1. A method for calibrating an oxygen field of a tail flue of a power station boiler is characterized by comprising the following steps: adjusting the stable operation of the boiler under various loads, sampling and analyzing the smoke of each grid measuring point on a flue measuring section to obtain the smoke oxygen content of each grid measuring point under the corresponding load state, calculating the spatial mean value of the smoke oxygen content of each measuring section under various loads, and calculating to obtain the average absolute deviation between the smoke oxygen content of each grid measuring point of each measuring section under various loads and the spatial mean value; and determining the minimum value of the average absolute deviation in all the grid measuring points, if the minimum value of the average absolute deviation does not exceed a set value, determining the corresponding grid measuring points as calibration points, and installing a DCS (distributed control system) oxygen sensor at the positions of the calibration points for correction.

2. The method for calibrating the oxygen field of the tail flue of the power station boiler as claimed in claim 1, wherein the method comprises the following steps:

the method for calibrating the oxygen field of the tail flue of the power station boiler comprises the following steps:

step 1: according to the requirements of test regulations, test holes are formed in a tail flue of the power station boiler according to the size of the flue, and the number of the test holes is m;

step 2: adjusting the boiler to stably run at 100% rated load, and sampling and analyzing the flue gas of each grid measuring point i on the section where the test measuring hole is located by using a flue gas analyzer according to the requirements of the test specification by adopting an m × n grid method, wherein the i is 1,2,3 … m × n, and obtaining the oxygen content D of the flue gas of each grid measuring point i under 100% rated load_1,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under the 100 percent rated load is obtained by the calculation of the formula (1)₁：

And step 3: adjusting the boiler to stably run at 75% rated load, and sampling and analyzing the flue gas of each grid measuring point i in sequence in the same manner as the step 2 to obtain the oxygen content D of the flue gas of each grid measuring point i at 75% rated load_2,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under 75 percent rated load is calculated and obtained by the formula (2)₂：

And 4, step 4: adjusting the boiler to stably run at 50% rated load, and sampling and analyzing the flue gas of each grid measuring point i in sequence in the same manner as the step 2 to obtain the oxygen content D of the flue gas of each grid measuring point i at 50% rated load_3,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under 50 percent rated load is obtained by the formula (3)₃：

And 5: calculating and obtaining the average absolute deviation S between the oxygen content of the flue gas of each grid measuring point i of the cross section of the tail flue of the boiler and the space mean value under three different loads by the formula (4)_i；

Step 6: determining the average absolute deviation S between the oxygen content of the smoke of all grid measuring points i and the space mean value obtained by calculation_iMinimum value of S_xWill be equal to the minimum value S_xMarking the corresponding grid measuring point as a grid measuring point x;

if: s_xIf the grid measuring point x is not greater than the deviation set value Q, judging that the grid measuring point x meets the calibration precision requirement of the flue gas oxygen field, taking the grid measuring point x as a calibration point, and installing a DCS oxygen sensor at the position of the calibration point for correction;

if: s_xIf the deviation is greater than the deviation set value Q, entering a step 7;

and 7: defining the central point of every four adjacent grid measuring points in all grid measuring points as a measuring point central point j, wherein j is 1,2,3 … (m-1) × (n-1); the oxygen content M of the position of the central point j of each measuring point in the cross section of the flue under each working condition of 100 percent, 75 percent and 50 percent of rated load is obtained by one-to-one corresponding calculation by adopting a linear interpolation method_1,j，M_2,jAnd M_3,j；

And 8: calculating and obtaining the average absolute deviation S between the oxygen content of the flue gas of the central point j of each measuring point in the cross section of the tail flue of the boiler and the space mean value under three different loads in the same way as the steps 2 to 5_j；

And step 9: determining the average absolute deviation S between the oxygen content of the smoke of the central point j of all the measuring points and the space mean value in the same way as the step 6_jMinimum value of S_a(ii) a Will be equal to the minimum value S_aThe corresponding measuring point center point is marked as a measuring point center point a;

if: s_aIf the measured point center point a is not greater than the deviation set value Q, judging that the measured point center point a meets the calibration precision requirement of the flue gas oxygen field, taking the measured point center point a as a calibration point, and installing a DCS oxygen sensor at the position of the calibration point for correction;

if: s_aIf the deviation is greater than the set value Q, the result indicates thatThe deviation of the oxygen content of the flue gas of each grid measuring point in the flue section is large, the distribution is extremely uneven, a proper flue section position needs to be selected again at the tail of the boiler to be additionally provided with a test measuring hole, and the oxygen field of the flue section is calibrated again according to the method from the step 1 to the step 9.

3. The method for calibrating the oxygen field of the tail flue of the power station boiler as claimed in claim 1, wherein the method comprises the following steps: the value of the deviation set value Q is 0.2.

4. The method for calibrating the oxygen field of the tail flue of the power station boiler as claimed in claim 1, wherein the method comprises the following steps: the test procedures include GB/T10184-.

5. The method for calibrating the oxygen field of the tail flue of the power station boiler as claimed in claim 1, wherein the method comprises the following steps: the calibration method is used for measuring and calibrating other physical quantity space fields including the exhaust gas temperature field of the power station boiler.

Background

The measurement of the spatial mean value of the oxygen content of the flue gas in the tail flue of the power station boiler is an important means for monitoring the stable, safe and economic operation of the boiler. Through measurement, whether the fuel is completely combusted and the air distribution amount is reasonable can be judged. If the oxygen content is too low, the fuel can be burnt insufficiently, so that the combustion is unstable, and in severe cases, the boiler hearth can extinguish fire. If the oxygen content is too high, more flue gas can take away heat excessively, and the heat loss of the flue gas is increased, so that the operation efficiency of the boiler is reduced. In the intelligent combustion system developed in recent years, the oxygen content of the flue gas in the tail flue of the power station boiler is introduced into an automatic combustion control system as an important parameter for controlling fuel and air supply quantity, so that the aim of intelligently controlling the optimal combustion is fulfilled. In addition, the oxygen content of the flue gas in the tail flue of the power station boiler is a very important assessment index in monitoring of the atmospheric pollutants, and the key for determining whether the emission concentration of the pollutants reaches the standard is achieved to a certain extent.

However, the oxygen content of the flue gas in the tail flue of the power station boiler is not uniformly distributed in a larger flue space, and the measurement result and the actual value of the flue gas often have larger deviation, so that the boiler can not be well guided to be stably, safely and economically combusted, the intelligent combustion control is greatly restricted, and the optimal combustion purpose is difficult to realize. Besides, the pollutant emission concentration monitoring result deviates from the actual value greatly, and the assessment of the atmospheric pollutant monitoring is influenced. In order to solve the problem, the power plant mainly adopts a representative point method to carry out single-point or multi-point measurement at present. The method for taking the representative point is essentially to carry out space measurement on the oxygen field, calculate the position which can represent the space mean value and install the zirconia measuring instrument. The method generally performs a test of the oxygen content in the space under a full-load working condition, then calculates an average value, and finds a position closest to the average value of the space to install a zirconia measuring instrument. The method is often influenced by the position of a test measuring point and load change, the measured value cannot well reflect the actual situation, and the application effect is poor. In order to ensure the safe, stable and economic operation of the boiler and promote the development of intelligent combustion, the accurate measurement of the spatial mean value of the oxygen content of the flue gas in the tail flue of the power station boiler becomes a difficult problem to be solved urgently.

Disclosure of Invention

In order to avoid the defects in the prior art, the invention provides the method for calibrating the oxygen field of the tail flue of the power station boiler, so that the problem of accurate measurement of the spatial mean value of the oxygen content of the flue gas in the tail flue of the power station boiler is solved, the safe and economic operation of the boiler is ensured, and the development of intelligent combustion is promoted.

The technical problem is that the invention adopts the following technical scheme:

the method for calibrating the oxygen field of the tail flue of the power station boiler is characterized by comprising the following steps: adjusting the stable operation of the boiler under various loads, sampling and analyzing the smoke of each grid measuring point on a flue measuring section to obtain the smoke oxygen content of each grid measuring point under the corresponding load state, calculating the spatial mean value of the smoke oxygen content of each measuring section under various loads, and calculating to obtain the average absolute deviation between the smoke oxygen content of each grid measuring point of each measuring section under various loads and the spatial mean value; and determining the minimum value of the average absolute deviation in all the grid measuring points, if the minimum value of the average absolute deviation does not exceed a set value, determining the corresponding grid measuring points as calibration points, and installing a DCS (distributed control system) oxygen sensor at the positions of the calibration points for correction.

The method for calibrating the oxygen field of the tail flue of the power station boiler is also characterized in that:

the method for calibrating the oxygen field of the tail flue of the power station boiler comprises the following steps:

step 1: according to the requirements of test regulations, test holes are formed in a tail flue of the power station boiler according to the size of the flue, and the number of the test holes is m;

step 2: adjusting the boiler to stably run at 100% rated load, and sampling and analyzing the flue gas of each grid measuring point i on the section where the test measuring hole is located by using a flue gas analyzer according to the requirements of the test specification by adopting an m × n grid method, wherein the i is 1,2,3 … m × n, and obtaining the oxygen content D of the flue gas of each grid measuring point i under 100% rated load_1,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under the 100 percent rated load is obtained by the calculation of the formula (1)₁：

And step 3: adjusting the boiler to stably run at 75% rated load, and sampling and analyzing the flue gas of each grid measuring point i in sequence in the same manner as the step 2 to obtain the oxygen content D of the flue gas of each grid measuring point i at 75% rated load_2,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under 75 percent rated load is calculated and obtained by the formula (2)₂：

And 4, step 4: adjusting the boiler to stably run at 50% rated load, and sampling and analyzing the flue gas of each grid measuring point i in sequence in the same manner as the step 2 to obtain the oxygen content D of the flue gas of each grid measuring point i at 50% rated load_3,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under 50 percent rated load is obtained by the formula (3)₃：

And 5: the oxygen content of the smoke of each grid measuring point i of the cross section of the tail flue of the boiler under three different loads and the oxygen content of the smoke at each grid measuring point i are obtained by calculation according to the formula (4)Mean absolute deviation of spatial mean S_i；

Step 6: determining the average absolute deviation S between the oxygen content of the smoke of all grid measuring points i and the space mean value obtained by calculation_iMinimum value of S_xWill be equal to the minimum value S_xMarking the corresponding grid measuring point as a grid measuring point x;

if: s_xIf the grid measuring point x is not greater than the deviation set value Q, judging that the grid measuring point x meets the calibration precision requirement of the flue gas oxygen field, taking the grid measuring point x as a calibration point, and installing a DCS oxygen sensor at the position of the calibration point for correction;

if: s_xIf the deviation is greater than the deviation set value Q, entering a step 7;

and 7: defining the central point of every four adjacent grid measuring points in all grid measuring points as a measuring point central point j, wherein j is 1,2,3 … (m-1) × (n-1); the oxygen content M of the position of the central point j of each measuring point in the cross section of the flue under each working condition of 100 percent, 75 percent and 50 percent of rated load is obtained by one-to-one corresponding calculation by adopting a linear interpolation method_1,j，M_2,jAnd M_3,j；

And 8: calculating and obtaining the average absolute deviation S between the oxygen content of the flue gas of the central point j of each measuring point in the cross section of the tail flue of the boiler and the space mean value under three different loads in the same way as the steps 2 to 5_j；

And step 9: determining the average absolute deviation S between the oxygen content of the smoke of the central point j of all the measuring points and the space mean value in the same way as the step 6_jMinimum value of S_a(ii) a Will be equal to the minimum value S_aThe corresponding measuring point center point is marked as a measuring point center point a;

if: s_aIf the measured point center point a is not greater than the deviation set value Q, judging that the measured point center point a meets the calibration precision requirement of the flue gas oxygen field, taking the measured point center point a as a calibration point, and installing a DCS oxygen sensor at the position of the calibration point for correction;

if: s_aIf the oxygen content of the flue gas at each grid measuring point in the flue section is larger than the deviation set value Q, the flue gas oxygen content deviation is large, the distribution is extremely uneven, a proper flue section position needs to be selected again at the tail of the boiler to be additionally provided with the test measuring hole, and the flue section oxygen field is calibrated again according to the method from the step 1 to the step 9.

The method for calibrating the oxygen field of the tail flue of the power station boiler is also characterized in that: the value of the deviation set value Q is 0.2.

The method for calibrating the oxygen field of the tail flue of the power station boiler is also characterized in that: the test procedures include GB/T10184-2015 Power station boiler Performance test procedure.

The method for calibrating the oxygen field of the tail flue of the power station boiler is also characterized in that: the calibration method is used for measuring and calibrating other physical quantity space fields including the exhaust gas temperature field of the power station boiler.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention adopts three different load working conditions covering the whole operation load range to carry out calibration test, and eliminates the influence of the load change of the unit on the calibration result.

2. The invention adopts a mathematical method with minimum square error to search the calibration point and install the DCS on-line measuring point, can quickly and accurately find the optimal installation position and calculate the calibration precision.

3. The invention adopts a test measurement data space linear interpolation method for calibration based on space continuity characteristics, and eliminates the adverse effect of the test measurement point position on the calibration result.

Drawings

FIG. 1 is a schematic view of the operation flow of the calibration method of the oxygen field of the tail flue of the power station boiler.

Detailed Description

The method for calibrating the oxygen field of the tail flue of the power station boiler in the embodiment comprises the steps of adjusting the boiler to stably run under various loads, carrying out sampling analysis on flue gas of each grid measuring point on a flue measuring section to obtain the oxygen content of the flue gas of each grid measuring point under the corresponding load state, calculating the space mean value of the oxygen content of the flue gas of each measuring point of the measuring section under various loads, and calculating to obtain the average absolute deviation of the oxygen content of the flue gas of each grid measuring point of the measuring section under various loads and the space mean value; and determining the minimum value of the average absolute deviation in all the grid measuring points, if the minimum value of the average absolute deviation does not exceed a set value, determining the corresponding grid measuring points as calibration points, and installing a DCS (distributed control system) oxygen sensor at the positions of the calibration points for correction.

The spatial mean value of the oxygen content of the flue gas of the boiler tail flue is a key parameter for energy-saving monitoring and intelligent combustion control of a power plant. In consideration of the cost of setting measuring points in a power plant, the single-point measurement is combined with the calibration method in the embodiment, so that the accurate measurement with higher precision can be realized, and the general requirements of industrial application are met.

In order to eliminate the influence of the change of the electrical load on the distribution characteristics of the oxygen content of the flue gas in the flue, the calibration is performed for three different loads in the embodiment. Meanwhile, considering the influence of the positions of the discrete grid points, the oxygen content of the smoke at the central point of the measuring point is obtained by a mathematical method according to the principle of space continuity for calibration.

Referring to fig. 1, the method for calibrating the oxygen field of the tail flue of the utility boiler in the embodiment is performed according to the following steps:

step 1: according to the requirements of test regulations, test holes are formed in a tail flue of the power station boiler according to the size of the flue, and the number of the test holes is m; relevant test protocols include GB/T10184-.

Step 2: adjusting the boiler to stably run at 100% rated load, utilizing a flue gas analyzer to sample and analyze the flue gas of each grid measuring point i on the section where the test measuring hole is located by adopting an m multiplied by n grid method according to the requirements of test regulations, wherein i is 1,2,3 … m multiplied by n, and obtaining the oxygen content D of the flue gas of each grid measuring point i under 100% rated load_1,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under the 100 percent rated load is obtained by the calculation of the formula (1)₁：

And step 3: adjusting the boiler to stably run at 75% rated load, and sampling and analyzing the flue gas of each grid measuring point i in sequence in the same manner as the step 2 to obtain the oxygen content D of the flue gas of each grid measuring point i at 75% rated load_2,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under 75 percent rated load is calculated and obtained by the formula (2)₂：

And 4, step 4: adjusting the boiler to stably run at 50% rated load, and sampling and analyzing the flue gas of each grid measuring point i in sequence in the same manner as the step 2 to obtain the oxygen content D of the flue gas of each grid measuring point i at 50% rated load_3,i(ii) a The space average value A of the oxygen content of the smoke of the measuring section under 50 percent rated load is obtained by the formula (3)₃：

And 5: calculating and obtaining the average absolute deviation S between the oxygen content of the flue gas of each grid measuring point i of the cross section of the tail flue of the boiler and the space mean value under three different loads by the formula (4)_i；

Step 6: determining the average absolute deviation S between the oxygen content of the smoke of all grid measuring points i and the space mean value obtained by calculation_iMinimum value of S_xWill be compared with the minimum value S_xMarking the corresponding grid measuring point as a grid measuring point x;

if: s_xIf the grid measuring point x is not greater than the deviation set value Q, judging that the grid measuring point x meets the calibration precision requirement of the flue gas oxygen field, taking the grid measuring point x as a calibration point, and installing a DCS oxygen sensor at the position of the calibration point for correction;

if: s_xIf the deviation is greater than the deviation set value Q, entering a step 7;

and 7: defining the central point of every four adjacent grid measuring points in all grid measuring points as a measuring point central point j, wherein j is 1,2,3 … (m-1) × (n-1); the oxygen content M of the position of the central point j of each measuring point in the flue section under each working condition of 100 percent, 75 percent and 50 percent of rated load is obtained by one-to-one corresponding calculation by adopting a linear interpolation method_1,j，M_2,jAnd M_3,j；

And 8: calculating and obtaining the average absolute deviation S between the oxygen content of the flue gas of the central point j of each measuring point in the cross section of the tail flue of the boiler and the space mean value under three different loads in the same way as the steps 2 to 5_j；

And step 9: determining the average absolute deviation S between the oxygen content of the smoke of the central point j of all the measuring points and the space mean value in the same way as the step 6_jMinimum value of S_a(ii) a Will be summed with the minimum value S_aThe corresponding measuring point center point is marked as a measuring point center point a;

if: s_aIf the measured point center point a is not greater than the deviation set value Q, judging that the measured point center point a meets the calibration precision requirement of the flue gas oxygen field, taking the measured point center point a as a calibration point, and installing a DCS oxygen sensor at the position of the calibration point for correction;

if: s_aIf the oxygen content of the flue gas at each grid measuring point in the flue section is larger than the deviation set value Q, the flue gas oxygen content deviation is large, the distribution is extremely uneven, a proper flue section position needs to be selected again at the tail of the boiler to be additionally provided with the test measuring hole, and the flue section oxygen field is calibrated again according to the method from the step 1 to the step 9.

Considering that the measurement accuracy of the oxygen content of the conventional flue gas analyzer is ± 0.2% Vol, the deviation set value Q in this embodiment is set to be a predetermined value of 0.2 (unit%),

the calibration method of the invention can be applied to the measurement calibration of space fields of other physical quantities including the exhaust gas temperature field of a power station boiler.

Application example:

the measurement results of the oxygen content of the flue gas at discrete grid measuring points in the flue gas of a certain flue section of a certain power plant under three different loads are shown in table 1, table 2 and table 3. The number m of the smoke channel test measuring holes is 6, and the number of the discrete grid measuring points is 60.

TABLE 1 measurement of oxygen content in flue gas at each discrete space measurement point of a unit at 100% rated load

Measuring point	1	2	3	4	5	6	7	8	9	10
											O2(％)	5.0	5.0	5.0	5.0	5.0	4.9	4.9	4.8	4.8	4.8
Measuring point	11	12	13	14	15	16	17	18	19	20
											O2(％)	3.8	3.8	3.8	3.7	3.7	3.7	3.7	3.7	3.7	3.7
Measuring point	21	22	23	24	25	26	27	28	29	30
											O2(％)	3.0	3.1	3.1	3.0	3.1	3.0	3.0	3.0	3.0	3.0
Measuring point	31	32	33	34	35	36	37	38	39	40
											O2(％)	4.1	4.0	4.1	4.0	4.1	4.0	4.0	4.0	4.0	4.0
Measuring point	41	42	43	44	45	46	47	48	49	50
											O2(％)	3.4	3.4	3.4	3.4	3.5	3.5	3.4	3.4	3.4	3.4
Measuring point	51	52	53	54	55	56	57	58	59	60
											O2(％)	3.9	4.0	4.0	4.0	4.0	4.1	4.1	4.0	4.0	4.0

TABLE 2 flue gas oxygen content measurement results of each discrete grid measuring point under 75% rated load of the unit

Measuring point	1	2	3	4	5	6	7	8	9	10
											O2(％)	5.4	5.4	5.5	5.5	5.5	5.5	5.6	5.5	5.4	5.4
Measuring point	11	12	13	14	15	16	17	18	19	20
											O2(％)	3.7	3.7	3.7	3.7	3.7	3.8	3.8	3.7	3.7	3.7
Measuring point	21	22	23	24	25	26	27	28	29	30
											O2(％)	3.5	3.5	3.6	3.6	3.6	3.7	3.7	3.6	3.6	3.6
Measuring point	31	32	33	34	35	36	37	38	39	40
											O2(％)	2.8	2.8	2.8	2.8	2.9	2.9	2.9	2.8	2.8	2.8
Measuring point	41	42	43	44	45	46	47	48	49	50
											O2(％)	3.1	3.2	3.2	3.2	3.2	3.2	3.1	3.1	3.1	3.1
Measuring point	51	52	53	54	55	56	57	58	59	60
											O2(％)	3.9	3.9	3.9	3.9	4.0	4.0	3.9	3.9	3.9	3.9

TABLE 3 measurement of oxygen content in flue gas at each discrete grid measurement point for a unit at 50% rated load

Measuring point	1	2	3	4	5	6	7	8	9	10
											O2(％)	7.7	7.8	7.9	8.0	8.0	8.0	7.9	7.9	7.9	7.9
Measuring point	11	12	13	14	15	16	17	18	19	20
											O2(％)	5.0	5.0	5.2	5.2	5.3	5.3	5.3	5.2	5.2	5.2
Measuring point	21	22	23	24	25	26	27	28	29	30
											O2(％)	5.4	5.4	5.4	5.4	5.5	5.6	5.5	5.4	5.3	5.4
Measuring point	31	32	33	34	35	36	37	38	39	40
											O2(％)	3.1	3.0	3.0	2.8	2.8	2.8	2.9	2.9	2.8	2.8
Measuring point	41	42	43	44	45	46	47	48	49	50
											O2(％)	3.5	3.3	3.2	3.3	3.4	3.5	3.5	3.6	3.5	3.5
Measuring point	51	52	53	54	55	56	57	58	59	60
											O2(％)	4.2	4.2	4.2	4.2	4.2	4.2	4.2	4.2	4.2	4.2

The data are processed according to the above operation procedures, and the average absolute deviation between the flue gas oxygen content of each discrete grid measuring point and the space mean value is calculated, as shown in table 4.

TABLE 4 mean absolute deviation of oxygen content of flue gas and space mean value at each discrete grid measuring point

Measuring point	1	2	3	4	5	6	7	8	9	10
											Mean absolute deviation (%)	2.01	2.06	2.13	2.18	2.18	2.16	2.14	2.10	2.07	2.07
Measuring point	11	12	13	14	15	16	17	18	19	20
											Mean absolute deviation (%)	0.11	0.11	0.22	0.23	0.28	0.28	0.28	0.23	0.23	0.23
Measuring point	21	22	23	24	25	26	27	28	29	30
											Mean absolute deviation (%)	0.61	0.57	0.55	0.60	0.59	0.66	0.63	0.60	0.57	0.60
Measuring point	31	32	33	34	35	36	37	38	39	40
											Mean absolute deviation (%)	1.16	1.21	1.21	1.31	1.29	1.29	1.23	1.26	1.31	1.31
Measuring point	41	42	43	44	45	46	47	48	49	50
											Mean absolute deviation (%)	0.91	0.99	1.04	0.99	0.92	0.87	0.91	0.86	0.91	0.91
Measuring point	51	52	53	54	55	56	57	58	59	60
											Mean absolute deviation (%)	0.38	0.38	0.38	0.38	0.40	0.41	0.40	0.38	0.38	0.38

As can be seen from Table 4, the average absolute deviation between the oxygen content of the flue gas at the discrete grid measuring points 11 and 12 and the space mean value is the minimum, and the average absolute deviation value is 0.11 (unit%), and is less than 0.2 (unit%), then the measuring points 11 and 12 can be used as calibration points, a DCS oxygen sensor is installed at any calibration point position, the DCS measurement value is calibrated, and the calibration work is completed.