Steam turbine and power generation plant, as well as operation method of steam turbine

Abstract

To satisfy a requested amount of power generation of a generator and stabilize operation of a boiler.SOLUTION: A steam turbine 111 receives steam generated by a boiler and drives a generator 113 by rotary drive using the supplied steam. The steam turbine 111 includes: a compartment 111a in which the steam is circulated; a rotating shaft 111b that can be rotated with a center axis C1 extending in a predetermined direction as a center and is mounted to the compartment 111a; multiple blades mounted to an outer peripheral surface of the rotating shaft 111b; and an angle changing section capable of changing an amount of generation of the generator 113. The rotating shaft 111b is rotated along with the blade when the steam circulated inside the compartment 111a collides with the blade. A gap through which the steam passes is formed between the blades. When a requested amount of generation of the generator 113 is a requested amount of generation corresponding to a load that is equal to or less than the minimum stable load of the boiler, the angle changing section changes the gap and reduces the amount of generation of the generator 113.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to steam turbines and power plants, and methods of operating steam turbines. [Background technology]

[0002] A large boiler such as a power generation boiler has a hollow furnace that is installed vertically, and a plurality of burners are arranged on the furnace wall along the circumferential direction of the furnace. In addition, a flue is connected to the large boiler vertically above the furnace, and a heat exchanger for generating steam is arranged in the flue. Then, a flame is formed by the burner injecting a mixture of fuel and air (oxidizing gas) into the furnace, and combustion gas is generated and flows into the flue. A heat exchanger is installed in the area where the combustion gas flows, and water and steam flowing in a heat transfer tube that constitutes the heat exchanger are heated to generate superheated steam. As such a boiler, the boiler described in Patent Document 1 is known. The steam generated in the boiler described in Patent Document 1 is supplied to a steam turbine provided in the power plant to rotate the steam turbine, which then drives a generator to generate electricity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-65375 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, with the increase in the use of renewable energy, power plants that generate electricity by burning fuel (thermal power plants) are required to reduce the amount of power generated by their generators during the daytime. One method for reducing the amount of power generated by a power plant is to temporarily shut down the plant, but this method has the problem of being inefficient, considering the time required to shut down and restart the power plant and the need to store the plant while it is shut down.

[0005] In addition, as a method for reducing the power generation amount of a power plant, a method of reducing the load of the boiler is considered. However, in order to operate the boiler stably, a minimum stable load is set for the boiler. Therefore, when the required power generation amount for the power plant corresponds to a load lower than the minimum stable load of the boiler, it is not recommended to operate the boiler at a load lower than the minimum stable load of the boiler. Therefore, it may not be possible to reduce the power generation amount to the required power generation amount. In addition, coal, which is inexpensive as fuel, is widely used in power plants, and a coal pulverizer is installed to pulverize the coal. A lower limit of the fuel supply amount is set for the coal pulverizer in order to pulverize the coal stably and efficiently, and it may not be possible to reduce the power generation amount to the required power generation amount of the power plant. To solve this problem, it is possible to switch from coal to heavy oil, light oil, gas, etc. as fuel and reduce the amount of power generated to the required level of the power plant. However, in this case, there is a problem that the fuel cost increases.

[0006] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a steam turbine, a power plant, and a method for operating a steam turbine that can suitably satisfy the required power generation amount of the generator. [Means for solving the problem]

[0007] In order to solve the above problems, the steam turbine, power plant, and steam turbine operating method disclosed herein employ the following measures. a rotating shaft housed inside the housing and attached to the housing so as to be rotatable about a central axis extending in a predetermined direction and connected to the generator; a plurality of blades housed inside the housing and attached to an outer circumferential surface of the rotating shaft so as to be aligned at predetermined intervals along the circumferential direction; and an output change unit that can change the amount of power generated by the generator when the amount of steam introduced into the housing is constant, wherein the rotating shaft rotates together with the blades as the steam circulating inside the housing collides with the blades, and gaps are formed between the blades adjacent in the circumferential direction through which the steam circulating inside the housing can pass, and when the amount of power generated by the generator is the amount of power generated according to a load that is less than the minimum stable load of the boiler, the output change unit changes the gap to reduce the amount of power generated by the generator.

[0008] and a step of changing the gap to reduce the amount of power generated by the generator when the amount of power generated by the generator is constant. The method of operating a steam turbine according to one aspect of the present disclosure is a method of operating a steam turbine that is supplied with steam generated in a boiler and that drives a generator by rotating the steam generated by the supplied steam, the steam turbine comprising: a casing forming an outer shell into which steam is introduced and through which the steam flows; a rotating shaft that is housed inside the casing and attached to the casing so as to be rotatable about a central axis extending in a predetermined direction and that is connected to the generator; a plurality of blades that are housed inside the casing and attached to an outer circumferential surface of the rotating shaft so as to be aligned at predetermined intervals along the circumferential direction; and an output changing unit that can change the amount of power generated by the generator when the amount of power generated by the generator is constant, the rotating shaft rotates together with the blades when the steam flowing inside the casing collides with the blades, and gaps are formed between the blades that are adjacent in the circumferential direction, through which the steam flowing inside the casing can pass, the method comprising: a step of changing the gap to reduce the amount of power generated by the generator when the amount of power generated by the generator is an amount of power generated corresponding to a load that is less than a minimum stable load of the boiler. Effect of the Invention

[0009] According to the present disclosure, it is possible to stabilize the operation of the boiler while satisfying the required power generation amount of the generator. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram illustrating a coal-fired boiler according to an embodiment of the present disclosure. FIG. [Diagram 2] FIG. 1 is a schematic diagram showing a steam, condensate, and feedwater system in a coal-fired boiler (once-through boiler) according to an embodiment of the present disclosure. [Diagram 3] FIG. 1 is a schematic vertical cross-sectional view illustrating a steam turbine according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a schematic perspective view showing a rotor blade provided in a steam turbine according to an embodiment of the present disclosure. [Diagram 5]1 is a graph showing the relationship between a generator output command value, fuel / water / air command values, rotor blade opening, and generator output in a power plant according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to this embodiment, and when there are multiple embodiments, the present disclosure also includes a configuration in which each embodiment is combined. In the following description, up and above refer to the upper side in the vertical direction, and down and below refer to the lower side in the vertical direction, and the vertical direction is not precise and includes an error.

[0012] FIG. 1 is a schematic diagram showing the configuration of a boiler using solid fuel as the main fuel according to this embodiment.

[0013] The boiler 10 of this embodiment is a boiler that can generate superheated steam by burning pulverized fuel made by pulverizing solid fuel with a burner and exchanging the heat generated by this combustion with feed water or steam. Biomass fuel, coal, etc. are used as the solid fuel.

[0014] The boiler 10 has a furnace 11, a combustion device 20, and a combustion gas passage 12. The furnace 11 has a hollow rectangular cylinder shape and is installed vertically. The furnace wall 101 constituting the inner wall surface of the furnace 11 is composed of a plurality of heat transfer tubes and fins connecting the heat transfer tubes, and recovers heat generated by the combustion of pulverized fuel by heat exchange with water and steam flowing inside the heat transfer tubes, while suppressing the temperature rise of the furnace wall 101.

[0015] The combustion device 20 is installed in the lower region of the furnace 11. In this embodiment, the combustion device 20 has a plurality of burners 21A, 21B, 21C, 21D, 21E, and 21F (hereinafter, they may be collectively referred to as "burners 21") attached to the furnace wall 101. The burners 21 are arranged in a plurality of stages along the vertical direction, with each set being arranged at equal intervals along the circumferential direction of the furnace 11 (for example, four burners installed at each corner of the rectangular furnace 11). For convenience of illustration, only two burners of one set are shown in FIG. 1, and each set is denoted by the reference numerals 21A, 21B, 21C, 21D, 21E, and 21F. The shape of the furnace, the number of burner stages, the number of burners in one stage, the arrangement of the burners, and the like are not limited to this embodiment.

[0016] The burners 21A, 21B, 21C, 21D, 21E, and 21F are connected to a plurality of mills (pulverizers) 31A, 31B, 31C, 31D, 31E, and 31F (hereinafter, sometimes collectively referred to as "mills 31") via a plurality of pulverized fuel supply pipes 22A, 22B, 22C, 22D, 22E, and 22F (hereinafter, sometimes collectively referred to as "pulverized fuel supply pipes 22"). The mill 31 is, for example, a vertical roller mill in which a pulverizing table (not shown) is supported inside so as to be rotatable and a plurality of pulverizing rollers (not shown) are supported above the pulverizing table so as to be rotatable in conjunction with the rotation of the pulverizing table. The solid fuel pulverized by the cooperation of the pulverizing rollers and the pulverizing table is transported to a classifier (not shown) provided in the mill 31 by primary air (transport gas, oxidizing gas) supplied to the mill 31. In the classifier, the fuel particles are classified 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 that. The pulverized fuel passes through the classifier and is supplied to the burner 21 together with 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 re-ground.

[0017] An air register 23 is provided on the outside of the furnace 11 at the mounting position of the burner 21, and one end of an air duct 24 is connected to the air register 23. A forced draft fan (FDF: Forced Draft Fan) 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 air register 23 as secondary air (combustion air, oxidizing gas), and is introduced into the furnace 11.

[0018] The combustion gas passage 12 is connected to the vertical upper part of the furnace 11. In the combustion gas passage 12, a first superheater 102A, a second superheater 102B, a third superheater 102C (hereinafter, sometimes collectively referred to as "superheater 102"), a first reheater 103A, a second reheater 103B (hereinafter, sometimes collectively referred to as "reheater 103"), and a coal economizer 104 are provided as heat exchangers for recovering heat from the combustion gas, and heat is exchanged between the combustion gas generated in the furnace 11 and 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. 1.

[0019] A flue 13 is connected to the downstream side of the combustion gas passage 12, and discharges the combustion gas whose heat has been recovered by the heat exchanger. An air preheater (air heater) 42 is provided between the flue 13 and the air duct 24, and heat is exchanged between the air flowing through the air duct 24 and the combustion gas flowing through the flue 13, thereby heating the primary air supplied to the mill 31 and the secondary air supplied to the burner 21, thereby recovering further heat from the combustion gas after heat exchange with water and steam.

[0020] Furthermore, 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 having an effect of reducing nitrogen oxides, such as ammonia or urea water, to the combustion gas flowing through the flue 13, and promotes a reaction between the nitrogen oxides (NOx) in the combustion gas to which the reducing agent has been supplied and the reducing agent by the catalytic action of a denitration catalyst provided 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 equipment 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.

[0021] In the boiler 10, when the multiple mills 31 are driven, the pulverized and classified pulverized fuel is supplied to the burner 21 together with the primary air through the pulverized fuel supply pipe 22. In addition, secondary air heated by the air preheater 42 is supplied to the burner 21 through the wind duct 24 and the wind box 23. The burner 21 blows a pulverized fuel mixture, which is a mixture of the pulverized fuel and the primary air, into the furnace 11, and also blows secondary air into the furnace 11. The pulverized fuel mixture blown into the furnace 11 ignites and reacts with the secondary air to form a flame. A flame is formed in the lower region of the furnace 11, and the high-temperature combustion gas rises inside 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 ratio than air, and stable combustion in the furnace 11 is achieved by adjusting the ratio of the amount of oxygen to the amount of fuel supplied to an appropriate range.

[0022] Moreover, above the mounting position of the burner 21 of the furnace 11, a plurality of additional air ports (AA ports) 25 for supplying additional air for combustion (AA) into the furnace 11 are provided. An end of an additional air duct (AA duct) 26 branched off from the air duct 24 is connected to the additional air port 25, and a part of the air supplied from the forced draft fan 32 can be supplied to the additional air port 25 via the additional air duct 26 as additional air for combustion.

[0023] In region A (corresponding to the installation range of the wind box 23 in the height direction) inside the furnace 11 shown in FIG. 1, a flame is formed by the combustion of a mixture of primary air and pulverized fuel with secondary air. Here, the air ratio in region A is set to be 1 or less, specifically, the amount of air (total amount of primary air and secondary air) supplied to the burner 21 is set to be less than the theoretical amount of air for the amount of fuel supplied to the burner 21, so that region A and region B (region between the top of the burner 21 and the bottom of the additional air port 25) inside the furnace 11 become reducing atmospheres, and nitrogen oxides (NOx) generated by combustion are reduced inside the furnace 11. After that, in region C (region above the bottom of the additional air port 25), additional air for combustion is supplied from the additional air port 25 to the combustion gas in which NOx has been reduced, and the combustion is completed, but the amount of NOx generated is reduced by the amount of the reduction effect in region A and region B.

[0024] The combustion gas flowing 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, and the combustion gas exchanges heat with primary air and secondary air in an air preheater 42, and is then 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. Note that the arrangement of the heat exchangers in the combustion gas passage 12 and the devices from the flue 13 to the gas duct 41 with respect to the combustion gas flow does not necessarily have to be in the order described above.

[0025] Next, a detailed description will be given of the superheater 102, the reheater 103, and the economizer 104 provided in the combustion gas passage 12 as heat exchangers. FIG. Note that Figure 1 does not accurately show the positions of each heat exchanger (first superheater 102A, second superheater 102B, third superheater 102C, first reheater 103A, second reheater 103B, and economizer 104) in the combustion gas passage 12, and the arrangement order of each heat exchanger with respect to the combustion gas flow is not limited to that shown in Figure 1.

[0026] As shown in FIG. 2, the power plant 1 of this embodiment includes heat exchangers provided in a boiler 10, a steam turbine 111 that is rotationally driven by steam generated in the boiler 10, and a generator 113 that is connected to the steam turbine 111 and generates electricity by the rotational force of the steam turbine 111.

[0027] The steam turbine 111 is composed of, for example, a high-pressure turbine 111A, an intermediate-pressure turbine 111B, and a low-pressure turbine 111C. After steam heated by the superheater 102 of the boiler 10 drives the high-pressure turbine 111A, it is reheated by the reheater 103 of the boiler 10 and drives the intermediate-pressure turbine 111B and 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 feedwater line L1. For example, a condensate pump (CP) 121, a low-pressure feedwater heater 122, a boiler feedwater pump (BFP) 123, and a high-pressure feedwater heater 124 are provided on the feedwater line L1. A portion of the steam that drives the steam turbine 111 is extracted and supplied to the low-pressure feedwater heater 122 and the high-pressure feedwater heater 124 as a heat source via an extraction line (not shown), and the feedwater supplied to the economizer 104 is heated.

[0028] For example, a case where the boiler 10 is a once-through boiler will be described. The economizer 104 is connected to a heat transfer tube constituting the furnace wall 101. The feed water heated by the economizer 104 is heated by radiation from the flame in the furnace 11 while passing through the heat transfer tube constituting the furnace wall 101, and is led to the steam separator 125. The steam separated by the steam separator 125 is supplied to the superheater 102, and the drain water separated by the steam separator 125 flows into the steam separator drain tank 126 and is led to the condenser 112 via the drain water line L2.

[0029] Furthermore, during startup or low load operation of the once-through boiler, the feedwater supplied from the economizer 104 may not be fully evaporated as it passes through the heat transfer tubes constituting the furnace wall 101, resulting in an operating state (wet operating state) in which the water level exists in the steam separator 125. In this wet operating state, the drain water separated in the steam separator 125 and discharged to the steam separator drain tank 126 may be circulated and supplied from the economizer 104 to the heat transfer tubes constituting the furnace wall 101 by merging it midway through the feedwater line L1 using the boiler circulation pump (BCP) 127 via the circulation line L6.

[0030] When the combustion gas flows through the combustion gas passage 12, the 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 (BFP) 123 is preheated by the economizer 104, and then heated to become steam when passing through the heat transfer tubes constituting the furnace wall 101, and is guided to the steam separator 125. The steam separated by the steam separator 125 is guided to the first superheater 102A, the second superheater 102B, and the third superheater 102C, and is superheated by the combustion gas. The superheated steam generated by the superheater 102 is supplied to the high-pressure turbine 111A via the steam line L3, and rotates and drives the high-pressure turbine 111A. The steam discharged from the high-pressure turbine 111A is guided to the first reheater 103A and the second reheater 103B, and is superheated again. The re-superheated steam is supplied to the low-pressure turbine 111C via the steam line L5 and the intermediate-pressure turbine 111B, and rotates and drives the intermediate-pressure turbine 111B and the low-pressure turbine 111C. The rotating shaft of the steam turbine 111 rotates and drives the generator 113 to generate electricity. The steam discharged from the low-pressure turbine 111C is cooled in the condenser 112 to become condensed water, and is sent again to the economizer 104 via the water supply line L1.

[0031] The superheater 102 and the reheater 103 may be provided with a means for controlling the temperature of the steam superheated in each heat exchanger (hereinafter, the temperature of the superheated steam at the outlet of the third superheater 102C is referred to as the "main steam temperature", and the temperature of the superheated steam at the outlet of the second reheater 103B is referred to as the "reheated steam temperature"). For example, a superheater spray valve (not shown) or a reheater spray valve (not shown) may be provided for controlling the steam temperature by adjusting the amount of water mixed and injected into the superheated steam (hereinafter, the water injected for controlling the main steam temperature is referred to as the "superheater spray water", and the water injected for controlling the reheated steam temperature is referred to as the "reheater spray water"). The superheater spray water and the reheater spray water are supplied, for example, by branching a part of the water supplied to the boiler 10 from the outlet of the boiler feed water pump 123. The position where the superheater spray water is mixed and injected is not limited to the outlet of the third superheater 102C, and may be any position where the main steam temperature can be controlled, for example, it is installed at any position between the outlet of the steam separator 125 and the inlet of the high-pressure turbine 111A. Similarly, the position where the reheater spray water is mixed and injected is not limited to the outlet of the second reheater 103B, and may be any position where the reheat steam temperature can be controlled, for example, it is installed at any position between the outlet of the high-pressure turbine 111A and the inlet of the intermediate-pressure turbine 111B.

[0032] Next, the steam turbine 111 will be described with reference to Figures 3 and 4. Note that, for ease of illustration, stationary blades are omitted in Figure 3. The steam turbine 111 described below is applied to a high-pressure turbine 111A and / or an intermediate-pressure turbine 111B and / or a low-pressure turbine 111C.

[0033] As shown in FIG. 3, the steam turbine 111 has a casing 111a which forms an outer shell and has a space therein, a rotating shaft 111b which penetrates the casing 111a, stationary vanes (not shown) which are provided inside the casing 111a and fixed to the inner surface of the casing 111a, and a plurality of rotor blades 111c which are provided inside the casing 111a and attached to the outer surface of the rotating shaft 111b.

[0034] In the steam turbine 111, steam supplied from a steam line L3 or the like is introduced into a space formed between a casing 111a and a rotating shaft 111b. When the steam is introduced into the space, the rotor blades 111c and the rotating shaft 111b are rotationally driven by the energy of the steam flowing through the space. This rotates and drives a generator 113 (see FIG. 1) connected to the rotating shaft 111b to generate electricity. The electricity generated by the generator 113 is sent to a power transmission device 115 via a transformer 114.

[0035] The casing 111a forms an outer shell, into which steam is introduced and through which steam circulates. The rotating shaft 111b is housed inside the casing 111a. The rotating shaft 111b is attached to the casing 111a so as to be rotatable around a central axis C1 extending in a predetermined direction. In addition, an end of the rotating shaft 111b in the predetermined direction is connected to the generator 113. The rotating shaft 111b rotates together with the blades 111d when the steam flowing inside the casing 111a collides with the rotor blades 111c (more specifically, the blades 111d described later).

[0036] A plurality of stator blades are provided. The plurality of stator blades are arranged side by side at predetermined intervals along a predetermined direction. For example, the plurality of stator blades are fixed to an inner peripheral surface of the casing 111a. The plurality of stator blades are arranged side by side at predetermined intervals along the circumferential direction. The stationary blades and the rotor blades 111c are arranged alternately in a predetermined direction.

[0037] The rotor blade 111c is fixed to the outer circumferential surface of the rotating shaft 111b. A plurality of rotor blades 111c are provided. The plurality of rotor blades 111c are arranged in a line at a predetermined interval along a predetermined direction. Each rotor blade 111c has a plurality of blades 111d attached to the outer circumferential surface of the rotating shaft 111b so as to be arranged in a line at a predetermined interval in the circumferential direction. Between the blades 111d adjacent in the circumferential direction, a gap is formed through which steam flowing inside the casing 111a passes.

[0038] The blade 111d extends in a radial direction from the outer circumferential surface of the rotating shaft 111b. That is, the blade 111d extends radially with respect to the rotating shaft 111b. As shown in Fig. 4, the blade 111d has a plate surface. The blade 111d is provided so that the plate surface forms a predetermined angle with respect to a plane perpendicular to a predetermined direction (axial direction).

[0039] Furthermore, as shown in FIG. 4, the blade 111d has an angle change section (output change section) 111e that changes the angle of the blade 111d with respect to a plane perpendicular to a predetermined direction so as to change the size of the gap formed between the blades 111d.

[0040] The angle changer 111e supports the blades 111d to be rotatable about a central axis C2 extending in the radial direction. The angle changer 111e can increase the gap formed between the blades 111d (i.e., open the gap) by changing the angle of the blades 111d. The angle changer 111e can also decrease the gap formed between the blades 111d (i.e., close the gap) by changing the angle of the blades 111d.

[0041] When the angle changer 111e changes the angle of the blades 111d to change the size of the gap formed between adjacent blades 111d through which steam passes, the amount of steam colliding with the blades 111d also changes. This changes the driving force that rotates the rotor blades 111c and the rotating shaft 111b. The change in the driving force that rotates the rotating shaft 111b also changes the output from the steam turbine 111 to the generator 113. In other words, the amount of power generated by the generator 113 changes. In this way, the angle changer 111e can change the amount of power generated in the generator 113 by changing the angle of the blades 111d.

[0042] The power plant also includes a control unit that controls the behavior of the angle change unit 111e. Furthermore, the control unit determines the load of the boiler 10 based on the required amount of power generation of the generator 113, and controls the boiler 10 to achieve that load. Furthermore, when the required amount of power generation of the generator 113 corresponds to a load less than the minimum stable load of the boiler 10, the control unit reduces the driving force with which the angle changer 111e rotates the rotating shaft 111b.

[0043] The control unit has two operation modes for the boiler 10. In detail, as described above, the control unit has two operation modes: a once-through operation mode (dry operation mode) in which the feedwater is not circulated in the boiler 10, and a circulation operation mode (wet operation mode) in which the feedwater is circulated.

[0044] The control unit selects the circulation operation mode when the load on the boiler 10 is low (e.g., less than 30% of the rated load), and operates the boiler 10 in the once-through operation mode when the load on the boiler 10 is medium or higher (e.g., 30% or more of the rated load).

[0045] In addition, a minimum stable load is set for the boiler 10. The minimum stable load is set from the following viewpoints. As described above, the control unit has a plurality of operation modes according to the load of the boiler 10. Since the set values ​​and control methods of various parameters such as the feedwater supply amount, the air supply amount, and the fuel supply amount are different in each operation mode, when the load changes passing through the switching point for switching the operation mode, the balance of various parameters changes more significantly than when the load changes in the region above the minimum stable load, which may cause the operation of the boiler 10 to become unstable. For this reason, during normal operation of the boiler 10, the load of the switching point (e.g., a load of 30% of the rated load) is set as the minimum stable load so that the switching point of the operation mode is not passed. By setting the minimum stable load of the boiler 10 in this way, the operation mode is not switched during the operation of the boiler 10, so that the boiler 10 can be operated stably.

[0046] Next, the relationship between the generator output command value, the fuel / water / air command value, the rotor blade opening, and the generator output in the power plant 1 according to this embodiment will be described with reference to FIG. 5 shows the change over time in the generator output command value (required power generation amount of the generator 113), with the vertical axis showing the generator output command value. Also, the dashed line shows the change over time in the fuel, feedwater, and air command values ​​for the boiler 10, with the vertical axis showing the fuel, feedwater, and air command values. Also, the dashed line shows the change over time in the opening degree of the rotor blades 111c, with the vertical axis showing the opening degree of the rotor blades 111c. Also, the two-dot chain line shows the change over time in the power generation amount (output) of the generator 113, with the vertical axis showing the power generation amount of the generator 113.

[0047] In the section from t1 to t2, when the generator output command value gradually decreases, the fuel, feedwater, and air command values ​​for the boiler 10 are gradually decreased accordingly. That is, the fuel supply amount (the supply amount of pulverized coal fuel supplied from the mill 31 to the boiler 10), the feedwater amount, and the air supply amount for the boiler 10 are gradually decreased. This reduces the load on the boiler 10, and the power generation amount of the generator 113 also gradually decreases. At this time, the opening degree of the rotor blades 111c (i.e., the angle of the blades 111d) is not changed. In this way, the power plant 1 according to this embodiment responds to a reduction in the required amount of power generation by reducing the load on the boiler 10 before the degree of opening of the rotor blades 111c.

[0048] In the section from t2 to t3, when the reduction in the generator output command value stops, the reduction in the fuel, feedwater, and air command values ​​for the boiler 10 also stops. In response to this, the reduction in the power generation amount of the generator 113 also stops. In this embodiment, the fuel, feedwater, and air command values ​​in the section from t2 to t3 are set to the lower limits of the fuel supply amount, the feedwater amount, and the air supply amount in the boiler 10. In other words, the boiler 10 is in a state of the minimum stable load, and the fuel supply amount, the feedwater amount, and the air supply amount cannot be reduced any more.

[0049] In the section from t3 to t4, when the generator output command value is further gradually reduced, the opening degree of the rotor blades 111c is gradually increased. That is, the angle of the blades 111d is changed to gradually increase the gap formed between the blades 111d. This reduces the driving force that rotates the rotating shaft 111b, and the output to the generator 113 is reduced. Therefore, the amount of power generated by the generator 113 is also gradually reduced.

[0050] In the section from t4 to t5, when the reduction in the generator output command value stops, the increase in the opening degree of the rotor blades 111c also stops. Accordingly, the reduction in the power generation amount of the generator 113 also stops. The power generation amount of the generator 113 at this time is set to the power generation amount corresponding to a load lower than the minimum stable load of the boiler 10. In other words, the power generation amount of the generator 113 cannot be reduced to this extent by simply operating the boiler 10 at the minimum stable load.

[0051] In the section from t5 to t6, when the generator output command value gradually increases, the opening degree of the rotor blades 111c is gradually decreased. That is, the angle of the blades 111d is changed to gradually decrease the gap formed between the blades 111d. This increases the driving force that rotates the rotating shaft 111b, and increases the output to the generator 113. Therefore, the amount of power generated by the generator 113 also gradually increases.

[0052] In the section from t6 to t7, when the increase in the generator output command value stops, the decrease in the opening degree of the rotor blades 111c also stops. Accordingly, the amount of power generated by the generator 113 also stops increasing.

[0053] In the section from t7 to t8, when the generator output command value increases gradually further, the fuel, feedwater, and air command values ​​for the boiler 10 are correspondingly increased gradually. That is, the fuel supply amount (the supply amount of pulverized coal fuel supplied from the mill 31 to the boiler 10), the feedwater amount, and the air supply amount for the boiler 10 are gradually increased. This increases the load on the boiler 10, and the power generation amount of the generator 113 also gradually increases. At this time, the opening degree of the rotor blades 111c (i.e., the angle of the blades 111d) is not changed.

[0054] According to this embodiment, the following advantageous effects are obtained. The rotating shaft 111b is connected to the generator 113. As a result, the amount of power generated by the generator 113 corresponds to the driving force that rotates the rotating shaft 111b. In this embodiment, the angle changer 111e is provided, which can change the driving force that rotates the rotating shaft 111b by changing the angle of the blades 111d when the amount of steam introduced into the casing 111a is constant. As a result, the amount of power generated by the generator 113 can be changed by changing the driving force that rotates the rotating shaft 111b (in other words, the output from the steam turbine 111 to the generator 113) with the angle changer 111e. In this way, since the amount of power generated by the generator 113 can be changed by the steam turbine 111, the correspondence between the boiler load and the amount of power generated by the generator 113 can be separated. In other words, the amount of power generated by the generator 113 can be changed from the amount of power generated according to the boiler load. Therefore, for example, even if the required amount of power generation of the generator 113 corresponds to a load band that is not preferable for the boiler 10 (for example, a load band below the minimum stable load), the boiler 10 can be operated at a load other than the load band by adjusting the amount of power generation of the generator 113 by the angle changer 111e. Thus, the operation of the boiler 10 can be stabilized. In this manner, in this embodiment, the required amount of power generation of the generator 113 can be satisfied, while the operation of the boiler 10 can be stabilized.

[0055] Furthermore, in this embodiment, when the required amount of power generation of the generator 113 corresponds to a load less than the minimum stable load of the boiler 10, the angle changer 111e reduces the driving force for rotating the rotating shaft 111b. As a result, even when the required amount of power generation of the generator 113 corresponds to a load less than the minimum stable load of the boiler 10, the boiler 10 can maintain the minimum stable load and does not pass through the switching point at which the operation mode is switched. This makes it possible to avoid the unstable region near the switching point, thereby stabilizing the operation of the boiler 10.

[0056] Furthermore, in this embodiment, the amount of power generated by the generator 113 is adjusted by controlling the opening of the turbine rotor blades 111c, which has good responsiveness without affecting the control aspect of the boiler, and therefore, the responsiveness when changing the amount of power generated by the generator 113 can be improved.

[0057] In addition, since the amount of electricity generated by the generator 113 is adjusted by controlling the opening of the rotor blades 111c, it is possible to suppress an increase in running costs compared to adjusting the amount of electricity generated by the generator 113 by switching the fuel from coal to heavy oil, light oil, gas, etc.

[0058] Also, in order to lower the minimum stable load of the boiler, it is possible to reduce the number of mills 31 in operation, for example, by operating only one mill 31. However, when only one mill 31 is operated, there is a possibility that it will not be possible to adequately follow the load change speed, so it is necessary to operate an oil burner or gas burner as an auxiliary. Since oil fuel and gas fuel are more expensive than coal, there is a problem in that fuel costs increase when an oil burner or gas burner is operated as an auxiliary. On the other hand, in this embodiment, since the amount of power generated can be adjusted according to the amount of power required by the generator 113 without reducing the number of operating mills 31, there is no need to operate auxiliary oil burners or gas burners, etc. Therefore, it is possible to suppress an increase in fuel costs.

[0059] In addition, during AFC (Automatic Frequency Control: system frequency concentration control) operation, the output of the generator 113 was adjusted by opening and closing the aperture of a control valve (not shown) installed at the inlet of the high-pressure turbine 111A. Therefore, in the power generation plant 1 composed of the high-pressure turbine 111A, the intermediate-pressure turbine 111B, and the low-pressure turbine 111C, there was a problem that a certain time delay occurred before the output of the generator 113 changed even if the aperture of the control valve was increased or decreased. On the other hand, in this embodiment, as described above, it is possible to improve the responsiveness when changing the amount of power generated by the generator 113. Therefore, this is particularly effective in control such as AFC, in which responsiveness is important.

[0060] In this embodiment, the angle changer 111e has an angle changer 111e that changes the angle of the blade 111d with respect to a plane perpendicular to the predetermined direction so as to change the size of the gap. This allows the size of the gap formed between adjacent blades 111d and through which steam passes to be changed by changing the angle of the blade 111d. The change in the size of the gap also changes the amount of steam that collides with the blade 111d. Therefore, by changing the angle of the blade 111d, the driving force that rotates the blade 111d and the rotating shaft 111b changes, and the amount of power generated by the generator 113 can be changed.

[0061] The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit and scope of the present disclosure.

[0062] In the above-described embodiment, the boiler of the present disclosure has been described as a boiler that uses solid fuel as fuel. The solid fuel used in the boiler may be coal, biomass fuel, petroleum coke (PC) fuel, petroleum residue, or the like. The fuel for the boiler is not limited to solid fuels, and can also be petroleum such as heavy oil, light oil, and heavy oil, industrial wastewater, liquid ammonia, etc. Also, gaseous fuels such as natural gas, various petroleum gases, by-product gases generated in the steelmaking process, hydrogen gas, and ammonia gas can also be used. Furthermore, the present invention can be applied to a multi-fuel boiler that uses a combination of these various fuels.

[0063] Also, for example, in the above embodiment, an example has been described in which the driving force for rotating the rotating shaft 111b is changed by changing the angle of the blade 111d, but the present disclosure is not limited to this. For example, the rotation speed of the rotating shaft 111b may be changed by changing the size of the gap formed between the casing 111a and the blades 111d. By changing the size of the gap formed between the casing 111a and the blades 111d, the amount of steam passing outside the blades 111d can be changed. In other words, by changing the size of the gap, the amount of steam colliding with the blades 111d can be changed. Therefore, the driving force that rotates the blades 111d and the rotating shaft 111b can be changed, and the amount of power generated by the generator 113 can be changed.

[0064] Furthermore, for example, when the required amount of power generation of the generator 113 increases, the angle of the blades 111d may be changed so that the gap between the blades 111d decreases, thereby increasing the driving force for rotating the rotating shaft 111b. This allows the amount of power generation of the generator 113 to be improved in the steam turbine 111 as well, so that the required amount of power generation can be more suitably achieved.

[0065] The steam turbine, the power plant, and the method of operating the steam turbine according to the above-described embodiments can be understood, for example, as follows. A steam turbine according to a first aspect of the present disclosure is a steam turbine (111) that is supplied with steam generated in a boiler (10) and that drives a generator (113) by being rotated by the supplied steam. The steam turbine includes a casing (111a) that forms an outer shell and into which steam is introduced and through which steam flows, a rotating shaft (111b) that is housed inside the casing (111a), attached to the casing (111a) so as to be rotatable about a central axis extending in a predetermined direction, and connected to the generator (113), a plurality of blades (111d) that are housed inside the casing (111a) and attached to the outer circumferential surface of the rotating shaft (111b) so as to be aligned at predetermined intervals along the circumferential direction, and ...). and an output change unit (111e) capable of changing the output of the generator (113) when the amount of steam introduced into the housing (111a) is constant, wherein the rotating shaft (111b) rotates together with the blades (111d) as a result of the steam circulating inside the housing (111a) colliding with the blades (111d), and between the blades (111d) adjacent in the circumferential direction, a gap is formed through which the steam circulating inside the housing (111a) can pass, and when the amount of power generation required by the generator (113) is an amount corresponding to a load that is less than a minimum stable load of the boiler (10), the output change unit (111e) changes the gap to reduce the amount of power generation of the generator (113).

[0066] In the above configuration, the power generation amount of the generator is changed when the amount of steam introduced into the casing is constant. This allows the power generation amount of the generator to be changed by the output change unit. Since the power generation amount of the generator can be changed by the steam turbine in this way, the correspondence between the boiler load and the power generation amount of the generator can be separated. That is, the power generation amount of the generator can be changed from the power generation amount corresponding to the boiler load. Therefore, for example, even if the required power generation amount of the generator is the power generation amount corresponding to a load band that is not preferable for the boiler (for example, a load band below the minimum stable load), the boiler can be operated at a load other than the load band by adjusting the power generation amount of the generator by the output change unit. Therefore, the operation of the boiler can be stabilized. In this way, the required power generation amount of the generator can be preferably satisfied in the above configuration. Also, the operation of the boiler can be stabilized while satisfying the required power generation amount of the generator.

[0067] Furthermore, in the above configuration, when the required amount of power generation of the generator corresponds to a load that is less than the minimum stable load of the boiler, the output change unit changes the gap to reduce the amount of power generation of the generator. As a result, when the required amount of power generation of the generator corresponds to a load that is less than the minimum stable load of the boiler, the load of the boiler can be increased by the amount by which the steam turbine (output change unit) reduces the amount of power generation of the generator. Therefore, when the amount of power generation of the generator is adjusted by the steam turbine so that the load of the boiler is equal to or greater than the minimum stable load, the boiler can be operated at a load equal to or greater than the minimum stable load. This makes it possible to stabilize the operation of the boiler.

[0068] In addition, in a steam turbine according to a second aspect of the present disclosure, in the above-mentioned first aspect, the output change section (111e) has an angle change section (111e) that changes the angle of the blade (111d) with respect to a plane perpendicular to the specified direction so as to change the size of the gap.

[0069] In the above configuration, the output change unit has a blade angle change unit that changes the angle of the blade with respect to a plane perpendicular to the predetermined direction so as to change the size of the gap. This makes it possible to change the size of the gap formed between adjacent blades and through which steam passes by changing the angle of the blade. Changing the size of the gap also changes the amount of steam that collides with the blade. Therefore, changing the angle of the blade changes the rotation speed of the blade and the rotating shaft, and therefore the amount of power generated by the generator can be changed.

[0070] In addition, in a steam turbine according to a third aspect of the present disclosure, in the first or second aspect described above, the output change unit (111e) has a gap change unit that changes the size of the gap formed between the casing (111a) and the blades (111d).

[0071] In the above configuration, the output change unit has a gap change unit that changes the size of the gap formed between the housing and the blades. This allows the amount of steam passing outside the blades to be changed by changing the size of the gap. In other words, the amount of steam that collides with the blades can be changed by changing the size of the gap. Therefore, the rotation speed of the blades and the rotating shaft can be changed, and the amount of power generated by the generator can be changed.

[0072] In addition, in a steam turbine according to a fourth aspect of the present disclosure, in any one of the first to third aspects described above, when the required power generation amount of the generator (113) increases, the output change unit (111e) increases the power generation amount of the generator (113).

[0073] In the above configuration, when the required amount of electricity generated by the generator increases, the output varying unit increases the rotation speed of the rotating shaft. This allows the amount of electricity generated by the generator to be improved even in the steam turbine, making it possible to more appropriately achieve the required amount of electricity generated.

[0074] Furthermore, a power plant according to a first aspect of the present disclosure includes a steam turbine (111) according to any one of the first to fourth aspects, a boiler (10) that generates steam to be supplied to the steam turbine (111), and a generator (113) that generates electricity using the rotational driving force of the steam turbine (111).

[0075] A method for operating a steam turbine according to a first aspect of the present disclosure is a method for operating a steam turbine (111) that is supplied with steam generated in a boiler (10) and that drives a generator (113) by being rotated by the supplied steam, in which the steam turbine (111) includes a casing (111a) that forms an outer shell and into which steam is introduced and through which the steam flows, a rotating shaft (111b) that is housed inside the casing (111a), attached to the casing (111a) to be rotatable about a central axis extending in a predetermined direction, and connected to the generator (113), and a plurality of blades (111b) that are housed inside the casing (111a) and attached to an outer circumferential surface of the rotating shaft (111b) so as to be arranged at predetermined intervals along a circumferential direction. the rotating shaft (111b) rotates together with the blades (111d) when the steam circulating inside the housing (111a) collides with the blades (111d), and gaps are formed between the blades (111d) adjacent in the circumferential direction, through which the steam circulating inside the housing (111a) passes, and when the required amount of power generation of the generator (113) is a required amount of power generation corresponding to a load that is less than a minimum stable load of the boiler (10), the output changing unit (111e) changes the gap to reduce the amount of power generation of the generator (113). [Explanation of symbols]

[0076] 1: Power plant 10: Boiler 11: Furnace 12: Combustion gas passage 13: Flue 20: Combustion equipment 21: Burna 22:Powdered fuel supply pipe 22A: Fine powder fuel supply pipe 22B: Fine powder fuel supply pipe 22C: Fine powder fuel supply pipe 22D: Fine powder fuel supply pipe 22E: Fine fuel supply pipe 22F: Fine powder fuel supply pipe 23: Wind box 24: Wind road 25: Additional air port 26: Additional air duct 31: Mill 32: Forced ventilation fan 41: Gas duct 42: Air preheater 43: Denitration equipment 44: Dust collection device 46: Desulfurization equipment 47: Chimney 101: Furnace wall 102:Superheater 102A: 1st superheater 102B: 2nd superheater 102C: 3rd superheater 103 :Reheater 103A: 1st reheater 103B:Second reheater 104: Economizer 111: Steam turbine 111A: High pressure turbine 111B: Intermediate pressure turbine 111C: Low pressure turbine 111a: Vehicle interior 111b: Rotation axis 111c: Moving blade 111d: Blade 111e: Angle change unit (output change unit) 112: Condenser 113: Generator 114: Transformer 115: Power transmission equipment 122: Low pressure water heater 123: Boiler feed pump 124: High pressure water heater 125:Brackish water separator 126: Brackish water separator drain tank L1: Water supply line L2: Drain water line L3: Steam line L5: Steam line L6: Circulation line

Claims

1. A steam turbine that is supplied with steam generated in a boiler and drives a generator by being rotated by the supplied steam, a housing forming an outer shell, into which steam is introduced and through which steam circulates; a rotating shaft that is accommodated inside the housing, that is attached to the housing so as to be rotatable about a central axis line extending in a predetermined direction, and that is connected to the generator; A plurality of blades are housed inside the housing and attached to the outer circumferential surface of the rotating shaft so as to be arranged at predetermined intervals along the circumferential direction; an output change unit that changes the amount of power generated by the generator while the amount of steam introduced into the housing is constant; the rotating shaft rotates together with the blades as steam flowing inside the housing collides with the blades, A gap is formed between the blades adjacent to each other in the circumferential direction, through which steam circulating inside the housing passes, When the required amount of power generation of the generator corresponds to a load less than a minimum stable load of the boiler, the output changing unit changes the gap to reduce the amount of power generation of the generator.

2. The steam turbine according to claim 1 , wherein the output varying unit has an angle changing unit that changes an angle of the blade with respect to a plane perpendicular to the predetermined direction so as to change the size of the gap.

3. The steam turbine according to claim 1 , wherein the output varying unit has a clearance changing unit that varies a size of a clearance formed between the casing and the blades.

4. The steam turbine according to claim 1 , wherein the output varying unit increases the amount of power generated by the generator when a required amount of power generation of the generator increases.

5. A steam turbine according to any one of claims 1 to 4; a boiler for generating steam to be supplied to the steam turbine; a generator that generates electricity using the rotational driving force of the steam turbine.

6. A method for operating a steam turbine in which steam generated in a boiler is supplied to rotate and drive a generator using the supplied steam, comprising the steps of: The steam turbine includes: a housing forming an outer shell, into which steam is introduced and through which steam circulates; a rotating shaft that is accommodated inside the housing, that is attached to the housing so as to be rotatable about a central axis line extending in a predetermined direction, and that is connected to the generator; A plurality of blades are housed inside the housing and attached to the outer circumferential surface of the rotating shaft so as to be arranged at predetermined intervals along the circumferential direction; an output change unit that changes the amount of power generated by the generator while the amount of steam introduced into the housing is constant; the rotating shaft rotates together with the blades as steam flowing inside the housing collides with the blades, A gap is formed between the blades adjacent to each other in the circumferential direction, through which steam circulating inside the housing passes, A method for operating a steam turbine comprising a step of, when the required amount of power generation of the generator corresponds to a load less than a minimum stable load of the boiler, changing the gap by the output changing unit to reduce the amount of power generation of the generator.

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