JP2024077776A - Method for operating power plant and power plant - Google Patents

Abstract

[Problem] To provide a power plant operating method and power plant that can reduce the possibility of the reheater being overheated and damaged by combustion gas. [Solution] When the flow rate of steam generated in the boiler 10 flowing through reheaters 103A, 103B installed in the combustion gas passage 12 of the boiler 10 is equal to or less than a reference flow rate value and combustion gas is flowing through the combustion gas passage 12, external steam different from the steam generated in the boiler 10 is supplied to the reheaters 103A, 103B. Also, when the temperature of the combustion gas flowing through the combustion gas passage 12 is equal to or higher than a reference temperature value, external steam is supplied to the reheaters 103A, 103B. [Selected Figure] Figure 2

Description

The present disclosure relates to a method for operating a power plant and a power plant.

For example, FIG. 2 of Patent Document 1 discloses a configuration in which steam generated in a boiler is supplied to a high-pressure turbine and then supplied to a reheater installed in the flue of the boiler.

JP 2022-123455 A

When a thermal power plant starts up, there is a certain period of time after combustion in the boiler has begun in which combustion gas flows through the flue but steam is not supplied to the high-pressure turbine used for generating electricity. In this state, since steam is not supplied to the reheater, in order to prevent the reheater from being overheated and damaged by the combustion gas (overheating damage), the temperature of the combustion gas that comes into contact with the reheater must be kept lower than the heat resistance temperature of the reheater. Specifically, the amount of fuel fed into the boiler must be limited. As a result, it can take a long time to start up the boiler.

In addition, if power generation is stopped by stopping the steam supply to the steam turbine (high-pressure turbine) due to a problem with the power system connected to the thermal power plant and the boiler is operated alone, no steam will be supplied to the high-pressure turbine. In this case, too, since no steam is supplied to the reheater, the temperature of the combustion gas that comes into contact with the reheater must be lowered to a temperature lower than the heat resistance temperature of the reheater in order to avoid overheating damage. Specifically, it was necessary to limit the amount of fuel fed into the boiler, and in some cases to make an emergency shutdown of the boiler. As a result, it sometimes took a long time to restart the thermal power plant after recovery from the problem.

The present disclosure has been made in consideration of these circumstances, and aims to provide a power plant operation method and a power plant that can reduce the possibility of the reheater being overheated and damaged by combustion gas.

In order to solve the above problems, the power plant operation method and the power plant disclosed herein employ the following measures.
In other words, a method of operating a power plant according to one embodiment of the present disclosure supplies external steam, different from the steam generated in the boiler, to the reheater when the flow rate of steam generated in the boiler flowing through a reheater installed in a combustion gas passage of the boiler is below a reference flow rate value and combustion gas is flowing in the combustion gas passage.

In addition, a power plant according to one aspect of the present disclosure includes a reheater that is installed in a combustion gas passage of a boiler and is supplied with steam generated in the boiler, an external steam generating device that is installed outside the boiler and generates external steam different from the steam generated in the boiler, and a control unit that controls the flow rate of the external steam supplied from the external steam generating device to the reheater, and when the flow rate of the steam flowing through the reheater is equal to or less than a reference flow rate value and combustion gas is flowing in the combustion gas passage, the control unit supplies the external steam from the external steam generating device to the reheater.

This disclosure reduces the possibility of the reheater being overheated and damaged by combustion gases.

FIG. 2 is a schematic configuration diagram showing a boiler provided in a power plant according to an embodiment of the present disclosure. FIG. 1 is a diagram illustrating a steam system (water system) of a power plant according to an embodiment of the present disclosure. 4 is a timing chart showing the pressure of main steam, the rotation speed of the high-pressure turbine, the output of the generator, and the open/closed state of each valve when the boiler is started up. 4 is a timing chart showing the command value for the generator output, the rotation speed of the high-pressure turbine, the command value for the main steam pressure, and the open/closed state of each valve during independent operation of the boiler.

Below, a method for operating a power plant and a power plant according to one embodiment of the present disclosure will be described with reference to the drawings.

However, the present disclosure is not limited to this embodiment.
Furthermore, when there are a plurality of embodiments or examples, the embodiments or examples may be combined together.
Additionally, "up" and "above" refer to the top in the vertical direction, and "down" and "below" refer to the bottom in the vertical direction. However, the vertical direction may include an error.

[Power plant configuration]
FIG. 1 is a schematic diagram showing the configuration of a boiler 10 provided in a power plant 1 .
The boiler 10 is a boiler that burns pulverized fuel obtained by pulverizing solid fuel using a plurality of burners 21 and exchanges heat generated by the combustion with feed water or steam to generate superheated steam.
Examples of solid fuels include biomass fuels and coal.
The boiler 10 has a furnace 11 , a combustion device (not shown), and a combustion gas passage 12 .

The furnace 11 has a hollow rectangular cylinder shape and is installed along the vertical direction.
The furnace wall 101 constituting the inner wall surface of the furnace 11 has a plurality of heat transfer tubes and fins connecting the heat transfer tubes, and recovers heat generated by the combustion of the pulverized fuel by heat exchange with water or steam flowing inside each heat transfer tube, while suppressing a temperature rise of the furnace wall 101. The furnace wall 101 is sometimes called a "water-cooled wall."

The combustion device is installed in the lower region of the furnace 11 .
The combustion device has a plurality of burners 21A, 21B, 21C, 21D, 21E, and 21F (which may be collectively referred to as "burners 21") attached to a furnace wall 101.
The burners 21 are arranged in a plurality of vertical rows, each of which is a set of burners that are equally spaced around the periphery of the furnace 11. In the case of Fig. 1, for example, each set of four burners 21 is arranged at each corner of the rectangular furnace 11, and six such sets are arranged in a vertical row.

For convenience of illustration, FIG. 1 shows only two of the burners included in one set, and each set is denoted by reference numerals 21A, 21B, 21C, 21D, 21E, and 21F.
Furthermore, the shape of the furnace 11, the number of stages of the burners 21, the number of burners 21 in one stage, the arrangement of the burners 21, etc. are not limited to the above-mentioned form.

The burners 21A, 21B, 21C, 21D, 21E, and 21F are respectively connected to a plurality of mills 31A, 31B, 31C, 31D, 31E, and 31F (which may be collectively referred to as "mills 31") via a plurality of pulverized fuel supply pipes 22A, 22B, 22C, 22D, 22E, and 22F (which may be collectively referred to as "pulverized fuel supply pipes 22").
The mill 31 is, for example, a vertical roller mill in which a grinding table (not shown) is supported inside so as to be rotatable, and a plurality of grinding rollers (not shown) are supported above the grinding table so as to be rotatable in conjunction with the rotation of the grinding table. The solid fuel pulverized by the cooperation of the grinding rollers and the grinding table is transported to a classifier (not shown) provided in the mill 31 by primary air (carrier gas, oxidizing gas) supplied to the mill 31. The classifier classifies the solid fuel into pulverized fuel having a particle size equal to or smaller than that suitable for combustion in the burner 21 and coarse pulverized fuel having a particle size larger than the particle size. The pulverized fuel passes through the classifier and is supplied to the burner 21 together with the primary air via the pulverized fuel supply pipe 22. The coarse pulverized fuel that does not pass through the classifier falls onto the grinding table by its own weight inside the mill 31 and is pulverized again.

An air register 23 is provided outside the furnace 11 at the mounting position of the burner 21, and one end of an air passage 24 (air duct) is connected to the air register 23.
A forced draft fan (FDF) 32 is connected to the other end of the air duct 24. The air supplied from the forced draft fan 32 is heated by an air preheater 42 installed in the air duct 24 (details will be described later), and is supplied to the burner 21 via the wind box 23 as secondary air (combustion air, oxidizing gas), and is introduced into the furnace 11.

The combustion gas passage 12 is connected to the vertical upper part of the furnace 11 .
The combustion gas passage 12 is provided with superheaters 102A, 102B, 102C (which may be collectively referred to as "superheaters 102"), reheaters 103A, 103B (which may be collectively referred to as "reheater 103"), and a coal economizer 104 as heat exchangers for recovering heat from the combustion gas, and heat is exchanged between the combustion gas generated in the furnace 11 and the feed water or steam flowing inside each heat exchanger.
The arrangement and shape of each heat exchanger are not limited to the form shown in FIG.

A flue 13 is connected downstream of the combustion gas passage 12, through which the combustion gas from which heat has been recovered in each heat exchanger is discharged.
An air preheater 42 (air heater) is provided in the flue 13, and is configured to perform heat exchange between the air flowing through the air duct 24 and the combustion gas flowing through the flue 13. By heating the primary air supplied to the mill 31 and the secondary air supplied to the burner 21 by the air preheater 42, it is possible to further recover heat from the combustion gas after heat exchange with water or steam.

Further, a denitration device 43 may be provided in the flue 13 at a position upstream of the air preheater 42 .
The denitration device 43 supplies a reducing agent, such as ammonia or urea water, which has the effect of reducing nitrogen oxides, to the combustion gas flowing through the flue 13, and promotes the reaction between the nitrogen oxides (NOx) in the combustion gas to which the reducing agent has been supplied and the reducing agent through the catalytic action of a denitration catalyst installed in the denitration device 43, thereby removing and reducing the nitrogen oxides in the combustion gas.

A gas duct 41 is connected to the flue 13 downstream of the air preheater 42 .
The gas duct 41 is provided with environmental equipment such as a dust collector 44, such as an electrostatic precipitator, for removing ash and the like from the combustion gas, a desulfurization device 46 for removing sulfur oxides, and an induced draft fan (IDF) 45 for directing the exhaust gas to these environmental equipment. The downstream end of the gas duct 41 is connected to a chimney 47, and the combustion gas treated in the environmental equipment is discharged to the outside of the system as exhaust gas.

In the boiler 10, when the multiple mills 31 are driven, the pulverized and classified pulverized fuel is supplied together with the primary air to the burner 21 through the pulverized fuel supply pipe 22. In addition, secondary air heated by the air preheater 42 is supplied from the air duct 24 through the wind box 23 to the burner 21.
The burner 21 blows a pulverized fuel mixture, which is a mixture of pulverized fuel and primary air, into the furnace 11 and also blows secondary air into the furnace 11 .
The pulverized fuel mixture injected into the furnace 11 is ignited and reacts with the secondary air to form a flame.
A flame is formed in the lower region within the furnace 11 , and high-temperature combustion gas rises within the furnace 11 and flows into the combustion gas passage 12 .
In this embodiment, air is used as the oxidizing gas (primary air, secondary air), but the oxidizing gas may have a higher or lower oxygen content than air, and stable combustion in the furnace 11 can be achieved by adjusting the ratio of the amount of oxygen to the amount of fuel supplied within an appropriate range.

The combustion gas that has flowed into the combustion gas passage 12 exchanges heat with water and steam in a superheater 102, a reheater 103, and a coal economizer 104 arranged inside the combustion gas passage 12, and is then discharged into the flue 13, where nitrogen oxides are removed in a denitration device 43, the combustion gas exchanges heat with primary air and secondary air in an air preheater 42, and is further discharged into a gas duct 41, where ash and the like are removed in a dust collector 44, and sulfur oxides are removed in a desulfurization device 46, and the combustion gas is then discharged to the outside of the system from a chimney 47.
The heat exchangers in the combustion gas passage 12 and the devices from the flue 13 to the gas duct 41 do not necessarily have to be arranged in the above-mentioned order with respect to the combustion gas flow.

Next, a detailed description will be given of the superheater 102, the reheater 103, and the economizer 104 provided as heat exchangers in the combustion gas passage 12. FIG.
Note that FIG. 1 does not accurately show the positions of the heat exchangers (superheaters 102A, 102B, 102C, reheaters 103A, 103B, and economizer 104) in the combustion gas passage 12, and the arrangement order of the heat exchangers with respect to the combustion gas flow is not limited to that shown in FIG. 1.

As shown in FIG. 2, the power plant 1 includes heat exchangers provided in the boiler 10, a steam turbine 111 that is driven to rotate by steam generated in the boiler 10, and a generator 113 that is connected to the steam turbine 111 and generates electricity using the rotational force of the steam turbine 111.

The steam turbine 111 includes, for example, a high-pressure turbine 111A, an intermediate-pressure turbine 111B, and a low-pressure turbine 111C.
The steam heated by the superheater 102 of the boiler 10 drives the high-pressure turbine 111A to rotate.
The steam that has passed through the high-pressure turbine 111A is reheated in the reheater 103 of the boiler 10, and drives the intermediate-pressure turbine 111B to rotate.
The steam that has passed through the intermediate-pressure turbine 111B drives and rotates the low-pressure turbine 111C.

A condenser 112 is connected to the low-pressure turbine 111C, and the steam that drives the low-pressure turbine 111C is condensed by heat exchange with cooling water (e.g., seawater or river water) in the condenser 112 to become condensed water.
The condenser 112 is connected to the economizer 104 via a water supply line L1.

The water supply line L1 is provided with, for example, a condensate pump 121 (CP), a low-pressure water supply heater 122, a boiler water supply pump 123 (BFP), and a high-pressure water supply heater 124.
A portion of the steam that drives the intermediate-pressure turbine 111B is supplied to the low-pressure feed water heater 122 via a steam extraction line L12.
A portion of the steam that drives the high-pressure turbine 111A is supplied to the high-pressure feed water heater 124 via a steam extraction line L13.
The low pressure feed water heater 122 and the high pressure feed water heater 124 are devices that use steam extracted from the steam turbine 111 as a heat source to heat the feed water supplied to the economizer 104 .

For example, when the boiler 10 is a once-through boiler, the economizer 104 is connected to a heat transfer tube that constitutes the furnace wall 101 .
The feed water heated in the economizer 104 is heated by radiation from the flame in the furnace 11 as it passes through the heat transfer tubes that make up the furnace wall 101 , and is then led to the steam separator 125 .
The steam separated in the steam separator 125 is supplied to the superheater 102. On the other hand, the drain water separated in the steam separator 125 flows into a steam separator drain tank 126 and is guided to the condenser 112 via a drain water line L2.

In addition, when the once-through boiler is started up or in low-load operation, the feedwater supplied from the economizer 104 may not evaporate completely as it passes through the heat transfer tubes that make up the furnace wall 101, resulting in an operating state (wet operating state) in which the water level is present in the steam separator 125. In this wet operating state, the drain water separated in the steam separator 125 and guided to the steam separator drain tank 126 may be circulated and supplied from the economizer 104 to the heat transfer tubes that make up the furnace wall 101 by merging it midway through the feedwater line L1 via the circulation line L6 using the boiler circulation pump 127 (BCP).

When the combustion gas flows through the combustion gas passage 12, heat of the combustion gas is recovered by the superheater 102, the reheater 103, and the economizer 104. On the other hand, the feed water supplied from the boiler feed pump 123 (BFP) is preheated by the economizer 104, and then heated to become steam while passing through the heat transfer tubes constituting the furnace wall 101. The steam is then led to the steam separator 125.
The steam separated in the steam separator 125 is introduced into the first superheater 102A, the second superheater 102B, and the third superheater 102C, and is superheated by the combustion gas.
The superheated steam generated in the superheater 102 is supplied to the high-pressure turbine 111A via a steam line L3, and drives the high-pressure turbine 111A to rotate.
The steam discharged from the high-pressure turbine 111A is introduced into the first reheater 103A and the second reheater 103B via a steam line L4 and is superheated again.
The steam resuperheated in each reheater is supplied via a steam line L5 through the intermediate-pressure turbine 111B to the low-pressure turbine 111C, and drives the intermediate-pressure turbine 111B and the low-pressure turbine 111C to rotate.
The rotating shaft of the steam turbine 111 rotates and drives a generator 113 to generate electricity. The steam discharged from the low-pressure turbine 111C is cooled in a condenser 112 to become condensed water, and is sent to the economizer 104 via a water supply line L1.

The power plant 1 of this embodiment includes a bypass line L7 that connects the steam line L3 and the condenser 112, and a bypass line L8 that connects the steam line L5 and the condenser 112.
The bypass line L7 is a line that leads the steam (main steam) from the boiler 10 (superheater 102) flowing through the steam line L3 directly to the condenser 112 without passing through the steam turbine 111 (high-pressure turbine 111A, intermediate-pressure turbine 111B, and low-pressure turbine 111C).
The bypass line L8 is a line that leads the steam (reheated steam) from the boiler 10 (reheater 103) flowing through the steam line L5 directly to the condenser 112 without passing through the steam turbine 111 (intermediate-pressure turbine 111B and low-pressure turbine 111C).

As described above, each of the steam lines L3 to L5 and the bypass lines L7 and L8 is provided with a valve that adjusts the flow rate of the steam generated in the boiler 10 as appropriate. The open/close state of each valve is controlled by the control unit 81. The open/close state of the regulating valve, which will be described later, is also controlled by the control unit 81.

The control unit 81 includes, for example, a CPU (Central Processing Unit: processor), a main memory, a secondary storage, etc. Furthermore, the control unit 81 may include a communication unit for transmitting and receiving information to and from other devices. Here, the other devices include, for example, each valve, and a temperature sensor, a flow rate sensor, etc., that are required for controlling each valve provided at each location.
The main storage device is composed of writable memory such as cache memory and RAM (Random Access Memory), and is used as a working area for reading execution programs of the CPU and writing processing data by the execution programs.
The secondary storage device is a non-transitory computer readable storage medium, such as a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, or a semiconductor memory.
As an example, a series of processes for realizing various functions is stored in a secondary storage device in the form of a program, and the CPU reads this program into the main storage device and executes information processing and arithmetic processing to realize various functions. Note that the program may be pre-installed in the secondary storage device, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

A main steam cutoff valve 51 and a main steam control valve 52 (governor valve) are provided on the steam line L3.
The main steam cutoff valve 51 is a valve that can cut off steam from the boiler 10 (superheater 102) that is supplied to the high-pressure turbine 111A.
The main steam control valve 52 is a valve that can adjust the flow rate of steam from the boiler 10 (superheater 102) supplied to the high-pressure turbine 111A. The main steam control valve 52 is provided downstream of the main steam shutoff valve 51 in the steam flow direction.

A reheat steam cutoff valve 53 is provided on the steam line L5.
The reheat steam cutoff valve 53 is a valve that can cut off steam from the boiler 10 (reheater 103) that is supplied to the intermediate-pressure turbine 111B.

A high-pressure turbine bypass valve 54 is provided in the bypass line L7.
The high-pressure turbine bypass valve 54 is a valve that can adjust the flow rate of steam (main steam) from the boiler 10 (superheater 102) that is supplied to the condenser 112. By opening the high-pressure turbine bypass valve 54, at least a portion of the steam from the boiler 10 can be supplied to the condenser 112.
The high-pressure turbine bypass valve 54 may be controlled together with the main steam cutoff valve 51 and the main steam regulating valve 52, and the flow rate of steam supplied from the boiler 10 to the condenser 112 can also be determined by a combination of the high-pressure turbine bypass valve 54 and the main steam cutoff valve 51 and/or the main steam regulating valve 52. For example, the entire amount of steam from the boiler 10 can be caused to bypass the high-pressure turbine 111A.

A low-pressure turbine bypass valve 55 is provided in the bypass line L8.
The low-pressure turbine bypass valve 55 is a valve that can adjust the flow rate of steam (reheated steam) from the boiler 10 that is supplied to the condenser 112. By opening the low-pressure turbine bypass valve 55, at least a portion of the steam from the boiler 10 can be supplied to the condenser 112.
The low-pressure turbine bypass valve 55 may be controlled together with the reheat steam cutoff valve 53, and the flow rate of steam supplied from the boiler 10 to the condenser 112 can be determined by a combination of the low-pressure turbine bypass valve 55 and the reheat steam cutoff valve 53. For example, the entire amount of steam from the boiler 10 can be caused to bypass the intermediate-pressure turbine 111B and the low-pressure turbine 111C.

[External steam generating device]
The power plant 1 of this embodiment further includes an external steam generating device 71 and an external steam header 73 .
The external steam is steam generated in a system different from the steam generated in the boiler 10 (specifically, the furnace wall 101, the superheater 102, and the reheater 103). When simply described as "external steam", it is distinguished from the steam generated in the boiler 10.

The external steam generating device 71 is a device for generating external steam.
Examples of the external steam generating device 71 include an auxiliary boiler provided in a power plant including the power plant 1, and a steam generating device that uses renewable energy such as solar power and is installed in or near the power plant.
However, the present invention is not limited to this as long as the external steam generating device 71 is capable of generating external steam. The number of the external steam generating devices 71 may be one or three or more. Different types of devices may be combined.

The external steam header 73 is where the external steam generated by the multiple external steam generating devices 71 is collected.

External steam line L9, external steam line L10, and external steam line L11 are connected to the external steam header 73.

The external steam line L9 is a line that supplies the external steam collected in the external steam header 73 to the steam line L4. However, the external steam line L9 does not necessarily need to be connected to the steam line L4, and it is sufficient that the external steam line L9 is configured to be able to supply the external steam to the reheater 103.
The external steam line L9 is provided with a control valve 61. The control valve 61 is a valve that can adjust the flow rate of the external steam supplied to the reheater 103.

The external steam line L10 is a line that supplies the external steam collected in the external steam header 73 to the low-pressure feed water heater 122. This makes it possible to use the external steam as a heat source for the low-pressure feed water heater 122.
The external steam line L10 is provided with an adjustment valve 62. The adjustment valve 62 is a valve that can adjust the flow rate of the external steam supplied to the low-pressure feedwater heater 122.

The external steam line L11 is a line that supplies the external steam collected in the external steam header 73 to the high-pressure feed water heater 124. This makes it possible to use the external steam as a heat source for the high-pressure feed water heater 124.
The external steam line L11 is provided with an adjustment valve 63. The adjustment valve 63 is a valve that can adjust the flow rate of the external steam supplied to the high-pressure feedwater heater 124.

[Timing for supplying external steam]
During normal operation of the power plant 1, steam generated in the boiler 10 (furnace wall 101 and superheater 102) is supplied to the reheater 103 via the high-pressure turbine 111A.
At this time, if the flow rate of steam supplied to the reheater 103 decreases or is low from the beginning for some reason, the reheater 103, which is exposed to the combustion gas in the combustion gas passage 12, may be overheated and damaged by the combustion gas.
Therefore, in this embodiment, in certain cases, external steam is supplied to the reheater 103 instead of steam (generated by the boiler 10), thereby preventing overheating damage to the reheater 103.
The "predetermined case" here refers to, for example, a case where the flow rate of steam flowing through the reheater 103 is equal to or lower than the reference flow rate value (including the case where it is zero), where the reference flow rate value is set to a flow rate of steam that will not cause overheating damage to the reheater 103 even if exposed to combustion gas, the flow rate being determined taking into consideration the state quantities (temperature, flow rate, etc.) of the combustion gas corresponding to the amount of fuel input to the boiler 10 and the heat resistance of the reheater 103. Note that this is merely an example, and external steam may be supplied at a timing that can prevent overheating damage to the reheater 103, taking into consideration the flow rate of steam supplied to the reheater 103.

An embodiment of the timing of supplying external steam will be described below.
In addition to the timing for supplying external steam to the reheater 103, the timing for supplying external steam to the low-pressure feed water heater 122 and the timing for supplying external steam to the high-pressure feed water heater 124 will also be explained.

Example 1: At the start of the boiler
FIG. 3 is a timing chart showing the pressure of the main steam, the rotation speed of the high-pressure turbine 111A, the output of the generator 113, and the open/closed state of each valve when the boiler 10 is started up.

As shown in Figures 2 and 3, when starting up the boiler 10, the control unit 81 first resets the fuel shutoff (MFT) circuit to enable ignition of the boiler 10. Note that at this stage, it is assumed that a sufficient amount of external steam is supplied to the external steam header 73.

Next, the control unit 81 controls so as to open the adjustment valves 62 and 63. As a result, external steam as a heat source is supplied to the low-pressure feed water heater 122 and the high-pressure feed water heater 124, and the feed water flowing through the feed water line L1 is heated.
The bleed valve 56 provided in the bleed line L12 and the bleed valve 57 provided in the bleed line L13 are closed.

Next, the control unit 81 ignites the boiler 10 (burner 21). As a result, the combustion gas starts to flow through the combustion gas passage 12. At this time, steam starts to be generated in the boiler 10, but the amount of steam generated is significantly smaller than the amount generated during normal operation (at least equal to or less than the reference flow rate value).
At approximately the same time, the control unit 81 controls the adjustment valve 61 to open. As a result, the external steam collected in the external steam header 73 is supplied to the reheater 103 exposed to the combustion gas via the external steam line L9. This makes it possible to prevent the reheater 103 from being overheated and damaged by the combustion gas.
At approximately the same time, the control unit 81 controls the low-pressure turbine bypass valve 55 to open. At this time, the reheat steam cutoff valve 53 is closed. As a result, the external steam supplied to the reheater 103 is guided to the condenser 112 via the bypass line L8.

Next, after the pressure of the main steam reaches a predetermined pressure value, the control unit 81 controls the main steam shutoff valve 51 and the main steam regulating valve 52 to open, and starts venting to the high-pressure turbine 111A. As a result, the high-pressure turbine 111A starts to rotate, and the steam supplied to the high-pressure turbine 111A is supplied to the reheater 103 via the steam line L4. The pressure of the main steam is measured, for example, near the inlet of the main steam shutoff valve 51.
When the steam (main steam) generated by the boiler 10 starts to flow into the reheater 103 and reaches the reference flow rate value, it becomes unnecessary to supply external steam to the reheater 103. Therefore, the control unit 81 controls the adjustment valve 61 to close. Note that, when the rotation speed of the high-pressure turbine 111A becomes approximately constant, the flow rate of the steam flowing through the reheater 103 reaches the reference flow rate value, and the adjustment valve 61 is fully closed.
Thereafter, the generator 113 starts generating electricity (concurrently connected), and the power plant 1 starts transmitting electricity to the power grid.

<Example 2: When the boiler is operating alone>
FIG. 4 is a timing chart showing the command value for the output of the generator 113, the rotation speed of the high-pressure turbine 111A, the command value (set value) for the main steam pressure, and the open/close state of each valve when the boiler 10 is operating alone.
Here, "independent operation of the boiler 10" refers to a state in which the steam turbine 111 is stopped to stop power generation due to a power supply system trouble or the like, but the generation of steam by the boiler 10 (i.e., combustion in the furnace 11) continues. In addition, "stopping the steam turbine 111" includes not only a state in which the rotation speed is zero, but also a state in which the supply of steam to the steam turbine 111 is stopped and the rotation speed is reduced below that during normal operation.

As shown in Figs. 2 and 4, when the boiler 10 is shifted to an independent operation, first, the control unit 81 sets the command value of the output of the generator 113 to zero.
At substantially the same time, the control unit 81 changes the set value so that the main steam pressure gradually decreases at a specified rate.

At approximately the same time, the control unit 81 controls the high-pressure turbine bypass valve 54 and the low-pressure turbine bypass valve 55 to open. At this time, the control unit 81 controls the main steam shutoff valve 51, the main steam control valve 52, and the reheat steam shutoff valve 53 to close. Through these controls, the flow rate and pressure of the main steam supplied to the steam turbine 111 are reduced, and the flow rate of the steam guided to the condenser 112 via the bypass line L7 and the bypass line L8 is increased. When the flow rate of the steam supplied to the high-pressure turbine 111A is reduced, the rotation speed of the high-pressure turbine 111A is reduced. Furthermore, when the flow rate of the steam supplied to the high-pressure turbine 111A is reduced, the flow rate of the steam (generated in the boiler 10) supplied to the reheater 103 is also reduced (to at least a reference flow rate value or less).
At approximately the same time, the control unit 81 controls the adjustment valve 61 to open. As a result, the external steam collected in the external steam header 73 is supplied to the reheater 103 exposed to the combustion gas via the external steam line L9. This makes it possible to prevent the reheater 103 from being overheated and damaged by the combustion gas.

During independent operation of the boiler 10, the control valves 62 and 63 are controlled taking into consideration the margin of external steam generation capacity.
Specifically, if there is a margin in the external steam generation capacity, the control valves 62 and 63 may be opened to heat the feed water. This allows the feed water to be circulated while maintaining it at a high temperature, so that the boiler 10 can be started up quickly when switching from standalone operation to normal operation.
On the other hand, if there is no spare capacity in the generation capacity of external steam, the control valve 62 and the control valve 63 may be closed. This allows a sufficient amount of external steam to be supplied to the reheater 103 to prevent overheating damage.

<Modification 1>
Not only when the boiler 10 is started up or when the boiler 10 is operating alone, but also when combustion gas is flowing through the combustion gas passage 12, external steam can be supplied to the reheater 103 in cases where the steam flowing through the reheater 103 alone at that time is likely to cause damage to the reheater 103 due to overheating.
For example, this may be an in-house isolated operation state in which power transmission to an external system is stopped and only the power required for the power plant 1 to continue operating is generated.
<Modification 2>
In addition, external steam may be supplied to the reheater 103 on the condition that the main steam shutoff valve 51 and/or the main steam control valve 52 have begun to close/have reached a fully closed state.
<Modification 3>
Even if the combustion gas flows through the combustion gas passage 12, there is no need to supply external steam while the temperature of the combustion gas is maintained at or below the heat resistance temperature of the reheater 103. In other words, external steam may be supplied to the reheater 103 on the condition that the temperature of the combustion gas becomes equal to or higher than a reference temperature value that is lower than the heat resistance temperature of the reheater 103.
Even if the temperature of the combustion gas is equal to or lower than the reference temperature value, external steam may be supplied to the reheater 103 so as to maintain the temperature of the reheater 103 at or below the heat-resistant temperature.

In either case, when the flow rate of steam supplied from the boiler 10 to the high-pressure turbine 111A becomes equal to the supply amount expected during normal operation, the supply of external steam to the reheater 103 may be stopped.

According to this embodiment, the following effects are obtained.
In cases where the flow rate of steam (generated in the boiler 10) flowing through the reheater 103, which is exposed to high-temperature combustion gas, is reduced or is low to begin with, which may cause the reheater 103 to be overheated and damaged, the possibility of the reheater 103 being overheated and damaged by the combustion gas can be reduced by flowing external steam into the reheater 103 instead of the steam (generated in the boiler 10).
This, for example, eliminates the need to limit the amount of fuel input to the boiler 10 in order to prevent the combustion gas from becoming too hot when the boiler 10 is started, thereby realizing a reduction in the time required to start up the boiler 10. In addition, for example, when power generation is stopped (i.e., the steam turbine 111 is stopped) due to some kind of trouble and the boiler 10 is operated independently, it is no longer necessary to limit the amount of fuel input to the boiler 10 or to perform an emergency stop of the boiler 10 in order to lower the temperature of the combustion gas, thereby realizing a reduction in the time required for restart.

In addition, when the water (feedwater) supplied to the boiler 10 is heated with external steam, it is possible to supply relatively high-temperature water to the boiler 10. This makes it possible to shorten the time required to start and restart the boiler 10.

In addition, when steam is supplied to the high-pressure turbine 111A connected to the steam inlet of the reheater 103, the external steam supplied to the reheater 103 is stopped, so that switching from external steam to steam (generated by the boiler 10) can be performed smoothly.

In the above-described embodiment, the boiler 10 of the present disclosure has been described as a boiler 10 that uses solid fuel as fuel. The solid fuel used in the boiler 10 may be coal, biomass fuel, petroleum coke (PC) fuel, petroleum residue, or the like.
The fuel for the boiler 10 is not limited to solid fuel, and may also be petroleum such as heavy oil, light oil, heavy oil, etc., industrial waste liquid, liquefied ammonia, etc. Gas fuels such as natural gas, various petroleum gases, by-product gases generated in the steelmaking process, hydrogen gas, ammonia gas, etc. may also be used.
The present invention can also be applied to a multi-fuel boiler that uses a combination of these various fuels.

The power plant operation method and the power plant according to the present embodiment described above can be understood, for example, as follows.
That is, in the method of operating a power plant according to the first aspect of the present disclosure, when the flow rate of steam generated in a boiler (10) flowing through a reheater (103) installed in a combustion gas passage (12) of the boiler (10) is equal to or less than a reference flow rate value and combustion gas is flowing in the combustion gas passage (12), external steam different from the steam generated in the boiler (10) is supplied to the reheater (103).

According to the operation method of the power plant (1) of this embodiment, when the flow rate of steam generated in the boiler (10) flowing through the reheater (103) installed in the combustion gas passage (12) of the boiler (10) is equal to or less than a reference flow rate value and combustion gas is flowing through the combustion gas passage (12), external steam different from the steam generated in the boiler (10) is supplied to the reheater (103). Therefore, in a case where the flow rate of the steam (generated in the boiler (10)) flowing through the reheater (103) exposed to high-temperature combustion gas is reduced/is low from the beginning, and there is a possibility that the reheater (103) will be overheated and damaged, the external steam is flowed into the reheater (103) instead of the steam (generated in the boiler (10)), thereby reducing the possibility that the reheater (103) will be overheated and damaged by the combustion gas.
This, for example, eliminates the need to limit the amount of fuel fed to the boiler (10) in order to avoid an increase in the temperature of the combustion gas when the boiler (10) is started, thereby realizing a reduction in the time required to start the boiler (10). Also, for example, when power generation is stopped (i.e., the power generation turbine is stopped) due to some kind of trouble and the boiler (10) is operated independently, it is no longer necessary to limit the amount of fuel fed to the boiler (10) or to perform an emergency stop of the boiler (10) in order to lower the temperature of the combustion gas, thereby realizing a reduction in the time required for restart.

The power plant operation method according to the second aspect of the present disclosure supplies the external steam to the reheater (103) when the temperature of the combustion gas flowing through the combustion gas passage (12) is equal to or higher than a reference temperature value in the first aspect.

According to the operating method of the power plant (1) of this embodiment, when the temperature of the combustion gas flowing through the combustion gas passage (12) is equal to or higher than a reference temperature value, external steam is supplied to the reheater (103), so that the temperature of the combustion gas that may cause overheating damage to the reheater (103) can be used as one of the criteria.

The power plant operation method according to the third aspect of the present disclosure supplies the external steam to the reheater (103) when the supply of the steam to the turbine connected to the steam inlet of the reheater (103) is stopped in the first or second aspect.

According to the operating method of the power plant (1) of this embodiment, when the supply of steam to the turbine connected to the steam inlet of the reheater (103) is stopped, external steam is supplied to the reheater (103), so that external steam can be supplied to the reheater (103) before the supply of steam (generated in the boiler (10)) to the turbine is stopped and the amount of steam (generated in the boiler (10)) supplied to the reheater (103) becomes approximately zero.

The power plant operation method according to the fourth aspect of the present disclosure, in any one of the first to third aspects, supplies the external steam to the reheater (103) when the boiler (10) is started up or when the boiler (10) is operating independently.

According to the operating method of the power plant (1) of this embodiment, external steam is supplied to the reheater (103) when the boiler (10) is started up or when the boiler (10) is operating alone, so that external steam can be supplied to the reheater (103) when there is a high possibility that the reheater (103) will be overheated and damaged by the combustion gas if the amount of fuel input to the boiler (10) is not limited.

The power plant operation method according to the fifth aspect of the present disclosure is any one of the first to fourth aspects, in which the water supplied to the boiler (10) is heated with the external steam.

According to the method for operating the power plant (1) of this embodiment, the water supplied to the boiler (10) is heated by external steam, so that relatively high-temperature water can be supplied to the boiler (10). This makes it possible to reduce the time required to start and restart the boiler (10).

The power plant operation method according to the sixth aspect of the present disclosure, in any one of the first to fifth aspects, stops the external steam supplied to the reheater (103) when the steam is supplied to the turbine (111) connected to the steam inlet of the reheater (103).

According to the operating method of the power plant (1) of this embodiment, when steam is supplied to the turbine (111) connected to the steam inlet of the reheater (103), the external steam supplied to the reheater (103) is stopped, so that the switch from external steam to steam (generated in the boiler (10)) can be smoothly performed.

The power plant according to the seventh aspect of the present disclosure includes a reheater (103) that is installed in the combustion gas passage (12) of a boiler (10) and is supplied with steam generated in the boiler (10), an external steam generating device (71) that is installed outside the boiler (10) and generates external steam different from the steam generated in the boiler (10), and a control unit (81) that controls the flow rate of the external steam supplied from the external steam generating device (71) to the reheater (103). When the flow rate of the steam flowing through the reheater (103) is equal to or less than a reference flow rate value and combustion gas is flowing in the combustion gas passage (12), the control unit (81) supplies the external steam from the external steam generating device (71) to the reheater (103).

In the power plant according to the eighth aspect of the present disclosure, in the seventh aspect, the external steam generating device (71) uses solar energy.

10 Boiler 11 Furnace 12 Combustion gas passage 13 Flue 21 (21A to 21F) Burner 22 (22A to 22F) Pulverized fuel supply pipe 23 Wind box (air register)
24 Air duct
31 (31A to 31F) Mill (crusher)
32 Forced draft fan (FDF)
41 Gas duct 42 Air preheater 43 Denitrification device 44 Dust collector 45 Induced draft fan (IDF)
46 Desulfurization device 47 Chimney 51 Main steam cutoff valve 52 Main steam control valve (governor valve)
53 Reheat steam cutoff valve 54 High pressure turbine bypass valve 55 Low pressure turbine bypass valve 56 Extraction valve (installed at L12)
57 Bleed valve (installed at L13)
61 Control valve (installed at L9)
62 Control valve (installed at L10)
63 Control valve (installed at L11)
71 External steam generating device 73 External steam header 81 Control unit 101 Furnace wall 102 Superheater 102A First superheater 102B Second superheater 102C Third superheater 103 Reheater 103A First reheater 103B Second reheater 104 Economizer 111 Steam turbine 111A High pressure turbine 111B Intermediate pressure turbine 111C Low pressure turbine 112 Condenser 113 Generator 121 Condensate pump (CP)
122 Low pressure feed water heater 123 Boiler feed water pump (BFP)
124 High pressure feed water heater 125 Steam separator 126 Steam separator drain tank 127 Boiler circulation pump (BCP)
L1: Feed water line L2: Drain water line L3-L5: Steam line L6: Circulation line L7, L8: Bypass line L9-L11: External steam line L12, L13: Extraction line

Claims (8)

A method for operating a power plant, in which, when a flow rate of steam generated in a boiler flowing through a reheater installed in a combustion gas passage of the boiler is equal to or less than a reference flow rate value and combustion gas is flowing in the combustion gas passage, external steam different from the steam generated in the boiler is supplied to the reheater. 2. The method for operating a power plant according to claim 1, further comprising the step of: supplying the external steam to the reheater when a temperature of the combustion gas flowing through the combustion gas passage is equal to or higher than a reference temperature value. 2. The method for operating a power plant according to claim 1, further comprising the step of: supplying the external steam to the reheater when the supply of the steam to a turbine connected to a steam inlet of the reheater is stopped. 2. The method for operating a power plant according to claim 1, further comprising the step of supplying the external steam to the reheater when the boiler is started up or when the boiler is in an independent operation. 2. The method of claim 1, wherein water supplied to the boiler is heated by the external steam. 6. The power plant operation method according to claim 1, wherein the external steam supplied to the reheater is stopped when the steam is supplied to a turbine connected to a steam inlet of the reheater. a reheater provided in a combustion gas passage of the boiler and supplied with steam generated in the boiler;
an external steam generating device that is installed outside the boiler and generates external steam different from the steam generated in the boiler;
A control unit that controls a flow rate of the external steam supplied from the external steam generating device to the reheater;
Equipped with
The control unit supplies the external steam from the external steam generating device to the reheater when the flow rate of the steam flowing through the reheater is equal to or less than a reference flow rate value and combustion gas is flowing in the combustion gas passage. The power plant according to claim 7, wherein the external steam generating device utilizes solar energy.