U.S. patent application number 09/866621 was filed with the patent office on 2001-09-27 for cooling steam supply method of a combined cycle power generation plant.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Nagashima, Takayuki.
Application Number | 20010023577 09/866621 |
Document ID | / |
Family ID | 12001847 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010023577 |
Kind Code |
A1 |
Nagashima, Takayuki |
September 27, 2001 |
Cooling steam supply method of a combined cycle power generation
plant
Abstract
A combined cycle power generation plant includes a gas turbine
plant, a steam turbine plant operatively connected to the gas
turbine plant, an exhaust gas heat recovery boiler for generating
steam for driving the steam turbine plant by an exhaust gas of the
gas turbine plant, an evaporator unit accommodated in the exhaust
gas heat recovery boiler, the evaporator unit being divided into a
first evaporator and a second evaporator, and a superheater
provided for at least one of an intermediate portion between the
first evaporator and the second evaporator and a portion on a
downstream side of the second evaporator.
Inventors: |
Nagashima, Takayuki;
(Yokohama-shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Kabushiki Kaisha Toshiba
72, Horikawa-cho, Saiwai-ku, Kanagawa-ken
Kawasaki-shi
JP
|
Family ID: |
12001847 |
Appl. No.: |
09/866621 |
Filed: |
May 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09866621 |
May 30, 2001 |
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09016726 |
Jan 30, 1998 |
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6263662 |
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Current U.S.
Class: |
60/772 ;
60/39.182 |
Current CPC
Class: |
Y02E 20/18 20130101;
F02C 6/18 20130101; F05D 2220/74 20130101; Y02E 20/16 20130101;
F02C 7/16 20130101; F01K 23/106 20130101; F05D 2220/72 20130101;
F05D 2260/2322 20130101 |
Class at
Publication: |
60/39.02 ;
60/39.182 |
International
Class: |
F02C 006/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 1997 |
JP |
9-019528 |
Claims
1. A combined cycle power generation plant comprising: a gas
turbine plant; a steam turbine plant operatively connected to the
gas turbine plant; an exhaust gas heat recovery boiler configured
to generate steam for driving the steam turbine plant by an exhaust
gas of the gas turbine plant; an evaporator unit accommodated in
the exhaust gas heat recovery boiler, said evaporator unit being
divided into a first evaporator disposed on an upstream side with
respect to an exhaust gas flow and a second evaporator disposed on
a downstream side thereof; a high pressure superheater unit
including first, second and third high pressure superheaters
disposed in series in this order from the downstream side with
respect to the exhaust gas flow, said first high pressure
superheater being disposed at at least one of an intermediate
position between the first evaporator and the second evaporator and
a position on the downstream side of the second evaporator with
respect to the exhaust gas flow; and a bypass pipe configured to
bypass the second high pressure superheater and to connect the
first high pressure superheater with the third high pressure
superheater.
2. A combined cycle power generation plant according to claim 1,
further comprising: one low pressure evaporator and one
intermediate pressure evaporator disposed in the exhaust gas heat
recovery boiler; and wherein said first and second evaporators are
high pressure evaporators.
3. A combined cycle power generation plant according to claim 1,
wherein said superheater unit is located to a portion, at which a
superheated steam having a low degree of superheat is generated, at
an intermediate portion between the first and second
evaporators.
4. A combined cycle power generation plant according to claim 1,
further comprising another superheater unit disposed on an upstream
side of the first mentioned superheater unit and a bypass pipe
connected said first mentioned superheater unit and adapted to join
a superheated steam generated from the another superheater unit to
a superheated steam generated from the first mentioned superheater
unit.
5. A combined cycle power generation plant according to claim 1,
wherein said bypass pipe is provided with a bypass valve.
6. A combined cycle power generation plant according to claim 1,
wherein said high pressure superheater unit uses a superheated
steam generated therefrom as a process steam for another plant.
7. A combined cycle power generation plant according to claim 1,
wherein said high pressure superheater unit utilizes generated
superheated steam as a cooling steam for a gas turbine constituting
the gas turbine plant.
8. A combined cycle power generation plant according to claim 1,
further comprising: a pipe configured to supply a steam composed of
a steam from the exhaust gas heat recovery boiler and a steam from
the steam turbine to the gas turbine plant as a cooling steam; and
a device configured to control steam supply of the pipe to the gas
turbine plant.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a combined cycle power
generation plant capable of setting a steam generated from an
exhaust gas heat recovery boiler to a proper temperature and
supplying the steam to a steam turbine plant while supplying the
steam generated from the exhaust gas heat recovery boiler to a gas
turbine plant as a cooling steam, and also relates to a cooling
steam supply method for the combined cycle power generation
plant.
[0003] 2. Description of the Related Art
[0004] In recent years, a study and development for obtaining high
power and achieving high heat efficiency has been made in a
combined cycle power generation plant. With the study and
development, there has been made a plan to raise a combustion gas
temperature of at least a portion of a gas turbine inlet from a
temperature of 1300.degree. C., obtained in the prior art, to a
temperature of 1500.degree. C. or more.
[0005] In the case of creating a high temperature of the combustion
gas of the gas turbine inlet, for example, a high chromium steel
has been conventionally used as a component of a gas turbine plant,
and part of the compressed air from an air compressor has been
supplied to the component of the gas turbine plant as a cooling
medium. However, in the prior art as described above, the strength
of the component has been close to its limit. For this reason, in
order to discover a cooling medium substituting for the compressed
air used in the prior art, it has been attempted to study and
develop a new cooling medium to be supplied to the components of
the gas turbine plant, and steam has been selected as one of the
cooling medium. A combined cycle power generation plant which takes
advantage of steam cooling has been already disclosed in, for
example, Japanese Laid-Open Patent Publication Nos. 5-163960 and
6-93879.
[0006] Steam has a higher specific heat as compared with compressed
air and is adapted to an absorption of heat generated in
components, for example, in a gas turbine stationary blade and a
movable blade, accompanying with high temperature of the gas
turbine plant. However, each of the gas turbine stationary blade
and the movable blade has a structure in which a complicatedly
meandering narrow passage is defined in the interior of these
blades. For this reason, if impurities such as silica or the like
are contained in a steam passing through the above passage,
unbalanced cooling occurs because of the possibility of clogging
the passage with silica or the like. As a result, these blades are
broken down due to thermal strain accompanying the unbalanced
cooling. Therefore, cooling steam is required having a high
cleanliness factor.
[0007] Further, in the case where a cooling steam is supplied to
components of the gas turbine plant, it is necessary to provide a
steam supply source which can supply a steam of proper temperature.
If not so, the component of the gas turbine plant generates an
excessive thermal stress resulting from the difference in
temperature between a combustion gas as a driving fluid and these
components, which difference may result in a possibility that these
components are broken down. For this reason, in the components of
the gas turbine plant, a steam supply source, which can supply a
steam of proper temperature, is securely required.
[0008] On the other hand, with a temperature of the gas turbine
plant being high, a steam supplied from the exhaust gas heat
recovery boiler to a steam turbine plant also has a high
temperature. In this case, if the steam temperature is too high, an
excessive thermal stress is generated in the steam turbine plant,
and as a result, it becomes difficult to maintain a material
strength of the components of the steam turbine plant. For this
reason, in the steam turbine plant, it is necessary to provide a
steam supply source which can supply a steam of a proper
temperature.
[0009] As described above, in the combined cycle power generation
plant, a first high pressure superheater of the exhaust gas heat
recovery boiler is selected and set as a steam supply source,
taking into consideration the cleanliness of cooling steam, supply
of proper temperature steam, and technical matters indispensable to
the gas turbine and steam turbine plant. As one example, a combined
cycle power generation plan as shown in FIG. 6 has been already
proposed.
[0010] The combined cycle power generation plant shown in FIG. 6
has an arrangement in which a gas turbine plant 1 and a steam
turbine plant 2 are combined by a common rotary shaft 3 and an
exhaust gas heat recovery boiler 4 is located independently from
these plants.
[0011] The gas turbine plant 1 includes a generator 5, an air
compressor 6, a combustor 7 and a gas turbine 8. Air AR sucked by
the air compressor 6 is made into a high pressure compressed air,
and is guided to the combustor 7. In the combustor 7, a fuel is
added to the compressed air so that a combustion gas is generated,
and then, the combustion gas is expanded by the gas turbine 8, thus
the generator 5 is driven by the power generated in the above
manner.
[0012] The steam turbine plant 2 includes a high pressure turbine
9, an intermediate pressure turbine 10, a low pressure turbine 11
and a condenser 12. An exhaust steam, after being expanded by the
high pressure turbine 9, is led to a reheater 13 of the exhaust gas
heat recovery boiler 4 and is superheated therein. Then, the
exhaust steam is led to the intermediate pressure turbine 10 and is
expanded as a reheat steam. Further, the exhaust steam is again
expanded by the low pressure turbine 11, and thereafter, is
condensed into a condensate by the condenser 12. The condensate is
supplied as a feed water to the exhaust gas heat recovery boiler 4
via a pump 100.
[0013] Meanwhile, the exhaust gas heat recovery boiler 4 is
provided with a third high pressure superheater 14, the reheater
13, a second high pressure superheater 15, a first high pressure
superheater 16, a high pressure evaporator 18 including a high
pressure drum 17, an intermediate pressure superheater 19, a high
pressure economizer 20, a low pressure superheater 21, an
intermediate pressure evaporator 23 including an intermediate
pressure drum 22, an intermediate pressure economizer 24, a low
pressure evaporator 26 including a low pressure drum 25, and a low
pressure economizer 27. These components or elements are arranged
in order from an upstream side toward a downstream side along a
flow of an exhaust gas G of the gas turbine plant 1, and steam is
generated through the heat exchanging operation between each heat
exchanger and the exhaust gas G.
[0014] Specifically, in the exhaust gas heat recovery boiler 4, a
feed water supplied from the condenser 12 of the steam turbine
plant 2 via the pump 100 is preheated by the low pressure
economizer 27 and is led to the low pressure drum 25. Then, by
taking advantage of a difference in density of drum water, the feed
water is circulated through the low pressure evaporator 26 to
generate steam, and the generated steam is supplied to the low
pressure turbine 11 via the low pressure superheater 21.
[0015] The low pressure economizer 27 leads part of the feed water,
which is diverted (divided) on an outlet side of the economizer 27,
to the low pressure drum 22 by a low pressure pump 28 and the
intermediate pressure economizer 24. Due to a difference in density
of drum water, a part of the saturated water is circulated through
the low pressure evaporator 23 to generate steam, and then, the
generated steam is supplied to the gas turbine plant 1 via the
intermediate pressure superheater 19 so as to cool the components
of the gas turbine 8.
[0016] Further, the low pressure economizer 27 leads the remaining
feed water to the high pressure drum 17 by a high pressure pump 29
and the high pressure economizer 20. Then, the remaining saturated
water is circulated through the high pressure evaporator 18 to
generate steam, and the generated steam is led to the first high
pressure superheater 16.
[0017] This first high pressure superheater 16 includes a steam
pipe 30 for leading steam to the second high pressure superheater
15, and a bypass pipe 32 between which a bypass valve 31 is
interposed. Steam passed through the bypass pipe 32 is joined
together with a superheated steam generated by the second high
pressure superheater 15, and after the temperature of the steam has
been decreased to a proper temperature, the steam is supplied to
the high pressure turbine 9 of the steam turbine plant 2 via the
third high pressure superheater 14.
[0018] As described above, in the known combined cycle power
generation plant, in the case where steam is supplied from the
exhaust gas heat recovery boiler 4 to the high pressure turbine 9,
the first high pressure superheater 16 is set as the steam supply
source. When the steam generated from the first high pressure
superheater 16 is made into a superheated steam by the second high
pressure superheater 15, the steam temperature is decreased by the
bypass pipe 32, and then, the superheated steam having a proper
temperature is supplied from the third high pressure superheater 14
to the high pressure turbine 9.
[0019] Moreover, when supplying a cooling steam to the components
of the gas turbine 8, in the exhaust gas heat recovery boiler 4, a
superheated steam generated by the intermediate pressure
superheater 19 and an exhaust steam of the high pressure turbine 9
are joined together, and then, the joined steam is supplied to the
gas turbine 8 so that the strength of the gas turbine members can
be maintained so as to adapt to high temperature of a combustion
gas on an inlet of the gas turbine 8. Further, a steam, which
cooled the components of the gas turbine 8, is then led to the
intermediate pressure turbine 10 together with a reheated steam of
the reheater 13.
[0020] Meanwhile, in the combined cycle power generation plant
shown in FIG. 6, during the start-up operation, the steam is still
not generated from the exhaust gas heat recovery boiler, and for
this reason, a cooling steam cannot be supplied to the gas turbine
8 from the intermediate pressure superheater 19 and the high
pressure turbine 9. Thus, in order to cool the components of the
gas turbine 8, there is the following plan for making use of the
steam remaining in the high pressure drum 17 of the exhaust gas
heat recovery boiler 4. Specifically, in this case, the exhaust gas
heat recovery boiler 4 can make use of a residual heat of the first
high pressure superheater 16, the second high pressure superheater
15 and the third high pressure superheater 14. Therefore, as shown
in FIG. 7, an outlet side of the first high pressure superheater 16
is provided with a cooling steam pipe 34 which is arranged parallel
to the bypass pipe 32 and includes a control valve 33.
[0021] The residual steam of the high pressure drum 17 is led to
the first high pressure superheater 16 so as to be superheated, and
then, part of the residual steam is guided to the second high
pressure superheater 15 and the first high pressure superheater 14
while the remaining steam thereof is led to the cooling steam pipe
34. Subsequently, the two flows of steams are joined together on
the outlet side of the third high pressure superheater 14, and a
high-temperature portion of the gas turbine 8 is temporarily cooled
by the joined steam. When the gas turbine plant 1 is in a high-load
state, the components of the gas turbine 8 are cooled by the joined
steam of the intermediate pressure superheater 19 and the high
pressure turbine 9.
[0022] As described above, in the combined cycle power generation
plant shown in FIG. 6, the known plan mentioned above has been
performed such that a steam of a proper temperature is supplied
from the exhaust gas heat recovery boiler 4 to the high pressure
turbine 9 during the rated operation. However, when the gas turbine
plant 1 is in a state of a partial load operation, the exhaust gas
G supplied from the gas turbine 8 to the exhaust gas heat recovery
boiler 4 is further increased in its temperature.
[0023] In general, in the case where the partial load operation of
the gas turbine plant 1 is carried out, as shown by a broken line
in FIG. 8, a temperature of the exhaust gas G rises. In contrast to
the rising of the temperature of the exhaust gas G, the steam
temperature of the first high pressure superheater 16 is
substantially constant as shown by a dotted chain line in FIG. 8.
On the other hand, the steam temperature of the second high
pressure superheater 15 becomes high as shown by a solid line in
FIG. 8. The steam temperature of the third high pressure
superheater 14 rises, not shown, like the second high pressure
superheater 15. In this case, the exhaust gas heat recovery boiler
4 sets the superheated steam of the third high pressure super
heater 14 at a proper temperature and supplies it to the high
pressure turbine 9. Thus, when supplying the superheated steam of
the first high pressure superheater 16 to the third high pressure
superheater 14 via the bypass pipe 32, a bypass steam flow rate is
increased as shown by a solid line in FIG. 8. For this reason, a
heat exchange quantity of the second high pressure superheater 15
is increased as the exhaust gas reaches high temperature. However,
a steam quantity of any heated object remarkably decreases, and
during the heat exchange, an excessive thermal stress is generated
due to a biased temperature distribution. As a result, a problem is
caused such that a heat transfer pipe is burned or broken down.
[0024] On the other hand, the combined cycle power generation plant
shown in FIG. 7 is constructed as follows. Specifically, during a
start-up operation, the outlet side of the first high pressure
superheater 16 is provided with the cooling steam pipe 34 which is
arranged parallel to the bypass pipe 32. Due to the steam remaining
in the high pressure drum 17, the steam is led to the first high
pressure superheater 15, which is used as a cooling steam supply
source. Further, part of the steam is supplied to the cooling steam
pipe 34 while the remainder thereof is supplied to the third high
pressure superheater 14 via the second high pressure superheater
15. Subsequently, both the steam flows are joined together on the
outlet side of the third high pressure superheater 14, and the
joined steam is supplied to the gas turbine 8 so as to cool the
components of the gas turbine 8.
[0025] However, even during the start-up operation, for example,
when the gas turbine plant 1 is in a hot start or a very hot start
state, a residual heat of each heat exchanger is still at a high
temperature, and for this reason, there sometimes arises a case
where the temperature of the cooling steam exceeds a proper cooling
steam temperature of the gas turbine 8. In order to realize a
proper temperature of the cooling steam, as shown in FIG. 7, it is
necessary to locate a steam generating apparatus 35, which
generates a steam having a relatively low temperature, on an inlet
side of the gas turbine 8. However, this arrangement is not
advantageous when the cost of facilities is considered.
[0026] In FIG. 7, the outlet side of the gas turbine 8 is provided
with a first bypass pipe 12a connected to the condenser 12.
Further, the inlet side of the high pressure turbine 9 is provided
with a second bypass pipe 12b connected to the condenser 12.
[0027] As described above, in the known combined cycle power
generation plants shown in FIGS. 6 and 7, the following plan has
been made. Specifically, the first high pressure superheater 16,
which generates steam having a stable temperature with respect to a
load variation as shown in FIG. 8, is set as a steam supply source,
and steam having a proper temperature is supplied to the high
pressure turbine 9 therefrom while a cooling steam having a proper
temperature is supplied to the gas turbine 8. Considering the
details, however, the conventional combined cycle power generation
plants have various problems as described above, and it is required
to achieve improvements for sufficiently coping with the high
temperature of the gas turbine plant.
SUMMARY OF THE INVENTION
[0028] A primary object of the present invention is to
substantially eliminate defects or drawbacks encountered in the
prior art mentioned above and to provide a combined cycle power
generation plant which can stably supply steam having a proper
temperature from an exhaust gas heat recovery boiler to a steam
turbine plant even during a partial load operation of the turbine
plant.
[0029] Another object of the present invention is to provided a
combined cycle power generation plant which can supply a cooling
steam having a proper temperature from an exhaust gas heat recovery
boiler to a gas turbine plant even during a start-up operation.
[0030] A further object of the present invention is to provide a
cooling steam supply method of a combined cycle power generation
plant capable of supplying a cooling steam generated from an
exhaust gas heat recovery boiler to another plant.
[0031] These and other objects can be achieved according to the
present invention by providing, in one aspect, a combined cycle
power generation plant comprising:
[0032] a gas turbine plant;
[0033] a steam turbine plant operatively connected to the gas
turbine plant;
[0034] an exhaust gas heat recovery boiler for generating steam for
driving the steam turbine plant by an exhaust gas of the gas
turbine plant;
[0035] an evaporator unit accommodated in the exhaust gas heat
recovery boiler, said evaporator unit being divided into a first
evaporator disposed on an upstream side of an exhaust gas flow and
a second evaporator disposed on a downstream side thereof; and
[0036] a superheater unit provided at at least one of an
intermediate position between the first evaporator and the second
evaporator and a position on a downstream side of the exhaust gas
flow of the second evaporator.
[0037] In preferred embodiments, the evaporator unit includes at
least one low pressure evaporator and one high pressure evaporator
of a pressure higher than that of the lower pressure evaporator and
the superheater unit includes at least one low pressure superheater
and one high pressure superheater of a pressure higher than that of
the lower pressure superheater. The superheater unit is located
adjacent to a portion, at which a superheated steam having a low
degree of superheat is generated, at an intermediate portion
between the first and second evaporators.
[0038] There is further provided with another superheater unit
disposed on an upstream side of the first mentioned superheater
unit and a bypass pipe connected to the first mentioned superheater
unit and adapted to join a superheated steam generated from the
another superheater unit to a superheated steam generated from the
first mentioned superheater unit. The bypass pipe is provided with
a bypass valve.
[0039] The superheater unit makes use of a superheated steam
generated therefrom as a process steam for another plant. The
superheater unit utilizes the generated superheated steam as a
cooling steam for a gas turbine constituting a gas turbine
plant.
[0040] The combined cycle power generation plant further comprises
a steam supply means for supplying a steam composed of a steam from
the exhaust gas heat recovery boiler and a steam from the steam
turbine to the gas turbine plant as a cooling steam and a control
means for controlling the steam supply of the steam supply means to
the gas turbine plant.
[0041] In another aspect of the present invention, there is
provided a cooling steam supply method of a combined cycle power
generation plant, comprising a gas turbine plant, a steam turbine
plant, a superheater, an evaporator unit and an exhaust gas heat
recovery boiler having a drum, which are operatively connected
together, in which a cooling steam is supplied from the drum of the
exhaust gas heat recovery boiler to the gas turbine plant, said
method comprising the steps of:
[0042] supplying a steam remaining in the exhaust gas heat recovery
boiler to the gas turbine plant during a start-up operation
thereof;
[0043] joining an exhaust steam generated from the steam turbine
plant and a steam generated from the exhaust gas heat recovery
boiler together after opening a steam turbine inlet valve and
leading the steam to the steam turbine; and
[0044] supplying the joined steam to the gas turbine plant as a
cooling steam.
[0045] In performing the above method, in preferred embodiments,
the evaporator unit is divided into two evaporators and the drum is
a high pressure drum. Steam remaining in the high pressure drum is
supplied to the superheater disposed at an intermediate portion
between the divided two evaporators and a steam generated from the
superheater is supplied to the gas turbine plant as a cooling
steam. The superheater joins the steam generated therefrom and a
steam generated from another superheater located on an upstream
side of the first mentioned superheater when supplying the
generated steam to the gas turbine plant as a cooling steam. The
generated steam is supplied through a bypass pipe connected to the
first mentioned superheater.
[0046] According to the characteristic features and structures of
the present invention mentioned above, the high pressure evaporator
is divided into two high pressure evaporators. and the first high
pressure superheater is provided on a position where a superheated
vapor having a relatively low degree of superheat is generated in
the middle portion between these high pressure evaporators.
Further, the superheated steam generated from the first high
pressure superheater is controlled, and thereafter, is supplied to
the high pressure turbine. Therefore, even during a partial load
operation, the superheated steam can be supplied to the high
pressure turbine as a driving steam having a proper temperature
without specially providing temperature reducing means.
[0047] Further, in the cooling steam supply method of the combined
cycle power generation plant according to the present invention, by
making use of the steam of the high pressure drum, a superheated
steam having a relatively low degree of superheat is generated by
the first high pressure superheater, and then, the superheated
steam is controlled and is supplied to the gas turbine. Therefore,
even if during a start-up operation, steam is not still generated
from each heat exchanger of the exhaust gas heat recovery boiler, a
cooling steam having a proper temperature can be securely supplied
to the components of the gas turbine.
[0048] Furthermore, in the combined cycle power generation plant
according to the present invention, the superheated steam generated
from the high pressure superheater is supplied to other plants as a
process steam, so that an effective heat use can be achieved.
[0049] Still furthermore, according to the present invention, the
superheater utilizes the generated superheated steam as a cooling
steam for a gas turbine constituting the gas turbine plant.
[0050] The nature and further characteristic features of the
present invention will be made clear from the following
descriptions made with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] FIG. 1 is a schematic system diagram showing a combined
cycle power generation plant according to a first embodiment of the
present invention;
[0052] FIG. 2 is a view for explaining a position where a first
high pressure superheater according to the present invention is
located;
[0053] FIG. 3 is a graph showing a steam temperature and a bypass
steam flow rate distribution with respect to a load variation
obtainable from the present invention;
[0054] FIG. 4 is a schematic system diagram for explaining a
cooling steam supply method of the combined cycle power generation
plant according to the present invention;
[0055] FIG. 5 is a schematic system diagram showing a combined
cycle power generation plant according to a second embodiment of
the present invention;
[0056] FIG. 6 is a schematic system diagram showing a combined
cycle power generation plant of the prior art;
[0057] FIG. 7 is a schematic system diagram showing another
combined cycle power generation plant in the prior art; and
[0058] FIG. 8 is a graph showing a steam temperature and a bypass
steam flow rate distribution with respect to a load variation in
the prior art.
DETAILED DESCRIPTION OF THF PREFERRED EMBODIMENTS
[0059] A first embodiment of the present invention will be
described hereunder with reference to FIGS. 1 to 3.
[0060] Referring to FIG. 1, the combined cycle power generation
plant according to the first embodiment has a construction in which
a steam turbine plant 37 is combined with a gas turbine plant 36 by
a drive shaft 38 so that a cooling steam is supplied to the gas
turbine plant 36, and an exhaust gas heat recovery boiler 39 which
supplies a driving steam to the steam turbine plant 37 is provided
independently from these plants.
[0061] The gas turbine plant 36 includes a generator 40, an air
compressor 41, a combustor 42, and a gas turbine 43. Air AR sucked
by the compressor 41 is made into a high pressure compressed air
and is guided to the combustor 42. In the combustor 42, a fuel is
added to the compressed air so that a combustion gas is generated,
and then, the combustion gas is expanded by the gas turbine 43,
thus the generator 40 is driven by the power generated in the above
manner.
[0062] The steam turbine plant 37 includes a high pressure turbine
44, an intermediate pressure turbine 45, a low pressure turbine 46
and a condenser 47. An exhaust steam after being expanded by the
high pressure turbine 44 is guided to a reheater 48 of the exhaust
gas heat recovery boiler 39 and is heated therein. Then, the
exhaust steam is led to the intermediate pressure turbine 45 and is
expanded as reheated steam. Further, the exhaust steam is again
expanded by the low pressure turbine 46, and thereafter, is
condensed into a condensate by the condenser 47. The condensate is
supplied as a feed water to the exhaust gas heat recovery boiler 39
via a pump 49.
[0063] Meanwhile, the exhaust gas heat recovery boiler 39 is
provided with a third high pressure superheater 50, a reheater 48,
a second high pressure superheater 51, a high pressure evaporator
53 including a high pressure drum 52, an intermediate pressure
superheater 57, a high pressure economizer 58, a low pressure
superheater 59, an intermediate pressure evaporator 61 including an
intermediate pressure drum 60, an intermediate pressure economizer
62, a low pressure evaporator 64 including a low pressure drum 63,
and a low pressure economizer 65. These component elements are
arranged in order from an upstream side toward a downstream side
along a flow of an exhaust gas G of the gas turbine plant 43. Steam
is generated through the heat exchanging operation between each
heat exchanger and the exhaust gas G. Further, a low pressure pump
68 supplies part of a saturated water of the low pressure
economizer 65 to the intermediate pressure economizer 62, and a
high pressure pump 69 supplies a remaining part of the saturated
water of the low pressure economizer 65 to the high pressure
economizer 58.
[0064] The high pressure evaporator 53 includes two divisional
evaporators, that is, a second high pressure evaporator 54 and a
first high pressure evaporator 55, and is further provided with a
first high pressure superheater 56 which is arranged on a middle
portion between the second high pressure evaporator 54 and the
first high pressure evaporator 55. The first high pressure
superheater 56 is provided on a middle portion between the second
high pressure evaporator 54 and the first high pressure evaporator
55. The reason for taking the above arrangement is as follows.
[0065] As shown in FIG. 2, it has been known that the exhaust gas G
passing through the high pressure evaporator 53 has a saturation
temperature of +170.degree. C. on an inlet side of the high
pressure evaporator 53, and the difference in saturation
temperature becomes small on the downstream side from the central
portion thereof. For this reason, in this first embodiment, if the
first high pressure superheater 56 is provided in a region A where
the exhaust gas has a saturation temperature of +30.degree. C. to
10.degree. C., it is possible to limit a degree of superheat of
superheated steam generated from the first high pressure
superheater 56 within a relatively low temperature range from
10.degree. C to 20.degree. C. In this case, a pinch point of the
superheated steam and exhaust gas G generated from the first high
pressure superheater 56 is about 8.degree. C. according to a test
calculation. Further, in the case where the steam turbine plant 37
requires a superheated steam of a low degree of superheat such as
5.degree. C. to 10.degree. C., it is preferable that the first high
pressure superheater 56 is provided on the downstream side of the
first high pressure evaporator 55 which is one of the two divided
evaporators of the high pressure evaporator 53.
[0066] An operation of the combined cycle power generation plant
according to the first embodiment of the present invention shown in
FIG. 1 will be described hereunder.
[0067] When the combined cycle power generation plant is in a
partial load operation state, the temperature of the exhaust gas G
supplied from the gas turbine plant 36 to the exhaust gas heat
recovery boiler 39 rises, and with the rise of temperature, the
temperature of steam generated from each of the third high pressure
superheater 50, the second high pressure superheater 51 and the
first high pressure superheater 56 also rises and exceeds a
temperature of a driving steam required for the high pressure
turbine 44 of the steam turbine plant 37.
[0068] However, in the present embodiment, the high pressure
evaporator 53 is divided into the second high pressure evaporator
54 and the first high pressure evaporator 55, and further, the
first high pressure superheater 56 is provided at the intermediate
portion between the two divided high pressure evaporators 54 and
55. In this manner, the degree of superheat of the superheated
steam generated from the first high pressure superheater 56 is
limited within a range from 10.degree. C. to 20.degree. C. as shown
in FIG. 2. In the case where part of the superheated steam
generated in FIG. 1 from the first high pressure superheater 56 is
supplied to a bypass pipe 67 including a bypass valve 66 as bypass
steam, the flow rate of the steam can be reduced, and also, the
remaining superheated steam is supplied to the second high pressure
superheater 51 so as to make low a temperature of the superheated
steam generated from the second high pressure superheater 51.
According to a test calculation, the temperature of the superheated
steam generated from the first high pressure superheater 56 of the
present embodiment is about 100.degree. C., which is lower than the
temperature (400.degree. C. or more) of superheated steam generated
from the known first high pressure superheater 16 shown in FIG.
6.
[0069] FIG. 3 is a characteristic chart showing a temperature
distribution of the exhaust gas G shown by a broken line, a
temperature distribution of the superheated vapor generated from
the second high pressure superheater 51 shown by a solid line, a
temperature distribution of the superheated steam generated from
the first high pressure superheater 56 shown by a dotted chain
line, and a bypass steam flow rate shown by a solid line, with
respect to a load variation of the gas turbine plant 36.
[0070] As seen from FIG. 3, the temperature of the exhaust gas G
rises with respect to a load variation of the gas turbine plant 1.
However, a temperature of the superheated steam generated from the
second high pressure superheater 51 is lowered as compared with the
rise of the exhaust gas temperature, and also, a bypass steam flow
rate is reduced.
[0071] As described above in regard to FIG. 1, the first high
pressure superheater 56 generates a superheated steam having a
relatively low degree of superheat. Much of the superheated steam
is supplied to the second high pressure superheater 51, and then,
is supplied to the bypass pipe 67 so that the bypass steam flow
rate becomes relatively low. Further, the bypass steam flow is
joined together with the superheated steam generated from the
second high pressure superheater 51 to lower the temperature of the
steam. Subsequently, the low-temperature joined steam is changed
into a proper temperature driving steam necessary for a partial
load operation by the third high pressure superheater 50, and then,
is supplied to the high pressure turbine 44, and thus, the high
pressure turbine 44 is driven. The high pressure turbine 44 expands
the driving steam so as to drive the generator 40 while joining the
exhaust steam with steam generated from the intermediate pressure
superheater 57, and then, supplies the joined steam to the gas
turbine 43. The joined steam cools the components of the gas
turbine 43, and thereafter, is joined with a reheated steam
generated from the reheater 48. Further, the joined steam is
expanded by the intermediate pressure turbine 45, and thereafter,
is supplied to the low pressure turbine 46.
[0072] In the present embodiment, the high pressure evaporator 53
is divided into two, that is, the second high pressure evaporator
54 and the first high pressure evaporator 55, and the first high
pressure superheater 56 is located at an intermediate portion
between these high pressure evaporators 54 and 55. Further, the
degree of superheat of the superheated steam generated from the
first high pressure superheater 56 is made lower, whereby much of
the superheated steam is supplied to the second high pressure
superheater 51, so that a relatively little superheated steam can
be supplied to the bypass pipe 67 and that a driving steam of a
proper temperature can be supplied to the high pressure turbine 44
without providing any temperature reducing means in the third high
pressure superheater 50.
[0073] At this time, since much of the superheated steam flows
through the second high pressure superheater 51, it is possible to
provide a uniform temperature distribution such that a thermal
stress is almost not generated during heat exchange. Therefore, the
material strength of the heat transfer pipe can be maintained for
the long term. Further, since little of the superheated steam flows
through the bypass pipe 67 as compared with the conventional one,
when selecting the bypass valve 66, it is possible to select a
valve having a relatively smaller diameter, contributing to a
reduction of cost.
[0074] In general, since the first high pressure superheater 56 is
constructed so that impurities such as silica contained in the
saturated steam supplied from the high pressure drum 52 adhere to
the heat transfer pipe thereof, the first high pressure superheater
56 has a function of improving the cleanliness of the saturated
steam. Thus, when supplying a cooling steam to the components of
the gas turbine 43, a cooling steam having a relatively high
cleanliness can be supplied thereto, so that the components of the
gas turbine 43 can be prevented from being clogged with silica or
the like.
[0075] FIG. 4 is a schematic system diagram showing a cooling steam
supply method of a combined cycle power generation plant according
to another embodiment of the present invention. For simplification
of explanation, like reference numerals are used to designate the
same portions as the components of the combined cycle power
generation plant shown in FIG. 1.
[0076] Prior to an explanation about a cooling steam supply method
of a combined cycle power generation plant according to this
embodiment, first, the construction will be described below.
[0077] The high pressure evaporator 53 is divided into two, that
is, the second high pressure evaporator 54 and the first high
pressure evaporator 55, and the first high pressure superheater 56
is provided at the intermediate portion between these high pressure
evaporators 54 and 55. An outlet side of the first high pressure
superheater 56 is provided with a cooling steam pipe 71 between
which a control valve 70 connected to an inlet side of the gas
turbine 43 is interposed. Further, the outlet side of the gas
turbine 43 is provided with a first bypass pipe 72 connected to the
condenser 47, and on the other hand, the inlet side of the high
pressure turbine 44 is provided with a second bypass pipe 73
connected to the condenser 47.
[0078] In the combined cycle power generation plant, a daily
start/stop (DSS) operation is frequently carried out unlike a
conventional power generation plant. In the case of the DSS
operation, the third high pressure superheater 50, the second high
pressure superheater 51, the second high pressure evaporator 54 and
the first high pressure evaporator 55 which divides the high
pressure evaporator 53 into two, are accommodated in the exhaust
gas heat recovery boiler 39, and these elements are respectively
kept at a warming state before the start-up operation of the
exhaust gas heat recovery boiler 39. Further, the residual heat of
these elements is at high temperature.
[0079] The high pressure drum 52, the intermediate drum 60 and the
low pressure drum 63 have a steam pressure of about 60 kg/cm.sup.2,
12 kg/cm.sup.2 and 4 kg/cm.sup.2, respectively.
[0080] In the case where a cooling steam is supplied to the
components of the gas turbine 43, according to the test calculation
taking various losses into consideration, the cooling steam is
required to have a steam pressure of 20 kg/cm.sup.2. Further, the
first high pressure superheater 56 can reduce a degree of superheat
of a steam supplied from the high pressure drum 52 from 10.degree.
C. to 20.degree. C. Thus, since the first high pressure superheater
56 can set a temperature of the cooling steam to about 300.degree.
C. during the hot start-up operation, the cooling steam meets the
condition of 350.degree. C. or less cooling steam temperature
required for the components of the gas turbine 43. Therefore, the
cooling steam can be sufficiently supplied to the gas turbine
43.
[0081] The construction of this embodiment is based on the test
calculation as described above, and a cooling steam supply method
will be described hereunder.
[0082] Before the start-up operation of the combined cycle power
generation plant, first, the first high pressure superheater 56
supplies the steam of the high pressure drum 52 to the condenser 47
through the second bypass pipe 73 by the second high pressure
superheater 51 and the third high pressure superheater 50 so as to
blow out impurities such as silica contained in the respective high
pressure superheaters 51 and 50. Next, the bypass valve 66 of the
bypass pipe 67 is throttled to open the control valve 70 of the
cooling steam pipe 71, and then, the steam of the high pressure
drum 52 is supplied to the gas turbine 43 as a cooling steam. At
this time, in the case where a thermal stress is generated in the
components of the gas turbine 43 because the cooling steam
temperature is too low, the control valve 74 provided on the outlet
side of the third high pressure superheater 50 is opened so that
the cooling steam is joined together with the steam of the third
high pressure superheater 50, and thus, the joined steam
temperature is controlled so that the cooling steam becomes a
proper temperature. The cooling steam cools the components of the
gas turbine 43, and thereafter, is supplied from the first bypass
pipe 72 to the condenser 47, or is discharged from a chimney (not
shown) of the exhaust gas heat recovery boiler 39.
[0083] When the start-up operation of the gas turbine 43 has been
completed and the steam turbine inlet valve is opened, the exhaust
steam of the high pressure turbine 44 and the superheated steam of
the intermediate pressure superheater 57 are joined together, and
then, an operation for cooling the components of the gas turbine 43
is carried out with the use of the joined steam.
[0084] According to this method, the steam remaining in the high
pressure drum 52 is used, and when the steam is supplied from the
first high pressure superheater 56 to the components of the gas
turbine 43 as the cooling steam, the cooling steam is controlled so
as to become a proper temperature. Thus, even if each heat
exchanger of the exhaust gas heat recovery boiler 39 still does not
generate a steam, it is possible to cool securely the components of
the gas turbine 43, whereby a stable operation of the gas turbine
43 can be carried out.
[0085] FIG. 5 is a schematic system diagram showing a combined
cycle power generation plant according to a second embodiment of
the present invention. In this second embodiment, like reference
numerals are used to designate the same portions as the components
used in the first embodiment shown in FIG. 1.
[0086] In the second embodiment, the high pressure evaporator 53 is
divided into two, that is, the second high pressure evaporator 54
and the first high pressure evaporator 55, and the first high
pressure superheater 56 located at the intermediate portion between
these evaporators 54 and 55 is provided with a process steam supply
pipe 75. Thus, it is possible to supply the steam of the first high
pressure superheater 56 to a gasification furnace such as a coal
gasification, residual oil gasification plant or the like.
[0087] In the combined cycle power generation plant which does not
supply a cooling steam from the exhaust gas heat recovery boiler 39
to the components of the gas turbine 43, in the case of making the
steam of the third high pressure superheater 50 into a proper
temperature driving steam and supplying it to the high pressure
turbine 44, the outlet side of the second high pressure superheater
51 is provided with a temperature reducer 76. Then, the steam from
the high pressure economizer 58 is supplied from a high-pressure
superheater temperature-reducing water pipe 77 to the temperature
reducer 76 through a valve 78 which is controlled depending upon
the outlet temperature of the second or third high pressure
superheater 51 or 50. Further, the superheated vapor temperature of
the second high pressure superheater 51 is decreased, and the steam
is supplied to the third high pressure superheater 50. For this
reason, the superheated steam generated from the first high
pressure superheater 56 has a steam pressure of 100 kg/cm.sup.2 and
a temperature of about 350.degree. C.
[0088] In this embodiment, the superheated steam generated from the
first high pressure superheater 56 is supplied to a gasification
furnace such as a coal gasification plant as process steam, so that
the superheated steam generated from the exhaust gas heat recovery
boiler can be effectively used. In particular, a gasification power
generation plant recently receives much attention, and it is very
advantageous in a thermal efficiency calculation if the plant would
received a superheated steam generated from the exhaust gas heat
recovery boiler.
[0089] It is to be noted that the present invention is not limited
to the described embodiments and many other changes and
modifications may be made without departing from the scope and
spirit of the appended claims.
* * * * *