The level control of the boiler drum Chenhui He Bachelor’s degree (UAS)

The level control of the boiler drum  Chenhui He Bachelor’s degree (UAS)
The level control of the boiler drum
Chenhui He
Bachelor’s Thesis
30.10.2014
Bachelor’s degree (UAS)
Engineering and Technology, Varkaus
SAVONIA UNIVERSITY OF APPLIED SCIENCES
THESIS
Abstract
Field of Study
Technology, Communication and Transport
Degree Programme
Degree Programme in Industrial Management
Author(s)
Chenhui He
Title of Thesis
The level control of the boiler drum
Date
1.10.2014
Pages/Appendices
33
Supervisor(s)
Principal Lecturer Harri Heikura
Client Organisation/Partners
Abstract
Level control uses the boiler drum as a controlled object, and uses the level as a controller value.
By making sure the level control is attached accurately we get better dynamic performance. I use
the cascade control to make the difference to the traditional control.
In this thesis, I summarize many problems with the level control in the steam boiler field as the
false level phenomenon. I design three methods for the level control process system with different
ways. I make the final choice at the end. I also do the SAMA figure to show the systems way of
running.
The automation is one of the main points with the level controlling system in the thesis.
At the end of this thesis, I was able to achieve the automatic controlling for the steam level.
Keywords
Level control, Automation, SAMA figure, Steam boiler
CONTENTS
1 INTRODUCTION ............................................................................................. 5
1.1 Thesis goal .............................................................................................. 5
1.2 Thesis background .................................................................................... 5
1.2.1 The feature of the process control .................................................... 5
1.2.2 Development status of the level control system ................................. 6
2 DYNAMICS OF THE BOILER DRUM LEVEL PROCESS ........................................... 7
2.1 The total introduction................................................................................ 7
2.2 The formation of the false level phenomenon.............................................. 7
2.3 The factors of influence steam level ........................................................... 8
2.3.1 Feed water disturbance influence ..................................................... 8
2.3.2 The influence of consumption of turbine ........................................... 9
2.3.3 The influence of the fuel disturbance .............................................. 10
3 DRUM LEVEL CONTROL SYSTEM DESIGN ....................................................... 12
4 ENGINEERING OF LEVEL CONTROL SYSTEM ................................................... 18
4.1 Whole feed water process introductions.................................................... 18
5 AUTOMATION APPLICATION OF DRUM LEVEL CONTROL SYSTEM .................... 20
5.1 Drum level measurement and correction................................................... 20
5.2 Measurement and correction for steam flow signals ................................... 22
5.3 Measurement and correction for main feeding water flow signals ................ 23
5.4 Single impulse and three impulse control figure......................................... 23
5.5 Feeding water SAMA figure...................................................................... 24
5.6 Introduction about the SAMA figure ......................................................... 24
5.7 Parameters tuning and feeding water system process ................................ 26
5.8 Feeding water controlling system tuning ................................................... 26
5.9 Feeding water three impulse controlling system tuning .............................. 26
6 CONCLUSION ............................................................................................... 27
REFERENCES .................................................................................................... 28
Appendix .......................................................................................................... 29
Appendix 1 Feeding water SAMA figures ......................................................... 29
Appendix 2 Measurement and correction for steam flow signals ........................ 30
Appendix 3 Measurement and correction for main feeding water flow signals ..... 31
Appendix 4 Single impulse or three impulse controlling switch figure ................. 32
32
4
SYMBOLS AND ABBREVIATIONS
FC
Flow Controller
FT
Flow Transmitter
LC
Level Controller
LT
Level Transmitter
Σ
Sum
5
1
INTRODUCTION
This part includes thesis goal and background information on the stream drum level
control and also on the level control of the boiler drum in power plants.
1.1
Thesis goal
The main research part in this thesis involves boiler drum feed water control system,
level control method, feed control system operation. The designing of an automation
system for the level control in drum is the main goal in this thesis.
1.2
Thesis background
In this part, I introduce the background of the level control history and the previous
system about the drum boiler. After that, I can find the reasons for designing this system.
1.2.1
The feature of the process control
Level control system means the automatic control system controlling the level as a
variable value in the industrial producing process. As goals that guarantee the quality
and working safety, I should control the level value in a determine value or changing
follow a discipline.
The level value changes not only caused by the external influences, but also it
caused by the internal influences. In the process the influence parameter should be
more than one value. The functions are also very different. It increases the complexity in the process parameter control. As a result of that, I can get the features below:
1) The object hysteresis
The hot productions always happen in huge production equipment, the objects have
huge storage capacity and inertia. There are some resistances during the media flow
or hot energy transfer, and they have the trend to get the balance. In a word, when
flow in (or out) objects‟ weight or energy has changed, cause of the capacity, inertia
and resistances, the parameter cannot change immediately. System called the phenomenon as hysteresis.
6
2) The object nonlinear
The features of the object always change by the load. The most of the production are
nonlinear. To guarantee the nonlinear production reasons the properties of the nonlinear are very significant.
3) The control system complexity
When thinking the safety production, system tries very hard to guarantee the steadiness of the design and production process, and the parameters changed cannot go
over the limit range. There is more than one parameter which needs to be controlled,
and all of them have different features. I need to make different control systems for
the different parameters.
1.2.2
Development status of the level control system
Because of the developments of the science technology, the control system becomes
huge nowadays. To guarantee the industrial production under safety and efficient,
there is a hot point which I research in the process control area that I monitor online
and control the production situation in time and accurately. In the light industry, it is
very normal that I use the level control. There are many examples like the simple float
level switch, ultrasonic wave level test and high accuracy isotope level test system.
It is very normal that I use the level control system in the different areas in our daily
lives. However, from the controller of the level control in China, there is still the gap
with some developed country. [Liu Zhenjiang, 2007]
7
2
DYNAMICS OF THE BOILER DRUM LEVEL PROCESS
The drum is very important power equipment whose task is to supply qualified stable
steam to support load need. The level of the boiler drum is the most significance value to guarantee the process safety.
2.1
The total introduction
The following system is controlling to level, with the knowledge I have learned.
Application area: using the element with detector, controller and actuators etc. to control the level.
Function introduction with this system: it can show the value of the level. When the
disturbances get in the system, the value can be made to the stable value without
any kind of manual work.
2.2
The formation of the false level phenomenon
The false level means that the untrue level value in the boiler running process. When
the pressure dramatic decreases are saturation temperature decreases to the low
pressure temperature value. It will make the boiler water exothermic and to evaporate,
and form a lot of bubbles. The volume of the mixed water and air expand a lot. As a
result of that, it makes the level increase a lot, and I get the false level.
When the heat load is changed, the fire is extinguished safety valve behaviour and
combustion instability also can result in the false level. When the load is changed
rapidly, the pressure of the steam also will change, and it will be the false level. More
rapid the load is changed higher the false level it will be.
As the solution for the false level, I can lead a steam flow signal to the input port and
designing feed forward adjustment for the level system. When the steam flow increases, it can put more water inside and the temperature will become lower. It will
infect the false level.
8
2.3
The factors of influence steam level
First of all, I should analyse the dynamic characteristics of the steam. Figure 1 shows
it below. The feed water adjustment in the inverter adjusts feed water value W, the
steam turbine valve angle controls the steam turbine consumption D.
H
Figure 1. Boiler process and feed water regulating object
At first glance, a dynamic characteristic of steam level is the same with the single
packaging sink. Feed water flow and steam flow influence the drum level. However,
the true situation is not like that. The most different point is the water cycle system full
of the steam water, and the Volume V of the steam is changed with the drum pressure and furnace heat load changing too. If some reasons influence, the total volume
is changed. Although the water value in the water cycle has not changed, the drum
level will also change and influence the stability of the water level.
The most significant influence factor for the drum level H is feed water value W, consumption of turbine D and the amount of fuel B.
2.3.1
Feed water disturbance influence
If I make the drum and its water cycle system as a single packaging sink, curve of the
feeding water disturbance response should be like Figure 2 curve H1 shows. I think
about the feeding water temperature lower than the saturated water in the drum.
When it enters the drum, the water absorbs some heat from the original saturated
water in the drum. The steam flow in the boiler will decline. Total volume of the steam
under the level will decline and the water level will decline too. It is like Figure 2 curve
9
H2 shows. Actually the response curve should between curve H1 and H2 like H. It is
integral part with the delay time, the higher sub cooling value, the longer the responds time it will be. The transfer functions should be like in formula 1 [Lin Zunji]
(1)
In the (1), there are
ε1= Gain
τ= Process time constant,[Second]
G1(s)=Transfer functoin=H(s)/W(s)
s=Laplace operator
Figure 2. Feeding water responding level curves in drum [Li Zunji, 2010]
2.3.2
The influence of consumption of turbine
When the consumption D of the turbine increases, it changes the substances balance
situation to make liquid in the drum evaporation and level become lower. I can see
the curve H1 in Figure 3. At the same time, the consumption of turbine D increases
and the bubbles become more. Because of the amount of fuel unchanged the pressure of the bubbles become lower. It will make the bubble under the water expand
and total volume V increase. The result is the drum level increases. I can get the
curve like H2 in Figure 3. The true level response curve should be H which is the sum
of the H1 and H2. If I talk about the huge size of the boiler, the influence is bigger of
H2 situation than in H1. As the result of that, when the load increases in a period of
10
time, the level will be increased instead of decrease. This is a phenomenon I called
“false level phenomenon”. That the function should be like below [Lin Zunji]:
(2)
In the (2), there are
ε2 = The speed of steam flow increase
T0 = The postpone time of “false level phenomenon”.
K= Gain
s=Laplace operator
Level
Time
Figure 3. Consumption of turbine respond curve
2.3.3
The influence of the fuel disturbance
The fuel disturbance must make the change of steam flow D to change. System can
also get the “false level phenomenon”. However, there is lot of water in the drum water cycle system, and there is lot of heat storage in the drum and water-cold system.
As the result of that, it has the thermal inertia. The increase of fuel can just make the
amount of steam increase slowly. At the same time, the pressure of the steam will
increase slowly. It will make the volume of bubble decrease. The “false level phenomenon” under the fuel disturbance is more alienated with load disturbance.
From the analysis, I can get the response of feed water disturbance that is hysteresis.
The load disturbance has “false level phenomenon”. Those kinds of characteristics
11
make the drum level change under a lot of factors, and it is hard and complex to control it.
12
3
DRUM LEVEL CONTROL SYSTEM DESIGN
From the feedback I can easily get that the drum level as a feedback value. The feed
water value is a controlled value. I get a single-loop feedback control system. It is
also the level single impulse control system. P&ID-diagram should be like Figure 4,
and it is a basic control plan. The block diagram is Figure 5. For the small capacity
boiler, because the volume of the water is bigger, the volume under the drum that is
under level that cannot occupy large rate is not very big. The false level phenomenon
is not very obvious. I can use the drum level single impulse control system to control
the drum level.
H
Inverter
LC
LT
Figure 4. Drum level single impulse control systems P&ID-diagram
However, for the middle size or the huge size boiler, the plan cannot be suitable for
the control requirement. The steam value of turbine load disturbance will lead to the
false level phenomenon and make the malfunction of the feed water system. It will
lead to the drum level fluctuating deeply and influence the equipment lifetime and
safety. The middle or huge boiler cannot use only the drum level single impulse control system to control. System should find other method to control the level.
13
Level
setponit
Figure 5. Drum level single impulse control system block diagram
Analysis can start from the Mass Balance theory. If I can make sure that the feed
water value always equal to the evaporation of the steam, system can make sure the
drum level is stable.
H
Figure 6. Steam flow servo control systems P&ID-diagram
System can use the steam flow servo control system, and for the flow regulator I use
a PI controller. It makes the steam value of the turbine as a system set point, and the
water flow changed follow the steam flow changed. It established a servo control
system to make sure the drum level remains constant. You can see the block
diagram as Figure 7.
14
Level
setponit
Figure 7. Steam flow servo control system block diagram
The advantage of this system is that it is based on the Mass Balance to work; the
feed water flow is based on the turbine steam consumption. The false value will not
affect the feed water adjustment system. However, the system is an open loop control system for the drum level. Because the feed water and steam flow are inaccurate
measurements and other disturbance of the boiler make the ratio of the steam flow
and feed water value is not exact. Because the deviation for the two values is integral
relation, so the small difference will lead to huge level difference. As a result of that, I
cannot use the steam flow servo control system.
If I combine the two systems, system can get the drum level double impulse control
system as in Figure 8 and in the block diagram in Figure 9. The double impulse
means that system use two measurement signals: the drum level and steam flow.
H
Figure 8. Drum level double impulse control systems P&ID-diagram
15
Figure 9. Drum level double impulse control system block diagram
This system can improve high quality of the drum level control. When the steam consumption of the turbine becomes high, the “false level phenomenon”, the drum level
becomes high temporarily, and it makes malfunction to reduce the feed water value.
On the other hand, the higher of the consumption of the turbine it will increase the
feed water value with the control of the ratio control system. The actual feed water
situation should make sure with parameter tuning based on the actual situation.
When the false level phenomenon disappears, the level and steam signal will control
the adjustment action. If the parameter tuning is right, the feed water value must
equal with the steam water value to make the level constant.
In this point, I consider that the change of the feed water flow can be adjusted
through inner loop by itself with a cascade controller. The system like Figure 10
shows the three impulse control systems. The block diagram shows it in Figure 11.
16
H
Figure. 10 Drum level three impulse control systems P&ID-diagram
It is a feed forward-feedback-cascade mixed controlled system. This three impulse
control system includes a water flow control loop and a drum level control loop with a
steam flow feed forward passage. In fact, it is a steam flow feed forward-flow cascade
composed of a mixed control system.
Level
Controll
er
Figure 11. Drum level three impulse control systems block diagram
17
In this cascade control system, the main parameter is drum level, the amplitude parameter is the feed water flow, the main regulator is the feed water flow regulator, the
amplitude regulator is the level regulator. On the one hand, it can overcome feed water disturbance, and make feed water flow self-regulation. On the other hand, it can
overcome the “false level phenomenon”. When the steam flow changes, the feed
water flow control loop in the boiler drum level control system can change the feed
water value immediately to accomplish controlling. After that, the drum level regulator
accomplishes fine tuning to keep the drum level stable.
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4
ENGINEERING OF LEVEL CONTROL SYSTEM
Feed water process automation means that the process for feeding water in the boiler
is totally automated. It means that when the controlling equipment is running normally,
company do not need other resources for working with this system
4.1
Whole feed water process introductions
System should make sure that the drum level is in the range of the system. It is more
complex with the normal feed water system. As a result of that, I present some requirements about the automation control system below [SAMA, 2006]:
1.
I can change the adjusting door degree of opening to accomplish the feeding
water process control. It means that I can change the resistance in the pipes to
change the water volume to change the pumps speed. It also means that the
change in the pressure of water is reduced to change the feed water value. The
first method will lead to a big loss with the throttling. There is too much power
consumption in the pumps. It is not economic. As a result of that, I use the second method in many big boilers. In the whole process of feeding water, not only
I should feed the requirements of feeding water value adjustment, but also I
should make sure that the pump is working in the safety range. In most of the
time, it should be two controlling systems to accomplish this process. It is what I
call two part adjustment.
2.
Because the unit will show different object properties in different loads, the controlling system should fit for this property. With the load changing, the system will
begin with a single impulse to change to three impulses, or begin with three impulses to change to a single impulse. It will bring the problems about the shift of
system. System must be two controlling circuits without any interference between
each other with these two systems.
3.
Because the big working ranges of the whole controlling system, it should be
higher requirements about the measurement.
4.
In the complex switching processes in different adjustment mechanisms, the
feeding water system must be without any interference. High and low loads need
different regulating valves. I should solve the problems with switching. The sectional doors switching need a period of time, and it bring troubles with keeping
the water level. At the same time, it brings the over switching problems between
regulating valve and a regulating speed pump. The pressure is growing a lot. Because the boiler is without any output steam value, the feed water value changed
19
very little, so the single impulse adjustment system is not very good. System
should use the method with opening regulating valve to control the water level.
5.
The feeding water system should be suitable with aircrew in constant pressure or
sliding pressure. At the same time, I should make the system adapt cold starting
or warm starting.
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5
AUTOMATION APPLICATION OF DRUM LEVEL CONTROL SYSTEM
I use a 600 MW unit aircrew feeding water system as an example to introduce the
whole process of feeding water system running principle and characteristics. There
are some important parts in the feeding water system like drum level, main stream
flow, main feeding water flow and water pumps controlling. I will introduce each part
with the function and operating principle. At the end of this part, it will be a SAMA
figure to show the system. [TAKEO IMANAKA, 2000.]
5.1
Drum level measurement and correction
When the boiler starts normal running process, the steam pressure changed all the
time. Because the density of saturated water and saturated stream in drum changed
with the pressure changed. It will influence the accuracy of measurement about the
drum level. For the measurement saturated water with differential pressure principle
system, system should make pressure with differential pressure signal, and correct
temperature before system can get a true drum level.
The key point of differential pressure type level gauge when measuring drum level
correctly is the accurate conversion between level and differential pressure. This kind
of conversion uses the balance container to stride the reference water column to accomplish the task.
When the differential pressure type level gauges work, it will compare the drum level
water column pressure with the water column level together with balanced ratio of a
container. The basic point of comparison is the water side of the centreline water table sampling hole. Because the reference height in the column is kept constant, the
measured pressure can directly reflect the drum level. After installing the balance
container, the reference height of the water column is a fixed value. The differential
pressure transmitter range is equal with the height of the reference level.
21
Measuring
Tube
Figure 12. Drum level measurement
ρs=Density of saturated steam inside the drum, single-valued function of drum pressure
(kg/m3)
ρw=Density of saturated water inside the drum, single-valued function of drum pressure (kg/m3)
ρa=Density of balance within the single-chamber container unsaturated water, it is a
function with pressure and temperature (baseline water column) (kg/m3)
L=Differential pressure level range (mm)
Hyc=Single room balancing container extraction pipe center distance (mm)
H=drum actual level (mm)
ΔP=single room balancing the measured differential pressure vessel (Pa)
T=Drum pressure corresponding saturation temperature (0c)
Ta=Unsaturated water temperature in Single room balancing container (0c)
From the FIGURE 12 that the differential pressure measured by the differential pressure transmitter is:
ΔP=(P+g×L×ρa)-[P+g×(L-H)×ρs+g×H×ρw]
(3)
H=[L(ρa-ρs)×g- ΔP]/( ρw-ρs)×g
(4)
In (3) and (4)
g=gravity (m/s2)
From the above equation, the water Level Range L is a known value as a constant.
ΔP is measurement of differential pressure transmitter, ρw, ρs is single-valued function
of the drum pressure. Based on the saturated water and saturated steam nature table,
I can use the function module in the control system. Not only has the pressure influ-
22
enced the ρa, but also the balance container cooling conditions and environment
temperature. When the pressures of steam and environment temperature are
changed, this value will also change. As a result of that, system should make up
those two factors.
Figure 13. Drum level measurement and correction instrumentation
In this figure, the “2XMTR” means the dual measurement processing algorithms. The
function is to choose two in one. 2XMTR is a text algorithm in WDPF. It monitors two
analogy transmitters input, and checks their quality and deviation. The output of this
kind of algorithm should be either a or b. Also it could be bigger value, smaller value
or average value. Operating persons can choose them by WDPF provided Graphical
interface.
5.2
Measurement and correction for steam flow signals
Steam flow is the steam flow in the boiler outlet. The steam flow in the boiler outlet is
the sum of turbine inlet flow and bypass flow. Middle or small size generators main
stream flow measurement always use throttling element marked----standard nozzle
23
(differential pressure method). However, in the huge size of the generator, the steam
flow is big and diameter of pump is big. It needs big size of nozzle and it is hard to
install. As a result of that, I do not use this method to measure the flow.
Friuli Siegel flow formula is the most common way in the steam flow calculation nowadays. The measuring principle is: When each level turbine has enough level inside,
each level steam pressure, temperature and steam flows have this kind of relationship.
(4)
In equation (4)
T1 =speed temperature (0c)
T01 =speed temperature under rated pirating conditions (0c)
P1 = pressure for speed temperature. (Pa)
Figure measurement and correction for steam flow signals can be found in the Appendix 2.
5.3
Measurement and correction for main feeding water flow signals
Because the flow of superheater spray desuperheater is reducing warm water and
flow of reheater spray is reducing warm water there will be steam flow in the end, so
the main feeding water flow is boiler feeding water flow plus superheater and reheater reducing warm water flow. This system with reducing warm water through superheater has 1, 2 level desuperheater (each level with A, B two side), which have four
reducing warm water flow signals totally and one reheater reducing warm water flow.
Figure measurement and correction for main feeding water flow signals is shown in
the Appendix 3.
5.4
Single impulse and three impulse control figure
Single impulse or three impulse controlling switch figure can be found in appendix 4.
In the low load situation, system just uses the drum level signal to controlling. It is
single impulse way for controlling. When it is in the high load situation, I use the three
impulses to controlling. The drum level signal works in the main controller input to
correct level deviation. The steam flow signal which as a feed forward signal works in
deputy controller input to overcome the false water level. Feed water signal is a feedback signal in inner closed loop.
24
5.5
Feeding water SAMA figure
The SAMA figure shows in Appendix 1.
This example is a 600 MW generator with three pumps. Rate is 30% electric water
pump; each has 50% TDBFP (steam pump). Electric water pumps are always start
pumps and standby pumps. There are two TDBFPs in normal running time.
In the low load, when the electric pump is running, system uses the single impulse
controlling method. When the load decreases, steam pumps start running. I use the
three impulses controlling method. When in the unusual circumstances, system
switches to manual method.
Manual, automation switching conditions:
1 Steam level deviation is big.
2 Steam level signals have problems.
3 Electricity pumps do not run.
4 Inputs signals problems in electricity pump
5 Feeding water flow signals have problems when underling three impulse controlling.
6 Steam flow signals have problem when underling three impulse controlling.
5.6
Introduction about the SAMA figure
SAMA (Scientific Apparatus Makers Association) figure is a control system structure
which includes all control devices. SAMA legend is easy to understand and it can
clearly indicate that the system functions. SAMA figure can reflect all the control and
signal processing functions of the control system and design ideas by designers.
[SAMA, 2006]
When I compose the system, I must first control process according to the requirements and a process control block diagram is drawn in accordance with SAMA legend. Then I select the appropriate rack-mounted instruments and instrument panel
mounted under the block diagram.
Legend shape meaning SAMA is featured in four categories, each of which has a
definite meaning,
① ○ Measurement or signal readout
②
Auto Signal Processing, generally expressed in the instrument function control
cabinet.
③ ◇ Manual Signal Processing, generally expressed in the operating device.
④
Actuator
25
When the control system block diagram expresses SAMA legend, I often draws together some of the symbols representing a specific module (meter) what are the
functions. Such a block diagram of the control system and the main diagram clearly
express how big specific module (meter is).
The SAMA figure will show those function below:
1. Signal Processing
A) Live signal and the control room signal conversion;
B) The quality of the signal inspection, testing whether it is within the valid range;
C) The important parameters should be multi-point measurement, integrated treatment
D) Compensation processing the measurement signal.
2. Automatic Control
A) Reflects the control of the control structure diagram of
B) Reflect the dynamic rule Controller
C) Reflect the direction of a controller action
D) When the system is run manually, the regulator should have the tracking function
to enable the system to achieve bump less switching.
3. Control system hand / auto switch and manual operation
A) In the control system generally each actuator should be equipped with an operator; operator may need to run manually according to the system / automatic
switch, manual operation and valve position are displayed, the value and the
measured value display are set.
B) Control system Hand / automatic switching of the basic principles:
System is normal. The operators on the operator by pressing keys „automatically‟
are put into automatic mode the system. In system failure or poor quality control
system control, the control system should be automatic state automatically switch
to manual states.
C) When the regulators of output corresponding operators to manually cut the corresponding output of the regulator should be cut to track status. The goal of that is
to enable the system to achieve bump less switching.
4. Signal alarm
For critical parameters, system should make sure the provisions of its high and
low alarm value according to process requirements.
5 Chain protections
Chain protection system means that when the production faces a serious failure, in
order to ensure equipment and personal safety, all devices stop operation in a certain order or operation of the emergency in a particular state.
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5.7
Parameters tuning and feeding water system process
This unit is about the parameters tuning for this final method process system.
5.8
Feeding water controlling system tuning
The feeding water controlling system includes feeding water three impulses controlling system, feeding water single impulse controlling system and the pressure controlling system in the output of pumps. When system begins to run, system should tune
these three parts.
5.9
Feeding water three impulse controlling system tuning
In the system prototype, like Figure 14 shows, there are three loops tandem with
each other. They are input flow regulation loops, (total) feeding water flow regulation
loops and level regulation loops. The parameter tuning of regulator (adjustment assembly) is based on dynamic characteristics of objects. In a normal cascade control
system, the vice-loop adjustment process is much faster than the main circuit. As a
result of that, when the vice-loop perturb ate by leapfrog, the adjustment process
could end in a short time. At the same time, basically it does not participate in the
operation of the main circuit. When the main circuit join the adjustment, the main-loop
operation has prefect action with function. In other words, the main loop can be seen
as an approximate percentage of links in the main circuit. As a result of that, the parameters of two adjustments can be respectively tuned.
Figure 14. Feeding water system prototypes block diagram
27
6
CONCLUSION
This thesis introduced the design of the level controlling system in the drum boiler. I
have compared many methods for the controlling system and I made the choice in
the end.
In the process of building the level control system, there are still some variability
points in this process. There is huge development about the level control system that
I found some new types of the level controller, like the ultrasonic wave level controller,
radar level controller and optical level switch. Most of them are used the radio waves
refraction and reflection theories. The light could be refraction and reflection in the
sub-interfaces between different media. These kinds of the controllers appeared to
develop the control system accuracy a lot and to complete the diversity of the control
system.
I use the SAMA figure to show the process and controlling method.
In this design process about this system, I have studied so many new things on Industrial Management. I use the knowledge about the automation and process controlling. This knowledge is very important parts in Industrial Management. I have learned
more and got some new knowledge that could further influence my future work and
career.
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REFERENCES
Liu Zhenjiang “coordination and feeding water process controlling” 2007 China Electric Power Press
Li Zunji “Thermal automatic control system” 2010 North China Electric Power University Press
600MW Coordinated Control System SAMA figure 2006
TAKEO IMANAKA, A study on locational configuration of DCS, Electrical engineering
in Japan, 2000
29
Appendix
Appendix 1 Feeding water SAMA figures
30
Appendix 2 Measurement and correction for steam flow signals
Temperture
transmitter
Temperture
setpoint
Turbine first
transmitter
level
pressure
Bypass
flow
Steam flow
31
Appendix 3 Measurement and correction for main feeding water flow signals
Temperature
setpoint
pressure
setpoint
Temperature
Pressure
compensator
Economizer
inlet flow
transmitter
Second level reducing
Frist level reducing
warm water flow
warm water flow
transmitter
Reheater reduc-
ing warm water
flow
Transmitter
32
Appendix 4 Single impulse or three impulse controlling switch figure
level
setpoint
Steam flow
Drum level
Feeding
Water
Flow
Main
controller
Single
impluse
controller
Deputy
controller
Manually
switch
Single impulse or
three impulse control instructions
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