U.S. patent application number 12/787176 was filed with the patent office on 2010-12-30 for steam turbine power plant and operation method thereof.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Nobuhiko Hattori, Yasunori Matsuura, Nobuo OKITA.
Application Number | 20100326074 12/787176 |
Document ID | / |
Family ID | 42341210 |
Filed Date | 2010-12-30 |
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United States Patent
Application |
20100326074 |
Kind Code |
A1 |
OKITA; Nobuo ; et
al. |
December 30, 2010 |
STEAM TURBINE POWER PLANT AND OPERATION METHOD THEREOF
Abstract
According to one aspect of the embodiment, a steam turbine power
plant 10 is provided with a steam turbine system 20 which generates
electricity by driving a steam turbine by the steam from a boiler
21 or the like which generates the steam by combustion heat, and a
carbon dioxide recovery system 50 which recovers carbon dioxide
contained in the combustion gas from the boiler 21 or the like. In
the steam turbine system 20, part of the steam having performed the
expansion work in a high-pressure turbine 22 is introduced into a
back-pressure turbine 27. The steam introduced into the
back-pressure turbine 27 performs the expansion work and partly
supplied to the carbon dioxide recovery system 50 through a pipe 42
to heat an absorption liquid 90 in a regeneration tower 70.
Inventors: |
OKITA; Nobuo; (Yokohama-shi,
JP) ; Matsuura; Yasunori; (Tokyo, JP) ;
Hattori; Nobuhiko; (Tokyo, JP) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
|
Family ID: |
42341210 |
Appl. No.: |
12/787176 |
Filed: |
May 25, 2010 |
Current U.S.
Class: |
60/648 ; 60/649;
60/653 |
Current CPC
Class: |
Y02E 20/326 20130101;
F01K 7/04 20130101; B01D 53/1475 20130101; B01D 2257/504 20130101;
Y02C 10/06 20130101; Y02C 20/40 20200801; Y02E 20/32 20130101; F01K
7/025 20130101; Y02C 10/04 20130101; B01D 53/62 20130101; F22B
37/008 20130101; B01D 53/1425 20130101; F01K 17/06 20130101; B01D
2251/80 20130101 |
Class at
Publication: |
60/648 ; 60/653;
60/649 |
International
Class: |
F01K 7/38 20060101
F01K007/38; F01K 7/16 20060101 F01K007/16; F01K 17/00 20060101
F01K017/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2009 |
JP |
P2009-129068 |
Claims
1. A steam turbine power plant, comprising: a steam turbine system,
the steam turbine system comprises: a boiler comprising a
superheater; a first steam turbine into which main steam is
introduced from the superheater of the boiler; a reheater which
reheats the steam discharged fluid the first steam turbine; a
second steam turbine into which the steam reheated by the reheater
is introduced; a third steam turbine into which the steam
discharged from the second steam turbine is introduced; a first
electric generator which is driven by the third steam turbine; a
condenser which condensates the steam discharged from the third
steam turbine into a condensate; a feed water heater which heats
the condensate to introduce into the boiler as feed water and a
fourth steam turbine into which part of the steam discharged from
the first steam turbine is introduced, and a carbon dioxide
recovery system, the carbon dioxide recovery system comprises: an
absorption tower which absorbs the carbon dioxide contained in
combustion gas from the boiler by an absorption liquid; a
regeneration tower which separates the carbon dioxide from the
absorption liquid by heating the absorption liquid having absorbed
the carbon dioxide by the steam discharged from the fourth steam
turbine; and a recovery apparatus which recovers the carbon dioxide
separated by the regeneration tower.
2. The steam turbine power plant according to claim 1, wherein the
second steam turbine is composed of two steam turbines, one of the
two steam turbines is introduced with the steam obtained by
reheating by the reheater the steam discharged from the first steam
turbine, the other of the two steam turbines is introduced with the
steam obtained by reheating by the reheater the steam discharged
from the one of the two steam turbines, and the steam discharged
from the other of the two steam turbines is introduced into the
third steam turbine.
3. The steam turbine power plant according to claim 1, further
comprising, a second electric generator which is driven by the
fourth steam turbine.
4. The steam turbine power plant according to claim 1, wherein the
steam extracted from the fourth steam turbine is guided to the feed
water heater.
5. The steam turbine power plant according to claim 1, further
comprising, a pressure regulating valve which adjusts the pressure
of the steam discharged from the fourth steam turbine.
6. The steam turbine power plant according to claim 1, further
comprising, a flow rate regulating valve which introduces part of
the steam discharged from the second steam turbine into a
predetermined stage of the fourth steam turbine while adjusting the
flow rate.
7. The steam turbine power plant according to claim 2, further
comprising, a flow rate regulating valve which introduces part of
the steam discharged from the one of the two steam turbines into a
predetermined stage of the fourth steam turbine while adjusting the
flow rate.
8. The steam turbine power plant according to claim 1, further
comprising, a flow rate regulating valve which adjusts the flow
rate of the steam, which is discharged from the fourth steam
turbine and used to heat the absorption liquid in the regeneration
tower based on the temperature of the absorption liquid in the
regeneration tower.
9. The steam turbine power plant according to claim 1, further
comprising, a flow rate regulating valve which adjusts the flow
rate of the steam, which is discharged from the fourth steam
turbine and used to heat the absorption liquid in the regeneration
tower based on the flow rate of the absorption liquid in the
regeneration tower.
10. An operation method of a steam turbine power plant comprising:
a boiler having a superheater and a reheater; a first steam turbine
which is driven by steam introduced form the superheater of the
boiler and discharges the steam to the reheater; a second steam
turbine which is driven by the steam from the reheater; a third
steam turbine which is driven by the steam discharged from the
second steam turbine; a fourth steam turbine which is driven by
part of the steam discharged from the first steam turbine; a
condenser which condensates the steam discharged from the third
steam turbine into a condensate; a feed water heater which is
disposed on a feed water system between the condenser and the
boiler and heats the feed water guided from the condenser; an
absorption tower which has combustion gas guided into it from the
boiler and an absorption liquid supplied into it and which absorbs
the carbon dioxide contained in the combustion gas by the
absorption liquid; and a regeneration tower which diffuses the
absorbed carbon dioxide by heating the absorption liquid having
absorbed the carbon dioxide in the absorption tower, wherein the
steam extracted from the fourth steam turbine is used as a heat
source for the feed water by the feed water heater, and the steam
discharged from the fourth steam turbine is used as a heat source
for heating the absorption liquid in the regeneration tower.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2009-129068
filed on May 28, 2009; the entire contents of which are
incorporated herein by reference.
FIELD
[0002] Embodiments described herein relates generally to a steam
turbine power plant comprising a steam turbine, a boiler, a turbine
generator and the like and an operation method thereof, more
particularly to a steam turbine power plant provided with an
apparatus which increases a steam temperature to improve power
generation efficiency and separates CO.sub.2 contained in the
combustion gas exhausted from the boiler to recover it, and an
operation method thereof.
BACKGROUND
[0003] Since a conventional steam turbine power plant has steam
temperature conditions including 600.degree. C. or below, the
configuration members, such as a turbine rotor, a rotor blade, a
nozzle and the like which are exposed to high temperatures, are
made of a ferritic heat-resistant steel having outstanding
productivity and economical efficiency. On the other hand, carbon
steel has been used for materials configuring, for example, a feed
water heater which is not exposed to high temperatures.
[0004] Meanwhile, the provision of high efficiency to the steam
turbine power plant is being performed vigorously in view of fuel
saving and environmental protection in these years. For example, a
steam turbine using high-temperature steam at a temperature of
about 600.degree. C. (620.degree. C. or below) is being operated.
The steam turbine using such high-temperature steam has quite a few
parts which cannot satisfy the demanded properties by the various
properties of the ferritic heat-resistant steels. Therefore, there
are used austenitic heat-resistant steels or the like more
excelling in high-temperature properties. But, the use of the
austenitic heat-resistant steels increases the facility cost. In
addition, since the austenitic heat-resistant steels have a low
thermal conductivity and a large coefficient of linear expansion in
comparison with those of the ferritic heat-resistant steels, there
is a problem that a thermal stress tends to occur at the time of a
change in load when the plant is activated or stopped.
[0005] In addition, a 700.degree. C. advanced ultra-supercritical
pressure power-generation system having a steam temperature of
700.degree. C. or higher, so-called A-USC (Advanced
Ultra-Supercritical.), is now being considered. When the steam
turbine has an inlet steam temperature of 650.degree. C. or higher,
there is caused a portion where a turbine extraction steam exceeds
580.degree. C., and it is necessary to use the heat-resistant steel
for the feed water heater which heats by the extraction steam. But,
the introduction of the turbine extraction steam exceeding
580.degree. C. into the feed water heater is not preferable in view
of a thermal stress generated in proportion to a difference between
the feed-water temperature and the extraction steam temperature. To
prevent it, there is proposed a cycle that part of the steam
discharged from the high-pressure turbine is introduced once into a
back-pressure extraction turbine to take out a work, and the steam
extracted from the back-pressure extraction turbine and having a
lowered pressure and temperature is supplied to the feed water
heater. This back-pressure extraction turbine is conventionally in
direct connection with a water feed pump to drive it.
[0006] And, the greenhouse effect due to carbon dioxide (CO.sub.2)
is being pointed out as one of causes of the global warming
phenomenon. Therefore, a method of recovering carbon dioxide from
the combustion exhaust gas by contacting the combustion exhaust gas
to an absorption liquid has been studied vigorously for a thermal
power plant using, for example, a large amount of fossil fuel.
[0007] FIG. 8 is a diagram showing one example of a conventional
carbon dioxide recovery system 300 which recovers carbon dioxide by
removing it from the combustion exhaust gas.
[0008] In the conventional carbon dioxide recovery system 300 shown
in FIG. 8, for example, the combustion exhaust gas discharged by
burning a fossil fuel in a boiler is guided through a combustion
exhaust gas supply port 311 into an absorption tower 310. An
absorption liquid 320 which absorbs the carbon dioxide is supplied
to an upper part of the absorption tower 310, and the supplied
absorption on liquid 320 comes into gas-liquid contact with the
introduced combustion exhaust gas to absorb the carbon dioxide
contained in the combustion exhaust gas.
[0009] The absorption liquid 320 which has absorbed the carbon
dioxide is guided through the bottom of the absorption tower 310 to
a regeneration tower 350 via a heat exchanger 340 by an absorption
liquid circulating pump 330. The absorption liquid 320 having
absorbed the carbon dioxide has a temperature which becomes higher
than that of the absorption liquid 320, which has not absorbed the
carbon dioxide, by the reaction heat due to the absorption and the
sensible heat possessed by the combustion exhaust gas.
[0010] Meanwhile, the combustion exhaust gas from which the
absorption liquid 320 has absorbed the carbon dioxide is released
into the atmosphere through the top of the absorption tower
310.
[0011] The absorption liquid 320 guided to the regeneration tower
350 is heated by a reboiler 360 to diffuse the absorbed carbon
dioxide and regenerated into the absorption liquid 320 capable of
absorbing the carbon dioxide again. The regenerated absorption
liquid 320 is returned to the upper part of the absorption tower
310 by an absorption liquid circulating pump 331 via the heat
exchanger 340.
[0012] Meanwhile, the carbon dioxide diffused from the absorption
liquid 320 is guided to a steam separator 370 via a cooler 341 to
remove moisture, and the resultant is guided to and recovered by a
carbon dioxide compressor 380. And, the condensed water separated
by the steam separator 370 is guided to the regeneration tower 350.
As the heat source for the reboiler 360, the steam extracted from
the steam turbine cycle in the thermal power plant or the like is
mainly used as described in, for example, JP-B2 2809381 (Patent
Registration) and JP-A 2004-323339 (KOKAI), but carbon dioxide gas
increased to a high temperature in the process of compressing the
carbon dioxide can also be used.
[0013] For example, JP-A 2004-323339 (KOKAI) discloses a technology
that part of the steam discharged from the high-pressure turbine is
introduced into the back-pressure turbine for driving the carbon
dioxide compressor, part of the steam discharged from the
intermediate-pressure turbine is introduced into the back-pressure
turbine for driving an auxiliary machine (e.g., for driving the
water feed pump), and the steam discharged from the individual
steam turbines is used for heating the carbon dioxide recovery
system.
[0014] The conventional back-pressure extraction turbine which
introduces part of the steam discharged from the high-pressure
turbine as a working steam had been applied as a drive source for a
water feed pump in order to improve the cycle efficiency. Each
extraction steam pressure in this back-pressure extraction turbine
is substantially proportional to the steam flow rate which results
from sequential subtraction of each extraction steam flow rate
(about 3-5% of the feed water flow rate), which is to the feed
water heater, from the working steam flow rate after the extraction
stage of the back-pressure extraction turbine, namely a drive steam
flow rate (about 15 of the feed water flow rate) appropriate to the
power of the water feed pump, so that it has a drawback that it is
easily variable and its operability is low. Therefore, the steam
extracted in the back-pressure extraction turbine is not adopted as
the steam for heating in the feed water heater recently.
[0015] In the above-described carbon dioxide recovery system, part
of the steam discharged from the high-pressure turbine is
introduced into the hack-pressure turbine for driving the carbon
dioxide compressor, part of the steam discharged from the
intermediate-pressure turbine is introduced into the back-pressure
turbine for driving the auxiliary machine, and the steam discharged
from the back-pressure turbines is used as the steam for heating
the absorption liquid, but a total of drive steam flow rates
necessary for the carbon dioxide compressor and the auxiliary
machine does not necessarily agree with the heating steam flow rate
necessary for the carbon dioxide recovery system. Therefore, when
the drive steam flow rate is higher than the necessary steam flow
rate, excess steam is discarded into the condenser or the like. In
this case, an energy loss is caused because steam having high
energy is directly supplied to the carbon dioxide recovery
system.
[0016] In the conventional carbon dioxide recovery system, carbon
dioxide must be recovered by separating it from the absorption
liquid having absorbed the carbon dioxide contained in the
combustion exhaust gas by a certain method. For the separation of
the carbon dioxide, heating of the absorption liquid is the
simplest way, so that a heat diffusion method has been adopted
conventionally. But, since a heat quantity used for separation of
the carbon dioxide is large, it is said that the power generation
efficiency drops by about 30% in a relative value when the steam in
the steam turbine cycle is extracted.
[0017] For example, when an amine based absorption liquid having
high carbon dioxide absorption performance is used as an absorption
liquid, a temperature to separate the carbon dioxide by heating the
carbon dioxide-absorbed absorption liquid is about 100-150.degree.
C. It is said that the heat quantity required here is 2.5-3.5
MJ/(kg-CO.sub.2), namely 2.5-3.5 MJ/kg of carbon dioxide. For
example, this heat quantity corresponds to about 10-20% of the
heating value of coal when the coal is used as a boiler fuel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The embodiments are described with reference to the
drawings, which are provided for illustration only and do not limit
the present invention in any respect.
[0019] FIG. 1 is a diagram showing an overview of the steam turbine
power plant according to a first embodiment of the invention.
[0020] FIG. 2 is a diagram showing an overview of a carbon dioxide
recovery system of the steam turbine power plant according to the
first embodiment of the invention.
[0021] FIG. 3 is a diagram showing a T-s curve (temperature-entropy
curve) of a steam condition change in the steam turbine power plant
according to the first embodiment of the invention.
[0022] FIG. 4 is a diagram showing an overview of the steam turbine
power plant according to a second embodiment of the invention.
[0023] FIG. 5 is a diagram showing a T-s curve (temperature-entropy
curve) of a steam condition change in the steam turbine power plant
according to the second embodiment of the invention.
[0024] FIG. 6 is a diagram showing an overview of the steam turbine
power plant according to a third embodiment of the invention.
[0025] FIG. 7 is a diagram showing a T-s curve (temperature-entropy
curve) of a steam condition change in the steam turbine power plant
according to the third embodiment of the invention.
[0026] FIG. 8 is a diagram showing one example of a conventional
carbon dioxide recovery system which recovers carbon dioxide by
removing it from a combustion exhaust gas.
DETAILED DESCRIPTION
[0027] The embodiments provide a steam turbine power plant and an
operation method thereof to suppress an energy loss and to obtain
high power generation efficiency by using, as an energy source
necessary for a carbon dioxide recovery system, the discharged
steam having low exergy after generating electricity by a
back-pressure turbine.
[0028] According to an aspect of the embodiments, there is provided
a steam turbine system, the steam turbine system comprises a boiler
comprising a superheater; a first steam turbine into which main
steam is introduced from the superheater of the boiler; a reheater
which reheats the steam discharged from the first steam turbine; a
second steam turbine into which the steam reheated by the reheater
is introduced; a third steam turbine into which the steam
discharged from the second steam turbine is introduced; a first
electric generator which is driven by the third steam turbine; a
condenser which condensates the steam discharged from the third
steam turbine into a condensate; a feed water heater which heats
the condensate to introduce into the boiler as feed water and a
fourth steam turbine into which part of the steam discharged from
the first steam turbine is introduced, and a carbon dioxide
recovery system, the carbon dioxide recovery system comprises an
absorption tower which absorbs the carbon dioxide contained in
combustion gas from the boiler by an absorption liquid; a
regeneration tower which separates the carbon dioxide from the
absorption liquid by heating the absorption liquid having absorbed
the carbon dioxide by the steam discharged from the fourth steam
turbine; and a recovery apparatus which recovers the carbon dioxide
separated by the regeneration tower.
[0029] According to another aspect of the embodiments, there is
provided an operation method of a steam turbine power plant
comprising a boiler having a superheater and a reheater, a first
steam turbine which is driven by steam introduced form the
superheater of the boiler and discharges the steam to the repeater,
a second steam turbine which is driven by the steam from the
repeater, a third steam turbine which is driven by the steam
discharged from the second steam turbine, a fourth steam turbine
which is driven by part of the steam discharged from the first
steam turbine, a condenser which condensates the steam discharged
from the third steam turbine into a condensate, a feed water heater
which is disposed on a feed water system between the condenser and
the boiler and heats the feed water guided from the condenser, an
absorption tower which has combustion gas guided into it from the
boiler and an absorption liquid supplied into it and which absorbs
the carbon dioxide contained in the combustion gas by the
absorption liquid, and a regeneration tower which diffuses the
absorbed carbon dioxide by heating the absorption liquid having
absorbed the carbon dioxide in the absorption tower, wherein the
steam extracted from the fourth steam turbine is used as a heat
source for the feed water by the feed water heater, and the steam
discharged from the fourth steam turbine is used as a heat source
for heating the absorption liquid in the regeneration tower.
[0030] Detailed embodiments will be described below with reference
to the drawings.
First Embodiment
[0031] FIG. 1 is a diagram showing an overview of a steam turbine
power plant 10 according to a first embodiment of the
invention.
[0032] The steam turbine power plant 10 of the first embodiment is
provided with a steam turbine system 20 which generates electricity
by driving a steam turbine by steam from a boiler 21 or the like
which generates the steam by utilizing combustion heat, and a
carbon dioxide recovery system 50 which recovers the carbon dioxide
contained in the combustion gas from the boiler 21 or the like.
[0033] First, the steam turbine system 20 is described below.
[0034] As shown in FIG. 1, the steam turbine system 20 is provided
with the boiler 21, a superheater 21a disposed within the boiler
21, a high-pressure turbine 22 which functions as a first steam
turbine, a reheater 23, an intermediate-pressure turbine 24 which
functions as a second steam turbine, a low-pressure turbine 25
which functions as a third steam turbine, an electric generator 26
for the low-pressure turbine 25, a back-pressure turbine 27 which
functions as a fourth steam turbine, a condenser 28, a condensate
pump 29, a gland steam condenser 30, a low-pressure feed water
heater 31, a deaerator 32, a boiler feed pump 33, and a
high-pressure feed water heater 34. Here, the reheater 23 is also
disposed together with the superheater 21a within the boiler
21.
[0035] The back-pressure turbine 27 is provided with an electric
generator 35 for the back-pressure turbine 27. Part of the steam
discharged from the back-pressure turbine 27 is supplied to the
carbon dioxide recovery system 50.
[0036] In this steam turbine system 20, the high-temperature steam
generated by the superheater 21a of the boiler is introduced into
the high-pressure turbine 22 to perform en expansion work and then
introduced into the reheater 23. Here, the temperature of the steam
introduced from the superheater 21a into the high-pressure turbine
22 is preferably determined to be 650.degree. C. or higher in view
of improvement of the power generation efficiency. For example,
steam having a temperature of about 700.degree. C. or higher can
also be introduced into the high-pressure turbine 22.
[0037] The steam heated by the reheater 23 to become a
high-temperature steam again is introduced into the
intermediate-pressure turbine 24 to perform an expansion work and
then introduced into the low-pressure turbine 25. Here, the
temperature of the steam which is heated by the reheater 23 and
introduced into the intermediate-pressure turbine 24 is preferably
determined to be 650.degree. C. or higher in view of the
improvement of the power generation efficiency. Similar to the
high-pressure turbine 22, high-temperature steam of, for example,
about 700.degree. C. or higher can also be introduced into the
intermediate-pressure turbine 24. And, part of the steam discharged
from the intermediate-pressure turbine 24 may also be introduced
into the deaerator 32 to provide a heat source necessary for the
deaerator 32.
[0038] The steam introduced into the low-pressure turbine 25 and
performed the expansion work is introduced into the condenser 28 to
become a condensate. The steam extracted from the low-pressure
turbine 25 is guided to the low-pressure feed water heater 31 to
heat the feed water. And, the low-pressure turbine 25 drives the
electric generator 26 to generate electricity.
[0039] The condensate in the condenser 28 is sent by the condensate
pump 29 to the gland steam condenser 30, the low-pressure feed
water heater 31 and the deaerator 32, has its pressure increased by
the boiler feed pump 33 and is fed to the boiler 21 via the
high-pressure feed water heater 34.
[0040] Part of the steam having performed the expansion work in the
high-pressure turbine 22 is introduced into the back-pressure
turbine 27. To guide the part of the steam discharged from the
high-pressure turbine 22 to the back-pressure turbine 27, a pipe 41
is disposed to branch from a pipe 40 for guiding the steam
discharged from the high-pressure turbine 22 to the reheater 23.
The steam guided to the back-pressure turbine 27 performs the
expansion work and its part is supplied to the carbon dioxide
recovery system 50 through a pipe 42, and its remaining is guided
to the low-pressure feed water heater 31 together with the steam
extracted from the low-pressure turbine 25 through a pipe 43
branched from the pipe 42.
[0041] The steam extracted from the back-pressure turbine 27 is
guided to the high-pressure feed water heater 34 to heat the feed
water. And, the back-pressure turbine 27 drives the electric
generator 35 to generate electricity.
[0042] Part of the steam having performed the expansion work in the
high-pressure turbine 22 is supplied to the high-pressure feed
water heater 34 to heat the feed water.
[0043] For example, when the main steam introduced into the
high-pressure turbine 22 has a temperature of about 700.degree. C.,
the steam having performed the expansion work in the high-pressure
turbine 22 and having a temperature of about 590.degree.
C.-620.degree. C. can be introduced into the back-pressure turbine
27. Therefore, since the steam extracted from the back-pressure
turbine 27 can be made to have a temperature of 580.degree. C. or
below, the same material as the material such as carbon steel which
has been used conventionally can be used as a material forming the
steam extraction pipe between the back-pressure turbine 27 and the
high-pressure feed water heater 34 and the high-pressure feed water
heater 34. And, it is possible to prevent an increase of thermal
stress which results from a difference between the temperature of
the feed water flowing through the high-pressure feed water heater
34 and that of the extraction steam guided to the high-pressure
feed water heater 34.
[0044] When the steam having performed the expansion work in the
high-pressure turbine 22 and having a temperature of about
590.degree. C.-620.degree. C. is introduced into the high-pressure
feed water heater 34, it is desirable to dispose, for example, a
heat exchanger (not shown) which can perform heat exchange between
the feed water flowing through the pipe between the high-pressure
feed water heater 34 and the boiler 21 and the steam flowing
through the pipe which guides the steam discharged from the
high-pressure turbine 22 to the high-pressure feed water heater 34.
Thus, the temperature of the steam introduced into the
high-pressure feed water heater 34 can be determined to be
580.degree. C. or below.
[0045] Here, the pipe 41 is provided with a flow rate regulating
valve V1 for adjusting the flow rate of the steam guided to the
back-pressure turbine 27. The pipe 43 is provided with a pressure
regulating valve V2 for adjusting the pressure of the steam
discharged from the back-pressure turbine 27. The pipe 42 is
provided with a steam flow rate detector F1 for detecting
information on the flow rate of the steam flowing through the pipe
42. And, the pipe 42 is provided with a steam temperature detector
T1 for detecting information on the temperature of the steam
flowing through the pipe 42.
[0046] Detection information from the steam flow rate detector F1
and the steam temperature detector T1 is outputted to an unshown
control device. And, the control device is disposed to be capable
of controlling the flow rate regulating valve V1 and the pressure
regulating valve V2, and adjusts the opening/closing and the
opening degree of the flow rate regulating valve V1 and the
pressure regulating valve V2 based on the detection information
from the steam flow rate detector F1 and the steam temperature
detector T1. For example, the control device controls the flow rate
regulating valve V1 based on the detection information from the
steam flow rate detector F1 and controls the pressure regulating
valve V2 based on the detection information from the steam
temperature detector T1. Thus, the provision of the detector, the
regulating valves and the control device allows controlling
appropriately the flow rate and temperature of the steam introduced
into the carbon dioxide recovery system 50 through the pipe 42.
[0047] And, the temperature of the steam introduced into the carbon
dioxide recovery system 50 must be controlled to a predetermined
temperature. The flow rate regulating valve V1 and the pressure
regulating valve V2 are adjusted, and feedback control is performed
based on the detection information from the steam flow rate
detector F1 and the steam temperature detector T1, so that the
temperature of the steam discharged from the back-pressure turbine
27, namely the temperature of the steam introduced into the carbon
dioxide recovery system 50, can be controlled to a predetermined
temperature. Specifically, when the temperature of the steam
discharged from the back-pressure turbine 27 is lower than the
temperature of the steam required by the carbon dioxide recovery
system 50, the pressure of the steam discharged from the
back-pressure turbine 27 is raised by closing the pressure
regulating valve V2. Thus, the temperature of the steam discharged
from the back-pressure turbine 27 can be raised to become closer to
a predetermined temperature. If it is necessary to make fine
adjustment of the temperature, the temperature may be adjusted by,
for example, cooling a part of the pipe 42 by spraying water or the
like. When the flow rate of the steam introduced into the carbon
dioxide recovery system 50 is lower than a predetermined flow rate,
it can be made closer to the predetermined flow rate by increasing
an opening degree of the flow rate regulating valve V1.
[0048] One example of adjusting the flow rate regulating valve V1
and the pressure regulating valve V2 based on the temperature of
the steam introduced into the carbon dioxide recovery system 50 was
described above, but for example, the flow rate regulating valve V1
and the pressure regulating valve V2 may be adjusted based on the
temperature of the absorption liquid in the regeneration tower of
the carbon dioxide recovery system 50 described later. Thus, a time
delay for appropriate control can be decreased by adjusting the
flow rate regulating valve V1 and the pressure regulating valve V2
based on the temperature of the absorption liquid. For
stabilization of the control, the flow rate regulating valve V1 and
the pressure regulating valve V2 may be controlled with the flow
rate of the absorption liquid determined as a function.
[0049] Here, power generation output of the steam turbine power
plant 10 is controlled by a steam control valve (not shown) which
adjusts the flow rate of the main steam introduced into the
high-pressure turbine 22 such that a total output of the electric
generator 26 for the low-pressure turbine 25 and the electric
generator 35 for the back-pressure turbine 27 meets a target
output.
[0050] The carbon dioxide recovery system 50 is described
below.
[0051] FIG. 2 is a diagram showing an overview of the carbon
dioxide recovery system 50 of the steam turbine power plant 10
according to the first embodiment of the invention.
[0052] As shown in FIG. 2, the carbon dioxide recovery system 50 is
provided with an absorption tower 60, a regeneration tower 70, and
a carbon dioxide recovery apparatus 80.
[0053] The absorption tower 60 is a tower for absorbing the carbon
dioxide contained in the combustion gas by an absorption liquid 90
by introducing the combustion gas discharged from the boiler 21 and
the reheater 23, and making gas-liquid contact of the absorption
liquid 90 with the combustion gas.
[0054] The regeneration tower 70 is a tower to separate the carbon
dioxide from the absorption liquid 90 by heating the absorption
liquid 90 which has absorbed the carbon dioxide in the absorption
tower 60 by the heat of the steam discharged from the back-pressure
turbine 27.
[0055] The carbon dioxide recovery apparatus 80 is an apparatus for
recovering the carbon dioxide separated by the regeneration tower
70. The carbon dioxide recovery apparatus 80 is configured of, for
example, a compression recovery apparatus which compresses the
separated carbon dioxide to recover it.
[0056] Here, any liquid can be used as the absorption liquid if it
can absorb carbon dioxide and diffuse it under prescribed
conditions and, for example, an amine based aqueous solution can be
used. Specifically, examples of the amine based aqueous solution
include an aqueous solution of any one of alkanolamines such as
monoethanolamine, diethanolamine, triethanolamine,
methyldiethanolamine, diisopropanolamine, diglycolamine and the
like, or an aqueous solution of a mixture of two or more of
them.
[0057] In the above-described carbon dioxide recovery system 50,
for example, the combustion exhaust gas discharged by burning a
fossil fuel in the boiler 21 and the reheater 23 is guided into the
absorption tower 60 through a combustion exhaust gas supply port
61. The absorption liquid 90 which absorbs the carbon dioxide is
supplied to the upper part of the absorption tower 60. For example,
the supplied absorption liquid 90 is sprayed downward to make
gas-liquid contact with the introduced combustion exhaust gas to
absorb the carbon dioxide contained in the combustion exhaust
gas.
[0058] The absorption liquid 90 which has absorbed the carbon
dioxide is guided through the bottom of the absorption tower 60 to
the regeneration tower 70 via a heat exchanger 110 by an absorption
liquid circulating pump 100. The absorption liquid 90 which is
flowing through the heat exchanger 110 is heated by the absorption
liquid 90 which is guided from the regeneration tower 70 to the
absorption tower 60. The absorption liquid 90 which has absorbed
the carbon dioxide has a temperature which becomes higher than that
of the absorption liquid 90, which has not absorbed the carbon
dioxide, by the reaction heat by the absorption and the sensible
heat possessed by the combustion exhaust gas.
[0059] Meanwhile, the combustion exhaust gas from which the carbon
dioxide has been absorbed by the absorption liquid 90 is released
into the atmosphere from the top of the absorption tower 60.
[0060] The absorption liquid 90 guided to the regeneration tower 70
is heated by a reboiler 120 to diffuse the absorbed carbon dioxide
and regenerated into the absorption liquid 90 capable of absorbing
the carbon dioxide again. The steam discharged from the back
pressure turbine 27 is introduced into the reboiler 120 through the
pipe 42. The absorption liquid 90 having absorbed the carbon
dioxide is heated by the steam discharged from the back-pressure
turbine 27.
[0061] Here, the temperature of the steam discharged from the
back-pressure turbine 27 and introduced into the reboiler 120 is
set to a predetermined temperature under control by the
above-described steam turbine system 20. Therefore, the
predetermined temperature is a temperature necessary to heat the
absorption liquid 90 to a temperature that the carbon dioxide can
be diffused effectively in the regeneration tower 70, and it is
appropriately set in correspondence with the used absorption liquid
90. For example, when the above-described amine based aqueous
solution is used as the absorption liquid 90, the temperature that
the carbon dioxide can be diffused effectively is in a range of 100
to 120.degree. C. In other words, it is adequate if a heat quantity
capable of raising the temperature of the absorption liquid 90
introduced into the regeneration tower 70 to 100-120.degree. C. can
be applied to the absorption liquid 90 by the reboiler 120. Namely,
the predetermined temperature of the steam introduced into the
carbon dioxide recovery system 50 is variable depending on the flow
rate of the heated absorption liquid 90 or the flow rate of the
steam introduced into the reboiler 120, but it is preferable that
the temperature is set to about 130-150.degree. C. in view of the
above flow rates.
[0062] The steam, which is caused to discharge heat to the
absorption liquid 90 by the reboiler 120, is guided to the
condenser 28 to become a condensate as shown in FIG. 1.
[0063] The absorption liquid 90, which has diffused the carbon
dioxide and is regenerated, is returned to the upper part of the
absorption tower 60 again via the heat exchanger 110 by an
absorption liquid circulating pump 101. Here, the absorption liquid
90 passes through the heat exchanger 110 and simultaneously heats
the absorption liquid 90 guided from the absorption tower 60 to the
regeneration tower 70. Thus, the temperature of the absorption
liquid 90 returned to the absorption tower 60 is determined to be a
temperature lower than the temperature in the regeneration tower 70
and suitable for absorption of the carbon dioxide in the combustion
exhaust gas in the absorption tower 60. In other words, the heat
exchanger 110 is a regenerative heat exchanger which regenerates
the heat of the regenerated absorption liquid 90, which is supplied
from the regeneration tower 70 by the absorption liquid circulating
pump 101 and has a relatively high temperature, into the absorption
liquid 90 having absorbed the carbon dioxide requiring heating to
diffuse the absorbed carbon dioxide which is supplied from the
bottom of the absorption tower 60 via the absorption liquid
circulating pump 100 and has a relatively low temperature.
[0064] Meanwhile, the carbon dioxide diffused from the absorption
liquid 90 in the regeneration tower 70 is guided to a steam
separator 130 via a cooler 111 to remove moisture, and the
resultant is guided to and recovered by the carbon dioxide recovery
apparatus 80. And, the condensed water separated by the steam
separator 130 is guided to the regeneration tower 70.
[0065] The absorption liquid circulating pump 100, the absorption
liquid circulating pump 101, the carbon dioxide recovery apparatus
80 and the like are controlled by the above-described control
device (not shown).
[0066] The cycle efficiency of the steam turbine power plant 10 of
the first embodiment is described below.
[0067] FIG. 3 is a diagram showing a T-s curve (temperature-entropy
curve) of a steam condition change in the steam turbine power plant
10 according to the first embodiment of the invention. FIG. 3 also
shows a condition change in a conventional one stage reheat cycle
for comparison. There is shown an example that the temperature of
the steam introduced into the high-pressure turbine 22 in the steam
turbine power plant 10 according to the first embodiment is
determined to be 650.degree. C., and the temperature of the steam
introduced into the high-pressure turbine in a conventional steam
turbine power plant is determined to be 620.degree. C. It is
assumed in FIG. 3 that the expansion process in each turbine is
adiabatic expansion.
[0068] In the conventional steam turbine power plant, it is
indicated that 6.fwdarw.1 is isobaric heating by the boiler 21,
1.fwdarw.2 is adiabatic expansion by the high-pressure turbine,
2.fwdarw.3 is isobaric reheating by the reheater, and 3.fwdarw.4 is
adiabatic expansion by the intermediate-pressure turbine and the
low-pressure turbine. And, it is indicated that 4.fwdarw.5 is
isothermal condensation by the condenser, and 5.fwdarw.6 is a
pressure increase and a temperature increase by the water feed pump
and the feed water heater.
[0069] Meanwhile, in the steam turbine power plant 10 of the first
embodiment, the temperature of the steam introduced into the
high-pressure turbine 22 is higher than the temperature of the
steam introduced into the high-pressure turbine of the conventional
steam turbine power plant, so that the adiabatic expansion by the
high-pressure turbine 22 becomes 1a.fwdarw.2a. And, the adiabatic
expansion by the intermediate-pressure turbine 24 and the
low-pressure turbine 25 becomes 3a.fwdarw.4a.
[0070] In FIG. 3, the area (area of the shaded portion in FIG. 3)
surrounded by a steam condition value higher than the conventional
steam condition value is an increase in energy which can be taken
out as a work, namely an extent of a contribution to efficiency
improvement by an increase in temperature.
[0071] The adiabatic expansion by the back-pressure turbine 27 is
indicated by 2a.fwdarw.7, and the temperature of the steam
discharged from the back-pressure turbine 27 is determined by
pressure Pex of the discharged steam. For example, when the
temperature of the steam discharged from the back-pressure turbine
27 is lower than the temperature (e.g., 150.degree. C.) of the
steam required by the carbon dioxide recovery system 50, the
pressure Pex of the steam discharged from the back-pressure turbine
27 is raised by closing the pressure regulating valve V2. Thus, the
temperature of the steam discharged from the back-pressure turbine
27 can be raised to become closer to a predetermined temperature.
When the flow rate of the steam introduced into the carbon dioxide
recovery system 50 is lower than a predetermined flow rate, it can
be made closer to the predetermined flow rate by increasing the
opening degree of the flow rate regulating valve V1.
[0072] At this time, the flow rate of the extraction steam from the
back-pressure turbine 27, which is supplied to the high-pressure
feed water heater 34, is controlled by the ability of the
high-pressure feed water heater 34 depending on a feed water flow
rate (substantially proportional to the boiler load) and an
extraction steam pressure and substantially proportional to the
feed water flow rate similar to the prior art. In other words, the
flow rate of the steam introduced into the back-pressure turbine 27
through the pipe 41 is a total of the flow rate of the steam
discharged from the back-pressure turbine 27 and the flow rate of
the extraction steam supplied to the high-pressure feed water
heater 34. This total flow rate is substantially proportional to
the feed water flow rate (boiler load).
[0073] Generally, the extraction steam flow rate is about 5% of the
feed water flow rate per stage of the feed water heater. For
example, when the steam extraction to the three stages of the
high-pressure feed water heater 34 is made as shown in FIG. 1 and
the flow rate of the steam introduced into the carbon dioxide
recovery system 50 is determined to be 40% of the feed water flow
rate, a steam flow rate of "40%+3stages.times.5%=55%" is introduced
into the back-pressure turbine 27. It is a steam flow rate
sufficient to overcome a variation or low operability of an
extraction steam pressure, which is proportional to a stage steam
flow rate and caused because the load of the conventional
back-pressure extraction turbine for driving the water feed pump
described above is small to about 2% (about 15% of the feed water
flow rate in terms of the drive steam flow rate) of the boiler
load. And, since the flow rate of the steam for driving the
back-pressure turbine 27 is substantially proportional to the feed
water flow rate (namely, substantially proportional to the boiler
load) in the steam turbine power plant 10 according to the first
embodiment, the extraction steam pressure is substantially
proportional to the boiler load. Therefore, the extraction steam
pressure has the same property as that of a change of the
extraction steam pressure of the normal steam turbine power plant,
and a problem of operability is not produced.
[0074] By the above-described control, the output of the electric
generator 35 for the back-pressure turbine 27 is controlled by
adjusting the flow rate regulating valve V1 and the pressure
regulating valve V2, and the output of the entire steam turbine
power plant 10 is determined by a total of the electric generator
26 for the low-pressure turbine and the electric generator 35 for
the back-pressure turbine 27. Therefore, it becomes possible to
obtain a predetermined output by controlling the flow rate of the
steam introduced into the high-pressure turbine by a steam control
valve (not shown) to control the output of the electric generators
26 and 35. The output of the electric generator 35 is substantially
proportional to that of the boiler load, so that it is also
substantially proportional to the output of the electric generator
26 and excellent in controllability.
[0075] In a case where the steam turbine power plant 10 is operated
with the steam introduced into the reboiler 120 blocked in order to
make the exchange of the absorption liquid 90 of the carbon dioxide
recovery apparatus 80, the flow rate regulating valve V1 is
controlled such that the output of the back-pressure turbine 27
becomes a minimum output capable of performing a stable operation
to adjust the flow rate of the steam introduced into the
back-pressure turbine 27. And, a shutoff valve (not shown) disposed
on the pipe 42 is closed to stop the steam from flowing into the
carbon dioxide recovery apparatus 80. In addition, it is controlled
to fully open the pressure regulating valve V2 to introduce the
total amount of the steam discharged from the back-pressure turbine
27 into the low-pressure feed water heater 31.
[0076] As described above, the steam turbine power plant 10
according to the first embodiment uses the steam discharged from
the high-pressure turbine 22 to drive the back-pressure turbine 27
and can generate electricity by driving the electric generator 35
disposed on the back-pressure turbine 27. In addition, as energy
necessary for the regeneration tower 70 of the carbon dioxide
recovery apparatus 80, it is possible to use the steam having low
exergy which has performed the expansion work by the back-pressure
turbine 27. Thus, an energy loss can be suppressed, and high power
generation efficiency can be obtained.
[0077] In addition, the steam extracted from the back-pressure
turbine 27 can be made to have a temperature of 580.degree. C. or
below. Therefore, as the material configuring the steam extraction
pipe between the back-pressure turbine 27 and the high-pressure
feed water heater 34 and the high-pressure feed water heater 34,
the same material as the material such as carbon steel which has
been used for them can be used. And, a thermal stress generated due
to a difference between the temperature of the feed water flowing
through the high-pressure feed water heater 34 and the temperature
of the extraction steam guided to the high-pressure feed water
heater 34 can be prevented from increasing.
Second Embodiment
[0078] FIG. 4 is a diagram showing an overview of a steam turbine
power plant 11 according to a second embodiment of the invention.
FIG. 5 is a diagram showing a T-s curve (temperature-entropy curve)
of a steam condition change in the steam turbine power plant 11
according to the second embodiment of the invention. FIG. 5 also
shows a condition change in a conventional one stage reheat cycle
for comparison. Like component parts corresponding to those of the
steam turbine power plant 10 of the first embodiment are denoted by
like reference numerals, and overlapped descriptions will be
omitted or simplified. It is assumed in FIG. 5 that the expansion
process in each turbine is adiabatic expansion in the same manner
as in FIG. 3.
[0079] The steam turbine power plant 11 of the second embodiment is
provided with the steam turbine system 20 which generates
electricity by driving the steam turbine by steam from the boiler
which generates the steam by utilizing the combustion heat, and the
carbon dioxide recovery system 50 which recovers the carbon dioxide
contained in the combustion gas from the boiler.
[0080] The steam turbine power plant 11 according to the second
embodiment of the invention has the same structure as that of the
steam turbine power plant 10 according to the first embodiment
except that a predetermined stage of the back-pressure turbine 27
of the steam turbine system 20 is provided with a structure that
part of the steam discharged from the intermediate-pressure turbine
24 is introduced. The different structure is mainly described
below. The structure of the carbon dioxide recovery apparatus 80 is
similar to that of the carbon dioxide recovery apparatus 80 in the
steam turbine power plant 10 according to the first embodiment.
[0081] It is assumed here that the temperature of the steam
introduced into the high-pressure turbine 22 is lower than
650.degree. C., the temperature of the steam discharged from the
high-pressure turbine 22 is lower than the temperature of the steam
discharged from the high-pressure turbine 22 of the steam turbine
power plant 10 of the above-described first embodiment, and a state
of the steam discharged from the back-pressure turbine 27 belongs
to a wet region (region below the saturated vapor line shown in
FIG. 5).
[0082] When the state of the steam discharged from the
back-pressure turbine 27 belongs to the wet region, there is a
problem such as erosion of the turbine last-stage blade, and the
reliability of the steam turbine decreases.
[0083] When the steam discharged from the back-pressure turbine 27
is in the wet region, the pressure of the steam discharged from the
back-pressure turbine 27 can be increased to make the steam
temperature higher than the saturated vapor temperature. But, when
the temperature of the steam discharged from the back-pressure
turbine 27 is made to be the temperature (e.g., 150.degree. C.) of
the steam necessary for the carbon dioxide recovery system 50, it
is necessary to make pressure reduction and temperature decrease of
the steam discharged from the back-pressure turbine 27, resulting
in an energy loss.
[0084] Accordingly, in the steam turbine power plant 11 according
to the second embodiment, part of the steam discharged from the
intermediate-pressure turbine 24 is introduced into a predetermined
stage of the back-pressure turbine 27 to raise the steam
temperature. Thus, the temperature of the steam discharged is
properly controlled.
[0085] The steam turbine power plant 11 according to the second
embodiment is provided with a pipe 45 which separates part of the
steam, which is discharged from the intermediate-pressure turbine
24, from a pipe 44 guiding to the deaerator 32 and guides to a
predetermined stage of the back-pressure turbine 27. And, the pipe
45 is provided with a flow rate regulating valve V3 for adjusting
the flow rate of the steam guided to the back-pressure turbine 27.
This flow rate regulating valve V3 is controlled by a control
device (not shown) based on the detection information from the
steam temperature detector T1 disposed on the pipe 42. And, the
pipe 42 is provided with a pressure detector P1 for detecting
information on the pressure within the pipe 42. The detection
information from the pressure detector P1 is outputted to the
control device. The pressure regulating valve V2 disposed on the
pipe 43 is controlled by a control device (not shown) based on the
detection information from the pressure detector P1.
[0086] The predetermined stage in the back-pressure turbine 27 with
which the pipe 45 is communicated is a stage that the pressure of
the stage with which the pipe 45 is communicated becomes lower than
that of the steam guided by the pipe 45. In other words, the pipe
45 is disposed to communicate with the stage such that the steam
flowing through the pipe 45 from the intermediate-pressure turbine
24 can flow into it without applying a pressure by a pressure
device or the like.
[0087] In the above-configured steam turbine power plant 11
according to the second embodiment, the pressure regulating valve
V2 is controlled such that the pressure of the steam discharged
from the back-pressure turbine 27 becomes constant (e.g., about 400
kPa). In addition, the flow rate regulating valve V3 is controlled
such that the temperature of the steam discharged from the
back-pressure turbine 27 becomes a predetermined temperature (e.g.,
150.degree. C.) required by the carbon dioxide recovery system 50.
And, the flow rate of the steam discharged from the back-pressure
turbine 27 is adjusted by the flow rate regulating valve V1 in the
same manner as in the steam turbine power plant 10 according to the
first embodiment. The output of the electric generator 35 for the
back-pressure turbine 27 can be adjusted by controlling the flow
rate regulating valve V1, the pressure regulating valve V2 and the
flow rate regulating valve V3. In addition, the output of the
entire steam turbine power plant 11 can be adjusted by controlling
the flow rate of the steam introduced into the high-pressure
turbine 22 by a steam control valve (not shown).
[0088] One example of adjusting the flow rate regulating valve V1,
the pressure regulating valve V2 and the flow rate regulating valve
V3 based on the temperature of the steam introduced into the carbon
dioxide recovery system 50 was described above. But the flow rate
regulating valve V1, the pressure regulating valve V2 and the flow
rate regulating valve V3 may be adjusted based on, for example, the
temperature of the absorption liquid 90 in the regeneration tower
70 of the carbon dioxide recovery system 50. Thus, the flow rate
regulating valve V1, the pressure regulating valve V2 and the flow
rate regulating valve V3 are adjusted based on the temperature of
the absorption liquid 90, so that a time delay for proper control
can be decreased. To stabilize the control, the flow rate
regulating valve V1, the pressure regulating valve V2 and the flow
rate regulating valve V3 can be controlled with the flow rate of
the absorption liquid 90 used as a function.
[0089] The cycle efficiency of the steam turbine power plant 11
according to the second embodiment is described below with
reference to FIG. 5.
[0090] The temperature (temperature at of the steam introduced into
the back-pressure turbine 27 in the steam turbine power plant 11
according to the second embodiment becomes lower than the
temperature (temperature at 2a in FIG. 3) of the steam introduced
into the back-pressure turbine 27 of the steam turbine power plant
10 according to the first embodiment because the temperature of the
steam introduced into the high-pressure turbine 22 is lower than
650.degree. C. And, it is presumed that the state of the steam
discharged from the back-pressure turbine 27 in the steam turbine
power plant 11 according to the second embodiment belongs to the
wet region (region below the saturated vapor line shown in FIG.
5).
[0091] Accordingly, in the steam turbine power plant 11 according
to the second embodiment, the flow rate regulating valve V3 is
adjusted to mix the steam discharged from the intermediate-pressure
turbine 24 into a turbine stage which is in the steam condition (7a
here) on the side having a higher temperature (upper than the
saturated vapor line in FIG. 5) than the saturated vapor line. The
temperature of the steam resulting from mixing of the steam is
determined to be a temperature of the steam condition shown at 7b
(mixed steam pressure Pm), and the temperature of the steam
discharged from the back-pressure turbine 27 is determined to be a
temperature of the steam condition shown at 7c. Thus, the condition
of the steam discharged from the back-pressure turbine 27 can be
determined to be in a steam condition on the side of higher
temperature (upper side than the saturated vapor line in FIG. 5)
than the saturated vapor line.
[0092] Thus, in addition to the action and effect of the steam
turbine power plant 10 according to the first embodiment, even when
the temperature of the steam introduced into the high-pressure
turbine 22 is lower than 650.degree. C. in the steam turbine power
plant 11 according to the second embodiment, the condition of the
steam discharged from the back-pressure turbine 27 can be
determined to be a condition of steam on the high-temperature side
(upper side than the saturated vapor line in FIG. 5) than the
saturated vapor line. Thus, the steam discharged from the
back-pressure turbine 27 can keep a condition of overheat steam.
Therefore, there can be obtained a steam turbine power plant having
high reliability free from a problem such as erosion of the turbine
last stage blade.
Third Embodiment
[0093] FIG. 6 is a diagram showing an overview of a steam turbine
power plant 12 according to a third embodiment of the invention.
Like component parts corresponding to those of the steam turbine
power plant 10 of the first embodiment are denoted by like
reference numerals, and overlapped descriptions will be omitted or
simplified.
[0094] The steam turbine power plant 12 according to the third
embodiment is provided with the steam turbine system 20 which
generates electricity by driving a steam turbine by steam from the
boiler 21 or the like which generates the steam by utilizing
combustion heat, and the carbon dioxide recovery system 50 which
recovers the carbon dioxide contained in the combustion gas from
the boiler 21 or the like.
[0095] First, the steam turbine system 20 is described below.
[0096] As shown in FIG. 6, the steam turbine system 20 is provided
with the boiler 21, the superheater 21a disposed within the boiler
21, a superhigh-pressure turbine 36 which functions as a first
steam turbine, the high-pressure turbine 22 which functions as one
steam turbine of a second steam turbine configured of two steam
turbines, reheaters 23a and 23b, the intermediate-pressure turbine
24 which functions as the other steam turbine of the second steam
turbine, the low-pressure turbine 25 which functions as the third
steam turbine, the electric generator 26 for the low-pressure
turbine 25, the back-pressure turbine 27 which functions as the
fourth steam turbine, the condenser 28, the condensate pump 29, the
gland steam condenser 30, the low-pressure feed water heater 31,
the deaerator 32, the boiler feed pump 33, and the high-pressure
feed water heater 34. Here, the reheaters 23a and 23b are also
disposed together with the superheater 21a within the boiler
21.
[0097] The back-pressure turbine 27 is provided with an electric
generator 35 for the back-pressure turbine 27. Part of the steam
discharged from the back-pressure turbine 27 is supplied to the
carbon dioxide recovery system 50.
[0098] In this steam turbine system 20, the high-temperature steam
generated by the superheater 21a of the boiler 21 is introduced
into the superhigh-pressure turbine 36 to perform the expansion
work and then introduced into the reheater 23a. Here, the
temperature of the steam introduced into the superhigh-pressure
turbine 36 is preferably determined to be 650.degree. C. or higher
in view of improvement of the power generation efficiency. For
example, steam having a temperature of about 700.degree. C. or
higher can also be introduced into the superhigh-pressure turbine
36.
[0099] The steam heated again by the reheater 23a to become a
high-temperature steam is introduced into the high-pressure turbine
22 to perform the expansion work and then introduced into the
reheater 23b.
[0100] The steam heated again by the reheater 23b to become a
high-temperature steam is introduced into the intermediate-pressure
turbine 24 to perform the expansion work and introduced into the
low-pressure turbine 25.
[0101] Here, at least one of the temperatures of the steam which is
heated by the reheaters 23a and 23b and introduced into the
high-pressure turbine 22 and the intermediate-pressure turbine 24
is preferably 650.degree. C. or higher in view of improvement of
the power generation efficiency. The temperatures of the steam
introduced from the reheaters 23a and 23b into the high-pressure
turbine 22 and the intermediate-pressure turbine 24 can also be
determined to be temperature of about 700.degree. C. or higher.
[0102] The steam introduced into the low-pressure turbine 25 and
performed the expansion work is guided into and becomes a
condensate in the condenser 28. The steam extracted from the
low-pressure turbine 25 is guided into the low-pressure feed water
heater 31 to heat the feed water. And, the low-pressure turbine 25
drives the electric generator 26 to generate electricity.
[0103] The condensate in the condenser 28 is sent by the is
condensate pomp 29 to the gland steam condenser 30, the
low-pressure feed water heater 31 and the deaerator 32, has its
pressure increased by the boiler feed pump 33, and is fed to the
boiler 21 via the high-pressure feed water heater 34.
[0104] Part of the steam having performed the expansion work in the
superhigh-pressure turbine 36 is introduced into the back-pressure
turbine 27. Therefore, a pipe 151 is disposed to branch from the
pipe 150 for guiding the steam discharged from the
superhigh-pressure turbine 36 to the reheater 23a to guide part of
the steam discharged from the superhigh-pressure turbine 36 to the
back-pressure turbine 27. The steam guided to the back-pressure
turbine 27 performs the expansion work and its part is supplied to
the carbon dioxide recovery system 50 through the pipe 42, and its
remaining is guided together with the steam extracted from the
above-described low-pressure turbine 25 to the low-pressure feed
water heater 31 through the pipe 43 branched from the pipe 42. And,
the part of the steam discharged from the back-pressure turbine 27
through a pipe 152 branched from the pipe 42 is guided to the
deaerator 32 and used as a heat source necessary for the deaerator
32.
[0105] Here, the steam introduced into the back-pressure turbine 27
has a temperature of about 590.degree. C. to 620.degree. C. The
steam extracted from the back-pressure turbine 27 is guided to the
high-pressure feed water heater 34 to heat the feed water. And, the
back-pressure turbine 27 drives the electric generator 35 to
generate electricity.
[0106] Part of the steam having performed the expansion work in the
sup high-pressure turbine 36 is supplied to the high-pressure feed
water heater 34 to heat the feed water.
[0107] For example, when the main steam introduced into the
superhigh-pressure turbine 36 has a temperature of about
700.degree. C., the steam having performed the expansion work in
the superhigh-pressure turbine 36 and having a temperature of about
590.degree. C. to 620.degree. C. can be introduced into the
back-pressure turbine 27. Therefore, since the steam extracted from
the back-pressure turbine 27 can be made to have a temperature of
580.degree. C. or below, the same material as the material such as
carbon steel which has been used conventionally can be used as a
material forming the steam extraction pipe between the
back-pressure turbine 27 and the high-pressure feed water heater 34
and the high-pressure feed water heater 34. And, it is possible to
prevent an increase of a thermal stress which results from a
difference between the temperature of the feed water flowing
through the high-pressure feed water heater 34 and that of the
extraction steam guided to the high-pressure feed water heater
34.
[0108] Generally, the temperature (temperature at 2a in FIG. 7
described later) of the steam discharged from the
superhigh-pressure turbine 36 of a two stage reheat cycle is higher
than the temperature (temperature at 2a in FIG. 3) of the steam
discharged from the high-pressure turbine 22 of the one stage
reheat cycle as described in, for example, the first embodiment.
Therefore, the temperature of the steam discharged from the
superhigh-pressure turbine 36 has a high possibility of exceeding
580.degree. C. When the temperature of the steam discharged from
the superhigh-pressure turbine 36 exceeds 580.degree. C., it is
preferable to dispose, for example, a heat exchanger 160 which can
perform heat exchange between the feed water flowing through the
pipe between the high-pressure feed water heater 34 and the boiler
21 and the steam flowing through the pipe guiding the steam
discharged from the superhigh-pressure turbine 36 to the
high-pressure feed water heater 34 as shown in FIG. 6. Thus, the
temperature of the steam introduced into the high-pressure feed
water heater 34 can be made to be 580.degree. C. or below.
[0109] Here, the pipe 151 is provided with the flow rate regulating
valve V1 for adjusting the flow rate of the steam guided to the
back-pressure turbine 27. The pipe 43 is provided with the pressure
regulating valve V2 for adjusting the pressure of the steam
discharged from the back-pressure turbine 27. The pipe 42 is
provided with the steam flow rate detector F1 for detecting
information on the flow rate of the steam flowing through the pipe
42. The pipe 42 is also provided with the steam temperature
detector T1 for detecting information on the temperature of the
steam flowing through the pipe 42.
[0110] Detection information from the steam flow rate detector F1
and the steam temperature detector T1 is outputted to an unshown
control device. And, the control device is disposed to be capable
of controlling the flow rate regulating valve V1 and the pressure
regulating valve V2 and adjusts the opening/closing and the opening
degree of the flow rate regulating valve V1 and the pressure
regulating valve V2 based on the detection information from the
steam flow rate detector F1 and the steam temperature detector T1.
For example, the control device controls the flow rate regulating
valve V1 based on the detection information from the steam flow
rate detector F1 and controls the pressure regulating valve V2
based on the detection information from the steam temperature
detector T1. Thus, the provision of the detector, the regulating
valves and the control device allows controlling appropriately the
flow rate and temperature of the steam introduced into the carbon
dioxide recovery system 50 through the pipe 42.
[0111] And, the temperature of the steam introduced into the carbon
dioxide recovery system 50 must be controlled to a predetermined
temperature. The flow rate regulating valve V1 and the pressure
regulating valve V2 are adjusted, and feedback control is performed
based on the detection information from the steam flow rate
detector F1 and the steam temperature detector T1, so that the
temperature of the steam discharged from the back-pressure turbine
27, namely the temperature of the steam introduced into the carbon
dioxide recovery system 50, can be controlled to a predetermined
temperature. Specifically, when the temperature of the steam
discharged from the back-pressure turbine 27 is lower than the
temperature of the steam required by the carbon dioxide recovery
system 50, the pressure of the steam discharged from the
back-pressure turbine 27 is raised by closing the pressure
regulating valve V2. Thus, the temperature of the steam discharged
from the back-pressure turbine 27 can be raised to become closer to
a predetermined temperature. If it is necessary to make fine
adjustment of the temperature, the temperature may be adjusted by,
for example, cooling a part of the pipe 42 by spraying water or the
like. When the flow rate of the steam introduced into the carbon
dioxide recovery system 50 is lower than the predetermined flow
rate, it can be made closer to the predetermined flow rate by
increasing an opening degree of the flow rate regulating valve
V1.
[0112] One example of adjusting the flow rate regulating valve V1
and the pressure regulating valve V2 based on the temperature of
the steam introduced into the carbon dioxide recovery system 50 was
described above, but for example, the flow rate regulating valve V1
and the pressure regulating valve V2 may be adjusted based on the
temperature of the absorption liquid in the regeneration tower of
the carbon dioxide recovery system 50. Thus, a time delay for
appropriate control can be decreased by adjusting the flow rate
regulating valve V1 and the pressure regulating valve V2 based on
the temperature of the absorption liquid. For stabilization of the
control, the flow rate regulating valve V1 and the pressure
regulating valve V2 may be controlled with the flow rate of the
absorption liquid determined as a function.
[0113] Here, power generation output of the steam turbine power
plant 12 is controlled by a steam control valve (not shown) which
adjusts the flow rate of the main steam introduced into the
superhigh-pressure turbine 36 such that a total output of the
electric generator 26 for the low-pressure turbine 25 and the
electric generator 35 for the back-pressure turbine 27 meets a
target output.
[0114] The cycle efficiency of the steam turbine power plant 12 of
the third embodiment is described below.
[0115] FIG. 7 is a diagram showing a T-s curve (temperature-entropy
curve) of a steam condition change in the steam turbine power plant
12 according to the third embodiment of the invention. FIG. 7 also
shows a condition change in a conventional two stage reheat cycle
for comparison. There is shown an example that the temperature of
the steam introduced into the superhigh-pressure turbine 36 in the
steam turbine power plant 12 according to the third embodiment is
determined to be 650.degree. C., and the temperature of the steam
introduced into the superhigh-pressure turbine in a conventional
steam turbine power plant is determined to be 620.degree. C. It is
assumed in FIG. 7 that the expansion process in each turbine is
adiabatic expansion in the same manner as in FIG. 3 and FIG. 5.
[0116] In the conventional steam turbine power plant, is indicated
that 8.fwdarw.1 is an isobaric heating by the boiler, 1.fwdarw.2 is
adiabatic expansion by the superhigh-pressure turbine, 2.fwdarw.3
is isobaric reheating by the reheater, 3.fwdarw.4 is adiabatic
expansion by the high-pressure turbine, 4.fwdarw.5 is isobaric
reheating by the reheater, and 5.fwdarw.6 is adiabatic expansion by
the intermediate-pressure turbine and the low-pressure turbine.
And, it is indicated that 6.fwdarw.7 is isothermal condensation by
the condenser, and 7.fwdarw.8 is a pressure increase and a
temperature increase by the water feed pump and the feed water
heater.
[0117] Meanwhile, in the steam turbine power plant 12 of the third
embodiment, the temperature of the steam introduced into the
superhigh-pressure turbine 36 is higher than the temperature of the
steam introduced into the superhigh-pressure turbine of the
conventional steam turbine power plant, so that the adiabatic
expansion in the superhigh-pressure turbine 36 becomes
1a.fwdarw.2a. The adiabatic expansion by the high-pressure turbine
22 becomes 3a.fwdarw.4a. And, the adiabatic expansion by the
intermediate-pressure turbine 24 and the low-pressure turbine 25
becomes 5a.fwdarw.6a.
[0118] In FIG. 7, the area (area of the shaded portion in FIG. 7)
surrounded by a steam condition value higher than the conventional
steam condition value is an increase in energy which can be taken
out as a work, namely an extent of a contribution to efficiency
improvement by an increase in temperature.
[0119] The adiabatic expansion by the back-pressure turbine 27 is
indicated by 2a.fwdarw.9, and the temperature of the steam
discharged from the back-pressure turbine 27 is determined by
pressure Pex of the discharged steam. For example, when the
temperature of the steam discharged from the back-pressure turbine
27 is lower than the temperature (e.g., 150.degree. C.) of the
steam required by the carbon dioxide recovery system 50, the
pressure Pex of the steam discharged from the back-pressure turbine
27 is raised by closing the pressure regulating valve V2. Thus, the
temperature of the steam discharged from the back-pressure turbine
27 can be raised to become closer to a predetermined temperature.
When the flow rate of the steam introduced into the carbon dioxide
recovery system 50 is lower than a predetermined flow rate, it can
be made closer to the predetermined flow rate by increasing the
opening degree of the flow rate regulating valve V1.
[0120] At this time, the flow rate of the extraction steam from the
back-pressure turbine 27, which is supplied to the high-pressure
feed water heater 34, is controlled by the ability of the
high-pressure feed water heater 34 depending on a feed water flow
rate (substantially proportional to the boiler load) and an
extraction steam pressure and substantially proportional to the
feed water flow rate similar to the prior art. In other words, the
flow rate of the steam introduced into the back-pressure turbine 27
through the pipe 151 is a total of the flow rate of the steam
discharged from the back-pressure turbine 27 and the flow rate of
the extraction steam supplied to the high-pressure feed water
heater 34. This total flow rate is substantially proportional to
the feed water flow rate (boiler load).
[0121] Generally, the extraction steam flow rate is about 5% of the
feed water flow rate per stage of the feed water heater. For
example, when the steam extraction to the four stages of the
high-pressure feed water heater 34 is made as shown in FIG. 6 and
the flow rate of the steam introduced into the carbon dioxide
recovery system 50 is determined to be 40% of the feed water flow
rate, a steam flow rate of "40%+4 stages.times.5%=60%" is
introduced into the back-pressure turbine 27. It is a steam flow
rate sufficient to overcome a variation or low operability of an
extraction steam pressure, which is proportional to a stage steam
flow rate and caused because the load of the conventional
back-pressure extraction turbine for driving the water feed pump
described above is small to about 2% (about 15% of the feed water
flow rate in terms of the drive steam flow rate) of the boiler
load. And, since the flow rate of the steam for driving the
back-pressure turbine 27 is substantially proportional to the feed
water flow rate (namely, substantially proportional to the boiler
load) in the steam turbine power plant 12 according to the third
embodiment, the extraction steam pressure is substantially
proportional to the boiler load. Therefore, the extraction steam
pressure has the same property as that of a change of the
extraction steam pressure of the normal steam turbine power plant,
and a problem of operability is not produced.
[0122] By the above-described control, the output of the electric
generator 35 for the back-pressure turbine 27 is controlled by
adjusting the flow rate regulating valve V1 and the pressure
regulating valve V2, and the output of the entire steam turbine
power plant 10 is determined by a total of the electric generator
26 for the low-pressure turbine and the electric generator 35 for
the back-pressure turbine 27. Therefore, it becomes possible to
obtain a predetermined output by controlling the flow rate of the
steam introduced into the high-pressure turbine by a steam control
valve (not shown) to control the output of the electric generators
26 and 35. The output of the electric generator 35 is substantially
proportional to that of the boiler load, so that it is also
substantially proportional to the output of the electric generator
26 and excellent in controllability.
[0123] In a case where the steam turbine power plant 12 is operated
with the steam introduced into the reboiler 120 blocked in order to
make the exchange of the absorption liquid 90 of the carbon dioxide
recovery apparatus 80, the flow rate regulating valve V1 is
controlled such that the output of the back-pressure turbine 27
becomes a minimum output capable of performing a stable operation
to adjust the flow rate of the steam introduced into the
back-pressure turbine 27. And, a shutoff valve (not shown) disposed
on the pipe 42 is closed to stop the steam from flowing into the
carbon dioxide recovery apparatus 80. In addition, it is controlled
to fully open the pressure regulating valve V2 to introduce the
total amount of the steam discharged from the back-pressure turbine
27 into the low-pressure feed water heater 31.
[0124] As described above, the steam turbine power plant 12
according to the third embodiment uses the steam discharged from
the superhigh-pressure turbine 36 to drive the back-pressure
turbine 27 and can generate electricity by driving the electric
generator 35 disposed on the back-pressure turbine 27. In addition,
as energy necessary for the regeneration tower 70 of the carbon
dioxide recovery apparatus 80, it is possible to use the steam
having low exergy which has performed the expansion work by the
back-pressure turbine 27. Thus, an energy loss can be suppressed,
and high power generation efficiency can be obtained.
[0125] In addition, the steam extracted from the back-pressure
turbine 27 can be made to have a temperature of 580.degree. C. or
below. Therefore, as the material configuring the steam extraction
pipe between the back-pressure turbine 27 and the high-pressure
feed water heater 34 and the high-pressure feed water heater 34,
the same material as the material such as carbon steel which has
been used for them can be used. And, a thermal stress generated due
to a difference between the temperature of the feed water flowing
through the high-pressure feed water heater 34 and the temperature
of the extraction steam guided to the high-pressure feed water
heater 34 can be prevented from increasing.
[0126] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
methods and systems described herein may be embodied in a variety
of other forms; furthermore, various omissions, substitutions and
changes in the form of the methods and systems described herein may
be made without departing from the spirit of the inventions. The
accompanying claims and their equivalents are intended to cover
such forms or modifications as would fall within the scope and
sprit of the inventions.
* * * * *