CN113378353B - Method for evaluating similarity of NOx flux distribution based on gridding test - Google Patents

Abstract

The invention discloses a method for evaluating NOx flux distribution similarity based on a gridding test, which comprises the following steps: step 1: dividing grids on the cross section of the flue, respectively testing the speed and NOx concentration of each grid under different working conditions by using a pitot tube and a flue gas analyzer, and correspondingly calculating NOx flux distribution under different working conditions; step 2: calculating the total flux of NOx of the cross section of the flue and the standard deviation of a NOx flux distribution matrix under different working conditions, calculating a conversion coefficient according to the principle that the total flux is consistent, and solving a point division matrix; and step 3: respectively defining 3 indexes of a relation degree, a concentration degree and a contrast degree according to a mathematical statistics theory; and 4, step 4: and establishing a similarity comprehensive evaluation function by combining the indexes, and giving a similar criterion. According to the invention, by constructing the NOx flux distribution similarity evaluation method, the similarity of the internal flue gas conditions of the flue gas denitration device under different operation conditions is evaluated, and a guiding direction is provided for the multi-condition collaborative optimization and reconstruction of the flue gas conditions.

Description

Method for evaluating similarity of NOx flux distribution based on gridding test

Technical Field

The invention relates to a grid test-based NOx flux distribution similarity evaluation method, and belongs to the technical field of coal-fired unit flue gas treatment.

Background

With the normalization of the ultra-low emission operation management mode of the flue gas of the coal-fired unit, the strict real-time monitoring and control of the emission of the atmospheric pollutants and the improvement of the working enthusiasm of energy conservation and consumption reduction promoted by each enterprise, the seeking of the high-efficiency, economic and stable operation of the flue gas denitration facility becomes the topic of wide attention of each coal-fired power generation enterprise. The realization of the uniform distribution of the ammonia nitrogen molar ratio at the inlet of the denitration catalyst is the key for solving the problem of cooperative optimization of reaching the emission standard and reducing the consumption of reducing agent. Usually, a mixing device is additionally arranged behind an ammonia injection device and in front of a denitration catalyst to generate vortex to enhance the mixing of the denitration reducing agent and NOx in flue gas, and the matching relation between the denitration reducing agent amount injected into a flue by each partition and the NOx content in the flue gas is adjusted by adjusting the opening degree of each partition valve of the ammonia injection device. Tests show that the upstream flue gas flow rate of each partition of the ammonia injection device and the concentration of NOx in the flue gas can be adjusted to change along with the change of coal quality and combustion. At present, the flow field distribution characteristics of all working conditions are analyzed by adopting the flue gas flow velocity, the NOx concentration or the relative standard deviation of the ammonia nitrogen molar ratio in an isolated manner, the time-varying relation of the NOx flux distribution in the flue gas of all subareas of the ammonia spraying device is ignored, namely the relation degree of the composite index NOx flux distribution characteristics of the flue gas flow velocity, the NOx concentration and the subarea area among different working conditions, and the possibility of realizing the uniform distribution of the ammonia nitrogen molar ratio under all working conditions is reflected more visually and more accurately. It is therefore a meaningful task to study and evaluate the similarity of NOx flux distribution upstream of the ammonia injection grid under various conditions.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, and provides a method for evaluating NOx flux distribution similarity based on a gridding test, which is used for comprehensively analyzing the similar conditions of NOx flux distribution under multiple working conditions.

The technical scheme adopted by the invention for solving the problems is as follows: a NOx flux distribution similarity evaluation method based on a gridding test is characterized by comprising the following steps:

step 1: dividing grids on the cross section of the flue, respectively testing the speed and NOx concentration of each grid under different working conditions by using a pitot tube and a flue gas analyzer, and correspondingly calculating NOx flux distribution under different working conditions;

step 2: calculating the total flux of NOx of the cross section of the flue and the standard deviation of a NOx flux distribution matrix under different working conditions, calculating a conversion coefficient according to the principle that the total flux is consistent, and solving a point division matrix;

and step 3: respectively defining 3 indexes of a relation degree, a concentration degree and a contrast degree according to a mathematical statistics theory;

and 4, step 4: and establishing a similarity comprehensive evaluation function by combining the indexes, and giving a similar criterion.

In the step 1, the cross section of the flue is divided into grids with m multiplied by n (length multiplied by width) areas a, the geometric center of each grid is taken as a measurement point, and the speed V of each grid is tested_ijAnd NOx concentration C_ij(i-1 … m, j-1 … n); the distribution expression matrix of the NOx flux of the flue section of the working condition 1 is as follows:

the distribution expression matrix of NOx flux of the flue section of the working condition 2 is as follows:

in step 2, the matrix Φ is expressed according to the NOx flux distribution₁Calculating the total flux phi' and standard deviation sigma of NOx in the section of the flue under the working condition 1₁：

Representation matrix phi from NOx flux distribution₂Calculating the total NOx flux phi' and standard deviation sigma of the section of the flue under the working condition 2₂：

Calculating a conversion coefficient alpha and a point division matrix psi according to the total NOx flux under different working conditions:

α＝Φ′Φ″

in the step 3: satisfaction in the elements of the point division matrix Ψ

Counting the number of the first and second groups, namely the same number K;

satisfaction in the elements of the point division matrix Ψ

Counting the number of the adjacent numbers P;

satisfaction in the elements of the point division matrix Ψ

Counting the number of the pairs, namely counting the pairs Q;

obviously, the sum of the same number, the adjacent number and the opposite number is the number of the dot division matrix elements, i.e., K + P + Q ═ mn;

introducing degree of relation which is a linear function of identity number, adjacent number and opposite number, i.e.

Introducing a concentration degree which is an exponential function on the point divided matrix elements, i.e.

Contrast is introduced as an exponential function representing the standard deviation of the matrix with respect to NOx flux distribution

In step 4, establishing a similar comprehensive evaluation function f ═ r + s + t)/3;

when the value range of the comprehensive evaluation function is within [0.7,1], the NOx flux distribution under two working conditions is determined to be similar, and the design requirement that the flue gas condition of the flue section is basically unchanged is met.

Compared with the prior art, the invention has the following advantages and effects: according to the invention, by constructing the NOx flux distribution similarity evaluation method, the similarity of the internal flue gas conditions of the flue gas denitration device under different operation conditions is evaluated, and a guiding direction is provided for the multi-condition collaborative optimization and reconstruction of the flue gas conditions.

Drawings

FIG. 1 is a schematic diagram of a cross-sectional meshing of a flue in an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail below by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and are not to be construed as limiting the present invention.

Examples are given.

Referring to fig. 1, in this embodiment, a method for evaluating NOx flux distribution similarity based on a gridding test includes the following specific steps:

step 1: carrying out grid division on the cross section of the flue, respectively testing the speed and the NOx concentration of the central point of each grid under different working conditions by using a pitot tube and a flue gas analyzer, and correspondingly calculating the NOx flux distribution under different working conditions;

and 2, step: calculating the total flux of NOx of the cross section of the flue and the standard deviation of a NOx flux distribution matrix under different working conditions, calculating a conversion coefficient according to the principle that the total flux is consistent, and solving a point division matrix;

and step 3: respectively defining 3 indexes of a relation degree, a concentration degree and a contrast degree according to a mathematical statistics theory;

and 4, step 4: and establishing a similar comprehensive evaluation function by combining the indexes, and giving a similar criterion.

The invention is further illustrated with reference to fig. 1 as follows:

under the working condition 1, the actual measurement results of the flue section speed distribution, the NOx concentration distribution, the NOx flux distribution, the flux distribution matrix standard deviation and the total flux are respectively as follows:

σ₁＝0.58

Φ′＝179

under the working condition 2, the actual measurement results of the flue section speed distribution, the NOx concentration distribution, the NOx flux distribution, the flux distribution matrix standard deviation and the total flux are respectively as follows:

σ₂＝0.51

Φ″＝120

next, the conversion coefficients, the dot division matrix, and the respective analysis indexes are calculated.

Conversion coefficient:

α＝179/120＝1.49

dot division matrix:

the number of elements in the dot division matrix is 30;

satisfies | Φ in the elements of the dot division matrix_ij-14 identical numbers K | < 0.1;

the element of the difference matrix satisfies | phi more than or equal to 0.1_ij-12, the number of neighbors P ═ 1| < 0.3;

satisfies | Φ in elements of the difference matrix_ij-4 as many as 1 ≧ 0.3 or the number of opponents Q;

and (3) calculating the contact degree:

and (3) calculating the concentration ratio:

calculating the contrast ratio:

similar comprehensive evaluation function:

f＝(r+s+t)/3＝0.75

when the value range of the comprehensive evaluation function is within [0.7,1], the NOx flux distributions under the two working conditions are considered to have high similarity. From the similar comprehensive evaluation function calculated value of this embodiment, the flue gas distribution condition under the different operating modes is similar, and is comparatively stable to operating mode change flue gas distribution promptly, and the fluctuation is less.

Those not described in detail in this specification are well within the skill of the art.

Although the present invention has been described with reference to the above embodiments, it should be understood that the scope of the present invention is not limited thereto, and that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims (1)

1. A NOx flux distribution similarity evaluation method based on a gridding test is characterized by comprising the following steps:

step 1: dividing grids on the cross section of the flue, respectively testing the speed and NOx concentration of each grid under different working conditions by using a pitot tube and a flue gas analyzer, and correspondingly calculating NOx flux distribution under different working conditions;

step 2: calculating the total flux of NOx of the cross section of the flue and the standard deviation of a NOx flux distribution matrix under different working conditions, calculating a conversion coefficient according to the principle that the total flux is consistent, and solving the matrix;

and step 3: respectively defining 3 indexes of a link ratio, a concentration ratio and a contrast ratio according to a mathematical statistics theory;

and 4, step 4: establishing a similarity comprehensive evaluation function by combining the indexes, and giving a similar criterion;

in the step 1, the cross section of the flue is divided into grids with m multiplied by n areas of a, the geometric center of each grid is taken as a measuring point, and the speed V of each grid is tested_ijAnd NOx concentration C_ij(i-1 … m, j-1 … n); the distribution expression matrix of NOx flux of the flue section of the working condition 1 is as follows:

under the working condition 2, the distribution expression matrix of the NOx flux of the flue section is as follows:

in step 2, the matrix Φ is expressed according to the NOx flux distribution₁Calculating the total flux phi' and standard deviation sigma of NOx in the section of the flue under the working condition 1₁：

Representation matrix phi from NOx flux distribution₂Calculating the total NOx flux phi' and standard deviation sigma of the section of the flue under the working condition 2₂：

Calculating a conversion coefficient alpha and a matrix psi according to the total NOx flux under different working conditions:

α＝Φ′/Φ″

in the step 3:

for satisfaction of the elements of the matrix Ψ

Counting the number of the first and second groups, namely the same number K;

for satisfaction of the elements of the matrix Ψ

Counting the number of the adjacent numbers P;

for satisfaction of the elements of the matrix Ψ

Counting the number of the pairs, namely counting the pairs Q;

the sum of the same number, the adjacent number and the opposite number is the number of matrix elements, namely K + P + Q ═ mn;

the degree of relation is introduced, which is a linear function of the same number, the adjacent number and the opposite number,namely, it is

Introducing a concentration which is an exponential function with respect to the matrix elements, i.e.

Contrast is introduced as an exponential function representing the standard deviation of the matrix with respect to NOx flux distribution

In step 4, establishing a similar comprehensive evaluation function f ═ r + s + t)/3;

when the value range of the comprehensive evaluation function is within [0.7,1], the NOx flux distribution under two working conditions is determined to be similar, and the design requirement that the flue gas condition of the flue section is basically unchanged is met.

Images