Premixing device, boiler, and method for modifying boiler

Abstract

Provided is a premixing device for forming a premixed gas of heated air and ammonia, the premixing device comprising an injection unit configured to inject liquid ammonia into a heated-air flow path, which communicates with a furnace and through which heated air flows.

Description

Premixing device, boiler, and boiler modification method

[0001] This application claims priority to Japanese Patent Application No. 2023-105020, filed with the Japan Patent Office on June 27, 2023, the contents of which are incorporated herein by reference.

[0002] Combustion devices such as boilers that burn ammonia as fuel are known.

[0003] Patent Document 1 describes a boiler that burns ammonia fuel. In this boiler, ammonia vaporized in a vaporizer is mixed with air heated by an air heater and then combusted.

[0004] International Publication No. 2023 / 002814

[0005] Ammonia has a slower burning speed and is more difficult to ignite and burn than common hydrocarbon fuels such as methane, so a premixed combustion method may be adopted to ensure ignition.

[0006] On the other hand, as described in Patent Document 1, for example, a large flow path area is required to supply gaseous ammonia to a combustion device, and increasing the amount of ammonia supplied results in a larger facility. Also, considering that both pulverized fuel and ammonia are used as fuels in a combustion device such as a boiler, if an ammonia injection unit (nozzle) is disposed in the pulverized fuel transport path, the injection unit may be damaged by wear.

[0007] In view of the above circumstances, at least one embodiment of the present invention aims to provide a premixing device, a boiler, and a boiler modification method that can increase the amount of ammonia input while suppressing an increase in the size of the equipment and reduce the risk of damage due to wear of the ammonia injection unit.

[0008] A premixing device according to at least one embodiment of the present invention is a premixing device for forming a premixed gas of heated air and ammonia, and includes an injection unit that communicates with a furnace and is configured to inject liquid ammonia into a heated air flow path through which heated air flows.

[0009] A boiler according to at least one embodiment of the present invention includes: the premixing device; and a furnace for burning the premixed gas of heated air and ammonia formed by the premixing device.

[0010] Furthermore, a boiler retrofitting method according to at least one embodiment of the present invention includes a step of installing a premixing device in a boiler including a furnace, the premixing device forming a premixed gas of heated air and ammonia, the premixing device including an injection unit communicating with the furnace and for injecting liquid ammonia into a heated air flow path through which heated air flows.

[0011] According to at least one embodiment of the present invention, a premixing device, a boiler, and a boiler modification method are provided that can increase the amount of ammonia input while suppressing an increase in the size of the equipment and reduce the risk of damage due to wear of the ammonia injection section.

[0012] FIG. 1 is a schematic configuration diagram showing a boiler according to an embodiment. FIG. 2 is a schematic diagram of a burner constituting a boiler according to an embodiment. FIG. 3 is a schematic diagram of a premixing device according to an embodiment. FIG. 4 is a schematic diagram of a premixing device according to an embodiment. FIG. 5 is a schematic diagram of a premixing device according to an embodiment. FIG. 6 is a schematic diagram of a premixing device according to an embodiment. FIG. 7 is a schematic diagram of a premixing device according to an embodiment. FIG. 8 is a graph showing an example of the correlation between the temperature of the premixed gas and the air ratio.

[0013] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0014] 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.

[0015] (Configuration of Boiler) FIG. 1 is a schematic configuration diagram showing a boiler to which a premixing device according to some embodiments is applied.

[0016] 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.

[0017] 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.

[0018] 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.

[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 to which the premixing device according to the embodiment described below is applied is a co-firing boiler capable of co-firing pulverized fuel such as coal and ammonia in a combustion device.

[0030] Fig. 2 is a schematic diagram of a burner 21 constituting a boiler according to one embodiment. As shown in Fig. 2, the burner 21 (each of the burners 21A to 21F described above) according to one embodiment includes a central burner 60 located in the center in the vertical direction, 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).

[0031] 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.

[0032] The central burner 60 is adapted to inject fuel for diffusion combustion into the furnace 11 together with air.

[0033] 2 , the central burner 60 includes an oil fuel nozzle 62 configured to inject oil fuel into the furnace 11, and an air nozzle 66 provided to surround the periphery of the oil fuel 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] A typical pulverized coal-fired boiler may use a burner having the configuration shown in Fig. 2. By installing a premixing device according to an embodiment described below in a burner having such a configuration (for example, by modifying an existing boiler), a boiler according to an embodiment can be obtained.

[0036] (Configuration of Premixing Device) Next, a premixing device according to several embodiments will be described. Figures 3 to 9 are each a schematic diagram of a premixing device according to one embodiment.

[0037] A premixing device 72 according to one embodiment is a premixing device for forming a premixed gas of heated air and ammonia. As shown in Figures 3 to 9, the premixing device 72 includes an injection unit 76 configured to inject liquid ammonia into a heated air flow path 74 that communicates with the furnace 11 and through which heated air flows.

[0038] In this specification, heated air refers to air heated by a heater. The temperature of the heated air may be 200° C. or higher. The heated air may be the above-mentioned secondary air heated by, for example, the air heater 42.

[0039] 3 to 9 , as shown in FIG. 3 as an example, liquid ammonia from a liquid ammonia reservoir 118 may be supplied to the injection unit 76 via a liquid ammonia supply line 120. The liquid ammonia supply line 120 may be provided with a valve 122 for adjusting the amount of liquid ammonia supplied to the injection unit 76. Furthermore, secondary air (heated air) from the air duct 24 may be supplied to the heated air flow path 74 via a heated air line 124. The heated air line 124 may be provided with a valve 126 for adjusting the amount of heated air supplied to the heated air flow path 74.

[0040] In the above-described embodiment, liquid ammonia is injected into the heated air flow path 74 communicating with the furnace 11. Therefore, liquid ammonia, which has a relatively large heat of vaporization, is easily vaporized in the high-temperature heated air flow path 74, and a premixed gas of ammonia and air can be smoothly formed. Therefore, premixed combustion using liquid ammonia fuel can be realized. Furthermore, pulverized fuel (such as pulverized coal) does not usually flow through the heated air flow path 74 communicating with the furnace 11. That is, in the above-described embodiment, liquid ammonia is injected into a flow path that does not allow pulverized fuel to pass through, so that wear of the injection unit 76 (nozzle) that injects the liquid ammonia due to the pulverized fuel can be suppressed. Therefore, according to the above-described embodiment, it is possible to increase the amount of ammonia input while suppressing an increase in the size of the equipment, and to reduce the risk of damage due to wear of the injection unit 76.

[0041] If liquid components of ammonia remain in the combustion device, there is a possibility that ignition performance may deteriorate or unburned ammonia may be discharged. In this regard, in the above-described embodiment, liquid ammonia is easily vaporized because liquid ammonia is injected into the heated air flow path 74 through which high-temperature heated air flows, and such problems are unlikely to occur.

[0042] 3, the heated air flow path 74 is formed by a premixing pipe 78 connected to a pulverized fuel supply pipe 22 for supplying pulverized fuel to the furnace 11. The injection section 76 also includes a first liquid ammonia nozzle 80 configured to inject liquid ammonia into the premixing pipe 78.

[0043] In the above-described embodiment, the premixing pipe 78 connected to the pulverized fuel supply pipe 22 for supplying pulverized fuel to the furnace 11 forms the heated air flow path 74, and the injection unit 76 (first liquid ammonia nozzle 80) injects liquid ammonia into the heated air flow path 74. That is, since liquid ammonia is injected from the injection unit 76 into the premixing pipe 78 through which the pulverized fuel does not pass, wear of the injection unit 76 due to the pulverized fuel can be suppressed.

[0044] 3, the premixing device 72 may include a communication state switching unit 82 for switching the communication state between the premixing air pipe 78 and the furnace 11 and the communication state between the pulverized fuel supply pipe 22 and the furnace 11. In the exemplary embodiment shown in FIG. 3, the communication state switching unit 82 includes a premixed air valve 86 provided in the premixing air pipe 78, and a pulverized fuel valve 84 provided in the pulverized fuel supply pipe 22 at a position upstream of the connection with the premixing air pipe 78. By appropriately operating the communication state switching unit 82, the fuel supplied to the pulverized fuel burners 50A, 40B can be switched between the pulverized fuel from the pulverized fuel supply pipe 22 and the premixed air from the premixing air pipe 78.

[0045] 4, 5, 7, and 8, the heated air flow path 74 is formed by the air nozzle 66 constituting the central burner 60 of the burner 21. The injection portion 76 is provided in the heated air flow path 74 so as to extend around the diffusion nozzle (oil fuel nozzle 62 in FIG. 2) for ejecting fuel for diffusion combustion along the axial direction of the nozzle.

[0046] 4 and 5, the diffusion nozzle is an oil fuel nozzle 62 configured to supply oil fuel to the furnace 11. The injection unit 76 also includes at least one (two in FIGS. 4 and 5) second liquid ammonia nozzle 88 provided around the oil fuel nozzle 62. A nozzle hole for ejecting liquid ammonia is provided at the tip of the second liquid ammonia nozzle 88.

[0047] 7 and 8, the diffusion nozzle is an ammonia diffusion combustion nozzle 68 configured to supply ammonia to the furnace 11. The injection section 76 also includes at least one (two in FIGS. 7 and 8) fourth liquid ammonia nozzle 89 provided around the ammonia diffusion combustion nozzle 68. A nozzle hole for ejecting liquid ammonia is provided at the tip of the fourth liquid ammonia nozzle 89.

[0048] In the exemplary embodiments shown in Figures 4, 5, 7, and 8, the diffusion nozzle (oil fuel nozzle 62 in Figures 4 and 5, ammonia diffusion combustion nozzle 68 in Figures 7 and 8) includes tip portions 90, 114 in which injection ports 63, 69 for injecting fuel (oil or ammonia) are formed. Furthermore, the tip portions 90, 114 are provided with vortex forming portions 92 for forming vortices of heated air blown into the furnace 11 from the air nozzle 66. By providing such vortex forming portions 92, vortices of heated air are formed near the diffusion nozzle tips 90, 114, facilitating flame stabilization in the burner 21.

[0049] In the exemplary embodiment shown in Figures 4 and 7, the vortex generating section 92 includes a dish-shaped diffuser 94 and a cylindrical guide section 96 provided upstream of the diffuser 94. A vortex is generated when the heated air flows through a gap between the guide section 96 and the diffuser 94. In the exemplary embodiment shown in Figures 5 and 8, the vortex generating section 92 includes a swirler 98. A vortex is generated when the heated air passes through the swirler 98.

[0050] As shown in Figures 4, 5, 7, and 8, the second liquid ammonia nozzle 88 or the fourth liquid ammonia nozzle 89 may be configured to inject liquid ammonia at a position upstream of the vortex forming section 92 in the flow direction of the heated air in the heated air flow path 74.

[0051] In this case, the second liquid ammonia nozzle 88 or the fourth liquid ammonia nozzle 89 is provided at a position upstream of the vortex generating section 92 for forming a vortex of the heated air, so there is a certain distance between the second / fourth liquid ammonia nozzles 88, 89 and the vortex generating section 92. Therefore, the liquid ammonia sprayed from the second / fourth liquid ammonia nozzles is more likely to vaporize before reaching the vortex generating section 92. Furthermore, mixing of the ammonia sprayed from the second / fourth liquid ammonia nozzles 88, 89 and the heated air is promoted in the vortex generating section 92. Therefore, a premixture of ammonia and heated air can be smoothly formed.

[0052] 7 and 8, as described above, the diffusion nozzle includes the ammonia diffusion combustion nozzle 68. That is, ammonia is added to the injection section 76 (fourth liquid ammonia nozzle 89) for forming a premixed gas with heated air, and the ammonia diffusion combustion nozzle 68 for diffusively burning the ammonia in the furnace 11 is provided, so that a larger amount of ammonia fuel can be supplied to the furnace 11.

[0053] The ammonia fuel supplied from the ammonia diffusion combustion nozzle 68 to the furnace 11 may be liquid or gas. In the case of gaseous ammonia, it may be obtained by vaporizing liquid ammonia using a vaporizer.

[0054] Air flows through the air nozzle 66 that constitutes the central burner 60, but pulverized fuel is not generally present inside. Therefore, even if an injection part 76 is provided in the heated air flow path 74 formed by the air nozzle 66, there is little possibility that the injection part 76 will be worn due to contact with the pulverized fuel, etc.

[0055] In some embodiments, as shown in Figure 6, for example, the heated air flow path 74 includes a combustion air supply pipe for supplying combustion air to the furnace for combusting fuel, and the injection unit 76 includes a third liquid ammonia nozzle 112 configured to inject liquid ammonia into the combustion air supply pipe. In the exemplary embodiment shown in Figure 6, the combustion air supply pipe includes the combustion air nozzle 56. In another embodiment, the combustion air supply pipe may include an air nozzle 54 that constitutes the pulverized fuel burner 50A, and the injection unit 76 may include a nozzle configured to inject liquid ammonia into the air nozzle 54.

[0056] In the above-described embodiment, the third liquid ammonia nozzle 112 (injection unit 76) for injecting liquid ammonia into the combustion air supply pipe is provided. That is, the injection unit 76 is provided in the heated air flow path 74 through which the pulverized fuel does not pass, so that wear of the injection unit 76 due to the pulverized fuel can be suppressed.

[0057] In some embodiments, for example as shown in FIG. 9 , the heated air flow path 74 includes an air duct for supplying combustion air to each of the at least one combustion air supply pipe, and the injection unit 76 is configured to inject liquid ammonia into the air duct.

[0058] As shown in Fig. 9, the air duct 24 includes a plurality of branch pipes 24A to 24C, and supplies combustion air (secondary air, heated air) to each of a plurality of burners 21 (21A to 21C) arranged in the vertical direction via the plurality of branch pipes 24A to 24C. In the exemplary embodiment shown in Fig. 9, a fifth liquid ammonia nozzle 116 is provided as an injection unit 76 that injects liquid ammonia at a position in the air duct 24 between the branch point of the branch pipe 24A and the branch point of the branch pipe 24B. As a result, a premixture of ammonia and heated air (combustion air) formed in the air duct 24 is supplied to the combustion air supply pipes (the air nozzles 54 of the pulverized fuel burners 50, the air nozzles 66 of the central burners 60, and / or the combustion air nozzles 56) of the burners 21B and 21C located above the injection unit 76.

[0059] In the above-described embodiment, a fifth liquid ammonia nozzle 116 (injection unit 76) for injecting liquid ammonia is provided inside an air duct 24 (i.e., an air duct 24 upstream of a plurality of burners 21) for supplying combustion air (secondary air) to at least one combustion air supply pipe. That is, the injection unit 76 is provided in a heated air flow path through which pulverized fuel does not pass, so that wear of the injection unit 76 due to pulverized fuel can be suppressed. Furthermore, compared to the case where liquid ammonia nozzles are provided in each individual combustion air supply pipe, installation is relatively easy because it is sufficient to install a common fifth liquid ammonia nozzle 116.

[0060] In some embodiments, the premixing device 72 includes an adjusting section configured to adjust the flow rate of heated air in the heated air passage 74 depending on the amount of liquid ammonia supplied from the injection section 76 to the heated air passage 74.

[0061] 1, the adjustment unit may include a control device 200 for controlling the aperture of a valve 122 provided in the liquid ammonia supply line 120 and a valve 126 provided in the heated air line 124. The control device 200 may be configured to control the aperture of the valve 122 so that the amount of liquid ammonia supplied to the heated air flow path 74 (premixing air pipe 78 in FIG. 1) becomes a separately determined required value, and to control the aperture of the valve 126 so that an amount of heated air capable of vaporizing all of the supplied amount of liquid ammonia is supplied to the heated air flow path 74 (premixing air pipe 78 in FIG. 1).

[0062] 10 is a graph showing an example of the correlation between the temperature of the premixed gas and the air ratio (the ratio of the air flow rate to the air flow rate required for the amount of liquid ammonia to be introduced) when it is assumed that the temperature of the heated air and the temperature of the liquid ammonia are fixed predetermined values. As shown in the graph of Fig. 10, the smaller the air ratio, the lower the temperature of the premixed gas of ammonia and air, and when the air ratio is smaller than a predetermined value ra, the temperature of the premixed gas becomes lower than the boiling point of ammonia (approximately -33.3°C), and not all of the ammonia vaporizes.

[0063] Therefore, the above-mentioned adjusting unit may be configured to adjust the flow rate of heated air in the heated air flow path 74 so that the air ratio does not become smaller than the above-mentioned predetermined value ra.

[0064] According to the above-described embodiment, the flow rate of heated air in the heated air flow path 74 is adjusted in accordance with the amount of liquid ammonia supplied from the injection unit 76 to the heated air flow path 74, so that an amount of heated air sufficient to vaporize the supplied liquid ammonia can be supplied to the heated air flow path 74. This makes it possible to suppress deterioration of ignition due to remaining liquid components of ammonia, emission of unburned ammonia, and the like.

[0065] Next, a method for modifying a boiler according to one embodiment will be described.

[0066] A boiler retrofitting method according to one embodiment includes a step of installing a premixing device 72 for forming a premixed gas of heated air and ammonia in a boiler 10 (see FIG. 1) including a furnace 11. The premixing device 72 includes an injection unit 76 that communicates with the furnace 11 and that injects liquid ammonia into a heated air flow path 74 through which heated air flows, and may be, for example, one of those described with reference to FIGS.

[0067] In the boiler 10 obtained by the above method, liquid ammonia is injected into the heated air flow path 74 communicating with the furnace 11. Therefore, liquid ammonia, which has a relatively large heat of vaporization, is easily vaporized in the high-temperature heated air flow path 74, allowing a premixed gas of ammonia and air to be smoothly formed. This allows premixed combustion using liquid ammonia fuel to be realized. Furthermore, pulverized fuel (such as pulverized coal) does not normally flow through the heated air flow path 74 communicating with the furnace 11. In other words, in the boiler 10 obtained by the above method, liquid ammonia is injected into a flow path through which pulverized fuel does not pass. This prevents wear on the injection unit 76 (nozzle) that injects the liquid ammonia, which is caused by the pulverized fuel. Therefore, the above method allows for a boiler 10 to be obtained that can increase the amount of ammonia input while minimizing the size of the equipment and reduces the risk of damage due to wear on the ammonia injection unit.

[0068] The contents described in each of the above embodiments can be understood, for example, as follows.

[0069] [1] A premixing device (72) according to at least one embodiment of the present invention is a premixing device for forming a premixed gas of heated air and ammonia, and includes an injection unit (76) configured to inject liquid ammonia into a heated air flow path (74) that communicates with a furnace (11) and through which heated air flows.

[0070] In the configuration [1] above, liquid ammonia is injected into the heated air flow path communicating with the furnace. Liquid ammonia, which has a relatively large heat of vaporization, is easily vaporized in the high-temperature heated air flow path, allowing a premixed gas of ammonia and air to be smoothly formed. This allows premixed combustion using liquid ammonia fuel to be realized. Furthermore, pulverized fuel (such as pulverized coal) does not usually flow through the heated air flow path communicating with the furnace. In other words, in the configuration [1] above, liquid ammonia is injected into a flow path through which pulverized fuel does not pass, thereby suppressing wear of the injection unit (nozzle) that injects the liquid ammonia due to the pulverized fuel. Therefore, the configuration [1] above allows the amount of ammonia input to be increased while suppressing an increase in the size of the equipment, and also reduces the risk of damage due to wear of the ammonia injection unit.

[0071] [2] In some embodiments, in the configuration of [1] above, the heated air flow path includes a premixing pipe (78) connected to a pulverized fuel supply pipe for supplying pulverized fuel to the furnace, and the injection unit includes a first liquid ammonia nozzle (80) configured to inject the liquid ammonia into the premixing pipe.

[0072] In the configuration [2] above, a premixing pipe connected to a pulverized fuel supply pipe for supplying pulverized fuel to the furnace forms a heated air flow path, and the injection unit (first liquid ammonia nozzle) injects liquid ammonia into the heated air flow path. That is, liquid ammonia is injected from the injection unit into the premixing pipe through which pulverized fuel does not pass, so that wear of the injection unit due to pulverized fuel can be suppressed.

[0073] [3] In some embodiments, in the configuration of [2] above, a communication state switching unit (82) is provided for switching the communication state between the premixing pipe and the furnace, and the communication state between the pulverized fuel supply pipe and the furnace.

[0074] According to the configuration [3] above, a communication state switching unit is provided for switching the communication state between the premixing pipe and the furnace, and the communication state between the pulverized fuel supply pipe and the furnace, so that the operation of a combustion device (boiler, etc.) equipped with a premixing device can be flexibly switched between pulverized fuel combustion and ammonia combustion depending on the fuel availability situation, etc.

[0075] [4] In some embodiments, in the configuration of any one of [1] to [3] above, the injection unit includes a second liquid ammonia nozzle (88) that is provided in the heated air flow path around an oil fuel nozzle (62) for supplying oil fuel to the furnace and extends along the axial direction of the oil fuel nozzle.

[0076] In the configuration [4] above, a second liquid ammonia nozzle (injection unit) for injecting liquid ammonia is provided in the heated air flow path in which the oil fuel nozzle is provided. That is, the injection unit is provided in the heated air flow path through which the pulverized fuel does not pass, so that wear of the injection unit due to the pulverized fuel can be suppressed.

[0077] [5] In some embodiments, in the configuration of [4] above, the oil fuel nozzle includes a tip portion (90) in which an injection port for injecting the oil fuel is formed, and a vortex forming portion (92) is provided at the tip portion for forming a vortex of the heated air, and the second liquid ammonia nozzle is configured to inject the liquid ammonia at a position upstream of the vortex forming portion in the flow direction of the heated air in the heated air flow path.

[0078] According to the configuration [5] above, the second liquid ammonia nozzle (injection unit) is provided upstream of the vortex generating unit for forming a vortex in the heated air, so there is a certain distance between the second liquid ammonia nozzle and the vortex generating unit. This makes it easier for the liquid ammonia injected from the second liquid ammonia nozzle to vaporize before reaching the vortex generating unit. Furthermore, mixing of the ammonia and the heated air is promoted in the vortex generating unit. This allows for smooth formation of a premixed gas of ammonia and heated air.

[0079] [6] In some embodiments, in the configuration of any one of [1] to [5] above, the heated air flow path includes a combustion air supply pipe (e.g., a combustion air nozzle 56) configured to supply combustion air for combusting fuel to the furnace, and the injection unit includes a third liquid ammonia nozzle (112) configured to inject the liquid ammonia into the combustion air supply pipe.

[0080] In the configuration [6] above, a third liquid ammonia nozzle (injection part) for injecting liquid ammonia is provided inside the combustion air supply pipe. That is, the injection part is provided in the heated air flow path through which the pulverized fuel does not pass, so that wear of the injection part due to the pulverized fuel can be suppressed.

[0081] [7] In some embodiments, in the configuration of any of [1] to [6] above, an ammonia diffusion combustion nozzle (68) extending in the heated air flow path along the flow direction of the heated air and for supplying ammonia to the furnace is provided, and the injection unit includes a fourth liquid ammonia nozzle (89) provided in the heated air flow path around the ammonia diffusion combustion nozzle and extending along the axial direction of the ammonia diffusion combustion nozzle.

[0082] According to the configuration [7] above, ammonia is added to the injection section (fourth liquid ammonia nozzle) for forming a premixture of heated air, and an ammonia diffusion combustion nozzle for diffusively burning ammonia in the furnace is provided, so that a larger amount of ammonia fuel can be supplied to the furnace.

[0083] [8] In some embodiments, in the configuration of any of the above [1] to [7], the heated air flow path includes an air duct (24) for supplying combustion air to each of at least one combustion air supply pipe configured to supply the combustion air for combusting fuel to the furnace, and the injection unit includes a fifth liquid ammonia nozzle (116) configured to inject the liquid ammonia into the air duct.

[0084] In the configuration [8] above, a fifth liquid ammonia nozzle (injection unit) for injecting liquid ammonia is provided inside an air duct for supplying combustion air to at least one combustion air supply pipe. That is, the injection unit is provided in a heated air flow path through which pulverized fuel does not pass, so wear of the injection unit due to pulverized fuel can be suppressed. Furthermore, compared to installing liquid ammonia nozzles in individual combustion air supply pipes, only a common fifth liquid ammonia nozzle is installed, making installation relatively easy.

[0085] [9] In some embodiments, in the configuration of any one of [1] to [8] above, an adjusting unit (e.g., a control device 200) is provided that is configured to adjust the flow rate of the heated air in the heated air flow path according to the amount of the liquid ammonia supplied from the injection unit to the heated air flow path.

[0086] According to the configuration [9] above, the flow rate of the heated air in the heated air flow path is adjusted according to the amount of liquid ammonia supplied from the injection unit to the heated air flow path, so that an amount of heated air sufficient to vaporize the supplied liquid ammonia can be supplied to the heated air flow path. This makes it possible to effectively suppress deterioration of ignition ability due to remaining liquid components of ammonia, emission of unburned ammonia, etc.

[0087]

[10] A boiler (10) according to at least one embodiment of the present invention includes: the premixing device (72) according to any one of the above [1] to [9]; and a furnace (11) for combusting a premixed gas of heated air and ammonia formed by the premixing device.

[0088] In the configuration

[10] above, liquid ammonia is injected into the heated air flow path communicating with the furnace. Liquid ammonia, which has a relatively large heat of vaporization, is easily vaporized in the high-temperature heated air flow path, allowing a premixed gas of ammonia and air to be smoothly formed. This allows premixed combustion using liquid ammonia fuel to be realized. Furthermore, pulverized fuel (such as pulverized coal) does not usually flow through the heated air flow path communicating with the furnace. In other words, in the configuration

[10] above, liquid ammonia is injected into a flow path through which pulverized fuel does not pass, thereby suppressing wear of the injection unit (nozzle) that injects the liquid ammonia due to the pulverized fuel. Therefore, the configuration

[10] above allows the amount of ammonia input to be increased while preventing the equipment from becoming larger, and also reduces the risk of damage due to wear of the ammonia injection unit.

[0089]

[11] A method for modifying a boiler according to at least one embodiment of the present invention includes a step of installing a premixing device (72) for forming a premixed gas of heated air and ammonia in a boiler (10) including a furnace (11), wherein the premixing device includes an injection unit (76) for injecting liquid ammonia into a heated air flow path (74) that communicates with the furnace and through which heated air flows.

[0090] In the boiler obtained by the method

[11] above, liquid ammonia is injected into the heated air flow path communicating with the furnace. Liquid ammonia, which has a relatively large heat of vaporization, is easily vaporized in the high-temperature heated air flow path, allowing a premixed gas of ammonia and air to be smoothly formed. This allows premixed combustion using liquid ammonia fuel to be realized. Furthermore, pulverized fuel (such as pulverized coal) does not usually flow through the heated air flow path communicating with the furnace. In other words, in the boiler obtained by the method

[11] above, liquid ammonia is injected into a flow path that does not allow pulverized fuel to pass through. This prevents wear on the injection unit (nozzle) that injects the liquid ammonia due to the pulverized fuel. Therefore, the method

[11] above allows the ammonia input amount to be increased while preventing the equipment from becoming larger, and reduces the risk of damage due to wear on the ammonia injection unit.

[0091] 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.

[0092] 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.

[0093] 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 Air duct (air duct) 24A Branch pipe 24B Branch pipe 24C Branch pipe 31 Mill 32 Forced draft fan 40B Pulverized fuel burner 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 fuel nozzle 63 Injection nozzle 66 Air nozzle 68 Ammonia diffusion combustion nozzle 69 Injection port 72 Premixing device 74 Heated air flow path 76 Injection section 78 Premixing air pipe 80 First liquid ammonia nozzle 82 Communication state switching section 84 Pulverized fuel valve 86 Premixing air valve 88 Second liquid ammonia nozzle 89 Fourth liquid ammonia nozzle 90 Tip section 92 Swirl forming section 94 Diffuser 96 Guide section 98 Swirler 101 Furnace wall 102 Superheater 102A Superheater 102B Superheater 102C Superheater 103 Reheater 103A Reheater 103B Reheater 104 Economizer 112 Third liquid ammonia nozzle 114 Tip section 116 Fifth liquid ammonia nozzle 118 Liquid ammonia storage section 120 Liquid ammonia supply line 122 Valve 124 Heated air line 126 Valve 200 Control device

Claims

1. A premixing device for forming a premixture of heated air and ammonia, comprising an injection unit configured to inject liquid ammonia into a heated air flow path that communicates with a furnace and through which heated air flows.

2. The premixing device according to claim 1, wherein the heated air flow path includes a premixing pipe connected to a pulverized fuel supply pipe for supplying pulverized fuel to the furnace, and the injection unit includes a first liquid ammonia nozzle configured to inject the liquid ammonia into the premixing pipe.

3. A premixing device as set forth in claim 2, further comprising a communication state switching unit for switching a communication state between the premixing pipe and the furnace, and a communication state between the pulverized fuel supply pipe and the furnace.

4. A premixing device as claimed in any one of claims 1 to 3, wherein the injection section includes a second liquid ammonia nozzle provided within the heated air flow path around an oil fuel nozzle for supplying oil fuel to the furnace and extending along the axial direction of the oil fuel nozzle.

5. The premixing device described in claim 4, wherein the oil fuel nozzle includes a tip portion at which an injection port for injecting the oil fuel is formed, and a vortex forming portion is provided at the tip portion for forming a vortex of the heated air, and the second liquid ammonia nozzle is configured to inject the liquid ammonia at a position upstream of the vortex forming portion in the flow direction of the heated air in the heated air flow passage.

6. The premixing device according to any one of claims 1 to 3, wherein the heated air flow path includes a combustion air supply pipe configured to supply combustion air for combusting fuel to the furnace, and the injection unit includes a third liquid ammonia nozzle configured to inject the liquid ammonia into the combustion air supply pipe.

7. A premixing device as claimed in any one of claims 1 to 3, comprising an ammonia diffusion combustion nozzle extending within the heated air flow passage along the flow direction of the heated air and for supplying ammonia to the furnace, wherein the injection section includes a fourth liquid ammonia nozzle provided within the heated air flow passage around the ammonia diffusion combustion nozzle and extending along the axial direction of the ammonia diffusion combustion nozzle.

8. The premixing device according to any one of claims 1 to 3, wherein the heated air flow path includes an air duct for supplying combustion air to at least one combustion air supply pipe configured to supply the combustion air to the furnace for combusting fuel, and the injection unit includes a fifth liquid ammonia nozzle configured to inject the liquid ammonia into the air duct.

9. The premixing device according to any one of claims 1 to 3, further comprising an adjusting unit configured to adjust a flow rate of the heated air in the heated air passage in accordance with an amount of the liquid ammonia supplied from the injection unit to the heated air passage.

10. A boiler comprising: a premixing device according to any one of claims 1 to 3; and a furnace for combusting a premixture of heated air and ammonia formed by the premixing device.

11. A method for modifying a boiler, comprising the step of installing a premixing device in a boiler including a furnace for forming a premixture of heated air and ammonia, the premixing device including an injection unit that communicates with the furnace and for injecting liquid ammonia into a heated air flow path through which heated air flows.

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