Calibration method of flue gas online monitoring system

Abstract

The invention discloses a calibration method of a flue gas on-line monitoring system, which is used for calibrating the flue gas on-line monitoring system periodically, and comprises the following calibration steps in each calibration period: a control system sends a calibration request to a programmable controller, the programmable controller stops the flue gas on-line monitoring system to perform normal sampling after receiving the calibration request, and the calibration is completed after the calibration request is received by the programmable controller. A calibration feedback signal is sent to the control system; the programmable controller sends an automatic calibration instruction to the flue gas on-line monitoring system to trigger a calibration program of the flue gas on-line monitoring system; the programmable controller controls the calibration gas supply system to provide zero calibration gas for the flue gas on-line monitoring system to complete zero calibration; the programmable controller controls the calibration gas supply system to provide range calibration gas for the flue gas on-line monitoring system to complete range calibration; and the programmable controller controls the flue gas on-line monitoring system to recover sampling and stops sending the calibration feedback signal to the control system.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas monitoring system calibration, and in particular to a calibration method for a flue gas online monitoring system. Background Art

[0002] The flue gas online monitoring system is widely used in the monitoring of flue gas emissions from fixed pollution sources such as thermal power plant boilers, industrial / civilian boilers, and industrial kilns. With the development of modern industry and the improvement of environmental protection standards, the daily calibration cycle of the flue gas online monitoring system is getting shorter and shorter. Usually, the analytical instruments of the flue gas online monitoring system need to be calibrated once a week to ensure the accuracy of the measurement parameters. At present, the calibration of the flue gas analyzer in the flue gas online monitoring system is manually operated, involving moving gas cylinders, introducing standard gas, waiting for the measurement to stabilize, etc., and the maintenance cost is high. Summary of the invention

[0003] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a calibration method for a flue gas online monitoring system, aiming to solve the problem of high maintenance cost of manual calibration.

[0004] Technical solution: To achieve the above-mentioned purpose, a calibration method for a flue gas online monitoring system of the present invention comprises a control system, a programmable controller and a calibration gas supply system cooperating with each other to periodically calibrate the flue gas online monitoring system; in each calibration cycle, the following calibration steps are included: Step S1: the control system sends a calibration request to the programmable controller. After receiving the calibration request, the programmable controller stops the normal sampling of the flue gas online monitoring system and sends a calibration feedback signal to the control system; Step S2: the programmable controller sends an automatic calibration instruction to the flue gas online monitoring system to trigger the calibration program of the flue gas online monitoring system; Step S3: the programmable controller controls the calibration gas supply system to provide zero-position calibration gas for the flue gas online monitoring system to complete the zero-position calibration; Step S4: the programmable controller controls the calibration gas supply system to provide range calibration gas for the flue gas online monitoring system to complete the range calibration; Step S5: the programmable controller controls the flue gas online monitoring system to resume sampling and stop sending calibration feedback signals to the control system.

[0005] Furthermore, the calibration gas supply system has three gas supply modules, which respectively supply zero standard gas, range standard gas and mixed gas; wherein the mixed gas is formed by mixing high-concentration standard gas and zero standard gas in a certain ratio, and after adjusting the ratio, the concentration of the mixed gas can be consistent with that of the range standard gas; in step S3, the calibration gas supply system provides zero standard gas as zero calibration gas; in step S4, the calibration gas supply system provides range standard gas or mixed gas as range calibration gas.

[0006] Further, in any two adjacent calibration cycles, the calibration gas supply system provides the range standard gas and the mixed gas as the range calibration gas respectively.

[0007] Furthermore, in a calibration cycle, if a range standard gas is provided as the range calibration gas, step S4.5 is added after the range calibration is completed; in step S4.5, the ratio of the mixed gas is adjusted by the flue gas online monitoring system that has completed the range calibration, so that the concentration of the mixed gas is adjusted to be consistent with the concentration of the range standard gas.

[0008] Furthermore, in the mixed gas supply module, there are two gas distribution branches connected to the gas mixer, on which are respectively provided a high-concentration gas cylinder and a zero-point gas cylinder, and both gas distribution branches are provided with flow regulating valves and gas flow meters; the high-concentration standard gas in the high-concentration gas cylinder enters the gas mixer after passing through the flow regulating valve and the gas flow meter, and the zero-point standard gas in the zero-point gas cylinder enters the gas mixer after passing through the flow regulating valve and the gas flow meter, and the high-concentration standard gas and the zero-point standard gas are mixed in the gas mixer and provided to the flue gas online monitoring system.

[0009] Furthermore, in step S4.5, when the concentration of the mixed gas is adjusted to be consistent with the concentration of the range standard gas and the concentration of the mixed gas remains stable, the opening value of the flow regulating valve relative to the high-concentration standard gas is recorded, and the flow measured value of the gas flowmeter relative to the zero standard gas is recorded; in the next calibration cycle, when the mixed gas is provided as the range calibration gas, the opening value and the flow measured value recorded in step S4.5 of the previous calibration cycle are used as unchanged parameter values ​​to mix the mixed gas.

[0010] Beneficial effects: The calibration method of a flue gas online monitoring system of the present invention has the following beneficial effects:

[0011] 1) The control system, programmable controller and calibration gas supply system cooperate with each other to periodically calibrate the flue gas online monitoring system, which can realize automatic calibration and reduce labor costs;

[0012] 2) In different calibration cycles, the range standard gas and the mixed gas are used alternately as the range calibration gas, which can reduce the use of standard gas and reduce costs;

[0013] 3) When the range standard gas is used as the range calibration gas, after the range calibration is completed, the ratio of the mixed gas is adjusted through the flue gas online monitoring system that has completed the range calibration, and the concentration of the mixed gas is adjusted to be consistent with the concentration of the range standard gas, which can solve the problem of large error in the mixed gas ratio caused by the limited accuracy of the flow control valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Attached Figure 1 is a flow chart of the steps of the calibration method of the present invention;

[0015] Attached Figure 2 This is a schematic diagram of the calibration gas supply system. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings.

[0017] As attached Figures 1 to 2 The calibration method of a flue gas online monitoring system is characterized in that a control system, a programmable controller and a calibration gas supply system cooperate with each other to periodically calibrate the flue gas online monitoring system. Specifically, the control system is a DCS control system, which is used to send an automatic calibration request to the programmable controller. The programmable controller is a PLC programmable controller, which is used to send an automatic calibration instruction to the flue gas online monitoring system to trigger the flue gas online monitoring calibration program. The calibration gas supply system is used to provide a stable flow of calibration gas to the flue gas online monitoring system.

[0018] In each calibration cycle, the following calibration steps are included:

[0019] Step S1: The control system prompts the operator to calibrate the flue gas online monitoring system, and the control system determines whether the automatic calibration conditions are met. If the automatic calibration conditions are met, the operator presses the "one-key automatic calibration" button on the operation screen to make the control system send an automatic calibration request to the programmable controller. After receiving the automatic calibration request, the programmable controller stops the flue gas online monitoring system for normal sampling and sends a calibration feedback signal to the control system;

[0020] Step S2: the programmable controller sends an automatic calibration instruction to the flue gas online monitoring system, triggering the calibration procedure of the flue gas online monitoring system;

[0021] Step S3: the programmable controller controls the calibration gas supply system to provide zero calibration gas for the flue gas analyzer in the flue gas online monitoring system, and completes the zero calibration according to the calibration sequence of the flue gas analyzer;

[0022] Step S4: the programmable controller controls the calibration gas supply system to provide the range calibration gas for the flue gas analyzer in the flue gas online monitoring system, and completes the range calibration according to the calibration sequence of the flue gas analyzer;

[0023] Step S5: the programmable controller restarts the flue gas online monitoring system, controls the flue gas online monitoring system to resume sampling, and the programmable controller stops sending calibration feedback signals to the control system.

[0024] In the present invention, the automatic calibration of the flue gas online monitoring system is realized through the cooperation of the control system, the programmable controller and the calibration gas supply system, thereby reducing the labor cost.

[0025] During the calibration process, the cost of the standard gas used for calibration is relatively high, so it is necessary to reduce the amount of standard gas used. In the present invention, the calibration gas supply system has three gas supply modules, which respectively supply zero standard gas, range standard gas and mixed gas; wherein the mixed gas is a mixture of high-concentration standard gas and zero standard gas, and the concentration of the high-concentration standard gas is 5 to 2 times that of the range standard gas. After adjusting the ratio, the mixed gas can be consistent with the concentration of the range standard gas. The zero standard gas is generally nitrogen.

[0026] In step S3, the calibration gas supply system provides zero standard gas as zero calibration gas; in step S4, the calibration gas supply system provides span standard gas or mixed gas as span calibration gas. In part of the calibration cycle, mixed gas is used to replace span standard gas as span calibration gas, thereby reducing the consumption of span standard gas and thus reducing calibration costs.

[0027] In any two adjacent calibration cycles, the calibration gas supply system provides the range standard gas and the mixed gas as the range calibration gas, that is, in each consecutive calibration cycle, the calibration gas supply system alternately provides the range standard gas and the mixed gas as the range calibration gas.

[0028] If the range standard gas is completely replaced by a mixed gas, although the consumption of the range standard gas will be further reduced, in actual application, the ratio accuracy of the mixed gas is difficult to guarantee, which can easily lead to deviations in the calibration results, and the higher the concentration of the high-concentration standard gas, the greater the error in the ratio. Therefore, in the present invention, in a calibration cycle, if a range standard gas is provided as a range calibration gas, step S4.5 is added after the range calibration is completed. In step S4.5, the ratio of the mixed gas is adjusted by the flue gas online monitoring system that has completed the range calibration, so that the concentration of the mixed gas is adjusted to be consistent with the concentration of the range standard gas, thereby increasing the ratio accuracy of the mixed gas.

[0029] Specifically, in the mixed gas supply module, there are two gas distribution branches connected to the gas mixer 37, and the gas supply sources of the two gas distribution branches are respectively the high-concentration gas cylinder 34 and the zero-position gas cylinder. The high-concentration gas cylinder 34 provides high-concentration standard gas, and the zero-position gas cylinder provides zero-position standard gas. In addition, flow regulating valves and gas flow meters are provided on the two gas distribution branches. The programmable control can adjust the gas flow of the high-concentration gas cylinder 34 and the zero-position gas cylinder through the flow regulating valve, and the gas flow meter can monitor the gas flow and feed back the flow information to the programmable controller.

[0030] The high-concentration standard gas in the high-concentration gas cylinder 34 enters the gas mixer 37 after passing through a flow regulating valve and a gas flow meter, and the zero-point standard gas in the zero-point gas cylinder enters the gas mixer 37 after passing through a flow regulating valve and a gas flow meter. The high-concentration standard gas and the zero-point standard gas are mixed in the gas mixer 37 and provided to the flue gas online monitoring system.

[0031] In practical applications, it is precisely because of the limitation of the accuracy of the flow control valve that errors are prone to occur when the mixed gas is proportioned. To solve this problem, in step S4.5, when the concentration of the mixed gas is adjusted to be consistent with the concentration of the range standard gas and the concentration of the mixed gas remains stable, the opening value of the flow control valve relative to the high-concentration standard gas is recorded, and the flow measured value of the gas flowmeter relative to the zero standard gas is recorded. In the next calibration cycle, when the mixed gas is provided as the range calibration gas, the opening value and the flow measured value recorded in step S4.5 of the previous calibration cycle are used as unchanged parameter values ​​to proportion the mixed gas.

[0032] The internal structure of the calibration gas supply system is shown in the attached Figure 2 As shown in , it is divided into a zero-position standard gas supply module, a range standard gas supply module, and a mixed gas supply module. The gas circuit of the zero-position standard gas supply module is connected in sequence with a zero-position gas cylinder 11, a flow regulating valve 12, a gas flow meter 13, and a first opening and closing valve 14; the gas circuit of the range standard gas supply module is connected in sequence with a range standard gas cylinder 21, a flow regulating valve 22, a gas flow meter 23, and a second opening and closing valve 24; the mixed gas supply module is divided into two gas distribution branches, one of which is connected in sequence with a zero-position gas cylinder 31, a flow regulating valve 32, and a gas flow meter 33, and the other is connected in sequence with a high-concentration gas cylinder 34, a flow regulating valve 35, and a gas flow meter 36. The two gas distribution branches are connected to the main gas distribution circuit, and a gas mixer 37 and a third opening and closing valve 38 are provided on the main gas distribution circuit.

[0033] When the zero-point standard gas is supplied in step S3 , the No. 1 on-off valve 14 is opened, and the No. 2 on-off valve 24 and the No. 3 on-off valve 38 are closed.

[0034] When the range standard gas is provided as the range calibration gas in step S4, the No. 2 on-off valve 24 is opened, and the No. 1 on-off valve 14 and the No. 3 on-off valve 38 are closed. In step S4.5, the No. 3 on-off valve 38 is opened, the No. 1 on-off valve 14 and the No. 2 on-off valve 24 are closed, and the ratio of the mixed gas is adjusted using the calibrated flue gas analyzer, and the openings of the No. 3 flow regulating valve 32 and the No. 4 flow regulating valve 35 are adjusted so that the mixed gas supply module can stably supply the mixed gas consistent with the concentration of the range standard gas, and the flow measured value of the No. 3 gas flow meter 33 is recorded. In step S4 of the next calibration cycle, the opening of the No. 4 flow regulating valve 35 is kept unchanged, and the No. 3 flow regulating valve 32 is adjusted so that the actual flow value of the No. 3 gas flow meter 33 is consistent with the flow measured value recorded in the previous calibration cycle.

[0035] In the process of mixing the mixed gas, the amount of high-concentration standard gas consumed is much smaller than the zero-point standard gas. Due to the accuracy of the flow control valve, it is difficult to accurately provide the required amount of high-concentration standard gas, which will result in a large error. In the present invention, since the opening of the No. 4 flow control valve 35 has been determined in advance by the calibrated flue gas analyzer in the previous calibration cycle, the error caused by the accuracy of the flow control valve can be solved. Since the No. 2 zero-point gas cylinder 31 consumes more gas, even if the opening of the No. 3 flow control valve 32 remains unchanged, the gas flow rate will change. Therefore, it is necessary to use the flow value measured by the No. 3 gas flowmeter 33 as a reference to keep the measured flow value consistent with the flow measured value recorded in the previous calibration cycle.

[0036] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A calibration method for a flue gas online monitoring system, characterized in that: The control system, programmable controller and calibration gas supply system cooperate with each other to periodically calibrate the flue gas online monitoring system; in each calibration cycle, the following calibration steps are included: Step S1: The control system sends a calibration request to the programmable controller. After receiving the calibration request, the programmable controller stops the flue gas online monitoring system for normal sampling and sends a calibration feedback signal to the control system. Step S2: the programmable controller sends an automatic calibration instruction to the flue gas online monitoring system to trigger the calibration procedure of the flue gas online monitoring system; Step S3: the programmable controller controls the calibration gas supply system to provide zero-position calibration gas to the flue gas online monitoring system to complete the zero-position calibration; Step S4: the programmable controller controls the calibration gas supply system to provide the range calibration gas for the flue gas online monitoring system to complete the range calibration; Step S5: The programmable controller controls the flue gas online monitoring system to resume sampling and stops sending calibration feedback signals to the control system.

2. The calibration method of a flue gas online monitoring system according to claim 1, characterized in that: The calibration gas supply system has three gas supply modules, which respectively supply zero standard gas, range standard gas and mixed gas; wherein the mixed gas is a mixture of high-concentration standard gas and zero standard gas, and after adjusting the ratio, the concentration of the mixed gas can be consistent with that of the range standard gas; In step S3, the calibration gas supply system provides zero standard gas as zero calibration gas; In step S4 , the calibration gas supply system provides a range standard gas or a mixed gas as a range calibration gas.

3. The calibration method of a flue gas online monitoring system according to claim 2, characterized in that: In any two adjacent calibration cycles, the calibration gas supply system provides the range standard gas and the mixed gas as the range calibration gas respectively.

4. The calibration method of a flue gas online monitoring system according to claim 3, characterized in that: In a calibration cycle, if a range standard gas is provided as the range calibration gas, step S4.5 is added after the range calibration is completed; in step S4.5, the ratio of the mixed gas is adjusted by the flue gas online monitoring system that has completed the range calibration, so that the concentration of the mixed gas is adjusted to be consistent with the concentration of the range standard gas.

5. The calibration method of a flue gas online monitoring system according to claim 4, characterized in that: In the mixed gas supply module, there are two gas distribution branches connected to the gas mixer (37), the two gas distribution branches are respectively provided with a high-concentration gas cylinder (34) and a zero-position gas cylinder, and both gas distribution branches are provided with a flow regulating valve and a gas flow meter; The high-concentration standard gas in the high-concentration gas cylinder (34) enters the gas mixer (37) after passing through a flow regulating valve and a gas flow meter, and the zero-point standard gas in the zero-point gas cylinder enters the gas mixer (37) after passing through a flow regulating valve and a gas flow meter. The high-concentration standard gas and the zero-point standard gas are mixed in the gas mixer (37) and provided to the flue gas online monitoring system.

6. The calibration method of a flue gas online monitoring system according to claim 5, characterized in that: In step S4.5, when the concentration of the mixed gas is adjusted to be consistent with the concentration of the range standard gas and the concentration of the mixed gas remains stable, the opening value of the flow control valve relative to the high-concentration standard gas is recorded, and the flow measured value of the gas flowmeter relative to the zero standard gas is recorded; in the next calibration cycle, when the mixed gas is provided as the range calibration gas, the opening value and flow measured value recorded in step S4.5 of the previous calibration cycle are used as unchanged parameter values ​​to mix the mixed gas.

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