Low-nitrogen combustion system for boiler

Abstract

The utility model provides a low-nitrogen combustion system for a boiler, which belongs to the technical field of combustion devices and comprises a boiler provided with a main combustion area and an over-fire air combustion area, and the over-fire air combustion area is provided with a lower-layer low-position air area and an upper-layer high-position air area; the low-position air area and the high-position air area are each provided with a layer of over-fire air nozzles which are arranged in a four-corner tangential mode. A nozzle structure of the over fire air nozzle is formed by combining a direct flow air nozzle and a rotational flow air nozzle which are coaxially arranged, and the direct flow air nozzle is located in the rotational flow air nozzle. An air inlet of the over fire air nozzle is a reducing pipe, and the air inlet is connected with the nozzle structure through a straight pipe; the rotational flow air nozzle comprises a guide pipe and a plurality of rotational flow blades, and the rotational flow blades are arranged between the outer wall of the direct flow air nozzle and the inner wall of the guide pipe in the circumferential direction. According to the system, by optimizing the over-fire air nozzle structure of the over-fire air combustor, the combustion efficiency of the boiler is improved, nitrogen oxide emission is effectively controlled, and low-nitrogen combustion of the boiler is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of combustion devices, in particular to a low-nitrogen combustion system for boilers. Background Art

[0002] In recent years, my country's economy has grown rapidly, energy consumption has increased significantly, and the resulting environmental pollution has become increasingly severe. my country's environmental protection department has set higher and higher requirements for pollutant emissions from combustion. In response to the country's call for "energy conservation and emission reduction", reducing nitrogen oxide emissions is one of the goals of the current coal-fired boiler low nitrogen oxide combustion technology transformation.

[0003] In the use of boilers, pulverized coal burners must first have a high combustion efficiency, and overburnt air burners are used to control nitrogen oxide emissions in addition to improving boiler combustion efficiency. However, the air outlet structure of existing overburnt air burners is relatively simple, and the position of overburnt air burners is relatively fixed, making it difficult to conveniently adjust the wind direction of the overburnt air outlet. The combustion, smoke temperature, and nitrogen oxide emissions can only be controlled by adjusting the air volume and swirl intensity of the overburnt air. The adjustment means are limited, resulting in the inability to take into account both combustion efficiency and control of nitrogen oxide emissions, making it difficult to better meet the use requirements of low-nitrogen combustion in existing boiler systems. Utility Model Content

[0004] The utility model provides a low-nitrogen combustion system for a boiler, which is used to solve the problems of low combustion efficiency, high nitrogen oxide emission and environmental pollution of coal-fired boilers in the prior art.

[0005] Specifically, the utility model provides a low-nitrogen combustion system for a boiler, comprising: a boiler, the boiler is provided with a main combustion zone and a burnout air combustion zone, the burnout air combustion zone is arranged above the main combustion zone; the burnout air combustion zone is provided with a lower low-level air zone and an upper high-level air zone; the low-level air zone and the high-level air zone are both provided with a layer of burnout air nozzles, the burnout air nozzles are arranged in a four-corner tangential circle, each burnout air nozzle is connected to a burnout air burner, and each burnout air burner is connected to the side wall of the boiler furnace.

[0006] Furthermore, the nozzle structure of the burnout air nozzle is formed by a combination of a direct current air nozzle and a swirl air nozzle, the direct current air nozzle and the swirl air nozzle are coaxially arranged, and the direct current air nozzle is located inside the swirl air nozzle; the side of the burnout air nozzle away from the nozzle structure is an air inlet, the air inlet is a tapered pipe, the small diameter of the air inlet is connected to the nozzle structure by a straight pipe, the diameter of the straight pipe is the diameter of the small diameter of the air inlet; the swirl air nozzle includes a guide pipe and a plurality of swirl blades, the swirl blades are circumferentially arranged between the outer wall of the direct current air nozzle and the inner wall of the guide pipe, and the swirl blades are extended and arranged in a spiral trajectory relative to the direct current air nozzle.

[0007] Furthermore, the main combustion zone is provided with a primary air zone and a secondary air zone. The primary air zone is provided with five layers of primary air nozzles arranged in a four-corner tangential circle, and the secondary air zone is provided with three layers of secondary air nozzles arranged in a four-corner tangential circle; the primary air nozzles and the secondary air nozzles are arranged alternately in the upper and lower layers, and the uppermost layer is the secondary air nozzle; each primary air nozzle and secondary air nozzle is correspondingly connected to a main burner, and each main burner is connected to the side wall of the boiler furnace.

[0008] Furthermore, the four-corner tangential circle arrangement of the burnout air nozzle is a reverse tangential arrangement relative to the secondary air nozzle of the uppermost layer, and the reverse tangential angle is 20°.

[0009] Furthermore, the guide tube is a tapered hollow structure, and the diameter of one end of the guide tube close to the straight tube is the same as that of the straight tube.

[0010] Furthermore, the DC air nozzle is a gradually expanding hollow structure, and the diameter of the DC air nozzle at one end away from the straight pipe is 1 / 2 of the diameter of the straight pipe.

[0011] Furthermore, the burnout air nozzle is also provided with an auxiliary combustion component, which includes an annular air outlet pipe and multiple distribution pipes; the multiple distribution pipes are evenly distributed on the outside of the straight pipe, and one end of each distribution pipe is connected to the side wall of the straight pipe, and the other end is connected to the annular air outlet pipe; the annular air outlet pipe is arranged on the outside of the guide pipe and is coaxially arranged with the guide pipe; and multiple air outlet holes are evenly distributed on the annular air outlet pipe.

[0012] Furthermore, the plurality of air outlet holes on the annular air outlet pipe are arranged in multiple layers in annular spacing, and the apertures of the air outlet holes gradually increase from the center to the edge.

[0013] Furthermore, the angle between each distribution pipe and the pipe wall of the straight pipe is 30°-60°.

[0014] The low-nitrogen combustion system for boilers provided by the utility model optimizes the overburnt air nozzle structure of the overburnt air burner and uses the external swirl wind to wrap the central direct air spray mode, so that the unburned coal powder particles in the furnace, CO and NO in the flue gas can be reduced. X The gases can be further burned and completely combusted, thereby improving the boiler's combustion efficiency, reducing the emission of boiler pollutants such as nitrogen oxides, and achieving low-nitrogen combustion in the boiler.

[0015] The boiler of this system adopts the method of supplying air in the main combustion area and the high-position overburnt air combustion area, rationally organizes the combustion air in a graded manner, realizes graded air supply in the vertical direction of the air, and ensures the optimization of the air distribution in the furnace. The existence of the overburnt air allows the combustibles to be further burned out in the later stage, thereby improving the combustion efficiency, reducing the carbon content of the fly ash, and reducing the generation of nitrogen oxides. The environmental protection benefits are significant and the boiler performance is improved.

[0016] The system has a simple structure, reasonable design, flexible configuration and stable operation. It effectively solves the problems of incomplete combustion and unreasonable combustion, effectively reduces the generation of nitrogen oxides, and the NOx emission concentration is no more than 200mg / Nm 3 (6% oxygen content, calculated as NO2), boiler efficiency is not less than 93%, unburned carbon heat loss is not more than 1.0%, slag carbon content is not more than 1%, CO emission concentration is not higher than 100μL / L, boiler exhaust temperature is not higher than 128℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic structural diagram of a low-nitrogen combustion system for a boiler provided in one embodiment of the utility model;

[0019] Figure 2 The airflow distribution diagram of the secondary air nozzle and the burnout air nozzle provided in one embodiment of the utility model;

[0020] Figure 3 A schematic diagram of the structure of a burnout air nozzle provided in one embodiment of the utility model;

[0021] Figure 4 for Figure 3 Cross-sectional view in the AA direction;

[0022] Figure 5 A schematic diagram of the connection between the nozzle structure and the auxiliary combustion component provided in one embodiment of the utility model.

[0023] Description of reference numerals:

[0024] 1-boiler, 2-main combustion zone, 3-overburnt air combustion zone, 4-overburnt air nozzle, 5-primary air nozzle, 6-secondary air nozzle, 21-main burner, 31-overburnt air burner, 41-direct current air nozzle, 42-air inlet, 43-straight pipe, 44-guide pipe, 45-swirl blade, 46-annular outlet pipe, 47-distribution pipe, 48-outlet. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the utility model clearer, the technical solution in the embodiments of the utility model is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work also fall within the scope of protection of the utility model.

[0026] like Figure 1 The utility model provides a low-nitrogen combustion system for a boiler 1, comprising: a boiler 1, wherein the boiler 1 is provided with a main combustion zone 2 and a burnout air combustion zone 3, wherein the burnout air combustion zone 3 is arranged above the main combustion zone 2; the burnout air combustion zone 3 is provided with a lower low-level air zone and an upper high-level air zone; both the low-level air zone and the high-level air zone are provided with a layer of burnout air nozzles 4, wherein the burnout air nozzles 4 are arranged in a four-corner tangential circle, each burnout air nozzle 4 is connected to a burnout air burner 31, and each burnout air burner 31 is connected to the side wall of the furnace of the boiler 1.

[0027] The air supply of the furnace of boiler 1 is divided into two routes, including the air supply of the main combustion zone 2 and the high-level burnout air combustion zone 3. The main air is ejected from the gap between the grates, and the burnout air is ejected from the appropriate positions in the middle and upper parts of the furnace flame to form low-level burnout air and high-level burnout air, so as to realize graded air supply in the vertical direction of the air, organize the combustion air in a reasonable graded manner, and ensure the optimization of the air distribution in the furnace. The existence of the burnout air makes the combustibles further burn out in the later stage, expands the combustion area of ​​the flame in the furnace, reduces the local oxygen concentration in the furnace, improves the combustion efficiency, reduces the carbon content of the fly ash, and reduces the generation of nitrogen oxides. The environmental protection benefits are remarkable, the low-nitrogen combustion of boiler 1 is realized, and the performance of boiler 1 is improved.

[0028] like Figure 3 and Figure 4 Preferably, the nozzle structure of the burnout air nozzle 4 is formed by a combination of a direct current air nozzle 41 and a swirl air nozzle, the direct current air nozzle 41 and the swirl air nozzle are coaxially arranged, and the direct current air nozzle 41 is located inside the swirl air nozzle; the side of the burnout air nozzle 4 away from the nozzle structure is an air inlet 42, the air inlet 42 is a tapered tube, the small diameter of the air inlet 42 is connected to the nozzle structure through a straight tube 43, the diameter of the straight tube 43 is the diameter of the small diameter of the air inlet 42; the swirl air nozzle includes a guide pipe 44 and a plurality of swirl blades 45, the swirl blades 45 are circumferentially arranged between the outer wall of the direct current air nozzle 41 and the inner wall of the guide pipe 44, and the swirl blades 45 are extended and arranged in a spiral trajectory relative to the direct current air nozzle 41.

[0029] The air inlet 42 of the burnout air nozzle 4 is designed as a tapered pipe, which can increase the flow rate of the airflow entering the burnout air nozzle 4, so that it can quickly pass through the straight pipe 43 and enter the nozzle structure. Since the swirl blades 45 are arranged in a spiral trajectory relative to the DC air nozzle 41, the burnout air passing through the swirl blades 45 can form a swirl. The swirl blades 45 fix the DC air nozzle 41 inside the guide pipe 44, and also play a certain supporting and fixing role. At the nozzle structure, a part of the burnout air is directly ejected through the DC air nozzle 41, and the other part of the burnout air is guided by the swirl blades 45 and ejected from the channel between the outer wall of the DC air nozzle 41 and the inner wall of the guide pipe 44. The central DC wind has jet rigidity and a long range. It uses the rigidity of the DC wind to penetrate the center of the flame to accelerate combustion. The external swirl wind not only supplements the air volume and improves the uniformity of the mixture of the burnt air and fuel in the furnace, but also uses the slight negative pressure formed by the swirl wind to concentrate the airflow around the flame and the unburned fly ash to the center of the flame to improve the combustion effect. The external swirl wind wraps the central DC wind and can make the unburned coal powder particles in the furnace, CO and NO in the flue gas be dispersed. X The gases can be further burned and burnt out, thereby improving the combustion efficiency of the boiler 1, reducing the emission of pollutants such as nitrogen oxides from the boiler 1, and achieving low-nitrogen combustion of the boiler 1.

[0030] It should be noted that, as in the prior art, the burnout air nozzle 4 in this system can be provided with a commonly used swinging assembly so that it can swing back and forth up and down and left and right, flexibly adjust the direction of the burnout air flow, and increase the burnout air coverage. Similarly, the inlet of the burnout air nozzle 4 can be provided with an adjustable baffle according to the conventional setting to control the air volume of the burnout air nozzle 4. Of course, the above conventional settings can be adjusted in real time by technicians in this field according to the operating conditions of the boiler 1 to greatly improve the adjustment range of the burnout air.

[0031] like Figure 1 Preferably, the main combustion zone 2 is provided with a primary air zone and a secondary air zone, the primary air zone is provided with five layers of primary air nozzles 5 arranged in a four-corner tangential circle, and the secondary air zone is provided with three layers of secondary air nozzles 6 arranged in a four-corner tangential circle; the primary air nozzles 5 and the secondary air nozzles 6 are arranged alternately in upper and lower layers, and the uppermost layer is the secondary air nozzle 6; each primary air nozzle 5 and secondary air nozzle 6 is correspondingly connected to a main burner 21, and each main burner 21 is connected to the side wall of the furnace of the boiler 1.

[0032] The main combustion zone 2 includes five layers of primary air nozzles 5 and three layers of secondary air nozzles 6. The specific number of nozzles can also be flexibly adjusted according to the working conditions. The main burner 21 adopts a large wind box structure. The primary air nozzles 5 and secondary air nozzles 6 at different heights in the same corner are respectively connected to the same corner wind box. The primary air boxes and secondary air boxes at the four corners are respectively connected to the primary air main duct and the secondary air main duct through branch air ducts to ensure that the air supply of each layer of nozzles in the same corner is relatively uniform.

[0033] like Figure 2 Preferably, the four-corner tangent circle arrangement of the burnout air nozzle 4 is a counter-tangent arrangement relative to the secondary air nozzle 6 of the uppermost layer, and the counter-tangent angle is 20°, wherein the dotted line with an arrow is the secondary air flow direction, and the solid line is the burnout air flow direction. The airflow direction of the burnout air nozzle 4 is counter-tangently arranged relative to the secondary air nozzle 6 of the uppermost layer, and the airflow ejected from the burnout air nozzle 4 forms an angle of -20° with the rising airflow of the main combustion zone 2 and is sprayed into the furnace. The upper and lower airflow directions are different, which can effectively reduce the rotation residue at the furnace outlet, alleviate the smoke temperature deviation on both sides of the furnace, and is not easy to cause furnace coking. It can also ensure that the fuel is fully burned, reduce the heat loss of incomplete combustion of solids in the boiler, reduce energy waste, improve combustion efficiency, and reduce nitrogen oxide emissions.

[0034] like Figure 3 Preferably, the guide pipe 44 is a tapered hollow structure, and the end of the guide pipe 44 close to the straight pipe 43 has the same diameter as the straight pipe 43. The tapered guide pipe 44 can increase the flow rate of the burnout wind inside the tank body, so that the swirl burnout wind formed by the swirl blades 45 can be ejected faster, enhance the micro-negative pressure effect on the flow path of the swirl wind, and enhance the combustion effect of the burnout wind combustion zone 3.

[0035] like Figure 3 Preferably, the DC air nozzle 41 is a gradually expanding hollow structure, and the diameter of the end of the DC air nozzle 41 away from the straight tube 43 is 1 / 2 of the diameter of the straight tube 43. The DC air nozzle 41 with a gradually expanding structure delivers the DC air into the furnace along its axial direction, and can also increase the coverage area of ​​the DC air when it is ejected, thereby improving the mixing degree of the burnout air and the fuel.

[0036] like Figure 5 Preferably, the burnout air nozzle 4 is also provided with an auxiliary combustion component, which includes an annular air outlet pipe 46 and a plurality of distribution pipes 47; the plurality of distribution pipes 47 are evenly distributed on the outside of the straight pipe 43, and one end of each distribution pipe 47 is connected to the side wall of the straight pipe 43, and the other end is connected to the annular air outlet pipe 46; the annular air outlet pipe 46 is arranged on the outside of the guide pipe 44 and is coaxially arranged with the guide pipe 44; a plurality of air outlet holes 48 are evenly distributed on the annular air outlet pipe 46.

[0037] An annular air outlet pipe 46 is provided outside the guide pipe 44 of the burnout air nozzle 4. The air volume of the annular air outlet pipe 46 can be used to fill the burnout air near the nozzle structure, and the residual combustion products at the nozzle structure can flow to the peripheral combustion area for secondary combustion, thereby forming a peripheral combustion area at the nozzle structure, expanding the coverage of the burnout air, reducing the uneven distribution of oxygen near the nozzle structure, strengthening the disturbance of the air flow to the flame, and also strengthening the combustion effect of the nozzle structure of the burnout air nozzle 4. The combustion is more complete, the formation of nitrogen oxides is suppressed, and the pollutants and fly ash combustible content in the exhaust gas of the boiler 1 are reduced, and the thermal efficiency of the boiler 1 is improved. The multiple air outlet holes 48 evenly arranged on the annular air outlet pipe 46 can make the temperature of the peripheral combustion more uniform, avoid local high temperature, and enable the fuel in the furnace to burn continuously, stably and fully.

[0038] like Figure 5 Preferably, the plurality of outlet holes 48 on the annular outlet pipe 46 are arranged in a multi-layer annular space, and the apertures of the outlet holes 48 gradually increase from the center to the edge. The apertures at the outermost part are larger, which is conducive to increasing the mixing degree of the burnout air and the fuel, so that the combustion is more complete.

[0039] Preferably, the angle between each distribution pipe 47 and the pipe wall of the straight pipe 43 is 30°-60°. The distribution pipe 47 and the straight pipe 43 are arranged obliquely, so that the burnout air in the straight pipe 43 can enter the distribution pipe 47 and the annular air outlet pipe 46 faster and more smoothly, thereby forming an aerodynamic field that is conducive to continuous combustion at the periphery of the nozzle structure and enhancing the combustion effect.

[0040] It should be noted that arrows without reference numerals indicate the flow direction of the gas phase.

[0041] The present invention is further described in detail below in conjunction with specific embodiments.

[0042] Example 1

[0043] The low-nitrogen combustion system for boiler 1, when in operation, air enters the furnace through the primary air nozzle 5 of the main burner 21, and at the same time, fuel enters the boiler 1 through the ignition channel of the main burner 21, and is ignited by the ignition component in the primary air zone, and the primary air energy assists the combustion of the fuel. In the main combustion zone 2, secondary air is also introduced through the secondary air nozzle 6, so that the amount of air in the furnace is increased and the combustion efficiency is improved. Above the main combustion zone 2, the low-level burnout air and the high-level burnout air are introduced through the burnout air nozzle 4 connected to the burnout air burners 31 in the low-level wind zone and the high-level wind zone, so as to reduce the unburned coal powder particles in the furnace, CO and NO in the flue gas. X The gases undergo secondary combustion, reducing the emission of nitrogen oxides.

[0044] When the burnout air passes through the burnout air nozzle 4, it first enters the air inlet 42 of the tapered tube structure to increase the flow rate, then quickly passes through the straight tube 43, and finally enters the nozzle structure. At the nozzle structure, part of the burnout air is directly ejected through the DC air nozzle 41, and the other part of the burnout air is guided by the swirl blades 45 and ejected from the channel between the outer wall of the DC air nozzle 41 and the inner wall of the guide tube 44, forming an ejection mode in which the external swirl wind wraps the central DC air, so that the unburned coal powder particles in the furnace, CO and NO in the flue gas are X The gases are further burned and completely combusted, thus achieving low-nitrogen combustion in boiler 1.

[0045] Example 2

[0046] On the basis of the above embodiment, this embodiment further includes: an annular air outlet pipe 46 is arranged outside the straight pipe 43 of the burnout air nozzle 4, and when the burnout air passes through the straight pipe 43, part of the burnout air is sent into the annular air outlet pipe 46 through the distribution pipe 47 obliquely connected thereto, and is ejected through the air outlet holes 48 thereon, filling the burnout air near the nozzle structure, forming a peripheral combustion zone at the nozzle structure, expanding the coverage of the burnout air, and also enhancing the combustion effect of the nozzle structure of the burnout air nozzle 4. Among them, the multiple air outlet holes 48 on the annular air outlet pipe 46 are arranged in multiple layers of annular intervals, and the aperture of the air outlet holes 48 from the center to the edge gradually increases, which is conducive to increasing the mixing degree of the burnout air and the fuel, so that the combustion is more complete.

[0047] It should be noted that in the present invention, the detailed structure of some devices is not described in detail, but belongs to the prior art known to those skilled in the art, so it will not be repeated here. In addition, the parts not involved in the device are the same as the prior art or can be implemented by the prior art.

[0048] It should be noted that pressure sensors, flow meters or temperature sensors are installed on the transmission pipelines inside the system between different units, devices or equipment. Different valves are also installed, such as pressure relief valves, pressure regulating valves, safety valves, etc., which are used to adjust and stabilize the pressure of the entire system.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it; although the utility model has been described in detail with reference to the aforementioned embodiments, ordinary technicians in the field should understand that it is still possible to modify the technical solutions recorded in the aforementioned embodiments, or to replace some or all of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the utility model.

Claims

1. A low nitrogen combustion system for a boiler, characterized in that: include: A boiler, wherein the boiler is provided with a main combustion zone and an overburnt air combustion zone, wherein the overburnt air combustion zone is arranged above the main combustion zone; the overburnt air combustion zone is provided with a lower low-level air zone and an upper high-level air zone; the low-level air zone and the high-level air zone are each provided with a layer of overburnt air nozzles, the overburnt air nozzles are arranged in a four-corner tangential circle, each of the overburnt air nozzles is connected to an overburnt air burner, and each of the overburnt air burners is connected to the side wall of the boiler furnace; The nozzle structure of the burnout air nozzle is formed by a combination of a direct current air nozzle and a swirl air nozzle, the direct current air nozzle and the swirl air nozzle are coaxially arranged, and the direct current air nozzle is located inside the swirl air nozzle; the side of the burnout air nozzle away from the nozzle structure is an air inlet, and the air inlet is a tapered pipe, and the small diameter of the air inlet is connected to the nozzle structure through a straight pipe, and the diameter of the straight pipe is the diameter of the small diameter of the air inlet; the swirl air nozzle includes a guide pipe and a plurality of swirl blades, and the swirl blades are arranged circumferentially between the outer wall of the direct current air nozzle and the inner wall of the guide pipe, and the swirl blades are extended and arranged in a spiral trajectory relative to the direct current air nozzle.

2. The low nitrogen combustion system for boiler according to claim 1, characterized in that: The main combustion zone is provided with a primary air zone and a secondary air zone. The primary air zone is provided with five layers of primary air nozzles arranged in a four-corner tangential circle, and the secondary air zone is provided with three layers of secondary air nozzles arranged in a four-corner tangential circle; the primary air nozzles and the secondary air nozzles are arranged alternately in upper and lower layers, and the uppermost layer is the secondary air nozzle; each of the primary air nozzles and the secondary air nozzles is correspondingly connected to a main burner, and each of the main burners is connected to the side wall of the boiler furnace.

3. The low nitrogen combustion system for boiler according to claim 2, characterized in that: The four-corner tangential circle arrangement of the burnout air nozzle is a reverse tangential arrangement relative to the secondary air nozzle of the uppermost layer, and the reverse tangential angle is 20°.

4. The low nitrogen combustion system for boiler according to claim 1, characterized in that: The guide tube is a tapered hollow structure, and the diameter of one end of the guide tube close to the straight tube is the same as that of the straight tube.

5. The low nitrogen combustion system for boiler according to claim 1, characterized in that: The direct current air nozzle is a gradually expanding hollow structure, and the diameter of the end of the direct current air nozzle away from the straight pipe is 1 / 2 of the diameter of the straight pipe.

6. The low nitrogen combustion system for a boiler according to any one of claims 1 to 5, characterized in that: The burnout air nozzle is also provided with an auxiliary combustion component, which includes an annular air outlet pipe and a plurality of distribution pipes; the plurality of distribution pipes are evenly distributed on the outside of the straight pipe, and one end of each distribution pipe is connected to the side wall of the straight pipe, and the other end is connected to the annular air outlet pipe; the annular air outlet pipe is arranged on the outside of the guide pipe and is coaxially arranged with the guide pipe; the annular air outlet pipe is evenly distributed with a plurality of air outlet holes.

7. The low nitrogen combustion system for boiler according to claim 6, characterized in that: The plurality of air outlet holes on the annular air outlet pipe are arranged in multiple layers in annular spacing, and the apertures of the air outlet holes gradually increase from the center to the edge.

8. The low nitrogen combustion system for boiler according to claim 6, characterized in that: The angle between each distribution pipe and the pipe wall of the straight pipe is 30°-60°.

Images