A method for controlling the opening degree of the air damper under deep peak shaving

Abstract

The present invention provides a method for controlling the opening degree of the air damper under deep peak shaving, which includes the following steps: S1 selection of data parameters; S2 analysis of deep peak shaving data; S3 modification of the logical control value of the air damper opening degree; S4 verification of the air damper opening degree control curve; it is simple to operate, and on the premise of ensuring the stable combustion of the unit, through reasonable control of the air damper opening degree, the NO x emission concentration is controlled at a low level.

Description

Technical Field

[0001] The present invention relates to the technical field of deep peak regulation, and in particular to a method for controlling the opening of an air damper under deep peak regulation. Background Art

[0002] As large-scale units participate in peak load regulation more and more frequently and the load drops lower and lower, the boiler side faces several major challenges as follows: First, the problem of stable combustion of the boiler at low load; second, the problem of dry-wet state conversion on the steam-water side of the boiler; third, the flue gas temperature of the denitrification system cannot meet the minimum temperature required for the catalyst reaction; fourth, the NO x The emission concentration is high, the amount of ammonia sprayed by the denitrification system is large, and the ammonia escape is large. In response to the above problems, scholars have carried out a lot of research, including low-load stable combustion and NO x The contradiction between high emission concentration and low load stability is particularly prominent. From the perspective of safe operation of the unit, power plants have chosen low-load stable combustion, which will lead to NO x High emission concentration and large ammonia injection volume can easily cause excessive ammonia escape, forming ammonium bisulfate to block the air preheater.

[0003] Stable combustion and NO during deep peak load regulation x The problem of high emission concentration and inability to take into account the other issues is particularly prominent. How to balance low-load stable combustion and NO x Therefore, a method for controlling the opening of the damper under deep peak regulation is urgently needed. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for controlling the opening of the damper under deep peak regulation, which is simple to operate. Under the premise of ensuring stable combustion of the unit, the NO x The emission concentration is controlled at a low level.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] The present invention provides a method for controlling the opening of a damper under deep peak regulation, comprising the following steps:

[0007] S1 data parameter selection, collection and transfer of unit load parameters, economizer outlet oxygen parameters, NO x The emission concentration parameters, air damper opening parameters and flame signal parameters are used as deep peak regulation data;

[0008] S2 analyzes the deep peak regulation data, selects the parameters of the unit under rated load operation for key analysis, and analyzes the air damper opening parameters, economizer outlet oxygen parameters, NO x The corresponding relationship between the emission concentration parameters and the flame signal parameters is analyzed to obtain analytical data;

[0009] Modify the logical control value of the S3 damper opening. According to the analysis data, the influence degree of the key damper opening on the NO x emission concentration is determined. By repeating step S2 to modify the logical control value of the damper opening multiple times, the purpose of reducing the NO x emission concentration under deep peak shaving is achieved;

[0010] Verify the damper opening control curve in S4. Under deep peak shaving, while taking into account the stable combustion of the unit, when the unit is operating at the rated load, the logical control value of the damper opening is used to calculate the damper opening value through linear interpolation. According to the damper opening value, verify the adaptability of the damper opening control curve and solidify it for controlling the damper opening under deep peak shaving.

[0011] A method for controlling the damper opening under deep peak shaving provided by the present invention is simple to operate. On the premise of ensuring the stable combustion of the unit, through reasonable control of the damper opening, the NO x emission concentration is controlled at a low level.

[0012] As a preferred technical solution, the analysis of the deep peak shaving data in step S2 specifically includes the following steps: When the unit is operating at the rated load, the NO x emission concentration has a positive correlation with the oxygen content at the economizer outlet, and the oxygen content at the economizer outlet has an inverse correlation with the opening of the upper overfire air damper.

[0013] As a preferred technical solution, in step S3, according to the analysis data, the opening of the sub-upper overfire air damper and the opening of the top overfire air damper are determined as the key damper openings to be able to control the NO x emission concentration under deep peak shaving.

[0014] As a preferred technical solution, the verification of the damper opening control curve in step S4 specifically includes the following steps: When the unit is operating at the rated load, under deep peak shaving, the flame signal is stable. Collect the preset value and the actual value of the operating oxygen content of the unit in this rated load range, calculate the difference between the actual value and the preset value of the operating oxygen content, obtain the corresponding oxygen content range through the difference calculation, and calculate the logical control value of the damper opening according to the corresponding oxygen content range by linear interpolation. According to the logical control value of the damper opening, obtain the damper opening value through linear interpolation. According to the damper opening value, verify the adaptability of the damper opening control curve and solidify it for controlling the damper opening under deep peak shaving, so as to gradually reduce the actual value of the operating oxygen content to the preset value of the operating oxygen content to achieve the purpose of reducing the NO x emission concentration.

[0015] As a preferred technical solution, the rated load is 20% to 50%.

[0016] As a preferred technical solution, the unit includes: a main air box, in which there are at least 6 layers of enhanced ignition pulverized coal nozzles, and fuel air is arranged around the pulverized coal nozzles, and the differential pressure of the main air box of the unit is 30 - 110 mmH2O.

[0017] As a preferred technical solution, a layer of auxiliary air nozzles is arranged between every two adjacent layers of pulverized coal nozzles, and the auxiliary air nozzles include: auxiliary air nozzles with horizontally deflected angles arranged oppositely.

[0018] As a preferred technical solution, a layer of top combustion air damper baffle and two layers of compact burnout air damper baffles are arranged on the upper part of the main air box, and a layer of bottom combustion air damper baffle and a layer of under-fire air damper baffle are arranged on the lower part of the main air box.

[0019] As a preferred technical solution, four layers of independent horizontally swingable low-level burnout air damper baffles are respectively arranged at positions 4.0 m to 4.5 m from the center line of the upper burner on the upper part of the main air box, and four layers of independent horizontally swingable high-level burnout air damper baffles are respectively arranged at positions 8.5 m to 9.0 m from the center line of the upper burner.

[0020] As a preferred technical solution, the high-level burnout air damper baffle is successively provided with the topmost high-level burnout air baffle, the second topmost high-level burnout air baffle, the middle-level high-level burnout air baffle and the lower-level high-level burnout air baffle from top to bottom along the height direction of the unit.

[0021] A method for controlling the opening degree of the air damper baffle under deep peak shaving provided by the present invention is simple to operate. On the premise of ensuring the stable combustion of the unit, by reasonably controlling the opening degree of the air damper baffle, the NO x emission concentration is controlled at a low level. Description of the Drawings

[0022] Figure 1 It is the NO x change data curve of the unit under rated load conditions (not processed by the method for controlling the opening degree of the air damper baffle under deep peak shaving of the present invention);

[0023] Figure 2 It is the NO x change data curve of the unit provided by the present invention under rated load conditions (processed by the method for controlling the opening degree of the air damper baffle under deep peak shaving of the present invention). Detailed Embodiments

[0024] The preferred embodiments of the present invention will be described in detail below with reference to the drawings.

[0025] It is understandable that the present invention achieves the object of the present invention through some embodiments. The present invention provides a method for controlling the opening degree of the air damper under deep peak shaving, including the following steps:

[0026] S1 Selection of data parameters, collecting and retrieving the unit load parameter, the oxygen content parameter at the economizer outlet, NO x emission concentration parameter, air damper opening degree parameter, and flame signal parameter as deep peak shaving data;

[0027] S2 Analysis of deep peak shaving data, selecting the parameters of the unit load at the rated load of the unit for key analysis, and analyzing the corresponding relationship between the air damper opening degree parameter, the oxygen content parameter at the economizer outlet, NO x emission concentration parameter, and flame signal parameter to obtain analysis data;

[0028] Under the condition of 20% - 50% of the rated load, NO x emission concentration has a positive correlation with the oxygen content at the economizer outlet, that is, the higher the oxygen content at the economizer outlet, the higher the NO x emission concentration; the oxygen content at the economizer outlet has an inverse correlation with the opening degree of the overfire air damper, that is, when the opening degree of the overfire air damper is increased, the oxygen content at the economizer outlet decreases; through the above data analysis, it is found that under deep peak shaving, while ensuring that the flame signal does not flicker, in order to control the NO x emission concentration, it is necessary to increase the opening degree of the overfire air damper and reduce the operating oxygen content;

[0029] S3 Modification of the logical control value of the air damper opening degree. According to the analysis data, it is determined that the key air damper opening degree has a greater impact on the NO x emission concentration. By repeating step S2 to modify the logical control value of the air damper opening degree multiple times, the purpose of reducing the NO x emission concentration under deep peak shaving is achieved;

[0030] According to the analysis data, the opening degree of the sub - upper overfire air damper and the opening degree of the top - most overfire air damper are determined as the key air damper opening degrees to be able to control the NO x emission concentration under deep peak shaving;

[0031] S4 Verification of the air damper opening degree control curve. Under deep peak shaving, taking into account the stable combustion of the unit, in the range of 20% - 50% of the rated load of the unit, the air damper opening degree value is calculated by linear interpolation according to the logical control value of the air damper opening degree, and the adaptability of the air damper opening degree control curve is verified and solidified for controlling the air damper opening degree under deep peak shaving;

[0032] When the unit operates at 20% - 50% of the rated load and under deep peak shaving, the flame signal is stable. The preset value and the actual value of the operating oxygen content of the unit in this rated load range are collected, and the difference between the actual value and the preset value of the operating oxygen content is calculated. The corresponding oxygen content range is obtained through the difference calculation, and the logical control value of the damper opening is calculated according to the corresponding oxygen content range by linear interpolation. According to the logical control value of the damper opening, the damper opening value is obtained through linear interpolation. According to the damper opening value, the adaptability of the damper opening control curve is verified and solidified, which is used to control the damper opening under deep peak shaving, so as to gradually reduce the actual value of the operating oxygen content to the preset value of the operating oxygen content in order to achieve the reduction of NO x emission concentration.

[0033] A damper opening control method under deep peak shaving provided by the present invention has simple operation. On the premise of ensuring the stable combustion of the unit, through the reasonable control of the damper opening, the NO x emission concentration is controlled at a low level.

[0034] The combustion mode of the unit adopts the TFS2000 combustion system. The main purpose of the system design is to reduce the conversion of volatile nitrogen into NO x , and its main method is to establish early ignition and use fuel / air staged combustion technology with oxygen content control.

[0035] The main components of the unit include: a compact overfire air damper (CCOFA), a horizontally swingable separated overfire air damper (SOFA), an auxiliary air nozzle (CFS) with a preset horizontal deflection angle, and an enhanced ignition pulverized coal nozzle. The unit includes: a primary air box, in which there are at least 6 layers of enhanced ignition pulverized coal nozzles. Fuel air is arranged around the pulverized coal nozzles, and one layer of auxiliary air nozzles is arranged between every two adjacent layers of pulverized coal nozzles. The auxiliary air nozzles include: auxiliary air nozzles with horizontally deflected angles arranged relatively; on the upper part of the primary air box, there is one layer of top combustion air damper and two layers of compact overfire air dampers, and on the lower part of the primary air box, there is one layer of bottom combustion air damper and one layer of underfire air damper; at positions 4.0m - 4.5m from the center line of the upper burner in the upper part of the primary air box, four layers of independently horizontally swingable low-level overfire air dampers are arranged respectively, and at positions 8.5m - 9.0m from the center line of the upper burner, four layers of independently horizontally swingable high-level overfire air dampers are arranged respectively; the high-level overfire air dampers are successively provided with the topmost high-level overfire air damper, the sub-topmost high-level overfire air damper, the middle-level high-level overfire air damper, and the lower-level high-level overfire air damper from top to bottom along the height direction of the unit.

[0036] Number the damper plates from bottom to top along the height of the unit in sequence as: UFA, AA, A, ABA, AB, ABB, B, BCB, BC, BCC, C, CDC, CD, CDD, D, DED, DE, DEE, E, EFE, EF, EFF, F, FF, CCOFA A, CCOFAB, LSOFA-A, LSOFA-B, LSOFA-C, LSOFA-D, HSOFA-A (lower-layer over-fire air damper), HSOFA-B (middle-layer over-fire air damper), HSOFA-C (sub-upper-layer over-fire air damper), and HSOFA-D (uppermost-layer over-fire air damper), a total of 34 layers. Among them, the proportion of over-fire air in the secondary air volume is 40%. A hypothetical tangential circle is formed at the center of the furnace of the unit, rotating clockwise when viewed from top to bottom.

[0037] A method for controlling the opening of the damper plate under deep peak shaving provided by the present invention includes the following steps:

[0038] S1: Selection of data parameters;

[0039] Collect and retrieve the unit load parameter, oxygen content parameter at the outlet of the economizer, NO x emission concentration parameter, damper plate opening parameter, and flame signal parameter as deep peak shaving data;

[0040] S2: Analysis of deep peak shaving data;

[0041] For the analysis of deep peak shaving data, select the parameters of the unit under the rated load condition for key analysis, and analyze the corresponding relationship between the damper plate opening parameter, oxygen content parameter at the outlet of the economizer, NO x emission concentration parameter, and flame signal parameter to obtain analysis data;

[0042] Under the rated load condition of 20% - 50%, from Figure 1 the data, it is found that the NO x emission concentration has a positive correlation with the oxygen content at the outlet of the economizer, that is, the higher the oxygen content, the higher the NO x emission concentration, that is, the higher the oxygen content at the outlet of the economizer, the higher the NO x emission concentration, especially under low load conditions; historical data analysis also finds that the oxygen content at the outlet of the economizer has an inverse correlation with the opening of the uppermost-layer over-fire air damper (HSOFA-D) and the opening of the sub-upper-layer over-fire air damper (HSOFA-C), that is, when the opening of the uppermost-layer over-fire air damper (HSOFA-D) and the opening of the sub-upper-layer over-fire air damper (HSOFA-C) are increased, the oxygen content at the outlet of the economizer decreases; through the above data analysis, it is found that under deep peak shaving, while ensuring that the flame signal does not flicker, to control NO xFor the emission concentration, it is necessary to increase the opening degrees of the topmost overfire air damper (HSOFA-D) and the second topmost overfire air damper (HSOFA-C), and reduce the operating oxygen content;

[0043] S3: Modification of the logic control value of the damper opening degree; Based on the analysis data, it is determined that the key damper opening degrees have a greater impact on the NO x emission concentration. By repeating step S2 multiple times to modify the logic control value of the damper opening degree, the purpose of reducing the NO x emission concentration under deep peak shaving is achieved;

[0044] Based on the analysis data, it is determined that the opening degrees of the second topmost overfire air damper (HSOFA-C) and the topmost overfire air damper (HSOFA-D) are used as the key damper opening degrees to be able to control the NO x emission concentration under deep peak shaving;

[0045] By repeating step S2 multiple times to modify the logic control value of the damper opening degree, it specifically includes the following steps:

[0046] During the operation of the unit, the differential pressure between the furnace wind box of the unit maintains the opening degrees of the main combustion zone (UFA, AA, A, ABA, AB, ABB, B, BCB, BC, BCC, C, CDC, CD, CDD, D, DED, DE, DEE, E, EFE, EF, EFF, F, FF) dampers within a certain range to ensure that the flame signal does not flicker under deep peak shaving. The control value of the differential pressure between the furnace wind box of the unit is 30 - 110 mmH2O, as shown in Table 1 below, and is used to control the opening degrees of dampers such as ABA, AB, ABB, BCB, BC, BCC, CDC, CD, CDD, DED, DE, DEE, EFE, EF, EFF, etc.;

[0047] Table 1 Control value of the differential pressure between the furnace wind box

[0048]

[0049] Among them, the control values of the opening degrees of the under-fire air UFA and the bottom combustion air AA dampers are as shown in Tables 2 - 3 below;

[0050] Table 2 Control value of the UFA / AA damper opening degree (when A mill is in operation)

[0051]

[0052] Table 3 Control value of the UFA / AA damper opening degree (when A mill is not in operation)

[0053]

[0054] The opening control values of the perimeter air dampers A, B, C, D, and E are as shown in Table 4 below;

[0055] Table 4 Fuel Air (Perimeter Air) Damper Control Values

[0056]

[0057] The opening control values of the top combustion air damper FF and the compact overfire air damper CCOFA are as shown in Tables 5 to 6;

[0058] Table 5 FF / CCOFA Damper Opening Control Values (When F Coal Mill is in Operation)

[0059]

[0060] Table 6 FF / CCOFA Damper Opening Control Values (When F Coal Mill is not in Operation)

[0061]

[0062] The opening control value of the low overfire air (LSOFA) damper is as shown in Table 7;

[0063] Table 7 Low Overfire Air (LSOFA) Damper Control Values

[0064]

[0065] The opening control values of the high overfire air HSOFA-A and HSOFA-B dampers are as shown in Table 8;

[0066] Table 8 High Overfire Air (HSOFA-A, HSOFA-B) Damper Control Values

[0067]

[0068] Analyze the above data. According to the analysis data, the opening of the second upper high overfire air damper and the opening of the top high overfire air damper are used as important means to control the NO x emission concentration during deep peak shaving. The difference between the measured value of the operating oxygen content and the preset value of the operating oxygen content, and the difference between the measured value of the operating oxygen content and the pre-preset value of the operating oxygen content are used to calculate the logic control value of the damper opening as shown in Table 8 below. The specific modified logic control value of the damper opening after calculation is shown in Tables 9 to 10;

[0069] Table 8 Calculate the Logic Control Value of the Damper Opening Based on the Difference between the Measured Value of the Operating Oxygen Content and the Preset Value of the Operating Oxygen Content

[0070]

[0071] Table 9 Logic Control Value of HSOFA-C Damper Opening

[0072]

[0073] Table 10 Logic control values for the opening of the HSOFA-D damper

[0074]

[0075] S4: Verification of the optimal air damper opening control curve;

[0076] The rated load preferably ranges from 30% to 50%. When the unit operates at 30% - 50% of the rated load, under deep peak shaving, the flame signal is stable, but the NO x emission concentration level is between 310 mg / m 3 and 350 mg / m 3 (as shown in Figure 1 ). At this rated load, the pre-set value of the collected operating oxygen content is 5.50%, and the actual value of the collected operating oxygen content is 7.80%. The difference between the actual value and the pre-set value of the operating oxygen content is calculated as 7.80% - 5.00% = 2.80%. The corresponding oxygen content range is obtained through the difference calculation. The calculation formula for the 21.0% oxygen content range is 2.80% / 21.0% = 13.3%. The logic control value of the air damper opening is obtained by linear interpolation according to Table 8. The calculation formula for the logic control value of the air damper opening is 30 * (13.3 - 10) / 90 + 50 = 51.1. At this time, according to Table 9, the opening value of the upper secondary overfire air damper (HSOFA-C) is calculated by linear interpolation according to the logic control value of the air damper opening, and the upper secondary overfire air damper (HSOFA-C) is fully opened. At this time, according to Table 10, the opening value of the top overfire air damper (HSOFA-D) is calculated by linear interpolation according to the logic control value of the air damper opening. The calculation formula for the opening value of the top overfire air damper (HSOFA-D) is 75 * (51.1 - 50) / 50 + 5 = 6.65%. The top overfire air damper (HSOFA-D) is slightly opened, so that the measured value of the operating oxygen content is gradually reduced to the pre-set value of the operating oxygen content of 5.50%, thereby achieving the purpose of reducing the NO x emission concentration. According to the air damper opening value, verify the adaptability of the air damper opening control curve and solidify it. When the unit operates at 30% - 50% of the rated load, the flame signal is stable. Under deep peak shaving, the NO x emission concentration level is between 145 mg / m 3 and 175 mg / m 3 (as shown in Figure 2 ), which is beneficial to the control of ammonia escape. From Figure 2In this case, we can observe that the NO emission concentration can be reduced by the air damper opening control method for deep peak shaving of the present invention. x Therefore, the air damper opening control method for deep peak shaving provided by the present invention, on the premise of ensuring the stable combustion of the unit, through reasonable control of the air damper opening, controls the NO at the denitration inlet x at a relatively low level.

[0077] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all changes or equivalent replacements that fall within the scope of the claims of this application. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments that fall within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A control method for the opening degree of the air damper under deep peak shaving, characterized in that, It includes the following steps: Selection of S1 data parameters, collecting and retrieving unit load parameters, economizer outlet oxygen content parameters, NO x emission concentration parameters, damper opening parameters and flame signal parameters as deep peak shaving data; Analysis of the deep peak shaving data, selecting the parameters of the unit operating at the rated load for key analysis, and analyzing the corresponding relationships of the damper opening parameters, the oxygen content at the economizer outlet, the NO x emission concentration parameters and the flame signal parameters to obtain the analysis data; Modification of the S3 damper opening logic control value. Based on the analysis data, the influence degree of the key damper opening on the NO x emission concentration was determined. By repeating step S2 and modifying the damper opening logic control value multiple times, the purpose of reducing the NO x emission concentration under deep peak shaving was achieved; Verification of the air damper opening control curve. Under deep peak shaving, while taking into account the stable combustion of the unit, when the unit is operating at the rated load, the logical control value of the air damper opening is used to calculate the air damper opening value through linear interpolation. According to the air damper opening value, the adaptability of the air damper opening control curve is verified and solidified for controlling the air damper opening under deep peak shaving.

2. The damper opening control method for deep peak shaving under the premise of claim 1, characterized in that Analysis of the deep peak shaving data in step S2, specifically including the following steps: When the unit is operating at the rated load, the NO x emission concentration is positively correlated with the oxygen content at the economizer outlet, and the oxygen content at the economizer outlet is inversely correlated with the opening degree of the over-fire air damper.

3. The damper opening control method for deep peak shaving according to claim 1, wherein In step S3, according to the analysis data, the opening degrees of the second upper overfire air damper and the topmost overfire air damper are determined as the key damper opening degrees to enable the control of the NO x emission concentration.

4. The damper opening control method for deep peak shaving under the premise of claim 1, characterized in that, Verification of the air damper opening control curve in step S4 specifically includes the following steps: Under the condition of the unit operating at the rated load and during deep peak shaving, with the flame signal stable, collect the pre-set value and the actual value of the operating oxygen content of the unit in the rated load range, calculate the difference between the actual value and the pre-set value of the operating oxygen content, obtain the corresponding oxygen content range through the difference calculation, calculate the logical control value of the air damper opening according to the corresponding oxygen content range by linear interpolation, obtain the air damper opening value through linear interpolation according to the logical control value of the air damper opening, verify the adaptability of the air damper opening control curve according to the air damper opening value and solidify it, which is used to control the air damper opening during deep peak shaving, so as to gradually reduce the actual value of the operating oxygen content to the pre-set value of the operating oxygen content in order to achieve the purpose of reducing the NO x emission concentration.

5. The damper opening control method for deep peak shaving under the windward side according to claim 1, characterized in that, The rated load is 20% - 50%.

6. The method for controlling the opening degree of the air damper under deep peak shaving according to claim 1, characterized in that, The unit includes: a primary air box, in which there are at least 6 layers of enhanced ignition pulverized coal nozzles, and fuel air is arranged around the pulverized coal nozzles. The differential pressure of the primary air box of the unit is 30 - 110 mmH2O.

7. The method for controlling the opening degree of the downwind damper according to claim 6, wherein One layer of auxiliary air nozzles is arranged between every two adjacent layers of pulverized coal nozzles. The auxiliary air nozzles include: auxiliary air nozzles with horizontally deflected angles arranged oppositely.

8. The damper opening control method for deep peak shaving under the windward side according to claim 7, characterized in that One layer of top combustion air damper and two layers of compact overfire air dampers are arranged at the upper part of the primary air box, and one layer of bottom combustion air damper and one layer of underfire air damper are arranged at the lower part of the primary air box.

9. The damper opening control method for deep peak shaving under the downwind as claimed in claim 8, wherein, Four layers of independent horizontally swingable low-level overfire air dampers are respectively arranged at the position 4.0 m - 4.5 m from the center line of the upper burner at the upper part of the primary air box, and four layers of independent horizontally swingable high-level overfire air dampers are respectively arranged at the position 8.5 m - 9.0 m from the center line of the upper burner.

10. The method for controlling the opening degree of the air damper under deep peak shaving according to claim 9, wherein The high-level overfire air dampers are successively provided with the uppermost high-level overfire air damper, the second uppermost high-level overfire air damper, the middle high-level overfire air damper, and the lower high-level overfire air damper from top to bottom along the height direction of the unit.

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