Flue gas internal circulation low-nitrogen combustion head

Abstract

This invention discloses a low-NOx burner with internal flue gas recirculation, comprising a conical combustion air guide that directs the combustion air flow towards the furnace wall of the combustion chamber, forming two independent swirling airflow vortex zones. The combustion gas is divided into a front center and a rear outer ring. By rationally arranging the injection position and direction of the combustion gas, it is pre-mixed with the flue gas swirling in the two vortex zones before being mixed with air for combustion, thus reducing the formation of nitrogen oxides. An annular gap is left between the flame tube and the air guide plate. The flue gas in the combustion chamber is drawn into the negative pressure zone through the annular gap and then drawn into the flame tube by the combustion air flow, mixing with the combustion air inside the flame tube. This invention, by pre-diluting the combustible material and oxidant separately before mixing and burning, reduces the intensity of the combustion reaction, expands the combustion reaction zone, ensures a more uniform temperature inside the combustion chamber, avoids localized high temperatures, and reduces the generation of nitrogen oxides.

Description

Technical Field

[0001] This invention belongs to the technical field of burners and related air-fuel-flue gas mixing devices, specifically relating to a low-NOx burner head with internal flue gas recirculation. This invention relates to associated industrial burners, encompassing types including burners mounted on a combustion chamber, using natural gas as fuel, for systems without external flue gas recirculation. Background Technology

[0002] As is well known, nitrogen oxides (NOx) are toxic and harmful gases. During combustion, thermal nitrogen oxides are the main type. A key characteristic of NOx emissions is that as the temperature of the flame and combustion zone increases, the emissions of nitrogen oxides also increase exponentially. Controlling and reducing the flame temperature during combustion has become the main technical means to reduce thermal nitrogen oxide emissions.

[0003] Flue gas recirculation (FGR) technology is a low-NOx combustion technology widely used in boiler systems. FGR utilizes the flue gas produced during combustion, whose main components are carbon dioxide, water vapor, and nitrogen. By circulating the non-combustible flue gas back to the combustion zone, the combustibles and oxidizers are diluted by the flue gas before combustion during the chemical reaction that occurs. This reduces the intensity of the combustion reaction, lowers the flame temperature, and also lowers the temperature of the combustion zone. This effectively reduces the conditions for the formation of thermal nitrogen oxides from oxygen and nitrogen, thereby reducing the formation of nitrogen oxides.

[0004] Flue gas recirculation (FGR) technology is basically divided into two categories: external FGR and internal FGR. External FGR involves drawing a portion of the flue gas from the boiler's tail outlet and mixing it with combustion air before it enters the combustion zone. Internal FGR utilizes a swirling airflow created within the boiler's combustion chamber to directly circulate the flue gas into the combustion zone. The difference between internal and external FGR refers to whether the recirculation occurs inside or outside the combustion chamber. Often, a combination of internal and external FGR is used. Internal FGR technology is relatively mature for NOx ≤ 80 mg / m³, and when combined with external FGR, it can achieve NOx ≤ 30 mg / m³.

[0005] The most widely used type of burner on the market is the diffusion burner with external flue gas recirculation technology, which reduces nitrogen oxide emissions. This type of burner has a relatively simple burner head structure and is relatively reliable in operation. However, because its working principle involves using a fan to circulate and burn the flue gas, it requires increased blower power or the use of a flue gas recirculation fan, which increases investment costs.

[0006] Furthermore, most on-site flue gas return ducts connect to the burner blower inlet side. Since the flue gas temperature is high and the combustion air temperature is low, water vapor in the flue gas condenses into water when they meet, causing corrosion at the junction. In severe cases, condensate can enter the burner, leading to malfunctions in the flame detector sensing components and ignition elements, creating safety hazards. Additionally, condensate entering the burner casing corrodes the blower impeller, internal burner components, and the casing itself, affecting the burner's service life.

[0007] To achieve the desired reduction of nitrogen oxides, commercially available flue gas recirculation boilers typically require a sufficiently large combustion chamber diameter and ample recirculation space to ensure adequate flue gas volume for effective recirculation. Increasing the furnace size significantly increases boiler costs.

[0008] These flue gas recirculation burners achieve the goal of reducing nitrogen oxides by sending flue gas into the combustion zone through recirculation. However, in pursuit of even lower emission standards, it is necessary to increase the amount of flue gas recirculated, which further reduces the intensity of the combustion flame. These practices lead to a decrease in combustion stability, making it prone to combustion surges, flame instability, and an increase in the failure rate of the burner.

[0009] Patent document DE 3811477 A1 describes a gas burner where gas and air are mixed at the combustion chamber inlet, with the gas entering through several mixing pipes. Specifically, the gas is directly fed into the combustion chamber inlet via the mixing pipes and their nozzles, mixing with the combustion air before entering the combustion chamber. The gas pipe outlets are distributed across different cross-sections within the burner's mixing chamber according to the divergence direction.

[0010] The patent document DE 195 09 219 describes a method and its burner head that supplies combustion air while fuel gas is burning, using inert gases to reduce nitrogen oxides. The fuel gas is divided into two stages, with one stage superimposed on the other. It is blown in from the root of the flame in the direction of the flow of the combustion air. The mixture of combustion air and fuel gas with a superchemical reaction ratio in the first stage flows to the flame. The supplementary fuel gas is added to the cross section of the second stage. The flue gas that is recycled there is added to the second stage as an inert gas. A portion of the combustion gas is injected into the second stage and forms a mixture with the recycled flue gas with a reaction ratio lower than the chemical reaction ratio. The mixture is mixed before reaching the flame.

[0011] Patent EP 0 635 676 describes a method for use in a low-NOx combustion device for liquid or gaseous fuels. The burner extends into the combustion chamber of a boiler, and its burner tube has at least one fuel nozzle for supplying fuel and is adjacent to a flame stabilizer. This method delivers a large amount of gas from the flame stabilizer to the inner wall area of ​​the burner tube. The fast airflow flowing through the gap between the burner tube and the flame stabilizer creates a negative pressure at the leading edge of the burner tube. The flue gas generated in the combustion chamber is sent to this negative pressure zone through internal circulation. The burner tube has multiple guide points that extend into the negative pressure zone.

[0012] Chinese patent CN112178626B describes an internal circulation low-NOx gas burner. A cyclone separator is fitted onto one end of a first gas pipe, an annular gas head is fitted onto the outside of the cyclone separator with a clearance fit, a second gas pipe supplies gas to the annular gas head, a diverter is fitted onto the outside of the annular gas head, and a flow divider is fitted onto the outside of the diverter, forming a flue gas passage with the diverter. Multiple sets of inner ring gas assemblies are located within the flue gas passage, and multiple sets of outer ring gas assemblies are installed around the flow divider. The diverter is used to divert air to form mixed-smoke air and mixed-combustion air. When the mixed-smoke air flows through the flue gas passage, a negative pressure is generated at the flue gas inlet, thereby drawing in the flue gas from the combustion chamber and re-participating in combustion. Because it utilizes a vacuum method to directly recover flue gas, it not only eliminates the need for a flue gas passage and removes safety hazards, but also reduces operating costs.

[0013] Chinese patent CN107120652 discloses a staged gas low-NOx burner, relating to the field of burner technology. The staged gas low-NOx burner includes a distributor, a guide plate, an ignition electrode, an ignition fuel pipe, and a combustion cylinder. The distributor provides flow paths for gas and air, and includes a body, multiple gas nozzles, a gas distribution ring, and multiple air distribution pipes. The body is a cylinder with a first interlayer; gas enters the gas pipe through the body and is then ejected by the gas distribution ring. Air flows through the hollow part of the body, the air distribution pipes, and the outside of the distributor to form an airflow path, providing combustion-supporting gas to the gas. The distribution ring in CN107120652 is relatively thin, shown in the figure as no more than four times the diameter of the gas distribution hole; it only distributes gas as inner and outer rings and does not separate air. The guide plate in CN107120652 guides the air introduced by the multiple air distribution pipes, forming a rotating airflow; the main component is air, and no gas distribution device is provided.

[0014] The aforementioned known patented methods and structures are insufficient to meet the increasing demand for reduced pollutant emissions from combustion equipment, especially when legal requirements for nitrogen oxide emissions are further reduced. These methods and structures are limited and still suffer from problems such as excessive nitrogen oxide emissions or unstable combustion, making it difficult to meet environmental emission standards.

[0015] This invention utilizes a combustion air guide to direct combustion air towards the combustion chamber wall, creating two vortex zones that fully utilize the combustion chamber space and enable internal flue gas recirculation. The rational arrangement of the gas outflow position and direction allows the gas to be mixed and diluted with a portion of the flue gas before meeting the airflow for combustion. Furthermore, before meeting the gas at the combustion head, the combustion air is also mixed and diluted with the flue gas drawn in at the guide plate on the front wall of the combustion chamber within the flame tube. This method of pre-mixing the combustible material and oxidizer with the flue gas, followed by the diluted combustible material and oxidizer for combustion, effectively improves the flue gas mixing efficiency, reduces combustion intensity and flame temperature, and minimizes the generation of nitrogen oxides.

[0016] The purpose of this invention is to overcome the aforementioned shortcomings of existing burners. The flue gas recirculation low-NOx burner of this invention utilizes a structure consisting of a combustion air cone guide, a central gas distributor, a guide plate, and an outer gas ring to form two vortex zones inside the combustion chamber. By utilizing the relatively static airflow area at the center of the vortex, similar to the eye of a typhoon, the flame remains stationary. Simultaneously, the high airflow velocity and large volume at the outer ring of the vortex ensure effective mixing of flue gas and fuel gas. This guarantees flame stability while effectively providing sufficient internally recirculated flue gas to the combustion zone, reducing the formation of nitrogen oxides. Summary of the Invention

[0017] This invention was made to solve the above-mentioned problems, and its purpose is to provide a stable, safe, and efficient flue gas recirculation low-NOx gas burner.

[0018] The technical solution of this invention is a low-NOx combustion head with internal flue gas recirculation, comprising an air guide duct, a flame tube, a gas collector, and a central gas distributor. The air guide duct and the flame tube are coaxially arranged. The gas collector axially passes through the interior of the air guide duct, and the central gas pipe of the central gas distributor axially passes through the interior of the flame tube. The central gas pipe is connected to the gas collector. A combustion air guide plate is provided at the air outlet of the air guide duct, and the combustion air guide plate has guide holes. A gap exists between the combustion air guide plate and the flame tube. An annular arrangement is provided on the outer wall of the flame tube. An outer gas ring is axially connected to the gas distributor via one or more outer gas pipes. An axial gas nozzle is provided on the outer gas ring. A combustion air guide is provided at the front end outlet of the flame tube. The combustion air guide is installed on the central gas pipe. The combustion air guide includes a guide surface. The guide surface cooperates with the front end of the flame tube to form a channel that guides the combustion air to the combustion chamber wall to form a vortex zone. A radial nozzle pipe and an axial nozzle pipe of the central gas distributor are provided on the back side of the guide surface. The axial nozzle pipe has a gas hole opened radially.

[0019] Furthermore, the guiding surface of the combustion air guide is a conical guiding surface, and the combustion air guide also includes a guide end disc. The conical guiding surface is installed on the guide end disc, and the central gas pipe passes through the cone apex of the conical guiding surface and exits from the center of the guide end disc.

[0020] Furthermore, the central gas pipe passes through one side of the combustion chamber on the coaxial axis of the end disc of the diffuser and connects to the radial nozzle pipe or axial nozzle pipe of the central gas distributor.

[0021] Furthermore, the combustion air guide plate is conical or flat, and one or more triangular, trapezoidal or circular air guide holes are provided on the combustion air guide plate, and triangular air guide vanes are provided on the air guide holes.

[0022] Furthermore, the gap between the combustion air guide plate and the flame tube is an annular gap. This annular gap is located inside the combustion chamber and connects the inside and outside of the flame tube. The starting point of the annular gap is the combustion air guide plate, and the ending point of the annular gap is the rear end face of the flame tube.

[0023] Furthermore, the gas distributor includes a central gas connector and an outer ring gas connector. The inlet end of the gas distributor is connected to the main gas pipe. The central gas connector passes through the center of the combustion air guide plate and is connected to the central gas pipe of the central gas distributor. The outer ring gas connector is connected to the outer ring gas ring.

[0024] Furthermore, the conical air guide is arranged coaxially with the flame tube and located at the front end of the flame tube. Combustion air and circulating flue gas are mixed inside the flame tube, and the mixed airflow is guided to flow out towards the furnace wall of the combustion chamber through the channel between the front end of the flame tube and the conical air guide.

[0025] Furthermore, the gas enters the central gas connector and the outer ring gas connector of the gas distributor through the gas main pipe. The central gas enters the central gas pipe through the central gas connector, and then flows into the radial nozzle pipe and the axial nozzle pipe before being ejected through the nozzles to form the front central gas section. The outer ring gas enters the outer ring gas ring through the outer ring gas connector and is ejected along the outer wall of the flame tube through the nozzles on the outer ring gas ring to form the rear outer ring gas section.

[0026] Furthermore, the channel formed between the combustion air guide and the flame tube guides the combustion air flow towards the combustion chamber wall, where it splits at the combustion chamber wall to form two independent swirling airflow vortex zones: a front vortex zone and a rear vortex zone.

[0027] Furthermore, the gas ejected from the nozzles on the radial and axial nozzles of the central gas distributor mixes with the flue gas swirling in the front vortex zone and then merges with the combustion air flow.

[0028] This invention utilizes the separate mixing of fuel gas and flue gas, and air and flue gas, followed by combustion. The combustible material and oxidant are first diluted and preheated. When the mixture reaches its natural temperature, the oxygen content is below 10%, and the combustion chamber temperature reaches 1000°C, the conditions for flameless combustion are met in this part of the space. The mixture will then transition to a flameless combustion state. It can be observed that there is no obvious flame in this part of the combustion chamber, the reaction zone is significantly expanded and becomes transparent, the combustion is gentle, the noise is reduced, the temperature inside the combustion chamber is more uniform, and the thermal efficiency is improved while nitrogen oxides are further reduced.

[0029] In summary, the beneficial effects of the present invention are as follows: The flue gas internal circulation burner head technology with combustion air diversion method provided by the present invention can achieve low nitrogen oxide emissions, higher combustion efficiency, uniform combustion chamber temperature, better heat exchange effect, lower boiler energy consumption, and lower boiler manufacturing cost when the combustion chamber diameter is small. Attached Figure Description

[0030] Figure 1 The diagram shows a schematic of the low-NOx burner head for internal flue gas recirculation placed in the combustion chamber according to the present invention.

[0031] Figure 2 The diagram shows the structure of the flue gas internal circulation low-NOx burner head of the present invention placed in the combustion chamber, which shows the flow channels and directions of the fuel gas, air and flue gas, as well as the area of ​​the flame.

[0032] Figure 3 The image shown is a cross-sectional view of the low-NOx combustion head with internal flue gas recirculation according to the present invention.

[0033] Figure 4 The diagram shown is a structural schematic of the combustion air guide device for the flue gas internal circulation low-NOx burner head of the present invention.

[0034] Figure 5 The diagram shows the outer gas ring and combustion air guide plate of the flue gas internal circulation low-NOx burner of the present invention.

[0035] Reference numerals: 1. Combustion chamber; 2. Burner head; 3. Combustion air guide; 4. Central gas distributor; 5. Outer gas ring; 6. Combustion air guide plate; 7. Flame tube; 8. Gap; 9. Gas collector; 11. Front wall; 12. Combustion chamber wall; 13. Heat medium; 21. Connecting flange; 22. Air guide tube; 31. Guide surface; 32. End disc of guide; 41. Radial nozzle pipe; 42. Axial nozzle pipe; 43. Gas nozzle; 44. Central gas pipe; 51. Gas nozzle; 52. Outer gas connecting pipe; 61. Air guide hole; 62. Air guide vane; 71. Flame tube outer wall; 72. Flame tube inner wall; 73. Flame tube front end; 74. Flame tube rear end; 91. Main gas pipe; 92. Central gas pipe; 93. Outer ring gas pipe; A. Combustion air; B. Gas; C. Flue gas; D. Vortex zone; F. Flame; A1. Mixture of combustion air and flue gas; B1. Central gas; B2. Outer ring gas; C1. Front swirling flue gas; C2. Rear swirling flue gas; C3. Flue gas returning to the guide vane; D1. Front vortex zone; D2. Rear vortex zone; F1. Front flame zone; F2. Rear flame zone; F3. Diversion point flame zone. Implementation

[0036] To make the technical means, technical features, objectives and technical effects of the present invention easy to understand, the present invention will be specifically described below in conjunction with embodiments and accompanying drawings.

[0037] like Figures 1 to 5 As shown, it illustrates the specific principle and structure of the internal circulation low-NOx combustion head of the present invention.

[0038] like Figure 1 and Figure 2 As shown, an internal circulation low-NOx burner head 2 of the present invention is installed on the front wall 11 of the combustion chamber 1 via a connecting flange 21. The outer side of the combustion chamber furnace wall 12 is the heat medium 13, and the internal circulation component of the burner head 2 extends into the interior of the combustion chamber 1.

[0039] like Figure 3 and Figure 4As shown, a specific structure of an internal circulation low-NOx burner head is disclosed. The burner head includes an air guide duct 22, a flame tube 7, a gas distributor 9, and a central gas distributor 4. The air guide duct 22 and the flame tube 7 are coaxially arranged. The gas distributor 9 axially passes through the interior of the air guide duct 22, and the central gas pipe 44 of the central gas distributor 4 axially passes through the interior of the flame tube 7. The central gas pipe 44 is connected to the central gas pipe 92 of the gas distributor 9. A combustion air guide plate 6 is provided at the air outlet of the air guide duct 22, and an air guide hole 61 is provided on the combustion air guide plate 6. Combustion air A can enter the interior of the flame tube 7 through the air guide hole 61. An annular gap 8 exists between the combustion air guide plate 6 and the flame tube 7. An annular outer ring of gas is arranged on the outer wall of the flame tube 7. The outer ring of gas 5 is axially connected to the outer ring of gas pipe 93 of the gas distributor 9 through one or more outer ring of gas pipes 52. An axial gas nozzle 51 is provided on the outer ring of gas 5. A combustion air guide 3 is provided at the outlet of the front end 73 of the flame tube. The combustion air guide 3 is installed on the central gas pipe 44. The combustion air guide 3 includes a guide surface 31. The guide surface 31 cooperates with the front end 73 of the flame tube to form a channel that guides the combustion air to the combustion chamber wall 12 to form a vortex zone. A radial nozzle pipe 41 and an axial nozzle pipe 42 of the central gas distributor 4 are provided on one side of the back of the guide surface 3. The axial nozzle pipe 42 has a gas injection hole 43 opened radially. Of course, the central gas distributor 4 is not limited to axial and radial gas distribution. It can include gas distribution at any angle at the front end of the conical combustion air guide 3, for the method of gas mixing with swirling flue gas before gas mixing with air.

[0040] like Figure 4 As shown, the combustion air guide 3 includes a guide surface 31 and a guide end disc 32. The guide surface 31 is conical (or trumpet-shaped). The central gas pipe 44 of the central gas distributor 4 passes through the cone apex of the conical guide surface 31 and through the center of the guide end disc 32 towards the combustion chamber 1. The guide end disc 32 is a circular flat plate, but is not limited to a flat plate shape. It includes structural shapes with folded edges, openings, and guide fins that have a guiding function. The outer edge size is not limited to being equal to, greater than, or less than the flame tube diameter. The diameter of the guide end disc 32 satisfies the function of guiding the combustion air to the outer wall of the combustion chamber, forming the structural size of two vortex zones. The central gas pipe 44 of the central gas distributor 4 connects the radial nozzle pipe 41 and the axial nozzle pipe 42. The axial nozzle pipe 42 has gas injection holes 43 radially opened. An annular outer ring gas ring 5 is arranged on the outer wall 71 of the burner flame tube 7. The outer ring gas ring 5 is axially connected to the outer ring gas pipe 93 of the gas distributor 9 through one or more outer ring gas pipes 52. Multiple gas nozzles 51 are distributed axially at the other end of the outer ring gas ring 5.

[0041] A combustion air guide plate 6 is arranged at the outlet of the air guide duct 22. The combustion air guide plate 6 can be set as a cone or a flat plate, but is not limited to cone and flat plate shapes. It can be any shape used to intercept the combustion air. One or more triangular, trapezoidal, circular or unrestricted air guide holes 61 are opened on the combustion air guide plate 6. In this specific embodiment, the air guide hole 61 is triangular and has triangular air guide vanes 62. The combustion air A enters the flame tube 7 of the burner head through the air guide hole 61 along the inner wall 72 of the flame tube.

[0042] A gap 8 is left between the combustion air guide plate 6 and the flame tube 7, forming an annular gap 8 for flue gas recirculation. In the axial direction of the burner head, this gap 8 is located inside the combustion chamber 1, connecting the inside and outside of the flame tube 7. The shape is annular, but not limited to any annular shape. The starting point of the annular gap 8 is the combustion air guide plate 6, and the ending point of the annular gap is the rear end 74 of the flame tube.

[0043] When the combustion air A delivered by the blower enters the burner head through the air guide hole 61 of the combustion air guide plate 6, the air velocity at the air guide hole 61 is accelerated due to the interception effect of the combustion air guide plate 6, forming a negative pressure zone on the back of the air guide plate 6 on one side of the combustion chamber 1. The flue gas C3 returning from the guide plate in the furnace is drawn into the negative pressure zone through the annular gap 8 between the flame tube 7 and the combustion air guide plate 6, and then is drawn into the flame tube 7 of the burner head by the combustion air A. The flue gas C3 drawn in from the guide plate mixes with the combustion air A inside the flame tube 7, forming a mixture of combustion air and flue gas A1. The mixture flows out of the burner head through the channel between the front end 73 of the flame tube and the combustion air guide 3, and then meets and merges with the central combustion gas B1 airflow that has been mixed with flue gas at the front end of the combustion air guide 3 and the outer ring combustion gas B2 airflow that has been mixed with flue gas on the outer wall 71 of the flame tube, and they are mixed and burned.

[0044] The flue gas C3 returning to the guide plate flows back through the space between the outer wall 71 of the flame tube and the furnace wall 12 of the combustion chamber to the annular gap 8 in front of the combustion air guide plate 6. This is because the negative pressure on the back of the combustion air guide plate 6 generates the power of flue gas recirculation, which enhances the power of the combustion air to be diverted backward when it flows out of the combustion air guide 3, ensuring successful front and rear diversion and enabling the formation of the rear vortex zone D2. The amount of this recirculated flue gas will affect the swirling intensity of the rear vortex zone.

[0045] like Figure 3 The diagram illustrates the specific structure of the gas distributor 9 of the invention. The gas distributor 9 includes a central gas pipe 92 and outer ring gas pipes 93. The inlet end of the gas distributor 9 is connected to the main gas pipe 91. The central gas pipe 92 passes through the center of the combustion air guide plate 6 and then connects to the central gas pipe 44 of the central gas distributor 4. The outer ring gas pipes 93 have four branches, each connected to... Figure 5 The outer ring gas ring 5 shown has four outer ring gas pipes 52.

[0046] The specific flow direction principle of the combustion air, fuel gas, and flue gas in this invention is as follows:

[0047] like Figure 1 and 2 As shown, the combustion air A first enters the burner head flame tube 7 through the combustion air guide plate 6 of the guide tube 22, and then flows out towards the combustion chamber furnace wall 12 through the channel formed by the front end 73 of the flame tube and the guide surface 31 of the combustion air guide 3. After reaching the combustion chamber furnace wall 12, as mentioned above, due to the negative pressure zone at the annular gap 8, the front and rear flows will be split, forming two independent swirling airflow vortex zones, the front vortex zone D1 and the rear vortex zone D2.

[0048] Meanwhile, when the (conical or trumpet-shaped) combustion air guide 3 guides the combustion air and flue gas mixture A1 to the combustion chamber wall 12, a negative pressure zone is formed at the end disk 32 of the combustion air guide 3, which is the area of ​​the central gas distributor 4. The front vortex zone D1 allows a portion of the front swirling flue gas C1 generated by combustion to swirl through the central space of the combustion chamber to the central gas distributor 4, and mix with the central gas B1 flowing out of the central gas distributor nozzle, and then merge with the combustion air and flue gas mixture A1 along the vortex direction.

[0049] The rear vortex zone D2 allows a portion of the rear swirling flue gas C2 generated by combustion to swirl through the space between the combustion chamber wall 12 and the outer wall 71 of the burner flame tube to the gas nozzle 51 at the front end of the outer ring gas ring 5 of the outer wall 71 of the flame tube, and mix with the outer ring gas B2 flowing out of the nozzle, and then merge with the combustion air and flue gas mixture A1 along the vortex direction of the outer wall of the flame tube.

[0050] Gas B enters the gas distributor 9 via the gas main pipe 91. The central gas B1 is sent to the nozzle of the central gas distributor 4 through the central gas connector 92 and the central gas pipe 44. The central gas B1 is then sent to the front vortex zone D1 through the nozzles of the axial nozzle pipe 42 and the radial nozzle pipe 41. These gas nozzles are the top parts of the burner head that extend into the combustion chamber. The gas flowing out of the nozzles mixes with the front swirling flue gas C1 swirling in the front vortex zone D1 and then merges with the combustion air and flue gas mixture A1. The mixture is then burned to form the front flame zone F1.

[0051] Gas B enters the gas distributor 9 via the gas main pipe 91, and is then fed into the outer ring gas ring 5 through the outer ring gas connector 93 and outer ring gas pipe 52. The outer ring gas B2 is then sent into the rear vortex zone D2 through the nozzle 52, where it mixes with air and burns, forming the rear flame zone F2. Since the front and rear branch point areas are relatively static, a stable stagnant flame forms here, creating a stable flame band on the furnace wall, which is the branch point flame zone F3.

[0052] Furthermore, the flue gas generated in the front flame zone F1, under the vortex action of the front vortex zone D1, passes through the central area of ​​the combustion chamber and becomes the front swirling flue gas C1, which flows back to the central gas distributor 4. After further mixing with the central gas B1, it enters the front vortex zone D1, realizing the internal circulation combustion of the front flue gas.

[0053] Furthermore, the flue gas generated in the rear flame zone F2, under the vortex action of the rear vortex zone D2, passes through the combustion chamber wall 12 and the outer wall space of the flame tube 7, and becomes the rear swirling flue gas C2, which flows back to the gas nozzle 51 of the outer ring gas ring 5. After further mixing with the outer ring gas B2, it enters the rear vortex zone D2, realizing the internal circulation combustion of the rear flue gas.

[0054] Furthermore, when the combustion air supplied by the blower enters the burner head through the air guide hole 61 of the combustion air guide plate 6, a negative pressure zone is formed on one side of the flame tube 7 of the combustion air guide plate 6 due to the interception effect of the combustion air guide plate 6. Figure 2 As shown, a portion of the flue gas flow from the rear flame zone F2 and the diversion point flame zone F3 flows into the negative pressure zone of the annular gap 8 through the space between the furnace wall 12 and the outer wall 71 of the flame tube. This portion of flue gas is the return flue gas C3 from the guide plate. After the combustion air flow A passes through the guide hole 61 of the combustion air guide plate 6, it will entrain the return flue gas C3 into the flame tube 7, where they mix to become a mixture of combustion air and flue gas A1. This mixture then flows through the channel between the front end 73 of the flame tube and the combustion air guide 3 to the furnace wall 12, and then enters the front flame zone F1, the rear flame zone F2, and the diversion point flame zone F3 to participate in combustion. Ultimately, this achieves an internal circulation low-NOx combustion method where the fuel gas and flue gas are premixed, and the air and flue gas are premixed before being mixed and burned.

[0055] The present invention utilizes a method of separately mixing fuel gas and flue gas, and air and flue gas before mixing and burning them. This method reduces the intensity of the combustion reaction, promotes regional diffusion, and ensures a more uniform temperature inside the combustion chamber, avoiding localized high temperatures and reducing the generation of nitrogen oxides. Combustion occurs in two independent swirling vortex zones, forming two flame zones. This staged and zoned combustion method reduces the overall combustion intensity and further reduces the generation of nitrogen oxides.

[0056] This invention utilizes a conical combustion air guide to create two vortex zones inside the combustion chamber. The relatively still airflow at the center of the vortex, similar to the eye of a typhoon, keeps the flame stationary. Simultaneously, the high velocity and large flow rate of the airflow on the outer edge of the vortex ensure effective mixing of flue gas and combustion fuel. This approach guarantees flame stability while effectively providing sufficient internally recirculated flue gas to the combustion zone, reducing the formation of nitrogen oxides.

[0057] This invention uses a conical combustion air guide to form two vortex zones inside the combustion chamber. When the combustion air is split, a relatively static area is formed at the split point on the combustion chamber wall. This part forms a flame stagnation point, and a stable flame ring is formed at this position on the combustion chamber wall, which greatly improves the overall combustion stability.

[0058] The partially burning flames adhere closely to the inner furnace wall of the combustion chamber, which is covered by the heat transfer medium. The flames adhering to the furnace wall improve the efficiency of heat transfer to the heat transfer medium, while the cooling effect of the heat transfer medium on the flames reduces the generation of nitrogen oxides.

[0059] This invention utilizes the separate mixing of fuel gas and flue gas, and air and flue gas, followed by combustion. The combustible material and oxidant are first diluted and preheated. When the mixture reaches its natural temperature, the oxygen content is below 10%, and the combustion chamber temperature reaches 1000°C, the conditions for flameless combustion are met in this part of the space. The mixture will then transition to a flameless combustion state. It can be observed that there is no obvious flame in this part of the combustion chamber, the reaction zone is significantly expanded and becomes transparent, the combustion is gentle, the noise is reduced, the temperature inside the combustion chamber is more uniform, and the thermal efficiency is improved while nitrogen oxides are further reduced.

Claims

1. A low NOx combustion head with internal flue gas recirculation, characterized in that, The device includes an air guide duct, a flame tube, a gas collector, and a central gas distributor. The air guide duct and the flame tube are coaxially arranged. The gas collector axially passes through the interior of the air guide duct, and the central gas pipe of the central gas distributor axially passes through the interior of the flame tube. The central gas pipe is connected to the gas collector. A combustion air guide plate is provided at the air outlet of the air guide duct, and the combustion air guide plate has guide holes. An annular gap exists between the combustion air guide plate and the flame tube. An annular outer ring of gas is arranged on the outer wall of the flame tube. The gas ring is axially connected to the gas distributor via one or more outer ring gas pipes. An axial gas nozzle is provided on the outer ring gas ring. A combustion air guide is provided at the front end outlet of the flame tube. The combustion air guide is installed on the central gas pipe. The combustion air guide includes a guide surface. The guide surface cooperates with the front end of the flame tube to form a channel that guides the combustion air to the combustion chamber wall to form a vortex zone. A radial nozzle pipe and an axial nozzle pipe of the central gas distributor are provided on the back side of the guide surface. The axial nozzle pipe has gas injection holes opened radially. The guiding surface of the combustion air guide is a conical guiding surface. The combustion air guide also includes a guide end disc. The conical guiding surface is installed on the guide end disc. The central gas pipe passes through the cone apex of the conical guiding surface and exits from the center of the guide end disc.

2. The combustion tip of claim 1, wherein The central gas pipe passes through one side of the combustion chamber on the coaxial axis of the end disc of the diffuser and connects to the radial nozzle pipe or axial nozzle pipe of the central gas distributor.

3. The low-NOx combustion head of claim 1, wherein, The combustion air guide plate is conical or flat, and one or more triangular, trapezoidal or circular air guide holes are provided on the combustion air guide plate, and triangular air guide vanes are provided on the air guide holes.

4. The low-NOx combustion head of claim 1, wherein, The annular gap is located inside the combustion chamber, connecting the inside and outside of the flame tube. The starting point of the annular gap is the combustion air guide plate, and the ending point of the annular gap is the rear end face of the flame tube.

5. The low-NOx combustion head of claim 1, wherein, The gas distributor includes a central gas inlet and an outer ring gas inlet. The inlet of the gas distributor is connected to the main gas pipe. The central gas inlet passes through the center of the combustion air guide plate and is connected to the central gas pipe of the central gas distributor. The outer ring gas inlet is connected to the outer ring gas ring.

6. The low-NOx combustion head with internal flue gas recirculation according to claim 1, characterized in that, The combustion air guide is arranged coaxially with the flame tube and located at the front end of the flame tube. Combustion air and circulating flue gas are mixed inside the flame tube, and the mixed airflow is guided to flow out towards the furnace wall of the combustion chamber through the channel between the front end of the flame tube and the combustion air guide.

7. The low-NOx combustion head with internal flue gas recirculation according to claim 5, characterized in that, Gas enters the central gas connector and outer ring gas connector of the gas distributor through the gas main pipe. The central gas enters the central gas pipe through the central gas connector, then flows into the radial nozzle pipe and the axial nozzle pipe, and is ejected through the nozzle to form the front central gas section. The outer ring gas enters the outer ring gas ring through the outer ring gas connector, and is ejected along the outer wall of the flame tube through the nozzle on the outer ring gas ring to form the rear outer ring gas section.

8. The low-NOx combustion head with internal flue gas recirculation according to claim 1, characterized in that, The channel formed between the combustion air guide and the flame tube guides the combustion air flow towards the combustion chamber wall. Upon reaching the combustion chamber wall, the flow splits into two independent swirling airflow vortex zones: a front vortex zone and a rear vortex zone.

9. The low-NOx combustion head with internal flue gas recirculation according to claim 8, characterized in that, The gas ejected from the nozzles on the radial and axial nozzles of the central gas distributor mixes with the flue gas swirling in the front vortex zone and then merges with the combustion air flow.

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