A multi-stage louvered swirl pure ammonia pre-decomposition burner

Abstract

This invention discloses a multi-stage louvered swirl-type pure ammonia pre-decomposition burner, comprising a central ignition assembly, a silicon carbide heating assembly, a multi-stage louvered swirl pre-decomposition assembly, and a mixing chamber arranged coaxially from the inside out; the main combustion gas flow direction is forward; the central ignition assembly is used to introduce ammonia gas to achieve ignition and flame stabilization; the inner wall surface of the silicon carbide cylinder is smooth, and the outer wall surface is coated with a catalyst coating and has irregularly protruding small blocks; the multi-stage louvered swirl pre-decomposition assembly is arranged in the pre-decomposition channel between the silicon carbide cylinder wall and the mixing chamber cylinder wall, each stage including multiple guide rings and guide vanes; the inner diameter of each stage of the guide ring gradually decreases along the airflow direction; the guide vanes are arc-shaped, and their axes are inclined at an angle to the burner axis, with the inclination directions of adjacent stages being opposite. This invention achieves self-stabilized ignition of pure ammonia, significantly improves pre-decomposition efficiency, and achieves low nitrogen emissions.

Description

Technical Field

[0001] This invention relates to the field of ammonia fuel combustion equipment, and more particularly to a multi-stage louvered swirl pure ammonia pre-decomposition burner, which improves the stability and efficiency of pure ammonia combustion through fuel grading and swirl-enhanced pre-decomposition technology. Background Technology

[0002] Ammonia, as a carbon-neutral fuel, produces only nitrogen and water as combustion products. Under the "dual-carbon" goal, it has become one of the core directions for replacing fossil fuels and achieving a zero-carbon transition in the energy system, and is widely used in industrial furnaces, gas turbines, and marine propulsion. However, the combustion characteristics of pure ammonia itself restrict its large-scale application: on the one hand, ammonia has a high ignition energy and a slow flame propagation speed (only 1 / 10 that of hydrogen), leading to problems such as ignition failure, flame de-flame, or incomplete combustion when pure ammonia is directly burned; on the other hand, ammonia combustion is prone to generating NOx (especially thermal NOx) due to local high temperatures or uneven atmosphere, and if ammonia is not completely burned, there is also a risk of NH3 escape, causing secondary pollution. In existing technologies, "pre-decomposition" is used to decompose part of ammonia into H2 and N2 (2NH3→3H2+N2, endothermic reaction), utilizing the high flammability of H2 to improve the combustion performance of ammonia, which is a key means to solve the above problems. However, existing pre-decomposition burners have the following shortcomings: (1) Low pre-decomposition efficiency: Single-stage swirl or straight tube heating structure is mostly used, the contact time between ammonia and high temperature heat source is short and the heat transfer is uneven, resulting in low decomposition efficiency. (2) Poor flame stability: It relies on external fuel to maintain ignition or combustion. The heat matching between the central ignition zone and the peripheral pre-decomposition zone is unreasonable, which easily leads to ignition failure or unstable secondary combustion of pre-decomposition products. (3) Structural design defects: The pre-decomposition components have insufficient high temperature resistance and the swirl intensity is uncontrollable, resulting in uneven mixing of ammonia decomposition products and affecting subsequent combustion efficiency.

[0003] In summary, while existing ammonia burner technology has made breakthroughs in individual dimensions such as mixing, low-NOx combustion, and pre-decomposition, it still has core shortcomings. It cannot achieve self-stable ignition of pure ammonia without auxiliary fuel, and suffers from low pre-decomposition efficiency, poor combustion stability, and weak load adaptability. Therefore, to address these technical bottlenecks, there is an urgent need to design a pure ammonia burner structure that can achieve efficient pre-decomposition, stable ignition, and enhanced mixing. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a multi-stage louvered swirl-type pure ammonia pre-decomposition burner.

[0005] The specific technical solution is as follows: A multi-stage louvered swirl-type pure ammonia pre-decomposition burner includes a central ignition assembly, a silicon carbide heating assembly, a multi-stage louvered swirl-type pre-decomposition assembly, and a mixing chamber arranged coaxially from the inside to the outside; with the main gas flow direction as the front; the mixing chamber includes: a mixing chamber cylinder wall, a secondary air passage, and swirl blades; a front-guided inner nozzle is provided on the inner side of the middle section of the mixing chamber cylinder wall, a front-guided outer nozzle is provided at the front end, and a secondary air passage is sleeved on the outer side of the front section, in which swirl blades are provided; the outlet of the silicon carbide heating assembly is located behind the nozzle inside the mixing chamber; The central ignition assembly includes a primary ammonia gas channel, a primary air channel, an annular disk, and a blunt body arranged coaxially. The front section of the primary ammonia gas channel passes through the annular disk, and multiple primary ammonia gas outlets are evenly opened circumferentially on the outer wall of this section. A blunt body is provided at the front end. The primary air channel is sleeved around the outside of the primary ammonia gas channel, and its front end is fixedly connected to the annular disk. Multiple oblique swirling holes are evenly opened circumferentially on the outer circumference of the swirling air disc at the center of the annular disk, and multiple central air outlets are evenly opened circumferentially on the inner circumference. The silicon carbide heating assembly includes a silicon carbide cylinder wall; the silicon carbide cylinder wall is coaxially fixed to the inner side of the mixing chamber cylinder wall, and there is a pre-decomposition channel between the two, and ammonia gas is introduced into the inlet of the pre-decomposition channel; the inner wall surface of the silicon carbide cylinder wall is a smooth surface, the outer wall surface is coated with a catalyst coating that promotes the decomposition of ammonia gas, and irregular protruding small blocks are provided, and a central combustion nozzle is provided at the front end. The multi-stage louvered swirl pre-decomposition assembly is arranged in the pre-decomposition channel and includes a multi-stage louvered swirl assembly. Each stage includes a guide ring and multiple guide blades. The inner diameter of each stage of the guide ring gradually decreases along the airflow direction. The guide blades are arc-shaped metal sheets with their axes at an angle to the burner axis, and the angles of adjacent louvered swirl assemblies are opposite.

[0006] Furthermore, the primary ammonia outlet is composed of multiple radially distributed oblique holes along the outer wall of the primary ammonia channel, with each layer having multiple evenly distributed oblique holes circumferentially. The axis of the oblique holes forms a 30°~60° counter-current injection angle with the burner axis, and the injection direction is opposite to the direction of the main gas flow. The oblique holes have an overall rotation angle, and their rotation direction is consistent with the rotation direction of the primary air flow output from the oblique swirl holes on the swirl fan plate.

[0007] Furthermore, the swirl number of the oblique swirl holes opened on the swirl fan disk is 0.6~0.8; the blunt body has a frustum structure, with its virtual cone apex pointing backward and a cone angle of [missing information]. .

[0008] Furthermore, the silicon carbide heating assembly also includes: a fixed boss and side holes in the cylinder wall; the fixed boss is an annular bracket, coaxially fixed to the inner side of the cylinder wall of the mixing chamber, for supporting the silicon carbide cylinder wall, that is, the silicon carbide cylinder wall is coaxially fixed to the mixing chamber through the fixed boss; the front end wall surface of the silicon carbide cylinder wall is provided with a plurality of side holes in the cylinder wall that are uniformly opened circumferentially and communicate with the pre-decomposition channel.

[0009] Furthermore, the catalyst coating that aids in the decomposition of ammonia is applied to the outer wall of the silicon carbide cylinder. The catalyst is Ni-ZrO2, the coating thickness is 7-9 μm, and the mass ratio of Ni to ZrO2 is 1:3.

[0010] Furthermore, the central combustion nozzle of the silicon carbide heating assembly is a conical annular channel with a taper of 15°~30°; the inner nozzle of the mixing chamber is a conical annular shape with a taper of 20°~30°, and the outer nozzle is a conical opening with a taper of 30°~45°.

[0011] Furthermore, the mixing chamber also includes a turbulence blunt body; the turbulence blunt body is trapezoidal or hemispherical and coaxially fixed to the outlet end of the nozzle in the mixing chamber to form a secondary recirculation zone; the swirl number of the swirl blades in the secondary air duct is adjusted according to the burner load. If the burner load is less than 50% of the rated load, it is 1.2-1.5, otherwise it is 0.8-1.0.

[0012] Furthermore, in the multi-stage louvered swirl pre-decomposition assembly, the angle between the axis of the guide vanes and the axis of the burner is 15°~45°. Furthermore, in the pre-decomposition channel, after the three-stage louvered swirl assembly, a swirl blade is coaxially arranged to guide the mixed gas swirl out of the pre-decomposition channel.

[0013] Furthermore, the ammonia flow rate introduced into the central ignition assembly is 15%-20% of the total ammonia flow rate of the burner, and the ammonia flow rate introduced into the multi-stage louvered swirl pre-decomposition assembly is 85%-80% of the total ammonia flow rate of the burner.

[0014] The beneficial effects of this invention are: (1) This invention achieves self-stabilized ignition of pure ammonia without dependence on auxiliary fuels. Through the synergy of "multi-layer reverse injection of ammonia + swirling air + blunt body reflux", the high-temperature flue gas is entrained to reduce the ignition energy of ammonia, eliminating the need for auxiliary fuels such as natural gas and hydrogen, reducing fuel costs and simplifying the system structure.

[0015] (2) The burner of the present invention has high pre-decomposition efficiency and significantly improved combustion performance. The three-stage reverse louvered swirl pre-decomposition component extends the ammonia residence time to ≥1.5s, and the silicon carbide cylinder wall is coated with a catalyst coating to enhance heat transfer and catalysis, thus significantly improving the pre-decomposition rate.

[0016] (3) The burner of this invention has excellent mixing uniformity, achieving low NOx emissions. The turbulent bluff body and adjustable swirl secondary air work together to reduce the concentration deviation of ammonia-air and lower NOx emissions. Attached Figure Description

[0017] Figure 1 This is a schematic cross-sectional view of the multi-stage louvered swirl pure ammonia pre-decomposition burner in an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the structure of the center ignition assembly provided in an embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the silicon carbide heating assembly in an embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram of the mixing chamber in an embodiment of the present invention.

[0021] Figure 5 This is a schematic diagram of the structure of the multi-stage louvered swirl pre-decomposition component in an embodiment of the present invention.

[0022] In the figure, the components are: central ignition assembly 100, primary ammonia channel 101, primary air channel 102, annular disk 103, swirl fan disk 104, blunt body 105, primary ammonia outlet 106, and central air outlet 107; silicon carbide heating assembly 200, fixed boss 201, silicon carbide cylinder wall 202, central combustion nozzle 203, and cylinder wall side hole 204; multi-stage louvered swirl pre-decomposition assembly 300, first-stage louvered swirl assembly 301, second-stage louvered swirl assembly 302, third-stage louvered swirl assembly 303, guide vane 304, and guide ring 305; mixing chamber 400, mixing chamber cylinder wall 401, mixing chamber nozzle 402, turbulence blunt body 403, secondary air channel 404, swirl vane 405, and mixing chamber outlet nozzle 406. Detailed Implementation

[0023] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The objectives and effects of the present invention will become clearer as a result. The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] This embodiment proposes a multi-stage louvered swirl-type pure ammonia pre-decomposition burner. Through the synergistic design of "center reverse injection ignition - silicon carbide nozzle heat transfer - multi-stage louvered swirl pre-decomposition," it improves the efficiency and combustion stability of pure ammonia pre-decomposition, making it suitable for small industrial furnaces and distributed energy equipment. Figure 1As shown, the burner includes, from the inside out, the following components arranged coaxially: a center ignition assembly 100, a silicon carbide heating assembly 200, a multi-stage louvered swirl pre-decomposition assembly 300, and a mixing chamber 400. The direction of the main gas flow is considered the front, and vice versa. The outlet of the center ignition assembly 100 is located in the rear section of the cavity inside the silicon carbide heating assembly 200, and the outlet of the silicon carbide heating assembly 200 is located in the middle section of the cavity inside the mixing chamber 400.

[0025] like Figure 2 As shown, the central ignition assembly 100, as the core ignition and flame stabilization unit, includes the following components arranged along the burner axis: a primary ammonia passage 101, a primary air passage 102, an annular disc 103, a swirl fan disc 104, a blunt body 105, a primary ammonia outlet 106, and a central air outlet 107.

[0026] The primary ammonia channel 101 is a coaxially arranged metal tube (made of 310s stainless steel, with an inner diameter of 15-25mm). One end (i.e., the inlet end) is connected to the pure ammonia supply system, and the other end (i.e., the outlet end, which is the front end according to the direction definition rule) passes through the annular disk 103. The front end passes through the outer periphery of the wall of the annular disk 103 and opens the primary ammonia outlet 106. The primary ammonia outlet 106 is a radially distributed multi-layer (3-5 layers) of inclined holes along the outer wall of the primary ammonia channel 101, with multiple (6-8) inclined holes evenly distributed circumferentially in each layer. The axis of the inclined holes is at a 30°-60° counter-injection angle with the burner axis (opposite to the direction of the main gas flow). The inclined holes have a rotation angle, and their rotation direction is consistent with the rotation direction of the primary air flow. This is used to back-inject pure ammonia for ignition into the ignition zone in multiple dimensions, thereby improving the initial mixing uniformity of ammonia and air. Furthermore, the reverse injection angle of the primary ammonia outlet 106 is preferably 30°, the radial layer number is preferably 3 layers, and the orifice diameter is preferably 3mm; the ammonia flow rate entering the primary ammonia channel 101 is 15%-20% of the total ammonia flow rate of the burner, to ensure stable ignition flame and the highest ammonia fuel utilization rate.

[0027] The primary air duct 102 is encircled by the outer side of the primary ammonia duct 101. One end (i.e., the inlet end) is connected to the combustion air system, and the other end (i.e., the outlet end) is connected to the swirl fan plate 104. The plane at the center of the annular disc 103 is designated as the swirl fan plate 104. Multiple (8-12) oblique swirl holes are evenly distributed around the outer circumference of the swirl fan plate 104 to convert the primary air input through the primary air duct 102 into a swirl airflow, which is then efficiently mixed with the reverse-sprayed ammonia ejected from the primary ammonia outlet 106. The thickness of the swirl fan plate 104 (i.e., the depth of the swirl holes) is 5-8 mm, and the swirl number is 0.6-0.8. A high-energy igniter is arranged on the surface of the swirl fan plate 104 for ignition.

[0028] The swirl fan plate 104 has multiple through holes evenly distributed around its inner circumference, communicating with the primary air channel 102, serving as a central air outlet 107. This outlet is used to inject a small amount of direct current air to prevent localized heat accumulation in the central ignition area, which could lead to NOx generation, while also stabilizing the flame shape in the primary recirculation zone. Furthermore, the aperture of the primary air channel 102 is 5~8mm.

[0029] The blunt body 105 is a frustum structure, coaxially fixed to the front end face of the primary ammonia channel 101. The virtual cone vertex of the blunt body 105 points rearward, and the cone angle is... It is used to form a stable primary reflux zone behind it, entraining the high-temperature flue gas from the combustion of pure ammonia in the center, and reducing the energy requirement for ammonia ignition.

[0030] like Figure 3 As shown, the silicon carbide heating assembly 200 is arranged around the central ignition assembly 100 to provide a high-temperature heat source for the pre-decomposition of ammonia in the outer layer, and includes: a fixed boss 201, a silicon carbide cylinder wall 202, a central combustion nozzle 203, and a cylinder wall side hole 204.

[0031] The fixed boss 201 is an annular support made of silicon carbide body, which is coaxially fixed to the inner side of the cylinder wall of the mixing chamber 400 along the radial direction of the burner to support the silicon carbide cylinder wall 202.

[0032] The silicon carbide cylinder wall 202 is an annular cylinder made of high-density silicon carbide material, coaxially fixed to the inside of the mixing chamber 400 by a fixing boss 201. The silicon carbide cylinder wall 202 can withstand high temperatures of 1600℃ and above, with a thermal conductivity ≥80W / (m・K). The inner wall surface of the silicon carbide cylinder wall 202 (facing the central ignition assembly 100) is a smooth surface, used to efficiently absorb the radiant and convective heat of the central ignition flame. The outer wall surface is coated with a Ni-ZrO2 catalyst coating (coating thickness 5-10μm) to enhance heat transfer and catalysis. Irregularly protruding small pieces (not shown in the figure) are also provided on the outer wall surface, which, together with the catalyst coating, significantly increase the heat exchange and catalytic reaction area, disturb the airflow, and enhance the mixing effect of ammonia and high-temperature airflow, accelerating the ammonia decomposition reaction. Preferably, the Ni-ZrO2 catalyst coating on the outer wall surface of the silicon carbide cylinder wall 202 has a thickness of 7-9μm, and the mass ratio of Ni to ZrO2 is 1:3, resulting in the optimal ammonia decomposition catalytic efficiency.

[0033] The central combustion nozzle 203 is located at the front end of the silicon carbide cylinder wall 202 and is a conical annular channel with a taper of 15°~30°, used to guide the high-temperature flame generated by the central ignition assembly 100.

[0034] The side holes 204 are multiple circumferentially uniformly opened through holes on the front wall surface of the silicon carbide cylinder wall 202, with a diameter of 8-12mm. The high-temperature exhaust gas from the central combustion will enter the pre-decomposition channel between the silicon carbide cylinder wall 202 and the mixing chamber cylinder wall 401 through the side holes 204 to achieve heat exchange and maintain the temperature of the silicon carbide cylinder wall 202 stable (preferably stable at 800-900℃).

[0035] like Figure 4 As shown, the mixing chamber 400 includes: a mixing chamber wall 401, an inner mixing chamber nozzle 402, a turbulence blunt body 403, a secondary air passage 404, a swirl vane 405, and an outer mixing chamber nozzle 406.

[0036] The mixing chamber wall 401 is a high-temperature resistant metal cylinder (made of 310s stainless steel), and its inner wall surface is coated with a high-temperature heat-insulating coating (10~15μm thick) to reduce combustion heat loss. An annular channel is formed between the outer wall surface of the silicon carbide cylinder wall 202 and the inner wall surface of the mixing chamber wall 401, which is referred to as the pre-decomposition channel.

[0037] The nozzle 402 inside the mixing chamber is a conical opening (contraction angle 20°~30°) located on the inner side of the middle section of the mixing chamber wall 401 to avoid airflow dispersion. The central combustion nozzle 203 is located behind the nozzle 402 inside the mixing chamber and works in conjunction with it to serve as the outlet of the pre-decomposition channel. The pre-decomposed ammonia-hydrogen mixture is introduced into the ammonia-hydrogen mixing chamber through the conical constriction structure. The ammonia-hydrogen mixing chamber is a highly efficient mixing area for the high-temperature exhaust gas and ammonia decomposition gas from the burner.

[0038] The turbulence blunt body 403 has a trapezoidal or hemispherical structure and is coaxially fixed to the outlet end of the nozzle 402 in the mixing chamber. It is used to form a secondary reflux zone in the ammonia-hydrogen mixing chamber, break the concentration stratification of the mixed gas, and promote the uniform mixing of the mixed gas.

[0039] The mixing chamber outdoor nozzle 406 is a conical opening located at the front end of the mixing chamber cylinder wall 401, with a contraction angle of 30°~45°. It is used to guide the flame after stable combustion, and the conical contraction structure can enhance the flame rigidity, adapting to the flame shape requirements of different combustion equipment such as industrial furnaces, gas turbines, etc., and adapting to the heating requirements of small industrial furnaces.

[0040] The secondary air duct 404 is an annular channel surrounding the front outer side of the mixing chamber wall 401. One end (the inlet end) is connected to the secondary air supply system, and the other end (the outlet end) is flush with the front end of the mixing chamber wall 401 and connected to the swirl vanes 405. The swirl vanes 405 are 16-20 arc-shaped blades (swirl number 0.8-1.5) evenly arranged circumferentially outside the mixing chamber nozzle 406. They are used to convert the secondary air into swirling airflow, precisely matching the amount of air required for the combustion of the pre-decomposed mixture, and controlling the excess air coefficient of combustion to 1.1-1.3. Furthermore, the swirl number of the swirl vanes 405 can be adjusted according to the burner load. The adjustment logic is as follows: 1.2-1.5 at low load (<50% rated load) to enhance mixing and prevent flameout; 0.8-1.0 at high load (≥50% rated load) to reduce the peak combustion temperature and suppress NOx formation.

[0041] like Figure 5 As shown, the multi-stage louvered swirl pre-decomposition assembly 300 is fitted outside the silicon carbide heating assembly 200 and located inside the mixing chamber 400 (i.e., arranged in the pre-decomposition channel). It provides swirl enhancement disturbance for ammonia pre-decomposition and includes: a first-stage louvered swirl assembly 301, a second-stage louvered swirl assembly 302, and a third-stage louvered swirl assembly 303. Each stage of the louvered swirl assembly includes multiple guide vanes 304 and guide rings 305. After the ammonia gas to be decomposed enters from the annular ammonia inlet of the pre-decomposition channel, it forms a strong swirl under the guidance of the first-stage louvered swirl assembly 301, the second-stage louvered swirl assembly 302, and the third-stage louvered swirl assembly 303 in sequence, prolonging the residence time of ammonia in the pre-decomposition channel (≥1.5s). At the same time, under the directional action of the gradually narrowing guide rings 305, the contact frequency between ammonia and the outer wall surface of the silicon carbide cylinder wall 202 is enhanced, significantly improving the pre-decomposition efficiency.

[0042] The guide ring 305 is a concentric annular metal frame, arranged at intervals of 50~80mm along the burner axis, and coaxially fixed to the inner side of the mixing chamber cylinder wall 401. The inner diameter of the guide ring 305 gradually decreases along the airflow direction (e.g., 200mm, 180mm, 160mm in sequence), forming a "gradually narrowing guide channel" to guide the ammonia to be decomposed to the outer wall surface of the silicon carbide cylinder wall 202. At the same time, the guide ring 305 can be used to support the swirl assembly of each stage of louvers.

[0043] Each guide ring 305 has 8-12 guide blades 304 uniformly welded circumferentially; the guide blades 304 are arc-shaped metal sheets (2-3 mm thick, made of 310s stainless steel) (preferably 30°). The guide blades 304 of adjacent louvered swirl assemblies have opposite tilt angles, forming a multi-stage swirl of "inner swirl-outer swirl-inner swirl". Preferably, the tilt angle of the guide blades 304 is 30°, with the first-stage louvered swirl assembly 301 having a clockwise tilt angle, the second stage having a counterclockwise tilt angle, and the third stage having a clockwise tilt angle. At this point, the swirl disturbance intensity and airflow resistance are optimally balanced, and the ammonia residence time can reach 2 seconds.

[0044] As a core component for airflow guidance and swirl formation, the guide vane 304 plays a crucial role in airflow guidance, swirl enhancement, and mixing promotion. In existing technologies, guide vanes are mostly used in single or two-stage swirl components, and their simple structure only achieves basic airflow guidance. In this embodiment, the guide vane 304 is adapted to each stage of the louvered swirl component. Through multi-stage counter-tilt angle coordination, the airflow swirl intensity and mixing effect can be precisely controlled, significantly reducing ammonia mixing dead zones, minimizing ammonia escape, promoting full contact between the mixed airflow and the silicon carbide cylinder wall, and fully utilizing the heat of the combustion system.

[0045] In the pre-decomposition channel, after the three-stage louvered swirl assembly and before the side hole 204 of the cylinder wall, a swirl blade is coaxially arranged to guide the thermally decomposed mixed gas swirling out of the pre-decomposition channel; furthermore, the swirl blade is fixed to the inner wall of the mixing chamber cylinder wall 401 by welding.

[0046] The working principles of each stage of the above-mentioned multi-stage louvered swirl pure ammonia pre-decomposition burner are as follows: (1) Center ignition stage.

[0047] The liquid ammonia supply system delivers 15%-20% pure ammonia to the primary ammonia channel 101, which is then sprayed out in multiple dimensions through the primary ammonia outlet 106 (45° back-injection, 3 layers of oblique holes). The primary air channel 102 delivers combustion air (excess air coefficient 1.2), which forms a vortex through the swirl fan 104 (swirl number 0.7). The back-injection design of the primary ammonia channel 101 causes the ammonia flow to oppose the main combustion direction, and the primary air and back-injected ammonia mix rapidly behind the blunt body 105. A high-energy igniter (such as a plasma igniter) ignites the mixture, forming a central flame at 1000-1200℃. The flame flow forms a stable primary recirculation zone behind the conical blunt body 105, entraining the high-temperature flue gas in the central combustion zone, thus reducing the ignition energy of the pure ammonia and achieving self-stabilized ignition of pure ammonia without auxiliary fuel. During this process, a small amount of direct-flow air is injected from the central air outlet 107 to avoid localized high temperatures in the ignition zone and reduce the NOx concentration in the central combustion zone.

[0048] (2) Pre-decomposition stage.

[0049] The central flame heats the silicon carbide cylinder wall 202 and directs it to the ammonia-hydrogen mixing chamber through the central combustion nozzle 203 (25° taper). The inner wall surface of the silicon carbide cylinder wall 202 absorbs the radiant heat and convective heat of the flame, causing the cylinder wall temperature to rise. The liquid ammonia supply system introduces 85%-80% of the total flow of ammonia gas to be decomposed into the pre-decomposition channel through the annular ammonia inlet. Under the guidance of the reverse-angle guide vanes 304 (inner swirl-outer swirl-inner swirl) of the three-stage louvered swirl assembly, a multi-stage swirl is formed. Specifically, the ammonia gas flow is guided by the first-stage louvered swirl assembly 301 to the outer wall surface of the silicon carbide cylinder wall 202, and a swirl is formed under the action of the clockwise guide vanes 304, extending the contact time. Subsequently, the ammonia gas flow enters the second-stage louvered swirl assembly 302, and a swirl is formed under the action of the counterclockwise guide vanes 304, breaking the gas flow boundary layer. Finally, the gas flow passes through the third-stage louvered swirl assembly 303, and a swirl is formed again under the action of the clockwise guide vanes 304. Simultaneously, under the directional action of the gradually narrowing guide ring 305 (200mm→180mm→160mm), it continuously contacts the outer wall surface of the silicon carbide cylinder wall 202 (with a Ni-ZrO2 coating), absorbing heat and decomposing into an ammonia-hydrogen mixture (decomposition rate ≥85%). Ni-ZrO2 reduces the activation energy of ammonia decomposition to 29kJ / mol, accelerating the 2NH3→3H2+N2 reaction. Under the combined action of the high temperature of the silicon carbide cylinder wall 202, deep pre-decomposition of ammonia is achieved.

[0050] The flue gas at the outlet of the pre-decomposition channel (hereinafter referred to as the pre-decomposition mixed gas) mainly consists of N2, H2, H2O, NH3, etc., and is introduced into the ammonia-hydrogen mixing chamber through the nozzle 402 in the mixing chamber. The unreacted NH3 can also undergo a reduction reaction with the NO produced by the central flame combustion, further reducing nitrogen oxide emissions. The exhaust gas from the central flame combustion enters the pre-decomposition channel through the side hole 204 of the cylinder wall to achieve heat transfer and maintain the outer wall temperature of the silicon carbide cylinder wall 202 at 800-900℃.

[0051] (3) Mixed combustion stage.

[0052] The pre-decomposed gas mixture enters the ammonia-hydrogen mixing chamber through nozzle 402 within the mixing chamber. Under the action of the turbulence blunt body 403, a secondary reflux zone is formed, breaking the concentration stratification of the pre-decomposed gas mixture and significantly improving the mixing uniformity of the hydrogen-ammonia mixture with the secondary air, ensuring complete combustion at low flow rates. The mixed combustible gas undergoes partial oxygen-deficient combustion in the ammonia-hydrogen mixing chamber under the ignition of the central flame, and the flame is finally discharged through nozzle 406 (contraction angle 40°) outside the mixing chamber. The secondary air supplied by the secondary air system forms a vortex through the secondary air channel 404 and swirl blades 405 (the swirl number is adjusted according to the load), and is uniformly mixed with the gas mixture output from the ammonia-hydrogen mixing chamber (concentration deviation <10%), resulting in NOx emissions ≤80ppm (@6%O2) and a burnout rate ≥98%.

[0053] This led to the completion of a multi-stage louvered swirl pure ammonia pre-decomposition burner, achieving efficient, stable, and clean combustion of pure ammonia.

[0054] This implementation case, through a fuel distribution strategy of "15% primary ammonia ignition + 85% multi-stage swirl pre-decomposition", can be directly integrated into small industrial furnaces and distributed energy equipment, providing a practical technical solution for the combustion of pure ammonia at small and medium power.

[0055] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A multi-stage louvered swirl-type pure ammonia pre-decomposition burner, characterized in that, It includes a central ignition assembly, a silicon carbide heating assembly, a multi-stage louvered swirl pre-decomposition assembly, and a mixing chamber, arranged coaxially from the inside out. With the main gas flow direction as the front; the mixing chamber includes: a mixing chamber cylinder wall, a secondary air passage, and swirl blades; a front-guided inner nozzle is provided on the inner side of the middle section of the mixing chamber cylinder wall, a front-guided outer nozzle is provided at the front end, and a secondary air passage is sleeved on the outer side of the front section, in which swirl blades are provided; the outlet of the silicon carbide heating component is located behind the nozzle inside the mixing chamber; The central ignition assembly includes a primary ammonia gas channel, a primary air channel, an annular disk, and a blunt body arranged coaxially. The front section of the primary ammonia gas channel passes through the annular disk, and multiple primary ammonia gas outlets are evenly opened circumferentially on the outer wall of this section. A blunt body is provided at the front end. The primary air channel is sleeved around the outside of the primary ammonia gas channel, and its front end is fixedly connected to the annular disk. Multiple oblique swirling holes are evenly opened circumferentially on the outer circumference of the swirling air disc at the center of the annular disk, and multiple central air outlets are evenly opened circumferentially on the inner circumference. The silicon carbide heating assembly includes a silicon carbide cylinder wall; the silicon carbide cylinder wall is coaxially fixed to the inner side of the mixing chamber cylinder wall, and there is a pre-decomposition channel between the two, and ammonia gas is introduced into the inlet of the pre-decomposition channel; the inner wall surface of the silicon carbide cylinder wall is a smooth surface, the outer wall surface is coated with a catalyst coating that promotes the decomposition of ammonia gas, and irregular protruding small blocks are provided, and a central combustion nozzle is provided at the front end. The multi-stage louvered swirl pre-decomposition assembly is arranged in the pre-decomposition channel and includes a multi-stage louvered swirl assembly. Each stage includes a guide ring and multiple guide blades. The inner diameter of each stage of the guide ring gradually decreases along the airflow direction. The guide blades are arc-shaped metal sheets with their axes at an angle to the burner axis, and the angles of adjacent louvered swirl assemblies are opposite.

2. The multi-stage louvered swirl-type pure ammonia pre-decomposition burner according to claim 1, characterized in that, The primary ammonia outlet consists of multiple radially distributed oblique holes along the outer wall of the primary ammonia channel, with each layer having multiple evenly distributed oblique holes circumferentially. The axis of the oblique holes forms a 30°~60° counter-current injection angle with the burner axis, and the injection direction is opposite to the direction of the main gas flow. The oblique holes have an overall rotation angle, and their rotation direction is consistent with the rotation direction of the primary air flow output from the oblique swirl holes on the swirl fan disc.

3. The multi-stage louvered swirl-type pure ammonia pre-decomposition burner according to claim 1, characterized in that, The swirl number of the oblique swirl holes on the swirl fan is 0.6~0.8; the blunt body has a frustum structure, with its virtual cone apex pointing backward and a cone angle of [missing information]. .

4. The multi-stage louvered swirl-type pure ammonia pre-decomposition burner according to claim 1, characterized in that, The silicon carbide heating assembly further includes: a fixed boss and side holes in the cylinder wall; the fixed boss is an annular bracket, coaxially fixed to the inner side of the cylinder wall of the mixing chamber, and is used to support the silicon carbide cylinder wall, that is, the silicon carbide cylinder wall is coaxially fixed to the mixing chamber through the fixed boss; the front wall surface of the silicon carbide cylinder wall is provided with a plurality of side holes in the cylinder wall evenly distributed around the circumference and communicating with the pre-decomposition channel.

5. The multi-stage louvered swirl-type pure ammonia pre-decomposition burner according to claim 1, characterized in that, The catalyst coating on the outer wall of the silicon carbide cylinder, which aids in the decomposition of ammonia, is made of Ni-ZrO2 catalyst, with a coating thickness of 7-9 μm and a mass ratio of Ni to ZrO2 of 1:

3.

6. The multi-stage louvered swirl pure ammonia pre-decomposition burner according to claim 1, characterized in that, The central combustion nozzle of the silicon carbide heating assembly is a conical annular channel with a taper of 15°~30°; the inner nozzle of the mixing chamber is a conical annular shape with a taper of 20°~30°, and the outer nozzle is a conical opening with a taper of 30°~45°.

7. The multi-stage louvered swirl-type pure ammonia pre-decomposition burner according to claim 1, characterized in that, The mixing chamber also includes a turbulence blunt body; the turbulence blunt body is trapezoidal or hemispherical and is coaxially fixed to the outlet end of the nozzle in the mixing chamber to form a secondary recirculation zone; the swirl number of the swirl blades in the secondary air duct is adjusted according to the burner load. If the burner load is less than 50% of the rated load, it is 1.2-1.5, otherwise it is 0.8-1.

0.

8. The multi-stage louvered swirl-type pure ammonia pre-decomposition burner according to claim 1, characterized in that, In the multi-stage louvered swirl pre-decomposition assembly, the angle between the axis of the guide vanes and the axis of the burner is 15°~45°.

9. The multi-stage louvered swirl-type pure ammonia pre-decomposition burner according to claim 1, characterized in that, In the pre-decomposition channel, after the three-stage louvered swirl assembly, there are also swirl blades coaxially arranged to guide the mixed gas swirl out of the pre-decomposition channel.

10. The multi-stage louvered swirl-type pure ammonia pre-decomposition burner according to claim 1, characterized in that, The ammonia flow rate introduced into the center ignition assembly is 15%-20% of the total ammonia flow rate of the burner, and the ammonia flow rate introduced into the multi-stage louvered swirl pre-decomposition assembly is 85%-80% of the total ammonia flow rate of the burner.

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