Boiler system, power generation plant and method for operating boiler system

Abstract

To supply a sufficient air flow rate for cooling of unused burners in a high-load band to protect burner devices, and supply an appropriate air flow rate in a low-load band according to decrease in thermal load of a furnace, thereby ensuring a suitable operating state in the entire load band.SOLUTION: A boiler system 2 comprises: a boiler 10 having a plurality of burners 21; an air supply unit that supplies air to the burners 21; a cold gas damper 30d that adjusts an amount of air supplied to the burners 21 by the air supply unit; and a control unit 50 that controls the cold gas damper 30d so as to supply an amount of cooling air according to a load of the boiler 10 when cooling air is supplied by the air supply unit to the burners 21 that are not forming a flame.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a boiler system and a power plant, as well as a method of operating a boiler system. [Background technology]

[0002] A large boiler such as a power generation boiler has a hollow furnace that is installed vertically, and a plurality of burners are arranged on the furnace wall along the circumferential direction of the furnace. In addition, a flue is connected to the large boiler vertically above the furnace, and a heat exchanger for generating steam is arranged in the flue. The burner injects a mixture of fuel and air (oxidizing gas) into the furnace to form a flame, and combustion gas is generated and flows into the flue. A heat exchanger is installed in the area where the combustion gas flows, and water or steam flowing inside a heat transfer tube that constitutes the heat exchanger is heated to generate superheated steam.

[0003] Such boilers are provided with multiple burners (for example, Patent Document 1). The boiler also changes the number of burners that form flames depending on the load. At this time, burners that are not forming a flame may be subject to a shortened lifespan or damage due to radiant heat from the furnace. In particular, burners equipped with a flame-holding mechanism that is installed facing the inside of the furnace may be susceptible to a shortened lifespan or damage as the metal temperature is easily increased by receiving radiant heat from the flame holder surface. For this reason, cooling air is supplied to burners that are not forming a flame to cool the burners, thereby preventing the shortened lifespan and damage to the burners. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-76868 A Summary of the Invention [Problem to be solved by the invention]

[0005] Unlike the combustion air supplied to burners that do not form a flame, the cooling air supplied to burners that form a flame is unlikely to directly contribute to combustion in the boiler. For this reason, depending on the boiler load, the ratio of cooling air to the total amount of air (total air volume) supplied to the boiler may increase, causing the air ratio near the flame to deviate from the specified range, which may affect the performance and operability of the boiler, such as increasing the concentration of nitrogen oxides (NOx) in the combustion exhaust gas and increasing the exhaust gas temperature at the air preheater outlet due to an increase in the amount of air bypassing the air preheater.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a boiler system, a power generation plant, and an operating method for a boiler system that can provide a sufficient air flow rate for cooling unused burners and protecting the burner equipment during high load ranges, while at the same time providing an appropriate air flow rate in response to a decrease in the thermal load of the furnace during low load ranges, thereby achieving suitable operating conditions over the entire load range. [Means for solving the problem]

[0007] In order to solve the above problems, the boiler system, power generation plant, and boiler system operating method of the present disclosure employ the following measures. A boiler system according to one embodiment of the present disclosure includes a boiler having a plurality of burners, an air supply unit that supplies air to the burners, an adjustment unit that adjusts the amount of air supplied to the burners by the air supply unit, and a control unit that controls the adjustment unit so that an amount of cooling air corresponding to the load of the boiler is supplied when cooling air is supplied by the air supply unit to the burners that are not forming a flame.

[0008] A method of operating a boiler system according to one embodiment of the present disclosure includes a boiler system comprising a boiler having a plurality of burners, an air supply unit that supplies air to the burners, and an adjustment unit that adjusts the amount of air supplied to the burners by the air supply unit, and includes a control step of controlling the adjustment unit so that when cooling air is supplied by the air supply unit to the burners that are not forming a flame, an amount of cooling air corresponding to the load of the boiler is supplied. Effect of the Invention

[0009] According to the present disclosure, at high loads, sufficient air flow is supplied to cool unused burners and protect the burner equipment, while at low loads, an appropriate air flow is set in response to the decrease in thermal load on the furnace, thereby forming a flame with an appropriate combustion state at each load and optimizing the boiler as a whole. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram illustrating a boiler system according to an embodiment of the present disclosure. [Diagram 2] 1 is a schematic configuration diagram illustrating a boiler system according to an embodiment of the present disclosure. [Diagram 3] FIG. 2 is a block diagram illustrating a control unit according to an embodiment of the present disclosure. [Figure 4] 1 is a graph showing a relationship between a boiler load and an opening degree of a cold gas damper in a boiler system according to an embodiment of the present disclosure. [Diagram 5] 13 is a graph showing the relationship between the boiler load and the opening degree of the cold gas damper for each solid fuel in a boiler system according to a modified example of an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0012] The power plant 1 of this embodiment includes a boiler system 2 that generates steam, a steam turbine (not shown) that is driven by the steam generated in the boiler system 2, and a power generation section (not shown) that generates power using the driving force of the steam turbine.

[0013] 1 is a schematic configuration diagram showing a boiler system 2 using solid fuel as a main fuel according to the present embodiment. The boiler system 2 includes a boiler 10 and a mill 31. The boiler system 2 will be described in detail later.

[0014] The boiler 10 of this embodiment is a boiler that can generate superheated steam by burning pulverized fuel made by pulverizing solid fuel with a burner and exchanging the heat generated by this combustion with feed water or steam. Biomass fuel, coal, etc. are used as the solid fuel.

[0015] The boiler 10 has a furnace 11, a combustion device, and a combustion gas passage 12. The furnace 11 has a hollow rectangular cylinder shape and is installed vertically. The furnace wall 101 constituting the inner wall surface of the furnace 11 is composed of a plurality of heat transfer tubes and fins connecting the heat transfer tubes, and recovers heat generated by the combustion of pulverized fuel by heat exchange with water and steam flowing inside the heat transfer tubes, while suppressing the temperature rise of the furnace wall 101.

[0016] The combustion device is installed in the lower region of the furnace 11. In this embodiment, the combustion device has a plurality of burners 21A, 21B, 21C, 21D, 21E, and 21F (hereinafter, they may be collectively referred to as "burners 21") attached to the furnace wall 101. The burners 21 are arranged in a plurality of stages along the vertical direction, with each set being arranged at equal intervals along the circumferential direction of the furnace 11 (for example, four burners installed at each corner of the rectangular furnace 11). For convenience of illustration, only two burners of one set are shown in FIG. 1, and each set is denoted by the reference numerals 21A, 21B, 21C, 21D, 21E, and 21F. The shape of the furnace 11, the number of burner stages, the number of burners in one stage, the arrangement of the burners, and the like are not limited to this embodiment.

[0017] The burners 21A, 21B, 21C, 21D, 21E, and 21F are connected to a plurality of mills (pulverizers) 31A, 31B, 31C, 30D, 31E, and 31F (hereinafter, sometimes collectively referred to as "mills 31") via a plurality of pulverized fuel supply pipes 22A, 22B, 22C, 22D, 22E, and 22F (hereinafter, sometimes collectively referred to as "pulverized fuel supply pipes 22"). The mill 31 is, for example, a vertical roller mill in which a pulverizing table (not shown) is supported inside so as to be rotatable and a plurality of pulverizing rollers (not shown) are supported above the pulverizing table so as to be rotatable in conjunction with the rotation of the pulverizing table. The solid fuel pulverized by the cooperation of the pulverizing rollers and the pulverizing table is transported to a classifier (not shown) provided in the mill 31 by primary air (transport gas, oxidizing gas) supplied to the mill 31. In the classifier, the fuel is classified into pulverized fuel having a particle size equal to or smaller than that suitable for combustion in the burner 21, and coarse pulverized fuel having a particle size larger than that. The pulverized fuel passes through the classifier and is supplied to the burner 21 via the pulverized fuel supply pipe 22 together with primary air. The coarse pulverized fuel that does not pass through the classifier falls onto the grinding table by its own weight inside the mill 31 and is re-ground. The burner 21 also has a flame-holding mechanism (not shown) at its tip, which is installed so as to face the inside of the furnace 11.

[0018] An air register 23 is provided on the outside of the furnace 11 at the mounting position of the burner 21, and one end of an air duct 24 is connected to the air register 23. A forced draft fan (FDF: Forced Draft Fan) 32 is connected to the other end of the air duct 24. The air supplied from the forced draft fan 32 is heated by an air preheater 42 installed in the air duct 24 (details will be described later), and is supplied to the burner 21 via the air register 23 as secondary air (combustion air, oxidizing gas), and is introduced into the furnace 11.

[0019] 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 feed water or steam flowing inside each heat exchanger. The arrangement and shape of each heat exchanger are not limited to the form shown in FIG. 1.

[0020] A flue 13 is connected to the downstream side of the combustion gas passage 12, and discharges the combustion gas whose heat has been recovered by the heat exchanger. An air preheater (air heater) 42 is provided between the flue 13 and the air duct 24, and heat is exchanged between the air flowing through the air duct 24 and the combustion gas flowing through the flue 13, thereby heating the primary air supplied to the mill 31 and the secondary air supplied to the burner 21, thereby recovering further heat from the combustion gas after heat exchange with water and steam.

[0021] Furthermore, a denitration device 43 may be provided in the flue 13 at a position upstream of the air preheater 42. The denitration device 43 supplies a reducing agent having an effect of reducing nitrogen oxides, such as ammonia or urea water, to the combustion gas flowing through the flue 13, and promotes a reaction between the nitrogen oxides (NOx) in the combustion gas to which the reducing agent has been supplied and the reducing agent by the catalytic action of a denitration catalyst provided in the denitration device 43, thereby removing and reducing the nitrogen oxides in the combustion gas. A gas duct 41 is connected to the flue 13 downstream of the air preheater 42. The gas duct 41 is provided with environmental equipment such as a dust collector 44, such as an electrostatic precipitator, for removing ash and the like from the combustion gas, a desulfurization equipment 46 for removing sulfur oxides, and an induced draft fan (IDF) 45 for directing the exhaust gas to these environmental equipment. The downstream end of the gas duct 41 is connected to a chimney 47, and the combustion gas treated in the environmental equipment is discharged to the outside of the system as exhaust gas.

[0022] In the boiler 10, when the multiple mills 31 are driven, the pulverized and classified pulverized fuel is supplied to the burner 21 together with the primary air through the pulverized fuel supply pipe 22. In addition, secondary air heated by the air preheater 42 is supplied to the burner 21 through the wind duct 24 and the wind box 23. The burner 21 blows a pulverized fuel mixture, which is a mixture of the pulverized fuel and the primary air, into the furnace 11, and also blows secondary air into the furnace 11. The pulverized fuel mixture blown into the furnace 11 ignites and reacts with the secondary air to form a flame. A flame is formed in the lower region of the furnace 11, and the high-temperature combustion gas rises inside the furnace 11 and flows into the combustion gas passage 12. In this embodiment, air is used as the oxidizing gas (primary air, secondary air), but the oxidizing gas may have a higher or lower oxygen ratio than air, and stable combustion in the furnace 11 is achieved by adjusting the ratio of the amount of oxygen to the amount of fuel supplied to an appropriate range.

[0023] The combustion gas flowing into the combustion gas passage 12 exchanges heat with water and steam in a superheater 102, a reheater 103, and a coal economizer 104 arranged inside the combustion gas passage 12, and is then discharged into the flue 13, where nitrogen oxides are removed in a denitration device 43, and the combustion gas exchanges heat with primary air and secondary air in an air preheater 42, and is then discharged into a gas duct 41, where ash and the like are removed in a dust collector 44, and sulfur oxides are removed in a desulfurization device 46, and the combustion gas is then discharged to the outside of the system from a chimney 47. Note that the arrangement of the heat exchangers in the combustion gas passage 12 and the devices from the flue 13 to the gas duct 41 with respect to the combustion gas flow does not necessarily have to be in the order described above.

[0024] Next, the boiler system 2 will be described in detail with reference to FIGS. The boiler system 2 includes the above-mentioned boiler 10 and a plurality of mills 31 that pulverize the solid fuel to be supplied to the burner 21 of the boiler 10.

[0025] The mill 31 pulverizes the solid fuel supplied from the fuel supply unit 31a inside, and discharges the pulverized solid fuel to the outside together with the primary air (carrier gas, oxidizing gas) supplied to the mill 31. The primary air and pulverized fuel discharged to the outside are led to the burner 21 of the boiler 10 via the pulverized fuel supply pipe 22.

[0026] The boiler system 2 includes a blower section 30 that directs primary air to a mill 31 . The blower 30 is a device that blows primary air into the mill 31 to dry and transport the pulverized fuel. In order to appropriately adjust the flow rate and temperature of the primary air blown into the inside of the mill 31, in this embodiment, the blower section 30 is equipped with a primary air fan (PAF) 33, a hot gas flow path 30a, a cold gas flow path (air piping) 30b, a hot gas damper 30c, and a cold gas damper (adjustment section) 30d.

[0027] The hot gas passage 30a branches off from the cold gas passage 30b. The hot gas passage 30a supplies a part of the air sent out from the primary air ventilator 33 as hot gas heated by passing through the air preheater 42. The hot gas passage 30a is provided with a hot gas gate valve 30e and a hot gas damper 30c downstream of the air preheater 42. The hot gas gate valve 30e is an opening / closing valve, and is switched between an open state and a closed state by the control unit 50. The opening degree of the hot gas damper 30c is controlled by the control unit 50. The flow rate of the hot gas supplied from the hot gas passage 30a is determined by the opening degree of the hot gas damper 30c. The hot gas heated by the air preheater 42 is also led to other mills 31 via the hot gas passage 30a.

[0028] The cold gas flow path 30b supplies a portion of the air sent out from the primary air ventilator 33 as cold gas at room temperature. A cold gas gate valve 30f and a cold gas damper 30d are provided in the cold gas flow path 30b. The cold gas gate valve 30f is an opening / closing valve that is switched between an open state and a closed state by the control unit 50. The opening degree of the cold gas damper 30d is controlled by the control unit 50. The flow rate of cold gas supplied from the cold gas flow path 30b is determined by the opening degree of the cold gas damper 30d. The cold gas sent out from the primary air ventilator 33 is also guided to other mills 31 via the cold gas flow path 30b.

[0029] The hot gas flow path 30a and the cold gas flow path 30b join at the downstream end to form a primary air flow path 35. The flow rate of the primary air (i.e., the amount of air flowing through the primary air flow path 35) is the sum of the flow rate of the hot gas supplied from the hot gas flow path 30a and the flow rate of the cold gas supplied from the cold gas flow path 30b, and the temperature of the primary air is determined by the mixing ratio of the hot gas supplied from the hot gas flow path 30a and the cold gas supplied from the cold gas flow path 30b, and is controlled by the control unit 50. The primary air flow passage 35 is provided with a flow meter (air amount detection section) 35a that measures the flow rate of the primary air flowing therethrough.

[0030] In this embodiment, the blower section 30, the primary air passage 35, the mill 31 and the pulverized fuel supply pipe 22 are included in an air supply section that supplies air (including primary air for combustion and cooling air) to the burner 21 of the boiler 10.

[0031] The boiler system 2 according to this embodiment does not always form flames in all burners 21 (burners 21A, 21B, 21C, 21D, 21E, 21F), but changes the number of burners 21 that form flames depending on the load of the boiler 10, etc. Specifically, the higher the load of the boiler 10, the more burners 21 that form flames are increased. As a result, in the boiler 10, there are burners 21 that form flames and burners 21 that do not form flames.

[0032] The burner 21 forming a flame and the mill 31 connected via the pulverized fuel supply pipe 22 are in an operating state. On the other hand, the burner 21 not forming a flame and the mill 31 connected via the pulverized fuel supply pipe 22 are in a stopped state.

[0033] The burners 21 that form a flame are supplied with a mixture of pulverized fuel and primary air for combustion by the air supply unit, while the burners 21 that do not form a flame are supplied with cooling air by the air supply unit.

[0034] 3, the boiler system 2 includes a control unit 50. The control unit 50 controls the hot gas gate valve 30e, the hot gas damper 30c, the cold gas gate valve 30f, the cold gas damper 30d, etc. The control unit 50 also receives information detected by the flow meter 35a.

[0035] When supplying cooling air to the burners 21 not forming a flame, the control unit 50 controls the opening degree of the cold gas damper 30d so as to supply an amount of cooling air according to the load of the boiler 10. Specifically, the control unit 50 controls the opening degree of the cold gas damper 30d so that the amount of cooling air supplied to the burners 21 not forming a flame decreases as the load of the boiler 10 decreases.

[0036] In addition, the control unit 50 may determine the amount of cooling air based on a map or the like that specifies the relationship between the load of the boiler 10 and the amount of cooling air that is stored in advance, and control the opening degree of the cold gas damper 30d so that the amount of cooling air is determined. At this time, the method of controlling the opening degree of cold gas damper 30d so as to obtain the determined amount of cooling air is not particularly limited. For example, control unit 50 may control the opening degree of cold gas damper 30d based on a map or the like that defines the relationship between the amount of cooling air and the opening degree of cold gas damper 30d that is stored in advance. Control unit 50 may also control the opening degree of cold gas damper 30d based on the amount of cooling air detected by flow meter 35a.

[0037] Furthermore, the method in which the control unit 50 acquires the load of the boiler 10 is not limited. For example, the load command value of the boiler 10 may be the load of the boiler 10. Furthermore, the control unit 50 may derive the load of the boiler 10 based on the amount of solid fuel supplied to all the mills 31, i.e., the total amount of fuel supplied to the boiler 10.

[0038] The control unit 50 (Controller) includes, for example, a CPU (Central Processing Unit: Processor), a main memory, a secondary storage, etc. Furthermore, the control unit 50 may include a communication unit for transmitting and receiving information to and from other devices. The main storage device is composed of writable memory such as cache memory and RAM (Random Access Memory), and is used as a working area for reading out programs executed by the CPU and writing data processed by the programs. The secondary storage device is a non-transitory computer readable storage medium, such as a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, or a semiconductor memory. A series of processes for realizing various functions is stored in a secondary storage device in the form of a program, for example, and various functions are realized by the CPU reading the program into the main storage device and executing information processing and arithmetic processing. The program may be installed in the secondary storage device in advance, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0039] Next, the flow of air supplied to the burners 21 which are generating a flame and the burners 21 which are not generating a flame will be described.

[0040] [Burner forming the flame (ignition burner)] The mill 31 corresponding to the burner 21 which is forming the flame is in an operational state as described above. In the operating state, the mill 31 is supplied with primary air, which is a mixture of hot gas flowing through the hot gas flow path 30a and cold gas flowing through the cold gas flow path 30b, from the blower 30 via the primary air flow path 35. At this time, the openings of the hot gas damper 30c and the cold gas damper 30d are controlled by the control unit 50 so that the primary air has a predetermined temperature (the temperature at the outlet or inlet of the mill 31) and flow rate. In addition, the hot gas gate valve 30e and the cold gas gate valve 30f are opened by the control unit 50.

[0041] The mill 31 in operation is supplied with solid fuel by the fuel supply unit 31a and pulverizes the solid fuel inside. The mill 31 in operation discharges the pulverized solid fuel (pulverized fuel) together with the supplied primary air to the outside. The mixture of the pulverized fuel and the primary air discharged to the outside of the mill 31 is led to the burner 21 of the boiler 10 via the pulverized fuel supply pipe 22.

[0042] Secondary air preheated by an air preheater 42 is supplied to the wind box 23 of the boiler 10 via an air duct 24. A wind box damper (not shown) for adjusting the flow rate of secondary air supplied to each burner 21 is provided in the wind box 23 corresponding to each burner 21. The opening degree of the wind box damper is adjusted by the control unit 50 in accordance with the operating state of each burner 21 (ignition / extinguishing, load of the boiler 10, amount of fuel supply, etc.).

[0043] The burner 21 for forming the flame uses the supplied primary air and secondary air as combustion air to burn the supplied pulverized fuel to form the flame. At this time, the amount of secondary air is adjusted by the opening degree of the wind box damper so that the air ratio in the vicinity of the flame falls within a predetermined range.

[0044] [Burner that does not form a flame (extinguishing burner)] The mill 31 corresponding to the burner 21 that is not generating a flame is in a stopped state as described above. To the mill 31 in a stopped state, only cold gas flowing through the cold gas passage 30b from the blower 30 is supplied as cooling air via the primary air passage 35. At this time, the opening degree of the cold gas damper 30d is controlled by the control unit 50 so that the amount of cooling air supplied decreases as the load of the boiler 10 decreases. An example of the control performed by the control unit 50 will be described with reference to Fig. 4. As shown in Fig. 4, the control unit 50 gradually reduces the opening degree of the cold gas damper 30d when the load of the boiler 10 is low. In detail, the opening degree of the cold gas damper 30d is reduced when the load of the boiler 10 is low, compared with the case where the opening degree of the cold gas damper 30d is constant in accordance with the load of the boiler 10 when it is high (see the dashed line). Note that the control performed by the control unit 50 is not limited to this. For example, the control unit 50 may control the cold gas damper 30d so that the opening degree is gradually reduced as the load of the boiler 10 decreases.

[0045] 2, the hot gas gate valve 30e is closed by the control unit 50, and no air flows through the hot gas passage 30a. On the other hand, the cold gas gate valve 30f is opened by the control unit 50.

[0046] Moreover, the mill 31 in the stopped state is not supplied with solid fuel by the fuel supply unit 31a. The cooling air supplied to the mill 31 in the stopped state passes through the mill 31 and is discharged to the outside. The cooling air discharged to the outside of the mill 31 is led to the burner 21 of the boiler 10 via the pulverized fuel supply pipe 22.

[0047] Secondary air preheated by an air preheater 42 is supplied to the wind box 23 of the boiler 10 via an air duct 24 .

[0048] The burner 21 that is not forming a flame cools the burner nozzle and the like with the supplied cooling air, thereby suppressing damage caused by radiant heat. The cooling air that has cooled the burner 21 is discharged into the furnace 11 of the boiler 10.

[0049] According to this embodiment, the following advantageous effects are obtained. In the boiler system 2, combustion air is supplied to the burners 21 that are forming a flame via an air supply unit, and cooling air is supplied to the burners 21 that are not forming a flame via an air supply unit to suppress damage to the burners 21 due to radiation. Therefore, the total amount of air supplied to the boiler 10 (total air amount) includes the combustion air supplied to the burners 21 that are forming a flame and the cooling air supplied to the burners 21 that are not forming a flame. In this embodiment, a control unit 50 is provided that controls the cold gas damper 30d so as to supply cooling air to the burners 21 not forming a flame in an amount corresponding to the load of the boiler 10. This allows the amount of cooling air supplied to the burners 21 not forming a flame to be an amount corresponding to the load of the boiler 10. Therefore, the ratio of the amount of cooling air to the total amount of air can be set to a ratio corresponding to the load of the boiler 10. In other words, since the ratio of the amount of combustion air to the total amount of air can be set to a ratio corresponding to the load of the boiler 10, a suitable combustion state can be formed in the boiler 10 and a stable state can be secured as a boiler system. Therefore, the performance and operability of the boiler 10 can be improved. Furthermore, since the burner 21 can be cooled with an appropriate amount of cooling air, damage to the burner 21 due to heat can be suppressed, and the life of the burner 21 can be extended.

[0050] Furthermore, the lower the load of the boiler 10, the fewer the number of burners 21 that form flames, and therefore the number of burners 21 to which cooling air is supplied increases. Therefore, when the amount of cooling air supplied to the burners 21 is constant, the lower the load of the boiler 10, the greater the ratio of the amount of cooling air to the total amount of air. On the other hand, in this embodiment, the control unit 50 controls the cold gas damper 30d so that the amount of air supplied to the burner 21 that is not forming a flame decreases as the load of the boiler 10 decreases. This makes it possible to suppress an increase in the ratio of the amount of cooling air to the total amount of air even when the boiler 10 is operating in a low load region.

[0051] Specifically, as the ratio of the amount of cooling air to the total amount of air increases, the following points (1) to (3) become a concern.

[0052] (1) Since the cooling air is supplied to the burner 21 in the same system as the primary air, an increase in the ratio of the cooling air volume is the same as an increase in the primary air volume. When the ratio of the primary air volume to the total air volume increases, the ratio of the secondary air volume to the total air volume decreases accordingly. This reduces the amount of secondary air supplied to the wind box 23, and the pressure in the wind box 23 decreases. Therefore, the pressure difference between the furnace 11 of the boiler 10 and the wind box 23 decreases, and even if the opening of the wind box damper is adjusted, the secondary air may not be introduced from the wind box 23 to the furnace 11 of the boiler 10. Therefore, the air ratio near the flame may deviate from the specified range, which may affect the performance of the boiler 10, such as increasing the concentration of nitrogen oxides (NOx) in the combustion exhaust gas. On the other hand, in this embodiment, even when the boiler 10 is operated in a low load region, an increase in the ratio of the amount of cooling air to the total amount of air can be suppressed, so that secondary air can be suitably introduced from the wind box 23 to the furnace 11 of the boiler 10. Therefore, a flame can be suitably formed in the boiler 10.

[0053] (2) Furthermore, when the amount of cooling air increases, the amount of air bypassing the air preheater 42 (i.e., flowing through the cold gas flow path 30b) also increases, and the exhaust gas is not sufficiently cooled in the air preheater 42, so the temperature of the exhaust gas discharged from the air preheater 42 to the gas duct 41 rises. As a result, high-temperature exhaust gas is introduced into the equipment (dust collector 44, induced draft fan 45, desulfurizer 46, etc.) provided downstream in the exhaust gas flow from the air preheater 42, which may result in the upper limit of the gas temperature of the equipment being reached or the efficiency of the boiler 10 being deteriorated. On the other hand, in this embodiment, when the boiler 10 operates in the low load region, the amount of cooling air is reduced, so that it is possible to suppress an increase in the amount of air bypassing the air preheater 42. Therefore, it is possible to suppress an increase in the temperature of the exhaust gas discharged from the air preheater 42 to the gas duct 41.

[0054] (3) Furthermore, when the forced draft fan 32 and the primary air fan 33 are arranged in parallel, the proportion of the air discharged by the primary air fan 33 increases and the proportion of the air discharged by the forced draft fan 32 decreases, so that the blade opening of the forced draft fan 32 becomes close to fully closed, which may deteriorate the controllability. On the other hand, in this embodiment, when the boiler 10 operates in the low load region, the amount of cooling air is reduced, so that it is possible to prevent an increase in the proportion of the discharge air amount of the primary air fan 33. Therefore, the blade opening degree of the forced draft fan 32 is unlikely to approach the fully closed state, so that it is possible to prevent the controllability of the forced draft fan 32 from deteriorating.

[0055] In this embodiment, the control unit 50 controls the opening degree of the cold gas damper 30d so as to supply cooling air to the burners 21 that are not forming flames in an amount corresponding to the load of the boiler 10. In this way, the amount of cooling air to be supplied can be adjusted simply by controlling the opening degree of the cold gas damper 30d. Therefore, the amount of cooling air can be easily adjusted.

[0056] Furthermore, when the control unit 50 controls the cold gas damper 30d based on the amount of air detected by the flowmeter 35a, the amount of cooling air supplied to the burners 21 that are not forming a flame can be more accurately set to an amount corresponding to the load of the boiler 10. Therefore, the ratio of the amount of cooling air to the total amount of air can be more accurately set to a ratio corresponding to the load of the boiler 10.

[0057] In addition, in this embodiment, the control unit 50 stops the supply of solid fuel from the mill 31 to the burner 21 that does not form a flame, and controls the cold gas damper 30d so that the mill 31 supplies air in an amount corresponding to the load of the boiler 10. This allows an appropriate amount of cooling air to be supplied to the burner 21 that does not form a flame in the boiler 10 to which solid fuel is supplied from the mill 31, thereby suppressing damage to the burner 21 due to radiant heat. In addition, the amount of cooling air supplied to the burner 21 that does not form a flame can be set to an amount corresponding to the boiler 10 load. Therefore, the ratio of the amount of cooling air to the total amount of air can be set to a ratio corresponding to the boiler 10 load more accurately.

[0058] [Variations] Next, a modified example of this embodiment will be described with reference to Fig. 5. In this modified example, the control performed by the control unit 50 is different. In the above embodiment, an example has been described in which the control unit 50 performs control to adjust the opening degree of the cold gas damper 30d so as to supply an amount of cooling air corresponding to the load of the boiler 10 when supplying cooling air to the burner 21 not forming a flame. In this modified example, in addition to the above control, the control unit 50 performs control to adjust the opening degree of the cold gas damper 30d so as to supply an amount of cooling air corresponding to the type of solid fuel supplied to the mill 31 when supplying cooling air to the burner 21 not forming a flame.

[0059] An example of the control performed by the control unit 50 of this modified example will be described. First, the control unit 50 determines the type of solid fuel used in the boiler 10 based on a value calculated from a heat absorption index (HAI) which is the ratio of the amount of heat exchanged in the superheater 102, reheater 103, and economizer 104, which are convective heat transfer parts, to the amount of heat exchanged in the furnace 11, which is a radiative heat transfer part. Specifically, if the calculated value is 0.9, it is determined to be a solid fuel with a low fuel ratio, if the calculated value is 1.0, it is determined to be a solid fuel with a medium fuel ratio, and if the calculated value is 1.1, it is determined to be a solid fuel with a high fuel ratio. The fuel ratio is calculated as fixed carbon / volatile matter, and the lower the fuel ratio, the more volatile matter is contained, so the higher the combustibility and the earlier the combustion is completed, so the amount of radiative heat transfer in the furnace 11 becomes relatively large, and the HAI tends to become small.

[0060] Next, the control unit 50 performs control to adjust the opening of the cold gas damper 30d so as to supply an amount of cooling air according to the fuel ratio of the determined solid fuel. Specifically, as shown in FIG. 5, when the solid fuel is determined to be a low fuel ratio solid fuel, the temperature in the furnace 11 becomes high, so the opening of the cold gas damper 30d is made larger than in the case of solid fuels with other fuel ratios. Also, when the solid fuel is determined to be a medium fuel ratio solid fuel, the opening of the cold gas damper 30d is made larger than in the case of solid fuels with high fuel ratios. In this way, the control unit 50 controls the cold gas damper 30d so that the opening becomes larger as the fuel ratio of the solid fuel becomes lower.

[0061] For solid fuels with a calculated value greater than 0.9 and less than 1.0, or greater than 1.0 and less than 1.1, parameters obtained by dividing the set values ​​for each calculated value are used. Specifically, for example, if the calculated value is 0.95, the intermediate value between the parameter when the calculated value is 0.9 and the parameter when the calculated value is 1.0 is reflected as the parameter.

[0062] Also, as shown in FIG. 4, regardless of the fuel ratio of the solid fuel, the control unit 50 may control the cold gas damper 30d so that the opening degree gradually decreases as the load on the boiler 10 decreases. In the example of FIG. 4, the opening degree of the cold gas damper 30d is set not to be smaller than the minimum opening degree m.

[0063] This modified example provides the following advantageous effects. Since the fuel ratio (ease of combustion) differs depending on the type of solid fuel, the temperature of the furnace 11 of the boiler 10 changes depending on the type of solid fuel supplied to the boiler 10. Therefore, the radiant heat to the burner 21 also changes depending on the type of solid fuel. Therefore, the amount of cooling air required to cool the burner 21 that is not forming a flame also changes depending on the type of solid fuel. In this embodiment, the control unit 50 controls the opening degree of the cold gas damper 30d so as to supply an amount of cooling air according to the type of solid fuel supplied to the mill 31. This allows the amount of cooling air supplied to the burner 21 that is not forming a flame to be an amount according to the type of solid fuel. Therefore, the ratio of the amount of cooling air to the total air amount can be set to a ratio according to the type of solid fuel. Therefore, it is possible to form a suitable combustion state in the boiler 10 and ensure an amount of cooling air according to the type of solid fuel.

[0064] The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit and scope of the present disclosure. For example, in the above embodiment, an example in which the forced draft fan 32 and the primary air fan 33 are provided in parallel has been described, but the present disclosure is not limited to this. For example, the forced draft fan 32 and the primary air fan 33 may be provided so that a portion of the air pressurized by the forced draft fan 32 is guided to the primary air fan 33.

[0065] The boiler system, the power plant, and the method of operating the boiler system described in the above-described embodiments can be understood, for example, as follows. A boiler system according to a first aspect of the present disclosure includes a boiler (10) having a plurality of burners (21), an air supply unit that supplies air to the burners (21), an adjustment unit (30d) that adjusts the amount of air supplied to the burners (21) by the air supply unit, and a control unit (50) that controls the adjustment unit (30d) so as to supply an amount of cooling air corresponding to the load of the boiler (10) when cooling air is supplied by the air supply unit to the burners (21) that are not forming a flame.

[0066] In a boiler system, combustion air is supplied to burners that form flames via an air supply unit, and cooling air is supplied to burners that do not form flames via an air supply unit to prevent damage to the burners due to radiation. Therefore, the total amount of air supplied to the boiler (total air amount) includes the combustion air supplied to burners that form flames and the cooling air supplied to burners that do not form flames. In the above configuration, a control unit is provided that controls the adjustment unit so as to supply cooling air to the burners not forming a flame in an amount corresponding to the boiler load. This allows the amount of cooling air supplied to the burners not forming a flame to be an amount corresponding to the boiler load. Therefore, the ratio of the amount of cooling air to the total amount of air can be set to a ratio corresponding to the boiler load. In other words, the ratio of the amount of combustion air to the total amount of air can be set to a ratio corresponding to the boiler load, so that a suitable combustion state can be achieved in the boiler and the boiler system as a whole can be optimized.

[0067] In addition, in the boiler system according to a second aspect of the present disclosure, in the above-mentioned first aspect, the control unit (50) controls the adjustment unit (30d) to supply less cooling air to the burner (21) not forming a flame as the load of the boiler (10) becomes lower.

[0068] The lower the boiler load, the fewer the number of burners that form flames, and the more burners to which cooling air is supplied. Therefore, if the amount of cooling air supplied to the burners is constant, the lower the boiler load, the greater the ratio of the amount of cooling air to the total amount of air. On the other hand, in the above configuration, the control unit controls the adjustment unit so that the amount of air supplied to the burner that is not forming a flame decreases as the boiler load decreases. This makes it possible to suppress an increase in the ratio of the amount of cooling air to the total amount of air even when the boiler is operating in a low load range.

[0069] Furthermore, in a boiler system according to a third aspect of the present disclosure, in the above-mentioned first or second aspect, the air supply unit has an air piping (30b) that transports air to the burner (21), the adjustment unit (30d) has a damper (30d) that is provided in the air piping (30b) and adjusts the amount of air flowing through the air piping (30b) by changing the opening degree, and the control unit (50) controls the opening degree of the damper (30d) so as to supply cooling air in an amount corresponding to the load of the boiler (10) to the burner (21) that is not forming a flame.

[0070] In the above configuration, the control unit controls the opening of the damper so as to supply the amount of cooling air corresponding to the load of the boiler to the burners that are not generating flames. In this way, the amount of cooling air supplied can be adjusted simply by controlling the opening of the damper. Therefore, the amount of cooling air can be easily adjusted.

[0071] Furthermore, the boiler system according to a fourth aspect of the present disclosure is the boiler system of any of the first to third aspects, further comprising an air amount detection unit (35a) that detects an amount of air supplied to the burner (21), and the control unit (50) controls the adjustment unit (30d) on the basis of the amount of air detected by the air amount detection unit (35a).

[0072] In the above configuration, the control unit controls the adjustment unit based on the amount of air detected by the air amount detection unit. This makes it possible to more accurately adjust the amount of cooling air supplied to the burners that are not forming a flame to an amount that corresponds to the boiler load. Therefore, it is possible to more accurately adjust the ratio of the amount of cooling air to the total amount of air to a ratio that corresponds to the boiler load.

[0073] In addition, a boiler system according to a fifth aspect of the present disclosure, in any one of the first to fourth aspects, includes a plurality of mills (31) capable of supplying air or a mixture of pulverized solid fuel and air to a specific burner (21) via the air supply unit, and the control unit (50) controls the adjustment unit (30d) to stop the supply of solid fuel from the mill (31) to the burner (21) that does not form a flame, and to supply cooling air from the mill (31) in an amount corresponding to the load of the boiler (10).

[0074] In the above configuration, the control unit stops the supply of solid fuel from the mill to the burners that do not form a flame, and controls the adjustment unit to supply air from the mill in an amount corresponding to the boiler load. This allows cooling air to be supplied to the burners that do not form a flame in the boiler to which solid fuel is supplied from the mill, thereby suppressing damage to the burners due to radiant heat. In addition, the amount of cooling air supplied to the burners that do not form a flame can be set to an amount corresponding to the boiler load. Therefore, the ratio of the amount of cooling air to the total amount of air can be more accurately set to a ratio corresponding to the boiler load.

[0075] Further, in the boiler system according to a sixth aspect of the present disclosure, in the above-mentioned fifth aspect, the load of the boiler (10) is the amount of solid fuel supplied to the boiler (10).

[0076] In the above configuration, the load of the boiler is the amount of solid fuel supplied to the mill, so that the amount of cooling air corresponding to the amount of solid fuel supplied to the mill can be supplied to the burners that are not forming a flame.

[0077] In addition, in the boiler system according to a seventh aspect of the present disclosure, in the above-mentioned fifth or sixth aspect, the control unit (50) controls the adjustment unit (30d) to supply cooling air in an amount corresponding to the type of solid fuel supplied to the boiler (10) when supplying cooling air to the burner (21) that is not forming a flame.

[0078] Since the fuel ratio (ease of combustion) differs depending on the type of solid fuel, the temperature of the boiler furnace changes depending on the type of solid fuel supplied to the boiler. Therefore, the radiant heat to the burner also changes depending on the type of solid fuel. Therefore, the amount of cooling air required to cool the burner that is not forming a flame also changes depending on the type of solid fuel. In the above configuration, the control unit controls the adjustment unit to supply an amount of cooling air according to the type of solid fuel supplied to the boiler. This makes it possible to adjust the amount of cooling air supplied to the burner that is not forming a flame to an amount according to the type of solid fuel. Therefore, the ratio of the amount of cooling air to the total amount of air can be adjusted to a ratio according to the type of solid fuel.

[0079] A power plant according to a first aspect of the present disclosure includes a boiler system (2) described in any one of the first to seventh aspects, and a power generation section that generates power using steam generated in the boiler system (2).

[0080] In a first aspect of the present disclosure, a method for operating a boiler system includes a boiler system (2) including a boiler (10) having a plurality of burners (21), an air supply unit that supplies air to the burners (21), and an adjustment unit (30d) that adjusts the amount of air supplied to the burners (21) by the air supply unit, and includes a control step of controlling the adjustment unit (30d) to supply an amount of cooling air corresponding to a load of the boiler (10) when cooling air is supplied by the air supply unit to the burners (21) that are not forming a flame. [Explanation of symbols]

[0081] 1: Power plant 2: Boiler system 10: Boiler 11: Furnace 12: Combustion gas passage 13: Flue 20: Combustion equipment 21: Burna 21A: Burner 21B: Burner 21C: Burner 21D: Burner 21E: Burner 21F: Burner 22:Powdered fuel supply pipe 22A: Fine powder fuel supply pipe 22B: Fine powder fuel supply pipe 22C: Fine powder fuel supply pipe 22D: Fine powder fuel supply pipe 22E: Fine fuel supply pipe 22F: Fine powder fuel supply pipe 23: Wind box 24: Wind road 30: Blower section 30a: Hot gas flow path 30b: Cold gas flow path (air piping) 30c: Thermal gas damper 30d: Cold gas damper (adjustment part) 30e: Hot gas gate valve 30f: Cold gas gate valve 31: Mill 31a: Fuel supply section 32: Forced ventilation fan 33: Primary air ventilator 35: Primary air passage 35a: Flow meter (air volume detection section) 41: Gas duct 42: Air preheater 43: Denitration equipment 44: Equipment 45: Induced draft fan 46: Desulfurization equipment 47: Chimney 50: Control section 101: Furnace wall 102:Superheater 102A :Superheater 102B :Superheater 102C :Superheater 103: Reheater 103A : Reheater 103B : Reheater 104: Carbon saver

Claims

1. A boiler having a plurality of burners; an air supply unit that supplies air to the burner; an adjustment unit that adjusts the amount of air supplied to the burner by the air supply unit; A boiler system comprising: a control unit that controls the adjustment unit so as to supply an amount of cooling air corresponding to the load of the boiler when the air supply unit supplies cooling air to the burner that is not forming a flame.

2. 2. The boiler system according to claim 1, wherein the control unit controls the adjustment unit so that the amount of cooling air supplied to the burner that is not forming a flame decreases as the load of the boiler decreases.

3. The air supply unit has an air pipe that conveys air to the burner, The adjustment unit has a damper that is provided in the air piping and adjusts the amount of air flowing through the air piping by changing an opening degree of the damper, 2. The boiler system according to claim 1, wherein the control unit controls an opening degree of the damper so as to supply cooling air to the burners not forming a flame in an amount corresponding to a load of the boiler.

4. an air amount detection unit that detects the amount of air supplied to the burner, The boiler system according to claim 1 , wherein the control unit controls the adjustment unit based on the amount of air detected by the air amount detection unit.

5. a plurality of mills capable of supplying air or a mixture of pulverized solid fuel and air to specific burners via the air supply; The boiler system according to claim 1, wherein the control unit stops the supply of solid fuel from the mill to the burner that is not forming a flame, and controls the adjustment unit to supply cooling air from the mill in an amount corresponding to the load of the boiler.

6. The boiler system according to claim 5 , wherein the load of the boiler is an amount of solid fuel supplied to the boiler.

7. The boiler system according to claim 5, wherein the control unit controls the adjustment unit so as to supply an amount of cooling air corresponding to the type of solid fuel supplied to the boiler when supplying cooling air to the burner that is not forming a flame.

8. A boiler system according to any one of claims 1 to 7, a power generation unit that generates electricity using the steam generated in the boiler system.

9. 1. A method for operating a boiler system, comprising: The boiler system includes: A boiler having a plurality of burners; an air supply unit that supplies air to the burner; an adjustment unit that adjusts the amount of air supplied to the burner by the air supply unit, A method for operating a boiler system comprising a control step of controlling the adjustment unit so as to supply an amount of cooling air corresponding to the load of the boiler when the air supply unit supplies cooling air to the burner that is not forming a flame.

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