Low-nitrogen staged combustion burner and staged control method

Abstract

The application discloses a low-nitrogen staged combustor and a staged control method, and relates to the technical field of combustors.The combustor comprises an axially connected first shell and a second shell, a mixed cylinder is connected between the first shell and the second shell, and a main gas passage is sequentially penetrated through the first shell and the mixed cylinder and inserted into the second shell; a smoke chamber is arranged in the first shell, a ignition chamber is arranged in the second shell, an air pipeline is arranged in the mixed cylinder, the air pipeline is connected with external air, the ignition chamber and the main gas passage, a preheating pipeline is arranged outside the mixed cylinder, and the preheating pipeline is connected with the smoke chamber and the ignition chamber.The combustor mixes air and gas in multiple stages, improves the utilization rate of gas and improves the combustion degree of the flame.The preheating pipeline and the air pipeline are used to preheat the air with the smoke, so that the air and the gas can be fully mixed under low-temperature conditions.The opening degrees of the first valve and the second valve are controlled in a programmed mode, so that the gas flow rate control and the staged control requirements of the gas and the air are simultaneously met.

Description

Technical Field

[0001] This invention relates to the field of burner technology, and in particular to a low-NOx staged burner and a staged control method. Background Technology

[0002] Nitrogen oxides (NOx) are widely present in industrial exhaust gases and are a major source of environmental pollution, including acid rain and smog. They are also one of the main industrial pollutants threatening public health. To reduce NOx emissions, the government has revised emission standards for industrial boilers and burners, raising emission standards for combustion gases and using economical and effective methods to meet environmental requirements for burner emissions. Existing low-NOx combustion technologies are typically based on technologies such as rich-lean combustion, staged combustion, premixed combustion, flameless combustion, chemical looping combustion, flue gas recirculation, and porous media combustion.

[0003] Staged combustion, such as CN106524152B - a staged low-NOx burner, typically involves classifying the combustion of the gas mixture into stages and forming relatively low-temperature rich and lean flames through corresponding channels. This reduces the content of nitrogen oxides generated, achieving a certain degree of nitrogen reduction and meeting environmental protection requirements. However, the staged combustion in this type of staged combustion reduces the degree of flame combustion and cannot achieve stable combustion.

[0004] By setting a premixed combustion mode, the damage to the carrier caused by high-temperature combustion and the emission of nitrogen oxides caused by local high temperature can be reduced to a large extent. However, the existing premixed mode is prone to risks such as explosion, causing safety hazards. Moreover, the premixing method is simple, and the air and gas are not fully premixed, resulting in low gas utilization and insufficient flame combustion. Summary of the Invention

[0005] The purpose of this invention is to provide a low-NOx staged burner and a staged control method, which can ensure the NOx emission of the burner and the long-term stable operation of the burner; and by adjusting the air intake of the burner according to the smoke generation, the fuel combustion is more complete.

[0006] This invention provides a low-NOx staged burner, comprising an axially connected first shell and a second shell, with a mixing cylinder internally connected between the first shell and the second shell, and a main gas combustion channel sequentially passing through the first shell and the mixing cylinder and inserted into the second shell; a smoke chamber is provided inside the first shell, and an ignition chamber is provided inside the second shell; an air pipe is provided inside the mixing cylinder, the air pipe connecting outside air to the ignition chamber and the main gas combustion channel; a preheating pipe is provided outside the mixing cylinder, the preheating pipe connecting the smoke chamber and the ignition chamber.

[0007] Furthermore, there is an annular interlayer between the mixing cylinder and the first and second shells, and a plurality of the preheating pipes are arranged around the annular interlayer. The air pipes pass through the mixing cylinder and communicate with the first and second shells to the outside air.

[0008] Furthermore, the main gas passage is inserted into the air duct, and the downstream sidewall of the main gas passage is connected to the air duct by opening a plurality of mixing holes, the diameter of the mixing holes increasing sequentially in the downstream direction.

[0009] Furthermore, the downstream end of the main gas passage is connected to the ignition chamber via a diversion channel.

[0010] Furthermore, the main gas passage is circumferentially connected to several secondary gas passages, and these secondary gas passages extend to the ignition chamber.

[0011] Furthermore, the ignition chamber is connected to a flow divider, and a swirl vane is connected to the flow divider.

[0012] Furthermore, the ignition chamber has a plurality of openings along the circumferential direction, and the diameter of the plurality of openings decreases sequentially from the center of the ignition chamber outward.

[0013] The present invention also provides a staged control method for a low-NOx staged burner, wherein a first valve is provided on the main gas passage, a second valve is provided on the air duct, and a controller is provided on the first housing and / or the second housing and / or the mixing cylinder, the controller being used to control the first valve and the second valve.

[0014] Furthermore, a smoke detector is provided in the smoke chamber. The smoke detector detects smoke parameters and transmits them to the central control unit, which then sends control commands to the controller.

[0015] Further, the process includes the following steps: S1, setting the opening degrees of the first valve and the second valve sequentially from large to small to level one, level two, and level three, with the level controlled by the controller; S2, the central control unit acquires the historical smoke concentration parameter C from the smoke detector. smo , and smoke temperature parameter T, and calculate the control coefficient K using the following formula; Among them, C smo(t) is the dynamic smoke concentration range, δ and ∈ are dynamic coefficients, Δt = t2 - t1, where Δt is the preset time period, t2 is the current time, and t1 is the historical change time deduced from the current time; S3, compare the control coefficient K with the preset threshold range [K1, K2], where 0 < K1 < K2: if K ∈ [K1, K2], the central control unit sends a synchronous control instruction to the controller and adjusts the first valve and the second valve to the first gear; if K > K2, the central control unit sends an asynchronous control instruction to the controller, adjusts the first valve to the third gear, and adjusts the second valve to the second gear; if K < K1, the central control unit sends an asynchronous control instruction to the controller, adjusts the first valve to the second gear, and adjusts the second valve to the third gear.

[0016] Advantages of the present invention:

[0017] (1) In the present invention, air and gas are pre-mixed by connecting the air pipeline with the main gas passage, and air and gas are re-mixed by connecting the air pipeline with the ignition chamber. The air and gas are mixed in multiple stages, improving the gas utilization rate and the degree of flame combustion.

[0018] (2) In the present invention, combustion exhaust gas (mainly flue gas) is transmitted through the preheating pipeline. During the process of transporting the flue gas to the smoke chamber, the preheating pipeline and the air pipeline are used to preheat the air with the flue gas, ensuring that air and gas are fully mixed and preheated under low temperature conditions.

[0019] (3) In the present invention, by arranging the mixing cylinder and the air pipeline in the first housing and the second housing, it is ensured that the fuel and air in the burner are shunted, ensuring low emissions of nitrogen oxides and the stable operation of the burner.

[0020] (4) In the present invention, by setting control valves in the main gas passage and the air pipeline, it is ensured that the intake air volume of the gas and air input into the pipeline is controlled. Through the parameter data programming of the smoke detector in the smoke chamber, the opening degrees of the first valve and the second valve are controlled, ensuring the control of the gas flow rate and meeting the requirements of hierarchical control of gas and air at the same time.

[0021] Of course, it is not necessary for any product implementing the present invention to achieve all the above-mentioned advantages simultaneously. Description of the Drawings

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0023] Figure 1 This is a schematic diagram of the overall structure of the low-NOx staged burner of the present invention;

[0024] Figure 2 This is a schematic diagram of the internal structure of the low-NOx staged burner of the present invention;

[0025] Figure 3 This is a schematic diagram of the control valve structure in the air duct and main gas passage of the present invention;

[0026] Figure 4 This is a schematic diagram of the swirl vane of the present invention.

[0027] Figure 5 This is a schematic plan view of the ignition chamber of the present invention;

[0028] Figure 6 This is a schematic diagram of the hierarchical control method of the present invention.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1-First shell; 101-Smoke chamber; 102-Smoke inlet; 2-Second shell; 201-Ignition chamber; 202-Opening; 3-Mixing cylinder; 4-Main gas passage; 401-Mixing hole; 5-Air pipe; 6-Preheating pipe; 7-Drainage passage; 8-Secondary gas passage; 9-Diverter plate; 901-Swirl vane; 10-Controller; 11-First valve; 12-Second valve; 13-Smoke detector. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Example 1

[0035] like Figures 1-2 As shown, the present invention provides a low-NOx staged burner, comprising a first housing 1 and a second housing 2 connected axially, a mixing cylinder 3 connected between the first housing 1 and the second housing 2, and a main gas passage 4 passing through the first housing 1 and the mixing cylinder 3 in sequence and inserted into the second housing 2; a smoke chamber 101 is provided inside the first housing 1, an ignition chamber 201 is provided inside the second housing 2, an air pipe 5 is provided inside the mixing cylinder 3, the air pipe 5 connects the outside air with the ignition chamber 201 and the main gas passage 4, and a preheating pipe 6 is provided outside the mixing cylinder 3, the preheating pipe 6 connects the smoke chamber 101 and the ignition chamber 201.

[0036] Specifically, a mixing cylinder 3 is connected within the first housing 1 and the second housing 2, with the main gas supply channel 4 flowing from the first housing 1 to the second housing 2. That is, the first housing 1 is the upstream end of the device, and the second housing 2 is the downstream end. The mixing cylinder 3 is a hollow structure, with its upstream side connected to the first housing 1 and its downstream side connected to the second housing 2. The main gas supply channel 4 and the mixing cylinder 3 pass through each other to supply gas. An air channel is located inside the mixing cylinder 3 to supply outside air to the ignition chamber 201. The main gas supply channel 4 also communicates with the air channel as it passes through the mixing cylinder 3. This allows the air in the air pipe 5 to mix with the gas in the main gas supply channel 4 for the first time. After the mixed gas reaches the ignition chamber 201, it can be directly used for combustion. Since the air pipe 5 also directly supplies air to the ignition chamber 201, the gas that has not been fully burned mixes with the air a second time for complete combustion. This improves the completeness of combustion and reduces the flue gas output.

[0037] Meanwhile, the high-temperature flue gas generated by combustion in the ignition chamber 201 is transported to the smoke chamber 101 of the first housing 1 through the preheating pipe 6, and discharged through the smoke outlet 102 on the first housing 1 that is connected to the smoke chamber 101. During this process, the preheating pipe 6 is in contact with the air pipe 5 but not connected, so that the high-temperature flue gas exchanges heat with the air through the pipe wall, the flue gas is cooled, and the preheated air and the fuel gas are fully mixed to improve the combustion efficiency.

[0038] The above technical solutions separate fuel and air in the burner, ensuring low emissions of nitrogen oxides and stable operation of the burner.

[0039] Example 2

[0040] This embodiment 2 specifically describes the preheating pipe 6 and the air pipe 5.

[0041] like Figures 1-2 As shown, there is an annular interlayer between the mixing cylinder 3 and the first shell 1 and the second shell 2. Several preheating pipes 6 are arranged around the annular interlayer. An air pipe 5 passes through the mixing cylinder 3 and connects to the outside air through the first shell 1 and the second shell 2.

[0042] Specifically, both the first shell 1 and the second shell 2 are cylindrical shells, connected to form a hollow cylindrical structure. The mixing cylinder 3 is a cylindrical structure open at both ends, and the outer diameter of the mixing cylinder 3 is smaller than the inner diameter of the first shell 1 and the second shell 2, thus forming an annular sandwich. The preheating pipe 6 is fitted onto the outer wall of the mixing cylinder 3 and connects to the smoke chamber 101 inside the first shell 1 and the ignition chamber 201 inside the second shell 2. Multiple preheating pipes 6 are arranged around the circumference of the mixing cylinder 3. The air pipe 5 is a cylindrical structure set inside the mixing cylinder 3. A radial short pipe is connected to the air pipe 5, passing through the mixing cylinder 3, the first shell 1, and the second shell 2, and extending to the outside. In this way, heat exchange occurs between the high-temperature flue gas and the air through the pipe walls of the preheating pipe 6, the mixing cylinder 3, and the air pipe 5.

[0043] Example 3

[0044] This embodiment 3 specifically describes the initial premixing structure of air and gas.

[0045] like Figures 1-2 As shown, the main gas passage 4 is inserted into the air duct 5. The downstream sidewall of the main gas passage 4 is connected to the air duct 5 by opening a number of mixing holes 401. The diameter of the mixing holes 401 increases sequentially in the downstream direction.

[0046] Specifically, the main gas passage 4 is directly inserted into the air duct 5, and a mixing hole 401 is opened in a section of the main gas passage 4 on the downstream side. The gas in the main gas passage 4 and the air in the air duct 5 are pre-mixed through these mixing holes 401. An ignition device is installed in the ignition chamber 201 to ensure that the mixed gas is fully ignited. The ignition chamber 201 is connected to the mixing cylinder 3 to ensure that the pre-mixed gas is fully combusted in the ignition chamber 201.

[0047] Example 4

[0048] This embodiment 4 specifically describes the secondary and tertiary premixing structures of air and gas.

[0049] like Figures 1-2 , Figures 4-5 As shown, the downstream end of the main gas passage 4 is connected to the ignition chamber 201 via the diversion passage 7. Several secondary gas passages are circumferentially connected to the main gas passage 4, extending to the ignition chamber 201. The ignition chamber 201 is connected to a flow divider 9, on which a swirl vane 901 is connected. Several openings 202 are formed circumferentially inside the ignition chamber 201, with the diameter of the openings decreasing sequentially from the center of the ignition chamber 201 outwards.

[0050] Specifically, the diversion channel 7 ensures the directional diversion of gas in the main gas channel 4. The mixing hole 401 is located in a section of the downstream end of the main gas channel 4 connected to the diversion channel 7, ensuring initial premixing with the air in the mixing cylinder 3. At the same time, the remaining gas in the main gas channel 4 and a small amount of air mix and reach the ignition chamber 201 through the diversion channel 7 for combustion, and undergo a second mixing and combustion.

[0051] The main gas passage 4 is provided with a secondary gas passage 8 upstream of the first valve 11. The gas is transported downstream through the secondary gas passage 8 to the top of the combustion plate and mixed with the gas in the mixing cylinder 3 for a third mixing and combustion. The gas is mixed with the split fuel and then the premixed gas is ignited in the ignition chamber 201 to ensure safe and stable combustion of the flame.

[0052] By opening a flow divider plate 9 at the bottom of the ignition chamber 201, and setting swirl vanes 901 inside the flow divider plate 9, the multiple swirl vanes 901 are arranged in a circle, which facilitates the diversion of the flame in the ignition chamber 201, ensuring that the flame is evenly distributed and facilitating uniform heating of the heated object.

[0053] It should be noted that, in this embodiment 4 and the above embodiment 3, the structure for supplying mixed gas to the ignition chamber 201 from the center outwards consists of a diversion channel 7, an air duct 5, and a secondary gas duct 8. Correspondingly, the opening 202 in the middle of the ignition chamber 201 is the largest, ensuring that the gas in the main gas duct 4 burns in a relatively oxygen-demanding environment through the diversion channel 7. As the air duct 5 and the secondary gas duct 8 gradually extend outwards from the ignition chamber 201, the mixed gas volume gradually decreases, and the diameter of the opening 202 also gradually decreases, ensuring the classified combustion of the gas while ensuring a sufficient flame area.

[0054] Example 5

[0055] like Figures 1-6 As shown, the present invention also provides a graded control method for a low-NOx graded burner. A first valve 11 is provided on the main gas passage 4, a second valve 12 is provided on the air duct 5, and a controller 10 is provided on the first housing 1 and / or the second housing 2 and / or the mixing cylinder 3. The controller 10 is used to control the first valve 11 and the second valve 12. A smoke detector 13 is provided in the smoke chamber 101. The smoke detector 13 detects smoke parameters and transmits them to the central control unit. The central control unit sends control commands to the controller 10. The graded control method includes the following steps: S1, the opening degrees of the first valve 11 and the second valve 12 are set sequentially from large to small to level one, level two, and level three, and the level is controlled by the controller 10; S2, the central control unit obtains the historical smoke concentration parameter C from the smoke detector 13. smo , and smoke temperature parameter T, and calculate the control coefficient K using the following formula; Among them, C smo (t) represents the dynamic smoke concentration range, δ and ∈ represent dynamic coefficients, Δt = t2 - t1, where Δt is the preset time period, t2 is the current time, and t1 is the historical change time derived from the current time; S3, compare the control coefficient K with the preset threshold range [K1, K2], where 0 < K1 < K2: If K ∈ [K1, K2], the central control unit sends a synchronous control command to the controller 10 and adjusts the first valve 11 and the second valve 12 to level one; if K > 2, the central control unit sends an asynchronous control command to the controller 10, adjusts the first valve 11 to level three, and adjusts the second valve 12 to level two; if K < 1, the central control unit sends an asynchronous control command to the controller 10, adjusts the first valve 11 to level two, and adjusts the second valve 12 to level three.

[0056] Specifically, both the first valve 11 and the second valve 12 are ball valves. The controller 10 controls the size of the overlap area between the ball valve rotation and the passage, thereby controlling the amount of gas and air entering the system. The two ball valves are fitted with spherical cavities, which are located within the main gas passage 4 and the air duct 5. The ball valves rotate under driving force, and are connected to the controller 10 via a rotating rod passing through the outside of the first housing 1. The ball valves rotate under the control of the controller 10, ensuring that the controller 10 drives the drive motor to rotate the two ball valves, thus adjusting the amount of gas in the air duct 5 and the main gas passage 4. The overlap areas of the openings of the first valve 11 and the second valve 12 with the main gas passage 4 and the air duct 5 are sequentially set to three levels, from largest to smallest: level one, level two, and level three. The higher the level, the smaller the overlap area. A smoke detector 13 is installed on the top inner side of the smoke chamber 101 near the smoke inlet 102. The smoke detector 13 detects the smoke concentration parameters and transmits them to the central control unit. The controller 10 receives and executes the control commands from the central control unit.

[0057] The dynamic coefficient δ is obtained based on the air-to-gas mixing ratio, where Δt = t2 - t1, Δt is a preset time period obtained through historical experience, t2 is the current time, and t1 is the historical change time derived from the current time. It should be noted that the dynamic coefficients δ and ∈ in the above scheme are selectively set based on experimental data of different air-to-gas mixing ratios, and the preset threshold range in the above scheme is selectively set based on historical data, which will not be elaborated upon here.

[0058] In this embodiment 5, the smoke detector 13 detects historical smoke concentration and temperature parameters within the smoke chamber 101. The central control unit analyzes the data and generates control commands, instructing the controller 10 to adjust its position. This adjustment controls the air intake by regulating the opening of the first valve 11 and the second valve 12, simultaneously controlling and individually adjusting the intake of both fuel gas and air. This achieves stratified air intake, ensuring stable combustion in the burner based on smoke conditions, and is achieved through formulas. Calculate the control coefficients K and C. smo (t) represents the dynamic smoke concentration range, and δ and ∈ represent the dynamic coefficients obtained by the mixing ratio of air and gas. Then, the control coefficient K is compared with the preset threshold range [K1,K2], and synchronous and asynchronous control commands are issued to ensure that the size of the ball valve opening and the overlapping area of ​​the channel are adjusted, thereby changing the gas flow rate and performing graded control of gas and air.

[0059] Working principle of the invention:

[0060] This invention achieves initial premixing of fuel gas and air by setting up a main fuel gas channel 4 and an air duct 5. The main fuel gas channel 4, through a guide channel 7, sends the gas into the combustion chamber 201 for secondary mixing with the air in the air duct 5. A secondary fuel gas channel 8 is connected to the main fuel gas channel 4 and extends into the combustion chamber 201 for tertiary mixing with the air in the air duct 5, improving the mixing degree of fuel gas and air and facilitating combustion at the bottom of the pipe. High-temperature flue gas is transported to the smoke chamber 101 via a preheating pipe 6. The high-temperature flue gas in the preheating pipe 6 exchanges heat with the air in the air duct 5, preheating the air and ensuring thorough mixing of air and fuel gas at a lower temperature. The overall scheme ensures complete combustion of fuel and reduces flue gas production.

[0061] This invention controls the intake volume of gas and air by installing a first valve 11 and a second valve 12 in the main gas passage 4 and the air duct 5. A controller 10 controls the opening of the first valve 11 and the second valve 12. A smoke detector 13 in the smoke chamber 101 detects smoke parameters and transmits them to the central control unit. The central control unit instructs the controller 10 to adjust the first valve 11 and the second valve 12 according to the smoke conditions, thereby adjusting the input volume of air and gas to keep the smoke conditions within a reasonable range. This achieves the control of gas flow rate and meets the requirements for graded control of gas and air.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A staged control method for a low-NOx staged burner, characterized in that, The low-nitrogen staged combustion burner includes a first housing and a second housing connected axially. A mixing cylinder body is internally connected between the first housing and the second housing. The main gas channel sequentially passes through the first housing and the mixing cylinder body and inserts into the second housing. A smoke chamber is provided in the first housing, a ignition chamber is provided in the second housing, an air duct is provided in the mixing cylinder body, and the air duct connects the outside air with the ignition chamber and the main gas channel. A preheating duct is provided outside the mixing cylinder body, and the preheating duct connects the smoke chamber with the ignition chamber. A first valve is provided on the main gas channel, a second valve is provided on the air duct, and a controller is provided on the first housing and / or the second housing and / or the mixing cylinder body. The controller is used to control the first valve and the second valve. A smoke detector is provided in the smoke chamber. The smoke detector detects smoke parameters and transmits them to the central control unit, and the central control unit sends a control instruction to the controller. The method includes the following steps: S1, set the opening degrees of the first valve and the second valve from large to small as the first gear, the second gear, and the third gear in sequence, and the gears are controlled by the controller. S2, The central control unit acquires historical smoke concentration parameters from the smoke detector. , and smoke temperature parameter T, and calculate the control coefficient K using the following formula; in, The dynamic smoke concentration range is given by δ and ∈, where δ and ∈ are dynamic coefficients. =t2-t1, where Δt is the preset time period, t2 is the current time, and t1 is the historical change time derived from the current time; S3, compare the control coefficient K with the preset threshold interval [K1, K2], where 0 < K1 < K2: If K ∈ [K1, K2], the central control unit issues a synchronous control instruction to the controller and adjusts the first valve and the second valve to the first gear. If K > K2, the central control unit issues an asynchronous control instruction to the controller, adjusts the first valve to the third gear, and adjusts the second valve to the second gear. If K < K1, the central control unit issues an asynchronous control instruction to the controller, adjusts the first valve to the second gear, and adjusts the second valve to the third gear.

2. The staged control method for a low-NOx staged burner according to claim 1, characterized in that, There is an annular interlayer between the mixing cylinder body and the first housing and the second housing. A plurality of the preheating ducts are arranged around in the annular interlayer, and the air duct passes through the mixing cylinder body and is connected to the outside air through the first housing and the second housing.

3. The staged control method for a low-NOx staged burner according to claim 1, characterized in that, The main gas channel inserts into the air duct, and the downstream side wall of the main gas channel is connected to the air duct through a plurality of mixing holes, and the aperture of the mixing holes increases sequentially in the downstream direction.

4. The staged control method for a low-NOx staged burner according to claim 1, characterized in that, The downstream end of the main gas channel is connected to the ignition chamber through a diversion channel.

5. The staged control method for a low-NOx staged burner according to claim 1, characterized in that, A plurality of secondary gas channels are circumferentially connected along the main gas channel, and the plurality of secondary gas channels extend to the ignition chamber.

6. The staged control method for a low-NOx staged burner according to claim 1, characterized in that, The ignition chamber is connected with a shunt plate, and a swirl vane is connected to the shunt plate.

7. The staged control method for a low-NOx staged burner according to claim 6, characterized in that, A plurality of openings are arranged in the ignition chamber along the circumferential direction, and the aperture of the plurality of openings decreases sequentially from the center of the ignition chamber to the outside.

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