Small low-nitrogen burner and combustion method

Abstract

The present application relates to a kind of small low-nitrogen combustor and combustion method, including head air inlet assembly, combustion cylinder assembly and connecting assembly, head air inlet assembly includes primary air inlet pipe, center air distribution body module, axial swirler, radial swirler, fuel pipe and premixed gas pipeline;Primary air inlet pipe is arranged at the inlet end of center air distribution body module;Premixed gas pipeline is sleeved in the outlet end of center air distribution body module, the axial swirler is arranged between the premixed gas pipeline and the outlet end;Fuel pipe and radial swirler are respectively arranged in other positions of the center air distribution body module;Connecting assembly connects the head air inlet assembly and combustion cylinder assembly together.The present application is obvious in nitrogen reduction effect, and flame stability is high.By controlling the air amount of premixed gas and the internal swirl angle of combustor, the outlet nitrogen oxide is reduced, and the inner circulation zone can ensure the stability of combustion center flame.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of low-nitrogen combustion, and particularly relates to a small low-nitrogen combustor and a combustion method. BACKGROUND

[0002] Nitrogen oxides (NO x ) are a class of compounds generated by nitrogen and oxygen in the high-temperature combustion process. The main components include nitric oxide (NO) and nitrogen dioxide (NO2). NO x is one of the atmospheric pollutants, which has serious harm to the environment and human health. The emission of NO x mainly comes from transportation and energy consumption activities. 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 human health, it is necessary to improve and optimize the combustion process of fossil fuels to reduce the generation and release of NO x . The current low-nitrogen combustor is mainly aimed at large and medium-sized industrial or civil equipment such as boilers, while small low-nitrogen combustors lack supervision. With the rapid development of distributed energy, the demand for small combustors is also growing rapidly.

[0003] Prior art one (CN 212746469 U) is a low-nitrogen combustor. The combustor has good gas and air mixing effect, high combustion efficiency, and certain effect on reducing NO x However, the combustor has the following main problems: (1) the adopted nitrogen reduction technology is too single, only the method of fuel and air grading is used to reduce NO x , which has limited effect on high NO x emission reduction; (2) the primary gas nozzle is too close to the air inlet pipe, which easily leads to high temperature of the air inlet pipe and reduces the service life; (3) the structure design of the combustor head is complex, different size and direction conical nozzles need to be manufactured on the head of the combustor, which has high manufacturing cost of the combustor and no economic advantage for small combustors.

[0004] Prior art two (CN 114811582 A) is a double-swirl low-nitrogen combustor. It sets multiple secondary swirl vanes in the secondary air passage to promote the mixing of ammonia and air, thereby reducing the generation of NO x Although the nitrogen reduction method of this patent is the same as that of the present patent, the nitrogen reduction principle is different, that is, the patent does not consider the influence of the installation angle of the swirl vane on NO x . At the same time, the combustor does not consider the influence of high temperature combustion on the wall temperature.

[0005] The prior art three (CN 221005049 U) is an atomized cyclone low-nitrogen burner. It forms an umbrella-shaped combustion flame through a cyclone nozzle to achieve sufficient combustion effect. Its nitrogen reduction principle is different from that of the present patent.

[0006] The prior art four (CN 113739149 A) and the prior art five (CN 110822430 A) are both low-nitrogen burners with cyclones. By setting axial cyclones at different air outlets, a low-speed backflow area is formed at the combustion center to reduce NO x emissions. Although the nitrogen reduction principle of this patent is similar to that of the present patent, its design is more complex and is generally used in industrial boilers equipped with external denitration devices such as selective catalytic reduction (SCR), which is not suitable for small-scale heating systems. Small burners need to better organize 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 scale down for use in small equipment. Small burners generally face problems such as unstable combustion, excessive pollutant emissions, and local overheating leading to short service life. 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 application. On the one hand, due to space limitations, industrial high-power burners cannot be directly scaled down for use in low-power scenarios, especially for devices with power less than 40kW. On the other hand, some small burners perform poorly under high-temperature conditions, and key parts such as nozzle walls are prone to overheating, affecting service life. In addition, the nitrogen reduction technology of existing small burners is relatively simple, making it difficult to meet increasingly stringent emission requirements, and more advanced nitrogen reduction solutions are urgently needed. SUMMARY

[0008] To overcome the problems of the prior art, the present application provides a small low-nitrogen burner and a combustion method.

[0009] A small low-nitrogen burner, comprising a head air inlet assembly, a combustion cylinder assembly, and a connecting assembly,

[0010] The head air inlet assembly comprises a primary air inlet pipe, a central air distribution body module, an axial cyclone, a radial cyclone, 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 to guide external air into the central air distribution body module;

[0012] The premixed gas pipeline is sleeved on the outlet end of the central air distribution body module, and the axial cyclone 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 center air distribution body module, and are respectively used for providing gaseous fuel to the combustor and mixing the gaseous fuel and external air;

[0014] The connecting assembly connects the head air inlet assembly and the combustor barrel assembly together.

[0015] According to the aspect and any possible implementation manner as described above, further provided is an implementation manner, the center air distribution body module is an integrated stepped circular truncated cone, externally comprising a first convex platform and a second convex platform, the first convex platform is provided with a plurality of bolt holes, the radial swirler is arranged on the second convex platform, and the fuel pipe is clamped on the radial swirler and fixed with the first convex platform through the plurality of bolt holes; a center cooling air passage is arranged at a central position in the interior, and a plurality of premixing air passages are arranged around the center cooling air passage in a ring shape, and the center cooling air passage is in communication with the inlet end and the outlet end.

[0016] According to the aspect and any possible implementation manner as described above, further provided is an implementation manner, the connecting assembly is a chamber shoulder, an expanding angle of the chamber shoulder is 30° to 35°, and the chamber shoulder is directed towards the combustor barrel assembly.

[0017] According to the aspect and any possible implementation manner as described above, further provided is an implementation manner, the cooling air passage is arranged in an expanding form at the outlet end, and an expanding angle is 30° to 60°.

[0018] According to the aspect and any possible implementation manner as described above, further provided is an implementation manner, the combustor barrel assembly further comprises an outer barrel and an inner barrel, the outer barrel is arranged at an outer periphery of the inner barrel, the inner barrel comprises a jet cooling section, a mixing section and an extension section, the inner barrel extension section is arranged outside the outer barrel, and a space surrounded by the chamber shoulder and the inner barrel forms a combustion chamber.

[0019] According to the aspect and any possible implementation manner as described above, further provided is an implementation manner, a wall surface of the jet cooling section is provided with a plurality of vertical jet holes or inclined jet holes.

[0020] According to the aspect and any possible implementation manner as described above, further provided is an implementation manner, a mixing hole is arranged on a wall surface of the mixing section.

[0021] According to the aspect and any possible implementation manner as described above, further provided is an implementation manner, the combustor further comprises a secondary air inlet pipe welded on the outer barrel.

[0022] Aspects and any possible implementation mentioned above, further provide an implementation, the fuel pipe comprises a fuel inlet pipe, which is welded on the outer cylinder.

[0023] The application also provides a combustion method of the small-sized low-nitrogen combustor, which is achieved by using the combustor and comprises the following steps:

[0024] When the combustor starts to work, primary air enters through the primary air inlet pipe, and the amount of the primary air is distributed through the central cooling air channel and the premixing air channel on the central air distribution body module;

[0025] Meanwhile, 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 being rotated by the radial swirler, the fuel is mixed with the premixing air to form mixed gas, which is then collected into the mixing channel formed by the premixing gas pipe and the central air distribution body module, and after flowing and mixing, the mixed gas is sent into the combustion chamber through the axial swirler, and in the combustion chamber, the mixed gas is combusted at high temperature or ignited to combust; the central cooling air flows out of the central cooling air channel and flows to 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 hole and the mixing hole on the inner cylinder, and after complete combustion and mixing, the secondary air is discharged through the extended section of the inner cylinder.

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

[0028] The combustor of the application is a small-sized low-nitrogen combustor for distributed energy systems, small-sized heating systems and the like; the combustor has high flame stability, and the nitrogen oxide emission at the outlet is lower than 30 mg / m 3 , which meets the emission standard of gas combustors, and has high thermal efficiency and complete combustion; the combustor integrates air staging, premixing combustion and flue gas internal circulation, and has a compact structure; through the design of the jet hole of the combustor, the maximum temperature of the wall surface of the combustion chamber is lower than 1000K, thereby improving the service life of the combustor. The application reduces the nitrogen oxide at the outlet by controlling the air amount of the premixed gas and the internal swirling angle of the combustor. Meanwhile, the internal circulation zone can ensure the stability of the central flame. The inner wall surface temperature of the flame cylinder of the combustor is low, and the service life is improved. Through the design of the jet hole on the inner wall of the combustion cylinder, a layer of cooling gas film is formed, thereby reducing the thermal stress on the inner cylinder near the combustion center. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The figure is a three-dimensional view of the combustor of the application;

[0030] Figure 2 The figure is a position view of the A-A section of the combustor of the application;

[0031] Figure 3 Figure 1 is a central sectional view of the combustor of the present application;

[0032] Figure 4 Figure 2 is a front view of the central air distribution body of the combustor of the present application;

[0033] Figure 5 Figure 3 is a B-B sectional view of the central air distribution body of the present application;

[0034] Figure 6 Figure 4 is a B-B sectional view;

[0035] Figure 7 Figure 5 is a C-C sectional view of the air intake assembly of the present application;

[0036] Figure 8 Figure 6 is a C-C sectional view;

[0037] Figure 9 Figure 7 is a simplified 3D view of the combustor;

[0038] Figure 10 Figure 8 is a simplified central flow streamline view of the combustor;

[0039] Figure 11 Figure 9 is a simplified central cross-sectional temperature distribution contour plot of the combustor;

[0040] Figure 12 Figure 10 is a simplified central cross-sectional NOx x mole fraction distribution contour plot of the combustor;

[0041] Figure 13 Figure 11 is a temperature profile near the inner flame tube wall. DETAILED DESCRIPTION

[0042] In order to better understand the technical solutions of the present application, the present application includes but is not limited to the following detailed description, and similar techniques and methods should be considered as falling within the scope of the present application. In order to make the technical problems, technical solutions and advantages of the present application more clear, the following will be described in detail in conjunction with the drawings and specific embodiments.

[0043] It should be clear that the embodiments described in the present application are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

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

[0045] The application provides a small-sized low-nitrogen combustor, comprising a head air inlet assembly, a combustion cylinder assembly and a connecting assembly,

[0046] The head air inlet assembly comprises 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 an inlet end of the central air distribution body module and used for guiding external air into the central air distribution body module.

[0048] The premixed gas pipeline is sleeved at an 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 arranged at other positions of the central air distribution body module respectively and used for providing gaseous fuel to the combustor and mixing the gaseous fuel and external air respectively.

[0050] The connecting assembly connects the head air inlet assembly and the combustion cylinder assembly together.

[0051] Further, the central air distribution body module is an integrated stepped circular truncated cone, which comprises a first convex platform and a second convex platform, a plurality of bolt holes are arranged on the first convex platform, the radial swirler is arranged on the second convex platform and fixed with the second convex platform through threads, the fuel pipe is clamped on the radial swirler and fixed with the first convex platform through the plurality of bolt holes, and a central cooling air channel is arranged at a central position in the interior and a plurality of premixing air channels are arranged around the central cooling air channel in a ring shape, and the central cooling air channel is communicated with the inlet end and the outlet end.

[0052] Further, the connecting assembly is a chamber shoulder, the flaring angle of which is 30°-35° and the chamber shoulder is directed towards the combustion cylinder assembly.

[0053] Further, the cooling air channel is arranged in a flared form at the outlet end, and the flaring angle is 30°-60°.

[0054] Further, the combustion cylinder assembly further comprises an outer cylinder and an inner cylinder, the outer cylinder is arranged at the outer periphery of the inner cylinder, the inner cylinder comprises a jet cooling section, a mixing section and an extension section, the inner cylinder extension section is arranged outside the outer cylinder, and optionally, the extension section can also be a part independent of the inner cylinder and the outer cylinder, and the application can be realized in both the two modes without limitation.

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

[0056] Further, a mixing hole is arranged on the wall of the mixing section of the inner cylinder.

[0057] Further, the combustor further comprises a secondary air inlet pipe welded on the outer cylinder.

[0058] Further, the fuel pipe comprises a fuel inlet pipe welded on the outer cylinder, and the combustor further comprises a secondary air inlet pipe welded on the outer cylinder.

[0059] Specifically, as shown in Figures 1-8 , the combustor comprises a head air intake assembly, a combustion cylinder assembly and a connecting assembly, the head air intake assembly, as shown in Figure 7 and Figure 8 , comprises 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 pipe 6. The central air distribution body module 2, as shown in Figure 4 , Figure 5 and 6The shown is an integrated stepped circular cone, and the primary air inlet pipe 1 is arranged at the inlet end of the central air distribution body module 2, wherein the 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 arranged in the form of an expanded mouth at the outlet end, with an expansion angle of 30°-60°, which can ensure that the backflow of high-temperature flue gas does not overheat it. The premixing air channels 21 are arranged in a ring shape around the central cooling air channel 22, and the number of the premixing air channels 21 is six, and the specific number can be determined according to different working conditions. The axial cyclone 3 is installed at the rightmost end of the central air distribution body module 2, that is, the outlet end, and the axial cyclone 3 is connected to the central air distribution body module 2 by welding or as a whole by a threaded connection, and the axial cyclone 3 is provided with an axial cyclone support 31, which has a diameter slightly smaller than the premixing gas pipe 6, and the premixing gas pipe 6 is sleeved outside the inlet end to support the premixing gas pipe 6. The primary air inlet pipe 1 is fixed on the left side wall of the inlet end of the central air distribution body module 2 by welding, and is used to guide the external air into the central air distribution body module 2. The outer side of the central air distribution body module 2 includes the boss I surface 23 and the boss II surface 24, that is, the first boss surface and the second boss surface, and the radial cyclone 4 is fixed to the boss II surface 24 of the central air distribution body module 2 by threading. The blades of the axial cyclone 3 can adopt straight blades or curved blades and other structural types to reduce resistance. The straight blades control the size of the backflow area of the flue gas in the burner by controlling the installation angle of the cyclone blades, which is 35° in the present application, to control the oxygen concentration in the combustion area, further reduce the emission of nitrogen oxides of the burner, improve the uniformity of the outlet temperature of the burner, and further ensure uniform mixing, generate a high-temperature flue gas backflow area in the furnace, and maintain the high temperature of the combustion area by heating the premixed fuel gas and the secondary air with the high-temperature flue gas to ensure the stability of the flame. The radial cyclone 4 increases the disturbance of the gas fuel and the premixed air, so that they are more uniformly mixed.

[0060] The fuel pipe 5 is bolted at the bottom of the central air distribution body module 2, and is locked by bolts, and the boss I surface 23 is provided with six bolt holes, as shown in Figure 4 When the fuel pipe 5 is fixed, the fuel pipe 5 clamps the radial cyclone 4 and is fixedly connected with the bolt holes of the boss I surface 23, further ensuring the stability of the radial cyclone 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 premixing gas pipe 6 is fixed to the fuel pipe 5 by threading or welding, is coaxially arranged with the axial cyclone 3, and is supported by the support 31 on the axial cyclone 3.

[0061] The combustion cylinder assembly comprises an outer cylinder 8 and an inner cylinder 9, the outer cylinder 8 is fixed with the center air distribution body module 2 through 6 bolts passing through the fuel pipe 5, while clamping the fuel pipe 5, so as to ensure the stability of the whole structure of the burner. The secondary air inlet pipe 81 is fixed on the outer cylinder 8 by welding.

[0062] The chamber shoulder 7 is used for connecting the head air inlet assembly and the combustion cylinder assembly, and the angle of the chamber shoulder is 30°-35°, so as to reduce the area of the corner backflow area in the combustion chamber. The head left end of the chamber shoulder 7 is connected with the premixed gas pipeline 6 through a flange or welding, and the right end of the chamber shoulder 7 is connected with the inner cylinder 9 through welding. The inner cylinder 9 of the combustion cylinder is welded with a supporting rib, and a screw rod is added to 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. The jet cooling section is arranged on the inner cylinder 9, a plurality of vertical jet holes or inclined jet holes 91 are arranged on the wall surface of the jet cooling section, the arrangement mode is not limited, and in addition to the vertical jet, the inclined jet mode can also be adopted, so that the gas film length is longer and the protection area is larger. In this position, the dense staggered jet holes are adopted, the wall surface temperature of the inner cylinder where the flame is located is effectively reduced, the highest temperature is controlled below 750℃, the requirement for the material is significantly reduced, the ordinary stainless steel can be used to replace the high-temperature alloy, so that the manufacturing cost of the burner is greatly reduced.

[0063] Meanwhile, in addition to the screw rod for fixing the inner cylinder 9, the outer cylinder 8 can also adopt a semi-open design, and the supporting rib is arranged on the inner wall of the outer cylinder 8 to fix the inner cylinder 9.

[0064] The mixing holes 92 are arranged on the wall surface of the mixing section of the inner cylinder 9, and the design of the mixing holes of 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 further comprises a secondary air inlet pipe 81 welded on the outer cylinder, and the fuel pipe 5 comprises a fuel inlet pipe 51 welded on the outer cylinder 8.

[0065] As an embodiment disclosed by the application, the application provides a combustion method of a small low-nitrogen burner, the method is realized by using the burner, and comprises 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 amount is completed through the center cooling air channel and the premixing air channel on the center air distribution body module;

[0067] Meanwhile, the gas fuel enters the annular flow channel formed by the fuel pipe and the center air distribution body module through the fuel inlet pipe, and after being rotated by the radial swirler, the fuel is mixed with the premixing air to form mixed gas, which is collected into the mixing channel formed by the premixing gas pipe and the center air distribution body module, and after flow mixing, is sent into the combustion chamber through the axial swirler, and in the combustion chamber, the mixed gas is burned or ignited; the center cooling air flows out from the center cooling air channel and flows to the combustion chamber to prevent the high-temperature flue gas from flowing back to cause local overheating.

[0068] 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 hole and the mixing hole on 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 different cross-sectional areas of the center cooling air channel 22 and the premixing air channel 21 on the center air distribution body module 2 complete the distribution of the amount of primary air; meanwhile, the gas fuel (such as methanol vapor, methane, hydrogen-rich gas fuel, etc.) enters the annular flow channel formed by the fuel pipe 5 and the center air distribution body module 2 through the fuel inlet pipe 51, and after being rotated by the radial swirler 4, the fuel is mixed with the premixing air to form mixed gas, which is collected into the mixing channel formed by the premixing gas pipe 6 and the center air distribution body module 2, and after flow mixing, is sent into the combustion chamber 11 through the axial swirler 3, and the combustion chamber 11 is the space surrounded by the chamber shoulder 7 and the inner cylinder 9. In the combustion chamber 11, the mixed gas is burned or ignited. The center cooling air flows out from the center cooling air channel 22 and flows to the combustion chamber 11 at a certain angle to prevent the high-temperature flue gas from flowing back to cause local overheating, and the angle is related to the expansion angle of the center cooling air channel 22. The secondary air enters the flow channel between the outer cylinder 8 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 hole 91 and the mixing hole 92 on the inner cylinder 9 of the combustion cylinder. After complete combustion and mixing, the burner is discharged through the extended section 10 of the inner cylinder. The present application reduces the outlet nitrogen oxide by controlling the air amount of the premixed gas and the internal rotational angle of the burner. At the same time, the inner circulation area can ensure the stability of the central flame, so the nitrogen reduction effect is obvious, the flame stability is high, and by arranging the jet hole 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 hole, so that the jet cooling section of the inner cylinder 9 is covered with a layer of cooling gas film, thereby reducing the thermal stress on the inner cylinder 9 near the combustion center, the inner wall surface temperature is low, and the service life of the burner is improved.

[0071] The combustor of the present application adopts air staging, controls the temperature in the combustion process by feeding air into the combustor in batches, adopts premixed combustion method, increases the excess air coefficient in the premixed gas, reduces the maximum temperature in the high-temperature region, and reduces the generation of thermal NO x The axial swirler is adopted to make the premixed gas produce a central low-pressure backflow area in the hearth of the combustor, so that the burned high-temperature flue gas flows back to the center of the hearth, thereby reducing the oxygen and fuel concentration in the combustion region, and further reducing the thermal and rapid NO x， The present application solves the problems of single nitrogen reduction technology of the existing combustor, and the low NO x reduction effect.

[0072] In addition, the combustor is provided with a central cooling air passage 22 and a jet hole 91, and part of the central air is sent into the front end of the combustion chamber 11 through the central cooling air passage 22, so as to reduce the temperature at the burner position, and at the same time, the secondary air forms a cooling gas film on the wall surface of the combustion cylinder inner cylinder 9, greatly reducing the temperature near the wall surface, so that the temperature is lower than 750 DEG C, and the service life is improved.

[0073] CFD simulation results:

[0074] In addition, the present application establishes a simplified three-dimensional model of the combustor, combines appropriate physical models and boundary conditions, takes methanol fuel as an example, and uses Fluent software to numerically simulate the combustion process. Through in-depth analysis of the simulation results, the influence of different parameters on the combustion performance is quantified, so as to show the rationality of the structure of the combustor of the present application. As shown in the following simulation calculation steps and results of the present application. Figures 9-13

[0075] I. Model establishment

[0076] (1) Turbulence model

[0077] Realizable k-ε model combined with standard wall function method is adopted.

[0078] (2) Combustion model and radiation model

[0079] Taking methanol steam fuel as an example, two-step oxidation reaction of methanol steam and oxygen in air occurs, that is, methanol is first oxidized to carbon monoxide, and carbon monoxide is further oxidized to carbon dioxide, and the pyrolysis reaction of carbon dioxide is also considered. Due to the high temperature in the combustion process, the influence of gas radiation cannot be ignored, and the DO radiation model which is more accurate for simulating gas radiation in the combustion process is adopted.

[0080] (3) Physical model of the combustor

[0081] ​It is assumed that the methanol vapor has been mixed with air completely in the mixing channel. The simulation region is a cylindrical region 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 condition

[0083] (1) Solution method

[0084] In the Fluent commercial software, the SIMPLE algorithm is used to solve the velocity pressure coupling equation, the PRESTO is selected for pressure interpolation format, and the second order upwind format is used for the rest of the momentum, component and energy equations. In order to ensure the accuracy of the steady-state calculation, the continuity equation residual is set to 10 -4 , the energy equation and the radiation model residual are set to 10 -5 , and the rest of the component residual is set to 10 -6 , while monitoring the temperature at the outlet of the burner and the CO concentration.

[0085] (2) Boundary condition

[0086] The burner inlet adopts velocity inlet, the total air excess coefficient is 3.6, the premixed gas air excess coefficient is 1.2, the outlet is pressure outlet, and the specific burner inlet boundary condition is shown in Table 1. The wall surface adopts no-slip fixed wall, and the wall blackness value is 0.6.

[0087]

[0088] Table 1: Boundary conditions of each inlet of the burner

[0089] Simulation results

[0090] After the design of the swirl burner, the high temperature area of the burner is relatively concentrated; two low pressure backflow zones are formed in the center of the burner, which ensures that the burner can also ensure flame stability under a larger air excess coefficient while reducing NO x emission. The NO x emission of the gas burner is 12 mg / m 3 (oxygen concentration 3.5%, has been converted), which is much lower than the limit of 30 mg / m 3 specified by Beijing; the axial velocity of the airflow in the swirl burner decays quickly, which can reduce the flame length, shorten the length of the burner, and reduce the volume; staggered jet holes are designed in the combustion section of the flame tube to reduce the wall temperature of the combustion section of the flame tube, so that the maximum temperature is lower than 750℃.

[0091] The foregoing description illustrates and describes several preferred embodiments of the present application, but it is to be understood that the application is not limited to the above-described forms, and that it should not be seen as excluding other embodiments, but rather as being applicable in a variety of other combinations, modifications and environments, and capable of being altered in various ways within the scope of the application as described in the claims, by the teaching or knowledge of the relevant art. Any alterations and further modifications in the application and any further applications of the principles of the application are to be considered within the scope of the present application as defined in the following claims.

Claims

1. A small scale low NOx combustor characterized by, The combustion device comprises a head air intake assembly, a combustion cylinder assembly and a connecting assembly, The head air intake assembly comprises a primary air inlet pipe, a central air distribution body module, an axial swirler, a radial swirler, a fuel pipe and a premix gas pipeline. The primary air inlet pipe is arranged at an inlet end of the central air distribution body module for guiding external air into the central air distribution body module. The premix gas pipeline is sleeved at an outlet end of the central air distribution body module, and the axial swirler is arranged between the premix gas pipeline and the outlet end. The fuel pipe and the radial swirler are arranged at other positions of the central air distribution body module respectively for providing gaseous fuel to the combustor and mixing the gaseous fuel and external air respectively. The connecting assembly connects the head air intake assembly and the combustion cylinder assembly together.

2. The compact low-nitrogen burner according to claim 1, characterized in that, The central air distribution body module is an integrated stepped circular truncated cone, which comprises a first convex platform and a second convex platform.

3. The compact low-nitrogen burner according to claim 1, characterized in that, The radial swirler is arranged on the second convex platform, and the fuel pipe is clamped on the radial swirler and fixed on the first convex platform through the bolt holes.

4. The compact low-nitrogen burner according to claim 2, wherein A central cooling air channel is arranged at a central position inside the central air distribution body module, and a plurality of premix air channels are arranged around the central cooling air channel in a ring shape.

5. The compact low-nitrogen burner according to claim 4, characterized in that The connecting assembly is a chamber shoulder, which has an expansion angle of 30°-35° and is directed towards the combustion cylinder assembly.

6. The compact low-nitrogen burner of claim 4, wherein The cooling air channel is arranged in an expansion form at the outlet end, and has an expansion angle of 30°-60°.

7. The compact low-nitrogen burner of claim 4, wherein The combustion cylinder assembly further comprises an outer cylinder and an inner cylinder.

8. The compact low-nitrogen burner of claim 4, wherein The inner cylinder comprises a jet cooling section, a mixing section and an extension section.

9. A combustion method of a small-sized low-nitrogen combustor, characterized by, The space surrounded by the chamber shoulder and the inner cylinder forms a combustion chamber. A plurality of vertical jet holes or inclined jet holes are arranged on the wall surface of the jet cooling section. Mixing holes are arranged on the wall surface of the mixing section. The combustor further comprises a secondary air inlet pipe welded on the outer cylinder. The fuel pipe comprises a fuel inlet pipe welded on the outer cylinder. The method is realized by using the combustor according to any one of claims 1-8, and comprises the following steps: When the combustor starts to work, primary air enters through the primary air inlet pipe and is distributed through the central cooling air channel and the premix air channel of the central air distribution body module; 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, is rotated by the radial swirler, and then is mixed with premix air to form mixed gas, which is then sent into the combustion chamber through the axial swirler after flowing and mixing, and burns or ignites in the combustion chamber; and central cooling air flows out from the central cooling air channel and flows to the combustion chamber. 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 the mixing holes on the inner cylinder, and is discharged through the extension section of the inner cylinder after complete combustion of the mixture.

Images