Combustor, combustion system, and combustion method

Abstract

Provided are a combustor, a combustion system, and a combustion method capable of reducing the amount of unburned fuel emitted. A combustor (AA) includes: a first combustion cylinder (10) which has one end that is closed by a bottom portion (13); a second combustion cylinder (20) which is connected to the first combustion cylinder (10) and which has an inner diameter greater than that of the first combustion cylinder (10); a first nozzle (41) which ejects first fuel from a first ejection port (16) formed in a side wall of the first combustion cylinder (10) in a direction toward the bottom portion (13) along an inner peripheral surface of the side wall; and a second nozzle (42) which ejects second fuel from a second ejection port (26) formed in a side wall of the second combustion cylinder (20) in a direction along an inner peripheral surface of the side wall. Since a swirling flow of the first fuel is reflected by the bottom portion (13), the residence time of the first fuel is increased, and a high-temperature reaction zone can be generated in a central portion of the combustion chamber. In addition, high-temperature air supply employing ultra-lean combustion in the second combustion cylinder (20) is performed. As a result, combustion of the fuel is promoted, and the amount of unburned fuel emitted can be reduced.

Description

COMBUSTOR, COMBUSTION SYSTEM, AND COMBUSTION METHOD

[0001] The present invention relates to a combustor, a combustion system, and a combustion method, and more particularly to a combustor, a combustion system, and a combustion method for burning a non-flammable fuel such as ammonia.

[0002] In light of global warming, efforts are underway to move toward a decarbonized society. Ammonia, in particular, is attracting attention as a next-generation energy source because it does not emit carbon dioxide when burned. However, ammonia is a flame-retardant fuel, making it difficult to burn stably. Therefore, it has been proposed to use high-calorie city gas as a combustion support fuel.

[0003] In response to this, the present inventors have proposed a combustor that improves fuel combustibility without using high-calorie fuel gas (Patent Document 1). This combustor has a main jet section formed at the center of the bottom of the combustion chamber and a swirl-flow generating jet section formed on the side wall. A first fuel jetted from the main jet section forms a main jet, and a second fuel jetted from the swirl-flow generating jet section forms a swirl flow. The swirl flame supplies the active chemical species and thermal energy necessary for combustion to the main jet, improving fuel combustibility. This makes ammonia combustion possible.

[0004] International Publication No. 2023 / 140290

[0005] However, the combustor disclosed in Patent Document 1 has a problem in that it emits a large amount of unburned ammonia. Specifically, although it depends on the flow rates of the first fuel and the second fuel, the ammonia concentration in the space around the combustor reaches 1,000 to 2,500 ppm.

[0006] In view of the above circumstances, an object of the present invention is to provide a combustor, a combustion system, and a combustion method that can reduce the amount of unburned fuel discharged.

[0007] A first aspect of the combustor includes a cylindrical first combustion liner having one end closed at a bottom and the other end open, a cylindrical second combustion liner having one end connected to the open end of the first combustion liner and an inner diameter larger than that of the first combustion liner, a first nozzle configured to eject a first fuel from a first outlet formed in a first side wall of the first combustion liner in a direction along an inner circumferential surface of the first side wall toward the bottom, and a second nozzle configured to eject a second fuel from a second outlet formed in a second side wall of the second combustion liner in a direction along the inner circumferential surface of the second side wall.A second aspect of the combustor includes the first aspect of the combustor, further including a constriction portion connected to the second combustion liner and having a flame port whose inner diameter at an open end is smaller than that of the second combustion liner.A third aspect of the combustor includes the first or second aspect of the combustor, further including a plurality of first nozzles configured to eject the first fuel from each of a plurality of first outlets formed in the first combustion liner in a circumferential direction and / or in multiple stages in the axial direction. A fourth aspect of the combustor is the combustor of any of the first to third aspects, characterized in that it includes a plurality of second nozzles that eject the second fuel from each of a plurality of second injection ports that are arranged side by side in the circumferential direction of the second combustion liner and / or that are formed in multiple stages in the axial direction.A fifth aspect of the combustor is the combustor of any of the first to fourth aspects, characterized in that the first fuel is a first mixed fuel obtained by mixing a low-flammability fuel with air, and the second fuel is a second mixed fuel obtained by mixing the low-flammability fuel or a combustion-supporting fuel with the air.A sixth aspect of the combustor is the combustor of the fifth aspect, characterized in that the low-flammability fuel is ammonia. A combustion system of a seventh aspect includes the combustor of any one of the first to fourth aspects, a flame-retardant fuel supply source that supplies flame-retardant fuel, an air supply source that supplies air, and a fuel flow path that supplies a first mixed fuel obtained by mixing the flame-retardant fuel and the air to the first nozzle as the first fuel, and that supplies a second mixed fuel obtained by mixing the flame-retardant fuel and the air to the second nozzle as the second fuel.The combustion system of an eighth aspect is the combustion system of the seventh aspect, further comprising a flow rate control unit that controls the flow rates of the low-flammability fuel and the air so that an overall equivalence ratio of the first mixed fuel and the second mixed fuel is 1.0 to 1.2, the equivalence ratio of the first mixed fuel is greater than 1.0, and the equivalence ratio of the second mixed fuel is lower than the equivalence ratio of the first mixed fuel.The combustion system of a ninth aspect is characterized by comprising the combustor of any of the first to fourth aspects, a low-flammability fuel supply source that supplies a low-flammability fuel, a combustion supporting fuel supply source that supplies a combustion supporting fuel, an air supply source that supplies air, and a fuel flow path that supplies the first mixed fuel obtained by mixing the low-flammability fuel and the air to the first nozzle as the first fuel and that supplies the second mixed fuel obtained by mixing the combustion supporting fuel and the air to the second nozzle as the second fuel. A combustion system of a tenth aspect is the ninth aspect, further comprising a flow rate control unit that controls the flow rates of the non-flammable fuel, the combustion supporting fuel, and the air so that the overall equivalence ratio of the first mixed fuel and the second mixed fuel is 1.0 to 1.2, the equivalence ratio of the first mixed fuel is 1.2 or more, and the equivalence ratio of the second mixed fuel is lower than the equivalence ratio of the first mixed fuel. A combustion system of an eleventh aspect is the tenth aspect, characterized in that the flow rate control unit controls the flow rates of the non-flammable fuel and the combustion supporting fuel so that the ratio of the combustion supporting fuel to the total fuel, which is the combination of the non-flammable fuel and the combustion supporting fuel, is approximately 5 to 15 volume %. A twelfth aspect is the combustion system of any of the seventh to eleventh aspects, characterized in that the non-flammable fuel is ammonia. A combustion method of a thirteenth aspect is a combustion method using the combustor of any one of the first to fourth aspects, characterized in that a mixed fuel of a non-combustible fuel and air having an equivalence ratio of more than 1.0 is supplied to the first nozzle as the first fuel, a mixed fuel of a non-combustible fuel and air having an equivalence ratio lower than that of the first fuel is supplied to the second nozzle as the second fuel, and an overall equivalence ratio of the first fuel and the second fuel is 1.0 to 1.2.A combustion method of a 14th aspect is a combustion method using the combustor of any of the 1st to 4th aspects, characterized in that a mixed fuel of a low-flammability fuel and air having an equivalence ratio of 1.2 or more is supplied to the first nozzle as the first fuel, and a mixed fuel of a combustion-supporting fuel and air having an equivalence ratio lower than that of the first fuel is supplied to the second nozzle as the second fuel, and the overall equivalence ratio of the first fuel and the second fuel is 1.0 to 1.2. A combustion method of a 15th aspect is the 14th aspect, characterized in that the proportion of the combustion-supporting fuel to the total fuel, including the low-flammability fuel and the combustion-supporting fuel, is approximately 5 to 15 volume %. A combustion method of a 16th aspect is the 13th to 15th aspect, characterized in that the low-flammability fuel is ammonia.

[0008] According to the first aspect, activated chemical species can be supplied by the swirling flow of the first fuel and the second fuel. Furthermore, because the swirling flow of the first fuel is reflected at the bottom, the residence time of the first fuel is increased, and a high-temperature reaction zone can be generated in the center of the combustion chamber. As a result, fuel combustion is promoted and unburned fuel emissions can be reduced. According to the second aspect, the swirl radius of the fuel is narrowed by the constricted portion, and activated chemical species are concentrated at the swirl center, thereby improving combustion stability. According to the third aspect, by ejecting the first fuel from multiple first nozzles, the amount of fuel supplied to the combustor can be increased, thereby increasing combustion heat. According to the fourth aspect, by ejecting the second fuel from multiple second nozzles, the amount of fuel supplied to the combustor can be increased, thereby increasing combustion heat. According to the fifth aspect, combustion can be sustained even when a non-flammable fuel is supplied, thereby achieving high-load combustion. According to the sixth aspect, by using ammonia as fuel, thermal energy can be obtained without emitting carbon dioxide. According to the seventh aspect, combustion can be sustained even when a non-flammable fuel is supplied, thereby achieving high-load combustion. According to the eighth aspect, by providing a difference in equivalence ratio between the first mixed fuel and the second mixed fuel, unburned fuel emissions can be reduced, and nitrogen oxide emissions can also be reduced. According to the ninth aspect, combustion can be sustained even when a low-flammability fuel is supplied, thereby achieving high-load combustion. According to the tenth aspect, by using a mixed fuel of a combustion support fuel and air as the second fuel, unburned fuel emissions can be further reduced, and nitrogen oxide emissions can also be further reduced. According to the eleventh aspect, the proportion of the combustion support fuel to the total fuel is low, so carbon dioxide emissions can be reduced. According to the twelfth aspect, by using ammonia as the fuel, thermal energy can be obtained without emitting carbon dioxide. According to the thirteenth aspect, by providing a difference in equivalence ratio between the first mixed fuel and the second mixed fuel, unburned fuel emissions can be reduced, and nitrogen oxide emissions can also be reduced. According to the fourteenth aspect, by using a mixed fuel of a combustion support fuel and air as the second fuel, unburned fuel emissions can be further reduced, and nitrogen oxide emissions can also be further reduced. According to the fifteenth aspect, the ratio of the combustion supporting fuel to the total fuel is small, so that the amount of carbon dioxide emissions can be reduced.According to the sixteenth aspect, by using ammonia as fuel, thermal energy can be obtained without emitting carbon dioxide.

[0009] 1 is a perspective view of a combustor according to a first embodiment; 2 is a longitudinal sectional view of the combustor; 3 is a front view of the combustor; 4 is a plan view of the combustor; 5 is an explanatory diagram of a combustion system according to a first embodiment; and 6 is an explanatory diagram of a combustion system according to a second embodiment. 7 is a diagram showing fuel flow lines in a combustion chamber; and 8 is a graph showing a stable combustion region of a flame. 9 is a graph showing the relationship between the flow rate of a first mixed fuel and the unburned ammonia concentration; and 10 is a graph showing the relationship between the flow rate of the first mixed fuel and the nitrogen oxide concentration. 11 is a graph showing the NO concentration distribution when the equivalence ratios of the first mixed fuel and the second mixed fuel are both 1.0. 12 is a graph showing the NO concentration distribution when the equivalence ratio of the first mixed fuel is 1.3 and the equivalence ratio of the second mixed fuel is 0.7. 13 is a graph showing the relationship between the equivalence ratio of the first mixed fuel and the unburned ammonia concentration; and 14 is a graph showing the relationship between the equivalence ratio of the first mixed fuel and the nitrogen oxide concentration. Graph (A) is a graph showing the relationship between the flow rate of the first mixed fuel and the concentration of unburned ammonia, and graph (B) is a graph showing the relationship between the flow rate of the first mixed fuel and the concentration of nitrogen oxides.

[0010] Next, embodiments of the present invention will be described with reference to the drawings. [First Embodiment] (Combustor) As shown in Fig. 1, a combustor AA according to a first embodiment of the present invention has a first combustion liner 10, a second combustion liner 20, and a throttle portion 30. The combustor AA also has a first nozzle 41 and a second nozzle 42 that supply fuel to the inside of the combustor AA.

[0011] As shown in Figure 2, the first combustion liner 10 is a cylindrical member with a bottom. The first combustion liner 10 has a first combustion chamber 11 inside. The cylindrical side wall of the first combustion liner 10 is referred to as a first side wall 12. One end (the lower end in Figure 2) of the first combustion liner 10 is closed by a bottom 13, and the other end (the upper end in Figure 2) is open. Both the first side wall 12 and the bottom 13 are made of an outer shell 14 formed of steel or the like, and a heat insulating material 15 that covers the entire inside of the outer shell 14.

[0012] The second combustion liner 20 is a cylindrical member. The second combustion liner 20 has a second combustion chamber 21 inside. The cylindrical side wall of the second combustion liner 20 is referred to as the second side wall 22. Like the first side wall 12, the second side wall 22 is composed of an outer shell 24 made of steel or the like, and a heat insulating material 25 that covers the entire inside of the outer shell 24. The outer shell 14 of the first combustion liner 10 and the outer shell 24 of the second combustion liner 20 may be an integral member. Similarly, the heat insulating material 15 of the first combustion liner 10 and the heat insulating material 25 of the second combustion liner 20 may be an integral member.

[0013] The first combustion liner 10 and the second combustion liner 20 are connected with their central axes O aligned. More specifically, one end (the lower end in FIG. 2 ) of the second combustion liner 20 is connected to the open end (the upper end in FIG. 2 ) of the first combustion liner 10. Therefore, the first combustion chamber 11 and the second combustion chamber 21 form a continuous space. The combined space of the first combustion chamber 11 and the second combustion chamber 21 is referred to as the combustion chamber. The inner diameter of the second combustion liner 20 is larger than the inner diameter of the first combustion liner 10. The inner circumferential surfaces of the first combustion liner 10 and the second combustion liner 20 are connected via a second annular bottom surface 23.

[0014] The throttle portion 30 is a substantially plate-shaped member. The throttle portion 30 is connected to the open end (the upper end in FIG. 2 ) of the second combustion liner 20. The throttle portion 30 has a flame port 31 that penetrates from front to back. The flame port 31 is an opening with a circular cross section, and its center is located on the central axis O of the first combustion liner 10 and the second combustion liner 20. The throttle portion 30 is composed of an outer shell 34 made of steel or the like, and a heat insulating material 35 that covers the inner surface of the outer shell 34. The flame port 31 is formed in the heat insulating material 35.

[0015] The inner diameter of the open end of the flame port 31 (the opening on the upper surface in FIG. 2 ) is smaller than the inner diameter of the second combustion liner 20. It is preferable that the flame port 31 be cone-shaped with the inner diameter decreasing toward the open end, and that the inner diameter of the end connected to the second combustion liner 20 (the opening on the lower surface in FIG. 2 ) be equal to the inner diameter of the second combustion liner 20. In this case, the second combustion chamber 21 and the flame port 31 are connected without any steps. Alternatively, the flame port 31 may be an opening with a constant inner diameter in the axial direction. In this case, the second combustion chamber 21 and the flame port 31 are connected in a stepped manner.

[0016] The combustor AA has a throttle portion 30 connected to a device such as a boiler or furnace. The thermal energy of the flame emitted from the flame port 31 is utilized in the device such as a boiler or furnace.

[0017] An insertion hole into which a first nozzle 41 is inserted is formed in the first side wall 12 and the second side wall 22. One end of this insertion hole opens to the inner circumferential surface of the first side wall 12. This opening is referred to as a first injection port 16. The tip of the first nozzle 41 is disposed at the first injection port 16. The first fuel supplied to the first nozzle 41 is injected from the first injection port 16 into the first combustion chamber 11.

[0018] As shown in Fig. 3 , in a front view, the first nozzles 41 are disposed obliquely with respect to the central axis O of the combustor AA so that the ejection direction faces the bottom 13. Although not particularly limited, the angle θ of the first nozzles 41 with respect to the central axis O is preferably 30° to 75°. Furthermore, as shown in Fig. 4 , in a plan view, the ejection direction of the first nozzles 41 is perpendicular to the radial direction of the combustor AA. Therefore, the first fuel supplied to the first nozzles 41 is ejected in a direction toward the bottom 13 along the inner circumferential surface of the first sidewall 12. As a result, the first fuel forms a swirling flow that advances toward the bottom 13.

[0019] The number of first nozzles 41 and first ejection ports 16 may be one or more. The combustor AA of this embodiment has two first nozzles 41. Two first ejection ports 16 are formed in the first combustion liner 10 and are arranged side by side in the circumferential direction. The tips of the first nozzles 41 are disposed in the two first ejection ports 16, respectively. Therefore, the first fuel is ejected from each of the two first ejection ports 16. When multiple first ejection ports 16 are formed in the first combustion liner 10, the multiple first ejection ports 16 are preferably disposed at equal angular intervals in the circumferential direction of the first combustion liner 10.

[0020] The first injection ports 16 may be formed in multiple stages in the axial direction of the first combustion liner 10. In this case, the first combustion liner 10 may be elongated in the axial direction. The inner diameter of the first combustion liner 10 may be changed for each stage of the first injection ports 16. In this case, it is preferable to make the inner diameter smaller closer to the bottom 13. Even when the first injection ports 16 are provided in multiple stages, the tip of the first nozzle 41 is disposed in each of the multiple first injection ports 16. Therefore, the first fuel is injected from each of the multiple first injection ports 16.

[0021] As shown in Fig. 2, an insertion hole into which a second nozzle 42 (not shown in Fig. 2) is inserted is formed in the second side wall 22. One end of this insertion hole opens to the inner circumferential surface of the second side wall 22. This opening is referred to as the second ejection port 26. The second ejection port 26 is preferably located near the second bottom surface 23. The tip of the second nozzle 42 is located at the second ejection port 26. The second fuel supplied to the second nozzle 42 is ejected from the second ejection port 26 into the second combustion chamber 21.

[0022] As shown in Fig. 3, the second nozzle 42 is disposed in a plane perpendicular to the central axis O of the combustor AA. As shown in Fig. 4, the ejection direction of the second nozzle 42 is perpendicular to the radial direction of the combustor AA. Therefore, the second fuel supplied to the second nozzle 42 is ejected in a direction along the inner circumferential surface of the second side wall 22. As a result, the second fuel forms a swirling flow.

[0023] The number of second nozzles 42 and second ejection ports 26 may be one or more. The combustor AA of this embodiment has two second nozzles 42. Furthermore, two second ejection ports 26 are formed in the second combustion liner 20, side by side in the circumferential direction. The tip of the second nozzle 42 is disposed in each of the two second ejection ports 26. Therefore, the second fuel is ejected from each of the two second ejection ports 26. Note that, when multiple second ejection ports 26 are formed in the second combustion liner 20, the multiple second ejection ports 26 are preferably disposed at equal angular intervals in the circumferential direction of the second combustion liner 20.

[0024] The second injection ports 26 may be formed in multiple stages in the axial direction of the second combustion liner 20. In this case, the second combustion liner 20 may be elongated in the axial direction. The inner diameter of the second combustion liner 20 may be changed for each stage of the second injection ports 26. In this case, it is preferable to make the inner diameter smaller as it approaches the second bottom surface 23. Even when the second injection ports 26 are provided in multiple stages, the tip of the second nozzle 42 is disposed in each of the multiple second injection ports 26. Therefore, the second fuel is injected from each of the multiple second injection ports 26.

[0025] An igniter (not shown) that ignites the first fuel and the second fuel is disposed inside the combustor AA (combustion chamber). A spark plug, a glow plug, or the like may be used as the igniter. The location of the igniter is not particularly limited, but may be provided on the bottom portion 13, for example.

[0026] When the first and second fuels are supplied to the combustor AA, they form a swirling flow. This swirling flow supplies activated chemical species (e.g., OH radicals, H radicals, and O radicals) necessary for combustion. This improves combustion stability. Furthermore, the combustion reaction within the first combustion chamber 11 is uniform, suppressing the generation of nitrogen oxides. The swirling flow of the first fuel travels toward the bottom 13 within the first combustion chamber 11, reflects off the bottom 13, and travels toward the second combustion chamber 21. As the first fuel travels back and forth within the first combustion chamber 11, the residence time of the first fuel increases. This creates a high-temperature reaction zone in the center of the combustion chamber. The second fuel swirls around this high-temperature reaction zone, supplying excess high-temperature air. As a result, fuel combustion is promoted and unburned fuel emissions are reduced. Furthermore, the throttle section 30 reduces the swirling radius of the fuel, causing exhaust gases with different equivalence ratios to concentrate at the swirl center. This promotes mixing while maintaining combustion stability, improving exhaust gas purification.

[0027] The combustor AA can stably burn low-flammable fuel, so it can sustain combustion even when a large amount of low-flammable fuel is supplied. This allows for high-load combustion. Here, high-load combustion means high combustion heat per unit volume and per unit time.

[0028] The combustor AA of this embodiment is characterized in that a swirling flow of the first fuel travels back and forth within the first combustion chamber 11. From the viewpoint of increasing the streamline distance and residence time of the first fuel, it is preferable that the first injection port 16 be disposed closer to the second combustion chamber 21 than the center of the axial direction of the first combustion chamber 11. Furthermore, the residence time of the first fuel can be adjusted by adjusting the axial length of the first combustion chamber 11. It is preferable that the swirling direction of the first fuel and the swirling direction of the second fuel are the same.

[0029] If the first fuel is ejected from the multiple first nozzles 41, the amount of fuel supplied to the combustor AA can be increased, thereby increasing the combustion heat. Similarly, if the second fuel is ejected from the multiple second nozzles 42, the amount of fuel supplied to the combustor AA can be increased, thereby increasing the combustion heat.

[0030] (Combustion System) Next, a combustion system BB according to a first embodiment of the present invention will be described. As shown in FIG. 5 , the combustion system BB has a combustor AA. The combustion system BB also has a flame-retardant fuel supply source 51. The flame-retardant fuel supply source 51 supplies flame-retardant fuel. Ammonia, biogas, or the like can be used as the flame-retardant fuel. A gas cylinder or a liquefied gas tank that stores flame-retardant fuel can be used as the flame-retardant fuel supply source 51. The combustion system BB has an air supply source 53. The air supply source 53 is not particularly limited as long as it can supply air, and a compressor, for example, can be used.

[0031] The combustion system BB has a fuel flow path 54 that connects the combustor AA with a non-flammable fuel supply source 51 and an air supply source 53. The fuel flow path 54 mixes the non-flammable fuel supplied from the non-flammable fuel supply source 51 with air supplied from the air supply source 53 and supplies the resulting mixed fuel to the combustor AA. The mixed fuel supplied to the first nozzle 41 of the combustor AA is referred to as the first mixed fuel. Also, the mixed fuel supplied to the second nozzle 42 is referred to as the second mixed fuel. The fuel flow path 54 supplies the first mixed fuel to the first nozzle 41 as the first fuel and supplies the second mixed fuel to the second nozzle 42 as the second fuel.

[0032] A flow rate control unit 55 is provided in the fuel flow path 54. The flow rate control unit 55 is configured by combining a flow meter and a flow rate control valve. The flow rate control unit 55 controls the flow rates of the non-flammable fuel and air mixed as the first mixed fuel. By controlling the flow rates of the non-flammable fuel and air, the equivalence ratio and flow rate of the first mixed fuel can be controlled. Similarly, the flow rate control unit 55 controls the flow rates of the non-flammable fuel and air mixed as the second mixed fuel. By controlling the flow rates of the non-flammable fuel and air, the equivalence ratio and flow rate of the second mixed fuel can be controlled.

[0033] Here, the equivalence ratio is the reciprocal of the air ratio. The air ratio is an index that indicates how many times the theoretical amount of air is supplied in a fuel reaction. When the equivalence ratio is greater than 1, it means that there is an excess of fuel. When the equivalence ratio is less than 1, it means that there is an excess of air.

[0034] For example, the fuel reaction of ammonia is expressed by the following formula (1): When 4 mol of ammonia is mixed with air equivalent to 3 mol of oxygen, the air ratio is 1 and the equivalence ratio is 1. When 4 mol of ammonia is mixed with air equivalent to 6 mol of oxygen, the air ratio is 2 and the equivalence ratio is 0.5. 4NH ３ +30 ２ →2N ２ +6H ２ O... (1)

[0035] (Combustion Method) Next, the combustion method will be described. A first fuel is supplied to the first nozzle 41 of the combustor AA, and a second fuel is supplied to the second nozzle 42. When the fuel is ignited in this state, the fuel burns and a flame is emitted from the flame port 31.

[0036] The combustor AA of this embodiment has high combustion stability, so it can maintain combustion even when using a low-flammability fuel. If ammonia is used as the fuel, thermal energy can be obtained without emitting carbon dioxide. Moreover, the combustor AA of this embodiment can reduce the amount of unburned fuel emitted.

[0037] By controlling the flow rates of the non-flammable fuel and air using the flow rate control unit 55, the equivalence ratio of the first mixed fuel and the equivalence ratio of the second mixed fuel can be adjusted. For example, the equivalence ratio of the first mixed fuel may be set to 1.0, and the equivalence ratio of the second mixed fuel may be set to 1.0. The flow rate of the first mixed fuel may be the same as, less than, or greater than the flow rate of the second mixed fuel. Even in this case, the non-flammable fuel can be burned stably. If ammonia is used as the fuel, ammonia mono-combustion can be achieved.

[0038] While maintaining the overall equivalence ratio of the first mixed fuel and the second mixed fuel in the range of 1.0 to 1.2, the equivalence ratio of the first mixed fuel may be greater than 1.0, and the equivalence ratio of the second mixed fuel may be lower than that of the first mixed fuel. That is, while maintaining the overall equivalence ratio in the range of 1.0 to 1.2, a mixed fuel of non-combustible fuel and air having an equivalence ratio greater than 1.0 is supplied to the first nozzle 41 as the first fuel, and a mixed fuel of non-combustible fuel and air having an equivalence ratio lower than that of the first mixed fuel is supplied to the second nozzle 42 as the second fuel. In this way, by providing a difference in the equivalence ratio between the first mixed fuel and the second mixed fuel, it is possible to reduce unburned fuel emissions and nitrogen oxide emissions.

[0039] From the viewpoint of reducing unburned fuel emissions while maintaining stable combustion, the overall equivalence ratio is preferably 1.0 to 1.2, and more preferably 1.0 to 1.1. From the viewpoint of suppressing both unburned fuel and nitrogen oxides, the equivalence ratio of the first mixed fuel is preferably greater than 1.0, more preferably 1.1 or greater, and even more preferably 1.2 or greater. Furthermore, the equivalence ratio of the second mixed fuel is preferably 1.0 or less, more preferably 0.9 or less, and even more preferably 0.8 or less. Alternatively, the difference between the equivalence ratios of the first mixed fuel and the second mixed fuel is preferably 0.1 or greater, more preferably 0.2 or greater, and even more preferably 0.4 or greater.

[0040] The combustor AA has a two-stage combustion chamber configuration in which the first combustion chamber 11 and the second combustion chamber 21 are connected, thereby enabling lean combustion and ultra-lean combustion with a low equivalence ratio of the mixed fuel in the second combustion chamber 21. The combustor AA also has a throttle section 30. The throttle section 20 reduces the swirl radius of the fuel, so that the first mixed fuel and the second mixed fuel, which have different equivalence ratios, are concentrated at the swirl center, promoting their mixing. This effectively suppresses unburned ammonia.

[0041] Second Embodiment (Combustion System) Next, a combustion system CC according to a second embodiment of the present invention will be described. As shown in FIG. 6, the combustion system CC has a combustor AA. The combustion system CC also has a combustion supporting fuel supply source 52 in addition to a flame-retardant fuel supply source 51. The combustion supporting fuel supply source 52 supplies a combustion supporting fuel. The combustion supporting fuel may be methane, petroleum gas, ammonia off-gas (H ２ / NH ３ / N ２ A gas cylinder or the like that stores the combustion supporting fuel can be used as the combustion supporting fuel supply source 52. The combustion system CC also has an air supply source 53.

[0042] The combustion system CC has a fuel flow path 54 connecting the combustor AA with a non-combustible fuel supply source 51, a combustion supporting fuel supply source 52, and an air supply source 53. The fuel flow path 54 mixes the non-combustible fuel supplied from the non-combustible fuel supply source 51 with air supplied from the air supply source 53, and supplies the resulting first mixed fuel as the first fuel to the first nozzle 41. The fuel flow path 54 also mixes the combustion supporting fuel supplied from the combustion supporting fuel supply source 52 with air supplied from the air supply source 53, and supplies the resulting second mixed fuel as the second fuel to the second nozzle 42.

[0043] The fuel flow path 54 is provided with a flow rate control unit 55. The flow rate control unit 55 controls the flow rates of the non-flammable fuel and air mixed into the first mixed fuel. By controlling the flow rates of the non-flammable fuel and air, the equivalence ratio and flow rate of the first mixed fuel can be controlled. Similarly, the flow rate control unit 55 controls the flow rates of the combustion supporting fuel and air mixed into the second mixed fuel. By controlling the flow rates of the combustion supporting fuel and air, the equivalence ratio and flow rate of the second mixed fuel can be controlled.

[0044] (Combustion Method) Next, the combustion method will be described. A first mixed fuel is supplied to the first nozzle 41 of the combustor AA, and a second mixed fuel is supplied to the second nozzle 42. When the fuel is ignited in this state, the fuel burns and a flame is emitted from the flame port 31. In this embodiment, a mixed combustion is performed in which a low-flammability fuel and a combustion-supporting fuel are burned.

[0045] By controlling the flow rates of the non-combustible fuel, the combustion supporting fuel, and the air using the flow rate control unit 55, the equivalence ratio of the first mixed fuel and the equivalence ratio of the second mixed fuel can be adjusted. Here, it is preferable to set the equivalence ratio of the first mixed fuel to 1.2 or more and the equivalence ratio of the second mixed fuel lower than the equivalence ratio of the first mixed fuel while maintaining the overall equivalence ratio in the range of 1.0 to 1.2. That is, while maintaining the overall equivalence ratio in the range of 1.0 to 1.2, a mixed fuel of non-combustible fuel and air having an equivalence ratio of 1.2 or more is supplied to the first nozzle 41 as the first fuel, and a mixed fuel of combustion supporting fuel and air having an equivalence ratio lower than that of the first mixed fuel is supplied to the second nozzle 42 as the second fuel. This further reduces unburned fuel emissions and nitrogen oxide emissions. When ammonia is used as the non-combustible fuel and methane is used as the combustion supporting fuel, unburned ammonia emissions and nitrogen oxide emissions can be reduced.

[0046] From the viewpoint of reducing unburned fuel emissions while maintaining stable combustion, the overall equivalence ratio is preferably 1.0 to 1.2, more preferably 1.0 to 1.1. From the viewpoint of suppressing unburned fuel and nitrogen oxides, the equivalence ratio of the first mixed fuel is preferably 1.2 or more, more preferably 1.3 or more. Furthermore, the equivalence ratio of the second mixed fuel is preferably 0.8 or less, more preferably 0.7 or less. In other words, combustion in the second combustion chamber 21 is lean combustion or ultra-lean combustion. Such lean combustion can be achieved by employing a structure that swirls the second fuel. Alternatively, the difference between the equivalence ratios of the first mixed fuel and the second mixed fuel is preferably 0.4 or more, more preferably 0.6 or more. However, from the viewpoint of maintaining stable combustion, the equivalence ratio of the first mixed fuel is preferably 1.5 or less, and the equivalence ratio of the second mixed fuel is preferably 0.5 or more.

[0047] By controlling the flow rates of the non-combustible fuel and the combustion supporting fuel using the flow rate control unit 55, it is possible to adjust the ratio of the combustion supporting fuel to the total fuel, which is the combination of the non-combustible fuel and the combustion supporting fuel. Here, the ratio of the combustion supporting fuel to the total fuel is preferably 5 to 15% by volume. By reducing the ratio of the combustion supporting fuel to the total fuel, it is possible to reduce carbon dioxide emissions.

[0048] (Fuel flow lines) The fuel flow inside the combustor was confirmed using a computer simulation. Figure 7 shows the fuel flow lines inside the combustion chamber. As can be seen from Figure 7, the first fuel forms a swirling flow that descends toward the bottom near the outside of the first combustion chamber. This swirling flow is reflected at the bottom and becomes a swirling flow that ascends through the center of the first combustion chamber, and is supplied to the second combustion chamber. A swirling flow of the second fuel is formed outside the swirling flow of the first fuel that ascends through the center of the second combustion chamber.

[0049] In this way, the first fuel forms a swirling flow that travels back and forth within the first combustion chamber. This confirms that the residence time of the first fuel is longer. Furthermore, since active chemical species are continuously supplied to the center of the combustion chamber from the swirling flow formed near the outside of the combustion chamber, it is clear that it is possible to maintain combustion of the low-flammability fuel.

[0050] (Stable Fuel Region) A mixed fuel of ammonia and air was supplied to the combustor having the configuration shown in Figure 1 and burned. The equivalence ratio of both the first mixed fuel supplied to the first nozzle and the second mixed fuel supplied to the second nozzle was 1.0. Whether stable combustion was possible was confirmed by changing the flow rates of the first mixed fuel and the second mixed fuel.

[0051] The results are shown in Figure 8. The hatched area in Figure 8 is the stable combustion region. As can be seen from Figure 8, it was confirmed that ammonia combustion can be achieved over a wide range of total flow rates from 10 to 120 L / min. Note that the maximum value on the horizontal and vertical axes in Figure 8 is 60 L / min, but this is due to the performance limits of the fuel supply device. Ammonia combustion is also possible at flow rates greater than this.

[0052] (Unburned ammonia concentration, nitrogen oxide concentration) A mixed fuel of ammonia and air was supplied to a combustor having the configuration shown in Figure 1 and burned. The equivalence ratio of both the first mixed fuel supplied to the first nozzle and the second mixed fuel supplied to the second nozzle was 1.0. The flow rate of the second mixed fuel was set to 30 L / min. The ammonia concentration and nitrogen oxide concentration in the space surrounding the combustor were measured while changing the flow rate of the first mixed fuel. The ammonia concentration and nitrogen oxide concentration were measured using a laser absorption exhaust gas analyzer (MEXA-1400QL-NX, manufactured by Horiba, Ltd.).

[0053] Figure 9(A) shows the relationship between the flow rate of the first mixed fuel and the unburned ammonia concentration. As can be seen from Figure 9(A), the unburned ammonia concentration tends to increase as the flow rate of the first mixed fuel increases. However, it was confirmed that the unburned ammonia concentration can be reduced to 120 ppm or less even when the flow rate of the first mixed fuel is 50 L / min (the total flow rate of the first mixed fuel and the second mixed fuel is 80 L / min). This means that the unburned ammonia concentration can be reduced to about 1 / 100 of that of the combustor disclosed in Patent Document 1.

[0054] 9B shows the relationship between the flow rate of the first mixed fuel and the nitrogen oxide concentration. As can be seen from FIG. 9B, the nitrogen oxide concentration tends to increase as the flow rate of the first mixed fuel increases (as the total flow rate of the first mixed fuel and the second mixed fuel increases).

[0055] (Simulation of Nitrogen Oxide Concentration) Next, the nitric oxide (NO) concentration in the combustion chamber was confirmed by computer simulation. Figure 10(A) shows the NO concentration distribution when the equivalence ratios of the first and second mixed fuels were both set to 1.0. The flow rates of the first and second mixed fuels were both 60 L / min. As can be seen from Figure 10(A), the NO concentration in the central region of the combustion chamber was 3,000 to 4,000 ppm.

[0056] Figure 10(B) shows the NO concentration distribution when the equivalence ratio of the first mixed fuel is 1.3 and the equivalence ratio of the second mixed fuel is 0.7. The flow rates of the first and second mixed fuels are both 60 L / min. As can be seen from Figure 10(B), the NO concentration in the central region of the combustion chamber is suppressed to 1,000 to 1,500 ppm.

[0057] In both of the above two conditions, the overall equivalence ratio is 1.0 and the total flow rate is 120 L / min. However, by providing a difference between the equivalence ratio of the first mixed fuel and the equivalence ratio of the second mixed fuel, the generation of nitrogen oxides is suppressed. It was confirmed that, compared to when the equivalence ratios of the first mixed fuel and the second mixed fuel are both 1.0, nitrogen oxide emissions can be reduced by setting the equivalence ratio of the first mixed fuel to greater than 1.0 and the equivalence ratio of the second mixed fuel to less than 1.0.

[0058] (Actual Equivalence Ratio Test) A mixed fuel of ammonia and air was supplied to a combustor having the configuration shown in Figure 1 and burned. While maintaining the overall equivalence ratio at 1.0, the equivalence ratio of the first mixed fuel was varied in the range of 1.0 to 1.3, and the equivalence ratio of the second mixed fuel was varied in the range of 0.7 to 1.0. The flow rates of the first mixed fuel and the second mixed fuel were 30 L / min. The ammonia concentration and nitrogen oxide concentration in the space surrounding the combustor were measured at this time.

[0059] FIG. 11(A) shows the relationship between the equivalence ratio of the first mixed fuel and the unburned ammonia concentration. FIG. 11(B) shows the relationship between the equivalence ratio of the first mixed fuel and the nitrogen oxide concentration. As can be seen from FIGS. 11(A) and 11(B), the unburned ammonia concentration and the nitrogen oxide concentration tend to decrease as the equivalence ratio of the first mixed fuel increases (as the equivalence ratio of the second mixed fuel decreases). In other words, the greater the difference between the equivalence ratios of the first mixed fuel and the second mixed fuel, the more the unburned ammonia concentration and the nitrogen oxide concentration can be reduced. When the equivalence ratio of the first mixed fuel is 1.3 and the equivalence ratio of the second mixed fuel is 0.7, the unburned ammonia concentration is 84 ppm and the nitrogen oxide concentration (O ２ 5% conversion) was 945 ppm.

[0060] From the viewpoint of suppressing both unburned ammonia and nitrogen oxides, the equivalence ratio of the first mixed fuel is preferably greater than 1.0, more preferably 1.1 or greater, and even more preferably 1.2 or greater. The equivalence ratio of the second mixed fuel is preferably less than 1.0, more preferably 0.9 or less, and even more preferably 0.8 or less. Alternatively, the difference between the equivalence ratios of the first mixed fuel and the second mixed fuel is preferably 0.1 or greater, more preferably 0.2 or greater, and even more preferably 0.4 or greater.

[0061] Furthermore, this test confirmed that both unburned ammonia and nitrogen oxides can be suppressed at least when the equivalence ratio of the first mixed fuel is in the range of 1.0 to 1.3 and when the equivalence ratio of the second mixed fuel is in the range of 1.0 to 0.7.

[0062] (Methane co-combustion) A combustion test was carried out using a combustor having the configuration shown in Figure 1. A mixed fuel of ammonia and air was used as the first mixed fuel. Methane (CH ４A mixed fuel of methane and air was used. The total flow rate of the first and second mixed fuels was 60 L / min, and the volume ratio of methane to ammonia was 10:90. In other words, the ratio of methane to the total fuel was 10% by volume. The equivalence ratio of the first mixed fuel was adjusted so that the overall equivalence ratio was 1.0 while the air ratio of the second mixed fuel was changed within a range of 1.5 to 2.0. Furthermore, the equivalence ratio of the first mixed fuel was adjusted so that the overall equivalence ratio was 0.95 while the air ratio of the second mixed fuel was changed within a range of 1.5 to 2.0. The nitrogen oxide concentration in the space surrounding the combustor was measured at this time.

[0063] The results are shown in Figure 12. As can be seen from Figure 12, it was confirmed that the nitrogen oxide concentration decreased as the air ratio of the second mixed fuel increased (the equivalence ratio decreased). When the overall equivalence ratio was set to 1.0, it was confirmed that the nitrogen oxide concentration could be suppressed to 620 to 960 ppm when the air ratio of the second mixed fuel was in the range of 1.5 to 2.0 (the equivalence ratio was 0.5 to 0.67).

[0064] (Comparison with ammonia mono-fuel combustion) A mixed fuel of ammonia and air was supplied to a combustor having the configuration shown in Figure 1 and burned. The equivalence ratio of both the first mixed fuel supplied to the first nozzle and the second mixed fuel supplied to the second nozzle was 1.0. The flow rate of the second mixed fuel was set to 30 L / min. The ammonia concentration and nitrogen oxide concentration in the space around the combustor were measured while changing the flow rate of the first mixed fuel.

[0065] Next, a mixed fuel of ammonia and air was used as the first mixed fuel. ４ A mixed fuel of methane and air was used. The air ratio of the second mixed fuel was set to 1.5 (equivalence ratio 0.67) and the flow rate was set to 20 L / min. The equivalence ratio of the first mixed fuel was set to 1.4 and the flow rate was changed in the range of 40 to 80 L / min. The ammonia concentration and nitrogen oxide concentration in the space around the combustor were measured at this time. Table 1 shows the overall equivalence ratio, the ratio of methane to the total fuel, the ammonia concentration, and the nitrogen oxide concentration.

[0066]

[0067] Figure 13(A) shows the relationship between the flow rate of the first mixed fuel and the unburned ammonia concentration. Figure 13(B) shows the relationship between the flow rate of the first mixed fuel and the nitrogen oxide concentration. As can be seen from Figures 13(A) and 13(B), co-combustion with the addition of methane can reduce both unburned ammonia and nitrogen oxides compared to ammonia mono-combustion.

[0068] It was confirmed that the unburned ammonia concentration could be suppressed to 0.7 to 3 ppm when the flow rate of the first mixed fuel was in the range of 40 to 80 L / min.

[0069] AA Combustor 10 First combustion liner 11 First combustion chamber 12 First side wall 13 Bottom 16 First nozzle 20 Second combustion liner 21 Second combustion chamber 22 Second side wall 26 Second nozzle 30 Constriction portion 31 Flame nozzle 41 First nozzle 42 Second nozzle

Claims

1. A combustor comprising: a first cylindrical combustion liner having one end closed at a bottom and the other end open; a second cylindrical combustion liner having one end connected to the open end of the first combustion liner and having an inner diameter larger than that of the first combustion liner; a first nozzle that ejects a first fuel from a first ejection port formed in a first side wall of the first combustion liner in a direction along an inner circumferential surface of the first side wall toward the bottom; and a second nozzle that ejects a second fuel from a second ejection port formed in a second side wall of the second combustion liner in a direction along the inner circumferential surface of the second side wall.

2. A combustor as claimed in claim 1, further comprising a throttle portion connected to said second combustion liner and having a flame port whose open end has an inner diameter smaller than the inner diameter of said second combustion liner.

3. The combustor according to claim 1 or 2, characterized in that it is provided with a plurality of first nozzles which eject the first fuel from each of a plurality of first ejection ports which are arranged in a line in the circumferential direction of the first combustion tube and / or are arranged in multiple stages in the axial direction.

4. A combustor as set forth in any one of claims 1 to 3, characterized in that it is provided with a plurality of second nozzles which eject the second fuel from each of a plurality of second ejection ports which are arranged in a line in the circumferential direction of the second combustion tube and / or are formed in multiple stages in the axial direction.

5. A combustor as set forth in any one of claims 1 to 4, characterized in that the first fuel is a first mixed fuel obtained by mixing a non-flammable fuel with air, and the second fuel is a second mixed fuel obtained by mixing the non-flammable fuel or a combustion supporting fuel with the air.

6. The combustor according to claim 5, wherein the non-flammable fuel is ammonia.

7. A combustion system comprising: a combustor according to any one of claims 1 to 4; a flame-retardant fuel supply source for supplying flame-retardant fuel; an air supply source for supplying air; and a fuel flow path for supplying a first mixed fuel obtained by mixing the flame-retardant fuel and the air as the first fuel to the first nozzle, and for supplying a second mixed fuel obtained by mixing the flame-retardant fuel and the air as the second fuel to the second nozzle.

8. The combustion system according to claim 7, further comprising a flow control unit that controls the flow rates of the non-flammable fuel and the air so that an overall equivalence ratio of the first mixed fuel and the second mixed fuel is 1.0 to 1.2, the equivalence ratio of the first mixed fuel is greater than 1.0, and the equivalence ratio of the second mixed fuel is lower than the equivalence ratio of the first mixed fuel.

9. A combustion system comprising: a combustor according to any one of claims 1 to 4; a flame-retardant fuel supply source for supplying a flame-retardant fuel; a combustion supporting fuel supply source for supplying a combustion supporting fuel; an air supply source for supplying air; and a fuel flow path for supplying a first mixed fuel obtained by mixing the flame-retardant fuel and the air to the first nozzle as the first fuel, and for supplying a second mixed fuel obtained by mixing the combustion supporting fuel and the air to the second nozzle as the second fuel.

10. The combustion system according to claim 9, further comprising a flow control unit that controls the flow rates of the flame-retardant fuel, the combustion supporting fuel, and the air so that an overall equivalence ratio of the first mixed fuel and the second mixed fuel is 1.0 to 1.2, the equivalence ratio of the first mixed fuel is 1.2 or more, and the equivalence ratio of the second mixed fuel is lower than the equivalence ratio of the first mixed fuel.

11. The combustion system according to claim 10, characterized in that the flow rate control unit controls the flow rates of the flame-retardant fuel and the auxiliary fuel so that the ratio of the auxiliary fuel to the total fuel, which is the combination of the flame-retardant fuel and the auxiliary fuel, is 5 to 15 volume %.

12. The combustion system according to any one of claims 7 to 11, characterized in that the non-flammable fuel is ammonia.

13. A combustion method using a combustor as defined in any one of claims 1 to 4, comprising: supplying a mixed fuel of a non-combustible fuel and air having an equivalence ratio of more than 1.0 as the first fuel to the first nozzle; supplying a mixed fuel of a non-combustible fuel and air having an equivalence ratio lower than that of the first fuel to the second nozzle as the second fuel; and the overall equivalence ratio of the first fuel and the second fuel is 1.0 to 1.

2.

14. A combustion method using a combustor as defined in any one of claims 1 to 4, comprising the steps of: supplying a mixed fuel of a non-combustible fuel and air having an equivalence ratio of 1.2 or more as the first fuel to the first nozzle; supplying a mixed fuel of a combustion support fuel and air having an equivalence ratio lower than that of the first fuel to the second nozzle as the second fuel; and the overall equivalence ratio of the first fuel and the second fuel is 1.0 to 1.

2.

15. The combustion method according to claim 14, wherein the ratio of said combustion supporting fuel to the total fuel, which is the combination of said flame-retardant fuel and said combustion supporting fuel, is 5 to 15 volume %.

16. The combustion method according to any one of claims 13 to 15, characterized in that the non-flammable fuel is ammonia.

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