NOx concentration distribution monitoring system and monitoring method based on dilution method synchronous calibration

Abstract

The invention discloses a NOx concentration distribution monitoring system and a monitoring method based on dilution method synchronous calibration. The monitoring system includes an in-situ NOx online analyzer, a diluter, a sonic orifice, a standard gas pipe, a NOx standard gas bottle, a standard gas control valve, a zero gas generator, a zero gas pipe and a diluted standard gas main pipe; the sampling end of each set of in-situ NOx online analyzers extends into the flue, and is arranged equidistantly or by grid method in the flue measurement section; each set of in-situ NOx online analyzers is connected to a diluted standard gas branch pipe, and a standard gas branch pipe control valve is arranged on each diluted standard gas branch pipe; the diluter is a three-way structural member with a standard gas inlet, a zero gas inlet and a diluted standard gas outlet; the sonic orifice is installed on the standard gas inlet and is connected to the NOx standard gas bottle through the standard gas pipe, and the standard gas control valve is arranged on the standard gas pipe; the zero gas generator is connected to the zero gas inlet through the zero gas pipe; one end of the diluted standard gas main pipe is connected to the diluted standard gas outlet of the diluter, and the other end is connected to all the diluted standard gas branches. The invention is simple, reliable and accurate.

Description

Technical Field

[0001] The invention relates to a technology for measuring the distribution of flue gas components in a large coal-fired power station, and in particular to the field of measuring the NOx concentration distribution at an SCR outlet. Background Art

[0002] At present, large power plants generally use SCR denitrification devices to reduce the NOx emission concentration in flue gas. SCR uses the reduction characteristics of NH3 to NOx, and reduces NOx to environmentally friendly N2 and H2O under the action of a catalyst. In the actual operation process, the control of the amount of ammonia injection is particularly critical. Increasing the amount of ammonia injection is conducive to reducing the NOx emission concentration, but ammonia escape will increase, which will cause the downstream air preheater to be blocked and corroded due to ammonium bisulfate deposition. In terms of ammonia injection control, in addition to reasonably controlling the total amount of ammonia injection, attention should also be paid to the uniformity of ammonia injection to ensure that the NOx emission concentration meets the standard within the allowable ammonia escape range. At present, the power industry is fully implementing the ultra-low emission standards for coal-fired units, requiring that the NOx emission concentration be strictly controlled at 50mg / Nm 3 This puts more stringent requirements on the ammonia injection system, so the monitoring and timely adjustment of ammonia injection uniformity is particularly important.

[0003] The uniformity of ammonia injection is closely related to the NOx concentration distribution at the SCR outlet cross section. When there is no obvious fault in the SCR catalyst layer, if the NOx concentration is too high, it can be considered that the amount of ammonia injection in the corresponding upstream area is too small; if the local NOx concentration is too low, it is due to the excessive amount of ammonia injection in the corresponding upstream area; if the local NOx concentration is too low, ammonia slip will increase significantly, which will not only increase the operating cost of the SCR, but also pose a serious threat to the safe operation of the downstream air preheater (there is a risk of ash blockage). Therefore, it is necessary to avoid serious uneven analysis of the NOx concentration at the SCR outlet, and by optimizing the SCR upstream AIG (ammonia injection adjustment device), the SCR outlet NOx concentration can be adjusted to a relatively uniform state. If it is found that the adjustment range of AIG is too large, the catalyst module at the corresponding position may have obvious wear, collapse, ash blockage and other faults.

[0004] In view of the above analysis, under the background of the current comprehensive implementation of ultra-low emissions of coal-fired units in the power industry, the monitoring of NOx concentration distribution at the SCR outlet is particularly important for the safe operation and troubleshooting of boilers. According to current technical conditions, the technical solution of installing multiple instruments to measure the distribution of flue gas components at the SCR outlet has been made public, but this solution has an obvious drawback, that is, the measurement difference between the instruments affects the judgment of the uniformity of the NOx concentration distribution at the SCR outlet. Summary of the invention

[0005] In order to solve the problem of monitoring the uniformity of SCR ammonia injection and eliminate the defects of the prior art, the present invention provides a NOx concentration distribution monitoring system and a monitoring method based on dilution method synchronous calibration.

[0006] In order to solve the above technical problems, the technical solution of the present invention is:

[0007] The NOx concentration distribution monitoring system based on the dilution method synchronous calibration includes at least an in-situ NOx online analyzer, a diluted standard gas branch pipe, a standard gas branch pipe control valve, a diluter, a sonic orifice, a standard gas pipe, a NOx standard gas bottle, a standard gas control valve, a zero gas generator, a zero gas pipe and a diluted standard gas main pipe;

[0008] There are at least three sets of in-situ NOx online analyzers, the sampling end of each set of in-situ NOx online analyzers extends into the flue, and is arranged equidistantly or in a grid method in the flue measurement section; each set of in-situ NOx online analyzers is connected to a diluted standard gas branch pipe, and each diluted standard gas branch pipe is provided with a standard gas branch pipe control valve;

[0009] The diluter is a three-way structure with a standard gas inlet, a zero gas inlet and a diluted standard gas outlet. The dilution ratio of the diluter is between 15-150;

[0010] The sonic orifice is installed on the standard gas inlet of the diluter and connected to the NOx standard gas cylinder through the standard gas pipe. The standard gas control valve is set on the standard gas pipe. The initial concentration of NOx gas in the NOx standard gas cylinder is not less than 500mg / Nm 3 ;

[0011] The zero gas generator is connected to the zero gas inlet of the diluter through a zero gas pipe, and the gas source of the zero gas generator is compressed air;

[0012] One end of the diluted standard gas main pipe is connected to the diluted standard gas outlet of the diluter, and the other end is connected to all the diluted standard gas branch pipes.

[0013] The applicant has found through research that when multiple sets of in-situ NOx online analyzers are arranged equidistantly or in a grid method in the flue measurement section, although each set of meters directly measures the NOx concentration values ​​at different positions of the cross section, it is not equivalent to the NOx distribution monitoring data at the denitrification outlet, because each set of in-situ NOx online analyzers may have different zero drifts or linearity errors. For this reason, the same standard gas is introduced into each set of in-situ NOx online analyzers at the same time to obtain the relative mean deviation of the measurements of each set of in-situ NOx online analyzers. The value obtained by directly measuring the instrument after eliminating the influence of the relative mean deviation of the measurements of each set of in-situ NOx online analyzers is the true NOx distribution data at the denitrification outlet. Frequent calibration at regular intervals will consume more standard gas. For this reason, a high-concentration NOx standard gas cylinder is used in combination with a dilution method to ensure the long-term stable operation of the monitoring system. Theoretically, when the pressure difference before and after the sonic orifice exceeds the critical pressure difference, the standard gas velocity reaches the speed of sound and the dilution ratio tends to be stable. Although it is difficult to accurately dilute and determine the NOx concentration of the diluted standard gas, the NOx concentration of the diluted standard gas can be roughly selected within the range of 20-50 mg / Nm 3 Within the commonly used range, the absolute value of the NOx concentration distribution monitoring data at the denitrification outlet is not very meaningful because it is used for ammonia injection leveling. On the contrary, the relative deviation of the measurement values ​​of each set of in-situ NOx online analyzers is more significant.

[0014] In order to improve the stability of the dilution ratio, the above-mentioned diluter is a Venturi tube, and the standard gas inlet can generate a negative pressure of not less than -30kPa.

[0015] In order to improve the accuracy of calibration and monitoring data and reduce the frequency of replacing NOx standard gas cylinders, it is preferred that the initial concentration of NOx gas contained in the NOx standard gas cylinder is 3000-4000 mg / Nm 3 The NOx concentration range of the diluted standard gas is 20-50mg / Nm 3 Further preferably, the mean deviation between the NOx concentration of the diluted standard gas and the current in-situ NOx online analyzer measurement value is less than ±5 mg / Nm 3 .

[0016] In order to improve system reliability and avoid the impact of leakage of the standard gas branch pipe control valve on the in-situ NOx online analyzer, it is preferred to set a standard gas main pipe control valve on the dilution standard gas main pipe, and the standard gas main pipe control valve is opened or closed synchronously with all standard gas branch pipe control valves.

[0017] In order to obtain diluted standard gas of different concentrations, the above-mentioned monitoring system also includes a diluter bypass pipeline and a bypass flow regulating valve. The bypass flow regulating valve is arranged on the diluter bypass pipeline, and the two ends of the diluter bypass pipeline are respectively connected to the zero gas inlet and the diluted standard gas outlet; or a zero gas control valve is arranged on the zero gas pipe to change the diluted standard gas concentration by adjusting the zero gas flow and pressure.

[0018] The NOx concentration distribution monitoring method based on the synchronous calibration of the dilution method uses each set of in-situ NOx online analyzers to obtain the NOx concentration measurement value of the area, and then uses the same standard gas to calibrate all the in-situ NOx online analyzers at the same time to obtain the relative mean deviation of each set of in-situ NOx online analyzers. The sum of the measured value and the relative mean deviation is the true NOx concentration distribution data of the measurement section; during calibration, the high-concentration standard gas is diluted with zero gas to control the NOx concentration range of the diluted standard gas to be 20-50mg / Nm 3 .

[0019] The technologies not mentioned in the present invention are all referred to the prior art.

[0020] The present invention is a NOx concentration distribution monitoring system and method based on synchronous calibration using a dilution method. Multiple sets of in-situ NOx online analyzers are installed in a distributed manner on a flue measurement section to obtain NOx concentration values ​​in different areas. The multiple sets of in-situ NOx online analyzers are then calibrated simultaneously using the same standard gas to obtain a relative mean deviation of instrument measurement. The sum of the direct measurement value of the instrument and the relative mean deviation of the instrument measurement is the true NOx concentration distribution data of the measurement section, thereby eliminating the influence of the measurement difference between the instruments on the judgment of the uniformity of the NOx concentration distribution at the SCR outlet. In addition, by diluting the high-concentration NOx standard gas, a sufficient amount of standard gas is provided to ensure the long-term stable operation of the monitoring system. The standard gas concentration is also adjustable to make the standard gas concentration close to the actual measurement concentration, thereby obtaining a more accurate measurement value. The present system is simple, reliable, and has high measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the NOx concentration distribution monitoring system based on the dilution method synchronous calibration in Example 1 of the present invention;

[0022] Figure 2 Schematic diagram of the structure of the NOx concentration distribution monitoring system based on the dilution method synchronous calibration in Example 2 of the present invention;

[0023] Figure 3 Schematic diagram of the structure of the NOx concentration distribution monitoring system based on the dilution method synchronous calibration in Example 3 of the present invention;

[0024] Figure 4 It is a structural schematic diagram of a NOx concentration distribution monitoring system based on dilution method synchronous calibration in Example 4 of the present invention;

[0025] In the figure, 1 is the in-situ NOx online analyzer, 2 is the NOx standard gas cylinder, 3 is the sonic orifice, 4 is the diluter, 5 is the zero gas generator, 6 is the standard gas pipe, 7 is the standard gas control valve, 8 is the zero gas pipe, 9 is the diluted standard gas main pipe, 10 is the diluted standard gas branch pipe, 11 is the standard gas branch pipe control valve, 12 is the standard gas main pipe control valve, 13 is the diluter bypass pipe, 14 is the bypass flow regulating valve, and 15 is the zero gas control valve. DETAILED DESCRIPTION

[0026] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0027] Example 1

[0028] like Figure 1 As shown, the NOx concentration distribution monitoring system based on the synchronous calibration of the dilution method includes at least an in-situ NOx online analyzer, a diluted standard gas branch pipe, a standard gas branch pipe control valve, a diluter, a sonic orifice, a standard gas pipe, a NOx standard gas bottle, a standard gas control valve, a zero gas generator, a zero gas pipe and a diluted standard gas main pipe;

[0029] There are at least three sets of in-situ NOx online analyzers, the sampling end of each set of in-situ NOx online analyzers extends into the flue, and is arranged equidistantly or in a grid method in the flue measurement section; each set of in-situ NOx online analyzers is connected to a diluted standard gas branch pipe, and each diluted standard gas branch pipe is provided with a standard gas branch pipe control valve;

[0030] The diluter is a three-way structure with a standard gas inlet, a zero gas inlet and a diluted standard gas outlet. The dilution ratio of the diluter is between 15-150;

[0031] The sonic orifice is installed on the standard gas inlet of the diluter and connected to the NOx standard gas cylinder through the standard gas pipe. The standard gas control valve is set on the standard gas pipe. The initial concentration of NOx gas in the NOx standard gas cylinder is not less than 500mg / Nm 3 ;

[0032] The zero gas generator is connected to the zero gas inlet of the diluter through a zero gas pipe, and the gas source of the zero gas generator is compressed air;

[0033] One end of the diluted standard gas main pipe is connected to the diluted standard gas outlet of the diluter, and the other end is connected to all the diluted standard gas branch pipes.

[0034] During monitoring, each set of in-situ NOx online analyzers is used to obtain the NOx concentration measurement value in the area, and then the same standard gas is used to calibrate all the in-situ NOx online analyzers at the same time to obtain the relative mean deviation of each set of in-situ NOx online analyzers. The sum of the measured value and the relative mean deviation is the true NOx concentration distribution data of the measurement section; during calibration, the high-concentration standard gas is diluted with zero gas to control the NOx concentration of the diluted standard gas to be in the range of 20-50mg / Nm 3 .

[0035] The applicant has found through research that when multiple sets of in-situ NOx online analyzers are arranged equidistantly or in a grid method in the flue measurement section, although each set of meters directly measures the NOx concentration values ​​at different positions of the cross section, it is not equivalent to the NOx distribution monitoring data at the denitrification outlet, because each set of in-situ NOx online analyzers may have different zero drifts or linearity errors. For this reason, the same standard gas is introduced into each set of in-situ NOx online analyzers at the same time to obtain the relative mean deviation of the measurements of each set of in-situ NOx online analyzers. The value obtained by directly measuring the instrument after eliminating the influence of the relative mean deviation of the measurements of each set of in-situ NOx online analyzers is the true NOx distribution data at the denitrification outlet. Frequent calibration at regular intervals will consume more standard gas. For this reason, a high-concentration NOx standard gas cylinder is used in combination with a dilution method to ensure the long-term stable operation of the monitoring system. Theoretically, when the pressure difference before and after the sonic orifice exceeds the critical pressure difference, the standard gas velocity reaches the speed of sound and the dilution ratio tends to be stable. Although it is difficult to accurately dilute and determine the NOx concentration of the diluted standard gas, the NOx concentration of the diluted standard gas can be roughly selected within the range of 20-50 mg / Nm 3 Within the commonly used range, the absolute value of the NOx concentration distribution monitoring data at the denitrification outlet is not very meaningful because it is used for ammonia injection leveling. On the contrary, the relative deviation of the measurement values ​​of each set of in-situ NOx online analyzers is more significant.

[0036] Example 2

[0037] On the basis of Example 1, the following improvements were made: Figure 2 As shown, in order to improve system reliability and avoid the impact of leakage of the standard gas branch pipe control valve on the in-situ NOx online analyzer, a standard gas main pipe control valve is set on the diluted standard gas main pipe, and the standard gas main pipe control valve is opened or closed synchronously with all standard gas branch pipe control valves.

[0038] Example 3

[0039] On the basis of Example 2, the following improvements were made: Figure 3 As shown, in order to obtain diluted standard gas of different concentrations, the above-mentioned monitoring system also includes a diluter bypass pipeline and a bypass flow regulating valve. The bypass flow regulating valve is arranged on the diluter bypass pipeline. The two ends of the diluter bypass pipeline are respectively connected to the zero gas inlet and the diluted standard gas outlet.

[0040] Example 4

[0041] On the basis of Example 2, the following improvements were made: Figure 4 As shown, in order to obtain diluted standard gas of different concentrations, a zero gas control valve is set on the zero gas pipe, and the concentration of the diluted standard gas is changed by adjusting the zero gas flow and pressure.

[0042] Example 5

[0043] On the basis of Example 3 or 4, the following improvement is further made: in order to improve the stability of the dilution ratio, the above-mentioned diluter is a Venturi tube, and the standard gas inlet can generate a negative pressure of not less than -30 kPa.

[0044] Example 6

[0045] On the basis of Example 5, the following improvements were made: in order to improve the accuracy of calibration and monitoring data and reduce the frequency of replacing NOx standard gas cylinders, the initial concentration of NOx gas contained in the NOx standard gas cylinders was 3500 mg / Nm 3 The mean deviation between the NOx concentration of the diluted standard gas and the current NOx online analyzer measurement value is less than ±5mg / Nm 3 .

[0046] Through engineering practice, the above examples use multiple sets of in-situ NOx online analyzers distributedly installed on the flue measurement section to obtain NOx concentration values ​​in different areas, and then use the same standard gas to calibrate multiple sets of in-situ NOx online analyzers at the same time to obtain the relative mean deviation of the instrument measurement. The sum of the direct measurement value of the instrument and the relative mean deviation of the instrument measurement is the true NOx concentration distribution data of the measurement section, eliminating the influence of the measurement difference between the instruments on the judgment of the uniformity of the NOx concentration distribution at the SCR outlet; in addition, by diluting the high-concentration NOx standard gas, a sufficient amount of standard gas is provided to ensure the long-term stable operation of the monitoring system; further, the standard gas concentration is adjustable, so that the standard gas concentration is close to the actual measurement concentration, so as to obtain more accurate measurement values; this system is simple, reliable and has high measurement accuracy.

Claims

1. A NOx concentration distribution monitoring method based on dilution method synchronous calibration, characterized in that: The NOx concentration distribution monitoring system based on the dilution method and synchronous calibration is used for monitoring. The NOx concentration distribution monitoring system based on the dilution method and synchronous calibration includes at least an in-situ NOx online analyzer, a diluted standard gas branch pipe, a standard gas branch pipe control valve, a diluter, a sonic orifice, a standard gas pipe, a NOx standard gas bottle, a standard gas control valve, a zero gas generator, a zero gas pipe and a diluted standard gas main pipe; There are at least three sets of in-situ NOx online analyzers, the sampling end of each set of in-situ NOx online analyzers extends into the flue, and is arranged equidistantly or in a grid method in the flue measurement section; each set of in-situ NOx online analyzers is connected to a diluted standard gas branch pipe, and each diluted standard gas branch pipe is provided with a standard gas branch pipe control valve; The diluter is a three-way structure with a standard gas inlet, a zero gas inlet and a diluted standard gas outlet. The dilution ratio of the diluter is between 15-150; The sonic orifice is installed on the standard gas inlet of the diluter and connected to the NOx standard gas cylinder through the standard gas pipe. The standard gas control valve is set on the standard gas pipe. The initial concentration of NOx gas in the NOx standard gas cylinder is not less than 500mg / Nm 3 ; The zero gas generator is connected to the zero gas inlet of the diluter through a zero gas pipe, and the gas source of the zero gas generator is compressed air; One end of the diluted standard gas main pipe is connected to the diluted standard gas outlet of the diluter, and the other end is connected to all the diluted standard gas branch pipes. The NOx concentration distribution monitoring method based on the synchronous calibration of the dilution method uses each set of in-situ NOx online analyzers to obtain the NOx concentration measurement value of the area, and then uses the same standard gas to calibrate all the in-situ NOx online analyzers at the same time to obtain the relative mean deviation of the measurement of each set of in-situ NOx online analyzers. The sum of the measurement value and the relative mean deviation is the real NOx concentration distribution data of the measurement section. During calibration, dilute the high-concentration standard gas with zero gas and control the NOx concentration of the diluted standard gas to be within the range of 20-50mg / Nm 3 .

2. The NOx concentration distribution monitoring method based on dilution method synchronous calibration according to claim 1, characterized in that: The diluter is a Venturi tube, and the standard gas inlet generates a negative pressure of not less than -30kPa.

3. The NOx concentration distribution monitoring method based on dilution method synchronous calibration according to claim 1 or 2, characterized in that: The initial concentration of NOx gas in the NOx standard gas bottle is 3000~4000mg / Nm 3 .

4. The NOx concentration distribution monitoring method based on dilution method synchronous calibration according to claim 1 or 2, characterized in that: The mean deviation between the NOx concentration of the diluted standard gas and the current NOx online analyzer measurement value is less than ±5mg / Nm 3 .

5. The NOx concentration distribution monitoring method based on dilution method synchronous calibration according to claim 1 or 2, characterized in that: A standard gas main pipe control valve is provided on the dilution standard gas main pipe, and the standard gas main pipe control valve is opened or closed synchronously with all standard gas branch pipe control valves.

6. The NOx concentration distribution monitoring method based on dilution method synchronous calibration according to claim 1 or 2, characterized in that: It also includes a diluter bypass pipeline and a bypass flow regulating valve. The bypass flow regulating valve is arranged on the diluter bypass pipeline. Two ends of the diluter bypass pipeline are respectively connected to a zero gas inlet and a dilution standard gas outlet.

7. The NOx concentration distribution monitoring method based on dilution method synchronous calibration according to claim 1 or 2, characterized in that: A zero gas control valve is set on the zero gas pipe to change the concentration of the diluted standard gas by adjusting the zero gas flow and pressure.

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