Methane and propane component identification method based on laser absorption spectrum gas remote measurement

Abstract

The invention discloses a methane and propane component identification method based on laser absorption spectrum gas remote measurement, which comprises the following steps: S1, obtaining harmonic signals of gas to be detected, and searching a wave trough in the range of 100-350 harmonic signals; judging whether the gas to be detected is monopropane or not according to the trough width; when the to-be-detected gas is judged to be monopropane, identification is finished, and S2 is carried out to give a propane concentration value; otherwise, entering the step S3; and S3, determining that the gas is a gas mixture of methane and propane, and judging the ratio of the gas mixture. S4, acquiring a peak-valley difference value of the peak 1 and the peak 2, respectively acquiring a peak 1 concentration coefficient and a peak 2 concentration coefficient according to the peak-valley difference value and the standard gas calibration curve, acquiring the proportion of methane to propane according to the ratio of absolute values of the concentration values acquired by the peak 1 and the peak 2, and entering S4; and S4, respectively giving a methane concentration value and a propane concentration value according to the ratio of methane to propane. The method can realize component identification and accurate concentration detection, and has important guiding significance in the technical field of alkane gas remote measurement.

Description

Technical Field

[0001] The invention belongs to the technical field of laser gas remote sensing, and in particular relates to a methane and propane component identification method based on laser absorption spectrum gas remote sensing. Background Art

[0002] Application scenarios such as petrochemical plants that are dominated by polyalkanes and polyolefins have long lacked corresponding laser gas telemetry methods, making it impossible to achieve fast non-contact measurement. Based on the mid-infrared semiconductor interband cascade (ICL) laser, the tunable semiconductor laser absorption spectroscopy technology principle (WMS) is adopted. The gas to be measured has characteristic absorption peaks in the mid-infrared band, and non-contact and accurate detection of the concentration of the gas to be measured is achieved. In order to meet the needs of leak warning in petrochemical storage tank areas, the technical solution of tunable laser absorption spectroscopy (TDLAS) based on a cassette telephoto lens is adopted to achieve remote detection of leaks of alkane gases such as propane or n-butane in petrochemical storage tanks.

[0003] According to research, 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 three gases: 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 the partial least squares method to identify and invert the concentration of the two components. After analysis, it was found that the above bands are not suitable for laser gas telemetry, but only for online detection, because the absorption peaks of water vapor and carbon dioxide in the atmosphere seriously interfere with the absorption peaks of the gases to be measured in the above bands. Jiang Meng et al. used the 20-fold difference in the line shape of propane / butane and methane / ethane at 3464nm and different modulation parameters to propose a method of alternating scanning of two sets of different modulation depth parameters, which can realize the simultaneous remote sensing measurement of four single-component gases: methane, ethane, propane and n-butane. However, through the study of the spectral database, it was found that the broad absorption peak of propane is actually composed of 21 narrow spectral lines overlapping each other. Therefore, the difference in the modulation parameters of methane and propane is not as large as expected, but 1.4 times. Different methods based on modulation depth cannot accurately identify propane and methane. The biggest problem in the demonstration application of propane telemetry in petrochemical storage tank areas is that there is methane in the air background. The methane concentration value obtained by the telemetry sensor is the integral along the beam path. Therefore, the concentration value is related to the telemetry distance. As the telemetry distance increases, the methane concentration value also changes continuously. There is serious cross-interference between the propane spectral lines and the methane spectral lines. How to identify propane from the methane background that exists in large quantities in the air, that is, the telemetry of methane and propane mixtures, is an urgent problem that needs to be solved. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects and provide a method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing, which solves the technical problem that the overlap of methane and propane spectral lines makes it difficult to achieve remote sensing of methane and propane mixed gases. The present invention can achieve component identification and accurate concentration detection, and has important guiding significance in the field of alkane gas remote sensing technology.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention is a multi-alkane gas telemetry technology based on tunable semiconductor laser absorption spectroscopy technology, specifically a method for mixed gas component identification and simultaneous measurement. Long-distance telemetry is performed for petrochemical storage tanks (propane), but methane gas exists in the air background, and there is cross interference between methane and propane spectral lines, but the spectral line widths differ greatly. Through the analysis of the database spectral lines, it is found that the half-height full width of the propane absorption peak at 3468nm is 2.87nm, and the half-height full width of the methane absorption peak in this band is 0.15nm, which differs by 22 times. However, through simulation analysis, it is found that the propane spectral line is composed of 21 overlapping spectral lines, and the actual width is 0.21nm, which is 1.4 times the width of the methane spectral line. The line type of the second harmonic of the above two gases is also the overlap of multiple spectral line second harmonics. The actual difference in the spectral line width of the two gases is small, and there is no huge gap in modulation depth as traditionally believed. Based on the above analysis, a method is proposed to realize the identification of methane and propane mixed gas. For the second harmonic signals of methane, propane, and methyl-propane mixed gas, the characteristic absorption peaks and characteristic factors are found, and the concentration values ​​of the two gases in the mixed gas can be calculated based on the peak-to-valley difference of the absorption peak and their respective partition functions. The system is built to obtain the measured mixed gas harmonic data for verification.

[0007] Specifically, the present invention provides a methane and propane component identification method based on laser absorption spectroscopy gas remote sensing, which can realize propane, methane and methane propane mixed gas remote sensing, and selects the propane absorption peak of 3468nm, but this peak intersects with the methane gas spectrum line in the air background.

[0008] According to the spectral line data of the PNNL database, the absorption peak line shape of propane and methane is quite different, especially the spectral line width is one order of magnitude different, which makes it impossible to unify the modulation parameters, and the two parameters can only be scanned alternately. The present invention uses only one set of parameters to achieve simultaneous measurement of multi-component gases. By comparing the spectral lines of the PNNL database and the HITRAN database, the ultra-wide spectrum of propane is simulated and analyzed to find that it is composed of 21 adjacent spectral lines overlapping, and its second harmonic is also the superposition of multiple second harmonics. The actual propane spectral line and the methane spectral line width are 1.4 times different. Therefore, the same set of modulation parameters can achieve simultaneous measurement of methane and propane. Therefore, the modulation parameters for propane only need to be set according to the propane cross spectral line width.

[0009] Similarly, through the comparison of the PNNL database and the HITRAN database, the methane spectral lines all intersect with propane, and it is normally impossible to achieve component identification and concentration value measurement. The present invention finds that there is a significant difference between a methane harmonic signal and the overlapping propane harmonic signal, and can extract identification characteristic factors. First, it is determined whether it is methane, propane or a mixture of methyl and propane based on the trough width. If the trough width is 150≤W≤200, it is single propane, and the rest are propane and methyl and propane mixtures. The ratio of the absolute values ​​of peak 1 and peak 2 is determined, which is related to the ratio of the methane and propane mixture. The two different gases, methane and propane, have different contribution distribution functions to the peak-to-valley difference of harmonic peaks 1 and 2. The distribution function is calculated by concentration calibration. In actual measurements, the components of the methane and propane mixture are verified, and the concentration values ​​of methane and propane are calculated in real time.

[0010] The specific technical solutions of the present invention are as follows:

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

[0012] S1 obtains the second harmonic signal of the gas to be tested, and searches for the harmonic valley within the range of 100 to 300 of the second harmonic signal; determines whether the gas to be tested is monopropane according to the width W between the two harmonic valleys;

[0013] When 150≤W≤200, the gas to be tested is judged to be monopropane, and the process goes to S2;

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

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

[0016] S3 obtains the peak-to-valley difference between peak 1 and peak 2 in the range of 100 to 300 of the second harmonic signal of the gas to be measured;

[0017] The ratio R of propane to methane in the methane-propane mixture is obtained based on the peak-to-valley difference between peak 1 and peak 2;

[0018] S4 obtains the concentration values ​​of methane and propane according to the ratio R of propane to methane in the methane and propane mixed gas.

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

[0020] Under the conditions of fixed optical path and ambient temperature, different concentrations of propane standard gas are filled into the calibration test gas chamber to obtain the second harmonic signal of propane standard gas. The concentration inversion function K is obtained according to the linear fitting function of the harmonic peak-to-valley difference in the second harmonic signal of propane standard gas 100-300. 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 term and the zero-order term in the linear fitting curve of single propane.

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

[0022] The peak-to-valley difference of peak 1 in the range of 175 to 300 increases with the increase of methane concentration, and the peak-to-valley difference of peak 2 in the range of 100 to 225 decreases with the increase of propane concentration;

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

[0024] Furthermore, in step S3, peak 1 is located at abscissa 175-300; peak 2 is located at abscissa 100-225.

[0025] Further, the method for judging whether the gas to be tested is a mixture of methane and propane according to the ratio R of the two peak ordinates includes:

[0026] When R is a value much greater than 1, it is judged that the proportion of propane in the methane-propane mixture is much greater than that of methane;

[0027] When R is a value much smaller than 1, it is judged that the proportion of methane in the methane and propane mixture is much greater than that of propane, or it is pure methane;

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

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

[0030] The concentration value of propane is K1×R. 6. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing according to claim 1, characterized in that the same set of modulation parameters is used to achieve simultaneous measurement of methane and propane, and the same set of modulation parameters is set for the line width of the propane cross-spectral line.

[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 central wavelength of 3468nm. 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, and 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 be output at a fixed 1000 points per frame, the second harmonic real part 2fX is the first 500 points, and the second harmonic imaginary part 2fY is the last 500 points; the 2fR signal is obtained through 2fX and 2fY Adjust the X / Y phase difference in the digital phase lock to make 2fX the maximum. At this time, 2fX is the second harmonic signal. The horizontal axis of the second harmonic signal is the number of harmonic points, which is the same as the wave number ν (cm) scanned by the laser. -1 ) correspond one to one.

[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, the present invention provides a method for identifying methane and propane components based on laser absorption spectroscopy gas telemetry, including: S1 obtains the harmonic signal of the gas to be tested, wherein the second harmonic real part 2fX is the first 500 points, and the second harmonic imaginary part 2fY is the last 500 points. The 2fR signal is obtained through 2fX and 2fY, and the X / Y phase difference is adjusted to make 2fX the maximum, and 2fX at this time is S1. And find the trough in the range of 100 to 350 of the harmonic signal; judge whether the gas to be tested is single propane according to the trough width; when it is judged that the gas to be tested is single propane, the identification ends, and enters S2 to give the propane concentration value; otherwise, enters step S3; S3 considers that the gas is a mixture of methane and propane, and judges the proportion of the mixed gas. The peak-to-valley difference between peak 1 (abscissa 175-300) and peak 2 (abscissa 100-225) is obtained, and the peak 1 concentration coefficient and the peak 2 concentration coefficient are obtained according to the peak-to-valley difference and the standard gas calibration curve, respectively, and the ratio of methane and propane is obtained according to the ratio of the absolute values ​​of the concentration values ​​obtained for peak 1 and peak 2, and then S4 is entered; S4 gives the methane concentration value and the propane concentration value according to the ratio of methane and propane, and S2 gives the single propane concentration value. The present invention can realize component identification and accurate concentration detection, and has important 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 beneficial effects:

[0036] (1) The present invention provides a methane and propane component identification method based on laser absorption spectroscopy gas remote sensing, which can achieve high-sensitivity methane and propane remote sensing, and can realize component identification and accurate concentration detection, and is suitable for gas remote sensing scenarios such as chemical plant areas and tank area leaks;

[0037] (2) The present invention addresses the problem of a 20-fold difference in the spectral line widths between propane and methane. Through simulation, it is confirmed that the 2.87 nm wide 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 the superposition of 21 second harmonics, and the actual spectral line width difference is 1.5 times.

[0038] (3) To solve the serious problem of propane and methane spectral line crossover, the present invention cleverly utilizes the superposition of three characteristic absorption peaks of propane at 3468 nm, and forms a highly reliable and accurate component identification and concentration calibration method through trough width, peak 1 and peak 2 ratio, and peak-to-trough difference. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The propane absorption spectrum obtained by the simulation of the present invention is compared with the spectrum parameters of the PNNL database and the HITRAN database;

[0040] Figure 2 The propane absorption spectrum obtained by the simulation of the present invention is compared with the spectrum parameters of the PNNL database;

[0041] Figure 3 The present invention is based on Figure 1 and Figure 2 Spectral line data simulates methane harmonic signals, propane harmonic signals, and harmonic signals of methane and propane mixtures;

[0042] Figure 4 These are the harmonic signals of methane, propane, and the harmonic signals of a mixture of methane and propane obtained by actual measurement of the present invention. DETAILED DESCRIPTION

[0043] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0044] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0045] In view of the existence of an atmospheric transmission window between 3460nm and 4165nm, 3464nm is selected as the characteristic wavelength for remote sensing of light hydrocarbon gas. Propane has a relatively wide absorption peak in this band, with a central wavelength of 3463.8nm and a half-width of 2.87nm. Methane has 7 characteristic absorption peaks in this band, which are respectively set to set the driving current of the laser so that its scanning wavelength covers 3461.5nm to 3467.5nm, i.e., wave numbers 2883.9 to 2888.9cm -1 , that is, the absorption peaks of methane and propane in this band can be scanned simultaneously, and harmonic signals can be obtained respectively to judge the concentration. If the absorption peaks of the two gases are adjacent, they can be detected separately and the mixed gas can be identified. If the absorption peaks of the two gases overlap, they can be detected separately, but it is difficult to identify and measure the mixed gas. The present invention solves the problem of overlapping spectral lines of methane and propane.

[0046] In addition, the principle of tunable laser absorption spectroscopy (TDLAS) technology based on wavelength modulation technology (WMS) believes that the selection of modulation coefficient is calculated based on the spectral line width. The modulation depth m is the ratio of the amplitude Δv of the sinusoidal signal applied to the laser to the half-width γ of the spectrum line according to the absorption wavelength of the gas to be measured and the current wavelength coefficient of the laser. The maximum harmonic signal is obtained when the ratio is 2.2 times. The wavelength modulation technology (WMS) requires the superposition of the sawtooth signal and the 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 to be measured. The half-width of the absorption peak of methane is 0.15nm, and the half-width of the absorption peak of propane is 2.87nm, with a difference of 22 times. However, the actual propane absorption peak at 3464nm is the superposition of at least 21 adjacent absorption peaks. According to the fitting, it can be inferred that the half-width of the single absorption peak is about 0.21nm, which is actually 1.4 times different from the half-width of the absorption peak of methane. The methane concentration value can be accurately obtained by using the parameters of low modulation depth m, but the concentration value of methane and propane superimposed on each other can be obtained by using the parameters of deep modulation depth m. The relationship between the two waveforms is not a simple superposition, and there is a lack of a method to accurately deduct the methane concentration from the mixed propane and methane waveform.

[0047] The present invention focuses on solving the problem of methane and propane component identification and concentration calibration in multi-alkane remote sensing. After simulation analysis, the absorption peak of methane has 7 absorption peaks in this band, which are composed of 11 overlapping spectral lines, so 7 independent harmonic signals are obtained. Propane has at least 21 mutually intersecting absorption peaks in this band, so what is obtained is a waveform of 21 independent harmonic signals superimposed on each other. Therefore, if there is a mixture of methane and propane, the signal obtained is the superposition of the propane waveform and the methane harmonic signal, and with different debugging depths and different concentration ratios, the waveform finally obtained has no regularity.

[0048] For the harmonic signal of the methane and propane mixed gas, the trough width and the trough horizontal coordinate are selected as characteristic factors, and the minimum value, i.e., the trough, is found in the range of 0 to 500. The transparent gas chamber is filled with standard gas, single methane, single propane, and mixed gas of methane and propane with different ratios. The trough width and peak-to-trough difference are shown in Table 1.

[0049] Table 1 Test data of methane, propane and methane-propane mixture (trough width and peak-to-trough difference)

[0050]

[0051]

[0052] As can be seen from Table 1, each harmonic signal is obtained, the valley is found within the set range and the peak-to-valley difference between two peaks, peak 1 and peak 2, is calculated for concentration calculation.

[0053] When the trough width of 100-300 is 150≤W≤200, the component is judged to be single propane gas, and the propane concentration is deduced according to the inversion coefficient K0 of propane, and the methane concentration value is displayed as 0.

[0054] When the trough width of 100-300 is within the range of 78≤W≤90, it is consistent with single methane gas or methane-propane mixed gas, and the peak-to-valley difference of peak 1 and peak-to-valley difference of peak 2 are calculated respectively. Since the peak 1 methane concentration value is proportional to the peak-to-valley difference, the peak-to-valley difference increases with the increase of the methane concentration value. As shown in Table 1, the single methane concentration obtained by K1 inversion is consistent with the actual value. However, when there is a mixed gas of methane and propane in different proportions, the methane concentration inverted by K1 is different from the actual value of the standard gas charged. Other parameters need to be introduced for correction.

[0055] The peak-to-valley difference of peak 2 gradually decreases with the increase of propane concentration. Therefore, the propane value calibrated by K2 is inversely proportional to the peak-to-valley difference. The K2 coefficient is fitted according to the test value to obtain the K2 inversion value. As shown in the table, if the ratio R is much greater than 1, it is a high-concentration propane. If R is close to 1, the ratio of methane to propane is close to 1:1. If R is less than 1, it is a high-concentration methane or single methane. The propane value in the mixed gas is calculated based on the proportional coefficient, which is consistent with the concentration value of the methane and propane mixed gas in the standard gas filled into the gas chamber.

[0056] In summary, the present invention aims at the problem of 20 times difference in the spectral line width between propane and methane. Through simulation, it is confirmed that the 2.87nm width absorption peak of propane at 3464nm is formed by the superposition of at least 21 crossed absorption peaks. Therefore, the propane second harmonic in this band is also the superposition of 21 second harmonics, and the actual spectral line width difference is 1.5 times. The present invention provides a component identification and concentration calibration method for simultaneous measurement of methane and propane. In view of the serious problem of crossover of propane and methane spectral lines, the three characteristic absorption peaks of propane at 3468nm are superimposed. First, according to the trough width as a characteristic factor, it can be identified whether it is single propane, single methane, or methane-propane mixed gas. If it is single propane, the propane concentration is inverted according to K0. Under the conditions of propane and methane mixed gas, the peak-to-valley difference of the propane harmonic curve decreases with the increase of the concentration value under the methane background, which is completely opposite to the peak 1 of the methane harmonic curve, and the concentration proportional coefficient of methane and propane is obtained. Determine the proportion of propane based on the proportional coefficient and calculate the concentration values ​​of methane and propane in the mixed gas respectively.

[0057] In summary, the present invention relates to laser gas telemetry technology, especially to the field of petrochemical tank leakage warning, and is suitable for gas telemetry scenarios such as chemical plant area and tank area leakage. In view of the problem that methane gas exists in the atmospheric background in the laser gas telemetry system, and the methane absorption peak and propane interfere with each other, the absorption spectrum lines and harmonic wave curves of propane and methane are simulated to find adjacent spectrum lines that can realize component identification, and determine the corresponding modulation parameters. High-sensitivity methane and propane telemetry is achieved, and component identification and accurate concentration detection can be achieved.

[0058] Example:

[0059] Example 1

[0060] The present invention adopts a mid-infrared semiconductor ICL laser to simultaneously detect multi-component light hydrocarbon gases. The laser driving unit in the device controls the laser to emit a laser beam with a central wavelength of 3468nm. 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 figure, the red and black solid lines are the overall spectral lines fitted according to the PNNL database and the HITRAN database, and the dotted lines are the results of fitting each spectral line and the superposition of multiple spectral lines based on the single methane spectral line data provided by HITRAN. The horizontal axis is the wave number (cm -1 ), the ordinate is absorbance (ppm -1 ·m -1 ); Figure 2Since HITRAN does not provide single propane spectral line parameters, propane is the multiple spectral lines and their superposition results simulated and fitted by the present invention. The simulation is based on the speculation of spectral line data obtained from the actual test results of propane standard gas. The characteristic absorption peak curves of methane and propane gases in this band are obtained by fitting the data provided by PNNL database and HITRAN database. Figure 1 and Figure 2 The solid line is shown in the middle, and the dotted line is the self-fitted spectrum line. The laser beam is collimated and emitted in an open space, with the divergence angle controlled at 1.3mrad and the receiving angle at 2mrad. The laser beam irradiates the wall near the storage tank, and aluminum foil is pasted on the wall to increase the reflectivity. The diffusely reflected beam is received by the lens. In order to increase the telemetry distance, the size of the lens is 25cm, and the telemetry distance is 100.2m (aluminum foil). The harmonic signals of three gases, methane, propane, and methane-propane mixture, are telemetered, and the response time is 1.49s. According to Figure 3 The extracted characteristic factors and strategies are shown to judge the components, where ΣC1 represents methane (CH4) and ΣC3 represents propane (C3H8). Figure 1 and Figure 2 The multiple second harmonic curves obtained by fitting multiple spectral line data are superimposed. The actual measured harmonic curve is as follows Figure 4 Shown with Figure 3 The curve obtained by simulation is completely consistent with Figure 4 The unit of medium concentration value is ppm×m, which has the same meaning as ppm·m mentioned above, that is, multiplication.

[0061] Example 2

[0062] This embodiment adopts the above-mentioned methane and propane component identification method based on laser absorption spectroscopy gas telemetry to verify the single components of methane and propane and mixed gases of different proportions. The specific steps are as follows:

[0063] S1 obtains the harmonic signal of the gas to be tested, and fills the gas chamber with 62.5ppm·m and 625ppm·m methane standard gas, 125ppm·m and 625ppm·m propane standard gas, as well as 62.5ppm·m methane + 625ppm·m propane mixed gas, 625ppm·m methane + 625ppm·m propane mixed gas, and 625ppm·m methane + 125ppm·m propane mixed gas, respectively, to obtain different harmonic signals. And look for the trough in the range of 0 to 300 of the harmonic signal; if the trough width is >150, it is judged to be propane, and the propane concentration value is obtained according to K0 inversion. If the trough width is between 78 and 90, it is judged that the gas to be tested is methane alone or a mixture of methane and propane;

[0064] S2 obtains the ordinate ratio of peak 1 and peak 2 in the range of 0 to 300 of the harmonic signal of the gas to be measured; the ordinates of peak 1 and peak 2, the proportional coefficient, and the mixed gas concentration values ​​obtained by inversion are respectively as shown in Table 1, which are consistent with the concentration values ​​of the pre-charged mixed gas components within the allowable error range.

[0065] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0066] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for identifying methane and propane components based on laser absorption spectroscopy gas telemetry, characterized in that: include: S1 obtains the second harmonic signal of the gas to be tested, and searches for the harmonic valley within the range of 100 to 300 of the second harmonic signal; determines whether the gas to be tested is monopropane according to the width W between the two harmonic valleys; When 150≤W≤200, the gas to be tested is judged to be monopropane, and the process goes to S2; When 78≤W≤90, it is determined that the gas to be tested is a mixture of methane and propane, and the process goes to step S3; S2 obtains the concentration inversion coefficient K0 according to the second harmonic signal of the propane standard gas, and obtains the real-time single propane concentration value according to the concentration inversion coefficient K0; S3 obtains the peak-to-valley difference between peak 1 and peak 2 in the range of 100 to 300 of the second harmonic signal of the gas to be measured; The ratio R of propane to methane in the methane-propane mixture is obtained based on the peak-to-valley difference between peak 1 and peak 2; S4 obtains the concentration values ​​of methane and propane according to the ratio R of propane to methane in the methane and propane mixed gas.

2. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing according to claim 1 is characterized in that: In step S2, the method for obtaining the concentration inversion linear function K0 according to the second harmonic signal of the propane standard gas includes: Under the conditions of fixed optical path and ambient temperature, different concentrations of propane standard gas are filled into the calibration test gas chamber to obtain the second harmonic signal of propane standard gas. The concentration inversion function K is obtained according to the linear fitting function of the harmonic peak-to-valley difference in the second harmonic signal of propane standard gas 100-300. 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 term and the zero-order term 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: The specific method of step S3 includes: The peak-to-valley difference of peak 1 in the range of 175 to 300 increases with the increase of methane concentration, and the peak-to-valley difference of peak 2 in the range of 100 to 225 decreases with the increase of propane concentration; According to the peak-to-valley difference of peak 1 and the peak-to-valley difference of peak 2 in the second harmonic signal of the mixed standard gas, the inversion function of peak 1 is K1=a1x+b1, and the inversion function of peak 2 is K2=-a2x+b2. According to the inversion functions of peak 1 and peak 2, the ratio of the methane and propane mixed gas to be tested is judged as R=abs(K2) / K1; wherein x is the peak-to-valley difference obtained in real time, a1 and b1 are the first-order term and zero-order term coefficients in the linear fitting curve of peak 1, and a2 and b2 are the first-order term and zero-order term coefficients in the linear fitting curve of peak 2.

4. 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 S3, peak 1 is located at abscissa 175-300; peak 2 is located at abscissa 100-225.

5. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing according to claim 3, characterized in that: In step S4, the concentration value of methane is the inversion coefficient K1 of peak 1; The concentration of propane is K1×R.

6. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing according to claim 1, characterized in that: The same set of modulation parameters is used to achieve simultaneous measurement of methane and propane, and the same set of modulation parameters is set for the line width of the propane cross-spectral line.

7. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing according to claim 1, characterized in that: A mid-infrared semiconductor ICL laser is used to simultaneously detect the gases to be tested. The laser emits a laser beam with a central wavelength of 3468nm. 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, and obtaining the harmonic signal of the gas to be tested.

8. 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 a fixed output of 1000 points per frame, the second harmonic real part 2fX is the first 500 points, and the second harmonic imaginary part 2fY is the last 500 points; the 2fR signal is obtained through 2fX and 2fY Adjust the X / Y phase difference in the digital phase lock to make 2fX the maximum. At this time, 2fX is the second harmonic signal. The horizontal axis of the second harmonic signal is the number of harmonic points, which is the same as the wave number ν (cm) scanned by the laser. -1 ) correspond one to one.

9. The method for identifying methane and propane components based on laser absorption spectroscopy gas remote sensing according to claim 1, characterized in that: Applied to petrochemical tank telemetry for component identification of methane and propane.

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