Boiler system, control method and program

Abstract

The present invention efficiently lowers the surface temperature of pipes that make up a boiler system, thereby suppressing high-temperature corrosion of the pipes. A boiler system 1 comprises: a pipe (first connection pipe 14, second connection pipe 15, reheater pipe 40a) for circulating steam; and a steam temperature control unit (pump 7, pipes 7a, 7b, 7c, first regulating valve 18, second regulating valve 19, third regulating valve 60, control unit 30) that lowers the temperature (T1, T3, T5) of the steam circulating through the pipe below a predetermined temperature (T12, T34, T56) by supplying fluid to the interior of the pipe.

Description

[Technical field]

[0001] The present invention relates to a boiler system, a control method, and a program. [Background technology]

[0002] Various boiler systems have been proposed that generate steam using the heat of high-temperature exhaust gas obtained by burning fuel in a combustion furnace. Such boiler systems are equipped with a superheater that further superheats the steam generated in the steam drum to a high temperature and pressure. The steam superheated by the superheater is supplied to a steam turbine and used to drive a generator, etc.

[0003] Currently, in order to maximize the energy extracted from the thermal cycle (Rankine cycle) of a thermal power plant, a method is adopted in which the temperature of the steam at the boiler outlet (the temperature of the steam discharged from the most downstream superheater: hereinafter referred to as the "main steam temperature") is raised. However, raising the main steam temperature causes high-temperature steam to flow through the superheater tubes that constitute the superheater, and as a result, the surface temperature of the superheater tubes also becomes high. This may cause ash, consisting of chlorides, sulfides, etc. contained in the exhaust gas, to melt and adhere to the surface of the superheater tubes, accelerating high-temperature corrosion of the superheater tubes.

[0004] For this reason, in recent years, a technology has been proposed in which a corrosion detector is installed near the superheater, and when a corrosion signal exceeds a predetermined threshold, the operation of the combustion furnace is controlled to lower the temperature of the exhaust gas (see, for example, Patent Document 1). It is said that the adoption of such a technology makes it possible to suppress the adhesion of molten ash to the surface of the superheater tube, thereby mitigating the corrosive environment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-106822 A Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional technology such as that described in Patent Document 1 reduces the surface temperature of the superheater tube by lowering the temperature of the exhaust gas. However, because extremely high-temperature (e.g., 541°C) steam flows inside the superheater tube that constitutes the superheater (especially the superheater located at the most downstream position), it is not possible to efficiently lower the surface temperature of the superheater tube by simply lowering the temperature of the exhaust gas.

[0007] The present invention has been made in view of the above circumstances, and has an object to efficiently reduce the surface temperature of tubes that constitute a boiler system, thereby suppressing high-temperature corrosion of the tubes. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the boiler system of the present invention comprises a pipe through which steam flows, and a steam temperature control unit that reduces the temperature of the steam flowing through the pipe below a predetermined temperature by supplying a fluid inside the pipe.

[0009] In addition, the control method of the present invention is a method for controlling the steam temperature of a boiler system having a pipe through which steam circulates, and includes a steam temperature control step of lowering the temperature of the steam circulating through the pipe below a predetermined temperature by supplying a fluid inside the pipe.

[0010] In addition, the program of the present invention is a program that causes a computer to execute a method for controlling the steam temperature of a boiler system having a pipe through which steam circulates, the method including a steam temperature control step of lowering the temperature of steam circulating through the pipe below a predetermined temperature by supplying a fluid inside the pipe.

[0011] By adopting this configuration and method, the temperature of the steam flowing through the tubes can be lowered to below a predetermined temperature by supplying a fluid inside the tubes, so that the surface temperature of the tubes can be lowered more efficiently than with conventional methods for lowering the temperature of exhaust gases. This makes it possible to suppress adhesion of molten ash to the surface of the tubes and to suppress high-temperature corrosion of the tubes.

[0012] In the boiler system according to the present invention, a temperature detector for detecting the steam temperature can be provided. In such a case, the steam temperature control unit can have a supply unit for supplying a fluid into the pipe, a regulating valve for adjusting the amount of fluid supplied by the supply unit, and a control unit for controlling the flow rate of the fluid supplied into the pipe by controlling the regulating valve based on the steam temperature detected by the temperature detector.

[0013] With this configuration, the flow rate of the fluid supplied to the pipe can be controlled by the control unit by controlling the regulating valve based on the steam temperature detected by the temperature detection unit, thereby making it possible to perform appropriate control according to the steam temperature.

[0014] In the boiler system according to the present invention, when the steam temperature detected by the temperature detector exceeds a predetermined threshold, the control unit can control the regulating valve to lower the steam temperature in the tube below the threshold. Here, the threshold can be set according to the state of ash adhesion to the tube and the fuel properties of the ash.

[0015] By adopting such a configuration, when the steam temperature detected by the temperature detection unit exceeds a predetermined threshold value, the control unit can control the regulating valve so as to lower the steam temperature in the pipe below the threshold value.

[0016] The boiler system according to the present invention may include a superheater having a first superheating section, a second superheating section downstream of the first superheating section, and a third superheating section downstream of the second superheating section. In such a case, the tubes may include a first connecting tube connecting the superheater tube of the first superheating section and the superheater tube of the second superheating section, and a second connecting tube connecting the superheater tube of the second superheating section and the superheater tube of the third superheating section. The temperature detection unit may include a first temperature sensor detecting a steam temperature at an inlet of the superheater tube of the second superheater section, a second temperature sensor detecting a steam temperature at an outlet of the superheater tube of the second superheater section, a third temperature sensor detecting a steam temperature at an inlet of the superheater tube of the third superheater section, and a fourth temperature sensor detecting a steam temperature at an outlet of the superheater tube of the third superheater section, the supply unit may include a pump for supplying a fluid, a first feedwater pipe connecting the pump and the first connecting pipe, and a second feedwater pipe connecting the pump and the second connecting pipe, and the regulating valve may include a first regulating valve for regulating a supply amount of the fluid supplied to the first connecting pipe, and a second regulating valve for regulating a supply amount of the fluid supplied to the second connecting pipe. The control unit may control the first regulating valve based on the steam temperatures detected by the first and second temperature sensors to reduce the steam temperature in the superheater tube of the second superheater section below a first threshold value, and control the second regulating valve based on the steam temperatures detected by the third and fourth temperature sensors to reduce the steam temperature in the superheater tube of the third superheater section below a second threshold value. In this case, the second threshold value can be set to a value greater than the first threshold value.

[0017] When this configuration is adopted, the steam temperature in the superheater tube of the second superheater section can be reduced below the first threshold value by controlling the first adjustment valve based on the steam temperature (steam temperature at the inlet and outlet of the superheater tube of the second superheater section) detected by the first and second temperature sensors, and the steam temperature in the superheater tube of the third superheater section can be reduced below the second threshold value by controlling the second adjustment valve based on the steam temperature (steam temperature at the inlet and outlet of the superheater tube of the third superheater section) detected by the third and fourth temperature sensors. Therefore, high-temperature corrosion of the superheater tubes of the second and third superheater sections can be suppressed. At this time, since the second threshold value is set to a value larger than the first threshold value, it is possible to control the steam temperature to gradually increase.

[0018] The boiler system according to the present invention may include a reheater that reheats steam discharged from the turbine. In such a case, the tube may include a turbine extraction pipe that connects the turbine and a reheater pipe of the reheater. The temperature detection unit may include an inlet temperature sensor that detects a steam temperature at an inlet of the reheater pipe of the reheater and an outlet temperature sensor that detects a steam temperature at an outlet of the reheater pipe of the reheater, the supply unit may include a pump that supplies a fluid and a third feedwater pipe that connects the pump and the turbine extraction pipe, and the adjustment valve may include a third adjustment valve that adjusts the supply amount of the fluid supplied to the turbine extraction pipe. The control unit may control the third adjustment valve based on the steam temperatures detected by the inlet temperature sensor and the outlet temperature sensor, thereby reducing the steam temperature in the reheater pipe of the reheater below a third threshold value.

[0019] With this configuration, the third regulating valve is controlled based on the steam temperatures detected by the inlet and outlet temperature sensors (the steam temperatures at the inlet and outlet of the reheater tubes of the reheater), thereby making it possible to lower the steam temperature in the reheater tubes of the reheater below the third threshold value, thereby making it possible to suppress high-temperature corrosion of the reheater tubes of the reheater. Effect of the Invention

[0020] According to the present invention, it is possible to efficiently reduce the surface temperature of tubes constituting a boiler system, thereby suppressing high-temperature corrosion of the tubes. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic diagram showing an overall configuration of a boiler system according to a first embodiment of the present invention. [Diagram 2] 1 is a diagram showing a configuration of a superheater and its surroundings in a boiler system according to a first embodiment of the present invention. FIG. [Diagram 3] 4 is a flowchart for explaining a method for controlling a steam temperature in a boiler system according to the first embodiment of the present invention. [Figure 4] 4 is a graph showing an example of a change in steam temperature in the boiler system according to the first embodiment of the present invention. [Diagram 5] FIG. 6 is a diagram showing a configuration of a superheater and its surroundings in a boiler system according to a second embodiment of the present invention. [Figure 6] 6 is a flowchart for explaining a method for controlling a steam temperature in a boiler system according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are merely preferred application examples, and the scope of application of the present invention is not limited to these.

[0023] First Embodiment First, a boiler system 1 according to a first embodiment of the present invention will be described with reference to Figs. 1 to 4. The boiler system 1 according to this embodiment is a circulating fluidized bed boiler (circulating fluidized bed type) system, which burns fuel while circulating a circulating material (such as silica sand) that flows at high temperature, to generate steam. As the fuel for the boiler system 1, for example, non-fossil fuels (such as wood biomass, waste tires, waste plastics, sludge, etc.) can be used. The steam generated by the boiler system 1 is used to drive turbines 100 and 101, which will be described later.

[0024] The boiler system 1 is configured to burn fuel in a furnace 2, separate circulating materials from exhaust gas by a cyclone 3 functioning as a solid-gas separator, and return the separated circulating materials to the furnace 2 for circulation. The separated circulating materials are returned to the lower part of the furnace 2 via a circulating materials recovery pipe 4 connected to the lower part of the cyclone 3. The lower part of the circulating materials recovery pipe 4 and the lower part of the furnace 2 are connected via a loop seal part 4a with a narrowed flow path as shown in FIG. 1. As a result, a predetermined amount of circulating materials is stored in the lower part of the circulating materials recovery pipe 4. The exhaust gas from which the circulating materials have been removed by the cyclone 3 is supplied to the rear flue 5 via the exhaust gas flow path 3a.

[0025] The furnace 2 is a combustion furnace that burns fuel. A fuel supply port 2a for supplying fuel is provided in the middle of the furnace 2, and a gas outlet 2b for discharging combustion gas is provided in the upper part of the furnace 2. Fuel supplied to the furnace 2 from a fuel supply device (not shown) is supplied to the inside of the furnace 2 through the fuel supply port 2a. In addition, a furnace wall tube 6 for heating boiler feed water is provided on the furnace wall of the furnace 2. The boiler feed water flowing through the furnace wall tube 6 is heated by combustion in the furnace 2.

[0026] In the furnace 2, the solids containing the fuel supplied from the fuel supply port 2a are fluidized by the air for combustion and fluidization introduced from the air supply line 2c at the bottom, and the fuel is burned at about 800 to 900°C while flowing. The combustion gas generated in the furnace 2 is introduced into the cyclone 3 together with the circulating material. The cyclone 3 separates the circulating material from the gas by centrifugal separation, and returns the separated circulating material to the furnace 2 via the circulating material recovery pipe 4, while sending the combustion gas from which the circulating material has been removed through the exhaust gas flow path 3a to the rear flue 5 described later.

[0027] In the furnace 2, solid matter called the in-furnace bed material is generated and accumulates at the bottom, but it is necessary to suppress sintering and melting and solidifying of the bed material caused by the concentration of impurities (low melting point substances, etc.) in the in-furnace bed material, or malfunction due to non-combustible impurities. For this reason, the in-furnace bed material is continuously or intermittently discharged to the outside from the discharge port 2d at the bottom of the furnace 2. After removing inappropriate materials such as metals and coarse grains from the discharged bed material on a circulation line not shown, it is either supplied to the furnace 2 again or disposed of as is. The circulating material of the furnace 2 circulates in a circulation system consisting of the furnace 2, cyclone 3, and circulating material recovery pipe 4.

[0028] The rear flue 5 has a flow path for flowing the gas discharged from the cyclone 3 to the rear stage. The rear flue 5 has a superheater 10 for generating superheated steam and an economizer 20 for preheating boiler feed water as an exhaust heat recovery section for recovering heat from the exhaust gas. The exhaust gas flowing through the rear flue 5 is cooled by heat exchange with the steam and boiler feed water flowing through the superheater 10 and the economizer 20. The rear flue 5 also has a pump 7 for supplying boiler feed water to the economizer 20, and a steam drum 8 for storing the boiler feed water that has passed through the economizer 20 and connected to the furnace wall tube 6 of the furnace 2. The configuration of the superheater 10 will be described in detail later.

[0029] The economizer 20 transfers heat from the exhaust gas to the boiler feed water to preheat the boiler feed water. The economizer 20 is connected to the pump 7 via a pipe 21, and is also connected to the steam drum 8 via a pipe 22. The boiler feed water that is supplied from the pump 7 via the pipe 21 to the economizer 20 and preheated by the economizer 20 is supplied to the steam drum 8 via the pipe 22.

[0030] A downcomer pipe 8a and a furnace wall pipe 6 are connected to the steam drum 8. The boiler feed water in the steam drum 8 flows down the downcomer pipe 8a, is introduced into the furnace wall pipe 6 at the lower side of the furnace 2, and flows toward the steam drum 8. The boiler feed water in the furnace wall pipe 6 is heated by the combustion heat generated in the furnace 2, and evaporates in the steam drum 8 to become steam.

[0031] An exhaust pipe 8b for discharging the steam inside is connected to the steam drum 8. The exhaust pipe 8b connects the steam drum 8 and a superheater 10. The steam inside the steam drum 8 is supplied to the superheater 10 via the exhaust pipe 8b. The superheater 10 superheats the steam using the heat of the exhaust gas to generate superheated steam. The superheated steam passes through a pipe 10a and is supplied to turbines 100, 101 outside the boiler system 1 and is used for power generation.

[0032] Here, the configuration around the superheater 10 of the boiler system 1 according to this embodiment will be specifically described with reference to FIG.

[0033] As shown in Fig. 2, the superheater 10 has a first superheating section 11 that superheats steam introduced from an exhaust pipe 8b, a second superheating section 12 that further superheats the steam introduced from the first superheating section 11, and a third superheating section 13 that further superheats the steam introduced from the second superheating section 12. The first superheating section 11, the second superheating section 12, and the third superheating section 13 each have superheater tubes 11a, 12a, and 13a through which steam flows. The first superheating section 11 and the second superheating section 12 are connected by a first connecting tube 14, and the second superheating section 12 and the third superheating section 13 are connected by a second connecting tube 15.

[0034] A first temperature sensor 16a is provided upstream of the second superheating section 12 to detect a steam temperature T1 at the inlet of the superheater tube 12a, and a second temperature sensor 16b is provided downstream of the second superheating section 12 to detect a steam temperature T2 at the outlet of the superheater tube 12a of the second superheating section 12. A third temperature sensor 16c is provided upstream of the third superheating section 13 to detect a steam temperature T3 at the inlet of the superheater tube 13a, and a fourth temperature sensor 16d is provided downstream of the third superheating section 13 to detect a steam temperature T4 at the outlet of the superheater tube 13a. Information on the steam temperatures detected by the first temperature sensor 16a, the second temperature sensor 16b, the third temperature sensor 16c, and the fourth temperature sensor 16d is sent to a control section 30 described later and used for controlling various regulating valves. The first temperature sensor 16a, the second temperature sensor 16b, the third temperature sensor 16c, and the fourth temperature sensor 16d correspond to the temperature detection section in the present invention.

[0035] A first connecting pipe 14 connecting the first superheating section 11 and the second superheating section 12 is connected to the pump 7 by a first water supply pipe 7a, and a second connecting pipe 15 connecting the second superheating section 12 and the third superheating section 13 is connected by a second water supply pipe 7b. Water for cooling steam is supplied from the pump 7 to the first connecting pipe 14 via the first water supply pipe 7a, and is supplied from the pump 7 to the second connecting pipe 15 via the second water supply pipe 7b. The first water supply pipe 7a and the second water supply pipe 7b share a common pipe section 7ab on the upstream side (pump 7 side). The pump 7 and the first and second water supply pipes 7a, 7b correspond to the supply section in this invention.

[0036] A first regulating valve 18 is provided in the first water supply pipe 7a connecting the pump 7 and the first connecting pipe 14 to adjust the flow rate of water flowing through the first water supply pipe 7a, and a second regulating valve 19 is provided in the second water supply pipe 7b connecting the pump 7 and the second connecting pipe 15 to adjust the flow rate of water flowing through the second water supply pipe 7b. The first regulating valve 18 and the second regulating valve 19 function to adjust the amount of water supplied to the first connecting pipe 14 and the second connecting pipe 15 by being controlled by a control signal sent from the control unit 30 described later.

[0037] The boiler system 1 according to this embodiment includes a control unit 30 that performs integrated control of various components provided in the system. The control unit 30 includes a memory that stores various control programs and various control data, a processor that executes the various control programs, and the like.

[0038] The control unit 30 controls the first regulating valve 18 and the second regulating valve 19 based on the steam temperatures T1, T2, T3, T4 detected by the first temperature sensor 16a, the second temperature sensor 16b, the third temperature sensor 16c, and the fourth temperature sensor 16d, thereby controlling the flow rates of water supplied into the first connecting pipe 14 and the second connecting pipe 15. More specifically, the control unit 30 calculates whether the average values ​​of the steam temperatures T1, T2 (steam temperatures at the inlet and outlet of the superheater tube 12a of the second superheating section 12) detected by the first temperature sensor 16a and the second temperature sensor 16b and the average values ​​of the steam temperatures T3, T4 (steam temperatures at the inlet and outlet of the superheater tube 13a of the third superheating section 13) detected by the third temperature sensor 16c and the fourth temperature sensor 16d exceed first and second threshold values ​​T 12 , T 34 When the steam temperature exceeds the first threshold value T1, the steam temperature in the first connecting pipe 14 and the steam temperature in the second connecting pipe 15 are lowered. As a result, the steam temperature T1 at the inlet of the superheater tube 12a of the second superheating section 12 (the steam temperature in the first connecting pipe 14) and the steam temperature T3 at the inlet of the superheater tube 13a of the third superheating section 13 (the steam temperature in the second connecting pipe 15) are lowered to the first threshold value T2. 12 , T 34 The first regulating valve 18 and the second regulating valve 19 are controlled so as to lower the respective pressures to lower than the pressures.

[0039] Here, the first and second thresholds T 12 , T 34is a value that is appropriately determined based on the state of ash adhesion, the component analysis values ​​of the fuel and combustion ash, the state of ash adhesion to the tubes during periodic inspection, the corrosion state of the tubes, etc., and for example, the melting point of ash contained in the exhaust gas, a specific temperature set according to the requirements of the turbines 100, 101 connected to the boiler system 1, etc. can be adopted as the predetermined threshold value. The fuel may contain alkali metals (sodium, potassium, etc.) in addition to chlorine, and chlorides and sulfides generated from chlorine, sodium, potassium, etc. may have melting points lower than the combustion field temperature (about 870°C) in the furnace 2. Examples of low-melting point substances include sodium chloride, calcium chloride, potassium chloride, sodium sulfate, potassium sulfate, potassium pyrosulfate, and trisulfides of sodium or potassium (Na3Fe(SO4)3, K3Fe(SO4)3). The first and second threshold values ​​T 12 , T 34 is preferably appropriately determined in consideration of the low melting points of these substances. The threshold value in the second embodiment described later is also appropriately determined in the same manner.

[0040] In this embodiment, the pump 7, the first and second water supply pipes 7a, 7b (supply section), the first regulating valve 18 and the second regulating valve 19, and the control section 30 constitute a "steam temperature control section" that supplies water to the inside of the first connecting pipe 14 and the second connecting pipe 15, thereby lowering the temperature of the steam flowing through the first connecting pipe 14 and the second connecting pipe 15 below a predetermined temperature.

[0041] As shown in FIG. 2, the boiler system 1 according to this embodiment is connected to turbines (turbines 100 and 101 arranged on the same axis). Steam is supplied to the turbine 100 from the superheater 10 through a pipe 10a, and steam (reheated steam) is supplied to the turbine 101 from a reheater 40 described later, thereby rotating the turbines 100 and 101 to generate power. The pressure and temperature of the steam discharged from the turbine 100 are lower than those of the steam discharged from the superheater 10. Although not particularly limited, the pressure and temperature of the steam supplied to the turbine 100 are about 10 to 17 MPa, and the temperature is about 530 to 570° C. The pressure and temperature of the steam discharged from the turbine 100 are about 3 to 5 MPa, and the temperature is about 350 to 400° C. A condenser 102 is provided downstream of the turbine 101. The steam discharged from the turbine 101 is supplied to a condenser 102 where it is condensed back into saturated water and then supplied to the pump 7 .

[0042] As shown in FIG. 2, the boiler system 1 according to this embodiment includes a reheater 40 that reheats steam discharged from a turbine 100. The reheater 40 has a reheater tube 40a through which steam flows. The turbine 100 and the reheater 40 are connected by a turbine extraction pipe 100a for supplying the steam discharged from the turbine 100 to the reheater 40. The reheater 40 and the turbine 101 are also connected by a turbine intake pipe 101a for supplying the steam reheated in the reheater 40 to the turbine 101. Therefore, the steam supplied to the reheater 40 via the turbine extraction pipe 100a is reheated by heat exchange in the reheater 40, and then supplied to the downstream turbine 101 via the turbine intake pipe 101a.

[0043] An inlet temperature sensor 51 for detecting a steam temperature T5 at the inlet of the reheater tube 40a is provided upstream of the reheater 40, and an outlet temperature sensor 52 for detecting a steam temperature T6 at the outlet of the reheater tube 40a is provided downstream of the reheater 40. The inlet temperature sensor 51 and the outlet temperature sensor 52 also correspond to the temperature detection unit in the present invention. Information on the steam temperatures detected by the inlet temperature sensor 51 and the outlet temperature sensor 52 is sent to the control unit 30 and used for controlling a third adjustment valve 60, which will be described later. In addition, the turbine extraction pipe 100a connecting the turbine 100 and the reheater 40 is connected to the pump 7 by a third feedwater pipe 7c branched from the second feedwater pipe 7b, and water for steam cooling is supplied from the pump 7 to the turbine extraction pipe 100a (and thus to the reheater tube 40a) via the third feedwater pipe 7c. The pump 7 and the third feedwater pipe 7c correspond to the supply unit in the present invention.

[0044] The third feedwater pipe 7c is provided with a third regulating valve 60 that regulates the flow rate of water flowing through the third feedwater pipe 7c. The third regulating valve 60 functions to regulate the amount of water supplied to the turbine extraction pipe 100a (reheater pipe 40a) by being controlled by a control signal sent from the control unit 30. The control unit 30 controls the third regulating valve 60 based on the steam temperatures T5, T6 detected by the inlet temperature sensor 51 and the outlet temperature sensor 52, thereby controlling the flow rate of water supplied to the turbine extraction pipe 100a (reheater pipe 40a). More specifically, the control unit 30 controls the flow rate of water supplied to the turbine extraction pipe 100a (reheater pipe 40a) by controlling the third regulating valve 60 based on the steam temperatures T5, T6 detected by the inlet temperature sensor 51 and the outlet temperature sensor 52. 56 When the steam temperature T5 at the inlet of the reheater tube 40a of the reheater 40 (the steam temperature in the turbine extraction pipe 100a) exceeds the third threshold T 56 The third adjusting valve 60 is controlled so as to reduce the pressure to less than the third threshold T 56 are the first and second thresholds T 12 , T 34 Similarly, this value is appropriately determined based on the state of ash adhesion, etc.

[0045] In this embodiment, the pump 7, the third water supply pipe 7c (supply section), the third adjustment valve 60, and the control section 30 constitute a "steam temperature control section" that supplies water to the inside of the turbine extraction pipe 100a (reheater pipe 40a) to lower the temperature of the steam flowing through the turbine extraction pipe 100a (reheater pipe 40a) below a predetermined temperature.

[0046] Next, a method for controlling the steam temperature of the boiler system 1 according to this embodiment will be described with reference to the flowchart of FIG.

[0047] First, the control unit 30 of the boiler system 1 detects steam temperatures T1, T2 at the inlet and outlet of the superheater tube 12a of the second superheater section 12 using the first temperature sensor 16a and the second temperature sensor 16b (first second temperature detection step: S1), and detects steam temperatures T3, T4 at the inlet and outlet of the superheater tube 13a of the third superheater section 13 using the third temperature sensor 16c and the fourth temperature sensor 16d (third fourth temperature detection step: S2). Furthermore, the control unit 30 detects steam temperatures T5, T6 at the inlet and outlet of the reheater tube 40a of the reheater 40 using the inlet temperature sensor 51 and the outlet temperature sensor 52 (inlet and outlet temperature detection step: S3).

[0048] Next, the control unit 30 of the boiler system 1 detects whether the average value of the steam temperatures T1 and T2 detected in the first and second temperature detection steps S1 is equal to or smaller than the first threshold value T 12 When the flow rate of the water supplied to the first connecting pipe 14 is exceeded, the first regulating valve 18 is controlled to control the flow rate of the water supplied to the first connecting pipe 14, thereby lowering the steam temperature in the first connecting pipe 14. As a result, the steam temperature T1 at the inlet of the superheater tube 12a of the second superheating section 12 is lowered to a value lower than the first threshold value T 12 The control unit 30 also determines whether the average value of the steam temperatures T3 and T4 detected in the third and fourth temperature detection steps S2 is equal to or lower than the second threshold value T 34When the flow rate of the water supplied to the second connecting pipe 15 is exceeded, the second regulating valve 19 is controlled to control the flow rate of the water supplied to the second connecting pipe 15, thereby lowering the steam temperature in the second connecting pipe 15. As a result, the steam temperature T3 at the inlet of the superheater tube 13a of the third superheating section 13 is lowered to a value equal to or lower than the second threshold value T 34 (second steam temperature control step: S5). Furthermore, the control unit 30 determines whether the average value of the steam temperatures T5 and T6 detected in the inlet / outlet temperature detection step S3 is equal to or lower than a third threshold value T 56 When the flow rate of the water supplied to the turbine extraction pipe 100a (reheater pipe 40a) is controlled by controlling the third regulating valve 60, the steam temperature in the turbine extraction pipe 100a (reheater pipe 40a) is reduced, and as a result, the steam temperature T5 at the inlet of the reheater pipe 40a of the reheater 40 is reduced to a value lower than the third threshold value T 56 The temperature of the steam is lowered to a value lower than the third steam temperature control step S6.

[0049] In this embodiment, an example is shown in which the first regulating valve 18 (second regulating valve 19) is controlled based on the average value of the steam temperatures T1, T2 (T3, T4) at the inlet and outlet of the superheater tube 12a (13a) of the second superheating section 12 (third superheating section 13), but the control manner of the first regulating valve 18 (second regulating valve 19) is not limited to this. For example, the first regulating valve 18 (second regulating valve 19) can also be controlled based on the difference between the steam temperatures T1, T2 (T3, T4) at the inlet and outlet of the superheater tube 12a (13a) of the second superheating section 12 (third superheating section 13).

[0050] FIG. 4 shows an example of a change in steam temperature in the boiler system 1 according to this embodiment.

[0051] In the economizer 20 of the boiler system 1, the boiler feed water is preheated by the heat of the exhaust gas, and the temperature is raised to a predetermined temperature before being supplied to the steam drum 8. The steam of the boiler feed water supplied to the steam drum 8 is heated by the combustion in the furnace 2, and is supplied to the first superheating section 11 of the superheater 10 in a state in which it has risen to a saturated steam temperature. The steam supplied to the first superheating section 11 is supplied to the second superheating section 12 via the first connecting pipe 14 in a state in which it is superheated by the heat of the exhaust gas to a steam temperature of, for example, about 450°C.

[0052] The control unit 30 controls the first regulating valve 18 to supply water into the first connecting pipe 14, thereby lowering the steam temperature in the first connecting pipe 14. At this time, as already described, the control unit 30 controls the first regulating valve 18 based on the steam temperatures T1, T2 at the inlet and outlet of the superheater tube 12a of the second superheating section 12 to control the flow rate of water supplied into the first connecting pipe 14, thereby lowering the steam temperature in the first connecting pipe 14, and as a result, the steam temperature T1 at the inlet of the superheater tube 12a of the second superheating section 12 is lowered to a value equal to or lower than the first threshold value T 12 The first threshold value T 12 can be appropriately set according to the target main steam temperature (the temperature of the steam to be supplied to the turbine 100).

[0053] For example, when the target main steam temperature is a relatively high value (e.g., about 550° C.), the first threshold T 12 The steam temperature T1 at the inlet of the second superheating section 12 is set to a relatively high value (for example, about 450° C.) as shown in the upper graph G1 of FIG. 12 On the other hand, when the target main steam temperature is a relatively low value (for example, about 500° C.), the first threshold value T 12 The steam temperature T1 at the inlet of the second superheating section 12 is set to a relatively low value (for example, about 400° C.) as shown in the lower graph G2 of FIG. 12 In this way, in either case, the temperature of the steam flowing through the first connecting pipe 14 can be lowered, and the temperature of the steam flowing through the superheater pipe 12a of the second superheating section 12 can also be lowered.

[0054] In addition, the control unit 30 controls the second regulating valve 19 to supply water into the second connecting pipe 15, thereby lowering the steam temperature in the second connecting pipe 15. At this time, as already described, the control unit 30 controls the steam temperature T 3、The second control valve 19 is controlled based on T4 to control the flow rate of water supplied to the second connecting pipe 15, thereby lowering the steam temperature in the second connecting pipe 15. As a result, the steam temperature T3 at the inlet of the superheater tube 13a of the third superheating section 13 is lowered to a value equal to or lower than the second threshold value T 34 The second threshold value T 34 can be appropriately set according to the target main steam temperature (the temperature of the steam to be supplied to the turbine 100).

[0055] For example, when the target main steam temperature is a relatively high value (for example, about 550° C.), the second threshold T 34 The second threshold T 34 On the other hand, when the target main steam temperature is a relatively low value (for example, about 500° C.), the second threshold value T 34 The second threshold T 34 In this way, in either case, the temperature of the steam flowing through the second connecting pipe 15 can be lowered, and the temperature of the steam flowing through the superheater pipe 13a of the third superheating section 13 can also be lowered.

[0056] In the boiler system 1 according to the embodiment described above, by supplying water to the inside of the tubes (the first connecting tube 14, the second connecting tube 15, and the reheater tube 40a), the temperature of the steam flowing through the tubes can be lowered to a predetermined temperature or lower, so that the surface temperature of the tubes can be lowered more efficiently than with the conventional method of lowering the temperature of the exhaust gas. Therefore, adhesion of molten ash to the surface of the tubes can be suppressed, and high-temperature corrosion of the tubes can be suppressed.

[0057] Moreover, in the boiler system 1 according to the embodiment described above, the flow rate of water supplied to the pipes (first connecting pipe 14, second connecting pipe 15, reheater pipe 40a) can be controlled by the control unit 30 by controlling the regulating valves (first regulating valve 18, second regulating valve 19, third regulating valve 60) based on the steam temperatures (T1, T2, T3, T4, T5, T6) detected by the temperature detection units (first temperature sensor 16a, second temperature sensor 16b, third temperature sensor 16c, fourth temperature sensor 16d, inlet temperature sensor 51, outlet temperature sensor 52). Therefore, appropriate control can be performed according to the steam temperature. In particular, in the boiler system 1 according to this embodiment, the steam temperature detected by the temperature detection units is lower than a predetermined threshold value (T 12 , T 34 , T 56 ), the control unit 30 can control the regulating valve so as to reduce the steam temperature in the pipe below the threshold value.

[0058] In the boiler system 1 according to the embodiment described above, the first regulating valve 18 is controlled based on the steam temperatures T1 and T2 (the steam temperatures at the inlet and outlet of the superheater tube 12a of the second superheating section 12) detected by the first temperature sensor 16a and the second temperature sensor 16b, so that the steam temperatures T1 and T2 in the superheater tube 12a of the second superheating section 12 are adjusted to a value equal to or lower than the first threshold value T 12 The steam temperatures T3 and T4 in the superheater tube 13a of the third superheater section 13 are lowered below the second threshold value T 34 Therefore, it is possible to suppress high-temperature corrosion of the superheater tube 12a of the second superheating section 12 and the superheater tube 13a of the third superheating section 13. In addition, in this embodiment, the second threshold value T 34 The first threshold T 12 Since the temperature is set to a value larger than the predetermined value, it is possible to control the steam temperature so that it gradually increases.

[0059] In the boiler system 1 according to the embodiment described above, the third regulating valve 60 is controlled based on the steam temperatures (steam temperatures at the inlet and outlet of the reheater tube 40a of the reheater 40) T5 and T6 detected by the inlet temperature sensor 51 and the outlet temperature sensor 52, so that the steam temperature in the turbine extraction pipe 100a (in the reheater tube 40a of the reheater 40) is adjusted to a value equal to or lower than the third threshold value T 56 Therefore, high-temperature corrosion of the reheater tubes 40a of the reheater 40 can be suppressed.

[0060] Second Embodiment Next, a boiler system according to a second embodiment of the present invention will be described with reference to Figures 5 and 6. The boiler system according to this embodiment is substantially the same as the first embodiment in other respects, except that the configurations of the temperature sensor and the control unit of the boiler system 1 according to the first embodiment are changed. Therefore, configurations different from the first embodiment will be mainly described, and common configurations will be denoted by the same reference numerals and detailed descriptions thereof will be omitted.

[0061] 5, the superheater 10 of the boiler system according to this embodiment has a first superheating section 11, a second superheating section 12, and a third superheating section 13, and the first superheating section 11, the second superheating section 12, and the third superheating section 13 each have superheater tubes 11a, 12a, and 13a through which steam flows, and the first superheating section 11 and the second superheating section 12 are connected by a first connecting pipe 14, and the second superheating section 12 and the third superheating section 13 are connected by a second connecting pipe 15. These configurations are similar to those of the first embodiment, so detailed explanations will be omitted.

[0062] On the downstream side of the second superheating section 12, a steam temperature T 1A A first downstream temperature sensor 16 is provided on the downstream side of the third superheating section 13 to detect the steam temperature T 2AInformation about the steam temperatures detected by the first downstream temperature sensor 16 and the second downstream temperature sensor 17 is sent to a control unit 30A, which will be described later, and is used to control various regulating valves. The first downstream temperature sensor 16 and the second downstream temperature sensor 17 correspond to the temperature detection unit in the present invention.

[0063] A first connecting pipe 14 connecting the first superheating section 11 and the second superheating section 12 is connected to the pump 7 by a first water supply pipe 7a, a second connecting pipe 15 connecting the second superheating section 12 and the third superheating section 13 is connected by a second water supply pipe 7b, the first water supply pipe 7a connecting the pump 7 and the first connecting pipe 14 is provided with a first regulating valve 18 for adjusting the flow rate of water flowing through the first water supply pipe 7a, and the second water supply pipe 7b connecting the pump 7 and the second connecting pipe 15 is provided with a second regulating valve 19 for adjusting the flow rate of water flowing through the second water supply pipe 7b. The pump 7, the first and second water supply pipes 7a, 7b, the first and second connecting pipes 14 and 15, and the first and second regulating valves 18 and 19 are similar to those in the first embodiment, and therefore detailed description thereof will be omitted.

[0064] The control unit 30A in this embodiment is configured to control the steam temperature T 1A , T 2A The control unit 30A controls the flow rate of water supplied to the first connecting pipe 14 and the second connecting pipe 15 by controlling the first regulating valve 18 and the second regulating valve 19 based on the steam temperature T 1A , T 2A are the first and second thresholds T T1 , T T2 When the steam temperature exceeds the upper limit of the second superheating section 12, the steam temperature in the first connecting pipe 14 and the second connecting pipe 15 is lowered, and as a result, the steam temperature T 1A and the steam temperature T at the outlet of the superheater tube 13a of the third superheating section 13 2A The first and second thresholds T T1 , T T2The first and second regulating valves 18 and 19 are controlled so as to lower the first and second thresholds T T1 , T T2 As in the first embodiment, this is a value that is appropriately determined based on the state of ash adhesion, etc.

[0065] In this embodiment, the pump 7, the first and second water supply pipes 7a, 7b (supply section), the first regulating valve 18 and the second regulating valve 19, and the control section 30A constitute a "steam temperature control section" that supplies water to the inside of the first connecting pipe 14 and the second connecting pipe 15, thereby lowering the temperature of the steam flowing through the first connecting pipe 14 and the second connecting pipe 15 below a predetermined temperature.

[0066] Downstream of the reheater 40 in the boiler system according to this embodiment, a steam temperature T 3A The third downstream temperature sensor 50 also corresponds to the temperature detection section in the present invention. Information about the steam temperature detected by the third downstream temperature sensor 50 is sent to the control section 30A and used for controlling a third adjustment valve 60, which will be described later. The pump 7 and the third feedwater pipe 7c correspond to the supply section in the present invention.

[0067] The third feedwater pipe 7c is provided with a third regulating valve 60 for regulating the flow rate of water flowing through the third feedwater pipe 7c. The third regulating valve 60 is controlled by a control signal sent from the control unit 30A to regulate the amount of water supplied to the turbine extraction pipe 100a (reheater pipe 40a). The control unit 30A controls the steam temperature T 3A The control unit 30 controls the flow rate of water supplied to the turbine extraction pipe 100a (the reheater pipe 40a) by controlling the third regulating valve 60 based on the steam temperature T 3A is the third threshold T T3 When the steam temperature exceeds the upper limit of the reheater 40, the steam temperature in the turbine extraction pipe 100a (the reheater tube 40a) is lowered, and as a result, the steam temperature T 3AThe third threshold T T3 The third adjusting valve 60 is controlled so as to reduce the pressure to less than the third threshold T T3 are the first and second thresholds T T1 , T T2 Similarly, this value is appropriately determined based on the state of ash adhesion, etc.

[0068] In this embodiment, the pump 7, the third water supply pipe 7c (supply section), the third adjustment valve 60, and the control section 30A constitute a "steam temperature control section" that supplies water to the inside of the turbine extraction pipe 100a (reheater tube 40a) to lower the temperature of the steam flowing through the turbine extraction pipe 100a (reheater tube 40a) below a predetermined temperature.

[0069] Next, a method for controlling the steam temperature of the boiler system according to this embodiment will be described with reference to the flowchart of FIG.

[0070] First, the control unit 30A of the boiler system measures the steam temperature T 1A (first temperature detection step: S1A), and the steam temperature T at the outlet of the superheater tube 13a of the third superheating section 13 is detected by using the second downstream temperature sensor 17. 2A (a second temperature detection step: S2A). Furthermore, the control unit 30A detects the steam temperature T 3A (third temperature detection step: S3A).

[0071] Next, the control unit 30A of the boiler system detects the steam temperature T 1A is the first threshold T T1 When the steam temperature exceeds the upper limit of the second superheating section 12, the first regulating valve 18 is controlled to control the flow rate of water supplied to the first connecting pipe 14, thereby lowering the steam temperature in the first connecting pipe 14. As a result, the steam temperature T 1A The first threshold T T1The control unit 30A also reduces the steam temperature T 2A is the second threshold T T2 When the steam temperature exceeds the upper limit of the second connecting pipe 15, the second regulating valve 19 is controlled to control the flow rate of water supplied to the second connecting pipe 15, thereby lowering the steam temperature in the second connecting pipe 15. As a result, the steam temperature T 2A Threshold T T2 (second steam temperature control step: S5A). Furthermore, the control unit 30A reduces the steam temperature T 3A is the third threshold T T3 When the steam temperature exceeds the predetermined value, the third regulating valve 60 is controlled to control the flow rate of water supplied to the turbine extraction pipe 100a (reheater pipe 40a), thereby lowering the steam temperature in the turbine extraction pipe 100a (reheater pipe 40a). As a result, the steam temperature T 3A Threshold T T3 The temperature of the steam is lowered to a value lower than the third steam temperature control step S6A.

[0072] In the boiler system according to the embodiment described above, the same advantageous effects as those of the first embodiment can be obtained.

[0073] In each of the above embodiments, an example has been shown in which a superheater having three superheating parts is adopted, but the number of superheating parts is not limited to this. For example, a superheater having only one superheating part, a superheater having two superheating parts, or a superheater having four or more superheating parts may also be adopted.

[0074] In addition, in each of the above embodiments, an example has been shown in which "water" is used as the fluid for steam cooling, but a fluid other than "water" (e.g., low-temperature steam, etc.) can also be used as the fluid for steam cooling.

[0075] In addition, in each of the above embodiments, an example has been shown in which the second threshold value used to control the second adjustment valve 19 located downstream is set to a value greater than the first threshold value used to control the first adjustment valve 18 located upstream, but the second threshold value can also be set to the same value as the first threshold value.

[0076] The present invention is not limited to the above-described embodiments, and even if a person skilled in the art appropriately modifies the design of these embodiments, the same is included within the scope of the present invention as long as the features of the present invention are included. In other words, the elements of the above-described embodiments and their arrangements, materials, conditions, shapes, sizes, etc. are not limited to those exemplified, and can be appropriately modified. In addition, the elements of the above-described embodiments can be combined to the extent technically possible, and combinations of these can also be included within the scope of the present invention as long as they include the features of the present invention. [Explanation of symbols]

[0077] 1. Boiler system 7...Pump (supply section, part of steam temperature control section) 7a…First feedwater piping (supply section, part of steam temperature control section) 7b…Second feedwater piping (supply section, part of steam temperature control section) 7c…Third feedwater piping (supply section, part of steam temperature control section) 11...First overheating section 11a...Superheater tube 12...Second overheating section 12a…Superheater tube 13…Third overheating section 13a…Superheater tube 14…First connecting pipe 15...Second connecting pipe 16...First downstream temperature sensor (temperature detection part) 16a...First temperature sensor (temperature detection unit) 16b...Second temperature sensor (temperature detection unit) 16c...Third temperature sensor (temperature detection part) 16d...Fourth temperature sensor (temperature detection part) 17...Second downstream temperature sensor (temperature detection part) 18...First adjustment valve (part of the steam temperature control section) 19...Second regulating valve (part of steam temperature control section) 30·30A…Control unit (part of the steam temperature control unit) 40…Reheater 40a…Reheater tube 51...Inlet temperature sensor (temperature detection unit) 52...Outlet temperature sensor (temperature detection part) 60...Third regulating valve (part of steam temperature control section) 100a...Turbine extraction pipe S4 / S4A: First steam temperature control process S5 / S5A: Second steam temperature control process S6 / S6A: Third steam temperature control process

Claims

1. a superheater having a first superheating section, a second superheating section downstream of the first superheating section, and a third superheating section downstream of the second superheating section; a first connecting pipe connecting a superheater tube of the first superheating section and a superheater tube of the second superheating section, and a second connecting pipe connecting a superheater tube of the second superheating section and a superheater tube of the third superheating section, the pipes through which steam flows; a temperature detection unit that detects steam temperatures, the temperature detection unit including a first temperature sensor that detects a steam temperature at an inlet of a superheater tube of the second superheating unit, a second temperature sensor that detects a steam temperature at an outlet of the superheater tube of the second superheating unit, a third temperature sensor that detects a steam temperature at an inlet of the superheater tube of the third superheating unit, and a fourth temperature sensor that detects a steam temperature at the outlet of the superheater tube of the third superheating unit; A steam temperature control unit that supplies a fluid to the inside of the tube to reduce the temperature of the steam flowing through the tube to a value lower than a threshold value determined based on the fuel properties of the ash and / or the adhesion state of the ash to the tube, the threshold value includes a first threshold value and a second threshold value; The steam temperature control unit is A supply unit that supplies the fluid into the pipe; a first adjusting valve and a second adjusting valve for adjusting the amount of the fluid supplied by the supply unit; a control unit that controls the first regulating valve based on steam temperatures detected by the first temperature sensor and the second temperature sensor to reduce the steam temperature in the superheater tube of the second superheating section below the first threshold value, and controls the second regulating valve based on steam temperatures detected by the third temperature sensor and the fourth temperature sensor to control the flow rate of the fluid supplied into the tube so as to reduce the steam temperature in the superheater tube of the third superheating section below the second threshold value; A boiler system comprising:

2. the supply unit includes a pump that supplies the fluid, a first water supply pipe that connects the pump and the first connecting pipe, and a second water supply pipe that connects the pump and the second connecting pipe, The first adjusting valve adjusts the amount of the fluid supplied to the first connecting pipe, The boiler system according to claim 1 , wherein the second adjusting valve adjusts the amount of the fluid supplied to the second connecting pipe.

3. The boiler system according to claim 1 or 2, wherein the second threshold value is greater than the first threshold value.

4. A reheater is provided for reheating steam discharged from the turbine. the pipes include a turbine extraction pipe connecting the turbine and a reheater pipe of the reheater; The temperature detection unit includes an inlet temperature sensor that detects a steam temperature at an inlet of a reheater tube of the reheater, and an outlet temperature sensor that detects a steam temperature at an outlet of the reheater tube of the reheater, the steam temperature control unit includes a third adjustment valve that adjusts a supply amount of the fluid supplied to the turbine extraction piping, the supply unit includes a pump that supplies the fluid, and a third feedwater piping that connects the pump and the turbine extraction piping, 4. The boiler system according to claim 1, wherein the control unit controls the third regulating valve based on the steam temperatures detected by the inlet temperature sensor and the outlet temperature sensor, thereby lowering the steam temperature in the reheater tube of the reheater below a third threshold value.

5. a superheater having a first superheating section, a second superheating section downstream of the first superheating section, and a third superheating section downstream of the second superheating section; a first connecting pipe connecting a superheater tube of the first superheating section and a superheater tube of the second superheating section, and a second connecting pipe connecting a superheater tube of the second superheating section and a superheater tube of the third superheating section, the pipes through which steam flows; a temperature detection unit that detects steam temperatures, the temperature detection unit including a first temperature sensor that detects a steam temperature at an inlet of a superheater tube of the second superheating unit, a second temperature sensor that detects a steam temperature at an outlet of the superheater tube of the second superheating unit, a third temperature sensor that detects a steam temperature at an inlet of the superheater tube of the third superheating unit, and a fourth temperature sensor that detects a steam temperature at the outlet of the superheater tube of the third superheating unit; 1. A method for controlling steam temperature in a boiler system comprising: a temperature detection step in which the temperature detection unit detects the steam temperature; A steam temperature control process for supplying a fluid to the inside of the tube to lower the temperature of the steam flowing through the tube below a threshold value determined based on the fuel properties of the ash and / or the state of adhesion of the ash to the tube, the threshold value includes a first threshold value and a second threshold value; The steam temperature control step includes: a supplying step of supplying the fluid into the pipe; an adjusting step of adjusting a supply amount of the fluid by a first adjusting valve and a second adjusting valve; a control step of controlling a flow rate of the fluid supplied into the tubes so as to reduce the steam temperature in the superheater tube of the second superheating section below the first threshold value by controlling the first regulating valve based on the steam temperatures detected by the first temperature sensor and the second temperature sensor, and to reduce the steam temperature in the superheater tube of the third superheating section below the second threshold value by controlling the second regulating valve based on the steam temperatures detected by the third temperature sensor and the fourth temperature sensor; A control method comprising:

6. a superheater having a first superheating section, a second superheating section downstream of the first superheating section, and a third superheating section downstream of the second superheating section; a first connecting pipe connecting a superheater tube of the first superheating section and a superheater tube of the second superheating section, and a second connecting pipe connecting a superheater tube of the second superheating section and a superheater tube of the third superheating section, the pipes through which steam flows; a temperature detection unit that detects steam temperatures, the temperature detection unit including a first temperature sensor that detects a steam temperature at an inlet of a superheater tube of the second superheating unit, a second temperature sensor that detects a steam temperature at an outlet of the superheater tube of the second superheating unit, a third temperature sensor that detects a steam temperature at an inlet of the superheater tube of the third superheating unit, and a fourth temperature sensor that detects a steam temperature at the outlet of the superheater tube of the third superheating unit; A program for causing a computer to execute a method for controlling a steam temperature in a boiler system comprising: The method comprises: a temperature detection step in which the temperature detection unit detects the steam temperature; A steam temperature control process for supplying a fluid to the inside of the tube to lower the temperature of the steam flowing through the tube below a threshold value determined based on the fuel properties of the ash and / or the state of adhesion of the ash to the tube, the threshold value includes a first threshold value and a second threshold value; The steam temperature control step includes: a supplying step of supplying the fluid into the pipe; an adjusting step of adjusting a supply amount of the fluid by a first adjusting valve and a second adjusting valve; a control step of controlling a flow rate of the fluid supplied into the tubes so as to reduce the steam temperature in the superheater tube of the second superheating section below the first threshold value by controlling the first regulating valve based on the steam temperatures detected by the first temperature sensor and the second temperature sensor, and to reduce the steam temperature in the superheater tube of the third superheating section below the second threshold value by controlling the second regulating valve based on the steam temperatures detected by the third temperature sensor and the fourth temperature sensor; Including, the program.

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