U.S. patent application number 13/578642 was filed with the patent office on 2012-12-27 for coal-fired power plant, and method for operating coal-fired power plant.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Yoshiharu Hayashi.
Application Number | 20120324893 13/578642 |
Document ID | / |
Family ID | 44563276 |
Filed Date | 2012-12-27 |
![](/patent/app/20120324893/US20120324893A1-20121227-D00000.png)
![](/patent/app/20120324893/US20120324893A1-20121227-D00001.png)
![](/patent/app/20120324893/US20120324893A1-20121227-D00002.png)
United States Patent
Application |
20120324893 |
Kind Code |
A1 |
Hayashi; Yoshiharu |
December 27, 2012 |
Coal-Fired Power Plant, and Method for Operating Coal-Fired Power
Plant
Abstract
A coal-fired power plant having a control unit including a first
flow rate control valve for regulating a water flow rate of a water
feed bypass system, a second flow rate control valve installed in
an extraction pipe for extracting steam from a steam turbine, a
first temperature sensor on a downstream side of a heat recovery
device, and a second temperature sensor on a downstream side of a
heat exchanger and the control unit regulates opening of the first
and second flow rate control valves on the basis of an exhaust gas
temperature detected by the first temperature sensor and a feed
water temperature detected by the second temperature sensor.
Accordingly, even when a recovery heat quantity of the heat
recovery device installed on a gas duct is changed due to
deterioration with age of a boiler, a reduction in plant
reliability and plant efficiency can be suppressed.
Inventors: |
Hayashi; Yoshiharu;
(Hitachinaka, JP) |
Assignee: |
Hitachi, Ltd.
Chiyoda-ku, Tokyo
JP
|
Family ID: |
44563276 |
Appl. No.: |
13/578642 |
Filed: |
February 7, 2011 |
PCT Filed: |
February 7, 2011 |
PCT NO: |
PCT/JP2011/052472 |
371 Date: |
August 13, 2012 |
Current U.S.
Class: |
60/691 ; 60/645;
60/670; 60/690 |
Current CPC
Class: |
F22D 1/40 20130101; F23J
15/06 20130101; F01K 7/34 20130101; Y02E 20/363 20130101; F22D
1/003 20130101; F22D 1/12 20130101; F01K 7/40 20130101; F22D 1/32
20130101; Y02E 20/30 20130101; F22D 1/02 20130101; F01K 13/02
20130101; F22D 1/325 20130101 |
Class at
Publication: |
60/691 ; 60/670;
60/690; 60/645 |
International
Class: |
F01K 11/02 20060101
F01K011/02; F01K 9/00 20060101 F01K009/00; F01K 7/34 20060101
F01K007/34 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2010 |
JP |
2010-055229 |
Claims
1. A coal-fired power plant comprising: an exhaust gas discharge
system for flowing exhaust gas discharged from a boiler flow, a
steam supply system for driving a steam turbine by steam generated
by the boiler and feeding the steam to a condenser after driving
the steam turbine, and a water feed system for feeding water
condensed by the condenser to the boiler, wherein: the water feed
system includes a feed water heater having a heat exchanger for
heating the water by steam extracted from the steam turbine, and a
water feed bypass system is provided at an upstream side of the
heat exchanger to exchange heat between the exhaust gas flowing
through the exhaust gas discharge system and the water of the water
feed system by a heat recovery device which is installed in the
water feed bypass system, characterized in that: a control unit
including a first flow rate control valve for regulating a water
flow rate flowing in the water feed bypass system, a second flow
rate control valve installed in an extraction pipe for extracting
steam from the steam turbine, a first temperature sensor installed
on a downstream side of the heat recovery device, and a second
temperature sensor installed on a downstream side of the heat
exchanger, wherein the control unit regulates openings of the first
and second flow rate control valves on the basis of an exhaust gas
temperature detected by the first temperature sensor and a feed
water temperature detected by the second temperature sensor.
2. The coal-fired power plant according to claim 1, wherein: the
feed water heater comprises a plurality of heat exchangers and the
second temperature sensor is installed on the downstream side of
the respective heat exchangers.
3. The coal-fired power plant according to claim 1, wherein: the
first flow rate control valve controls an opening thereof on the
basis of an entrance gas temperature of an electric dust collector
installed on the downstream side of the heat recovery device.
4. The coal-fired power plant according to claim 1, wherein: the
second flow rate control valve controls an opening thereof on the
basis of the feed water temperature discharged from the heat
exchanger.
5. The coal-fired power plant according to claim 1, wherein a
plurality of the heat exchangers and a plurality of the heat
recovery devices are arranged as a pair, a water feed bypass system
for branching on the upstream side of each of the heat exchangers
is provided, and the control unit regulates a flow rate of feed
water to be fed to the heat recovery device positioned on a
high-temperature side of the water feed system from among the
plurality of heat recovery devices so as to increase the flow rate
thereof.
6. An operating method for a coal-fired power plant comprising: an
exhaust gas discharge system for flowing exhaust gas discharged
from a boiler flow, a steam supply system for driving a steam
turbine by steam generated by the boiler and feeding the steam to a
condenser after driving the steam turbine, and a water feed system
for feeding water condensed by the condenser to the boiler,
wherein: the water feed system includes a feed water heater having
a heat exchanger for heating the water by steam extracted from the
steam turbine, and a water feed bypass system is provided at an
upstream side of the heat exchanger to exchange heat between the
exhaust gas flowing through the exhaust gas discharge system and
the water of the water feed system by a heat recovery device which
is installed in the water feed bypass system, comprising a step of:
regulating a water flow rate flowing in the water feed bypass
system and an extraction rate for extracting steam from the steam
turbine on the basis of a exhaust gas temperature on a downstream
side of the heat recovery device and a feed water temperature on a
downstream side of the heat exchanger.
Description
TECHNICAL FIELD
[0001] The present invention relates to a coal-fired power plant
and an operating method for the coal-fired power plant.
BACKGROUND ART
[0002] The patent literature 1 discloses a feed water heater in a
combined cycle plant of an exhaust gas reheat system with a gas
turbine power plant additionally installed in a steam turbine power
plant. The combined cycle plant of the patent literature 1 installs
a bypass path in a condensate supply system, feeds condensate to a
heat recovery device (an exhaust gas cooler), thereby heats the
condensate. And, the heat of exhaust gas recovered by the heat
recovery device (the exhaust gas cooler) heats boiler feed water
and improves the plant efficiency. Further, the patent literature 1
discloses a feed water regulating valve for regulating the water
distribution rate to be fed to the feed water heater side and heat
recovery device (the exhaust gas cooler) side.
PRIOR ART LITERATURE
Patent Literature
[0003] {Patent Literature 1} Japanese Patent Application Laid-open
No. Hei 6 (1994)-2806
SUMMARY OF INVENTION
Technical Problem
[0004] However, the invention disclosed in the patent literature 1
fails to disclose a method for regulating the heat quantity of
exhaust gas recovered by the heat recovery device (the exhaust gas
cooler) and the heating rate of boiler feed water. Therefore, in
the invention disclosed in the patent literature 1, when the
exhaust gas temperature and exhaust gas flow rate are changed due
to a deterioration with age of the boiler, the temperature of
exhaust gas discharged from the boiler and the temperature of water
to be fed to the boiler cannot be controlled to predetermined
temperatures.
[0005] Therefore, when the temperature of exhaust gas discharged
from the boiler is shifted from the design value, there is a case
that the dust collection efficiency of an electric dust collector
on the downstream side may be reduced.
[0006] Further, in the boiler, a heat exchanger in which
evaporation of water in the flow path is not supposed in design is
installed. Therefore, when the temperature of water to be fed to
the boiler is higher than the design value, the feed water is
evaporated (steaming) by the heat exchanger of the boiler, which
can cause the heat exchanger to be damaged. On the other hand, when
the temperature of water to be fed to the boiler is lower than the
design value, the total quantity of water fed to the boiler is not
evaporated and some of it is discharged as drain.
[0007] As mentioned above, when the temperature of exhaust gas
discharged from the boiler and the temperature of water to be fed
to the boiler cannot be controlled to predetermined temperatures, a
problem arises that the plant reliability and plant efficiency are
reduced.
[0008] An object of the present invention is to suppress the
reduction in the plant reliability and plant efficiency even if the
exhaust gas temperature or exhaust gas flow rate is changed due to
a deterioration with age of the boiler and the recovery heat
quantity of the heat recovery device installed on a gas duct is
changed.
Solution to Problem
[0009] The present invention is characterized in that a control
unit including a first flow rate control valve for regulating the
water flow rate flowing in the water feed bypass system, a second
flow rate control valve installed in an extraction pipe for
extracting steam from the steam turbine, a first temperature sensor
installed on a downstream side of the heat recovery device, and a
second temperature sensor installed on a downstream side of the
feed water heater is installed, wherein the control unit regulates
the openings of the first and second flow rate control valves on
the basis of an exhaust gas temperature detected by the first
temperature sensor and a feed water temperature detected by the
second temperature sensor.
Advantageous Effects of Invention
[0010] According to the present invention, even if the exhaust gas
temperature or exhaust gas flow rate is changed due to a
deterioration with age of the boiler and the recovery heat quantity
of the heat recovery device installed on the gas duct is changed,
the reduction in the plant reliability and plant efficiency can be
suppressed.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a schematic view showing the low-pressure feed
water heater and the related devices among the constituent devices
of the coal-fired power plant. Embodiment 1
[0012] FIG. 2 is a schematic view showing the low-pressure feed
water heater and the related devices among the constituent devices
of the coal-fired power plant. Embodiment 2
[0013] FIG. 3 is a system diagram of a coal-fired power plant.
DESCRIPTION OF EMBODIMENTS
[0014] Generally, to remove an environmental restriction substance
included in exhaust gas discharged from a boiler until below the
restriction value, a coal-fired power plant includes an exhaust gas
treatment equipment. The exhaust gas treatment equipment includes
denitrification equipment for removing nitrogen oxide, an electric
dust collector for removing combustion ash, and a desulfurizer for
removing sulfur oxide. Further, in addition to these eliminators,
the exhaust gas treatment equipment is provided with heat
exchangers for using the surplus heat of exhaust gas. One of the
heat exchangers is an air preheater, which exchanges heat between
air to be fed to the boiler and exhaust gas. Exhaust gas heat can
be used to raise feed air in temperature, thereby improving the
heat efficiency of the boiler. Another heat exchanger is a gas-gas
heater (GGH), which exchanges heat between high-temperature gas
flowing on the upstream side of the gas duct and low-temperature
gas flowing on the downstream side of the gas duct. The GGH is a
device for preventing a phenomenon that water vapor included in
exhaust gas is discharged like white smoke from the chimney
positioned at the exit of the gas duct. Discharging of water vapor
itself is harmless. However, it causes visual uneasiness to
neighbors, so that in Japan, it is a restriction object (called
visual environmental pollution).
[0015] Further, the desulfurizer sprays a water solution of a
limestone slurry on the gas duct with a sprayer to remove the
sulfur oxide. Therefore, at the exit of the desulfurizer, the
moisture concentration in exhaust gas is increased and the gas
temperature is decreased. Therefore, if exhaust gas discharged from
the desulfurizer is discharged into the atmosphere as it is, water
vapor is condensed at the exit of the chimney into like white
smoke. The GGH raises low-temperature exhaust gas on the downstream
side of the desulfurizer to 100.degree. C. or higher by
high-temperature exhaust gas on the upstream side of the gas duct,
thereby suppressing the condensation of water vapor at the exit of
the chimney to prevent white smoke.
[0016] The GGH uses water as a heat transfer medium and exchanges
heat between the upstream side and the latterstream side of exhaust
gas. Namely, a heat recovery device for recovering heat from
high-temperature exhaust gas is installed on the upstream side of
the gas duct, and the heat recovery device recovers heat from the
high-temperature exhaust gas and raises water in temperature.
Furthermore, on the latterstream side of the gas duct (behind the
desulfurizer), a reheater for raising low-temperature exhaust gas
in temperature is installed. The reheater exchanges heat between
high-temperature water passing through the heat recovery device and
low-temperature exhaust gas to raise the low-temperature exhaust
gas in temperature. The water as a heat transfer medium circulates
through the heat recovery device and reheater. The heat recovery
device is often installed at the preceding stage of an electric
dust collector. The reason is that the dust collection efficiency
of an electric dust collector depends on gas temperature. And, the
heat recovery device of the GGH regulates (lowers) the exhaust gas
temperature and thereby can maximize the dust collection
efficiency.
[0017] Here, neither a power plant in a foreign country imposing no
white smoke prevention restrictions nor a CO.sub.2-collection type
coal-fired power plant provided with an apparatus for collecting
and storing CO.sub.2 in exhaust gas to suppress discharge of
CO.sub.2 is provided with a GGH.
[0018] When there is no GGH provided, it is impossible to regulate
exhaust gas temperature so that the efficiency of the electric dust
collector will be maximized. Therefore, a method of installing a
heat recovery device at the preceding stage of the electric dust
collector may be considered. However, unlike the GGH, there is no
need to heat exhaust gas at the exit of the chimney, so that no
reheater is mounted. Therefore, in place of the reheater, a system
provided with a feed water heater may be used. The feed water
heater is an apparatus of heating boiler feed water by the heat of
exhaust gas recovered by the heat recovery device and thereby
improving the plant efficiency.
[0019] The following embodiments relate to a coal-fired power plant
and more particularly to a plant including a feed water heater for
contributing to the efficiency improvement of a coal-fired power
plant.
Embodiment 1
[0020] FIG. 3 is a system diagram of a coal-fired power plant. A
boiler 50 generates combustion gas using coal as fuel. A gas duct
54 is an exhaust gas discharge system for leading exhaust gas
discharged from the boiler 50 to a chimney 58. An exhaust gas
treatment equipment 57 is an apparatus of removing an environmental
restriction substance included in exhaust gas discharged from the
boiler 50 until below the restriction value. The chimney 58
discharges outside exhaust gas treated by the exhaust gas treatment
equipment 57. Further, the exhaust gas treatment equipment 57
includes not only a heat recovery device 5 and an electric dust
collector 6 but also denitrification equipment.
[0021] A steam supply system 55 includes a steam turbine 12 and a
condenser 51. The steam turbine 12 is driven by steam generated by
the boiler 50. The condenser 51 condenses steam discharged from the
steam turbine 12 to water. The condensate discharged from the
condenser 51 is returned to the boiler 50 through a water feed
system 11. The water feed system 11 includes a condensate pump 52
for feeding condensate, a low-pressure feed water heater 10, and a
high-pressure feed water heater 53.
[0022] Between the steam turbine 12 and the low-pressure feed water
heater 10, steam extraction systems 23 and 24 through which
extraction steam from the steam turbine 12 flows are installed.
Drain steam pipes 25 and 26 are pipes through which drain from the
feed water heater flows.
[0023] FIG. 1 is a schematic view showing the low-pressure feed
water heater and the related devices among the constituent devices
of the coal-fired power plant shown in FIG. 3.
[0024] The coal-fired power plant raises the condensate from the
condenser 51 in pressure by the condensate pump 52 and feeds it
firstly to the low-pressure feed water heater 10 through the water
feed system 11. The low-pressure feed water heater 10 is composed
of a plurality of heat exchangers. These heat exchangers are called
a first heat exchanger 1, a second heat exchanger 2, a third heat
exchanger 3, and a fourth heat exchanger 4 successively from the
heat exchanger positioned on the condenser side. The feed water
heated by the low-pressure feed water heater 10 is fed to the
high-pressure feed water heater 53. Each heat exchanger of the
low-pressure feed water heater 10 heats feed water by the steam
extracted from the steam turbine 12. The steam extraction system 23
feeds extraction steam to the first heat exchanger 1 and the steam
extraction system 24 feeds extraction steam to the second heat
exchanger 2. The extraction pipes for feeding extraction steam to
the third and fourth heat exchangers are omitted. The extraction
steam fed to the second heat exchanger 2 exchanges heat with the
feed water and then becomes drain. This drain is fed to the first
heat exchanger 1 through the drain steam pipe 25. The first heat
exchanger 1 heats feed water using drain from the second heat
exchanger 2 and the extraction steam extracted from the steam
extraction system 23. And, the drain discharged from the first heat
exchanger 1 is fed finally to the condenser 51 through the drain
steam pipe 26. Each heat exchanger of the low-pressure feed water
heater 10 exchanges heat between the extraction steam from the
steam turbine 12 and feed water flowing through the water feed
system 11, though it does not mix the two.
[0025] The water feed system of this embodiment branches on the
upstream side of the low-pressure feed water heater 10. A part of
the feed water flowing through the water feed system 11 is fed to
the heat recovery device 5 installed on the gas duct through a
water feed bypass system 27. The heat recovery device 5 heats feed
water by high-temperature exhaust gas and then feeds water again to
the water feed system 11. The water feed system 11 of this
embodiment permits the water feed bypass system 27 to join on the
latter side of the second heat exchanger 2. However, the junction
position of the water feed bypass system 27 to the water feed
system 11 depends on the heat quantity that can be recovered from
exhaust gas. When the recovered heat quantity from exhaust gas is
large and the feed water temperature can rise to a high
temperature, it may be considered that the water feed bypass system
27 joins on a more slip-stream side relative to the water feed
system 11. Inversely, when the heat quantity recovered from exhaust
gas is small, it may be considered that the water feed bypass
system 27 joins on a more upstream side relative to the water feed
system 11 (that is, at the latter stage of the first heat exchanger
1). The heat quantity recoverable from exhaust gas depends on the
difference between the temperature of exhaust gas entering the heat
recovery device 5 and an appropriate value of the entrance exhaust
gas temperature decided on the basis of the dust collection
efficiency of the electric dust collector 6 installed at the latter
stage of the heat recovery device 5 and the exhaust gas flow
rate.
[0026] Next, in the aforementioned apparatus, a method for
executing feed water heating by exhaust gas and controlling the
feed water temperature and the exhaust gas temperature at the
entrance of the electric dust collector to predetermined values
will be explained.
[0027] At the feed water exit of each heat exchanger composing the
low-pressure feed water heater 10, a temperature sensor for
detecting the feed water temperature is installed. Further, FIG. 1
shows two temperature sensor 31 and 32 representatively. Further,
at the entrance of the electric dust collector, a temperature
sensor 33 for detecting the entrance gas temperature of the
electric dust collector is installed. Temperature signals detected
by the temperature sensors 31 to 33 are transmitted to a control
unit 7. The control unit 7 regulates the flow rate of extraction
steam so as to control the temperatures detected by these
temperature sensors to predetermined values.
[0028] A flow rate control valve 41 is a valve for regulating the
extraction steam flow rate to be fed from the steam turbine 12 to
the first heat exchanger 1. A flow rate control valve 42 is a valve
for regulating the extraction steam flow rate to be fed to the
second heat exchanger 2. A flow rate control valve 43 is a valve
for regulating the water feed bypass flow rate flowed to the water
feed bypass system 27. The control unit 7 transmits an
opening-angle signal to the flow rate control valves 41, 42, and 43
so as to control the temperatures detected by the temperature
sensors 31, 32, and 33 to the predetermined values.
[0029] Concretely, a part of the feed water fed from the condensate
pump 52 is fed to the heat recovery device 5 through the water feed
bypass system 27. For the gas temperature at the entrance of the
electric dust collector, a value is set so as to maximize the dust
collection efficiency. The control unit 7 controls the flow rate
control valve 43 to regulate the water feed bypass flow rate so
that the value of the temperature sensor 33 for detecting the gas
temperature at the entrance of the electric dust collector will be
the aforementioned set value. In the heat recovery device 5, as the
water feed bypass flow rate increases, the heat exchange quantity
from exhaust gas to feed water increases and the gas temperature at
the entrance of the electric dust collector lowers. Inversely, as
the water feed bypass flow rate decreases, the heat exchange
quantity from exhaust gas to feed water decreases and the gas
temperature at the entrance of the electric dust collector
rises.
[0030] On the other hand, if the water feed bypass flow rate
through the water feed bypass system 27 increases, the feed water
flow rate flowing through the first heat exchanger 1 and the second
heat exchanger 2 decreases. When the extraction steam flow rate
flowing from the steam turbine 12 is not changed, the first heat
exchanger 1 and the second heat exchanger 2 heat a small quantity
of feed water, so that the feed water temperature rises. For the
feed water temperature, an optimum value to each heat exchanger in
the boiler is set. Therefore, the control unit 7 controls the flow
rate control valves 41 and 42 to regulate the extraction steam flow
rate so that the values of the temperature sensors 31 and 32 for
detecting the feed water exit temperature of each heat exchanger
will be the aforementioned set values. As the extraction steam flow
rate decreases, the heat quantity fed from extraction steam to feed
water decreases and the feed water temperature falls. If the
extraction steam flow rate from the steam turbine decreases, steam
is accordingly used for power generation, resulting in an increase
in the plant efficiency.
[0031] According to this embodiment, the control unit 7 including
the flow rate control valve 43 for regulating the water flow rate
flowing in the water feed bypass system 27, the flow rate control
valves 41 and 42 installed in the extraction pipe for extracting
steam from the steam turbine 12, the temperature sensor 33
installed on the downstream side of the heat recovery device 5, and
the temperature sensors 31 and 32 installed on the downstream side
of the feed water heater is installed. The control unit 7 regulates
the opening angles of the flow rate control valves 41 to 43 on the
basis of the exhaust gas temperature detected by the temperature
sensor 33 and the feed water temperature detected by the
temperature sensors 31 and 32. In the coal-fired power plant, due
to a deterioration with age of the boiler, the exhaust gas
temperature and exhaust gas flow rate are changed. Therefore, in
the heat recovery device installed in the exhaust gas system (the
gas duct), the heat quantity recovered from exhaust gas is changed
and the dust collection efficiency of the electric dust collector
positioned on the downstream side is influenced. Further, by the
extraction steam quantity from the steam turbine, the heat
exchangers in the boiler are influenced. Therefore, by installing
the aforementioned control unit, the dust collection efficiency of
the electric dust collector is maintained and it can be suppressed
that water is evaporated (steaming) by the heat exchangers in the
boiler and the heat exchangers are damaged. Further, the phenomenon
that the total quantity of water fed to the boiler is not
evaporated and some of it is discharged as drain can be
avoided.
[0032] Further, in this embodiment, the feed water heater is
composed of a plurality of heat exchangers and the temperature
sensors are installed on the downstream side of each heat
exchanger. With the temperature sensors installed on the downstream
side of each heat exchanger, the heating quantity for heating feed
water by each heat exchanger using extraction steam can be
confirmed. Therefore, the steam quantity extracted from each steam
turbine can be regulated and the extraction steam quantity can be
minimized. If the extraction steam quantity can be reduced, the
generated energy of each steam turbine can be increased.
Embodiment 2
[0033] FIG. 2 is a schematic view showing the low-pressure feed
water heater and the related devices among the constituent devices
of the coal-fired power plant. Here, only the portions different
from the Embodiment 1 will be explained.
[0034] The Embodiment 1 uses one heat recovery device, though the
Embodiment 2 uses a plurality of heat recovery devices. A first
heat recovery device 8 is installed in parallel with the first heat
exchanger 1 and a second heat recovery device 9 is installed in
parallel with the second heat exchanger 2. Water feed bypass
systems 28 and 29 for feeding water to the respective heat recovery
devices and flow rate control valves 44 and 45 for regulating the
water feed bypass flow rate are installed. The plurality of flow
rate control valves are controlled by the control unit 7 and the
water feed bypass flow rate to each heat recovery device is
regulated independently.
[0035] The control unit 7 of this embodiment regulates the feed
water flow rate to be fed to the heat recovery device positioned on
the high-temperature side of the water feed system, from among the
plurality of heat recovery devices, in such a way that the feed
water rate will be more increased. As the water feed bypass flow
rate to the heat recovery device increases, the feed water flow
rate to the feed water heater (heat exchanger) installed in
parallel with the heat recovery device decreases. And, the heat
quantity necessary to heat feed water using extraction steam of the
steam turbine decreases, so that the flow rate of the extraction
steam of the steam turbine can be decreased. With respect to the
contribution degree for decreasing the extraction steam flow rate
and improving the turbine output, the second heat exchanger 2 is
larger than the first heat exchanger 1. The reason is that the feed
water temperature rises higher on the downstream side of the feed
water system than on the upstream side and, as a result, with
respect to the extraction steam for heating feed water, the second
heat exchanger 2 positioned on the high-temperature side of the
feed water system requires steam at a higher temperature and a
higher pressure than the first heat exchanger 1. Therefore, by
increasing the flow rate of the feed water to be fed to the heat
recovery device positioned on the high-temperature side of the feed
water system, it is possible to make use of high-temperature and
high-pressure steam not for heating feed water but for the rotation
power of the turbine and increase the range of turbine output.
[0036] In consideration of the aforementioned characteristics, in
this embodiment, when decreasing the extraction steam from the
steam turbine, it is possible to increase the contribution degree
to the increase in the turbine output by decreasing
higher-temperature and higher-pressure extraction steam
preferentially.
[0037] Next, the control method of this embodiment will be
explained. This embodiment is the same as the Embodiment 1 in that
the water feed bypass flow rate is regulated so that the entrance
gas temperature of the electric dust collector 6 in the exhaust gas
treatment equipment will be the predetermined value.
[0038] In this embodiment, when increasing the water feed bypass
flow rate because the entrance gas temperature of the electric dust
collector 6 is higher than the predetermined value, the control
unit 7, by operating the flow rate control valve 45 so that it
opens, increases the water feed bypass flow rate to the second heat
recovery device 9 preferentially. At this time, to prevent the exit
feed water temperature of the second heat exchanger 2 from rising,
the control unit 7, by controlling the flow rate control valve 42
of extraction steam so that it closes, decreases the extraction
steam flow rate to the second heat exchanger 2 and regulates the
exit feed water temperature to the predetermined value. Here, in
the control unit 7, a lower limit value of flow rate of extraction
steam to be fed to the second heat exchanger 2 is set. When the
extraction steam flow rate reaches the lower limit value or when
there is no lower limit value set, the control unit 7 totally
closes the flow rate control valve 42. Then, when the extraction
steam flow rate reaches zero, the control unit 7, while operating
the flow rate control valve 44 so that it opens, increases the
water feed bypass flow rate to the first heat recovery device 8. In
conjunction with this operation, the extraction steam flow rate to
the first heat exchanger 1 is decreased. As mentioned above, when
the heat quantity recovered from exhaust gas by only the second
heat recovery device 9 is insufficient and the entrance gas
temperature of the electric dust collector is not reduced to the
predetermined value, the first heat recovery device 8 has an
assistant role of recovering heat from exhaust gas.
[0039] When decreasing the water feed bypass flow rate because the
entrance gas temperature of the electric dust collector 6 is lower
than the predetermined value, the reverse procedure to the
aforementioned control method is used. Concretely, the control unit
7 operates the flow rate control valve 44 so that the water feed
bypass flow rate to the first heat recovery device 8 will be
decreased giving a priority over the second heat recovery device 9.
At this time, to prevent the exit feed water temperature of the
first heat exchanger 1 from decreasing, the control unit 7, by
controlling the flow rate control valve 41 of extraction steam so
that it opens, increases the extraction steam flow rate to the
first heat exchanger 1 and regulates the exit feed water
temperature to the predetermined value. Here, in the control unit
7, a lower limit value of the water feed bypass flow rate to the
first heat recovery device 8 is set. When the water feed bypass
flow rate reaches the lower limit value or when there is no lower
limit value set, the control unit 7 totally closes the flow rate
control valve 44. Then, when the water feed bypass flow rate
reaches zero, the control unit 7, by operating the flow rate
control valve 45 so that it closes, decreases the water feed bypass
flow rate to the second heat recovery device 9. In conjunction with
this operation, the control unit 7 increases the extraction steam
flow rate to the second heat exchanger 2.
[0040] According to this embodiment, in the coal-fired power plant
using exhaust gas heat to heat feed water, the water feed bypass
flow rate of the heat exchanger positioned on the downstream side
of the water feed system is increased preferentially. For this
reason, by decreasing turbine extraction steam at a higher
temperature and a higher pressure, it is possible to increase the
range of turbine output and thereby achieve a high-efficient plant
operation.
INDUSTRIAL APPLICABILITY
[0041] The present invention can be applied to a coal-fired power
plant including a feed water heater for heating feed water by
exhaust gas heat.
REFERENCE SIGNS LIST
[0042] 1 First heat exchanger [0043] 2 Second heat exchanger [0044]
3 Third heat exchanger [0045] 4 Fourth heat exchanger [0046] 5 Heat
recovery device [0047] 6 Electric dust collector [0048] 7 Control
unit [0049] 8 First heat recovery device [0050] 9 Second heat
recovery device [0051] 10 Low-pressure feed water heater [0052] 11
Water feed system [0053] 12 Steam turbine [0054] 23, 24 Steam
extraction system [0055] 25, 26 Drain steam pipe [0056] 27, 28, 29
Water feed bypass system [0057] 31, 32, 33 Temperature sensor
[0058] 41, 42, 43, 44 Flow rate control valve
* * * * *