CN116380838B - Greenhouse gas measurement system and method based on multipath infrared laser absorption spectrum - Google Patents
Greenhouse gas measurement system and method based on multipath infrared laser absorption spectrum Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
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- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
- G01N2021/392—Measuring reradiation, e.g. fluorescence, backscatter
- G01N2021/393—Measuring reradiation, e.g. fluorescence, backscatter and using a spectral variation of the interaction of the laser beam and the sample
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Abstract
The invention discloses a greenhouse gas measurement system and method based on multipath infrared laser absorption spectrum, and belongs to the technical field of gas measurement. The measuring system comprises a computer, a data acquisition card, a laser generating device, a light beam coupling and incidence adjusting device, an InAsSb detector, an InGaAs detector and a multi-reflection gas absorption cell. According to the content of CO 2、CH4、N2 O in the atmosphere, the distributed feedback type laser which works at three infrared wave bands of 2003nm, 1653nm and 4474nm is selected to respectively carry out on-line detection on three gases of CO 2、CH4、N2 O, and the greenhouse gas measurement system based on the multi-path infrared laser absorption spectrum is simple in structure and has the advantages of low detection cost and quick response time.
Description
Technical Field
The invention relates to the technical field of gas concentration measurement, in particular to a greenhouse gas measurement system and method based on multipath infrared laser absorption spectrum.
Background
The greenhouse gas species include CH 4、N2 O, HCFs, PFCs and SF 6 in addition to CO 2, and since the latter three greenhouse gases are properly controlled and the atmosphere is low, the contribution to the atmospheric temperature chamber effect is negligible over a short period of time compared to the first three gases. CO 2 is the most predominant long-life greenhouse gas affecting the earth's radiation balance, and the concentration in the atmosphere has exceeded 400ppm; the CO 2 with the capability of causing the greenhouse effect of CH 4 is 25 times, the influence on the greenhouse effect is inferior to CO 2, and the content of the current atmosphere is about 1.9ppm; n 2 O is very low in the atmosphere, but its effect on the greenhouse effect is 298 times that of CO 2, and in the last decades N 2 O has increased approximately at a rate of 0.8ppb each month, currently about 330ppb in the atmosphere. CO 2、CH4、N2 O has high content in the atmosphere and long existence time, and is a main research object for controlling greenhouse gases at present.
When the content of CO 2 and CH 4 in the atmosphere reaches the ppm level and concentration detection is carried out based on a spectrum technology, gas absorption lines in the near infrared band can be selected to detect CO 2 and CH 4 respectively. The N 2 O content in the atmosphere is only about 330ppb, the N 2 O is weak in the near infrared band, and the detection of the fundamental frequency absorption line of N 2 O in the middle infrared band is a better choice. Various spectroscopic techniques are also used for greenhouse gas detection, such as off-axis integrating cavity output spectra, cavity enhanced absorption spectra, cavity ring down spectra, and the like. The use of the above-mentioned spectroscopic techniques often requires accurate knowledge of the reflectivity of the lenses in the device, requires extremely high optical alignment, and requires high-speed electronics to complete signal acquisition and analysis, which results in relatively complex and costly devices that are not suitable for wide-ranging applications.
In order to guide the detection personnel in the carbon emission detection field to measure the concentration of CO 2、CH4、N2 O in various gas samples, the method is formally implemented from 3 months and 6 days of 2021 in gas chromatography (T/LCAA 005-2021) which is a group standard of measuring the concentration of methane, nitrous oxide and carbon dioxide in gas, issued by low-carbon agriculture Association in Beijing city. The gas chromatography is a chromatographic analysis method using gas as a mobile phase, can be used for high-precision detection of gas concentration, and is an important analysis means for detecting organic compounds in judicial identification. However, when the method is used for measuring the gas concentration, the signal output after detection is often required to be corrected by using a pure sample of a known object to be detected, and the device is expensive and large in size, so that the method is more suitable for laboratory detection and is not suitable for on-site on-line monitoring.
The patent of the invention with the application number of CN201110046054.8 provides a greenhouse gas tester and a testing method, wherein the method mainly adopts a detection system consisting of chemical reagents and a gas collecting device to measure the greenhouse gas. The method needs to complete operations such as gas sampling, chemical reagent repeated configuration and the like, and has complex and time-consuming process and can not achieve accurate online gas detection.
In summary, there is a need for a system that can simultaneously perform on-line rapid measurements of three greenhouse gases, CO 2、CH4、N2 O, and that is convenient for on-site applications in terms of cost and portability for use in the accounting and assessment of greenhouse gas emissions.
Disclosure of Invention
The invention aims to rapidly and online measure the concentration of three greenhouse gases, namely CO 2、CH4、N2 O, at low cost, and provides a greenhouse gas measurement system and method based on a multi-path infrared laser absorption spectrum.
To achieve the purpose, the invention adopts the following technical scheme:
The greenhouse gas measurement system based on the multi-path infrared laser absorption spectrum comprises a computer, a data acquisition card, a laser generating device, a light beam coupling and incidence adjusting device, an InAsSb detector, an InGaAs detector and a multi-reflection gas absorption tank, wherein a software program running on the computer calls a signal output channel of the data acquisition card to circularly output current signals to drive a first laser, a second laser and a third laser in the laser generating device to sequentially output laser,
The beam coupling and incidence adjusting device couples the laser output by the first laser and the second laser to the same light path, then the laser output by the first laser or the second laser is incident into the multi-reflection gas absorption tank at an angle which coincides with the incident optical axis of the multi-reflection gas absorption tank, and is used for coupling the laser output by the third laser and the He-Ne laser to the same light path, then the laser output by the third laser and the He-Ne laser is incident into the multi-reflection gas absorption tank at an angle which coincides with the incident optical axis of the multi-reflection gas absorption tank, and the multi-reflection gas absorption tank is filled with a gas sample to be measured containing CO 2、CH4、N2 O;
the outgoing light beam which is output by the first laser or the second laser and is subjected to multiple reflection by the multiple reflection gas absorption cell is collected by the InGaAs detector and converted into an electric signal, and then the electric signal is output to the data acquisition card; the emergent light beam which is output by the third laser and is subjected to multiple reflection by the multiple reflection gas absorption cell is collected by the InAsSb detector and converted into an electric signal, and then the electric signal is output to the data acquisition card;
and the data acquisition card correspondingly calculates the concentration of CO 2, the concentration of CH 4 or the concentration of N 2 O in the gas sample to be detected according to the received electric signals.
As a preferred scheme of the invention, the first laser and the second laser are distributed feedback semiconductor lasers packaged in a butterfly shape, and the third laser is a distributed feedback quantum cascade laser packaged in a HHL.
As a preferred scheme of the invention, the first laser works in the 2003nm infrared band and is used for detecting the concentration of CO 2 in the gas sample to be detected; the second laser works in the 1653nm infrared band and is used for carrying out CH 4 concentration detection on the gas sample to be detected; the third laser works in 4474nm infrared band and is used for detecting the concentration of N 2 O in the gas sample to be detected; the He-Ne laser is used for outputting 633nm visible laser.
As a preferable mode of the present invention, the laser generating device includes the first laser, the second laser, the third laser, and a first laser driver, a second laser driver, and a third laser driver for driving the first laser, the second laser, and the third laser to output laser light, respectively, and each laser driver receives the current signal and drives the laser operating in the corresponding infrared band to output laser light.
As a preferable mode of the invention, the light beam coupling and incidence adjusting device comprises a first light beam coupling device, a first incidence adjusting device, a second light beam coupling device and a second incidence adjusting device,
The first light beam coupling device comprises a first collimator, a second collimator, a first plane reflector and a light splitting sheet, wherein laser output by the first laser reaches the light splitting sheet through the reflection of the first plane reflector after being collimated by the first collimator, laser output by the second laser reaches the light splitting sheet after being collimated by the second collimator, the light splitting sheet couples the laser output by the first laser and the second laser to the same light path and reaches the first incidence adjusting device, and the deflection and pitching angles of the first incidence adjusting device are adjusted to enable the laser beam emitted by the first incidence adjusting device to coincide with the incidence optical axis of the multi-reflection gas absorption tank;
The second light beam coupling device comprises a third plane reflector, a dichroic beam splitter and an adjustable aperture, laser output by the third laser is coupled to the same light path through the dichroic beam splitter and visible laser output by the He-Ne laser by adjusting the deflection and pitching angles of the third plane reflector, the coupled light beam reaches the second incidence adjusting device after being shaped through the adjustable aperture, and the laser beam emitted by the second incidence adjusting device coincides with the incidence optical axis of the multi-reflection gas absorption tank by adjusting the deflection and pitching angles of the second incidence adjusting device.
As a preferred embodiment of the present invention, the first incident adjusting device is a second plane mirror; the second incidence adjusting device comprises a fourth plane reflector and a fifth plane reflector, and after the laser beam shaped by the adjustable light ring is reflected by the fourth plane reflector and the fifth plane reflector, the reflected beam is incident into the multi-reflection gas absorption tank at an angle which coincides with an incident optical axis of the multi-reflection gas absorption tank.
As a preferred embodiment of the present invention, the model numbers of the first laser driver and the second laser driver are LDTC0520; the model of the third laser driver is QCL500/PTC2.5K.
As a preferable scheme of the invention, the light splitting sheet is a long-wave-pass dichroic mirror, the reflectivity of the long-wave-pass dichroic mirror for 1653nm band infrared light is 98.91%, and the transmissivity for 2003nm band infrared light is 97.06%; the dichroic beam splitter is a low-pass filter, the low-pass filter has a transmittance of 70% for visible light in a 400-700nm wave band, and a reflectance of 95% for infrared light in a 3-12 mu m wave band.
As a preferred embodiment of the present invention, the first collimator and the second collimator are CFC2-C;
The model of the light splitting sheet is DMLP and 1800;
The model of the dichromatic beam splitter is BSP-DI-25;
The model of the data acquisition card is NI USB6363.
As a preferable scheme of the invention, the multi-reflection gas absorption cell comprises a first multi-reflection gas absorption cell and a second multi-reflection gas absorption cell, laser output by the first laser and the second laser is incident into the first multi-reflection gas absorption cell, laser output by the third laser and the He-Ne laser is incident into the second multi-reflection gas absorption cell, the first multi-reflection gas absorption cell is communicated with the second multi-reflection gas absorption cell through a hose, and the gas sample to be detected enters the second multi-reflection gas absorption cell through an air inlet of the second multi-reflection gas absorption cell and then is input into the first multi-reflection gas absorption cell through the hose;
The system further comprises a filter box, a first electromagnetic valve, a second electromagnetic valve and a gas sampling pump, wherein the filter box is arranged on an air inlet pipeline of the second multi-reflection gas absorption tank, the first electromagnetic valve is arranged on the air inlet pipeline between an air inlet of the second multi-reflection gas absorption tank and the filter box, the gas sampling pump is arranged on an air outlet pipeline of the first multi-reflection gas absorption tank, the second electromagnetic valve is arranged on the air outlet pipeline between the gas sampling pump and an air outlet of the first multi-reflection gas absorption tank, and the switch of the first electromagnetic valve and the switch of the second electromagnetic valve are controlled by the computer.
As a preferable mode of the invention, a wedge-shaped silicon window lens is arranged in the multi-reflection gas absorption cell, and laser light entering the multi-reflection gas absorption cell enters the multi-reflection gas absorption cell after penetrating through the wedge-shaped silicon window lens.
The invention also provides a greenhouse gas measurement method based on the multipath infrared laser absorption spectrum, which comprises the following steps:
Step S1, driving a first laser, a second laser and a third laser to sequentially output laser through the system and enabling the laser to enter a multi-reflection gas absorption tank at an angle which coincides with an incident optical axis of the multi-reflection gas absorption tank, wherein a gas sample to be detected containing CO 2、CH4、N2 O is arranged in the multi-reflection gas absorption tank;
s2, collecting outgoing light beams reflected for many times by the multi-reflection gas absorption cell by the InGaAs detector or the InAsSb detector, converting the collected light signals into electric signals and outputting the electric signals to a data acquisition card;
and step S3, the data acquisition card correspondingly calculates the concentration of CO 2, the concentration of CH 4 or the concentration of N 2 O of the gas sample to be detected according to the received electric signals.
According to the content of CO 2、CH4、N2 O in the atmosphere, the distributed feedback type laser which works at three infrared wave bands of 2003nm, 1653nm and 4474nm is selected to respectively carry out on-line detection on three gases of CO 2、CH4、N2 O, and the greenhouse gas measurement system based on the multi-path infrared laser absorption spectrum is simple in structure and has the advantages of low detection cost and quick response time.
Drawings
In order to more clearly illustrate the technical solution of the embodiments of the present invention, the drawings that are required to be used in the embodiments of the present invention will be briefly described below. It is evident that the drawings described below are only some embodiments of the present invention and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a schematic diagram of a greenhouse gas online measurement system based on multi-channel infrared laser absorption spectrum according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of drive signals for sequentially driving three lasers in a single detection period;
Fig. 3 is a step diagram of a method for detecting the concentration of three gases of CO 2、CH4、N2 O by using the system provided by the embodiment of the present invention.
Detailed Description
The technical scheme of the invention is further described below by the specific embodiments with reference to the accompanying drawings.
Wherein the drawings are for illustrative purposes only and are shown in schematic, non-physical, and not intended to be limiting of the present patent; for the purpose of better illustrating embodiments of the invention, certain elements of the drawings may be omitted, enlarged or reduced and do not represent the size of the actual product; it will be appreciated by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numbers in the drawings of embodiments of the invention correspond to the same or similar components; in the description of the present invention, it should be understood that, if the terms "upper", "lower", "left", "right", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, only for convenience in describing the present invention and simplifying the description, rather than indicating or implying that the apparatus or elements being referred to must have a specific orientation, be constructed and operated in a specific orientation, so that the terms describing the positional relationships in the drawings are merely for exemplary illustration and should not be construed as limiting the present patent, and that the specific meaning of the terms described above may be understood by those of ordinary skill in the art according to specific circumstances.
In the description of the present invention, unless explicitly stated and limited otherwise, the term "coupled" or the like should be interpreted broadly, as it may be fixedly coupled, detachably coupled, or integrally formed, as indicating the relationship of components; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between the two parts or interaction relationship between the two parts. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
The tunable laser infrared absorption spectrum technology uses a wavelength scanning method to detect a single absorption spectrum line of the gas to be detected, and calculates the concentration of the gas according to the infrared absorption spectrum of the gas to be detected. The tunable laser infrared absorption spectrum technology is widely applied to trace gas detection by the advantages of non-invasiveness, rapidness, high sensitivity and the like. For the tunable laser infrared absorption spectrum technology, the modulation spectrum technology and the multi-reflection gas absorption tank are combined, and the detection limit of the gas to be detected can reach ppm to ppb level. By utilizing software programming, the infrared absorption spectrum and the wavelength modulation spectrum technology can be conveniently combined and applied to high-precision on-line detection of gas concentration. According to the content of CO 2、CH4、N2 O in the atmosphere, three distributed feedback lasers working in 2003nm, 1653nm and 4474nm infrared bands are selected to respectively perform on-line detection on three gases of CO 2、CH4、N2 O, and the high-sensitivity detection on the three gases is realized by combining a modulation spectrum technology.
Firstly, the structure of the greenhouse gas measurement system based on multi-path infrared laser absorption spectrum provided by the embodiment of the invention is described, as shown in fig. 1 (solid lines in fig. 1 represent optical paths, dotted lines represent electric signal transmission directions, and dash-dot lines represent gas flow directions), the system comprises:
Computer 100, data acquisition card 200 (preferably, data acquisition card with model number USB6363 manufactured by National Instruments Co., ltd.), laser generator, beam coupling and incidence regulator, inAsSb detector 300, inGaAs detector 400 and multiple reflection gas absorption cell, software program running on computer 100 calls signal output channel of data acquisition card 200, circularly outputs current signal to drive first laser J1 (working in 2003nm infrared band for CO 2 concentration detection of gas sample to be tested), second laser J2 (working in 1653nm infrared band for CH 4 concentration detection of gas sample to be tested), third laser J3 (working in 4474nm infrared band for N 2 O concentration detection of gas sample to be tested) in turn output laser,
The beam coupling and incidence adjusting device couples the laser output by the first laser J1 and the second laser J2 to the same light path, then the laser output by the first laser J1 or the second laser J2 is incident into the multi-reflection gas absorption tank at an angle which coincides with the incident optical axis of the multi-reflection gas absorption tank, and is used for coupling the laser output by the third laser J3 and the He-Ne laser J4 (for outputting 633nm visible laser) to the same light path, then the laser output by the third laser J3 and the He-Ne laser J4 is incident into the multi-reflection gas absorption tank at an angle which coincides with the incident optical axis of the multi-reflection gas absorption tank, and a gas sample to be detected containing CO 2、CH4、N2 O is filled in the multi-reflection gas absorption tank; here, the addition of the He-Ne laser J4 is because the emergent light of the third laser J3 is invisible and belongs to the spatial free light output, and the laser light output by the He-Ne laser J4 is visible light, and by coupling the light paths of the He-Ne laser J4 and the third laser J3, the angle of the incident laser light output by the third laser J3 into the multiple reflection gas absorption cell and the emergent light after multiple reflections can be accurately located on the response surface of the InAsSb detector can be helped. The emergent light of the first laser J1 and the emergent light of the second laser J2 are output through optical fibers, and the optical path adjustment can be carried out by means of a laser pen and an optical fiber jumper, so that the He-Ne lasers are not required to be configured for the first laser J1 and the second laser J2.
The outgoing beam which is output by the first laser J1 or the second laser J2 and is subjected to multiple reflection by the multiple reflection gas absorption cell is collected by the InGaAs detector 400 and converted into an electric signal, and then the electric signal is output to the data acquisition card 200; the outgoing beam which is output by the third laser J3 and is subjected to multiple reflection by the multiple reflection gas absorption cell is collected by the InAsSb detector 300 and converted into an electric signal, and then the electric signal is output to the data acquisition card 200;
The data acquisition card 200 correspondingly calculates the concentration of CO 2, the concentration of CH 4 or the concentration of N 2 O in the gas sample to be detected according to the received electric signals.
In this embodiment, as shown in fig. 1, the laser generating device includes a first laser J1, a second laser J2, a third laser J3, and a first laser driver QJ1, a second laser driver QJ2, and a third laser driver QJ3 for driving the first laser J1, the second laser J2, and the third laser J3 to output laser light, respectively, where each laser driver receives a current signal and drives a laser operating in a corresponding infrared band to output laser light. In this embodiment, the first laser J1 and the second laser J2 are preferably distributed feedback semiconductor lasers in a butterfly package, and the third laser J3 is preferably a distributed feedback quantum cascade laser in a HHL package. The first laser driver QJ1 and the second laser driver QJ2 are laser drivers of model LDTC0520 manufactured by Wavelength corporation of America, and the third laser driver QJ3 is a laser driver of model QCL500/PTC2.5K manufactured by Wavelength corporation of America.
The beam coupling and incidence adjusting device comprises a first beam coupling device, a first incidence adjusting device, a second beam coupling device and a second incidence adjusting device,
The first beam coupling device comprises a first collimator 9 (preferably a collimator with the model CFC2-C manufactured by Thorlabs corporation in united states), a second collimator 10 (preferably a collimator with the model CFC2-C manufactured by Thorlabs corporation in united states), a first plane mirror 6 and a beam splitter 7 (preferably a beam splitter with the model DMLP1800 manufactured by Thorlabs corporation in united states), the laser beam output by the first laser J1 reaches the beam splitter 7 through the reflection of the first plane mirror 6 after being collimated by the first collimator 9, the laser beam output by the second laser J2 reaches the beam splitter 7 through the collimation of the second collimator 10, the beam splitter 7 couples the laser beams output by the first laser J1 and the second laser J2 to the same optical path and then reaches the first incidence adjusting device, and the deflection and the pitching angle of the first incidence adjusting device are adjusted so that the laser beam emitted by the first incidence adjusting device coincides with the incidence of the multiple reflection gas absorption cell; the first incidence adjusting means is preferably a second plane mirror 8 as shown in fig. 1;
The second beam coupling device comprises a third plane mirror 1, a dichroic beam splitter 2 (preferably a dichroic beam splitter with the model of BSP-DI-25 manufactured by ISP QPTICS company in the United states), and an adjustable optical ring 3, the deflection and the pitching angle of the third plane mirror are adjusted to enable the laser output by the third laser J3 to be coupled to the same optical path through the dichroic beam splitter 2 and the visible laser output by the He-Ne laser J4, the coupled beam reaches the second incidence adjusting device after being shaped through the adjustable optical ring 3, and the deflection and the pitching angle of the second incidence adjusting device are adjusted to enable the laser beam emitted by the second incidence adjusting device to coincide with the incidence optical axis of the multi-reflection gas absorption cell. The second incidence adjusting device is preferably a fourth plane mirror 4 and a fifth plane mirror 5 shown in fig. 1, and after the laser beam shaped by the adjustable aperture 3 is reflected by the fourth plane mirror 4 and the fifth plane mirror 5, the reflected beam is incident into the multiple reflection gas absorption cell at an angle coinciding with the incident optical axis of the multiple reflection gas absorption cell.
In order to improve convenience and accuracy of greenhouse gas measurement, preferably, in the system, the number of the multiple reflection gas absorption tanks is set to be 2, namely, the first multiple reflection gas absorption tank 14 and the second multiple reflection gas absorption tank 13 in fig. 1, laser light output by the first laser device J1 and the second laser device J2 is incident into the first multiple reflection gas absorption tank 14, laser light output by the third laser device J3 and the He-Ne laser device J4 is incident into the second multiple reflection gas absorption tank 13, the first multiple reflection gas absorption tank 14 and the second multiple reflection gas absorption tank 13 are communicated through a hose 17, and a gas sample to be measured is input into the first multiple reflection gas absorption tank 14 together through the hose 17 after entering into the second multiple reflection gas absorption tank through an air inlet 131 of the second multiple reflection gas absorption tank 13. It should be noted that, for the measurement system, the longer the absorption optical path is, the more obvious the absorption of the gas molecules to be measured to the laser is, the larger the amplitude of the output harmonic signal is, the higher the corresponding detection sensitivity is, and the lower the detection limit is, therefore, the incident light beam is collected by the corresponding detector after being reflected for multiple times by using the multiple reflection gas absorption cell, and the sensitivity of gas measurement is improved.
In order to facilitate the control of the inflation and deflation of the multiple reflection gas absorption cell (such as the control of the intake air flow rate and the intake air amount) and ensure the dryness of the gas to be measured, preferably, as shown in fig. 1, the system further comprises a filter box 11, a first electromagnetic valve 12, a second electromagnetic valve 15 and a gas sampling pump 16, wherein a desiccant for drying the gas to be measured is arranged in the filter box 11, the filter box 11 is arranged on the air inlet pipe of the second multiple reflection gas absorption cell 13, and the gas to be measured enters the second multiple reflection gas absorption cell 13 through the air inlet pipe after being dried and filtered by the filter box 11. The first electromagnetic valve 12 is arranged on an air inlet pipeline between the air inlet 131 of the second multi-reflection gas absorption tank 13 and the filter box 11, the gas sampling pump 16 is arranged on an air outlet pipeline of the first multi-reflection gas absorption tank 14, the second electromagnetic valve 15 is arranged on an air outlet pipeline between the gas sampling pump 16 and the air outlet 141 of the first multi-reflection gas absorption tank 14, and the switch of the first electromagnetic valve 12 and the second electromagnetic valve 15 is controlled by the computer 100. When the two multi-reflection gas absorption tanks need to be charged, a software program running in a computer controls the first electromagnetic valve 12 and the second electromagnetic valve 15 to be opened, and the gas sampling pump 16 is started in a manual or automatic control mode, and the gas sampling pump 16 pumps external gas into the two multi-reflection gas absorption tanks to serve as a gas sample to be detected.
In order to eliminate the influence of the optical interference fringes on the detection result accurately and avoid the influence of cavity feedback on the reflected laser, preferably, a wedge-shaped silicon window lens is arranged in the multi-reflection gas absorption tank, and the laser incident to the multi-reflection gas absorption tank enters the multi-reflection gas absorption tank after passing through the wedge-shaped silicon window lens.
The following specifically describes how the system provided in this embodiment performs greenhouse gas measurement based on multiple infrared laser absorption spectra, with reference to fig. 1-3:
The software program running on the computer firstly circularly outputs current signals to drive the 3 lasers (namely the first laser J1, the second laser J2 and the third laser J3) to work sequentially by calling an analog signal output channel of the data acquisition card. For a first laser J1 working in a near-infrared band and used for CO 2 concentration detection (2003 nm) and a second laser J2 working in a CH 4 concentration detection (1653 nm), coupling laser emitted by the first laser J1 or the second laser J2 into the same optical path, transmitting the laser emitted by the first laser J1 to a first collimator 9 through a single mode fiber, collimating by the first collimator 9, reaching a first plane mirror 6, reflecting the first plane mirror, and enabling the reflected light to reach a beam splitter 7; the laser emitted by the second laser J2 is transmitted to the second collimator 10 through a single mode fiber, is collimated by the second collimator 10 and reaches the beam splitter 7, the optical system couples 2003nm laser and 1653nm collimated laser to the same optical path through the beam splitter 7, the coupled light beam is reflected by the second plane mirror 8, the deflection and pitching angle of the second plane mirror 8 are adjusted to enable the reflected light beam to coincide with the incident optical axis of the multi-reflection gas absorption cell, and the incident light beam reaches the InGaAs detector after being reflected by the multi-reflection gas absorption cell. Since the laser beams output by the two optical fiber output lasers (i.e., the first laser J1 and the second laser J2) are coupled to the same optical path, in order to avoid interference between the laser beams emitted by the first laser J1 and the second laser J2, it is necessary to separate the two laser beams in the time domain, by outputting driving signals sequentially in time sequence to drive the laser beams one by one, as shown in fig. 2, for example, the first laser J1 is driven to operate, the InGaAs detector collects the reflected beam of the laser beam output by the first laser J1, then drives the second laser J2, and finally drives the third laser J3. After the driving of the 3 lasers is completed once and the reflected laser signals are collected, the detection period of the CO 2、CH4、N2 O concentration of the gas sample to be detected is considered to be finished.
A distributed feedback quantum cascade laser (i.e., a third laser J3) operating at room temperature is used to scan the N 2 O absorption line around 4474nm, which uses HHL packaging, a collimating lens built into the HHL packaging can collimate the output laser, and an adjustable ferrule 3 is placed in front of the laser exit for beam shaping. The output beam of the distributed feedback quantum cascade laser is aligned with the laser output by the He-Ne laser J3 through the dichromatic beam splitter 2, the aligned beam is reflected by two reflectors (namely a fourth plane reflector 4 and a fifth plane reflector 5), and the deflection and pitching angles of the two reflectors are adjusted to enable the reflected beam to coincide with the incident optical axis of the multi-reflection gas absorption tank, and the reflected beam is collected by the InAsSb detector after being subjected to multi-reflection by the multi-reflection gas absorption tank.
The InGaAs detector and the InAsSb detector convert the collected optical signals into electric signals and output the electric signals to a data acquisition card for digital processing, and the data acquisition card uses a LabVIEW-based software platform for data recording and analysis. The developed LabVIEW-based software platform is used for generating wavelength modulation signals, collecting signals detected by the InGaAs detector and the InAsSb detector, demodulating the detection signals and extracting harmonic signals. A method for calculating the concentration of the gas to be measured by the data acquisition card according to the signal collected by the detector will be briefly described herein: the photoelectric detector (i.e. InGaAs and InAsSb detector) has fixed responsivity, can convert laser power into current signals in proportion, and a transimpedance amplifier in the detector amplifies the current signals to output voltage signals, so that the output voltage signals are in direct proportion to the laser power received by the detector. The voltage signals output by the detector are collected through the data collection card, and the voltage signals are demodulated to obtain a first harmonic signal and a second harmonic signal. And combining the functional relation between the first harmonic normalized second harmonic signal peak value obtained by the pre-calibration and the standard gas concentration, and calculating to obtain the gas concentration to be measured.
In summary, when three gases of CO 2、CH4、N2 O are detected, the conventional spectroscopic techniques such as off-axis integrating cavity output spectrum, cavity enhanced absorption spectrum, cavity ring-down spectrum often require accurate information of the reflectivity of the lens in the solution device, the reflectivity information of the lens is critical to accurate calculation of the concentration of the gases, and if the lens is contaminated, the measurement result is inaccurate. In addition, these devices require extremely high optical standards and require high-speed electronics to complete signal acquisition and analysis, which results in their devices being relatively complex and costly. Although the measurement sensitivity is high, it is only suitable for laboratory analysis of sampled gases and not for popularization for field applications. In addition, when three greenhouse gases of CO 2、CH4、N2 O are measured by utilizing a gas chromatography technology and the like, the defects of complex device, complex pretreatment steps, long response time and the like are faced, and the technology is suitable for multi-component high-sensitivity analysis of sampling gases in a laboratory, but is difficult to meet the requirement of on-site on-line detection. The invention utilizes the absorption spectrum line of three gases of CO 2、CH4、N2 O in the infrared band, and can realize the accurate, quick and on-line measurement of the three gases by adopting a multi-path infrared laser absorption spectrum technology. By selecting proper absorption spectrum lines and a multi-reflection gas absorption tank, the measurement accuracy can reach ppm to ppb level, and more importantly, the method does not need to pretreat sample gas, so that the method is very suitable for being applied to actual sites for online measurement.
As shown in fig. 3, the invention further provides a greenhouse gas measurement method based on the multi-path infrared laser absorption spectrum, which comprises the following steps:
Step S1, driving a first laser, a second laser and a third laser to sequentially output laser and enabling the laser to enter a multi-reflection gas absorption tank at an angle which coincides with an incident optical axis of the multi-reflection gas absorption tank, wherein a gas sample to be detected containing CO 2、CH4、N2 O is arranged in the multi-reflection gas absorption tank;
S2, collecting outgoing light beams reflected for many times by the gas absorption cell by the InGaAs detector or the InAsSb detector, converting the collected light signals into electric signals and outputting the electric signals to the data acquisition card;
And S3, correspondingly calculating the concentration of CO 2, the concentration of CH 4 or the concentration of N 2 O of the gas sample to be detected by the data acquisition card according to the received electric signals.
It should be understood that the above description is only illustrative of the preferred embodiments of the present application and the technical principles employed. It will be apparent to those skilled in the art that various modifications, equivalents, variations, and the like can be made to the present application. Such variations are intended to be within the scope of the application without departing from the spirit thereof. In addition, some terms used in the description and claims of the present application are not limiting, but are merely for convenience of description.
Claims (6)
1. A greenhouse gas measurement system based on multipath infrared laser absorption spectrum is characterized by comprising a computer, a data acquisition card, a laser generating device, a light beam coupling and incidence adjusting device, an InAsSb detector, an InGaAs detector and a multiple reflection gas absorption tank, wherein a software program running on the computer calls a signal output channel of the data acquisition card to circularly output current signals to drive a first laser, a second laser and a third laser in the laser generating device to sequentially output laser,
The beam coupling and incidence adjusting device couples the laser output by the first laser and the second laser to the same light path, then the laser output by the first laser or the second laser is incident into the multi-reflection gas absorption tank at an angle which coincides with the incident optical axis of the multi-reflection gas absorption tank, and is used for coupling the laser output by the third laser and the He-Ne laser to the same light path, then the laser output by the third laser and the He-Ne laser is incident into the multi-reflection gas absorption tank at an angle which coincides with the incident optical axis of the multi-reflection gas absorption tank, and the multi-reflection gas absorption tank is filled with a gas sample to be measured containing CO 2、CH4、N2 O;
the outgoing light beam which is output by the first laser or the second laser and is subjected to multiple reflection by the multiple reflection gas absorption cell is collected by the InGaAs detector and converted into an electric signal, and then the electric signal is output to the data acquisition card; the emergent light beam which is output by the third laser and is subjected to multiple reflection by the multiple reflection gas absorption cell is collected by the InAsSb detector and converted into an electric signal, and then the electric signal is output to the data acquisition card;
The data acquisition card correspondingly calculates the concentration of CO 2, the concentration of CH 4 or the concentration of N 2 O in the gas sample to be detected according to the received electric signals;
The multi-reflection gas absorption tank comprises a first multi-reflection gas absorption tank and a second multi-reflection gas absorption tank, laser output by the first laser and the second laser is incident into the first multi-reflection gas absorption tank, laser output by the third laser and the He-Ne laser is incident into the second multi-reflection gas absorption tank, the first multi-reflection gas absorption tank is communicated with the second multi-reflection gas absorption tank through a hose, and a gas sample to be detected enters the second multi-reflection gas absorption tank through an air inlet of the second multi-reflection gas absorption tank and then is input into the first multi-reflection gas absorption tank through the hose;
The system further comprises a filter box, a first electromagnetic valve, a second electromagnetic valve and a gas sampling pump, wherein the filter box is arranged on an air inlet pipeline of the second multi-reflection gas absorption tank, the first electromagnetic valve is arranged on the air inlet pipeline between an air inlet of the second multi-reflection gas absorption tank and the filter box, the gas sampling pump is arranged on an air outlet pipeline of the first multi-reflection gas absorption tank, the second electromagnetic valve is arranged on the air outlet pipeline between the gas sampling pump and an air outlet of the first multi-reflection gas absorption tank, and the switch of the first electromagnetic valve and the switch of the second electromagnetic valve are controlled by the computer;
The light beam coupling and incidence adjusting device comprises a first light beam coupling device, a first incidence adjusting device, a second light beam coupling device and a second incidence adjusting device,
The first light beam coupling device comprises a first collimator, a second collimator, a first plane reflector and a light splitting sheet, wherein laser output by the first laser reaches the light splitting sheet through the reflection of the first plane reflector after being collimated by the first collimator, laser output by the second laser reaches the light splitting sheet after being collimated by the second collimator, the light splitting sheet couples the laser output by the first laser and the second laser to the same light path and reaches the first incidence adjusting device, and the deflection and pitching angles of the first incidence adjusting device are adjusted to enable the laser beam emitted by the first incidence adjusting device to coincide with the incidence optical axis of the multi-reflection gas absorption tank;
The second light beam coupling device comprises a third plane reflector, a dichroic beam splitter and an adjustable aperture, the laser output by the third laser is coupled to the same light path through the dichroic beam splitter and the visible laser output by the He-Ne laser by adjusting the deflection and the pitching angle of the third plane reflector, the coupled light beam reaches the second incidence adjusting device after being shaped through the adjustable aperture, and the laser beam emitted by the second incidence adjusting device coincides with the incidence optical axis of the multi-reflection gas absorption cell by adjusting the deflection and the pitching angle of the second incidence adjusting device;
The first incidence adjusting device is a second plane reflecting mirror; the second incidence adjusting device comprises a fourth plane reflector and a fifth plane reflector, and after the laser beam shaped by the adjustable light ring is reflected by the fourth plane reflector and the fifth plane reflector, the reflected beam is incident into the multi-reflection gas absorption tank at an angle which coincides with an incident optical axis of the multi-reflection gas absorption tank;
The multi-reflection gas absorption tank is internally provided with a wedge-shaped silicon window lens, and laser incident into the multi-reflection gas absorption tank enters the multi-reflection gas absorption tank after penetrating through the wedge-shaped silicon window lens.
2. The greenhouse gas measurement system based on multi-channel infrared laser absorption spectroscopy of claim 1, wherein the first laser and the second laser are butterfly-packaged distributed feedback semiconductor lasers and the third laser is a HHL-packaged distributed feedback quantum cascade laser.
3. The greenhouse gas measurement system based on multi-path infrared laser absorption spectroscopy according to claim 1, wherein the first laser operates in an infrared band of 2003nm for CO 2 concentration detection of the gas sample to be measured; the second laser works in the 1653nm infrared band and is used for carrying out CH 4 concentration detection on the gas sample to be detected; the third laser works in 4474nm infrared band and is used for detecting the concentration of N 2 O in the gas sample to be detected; the He-Ne laser is used for outputting 633nm visible laser.
4. The greenhouse gas measurement system based on the multi-path infrared laser absorption spectrum according to claim 1, wherein the laser generating device comprises the first laser, the second laser, the third laser, and a first laser driver, a second laser driver and a third laser driver for driving the first laser, the second laser and the third laser to output laser respectively, and each laser driver receives the current signal and drives the laser working in the corresponding infrared band to output laser;
the model of the first laser driver and the second laser driver is LDTC0520; the model of the third laser driver is QCL500/PTC2.5K.
5. The greenhouse gas measurement system based on the multi-path infrared laser absorption spectrum according to claim 1, wherein the beam splitter is a long-wave-pass dichroic mirror, the reflectivity of the long-wave-pass dichroic mirror for 1653nm band infrared light is 98.91%, and the transmittance for 2003nm band infrared light is 97.06%; the dichroic beam splitter is a low-pass filter, the transmittance of the low-pass filter for visible light in the wave band of 400-700nm is 70%, and the reflectivity for infrared light in the wave band of 3-12 mu m is 95%;
The model numbers of the first collimator and the second collimator are CFC2-C;
The model of the light splitting sheet is DMLP and 1800;
The model of the dichromatic beam splitter is BSP-DI-25;
The model of the data acquisition card is NI USB6363.
6. The greenhouse gas measurement method based on the multipath infrared laser absorption spectrum is characterized by comprising the following steps of:
Step S1, driving a first laser, a second laser and a third laser to sequentially output laser light through the system according to any one of claims 1-5 and enabling the laser light to enter a multi-reflection gas absorption tank at an angle which coincides with an incident optical axis of the multi-reflection gas absorption tank, wherein a gas sample to be detected containing CO 2、CH4、N2 O is arranged in the multi-reflection gas absorption tank;
s2, collecting outgoing light beams reflected for many times by the multi-reflection gas absorption cell by the InGaAs detector or the InAsSb detector, converting the collected light signals into electric signals and outputting the electric signals to a data acquisition card;
and step S3, the data acquisition card correspondingly calculates the concentration of CO 2, the concentration of CH 4 or the concentration of N 2 O of the gas sample to be detected according to the received electric signals.
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