A kind of laser sulfur trioxide concentration on-line monitoring system calibration device and method

Abstract

The application provides a kind of laser sulfur trioxide concentration on-line monitoring system calibration device and method, improve the accuracy and reliability of on-line monitoring. Mainly including gas tank, flowmeter, sampling gas circuit, high temperature furnace, catalytic chamber, laser, gas analysis cell, photodetector, water cooling device, vacuum pump, data acquisition and analysis module. Open the vacuum pump, nitrogen is imported to complete the zero gas calibration of laser sulfur trioxide concentration on-line monitoring system;Sulfur dioxide and air mixed gas is imported, and sulfur trioxide gas is generated in high temperature environment under the action of vanadium catalyst, passes through gas cell, records optical characteristic value, then collects sulfur trioxide in water cooling device, with off-line test results of national standard control condensation sulfur trioxide as reference basis, completes two-point calibration of monitoring system. Gas analysis cell and water cooling device are connected in series during calibration process, to ensure that sulfur trioxide flux is completely consistent.

Description

Technical Field

[0001] This invention relates to the field of coal-fired flue gas pollutant monitoring technology, and in particular to a calibration device and method for an online monitoring system for sulfur trioxide concentration using laser. Background Technology

[0002] Flue gas from coal-fired power plants and industrial boilers often contains sulfur trioxide (SO3). On one hand, SO3 is formed from the further oxidation of sulfur oxides generated during the combustion of fossil fuels. SO3 reacts with water to form sulfuric acid (H2SO4). When the flue gas temperature drops below the acid dew point, H2SO4 adheres to the pipe walls, causing low-temperature corrosion. If released into the atmosphere, it causes acid rain and other environmental pollution. On the other hand, most power plants are equipped with selective reduction (SCR) denitrification systems. In these systems, additional sulfur dioxide (SO2) may be oxidized to SO3 on the catalyst. Due to the presence of ammonia, a reduction product of nitrogen oxides, this SO3 forms ammonium sulfate and ammonium bisulfate salts, which are a few micrometers in diameter, leading to PM10 emissions. This also contaminates the microporous structure of the catalyst, limiting its reactivity. Therefore, accurately monitoring the SO3 concentration in industrial flue gas is crucial for preventing flue gas corrosion and controlling SO3 emissions in industrial production activities such as coal-fired power plants.

[0003] Currently, the main methods for SO3 detection include controlled condensation, isopropanol absorption, salt absorption, and absorption spectroscopy. Online measurement methods mainly include online monitoring based on isopropanol absorption and laser absorption spectroscopy. Different methods have different detection principles and advantages and disadvantages. Offline testing methods have drawbacks such as long measurement cycles, inability to reflect flue gas characteristics in real time, complex detection equipment and processes, and large human error. Online monitoring systems based on absorption spectroscopy require a stable concentration of SO3 gas for instrument calibration. Therefore, there is an urgent need for a calibration device and method for an online monitoring system of sulfur trioxide concentration using laser spectroscopy.

[0004] A calibration system for an SO3 standard substance generator and online analyzer, disclosed in document CN211825963U, relates to the field of flue gas monitoring technology. This system includes a gas cylinder connected to a reaction device via a pipeline equipped with a flow meter. The gas cylinder is also connected to a sampling device via a pipeline. A temperature control device is located outside the reaction device, which is also connected to the sampling device via a pipeline. The sampling device is connected to the analyzer and a water bath cooling device, which is connected to a laboratory analysis device. This patent uses four gas cylinders and a rotor flow meter to distribute the gas before it enters the reaction device, which is prone to human error. Furthermore, the parallel connection of the laboratory analysis device and the online analyzer makes it impossible to guarantee consistent gas flow and concentration between them. Additionally, the patent does not explicitly apply the principles of portable online instruments, failing to meet the requirement of maintaining negative pressure in laser absorption spectroscopy measurements. Summary of the Invention

[0005] The purpose of this invention is to address the needs of existing technologies by providing a calibration device and method for an online monitoring system of sulfur trioxide concentration using laser technology. SO3 is liquid at room temperature and solid under standard conditions, making it impossible to store a stable concentration of standard gas in a gas tank. Laser absorption spectroscopy can achieve online measurement without affecting the chemical properties of the gas; however, the commonly used sulfur trioxide absorption spectrum is interfered with by the absorption spectrum of nearby water at normal pressure, thus requiring measurement under negative pressure. This invention uses a stable SO3 generator, a water bath cooling device, and a vacuum pump to calibrate the online monitoring system of sulfur trioxide concentration using laser technology, and can quickly switch to sampling mode via a three-way valve.

[0006] To address the problems existing in the prior art, this invention provides a calibration device and method for an online monitoring system of sulfur trioxide concentration using laser technology, thereby improving the accuracy and reliability of online monitoring.

[0007] The main technical solution of this invention is a calibration device for an online monitoring system of sulfur trioxide concentration using laser technology. This device mainly includes a nitrogen cylinder and a mixed gas cylinder. The nitrogen cylinder is connected to a gas analysis device via a three-way valve, and the mixed gas cylinder is connected to a sulfur trioxide generator via a three-way valve, which in turn connects to a sampling gas path and the gas analysis device. The gas analysis device includes a laser, a gas analysis cell, a photodetector, and a data acquisition and analysis module. The sulfur trioxide generator includes a flow meter, a high-temperature furnace, and a catalytic chamber. The gas analysis cell is connected to a water bath cooling device and a vacuum pump.

[0008] This invention also provides a calibration method for an online monitoring system for sulfur trioxide concentration using laser: using the above-mentioned device, the following operations are performed: zero gas calibration, range calibration, and calibration function switching; the zero gas calibration uses a nitrogen cylinder, and the range calibration uses a standard mixed gas cylinder of sulfur dioxide and dry air, which catalytically generates sulfur trioxide gas at high temperature.

[0009] Generally, the nitrogen gas cylinder uses 99.999% high-purity nitrogen, and the mixed gas cylinder uses a standard mixed gas of SO2 and dry air at a specified concentration.

[0010] During the range calibration, the three-way valve is switched to connect the gas analysis cell, water bath cooling device, and vacuum pump in series.

[0011] After the calibration is completed, switch the three-way valve to connect the sampling gas path, gas analysis cell and vacuum pump in series.

[0012] The catalytic chamber is filled with vanadium catalyst (containing vanadium pentoxide) and placed in a high-temperature furnace at a temperature of 500°C. The generated gas is introduced into a gas analysis cell, and the entire gas path is kept warm by a heating tape at a temperature of 220°C.

[0013] The laser is selected as a mid-infrared quantum cascade laser with a laser wavelength range of around 7.323 micrometers, and the photodetector response wavelength is matched accordingly.

[0014] The data acquisition and analysis module includes a signal generator, a data acquisition card, and a computer. The signal generator outputs a voltage signal of a specific waveform to modulate the laser. The data acquisition card acquires the analog signal from the photodetector. The computer analyzes the data online and obtains optical characteristic values ​​containing gas concentration information using Lambert-Beer's law.

[0015] The water bath cooling device is connected in series with the gas analysis cell during range calibration. The system range concentration calibration is completed by using the offline test results of condensation control according to national standards as a reference.

[0016] The zero-gas calibration involves starting the gas analysis cell, opening the nitrogen tank, and introducing nitrogen into the gas analysis cell. Zero-gas calibration is then completed using a laser, photodetector, and data acquisition and analysis module. Preferably, the gas analysis cell is started and kept at a temperature of 220°C.

[0017] The range calibration involves starting the high-temperature furnace, starting the gas analysis cell, opening the mixed gas tank, reacting the gas in the catalytic chamber, and then introducing it into the gas analysis cell. The laser, photodetector, and data acquisition and analysis module complete the acquisition of optical characteristic values. The sulfur trioxide is condensed through a water bath cooling device. The system range concentration calibration is completed based on the offline test results of the condensation control according to national standards. Preferably, the high-temperature furnace is started and the temperature is maintained at 500°C, and the gas analysis cell is started and the temperature is maintained at 220°C.

[0018] After calibration is completed, the three-way valve is switched, and the concentration of sulfur trioxide can be monitored online through the sampling gas path.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] This invention uses a standard mixture of SO2 and dry air of a specified concentration to react and generate SO3 gas, eliminating the need for gas mixing during calibration and ensuring stable output concentration. During range calibration, a water bath cooling device is connected in series with the gas analysis cell to ensure a consistent SO3 gas flux. Simultaneously, a vacuum pump maintains a negative pressure environment, effectively lowering the gas's condensation point and allowing SO3 gas to fully condense inside the water bath cooling device, ensuring the accuracy and reliability of the calibration process. This invention's device and method, while providing calibration for an online laser sulfur trioxide concentration monitoring system, can be easily switched to sampling and analysis mode, making it suitable for periodic system calibration. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the calibration device for the laser-based online monitoring system for sulfur trioxide concentration described in the examples of this invention.

[0022] In the diagram: 1—Nitrogen tank, 2—Mixed gas tank, 3—Flow meter, 4—Sampling gas path, 5—High temperature furnace, 6—Catalytic chamber, 7—Laser, 8—Gas analysis cell, 9—Photodetector, 10—Water bath cooling device, 11—Vacuum pump, 12—Data acquisition and analysis module. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the following embodiments are illustrative and not limiting, and should not be used to limit the scope of protection of the present invention. Example

[0024] Reference Appendix: Calibration Device for an Online Monitoring System of Sulfur Trioxide Concentration Using Laser Figure 1 It mainly includes a nitrogen tank (1), a mixed gas tank (2), a flow meter (3), a sampling gas path (4), a high-temperature furnace (5), a catalytic chamber (6), a laser (7), a gas analysis cell (8), a photodetector (9), a water bath cooling device (10), a vacuum pump (11), and a data acquisition and analysis module (12).

[0025] In the embodiment, the nitrogen gas tank (1) is connected to the gas analysis device through a three-way valve, and the mixed gas tank (2) is connected to the sulfur trioxide generator through a three-way valve. The sampling gas path (4) and the gas analysis device are connected through a three-way valve. The gas analysis device includes a laser (7), a gas analysis cell (8), a photodetector (9), and a data acquisition and analysis module (12). The sulfur trioxide generator includes a flow meter (3), a high-temperature furnace (5), and a catalytic chamber (6). The gas analysis cell (8) is connected to a water bath cooling device (10) and a vacuum pump (11).

[0026] In the embodiment, the nitrogen gas tank (1) uses 99.999% high-purity nitrogen, and the mixed gas tank (2) uses a standard mixed gas of SO2 and dry air at a specified concentration.

[0027] In the embodiment, the catalytic chamber (6) is filled with vanadium catalyst (containing vanadium pentoxide) and built into a high-temperature furnace (5) with the temperature set at 500°C. The generated gas is introduced into the gas analysis cell, and the entire gas path is kept warm by a heat tracing cable with the temperature set at 220°C.

[0028] In the embodiment, the laser (7) is selected as a mid-infrared quantum cascade laser with a laser band range of around 7.323 micrometers, and the photodetector response band is matched.

[0029] In this embodiment, the data acquisition and analysis module (12) includes a signal generator, a data acquisition card and a computer. The signal generator outputs a voltage signal with a specific waveform to modulate the laser. The data acquisition card acquires the analog signal of the photodetector. The computer analyzes the data online and obtains optical feature values ​​containing gas concentration information through Lambert-Beer's law.

[0030] The calibration method for the calibration device of the laser-based online monitoring system for sulfur trioxide concentration is as follows.

[0031] Zero point calibration: Start the gas analysis cell (8) and maintain the temperature at 220°C. Open the nitrogen tank (1) and introduce it into the gas analysis cell (8). Complete the zero gas calibration through the laser (7), photodetector (9) and data acquisition and analysis module (12).

[0032] Range calibration: Start the high temperature furnace (5) and maintain the temperature at 500℃. Start the gas analysis cell (8) and maintain the temperature at 220℃. Open the mixed gas tank (2). The gas reacts in the catalytic chamber (6) and is introduced into the gas analysis cell (8). The laser (7), photodetector (9) and data acquisition and analysis module (12) complete the acquisition of optical characteristic values. The sulfur trioxide is condensed through the water bath cooling device (10). The system range concentration calibration is completed based on the offline test results of the condensation control according to national standards.

[0033] After calibration, the three-way valve of the embodiment device can be switched to perform online monitoring of sulfur trioxide concentration through the sampling gas path (4).

[0034] The specific calibration method is as follows: Zero gas calibration of the laser sulfur trioxide concentration online monitoring system: start the gas analysis cell and maintain the temperature at 220℃, open the nitrogen tank and introduce it into the gas analysis cell, maintain the pressure of the analysis cell at 60hPa with the vacuum pump, complete the zero gas calibration through the laser, photodetector and data acquisition and analysis module, and record the zero gas characteristic value H1.

[0035] The laser-based online monitoring system for sulfur trioxide concentration was calibrated by starting the high-temperature furnace and maintaining it at 500℃, and starting the gas analysis cell and maintaining it at 220℃. The mixed gas tank was opened, and the gas was reacted in the catalytic chamber and then introduced into the gas analysis cell. The vacuum pump maintained the pressure in the analysis cell at 60 hPa. The laser, photodetector, and data acquisition and analysis module completed the acquisition of optical characteristic values ​​and recorded the characteristic value H2. SO3 was condensed using a water bath cooling device, and the offline condensation test result C was controlled according to national standards. S For reference, complete the system range calibration, concentration C. S The corresponding feature value is H2.

[0036] The calibration function switching, after calibration, involves switching the three-way valve to enable online monitoring of sulfur trioxide concentration via the sampling gas path. At this point, the sampling gas is introduced, and the optical characteristic value H3 is obtained. Substituting this value into the calibration result, the concentration value C is obtained.

[0037] .

Claims

1. A calibration device for an online monitoring system of sulfur trioxide concentration using laser technology, characterized in that: The device comprises a nitrogen gas tank and a mixed gas tank, the nitrogen gas tank is connected with the gas analysis device through a three-way valve, the mixed gas tank is connected with the sulfur trioxide generating device, the sulfur trioxide generating device is connected with the sampling gas path and the gas analysis device through a three-way valve; the gas analysis device comprises a laser, a gas analysis cell, a photodetector and a data acquisition and analysis module; the sulfur trioxide generating device comprises a flow meter, a high-temperature furnace and a catalytic chamber; the gas analysis cell is connected with a water bath cooling device and a vacuum pump; the mixed gas tank uses a standard mixed gas tank of sulfur dioxide and dry air; the laser selects a mid-infrared waveband quantum cascade laser, the laser waveband range is near 7.323 microns, and the photodetector response waveband is matched; the data acquisition and analysis module comprises a signal generator, a data acquisition card and a computer; The calibration method of the above-mentioned laser sulfur trioxide concentration online monitoring system calibration device is as follows: zero gas calibration, range calibration and calibration function switching; the zero gas calibration uses the nitrogen gas tank, the range calibration uses the standard mixed gas tank of sulfur dioxide and dry air, and sulfur trioxide gas is generated by catalysis at high temperature; The zero gas calibration is performed as follows: the gas analysis cell is started to keep the temperature at 220 DEG C, the nitrogen gas tank is opened, the gas analysis cell is connected, the vacuum pump maintains the pressure of the analysis cell at 60 hPa, the zero gas calibration is completed through the laser, the photodetector and the data acquisition and analysis module, and the zero gas characteristic value H1 is recorded; The range calibration switches the three-way valve to connect the gas analysis cell, water bath cooling device and vacuum pump in series, starts the high temperature furnace to maintain the temperature at 500°C, starts the gas analysis cell to maintain the temperature at 220°C, opens the mixed gas tank, the gas is reacted in the catalytic chamber, is introduced into the gas analysis cell, the vacuum pump maintains the pressure of the analysis cell at 60 hPa, the laser, photodetector and data acquisition and analysis module complete the collection of optical characteristic values, record the characteristic value H2, and the water bath cooling device completes the condensation of SO3, and the off-line test result C is controlled according to the national standard S For reference, complete system range calibration, concentration C S The corresponding characteristic value is H2; The calibration function is switched, and after calibration, the three-way valve is switched to connect the sampling gas path, the gas analysis cell and the vacuum pump in series, and the sulfur trioxide concentration is monitored on line through the sampling gas path. At this time, the sampling gas is introduced, the optical characteristic value H3 is obtained, and the concentration value C is obtained by substituting the calibration: .

2. The calibration device for the laser SO3 concentration on-line monitoring system according to claim 1, characterized in that: The catalytic chamber is filled with vanadium catalyst containing vanadium pentoxide and is built in the high-temperature furnace, and the whole gas path is heat-insulated through a heat tracing band; the signal generator outputs a voltage signal with a specific wave form to modulate the laser, the data acquisition card acquires the analog signal of the photodetector, the computer analyzes the data online, and the optical characteristic value containing the gas concentration information is obtained through the Lambert-Beer law.

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