A method and system for distributing secondary air in a boiler windbox

Abstract

The present application provides a kind of boiler air bellow secondary air distribution method and system, belong to coal-fired boiler combustion and secondary air distribution control technical field, for the uneven air distribution of existing layer air bellow along the width direction of furnace, the problem that side burner is easy to lack oxygen and regional air volume is difficult to independently adjust.First air supply path and second air supply path respectively supply air to the side air supply area and the middle air supply area of layer air bellow;Total secondary air demand is determined according to the operation state of burner layer and benchmark distribution is carried out, side air supply demand, middle air supply reduction amount and path transfer amount are determined, the minimum value in three is used to determine actual transfer amount, according to which the side target air volume is increased and the middle target air volume is reduced, and the flow state of the two air supply paths is adjusted.The present application can redistribute furnace width direction air volume under the condition of keeping the total secondary air demand of burner layer unchanged, improve the oxygen deficiency and near-wall reducing atmosphere of side, and improve the controllability of regional air distribution and the safety of boiler operation.

Description

Technical Field

[0001] This invention belongs to the field of combustion and secondary air distribution control technology of coal-fired boilers, specifically relating to a method and system for secondary air distribution in a boiler air box. Background Technology

[0002] During the operation of a coal-fired boiler, secondary air is mainly used to supplement the air required for fuel combustion, organize the airflow in the furnace, and regulate the oxygen distribution in the combustion zone. Its supply status has a significant impact on combustion stability, burnout degree, nitrogen oxide generation, and the safe operation of the furnace heating surfaces. For opposed-wall combustion boilers, multiple burners are usually arranged in layers along the width of the furnace. Secondary air for the same burner layer is supplied to the secondary air layer air box through the secondary air layer duct, and then distributed to each burner in that layer by the secondary air layer air box.

[0003] Existing secondary air tiered wind boxes typically employ an end-inlet structure, meaning secondary air enters the tiered wind box through secondary air dampers located at one or both ends and is distributed along the width of the furnace within the tiered wind box. Due to the large width of the tiered wind box, and variations in damper outlet cross-section, air inlet direction, duct bends, and flow resistance at different burner positions, secondary air entering the tiered wind box easily forms localized high-speed jets, recirculation zones, and low-speed zones, resulting in uneven pressure and airflow distribution along the furnace width. In some boilers, this leads to a phenomenon where the secondary airflow to the central burners is excessive while that to the burners near the side walls is insufficient. The area near the side walls is prone to localized oxygen-deficient combustion and a reducing atmosphere, leading to increased levels of carbon monoxide, hydrogen sulfide, and other components, and increasing the risk of high-temperature corrosion of the side wall water-cooled walls. Furthermore, ash accumulation is easily generated in the recirculation and low-speed zones within the wind box.

[0004] To address the aforementioned issues, existing technologies typically employ methods such as installing baffles, guide vanes, or flow equalization structures within the air duct or air box, increasing secondary air branches or inlet positions, and altering the opening degrees of dampers corresponding to different burners to improve air distribution. Some control methods also adjust secondary dampers based on boiler load, coal feed rate, oxygen content, carbon monoxide concentration, air box pressure, or actual burner airflow. However, baffles, guide vanes, and multi-point inlet structures generally focus on improving the overall flow field or enhancing airflow uniformity, making it difficult to quantitatively allocate air according to the different actual air distribution needs of the side and central air supply areas. When only the opening degrees of individual dampers are adjusted within a shared air box, pressure coupling still exists between different burner areas, and the damper opening degree does not correspond to a fixed airflow; the same opening degree change may produce different airflow changes under different air box pressures and path resistance conditions.

[0005] Furthermore, existing side-mounted air supply and central-mounted air reduction methods typically lack clearly defined regional air volume transfer boundaries. When the flow capacity of the side-mounted air supply path is insufficient, further reducing the air supply to the central burner will not result in a corresponding increase in air volume for the side burner; on the contrary, it may lead to insufficient oxygen supply or decreased combustion stability in the central burner. Directly increasing the total secondary air volume of this burner layer may also alter the original air-coal ratio and staged combustion state of the boiler.

[0006] Therefore, existing technologies still need to address how to redistribute the secondary air in the furnace width direction in a constrained manner, taking into account the makeup air demand of the side area, the adjustment space of the central air supply area, and the flow state of different air supply paths, while meeting the total secondary air demand of the burner layer, and how to ensure that the redistribution results actually act on different burner areas through the corresponding air supply paths. Summary of the Invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art, and to provide a method and system for secondary air distribution in a boiler wind box.

[0008] This invention provides a method for secondary air distribution in a boiler air box. The method uses a first air supply path to supply air to the side air supply area of ​​the secondary air box, and uses a second air supply path to supply air to the central air supply area of ​​the secondary air box, which is separated from the side air supply area. The method includes the following steps: S1. Obtain the current operating status of the burner layer, determine the total secondary air demand of the current burner layer based on the operating status, and allocate the total secondary air demand between the side air supply area and the central air supply area to obtain the reference secondary air volume of each area. S2. Determine the side air supply demand and the middle reduction margin based on the operating status and the reference secondary air volume of each area, and determine the smaller of the air increase margin of the first air supply path under the current flow state and the air reduction margin of the second air supply path under the current flow state as the path transfer margin. S3. Determine the minimum value among the side air supply demand, the central reduction margin, and the path transfer margin as the actual transfer amount; determine the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area according to the relationship of adding the actual transfer amount to the benchmark secondary air volume of the side air supply area and reducing the actual transfer amount to the benchmark secondary air volume of the central air supply area. The sum of the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area is equal to the total secondary air demand. S4. Based on the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area, adjust the flow state of the first air supply path and the second air supply path respectively, so as to supply air to the corresponding air supply area according to the corresponding target secondary air volume.

[0009] Furthermore, based on the total secondary air demand and the fuel supply status of the burners corresponding to the side air supply area and the central air supply area, the corresponding reference secondary air volume is determined; based on the fuel supply status and regional combustion status of the burners corresponding to the side air supply area, the air distribution demand of the side air supply area is determined, and the portion of the air distribution demand of the side air supply area that exceeds its reference secondary air volume is determined as the side make-up air demand.

[0010] Specifically, the non-negative difference obtained by subtracting the sum of the minimum air distribution requirement and the safety margin of the central air supply area from the baseline secondary air volume of the central air supply area is determined as the central adjustment margin; the air increase margin is determined by subtracting the current air supply volume from the upper limit of the air supply volume of the first air supply path, and the air reduction margin is determined by subtracting the lower limit of the air supply volume from the current air supply volume of the second air supply path.

[0011] Specifically, based on the pressure difference between the first air supply path and the second air supply path, as well as the predetermined flow state and the correspondence between the pressure difference and the air supply volume, the target flow state corresponding to the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area are determined respectively, and the first air supply path and the second air supply path are adjusted according to the corresponding target flow state.

[0012] Preferably, the actual secondary air volume of the adjusted side air supply area and the central air supply area is obtained, the difference between the actual secondary air volume of the side air supply area and its reference secondary air volume is determined as the actual increase in air volume, the difference between the reference secondary air volume of the central air supply area and its actual secondary air volume is determined as the actual decrease in air volume, and the transfer matching deviation is determined based on the difference between the actual increase in air volume and the actual decrease in air volume.

[0013] Specifically, the actual transfer amount is corrected according to the transfer matching deviation, and the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area are re-determined based on the corrected actual transfer amount, and the flow state of the first air supply path and the second air supply path is further adjusted.

[0014] Furthermore, when the actual increase in air volume is less than the actual transfer volume, the second air supply path is controlled to ensure that the actual decrease in air volume does not exceed the actual increase in air volume, and the increase in the actual transfer volume is stopped.

[0015] Another aspect of the present invention provides a boiler air box secondary air distribution system, comprising: A secondary air layer air box is installed in the burner layer of the boiler. The secondary air layer air box has a central air supply area and a side air supply area along the width of the furnace. The central air supply area and the side air supply area are separated by a partition. The secondary air duct is connected to the side air supply area via the end secondary air damper to form the first air supply path; The diversion air box has its inlet connected to the secondary air layer duct upstream of the end secondary air damper, and its outlet connected to the central air supply area via the central air inlet located in the middle of the secondary air layer air box. The inlet of the diversion air box is provided with a diversion air box damper to form a second air supply path. The status acquisition unit is used to acquire the operating status of the burner layer and the flow status of the first air supply path and the second air supply path; and The control unit is signal-connected to the status acquisition unit, the actuator of the end secondary air damper, and the actuator of the diversion box damper, respectively. It is used to determine the total secondary air demand of the burner layer based on the operating status, and to perform a baseline allocation of the total secondary air demand between the side air supply area and the middle air supply area; to determine the side makeup air demand and the middle reduction margin based on the operating status and the baseline allocation result, and to determine the path transfer margin based on the current flow state of the first and second air supply paths; to determine the minimum value among the side makeup air demand, the middle reduction margin, and the path transfer margin as the actual transfer amount, and to increase the baseline secondary air volume of the side air supply area and decrease the baseline secondary air volume of the middle air supply area using the actual transfer amount, thereby obtaining the target secondary air volume for both air supply areas; and to control the actuators of the end secondary air damper and the diversion box damper respectively based on the corresponding target secondary air volume.

[0016] Furthermore, the side air supply area includes a left air supply area and a right air supply area located on both sides of the central air supply area. The first air supply path includes a left air supply branch and a right air supply branch that are connected to the left air supply area and the right air supply area respectively via two end secondary air dampers. The distribution box has two inlets connected to the secondary air layer duct. The two inlets are respectively provided with the distribution box dampers and supply air to the central air inlet together. The control unit controls the actuators of the two end secondary air dampers according to the make-up air demand of the left air supply area and the right air supply area, and coordinates the control of the actuators of the two distribution box dampers according to the target secondary air volume corresponding to the central air supply area.

[0017] Specifically, the system further includes a zone combustion status detection device and air supply status detection devices corresponding to the first air supply path and the second air supply path, respectively. The air supply status detection device is used to obtain the air supply volume and pressure difference of the corresponding air supply path. The zone combustion status detection device and the air supply status detection device are respectively signal-connected to the status acquisition unit. The control unit determines the side air supply demand based on the detection result of the zone combustion status detection device, determines the path transfer margin based on the detection result of the air supply status detection device, determines the transfer matching deviation based on the difference between the adjusted actual air increase volume and the actual air decrease volume, and corrects the actual transfer amount based on the transfer matching deviation.

[0018] The beneficial effects of this invention are as follows: This invention supplies air to the side and central air supply areas of the secondary air layer box via different air supply paths. While meeting the total secondary air demand of the burner layer, it transfers a portion of the central secondary air to the side based on the side air supply requirements, the central reduction margin, and the path transfer margin, thus redistributing the secondary air volume along the furnace width. By determining the damper flow state in conjunction with the air supply path pressure difference, and by limiting and correcting based on the matching relationship between the actual increase in air volume on the side and the actual decrease in air volume in the central area, it avoids regional air supply mismatch, improves oxygen-deficient combustion in the side burners and the reducing atmosphere near the side walls, and enhances the controllability of regional air distribution, combustion uniformity, and boiler operational safety. Attached Figure Description

[0019] Figure 1 This is a flowchart of a boiler wind box secondary air distribution method according to a specific embodiment of the present invention; Figure 2 This is a connection block diagram of a boiler wind box secondary air distribution system according to a specific embodiment of the present invention; Figure 3 This is a schematic diagram of a boiler wind box secondary air supply structure according to a specific embodiment of the present invention; Figure 4 This is a schematic diagram of the internal structure of a flow divider box according to a specific embodiment of the present invention; Figure 5 This is a schematic diagram of the secondary air layer wind box partition structure according to a specific embodiment of the present invention.

[0020] Among them, 11 is the front wall, 12 is the rear wall, 100 is the secondary air duct, 110 is the secondary air layer duct, 120 is the end secondary air damper, 200 is the secondary air layer air box, 210 is the left air supply area, 220 is the middle air supply area, 230 is the right air supply area, 240 is the second partition, 250 is the first partition, 260 is the burner, 270 is the middle air inlet, 300 is the split air box, 310 is the split air box inlet, 320 is the split air box damper, 330 is the split air box outlet, 340 is the first guide plate, 350 is the second guide plate, 400 is the first air supply path, and 500 is the second air supply path. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown in the figure, a boiler air box secondary air distribution method provided by a specific embodiment of the present invention supplies air to the side air supply area of ​​the secondary air layer air box through a first air supply path, and supplies air to the central air supply area of ​​the secondary air layer air box that is separated from the side air supply area through a second air supply path, including the following steps: S1. Obtain the current operating status of the burner layer, determine the total secondary air demand of the current burner layer based on the operating status, and allocate the total secondary air demand between the side air supply area and the central air supply area to obtain the reference secondary air volume of each area. S2. Determine the side air supply demand and the middle reduction margin based on the operating status and the reference secondary air volume of each area, and determine the smaller of the air increase margin of the first air supply path under the current flow state and the air reduction margin of the second air supply path under the current flow state as the path transfer margin. S3. Determine the minimum value among the side air supply demand, the central reduction margin, and the path transfer margin as the actual transfer amount; determine the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area according to the relationship of adding the actual transfer amount to the benchmark secondary air volume of the side air supply area and reducing the actual transfer amount to the benchmark secondary air volume of the central air supply area. The sum of the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area is equal to the total secondary air demand. S4. Based on the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area, adjust the flow state of the first air supply path and the second air supply path respectively, so as to supply air to the corresponding air supply area according to the corresponding target secondary air volume.

[0023] In one embodiment, the side air supply area can be a single air supply area located to one side of the central air supply area, or it can include a left air supply area and a right air supply area located on either side of the central air supply area. When the side air supply area includes a left air supply area and a right air supply area, the reference secondary air volume, air distribution requirement, target secondary air volume, and actual secondary air volume of the side air supply area are the sum of the corresponding air volumes of the left air supply area and the right air supply area, respectively. The central air supply area is used to supply secondary air to one or more burners located in the middle of the corresponding burner layer.

[0024] Specifically, the current operating state of the burner layer includes the fuel supply state characterizing the combustion load of the burner layer, the regional combustion state characterizing the combustion conditions of different air supply zones, and the flow state characterizing the air supply capacity of the first and second air supply paths. The flow state at least reflects the current air supply volume of the corresponding air supply path and its ability to increase or decrease the air supply volume within the allowable adjustment range.

[0025] Furthermore, in this embodiment, the reference secondary air volume, target secondary air volume, actual secondary air volume, and various air volume margins all use the same metering reference. The metering reference can be mass flow rate or volumetric flow rate corrected for temperature and pressure. The sum of the reference secondary air volume of the side air supply area and the reference secondary air volume of the central air supply area equals the total secondary air demand of the current burner layer, ensuring that the total target secondary air volume of the burner layer remains unchanged when the secondary air volume shifts from the central air supply area to the side air supply area.

[0026] Based on the above basic implementation method, the corresponding reference secondary air volume is determined according to the total secondary air demand and the fuel supply status of the burners corresponding to the side air supply area and the central air supply area; the air distribution demand of the side air supply area is determined according to the fuel supply status and regional combustion status of the burners corresponding to the side air supply area, and the portion of the air distribution demand of the side air supply area that exceeds its reference secondary air volume is determined as the side make-up air demand.

[0027] Furthermore, the total secondary air demand can be determined by the secondary air setting of the burner layer given by the boiler's original combustion control system, or it can be determined based on the fuel supply corresponding to the burner layer, the total air volume required for combustion, and the primary air volume and other combustion air volumes allocated to the burner layer. For boilers with multiple burner layers, the total combustion air demand of the boiler can be determined first, and then the secondary air volume borne by the burner layer air box can be allocated to the corresponding burner layer according to the fuel supply status of each burner layer.

[0028] Furthermore, the fuel supply status is used to characterize the amount of fuel or fuel heat input obtained by the burners in the corresponding air supply area. It can be obtained based on the pulverized coal supply of the corresponding burner, or determined based on the output of the coal mill and the fuel distribution relationship of each pulverized coal pipeline. The reference secondary air volume of the side air supply area and the central air supply area can be allocated proportionally according to the fuel supply status of their respective burners, or it can be allocated based on the pre-determined regional air distribution coefficient under normal boiler operating conditions. However, the sum of the reference secondary air volumes of each area after allocation remains equal to the total secondary air demand.

[0029] Specifically, when the fuel supply amounts corresponding to the side air supply area and the central air supply area are the same as the side fuel supply amount and the central fuel supply amount, respectively, the corresponding reference secondary air volume can be determined based on the proportion of the two to the fuel supply amount of the burner layer. For cases where the fuel supply amount is the same but the burner structure, duct resistance, or regional air distribution requirements are different, the above proportion can be corrected using the regional air distribution coefficient determined in advance through boiler commissioning or operation tests.

[0030] The zone combustion state is used to characterize whether there is insufficient secondary air in the side-supply air zone relative to its fuel supply state. The zone combustion state can be characterized by at least one of the following: oxygen content, reducing gas content, or incomplete combustion product content in the near-wall area of ​​the side wall or the area corresponding to the side burner. When the zone combustion state indicates that there is a tendency for oxygen deficiency in the side-supply air zone, the side zone air distribution demand is determined to be higher than the side baseline secondary air volume based on the fuel supply state and the zone combustion state; when there is no side make-up air demand, the side make-up air demand is determined to be zero; the correspondence between the zone combustion state and the air distribution demand of the side-supply air zone can be pre-established during the boiler commissioning stage according to the burner layer load range, fuel type, and fuel supply state. Specifically, under the condition of keeping the fuel supply state, primary air volume, and other combustion air volumes of the corresponding burner layer basically stable, the secondary air volume of the side-supply air zone is changed in stages, and the oxygen content, reducing gas content, or incomplete combustion product content in the near-wall area of ​​the side wall or the area corresponding to the side burner is obtained under each level of secondary air volume. The side secondary air volume when the combustion state of the zone meets the preset combustion safety requirements under the corresponding operating conditions and the combustion remains stable is determined as the air distribution demand for the corresponding operating conditions, and a corresponding relationship table or characteristic curve is formed according to the load range and fuel supply status.

[0031] During operation, the air distribution requirements of the side air supply area are determined from the corresponding relationship table or characteristic curve based on the current fuel supply status and the regional combustion status. When using multiple regional combustion status parameters, the larger value among the air distribution volumes required to meet various combustion safety requirements can be used as the air distribution requirements of the side air supply area to avoid one test result meeting the requirements while another still indicates regional oxygen deficiency.

[0032] In one specific implementation, the non-negative difference obtained by subtracting the sum of the minimum air distribution requirement and the safety margin of the central air supply area from the baseline secondary air volume of the central air supply area is determined as the central adjustment margin; the air increase margin is determined by subtracting the current air supply volume from the upper limit of the air supply volume of the first air supply path, and the air reduction margin is determined by subtracting the lower limit of the air supply volume from the current air supply volume of the second air supply path.

[0033] In this embodiment, the minimum air distribution requirement of the central air supply zone is the minimum secondary air volume required to maintain stable combustion of its corresponding burner, which can be determined based on the fuel supply of the corresponding burner and the minimum permissible secondary air-fuel ratio. The minimum permissible secondary air-fuel ratio can be derived from burner design data, boiler combustion adjustment tests, or stable combustion tests under different loads; when fuel heat input is used to characterize the fuel supply status, the minimum air distribution requirement can be determined according to the corresponding minimum secondary air heat input ratio.

[0034] The safety margin for the central air volume is determined based on the fluctuation range of fuel supply, the measurement error of air volume, the change in air volume during damper operation, and the requirements for stable combustion of the burner. It can be set according to a fixed air volume or according to a certain proportion of the minimum air distribution demand in the central area. The safety margin is used to form the reserved air distribution boundary of the central air supply area and is not calculated repeatedly with the flow capacity margin of the first and second air supply paths.

[0035] Furthermore, when the reference secondary air volume of the central air supply area is not greater than the sum of the minimum air distribution requirement of the central air supply area and the central air volume safety margin, the central reduction margin is determined to be zero. The upper limit of the air supply volume of the first air supply path is the air volume that can be provided to the side air supply area under the current air supply pressure and the maximum allowable flow conditions, and the lower limit of the air supply volume of the second air supply path is the air volume that should be retained under the condition of meeting the minimum air distribution requirements of the central air supply area and the allowable adjustment range of the damper.

[0036] The increase margin of the first air supply path is used to limit the actual increase in secondary air volume in the side air supply area, and the decrease margin of the second air supply path is used to limit the actual decrease in secondary air volume in the central air supply area. Determining the smaller of the two as the path transfer margin can avoid exceeding the actual adjustment capacity of any air supply path by determining the transfer amount solely based on the side air supply demand.

[0037] The actual transfer volume is constrained by the side air supply demand, the central reduction margin, and the path transfer margin. When any one of these is zero, the actual transfer volume is zero; when all three are greater than zero, the minimum value among them is taken as the actual transfer volume, so that the target secondary air volume increased on the side has a corresponding adjustable reduction air volume in the central section and the flow capacity of the air supply path. The actual transfer volume referred to in this specification is the execution setting determined by the current air distribution adjustment under the joint constraints of the side air supply demand, the central reduction margin, and the path transfer margin, used to form the target secondary air volume in the side air supply area and the central air supply area, and is not the realized air volume directly measured after the damper action. The actual transfer effect after the damper action is characterized by the actual increase in air volume in the side air supply area and the actual decrease in air volume in the central air supply area, and the degree of matching between the actual execution result and the actual transfer volume is evaluated by the transfer matching deviation.

[0038] In another specific embodiment, based on the pressure difference between the first air supply path and the second air supply path, as well as the predetermined flow state and the correspondence between the pressure difference and the air supply volume, the target flow state corresponding to the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area is determined respectively, and the first air supply path and the second air supply path are adjusted according to the corresponding target flow state.

[0039] In this embodiment, the pressure difference of the first air supply path is the difference between the pressure at the inlet side of the first air supply path and the pressure within the side air supply area, and the pressure difference of the second air supply path is the difference between the pressure at the inlet side of the second air supply path and the pressure within the central air supply area. The flow state includes the opening degree of the corresponding damper or the effective flow area formed by the damper opening degree.

[0040] Specifically, the correspondence between the flow state, pressure difference, and air supply volume can be predetermined through air supply path resistance calculation, boiler cold-state ventilation test, or damper characteristic test during unit commissioning, and stored as a correspondence table or characteristic curve. For operating conditions under different secondary air temperatures and pressures, the air supply volume can be converted according to the same measurement standard, so that the correspondence can be used to determine the target flow state under the current pressure difference condition. When determining the upper or lower limit of the air supply volume for the air supply path, the current pressure difference of the corresponding air supply path is first obtained, and then the air supply volume corresponding to the maximum allowable flow state of the damper and the minimum allowable flow state under that pressure difference is determined according to the correspondence table or characteristic curve. The upper limit of the air supply volume of the first air supply path adopts the air supply volume corresponding to its maximum allowable flow state, and the lower limit of the air supply volume of the second air supply path adopts the air supply volume corresponding to its minimum allowable flow state. When the air supply path includes multiple parallel air supply branches, the air supply capacity of each air supply branch is determined separately, and the air supply volume boundary of the air supply path is determined by the air supply volume that each parallel air supply branch can jointly achieve within its allowable flow range.

[0041] Furthermore, since the first and second air supply paths are formed by the same secondary air layer duct, adjusting one of the air supply paths may cause changes in the pressure of the secondary air layer duct and the air supply volume of the other air supply path. Therefore, the target flow state of the first and second air supply paths is determined according to their respective target secondary air volume and pressure difference, and the corresponding damper control commands are coordinated and output by the control unit, rather than directly using a fixed damper opening as a fixed air supply volume.

[0042] In another specific embodiment, the actual secondary air volume of the adjusted side air supply area and the middle air supply area is obtained, the difference between the actual secondary air volume of the side air supply area and its reference secondary air volume is determined as the actual increase in air volume, the difference between the reference secondary air volume of the middle air supply area and its actual secondary air volume is determined as the actual decrease in air volume, and the transfer matching deviation is determined based on the difference between the actual increase in air volume and the actual decrease in air volume.

[0043] Furthermore, the actual secondary air volume of the side air supply area can be determined by the actual air supply volume of the first air supply path. When the side air supply area includes a left air supply area and a right air supply area, the actual secondary air volume of the side air supply area is the sum of the actual air supply volumes of the left and right air supply branches. The actual secondary air volume of the central air supply area can be determined by the sum of the actual air supply volumes of each branch air supply branch entering the central air supply area; the air supply status detection device is set before the corresponding air supply path enters the corresponding air supply area and after other branch points; when there is measurable cross-zone crossflow in the separator, the measured air supply volume of the path is corrected according to the pre-calibrated cross-zone crossflow volume.

[0044] Specifically, the actual increase in air volume is the difference between the actual secondary air volume of the adjusted side air supply area and its reference secondary air volume, and the actual decrease in air volume is the difference between the reference secondary air volume of the central air supply area and its adjusted actual secondary air volume. The transfer matching deviation can be determined as the difference between the actual increase in air volume and the actual decrease in air volume. A positive transfer matching deviation indicates that the actual increase in secondary air volume in the side area is greater than the actual decrease in secondary air volume in the central area; a negative transfer matching deviation indicates that the actual decrease in secondary air volume in the central area is greater than the actual increase in secondary air volume in the side area.

[0045] Furthermore, considering the fluctuations in airflow measurement and the transient process of damper operation, an allowable deviation range can be set for the transfer matching deviation. When the transfer matching deviation is within the allowable deviation range, it is considered that the actual increase in airflow on the side matches the actual decrease in airflow in the middle; when it exceeds the allowable deviation range, a correction is performed on the actual transfer amount or the flow state of the corresponding air supply path. The allowable deviation range can be determined based on the airflow detection accuracy and boiler operation stability requirements, and is not limited to a specific value.

[0046] In another specific embodiment, the actual transfer amount is corrected according to the transfer matching deviation, and the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area are re-determined based on the corrected actual transfer amount. The flow state of the first air supply path and the second air supply path is further adjusted. When the transfer matching deviation exceeds the allowable deviation range, the smaller of the actual increase in air volume and the actual decrease in air volume is determined as the corrected actual transfer amount, and the target secondary air volume of the two areas is re-determined according to the corrected actual transfer amount.

[0047] Specifically, when the transfer matching deviation is positive and exceeds the allowable deviation range, it indicates that the actual air volume increase on the side is large, and the flow state of the first air supply path can be reduced to make the actual air volume increase on the side closer to the actual air volume decrease in the middle; when the transfer matching deviation is negative and exceeds the allowable deviation range, it indicates that the actual air volume decrease in the middle is large, and the flow state of the second air supply path can be increased to make the actual air volume decrease in the middle closer to the actual air volume increase on the side.

[0048] Furthermore, the corrected actual transfer amount still does not exceed the side air supply demand, the central reduction margin, and the path transfer margin. Based on the corrected actual transfer amount, it is added to the baseline secondary air volume of the side air supply area and subtracted from the baseline secondary air volume of the central air supply area to obtain the two target secondary air volumes again. Thus, the feedback correction changes the secondary air transfer amount between the two areas, but does not change the total target air volume limited by the total secondary air demand of the burner layer.

[0049] When the actual increase in air volume and the actual decrease in air volume match each other but neither reaches the actual transfer volume, the two air supply paths can be adjusted further, provided that the margins are still allowed, so that their actual air supply volumes approach the corresponding target secondary air volumes; this target tracking process does not change the determination relationship of the actual transfer volume.

[0050] In another specific embodiment, when the actual increase in air volume is less than the actual transfer volume, the second air supply path is controlled to ensure that the actual decrease in air volume does not exceed the actual increase in air volume, and the increase in the actual transfer volume is stopped. The actual increase in air volume, the actual decrease in air volume, and the transfer matching deviation are determined after the corresponding damper completes its target action, or after an evaluation period covering the main response process of the air supply path, to avoid judging normal transient responses as insufficient air supply capacity. The evaluation period can be determined through a damper step test during boiler commissioning. A flow state change command of a predetermined amplitude is input to the corresponding damper, and the time taken from the issuance of the control command to the actual air supply volume of the corresponding air supply path entering and remaining within the allowable deviation range of the target air supply volume is recorded. The larger value between the corresponding time of the first air supply path and the second air supply path is used as the basis for determining the evaluation period. The evaluation period does not need to be limited to a fixed value, but it should be sufficient to exclude normal transient processes caused by damper action and duct pressure propagation.

[0051] Furthermore, if the actual air volume increase is less than the actual transfer volume, it indicates that the first air supply path is limited by the current air supply pressure, damper flow capacity, or duct resistance, and fails to provide secondary air volume corresponding to the planned transfer volume to the side air supply area. If the air supply volume of the second air supply path is further reduced in this case, the actual total amount of secondary air obtained by the burner layer will decrease, and the air volume distribution in the central air supply area may be lower than the air volume required for stable combustion.

[0052] Specifically, the second air supply path is controlled so that the actual air reduction in the central air supply area does not exceed the actual air increase already achieved in the side area; for the actual air reduction in the central area that has exceeded the actual air increase in the side area, the corresponding air volume is restored by increasing the flow state of the second air supply path. At the same time, the increase in the target air supply volume of the first air supply path or the decrease in the target air supply volume of the second air supply path is stopped, and the two target secondary air volumes are re-determined based on the currently achievable matching transfer amount.

[0053] Furthermore, when the air supply path's boosting capacity is restored, and the redefined path transfer margin is greater than the current actual transfer volume, air volume transfer can continue as long as the side air supply demand and the central reduction margin still exist. This avoids prematurely reducing the central secondary air volume before side air supply has actually been generated.

[0054] In one specific implementation, such as Figure 2As shown, a boiler air box secondary air distribution system is provided, comprising: A secondary air layer air box is installed in the burner layer of the boiler. The secondary air layer air box has a central air supply area and a side air supply area along the width of the furnace. The central air supply area and the side air supply area are separated by a partition. The secondary air duct is connected to the side air supply area via the end secondary air damper to form the first air supply path; The diversion air box has its inlet connected to the secondary air layer duct upstream of the end secondary air damper, and its outlet connected to the central air supply area via the central air inlet located in the middle of the secondary air layer air box. The inlet of the diversion air box is provided with a diversion air box damper to form a second air supply path. The status acquisition unit is used to acquire the operating status of the burner layer and the flow status of the first air supply path and the second air supply path; and The control unit is signal-connected to the status acquisition unit, the actuator of the end secondary air damper, and the actuator of the diversion air box damper, respectively. It is used to determine the total secondary air demand of the burner layer based on the operating status, and to perform a baseline allocation of the total secondary air demand between the side air supply area and the middle air supply area. Based on the operating status and the baseline allocation result, it determines the side makeup air demand and the middle reduction margin, and determines the path transfer margin based on the current flow state of the first and second air supply paths. The minimum value among the side makeup air demand, the middle reduction margin, and the path transfer margin is determined as the actual transfer amount. The baseline secondary air volume of the side air supply area is increased and the baseline secondary air volume of the middle air supply area is decreased by the actual transfer amount to obtain the target secondary air volume for the two air supply areas. The control unit controls the actuators of the end secondary air damper and the diversion air box damper according to the corresponding target secondary air volume. The status acquisition unit and the control unit can be implemented as functional units in an existing distributed control system for the boiler, or they can be set in an independent controller. The status acquisition unit obtains fuel supply status, zone combustion status, air supply volume, pressure, and damper flow status through analog, digital, or communication interfaces, and transmits the acquired data to the control unit. The control unit performs zone baseline allocation, transfer margin determination, and target secondary air volume determination, and outputs control commands to the actuators of the end secondary air damper 120 and the diversion box damper 320. The signal connection includes wired connection or industrial communication connection, without limitation to a specific control platform or communication protocol.

[0055] In this embodiment, the secondary air from the secondary air layer duct forms two types of air supply paths upstream of the end secondary air damper. One portion of the secondary air enters the side air supply area of ​​the secondary air layer box through the end secondary air damper, forming the first air supply path; the other portion enters the distribution box through the distribution box damper and then enters the central air supply area through the central air inlet, forming the second air supply path. Thus, different air supply paths correspond to different air supply areas, reducing the mixing of the two types of secondary air before entering their respective air supply areas.

[0056] like Figure 3 As shown, the boiler has a front wall 11 and a rear wall 12 arranged opposite to each other, and the secondary air duct 100 is connected to multiple secondary air layer ducts 110 on one side of the front wall 11 and the rear wall 12 respectively. Figure 3 The illustration uses only two burner layers as an example; the actual number of burner layers is not limited by this. Each secondary air duct 110 corresponds to a secondary air box 200 for one burner layer, and multiple burners 260 are arranged within the secondary air box 200 along the width of the furnace. The secondary air ducts 110 are connected to the secondary air box 200 via end secondary air dampers 120 located at both ends of the secondary air box 200.

[0057] The air supply path 400 consists of air entering the secondary air layer box 200 from the secondary air layer duct 110 via the end secondary air damper 120, primarily supplying air to the left air supply area 210 and the right air supply area 230. The two branch box inlets 310 of the branch box 300 are connected to the secondary air layer duct 110 upstream of their respective end secondary air dampers 120, and each branch box inlet 310 is equipped with a branch box damper 320. The branch box outlet 330 of the branch box 300 is connected to the central air supply area 220 via the central air inlet 270. The second air supply path 500 consists of air entering the central air supply area 220 from the secondary air layer duct 110 via the branch box inlet 310, branch box damper 320, branch box 300, branch box outlet 330, and central air inlet 270.

[0058] Both the first air supply path 400 and the second air supply path 500 obtain hot secondary air from the secondary air layer duct 110, but they supply air to different air supply areas from the end and middle of the secondary air layer air box 200, respectively, thereby providing a structural basis for the redistribution of secondary air between the left air supply area 210, the right air supply area 230 and the middle air supply area 220.

[0059] Specifically, the separator is disposed between the central air supply area and the side air supply area to limit lateral flow between the different air supply areas, ensuring that secondary air entering through the first air supply path mainly supplies the side air supply area, and secondary air entering through the second air supply path mainly supplies the central air supply area. The relative separation refers to the separator's ability to effectively isolate the main airflow in each area, but does not exclude localized connections due to installation gaps, pressure balance, or maintenance needs; such as... Figure 5 As shown, the secondary air duct 200 forms a left air supply area 210, a middle air supply area 220, and a right air supply area 230 along the width of the furnace. The left air supply area 210 corresponds to the burner 260 near the furnace side, the right air supply area 230 corresponds to the burner 260 near the other side of the furnace, and the middle air supply area 220 corresponds to one or more burners 260 located in the middle of the furnace width direction. Figure 5 Taking four burners 260 set in the same burner layer as an example, the left air supply area 210 and the right air supply area 230 each correspond to one burner 260, and the middle air supply area 220 corresponds to two burners 260; the specific number of burners 260 and their distribution in each air supply area are not limited.

[0060] Two end secondary air dampers 120 are respectively disposed at the left and right ends of the secondary air layer box 200. A first baffle 250 is disposed in the end air inlet area adjacent to the end secondary air dampers 120 and forms an arc-shaped guide surface for guiding the hot secondary air. Since the end secondary air dampers 120 only occupy a part of the end air inlet section of the secondary air layer box 200 in the height direction, the hot secondary air entering through the end secondary air dampers 120 is prone to backflow in the end air inlet area. The first baffle 250 is used to guide the hot secondary air to flow to the corresponding left air supply area 210 or right air supply area 230 to reduce the backflow area and the dust accumulation it causes.

[0061] The second partition 240 is respectively located at the junction of the left air supply area 210 and the middle air supply area 220, and at the junction of the middle air supply area 220 and the right air supply area 230. Figure 5 The second baffle 240 shown includes two sets of four arc-shaped plates. The two arc-shaped plates in each set are arranged opposite each other to relatively separate the main air supply airflow of adjacent air supply areas and guide the hot secondary airflow to the corresponding burner 260. The second baffle 240 constitutes the main structure of the aforementioned separator. The second baffle 240 and the first baffle 250 jointly organize the airflow in the secondary air layer box 200, so that the left air supply area 210, the middle air supply area 220 and the right air supply area 230 form relatively independent air supply areas.

[0062] Hot secondary air entering the secondary air chamber 200 through the left and right end secondary air dampers 120 is mainly supplied to the left air supply area 210 and the right air supply area 230, respectively; hot secondary air entering the secondary air chamber 200 through the central air inlet 270 is mainly supplied to the central air supply area 220. The connection between the central air inlet 270 and the central air supply area 220 is as follows: Figure 3 As shown in the figure, Figure 5 To highlight the partitioning relationship of the secondary air layer air box 200 along the width of the furnace, the central air inlet 270 is not shown again.

[0063] Furthermore, the actuators of the end secondary air damper and the diversion box damper respectively receive control signals output by the control unit to change the effective flow area of ​​the corresponding air supply path. The control unit determines the control command based on the target secondary air volume and the current flow state of the air supply path, rather than judging the actual secondary air distribution volume solely based on the relative opening of the two dampers.

[0064] The outlet section of the diversion box can be equipped with a guide structure to direct secondary airflow toward the central air inlet. The secondary air layer box can also be equipped with a guide structure that works in conjunction with the separator to reduce backflow from the inlet jet and improve airflow distribution within each air supply zone. The specific shape of the guide structure does not affect the correspondence between the two types of air supply paths and different air supply zones.

[0065] like Figure 4 As shown, the diversion air box 300 extends along the width of the furnace. Diversion air box inlets 310 are formed at both ends of the diversion air box 300, and each inlet 310 is used to connect with the corresponding secondary air duct 110. A diversion air box damper 320 is provided at each diversion air box inlet 310 to adjust the volume of hot secondary air entering the diversion air box 300 from the corresponding secondary air duct 110. A diversion air box outlet 330 is formed in the middle of the diversion air box 300, and the outlet 330 connects to the central air inlet 270 located in the middle of the secondary air duct 200, allowing the hot secondary air from the two diversion air box inlets 310 to enter the central air supply area 220 through the outlet 330.

[0066] The outlet section of the splitter box 300 is provided with a first guide plate 340 and a second guide plate 350. There are two first guide plates 340, both of which are arc-shaped and are respectively positioned at the turning points on both sides of the second guide plate 350. These guide plates guide the hot secondary air flowing in from both ends of the splitter box 300 smoothly towards the splitter box outlet 330. The second guide plate 350 is a plate-like structure located in the middle of the splitter box outlet 330. It separates and guides the hot secondary air flowing from both sides of the splitter box 300 to the splitter box outlet 330, reducing backflow and localized low-speed areas caused by direct collision of the two streams of hot secondary air at the outlet section.

[0067] The first guide vane 340 and the second guide vane 350 together redirect and rectify the hot secondary air within the distribution box 300, causing the hot secondary air from the two distribution box inlets 310 to enter the central air supply area 220 via the distribution box outlet 330 and the central air inlet 270. The first guide vane 340 and the second guide vane 350 are used to improve the airflow organization within the second air supply path 500, but do not change the air supply correspondence between the second air supply path 500 and the central air supply area 220.

[0068] In one specific embodiment, the side air supply area includes a left air supply area and a right air supply area located on both sides of the central air supply area. The first air supply path includes a left air supply branch and a right air supply branch that are connected to the left air supply area and the right air supply area respectively via two end secondary air dampers. The distribution box has two inlets connected to the secondary air layer duct. The two inlets are respectively provided with the distribution box dampers and supply air to the central air inlet together. The control unit controls the actuators of the two end secondary air dampers according to the make-up air demand of the left air supply area and the right air supply area, and coordinates the control of the actuators of the two distribution box dampers according to the target secondary air volume corresponding to the central air supply area.

[0069] Specifically, when the makeup air requirements of the left and right air supply areas differ, the control unit determines the target secondary air volume corresponding to the left and right air supply areas respectively, and allocates the actual transfer volume of the side air supply areas to the left and right air supply branches without exceeding the air increase margin of the corresponding air supply branches. The allocation can be determined according to the ratio of makeup air requirements on both sides, or it can be preferentially allocated to the side where the combustion state indicates a higher degree of oxygen deficiency, but the sum of the target secondary air volumes increased on both sides shall not exceed the actual transfer volume.

[0070] Furthermore, the sum of the secondary air volumes allocated to the left and right air supply areas constitutes the target secondary air volume for the side air supply area. The control unit controls the actuators of the two end secondary air dampers respectively, so that the left and right side air supply branches supply air to the corresponding side air supply areas, thereby avoiding treating different combustion states on both sides as the same damper opening.

[0071] The two inlets of the split-flow box draw air from the secondary air layer duct upstream of the corresponding end secondary air dampers. The sum of the actual air supply volumes of the two inlets constitutes the actual secondary air volume of the central air supply area. The control unit can coordinate and adjust the dampers of the two split-flow box according to the pressure difference and air supply volume of the two inlets, so that the two inlets together meet the target secondary air volume corresponding to the central air supply area, and avoid air supply deviation inside the split-flow box due to pressure differences in the secondary air layer ducts on both sides.

[0072] In one specific embodiment, the system further includes a zone combustion status detection device and air supply status detection devices corresponding to the first air supply path and the second air supply path, respectively. The air supply status detection devices are used to obtain the air supply volume and pressure difference of the corresponding air supply path. The zone combustion status detection device and the air supply status detection device are respectively signal-connected to the status acquisition unit. The control unit determines the side air supply demand based on the detection result of the zone combustion status detection device, determines the path transfer margin based on the detection result of the air supply status detection device, determines the transfer matching deviation based on the difference between the adjusted actual air increase volume and the actual air decrease volume, and corrects the actual transfer amount based on the transfer matching deviation.

[0073] Specifically, the zone combustion state detection device can be installed in the near-wall area of ​​the furnace sidewall, the corresponding area of ​​the side burner, or a flue gas sampling location connected to the corresponding area, to obtain detection results that characterize the combustion state of the side-supply area. The detection results may include at least one of oxygen content, CO concentration, and H2S concentration, or other detection results that characterize regional oxygen-deficient combustion. The control unit determines the air distribution requirements of the side-supply area based on the degree of deviation of the detection results from the zone combustion state target under the corresponding operating conditions.

[0074] Furthermore, the air supply status detection device corresponding to the first air supply path is used to obtain the pressure difference between the inlet of the first air supply path and the side air supply area, as well as the air supply volume of the first air supply path; the air supply status detection device corresponding to the second air supply path is used to obtain the pressure difference between the inlet of the second air supply path and the central air supply area, as well as the air supply volume of the second air supply path. For an air supply path including multiple parallel air supply branches, its air supply volume is the sum of the air supply volumes of each parallel air supply branch.

[0075] The status acquisition unit collects signals from the zone combustion status detector and the air supply status detector, and transmits them to the control unit. The control unit determines the side air supply demand based on the zone combustion status, determines the path transfer margin based on the actual air supply volume, pressure difference, and allowable flow range of each air supply path, and determines the transfer matching deviation based on the actual air increase and actual air decrease after damper adjustment.

[0076] Furthermore, when the transfer matching deviation exceeds the allowable deviation range, the control unit corrects the actual transfer amount according to the principle of not expanding the side air supply demand, the central reduction margin, and the path transfer margin, and re-controls the actuator of the corresponding damper. This forms a control closed loop of "determining air supply demand based on zone combustion state—limiting transfer amount based on air supply capacity—implementing air volume transfer on two air supply paths—verifying transfer matching relationship based on actual air volume"; the statement in this specification that "side air increase and central air reduction are equal" means that their target values ​​are determined according to the same actual transfer amount; due to the influence of damper action time, duct pressure fluctuations, and measurement errors, their actual values ​​may have transient differences during the adjustment process, which are limited and corrected by the transfer matching deviation.

[0077] In one specific implementation, taking the first layer of burners on the front wall of a wall-mounted opposed-fired boiler as an example, this burner layer has four burners arranged along the width of the furnace. The secondary air layer air box is divided into a left air supply area, a middle air supply area, and a right air supply area by two partitions. The left and right air supply areas correspond to the burners closest to the two side walls, respectively, while the middle air supply area corresponds to the two burners located in the middle.

[0078] The secondary air duct is connected to the left and right air supply areas via end secondary air dampers located at both ends of the secondary air box, forming the first air supply path. The two inlets of the split air box are connected to the secondary air duct upstream of the corresponding end secondary air dampers, and each inlet is equipped with a split air box damper. The outlet of the split air box is connected to the central air supply area via a central air inlet located in the middle of the secondary air box, forming the second air supply path.

[0079] In this embodiment, the secondary air volume is measured using mass flow rate. The current fuel supply to the burner layer is 14 kg / s, with the fuel supply to the burners in the left, middle, and right air supply areas being 2.8 kg / s, 8.4 kg / s, and 2.8 kg / s, respectively. Based on the current boiler load, the fuel supply status of the burner layer, and the combustion air distribution relationship, the boiler combustion control system determines the total secondary air demand for the burner layer to be 40 kg / s. The following values ​​are used to illustrate the air volume distribution, margin constraints, and feedback correction relationships of this invention and do not constitute a limitation on boiler capacity, number of burners, fuel supply, or the range of secondary air volume. In practical applications, the total secondary air demand, regional air distribution demand, minimum air distribution demand, and air supply capacity boundaries of each air supply path for the burner layer should be determined based on the specific boiler design data, combustion adjustment tests, and operational commissioning results.

[0080] In this embodiment, the burners in each region use the same fuel, therefore the fuel mass flow rate is used to proportionally allocate the secondary air volume based on the region. When there are differences in the lower heating value of the fuel for burners in different regions, the fuel heat input of the burners in each region is used as a unified allocation benchmark.

[0081] In this embodiment, based on the proportion of the fuel supply to the burner in each air supply area to the fuel supply of the burner layer, the total secondary air demand of 40 kg / s is allocated on a benchmark basis, and the benchmark secondary air volume of the left air supply area is 8 kg / s. The baseline secondary air volume for the central air supply area is 24 kg / s; The baseline secondary air volume for the right-side air supply area is 8 kg / s.

[0082] Therefore, the baseline secondary air volume for the side air supply area is the sum of the baseline secondary air volumes for the left and right air supply areas, which is 16 kg / s. The sum of the baseline secondary air volumes for the side and central air supply areas is 40 kg / s, which is equal to the total secondary air requirement of this burner layer.

[0083] The combustion status detection device obtained the combustion status of the near-wall areas on the left and right sides. The test results showed that both air supply areas had insufficient secondary air relative to their fuel supply status, and the oxygen deficiency in the left air supply area was higher than that in the right air supply area.

[0084] Based on the pre-determined relationship between zone combustion status and air distribution demand established during boiler commissioning, the control unit determines the air distribution demand for the left air supply zone to be 11.5 kg / s and the air distribution demand for the right air supply zone to be 10.5 kg / s. Therefore: The makeup air requirement for the left-side air supply area is:

[0085] The makeup air requirement for the right-side air supply area is:

[0086] The makeup air requirement for the side air supply area is:

[0087] Based on the fuel supply status and stable combustion requirements of the burners in the central air supply area, the minimum air distribution demand in the central air supply area is determined to be 16 kg / s, and a safety margin of 2 kg / s for the central air volume is set.

[0088] The baseline secondary air volume for the central air supply area is 24 kg / s, therefore the adjustment margin for the central area is:

[0089] Therefore, the secondary air volume in the central air supply area can be reduced by a maximum of 6 kg / s. After the reduction, the target secondary air volume in the central air supply area is no less than 18 kg / s, thus preserving the secondary air volume and safety margin required for stable combustion of the central burner.

[0090] Before adjustment, the secondary air volume supplied by the first air supply path to the left air supply area and the right air supply area was 8 kg / s and 8 kg / s respectively, and the current total air supply volume of the first air supply path was 16 kg / s.

[0091] Based on the current pressure differential of the first air supply path, the allowable opening range of the end secondary air damper, and the pre-calibrated flow characteristics, it is determined that the left air supply branch can increase its flow rate by a maximum of 4 kg / s under the current flow conditions, and the right air supply branch can increase its flow rate by a maximum of 3 kg / s. Therefore, the air supply margin for the first air supply path is:

[0092] The current air supply volume of the second air supply path is 24 kg / s. Based on the current pressure difference of the second air supply path, the allowable adjustment range of the diversion box damper, and the minimum air supply volume that should be maintained in the central air supply area, the lower limit of the air supply volume of the second air supply path is determined to be 17 kg / s. Therefore, the air reduction margin of the second air supply path is:

[0093] The air increase margin for the first air supply path and the air decrease margin for the second air supply path are both 7 kg / s, therefore the path transfer margin is 7 kg / s. In this embodiment, 17 kg / s is the lower limit of the flow capacity of the second air supply path determined based on the current pressure difference and the allowable adjustment range of the split-flow box damper, used to calculate the air decrease margin of the second air supply path; 18 kg / s is the sum of the minimum air distribution demand of the central air supply area and the central air volume safety margin, used to limit the allowable reduction amount of the central air supply area. These two are respectively the air supply path flow capacity constraint and the central combustion safety constraint. The actual transfer amount is subject to both constraints simultaneously. In this embodiment, the more stringent central combustion safety constraint limits the target secondary air volume of the central air supply area to no less than 18 kg / s.

[0094] The minimum value among the side air supply demand of 6 kg / s, the central adjustment margin of 6 kg / s, and the path transfer margin of 7 kg / s is determined as the actual transfer volume. Therefore, the actual transfer volume is 6 kg / s.

[0095] The actual transfer volume of 6 kg / s is added to the baseline secondary air volume of the side air supply area and subtracted from the baseline secondary air volume of the central air supply area to obtain: The target secondary air volume for the side air supply area is:

[0096] The target secondary air volume for the central air supply area is:

[0097] The sum of the target secondary air volumes for the two areas is:

[0098] Therefore, this air distribution adjustment did not increase the total secondary air demand of the burner layer, but instead transferred the 6 kg / s secondary air volume of the central air supply area to the side air supply area, changing the secondary air distribution of the burner layer along the width of the furnace.

[0099] Based on the air supply requirements on the left and right sides, the actual transfer volume of 6 kg / s is allocated as an increase of 3.5 kg / s on the left and 2.5 kg / s on the right. Therefore, the target secondary air volumes for the left and right air supply areas are 11.5 kg / s and 10.5 kg / s, respectively.

[0100] Specifically, the control unit obtains the pressure difference between the first air supply path and the second air supply path, and determines the target flow state of the left end secondary air damper, the right end secondary air damper, and the two diversion air box dampers according to the predetermined damper flow state, the correspondence between the pressure difference and the air supply volume.

[0101] The control unit increases the flow rate of the secondary air dampers at the left and right ends, so that the first air supply path supplies air to the left and right air supply areas at target secondary air volumes of 11.5 kg / s and 10.5 kg / s, respectively; at the same time, it decreases the flow rate of the two split air box dampers, so that the second air supply path supplies air to the central air supply area at a target secondary air volume of 18 kg / s.

[0102] The sum of the air supply volumes at the inlets of the two branch air boxes constitutes the air supply volume for the central air supply area. When the pressure difference between the inlets of the two branch air boxes is different, the control unit determines the target flow state of the dampers of the two branch air boxes respectively, so that the total air supply volume of the two inlets meets the target secondary air volume of 18 kg / s for the central air supply area.

[0103] After the damper was adjusted, the air supply status detection device obtained actual secondary air volumes of 11.2 kg / s for the left air supply area and 9.9 kg / s for the right air supply area. Therefore, the actual secondary air volume in the side air supply area is 21.1 kg / s, and the actual increase in air volume in the side area is:

[0104] The actual secondary air volume in the central air supply area is 18.3 kg / s, and the actual air reduction volume in the central area is:

[0105] Subtracting the actual air reduction in the middle section from the actual air increase in the side section yields the transfer matching deviation:

[0106] In this embodiment, the allowable range of transfer matching deviation is set to... 0.3 kg / s to 0.3 kg / s. Due to The 0.6 kg / s reading is outside the allowable range, indicating that the actual reduction in secondary air volume in the middle section is greater than the actual increase in secondary air volume in the side section.

[0107] The control unit sets the corrected actual transfer rate at 5.1 kg / s and redetermines the target secondary air volumes for the side and central air supply zones, respectively:

[0108] as well as:

[0109] The control unit correspondingly increases the flow rate of the splitter box damper, adjusting the actual secondary air volume in the central air supply area from 18.3 kg / s to 18.9 kg / s. After correction, the actual secondary air volume in the side air supply area is 21.0 kg / s, and the actual secondary air volume in the central air supply area is 18.9 kg / s. The actual increase and decrease in air volume are 5.0 kg / s and 5.1 kg / s respectively, with a transfer matching deviation of [missing value]. The corrected side transfer volume is 0.1 kg / s, which is within the allowable range. The adjusted side transfer volume is allocated according to the proportion of unmet supplementary air demand on both sides or the current available air increase margin for each branch. The sum of the transfer volumes allocated to the two side air supply branches equals the corrected actual transfer volume. The sum of the corrected target secondary air volumes for the two areas remains 40 kg / s. The aforementioned 21.0 kg / s and 18.9 kg / s are the actual secondary air volumes obtained after adjustment. The 0.1 kg / s difference between their sum and the target total secondary air volume originates from air volume measurement errors, damper execution deviations, and duct pressure fluctuations, and does not indicate a change in the target total secondary air demand. When the deviation of the sum of the actual secondary air volumes of the two areas relative to the total secondary air demand exceeds the allowable range of the boiler's total air volume control, the original total air volume control of the boiler will adjust the total secondary air supply. The regional air volume transfer relationship is still determined according to the principle of matching the side air increase volume with the central air decrease volume.

[0110] In another operating state, if the actual transfer volume is still determined to be 6 kg / s, but the first air supply path can only increase the side air supply area by 4.2 kg / s due to the pressure of the secondary air layer duct or the flow capacity of the end secondary air damper, then the control unit limits the reduction volume of the second air supply path to no more than 4.2 kg / s.

[0111] At this time, the actual secondary air volume in the central air supply area is not less than:

[0112] The control unit stops increasing the actual transfer volume and redetermines the target secondary air volume for both zones based on the matched transfer volume of 4.2 kg / s. This avoids further reducing the secondary air volume in the central air supply zone before the side air supply is actually formed.

[0113] Through the above control process, while maintaining the total target secondary air volume of the burner layer at 40 kg / s, a portion of the secondary air volume in the central air supply area is transferred to the side air supply area, so that the side burners can obtain supplementary secondary air corresponding to the combustion state of their area, while avoiding the secondary air volume in the central air supply area from falling below the air volume boundary required for stable combustion.

[0114] In summary, this embodiment has at least the following technical effects: This invention sets up different air supply paths corresponding to the side air supply area and the middle air supply area respectively, and uses a separator to divide the secondary air layer air box into areas, so that different air supply paths mainly supply air to the corresponding burner area, reducing mutual interference of airflow in the common air box and improving the independent adjustment capability of secondary air volume in different areas of the same floor. This invention, while meeting the current total secondary air demand of the burner layer, transfers a portion of the secondary air volume from the central air supply area to the side air supply area, so that the increased air volume on the side corresponds to the decreased air volume in the central area. Thus, without simply increasing the total secondary air volume of the burner layer, the distribution of secondary air along the furnace width can be changed, avoiding an increase in the total excess air level in the boiler due to overall air increase. The present invention limits the actual transfer amount by combining the side air supply requirement, the middle adjustment margin, and the air supply path transfer margin. This satisfies the air supply requirements of the side burner, avoids the secondary air volume in the middle air supply area from being lower than the air distribution boundary required for stable combustion, and prevents the target air volume from exceeding the actual flow capacity of the air supply path. This invention determines the corresponding target flow state based on the pressure difference and flow state of the air supply path, as well as the correspondence between the pressure difference and the air supply volume. This avoids directly equating the damper opening with the actual air supply volume. It can adapt to changes in the pressure of the secondary air layer duct and different operating conditions with varying resistance of different air supply paths, thereby improving the reliability of the execution of the regional target secondary air volume. This invention determines the transfer matching deviation by comparing the actual air volume increase on the side with the actual air volume decrease in the middle, and corrects the actual transfer amount accordingly. When the side air supply path fails to achieve the predetermined air volume increase, the air volume decrease in the middle air supply path is limited, thereby avoiding the mismatch state of "the side not receiving enough make-up air while the secondary air in the middle has been reduced", and maintaining the stability of the actual secondary air supply in the burner layer; This invention can determine the air supply demand and adjust the corresponding end secondary air damper according to the different combustion states of the left and right sides, thereby adapting to the asymmetrical combustion state on both sides of the furnace, improving the oxygen-deficient combustion state of the burners near the side wall, and reducing the risk of strong reducing atmosphere and high-temperature corrosion of the water-cooled wall in the near wall area. The partitioned structure within the secondary air layer air box, along with the diversion air box, guide structure, and different air inlet positions, helps to reduce backflow and localized ash accumulation caused by end air inlets, improves the airflow and pressure distribution within each air supply area, and enables burners in each area to obtain secondary air volume that matches their combustion requirements, thereby improving the combustion uniformity in the furnace width direction and the boiler's operational stability.

[0115] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for secondary air distribution in a boiler wind box, characterized in that, The method supplies air to the side air supply area of ​​the secondary air layer box via a first air supply path, and supplies air to the central air supply area of ​​the secondary air layer box, which is separated from the side air supply area, via a second air supply path, including the following steps: S1. Obtain the current operating status of the burner layer, determine the total secondary air demand of the current burner layer based on the operating status, and allocate the total secondary air demand between the side air supply area and the central air supply area to obtain the reference secondary air volume of each area. S2. Determine the side air supply demand and the middle reduction margin based on the operating status and the reference secondary air volume of each area, and determine the smaller of the air increase margin of the first air supply path under the current flow state and the air reduction margin of the second air supply path under the current flow state as the path transfer margin. S3. Determine the minimum value among the side air supply demand, the central reduction margin, and the path transfer margin as the actual transfer amount; determine the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area according to the relationship of adding the actual transfer amount to the benchmark secondary air volume of the side air supply area and reducing the actual transfer amount to the benchmark secondary air volume of the central air supply area. The sum of the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area is equal to the total secondary air demand. S4. Based on the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area, adjust the flow state of the first air supply path and the second air supply path respectively, so as to supply air to the corresponding air supply area according to the corresponding target secondary air volume.

2. The boiler air box secondary air distribution method according to claim 1, characterized in that, Based on the total secondary air demand and the fuel supply status of the burners corresponding to the side air supply area and the central air supply area, the corresponding reference secondary air volume is determined; based on the fuel supply status and regional combustion status of the burners corresponding to the side air supply area, the air distribution demand of the side air supply area is determined, and the portion of the air distribution demand of the side air supply area that exceeds its reference secondary air volume is determined as the side make-up air demand.

3. The boiler air box secondary air distribution method according to claim 1, characterized in that, The non-negative difference obtained by subtracting the sum of the minimum air distribution requirement and the safety margin of the central air supply area from the baseline secondary air volume of the central air supply area is determined as the central adjustment margin; the air increase margin is determined by subtracting the current air supply volume from the upper limit of the air supply volume of the first air supply path, and the air reduction margin is determined by subtracting the lower limit of the air supply volume from the current air supply volume of the second air supply path.

4. The boiler air box secondary air distribution method according to claim 1, characterized in that, Based on the pressure difference between the first and second air supply paths, the predetermined flow state, and the correspondence between the pressure difference and the air supply volume, the target flow state corresponding to the target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area is determined respectively, and the first and second air supply paths are adjusted according to the corresponding target flow state.

5. The boiler air box secondary air distribution method according to claim 1, characterized in that, The actual secondary air volume of the adjusted side air supply area and the middle air supply area is obtained. The difference between the actual secondary air volume of the side air supply area and its reference secondary air volume is determined as the actual increase in air volume. The difference between the reference secondary air volume of the middle air supply area and its actual secondary air volume is determined as the actual decrease in air volume. The transfer matching deviation is determined based on the difference between the actual increase in air volume and the actual decrease in air volume.

6. The boiler air box secondary air distribution method according to claim 5, characterized in that, The actual transfer amount is corrected based on the transfer matching deviation. The target secondary air volume of the side air supply area and the target secondary air volume of the central air supply area are re-determined based on the corrected actual transfer amount. The flow state of the first air supply path and the second air supply path is further adjusted.

7. The boiler air box secondary air distribution method according to claim 5 or 6, characterized in that, When the actual increase in air volume is less than the actual transfer volume, the second air supply path is controlled to ensure that the actual decrease in air volume does not exceed the actual increase in air volume, and the increase in the actual transfer volume is stopped.

8. A boiler air box secondary air distribution system, characterized in that, include: A secondary air layer air box is installed in the burner layer of the boiler. The secondary air layer air box has a central air supply area and a side air supply area along the width of the furnace. The central air supply area and the side air supply area are separated by a partition. The secondary air duct is connected to the side air supply area via the end secondary air damper to form the first air supply path; The diversion air box has its inlet connected to the secondary air layer duct upstream of the end secondary air damper, and its outlet connected to the central air supply area via the central air inlet located in the middle of the secondary air layer air box. The inlet of the diversion air box is provided with a diversion air box damper to form a second air supply path. The status acquisition unit is used to acquire the operating status of the burner layer and the flow status of the first air supply path and the second air supply path; as well as The control unit is signal-connected to the status acquisition unit, the actuator of the end secondary air damper, and the actuator of the diversion air box damper, respectively. It is used to determine the total secondary air demand of the burner layer according to the operating status, and to perform a reference allocation of the total secondary air demand between the side air supply area and the middle air supply area to obtain the reference secondary air volume of each area. The side air supply demand and the central reduction margin are determined based on the operating status and the baseline secondary air volume of each area. The path transfer margin is determined based on the current flow status of the first air supply path and the second air supply path. The minimum value among the side air supply demand, the central reduction margin, and the path transfer margin is determined as the actual transfer amount. The target secondary air volume of each area is determined according to the relationship of adding the actual transfer amount to the baseline secondary air volume of the side air supply area and reducing the actual transfer amount to the baseline secondary air volume of the central air supply area. The corresponding actuators are controlled according to the target secondary air volume of each area.

9. The boiler air box secondary air distribution system according to claim 8, characterized in that, The side air supply area includes a left air supply area and a right air supply area located on both sides of the central air supply area; the first air supply path includes a left air supply branch and a right air supply branch, the left air supply branch and the right air supply branch respectively connected to the left air supply area and the right air supply area via corresponding end secondary air dampers; the distribution box has two inlets connected to the secondary air layer duct and respectively provided with the distribution box damper, the two inlets jointly supply air to the central air inlet; the control unit controls the actuators of the two end secondary air dampers respectively, and coordinates the control of the actuators of the two distribution box dampers.

10. The boiler air box secondary air distribution system according to claim 8 or 9, characterized in that, The system further includes a zone combustion status detection device and air supply status detection devices corresponding to the first air supply path and the second air supply path, respectively. The zone combustion status detection device is used to detect the combustion status of the side air supply zone, and the air supply status detection device is used to detect the air supply volume and pressure difference of the corresponding air supply path. The zone combustion status detection device and the air supply status detection device are respectively signal-connected to the status acquisition unit. The control unit determines the side air replenishment demand and the path transfer margin according to the detection results, and corrects the actual transfer amount according to the difference between the actual increase in side air volume and the actual decrease in central air volume after adjustment.

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