A secondary air structure conducive to low-nitrogen combustion in boilers

Abstract

A secondary air structure that is beneficial to low-nitrogen combustion of a boiler comprises: a furnace; a front wall secondary air duct assembly, the front wall secondary air duct assembly is arranged on the front wall side of the furnace; the front wall secondary air duct assembly is arranged in two layers, upper and lower, the upper layer is arranged with 4 secondary air ducts on the front wall and the lower layer is arranged with 2 secondary air ducts under the front wall; a rear wall secondary air duct assembly, the rear wall secondary air duct assembly is arranged on the rear wall side of the furnace; the rear wall secondary air duct assembly is arranged in two layers, upper and lower, the upper layer is arranged with 2 secondary air ducts on the rear wall and the lower layer is arranged with 3 secondary air ducts under the rear wall. The secondary air structure that is beneficial to low-nitrogen combustion of a boiler described in the utility model is designed with reasonable arrangement, number and angle of secondary air ports, etc., to ensure that the secondary air can be driven into the center of the furnace, avoid hypoxia in the middle of the furnace, reduce the carbon content of the tail fly ash, thereby facilitating low-nitrogen combustion of the boiler, reducing the concentration of nitrogen oxides produced, reducing the subsequent nitrogen oxides treatment costs, and reducing the concentration of nitrogen oxides emissions.

Description

Technical Field

[0001] The utility model relates to the technical field of boilers, in particular to a secondary air structure for low-nitrogen combustion which is beneficial to reducing the original concentration of nitrogen oxides produced by the boiler. Background Art

[0002] Pollutants emitted from boiler flue gas include nitrogen oxides (NOx). In addition to being harmful to human health, NOx is also the main driver of acid rain, photochemical smog, and ozone destruction, and is also an important culprit for the generation of ultrafine particles PM2.5 in the atmosphere.

[0003] The main components of haze are inhalable particulate matter, NOx and sulfur dioxide, which combine with fog to make the atmosphere turbid, resulting in reduced visibility. Due to the current severe atmospheric environmental protection situation, especially in autumn and winter, as people pay more and more attention to the living environment, stricter requirements are put forward for boiler flue gas emissions.

[0004] From the perspective of the NOx generation mechanism, boilers also focus on two aspects to control NOx generation: reducing the combustion flame temperature and reducing the O2 volume fraction. Therefore, it can be seen that an important measure to suppress NOx generation is to transform the boiler's secondary air device.

[0005] The secondary air device of the existing boiler has the following problems: 1. Since the secondary air device has a small branch pipe, it consumes a certain amount of wind pressure, and no nozzle is set at the secondary air inlet, resulting in poor secondary air penetration ability, resulting in the formation of a black core area (carbon black) in the center of the furnace, and insufficient combustion leads to an increase in the carbon content of the fly ash, resulting in high NOx generation; 2. The secondary air opening of the lower layer of the secondary air device is too low, resulting in too low temperature in the dense phase area and a large flue gas temperature difference in the furnace, which in turn affects the desulfurization efficiency; 3. The secondary air of the lower layer of the secondary air device is too close to the coal feed, causing the secondary air to become the primary air effect, and the bed temperature is not high. Especially when the coal quality is poor, the overall air volume in the dense phase area is too large, making it more difficult to maintain the bed temperature.

[0006] Therefore, in order to solve the above technical problems, the utility model transforms the secondary air device of the boiler, determines the reasonable arrangement, number and angle of the secondary air ports according to the type of coal used in the existing boiler and the combustion characteristics of the existing boiler in combination with thermal calculation and furnace dynamic simulation, to ensure that the secondary air can be injected into the center of the furnace, avoid oxygen deficiency in the middle of the furnace, reduce the carbon content of the tail fly ash, thereby reducing the NOx concentration generated and improving the desulfurization efficiency of calcium injection in the boiler. Utility Model Content

[0007] Purpose of the utility model: In order to overcome the above-mentioned deficiencies, the purpose of the utility model is to provide a secondary air structure for low-nitrogen combustion which is beneficial to reducing the original production concentration of nitrogen oxides in the boiler. Reasonable arrangement, number and angle of the secondary air inlets are designed to ensure that the secondary air can be injected into the center of the furnace, avoiding oxygen deficiency in the middle of the furnace and reducing the carbon content of the tail fly ash, thereby facilitating low-nitrogen combustion in the boiler and reducing the original production concentration of nitrogen oxides, and has broad application prospects.

[0008] Technical solution: A secondary air structure that is beneficial to low-nitrogen combustion in boilers, including:

[0009] furnace;

[0010] A front wall secondary air duct assembly, the front wall secondary air duct assembly is arranged on one side of the front wall of the furnace; the front wall secondary air duct assembly is arranged in two layers, the upper layer is arranged with 4 front wall secondary air ducts and the lower layer is arranged with 2 front wall lower secondary air ducts, the angle of the front wall secondary air duct and the front wall lower secondary air duct blowing into the furnace is 10-30°;

[0011] The rear wall secondary air duct assembly is arranged on one side of the rear wall of the furnace; the rear wall secondary air duct assembly is arranged in an upper and lower layer, wherein the upper layer is arranged with 2 rear wall secondary air ducts and the lower layer is arranged with 3 rear wall lower secondary air ducts, and the angle of the rear wall upper secondary air duct and the rear wall lower secondary air duct blowing into the furnace is 10-30°.

[0012] The secondary air structure beneficial to the low-nitrogen combustion of the boiler described in the utility model is based on the type of coal operated by the existing boiler (the existing boilers are all circulating fluidized bed boilers with a continuous evaporation capacity of 75t / h as an example), combined with thermal calculation and furnace dynamic simulation of the combustion characteristics of the existing boiler, and reasonable arrangement, number and angle of the secondary air inlets are designed to ensure that the secondary air can be injected into the center of the furnace, avoid oxygen deficiency in the middle of the furnace, reduce the carbon content of the tail fly ash, and thus facilitate the low-nitrogen combustion of the boiler.

[0013] Furthermore, in the above-mentioned secondary air structure which is beneficial to low-nitrogen combustion of the boiler, the elevation of the furnace is set to 8750mm, the elevations of the secondary air ducts on the front wall and the secondary air ducts on the rear wall are both set to 6000mm, and the elevations of the secondary air ducts under the front wall and the secondary air ducts under the rear wall are both set to 5400mm.

[0014] Furthermore, in the above-mentioned secondary air structure which is beneficial to low-nitrogen combustion in the boiler, the angles at which the secondary air ducts on the front wall and the secondary air ducts on the rear wall blow into the furnace are both set to 30°, and the angles at which the secondary air ducts under the front wall and the secondary air ducts under the rear wall blow into the furnace are both set to 20°.

[0015] The angle at which the secondary air duct blows into the furnace will affect the degree of mixing of air and fuel. According to the type of coal used in the existing boiler, combined with thermal calculations and furnace dynamic simulation of the boiler's combustion characteristics, the angles at which the secondary air ducts on the front wall and the rear wall blow into the furnace are set to 30°, and the angles at which the secondary air ducts under the front wall and the secondary air ducts under the rear wall blow into the furnace are set to 20°. This can reduce the problem of low temperature in the dense phase zone and large flue gas temperature difference in the furnace, which in turn affects the desulfurization efficiency.

[0016] Furthermore, the above-mentioned secondary air structure is beneficial to low-nitrogen combustion of the boiler, and the arrangement order of the front wall secondary air duct components is: 1 secondary air duct on the front wall, 1 secondary air duct under the front wall, and 1 secondary air duct on the front wall constitute a first group, which are arranged on the left side of the front wall of the furnace; 1 secondary air duct on the front wall, 1 secondary air duct under the front wall, and 1 secondary air duct on the front wall constitute a second group, which are arranged on the middle right part of the front wall of the furnace.

[0017] Furthermore, the above-mentioned secondary air structure is beneficial to low-nitrogen combustion of the boiler, and the arrangement order of the rear wall secondary air duct assembly is: 1 secondary air duct under the rear wall and the secondary air duct on the rear wall constitute the first group, which are arranged on the left side of the rear wall of the furnace; 1 secondary air duct under the rear wall constitutes the second group, which is arranged in the middle of the rear wall of the furnace; 1 secondary air duct on the rear wall and the secondary air duct under the rear wall constitute the third group, which is arranged on the right side of the rear wall of the furnace.

[0018] Furthermore, in the above-mentioned secondary air structure which is beneficial to low-nitrogen combustion of the boiler, the air outlets of the secondary air duct on the front wall, the secondary air duct under the front wall, the secondary air duct on the rear wall, and the secondary air duct under the rear wall are all provided with nozzles.

[0019] A nozzle is provided at the air inlet of the secondary air duct, which improves the penetration ability of the secondary air, facilitates the secondary air to enter the center of the furnace, reduces the lack of oxygen in the middle of the furnace, reduces the carbon content of the tail fly ash, and thus reduces the NOx concentration generated.

[0020] Furthermore, in the above-mentioned secondary air structure which is beneficial to low-nitrogen combustion of the boiler, the secondary air duct on the front wall, the secondary air duct under the front wall, the secondary air duct on the rear wall, and the secondary air duct under the rear wall are all provided with solenoid valves.

[0021] A single secondary air duct is provided with a solenoid valve, which mainly plays the role of controlling the air volume. By opening and closing the solenoid valve, the air volume in the secondary air duct can be adjusted, thereby achieving precise control of the combustion process in the furnace and ensuring that the secondary air can operate stably and economically under different load conditions.

[0022] The beneficial effects of the utility model are as follows: the secondary air structure which is beneficial to the low-nitrogen combustion of the boiler described in the utility model has a reasonable structural design. According to the existing coal types of the boiler, combined with thermal calculations and furnace dynamic simulation of the combustion characteristics of the existing boiler, reasonable arrangement, number and angle of the secondary air inlets are designed to ensure that the secondary air can be injected into the center of the furnace, avoid oxygen deficiency in the middle of the furnace, reduce the carbon content of the tail fly ash, and thus facilitate the low-nitrogen combustion of the boiler; a nozzle is provided at the air inlet of the secondary air duct to improve the penetration ability of the secondary air; an electromagnetic valve is provided in the secondary air duct, and the air volume in the secondary air duct can be adjusted by opening and closing the electromagnetic valve, thereby realizing precise control of the combustion process in the furnace, ensuring that the secondary air can operate stably and economically under different load conditions, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The main view of the secondary air structure of the utility model which is beneficial to the low nitrogen combustion of the boiler Figure 1 ;

[0024] Figure 2 The main view of the secondary air structure of the utility model which is beneficial to the low nitrogen combustion of the boiler Figure 2 ;

[0025] Figure 3 This is a top view of the secondary air structure that is beneficial to low-nitrogen combustion in the boiler according to the utility model;

[0026] Figure 4 This is a layout sequence diagram of the front wall secondary air duct assembly of the secondary air structure that is beneficial to low-nitrogen combustion of the boiler according to the utility model;

[0027] Figure 5 This is a diagram showing the arrangement sequence of the rear wall secondary air duct assembly of the secondary air structure that is beneficial to low-nitrogen combustion in the boiler according to the utility model;

[0028] In the figure: furnace 1, front wall secondary air duct assembly 2, secondary air duct 21 on the front wall, secondary air duct 22 under the front wall, rear wall secondary air duct assembly 3, secondary air duct 31 on the rear wall, secondary air duct 32 under the rear wall, elevation a of the furnace, elevation b of the secondary air duct on the front wall, elevation c of the secondary air duct under the front wall, elevation d of the secondary air duct on the rear wall, elevation e of the secondary air duct under the rear wall, angle f of the secondary air duct on the front wall blowing into the furnace, angle g of the secondary air duct under the front wall blowing into the furnace, angle h of the secondary air duct on the rear wall blowing into the furnace, angle i of the secondary air duct under the rear wall blowing into the furnace, and ground j. DETAILED DESCRIPTION

[0029] The following is combined with Figure 1 , 2 , 3, 4, 5 and Example 1 and Example 2 further illustrate the utility model.

[0030] Example 1

[0031] like Figure 1 , 3 As shown in Figures 4 and 5, the secondary air structure beneficial to the low-nitrogen combustion of the boiler described in the utility model is based on the existing boiler operating coal type, combined with thermal calculation and furnace dynamic simulation of the combustion characteristics of the existing boiler, and reasonable secondary air inlet arrangement, number and angle are designed for the secondary air structure to ensure that the secondary air can be injected into the center of the furnace 1, avoid oxygen deficiency in the middle of the furnace 1, reduce the carbon content of the tail fly ash, and thus facilitate the low-nitrogen combustion of the boiler.

[0032] Among them, the existing boiler is a 75t / h coal-fired high-temperature and high-pressure circulating fluidized bed boiler (its specific structure can refer to patent publication number: CN107940448A), the boiler fuel is bituminous coal, and the analysis of the current fuel coal used in the boiler is shown in the following table:

[0033]

[0034] Among them, Figure 1 As shown, the secondary air structure that is beneficial to low-nitrogen combustion of the boiler described in the utility model includes a furnace 1, a front wall secondary air duct assembly 2 arranged on one side of the front wall 11 of the furnace 1, and a rear wall secondary air duct assembly 3 arranged on one side of the rear wall 12 of the furnace 1. The front wall secondary air duct assembly 2 and the rear wall secondary air duct assembly 3 are evenly arranged in upper and lower layers, and the upper and lower two-layer arrangement can effectively realize the staged combustion of air in the furnace 1, which helps to improve combustion efficiency and reduce pollutant emissions, especially the generation of NOx.

[0035] Further, such as Figure 1 , 3 As shown in Figure 4, the upper layer of the front wall secondary air duct assembly 2 is arranged with 4 front wall upper secondary air ducts 21 and the lower layer is arranged with 2 front wall lower secondary air ducts 22, and the arrangement order of the front wall secondary air duct assembly 2 is: 1 front wall upper secondary air duct 21, 1 front wall lower secondary air duct 22, and 1 front wall upper secondary air duct 21 constitute a first group, which are arranged on the left side of the front wall 11 of the furnace 1; 1 front wall upper secondary air duct 21, 1 front wall lower secondary air duct 22, and 1 front wall secondary air duct 21 constitute a second group, which are arranged on the middle right part of the front wall 11 of the furnace 1, and the angle f of the front wall secondary air duct blowing into the furnace and the angle g of the front wall lower secondary air duct blowing into the furnace are 10-30°.

[0036] Further, such as Figure 1 , 3As shown in Figure 5, the upper layer of the rear wall secondary air duct assembly 3 is arranged with two rear wall upper secondary air ducts 31 and the lower layer is arranged with three rear wall lower secondary air ducts 32, and the arrangement order of the rear wall secondary air duct assembly 3 is: one rear wall lower secondary air duct 32 and the rear wall secondary air duct 31 constitute the first group, which are arranged at the left part of one side of the rear wall 12 of the furnace 1; one rear wall lower secondary air duct 32 constitutes the second group, which is arranged at the middle part of one side of the rear wall 12 of the furnace 1; one rear wall upper secondary air duct 31 and the rear wall lower secondary air duct 32 constitute the third group, which are arranged at the right part of one side of the rear wall 12 of the furnace 1, and the angle h at which the rear wall secondary air duct blows into the furnace and the angle i at which the rear wall lower secondary air duct blows into the furnace are 10-30°.

[0037] Furthermore, nozzles are provided at the air inlets of the secondary air duct 21 on the front wall, the secondary air duct 22 under the front wall, the secondary air duct 31 on the rear wall, and the secondary air duct 32 under the rear wall. By providing nozzles at the air inlets, the penetration ability of the secondary air is improved, which is beneficial for the secondary air to be injected into the center of the furnace 1, reducing the lack of oxygen in the middle part of the furnace 1, reducing the carbon content of the tail fly ash, and thus reducing the concentration of NOx generated.

[0038] Furthermore, the secondary air duct 21 on the front wall, the secondary air duct 22 under the front wall, the secondary air duct 31 on the rear wall, and the secondary air duct 32 under the rear wall are all provided with solenoid valves, which mainly play the role of controlling the air volume. By opening and closing the solenoid valve, the air volume in the secondary air duct can be adjusted, thereby achieving precise control of the combustion process in the furnace 1 and ensuring that the secondary air can operate stably and economically under different load conditions.

[0039] Example 2

[0040] Based on the structural basis of Example 1 above, Figure 1 , 2 , 3, 4, and 5.

[0041] like Figure 2 As shown, the secondary air structure that is beneficial to the low-nitrogen combustion of the boiler described in the utility model, the distance between the furnace 1 and the installation ground j, the layered arrangement of the secondary air ducts and the distance relative to the installation ground j and other designs are very important influencing factors for realizing the staged combustion of air in the furnace, forming the oxygen-deficient zone in the center of the furnace and controlling the amount of NOx generated. According to the type of coal used in the existing boiler, combined with thermal calculations and furnace dynamics simulation of the combustion characteristics of the existing boiler, the elevation a of the furnace is set to 8750mm, the elevation b of the secondary air duct on the front wall and the elevation d of the secondary air duct on the rear wall are both set to 6000mm, the elevation c of the secondary air duct under the front wall and the elevation e of the secondary air duct on the rear wall are both set to 5400mm, which is beneficial to the low-nitrogen combustion of the boiler.

[0042] Further, such as Figure 2As shown, the angle at which the secondary air duct blows into the furnace 1 will affect the degree of mixing of air and fuel. According to the type of coal used in the existing boiler, combined with thermal calculations and furnace dynamic simulation of the combustion characteristics of the existing boiler, the angle f of the secondary air duct on the front wall blowing into the furnace and the angle h of the secondary air duct on the rear wall blowing into the furnace are both set to 30°, the angle g of the secondary air duct under the front wall blowing into the furnace and the angle h of the secondary air duct on the rear wall blowing into the furnace are both set to 20°, which is beneficial to reducing the problem of too low temperature in the dense phase zone and large temperature difference of the flue gas in the furnace 1, thereby affecting the desulfurization efficiency.

[0043] The utility model transforms the secondary air structure of the existing boiler, solves the technical problems existing in the secondary air device of the existing boiler, obtains a reasonable secondary air speed and air volume, improves the combustion conditions, and realizes low-nitrogen combustion. The flue gas pressure at the outlet of the boiler furnace 1 is close to the design value; when burning the existing coal (the main analysis index deviates by ≯10%), the NOx emission after the transformation is lower than 20mg / Nm 3 .

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A secondary air structure that is beneficial to low-nitrogen combustion in boilers, characterized in that: include: Furnace (1); A front wall secondary air duct assembly (2), the front wall secondary air duct assembly (2) being arranged on one side of the front wall (11) of the furnace (1); the front wall secondary air duct assembly (2) being arranged in two layers, an upper layer having four front wall upper secondary air ducts (21) and a lower layer having two front wall lower secondary air ducts (22); the angle at which the front wall upper secondary air ducts (21) and the front wall lower secondary air ducts (22) blow into the furnace (1) is 10-30°; A rear wall secondary air duct assembly (3), the rear wall secondary air duct assembly (3) being arranged on one side of a rear wall (12) of a furnace (1); the rear wall secondary air duct assembly (3) being arranged in two layers, upper and lower, wherein the upper layer is arranged with two rear wall upper secondary air ducts (31) and the lower layer is arranged with three rear wall lower secondary air ducts (32), and the angle at which the rear wall upper secondary air ducts (31) and the rear wall lower secondary air ducts (32) blow into the furnace (1) is 10-30 degrees.

2. The secondary air structure that is beneficial to low-nitrogen combustion in boilers according to claim 1 is characterized in that: The elevation of the furnace (1) is set to 8750 mm, the elevations of the secondary air duct (21) on the front wall and the secondary air duct (31) on the rear wall are both set to 6000 mm, and the elevations of the secondary air duct (22) under the front wall and the secondary air duct (32) under the rear wall are both set to 5400 mm.

3. The secondary air structure that is beneficial to low-nitrogen combustion in boilers according to claim 1 is characterized in that: The angles at which the secondary air duct (21) on the front wall and the secondary air duct (31) on the rear wall blow into the furnace (1) are both set to 30°, and the angles at which the secondary air duct (22) under the front wall and the secondary air duct (32) under the rear wall blow into the furnace (1) are both set to 20°.

4. The secondary air structure that is beneficial to low-nitrogen combustion in boilers according to claim 1 is characterized in that: The arrangement order of the front wall secondary air duct assembly (2) is as follows: one front wall upper secondary air duct (21), one front wall lower secondary air duct (22), and one front wall upper secondary air duct (21) form a first group, which is arranged at the left part of one side of the front wall (11) of the furnace (1); one front wall upper secondary air duct (21), one front wall lower secondary air duct (22), and one front wall upper secondary air duct (21) form a second group, which is arranged at the middle right part of one side of the front wall (11) of the furnace (1).

5. The secondary air structure that is beneficial to low-nitrogen combustion in boilers according to claim 1 is characterized in that: The arrangement order of the rear wall secondary air duct assembly (3) is as follows: one rear wall lower secondary air duct (32) and one rear wall upper secondary air duct (31) form a first group, which are arranged at the left part of one side of the rear wall (12) of the furnace (1); one rear wall lower secondary air duct (32) form a second group, which are arranged at the middle part of one side of the rear wall (12) of the furnace (1); one rear wall upper secondary air duct (31) and one rear wall lower secondary air duct (32) form a third group, which are arranged at the right part of one side of the rear wall (12) of the furnace (1).

6. The secondary air structure that is beneficial to low-nitrogen combustion in boilers according to claim 1 is characterized in that: The air outlets of the secondary air duct (21) on the front wall, the secondary air duct (22) below the front wall, the secondary air duct (31) on the rear wall, and the secondary air duct (32) below the rear wall are all provided with nozzles.

7. The secondary air structure that is beneficial to low-nitrogen combustion in boilers according to claim 1 is characterized in that: The secondary air duct (21) on the front wall, the secondary air duct (22) below the front wall, the secondary air duct (31) on the rear wall, and the secondary air duct (32) below the rear wall are all provided with solenoid valves.

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