A low-nitrogen combustion adjustment method based on lignite boiler

Abstract

The present invention discloses a low-nitrogen combustion adjustment method based on a lignite-fired boiler, comprising adjusting a combustion air distribution mode. The method is characterized in that the combustion air distribution mode is adjusted by adjusting the air volume proportion of each layer of the low-nitrogen burner as the boiler load changes so as to maintain the temperature of the flame center inside the furnace at 1200°C-1300°C; thereby solving the problems of low combustion efficiency, incomplete mechanical treatment in ash, and large combustion heat loss in existing dual-scale low-nitrogen burners when burning lignite.

Description

Technical Field

[0001] The present disclosure relates to the field of combustion technology of power station boilers, and more particularly to the combustion technology of a lignite boiler with a dual-scale low-nitrogen burner. Background Art

[0002] In order to meet the requirements of low nitrogen combustion and environmental emission index of boiler, the dual-scale burner divides the furnace into three longitudinal zones from bottom to top, such as Figure 1 As shown in the figure, the burnout zone consists of the main combustion zone, the reduction and denitrification zone, and the burnout zone. In the main combustion zone, the pulverized coal undergoes initial combustion, raising the furnace temperature and promoting ignition and combustion. The reduction and denitrification zone is the burner's primary reduction zone, fully reducing NOx generated in the main combustion zone. The burnout zone introduces an appropriate amount of burnout air at a suitable location above the burner, supplemented by secondary air using multiple nozzles and angles.

[0003] The dual-scale low nitrogen burner structure is arranged as follows Figure 2 As shown, its structure is arranged with two layers of primary air nozzles A and B, with peripheral wind around the nozzles; eight rows of secondary air are arranged in the upper, middle and lower layers; and a double layer of burnout air is arranged on the top.

[0004] The dual-scale low-NOx burner achieves low-NOx combustion by combining localized oxygen-deficient combustion with a reduction in the center flame temperature. To achieve this, the burner employs a "waisted" air distribution system, as shown in Table 1. Oxygen-deficient combustion is used in the center, creating a reducing atmosphere, with oxygen added at the top. The secondary air gates at each corner of the boiler remain unchanged under varying loads. Depending on the load, the air volume entering the furnace is adjusted by adjusting the outlet dampers of the suction and supply fans to maintain an oxygen content of 4%-5% at the furnace outlet.

[0005] Table 1 Combustion air distribution adjustment method of the original combustion method

[0006] load 290t / h 320t / h 360t / h 410t / h Oxygen content 5.0% 5.0% 4.5±0.5% 4.5±0.5% Burnout Wind Angle 50 50 50 50 Upper burnout wind 100 100 100 100 Lower burnout wind 15 15 15 15 Upper secondary air 2 80 80 80 80 Upper secondary air 1 0 0 0 0 B perimeter wind 0 0 0 0 Mid-level secondary wind 0 0 0 0 Mid-level secondary wind 0 0 0 0 Grease gun wind 50 50 50 50 Mid-level secondary wind 0 0 0 0 Mid-level secondary wind 0 0 0 0 A perimeter wind 0 0 0 0 Lower secondary air 100 100 100 100 Lower secondary air 100 100 100 100

[0007] According to the combustion air distribution method described in Table 1 above, when burning other relatively high-quality pulverized coal, the purpose of full combustion can be achieved under the premise of meeting low-nitrogen combustion and environmentally friendly emissions. However, when burning lignite, the amount of air entering the middle and upper parts of the furnace is reduced, resulting in poor ignition of the lignite. Although the late-entering burnout air replenishes air for ignition, due to its late entry, the lignite pulverized coal combustion time is insufficient and cannot be completely burned out. Therefore, the center temperature of the furnace flame is not high, only about 1150°C.

[0008] For this reason, the oxygen-deficient environment leads to insufficient oxygen in the center of the furnace flame and low flame temperature. However, in order to maintain the oxygen-deficient atmosphere, the air distribution in the central combustion zone is strictly controlled, which leads to insufficient oxygen in the main combustion zone and low combustion temperature when burning lignite. The ignition and combustion effects of the coal powder are not good. Some coal powder particles fall into the bottom ash hopper and are washed away before being completely burned, resulting in a large amount of mechanical incomplete combustion and heat loss in the ash, and low boiler combustion efficiency. Summary of the Invention

[0009] In view of this, the present disclosure provides a low-nitrogen combustion adjustment method based on a lignite boiler to solve the problems of low combustion efficiency, mechanical incompleteness in ash and large combustion heat loss in existing dual-scale low-nitrogen burners when burning lignite.

[0010] To achieve the above-mentioned purpose of the invention, the low-nitrogen combustion adjustment method based on lignite boiler includes adjusting the combustion air distribution mode, which is characterized in that the adjustment method of the combustion air distribution mode is:

[0011] As the boiler load changes, the air volume ratio of each layer of the low-nitrogen burner is adjusted to keep the temperature of the flame center inside the furnace at 1200℃-1300℃.

[0012] Furthermore, the air volume proportion of each layer is adjusted by adjusting the opening of the air door of each layer.

[0013] Furthermore, when the boiler load is lower than or equal to 320 t / h, for the middle-layer secondary air and upper-layer secondary air below and above the oil gun air, the damper opening is greater than the damper opening corresponding to the load higher than 320 t / h.

[0014] Furthermore, for the peripheral wind of the burner nozzle of layer A, the air damper opening is 80% when the load is less than or equal to 320 t / h, and is 50% when the load is higher than 320 t / h.

[0015] Furthermore, for the middle-layer secondary air below and above the oil gun air, the damper opening is 30-40% when the load is less than or equal to 320t / h, and 40-50% when the load is higher than 320t / h.

[0016] Furthermore, for the peripheral wind of the B-layer burner nozzle, the damper opening is 80% or above when the load is less than or equal to 320t / h, and is 100% when the load is higher than 320t / h.

[0017] Furthermore, for the upper secondary air, the damper opening is 30% when the load is less than or equal to 320 t / h, and is 50-55% when the load is higher than 320 t / h.

[0018] Furthermore, for the overburn air, the damper opening decreases as the load increases.

[0019] Furthermore, when the load is 290 t / h, 320 t / h, 360 t / h, and 390 t / h, respectively, the corresponding damper opening is 70%, 60%, 50%, and 40%, respectively.

[0020] The present disclosure has the following beneficial effects:

[0021] The disclosed method adjusts the air damper opening of each layer and the air volume ratio of each layer according to the different combustion conditions in the furnace and the changes in the boiler load, so that the temperature of the flame center inside the furnace is always maintained at 1200℃-1300℃. Practice has shown that the amount of nitrogen oxides generated by lignite furnace combustion at this temperature is limited, and the nitrogen oxide concentration value of the flue gas is always maintained at 200-300mg / M 3 , meet the nitrogen oxide concentration requirements at the boiler SCR inlet (the design inlet concentration requirement is no more than 350mg / M 3 ), and the pulverized coal ignition and combustion speed also meet the requirements for complete combustion. Sampling of the fly ash and slag produced by combustion demonstrated an average carbon content of 1-1.5% in the ash and 4-5.5% in the slag, meeting the specified values. Therefore, the combustion air distribution adjustment method employed in the disclosed method not only meets the boiler's low-nitrogen combustion requirements and environmental emission standards, but also provides an appropriate amount of air for lignite combustion, achieving efficient combustion adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0023] Figure 1 This is a structural arrangement diagram of the dual-scale low-nitrogen burner described in the background technology;

[0024] Figure 2 This is a longitudinal three-zone distribution diagram of the boiler furnace described in the background art;

[0025] Figure 3 This is a diagram of the appearance of ash formed by the background technology method;

[0026] Figure 4 This is a diagram of the appearance of ash formed by the method disclosed herein;

[0027] Figure 5 An inspection report of the ash residue formed by the background technology method;

[0028] Figure 6 This is an inspection report of the ash formed by the method of the present disclosure. DETAILED DESCRIPTION

[0029] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts not described in detail, those skilled in the art can also fully understand the present disclosure.

[0030] At the same time, unless the context clearly requires otherwise, words such as "include", "comprising" and the like throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, as "including but not limited to".

[0031] The mechanism of the combustion adjustment method disclosed in the present invention is based on the characteristics of lignite. For pulverized coal boilers burning lignite, different combustion air distribution methods and means are adopted according to different combustion conditions in the furnace under different loads. Compared with the original air distribution method that remains basically unchanged under different loads, the combustion air distribution method disclosed in the present invention adjusts the opening of each layer of air dampers as the boiler load changes, thereby adjusting the proportion of air volume in each layer, so that the temperature of the flame center inside the furnace is always maintained at 1200℃-1300℃. This is because practice has shown that the amount of nitrogen oxides generated by lignite furnace combustion at this temperature is limited, and the flue gas nitrogen oxide concentration value is always maintained at 200-300mg / M 3 , meeting the nitrogen oxide concentration requirements at the boiler SCR inlet, and the pulverized coal ignition and combustion speed can also meet the requirements of complete combustion.

[0032] According to the above-mentioned invention mechanism, the combustion adjustment method disclosed in the present invention includes the following general principles for adjusting the combustion air distribution mode:

[0033] When the load is lower than 320 t / h, less oxygen is required in the lower and middle parts of the flame, the oxygen-deficient reducing atmosphere is insufficient, and the degree of reduction of nitrogen oxides is insufficient. Therefore, the ratio of the middle and upper secondary air is reduced, and the air volume and oxygen are mostly sent in from the upper burnout air position to delay the time for oxygen to enter the furnace; when the load is higher than 320 t / h, the amount of pulverized coal sent into the furnace increases, and more oxygen is consumed in combustion. Therefore, the oxygen-deficient reducing atmosphere in the lower part has been established, and the amount of nitrogen oxides produced at this time is relatively low. Therefore, the air volume ratio of the middle and upper secondary air can be increased, which is conducive to the complete combustion of pulverized coal.

[0034] On the basis of the above general principles, the specific technical solutions adopted by the disclosed method are summarized as shown in Table 2. The detailed technical solutions of the disclosed method are described below in conjunction with Table 2:

[0035] 1. The lower secondary air at the bottom is always kept in a fully open state. At this time, the air door opening is 100%. The fully open lower secondary air forms a tray-like bottoming effect on the pulverized coal at the bottom of the furnace, reducing the proportion of unburned pulverized coal falling into the cold ash hopper at the bottom.

[0036] 2. When the load is lower than 320t / h, the peripheral wind at the burner nozzle of layer A should maintain an 80% air damper opening to cool the burner nozzle and prevent the burner from burning. When the load is higher than 320t / h, the amount of pulverized coal fed into the furnace increases, and the temperature in this area is not high, so the air damper opening can be 50%.

[0037] 3. For the secondary air in the middle layer below and above the oil gun, when the load is less than 320t / h, the damper opening is 40% to meet the requirements of low-nitrogen combustion. When the load is higher than 320t / h, the damper opening is increased to 50% to increase the air supply volume, meet the combustion air volume required by the increase in pulverized coal, and facilitate the ignition and combustion of pulverized coal.

[0038] 4. The peripheral wind of the B layer burner nozzle is close to the center of the flame. The temperature of the area is higher than the tolerance temperature of its alloy steel material. Its damper opening is always maintained at more than 80%. Specifically, the damper opening can be maintained at 80% when the load is 290t / h, and opened to 100% when the load is above 360t / h to cool the burner.

[0039] 5. The opening steps of the upper secondary air and the middle secondary air are basically the same. When the load is lower than 320t / h, a 30% damper opening is adopted to meet the requirements of low-nitrogen combustion; when the load is higher than 320t / h, the damper opening is increased to 50% to increase the air supply volume to meet the combustion air volume required for the increase in pulverized coal.

[0040] 6. For the burnout air in the top layer, when the load is 290 t / h, 320 t / h, 360 t / h and 390 t / h respectively, the corresponding damper opening is 70%, 60%, 50% and 40% respectively. This can not only maintain the emission requirements of low-nitrogen combustion, but also provide the necessary oxygen for complete combustion and reduce the heat loss of incomplete combustion.

[0041] Table 2 Combustion air distribution adjustment method of the disclosed method

[0042] load 290t / h 320t / h 360t / h 390t / h Oxygen content at furnace outlet 3% 4.0±0.5% 4.0±0.5% 4±0.5% Burnout wind swing angle 50 50 50 50 Upper burnout wind 70 60 50 40 Lower burnout wind 70 60 50 40 Upper secondary air 2 30 30 50 55 Upper secondary air 1 30 30 50 55 B perimeter wind 80 90 100 100 Mid-level secondary wind 30 30 40 50 Mid-level secondary wind 30 40 40 50 Grease gun wind 20 20 30 50 Mid-level secondary wind 40 40 50 50 Mid-level secondary wind 40 40 50 50 A perimeter wind 80 80 50 50 Lower secondary air 100 100 100 100 Lower secondary air 100 100 100 100

[0043] The overburn air swing angle (Table 2) is adjusted based on the coal quality and calorific value of the boiler. When the coal has a high calorific value and the steam temperature meets the requirements, the swing angle is adjusted downward to improve combustion efficiency and reduce the proportion of incomplete combustion. When the steam temperature is low, the swing angle is adjusted upward to raise the flame height, increase the heat absorption of the superheater, and increase the boiler steam temperature. By adjusting the overburn air angle, the boiler's main steam temperature is adjusted to reduce dependence on desuperheating water.

[0044] It can be seen that the disclosed method achieves the purpose of meeting the requirements of low-nitrogen combustion and environmental protection emissions of the boiler while reducing mechanical incomplete combustion losses by improving the lignite boiler combustion air distribution adjustment method without changing the original burner structure of the boiler.

[0045] The disclosed method has been put into practical use and compared with the background technology method to test the ash residues produced by the two methods. Figure 3-6 .

[0046] from Figure 3-6 The ash appearance image and ash test report show that after improving the combustion adjustment method of the low-nitrogen burner of the lignite-fired boiler, the black carbon particles in the ash field have been significantly reduced. Sampling and testing also show that the carbon content in the ash, that is, the mechanical incomplete combustion loss, has been greatly reduced.

[0047] In actual operation, after two winters, the combustion adjustment method of the disclosed combustion method, when applied to lignite-fired boilers, has demonstrated significant coal-saving results. With the actual operating time remaining roughly the same each year, each boiler saves approximately 6,650 tons of lignite annually. Calculated at a lignite price of 300 yuan per ton, this translates to a lignite cost savings of approximately 1.99 million yuan per boiler. Furthermore, the disclosed method also produces the following beneficial effects, as detailed in Table 3.

[0048] Table 3 Effects of using after improving combustion mode

[0049]

[0050] The above-described embodiments are merely examples of implementation methods of the present disclosure, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications, equivalent substitutions, and improvements without departing from the scope of the present disclosure, and these modifications are all within the scope of protection of the present disclosure. Therefore, the scope of protection of the present invention shall be based on the appended claims.

Claims

1. A method for adjusting low-nitrogen combustion based on a lignite-fired boiler, wherein the lignite-fired boiler is structured with two layers of primary air nozzles, A and B, with peripheral air around the nozzles; eight rows of secondary air are arranged in the upper, middle and lower layers; a double layer of burnout air is arranged on the top; the eight rows of secondary air are two rows of lower secondary air, four rows of middle secondary air and two rows of upper secondary air, the A layer of primary air nozzles is arranged between the lower secondary air and the middle secondary air, and the B layer of primary air nozzles is arranged between the middle secondary air and the upper secondary air; an oil gun air is arranged in the middle of the four rows of middle secondary air; the method includes adjusting the combustion air distribution method, characterized in that: The adjustment method of the combustion air distribution mode is: The proportion of air volume in each layer of the boiler is adjusted as the boiler load changes so that the temperature of the flame center inside the furnace is maintained at 1200°C-1300°C. The method of adjusting the proportion of air volume in each layer of the boiler as the boiler load changes is: When the boiler load is less than or equal to 320 t / h, the damper openings for the middle secondary air and upper secondary air below and above the oil gun air are greater than the damper openings corresponding to the load being greater than 320 t / h; For the perimeter wind of the primary air nozzles in layer A, the damper opening is 80% when the load is less than or equal to 320t / h, and 50% when the load is greater than 320t / h; For the secondary air in the middle layer below and above the oil gun air, the air door opening is 30-40% when the load is less than or equal to 320t / h, and 40-50% when the load is higher than 320t / h; For the peripheral wind of the primary air nozzles on the B layer, the damper opening is 80% or above when the load is less than or equal to 320t / h, and 100% when the load is higher than 320t / h; For the upper secondary air, the damper opening is 30% when the load is less than or equal to 320t / h, and 50-55% when the load is higher than 320t / h; For the overburnt air, the damper opening decreases as the load increases.

2. The low-nitrogen combustion adjustment method based on a lignite boiler according to claim 1, characterized in that: The air volume proportion of each floor is adjusted by adjusting the opening of the air door on each floor.

3. The low nitrogen combustion adjustment method based on a lignite boiler according to claim 2, characterized in that: When the loads are 290 t / h, 320 t / h, 360 t / h and 390 t / h respectively, the corresponding burnout air damper openings are 70%, 60%, 50% and 40% respectively.

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