A control method for the secondary air box damper of a pulverized coal boiler with a coal pulverizing system

Abstract

This invention discloses a method for controlling the dampers of the secondary air boxes in a counter-firing pulverized coal boiler. For air boxes in non-operational burners, the damper opening is set to 10%~30%. For damper control of each air box in operation burners, the method includes: A) using the formula K = k cl k qh k g k pf The opening degree K of each damper is calculated by multiplying by 100%, where k cl =B i / B max This is a correction factor for the output of the coal mill, corresponding to the output B of the coal mill used in the burner layer. i Of all the coal mills in operation, the one with the highest output B max The ratio; k qh k is the correction factor for the position of the front and rear wall bellows. g k is the correction factor for the height of the wind box. pf: A) Correction coefficient for air distribution method; B) Input each K value into the damper control system and adjust each damper to the corresponding opening degree; This invention can improve the uniformity and rationality of the air-coal ratio of different layers of burners, improve combustion efficiency, reduce pollutant emissions, air supply system resistance and fan power consumption, and improve the overall operating performance of the boiler.

Description

Technical Field

[0001] This invention relates to a control method for the damper of the secondary air box in a pulverized coal combustion boiler. Background Technology

[0002] As a major type of large-capacity power generation equipment, the combustion system of counter-firing pulverized coal boilers typically consists of one to two layers of burners per coal mill. Burners on the front and rear walls at the same elevation are each considered a separate layer. Each layer of burners has an independent secondary air box (hereinafter referred to as the air box). Each air box has remotely operated dampers on both sides in the furnace width direction, and the air volume can be adjusted independently. The purpose of controlling the damper opening is to control the air-to-coal ratio (air volume to pulverized coal volume) of each burner layer. If the air volume measurement is accurate, it can be directly controlled. However, in actual operation, air volume measurement often has significant errors. Therefore, actual control generally involves adjusting the damper opening of each layer's air box.

[0003] Current airflow control in the secondary air boxes, i.e., damper opening control, mainly relies on the ratio of the output of the corresponding layer of coal mills (burners) to their rated output. For example, if the output of all five mills is 75% of their rated output, then the damper opening of the corresponding layer of air boxes will be 75%, with each damper actuator and position feedback sensor working together to adjust each damper to the corresponding opening. Alternatively, if one coal mill has an output of 70% of its rated output and the other four have an output of 100% of their rated output, then the damper opening of the layer of air boxes will be 100%. This approach does not take into account the differences in output of each coal mill, duct and air box structure, damper characteristics, and special air distribution methods. As a result, the accuracy of the damper opening of each secondary air box relative to the actual air distribution requirements is poor, which can easily lead to uneven air-coal ratios in different layers of burners, affecting combustion efficiency, reducing boiler efficiency, increasing pollutant emissions, increasing air supply system resistance and fan power consumption, and ultimately reducing the overall operating performance of the boiler. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned shortcomings of existing technologies by providing a method for controlling the dampers of the secondary air boxes in a counter-firing pulverized coal boiler. This method proposes a layer-by-layer damper opening control function, introducing correction coefficients for pulverizer output, front and rear wall air box positions, height-direction layer air box correction coefficients, and air distribution method correction coefficients. This improves the accuracy of the damper openings of each secondary air box relative to actual air distribution needs, enhances the uniformity and rationality of the air-coal ratio in different layers of burners, improves combustion efficiency, reduces pollutant emissions, air supply system resistance, and fan power consumption, and ultimately improves the overall operating performance of the boiler.

[0005] To achieve the above objectives, the present invention provides a method for controlling the dampers of the secondary air boxes in a counter-firing pulverized coal boiler. For each secondary air box corresponding to each burner on the front and rear walls, the damper opening of the air box for the non-operational burner is set to 10%~30%. The method is characterized by the following steps for controlling the dampers of each air box for the operational burners: A) using the formula K = k cl k qh k g k pf The opening degree K of each damper is calculated by multiplying by 100%, where k cl =B i / B max This is a correction factor for the output of the coal mill, corresponding to the output B of the coal mill used in the burner layer. i Of all the coal mills in operation, the one with the highest output B max The ratio; k qh The correction coefficient for the positions of the front and rear wall bellows is given by k. qh The value is 1.0, and the rear wall bellows is k. qh Smaller than the front wall bellows k qh ;k g The lower-level bellows height correction factor is k. g The value is 1.0, and the k values ​​of the bellows layers above it are... g Decreasing sequentially; k pf: A) The K value is used as the correction coefficient for the air distribution method; B) The K values ​​are input into the damper control system, and the damper actuators and position feedback sensors work together to adjust each damper to the corresponding opening degree.

[0006] This invention proposes a layered air box damper opening control function K = k cl k qh k g k pf ×100%, where the mill output correction coefficient can be adjusted to change the damper opening according to the output of each mill. The smaller the output, the smaller the corresponding opening and air volume. For counter-firing pulverized coal boilers, the secondary air ducts usually extend from the rear wall to the front wall, with the air source closer to the rear wall's air box. Secondary air on the same side of the wall enters each air box from top to bottom, with the air source closer to the upper air box, resulting in higher air pressure. Therefore, the correction coefficient k for the front and rear wall air box positions is... qh and layer air box height correction factor k g The front wall bellows, further away from the air source qh The value is 1.0, and the rear wall bellows is k. qh Smaller than the front wall bellows k qh The lower-level bellows, further away from the air source g The value is 1.0, and the k values ​​of the bellows layers above it are... gBy decreasing sequentially, more uniform airflow can be achieved in each layer of the wind box under the same pulverized coal output. Furthermore, for conventional counter-firing pulverized coal boilers with standard technical parameters, the rear wall wind box k... qh Take a value of 0.85-0.95, and set the k value for each layer of bellows above the lower bellows. g值 Decreasing by 0.05-0.15 sequentially is more accurate; to improve boiler efficiency when burning different coal types, reduce pollutant emissions, and control steam parameters, different air distribution methods may be needed along the furnace height, including: uniform air distribution, upright pagoda-shaped air distribution, inverted pagoda-shaped air distribution, constricted air distribution, and bulging air distribution. For conventional counter-firing pulverized coal boilers with standard technical parameters, uniform air distribution, and the k value of each layer of air box... pf: Both are 1.0; for the pagoda-type air distribution system, the lower air box k pf: The value is 1.0, and the k values ​​of the bellows layers above it are... pf: Decrease by 0.05-0.15 sequentially; inverted pagoda-shaped air distribution method, upper air box k pf: The value is 1.0, and the k values ​​of the bellows layers below it are... pf: Decrease sequentially by 0.05-0.15; for waist-shaped air distribution systems with three or more layers of air boxes, the lower and upper air boxes k pf: All are 1.0, intermediate layer bellows k pf: The value is 0.75-0.85, with a drum-shaped air distribution system and an intermediate layer air box (k). pf: The value is 1.0, and the lower and upper air boxes are k. pf: All are 0.75-0.85k pf: This is relatively accurate; the damper opening of the stratum air box for stratum burners not in operation should be maintained at 10%~30% to provide cooling air to the burner nozzles and prevent nozzle coking and overheating damage. This invention improves the accuracy of the opening degree of each secondary air box damper to the actual air distribution requirements by introducing the opening degree coefficient K of the damper of each air box and optimizing the control of air volume. It also improves the uniformity and rationality of the air-coal ratio of different layers of burners, which can improve combustion efficiency, reduce pollutant emissions, air supply system resistance and fan power consumption, and improve the overall operating performance of the boiler. As a further improvement of the present invention, several dead zone widths are set in the damper control system for the damper opening control logic of each layer of the air box. When the K value changes due to the change in the output of the coal mill but all changes are within the same dead zone width, the damper actuators do not operate and the dampers maintain the same opening. Only when the K value changes beyond the dead zone width, each damper actuator cooperates with the position feedback sensor to adjust each damper to the corresponding opening. In actual operation, the output of the coal mill often fluctuates. By setting several dead zone widths, the damper opening can be controlled in segments, which can avoid continuous operation of the damper actuators and extend their service life. In summary, this invention can improve the accuracy of the opening degree of each secondary air box damper with the actual air distribution requirements, improve the uniformity and rationality of the air-coal ratio of different layers of burners, improve combustion efficiency, reduce pollutant emissions, air supply system resistance and fan power consumption, and improve the overall operating performance of the boiler. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of the structure of a pulverized coal boiler burner system employing the present invention.

[0008] Figure 2 for Figure 1 Top view.

[0009] Figure 3 for Figure 1 The left view.

[0010] Figure 4 for Figure 1 The right view.

[0011] Figure 5 This is a logic curve diagram for controlling the damper opening of the lower air box on the front wall in an embodiment of the present invention. Detailed Implementation

[0012] The present invention will now be described in further detail with reference to the accompanying drawings.

[0013] like Figures 1 to 4 As shown, the counter-firing pulverized coal boiler burner system of the present invention includes a front wall air box 1, a rear wall air box 2, and secondary air ducts 3 on both sides. The front wall air box 1 is divided into a front wall upper air box 4, a front wall middle air box 5, and a front wall lower air box 6 by a partition. The rear wall air box 2 is divided into a rear wall upper air box 7, a rear wall middle air box 8, and a rear wall lower air box 9 by a partition. Each air box corresponds to eight burners 10, and each air box is provided with dampers 11 on both sides. During operation, the burner in the upper-level wind box 4 on the front wall is not in operation, while the other wind boxes 5 to 9 are all in operation. In this embodiment of the invention, a method for controlling the dampers of the secondary wind boxes in a counter-firing pulverized coal boiler involves setting the damper opening of the upper-level wind box 4 (which is not in operation) to 30% to provide cooling air to the burner nozzles, preventing nozzle coking and overheating damage. The damper control for the other wind boxes 5 to 9 includes the following steps: A) Using the formula K = k cl k qh k g k pf The opening degree K of each damper is calculated by multiplying by 100%, where k cl =B i / B max This is a correction factor for the output of the coal mill, corresponding to the output B of the coal mill used in the burner layer. i Of all the coal mills in operation, the one with the highest output B maxThe ratio of B to the middle layer air box 5 on the front wall, the lower layer air box 6 on the front wall, and the lower layer air box 9 on the rear wall. i All are 100%, B of the upper air box 7 on the rear wall. i , for 90%, the middle layer of the rear wall air box 8 of B i If it is 80%, then the k of the middle layer air box 5 on the front wall, the lower layer air box 6 on the front wall, and the lower layer air box 9 on the rear wall is... cl The value is 1.0, and the k value of the upper air box 7 on the rear wall is 7. cl The value is 0.9, and the k value of the middle layer air box in the rear wall is 8. cl It is 0.8; k qh The correction coefficients for the positions of the front and rear wall bellows are k, where k is the value of the two bellows layers 5 and 6 on the front wall. qh All are 1.0, and the three-layer bellows on the rear wall have k values ​​of 7, 8, and 9. qh Smaller than the front wall bellows k qh Both are 0.9; k g The k value is the correction factor for the height of the lower-level air box 6 on the front wall and the lower-level air box 9 on the rear wall. g The value is 1.0, and the k values ​​of the bellows layers above it are... g The k values ​​decrease sequentially, for the middle layer air box 5 on the front wall and the middle layer air box 8 on the rear wall. g Both are 0.9, and the k of the upper bellows on the rear wall is 7. g , is 0.8; k pf: As a correction factor for the air distribution method, in this embodiment, air boxes 5 to 9 on each floor adopt an equal air distribution method, and the air box k on each floor... pf: All are 1.0; therefore, the opening degree K of each damper corresponding to the middle layer air box 5, the lower layer air box 6, the upper layer air box 7, the middle layer air box 8, and the lower layer air box 9 of the rear wall is calculated to be 90%, 100%, 64.8%, 64.8%, and 90% respectively; B) In the damper control system, several dead zone widths are set for the damper opening control logic of each layer air box (the control logic curve of the damper opening K of the lower layer air box 6 of the front wall is as follows). Figure 5 As shown, the control logic curves for the damper opening K of the remaining air boxes are similar. The calculated K values ​​are input into the damper control system. Based on the dead zone width of each K value, the damper actuators, in conjunction with the position feedback sensors, adjust each damper to the corresponding opening. When the K value changes due to the change in the coal mill output but remains within the same dead zone width, the damper actuators do not operate, and the dampers maintain the same opening. Only when the K value changes beyond the dead zone width does the damper actuators, in conjunction with the position feedback sensors, adjust each damper to the corresponding opening. This invention proposes a layered air box damper opening control function K = k cl k qh k g k pf×100%, where the mill output correction coefficient can be adjusted to change the damper opening according to the output of each mill. The smaller the output, the smaller the corresponding opening and air volume. For counter-firing pulverized coal boilers, the secondary air duct 3 usually extends from the rear wall to the front wall. The air source is closer to the rear wall's layer air box. The air pressure of the upper layer air box 7, middle layer air box 8, and lower layer air box 9 on the rear wall is greater than that of the air boxes on the front wall. Similarly, the secondary air on the same side of the wall enters each layer air box from top to bottom. The air source is closer to the upper layer air box, and its air pressure is also greater. Therefore, the correction coefficient k for the position of the front and rear wall air boxes is... qh and layer air box height correction factor k g The front wall bellows, located further away from the wind source, will be placed... qh Set to 1.0, rear wall bellows k qh Smaller than the front wall bellows k qh The lower-level bellows, further away from the air source g Set to 1.0, and the bellows k of each layer above it g By decreasing sequentially, the airflow in each layer of the wind box can be made more uniform under the same pulverized coal output. Furthermore, for conventionally designed counter-firing pulverized coal boilers, the airflow calibration test under steady-state wind pressure can be used to measure the k value of the rear wall wind box. qh For 0.85-0.95, the k of each layer of air box above the lower air box g Decreasing the airflow by 0.05-0.15 sequentially can achieve relatively accurate uniformity of airflow in each layer of the bellows. To adapt to the combustion of coals of different qualities, improve combustion efficiency, reduce pollutant emission requirements, reduce air supply system resistance, fan power consumption, and control steam parameters, thereby improving the overall operating performance of the boiler, it is necessary to adopt different air distribution methods. Existing air distribution methods include: equal air distribution, upright pagoda-type air distribution, inverted pagoda-type air distribution, waist-reducing air distribution, and waist-bulging air distribution. For conventional counter-firing pulverized coal boilers with conventional technical parameters, the airflow calibration test under steady-state air pressure is used to measure the k of each layer of the bellows in the equal air distribution method. pf: Both are 1.0; for the pagoda-type air distribution system, the lower air box k pf: The value is 1.0, and the k values ​​of the bellows layers above it are... pf: Decrease by 0.05-0.15 sequentially; inverted pagoda-shaped air distribution method, upper air box k pf: The value is 1.0, and the k values ​​of the bellows layers below it are... pf: Decrease sequentially by 0.05-0.15; for waist-shaped air distribution systems with three or more layers of air boxes, the lower and upper air boxes k pf: All are 1.0, intermediate layer bellows k pf: The value is 0.75-0.85, with a drum-shaped air distribution system and an intermediate layer air box (k). pf: The value is 1.0, and the lower and upper air boxes are k. pf: All are 0.75-0.85k pf: This ensures more accurate uniformity of airflow in each layer of the bellows. This invention, by introducing an opening coefficient K for the dampers of each layer of the secondary air box and optimizing the control of air volume, can improve the accuracy of the damper opening of each secondary air box relative to the actual air distribution requirements, improve the uniformity and rationality of the air-coal ratio in different layers of burners, enhance combustion efficiency, reduce pollutant emissions, reduce air supply system resistance and fan power consumption, and improve the overall operating performance of the boiler; coefficient k qh k g The structural parameters of the air supply system can be obtained through experimental calibration within different load (air volume) ranges, with coefficient k. pf The three coefficients can also be determined through combustion optimization tests under different coal types fed into the boiler. These three coefficients are constant values ​​during the same combustion process in the boiler, but the output of the coal mill will often fluctuate during the same combustion process, i.e., coefficient k cl Fluctuations will frequently occur, causing frequent fluctuations in the damper opening K value. In this embodiment, the control logic curve diagram of the damper opening K of the lower air box 6 on the front wall is as follows: Figure 5 The stepped shape shown in the figure achieves segmented control of the damper opening by setting several dead zone widths, which can avoid continuous operation of the damper actuator and extend its service life; the damper opening control logic curves of the other layers of the air box are set in a similar way.

Claims

1. A method for controlling the dampers of the secondary air boxes in a counter-firing pulverized coal boiler, wherein the damper opening of the secondary air boxes corresponding to each layer of burners on the front and rear walls is set to 10%~30% for the layer of burners not in operation; characterized in that: For the damper control of each air box of the burner in operation, the following steps are included: A) Using the formula K = k cl k qh k g k pf The opening degree K of each damper is calculated by multiplying by 100%, where k cl =B i / B max This is a correction factor for the output of the coal mill, corresponding to the output B of the coal mill used in the burner layer. i Of all the coal mills in operation, the one with the highest output B max The ratio; k qh The correction coefficient for the positions of the front and rear wall bellows is given by k. qh The value is 1.0, and the rear wall bellows is k. qh Smaller than the front wall bellows k qh ;k g The lower-level bellows height correction factor is k. g The value is 1.0, and the k values ​​of the bellows layers above it are... g Decreasing sequentially; k pf: A) The K value is used as a correction coefficient for the air distribution method; B) The K values ​​are input into the damper control system, and each damper actuator, in conjunction with the position feedback sensor, adjusts each damper to the corresponding opening degree; wherein the rear wall air box k qh The value is 0.85-0.95; the value of each bellows above the lower bellows is k. g Decrease successively by 0.05-0.15; k pf: For a uniform air distribution method, the air box k of each floor pf: Both are 1.0; for the pagoda-type air distribution system, the lower air box k pf: The value is 1.0, and the k values ​​of the bellows layers above it are... pf: Decrease by 0.05-0.15 sequentially; inverted pagoda-shaped air distribution method, upper air box k pf: The value is 1.0, and the k values ​​of the bellows layers below it are... pf: Decrease sequentially by 0.05-0.15; for waist-shaped air distribution systems with three or more layers of air boxes, the lower and upper air boxes k pf: All are 1.0, intermediate layer bellows k pf: The value is 0.75-0.85, with a drum-shaped air distribution system and an intermediate layer air box (k). pf: The value is 1.0, and the lower and upper air boxes are k. pf: All are between 0.75 and 0.

85.

2. The method for controlling the damper of the secondary air box in a pulverized coal boiler with counter-firing combustion according to claim 1, characterized in that: The output of the coal mill B i and B max The output is measured by the output meter of each coal mill.

3. A method for controlling the damper of the secondary air box in a pulverized coal boiler with counter-firing combustion, as described in claim 1 or 2, characterized in that: In step B), several dead zone widths are set in the damper control system for the damper opening control logic of each layer of the air box. When the K value changes due to the change in the output of the coal mill but all within the same dead zone width, the damper actuators do not operate and the dampers maintain the same opening. Only when the K value changes beyond the dead zone width will each damper actuator cooperate with the position feedback sensor to adjust each damper to the corresponding opening.

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