A staged air-controlled low-NOx combustion jet burner

Abstract

This utility model discloses a staged air-controlled low-NOx combustion jet burner, comprising a fuel pipe coaxially extending within the burner housing, with a blind end at the outlet. A radial jet nozzle is connected to the side of the fuel pipe at the outlet end, and a flow gap is provided between the radial jet nozzle and the burner housing, allowing fuel and combustion air to cross-jet within the flow gap to form a mixture. A central jet pipe is located within the blind end of the fuel pipe, with its inlet radially passing through the fuel pipe upstream of the flame stabilizer and facing the inlet end. Its outlet passes through the blind end to form a jet nozzle. A combustion air inlet pipe is located on the burner housing near the inlet end. This utility model employs a fuel-combustion air cross-jet mixing technology to enhance the mixing effect of fuel and air, improve combustion efficiency, and reduce NOx emissions. Stable combustion is achieved under a wide range of operating conditions thanks to the flame stabilizer. The overall structure is simple, easy to manufacture, and low in cost.

Description

Technical Field

[0001] This utility model relates to the field of combustion device technology, specifically to a staged air-controlled low-NOx combustion jet burner. Background Technology

[0002] In industrial combustion equipment, the jet burner, as the core component for mixing and burning fuel and combustion air, directly affects combustion efficiency and pollutant emissions through its structural design. Existing jet burners typically employ a direct cross-jet mixing method, where fuel is ejected through a radial nozzle and rapidly mixes and burns with the combustion air flowing axially along the burner shell within the furnace. Specifically, in current technology, the combustion air typically enters the inner cavity of the burner shell through an inlet pipe perpendicular to the axis. Within the inner cavity, it forms a cross-jet with the fuel radially ejected from the fuel pipe head, allowing the mixture to directly enter the furnace for combustion. To stabilize the flame, a flame stabilizer is often installed at the burner head, utilizing the annular gap between it and the shell to create a low-pressure recirculation zone, preventing flame destabilization.

[0003] However, existing technologies have significant drawbacks: First, the mixing path and time between the combustion air and fuel after vertical intake are short and insufficient, leading to local air-fuel ratios that easily approach the theoretical combustion ratio, forming high-temperature concentration zones (often exceeding 1500℃). Under these temperature conditions, nitrogen is easily oxidized to generate large amounts of thermal nitric oxide, resulting in excessive nitrogen oxide emissions and seriously affecting environmental indicators. Second, the combustion air enters the mixing zone in one go, and the secondary air directly impacts the initial combustion zone, intensifying combustion and causing a sharp rise in flame temperature and flow rate, further promoting the generation of thermal nitric oxide. Third, although tertiary air is used to supplement the oxygen required for combustion, due to the large intake angle and insufficient flow rate control, it is difficult to effectively cover the high-temperature zone at the tail of the flame, resulting in limited cooling effect and inability to suppress the continuous generation of nitrogen oxides. In addition, the fuel injection flow uniformity of some burners is poor, leading to localized rich combustion or oxygen, which reduces combustion efficiency and exacerbates pollutant emissions due to localized high temperatures or incomplete combustion.

[0004] The core reason for the aforementioned defects lies in the fact that existing technologies do not provide graded control of the combustion air, resulting in a lack of precise guidance in the mixing and combustion processes. This leads to uneven air-fuel ratio distribution and difficulty in controlling high-temperature areas. Therefore, there is an urgent need for a jet burner structure that can optimize the combustion air supply method, improve mixing uniformity, and suppress localized high temperatures, in order to solve problems such as excessive nitrogen oxide emissions and insufficient combustion efficiency in existing technologies. Utility Model Content

[0005] The purpose of this invention is to overcome the defects in the existing technology and provide a staged air-controlled low-NOx combustion jet burner.

[0006] To achieve the above objectives, the technical solution of this utility model is as follows:

[0007] A staged air-controlled low-NOx combustion jet burner includes a burner shell, which is a cylindrical tube open at both ends, with one end being an inlet and the other an outlet. A fuel tube is coaxially inserted inside the burner shell, with the outlet end of the fuel tube being a blind end. Multiple radially arranged radial jet nozzles are connected to the side of the fuel tube at the outlet end. A flame stabilizing plate is provided on the side of the radial jet nozzles away from the outlet end. A flow gap is provided between the radial jet nozzles and the burner shell, allowing fuel and combustion air to cross-jet within the flow gap to form a mixture. A central jet tube is provided in the blind end of the fuel tube. The air inlet of the central jet tube passes radially through the fuel tube upstream of the flame stabilizing plate and faces the inlet end. Its air outlet passes through the blind end to form a jet nozzle. A combustion air inlet pipe is provided on the side of the burner shell near the inlet end.

[0008] Furthermore, it also includes a graded air intake system for graded control of combustion air. The graded air intake system includes a primary air structure, a secondary air structure, and a tertiary air structure, which divides the combustion air into primary air, secondary air, and tertiary air. The primary air is initially mixed with the fuel, the secondary air suppresses the combustion intensity, and the tertiary air precisely cools the fuel.

[0009] Furthermore, the primary air structure includes an annular premixing chamber, which is disposed within an annular flow gap. The annular premixing chamber has an outlet facing the outlet end, forming an annular outlet. A radial jet nozzle is connected to the inner ring of the annular premixing chamber. The outer ring of the annular premixing chamber is circumferentially connected with multiple air guide holes. The air guide holes enter the radial jet nozzle tangentially. The air guide holes form a rotating airflow within the annular premixing chamber, which forms a rotating cross jet with the radially injected fuel, and extends the mixing path under the rotational motion.

[0010] Furthermore, the secondary air structure includes an annular inner shell disposed on the outer periphery of the annular premixing chamber, an annular duct is formed between the annular inner shell and the burner shell, the air guide hole passes through the annular inner shell and connects to the annular duct, the annular duct enters the annular premixing chamber through the air guide hole to form primary air, and is ejected through the annular duct to form secondary air.

[0011] Furthermore, the annular duct is provided with a spiral air guide belt, which consists of multiple spiral air guide belts wound in the same direction; the annular inner shell is provided with a diversion ring, which is located downstream of the air guide hole inlet.

[0012] Furthermore, the tertiary air structure includes a porous cooling ring cavity, which is an annular cavity located on the outer periphery of the outlet end of the burner shell. The porous cooling ring cavity has several micro-spray holes evenly distributed circumferentially on the side facing the furnace. The porous cooling ring cavity is connected to the combustion air inlet pipe through an air inlet pipe.

[0013] Furthermore, the position of the porous cooling ring cavity in the axial direction of the burner shell is adjustable. The porous cooling ring cavity is slidably connected to the burner shell through an axial slide rail, and a driving mechanism for the porous cooling ring cavity is provided in the normal temperature zone of the outer wall of the burner shell.

[0014] Furthermore, the micro-nozzles are set at a radial outward tilt of 15°, so that the tertiary airflow covers the high-temperature area around the flame tail.

[0015] Furthermore, the central jet tube is provided with a reflux ejector structure, which includes a Venturi tube section disposed inside the central jet tube. The Venturi tube section is located at the radial jet nozzle. The narrow part of the Venturi tube passes radially through the fuel tube and is provided with a guide tube. The guide tube is located on the side of the flame stabilizer plate facing the outlet end, and the guide tube is provided with multiple guide holes on the side of the guide tube facing the outlet end.

[0016] The advantages and beneficial effects of this invention are as follows: This invention employs a fuel-combustion air cross-jet mixing technology to enhance the mixing effect of fuel and air, improve combustion efficiency, and reduce nitrogen oxide emissions. The flame stabilizer enables stable combustion under a wide range of operating conditions. The overall structure is simple, easy to manufacture, and low in cost.

[0017] The hierarchical collaborative design of this utility model forms a stepped regulation of "mixing-temperature control-cooling" through primary air swirl premixing, secondary air swirl wrapping, and tertiary air targeted cooling, breaking through the limitation of the single air path of traditional burners; the axial adjustment of the tertiary air and the distribution of the secondary air flow enable the burner to adapt to different fuels and loads, solving the problem of poor adaptability of traditional burners. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a graded air-controlled low-NOx combustion jet burner according to this utility model;

[0019] Figure 2 This is a longitudinal cross-sectional schematic diagram of the jet burner according to Embodiment 1 of this utility model;

[0020] Figure 3 This is a cross-sectional schematic diagram of the radial jet nozzle of the jet burner according to Embodiment 1 of this utility model;

[0021] Figure 4 This is an exploded view of the jet burner of Embodiment 2 of this utility model;

[0022] Figure 5 This is a longitudinal cross-sectional schematic diagram of the jet burner of Embodiment 2 of this utility model;

[0023] In the diagram: 1. Burner shell; 2. Outlet end; 3. Fuel pipe; 4. Blind end; 5. Radial jet nozzle; 6. Flame stabilizer; 7. Central jet pipe; 8. Jet nozzle; 9. Combustion air inlet pipe; 10. Annular premixing chamber; 11. Annular outlet; 12. Air guide hole; 13. Annular inner shell; 14. Annular duct; 15. Spiral air guide belt; 16. Flow divider ring; 17. Porous cooling annular cavity; 18. Micro nozzle; 19. Air inlet pipe; 20. Axial slide rail; 21. Venturi tube section; 22. Drain pipe; 23. Drain hole; 24. Circular hole; 25. Folded edge. Detailed Implementation

[0024] The specific embodiments of this utility model will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solution of this utility model and should not be construed as limiting the scope of protection of this utility model.

[0025] Example 1:

[0026] A staged airflow control low-NOx combustion jet burner, such as Figure 1-3 As shown, the device includes a burner housing 1, which is a cylindrical tube open at both ends, with one end being the inlet and the other end being the outlet 2. The main body of the burner housing 1 is a cylindrical structure. A combustion air inlet pipe 9 is provided on the side near the inlet end of the burner housing 1, and is connected to an external air supply system via a flange connection. A fuel pipe 3 is coaxially inserted inside the burner housing 1. The fuel pipe 3 is a straight fuel pipe located at the center of the burner housing 1, on the central axis of the burner, and is used to transport fuel to the burner head. The outlet end 2 of the fuel pipe 3 is a blind end 4. Multiple radially arranged radial jet nozzles 5 are connected to the side of the outlet end 2 of the fuel pipe 3. Specifically, near the head of the fuel pipe 3, six circumferentially evenly arranged radial fuel injection holes are opened on the surface of the fuel pipe 3. These uniform injection holes are installed one-to-one with the jet nozzles, allowing fuel to be uniformly sprayed circumferentially from the jet nozzles. The head of the fuel pipe 3 is plugged and welded to form the blind end 4.

[0027] A flame stabilizing disc 6 is provided on the side of the radial jet nozzle 5 away from the outlet end 2. The flame stabilizing disc 6 is located on the side of each radial jet nozzle 5 and is used to form a low-pressure zone. The flame stabilizing disc 6 has a disc structure, and its outer diameter is flush with the outlet of the radial jet nozzle 5, so that an annular gap is formed between the outer periphery of the radial jet nozzle 5 and the flame stabilizing disc 6 and the burner housing 1. The inner side is connected to the outer wall of the fuel pipe 3, and the front end face is close to the wall surface of the radial jet nozzle 5. The flame stabilizing disc 6 has multiple circular holes 24 of the same size arranged between the radial jet nozzles 5 to reduce the temperature of the radial jet nozzles 5 and the baffle wall surface. The flame stabilizing disc 6 forms a certain obstruction through its disc structure, which accelerates the airflow around it. Combined with the jet entrainment effect, a local low pressure is formed on its front side. Then, the pressure balance is maintained by the flue gas recirculation, and finally a stable low-pressure zone is formed near the front end face. This area can anchor the flame root and prevent the flame from becoming unstable due to airflow disturbance, thus achieving the function of stable combustion. In this embodiment, the size and position of the circular holes 24 between each radial jet nozzle 5 are the same. The circular holes 24 are arranged symmetrically between each radial jet nozzle 5. Three circular holes 24 of the same size are evenly arranged radially at the center position between two adjacent radial jet nozzles 5, and one circular hole 24 is set near the radial jet nozzle 5.

[0028] A flow gap is provided between the radial jet nozzle 5 and the burner housing 1, allowing the fuel and combustion air to cross-jet within the flow gap to form a mixture. Specifically, the radial jet nozzles 5 are evenly distributed circumferentially at the head of the fuel pipe 3. The fuel enters each radial jet nozzle 5 through circumferentially uniform small holes at the head and is directly ejected, crossing the combustion air to form a mixture, which then enters the furnace for combustion. A certain distance is maintained between the outlet position of the radial jet nozzle 5 and the burner housing 1 to form a transverse jet and ensure thorough mixing.

[0029] The fuel pipe 3 has a central jet pipe 7 within its blind end 4. The air inlet of the central jet pipe 7 passes radially through the fuel pipe upstream of the flame stabilizer 6 and faces the inlet end. Its outlet passes through the blind end 4 to form a jet nozzle 8. Specifically, the central jet pipe 7 is a connecting pipe between the blind end 4 and the wall of the fuel pipe 3, used to draw air from outside the fuel pipe 3 to the vicinity of the head of the fuel pipe 3. This pipe is flush with the head of the fuel pipe 3 at the blind end 4 and located at the central axis of the fuel pipe 3. It passes radially through the fuel pipe 3 at a certain distance from the nozzle, the distance from the nozzle mainly to reduce the impact on the uniformity of the flow rate of each nozzle. The inlet of the central jet pipe 7 is a certain distance from the surface of the fuel pipe 3 to reduce the influence of the wall surface, and the inlet of the central jet pipe 7 is parallel to the direction of the combustion air flow. The central jet pipe 7 introduces air from outside the fuel pipe 3 to the vicinity of the head of the fuel pipe 3. The air introduced by the central jet pipe 7 flows along the central axis of the burner, forming a cross airflow with the radial fuel jet. This increases the contact area and mixing intensity between the fuel and air, avoiding uneven mixing caused by insufficient local air in the initial stage of fuel injection. Through precise air injection and optimized position design, the central jet pipe 7 not only enhances the initial mixing effect of fuel and air but also ensures the uniformity of fuel injection, thereby achieving efficient and stable combustion of the burner.

[0030] Example 2:

[0031] This embodiment improves upon the structure of the aforementioned embodiment. By dividing the combustion air into primary air, secondary air, and tertiary air, this embodiment achieves coordinated control of staged mixing, temperature control, and cooling. It utilizes the effects of jet mixing, swirling enhancement, and targeted temperature control in fluid mechanics to solve the problem of excessive nitrogen oxides caused by uneven mixing and localized high temperatures in traditional burners.

[0032] Specifically, such as Figure 4 , 5 As shown, the primary air structure includes an annular premixing chamber 10, located within an annular gap (i.e., the annular space between the radial jet nozzle 5 and the burner housing 1). Its outlet is an annular opening facing the furnace. The fuel outlet of the radial jet nozzle 5 connects to the inner ring of the premixing chamber. Multiple guide holes 12 are evenly distributed circumferentially on the outer ring, entering the premixing chamber tangentially and forming a rotating, cross-jet with the radially injected fuel. In practical use, considering the need to increase injection intensity and fuel injection distance, the inner and outer rings of the annular opening can be designed with folded edges 25, forming a narrowed annular opening. Due to the shielding effect of the folded edges 25 on the mixed fluid, the mixing effect of the fuel and combustion air can be further enhanced.

[0033] The air guide holes 12 are arranged tangentially, causing the combustion air to form a rotating airflow when it enters the premixing chamber. This creates a swirling effect on the airflow through the tangential air guide holes 12, forming a "rotating cross jet" with the radially ejected fuel. The fuel diffuses outward along the radial direction, while the rotating airflow moves in a circular direction. The trajectories of the two overlap, extending the mixing path by 3-5 times compared to a straight jet, significantly improving mixing uniformity. The annular outlet 11 allows the premixed gas to flow smoothly into the furnace along the axial direction, avoiding local airflow impacting the furnace wall, and reserving space for subsequent replenishment of secondary air.

[0034] Specifically, the annular premixing chamber 10 has an inner diameter of 120mm, an outer diameter of 150mm, and an axial length of 80mm; there are 8 air guide holes 12 with diameters of 10mm (inlet) and 8mm (outlet), arranged tangentially along the outer ring of the premixing chamber to ensure moderate swirl intensity; there are 6 radial jet nozzles 5 with diameters of 8mm, evenly distributed circumferentially.

[0035] The secondary air structure includes an annular inner shell 13 disposed around the annular premixing chamber 10. The annular inner shell 13 fits around the annular premixing chamber 10, forming an annular duct 14 with the burner shell 1. Air guide holes 12 pass through the annular inner shell 13 and connect to the annular duct 14. Part of the combustion air entering the annular duct 14 enters the premixing chamber through the air guide holes 12 to become primary air, while part is directly ejected through the annular duct 14 to become secondary air. Multiple spiral air guides 15 with the same direction of rotation are provided inside the duct. A flow divider ring 16 is provided on the annular inner shell 13 downstream of the inlet of the air guide holes 12. The flow divider ring 16 is used to achieve flow distribution. Located downstream of the inlet of the air guide holes 12, the flow divider ring 16 can distribute the combustion air in the annular duct 14 as needed through its structural shape (such as an arc-shaped convex surface)—part enters the air guide holes 12, and the other part flows along the duct, avoiding airflow imbalance caused by local resistance differences.

[0036] The spiral guide belt 15 causes the combustion air entering the annular duct 14 to form a rotating airflow. When it flows along the burner axis to the furnace, it "wraps" oxygen from the outside of the flame, which not only avoids direct impact on the initial combustion zone to prevent a sudden increase in combustion intensity, but also extends the mixing time with unburned fuel through swirling flow, thus suppressing local high temperature.

[0037] Specifically, the annular inner shell 13 has an inner diameter of 150mm, forming a 50mm wide annular duct 14 with the burner shell 1 having an inner diameter of 200mm; there are three spiral air guides 15 with a pitch of 150mm and a clockwise rotation direction. Understandably, the air guide hole 12 is set in the same direction as the spiral air guide 15; the diversion ring 16 is an annular plate with a thickness of 5mm, used to guide 20-30% of the combustion air into the air guide hole 12 to form primary air, and 70-80% into the duct to form secondary air.

[0038] The tertiary air structure includes a porous cooling ring cavity 17, which is an annular cavity on the outer periphery of the burner shell 1 outlet end 2. It is connected to the combustion air inlet pipe 9 through the air inlet pipe 19. A micro-spray hole 18 is provided on the side facing the furnace, which is radially inclined outward at 15°. That is, the angle between the axis of the micro-spray hole 18 and the axis of the burner is 15°, and it is inclined away from the center of the burner. This ensures that the sprayed tertiary air can cover the outer area of ​​the flame tail (the area where high temperature is easily formed in traditional burners). The cavity is slidably connected to the burner shell 1 through an axial slide rail 20. The drive mechanism is located in the normal temperature zone of the outer wall of the burner shell 1.

[0039] The micro-nozzle 18 is radially outward tilted at 15°, allowing the tertiary airflow to precisely cover the high-temperature zone around the flame tail. In traditional burners, this area is the most likely to generate thermal nitric oxide. The high-speed jet, with a flow rate >80m / s, reduces the local temperature to below 1300℃ through forced convection, keeping the temperature below the nitrogen oxide generation threshold.

[0040] The axial position of the porous cooling ring cavity 17 can be adjusted by the drive mechanism to adapt to the flame shape under different loads. For example, when the flame is short under low load, the cavity moves towards the inside of the furnace; when the flame is long under high load, the cavity moves towards the burner end to ensure that the cooling zone always matches the high-temperature zone and avoids over-cooling or insufficient cooling.

[0041] The porous cooling ring cavity 17 has an outer diameter of 220mm, a width of 50mm, and 36 micro-spray holes with a diameter of 2mm, radially inclined outward at 15°. The air inlet pipe 19 has a diameter of 30mm, and the tertiary air accounts for 15-20% of the total combustion air volume. The axial slide rail 20 has a stroke of 0-100mm, and the drive mechanism adopts a magnetically coupled stepper motor with a control accuracy of ±1mm. The stepper motor drives the porous cooling ring cavity 17 to move axially through a lead screw rotating a nut pair. The lead screw is arranged along the axis of the burner shell 1, with one end fixed to the inner wall of the burner shell 1 away from the furnace by a bearing seat, and the other end suspended and not in contact with the furnace. The nut is set on the porous cooling ring cavity 17 and meshes with the lead screw. When the driven magnetic ring rotates, the nut moves axially along the lead screw, driving the porous cooling ring cavity 17 to move synchronously. The axial slide rail 20 has three parallel T-shaped tracks set along the axial direction on the burner housing 1 wall and is evenly distributed circumferentially. Three T-shaped sliders are welded to the outside of the porous cooling ring cavity 17. The sliders are embedded in the T-shaped grooves, which restrict the rotational freedom of the cooling ring cavity and only allow axial sliding to achieve directional movement in conjunction with the screw and nut pair.

[0042] The hierarchical collaborative design of this embodiment forms a stepped regulation of "mixing-temperature control-cooling" through primary air swirl premixing, secondary air swirl wrapping, and tertiary air targeted cooling, breaking through the limitations of the single air path of traditional burners; the adjustable axial direction of the tertiary air and the distribution of the secondary air flow enable the burner to adapt to different fuels and loads, solving the problem of poor adaptability of traditional burners.

[0043] Example 3:

[0044] As an improvement to the central jet tube 7, a recirculation ejector structure is provided on the central jet tube 7. This structure includes a Venturi tube section 21 disposed within the central jet tube 7. The Venturi tube section 21 is located at the radial jet nozzle 5. The narrow portion of the Venturi tube passes radially through the fuel pipe 3 and is provided with a guide pipe 22. The guide pipe 22 is located on the side of the flame stabilizer 6 facing the outlet end 2, and the guide pipe 22 has multiple guide holes 23 on the side facing the outlet end 2. This embodiment achieves efficient utilization of the recirculated flue gas near the flame stabilizer 6 through the throttling effect of the Venturi tube and the directional ejection of the guide pipe 22.

[0045] The Venturi tube section 21 is located inside the central jet tube 7. When the air in the central jet tube 7 flows through the narrow section, the flow velocity increases sharply, forming a local low-pressure area, which provides power for the drainage tube 22 to draw in the smoke without the need for an additional drive device.

[0046] The guide pipe 22 passes radially through the fuel pipe 3, with one end connected to the narrow section of the venturi tube and the other end extending to the side of the flame stabilizer 6 facing the outlet end 2, i.e., the low-pressure zone of the flame stabilizer 6 near the furnace. Multiple guide holes 23 are provided on the side of the guide pipe 22 facing the outlet end 2. The low-pressure zone formed by the flame stabilizer 6 attracts high-temperature flue gas from the furnace to flow back. This backflowing flue gas enters the guide pipe 22 through the guide holes 23. Under the suction effect of the low-pressure zone in the narrow section of the venturi tube, the flue gas enters the central jet pipe 7 through the guide pipe 22, mixes with the air inside the pipe, and is ejected from the end of the central jet pipe 7, ultimately mixing with the fuel ejected from the radial jet nozzle 5. The introduction of backflowing flue gas reduces the oxygen concentration in the initial mixing zone (inert components in the flue gas, such as CO2 and N2, dilute the oxygen), inhibits intense local combustion, and thus reduces nitrogen oxide generation. Simultaneously, the high-temperature flue gas provides preheating, promoting improved combustion efficiency, thereby achieving the goal of enhanced mixing and reduced nitrogen oxides.

[0047] Specifically, the guide tube 22 is a circular tube with a diameter of 4 mm, which passes through the fuel tube 3 radially and is welded to the narrow part of the venturi tube; the guide tube 22 extends to 10 mm from the flame stabilizer 6 towards the outlet end 2, and four guide holes 23 with a diameter of 1.5 mm are opened on the side of the tube body facing the outlet end 2. The guide tube 22 is set between two adjacent radial jet nozzles 5.

[0048] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A staged overfire low-NOx combustion jet burner characterized by, The device includes a burner housing, which is a cylindrical tube open at both ends, with one end being the inlet and the other the outlet. A fuel pipe is coaxially inserted through the burner housing, with the outlet end being a blind end. Multiple radially arranged radial jet nozzles are connected to the side of the fuel pipe at the outlet end. A flame stabilizer is provided on the side of each radial jet nozzle away from the outlet end. A flow gap is provided between the radial jet nozzles and the burner housing, allowing fuel and combustion air to cross-jet within the flow gap to form a mixture. A central jet pipe is provided in the blind end of the fuel pipe. The air inlet of the central jet pipe passes radially through the fuel pipe upstream of the flame stabilizer and faces the inlet end. Its air outlet passes through the blind end to form a jet nozzle. A combustion air inlet pipe is provided on the side of the burner housing near the inlet end.

2. A staged overfire low-NOx combustion jet burner according to claim 1, wherein It also includes a graded air intake system for graded control of combustion air. The graded air intake system includes a primary air structure, a secondary air structure, and a tertiary air structure, which divides the combustion air into primary air, secondary air, and tertiary air. The primary air is initially mixed with the fuel, the secondary air suppresses the combustion intensity, and the tertiary air precisely cools the fuel.

3. A staged overfire low-NOx combustion jet burner according to claim 2, wherein The primary air structure includes an annular premixing chamber, which is disposed within an annular flow gap. The annular premixing chamber has an outlet facing the outlet end, forming an annular outlet. A radial jet nozzle is connected to the inner ring of the annular premixing chamber. The outer ring of the annular premixing chamber is circumferentially connected with multiple air guide holes. The air guide holes enter the radial jet nozzle tangentially. The air guide holes form a rotating airflow in the annular premixing chamber, which forms a rotating cross jet with the radially injected fuel, and extends the mixing path under the rotational motion.

4. A staged overfire low-NOx combustion jet burner according to claim 3, wherein The secondary air structure includes an annular inner shell disposed on the outer periphery of the annular premixing chamber. An annular duct is formed between the annular inner shell and the burner shell. The air guide hole passes through the annular inner shell and connects to the annular duct. The air enters the annular premixing chamber through the air guide hole to form primary air and is ejected through the annular duct to form secondary air.

5. A staged overfire low-NOx combustion jet burner according to claim 4, wherein The annular duct is equipped with a spiral air guide belt, which consists of multiple spiral air guide belts wound in the same direction; the annular inner shell is equipped with a diversion ring, which is located downstream of the air guide hole inlet.

6. A staged overfire low-NOx combustion jet burner according to claim 4, wherein The tertiary air structure includes a porous cooling ring cavity, which is an annular cavity located on the outer periphery of the outlet end of the burner shell. Several micro-spray holes are evenly distributed circumferentially on the side of the porous cooling ring cavity facing the furnace. The porous cooling ring cavity is connected to the combustion air inlet pipe through an air inlet pipe.

7. A staged overfire low-NOx combustion jet burner according to claim 6, wherein The porous cooling ring cavity is adjustable in the axial direction of the burner shell. The porous cooling ring cavity is slidably connected to the burner shell through an axial slide rail. A drive mechanism for the porous cooling ring cavity is set in the normal temperature zone of the outer wall of the burner shell.

8. A staged overfire low-NOx combustion jet burner according to claim 6, wherein The micro-nozzles are set at a radial outward tilt of 15°, so that the tertiary wind covers the high-temperature area around the tail of the flame.

9. A staged overfire low-NOx combustion jet burner as defined in claim 6, wherein, The central jet tube is provided with a reflux ejector structure, which includes a Venturi tube section disposed inside the central jet tube. The Venturi tube section is located at the radial jet nozzle. The narrow part of the Venturi tube passes radially through the fuel tube and is provided with a guide tube. The guide tube is located on the side of the flame stabilizer plate facing the outlet end, and the guide tube is provided with multiple guide holes on the side of the guide tube facing the outlet end.

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