Boiler control device, boiler, power-generating plant, boiler control method, and boiler control program

Abstract

To provide a boiler control device, a boiler, a power-generating plant, a boiler control method, and a boiler control program that can be utilized as an adjusted electric power for renewable energy.SOLUTION: A boiler control device 50 which switches between a first operation state of a boiler and a second operation state lower in thermal efficiency than the first operation state in accordance with load and performs normal control to switch the first operation state to the second operation state when the load is below the first load, includes: a selection part 51 for selecting between a normal mode for performing normal control and an operation region expansion mode; and a parameter setting part 52 for setting a dedicated parameter regulated in prior with respect to each set value of the boiler when the operation region expansion mode is selected by the selection part 51. When the operation region expansion mode is selected by the selection part 51, the first operation state is maintained when the load is below the first load, and operation control of the boiler is performed by the dedicated parameter set by the parameter setting part 52.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a boiler control device, a boiler, a power generation plant, a boiler control method, and a boiler control program. [Background technology]

[0002] Large boilers, such as power generation boilers, have a hollow furnace installed vertically, with multiple burners arranged circumferentially around the furnace wall. Large boilers also have a flue connected vertically above the furnace, with a heat exchanger for generating steam located in the flue. The burner injects a mixture of fuel and air (oxidizing gas) into the furnace, forming a flame, generating combustion gas that flows down the flue. A heat exchanger is installed in the area where the combustion gas flows, and superheated steam is generated by heating water or steam flowing through the heat transfer tubes that make up the heat exchanger.

[0003] In recent years, power generation using renewable energy sources has become common. However, renewable energy sources have issues with stable power supply, and there are cases where a gap exists between power demand and the amount of power generated by renewable energy sources. Thermal power plants, especially coal-fired power plants, are being required to shift from their current baseload operation to an operation used for adjusting the gap between power demand and the amount of power generated by renewable energy sources. In particular, coal-fired power plants using supercritical pressure boilers, such as once-through boilers, are being considered for use as adjusting power sources, but are subject to load operation constraints, such as the minimum load at which they can be operated.

[0004] A once-through boiler operates in two modes depending on its operating load: dry operation and wet operation, which will be described later. Normal operation, where the boiler load (evaporation rate) is above a certain level, is dry operation (once-through operation), in which the amount of water fed to the boiler is approximately equal to the evaporation rate. On the other hand, during low-load operation, where the boiler load (evaporation rate) is lower than the minimum feedwater flow rate set to protect the furnace walls, the boiler operates in wet operation (circulation operation), in which part of the feedwater is circulated.

[0005] For example, in Patent Document 1, since it is difficult to continuously operate a once-through boiler at a constant load near the switching load between operation in a dry operating state (once-through operation) and operation in a wet operating state (recirculation operation), once-through operation is performed in the dry operating state based on a signal from the feedwater flow program and a numerically invariant signal corresponding to the minimum feedwater flow rate, and recirculation operation is performed in the wet operating state with the minimum feedwater flow rate always exceeding the signal from the feedwater flow program. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-19848 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the invention of Patent Document 1, the minimum feedwater flow rate is always set to a value that exceeds the signal of the feedwater flow rate program during wet operation, which results in a large surplus of feedwater flow rate and reduces boiler efficiency.Furthermore, the invention of Patent Document 1 does not consider the minimum load when used as regulating power for renewable energy.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to provide a boiler control device, a boiler, a power generation plant, a boiler control method, and a boiler control program that can be utilized as regulating power for renewable energy. [Means for solving the problem]

[0009] In order to solve the above problems, the boiler control device, boiler, power generation plant, boiler control method, and boiler control program of the present disclosure employ the following means. The boiler control device disclosed herein is a boiler control device that performs normal control by switching between a first operating state of a boiler and a second operating state that has lower thermal efficiency than the first operating state depending on the load, and by switching from the first operating state to the second operating state when the load falls below a first load, and is equipped with a selection unit that selects between a normal mode in which the normal control is performed and an expanded operating range mode, and a parameter setting unit that sets pre-defined dedicated parameters for each setting value of the boiler when the expanded operating range mode is selected by the selection unit, and when the load falls below the first load when the expanded operating range mode is selected by the selection unit, the first operating state is maintained, and operation of the boiler is controlled using the dedicated parameters set by the parameter setting unit.

[0010] The boiler of the present disclosure includes a heat exchanger including an economizer, a superheater, and a reheater, a furnace wall, a steam separator, a condenser, and the above-mentioned boiler control device.

[0011] The power generation plant of the present disclosure includes a boiler equipped with the above-mentioned boiler control device, a heat exchanger provided in the boiler, a steam turbine that is rotationally driven by steam generated in the boiler, and a generator connected to the steam turbine to generate electricity.

[0012] The boiler control method disclosed herein is a boiler control method in which a computer performs normal control, switching between a first operating state of a boiler and a second operating state having lower thermal efficiency than the first operating state depending on the load, and switching from the first operating state to the second operating state when the load falls below the first load. The method includes a selection step of selecting between a normal mode in which the normal control is performed and an expanded operating range mode, and a parameter setting step of setting predefined dedicated parameters for each setting value of the boiler when the expanded operating range mode is selected in the selection step, and when the load falls below the first load, the first operating state is maintained, and the computer performs operation control of the boiler using the dedicated parameters set in the parameter setting step.

[0013] The boiler control program of the present disclosure causes a computer to execute the above-described boiler control method. [Effects of the Invention]

[0014] According to the present disclosure, the boiler load can be appropriately adjusted, improving boiler efficiency and reducing the amount of fuel supplied (consumption) to the boiler. In addition, by lowering the minimum load, the use of renewable energy as regulating power can be expanded. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram illustrating a boiler that uses solid fuel as a primary fuel in some embodiments of the present disclosure. [Figure 2] FIG. 1 is a schematic diagram illustrating a heat exchanger in a coal-fired boiler according to some embodiments of the present disclosure. [Figure 3] FIG. 10 is a diagram illustrating the relationship between load and water supply flow rate in a wet operating condition in some embodiments of the present disclosure. [Figure 4] FIG. 10 is a diagram showing the relationship between load and water supply flow rate in a dry operation state in some embodiments of the present disclosure. [Figure 5] FIG. 2 illustrates switching between dry and wet operating states in some embodiments of the present disclosure. [Figure 6] FIG. 2 is a diagram illustrating an example of a hardware configuration of a control device according to some embodiments of the present disclosure. [Figure 7] FIG. 2 is a diagram illustrating an example of the functionality of a control device according to some embodiments of the present disclosure. [Figure 8] FIG. 10 illustrates a circuit for setting an operating range expansion mode in some embodiments of the present disclosure. [Figure 9] FIG. 10 illustrates a dedicated parameter setting circuit in some embodiments of the present disclosure. [Figure 10] FIG. 10 illustrates water supply flow rate settings corresponding to load indicators in some embodiments of the present disclosure. [Figure 11]FIG. 10 illustrates a circuit for enabling unused controls in some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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, it also includes configurations that combine the embodiments. In the following description, "up" and "upper" refer to the upper side in the vertical direction, and "lower" and "lower" refer to the lower side in the vertical direction, and the vertical direction is not precise and may include errors.

[0017] FIG. 1 is a schematic diagram illustrating a boiler that uses solid fuel as its main fuel according to some embodiments of the present disclosure.

[0018] The boiler (coal-fired 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 21 and exchanging the heat generated by this combustion with feedwater or steam. Biomass fuel, coal, etc. are used as the solid fuel.

[0019] The boiler 10 has a furnace 11, a combustion device 20, and a combustion gas passage 12. The furnace 11 has a hollow rectangular cylindrical shape and is installed vertically. The furnace wall 101 that forms the inner wall surface of the furnace 11 is composed of a plurality of heat transfer tubes and fins that connect the heat transfer tubes together, and recovers the heat generated by the combustion of pulverized fuel by heat exchange with water and steam circulating inside the heat transfer tubes, while suppressing the temperature rise of the furnace wall 101.

[0020] The combustion device 20 is installed in a 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, may be collectively referred to as "burners 21") attached to the furnace wall 101. The burners 21 are 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), and are arranged in multiple rows along the vertical direction. For convenience of illustration, only two burners 21 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 11, the number of rows of burners 21, the number of burners 21 in one row, the arrangement of the burners 21, and the like are not limited to this embodiment.

[0021] 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"). Mill 31 is, for example, a vertical roller mill having a pulverizing table (not shown) supported therein so as to be rotatable, and a plurality of pulverizing rollers (not shown) 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 mill 31 by primary air (carrier gas, oxidizing gas) supplied to mill 31. The classifier separates the pulverized fuel into pulverized fuel having a particle size 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 inside the mill 31 under its own weight and is re-ground.

[0022] An air register 23 is provided outside the furnace 11 at the installation 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) 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 introduced into the furnace 11.

[0023] The combustion gas passage 12 is connected to the vertical upper part of the furnace 11. The combustion gas passage 12 is provided with superheaters 102A, 102B, and 102C (hereinafter sometimes collectively referred to as "superheaters 102"), reheaters 103A and 103B (hereinafter sometimes collectively referred to as "reheaters 103"), and a coal economizer 104 as heat exchangers for recovering heat from the combustion gas, and heat is exchanged between the combustion gas generated in the furnace 11 and feedwater or steam flowing inside each heat exchanger. Note that the arrangement and shape of each heat exchanger are not limited to those shown in FIG. 1.

[0024] 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, 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.

[0025] 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, such as ammonia or urea water, which has the effect of reducing nitrogen oxides, to the combustion gas flowing through the flue 13, and promotes the reaction between the nitrogen oxides (NOx) in the combustion gas to which the reducing agent has been supplied and the reducing agent 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, that removes ash and the like from the combustion gas, and a desulfurization equipment 46 that removes sulfur oxides, as well as an induced draft fan (IDF) 45 that guides 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 that has been treated in the environmental equipment is discharged to the outside of the system as exhaust gas.

[0026] In the boiler 10, when the multiple mills 31 are driven, pulverized and classified pulverized fuel is supplied to the burner 21 together with primary air via the pulverized fuel supply pipe 22. Secondary air heated by the air preheater 42 is supplied to the burner 21 from the air duct 24 via the wind box 23. The burner 21 blows a pulverized fuel mixture, which is a mixture of pulverized fuel and primary air, into the furnace 11, and also blows secondary air into the furnace 11. The pulverized fuel mixture 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 high-temperature combustion gas rises within the furnace 11 and flows into the combustion gas passage 12. In this embodiment, air is used as the oxidizing gas (primary air, secondary air). However, the oxidizing gas may have a higher or lower oxygen content than air. By adjusting the ratio of the oxygen content to the amount of fuel supplied within an appropriate range, stable combustion in the furnace 11 is achieved.

[0027] Additionally, above the mounting position of the burners 21 in the furnace 11, a plurality of additional air ports (AA ports) 25 are provided for supplying additional air for combustion (AA) into the furnace 11. The additional air ports 25 are connected to the ends of additional air ducts (AA ducts) 26 branching off from the air duct 24, and a portion of the air supplied from the forced draft fan 32 can be supplied to the additional air ports 25 via the additional air ducts 26 as additional air for combustion.

[0028] 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 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 supplied to the burner 21 (the total amount of primary air and secondary air) is set to be less than the theoretical amount of air relative to the amount of fuel supplied to the burner 21. By doing so, regions A and B (regions 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. Thereafter, in region C (region above the bottom of the additional air port 25), additional combustion air is supplied from the additional air port 25 to the combustion gas in which NOx has been reduced, completing the combustion. However, the amount of NOx generated is reduced by the reduction effect in regions A and B.

[0029] The combustion gas that has flowed into the combustion gas passage 12 exchanges heat with water and steam in a superheater 102, a reheater 103, and an 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 gas exchanges heat with primary air and secondary air in an air preheater 42, and is then discharged into the 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 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 arrangement of the devices from the flue 13 to the gas duct 41 with respect to the combustion gas flow do not necessarily have to be in the order described above.

[0030] Next, the superheater 102, the reheater 103, and the economizer 104 provided in the combustion gas passage 12 as heat exchangers will be described in detail. FIG. 2 is a schematic diagram illustrating a heat exchanger provided in a coal-fired boiler according to some embodiments of the present disclosure. Note that Figure 1 does not accurately show the positions of the heat exchangers (superheaters 102A, 102B, 102C, reheaters 103A, 103B, and economizer 104) in the combustion gas passage 12, and the arrangement order of the heat exchangers relative to the combustion gas flow is not limited to that shown in Figure 1.

[0031] As shown in Figure 2, the power plant 1 of this embodiment includes a heat exchanger provided in the 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 using the rotational force of the steam turbine 111.

[0032] The steam turbine 111, which is rotationally driven by steam generated in the boiler 10, is composed of, for example, a high-pressure turbine 111A, an intermediate-pressure turbine 111B, and a low-pressure turbine 111C. Steam heated in the superheater 102 of the boiler 10 drives the high-pressure turbine 111A, is then reheated in 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 has driven the low-pressure turbine 111C is condensed into condensed water by heat exchange with cooling water (e.g., seawater or river water) in the condenser 112. The condenser 112 is connected to the economizer 104 via a water supply line L1. The feedwater line L1 is provided with, 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. 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 via an extraction line (not shown) as a heat source, and the feedwater that is supplied to the economizer 104 is heated.

[0033] The boiler 10 is a once-through boiler. The economizer 104 is connected to heat transfer tubes that make up the furnace wall 101. The feedwater heated by the economizer 104 is heated by radiation from the flame in the furnace 11 as it passes through the heat transfer tubes that make up the furnace wall 101, and is then led to the steam separator 125. The steam separated in the steam separator 125 is supplied to the superheater 102, and the drain water separated in the steam separator 125 flows into a steam separator drain tank 126 and is led to the condenser 112 via a drain water line L2 that is equipped with a drain water valve 128.

[0034] Furthermore, during startup or low-load operation of the once-through boiler, the feedwater supplied from the economizer 104 may not all evaporate as it passes through the heat transfer tubes that make up the furnace wall 101, resulting in a wet operation state (second operation state) in which a water level exists in the steam separator 125. In this wet operation 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 that make up the furnace wall 101 by using a boiler circulation pump (BCP) 127 to merge with the feedwater line L1 via a circulation line L6.

[0035] When the combustion gas flows through the combustion gas passage 12, heat of the combustion gas is recovered by the superheater 102, the reheater 103, and the economizer 104. Meanwhile, feedwater supplied from a boiler feed pump (BFP) 123 is preheated by the economizer 104, and then heated to become steam as it passes through the heat transfer tubes that make up the furnace wall 101, and is then guided to a steam separator 125. The steam separated in the steam separator 125 is introduced into the first superheater 102A, the second superheater 102B, and the third superheater 102C, where it is superheated by the combustion gas. The superheated steam generated in the superheater 102 is supplied to the high-pressure turbine 111A via a steam line L3, and rotates and drives the high-pressure turbine 111A. The steam discharged from the high-pressure turbine 111A is introduced into the first reheater 103A and the second reheater 103B, where it is superheated again. The resuperheated steam is supplied via steam line L5 to the low-pressure turbine 111C via 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, generating 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 feed line L1. When passing through the heat transfer tubes that make up the furnace wall 101, all of the steam evaporates and becomes dry steam, and an operating state in which there is no water level in the steam-water separator 125 is called a dry operating state (first operating state).

[0036] The superheater 102 and the reheater 103 may be provided with 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 to control the steam temperature by adjusting the amount of water mixed and injected into the superheated steam (hereinafter, the water injected to control the main steam temperature is referred to as the "superheater spray water," and the water injected to control 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 portion of the feedwater to the boiler 10 from the outlet of the boiler feedwater 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 may be 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 may be installed at any position between the outlet of the high-pressure turbine 111A and the inlet of the intermediate-pressure turbine 111B.

[0037] In addition, a soot blower (ash removal device) (not shown) may be disposed in the combustion gas passage 12 in the gaps between the heat transfer tubes constituting each heat exchanger, such as the superheater 102, reheater 103, and economizer 104, or in the gaps between each heat exchanger. The soot blower is disposed extending in a direction approximately perpendicular to the wall surface of the combustion gas passage 12. The soot blower is an injection device that injects steam (gas) in a direction perpendicular to the axial direction, with the axial direction being perpendicular to the wall surface of the combustion gas passage 12, and that can also change the injection direction. Steam injected from the soot blower toward heat exchangers, such as the superheater 102, reheater 103, and economizer 104, removes combustion ash that has adhered to and accumulated on the surfaces of the heat transfer tubes constituting the heat exchangers, thereby suppressing a decrease in the heat exchange efficiency of the heat transfer tubes.

[0038] As described above, there are two operating states of the boiler 10: a dry operating state (first operating state) and a wet operating state (second operating state). In the second operating state (wet operating state), the feedwater heated by the furnace wall 101 circulates inside the boiler 10 without being discharged outside the system, and therefore the thermal efficiency is lower than in the first operating state (dry operating state). In the dry operating state, superheated steam (dry steam) is produced at the outlet of the furnace wall 101 of the boiler 10. In the wet operating state, saturated steam (wet steam) is produced at the outlet of the furnace wall 101. In the wet operating state, drain in the moist air is separated in the steam separator 125 and discharged into the steam separator drain tank 126. During normal operation of the boiler 10, it is operated in the dry operating state at a certain load (evaporation amount) or above. In the boiler 10, a necessary feedwater flow rate is supplied according to the load (amount of evaporation). In the dry operation state, a feedwater flow rate of at least a certain amount must be ensured in order to protect the furnace wall 101 of the boiler 10. The lower limit of such a feedwater flow rate is defined as the minimum feedwater flow rate. If the load corresponding to the minimum feedwater flow rate is defined as the first load (minimum load), then operation is performed in the dry operation state above the first load, and a feedwater flow rate according to the load is supplied. On the other hand, when the load falls below the first load, operation is switched from the dry operation state to the wet operation state. At this time, a constant minimum feedwater flow rate is supplied regardless of the load in order to protect the furnace wall 101, as described above.

[0039] FIG. 3 is a diagram illustrating the relationship between the boiler load and the feedwater flow rate in a wet operating state in some embodiments of the present disclosure. 3, the vertical axis represents the feedwater flow rate, and the horizontal axis represents the load on the boiler 10. The solid line represents the minimum feedwater flow rate, and the dashed dotted line represents the feedwater flow rate according to the load (amount of evaporation). In wet operation, the feedwater flow rate is the minimum feedwater flow rate regardless of the load value. Normally, the feedwater flow rate required according to the load is supplied as shown by the dashed dotted line, but a larger amount, the minimum feedwater flow rate, is supplied. In Figure 3, the dark shading indicates the feedwater flow rate required according to the load, and the light shading indicates the surplus feedwater. The surplus feedwater is separated as drain in the steam separator 125 and discharged to the steam separator drain tank 126.

[0040] FIG. 4 is a diagram illustrating the relationship between the boiler load and the feedwater flow rate in a dry operation state in some embodiments of the present disclosure. 4, the vertical axis represents the feedwater flow rate, and the horizontal axis represents the load on the boiler 10. The solid line and the dashed-dotted line represent the feedwater flow rate according to the load (evaporation amount), and the dashed line represents the minimum feedwater flow rate. In the dry operation state, the required feedwater flow rate is supplied according to the load value, as shown by the solid line. In Fig. 4, the dark shading indicates the required feedwater flow rate according to the load, and since no surplus feedwater is generated, all of the dry steam that has passed through the steam separator 125 is supplied to the superheater 102, and no drain is collected in the steam separator drain tank 126.

[0041] FIG. 5 is a diagram illustrating switching between dry and wet operating states in some embodiments of the present disclosure. 5, the vertical axis represents the load of the boiler 10, the horizontal axis represents time, the solid line represents switching under conventional control, and the thick dashed line represents switching under the control of the embodiment of the present disclosure. As shown in Fig. 5, under conventional control, when the load decreases and falls below the first load, the operation state is switched from the first operating state (dry operating state) to the second operating state (wet operating state).

[0042] In conventional control, the region between a first load and a second load, which is a load smaller than the first load, is a region where control of the boiler 10 is unstable, and in this embodiment, this region is referred to as the switching load band. When the load enters the switching load band, the boiler 10 is controlled to operate at either the first load or the second load. In addition, in the switching load band, switching between a dry operating state and a wet operating state is performed, and this switching is performed based on a first operating state / second operating state determination circuit, which will be described later. Thus, in conventional control, the dry operating state is performed when the load is equal to or greater than the first load, and in the switching load band between the first load and the second load, switching between the dry operating state and the wet operating state is performed by the determination circuit, and the wet operating state is performed when the load is less than the second load. In the embodiment of the present disclosure, the range of loads that can be operated in a dry operation state is expanded.

[0043] FIG. 6 is a diagram illustrating an example of a hardware configuration of a control device according to some embodiments of the present disclosure. 6, the boiler control device (Controller) 50 is a computer system that includes, for example, a CPU (Central Processing Unit: Processor) 1100, a secondary storage device (ROM, Secondary storage: Memory) 1300, a main storage device (RAM, Main Memory) 1200, a communication I / F 1400 for connecting to a network or the like, and an input / output unit 1500. These units are connected via a bus 1800.

[0044] The CPU 1100 controls the entire boiler control device 50 using, for example, an operating system (OS) stored in a secondary storage device 1300 connected via a bus 1800, and executes various processes by executing various programs stored in the secondary storage device 1300. One or more CPUs 1100 may be provided, and may implement processes in cooperation with each other.

[0045] The main memory device 1200 is composed of writable memory such as cache memory and RAM (Random Access Memory), and is used as a working area for reading out programs executed by the CPU 1100 and writing data processed by the programs.

[0046] The secondary storage device 1300 is a non-transitory computer-readable storage medium. Examples of the secondary storage device 1300 include a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, and a semiconductor memory. Examples of the secondary storage device 1300 include a read-only memory (ROM), a hard disk drive (HDD), and a solid-state drive (SSD) flash memory. The secondary storage device 1300 stores, for example, an operating system (OS) for controlling the entire information processing device, such as Windows (registered trademark), iOS (registered trademark), or Android (registered trademark), a basic input / output system (BIOS), various device drivers for operating peripheral devices, various application software, and various data and files. The secondary storage device 1300 also stores programs for implementing various processes and various data required for implementing the various processes. A plurality of secondary storage devices 1300 may be provided, and the above-described programs and data may be stored separately in each secondary storage device 1300.

[0047] FIG. 7 is a diagram illustrating an example of the functionality of a control device in some embodiments of the present disclosure. As shown in FIG. 7, the boiler control device 50 includes a selection unit 51 and a parameter setting unit 52.

[0048] A series of processes for realizing the functions of the boiler control device 50 is stored in the form of a program in, for example, a secondary storage device 1300 (see FIG. 6), and the CPU (processor) 1100 (see FIG. 6) reads this program into the main storage device 1200 (see FIG. 6) and executes information processing and arithmetic processing to realize various functions. Note that the program may be pre-installed in the secondary storage device 1300, provided in a state stored in another non-transitory computer-readable storage medium, or distributed via wired or wireless communication means. Examples of non-transitory computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0049] 7 selects between a normal mode in which normal control is performed and an expanded operating range mode. Here, normal control refers to control in which, when the load falls below a first load, the boiler 10 is switched from a first operating state (dry operating state) to a second operating state (wet operating state) that has lower thermal efficiency than the first operating state. The expanded operating range mode refers to control in which the boiler 10 continues in the first operating state even when the load falls below the first load, and operation in the switching load range is performed according to the first operating state, thereby lowering the minimum load to a second load that is smaller than the first load, i.e., expanding the operating range of the first operating state.

[0050] The selection between the normal mode and the driving range expanded mode is made by the user, and the selection unit 51 selects either the normal mode or the driving range expanded mode based on the user's selection. The user does not select the expanded operating range mode while the boiler 10 is starting up or stopping the boiler 10. The user selects the expanded operating range mode when the boiler 10 is in a dry operating state after starting up, i.e., when the load is equal to or greater than the first load. In addition, when the boiler 10 is starting up or stopping, the expanded operating range mode cannot be selected, and conventional control shown in Figure 5 is performed as the normal mode, and in the switching load range, the determination circuit may switch between the dry operating state and the wet operating state.

[0051] In consideration of safety in the event that a unit stop mode is performed in which the unit including the boiler 10 is stopped while the user selects the operation range expansion mode and the selection unit 51 has selected the operation range expansion mode, the unit stop mode cannot be selected while the operation range expansion mode is selected so that the operation range expansion mode and unit stoppage are not possible at the same time.

[0052] When the selection unit 51 selects the expanded operating range mode, the parameter setting unit 52 sets dedicated parameters corresponding to the expanded operating range mode, which are predefined for each setting value of the boiler 10. Examples of the dedicated parameters for the boiler 10 include the steam temperature on various heat transfer surfaces inside the boiler 10, the fuel flow rate, the feedwater flow rate, the air flow rate, the flue gas O2 setting value, the boiler outlet superheat, the superheater spray water flow rate, the wind box damper opening, and the burner nozzle angle, but other parameters may also be used. The values of the dedicated parameters are predefined for the expanded operating range mode. The values of the dedicated parameters are predefined by the user according to the characteristics and operating conditions of the boiler 10.

[0053] For example, in normal mode, the wind box damper opening operates in the opening direction so that the amount of air sent to the boiler 10 increases in response to an increase in load. On the other hand, when the wind box damper opening is selected as a dedicated parameter in the expanded operating range mode, a value is set so that the wind box damper angle operates in the closing direction, i.e., a value that tends to reduce the amount of air sent to the boiler 10. In addition, a value that changes the position of the flame is set for the burner nozzle angle. An appropriate value is set for the burner nozzle angle depending on the characteristics of the boiler 10 in normal mode. For example, if the direction of fuel injection is changed upward by the burner nozzle angle, the flame position also moves upward. In contrast, when the burner nozzle angle is selected as a dedicated parameter in the expanded operating range mode, an appropriate value is set depending on the characteristics of the boiler 10 in the expanded operating range mode.

[0054] FIG. 8 is a diagram illustrating a setting circuit for the operating range expansion mode in some embodiments of the present disclosure. The selection signal for the operating range expansion mode 70 is added to the output of the determination circuit 64 for the dry operating state, which is the first operating state in the normal mode, and the wet operating state, which is the second operating state.

[0055] As shown in Fig. 8, a load index 61, a boiler outlet superheat degree 62, and a load change status 63 are input to a first operating state / second operating state determination circuit 64. The load index 61 is, for example, a required generator output (MWD, Mega Watt Demand) for the boiler 10. The boiler outlet superheat degree 62 is a value indicating the dryness fraction of steam supplied from the superheater 102 of the boiler 10 to the high-pressure turbine 111A. The load change status 63 indicates whether the load of the boiler 10 is changing. Based on these values, the first operating state / second operating state determination circuit 64 determines whether the boiler 10 should be in a dry operating state or a wet operating state.

[0056] When the first operating state / second operating state determination circuit 64 determines that the boiler 10 should be in the dry operating state, it inputs a switch signal to the dry operating state to an S / R (signal switch) 65. The S / R 65 switches between setting (SET) and resetting (RESET), and is set to "1" when a switch signal to the dry operating state is input. On the other hand, when the first operating state / second operating state determination circuit 64 determines that the boiler 10 should be in the wet operating state, it inputs a switch signal to the wet operating state to a logical operator 69. The logical operator 69 performs an AND (logical product) operation. If the result is true, a switch signal to the wet operating state is input to the S / R 65, and "0" is set.

[0057] When "1" is set in S / R65, i.e., when a switch signal to the dry operating state is input, the first operating state switch 66 is executed, and the logical operator 67 calculates NOT (negation), so the second operating state switch 68 is not executed. On the other hand, when "0" is set in S / R65, i.e., when a switch signal to the wet operating state is input, the first operating state switch 66 is not executed, and the logical operator 67 calculates NOT (negation), so the second operating state switch 68 is executed.

[0058] For such a circuit for determining whether the driving state is dry or wet, when the selection unit 51 selects the driving range expansion mode 70, a "1" is input to the logical operator 71. The logical operator 71 performs a NOT (negation) operation, and a "0" is input to the logical operator 69. The logical operator 69 performs an AND (logical product) operation, and outputs a "0" even if a switch signal to the wet driving state is input to the logical operator 69. In this way, when the driving range expansion mode 70 is selected, switching to the wet driving state is blocked, and transition to the wet driving state is not performed. In addition, a transition to the driving range expansion mode setting 72 occurs.

[0059] FIG. 9 is a diagram illustrating a dedicated parameter setting circuit in some embodiments of the present disclosure. Various setting values of the boiler 10 are set based on a load index 73. The load index 73 is an index indicating the magnitude of the boiler load and is expressed, for example, in terms of the power generation amount MW or the required power generation amount MWD. The acquired load index 73 is processed by a function unit 74, and various setting values of the boiler 10 corresponding to the load index 73 are output, and are set by a various setting value setting unit 77.

[0060] On the other hand, when the operation range expansion mode setting 72 in Fig. 8 is set, the setting is input to the control circuit 76 in Fig. 9. The control circuit 76 is, for example, a TRF (transversal filter) circuit. When the operation range expansion mode setting 72 is set in the control circuit 76, the control circuit 76 outputs the processing results of the function unit 75 to the various setting value setting 77, and each setting value of the boiler 10 is set.

[0061] The function unit 75 is set with dedicated parameters corresponding to the expanded operating range mode defined in advance for each set value of the boiler 10. The load index 73 is input to the function unit 75, processed, and dedicated parameters corresponding to the expanded operating range mode are output as each set value of the boiler 10. Examples of the various set values include a fuel flow rate setting, a feedwater flow rate setting, an air flow rate setting, and various steam temperature settings.

[0062] In this way, dedicated parameters are output as the respective set values of the boiler 10 according to the setting of the operation range expansion mode, and are output to the various set value setting 77, which sets the respective set values of the boiler 10. Since the various set values are for operation in a range where operation is not performed in normal mode, dedicated parameters that are parameters exclusive to the operation range expansion mode are required to switch the various set values.

[0063] FIG. 10 is a diagram illustrating water supply flow rate settings corresponding to load indicators in some embodiments of the present disclosure. The vertical axis of Fig. 10 is the feedwater flow rate setting (t / h), and the horizontal axis is the load index (MW). The solid line in Fig. 10 represents the feedwater flow rate setting that is the output of function generator 74, and the dashed line represents the feedwater flow rate setting that is the output of function generator 75.

[0064] A case will be described in which the operating range expansion mode is set in the dedicated parameter setting circuit of FIG. 9, dedicated parameters are set, and the feedwater flow rate setting is set as the set value. When the operating range expansion mode is not set, the feedwater flow rate setting shown by the solid line is output from the function unit 74. The feedwater flow rate setting shown by the solid line is set to increase steadily as the load index increases. On the other hand, when the operation range expansion mode is set, the output of function unit 75 is set. In the low load index region, function unit 75 outputs a feedwater flow rate setting that is lower than the output of function unit 74, as shown by the dashed line in Fig. 10. This is because the feedwater flow rate setting is set so as not to produce excess feedwater within a range that allows protection of furnace wall 101, in order to maintain a dry operation state in a region with a load index lower than the first load, i.e., in the low load range. Note that a similar tendency occurs when, for example, a fuel flow rate setting is used as the set value.

[0065] FIG. 11 illustrates a circuit for enabling unused controls in some embodiments of the present disclosure. In the operating range expanded mode below the first load, operation control is normally performed in the wet operating state in normal mode, so some of the controls required for the dry operating state associated with a reduction from the first load, which is the minimum load, are not used. Therefore, the control functions required to maintain (continue) the dry operating state in the operating range expanded mode are enabled.

[0066] The control permission conditions 78 set permission conditions for control functions that allow control in wet driving conditions. The control non-use conditions 79 set non-use conditions for control functions that do not allow control, i.e., do not use, in wet driving conditions. By inputting each condition into the various control functions 80, control is performed for control functions for which permission conditions are set, and control is not performed for control functions for which non-use conditions are set.

[0067] When the operating range expansion mode setting 72 in Fig. 8 is set, it is input to the control non-use condition 79 in Fig. 11. When the operating range expansion mode is set, the control non-use condition 79 changes (relaxes) the non-use condition so that the control functions that are not used in the wet operating state but are necessary in the dry operating state are permitted, so that the control functions that are not used in the wet operating state but are necessary in the dry operating state can be continued. Examples of control functions that are not used in the wet operating state but are necessary in the dry operating state include exhaust gas O2 control and steam separator drain tank level control.

[0068] In the air-fuel ratio control for maintaining the O2 concentration in the exhaust gas of the boiler 10, the control function is turned on / off according to the load of the boiler 10 so as to control only the dry operation state in which coal is exclusively fired. When the minimum load is lowered while the dry operation state continues as in this embodiment, it is also necessary to continue the air-fuel ratio control function according to the load. The steam separator drain tank level control controls the level (water level) of the steam separator drain tank 126. When the minimum load is lowered while the dry operation state continues as in this embodiment, the level control of the steam separator drain tank 126 must be continued because there is a possibility that a surplus of feedwater will occur due to the load reduction.

[0069] In this way, the control non-use conditions 79 and the control permission conditions 78 that have been changed according to the setting of the operating range expansion mode are input to the various control functions 80, and the control functions corresponding to the operating range expansion mode are implemented.

[0070] By performing these controls in the operating range expansion mode, the minimum load can be lowered to expand the operating range in the dry operating state, which has higher thermal efficiency than the wet operating state, thereby increasing the thermal efficiency of the boiler 10. As shown by the dashed line in Figure 5, in the control of this embodiment, even if the load decreases and falls below the first load, the first operating state (dry operating state) continues, and the operation in the dry operating state continues until the load further decreases and reaches the second load. In this way, the operation in the dry operating state is maintained even in the switching load range. Furthermore, the minimum load in the switching load band can be maintained at a desired load, and the balance with the amount of power generated by renewable energy can be appropriately adjusted. This reduces the amount of fuel supplied (consumption) and reduces the cost of power generation. Furthermore, since the load of the boiler 10 can be appropriately adjusted, the boiler efficiency can be improved.

[0071] <Additional Notes> The boiler control device, boiler, power plant, boiler control method, and boiler control program described in the above-described embodiments can be understood, for example, as follows.

[0072] A boiler control device (50) according to a first aspect of the present disclosure is a boiler control device (50) that switches between a first operating state of a boiler (10) and a second operating state having a lower thermal efficiency than the first operating state according to a load, and performs normal control to switch from the first operating state to the second operating state when the load falls below a first load. The boiler control device (50) includes a selection unit (51) that selects between a normal mode for performing the normal control and an expanded operating range mode, and a parameter setting unit (52) that sets dedicated parameters that are predefined for each set value of the boiler (10) when the expanded operating range mode is selected by the selection unit (51). When the expanded operating range mode is selected by the selection unit (51), the first operating state is maintained when the load falls below the first load, and the operation of the boiler (10) is controlled by the dedicated parameters set by the parameter setting unit (52).

[0073] By expanding the operating range in the first operating state (dry operating state) which has higher thermal efficiency than the second operating state (wet operating state), the thermal efficiency of the boiler can be increased. Furthermore, when the difference between the amount of power generated by renewable energy and the power demand is made up by thermal power generation equipped with a boiler, the desired load can be maintained within the expanded operating range, and the balance with the power generation by renewable energy can be appropriately adjusted. This reduces the amount of fuel supplied (consumption) and the cost of power generation. Furthermore, since the load of the boiler can be appropriately adjusted, the boiler efficiency can be improved.

[0074] In the boiler control device (50) of the second aspect of the present disclosure, in the first aspect, the first operating state may be a dry operating state in which dry steam is generated in a heat exchanger (104) upstream of a superheater (102), and the second operating state may be a wet operating state in which wet steam is generated in the heat exchanger (104) upstream of the superheater (102).

[0075] In the boiler control device (50) of a third aspect of the present disclosure, in the first or second aspect, the dedicated parameters may include at least one of a steam temperature of the boiler (10), a fuel flow rate, a feedwater flow rate, an air flow rate, an exhaust gas O2 set value, a boiler outlet superheat degree, a superheater spray water flow rate, a wind box damper opening, and a burner nozzle angle.

[0076] In any one of the first to third aspects, the boiler control device (50) of the fourth aspect of the present disclosure may be configured to activate a control that is not used in the first operating state in the normal mode when the operation range expansion mode is selected by the selection unit (51).

[0077] In the operating range below the first load in the operating range expansion mode, operation control is performed in the second operating state, which is normally the normal mode, so some of the controls required in the first operating state are not used.The control functions required to maintain (continue) the first operating state can be continued by enabling them.

[0078] In the boiler control device (50) of the fifth aspect of the present disclosure, in the fourth aspect, the controls that are enabled among the controls that are not used in the first operating state in the normal mode may include at least one of an exhaust gas O2 control and a steam separator drain tank level control.

[0079] In the boiler control device (50) of a sixth aspect of the present disclosure, in any of the first to fifth aspects, when the operation range expansion mode is selected by the selection unit (51), a unit stop mode for controlling the stop of a unit including the boiler (10) may be made unselectable.

[0080] Since the operating range expansion mode and the unit stop mode cannot coexist simultaneously, it is possible to prevent the unit from stopping in the first operating state due to the operating range expansion mode, thereby preventing an emergency stop of the unit or damage to the equipment.

[0081] A boiler according to a seventh aspect of the present disclosure includes a heat exchanger including an economizer (104), a superheater (102), and a reheater (103), a furnace wall (101), a steam separator (125), a condenser (112), and any one of the boiler control devices according to the first to sixth aspects.

[0082] A power plant (1) according to an eighth aspect of the present disclosure includes a boiler (10) equipped with the boiler control device according to any one of the first to sixth aspects, heat exchangers (102, 103, 104) provided in the boiler (10), a steam turbine (111) driven and rotated by steam generated in the boiler (10), and a generator (113) connected to the steam turbine (111) to generate electricity.

[0083] A boiler control method according to a ninth aspect of the present disclosure is a boiler control method (50) in which a computer performs normal control to switch between a first operating state of a boiler (10) and a second operating state having a lower thermal efficiency than the first operating state depending on a load, and to switch from the first operating state to the second operating state when the load falls below a first load. The method includes a selection step (51) of selecting between a normal mode for performing the normal control and an expanded operating range mode, and a parameter setting step (52) of setting, when the expanded operating range mode is selected in the selection step (51), predefined dedicated parameters for each set value of the boiler (10). When the expanded operating range mode is selected in the selection step (51), the first operating state is maintained when the load falls below the first load, and the computer performs operation control of the boiler (10) using the dedicated parameters set in the parameter setting step (52).

[0084] A boiler control program according to a tenth aspect of the present disclosure causes a computer to execute the boiler control method according to the ninth aspect.

[0085] In the above-described embodiment, the boiler of the present disclosure has been described as a boiler that uses solid fuel as fuel, such as coal, biomass fuel, petroleum coke (PC), petroleum residue, etc. The boiler can be fueled not only with solid fuels, but also with petroleum products such as heavy oil, light oil, and crude oil, industrial wastewater, liquefied ammonia, and other liquid fuels. It can also use gaseous fuels such as natural gas, various petroleum gases, by-product gases generated in steelmaking processes, hydrogen gas, and ammonia gas. Furthermore, the present invention can also be applied to a multi-fuel boiler that uses a combination of these various fuels.

[0086] In the above-described embodiment, the minimum load in the dry operation state in the normal mode is set as the first load, and a load lower than the first load is set as the second load, but the first load may be set to, for example, 30%, and the second load may be set to, for example, 20%. The values of the first load and the second load may be changed as appropriate depending on the characteristics of the boiler 10, etc. [Explanation of symbols]

[0087] 1. Power Plant 10. Boiler 11 Furnace 12 Combustion gas passage 13 Flue 20 Combustion equipment 21 Burner 22 Fine fuel supply pipe 23 Air register 24 Air duct 25 Additional air port 26 Additional air duct 31 Mill (Grinder) 32 Forced draft fan (FDF) 41 Gas duct 42 Air preheater 43 Denitration equipment 44 Dust collection device 45 Induced Draft Fan (IDF) 46 Desulfurization equipment 47 Chimney 50 Boiler control device 51 Selection section 52 Parameter setting section 101 Furnace wall 102 Superheater 102A 1st superheater 102B 2nd superheater 102C 3rd superheater 103 Reheater 103A 1st reheater 103B 2nd reheater 104 Economizer 111 Steam turbine 111A high pressure turbine 111B Intermediate Pressure Turbine 111C low pressure turbine 112 Condenser 113 Generator 121 Condensate pump (CP) 122 Low pressure water heater 123 Boiler Feed Pump (BFP) 124 High-pressure water heater 125 Brackish water separator 126 Steam separator drain tank 127 Boiler Circulation Pump (BCP) L1 water supply line L2 drain water line L3~L5 steam lines L6 Circulation Line 1100 CPU 1200 Main storage 1300 Secondary storage 1400 communication interface 1500 Input / output section 1800 Bus

Claims

1. switching between a first operating state of the boiler and a second operating state having a lower thermal efficiency than the first operating state according to a load; A boiler control device that performs normal control to switch from the first operating state to the second operating state when the load falls below a first load, a selection unit that selects between a normal mode in which the normal control is performed and an operating range expansion mode; a parameter setting unit that sets predefined dedicated parameters for each setting value of the boiler when the operation range expansion mode is selected by the selection unit; Equipped with When the operation range expansion mode is selected by the selection unit, the boiler control device maintains the first operation state when the load falls below the first load, and controls the operation of the boiler based on the dedicated parameters set by the parameter setting unit.

2. The first operating state is a dry operating state in which dry steam is produced in a heat exchanger upstream of a superheater, The boiler control device according to claim 1 , wherein the second operating state is a wet operating state in which the steam is converted into wet steam in the heat exchanger upstream of the superheater.

3. The dedicated parameters include the steam temperature of the boiler, the fuel flow rate, the feed water flow rate, the air flow rate, and the exhaust gas O ２ 2. The boiler control device according to claim 1, wherein the control unit includes at least one of a set value, a boiler outlet superheat degree, a superheater spray water flow rate, a wind box damper opening, and a burner nozzle angle.

4. When the operating range expansion mode is selected by the selection unit, The boiler control device according to claim 1 , wherein a control that is not used in the first operating state in the normal mode is enabled.

5. The control that is enabled among the controls that are not used in the first operating state in the normal mode is ２ 5. The boiler control device according to claim 4, further comprising at least one of a steam separator drain tank level control and a steam separator drain tank level control.

6. When the operating range expansion mode is selected by the selection unit, The boiler control device according to claim 1, wherein a unit stop mode for controlling the stop of a unit including the boiler is made unselectable.

7. a heat exchanger including an economizer, a superheater, and a reheater; The furnace wall and a steam separator; A condenser, A boiler comprising the boiler control device according to claim 1.

8. A boiler equipped with the boiler control device according to claim 1; a heat exchanger provided in the boiler; a steam turbine that is rotationally driven by steam generated in the boiler; a generator coupled to the steam turbine for generating electricity; A power plant comprising:

9. switching between a first operating state of the boiler and a second operating state having a lower thermal efficiency than the first operating state according to a load; A boiler control method in which a computer performs normal control to switch from the first operating state to the second operating state when the load falls below a first load, a selection step of selecting a normal mode in which the normal control is performed and an operating range expansion mode; a parameter setting step of setting predefined dedicated parameters for each setting value of the boiler when the operation range expansion mode is selected in the selection step; Equipped with When the operating range expansion mode is selected in the selection step, the first operating state is maintained when the load falls below the first load, and the computer controls the operation of the boiler using the dedicated parameters set in the parameter setting step.

10. A boiler control program that causes a computer to execute the boiler control method according to claim 9.

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