U.S. patent application number 09/829331 was filed with the patent office on 2001-11-08 for gas and steam turbine plant.
Invention is credited to Hannemann, Frank, Schiffers, Ulrich.
Application Number | 20010037641 09/829331 |
Document ID | / |
Family ID | 7883720 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037641 |
Kind Code |
A1 |
Hannemann, Frank ; et
al. |
November 8, 2001 |
Gas and steam turbine plant
Abstract
A gas and steam turbine plant includes a waste-heat steam
generator which is located downstream of a gas turbine on the
flue-gas side and which has heating surfaces that are connected
into a water/steam circuit of a steam turbine. A gasification
device is located upstream of a combustion chamber of the gas
turbine through a fuel line, for the integrated gasification of a
fossil fuel. The gas and steam turbine plant is to be operated with
particularly high plant efficiency even when oil is used as the
fossil fuel. Thus, a heat exchanger is connected on the primary
side into the fuel line upstream of a mixing apparatus for admixing
nitrogen to the gasified fuel, as seen in the direction of flow of
the gasified fuel. The heat exchanger is constructed on the
secondary side as an evaporator for a flow medium.
Inventors: |
Hannemann, Frank; (Spardorf,
DE) ; Schiffers, Ulrich; (Eckental, DE) |
Correspondence
Address: |
LERNER & GREENBERG, P.A.
Post Office Box 2480
Hollywood
FL
33022-2480
US
|
Family ID: |
7883720 |
Appl. No.: |
09/829331 |
Filed: |
April 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09829331 |
Apr 9, 2001 |
|
|
|
PCT/DE99/03222 |
Oct 6, 1999 |
|
|
|
Current U.S.
Class: |
60/39.12 ;
60/39.182 |
Current CPC
Class: |
F02C 3/32 20130101; F02C
3/20 20130101; F01K 23/10 20130101; F02C 3/30 20130101 |
Class at
Publication: |
60/39.12 ;
60/39.182 |
International
Class: |
F02C 003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 1998 |
DE |
198 46 225.5 |
Claims
We claim:
1. A gas and steam turbine plant, comprising: a gas turbine having
a flue-gas side; a combustion chamber connected to said gas
turbine; a steam turbine having a water/steam circuit; a waste-heat
steam generator disposed downstream of said gas turbine on said
flue-gas side, said steam generator having heating surfaces
connected into said water/steam circuit; a fuel line connected to
said combustion chamber; a gasification device for producing
gasified fuel, said gasification device connected into said fuel
line, upstream of said combustion chamber; a mixing apparatus
connected into said fuel line for admixing nitrogen to the gasified
fuel; and a heat exchanger having a primary side connected into
said fuel line, upstream of said mixing apparatus, as seen in a
flow direction of the gasified fuel, said heat exchanger having a
secondary side constructed as an evaporator for a flow medium, and
said heat exchanger having a steam side connected to said
combustion chamber.
2. The gas and steam turbine plant according to claim 1, wherein
said secondary side of said heat exchanger is constructed as a
medium-pressure evaporator for water.
3. The gas and steam turbine plant according to claim 1, wherein
said water/steam circuit has a low-pressure stage, a branch line is
connected between said steam side of said heat exchanger and said
low-pressure stage, and a regulating valve is connected in said
branch line.
4. The gas and steam turbine plant according to claim 1, including
a crude-gas waste-heat steam generator connected into said fuel
line upstream of said heat exchanger.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending
International Application No. PCT/DE99/03222, filed Oct. 6, 1999,
which designated the United States.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a gas and steam turbine plant with
a waste-heat steam generator which is located downstream of a gas
turbine on the flue-gas side and which has heating surfaces that
are connected into a water/steam circuit of a steam turbine. A fuel
gasification device is located upstream of a combustion chamber of
the gas turbine through a fuel line.
[0004] A gas and steam turbine plant with integrated gasification
of fossil fuel conventionally includes a fuel gasification device
which is connected on the outlet side to the combustion chamber of
the gas turbine through a number of components provided for gas
purification. In that case, a waste-heat steam generator is
connected downstream of the gas turbine, on the flue-gas side.
Heating surfaces of the waste-heat steam generator are connected
into the water/steam circuit of the steam turbine. A plant of that
type is known, for example, from UK Patent Application GB 2 234 984
A or from U.S. Pat. No. 4,697,415.
[0005] An apparatus for the removal of sulfur-containing
constituents is provided, in both plants, for the reliable
purification of the gasified fossil fuel. In the plant known from
UK Patent Application GB 2 234 984 A, a saturator for inerting the
fuel gas is located downstream of that apparatus in a supply line
for the gasified fuel which opens into the combustion chamber. The
gasified fuel is laden with steam in that saturator in order to
reduce pollutant emissions. For that purpose, the gasified fuel
flows through the saturator in countercurrent to a water stream
which is carried in a water circuit referred to as a saturator
circuit. A provision is made for feeding heat from the water/steam
circuit into the saturator circuit in that case, in order to
operate the saturator independently of the gas generation or gas
purification plant.
[0006] That plant is intended to operate with gasified coal or
gasified refinery residues, for example residual oil, as fossil
fuel and is therefore also adapted to process properties for the
gasification of coal or of residual oil with a view toward
achieving particularly high efficiency. In particular, the plant is
constructed in terms of the water/steam circuit of the steam
turbine, with a view toward cost-effective and operationally
reliable utilization of the heat occurring during gasification.
SUMMARY OF THE INVENTION
[0007] It is accordingly an object of the invention to provide a
gas and steam turbine plant, which overcomes the
hereinaforementioned disadvantages of the heretofore-known devices
of this general type, which has a particularly simple structure and
in which both high plant efficiency and independent and
simple-to-regulate operation for inerting fuel gas are ensured,
even when oil is used as a fossil fuel.
[0008] With the foregoing and other objects in view there is
provided, in accordance with the invention, a gas and steam turbine
plant, comprising a gas turbine having a flue-gas side. A
combustion chamber which is connected to the gas turbine has a
water/steam circuit. A waste-heat steam generator is disposed
downstream of the gas turbine on the flue-gas side. The steam
generator has heating surfaces connected into the water/steam
circuit. A fuel line is connected to the combustion chamber. A
gasification device for producing gasified fuel is connected into
the fuel line, upstream of the combustion chamber. A mixing
apparatus is connected into the fuel line for admixing nitrogen to
the gasified fuel. A heat exchanger has a primary side connected
into the fuel line, upstream of the mixing apparatus, as seen in a
flow direction of the gasified fuel. The heat exchanger has a
secondary side constructed as an evaporator for a flow medium, as
well as a steam side connected to the combustion chamber.
[0009] The invention disclosed herein is based on the concept that
for high plant efficiency, even when oil is used as a fossil fuel,
particularly effective utilization of the heat carried in the fuel
stream flowing off from the gasification device, which is also
referred to as crude gas, should be provided. At the same time,
precisely when oil is used as a fossil fuel, it should be kept in
mind that a large part of the crude-gas heat may occur in the form
of latent heat as a result of partial water condensation at
comparatively low temperature. It is precisely this heat which can
be extracted from the crude-gas stream in a particularly
advantageous way by the evaporation of a flow medium. The flow
medium is capable of being fed into the plant process at a suitable
point in a particularly simple and flexible way. In addition, and
for permitting the inerting system for the fuel gas to operate
independently of the water/steam circuit of the steam turbine
located downstream of the gas turbine, with a suitable choice of
the pressure level, the steam that is generated can be fed directly
as an inerting medium to the fuel gas or to the GT burner. In this
case, through the use of the heat exchanger, particularly favorable
operating parameters, in particular a particularly favorable
temperature level, of the crude gas can be established for the
subsequent mixing of the crude gas with nitrogen. This mixing is
intended for the purpose of adhering to particularly low NOx limit
values.
[0010] Supplying the steam generated in the heat exchanger into the
fuel stream makes it possible to fully ensure that the gasified
fuel is laden with steam sufficiently to adhere to even low
pollutant emission limit values. Therefore, complicated devices
normally provided for loading the gasified fuel with steam may be
dispensed with completely. In particular, a gas and steam turbine
plant of this type can be constructed so as to dispense with the
saturator which is normally provided, together with the further
components associated therewith, so that a particularly simple
structure is obtained. Moreover, feeding the evaporated flow medium
into the combustion chamber of the gas turbine ensures that the
heat extracted from the crude gas during the evaporation of the
flow medium is utilized particularly effectively for the plant
process. The apparatus also allows simple and operationally
reliable regulation of the steam content of the fuel gas in order
to adhere to the predetermined limit values for NOx emission.
[0011] In accordance with another feature of the invention, the
heat exchanger is constructed as a medium-pressure evaporator for
water as the flow medium. In this case, the heat exchanger is
constructed preferably for evaporating the water at a pressure
stage of about 20 to 25 bar. Thus, medium-pressure steam generated
in this way and not required to be fed into the combustion chamber
can also be utilized in a particularly advantageous way for the
plant process and may, for example, be fed into the water/steam
circuit of the steam turbine.
[0012] In accordance with a further feature of the invention, the
heat exchanger is connected to a low-pressure stage of the
water/steam circuit of the steam turbine on the steam side through
a branch line, into which a shut-off member and a throttle
apparatus are connected. In this case, the gas and steam turbine
plant may be constructed in such a way as to ensure that a steam
quantity which is sufficient for adhering to predetermined
pollutant emission limit values and which is to be supplied to the
fuel is produced in every operating state. Thus, after throttling,
possibly excess steam generated in the heat exchanger can be
utilized directly for energy generation in order to achieve
particularly high efficiency in the low-pressure stage of the
water/steam circuit. Conversely, if the NOx emission requirements
are particularly stringent, additional medium-pressure steam from
the water/steam circuit may also be admixed, preferably upstream of
the intermediate superheater of the waste-heat boiler.
[0013] In a further advantageous refinement, the heat exchanger for
medium-pressure steam generation has a further heat exchanger for
low-pressure steam generation disposed downstream thereof, so that
the maximum fraction of crude-gas heat at low temperature can be
utilized with high efficiency. The generated steam, together with
the throttled medium-pressure steam, may be delivered to the
low-pressure part of the water/steam circuit. A further heat
exchanger for cooling the crude gas may be provided, depending on
the gas purification requirements, in particular the temperature
level of possibly downstream COS hydrolysis.
[0014] In accordance with a concomitant feature of the invention,
for particularly high plant efficiency, there is provided a
crude-gas waste-heat steam generator preceding the medium-pressure
evaporator in the fuel line upstream of the heat exchanger. Through
the use of the crude-gas waste-heat steam generator, it is possible
for the crude gas or synthesis gas generated in the gasification
device to be precooled as required and in a manner which is
advantageous in material terms.
[0015] The advantages achieved through the use of the invention
are, on one hand, in particular, that even when oil is used as a
fossil fuel, particularly high overall efficiency of the plant can
be achieved. Utilizing the heat which is carried in the crude gas
and which may, in particular, take the form of latent heat at a
comparatively low temperature level in order to evaporate the flow
medium, makes it possible to supply this heat into the plant
process in a particularly effective and flexible way. Particularly
when water is evaporated as the flow medium and this steam is
subsequently fed into the mixed gas, it becomes possible for the
mixed gas to be sufficiently laden with steam, even without
connecting a saturator which per se, together with the further
components associated therewith, would entail a significant outlay
in terms of manufacture and assembly. On the other hand, admixing
the steam makes it possible to set the degree of saturation of the
fuel gas over a wide parameter range and to provide a simple and
quick-reacting concept for regulating the steam content. This
ensures that even low limit values for pollutant emission are
adhered to at a particularly low outlay.
[0016] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0017] Although the invention is illustrated and described herein
as embodied in a gas and steam turbine plant, it is nevertheless
not intended to be limited to the details shown, since various
modifications and structural changes may be made therein without
departing from the spirit of the invention and within the scope and
range of equivalents of the claims.
[0018] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIGS. 1A and 1B are left and right-hand portions of a
schematic and block diagram of a gas and steam turbine plant, as
illustrated in a legend in FIG. 1A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Referring now in detail to FIGS. 1A and 1B of the drawings
as a whole, there is seen a gas and steam turbine plant 1 including
a gas turbine plant 1a and a steam turbine plant 1b. The gas
turbine plant 1a includes a gas turbine 2 with a coupled air
compressor 4 and a combustion chamber 6 which is located upstream
of the gas turbine 2 and is connected to a compressed-air line 8 of
the compressor 4. The gas turbine 2 and the air compressor 4 as
well as a generator 10 are seated on a common shaft 12.
[0021] The steam turbine plant 1b includes a steam turbine 20 with
a coupled generator 22 as well as a water/steam circuit 24 in which
a condenser 26 located downstream of the steam turbine 20 and a
waste-heat steam generator 30 are disposed. The steam turbine 20 is
formed of a first pressure stage or high-pressure part 20a, a
second pressure stage or medium-pressure part 20b and a third
pressure stage or low-pressure part 20c which drive the generator
22 through a common shaft 32.
[0022] A waste-gas line 34 is connected to an inlet 30a of the
waste-heat steam generator 30 in order to supply working medium AM
or flue gas expanded in the gas turbine 2 into the waste-heat steam
generator 30. The expanded working medium AM from the gas turbine 2
leaves the waste-heat steam generator 30 through an outlet 30b
thereof in the direction of a non-illustrated chimney.
[0023] The waste-heat steam generator 30 includes a condensate
preheater 40 that has an inlet side for receiving condensate K from
the condenser 26 through a condensate line 42, into which a
condensate-pump unit 44 is connected. The condensate preheater 40
has an outlet side connected through a line 45 to a feedwater tank
46. Moreover, the condensate line 42 may be connected directly to
the feedwater tank 46 through a non-illustrated bypass line, in
order to bypass the condensate preheater 40, as required. The
feedwater tank 46 is connected through a line 47 to a high-pressure
feed pump 48 with medium-pressure extraction.
[0024] The high-pressure feed pump 48 brings feedwater S flowing
out of the feedwater tank 46 to a pressure level suitable for a
high-pressure stage 50 of the water/steam circuit 24. The
high-pressure stage 50 is associated with the high-pressure part
20a of the steam turbine 20. The feedwater S, which is under high
pressure, can be supplied to the high-pressure stage 50 through a
first feedwater preheater 52. The first feedwater preheater 52 has
an outlet side connected to a high-pressure drum 58 through a
feedwater line 56 that is capable of being shut off through the use
of a valve 54. The high-pressure drum 58 is connected, for the
formation of a water/steam recirculation 62, to a high-pressure
evaporator 60 disposed in the waste-heat steam generator 30. In
order to discharge fresh steam F, the high-pressure drum 58 is
connected to a high-pressure superheater 64 which is disposed in
the waste-heat steam generator 30. The high-pressure superheater 64
has an outlet side connected to a steam inlet 66 of the
high-pressure part 20a of the steam turbine 20.
[0025] A steam outlet 68 of the high-pressure part 20a of the steam
turbine 20 is connected through an intermediate superheater 70 to a
steam inlet 72 of the medium-pressure part 20b of the steam turbine
20. A steam outlet 74 of the medium-pressure part 20b is connected
through an overflow line 76 to a steam inlet 78 of the low-pressure
part 20c of the steam turbine 20. A steam outlet 80 of the
low-pressure part 20c of the steam turbine 20 is connected through
a steam line 82 to the condenser 26, so that the closed water/steam
circuit 24 is obtained.
[0026] Moreover, a branch line 84 branches off from the
high-pressure feed pump 48 at an extraction point at which the
condensate K has reached a medium pressure. This branch line is
connected through a second feedwater preheater 86 or
medium-pressure economizer to a medium-pressure stage 90 of the
water/steam circuit 24. The medium-pressure stage 90 is associated
with the medium-pressure part 20b of the steam turbine 20. For this
purpose, the second feedwater preheater 86 has an outlet side
connected to a medium-pressure drum 96 of the medium-pressure stage
90 through a feedwater line 94 that is capable of being shut off
through the use of a valve 92.
[0027] The medium-pressure drum 96 is connected to a heating
surface 98 disposed in the waste-heat steam generator 30 and
constructed as a medium-pressure evaporator, to form a water/steam
recirculation 100. In order to discharge medium-pressure fresh
steam F', the medium-pressure drum 96 is connected through a steam
line 102 to the intermediate superheater 70 and therefore to the
steam inlet 72 of the medium-pressure part 20b of the steam turbine
20.
[0028] A further line 110, which is provided with a low-pressure
feed pump 107 and is capable of being shut off through the use of a
valve 108, branches off from the line 47 and is connected to a
low-pressure stage 120 of the water/steam circuit 24 at a
connection VI. The low-pressure stage 120 is associated with the
low-pressure part 20c of the steam turbine 20. The low-pressure
stage 120 includes a low-pressure drum 122 which is connected to a
heating surface 124 disposed in the waste-heat steam generator 30
and constructed as a low-pressure evaporator, to form a water/steam
recirculation 126. In order to discharge low-pressure fresh steam
F", the low-pressure drum 122 is connected to the overflow line 76
through a steam line 128, into which a low-pressure superheater 129
is connected. The water/steam circuit 24 of the gas and steam
turbine plant 1 thus includes three pressure stages 50, 90, 120 in
the exemplary embodiment. Alternatively, however, fewer pressure
stages, in particular two, may also be provided.
[0029] The gas turbine plant la is constructed to operate with a
gasified synthesis gas SG which is generated by gasification of a
fossil fuel B. Gasified oil is provided as the synthesis gas in the
exemplary embodiment. For this purpose, an inlet side of the
combustion chamber 6 of the gas turbine 2 is connected through a
fuel line 130 to a gasification device 132. Oil which is used as
the fossil fuel B can be supplied to the gasification device 132
through a charging system 134.
[0030] In order to provide oxygen O.sub.2 required for gasifying
the fossil fuel B, an air separation plant 138 is located upstream
of the gasification device 132 through an oxygen line 136. The air
separation plant 138 has an inlet side which is capable of being
loaded with a partial stream T of the air compressed in the air
compressor 4. For this purpose, the air separation plant 138 is
connected on the inlet side to an extraction air line 140 which
branches off from the compressed-air line 8 at a branch point 142.
Moreover, a further air line 143, into which an additional air
compressor 144 is connected, opens into the extraction air line
140. Therefore, in the exemplary embodiment, a total air stream L
flowing into the air separation plant 138 is composed of the
partial stream T branched off from the compressed-air line 8 and
the air stream conveyed by the additional air compressor 144. A
set-up concept of this type is also referred to as a partly
integrated plant concept. In an alternative embodiment, a so-called
fully integrated plant concept, the further air line 143, together
with the additional air compressor 144, may also be dispensed with.
In that case, the air separation plant 138 is fed air completely
through the partial stream T extracted from the compressed-air line
8.
[0031] Nitrogen N.sub.2, which is obtained in the air separation
plant 138 during the separation of the air stream L, in addition to
the oxygen O.sub.2, is supplied to a mixing apparatus 146, through
a nitrogen line 145 connected to the air separation plant 138.
There, the nitrogen is admixed with the synthesis gas SG. In this
case, the mixing apparatus 146 is constructed for particularly
uniform strand-free mixing of the nitrogen N.sub.2 with the
synthesis gas SG.
[0032] The synthesis gas SG flowing off from the gasification
device 132 first passes through the fuel line 130 into a crude-gas
waste-heat steam generator 147, in which cooling of the synthesis
gas SG takes place by heat exchange with a flow medium.
High-pressure steam generated during this heat exchange is supplied
to the high-pressure stage 50 of the water/steam circuit 24 in a
non-illustrated manner.
[0033] A soot-washing apparatus 148 for the synthesis gas SG and a
desulfuration plant 149 are connected into the fuel line 130
downstream of the crude-gas waste-heat steam generator 147 and
upstream of the mixing apparatus 146, as seen in the direction of
flow of the synthesis gas SG.
[0034] A heat exchanger 150 has a primary side connected into the
fuel line 130 between the soot-washing apparatus 148 and the
desulfuration plant 149 and therefore upstream of the mixing
apparatus 146, as seen in the direction of flow of the gasified
fuel B. The heat exchanger 150 has a secondary side constructed as
an evaporator for water W acting as a flow medium. A connection V
connects the heat exchanger 150 to the feedwater line 94. At the
same time, the heat exchanger 150 is constructed as a
medium-pressure evaporator for the water W and therefore for
generating steam at a pressure of about 5 to 7 bar. In other words,
the pressure is still sufficient for admixing the steam to the
synthesis gas SG upstream of the combustion chamber 6.
[0035] The heat exchanger 150 has a steam side which is connected
through a steam line 152, having a valve 158, to a further mixing
apparatus 154 which is itself connected into the fuel line 130
downstream of the mixing apparatus 146, as seen in the direction of
flow of the synthesis gas SG. The heat exchanger 150 is thus
connected on the steam side to the combustion chamber 6 of the gas
turbine 2 through the steam line 152 and through the further mixing
apparatus 154. The medium-pressure steam generated in the heat
exchanger 150 can therefore be supplied to the synthesis gas SG
flowing into the combustion chamber 6, in which case the synthesis
gas SG is laden with steam. This ensures a particularly low
pollutant emission during the combustion of the synthesis gas SG.
At the same time, a heat exchanger 155 is connected into the fuel
line 130 between the mixing apparatus 146 and the further mixing
apparatus 154. Another line with a valve 157 is connected through a
connection VII to the steam line 102.
[0036] Moreover, the heat exchanger 150 is connected on the steam
side to the low-pressure stage 120 of the water/steam circuit 24
through a branch line 156 which branches off from the steam line
152 and through a connection I. At the same time, a regulating
valve 165 is connected into the branch line 156 in order to ensure
a pressure level suitable for the low-pressure stage 120 in an
outflow-side part of the branch line 156.
[0037] In order to provide for the further cooling of the crude
gas, a second heat exchanger 159 has a primary side connected into
the fuel line 130 downstream of the heat exchanger 150, in the
direction of flow of the synthesis gas SG. The heat exchanger 159
has a secondary side constructed as an evaporator for water W
acting as the flow medium. In this case, the heat exchanger 159 is
constructed as a low-pressure evaporator for the water W and
therefore for generating steam at about 6-7 bar. The heat exchanger
159 has a steam side connected to the branch line 156.
[0038] In order to provide for effective separation of sulfur
compounds from the synthesis gas SG, a COS hydrolysis device 160 is
connected into the fuel line 130 between the heat exchanger 159 and
the desulfuration plant 149. A further heat exchanger 161 for
further crude-gas cooling has a primary side located upstream of
the COS hydrolysis device 160 in order to establish a particularly
favorable temperature for COS hydrolysis. This heat exchanger 161
has a secondary side loaded with medium-pressure feedwater from the
water/steam circuit 24, as is illustrated by an arrow P.
[0039] A further heat exchanger 151 is located downstream of the
COS hydrolysis device 160 in order to cool the crude gas. The heat
exchanger 151 has a secondary side loaded with medium-pressure
feedwater from the water/steam circuit 24, as is illustrated by an
arrow P. In order to provide for the further cooling of the crude
gas, two further heat exchangers 153 and 167 are connected into the
fuel line 130 upstream of the desulfuration plant 149, as is seen
in the direction of flow of the crude gas. In the heat exchanger
153, the crude gas is cooled on the primary side and the
desulfurated crude gas is heated again on the secondary side. The
crude gas is cooled in the heat exchanger 167 to a temperature at
which desulfuration of the crude gas can take place in a
particularly advantageous way. At the same time, the heat exchanger
167 is loaded on the secondary side with cold condensate or cooling
water in a non-illustrated manner.
[0040] In order to provide for particularly low pollutant emissions
during the combustion of the gasified fuel in the combustion
chamber 6, there may be provision for loading the gasified fuel
with steam prior to entry into the combustion chamber 6. This may
take place in a saturator system in a particularly thermally
advantageous way. For this purpose, a saturator may be connected
into the fuel line 130 between the mixing apparatus 146 and the
heat exchanger 155. The gasified fuel would be carried in the
saturator in countercurrent to a heated water stream that is also
referred to as saturator water. In this case, the saturator water
or the water stream circulates in a saturator circuit which is
connected to the saturator and into which a circulating pump is
normally connected. At the same time, a feedline is connected to
the saturator circuit in order to compensate for the losses of
saturator water which occur during the saturation of the gasified
fuel.
[0041] In order to cool the partial stream T of compressed air to
be supplied to the air separation plant 138, which is also referred
to as extraction air, a heat exchanger 162 has a primary side
connected into the extraction air line 140 and a secondary side
constructed as a medium-pressure evaporator for a flow medium S'.
In order to form an evaporator recirculation 163, the heat
exchanger 162 is connected to a water/steam drum 164 constructed as
a medium-pressure drum. The water/steam drum 164 is connected
through lines 166, 168 at connections III, IV to the
medium-pressure drum 96 associated with to the water/steam
recirculation 100. Alternatively, however, the heat exchanger 162
may also be directly connected on the secondary side to the
medium-pressure drum 96. Therefore, in the exemplary embodiment,
the water/steam drum 164 is connected indirectly to the heating
surface 98 which is constructed as a medium-pressure evaporator.
Moreover, a feedwater line 170 is connected to the water/steam drum
164 for a make-up feed of evaporated flow medium S'.
[0042] A further heat exchanger 172, which has a secondary side
constructed as a low-pressure evaporator for a flow medium S", is
connected into the extraction air line 140 downstream of the heat
exchanger 162, as seen in the direction of flow of the partial
stream T of compressed air. In this case, in order to form an
evaporator recirculation 174, the heat exchanger 172 is connected
to a water/steam drum 176 that is constructed as a low-pressure
drum. In the exemplary embodiment, the water/steam drum 176 is
connected through lines 178, 180 at connections I, II to the
low-pressure drum 122 associated with the water/steam recirculation
126 and is thus connected indirectly to the heating surface 124
which is constructed as a low-pressure evaporator. Alternatively,
however, the water/steam drum 176 may also be connected in another
suitable way, in which the steam extracted from the water/steam
drum 176 is capable of being supplied as process steam and/or as
heating steam to a secondary consumer. In a further alternative
embodiment, the heat exchanger 172 may also be connected directly
on the secondary side to the low-pressure drum 122. Moreover, the
water/steam drum 176 is connected to a feedwater line 182.
[0043] The evaporator recirculations 163, 174 may each be
constructed as a forced recirculation, in which the recirculation
of the flow medium S' or S" is ensured by a circulating pump, and
the flow medium S', S" evaporates at least partially in the heat
exchanger 162 or 172 that is constructed as an evaporator. In the
exemplary embodiment, however, both the evaporator recirculation
163 and the evaporator recirculation 174 are each constructed as a
natural recirculation, in which the recirculation of the flow
medium S' or S" is ensured by pressure differences established
during the evaporation process and/or by a geodetic configuration
of the respective heat exchanger 162 or 172 and of the respective
water/steam drum 164 or 176. In this embodiment, only one
comparatively small-dimensioned, non-illustrated circulating pump
for starting up the system is connected into each of the evaporator
recirculation 163 or the evaporator recirculation 174.
[0044] A cooling-air line 192 branches off from the extraction air
line 140 downstream of the heat exchanger 172, as seen in the
direction of flow of the partial stream T. A partial quantity T' of
the cooled partial stream T is capable of being supplied to the gas
turbine 2 through the cooling-air line as cooling air for blade
cooling.
[0045] Even when oil is used as the fossil fuel B, the gas and
steam turbine plant 1 has particularly high overall efficiency.
Utilizing the heat which is carried in the crude gas and which may,
in particular, take the form of latent heat at a comparatively low
temperature level for evaporating the water W makes it possible to
supply this heat into the plant process in a particularly effective
and flexible way. In particular, supplying the steam which is
thereby generated into the synthesis gas SG flowing out of the
mixing apparatus 146 makes it possible for the mixed gas to be
laden sufficiently with steam, even without the connection of a
saturator which per se, together with the further components
associated therewith, would entail a significant outlay in terms of
manufacture and assembly. This ensures that even low limit values
for pollutant emissions are adhered to at a particularly low
outlay.
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