TECHNICAL FIELD
[0001] The present invention relates to a thermal power plant that uses steam generated in
a boiler and a control method for the thermal power plant.
This application claims the priority of Japanese Patent Application No. 2021-022766 filed
on February 16, 2021 and Japanese Patent Application No. 2021-169753 filed on October 15,
10 2021, the content of which is incorporated herein by reference.
BACKGROUND
[0002] A thermal power plant is known which uses steam generated in boiler (steam
generator) to drive steam turbine. As large-scale power source in a recent power grid,
15 thermal power plant mainly serves as base-load power plant and has contributed to stable supply
of domestic power together with GTCC (gas turbine combined cycle) plant, of its ability to
respond to load fluctuations.
[0003] Meanwhile, due to recent increase in amount of renewable energy-derived power
connected to power grid, the percentage of power supply of thermal power plant and GTCC
20 plant during daytime has been decreasing year by year and has already reached lower limit for
maintaining the frequency of the power grid and the balance of power supply and demand in
some area, however there is still a possibility that surplus renewable energy-derived power is
refused connection to the power grid.
[0004] In order to further expand renewable energy-derived power to the power grid, it is
25 essential to improve operability of the thermal power plant among large-scale power plants,
which has relatively large power output at its minimum load and a long starting-up time at DSS
(daily start stop) operation.
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Citation List
Patent Literature
[0005]
Patent Document 1: JPS64-54605 (Utility Model)
5
SUMMARY
Technical Problem
[0006] Patent Document 1 described above intends to increase an output of a steam turbine
by storing part of feed water in a hot water tank during a low load operation of the plant,
10 discharging the hot water to a high-pressure feed water heater group at the time of peak load of
power demand, and cutting or decreasing extraction steam to a high-pressure feed water heater.
[0007] Meanwhile, the low load operation of the plant in Patent Document 1 described
above is based on the premise that all main steam and reheat steam generated in the boiler are
introduced into the steam turbine through a governor to generate electric power, that is, a
15 minimum load that can be realized in the thermal power plant sets an amount, which is obtained
by subtracting extraction steam in the turbine from a heat amount of the main steam, the reheat
steam generated at the boiler minimum load and subsequently the plant inevitably outputs the
power of 25% load in general, even at the minimum not less than 10% load to the power grid.
[0008] It is desired to expand the range of renewable energy received into the power grid
20 during daytime by reducing power output from coal-fired thermal power plants (thermal power
plants) to the power grid from the recently achieved minimum load of 10% at the best practice
to almost 0% load (parallel no-power-transmission operation), as well as to maintain the
frequency of the power grid and adjustment of supply and demand by always paralleling a
turbine generator of the coal-fired thermal power plant (thermal power plant) to the grid so as
25 to be prepared to quickly increase the power output in response to a decrease in power
generation amount of the renewable energy associated with a change in weather.
[0009] Further, in a conventional thermal power plant that uses light oil for startup fuel and
is operated with DSS, it is desired to reduce fuel cost by allowing the plant to operate
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continuously with inexpensive coal, as well as to avoid wear in equipment and trouble at the
time of start-up associated with DSS operation.
[0010] In view of the above problems, an object of the present invention is to provide
technology for thermal power plant, enabling flexible response against change in power
generation amount of renewable energy and maintaining 5 high operability.
Solution to Problem
[0011] The present invention is characterized by a thermal power plant, which includes: a
boiler; a steam turbine driven by steam from the boiler; a turbine bypass line bypassing the
10 steam turbine to supply steam; a condenser for cooling exhaust steam of the steam turbine to
produce condensate water; a low-pressure feed water heater for heating the condensate water
with extraction steam from the steam turbine; and a deaerator for deaerating the condensate
water with the extraction steam, includes: a hot water heater for producing hot water from the
condensate water fed from the condenser, by using main steam of the turbine bypass line as a
15 heat source; a hot water tank for storing the hot water; and a hot water pump for feeding the hot
water stored in the hot water tank to downstream flow of the low-pressure feed water heater or
to the deaerator.
Advantageous Effects
20 [0012] According to the present invention, it is possible to provide a thermal power
technology enabling flexible response against change in power generation amount of renewable
energy and maintaining high operability.
BRIEF DESCRIPTION OF DRAWINGS
25 [0013] FIG. 1 is a schematic configuration diagram of a thermal power plant according to
an embodiment.
FIG. 2 is a schematic configuration diagram of the thermal power plant similar to an
embodiment.
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FIG. 3 is an example of an operation during a heat charge operation of the thermal power
plant according to an embodiment.
FIG. 4 is an example of an operation during a heat discharge operation of the thermal
power plant according to an embodiment.
FIG. 5 is a schematic configuration diagram showing the range of a 5 water heat storage
system according to an embodiment.
FIG. 6 is a schematic configuration diagram for describing auxiliary steam lines of the
thermal power plant according to an embodiment.
FIG. 7 is a schematic configuration diagram of a control system for the thermal power
10 plant according to an embodiment.
FIG. 8 is a schematic configuration diagram of the thermal power plant according to
Modification 1 of an embodiment.
FIG. 9 is a schematic configuration diagram of relevant parts of the thermal power plant
according to Modification 2 of an embodiment.
15 FIG. 10 is a flowchart of a confluent point switching process of the thermal power plant
according to Modification 2 of an embodiment.
FIG. 11 is an explanatory diagram for describing partial hot water feed to deaerator in the
thermal power plant according to Modification 3 of an embodiment.
FIG. 12 is a schematic configuration diagram of relevant parts of the thermal power plant
20 according to Modification 4 of an embodiment.
FIG. 13 is an explanatory diagram for describing the heat charge operation of the thermal
power plant according to Modification 4 of an embodiment.
FIG. 14 is an explanatory diagram for describing the heat discharge operation of the
thermal power plant according to Modification 4 of an embodiment.
25 FIG. 15 is a schematic configuration diagram of relevant parts of the thermal power plant
according to Modification 5 of an embodiment.
DETAILED DESCRIPTION
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[0014] Some embodiments of the present invention will be described below with reference
to the accompanying drawings. It is intended, however, that unless particularly identified,
dimensions, materials, shapes, relative positions and the like of components described or shown
in the drawings as the embodiments shall be interpreted as illustrative only and not intended to
limit the scope of the present 5 disclosure.
For instance, an expression of relative or absolute arrangement such as “in a direction”,
“along a direction”, “parallel”, “orthogonal”, “centered”, “concentric” and “coaxial” shall not
be construed as indicating only the arrangement in a strict literal sense, but also includes a state
where the arrangement is relatively displaced by a tolerance, or by an angle or a distance
10 whereby it is possible to achieve the same function.
For instance, an expression of an equal state such as “same”, “equal”, and “uniform” shall
not be construed as indicating only the state in which the feature is strictly equal, but also
includes a state in which there is a tolerance or a difference that can still achieve the same
function.
15 Further, for instance, an expression of a shape such as a rectangular shape or a tubular
shape shall not be construed as only the geometrically strict shape, but also includes a shape
with unevenness or chamfered corners within the range in which the same effect can be
achieved.
On the other hand, the expressions “comprising”, “including”, “having”, “containing”,
20 and “constituting” one constituent component are not exclusive expressions that exclude the
presence of other constituent components.
[0015] In the following embodiments, a thermal power plant 1 will be described as an
example of a coal-fired thermal power plant which is at least one embodiment of the present
invention. FIG. 1 is a schematic configuration diagram of the thermal power plant 1 according
25 to an embodiment.
[0016] The thermal power plant 1 includes a boiler 2, steam turbines 4, a condenser 13, a
water heat storage system 70, and a control system 80 (see FIG. 7). In the present embodiment,
a case is exemplified in which the thermal power plant 1 includes, as the steam turbines 4, a
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high-pressure turbine 4A, an intermediate-pressure turbine 4B, and a low-pressure turbine 4C.
However, the thermal power plant 1 may include one or two steam turbines 4, or may include
at least four steam turbines 4.
[0017] The boiler 2 is a steam generator that can generate superheated steam by exchanging
heat generated by burning pulverized fuel with feed water or steam. The 5 boiler 2 is, for
example, a coal-fired (pulverized coal-fired) boiler that uses pulverized coal obtained by
pulverizing coal (carbon-containing solid fuel) as pulverized fuel and burns the pulverized fuel
with a burner.
[0018] In the present embodiment, the coal-fired boiler is exemplified as the boiler 2.
10 However, the boiler 2 may use, as fuel, solid fuel such as biomass fuel, PC (petroleum coke)
fuel generated during petroleum refining, or petroleum residue. In addition, the boiler 2 can
use, as fuel, not only the solid fuel but also petroleum such as heavy oil, light oil, or heavy fuel,
or liquid fuel such as factory waste liquid, and can further use gas fuel (natural gas, by-product
gas, or the like) as fuel. Furthermore, the boiler 2 may be a mixed firing boiler that uses these
15 fuels in combination.
[0019] The steam (superheated steam) generated in the boiler 2 is supplied to the steam
turbines 4 via a main steam line 6. In the present embodiment, the steam from the boiler 2 is
first supplied to the high-pressure turbine 4A disposed upstream, thereby driving the highpressure
turbine 4A.
20 [0020] The steam having finished work in the high-pressure turbine 4A is reheated by a
reheater 35 via a reheat steam line 9 and supplied to the intermediate-pressure turbine 4B
disposed downstream, thereby driving the intermediate-pressure turbine 4B. The reheat steam
line 9 connects between the high-pressure turbine 4A and the intermediate-pressure turbine 4B.
The steam having finished work in the intermediate-pressure turbine 4B is supplied to the low25
pressure turbine 4C disposed downstream via an intermediate-pressure turbine exhaust steam
line 12, thereby driving the low-pressure turbine 4C. The intermediate-pressure turbine
exhaust steam line 12 connects between the intermediate-pressure turbine 4B and the lowpressure
turbine 4C. The steam having finished work in the low-pressure turbine 4C is
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discharged to the condenser 13, thereby producing condensate water.
[0021] A turbine bypass line 7 is also provided which connects the main steam line 6 and
the condenser 13. The turbine bypass line 7 is provided with a turbine bypass valve 8, and by
adjusting the opening degree of the turbine bypass valve 8, part of the steam flowing through
the main steam line 6 can be discharged to the condenser 13 while bypassing 5 the steam turbines
4.
[0022] The high-pressure turbine 4A, the intermediate-pressure turbine 4B, and the lowpressure
turbine 4C respectively include output shafts connected to a rotational shaft of a
generator 5. The generator generates electric power by being driven by power from these
10 steam turbines 4. The electric power generated by the generator is supplied to a power grid
(for example, a commercial grid) via a power transmission line (not shown).
[0023] The high-pressure turbine 4A, the intermediate-pressure turbine 4B, and the lowpressure
turbine 4C may include a common output shaft, and the output shaft may be connected
to a common generator, or a first generator, which is connected to the output shafts of the high15
pressure turbine 4A and the intermediate-pressure turbine 4B, and a second generator, which is
connected the output shaft of the low-pressure turbine 4C, may be provided as generators.
[0024] Further, as indicated by thick lines in FIG. 6, the steam extracted from the highpressure
turbine 4A and the intermediate-pressure turbine 4B (extraction steam; hb, ib) is
supplied to a second high-pressure feed water heater 21 and a first high-pressure feed water
20 heater 20, respectively. Part of the exhaust steam (he) of the high-pressure turbine 4A is also
supplied to the second high-pressure feed water heater 21. Saturated drain (condensation of
the extraction steam hb and the exhaust steam he) discharged from the second high-pressure
feed water heater 21 is supplied to the first high-pressure feed water heater 20. Drain
(saturated drain discharged from the second high-pressure feed water heater 21 and
25 condensation of the extraction steam ib) discharged from the first high-pressure feed water
heater 20 is supplied to a deaerator 17. Further, part of exhaust steam (ie) of the intermediatepressure
turbine 4B is supplied to the deaerator 17. Furthermore, steam extracted from the
low-pressure turbine 4C (low-pressure extraction steam; lb) is supplied to a low-pressure feed
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water heater 16. Saturated drain (condensation of the low-pressure extraction steam lb)
discharged from the low-pressure feed water heater 16 is supplied to the condenser 13.
Hereinafter, in order to avoid complication, auxiliary steam lines from the respective steam
turbines 4 to the respective high-pressure feed water heaters 21, 20 and the low-pressure feed
water heater 16 will be omitted as appropriate 5 in each diagram.
[0025] The condensate water produced in the condenser 13 is pressurized by a condensate
pump 14, supplied to the low-pressure feed water heater 16 through a condensate line 15, and
flows into the deaerator 17 after being heated with the extraction steam (lb) from the lowpressure
turbine 4C. In the deaerator 17, the condensate water is deaerated by part of the
10 exhaust steam (ie) of the intermediate-pressure turbine 4B. The condensate water deaerated
in the deaerator 17 is pressurized by a boiler feed water pump 18, supplied to the first highpressure
feed water heater 20, the second high-pressure feed water heater 21 via a water feed
line 19, and flows into the boiler 2 after being heated with the extraction steam (ib) of the
intermediate-pressure turbine 4B, the extraction steam and the exhaust steam (hb, he) of the
15 high-pressure turbine 4A.
[0026] The boiler 2 is operated in a subcritical state at low load conditions. At that time,
steam mixed water at a furnace outlet of the boiler 2 is separated from steam by a water drain
separator 31, the steam flows into a superheater 36, and the saturated drain flows into the
condenser 13 through a water drain separator drain line 33 and a water drain separator drain
20 control valve 32.
[0027] Next, the water heat storage system 70 provided in the thermal power plant 1 will
be described. The thermal power plant 1 of the present embodiment performs a low load
operation. The low load operation is an operation in which the boiler 2 and the steam turbines
4 are each at the minimum load. For example, the output of the boiler 2 is lowered to its
25 minimum load equivalent to 15% of the rated load, the outputs of the steam turbines 4 are
lowered to 5% of the rated load, and all the outputs of the steam turbines 4 are used for in-house
power. Thus, a so-called grid no-power-transmission operation (parallel no-powertransmission
operation) is realized in which a generator circuit breaker is closed and power
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transmission is set to 0 while maintaining the state of connection to the grid.
[0028] The water heat storage system 70 of the present embodiment stores, as hot water,
the above-described heat that is generated during the low load operation and corresponds to,
for example, the output of 10% which is a difference between 15% of the minimum load of the
boiler 2 and 5% of the loads of the steam turbines 4. More specifically, during 5 the low load
operation, the main steam in the turbine bypass line 7 is used as a heat source to heat the
condensate water fed from the condenser 13 and store it as hot water. Then, the stored hot
water is fed to the deaerator during the subsequent heat discharge operation (during the high
load operation).
10 [0029] Thus, the water heat storage system 70 realizes a reduction in grid transmission
power of the thermal power plant 1 over a long period of time. Further, the water heat storage
system 70 realizes cutting of the low-pressure extraction steam (lb) from the steam turbines 4
to the low-pressure feed water heater 16 during the high load operation after the low load
operation. By cutting the low-pressure extraction steam (lb), it is possible to increase the
15 outputs of the steam turbines 4 corresponding to a heat amount of the cut low-pressure
extraction steam (lb). Alternatively, since the boiler steam flow rate corresponding to the
increased outputs of the steam turbines 4 is reduced, it is possible to reduce the amount of fuel
input to the boiler 2. Hereinafter, the details of the water heat storage system 70 of the present
embodiment, which realizes this, will be described.
20 [0030] The water heat storage system 70 includes a hot water heater 51, hot water pumps
52, a hot water tank 53, and a cold water tank 59, as indicated by thick lines in FIG. 5. The
hot water pumps 52 include a first hot water pump 52A and a second hot water pump 52B.
Further, the water heat storage system 70 includes a TES storage steam line 55, a TES water
drain separator drain line 57, a cold water feed line 49, a cold water storage line 58, and a make25
up water line 60.
[0031] The TES steam line 55 is a line for supplying steam that passes through the turbine
bypass line 7 branched from the main steam line 6 to the hot water heater 51, and includes TES
steam flow control valve 54. Further, the TES water drain separator drain line 57 is a line for
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supplying the saturated drain separated by the water drain separator 31 to the hot water heater
51, and includes a TES water drain separator drain flow control valve 56.
[0032] The cold water feed line 49 is a line branched from the condensate line 15 for
supplying the condensate water fed by the condensate pump 14 to the hot water heater 51, and
includes a cold water flow 5 control valve 50.
[0033] The hot water heater 51 brings the incoming main steam and saturated drain into
contact with the fed cold water to produce hot water. The temperature of the produced hot
water is, for example, 140°C. The hot water heater 51 is, for example, a direct contact type
feed water heater for mixing the incoming condensate water (cold water) with main steam and
10 saturated drain, and heating the mixture.
[0034] The water heat storage system 70 shown in FIGs. 1 and 5 includes, as the hot water
pumps 52, the first hot water pump 52A and the second hot water pump 52B. The first hot
water pump 52A feeds the hot water produced in the hot water heater 51 to the hot water tank
53. The second hot water pump 52B feeds the hot water stored in the hot water tank 53 to the
15 deaerator 17. The hot water may be fed to the deaerator 17 alone, or may be fed together with
the low-pressure feed water at the outlet of the low-pressure feed water heater 16.
[0035] The first hot water pump 52A and the second hot water pump 52B are not
necessarily disposed separately, but an operation may be adopted in which one or a plurality of
hot water pumps 52 having roles of both the first hot water pump 52A and the second hot water
20 pump 52B are installed, and outlet lines of the hot water heater 51 and the hot water tank 53 are
respectively connected to inlets of the hot water pumps 52 and switched as appropriate.
[0036] The hot water tank 53 is a tank for storing the hot water produced in the hot water
heater 51. Since the temperature of the hot water stored in the hot water tank 53 is
approximately 140°C, the hot water tank 53 needs to have a structure capable of withstanding
25 a saturation vapor pressure of such hot water, as well as needs to appropriately be thermally
insulated in order to minimize heat dissipation from the stored hot water. The capacity of the
hot water tank 53 may optionally be determined at a design stage according to a daily low load
operation time required for the thermal power plant 1.
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[0037] The cold water storage line 58 is a line for feeding the condensate water fed by the
condensate pump 14 to the cold water tank 59. The fed condensate water is stored in the cold
water tank 59.
[0038] The make-up water line 60 is a line for feeding the cold water stored in the cold
water tank 59 to 5 the condenser 13.
[0039] The cold water tank 59 is a tank for storing surplus water in the condenser 13 for
make-up water feed to the condenser 13. In the present embodiment, the cold water tank 59
has a water storage amount equal to or greater than the water storage amount of the hot water
tank 53.
10 [0040] As shown in FIG. 7, the control system 80 controls opening and closing of each
control valve (valve) in the thermal power plant 1 in accordance with an instruction from the
outside (such as a control console 81 placed in the power plant) or signals from various sensors
including a temperature sensor and a water level sensor installed in the thermal power plant 1.
Opening and closing of the control valve is controlled in accordance with, for example, a heat
15 charge operation (low load operation), a heat discharge operation (high load operation) which
will be described later. Further, the control system 80 also controls the output of each pump.
The control system 80 includes, for example, a CPU, a memory, and a storage device, and
implements the above-described control by causing the CPU to load programs stored in the
storage device in advance into the memory and execute the programs.
20 [0041] As with the thermal power plant 1 shown in FIG. 2, the thermal power plant 1 may
discharge part of the steam flowing through the reheat steam line 9 to the condenser 13 while
bypassing the steam turbines 4. In this case, with the connection destination of the turbine
bypass line 7 being the outlet of the high-pressure turbine 4A on the reheat steam line 9, the
low-pressure turbine bypass line 10 is branched from the upstream of the inlet of the
25 intermediate-pressure turbine 4B on the reheat steam line 9 and connected to condenser 13 via
the low-pressure turbine bypass valve 11.
[0042]
FIG. 3 shows the storage form of hot water during the heat charge operation, that is, the
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low load operation of the thermal power plant 1. During the low load operation, the amount
of main steam generated in the boiler 2 is greater than the amount of main steam consumed for
power generation in the steam turbines 4, resulting in surplus steam. Further, the boiler 2 is
operated in the subcritical state, and saturated drain continuously flows into the water drain
5 separator 31.
[0043] Upon receiving an instruction to perform the heat charge operation, the control
system 80 opens the TES steam flow control valve 54, the TES water drain separator drain flow
control valve 56, and the cold water flow control valve 50. Thus, as indicated by thick lines
in FIG. 3, all or part of the main steam which is surplus on the main steam line 6 is supplied to
10 the hot water heater 51 via the TES steam line 55 and the TES steam flow control valve 54.
Further, all or part of the saturated drain flowing out of the water drain separator 31 is supplied
to the hot water heater 51 via the TES water drain separator drain line 57 and the TES water
drain separator drain flow control valve 56. Furthermore, as indicated by thick lines in FIG.
3, all or part of the condensate water fed by the condensate pump 14 is fed as cold water to the
15 hot water heater 51 via the cold water feed line 49 and the cold water flow control valve 50.
[0044] The hot water heater 51 brings the incoming main steam and saturated drain into
contact with the cold water to produce hot water of approximately 140°C. The amounts of the
incoming main steam and saturated drain are uniquely decided by the operating states of the
boiler 2 and the steam turbines 4. By controlling the cold water flow control valve 50, the
20 control system 80 always controls the flow rate of the cold water such that the temperature of
the hot water at the outlet of the hot water heater 51 is approximately 140°C. Further, by
controlling the first hot water pump 52A, the control system 80 always controls the water level
of the hot water heater 51. If the main steam pressure rises temporarily or the water level of
the water drain separator 31 rises temporarily due to, for example, a change in operating state
25 of the boiler 2, the control system 80 opens the turbine bypass valve 8 and the water drain
separator drain control valve 32 to discharge surplus steam and saturated drain to the condenser
13 through these control valves. Thus, the hot water heater 51 can maintain the constant
operation.
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[0045] The hot water fed by the first hot water pump 52A is stored in the hot water tank 53.
The heat charge operation is completed when the hot water tank 53 is full or when the low load
operation of the thermal power plant 1 ends. The control system 80 monitors the water level
of the hot water tank 53 and if the control system 80 determines that the hot water tank 53 is
full or if the control system 80 receives a signal indicating that the low load operation 5 has ended,
the control system 80 closes the respective control valves, namely, the TES steam flow control
valve 54, the TES water drain separator drain flow control valve 56, and the cold water flow
control valve 50. The water level of the hot water tank 53 is acquired from a water level sensor
provided in the hot water tank 53.
10 [0046] While the hot water is stored in the hot water tank 53, a considerable amount of
water is fed to the condenser 13 from the cold water tank 59 via the make-up water line 60 due
to, for example, a differential pressure, as indicated by thick lines in FIG. 3.
[0047] If the outputs of the steam turbines 4 are in the low load operation of approximately
5% of the rated load, the control system 80 performs controls so as to cut the extraction steam
15 from the high-pressure turbine 4A, the intermediate-pressure turbine 4B, the low-pressure
turbine 4C to the second high-pressure feed water heater 21, the first high-pressure feed water
heater 20, and the low-pressure feed water heater 16. This is because, during the low load
operation, in each steam turbine 4, a sufficient pressure is not obtained to sweep away the
saturated drain generated in each feed water heater to the deaerator or the condenser.
20 [0048] Further, if the steam turbines 4 are in the low load operation, a main steam
temperature at the inlet of the high-pressure turbine 4A and a reheat steam temperature at the
inlet of the intermediate-pressure turbine 4B need to appropriately be adjusted to avoid a
situation where the exhaust steam of the low-pressure turbine 4C enters a dry region. For this
purpose, a desuperheater may be installed in each of the main steam line 6 and the reheat steam
25 line 9 at the outlet of the boiler 2 to supply a desuperheating spray.
[0049] In a case where the low load operation of the thermal power plant 1 cannot be ended
even if the hot water tank 53 is full, and the surplus state of the main steam from the boiler 2
and the saturated drain from the water drain separator 31 continues, the low load operation of
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the thermal power plant 1 can be continued by supplying the surplus main steam and saturated
drain to the condenser 13 via the turbine bypass line 7 and the water drain separator drain line
33. At that time, however, the heat of the steam and the drain that have flowed into the
condenser 13 is released to a condenser cooling medium such as seawater.
[0050]
FIG. 4 shows the discharge form of hot water during the heat discharge, that is, the high
load operation of the thermal power plant 1. The high load operation here generally refers to
an operation at not less than 30% of the rated load of the thermal power plant.
[0051] The control system 80 operates the second hot water pump 52B upon receiving the
10 instruction for the heat discharge operation. Consequently, the hot water stored in the hot
water tank 53 is fed to the condensate line 15 by the second hot water pump 52B and flows into
the deaerator 17. In this case, as indicated by thick dashed lines in FIG. 4, the condensate
water from the condenser 13 may be fed to the deaerator 17 together with the hot water after
being heated by the low-pressure feed water heater 16 via the condensate line 15, or all or part
15 of the condensate water may be stored in the cold water tank 59 via the cold water storage line
58.
[0052] During the heat discharge operation, the supply of the extraction steam from the
low-pressure turbine 4C to the low-pressure feed water heater 16 under the high load operation
is stopped (cut) to realize the increase in output of the generator 5 or a reduction in fuel
20 consumption of the boiler 2. More specifically, the control system 80 switches all or part of
the condensate water flowing into the deaerator 17 to hot water, if the steam turbines 4 are in
the high load operation state. As a result, since the amount of the condensate water passing
through the low-pressure feed water heater 16 is reduced or cut off, the extraction steam
supplied from the low-pressure turbine 4C to the low-pressure feed water heater 16 is reduced
25 or cut. Thus, the steam turbines 4 can be operated at an increased output corresponding to the
reduction in extraction steam, making it possible to increase the output of the generator 5. At
this time, if the increased output operation is not required in this operating state, the main steam
flow rate from the boiler 2 is reduced to keep the load on the steam turbines 4 constant, and the
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fuel consumption in the boiler 2 may also be reduced.
[0053] If the operating load is low and an internal temperature of the deaerator 17 decreases
below the hot water temperature, it is necessary to reduce the temperature of the water flowing
into the deaerator 17 in accordance with the internal temperature of the deaerator 17. In such
case, the condensate water is fed through the low-pressure feed water heater 5 16 and mixed with
hot water fed from the hot water tank 53.
[0054] The heat discharge operation ends when the water level of the hot water tank 53
reaches the minimum water level. That is, during the heat discharge operation, the control
system 80 monitors the water level of the hot water tank 53 and stops the second hot water
10 pump 52B when the water level reaches the predetermined minimum water level.
Consequently, the thermal power plant 1 transitions to a normal plant operation. In the normal
plant operation, feeding of hot water via the second hot water pump 52B is stopped, as well as
feeding of cold water from the outlet of the condensate pump 14 to the cold water tank 59 is
also stopped, and all the condensate water is fed to deaerator 17 via low-pressure feed water
15 heater 16.
[0055]
FIG. 5 is an explanatory diagram of an additional installation range in a case where the
water heat storage system 70 is additionally installed in the thermal power plant 1. The
additional installation range of the water heat storage system 70 is a range illustrated by thick
20 lines in the diagram. As described above, the water heat storage system 70 is mainly
composed of the hot water heater 51, the hot water tank 53, the cold water tank 59, and the hot
water pump 52. A construction cost can be reduced by additionally installing the water heat
storage system 70 to the existing thermal power plant 1 by utilizing an empty space of the site.
[0056] Next, the schematic specifications of the water heat storage system 70 in the 1,000
25 MW class coal-fired unit will be exemplified below. The cold water tank 59 has a water
storage amount equal to or greater than the water storage amount of the hot water tank 53.
This is so that if the hot water stored in the hot water tank 53 is fed to the boiler feed water line,
the condensate water corresponding to that feed amount can be stored in the cold water tank 59.
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Hot water heater: direct contact type feed water heater
Capacity of hot water tank: 5 × 3,300 m3 (0.3 MPa), total 16,500 m3
Capacity of hot water tank capacity: 2 × 8,300 m3 (atmospheric pressure), total 16,600
m3
Heat charging time: approximately 5 6.0 hours
Heat discharging time: approximately 5.0 hours (100% ECR)
[0057] According to the above-described specifications, in the case of the 1,000 MW class
coal-fired unit, when the boiler is operated at the minimum load of 15%, the heat of the
steam/saturated drain equivalent to 10% load (100 MW) excluding 5% (50 MW) of the in-house
10 power is stored, allowing for the parallel non-power-transmission operation (the operation at
0% of external power transmission) with an inertia remaining.
[0058] Since the water heat storage system 70 adopts the method of returning the stored
heat to the deaerator 17 together with the heat medium, it is possible to recover substantially all
of the heat into the cycle. It is unnecessary to consider, in water heat storage, a heat exchange
15 loss between water and/or steam and the heat medium which has to be considered in molten
salt heat storage or metal PCM heat storage. However, it is necessary to consider heat
dissipation during the storage in the hot water tank 53 and a heat loss due to piping warming at
the start of heat storage (3% to 5% in total, depending on the time until heat discharge operation).
Due to a limit of the amount of water that can be fed to the deaerator 17 during heat discharge
20 operation (limit on mass balance), the heat charging time is approximately 6.0 hours, whereas
the heat discharge time is approximately 5.0 hours at 100% ECR.
[0059] Operation images of the conventional plant assuming the daytime DSS operation
and the thermal power plant 1 of the present embodiment including the water heat storage
system 70 in the coal-fired thermal power plant are compared. Three units of Plants A, B, C
25 are connected to the grid. An assumed operation during a time period (for example, daytime)
when a power generation amount of renewable energy is large and surplus power is generated
can be exemplified as follows.

17
21-00188PCT_specification
- 17 -
Plant A: Minimum load 15% operation (5% in-house power, 10% power transmission)
Plant B: DSS operation (temporary stop and restart of plant)
Plant C: DSS operation (temporary stop and restart of plant)
Total power transmission amount: equivalent to 10% load

Plant A: parallel no-power-transmission operation (minimum load 15% operation (5% inhouse
power, 10% heat storage))
Plant B: parallel no-power-transmission operation (minimum load 15% operation (5% inhouse
power, 10% heat storage))
10 Plant C: parallel no-power-transmission operation (minimum load 15% operation (5% inhouse
power, 10% heat storage))
Total power transmission amount: no power transmission (0% load)
[0060] As described above, in the case of the conventional plant, the one plant (here, Plant
A) operates at the minimum load of 15% and the remaining two plants (Plants B and C) operate
15 in DSS. Even in that case, 10% of power is transmitted to the grid. On the other hand, the
thermal power plant 1 of the present embodiment is capable of the parallel no-powertransmission
operation in all the thermal power plants.
[0061] That is, by using the thermal power plant 1 of the present embodiment, all the three
plants can reduce the power transmission amount to no power transmission. Thus, it is
20 possible to avoid the DSS operation while increasing the receiving amount of renewable energy.
Further, in the thermal power plant 1 of the present embodiment, by discharging the stored heat
during peak demand hours (for example, in the evening), fuel consumption can be reduced
(approximately 3% to 4%) during the peak demand hours.
[0062] The advantages of introducing the water heat storage system 70 of the present
25 embodiment into the thermal power plant 1 are as follows.
(1) Contribution to expanding introduction of renewable energy
By lowering the plant minimum load, it is possible to expand the room for receiving
renewable energy while maintaining a grid inertia.
18
21-00188PCT_specification
- 18 -
(2) Reduction in plant start-up cost by low load continuous operation
By performing a continuous low load operation with inexpensive coal, it is possible to
significantly reduce a cost of start-up light oil which is unavoidable in the DSS operation.
(3) Avoidance of equipment wear/start-up trouble due to DSS operation
By continuously operating the power generation unit, it is possible to avoid 5 various risks
associated with the DSS operation.
(4) Response to immediate load increase request, etc.
Since the generator 5 is continuously operated at an extremely low load while maintaining
grid parallelism, it is possible to respond to even an immediate load increase request due to a
10 sudden accident or the like.
(5) Heat recovery at plant start-up
It is possible to recover/utilize heat that has conventionally been thrown away as a starting
loss.
[0063] As described above, the thermal power plant 1 of the present embodiment includes
15 the water heat storage system 70 and during the low load operation, the heat of the main steam
and the saturated drain corresponding to the difference between the steam generated from the
boiler 2 and the steam consumed in the steam turbines 4 is stored in the hot water tank 53 as
the hot water. Further, during the high load operation, the stored hot water is fed to the
deaerator 17.
20 [0064] Thus, during the low load operation, even if the operating load of the generator 5
(steam turbines 4) is reduced below the minimum load of the boiler 2, the thermal power plant
1 of the present embodiment can store the heat corresponding to the difference as the hot water.
That is, during the low load operation, the operating load of the generator 5 (steam turbines 4)
can be reduced below the minimum load of the boiler 2 without wasting heat. Thus, it is
25 possible to realize the reduction in grid transmission power of the thermal power plant 1 over a
long period of time. Further, during the low load operation, it is possible to reduce the power
transmitted from the coal-fired thermal power plant to the power grid to almost 0% load
(parallel no-power-transmission operation).
19
21-00188PCT_specification
- 19 -
[0065] Furthermore, since the hot water stored during the low load operation is fed to the
deaerator 17 during the high load operation, it is possible to reduce the load on the low-pressure
feed water heater 16. Thus, it is possible to reduce or cut the low-pressure extraction steam
from the steam turbines 4 during the high load operation. Then, it is possible to increase the
outputs of the steam turbines 4 corresponding to the heat amount of the 5 reduced or cut lowpressure
extraction steam. Alternatively, if the outputs of the steam turbines 4 are maintained,
it is possible to reduce the steam flow rate from the boiler 2 by the amount corresponding to the
heat amount of the reduced or cut low-pressure extraction steam and as a result, it is possible
to reduce the amount of fuel input to the boiler 2.
10 [0066] That is, according to the present embodiment, since the plant power transmission
amount is decreased by reducing the operating load of the generator 5 (steam turbines 4) in the
thermal power plant below the boiler minimum load, it is possible to provide the thermal power
technology, enabling flexible response against change in power generation amount of renewable
energy and maintaining high operability.
15 [0067]
In the above-described embodiment, the case is described as an example in which the
thermal power plant 1 includes the one low-pressure feed water heater 16 and the one second
high-pressure feed water heater 21. However, the thermal power plant 1 may include a
plurality of low-pressure feed water heaters 16 and a plurality of second high-pressure feed
20 water heaters 21.
[0068] FIG. 8 shows a configuration example in which the thermal power plant 1 includes
four low-pressure feed water heaters 16 and two second high-pressure feed water heaters 21.
[0069] In this case, part of the extraction steam extracted from each steam turbine 4 and
part of the exhaust steam exhausted from each steam turbine 4 are supplied to different locations
25 depending on their temperatures, respectively.
[0070] For example, the high-pressure extraction steam hb of the high-pressure turbine 4A
is supplied to the second high-pressure feed water heater 21 on the downstream side. The
saturated drain (the condensation of the high-pressure extraction steam hb) discharged from the
20
21-00188PCT_specification
- 20 -
second high-pressure feed water heater 21 on the downstream side is supplied to the second
high-pressure feed water heater 21 on the upstream side. Part of the high-pressure exhaust
steam he of the high-pressure turbine 4A is supplied to the second high-pressure feed water
heater 21 on the upstream side. The saturated drain (the condensation of the high-pressure
extraction steam hb and the high-pressure exhaust steam he) discharged from 5 the second highpressure
feed water heater 21 on the upstream side is supplied to the first high-pressure feed
water heater 20. The intermediate-pressure extraction steam ib of the intermediate-pressure
turbine 4B is supplied to the first high-pressure feed water heater 20. The saturated drain (the
condensation of the high-pressure extraction steam hb and the intermediate-pressure extraction
10 steam ib, as well as the high-pressure exhaust steam he) discharged from the first high-pressure
feed water heater 20 is supplied to the deaerator 17. Part of the intermediate-pressure exhaust
steam ie of the intermediate-pressure turbine 4B is supplied to the deaerator 17. Extraction
steams (lb1, lb2, lb3, lb4) of the low-pressure turbine 4C are supplied from downstream of the
respective low-pressure feed water heaters 16 in descending order of temperature. Saturated
15 drains (condensations of the extraction steams) discharged from the respective low-pressure
feed water heaters 16 are supplied to the low-pressure feed water heater 16 on the upstream side
of the respective low-pressure feed water heaters 16. The saturated drain (the condensation
of the extraction steam lb1, lb2, lb3, lb4) discharged from the low-pressure feed water heater
16 on the most upstream side is supplied to the condenser 13.
20 [0071] Thus, steam can be supplied to the optimum feed water heater according to the steam
temperature, and efficient operation can be achieved without wasting heat.
[0072]
Further, in the above-described embodiment or Modification 1, during the heat discharge
operation, the confluent point of the hot water fed from the hot water tank 53 is disposed on the
25 outlet side of the most downstream low-pressure feed water heater 16. For example, if the
plurality of low-pressure feed water heaters 16 are provided, it may be configured such that a
plurality of confluent points are disposed and switched according to the temperature of the hot
water.
21
21-00188PCT_specification
- 21 -
[0073] In the present modification, the confluent point where the hot water from the hot
water tank 53 joins the condensate line 15 is disposed on the outlet side of each low-pressure
feed water heater 16. The temperature of the condensate water fed by the condensate pump
14 rises as the condensate water passes through the low-pressure feed water heater 16. In the
present modification, the hot water is joined at the confluent point where the 5 temperature of the
condensate water on the outlet side of the low-pressure feed water heater 16 is not lowered.
[0074] In order to achieve this, the control system 80 monitors the temperature of the hot
water and when the temperature of the hot water decreases, sequentially switches the confluent
point to a low-temperature side (the low-pressure feed water heater 16 on one step upstream
10 side). The switching of the confluent point to the low-temperature side is performed, for
example, when the temperature of the hot water flowing out of the hot water tank 53 falls below
the outlet temperature of each low-pressure feed water heater 16 for a certain period of time.
[0075] Hereinafter, as with Modification 1, a detailed description will be given by taking,
as an example, a case where four low-pressure feed water heaters 16A, 16B, 16C, 16D are
15 sequentially provided in series from the downstream side downstream of the condensate pump
14 on the condensate line 15. FIG. 9 shows only the relevant parts extracted.
[0076] As shown in FIG. 9, in the present modification, the thermal power plant 1 includes
a hot water feed line 71 for causing the hot water in the hot water tank 53 to join the condensate
line 15, and temperature sensors 72A, 72B, 72C, 72D, 72E for measuring the temperature of
20 the condensate water, switching valves 73A, 73B, 73C, 73D, 73E, 73F, and the flow control
valve 76. Further, the hot water feed line 71 includes three branch points 74A, 74B, 74C.
Furthermore, the hot water feed line 71 joins at confluent points 75A, 75B, 75C, 75D disposed
on the outlet sides of the low-pressure feed water heaters 16A, 16B, 16C, 16D, respectively.
[0077] Hereinafter, if no distinction is needed, a description will be given by
25 representatively referring to the low-pressure feed water heater 16, the temperature sensor 72,
the switching valve 73, the branch point 74, and the confluent point 75.
[0078] The branch point 74A is a branch point where the hot water feed line 71 toward the
low-pressure feed water heaters 16B, 16C, 16D branches from the hot water feed line 71 toward
22
21-00188PCT_specification
- 22 -
the outlet of the low-pressure feed water heater 16A. The branch point 74B is a branch point
where the hot water feed line 71 toward the low-pressure feed water heaters 16C, 16D branches
from the hot water feed line 71 toward the outlet of the low-pressure feed water heater 16B.
The branch point 74C is a branch point where the hot water feed line 71 toward the low-pressure
feed water heater 16D branches from the hot water feed line 71 toward the 5 outlet of the lowpressure
feed water heater 16C.
[0079] The temperature sensors 72A, 72B, 72C, 72D are respectively disposed near the
outlets of the low-pressure feed water heaters 16A, 16B, 16C, 16D, and measure the
temperature of the condensate water near the outlets. The temperature sensor 72E is disposed
10 between the outlet of the hot water tank 53 and the branch point 74A, and measures the
temperature of the hot water fed from the hot water tank 53. In FIG. 9, the temperature sensor
72E is disposed between the second hot water pump 52B and the branch point 74.
[0080] Further, the switching valve 73A is disposed between the branch point 74A and the
confluent point 75A, and controls the inflow into the hot water feed line 71 toward the outlet of
15 the low-pressure feed water heater 16A. The switching valve 73B is disposed between the
branch point 74B and the confluent point 75B, and controls the inflow into the hot water feed
line 71 toward the outlet of the low-pressure feed water heater 16B. The switching valve 73C
is disposed between the branch point 74C and the confluent point 75C, and controls the inflow
into the hot water feed line 71 toward the outlet of the low-pressure feed water heater 16C.
20 The switching valve 73D is disposed between the branch point 74C and the confluent point
75D, and controls the inflow into the hot water feed line 71 toward the outlet of the low-pressure
feed water heater 16D. The flow control valve 76 is disposed in a downstream flow of the
second hot water pump 52B, and controls the flow rate of hot water.
[0081] At predetermined time intervals, the control system 80 receives temperature
25 information from the respective temperature sensors 72, sequentially compares the hot water
temperature received from the temperature sensor 72E with the outlet temperatures received
from the respective temperature sensors 72A, 72B, 72C, 72D, and switches the confluent point
according to the comparison result.
23
21-00188PCT_specification
- 23 -
[0082] Herein, the flow of a confluent point switching process by the control system 80
will be described. FIG. 10 is a processing flow of the confluent point switching process of the
present modification.
[0083] Herein, both the confluent points and the low-pressure feed water heaters 16 are
numbered consecutively from the downstream side. Further, the N (N is an 5 integer not less
than 1) confluent point and the N low-pressure feed water heater 16 are provided. Furthermore,
n is a counter. Then, T1 is a "certain period of time" for making switching determination.
Moreover, the temperature of the hot water and the temperature on the outlet side of the lowpressure
feed water heater 16 are measured at predetermined time intervals.
10 [0084] The control system 80 first initializes the counter (n=1) and initializes a temporal
counter Δt (Δt=0) (step S1001).
[0085] First, the control system 80 sets the first confluent point to a confluent point to be
used (referred to as a use confluent point) (step S1002), and controls each switching valve 73
such that the hot water joins at the use confluent point.
15 [0086] Next, the control system 80 acquires a hot water temperature TH and an outlet-side
temperature TLn of the n-th low-pressure feed water heater 16 (comparison target heater) (step
S1003).
[0087] The control system 80 determines whether the acquired hot water temperature TH
is lower than the outlet-side temperature TLn (step S1004). If the hot water temperature TH
20 is not lower than the outlet-side temperature TLn (No), the control system 80 initializes the
temporal counter Δt (step S1009) and the process returns to step S1003.
[0088] On the other hand, if the hot water temperature TH is lower than the outlet-side
temperature TLn (Yes), the control system 80 determines whether this state has elapsed for the
certain period of time T1 (step S1005). If this state has not yet elapsed for the certain period
25 of time (No), the process returns to step S1003.
[0089] On the other hand, if the certain period of time has elapsed (Yes), the control system
80 switches the use confluent point to the confluent point disposed on the outlet side of the lowpressure
feed water heater 16 one stage upstream (step S1006), and controls each switching
24
21-00188PCT_specification
- 24 -
valve 73 such that the hot water joins at the use confluent point after the switching.
[0090] Thereafter, the control system 80 increments the counter n by 1, initializes the
temporal counter Δt (step S1007), and determines whether the use confluent point becomes the
most upstream confluent point (n=N?) (step S1008). If the confluent point set as the use
confluent point is not the most upstream confluent point, the process returns 5 to step S1003 to
repeat the process. On the other hand, if the most upstream confluent point is set as the use
confluent point, the process ends.
[0091] A specific example of the above-described confluent point switching process will
be described. First, the control system 80 compares the hot water temperature with an outlet
10 temperature (TLA) acquired by the temperature sensor 72A. If the hot water temperature is
not lower than the outlet temperature TLA, the control system 80 opens the switching valve
73A and closes the switching valves 73B, 73C, 73D. Consequently, the hot water joins the
condensate line 15 at the confluent point 75A, that is, on the outlet side of the low-pressure feed
water heater 16A.
15 [0092] If the hot water temperature remains below the outlet temperature TLA for a certain
period of time, the control system 80 compares the hot water temperature with an outlet
temperature (TLB) acquired by the temperature sensor 72B. If the hot water temperature is
not lower than the outlet temperature TLB, the control system 80 opens the switching valve
73B and closes the switching valves 73A 73C, 73D. Consequently, the hot water joins the
20 condensate line 15 at the confluent point 75B, that is, between the outlet of the low-pressure
feed water heater 16B and the inlet of the low-pressure feed water heater 16A.
[0093] If the hot water temperature remains below the outlet temperature TLB for a certain
period of time, the control system 80 compares the hot water temperature with an outlet
temperature (TLC) acquired by the temperature sensor 72C. If the hot water temperature is
25 not lower than the outlet temperature TLC, the control system 80 opens the switching valve
73C and closes the switching valves 73A, 73B, 73D. Consequently, the hot water joins the
condensate line 15 at the confluent point 75C, that is, between the outlet of the low-pressure
feed water heater 16C and the inlet of the low-pressure feed water heater 16B.
25
21-00188PCT_specification
- 25 -
[0094] If the hot water temperature remains below the outlet temperature TLC for a certain
period of time, the control system 80 opens the switching valve 73D and closes the switching
valves 73A, 73B, 73C. Consequently, the hot water joins the condensate line 15 at the
confluent point 75D, that is, between the outlet of the low-pressure feed water heater 16C and
the inlet of the low-pressure feed 5 water heater 16B.
[0095] The control system 80 may be configured to start control by the switching valve 73,
if the temperature of the hot water fed from the hot water tank 53 is less than a predetermined
threshold. More specifically, the above-described confluent point switching process is started,
if the temperature of the hot water fed from the hot water tank 53 decreases from 140°C to
10 100°C.
[0096] Further, in the present modification, the hot water temperature and the outlet
temperatures of the respective low-pressure feed water heaters 16 are sequentially compared
from the downstream side of the low-pressure feed water heaters 16 to control the switching
valves 73. However, the opening and closing control is not limited to this. For example, the
15 control system 80 may compare the hot water temperature with the outlet temperatures of all
the low-pressure feed water heaters 16 to decide the use confluent point. In this case, the
respective switching valves 73 are controlled such that the hot water joins at the confluent point
75 on the outlet side of the low-pressure feed water heater 16 having the outlet temperature
lower than the hot water temperature and closest to the hot water temperature.
20 [0097] In the example of FIG. 9, in the case where the hot water temperature is lower than
the outlet temperature of the low-pressure feed water heater 16C, even if the hot water
temperature is lower than the outlet temperature of the low-pressure feed water heater 16D, the
hot water is joined at the confluent point 75D. For example, furthermore, a confluent point
may further be disposed on the inlet side of the low-pressure feed water heater 16D and if the
25 hot water temperature is lower than the outlet temperature of the low-pressure feed water heater
16D, control may be performed so as to cause the hot water to join at the said confluent point.
In this case, since the number of confluent points is N+1, it is determined whether n=N+1 in
step S1008 of the processing flow of the confluent point switching process shown in FIG. 10.
26
21-00188PCT_specification
- 26 -
[0098] According to the present modification, during the heat discharge operation, when
the hot water in the hot water tank 53 is joined to the condensate line 15, the confluent point is
changed according to the temperature. That is, the hot water is joined at the outlet side of the
low-pressure feed water heater 16 having the outlet temperature lower than the hot water
temperature and closest to the hot water temperature. Thus, the temperature 5 of the condensate
water heated by the low-pressure feed water heater 16 is not lowered by the joined hot water,
making it possible to efficiently utilize the low-pressure feed water heater 16 and the hot water.
[0099]
In the above-described embodiment, during the heat charging operation, the hot water
10 produced in the hot water heater 51 is stored in the hot water tank 53. In the present
modification, control is performed such that part of the hot water produced in the hot water
heater 51 is fed to not the hot water tank 53 but the deaerator 17.
[0100] During the heat charging operation, since the steam turbines 4 are operated at the
extremely low load, the extraction steam aiming at heating the feed water may be cut and at the
15 same time, the steam for heating the deaerator 17 may be supplied from the auxiliary steam
system. This is because even during the low load operation, it is necessary that an exhaust gas
temperature of the boiler 2 is maintained above a certain temperature and it is essential that the
feed water is deaerated. In this operating state, since the temperature of the condensate water
flowing into the deaerator 17 decreases as the extraction steam of the low-pressure feed water
20 heater 16 is cut, in order to compensate therefor, the amount of auxiliary steam needs to be
increased. In the present modification, the decrease in temperature of the condensate water
flowing into the deaerator 17 due to the cutting of the extraction steam is compensated by
feeding outlet hot water of the hot water heater 51. Thus, it is possible to suppress the increase
in auxiliary steam consumption of the thermal power plant 1.
25 [0101] FIG. 11 shows parts of the thermal power plant 1 related to the present modification.
As indicated by a thick dotted line in the diagram, in the present modification, part of the hot
water produced in the hot water heater 51 is fed to the deaerator 17 during the heat charging
operation.
27
21-00188PCT_specification
- 27 -
[0102] A predetermined amount of water may continuously be fed from the hot water heater
51 to the deaerator 17 during the heat charging operation. Further, control may be performed
such that hot water is fed, if the temperature of the condensate water fed to the deaerator 17 is
decreased.
[0103] In the latter case, the thermal power plant 1 includes the temperature 5 sensor 72 and
the flow control valve 76. The temperature sensor 72 is disposed on the outlet side of the lowpressure
feed water heater 16 to measure the temperature of the condensate water on the outlet
side of the low-pressure feed water heater 16. Further, the flow control valve 76 is disposed
on the hot water feed line 71 connecting the hot water tank 53 and the condensate line 15 to
10 control the feeding of the hot water from the hot water heater 51 to the deaerator 17.
[0104] The control system 80 acquires temperature data measured by the temperature
sensor 72 at predetermined time intervals and if the temperature is less than a predetermined
threshold, issues an instruction to open the flow control valve 76, and feeds the hot water from
the hot water heater 51 to the deaerator 17.
15 [0105] Thus, the hot water from the hot water heater 51 is mixed with the condensate water
and fed to the deaerator 17, making it possible to increase the temperature of the condensate
water flowing into the deaerator and making it possible to suppress the auxiliary steam
consumption.
[0106] Further, the above-described operation is particularly useful when an existing unit
20 is remodeled which has a restriction on a piping size on the auxiliary steam line due to its layout
or in a case where an unnecessary increase in diameter of the piping on the auxiliary steam line
is to be avoided when a unit is newly installed. Furthermore, instead of performing feeding
of condensate water to the hot water heater 51 and water feed to the deaerator 17 independently
of each other, by diverting part of the hot water to the water feed to the deaerator 17, it is
25 possible to perform the operation within the capacity of the condensate pump 14 or a condensate
demineralizer when the existing unit is remodeled. When the unit is newly installed, it is also
possible to design the capacities of pumps/devices to simultaneously satisfy the feeding of
condensate water to the hot water heater 51 and the water feed to the deaerator 17. However,
28
21-00188PCT_specification
- 28 -
in view of the fact that a cost is expected to increase due to the increased capacities of the
pumps/devices, it is desirable to adopt the operation where part of the hot water is diverted to
the water feed to the deaerator 17, as when the existing unit is remodeled.
[0107]
In the above-described embodiment, two tanks, namely, the hot water tank 5 53 and the cold
water tank 59 are provided to store the hot water in the hot water tank 53 at the time of heat
charging operation and to store the used hot water in the cold water tank 59 at the time of heat
discharging operation. However, the present invention is not limited to this configuration.
For example, one thermocline tank 61 may be provided to have the functions of the hot water
10 tank 53 and the cold water tank 59.
[0108] The thermocline tank 61 is a single tank type tank which includes a hot water section,
a cold water section, and a thermocline in one tank and can store hot water and cold water.
The hot water section is located in an upper portion of the tank, the cold water section is located
in a lower portion of the tank, and the hot water section and the cold water section are separated
15 by the thermocline.
[0109] FIG. 12 shows parts of the thermal power plant 1 related to the present modification.
As shown in the diagram, the thermocline tank 61 includes a hot water inlet/outlet through
which hot water is fed/discharged and a cold water inlet/outlet through which cold water is
fed/discharged.
20 [0110] As indicated by a thick line in FIG. 12, the hot water inlet/outlet is connected to the
hot water feed line 71 and a hot water storage line 64 for feeding hot water from the hot water
heater 51. On the other hand, the cold water inlet/outlet is connected to a cold water return
line 62 connected to the condenser 13 and a second cold water storage line 63 branched from
the cold water feed line 49.
25 [0111] During the heat charging operation, in the above-described embodiment, condensate
water is fed from the condenser 13 to the hot water heater 51, and hot water is produced in the
hot water heater 51 and stored in the hot water tank 53. Then, while condensate water is fed
from the condenser 13 to the hot water heater 51, an amount of water corresponding to the fed
29
21-00188PCT_specification
- 29 -
condensate water is fed from the cold water tank 59 to the condenser 13.
[0112] In the present modification, as in the above-described embodiment, water is fed
from the condenser 13 to the hot water heater 51, and hot water is produced in the hot water
heater 51 and stored in the hot water section of the thermocline tank 61 through the hot water
storage line 64. However, in the present modification, as indicated by a thick 5 dashed line in
FIG. 13, the amount of water corresponding to the fed condensate water is fed from the cold
water section of the thermocline tank 61 to the condenser 13 via the cold water return line 62.
Further, as indicated by a dotted line, water partially passes from the hot water heater 51 to the
deaerator 17.
10 [0113] Furthermore, during the heat discharging operation, in the above-described
embodiment, hot water is fed from the hot water tank 53 to the deaerator 17 and accordingly,
the condensate water in the condenser 13 is stored to the cold water tank 59 via the cold water
storage line 58. On the other hand, in the present modification, as indicated by a thick line in
FIG. 14, if hot water is fed from the hot water section of the thermocline tank 61 to the deaerator
15 17, water is accordingly fed from the condenser 13 to the cold water section of the thermocline
tank 61 via the second cold water storage line 63 branched downstream of the condensate pump
14 on the condensate line 15, as indicated by a thick dashed line.
[0114] In the present modification, the capacity of the thermocline tank 61 is an addition
of a capacity corresponding to the thermocline that does not contribute to the tank capacity to
20 a required capacity of the hot water tank 53 or the cold water tank 59, and is always operated
in a full water state.
[0115] According to the present modification, by using the thermocline tank 61, it is
possible to save space related to installation of the tank, which is effective especially in a case
where there are restrictions on a power generation site. Further, if the thermocline tank 61 is
25 inexpensive, it is possible to reduce a cost compared to installing tanks separately.
[0116] In order to allow the thermocline tank 61 to have a structure that can withstand the
saturation pressure of hot water, and to allow the hot water and the cold water to flow in and
out while avoiding mixing thereof in the tank, the configuration and operation of the line
30
21-00188PCT_specification
- 30 -
connected to the hot water section and the cold water section of the thermocline tank 61 are the
same as the case where the hot water tank 53 and the cold water tank 59 are separately installed.
[0117]
In the above-described embodiment, the case has been described as an example where, as
the boiler 2, the supercritical boiler is used in a supercritical state except 5 under the low load
conditions. However, the type of boiler is not limited to this. For example, a subcritical
boiler may be used which is operated in the subcritical state at all loads.
[0118] The subcritical boiler includes a steam drum 34, a continuous blow tank 37, a flash
tank 38, and an intermittent blow line 39 instead of the water drain separator 31, as indicated
10 by thick lines in FIG. 15.
[0119] The steam drum 34 separates steam and saturated water (saturated drain). The
separated steam flows into the superheater 36, and the saturated drain flows into the continuous
blow tank 37. The saturated drain flows into the flash tank 38 after undergoing steam
separation and steam recovery in the continuous blow tank 37. The intermittent blow line 39
15 disposed in the steam drum 34 is used to avoid an increase in drum level due to boiler water
swelling at startup and to blow boiler water when quality of the boiler water deteriorates.
[0120] Part of the saturated drain having flowed into the continuous blow tank 37 becomes
flash steam, is supplied to the deaerator 17, and is used as part of heating steam of the deaerator
17.
20 [0121] When a subcritical drum is used, the TES water drain separator drain line 57 is
branched from the intermittent blow line 39. Then, during the heat charging operation, all or
part of the saturated drain separated in the steam drum 34 is supplied to the hot water heater 51
via the TES water drain separator drain line 57 branched from the intermittent blow line 39 and
the TES water drain separator drain flow control valve 56.
25 [0122] During the heat charging operation, also in the subcritical boiler, as in the case where
the supercritical boiler is used, all or part of the main steam which is surplus on the main steam
line 6 is supplied to the hot water heater 51 via the TES steam line 55 and the TES steam flow
control valve 54. During the heat charging operation, the hot water heater 51 uses the main
31
21-00188PCT_specification
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steam and the saturated drain supplied from the steam drum 34 as heat sources, and produces
hot water from condensate water fed from the condenser 13.
[0123] In the subcritical boiler, the amount of drain drawn from the steam drum 34 is
decided based on the amount of fuel input and the flow rate of the main steam. The level of
the steam drum 34 is controlled by a drum level control valve. If the drum 5 level temporarily
increases due to fluctuations in operating state, in addition to the control by the drum level
control valve, an intermittent blow valve is opened and closed as necessary.
[0124] That is, the control system 80 monitors the drum level and if the drum level exceeds
a predetermined threshold for not shorter than a certain period of time, decreases the opening
10 degree of the drum level control valve to suppress an inflow feed water amount. Alternatively,
the control system 80 may open the intermittent blow valve to extract saturated drain as
intermittent blow. The drum level is acquired from a water level sensor provided in the steam
drum 34.
[0125]
15 The heat source of the hot water heater 51 is not limited to turbine bypass steam. The
heat source may be, for example, reheated steam passing through the reheated steam line, or
extraction steam or exhaust steam from each steam turbine 4.
[0126] The respective modifications may be combined. For example, the thermal power
plant 1 of the above-described embodiment includes the plurality of low-pressure feed water
20 heaters 16, and can include at least one of the configuration where the confluent destination of
the hot water feed line 71 is switched according to the temperature of the hot water, the
configuration where water can partially pass, the configuration where the thermocline tank 61
is used instead of the hot water tank 53 and the cold water tank 59, the configuration where the
subcritical boiler is used, and the configuration where various kinds of steam are used as the
25 heat source of the hot water heater 51.
Reference Signs List
[0127]
32
21-00188PCT_specification
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1 Thermal power plant
2 Boiler
4 Steam turbine
4A High-pressure turbine
4B Intermediate-5 pressure turbine
4C Low-pressure turbine
5 Generator
6 Main steam line
7 Turbine bypass line
10 8 Turbine bypass valve
9 Reheat steam line
10 Low-pressure turbine bypass line
11 Low-pressure turbine bypass valve
12 Intermediate-pressure turbine exhaust steam line
15 13 Condenser
14 Condensate pump
15 Condensate line
16 Low-pressure feed water heater
16A Low-pressure feed water heater
20 16B Low-pressure feed water heater
16C Low-pressure feed water heater
16D Low-pressure feed water heater
17 Deaerator
18 Boiler feed water pump
25 19 Boiler feed water line
20 First high-pressure feed water heater
21 Second high-pressure feed water heater
31 Water drain separator
33
21-00188PCT_specification
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32 Water drain separator drain control valve
33 Water drain separator drain line
34 Steam drum
35 Reheater
5 36 Superheater
37 Continuous blow tank
38 Flash tank
39 Intermittent blow line
49 Cold water feed line
10 50 Cold water flow control valve
51 Hot water heater
52 Hot water pump
52A First hot water pump
52B Second hot water pump
15 53 Hot water tank
54 TES steam flow control valve
55 TES steam line
56 TES water drain separator drain flow control valve
57 TES water drain separator drain line
20 58 Cold water storage line
59 Cold water tank
60 Make-up water line
61 Thermocline tank
62 Cold water return line
25 63 Second cold water storage line
64 Hot water storage line
70 Water heat storage system
71 Hot water feed line
34
21-00188PCT_specification
- 34 -
72 Temperature sensor
72A Temperature sensor
72B Temperature sensor
72C Temperature sensor
72D 5 Temperature sensor
72E Temperature sensor
73A Switching valve
73B Switching valve
73C Switching valve
10 73D Switching valve
74 Branch point
74A Branch point
74B Branch point
74C Branch point
15 75 Confluent point
75A Confluent point
75B Confluent point
75C Confluent point
75D Confluent point
20 76 Flow control valve
80 Control system
81 Control console

1. A thermal power plant, comprising:
a boiler; a steam turbine driven by steam from the boiler; a turbine bypass line bypassing
the steam turbine to supply steam; a condenser for cooling exhaust steam of 5 the steam turbine
to produce condensate water; a low-pressure feed water heater for heating the condensate water
with extraction steam from the steam turbine; and a deaerator for deaerating the condensate
water with the extraction steam,
wherein the thermal power plant comprises:
10 a hot water heater for producing hot water from the condensate water fed from the
condenser, by using main steam of the turbine bypass line as a heat source;
a hot water tank for storing the hot water; and
a hot water pump for feeding the hot water stored in the hot water tank to a downstream
flow of the low-pressure feed water heater or to the deaerator.
15
2. The thermal power plant according to claim 1,
wherein the hot water heater is a direct contact type feed water heater for mixing the
condensate water and the main steam.
20 3. The thermal power plant according to claim 1 or 2,
wherein the boiler includes a water drain separator for separating steam mixed water at a
furnace outlet from steam, and
wherein the hot water heater also uses saturated drain separated from steam by the water
drain separator as the heat source.
25
4. The thermal power plant according to claim 1 or 2,
wherein the boiler includes a steam drum for separating steam and saturated water, and
wherein the hot water heater also uses an intermittent blow from the steam drum as the
36
21-00188PCT_specification
- 36 -
heat source.
5. The thermal power plant according to any one of claims 1 to 4, further comprising:
a cold water tank for storing surplus water in the condenser for make-up water feed to the
condenser, the cold water tank having a water storage amount equal to or greater 5 than a water
storage amount of the hot water tank.
6. The thermal power plant according to any one of claims 1 to 4,
wherein the hot water tank is a thermocline tank capable of storing the hot water and cold
10 water on opposite sides of a thermocline, the hot water tank storing, as the cold water, surplus
water in the condenser for make-up water feed to the condenser.
7. The thermal power plant according to any one of claims 1 to 6,
wherein the thermal power plant comprises a plurality of the low-pressure feed water
15 heaters in series on a condensate line for feeding the condensate water from the condenser to
the deaerator,
wherein the thermal power plant further comprises a hot water feed line for causing the
hot water to join at a confluent point where a temperature of the condensate water on an outlet
side is least lowered among confluent points of the plurality of low-pressure feed water heaters,
20 according to a hot water temperature which is a temperature of the hot water, and
wherein the confluent points are disposed on the condensate line on outlet sides of the
plurality of low-pressure feed water heaters, respectively.
8. A control method for the thermal power plant according to any one of claims 1 to 7,
25 comprising:
producing the hot water by using main steam, which corresponds to a difference between
steam generated in the boiler and steam consumed in the steam turbine, as the heat source and
storing the produced hot water in the hot water tank, during a low load operation of the thermal
37
21-00188PCT_specification
- 37 -
power plant; and
feeding the hot water stored in the hot water tank to the deaerator, during a high load
operation of the thermal power plant.
9. The control method for the thermal power plant according to claim 8, further 5 comprising:
feeding part of the hot water produced in the hot water heater to the deaerator according
to a temperature of the deaerator, during a low load operation of the steam turbine.
10. The control method for the thermal power plant according to claim 8 or 9,
10 wherein the thermal power plant includes a plurality of the low-pressure feed water
heaters in series on a condensate line for feeding the condensate water from the condenser to
the deaerator, and the thermal power plant further includes confluent points, at which the hot
water joins, respectively disposed on the condensate line on outlet sides of the plurality of lowpressure
feed water heaters where the hot water joins, and
15 wherein the control method comprises causing the hot water to join at a confluent point
where a temperature of the condensate water on an outlet side is least lowered among the
confluent points of the plurality of low-pressure feed water heaters, according to a temperature
of the hot water, during the high load operation of the thermal power plant.
20 11. The control method for the thermal power plant according to claim 10, comprising:
with a most downstream low-pressure feed water heater among the plurality of lowpressure
feed water heaters being a comparison target heater, setting the confluent point at
which the hot water joins to a confluent point on an outlet side of the comparison target heater;
and
25 repeating a process for comparing the temperature of the hot water with the temperature
of the condensate water on the outlet side of the comparison target heater at predetermined time
intervals, switching the confluent point at which the hot water joins to an outlet side of the lowpressure
feed water heater on one step upstream side of the comparison target heater if the
38
21-00188PCT_specification
- 38 -
temperature of the hot water is lower than the temperature of the condensate water for a
predetermined period, and setting the low-pressure feed water heater on one step upstream side
as the comparison target heater.