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

Abstract

To improve the efficiency of a whole system.SOLUTION: A boiler system 2 comprises: a boiler 10 comprising a first burner 21A for burning a first fuel, a second burner 21B for burning a second fuel, and a wind box 23 for supplying air to the first burner 21A and the second burner 21B; a mill 31 for pulverizing the first fuel; an air heating part 42 for heating air by exchanging heat between exhaust gas discharged from the boiler 10 and the air; a hot gas flow passage 30a for guiding the air heated by the air heating part 42, to the mill 31; a pulverized fuel supply pipe 22 for supplying the air supplied to the mill 31, and the first fuel pulverized by the mill 31, to the first burner 21A; an ammonia fuel supply flow passage 26 for supplying the second fuel to the second burner 21B; a secondary air supply line 24 for guiding the air heated by the air heating part 42, to the wind box 23; and a fuel heating part 50 for extracting a portion of the air flowing through the hot gas flow passage 30a, and heating the second fuel to be supplied to the second burner 21B.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 boilers designed to use solid fuel as fuel, such as the boiler described in Patent Document 1, the solid fuel may be mixed with other fuels. In such cases, the amount of solid fuel burned is reduced, and the amount of fuel other than the solid fuel (hereinafter referred to as "other fuel") burned is increased accordingly. In such cases, the heat absorption balance in the air heater (air preheater) that recovers the exhaust heat of the exhaust gas deteriorates, and the air heater cannot sufficiently recover the exhaust heat, which may cause the exhaust gas temperature at the outlet of the air heater to rise.

[0005] This is because, with a change in the mixed-fuel ratio (an increase in the mixed-fuel ratio of other fuels), the amount of conveying gas (primary air) supplied to the mill that crushes and dries the solid fuel decreases, and the amount of air (secondary air) for combustion of other fuels increases accordingly. In detail, the heat absorption imbalance in the air heater occurs because the amount of air passing through the primary air system decreases and the amount of air passing through the secondary air system increases. In other words, the amount of heat that can be exchanged in the secondary air system is determined by the heat transfer area of ​​the system, so heat exchange cannot exceed the determined amount of heat. For this reason, if the amount of secondary air increases more than expected and the amount of primary air decreases, the secondary air system is unable to fully 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 fully 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 embodiment of the present disclosure includes a boiler having a first burner that burns a first fuel, a second burner that burns a second fuel, and a wind box that supplies air to the first burner and the second burner, a pulverizer that pulverizes the first fuel to be supplied to the first burner, an air heating unit that heats the air by exchanging heat between 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 pulverizer, a first fuel supply line that supplies the air supplied to the pulverizer via the air supply line and the first fuel pulverized by the pulverizer to the first burner, a second fuel supply line that supplies a second fuel to the second burner, a secondary air supply line that guides the air heated by the air heating unit to the wind box, and a fuel heating unit that extracts a portion of the air heated by the air heating unit that flows through the air supply line and heats a second fuel supplied to the second burner with the extracted air.

[0009] In one embodiment of the present disclosure, there is provided a method for operating a boiler system, the boiler system comprising: a boiler having a first burner that burns a first fuel, a second burner that burns a second fuel, and a wind box that supplies air to the first burner and the second burner; a pulverizer that pulverizes the first fuel to be supplied to the first burner; an air heating unit that heats the air by exchanging heat 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 pulverizer; a first fuel supply line that supplies the air supplied to the pulverizer via the air supply line and the first fuel pulverized by the pulverizer to the first burner; a second fuel supply line that supplies a second fuel to the second burner; and a secondary air supply line that guides the air heated by the air heating unit to the wind box, the boiler system further comprising a fuel heating step of extracting a portion of the air heated by the air heating unit that flows through the air supply line, and heating a second fuel supplied to the second burner with the extracted air. 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 a first embodiment of the present disclosure. [Diagram 2] 1 is a block diagram showing a boiler system according to a first embodiment of the present disclosure. [Diagram 3] FIG. 4 is a schematic configuration diagram showing a boiler system according to a second embodiment 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] [First embodiment] 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, an ammonia fuel supply passage 26 that supplies ammonia as fuel to the boiler 10, and a fuel heating section 50 that heats the ammonia fuel.

[0015] The boiler 10 of this embodiment is a boiler that can generate steam by burning pulverized fuel made by pulverizing solid fuel and ammonia with a burner and exchanging the heat generated by this combustion with feed water or steam. As the solid fuel, biomass fuel, coal, etc. are used. The ammonia fuel may be liquid or gas.

[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 the mill 31 via a pulverized fuel supply pipe 22. The first burner 21A burns solid fuel (first fuel) dried and pulverized by the mill 31 as fuel.

[0018] The second burner 21B is supplied with ammonia via an ammonia fuel supply passage 26. The second burner 21B burns ammonia (second fuel) 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 combustion gas (hereinafter, may be 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 passage 30a (air supply line) and the secondary air supply line 24 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 14 for measuring 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 mill 31 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 solid fuel pulverized by the cooperation of the grinding rollers and the grinding table is transported to a classifier (not shown) provided in the mill 31 by primary air (carrier gas, oxidizing gas) supplied to the mill 31. The classifier classifies the solid fuel into 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 pulverized fuel passes through the classifier and is supplied to the first burner 21A together with the primary air via the pulverized fuel supply pipe 22. The coarse pulverized fuel that does not pass through the classifier falls onto the grinding table by its own weight inside the mill 31 and is re-pulverized.

[0025] The blower 30 is a device that blows primary air for drying and transporting the pulverized fuel into the inside of the mill 31. The amount of primary air supplied to the boiler 10 is determined according to the amount of fuel used by the first burner 21A. 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 (air supply line) 30a, a cold gas flow path 30b, a hot gas damper 30c, and a cold gas damper 30d.

[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 as hot gas heated by passing through the air preheater 42. The hot gas passage 30a is provided with a hot gas damper 30c downstream of the air preheater 42. The opening degree of the hot gas damper 30c is controlled by the control unit 60. 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.

[0027] 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 damper 30d is provided in the cold gas flow path 30b. The opening degree of the cold gas damper 30d is controlled by the control unit 60. The flow rate of the 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.

[0028] 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 60.

[0029] The ammonia fuel supply passage 26 is connected to the second burner 21B. The ammonia fuel supply passage 26 guides ammonia fuel from an ammonia supplier (not shown) to the second burner 21B.

[0030] The fuel heating section 50 has a branch passage 51 branching off from the hot gas passage 30a of the blower section 30, and an ammonia heater 52 that performs heat exchange between the air flowing through the branch passage 51 and the second fuel flowing through the ammonia fuel supply passage 26.

[0031] The branch passage 51 guides a portion of the air heated by the air preheater 42 to the ammonia heater 52. The branch passage 51 connects the hot gas passage 30a and the ammonia heater 52. The branch passage 51 is provided with a damper 51a that adjusts the flow rate of air flowing inside the hot gas passage 30a. The opening degree of the damper 51a is controlled by the control unit 60.

[0032] The ammonia heater 52 exchanges heat between the air flowing through the branch flow passage 51 and the ammonia flowing through the ammonia fuel supply flow passage 26. The ammonia heater 52 heats the ammonia flowing through the ammonia fuel supply flow passage 26 by heat exchange with the air flowing through the branch flow passage 51. The air that has been heat exchanged in the ammonia heater 52 is guided to the secondary air supply line 24 via an air flow passage (air line) 53. The air flow passage 53 connects the ammonia heater 52 and the secondary air supply line 24.

[0033] The control unit 60 may, for example, control the opening degree of the damper 51a so that the balance of the flow rates of the air (primary air) and secondary air passing through the air preheater 42 is the same as when only solid fuel (coal, etc.) is burned in the boiler 10. Also, as shown in FIG. 2, for example, the control unit 60 may control the opening degree of the damper 51a so that the temperature of the exhaust gas discharged from the air preheater 42 measured by the exhaust gas thermometer 14 is equivalent to that when only solid fuel (coal, etc.) is burned in the boiler 10.

[0034] 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.

[0035] 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.

[0036] 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 mill 31 by the blower 30. The blower 30 mixes air flowing through the hot gas passage 30a with air flowing through the cold gas passage 30b to generate primary air of a predetermined amount and temperature. When the mill 31 is driven, the pulverized and classified pulverized fuel is supplied to the first burner 21A together with the primary air via the pulverized fuel supply pipe 22. Secondary air heated by the air preheater 42 is supplied to the first burner 21A from the secondary air supply line 24 via 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.

[0037] A portion of the air flowing through the hot gas flow passage 30a is guided to the ammonia heater 52 via the branch flow passage 51. The air guided to the ammonia heater 52 is cooled by heat exchange with the ammonia flowing through the ammonia fuel supply flow passage 26. The air that has completed the heat exchange in the ammonia heater 52 is guided to the secondary air supply line 24 via the air flow passage 53. The air guided to the secondary air supply line 24 is guided to the wind box 23 as secondary air.

[0038] In addition, ammonia fuel is supplied to the second burner 21B through the ammonia fuel supply passage 26. The ammonia fuel is heated by heat exchange with air flowing through the branch passage 51 in the ammonia heater 52. The heated ammonia fuel is supplied to the second burner 21B. In addition, secondary air heated by the air preheater 42 is supplied to the second burner 21B from the secondary air supply line 24 via the wind box 23. The second burner 21B blows ammonia fuel into the furnace and also blows secondary air into the furnace. The ammonia fuel blown into the furnace is ignited and reacts with the secondary air to form a flame.

[0039] 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.

[0040] 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.

[0041] Next, the air flow rate of the boiler system 2 according to this embodiment will be described. 1, in this embodiment, the amount of primary air supplied to the first burner 21A is determined according to the amount of fuel 31a, and is about 20% 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 supplied to the wind box 23 is about 80% of the amount of hot air supplied to the boiler 10.

[0042] The first heat exchange section 42a of the air preheater 42 is supplied with 40% of the amount of hot air through the hot gas flow path 30a. The second heat exchange section 42b is supplied with 60% of the amount of hot air through the secondary air supply line 24. That is, the first heat exchange section 42a and the second heat exchange section 42b are supplied with air in amounts that are their upper limit heat amounts. In other words, the first heat exchange section 42a and the second heat exchange section 42b are supplied with the same amount of air as the amount of air supplied to the first heat exchange section 42a and the second heat exchange section 42b when only solid fuel is burned in the boiler 10.

[0043] 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. 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 led to the mill 31.

[0044] The amount of air flowing into the branch passage 51 is adjusted by adjusting the opening of the damper 51a as described above. In this embodiment, the amount of air flowing into the branch passage 51 and the amount of air led to the mill 31 are both controlled to be 20% of the amount of hot air by adjusting the damper 51a.

[0045] The entire amount of air introduced to the mill 31 is introduced to the first burner 21A via the pulverized fuel supply pipe 22. In this manner, 20% of the amount of hot air is introduced to the first burner 21A as primary air.

[0046] On the other hand, the air that has flowed into the branch passage 51 is guided to the ammonia heater 52. In the ammonia heater 52, the air that has completed heat exchange with the ammonia fuel flows through an air passage 53 and merges with the secondary air supply line 24.

[0047] Air that has completed heat exchange in the second heat exchange section 42b of the air preheater 42 flows through the secondary air supply line 24. The amount of air flowing through the secondary air supply line 24 is 80% of the amount of hot air because the air that has completed heat exchange in the ammonia heater 52 joins the secondary air supply line 24. In this way, 80% of the amount of hot air is introduced to the wind box 23 as secondary air.

[0048] According to this embodiment, the following advantageous effects are obtained. As described above, in the boiler system 2 of the present embodiment, it is possible to supply air in an amount that is the upper limit heat quantity to the first heat exchange section 42a and the second heat exchange section 42b of the air preheater 42 while satisfying the required primary air quantity and secondary air quantity. In other words, it is possible to supply air in an amount that is the upper limit heat quantity to the first heat exchange section 42a and the second heat exchange section 42b of the air preheater 42, regardless of the required primary air quantity and secondary air quantity. This makes it possible to maximize the exhaust heat recovery efficiency in the air preheater 42, regardless of the required primary air quantity and secondary air quantity. In this way, the air preheater 42 can sufficiently recover the exhaust heat of the exhaust gas (i.e., the exhaust gas can be sufficiently cooled), so that the increase in the temperature of the exhaust gas discharged from the air preheater 42 to the gas duct 41 can be suppressed. This prevents a decrease in the thermal efficiency of the boiler system 2, and also prevents exhaust gas with a temperature above the upper limit from being led to equipment (e.g., a dust collection device (not shown) or a desulfurization device (not shown)) located downstream in the exhaust gas flow of the air preheater 42.

[0049] In addition, in this embodiment, the exhaust heat recovered by the air preheater 42 is utilized to heat the ammonia fuel in the ammonia heater 52. Therefore, compared to a case where the exhaust heat of the exhaust gas is not utilized, it is possible to improve the energy efficiency of the entire boiler system 2 while satisfying the required amounts of primary air and secondary air.

[0050] In addition, in this embodiment, an air flow path 53 is provided that guides the air that has completed heat exchange in the ammonia heater 52 to the secondary air supply line 24. 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 primary air supplied to the first burner 21A and the 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 the primary air supplied to the first burner 21A and the amount of the 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.

[0051] 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.

[0052] 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.

[0053] [Second embodiment] Next, a second embodiment of the present disclosure will be described with reference to Fig. 3. In this embodiment, the configuration of the fuel heating unit is different from that of the first embodiment. Since the other configurations are the same as those of the first embodiment, the same reference numerals are used for the similar configurations and detailed description thereof will be omitted.

[0054] In this embodiment, the downstream end of the branch passage 51 is connected to a fuel heating section (premixing section) 55 of the second burner 21B. Air heated by the air preheater 42 is directly supplied to the second burner 21B via the branch passage 51.

[0055] The second burner 21B is provided with a premixing section 55. The premixing section 55 mixes the supplied air and ammonia fuel. The second burner 21B sprays a mixed fluid obtained by mixing the air and ammonia fuel into the furnace.

[0056] According to this embodiment, the following advantageous effects are obtained. In the present embodiment, in the premixing section, the second fuel can be heated by utilizing the exhaust heat of the exhaust gas recovered in the air preheater 42. Therefore, the energy efficiency of the entire boiler system 2 can be improved compared to a case in which the exhaust heat of the exhaust gas is not utilized. Furthermore, when the second fuel is a liquid fuel, the second fuel is vaporized when the second fuel is supplied from the second burner 21B into the furnace of the boiler 10. Therefore, when the second fuel is a liquid fuel, heat of vaporization is required, but in this embodiment, the heat of the air supplied via the branch passage 51 can be used as the heat of vaporization of the second fuel. Therefore, the energy efficiency of the entire boiler system 2 can be improved.

[0057] 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.

[0058] 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.

[0059] 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 degree of the cold gas damper 30d. 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 the cold gas damper according to the temperature of the air discharged from the air preheater 42. In this way, the opening degree of the cold gas damper 30d is determined according to the heat amount of the hot air, so that the amount of heat exchange in the air heating section can be detected from the opening degree of the cold gas damper 30d. 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, etc. based on the opening degree of the cold gas damper 30d.

[0060] 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 fuel, a second burner (21B) that burns a second fuel, and a wind box (23) that supplies air to the first burner (21A) and the second burner (21B), a pulverizer (31) that pulverizes the first fuel to be supplied to the first burner (21A), an air heating section (42) that heats the air by performing heat exchange between an exhaust gas discharged from the boiler (10) and the air, an air supply line (30a) that guides the air heated by the air heating section (42) to the pulverizer (31), and a wind box (23) that supplies air to the first burner (21A) and the second burner (21B). the first burner (21A), a first fuel supply line (22) that supplies the air supplied to the pulverizer (31) through the first fuel supply line (22) and the first fuel pulverized by the pulverizer (31), a second fuel supply line (26) that supplies a second fuel to the second burner (21B), a secondary air supply line (24) that guides the air heated by the air heating section (42) to the wind box (23), and a fuel heating section (50) that extracts a portion of the air heated by the air heating section (42) flowing through the air supply line (30a) and heats the second fuel supplied to the second burner (21B) with the extracted air.

[0061] The above-mentioned configuration includes a fuel heating section that extracts a portion of the air that flows through the air supply line and is heated by the air heating section, and heats the second fuel that is supplied to the second burner with the extracted air. This makes it possible to heat the second fuel by utilizing the exhaust heat of the exhaust gas recovered by the air heating section. Therefore, the energy efficiency of the entire system can be improved compared to a case in which the exhaust heat of the exhaust gas is not utilized.

[0062] In the boiler system according to a second aspect of the present disclosure, in the above-mentioned first aspect, the fuel heating section (50) includes a branch line (51) branched from the air supply line (30a) and through which a portion of the air heated in the air heating section (42) flows, and a heat exchange section (52) that performs heat exchange between the air flowing through the branch line (51) and the second fuel flowing through the second fuel supply line (26), and further includes an air line (53) that guides the air that has completed heat exchange in the heat exchange section (52) to the secondary air supply line (24).

[0063] In the above configuration, the fuel heating unit has a branch line through which a portion of the air branched from the air supply line and heated by the air heating unit flows, and a heat exchange unit that exchanges heat between the air flowing through the branch line and the second fuel flowing through the second fuel supply line. This allows the heat exchange unit to heat the second fuel supplied to the second burner by utilizing 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 a case in which the exhaust heat of the exhaust gas is not utilized.

[0064] In addition, the above configuration includes an air line that guides the air that has completed heat exchange in the heat exchange section to 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 primary air supplied to the first burner and the 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 the primary air supplied to the first burner and the 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.

[0065] In a boiler system according to a third aspect of the present disclosure, in the above-described first aspect, the fuel heating section (50) includes a branch line (51) branching from the air supply line (30a) and a premixing section that mixes the air flowing through the branch line (51) with the second fuel flowing through the second fuel supply line (26).

[0066] In the above configuration, the fuel heating section has a branch line branching off from the air supply line, and a premixing section that mixes air flowing through the branch line with the second fuel flowing through the second fuel supply line. This allows the premixing section to heat the second fuel by utilizing the exhaust heat of the exhaust gas recovered by the air heating section. This improves the energy efficiency of the entire system compared to a case in which the exhaust heat of the exhaust gas is not utilized.

[0067] Furthermore, when the second fuel is a liquid fuel, the second fuel vaporizes when it is supplied from the second burner into the furnace of the boiler. Therefore, when the second fuel is a liquid fuel, heat of vaporization is required, but in the above configuration, the heat of the air supplied through the branch line can be used as the heat of vaporization of the second fuel. Therefore, the energy efficiency of the entire system can be improved.

[0068] A boiler system according to a fourth aspect of the present disclosure is any one of the first to third aspects, wherein the fuel heating section (50) has a branch line (51) branched from the air supply line (30a) and through which a part of the air heated in the air heating section (42) flows, and a flow rate adjustment section (51a) adjusting the amount of air flowing through the branch line (51), and further includes a temperature detection section (14, 24a) for detecting an amount of heat exchange in the air heating section (42), and a control section (60) for controlling the flow rate adjustment section (51a) based on the amount of heat exchange detected by the temperature detection section (14, 24a,).

[0069] In the above configuration, a control unit is provided 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.

[0070] In a boiler system according to a fifth aspect of the present disclosure, in the above-described fourth aspect, 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).

[0071] 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.

[0072] In a boiler system according to a sixth aspect of the present disclosure, in the above-described fourth 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) based on the air temperature detected by the air outlet temperature detection unit (24a).

[0073] 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.

[0074] The boiler system according to a seventh aspect of the present disclosure is the same as in the fourth aspect, except that it includes a cold air supply line (30bA) that guides cold air to the grinder (31A), and the temperature detection unit has a cold air amount adjustment unit (30d) that adjusts the flow rate of cold air flowing through the cold air supply line (30bA) by adjusting its opening, and the control unit (60) controls the flow rate adjustment unit (51a) based on the opening of the cold air amount adjustment unit (30d).

[0075] 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 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 amount 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 amount adjustment section. In the above configuration, the control unit controls the flow rate regulator based on the opening degree of the cold air amount regulator, which allows the air heater to effectively recover the exhaust heat of the exhaust gas, thereby improving the energy efficiency of the entire system.

[0076] A boiler system according to an eighth aspect of the present disclosure is any one of the first to seventh aspects, wherein the second fuel includes ammonia.

[0077] With the above configuration, in a boiler system that uses a fuel containing ammonia as the second fuel, it is possible to improve the energy efficiency of the entire system.

[0078] A ninth aspect of the present disclosure relates to the boiler system of the above-mentioned eighth aspect, wherein the second fuel is a gaseous fuel containing ammonia.

[0079] With the above configuration, in a boiler system that uses a gaseous fuel containing ammonia as the second fuel, it is possible to improve the energy efficiency of the entire system.

[0080] A boiler system according to a tenth aspect of the present disclosure is the boiler system of the eighth aspect, wherein the second fuel is a liquid fuel containing ammonia.

[0081] With the above configuration, in a boiler system that uses a liquid fuel containing ammonia as the second fuel, it is possible to improve the energy efficiency of the entire system.

[0082] A power plant according to a first aspect of the present disclosure includes the boiler system according to any one of the first to tenth aspects, and a power generation unit that generates power using steam generated by the boiler system.

[0083] 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 fuel, a second burner (21B) that burns a second fuel, and a wind box (23) that supplies air to the first burner (21A) and the second burner (21B), a pulverizer (31) that pulverizes the first fuel to be supplied to the first burner (21A), an air heating section (42) that heats the air by performing heat exchange between an exhaust gas discharged from the boiler (10) and the air, an air supply line (30a) that guides the air heated by the air heating section (42) to the pulverizer (31), and a wind box (23) that supplies air to the first burner (21A) and the second burner (21B). The combustion apparatus includes a first fuel supply line (22) that supplies the air supplied to the pulverizer (31) via a supply line (30a) and the first fuel pulverized by the pulverizer (31) to the first burner (21A), a second fuel supply line (26) that supplies a second fuel to the second burner (21B), and a secondary air supply line (24) that guides the air heated in the air heating section (42) to the wind box (23), and includes a fuel heating step of extracting a part of the air heated in the air heating section (42) flowing through the air supply line (30a) and heating the second fuel supplied to the second burner (21B) with the extracted air. [Explanation of symbols]

[0084] 1: Power plant 2: Boiler system 10: Boiler 13: Flue 14: Exhaust gas thermometer 21A: First burner 21B: Second burner 22: Pulverized fuel supply pipe (first fuel supply line) 23: Wind box 24: Secondary air supply line 26: Ammonia fuel supply passage (second fuel supply line) 30: Blower section 30a: Hot gas flow path (air supply line) 30b: Cold gas passage 30c: Thermal gas damper 30d: Cold gas damper 31: Mill 32: Forced ventilation fan 33: Primary air ventilator 35: Primary air passage 41: Gas duct 42: Air preheater (air heating section) 42a: 1st heat exchange section 42b: Second heat exchange section 50:Fuel heating section 51: Branch flow path (branch line) 51a: Damper 52: Ammonia heater (heat exchange section) 53: Air flow path (air line) 55: Fuel heating section (premixing section) 60: Control section

Claims

1. a boiler having a first burner that burns a first fuel, a second burner that burns a second fuel, and a wind box that supplies air to the first burner and the second burner; a pulverizer for pulverizing a first fuel to be supplied to the first 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 pulverizer; a first fuel supply line that supplies the air supplied to the pulverizer through the air supply line and the first fuel pulverized by the pulverizer to the first burner; a second fuel supply line for supplying a second fuel to the second burner; a secondary air supply line for guiding the air heated by the air heating unit to the wind box; a fuel heating section that extracts a portion of the air heated by the air heating section that circulates through the air supply line and heats a second fuel supplied to the second burner using the extracted air.

2. the fuel heating unit includes a branch line branching from the air supply line and through which a portion of the air heated by the air heating unit flows, and a heat exchange unit performing heat exchange between the air flowing through the branch line and a second fuel flowing through the second fuel supply line, The boiler system according to claim 1 , further comprising an air line that guides the air that has completed heat exchange in the heat exchange section to the secondary air supply line.

3. 2. The boiler system according to claim 1, wherein the fuel heating unit has a branch line branching off from the air supply line, and a premixing unit that mixes air flowing through the branch line with a second fuel flowing through the second fuel supply line.

4. the fuel heating unit includes a branch line branching from the air supply line and through which a portion of the air heated by the air heating unit flows, and a flow rate adjusting unit adjusting an amount of air flowing through the branch line, A temperature detection unit for detecting a heat exchange amount in the air heating unit; The boiler system according to claim 1 , further comprising: a control unit that controls the flow rate regulator based on an amount of heat exchange detected by the temperature detector.

5. 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 4 , 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.

6. 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 4 , wherein the control unit controls the flow rate adjustment unit based on the air temperature detected by the air outlet temperature detection unit.

7. A cold air supply line is provided for conducting cold air to the grinder; The temperature detection unit has a cold air amount adjustment unit that adjusts the flow rate of cold air flowing through the cold air supply line by adjusting an opening degree, The boiler system according to claim 4 , wherein the control unit controls the flow rate adjustment unit based on an opening degree of the cold air amount adjustment unit.

8. The boiler system of claim 1 , wherein the second fuel comprises ammonia.

9. The boiler system according to claim 8 , wherein the second fuel is a gaseous fuel containing ammonia.

10. The boiler system according to claim 8 , wherein the second fuel is a liquid fuel containing ammonia.

11. A boiler system according to any one of claims 1 to 10; a power generation unit that generates electricity using the steam generated in the boiler system.

12. 1. A method for operating a boiler system, comprising: The boiler system includes: a boiler having a first burner that burns a first fuel, a second burner that burns a second fuel, and a wind box that supplies air to the first burner and the second burner; a pulverizer for pulverizing a first fuel to be supplied to the first 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 pulverizer; a first fuel supply line that supplies the air supplied to the pulverizer through the air supply line and the first fuel pulverized by the pulverizer to the first burner; a second fuel supply line for supplying a second fuel to the second burner; a secondary air supply line for guiding the air heated by the air heating unit to the wind box; A method for operating a boiler system comprising a fuel heating step of extracting a portion of the air heated in the air heating section circulating through the air supply line and using the extracted air to heat a second fuel supplied to the second burner.

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