In-situ online measurement device for concentration of CO2 in flue gas based on infrared absorption spectrum

Abstract

The utility model discloses an in-situ online measurement device for CO2 concentration in flue gas based on an infrared absorption spectrum. The in-situ online measurement device comprises an equipment shell, an infrared light source and a receiving module, wherein the infrared light source and the receiving module are arranged in the equipment shell; the equipment shell comprises a first mounting area, a second mounting area and a flue gas detection area, and the flue gas detection area is located between the first mounting area and the second mounting area; the infrared light source and the receiving module are arranged in the first mounting area, and a light source reflecting module is arranged in the second mounting area; detection windows are arranged on the two sides of the flue gas detection area, and each detection window is provided with an air curtain device. The infrared light source and the receiving module are positioned on the same side through the light source reflecting module, so that the in-situ online measurement device for the CO2 concentration in the flue gas is convenient to mount in a flue gas pipeline, and the in-situ measurement of the CO2 concentration in the flue gas is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of absorption spectroscopy gas measurement, and particularly relates to an in-situ online measurement device for CO2 concentration in flue gas based on infrared absorption spectroscopy. Background Technique

[0002] Implementing online monitoring of CO2 concentration in the flue gas of coal-fired power plants is of great significance for energy conservation, emission reduction of power station units and the establishment of the carbon trading market. By accurately measuring the CO2 concentration in the flue gas and combining it with the flue gas flow rate, the CO2 emission intensity of the unit can be accurately calculated, thus providing data support for optimizing the boiler combustion process, improving energy utilization efficiency and achieving the carbon emission reduction goal. In addition, the monitoring data of CO2 emission concentration is also the basis for calculating and trading carbon quotas in the carbon trading market of coal-fired power plants, which is of great significance for realizing carbon emission accounting and compliance management and improving the economic benefits and market competitiveness of coal-fired power stations.

[0003] In recent years, a large number of studies have been carried out on CO2 concentration measurement technologies, which can be divided into spectroscopic methods and non-spectroscopic methods according to the measurement principle. Non-spectroscopic methods mainly include gas chromatography, chemical analysis methods, etc. Most of these methods belong to single-point test methods and need to sample point by point. Therefore, the measurement takes a long time, rapid online monitoring cannot be achieved, and the measurement accuracy is easily interfered by the on-site environment, making it difficult to be applied to the harsh high-temperature flue gas environment in industrial sites.

[0004] Spectroscopic methods include fluorescence method, colorimetric method, infrared absorption spectroscopy method, etc. Among them, the infrared absorption spectroscopy method has received extensive attention due to its strong selectivity, high sensitivity, fast response speed and non-invasive characteristics. The infrared absorption spectroscopy method realizes selective measurement of the concentration of specific gas species by using the specificity of gas having absorption peaks in the infrared band. According to the molecular spectroscopy theory, when a beam of infrared light passes through the gas to be measured, the light intensity will attenuate due to the absorption of gas molecules. The attenuation amount of the light intensity is related to the absorption coefficient, concentration, effective optical path length, etc. of gas molecules. Therefore, the type and concentration of gas molecules can be inversely calculated according to the absorption spectrum. Lambert-Beer's law reveals the relationship between the change amount of light intensity after light passes through a certain gas and the gas concentration and effective optical path. When the optical path is known, the gas concentration can be calculated through the change amount of light intensity.

[0005] Current research on CO2 concentration measurement by infrared absorption spectroscopy is mainly limited to laboratories or simple gas environments after pretreatment. Although it can accurately measure CO2 in different concentration ranges, the measurement stability has high requirements for environmental stability and cannot meet the need for on-line monitoring of CO2 concentration in the complex gas environment of coal-fired power plant flue gas. The actual flue gas in coal-fired power plant flue has characteristics such as high temperature, fast flow rate, and high humidity, and at the same time contains complex gas components such as dust, nitrogen oxides, sulfides, CO, and CO2. Moreover, the flue has great limitations on the sensor layout method. Therefore, there are high requirements for the accuracy and stability of the measurement method and the simplicity of the optical path of the measurement system. How to achieve in-situ on-line measurement of CO2 concentration in such a complex environment is still an important problem that needs to be solved urgently at present. Summary of the Invention

[0006] The technical problem to be solved by the utility model is to provide an in-situ on-line measurement device for CO2 concentration in flue gas based on infrared absorption spectroscopy, which can improve the measurement accuracy and stability of CO2 concentration in flue gas under complex industrial site environments.

[0007] To solve the above technical problems, the technical solution adopted by the utility model is as follows:

[0008] An in-situ on-line measurement device for CO2 concentration in flue gas based on infrared absorption spectroscopy includes a device housing and an infrared light source and a receiving module arranged in the device housing. It is characterized in that the device housing includes a first installation area, a second installation area, and a flue gas detection area, and the flue gas detection area is located between the first installation area and the second installation area; the infrared light source and the receiving module are arranged in the first installation area, and a light source reflection module is arranged in the second installation area;

[0009] Detection windows are arranged on both sides of the flue gas detection area, and an air curtain device is arranged at each detection window;

[0010] A fan is also arranged in the first installation area, and the fan is connected to the air curtain device to form an air curtain at the detection window;

[0011] The emitted light of the infrared light source enters the detection window of the flue gas detection area after being reflected by the light source reflection module, and is received by the receiving module.

[0012] An air path is arranged in the device housing, and the fan and the air curtain device are connected through the air path; an air filter is arranged at the inlet of the air path.

[0013] The air curtain device includes a frame, and a circle of air injection holes are arranged on the side of the frame; the air injection holes are communicated with the air path.

[0014] The receiving module includes an MCU microcontroller unit, a first filter, a second filter, a converging lens, a reference optical path detector, a measurement optical path detector, and an amplifier circuit; the first filter, the second filter, the converging lens, the reference optical path detector, and the measurement optical path detector are sequentially arranged on the reflected light path of the light source reflection module; the amplifier circuit is used to amplify the voltage signals generated by the reference optical path detector and the measurement optical path detector, and the amplified voltage signals enter the microcontroller unit.

[0015] The first filter is a filter with a central wavelength of 4.26 μm, and the second filter is a filter with a central wavelength of 3.96 μm.

[0016] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0017] 1. The present utility model proposes an in-situ online measuring device for CO2 concentration in flue gas based on infrared absorption spectroscopy. Through the light source reflection module, the infrared light source and the receiving module are located on the same side, which facilitates the installation of the in-situ online measuring device for CO2 concentration in flue gas of the present utility model in the flue gas pipeline and realizes the in-situ measurement of CO2 concentration in flue gas.

[0018] 2. To prevent the flue gas from polluting the detection window and causing attenuation of the infrared light intensity, clean air is introduced into the measurement system to form an air film on the detection window to provide real-time flue gas isolation protection for the window.

[0019] 3. A single optical path and dual wavelength measurement system is built, and appropriate infrared bands are selected to basically eliminate the influences of changes in light source radiation intensity, contamination of optical components, and detector drift, etc., greatly improving the stability of the sensor and realizing the real-time in-situ online monitoring of CO2 concentration in high-temperature flue gas. Description of the Drawings

[0020] Figure 1 is the schematic diagram of the main structure and installation of the in-situ online measuring device for CO2 concentration in flue gas based on infrared absorption spectroscopy of the present utility model;

[0021] Figure 2 is the detailed structure diagram of the in-situ online measuring device for CO2 concentration in flue gas based on infrared absorption spectroscopy of the present utility model;

[0022] Figure 3 is the structure diagram of the air curtain device of the present utility model;

[0023] In the figure, 1 is the control and monitoring module; 1-1 is the infrared light source; 1-2 is the MCU microcontroller unit; 1-3 is the fan; 1-4 is the power supply module; 1-5 is the air dehumidification filter; 1-6 is the gas path; 1-7 is the flue gas temperature and humidity sensor; 1-8 is the 4.26μm filter; 1-9 is the 3.96μm filter; 1-10 is the converging lens; 1-11 is the reference optical path detector; 1-12 is the measurement optical path detector; 1-13 is the amplifier circuit; 2 is the light source reflection module; 2-1 is the corner cube reflector; 3 is the flue gas detection area; 3-1 is the left window; 3-2 is the right window; 3-3 is the air curtain device; 3-3-1 is the air injection hole; 3-4 is the flue gas temperature and humidity probe; 4 is the equipment housing; 5 is the flue duct wall; 6 is the flange; 7 is the signal connection wire; 8 is the circuit connection wire; 9 is the wide infrared beam. Detailed implementation mode

[0024] As Figure 1 shown, the in-situ online measurement device for flue gas CO2 concentration based on infrared absorption spectroscopy proposed by the present utility model includes a control and monitoring module 1, a light source reflection module 2, a flue gas detection area 3 and an equipment housing 4. The in-situ online measurement device for flue gas CO2 concentration based on infrared absorption spectroscopy is installed on the flue duct wall 5 of the area to be measured through a flange 6; the control and monitoring module 1 is installed outside the flue duct wall 5; the light source reflection module 2 and the flue gas detection area 3 are inside the flue duct wall 5.

[0025] In one embodiment, the control and monitoring module 1 includes an infrared light source 1-1, an MCU microcontroller unit 1-2, a fan 1-3, a power supply module 1-4, an air filter 1-5, a gas path 1-6, a flue gas temperature and humidity sensor 1-7, a 4.26μm filter 1-8, a 3.96μm filter 1-9, a converging lens 1-10, a reference optical path detector 1-11, a measurement optical path detector 1-12 and an amplifier circuit 1-13; the light source reflection module 2 is composed of a corner cube reflector 2-1; the flue gas detection area 3 is composed of a left window 3-1, a right window 3-2, an air curtain device 3-3 and a flue gas temperature and humidity probe 3-4.

[0026] As Figure 2 shown, the MCU microcontroller unit 1-2 is respectively connected to the infrared light source 1-1, the fan 1-3, the amplifier circuit 1-13, the power supply module 1-4 and the flue gas temperature and humidity sensor 1-7 through a signal connection wire 7;

[0027] As Figure 2 shown, the power supply module 1-4 is respectively connected to the infrared light source 1-1, the MCU microcontroller unit 1-2, the fan 1-3, the flue gas temperature and humidity sensor 1-7, the reference optical path detector 1-11 and the measurement optical path detector 1-12 through a circuit connection wire 8.

[0028] As Figure 2As shown, the reference optical path detector 1-11 is connected to the amplifier circuit 1-13 through the signal connection line 7.

[0029] As Figure 2 shown, the measurement optical path detector 1-12 is connected to the amplifier circuit 1-13 through the signal connection line 7.

[0030] As Figure 2 shown, the front side of the fan 1-3 is fixedly connected to the air curtain spraying mechanism 3-3 through the air path 1-6, and the rear side of the fan 1-3 is fixedly connected to the air filter 1-5 through the air path 1-6.

[0031] As Figure 2 shown, the left window 3-1 is embedded and installed on the equipment shell 4, and there is a ring of air curtain devices 3-3 on the outside of the left window 3-1;

[0032] As Figure 3 shown, there is a ring of air jet holes 3-3-1 on the outer wall of the air curtain device 3-3.

[0033] As Figure 2 shown, the flue gas temperature and humidity probe 3-4 is installed inside the flue duct wall 5 and is connected to the flue gas temperature and humidity sensor 1-7 through the signal connection line 7.

[0034] As Figure 2 shown, the infrared light source 1-1 emits a wide infrared beam 9 to the corner cube reflector 2-1; the wide infrared beam 9 passes through the corner cube reflector 2-1 and refracts through the left window 3-1 into the flue gas detection area 3, and then passes through the right window 3-2 again; the upper half of the optical path of the wide infrared beam 9 finally passes through the 3.96μm filter 1-9, and then passes through the converging lens 1-10 and is incident on the reference optical path detector 1-11, and the lower half of the optical path of the wide infrared beam 9 finally passes through the 4.26μm filter 1-8, and then passes through the converging lens 1-10 and is incident on the measurement optical path detector 1-12.

[0035] As Figure 2 shown, the reference optical path detector 1-11 converts the optical signal incident by the infrared beam passing through the 3.96μm filter 1-9 into an electrical signal and transmits the signal to the amplifier circuit 1-13 through the signal connection line 7; the amplifier circuit 1-13 sends the final signal to the MCU micro-control unit 1-2 through the signal connection line 7.

[0036] As Figure 2 shown, the measurement optical path detector 1-12 converts the optical signal incident by the infrared beam passing through the 4.26μm filter 1-9 into an electrical signal and transmits the signal to the amplifier circuit 1-13 through the signal connection line 7; the amplifier circuit 1-13 sends the final signal to the MCU micro-control unit 1-2 through the signal connection line 7.

[0037] An in-situ online measurement device for CO2 concentration in flue gas based on infrared absorption spectroscopy proposed by the present utility model emits a beam of light from an infrared light source. After being reflected by a corner cube reflector, it propagates in the reverse direction, passes through the left window and enters the flue gas flow region. CO2 in the flue gas absorbs the spectrum of a specific wavelength. After the infrared light absorbed by the flue gas passes through the right window, it passes through filters with different center wavelengths respectively to obtain two infrared lights of specific wavelengths, and then propagates through a converging lens to a photodetector (reference optical path detector, measurement optical path detector) to generate corresponding voltage signals. The voltage signals are amplified by an amplifier circuit and then collected by a microcontroller unit (MCU). At the same time, in order to reduce the influence of changes in flue gas temperature and humidity on the measurement results, a flue gas temperature and humidity probe is provided in the flue gas flow region to monitor the flue gas temperature and humidity, and the sensor signal is transmitted to the MCU microcontroller unit to correct the measurement results, so as to improve the measurement accuracy and stability of the system.

[0038] To prevent flue gas from polluting the left and right windows, resulting in attenuation of the infrared light intensity, clean air is introduced into the measurement system to form an air film on the windows to provide real-time flue gas isolation protection for the windows. Specifically, air is introduced by a fan. After being dehumidified and dust-removed by an air dehumidification filter, it is supplied to the air curtain device through an air path. The air injection holes of the air curtain device spray annular gas towards the windows, and then a flue gas isolation air film is formed on the windows.

[0039] The single-beam double-optical-path design is adopted in the measurement device and the dynamic reference technology (this technology is a conventional technology in this field) is introduced. By obtaining real-time reference signals to correct and compensate the measurement signals, the errors caused by environmental changes, interference of other components in the flue gas, and instrument temperature drift are eliminated. One optical path is used for the actual measurement optical path, and the other optical path is used as a reference. By comparing the signals of the two optical paths, the influence of dust, temperature, and flow rate changes in the flue gas is compensated to improve the measurement accuracy and stability, so as to realize high-precision in-situ online monitoring of CO2 concentration in a complex flue environment.

[0040] According to the attenuation degree of the infrared light intensity of specific wavelengths before and after the gas, the concentration of the gas can be calculated based on the Lambert-Beer law;

[0041] I(λ) = I0(λ)e -α(λ)kl #(1)

[0042] In the formula, I0(λ) and I(λ) are the incident light intensity and transmitted light intensity of the infrared light of wavelength λ respectively; α(λ) is the absorption coefficient of the gas for the infrared light of wavelength λ; k is the concentration of the gas to be measured, and l is the finite path length that the light passes through.

[0043] Since the actual flue gas contains dust and moisture, a correction factor m(λ) is introduced into Equation (1):

[0044] I(λ) = I0(λ)e-α(λ)kl+m(λ)l #(2)

[0045] m(λ)I = a(λ)l + b(λ)l + c(λ)l#(3)

[0046] Wherein, a(λ) is the Rayleigh scattering coefficient of other gas molecules, b(λ) is the Mie scattering coefficient of dust, and c(λ) is the water absorption coefficient.

[0047] When measuring the CO2 concentration based on the infrared absorption spectroscopy technique, from the infrared absorption spectrum of CO2, it can be seen that its main absorption is in the band around 4.26 μm, and it hardly absorbs the infrared radiation in the band around 3.96 μm. Therefore, a filter with a central wavelength of λ1 = 4.26 μm is selected for the measurement optical path, and a filter with a central wavelength of λ2 = 3.96 μm is selected for the reference optical path. The intensities of the two wavelengths in the light emitted by the infrared light source are I0(λ1) and I0(λ2), and the intensities of the infrared light absorbed by the flue gas received by the two photodetectors are I(λ1, l) and I(λ2, l). The calculation relationships of the light intensities before and after the interference absorption of CO2 and other components in the flue gas are as follows:

[0048]

[0049] From equations (4) and (5), the gas concentration k can be obtained as:

[0050]

[0051] Since CO2 hardly absorbs the infrared radiation in the band around 3.96 μm, α(λ2) ≈ 0. At the same time, since the two selected wavelengths are relatively close, the attenuation of the infrared light of the two wavelengths caused by the flue gas dust and water vapor is almost the same, that is, m(λ1) ≈ m(λ2), and equation (6) can be simplified as:

[0052]

[0053] It can be seen that through the single-beam dual-wavelength method and using the ratio method for processing, the CO2 concentration can be accurately obtained theoretically, which has nothing to do with the component performance of the sensor system, and basically eliminates the influences such as the change of the light intensity of the light source radiation, the interference of background components, the pollution of optical elements, and the drift of the detector, greatly improving the stability of the measuring device.

Claims

1. An in-situ online measuring device for the CO2 concentration in flue gas based on infrared absorption spectroscopy, comprising an equipment housing and an infrared light source and a receiving module arranged inside the equipment housing; characterized in that, The device housing includes a first installation area, a second installation area, and a flue gas detection area, and the flue gas detection area is located between the first installation area and the second installation area; the infrared light source and the receiving module are arranged in the first installation area, and a light source reflection module is arranged in the second installation area; Detection windows are arranged on both sides of the flue gas detection area, and an air curtain device is arranged at each detection window; A fan is also arranged in the first installation area, and the fan is connected to the air curtain device for forming an air curtain at the detection window; The emitted light of the infrared light source enters the detection window of the flue gas detection area after being reflected by the light source reflection module and is received by the receiving module.

2. The in-situ online measuring device for CO2 concentration in flue gas based on infrared absorption spectroscopy according to claim 1, characterized in that, An air path is arranged in the device housing, and the fan and the air curtain device are connected through the air path.

3. The in-situ on-line measuring device for the CO2 concentration in flue gas based on infrared absorption spectroscopy according to claim 2, wherein, An air filter is arranged at the inlet of the air path.

4. The in-situ online measuring device for the CO2 concentration in flue gas based on infrared absorption spectroscopy according to claim 3, wherein, The air curtain device includes a frame, and a circle of air injection holes are arranged on the side surface of the frame; the air injection holes are communicated with the air path.

5. The in-situ online measuring device for CO2 concentration in flue gas based on infrared absorption spectroscopy according to claim 4, wherein The frame is a square frame.

6. The in-situ online measuring device for CO2 concentration in flue gas based on infrared absorption spectrum according to any one of claims 1-5, characterized in that, The receiving module includes an MCU micro-control unit, a first filter, a second filter, a converging lens, a reference optical path detector, and a measurement optical path detector; the first filter, the second filter, the converging lens, the reference optical path detector, and the measurement optical path detector are sequentially arranged on the reflection optical path of the light source reflection module.

7. The in-situ online measuring device for the CO2 concentration in flue gas based on infrared absorption spectroscopy according to claim 6, wherein The receiving module further includes an amplifier circuit, and the amplifier circuit is used for amplifying the voltage signals generated by the reference optical path detector and the measurement optical path detector, and the amplified voltage signals enter the MCU micro-control unit.

8. The in-situ online measuring device for CO2 concentration in flue gas based on infrared absorption spectroscopy according to claim 6, characterized in that, The first filter is a filter with a central wavelength of 4.26 .

9. The in-situ on-line measuring device for the CO2 concentration in flue gas based on infrared absorption spectroscopy according to claim 6, wherein The second filter is a filter with a central wavelength of 3.96 .

10. The in-situ online measuring device for CO2 concentration in flue gas based on infrared absorption spectroscopy according to claim 1, wherein The receiving module further includes a flue gas temperature and humidity sensor for obtaining the temperature and humidity of the flue gas in the flue gas detection area.

Images