TDLAS (Tunable Diode Laser Absorption Spectroscopy)-based online monitoring system for greenhouse gas emission of gas turbine

Abstract

The invention discloses a TDLAS (tunable diode laser absorption spectroscopy)-based online monitoring system for greenhouse gas emission of a gas turbine, and relates to a gas turbine emission gas concentration monitoring technology. In the system, a laser generating device generates laser with at least two wavelengths, and the wavelengths correspond to characteristic absorption spectral lines of gas to be detected; the rectangular rack is arranged on an exhaust pipeline of the gas turbine, the mounting rail is arranged on the periphery of the rectangular rack, the laser collimator transmitting end, the laser collimator receiving end and the lens are arranged on the mounting rail, and the laser collimator transmitting end is connected with the output end of the laser generating device; the detector converts an optical signal output by the transmitting end of the laser collimator into an electric signal, the electric signal is transmitted to the data processing module after being acquired by the data acquisition card, and the data processing module gives the concentration of the gas to be detected. The invention provides a specific scheme for online monitoring of the greenhouse gas emission of the gas turbine based on TDLAS, and non-contact online measurement of the greenhouse gas emission of the gas turbine is realized.

Description

Technical Field

[0001] The present invention relates to the technology for monitoring the concentration of exhaust gas of gas turbines, and particularly to an online monitoring system for greenhouse gas emissions of gas turbines based on TDLAS. Background Art

[0002] As a core device in modern industrial and energy systems, the problem of greenhouse gas emissions from power plants has become an important issue in global climate governance. As a key component of power plants, gas turbines are widely used in the fields of electricity, aviation, ships, oil and gas exploration, etc. due to their high efficiency, high power density and flexible peak shaving ability. However, the combustion characteristics mainly using fossil fuels such as natural gas and diesel during their operation will lead to the emissions of a large amount of greenhouse gases and pollutants such as carbon dioxide and nitrogen oxides.

[0003] Tunable Diode Laser Absorption Spectroscopy (TDLAS) is a non-invasive gas detection technology based on the principle of laser absorption, which can accurately measure the concentration, temperature, pressure and velocity of gases. According to the Beer-Lambert theorem, it tunes the output wavelength of the diode laser to be consistent with the specific absorption line of the gas to be measured, so as to achieve highly sensitive and highly selective gas detection. This technology has the advantages of fast response, non-contact measurement, high precision and wide dynamic range in gas detection, and can be applied to various harsh environments. Summary of the Invention

[0004] The purpose of the present invention is to meet the development needs of the existing technology and provide an online monitoring system for greenhouse gas emissions of gas turbines based on TDLAS.

[0005] The online monitoring system for greenhouse gas emissions of gas turbines based on TDLAS of the present invention includes a laser generating device, a detector, a data acquisition card and a data processing module, and also includes a rectangular test device;

[0006] The laser generating device is used to generate lasers with at least two wavelengths, and the wavelengths correspond to the characteristic absorption lines of the gas to be measured;

[0007] The rectangular test device includes a rectangular bench, mounting rails, a transmitting end of a laser collimator, a receiving end of the laser collimator, and a lens. The rectangular bench is arranged on the exhaust duct of the gas turbine. The mounting rails are arranged around the rectangular bench. The transmitting end of the laser collimator, the receiving end of the laser collimator, and the lens are arranged on the mounting rails. The transmitting ends of the laser collimators and the receiving ends of the laser collimators correspond one by one. A lens is arranged in front of each transmitting end of the laser collimator and each receiving end of the laser collimator. The transmitting end of the laser collimator is connected to the output end of the laser generating device;

[0008] The detector is used to measure the output signal of the receiving end of the laser collimator. The signal output end of the detector is connected to the signal input end of the data acquisition card;

[0009] The data processing module is used to process the output signal of the data acquisition card and give the concentration of the gas to be measured.

[0010] Optionally, the exhaust duct is divided into two parts, and the rectangular bench is installed between the two parts.

[0011] Optionally, the transmitting ends of the laser collimators are evenly distributed on two adjacent mounting rails.

[0012] Optionally, stepped through-holes are evenly distributed on the mounting rails. One end of the stepped through-hole is used to install the transmitting end of the laser collimator / the receiving end of the laser collimator, and the other end is used to install the lens.

[0013] Optionally, the mounting rails are installed outside the rectangular bench, and an optical window is opened at a position on the rectangular bench corresponding to the lens.

[0014] Optionally, the laser generating device is connected to the transmitting end of the laser collimator through an optical fiber combiner and an optical fiber splitter.

[0015] Optionally, the laser generating device includes a signal generator, at least two laser controllers, and at least two semiconductor lasers. The laser controllers and the semiconductor lasers correspond one by one. The signal output end of the signal generator is connected to the control signal input end of the laser controller, and the drive signal output end of the laser controller is connected to the drive signal input end of the laser.

[0016] Optionally, the drive signal output by the laser controller is a sawtooth wave signal or a sine wave signal.

[0017] The on-line monitoring system for greenhouse gas emissions of gas turbines based on TDLAS of the present invention can achieve non-contact on-line measurement of greenhouse gas emissions of gas turbines. By passing multiple groups of lasers through the rectangular flow field of the gas to be measured, on-line and real-time detection and display of the content of greenhouse gases in the exhaust gas of gas turbines can be realized without disturbing the existing flow field of the gas turbines at all, so as to guide the further energy conservation and emission reduction optimization of gas turbines. Description of the Drawings

[0018] Figure 1 is a schematic diagram of the principle of an on-line monitoring system for greenhouse gas emissions of a gas turbine based on TDLAS according to an embodiment of the present application;

[0019] Figure 2 is a schematic structural diagram of a rectangular test device according to an embodiment of the present application. Only one mounting rail is shown in the figure, and the emitting end of the laser collimator in the figure can be replaced by the receiving end of the laser collimator;

[0020] Figure 3 is a schematic structural diagram of a rectangular bench according to an embodiment of the present application. Among them, (a) is an isometric view of the rectangular bench, (b) is the front view of the rectangular bench, (c) is the top view of (b), and (d) is the left view of (b);

[0021] Figure 4 is a schematic structural diagram of an on-line monitoring system for greenhouse gas emissions of a gas turbine based on TDLAS according to an embodiment of the present application. Detailed Embodiments

[0022] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0023] As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It should be further understood that the terms "comprises" and "comprising" specify the presence of the stated features, operations, elements, components, items, species, and / or groups, but do not preclude the presence, occurrence or addition of one or more other features, operations, elements, components, items, species, and / or groups. The terms "or" and "and / or" used herein are to be construed as inclusive, meaning either or any combination. Thus, "A, B or C" or "A, B and / or C" means "any of the following: A; B; C; A and B; A and C; B and C; A, B and C". An exception to this definition occurs only when the combination of elements, functions or operations are mutually exclusive in some way.

[0024] TDLAS technology has good application prospects in the field of on-line monitoring of greenhouse gas emissions from gas turbines. This application provides a specific solution for on-line monitoring of greenhouse gas emissions from gas turbines using TDLAS technology.

[0025] A beam of monochromatic light propagates in the gas to be measured. The gas to be measured will absorb a part of the laser radiation, resulting in the attenuation of the incident light intensity. The Beer-Lambert law describes the relationship between the incident spectral intensity and the transmitted spectral intensity. For a beam of monochromatic light with a frequency of ν, the spectral intensity of the incident light is I0. When passing through a region with a optical path length of L and a uniform distribution of the gas to be measured without scattering effect, the spectral intensity I of the transmitted light measured by the detector t and the spectral intensity I0 of the incident light conform to the following formula:

[0026] I t (ν) = I0(ν)exp[-α(ν)L] (1)

[0027] where α(ν), the absorption coefficient of the gas to be measured, can be expressed as:

[0028]

[0029] The above formula is the classical Lambert-Beer absorption theorem, which is the theoretical basis of the TDLAS test method. Where P is the pressure of the gas to be measured, in atm, X is the volume concentration of the molecules of the gas to be measured, is the line shape function of the gas absorption spectrum normalized by the integral area, in cm, S(T) is the absorption line intensity, which is a single-valued function of temperature T. The value of the absorption line intensity S(T0) at the reference temperature T0 is obtained through the HITRAN database, and then the line intensity S(T) at temperature T is calculated by formula (3).

[0030]

[0031] Among them, h is Planck's constant, c is the speed of light, k is Boltzmann's constant, and v0 is the transition frequency; E″ is the energy of the low transition state, and Q is the total internal molecular partition function, which is usually obtained by the method of polynomial fitting.

[0032] As a classic gas detection technology, the direct absorption method is widely used due to its convenient operation and good engineering applicability. This method is based on the tunable characteristics of semiconductor lasers. By applying a periodic modulation current (such as a sawtooth wave or a sine wave) to the semiconductor laser through a signal generator and a laser driver, the laser output wavelength is periodically scanned across the characteristic absorption lines of the target gas. When the tuned laser passes through the gas to be measured, the intensity of the laser with a specific wavelength will be attenuated due to the absorption of gas molecules. The photodetector converts the remaining light intensity carrying absorption information into an electrical signal. After being digitized by the data acquisition system, the absorption spectrum is quantitatively analyzed in combination with the Beer-Lambert law, and finally the gas concentration, temperature, and pressure are calculated.

[0033] By transforming formula (1), the expression of the integrated absorbance A, that is, the area covered by the absorption line, can be obtained:

[0034]

[0035] Among them, f(v - v0) is the line shape function of the absorption line From this, the greenhouse gas emission concentration χ is obtained:

[0036]

[0037] Figure 1 is a schematic diagram of the principle of the online monitoring system for greenhouse gas emissions of gas turbines based on TDLAS according to the embodiments of the present application. As Figure 1 shown, the online monitoring system for greenhouse gas emissions of gas turbines based on TDLAS according to the embodiments of the present application includes a laser generating device 1, a rectangular test device 2, a detector 3, a data acquisition card 4, and a data processing module 5. Among them, the rectangular test device 2 is arranged in the exhaust pipeline of the gas turbine and is located at the position where the cross-section of the exhaust pipeline is rectangular. The size of the rectangular test device 2 should match the size of the exhaust pipeline. The area enclosed by the rectangular test device 2 is the gas flow field to be measured. A laser emitting end and a laser receiving end are arranged on the rectangular test device 2. The laser generated by the laser generating device 1 enters the internal area of the rectangular test device 2 through the laser emitting end, passes through the gas flow field to be measured, and then enters the laser receiving end. After being emitted from the laser receiving end, it is detected by the detector 3. The detector 3 converts the received optical signal into an electrical signal and outputs it to the data acquisition card 4. The data acquisition card 4 outputs the collected data to the data processing module 5. The data processing module 5 calculates the concentration, temperature, and pressure of the gas to be measured according to the Beer-Lambert law.

[0038] The above laser generating device 1 generates lasers of at least two wavelengths. The laser wavelengths are determined by the gas to be measured. For each gas to be measured, two characteristic absorption lines of the gas under greenhouse conditions need to be determined. The laser generating device 1 outputs lasers of two wavelengths, and these two wavelengths respectively coincide with the two characteristic absorption lines of the gas under greenhouse conditions. Taking two gases, CO2 and NO2, as an example, the laser generating device 1 needs to output lasers of 4 wavelengths, where two wavelengths correspond to the two characteristic absorption lines of CO2, and the other two wavelengths correspond to the two characteristic absorption lines of NO2.

[0039] In one implementation, the laser generating device 1 includes a signal generator, at least two laser controllers, and at least two semiconductor lasers. The signal generator outputs a sawtooth wave or sine wave electrical signal to the laser controllers. Under the action of the sawtooth wave or sine wave electrical signal, the laser controllers output electrical signals of the same waveform, and this electrical signal will be used as the drive signal for the semiconductor lasers. The number of laser controllers 1 and semiconductor lasers is determined by the gas to be measured. Each laser controller is used to control a semiconductor laser to output a laser of one wavelength.

[0040] Figure 2 is a schematic structural diagram of a rectangular test device according to an embodiment of the present application. As Figure 2 shown, the rectangular test device 2 includes a rectangular frame 21, a mounting rail 22, a laser collimator transmitting end 23, a laser collimator receiving end, and a lens 25. Among them, the rectangular frame 21 is arranged on the exhaust pipe of the gas turbine. Specifically, the exhaust pipe of the gas turbine can be divided into two sections, the rectangular frame 21 is arranged between the two exhaust pipe sections, and sealing treatment is performed at the connection of the rectangular frame 21 and the exhaust pipes on both sides. Threaded holes for fixing the frame are provided on the four sides of the rectangular frame 21, and the threaded holes for fixing the frame are used to fix the rectangular frame 21 to the exhaust pipe.

[0041] The rectangular frame 21 can adopt the structure shown in Figure 3 (a) to Figure 3 (d). Threaded holes 211 for fixing the frame are provided on the four sides of the rectangular frame 21, and the threaded holes 211 for fixing the frame are used to fix the rectangular frame 21 to the exhaust pipe, so as to Figure 3For example, each side of the rectangular frame 21 is provided with 5 frame fixing threaded holes 211, and the central axis of the frame fixing threaded holes 211 is parallel to the central axis of the exhaust pipe. Each side of the rectangular frame 21 is also provided with 5 stepped through holes and 6 mounting rail fixing threaded holes 213. The stepped through holes are used as the optical windows 212. The optical windows 212 and the frame fixing threaded holes 211 are arranged in an interspersed manner. The central axis of the optical windows 212 is perpendicular to the central axis of the frame fixing threaded holes 211. The diameter of the end of the optical window 212 facing the outside of the rectangular frame 21 is slightly larger, which is used to install the lens 25. The mounting rail fixing threaded holes 213 are used to fix the mounting rail 22, and the central axis of the mounting rail fixing threaded holes 213 is parallel to the central axis of the optical windows 212.

[0042] The laser collimator emitting end 23, the laser collimator receiving end, and the lens 25 are arranged on the mounting rail 22. The laser collimator emitting ends 23 and the laser collimator receiving ends correspond one by one. A lens 25 is arranged in front of each laser collimator emitting end 22 and each laser collimator receiving end. The laser collimator emitting end 23 is connected to the laser output end of the laser generating device 1. Usually, the laser collimator emitting end 23 and the laser collimator receiving end have the same size, but the diameter of the laser collimator emitting end 23 / laser collimator receiving end is different from the diameter of the lens 25. Mounting holes are provided on the mounting rail 22. One side of the mounting hole is used to mount the laser collimator emitting end 23 / laser collimator receiving end, and the other side is used to mount the lens 25. Along Figure 2 the direction indicated by the arrow in the figure, the mounting rail 22 is fixed on the rectangular frame 21. In the embodiment of the present application, the laser collimator emitting end 23, the laser collimator receiving end, and the lens 25 are mounted on the mounting rail 22 instead of directly on the rectangular frame 21. When the laser collimator and the lens 25 need to be maintained or repaired, only the mounting rail 22 needs to be disassembled, and there is no need to disassemble the rectangular frame 21 from the exhaust pipe.

[0043] The laser output by the laser generating device 1 can enter the laser collimator emitting end 23 through the beam combiner and the beam splitter. Taking two gases as an example, a total of four semiconductor lasers are required. The output wavelengths of two of the semiconductor lasers are respectively the two absorption peaks of the first gas. The lasers output by these two semiconductor lasers are combined through an optical fiber beam combiner and then enter an optical fiber beam splitter. After being split into several beams of laser by the optical fiber beam splitter, they enter a group of laser collimator emitting ends 23. The output wavelengths of the other two semiconductor lasers are respectively the two absorption peaks of the second gas. The lasers output by these two semiconductor lasers are combined through another optical fiber beam combiner and then enter another optical fiber beam splitter. After being split into several beams of laser by the optical fiber beam splitter, they enter another group of laser collimator emitting ends 23.

[0044] In the first implementation, the transmitting ends 23 of the laser collimators are divided into two groups. One group of the transmitting ends 23 of the laser collimators are fixedly arranged at equal intervals on an installation rail 22, and the other group of the transmitting ends 23 of the laser collimators are fixedly arranged at equal intervals on another installation rail 22. The two installation rails 22 are respectively arranged on two adjacent sides of the rectangular platform 21. For example, one group of the transmitting ends 23 of the laser collimators with an output wavelength at the CO2 absorption peak are fixedly arranged at equal intervals on an installation rail 22, and one group of the transmitting ends 23 of the laser collimators with an output wavelength at the NO2 absorption peak are fixedly arranged at equal intervals on another installation rail 22. The two installation rails 22 are arranged on two adjacent sides of the rectangular platform 21. The transmitting ends 23 of the laser collimators correspond one-to-one with the receiving ends of the laser collimators. Therefore, the receiving ends of the laser collimators are also divided into two groups and are fixed on the other two adjacent sides of the rectangular platform 21. Multiple laser propagation paths form a grid within the rectangular gas flow field to be measured.

[0045] In the second implementation, all the transmitting ends 23 of the laser collimators are fixedly arranged at equal intervals on an installation rail 22, and all the receiving ends of the laser collimators are fixedly arranged at equal intervals on another installation rail 22. The two installation rails 22 are respectively fixed on two opposite sides of the rectangular platform 21, and multiple laser propagation paths are parallel and evenly distributed throughout the entire rectangular gas flow field to be measured.

[0046] Figure 4 is a schematic structural diagram of an on-line monitoring system for greenhouse gas emissions from a gas turbine based on TDLAS according to an embodiment of the present application, as Figure 4As shown, the output wavelengths of the four semiconductor lasers 13 are 2001 nm, 2004 nm, 6154 nm, and 6157 nm respectively. Among them, 2001 nm and 2004 nm are the absorption peaks of CO2, and 6154 nm and 6157 nm are the absorption peaks of NO2. The lasers with wavelengths of 2001 nm and 2004 nm are emitted from the semiconductor lasers 13 and then coupled into an optical fiber combiner 6. After being combined by the optical fiber combiner 6, they enter an optical fiber splitter 7. The optical fiber splitter 7 has five output ports, and each of the five output ports is connected to a transmitting end 23 of a laser collimator. This group of transmitting ends 23 of the laser collimators is arranged on the upper side of the rectangular bench 21, and the corresponding receiving ends 24 of the laser collimators are arranged on the lower side of the rectangular bench 21. The lasers with wavelengths of 6154 nm and 6157 nm are emitted from the semiconductor lasers 13 and then coupled into another optical fiber combiner 6. After being combined by the optical fiber combiner 6, they enter another optical fiber splitter 7. The optical fiber splitter 7 also has five output ports, and each of the five output ports is connected to a transmitting end 23 of a laser collimator. This group of transmitting ends 23 of the laser collimators is arranged on the left side of the rectangular bench 21, and the corresponding receiving ends 24 of the laser collimators are arranged on the right side of the rectangular bench 21. The distance between adjacent transmitting ends 23 of the laser collimators is 5 cm, and the distance between adjacent receiving ends 24 of the laser collimators is 5 cm. The laser output from each receiving end 24 of the laser collimator is detected by a detector 3, and all the detectors 3 form a detector array.

[0047] In Figure 4In the structure shown, under the action of the signal generator 11, four independent laser controllers 12 respectively control four semiconductor lasers 13 to output lasers with different wavelengths. The generated laser beams are first combined in pairs, and then are respectively guided to the emission ends 23 of the laser collimators arranged on two side edges of the rectangular frame 21. The rectangular frame 21 is arranged in the vertical direction, and these laser beams are simultaneously emitted in an array form and horizontally pass through the entire exhaust plume region discharged by the gas turbine. When the laser passes through the exhaust plume region containing greenhouse gases, the photon energy of a specific wavelength will be absorbed by gas molecules, resulting in the attenuation of the intensity of the laser of that wavelength. The attenuation degree is proportional to the gas concentration and the optical path length. The receiving ends 24 of the laser collimators receive the laser beams whose intensities have been attenuated after passing through the exhaust plume in an array, and the detector 3 converts the received optical signal into an electrical signal. To ensure the accuracy and synchronization of the measurement, a timing synchronization generation module is used to control the sequential excitation of the two lasers after beam combination, coordinate the entire system, and send the electrical signals output by the detector array to the data acquisition card 4 for synchronous acquisition. The raw data collected by the data acquisition card 4 can be preprocessed in real time by a signal processing unit, and the preprocessing includes processes such as filtering and demodulation. The preprocessed data is sent to the data processing module 5, which can be implemented by software embedded in a computer. The data processing module 5 uses the built-in algorithm to analyze the absorption rates of lasers with different wavelengths, and inversely calculates the gas concentrations on each measurement path based on this. After data interpolation and smoothing, the concentrations of various gases at each position of the exhaust pipe cross-section are obtained, and the concentration data is fused to generate a greenhouse gas concentration distribution map of the exhaust pipe cross-section, realizing the precise quantification and visual monitoring of the emission concentration of the gas to be measured.

[0048] The embodiment of this application proposes a specific scheme for on-line monitoring of greenhouse gas emissions from gas turbines based on the TDLAS principle. This scheme constructs a rectangular test field through a rectangular test device. Compared with a circular frame or a special-shaped frame, the rectangular frame of the embodiment of this application has the following advantages:

[0049] 1. When facing lateral vibration, the circular frame is prone to torsional deformation, resulting in the optical path deviation of the internal optical elements. However, due to its right-angle symmetry and closed-frame design, the rectangular frame performs excellently in a dynamic load environment and has stronger anti-vibration performance;

[0050] 2. In terms of spatial layout and functional expandability, the arc edge of the circular frame requires a customized arc bracket installation component, and it is difficult to effectively utilize the central area when stacked vertically, resulting in space waste. However, the planar right-angle characteristic of the rectangular frame provides a natural advantage for modular design, not only simplifying the optical path calibration process but also facilitating the integration of various auxiliary devices;

[0051] 3. In terms of manufacturing, the circular bench needs to be formed through bending or casting processes, with a relatively high material loss rate during processing. In contrast, the processing flow of the rectangular bench is mature, and the material utilization rate is high, which can significantly reduce the manufacturing cost.

[0052] 4. Regarding maintenance, the arc-shaped panel of the circular bench is difficult to disassemble, and it is difficult to access the components in the central area during maintenance, which may double the downtime. On the other hand, the flat panel design of the rectangular bench supports quick disassembly, allowing technicians to easily access the internal components for mirror cleaning or optical element replacement.

[0053] In summary, due to its structural stability, space efficiency, maintenance convenience, and cost advantages, the rectangular bench 21 has become an ideal carrier for the precision measurement system. In harsh industrial environments such as gas turbine greenhouse gas monitoring, the rectangular bench 21 has significantly improved the reliability of system measurement, system life, and operation and maintenance efficiency, providing a solid hardware foundation for real-time online monitoring.

[0054] The on-line monitoring system for gas turbine greenhouse gas emissions based on TDLAS in the embodiments of this application realizes non-contact on-line measurement of gas turbine greenhouse gas emissions. By passing multiple laser beams through the rectangular flow field of the measured gas, on-line and real-time detection can be achieved without disturbing the existing flow field of the gas turbine at all, and the content of greenhouse gases in the gas turbine exhaust gas can be displayed, thereby guiding the gas turbine to further achieve energy conservation, emission reduction, and optimization.

[0055] The various technologies described here can be implemented in combination with hardware or software, or a combination of both. Thus, the methods and devices of the present invention, or certain aspects or parts of the methods and devices of the present invention, can take the form of program code (i.e., instructions) embedded in a tangible medium, such as a removable hard disk, USB flash drive, floppy disk, CD-ROM, or any other machine-readable storage medium. When the program is loaded into a machine such as a computer and executed by the machine, the machine becomes a device for practicing the present invention.

Claims

1. An online monitoring system for greenhouse gas emissions from gas turbines based on TDLAS, comprising a laser generating device, a detector, a data acquisition card, and a data processing module, characterized in that, It further includes a rectangular test device; The laser generating device is used to generate lasers of at least two wavelengths, and the wavelengths correspond to the characteristic absorption spectral lines of the gas to be measured; The rectangular test device includes a rectangular bench, mounting rails, a transmitting end of a laser collimator, a receiving end of the laser collimator, and a lens. The rectangular bench is arranged on the exhaust duct of the gas turbine, the mounting rails are arranged around the rectangular bench, the transmitting end of the laser collimator, the receiving end of the laser collimator, and the lens are arranged on the mounting rails. The transmitting ends of the laser collimators and the receiving ends of the laser collimators are in one-to-one correspondence, and a lens is arranged in front of each transmitting end of the laser collimator and each receiving end of the laser collimator. The transmitting end of the laser collimator is connected to the output end of the laser generating device; The detector is used to measure the output signal of the receiving end of the laser collimator, and the signal output end of the detector is connected to the signal input end of the data acquisition card; The data processing module is used to process the output signal of the data acquisition card and give the concentration of the gas to be measured.

2. The system according to claim 1, wherein The exhaust duct is divided into two parts, and the rectangular bench is installed between the two parts.

3. The system according to claim 1 or 2, characterized in that, The transmitting ends of the laser collimators are evenly distributed on two adjacent mounting rails.

4. The system according to claim 3, wherein Step-shaped through holes are evenly distributed on the mounting rails. One end of the step-shaped through hole is used to install the transmitting end of the laser collimator / the receiving end of the laser collimator, and the other end is used to install the lens.

5. The system according to claim 4, characterized in that, The mounting rails are installed outside the rectangular bench, and an optical window is opened at a position on the rectangular bench corresponding to the lens.

6. The system according to claim 1, wherein The laser generating device is connected to the transmitting end of the laser collimator through an optical fiber combiner and an optical fiber splitter.

7. The system according to claim 1, wherein The laser generating device includes a signal generator, at least two laser controllers, and at least two semiconductor lasers. The laser controllers and the semiconductor lasers are in one-to-one correspondence. The signal output end of the signal generator is connected to the control signal input end of the laser controller, and the drive signal output end of the laser controller is connected to the drive signal input end of the laser.

8. The system according to claim 7, wherein The drive signal output by the laser controller is a sawtooth wave signal or a sine wave signal.

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