Method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing

Abstract

The application discloses a kind of methane and propane component identification method based on laser absorption spectrum gas telemetry, comprising: S1 obtains the harmonic signal of the gas to be measured, and looks for wave trough in the range of harmonic signal 100~350;According to the width of wave trough, judge whether the gas to be measured is single propane;When judging that the gas to be measured is single propane, identification ends, enters S2 and gives propane concentration value;Otherwise, enter step S3;S3 considers that the gas is methane and propane mixed gas, judges the proportion of mixed gas. The peak valley difference of peak 1 and peak 2 is obtained, the concentration coefficient of peak 1 and peak 2 is obtained according to the peak valley difference and standard gas calibration curve, the ratio of the absolute value of concentration value obtained according to peak 1 and peak 2 is obtained, and the ratio of methane and propane is obtained, enters S4;S4 gives methane concentration value and propane concentration value according to the ratio of methane and propane respectively.The application can realize component identification and accurate concentration detection, and has important guiding significance in the field of alkane gas telemetry technology.

Description

Technical Field

[0001] This invention belongs to the field of laser gas telemetry technology, and specifically relates to a method for identifying methane and propane components based on laser absorption spectroscopy gas telemetry. Background Technology

[0002] In petrochemical plants and other applications primarily involving polyalkane and polyolefin gases, there has long been a lack of corresponding laser gas remote sensing methods, hindering rapid non-contact measurement. Based on a mid-infrared interband cascaded (ICL) semiconductor laser, and employing the principle of tunable semiconductor laser absorption spectroscopy (WMS), this technology targets the characteristic absorption peaks of the gas being measured in the mid-infrared band, enabling precise non-contact detection of the gas concentration. To meet the leakage early warning needs of petrochemical storage tank areas, a tunable laser absorption spectroscopy (TDLAS) solution based on a cassette telescope head is adopted to achieve remote sensing of propane or n-butane leaks in petrochemical storage tanks.

[0003] Studies have shown that P. Kluczynski used a 3370nm ICL laser to detect propane. Angelo Sampaolo et al. used a 3342-3349nm ICL laser combined with photoacoustic spectroscopy to simultaneously measure methane, ethane, and propane. Wang Yin et al. used a 1678.7-1686.1nm near-infrared laser to simultaneously measure propane and butane, and used partial least squares to identify and invert the concentrations of the two components. Analysis revealed that these wavelengths are not suitable for laser gas remote sensing, but only for online detection, because the absorption peaks of water vapor and carbon dioxide in the atmosphere severely interfere with the absorption peaks of the target gases in these wavelengths. Jiang Meng et al., utilizing the 20-fold difference in linearity between propane / butane and methane / ethane at 3464nm and different modulation parameters, proposed a method of alternating scanning with two sets of different modulation depth parameters, which can achieve simultaneous remote sensing measurement of single components of four gases: methane, ethane, propane, and n-butane. However, research published on spectral databases revealed that the broad absorption peak of propane is actually formed by the overlapping of 21 narrow spectral lines. Therefore, the difference in modulation parameters between methane and propane is not as large as expected, differing by only 1.4 times. Methods based on different modulation depths cannot accurately distinguish between propane and methane. The biggest problem in the demonstration application of propane remote sensing in petrochemical storage tank areas is the presence of methane in the background air. The methane concentration value obtained by the remote sensing sensor is the integral along the beam path, thus the concentration value is related to the remote sensing distance. As the remote sensing distance increases, the methane concentration value also changes continuously, resulting in severe cross-interference between propane and methane spectral lines. How to identify propane from the abundant methane background in the air, i.e., remote sensing of a mixture of methane and propane, is a problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned shortcomings and provide a method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing. This method solves the technical problem of difficulty in remote sensing methane and propane mixtures due to overlapping spectral lines. This invention enables component identification and accurate concentration detection, and has significant guiding significance in the field of alkane gas remote sensing technology.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention relates to a remote sensing technology for polyalkane gases based on tunable semiconductor laser absorption spectroscopy, specifically a method for identifying and simultaneously measuring components in a mixed gas. The invention targets long-distance remote sensing of a petrochemical storage tank (propane), where methane gas is present in the background air, and the methane and propane spectral lines exhibit cross-interference, despite significant differences in linewidth. Analysis of the database reveals that propane has a full width at half maximum (FWHM) of 2.87 nm at its 3468 nm absorption peak, while methane has an FWHM of 0.15 nm at the same wavelength, a difference of 22 times. However, simulation analysis shows that the propane spectral line is composed of 21 overlapping lines, with an actual width of 0.21 nm, a difference of 1.4 times compared to the methane spectral line width. Furthermore, the second harmonics of both gases are also composed of overlapping second harmonics of multiple spectral lines. Therefore, the actual difference in linewidth between the two gases is relatively small, and the previously assumed large difference in modulation depth does not exist. Based on the above analysis, a method is proposed to identify methane and propane mixtures. For the second harmonic signals of methane, propane, and methane-propane mixtures, characteristic absorption peaks and characteristic factors are identified. Based on the peak-to-valley difference of the absorption peaks and their respective partition functions, the concentrations of the two gases in the mixture can be calculated. The method was validated by obtaining measured harmonic data of the mixed gas through a system.

[0007] Specifically, the present invention provides a method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing, which can realize remote sensing of propane, methane, and methane-propane mixtures. The propane absorption peak at 3468 nm is selected, but this peak intersects with the methane gas spectral lines in the background air.

[0008] According to spectral data from the PNNL database, propane and methane exhibit significant differences in absorption peak line shapes, particularly in linewidth, which differs by an order of magnitude. This makes it impossible to unify modulation parameters, necessitating alternating scans with the two sets of parameters. This invention aims to achieve simultaneous measurement of multiple gas components using only one set of parameters. Through comparison of spectral lines from the PNNL and HITRAN databases, simulation analysis revealed that the ultra-wide spectrum of propane is composed of 21 overlapping adjacent lines, and its second harmonic is also a superposition of multiple second harmonics. The actual linewidth difference between propane and methane is 1.4 times. Therefore, the same set of modulation parameters can achieve simultaneous measurement of both methane and propane. Thus, the modulation parameters for propane only need to be set according to the linewidth of the propane cross-spectral lines.

[0009] Similarly, by comparing the PNNL and HITRAN databases, methane spectral lines all intersect with propane, making component identification and concentration measurement impossible under normal circumstances. This invention identifies a methane harmonic signal that significantly differs from the overlapping propane harmonic signals, allowing for the extraction of identification feature factors. First, the valley width is used to determine whether it is methane, propane, or a methane-propane mixture. If the valley width is 150 ≤ W ≤ 200, it is propane alone; otherwise, it is a mixture of propane and methane-propane. The ratio of the absolute values ​​of peak 1 and peak 2 is determined, as it is related to the ratio of methane to propane in the mixture. The contribution functions of methane and propane to the peak-valley difference of harmonic peaks 1 and 2 differ between the two gases, and these contribution functions are calculated through concentration calibration. In actual measurements, the results are verified for the methane-propane mixture, with real-time calculation of the concentrations of methane and propane.

[0010] The specific technical solution of this invention is as follows:

[0011] A method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing includes:

[0012] S1 acquires the second harmonic signal of the gas to be tested and finds the harmonic valleys within the range of 100~300 of the second harmonic signal; the width W between the two harmonic valleys determines whether the gas to be tested is monopropane.

[0013] When 150≤W≤200, the gas to be tested is determined to be propane, and it enters S2;

[0014] When 78≤W≤90, the gas to be tested is determined to be a mixture of methane and propane, and proceed to step S3;

[0015] S2 obtains the concentration inversion coefficient K0 based on the second harmonic signal of propane standard gas, and obtains the real-time single propane concentration value based on the concentration inversion coefficient K0.

[0016] S3 acquires the peak-valley difference between peak 1 and peak 2 within the range of 100~300 for the second harmonic signal of the gas under test;

[0017] The ratio R of propane and methane in the methane and propane mixture can be obtained from the peak-valley difference between peak 1 and peak 2.

[0018] S4 obtains the concentration values ​​of methane and propane based on the ratio R of propane and methane in the methane and propane mixture.

[0019] Furthermore, in step S2, the method for obtaining the concentration inversion linear function K0 based on the second harmonic signal of propane standard gas includes:

[0020] Under fixed optical path and ambient temperature conditions, propane standard gas of different concentrations was filled into the calibration test gas chamber, and the second harmonic signal of the propane standard gas was obtained. The concentration inversion function K was obtained by linearly fitting the harmonic peak-valley difference of the second harmonic signal of the propane standard gas from 100 to 300. 0= a0x+b0, where x is the peak-to-valley difference obtained in real time, and a0 and b0 are the coefficients of the first-order and zero-order terms in the linear fitting curve of propane.

[0021] Furthermore, the specific method of step S3 includes:

[0022] The peak-to-valley difference of peak 1 in the range of 175~300 increases with increasing methane concentration, while the peak-to-valley difference of peak 2 in the range of 100~225 decreases with increasing propane concentration.

[0023] Based on the peak-valley difference of peak 1 and peak-valley difference of peak 2 in the second harmonic signal of the mixed standard gas, the inversion function of peak 1 is obtained as K1=a1x+b1, and the inversion function of peak 2 is obtained as K2=-a2x+b2. Based on the inversion functions of peak 1 and peak 2, the ratio of the methane and propane mixture to be tested is determined as R=abs(K2) / K1; where x is the peak-valley difference obtained in real time, a1 and b1 are the coefficients of the first and zeroth degree terms in the linear fitting curve of peak 1, and a2 and b2 are the coefficients of the first and zeroth degree terms in the linear fitting curve of peak 2.

[0024] Furthermore, in step S3, peak 1 is located at the x-coordinate of 175~300; peak 2 is located at the x-coordinate of 100~225.

[0025] Furthermore, methods for determining whether the gas to be tested is a mixture of methane and propane based on the ratio R of the two peak ordinates include:

[0026] When R is much greater than 1, it is determined that the proportion of propane in the methane and propane mixture is much greater than that of methane.

[0027] When R is much less than 1, it is determined that the proportion of methane in the methane and propane mixture is much greater than that of propane, or that it is pure methane.

[0028] When R is approximately equal to 1, it is determined that the ratio of methane to propane in the methane-propane mixture is close to 1, indicating that the ratio of methane to ethane is close.

[0029] Furthermore, in step S4, the concentration value of methane is the inversion coefficient K1 of peak 1;

[0030] The concentration of propane is K1×R.

[0031] Furthermore, a mid-infrared semiconductor ICL laser is used to simultaneously detect the gas to be tested. The laser emits a laser beam with a center wavelength of 3468nm, and the wavelength scanning range is from 3466 to 3470nm with a width of 4nm, covering the absorption peaks of methane and propane in this band, thereby obtaining the harmonic signal of the gas to be tested.

[0032] Furthermore, in step S1, the harmonic signal obtained by the digital lock-in amplifier is filtered and downsampled to output a fixed 1000 points per frame, with the real part of the second harmonic being 2. f X represents the first 500 points, and the imaginary part of the second harmonic is 2. f Y represents the last 500 points; through 2 f X and 2 f Y gets 2 f R signal ( Adjusting the X / Y phase difference in the digital phase-locked loop makes 2 f X is at its maximum, at which point 2 f X represents the second harmonic signal, and the horizontal axis of the second harmonic signal represents the number of harmonic points, which is related to the wavenumber ν (cm) scanned by the laser. -1 One-to-one correspondence.

[0033] Furthermore, the above method is applied to the remote sensing of petrochemical storage tanks to identify the components of methane and propane.

[0034] In summary, this invention provides a method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing, comprising: S1 acquiring the harmonic signal of the gas to be measured, wherein the real part of the second harmonic is 2 f X represents the first 500 points, and the imaginary part of the second harmonic is 2. f Y represents the last 500 points. (Through 2...) f X and 2 f Y gets 2 f R signal, adjust the X / Y phase difference to make 2 f X is at its maximum, at which point 2 fX represents S1. The process involves searching for troughs within the harmonic signal range of 100-350 Hz; determining whether the gas being tested is propane based on the trough width; if propane is identified, the identification process ends, and the process proceeds to S2 to provide the propane concentration value; otherwise, it proceeds to step S3; S3 assumes the gas is a mixture of methane and propane and determines the mixture ratio. The peak-trough difference between peak 1 (horizontal axis 175-300) and peak 2 (horizontal axis 100-225) is obtained. Based on the peak-trough difference and the standard gas calibration curve, the concentration coefficients for peak 1 and peak 2 are obtained respectively. The ratio of the absolute concentration values ​​of peak 1 and peak 2 is used to obtain the methane-propane ratio, and the process proceeds to S4; S4 provides the methane and propane concentration values ​​based on the methane-propane ratio, while S2 provides the propane concentration value. This invention enables component identification and accurate concentration detection, and has significant guiding significance in the field of alkane gas remote sensing technology.

[0035] Compared with the prior art, the present invention has at least one of the following advantages:

[0036] (1) This invention provides a method for identifying methane and propane components based on laser absorption spectroscopy gas telemetry, which can achieve high-sensitivity methane and propane telemetry, and can achieve component identification and accurate concentration detection. It is applicable to gas telemetry scenarios such as leaks in chemical plant areas and storage tank areas.

[0037] (2) In response to the problem of a 20-fold difference in the spectral line width between propane and methane, the present invention confirmed through simulation that the 2.87 nm width absorption peak of propane at 3464 nm is composed of 21 overlapping absorption peaks. Therefore, the second harmonic of propane in this band is also a superposition of 21 second harmonics, and the actual spectral line width difference is 1.5 times.

[0038] (3) In view of the serious problem of the crossover of propane and methane spectral lines, this invention cleverly utilizes the superposition of three characteristic absorption peaks of propane at 3468nm. By using the valley width, the ratio of peak 1 to peak 2 and the peak-valley difference, a highly reliable and accurate method for component identification and concentration calibration is formed. Attached Figure Description

[0039] Figure 1 To compare the propane absorption spectrum obtained by simulation in this invention with the spectral parameters of the PNNL and HITRAN databases;

[0040] Figure 2 To compare the propane absorption spectrum obtained from the simulation of this invention with the spectral parameters in the PNNL database;

[0041] Figure 3 According to the present invention Figure 1 and Figure 2 The spectral data simulation includes methane harmonic signals, propane harmonic signals, and harmonic signals of a mixture of methane and propane.

[0042] Figure 4 The harmonic signals of methane, propane, and a mixture of methane and propane obtained by actual measurement in this invention are shown. Detailed Implementation

[0043] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0044] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0045] Considering the atmospheric transmission window between 3460 nm and 4165 nm, 3464 nm was selected as the characteristic wavelength for remote sensing of light hydrocarbon gases. Propane exhibits a broad absorption peak in this band, with a center wavelength of 3463.8 nm and a full width at half maximum (FWHM) of 2.87 nm. Methane exhibits seven characteristic absorption peaks in this band. The laser's driving current was adjusted to cover the scanning wavelength range of 3461.5 nm to 3467.5 nm, i.e., wavenumbers 2883.9 to 2888.9 cm⁻¹. -1 This invention allows for the simultaneous scanning of the absorption peaks of methane and propane in this wavelength range, obtaining harmonic signals for concentration determination. If the absorption peaks of the two gases are adjacent, they can be detected individually or used to identify a mixture. If the absorption peaks of the two gases overlap, they can be detected individually, but it is difficult to identify and measure a mixture. This invention addresses the problem of overlapping methane and propane spectral lines.

[0046] Furthermore, the principle of Tunable Laser Absorption Spectroscopy (TDLAS) based on wavelength modulation (WMS) technology posits that the modulation coefficient is calculated based on the spectral linewidth, and the modulation depth *m* is the amplitude of the sinusoidal signal applied to the laser based on the absorption wavelength of the gas being measured and the laser's current wavelength coefficient. The maximum harmonic signal is obtained when the ratio of v to the half-width at half-maximum (WHM) γ is 2.2. Wavelength modulation technique (WMS) requires the superposition of a sawtooth signal and a sinusoidal signal to modulate the laser signal. The amplitude of the sinusoidal signal is the modulation depth m, which is related to the line shape of the gas being measured. The WHM of methane absorption peak is 0.15 nm, while that of propane absorption peak is 2.87 nm, a difference of 22 times. However, the actual propane absorption peak at 3464 nm is the superposition of at least 21 adjacent absorption peaks. Based on fitting, the WHM of a single absorption peak can be inferred to be approximately 0.21 nm, which is approximately 1.4 times different from the actual WHM of methane absorption peak. Using a parameter with a low modulation depth m can accurately obtain the methane concentration value, but using a parameter with a high modulation depth m yields the concentration value of the superimposed methane and propane. These two waveforms are not a simple superposition relationship, and there is a lack of a method to accurately subtract the methane concentration from the waveforms of the mixed propane and methane.

[0047] This invention focuses on solving the problem of methane and propane component identification and concentration calibration in polyalkane remote sensing. Simulation analysis reveals that methane has seven absorption peaks in this band, formed by the overlap of 11 spectral lines, thus yielding seven independent harmonic signals. Propane has at least 21 intersecting absorption peaks in this band, resulting in a waveform of 21 superimposed independent harmonic signals. Therefore, if a methane and propane mixture is present, the obtained signal is a further superposition of the propane waveform and methane harmonic signals. Furthermore, the final waveform exhibits no discernible pattern depending on the depth of calibration and the concentration ratio.

[0048] For the harmonic signal of a methane and propane mixture, the trough width and trough abscissa were selected as characteristic factors, and the minimum value (trough) was found in the range of 0 to 500. Standard gases, including single methane, single propane, and mixtures of methane and propane in different proportions, were filled into a transparent gas chamber. The trough width and peak-to-trough difference are shown in Table 1.

[0049] Table 1 Test data for methane, propane, and methane-propane mixtures (valley width and peak-valley difference).

[0050]

[0051] As shown in Table 1, each harmonic signal is obtained, the valley is found within the set range, and the peaks are calculated. The peak-valley difference between peak 1 and peak 2 is used for concentration calculation.

[0052] When the trough width is 150≤W≤200 in the range of 100~300, the component is determined to be a single propane gas. The propane concentration is then derived according to the propane inversion coefficient K0, and the methane concentration value is displayed as 0.

[0053] When the valley width is within the range of 100~300 and 78≤W≤90, it conforms to either a single methane gas or a methane-propane mixture. The peak-valley difference for peak 1 and peak valley difference for peak 2 are calculated separately. Since the methane concentration at peak 1 is proportional to the peak-valley difference, the peak-valley difference increases with increasing methane concentration, as shown in Table 1. The single methane concentration obtained from K1 inversion matches the actual value. However, when there are different proportions of methane and propane mixtures, the methane concentration obtained from K1 inversion differs from the actual standard gas value. Other parameters need to be introduced for correction.

[0054] The peak-to-valley difference of peak 2 gradually decreases with increasing propane concentration. Therefore, the propane value calibrated according to K2 is inversely proportional to the peak-to-valley difference. The K2 coefficient is fitted based on the test values ​​to obtain the K2 inversion value. As shown in the table, if the ratio R is much greater than 1, it indicates high-concentration propane; if R is close to 1, the methane to propane ratio is close to 1:1; if R is less than 1, it indicates high-concentration methane or methane alone. The propane value in the mixed gas calculated based on the ratio coefficient matches the concentration values ​​of the methane and propane mixture in the standard gas charged into the gas chamber.

[0055] In summary, this invention addresses the issue of a 20-fold difference in the spectral linewidths of propane and methane. Simulations confirm that the 2.87 nm width absorption peak of propane at 3464 nm is composed of at least 21 overlapping absorption peaks. Therefore, the second harmonic of propane in this band is also a superposition of 21 second harmonics, resulting in an actual spectral linewidth difference of 1.5 times. This invention provides a method for component identification and concentration calibration applied to the simultaneous measurement of methane and propane. Addressing the severe crossover of propane and methane spectral lines, it cleverly utilizes the superposition of three characteristic absorption peaks of propane at 3468 nm. First, the valley width is used as a characteristic factor to identify whether it is propane alone, methane alone, or a methane-propane mixture. If it is propane alone, the propane concentration is inverted based on K0. Under propane and methane mixture conditions, the peak-valley difference of the propane harmonic curve decreases with increasing concentration against a methane background, exhibiting a completely opposite characteristic to peak 1 of the methane harmonic curve, thus obtaining the concentration ratio coefficient of methane and propane. Determine the proportion of propane based on the proportion coefficient and calculate the concentrations of methane and propane in the mixture.

[0056] In summary, this invention relates to laser gas telemetry technology, particularly for early warning of leaks in petrochemical storage tanks, and is applicable to gas telemetry scenarios such as leaks in chemical plant areas and storage tank areas. Addressing the issue of methane gas present in the atmospheric background and the interference between methane absorption peaks and propane in laser gas telemetry systems, this invention uses simulation of the absorption spectra and harmonic curves of propane and methane to identify adjacent spectral lines capable of component identification and determine the corresponding modulation parameters. This achieves highly sensitive remote sensing of methane and propane, enabling component identification and accurate concentration detection.

[0057] Example:

[0058] Example 1

[0059] This invention employs a mid-infrared semiconductor ICL laser to simultaneously detect multiple components of light hydrocarbon gas. The laser driving unit in the device controls the laser to emit a laser beam with a center wavelength of 3468nm, and the wavelength scanning range is from 3466 to 3470nm with a width of 4nm, covering the absorption peaks of methane and propane in this band. Figure 1 In the diagram, the solid red and black lines represent the overall spectral lines fitted from the PNNL and HITRAN databases, while the dashed lines represent the individual spectral lines fitted from single methane spectral data provided by HITRAN, as well as the superposition results of multiple spectral lines. The horizontal axis represents the wavenumber (cm²). -1 The vertical axis represents absorbance (ppm). -1 •m -1 ); Figure 2 Since HITRAN does not provide parameters for a single propane spectral line, the propane data presented in this invention consists of multiple spectral lines simulated and fitted by the author, and their superposition. The simulation is based on inferences from spectral data obtained from actual test results of propane standard gas. The characteristic absorption peak curves of methane and propane gases in this band are obtained by fitting data from the PNNL and HITRAN databases, as shown below. Figure 1 and Figure 2 The solid line represents the solid line, and the dashed line represents the self-fitted spectral line. The laser beam, after collimation, is emitted in open space with a divergence angle controlled at 1.3 mrad and a reception angle of 2 mrad. The laser beam illuminates the wall near the storage tank, which is covered with aluminum foil to increase reflectivity. The diffusely reflected beam is received by a lens. To improve the telemetry distance, the lens size is 25 cm, achieving a telemetry distance of 100.2 m (aluminum foil). The response time for telemetry of harmonic signals for methane, propane, and a methane-propane mixture is 1.49 s. According to... Figure 3 The extracted feature factors and strategies are used to determine the components, where ΣC1 represents methane (CH4) and ΣC3 represents propane (C3H8). Figure 1 and Figure 2 Multiple second-harmonic curves calculated by fitting multiple spectral line data are superimposed. The actual measured harmonic curves are as follows: Figure 4 As shown Figure 3 The simulated curves match perfectly, where Figure 4 The medium concentration value uses the unit ppm×m, which has the same meaning as ppm•m mentioned earlier; both involve multiplication.

[0060] Example 2

[0061] This embodiment employs the aforementioned method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing to verify single components of methane and propane, as well as mixtures of different proportions. The specific steps are as follows:

[0062] S1 acquires the harmonic signals of the gas to be tested. Methane standard gases of 62.5 ppm•m and 625 ppm•m, propane standard gases of 125 ppm•m and 625 ppm•m, and mixtures of 62.5 ppm•m methane + 625 ppm•m propane, 625 ppm•m methane + 625 ppm•m propane, and 625 ppm•m methane + 125 ppm•m propane are introduced into the gas chamber, respectively, yielding different harmonic signals. Valleys are searched within the harmonic signal range of 0~300. If the valley width is >150, it is identified as propane, and the propane concentration value is obtained through K0 inversion. If the valley width is in the range of 78 and 90, the gas to be tested is identified as either methane alone or a mixture of methane and propane.

[0063] S2 acquires the ratio of the ordinates of peak 1 and peak 2 within the range of 0~300 for the harmonic signal of the gas to be measured; the ordinates of peak 1 and peak 2, the scaling factor, and the inverted mixed gas concentration values ​​are shown in Table 1, which are consistent with the pre-charged mixed gas component concentration values ​​within the allowable error range.

[0064] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0065] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing, characterized in that, include: S1 acquires the second harmonic signal of the gas to be tested and searches for harmonic valleys within the range of 100~300 of the second harmonic signal. The width W between the two harmonic valleys determines whether the gas to be tested is monopropane; When 150≤W≤200, the gas to be tested is determined to be propane, and it enters S2; When 78≤W≤90, the gas to be tested is determined to be a mixture of methane and propane, and proceed to step S3; S2 obtains the concentration inversion coefficient K0 based on the second harmonic signal of propane standard gas, and obtains the real-time single propane concentration value based on the concentration inversion coefficient K0. S3 acquires the peak-valley difference between peak 1 and peak 2 within the range of 100~300 for the second harmonic signal of the gas under test; The ratio R of propane and methane in the methane and propane mixture can be obtained from the peak-valley difference between peak 1 and peak 2. S4 obtains the concentration values ​​of methane and propane based on the ratio R of propane and methane in the methane and propane mixture; The specific methods for step S3 include: The peak-to-valley difference of peak 1 in the range of 175~300 increases with increasing methane concentration, while the peak-to-valley difference of peak 2 in the range of 100~225 decreases with increasing propane concentration. Based on the peak-valley difference of peak 1 and peak-valley difference of peak 2 in the second harmonic signal of the mixed standard gas, the inversion function of peak 1 is obtained as K1=a1x+b1, and the inversion function of peak 2 is obtained as K2=-a2x+b2. Based on the inversion functions of peak 1 and peak 2, the ratio of the methane and propane mixture to be tested is determined as R=abs(K2) / K1; where x is the peak-valley difference obtained in real time, a1 and b1 are the coefficients of the first and zeroth degree terms in the linear fitting curve of peak 1, and a2 and b2 are the coefficients of the first and zeroth degree terms in the linear fitting curve of peak 2. In step S3, peak 1 is located at 175~300 on the horizontal axis; peak 2 is located at 100~225 on the horizontal axis; in step S4, the concentration value of methane is the inversion coefficient K1 of peak 1. The concentration of propane is K1×R; Simultaneous measurement of methane and propane is achieved using the same set of modulation parameters, which are set for the linewidth of the cross-spectral lines of propane. The gas to be tested is detected simultaneously using a mid-infrared semiconductor ICL laser. The laser emits a laser beam with a center wavelength of 3468nm, and the wavelength scanning range is from 3466 to 3470nm with a width of 4nm. This band covers the absorption peaks of methane and propane, and the harmonic signal of the gas to be tested is obtained.

2. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing according to claim 1, characterized in that, In step S2, the method for obtaining the concentration inversion linear function K0 based on the second harmonic signal of propane standard gas includes: Under fixed optical path and ambient temperature conditions, propane standard gas of different concentrations was filled into the calibration test gas chamber, and the second harmonic signal of the propane standard gas was obtained. The concentration inversion function K0=a0x+b0 was obtained by fitting the linear function of the harmonic peak-valley difference in the second harmonic signal of propane standard gas from 100 to 300. Here, x is the peak-valley difference obtained in real time, and a0 and b0 are the coefficients of the first and zeroth terms in the linear fitting curve of single propane.

3. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing according to claim 1, characterized in that, In step S1, the harmonic signal obtained by the digital lock-in amplifier is filtered and downsampled to output a fixed 1000 points per frame, with the real part of the second harmonic being 2. f X represents the first 500 points, and the imaginary part of the second harmonic is 2. f Y represents the last 500 points; through 2 f X and 2 f Y gets 2 f R signal Adjusting the X / Y phase difference in the digital phase-locked loop makes 2 f X is at its maximum, at which point 2 f X represents the second harmonic signal, and the horizontal axis of the second harmonic signal represents the number of harmonic points, which is related to the wavenumber νcm scanned by the laser. -1 One-to-one correspondence.

4. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing as described in claim 1, characterized in that, It is used for component identification of methane and propane in remote sensing of petrochemical storage tanks.

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