A method for inhibiting coking of a tangentially fired high basicity coal boiler by controlling the air distribution

Abstract

The application discloses a kind of inhibiting the air distribution control method of coking of high alkali coal four corner tangential boiler, including with meet following condition I to condition III as control principle to the opening of secondary air door, overfire air door and perimeter air door is controlled: condition I, the differential pressure of secondary air box and boiler furnace is 0.4KPa~0.95KPa, operating oxygen content is 3.0%~6.5%;Secondary air ratio is 60%~70%, overfire air ratio is 25%~35%, perimeter air ratio is 4%~5%;Condition II, the opening of multiple secondary air doors sequentially arranged from bottom to top along boiler furnace forms two-section double waist type air distribution mode;Condition III, the opening of multiple overfire air doors arranged at the top of boiler furnace is in equilateral triangle distribution.The air distribution control method of the application can improve the oxygen content of main combustion zone, increase the residence time of coal particles in the furnace, reduce the flame center, strengthen the burnout characteristics of coal, inhibit the coking of heating surface, and improve the blending ratio of high alkali coal.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal-fired power plant boiler operation, and particularly relates to a method for controlling air distribution to suppress coking of a tangentially fired boiler burning high-alkali coal. BACKGROUND

[0002] A tangentially fired coal-fired boiler is generally designed to have primary air, secondary air, overfire air and perimeter air. The secondary air is hot air sent into the furnace through a separate channel of the burner, and is gradually mixed with the primary air after entering the furnace. The secondary air provides oxygen for the combustion of coal powder and can enhance the disturbance of the airflow, promote the backflow of high-temperature flue gas, and promote the mixing of combustibles and oxygen to provide conditions for complete combustion. The overfire air is used to reduce the generation of NO x , and hot air is separately sent into the furnace above the main burner in a staged air supply manner to further burn out the combustibles in the later stage. The perimeter air mainly forms an air curtain around the primary air flow to cool the primary air port and prevent coal powder torches from sticking to the wall and coal powder from separating from the airflow. After the coal powder airflow ignites, a small amount of secondary air can be supplied in time to facilitate the development of the combustion process.

[0003] In actual boiler operation, the secondary air, overfire air and perimeter air are all sourced from the secondary air plenum, and the distribution ratio, flow characteristics and rigidity of the three are mainly adjusted by the damper opening. Different distribution characteristics affect the combustion conditions in the furnace. Among them, the control scheme of the secondary air damper opening is generally to set the damper opening to follow the plenum and furnace differential pressure, and the differential pressure is set to follow the boiler command (fuel quantity setting). The control scheme of the overfire air damper opening is generally open-loop control, that is, the damper opening is set to follow the total air quantity. The control strategies described above are suitable for conventional coal-fired boilers and can ensure the synchronous change of damper opening and fuel and enhance the combustion responsiveness, but for boilers burning high-alkali coal, it is easy to cause oxygen deficiency in the main burner area, the flame center moves upward, and then causes large-area coking of the heating surface, which greatly affects the safe and stable operation of the unit. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a method for controlling air distribution to suppress coking of a tangentially fired boiler burning high-alkali coal, to solve the problem of coking of the heating surface of the existing tangentially fired boiler burning high-alkali coal.

[0005] To solve the above problems, the present application adopts the following technical scheme:

[0006] The application discloses a method for inhibiting coking of a high-alkali coal-fired four-corner tangential circle boiler, and the boiler furnace of the four-corner tangential circle boiler is provided with multilayer secondary air dampers for providing secondary air, multilayer overfire air dampers for providing overfire air and multilayer perimeter air dampers for providing perimeter air, wherein the secondary air, the overfire air and the perimeter air are all derived from a secondary air box, and the method comprises controlling the opening degrees of the multilayer secondary air dampers, the multilayer overfire air dampers and the multilayer perimeter air dampers according to the following conditions I-III:

[0007] Condition I: the differential pressure of the secondary air box and the boiler furnace is 0.4-0.95 KPa, the operation oxygen content is 3.0%-6.5%, the secondary air accounts for 60%-70%, the overfire air accounts for 25%-35%, and the perimeter air accounts for 4%-5%;

[0008] Condition II: the multilayer secondary air dampers arranged in the boiler furnace from bottom to top are divided into two groups, each group comprises a plurality of layers of secondary air dampers, the opening degrees of the secondary air dampers in each group are controlled in a waist-shaped air distribution mode with high ends and low middle, and the two groups of secondary air dampers form a two-section double-waist-shaped air distribution mode;

[0009] Condition III: the opening degrees of the multilayer overfire air dampers arranged at the top of the boiler furnace gradually decrease from bottom to top, so that the opening degrees of the multilayer overfire air dampers are distributed in a regular triangle shape.

[0010] In specific schemes, the boiler furnace is provided with multilayer pulverized coal nozzles, the multilayer perimeter air dampers correspond to the multilayer pulverized coal nozzles one by one, and each layer of pulverized coal nozzle is connected to a coal mill; wherein, on the basis of the control principles of the conditions I-III, the opening degree of each layer of secondary air damper is specifically regulated in the following mode:

[0011] determining an opening degree base of the secondary air damper;

[0012] correcting the opening degree base according to the coal quantity of the coal mill corresponding to the secondary air damper and the coal quantity of the adjacent coal mill, and determining the opening degree of the secondary air damper.

[0013] More specifically, the determination of the opening degree base of the secondary air damper comprises:

[0014] obtaining a functional relationship between the boiler load and the opening degree of the secondary air damper;

[0015] determining the opening degree base of the secondary air damper based on the input value of the boiler load and the functional relationship.

[0016] More specifically, the correction of the opening degree base according to the coal quantity of the coal mill corresponding to the secondary air damper and the coal quantity of the adjacent coal mill comprises:

[0017] obtain a first correction function relationship between the coal quantity of the corresponding coal mill and the opening degree of the secondary air damper, and obtain a second correction function relationship between the coal quantity of the adjacent coal mill and the opening degree of the secondary air damper;

[0018] a first correction value is calculated based on the coal quantity input value of the corresponding coal mill and the first correction function relationship, a second correction value is calculated based on the coal quantity input value of the adjacent coal mill and the second correction function relationship, and the opening degree base value is corrected according to the first correction value and the second correction value.

[0019] In a specific scheme, on the basis of the control principles of the conditions I to III, the opening degree of the overfire air damper is specifically regulated in the following manner:

[0020] obtain a function relationship between the boiler load and the NOx concentration at the furnace outlet, determine the NOx target concentration value based on the boiler load input value and the function relationship, and obtain a function relationship between the NOx concentration deviation set value input by the operator and the NOx concentration measured value at the furnace outlet. x x obtain a function relationship between the boiler load and the NOx concentration at the furnace outlet, determine the NOx target concentration value based on the boiler load input value and the function relationship, and obtain a function relationship between the NOx concentration deviation set value input by the operator and the NOx concentration measured value at the furnace outlet.

[0021] obtain a function relationship between the boiler load and the NOx concentration at the furnace outlet, determine the NOx target concentration value based on the boiler load input value and the function relationship, and obtain a function relationship between the NOx concentration deviation set value input by the operator and the NOx concentration measured value at the furnace outlet. x x obtain a function relationship between the boiler load and the NOx concentration at the furnace outlet, determine the NOx target concentration value based on the boiler load input value and the function relationship, and obtain a function relationship between the NOx concentration deviation set value input by the operator and the NOx concentration measured value at the furnace outlet. x obtain a function relationship between the boiler load and the NOx concentration at the furnace outlet, determine the NOx target concentration value based on the boiler load input value and the function relationship, and obtain a function relationship between the NOx concentration deviation set value input by the operator and the NOx concentration measured value at the furnace outlet.

[0022] In a specific scheme, on the basis of the control principles of the conditions I to III, the opening degree of the overfire air damper is specifically regulated in the following manner:

[0023] The opening degree of the overfire air damper is set to follow the operation mode of the corresponding coal mill: when the corresponding coal mill is running, the opening degree of the overfire air damper is 4% to 6%; when the corresponding coal mill is not running, the opening degree of the overfire air damper is 18% to 22%.

[0024] Compared with the prior art, the present application has the following technical effects:

[0025] (1) The distribution ratios of the secondary air, the overfire air and the peripheral air are considered as a whole, the damper opening degrees of the secondary air, the overfire air and the peripheral air are controlled, the differential pressure between the secondary air box and the boiler furnace is controlled to be between 0.4 KPa and 0.95 KPa, the oxygen content is controlled to be between 3.0% and 6.5%, and problems such as too high overfire air ratio, insufficient secondary air rigidity and insufficient combustion are avoided.

[0026] ​​(2) The secondary air adopts a two-stage double waist-shaped air distribution method, which can increase the oxygen content in the main combustion zone, increase the residence time of pulverized coal particles in the furnace, lower the flame center, enhance the combustion characteristics of pulverized coal, inhibit coking on the heating surface, and also increase the blending ratio of high-alkali coal. The blending ratio of high-alkali coal can be increased by 5% to 10% on the original basis.

[0027] (3) The burnout air adopts an air distribution method in which the damper opening gradually decreases from bottom to top, forming an equilateral triangle. This can reduce NO at the furnace outlet. x Generation amount. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the damper arrangement structure of the four-corner tangential boiler in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of a two-section double-waisted air distribution method for secondary air in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the burnout air distribution method in an embodiment of the present invention, which adopts an equilateral triangular distribution.

[0031] Figure 4 This is a schematic diagram of the secondary air damper opening control strategy in an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the burnout air damper opening control strategy in an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of the perimeter wind damper opening control strategy in an embodiment of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the drawings. The embodiments of the present invention shown in and described with reference to the drawings are merely exemplary, and the present invention is not limited to these embodiments.

[0035] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0036] This invention provides an air distribution control method for suppressing coking in a tangentially circular boiler burning high-alkali coal. The boiler furnace of the tangentially circular boiler is provided with multiple layers of pulverized coal nozzles arranged sequentially from bottom to top, and each layer of pulverized coal nozzles is equipped with a corresponding coal mill.

[0037] The boiler furnace of the four-corner tangential boiler is also equipped with multi-layer secondary air dampers for providing secondary air, multi-layer burnout air dampers for providing burnout air, and multi-layer perimeter air dampers for providing perimeter air. The secondary air, burnout air, and perimeter air all originate from the secondary air box. (See reference...) Figure 1 Damper unit 1 is a secondary air damper, damper unit 2 is a perimeter air damper, and damper unit 3 is a burnout air damper. The multi-layered secondary air dampers are arranged sequentially from bottom to top along the vertical direction of the boiler furnace. The multi-layered burnout air dampers are arranged sequentially from bottom to top at the top of the boiler furnace. The multi-layered perimeter air dampers are arranged sequentially from bottom to top along the vertical direction of the boiler furnace, and each multi-layered perimeter air damper corresponds one-to-one with a multi-layered pulverized coal nozzle.

[0038] Taking a commonly used 660MW ultra-supercritical tangential-circular boiler in existing production as an example, this boiler has six layers of pulverized coal nozzles, and six layers of perimeter air dampers A, B, C, D, E, and F correspond one-to-one with the six layers of pulverized coal nozzles. Fifteen layers of secondary air dampers AA, AB1, AB2, BC1, BC2, BC3, CC, DD, DE1, DE2, DE3, EF1, EF2, EF3, and FF are arranged sequentially from bottom to top along the vertical direction of the boiler furnace. Seven layers of burnout air dampers UA, UB, UC, UD, UE, UF, and UG are arranged sequentially from bottom to top at the top of the boiler furnace.

[0039] The air distribution control method provided in this embodiment of the invention includes controlling the opening degree of the multi-layer secondary air damper, the multi-layer burnout air damper, and the multi-layer perimeter air damper based on the following conditions I to III.

[0040] Condition I: The differential pressure between the secondary air box and the boiler furnace is 0.4 kPa to 0.95 kPa, and the operating oxygen content is 3.0% to 6.5%; the proportion of secondary air is 60% to 70%, the proportion of burnout air is 25% to 35%, and the proportion of perimeter air is 4% to 5%.

[0041] Condition II: The multi-layered secondary air dampers arranged sequentially from bottom to top along the boiler furnace are divided into upper and lower groups. Each group includes several layers of secondary air dampers. The opening of the several layers of secondary air dampers in each group adopts a waist-shaped air distribution method with high ends and low middle, forming two sections of double waist-shaped air distribution.

[0042] For example Figure 1 Taking the secondary air damper shown as an example, refer to... Figure 2The 15-layer secondary air damper is divided into two groups: the lower group corresponds to the lower 3 layers of pulverized coal nozzles, including 7 layers of secondary air dampers AA, AB1, AB2, BC1, BC2, BC3, and CC; the upper group corresponds to the upper 3 layers of pulverized coal nozzles, including 8 layers of secondary air dampers DD, DE1, DE2, DE3, EF1, EF2, EF3, and FF. In the first group, the opening of the 7 layers of secondary air dampers gradually decreases from damper AA to damper BC1, and then gradually increases from damper BC1 to damper CC, forming a waist-shaped air distribution pattern that is high at both ends and low in the middle. Similarly, in the second group, the opening of the 8 layers of secondary air dampers gradually decreases from damper DD to damper DE3, and then gradually increases from damper DE3 to damper FF, also forming a waist-shaped air distribution pattern that is high at both ends and low in the middle. Therefore, the 15-layer secondary air damper as a whole adopts a two-stage double-waist-shaped air distribution pattern.

[0043] Condition III: The opening of the multi-layer burnout air damper located at the top of the boiler furnace gradually decreases from bottom to top, so that the opening of the multi-layer burnout air damper is distributed in an equilateral triangle.

[0044] For example Figure 1 For example, refer to the burnout air damper shown below. Figure 3 The 7-layer burnout air dampers gradually decrease in size from bottom to top, from damper UA to damper UG, and the opening of the 7-layer burnout air dampers is distributed in an equilateral triangle.

[0045] Based on condition I, the air distribution control method provided in this embodiment of the invention comprehensively considers the distribution ratio among secondary air, burnout air, and perimeter air. By controlling the opening of the dampers for secondary air, burnout air, and perimeter air, the differential pressure between the secondary air box and the boiler furnace is controlled between 0.4 kPa and 0.95 kPa, and the operating oxygen content is controlled between 3.0% and 6.5%. This avoids problems such as excessively high burnout air ratio, insufficient rigidity of secondary air, and incomplete combustion.

[0046] Based on condition II, the air distribution control method provided in this embodiment of the invention adopts a two-stage double-waisted air distribution method for secondary air, which can increase the oxygen content in the main combustion zone, increase the residence time of pulverized coal particles in the furnace, lower the flame center, enhance the combustion characteristics of pulverized coal, suppress coking on the heating surface, and also increase the blending ratio of high-alkali coal.

[0047] Based on condition III, the air distribution control method provided in this embodiment of the invention uses an equilateral triangular distribution pattern where the damper opening gradually decreases from bottom to top to distribute the burnout air, which can reduce NO at the furnace outlet. x Generation amount.

[0048] In the specific scheme, based on satisfying the control principles of conditions I to III, the opening degree of the secondary air damper on each floor is specifically adjusted in the following manner:

[0049] Determine the base opening degree of the secondary air damper. Specifically, refer to... Figure 4 First, obtain the functional relationship f(x1) between the boiler load and the opening of the secondary air damper. Then, determine the base number of the opening of the secondary air damper based on the boiler load input value x1 and the functional relationship f(x1).

[0050] The opening degree of the secondary air damper is determined by correcting the base value based on the coal quantity of the pulverizer corresponding to the secondary air damper and the coal quantity of the adjacent pulverizers. Specifically, see [link to relevant documentation]. Figure 4 First, obtain the first correction function relationship f(x2) between the coal quantity of the pulverizer corresponding to the secondary air damper and the opening degree of the secondary air damper, and obtain the second correction function relationship f(x3) between the coal quantity of the pulverizer adjacent to the secondary air damper and the opening degree of the secondary air damper; then, calculate the first correction value based on the coal quantity input value x2 of the corresponding pulverizer and the first correction function relationship f(x2), and calculate the second correction value based on the coal quantity input value x3 of the adjacent pulverizer and the second correction function relationship f(x3).

[0051] The aperture base is adjusted based on the first and second correction values. Specifically, see [link to relevant documentation]. Figure 4 The opening base, the first correction value, and the second correction value are summed by the summation module ∑, and the opening of the secondary air damper is finally determined and output from the output module OUT.

[0052] It should be noted that the above functional relationships f(x1), f(x2), and f(x3) are all derived from the actual adjustment test results, and the functional relationship corresponding to each secondary damper is different.

[0053] In the specific scheme, based on satisfying the control principles of conditions I to III, the opening degree of the burnout air damper is specifically adjusted in the following manner:

[0054] See Figure 5 First, obtain the boiler load and furnace outlet NO. x The concentration is determined by the functional relationship f(x4), and then NO is determined based on the boiler load input value x4 and the functional relationship f(x4). x Target concentration value.

[0055] See Figure 5 The NO input by the operator x Concentration deviation setpoints y and NO x The target concentration value is summed by the summation module (∑) and then input into the PID controller to control the NO concentration at the furnace outlet. xThe measured concentration value x5 is input to the PID controller via the delay module Lag. The PID controller calculates and outputs control parameters based on the input parameters to control the opening degree of the burnout air dampers UA to UG on each floor.

[0056] In this embodiment of the invention, NO is used. x Closed-loop PID control of NO concentration is used to control the burnout air damper opening. x The concentration setting is automatically set based on the boiler load, with operator bias correction. A sequential control principle of increasing opening size is used for deviation adjustment control, ultimately determining the burnout air damper opening. The entire burnout air damper distribution forms an equilateral triangle, thereby lowering the flame center and simultaneously reducing NO. x The role of production volume.

[0057] In the specific scheme, based on satisfying the control principles of conditions I to III, the opening degree of the perimeter wind damper is specifically adjusted in the following manner:

[0058] The opening degree of the perimeter air damper is set to be adjusted according to the corresponding coal mill operating mode. The perimeter air damper opening degree control function is determined based on whether the coal mill is running or not. Figure 6 As shown, the functional relationship between the coal mill's operating status and the opening of the perimeter air damper is f(x6). Based on the coal mill's operating status input value x6 and the functional relationship f(x6), the opening of the perimeter air damper is determined and output from the output module OUT. Preferably, when the corresponding coal mill is running, the opening of the perimeter air damper is 4%~6%, more preferably 5%; when the corresponding coal mill is not running, the opening of the perimeter air damper is 18%~22%, more preferably 20%.

[0059] In a specific case study, a 660MW ultra-supercritical tangential boiler is used as the object for air distribution, and the damper configuration is as follows: Figure 1 As shown, the main implementation steps of its air distribution process are as follows:

[0060] Step 1: During shutdown, modify and download the control logic strategy. Based on the existing conventional DCS distributed control system design concept, and combined with the air distribution control method of this invention, modify the control strategies for secondary air dampers, burnout air dampers, and perimeter air dampers, and download the compiled logic control method to the DCS distributed control system. The optimized control logic is designed according to the current typical logic design specifications for units, and a switching function with the original configuration logic is set up. The original DCS configuration logic is retained, and the new optimized logic will only be gradually activated during combustion optimization and commissioning.

[0061] Step 2: After start-up, conduct combustion optimization adjustments to determine the relationships between various control functions. During the combustion optimization adjustment test, secondary air is distributed in a two-stage double "waist" configuration to lower the flame center in the furnace, increase the residence time of pulverized coal and the burnout rate. The uniformity of the combustion process in the furnace is judged by the deviation of the flue gas temperature at the furnace outlet, and the degree of burnout of pulverized coal reaching the furnace outlet is judged by the flue gas temperature at the furnace outlet, thus determining the final control function relationships.

[0062] Step 3: Modify the control function relationship and switch to the new control strategy to achieve automated control of boiler combustion and air distribution. Modify the control function relationship described above in the DCS system, and switch the control methods for secondary air, burnout air, and perimeter air to the new control logic. At this point, the opening control of secondary air, burnout air, and perimeter air enters the DCS closed-loop control.

[0063] Ultimately, after the new air distribution control method was put into operation, the flue gas temperature in the furnace was significantly controlled, coking on the heating surfaces was significantly alleviated and controlled, the proportion of high-alkali coal blending could be increased by 5% to 10% on the original basis, and the NO at the furnace outlet was reduced. x The generation rate was reduced by 5% to 10%, achieving the expected optimization goal.

[0064] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for controlling air distribution to suppress coking in a tangentially circular boiler burning high-alkali coal, wherein the boiler furnace of the tangentially circular boiler is equipped with multi-layer secondary air dampers for providing secondary air, multi-layer burnout air dampers for providing burnout air, and multi-layer perimeter air dampers for providing perimeter air, wherein the secondary air, burnout air, and perimeter air all originate from the secondary air box, characterized in that, The air distribution control method includes controlling the opening degree of the multi-layer secondary air damper, multi-layer burnout air damper, and multi-layer perimeter air damper based on the following conditions I to III: Condition I: The differential pressure between the secondary air box and the boiler furnace is 0.4 kPa to 0.95 kPa, and the operating oxygen content is 3.0% to 6.5%; the proportion of secondary air is 60% to 70%, the proportion of burnout air is 25% to 35%, and the proportion of perimeter air is 4% to 5%. Condition II: The multi-layer secondary air dampers arranged sequentially from bottom to top along the boiler furnace are divided into upper and lower groups. Each group includes several layers of secondary air dampers. The opening of the several layers of secondary air dampers in each group adopts a waist-shaped air distribution method with high ends and low middle, forming two sections of double waist-shaped air distribution. Condition III: The opening of the multi-layer burnout air damper located at the top of the boiler furnace gradually decreases from bottom to top, so that the opening of the multi-layer burnout air damper is distributed in an equilateral triangle.

2. The air distribution control method according to claim 1, characterized in that, The boiler furnace is equipped with multiple layers of pulverized coal nozzles, and each layer of peripheral air dampers corresponds one-to-one with a pulverized coal nozzle. Each layer of pulverized coal nozzles is connected to a coal mill. Based on the control principles of conditions I to III, the opening degree of each layer of secondary air dampers is specifically adjusted as follows: Determine the base opening degree of the secondary air damper; The opening degree of the secondary air damper is determined by correcting the base value of the opening degree based on the coal quantity of the coal mill corresponding to the secondary air damper and the coal quantity of the adjacent coal mill.

3. The air distribution control method according to claim 2, characterized in that, The determination of the opening base value of the secondary air damper includes: Obtain the functional relationship between boiler load and the opening of the secondary air damper; The opening base value of the secondary air damper is determined based on the boiler load input value and the aforementioned functional relationship.

4. The air distribution control method according to claim 2, characterized in that, The step of correcting the opening base value based on the coal quantity of the coal mill corresponding to the secondary air damper and the coal quantity of the adjacent coal mills includes: Obtain the first correction function relationship between the coal quantity of the pulverizer corresponding to the secondary air damper and the opening degree of the secondary air damper; obtain the second correction function relationship between the coal quantity of the pulverizer adjacent to the secondary air damper and the opening degree of the secondary air damper. A first correction value is calculated based on the coal quantity input value of the corresponding coal mill and the first correction function relationship. A second correction value is calculated based on the coal quantity input value of the adjacent coal mill and the second correction function relationship. The opening base number is then corrected according to the first correction value and the second correction value.

5. The air distribution control method according to any one of claims 2-4, characterized in that, Based on the control principles of conditions I to III, the opening degree of the burnout air damper is specifically adjusted in the following manner: Obtain boiler load and furnace outlet NO x The concentration of NO is determined based on the boiler load input value and the functional relationship. x Target concentration value; The NO entered by the operator x Concentration deviation setpoint, furnace outlet NO x Measured concentration values ​​and the NO x The target concentration value is input into the PID controller, which calculates and outputs the opening degree of the burnout air damper.

6. The air distribution control method according to claim 5, characterized in that, Based on the control principles of conditions I to III, the opening degree of the perimeter wind damper is specifically adjusted in the following manner: The opening degree of the perimeter air damper is set to be adjusted according to the corresponding coal mill operation mode: when the corresponding coal mill is running, the opening degree of the perimeter air damper is 4%~6%; when the corresponding coal mill is not running, the opening degree of the perimeter air damper is 18%~22%.

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