Multistage micro-decomposition swirling flow burner for ammonia-mixed fuel and low NOx control method

Abstract

This invention discloses a multi-stage, micro-swirl burner for ammonia-mixed fuel and a low-NOx control method. The burner includes a natural gas center tube, a primary air duct, and a burner shell, which are fitted from inside to outside to form a spaced-apart primary air passage and an overfire air duct. Natural gas is injected from the natural gas center tube, and swirl vanes are positioned within the primary air passage to swirl the primary air and mix it with the central natural gas. A diffusion flame is then formed under the action of an ignition device, forming a sustainably combustible pilot flame at the center of the burner's injection end. The ammonia-mixed fuel, formed by premixing ammonia gas and natural gas, generates negative pressure when ejected at high speed through a micro-swirl nozzle. The surrounding overfire air is constantly sucked in, while the ammonia is injected into the high-temperature combustion zone of the pilot flame at the center of the burner. This allows the ammonia to rapidly decompose, producing a large amount of hydrogen and improving combustion stability. This invention's novel and rational structural layout improves combustion stability and reduces NOx emissions.

Description

【Technical Field】 【0001】 The present invention belongs to the field of combustion devices, relates to a burner for burning gas fuel, and particularly Multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel relates to a low NOx control method. 【Background Art】 【0002】 In a premixed swirl burner, the mixing ratio and mixing uniformity of the ammonia mixed fuel and the oxidant during combustion directly determine the NOx (combustion nitrogen oxides) emission effect of the burner. In conventional swirl burners, the ammonia mixed fuel and the oxidant are not sufficiently mixed, the flame effect is not ideal, and the nitrogen oxide emission is high, so the safety and environmental protection requirements required by current burners cannot be met. 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0003】 In order to solve the problems existing in conventional burners, such as insufficient mixing of the ammonia mixed fuel and the oxidant, non-ideal flame effect, and high nitrogen oxide emission, the present invention aims to provide a multi-stage microdecomposition swirl burner for ammonia mixed fuel with high combustion stability and low NOx emission and a low NOx control method. 【Means for Solving the Problems】 【0004】 To achieve the above object, the present invention provides the following technical solutions. 【0005】 The present invention provides a multi-stage microdecomposition swirl burner for ammonia mixed fuel, including a natural gas central pipe, a primary air duct, and a burner shell that are sequentially fitted from the inside to the outside. A primary air passage is formed between the outer wall of the natural gas central pipe and the inner wall of the primary air duct, and an overfire air duct is formed between the outer wall of the primary air duct and the inner wall of the burner shell. An ignition device and a swirling flow vane are provided in the primary air passage, the swirling flow vane is attached to the outer circumference of the outlet end of the natural gas central pipe, the swirling flow vane is arranged to create a swirling flow state in the primary air passage and mix it with the natural gas injected from the outlet end of the natural gas central pipe, the ignition device ignites and burns the mixed primary air and natural gas to form a sustained pilot flame at the outlet end of the natural gas central pipe, A fuel distribution nozzle is provided within the overfire air duct, and the fuel distribution nozzle is positioned near the outlet end of the natural gas central pipe, and the outlet end of the fuel distribution nozzle is Multiple holes, each having an opening smaller than the nozzle diameter of the fuel distribution nozzle, capable of injecting fuel at high speed. A pilot flame is provided to inject an ammonia-mixed fuel at high speed, and the ammonia in the ammonia-mixed fuel burns under the action of the pilot flame. When the ammonia-mixed fuel is injected at high speed, a negative pressure is formed at the end of the overfire air duct, and the overfire air generated by the combustion of the ammonia-mixed fuel is drawn in. 【0006】 Furthermore, a primary air distribution pipe communicating with the primary air passage is provided on the outer wall of the primary air pipe, the primary air distribution pipe is located inside the overfire air duct, the outlet end of the primary air distribution pipe is located on the outer circumference of the outlet end of the primary air pipe, and the outlet end of the primary air distribution pipe is longer than the natural gas central pipe and the outlet end of the primary air pipe. 【0007】 In a selective modification, a distribution nozzle is provided at the outlet end of the primary air distribution pipe, and the angle between the distribution nozzle and the axial direction of the primary air pipe is adjustable. 【0008】 In the selective modification, a plurality of primary air distribution pipes are evenly arranged along the circumferential direction of the outer wall of the primary air pipe. 【0009】 In the selective modification, the overfire air duct is provided with a plurality of fuel distribution nozzles, all of which are evenly arranged along the circumferential direction of the primary air duct, and in any of the fuel distribution nozzles said hole They are evenly distributed. 【0010】 In a selective variation, the ignition device is an ignition gun. 【0011】 In a selective variation, the swirling vane includes a plurality of rotary vanes evenly arranged along the circumferential direction, the angle between each rotary vane and the axial direction of the primary air duct is 30° to 45°. 【0012】 In selective deformation, either said hole The hole diameter is 3mm to 7mm. 【0013】 The present invention further provides a low NOx control method, which includes the steps of: implementing the low NOx control method using a multi-stage micro-decomposition swirling flow burner for ammonia mixed fuel described in any one of the above items, injecting a portion corresponding to 20% of the volume ratio of natural gas from the outlet end of the natural gas central pipe and mixing and burning it with the primary wind under the action of the ignition device to form the pilot flame; and premixing the remaining portion corresponding to 80% of the volume ratio of natural gas with ammonia gas to obtain an ammonia mixed fuel, premixing it at a predetermined equivalence ratio, injecting it from the fuel distribution nozzle into the flame region of the pilot flame, and burning and decomposing the ammonia in the ammonia mixed fuel under the action of the pilot flame. 【0014】 In the selective modification, during the combustion process of the ammonia-mixed fuel, the overall equivalent ratio between the ammonia-mixed fuel and the multi-stage micro-decomposition swirling flow burner for the ammonia-mixed fuel is controlled to a lean combustion state, while the local equivalent ratio between the overfire air and the ammonia-mixed fuel is controlled to a rich combustion state. 【0015】 In the selective modification, during the combustion process of the ammonia-mixed fuel, the overall equivalent ratio between the ammonia-mixed fuel and the multi-stage micro-decomposition swirling flow burner for the ammonia-mixed fuel is controlled to 0.7 to 0.8, and the local equivalent ratio between the overfire air and the ammonia-mixed fuel is controlled to 1.0 to 1.3. [Effects of the Invention] 【0016】 Compared to the prior art, the present invention achieves the following technical advantages. 【0017】 The multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel proposed in this invention is constructed by fitting a natural gas central tube, a primary air tube, and a burner shell in sequence from the inside out, thereby forming a spaced-out primary air passage and an overfire air duct. Natural gas is injected from the natural gas central tube, and the swirling flow vanes are positioned within the primary air passage and around the natural gas central tube, mixing the primary air with the central natural gas in a swirling flow state. Subsequently, under the action of an ignition device, a diffusion flame is formed, thus creating a single sustainably combustible pilot flame at the injection end center of the multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel. The ammonia-mixed fuel, obtained by pre-mixing ammonia gas and natural gas, is injected at high speed from the micro-decomposition holes, creating negative pressure. This constantly draws in surrounding overfire air, and simultaneously, the injected ammonia-mixed fuel enters the high-temperature combustion region of the pilot flame at the center of the burner. Consequently, the ammonia is rapidly decomposed, and the large amount of hydrogen produced contributes to improving combustion stability. This multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel has a novel and rational structural arrangement, which can improve combustion stability and reduce NOx emissions. 【0018】 In some of the technical solutions disclosed by the present invention, a primary air distribution pipe with an adjustable nozzle angle is positioned outside the primary air pipe, and the outlet end of the primary air distribution pipe is longer than the outlet end of the natural gas central pipe and the primary air pipe. This delays the inflow of some of the primary air into the combustion area, ensuring complete combustion of the fuel and further improving combustion stability. [Brief explanation of the drawing] 【0019】 To more clearly illustrate embodiments of the present invention or the technical concepts of the prior art, the necessary drawings for use in the embodiments are briefly introduced below. However, obviously, the drawings described below represent only a portion of embodiments of the present invention, and those skilled in the art can obtain other drawings based on these without expending any creative effort. [Figure 1] This is a schematic structural diagram of a multi-stage micro-decomposition swirling flow burner for ammonia mixed fuel disclosed in an embodiment of the present invention. [Figure 2] This is a front view of a multi-stage micro-decomposition swirling flow burner for ammonia mixed fuel disclosed in an embodiment of the present invention. [Figure 3] This is a side view of a multi-stage micro-decomposition swirling flow burner for ammonia mixed fuel disclosed in an embodiment of the present invention. 【Embodiment for Carrying out the Invention】 【0020】 Hereinafter, while referring to the drawings according to the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments described in the present invention, all other embodiments obtained by those skilled in the art without creative efforts are also included in the protection scope of the present invention. 【0021】 One of the objects of the present invention is to provide a multi-stage micro-decomposition swirling flow burner for ammonia mixed fuel with high combustion stability and low NOx emissions in order to solve the problems existing in conventional burners, such as insufficient mixing of ammonia mixed fuel and oxidant,不理想 flame effect, and high nitrogen oxide emissions. 【0022】 Another object of the present invention is to provide a low NOx control method implemented using a multi-stage micro-decomposition swirling flow burner for ammonia mixed fuel with high combustion stability and low NOx emissions in order to solve the problems existing in conventional burners, such as insufficient mixing of ammonia mixed fuel and oxidant,不理想 flame effect, and high nitrogen oxide emissions. <00​​​​​​​​​ As shown in Figures 1 to 3, this embodiment provides a multi-stage micro-decomposition swirling flow burner 100 for ammonia mixed fuel, which includes a natural gas central tube 1, a primary air duct 2, and a burner shell 3 fitted in order from the inside to the outside. A primary air passage 4 is formed between the outer wall of the natural gas central tube 1 and the inner wall of the primary air duct 2, and an overfire air duct 5 is formed between the outer wall of the primary air duct 2 and the inner wall of the burner shell 3. An ignition device 6 and a swirling flow vane 7 are provided in the primary air passage 4. The swirling flow vane 7 is attached to the outer circumference of the outlet end of the natural gas central tube 1, and is positioned to make the primary air in the primary air passage 4 into a swirling flow state and mix it with the natural gas injected from the outlet end of the natural gas central tube 1. The ignition device 6 ignites and burns the mixed primary air and natural gas to form a sustained pilot flame at the outlet end of the natural gas central tube 1. A fuel distribution nozzle 8 is provided inside the overfire air duct 5, positioned near the outlet end of the natural gas central pipe 1. Multiple micro-decomposition holes 81 are provided at the outlet end of the fuel distribution nozzle 8 to inject ammonia-mixed fuel at high speed. As a result, the ammonia in the ammonia-mixed fuel burns under the action of the pilot flame, and when the ammonia-mixed fuel is injected at high speed, a negative pressure is created at the end of the overfire air duct 5, drawing in the overfire air generated by the combustion of the ammonia-mixed fuel. 【0026】 In this embodiment, a primary air distribution pipe 10 is provided on the outer wall of the primary air duct 2, which communicates with the primary air passage 4. The primary air distribution pipe 10 is located inside the overfire air duct 5, and its outlet end is on the outer circumference of the outlet end of the primary air duct 2. Furthermore, the outlet end of the primary air distribution pipe 10 is longer than the outlet ends of the natural gas central pipe 1 and the primary air duct 2. As a result, the primary air injected from the primary air distribution pipe 10 enters the combustion region later than the primary air injected from the primary air duct 2, ensuring complete combustion of the fuel. The inlet end of the primary air distribution pipe 10 is usually connected near the tail end of the primary air duct 2, and when primary air is passed through the primary air duct 2, the primary air immediately flows into the primary air distribution pipe 10. 【0027】 In this embodiment, a distribution nozzle is provided at the outlet end of the primary air distribution pipe 10, and the angle between the distribution nozzle and the axial direction of the primary air pipe 2 is adjustable, with the adjustment angle generally being -45° to 45°. Regarding the angle adjustment of the distribution nozzle, a nozzle with an angle adjustment function, such as a universal nozzle or a spherical angle adjustment nozzle disclosed in Patent Document CN95106474.6, can be directly used. Alternatively, by attaching the nozzle using an existing spray angle adjustment structure, the angle between the distribution nozzle and the axial direction of the primary air pipe 2 can be adjusted using the spray angle adjustment structure. Examples of spray angle adjustment structures include universal valves, universal adjusters, and structures disclosed in Patent Document CN101121157A. 【0028】 In this embodiment, the ratio of the airflow rate through any of the primary wind distribution pipes 10 to the total amount of primary wind is the ratio of the cross-sectional area of ​​the primary wind distribution pipe 10 to the cross-sectional area of ​​the primary wind pipe 2. 【0029】 In this embodiment, multiple primary air distribution pipes 10 are evenly arranged along the circumferential direction of the outer wall of the primary air pipe 2. 【0030】 In this embodiment, multiple fuel distribution nozzles 8 are provided within the overfire air duct 5, and all fuel distribution nozzles 8 are arranged at equal intervals along the circumferential direction of the primary air pipe 2. The micro-dissolution holes 81 in each fuel distribution nozzle 8 are uniformly arranged, which allows for the homogenization of the burner outlet airflow field. In a more preferred technical configuration, the fuel distribution nozzles 8 are arranged on the outer circumference of multiple primary air distribution pipes 10, as shown in Figures 1 and 2, and the outlet ends of the primary air distribution pipes 10 are longer than the outlet ends of the fuel distribution nozzles 8. 【0031】 In this embodiment, each fuel distribution nozzle 8 is connected to a fuel supply pipe 9. Preferably, the fuel supply pipes 9 connected to all fuel distribution nozzles 8 have the same diameter, are parallel to each other, and are arranged at equal intervals. The load of the multi-stage micro-decomposition swirling flow burner 100 for ammonia-mixed fuel can be adjusted by the number of times the fuel supply pipes 9 are opened or closed. 【0032】 In this embodiment, the ignition device 6 is preferably an ignition gun. After ignition, the ignition gun can also be used as a gas inlet channel for other fuels. 【0033】 In this embodiment, the swirling air vane 7 includes a plurality of rotary vanes evenly arranged along the circumferential direction, and the angle between each rotary vane and the axial direction of the primary air duct is 30° to 45°. 【0034】 In this embodiment, the diameter of each micro-decomposition hole 81 is 3 mm to 7 mm. More specifically, the diameter of each micro-decomposition hole 81 may be 3 mm, 5 mm, or 7 mm. 【0035】 In this embodiment, as shown in Figures 1 to 3, the entire natural gas central pipe 1 has a curved pipe structure, with one end located inside the primary air pipe 2 and arranged coaxially with the primary air pipe 2, and the other end extending outside the primary air pipe 2 by penetrating its side wall. This structural arrangement facilitates simultaneous ventilation of the natural gas central pipe 1 and the primary air pipe 2, and avoids interference between the two due to simultaneous ventilation. The inner wall of the outlet end of the natural gas central pipe 1 is provided with an obtuse body shape 11 to match the aerodynamic properties of an obtuse body. The arrangement of the obtuse body 11 is a conventional technical method in the field of burners and will not be described in detail here. 【0036】 The multi-stage micro-decomposition swirling flow burner 100 for ammonia-mixed fuel is configured by fitting a natural gas central tube 1, a primary air tube 2, and a burner shell 3 in sequence from the inside out to form a primary air passage 4 and an overfire air duct 5 that are spaced apart from each other. Natural gas is injected from the natural gas central tube 1, which accounts for approximately 20% of the volume of natural gas. The swirling flow vanes 7 are positioned within the primary air passage 4 and around the natural gas central tube 1, mixing the primary air with the central natural gas in a swirling flow state. Subsequently, under the action of the ignition device 6, a diffusion flame is formed. In this way, a single sustained-burn pilot flame is formed at the center of the injection end of the multi-stage micro-decomposition swirling flow burner 100 for ammonia-mixed fuel. A primary air distribution pipe 10 with an adjustable nozzle angle is positioned outside the primary air pipe 2, and the outlet end of the primary air distribution pipe 10 is longer than the outlet ends of the natural gas central pipe 1 and the primary air pipe 2, thereby delaying the inflow of some primary air into the combustion area and ensuring complete combustion of the fuel. A fuel distribution nozzle 8, consisting of multiple microdecomposition holes 81, is positioned on the outer circumference of the primary air distribution pipe 10. 100% ammonia and the remaining 80% natural gas are premixed to form an ammonia-mixed fuel, which is rectified by a fuel supply pipe 9 connected to the fuel distribution nozzle 8 and injected at high speed from the microdecomposition holes 81, generating negative pressure to continuously draw in surrounding overfire air. At the same time, the ammonia-mixed fuel is injected into the high-temperature combustion area of ​​the pilot flame at the center of the burner, so that the ammonia is rapidly decomposed, and the large amount of hydrogen produced helps to improve combustion stability. In the combustion process of ammonia-mixed fuel, the overall equivalent ratio of the ammonia-mixed fuel to the multi-stage micro-decomposition swirling flow burner 100 for the ammonia-mixed fuel is generally controlled to a lean combustion state, for example, by controlling the overall equivalent ratio of the ammonia-mixed fuel to the multi-stage micro-decomposition swirling flow burner 100 for the ammonia-mixed fuel to 0.7 to 0.8, while simultaneously controlling the local equivalent ratio of the overfire air to the ammonia-mixed fuel to a rich combustion state, for example, by controlling the local equivalent ratio of the overfire air to the ammonia-mixed fuel to 1.0 to 1.3. A more preferred technical approach is to generally control the local equivalent ratio of the overfire air to the ammonia-mixed fuel to approximately 1.2 during the combustion process of ammonia-mixed fuel. 【0037】 Based on the above, in the multi-stage micro-decomposition swirling flow burner 100 for ammonia-mixed fuel proposed in this technology, during operation, the natural gas in the center and the swirling flow air first form a stable high-temperature pilot flame by the ignition device 6, and the remaining natural gas, after being pre-mixed with ammonia, is injected at a constant equivalence ratio through the micro-decomposition holes 81 into the high-temperature region formed by the combustion of the high-temperature pilot flame. By combining this with the setting of the primary air distribution piping, complete combustion of the fuel can be achieved, combustion stability can be improved, and NOx emissions can be reduced. Compared with conventional technology, this technology proposal has the following beneficial technical effects. 【0038】 (1) A multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel that enables precise control of NOx emissions, and can solve the problem of high NOx emissions in current ammonia-mixed fuels. 【0039】 (ii) During combustion, a flame region consisting of different internal and external passages is formed, and the flame field generated by the central pilot flame provides a stable high-temperature environment for the decomposition of ammonia fuel, resulting in high combustion stability and low NOx emissions. 【0040】 (3) The combustion output of the burner can be freely controlled by adjusting the number of times the fuel supply pipe 9 is opened and closed. 【0041】 (iv) The design of the micro-decomposition holes increases the fuel flow rate, which effectively prevents flashback during combustion. 【0042】 (5) Because the primary air passage 4, the overfire air duct 5, and the primary air distribution pipe 10 are partitioned in a sealed connection, the fuel and oxidizer in each stage can reach a uniform mixture state when they reach the planar position of the burner outlet, thus avoiding premixing of fuel and oxidizer. At the same time, the ratio of fuel to oxidizer can be precisely controlled according to the required operating conditions, enabling rapid decomposition of the ammonia-mixed fuel and achieving low NOx combustion technology. 【0043】 The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be within the scope of protection of the present invention. [Explanation of symbols] 【0044】 100 Multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel 1. Natural gas central pipe 2 Primary wind pipe 3 burner shells 4 Primary air path 5. Overfire air duct 6 Ignition device 7 Swirling Flow Blades 8 Fuel distribution nozzles 81 Differential resolution hole 9 Fuel supply pipe 10 Primary air distribution piping 11 Blunt body

Claims

[Claim 1] A multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel, comprising a natural gas central tube (1), a primary air duct (2), and a burner shell (3) fitted in order from the inside to the outside, A primary air passage (4) is formed between the outer wall of the natural gas central pipe (1) and the inner wall of the primary air pipe (2), and an overfire air duct (5) is formed between the outer wall of the primary air pipe (2) and the inner wall of the burner shell (3). An ignition device (6) and a swirling flow vane (7) are provided within the primary air passage (4). The swirling flow vane (7) is attached to the outer circumference of the outlet end of the natural gas central pipe (1). The swirling vane (7) is positioned to create a swirling flow in the primary air passage (4) and mix it with the natural gas injected from the outlet end of the natural gas central pipe (1). The ignition device (6) ignites and burns the mixed primary air and natural gas to form a sustained pilot flame at the outlet end of the natural gas central pipe (1). A fuel distribution nozzle (8) is provided inside the overfire air duct (5). The fuel distribution nozzle (8) is located near the outlet end of the natural gas central pipe (1), The outlet end of the fuel distribution nozzle (8) is provided with a plurality of holes (81) having an opening smaller than the nozzle diameter of the fuel distribution nozzle (8) and capable of injecting fuel at high speed. Ammonia-mixed fuel is injected at high speed, and the ammonia in the ammonia-mixed fuel burns under the action of a pilot flame. When the ammonia-mixed fuel is injected at high speed, a negative pressure is formed at the end of the overfire air duct (5), and the overfire air generated by the combustion of the ammonia-mixed fuel is drawn in. A primary air distribution pipe (10) is further provided on the outer wall of the primary air pipe (2) and communicates with the primary air passage (4). The primary air distribution pipe (10) is located inside the overfire air duct (5). A multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel, characterized in that the outlet end of the primary air distribution pipe (10) is located on the outer circumference of the outlet end of the primary air pipe (2), and the outlet end of the primary air distribution pipe (10) is longer than the outlet end of the natural gas central pipe (1) and the primary air pipe (2). [Claim 2] A distribution nozzle is provided at the outlet end of the primary air distribution pipe (10), and The multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel according to claim 1, characterized in that the angle between the distribution pipe nozzle and the axial direction of the primary air pipe (2) is adjustable. [Claim 3] The multi-stage micro-decomposition swirling flow burner for ammonia mixed fuel according to claim 1 or 2, characterized in that a plurality of primary air distribution pipes (10) are evenly arranged along the circumferential direction of the outer wall of the primary air pipe (2). [Claim 4] Multiple fuel distribution nozzles (8) are provided within the overfire air duct (5). All of the fuel distribution nozzles (8) are evenly arranged along the circumferential direction of the primary air duct (2), The multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel according to claim 1 or 2, characterized in that the holes (81) in each of the fuel distribution nozzles (8) are evenly spaced. [Claim 5] The multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel according to claim 1 or 2, characterized in that the ignition device (6) is an ignition gun. [Claim 6] The swirling flow vane (7) includes a plurality of rotary vanes evenly arranged along the circumferential direction, The multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel according to claim 1 or 2, characterized in that the angle between each of the rotary vanes and the axial direction of the primary air duct (2) is 30° to 45°. [Claim 7] A multi-stage micro-decomposition swirling flow burner for ammonia mixed fuel according to claim 1 or 2, characterized in that the diameter of each of the holes (81) is 3 mm to 7 mm. [Claim 8] A low NOx control method, The process involves injecting a portion of the natural gas, equivalent to 20% by volume, from the outlet end of the natural gas central pipe (1), and mixing and burning it with the primary air under the action of the ignition device (6) to form the pilot flame, A low NOx control method performed using a multi-stage micro-decomposition swirling flow burner for ammonia-mixed fuel according to claim 1, characterized by comprising the steps of: pre-mixing an ammonia-mixed fuel obtained by pre-mixing the remaining portion of natural gas, which accounts for 80% of the volume, with ammonia gas at a predetermined equivalence ratio, injecting the mixture from the fuel distribution nozzle (8) into the flame region of the pilot flame, and burning and decomposing the ammonia in the ammonia-mixed fuel under the action of the pilot flame. [Claim 9] In the combustion process of the ammonia-mixed fuel, The low NOx control method according to claim 8, characterized in that the overall equivalent ratio of the ammonia mixed fuel and the multi-stage micro-decomposition swirling flow burner for the ammonia mixed fuel is controlled to a lean combustion state, and the local equivalent ratio of the overfire air and the ammonia mixed fuel is controlled to a rich combustion state.

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