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UFC 3-430-02FA
15 May 2003
Including change 1, December 2007
UNIFIED FACILITIES CRITERIA (UFC)
CENTRAL STEAM BOILER PLANTS
APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED
UFC 3-430-02FA
15 May 2003
Including change 1, December 2007
UNIFIED FACILITIES CRITERIA (UFC)
CENTRAL STEAM BOILER PLANTS
Any copyrighted material included in this UFC is identified at its point of use.
Use of the copyrighted material apart from this UFC must have the permission of the
copyright holder.
U.S. ARMY CORPS OF ENGINEERS (Preparing Activity)
NAVAL FACILITIES ENGINEERING COMMAND
AIR FORCE CIVIL ENGINEER SUPPORT AGENCY
Record of Changes (changes are indicated by \1\ ... /1/)
Change No.
1
Date
Dec 2007
Location
Pages 8-10 & 8-11, Chapter 8, Para 8-4b(2)
This UFC supersedes TM 5-810-15, dated 1 August 1995. The format of this UFC does not
conform to UFC 1-300-01; however, the format will be adjusted to conform at the next revision.
The body of this UFC is a document of a different number.
1
UFC 3-430-02FA
15 May 2003
Including change 1, December 2007
FOREWORD
\1\
The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides
planning, design, construction, sustainment, restoration, and modernization criteria, and applies
to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordance
with USD(AT&L) Memorandum dated 29 May 2002. UFC will be used for all DoD projects and
work for other customers where appropriate. All construction outside of the United States is
also governed by Status of forces Agreements (SOFA), Host Nation Funded Construction
Agreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA.)
Therefore, the acquisition team must ensure compliance with the more stringent of the UFC, the
SOFA, the HNFA, and the BIA, as applicable.
UFC are living documents and will be periodically reviewed, updated, and made available to
users as part of the Services’ responsibility for providing technical criteria for military
construction. Headquarters, U.S. Army Corps of Engineers (HQUSACE), Naval Facilities
Engineering Command (NAVFAC), and Air Force Civil Engineer Support Agency (AFCESA) are
responsible for administration of the UFC system. Defense agencies should contact the
preparing service for document interpretation and improvements. Technical content of UFC is
the responsibility of the cognizant DoD working group. Recommended changes with supporting
rationale should be sent to the respective service proponent office by the following electronic
form: Criteria Change Request (CCR). The form is also accessible from the Internet sites listed
below.
UFC are effective upon issuance and are distributed only in electronic media from the following
source:
•
Whole Building Design Guide web site http://dod.wbdg.org/.
Hard copies of UFC printed from electronic media should be checked against the current
electronic version prior to use to ensure that they are current.
AUTHORIZED BY:
______________________________________
DONALD L. BASHAM, P.E.
Chief, Engineering and Construction
U.S. Army Corps of Engineers
______________________________________
DR. JAMES W WRIGHT, P.E.
Chief Engineer
Naval Facilities Engineering Command
______________________________________
KATHLEEN I. FERGUSON, P.E.
The Deputy Civil Engineer
DCS/Installations & Logistics
Department of the Air Force
______________________________________
Dr. GET W. MOY, P.E.
Director, Installations Requirements and
Management
Office of the Deputy Under Secretary of Defense
(Installations and Environment)
2
TM 5-810-15
CHAPTER 1
INTRODUCTION
1-1. Purpose
This manual provides guidance for the design of
central steam plants for Army installations.
1-2. Scope.
This manual considers steam plants with capacities
from one to three boilers, each rated between
20,000 and 250,000 pounds per hour (pph). Where
special conditions and problems are not specifically
covered in this manual, acceptable industry standards will be followed. Modifications or additions
to existing systems solely for the purpose of meeting criteria in this manual are not authorized. The
guidance and criteria herein are not intended to be
retroactively mandatory. Clarification of the basic
standards and guidelines for a particular application
and supplementary standards which may be
required for special cases may be obtained through
normal channels from HQUSACE, WASH DC
20314-1000.
1-3. References.
Appendix A contains a list of references used in this
manual.
1-4. Economic considerations.
The selection of one particular type of design for a
given application, when two or more types of
design are known to be feasible, will be based on
the results of an economic study.
1-5. Design philosophy.
a. General. Steam plants considered in this
manual will be fired by gas, oil, gas-and-oil, coal,
or waste fuels. Coal fired plants will use any
combination of three commercially proven coal
firing technologies. These include atmospheric circulating fluidized bed (ACFB), pulverized coal and
stoker fired boilers. Stokers are designed to burn
any one of the different types of anthracite, bituminous, sub-bituminous or lignite type coals.
ACFB boilers offer reduced sulfur dioxide emissions without use of scrubbers while firing a wide
range of lower cost fuels such as high sulfur coal
and waste fuels. To provide a quick scale for the
plants under review here, several categories have
been developed, as shown in table 1-1.
b. Reliability. Steam plant reliability standards
will be equivalent to a 1-day forced outage in 10
years with equipment quality and redundancy
Table 1-1. Central Steam Plant Sizes.
Category
Small
Medium
Large
Size
0-100,000 pph
100,000-300,000 pph
300,000-750,000 pph
selected during plant design to conform to this
standard. This standard also requires quality engineering, equipment, and operations and maintenance personnel. In order for boilers to have high
availability it is mandatory that a good water
treatment program be implemented. Availability
guarantees offered by boiler manufacturers for coal
fired units are in the range of 85 to 90 percent and
are in the range of 90 to 95 percent for gas fired
boilers. A planned outage of a minimum of one day
per year is normal for waterside inspection.
c. Maintenance. Steam plant arrangement will
permit reasonable access for operation and maintenance of equipment. Careful attention will be given
to the arrangement of equipment, valves,
mechanical specialties, and electrical devices so that
rotors, tube bundles, inner valves, top works,
strainers, contactors, relays, and like items can be
maintained or replaced. Adequate platforms, stairs,
handrails, and kickplates will be provided so that
operators and maintenance personnel can function
conveniently and safely.
d. Future expansion. The specific site selected
for the steam plant and the physical arrangement of
the plant equipment, building, and support facilities
such as natural gas supply lines, coal and ash
handling systems, coal storage, circulating water
system, trackage, and access roads will be arranged
insofar as practicable to allow for future expansion.
1-6. Design criteria.
a. General requirements. The design will provide
for a steam plant which has the capacity to provide
the quantity and type of steam required.
b. Steam loads. The following information, as
applicable, is required for design:
(1) A forecast of annual and monthly diversified peak loads to be served by the project.
(2) Typical, seasonal, weekly and daily load
curves and load duration curves of the load to be
served. Figures 1-1 and 1-2 show example load
duration curves.
1-1
TM 5-810-15
1-2
TM 5-810-15
(3) A forecast of peak loads encountered during the steam plant full mobilization.
(4) If the plant is to operate in conjunction
with any existing steam generation on the base or
is an expansion of an existing facility, the designer
will also need the following:
(a) An inventory of major existing steam
generation equipment giving principle characteristics such as type, capacities, steam characteristics,
pressures and like parameters.
(b) Incremental thermal efficiency of existing boiler units.
(c) Historical operating data for each existing steam generating unit giving energy generated,
fuel consumption, and other related information.
(5) Existing or recommended steam distribution systems to support base operations.
(6) A complete fuel analysis for each fuel
being considered for use in the plant. Coal analyses
shall include proximate analysis, ultimate analysis,
grindability, higher heating value, ash analysis, ash
fusion
temperature,
and
agglomerating
classification.
(7) Plant site conditions must be identified to
include ambient temperature ranges, maximum
expected wind conditions, snow load, seismic
conditions and any other site conditions that could
affect the design of the boiler and its accessories.
(8) Water quality available to the boiler to
include such things as total dissolved solids, pH,
etc.
(9) All codes that pertain to design, construction and placing of the boiler and its accessories
into operation need to be identified.
(10) If any of the above data which is
required for performing the detailed design is
unavailable, the designer will develop this data.
c. Fuel source and cost. The type, availability,
and cost of fuel will be determined in the early
stages of design, taking into account environmental
regulatory requirements that may affect fuel and
fuel characteristics of the plant.
d. Water supply. Fresh water is required for the
boiler cycle makeup. Quantity of makeup will vary
with the type of boiler plant, amount of condensate
return for any export steam, and the maximum heat
rejection from the cycle.
e. Stack emissions. A steam plant will be designed for the type of stack gas cleanup equipment
which meets federal, state, and local emission
requirements. For a coal fired boiler, this will
involve an electrostatic precipitator or baghouse for
particulates or fly ash removal, and a scrubber for
flue gas desulfurization (FGD) unless fluidized bed
combustion or compliance coal is employed. If
design is based on compliance coal, the design will
include space and other required provisions for the
installation of equipment. Boiler design will be
specified as required for nitrous oxides (NOx)
control. ACFB boilers have low nitrogen oxide
(NOx) emissions because of their relatively low
combustion temperatures. Selective noncatalytic
reduction (SNCR) systems are now being required
by several states even on ACFB boiler installations
to meet new NOx allowable emissions limits (AEL)
that are more stringent.
f. Waste disposal. Both solid and liquid wastes
will be handled and disposed of in an environmentally acceptable manner. The wastes can be categorized generally as follows:
(1) Solid wastes. These include both bottom
ash and fly ash from boilers.
(2) Liquid wastes. These include boiler blowdown, cooling tower blowdown, acid and caustic
water treating wastes, coal pile runoff, and various
contaminated wastes from chemical storage areas,
sanitary sewage and yard areas.
g. Other environmental considerations. Other
environmental considerations include noise control
and aesthetic treatment of the project. The final
location of the project within the site area will be
reviewed in relation to its proximity to hospital and
office areas and the civilian neighborhood, if
applicable. Also, the general architectural design
will be reviewed in terms of coordination and
blending with the style of surrounding buildings.
Any anticipated noise or aesthetics problem will be
resolved prior to the time that final site selection is
approved.
h. Construction cost estimate. The following
items should be considered in the construction cost
estimate for a boiler plant.
(1) Substructure
(2) Structural Steel
(3) Superstructure
(4) Painting
(5) Coal, Limestone, Inert Bed Material &
Ash Handling Systems Foundations
(6) Stack Foundations
(7) Air Pollution Control Equipment Foundations
(8) Roads, Grading & Site Improvements
(9) Ash Pond, Coal Runoff Pond & Coal Pile
Stabilization
(10) Railroad Siding
(11) Water & Sewers
(12) Fencing
(13) Steam Generators
(14) Particulate Control Equipment
(15) Sulfur Removal Equipment
1-3
TM 5-810-15
(16)
(17)
ment
(18)
(19)
(20)
(21)
(22)
(23)
(24)
(25)
(26)
(27)
1-4
Stacks
Continuous Flue Gas Monitoring EquipCoal Handling System
Limestone Handling System
Inert Bed Handling System
Ash Handling System
Panels, Instruments & Controls
Water Treatment Equipment
Deaerators
Feedwater Heaters
Boiler Feed Pumps
Fire Protection
(28)
(29)
(30)
(31)
(32)
(33)
(34)
(35)
(36)
Air Compressors
Power Piping
Electrical Equipment
Power Wiring
Plant Substation
Operator Training
Fuels
Chemicals
Fuel Storage
1-7. Explanation of abbreviations and terms.
Abbreviations and special terms used in this regulation are explained in the glossary.
TM 5-810-15
Table 3-3. Analysis of Typical U.S. Coals. (As Mined) (Continued).
% Proximate Analysis
VM
FC
Ash
H2O
C
% Ultimate Analysis
H2
S
State
Rank
Btu/lb
H2O
O2
N2
NM
NM
B
F
13,340
12,650
2.9
2.0
5.5
33.5
82.7
50.6
8.9
13.9
2.9
2.0
82.3
70.6
2.6
4.8
0.8
1.3
1.3
6.2
1.2
1.2
OH
OH
F
G
12,990
12,160
4.9
8.2
36.6
36.1
51.2
48.7
7.3
7.0
4.9
8.2
71.9
68.4
4.9
4.7
2.6
1.2
7.0
9.1
1.4
1.4
OK
OK
D
F
13,800
13,630
2.6
2.1
16.5
35.0
72.2
57.0
8.7
5.9
2.6
2.1
80.1
76.7
4.0
4.9
1.0
0.5
1.9
7.9
1.7
2.0
PA*
PA**
PA***
PA
PA
PA
B
B
B
C
E
F
11,950
13,540
12,820
13,450
14,310
13,610
5.4
2.3
4.9
3.0
3.3
2.6
3.8
3.1
3.7
8.4
20.5
30.0
77.1
87.7
82.2
78.9
70.0
58.3
13.7
6.9
9.2
9.7
6.2
9.1
5.4
2.3
4.9
3.0
3.3
2.6
76.1
86.7
81.6
80.2
80.7
76.6
1.8
1.9
1.8
3.3
4.5
45.9
0.6
0.5
0.5
0.7
1.8
1.3
1.8
0.9
1.3
2.0
2.4
3.9
0.6
0.8
0.7
1.1
1.1
1.6
RI
A
9,313
13.3
2.5
65.3
18.9
13.3
64.2
0.4
0.3
2.7
0.2
TN
F
13,890
1.8
35.9
56.1
6.2
1.8
77.7
5.2
1.2
6.0
1.9
TX
TX
F
J
12,230
7,350
4.0
33.7
48.9
29.3
34.9
29.7
12.2
7.3
4.0
33.7
65.5
42.5
5.9
3.1
2.0
0.5
9.1
12.1
1.3
0.8
UT
F
12,990
4.3
37.2
51.8
6.7
43.0
72.2
5.1
1.1
9.0
1.6
VA
VA
VA
C
E
F
11,850
14,030
14,510
3.1
3.1
2.2
10.6
21.8
36.0
66.7
67.9
58.0
19.6
7.2
3.8
3.1
3.1
2.2
70.5
80.1
80.6
3.2
4.7
5.5
0.6
1.0
0.7
2.2
2.4
5.9
0.8
1.5
1.3
WA
F
12,610
4.3
37.7
47.1
10.9
4.3
68.9
5.4
0.5
8.5
1.5
WV
WV
D
F
14,730
14,350
2.7
2.4
17.2
33.0
76.1
60.0
4.0
4.6
2.7
2.4
84.7
80.8
4.3
5.1
0.6
0.7
2.2
4.8
1.5
1.6
WY
WY
G
I
12,960
9,420
5.1
23.2
40.5
33.3
49.8
39.7
4.6
3.8
5.1
23.2
73.0
54.6
5.0
3.8
0.5
0.4
10.6
13.2
1.2
1.0
*Orchard Bed. **Mammoth Bed. ***Holmes Bed.
RANK KEY: A-Meta-anthracite
B-Anthracite
C-Semianthracite
D-Low Volatile Bituminous
E-Medium Volatile Bituminous
F-High Volatile Bituminous A
G-High Volatile Bituminous B
H-High Volatile Bituminous C
1-Subbituminous
J-Lignite
Table 3-4. Typical coal and ash analysis information suitable for boiler design.
Typical
As Received (Raw)
Range
Proximate Analysis
Moisture (%)
Ash (%)
Fixed Carbon (%)
Total
Btu per pound (as received)
Btu per pound (dry)
Sulfur (%)
________
________
________
100.0
________
________
________
________to________
________to________
________to________
Ultimate Analysis
Carbon (%)
Hydrogen (%)
Nitrogen (%)
________
________
________
3-6
Washed
Typical
Range
________to________
________to________
________to________
________to________
________to________
________to________
________
________
________
100.0
________
________
________
________to________
________to________
________to________
________
________
________
________to________
________to________
________to________
________to________
________to________
________to________
TM 5-810-15
(4) If extensive or repetitive dredging of waterway will be necessary for plant operations.
(5) The historical maximum and minimum
water level and flow readings. Check that adequate
water supply is available at minimum flow and if
site will flood at high level.
2-4. Site development.
a. Soils investigation. An analysis of existing
soils conditions will be made to determine the
proper type of foundation. Soils data will include
elevation of each boring, water table level, description of soil strata including the group symbol based
on the Unified Soil Classification System, and
penetration data (blow count). Geological conditions must support the foundations of plant
structures at a reasonable cost with particular
attention being paid to bedrock formations and
faults. The soils report will include recommendations as to type of foundations for various purposes; excavation, dewatering and fill procedures;
and suitability of on site material for fill and earthen
dikes including data on soft and organic materials,
rock and other pertinent information as applicable.
b. Grading and drainage.
(1) Basic criteria. Determination of final
grading and drainage scheme for a new steam plant
will be based on a number of considerations
including size of property in relationship to the size
of plant facilities, desirable location on site, and
plant access based on topography.
(2) Drainage. Storm water drainage will be
evaluated based on rainfall intensities, runoff
characteristics of soil, facilities for receiving storm
water discharge, and local regulations.
(3) Erosion prevention. All graded areas will
be stabilized to control erosion by designing shallow slopes to the greatest extent possible and by
means of soil stabilization such as seeding, sod,
stone, riprap and retaining walls.
c. Meteorology. Precipitation, wind conditions,
evaporation, humidity and temperature will affect
emissions dispersion, coal storage and handling,
and other aspects of plant operation.
d. Area requirements. Plant area requirements
will be figured on the type of plant; capacity; urban,
suburban or rural location; design of fuel storage
and handling facilities; disposal of soil waste and
treatment of wastewater; condenser cooling; and
the plant structure and miscellaneous requirements.
Acquisition of land should include plant access
roads, rail access and space for future additions to
the plant.
(1) Space must be provided for the long
term coal storage pile. Maximum allowable height
2-2
of the coal pile and methods of stockout and
reclaim will further affect space requirements. If oil
is used as primary fuel or as a backup fuel, storage
tank space must be calculated.
(2) Space for the disposal of wet and dry ash
will be provided.
(3) Control of runoff from material storage
areas is required by EPA regulations. Space for
retention ponds must be provided.
e. Flood protection. Site protection for flood frequency of once every 500 years will be calculated
into area requirements.
f. Other requirements. Space for parking, warehouses, cooling water systems, environmental systems, construction laydown areas and other requirements will be provided.
2-5. Plant access.
a. Plant roadway requirements. Layout of plant
roadway will be based on volume and type of
traffic, speed, and traffic patterns. Proximity to
principle highways should permit reasonably easy
access for construction crews and deliveries. Roadway design will be in accordance with American
Association of State Highway and Transportation
Officials (AASHTO) standard specifications. Roadway material and thickness will be based on
economic evaluations of feasible alternatives. Vehicular parking for plant personnel and visitors will
be located in areas that will not interfere with the
safe operation of the plant. Turning radii will be
adequate to handle all vehicle categories.
b. Railroads. If a railroad spur is selected to
handle fuel supplies and material and equipment
deliveries during construction or plant expansion,
the design will be in accordance with American
Railway Engineering Association (AREA) Manual.
(1) Spur layout will accommodate coal handling facilities including a storage track or loop
track for empty cars. Refer to chapter 5 for
additional information.
(2) If liquid fuel is to be handled, unloading
pumps and steam connections for tank car heaters
may be required in frigid climates.
2-6. Plant structures.
a. Size and arrangements. The steam plant main
building size and arrangement depend on the
selected plant equipment and facilities including:
whether steam generators are indoor or outdoor
type; coal bunker or silo arrangement in the cases
of pulverized coal and stoker fired plants; coal,
limestone and inert bed silo arrangement in the case
of atmospheric circulating fluidized bed (ACFB)
boiler plants; source of cooling water supply
relative to the plant; provisions for future
expansion; and aesthetic and environmental con-
TM 5-810-15
siderations. Generally, the main building will consist of: a steam generator bay (or firing aisle the
semi-outdoor units); an auxiliary bay for feedwater
heaters, pumps, and switchgear; and general spaces
as may be required for machine shop, locker room,
laboratory and office facilities. For very mild
climates the steam generators may be outdoor type
(in a weather protected, walk-in enclosure)
although this arrangement presents special
maintenance problems. If incorporated, the elevator
will have access to the highest operating level of
the steam generator (drum levels).
b. Layout considerations. The layout of the
structural system will identify specific requirements
relative to vertical and horizontal access, personnel
needs and convenience, equipment and respective
maintenance areas, floors and platforms.
c. Soil investigation requirements. A subsurface
exploration program will be conducted. Design
information regarding the interaction of the structure and the surrounding ground is required. In
addition, an investigation should furnish information as to the source of construction materials and
the types and extent of materials which will be
encountered during construction will be investigated. Information required for design includes:
extent of each identifiable soil stratum, depth to top
of rock and character of the rock, elevation of
normal ground water at site, and engineering
properties of the soil and rock.
d. Foundation design. Selection of the type of
foundation to be used for each component of the
plant (i.e., main building, boiler, stacks and coal
handling structure) will be determined from the
subsurface exploration data, cost considerations
and availability of construction trades.
e. Structural design. Thermal stations will be
designed utilizing conventional structural steel for
the main steam station building. Separate structural
steel will be provided to support building floors and
platforms; boiler steel will not be used in support
building structure. The pedestal for supporting the
turbine driven boiler feed pump if utilized will be of
reinforced concrete. Reinforced concrete or
masonry construction may be used for the building
framing (not for boiler framing); special concrete
inserts or other provisions must be made in such
event for support of piping, trays and conduits. An
economic evaluation will be made of these
alternatives.
f. Structure loading.
(1) Buildings, structures and all portions
thereof will be designed and constructed to support
all live and dead loads without exceeding the
allowable stresses of the selected materials in the
structural members and connections. Typical live
loads for steam plant floors are as follows:
Basement and operating floors
Mezzanine, deaerator, and miscellaneous
operating floors
Office, laboratories, instrument shops,
and other lightly loaded areas
200 psf
200 psf
100 psf
Live loads for actual design will be carefully
reviewed for any special conditions and actual
loads applicable.
(2) Live loads for equipment floors will be
based on the assumption that the floor will be
utilized as laydown for equipment parts during
maintenance. Load will be based on heaviest piece
removed during maintenance.
(3) Live load assumptions will be in accordance with TM 5-809-1.
g. Other loads. In addition to the live and dead
loads, the following loadings will be provided for:
(1) Piping load. Weight of major piping
sized and routed will include weight of pipe,
insulation, hydraulic weight (pipe full of water) in
addition to any shock loads. Pipe hanger loads will
be doubled for design of supporting steel. In
congested piping areas increase live load on the
supporting floor by 100 pounds per square foot
(psf). Structural steel will be provided to
adequately support all mechanical piping and
electrical conduit. Provision will be made to
accommodate expansion and contraction and
drainage requirements of the pipe. Piping
connections must be made to preclude rupture
under the most adverse conditions expected. Pipe
supports will be close coupled to supporting structures when the more severe seismic conditions are
expected.
(2) Wind loading. Building will be designed
to resist the horizontal wind pressure available for
the site on all surfaces exposed to the wind. Wind
load assumptions will be in accordance with TM 5809-1.
(3) Seismic loading. Buildings and other
structures will be designed to resist seismic loading
in accordance with the zone in which the building
is located. Seismic design will be in accordance
with
TM 5-809-10.
(4) Equipment loading. Equipment loads are
furnished by the various manufacturers of each
equipment item. In addition to equipment dead
loads, impact loads, short circuit forces for generators, and other pertinent special loads prescribed by
the equipment function or requirements will be
included. Dead load assumptions will be in accordance with TM 5-809-1. Ductwork, flue gas breeching, stacks, and other hot equipment must be
2-3
TM 5-810-15
supported such that expansion and contraction will
not impose detrimental loads and stresses on
related structures.
(5) Snow loading. Snow load assumptions
will be in accordance with TM 5-809-1.
h. Architectural treatment.
(1) The architectural treatment will be developed to harmonize with the site conditions, both
natural and manmade. Depending on location, the
environmental compatibility may be the determining
factor. In other cases the climate or user
preference, tempered with aesthetic and economic
factors, will dictate architectural treatment.
(2) For special circumstances, such as areas
where extended periods of very high humidity,
frequently combined with desert conditions giving
rise to heavy dust and sand blasting action, indoor
construction with pressurized ventilation will be
required.
(3) Control rooms, offices, locker rooms,
and some outbuildings will be enclosed regardless
of enclosure selected for main building.
(4) Equipment room size will provide
adequate space for equipment installation,
maintenance and removal. A minimum of aisle
space between items will be 4 feet if feasible.
Provide a minimum of 8 feet clearance between
boilers 60,000 pph and larger. If future expansion
is planned, size of room will be based on future
requirements. Equipment room construction will
allow for equipment removal and include double
doors and steel supports for chain hoists. Adequate
ventilation and heating will be included.
Attenuation of noise will be considered in room
design.
(5) Provide openings or doorways for
passage of the largest equipment units. Make
openings for ventilation louvers, breechings, and
piping where necessary. Fire doors, fire shutters or
a combination of both, may be required.
(6) On multiple floor installations, provide a
freight elevator.
(7) Furnish necessary shower room, toilet
room facilities and lockers for operating personnel
for both sexes in buildings. The plant should
contain a sampling laboratory space, storage area,
small repair area, control room (in larger plants),
generator room, lunch room, compressor room,
chemical storage area, office space for supervisors
and clerks. Parking spaces for plant personnel and
visitors should be provided near the boiler plant.
(8) Finish of plant interior walls and tunnels
will have a coating which will permit hose down or
scrubbing of areas.
(9) Concrete will be in accordance with TM
5-805-1, American Concrete Institute (ACI) 318
and 301.
2-4
i. Special considerations.
(1) Crane bay-provide removable openings
in floor above major equipment for removal by station crane (if provided).
(2) Provide hoists and supports for maintenance on pumps, fans and other heavy equipment.
Provide a beam into the plant to hoist equipment to
an upper level.
(3) All anchor bolts for equipment will be
sleeved to allow adjustment for final alignment of
equipment.
2-7. Heating, ventilating and air conditioning
systems (HVAC).
a. General. System analysis and design procedures provided in the American Society of Heating,
Refrigeration and Air Conditioning Engineers
(ASHRAE) Guide for Data books and TM 5-810-1
should be followed, unless otherwise stated or
specifically directed by other criteria.
b. Design considerations. When a computer program is required, provisions for showing an estimate of the hourly space heating and cooling
requirements, and hourly performance of the heating and cooling system can be structured. When
manual computation is used, the heating and
cooling load estimates will be in accordance with
the current edition of the ASHRAE Handbook of
Fundamentals.
2-8. Drainage.
a. Drains which may contain coal or oil will have
suitable separators to separate coal or oil from
drainage before being connected to sewer lines.
b. Provide drains and connect to storm water
drainage system for diked areas for above ground
oil storage.
c. Maximum temperature of effluent to the drain
system will be as required by governing codes. A
temperature regulating valve will be used to inject
potable water into the high temperature waste
stream from the blowdown tank. This technique
will also be used on other equipment as required.
2-9. Plant design safety.
a. Introduction. The safety features described in
the following paragraphs will be incorporated into
the steam plant design to assist in maintaining a
high level of personnel safety.
b. Design safety features. In designing a steam
plant, the following general recommendations on
safety will be given attention:
(1) Equipment will be arranged with
adequate access space for operation and for
maintenance.
TM 5-810-15
Wherever possible, auxiliary equipment will be
arranged for maintenance handling by monorails,
wheeled trucks, or portable A-frames if disassembly
of heavy pieces is required for maintenance.
(2) Safety guards will be provided on
moving or rotating parts of all equipment.
(3) All valves, specialties, and devices
needing manipulation by operators will be
accessible without ladders, and preferably without
using chain-wheels.
(4) Valve centers will be mounted approximately 7 feet above floors and platforms so that
rising stems and bottom rims of handwheels will
not be a hazard. Provide access platforms for
operations and maintenance of all valves and
equipment over 7 feet above the floor.
(5) Stairs with conventional riser-tread
proportions will be used. Vertical ladders should be
installed only as a last resort.
(6) All floors, gratings and checkered plates
will have nonslip surfaces.
(7) No platform or walkway will be less than
30-inches wide.
(8) Toe plates, fitted closely to the edge of
all floor openings, platforms and stairways, will be
provided in all cases. Handrails will be provided on
platforms and floor openings.
(9) Not less than two exits will be provided
from catwalks, platforms longer than 10 to 15 feet
in length, boiler aisles, floor levels and the steam
plant. Emergency lighting will be provided for all
modes of egress.
(10) All floors subject to washdown or leaks
will be sloped to floor drains.
(11) All areas subject to lube oil or chemical
spills will be provided with curbs and drains.
(12) If plant is of semioutdoor or outdoor
construction in a climate subject to freezing
weather, weather protection will be provided for
critical operating and maintenance areas such as the
firing aisle, boiler steam drum ends and soot blower
locations.
(13) Adequate illumination will be provided
throughout the plant. Illumination will comply with
requirements of the Illuminating Engineers Society
(TES) Lighting Handbook.
(14) Comfort air conditioning will be
provided throughout control rooms, laboratories,
offices and similar spaces where operating and
maintenance personnel spend considerable time.
(15) Mechanical supply and exhaust ventilation will be provided for all of the steam plant
equipment areas to alleviate operator fatigue and
prevent accumulation of fumes and dust.
(16) Noise level will be reduced to at least the
recommended maximum levels of OSHA. Use of
fan silencers, compressor silencers, mufflers on
internal combustion engines, and acoustical material is required as discussed in TM 5-805-4 and TM
5-805-9.
(17) Color schemes will be psychologically
restful except where danger must be highlighted
with special bright primary colors.
(18) Each equipment item will be clearly labeled in block letters identifying it both by equipment item number and name.
2-5
TM 5-810-15
segregation. Approximately 25 to 50 percent of the
coal is burned in suspension by this method. This
spreader feed has a larger grate heat release rate
than the cross feed type; requires a smaller furnace
envelope; and has a quicker response time for load
changes. This type of fuel feed must have a uniform
air flow through the grates due to the large amount
of suspension burning. For best results, the fuel fed
to this type of unit should be properly sized. Refer
to Figure 3-12 illustrating coal size.
d. Stoker selection considerations. Table 3-6
provides a summary of factors to be considered
when selecting a stoker for a boiler within the
range of 20,000 to 250,000 pph of steam. Prior to
submitting a set of specifications to the boiler or
stoker manufacturers, the type of coal that is to be
burned must be known. Selection of the design coal
is required so that these manufacturers are able to
guarantee their equipment performance. When the
coal is not known, or when the possibility exists
that many different types of coals will be burned
over the life of the stoker, the selection emphasis
3-18
should lean toward spreader stokers. This type of
stoker is more flexible in its capability to efficiently
burn a wider range of coals.
3-13.
Fly ash reinjection for coal firing.
a. General. A fly ash reinjection system for coal
fired boilers is used to return coarse, carbon
bearing particulate back into the furnace for further
combustion. This is only economically justified in
stoker fired boilers with steam capacities over
70,000 pph. Fly ash reinjection from the boiler,
economizer, air heater and dust collector hoppers
can improve boiler thermal efficiency by 3 to 5
percent. However, fly ash recirculation within the
boiler is significantly increased.
b. Equipment sizing. Tube erosion and other
maintenance costs in addition to requiring an
increase in the capability of the air pollution control
equipment are to be expected and must be taken
into consideration when sizing the air pollution
control equipment.
TM 5-810-15
fired units may be specified for boilers with
capacities of 100,000 pph and above. Field erected
atmospheric circulating fluidized bed boilers
(ACFB) are 80,000 pph or larger. Gas and oil fired
boilers and field erected for capacities of 200,000
pph or larger. Field erected units are the only
boilers available for any of these technologies
above 200,000 pph.
3-4. Available fuels.
a. Natural gas. Natural gas is the cleanest
burning of the widely used commercially available
fuels. It contains virtually no ash which reduces
design, building and operating costs. This also
eliminates the need for particulate collection
equipment such as baghouses or electrostatic precipitators. Thorough mixing with combustion air
allows low excess air firing. The high hydrogen
content of natural gas compared to the oil or coal
causes more water vapor to be formed in the flue
gas. This water takes heat away from the combustion process, making less heat available for steam
generation which lowers the boiler efficiency.
b. Natural gas analysis. Two types of analyses of
natural gas are commonly used. Proximate analysis
provides the percentage content by volume of
methane, ethane, carbon dioxide and nitrogen.
Ultimate analysis provides the percentage content
by weight of hydrogen, carbon, nitrogen and
oxygen. Table 3-1 gives natural gas analyses from
selected United States fields.
c. Fuel oil. Compared to coal fuel oils are relatively easy to handle and burn. Ash disposal and
emissions are negligible. When properly atomized
oil characteristics are similar to natural gas. Even
though oil contains little ash, other constituents
such as sulfur, sodium and vanadium present
problems. These concerns include emission of
pollutants, external deposits and corrosion.
d. Fuel oil analysis. Historically petroleum refineries have produced five different grades of fuel
oil. Fuel oils are graded according to gravity and
viscosity as defined by ASTM standard specifications with No. 1 being the lightest and No. 6 being
the heaviest. Table 3-2 lists typical analyses of the
various grades.
e. Coal types. For the purpose of boiler design,
domestic U.S. coals are divided into four basic
classifications: lignite, subbituminous, bituminous,
and anthracite. Anthracite, however, requires special furnace and burner designs due to its low
volatile content and is not normally used in the U.S.
for boiler fuel. Note the following illustrations,
figures 3-1 and 3-2. In general, these coal
classifications refer to the ratio of fixed carbon to
volatile matter and moisture contained in the coal,
which increases with the action of pressure, heat,
and other agents over time as coal matures. The
changes in this ratio over the stages of coal
information are illustrated in figure 3-3. Volatile
matter consists of hydrocarbons and other compounds which are released in gaseous form when
coal is heated. The amount present in a particular
coal is related to the coal*s heating value and the
rate at which it burns. The volatile matter to fixed
carbon ratio greatly affects boiler design, since the
furnace dimensions must allow the correct retention
time to properly burn the fuel.
Table 3-1. Analyses of Natural Gas from Selected United States Fields.
Pittsburg
So. Cal.
Birmingham
Proximate, % by Volume
Methane CH4
Ethane C2 H6
Carbon D.C02
Nitrogen N2
Total
83.40
15.80
—
0.80
100.00
84.00
14.80
0.70
0.50
100.00
5.00
100.00
Ultimate % by Weight
Hydrogen H2
Carbon C
Nitrogen N2
Oxygen 02
Total
Sp Gr (Air= 1.0)
HHV Btu/ft3*
Btu/lb
Fuel lb/10,000 Btu
Theoretical Air lb/10,000 Btu
Total Moisture lb/10,O00 Btu
25.53
75.25
1.22
—
100.00
0.610
1,129
23,170
0.432
7.18
0.915
23.30
74.72
0.76
1.22
100.00
0.636
1,116
22,904
0.437
7.18
0.917
22.68
69.26
8.06
—
100.00
0.600
1,000
21,800
0.459
7.50
0.971
*At 60 degree F and 30 in. Hg
3-2
90.00
5.00
Kansas City
Los Angeles
84.10
6.70
0.80
8.40
100.00
77.50
16.00
6.50
—
100.00
20.85
64.84
12.90
20.35
69.28
1.41
10.37
100.00
0.630
974
20,160
0.496
7.19
0.933
100.00
0.697
1,073
20,090
0.498
7.18
0.911
TM 5-810-15
(8) A static and dynamic structural analyses
must be made of the wind, earthquake, dead, and
thermal loads. Vortex shedding of wind loads must
be considered to be assured that destructive natural
frequency harmonics are not built into the stack.
d. Stack construction. The stack height and diameter, support, corrosion resistance, and economic factors dictate the type of construction to be
utilized.
(1) Stacks are generally made of concrete or
steel because of the high cost of radial brick
construction. If stack gases are positively pressurized, or if flue gases will be at or below the dew
point of the gases, corrosion resistant linings must
be provided; linings must be able to withstand
temperature excursions which may be experienced
in the flue gas if flue gas scrubbers are bypassed.
(2) Stacks of steel or concrete construction
will be insulated to avoid condensation by not
allowing
the internal surfaces to drop below 250 degrees F.
This requirement does not apply when scrubbers
are used with low temperature discharge (150 to
180 degrees F) into the stack because the flue gas
is already below dew point temperature.
(3) A truncated cone at the top of the stack
will decrease cold air downdrafts at the periphery
of the stack and will thus help maintain stack
temperature, but stack draft will decrease considerably.
3-19.
Adjustable Speed Drives.
Significant electrical power savings can be realized
at reduced boiler loads by installing adjustable
speed drives (ASD) on ID and FD fans. The
economics of ASD*s depend on the boiler load
profile (number of hours at different loads). The
feasibility of ASD installation should be verified by
an LCCA.
3-29
TM 5-810-15
f. Coal analysis. Two analyses of coal are commonly used to determine the classification and
constituents of coal: proximate analysis and ultimate analysis. Proximate analysis provides the percentage content by weight of fixed carbon, volatile
matter, moisture, and ash, and the heating value in
Btu per pound. These classifications are shown in
table 3-3. Ultimate analysis provides the percentage
content by weight of carbon, hydrogen, nitrogen,
oxygen, and sulfur. These data are used to
determine air requirements and the weight of
combustion by-products, both of which are used to
determine boiler fan sizes. Table 3-4 lists coal and
ash analysis together, ash fusion temperatures and
other data needed by boiler manufacturers for the
design and guarantee of boiler performance.
g. Alternate ACFB boiler fuels. ACFB systems
when properly designed can burn a wide variety of
materials that contain carbon. Many can be utilized
by themselves, while others are limited to a certain
percentage of total heat input as part of a mixture
with another fuel. Fuels with sulfur are burned in
combination with a calcium rich material such as
dolomite or limestone. Sulfur is removed as
calcium sulfate in the baghouse and either landfilled
3-4
or sold. If sulfur capture is not required then
another maufacturer recommended inert material
such as sand may be used. ACFB fuel flexibility
includes the following list of potential fuels—
(1) Anthracite coal
(2) Anthracite culm
(3) Bark and woodwaste
(4) Bituminous coal
(5) Bituminous gob
(6) Gasifier char
(7) Industrial sludges, wastes, residues
(8) Lignite
(9) Municipal refuse
(10) Oil
(11) Oil shale
(12) Paper products waste
(13) Peat
(14) Petroleum coke
(15) Phenolic resins
(16) Plastics
(17) Sewage sludge
(18) Subbituminous coal
(19) Textile waste
(20) Shredded tires
TM 5-810-15
Table 3-3. Analysis of Typical U.S. Coals. (As Mined)
State
% Proximate Analysis
VM
FC
Rank
Btu/lb
H2O
AL
F
14,210
5.5
30.8
AR
AR
C
D
13,700
13,700
2.1
3.4
CO
CO
CO
B
F
1
13,720
13,210
10,130
IA
H
IL
IL
C
% Ultimate Analysis
H2
S
Ash
H2O
O2
N2
60.9
2.8
5.5
80.3
4.9
0.6
4.2
1.7
9.8
16.2
78.8
71.8
9.3
8.6
2.1
3.4
80.3
79.6
3.4
3.9
1.7
1.0
1.7
1.8
1.5
1.7
2.5
1.4
19.6
5.7
32.6
30.5
83.8
54.3
45.9
8.0
11.7
4.0
2.5
1.4
19.6
83.9
73.4
58.8
2.9
5.1
3.8
0.7
0.6
0.3
0.7
6.5
12.2
1.3
1.3
1.3
10,720
14.1
35.6
39.3
11.0
14.1
58.5
4.0
4.3
7.2
0.9
G
H
12,130
11,480
8.0
12.1
33.0
40.2
50.6
39.1
8.4
8.6
8.0
12.1
68.7
62.8
4.5
4.6
1.2
4.3
7.6
6.6
1.6
1.0
IN
H
11,420
12.4
36.6
42.3
8.7
12.4
63.4
4.3
2.3
7.6
1.3
KS
F
12,670
7.4
31.8
52.4
8.4
7.4
70.7
4.6
2.6
5.0
1.3
KY
KY
F
G
14,290
12,080
3.1
7.5
35.0
37.7
58.9
45.3
3.0
9.5
3.1
7.5
79.2
66.9
5.4
4.8
0.6
3.5
7.2
6.4
1.5
1.4
MD
D
13,870
3.2
18.2
70.4
8.2
3.2
79.0
4.1
1.0
2.9
1.6
MI
H
11,860
12.4
35.0
47.0
5.6
12.4
65.8
4.5
2.9
7.4
1.4
MO
MO
F
G
12,990
11,300
5.4
10.5
32.1
32.0
53.5
44.6
9.0
12.9
5.4
10.5
71.6
63.4
4.8
4.2
3.6
2.5
4.2
5.2
1.4
1.3
ND
J
7,210
34.8
28.2
30.8
6.2
34.8
42.4
2.8
0.7
12.4
0.7
3-5
TM 5-810-15
Table 3-3. Analysis of Typical U.S. Coals. (As Mined) (Continued).
% Proximate Analysis
VM
FC
Ash
H2O
C
% Ultimate Analysis
H2
S
State
Rank
Btu/lb
H2O
O2
N2
NM
NM
B
F
13,340
12,650
2.9
2.0
5.5
33.5
82.7
50.6
8.9
13.9
2.9
2.0
82.3
70.6
2.6
4.8
0.8
1.3
1.3
6.2
1.2
1.2
OH
OH
F
G
12,990
12,160
4.9
8.2
36.6
36.1
51.2
48.7
7.3
7.0
4.9
8.2
71.9
68.4
4.9
4.7
2.6
1.2
7.0
9.1
1.4
1.4
OK
OK
D
F
13,800
13,630
2.6
2.1
16.5
35.0
72.2
57.0
8.7
5.9
2.6
2.1
80.1
76.7
4.0
4.9
1.0
0.5
1.9
7.9
1.7
2.0
PA*
PA**
PA***
PA
PA
PA
B
B
B
C
E
F
11,950
13,540
12,820
13,450
14,310
13,610
5.4
2.3
4.9
3.0
3.3
2.6
3.8
3.1
3.7
8.4
20.5
30.0
77.1
87.7
82.2
78.9
70.0
58.3
13.7
6.9
9.2
9.7
6.2
9.1
5.4
2.3
4.9
3.0
3.3
2.6
76.1
86.7
81.6
80.2
80.7
76.6
1.8
1.9
1.8
3.3
4.5
45.9
0.6
0.5
0.5
0.7
1.8
1.3
1.8
0.9
1.3
2.0
2.4
3.9
0.6
0.8
0.7
1.1
1.1
1.6
RI
A
9,313
13.3
2.5
65.3
18.9
13.3
64.2
0.4
0.3
2.7
0.2
TN
F
13,890
1.8
35.9
56.1
6.2
1.8
77.7
5.2
1.2
6.0
1.9
TX
TX
F
J
12,230
7,350
4.0
33.7
48.9
29.3
34.9
29.7
12.2
7.3
4.0
33.7
65.5
42.5
5.9
3.1
2.0
0.5
9.1
12.1
1.3
0.8
UT
F
12,990
4.3
37.2
51.8
6.7
43.0
72.2
5.1
1.1
9.0
1.6
VA
VA
VA
C
E
F
11,850
14,030
14,510
3.1
3.1
2.2
10.6
21.8
36.0
66.7
67.9
58.0
19.6
7.2
3.8
3.1
3.1
2.2
70.5
80.1
80.6
3.2
4.7
5.5
0.6
1.0
0.7
2.2
2.4
5.9
0.8
1.5
1.3
WA
F
12,610
4.3
37.7
47.1
10.9
4.3
68.9
5.4
0.5
8.5
1.5
WV
WV
D
F
14,730
14,350
2.7
2.4
17.2
33.0
76.1
60.0
4.0
4.6
2.7
2.4
84.7
80.8
4.3
5.1
0.6
0.7
2.2
4.8
1.5
1.6
WY
WY
G
I
12,960
9,420
5.1
23.2
40.5
33.3
49.8
39.7
4.6
3.8
5.1
23.2
73.0
54.6
5.0
3.8
0.5
0.4
10.6
13.2
1.2
1.0
*Orchard Bed. **Mammoth Bed. ***Holmes Bed.
RANK KEY: A-Meta-anthracite
B-Anthracite
C-Semianthracite
D-Low Volatile Bituminous
E-Medium Volatile Bituminous
F-High Volatile Bituminous A
G-High Volatile Bituminous B
H-High Volatile Bituminous C
1-Subbituminous
J-Lignite
Table 3-4. Typical coal and ash analysis information suitable for boiler design.
Typical
As Received (Raw)
Range
Proximate Analysis
Moisture (%)
Ash (%)
Fixed Carbon (%)
Total
Btu per pound (as received)
Btu per pound (dry)
Sulfur (%)
________
________
________
100.0
________
________
________
________to________
________to________
________to________
Ultimate Analysis
Carbon (%)
Hydrogen (%)
Nitrogen (%)
________
________
________
3-6
Washed
Typical
Range
________to________
________to________
________to________
________to________
________to________
________to________
________
________
________
100.0
________
________
________
________to________
________to________
________to________
________
________
________
________to________
________to________
________to________
________to________
________to________
________to________
TM 5-810-15
Table 3-4. Typical coal and ash analysis information suitable for boiler design. (Continued)
Typical
As Received (Raw)
Range
Washed
Typical
Range
Chlorine (%)
Sulfur (%)
Ash (%)
Oxygen (%)
________
________
________
________
________to________
________to________
________to________
________to________
________
________
________
________
________to________
________to________
________to________
________to________
Moisture (%)
________
________to________
________
________to________
Mineral Analysis
Phos. Penioxide, P205
Silica, SiO2
Ferric Oxide, Fe2O3
Alumina, Al2O3
Titania, TiO2
Calcium Oxide, CaO
Magnesium Oxide, MgO
Sulfur Trioxide, SO3
Potassium Oxide, K2O
Sodium Oxide, Na2O
Undetermined
Total
________
________
________
________
________
________
________
________
________
________
________
100.0
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________
________
________
________
________
________
________
________
________
________
________
100.0
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________to________
________to________
Reducing
Oxidizing
Fusion Temperature of Ash, deg. F
Initial Deformation (IT)
Softening (H=W)
Hemispherical (H= 1/2W)
Fluid (FT)
Free Swelling Index
Viscosity T250, deg. F
Silica Value
Base/Acid Ratio
________
________
________
________
________to________
________to________
________to________
____________
____________
____________
____________
________
________
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________to________
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Sulfur Forms
Pyritic Sulfur (%)
Sulfate Sulfur (%)
Organic Sulfur (%)
________
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________to________
________to________
________to________
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________to________
________to________
________to________
Water Soluble Alkalis
Water Soluble Na2O
Water Soluble K20
Equilibrium Moisture
Hardgrove Grindability Index
________
________
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________to________
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3-5. Coal ash characteristics.
a. Slagging and fouling potential. The slagging
potential of ash is the tendency to form fused deposits on tube surfaces exposed to high
temperature radiant heat. The fouling potential is
the tendency of ash to bond to lower temperature
convection surfaces. The slagging and the fouling
potential of the coal also directly affects furnace
design. Ash analyses of the expected fuel source
must be performed before undertaking the boiler
design, using ash prepared according to ASTM D
3174.
(1) Fusion temperature. Many comparisons
of chemical makeup have been developed to
analyze the behavior of ash in boilers, empirical
testing of ash fusion temperature is still the most
basic way of predicting slagging and fouling
potential. One testing method of determining ash
fusion temperature is prescribed in ASTM D 1857.
The test consists of observing the gradual thermal
deformation (melting) of a pyramid shaped ash
sample and recording the Initial Deformation
Temperature (IT), Softening Temperature (ST),
Hemispherical Temperature (HT), and Fluid
Temperature (FT). The stages at which these
temperatures are recorded are shown in figure 3-4.
(2) Chemical analyses. The fusion
temperature of ash is influenced by the interaction
of the acidic oxide constituents silica dioxide
(SiO2), aluminum oxide (Al2O3), and titanium
dioxide (TiO2) with the basic oxides; ferric oxide
(Fe2O3), calcium oxide (CaO), magnesium oxide
(MgO), and potassium oxide (K2O)—all of which
are present in the coal ash in widely varying
3-7
TM 5-810-15
proportions. Depending on their relative
proportions they can combine during combustion to
form compounds with melting temperatures
ranging from 1610 degrees F for sodium silicate
(Na2SiO3) to 2800 degrees F for calcium silicate
(CaSiO3). In determining the slagging potential and
fouling potential of ash, studying the base/acid
3-8
ratio, silica/alumina ratio, iron/calcium ratio,
iron/dolomite ratio, dolomite percentage, silica
percentage, total alkalies, and the role of iron in
coal ash can all be useful, as shown in figure 3-5.
The chemical elements found in coal, their oxidized
forms, and the ranges in which they may be present
in coal ash are listed in table 3-5.
TM 5-810-15
Table 3—5. Chemical Constituents of Coal Ash.
required for wet bottom boilers to prevent solidification of the ash during low load operation. Furnace volume must be increased for coals producing
ash with high fouling and slagging potentials, or to
counteract the erosive effects of large quantities of
ash or very abrasive ash. The greater furnace
volume results in both lower exit gas temperaturesreducing fouling and slagging-and lower exit gas
velocities, reducing tube erosion. The relationship
between coal classification and furnace volume is
shown in figure 3-6.
3-6. Combustion technology selection.
b. Ash characteristics and boiler design. The
characteristics and quantity of ash produced by a
specific coal strongly influence several aspects of
pulverized coal, ACFB and stoker boiler design,
including the selection of a bottom ash handling
system and furnace sizing. Ash with a high (2400
degrees F and above of a reducing basis) fusion
temperature is most suitable for dry bottom boilers,
while lower (1900 degrees F to 2400 degrees F on
a reducing basis) ash fusion temperatures are
a. Exclusionary factors. Gas and oil fired boilers
are available over the entire size range. Their use is
limited to areas where these fuels are economically
available. Stoker-fired boilers are available for the
entire load range covered by this manual.
Pulverized coal (PC) boilers are available in capacities of 100,000 pph and above. Atmospheric circulating fluidized bed (ACFB) boilers are available in
capacities of 80,000 pph and above. PC fired units
were used in capacity ranges below 100,000 pph
prior to the advent of package boilers, but with the
new designs it became more difficult to evaluate
PC firing as a preferred method of firing coal and
hence have essentially become obsolete. When
3-9
TM 5-810-15
rapid load swings are expected, stoker-fired units
may be eliminated because of their inferior response
to these conditions. When economics dictate the
use of low grade fuels including those of high or
variable ash content or high sulfur content then
stoker-fired and PC systems may be eliminated in
favor of ACFB systems. If none of these firing
systems are excluded by these factors, then the
choice between firing systems must be made on the
basis of a life cycle cost analysis (LCCA).
b. Base capital cost. The base capital cost of a
dual firing system is the total price of purchasing
and installing the entire system, including the boiler,
furnace, either stoker, pulverizer or fluidization
system, fans, flues, ducts, and air quality control
equipment. PC fired and ACFB boilers are more
expensive than stoker-fired boilers of a given
capacity, in part because they have a larger furnace
to provide space and time for the combustion
process to go to completion. Approximately 60 to
90 percent of the ash content of the coal passes
through the unit along with the gases of combustion. Tube spacing within the unit has to be
provided in order to accommodate this condition
and the ability of this ash to cause slagging and
fouling of the heating surface. These factors can
increase the size of the boiler and its cost. PC fired
units have been replaced by packaged boilers in
capacity ranges below 100,000 pph. Gas, oil and
PC boilers require a flame failure system which
increases their cost. The total cost of an ACFB
boiler addition is offset by not requiring flue gas
desulfurization (FGD) or selective catalytic reduction (SCR). Selective noncatalytic reduction
(SNCR) is required on ACFB boilers in place of
SCR.
c. Average boiler duty. The remaining expenses
calculated for an LCCA are all functions of the
average boiler duty. This value is based on the
estimated annual boiler load during the expected
life of the plant. It is calculated as follows:
average load (pph)
hours of operation
X
' averageboilerduty
rated capacity
8,760 hours
For example, if a 100,000 pph boiler operates at an
average load of 75,000 pph for 8,000 hours per
year out of a possible 8,760 hours, the average
boiler duty is 68 percent.
d. Fuel flexibility. When economically feasible
the ability to satisfy steam requirements with more
then one type of fuel offers significant advantages.
Problems with only one fuel*s source, transportation, handling or firing system will not stop
steam production. The flexibility of alternate fuel
supplies can be a powerful bargaining tool when
3-10
negotiating fuel supply contracts.
e. Fuel selection considerations. The use of
natural gas has the lowest first cost provided there
is adequate supply in a nearby supplier*s pipeline.
Natural gas does not require storage facilities;
however, it is subject to interruption and possible
curtailment. Although diesel oil burns more efficiently than natural gas, oil requires on site storage
and pumping facilities. Because oil has the potential
to contaminate ground water, storage facilities are
required to include spill containment and leak
detection systems. Coal can be stored in piles
outdoors. Steel tanks and spill containment are not
required. Coal pile runoff (coal fines in rain water)
into surrounding waters and airborne fugitive dust
emissions are concerns that have to be addressed.
Transportation of coal from stockpiles to the
bunkers requires dedicated labor to operate
unloading, storage, reclaim, and handling systems.
These needs along with sizing, ash handling, and
particulate emissions reduction requirements make
coal firing the highest capital investment
alternative.
f. Solid fuel considerations. Due to the special
coal sizing requirements of stoker and ACFB fuel
for such a unit may cost (5 to 15 percent) more
than the unsized coal that could be purchased for a
PC fired unit. However, if unwashed or run-ofmine (ROM) coal is purchased for a PC fired unit,
a crusher and motor should also be included in the
coal handling system in order to reduce the coal
particle size to approximately 1-1/4 by 0-inch.
Another consideration is that it may be difficult to
obtain the size stoker or ACFB coal due to either
transportation difficulties or lack of equipment at a
mine site. When using the same bituminous quality
coal, PC and ACFB fired units have a higher
thermal efficiency (86 to 88 percent) compared to
stoker fired units (80 to 84 percent) that effectively
lowers their fuel usage costs. The primary reason
for these differences is unburned carbon loss and
dry gas (exit gas temperature) losses and amount of
fly ash reinjection. These efficiency percentages will
vary with the quality of the fuel. With low sulfur
western fuels having a high moisture content (20 to
30 percent), a PC fired unit efficiency may be as
low as 82 to 85 percent. A particular ACFB boiler
can fire a wide range of low grade inexpensive
fuels. These include high sulfur coal, petroleum
coke, refuse derived fuel, waste water plant
treatment sludge and mixtures of coal with various
scraps such as shredded tires, wood chips and
agricultural waste. Another feature of PC and
ACFB fired units that results in increased costs and
must also be considered in the overall evaluation is
TM 5-810-15
the natural gas or No. 2 fuel oil burner lighters
which are normally in the range of 3 million to 10
million Btu per hour for each device. Stoker fired
units are normally started by spreading kerosene or
other waste oil and scrap wood over a coal bed and
lighting it. Annual fuel cost is based on the cost of
the fuel, in dollars and cents per million Btu
multiplied by the hours of operation and average
load and divided by the percent boiler efficiency.
g. Power cost. Gas fired boilers have the lowest
electrical energy requirements. Oil fired units are
next due to oil pumping and heating needs. Auxiliary power requirements for gas and oil boilers are
considerably less than coal fired units because ash
handling, coal handling, sorbent handling and
pollution control systems are not needed. A comparison can be approximated by listing the fan and
drives with their respective duties and the sizes of
each. For example, on a PC fired unit there are
forced draft (FD) and induced draft (ID) fans and
drives, primary air (PA) fan(s) and exhauster(s) and
drive(s) and pulverizer drive motor(s). It is possible
the primary air fan or exhauster drive and
pulverizer drive motor may be combined so there is
a single motor driving both devices. Normally,
there would be two or more pulverizers and PA or
exhauster fans per boiler unit. For the stoker fired
unit, there are also an FD and ID fan drive, and an
overfire air and ash reinjection system that likewise
may be combined as a single piece of equipment.
The pulverizer drive and primary air fan and
exhauster drive are relatively high duty or
horsepower (hp) consumers compared to the stoker
overfire air and ash reinjection system fan drive
together with the stoker drive motor. Annual
power costs, kilowatthours per year, is directly
related to average boiler duty. Sootblower motors
are fractional horsepower and generally are not
included in any power comparison. ACFB boilers
also have high electrical power requirements. The
fluidized bed is suspended on air that is provided by
a primary air fan. The solids reinjection device has
fluidizing air needs which are provided by blowers.
Limestone handling is another electrical user which
is unique to ACFB. Inert bed handling is also in this
category. ACFB boilers, however, unlike PC and
stoker boilers, may not require sulfur removal
equipment such as scrubbers. This must be
considered when evaluating power cost.
h. Maintenance costs. Gas fired boilers have the
lowest maintenance cost. Oil fired boiler installations are higher than gas fired systems due to oil
pumping needs, oil storage requirements and boiler
corrosion and external deposits on heat transfer
surfaces resulting from sulfur, sodium and
vanadium in the oil. ACFB boilers have higher
maintenance when compared to PC boilers. The
abrasive action of the solids circulating through the
combustor and solids separator causes wear. ACFB
systems are more complicated with more
components which add to the maintenance cost. As
more ACFB experience is gained, maintenance
costs can be expected to decrease as improvements
are made. Maintenance costs for a PC fired unit are
generally higher than that for a stoker fired boiler
due to the higher duty requirements of such items
as the pulverizers, primary air fans or exhausters,
electric motors, coal lines and greater number of
sootblowers. Maintenance costs are also a
reflection of the hours of operation and average
boiler duty.
i. Operating costs. These expenses include manpower, sorbent, and other costs incurred on a
continuing basis while the plant is in operation.
Manpower requirements for oil fired boilers are
somewhat higher than gas boilers, because of the
fuel storage and increased handling concerns associated with oil. Coal fired technologies require
considerably more manpower than either oil or gas.
Fuel handling, ash handling and pollution control
systems account for the majority of the increase in
operating costs. Even though stoker fired and PC
boilers are less complicated than ACFB boilers,
stoker and PC boilers, unlike ACFB boilers, must
include scrubbers. The evaluation of operating
costs among coal firing technologies is site specific
and must include all relevant factors.
3-7. Pulverizers (Mills).
a. Types. There are four basic types of pulverizers frequently used on industrial sized boilers. They
are commonly referred to by the type of grinding
elements, i.e., ball and tube, attrita, ball-and-race,
and ring-and-roll.
(1) The ball and tube type mill is commonly
used on boilers that use coal as the principle fuel.
They require more space and use more power input
than the other types, so they are at an economic
disadvantage unless only one mill is used.
(2) Attrita type mills are usually used on
boilers that use gas or oil as the primary fuel with
coal as a backup fuel. These mills are subject to
high maintenance due to the use of unwashed
(ROM) coal and foreign objects (rail, spikes, rebar,
wood) getting into the coal stream. This mill
combines the pulverizer and the exhauster in a
single package.
(3) The following information and
illustrations primarily pertain to the more frequently
used ball-and-race and ring-and-roll type mills.
3-11
TM 5-810-15
Figures 3-7 and 3-8 illustrate the two more
commonly used pulverizer types.
b. Capacity. Pulverizer capacity is a function of
coal type, based on a grindability index, moisture
content, and fineness of the product. At least two
pulverizers should be provided, and with one pulverizer off line for maintenance the remaining
pulverizers should be capable of supplying coal to
the boiler at the desired load with worst case coal.
Figures 3-9, 3-10 and 3-11 show the influence of
grindability and moisture content of coal on pulverizer operation.
has to be stabilized should be investigated in the
design stage so that suitable auxiliary fuel
provisions can be designed into the plant. If oil
ignitors are used, either compressed air or steam
atomizers are used. Pressure on mechanical atomization should not be considered due to safety
factors.
b. Cost. The cost of these ignitors and the labor
required for their installation plus the fuel system
required should be included in the LCCA. Ignitors
will be lit by high energy spark plug type lighters.
3-9. Burners and NOx control.
3-8. Coal burner ignitors.
a. Types. Natural gas or No. 2 fuel oil ignitors
are required for firing pulverized coal. These ignitors will be capable of preheating the boiler prior to
starting the pulverizer and firing coal. The ignitors
should be able to carry about 10 percent of
maximum continuous rating (MCR) and are also
used to stabilize the coal flame when the burner
load is less than approximately 40 to 50 percent or
other adverse fuel conditions such as high moisture.
The steam load at which the pulverized coal flame
3-12
a. Burner design. State-of-the-art burner design
calls for low excess air operation to improve the
boiler thermal efficiency (reduced exit gas temperature and dry gas loss) as well as to reduce NOx
emissions. Coal burners will be specifically designed for pulverized coal and compatible with the
gas or oil ignitors to be supplied and produced by
a qualified manufacturer. Note, in the case of gas,
oil and pulverized coal fired units, a flame safety
system is also required.
TM 5-810-15
b. Flame safety detectors.
(1) Ultra violet type detectors are used on
natural gas and some oil fuels, but will not be used
on pulverized coal boilers since the flame masks
most of the light rays of that type.
(2) Infrared type detectors are used on
pulverized coal boilers to detect coal fire.
(3) For reliability, with a suitable life span,
solid state type controls should be used for the
detectors.
c. NOx control options and considerations. Many
options are available to reduce NOx emissions as
mandated by recent regulations. The nitrogen
content of fuels, especially oil and even coal,
should be specified in the fuel purchase contract.
Restrictions on the nitrogen content will limit fuel
flexibility. A careful analysis of proposed NOx
reduction technologies must be performed to account for any required changes to auxiliary equipment and to identify future increases in O&M costs.
Important questions that should be answered and
be a part of the evaluation include the performance
of NOx reduction over the entire load range,
performance during backup fuel firing, and the
performance over the lifetime of the unit.
(1) Harmful effects of NOx on the environment include contributions to acid rain, to the
destruction of the ozone layer, to global warming,
and to smog.
(2) Components of NOx include nitric oxide
(NO), nitrogen dioxide (NO2), and nitrous oxide
(N2O) as a residual pollutant of some NOx control
processes. Emissions from combustion processes
are 90 to 95% NO with the balance being NO2.
(3) Title IV of the Clean Air Act
Amendments of 1990 (CAAA) requires application
of low NOx, burner (LNB) technology. Title I of
the CAAA has more impact in ozone nonattainment
areas which are near the nation*s largest cities.
State implementation plans may place even more
strict limits on NOx Flexibility may be allowed by
having provisions for averaging NOx emissions
over the system.
(4) NOx is formed as a result of oxidizing
various sources of nitrogen. Fuel NOx is formed
when the nitrogen contained in the fuel is oxidized.
3-13
TM 5-810-15
Thermal NOx results from the oxidation of nitrogen
in the combustion air at high temperatures. At very
low levels of NOx prompt NOx is formed when
intermediate hydrocarbons present in the flames
oxidize.
(5) NOx control techniques can be defined as
either combustion modifications or post combustion reduction. The goals of combustion modification include redistribution of air and fuel to slow
mixing, reduction of O2 in NOx formation zones,
and reduction of the amount of fuel burned at peak
flame temperatures.
3-14
(6) Combustion modifications primarily deal
with the control of fuel and air. Vertical staging
includes overfire air (OFA) ports above the main
combustion zone. Horizontal staging use registers
or other devices to introduce air at different points
along the flame. Fuel staging establishes a fuel rich
zone above an air lean main combustion zone.
Burner out of service (BOOS) techniques direct
fuel to lower burner levels, while operating upper
burners with air only. Flue gas recirculation (FGR)
reduces O2 available to react with nitrogen and
cools the flame. In addition to low NOx burners
TM 5-810-15
CHAPTER 7
MECHANICAL AUXILIARY EQUIPMENT
7-1. General.
This chapter addresses the criteria for the major
steam plant auxiliary equipment.
7-2. Closed
(CFHE).
feedwater
heat
exchangers
a. Applications. CFHE may be used to raise
feedwater temperature to the plant economizer and
thus maintain the exit flue gas temperature above
the acid dew point during low load operation. This
application is possible for plant design in all size
ranges. Other methods for keeping the exit flue gas
temperature above the acid dew point are
bypassing flue gas around the economizer or
bypassing a portion of feedwater around the economizer which needs to be avoided. Bypassing the
feedwater around the economizer at low load operation creates a potential for steam formation in the
economizer. The CFHE is the most positive
approach to maintaining the exist flue gas temperature. An evaluation will be made to determine the
economic practicality of each method.
b. CFHE design. Each CFHE will be a U-tube
type heater to minimize stresses caused by thermal
expansion. Tube material selection is dependent on
the quality of the water. Tubes of stainless steel
construction will minimize the possibility of
corrosion and erosion. High quality water will
allow the use of 90/10 and 70/30 copper nickel
(CuNi) material tubing.
c. CFHE design criteria. Data listed in table 7-1
are necessary to size CFHE.
Table 7-1. Closed Feedwater Heat Exchanger Design
Parameters.
Parameter
Engineering Units
Feedwater flow
Feedwater inlet temperature
Feedwater outlet temperature
Maximum feedwater velocity
Maximum allowable tube side pressure
drop
Maximum tube side operating pressure
Maximum shell side operating pressure
pph
degrees F
degrees F
fps
psi
psig
psig
Minimum recommended feedwater temperatures to
the economizer are shown in figure 7-1. Minimum
feedwater velocities are shown in figure 7-2.
7-3. Steam deaerators.
a. General. The steam deaerator (DA) heats
boiler feedwater to improve plant efficiency and
lowers dissolved oxygen and gasses that are corrosive to internal metal surfaces of the boiler. The
standards of the Heat Exchange Institute (HEI),
1992, Fifth Edition, state that a DA should be
guaranteed to remove all dissolved oxygen in
excess of 0.005 cc/i.
b. Deaerator types. There are several types of
steam DA with three acceptable types being:
spray/tray type, atomizer or scrubber spray type
and recycle type. DA heater should be counterflow
design. Although some tray and recycle type DA*s
have a higher first cost, they will operate properly
under rapid load changes and only require a 10 to
30 degrees F rise across the DA (inlet water
temperature 10 to 30 degrees F lower than the DA
outlet water temperature). Spray or atomizing type
DA*s can be used when steam loads are steady and
the temperature rise across the DA is 30 to 50
degrees F or greater. Because of this performance
limitation, tray or recycle type DA*s will be used
unless there is a steady steam load and the
temperature rise in the DA is 50 degrees F or
greater. If the latter conditions exist, the DA
selection will be decided by a LCCA.
c. Deaerator design criteria. Deaerating heaters
and storage tanks will comply with the ASME
Unfired Pressure Vessel Code, ASME Power Test
Code for Deaerators, Heat Exchange Institute,
American National Standards Institute, and National Association of Corrosion Engineers Recommendations. One steam plant DA can be sized for
multiple boiler units. At full load conditions, the
water from the DA will have a temperature
sufficiently high to prevent acid dew point corrosion of the economizer. In no case will the temperature rise in the DA be less than 20 degrees F or
the minimum storage capacity at normal operating
level be less than 10 minutes at the DA*s maximum
continuous load rating or less than 12 minutes full.
Information contained in table 7-2 will be specified
after a heat balance around the DA has been
determined at full load conditions.
7-1
TM 5-810-15
Table 7-2. Specified Deaerator Information.
Item
Engineering Units
Maximum plant capacity
Maximum DA outlet capacity
Make-up water temperature
Condensate temperature
Make-up water flow
Condensate flow
Steam temperature to DA
Steam pressure to DA prior to control
valve
DA design pressure
DA outlet water temperature
DA outlet water flow
pph
pph
degrees F
degrees F
pph
pph
degrees F
psig
psig
degrees F
pph
7-4. Boiler feed pumps.
a. General. Boiler feed pumps convey water
from the DA to the boiler.
b. Design requirements. Boiler feed pumps will
comply with the latest revisions of Hydraulics
Institute (HI) and ANSI. A minimum of one pump
per boiler and one backup pump will be provided
for all cases. The ASME Boiler and Pressure
Vessel Code requires that coal fired boiler plants in
this size range be provided with at least two means
of feeding water. For stoker fired boilers, one
source will supply sufficient water to prevent boiler
damage during an interruption. A steam turbine
driven pump is one method that is frequently used
to meet this requirement. Multiple pumps permit
backup capacity for individual pump failures or
scheduled maintenance and increase efficiency of
pump operations at reduced loads. Multiple pumps
are usually more cost effective for boilers subjected
to large daily load swings. This arrangement allows
the pumps to operate in a more efficient range and
gives the system more flexibility. The use of
multiple pumps will provide for between 50 and
100 percent of additional capacity beyond the
expected operating loads.
c. Steam turbine drives vs electric motor drives.
Steam turbine drives provide a more thermally
efficient system, but in this size range they can be
less economical on a LOCA than electric motor
drives. However, as noted above, the ASME Boiler
and Pressure Vessel Code requires that both steam
turbine and motor drives be used in stoker fired
bailer plants with capacities of 35,000 pph and
above. Steam turbine drives will not be used
exclusively. An electric motor drive makes it easier
to bring a boiler on line from a cold start.
d. Boiler feed pump sizing. Boiler feed pumps
will be sized to deliver the desired flow and
pressure to the boilers from the DA. A 10 percent
flow margin for wear allowance will be included
when sizing the pump. These conditions are determined by first defining the items listed in table 7-3.
Table 7-3. Boiler Feed Pumps Capacity Criteria.
Item
Engineering Units
Boiler steam outlet pressure
psig
Boiler water side pressure losses
psi
Water temperature entering pump
degrees F
Piping losses
psi
DA operating pressure
psig
Pump elevation relative to boiler and DA ft
Net positive suction head required
ft
(NPSHR)
(1) Calculation of net positive suction head
available (NPSHA). Determining the NPSHA is an
important design consideration for boiler feed
pumps because they take water from the DA at
saturated conditions. To prevent cavitation of a
pump operating at elevated temperatures, the DA
is elevated to increase the static pressure at the
pump suction and overcome the vapor pressure.
The boiler feed pump vapor pressure is equal to the
DA operating pressure and cancel out each other.
Thus, boiler feed pump NPSHA is the head of
water from the DA to the pump inlet minus the
pipe friction loss. A safety margin of at least one
foot of head will be subtracted from the calculated
NPSHA to obtain the net positive suction head
required (NPSHR).
(2) Discharge head calculation. The boiler
feed pump discharge head will be designed to
overcome the boiler drum pressure, valve and
piping losses within the boiler and external to the
boiler as well as the head of the water column.
e. Pump construction. The boiler feed pumps will
be constructed to provide continuous operation for
the expected plant life. Pump manufacturers should
be consulted regarding specific features of
construction for a particular application. In general,
lower pressures and flows could use vertical in-line
pumps with stainless steel shaft, impellers, and
impeller casings. Suction and discharge chambers
on vertical pumps will be cast iron. For higher
pressure and flow applications casings will be 11 to
13 percent chrome steel, split on the horizontal
centerline with suction nozzles, discharge nozzles
and feet on the lower half of the casing so the top
half of the casings can be removed without
7-3
TM 5-810-15
disturbing the main piping. These applications will
also include shafts constructed of stainless steel,
containing not less than 11 percent chrome. The
impellers will be of the closed type, cast in one
piece. All internal parts of the pumps including
impellers, sleeves and wearing rings, will be
constructed of stainless steel containing not less
than 11 percent chrome.
7-5. Condensate pumps.
a. General. The condensate pumps convey condensate from condensate return storage tank to the
DA.
b. Design requirements. A minimum of two condensate pumps will be used, each sized for at least
two thirds of the maximum steam plant demand.
This configuration will provide backup capacity for
individual pump failures or scheduled maintenance
and will increase pump operation efficiency at
reduced loads. Steam turbine driven pumps may be
more economical than electric motor driven pumps.
However, one electric motor driven pump
facilitates cold start-up of the boiler plant. A LCCA
will be made to determine the most practical
combination of condensate pumps.
c. Condensate pump sizing. The condensate
pump discharge head needs to be designed to
overcome the water static head to the DA, the
piping losses and the DA operating pressure. A 10
percent flow margin for wear allowance will be
included when sizing the pump. The condensate
pump discharge head and suction head available
will be determined when the operating conditions
are defined, an arrangement of the equipment has
been made, and a pipe size and routing has been
made.
d. Pump construction. Pumps will be constructed
so they will provide continuous operation for the
expected plant life. Pump manufacturers should be
consulted regarding specific features of
construction for a particular application. The pump
impellers will be split ring key type. Bearings will
be of the water lubricated sleeve type. The
baseplate, outer barrel, inner column and discharge
head will be carbon steel. The impeller will be
bronze and the pump bearings graphalloy. The
stage bowl will be cast iron. The shaft, shaft sleeves
and wearing rings will be 11 to 13 percent chrome
stainless steel. When the pump design conditions
do not require a vertical can type pump as
described above, the pump may be centrifugal,
horizontal end suction, top discharge type as described below. The pump impellers will be totally
open type, screw mounted directly to the shaft with
0-ring seal and constructed of ductile iron.
Impellers will be dynamically balanced to the
7-4
maximum rated speed. The pump construction will
include antifriction bearings that operate in an oil
bath. Pump and bearing frame and housing will be
constructed of cast iron. Casing will be constructed
of ductile iron. Minimum casing thickness will be ½
inch with an additional 1/8 inch corrosion
allowance. The shaft, shaft sleeves and wearing
rings will be 316 stainless steel.
e. Turbine drives. The turbine drives will be
sized to match the runout hp of the pump. Turbine
drives will be horizontal split case construction.
The steam chest will be case iron or cast steel. The
rotor shaft will be annealed carbon steel and the
rotor disc a high strength alloy steel.
7-6. Air compressors.
a. Applications. Two compressor applications
are used in a steam plant: plant air and instrument
air. Plant air is the dry air used to atomize fuel oil,
blow soot deposits from the boiler furnace and heat
recovery equipment, run plant pneumatic tools, and
perform other general plant functions. Instrument
air is oil free, dry air supplied to instruments and
pneumatic controls control valves and control
drives. Instrument air is also used to clean fly ash
baghouse filter bags.
b. Compressor types. Compressors are available
in two types. The first type is positive displacement, such as the reciprocating piston compressor.
The second type is dynamic, such as the centrifugal
compressor. Each type can be furnished with single
stage or multiple stage design. Reciprocal and
centrifugal compressors are the industry standard
for compressors used in boiler plants. Centrifugal
compressors are usually considered for selection
when the compressed air demand is uniform and is
equal to or above 400 standard cubic feet per
minute (scfm). Otherwise reciprocating compressors are usually used.
c. Instrument air compressor sizing criteria.
(1) Required volume of air. The required
volume of air needed is found by adding all simultaneous air usages together. With instrument air, the
highest usages generally occur during boiler start
up when lighters are inserted or when fly ash
baghouse filter bags are being cleaned.
(2) Outlet pressure. The compressor outlet
pressure will be sufficient to supply air at the
required pressure, after line losses, to the device
requiring the highest pressure in the instrument air
system. Pressure regulators will limit the pressure
to devices operating at lower pressures.
d. Plant air compressor sizing criteria.
(1) Required volume of air. The required
volume of air needed is found by adding all simultaneous air usages together. One of the highest
TM 5-810-15
segregation. Approximately 25 to 50 percent of the
coal is burned in suspension by this method. This
spreader feed has a larger grate heat release rate
than the cross feed type; requires a smaller furnace
envelope; and has a quicker response time for load
changes. This type of fuel feed must have a uniform
air flow through the grates due to the large amount
of suspension burning. For best results, the fuel fed
to this type of unit should be properly sized. Refer
to Figure 3-12 illustrating coal size.
d. Stoker selection considerations. Table 3-6
provides a summary of factors to be considered
when selecting a stoker for a boiler within the
range of 20,000 to 250,000 pph of steam. Prior to
submitting a set of specifications to the boiler or
stoker manufacturers, the type of coal that is to be
burned must be known. Selection of the design coal
is required so that these manufacturers are able to
guarantee their equipment performance. When the
coal is not known, or when the possibility exists
that many different types of coals will be burned
over the life of the stoker, the selection emphasis
3-18
should lean toward spreader stokers. This type of
stoker is more flexible in its capability to efficiently
burn a wider range of coals.
3-13.
Fly ash reinjection for coal firing.
a. General. A fly ash reinjection system for coal
fired boilers is used to return coarse, carbon
bearing particulate back into the furnace for further
combustion. This is only economically justified in
stoker fired boilers with steam capacities over
70,000 pph. Fly ash reinjection from the boiler,
economizer, air heater and dust collector hoppers
can improve boiler thermal efficiency by 3 to 5
percent. However, fly ash recirculation within the
boiler is significantly increased.
b. Equipment sizing. Tube erosion and other
maintenance costs in addition to requiring an
increase in the capability of the air pollution control
equipment are to be expected and must be taken
into consideration when sizing the air pollution
control equipment.
TM 5-810-15
Table 3-6. Stoker Selection Factors.
Vibrating
Grate Stoker
Crossfeed
Traveling
Grate Stoker
Applicable
Boiler Size, pph
100,000150,000
Spreader
Feed
20,000150,000
Maximum Grate
Heat Release,
Btu/ft2-hr
400,000
600,000
450,000
750,000
450,000
Maximum Furnace
Heat Release,
Btu/ft3-hr
25,000
25,000
25,000
25,000
25,000
0-10
0-10
2-15
0-10
2-15
30-40
40-50
5-10
12,500
30-40
40-50
5-10
30-45
40-55
6
11,000
30-40
40-50
5-15
30-45
40-55
6
11,000
5
Ash Softening
Temp, F (Reducing
Stimulus)
2,300
2,300
2,200
2,300
1,900
Coal Size
1”x0”
1-1/4"x3/4”
1”x0”
1-1/4"x3/4”
1”x0”
40%
50%
60%
40%
60%
3:1
3:1
3:1
3:1
3:1
1.0-1.5
1.4-10
0.6-1.5
1.4-10
0.6-1.5
Coal Parameters
Moisture %
Volatile
Matter %
Fixed Carbon %
Ash %
Btu/lb (Mm)
Free Swelling
Index (Max)
Max Fines thru
1/4” Screen Max
1
Stoker Turndown
(Stable Fire)
Particulate
Emissions
106 Btu
Crossfeed
Traveling
Chain Grate
Stoker
Crossfeed
100,000250,000
Spreader
Feed
50,000250,000
20,00075,000
1
To achieve this turndown rate, reference should be considered in the construction of the boiler for either membrane or welded
wall construction or tube and tile type construction. Note some loss in boiler thermal efficiency will occur at lower loads.
Note: Coal sizing and quality have a direct influence on the efficiency of stoker fire boilers. These selection factors do not apply
to those western fuels which have high moisture 25 percent or more content and have a lignite type ash characteristic.
3-14.
Overfire air.
a. General. Overfire air is the ambient air supplied by either the FD fan or a separate fan that
may also be used for fly ash reinjection and is used
on all types of stoker fired boilers. The purpose is
to aid combustion and to insure the coal particles
are as completely burned as possible.
b. Port location. Overfire air ports are located on
either or both the front and rear furnace walls.
3-15. Atmospheric circulating fluidized bed
(ACFB) boiler components.
a. Lower combustor. Fuel is fed into the refractory lined lower combustor section where fluidizing
air nozzles on the floor of the combustor introduce
air which controls the velocity of solids through the
combustor. Ash must be removed from the bottom
of the combustor to control solids inventory, bed
quality, and prevent agglomeration of solids.
Arrangement of tuyeres or air distribution devices
must direct ash flow toward bed drains. Figure 313 shows the major ACFB boiler components.
b. Upper combustor and transition zone. The
upper combustor is waterwall design. Solids and
gases leave the combustor through a transition
section which must account for three dimensional
thermal expansion between the major boiler components.
c. Solids separator. The transition section with
expansion joint connects the combustor to a solids
separator. Two different separator designs include
3-19
TM 5-810-15
mechanical cyclone type and U beam. Cyclone
separators are more common. Cyclones can be
either water or steam cooled to reduce refractory
thickness.
d. Solids reinjection device. Solids that have
been removed in the separator are reintroduced into
the combustor for additional carbon burnout and
increased combustion efficiency. This recirculating
loop is sometimes referred to as the “thermal fly
wheel.” Solids reinjection devices consist of a
refractory lined pipe with fluidizing air nozzles.
This device is frequently called either a J-valve, Lvalve or loop seal. Sorbent for sulfur capture enters
the boiler either through the reinjection device or
through separate feeders into the lower combustor
section.
e. External heat exchanger (EHE). One design
includes the use of an EHE to recover heat from
recycled solids. Most manufacturers do not use an
EHE due to problems encountered.
3-16.
Boiler components.
a. Superheaters. Superheaters receive saturated
steam from the boiler steam drum after having gone
through the steam and water separating
components within the steam drum. This steam
should have a purity of 1 part per million (ppm) or
better depending on the quality of the boiler water.
The superheater is sized so as to add sufficient heat
to the steam to obtain the desired final steam
temperature. For units with a final steam
3-20
temperature of no more than 700 degrees F, boiler
manufacturers will normally use a single section
style superheater. Superheaters on coal fired units
are of the pendant type and hence are not drainable.
Further, superheaters are either exposed to the
radiation of the fire in the furnace, or are located
above a "nose" usually on the rear furnace wall that
provides for a radiant-convection superheater
surface. The design and construction of
superheaters is in accordance with the ASME
Boiler and Pressure Vessel Code that applies to the
boiler. Normally, superheaters for boilers covered
by this manual, will have tubes made of carbon
steel, either SA-210 or SA-192, whereas the
saturated or water carrying tubes of the boiler and
furnace will be made of carbon steel type SA-178.
(1) For proper operation, particularly of pendant, nondrainable type superheaters, fluid pressure
drop is needed to provide proper distribution of the
steam through the tubes. It is desirable to locate the
steam outlet connection at the center of the
superheater outlet header for proper steam
distribution, but end outlets are acceptable if proper
design consideration is given to the flow
distribution imbalances caused by the header configuration.
(2) A factor to be considered about superheater pressure drop is the power cost required for
the boiler feed pump. The higher the pressure drop,
the more pump power required.
TM 5-810-15
Table 7-8. Blowdown Tank Pressure.
Maximum Allowable Boiler
Pressure, psig
Blowdown Tank Design
Pressure, psig
50
100
200
300
500
750
1000
1500
2250
2500
25
50
70
90
125
165
200
275
325
400
b. Design. Heat is recovered in a blowdown heat
recovery system by passing the blowdown water
from the blowdown tank through a heat exchanger
to recover the sensible heat of the water and
transferring blowdown tank steam to the DA. The
heat exchanger will be sized to reduce the temperature of the blowdown main to 20 degrees F above
the inlet temperature of the fluid being heated,
typically feedwater heating, makeup water heating,
building heating, oil heating or process steam
generation. The blowdown tank for a heat recovery
system will be smaller to allow the blowdown drain
water to be hotter for an effective heat recovery
system. If flash steam is used in the DA, the
blowdown tank will be designed to minimize
carryover. A normal blowdown system consisting
of a large blowdown tank venting to atmosphere
and draining directly to waste may have to be
available to allow maintenance on the heat recovery
equipment during operation. There are several
package blowdown heat recovery systems available
consisting of blowdown tanks, heat exchangers,
flow control valves, thermostatic control valves,
sample coolers and high level float switches.
7-10.
Steam coil air heater.
a. Application. The steam coil air heater preheats
the combustion air before it enters the main air
heater. The heat dries the air and reduces corrosion
of the air heater tube metals.
b. Design. The installation will be designed for
reasonable air velocities with pressure loss not to
exceed one inch of water. The heating coils will be
designed in multiple elements to maintain average
cold and metal temperatures of the air heater
surfaces above 180 degrees F at all loads up to 15
percent above full rated load. The uncorrected air
heater gas outlet temperature should be used to
determine the average cold end metal temperature.
A typical steam coil would have seamless type 321
stainless steel tubes, outer tubes 1 inch outside
diameter and 0.049-inch minimum wall thickness
and inner tubes 5/8-inch outside diameter and
0.022-inch minimum wall thickness. The supply and
return connections are to be on the same end of the
coil. Tubes will be pitched to the drain. The coil
should be removable in a manner that does not
disturb connecting ends of breeching. The coil
outer casing is typically 10 gauge steel welded into
an airtight structure. The core header plate will be
gasket sealed to the casing.
7-11.
Steam coil drain tank.
a. Application. The steam coil drain tank will
collect the condensate from the steam coil air
heater for transfer to the DA.
b. Design. The steam coil drain system must be
sized large enough to drain the maximum expected
steam flow rate to the air heater and to maintain a
reasonable condensate level allowing proper
operation of the steam coil drip return pumps (if
included). Another consideration is the possibility
of freezing. The steam coil tank should be located
indoors, if possible, and sized small enough that
outdoor drain piping is not allowed to fill with
condensate. The steam coil drain tank is normally
equipped with a level controller, gauge glass and
high level alarm. The steam coil drain tank will be
designed and constructed in accordance with the
ASME Boiler and Pressure Vessel Code, Section
VIII.
7-12.
Fans.
a. Applications. Boiler furnaces are either pressurized or have balanced draft for combustion. Gas
and oil fired boilers are normally of the pressurized
furnace design. Modern coal fired boilers have
balanced draft type furnaces. Balanced draft type
boilers use FD fans to supply combustion air to the
furnace and ID fans exhaust the products of
combustion or flue gas. The furnace is kept at a
slightly negative pressure ranging from 0.1 to 0.25inches w.g., by the ID fan which is located
downstream of the particulate removal equipment.
b. Forced draft fans. FD fans operate with reasonably clean, cool or warm air and will be
designed for quietness and efficiency. This source
of combustion air is frequently taken from within
the steam plant to promote ventilating and to take
advantage of the higher ambient temperatures.
Inlets for the fans will have silencers with screens
to attenuate entrance noises and to keep birds and
other objects from entering the system. The static
pressure of the FD fan will be calculated for the
pressure drop through the inlet air duct, steam coil
air heater, air heater (if used), air metering devices,
dampers or vanes, air ducts, static fuel bed or
7-11
TM 5-810-15
construction of the coolers will allow the
circulating water or dirtier water to pass through
the tubes allowing more practical cleaning. The
cooler tubing and tube sheet material selection will
be based on water quality. Materials can be
admiralty, copper nickel, or for corrosive
applications stainless steel. The coolers will be the
straight tube type with fixed tubesheet, removable
channel construction. The shell will be carbon steel
and the channel heads will be fabricated steel. The
shell will have 150 pound raised face flanged or
3000 pound screwed connections. The channel will
have 150 pound flat faced flanged or 3000 pound
screwed connections. The coolers will be
manufactured with shell, channel vent and drain
connection.
mendations of the boiler manufacturer. Depending
on the boiler and down period, such steam parts
filled with treated water or a nitrogen purge are the
economizer, water walls, superheater, reheater,
feedwater heater (tube side-water; shell sidenitrogen) and drum. In some cases freezing may be
a problem and treated water can be replaced with
nitrogen. The amount of nitrogen required, for
boiler purging will be given by the boiler
manufacturer or can be calculated from the volume
of the steam parts. The nitrogen system is a low
pressure system. However, the nitrogen is stored in
high pressure cylinder bottles and the piping will be
connected to a high pressure boiler. A pressure
regulator and high pressure valving will be
required.
7-16.
7-18.
Ignitor fuel oil pumps.
a. Design. Ignitor fuel oil pumps will be rotary
screw type pumps. Two pumps will be provided,
each rated at 100 percent capacity, with one pump
used for backup service. A fuel oil unloading pump
will be applied if required and will have the same
characteristics as the ignitor fuel oil pumps. No. 2
fuel oil is more commonly used for ignitor systems
and will be assumed herein. The pumps will be able
to pump oil with a viscosity of 200 Saybolt
Seconds Universal (SSU) against the design discharge pressure at the design capacity. Fuel oil
viscosity will be expected to vary between 33 and
200 SSU. Pump motors will be totally enclosed and
explosionproof.
b. Types. Unlike a centrifugal pump, a rotary
screw pump is a positive displacement pump, that
will displace its capacity to the point of failure
regardless of the resisting pressure. A fuel oil
recirculation system will be designed to allow the
pump to recirculate the fuel oil as the ignitor fuel
oil is modulated according to demand. In a fuel oil
loading system the fuel oil is not modulated and a
recirculation system is not necessary. In sizing the
fuel oil pump, the pressure to overcome will be
calculated from piping losses and elevation change
to get the required pump discharge pressure. The
ignitor fuel oil pump capacity is determined from
maximum fuel oil demand plus 20 percent for pump
wear and safety factor.
7-17.
Nitrogen system.
a. Application. The nitrogen system is used to
purge the boiler for protection from corrosion
between hydrostatic test and initial operation and
after chemical cleaning periods and outages.
b. Design. The boiler steam parts are filled with
treated water until overflowing and then capped off
with 5 psig of nitrogen according to the recom-
Carbon dioxide (CO2) system.
a. Application. A carbon dioxide system in a
boiler plant is most commonly used to extinguish
fires in coal bunkers. A CO2 system can also be
used to extinguish electrical hazards, such as
transformers, oil switches and circuit breakers, and
rotating equipment. CO2 extinguishes fire by
reducing the concentration of oxygen and the
gaseous phase of the fuel in the air to the point
where combustion stops.
b. Design. The CO2 systems are classified as
automatic, manual or automatic-manual. Fires or
conditions likely to produce fires may be detected
by visual (human senses) or by automatic means. In
the case of coal bunkers, methane detectors can be
used to alarm a fire or actuate the CO2 system and
an alarm. CO2 can be stored in cylinder bottles and
pipes through a pressure regulated system to
discharge nozzles at the area of combustion. The
amount of CO2 in the system will be at least
sufficient for the largest single hazard protected or
group of hazards to be protected simultaneously.
The CO2 system will be designed and erected in
accordance with NFPA 12 of the National Fire
Codes.
7-19.
Chemical feed pumps.
a. Application. Chemical feed pumps are small
capacity pumps used to inject chemicals into the
condensate, feedwater and steam system at a
controlled rate. Most chemical feed pumps are
specified and purchased as a chemical feed unit that
includes a pump, tank, mixer and piping. Typical
chemical systems used in a boiler plant are
hydrazine, morpholine, phosphate and a metal
surface passivating agent.
b. Design. The pump selection will have the
capacity and discharge head to inject the chemical
into the system. Pumps are rated by capacity in
7-15
TM 5-810-15
gallons per hour (gph), discharge head in psig and
piston strokes per minute. The chemical feed
pumps will be positive displacement metering type.
The pumps will have hydraulically balanced
diaphragms, mechanically actuated air venting; all
rotating parts to run in an oil bath with roller
bearings; double ball check valves with Teflon 0ring seats on both suction and discharge. The
pumps will have micrometer capacity adjustment
from 0—100 percent while the pump is running and
to have metering accuracy within plus or minus 1
percent.
c. Chemical feed unit. Chemical feed tanks for
the mentioned chemicals will be 16 gage type 304
stainless steel with agitator, gage glass and low
level alarm system. Piping will be stainless steel and
valves will have Teflon seats. The chemical feed
system will include a back pressure valve to insure
accurate and consistent metering at all flows and
will include a safety valve.
7-20.
Laboratory.
a. General. A laboratory is needed in every boiler
plate to assist in analyzing chemical treatment and
in early detection of problems. Samples of water
and steam are taken from various systems and parts
of systems to evaluate the system*s condition.
b. Sample coolers. Sample coolers are required
to condense steam and cool water to be handled.
Sample coolers are heat exchangers that will be
sized to maintain the temperature at 77 degrees F.
7-16
Coolers for individual samples are either doubletube helical coils with cooling water counterflow
cooling or submerged helical coils properly baffled
to effect counterflow cooling. If a coil type of
exchanger or a coil and condenser type of exchanger are used, they will meet the intention of
ASTM D 1192. If a multicircuit heat exchanger is
used, it will meet the requirements of Section VIII,
ASME Boiler and Pressure Vessel Code.
7-21.
Sump pumps.
a. Application. Sump pumps are required in
several applications at a boiler plant. Sump pumps
primarily are used for storm water removal but also
are used for ash hopper water overflow or any
condition requiring removal of water from a sump.
b. Design. The pump will be sized for one and
one-half times the maximum amount of expected
drain rate. Two 100 percent capacity pumps will be
used to supply full backup if overflow is dangerous.
The suction line between the suction vessel and the
pump must be properly designed to prevent air
pockets and cavitation. Sufficient NPSH must be
available at the pump suction flange.
c. Construction. The pumps will be motor
driven, vertical shaft configuration with bottom
suction and open impeller. The pump will include a
flanged column, discharge pipe flanged over
soleplate, bearing lubrication piping and connections on the soleplate to support the pump and
motor.
TM 5-810-15
surface replaced the refractory setting. Casing,
frequently 10 gage, was used to seal the refractory
placed adjacent to the furnace tubes and backed
with block type insulation. This construction is still
in use on some small boilers applicable to this
manual. However; the products of combustion,
particularly with coal fired boilers, will cause
corrosion to take place and air leaks will develop
when the corrosive (mainly sulfur) substances come
in contact with the relatively cool casing. The first
signs of leakage will be the gases condensing and
dripping through the casing. This condition led the
manufacturers to place the casing behind the
refractory and then insulating over the casing and
protecting the insulation with galvanized or
aluminum lagging. However, the latest and to date
best design is the use of welded wall construction.
Welded-wall construction positively contains
internal flue gas pressure by seal welding metal
plates between the tubes. Insulating materials cover
the outside of the welded-wall tubes. Lagging is
then placed over the insulation.
(2) The advantage of the welded wall
construction currently being used by all major
boiler manufacturers is that it virtually eliminates
the flue gas corrosion that has taken place on the
boiler casing. Another advantage is that it reduces
air infiltration which in turn reduces exit gas
temperature and fuel costs as well as the maintenance costs that were involved in repair of the
refractory and insulation that previously existed.
The design of boiler settings will include several
considerations. High temperature air and corrosive
gases will be safely contained. Air leakage will be
held to a minimum. Heat loss is reduced to an
acceptable level. Differential expansion of the component parts will be provided. The surface temperature should be such that it would not be a source
of hazard or discomfort to operating personnel. If
located outdoors, should be weatherproofed. The
probability of injury or plant damage in the event of
an explosion will be reduced. The use of welded
wall construction and its inherent strength is
probably the most imperative reason for the current
design of boiler settings.
g. Flue and ducts. Flues and ducts will be
designed to operate at the pressure and temperature to which they are subjected. As a general rule,
the following velocities will be used in arriving at
the cross-sectional flow area of boiler flues and
ducts. Cold air ducts—2000 to 2500 fpm. Hot air
ducts—3000 to 3500 fpm. Gas flues upstream of
particulate collection equipment—2,500 to 3,000.
Gas flues—3500 to 4000 fpm. It should be noted
that velocities can be higher at elevated temperatures because the air or gas is less dense and
3-24
therefore has less impact energy. Directional or
straightening vanes should be used at bends in
ductwork to minimize turbulence or draft loss.
h. Desuperheaters. Normally on boilers with an
outlet superheat temperature of no more than 750
degrees F, desuperheaters will not be used. However, if the steam is used for a process at a lower
pressure and the temperature may be harmful or
unwanted, a desuperheater can be installed in the
steam line to control the desired temperature. Water for this device will normally be obtained from
the boiler feed pump or a separate pump. The
source of the water used by the desuperheater will
be such as deaerating heater and will be of the same
quality as used in the boiler. If a desuperheater is
used and the discharge of the device is into the
superheater, the water and entrained impurities will
be sprayed into the superheater tubes.
i. Fan blades and applications. Table 3-7 provides a summary of available fan blade types and
their respective applications. Individual fan types
are more fully described in paragraph 7-12 of this
manual. Items that must be identified for the design
of a particular fan application include: anticipated
flow of air or combustion gas (pph), temperature of
air or gas (degrees F), density of air or gas (pounds
per cubic foot, lb/ft3), fan inlet pressure (inches
water gauge, in. wg), fan outlet pressure (in. wg),
and fan curves of applicable fan types.
Table 3-7. Fan Blades and Applications.
Fan Blade Type
Application
Backware Inclined
Hot Primary Air (HPA)
Cold Primary Air (CPA)
FD, ID, CPA, OFA, BF
FD, OFA, ID, BF
HPA, OFA, ID, FTB
Pulverizer Exhauster
CPA, ID
Backward Curved
Hollow Air Foil
Radial
Open Radial
Radial Tip
FD - Forced Draft.
ID - Induced Draft.
HPA - Hot Primary Air.
CPA - Cold Primary Air.
OFA - Overfire Air.
BF - Booster Fan.
FTB - Fly Ash Transport.
j. Fan inlet. The following guidelines apply to
the fan inlet design.
(1) Intake areas will be at least 20 percent
greater than the fan wheel discharge areas.
(2) Fans positioned next to each other will
be separated by at least six fan diameters and a
separation baffle.
TM 5-810-15
(3) Fans will have turning vanes or inlet
boxes, or four to five diameters of straight duct at
the inlet. The FD, PA, or Overfire Air (OFA) fan
inlets located too close to building walls will have
splitters.
(4) Where the duct arrangement imparts a
swirl to the inlet of the air or gas, the swirl will be
in the same direction as the fan rotation.
(5) All fans will use inlet bells to insure a
smooth air or gas flow at the fan inlet.
k. Fan outlet. For a minimum pressure drop,
there will be three to six diameters of straight duct
at the fan outlet.
3-17.
Boiler water circulation and chemical
treatment.
a. Water circulation. A description of the internal or water/steam-circulation features of watertube boilers is listed below:
(1) The limits of the capability of a boiler is
determined by water circulation and the feedwater
and boiler water treatment. Boilers that do not
circulate properly will rupture tubes in a very short
period of time when operated at or near rated load.
Such items as superheat and tube metal
temperatures as well as fire side design
considerations, physical limits of firing equipment
and air and gas fan and their physical limits are not
being overlooked.
(2) The basic design of boilers and the size
pressure and temperature range of this manual are
at the lower end of the technology scale.
(3) The American Boilers Manufacturers
Association has set certain standards for boiler
water limits. Table 3-8 shows the allowable
concentrations for boiler water. These conditions
are normally stated in proposals submitted by those
manufacturers. They should be considered
minimums for feedwater and boiler water
treatment. All reputable feedwater treatment
consultants or vendors will be able to meet and
improve on the conditions required for the
operating conditions of boilers covered by this
manual.
Table 3-8. Boiler Water Concentrations.
Operating
Pressure
psig
Total
Solids
ppm
Total
Alkalinity
ppm
Suspended
Solids
ppm
0-300
3500
700
300
301-450
3000
600
250
451-600
2500
500
150
601-750
2000
400
100
751-900
1500
300
60
901-1000
1250
250
40
American Boiler Manufacturers Association
Stipulation in Standard Guarantees on Steam Purity
(4) Boilers should not be operated at capacities or pressure and temperature conditions not
anticipated by the manufacturer.
(5) As previously stated, boilers with superheaters are guaranteed to meet a 1 ppm steam
purity condition leaving the steam drum. Boilers
without superheaters can be guaranteed to meet a
3 ppm steam purity limit; or in the case of some
low pressure, 150 psig saturated and lower, boilers
used for heating or similar conditions may only be
required to meet a 0.5 percent moisture condition.
These limits are not. stringent if the proper feedwater treatment is used and the proper equipment
incorporated in the plant design. In addition, the
operators must make proper use of the boiler water
blowdown and the addition of the chemical
treatment. Steam drum internals are revised when
lower guarantee limits are stated. In fact at times,
manufacturers may rely on natural separation of
steam and water within the steam drum. In this case
they may eliminate all steam drum internals except
a dry pipe or other such collecting device.
(6) In referring to the proper feedwater
treatment and operation of the boiler blowdown
and chemical treatment, attention to these items
will pay off in the long run in reduced maintenance,
retention of design efficiency and minimum cost of
feedwater treatment chemicals through elimination
of tube deposits and steam carryover problems.
(7) Figure 3-16 graphically describes the difference in the specific weights per cubic foot of
water and saturated steam at various pressures up
to approximately 3200 psig. This chart illustrates
their ratio which may be considered a margin of
safety. For boilers operating in the range of 150 to
400 psig, depending on the boiler design, location
of the tube in the furnace or boiler area, slope, and
other similar conditions, the ratio of pounds of
water circulated to the pounds of steam entrained
and then released from the steam drum is very
approximately 30 to 15 to 1. This ratio decreases
quite rapidly as the operating pressure rises.
Circulation is assisted by the height of the boiler as
well as the burner heat input located at the bottom
of the U-tube which acts as a thermal pump.
b. Chemical treatment.
(1) Oxygen (O2) is one of the more troublesome components of feedwater. It is readily removed by proper operation of the deaerating heater
together with a minimum water temperature of
approximately 220 degrees F leaving that heater.
Frequently a chemical O2 scavenger such as sodium
sulfite or hydrazine is used in the boiler feedwater
3-25
TM 5-810-15
to make sure any residual dissolved 02 is not
permitted to pit the tubes.
(2) Water hardness, expressed as calcium
carbonate (CaCo3) in ppm should be as close to
zero as possible under all conditions. This can be
accomplished by proper feedwater treatment and
boiler water testing.
(3) Another item of importance is to
maintain the proper acidity or alkalinity (pH value)
reading of the boiler water. For boilers in the range
of this manual, a pH reading of 9.0 to 10.5 should
be acceptable depending on the chemical
composition of the water source and the type of
treatment used. In the latter category, some of the
more common types of treatment are: sodium
zeolite, hot lime zeolite, phosphate hydroxide and
coordinated phosphate. In some cases the use of a
demineralizer or evaporation may be desirable.
These latter methods are more appropriate for
higher pressures and temperatures in a steam cycle
that has more complex problems due to the source
of water for the boiler or boilers. These water
treatment methods are addressed in more detail in
chapter 7.
c. Boiler internals. Figures 3-17 and 3-18 indi3-26
cates the steam drum internals showing the chemical feed line and the continuous blow pipe in
addition to the feedwater line. The diameter and
length of the drum are determined by the capacity
of the boiler in the number of primary or cyclone
separators needed. These devices in addition to
separating steam and water, aid water circulation
by a reactive (pumping) action that promotes water
flow along the length of the steam drum.
(1) The drying screen or secondary
scrubbers further separates the steam and water
particles so that the steam leaving the drum meets
the desired steam purity condition. Another feature
of the steam drum is the reserve water holding
capacity which permits load swings besides being
the collecting and distribution point of the steam.
(2) The primary function of the lower (mud)
drum is to complete the circuit for the tubes in the
boiler section and generally to act as a water
reservoir and supply source for the lower furnace
wall headers and tubes connected thereto. Except
in unusual cases, the lower drum has no internals.
It should be sized so that maintenance people can
roll tubes into the drum holes as well as inspect
those tubes. Some designs may permit rolling of
TM 5-810-15
Table 8-2. Valve Types.
Valve Type
Application
Fluid
Globe
Throttling and flow regulation service, control valves
Steam, water, air gas, oil
Gate
Isolating nonthrottling service
Steam, water, air, gas suitable for high temperature
and pressure
Butterfly
Isolating service, intermittent throttling, limited control valve application
Low pressure and temperature water and other fluids
Plug
Isolating service, intermittent throttling
Natural gas, fuel oil and other viscous fluids
Ball
Isolating service, intermittent throttling
Water, air, gas—low pressure applications
Check
Allows flow in one direction only, pump discharge piping
Steam, water, air, gas, oil
Diaphragm
Provide flow control and leaktight closure
Corrosive, abrasive and solids in suspension
Pinch
Isolating service for large amounts of solids in suspension
Low pressure and temperature, noncorrosive fluids
Needle
Volume control valve used in small instrument, gage
and meter lines
Water, air, gas
Relief or safety
Prevents excessive overpressure in process and piping
Steam, water, air, gas system
8-9
TM 5-810-15
(5) After structural adequacy has been determined, both static and dynamic analyses should be
made of the loads.
(6) With welded steel stacks, a steady wind can
produce large deflections due to Karmen Vortices
phenomenon. If the frequency of these pulsations is
near the stacks natural frequency, severe
deflections can result due to resonance.
(7) The plant location, adjacent structures,
and terrain will all affect the stack design.
(8) Cleanout doors, ladders, painter trolleys,
EPA flue gas testing ports and platforms, lightning
protection and aviation warning lights will be
provided, as required.
b. Stack design. The stack height calculations are
for the effective stack height rather than the actual
height, this is the distance from the top of the stack
to the centerline of the opening of the stack where
the flue gas enters. Air and gas flow losses through
the inlet air duct, air heater (air side), windbox,
furnace and passes, air heater (gas side) or
economizer, gas cleanup equipment and other
losses through duct and breeching should be
plotted and overcome with the fans. The kinetic
discharge head, the friction losses at the entrance to
3-28
the stack, and friction losses in the stack should be
provided by the natural draft of the stack.
Barometric pressures adjusted for altitude and
temperature must be considered in determining air
pressure. The following stack parameters must be
determined:
(1) The extreme and average temperatures
of ambient air and gas entering the stack.
(2) All heat losses in the stack (to find mean
stack temperature).
(3) Altitude and barometric corrections for
specific volume.
(4) Gas weight to be handled. The
infiltration of air and combustion air into the stack
casing and ductwork must also be considered.
(5) Stack draft losses due to fluid friction in
the stack and kinetic energy of gases leaving the
stack.
(6) The most economical stack diameter and
the minimum stack height to satisfy dispersion
requirements of gas emissions.
(7) The stack height for required draft.
(Where scrubbers are used, the temperature may be
too low for sufficient buoyancy to overcome the
stacks internal pressure losses.)
TM 5-810-15
(8) A static and dynamic structural analyses
must be made of the wind, earthquake, dead, and
thermal loads. Vortex shedding of wind loads must
be considered to be assured that destructive natural
frequency harmonics are not built into the stack.
d. Stack construction. The stack height and diameter, support, corrosion resistance, and economic factors dictate the type of construction to be
utilized.
(1) Stacks are generally made of concrete or
steel because of the high cost of radial brick
construction. If stack gases are positively pressurized, or if flue gases will be at or below the dew
point of the gases, corrosion resistant linings must
be provided; linings must be able to withstand
temperature excursions which may be experienced
in the flue gas if flue gas scrubbers are bypassed.
(2) Stacks of steel or concrete construction
will be insulated to avoid condensation by not
allowing
the internal surfaces to drop below 250 degrees F.
This requirement does not apply when scrubbers
are used with low temperature discharge (150 to
180 degrees F) into the stack because the flue gas
is already below dew point temperature.
(3) A truncated cone at the top of the stack
will decrease cold air downdrafts at the periphery
of the stack and will thus help maintain stack
temperature, but stack draft will decrease considerably.
3-19.
Adjustable Speed Drives.
Significant electrical power savings can be realized
at reduced boiler loads by installing adjustable
speed drives (ASD) on ID and FD fans. The
economics of ASD*s depend on the boiler load
profile (number of hours at different loads). The
feasibility of ASD installation should be verified by
an LCCA.
3-29
TM 5-810-15
sized for the maximum expected condensate load
and a safety factor. Oversizing a trap can increase
losses, both for good traps as well as traps that fail
open. It is recommended that a safety factor of 2:1
be used to size a trap in a constant pressure usage
and safety factor of 3:1 be used if the pressure
varies. The major steam loss from a trap is at a
failed-open condition and can cost thousands of
dollars a year if not detected. However, a failed
close trap may cause extensive damage because of
corrosion or water hammer from condensate that is
not discharged. Selection of the failure mode
depends on the design conditions and maintenance
practices. All traps are subject to freezing,
particularly due to condensate flow blockage. Of all
types of traps, float traps are most subject to
freezing. Steel bodied traps resist freezing better
than iron. Trap cost is an important consideration
as initial expense may not justify selection because
of maintenance characteristics and life span. The
inverted bucket type of trap has the longest life,
followed by the float trap, thermostatic trap and the
thermodynamic trap consecutively for long life.
d. Types. There are four basic types of steam
traps: inverted bucket, float, thermostatic and
thermodynamic.
(1) Inverted bucket. This type of steam trap is
the most widely used. When properly sized, steam
loss is kept to a minimum. The inverted bucket trap
contains an inverted bucket inside the trap body.
The inverted bucket is fastened to a linkage in such
a manner that it will close the trap outlet when
steam enters from beneath the bucket. As the steam
cools and condenses (assisted by a bucket vent),
the bucket loses its buoyancy and the trap opens
releasing the condensate. Gases mixed with the
steam pass through the inverted bucket trap partly
by way of the bucket vent and partly in any steam
discharged by the trap. The discharge from the
inverted bucket trap is intermittent and requires a
differential pressure between the inlet and discharge
of the trap to lift the condensate from the bottom of
the trap to the discharge connection. They are
resistant to water hammer, operate well at low
loads, and fail open. Bucket traps may be subject to
damage from freezing and have only fair ability to
handle start-up air loads. Inverted bucket traps are
well suited for draining condensate from steam
lines or equipment where an abnormal amount of
air is to be discharged and where dirt may drain
into the trap.
(2) Float. A float trap has a small chamber
containing a float and linkage that multiplies the
float*s buoyancy. The condensate will cause the
8-12
float to open the trap until it is drained and the float
loses buoyancy. A float trap does not have to be
primed as an inverted bucket trap does. However,
buildup of solids and sludge in the trap body can
prevent the float from sinking and closing the
valve. The discharge from the float trap is generally
continuous. This type is used for draining
condensate from steam headers, steam heating
coils, and other similar equipment. When a float
trap is used for draining a low pressure steam
system, it will be equipped with a thermostatic air
vent.
(3) Thermostatic. The thermostatic trap opens
and closes by means of a force developed by a
temperature sensitive actuator. A basic problem for
all thermostatic traps is keeping the actuating
temperature close to the saturation temperature so
the condensate will be hot, but not allow live steam
to blow out the trap. If the actuating temperature is
not close to the saturation temperature, there is a
possibility that O2 and CO2 may dissolve in the
water, and also, that the condensate may back up
to an unacceptable level. The discharge from this
type of trap is intermittent. Thermostatic traps are
used to drain condensate from steam heating coils,
unit heaters and other similar equipment. Strainers
are normally installed on the inlet side of the steam
trap to prevent dirt and pipe scale from entering the
trap. The thermostatic trap is the most common of
all trap types used for two pipe steam heating systems. When this type of trap is used for a heating
system, at least 2 feet of pipe will be provided
ahead of the trap to cool the condensate. This
permits condensate to cool in the pipe rather than
in the coil, and thus maintains maximum coil
efficiency. Thermostatic traps are recommended for
low pressure systems up to a maximum of 15 psi.
When used in medium or high pressure systems,
they must be selected for the specific design
temperature. In addition, the system must be
operated continuously at that design temperature.
(4) Thermodynamic disc traps. Thermodynamic disc traps are used for intermittent service,
where they operate well under variable pressure
conditions, are resistant to damage from freezing
and water hammer, and fail open. A disadvantage
of the thermodynamic trap or disc trap is poor gas
handling. The pressure drop when air or 002 are
flowing in the trap resembles that of steam, so that
large amounts of air will close the trap. Therefore,
another air removal method is necessary for startup
of a steam system. Thermodynamic disc traps will
not be used where high back pressures, or low load
conditions might occur. They are best suited for
TM 5-810-15
the primary air to fuel ratio above a minimum level
for all pulverizer loads.
g. Gas/oil system controls.
(1) Fuel flow control. Fuel flow in gas/oil fired
boilers is controlled by operation of gas or oil
control valves in the supply lines to the burners.
The gas or oil control valves are modulated to
control fuel flow based on the demand signal
generated by the combustion control system. Gas
flow to the burner is measured by taking the
differential pressure across an orifice. Oil flow to
the burners will be measured by a rotating disk type
meter. Metering type control systems utilize the
fuel flow and unit load in the combustion control
9-6
system to properly modulate fuel flow in response
to the system demand.
(2) Combustion air control. The combustion
air is normally controlled at the FD fan. Air flow
for package boilers is normally controlled by outlet
dampers at the FD fan. Other methods that are
used include control of the FD fan inlet vanes or
control of the FD fan inlet damper. The relationship
between inlet vane or damper position and air flow
will be determined for characterizing the final
control element. When a metering type control
system is used air flow is measured downstream of
the FD fan or a piezometer may be installed at the
FD fan inlet.
TM 5-810-15
(3) Combustion air flow measurement. Accurate combustion air flow measurement is also
important in metering type combustion control
systems for gas/oil fired boilers. A venturi section
or air foil flow element should be provided in the
ductwork between the FD fan and the burner
windbox or a piezometering may be installed at the
FD fan inlet. The flow element will be designed to
provide a design differential pressure across the
flow element of not less than 2 inches wg at full
load conditions. The flow transmitter selected for
combustion air flow will be a differential pressure
transmitter that is accurate in the range of
differential pressure developed by the flow element.
(4) Oil atomization. The oil to the burner will
be atomized utilizing steam or compressed air. A
control valve installed in the atomizing steam or air
line will be controlled to maintain the atomizing
medium pressure above the oil supply pressure to
the burner.
h. Atmospheric circulating fluidized bed (ACFB)
boiler.
(1) Fuel flow control. Main fuel flow in an
ACFB system is established by fuel flow through
the feeder to the combustor. The volumetric rate of
fuel flow is directly related to feeder speed. The
coal feed demand speed utilizes the lower of the
total air flow or firing rate demand as the set
point and compares the set point to total fuel flow
to develop the demand signal for the feeder master.
The feeder master demand signal is applied to all
feeders which have duplicate controls. Therefore,
as firing rate demand is increased or decreased the
feeder speed is increased or decreased. Coal chute
air flow compares measured air flow to load flow
to operate the coal chute air damper. A feed
forward signal based on rate of change is also used
to modulate the coal chute air control damper. Coal
feeder and coal chute air damper control is shown
in figure 9-5.
(2) Combustion air control. Combustion air
flow in ACFB systems consists of primary air flow,
overfire air flow, stripper cooler air flow, and main
fuel chute air flow. Primary air is introduced below
the bed and keeps the fuel and bed in suspension.
Overfire air is delivered by the FD fan and is
utilized at loads above 50 percent to control
furnace exit gas temperature. The stripper cooler
air flow is utilized to cool the excess bed material
which is removed in the stripper section. Main fuel
chute air flow is utilized to sweep the fuel tube to
the combustor. Total air flow is the sum of primary
air, overfire air, stripper cooler air, and coal chute
air flow. All air can be supplied by the FD fan or
separate primary air and FD fans may be utilized.
The primary air, overfire air and stripper cooler are
controlled by positioning the appropriate damper.
9-7
TM 5-810-15
CHAPTER 5
FUEL AND SORBENT HANDLING AND STORAGE
5-1. General.
This chapter addresses requirements for fuel handling and storage systems for gas, oil and coal fired
boiler plants. Solid fuel policies and procedures are
discussed in AR 420-49. Criteria for petroleum
product storage and distribution is also prescribed
in AR 420-49. While not intended to give the
reader a complete in-depth study of handling and
storage system design, it is written to give a basic
understanding of how to select handling and
storage system equipment for a small to medium
size boiler plant.
5-2. Gas design considerations.
a. Natural gas is not stored on site. It is furnished
through the supplier*s pipeline. The takeoff line
from the pipe is either furnished by the customer or
subsidized by the gas company depending upon
how the contract is negotiated. Liquified petroleum
gas (LPG) is stored on site in specially built tanks
that can either be leased or purchased.
b. Gas piping will be in accordance with ASME
B31.8, Gas Transmission and Distribution Piping
Systems.
5-3. Oil design considerations.
a. Fuel oil piping systems require special consideration for connections on small pipes. Small
threaded fuel oil piping tends to leak due to the
penetrating action of oil under pressure. For this
reason it is recommended that pipe 2 inches and
smaller be socket welded.
b. Fuel oil storage tank design and installation
will include spill containment and leak detection.
Spill containment can be in the form of a double
wall tank or a berm as in the case of above ground
installations. Leak detection can be electronic using
alarms or it can be visual. An example of a visual
system is the leak detection technique of providing
underground drainage to a single point next to an
above ground storage. A vertical pipe is routed
from this point to above ground for periodic visual
inspection. A removable cap is used to prevent rain
water from entering the pipe.
5-4. Sorbent and alternate fuel considerations.
a. Sorbent or limestone is used for sulfur emissions reduction on atmospheric circulating fluidized
bed (ACFB) boilers. Sorbent is transported to the
site by truck or rail cars. Sorbent is conveyed
pneumatically beginning with site storage if required in a silo and plant storage in a limestone
bunker. Pneumatic systems are further discussed in
this chapter and also in chapter 6. Bunker design
should accommodate all possible sorbents being
considered. Cylindrical silos and bunkers are
commonly used for sorbent storage. Bunker design
considerations for sorbent are similar to coal and
are discussed in more detail later in this chapter. It
is important to measure the amount of limestone
going into the combustor. This is done using a belt
scale at the outlet of the bunker. The belt scale
discussion later in this chapter is applicable.
b. Alternate fuels such as petroleum coke can be
handled similar to coal. Because of the variance of
properties within a single fuel type and especially
between fuel types, each system will be designed
for the fuel being considered and the unique site
conditions and operating scenarios.
5-5. Coal handling design considerations.
a. Developing conceptual designs. The process
of selecting and laying out coal handling system
components should systematically proceed through
three preliminary phases before any detailed design
work is performed: setting design criteria,
evaluating design alternatives, and developing a
flow schematic. The design criteria should address
such factors as plant location, climatic conditions,
available land, system requirements, types of boiler
(stoker or pulverized coal) amount of coal storage,
conveying rate and method of coal delivery. After
these basic criteria have been established, the
designer should present a number of different
options that will fit them. The feasibility of each
option should be examined, and its advantages and
disadvantages should be listed and compared to the
other alternatives. Because the lowest capital cost
system is not always the most economical system,
an LCCA will then be made for each of the
different design alternatives, taking into account the
following considerations: Capital investment costs,
operating costs, and maintenance costs. As a final
stage of the preliminary design effort, a coal flow
schematic as shown in figure 5-1 will be prepared
showing each process and piece of equipment the
coal is moved through before reaching the plant
storage bunkers.
5-1
TM 5-810-15
allows a hot restart which bypasses the purge,
ignitors and warm burners and allows the introduction of solid fuel provided certain conditions are
met. Figure 9-12 shows sequential logic for burner
control.
b. Feedwater flow and drum level control.
(1) Two element control. Two element feedwater control systems as shown in figure 9-13(a)
are characterized by the use of steam flow as a
feed-forward signal to reduce the effect of shrink
9-14
and swell of the boiler drum level during load
changes. Without the steam flow feed-forward signal, load changes will momentarily cause the drum
level to change in a direction opposite to the load
change. The feed-forward signal provides the
correct initial response of the feedwater valve.
(2) Three element control. Three element
feedwater control as shown in figure 9-13(b) uses
feedwater flow in addition to steam flow to improve drum level control. In this system feedwater
TM 5-810-15
belt size larger than recommended i.e. if a conveyor
is sized at 30 inches wide to handle a certain
capacity, then use a 36-inch wide belt. Conveyor
speeds in excess of 700 fpm are not recommended
for western type coal.
5-6. Coal delivery.
a. General. The method of delivering coal to the
plant can be a significant cost in the delivered price
of the coal and will affect the design, operation and
cost of the coal receiving system. The delivery
mode depends on such factors as, plant location,
distance from mine to plant, daily “burnrate” under
full load conditions, available coal storage area and
the cost of competitive transportation methods.
The ability to receive coal by either truck or rail can
be advantageous and create a competitive pricing
atmosphere. The ability to accommodate 10-15
railcars or higher multiple car shipments can enable
the user to obtain lower shipping rates and reduce
demurrage on the railcars due to the amount of
time a car spends at the plant. Enough track must
be provided at the plant site to allow for the loaded
and empty railcars and the unloading area. The
economic justification for a loop track or spur track
rail storage system can be made as a result of
savings in freight rates, if space permits.
b. Truck delivery. Trucks are an extremely convenient form of coal transportation, but due to the
high manpower and fuel costs, this type of transportation has become expensive. Over-the-road
trucks vary in net carrying capacity from 10 to 40
tons. Trucking coal more than 150 to 200 miles to
a plant site usually increases the delivered price of
coal to a cost that is financially unacceptable for
efficient operation. Truck delivery of coal can
usually be incorporated into the design of a railcar
unloading hopper. If trucks are the sole method of
coal delivery, the designer should investigate the
economics of a covered shed over the unloading
hopper. Truck hopper should be a minimum of 12
feet by 12 feet with a steel grating covering the
dump area. Maximum grating opening should be 6
inches square. Grating should be designed to
withstand the loads imposed by the fully loaded
truck. Truck weighing scales are optional subject to
both economics and justification.
c. Railroad car delivery. This is the most common form of coal delivery to the boiler plant. If a
plant has good access to a rail network, the
delivery of coal in 70-100 ton railcars is usually
more efficient and economical than delivery by
trucks. The most common size of railcar is the 100
ton capacity car. The designer should also take into
consideration any requirements for the smaller 50
and 80 ton capacity cars which are more popular at
smaller sized plants.
5-7. Railcar unloading system components.
a. Railcar scales. Railcar scales are optional for
large plants if their use can be justified. These
scales are usually not installed in a coal handling
system.
b. Railcar haulage. The designer can select from
capstan type, drum type, or hydraulic type car
pullers. Cost is dependent upon the type of car
puller arrangement and accessories provided. The
capstan type puller is the cheapest, and is used
where one or two cars have to be moved. The
capstan puller can only be used on level track, and
has very limited capabilities. An alternative for very
small systems where three to four cars are moved
per week, a front end loader fitted with a railcar
moving device should be considered. Drum or
reversible type railcar pullers provide more
versatility and are becoming the most commonly
selected units. The operator makes one connection
to a “string” of railcars and pulls them backward or
forward, up or down grades, and around curves
with a car puller. The designer will ensure that the
operator and control panel is well protected from
the railcar pulling rope. A railcar string is usually
one to twelve fully loaded cars. Hydraulic car
pullers are usually the most expensive. They are
used at larger plants where high volume railcar
moving is required. In making a selection, the
designer must take number of loaded railcars, track
grade, radius of curvature of track (straight
preferred), track condition (new or old), operating
temperature, and amount of travel distance required into consideration. The designer should
consult a railcar manufacturer for final equipment
selection.
c. Railcar shaker. Railcar shakers are used to
vibrate the railcar for fast removal of coal from the
railcar without the operator having to get inside the
car and manually clear the material out, thus
reducing unloading time and manpower
requirements. Car shakers can be the overhead or
side mounted type. Side mounted car shakers
require a foundation outside of the rails, and this
becomes a problem if there are two or more
railroad tracks spaced close together. This type of
shaker is more expensive than the overhead type.
The overhead shaker is the more common of the
two types of shaker, having been in proven use for
many years. The designer must ensure that suitable
electrical interlocks are provided for the hoist and
shaker to prevent incorrect use.
5-3
TM 5-810-15
Table 9-4. Operator lnterface lnstrumentation Requirements. (Continued)
ACFB Fired Boilers
16. J-valve plenum air flow
upleg
17. J-valve plenum air flow
downleg
18. Total air flow
19. Steam flow
20. Spray water flow
21. Feedwater flow
22. Gas flow
Operator Stations:
1. Boiler master
2. Primary air flow
3. Overfire air flow
4. Oxygen trim
5. Fuel master
6. Fuel flow
7. Airflow
8. Furnace pressure
9. FD fan discharge pressure
10. Stripper cooler air flow
11. Solids cooler spray water
12. J-valve blower discharge
pressure
13. J-valve aeration control
Recorder Requirements:
1. Furnace pressure
pressure
3. J-valve inlet static pressure
4. J-valve discharge pressure
5. Over furnace bed static
pressure
6. Furnace plenum pressure
7. Steam pressure
8. Spray water pressure
9. J-valve diplet (duff press)
10. J-valve density (duff press)
11. Valve solids flow
(diff press)
12. Bed differential pressure
13. Total furnace differential
pressure
14. Primary air flow
15. Overfire air flow
16. J-valve plenum air flow
upleg
17. J-valve plenum air flow
downieg
18. Total air flow
19. Steam flow
20. Spray water flow
21. Feedwater flow
22. Gas flow
23. Fuel flow
24. Sorbent (limestone) flow
25. Steam temperature
26. Furnace exit gas temperature
27. Solids cooler stripper
section temperature
28. Solids cooler cooler
section temperature
R
38.
39.
R
40.
Deaerator level
Cyclone level (uses diff
press transmitters)
Chute air flow
X
R
J-valve plenum air control
Sorbent (limestone) feed
Furnace bed inventory
control
Drum level
Steam temperature (SH only)
Warm-up burner control
Deaerator pressure
Deaerator level
Feedwater heater
Steam coil preheater
R
R
R
R
R
R
R
X
R
X
R
J-valve fluid temperature
Furnace bed individual TC
temperature
Furnace bed average
temperature
Furnace plenum temperature
Finish SH inlet temperature
Feedwater temperature
Oxygen
SO[sub]2
Drum level
Deaerator pressure
Deaerator level
Cyclone level (uses duff
press transmitters)
FD fan discharge pressure
Solids cooler stripper
airflow
Solids cooler solids air
flow
Drum pressure
Warmup burner discharge
temperature
Air heater inlet air
temperature
Air heater gas temperature
Air heater cold end
temperature
ID fan amps
FD fan amps
Boiler feed pump amps
Sootblower pressure
R
X
R
R
R
X
R
R
R
R
R
R
X
R
R
R
R
R
R
R
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
R
R
R
R'
R
R
R
X
R
R
R
R
R
R
R
R
R
R
R
X
R
R
R
R
R
R
R
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
R
R
X
X
R
R
R
X
X
R
R
R
R
R
R
R
R
R
R
R
R
R
X
R
9-27
TM 5-810-15
FGR
lb/ft3
Flue Gas Recirculation
Pounds per cubic foot
FM
LCCA
Factory Mutual
Life Cycle Cost Analysis
fpm
LEA
Feet per minute
Low Excess Air
fps
LED
Feet per second
Light Emitting Diode
FS
LNB
Full Scale
Low NOx burner
FT
LOI
Fluid Temperature
Loss on ignition
FW
LPG
Feedwater
Liquified Petroleum Gas
gph
mA
Gallons per hour
Milliamp
HEI
MB
Heat Exchange Institute
Million Btu
HEMA
MFT
Heat Exchanger Manufacturers Association
Main Fuel Trip
HI
Mg
Hydraulics Institute
Magnesium
Hg
MgO
Mercury
Magnesium Oxide
hp
O
Na2Si 3
Horsepower
Sodium Silicate
HRA
NaZ
Heat Recovery Area
Sodium Zeolite
HY
NEMA
Hemispherical Temperature
National Electrical Manufacturers Association
HVAC
NFPA
Heat, Ventilating and Air Conditioning
National Fire Protection Association
ID
NO
Induced Draft
Nitric Oxide
IES
NO2
Illuminating Engineers Society
Nitrogen Dioxide
IR
N2O
Infrared
Nitrous Oxide
ISA
NOx
Instrument Society of America
Oxides of Nitrogen
IT
NPDES
Initial Deformation Temperature
National Pollutant Discharge Elimination System
K2O
NPSH
Potassium Oxide
Net Positive Suction Head
kv
NPSHA
Thousand volt
Net Positive Suction Head Available
lb
NPSHR
Pound
Net Positive Suction Head Required
Glossary-2
TM 5-810-15
f. Idlers. Idlers will be selected for a specific
condition since they provide the support and protection for the belt and material load and also
influence the overall design of the conveyor. Improper idler selection directly affects the belt
tensions and thus the final horsepower requirements.
(1) Troughing idlers will have a minimum of
three 5-inch diameter equal length interchangeable
rolls, with the two outside rolls inclined at 35
degrees from the horizontal.
(2) At least 3 rubber type impact idlers,
spaced a maximum of one foot apart or urethane
bar loading sections will be placed under each
conveyor belt loading point. As an alternative,
cradles composed of energy absorbing bars may be
used under the loading zone to cushion the impact.
In installations where more than one cradle is
required to cover the length of the loading zone, an
impact idler will be placed between the cradles to
assure proper belt carriage.
(3) Self aligning carrying and return idlers
should be placed at 80-foot centers along the length
of the conveyor.
(4) All idlers will have a single point grease
lubrication system that is accessible from the
walkway side of the conveyor.
(5) Idler construction, selection and spacing
will be based upon Conveyor Equipment Manufacturers Association (CEMA) standards.
g. Belt take-ups. Belt take-ups are necessary to
maintain the proper belt tensions for the drive
pulley traction and to maintain correct amount of
belt sage between idlers. Gravity type take-ups
should be provided on all conveyors with adjust5-6
ment of at least three percent of the conveyor
terminal centers.
(1) Counterweight will be adjustable +/-20
percent from the calculated weight. Counterweight
will be designed to limit conveyor belt sag to 2
percent and provide adequate traction for the drive
pulley. Loading zone belt sag will be maximum 1
percent.
(2) Screw type takeups are satisfactory for
conveyors less than 40 feet in length, but should be
avoided if at all possible.
h. Conveyor belt selection. One of the most important design considerations is the selection of the
conveyor belt. The belt has to withstand both the
initial start up and operating tensions that are
encountered within the system, be impact resistant and be suitable for the material being conveyed.
(1) The conveyor belt selection must be
capable of transmitting the maximum belt tension in
the conveyor, include the minimum number of belt
plies to support the load, pulley series, take into
account the type of material to be conveyed, and
minimize belt cost to cover the above items.
(2) Conveyor minimum belt cover
thicknesses will be 1/16-inch thick bottom cover
(belt side which contacts the idlers and pulleys) and
c-inch thick top cover (belt side in contact with
the material).
(3) The conveyor belt selected must be
capable of withstanding all startup and operating
tensions that will be encountered within the
conveyor. For a multiple ply conveyor belt, the unit
tension is expressed in pounds per inch belt width
(piw) or pounds per ply inch (ppi). A 30-inch wide,
TM 5-810-15
3 ply belt with a maximum calculated operating
tension of 5000 pounds, will have a unit tension of:
5000 = 167 piw or 56 ppi
30
(4) Conveyor belt sag between carrying
idlers should be limited to two percent, except at
load zones limited to 1 percent.
(5) Belt tension will not exceed 70 percent
of the Rubber Manufacturers Association (RMA)
tension ratings under normal operating conditions
with a vulcanized splice.
(6) Conveyor belt will be fire and oil
resistant conforming to United States Bureau of
Mines Standards.
(7) Consideration should be given in applications of limited takeup or long conveyors to provide a mechanical splice when the belt is first
installed so initial stretch can be taken out before
doing the vulcanized splice. In these cases run-in
time will be long enough to eliminate manufacturer*s stretch. Vulcanized belt splices generally last
close to the life of the belt. Mechanical splices last
two to three years.
i. Skirtboards. Skirtboards will be provided at all
conveyor loading points. Coal handling system
design, especially when handling lignite or western
coal requires examination of flow velocity
differences between conveyors, vertical drop at
transfer points, and angular relationship of conveyors. The width of the skirtboards will be maximum 3/4 belt width.
(1) Skirtboard length will be at least 2 feet
for every 100 fpm of belt speed plus 3 feet at tail
end. Minimum skirt length will be 8 feet. The skirtboard will terminate above an idler roll, not
between.
(2) Skirtboard rubber strips with easy adjustable clamps will be provided on the lower edge of
the skirtboards to prevent the escape of fines.
Wearable liners inside the chute will be installed as
a dam to keep the material load off the rubber, so
it can effectively serve as a fines barrier. Provide
continuous skirtboards on feeder conveyors.
j. Belt cleaners. Belt cleaner units on a troughed
conveyor belt will consist of a primary scraper on
the face of the head pulley and one or more
secondary arm and blade type multiple blade
cleaner to scrape and remove the material that
bypasses the primary cleaner. Each belt cleaner will
be held in an easily serviceable mounting system
allowing fast and easy blade replacement. The
cleaners will be held in position against the belt by
means of a tensioner which rotates the blades
against the belt yet which allows for relief when
mechanical splices or other obstructions pass. Do
not use counter-weighted type cleaning devices on
conveyors faster than 350 fpm or larger than 36inch as they become ineffective very quickly. V
type belt cleaners will be provided on the clean side
of the belt before belt take ups and tail pulleys.
5-9. Other conveying methods.
a. Bucket elevators. These are used to elevate
coal to overhead storage or conveyors, where there
is little available space for a belt conveyor. Malleable iron, steel, stainless steel, aluminum or plastic
buckets can be selected depending on the material
conveyed. Care should be taken when selecting
nonmetallic type buckets for use in a combustible
environment, due to their ability to retain a static
electrical charge. Capacity of the bucket elevator
will be based upon buckets filled to 75 percent
theoretical capacity for loading. Drive horsepower
will be based upon 100 percent full buckets. There
are two common types of elevator used for coal
handling: centrifugal and continuous.
(1) Centrifugal type. Centrifugal discharge
elevators are the most frequently used type for free
flowing, fine or small lump materials. Buckets
should be type A or AA as designated by CEMA,
spaced at intervals to chain or belt. Buckets are
loaded by a combination of material flowing into
the buckets and material that is scraped up by the
digging action as the buckets pass around the tail
pulley. Speeds are relatively high and the centrifugal action controls the discharge from the buckets.
Capacities range from 5 to 80 tons per hour (tph).
Elevator will be completely self supporting. Centrifugal type elevators are used extensively in grain
service and other free flowing materials.
Centrifugal elevators tend to create more dust and
cause breaking of friable material, which creates
problems with boiler requiring a particular size
distribution. Centrifugal elevators if used should be
vented, and include a filter to relieve the “air
pumping” phenomena at discharge.
(2) Continuous type. Continuous bucket
elevators are recommended for high capacity heavy
duty service. The buckets are steel, continuously
space on single or double strand chain or on a belt.
At the head, the discharge from each bucket is over
the back of the preceding bucket which forms a
chute to lower the material to the fixed discharge
spout. This method of discharge, plus the slow
speed, minimizes breakage of fragile material.
These types of elevator are not the self digging
type, so a loading leg must be used, requiring a
deeper pit than that needed for a centrifugal
discharge elevator. Capacities from 15 to 300 tph
are available. Elevator will be completely self
5-7
TM 5-810-15
supporting. Bucket elevators are usually high
maintenance items and should only be used where
space restrictions apply. Manufacturers have to
take particular care when designing the track and
load shoe.
b. Apron conveyors. Apron and pan conveyors
consist of overlapped steel pans which are supported between two strands of chain that pass
around head and tail sprockets. This type of
conveyor is usually short, slow speed, and used for
removing granular or lumpy material from under
the track hopper. An apron conveyor is a very high
maintenance item and should be avoided when
possible. Maximum conveyor incline is usually up
to 25 degrees or 45 degrees with pusher plates.
One distinct advantage of this type of conveyor is
they can carry hot materials.
c. Screw conveyors. Screw conveyors are an economical short, low tonnage type of conveyor which
can be used in areas with low headroom. Screw
conveyors are not usually used when their capacities exceed 50 tph. They are used to handle
pulverized, granular or noncorrosive materials
where product agitation or degradation can be
tolerated. Where mixing or blending is required,
numerous conveyor screw configurations are available. The conveyor is completely enclosed with
only one moving part and can be fitted with
multiple or single discharge openings. Extreme
caution must be taken when handling abrasive
materials, as excessive wear will lead to premature
equipment failure. As the screw conveyor is
inclined, the carrying capacity decreases. Trough
loading should not exceed 30 percent of the trough
cross sectional area for coal, even though higher
loading is possible.
d. Flight conveyors. Flight conveyors are used to
move granular, lumpy or pulverized material along
both horizontal and inclined paths. Inclines are
limited to approximately 40 degrees, with capacity
decreasing as incline increases. One percent of
capacity should be deducted for each degree of
incline over 30 degrees. Flight conveyor is a high
wear, very noisy and high maintenance item. With
abrasive materials, the trough design should
provide for renewal of the bottom plate without
disturbing or removing the side plates or flights. A
method of compensating for unequal chain wear or
stretching must be incorporated into the design.
Flight conveyors are well suited to conveying
bottom ash from boilers and sludge from tanks and
ponds.
5-10.
Drive units and couplings.
a. Conveyor drive units. The conveyor drive unit
should be located at the discharge or head end of
5-8
inclined and horizontal conveyors. The designer
may find it preferable to locate the drive internally
or at the tail end of the conveyor if required by
accessibility or maintenance, but should be avoided
if possible. The drive arrangement should be
designed with the minimum amount of compact
components as possible. Reducers, couplings and
motors should be the same size as far as practical
for ease of maintenance and to reduce spare parts
inventories. On conveyor drives over 300 hp the
designer should investigate the economical justification of dual drives. This type of drive allows the
conveyor to be operated at reduced capacity when
one of the drive units fails. V belts will not be used.
b. Reducers. The conveyor drive reducer will be
American Gear Manufacturers Association
(AGMA) rated using a service factor of 1.5 of the
input motor design hp. The thermal hp rating of the
reducer will not be less than the full load hp of the
motor. Bearings will be Anti Friction Bearing
Manufacturers Association (AFBMA) 100,000
hour L-10 minimum life. All conveyor drives will
be capable of starting under full loaded conditions.
V belts will not be used.
c. Couplings. Power from the reducer drive low
speed shaft is transmitted to the conveyor head or
drive pulley by the use of a flexible coupling. The
coupling will be capable of withstanding parallel,
axial and angular misalignment of the drive shafts.
The coupling will be incapable of transmitting axial
loading and the use of torque limiting couplings
will not be permitted. Couplings will be rated using
a minimum service factor of 2.0 for the input hp.
d. Fluid couplings. Fluid coupling will be provided between the drive motor and the reducer
which allows a controlled amount of slip to occur
without causing excessive tension and shock loading to the drive components and conveyor belt. A
fluid coupling will allow the motor to run rapidly
up to full speed, but will allow the conveyor a
smooth controlled acceleration start curve when
starting from rest when either empty or fully
loaded. This type of coupling is also beneficial in
extremely cold climates where a controlled acceleration start is required to prevent coal from backsliding on inclined conveyors. Fluid couplings permit the use of standard motors with across-the-line
starting capabilities which allows the use of less
expensive motors.
5-11.
Belt scales.
a. Scales. General Belt scales are used to constantly measure the rate at which a bulk material is
being delivered to the plant on a moving conveyor
belt, and to make a record of the delivered amount
TM 5-810-15
for inventory purposes. It is important to weigh the
coal as it is delivered to the plant, and again before
it is burned.
b. Type. A belt scale of the weighbridge type
which incorporate electronic precision strain gauge
load cell and microprocessor based technology with
automatic calibration capabilities should be selected. The belt scale, including weighbridge assembly will be capable of withstanding at least 250
percent material overload without damage to any
mechanical or electrical components.
c. Scale accuracy. If a belt scale is to be used for
basis-of-payment contracts between the coal supplier and the plant, the coal supplier may require a
scale with 0.125 or 0.25 percent repeatability
accuracy. For general plant inventory purposes, a
0.5 percent accuracy is usually acceptable. If a
scale is used for billing purposes or invoicing
freight, approval and certification by the weighing
bureau which has jurisdiction for that particular
geographical area must be obtained.
d. Readout. The scale can be connected to a
computer or a printer to provide a readout of the
quantity of material delivered to the plant. The
readout will be easily readable by the operator and
be such that he does not have to do any manual
calculations to find the amount of coal received.
5-12.
Sampling system.
a. General. When a given consignment of coal is
delivered to the plant, it may be advantageous to
the plant to determine by laboratory analysis some
of the characteristics of the delivered coal. Sampling is used to take a representative sample from
the complete coal consignment lot and provide a
quality evaluation of that sample. Because of the
variability of the chemical composition of the coal,
the analytical results from a sampling system can be
used to determine coal contract rates, reliable and
efficient quality assurance, plant operating
efficiency and compliance with environmental
standards.
b. Design conditions. Each sampling system will
be designed for a specific location and on an
individual plant basis. One sampling system cannot
necessarily be used for another similar system.
Depending on the capacity of system, one or more
sampling stages may be required to obtain the
volume of the final sample required for analysis.
ASTM standards establish the requirements of the
final sample for each particular system. A good rule
of thumb for selection is a three stage system is
used for flow rates which exceed 2000 tph and
when product size is greater than 3 inches, while a
two stage system is used where flow rates are
below 2000 tph and product size is below 3 inches.
Sample system manufacturers will provide help
with system sizing and requirements. Due to the
complexity and high cost of sampling system, the
designer must decide if a sample system is a
justifiable piece of equipment to meet the end
results.
c. Sweep type sampling. Sweep type (or hammer
type) are relatively new and have different design
conditions than given above. This type takes less
sample than a cross stream type, usually from 1/3
to 1/6 less, depending on conveyor speed, material
size and flow rate. This allows two stage sampling
systems to be employed with virtually any flow rate
using sweep samplers for the first and second
stages. Also, for low capacity installations of approximately 50 tph and below, a single sweep
sampler with sample collector can be used to meet
ASTM D 2234. At these low flow rates, a manageable amount of sample is collected for laboratory
analysis with a minimal capital investment.
5-13.
Magnetic separators and detectors.
a. Magnetic separators. Magnetic separators are
installed to remove potentially damaging magnetic
tramp iron from the material on the conveyor belt.
Tramp iron is removed from the conveyed material
by the separator and can be automatically or
manually discharged to a collection hopper. A
single unit mounted ahead of the crusher on the
conveyor is usually all that is required to protect a
complete conveying system. A small piece of tramp
iron can put an expensive crusher out of action
very easily. The separator will also protect the
conveyor belts from being ripped by large pieces of
tramp iron. A separator is a relatively inexpensive
and necessary method for protecting crushing machinery, conveyors and the plant boilers.
b. Detectors. Detectors are used to detect both
magnetic and nonmagnetic tramp iron and are
usually installed in conjunction with a magnetic
separator to provide additional protection for all
downstream equipment. When tramp metal is
detected, the unit automatically die marks the
location and shuts down the conveyor before any
damage is done. The operator has to manually
remove the foreign material before restarting the
conveyor.
c. Magnetic pulleys. Magnetic pulleys can also
be used to remove tramp iron, but are usually not
as effective as a magnetic separator, and are seldom
used in coal handling systems.
5-14.
Coal crushing equipment.
a. General. Stoker fired or pulverized coal boiler
plants install crushers for use when a larger and
5-9
TM 5-810-15
more coarse ROM coal has been purchased for use
in the boiler plant. A separate crusher bypass chute
should be provided to divert coal around the
crusher when properly sized coal is purchased and
no crushing is required. The separate bypass chute
is also advantageous when maintenance work has
to be performed, requiring the shutdown or removal of the crusher from the coal handling system.
In boiler plants that have both pulverized coal and
stoker fired boilers, all the coal supplied is sized to
suit the stokers, with coal going to pulverizers
when required. This simplifies the storage and
handling facilities required for the system. The
crusher will be selected to handle the hardest
material that may be encountered in the system. A
stationary or vibrating grizzly screen placed ahead
of the crusher reduces the crusher size. This can be
part of the feed chute to the crusher.
b. Crusher sizing. Generally, crusher drive motor
sizing is 1/2 hp per tph for roll crushers,
granulators and hammermills and one hp per tph is
used for sizing impactors.
c. Coal reduction methods. Reducing coal to
smaller size can be separated into the two categories of breaking and crushing. Breakers reduce raw
mine coal into a manageable size, while crushers
break the coal down to small manageable particles.
Rotary breakers are used to crush or size run-ofmine coal by gravity impact and are often used to
clean debris from coal which has already been
sized. This type of breaker is usually used at the
mine site and not at the boiler plant location. When
used at a boiler plant, a built in hammer mill is
included.
d. Crusher types.
(1) Roll crushers. Roll crushers compress
the coal between a roll and a breaker plate. Teeth
on the roll help to split the coal through impact and
toward the bottom of the breaker plate, the teeth
shear the coal, which minimizes product fines and
reduces power demand. Adjustable clearance between the breaker plate and roll determine the
finished product size. The breaker plate is usually
spring loaded for protection against uncrushable
debris and adjustable from outside the machine.
Roll crushers are well suited for western coal due
to control on minimum size of product.
(2) Hammermills. Hammermills break the
coal by the impact of rotating hammers throwing
the coal against breaker bars and then dragging the
coal against the screen bars. This type of crusher is
used as a primary reduction of dry or friable
material where uniform product size is required and
large amounts of fines are not objectionable.
Hammermill crushers must be provided with a vent
arrangement because of the air being displaced by
5-10
the high speed rotating hammers.
(3) Granulators. Granulators crush coal with
a slow, positive rolling action which produces a
granular product with a minimum amount of fines.
Power plants particularly choose this type of
crusher for its high reduction ratio and high
capacity. The product size is externally adjusted by
changing the clearance between the case assembly
and the ring hammers.
(4) Impactors. Impactors break the material
by dropping it centrally into the path of the rotating
hammers. The material then impacts against
breaker plates and rebounds back into the rotating
hammers. A variety of product sizes can be attained
by adjustment of the breaker plates. Impactors are
usually recommended for secondary and tertiary
crushing applications where high reduction ratios,
high capacity and a well shaped and graded product
are required.
5-15.
Vibrating feeders.
a. General. Vibrating pan feeders consist of a
pan or trough to which is imparted a vibrating
motion so that material moves in a controlled flow.
Feeders are instantly adjustable for capacity and
controllable from any near or remote point. Feeders
are normally positioned under track hopper
openings, the bottom of a bin or under a storage
pile to induce and regulate the flow of material
onto a belt conveyor or other means of moving
coal. Vibrating feeders are used for handling practically all kinds of bulk materials, but will be
avoided where the material has a tendency to stick
to the pan. The feed rate in tons per hour of the
feeder is a function of bulk density, material size,
material angle of repose, angle of decline, frequency of vibration, trough stroke and feeder
length.
b. Feeder design. Feeders will be the electro
mechanical type which employ easily adjustable,
rotating eccentric weights driven by a heavy duty
electric motor which transmits power to the feeder
pan through heavy duty springs, which in turn
induces the material to flow. Electromagnetic type
feeders will be avoided where possible. These type
of feeders have an extremely high noise level when
installed in underground pits and tunnels, and have
trouble meeting explosionproof atmosphere
requirements.
(1) Each feeder will be designed and sized
for nonflushing operation.
(2) Hopper design and inlet arrangement to
the vibrating feeder are very important in obtaining
the required capacity and preventing overloading
and choking of the pan. An adjustable depth
TM 5-810-15
limiting gate will be provided to control the depth
of material on the feeder pan.
(3) Maximum recommended feeder angle of
slope is 10 degrees down from the horizontal.
Larger slopes are possible, but care must be taken
to prevent the material from “flushing” (self emptying), when the feeder is shut down.
(4) The more common type of primary
feeder supports consist of steel cable or bar hangers
supported from the hopper or roof support steel
above, with spring type shock absorbers in each
hanger. A support frame can be used to support the
feeder from below if the feeder cannot be
supported from the hopper or overhead support
steel. The feeder will be provided with at least two
safety slings to prevent the feeder from falling in
the event of a primary support failure. Application
of suspended feeders will take into account “back
out” action of the feeder.
c. Feeder construction. Feeder pan will be constructed from a minimum of 3/8-inch thick, type
304 solid stainless steel plate. Replaceable stainless
steel liner plates can be used, but are far more
expensive to install. Plastic type liner plates should
be investigated when a sticky material is being
handled.
d. Controls. There are two common types of
control systems which are used to control the
vibrating feed rate; Silicon Controlled Rectifier and
Variable Auto-Transformer. The control system
will be capable of adjusting the feed rate from 0 to
100-percent of the vibrating feeder capacity.
(1) Silicon Controlled Rectifier (SCR). This
is the more commonly preferred method of
vibrating feeder control. The SCR is a solid state,
variable voltage, soft start control device that can
be used for both local and remote operation where
a manual or electronic process control signal input
is used. A full voltage start circuit is recommended
to protect against full inrush starting current.
(2) Variable auto transformer. This is a
variable voltage device that is used for local,
manual control of the feeder feedrate. The auto
transformer requires that a servo device be used for
dial adjustment. This type of control is being
replaced by the solid state circuitry of the SCR,
which is capable of both local and remote control.
5-16.
Trippers.
a. General. Tippers are used in conjunction with
a horizontal belt conveyor to discharge material
from the belt at points along its length. Trippers
can be stationary or fixed position, arranged with
suitable chutework to discharge material to either
side of the conveyor or back onto the conveyor
belt.
b. Stationary type. Stationary trippers are used to
discharge material at a specific fixed location into
a bin or silo, or direct the material back onto the
conveyor belt to the next point of discharge.
c. Motor driven. Motor driven movable trippers
have the tripper frame mounted on wheels, which
engage parallel rails supported on either side of the
belt. This type of tripper can remain in a specific
location for a short time or locked in position for
longer periods. Provide a cable reel or festoon
cable system to provide power to controls and
motor drives. The designer must provide safety
devices at each end of the tripper travel to reverse
or stop the tripper car. Dust seals will be provided
near the lower end of the discharge chutes to
prevent the escape of dust from the covered bins or
hoppers. For a clean operation hoppers or bins
must be vented to release air displaced by incoming
coal. Belt propelled tripper cars will be avoided.
Traveling trippers are installed in stream plants
where material is discharged into multiple bins,
hoppers or silos.
d. Winch type. Winch trippers have positive
drives using cable connected to both ends of the
conveyor, and looped up through winch. No power
is required on the tripper. Winch trippers should be
used when conveyor would be exposed to weather.
Wind can fold the belt which could cause a selfpropelled tripper to come off the tracks. Rain or
handling material that absorbs moisture could make
the rails slippery, which would not adversely affect
a positive drive unit such as a winch tripper.
5-17.
Conveyor chutework.
a. Chutework design. Design of conveyor transfer and headchutes depends upon the accurate
prediction of the material trajectory path as it
discharges over the end of the pulley. The curvature of the material trajectory is dependent on the
material depth on the conveyor belt, the belt speed,
the angle of the conveyor, pulley size and the force
of gravity on the material. All the above factors
should be considered during the design stage to
prevent the material from choking or plugging the
chutework and causing material spillage.
b. Chute slope. For good coal flow all chutework
side plates will be as steep as possible but will have
a slope no less than 55 degrees off horizontal. For
western coal slope will be minimum 60 degrees,
preferably 70 degrees. The designer must eliminate
offsets, turns or changes in direction of chutework
as much as possible.
c. Chute liners. Stainless steel or Ultra High
Molecular Weight (UHMW) liner plates will be
installed on all surface subject to wear or slide,
such as “dribble” from belt scrapers landing on
5-11
TM 5-810-15
chute back plates. Impact type liners or bars will be
installed at material discharge impact points.
d. Construction. Headchutes and transfer chutes
will be totally enclosed to reduce spillage and
fugitive dust. Rubber dust curtains and seals will be
provided around the conveyor belt as it enters and
exits the headchute. Conveyor headchutes will have
at least 2 inches clearance between the edge of the
head pulley and the inside of the chute. For belt
widths up to 42-inch and 48-inch through 72-inch
clearance will be 3-inch. Headchute construction
should have provisions to remove the entire pulley
assembly and frame so maintenance can be done in
the shop. Chutework will be flanged and bolted
design with externally mounted bearings and hinged
access doors for ease of maintenance. Provide
hinged, access doors on both sides or front (above
material impact point) of headchutes.
e. Chute pluggage detectors. A tilt type plugged
chute detector will be furnished at each transfer
point to protect the conveyor from damage. Pressure or resistance type plug chute switches are not
as reliable as the tilt type switches and will not be
used.
5-18.
Coal reclaim.
a. General. Reclaim systems can be classified
into two categories, below grade and above grade
coal reclaim systems. Small size steam plants
usually cannot economically justify the types of
reclaim systems employed by the larger power
plants such as the above grade reclaimers, bucket
wheels, boom mounted bucket wheels, barrel and
bridge reclaimers, and the below grade system such
as V-shaped slot bunkers, glory holes and
underground reclaim tunnels with vibratory or
rotary plow devices. These type of reclaim devices
require a very large capital outlay. Smaller plants
usually employ a combination of both the above
and below grade systems.
b. Reclaim hopper. This is the cheapest and
simplest form of reclaiming coal from long term
storage. In this method an above ground bulldozer
moves coal from the storage pile to a below grade
reclaim hopper. The hopper will be approximately
12 foot square and covered with a steel grizzly or
grillage with maximum 6-inch square openings. The
hopper and grillage will be designed for a fully
loaded hopper and the weight of a bulldozer, frontend loader or truck. A vibrating apron or belt
feeder under the hopper outlet and a manually
adjustable strike off gate on the hopper regulate the
amount of coal loaded onto the reclaim conveyor.
This method of coal reclaim is solely dependent on
the front-end loader or bulldozer to move coal to
5-12
the hopper. There is no “live” reclaim ability with
this method.
c. Drawdown hopper. A more expensive method
of reclaiming coal is with the use of a vibrating
drawdown hopper or pile discharger. The drawdown hopper is located directly under the coal
storage pile and is designed to operate on a timed
cycle basis, which transmits controlled vibration
energy into the coal pile, generating fracture lines,
causing the control column of flow to be drawn
down into the hopper and onto the conveyor belt.
This method of coal reclaim can provide the plant
with a certain amount of “live” reclaim from the
coal pile minimizing the use of mobile coal moving
machinery.
5-19.
Wet and dry dust control.
a. General. Whenever a dry material such as coal
is moved or changes its direction during a process,
the result is fugitive airborne dust. Fugitive dust
emissions can be significantly reduced by the
addition of an effective dry dust collection system,
wet suppression system or combination of both.
With the evolution of more stringent air pollution
control regulations, coal handling systems are being
required to meet these standards for the
geographical area they are located in. Federal, State
or local clean air codes can rule out the use of one
or the other types of dust control systems.
b. Wet dust suppression system. Wet dust suppression system is usually used where the dust
producing area is complex, large and unconfined,
such as stockpiles or track hoppers.
(1) This type of system uses a proprietary
water soluble, surface active, proportioned chemical additive, to dampen and agglomerate fugitive
dust particles at the source making them too heavy
to be airborne.
(2) The effectiveness of wet suppression systems can range from total suppression in warm
weather to questionable operation in cold subfreezing temperatures. Additional moisture can cause
coal to stick together complicating the flow characteristics of the material being conveyed, and can
reduce the burning characteristics of the coal and
are only as effective as the amount of dust that is
contacted by the suppressing agent.
(3) A wet suppression system is a simple
solution to dust control, that does not require the
use of costly or elaborate enclosures or hoods, are
cheaper to install and require far less space than a
dry dust collection system. Changes or alterations
required after startup can be made with the
minimum of expense and system downtime.
TM 5-810-15
(4) Foam suppression is simple and efficient.
Foaming chemicals have to be purchased. It is ideal
where low moisture is necessary. Foam type
systems typically add less than ½ percent moisture
as compared to up to 4 percent with standard water
spray systems. One foam unit is needed for each
central application location. No electricity is
required. Water and compressed air are required.
c. Dry dust collection systems. Dry dust collection systems utilize dry type bag filters which are
designed to remove dust-laden air from unloading
areas and transfer points throughout the coal
handling system, as well as to provide ventilation
for bins, storage silos or bunkers. The main advantage of this type of system is that it can be operated
in both warm and cold climates.
(1) A dry dust collection system requires a
large amount of space for equipment and ductwork, which makes it more expensive to install
than a wet type dust suppression system. Operating
and maintenance costs are compounded as the size
of the system increases. Changes or alterations
required after startup are virtually impossible
without completely modifying the entire system.
Filter bag replacement for the dust collector units
is very time consuming and costly.
(2) The collected dust from the dust
collector must be returned to the material flow
which allows reentrainment of the dust at the next
pick-up point location.
(3) Table 5-1 shows a comparison of dry
dust collection versus wet dust suppression
systems.
5-20.
Conveyor safety and safety devices.
a. General. Conveying system safety begins with
good design which, as far as is practical, tries to
protect the operator from dangerous or hazardous
areas associated with conveyors. Safety should be
considered in all phases of conveyor design, manufacture, installation, operation and maintenance
procedures. Conveyor operators must be properly
trained and made aware of possible recognizable
equipment hazards, safety procedures and devices,
before they become involved in an accident. Conveyor safety is covered in ANSI B20.1. In addition,
the following safety devices will be included for all
conveyors:
Table 5-1. Comparison of Dry Dust Collection Versus Wet Dust Suppression Systems.
Dry dust collection
Wet dust suppression
Foam suppression
When recommended
Enclosed hoppers, bins, silos,
transfer/crusher houses.
Silo, bunker or bin venting
Enclosed track hopper
buildings
Open coal storage piles
Open or enclosed track hopper
buildings.
Op en or enclosed conveyor.
Transfer points
Stock piles
Crushers
Enclosed transfer points
Note: Where an item is listed under both dry dust collection and wet suppression, an LCCA should be conducted to determine which
system should be used.
Disadvantages
More expensive.
High operating and
maintenance costs.
Changes or alteration to
system are costly.
Time consuming filter bag
replacement.
Large amount of space
required.
Collected dust must be
returned to the material
flow.
Chemical additive be
purchased.
Questionable cold-weather
operation.
Moisture is added to coal.
Requires a water supply.
Requires freeze protection
supply.
Foaming chemicals must be
purchased
Advantages
Can be operated in warm and Less expensive.
cold climates.
Does not require costly or
Does not add moisture to coal.
elaborate enclosures.
Can be used for bin or silo
Small space required for
venting,
installation.
Changes to system easily made.
Same advantages as wet dust
suppression.
5-13
TM 5-810-15
b. Safety devices. Each conveyor in a conveying
system will incorporate electrical safety devices to
provide protection to the operating personnel as
well as to prevent damage to the conveyors*
mechanical components.
(1) All electrical safety devices will be
electrically interlocked so that when a “trip” signal
is received from the device at the point of failure,
all the downstream conveyors and feed devices,
such as crushers and feeders, back to the initial
conveyor feed source will shut down immediately.
(2) No conveyor can be started until the
safety device has been checked and put back into
proper service. Only then can the complete
conveying system be put back into operation.
c. Emergency stop switches. Pull cord switches
and pull cords will be located along all walkways or
areas that are accessible to conveyors to protect
personnel from falling into any rotating or moving
machinery. Once “tripped” these switches have to
be manually reset before the conveyor can be
restarted.
d. Belt overtravel switches. Belt misalignment
switches will be provided on both sides of the belt
at the head and tail end of each conveyor and the
tripper, to detect conveyor belt misalignment,
which can result in serious damage to expensive
belts, drive equipment and structures. Extra
switches will be installed at selected intervals, no
more than 500 feet apart on long conveyors.
e. Conveyor zero speed switch. A zero speed
switch will be provided for each conveyor in the
system. They are installed on a nondrive pulley,
preferably the tail pulley to detect a decrease in
conveyor belt speed, from a given set value.
f. Plug chute switches. A plug chute switch will
be installed at each conveyor transfer point. They
operate when a plugged chute condition occurs,
and are arranged to stop the downstream equipment from continuing to feed the plugged chute.
Similar type switches are used in hoppers, bins,
silos and chute discharge points. Tilt type switches
are the most common type used.
g. Warning horns. Horns are used prior to the
conveyor start sequence to warn operating or
maintenance personnel that the equipment is being
placed into operation. Horns will be operated for at
least 15 seconds, before starting any conveyor.
Provide enough horns to cover all conveyor areas
in the plant.
h. Guards. Rotating or moving machinery which
provides a safety hazard to the operator will be
provided with a guard or guards to warn the
operator that a particular hazard does exist. ANSI
B20. 1 gives the conveyor designer guidance on
conveyor safety guards.
5-14
i. Conveyor backstops. A backstop is a mechanical device which allows a conveyor or bucket
elevator drive shaft to rotate in one direction only.
An automatic backstop will be installed on all
conveyors or bucket elevators subject to reversal
under loaded conditions. Backstop will be sized
according to conveyor drive motor stall torque, and
be provided with a removable torque arm. The
backstop will be installed on the conveyor drive
pulley shaft and not in the drive reducer.
j. Methane detectors. Install methane detectors
and vent system anywhere that coal is stored in an
enclosure.
5-21.
Spontaneous combustion of coal.
a. General. A major problem with the bulk
storage of coal is its ability to release enough heat,
through slow oxidation, to raise its temperature
gradually until self-ignition or spontaneous combustion occurs. The tendency of stockpiled or
stored coal to self ignite increases as the coal
ranking decreases.
b. Coal ranking. Lower rank coals tend to be
very fragile, resulting in faster degradation and
particle size reduction during the handling process.
Anthracite type coals, which are the highest ranking
coals have few problems and are very easy to
handle. Lignite and subbituminous type coals tend
to degrade quickly leading to spontaneous
combustion.
(1) When these types of coal are stored,
provisions must be made to monitor the conditions
in the silo, bunker or stockpile to reduce the occurrence of spontaneous combustion.
(2) Precautions must be taken so that material in a silo, bunker or stockpile can be evacuated
in the event of material self ignition. Without
oxygen, the oxidation process cannot take place, so
it is important that the total coal surface exposure
to air be as low as possible. Coal should be stored
so that air cannot infiltrate or move through the
storage pile. Spontaneous combustion usually only
results from careless storage procedures. Where
coal is properly stored, this likelihood is remote.
5-22.
Coal bunkers.
a. General. In the design of bunkers, careful
consideration will be given to the capacity, shape,
bunker material, and bunker location within the
steam plant.
b. Storage capacity. Bunker will be sized for a
minimum of 30 hours supply for maximum boiler
capacity.
c. Shape. The shape of the bunkers are usually a
compromise between space restrictions and optimum design for coal flow. The more common
TM 5-810-15
bunker designs are the square upside down pyramid
and silo types. Cantenary, straight, or parabolic
type bunkers will not be used because the flow of
coal from all outlets is not uniform which creates
dead pockets and causes a spontaneous combustion
hazard. Cylindrical or silo type bunkers are used to
reduce danger of spontaneous ignition of coals. To
reduce stagnation and coal segregation, separate
bunkers will be provided for each boiler. At least
the bottom of each bunker should be in the building
to preclude bottom freezing. Discharge hoppers
will be sloped at least 55 degrees. An emergency
discharge chute will be provided for each bunker to
remove coal from the bunker in emergency
situations. Silo design type bunkers are more
frequently used because they have been found to be
less susceptible to rat holing and hangups than
other shapes.
d. Material. The designer will carefully analyze
the type of material being used for the bunker, to
insure the material is compatible with the type of
coal being stored.
e. Location. Coal bunkers should be located to
provide a coal flow which is as vertical as possible.
Current trend is to replace plant storage bunkers
with inside silos which require less building volume
and structural support steel. On the average, it has
been determined that the silo and related support
steel structure were less expensive than a bunker of
the same capacity. The cylindrical shape of a silo
has an inherent strength advantage. A properly
designed bunker generally can match a silo*s flow
efficiency, therefore such factors as moisture
content, temperature and storage time have the
greatest influence on the type of silo or bunker that
is selected.
5-23.
Long term coal storage.
a. General. The long term coal storage pile is
created for the sole purpose of having an adequate
supply of coal on hand to supply coal to the boilers
in the event of an interruption of coal supplies to
the plant.
(1) The reserve or long term coal storage
pile should be maintained at the boiler plant. Refer
to TM 5-848-3 for the criteria for determining the
quantity of coal to be stored.
(2) The method of storing and reclaiming
coal in an outside storage pile should be determined
to satisfy regulatory environmental restraints.
Drainage and collection of rainwater runoff,
treatment, coal water separation and neutralizing
effluent will be included in design. Local, State and
Federal environmental regulations will determine
limits for suspended solids and pH of coal pile
runoff water and leachate. Treatment facilities will
be provided if required.
(3) Care must be taken in the method of
constructing the coal pile. Coal is placed in maximum 18-inch thick layers and then compacted with
the use of a front-end loader or rubber tired dozer
to eliminate air spaces within the pile.
(4) The designer will take into account the
“weathering” process or loss of coal heating value,
that takes place with long term storage of coal.
(5) Coal handling personnel will be assigned
to check a long term storage pile on a daily basis,
to guard against localized hot spots caused by
spontaneous combustion.
(6) A liner may be required underneath the
coal pile to prevent coal pile runoff from being
absorbed by surrounding subsoil. Soil permeability
tests will be taken in the area where the coal pile is
to be located.
b. Environmental regulations. Local and State
Regulation Agencies may have environmental regulations which prohibit open storage of coal, because of fugitive dust emissions and runoff. In this
case the designer should investigate the use of
outside coal storage silos or covered barn structures. Both silos and barns are high capital expense
items. Some agencies will allow open storage of
coals with wet suppression.
5-24.
Fire protection and prevention.
a. General. Fire protection and prevention for a
conveying system and its related structures, requires that the designer ensure careful planning
during the initial design stage to reduce coal dust.
Fire protection systems are playing a more important role in the design of conveying systems. New
code standards developed by the NFPA and industry requirements are forcing designers to reexamine
coal handling system design and the suitability of
the fire protection system. A fire protection system
can make a difference between minor damage and
total destruction.
(1) Western subbituminous type coals are
less dense, more susceptible to spontaneous
combustion than the eastern coals. The amount of
fire protection required for any system largely
depends on the type of coal to be burned at the
facility. Some coals can be stored in bunkers for
years without any spontaneous combustion
generated fires, while other coals such as some
types of western subbituminous C type coals
cannot be left in a bunker for a period over 30
days. An emergency bunker unloading system will
be included in the design to enable the bunkers to
be emptied. Western coals tend to produce a higher
5-15
TM 5-810-15
percentage of fines during the handling, conveying
and stockpiling process, thus causing particles to
become airborne, creating a more dusty
environment. Coal dust can impair the operation of
coal conveying equipment and create an unhealthy
working environment which increases the risk of
fires and explosions. Methane detectors and a vent
system should be installed in coal storage
enclosures to reduce danger of explosion.
(2) Conveyor fires are usually started by friction between seized idlers and the conveyor belt,
seized bearings or improperly aligned or maintained
equipment. If a fire on a conveyor should occur,
the conveyor, the upstream and downstream
conveyors, auxiliary feed equipment such as crushers and dust collectors must all be stopped immediately.
b. Design. The following items will be given
consideration when designing a conveyor fire protection system:
(1) An automatic wet or dry pipe sprinkler
system should be installed along conveyors, to
protect the carrying and return belts, conveyor
drives, underground tunnels and control areas.
(2) Automatic deluge systems require large
flow rates to protect the conveyor and the
conveyor galleries. The water supply system will be
investigated to see if it can support the required
flow rates when a fire protection system is
determined to be necessary.
(3) Adequate means of removing fire protection water from below grade tunnels must be
provided to ensure that personnel can be evacuated
before a hazardous water build up occurs.
(4) A dry pipe or preaction type system,
which employ a fusible link or glass bulb sprinkler
heads, are usually used in areas that are subject to
freezing conditions. This type of system is the more
popular type of fire protection system.
(5) A wet pipe system, which is basically the
same as dry pipe, except that water is in the system
piping at all times, is usually suitable for areas not
subject to freezing.
(6) A fire detection and evacuation alarm
system will be provided throughout all facilities
with pull stations at all exterior exits and sufficient
evacuation alarms to overcome the normally higher
level of noise found in power plants. The fire
detection and evacuation alarms will give indication
in main and auxiliary control roams and into the
plant main fire alarm system.
(7) Adequate fire hydrant protection will be
provided for all coal piles and consideration will be
given to the long term methods of coal pile storage
to minimize spontaneous combustion.
(8) Draft barriers or fire walls will be provided at each end of conveyor galleries.
5-16
(9) Safety escapes. Conveyors will include
means of egress that comply with all applicable
codes. In no case will the distance from any
location on the conveyor to a safety escape to
grade level exceed 200 feet.
(10) Carbon dioxide, or steam protection
should be considered for bunkers, bins and silos. A
method of transporting coal from a silo to a remote
yard area in the event of a fire will be considered in
the design.
(11) There are numerous types of fire detection sensors and detectors such as heat, continuous
thermal sensor, fixed temperature spot sensor,
fusible thermal wire, pneumatic rate of rise, series
thermal detector, smoke detectors, ionization detectors, flame, ultraviolet, infrared and numerous
others. There is no single, all purpose sensor or
detector for a fire protection system and a well
designed system usually requires a wide range of
sensors for maximum system protection. Matching
the specific type and configuration of the detector
or sensor to a particular hazard is very difficult and
a professional fire protection systems engineer who
has experience with the design and operation of
coal handling fire protection systems should be
consulted.
5-25.
Control system.
a. General. Control of the individual conveying
system operations should be conducted from a
single control room. The following items should be
considered:
(1) The control system will be capable of
providing a local manual, remote manual or fully
automatic control of the conveying system.
(2) Conveyor controls will be interlocked to
prevent coal spills in the event of a system
malfunction and to shut the conveying systems
down in a set sequence. The controls will provide
a foolproof sequential method of starting and stopping upstream and downstream equipment in the
conveying system.
(3) A locked remote control panel will be
located next to each piece of equipment they
control, so that the equipment can be locally
operated by maintenance personnel. Local panels
will be interlocked with main control panel so that
both panels cannot be operated at the same time.
(4) Each system will be adequately
monitored with alarm and control devices so that
the operating status of the system can be
determined from indicating lights on the control
room graphic or mimic display panel.
(5) Indicating lights will be provided on a
separate annunciator panel for belt misalignment,
plugged chute, drive motor overload, emergency
stop, zero speed, or any other safety device. The
TM 5-810-15
lights tell the operator at the control panel which
piece of equipment has tripped and also the reason.
(6) Motor operated gates and valves will be
provided in locations requiring frequent operation,
and properly interlocked for starting and stopping
in the proper sequence.
b. Computerized
control
systems.
A
computerized control system such as a
programmable controller (PC) is the most cost
effective where logic functions must be
accomplished. Advances in micro technology make
the cost of computer type controls more
economical than the relay based control systems.
Field changes to the logic in a PC system can be
made without wiring changes. Most units allow a
program simulation mode, whereby the PC will
diagnose the program and check the logic that has
been entered. The computerized system is the
preferred method of control.
5-26.
En masse conveying system.
a. General. This type of system uses a conveying
chain which utilizes the skeletal flight as opposed to
a paddle flight, which can greatly reduce the
horsepower requirements for the conveyor. The
conveyor chain runs in a completely enclosed and
sealed trough. The effective conveying capacity can
reach as high as 90 percent of the cross sectional
area. These conveyors have the ability to convey
horizontally, inclined or vertically, which makes
them extremely versatile.
(1) En masse type conveyors require
approximately twice as much horsepower as a
regular belt conveyor to move the same amount of
material the same distance. They are also very
susceptible to foreign material, which is not the
case with belt conveyors. Special care has to be
taken when handling abrasive or corrosive
materials.
(2) En masse conveyors are advantageous
for overbunker distribution systems, offering totally
enclosed, multiple or individual discharges which
do not require complicated or extensive chutework
at the discharge points.
b. Chain. Use short pitch, drop forged alloy
steel, carburized or case hardened to 500-600
Brinell Hardness Number (BHN). Each link should
be easily removable without cutting any part.
c. Trough. Provide symmetrical panels for wear
and maintenance. Sides and bottom plates will be
abrasion resistant and bolted for easy replacement.
d. Return rails. Hardness of rails will match the
hardness of the conveying chain.
e. Drive sprockets. Provide a segmental type
with reversible teeth sections, so that the complete
drive shaft assembly does not have to be removed
for maintenance. Teeth hardness will match chain
hardness.
5-27.
Pneumatic conveying systems.
a. General. Pneumatic conveying involves the
movement of powdered, granular or other free
flowing bulk materials along the pipeline with the
aid of compressed air. Pneumatic conveying can be
very basically categorized into two areas—dense
phase and dilute phase. Suitable materials that can
become fluid-like or fluidized are usually only
suitable for pneumatic conveying. The product size
can also restrict the use of this type of conveying
medium. This type of system is sometimes used for
moving small tonnages, up to about 50 tph.
(1) Materials that have a high moisture content, such as wet coal are difficult if not impossible
to handle in a pneumatic type system.
(2) Pneumatic conveying systems are extremely inefficient when comparing tonnage moved
to hp required to move the material with energy
consumption as much as five times that of a belt
conveyor.
(3) Exotic auxiliary equipment and very
costly control components have to be compared
with the minimal roam requirements and ease of
installation for this type of system.
b. Advantages and disadvantages.
(1) Advantages of pneumatic conveying systems are that they require little maintenance, take
up less space than belt conveying equipment, are
usually automatic (eliminating manual operations)
and are totally enclosed, thus avoiding
environmental fugitive emission problems, spillage
and dust.
(2) Disadvantages of pneumatic systems are
that they usually have a higher operating cost than
belt conveying systems because compressed air is
used to convey the material and there is a limitation
on the maximum size material and the amount of
fines that can be conveyed. Coal fines in excess of
40 percent will cause pluggage problems in the
conveying pipe. Pneumatic conveying tends to
create additional coal fines.
5-17
TM 5-810-15
CHAPTER 6
ASH HANDLING
6-1. General.
This chapter addresses the requirements for the ash
handling system for a coal fired boiler plant.
a. Design criteria. Ash handling systems were
relatively simple prior to the enactment of stringent
environmental regulations during the past twenty
years. The ash was commonly quenched in wet ash
pits and hydraulically discharged through ash sluice
trenches to a sump pit and from there were pumped
to an ash fill area. Bottom ash, pulverizer or mill
pyrite rejects (pulverized coal fired plants only),
economizer ash and fly ash are sometimes handled
by individual, independent systems in plants now
being designed.
b. Methods. A well accepted method of handling
bottom ash and fly ash today is by the use of
pneumatic conveying systems in stoker fired boilers. Ash is pneumatically conveyed to a storage silo
without coming in contact with steam or liquid.
Figure 6-1 shows a typical bottom ash and fly ash
conveying system. Ash dust control conditioners
have been developed to mix water with dry bottom
ash and fly ash in the proper proportions to reduce
the fugitive dust emissions during the transfer of
ash from the storage silo to either trucks or railcars.
Because of higher furnace temperatures and larger
ash quantities in pulverized coal fired boilers,
bottom ash has been water quenched and
hydraulically conveyed. Dry bottom ash systems
have been limited in quantity because of dry gravity
flow. Continuous removal dry bottom ash systems
are becoming available and allow reconsideration of
dry bottom ash handling. Water filled bottom ash
storage hoppers have been designed to
accommodate large ash quantities. Bottom ash is
periodically removed from the bottom ash hopper
and hydraulically sluiced to an ash pond or to
dewatering bins. Quantity and characteristics of ash
produced in a coal fired boiler, and the ratio of fly
to bottom ash depends on the coal being used,
steaming rate, and method of burning. These
factors, along with a LCCA of available ash
handling systems will determine equipment selection. This chapter will consider hydraulic, mechanical and pneumatic ash handling systems.
6-2. System design.
a. General. There are many considerations involved in selecting an ash handling system for a
coal fired boiler plant. These are as follows:
b. Boiler design and configuration. The boiler
determines the amount of coal to be burned, and
the percentage of fly ash to bottom ash. In a
pulverized coal-fired boiler approximately 80 percent of all ash is fly ash and the remainder 20
percent is bottom ash. In a stoker fired boiler
approximately 20 to 30 percent of the total ash
content in the coal is fly ash with the remaining amount being bottom ash. The versatility of the
boilers to burn a wide range of coals should be
considered to determine the highest ash production rate when sizing the system conveying capacity.
c. Disposal conditions. Disposal to an ash pond
or, alternatively, to storage bins or silos is a factor
in selection of equipment. Ash ponds require large
areas of land and must meet environmental regulatory restrictions. Ash storage bins require less
space and are environmentally more compatible
than ash ponds; however, the ash must ultimately
be removed from the bin and disposed.
d. Water availability. The availability of water
as a source for conveying ash, its pH rating and
other chemical characteristics must be considered.
If the water is not recycled, the environmental
regulations of the discharged water must be considered. In most localities, untreated overflow is
not permitted.
e. Type of coal. The type of coal to be burned, its
ash content, sulfur content and its chemical
constituents have an effect on the selection of the
ash handling system. The coal with the highest ash
content at the maximum continuous boiler steam
output rating will be anticipated to assure adequate
ash handling capacity. Ash from some coals with
high calcium oxide content, such as western
subbituminous coal, has a tendency to solidify when
it comes in contact with water and should be
handled dry to the disposal areas where it can be
blown underwater from a closed bed truck.
f. Design capacity. The design criteria for selection of conveying capacity will be made to require
the system to operate no more than 50 percent of
the time or four hours in an eight hour shift. The
remaining time is used for maintenance or catch up
time on the ash handling system. The conveying
time is based on the coal with the highest ash
content which can be used in the boilers and with a
10 percent reserve margin on the estimated percent
fly ash and bottom ash.
6-1
TM 5-810-15
6-3. Bottom ash hydraulic conveying systems.
a. General. Hydraulic conveying systems are
generally used for only bottom ash handling systems. Bottom ash is collected in a water impounded
refractory lined steel hopper, which will be sized to
store a minimum of twelve hours production of ash
under the worst coal conditions at maximum
continuous boiler steam output rating. The water
impounded bottom ash hopper allows ash to fall
through a clinker grinder or crusher where the ash
is ground to a predetermined size prior to entry
into a hydraulic ejector or in some instances to
material handling pumps. The ash is sluiced from
the plant to ash ponds or to dewatering bins. Figure
6-2 shows a typical sluice conveyor arrangement.
The ash slurry is conveyed by a system of ash sluice
centrifugal pumps. Ash handling pumps are
discussed in paragraph 7-13. Most hydraulic
ejectors are jet pumps requiring high pressure ash
sluice centrifugal pumps to supply the water that is
used to convey the ash to the storage area. This
arrangement eliminates the need for a downstream
transfer tank and the use of pumps to convey the
abrasive ash slurry as shown in figure 6-3. The high
pressure ash sluice pumps are also used for hopper
washdown nozzles. Low pressure ash sluice
centrifugal pumps supply water for bottom ash
hopper furnace sealing and for coaling the refractory lined hoppers, and inspection windows.
b. Ash ponds. The ash ponds receive the ash
slurry from the bottom ash hopper. Ash ponds must
be sealed to prevent seepage into ground water.
Ash ponds can be constructed in a manner to allow
the water to be stored and returned to the plant for
6-2
reuse. The ash ponds which act as a solid liquid
separator must have a considerable area since
retention time is the only means to allow ash to
settle and separate from the conveying water. If fly
ash is conveyed to the ash pond, the pond must be
greatly enlarged because of the extremely slow
settling rate.
c. Dewatering bins. Dewatering bins receive the
ash water slurry and drain the water from the
accumulated ash. Dewatering bins, like the ash
ponds, can work in a closed system or an open
system where water is allowed to drain to waste. In
most cases the discharge of water is not allowed by
regulation, so a closed recycling dewatering system
will be discussed. After passing through the bottom
ash hopper the ash is pumped to two dewatering
bins. While one bit receives ash slurry the other bin
is draining or decanting to separate the solids and
liquids. The dewatered bottom ash is discharged
from the bin to trucks or railcars as shown in figure
6-4. Each dewatering bin will be sized for at least
36 hour storage for a total of 72 hours storage for
long weekends when trucks or rail service is not
available. The dewatering bins will be designed
with a 30-degree angle of repose for the ash at the
top of the bins. The dewatering bins will be
designed to hold the determined ash capacity at an
ash/water density of 62.4 pounds per cubic foot
(pcf) and be designed structurally for an ash/water
density of 110 pcf. From the dewatering bins which
act as the solid/liquid separator, the decanted water
with some entrained ash fines flows by gravity into
a settling tank for the second stage of separating
the ash from the sluicing water. The settling tank
TM 5-810-15
overflows into a surge tank which is the third and
final stage of the closed recirculation system. The
surge tank is sized to accommodate the overall
coaling and conveying water demands of the
bottom ash system. The decanted ash sluice water
is returned to the ash conveying system for
recycling. The ash sludge which is collected in the
settling and surge tanks are returned to the
dewatering bins by the use of sludge return pumps.
A dewatering system is much more compact but
usually more expensive to purchase and operate
than an ash pond system. Climatic conditions may
require this system to be enclosed and piping heat
traced to avoid freeze up problems.
6-4. Bottom ash handling system alternatives.
a. Submerged drag chain mechanical transport
system. Mechanical transport systems collect bottom ash in a water impounded hopper. The hopper
includes a water seal to prevent escape of the boiler
furnace flue gases into the environment and to
prevent ambient air from entering the boiler. The
6-3
TM 5-810-15
ash is continuously removed by a submerged
scraper conveyor. The ash is then conveyed to
either a storage bin with a capacity of up to three
days or to a bunker for front end loader/truck
removal. The water is recirculated into and out of
the submerged trough to maintain a temperature
below 140 degrees F. Overflow water from the
trough is filtered through tanks before it is recirculated into the system. Surge tanks are small
compared to the dewatering system tanks.
b. Sizing. The submerged scraper conveyor must
be sized so that the rate of ash removal will be at
least as great as ash production at maximum
continuous boiler steam output rating under worst
fuel conditions. Mechanical transport has several
advantages over hydraulic transport. The ash removed is dewatered, it requires a lower boiler
setting height and reduces power and water consumption. However, ash storage in a submerged
scraper conveyor is limited and maintenance must
be done in a relatively short period of time.
Expensive standby conveyors and transition hoppers are often needed to provide time to perform
maintenance. The submerged scraper conveyor is
not commonly used in the United States because
the reliability of the system in past years has been
too low. There is some renewed interest by industry in the use of this type of system because of the
recent improvements in the reliability and its wider
acceptance in the European countries. Also in
current use in Europe is a continuous dry removal
system utilizing moving stainless steel belting and
introduction of additional air to complete
combustion and cool the ash.
6-4
6-5. Fly ash pneumatic systems.
a. Pneumatic systems. This type of system is
usually used to transport fly ash from the fly ash
collection equipment storage hoppers to the ash
storage silo. The tendency of some types of fly ash
to form scale inside hydraulic fly ash conveying
lines and its extremely slow settling rate in water
when coupled with the environmental liquid discharge limitations have severely restricted the use
of the wet type fly ash conveying system. An
advantage of pneumatic systems is they can be
applied to both fly ash and bottom ash for stoker
fired or fluidized bed boilers simplifying ash conveying and storage as shown in figure 6-5. Pneumatic systems are either vacuum or pressure types
of system. A vacuum system pulls ash from the fly
ash storage hoppers by means of mechanical, steam
or water powered exhausters and a filtering system.
Vacuum systems, depending on capacity
requirements, line configuration and plant altitude
may be designed for vacuum levels ranging from 8
to 20 inches Mercury (Hg). Vacuum systems are
generally preferable to pressure systems because
the system piping joint leaks pull air into the system
leaving a cleaner environment. A vacuum system is
recommended for capacities of less than 60 tph per
system. If the conveying distance is at a remote
location of over 800 feet from the boiler plant an
evaluation will be made to determine whether a
vacuum or pressure system is more feasible. A
comparison of vacuum systems and pressure
systems are shown in table 6-1.
b. Pressure systems. A pressure system engages
a positive displacement blower producing pressures
TM 5-810-15
up to 20 psig for the conveying system as shown in
figure 6-6. System capacity and long conveyor
distances sometimes require higher blower
pressures. Pressure systems may be used in lieu of
vacuum systems because of higher capacities or
longer conveying distances. Pressure type system
should be avoided where possible because leaks of
fine ash particles usually occur at the piping joints.
Silo storage design is the same for a pressure
system as for a vacuum system except that ash
collectors are not required at the silo and fly ash is
redeposited directly into the silo. There are two
types of pressure systems, the dilute phase and
dense phase. The dilute phase system usually has an
ash to air volumetric ratio of 15 to 1 and sometimes
it is as high as 30 to 1. A dense phase system has an
ash to air ratio of 40 to 50 to 1 and is sometimes as
high as 80 to 1. Vacuum systems are classified as
dilute phase. A comparison of pressure dilute phase
and dense phase systems is shown in table 6-2. The
dilute phase pressure system is the more widely
used pressure system. Dense phase pressure
systems utilize a fluidizing transporter, a vessel in
which air and ash is mixed, fluidizing the ash so
that flow characteristics resemble that of a liquid.
c. Vacuum/pressure systems. In some rare cases,
it may be more economical to combine a vacuum
system with a pressure system where distance rules
out the use of a vacuum system alone. Figure 6-7
shows a typical vacuum/pressure system. The
vacuum system, with its simplified controls,
removes ash at an optimum rate. The pressure
system, reduced to one transfer point with a
minimum of controls, then delivers collected ash to
any terminal point at a distance of several thousand
feet. The vacuum pressure system provides the
least complex controls of any long distance
pneumatic conveying system.
d. Ash storage silos. Storage silos are usually
constructed of carbon steel because of its lower
cost and durability. Hollow concrete stave construction or reinforced concrete construction are
sometimes used. The bottom of ash storage silos
are equipped with aeration stones to fluidize the
ash and induce flow from the silo to the discharge
outlets. Silos will be designed for a minimum of
sixty hours of storage, based on the design and
production rate, utilizing an ash density of 60 pcf.
The actual ash density can vary from 60 pcf
depending on the coals being fired. The silo support structure will be designed for a full silo with
fly ash density 100 pcf.
6-6. Controls
a. General. Programmable type control systems
are used for both automatic and semi-automatic
control. Older systems used electromechanical type
control systems, many of which are still in operation.
b. Types.
(1) Programmable controllers (PC) have
been applied to ash handling systems with good
success during the last fifteen years and are the
6-5
TM 5-810-15
Table 6-1. Comparison of Pneumatic Vacuum Versus Pressure Ash Conveying Systems.
Vacuum Systems
Pressure Systems
Convey systems less than 60 TPH per system.
Reasonable conveying distance.
High system capacity.
Long conveying distances (greater than 1000 to
2000 feet).
Less maintenance at hoppers.
System leaks inward for cleaner environment.
Multiple collecting points.
Simpler control scheme.
Relative unlimited capacity.
Relative unlimited conveying distance.
No separating equipment.
Clean air blowers multiple disposal points.
Requires separating equipment and process bag
filter.
Blower life dependent on separating equipment
reliability.
Double gates required with air lock.
Air lock pressurizing and venting requires
additional piping and valving.
Ash leaks outward into the plant.
Higher maintenance costs.
When Recommended
Advantages
Disadvantages
most preferable type of control. The PC*s ability to
perform relay logic, timing, counting, and sequencing functions, provides a way to perform the
tasks required for ash handling system control. A
number of higher level PC*s also offer more
enhanced capabilities such as instruction,
sophisticated report generation and off-line programming. The PC performs all ash handling
controls and allows flexibility in control schemes
giving the user many benefits. The PC has a
memory and is programmable, providing the user
with the ability to change the ash handling sequence
6-6
and timing and gives him the ability to
troubleshoot, modify and expand with the system.
(2) Before the advent of the PC, both the
bottom ash and fly ash made extensive use of the
drum sequencer, electromagnetic timers and
counters, and relay logic. The disadvantage of the
electromechanical system is the large amount of
relay control required for the drum sequencer; the
periodic maintenance required for the drum sequencer, the large amount of panel area required;
the extensive wiring; and the inflexibility of the
system when changes are required.
TM 5-810-15
Table 6-2. Comparison of Pressure Dilute Phase and Dense Phase Pneumatic Ash Conveying Systems.
Dilute Phase
Dense Phase
Design Criteria
Evenly loaded single conveying line.
Loading ratio (5 to 22) lbs. of ash to lb. of air.
10 to 30 psig operating pressure.
2000 to 3500 ft per mm starting velocity.
Typically multiple convey lines.
Loading ratio (20 to 200) lbs. of ash to lb. of air.
30 to 100 psig operating pressure.
600 to 3000 ft per min starting velocity.
High conveying capacity (greater than 30 TPH)
Long conveying distances (greater than 1000 ft).*
Multiple disposal points.
Minimum collection points.
Short conveying distances (200 to 500 ft).*
Medium capacities (10 to 50 TPH).
Minimum collection points.
Minimum disposal points.
Greater capacities and distances with single line.
Not affected by material changes with gravity flow.
Stable velocity range provides material re-entrainment.
Transfer stations normally not required.
Low initial cost air handling equipment
Components subjected to lower pressure.
Smaller conveyor lines, bag filters and hoppers.
Lower conveying velocity.
Normally lower horsepower.
Carbon steel pipe.
Higher airflow, larger pipe, and hoppers.
Often higher horsepower.
Components subjected to higher velocity,
Special pipe required-alloy pipe or ceramic lined pipe.
Material consistency greatly affects conveying
parameters and granular material remains in
airlock with top exist.
Positive sealing high differential discharge valve is
critical to system performance.
Transfer stations normally required.
Parallel compressed air lines required to free line plugs.
Multiple conveyor lines.
Expensive initial cost air compressors.
Components subject to higher pressure.
When
Recommended
Advantages
Disadvantages
*An evaluation should be made for conveying distances of 500 to 1000 ft to determine whether Dilute Phase or Dense Phase pneumatic ash conveying systems are more feasible.
6-7
TM 5-810-15
CHAPTER 7
MECHANICAL AUXILIARY EQUIPMENT
7-1. General.
This chapter addresses the criteria for the major
steam plant auxiliary equipment.
7-2. Closed
(CFHE).
feedwater
heat
exchangers
a. Applications. CFHE may be used to raise
feedwater temperature to the plant economizer and
thus maintain the exit flue gas temperature above
the acid dew point during low load operation. This
application is possible for plant design in all size
ranges. Other methods for keeping the exit flue gas
temperature above the acid dew point are
bypassing flue gas around the economizer or
bypassing a portion of feedwater around the economizer which needs to be avoided. Bypassing the
feedwater around the economizer at low load operation creates a potential for steam formation in the
economizer. The CFHE is the most positive
approach to maintaining the exist flue gas temperature. An evaluation will be made to determine the
economic practicality of each method.
b. CFHE design. Each CFHE will be a U-tube
type heater to minimize stresses caused by thermal
expansion. Tube material selection is dependent on
the quality of the water. Tubes of stainless steel
construction will minimize the possibility of
corrosion and erosion. High quality water will
allow the use of 90/10 and 70/30 copper nickel
(CuNi) material tubing.
c. CFHE design criteria. Data listed in table 7-1
are necessary to size CFHE.
Table 7-1. Closed Feedwater Heat Exchanger Design
Parameters.
Parameter
Engineering Units
Feedwater flow
Feedwater inlet temperature
Feedwater outlet temperature
Maximum feedwater velocity
Maximum allowable tube side pressure
drop
Maximum tube side operating pressure
Maximum shell side operating pressure
pph
degrees F
degrees F
fps
psi
psig
psig
Minimum recommended feedwater temperatures to
the economizer are shown in figure 7-1. Minimum
feedwater velocities are shown in figure 7-2.
7-3. Steam deaerators.
a. General. The steam deaerator (DA) heats
boiler feedwater to improve plant efficiency and
lowers dissolved oxygen and gasses that are corrosive to internal metal surfaces of the boiler. The
standards of the Heat Exchange Institute (HEI),
1992, Fifth Edition, state that a DA should be
guaranteed to remove all dissolved oxygen in
excess of 0.005 cc/i.
b. Deaerator types. There are several types of
steam DA with three acceptable types being:
spray/tray type, atomizer or scrubber spray type
and recycle type. DA heater should be counterflow
design. Although some tray and recycle type DA*s
have a higher first cost, they will operate properly
under rapid load changes and only require a 10 to
30 degrees F rise across the DA (inlet water
temperature 10 to 30 degrees F lower than the DA
outlet water temperature). Spray or atomizing type
DA*s can be used when steam loads are steady and
the temperature rise across the DA is 30 to 50
degrees F or greater. Because of this performance
limitation, tray or recycle type DA*s will be used
unless there is a steady steam load and the
temperature rise in the DA is 50 degrees F or
greater. If the latter conditions exist, the DA
selection will be decided by a LCCA.
c. Deaerator design criteria. Deaerating heaters
and storage tanks will comply with the ASME
Unfired Pressure Vessel Code, ASME Power Test
Code for Deaerators, Heat Exchange Institute,
American National Standards Institute, and National Association of Corrosion Engineers Recommendations. One steam plant DA can be sized for
multiple boiler units. At full load conditions, the
water from the DA will have a temperature
sufficiently high to prevent acid dew point corrosion of the economizer. In no case will the temperature rise in the DA be less than 20 degrees F or
the minimum storage capacity at normal operating
level be less than 10 minutes at the DA*s maximum
continuous load rating or less than 12 minutes full.
Information contained in table 7-2 will be specified
after a heat balance around the DA has been
determined at full load conditions.
7-1
TM 5-810-15
7-2
TM 5-810-15
Table 7-2. Specified Deaerator Information.
Item
Engineering Units
Maximum plant capacity
Maximum DA outlet capacity
Make-up water temperature
Condensate temperature
Make-up water flow
Condensate flow
Steam temperature to DA
Steam pressure to DA prior to control
valve
DA design pressure
DA outlet water temperature
DA outlet water flow
pph
pph
degrees F
degrees F
pph
pph
degrees F
psig
psig
degrees F
pph
7-4. Boiler feed pumps.
a. General. Boiler feed pumps convey water
from the DA to the boiler.
b. Design requirements. Boiler feed pumps will
comply with the latest revisions of Hydraulics
Institute (HI) and ANSI. A minimum of one pump
per boiler and one backup pump will be provided
for all cases. The ASME Boiler and Pressure
Vessel Code requires that coal fired boiler plants in
this size range be provided with at least two means
of feeding water. For stoker fired boilers, one
source will supply sufficient water to prevent boiler
damage during an interruption. A steam turbine
driven pump is one method that is frequently used
to meet this requirement. Multiple pumps permit
backup capacity for individual pump failures or
scheduled maintenance and increase efficiency of
pump operations at reduced loads. Multiple pumps
are usually more cost effective for boilers subjected
to large daily load swings. This arrangement allows
the pumps to operate in a more efficient range and
gives the system more flexibility. The use of
multiple pumps will provide for between 50 and
100 percent of additional capacity beyond the
expected operating loads.
c. Steam turbine drives vs electric motor drives.
Steam turbine drives provide a more thermally
efficient system, but in this size range they can be
less economical on a LOCA than electric motor
drives. However, as noted above, the ASME Boiler
and Pressure Vessel Code requires that both steam
turbine and motor drives be used in stoker fired
bailer plants with capacities of 35,000 pph and
above. Steam turbine drives will not be used
exclusively. An electric motor drive makes it easier
to bring a boiler on line from a cold start.
d. Boiler feed pump sizing. Boiler feed pumps
will be sized to deliver the desired flow and
pressure to the boilers from the DA. A 10 percent
flow margin for wear allowance will be included
when sizing the pump. These conditions are determined by first defining the items listed in table 7-3.
Table 7-3. Boiler Feed Pumps Capacity Criteria.
Item
Engineering Units
Boiler steam outlet pressure
psig
Boiler water side pressure losses
psi
Water temperature entering pump
degrees F
Piping losses
psi
DA operating pressure
psig
Pump elevation relative to boiler and DA ft
Net positive suction head required
ft
(NPSHR)
(1) Calculation of net positive suction head
available (NPSHA). Determining the NPSHA is an
important design consideration for boiler feed
pumps because they take water from the DA at
saturated conditions. To prevent cavitation of a
pump operating at elevated temperatures, the DA
is elevated to increase the static pressure at the
pump suction and overcome the vapor pressure.
The boiler feed pump vapor pressure is equal to the
DA operating pressure and cancel out each other.
Thus, boiler feed pump NPSHA is the head of
water from the DA to the pump inlet minus the
pipe friction loss. A safety margin of at least one
foot of head will be subtracted from the calculated
NPSHA to obtain the net positive suction head
required (NPSHR).
(2) Discharge head calculation. The boiler
feed pump discharge head will be designed to
overcome the boiler drum pressure, valve and
piping losses within the boiler and external to the
boiler as well as the head of the water column.
e. Pump construction. The boiler feed pumps will
be constructed to provide continuous operation for
the expected plant life. Pump manufacturers should
be consulted regarding specific features of
construction for a particular application. In general,
lower pressures and flows could use vertical in-line
pumps with stainless steel shaft, impellers, and
impeller casings. Suction and discharge chambers
on vertical pumps will be cast iron. For higher
pressure and flow applications casings will be 11 to
13 percent chrome steel, split on the horizontal
centerline with suction nozzles, discharge nozzles
and feet on the lower half of the casing so the top
half of the casings can be removed without
7-3
TM 5-810-15
disturbing the main piping. These applications will
also include shafts constructed of stainless steel,
containing not less than 11 percent chrome. The
impellers will be of the closed type, cast in one
piece. All internal parts of the pumps including
impellers, sleeves and wearing rings, will be
constructed of stainless steel containing not less
than 11 percent chrome.
7-5. Condensate pumps.
a. General. The condensate pumps convey condensate from condensate return storage tank to the
DA.
b. Design requirements. A minimum of two condensate pumps will be used, each sized for at least
two thirds of the maximum steam plant demand.
This configuration will provide backup capacity for
individual pump failures or scheduled maintenance
and will increase pump operation efficiency at
reduced loads. Steam turbine driven pumps may be
more economical than electric motor driven pumps.
However, one electric motor driven pump
facilitates cold start-up of the boiler plant. A LCCA
will be made to determine the most practical
combination of condensate pumps.
c. Condensate pump sizing. The condensate
pump discharge head needs to be designed to
overcome the water static head to the DA, the
piping losses and the DA operating pressure. A 10
percent flow margin for wear allowance will be
included when sizing the pump. The condensate
pump discharge head and suction head available
will be determined when the operating conditions
are defined, an arrangement of the equipment has
been made, and a pipe size and routing has been
made.
d. Pump construction. Pumps will be constructed
so they will provide continuous operation for the
expected plant life. Pump manufacturers should be
consulted regarding specific features of
construction for a particular application. The pump
impellers will be split ring key type. Bearings will
be of the water lubricated sleeve type. The
baseplate, outer barrel, inner column and discharge
head will be carbon steel. The impeller will be
bronze and the pump bearings graphalloy. The
stage bowl will be cast iron. The shaft, shaft sleeves
and wearing rings will be 11 to 13 percent chrome
stainless steel. When the pump design conditions
do not require a vertical can type pump as
described above, the pump may be centrifugal,
horizontal end suction, top discharge type as described below. The pump impellers will be totally
open type, screw mounted directly to the shaft with
0-ring seal and constructed of ductile iron.
Impellers will be dynamically balanced to the
7-4
maximum rated speed. The pump construction will
include antifriction bearings that operate in an oil
bath. Pump and bearing frame and housing will be
constructed of cast iron. Casing will be constructed
of ductile iron. Minimum casing thickness will be ½
inch with an additional 1/8 inch corrosion
allowance. The shaft, shaft sleeves and wearing
rings will be 316 stainless steel.
e. Turbine drives. The turbine drives will be
sized to match the runout hp of the pump. Turbine
drives will be horizontal split case construction.
The steam chest will be case iron or cast steel. The
rotor shaft will be annealed carbon steel and the
rotor disc a high strength alloy steel.
7-6. Air compressors.
a. Applications. Two compressor applications
are used in a steam plant: plant air and instrument
air. Plant air is the dry air used to atomize fuel oil,
blow soot deposits from the boiler furnace and heat
recovery equipment, run plant pneumatic tools, and
perform other general plant functions. Instrument
air is oil free, dry air supplied to instruments and
pneumatic controls control valves and control
drives. Instrument air is also used to clean fly ash
baghouse filter bags.
b. Compressor types. Compressors are available
in two types. The first type is positive displacement, such as the reciprocating piston compressor.
The second type is dynamic, such as the centrifugal
compressor. Each type can be furnished with single
stage or multiple stage design. Reciprocal and
centrifugal compressors are the industry standard
for compressors used in boiler plants. Centrifugal
compressors are usually considered for selection
when the compressed air demand is uniform and is
equal to or above 400 standard cubic feet per
minute (scfm). Otherwise reciprocating compressors are usually used.
c. Instrument air compressor sizing criteria.
(1) Required volume of air. The required
volume of air needed is found by adding all simultaneous air usages together. With instrument air, the
highest usages generally occur during boiler start
up when lighters are inserted or when fly ash
baghouse filter bags are being cleaned.
(2) Outlet pressure. The compressor outlet
pressure will be sufficient to supply air at the
required pressure, after line losses, to the device
requiring the highest pressure in the instrument air
system. Pressure regulators will limit the pressure
to devices operating at lower pressures.
d. Plant air compressor sizing criteria.
(1) Required volume of air. The required
volume of air needed is found by adding all simultaneous air usages together. One of the highest
TM 5-810-15
usages of plant air occurs when air soot blowers
are used in the boiler. Steam soot blowers may be
used eliminating the need for air soot blowers.
Other usages which must be considered are air tool
demand and cleaning coal handling dust bags.
(2) Outlet pressure. The compressor outlet
pressure will be sufficient to supply air at the
required pressure, after line losses, to the device
requiring the highest pressure in the plant air
system. Pressure regulators will limit the pressure
to devices operating at lower pressures.
e. Compressor auxiliaries.
(1) Aftercoolers/intercoolers. Intercoolers
are used on any compressor having more than one
stage, and all compressors will have aftercoolers.
Aftercoolers will be pipeline type units with air-intube, water-in-shell construction and designed with
a 20 degrees F approach.
(2) Air dryers. All air compressors will have
air dryers installed immediately downstream of the
aftercoolers. The dryers will be designed to
maintain a dew point at line pressure which is lower
than any ambient temperature to which pressurized
air lines are exposed.
(3) Receivers. Receivers will be sized based
upon a timed usage of a volume of air. The
required tank volume will be determined using
equation 7-1:
T ' V x (P1 & P2)
(eq 7-1)
C x P0
T = time in minutes receiver will supply air from
upper to lower pressure limits (use 15 seconds)
V = volume of tank, in cubic feet
P0 = absolute atmospheric pressure, psia
P1 = maximum tank pressure, psia (compressor
discharge pressure)
P2 = minimum tank pressure, psia (pressure required to operate tool)
C = amount of cubic feet of free air needed per
minute, cfm (air at ambient temperature and
pressure)
f. General design criteria.
(1) The total air capacity will be increased by
a factor of 1.1 to 1.2 to account for leakage.
(2) Both the instrument air and the plant air
systems will consist of two compressors tied to a
common header. Backup capacity of 100 percent
will be provided so maximum compressed air
demand can be satisfied with one compressor out
of service.
(3) The headers for instrument air and plant
air will have an emergency cross-connection
equipped with oil removal equipment to protect the
instrument air system.
(4) Plant air compressor will be designed to
be loaded 50 percent of the time at maximum load.
Instrument air compressor is to be sized for 40
percent loading at maximum load. Centrifugal
compressors can be loaded 100 percent of the time.
(5) Provisions will be made to allow
drainage of water from all coolers and receivers by
means of traps or manual valving.
(6) Separate receivers will be placed near
area of large air demands. It may be more
economical to supply separate air systems for air
soot blowers and baghouse cleaning systems.
7-7. Boiler feedwater treatment.
a. General. Feedwater treatment is necessary to
prevent corrosion of metals, formation of deposits
and to minimize boiler water solids carryover.
Boiler water treatment guidelines are discussed in
AR 42049. For boilers operating at 400 psig,
constituents in the feedwater must be controlled so
that the maximum water limits for boiler feed-water
and boiler water shown in tables 7-4 and 7-5 can be
maintained with minimal boiler blow-down, since
the higher the blowdown rate, the greater the
thermal loss. An evaluation will be made to
determine the costs of thermal losses due to
blowdown versus the costs of high quality treated
water.
Table 7-4. Boiler Feedwater Limits.
Drum
Pressure
(psig)
Iron
(ppm Fe)
Copper
(ppm Cu)
Total hardness
Calcium
carbonate
(ppm CaCo3)
0-300
3010-450
0.100
0.050
0.050
0.025
0.300
0.300
Table 7-5. Boiler Water Limits.
Drum
pressure
(psig)
0-300
301-450
Total
Alkalinity
Silica
calcium
Specific
silicon dioxide carbonate
conductance
(ppm SiG) (ppm CaCo3) (micromhos./cm)
150
90
700
600
7000
6000
b. Design requirements. Before a plant water
treatment system is designed, a thorough raw water
analysis will be obtained as shown in table 7-6.
The raw water condition can vary widely even
within a small regional area and can greatly effect
the options and economics available for water
treatment equipment. Also, the purity and quantity
7-5
TM 5-810-15
of condensate available as feedwater is to be
established. From this information the actual
feedwater constituents to be treated can be determined. The water treatment requirements for the
plant can then be identified based on the allowable
boiler water limits and the desired amount of
continuous boiler blowdown (use 1 percent of
boiler maximum continuous rating as a starting
blow-down value).
Table 7-6. General Raw Water Analysis.
Water properties
Calcium
Silica
Magnesium
Sodium
Sulfate
Chloride
Bicarbonate
Nitrate
Total hardness
Carbonate hardness
Noncarbonate hardness
Total alkalinity
Conductivity - microseim per
per centimeter
pH
Milligrams/Liter
As the ion or as
Shown
64.5
9.1
20.7
70.0
182.0
23.3
211.0
4.0
248.0
173.0
73.0
166
731
8.2
Note: Water characteristics will vary by location.
c. Treatment. Water treatment is generally categorized by external treatment or internal treatment.
External treatment dampens, softens, or purifies
raw water prior to introducing the water into the
feedwater system. Internal methods introduce
chemicals directly into the feedwater or boiler
7-6
water where they regulate the undesirable effects of
water impurities. Blowdown is used in the
evaporative process to control the concentration of
dissolved and suspended solids. Methods of water
treatment include filtration (reverse osmosis),
deaeration (para 7-3 above) and degasification,
cold or hot lime softening, sodium zeolite ion
exchange, chloride cycle dealkalization, demineralization, internal chemical treatment, and blowdown. Several internal treatment methods commonly used to treat boiler water include phosphate
hydroxide or conventional treatment method, chelent method, polymer method (feedwater < 1.0
ppm Ca as Ca CO3), and coordinated phosphate/pH
(high purity # 15 mirohms conductivity). These
chemical internal treatment methods can be used in
conjunction with external treatment methods. After
a raw water analysis has been made, a water
treatment specialist should be consulted and an
evaluation should be made on the practicability of
a combination of internal and external treatment
methods. It is usually more cost effective to
externally pretreat the feedwater as much as
practical. This discussion concerns boiler feedwater
treatment equipment. It is assumed that water
delivered to the feedwater equipment is of a
pretreated, clear, potable quality free of organic
materials.
d. Boiler feedwater treatment equipment. The
industry standards for reducing water constituents
in boilers with an operating pressure of 400 psig
are reverse osmosis, ion exchangers, or combinations of the two.
(1) Reverse osmosis (RO) is a filtration
method which removes approximately 90 percent
of all inorganic dissolved solids from the feedwater.
Reverse osmosis can be used alone, as shown in
figure 7-3, but is more generally used with regenerative ion exchange equipment (demineralizer) as
shown in figure 7-4. The viability of using reverse
osmosis will be determined by a LCCA.
TM 5-810-15
(2) Sodium zeolite (NaZ) softeners are
used to remove calcium (Ca) and magnesium (Mg)
from the feedwater. NaZ softeners do not remove
silica, bicarbonate, or carbonate, and should be
used alone when these constituents are not a
problem in the boiler feedwater. A typical NaZ
softener is shown in figure 7-5.
(3) A split stream softener with degasifier
should be used when it is necessary to remove
hardness (Ca, Mg) and carbon dioxide (CO2)
formed from bicarbonate and carbonates. A typical
split stream system is shown in figure 7-6. The use
of split stream versus other options will be decided
by means of a LCCA and an evaluation of applicable safety restrictions. This particular type system
will result in a reduction of total dissolved solids
(TDS).
(4) Chloride
anion
exchangers
(dealkalizer) may be used in conjunction with NaZ
softener to remove carbonate, bicarbonate and
CO2. Used in this manner, the dealkalizer takes the
place of a hydrogen cycle softener and degasifier in
the split stream system. A dealkalizer application is
shown in figure 7-7. This particular type system
will not reduce TDS.
(5) A weak cation exchanger, regenerated
with acid, followed by a strong acid cation exchanger, salt regenerated, can be used in conjunction with a degasifier. The weak acid exchanger
will remove the alkalinity and the hardness associated with alkalinity, and the salt regenerated strong
acid cation exchanger will remove the balance of
the hardness. This balance will depend on. the
hardness to alkalinity ratio of the raw water. The
degasifier will be used to strip the CO2 formed in
the weak acid exchange process.
7-7
TM 5-810-15
(6) Demineralizers produce very high
quality water—higher than is generally required for
a boiler operating at 400 psig.
7-8. Blowdown tank.
a. Application. Pure water vapor is generated in
a bailer and the impurities (dissolved solids) of the
boiler feed water remain and become concentrated.
The concentration of dissolved solids can be
controlled by withdrawing the boiler water with a
high concentration of dissolved solids as blowdown
and discharging it safely to waste through a
blowdown tank. Every boiler - system has two
types of blowdowns. The upper blow-down of
7-8
either intermittent or continuous operation is used
to control concentrations of dissolved solids. It is
connected to the stream drum of a water tube
boiler in such location as to minimize the inclusion
of feedwater, chemical feed and steam entrainment.
The other blowdowns from the mud drum or the
water walls are intermittent or mass blowdowns
which removes accumulated solids and sludge from
stagnated areas of the boiler, usually at reduced
steam loads. A blowdown tank allows the hot
water to flash to steam leaving the concentrated
impurities to be more safely drained to waste. The
flashed steam can be vented to atmosphere or can
be used in a heat recovery system.
b. Design.
TM 5-810-15
(1) Blowdown tanks will be designed and
constructed in accordance with the ASME Boiler
and Pressure Vessel Code, Section VIII. The
amount of boiler blowdown capacity is determined
to be a percentage of the boiler firing rate. The
percent of boiler blowdown is governed by the
allowable concentration ratio (CR) or the number
of times a dissolved solid may be concentrated over
the amount of dissolved solid in the feedwater. The
allowable concentration ratios are determined by a
chemical analysis of the boiler feedwater and by the
type of makeup water treatment. The continuous
blowdown rate can be determined using equation
7-2:
R '
B
x Q
A&B
(eq 7-2)
R = Blowdown rate (pph)
A = Predetermined bailer water concentration as total
solids (ppm)
B = Total solids in feedwater to boiler (ppm)
Q = Steam output (pph)
A boiler operated on exceptionally high quality
feedwater will have very little blowdown. The size
of the blowdown tank will be determined from
table 7-7. Blowdown, steam and water connection
sizes are shown in table 7-7. The tank will have
openings to allow cleaning and inspection. The
blowdown tank should have a blowdown inlet
connection, a water outlet connection, a vent connection, a cold water supply line, a drain connection, a thermometer connection, and a pressure
gauge.
Table 7-7. Blowdown Tank Size.
Boiler
Design
Pressure
(psig)
20
to
50
51
to
100
101
to
150
151
to
200
201
to
300
301
to
400
*Blowdown
Size
(Inches)
¾
1
1½
1½
2
2½
Cold
Steam
Vent
Size
(Inches)
2
2
2
2½
3
4
Water
Inlet
Size
(Inches)
¾
1
1¼
1¾
2
2
¾
1
1¼
1½
2
2½
2
2½
3
4
5
6
¾
1
1¼
1½
2
2½
¾
1
1¼
1½
2
2½
¾
1
1¼
1½
2
2½
¾
1
1¼
1½
2
2½
Water
Outlet
Size
(Inches)
1½
1½
2½
2½
4
4
**Blowdown
Tank
Size
(Dia x Ht.)
14” x 5'6”
14” x 5'6”
14” x 5'6”
14” x 5'6”
18" x 6*0”
20” x 6'0
1
1¾
1½
2
2½
2½
1½
2
3
4
4
5
14”
14"
18”
18”
24"
30"
2½
3
4
5
6
8
1
1¼
1½
2
2½
3
2
3
3
4
4
5
14” x 5*6”
14” x 5*6”
20” x 6*0”
24” x 6*0”
33” x 6*0”
39” x 66”
3
4
5
6
8
8
4
5
6
6
8
10
4
5
6
8
10
10
1
1¼
2
2
2½
3
1¼
1½
2
2½
3
3
1¼
1½
2
2½
3
4
2
2½
3
4
4
5
2
2½
4
4
5
6
2½
3
4
4
5
6
14" x 5*6”
18” x 6*0”
24” x 6*0”
30" x 6*6”
39" x 6*6”
48” x 6'6"
18” x 60”
24" x 6*0”
30" x 6*6”
36" x 6*6”
48" x 6*6”
54” x 7*0”
20" x 6*0”
24” x 6'0"
33” x 6*6”
42" x 6*6”
54" x 7*0”
66” x 7*0”
x 56”
x 5*6”
x 6*0”
x 6*0”
x 6*0”
x 6*6”
7-9
TM 5-810-15
Table 7-7. Blowdown Tank Size. (Continued).
*Blowdown
Size
(inches)
Cold
Steam
Vent
Size
(Inches)
Water
inlet
Size
(Inches)
Water
Outlet
Size
(inches)
**Blowdown
Tank
Size
(Dia x Ht.)
¾
1
1¼
1½
2
2½
4
5
8
8
10
12
1¼
1½
2
2½
3
4
2½
3
4
4
5
8
20” x 6*0”
27” x 6*6”
39” x 6*6”
48” x 6*6”
60” x 7*0”
72” x 7*0”
¾
1
1¼
1½
2
2½
5
6
8
10
12
12
1¼
1½
2½
2½
3
4
2½
3
4
5
6
8
24” x 6*0”
30" x 6*6”
42” x 6*6”
54” x 7*0”
66” x 7*0”
72” x 7*0”
¾
1
1¼
1½
2
2½
5
6
8
10
12
12
1¼
1½
2
2½
3
4
2½
3
4
5
6
8
27” x 6*6”
36" x 6*6”
48” x 6*6”
60” x 7*0”
72" x 7*0”
72" x 7*0”
801
to
1000
¾
1
1¼
1½
2
6
8
10
10
12
1¼
1½
2½
3
4
2½
3
4
5
6
30” x 6*6”
42" x 6*6”
54" x 7*0”
66" x 7*0”
72" x 7*0”
1001
to
1500
¾
1
1¼
1½
8
8
10
12
1¼
2
2½
3
2½
4
4
5
36" x 6*6”
48" x 6*6”
66" x 7*0”
72” x 7*0”
1505
to
2000
¾
1
1¼
1½
8
10
10
12
1¼
1½
2½
3
2½
4
5
5
42" x 6*6”
48" x 6*6”
66” x 7*0”
72” x 7*0”
2001
to
2500
¾
1
1¼
1½
8
10
12
12
1½
2
2½
3
4
4
5
6
48” x 6*6”
66” x 7*0"
72” x 7*0”
72" x 7*0”
Boiler
Design
Pressure
(psig)
401
to
500
501
to
600
601
to
800
*Size of blow-off connection on boiler or size of blow-off header, whichever is larger.
**The sizes tabulated are based on the minimum diameter and minimum volume that can be used. Larger diameter tanks with
equivalent or larger volume may be used.
(2) The pressure for which the tank should
be designed is shown in table 7-8. The blowdown
tank will have a wear plate between the tank water
level and the top of the tank. The blowdown will
enter tangentially and the wear plate attached to the
shell at the point of impact from the blowdown.
The wear plate will be the same thickness of the
tank and extend approximately one-third of the
tank circumference. The blowdown tank vent will
allow steam to escape from the highest possible
location on the tank and will be as direct as
possible to the outside atmosphere without
intervening stop valves. The water discharge
7-10
temperature should not exceed 140 degrees F. The
pressure of the blowdown leaving any type of
blowdown equipment will not exceed 5 psig. The
Boiler Law and Rules & Regulations Code administered by the Bureau of Safety & Regulation in
Lansing, Michigan can be used as a guide in
designing blowdown tanks. Each state will be
consulted to determine their design criteria.
7-9. Slowdown heat recovery.
a. Application. A LCCA will be conducted to
determine if a blowdown heat recovery system is a
justifiable capital investment.
TM 5-810-15
Table 7-8. Blowdown Tank Pressure.
Maximum Allowable Boiler
Pressure, psig
Blowdown Tank Design
Pressure, psig
50
100
200
300
500
750
1000
1500
2250
2500
25
50
70
90
125
165
200
275
325
400
b. Design. Heat is recovered in a blowdown heat
recovery system by passing the blowdown water
from the blowdown tank through a heat exchanger
to recover the sensible heat of the water and
transferring blowdown tank steam to the DA. The
heat exchanger will be sized to reduce the temperature of the blowdown main to 20 degrees F above
the inlet temperature of the fluid being heated,
typically feedwater heating, makeup water heating,
building heating, oil heating or process steam
generation. The blowdown tank for a heat recovery
system will be smaller to allow the blowdown drain
water to be hotter for an effective heat recovery
system. If flash steam is used in the DA, the
blowdown tank will be designed to minimize
carryover. A normal blowdown system consisting
of a large blowdown tank venting to atmosphere
and draining directly to waste may have to be
available to allow maintenance on the heat recovery
equipment during operation. There are several
package blowdown heat recovery systems available
consisting of blowdown tanks, heat exchangers,
flow control valves, thermostatic control valves,
sample coolers and high level float switches.
7-10.
Steam coil air heater.
a. Application. The steam coil air heater preheats
the combustion air before it enters the main air
heater. The heat dries the air and reduces corrosion
of the air heater tube metals.
b. Design. The installation will be designed for
reasonable air velocities with pressure loss not to
exceed one inch of water. The heating coils will be
designed in multiple elements to maintain average
cold and metal temperatures of the air heater
surfaces above 180 degrees F at all loads up to 15
percent above full rated load. The uncorrected air
heater gas outlet temperature should be used to
determine the average cold end metal temperature.
A typical steam coil would have seamless type 321
stainless steel tubes, outer tubes 1 inch outside
diameter and 0.049-inch minimum wall thickness
and inner tubes 5/8-inch outside diameter and
0.022-inch minimum wall thickness. The supply and
return connections are to be on the same end of the
coil. Tubes will be pitched to the drain. The coil
should be removable in a manner that does not
disturb connecting ends of breeching. The coil
outer casing is typically 10 gauge steel welded into
an airtight structure. The core header plate will be
gasket sealed to the casing.
7-11.
Steam coil drain tank.
a. Application. The steam coil drain tank will
collect the condensate from the steam coil air
heater for transfer to the DA.
b. Design. The steam coil drain system must be
sized large enough to drain the maximum expected
steam flow rate to the air heater and to maintain a
reasonable condensate level allowing proper
operation of the steam coil drip return pumps (if
included). Another consideration is the possibility
of freezing. The steam coil tank should be located
indoors, if possible, and sized small enough that
outdoor drain piping is not allowed to fill with
condensate. The steam coil drain tank is normally
equipped with a level controller, gauge glass and
high level alarm. The steam coil drain tank will be
designed and constructed in accordance with the
ASME Boiler and Pressure Vessel Code, Section
VIII.
7-12.
Fans.
a. Applications. Boiler furnaces are either pressurized or have balanced draft for combustion. Gas
and oil fired boilers are normally of the pressurized
furnace design. Modern coal fired boilers have
balanced draft type furnaces. Balanced draft type
boilers use FD fans to supply combustion air to the
furnace and ID fans exhaust the products of
combustion or flue gas. The furnace is kept at a
slightly negative pressure ranging from 0.1 to 0.25inches w.g., by the ID fan which is located
downstream of the particulate removal equipment.
b. Forced draft fans. FD fans operate with reasonably clean, cool or warm air and will be
designed for quietness and efficiency. This source
of combustion air is frequently taken from within
the steam plant to promote ventilating and to take
advantage of the higher ambient temperatures.
Inlets for the fans will have silencers with screens
to attenuate entrance noises and to keep birds and
other objects from entering the system. The static
pressure of the FD fan will be calculated for the
pressure drop through the inlet air duct, steam coil
air heater, air heater (if used), air metering devices,
dampers or vanes, air ducts, static fuel bed or
7-11
TM 5-810-15
burners and any other resistance between the fan
and the furnace at the air flow rate required for
proper combustion. The volume of the air to be
handled is dependent on the air pressure
(elevation), moisture content if moisture exceeds 1
or 2 percent by weight, temperature and excess air
required. Factors of safety to be added to the air
flow requirements to obtain test blockrating are 20
percent excess volume and 32 percent excess pressure for coal fired boilers. Add 25 degrees F to
temperature of the air being handled as a safety
factor.
(1) FD fan will be airfoil type to provide
lower power consumption. Airfoil fans will have
inlet vane controls to provide low part load power
consumption.
(2) FD fan design will include the following
features. Shafts will be designed to have critical
speeds not less than 1.4 times the operating speed.
Bearings will be antifriction type with L10 life of
100,000 hours. Wheel stresses should not exceed
50 to 60 percent of yield strength while using finite
difference methods and 75 percent of yield strength
at operating temperature while using finite element
methods. Stress rupture should be considered for
elevated temperature. Variable speed fan fatigue
life should be evaluated to avoid premature failure
due to low cycle fatigue. An impact response test
should be performed to avoid high cycle fatigue
due to resonance. Resonance speed of fan support
system should not be less than 1.2 times operating
speed.
c. Induced draft fans. ID fans can operate under
erosive conditions even though these fans are
located downstream of the particulate (fly ash)
collection equipment. Erosion is controlled by using abrasion resistant material and limiting top
speed. The ID fans move the gas from the furnace,
through the superheater if required, boiler bank,
economizer, ductwork, scrubbers, baghouse and
stack. Corrosion must be considered if temperatures of flue gas are within 30 degrees F of the dew
point. The type of fan is usually straight radial with
shrouds (modified radial) or radial tip design
(forward curved, backware inclined) with wearing
strips when dust burden is high. Maximum speed
should be 1200 revolutions per minute (rpm). Even
when flue gases are normally cleaned through a
baghouse before they reach the fan dirty gases can
be bypassed around the baghouse and impinge on
the fan blades or wheel. Therefore, the fan must be
constructed to resist fly ash and dust buildup and to
give better wear resistance. Factors of safety to be
added to the air flow requirements to obtain test
block rating are 20 percent excess volume and 32
percent excess pressure for coal fired boilers. Add
a minimum of 25 degrees F to the temperature of
7-12
entering gas being handled as a safety factor. ID fan
type will be selected based on grain loading
according to table 7-9.
Table 7-9. ID Fan Type.
Grains/actual cubic feet
ID fan type
0.1 to 0.2
>0.2
Airfoil
Radial tipped, backward inclined, or radial bladed
ID fan control type will be selected based on
temperature and grain loading according to table
7-10.
Table 7-10. ID Fan Control Type.
Temperature
#500 F
>500 F
Grains/actual
cubic foot
Type ID fan control
#0.2
>0.2
inlet vane
inlet box dampers
ID Fan design will include the following features.
Shafts will be designed to have critical speeds not
less than 1.4 to 1.5 times the operating speed.
Bearings shall be antifriction type with L10 life of
100,000 hours. Partial liners will be included for
airfoil or backward curved fans. Partial or full
width liners will be included for other blade types
based on dust loading and velocities. Housings will
be provided with liners or replaceable heavier scroll
for fans with severe dust loading. Wheel stresses
should not exceed 50 to 60 percent of yield
strength while using finite difference methods and
75 percent of yield strength at operating temperature while using finite element methods. Stress
rupture should be considered for elevated temperature. Variable speed fan fatigue life should be
evaluated to avoid premature failure due to low
cycle fatigue. An impact response test should be
performed to avoid high cycle fatigue due to
resonance. Resonance speed of fan support system
should not be less than 1.25 times operating speed.
d. Fan control methods.
(1) Dampers are used on the fan discharge at
either the stoker plenum, the boiler outlet or in
ducting and function to raise system resistance,
thus raising operating points higher on the fan
curves and altering fan output. Input power can
decrease somewhat on decreased volume output if
fan efficiency increases. Dampers are closed on
startup of the boiler to reduce the starting load on
the motor.
(2) Variable inlet vanes are used to change
characteristic curves of FD fans. Vanes impart a
prespin to the gas and by the alteration of the pitch
TM 5-810-15
of the vanes, fan discharge volume and pressure are
changed to give new system operating points. With
fixed speed motors, power usage only slightly
diminishes as air volume is reduced; this system will
operate economically if air volume is 75 percent or
above the design volume. Movement of vanes is
non linear so they have to move more at low loads.
(3) Two speed motors, generally of speed
ratios of 4:3 or 3:2 with variable inlet vanes will
provide economical operation down to 40 percent
of the design volume.
(4) Variable speed drive on ID fan, two
speed or variable speed motor on FD fan, with
variable inlet vanes on boiler outlet damper, are
generally required for most efficient operation of
heating plant boiler systems with power drive
requirements in excess of 10 hp. The benefits of a
variable speed drive are greater when the boiler is
operated at lower loads. A life cycle cost analysis
(LCCA) should be performed based on the number
of hours at each load to justify the use of a variable
speed drive. The variable speed gives an infinite
series of fan curves from which the points of
highest system efficiency can be chosen. Fans with
both adjustable speed capability and control inlet
vanes provide the most energy efficient operation.
Control dampers may be provided for multiple coal
fired units with auxiliary oil firing for startup of
boiler and adjustment of air flow. If oil is fired in a
boiler designed for coal firing, excessive dampering
may set up objectionable vortexing of the air
currents in the breeching and ductwork unless
variable speed drives are used in the system.
e. Fan motors. Motors will be selected for the
maximum duty required by the fan under most
severe anticipated operating conditions. Motor selection is discussed in chapter 10.
7-13.
Hydraulic ash handling pumps.
a. Application. Bottom ash can be conveyed
hydraulically from a bottom ash hopper by means
of mechanical pumps. Hydraulic ash handling
systems are discussed in chapter 6.
b. Ash sluice pump.
(1) Application. The ash sluice pump pumps
recycle sluice water through the bottom ash hopper
outlet to be disposed.
(2) Sizing. Two 100 percent capacity pumps
will be used to provide full backup. The capacity of
the ash sluice pumps will depend on the hydraulic
ash handling system demands. The discharge head
of the ash sluice pump will be designed to overcome the piping losses and static head to a
dewatering bin or surge tank. A jet pump hydraulic
system will demand higher pressure pumps to allow
the jet pump to function properly. A surge tank is
required to make available adequate NPSH for an
effective pump.
(3) Construction. The pumps will be constructed in a horizontal split case configuration
with a heavy duty slurry type enclosed impeller.
Replaceable shaft sleeves, suction sideplates and
rear sideplates will be provided. The pump will
include oil lubricated bearings and a stuffing box
packing for external clean water injection.
(4) Pump materials. Ash sluice pumps will
be designed of abrasion resistant alloys to provide
an acceptable life.
c. Bottom ash pump.
(1) Application. The bottom ash pump
transfers the slurry from the bottom ash hopper discharge to a disposal area, either dewatering bins or
ash handling ponds. The bottom ash pump is not
needed if the ash sluice pumps are designed to
pump the water through the hopper discharge to
the disposal system.
(2) Sizing. The bottom ash pump is most
generally used with a surge tank downstream of the
ash hopper offering a controlled NPSH. Two 100
percent capacity pumps will be used to provide full
backup. The capacity of the bottom ash pumps
depend on the hydraulic ash handling system
demands. The capacity must be greater than the ash
sluice pump capacity. The discharge head of the
bottom ash pump will be designed to overcome the
piping losses and static head to a dewatering bin.
(3) Construction. The pumps will be constructed in a horizontal, vertical split case, end
suction back pullout configuration with a heavy
duty, slurry type enclosed impeller. Replaceable
shaft sleeves, suction sideplates and rear side-plates
will be provided. The pump will include oil
lubricated bearings and a stuffing box packing for
external clear water injection.
(4) Pump materials. Bottom ash pumps will
be designed of abrasion resistant alloys to provide
an acceptable life.
d. Ash sluice water recirculation pumps.
(1) Application.
Ash
sluice
water
recirculation pumps are used for returning ash pond
water to a surge tank for the ash sluice pump
suction.
(2) Sizing. Two 100 percent capacity pumps
will be used to provide full backup. The capacity of
the recirculation pumps must exceed the ash sluice
pump capacities. The NPSH available will be the
atmospheric pressure of the ash pond plus the
depth of the impeller minus the resistance of the
suction bell piping. The discharge head of the
recirculation pumps must overcome piping losses
and the surge tank static head.
7-13
TM 5-810-15
(3) Construction. The pumps will be vertical
shaft configuration with bottom suction. Replaceable suction sideplates and rear sideplates will be
provided.
(4) Pump materials. The ash sluice water recirculation pumps will be designed of abrasion
resistant alloys to provide an acceptable life.
e. Sludge return pump.
(1) Application. The sludge pump is used on
a hydraulic ash handling system using a dewatering
bin. A tank or series of tanks collect and store the
water discharge from the dewatering bins. Remaining ash particles settle in these conical shaped
tanks and are pumped from the tank bottom back
to the dewatering bins by sludge return pumps.
(2) Design. The sludge return pumps have
the same design characteristics as the bottom ash
pumps.
7-14.
Bearing cooling water pumps.
a. Application. Bearing cooling water pumps will
supply cooling water to all plant equipment with a
cooling water demand. Typical equipment requiring
cooling water are pulverizers, pump bearings and
seals, air compressors and after coolers, fan drives,
lube oil coolers and chemical feed sample coolers,
boilers access doors and scanning fire detectors.
Smaller boiler plants may have processed water
available and may not require cooling water pumps.
Boiler plants with a plentiful water supply will
sometimes allow cooling water to be discharged
without recirculation.
b. Design. Two 100 percent capacity pumps will
be used to provide full backup. The required flow
rate needed is found by adding all equipment
coincident demands. The future expansion of the
plant will also be considered. The cooling water
system may be an open (once through) or closed
(recirculating) type of system depending on the
availability of clear water. The system head required must be determined by adding the system
piping friction losses and the static head required.
When the flowrate and total head required are
known, add 10 percent tot he total head for wear
allowance. This will be the rated capacity and total
dynamic head for the pump selection.
c. Construction. The pumps will be motor
driven, horizontal, vertical split case, end suction,
centrifugal type, back pullout configuration, single
stage design.
7-15.
Bearing cooling water heat exchangers.
a. Application. Bearing cooling water heat exchangers are required for a closed loop system in
which clean water is not available in unlimited
quantities. A heat exchanger will transfer heat
7-14
absorbed by the clean bearing cooling water and
transfer it to a circulating water system. The
circulating water system may use river water, lake
water, or a cooling tower system where absorbed
heat can be discharged. An evaluation must be
made to determine the feasibility of using a heat
exchanger versus using a cooling tower where
bearing water is directly pumped through the
cooling system. A plentiful supply of dirty water
from a lake or river may make a heat exchanger
more economical. Consideration will be given to
water treatment as a cooling tower bearing water
system would have to be constantly monitored and
treated as water is made up for evaporation.
b. Design. The heat exchanger must be sized to
transfer all the heat generated from the fully
operational plant at the maximum continuous
rating. Two heat exchangers will be used so one
can be removed from service, each having 100
percent of the flow capacity. The heat exchanger
will be designed to conform to the ASME Boiler
and Pressure Vessel Code, Section VIII. The heat
exchanger manufacturer must be given the information for both the shell side and the tube as
shown in table 7-11. The amount of cooling water
required depends on the equipment cooling water
demand. The equipment manufacturers will be
asked how many gallons of cooling water per
minute is required for equipment cooling at a given
inlet temperature of 95 degrees F allowing the
outlet temperature to be no more than 10 degrees
F higher. The heater cooling water rated flow
capacity will be the total equipment demand of all
equipment to be operating simultaneously plus a 20
percent design margin. The circulating water rated
flow capacity will be twice the cooling water rated
flow capacity.
c. Construction. The coolers will be designed
and constructed to conform with the ASME Boiler
and Pressure Vessel Code, Section VIII. The
Table 7-11. Heat Exchanger Design Information.
Typical Values
Shell Side
Tube Side
Cooling Water
Water
Number of passes
.1
1
Temperature in, degrees F
115
85
Temperature out, degrees F
95
95
Flow gpm.
demand
demand
Maximum pressure drop,
2
5
psi
Design pressure, psig
150
75
Fouling factor
.0005
001
Maximum velocity, fps
3.0
5.0
TM 5-810-15
construction of the coolers will allow the
circulating water or dirtier water to pass through
the tubes allowing more practical cleaning. The
cooler tubing and tube sheet material selection will
be based on water quality. Materials can be
admiralty, copper nickel, or for corrosive
applications stainless steel. The coolers will be the
straight tube type with fixed tubesheet, removable
channel construction. The shell will be carbon steel
and the channel heads will be fabricated steel. The
shell will have 150 pound raised face flanged or
3000 pound screwed connections. The channel will
have 150 pound flat faced flanged or 3000 pound
screwed connections. The coolers will be
manufactured with shell, channel vent and drain
connection.
mendations of the boiler manufacturer. Depending
on the boiler and down period, such steam parts
filled with treated water or a nitrogen purge are the
economizer, water walls, superheater, reheater,
feedwater heater (tube side-water; shell sidenitrogen) and drum. In some cases freezing may be
a problem and treated water can be replaced with
nitrogen. The amount of nitrogen required, for
boiler purging will be given by the boiler
manufacturer or can be calculated from the volume
of the steam parts. The nitrogen system is a low
pressure system. However, the nitrogen is stored in
high pressure cylinder bottles and the piping will be
connected to a high pressure boiler. A pressure
regulator and high pressure valving will be
required.
7-16.
7-18.
Ignitor fuel oil pumps.
a. Design. Ignitor fuel oil pumps will be rotary
screw type pumps. Two pumps will be provided,
each rated at 100 percent capacity, with one pump
used for backup service. A fuel oil unloading pump
will be applied if required and will have the same
characteristics as the ignitor fuel oil pumps. No. 2
fuel oil is more commonly used for ignitor systems
and will be assumed herein. The pumps will be able
to pump oil with a viscosity of 200 Saybolt
Seconds Universal (SSU) against the design discharge pressure at the design capacity. Fuel oil
viscosity will be expected to vary between 33 and
200 SSU. Pump motors will be totally enclosed and
explosionproof.
b. Types. Unlike a centrifugal pump, a rotary
screw pump is a positive displacement pump, that
will displace its capacity to the point of failure
regardless of the resisting pressure. A fuel oil
recirculation system will be designed to allow the
pump to recirculate the fuel oil as the ignitor fuel
oil is modulated according to demand. In a fuel oil
loading system the fuel oil is not modulated and a
recirculation system is not necessary. In sizing the
fuel oil pump, the pressure to overcome will be
calculated from piping losses and elevation change
to get the required pump discharge pressure. The
ignitor fuel oil pump capacity is determined from
maximum fuel oil demand plus 20 percent for pump
wear and safety factor.
7-17.
Nitrogen system.
a. Application. The nitrogen system is used to
purge the boiler for protection from corrosion
between hydrostatic test and initial operation and
after chemical cleaning periods and outages.
b. Design. The boiler steam parts are filled with
treated water until overflowing and then capped off
with 5 psig of nitrogen according to the recom-
Carbon dioxide (CO2) system.
a. Application. A carbon dioxide system in a
boiler plant is most commonly used to extinguish
fires in coal bunkers. A CO2 system can also be
used to extinguish electrical hazards, such as
transformers, oil switches and circuit breakers, and
rotating equipment. CO2 extinguishes fire by
reducing the concentration of oxygen and the
gaseous phase of the fuel in the air to the point
where combustion stops.
b. Design. The CO2 systems are classified as
automatic, manual or automatic-manual. Fires or
conditions likely to produce fires may be detected
by visual (human senses) or by automatic means. In
the case of coal bunkers, methane detectors can be
used to alarm a fire or actuate the CO2 system and
an alarm. CO2 can be stored in cylinder bottles and
pipes through a pressure regulated system to
discharge nozzles at the area of combustion. The
amount of CO2 in the system will be at least
sufficient for the largest single hazard protected or
group of hazards to be protected simultaneously.
The CO2 system will be designed and erected in
accordance with NFPA 12 of the National Fire
Codes.
7-19.
Chemical feed pumps.
a. Application. Chemical feed pumps are small
capacity pumps used to inject chemicals into the
condensate, feedwater and steam system at a
controlled rate. Most chemical feed pumps are
specified and purchased as a chemical feed unit that
includes a pump, tank, mixer and piping. Typical
chemical systems used in a boiler plant are
hydrazine, morpholine, phosphate and a metal
surface passivating agent.
b. Design. The pump selection will have the
capacity and discharge head to inject the chemical
into the system. Pumps are rated by capacity in
7-15
TM 5-810-15
gallons per hour (gph), discharge head in psig and
piston strokes per minute. The chemical feed
pumps will be positive displacement metering type.
The pumps will have hydraulically balanced
diaphragms, mechanically actuated air venting; all
rotating parts to run in an oil bath with roller
bearings; double ball check valves with Teflon 0ring seats on both suction and discharge. The
pumps will have micrometer capacity adjustment
from 0—100 percent while the pump is running and
to have metering accuracy within plus or minus 1
percent.
c. Chemical feed unit. Chemical feed tanks for
the mentioned chemicals will be 16 gage type 304
stainless steel with agitator, gage glass and low
level alarm system. Piping will be stainless steel and
valves will have Teflon seats. The chemical feed
system will include a back pressure valve to insure
accurate and consistent metering at all flows and
will include a safety valve.
7-20.
Laboratory.
a. General. A laboratory is needed in every boiler
plate to assist in analyzing chemical treatment and
in early detection of problems. Samples of water
and steam are taken from various systems and parts
of systems to evaluate the system*s condition.
b. Sample coolers. Sample coolers are required
to condense steam and cool water to be handled.
Sample coolers are heat exchangers that will be
sized to maintain the temperature at 77 degrees F.
7-16
Coolers for individual samples are either doubletube helical coils with cooling water counterflow
cooling or submerged helical coils properly baffled
to effect counterflow cooling. If a coil type of
exchanger or a coil and condenser type of exchanger are used, they will meet the intention of
ASTM D 1192. If a multicircuit heat exchanger is
used, it will meet the requirements of Section VIII,
ASME Boiler and Pressure Vessel Code.
7-21.
Sump pumps.
a. Application. Sump pumps are required in
several applications at a boiler plant. Sump pumps
primarily are used for storm water removal but also
are used for ash hopper water overflow or any
condition requiring removal of water from a sump.
b. Design. The pump will be sized for one and
one-half times the maximum amount of expected
drain rate. Two 100 percent capacity pumps will be
used to supply full backup if overflow is dangerous.
The suction line between the suction vessel and the
pump must be properly designed to prevent air
pockets and cavitation. Sufficient NPSH must be
available at the pump suction flange.
c. Construction. The pumps will be motor
driven, vertical shaft configuration with bottom
suction and open impeller. The pump will include a
flanged column, discharge pipe flanged over
soleplate, bearing lubrication piping and connections on the soleplate to support the pump and
motor.
TM 5-810-15
CHAPTER 8
PIPING SYSTEMS
8-1. General.
This chapter addresses the criteria for the steam
plant piping systems. The design of the steam plant
piping will be in accordance with the ASME B31.1.
Gas piping will be in accordance with ASME
B31.8. Reference table 8-1 for piping system
design notes.
8-2. System descriptions.
a. Main steam. The main steam system delivers
steam from the boiler outlet connections to the
process. The main steam system consists of: piping
from each boiler outlet connection, superheating
equipment (superheated boilers only), a common
main steam line headered to the individual boiler
outlets, and piping which transports the steam to
the process. On superheated steam units the superheating equipment, which is an integral part of the
boiler, consists of a primary superheater section, a
desuperheater, and a secondary superheater. The
system diagram is shown in figure 8-1.
b. Low pressure steam. The low pressure steam
system provides steam for use within the steam
plant. These uses include deaerator (DA) pegging
steam, sootblowing steam, steam coil air preheaters, boiler feed pump turbine drives, and feedwater heaters. The low pressure steam system
consists of: steam pressure reducing station, DA,
sootblowers, steam coils, turbine drives, feedwater
heaters, and interconnecting piping. The system
diagram is shown in figure 8-2.
c. Feedwater. The feedwater system collects returning process condensate, treats raw water for
makeup to the boiler, collects returning condensate
from in-plant processes, conditions the condensate
and makeup to remove corrosive gases, heats the
water, and delivers it to the boiler economizer. The
feedwater system consists of: water treatment
equipment to condition raw water for makeup to
the boiler, a treated water and condensate storage
tank, treated water and condensate pumps to
deliver water to the DA, a blowdown recovery heat
exchanger, a DA to remove the entrained corrosive
gases from the water, boiler feed pumps to increase
the pressure of the water and deliver it to the
boiler, feedwater heaters to heat the water and
protect the boiler economizer against acid condensation of the flue gas at low loads, flow regulating
stations, and interconnecting piping. The system
diagram is shown in figure 8-3.
d. Fuel gas. The fuel gas system reduces gas
pressure from the supplier*s pipeline, totalizes flow
to the plant, removes impurities from the gas,
allows manual isolation of the plant from the
supply, provides visual indication of plant gas
pressure, and electrically isolates the plant piping
from the buried supply piping.
e. Fuel oil. The fuel oil system includes pumps to
move oil from outdoor storage tanks to the plant
header. The functions performed by the fuel oil
system are similar to those listed for the gas
system. Since oil is stored on site and since there is
recirculation back to the fuel oil storage tank, more
than one totalizing flow meter is needed to
calculate the amount of oil burned.
f. Blowdown heat recovery. The blowdown heat
recovery system recovers part of the heat available
in boiler blowdown water and discharges the unusable high-solids content water. The blowdown heat
recovery system consists of: blowdown regulation
equipment, a flash tank, a blowdown recovery heat
exchanger, and interconnecting piping. The system
diagram is shown in figure 8-4.
g. Instrument air. The instrument air system
supplies air to the pneumatic instruments and
control devices throughout the plant. The instrument air system consists of: instrument air compressors, aftercoolers, air drying equipment, instrument air receiver, baghouse air receiver (when
required), and interconnecting and distribution
piping. The system diagram is shown in figure 8-5.
h. Plant air. The plant air system supplies air for
pneumatic tools, maintenance uses, and other uses
throughout the plant. Plant air may also be used for
sootblowing and igniter atomizing purposes when
required. The plant air system consists of: plant air
compressors, aftercoolers, oil separating equipment
on crosstie to instrument air system, plant air
receiver, sootblower air receiver (when required),
atomizing air regulating station (when required),
and interconnecting piping. The system diagram is
shown in figure 8-6.
i. Boiler vents and drains. Boiler vents and
drains provide the means by which the boiler is
vented and drained during startup and maintenance
operations. The system consists of piping from the
vent and drain connections on the boiler to the
appropriate disposal points.
8-1
TM 5-810-15
Table 8-1. Piping Design Notes,
Typical Design
Press. & Temp.
400 psig
450 degrees F
System
Main steam
(Saturated)
Origin
Boiler outlet
Termination
Process
Main steam
(superheated)
Boiler outlet
Process
400 psig
750 degrees F
Slope pipe ¼" per 100 ft. Thermal expansion compensation required. Traps and drains required. Insulate for
thermal efficiency.
Auxiliary
(low pressure)
steam
Pressure reducing station
Deaerator. feedwater heaters
steam coils BFP
turbine sootblowers
150 psig
375 degrees F
Slope pipe ¼” per 100 ft. Thermal expansion compensation required. Traps and drains required. Insulate for
thermal efficiency.
Steam coil
steam supply
Auxiliary steam
header
Steam coil inlet
150 psig
375 degrees F
Slope pipe ¼” per 100 ft. Thermal expansion compensation required. Insulate for thermal efficiency. Traps and
drains required.
Building heat
Auxiliary steam
system (reducing
station)
Building heating
equipment
150 psig
375 degrees F
Slope pipe ¼” per 100 ft. Thermal expansion compensation required. Traps and drains required. Insulate for
thermal efficiency.
Boiler feed pump
discharge
Boiler feed pump
Boiler economizer 450 psig
230 degrees F
Check valve required on each pump. Insulate for thermal efficiency.
Boiler feed pump
suction
Deaerator storage tank
Boiler feed pump
5 psig
225 degrees F
Strainer required on each pump. Insulate for thermal
efficiency.
Boiler feed pump
recirculation
Boiler feed pump
discharge
Deaerator
450 psig
230 degrees F
Breakdown orifice required for each pump. Insulate for
thermal efficiency.
Main steam desuperheater
Boiler feed pump
discharge
Main steam desuperheater
450 psig
230 degrees F
Insulate for thermal efficiency.
Sootblower steam
Auxiliary steam
system (reducing
station)
Sootblowers
150 psig
375 degrees F
Slope pipe ¼” per 100 ft. Thermal expansion compensation required. Traps and drains required. Insulate for
thermal efficiency.
Boiler continuous
blowdown
Boiler drum
Flash tank
400 psig
450 degrees F
Compensation for thermal expansion and boiler movement required. Insulate for thermal efficiency.
Instrument air
Instrument air
compressors
Instrument sir
piping system
100 psig
100 degrees F
No insulation required.
Plant air
Plant air compressors
Plant air piping
system
100 psig
100 degrees F
No insulation required.
Atomizing air
Plant air system
Ignitors
100 psig
100 degrees F
No insulation required.
Boiler drains and
vents
Boiler drum mud
drum, waterwall
headers
Atmosphere,
drain
400 psig
450 degrees F
Compensation for boiler movement required. Insulate
for burn protection.
Steam coil drain
& vent
Steam coil outlet
Deaerator (drain) 10 psig
atmosphere (vent) 240 degrees F
Insulate for thermal efficiency.
Deaerator vents
Deaerator
Atmosphere
5 psig
220 degrees F
Insulate for burn protection.
Safety valve vents
lets
Safety valve out-
Atmosphere
As required
bends or turns.
Use drip pan elbows on steam safety valves. Avoid
Condensate
makeup pump
discharge
Condensate
makeup pump
Deaerator
10 psig
100 degrees F
Check valve required on each pump. Insulate for thermal efficiency.
Condensate
makeup pump
suction
Condensate storage tank
Condensate
makeup pump
5 psig
100 degrees F
Strainer required on each pump. Insulate for thermal
efficiency.
8-2
Design Notes
Slope pipe ¼” per 100 ft. Thermal expansion compensation required. Traps and drains required. Insulate for
thermal efficiency.
TM 5-810-15
Table 8-1. Piping Design Notes. (Continued)
Typical Design
System
Origin
Termination
Press. & Temp.
Condensate
makeup pump
recirculation
Condensate
makeup pump
discharge
Condensate storage tank
10 psig
100 degrees
Breakdown orifice required for each pump.
Treated water
Water treatment
system
Condensate storage tank
10 psig
60 degrees F
No insulation required.
Condensate return
Process
Condensate storage tank
As required
Insulate for thermal efficiency.
Potable water
Water main
Restrooms, lockers, drinking
fountains, etc.
50 psig
60 degrees F
Piping must be sanitized before use. No insulation required.
Service water
Water main
Air compressors,
aftercoolers
50 psig
60 degrees F
No insulation required.
Trap return
Steam traps
Waste or drain
150 psig
375 degrees F
Insulate for burn protection.
Fire protection
Water main or
service water
Sprinklers and
hose stations
150 psig
60 degrees F
No insulation required. All valves OS&Y type FM approved.
Floor and roof
drains
Drain hubs
Within 15 feet
outside building
50 psig
60 degrees F
Slope pipe ¼” per 100 ft. Provide cleanouts, use lateral
fittings, avoid sharp turns. Coat where buried.
Sanitary drains
Restrooms,
lockers, drinking
fountains, etc.
Drainage
100 psig
60 degrees F
Slope pipe ¼” per 100 ft. Provide cleanouts, use lateral
fittings, avoid sharp turns.
Ash sluice water
Ash pond
Bottom ash hopper
60 degrees F
No insulation required.
Bottom ash water Bottom ash
hopper
Ash handling
equipment
150 psig
100 degrees F
No insulation required.
Nitrogen
Nitrogen bottle
manifold
Boiler drums
150 psig
60 degrees F
No insulation required.
Coal bunker &
pulverizer inerting gas
Gas bottle
manifold
Coal bunkers &
pulverizers
150 psig
60 degrees F
No insulation required.
Ignitor fuel
Fuel oil storage
tank
Ignitors
As required
No insulation required.
Chemical feed
Chemical feed
pumps
Boiler drum, deaerator
450 psig
(boiler drum)
10 psig
(deaerator)
60 degrees F
Strainers on pump suction and check valves on pump
discharge required. No insulation required.
Samples
Boiler drum,
deaerator
feedwater
Water analysis
equipment
400 psig
(boiler drum
main steam)
450 psig FW
450 degrees F
boiler drum
230 degrees F
DA FW
Sample coolers required on boiler drum.
Fly ash
Fly ash hoppers
Ash handling
As required
Insulate where cooler climates may develop condensation in pipe.
Design Notes
8-3
TM 5-810-15
j. Deaerator vent. The DA vent piping provides
the means by which the entrained gases removed by
the DA are vented to the atmosphere. The system
will contain an orifice sized for the venting
requirements determined from operating conditions
and DA design.
k. Safety valve vents. Safety valve vent piping
provides for the safe discharge of fluids from safety
valves. Water safety valves require piping from the
safety valve outlet to drain. Air and gas safety
valves require piping from the safety valve outlet to
atmosphere or to a safe location. Steam safety
valves require piping from the safety valve outlet to
a safe location that is outside the building. Steam
safety valve vents also require provisions for
removal of water condensed under the safety valve
seat and in the vent piping itself. Safety valve
8-4
piping must be designed to pass the required flow
without adversely effecting safety valve operation.
l. Miscellaneous water systems. Miscellaneous
water systems include service and potable water
and ash sluice water. The service and potable water
system will provide water for the various cooling
requirements in the plant, such as air compressor
intercoolers and aftercoolers, and will provide
water for personnel usages. The ash sluice water
system is required when a hydraulic bottom ash
system is used. Ash sluice water provides the water
for ash jet pumps and bottom ash hopper filling and
sealing water requirements.
m.
Miscellaneous gas systems. Miscellaneous
gas systems include nitrogen system and coal
bunker and pulverizer inerting systems. The
nitrogen system is used to fill any of the boilers
TM 5-810-15
with nitrogen when it is to be out of service for an
extended period. The system consists of nitrogen
bottles, manifold, and interconnecting piping. The
coal bunker and pulverizer inerting system is used
to fill coal bunkers and pulverizers with an inert
gas, usually 002 when fires are detected in the
equipment or when the equipment is to be out of
service for an extended period. The system consists
of gas bottles, manifold, and interconnecting piping.
n. Ignitor fuel. The ignitor fuel system provides
fuel for burner ignitors. Ignitors are used on gas,
oil, pulverized coal, and ACFB boilers. The ignition
fuel may be oil, natural gas or liquified petroleum
gas based on the type of ignitors used. The system
consists of pressure regulating stations and
interconnecting piping.
o. Chemical feed. The chemical feed system supplies chemicals to the feedwater system at the DA
storage tank to maintain water quality. The system
consists of chemical feed tanks for mixing and
storage of chemical solutions; positive displacement
metering type chemical feed pumps; and stainless
steel piping or tubing for interconnection of system
components and the DA storage tank.
p. Samples. The samples system collects samples
from various points in the plant for use in
determining chemical feed requirements based on
water quality. Sample points will include boiler
drum, feedwater, and condensate. The system consists of sample coolers (boiler drum) and tubing
from the sample point to a central location when
desired.
8-3. Valves.
a. General. All valves installed in piping systems
must be suitable for the pressure and temperature
of the piping system in which they are installed.
Valves will be selected based on type of service
(throttling or isolation), type of process fluid
(water, steam, air), and special conditions
(corrosive or abrasive process). Consideration must
be given to materials of construction and packing
materials. Table 8-2 summarizes the types of valves
and their application.
8-5
TM 5-810-15
8-6
TM 5-810-15
8-7
TM 5-810-15
8-8
TM 5-810-15
Table 8-2. Valve Types.
Valve Type
Application
Fluid
Globe
Throttling and flow regulation service, control valves
Steam, water, air gas, oil
Gate
Isolating nonthrottling service
Steam, water, air, gas suitable for high temperature
and pressure
Butterfly
Isolating service, intermittent throttling, limited control valve application
Low pressure and temperature water and other fluids
Plug
Isolating service, intermittent throttling
Natural gas, fuel oil and other viscous fluids
Ball
Isolating service, intermittent throttling
Water, air, gas—low pressure applications
Check
Allows flow in one direction only, pump discharge piping
Steam, water, air, gas, oil
Diaphragm
Provide flow control and leaktight closure
Corrosive, abrasive and solids in suspension
Pinch
Isolating service for large amounts of solids in suspension
Low pressure and temperature, noncorrosive fluids
Needle
Volume control valve used in small instrument, gage
and meter lines
Water, air, gas
Relief or safety
Prevents excessive overpressure in process and piping
Steam, water, air, gas system
8-9
TM 5-810-15
b. Valve types. Numerous types of valves are
available including globe, gate, butterfly, plug, ball
and check valves. Valves can be furnished with
flanged, butt welded, socket welded, or screwed
end connections.
c. Valve construction. Valves must be constructed of suitable materials for the pressures,
temperatures, and fluids for which they will be
used. Table 8-3 summarizes body and packing
materials and their application. Consideration will
be given to special disc and seat materials and valve
bonnet types when required by special process
conditions.
8-4. Pipe insulation.
a. Acceptable types. Table 8-4 shows the acceptable types of insulation material.
b. Applications.
(1) Burn protection. Where applicable, insulation will be sufficiently thick to provide burn
protection as required by OSHA regulations.
Table 8-3. Valve Construction.
Application
Body Material:
Cast Iron
Pressure up to 250 psi, temperature up to 267
degrees F, water, oil, gas
Steel
Pressure up to 9000 psi, temperature up to
800 degrees F, water, oil, gas, steam
Stainless
Steel
Pressure up to 9000 psi, temperature up to
1200 degrees F, corrosive fluids
Bronze
Pressure up to 300 psi, temperature up to 400
degrees F, water, air gas
Packing
Material:
Teflon
Graphite
Temperature up to 450 degrees F, water, oil,
gas
Temperature up to 1000 degrees F, water, oil,
gas, steam
Table 8-4. Acceptable Insulation Types.
Insulation Type
Advantages
Disadvantages
Asbestos free calcium silicate ASTM C
533 and expanded silica (perlite)
Inexpensive, easy to handle, numerous
manufacturers, for use from 100
degrees F to 1500 degrees F.
Deteriorates in moist conditions, not very
compressible, unsuitable for direct buried
applications.
Fiberglass ASTM E-84
Inexpensive, easy to handle, numerous
manufacturers, for use from -40
degrees F to 1200 degrees F.
Loses insulating value in moist conditions,
unsuitable for direct buried applications.
Cellular Glass
Impervious to moisture, easy to handle,
for use from -40 degrees F to 1200
degrees F can be used above and below
ground.
Not compressible, few manufacturers.
*Insulation systems using composite of two or more acceptable insulations may also be acceptable.
(2) Thermal efficiency. For purposes of efficiency,\1\ the recommended economic thickness of pipe
insulation shall meet or exceed the requirements of ASHRAE 90.1.
Table 8-5. Recommended Economic Thickness for Pipe insulation.
Temperature of pipe F
Nominal Pipe
size, in.
100-199
l½ and less
2
2½
3
3¼
4
4½
5
6
8-10
1
1
1
1
1
1
1
1
1
200-299
300-399
1
1
1
1
1½
1½
1½
1½
1½
1
1
1½
1½
1½
1½
1½
1½
2
400-499 500-599 600-699 700-799
UTILITY—STEAM GENERATION
1½
1½
1½
2
1½
1½
1½
2
1½
2
2
2½
1½
2
2
2½
2
2
2½
3
2
2
2½
3
2
2
2½
3
2
2½
2½
3
2
2½
2½
3
800-899
2½
2½
2½
2½
3
3
3
3½
3½
900-999 1000-1099 1100-1200
2½
1½
3
3
3
3½
3½
3½
3½
2½
2½
3
3
3½
3½
3½
4
3½
3
3
3½
3½
4
4
4
4
4
TM 5-810-15
Table 8-5. Recommended Economic Thickness for Pipe Insulation. (Continued)
Temperature of pipe F
Nominal Pipe
size, in.
100-199
7
8
9
10
11
12
l4 and up
1½
1½
1½
1½
1½
1½
1½
200-299
1½
1½
1½
1½
1½
1½
1½
300-399
2
2
2
2
2
2
2
400-499 500-599 600-699 700-799
UTILITY—STEAM GENERATION
2
2½
2½
3
2
2½
2½
3½
2½
2½
3
3½
2½
3
3
3½
2½
3
3
3½
2½
3
3
3½
2½
3
3
4
/1/ 8-5. Pipe hangers, anchors and supports.
a. Design. Hangers, anchors and pipe supports
will be designed to meet ASME B31.1 requirements where applicable. Pipe hangers will be in
accordance with MSS SP-69.
b. Spacing. Guidelines for pipe support spacing
and carrying capacities are provided in ASME
B31.1
8-6. Pipe expansion compensation.
a. Design. The thermally induced expansion of
piping materials can be compensated for with
normal pipe bends and the proper placement of
anchors. The thermal expansion of common piping
materials is shown in Appendix B of the ASME
B31.1.
b. Expansion devices. When piping system design is unable to compensate for pipe expansion,
expansion bends or expansion joints will be used.
Expansion joints and bends will conform to ASME
standards.
8-7. Pipe sizing.
a. General. Selection of the proper pipe size for
any particular application is dependent upon numerous variables. Pipe sizing is based on velocity,
pressure loss, and friction loss calculations.
b. Data requirements. In order to properly size
piping, pertinent data must be organized for use in
the required calculations. This data includes pipe
material (friction factor), process fluid, flow requirements, design pressures and temperatures,
allowable pressure drop, velocity requirements, and
preliminary piping layout.
c. Velocity guidelines. General guidelines for
allowable velocities in piping systems are shown in
table 8-6.
d. Pipe sizing philosophy. Piping will be sized to
obtain a maximum velocity that corresponds to the
allowable pressure drop for the system. It is
desirable to keep velocities as high as possible
800-899
3½
3½
3½
4
4
4
4
900-999 1000-1099 1100-1200
3½
4
4
4
4
4
4½
4
4
4
4
4½
4½
4½
4
4½
5
5
5
5
5
Table 8-6. Piping Velocity Guidelines.
Fluid
Application
Velocity
Steam
Superheated steam, boiler leads
150-333 fps
Auxiliary steam, exhaust lines
100-250 fps
Saturated and low pressure steam
100-167 fps
Centrifugal pump suction lines
3-5 fps
Feedwater
8-15 fps
General service
4-10 fps
Potable water
Up to 7 fps
Water
without exceeding maximum allowable velocities or
causing excessive pressure drops.
e. Sizing calculations. Empirical equations and
charts have been devised to calculate pressure
drops with reasonable accuracy. The Darcy Equation has been shown to produce accurate results.
8-8. Steam traps.
a. Application. Steam traps are devices that are
used to accomplish the following functions:
(1) Allow condensate resulting from loss of
latent heat in steam to flow from the steam system
to a lower pressure system or to atmosphere.
(2) Vent air and other gases from the steam
system to maintain steam temperature and reduce
corrosion.
(3) Prevent escape of steam from the steam
system.
b. Selection. The factors to be considered when
selecting the proper steam trap include condensate
load, continuous or intermittent operation, system
pressure, constant or variable pressure and load,
indoor or outdoor installation, failure mode (open
or closed), air and noncondensible gas venting, and
resistance to water hammer.
c. Design. Trap selection and sizing depends on
many factors. The condensate load on a trap
involves range of load as well as rate of change.
Nearly all traps service a long range. A trap will be
8-11
TM 5-810-15
sized for the maximum expected condensate load
and a safety factor. Oversizing a trap can increase
losses, both for good traps as well as traps that fail
open. It is recommended that a safety factor of 2:1
be used to size a trap in a constant pressure usage
and safety factor of 3:1 be used if the pressure
varies. The major steam loss from a trap is at a
failed-open condition and can cost thousands of
dollars a year if not detected. However, a failed
close trap may cause extensive damage because of
corrosion or water hammer from condensate that is
not discharged. Selection of the failure mode
depends on the design conditions and maintenance
practices. All traps are subject to freezing,
particularly due to condensate flow blockage. Of all
types of traps, float traps are most subject to
freezing. Steel bodied traps resist freezing better
than iron. Trap cost is an important consideration
as initial expense may not justify selection because
of maintenance characteristics and life span. The
inverted bucket type of trap has the longest life,
followed by the float trap, thermostatic trap and the
thermodynamic trap consecutively for long life.
d. Types. There are four basic types of steam
traps: inverted bucket, float, thermostatic and
thermodynamic.
(1) Inverted bucket. This type of steam trap is
the most widely used. When properly sized, steam
loss is kept to a minimum. The inverted bucket trap
contains an inverted bucket inside the trap body.
The inverted bucket is fastened to a linkage in such
a manner that it will close the trap outlet when
steam enters from beneath the bucket. As the steam
cools and condenses (assisted by a bucket vent),
the bucket loses its buoyancy and the trap opens
releasing the condensate. Gases mixed with the
steam pass through the inverted bucket trap partly
by way of the bucket vent and partly in any steam
discharged by the trap. The discharge from the
inverted bucket trap is intermittent and requires a
differential pressure between the inlet and discharge
of the trap to lift the condensate from the bottom of
the trap to the discharge connection. They are
resistant to water hammer, operate well at low
loads, and fail open. Bucket traps may be subject to
damage from freezing and have only fair ability to
handle start-up air loads. Inverted bucket traps are
well suited for draining condensate from steam
lines or equipment where an abnormal amount of
air is to be discharged and where dirt may drain
into the trap.
(2) Float. A float trap has a small chamber
containing a float and linkage that multiplies the
float*s buoyancy. The condensate will cause the
8-12
float to open the trap until it is drained and the float
loses buoyancy. A float trap does not have to be
primed as an inverted bucket trap does. However,
buildup of solids and sludge in the trap body can
prevent the float from sinking and closing the
valve. The discharge from the float trap is generally
continuous. This type is used for draining
condensate from steam headers, steam heating
coils, and other similar equipment. When a float
trap is used for draining a low pressure steam
system, it will be equipped with a thermostatic air
vent.
(3) Thermostatic. The thermostatic trap opens
and closes by means of a force developed by a
temperature sensitive actuator. A basic problem for
all thermostatic traps is keeping the actuating
temperature close to the saturation temperature so
the condensate will be hot, but not allow live steam
to blow out the trap. If the actuating temperature is
not close to the saturation temperature, there is a
possibility that O2 and CO2 may dissolve in the
water, and also, that the condensate may back up
to an unacceptable level. The discharge from this
type of trap is intermittent. Thermostatic traps are
used to drain condensate from steam heating coils,
unit heaters and other similar equipment. Strainers
are normally installed on the inlet side of the steam
trap to prevent dirt and pipe scale from entering the
trap. The thermostatic trap is the most common of
all trap types used for two pipe steam heating systems. When this type of trap is used for a heating
system, at least 2 feet of pipe will be provided
ahead of the trap to cool the condensate. This
permits condensate to cool in the pipe rather than
in the coil, and thus maintains maximum coil
efficiency. Thermostatic traps are recommended for
low pressure systems up to a maximum of 15 psi.
When used in medium or high pressure systems,
they must be selected for the specific design
temperature. In addition, the system must be
operated continuously at that design temperature.
(4) Thermodynamic disc traps. Thermodynamic disc traps are used for intermittent service,
where they operate well under variable pressure
conditions, are resistant to damage from freezing
and water hammer, and fail open. A disadvantage
of the thermodynamic trap or disc trap is poor gas
handling. The pressure drop when air or 002 are
flowing in the trap resembles that of steam, so that
large amounts of air will close the trap. Therefore,
another air removal method is necessary for startup
of a steam system. Thermodynamic disc traps will
not be used where high back pressures, or low load
conditions might occur. They are best suited for
TM 5-810-15
use on high pressure superheated steam mains and
steam tracer lines.
8-9. Piping accessories.
a. Strainers. Strainers are a filtering device used
to remove solids from liquid piping systems and to
protect equipment. Strainers are normally placed in
the line at the inlet to pumps, control valves or
other types of equipment that are to be protected
against damage.
(1) Y-type strainers. Y-type strainers are used
in small piping for protection of in-line devices such
as steam traps. Y-type strainers may also be used in
pump suction lines on small pumps such as
chemical feed pumps. Y-type strainers utilize a
screen mesh to remove solids and will have a blowoff valve and a means for removing the screen for
cleaning.
(2) T-type strainers. T-type strainers are used
in large piping on pump suction lines to protect the
pump. T-type strainers will utilize a perforated
basket to remove solids and will have inlet and
outlet pressure gauges or a differential pressure
gauge to indicate when the basket requires cleaning. Strainers for pump protection should be not
less than 40 mesh. Screen material will be suitable
for liquid or gas in line. Strainer body will be equal
to material specified for the valves in the same
service.
(3) Duplex strainers. Duplex strainers are
used on low pressure systems and contain two
sections which can be individually cleaned while the
process is in operation. One section is operable
while the other section is isolated. Duplex strainers
will have inlet and outlet pressure gauges or a
differential pressure gauge to indicate when a
basket requires cleaning.
b. Safety valves. Safety valves must be provided
in accordance with the ASME Boiler and Pressure
Vessel Code. Safety valves are pre-set to open fully
at a certain pressure and to pass a certain flow
capacity. The pressures and capacities are determined from code requirements. Safety valves on
the boiler proper are normally provided by the
boiler manufacturer. Other equipment requiring
safety valves includes the DA, feedwater heater
shell, feedwater heater channel, and air receivers.
Pressures and capacities for this equipment is also
determined from code requirements.
8-13
TM 5-810-15
CHAPTER 9
INSTRUMENTS AND CONTROLS
9-1. General.
This chapter addresses the criteria for the selection
of instruments and controls to meet the
requirements of the steam plant.
a. Pneumatic controls. Most control system
manufacturers have discontinued production of
pneumatic controls systems. Replacement parts and
qualified service for the equipment are difficult to
procure. For these reasons pneumatic controls
should not be used for new installation.
b. Electronic controls. Electronic systems have
been made obsolete by the microprocessor based
control systems. Manufacturers no longer make
electronic control systems and they should not be
specified for new installations.
c. Microprocessor based controls. Microprocessor based control systems can provide sequential
logic control and modulating control in one control
device. This capability makes available boiler control systems, which use both sequential logic and
modulating control, that are more flexible and
reliable as well as more cost effective. Processing
units can be utilized as single loop controllers or
more powerful processing units can be applied to
individual control subsystems, such as combustion
control of ash handling control.
(1) Inputs from and outputs to field devices
may be multiplexed. Data highways connect all
processing units to data storage and acquisition
components, cathode ray tube (CRT) displays and
operator consoles, loggers, and printers, providing
communication among all components. Communications between modulating control devices and
sequential logic flow freely and are not subject to
the restrictions inherent with analog and mechanical
relay electronic systems which require hard-wiring
between components. Data acquisition and
operator interface for control may be accomplished
using CRT*s, keyboards and printers or through
control stations indicators and recorders mounted
on an operator console. When CRT*s, keyboards
and printers are utilized redundant microprocessors
are sometimes utilized depending on unit size.
(2) Program logic can be changed or expanded
readily with limited hardware revisions. System
selection can range from programmable controller
systems to fully distributed digital control systems.
The criteria for selection of the proper
microprocessor based system will include unit size,
the amount and type of modulating control and
sequential logic required, operator interface re-
quirements, system security requirements, and
LCCA.
(3) Distributed control systems include the
process input output sensors and actuators which
are connected to the termination units which
condition and multiplex the signals for communication to the microprocessor unit controllers where
the logic resides for control of the process variable.
All microprocessor unit controllers communicate
with each other and to a data highway which
includes nodes for the operator interface station,
engineering work station, and programmable logic
controllers for balance of plant controls.
(4) The distributed control system logic for the
controls and the 110 for the process are located in
the vicinity of the process. This process controller
will communicate with other process controllers,
engineers work station, data acquisition system and
the operator interface. The control system will be
configured to allow the process controller to
continue to function upon loss of communication
with the operator interface, data acquisition system
and other process controllers.
d. Control system reliability. The methods used
to ensure control system reliability will be based on
unit size, importance to plant operation, and the
cost of control system failure versus the cost of
backup hardware.
(1) Power sources. Power to the control
system must have a backup supply. Microprocessor
based systems must have a backup power supply
either from a separate ac source or an
uninterruptable power supply (UPS). Loss of either
the primary power source or the backup power
service must be detected and alarmed. Loss of
either supply alone must not affect operation of the
controls. Distributed control systems will include
power supplies which are redundant or backed up
so that loss of any power supply will not cause loss
of power to the control logic. Loss of power supply
should be alarmed.
(2) Control
system
safeguards.
Microprocessor based controls are highly reliable
but safeguards must be provided to limit the effects
of component failure. Microprocessor based
control systems require grounding to a ground mat
with an impedance of three ohms or less for
protection of system components to reduce forced
plant outages. Spare circuit cards for critical
components are to be available at the boiler plant,
as well as spare microprocessing units that can be
9-1
TM 5-810-15
substituted for faulty units which are encountered
during start-up and operation of the plant. For
critical subsystems consideration should be given to
redundant microprocessors with automatic
switching of inputs and outputs from one
microprocessor to another. The data highway
should be looped or redundant so that failure of a
segment of the data highway will not result in the
loss of communications. Control elements should
be designed to fail in a safe condition upon loss of
the electric or pneumatic power to the actuators or
input signal. The loss of power at the component or
subsystem levels must cause the associated
auto/manual stations to switch to the manual mode
of operation. The control logic should have
continuous self diagnostic capability and, upon
detection of component failure, transfer to manual
and indicate the cause of the failure.
Microprocessors are to contain nonvolatile memory
which will not be erased on power failure.
e. Control system expansion. The control system
architecture should allow expansion at all levels of
the system. The 110 can be expanded by installing
additional cards or racks with signal conditioning
for communication to the control system processing units. Additional nodes can be added to the
data highway to allow additional processing units,
engineering work stations, and operator interface
CRT*s to be added to the control system.
f. Data link. The process 110 signals are connected to the termination units and through signal
conditioners to the microprocessor controllers. The
control system data highway for exchange of data
between microprocessor based controllers and between microprocessor based controllers, data
acquisition systems, operator interface and
engineering work stations will be redundant. The
data highways will utilize coax, twines of fiber
optic cabling. The speed of data transmission is
increasing and should be investigated prior to
9-2
writing specifications. Data rates of approximately
1 mega baud are available.
9-2. Combustion controls.
a. General. The purpose of combustion control
systems is to modulate the quantity of fuel and
combustion air inputs to the boiler in response to a
load index or demand (steam pressure or steam
flow) and to maintain the proper fuel/air ratio for
safe and efficient combustion for the boiler*s entire
load range.
b. System types. Three types of combustion control systems are available: series, parallel, and
series-parallel. Each of these types are schematically represented in figure 9-1.
(1) Series control. A series control system as
shown in figure 9-1(a) uses variation in the steam
header pressure (or any other master demand
signal) from the setpoint to cause a change in the
combustion air flow which, in turn, results in a
sequential change in fuel flow. The use of series
control is limited to boilers of less than 100,000
pph that have a relatively constant steam load and
a fuel with a constant Btu value.
(2) Parallel control. A parallel control system
as shown in figure 9-1(b) uses a variation from
setpoint of the master demand signal (normally
steam pressure) to simultaneously adjust both the
fuel and combustion air flows in parallel. This type
of system is applicable to stoker-fired boilers,
pulverized coal fired boilers, gas/oil fired boilers
and atmospheric circulating fluidized bed (ACFB)
boilers.
(3) Series-parallel control. A series-parallel
control system as shown in figure 9-1(c) should be
used to maintain the proper fuel/air ratio if the Btu
value of the fuel varies by 20 percent or more, if
the Btu input rate of the fuel is not easily
monitored, or if both of these conditions are
present. These conditions normally exist on pulver-
TM 5-810-15
ized coal fired and ACFB boilers. Variations in the
steam pressure setpoint adjust the fuel flow input.
Since steam flow is directly related to heat release
of the fuel, and because a relationship can be
established between heat release and combustion
air requirements, steam flow can be used as an
index of required combustion air. Note however
that this relationship is true only at steady load
conditions.
c. System categories. Combustion controls can
be further divided into two categories within the
basic types: positioning control and metering control, as shown in figure 9-2.
(1) Positioning control. Positioning systems
require that the final control elements move to a
preset position in response to steam pressure
variations from a setpoint. Series positioning control will not be covered here since it is only used on
very small boilers operating at constant loads.
Parallel positioning systems that use a mechanical
jackshaft to simultaneously position fuel feed and
air flow from a single actuator apply to packaged
type gas/oil fired boilers in the 20,000 to 70,000
pph size and is shown in figure 9-2a. This system
allows the operator to load the boiler over its
complete operating range. The fuel valves and air
damper are operated by the same drive through a
mechanical linkage. The gas and oil valves include
cams which are adjusted at start up to maintain
proper fuel air ratio over the operating range of the
boiler. Parallel positioning systems with fuel/air
ratio control as shown in figure 9-2(b) are suitable
for use on gas/oil and stoker fired units. This
system allows the operator to adjust the fuel/air
ratio for the entire load range of the boiler. The
addition of steam flow correction of air flow to
parallel positioning with fuel/air ratio control
creates a system suitable for use on ACFB, gas/oil
and pulverized coal fired units as shown in figure 92(c). This system uses variation of steam pressure
from a setpoint to initially control fuel and air
inputs. The system recorrects combustion air flow
using steam flow as a setpoint for air flow, since
steam flow is a function of fuel Btu input (inferred
fuel flow). This system relates directly to a seriesparallel type control with the addition of a feedforward signal from the steam pressure controller
to the combustion air control.
9-3
TM 5-810-15
(2) Metering control. Metering control
systems regulate combustion based on metered fuel
and air flows as shown in figure 9-3. The master
demand developed from steam pressure error
establishes the setpoints for fuel and combustion air
flows at the controllers. The controllers drive the
final control elements to establish proper fuel and
flows which are fed back to the controllers.
Maximum and minimum signal selectors are used to
prevent the fuel input from exceeding available
combustion air on a boiler load increase and to
prevent combustion air from decreasing below fuel
flow requirements on load reduction. This system
is a cross-limiting flow tie back system with air
leading fuel on load increase and fuel leading air on
load reduction. This system is applicable to gas and
oil, pulverized coal, and ACFB fired units.
d. System selection. Table 9-1 summarizes the
combustion control systems discussed and their
application to the various types of boilers.
9-4
e. Stoker system controls.
(1) Fuel flow control. The components of a
stoker system must respond to the fuel flow demand signals generated by the combustion control
system. For spreader stokers the coal feed to the
overthrow rotor will vary with the demand signal.
Grate speed on traveling grate and traveling chain
grate stokers will respond to the demand signal.
The frequency and duration of vibration cycles on
vibrating grate stokers will vary with the demand
signal. In all cases the relationship between fuel
flow and unit load will be determined for use in the
combustion control system to properly control fuel
flow in response to the demand signal.
(2) Combustion air control. The combustion
air flow is normally controlled at the FD fan. Two
methods that are commonly used are control of
inlet vanes on the FD fan or control of the FD fan
inlet damper. If a metering control system is used
the combustion air flow should be measured down
TM 5-810-15
Table 9-1. Combustion Control System Selection Guide.
Boiler Type
Gas/
Control System Oil
Jackshaft
positioning
X*
Series control
X**
Parallel
positioning
Stoker
Pulverized
Coal (PC)
Multiple
Burner
PC
ACFB
X**
X
X
Parallel
positioning
with steam
flow correction
of air
X
X
X
Parallel metering with cross
limiting and
flow tie-back
X
X
X
X Recommended Application
*Restricted to use on boilers 70,000 pph and under.
**Restricted to use on boilers under 100,000 pph with constant
load and constant Btu value fuel.
stream from the fan outlet. The relationship between inlet vane or damper position and air flow
will be determined for use in the combustion
control system or for characterizing the final control element. Overfire air flow on stoker fired units
normally is not measured. If overfire air is to be
controlled the air flow demand signal will be used
to control overfire air in parallel with combustion
air.
(3) Combustion air flow measurement. Accurate combustion air flow measurement is extremely
important in combustion control systems for stoker
fired boilers. A venturi section of air foil flow
element should be provided in the ductwork
between the FD fan and the stoker or a Piezometer
ring may be installed at the FD fan inlet. The flow
element will be designed to provide a design
differential pressure across the flow element of not
less than 2 inches wg at full load conditions. The
flow transmitter selected for combustion air flow
will be a differential pressure transmitter that is
accurate in the range of differential pressure
developed by the flow element.
f. Pulverized coal system controls.
(1) Fuel flow control. Fuel flow in pulverized
coal systems is established by coal feeder inputs to
the pulverizer. Coal feeder speed controls the fuel
flow to the pulverizer. The volumetric rate of coal
flow delivered to the pulverizer is directly related
to feeder speed. Feeder speed varies with fuel flow
demand.
(2) Combustion air control. Combustion air
flow in pulverized coal systems consists of primary
air flow and secondary air flow. Primary air is the
air which transports the pulverized coal to the
burner or burners. Secondary air is the air delivered
by the FD fan to the boiler to support combustion.
Total air flow is the sum of secondary air flow and
all primary air flows. Secondary air is measured
downstream of the FD fan and controlled by
positioning FD fan inlet vanes or inlet damper.
Primary air can be supplied by the FD fan or by a
primary air fan. Primary air is normally measured
on each pulverizer.
(3) Combustion air flow measurement. Accurate combustion air flow measurement is essential
for combustion control systems of pulverized coal
fired boilers. Secondary air flow will be measured
with a venturi section or air foil flow element in the
ductwork between the FD fan and the boiler
windbox. The flow element should be designed to
provide a design differential pressure across the
flow element of not less than 2-inches wg at full
load conditions. Primary air flow will be measured
on each pulverizer with a venturi section or pilot
tube between the primary air fan and the pulverizer.
The design pressure differential pressure across the
primary air flow elements should not be less than 2inches wg at full load. The transmitters selected for
primary air flow and secondary air flow will be
differential pressure transmitters that are accurate
in the range of differential pressure developed by
the flow elements.
(4) Pulverizer controls. Figure 9-4 shows one
multiple pulverizer control scheme. In this arrangement the firing rate demand is compared to
total fuel flow, which is the sum of all feeders to
develop the demand to the pulverizer master. The
pulverizer master demand signal is applied in
parallel to all pulverizers which have duplicate
controls. If an upset occurs in the fuel/air ratio such
that total air flow is low, an error signal from air
flow control reduces the firing rate demand to the
pulverizer master to restore the proper fuel/air
ratio. Since coal flow to the burner is a function of
primary air flow the primary air damper and coal
feeder speed control receive the same demand
signal. If an error develops between demand and
measured primary air flow or coal feeder speed, the
controllers adjust the primary air flow or feeder
speed to eliminate the error. If primary air flow is
less than feeder speed demand, the feeder speed
demand is made equal to the primary air flow by
the low select auctioneer. A minimum pulverizer
loading and a minimum primary air flow limit
should be used to maintain the pulverizers above
the minimum safe operating load to maintain
adequate burner nozzle velocities and to maintain
9-5
TM 5-810-15
the primary air to fuel ratio above a minimum level
for all pulverizer loads.
g. Gas/oil system controls.
(1) Fuel flow control. Fuel flow in gas/oil fired
boilers is controlled by operation of gas or oil
control valves in the supply lines to the burners.
The gas or oil control valves are modulated to
control fuel flow based on the demand signal
generated by the combustion control system. Gas
flow to the burner is measured by taking the
differential pressure across an orifice. Oil flow to
the burners will be measured by a rotating disk type
meter. Metering type control systems utilize the
fuel flow and unit load in the combustion control
9-6
system to properly modulate fuel flow in response
to the system demand.
(2) Combustion air control. The combustion
air is normally controlled at the FD fan. Air flow
for package boilers is normally controlled by outlet
dampers at the FD fan. Other methods that are
used include control of the FD fan inlet vanes or
control of the FD fan inlet damper. The relationship
between inlet vane or damper position and air flow
will be determined for characterizing the final
control element. When a metering type control
system is used air flow is measured downstream of
the FD fan or a piezometer may be installed at the
FD fan inlet.
TM 5-810-15
(3) Combustion air flow measurement. Accurate combustion air flow measurement is also
important in metering type combustion control
systems for gas/oil fired boilers. A venturi section
or air foil flow element should be provided in the
ductwork between the FD fan and the burner
windbox or a piezometering may be installed at the
FD fan inlet. The flow element will be designed to
provide a design differential pressure across the
flow element of not less than 2 inches wg at full
load conditions. The flow transmitter selected for
combustion air flow will be a differential pressure
transmitter that is accurate in the range of
differential pressure developed by the flow element.
(4) Oil atomization. The oil to the burner will
be atomized utilizing steam or compressed air. A
control valve installed in the atomizing steam or air
line will be controlled to maintain the atomizing
medium pressure above the oil supply pressure to
the burner.
h. Atmospheric circulating fluidized bed (ACFB)
boiler.
(1) Fuel flow control. Main fuel flow in an
ACFB system is established by fuel flow through
the feeder to the combustor. The volumetric rate of
fuel flow is directly related to feeder speed. The
coal feed demand speed utilizes the lower of the
total air flow or firing rate demand as the set
point and compares the set point to total fuel flow
to develop the demand signal for the feeder master.
The feeder master demand signal is applied to all
feeders which have duplicate controls. Therefore,
as firing rate demand is increased or decreased the
feeder speed is increased or decreased. Coal chute
air flow compares measured air flow to load flow
to operate the coal chute air damper. A feed
forward signal based on rate of change is also used
to modulate the coal chute air control damper. Coal
feeder and coal chute air damper control is shown
in figure 9-5.
(2) Combustion air control. Combustion air
flow in ACFB systems consists of primary air flow,
overfire air flow, stripper cooler air flow, and main
fuel chute air flow. Primary air is introduced below
the bed and keeps the fuel and bed in suspension.
Overfire air is delivered by the FD fan and is
utilized at loads above 50 percent to control
furnace exit gas temperature. The stripper cooler
air flow is utilized to cool the excess bed material
which is removed in the stripper section. Main fuel
chute air flow is utilized to sweep the fuel tube to
the combustor. Total air flow is the sum of primary
air, overfire air, stripper cooler air, and coal chute
air flow. All air can be supplied by the FD fan or
separate primary air and FD fans may be utilized.
The primary air, overfire air and stripper cooler are
controlled by positioning the appropriate damper.
9-7
TM 5-810-15
Air supply is maintained by modulating the FD fan
and primary air fan inlet vanes or dampers to
maintain pressure in the FD fan outlet duct.
(3) Combustion air flow measurement. Accurate combustion air flow measurement is also
important in combustion control systems for ACFB
boilers. Measurement of primary air flow, overfire
air flow, stripper cooler air flow, and coal chute air
flow will be measured with a venturi section or air
flow element in the ductwork to the various
equipment. The design pressure differential pressure across the air flow elements will be not less
than 2-inches wg at full load. The transmitters
selected for primary air flow and secondary air flow
will be differential pressure transmitters that are
accurate in the range of differential pressure
developed by the flow elements.
(4) Primary and overfire air flow control. Figure 9-6 shows the primary and overfire air flow.
The firing rate demand signal serves as an index for
air flow demand. The fuel feed signal and firing rate
demand signal are cross limited by a high selector
to serve as the setpoint for the total air flow
controller. The output of the total air flow
controller becomes the setpoint for the primary and
overfire air flow controllers. The setpoint is
9-8
characterized based on load to obtain the proper
primary-to-overfire air flow ratio. The upper overfire air dampers are closed below 50 percent load.
The primary air controller setpoint is low limited by
a minimum primary air setpoint. Each primary and
upper air flow controller compares measured air
flow to setpoint. The controller output becomes the
demand to its respective air flow control damper.
All air flow measurements should be temperature
corrected. Furnace exit gas temperature should be
monitored and at high temperature alarmed to
allow the operator to make the proper air flow
adjustment to bring the temperature back to
normal. A bias adjustment normally is provided for
each controller.
(5) Furnace bed inventory control and solids
cooler temperature, air flow and spray water control. Furnace bed inventory control requires removal of excess bed material from the furnace. The
solids cooler cools the excess bed material to a
temperature which allows it to be disposed of via
the ash system. Solids are removed from the
furnace either by operator action or automatically
on high furnace plenum pressure. The furnace bed
static pressure, total furnace differential pressure,
TM 5-810-15
furnace plenum static pressure and lower furnace
differential are all monitored to give the operator
an indication that the furnace bed inventory should
be reduced. When a sequence for removal of
materials is initiated the solids cooler air flow
control dampers are opened to a preset position.
The air flow dampers position will start a cycle
timer and open the bed material transfer line. At the
end of the timed period the transfer line is closed.
The material is cooled by spray water and air flow
to a temperature suitable for the ash system. The
spray water valve opens and closes automatically
based on cooler bed temperature. After the bed
material is cooled it is placed in a hopper for
removal by the ash system. The air flow dampers
and solid spray water valve can be opened and
closed manually by a hand auto station. Figure 9-7
shows the solids cooler temperature and flow
control.
(6) J-valve blower control. The J-valve blower
control maintains air flow for fluidization and
transport of material from the hot cyclone to the
furnace. The J-valve control is shown on figure 98. The system includes J-valve blower dischargepressure control valve, upleg aeration and plenum
control valve and downleg aeration and plenum
control valves.
(a) J-valve pressure control. The J-valve
blower pressure is maintained by sensing pressure
downstream of the J-valve blower discharge
damper. The discharge damper is modulated to
maintain a constant pressure of approximately
170”. The upleg and downleg plenum air is maintained at a constant value of approximately 400
lb/hr. The setpoint is constant throughout the load
range. Upleg and downleg plenum air flow will be
measured with a Venturi section or air foil flow
element in the ductwork to the plenums. The flow
element will be designed to provide a design
differential pressure across the flow element of not
less than 2 inches wg.
(b) J-valve aeration valve control. The
measured air flow is compared to the constant
setpoint and the control dampers modulated to
maintain the air flow at setpoint. The downleg
static pressure, inlet static pressure, and upleg
static pressure outlet as well as differential pressure
across portions of the J-valve indicate solids flow,
density and dipleg differential are measured and are
utilized to allow the operator to manually control
9-9
TM 5-810-15
the aeration valves. The aeration control is
normally only required during start-up and are
manually controlled.
(7) Sorbent (limestone) feeder control.
The sorbent feeder control provides the proper
amount of sorbent to capture the SO2 generated in
the combustion process. The sorbent feeder control
is shown in figure 9-9. Sorbent feeder speed
controls the sorbent flow to the combustor. The
volumetric rate of sorbent delivered to the
combustor is directly related to feeder speed.
Feeder speed setpoint is based on SO2 in the stack
flue gases, modified by oxygen in the flue gas, total
fuel flow and a correction factor. The SO2
measurement is provided by a flue gas analyzer or
analyzers, total fuel flow is taken from the main
fuel feeders and oxygen from the flue gas O2
analyzer. The setpoint value is compared to the
actual sorbent (limestone) flow. A low limit is
applied to the controller output to prevent the
value from falling below a minimum value.
(8) Warmup burner control. A gas/oil fired
burner or in-bed lances are utilized to warm the bed
material to the value where main fuel combustion
occurs. When gas/oil fire burners are utilized they
normally are placed in the primary air duct. Fuel
flow is regulated by a controller comparing primary
9-10
air temperature at the burner outlet to the selected
temperature. A low limit select limits the fuel to the
available primary air flow through the duct burner.
When in-bed lances are utilized the fuel flow
setpoint is compared to the actual fuel flow to
modulate the burner valve. Position of the fuel
valve is limited by a low selector to the available air
flow to the combustor. The warmup burner and inbed lance control is shown in figure 9-10.
i. Oxygen trim. Boiler efficiency can be improved by minimizing excess air levels. Excess air
is required to ensure complete combustion and
optimum heat release from the fuel. However
excess air adds to heat loss and reduces boiler
thermal efficiency. Oxygen trim controls are used
to operate the boiler at low excess air levels. An
oxygen analyzer is installed to monitor the amount
of oxygen in the boiler flue gas. The signal from the
analyzer is used to correct the combustion air flow
to maintain the proper oxygen level in the flue gas
exiting the boiler. The boiler manufacturer*s
recommendations for flue gas oxygen content
versus boiler load for optimum boiler efficiency
should be used to establish the proper oxygen
content in the flue gas at all boiler loads. Oxygen
trim controls applied to a parallel metering system
TM 5-810-15
are shown in figure 9-11. The oxygen setpoint is
calculated from boiler load by a characterizing
function generator applied to steam flow. Signal
limiters are used to establish minimum and
maximum corrections to the fuel/air ratio since
major excursions are possible due to malfunctions
of the oxygen analyzer. Automatic oxygen trim
controls should not be used on stoker fired units.
Since the fuel bed on a stoker cannot be increased
or decreased quickly the firing rate on a stoker is
varied primarily by changes in combustion air flow.
Changes in combustion air flow will cause similar
changes in flue gas oxygen content. Automatic
oxygen trim would attempt to correct the air flow
and would cause unstable operation during load
changes. Stoker fired units should be provided with
manual oxygen trim.
9-3. Boiler controls.
a. Furnace safety system.
(1) General requirements. The main function
of a furnace safety system is to prevent unsafe
conditions to exist in the boiler including prevention of the formation of explosive mixtures of fuel
and air in any part of the boiler during all phases of
operation. The system must be made to comply
with the appropriate NFPA regulations and the
recommendations of the boiler manufacturer.
(2) Purging and interlocks. The specific purging and interlock requirements will depend on
whether the boiler is gas/oil fired, stoker fired,
pulverized coal fired or ACFB fired. Regardless of
the type of firing system, certain functions must be
included in the furnace safety system. These
functions include a prefiring purge of the furnace,
establishment of permissives for fuel firing, emergency shutdown of the firing system when required,
and a post firing purge. Pulverized coal, ACFB and
gas/oil firing require additional functions such as
establishment of permissives for firing the ignition
system and continuous monitoring of firing
conditions. The prefiring purge is required to
ensure that all unburned fuel accumulated in the
furnace is completely removed and is accomplished
by passing a minimum of 25 to 30 percent air flow
through the furnace for five minutes. The
conditions that would cause an emergency
shutdown (trip) for pulverized coal, gas/oil and
ACFB boilers are shown in table 9-2. The furnace
safety system can be either deenergize-to-trip to
9-11
TM 5-810-15
energize-to-trip. The energize-to-trip philosophy is
more desirable since it reduces nuisance trips, is
operable on loss of power, and is more reliable.
(3) Flame detection and management. Stoker
fired boilers do not utilize flame detection or flame
management. Pulverized coal and gas/oil fired
systems do require flame detection, which is the
key to proper flame management. The basic requirements of flame detectors are detection of the
high energy zone of a burner flame, ability to
distinguish between ignitor and main flames, and
discrimination between the source flame, adjacent
flames, and background radiation. Ultraviolet (UV)
detectors are suited for flame detection of gas or
light oil ignitor and main gas flames. Infrared (IR)
detectors are used for pulverized coal flames. Self
checking or redundant detectors should be used to
ensure reliability. Location of the flame detectors is
critical to proper flame management and must be
given careful consideration. Flame detection
systems will be on-off type based on the presence
or absence of flame.
(4) Burner controls. Burner controls are the
permissives, interlocks, and sequential logic which
are required for safe startup and operation of
pulverized coal, ACFB and gas/oil burners. Burner
controls range from manual to fully automatic.
9-12
Regardless of the level of automation incorporated
into the burner controls, the system logic must
insure that the operator commands are performed
in the correct sequence with intervention only when
required to prevent a hazardous condition.
Pulverized coal burner controls must provide the
proper sequential logic to completely supervise
burner startup and operation including coal feeders,
pulverizers, air registers, ignitors, and flame
detectors. Gas/oil burner controls must provide the
proper sequential logic to completely supervise
burner startup and operation including gas/oil fuel
valves, air registers, ignitors and flame detectors.
The ACFB boiler includes utilizing a main gas
burner or gas lances and ignitor system to warm the
boiler and bed temperature above minimum
required for solid fuel firing. This burner operation
is identical to a gas/oil burner operation. The
ACFB boiler does not have a main fuel burner;
however, the introduction of fuel is completely
supervised to provide the proper sequence for
purge, ignitors, warm-up burners, flame detection,
coal feeders, sorbent feeders and bed temperature
monitoring. Note the bed temperature monitor
insures that adequate temperature is present to
ignite the solid fuel. Adequate bed temperature
TM 5-810-15
Table 9-2. Emergency Trip for Boilers.
Item
Loss of all FD fans
Loss of all ID fans (if used)
High-low drum level
High steam pressure
High furnace pressure or draft
Low air flow
Loss of power to safety system
Flame failure
Gas or oil pressure/temperature out of limits
High cyclone level
All solids fuel feeders trip
Bed temperature greater than maximum
Bed temperature less than minimum
Emergency trip pushbutton
Trips recommended by boiler supplier
Pulverized Coal
X
X
X
X
X
X
X
X
Gas/Oil
ACFB
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
9-13
TM 5-810-15
allows a hot restart which bypasses the purge,
ignitors and warm burners and allows the introduction of solid fuel provided certain conditions are
met. Figure 9-12 shows sequential logic for burner
control.
b. Feedwater flow and drum level control.
(1) Two element control. Two element feedwater control systems as shown in figure 9-13(a)
are characterized by the use of steam flow as a
feed-forward signal to reduce the effect of shrink
9-14
and swell of the boiler drum level during load
changes. Without the steam flow feed-forward signal, load changes will momentarily cause the drum
level to change in a direction opposite to the load
change. The feed-forward signal provides the
correct initial response of the feedwater valve.
(2) Three element control. Three element
feedwater control as shown in figure 9-13(b) uses
feedwater flow in addition to steam flow to improve drum level control. In this system feedwater
TM 5-810-15
flow to the boiler is metered and the feedwater
valve is positioned by summing steam flow and
drum level error through a controller. This system
should be used when multiple boilers are connected
to a common feedwater supply system since
feedwater flow is a metered feedback signal and the
control system demands a feedwater flow.
(3) System selection. Table 9-3 summarizes
the types of feedwater control systems and the
parameters which should be used for selection of
the proper system.
c. Furnace pressure controls.
(1) Single element control. Furnace pressure
controls are primarily single element type. The final
control element is the ID fan inlet damper, ID fan
inlet vanes or adjustable speed drive for ID fan.
The control loop shown in figure 9-14 also uses a
feed-forward demand signal that is representative
Table 9-3. Feedwater Control System Selection Guide
Control System
Two-element
Three-element
Boiler Requirements
Steady-State
Swinging
Multiple
Load
Load
Boiler
X
X
X
X
9-15
TM 5-810-15
of boiler air flow demand. This feed-forward signal
may be fuel flow, boiler master, or other demand
index, but will not be a measured air flow signal.
(2) Furnace implosion protection. Boilers that
have a large capacity and large draft losses due to
air quality control equipment may require ID fans
with a head capacity large enough to exceed design
pressure limits of the furnace and ductwork. If this
possibility exists, the furnace pressure control
system must include furnace implosion protection.
The furnace implosion protection system will
comply with the guidelines established by NFPA
85G. These guidelines include redundant furnace
pressure transmitters and transmitter monitoring
system, fan limits or run-backs on large furnace
draft error, feed-forward action initiated by a main
fuel trip, operating speed requirements for final
control elements, and interlock systems.
d. Steam controls.
(1) Steam pressure control. Steam pressure is
controlled by boiler firing rate. As discussed in
combustion control, steam pressure is used to
establish the master demand signal that controls
fuel and combustion air flow.
(2) Steam flow control. Steam flow is a function of boiler load demand. Steam flow is also a
function of fuel Btu input and can be used to trim
combustion air flow as discussed in combustion
control. Steam flow is also used to calculate boiler
load for use in oxygen trim controls and as a feedforward signal in feedwater controls.
(3) Steam temperature control. Boilers that
produce saturated steam do not require steam
temperature controls. Boilers that produce superheated steam require a control loop to maintain
superheater outlet temperature. A single element
loop with feedback as shown in figure 9-15 is
normally adequate for control of steam temperature.
e. Blowdown controls.
(1) Continuous blowdown. Continuous blowdown is the continuous removal of concentrated
water from the boiler. The rate of blowdown is
controlled by manually adjusting the setting of the
continuous blowdown control valve. Continuous
blowdown can be used on boilers of any capacity
and permits heat recovery of the blowdown. The
use of continuous blowdown heat recovery is dependent upon life cycle cost evaluation.
(2) Automatic
blowdown.
Automatic
blowdown systems as shown in figure 9-16
continuously monitor the boiler water and adjust
the rate of blowdown to maintain the conductance
of the boiler water at the proper level. Control
action can be two-position or modulating. The use
9-16
of automatic blowdown will be dependent on
whether blowdown heat is to be recovered and a
LCCA.
f. Sootblower control. Sootblower control
should be an operator-initiated automated sequence
control. After the start command the system should
step through the sequence for all sootblowers
including opening the valve for the sootblowing
medium, timing the length of the blow and closing
the valve. The system should automatically move to
the next sootblower and continue the sequence
until all sootblowers have been completed.
9-4. Nonboiler controls.
a. Low pressure steam controls.
TM 5-810-15
(1) Turbine drives. The boiler feed pump turbine drive is controlled by feedwater header pressure. The steam control valve on the turbine drive
inlet is controlled by a pressure transmitter on the
feedwater header acting through a controller as
shown in figure 9-17. The setpoint pressure will be
lower than the normal operating feedwater pressure
to prevent turbine drive operation during normal
operating conditions.
(2) Sootblowers. Sootblower steam controls
are normally a pressure control system to maintain
the proper steam pressure at the sootblower inlet.
If remote indication of the sootblower steam header
pressure is desired a transmitter and controller will
be used as shown in figure 9-18(a). If remote
indication is not required a pressure controller
mounted on the control valve can be used as shown
in figure 9-18(b).
(3) Steam coil air heater. The steam coil air
heater controls are based on maintaining the flue
gas leaving the air heater above the acid dew point
temperature. This is accomplished by using an
average cold end temperature control system as
shown in figure 9-19. Air heater average inlet air
temperature and average gas outlet temperature are
calculated. These two signals are averaged to arrive
at the average cold end temperature, which is used
to control the steam coil control valve. Also, the
control system should include an interlock that
opens the steam coil control valve 100 percent
when the ambient air is below a set temperature,
usually 35 degrees F.
(4) Deaerator. The DA steam controls are a
pressure control system to maintain DA pressure.
A single element loop with feedback as shown in
figure 9-20 is adequate for controlling DA pressure.
(5) Feedwater heater. The feedwater heater
controls as shown in figure 9-21 are used to protect
the economizer against acid condensation. The
economizer outlet gas temperature and economizer
inlet feedwater temperature are averaged. The
average is used to control the feedwater
temperature by regulating the steam input to the
feedwater heater.
9-17
TM 5-810-15
(2) Three element control. A three element
DA level control system as shown in figure 9-22(b)
uses a metered condensate flow feedback signal in
a cascaded control loop. This system will maintain
DA level on units that operate under swinging load
conditions.
c. Pump recirculat ion control. Pump recirculation controls are necessary to maintain the minimum flow through a pump when required by the
manufacturer. A breakdown orifice plate sized to
pass the required minimum flow can be installed in
a line from the pump discharge to the pump suction
source. Since this system is a constant recirculation
type, it is a source of lost pump hp. The lost hp can
be eliminated by using automatic pump
recirculation controls. This system requires pump
flow to be metered and an automatic valve to open
when pump flow is at or below the minimum flow
requirement. Automatic recirculation control will
be used only when justified by LCCA evaluation.
b. Deaerator level controls.
(1) Two element control. A two element DA
level control system as shown in figure 9-22(a) uses
feedwater flow as a feedwater signal to make the
system responsive to load changes. A two element
system for DA level control can be used for most
multiple unit installations that operate under steady
load conditions.
9-18
9-5. Control panels.
a. Control room. A control room isolated from
the plant environment complete with heating and
air conditioning should be provided for all boiler
plants. The boiler panels and auxiliaries may be
located at the boiler front for packaged boilers up
to 70,000 pph and for stoker fired units. A recorder
panel should be located in the control room. The
TM 5-810-15
control room will be located at a central location in
the plant to allow operating personnel good access
to the boilers and the auxiliary equipment. The
control room will be large enough for the operator
interface for the boiler and auxiliaries and also
allow room for a desk to be used by operating
personnel.
b. Operator interface. The operator interface to
the boiler and auxiliaries may be via CRT*s and
printer housed in a control console or operator
stations, recorders, indicators, annunciators and
start/stop controls mounted on a control panel.
(1) Distributed control system. Operator interface via CRT and printers are normally used on
larger units and are part of the distributed control
system. This system should always utilize redundant microprocessors, ORT*s and printers. The
system will automatically switch to the back-up
system and annunciate failure of a component. The
system will be utilized to perform combustion
control, data acquisition and trending, boiler efficiency calculations, graphic displays, boiler control
motor start/stop and ash system controls. An auxiliary panel will also be required to mount critical
controls and monitoring equipment.
(a) I/O racks. The system will include remote
mounted input/output racks with redundant
microprocessors for control. The information at the
I/O rack will be multiplexed to allow communica-
tion with other I/O racks and the central control
console. Redundant communication links should be
provided to allow communication when one link is
lost. All field wiring entering or leaving the I/O
racks is to be connected to terminal blocks with
spare terminals provided. The equipment in the 110
racks will be designed for installation in a dusty
atmosphere with maximum ambient temperatures
of 50 degrees C.
(b) Operator interface. The control console
will include the appropriate number of CRT*s and
printers required by the size and complexity of the
system. A minimum of two CRT*s and two printers
should be installed. The CRT*s and keyboard or
other means of operation will be mounted in a
console which allows the operators to access and
operate the controls while sitting at a chair in front
of the CRT.
(c) Auxiliary panel. Auxiliary panel construction must conform to the requirements of the
National Electrical Code, the National Fire Protection Association, and NEMA standards. It will be
constructed of steel plate with adequate internal
reinforcement to maintain flat surfaces and to
provide rigid support for the instrumentation to be
installed. The panel interior will have adequate
bracing and brackets for mounting of equipment to
be installed within the panel. Electrical outlets will
be provided in the panel. No pressure piping of
9-19
TM 5-810-15
process fluids is to be run in control panels. All
field wiring entering or leaving control panels is to
be connected to terminal blocks with spare terminals provided. The items to be mounted in the
auxiliary panel will include hardwired main fuel trip
(MFT) pushbutton, fan trips, drum level indication,
soot blower controls and annunciation of critical
items. The annunciator should include items listed
below.
1. Main fuel trip (MFP)
2. Drum level high-low.
3. Furnace pressure high.
4. Boiler FW pressure low.
5. Control system power failure.
(2) Panel mounted control system. The
control and auxiliaries panel where used will
include operator stations, recorders, indicators,
equipment start-stop controls and annunciation.
The arrangement of the panel will not be addressed
here since panel arrangements are normally based
on the preferences of operating personnel and
management.
(a) Control panel construction. Control
panel construction must conform to the
requirements of the National Electrical Code, the
National Fire Protection Association, and NEMA
standards. Panels will be constructed of steel plate
with adequate internal reinforcement to maintain
flat surfaces and to provide rigid support for the
instrumentation to be installed. The panel interior
will have adequate bracing and brackets for
mounting of equipment to be installed within the
panel. A walk-in door for access to the panel
interior will be provided on both ends of the panel
where possible and on at least one end of the panel.
Electrical outlets will be provided in the panel. No
pressure piping of process fluids is to be run in
control panels. All field wiring entering or leaving
control panels is to be connected to terminal blocks
with spare terminals provided.
c. Instrumentation requirements. The boiler and
auxiliaries panel or control console will provide
operator interface required to properly control and
monitor the operation of the boilers and auxiliary
equipment in the steam plant. This will include
operator interface to stations, recorders or trending, indication, equipment start/stop controls, and
annunciation. Table 9-4 summarizes the instrumentation requirements for the operator interface.
(1) Operator stations. Operator stations are to
be provided as shown in table 9-4. Operator
stations on control consoles will be accessed
through the CRT or through individual operator
station on control panels. Hand automatic operator
stations will provide bumpless transfer from hand
to automatic and automatic to hand without manual
9-20
balancing for transfer; and have antireset windup
characteristics. Operator stations with set point will
indicate set point in engineering units. Operator
stations with ratio or bias are to indicate the
magnitude of the ratio or bias at all times. Operator
stations are to indicate the measured variable on a
continuously in engineering units and will indicate
station output continuously in percent. The
indications on a station should be consistent with
all other stations such that all final control elements
move closed to open from zero to 100 percent. For
hardwired operator stations, the position of final
control elements will not change when an operator
station is disconnected from or reconnected to its
plug-in cable. Changes in ratio or bias settings will
not cause a process upset.
(2) Records. Records will be kept for the parameters indicated in table 9-4. Records will be
stored on floppy disks when a control console is
used. The operator will have access through the
CRT to display trends for parameter for which
records are kept. When the operator interface
utilizes boiler and auxiliaries panels recorders will
be used. Recorders may be strip chart recorders or
circular chart recorders. The recorders will have
scale markings consistent with the measured variables and associated field transmitters. The use of
circular chart recorders will be restricted to steam
pressure, steam flow, air flow, and exit gas temperature. Circular chart recorders will not be used
when conservation of panel space is critical or
desirable. Allowances should be made to provide
spare pens for future use.
(3) Indicators. Indicators will be provided for
the parameters shown in table 9-4. When a control
console is utilized the parameter will be displayed
on the CRT. The display may be digital or graphic
and the displays should have scale markings
consistent with the measured variable and
associated field transmitter. When indicators are
located on a panel the indicators may be digital
indicators or analog indicators. Digital indicators
will have Light Emitting Diode (LED) uniplaner
numerals, zero instrument zero drift with time, and
0.1 percent Full Scale (FS) or less span drift per
year. Analog indicators will have vertical edgewise
scales, plus or minus 2 percent full scale accuracy,
and scale markings consistent with the measured
variable and the associated field transmitter.
Integrators are shown in table 9-4 and should
include the signal converters necessary to provide
scaled integrated readings. Integrators will have at
least six digit readout.
(4) Equipment start/stop controls. Equipment
start/stop controls will be provided for all major
TM 5-810-15
equipment as shown in table 9-4. Start/stop controls on a control console will be performed utilizing the ORT. Indication of motor operation should
be indicated on the CRT. Start/stop controls will be
indicating control switches or indicating push
button when boiler and auxiliary panels are used for
the operator interface.
(5) Annunciator. Annunciators will be provided on the boiler and auxiliaries panel for visual
and audible indication of alarm conditions. Annunciator windows will have alarm legends etched on
the windows and will be backlighted in alarm or
test state. Each window will have at least two
parallel connected bulbs and front access for ease
of bulb replacement. All annunciator circuits will be
solid state and compatible with microprocessor
based controls. The annunciator will have an
adjustable tone and volume horn. Split windows
will be avoided unless conservation of panel space
is critical. The annunciator system will have one of
the alarm sequences specified in Instrument Society
of America (ISA) S18.1. Test and acknowledge
pushbuttons will be provided on the panel. All
alarms, except for critical alarms, will be displaced
on the ORT and printed on the printer when CRT*s
are utilized as the operator interface.
d. Ash handling control for stoker, pulverized
coal and ACFB boilers.
(1) General requirements. Control of the fly
ash system will be from the control room via ORT
or control panel. A bottom ash panel will be
located near the boilers. The control of the bottom
ash system may also be controlled from the control
room. The operator interface will contain all devices required to properly control and monitor the
operation of the ash handling system. This will
include start/stop control, selector controls, indication, and annunciator.
(2) Start/stop controls. Controls will include
start/stop controls for the vacuum producing equipment, initiation of system operation, emergency
stop, selection of manual or automatic system
operation and manual operation of hopper valves
and vibrators. This control may be through a CRT
or panel mounted indicating control switches or
indicating pushbuttons, pushbuttons and selector
switches.
(3) Indicators. Indication of system vacuum,
primary and secondary bag filter pressures and
temperature and vacuum pumps inlet temperature,
valve position, bag filter operation, system
operation and hopper being emptied should be
displayed in the control room. The display may be
via CRT or panel mounted indicators and indicating
lights.
(4) Annunciation. Alarm conditions of the ash
handling system should be audible and visually
annunciated in the control room. Annunciation may
be via CRT and printer or a panel mounted
annunciator of the same type described in c(5)
above.
f. Air quality control system for stoker, pulverized coal and ACFB boilers.
(1) General requirements. Control of the air
quality control equipment will be from the control
room via CRT or control panel. The operator
interface will contain all devices required to control
and monitor the operation of the air quality control
system. This will include start/stop controls,
selector controls, indication and annunciation.
(2) Start-stop controls. Start/stop controls will
be provided for manual operation of baghouse
cleaning via the CRT or panel mounted control
switches.
(3) Selection controls. Selection controls will
be provided for selection of manual, pressure initiated, or time sequenced baghouse cleaning. Operation of compartment isolation dampers and baghouse bypass dampers will be provided. The
control will be via CRT or panel mounted selector
switches.
(4) Indication. Indication will be provided for
compartment pressures and temperatures, baghouse inlet pressures and temperatures, and baghouse outlet pressures and temperatures. The indication will be via CRT or panel mounted indicators.
(5) Annunciation. Alarm conditions of the air
quality control system should be audible and
visually annunciated in the control room. Annunciation may be via CRT and printer or a panel
mounted annunciator as described in c(5) above.
g. Continuous emissions monitoring systems
controls. The continuous emissions monitoring
system (CEMS) controls will be located in an air
conditioned and heated environment. The controls
will be microprocessor based and include all
printers, displays and equipment necessary to save
all data and generate reports required by the EPA.
Malfunction of equipment will be annunciated in
the control room.
9-6. Field Instrumentation.
a. General. Transmitters, control drives, control
valves and piping instrumentation will be provided
to sense the process variables and allow the control
system to position the valves and dampers to
control the process. All field devices shall be
designed to operate in a dust laden atmosphere
with temperature conditions varying from 20 to
160 degrees F.
9-21
TM 5-810-15
b. Field transmitters.
(1) General. Electronic transmitters should
produce a 4-20 mA dc signal that is linear with the
measured variable. Electronic transmitters will be
the two wire type except when unavailable for a
particular application. Encapsulated electronics are
unacceptable in any transmitter. Transmitters will
be selected such that the output signal represents a
calibrated scale range that is a standard scale range
between 110 and 125 percent of the maximum
value of the measured process variable.
Transmitters will be designed for the service
required and will be supplied with mounting
brackets. Purge meters and differential regulators
will be used on transmitters for boiler gas service or
coal-air mixture service. A change in the load on a
transmitter within the transmitter load limits will
not disturb the transmitted signal. The load limits of
the transmitter will be a minimum of 600 ohms.
Transmitters can be supplied with local indicators,
either integral or field mounted, if desired.
Transmitters used for distributed control systems
should be the “smart” type which have duplex
digital communications ability transparent to the
analog signal. Smart transmitters may be remotely
calibrated via a hand held terminal. Data available
at the hand held terminal should include
programmed instrument number, instrument ID or
serial number, instrument location, date of last
calibration, calibrated range and diagnostics.
(2) Flow transmitters. Numerous types of flow
transmitters are available. These include differential
pressure with square root extractor, turbine
flowmeters, nutating disk type transmitter, ultrasonic flow transmitters, and magnetic flowmeters.
The most common method for measuring flow is to
measure differential pressure across an orifice, flow
nozzle, venturi, pitot tube, or piezometer ring.
Square root extraction is necessary to linearize the
output signal. Differential pressure measurement
should be used for most steam plant flow applications. Nutating disk with pulse to 4-20 mA transmitters are normally used for fuel oil flow measurement. Flow transmitters will be accurate within
0.5 percent of span from 20 to 100 percent span
with ambient temperature effect not to exceed 1.0
percent per 100 degrees F variation.
(3) Level transmitters. Measuring elements for
level transmitters will be diaphragm, bellows,
bourdon tube, strain gage transducer, caged float,
or sealed pressure capsule. Level transmitters will
be accurate within 0.5 percent of span with ambient
temperature effect not to exceed 1.0 percent of
span per 100 degrees F variation. The output signal
will be linear with the sensed level.
9-22
(4) Pressure transmitters. Measuring elements
for pressure transmitters will be diaphragm, bellows, bourdon tube, or strain gage transducers.
Pressure transmitters will be accurate within 0.5
percent of span with ambient temperature effect not
to exceed 1.0 percent of span per 100 degrees F
variation. Measuring elements for pressure differential transmitters will be diaphragm, bellows, or
sealed pressure capsule. Pressure differential
transmitters will be accurate within 0.25 percent of
span with ambient temperature effect not to exceed
1.0 percent of span per 100 degrees F variation.
Output signals for pressure and pressure differential
transmitters will be linear with the sensed pressure
or differential pressure.
(5) Temperature sensors. Several types of sensors can be used for temperature measurement.
Thermocouples sense temperature by a thermoelectric circuit which is created when two dissimilar
metals are joined at one end. A wide variety of
thermocouples are available for temperature sensing. Type J (iron-constantan) and type K (chromelalumel) are the most common types of thermocouples for boiler plant applications. Type J
thermocouples can be used for temperatures from
32 to 1382 degrees F. Type K thermocouples can
be used for temperatures from -328 to 2282
degrees F. The type of thermocouple to be used,
Type J or Type K, will be selected based upon the
temperatures to be sensed. All thermocouples in the
boiler plant will be of the same type. Resistance
Temperature Detectors (RTD) sense temperature
based upon the relationship between the resistivity
of a metal and its temperature. The most common
RTD used in boiler plant applications is a platinum
RTD with a resistance of 100 ohms at 0 degrees C.
Sealed bulb and capillary sensors detect
temperature by sensing the change in volume due
to changes in temperature of a fluid in a sealed
system.
(6) Temperature transmitters. Measuring elements for temperature transmitters should be
thermocouple, RTD, or sealed bulb and capillary.
Temperature transmitters will be accurate within
0.5 percent of span with ambient temperature effect
not to exceed 1.0 percent of span per 100 degrees
F degree variation. Output signals for temperature
transmitters will be linear with the sensed
temperature.
(7) Oxygen analyzers. Oxygen analyzers will
be direct probe type utilizing an in situ zirconium
sensing element. The element will be inserted
directly into the gas stream and will directly contact
the process gases. The sensing element will be
provided with a protective shield to prevent direct
TM 5-810-15
impingement of fly ash on the sensing element. The
analyzer should be equipped to allow daily
automatic calibration checks without removing the
analyzer from the process. The cell temperature in
the analyzer will be maintained at the proper
temperature by a temperature controller. The
analyzer will be certified for “in stack” analysis
technique in accordance with the Factory Mutual
(FM) approval guide. The analyzer will be
furnished with all accessories necessary for a
complete installation.
(8) Opacity monitors. Opacity monitors use
the principal of transmissometry to indicate level of
particulate emissions. A beam of light is projected
across the flue gas stream and a detector registers
variations in the light transmittance caused by the
particulate in the flue gas.
(9) Flue gas monitors. Flue gas monitors will
be provided for all items required for EPA reports.
Flue gas monitors are either in situ or extractive. In
situ monitors are attached directly to the stack or
breeching and access for maintenance should be
provided. Extractive systems are wet, dry or diluted. Wet extractive system sample line should be
heated to avoid corrosion. Dry systems utilize a
cooler to remove water. Dilution systems utilize
clean dry air to dilute the sample eliminating the
need to heat the sample lines or dry the sample.
Either in situ or extractive flue gas monitors should
be used and not a mixture of the two for the
various gases to be analyzed. All analyzers should
be provided with self calibration features and have
contact outputs for control room annunciation.
c. Control drives. Control drives will be used for
positioning of control dampers, isolating dampers,
and other devices requiring mechanical linkages.
Control drives may be pneumatic or electric and are
either open-shut type or modulating type depending
on the application. Modulating drives may include
position transmitters. Control drives will have
adjustable position limit switches wired to terminal
blocks, handwheels or levers for manual operation,
hand locks or be self locking, position indicators,
and adjustable limit stops at maximum and
minimum positions. Drive arms and connecting
linkages will be supplied with the damper drives.
Control drives will have stroking times as required
by the service and by NFPA recommendations.
(1) Pneumatic control drives. Pneumatic control drives should consist of a double acting air
cylinder with rigid support stand and weatherproof
enclosure. Pneumatic control drives for outdoor
service will have thermostat controlled space heaters installed and wired to terminal blocks. Pneumatic control drives for modulating service will
have positioners with characterizable cams. Open/
shut control drives should have internally mounted
four-way solenoid valves. Control drives will be
designed to provide the rated torque with a
maximum 50 psig air supply. The control drive will
be sized to provide 150 percent of the torque
required to drive controlled device.
(2) Electric control drives. Electric control
drives will consist of an electric motor, gear box,
rigid support stand, and wiring termination enclosure. Electric control drives will be weatherproof.
The gear box will be dust tight, weather tight, and
totally enclosed. Electric control drives will be selflocking on loss of control or drive power. Drives
for outdoor installation will be designed to operate
with ambient conditions of -20 degrees F and a 40
miles per hour wind. Drives will have adjustable
torque limit switches and position limit switches.
Electric drives will be supplied with motor starters,
position
controllers,
speed
controllers,
characterizable positioners, transformers, and other
accessories as required. The control drive will be
sized to provide 150 percent of the torque required
to drive the controlled device.
d. Control valves.
(1) Valve bodies. Control valve bodies will be
constructed in accordance with the applicable
ANSI codes. Control valves will be globe type
unless otherwise required for the particular process.
Butterfly valves may be used in low pressure water
systems. Globe valves will have a single port
designed to meet the design conditions. Restricted
ports should be used when necessary for stable
regulation at all loads. Special consideration will be
given to valves which pass flashing condensate to
assure adequate port and body flow area. The valve
body size may be smaller than the line size if the
plug guide is sufficiently rugged to withstand the
increased inlet velocity, but valve body size will not
be smaller than one half the line size. End
preparations will be suitable for the applicable
piping system. Valves will have teflon packing for
temperatures not exceeding 450 degrees F. Bonnet
joints will be flanged and bolted type and designed
for easy disassembly and assurance of correct valve
stem alignment. Valve trim will be cage guided and
removable through the top after bonnet removal.
Seat rings will be easily replaceable. Flow direction
should be flow opening unless otherwise required.
(2) Valve operators. Control valve operators
will be pneumatic diaphragm actuated type except
where piston actuators are required. Valve operators will be adequate to handle unbalanced forces
that occur from flow conditions or maximum differential. Allowances for stem force based on seating
9-23
TM 5-810-15
surface will be made to assure tight seating.
Diaphragms will be molded rubber and diaphragm
housing will be pressed steel. Piston operators will
use cast pistons and cylinders with 0-ring seals.
Each valve operator will have an air supply
pressure filter regulator. Valve operators for modulating service valves in fast response control
loops, such as flow control or pressure control, will
have electropneumatic valve positioners. Limit
switches will be provided if needed for remote
indication or control logic.
(3) Control valve sizing. Proper control valve
sizing requires careful analysis of the process and
piping system in which each valve is to be used. It
is necessary to calculate the required valve flow
coefficients based upon flow, valve inlet pressure,
valve outlet pressure, and process fluid conditions.
Calculations will be based on ISA S75.01. Valve
flow coefficients will be calculated at the maximum,
intermediate, and minimum process flow
conditions. The control valves will be selected such
that the maximum flow coefficient occurs at a valve
travel between 70 and 80 percent. The minimum
flow coefficient will occur at a valve travel between
10 and 20 percent. Control valves will be selected
with a flow characteristic which provides uniform
control loop stability over the range of process
operating conditions. A quick opening flow
characteristic provides large changes in flow at
small valve travels and should primarily be used for
on-off service applications. With a linear flow
characteristic, the flow rate is directly proportional
to valve travel. Valves with linear flow
characteristics will be used for liquid level control
where the ratio of the maximum valve pressure
differential to the minimum valve pressure
differential is less than five to one. Linear flow
characteristic valves will also be used for pressure
control of compressible fluids and for flow control
when the flow rate varies but the valve pressure
differential is constant. With an equal percentage
flow characteristic, equal increments of valve travel
produce equal percentage changes in the existing
flow rate. Equal percentage flow characteristic
valves will be used for liquid level control when the
ratio of the maximum valve pressure differential to
the minimum valve pressure differential is greater
than or equal to five to one. Equal percentage flow
characteristic valves will also be used for pressure
control of liquids and for flow control when the
valve pressure differential varies but the flow rate
is constant. Special inner valve trim characteristics
are required on applications where flashing or
cavitation exist in liquid service and for noise
control in steam or gas service.
9-24
(4) Control valve stations. Control valve stations are used to install control valves in piping
systems and to provide a means of isolating and
bypassing the control valve for maintenance purposes. Control valve stations will conform to the
recommendations of ISA RP 75.06. Control valve
stations consist of a control valve, isolating valves,
bypass valve, and bypass line. Since control valves
are normally smaller than the line size, reducers are
required and can be integral to the control valve on
valves with butt weld end connections. Isolation
valves are required to isolate the control valve for
repair, removal, or calibration and will be installed
on the inlet and outlet sides of the control valve.
Isolation valves will be gate valves or other nonthrottling type valves. A bypass valve is necessary
to provide a means of controlling the process when
the control valve is not operable. The bypass valve
will be identical to the control valve except it will
be manually operated. Using an identical valve on
the bypass provides better control during manual
operation since the valve will have the proper flow
coefficient and special valve trim. The bypass line
which contains the bypass valve must be smaller
than the main line size. The bypass line may be the
same size as the bypass valve but in no case will the
bypass line be smaller than one half the main line
size.
e. Piping instrumentation.
(1) Pressure switches. Pressure switches are
used to monitor pressures for remote indications,
interlocking functions, and alarm conditions. Pressure switches may have snap acting switch contacts
or mercury switch contacts. Shutoff valves of the
same pressure and temperature rating as the
process piping will be provided on each switch for
isolation purposes. Snubbers will be provided on
switches when the pressure connection is located
within 15 pipe diameters of a pump or compressor
discharge.
(2) Pressure gauges. Pressure gauges are used
to provide local and remote indication of process
pressures. Scale ranges will be selected such that
the normal operating pressure is at approximately
mid-scale. Shutoff valves of suitable rating will be
provided on each gauge for isolation purposes.
Snubbers will be provided on gauges when the
pressure connection is located within 15 pipe
diameters of a pump or compressor discharge.
Siphons will be provided on pressure gauges for
steam service. Pressure gauges will be provided on
the discharge of all pumps and compressors, all
boiler drums, all main process headers, and other
locations as required to monitor equipment and
process operation.
TM 5-810-15
(3) Thermometers. Thermometers are used to
provide local indication of process temperatures.
Thermometers are normally the bimetallic type for
most applications. Scale ranges will be selected
such that the normal operating temperature is at
approximately mid-scale. Thermometers will be
provided with thermowells so the thermometer
sensing element is not inserted directly into the
process. Thermowells will be designed to withstand
the pressure, temperature, and fluid velocities of
the process in which they are inserted. Thermowells
installed in piping will be long enough to extend to
approximately the pipe centerline. Thermowells will
have extensions to clear insulation and lagging.
(4) Thermocouples. Thermocouples are used
to provide remote indication and control of process
temperatures. Type J or Type K thermocouples are
normally suitable for steam plant applications as
discussed in paragraph 9-6b(5). Thermocouples
will be provided with thermowells or protection
tubes of suitable rating. Thermowell or protection
tube length will be sufficient to provide the necessary insertion length plus the desired nipple length.
Thermocouple assemblies will also include
insulators and terminal head with cover.
(5) Temperature switches. Temperature
switches are used to monitor temperatures for
remote indications, interlocking functions, and
alarm conditions. Temperature switches may have
snap acting switch contacts or mercury switch
contacts and may be bulb and capillary type or
direct insertion type. Thermowells of suitable rating
will be supplied so the sensing element is not
inserted directly into the process.
(6) Pressure controllers. Pressure controllers
will be pneumatic with bourdon tube or bellows
sensing element. The sensing element will be
suitable for the pressure and temperature of the
process fluid to be controlled and will be an integral
part of the controller assembly. The sensing
element will have adequate sensitivity and be able
to withstand the maximum pressure under all
conditions. Pressure controllers will have adjustable
proportional and reset control action, control point
adjustment, calibrated pressure setting dial, air
supply filter regulator, and gauges which indicate
air supply and controller output pressures. Pressure
controllers will be mounted on the operator of the
valve to be regulated.
Table 9-4. Operator Interface Instrumentation Requirements.
Gas/Oil Fired Boilers
Operator Stations:
1. Boiler Master
2. Air Flow
3. Fuel flow
4. Drum Level
5. Oxygen Trim
6. Furnace Pressure
7. Steam Temperature
(SH only)
8. Deaerator
Pressure
9. Deaerator Level
10. Feedwater Heater
Recorder Requirements:
1. Steam Pressure
2. Steam Flow
3. Fuel Flow
4. Drum Level
5. Percent Oxygen
6. Steam Temperature
(SH only)
7. Deaerator
Pressure
8. Deaerator Level
9. Feedwater Temp
10. Exit Gas Temp
11. Feedwater Flow
12. Air Flow
Pulverized Coal Fired
Boiler
Stoker Fired Boilers
R
X
X
R
X
R
X
X
X
R
X
X.
R
R
R
X
K
X
R
R
X
1.
2.
3.
4.
5.
6.
7.
Boiler Master
Air Flow
Fuel Flow
Drum Level
Oxygen Trim
Furnace Pressure
Steam Temperature
(SH only)
8. Deaerator
Pressure
9. Deaerator Level
10. Feedwater Heater
11. Steam Coil
Preheater
1.
2.
3.
Steam Pressure
Steam Flow
Steam Temperature
(SH only)
4. Feedwater Flow
5. Feedwater
Temperature
6. Deserator
Pressure
7. Deaerator Level
8. Drum Level
9. Air Flow
10. Percent Oxygen
11. Fuel Flow
R
R
R
R
X
R
R
X
R
X
R
R
R
R
R
X
K
X
R
R
R
K
1.
2.
3.
4.
5.
6.
7.
8.
9.
Boiler Master
Air Flow
Pulverizer Master
Pulverizers
Primary Air
Drum Level
Oxygen Trim
Furnace Pressure
Steam Temperature
(SH only)
Deaerator Pressure
Deaerator Level
Feedwater Heater
Steam Coil
Preheater
R
R
X
R
R
R
R
R
Steam Pressure
Steam Flow
Steam Temperature
(SH only)
4. Feedwater Flow
5. Feedwater
Temperature
6. Deaerator
Pressure
7. Deaerator Level
8. Drum Level
9. Total Air Flow
10. Percent Oxygen
11. Total Fuel Flow
R
R
10.
11.
12.
13.
1.
2.
3.
R
X
R
X
R
R
R
X
X
K
R
R
R
K
9-25
TM 5-810-15
Table 9-4. Operator lnterface lnstrumentation Requirements. (Continued)
Gas/Oil Fired Boilers
Indicators:
1. Steam Pressure
2. Drum Level
3. Furnace Pressure
4. Combustion Air
Pressure
5. Exit Air
Pressures
6. Feedwater
Pressures
7. Feedwater
Temperature
8. FD Fan Amps
9. Boiler Feed Pump
Amps
10. Sootblower
Pressure
11. Gas Pressure
12. Oil Pressure
Stoker Fired Boilers
12. Combustion Air
Temperatures
13. Exit Gas
Temperatures
R
R
R
R
R
R
R
R
R
X
X
X
X
R
Pulverized Coal Fired
Boiler
12 Combustion Air
Temperatures
13. Exit Gas
R
R
R
R
1.
2.
3.
4.
R
R
R
R
R
5.
R
6.
R
7.
R
R
R
8.
X
1.
2.
3.
4.
Steam Pressure
Drum Level
Furnace Pressure
Combustion Air
Pressures
5. ExitGas
Pressure
6. Feedwater
Pressures
7. Feedwater
Temperature
8. ID Fan Amps
9. FD Fan Amps
10. Boiler Feed Pump
Amps
11. Sootblower
Pressure
K
9.
10.
11.
12.
13.
Integrators:
1. Steam Flow
2. Fuel Flow
3. Feedwater Flow
Equipment start-stop controls:
1. FDFans
2. Boiler Feed Pumps
Steam Pressure
Drum Level
Furnace Pressure
Combustion Air
Pressures
ExitGas
Pressures
Feedwater
Pressures
Feedwater
Temperature
Pulverizer Outlet
Temperature
ID Fan Amps
FD Fan Amps
PA Fan Amps
Boiler Feed Pump
Amps
Sootblower
Pressure
R
R
R
R
R
R
R
R
R
R
X
X
X
X
1. Steam Flow
2. Fuel Flow
3. Feedwater Flow
X
X
K
1. Steam Flow
2. Fuel Flow
3. Feedwater Flow
X
X
X
R
R
1.
2.
3.
R
R
R
1.
2.
3.
4.
5.
6.
R
R
R
R
R
R
ID Fans
FD Fans
Boiler Feed Pumps
IDFans
FD Fans
PA Fans
Boiler Feed Pumps
Pulverizers
Coal Feeders
ACFB Fired Boilers
Indicators:
1. Furnace pressure
2. J-valve outlet static
pressure
3. J-valve inlet static pressure
4. J-valve discharge pressure
5. Over furnace bed static
pressure
6. Furnace plenum pressure
7. Steam pressure
8. Spray water pressure
9. J-valve dipleg (diff press)
10. J-valve density (duff press)
11. Valve solids flow
(diff press)
12. Bed differential pressure
13. Total furnace differential
pressure
14. Primary air flow
15. Overfire air flow
9-26
R
R
R
R
R
23.
24.
25.
26.
27.
28.
R
R
K
R
R
R
R
R
R
R
29.
30.
31.
32.
33.
34.
35.
36.
37.
Fuel flow
Sorbent (limestone) flow
Steam temperature
Furnace exit gas temperature
Solids cooler stripper
section temperature
Solids cooler cooler
cooler section temperature
J-valve fluid temperature
Furnace bed individual TC
temperature
Furnace bed average
temperature
Furnace plenum temperature
Feedwater temperature
Oxygen
SO2
Drum level
Deasrator pressure
R
R
R
R
R
R
R
X
R
R
K
R
R
R
X
TM 5-810-15
Table 9-4. Operator lnterface lnstrumentation Requirements. (Continued)
ACFB Fired Boilers
16. J-valve plenum air flow
upleg
17. J-valve plenum air flow
downleg
18. Total air flow
19. Steam flow
20. Spray water flow
21. Feedwater flow
22. Gas flow
Operator Stations:
1. Boiler master
2. Primary air flow
3. Overfire air flow
4. Oxygen trim
5. Fuel master
6. Fuel flow
7. Airflow
8. Furnace pressure
9. FD fan discharge pressure
10. Stripper cooler air flow
11. Solids cooler spray water
12. J-valve blower discharge
pressure
13. J-valve aeration control
Recorder Requirements:
1. Furnace pressure
pressure
3. J-valve inlet static pressure
4. J-valve discharge pressure
5. Over furnace bed static
pressure
6. Furnace plenum pressure
7. Steam pressure
8. Spray water pressure
9. J-valve diplet (duff press)
10. J-valve density (duff press)
11. Valve solids flow
(diff press)
12. Bed differential pressure
13. Total furnace differential
pressure
14. Primary air flow
15. Overfire air flow
16. J-valve plenum air flow
upleg
17. J-valve plenum air flow
downieg
18. Total air flow
19. Steam flow
20. Spray water flow
21. Feedwater flow
22. Gas flow
23. Fuel flow
24. Sorbent (limestone) flow
25. Steam temperature
26. Furnace exit gas temperature
27. Solids cooler stripper
section temperature
28. Solids cooler cooler
section temperature
R
38.
39.
R
40.
Deaerator level
Cyclone level (uses diff
press transmitters)
Chute air flow
X
R
J-valve plenum air control
Sorbent (limestone) feed
Furnace bed inventory
control
Drum level
Steam temperature (SH only)
Warm-up burner control
Deaerator pressure
Deaerator level
Feedwater heater
Steam coil preheater
R
R
R
R
R
R
R
X
R
X
R
J-valve fluid temperature
Furnace bed individual TC
temperature
Furnace bed average
temperature
Furnace plenum temperature
Finish SH inlet temperature
Feedwater temperature
Oxygen
SO[sub]2
Drum level
Deaerator pressure
Deaerator level
Cyclone level (uses duff
press transmitters)
FD fan discharge pressure
Solids cooler stripper
airflow
Solids cooler solids air
flow
Drum pressure
Warmup burner discharge
temperature
Air heater inlet air
temperature
Air heater gas temperature
Air heater cold end
temperature
ID fan amps
FD fan amps
Boiler feed pump amps
Sootblower pressure
R
X
R
R
R
X
R
R
R
R
R
R
X
R
R
R
R
R
R
R
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
R
R
R
R'
R
R
R
X
R
R
R
R
R
R
R
R
R
R
R
X
R
R
R
R
R
R
R
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
R
R
X
X
R
R
R
X
X
R
R
R
R
R
R
R
R
R
R
R
R
R
X
R
9-27
TM 5-810-15
Table 9-4. Operator lnterface Instrumentation Requirement. (Continued)
ACFB Fired Boilers
Integrator
1. Steam flow
2. Fuel flow
3. Feedwater flow
4. Sorbent flow
R - Required
X - Optional
9-28
R
R
R
R
Equipment Start-Stop Controls
1.
ID fans
2.
FD fans
3.
PA fans
4.
Boiler feed pumps
5.
Coal feeders
6.
Sorbent (limestone) feeders
7.
-valve blowers
R
R
R
R
R
R
R
TM 5-810-15
CHAPTER 10
ELECTRIC SYSTEMS
This chapter addresses the criteria for the electric power system in a steam plant.
a. Design requirements. The electrical requirements for the steam plant are the same as those for the steam
generating equipment of an electric power generating station as covered by TM 5-811-6.
b. The following sections of chapter 4 of TM 5-811-6 are applicable to the design of the steam boiler plant
electrical requirements:
(1) Station service power system (section VL). Station service power systems for a 200,000 pph boiler
addition is about the equivalent to a 20,000 kw power plant steam turbo-generator addition. Steam
generators of 200,000 pph and above will require a 4.16 kv auxiliary bus to supply the larger motors—
particularly boiler draft fans. Boilers below 200,000 pph can be accommodated with a 480 volt power supply.
(2) Emergency power system (section VII). Emergency power system applies to the steam boiler plant
with the exception that the battery requirements will be less because the system will not be required to supply
emergency power to any lube oil pumps.
(3) Motors (section VIII). This section covers the motor requirements to be used in the steam boiler
plant design.
(4) Communication systems (section IX). This section covers the communication system requirements
to be used in the steam boiler plant design.
10-1
TM 5-810-15
APPENDIX A
REFERENCES
Government Publications.
29 CFR 1910
Department of the Army.
AR 420-49
TM 5-805-1
TM 5-805-4
TM 5-805-9
TM 5-809-1
TM 5-809-10
TM 5-810-1
TM 5-811-6
TM 5-815-1
TM 5-848-3
Part 1910: Occupational Safety and Health Standards
Heating, Energy Selection and Fuel Storage, Distribution,
and Dispensing Systems
Standard Practice for Concrete Military Structures
Noise Control for Mechanical Equipment
Power Plant Acoustics
Load Assumptions for Buildings
Seismic Design for Buildings
Mechanical Design/Heating, Ventilating and Air
Conditioning
Electric Power Plant Design
Air Pollution Control Systems Boilers and Incinerators
Ground Storage of Coal
Non-Government Publications.
American Association of State Highway and Transportation Officials, (AASHTO)
444 North Capital Street, N.W., Suite 249
Washington, DC 20001
American Boiler Manufacturers Association (ABMA)
950 N. Glebe Road, Suite 160
Arlington, VA 22203
American Concrete Institute (ACI)
P. 0. Box 19150, Redford Station
Detroit, MI 48219-0150
ACI 301
(1989) Structural Concrete for Buildings
ACI 318
(1989; Rev 1992; Errata) Building Code Requirements for
Reinforced Concrete
American Gear Manufacturers Association (AGMA)
1500 King Street, Suite 201
Alexandria, VA 22314
American National Standards Institute, Inc. (ANSI)
11 West 42nd Street
New York, NY 10036
ANSI B20.1
(1990) Safety Standards for Conveyors and Related
Equipment
American Railway Engineering Association (AREA)
50 F Street, N.W., Suite 7702
Washington, DC 20001
American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
Publication Dept.
1791 Tullie Circle, N.E.
Atlanta, GA 30329
ASHRAE (1991) Handbook, HVAC Applications
ASHRAE (1992) Handbook, HVAC Systems and Equipment
ASHRAE (1993) Handbook, Fundamentals
ASHRAE (1990) Handbook, Refrigeration Systems and Applications
A-1
TM 5-810-15
American Society of Mechanical Engineers (ASME)
22 Law Drive
Box 2300
Fairfield, NJ 07007.2300
Boiler and Pressure Vessel Code, and Interpretations:
ASME
Section I: Power Boilers (1992; Addenda Dec 1992)
ASME 08
Section VIII: Pressure Vessels, Division 1 (1992;
Addenda Dec 1992)
ASME B31.1
(1992; b31.la) Power Piping
ASME B31.8
(1992) Gas Transmission and Distribution Piping Systems
American Society for Testing and Materials (ASTM)
1916 Race Street
Philadelphia, PA 19103
ASTM A 36
(1991) Structural Steel M-Grades
ASTM A 48
(1990) Gray Iron Castings
ASTM A 536
(1984) Ductile Iron Castings
ASTM A 588
(1991a) High-Strength Low-Alloy Structural Steel with
50 ksi (345 MPa) Minimum Yield Point to 4 in. (100
mm) Thick
ASTM D 395
(1988) Ferritic Ductile Iron Pressure-Retaining Castings
for Use at Elevated Temperature
ASTM D 1192
(1970; R 1977) Equipment for Sampling Water and Steam
ASTM D 1857
(1989) Test Method for Fusibility of Coal and Coke Ash
ASTM D 2234
(1989) Test Methods for Collection of a Gross Sample of
Coal
ASTM D 3174
(1989) Test Method for Ash in the Analysis Sample of
Coal and Coke from Coal
ASTM D 3176
(1989) Practice for Ultimate Analysis of Coal and Coke
Anti-Friction Bearing Manufacturers Association (AEBMA)
1101 Connecticut Ave., NW, Suite 700
Washington, DC 20036
Boiler Law and Rules and Regulations
The Bureau of Safety and Regulation
7150 Harris Drive
P 0 Box 30015
Lansing, MI 48909
Conveyor Equipment Manufacturers Association (CEMA)
932 Hungerford Dr., No. 36
Rockville, MD 20850
Factory Mutual Engineering and Research (FM)
1151 Boston-Providence Turnpike
P0 Box 9102
Norwood, MA 02062-9957
Heat Exchange Institute (HEI)
1300 Sumner Ave.
Cleveland, OH 44115-2851
Hydraulic Institute (HI)
9 Sylvan Way, Suite 180
Parsippany, NJ 07054-3802
Instrument Society of America (ISA)
P.O. Box 3561
Durham, NC 27702
ISA S18.1
(1979; R1992) Annunciator Sequences and Specification
ISA S75.01
(1985) Control Valve Sizing Equations
ISA RP 75.06
(1981) Control Valve Manifold Designs
A-2
TM 5-810-15
Manufacturers Standardization Society of the Valve and Fittings Industry (MSS)
127 Park Street, NE
Vienna, VA 22180
MSS SP-69
(1991) Pipe Hangers and Supports-Selection and Application
National Association of Corrosion Engineers (NACE)
P 0 Box 218340
Houston, TX 77218-8340
National Electric Code
P0 Box 9146
Quincy, MA 02269
National Electrical Manufacturers Association (NEMA)
2101 L St., NW
Washington, DC 20037
National Fire Protection Association (NFPA)
P.O. Box 9146
Quincy, MA 02269
NFPA 85G
(1987) Prevention of Furnace Implosions in Multiple
Burner Boiler-Furnaces
Rubber Manufacturers Association
1400 K Street NW
Washington, DC 20005
A-3
TM 5-810-15
GLOSSARY
AAP
Army Ammunition Plant
AASHTO
CaCO3
C03 Calcium Carbonate
American Association of State Highway and
Transportation Officials
CaO
ACFB
CaSiO3
Calcium Oxide
Atmospheric Circulating Fluidized Bed
Calcium Silicate
ACI
CEMA
American Concrete Institute
Conveyor Equipment Manufacturers Association
AEI
CEMS
Architectural and Engineering Instructions
Continuous Emissions Monitoring Systems
AEL
CFHE
Allowable Emissions Limit
Closed Feedwater Heat Exchangers
AFBMA
cfm
Anti Friction Bearing Manufacturers Association
Cubic feet per minute
AGMA
CO2
American Gear Manufacturers Association
Carbon Dioxide
Al203
CPU
Aluminum Oxide
Central Processing Unit
ANSI
CR
American National Standards Institute
Concentration Ratio
APHA
CRT
American Public Health Association
Cathode Ray Tube
AREA
Cu
American Railway Association Standards
Copper
ASHREA
CuNi
American Society of Heating, Refrigeration and Air
Conditioning Engineers
DA
Copper Nickel
ASME
Deaerator
American Society of Mechanical Engineers
DAS
ASYM
American Society for Testing and Materials
BHN
Brinell Hardness Number
BOD
Biochemical Oxygen Demand
BOOS
Data Acquisition System
EHE
External Heat Exchanger
EPA
Environmental Protection Agency
F
Fahrenheit
Burner Out of Service
FAC
Btu
Fe
British thermal units
C
Centigrade
Free Available Chlorine
Iron
FeO3
Ferric Oxide
Ca
FD
Calcium
Forced Draft
CAAA
FGD
Clean Air Act Amendments of 1990
Flue Gas Desulfurization
Glossary-1
TM 5-810-15
FGR
lb/ft3
Flue Gas Recirculation
Pounds per cubic foot
FM
LCCA
Factory Mutual
Life Cycle Cost Analysis
fpm
LEA
Feet per minute
Low Excess Air
fps
LED
Feet per second
Light Emitting Diode
FS
LNB
Full Scale
Low NOx burner
FT
LOI
Fluid Temperature
Loss on ignition
FW
LPG
Feedwater
Liquified Petroleum Gas
gph
mA
Gallons per hour
Milliamp
HEI
MB
Heat Exchange Institute
Million Btu
HEMA
MFT
Heat Exchanger Manufacturers Association
Main Fuel Trip
HI
Mg
Hydraulics Institute
Magnesium
Hg
MgO
Mercury
Magnesium Oxide
hp
O
Na2Si 3
Horsepower
Sodium Silicate
HRA
NaZ
Heat Recovery Area
Sodium Zeolite
HY
NEMA
Hemispherical Temperature
National Electrical Manufacturers Association
HVAC
NFPA
Heat, Ventilating and Air Conditioning
National Fire Protection Association
ID
NO
Induced Draft
Nitric Oxide
IES
NO2
Illuminating Engineers Society
Nitrogen Dioxide
IR
N2O
Infrared
Nitrous Oxide
ISA
NOx
Instrument Society of America
Oxides of Nitrogen
IT
NPDES
Initial Deformation Temperature
National Pollutant Discharge Elimination System
K2O
NPSH
Potassium Oxide
Net Positive Suction Head
kv
NPSHA
Thousand volt
Net Positive Suction Head Available
lb
NPSHR
Pound
Net Positive Suction Head Required
Glossary-2
TM 5-810-15
02
RO
Oxygen
Reverse Osmosis
OFA
ROM
Overfire Air
Run-of-mine
OSHA
rpm
Occupational Safety and Health Act
PA
Primary Air
PC
Revolutions per minute
RTD
Resistance Temperature Detector
Personal Computer
scfm
PC
SCR
Programmable Controller
Standard cubic feet per minute
PC
Selective Catalytic Reduction Silicon Controlled
Rectifier
Pulverized Coal
SH
PCB
Superheat
Polychlorinated Biphenyl
SiO2
pcf
Silica Dioxide
Pounds per cubic foot
SNCR
piw
Selective Noncatalytic Reduction
Pounds per inch width
SO2
pph
Sulfur Dioxide
Pounds per hour
SSU
ppi
Saybolt Seconds Universal
Pounds per ply inch
ST
ppm
Softening Temperature
Parts per million
TDS
psf
Pounds per square foot
psi
Pounds per square inch
psig
Pounds per inch gauge
RA
Relative Accuracy
RATA
Total Dissolved Solids
TiO2
Titanium Dioxide
tph
Tons per hour
TSS
Total Suspended Solids
UHMW
Ultra High Molecular Weight
Relative Accuracy Test Audit
UPS
RDF
uv
Refuse Derived Fuel
RMA
Rubber Manufacturers Association
Uninterruptable Power Supply
Ultraviolet
wg
Water gauge
Glossary-3
TM 5-810-15
The proponent agency of this publication is the Office of the
Chief of Engineers, United States Army. Users are invited to
send comments and suggested improvements on DA Form
2028 (Recommended Changes to Publications and Blank
Forms) to HQUSACE (CEMP-ET), WASH DC 20314-1000.
By Order of the Secretary of the Army:
Official:
DENNIS J. REIMER
General, United States Army
Chief of Staff
JOEL B. HUDSON
Acting Administrative Assistant
to the Secretary of the Army
Distribution:
To be distributed in accordance with DA Form 12-34-E, Block 1685,
requirements for TM 5-810-15.
U.S. G.P.O.:1995-386-731:290
PIN: 061328-000
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