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United States Patent 119]
Kamberger et a1.
[11]
Patent Number:
[45]
Date of Patent:
[54] CHEMICAL MODE OF OPERATION OF A
WATER/STEAM CYCLE
3,415,692
[75] Inventors: Werner Kamberger. Ober-Ohringen.
Switzerland; Erhard Liebig, Ditzingen.
Germany
[21] Appl. N0.: 743,181
[51]
[DE]
Germany ...................... .. 195 44 224.5
F02G 1/00
[52]
US. Cl. ........................ .. 422”; 60/39182; 60139.53;
[58]
Field of Search ............................ .. 422/7 ; 6059.182.
122/460; 122/472; 122/488
60/3953; 122/460. 472. 488; 203/10
References Cited
U.S. PATENT DOCUMENTS
2,727,069
2,947,686
3,162,550
290/4011
4,693,213
9/1987 Yanai et al. ........................... .. 122/7 R
4,753,311
7/1988 Pagani et 31..
60/3912
2/1988
4/1988
2/1989
3/1995
Germany .
Germany .
Germany .
United Kingdom .
Mathis. L.L.P.
Int. Cl.6 ............................. .. C23F 11/00; F02C 6/00;
[56]
7/1978 Foster-Pegg ..
Primary Examiner—Nina Bhat
Attorney, Agent, or Firm—Burns. Doane. Swecker &
Nov. 5, 1996
Foreign Application Priority Data
Nov. 28, 1995
6/1977 Martz et al. .... ..
4,099,374
3627344A1
3635411A1
3724947A1
2281742
Switzerland
[30]
12/1968 Armentano ........................... .. 143/614
4,031,404
FOREIGN PATENT DOCUMENTS
[73] Assignee: Asea Brown Boveri AG. Baden.
[22] Filed:
Jul. 7, 1998
12/1955 Van Waes ............................... .. 260/55
8/1960 Phillips. Jr,
[57]
ABSTRACT
A multi-pressure waste-heat boiler (7) comprises at least one
circulation steam generator, having a low-pressure econo
mizer (15), a low-pressure drum (17) and a low-pressure
evaporator (16), and at least one once-through steam gen
erator having a high-pressure economiz/er (21). a high
pressure evaporator (22) and a high-pressure superheater
(23). An oxygen addition (32) is arranged between the steam
drum (17) of the circulation steam generator and the high
pressure economizer (21) of the once-through steam gen
erator. An ammonia addition (31) is arranged in the feed line
(33) leading to the circulation steam generator.
208/340
12/1964 Dvoracek etal, ................... .. 148/614
2 Claims, 1 Drawing Sheet
US. Patent
5,776,413
Jul. 7, 1998
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5.776.413
1
2
CHEMICAL MODE OF OPERATION OF A
WATER/STEAM CYCLE
FIG. 2 is a graph showing oxygen concentration versus
ammonia concentration of condensate X. steam Y. and high
pressure feedwater Z for the method of the invention in
comparison with conventional methods.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a multi-pressure waste-heat boiler
having at least one circulation steam generator. essentially
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
Referring now to the drawings. wherein like reference
comprising a low-pressure economizer. a low-pressure drum
and a low-pressure evaporator. and at least one once-through
numerals designate identical or corresponding parts
throughout the several views. only the elements required for
steam generator. essentially comprising a high-pressure
understanding the invention are shown. and the direction of
?ow of the working media is shown by arrows. in FIG. 1
economizer. a high~pressure evaporator and a high-pressure
superheater. It also relates to a method of operating such a
fresh air drawn in via a line 1 is compressed in a compressor
plant.
2 to me working pressure in the gas-turbine system. The
compressed air is greatly heated in a combustion chamber 3.
?red for example with natural gas. and the fuel gas thus
developed is expanded in a gas turbine 4 to perform work.
2. Discussion of Background
Waste-heat boilers for utilizing the waste heat of energy or
process plants producing hot gas are designed either as
circulation boilers with drum or else as once-through forced
?ow boilers. The chemical mode of operation corresponds to
the conventional speci?cations for conventional steam
20
The energy obtained in the process is delivered to a gen
erator 5 or the compressor 2. The still hot exhaust gas from
the gas turbine is fed via a line 6 from the outlet of the gas
generating plants (e.g. TRD 611. VGB-R 450 L. EPRI
Guidelines). The alkaline mode of operation. the neutral
turbine to a waste-heat steam-generating plant 7 and is
passed from there. after delivery of its heat. into the open via
mode of operation and the combined mode of operation. as
used without exception. are brie?y explained in FIG. 2 to be
a line 8 and a ?ue (not shown).
In the water/steam cycle. a three- stage steam turbine 9. 10
and 11 is arranged on the same shaft as the gas turbine. The
described later. Problems arise if a waste-heat boiler is 25
equipped with a circulation low-pressure system and a
working steam expanded in the low-pressure turbine 11
once-through high-pressure system. If. for example. the
condenses in a condenser 13. The condensate is delivered
directly into the steam generator 7 by means of a condensate
conventional alkaline mode of operation is used. the
ammonia. on account of its ditferent solubility in steam and
water. increases in concentration in the steam region of the
low-pressure drum. Inside the drum. the ammonia content is
pump 14. It is remarkable that the plant has no low-pressure
30
heated as a rule by bleed steam.
then disproportionately high in the steam and accordingly
The waste-heat steam-generating plant 7 is constructed as
too low in the water. If the once-through steam generator is
now fed with water from the low-pressure drum. its
exchange surfaces are insu?iciently protected against cor
rosion and sediments. since no optimum oxide protection
an upright boiler and in the present case works according to
35
?lm can build up.
SUMMARY OF THE INVENTION
Accordingly. one object of the invention is to provide a
novel plant and an operating method of the type mentioned
at the beginning in which all parts of the plant can be
protected against corrosion and the formation of sediments.
This is achieved according to the invention in that an
oxygen addition is arranged between the low-pressure drum
of the circulation steam generator and the high-pressure
economizer of the once-through steam generator. and in that
an ammonia addition is arranged in the condensate line
leading to the circulation steam generator.
A method of operating such a plant is distinguished by the
45
could also be used.
The low-pressure system is constructed as a circulation
system with drum. in which case a forced circulation system
has been selected here. In the ?uegas path of the boiler. it
consists of a low-pressure economizer 15 into which the
condensate is directed. a low-pressure evaporator 16. and a
connected to a drum 17 via a circulating pump 18. The
superheated steam is transferred via a low-pressure steam
line 28 into a suitable stage of the intermediate-pressure
steam turbine 10.
The high-pressure system is constructed as a once
through forced_flow system and can thus be designed for
50
55
both subcritical and supercritical parameters. In the ?ue-gas
path of the boiler. it essentially comprises the high-pressure
economizer 21. the high-pressure evaporator 22 and the
high-pressure superheater 23. The working medium is fed to
the high-pressure economizer 21 from the low-pressure
drum 17 via a high-pressure feedpump 20. In this way. the
hitherto conventional feedwater tank can be dispensed with.
The superheated steam is transferred via a livesteam line 24
into the high-pressure part 9 of the steam turbine.
For the phase separation. a separator 25 is provided into
which the discharge of the high-pressure evaporator 22
leads. At its top end. the separator is connected to the
high-pressure superheater 23. At its bottom end. it is addi
BRIEF DESCRIPTION OF THE DRAWINGS
tionally provided with a sludge drain line 29. Arecirculation
A more complete appreciation of the invention and many
of the attendant advantages thereof will be readily obtained
line 26 likewise branches oil‘ from the bottom end of the
separator. which recirculation line 26 contains a shut-01f
as the same becomes better understood by reference to the
following detailed description when considered in connec
tion with the accompanying drawings FIG. 1 is a schematic
representation of a combined gas/steam power station plant.
a dual-pressure steam process. Of course. a horizontal boiler
low-pressure superheater 19. The low-pressure evaporator is
fact that so much ammonia solution is added in a dosed
quantity to the condensate. which has a pH value between
8.8 and 9.4. that a pH value between 9.4 and 9.7 is reached
in the steam phase of the low-pressure drum. and in that so
much gaseous oxygen is introduced into the water ?owing to
the once-through steam generator that its oxygen content
ranges between 50 and 150 ppb at a pH value between 8.8
and 9.2.
preheaters. feedwater tanks and high-pressure preheaters
65
member 30 and leads into the low-pressure drum 17.
After the partial expansion in the high-pressure part 9 of
the turbine. the steam is reheated before transfer into the
5,776,413
3
4
intermediate-pressure turbine 10. In the example. this
reheating is effected in heat-exchange surfaces 27 which are
arranged in the ?ue-gas path of the steam generator above
from oxygen pressure bottles or from an existing oxygen gas
network. and the ammonia addition may be effected in the
form of diluted ammonia solution by means of dosing
pumps.
The novel mode of operation can be recognized in the
diagram in FIG. 2. The pH value is plotted on the abscissa
and the oxygen content in [ppb] is plotted on the ordinate.
The three dotted regions in each case represent the conven
tional modes of operation mentioned at the beginning;
namely A the neutral mode of operation. 2 the combined
mode of operation and C the alkaline mode of the operation.
The novel mode of operation is shown in the shaded regions.
The initial position is the region X. which represents the
oxygen content and the pH value of the condensate after the
ammonia dosing at the boiler inlet. Region Y shows the state
of the low-pressure steam enriched with ammonia. and
region Z shows that of the high-pressure feedwater enriched
the high-pressure superheater 23.
By variation of the pressures and mass flows in the
circulation system and in the once-through system. a wide
range of combined processes can be covered with such a
steam generator.
In the case of the plant working by the variable-pressure
method. a boiler having a division of the mass ?ows in the
low-pressure system and the high-pressure system in a ratio
of 1:4 or 1:5 is considered to be appropriate.
The steam production starts in the boiler when the respec
tive temperatures of ebullition are reached. The initial steam
in the low-pressure system is generated by expansion of
recirculated high-pressure saturated water from the separa
tor.
The separator ensures that the high-pressure superheater
remains dry at all times during normal operation and steam
superheated in good time is available at the boiler outlet.
It is apparent from FIG. 1 that a condensate-purifying
plant is dispensed with. Underlying this fact is the idea that
the contaminants in the steam/water cycle can be drawn off
in the region of the separator. The purifying of the stearn/
with oxygen.
The result of the separate addition of ammonia (31)
upstream of the low-pressure drum 17. preferably into the
feed line 33 downstream of the condensate pump 14. and of
oxygen (32) downstream of the low-pressure drum 17.
preferably upstream of the high-pressure feedpump 20. is
25
water cycle can be etfected at both full load and part load.
To this end. the high-pressure system is overfed. Le. a larger
quantity of water than necessary is delivered through the
once-through steam generator via the high-pressure feed
pump. It goes without saying that the high-pressure feed
pump has to be of correspondingly larger design for the extra
quantity. The delivered water quantity is set in such a way
that wet steam passes into the separator in any case. The
contaminants are bound in the water droplets of the water!
steam mixture. The water portion of the steam is separated
in the separator by suitable means and drawn o? via the
30
35
sludge drain line 29. Of advantage in this method is the fact
According to the invention. measures are now to be taken
in order to reduce the susceptibility to corrosion mentioned
at the beginning in such boilers. in particular in the once
through steam generator. To this end. a novel chemical mode
evaporator. but not for the formation of a proper oxide
protection ?lm on the once-through mbing. which is fed with
the same drum water. In order to now create ideal protective
?lm conditions here. so much gaseous oxygen 32 is fed into
the feedwater ?owing to the high-pressure economizer that
an oxygen content between 50 and 150 ppb becomes estab
lished.
The apparatus for this method is extremely simple. The
oxygen addition 32 may be elfected volumetrically directly
wise than as speci?cally described herein.
What is claimed as new and desired to be secured by
Letters Patent of the United States is:
l. A method of operating a multi-pressure waste-heat
boiler having at least one circulation steam generator includ
ing a low-pressure eoonomizer. a low-pressure drum and a
low-pressure evaporator. and at least one once-through
steam generator. including a high-pressure economizer. a
the method comprising the steps of:
45
50
via the low-pressure economizer 15. The result of the
different solubility is that the ammonia increases in concen
tration in the steam. If. for example. the pH value of the
water is still 9.25 upon entering the drum. the pH value in
concentration. whereas the drum water only has a pH value
of 9.0. This value is sufficient for the requirements of the LP
quantity of conditioning chemicals. the vacuum degassing in
the condenser. and the desalting. described in connection
with the purifying of the cycle. from the separator 25.
Obviously. numerous modi?cations and variations of the
present invention are possible in light of the above teach
ings. It is therefore to be understood that within the scope of
high-pressure evaporator and a high-pressure superheater.
of operation having the following method steps is selected:
the steam increases to about 9.6 as a result of the increase in
speci?ed water/steam quality is regulated via the dosed
the appended claims. the invention may be practiced other
that contaminants are largely removed from the cycle even
after a few passes. i.e. within the shortest time.
Downstream of the condenser 13. the condensate as a rule
has an oxygen content 60 ppb and a pH value between 8.8
and 9.4. So much ammonia solution is now introduced into
this condensate by means of a dosing unit that it has a pH
value between 9.1 and 9.4 in the feed line to the boiler. The
water passes with this value into the low-pressure drum 17
that all parts of the plant are e?ectively protected. The
introducing an amount of dissolved ammonia into con
densate ?owing into the circulation steam generator.
said condensate having a pH value between 8.8 and 9.4.
su?icient to obtain a pH of steam in the steam space of
the low-pressure drum at a value between 9.4 and 9.7.
and
introducing an amount of gaseous oxygen into water
?owing to the once-through steam generator su?icient
to obtain an oxygen content in a range between 50 and
55
150 ppb at a pH value between 8.8 and 9.2.
2. A multi-pressure waste-heat boiler comprising at least
one circulation steam generatorincluding a low-pressure
economizer. a low-pressure drum and a low-pressure
evaporator. and at least one once-through steam generator.
including a high-pressure economizer fed by a line from the
low-pressure drum. a high-pressure evaporator and a high
pressure superheater. means for introducing oxygen in the
line between the low-pressure drum of the circulation steam
generator and the high-pressure economizer of the once
through steam generator and means for introducing ammo
nia in a feed line leading to the circulation steam generator.

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