Recycled flue gas denitration load reduction evaluation method

Abstract

The invention provides a recirculation flue gas denitration load reduction evaluation method, which comprises the following steps: acquiring flue gas temperature, residual oxygen concentration and recirculation flow transmitted by a multi-point temperature collector and an oxygen content monitoring device, and performing data fusion processing to obtain temperature gradients and oxygen concentration gradients corresponding to different extraction positions; a preset target oxygen concentration threshold value of the denitration system is obtained, the deviation degree of the local oxidizing atmosphere strengthening degree grade and the target oxygen concentration threshold value is evaluated, the oxygen content proportion of the hearth is adjusted according to the deviation degree, and a wind pressure set value is obtained; and the recirculation flow and the residual oxygen concentration variation corresponding to the optimal extraction scheme are extracted, the oxygen concentration reduction amplitude is evaluated, the denitration load reduction proportion is quantified according to the oxygen concentration reduction amplitude, and denitration load reduction is evaluated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of information technology, and in particular to a recirculated flue gas denitration load reduction evaluation method. BACKGROUND

[0002] Recirculated flue gas denitration technology plays a key role in environmental protection control of coal-fired power plants, as it can effectively reduce nitrogen oxide emissions while maintaining boiler combustion efficiency, which is of great significance to clean energy production. Current methods mainly rely on fixed extraction positions to improve recirculation rates to dilute the oxygen concentration in the furnace, thereby reducing the denitration load. However, this approach ignores the impact of extraction point position changes on flue gas composition, resulting in a large deviation between the evaluation results and actual effects. When the extraction position moves forward from the tail flue to the furnace outlet, the recirculation rate should be improved to reduce the oxygen concentration, but the high-temperature flue gas carries more residual oxygen back into the furnace, intensifying the local oxidation atmosphere and making the reduction effect unpredictable. Residual oxygen concentration is a key factor because it increases with the forward movement of the extraction position, directly related to the change in oxygen-carrying capacity of recirculated flue gas, and thus affecting the uniformity of oxygen distribution in the furnace. For example, in power plant tests, the recirculation rate is improved when extracting from the tail, and the oxygen concentration uniformly decreases, resulting in significant denitration load reduction. However, after the extraction point moves forward, the residual oxygen carried by the high-temperature flue gas increases the local oxygen concentration in the furnace, and the expected reduction improvement becomes ineffective or even worsens. This correlation between oxygen-carrying capacity and position makes it difficult for evaluation models to accurately capture the dynamics of the oxidation atmosphere. Therefore, how to quantify the impact of residual oxygen concentration and adjust the evaluation parameters in the interaction between the forward movement of the extraction position and the improvement of the recirculation rate has become a key problem in accurately determining the denitration load reduction. SUMMARY

[0003] The present application provides a recirculated flue gas denitration load reduction evaluation method, comprising:

[0004] Obtain the flue gas temperature, residual oxygen concentration, and recirculation flow rate transmitted by the multi-point temperature collector and oxygen content monitoring device, and obtain the temperature gradient and oxygen concentration gradient corresponding to different extraction positions through data fusion processing;

[0005] Identify the residual oxygen concentration change corresponding to the extraction position according to the temperature gradient and oxygen concentration gradient corresponding to different extraction positions, extract the correlation strength between the residual oxygen concentration change and the recirculation flow rate, and obtain the local oxidation atmosphere intensification degree grade;

[0006] Obtain the target oxygen concentration threshold preset by the denitration system, evaluate the deviation of the local oxidation atmosphere intensification degree grade and the target oxygen concentration threshold, adjust the oxygen content ratio of the furnace according to the deviation, and obtain the wind pressure set value;

[0007] Adjust the fan according to the wind pressure set value, identify the change range of the pipeline resistance after the fan is adjusted, extract the difference of the pipeline resistance at different extraction positions, obtain the resistance balance reference of each extraction position, compare the recirculation flow with the resistance balance reference, and obtain the flow matching degree of each extraction position;

[0008] Fuse the flow matching degree, temperature gradient, oxygen concentration gradient and resistance balance reference of each extraction position, evaluate the comprehensive reduction value of each extraction position, sort the comprehensive reduction value, and identify the extraction position with the highest comprehensive reduction value as the optimal extraction scheme;

[0009] Extract the recirculation flow and residual oxygen concentration change corresponding to the optimal extraction scheme, evaluate the oxygen concentration reduction amplitude, and quantify the denitration load reduction ratio according to the oxygen concentration reduction amplitude.

[0010] Further, the residual oxygen concentration change corresponding to the extraction position is identified according to the temperature gradient and oxygen concentration gradient corresponding to different extraction positions, and the correlation strength between the residual oxygen concentration change and the recirculation flow is extracted to obtain the local oxidation atmosphere strengthening degree grade, including:

[0011] According to the temperature gradient and oxygen concentration gradient corresponding to different extraction positions, the gradient change rate in the adjacent sampling period is calculated, the gradient change rate is multiplied by the corresponding position of the flue gas flow rate, and the residual oxygen concentration change of each extraction position is obtained;

[0012] The recirculation flow value at the moment corresponding to the residual oxygen concentration change is obtained, the correlation coefficient between the residual oxygen concentration change and the recirculation flow value is calculated by using Pearson correlation coefficient, and the coupling degree of oxygen content and flow is obtained;

[0013] According to the coupling degree of oxygen content and flow, the oxygen concentration fluctuation amplitude of the corresponding area in the furnace per unit time is calculated, the area ratio of the enhanced area in the oxidation atmosphere distribution map and the oxygen content increment rate in each enhanced area are mapped to five classification standards by using fuzzy membership function, and the local oxidation atmosphere strengthening degree grade is determined.

[0014] Further, the fusion of the flow matching degree, temperature gradient, oxygen concentration gradient and resistance balance reference of each extraction position, the evaluation of the comprehensive reduction value of each extraction position, the sorting of the comprehensive reduction value, and the identification of the extraction position with the highest comprehensive reduction value as the optimal extraction scheme, including:

[0015] Obtain the flow matching degree, temperature gradient and oxygen concentration gradient of each extraction position and the resistance balance reference, and perform normalization processing respectively to obtain a set of standardized parameters;

[0016] According to the standardized parameter set, a judgment matrix is constructed by using an analytic hierarchy process, and by calculating a characteristic vector corresponding to a maximum eigenvalue of the judgment matrix, weight coefficient values of the flow matching degree, the temperature gradient, the oxygen concentration gradient and the resistance balance benchmark are determined respectively;

[0017] By summing the product of the weight coefficient values and the corresponding standardized parameters, a weighted comprehensive score of each extraction position is calculated, the weighted comprehensive score is taken as a comprehensive reduction value of each extraction position, the comprehensive reduction values are sorted from large to small, the position identifier with the highest comprehensive reduction value after sorting is selected, and an optimal extraction scheme is determined.

[0018] Further, the flue gas temperature, the residual oxygen concentration and the recirculation flow transmitted by the multi-point temperature collector and the oxygen content monitoring device are obtained, and the temperature gradient and the oxygen concentration gradient corresponding to different extraction positions are obtained through data fusion processing, including:

[0019] The flue gas temperature value transmitted by the multi-point temperature collector in the flue and the residual oxygen concentration output by the oxygen content monitoring device are obtained, the data synchronization is judged according to the collection time stamp of the flue gas temperature value and the residual oxygen concentration, the time sequence is aligned, and a time sequence synchronized temperature oxygen data set is obtained;

[0020] According to the time sequence synchronized temperature oxygen data set, the temperature and the oxygen concentration between different extraction position points are calculated by using the Kriging spatial interpolation method, and a continuously distributed temperature field and an oxygen concentration field are obtained;

[0021] For the continuously distributed temperature field and the oxygen concentration field, the temperature change rate and the oxygen concentration change rate of adjacent extraction position points are calculated by using the finite difference method, and the temperature gradient and the oxygen concentration gradient corresponding to different extraction positions are obtained.

[0022] Further, the target oxygen concentration threshold preset by the denitration system is obtained, the deviation degree of the local oxidation atmosphere strengthening degree grade and the target oxygen concentration threshold is evaluated, the oxygen content ratio of the hearth is adjusted according to the deviation degree, a wind pressure set value is obtained, including:

[0023] The target oxygen concentration threshold preset by the denitration system is obtained, the difference between the actual value and the target threshold is calculated according to the actual oxygen concentration value corresponding to the local oxidation atmosphere strengthening degree grade, and the oxygen concentration deviation degree is obtained;

[0024] According to the oxygen concentration deviation degree, the preset proportion coefficient corresponding to the increase or decrease of the air supply amount per percentage point deviation degree is adjusted, and a corrected oxygen content ratio is obtained;

[0025] The required air supply flow is determined by the corrected oxygen content ratio, the fan outlet pressure required to maintain the air supply flow is calculated by using the Bernoulli equation according to the air supply flow, and a wind pressure set value is obtained.

[0026] Furthermore, the process of adjusting the fan according to the wind pressure setpoint, identifying the change in pipe resistance after fan adjustment, extracting the pipe resistance difference at different extraction locations, obtaining the resistance balance benchmark for each extraction location, and comparing the recirculation flow rate with the resistance balance benchmark to obtain the flow rate matching degree for each extraction location includes:

[0027] Adjust the output frequency of the fan inverter according to the wind pressure setpoint, collect the static pressure difference in the pipeline before and after the fan adjustment, and calculate the change in pipeline resistance by the ratio of the static pressure difference to the pipeline length.

[0028] Obtain pressure sensor readings at different extraction locations. Based on the pressure sensor readings and the variation in pipeline resistance, calculate the actual resistance value at each extraction location. Determine the resistance balance benchmark at each extraction location by the difference between the actual resistance value and the design resistance value.

[0029] Collect the measured recirculation flow rate at each extraction location, and determine the flow rate matching degree at each extraction location based on the ratio of the measured recirculation flow rate to the resistance balance benchmark at the corresponding location.

[0030] Furthermore, the extraction of the recirculation flow rate and residual oxygen concentration change corresponding to the optimal extraction scheme, the assessment of the oxygen concentration reduction rate, and the quantification of the denitrification load reduction ratio based on the oxygen concentration reduction rate, thereby assessing the denitrification load reduction, include:

[0031] Extract the recirculation flow rate and the change in residual oxygen concentration corresponding to the optimal extraction scheme, calculate the ratio of the change in residual oxygen concentration to the measured value of oxygen concentration before extraction, and obtain the reduction in oxygen concentration.

[0032] Based on the decrease in oxygen concentration, the denitrification load reduction ratio is determined by converting the percentage decrease in oxygen concentration with the corresponding percentage decrease in denitrification load using empirical methods, thus obtaining the denitrification load reduction amount.

[0033] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0034] This invention discloses a method for assessing the load reduction of denitrification in recirculated flue gas. By collecting flue gas temperature, residual oxygen concentration, and recirculation flow rate, and integrating temperature and oxygen concentration gradients at different extraction locations, the method identifies the correlation strength between changes in residual oxygen concentration and recirculation flow rate, assesses the degree of localized oxidation atmosphere enhancement, and adjusts the furnace oxygen content ratio and wind pressure setpoint in conjunction with a target oxygen concentration threshold. This invention calculates the comprehensive reduction value at each extraction location through fan adjustment, pipeline resistance change analysis, and flow matching degree assessment, comprehensively considering temperature gradients, oxygen concentration gradients, and resistance balance benchmarks, determining the optimal extraction scheme, and ultimately quantifying the denitrification load reduction ratio. This invention achieves precise control of the denitrification system, significantly reduces oxygen concentration deviation, improves system operating efficiency and load reduction effect, and provides a scientific basis for optimizing the industrial furnace environment. Attached Figure Description

[0035] Fig. 1 This is a flowchart of a method for evaluating the reduction of recirculated flue gas denitrification load according to the present invention.

[0036] Fig. 2 This is a schematic diagram of a method for evaluating the load reduction of recirculated flue gas denitrification according to the present invention.

[0037] Fig. 3 This is another schematic diagram of a method for evaluating the reduction of recirculated flue gas denitrification load according to the present invention. Detailed Implementation

[0038] To further understand the content of this invention, a detailed description of the invention is provided in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. It should also be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0039] like Figs. 1-3 The method for assessing the reduction of recirculated flue gas denitrification load in this embodiment may specifically include:

[0040] S101. Obtain the flue gas temperature, residual oxygen concentration, and recirculation flow rate transmitted by the multi-point temperature acquisition device and the oxygen content monitoring device, and obtain the temperature gradient and oxygen concentration gradient corresponding to different extraction locations through data fusion processing.

[0041] The process involves acquiring flue gas temperature values ​​transmitted by multi-point temperature acquisition devices within the flue and residual oxygen concentration output by oxygen content monitoring devices. Data synchronization is determined based on the acquisition timestamps of these values. When the time deviation exceeds a preset threshold, time alignment processing is performed to obtain a time-synchronized temperature and oxygen content dataset. Based on this dataset, Kriging space interpolation is used to calculate the temperature and oxygen concentration between different extraction points, resulting in a continuously distributed temperature and oxygen concentration field. For this continuously distributed field, the finite difference method is used to calculate the rate of temperature change and the rate of oxygen concentration change between adjacent extraction points, yielding the temperature gradient and oxygen concentration gradient corresponding to different extraction locations.

[0042] In one embodiment, specifically, the data acquisition device includes a thermocouple array and zirconia probes. The thermocouple array is arranged in a matrix along the cross-section of the flue, with the spacing between each measuring point maintained within the range of 0.8 meters to 1.2 meters. The zirconia probes are distributed at the same spacing. Time alignment processing employs a linear interpolation method. When the thermocouple acquisition timestamp is t1 and the zirconia probe acquisition timestamp is t2, if |t1-t2| exceeds a preset threshold of 1 second, the corresponding time value is calculated based on the slope of the two valid data points, aligning the temperature and oxygen concentration values ​​on the time axis. In one embodiment, the thermocouple array is arranged in a matrix along the cross-section of the flue, with the spacing between each measuring point maintained within the range of 0.8 meters to 1.2 meters. The zirconia probes are distributed at the same spacing. Since the thermocouple response time is approximately 3 seconds, while the zirconia probe response time reaches 5 seconds, there is an inherent time delay difference between the two types of sensors.

[0043] Specifically, the time deviation value is obtained by calculating the difference in timestamps between two adjacent samples. When the thermocouple sampling timestamp is t1 and the zirconia probe sampling timestamp is t2, if |t1-t2| exceeds a preset threshold of 1 second, linear interpolation alignment is initiated. The linear interpolation process calculates the corresponding values ​​based on the slope of the two valid data points, aligning the temperature and oxygen concentration values ​​on the time axis.

[0044] It should be noted that the Kriging spatial interpolation method has unique advantages in handling the spatial distribution within flue gas ducts. This method first constructs a semi-variogram function, establishing a spherical or Gaussian model by calculating the spatial correlation between data from different measuring points. In the flue gas environment, due to the continuity of flue gas flow, the temperature and oxygen concentration at adjacent locations exhibit strong spatial correlation. During interpolation, the estimated values ​​of unknown points are obtained by solving the Kriging equations based on the weighting coefficients λi of known measuring points. These weighting coefficients consider the distance, directionality, and flue gas flow characteristics between measuring points. The input is a time-synchronized temperature and oxygen dataset, formatted as an array containing location coordinates (x, y, z) and corresponding temperature and oxygen concentration data, with a dimension of N×5 (N being the number of measuring points). This method enables the reconstruction of continuous temperature and oxygen concentration fields from discrete measuring point data, providing a continuous spatial data foundation for subsequent gradient calculations. The output continuous field is represented by a grid, using a spatial step size Δx = 0.1 meters for gradient calculation using the finite difference method. The construction of this continuous field is crucial for accurately assessing the characteristics of flue gas at different extraction locations, because discrete measurement points cannot fully reflect the complex distribution inside the flue.

[0045] Preferably, the finite difference method uses the central difference scheme to calculate the gradient. For the temperature field T(x,y), the component of the temperature gradient in the x-direction is [T(x+Δx,y)-T(x-Δx,y)] / (2Δx), where Δx is the spatial step size. The oxygen concentration gradient is calculated using the same method.

[0046] In one embodiment, when the flue outlet temperature reaches 380 degrees Celsius, the temperature gradient can reach 15 degrees Celsius per meter in the vertical direction, while the oxygen concentration gradient in the same area is 0.3 percentage points per meter. These gradient values ​​directly reflect the flue gas stratification characteristics at different extraction locations, providing a quantitative basis for assessing the oxygen-carrying capacity of recirculated flue gas.

[0047] S102. Identify the change in residual oxygen concentration at the extraction location based on the temperature gradient and oxygen concentration gradient corresponding to different extraction locations, extract the correlation strength between the change in residual oxygen concentration and the recirculation flow rate, and obtain the level of local oxidation atmosphere enhancement.

[0048] Based on the temperature and oxygen concentration gradients corresponding to different sampling locations, the gradient change rate within adjacent sampling periods is calculated. This gradient change rate is multiplied by the flue gas velocity at the corresponding location to obtain the residual oxygen concentration change at each sampling location. The recirculation flow rate value at the time corresponding to the residual oxygen concentration change is obtained. The Pearson correlation coefficient is used to calculate the correlation value between the residual oxygen concentration change and the recirculation flow rate value, obtaining the coupling degree between oxygen quantity and flow rate. Based on the coupling degree between oxygen quantity and flow rate, when the coupling degree exceeds a preset threshold, the oxygen concentration fluctuation amplitude in the corresponding area within the furnace is calculated per unit time. If the fluctuation amplitude exceeds another preset threshold, the area is marked as an oxidizing atmosphere enhancement zone, resulting in an oxidizing atmosphere distribution map. Using the area ratio of the enhancement zone and the oxygen increase rate within each enhancement zone in the oxidizing atmosphere distribution map, a fuzzy membership function is used to map to a five-level classification standard to determine the level of local oxidizing atmosphere enhancement.

[0049] For example, in one implementation, the gradient rate of change is calculated based on differential operations over consecutive sampling periods.

[0050] Specifically, when the temperature gradient in the k-th sampling period is ∇T_k and the temperature gradient in the (k+1)-th sampling period is ∇T_(k+1), the gradient change rate is calculated as (∇T_(k+1)-∇T_k) / Δt, where Δt is the sampling period, typically set to 10 seconds. The oxygen concentration gradient change rate is calculated in the same way. The flue gas velocity is obtained by measuring with a Pitot tube installed in the flue, and the velocity range is typically between 8 and 15 m / s.

[0051] It should be noted that the physical meaning of the change in residual oxygen concentration lies in reflecting the dynamic transport characteristics of oxygen during flue gas recirculation. Specifically, the formula for calculating the change in residual oxygen concentration is: ΔC = dC / dt × v, where ΔC is the change in residual oxygen concentration, dC / dt is the rate of change of oxygen concentration gradient, and v is the flue gas velocity. When the oxygen concentration gradient in the k-th sampling period is ∇C_k, and the (k+1)-th sampling period is ∇C_(k+1), the rate of change of gradient dC / dt = (∇C_(k+1) - ∇C_k) / Δt, where Δt is the sampling period (usually 10 seconds). The rate of change of gradient characterizes the time-varying characteristics of the spatial distribution of oxygen concentration, while the flue gas velocity represents the oxygen transport rate. The product of the two essentially reflects the change in oxygen flux through a specific extraction location per unit time. When the rate of change of gradient is positive and the flue gas velocity is high, it means that the extraction location is delivering more residual oxygen into the furnace.

[0052] Preferably, a sliding window method is used to process the data sequence during the calculation of the Pearson correlation coefficient. The formula for calculating the Pearson correlation coefficient r is:

[0053] Where xi is the i-th value in the residual oxygen concentration change sequence, and yi is the i-th value in the recirculation flow rate sequence. and These are the means of the two sequences. A sliding window method was used, with a window length of 30 sampling points (corresponding to 5 minutes of data). Strong coupling was defined as |r| > 0.7. This coupling quantifies the sensitivity of oxygen concentration changes to recirculation flow rate; strong coupling implies that flow rate regulation has a significant impact on oxygen concentration distribution.

[0054] In one embodiment, the peak-to-peak value method is used to calculate the oxygen concentration fluctuation amplitude. Typically, a 1-minute period is selected as the statistical period to record the maximum oxygen concentration O within that region. max and minimum value O min The fluctuation amplitude is defined as O max -O min When the coupling degree exceeds a preset threshold of 0.6, fluctuation amplitude calculation is initiated. If the fluctuation amplitude exceeds another preset threshold of 0.5 percentage points, the region is marked as an oxidation atmosphere enhancement zone.

[0055] For example, the oxidizing atmosphere distribution map is constructed using a gridding method. The furnace cross-section is divided into 10×10 grid cells, each cell corresponding to a monitoring area. Different colors are used for visualization based on the oxidizing atmosphere enhancement status of each cell: red indicates a strong enhancement area, yellow indicates a moderate enhancement area, and green indicates a normal area. The distribution map is updated in real time, with a refresh frequency of once every 30 seconds, and can intuitively reflect the spatial distribution characteristics of the oxidizing atmosphere within the furnace.

[0056] Understandably, the design of the fuzzy membership function considers two key input variables: the area ratio of the oxidizing atmosphere enhancement zone and the oxygen increment rate. The area ratio is obtained by dividing the number of grids in the enhancement zone by the total number of grids, ranging from 0 to 1. The oxygen increment rate is defined as the rate of increase in oxygen concentration per minute, expressed as percentage points per minute. Oxygen concentration is sampled in real-time by an oxygen concentration sensor installed inside the furnace, once per minute, and the average value of multiple sampling points in the enhancement zone is taken. The calculation formula is R = (C t -C {t-1} ) / Δt, where R is the rate of increase, C t C represents the current oxygen concentration. {t-1}The oxygen concentration at the previous moment is represented by Δt, which is the time interval (1 minute). The fuzzy membership function adopts a trapezoidal function form, and corresponding membership curves are designed for different classification standards. Through fuzzy inference rules, the membership values ​​of the two input variables are combined to output the final enhancement level. This hierarchical evaluation provides a quantitative basis for subsequent air pressure adjustment and flow optimization, achieving precise control of the furnace oxidizing atmosphere. Furthermore, in actual operation, when a level four or five enhancement level is detected, the control system will automatically trigger an early warning mechanism, prompting operators to adjust the extraction position of the recirculated flue gas or reduce the recirculation flow rate. Through this dynamic evaluation and hierarchical management, it is possible to ensure denitrification efficiency while avoiding combustion instability caused by excessively strong local oxidizing atmospheres.

[0057] S103. Obtain the preset target oxygen concentration threshold of the denitrification system, evaluate the deviation between the local oxidation atmosphere enhancement level and the target oxygen concentration threshold, adjust the oxygen content ratio of the furnace according to the deviation, and obtain the wind pressure set value.

[0058] The target oxygen concentration threshold preset for the denitrification system is obtained. Based on the actual oxygen concentration value corresponding to the local oxidation atmosphere enhancement level, the difference between the actual value and the target threshold is calculated to obtain the oxygen concentration deviation. According to the oxygen concentration deviation, when the deviation is in the negative range, the air supply volume is increased by a preset proportional coefficient corresponding to each percentage point of deviation; when the deviation is in the positive range, the air supply volume is decreased by a preset proportional coefficient corresponding to each percentage point of deviation, resulting in a corrected oxygen content ratio. The required air supply flow rate is determined based on the corrected oxygen content ratio. The fan outlet pressure required to maintain this flow rate is calculated using Bernoulli's equation, resulting in the air pressure setpoint.

[0059] For example, in one embodiment, the target oxygen concentration threshold is determined based on the selective catalytic reduction (SCR) characteristics of the denitrification system. When the oxygen concentration in the flue gas is maintained in the range of 3.5% to 4.5%, the catalyst activity is at a high level, and the nitrogen oxide conversion efficiency reaches its peak. The target oxygen concentration threshold is typically set at 4.0%, a value that balances the requirements of denitrification efficiency and furnace combustion stability.

[0060] Specifically, the oxygen concentration deviation is calculated using a relative deviation method. When the actual oxygen concentration is 4.8% and the target threshold is 4.0%, the deviation is calculated as (4.8-4.0) / 4.0×100%=20%. A positive deviation indicates that the oxygen concentration is too high, requiring a reduction in air supply; a negative deviation indicates that the oxygen concentration is insufficient, requiring an increase in air supply. This relative deviation calculation method eliminates the influence of absolute value differences under different load conditions.

[0061] It should be noted that the preset proportional coefficient is determined based on the response characteristics of the furnace volume and the air supply system. In the negative deviation range, the air supply volume increase coefficient corresponding to each percentage point of deviation is set to 1.2 cubic meters per second; in the positive deviation range, the air supply volume decrease coefficient corresponding to each percentage point of deviation is set to 1.5 cubic meters per second. Different coefficients are used in the positive and negative ranges because the response speed of reducing oxygen is faster than that of increasing oxygen, which is related to the kinetic characteristics of the combustion reaction in the furnace. When the deviation is -10%, the air supply volume increases by 12 cubic meters per second; when the deviation is +15%, the air supply volume decreases by 22.5 cubic meters per second. Preferably, the air pressure calculation uses Bernoulli's equation and considers the resistance characteristics of the duct system. The fan outlet pressure P consists of three parts: dynamic pressure, friction loss, and local resistance loss, and the calculation formula is P = ρv² / 2 + ΔP. f +ΔP l Where ρ is air density, v is flow velocity, and ΔP f For friction loss along the friction path, ΔP l This is a local resistance loss.

[0062] In one embodiment, when the corrected oxygen content ratio determines that a supply airflow of 150 cubic meters per second is required, the flow velocity is calculated based on the cross-sectional area of ​​the air duct. This flow velocity, combined with the air duct length, roughness coefficient, and local resistance coefficient (elbows, valves, etc.), is then used to calculate the setpoint air pressure using Bernoulli's equation. This air pressure value serves as the control target for the blower frequency converter, enabling precise adjustment of the oxygen content in the furnace.

[0063] S104. Adjust the fan according to the wind pressure setpoint, identify the change in pipeline resistance after the fan adjustment, extract the pipeline resistance difference at different extraction positions, obtain the resistance balance benchmark for each extraction position, compare the recirculation flow rate with the resistance balance benchmark, and obtain the flow matching degree for each extraction position.

[0064] The output frequency of the fan inverter is adjusted according to the set wind pressure. The static pressure difference in the pipeline before and after the fan adjustment is collected. The pipeline resistance change is calculated by the ratio of the static pressure difference to the pipeline length. Pressure sensor readings are obtained at different extraction locations. Based on the pressure sensor readings and the pipeline resistance change, the actual resistance value at each extraction location is calculated. The resistance balance benchmark for each extraction location is determined by the difference between the actual resistance value and the design resistance value. The measured recirculation flow rate at each extraction location is collected. The flow matching degree is obtained by comparing the measured recirculation flow rate with the corresponding resistance balance benchmark. A high flow matching degree is achieved when the ratio is between 0.8 and 1.2, and a low flow matching degree is achieved when the ratio exceeds this range.

[0065] For example, in one implementation, the fan inverter adjusts the fan speed by changing the output frequency, thereby changing the system air pressure. When the inverter frequency is adjusted from 50 Hz to 45 Hz, the fan speed decreases proportionally. According to the fan similarity law, the air pressure is proportional to the square of the speed. The pipeline static pressure difference is obtained by measuring differential pressure transmitters installed at the pipeline inlet and outlet.

[0066] It should be noted that the variation in pipe resistance reflects the impact of fan adjustments on the overall pipe network resistance characteristics. Pipe resistance consists of frictional resistance and local resistance, and it changes quadratically with varying airflow. The resistance gradient per unit length can be calculated by dividing the static pressure difference by the pipe length; this gradient multiplied by the total pipe length gives the variation in pipe resistance. This parameter provides fundamental data for subsequent resistance assessments at each extraction location.

[0067] Specifically, the pressure sensors at different extraction locations employ piezoresistive sensors, achieving a measurement accuracy of 0.5%. The design resistance value is a theoretical value calculated during the system design phase based on parameters such as pipe layout, pipe diameter, and number of bends. In actual operation, due to factors such as dust accumulation and corrosion, the actual resistance value will deviate from the design value. By calculating the difference between the actual resistance value and the design resistance value, the degree of resistance deviation at each extraction location can be quantified; this difference serves as the resistance balance benchmark.

[0068] Preferably, the flow matching degree is evaluated using the ratio method. When the ratio of the measured recirculation flow rate to the resistance balance benchmark is within the range of 0.8 to 1.2, it indicates that the flow and resistance characteristics at the extraction location are well matched, and the system is operating stably. A ratio less than 0.8 indicates insufficient flow, which may lead to inadequate flue gas recirculation; a ratio greater than 1.2 indicates excessive flow, which will increase fan power consumption and may cause duct vibration.

[0069] S105. By integrating the flow matching degree, temperature gradient, oxygen concentration gradient and resistance balance benchmark of each extraction location, the comprehensive reduction value of each extraction location is evaluated. The comprehensive reduction values ​​are sorted, and the extraction location with the highest comprehensive reduction value is identified as the optimal extraction scheme.

[0070] The flow matching degree, temperature gradient, oxygen concentration gradient, and resistance balance benchmark are obtained for each extraction location. These four parameters are then normalized to map their values ​​to a dimensionless range of 0 to 1, resulting in a standardized parameter set. Based on this standardized parameter set, a judgment matrix is ​​constructed using the analytic hierarchy process (AHP). By calculating the eigenvector corresponding to the largest eigenvalue of the judgment matrix, the weighting coefficients for the four parameters (flow matching degree, temperature gradient, oxygen concentration gradient, and resistance balance benchmark) are determined. The weighted comprehensive score for each extraction location is calculated by summing the products of these weighting coefficients and their corresponding standardized parameters. This weighted comprehensive score is used as the comprehensive reduction value for each extraction location. The comprehensive reduction values ​​are sorted from largest to smallest. The sorted sequence of location identifiers is extracted, and the location identifier with the highest comprehensive reduction value in the sequence is selected as the optimal extraction location.

[0071] For example, in one implementation, the normalization process is achieved using an extreme value normalization method. For the flow matching parameter, assuming its original value range is [0.5, 1.5], it is normalized using formula (xx... min ) / (x max -x min This is mapped to the [0,1] interval. Temperature gradient, oxygen concentration gradient, and drag balance baseline are treated in the same way. Normalization aims to eliminate the influence of different dimensions on the overall evaluation, allowing parameters to be compared on the same scale.

[0072] It should be noted that the analytic hierarchy process (AHP) constructs the judgment matrix by comparing parameters pairwise. The judgment matrix is ​​a 4×4 positive and negative matrix, where the element aij represents the importance of the i-th parameter relative to the j-th parameter, determined using a 1-9 scale: 1 indicates equal importance, 3 indicates slightly important, 5 indicates significantly important, 7 indicates strongly important, and 9 indicates extremely important.

[0073] Specifically, the judgment matrix is ​​constructed based on the degree of influence of each parameter on the reduction of denitrification load. Flow matching degree directly determines the conveying efficiency of recirculated flue gas, and oxygen concentration gradient reflects the non-uniformity of oxygen distribution in the furnace; both have a direct impact on denitrification load and are given high relative importance. Temperature gradient affects the thermodynamic characteristics and chemical reaction rate of flue gas, and resistance balance benchmark relates to system energy consumption; their relative importance is secondary. A complete judgment matrix is ​​formed through pairwise comparisons. Preferably, the maximum eigenvalue and corresponding eigenvector of the judgment matrix are calculated iteratively using the power method. The initial vector is set to [1,1,1,1]T, and continuous multiplication of the matrix and vector is performed. Convergence is considered achieved when the vector difference between two adjacent iterations is less than 0.001. The obtained eigenvector, after normalization, becomes the weight coefficient of each parameter. Simultaneously, a consistency check is performed, and the consistency index CI=(λ) is calculated. max-n ) / (n-1), where λ maxThe largest eigenvalue is denoted by , and n=4 represents the number of parameters. When the consistency ratio CR=CI / RI<0.1, the consistency of the judgment matrix is ​​considered acceptable, where RI is the random consistency index (RI=0.90 for a 4th-order matrix). If the consistency test fails, the comparison values ​​in the judgment matrix need to be readjusted.

[0074] In one embodiment, a power plant boiler was configured with five candidate extraction locations. After normalization, the standardized parameter set for location A was: flow matching degree 0.85, temperature gradient 0.62, oxygen concentration gradient 0.78, and resistance balance benchmark 0.71. The weighting coefficients obtained through the analytic hierarchy process were 0.35, 0.18, 0.32, and 0.15, respectively. The weighted summation yielded a comprehensive reduction value of 0.85×0.35+0.62×0.18+0.78×0.32+0.71×0.15=0.764.

[0075] For example, the combined reduction values ​​for the other four positions are calculated as follows: 0.682 for position B, 0.735 for position C, 0.591 for position D, and 0.708 for position E. The five combined reduction values ​​are sorted in descending order to obtain the sequence [0.764, 0.735, 0.708, 0.682, 0.591], and the corresponding position identifier sequence is [A, C, E, B, D].

[0076] Understandably, the physical meaning of the comprehensive reduction value lies in quantitatively assessing the reduction potential of each extraction location for the denitrification load. A higher value indicates that when flue gas is recirculated at that location, the oxygen concentration in the furnace can be reduced more effectively, nitrogen oxide generation reduced, and the system's operational economy maintained. The comprehensive reduction value considers multiple factors such as flow, heat transfer, mass transfer, and resistance, representing a multi-objective optimization result. This comprehensive evaluation method allows for the scientific selection of optimal extraction locations in complex flue gas systems, achieving optimized operation of the denitrification system. Furthermore, the establishment of a location identifier sequence provides a basis for dynamic system adjustments. When the optimal location A is unavailable due to maintenance or other reasons, the second-best location C can be selected as an alternative according to the sequence order. This alternative mechanism improves the system's reliability and flexibility.

[0077] In one possible implementation, the calculation of the overall reduction value can also incorporate time-varying factors. When the boiler load changes, the weighting coefficients of each parameter can be dynamically adjusted according to the load rate. Under high load conditions, the weight of the oxygen concentration gradient increases; under low load conditions, the weight of the resistance balance benchmark increases. Through this adaptive adjustment, the optimal extraction scheme can adapt to different operating conditions.

[0078] S106. Extract the recirculation flow rate and residual oxygen concentration change corresponding to the optimal extraction scheme, evaluate the oxygen concentration reduction rate, quantify the denitrification load reduction ratio based on the oxygen concentration reduction rate, and evaluate the denitrification load reduction.

[0079] Extract the recirculation flow rate and residual oxygen concentration change corresponding to the optimal extraction scheme, calculate the ratio of the residual oxygen concentration change to the measured oxygen concentration before extraction, and obtain the oxygen concentration reduction rate. Based on the oxygen concentration reduction rate, and using the empirical relationship that a 1% decrease in oxygen concentration corresponds to a 2% reduction in denitrification load, determine the denitrification load reduction ratio and obtain the denitrification load reduction amount.

[0080] For example, in one implementation, the oxygen concentration measurement before extraction is obtained by a zirconia probe installed at the furnace outlet, which is typically in the range of 4.5% to 5.5% under normal operating conditions. When the optimal extraction scheme is implemented, the change in residual oxygen concentration is negative, indicating a decrease in oxygen concentration.

[0081] Specifically, the reduction in oxygen concentration is calculated using a relative rate of change. If the oxygen concentration before extraction is 5.0% and drops to 4.2% after recirculation, the change in residual oxygen concentration is -0.8%, and the reduction in oxygen concentration is calculated as 0.8 / 5.0 × 100% = 16%. This relative calculation method eliminates the influence of different initial oxygen concentration levels.

[0082] It should be noted that the relationship between oxygen concentration and denitrification load stems from the chemical kinetics of selective catalytic reduction (SCR). The formation rate of nitrogen oxides (NOx) is positively correlated with oxygen concentration; when the oxygen concentration in the furnace decreases, the formation of thermal NOx is inhibited. According to statistical data from numerous coal-fired boilers, for every 1 percentage point decrease in oxygen concentration, the average NOx formation decreases by 2%. Therefore, the denitrification load reduction ratio K = 2 × ΔO%, where ΔO% represents the decrease in oxygen concentration. For example, when the oxygen concentration decreases by 16%, the denitrification load reduction ratio is 32%, meaning the amount of NOx treated by the denitrification system is reduced by approximately one-third.

[0083] Preferably, in practical applications, the delayed volumetric flow rate is obtained to get the flue gas flow rate. This flue gas flow rate is then used to correct the denitrification load reduction. The final reduction effect is verified by monitoring the nitrogen oxide concentration at the chimney inlet. Specifically, the corrected reduction is: Qcorrected = Qinitial × (Factual / Fstandard), where Qinitial is the initial reduction, Qcorrected is the corrected reduction, Factual is the actual flue gas flow rate, and Fstandard is the standard flue gas flow rate.

[0084] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for assessing the reduction in denitrification load of recirculated flue gas, characterized in that, include: The flue gas temperature, residual oxygen concentration, and recirculation flow rate transmitted by the multi-point temperature acquisition device and oxygen content monitoring device are obtained, and the temperature gradient and oxygen concentration gradient corresponding to different extraction locations are obtained through data fusion processing. Based on the temperature gradient and oxygen concentration gradient corresponding to different extraction locations, the change in residual oxygen concentration at the extraction location is identified, and the correlation strength between the change in residual oxygen concentration and the recirculation flow rate is extracted to obtain the level of local oxidation atmosphere enhancement. Obtain the preset target oxygen concentration threshold of the denitrification system, assess the deviation between the local oxidation atmosphere enhancement level and the target oxygen concentration threshold, adjust the oxygen content ratio in the furnace according to the deviation, and obtain the wind pressure setpoint. Adjust the fan according to the wind pressure setpoint, identify the change in pipeline resistance after the fan adjustment, extract the pipeline resistance difference at different extraction positions, obtain the resistance balance benchmark at each extraction position, compare the recirculation flow rate with the resistance balance benchmark, and obtain the flow matching degree at each extraction position. By integrating the flow matching degree, temperature gradient, oxygen concentration gradient and resistance balance benchmark of each extraction location, the comprehensive reduction value of each extraction location is evaluated. The comprehensive reduction values ​​are ranked, and the extraction location with the highest comprehensive reduction value is identified as the optimal extraction scheme. Extract the recirculation flow rate and residual oxygen concentration change corresponding to the optimal extraction scheme, assess the oxygen concentration reduction rate, and quantify the denitrification load reduction ratio based on the oxygen concentration reduction rate.

2. The method for assessing the reduction of recirculated flue gas denitrification load according to claim 1, characterized in that, The method involves identifying the change in residual oxygen concentration at different extraction locations based on the temperature and oxygen concentration gradients, extracting the correlation strength between the change in residual oxygen concentration and the recirculation flow rate, and obtaining the level of local oxidation atmosphere enhancement, including: Based on the temperature gradient and oxygen concentration gradient corresponding to different sampling locations, the gradient change rate within adjacent sampling periods is calculated. The gradient change rate is then multiplied by the flue gas velocity at the corresponding location to obtain the change in residual oxygen concentration at each sampling location. Obtain the recirculation flow rate value at the time corresponding to the change in residual oxygen concentration, and use the Pearson correlation coefficient to calculate the correlation value between the change in residual oxygen concentration and the recirculation flow rate value to obtain the coupling degree between oxygen quantity and flow rate. Based on the coupling degree between oxygen quantity and flow rate, the fluctuation amplitude of oxygen concentration in the corresponding area of ​​the furnace per unit time is calculated. By using the area ratio of the enhanced zone and the oxygen quantity increase rate in each enhanced zone in the oxidation atmosphere distribution map, a fuzzy membership function is used to map to a five-level classification standard to determine the level of local oxidation atmosphere enhancement.

3. The method for assessing the reduction in recirculated flue gas denitrification load according to claim 1, characterized in that, The process integrates the flow matching degree, temperature gradient, oxygen concentration gradient, and resistance balance benchmark at each extraction location to evaluate the comprehensive reduction value at each extraction location. The comprehensive reduction values ​​are then ranked, and the extraction location with the highest comprehensive reduction value is identified as the optimal extraction scheme. This includes: The flow matching degree, temperature gradient, and oxygen concentration gradient at each extraction location are obtained in relation to the resistance balance benchmark, and then normalized to obtain a standardized parameter set. Based on the standardized parameter set, a judgment matrix is ​​constructed using the analytic hierarchy process (AHP). By calculating the eigenvector corresponding to the largest eigenvalue of the judgment matrix, the weight coefficients of flow matching degree, temperature gradient, oxygen concentration gradient, and resistance balance benchmark are determined respectively. The weighted comprehensive score of each extraction position is calculated by summing the products of the weight coefficients and the corresponding standardized parameters. The weighted comprehensive score is used as the comprehensive reduction value of each extraction position. The comprehensive reduction values ​​are sorted from largest to smallest. The position identifier with the highest comprehensive reduction value after sorting is selected to determine the optimal extraction scheme.

4. The method for assessing the reduction of recirculated flue gas denitrification load according to claim 1, characterized in that, The process of acquiring flue gas temperature, residual oxygen concentration, and recirculation flow rate transmitted by the multi-point temperature acquisition device and oxygen content monitoring device, and obtaining the temperature gradient and oxygen concentration gradient corresponding to different extraction locations through data fusion processing, includes: The flue gas temperature value transmitted by the multi-point temperature acquisition device in the flue and the residual oxygen concentration output by the oxygen content monitoring device are obtained. The data synchronization is judged according to the acquisition timestamp of the flue gas temperature value and residual oxygen concentration, and time alignment processing is performed to obtain a time-synchronized temperature and oxygen content dataset. Based on the time-synchronized temperature and oxygen data set, the Kriging spatial interpolation method is used to interpolate the temperature and oxygen concentration between different sampling points to obtain a continuously distributed temperature field and oxygen concentration field. For the continuously distributed temperature field and oxygen concentration field, the rate of temperature change and the rate of oxygen concentration change of adjacent extraction locations are calculated by the finite difference method to obtain the temperature gradient and oxygen concentration gradient corresponding to different extraction locations.

5. The method for assessing the reduction in recirculated flue gas denitrification load according to claim 1, characterized in that, The process of obtaining the preset target oxygen concentration threshold of the denitrification system, evaluating the deviation between the local oxidation atmosphere enhancement level and the target oxygen concentration threshold, adjusting the oxygen content ratio in the furnace according to the deviation, and obtaining the wind pressure setpoint includes: Obtain the preset target oxygen concentration threshold of the denitrification system, and calculate the difference between the actual value and the target threshold based on the actual oxygen concentration value corresponding to the level of local oxidation atmosphere enhancement, to obtain the oxygen concentration deviation. Based on the oxygen concentration deviation, the air supply volume is adjusted according to a preset proportional coefficient that increases or decreases the air supply volume for each percentage point of deviation, to obtain the corrected oxygen content ratio. The required air supply flow rate is determined by the corrected oxygen content ratio. The fan outlet pressure required to maintain the air supply flow rate is calculated using Bernoulli's equation based on the air supply flow rate, and the air pressure setpoint is obtained.

6. The method for assessing the reduction of recirculated flue gas denitrification load according to claim 5, characterized in that, The process involves adjusting the fan according to the wind pressure setpoint, identifying the change in pipe resistance after fan adjustment, extracting the pipe resistance difference at different extraction locations, obtaining the resistance balance benchmark for each extraction location, and comparing the recirculation flow rate with the resistance balance benchmark to obtain the flow rate matching degree for each extraction location. This includes: Adjust the output frequency of the fan inverter according to the wind pressure setpoint, collect the static pressure difference in the pipeline before and after the fan adjustment, and calculate the change in pipeline resistance by the ratio of the static pressure difference to the pipeline length. Obtain pressure sensor readings at different extraction locations. Based on the pressure sensor readings and the variation in pipeline resistance, calculate the actual resistance value at each extraction location. Determine the resistance balance benchmark at each extraction location by the difference between the actual resistance value and the design resistance value. Collect the measured recirculation flow rate at each extraction location, and determine the flow rate matching degree at each extraction location based on the ratio of the measured recirculation flow rate to the resistance balance benchmark at the corresponding location.

7. The method for assessing the reduction in recirculated flue gas denitrification load according to claim 1, characterized in that, The extraction of the optimal extraction scheme corresponds to the change in recirculation flow rate and residual oxygen concentration. The magnitude of the oxygen concentration reduction is assessed, and the denitrification load reduction ratio is quantified based on this reduction. The assessment of the denitrification load reduction includes: Extract the recirculation flow rate and the change in residual oxygen concentration corresponding to the optimal extraction scheme, calculate the ratio of the change in residual oxygen concentration to the measured value of oxygen concentration before extraction, and obtain the reduction in oxygen concentration. Based on the decrease in oxygen concentration, the denitrification load reduction ratio is determined by converting the percentage decrease in oxygen concentration with the corresponding percentage decrease in denitrification load using empirical methods, thus obtaining the denitrification load reduction amount.

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