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

Abstract

To improve energy efficiency of the whole system.SOLUTION: A boiler system 2 includes: a boiler 10 having a first burner 21A burning a first solid fuel, a second burner 21B burning a second solid fuel, and a wind box 23 for supplying the first burner 21A and the second burner 21B with air; a first mill 31A pulverizing the first solid fuel; a second mill 31B pulverizing the second solid fuel; an air preheater 42 performing heat exchange between exhaust gas exhausted by the boiler 10 and the air; a heat gas flow passage 30a guiding the air heated by the air preheater 42 to the first mill 31A and the second mill 31B; a secondary air supply line 24 for guiding the air heated by the air preheater 42 to the wind box 23; a branch flow passage 51 branched from the heat gas flow passage 30a; a damper 51a adjusting an amount of the air circulating in the branch flow passage 51; an exhaust gas thermometer 14 for detecting outlet temperature of the exhaust gas; and a control part for controlling the damper 51a on the basis of the exhaust gas temperature detected by the exhaust gas thermometer 14.SELECTED DRAWING: Figure 1

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] 2. Description of the Related Art Boilers that burn solid fuel (eg, coal) in a furnace to generate steam are known (eg, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 1-111925 Summary of the Invention [Problem to be solved by the invention]

[0004] In a boiler designed to use a specific solid fuel as fuel, such as the boiler described in Patent Document 1, the specific solid fuel may be mixed with another solid fuel having a different moisture content. In such a case, the amount of combustion of the specific solid fuel is reduced, and the amount of combustion of the other solid fuel is increased accordingly. If the moisture content of the other solid fuel is low, the amount of heat required for drying is less than that of the specific solid fuel. This may cause a deterioration in the heat absorption balance in an air heater (air preheater) that recovers exhaust heat from the exhaust gas, and the exhaust heat may not be sufficiently recovered by the air heater, resulting in a rise in the exhaust gas temperature at the outlet of the air heater.

[0005] As the co-firing ratio changes (the co-firing ratio of other solid fuels increases), the amount of conveying gas (primary air) supplied to the first mill, which pulverizes and dries the specified solid fuel, decreases, and the amount of conveying gas (primary air) supplied to the second mill, which pulverizes and dries the other solid fuel, increases accordingly. As described above, when the moisture content of the other solid fuel is low, the temperature of the conveying gas supplied to the second mill is lower than the temperature of the conveying gas supplied to the first mill. In this way, when the other solid fuel with a low moisture content is supplied to the second mill, the heat value of the entire conveying gas is lower than when the specified solid fuel is supplied to both the first and second mills. In this way, the heat absorption imbalance in the air heater occurs because the heat amount of the air passing through the primary air system decreases and the heat amount of the air passing through the secondary air system increases accordingly. In other words, the heat amount that can be exchanged in the secondary air system is determined by the heat transfer area of ​​the system, so heat exchange beyond the determined heat amount is not possible. Therefore, if the heat amount of the secondary air increases more than expected, the secondary air system is unable to sufficiently recover the exhaust heat, resulting in a decrease in the outlet air temperature of the air heater and an increase in the outlet exhaust gas temperature of the air heater. Since the exhaust heat of the exhaust gas cannot be sufficiently recovered in this way, there is a possibility that the energy efficiency of the entire system will decrease.

[0006] In Patent Document 1, adjustment of the amount of air passing through the primary air system and the amount of air passing through the secondary air system is taken into consideration, but the energy efficiency of the entire system is not taken into consideration.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide a boiler system, a power generation plant, and a method for operating a boiler system that can improve the energy efficiency of the entire system. [Means for solving the problem]

[0008] 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 aspect of the present disclosure includes a boiler having a first burner that burns a first solid fuel, a second burner that burns a second solid fuel having a moisture content different from that of the first solid fuel, and a wind box that supplies air to the first burner and the second burner, a first pulverizer that pulverizes the first solid fuel that is supplied to the first burner, a second pulverizer that pulverizes the second solid fuel that is supplied to the second burner, an air heating unit that heats the air by performing heat exchange between an exhaust gas discharged from the boiler and the air, an air supply line that guides the air heated by the air heating unit to the first pulverizer and the second pulverizer, and the air supplied to the first pulverizer via the air supply line and the first solid fuel pulverized by the first pulverizer. the first solid fuel supply line supplying air to the first burner, a second solid fuel supply line supplying air supplied to the second pulverizer via the air supply line and the second solid fuel pulverized by the second pulverizer to the second burner, a secondary air supply line directing the air heated in the air heating section to the wind box, a branch line branching off from the air supply line, extracting a portion of the air heated in the air heating section circulating through the air supply line and merging the extracted air into the secondary air supply line, a flow rate adjustment section adjusting the amount of air circulating through the branch line, a temperature detection section detecting an amount of heat exchange in the air heating section, and a control section controlling the flow rate adjustment section based on the amount of heat exchange detected by the temperature detection section.

[0009] In a method for operating a boiler system according to one aspect of the present disclosure, the boiler system includes a boiler having a first burner that burns a first solid fuel, a second burner that burns a second solid fuel having a moisture content different from that of the first solid fuel, and a wind box that supplies air to the first burner and the second burner, a first pulverizer that pulverizes the first solid fuel to be supplied to the first burner, a second pulverizer that pulverizes the second solid fuel to be supplied to the second burner, an air heating unit that heats air by performing heat exchange between an exhaust gas discharged from the boiler and the air, an air supply line that guides the air heated by the air heating unit to the first pulverizer and the second pulverizer, the air supplied to the first pulverizer via the air supply line, and the first solid fuel pulverized by the first pulverizer. the first solid fuel supply line supplies solid fuel to the first burner, a second solid fuel supply line supplies air supplied to the second pulverizer via the air supply line and the second solid fuel pulverized by the second pulverizer to the second burner, a secondary air supply line guides the air heated in the air heating section to the wind box, and a branch line branches off from the air supply line, extracts a portion of the air heated in the air heating section that flows through the air supply line and merges the extracted air into the secondary air supply line, and further comprises a heat exchange amount detection process for detecting a heat exchange amount in the air heating section, and a flow rate adjustment process for adjusting the amount of air flowing through the branch line based on the heat exchange amount detected in the heat exchange amount detection process. Effect of the Invention

[0010] According to the present disclosure, the energy efficiency of the entire system can be improved. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram showing a boiler system according to an embodiment of the present disclosure. [Diagram 2] FIG. 1 is a block diagram showing a boiler system according to an embodiment of the present disclosure. [Diagram 3] FIG. 2 is a schematic configuration diagram showing a boiler system according to a comparative example of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 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.

[0013] 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.

[0014] 1 is a schematic configuration diagram showing a boiler system 2 of this embodiment. The boiler system 2 includes a boiler 10, a plurality of mills (pulverizers) 31 that pulverize solid fuel to be supplied to the boiler 10, a blower section 30 that supplies air (primary air) to the mills 31, a secondary air supply line 24 that supplies secondary air to the boiler 10, and a branch flow path (branch line) 51 that extracts a portion of the air to be supplied to the mills 31 and merges the extracted air with the secondary air supply line 24.

[0015] The boiler 10 of this embodiment is a boiler that can burn pulverized fuel made by pulverizing multiple types of solid fuels with different moisture contents (e.g., a first solid fuel and a second solid fuel with a lower moisture content than the first solid fuel) using a burner and generate steam by exchanging heat generated by this combustion with feed water or steam. An example of the first solid fuel is coal, and an example of the second solid fuel is biomass fuel. Note that the first solid fuel and the second solid fuel are not limited to coal and biomass fuel.

[0016] The boiler 10 generates steam by exchanging heat between a combustion gas generated in a furnace (not shown) and feed water in a heat exchanger. The boiler 10 has a furnace (not shown) and a plurality of burners (including a first burner 21A and a second burner 21B. Hereinafter, they may be collectively referred to as "burners"). The burners are arranged at equal intervals along the circumferential direction of the furnace as one set, and are arranged in a plurality of stages along the vertical direction. For convenience of illustration, only one each of the first burner 21A and the second burner 21B is shown in FIG. 1. The shape of the furnace, the number of burner stages, the number of burners in one stage, the arrangement of the burners, and the like are not limited to this embodiment.

[0017] The first burner 21A is connected to a first mill 31A via a first pulverized fuel supply pipe 22A. The first burner 21A burns a first solid fuel (for example, coal) dried and pulverized in the first mill 31A as fuel.

[0018] The second burner 21B is connected to the second mill 31B via a second pulverized fuel supply pipe 22B. The second burner 21B burns the second solid fuel (for example, biomass fuel) dried and pulverized by the second mill 31B as fuel.

[0019] An air box 23 is provided outside the furnace at the mounting position of the first burner 21A and the second burner 21B. One end of a secondary air supply line 24 is connected to the air box 23. The air box 23 supplies air (secondary air) to all burners including the first burner 21A and the second burner 21B. A forced draft fan (FDF: Forced Draft Fan) 32 is connected to the other end of the secondary air supply line 24. The air supplied from the forced draft fan 32 is heated by an air preheater 42 installed in the secondary air supply line 24 (details will be described later), and is supplied as secondary air (combustion air, oxidizing gas) to the first burner 21A and the second burner 21B via the air box 23 and is introduced into the furnace. The amount of secondary air supplied to the air box 23 is determined according to the amount of air used by all burners. A secondary air thermometer (air outlet temperature detection unit) 24a that detects the temperature of the air (secondary air) discharged from the air preheater 42 is provided on the secondary air supply line 24 downstream of the air preheater 42.

[0020] The boiler 10 is connected to a flue 13 through which the combustion gas (hereinafter, sometimes referred to as "exhaust gas") whose heat has been recovered by a heat exchanger (not shown) is discharged. An air preheater 42 is provided in the flue 13. The air preheater 42 exchanges heat between the air flowing through the hot gas flow passage 30a (air supply line) and the secondary air supply line 24 of the blower section 30 and the combustion gas (exhaust gas) flowing through the flue 13. By performing this heat exchange, the air preheater 42 heats the primary air supplied to the mill 31 and the secondary air supplied to the first burner 21A and the second burner 21B, thereby recovering further heat from the combustion gas after heat exchange with water and steam.

[0021] The air preheater 42 has a first heat exchange section 42a into which air (primary air) flowing through the hot gas flow path 30a is introduced, and a second heat exchange section 42b into which air (secondary air) flowing through the secondary air supply line 24 is introduced.

[0022] The first heat exchanger 42a and the second heat exchanger 42b are each defined to have an upper limit of heat exchangeable therethrough. The upper limit of heat is defined, for example, based on the flow area of ​​the gas flowing through each heat exchanger. In the boiler system 2 according to the present embodiment, the upper limit of heat is defined for each heat exchanger in accordance with the amount of primary air and the amount of secondary air required when only solid fuel is burned in the boiler 10. That is, the first heat exchanger 42a and the second heat exchanger 42b are configured so that the total amount of heat exchanged in the first heat exchanger 42a and the second heat exchanger 42b is maximized for the amount of primary air and the amount of secondary air. The amount of primary air that is the upper limit of heat in the first heat exchanger 42a is, for example, 40% of the amount of hot air (the sum of the amount of primary air and the amount of secondary air) supplied to the boiler 10. The amount of secondary air that is the upper limit of heat in the second heat exchanger 42b is, for example, 60% of the amount of hot air (the sum of the amount of primary air and the amount of secondary air) supplied to the boiler 10.

[0023] A gas duct 41 is connected to the flue 13 downstream of the air preheater 42. The gas duct 41 is provided with an exhaust gas thermometer (exhaust gas outlet temperature detection unit) 14 that measures the temperature of the exhaust gas flowing inside. The downstream end of the gas duct 41 is connected to a chimney (not shown), and the exhaust gas treated by the environmental equipment is discharged to the outside of the system.

[0024] The first mill 31A and the second mill 31B have substantially the same configuration, so the following description will be given of the configuration of the first mill 31A as a representative. The first mill 31A is, for example, a vertical roller mill in which a grinding table (not shown) is supported inside so as to be driven and rotatable, and a plurality of grinding rollers (not shown) are supported above the grinding table so as to be rotatable in conjunction with the rotation of the grinding table. The first solid fuel that has been pulverized by the cooperation of the grinding rollers and the grinding table is transported to a classifier (not shown) provided in the first mill 31A by primary air (carrier gas, oxidizing gas) supplied to the first mill 31A. The classifier classifies the fuel into fine pulverized fuel having a particle size equal to or smaller than that suitable for combustion in the first burner 21A and coarse pulverized fuel having a particle size larger than the particle size. The fine pulverized fuel passes through the classifier and is supplied to the first burner 21A together with the primary air via the first fine pulverized fuel supply pipe 22A. The coarse pulverized fuel that has not passed through the classifier falls onto the grinding table by its own weight inside the first mill 31A and is re-pulverized.

[0025] The blower 30 is a device that blows primary air into the first mill 31A and the second mill 31B to dry and transport the pulverized fuel. The amount of primary air supplied to the boiler 10 is determined according to the amount of air used in the first burner 21A and the second burner 21B. In this embodiment, the blower section 30 is equipped with a primary air fan (PAF) 33, a hot gas flow path (air supply line) 30a, and a cold gas flow path 30b in order to appropriately adjust the flow rate and temperature of the primary air blown into the inside of the first mill 31A and the second mill 31B.

[0026] 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 to the first mill 31A and the second mill 31B as hot gas heated by passing through the air preheater 42. The hot gas heated by the air preheater 42 is also guided to the other mills 31 via the hot gas passage 30a.

[0027] The cold gas passage 30b also supplies a portion of the air sent out from the primary air fan 33 as cold gas at room temperature to the first mill 31A and the second mill 31B. The cold gas sent out from the primary air fan 33 is also guided to the other mills 31 via the cold gas passage 30b.

[0028] In addition, in order to appropriately adjust the flow rate and temperature of the primary air blown into the inside of the first mill 31A, the blower section 30 is equipped with a first hot gas flow path 30aA branching off from the downstream side of the air preheater 42 of the hot gas flow path 30a, a first cold gas flow path 30bA branching off from the cold gas flow path 30b, a first hot gas damper 30cA provided in the first hot gas flow path 30aA, and a first cold gas damper 30dA provided in the first cold gas flow path 30bA.

[0029] The first hot gas passage 30aA guides a portion of the hot gas flowing through the hot gas passage 30a to the first mill 31A. The first hot gas damper 30cA adjusts the flow rate of the hot gas flowing through the first hot gas passage 30aA by changing the opening degree. The opening degree of the first hot gas damper 30cA is controlled by the control unit 60.

[0030] The first cold gas passage 30bA guides a portion of the cold gas flowing through the cold gas passage 30b to the first mill 31A. The first cold gas damper 30dA adjusts the flow rate of the cold gas flowing through the first cold gas passage 30bA by changing the opening degree. The opening degree of the first cold gas damper 30dA is controlled by the control unit 60.

[0031] The first hot gas flow path 30aA and the first cold gas flow path 30bA join at the downstream end to form a first primary air flow path 35A. The flow rate of the primary air supplied to the first mill 31A (i.e., the amount of air flowing through the first primary air passage 35A) is the sum of the flow rate of the hot gas supplied from the first hot gas passage 30aA and the flow rate of the cold gas supplied from the first cold gas passage 30bA, and the temperature of the primary air is determined by the mixture ratio of the hot gas supplied from the first hot gas passage 30aA and the cold gas supplied from the first cold gas passage 30bA. In other words, the flow rate and temperature of the primary air supplied to the first mill 31A are controlled by the control unit 60.

[0032] In addition, in order to appropriately adjust the flow rate and temperature of the primary air blown into the inside of the second mill 31B, the blower section 30 is equipped with a second hot gas flow path 30aB branching off from the downstream side of the air preheater 42 of the hot gas flow path 30a, a second cold gas flow path 30bB branching off from the cold gas flow path 30b, a second hot gas damper 30cB provided in the second hot gas flow path 30aB, and a second cold gas damper 30dB provided in the second cold gas flow path 30bB.

[0033] The second hot gas passage 30aB guides a portion of the hot gas flowing through the hot gas passage 30a to the second mill 31B. The second hot gas damper 30cB adjusts the flow rate of the hot gas flowing through the second hot gas passage 30aB by changing the opening degree. The opening degree of the second hot gas damper 30cB is controlled by the control unit 60.

[0034] The second cold gas passage 30bB guides a portion of the cold gas flowing through the cold gas passage 30b to the second mill 31B. The second cold gas damper 30dB adjusts the flow rate of the cold gas flowing through the second cold gas passage 30bB by changing the opening degree. The opening degree of the second cold gas damper 30dB is controlled by the control unit 60.

[0035] The second hot gas flow path 30aB and the second cold gas flow path 30bB join at the downstream end to form a second primary air flow path 35B. The flow rate of the primary air supplied to the second mill 31B (i.e., the amount of air flowing through the second primary air passage 35B) is the sum of the flow rate of the hot gas supplied from the second hot gas passage 30aB and the flow rate of the cold gas supplied from the second cold gas passage 30bB, and the temperature of the primary air is determined by the mixture ratio of the hot gas supplied from the second hot gas passage 30aB and the cold gas supplied from the second cold gas passage 30bB. In other words, the flow rate and temperature of the primary air supplied to the second mill 31B are controlled by the control unit 60.

[0036] The branch passage 51 guides a portion of the air heated by the air preheater 42 to the secondary air supply line 24. The branch passage 51 connects the hot gas passage 30a upstream of the branch position of the first hot gas passage 30aA to the secondary air supply line 24. The branch passage 51 is provided with a damper (flow rate regulator) 51a that regulates the flow rate of air flowing through the branch passage 51. The opening degree of the damper 51a is controlled by the controller 60.

[0037] The control unit 60 may, for example, control the blowing volume of the forced draft fan 32 and the primary air fan 33 and the opening degree of the damper 51a so that the balance of the flow rate between the air (primary air) passing through the air preheater 42 and the secondary air is the same as when only the first solid fuel (coal, etc.) is burned in the boiler 10. 2, for example, the control unit 60 may control the airflow rates of the forced draft fan 32 and the primary air fan 33 and the opening degree of the damper 51a based on the temperature of the exhaust gas discharged from the air preheater 42 measured by the exhaust gas thermometer 14. The airflow rates of the forced draft fan 32 and the primary air fan 33 and the opening degree of the damper 51a may be adjusted manually.

[0038] Furthermore, the control unit 60 may derive the amount of heat exchange in the air preheater 42 based on the temperature of the exhaust gas detected by the exhaust gas thermometer 14. Furthermore, the control unit 60 may control the opening degree of the damper 51a based on the derived amount of heat exchange.

[0039] The control unit 60 (Controller) includes, for example, a CPU (Central Processing Unit: Processor), a main memory, a secondary storage, etc. Furthermore, the control unit 60 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.

[0040] Next, the behavior of the boiler system 2 according to this embodiment will be described. Air adjusted to a predetermined amount and temperature is introduced as primary air into the first mill 31A and the second mill 31B by the blower 30. The blower 30 mixes air flowing through the first hot gas passage 30aA with air flowing through the first cold gas passage 30bA to generate primary air of a predetermined amount and temperature (for example, about 280°C in this embodiment) and supplies the generated primary air to the first mill 31A. Similarly, the blower section 30 mixes the air flowing through the second hot gas flow path 30aB with the air flowing through the second cold gas flow path 30bB to generate primary air of a predetermined amount and temperature (in this embodiment, for example, approximately 150°C), and supplies the generated primary air to the second mill 31B.

[0041] When the first mill 31A is driven, the pulverized and classified pulverized fuel (first solid fuel) is supplied to the first burner 21A together with the primary air through the first pulverized fuel supply pipe 22A. The temperature of the primary air at this time is about 80°C. Secondary air (for example, about 300°C in this embodiment) heated by the air preheater 42 is supplied to the first burner 21A from the secondary air supply line 24 through the wind box 23. The first burner 21A blows a pulverized fuel mixture, which is a mixture of the pulverized fuel and the primary air, into the furnace, and also blows secondary air into the furnace. The pulverized fuel mixture blown into the furnace is ignited and reacts with the secondary air to form a flame. Similarly, when the second mill 31B is driven, the pulverized and classified pulverized fuel (second solid fuel) is supplied to the second burner 21B together with the primary air through the second pulverized fuel supply pipe 22B. The temperature of the primary air at this time is about 80°C. Secondary air (for example, about 300°C in this embodiment) heated by the air preheater 42 is supplied to the second burner 21B from the secondary air supply line 24 through the wind box 23. The second burner 21B blows the pulverized fuel mixture, which is a mixture of the pulverized fuel and the primary air, into the furnace, and also blows the secondary air into the furnace. The pulverized fuel mixture blown into the furnace is ignited and reacts with the secondary air to form a flame.

[0042] A part of the air flowing through the hot gas flow path 30a is led to the secondary air supply line 24 via the branch flow path 51. The air led to the secondary air supply line 24 merges with the secondary air flowing through the secondary air supply line 24 and is led to the wind box 23 as secondary air.

[0043] When a flame is formed in the lower region of the furnace, the high-temperature combustion gas rises in the furnace and flows into a combustion gas passage (not shown) in the boiler. In this embodiment, air is used as the oxidizing gas (primary air, secondary air), but the oxidizing gas may have a higher or lower oxygen content than air, and stable combustion in the furnace can be achieved by adjusting the ratio of the amount of oxygen to the amount of fuel supplied within an appropriate range.

[0044] The combustion gas that flows into the combustion gas passage exchanges heat with water or steam in a heat exchanger (superheater, reheater, economizer, etc.) (not shown) arranged inside the combustion gas passage, and is then discharged into the flue 13, where it exchanges heat with air (primary air) and secondary air in the air preheater 42, and is then discharged into the gas duct 41 and then exhausted to the outside of the system from the chimney.

[0045] Next, the air flow rate and temperature of the boiler system 2 according to this embodiment will be described. As shown in FIG. 1, in this embodiment, primary air is supplied to the first burner 21A so that the amount of primary air is 20% of the amount of hot air (the sum of the amount of primary air and the amount of secondary air passing through the air preheater 42) supplied to the boiler 10. Primary air is supplied to the second burner 21B so that the amount of primary air is 5% of the amount of hot air supplied to the boiler 10. Secondary air is supplied to the wind box 23 so that the amount of secondary air is 75% of the amount of hot air supplied to the boiler 10. That is, the amount of primary air required by the first burner 21A is set to 20% of the amount of hot air. The amount of primary air required by the second burner 21B is set to 5% of the amount of hot air. The amount of secondary air required by the wind box 23 is set to 75% of the amount of hot air.

[0046] To the first heat exchange section 42a of the air preheater 42, 40% of the amount of hot air is supplied by the primary air fan 33 through the hot gas flow path 30a. The temperature of the air guided to the first heat exchange section 42a by the primary air fan 33 is set to, for example, about 30°C. To the second heat exchange section 42b, 60% of the amount of hot air is supplied by the forced draft fan 32 through the secondary air supply line 24. The temperature of the air guided to the second heat exchange section 42b by the forced draft fan 32 is set to, for example, about 30°C. In this manner, the first heat exchange section 42a and the second heat exchange section 42b are supplied with an amount of air that is the upper limit heat quantity. In other words, the first heat exchange section 42a and the second heat exchange section 42b are supplied with an amount of air that is the same as the amount of air that is supplied to the first heat exchange section 42a and the second heat exchange section 42b when only the first solid fuel is combusted in the boiler 10.

[0047] The air that has completed heat exchange in the first heat exchange section 42a is discharged from the air preheater 42 to the hot gas flow path 30a. The temperature of the air discharged to the hot gas flow path 30a is set to about 300° C. A part of the air discharged to the hot gas flow path 30a flows into the branch flow path 51. The remaining air that does not flow into the branch flow path 51 is guided to the first mill 31A and the second mill 31B. The temperature of the exhaust gas introduced into the air preheater 42 is about 350°C, and the temperature of the exhaust gas discharged from the air preheater 42 is about 150°C.

[0048] The amount of air flowing into the branch flow passage 51 is adjusted by adjusting the opening degree of the damper 51a. The amount of air flowing into the branch flow passage 51 is determined based on the amount of primary air supplied to the first burner 21A and the second burner 21B. Specifically, the opening degree of the damper 51a is controlled so that the amount of air guided to the first mill 31A and the second mill 31B is the same as the amount of primary air supplied to the first burner 21A and the second burner 21B. In this embodiment, since the total amount of primary air supplied to the first burner 21A and the second burner 21B is 25% of the amount of hot air, the opening degree of the damper 51a is controlled so that the amount of air flowing into the branch flow passage 51 is 15% of the amount of hot air. In this way, by controlling the opening degree of the damper 51a, the amount of primary air that is 25% of the amount of hot air is guided to the first mill 31A and the second mill 31B. In addition, by controlling the opening of the first hot gas damper 30cA and the second hot gas damper 30cB, 20% of the amount of hot air is introduced to the first mill 31A, and 5% of the amount of hot air is introduced to the second mill 31B. At this time, the temperature of the primary air supplied to the first mill 31A is set to about 280°C, and the temperature of the primary air supplied to the second mill 31B is set to about 150°C.

[0049] The entire amount of air introduced to the first mill 31A is introduced to the first burner 21A via the first pulverized fuel supply pipe 22A. In this way, 20% of the amount of hot air is introduced to the first burner 21A as primary air. The entire amount of air introduced to the second mill 31B is introduced to the second burner 21B via the second pulverized fuel supply pipe 22B. In this manner, 5% of the amount of hot air is introduced to the second burner 21B as primary air.

[0050] On the other hand, the air that has flowed into the branch flow passage 51 is guided to the secondary air supply line 24. Air that has completed heat exchange in the second heat exchange section 42b of the air preheater 42 (for example, at about 300°C in this embodiment) flows through the secondary air supply line 24. The amount of air flowing through the secondary air supply line 24 is 75% of the amount of hot air because a part of the primary air (for example, at about 300°C in this embodiment) joins through the branch flow passage 51. In this way, 75% of the amount of hot air is guided to the wind box 23 as secondary air (for example, at about 300°C in this embodiment).

[0051] According to this embodiment, the following advantageous effects are obtained. In this embodiment, a branch flow path 51 is provided which branches off from the hot gas flow path 30a, extracts a portion of the air heated by the air preheater 42 flowing through the hot gas flow path 30a, and merges the extracted air with the secondary air supply line 24. This makes it possible to heat the secondary air by utilizing the exhaust heat of the exhaust gas recovered by the air preheater 42. Therefore, it is possible to improve the energy efficiency of the entire boiler system 2 compared to a case in which the exhaust heat of the exhaust gas is not utilized.

[0052] In addition, in this embodiment, a branch flow passage 51 is provided that merges the air that has completed heat exchange in the air preheater 42 with the secondary air supply line 24. This allows the primary air to be guided to the secondary air system (secondary air supply line 24). Since the primary air can be guided to the secondary air system in this manner, the amount of primary air supplied to the first burner 21A and the second burner 21B and the amount of secondary air supplied to the wind box 23 can be adjusted. Therefore, regardless of the balance between the primary air and the secondary air in the air preheater 42, the amount of primary air supplied to the first burner 21A and the second burner 21B and the amount of secondary air supplied to the wind box 23 can be set to a desired amount. Therefore, since the balance between the primary air and the secondary air in the air preheater 42 can be set to a desired balance, the exhaust heat of the exhaust gas can be suitably recovered in the air preheater 42. Therefore, the energy efficiency of the entire boiler system 2 can be improved.

[0053] Furthermore, in this embodiment, a control unit 60 is provided that controls the damper 51a based on the amount of heat exchange detected by the exhaust gas thermometer 14. This makes it possible to adjust the amount of primary air led to the secondary air system based on the amount of heat exchange in the air preheater 42. Therefore, the balance between the primary air and the secondary air in the air preheater 42 can be set to a desired balance based on the amount of heat exchange in the air preheater 42, so that the exhaust heat of the exhaust gas can be suitably recovered in the air preheater 42. This makes it possible to improve the energy efficiency of the entire boiler system 2.

[0054] Furthermore, the temperature of the exhaust gas discharged from the air preheater 42 changes depending on the amount of heat exchanged in the air preheater 42. Therefore, by detecting the temperature of the exhaust gas discharged from the air preheater 42, the amount of heat exchanged in the air preheater 42 can be detected. In this embodiment, the control unit 60 controls the damper 51a based on the temperature of the exhaust gas detected by the exhaust gas thermometer 14. This allows the air preheater 42 to suitably recover the exhaust heat of the exhaust gas. This improves the energy efficiency of the entire boiler system 2.

[0055] Next, the utilization of exhaust heat in the boiler system 2 according to this embodiment will be described in comparison with the temperatures of the air and exhaust gas in the boiler system 2 according to a comparative example shown in FIG. The boiler system 2 according to the comparative example differs from the boiler system 2 according to the present embodiment in that it is not provided with a branch passage 51. Other points are the same as those in the boiler system 2 according to the present embodiment, and therefore in Fig. 3, the same components as those in Fig. 1 are denoted by the same reference numerals as those in Fig. 1.

[0056] As shown in FIG. 1, in the boiler system 2 according to this embodiment, as described above, the first heat exchanger 42a and the second heat exchanger 42b are supplied with air in an amount that is the upper limit heat amount. That is, the first heat exchanger 42a is supplied with air in an amount that is 40% of the amount of hot air. The second heat exchanger 42b is supplied with air in an amount that is 60% of the amount of hot air. This allows the first heat exchanger 42a and the second heat exchanger 42b to recover the exhaust heat of the exhaust gas to the maximum extent. This allows the temperature of the air discharged from the first heat exchanger 42a and the second heat exchanger 42b to be 300°C. The exhaust gas discharged from the air preheater 42 is cooled to 150°C. In this way, the boiler system 2 according to this embodiment can sufficiently recover the exhaust heat of the exhaust gas.

[0057] On the other hand, as shown in Fig. 3, the boiler system 2 according to the comparative example cannot guide the primary air to the secondary air system, so the amount of air supplied to the first heat exchanger 42a and the second heat exchanger 42b is restricted by the required amount of primary air and secondary air. Therefore, the first heat exchanger 42a is supplied with an amount of air less than the upper limit of heat (specifically, 25% of the amount of hot air). The second heat exchanger 42b is supplied with an amount of air greater than the upper limit of heat (specifically, 75% of the amount of hot air). As a result, the second heat exchange section 42b cannot sufficiently recover the exhaust heat of the exhaust gas, so the temperature of the air discharged from the second heat exchange section 42b is set to about 280°C, which is lower than in this embodiment. Also, the temperature of the exhaust gas discharged from the air preheater 42 is set to about 160°C, which is higher than in this embodiment.

[0058] As described above, it is found that the boiler system 2 according to the comparative example is unable to sufficiently recover the exhaust heat of the exhaust gas, and the energy efficiency of the entire boiler system 2 is poor, compared to the boiler system 2 according to this embodiment.

[0059] 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.

[0060] In the above embodiment, the downstream end of the branch passage 51 is connected to the secondary air supply line 24, but the present disclosure is not limited to this. For example, the downstream end of the branch passage 51 may be connected to the wind box 23. Also, the downstream end of the branch passage 51 may be connected to the air register of each burner.

[0061] In the above embodiment, the control unit 60 controls the airflow rates of the forced draft fan 32 and the primary air fan 33 and the opening degree of the damper 51a based on the temperature of the exhaust gas discharged from the air preheater 42 measured by the exhaust gas thermometer 14, but the present disclosure is not limited to this. For example, the control unit 60 may control the airflow rates of the forced draft fan 32 and the primary air fan 33 and the opening degree of the damper 51a based on the temperature of the secondary air discharged from the air preheater 42 measured by the secondary air thermometer 24a. The temperature of the air discharged from the air preheater 42 changes depending on the amount of heat exchange in the air preheater 42. Therefore, the amount of heat exchange in the air preheater 42 can be detected by detecting the temperature of the air discharged from the air preheater 42. Therefore, the control unit 60 can suitably recover exhaust heat of the exhaust gas in the air preheater 42 by controlling the opening degree of the damper 51a, etc., based on the temperature of the secondary air.

[0062] Furthermore, the control unit 60 may control the airflow rates of the forced draft fan 32 and the primary air fan 33 and the opening degree of the damper 51a based on the opening degrees of the first cold gas damper 30dA and the second cold gas damper 30dB. The temperature of the air (hereinafter referred to as "hot air") discharged from the air preheater 42 changes depending on the amount of heat exchange in the air preheater 42. The temperature of the primary air led to each mill is determined based on the amount of hot air and the amount of cold air, so that the temperature of the primary air led to each mill is a predetermined temperature, the flow rate of the cold air is also changed by changing the opening degree of each cold gas damper according to the temperature of the air discharged from the air preheater 42. In this way, the opening degree of the first cold gas damper 30dA and the second cold gas damper 30dB is determined according to the heat amount of the hot air, so that the heat exchange amount in the air heating section can be detected from the opening degree of the first cold gas damper 30dA and the second cold gas damper 30dB. Therefore, the control unit 60 can appropriately recover the exhaust heat of the exhaust gas in the air preheater 42 by controlling the opening degree of the damper 51a based on the opening degree of the first cold gas damper 30dA and the second cold gas damper 30dB.

[0063] 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 first burner (21A) that burns a first solid fuel, a second burner (21B) that burns a second solid fuel having a moisture content different from that of the first solid fuel, and a wind box (23) that supplies air to the first burner (21A) and the second burner (21B), a first crusher (31A) that crushes the first solid fuel to be supplied to the first burner (21A), and a wind box (23) that crushes the second solid fuel to be supplied to the second burner (21B). The present invention relates to a first solid fuel pulverizer (31A), a second pulverizer (31B), an air heating section (42) that heats air by exchanging heat between the exhaust gas discharged from the boiler (10) and the air, an air supply line (30a) that introduces the air heated by the air heating section (42) to the first pulverizer (31A) and the second pulverizer (31B), and a first solid fuel pulverizer (31B) that supplies the air supplied to the first pulverizer (31) through the air supply line (30a) and the first solid fuel pulverized by the first pulverizer (31) to the first burner (21A). a fuel supply line (22A), a second solid fuel supply line (22B) for supplying the air supplied to the second pulverizer (31B) through the air supply line (30a) and the second solid fuel pulverized by the second pulverizer (31B) to the second burner (21B); a secondary air supply line (24) for introducing the air heated by the air heating section (42) as secondary air to the wind box (23); the secondary air supply line (51); a flow rate adjusting unit (51a) adjusting the amount of air flowing through the branch line; temperature detection units (14, 24a, 31dA, 31dB) detecting an amount of heat exchange in the air heating unit (42); and a control unit (60) controlling the flow rate adjusting unit (51a) on the basis of the amount of heat exchange detected by the temperature detection unit (14, 24a, 31dA, 31dB).

[0064] In the above configuration, a branch line is provided that branches off from the air supply line, extracts a portion of the air heated by the air heating unit that flows through the air supply line, and merges the extracted air into the secondary air supply line. This makes it possible to heat the secondary air using the exhaust heat of the exhaust gas recovered by the air heating unit. Therefore, the energy efficiency of the entire system can be improved compared to when the exhaust heat of the exhaust gas is not used.

[0065] In addition, the above configuration includes a branch line that merges the air that has completed heat exchange in the air heating section with the secondary air supply line. This allows the primary air to be guided to the secondary air system. Since the primary air can be guided to the secondary air system in this way, the amount of primary air supplied to the first burner and the second burner and the amount of secondary air supplied to the wind box can be adjusted. Therefore, regardless of the balance between the primary air and the secondary air in the air heating section, the amount of primary air supplied to the first burner and the second burner and the amount of secondary air supplied to the wind box can be set to a desired amount. Therefore, since the balance between the primary air and the secondary air in the air heating section can be set to a desired balance, the exhaust heat of the exhaust gas can be suitably recovered in the air heating section. Therefore, the energy efficiency of the entire system can be improved.

[0066] The above-mentioned configuration also includes a control unit that controls the flow rate adjustment unit based on the amount of heat exchange detected by the temperature detection unit. This makes it possible to adjust the amount of primary air led to the secondary air system based on the amount of heat exchange in the air heating unit. Therefore, the balance between the primary air and the secondary air in the air heating unit can be set to a desired balance based on the amount of heat exchange in the air heating unit, so that the exhaust heat of the exhaust gas can be suitably recovered in the air heating unit. This makes it possible to improve the energy efficiency of the entire system.

[0067] In addition, in the boiler system according to the first aspect of the present disclosure, the temperature detection unit has an exhaust gas outlet temperature detection unit (14) that detects the temperature of the exhaust gas discharged from the air heating unit (42), and the control unit (60) controls the flow rate adjustment unit (51 a) based on the temperature of the exhaust gas detected by the exhaust gas outlet temperature detection unit (14).

[0068] The temperature of the exhaust gas discharged from the air heating section changes depending on the amount of heat exchange in the air heating section. Therefore, the amount of heat exchange in the air heating section can be detected by detecting the temperature of the exhaust gas discharged from the air heating section. In the above configuration, the control unit controls the flow rate regulator based on the temperature of the exhaust gas detected by the exhaust gas outlet temperature detector. This allows the air heater to effectively recover the exhaust heat of the exhaust gas. This improves the energy efficiency of the entire system.

[0069] Furthermore, in a boiler system according to a third aspect of the present disclosure, in the above-described first or second aspect, the temperature detection unit has an air outlet temperature detection unit (24a) that detects the temperature of air discharged from the air heating unit (42), and the control unit (60) controls the flow rate adjustment unit (51a) on the basis of the air temperature detected by the air outlet temperature detection unit (24a).

[0070] The temperature of the air discharged from the air heating section varies depending on the amount of heat exchanged in the air heating section. Therefore, the amount of heat exchanged in the air heating section can be detected by detecting the temperature of the air discharged from the air heating section. In the above configuration, the control unit controls the flow rate regulator based on the air temperature detected by the air outlet temperature detector. This allows the air heater to effectively recover the exhaust heat from the exhaust gas. This improves the energy efficiency of the entire system.

[0071] Furthermore, a boiler system according to a fourth aspect of the present disclosure, in any one of the first to third aspects, includes a first cold air supply line (31bA) that guides cold air to the first pulverizer (31) and a second cold air supply line (30bB) that guides cold air to the second pulverizer (31B), the temperature detection unit has a first cold air quantity adjustment unit (31dA) that adjusts the flow rate of cold air flowing through the first cold air supply line (31bA) by adjusting its opening, and a second cold air quantity adjustment unit (30dB) that adjusts the flow rate of cold air flowing through the second cold air supply line (30bB) by adjusting its opening, and the control unit (60) controls the flow rate adjustment unit (51a) based on the openings of the first cold air quantity adjustment unit (31dA) and the second cold air quantity adjustment unit (30dB).

[0072] The temperature of the air discharged from the air heating section (hereinafter referred to as "hot air") changes depending on the amount of heat exchanged in the air heating section. The temperature of the primary air led to the pulverizer is determined based on the amount of hot air and the amount of cold air, so the flow rate of cold air is also changed by changing the opening of the cold air amount adjustment section according to the temperature of the air discharged from the air heating section so that the temperature of the primary air led to the pulverizer becomes a predetermined temperature. In this way, the opening of the cold air adjustment section is determined according to the heat amount of the hot air, so the amount of heat exchanged in the air heating section can be detected from the opening of the cold air adjustment section. In the above configuration, the control unit controls the flow rate adjustment unit based on the opening degree of the first cold air amount adjustment unit and the second cold air amount adjustment unit. This allows the air heating unit to effectively recover the exhaust heat of the exhaust gas. This improves the energy efficiency of the entire system.

[0073] A power plant according to a first aspect of the present disclosure includes a boiler system (2) according to any one of the first to fourth aspects, and a power generation section that generates power using steam generated in the boiler system (2).

[0074] In a method for operating a boiler system according to a first aspect of the present disclosure, the boiler system (2) includes a boiler (10) having a first burner (21A) that burns a first solid fuel, a second burner (21B) that burns a second solid fuel having a moisture content different from that of the first solid fuel, and a wind box (23) that supplies air to the first burner (21A) and the second burner (21B), and a first pulverizer (31A) that pulverizes the first solid fuel to be supplied to the first burner (21A). a second pulverizer (31B) for pulverizing the second solid fuel to be supplied to the second burner (21B); an air heating section (42) for heating air by performing heat exchange between the exhaust gas discharged from the boiler (10) and the air; an air supply line (30a) for introducing the air heated in the air heating section (42) to the first pulverizer (31A) and the second pulverizer (31B); a first solid fuel supply line (22) for supplying the first solid fuel pulverized by the pulverizer (31) to the first burner (21A); a second solid fuel supply line (26) for supplying air supplied to the second pulverizer via the air supply line (30a) and the second solid fuel pulverized by the second pulverizer to the second burner (21B); a secondary air supply line (24) for guiding the air heated by the air heating section (42) to the wind box (23); and a branch line (51) branching off from a supply line (30a), extracting a portion of the air heated in the air heating section (42) flowing through the air supply line (30a), and merging the extracted air into the secondary air supply line. The system further comprises a heat exchange amount detection step for detecting an amount of heat exchanged in the air heating section (42), and a flow rate adjustment step for adjusting the amount of air flowing through the branch line (51) on the basis of the amount of heat exchanged detected in the heat exchange amount detection step. [Explanation of symbols]

[0075] 1: Power plant 2: Boiler system 10: Boiler 13: Flue 14: Exhaust gas thermometer (exhaust gas outlet temperature detector) 21A: First burner 21B: Second burner 22A: 1st pulverized fuel supply pipe 22B:Second pulverized fuel supply pipe 23: Wind box 24: Secondary air supply line 24a: Secondary air thermometer (air outlet temperature detector) 30: Blower section 30a: Hot gas flow path 30aA: First hot gas passage 30aB: second hot gas passage 30b: Cold gas passage 30bA: First cold gas flow path (first cold air supply line) 30bB: Second cold gas flow path (second cold air supply line) 30cA: First hot gas damper 30cB: Second hot gas damper 30dA: 1st cold gas damper (1st cold air volume adjustment section) 30dB: Second cold gas damper (second cold air volume adjustment section) 31: Mill 31A: 1st mill 31B: 2nd Mill 32: Forced ventilation fan 33: Primary air ventilator 35A: First primary air passage 35B: Second primary air passage 41: Gas duct 42: Air preheater 42a: 1st heat exchange section 42b: Second heat exchange section 51: Branch flow path (flow rate control section) 51a: Damper 60: Control section

Claims

1. a boiler including a first burner for burning a first solid fuel, a second burner for burning a second solid fuel having a moisture content different from that of the first solid fuel, and a wind box for supplying air to the first burner and the second burner; a first pulverizer for pulverizing the first solid fuel to be supplied to the first burner; a second pulverizer for pulverizing the second solid fuel to be supplied to the second burner; an air heating section that heats the air by performing heat exchange between the exhaust gas discharged from the boiler and the air; an air supply line for guiding the air heated by the air heating unit to the first pulverizer and the second pulverizer; a first solid fuel supply line that supplies the air supplied to the first pulverizer through the air supply line and the first solid fuel pulverized by the first pulverizer to the first burner; a second solid fuel supply line that supplies the air supplied to the second pulverizer through the air supply line and the second solid fuel pulverized by the second pulverizer to the second burner; a secondary air supply line for guiding the air heated by the air heating unit to the wind box; a branch line that branches off from the air supply line, extracts a portion of the air that is heated by the air heating unit and flows through the air supply line, and merges the extracted air into the secondary air supply line; a flow rate adjusting unit that adjusts the amount of air flowing through the branch line; A temperature detection unit for detecting a heat exchange amount in the air heating unit; A control unit that controls the flow rate adjustment unit based on the amount of heat exchange detected by the temperature detection unit.

2. The temperature detection unit has an exhaust gas outlet temperature detection unit that detects the temperature of the exhaust gas discharged from the air heating unit, The boiler system according to claim 1 , wherein the control unit controls the flow rate adjustment unit based on the temperature of the exhaust gas detected by the exhaust gas outlet temperature detection unit.

3. The temperature detection unit has an air outlet temperature detection unit that detects the temperature of the air discharged from the air heating unit, The boiler system according to claim 1 , wherein the control unit controls the flow rate adjustment unit based on the air temperature detected by the air outlet temperature detection unit.

4. a first cold air supply line for conducting cold air to the first grinder; a second cold air supply line for directing cold air to the second grinder; the temperature detection unit includes a first cold air amount adjustment unit that adjusts a flow rate of cold air flowing through the first cold air supply line by adjusting an opening degree, and a second cold air amount adjustment unit that adjusts a flow rate of cold air flowing through the second cold air supply line by adjusting an opening degree, The boiler system according to claim 1 , wherein the control unit controls the flow rate adjustment unit based on opening degrees of the first cold air amount adjustment unit and the second cold air amount adjustment unit.

5. A boiler system according to any one of claims 1 to 4, a power generation unit that generates electricity using the steam generated in the boiler system.

6. 1. A method for operating a boiler system, comprising: The boiler system includes: a boiler including a first burner for burning a first solid fuel, a second burner for burning a second solid fuel, the second solid fuel being a solid fuel having a moisture content different from that of the first solid fuel, and a wind box for supplying air to the first burner and the second burner; a first pulverizer for pulverizing the first solid fuel to be supplied to the first burner; a second pulverizer for pulverizing the second solid fuel to be supplied to the second burner; an air heating section that heats the air by performing heat exchange between the exhaust gas discharged from the boiler and the air; an air supply line for guiding the air heated by the air heating unit to the first pulverizer and the second pulverizer; a first solid fuel supply line that supplies the air supplied to the first pulverizer through the air supply line and the first solid fuel pulverized by the first pulverizer to the first burner; a second solid fuel supply line that supplies the air supplied to the second pulverizer through the air supply line and the second solid fuel pulverized by the second pulverizer to the second burner; a secondary air supply line for guiding the air heated by the air heating unit to the wind box; a branch line that branches off from the air supply line, extracts a portion of the air that is heated by the air heating unit and flows through the air supply line, and merges the extracted air into the secondary air supply line; a heat exchange amount detection step of detecting a heat exchange amount in the air heating section; and a flow rate adjusting step of adjusting the amount of air flowing through the branch line based on the amount of heat exchange detected in the heat exchange amount detecting step.

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