Small low-nitrogen combustor and combustion method

Abstract

The invention relates to a small low-nitrogen combustor and a combustion method, the small low-nitrogen combustor comprises a head air inlet assembly, a combustion cylinder assembly and a connecting assembly, the head air inlet assembly comprises a primary air inlet pipe, a central air distributor module, an axial swirler, a radial swirler, a fuel pipe and a premixed gas pipeline; the primary air inlet pipe is arranged at the inlet end of the central air distributor module; the premixed gas pipeline is arranged at the outlet end of the central air distributor module in a sleeving manner, and the axial swirler is arranged between the premixed gas pipeline and the outlet end; the fuel pipe and the radial swirler are respectively arranged at other positions of the central air distributor module; the head air inlet assembly and the combustion cylinder assembly are connected together through the connecting assembly. The method is obvious in nitrogen reduction effect and high in flame stability. Nitric oxide at an outlet is reduced by controlling the air amount of premixed gas and the rotational flow angle in the combustor, and meanwhile, the flame stability of the combustion center can be guaranteed through the inner circulation area.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-nitrogen combustion, and particularly relates to a small low-nitrogen burner and a combustion method. Background Art

[0002] Nitrogen oxides (NO x ) are a class of compounds formed by nitrogen and oxygen during high-temperature combustion processes. The main components include nitric oxide (NO) and nitrogen dioxide (NO 2 ). NO x is one of the air pollutants and poses serious hazards to the environment and human health. The emission of NO x mainly comes from activities such as transportation and energy consumption. Among them, the combustion of fossil fuels in industrial production will emit a large amount of NO x . Therefore, in order to reduce the emission of NO x and reduce its harm to the environment and physical health, it is necessary to improve and optimize the fossil fuel combustion process to reduce the generation and release of NO x . The current low-nitrogen burners are mainly for large and medium-sized industrial or civil equipment such as boilers, while small low-nitrogen burners lack supervision. With the rapid development of distributed energy, the demand for small burners is also growing rapidly.

[0003] The prior art one (CN 212746469 U) is a low-nitrogen burner. This burner has a good mixing effect of gas and air and high combustion efficiency, which has a certain effect on reducing NO x . However, this burner has the following main problems: (1) The nitrogen reduction technology adopted is too single, only using the method of fuel and air staging to reduce NO x , and the emission reduction effect for high NO x is limited; (2) The primary gas nozzle is too close to the intake pipe, which easily causes the temperature of the intake pipe to be too high and reduces the service life; (3) The burner head structure is designed complexly, and it is necessary to manufacture conical nozzles of different sizes and directions at the burner head, and the manufacturing cost of the burner is high, which has no economic advantage for small burners.

[0004] The prior art two (CN 114811582 A) is a double-swirl low-nitrogen burner. It promotes the mixing of ammonia and air by setting multiple secondary swirl vanes in the secondary air channel, thereby reducing the generation of NO x . Although the nitrogen reduction method of this patent is the same as that of this patent, the nitrogen reduction principle is different, that is, the patent does not consider the influence of the installation angle of the swirl vanes on NO x . At the same time, this burner does not consider the influence of combustion high temperature on the wall temperature.

[0005] Prior Art Three (CN 221005049 U) is an atomizing swirl low-nitrogen burner. It forms an umbrella-shaped combustion flame through a swirl nozzle to achieve a full combustion effect. Similarly, its principle of reducing nitrogen is different from that of this patent.

[0006] Prior Art Four (CN 113739149 A) and Prior Art Five (CN 110822430 A) are both low-nitrogen burners with a swirler. They generate swirl at different air nozzles through axial swirlers, forming a low-speed recirculation zone at the combustion center to reduce NO x emissions. Although the nitrogen reduction principle of this patent is similar to that of this patent, its design is relatively complex and is generally applied to industrial boilers equipped with external denitration devices such as selective catalytic reduction (SCR), and is not suitable for small-scale system heating. Small burners need to better organize the internal flow, mass transfer, and combustion to meet the requirements of low-nitrogen emissions.

[0007] Currently, large industrial burners have complex structures and large supporting systems, making it difficult to directly reduce their scale for application in small devices. Small burners generally face problems such as unstable combustion, excessive pollutant emissions, and short service life due to local overheating. In addition, the nitrogen oxide emissions of current small burners have not been strictly regulated, which may exacerbate environmental pollution problems, and small burners face many challenges in applications. On the one hand, due to space limitations, it is difficult to directly reduce the size of industrial high-power burners for application in low-power scenarios, especially devices with a power below 40kW. On the other hand, some small burners perform poorly under high-temperature conditions, and key parts such as the nozzle wall are prone to overheating, affecting the service life. In addition, the current nitrogen reduction technology for small burners is relatively single and difficult to meet the increasingly strict emission requirements, and there is an urgent need to develop more advanced nitrogen reduction solutions. Summary of the Invention

[0008] In order to overcome the problems existing in the prior art, the present invention provides a small low-nitrogen burner and a combustion method.

[0009] A small low-nitrogen burner includes a head air intake assembly, a combustion cylinder assembly, and a connection assembly.

[0010] The head air intake assembly includes a primary air inlet pipe, a central air distribution body module, an axial swirler, a radial swirler, a fuel pipe, and a premixed gas pipeline.

[0011] The primary air inlet pipe is arranged at the inlet end of the central air distribution body module for guiding external air into the central air distribution body module.

[0012] The premixed gas pipeline is sleeved at the outlet end of the central air distribution body module, and the axial swirler is arranged between the premixed gas pipeline and the outlet end.

[0013] The fuel pipe and the radial swirler are respectively arranged at other positions of the central air distribution body module, and are respectively used for supplying gaseous fuel to the burner and mixing the gaseous fuel and external air;

[0014] The connecting component connects the head air inlet component and the combustion cylinder component together.

[0015] In the above-described aspects and any possible implementation manners, a further implementation manner is provided. The central air distribution body module is an integrated stepped frustum, including a first convex surface and a second convex surface on the outside. A plurality of bolt holes are provided on the first convex surface, the radial swirler is arranged on the second convex surface, the fuel pipe is clamped on the radial swirler and fixed to the first convex surface through a plurality of bolt holes; a central cooling air channel is arranged at the internal central position and a plurality of pre-mixing air channels distributed in a ring shape are arranged around it. The central cooling air channel is communicated with both the inlet end and the outlet end.

[0016] In the above-described aspects and any possible implementation manners, a further implementation manner is provided. The connecting component is a chamber shoulder, whose flaring angle is between 30° and 35°, and it faces the combustion cylinder component.

[0017] In the above-described aspects and any possible implementation manners, a further implementation manner is provided. The cooling air channel is set in a flared form at the outlet end, and the expansion angle is between 30° and 60°.

[0018] In the above-described aspects and any possible implementation manners, a further implementation manner is provided. The combustion cylinder component further includes an outer cylinder and an inner cylinder. The outer cylinder is arranged on the outer periphery of the inner cylinder. The inner cylinder includes a jet cooling section, a mixing section and an extension section. The extension section of the inner cylinder is arranged outside the outer cylinder. The space formed by the chamber shoulder and the inner cylinder forms a combustion chamber.

[0019] In the above-described aspects and any possible implementation manners, a further implementation manner is provided. A plurality of vertical jet holes or inclined jet holes are provided on the wall surface of the jet cooling section.

[0020] In the above-described aspects and any possible implementation manners, a further implementation manner is provided. Mixing holes are provided on the wall surface of the mixing section.

[0021] In the above-described aspects and any possible implementation manners, a further implementation manner is provided. The burner further includes a secondary air inlet pipe welded to the outer cylinder.

[0022] For the aspects and any possible implementation manners described above, a further implementation manner is provided. The fuel pipe includes a fuel inlet pipe which is welded to the outer cylinder.

[0023] The present invention also provides a combustion method for a small low-nitrogen burner, which is implemented by using the burner described above, and includes the following steps:

[0024] When the burner starts to work, primary air enters through the primary air inlet pipe, and the distribution of the primary air volume is completed through the central cooling air channel and the premixed air channel on the central air distribution body module;

[0025] At the same time, gaseous fuel enters the annular flow channel formed by the fuel pipe and the central air distribution body module through the fuel inlet pipe, and after swirling through the radial swirler, the fuel is mixed with the premixed air to form a mixed gas, which flows into the mixing channel formed by the premixed gas pipeline and the central air distribution body module, and after flowing and mixing, it is sent into the combustion chamber through the axial swirler to swirl. In the combustion chamber, the mixed gas burns when encountering high temperature or is ignited; the central cooling air flows out from the central cooling air channel and flows towards the combustion chamber;

[0026] Secondary air enters the flow channel between the outer cylinder and the inner cylinder through the secondary air inlet pipe on the outer cylinder, and enters the combustion chamber through the jet holes and mixing holes on the inner cylinder, and is discharged through the extended section of the inner cylinder after complete combustion and mixing.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The burner of the present invention is a small low-nitrogen burner for scenarios such as distributed energy systems and small heating systems; the burner has high flame stability, and the nitrogen oxide emission at the outlet is lower than 30mg / m 3 , meeting the emission standards of gas burners, with high thermal efficiency and complete combustion; the burner integrates multiple low-nitrogen technologies such as air staging, premixed combustion, and flue gas internal circulation, and has a compact structure; through the design of the jet holes of the burner, the highest temperature on the combustion chamber wall is lower than 1000K, improving the service life of the burner. The present invention reduces the nitrogen oxides at the outlet by controlling the air volume of the premixed gas and the swirl angle inside the burner. At the same time, the internal circulation area can ensure the flame stability of the combustion center. The inner wall temperature of the burner flame tube is low, and the service life is improved. By designing jet holes on the inner wall of the combustion tube, a cooling gas film is covered, reducing the thermal stress on the inner cylinder near the combustion center. Description of the Drawings

[0029] Figure 1 It is a three-dimensional view of the burner of the present invention;

[0030] Figure 2 It is a position diagram of the A-A section of the burner of the present invention;

[0031] Figure 3 This is the central sectional view of the burner of the present invention;

[0032] Figure 4 This is the front view of the central air distributor of the burner of the present invention;

[0033] Figure 5 This is the position diagram of the B-B section of the central air distributor of the present invention;

[0034] Figure 6 This is the B-B sectional view;

[0035] Figure 7 This is the position diagram of the C-C section of the air intake assembly of the present invention;

[0036] Figure 8 This is the C-C sectional view;

[0037] Figure 9 This is the 3D diagram of the simplified burner;

[0038] Figure 10 This is the central streamline diagram of the simplified burner;

[0039] Figure 11 This is the cloud diagram of the temperature distribution of the central section of the simplified burner;

[0040] Figure 12 This is for the central section of the simplified burner NO x mole fraction distribution cloud diagram;

[0041] Figure 13 This is a schematic diagram of the temperature curve near the wall of the inner flame tube. Detailed implementation manners

[0042] For a better understanding of the technical solution of the present invention, the content of the present invention includes but is not limited to the following detailed implementation manners, and similar technologies and methods should be regarded as within the scope of protection of the present invention. To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0043] It should be clear that the embodiments described in the present invention are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0044] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms of "a", "the" and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0045] The present invention provides a small low - nitrogen burner, which includes a head air intake assembly, a combustion cylinder assembly and a connection assembly.

[0046] The head air intake assembly includes a primary air inlet pipe, a central air distribution body module, an axial swirler, a radial swirler, a fuel pipe and a premixed gas pipeline;

[0047] The primary air inlet pipe is arranged at the inlet end of the central air distribution body module and is used to guide external air into the central air distribution body module;

[0048] The premixed gas pipeline is sleeved at the outlet end of the central air distribution body module, and the axial swirler is arranged between the premixed gas pipeline and the outlet end;

[0049] The fuel pipe and the radial swirler are respectively arranged at other positions of the central air distribution body module, and are respectively used to supply gaseous fuel to the burner and mix the gaseous fuel and external air;

[0050] The connection assembly connects the head air intake assembly and the combustion cylinder assembly together.

[0051] Further, the central air distribution body module is an integrated stepped frustum, including a first convex surface and a second convex surface on the outside. There are a number of bolt holes on the first convex surface. The radial swirler is arranged on the second convex surface and is fixed to the second convex surface by threads. The fuel pipe is clamped on the radial swirler and is fixed to the first convex surface through a number of bolt holes; at the central position inside, there is a central cooling air channel and a number of premixing air channels distributed in a ring around it. The central cooling air channel is communicated with both the inlet end and the outlet end.

[0052] Further, the connection assembly is a chamber shoulder, whose flaring angle is between 30° and 35°, and faces the combustion cylinder assembly.

[0053] Further, the cooling air channel is set in a flared form at the outlet end, and the expansion angle is between 30° and 60°.

[0054] Further, the combustion cylinder assembly further includes an outer cylinder and an inner cylinder. The outer cylinder is arranged on the outer periphery of the inner cylinder. The inner cylinder includes a jet cooling section, a mixing section and an extension section. The extension section of the inner cylinder is arranged outside the outer cylinder. Optionally, the extension section can also be a part independent of the inner cylinder and the outer cylinder. Both ways can be realized in the present invention without limitation.

[0055] Further, a number of vertical jet holes or inclined jet holes are arranged on the wall surface of the jet cooling section of the inner cylinder.

[0056] Furthermore, mixing holes are arranged on the wall surface of the mixing section of the inner cylinder.

[0057] Furthermore, the burner further includes a secondary air inlet pipe welded to the outer cylinder.

[0058] Furthermore, the fuel pipe includes a fuel inlet pipe welded to the outer cylinder, and the burner further includes a secondary air inlet pipe welded to the outer cylinder.

[0059] Specifically, as Figures 1-8 shown, the burner includes a head air intake assembly, a combustion cylinder assembly, and a connection assembly. The head air intake assembly, as Figure 7 and Figure 8 shown, includes a primary air inlet pipe 1, a central air distribution body module 2, an axial swirler 3, a radial swirler 4, a fuel pipe 5, and a premixed gas pipeline 6. The central air distribution body module 2, as Figure 4 , Figure 5 and 6Shown is an integrated stepped frustum. The primary air inlet pipe 1 is arranged at the inlet end of the central air distribution body module 2. A central cooling air channel 22 is arranged at the central position of the central air distribution body module 2, and the cooling air channel 22 is flared at the outlet end, with an expansion angle of 30° to 60°, which can ensure that the high-temperature flue gas in reflux will not overheat it. Around the central cooling air channel 22, there is a pre-mixed air channel 21 distributed in a ring shape. In the present invention, there are 6 such channels, and the specific number can be determined according to different working conditions. The axial swirler 3 is installed at the rightmost end, i.e., the outlet end position, of the central air distribution body module 2. The axial swirler 3 is connected to the central air distribution body module 2 by welding or as a whole by threading. An axial swirler support 31 is arranged on the axial swirler 3, and its diameter is slightly smaller than that of the pre-mixed gas pipeline 6. The pre-mixed gas pipeline 6 is sleeved on the outside of the inlet end, playing a supporting role for the pre-mixed gas pipeline 6. The primary air inlet pipe 1 is fixed on the left side wall surface of the inlet end of the central air distribution body module 2 by welding, and is used to guide external air into the central air distribution body module 2. The outside of the central air distribution body module 2 includes a convex platform I surface 23 and a convex platform II surface 24, that is, the first convex platform surface and the second convex platform surface. The radial swirler 4 is fixed to the convex platform II surface 24 of the central air distribution body module 2 by threading. The blades of the axial swirler 3 can adopt straight blades or curved blades and other structural forms to reduce resistance. By controlling the installation angle of the swirl blades, in the present invention, it is taken as 35°, the size of the flue gas reflux zone in the burner is controlled, and then the oxygen concentration in the combustion zone is controlled, further reducing the nitrogen oxide emissions of the burner and improving the temperature uniformity at the burner outlet. In addition to further ensuring uniform mixing, a high-temperature flue gas reflux zone is generated in the furnace, and the high-temperature flue gas heats the pre-mixed gas and secondary air to maintain the high temperature in the combustion zone, ensuring the stability of the flame. The radial swirler 4 increases the disturbance between the gaseous fuel and the pre-mixed air, making their mixing more uniform.

[0060] The bottom of the fuel pipe 5 is installed on the convex platform I surface 23 of the central air distribution body module 2 by bolts and locked by bolts. There are 6 bolt holes on the convex platform I surface 23, as Figure 4 shown. While fixing the fuel pipe 5, the fuel pipe 5 clamps the radial swirler 4 and is fixedly connected to the bolt holes on the convex platform I surface 23, further ensuring the stability of the radial swirler 4. The fuel inlet pipe 51 is fixed to the outer cylinder 8 of the combustion cylinder assembly by welding and is communicated with the fuel pipe 5. The pre-mixed gas pipeline 6 is fixed to the fuel pipe 5 by threading or welding, is coaxially installed with the axial swirler 3, and is supported by the support 31 on the axial swirler 3.

[0061] The combustion cylinder assembly includes: an outer cylinder 8 and an inner cylinder 9. The outer cylinder 8 is fixed to the central air distribution body module 2 through 6 bolts passing through the fuel pipe 5, and at the same time clamps the fuel pipe 5 to ensure the stability of the overall structure of the burner. The secondary air inlet pipe 81 is fixed to the outer cylinder 8 by welding.

[0062] The chamber shoulder 7 is used to connect the head air inlet assembly and the combustion cylinder assembly. The chamber shoulder angle is between 30° and 35°, thereby reducing the area of the corner recirculation zone in the combustion chamber. The left end of the head of the chamber shoulder 7 is connected to the premixed gas pipeline 6 by flange or welding, and the right end of the chamber shoulder 7 is connected to the inner cylinder 9 by welding. Support ribs are welded on the inner cylinder 9 of the combustion cylinder, and a screw is added to press the upper part of the outer cylinder 8 of the combustion cylinder to prevent vibration (not shown in the figure). The inner cylinder extension section 10 is sealed with the bottom of the outer cylinder 8 of the combustion cylinder through a sealing ring and a plug. A jet cooling section is provided on the inner cylinder 9. A number of vertical jet holes or inclined jet holes 91 are provided on the wall surface of this part. The arrangement method is not limited. In addition to using vertical jets for the installation of the jet holes, inclined jets can also be used, so that the air film length is longer and the protection area is larger. A denser staggered jet hole is adopted at this position, effectively reducing the wall temperature of the inner cylinder where the flame is located at the combustion center, and controlling the maximum temperature below 750°C, significantly reducing the requirements for materials, and ordinary stainless steel with lower cost can be used to replace the superalloy, thereby greatly reducing the manufacturing cost of the burner.

[0063] At the same time, in addition to using screws to fix the inner cylinder 9, the outer cylinder 8 of the burner can also adopt a semi-open design, and support ribs are installed on the inner wall of the outer cylinder 8 to fix the inner cylinder 9.

[0064] Mixing holes 92 are provided on the wall surface of the mixing section of the inner cylinder 9. At the same time, the design of the mixing holes in the mixing section optimizes the structure of the burner, shortens the overall length of the burner, makes the outlet temperature distribution more uniform, and improves the combustion efficiency. The burner also includes a secondary air inlet pipe 81 welded to the outer cylinder, and the fuel pipe 5 includes a fuel inlet pipe 51, and the fuel inlet pipe 51 is welded to the outer cylinder 8.

[0065] As an embodiment disclosed in the present invention, the present invention provides a combustion method for a small low-nitrogen burner, and the method is implemented by using the burner, including the following steps:

[0066] When the burner starts to work, the primary air enters through the primary air inlet pipe, and the distribution of the primary air volume is completed through the central cooling air channel and the premixing air channel on the central air distribution body module;

[0067] Meanwhile, the gaseous fuel enters the annular flow passage formed by the fuel pipe and the central air distribution body module through the fuel inlet pipe. After swirling through the radial swirler, the fuel mixes with the pre-mixed air to form a mixed gas, which then converges into the mixing passage formed by the pre-mixed gas pipeline and the central air distribution body module. After flowing and mixing, it is swirled by the axial swirler and sent into the combustion chamber, where the mixed gas undergoes high-temperature combustion or ignition combustion upon encountering high temperature; the central cooling air flows out from the central cooling air passage and flows towards the combustion chamber to prevent local overheating caused by the backflow of high-temperature flue gas;

[0068] The secondary air enters the flow passage between the outer cylinder and the inner cylinder through the secondary air inlet pipe on the outer cylinder, and enters the combustion chamber through the jet holes and mixing holes on the inner cylinder, and is discharged through the extended section of the inner cylinder after complete combustion and mixing.

[0069] Specifically, the working process of the burner is as follows:

[0070] When the burner starts to work, the primary air enters through the primary air inlet pipe 1, and the distribution of the primary air volume is completed through the different cross-sectional areas of the central cooling air passage 22 and the pre-mixed air passage 21 on the central air distribution body module 2; meanwhile, gaseous fuels (such as methanol vapor, methane, hydrogen-rich gaseous fuels, etc.) enter the annular flow passage formed by the fuel pipe 5 and the central air distribution body module 2 through the fuel inlet pipe 51. After swirling through the radial swirler 4, the fuel mixes with the pre-mixed air to form a mixed gas, which then converges into the mixing passage formed by the pre-mixed gas pipeline 6 and the central air distribution body module 2. After flowing and mixing, it is swirled by the axial swirler 3 and sent into the combustion chamber 11, which is the space surrounded by the chamber shoulder 7 and the inner cylinder 9. In the combustion chamber 11, the mixed gas undergoes high-temperature combustion or ignition combustion upon encountering high temperature. The central cooling air flows out from the central cooling air passage 22 and flows towards the combustion chamber 11 at a certain angle to prevent local overheating caused by the backflow of high-temperature flue gas, and this angle is related to the expansion angle of the central cooling air passage 22. The secondary air enters the flow passage between the outer cylinder 8 of the combustion cylinder and the inner cylinder 9 of the combustion cylinder through the secondary air inlet pipe 81 on the outer cylinder 8 of the combustion cylinder, and enters the combustion chamber 11 through the jet holes 91 and mixing holes 92 on the inner cylinder 9 of the combustion cylinder. After complete combustion and mixing, it is discharged from the burner through the extended section 10 of the inner cylinder of the combustion cylinder. The present invention reduces the outlet nitrogen oxides by controlling the air volume of the pre-mixed gas and the swirling angle inside the burner. At the same time, the inner circulation area can ensure the stability of the central flame of combustion. Therefore, the nitrogen reduction effect is obvious, and the flame stability is high. At the same time, by arranging jet holes on the wall surface of the inner cylinder 9, the air from between the outer cylinder 8 and the inner cylinder 9 enters the combustion chamber 11 through the jet holes, so that a cooling gas film covers the jet cooling section of the inner cylinder 9, thereby reducing the thermal stress on the inner cylinder 9 near the combustion center, with a low inner wall surface temperature and improving the service life of the burner.

[0071] The burner of the present invention adopts air staging, introducing air into the burner in batches to control the temperature during the combustion process; it uses the premixed combustion method to increase the air excess coefficient in the premixed gas, reduce the maximum temperature in the high-temperature area, and reduce the generation of thermal NO x ; it adopts an axial swirler to generate a central low-pressure recirculation zone for the premixed gas in the furnace of the burner, enabling the burned high-temperature flue gas to flow back to the center of the furnace, thereby reducing the oxygen and fuel concentrations in the combustion area, and further reducing the generation of thermal and prompt NO x， It solves the problem that the existing burners have a single NO reduction technology and the NO reduction effect is not obvious. x

[0072] In addition, the burner is provided with a central cooling air passage 22 and jet holes 91. Part of the central air is sent into the front end of the combustion chamber 11 through the central cooling air passage 22, reducing the temperature at the burner head position. At the same time, the secondary air forms a cooling gas film on the inner wall surface of the combustion cylinder 9, greatly reducing the temperature near the wall surface, making its temperature lower than 750 °C, and improving the service life.

[0073] CFD simulation results:

[0074] In addition, the present invention establishes a simplified three-dimensional model of the burner, combines appropriate physical models and boundary conditions, takes methanol fuel as an example, and uses Fluent software to numerically simulate the combustion process. By deeply analyzing the simulation results and quantifying the influence of different parameters on the combustion performance, the rationality of the structural setting of the burner of the present invention is demonstrated. As Figures 9-13 shown, the following are the simulation calculation steps and results of the present invention.

[0075] I. Model establishment

[0076] (1) Turbulence model

[0077] The Realizable k-ε model combined with the standard wall function method is used for solution.

[0078] (2) Combustion model and radiation model

[0079] Taking methanol vapor fuel as an example, methanol vapor undergoes a two-step oxidation reaction with oxygen in the air, that is: methanol is first oxidized to carbon monoxide, and carbon monoxide is further oxidized to carbon dioxide, while considering the pyrolysis reaction of carbon dioxide. Since the temperature is relatively high during the combustion process and the influence of gas radiation cannot be ignored, the DO radiation model, which is more accurate for simulating gas radiation during the combustion process, is adopted.

[0080] (3) Burner physical model

[0081] It is assumed that methanol vapor has been completely mixed with air in the mixing channel. The simulation area is a cylindrical area with a length of 300 mm and a diameter of 60 mm; an unstructured grid is selected for grid calculation.

[0082] II. Solution Method and Boundary Conditions

[0083] (1) Solution Method

[0084] In the Fluent commercial software, the SIMPLE algorithm is used to solve the velocity-pressure coupling equation, the pressure interpolation format is selected as PRESTO, and the second-order upwind format (Second Order Upwind) is used for the remaining momentum, component, and energy equations. To ensure the accuracy of the steady-state calculation, the continuity equation residual is set to 10 -4 , the energy equation and radiation model residuals are set to 10 -5 , and the remaining component residuals are set to 10 -6 , and at the same time, the burner outlet temperature and outlet CO concentration are monitored.

[0085] (2) Boundary Conditions

[0086] Velocity inlets are adopted at the burner inlets. The total air excess coefficient is 3.6, and the air excess coefficient of the premixed gas is 1.2. The outlet is a pressure outlet. The specific burner inlet boundary conditions are shown in Table 1. The wall surface adopts a non-slip fixed wall surface, and the wall surface emissivity is taken as 0.6.

[0087]

[0088] Table 1: Boundary Conditions of Each Burner Inlet

[0089] Simulation Results

[0090] After passing through the designed swirl burner, the high-temperature area of the burner is relatively concentrated; two low-pressure recirculation zones are formed in the center of the burner, ensuring that the flame is stable even at a large air excess coefficient and reducing NO x emissions. The NO x emitted by this gas burner is 12 mg / m 3 (oxygen concentration 3.5%, converted), far lower than the limit of 30 mg / m 3 specified in Beijing; the axial velocity of the gas flow in the swirl burner decays relatively fast, which can reduce the flame length, shorten the burner length, and reduce the volume; staggered jet holes are designed in the combustion section of the flame tube to reduce the wall temperature of the flame tube in the combustion section, making its maximum temperature lower than 750 °C.

[0091] The foregoing description has shown and described several preferred embodiments of the present invention. However, as previously mentioned, it should be understood that the present invention is not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the above teachings or the techniques or knowledge in the relevant field. Any alterations and changes made by those skilled in the art that do not depart from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A small low-nitrogen burner, characterized in that: It includes head air intake assembly, combustion tube assembly and connection assembly. The head air intake assembly includes a primary air inlet pipe, a central air distributor module, an axial swirler, a radial swirler, a fuel pipe and a premixed air pipeline; The primary air inlet pipe is arranged at the inlet end of the central air distribution module, and is used to guide external air into the central air distribution module; The premixed air pipeline is sleeved on the outlet end of the central air distributor module, and the axial swirler is arranged between the premixed air pipeline and the outlet end; The fuel pipe and radial swirler are respectively arranged at other positions of the central air distributor module, and are used to provide gas fuel to the burner and mix the gas fuel with external air respectively; The connecting assembly connects the head air intake assembly and the combustion cylinder assembly together.

2. The small low-nitrogen burner according to claim 1 is characterized in that: The central air distribution body module is an integrated stepped cone, and the outside includes a first boss surface and a second boss surface, the first boss surface is provided with a plurality of bolt holes, the radial swirler is provided on the second boss surface, the fuel pipe is clamped on the radial swirler and fixed to the first boss surface through a plurality of bolt holes; a central cooling air channel is provided at the internal center position and a plurality of premixing air channels are provided around it in an annular shape, and the central cooling air channel is connected with both the inlet end and the outlet end.

3. The small low-nitrogen burner according to claim 1 or 2, characterized in that: The connecting component is a chamber shoulder, the expansion angle of which is between 30° and 35° and faces the combustion tube component.

4. The small low-nitrogen burner according to claim 2 is characterized in that: The cooling air passage is arranged in a flared form at the outlet end, and the expansion angle is between 30° and 60°.

5. The small low-nitrogen burner according to claim 3 is characterized in that: The combustion tube assembly also includes an outer tube and an inner tube, the outer tube is arranged on the outer periphery of the inner tube, the inner tube includes a jet cooling section, a mixing section and an extension section, the extension section is arranged outside the outer tube, and the space enclosed by the chamber shoulder and the inner tube forms a combustion chamber.

6. The small low-nitrogen burner according to claim 5, characterized in that: A plurality of vertical jet holes or inclined jet holes are arranged on the wall surface of the jet cooling section.

7. The small low-nitrogen burner according to claim 5, characterized in that: Mixing holes are arranged on the wall surface of the mixing section.

8. The small low-nitrogen burner according to claim 5, characterized in that: The burner further includes a secondary air inlet pipe welded to the outer cylinder.

9. The small low-nitrogen burner according to claim 5, characterized in that: The fuel pipe comprises a fuel inlet pipe, and the fuel inlet pipe is welded to the outer cylinder.

10. A combustion method of a small low-nitrogen burner, characterized in that: The method is implemented by using the burner according to any one of claims 1 to 9, and comprises the following steps: When the burner starts working, primary air enters through the primary air inlet pipe, and the primary air volume is distributed through the central cooling air channel and the premixing air channel on the central air distributor module; At the same time, the gas fuel enters the annular flow channel formed by the fuel pipe and the central air distributor module through the fuel inlet pipe, and after being swirled by the radial swirler, the fuel is mixed with the premixing air to form a mixed gas, which is then merged into the mixing channel formed by the premixing gas pipeline and the central air distributor module. After flow mixing, the mixed gas is swirled by the axial swirler and sent into the combustion chamber. In the combustion chamber, the mixed gas encounters high temperature and burns or ignites. The central cooling air flows out from the central cooling air channel and flows to the combustion chamber. The secondary air enters the flow channel between the outer cylinder and the inner cylinder through the secondary air inlet pipe on the outer cylinder, and enters the combustion chamber through the jet holes and mixing holes on the inner cylinder. After the combustion and mixing are complete, the secondary air is discharged through the extension section of the inner cylinder.

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