A flue gas internal recirculation low-NOx burner

Abstract

This invention discloses a low-NOx burner head with internal flue gas recirculation, comprising a gas distributor, an air guide plate, a gas collector, and a central burner head. The gas distributor includes a cylindrical outer shell, one end of which is connected to the burner flange, and the other end has an annular cavity. The air guide plate is a hollow cone, and its outer edge is connected to the inner edge of the end of the annular cavity facing the combustion chamber. The outer edge of the air guide plate is on the same plane as the inner wall of the front wall of the combustion chamber. The central burner head extends into the combustion chamber through the central hole of the hollow inner edge of the air guide plate. This invention's low-NOx burner head with internal flue gas recirculation does not use components such as a flame tube, maximizing the use of the combustion chamber space for internal flue gas recirculation. This achieves effective mixing of flue gas, fuel gas, and air, reducing the intensity of the combustion reaction, expanding the combustion reaction area, resulting in a more uniform temperature inside the combustion chamber, avoiding localized high temperatures, and reducing 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 combustion chamber 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 eliminates the flame tube used in traditional burners. Utilizing the conical constriction structure of an air guide plate, a high-speed airflow is obtained, achieving internal flue gas recirculation. When the high-speed airflow enters the combustion chamber, it creates a surrounding vortex within the chamber. As the high-speed airflow passes over the conical air guide plate, a negative pressure zone is formed on its back. This negative pressure guides the vortex from the outer ring of the combustion chamber, flowing counter-currently towards the negative pressure zone on the back of the air guide plate. Upon reaching the negative pressure zone, the vortex naturally changes direction and merges with the airflow, flowing in the same direction as the combustion air towards the combustion chamber outlet. During combustion, the returning vortex contains the flue gas produced by combustion, thus constituting the internal flue gas recirculation mechanism.

[0016] The most important and different aspect of this invention is that, without using a traditional burner flame tube, the entire combustion chamber is treated as free space for airflow circulation. This naturally creates an optimized ratio of counter-current and co-current flue gas space, eliminating human interference and maximizing the utilization of the combustion chamber space. Through the rational arrangement of the gas nozzle positions, the gas flow smoothly merges with the flue gas and air flow, achieving good mixing and stable combustion. This reduces the intensity of the combustion reaction, expands the combustion reaction zone, ensures a more uniform temperature within the combustion chamber, avoids localized high temperatures, and reduces the generation of nitrogen oxides. Summary of the Invention

[0017] This invention is made to solve the above-mentioned problems, and aims to provide a stable, safe, compact, efficient and environmentally friendly flue gas internal circulation low-NOx gas burner.

[0018] The technical solution of this invention is a low-NOx burner head with internal flue gas circulation, which includes a gas distributor, an air guide plate, a gas collector, and a central burner head. The gas distributor is cylindrical and includes a cylindrical outer shell. One end of the cylindrical outer shell is connected to a burner flange, and the other end of the cylindrical outer shell has an annular cavity. The air guide plate is hollow and conical. The outer edge of the air guide plate is connected to the inner edge of the end of the annular cavity facing the combustion chamber. The outer edge of the air guide plate is on the same plane as the inner wall of the front wall of the combustion chamber. The central burner head extends into the combustion chamber through the central hole of the hollow inner edge of the air guide plate. One end of the annular cavity is connected to the gas collector, and the other end is connected to multiple gas nozzle pipes. The gas nozzle pipes extend into the combustion chamber, thereby forming a gas passage that introduces the gas from the gas collector into the combustion chamber.

[0019] Furthermore, the gas distributor includes a central gas connector and an outer ring gas connector. The inlet ends of the central gas connector and the outer ring gas connector are connected to the main gas pipe. The outlet end of the central gas connector is connected to the central burner. The outlet end of the outer ring gas connector is connected to the annular cavity.

[0020] Furthermore, the outer ring gas pipe consists of multiple pipes, which are evenly distributed in a ring and connected to the annular cavity.

[0021] Furthermore, the end face of the annular cavity connected to the gas nozzle pipe is provided with multiple evenly distributed circular openings for connecting the gas nozzle pipe to form a gas passage. The internal space enclosed by the cylindrical outer shell and the air guide plate forms a circulation channel for combustion air.

[0022] Furthermore, an annular gap channel for supplying combustion air is formed between the inner edge of the air guide plate and the central burner.

[0023] Furthermore, the central burner includes a central gas pipe and a sleeve. The sleeve is fitted over the central gas pipe, and an airflow channel is formed between the sleeve and the central gas pipe. An air vortex is provided at the outlet end of the sleeve, and a flame stabilizer and a gas distribution hole are provided at the outlet end of the central gas pipe. The central gas pipe is connected to the central gas connection pipe of the gas distributor.

[0024] In summary, the beneficial effects of this invention are as follows: The flue gas recirculation burner head technology provided by this invention, which eliminates the need for flame tubes and other components extending into the combustion chamber, maximizes the utilization of the entire combustion chamber as a recirculation space, achieving low nitrogen oxide emissions even with a relatively small combustion chamber diameter. Because the burner head of this invention does not use flame tubes or other components, the burner head structure is simplified, reducing manufacturing costs. The absence of flame tubes and other components exposed to the high temperature of the combustion chamber eliminates high-temperature wear on the burner head, extending the equipment's service life. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the flue gas internal circulation low-NOx burner head of the present invention placed in the combustion chamber.

[0026] Figure 2 This is a schematic diagram showing the flow direction of fuel gas, combustion air, and flue gas in the combustion chamber of the flue gas recirculation low-NOx burner head of the present invention.

[0027] Figure 3 This is a schematic diagram of the structure of the flue gas internal circulation low-NOx burner head of the present invention.

[0028] Figure 4 This is a cross-sectional view of the flue gas internal recirculation low-NOx burner head structure of the present invention.

[0029] Reference numerals: 1. Combustion chamber; 2. Burner head; 3. Gas distributor; 4. Gas collector; 5. Air guide plate; 6. Central burner head; 11. Front wall of combustion chamber; 12. Combustion chamber furnace wall; 13. Heat medium; 21. Burner flange; 31. Cylindrical outer shell; 32. Circular cavity; 33. Gas nozzle pipe; 41. Main air intake pipe; 42. Outer ring gas connection pipe; 43. Central gas connection pipe; 51. Outer edge of air guide plate; 52. Inner edge of air guide plate; 61. Central gas pipe; 62. Sleeve; 63. Swirl; 64. Gas nozzle; 65. Flame stabilizer. Detailed Implementation

[0030] 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.

[0031] like Figures 1 to 4 As shown, it illustrates the specific principle and structure of the internal circulation low-NOx combustion head of the present invention.

[0032] like Figure 1 and Figure 3 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 burner flange 21. The outer side of the combustion chamber furnace wall 12 is the heat medium 13. The outer edge 51 of the air guide plate 5 of the burner head 2 is on the same plane as the inner wall of the front wall 11 of the combustion chamber, that is, they are flush with each other. The gas nozzle pipe 33 and the central burner head 6 extend into the interior of the combustion chamber 1.

[0033] like Figure 3 and Figure 4As shown, this invention discloses a specific structure of an internal circulation low-NOx burner head. The burner head includes a gas distributor 3, a gas collector 4, an air guide plate 5, and a central burner head 6. The gas distributor 3 includes a cylindrical outer shell 31, one end of which is connected to the burner flange 21, and the other end is connected to the outer edge 51 of the air guide plate 5, forming an internal space that facilitates airflow. The central burner head 6 extends from the central hole of the hollow inner edge 52 of the air guide plate 5. The annular gap formed between the inner edge 52 of the air guide plate and the central burner head 6 serves as the air outlet for the burner, forming a combustion air flow channel. The cylindrical outer shell 31 of the gas distributor 3 contains an annular cavity 32 at the end facing the combustion chamber. One end of the annular cavity 32 is connected to the outer ring gas connection pipe 42 of the gas collector 4. The other end of the annular cavity 32 has multiple evenly distributed circular openings for connecting the gas nozzle pipe 33. The gas nozzle pipe 33 extends into the combustion chamber 1, forming a gas passage. The internal space enclosed by the cylindrical outer shell 31 and the air guide plate 5 forms a passage for combustion air. The air guide plate 5 is located on the inner wall of the front wall of the combustion chamber. Except for the gas nozzle pipe 33 and the central burner head 6 extending into the combustion chamber 1 beyond the air guide plate 5, no other components extend into the combustion chamber. The gas nozzle pipe 33, connected to the gas distributor, extends beyond the air guide plate 5 and into sufficient space within the combustion chamber 1. When the gas is ejected from the gas nozzle pipe 33, the surrounding flue gas flows in the same direction. As it flows towards the outlet of the combustion chamber 1, the gas, flue gas, and air merge and mix, and then burn in the recirculation zone. The central burner 6 provides a stable rooted flame for the entire combustion process, ensuring combustion stability.

[0034] like Figure 3 and Figure 4 As shown, the air guide plate 5 is located on the plane of the inner wall of the front wall of the combustion chamber. With this as the boundary, except for the gas nozzle 33 and the central burner 6 extending into the combustion chamber 1 beyond the air guide plate 5, no other components extend into the combustion chamber. The entire combustion chamber forms a complete flue gas internal circulation return space starting from the front wall.

[0035] like Figure 3As shown, the air guide plate 5 is a hollow conical structure. The outer edge 51 of the air guide plate is connected to the end face of the gas distributor 3 with the nozzle. The hollow part of the inner edge 52 of the air guide plate has a central burner 6 extending out from it. Due to the conical structure of the air guide plate 5, the highest airflow velocity can be obtained. The high-speed airflow is ejected into the combustion chamber 1 through the annular gap formed by the inner edge 52 of the air guide plate and the central burner 6. When the high-speed airflow blows into the combustion chamber, it will form an accompanying vortex surrounding the airflow inside the combustion chamber. At the same time, when the high-speed airflow passes over the conical air guide plate 5, a negative pressure zone will be formed on the back of the air guide plate 5. This negative pressure will guide the vortex from the outer ring of the combustion chamber to the negative pressure zone behind the air guide plate 5 in the opposite direction. After reaching the negative pressure zone, it will naturally turn and merge with the high-speed airflow, flowing in the same direction as the combustion air towards the outlet of the combustion chamber 11. During combustion, the swirling flow is the flue gas produced by combustion, which constitutes the internal circulation mode of the flue gas.

[0036] like Figure 2 The diagram illustrates the flow direction of the combustion gas and combustion air according to the present invention. Combustion air A enters the burner head 2 and enters the combustion chamber 11 through the air passage formed by the gas distributor 3 and the air guide plate 5. Due to the conical constriction structure of the air guide plate 5, the combustion air A reaches its maximum velocity upon passage. This high-velocity airflow, after entering the combustion chamber 11, forms an accompanying vortex D surrounding the airflow. Simultaneously, as the high-velocity airflow passes through the air guide plate 5, a negative pressure zone is formed on the back of the guide plate. This negative pressure guides the vortex D from the outer perimeter of the combustion chamber in a counter-current direction (C1) towards the air guide plate 5. Upon reaching the guide plate, it naturally changes direction and then merges with the airflow in a forward direction (C2), flowing together towards the outlet of the combustion chamber. During combustion, the returning vortices C1 and C2 represent the flue gas produced by combustion, constituting an internal flue gas circulation pattern. The outer ring gas B2 portion of gas B enters the gas distributor 3 through the outer ring pipe 42 of the gas distributor 4, and then enters the combustion chamber 1 through the nozzle pipe 33. When the outer ring gas B2 is ejected, it is located in the middle of the flow of the co-current flue gas C2. The converging gas B2, flue gas C2, and air remain and burn in the vortex zone. Except for the counter-current flue gas C1, the rest of the combusted flue gas C flows out of the combustion chamber in the co-current direction. The central gas B1 is sent to the central burner 6 through the central gas pipe of the gas distributor 4. The central flame F provides a stable root flame base for the overall combustion.

[0037] like Figure 4As shown, the gas distributor 3 has a cylindrical outer shell with an embedded annular cavity 32. One end of the annular cavity 32 is connected to the outer ring gas pipe 42 of the gas distributor 4, and the other end has multiple evenly distributed circular openings for connecting to the gas nozzle pipe 33. Gas enters from the main gas pipe 41 of the gas distributor 4, and then enters the annular cavity of the gas distributor 3 through four outer ring gas connecting pipes 42. Subsequently, it is distributed to the combustion chamber through the gas nozzle pipe 33, forming an outer ring gas passage. One end of the cylindrical outer shell 31 of the gas distributor 3 is connected to the burner flange 21. The internal space enclosed by the cylindrical outer shell 31 and the air guide plate 5 constitutes a channel for the circulation of combustion air.

[0038] like Figure 1 and Figure 3 As shown, the outlet of the gas nozzle pipe 33 extends beyond the air guide plate 5 and into the combustion chamber 1 with sufficient space to ensure that when the gas is ejected, the gas flow is located in the co-current flue gas flow of the flue gas internal circulation.

[0039] like Figure 4 As shown, the gas distributor 4 includes a central gas pipe 43 and an outer ring gas pipe 42. The inlet end of the gas distributor 4 is connected to the main gas pipe 41. The outlet end of the central gas pipe 43 is connected to the central gas pipe 61 of the central burner 6, and the outlet end of the outer ring gas pipe 42 is connected to the gas annular cavity 32 of the gas distributor 3.

[0040] like Figure 4 As shown, the central burner 6 includes a central gas pipe 61 and a sleeve 62. The sleeve 62 is fitted over the central gas pipe 61, forming a combustion air passage between the sleeve 62 and the central gas pipe 61. An air vortex 63 is provided at the outlet end of the sleeve 62, and a gas nozzle 64 is provided at the outlet end of the central gas pipe 61. A flame stabilizer baffle 65 is also provided at the outlet end. The central gas pipe 61 is connected to the outlet end of the central gas connector 43 of the gas distributor.

[0041] The sleeve 62 of the center burner 6 described in this invention can protect the center flame from being extinguished, providing a reliable base point for the entire combustion process and ensuring overall combustion stability. When a high-velocity airflow surrounds the sleeve 62 and is blown out, it can effectively cool the center flame and reduce the nitrogen oxides produced by the center flame.

[0042] The air guide plate 5 used in this invention is arranged on the inner wall 11 of the front wall of the combustion chamber. It provides a flue gas internal circulation combustion head technology without flame tubes or other components extending into the combustion chamber. Without using flame tubes or other components, it makes the maximum use of the combustion chamber space for flue gas circulation. It achieves effective mixing of flue gas, fuel gas and air even with a small combustion chamber diameter, reduces the intensity of the combustion reaction, expands the combustion reaction area, makes the internal temperature of the combustion chamber more uniform, avoids local high temperature, reduces the generation of nitrogen oxides, and achieves low nitrogen oxide emissions.

[0043] Furthermore, by eliminating the use of components such as flame tubes, the burner head structure is greatly simplified, reducing manufacturing costs. The absence of flame tubes and other components exposed to the high temperatures of the combustion chamber eliminates high-temperature wear on the burner head and extends the equipment's lifespan.

Claims

1. A low-NOx combustion head with internal flue gas recirculation, characterized in that, The device includes a gas distributor, an air guide plate, a gas collector, and a center burner. The gas distributor is cylindrical and includes a cylindrical outer shell. One end of the cylindrical outer shell is connected to a burner flange, and the other end of the cylindrical outer shell has an annular cavity. The air guide plate is hollow and conical. The outer edge of the air guide plate is connected to the inner edge of the end of the annular cavity facing the combustion chamber. The outer edge of the air guide plate is on the same plane as the inner wall of the front wall of the combustion chamber. The center burner extends into the combustion chamber through the central hole of the hollow inner edge of the air guide plate. One end of the annular cavity is connected to the gas collector, and the other end is connected to multiple gas nozzle pipes. The gas nozzle pipes extend into the combustion chamber, thereby forming a gas passage to introduce the gas in the gas collector into the combustion chamber. An annular gap channel for the flow of combustion air is formed between the inner edge of the air guide plate and the central burner.

2. The low-NOx combustion head with internal flue gas recirculation according to claim 1, characterized in that, The gas distributor includes a central gas inlet and an outer ring gas inlet. The inlet ends of the central gas inlet and the outer ring gas inlet are connected to the main gas pipe. The outlet end of the central gas inlet is connected to the central burner. The outlet end of the outer ring gas inlet is connected to the annular cavity.

3. The low-NOx combustion head with internal flue gas recirculation according to claim 2, characterized in that, The outer ring gas pipe consists of multiple pipes, which are evenly distributed in a ring and connected to the annular cavity.

4. The low-NOx combustion head with internal flue gas recirculation according to claim 1 or 2, characterized in that, The annular cavity is provided with a plurality of evenly distributed circular openings on the end face where it connects to the gas nozzle pipe to form a gas passage. The internal space enclosed by the cylindrical outer shell and the air guide plate forms a circulation channel for combustion air.

5. The low-NOx combustion head with internal flue gas recirculation according to claim 1, characterized in that, The central burner includes a central gas pipe and a sleeve. The sleeve is fitted over the central gas pipe, and an airflow channel is formed between the sleeve and the central gas pipe. An air vortex is provided at the outlet end of the sleeve. A flame stabilizer and a gas distribution hole are provided at the outlet end of the central gas pipe. The central gas pipe is connected to the central gas connection pipe of the gas distributor.

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