Boiler, method for modifying boiler, and method for operating boiler

Abstract

This boiler comprises: a furnace for burning fuel; an ammonia diffusion burner configured to eject liquid ammonia into the furnace; and an ammonia premix burner configured to inject a premixed gas of gaseous ammonia and air into the furnace.

Description

Boilers, methods for modifying boilers, and methods for operating boilers

[0001] This application claims priority to Japanese Patent Application No. 2023-107471, filed with the Japan Patent Office on June 29, 2023, the contents of which are incorporated herein by reference.

[0002] Boilers equipped with burners that burn ammonia as fuel are known.

[0003] Patent Document 1 describes a boiler equipped with a burner that burns ammonia and pulverized coal.

[0004] JP 2023-39881 A

[0005] Incidentally, in order to ensure the ammonia supply amount while suppressing the increase in size of fuel piping, etc., it is advantageous to supply ammonia as a liquid to the furnace and perform diffusion combustion, compared to supplying gaseous ammonia to the furnace. On the other hand, ammonia has a slower combustion rate than common hydrocarbon fuels such as methane, making it difficult to ignite and burn. Furthermore, liquid ammonia has a large heat of vaporization, which is thought to reduce ignition ability. Therefore, it is desirable for a boiler that uses ammonia as fuel to be able to both ensure the ammonia supply amount and ensure ignition stability.

[0006] In view of the above circumstances, at least one embodiment of the present invention aims to provide a boiler, a boiler modification method, and a boiler operation method that can ensure both an ammonia supply amount and ignition stability.

[0007] A boiler according to at least one embodiment of the present invention includes: a furnace for burning fuel; an ammonia diffusion burner configured to inject liquid ammonia into the furnace; and an ammonia premix burner configured to inject a premix of gaseous ammonia and air into the furnace.

[0008] Furthermore, at least one embodiment of the present invention provides a boiler retrofitting method for a boiler including a furnace, an oil burner for injecting oil into the furnace, and a pulverized fuel burner for injecting pulverized fuel together with air into the furnace, the method comprising the steps of: retrofitting the oil burner to an ammonia diffusion burner for injecting liquid ammonia into the furnace; and retrofitting the pulverized fuel burner to an ammonia premix burner for injecting a premix of gaseous ammonia and air into the furnace.

[0009] Furthermore, at least one embodiment of the present invention provides a boiler retrofitting method for a boiler including a furnace, an oil burner for injecting oil into the furnace, and a pulverized fuel burner for injecting pulverized fuel together with air into the furnace, the method comprising the steps of: retrofitting the oil burner to an ammonia premixing burner for injecting a premixture of gaseous ammonia and air into the furnace; and retrofitting the pulverized fuel burner to an ammonia diffusion burner for injecting liquid ammonia into the furnace.

[0010] Furthermore, a boiler operation method according to at least one embodiment of the present invention is the above-described boiler operation method, comprising a step of adjusting a diffusion ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia diffusion burner, and a premixed ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia premix burner, based on a required load of the boiler, wherein in the step, when the load of the boiler is reduced, the diffusion ammonia supply amount is reduced in preference to the premixed ammonia supply amount.

[0011] According to at least one embodiment of the present invention, there are provided a boiler, a boiler modification method, and a boiler operation method that can ensure both an ammonia supply amount and ignition stability.

[0012] FIG. 1 is a schematic diagram showing a boiler according to an embodiment; FIG. 2 is a schematic diagram of a burner applicable to the boiler shown in FIG. 1; FIG. 3 is a schematic diagram showing a part of a boiler according to an embodiment; FIG. 4 is a schematic diagram showing a part of a boiler according to an embodiment; FIG. 5 is a graph showing an example of time-varying boiler load and the rate of supply amount, on a calorie basis, of fuel (ammonia or pulverized fuel) supplied to each burner when a boiler operation method according to an embodiment is carried out; FIG. 6 is a graph showing an example of time-varying boiler load and the rate of supply amount, on a calorie basis, of fuel (ammonia or pulverized fuel) supplied to each burner when a boiler operation method according to an embodiment is carried out.

[0013] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. In the following description, "upper" and "upper" refer to the upper side in the vertical direction, and "lower" and "lower" refer to the lower side in the vertical direction, and the vertical direction is not precise and may include errors.

[0014] (Configuration of Boiler and Burner) FIG. 1 is a schematic configuration diagram showing a boiler according to one embodiment.

[0015] As shown in Figure 1, a boiler 10 according to one embodiment is a boiler that uses a burner to combust pulverized solid fuel, and exchanges the heat generated by the combustion with feedwater or steam to generate superheated steam. The solid fuel used can be biomass fuel, coal, or the like.

[0016] The boiler 10 has a furnace 11, a combustion device 20, and a combustion gas passage 12. The furnace 11 has a hollow rectangular cylindrical shape and is installed vertically. The furnace wall 101 that forms the inner wall surface of the furnace 11 is composed of a plurality of heat transfer tubes and fins that connect the heat transfer tubes together. The heat generated by the combustion of pulverized fuel is recovered by heat exchange with water and steam circulating inside the heat transfer tubes, and the temperature rise of the furnace wall 101 is suppressed.

[0017] The combustion device 20 is installed in the lower region of the furnace 11. In this embodiment, the combustion device 20 has a plurality of burners 21A, 21B, 21C, 21D, 21E, and 21F (hereinafter, sometimes collectively referred to as "burners 21") attached to the furnace wall 101. The burners 21 may be arranged in multiple vertical rows, with each set consisting of burners equally spaced along the circumferential direction of the furnace 11 (for example, four burners installed at each corner of the rectangular furnace 11). Note that, for convenience of illustration, only two burners from one set are shown in FIG. 1, and each set is denoted by the reference numerals 21A, 21B, 21C, 21D, 21E, and 21F. The shape of the furnace, the number of burner rows, the number of burners per row, and the arrangement of the burners are not limited to this embodiment.

[0018] For example, the combustion device 20 may be a swirl combustion type combustion device in which, as described above, multiple burners 21 are evenly arranged along the circumferential direction of the furnace 11 and are configured to spray fuel along the circumferential direction around a center line extending in the vertical direction of the furnace 11.

[0019] The burners 21A, 21B, 21C, 21D, 21E, and 21F are connected to a plurality of mills (pulverizers) 31A, 31B, 31C, 31D, 31E, and 31F (hereinafter, sometimes collectively referred to as "mills 31") via a plurality of pulverized fuel supply pipes 22A, 22B, 22C, 22D, 22E, and 22F (hereinafter, sometimes collectively referred to as "pulverized fuel supply pipes 22"). The mill 31 is, for example, a vertical roller mill having a rotatable grinding table (not shown) supported therein and a plurality of grinding rollers (not shown) 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 separates the pulverized fuel into pulverized fuel having a particle size smaller than that suitable for combustion in the burner 21 and coarse pulverized fuel having a particle size larger than that. The pulverized fuel passes through the classifier and is supplied to the burner 21 together with primary air via the pulverized fuel supply pipe 22. The coarse pulverized fuel that does not pass through the classifier falls onto the grinding table inside the mill 31 under its own weight and is re-ground.

[0020] An air register 23 is provided outside the furnace 11 at the installation position of the burner 21, and one end of an air duct 24 is connected to the air register 23. The other end of the air duct 24 is connected to a forced draft fan (FDF) 32. Air supplied from the forced draft fan 32 is heated by an air preheater 42 installed in the air duct 24 (details will be described later), and is supplied to the burner 21 via the air register 23 as secondary air (combustion air, oxidizing gas) and introduced into the furnace 11.

[0021] The combustion gas passage 12 is connected to the vertical upper part of the furnace 11. The combustion gas passage 12 is provided with superheaters 102A, 102B, and 102C (hereinafter sometimes collectively referred to as "superheaters 102"), reheaters 103A and 103B (hereinafter sometimes collectively referred to as "reheaters 103"), and an economizer 104 as heat exchangers for recovering heat from the combustion gas, and heat is exchanged between the combustion gas generated in the furnace 11 and feedwater or steam flowing through each heat exchanger. Note that the arrangement and shape of each heat exchanger are not limited to those shown in FIG. 1 .

[0022] A flue 13 is connected downstream of the combustion gas passage 12, and discharges the combustion gas whose heat has been recovered by the heat exchanger. An air preheater (air heater) 42 is provided between the flue 13 and the air duct 24, and heat is exchanged between the air flowing through the air duct 24 and the combustion gas flowing through the flue 13, thereby heating the primary air supplied to the mill 31 and the secondary air supplied to the burner 21, thereby recovering further heat from the combustion gas after heat exchange with water and steam.

[0023] A denitration device 43 may be provided in the flue 13 at a position upstream of the air preheater 42. The denitration device 43 supplies a reducing agent, such as ammonia or urea water, that has the ability to reduce nitrogen oxides to the combustion gas flowing through the flue 13. The denitration device 43 promotes a reaction between the nitrogen oxides (NOx) in the combustion gas to which the reducing agent has been supplied and the reducing agent through the catalytic action of a denitration catalyst provided in the denitration device 43, thereby removing and reducing the nitrogen oxides in the combustion gas. A gas duct 41 is connected to the flue 13 downstream of the air preheater 42. The gas duct 41 is provided with environmental devices, such as a dust collector 44, such as an electrostatic precipitator, that removes ash and the like from the combustion gas, and a desulfurization device 46 that removes sulfur oxides, as well as an induced draft fan (IDF) 45 that guides the exhaust gas to these environmental devices. The downstream end of the gas duct 41 is connected to a chimney 47, through which the combustion gas treated in the environmental device is discharged to the outside of the system as exhaust gas.

[0024] In the boiler 10, when the multiple mills 31 are driven, pulverized and classified pulverized fuel is supplied to the burner 21 together with primary air via the pulverized fuel supply pipe 22. Secondary air heated by the air preheater 42 is supplied to the burner 21 from the air duct 24 via the wind box 23. The burner 21 blows a pulverized fuel mixture, which is a mixture of pulverized fuel and primary air, into the furnace 11, and also blows secondary air into the furnace 11. The pulverized fuel mixture blown into the furnace 11 ignites and reacts with the secondary air to form a flame. A flame is formed in the lower region of the furnace 11, and high-temperature combustion gas rises within the furnace 11 and flows into the combustion gas passage 12. In this embodiment, air is used as the oxidizing gas (primary air, secondary air). However, oxidizing gases having a higher or lower oxygen content than air may also be used. Stable combustion in the furnace 11 can be achieved by adjusting the ratio of oxygen to the amount of fuel supplied within an appropriate range.

[0025] The combustion gas that has flowed into the combustion gas passage 12 exchanges heat with water and steam in a superheater 102, a reheater 103, and an economizer 104 arranged inside the combustion gas passage 12, and is then discharged into the flue 13, where nitrogen oxides are removed in a denitration device 43, and the combustion gas exchanges heat with primary air and secondary air in an air preheater 42, and is then discharged into the gas duct 41, where ash and the like are removed in a dust collector 44, and sulfur oxides are removed in a desulfurization device 46, and the combustion gas is then discharged to the outside of the system through a chimney 47. The arrangement of the heat exchangers in the combustion gas passage 12 and the arrangement of the devices from the flue 13 to the gas duct 41 with respect to the combustion gas flow do not necessarily have to be in the order described above.

[0026] In the above-described embodiment, the boiler of the present invention has been described as a boiler that uses solid fuel as fuel, such as coal, biomass fuel, petroleum coke (PC) fuel, petroleum residue, etc.

[0027] The boiler can be fueled not only with solid fuels, but also with petroleum products such as heavy oil, light oil, and crude oil, industrial wastewater, liquefied ammonia, and other liquid fuels. It can also use gaseous fuels such as natural gas, various petroleum gases, by-product gases generated in steelmaking processes, hydrogen gas, and ammonia gas.

[0028] Furthermore, the present invention can also be applied to a multi-fuel boiler that uses a combination of these various fuels.

[0029] The boiler 10, according to some embodiments, is configured to combust at least ammonia.

[0030] Fig. 2 is a schematic diagram of a burner 21' applicable to the boiler 10 shown in Fig. 1. The burner 21 according to some embodiments can be obtained by modifying the burner 21' described below.

[0031] 2, the burner 21' (corresponding to each of the burners 21A to 21F described above) includes a central burner 60 located in the vertical center, and pulverized fuel burners 50A and 50B (hereinafter collectively referred to as pulverized fuel burners 50) located above and below the central burner 60. Furthermore, combustion air nozzles 56 are provided above and below these burner groups (the central burner 60 and the pulverized fuel burners 50A and 50B).

[0032] The pulverized fuel burner 50 includes a pulverized fuel nozzle 52 and an air nozzle 54. The pulverized fuel nozzle 52 is configured to inject primary air supplied from the pulverized fuel supply pipe 22 and pulverized fuel (pulverized coal, etc.) carried by the primary air into the furnace 11. The air nozzle 54 is configured to inject secondary air (heated air heated by the air heater 42) supplied from the air duct 24 into the furnace 11.

[0033] The central burner 60 is configured to inject fuel for diffusion combustion together with air into the furnace 11. In the example shown in Fig. 2, the central burner 60 includes an oil nozzle 62 configured to inject oil fuel into the furnace 11, and an air nozzle 66 provided to surround the periphery of the oil nozzle 62. The air nozzle 66 may be configured to inject secondary air (heated air heated by the air heater 42) supplied from the air duct 24 into the furnace 11.

[0034] The combustion air nozzle 56 may be configured to blow secondary air (heated air heated by the air heater 42 ) supplied from the air duct 24 into the furnace 11 .

[0035] Next, the boiler and burner according to some embodiments will be described in more detail. Figures 3 to 5 are each a schematic diagram showing a part of a boiler according to one embodiment.

[0036] 3 to 5 includes an ammonia diffusion burner 70 for injecting liquid ammonia into the furnace 11, and an ammonia premixing burner 72 for injecting a premix of gaseous ammonia and air into the furnace 11. As shown in the drawings, the ammonia diffusion burner 70 and the ammonia premixing burner 72 may be provided adjacent to each other.

[0037] 3 to 5, the burner 21 includes a pulverized fuel burner 50 for injecting pulverized fuel (such as pulverized coal) together with air into the furnace 11. As shown, the pulverized fuel burner 50 may be provided adjacent to either an ammonia diffusion burner 70 or an ammonia premix burner 72.

[0038] In the exemplary embodiment shown in Figures 3 and 4, the burner 21 includes an ammonia diffusion burner 70 obtained by modifying the central burner 60 and an ammonia premix burner 72 obtained by modifying the pulverized fuel burner 50B.

[0039] That is, the burner 21 shown in Figures 3 and 4 can be obtained by modifying the oil burner (central burner 60) including the oil nozzle 62 in the burner 21' shown in Figure 2 into an ammonia diffusion burner 70, and by modifying the pulverized fuel burner 50B (pulverized fuel burner adjacent to the oil burner) in the burner 21' shown in Figure 2 into an ammonia premix burner 72.

[0040] The oil burner (central burner 60) including the oil nozzle 62 in the burner 21′ shown in FIG. 2 may be modified into the ammonia diffusion burner 70 by replacing the oil nozzle 62 of the burner 21′ with a liquid ammonia nozzle 74 (see FIGS. 3 and 4) for spraying liquid ammonia into the furnace 11.

[0041] The pulverized fuel burner 50B in the burner 21′ shown in FIG. 2 may be modified into the ammonia premixing burner 72 by providing the pulverized fuel burner 50B in the burner 21′ with a premixed gas forming section 82 (see FIGS. 3 and 4) for forming a premixed gas of gaseous ammonia and air.

[0042] 3 , the premixed gas forming unit 82 includes a premixing pipe 84 connected to the pulverized fuel supply pipe 22 and supplied with high-temperature (e.g., 200° C. or higher) heated air (e.g., secondary air from the air duct 24), and a liquid ammonia nozzle 86 for injecting liquid ammonia into the premixing pipe 84. The liquid ammonia injected into the heated air flow in the premixing pipe 84 is vaporized by the high-temperature heated air and mixed with the heated air to form a premixed gas. The premixed gas formed in this manner is supplied to the pulverized fuel nozzle 52 of the ammonia premixing burner 72 via the pulverized fuel supply pipe 22 and injected from the pulverized fuel nozzle 52 into the furnace 11.

[0043] The pulverized fuel supply pipe 22 may be provided with a gate valve 92 for switching between a supply state and a non-supply state of the pulverized fuel and primary air from the pulverized fuel supply pipe 22 to the furnace 11. The premixing air pipe 84 may be provided with a gate valve 94 for switching between a supply state and a non-supply state of the premixed air from the premixing air pipe 84 to the pulverized fuel supply pipe 22.

[0044] 4 , the premixed gas generating unit 82 includes a pulverized fuel supply pipe 22 and a gaseous ammonia supply pipe 110 connected to the pulverized fuel supply pipe 22 for supplying gaseous ammonia to the pulverized fuel supply pipe 22. The gaseous ammonia supply pipe 110 may be provided with a gate valve 112 for switching between a supply state and a non-supply state of gaseous ammonia from the gaseous ammonia supply pipe 110 to the pulverized fuel supply pipe 22. The gaseous ammonia supplied from the gaseous ammonia supply pipe 110 to the pulverized fuel supply pipe 22 is mixed with primary air flowing through the pulverized fuel supply pipe 22 together with the pulverized fuel, thereby forming a premixed gas. The premixed gas formed in this manner is supplied to the pulverized fuel nozzle 52 of the ammonia premixing burner 72 via the pulverized fuel supply pipe 22 and sprayed from the pulverized fuel nozzle 52 into the furnace 11.

[0045] In the exemplary embodiment shown in FIG. 5, the burner 21 includes an ammonia diffusion burner 70 obtained by modifying the pulverized fuel burner 50B and an ammonia premix burner 72 obtained by modifying the central burner 60.

[0046] That is, the burner 21 shown in FIG. 5 can be obtained by modifying the oil burner (central burner 60) including the oil nozzle 62 in the burner 21′ shown in FIG. 2 into an ammonia premix burner 72, and by modifying the pulverized fuel burner 50B (pulverized fuel burner adjacent to the oil burner) in the burner 21′ shown in FIG. 2 into an ammonia diffusion burner 70.

[0047] 2 , the oil burner (central burner 60) including the oil nozzle 62 may be modified into the ammonia premix burner 72 by removing the oil nozzle 62 from the burner 21′, installing a gaseous ammonia nozzle 120 for spraying gaseous ammonia in the space formed by removing the oil nozzle 62, and forming a heated air flow path 118 through which heated air (such as secondary air from the air duct 24) flows around the gaseous ammonia nozzle 120. The gaseous ammonia sprayed from the gaseous ammonia nozzle 120 is mixed with the heated air flowing through the heated air flow path 118 to form a premixed gas, and the premixed gas is sprayed into the furnace 11.

[0048] The pulverized fuel burner 50B in the burner 21' shown in FIG. 2 may be converted to an ammonia diffusion burner 70 by replacing the pulverized fuel burner 50B in the burner 21' with a diffusion burner including a liquid ammonia nozzle 74 and an air nozzle 116.

[0049] 3 to 5 , liquid ammonia from a liquid ammonia reservoir 76 is supplied to the ammonia diffusion burner 70 via an ammonia line 78. The ammonia line 78 may be provided with a first valve 80 capable of adjusting the amount of ammonia supplied to the ammonia diffusion burner 70.

[0050] 3 to 5 , a premixed gas of ammonia and air formed from liquid ammonia supplied from the liquid ammonia reservoir 76 via an ammonia line 88 is supplied to the ammonia premixed burner 72. A second valve 90 capable of adjusting the amount of ammonia supplied to the ammonia premixed burner 72 may be provided in the ammonia line 88.

[0051] In the exemplary embodiment shown in FIG. 3 , the liquid ammonia from the liquid ammonia reservoir 76 is supplied in a liquid state to the liquid ammonia nozzle 86 (premixed gas forming unit 82) via an ammonia line 88.

[0052] In the exemplary embodiment shown in FIGS. 4 and 5 , liquid ammonia from the liquid ammonia reservoir 76 is vaporized in a vaporizer 114, and then supplied to the gaseous ammonia supply pipe 110 (premixed gas formation unit 82) or the gaseous ammonia nozzle 120 via an ammonia line 88.

[0053] 3 to 5, the pulverized fuel burner 50A is supplied with pulverized fuel from a pulverized fuel reservoir 96 via a pulverized fuel line 98 and a pulverized fuel supply pipe 22. The pulverized fuel line 98 may be provided with a pulverized fuel valve 99 for adjusting the amount of pulverized fuel supplied to the pulverized fuel burner 50A.

[0054] 3 to 5, the boiler 10 may include a control device 200 (control unit) for adjusting the amount of ammonia supplied to the ammonia diffusion burner 70 via the ammonia line 78, the amount of ammonia supplied to the ammonia premix burner 72 via the ammonia line 88, and / or the amount of pulverized fuel supplied to the pulverized fuel burner 50A via the pulverized fuel line 98. The control device 200 may be configured to adjust the opening of the first valve 80, the second valve 90, and / or the pulverized fuel valve 99 so that the amount of each fuel supplied becomes a predetermined value.

[0055] The control device 200 may include a computer equipped with a processor (e.g., a CPU), a main memory device (e.g., a memory device; e.g., a RAM), an auxiliary memory device, an interface, etc. The control device 200 may be configured to receive target values ​​of the ammonia supply amount to the ammonia diffusion burner 70 via the ammonia line 78, the ammonia supply amount to the ammonia premix burner 72 via the ammonia line 88, and / or the pulverized fuel supply amount to the pulverized fuel burner 50A via the pulverized fuel line 98 from a higher-level control device, etc. The control device 200 may be configured to adjust the openings of the first valve 80, the second valve 90, and / or the pulverized fuel valve 99 so that each supply amount approaches the target value. Alternatively, the control device 200 may be configured to receive a required load of the boiler 10 from a higher-level control device, etc. The control device 200 may be configured to adjust the openings of the first valve 80, the second valve 90, and / or the pulverized fuel valve 99 so as to satisfy the required load.

[0056] In the boiler 10 according to the above embodiment, the ammonia diffusion burner 70 injects ammonia into the furnace 11 in liquid form, thereby increasing the amount of ammonia supplied while suppressing increases in the size of fuel piping and the like. Furthermore, the ammonia premixing burner 72, which has relatively good ignition performance, is provided together with the ammonia diffusion burner 70, thereby suppressing deterioration in ignition performance and combustibility due to the use of the ammonia diffusion burner 70 that injects liquid ammonia. Therefore, according to the above embodiment, it is possible to ensure both the amount of ammonia supplied and ignition stability. Furthermore, by providing the ammonia premixing burner 72 adjacent to the ammonia diffusion burner 70, deterioration in ignition performance and combustibility due to the use of the ammonia diffusion burner 70 that injects liquid ammonia can be more effectively suppressed.

[0057] Furthermore, in the boiler 10 according to the above embodiment, in addition to the ammonia diffusion burner 70 and the ammonia premix burner 72, the pulverized fuel burner 50A, which has relatively good ignition properties, is provided, so that the deterioration of ignition properties and combustibility caused by using the ammonia diffusion burner 70 that sprays liquid ammonia can be more effectively suppressed. Furthermore, by providing the pulverized fuel burner 50A adjacent to either the ammonia diffusion burner 70 or the ammonia premix burner 72, the deterioration of ignition properties and combustibility caused by using the ammonia diffusion burner 70 that sprays liquid ammonia can be more effectively suppressed. In the exemplary embodiments shown in FIGS. 3 and 4, the pulverized fuel burner 50A is provided adjacent to the ammonia diffusion burner 70. In the exemplary embodiment shown in FIG. 5, the pulverized fuel burner 50A is provided adjacent to the ammonia premix burner 72.

[0058] Next, a description will be given of a method for operating the above-described boiler 10 according to some embodiments. The operation method described below can be performed using the above-described control device 200 or manually.

[0059] 6 and 7 are graphs showing the boiler load and the ratio of the heat input of the ammonia diffusion burner 70, the ammonia premix burner 72, and the pulverized fuel burner 50A (i.e., the ratio of the fuel (ammonia (NH ３ 6 and 7 are graphs showing an example of the change over time in the rate of supply of fuel (or pulverized fuel) on a calorific value basis. In the graphs of Fig. 6 and Fig. 7, the boiler load is reduced in stages from 100% (rated load) to 25%.

[0060] In some embodiments, the method for operating the boiler 10 adjusts the diffusion ammonia feed rate, which is the amount of ammonia fed to the furnace 11 via the ammonia diffusion burner 70, and the premixed ammonia feed rate, which is the amount of ammonia fed to the furnace 11 via the ammonia premix burner 72, based on the required load of the boiler 10. Here, when the load of the boiler 10 is reduced based on the required load, the diffusion ammonia feed rate is reduced in preference to the premixed ammonia feed rate. That is, in this embodiment, when the load of the boiler 10 is reduced, as shown in FIGS. 6 and 7 , first, the diffusion ammonia feed rate is reduced while maintaining the premixed ammonia feed rate, and then, when the diffusion ammonia feed rate approaches zero, the premixed ammonia feed rate is reduced.

[0061] In the above-described operating method, when the load on the boiler 10 is reduced, the amount of diffused ammonia supplied to the ammonia diffusion burner 70, which has relatively low ignition ability, is reduced in preference to the amount of premixed ammonia supplied to the ammonia premix burner 72, which has relatively good ignition ability, and therefore the load on the boiler 10 can be reduced while maintaining ignition stability.

[0062] In one embodiment, when the load of the boiler 10 is reduced based on the required load, the diffusion ammonia feed rate is reduced in preference to the premixed ammonia feed rate, and the premixed ammonia feed rate is reduced in preference to the pulverized fuel feed rate. That is, in this embodiment, when the load of the boiler 10 is reduced, as shown in Fig. 6 , first, the diffusion ammonia feed rate is reduced while maintaining the premixed ammonia feed rate and the pulverized fuel feed rate, and then, when the diffusion ammonia feed rate approaches zero, the premixed ammonia feed rate is reduced while maintaining the pulverized fuel, and further, when the premixed ammonia feed rate approaches zero, the pulverized fuel feed rate is reduced.

[0063] According to the above-described embodiment, when the load on the boiler 10 is reduced, the amount of diffusion ammonia supplied to the ammonia diffusion burner, which has relatively low ignition characteristics, is reduced in preference to the amount of premixed ammonia supplied to the ammonia premixed burner, which has relatively good ignition characteristics, and the amount of premixed ammonia supplied to the ammonia premixed burner is reduced in preference to the amount of pulverized fuel supplied to the pulverized fuel burner, which has better ignition characteristics. As a result, the load on the boiler can be further reduced while maintaining ignition stability.

[0064] In one embodiment, when the load of the boiler 10 is reduced based on the required load, the diffusion ammonia feed rate is reduced in preference to the premixed ammonia feed rate while maintaining the ammonia co-firing ratio. Here, the ammonia co-firing ratio is the ratio, based on the calorific value, of the sum of the diffusion ammonia feed rate and the premixed ammonia feed rate to the total of the diffusion ammonia feed rate, the premixed ammonia feed rate, and the pulverized fuel feed rate. That is, in this embodiment, when the load of the boiler 10 is reduced, as shown in FIG. 7 , both the ammonia feed rate and the pulverized fuel feed rate are reduced while maintaining a constant ratio of the ammonia feed rate (the sum of the diffusion ammonia feed rate and the premixed ammonia feed rate). Regarding the ammonia feed rate, the diffusion ammonia feed rate is first reduced while maintaining the premixed ammonia feed rate, and then, when the diffusion ammonia feed rate approaches zero, the premixed ammonia feed rate is reduced.

[0065] According to the above-described embodiment, when the load on the boiler 10 is reduced, the amount of diffused ammonia supplied to the ammonia diffusion burner 70, which has relatively low ignition ability, is reduced in preference to the amount of premixed ammonia supplied to the ammonia premix burner 72, which has relatively good ignition ability, while maintaining the ammonia co-firing ratio. Therefore, the load on the boiler 10 can be reduced while maintaining ignition stability and while increasing the amount of ammonia input to the boiler 10 as much as possible.

[0066] The contents described in each of the above embodiments can be understood, for example, as follows.

[0067] [1] A boiler (10) according to at least one embodiment of the present invention comprises: a furnace (11) for burning fuel; an ammonia diffusion burner (70) configured to inject liquid ammonia into the furnace; and an ammonia premixing burner (72) configured to inject a premix of gaseous ammonia and air into the furnace.

[0068] In the configuration [1] above, the ammonia diffusion burner injects ammonia into the furnace in liquid form, making it possible to increase the amount of ammonia supplied while suppressing increases in the size of fuel piping, etc. Furthermore, since an ammonia premix burner with relatively good ignition properties is provided together with the ammonia diffusion burner, it is possible to suppress the deterioration of ignition properties and combustibility that would otherwise be caused by using an ammonia diffusion burner that injects liquid ammonia. Thus, the configuration [1] above makes it possible to ensure both the amount of ammonia supplied and ignition stability.

[0069] [2] In some embodiments, in the configuration of [1] above, the boiler further comprises a pulverized fuel burner (50A) configured to inject pulverized fuel together with air into the furnace.

[0070] According to the configuration [2], the pulverized fuel burner, which has relatively good ignition performance, is provided in addition to the ammonia diffusion burner and the ammonia premix burner, so that it is possible to more effectively suppress the deterioration of ignition performance and combustibility caused by using the ammonia diffusion burner that sprays liquid ammonia. Therefore, according to the configuration [2], it is possible to secure the ammonia supply amount and achieve ignition stability at the same time.

[0071] [3] In some embodiments, in the configuration of [1] or [2] above, the boiler includes a control unit (e.g., control device 200) configured to adjust a diffusion ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia diffusion burner, and a premixed ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia premix burner, based on a required load of the boiler, and the control unit is configured to reduce the diffusion ammonia supply amount in preference to the premixed ammonia supply amount when reducing the load of the boiler.

[0072] According to the configuration [3] above, when the load on the boiler is reduced, the amount of diffusion ammonia supplied to the ammonia diffusion burner, which has relatively low ignition ability, is reduced in priority to the amount of premixed ammonia supplied to the ammonia premixed burner, which has relatively good ignition ability. Therefore, the load on the boiler can be reduced while maintaining ignition stability.

[0073] [4] In some embodiments, in the configuration of [3] above, the boiler includes a pulverized fuel burner configured to inject pulverized fuel together with air into the furnace, and the control unit is configured to adjust the amount of pulverized fuel supplied to the furnace via the pulverized fuel burner in addition to the diffusion ammonia supply amount and the premixed ammonia supply amount, and the control unit is configured to reduce the diffusion ammonia supply amount in preference to the premixed ammonia supply amount and reduce the premixed ammonia supply amount in preference to the pulverized fuel supply amount when reducing the load on the boiler.

[0074] According to the configuration [4] above, when the load on the boiler is reduced, the amount of diffusion ammonia supplied to the ammonia diffusion burner, which has relatively low ignition ability, is reduced in preference to the amount of premixed ammonia supplied to the ammonia premixed burner, which has relatively good ignition ability, and the amount of premixed ammonia supplied to the ammonia premixed burner is reduced in preference to the amount of pulverized fuel supplied to the pulverized fuel burner, which has better ignition ability, so that the load on the boiler can be further reduced while maintaining ignition stability.

[0075] [5] In some embodiments, in the configuration of [3] above, the boiler includes a pulverized fuel burner configured to inject pulverized fuel together with air into the furnace, and the control unit is configured to adjust the amount of pulverized fuel supplied to the furnace via the pulverized fuel burner in addition to the diffusion ammonia supply amount and the premixed ammonia supply amount, and the control unit is configured to reduce the diffusion ammonia supply amount in preference to the premixed ammonia supply amount while maintaining an ammonia co-firing ratio when reducing the load on the boiler, and the ammonia co-firing ratio is a ratio, on a calorie basis, of the sum of the diffusion ammonia supply amount and the premixed ammonia supply amount to the total of the diffusion ammonia supply amount, the premixed ammonia supply amount, and the pulverized fuel supply amount.

[0076] According to the configuration [5] above, when the load on the boiler is reduced, the amount of diffused ammonia supplied to the ammonia diffusion burner, which has relatively low ignition ability, is reduced in priority to the amount of premixed ammonia supplied to the ammonia premixed burner, which has relatively good ignition ability, while maintaining the ammonia co-firing ratio. Therefore, the load on the boiler can be reduced while maintaining ignition stability and increasing the amount of ammonia fed to the boiler as much as possible.

[0077] [6] A method for retrofitting a boiler according to at least one embodiment of the present invention is a method for retrofitting a boiler including a furnace (11), an oil burner (e.g., a central burner 60) for injecting oil into the furnace, and a pulverized fuel burner (50B) for injecting pulverized fuel together with air into the furnace, the method comprising the steps of: retrofitting the oil burner to an ammonia diffusion burner (70) for injecting liquid ammonia into the furnace; and retrofitting the pulverized fuel burner to an ammonia premix burner (72) for injecting a premix of gaseous ammonia and air into the furnace.

[0078] According to the method [6] above, by converting the oil burner into an ammonia diffusion burner and the pulverized fuel burner into an ammonia premix burner, it is possible to obtain a boiler having the configuration [1] above. The boiler obtained in this way can ensure both a sufficient ammonia supply amount and ignition stability.

[0079] [7] In some embodiments, in the method of [6] above, in the step of modifying the oil burner, an oil nozzle of the oil burner is replaced with a liquid ammonia nozzle (74) for injecting liquid ammonia into the furnace, and in the step of modifying the pulverized fuel burner, a premixed gas forming unit (82) for forming a premixed gas of gaseous ammonia and air is installed in the pulverized fuel burner.

[0080] According to the method [7] above, by replacing the oil nozzle of the oil burner with an ammonia nozzle and installing a premixed gas generator in the pulverized fuel burner, it is possible to obtain a boiler having the configuration [1] above relatively easily.

[0081] [8] A method for retrofitting a boiler according to at least one embodiment of the present invention is a method for retrofitting a boiler including a furnace (11), an oil burner (e.g., a central burner 60) for injecting oil into the furnace, and a pulverized fuel burner (50B) for injecting pulverized fuel together with air into the furnace, the method comprising the steps of: retrofitting the oil burner to an ammonia premixing burner (72) for injecting a premix of gaseous ammonia and air into the furnace; and retrofitting the pulverized fuel burner to an ammonia diffusion burner (70) for injecting liquid ammonia into the furnace.

[0082] According to the method of [8] above, by converting the oil burner into an ammonia premix burner and the pulverized fuel burner into an ammonia diffusion burner, it is possible to obtain a boiler having the configuration of [1] above. The boiler obtained in this way can ensure both ammonia supply amount and ignition stability.

[0083] [9] A boiler operation method according to at least one embodiment of the present invention is the boiler operation method described in any one of [1] to [5] above, comprising a step of adjusting a diffusion ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia diffusion burner, and a premixed ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia premix burner, based on a required load of the boiler, wherein in the step, when the load of the boiler is reduced, the diffusion ammonia supply amount is reduced in preference to the premixed ammonia supply amount.

[0084] According to the method [9] above, when the load on the boiler is reduced, the amount of diffusion ammonia supplied to the ammonia diffusion burner, which has relatively low ignition ability, is reduced in priority to the amount of premixed ammonia supplied to the ammonia premixed burner, which has relatively good ignition ability, so that the load on the boiler can be reduced while maintaining ignition stability.

[0085] The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and also includes forms in which the above-described embodiment is modified, or forms in which these forms are appropriately combined.

[0086] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0087] 10 Boiler 11 Furnace 12 Combustion gas passage 13 Flue 20 Combustion device 21 (21A-21F) Burner 22 (22A-22F) Pulverized fuel supply pipe 23 Wind box 24 Wind duct (air duct) 31 Mill 32 Forced draft fan 41 Gas duct 42 Air preheater (air heater) 43 Denitrification device 44 Device 46 Desulfurization device 47 Chimney 50 Pulverized fuel burner 50A Pulverized fuel burner 50B Pulverized fuel burner 52 Pulverized fuel nozzle 54 Air nozzle 56 Combustion air nozzle 60 Central burner 62 Oil nozzle 66 Air nozzle 70 Ammonia diffusion burner 72 Ammonia premixing burner 74 Liquid ammonia nozzle 76 Liquid ammonia storage section 78 Ammonia line 80 First valve 82 Premixed gas formation section 84 Premixed gas pipe 86 Liquid ammonia nozzle 88 Ammonia line 90 Second valve 92 Gate valve 94 Gate valve 96 Pulverized fuel storage section 98 Pulverized fuel line 99 Pulverized fuel valve 101 Furnace wall 102 Superheater 102A Superheater 102B Superheater 102C Superheater 103 Reheater 103A Reheater 103B Reheater 104 Economizer 110 Gaseous ammonia supply pipe 112 Gate valve 114 Vaporizer 116 Air nozzle 118 Heated air flow path 120 Gaseous ammonia nozzle 200 Control device

Claims

1. A boiler comprising: a furnace for burning fuel; an ammonia diffusion burner configured to inject liquid ammonia into the furnace; and an ammonia premix burner configured to inject a premixture of gaseous ammonia and air into the furnace.

2. The boiler of claim 1, further comprising a pulverized fuel burner configured to inject pulverized fuel with air into said furnace.

3. A boiler as described in claim 1 or 2, further comprising a control unit configured to adjust a diffusion ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia diffusion burner, and a premixed ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia premixed burner, based on a required load of the boiler, wherein the control unit is configured to reduce the diffusion ammonia supply amount in preference to the premixed ammonia supply amount when the load of the boiler is reduced.

4. A boiler as described in claim 3, comprising a pulverized fuel burner configured to inject pulverized fuel together with air into the furnace, wherein the control unit is configured to adjust the amount of pulverized fuel supplied to the furnace via the pulverized fuel burner in addition to the diffusion ammonia supply amount and the premixed ammonia supply amount, and wherein the control unit is configured to reduce the diffusion ammonia supply amount in preference to the premixed ammonia supply amount and to reduce the premixed ammonia supply amount in preference to the pulverized fuel supply amount when the load on the boiler is reduced.

5. A boiler as described in claim 3, comprising a pulverized fuel burner configured to inject pulverized fuel together with air into the furnace, wherein the control unit is configured to adjust the amount of pulverized fuel supplied to the furnace via the pulverized fuel burner in addition to the diffusion ammonia supply amount and the premixed ammonia supply amount, and wherein the control unit is configured to reduce the diffusion ammonia supply amount in priority to the premixed ammonia supply amount while maintaining an ammonia co-firing ratio when reducing the load on the boiler, and wherein the ammonia co-firing ratio is a ratio on a heat value basis of the sum of the diffusion ammonia supply amount and the premixed ammonia supply amount to the sum of the diffusion ammonia supply amount, the premixed ammonia supply amount, and the pulverized fuel supply amount.

6. A method for modifying a boiler including a furnace, an oil burner for spraying oil into the furnace, and a pulverized fuel burner for spraying pulverized fuel together with air into the furnace, comprising the steps of: modifying the oil burner into an ammonia diffusion burner for spraying liquid ammonia into the furnace; and modifying the pulverized fuel burner into an ammonia premix burner for spraying a premix of gaseous ammonia and air into the furnace.

7. The boiler modification method as set forth in claim 6, wherein in the step of modifying the oil burner, an oil nozzle of the oil burner is replaced with a liquid ammonia nozzle for spraying liquid ammonia into the furnace, and in the step of modifying the pulverized fuel burner, a premixed gas forming unit for forming a premixed gas of gaseous ammonia and air is provided in the pulverized fuel burner.

8. A method for modifying a boiler including a furnace, an oil burner for spraying oil into the furnace, and a pulverized fuel burner for spraying pulverized fuel together with air into the furnace, comprising the steps of: modifying the oil burner into an ammonia premixed burner for spraying a premixture of gaseous ammonia and air into the furnace; and modifying the pulverized fuel burner into an ammonia diffusion burner for spraying liquid ammonia into the furnace.

9. A method for operating a boiler as claimed in claim 1 or 2, comprising a step of adjusting a diffusion ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia diffusion burner, and a premixed ammonia supply amount, which is the amount of ammonia supplied to the furnace via the ammonia premixed burner, based on a required load of the boiler, wherein in the step, when the load of the boiler is reduced, the diffusion ammonia supply amount is reduced in priority to the premixed ammonia supply amount.

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