Exhaust gas detection method and device for chimney pipeline

Abstract

The present application provides a method and device for detecting waste gas in a chimney pipeline, which relates to the field of detecting by tunable semiconductor laser absorption spectroscopy technology. The ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of H2O and O2 is obtained, and the ratio of the spectral line intensities of two adjacent absorption spectral lines of H2O and O2 is determined based on the ratio. The fitting correlation coefficient between the ratio of the spectral line intensities of two adjacent absorption spectral lines of O2 and H2O and the temperature is obtained, and the gas corresponding to the largest fitting correlation coefficient is used as the reference gas to determine the waste gas temperature value of the chimney pipeline. According to the waste gas temperature value and the second harmonic signals of two adjacent absorption spectral lines of the reference gas, the concentration value of O2 and the humidity value of the waste gas are determined based on the waste gas temperature value of the chimney pipeline and the waste gas pressure value of the chimney pipeline. This detection method can improve the detection accuracy of the temperature, pressure, humidity, and oxygen concentration value of the waste gas in the chimney pipeline.

Description

Technical Field

[0001] The present invention relates to the field of detecting by tunable semiconductor laser absorption spectroscopy technology, and particularly to a method and device for detecting waste gas in a chimney pipeline. Background Art

[0002] In the field of on-line monitoring of waste gas emissions from stationary pollution sources, in addition to the need to on-line monitor the concentrations of conventional pollutant factors (such as SO 2 , NO x , NMHC, etc.), it is also necessary to monitor waste gas parameters such as temperature, pressure, flow rate, humidity, and oxygen concentration. These parameters are important parameters for calculating the waste gas emission amount. Therefore, it is necessary to accurately monitor these parameters, which is of great significance for controlling the emission of pollutants in the waste gas.

[0003] In the related art, during the detection of waste gas, the tunable semiconductor laser absorption spectroscopy technology (TDLAS) is usually adopted, which has the characteristics of no need for pretreatment, strong selectivity, fast response speed, high accuracy and high precision, and has been widely used in the detection fields such as environment and medical treatment in recent years. TDLAS is mainly divided into direct absorption, frequency modulation and wavelength modulation technologies from the signal detection method. However, in the related art, when measuring waste gas parameters (temperature, pressure, humidity, oxygen concentration), the absorption spectroscopy technology and hardware such as sensors are often combined to determine the temperature, pressure, humidity, and oxygen concentration of the waste gas. Once the hardware fails or the detection accuracy of the hardware is different under different environmental conditions, the accuracy of the detected temperature, pressure, humidity, and oxygen concentration values will be affected. Summary of the Invention

[0004] Based on this, it is necessary to provide a method and device for detecting waste gas in a chimney pipeline for the above technical problems.

[0005] In a first aspect, the present application provides a method for detecting waste gas in a chimney pipeline, the method comprising:

[0006] Obtaining the ratio of the second harmonic signal amplitudes of two adjacent absorption spectral lines of H 2 O and the ratio of the second harmonic signal amplitudes of two adjacent absorption spectral lines of O 2 ; wherein, a first laser and a second laser are driven in time-sharing by a low-frequency triangular wave superimposed on a high-frequency sine wave, and the characteristic wavelength lasers emitted by the first laser and the second laser are both used to pass through the waste gas in the chimney pipeline. The characteristic wavelength laser emitted by one of the first laser and the second laser can cover two adjacent absorption spectral lines of H 2 O, and the characteristic wavelength laser emitted by the other can cover two adjacent absorption spectral lines of O 2Two adjacent absorption spectral lines;

[0007] Based on H 2 The ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of H 2 O to determine the ratio of the spectral line intensities of two adjacent absorption spectral lines of H 2 O, and based on the ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of O 2 To determine the ratio of the spectral line intensities of two adjacent absorption spectral lines;

[0008] Obtain the ratio of the spectral line intensities of two adjacent absorption spectral lines of O 2 The fitting correlation coefficient between the ratio of the spectral line intensities of two adjacent absorption spectral lines and temperature, and the ratio of the spectral line intensities of two adjacent absorption spectral lines of H 2 O, and use the gas corresponding to the largest fitting correlation coefficient as the reference gas, and determine the exhaust gas temperature value of the chimney duct based on the ratio of the spectral line intensities of two adjacent absorption spectral lines of the reference gas;

[0009] According to the exhaust gas temperature value and the second harmonic signals of two adjacent absorption spectral lines of the reference gas, determine the exhaust gas pressure value of the chimney duct through the broadening mechanism of the gas line shape function, and determine the concentration value of O based on the exhaust gas temperature value of the chimney duct and the exhaust gas pressure value of the chimney duct 2 And the humidity value of the exhaust gas.

[0010] In one embodiment, obtain the ratio of the spectral line intensities of two adjacent absorption spectral lines of O 2 The fitting correlation coefficient between the ratio of the spectral line intensities of two adjacent absorption spectral lines and temperature, and the ratio of the spectral line intensities of two adjacent absorption spectral lines of H 2 O, and use the gas corresponding to the largest fitting correlation coefficient as the reference gas, including:

[0011] According to the ratio of the spectral line intensities of two adjacent absorption spectral lines of O 2 And / or the ratio of the spectral line intensities of two adjacent absorption spectral lines of H 2 O, determine the target temperature range;

[0012] Obtain the corresponding fitting correlation coefficient of O in the target temperature range 2 And the fitting correlation coefficient of H 2 O, and use the gas corresponding to the largest fitting correlation coefficient as the reference gas.

[0013] In one embodiment, according to the ratio of the spectral line intensities of two adjacent absorption spectral lines of O 2 And / or the ratio of the spectral line intensities of two adjacent absorption spectral lines of H 2 O, determine the target temperature range, including:

[0014] Obtain a polynomial function; wherein, the polynomial function is a monotonic function, and there is a monotonic functional relationship between the temperature and the spectral line intensity ratio, and the polynomial coefficients of the polynomial function can be obtained by fitting the data points in a pre-set database. The data points include different temperatures and the corresponding spectral line intensities or spectral line intensity ratios at different temperatures;

[0015] Based on the monotonic functional relationship between the temperature and the spectral line intensity ratio, select, from multiple candidate temperature intervals, the candidate temperature interval that matches the spectral line intensity ratio of two adjacent absorption spectral lines adjacent to O 2 and / or the spectral line intensity ratio of two adjacent absorption spectral lines adjacent to H 2 O as the target temperature interval.

[0016] In one embodiment, determining the exhaust gas temperature value of the chimney duct based on the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas includes:

[0017] Substitute the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas into the polynomial function with known polynomial coefficients to obtain the exhaust gas temperature value of the chimney duct;

[0018] wherein, the polynomial function is: , a, b, c, d, e is the polynomial fitting coefficient;

[0019] The calculation method of the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas is:

[0020] ,

[0021] r is the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas, S(T) is the spectral line intensity of the absorption spectral line, K 21 , K 22 are the harmonic signal calibration coefficients of the first and second absorption spectral lines of the reference gas respectively, is the ratio of the second harmonic signal amplitudes of two adjacent absorption spectral lines of the reference gas.

[0022] In one embodiment, according to the exhaust gas temperature value and the second harmonic signals of two adjacent absorption spectral lines of the reference gas, determining the exhaust gas pressure value of the chimney duct through the broadening mechanism of the gas line shape function includes:

[0023] Substitute the exhaust gas temperature value into the full width at half maximum calculation formula of Doppler broadening to obtain the full width at half maximum of Doppler broadening σ g ;

[0024] Based on the second harmonic signals of two adjacent absorption spectral lines of the reference gas, obtain the full width at half maximum (FWHM) of the comprehensive broadening through the half-height value. Obtain the full width at half maximum (FWHM) of the comprehensive broadening. σ v ; where is the left bottom value of the second harmonic signal of one of the two adjacent absorption spectral lines of the reference gas, is the right bottom value of the second harmonic signal of this absorption spectral line, is the maximum value of the second harmonic signal of this absorption spectral line;

[0025] Based on the full width at half maximum (FWHM) of Doppler broadening σ g and the full width at half maximum (FWHM) of the comprehensive broadening σ v , determine the full width at half maximum (FWHM) of collision broadening σ l ;

[0026] According to the functional relationship between the full width at half maximum (FWHM) of collision broadening σ l and the pressure, obtain the pressure value.

[0027] In one embodiment, the calculation formula for determining the full width at half maximum (FWHM) of collision broadening σ g and the full width at half maximum (FWHM) of the comprehensive broadening σ v is as follows: σ l ;

[0028] ;

[0029] According to the functional relationship between the full width at half maximum (FWHM) of collision broadening σl and the pressure, the calculation formula for obtaining the pressure value is as follows:

[0030] ;

[0031] where P is the pressure value, T is the exhaust gas temperature value, T 0 is the reference temperature, n 1 、n 2 、 1、 2 、 1、 2They are the temperature correlation coefficient, air broadening coefficient, and self-broadening coefficient corresponding to the second harmonic signals of two adjacent gas absorption spectral lines of the reference gas, respectively.

[0032] In one embodiment, the second harmonic signals of two adjacent absorption spectral lines of H 2 O and O 2 are obtained respectively, including:

[0033] A driving signal in the form of a triangular wave is formed by superimposing a low-frequency triangular wave on a high-frequency sine wave. The second harmonic signals are collected at both the rising edge and the falling edge of the triangular wave driving signal to obtain the second harmonic signals of two adjacent absorption spectral lines of H 2 O and O 2 respectively; wherein, the driving signal in the form of a triangular wave drives the first laser or the second laser within each half cycle.

[0034] In one embodiment, the concentration value of O 2 and the humidity value of the waste gas are determined based on the waste gas temperature value and the waste gas pressure value of the chimney duct, including:

[0035] The waste gas temperature value and the waste gas pressure value of the chimney duct are substituted into the concentration calculation formula to obtain the concentration value of O 2 and the humidity value of the waste gas; wherein, the concentration calculation formula is:

[0036] ;

[0037] wherein, is the concentration value, y represents the gas type O 2 or H 2 O, is the left bottom value of the second harmonic signal of one of the two adjacent absorption spectral lines of O 2 or H 2 O, is the right bottom value of the second harmonic signal of this absorption spectral line, , the concentration value of H 2 O is equal to the humidity value of the waste gas, L represents the optical path, b 0 、K y are the zero absorption coefficient and the calibration coefficient respectively, v c is the center frequency output by the first laser or the second laser, S(T) is the spectral line intensity of the gas, and S(T) is related to the waste gas temperature value of the chimney duct.

[0038] In one embodiment, to determine H2 The amplitudes of the second harmonic signals of two adjacent absorption spectral lines adjacent to O and O 2 The amplitudes of the second harmonic signals of two adjacent absorption spectral lines, and select the maximum value from the amplitudes of the four second harmonic signals;

[0039] Obtain the frequency shift amount of the center frequency of the absorption spectral line corresponding to the maximum value Δυ , according to the frequency shift amount Δυ Determine the waste gas flow rate of the chimney pipe V ; The waste gas flow rate V The calculation formula is:

[0040] ;

[0041] Wherein, is the center frequency of the absorption spectral line, φ is the incident angle when the laser with the characteristic wavelength emitted by the first laser and the second laser is combined into one path by the coupler and then incident on the other side of the chimney pipe.

[0042] Second, the present application provides a device for detecting waste gas in a chimney pipe, and the device includes:

[0043] A signal generation circuit that generates a low-frequency triangular wave and a high-frequency sine wave in time-sharing;

[0044] Lasers, including a first laser and a second laser, the low-frequency triangular wave superimposed on the high-frequency sine wave drives the first laser and the second laser in time-sharing, and the lasers with the characteristic wavelength emitted by the first laser and the second laser are both used to pass through the waste gas in the chimney pipe. One of the first laser and the second laser emits a laser with a characteristic wavelength that can cover two adjacent absorption spectral lines adjacent to H 2 O, and the other emits a laser with a characteristic wavelength that can cover two adjacent absorption spectral lines adjacent to O 2 ;

[0045] A photodetector that receives the laser passing through the waste gas in the chimney pipe;

[0046] A signal processing circuit that performs the waste gas detection method in the above embodiments based on the laser passing through the waste gas in the chimney pipe.

[0047] In the above waste gas detection method and device for the chimney pipe, the first laser and the second laser are driven in time-sharing by superimposing a low-frequency triangular wave on a high-frequency sine wave. The lasers with the characteristic wavelength emitted by the first laser and the second laser are both used to pass through the waste gas in the chimney pipe. One of the first laser and the second laser emits a laser with a characteristic wavelength that can cover two adjacent absorption spectral lines adjacent to H 2 O, and the other emits a laser with a characteristic wavelength that can cover two adjacent absorption spectral lines adjacent to O 2Two adjacent absorption spectral lines. First, obtain H 2 The ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of H 2 O, and the ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of O, and respectively determine the corresponding spectral line intensity ratios based on the ratios of H 2 O, O 2 Corresponding ratios; further, respectively obtain the correlation coefficients of polynomial fitting based on the corresponding spectral line intensity ratios of H 2 O, O 2 Corresponding spectral line intensity ratios, and use the gas corresponding to the largest correlation coefficient as the reference gas. Determine the exhaust gas temperature value of the chimney pipe based on the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas. Furthermore, according to the exhaust gas temperature value and the second harmonic signals of two adjacent absorption spectral lines of the reference gas, determine the exhaust gas pressure value of the chimney pipe through the broadening mechanism of the gas line shape function. Determine the concentration value of O 2 And the humidity value of the exhaust gas based on the exhaust gas temperature value of the chimney pipe and the exhaust gas pressure value of the chimney pipe. The detection method and device are not affected by hardware failures and environmental conditions, and improve the detection accuracy of the temperature, pressure, humidity, and oxygen concentration value of the exhaust gas in the chimney pipe. Brief Description of the Drawings

[0048] Figure 1 Is a schematic flow chart of a method for detecting exhaust gas in a chimney pipe in an embodiment;

[0049] Figure 2 Is a diagram of the second harmonic signals of two adjacent absorption spectral lines of one of the gases in an embodiment;

[0050] Figure 3 Is a schematic flow chart of a method for determining polynomial coefficients and a reference gas in an embodiment;

[0051] Figure 4 Is a schematic flow chart of a method for determining polynomial coefficients and a reference gas for each temperature range in an embodiment;

[0052] Figure 5 Is a schematic flow chart of a method for determining the exhaust gas pressure in the pipe through the broadening mechanism in an embodiment;

[0053] Figure 6 Is a schematic diagram of collecting second harmonic signals by two lasers in an embodiment;

[0054] Figure 7 Is a device diagram of a method for detecting exhaust gas in a chimney pipe in an embodiment;

[0055] Figure 8 Is a specific flow chart of a method and device for detecting exhaust gas in a chimney pipe in an embodiment. Detailed Description of the Invention

[0056] In order to make the objectives, technical solutions and advantages of the present application clearer and more understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0057] In one embodiment, as Figure 1 shown, a waste gas detection method for a chimney pipe is provided, including the following steps:

[0058] Step 101: Obtain the ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of H 2 O and the ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of O 2 ; wherein, the first laser and the second laser are driven in time-sharing by a low-frequency triangular wave superimposed on a high-frequency sine wave, and the characteristic wavelength lasers emitted by the first laser and the second laser are both used to pass through the waste gas in the chimney pipe. The characteristic wavelength laser emitted by one of the first laser and the second laser can cover two adjacent absorption spectral lines of H 2 O, and the characteristic wavelength laser emitted by the other can cover two adjacent absorption spectral lines of O 2 .

[0059] Specifically, the first laser and the second laser are driven and modulated in time-sharing (1 - 10 s) by a low-frequency triangular wave (10 Hz - 100 Hz) superimposed on a high-frequency sine wave (10 kHz - 100 kHz). This driving method enables the lasers to emit light of specific wavelengths at different times and can cover the absorption spectral lines of H 2 O and O 2 . The light emitted by one of the lasers covers two adjacent absorption spectral lines of H 2 O, and the light emitted by the other laser covers two absorption spectral lines of O 2 . The lasers with the wavelengths emitted are both used to pass through the waste gas in the chimney pipe. Although each laser is specifically for one gas (H 2 O or O 2 ), it has the ability to scan two different characteristic wavelengths of this gas. That is, the same laser can scan two adjacent characteristic wavelengths in the same gas, so as to obtain two harmonic signals. By calculating the ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of H 2 O, the ratio of the amplitudes of the second harmonic signals of two absorption spectral lines of H 2 O is obtained , and by calculating the ratio of the amplitudes of the second harmonic signals of two absorption spectral lines of O 2 , the ratio of the amplitudes of the second harmonic signals of two absorption spectral lines of O 2 is obtained 。

[0060] Taking H 2 O as an example, the second harmonic signals of two adjacent absorption spectral lines of H 2 O are as follows Figure 2 shown M 1 is the maximum value of the second harmonic signal of one of the absorption spectral lines, M 2 is the maximum value of the second harmonic signal of the other absorption spectral line. F 1 and F 3 are the left and right bottom foot values of the second harmonic signal of one of the absorption spectral lines, F 2 and F 4 are the left and right bottom foot values of the second harmonic signal of the other absorption spectral line. Further, in Figure 2 , the abscissa represents the wave number, which can be understood as the change rate of the wavelength with distance. It should be noted that two adjacent absorption spectral lines can refer to two absorption spectral lines with close wave numbers and adjacent in sequence. The ordinate represents the second harmonic signals of two adjacent absorption spectral lines. V 0 represents the starting wave number value during laser scanning, V 1 and V 2 are the left and right wave numbers corresponding to the half-height value of the second harmonic signal of one of the absorption spectral lines; V c1 is the maximum value of the second harmonic signal of one of the absorption spectral lines M 1 corresponding to the wave number center point; V 3 and V 4 are the left and right wave numbers corresponding to the half-height value of the second harmonic signal of the other absorption spectral line; V c2 is the maximum value of the second harmonic signal of the other absorption spectral line M 2 corresponding to the wave number center point. It should be noted that taking H 2 O as an example, the amplitude of the second harmonic signal of one of the absorption spectral lines of H 2 O is the difference between the maximum value of the second harmonic signal of this absorption spectral line and the average value of the left and right bottom foot values of the second harmonic signal of this coefficient spectral line. In Figure 2 taking H 2 O as an example, the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of H 2 O can be M1 -( F 1 + F 3 ) / 2 and M 2 -( F 2 + F 4 ) / 2.

[0061] Step 102: Determine the spectral line intensity ratio of two adjacent absorption spectral lines of H 2 O based on the ratio of the second harmonic signal amplitudes of the two adjacent absorption spectral lines of H 2 O, and determine the spectral line intensity ratio of two adjacent absorption spectral lines of O 2 based on the ratio of the second harmonic signal amplitudes of the two adjacent absorption spectral lines of O 2 .

[0062] Specifically, for the spectral line intensity ratio of two adjacent absorption spectral lines of a gas (H 2 O or O 2 ), it can be determined by calibrating the ratio of the second harmonic signal amplitudes. The calibration process involves a gas with a known concentration to establish a proportional relationship by comparing the actual measured value and the theoretical value, and obtaining a calibration coefficient. Assume that a calibration coefficient 2 is obtained during the calibration process for H O, then the spectral line intensity ratio of H 2 O can be expressed as . Similarly, the spectral line intensity ratio of O 2 can be expressed as . It should be noted that the calibration coefficient needs to be determined through experiments, usually involving measuring the spectral line intensity ratios of H 2 O and O 2 with known concentrations under controlled conditions, and comparing them with the corresponding ratios of the second harmonic signal amplitudes. Through the least squares method or other statistical methods, the calibration coefficient suitable for the measured data can be found.

[0063] Step 103: Obtain the fitting correlation coefficient between the spectral line intensity ratio of two adjacent absorption spectral lines of O 2 and temperature, and the fitting correlation coefficient between the spectral line intensity ratio of two adjacent absorption spectral lines of H 2 O and temperature. Take the gas corresponding to the largest fitting correlation coefficient as the reference gas, and determine the exhaust gas temperature value of the chimney duct based on the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas.

[0064] Specifically, the fitting correlation coefficient between the spectral line intensity ratio of two adjacent absorption spectral lines of O 2The fitting correlation coefficient between the spectral line intensity ratio of two adjacent absorption spectral lines and temperature, and the fitting correlation coefficient between the spectral line intensity ratio of two adjacent absorption spectral lines of H 2 O. Among them, the database can be a system that centrally stores and manages scientific data on the characteristics of gas absorption spectral lines, and can provide the spectral line intensity ratio of gases such as O 2 and H 2 O at different temperatures. The spectral line intensity ratios of gases such as O 2 and H 2 O at different temperatures can be obtained through experimental measurements. That is, researchers use spectroscopic instruments to accurately record the absorption spectral lines of gases under controlled conditions and store the results in the database.

[0065] Compare the fitting correlation coefficients of O 2 and H 2 O, and select the gas corresponding to the maximum fitting correlation coefficient as the reference gas. Exemplarily, if the fitting correlation coefficient of O 2 is 0.88 and the fitting correlation coefficient of H 2 O is 0.93, compare the fitting correlation coefficients of the two, and select the gas with the maximum fitting correlation coefficient, that is, H 2 O as the reference gas. The actual temperature value of the waste gas in the chimney pipeline can be determined using the spectral line intensity ratio corresponding to the selected H 2 O. Among them, linear or non-linear regression analysis can be used to obtain the function of the spectral line intensity ratio changing with temperature, and the corresponding waste gas temperature can be calculated through this function.

[0066] Step 104: Determine the waste gas pressure value of the chimney pipeline through the broadening mechanism of the gas line shape function according to the waste gas temperature value and the second harmonic signals of two adjacent absorption spectral lines of the reference gas, and determine the concentration value of O 2 and the humidity value of the waste gas based on the waste gas temperature value of the chimney pipeline and the waste gas pressure value of the chimney pipeline.

[0067] Specifically, according to the obtained waste gas temperature value and the second harmonic signals of two adjacent absorption spectral lines of the reference gas, use the broadening mechanism of the gas function to determine the waste gas pressure value, which involves the calculations of Doppler broadening and collision broadening. Determine the waste gas pressure value through the broadening of the calculated second harmonic signals. Substitute the calculated waste gas temperature value and pressure value into the concentration calculation formula to obtain the humidity value of the waste gas and the concentration value of O 2 respectively.

[0068] In this embodiment, the first laser and the second laser are driven in time - divided manner by superimposing a low - frequency triangular wave on a high - frequency sine wave. The laser with characteristic wavelength emitted by the first laser and the second laser is used to pass through the waste gas in the chimney duct. The laser with characteristic wavelength emitted by one of the first laser and the second laser can cover two adjacent absorption spectral lines of H 2 O, and the laser with characteristic wavelength emitted by the other can cover two adjacent absorption spectral lines of O 2 First, obtain the ratio of the amplitudes of the second - harmonic signals of two adjacent absorption spectral lines of H 2 O and the ratio of the amplitudes of the second - harmonic signals of two adjacent absorption spectral lines of O 2 And respectively determine the corresponding spectral line intensity ratios based on the ratios of H 2 O and O 2 This method can accurately determine the spectral line intensity ratio of the reference gas (H 2 O or O 2 ). Further, based on the spectral line intensity ratio, polynomial fitting is performed to determine the correlation coefficient. By comparing the correlation coefficients, the reference gas is selected, and the temperature value of the waste gas is determined according to the spectral line intensity ratio of the reference gas, so that the most accurate temperature measurement results can be obtained under different working conditions, which is convenient for accurately calculating the temperature value of the waste gas in the chimney duct. Utilizing the broadening mechanism of the gas line - shape function and combining the determined waste gas temperature value, the pressure value of the waste gas in the chimney duct is determined. Based on the second - harmonic signal of the reference gas and the determined pressure and temperature, the concentration value of O 2 and the humidity value of the waste gas can be further determined. Thus, the detection method of this embodiment is not affected by hardware failures and environmental working conditions, and improves the detection accuracy of the temperature, pressure, humidity, and oxygen concentration value of the waste gas in the chimney duct.

[0069] In one embodiment, as Figure 3 shown, obtain the fitting correlation coefficient between the spectral line intensity ratio of two adjacent absorption spectral lines of O 2 and temperature and the fitting correlation coefficient between the spectral line intensity ratio of two adjacent absorption spectral lines of H 2 O and temperature. The gas corresponding to the largest fitting correlation coefficient is used as the reference gas, including the following steps:

[0070] Step 301: Determine the target temperature range according to the spectral line intensity ratio of two adjacent absorption spectral lines of O 2 and / or the spectral line intensity ratio of two adjacent absorption spectral lines of H 2 O;

[0071] Specifically, in the actual waste gas environment, use laser absorption spectroscopy technology to measure the intensities of two adjacent absorption spectral lines of O 2 and / or H 2 O, and calculate the intensity of O 2and / or H 2 The spectral line intensity ratio of two adjacent absorption spectral lines of O 2 and / or H 2 The spectral line intensity ratio of two adjacent absorption spectral lines of O at different temperature intervals. The different temperature intervals can be, for example, -100K to 0K, 0K to 100K, 100K to 200K, etc. Then, compare the measured spectral line intensity ratio with that in the database, find the spectral line intensity ratio in the database that is closest to the measured spectral line intensity ratio, determine the corresponding temperature interval, so as to determine that the temperature of the exhaust gas environment is within a certain interval, that is, determine the target temperature interval, such as 100K to 200K.

[0072] Step 302: Obtain the fitting correlation coefficient corresponding to O 2 and the fitting correlation coefficient corresponding to H 2 O, and use the gas corresponding to the largest fitting correlation coefficient as the reference gas.

[0073] Specifically, at the target temperature interval, use the spectral line intensity ratio of O 2 and temperature for polynomial fitting, and the fitting correlation coefficient of O 2 can be calculated; use the spectral line intensity ratio of H 2 O and temperature for polynomial fitting, and the fitting correlation coefficient of H 2 O can be calculated. Compare the magnitudes of the fitting correlation coefficients between O 2 and H 2 O, and the gas with the largest fitting correlation coefficient value can be selected as the reference gas. Exemplarily, at the target temperature interval, if the fitting correlation coefficient of O 2 is 0.91 and the fitting correlation coefficient of H 2 O is 0.88, and the fitting correlation coefficient of O 2 is greater than the fitting correlation coefficient of H 2 O, so O 2 is selected as the reference gas.

[0074] In this embodiment, the gas with the largest fitting correlation coefficient is selected as the reference gas. This can effectively identify the gas that is most closely related to temperature within a specific temperature interval, thereby improving the accuracy and reliability of temperature measurement.

[0075] In one embodiment, as Figure 4 shown, according to the spectral line intensity ratio of two adjacent absorption spectral lines of O 2 and / or the spectral line intensity ratio of two adjacent absorption spectral lines of H 2 O, to determine the target temperature interval, includes the following steps:

[0076] Step 401: Obtain a polynomial function; wherein, the polynomial function is a monotonic function, and there is a monotonic functional relationship between temperature and the spectral line intensity ratio. The polynomial coefficients of the polynomial function can be obtained by fitting the data points in a pre-set database. The data points include different temperatures and the corresponding spectral line intensities or spectral line intensity ratios at different temperatures;

[0077] Specifically, the database may contain data points of different temperatures and the corresponding spectral line intensity ratios at different temperatures. The data points can reflect the influence of temperature changes on the spectral line intensity ratio. There is a monotonic functional relationship between temperature and the spectral line intensity ratio, that is, as the temperature increases or decreases, the spectral line intensity ratio will correspondingly increase or decrease monotonically. By performing polynomial fitting on the data points, the fitted polynomial function can be made to approximate the actual data points as much as possible, so as to accurately describe the relationship between temperature and the spectral line intensity ratio. During the fitting process, the coefficients of each term of the polynomial function can be calculated, and the polynomial coefficients can determine the specific characteristics of the polynomial function.

[0078] Step 402: Based on the monotonic functional relationship between temperature and the spectral line intensity ratio, select, from multiple candidate temperature intervals, the candidate temperature interval that matches the spectral line intensity ratio of two adjacent absorption spectral lines adjacent to O 2 and / or the spectral line intensity ratio of two adjacent absorption spectral lines adjacent to H 2 O as the target temperature interval.

[0079] Specifically, based on the polynomial function obtained in Step 401, it is obtained that there is a monotonically increasing or decreasing relationship between temperature and the spectral line intensity ratio. In actual measurement, the spectral line intensity ratio of two adjacent absorption spectral lines adjacent to O 2 and / or H 2 can be obtained. Compare the measured spectral line intensity ratio of two adjacent absorption spectral lines adjacent to O 2 and / or H 2 with the spectral line intensity ratios calculated by the polynomial function within multiple candidate temperature intervals. In a specific temperature interval, the theoretical ratio is closest to the measured ratio, and this interval can be determined as the target temperature interval.

[0080] In this embodiment, obtain data points of different temperatures and their corresponding spectral line intensities or ratios from a pre-set database, and use these data points to fit a polynomial function to determine its fitting coefficients. Based on the monotonic functional relationship, select, from multiple candidate temperature intervals, the candidate temperature interval that matches the spectral line intensity ratio of two adjacent absorption spectral lines adjacent to O 2 and / or H 2The interval with the most matching spectral line intensity ratio of O is used as the target temperature interval. This method can effectively determine the temperature interval that is most consistent with the gas absorption characteristics, thereby improving the accuracy and reliability of temperature measurement. By selecting an appropriate target temperature interval, the temperature change in the exhaust gas can be monitored more precisely.

[0081] In one embodiment, determining the exhaust gas temperature value of the chimney duct based on the spectral line intensity ratio of two adjacent absorption spectral lines of a reference gas includes:

[0082] Substituting the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas into a polynomial function with known polynomial coefficients to obtain the exhaust gas temperature value of the chimney duct;

[0083] Wherein, the polynomial function is: , where a , b, c, d, e is the polynomial fitting coefficient;

[0084] The calculation method of the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas is:

[0085] ;

[0086] r is the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas, S ( T ) is the spectral line intensity of the absorption spectral line, K 21 , K 22 are the harmonic signal calibration coefficients of the first and second absorption spectral lines of the reference gas respectively, is the ratio of the second harmonic signal amplitudes of two adjacent absorption spectral lines of the reference gas.

[0087] Specifically, perform polynomial fitting on the relationship between the spectral line intensity ratio of the reference gas H 2 O or O 2 and temperature to determine the polynomial fitting coefficients a , b , c , d , e such that this function can best describe the relationship between the spectral line intensity ratio of the reference gas and temperature. Substitute the measured spectral line intensity of the reference gas into the polynomial function to calculate the temperature value of the exhaust gas in the chimney duct T , . Assume that H 2 O is the reference gas, the polynomial function coefficients of H 2 O are a = 0.01, b = 0.02, c = 0.03, d = 0.04, e = 25, and the H2 Spectral line intensity ratio of O r = 1.5. Substitute r = 1.5 into the polynomial function to calculate the temperature, and the obtained temperature T is 25.2451 K.

[0088] It should be noted that when measuring the exhaust gas parameters, the temperature value is calculated through the second harmonic signal of the double spectral lines. The specific process is as follows: Obtain the 2 H 2 Ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of two gases , calculate The formula for is as follows:

[0089] ;

[0090] In the formula, y represents the gas type H 2 O or O 2 ; and are the maximum values of the second harmonic signals of one of the absorption spectral lines of the reference gas and the maximum value of the second harmonic signal of another absorption spectral line. and are the left bottom foot values and right bottom foot values of the second harmonic signal of one of the absorption spectral lines of the reference gas, and are the left bottom foot values and right bottom foot values of the second harmonic signal of another absorption spectral line of the reference gas. Through calculation, the ratio of the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of the reference gas is obtained.

[0091] Furthermore, under the condition of weak absorption (absorbance ≤ 0.05), the spectral line intensities of two adjacent absorption spectral lines are approximately linearly related to the peak height values of the second harmonic signals of the two adjacent absorption spectral lines. At this time, it can be considered that the spectral line intensity ratio of two adjacent absorption spectral lines is equal to the peak height value ratio of the second harmonic signals of the two adjacent absorption spectral lines. The spectral line intensity ratio r can be as follows:

[0092] ;

[0093] In the formula, K 21 、K 22 are the harmonic signal calibration coefficients of one and another absorption spectral lines of the reference gas respectively. It should be noted that the peak height value of the second harmonic signal of the absorption spectral line can be calculated by subtracting the average value of the left bottom foot value and the right bottom foot value from the maximum value, that is, the peak height value of the second harmonic signal of the absorption spectral line can be expressed as .

[0094] Comparing with step 101, the peak height value of the second harmonic signal of the absorption line and the amplitude of the second harmonic of the absorption line are different names for the same definition. In the subsequent steps, both the amplitude of the second harmonic signal of the absorption line and the peak height value of the second harmonic signal of the absorption line represent the same meaning, that is, the highest value of the second harmonic signal of this absorption line minus the average value of the left and right base values. The formula can be expressed as .

[0095] Exemplarily, when introducing a known standard gas concentration, the calibration coefficient of the harmonic signal can be obtained K , and the calculation formula is as follows:

[0096] K= ;

[0097] In the formula, V pp is the amplitude of the second harmonic signal when introducing the standard gas, b 0 is the zero coefficient, and its value is the amplitude of the harmonic signal when no gas is introduced, is the concentration of the standard gas, is the pressure during calibration, is the calibration optical path, is the spectral line intensity at the calibration temperature, g ( T , P, C ) is the line shape compensation parameter in the calibration environment. It should be noted that all parameters of the standard gas can be obtained by querying the database.

[0098] In this embodiment, through polynomial fitting and precise measurement of the spectral line intensity ratio, this method can provide more accurate exhaust gas temperature measurement results. By determining the polynomial function through polynomial fitting and substituting the measured spectral line intensity of the reference gas into the polynomial function to calculate the temperature value of the exhaust gas in the chimney pipeline, the influence of random errors can be reduced and the reliability of the temperature data can be enhanced. This method can adapt to different working conditions because it is based on actual measurement data for fitting and can adapt to changes in temperature, pressure, and gas concentration. And compared with the contact temperature measurement method, the non-contact measurement method based on the absorption spectroscopy technology reduces the physical wear of the sensor and lowers the maintenance cost.

[0099] In one embodiment, as Figure 5 shown, according to the exhaust gas temperature value and the second harmonic signals of two adjacent absorption lines of the reference gas, the exhaust gas pressure value of the chimney pipeline is determined through the broadening mechanism of the gas line shape function, including the following steps:

[0100] Step 501: Substitute the waste gas temperature value into the full width at half maximum calculation formula for Doppler broadening to obtain the full width at half maximum of Doppler broadening σ g ;

[0101] Specifically, the waste gas temperature has been obtained through the above steps T , and the full width at half maximum of the Doppler broadening formula can be calculated by the following formula: . is the laser wavelength, c is the speed of light, k is the Boltzmann constant, m is the gas molecular mass. Substitute the waste gas temperature value T into the above formula to calculate the full width at half maximum of Doppler broadening σ g .

[0102] Step 502: Obtain the full width at half maximum of the comprehensive broadening through the half height value according to the second harmonic signals of two adjacent absorption spectral lines of the reference gas σ v ; where, is the left base value of the second harmonic signal of one of the two adjacent absorption spectral lines of the reference gas, is the right base value of the second harmonic signal of this absorption spectral line, is the highest value of the second harmonic signal of this absorption spectral line;

[0103] M Exemplarily, taking the reference gas as O 2 as an example, the highest value 2 of the second harmonic signal of one of the absorption spectral lines of O M 1 , the left base value F 1 and the right base value F 3 can be obtained through software; and the highest value M 2 of the second harmonic signal of the other absorption spectral line, the left base value F 2 and the right base value F 4 . Calculate the peak height values of the second harmonic signals of the two absorption spectral lines, compare the peak height values of the second harmonic signals of the two absorption spectral lines, and substitute the highest value and the base value of the larger second harmonic signal of the two absorption spectral lines into the formula to calculate the full width at half maximum of the comprehensive broadening σ v .

[0104] Further, the peak height value of the second harmonic signal of the absorption line of the reference gas can be calculated by subtracting the average value of the left and right base values from the maximum value. That is, the peak height value of the second harmonic signal of one of the absorption lines of the reference gas is M 1 - (F 1 + F 3 ) / 2, and the peak height value of the second harmonic signal of the other absorption line is M 2 - ( F 2 + F 4 ) / 2. Compare the peak height values of the second harmonic signals of the two absorption lines, and substitute the maximum value and the left and right base values in the larger second harmonic signal of one of the absorption lines into the formula to calculate the full width at half maximum of the comprehensive broadening σ v .

[0105] It should be noted that according to the second harmonic signals of two adjacent absorption lines of the reference gas obtained, the full width at half maximum of the comprehensive broadening is obtained through the half value Obtain the full width at half maximum of the comprehensive broadening σ v . Among them y represents the gas type H 2 O or O 2 , is the maximum value of the second harmonic signal of one of the two adjacent absorption lines of the reference gas, is the left base value of the second harmonic signal of one of the two adjacent absorption lines of the reference gas, the right base value of the second harmonic signal of this absorption line.

[0106] Further, i = 1 or 2; the value of i can be determined by comparing the peak height values of the second harmonic signals of the two absorption lines; if the peak height value of the second harmonic signal of one of the absorption lines is larger, then i = 1; if the peak height value of the second harmonic signal of the other absorption line is larger, then i = 2.

[0107] Step 503: Based on the full width at half maximum of the Doppler broadening σ g and the full width at half maximum of the comprehensive broadening σ v , determine the full width at half maximum of the collision broadening σ l ;

[0108] Specifically, a specific formula can be used to determine the full width at half maximum of the collision broadening σ l, this formula comprehensively considers the full width at half maximum σ of Doppler broadening g and the full width at half maximum σ of comprehensive broadening v . The formula is as follows:

[0109] ;

[0110] Among them, σ v is the comprehensive broadening, which is the result of the combined action of collision broadening σ l and Doppler broadening σ g . To calculate σ v and σ g from the known σ l . This formula needs to be rearranged to get:

[0111] ;

[0112] The full width at half maximum of collision broadening σ l can be obtained by solving this equation.

[0113] Step 504: Obtain the pressure value according to the functional relationship between the full width at half maximum of collision broadening σ l and the pressure.

[0114] Specifically, a specific formula can be used to calculate the exhaust gas pressure value in the chimney duct according to the full width at half maximum of collision broadening σ l . This formula considers the influence of the gas pressure P, the saturation pressure P S , the air broadening coefficient γ air , the self-broadening coefficient γ self , and the temperature ratio T 0 / T . The formula is as follows:

[0115] ;

[0116] In this formula, σ l represents the full width at half maximum of collision broadening. γ air is the broadening coefficient caused by collisions with air molecules. γ self is the broadening coefficient caused by self-collisions of molecules. P is the currently measured pressure. P Sis the saturation pressure, i.e., the pressure point at which the gas starts to condense. T 0 is the reference temperature, usually the standard temperature, such as 273K, T is the currently measured temperature. m is an exponent related to the gas properties and measurement conditions, and its value range and calculation formula can be changed according to the actual situation. is the introduced correction coefficient, which is used to make more accurate adjustments for different measurement environments.

[0117] Exemplarily, assume , γ air =0.01, γ self =0.02, P S =1000Pa, T 0 =298K, T = 320K, Substituting each parameter into this formula, the pressure P of the gas can be calculated to be 1227Pa.

[0118] In this embodiment, by using the accurate calculation of Doppler broadening and collision broadening, this method can provide more accurate exhaust gas pressure measurement results. By comprehensively considering Doppler broadening and collision broadening, this method can reduce the influence of random errors and enhance the reliability of pressure data. The non-contact measurement method based on absorption spectroscopy technology reduces the physical wear of the sensor and lowers the maintenance cost.

[0119] In one embodiment, based on the full width at half maximum σ g of Doppler broadening and the full width at half maximum σ v of the comprehensive broadening to determine the full width at half maximum σ l of the collision broadening, the calculation formula is as follows:

[0120] ;

[0121] According to the functional relationship between the full width at half maximum σ l of the collision broadening and the pressure, the calculation formula for the pressure value is as follows:

[0122] ;

[0123] Wherein, P is the pressure value, T is the exhaust gas temperature value, T 0 is the reference temperature, n 1、n 2 and 1 and 2 and 1 and 2 are respectively the temperature correlation coefficient, air broadening coefficient, and self-broadening coefficient corresponding to the second harmonic signals of two adjacent gas absorption spectral lines of the reference gas.

[0124] Specifically, obtained from the broadening mechanism of the gas line shape function, Doppler broadening can be represented by a Gaussian line shape function, and the full width at half maximum (FWHM) of Doppler broadening is:

[0125] ;

[0126] In the formula, m is the molecular mass; k is the Boltzmann constant; c is the speed of light, c = 3×10^10 cm / s. Collision broadening is represented by a Lorentz line shape function, and the full width at half maximum (FWHM) of collision broadening is:

[0127] ;

[0128] In the formula, P is the sample gas pressure; P S is the partial pressure of the absorbing gas; T 0 is the reference temperature, which is 296 K; n、 and are respectively the temperature correlation coefficient, air broadening coefficient, and self-broadening coefficient, obtained through the Hitran database. The Hitran (High-resolution Transmission Molecular Absorption Database) database is a widely used molecular absorption spectral database, which contains a large amount of molecular spectral data. These data are crucial for studying the molecular absorption characteristics in atmosphere and astrophysics. The Hitran database provides the absorption spectral parameters of molecules at different temperatures and pressures, and these parameters can be used to simulate and interpret molecular spectra.

[0129] In actual detection applications, both the full width at half maximum (FWHM) of gas Doppler broadening and the full width at half maximum (FWHM) of collision broadening exist. The full width at half maximum (FWHM) of the combined broadening of the two effects forms the gas spectral line broadening, which is represented by the Voigt line shape function. The full width at half maximum (FWHM) of the combined broadening is:

[0130] ;

[0131] In addition, another calculation method can be used to obtain σ g , σ v and σ l values. Substitute the calculated temperature value T into the full width at half maximum (FWHM) of Doppler broadening σ g formula, and the σ g value can be obtained. The full width at half maximum of Doppler broadening is:

[0132] ;

[0133] In the formula, c is the speed of light, m is the molecular mass; k is the Boltzmann constant; c is the speed of light, c = 3×10^10 cm / s.

[0134] According to the collected second harmonic signal, obtain the comprehensive broadening value through the half-height value σ v . Then, from σ g , σ v values, the σ l is:

[0135] ;

[0136] According to σ l and the functional relationship between

[0137] ;

[0138] where P is the pressure value, T is the exhaust gas temperature value, T 0 is the reference temperature, n 1 、n 2 , , are the temperature correlation coefficient, air broadening coefficient, and self-broadening coefficient corresponding to the second harmonic signals of two adjacent gas absorption lines of the reference gas, respectively.

[0139] Substitute and Compare and select the gas signal with the larger value for the next pressure calculation. Select the second harmonic signals of two adjacent gas absorption spectral lines to obtain the full width at half maximum (FWHM) of the comprehensive broadening and the FWHM of the Doppler broadening respectively. σ v value and the FWHM of the Doppler broadening σ g value, and obtain a system of binary linear equations about pressure P 、 P s :

[0140] ;

[0141] Further obtain the sample gas pressure P value:

[0142] ;

[0143] Among them, P is the pressure value, T is the waste gas temperature value, T 0 is the reference temperature, n 1 、n 2 、 1 、 2 、 1 、 2 are the temperature-related coefficients, air broadening coefficients, and self-broadening coefficients corresponding to the second harmonic signals of two adjacent gas absorption spectral lines of the reference gas respectively.

[0144] In this embodiment, the method accurately calculates the FWHM of the Doppler broadening σ g 、the FWHM of the comprehensive broadening σ v and the FWHM of the collision broadening σ l , so as to accurately calculate the pressure measurement result. By considering the temperature-related coefficient, air broadening coefficient, and self-broadening coefficient, this method can improve the accuracy of the measurement data. The non-contact measurement method reduces the dependence on physical sensors, thereby reducing the maintenance cost and potential failure risk.

[0145] In one embodiment, obtain H 2 O and O 2The second harmonic signals of two adjacent absorption spectral lines, including: a driving signal in the form of a triangular wave formed by superimposing a low-frequency triangular wave on a high-frequency sine wave, and collecting the second harmonic signals at both the rising edge and the falling edge of the triangular wave driving signal to respectively obtain H 2 O and O 2 The second harmonic signals of two adjacent absorption spectral lines; among them, the driving signal in the form of a triangular wave drives the first laser or the second laser within each half cycle (the schematic diagram of collecting the second harmonic signals by the two lasers is as shown in Figure 6 . Among them, signal 1 is the second harmonic signal collected by one of the lasers, signal 2 is the second harmonic signal collected by the other laser, and the two lasers respectively collect the second harmonic signals within a half cycle T).

[0146] Specifically, a low-frequency triangular wave (10 Hz - 100 Hz) is superimposed on a high-frequency sine wave (10 kHz - 100 kHz) to drive and modulate 2 lasers in time segments (1 s - 10 s). Considering that H 2 O and O 2 widely exists in most atmospheres and has a high concentration and a large absorption signal, the characteristic wavelength lasers emitted by the 2 lasers can respectively cover H 2 O and O 2 Two adjacent absorption spectral lines. Within each half cycle, only the first laser emits the characteristic wavelength laser or the second laser emits the characteristic wavelength laser. When emitting light, the driving is in the form of a triangular wave, and the second harmonic signals are collected at both the rising edge and the falling edge of the triangular wave, improving the duty cycle of effective data, reducing the time-consuming of digital average filtering to eliminate white noise, and enhancing the signal-to-noise ratio. After superimposition, the tuning current follows the following law within the cycle:

[0147] ;

[0148] where ， ， respectively represent the two driving currents, frequencies and phases, ， represents the triangular wave modulation coefficient. At the sine current modulation frequency of f m , the output frequency and optical intensity of the laser can be expressed as:

[0149] ,

[0150] .

[0151] In the formula, v c is the center frequency of the laser output;a is the sine modulation amplitude; I c is the light intensity at the laser center frequency; i 0 is the light intensity modulation amplitude; ζ is the phase difference between the frequency modulation and the light intensity modulation. Following the Lambert-Beer law, under weak absorption conditions, the laser light intensity after passing through the absorption medium can be expressed by the Fourier series as: ;

[0152] Let ω = 2πfmt , and further, the nth harmonic signal Hn is:

[0153] ;

[0154] In the formula, Kn is the calibration coefficient of the nth harmonic signal; S ( T ) is the spectral line intensity; P is the gas pressure; L is the measurement optical path; X is the gas concentration.

[0155] The present invention uses the second harmonic signal to measure the exhaust gas parameters, and the second harmonic signal is:

[0156] ;

[0157] In this embodiment, by collecting the second harmonic signal at both the rising edge and the falling edge of the triangular wave driving signal, the signal collection efficiency and quality can be improved, so as to obtain more accurate H 2 O and O 2 absorption spectral line data. This method can reduce the time-consuming of digital average filtering, eliminate white noise, thereby improving the signal-to-noise ratio and making the detection of absorption spectral lines more sensitive and accurate. Driving only one laser in each half cycle can optimize the use efficiency of the laser, reduce energy consumption, and extend the service life of the laser. By accurately collecting the H 2 O and O 2 absorption spectral line data, polynomial fitting can be performed more accurately, and then the temperature and pressure values of the exhaust gas can be determined. This method is applicable to harsh environments such as high temperature, high humidity, and high corrosion, improving the applicability of the monitoring system.

[0158] In one embodiment, determining the concentration value of O 2 and the humidity value of the exhaust gas based on the exhaust gas temperature value of the chimney pipe and the exhaust gas pressure value of the chimney pipe, including:

[0159] Substitute the exhaust gas temperature value and the exhaust gas pressure value of the chimney duct into the concentration calculation formula to obtain the concentration value of O 2 and the humidity value of the exhaust gas; among them, the concentration calculation formula is:

[0160] ;

[0161] Among them, is the concentration value, and y represents the gas type O 2 or H 2 O, is the left bottom foot value of the second harmonic signal of one of the adjacent two absorption spectral lines of O 2 or H 2 O, is the right bottom foot value of the second harmonic signal of this absorption spectral line, , H 2 The concentration value of O is equal to the humidity value of the exhaust gas, L represents the optical path, b 0 、K y are the zero absorption coefficient and the calibration coefficient respectively, v c is the central frequency output by the first laser or the second laser, S ( T ) is the spectral line intensity of the gas, and S ( T ) is related to the exhaust gas temperature value of the chimney duct.

[0162] Specifically, when the exhaust gas temperature value T and the exhaust gas pressure value P of the chimney duct are known, substitute the exhaust gas temperature value and the exhaust gas pressure value in the chimney duct into the concentration calculation formula to obtain the concentration value of O 2 and the humidity value of the exhaust gas. The concentration calculation formula is:

[0163] ;

[0164] Among them, is the concentration value, y represents the gas type O 2 or H 2 O, is the left bottom foot value of the second harmonic signal of one of the adjacent two absorption spectral lines of O 2 or H 2 O, is the right bottom foot value of the second harmonic signal of this absorption spectral line, . If the gas is H 2 O, the concentration value of H 2 O is equal to the humidity value of the exhaust gas; if the gas is O2 represents the concentration value of O 2 gas. L represents the optical path, b 0 , K y are the zero absorption coefficient and the calibration coefficient respectively, which are obtained when introducing the zero standard gas and the full-scale standard gas with known concentrations, and the values are stored in the hardware storage chip and automatically called during concentration calculation. v c is the central frequency output by the first laser or the second laser, S ( T ) is the spectral line intensity of the gas, and S ( T ) is related to the waste gas temperature value of the chimney duct. The S ( T ) parameters of conventional gases can be queried in the molecular spectroscopy database Hitran. The S ( T ) at a certain temperature can be calculated by the following formula:

[0165] ;

[0166] In the formula, Q ( T ) is the intramolecular partition function, is the reference temperature T 0 under which the intramolecular partition function, E is the intramolecular transition basic energy, h is the Planck constant, k is the Boltzmann constant, c is the speed of light, S ( T 0 ) is the spectral line intensity at the reference temperature T 0 under.

[0167] It should be noted that when calculating the concentration value of O 2 , it is necessary to compare the peak height values of the second harmonic signals of two adjacent absorption lines of O 2 to determine which absorption line has the highest value of the second harmonic signal and the left and right bottom values that can be substituted into the calculation formula to calculate the concentration of O 2 . Similarly, when calculating the humidity value of the waste gas, it is necessary to compare the peak height values of the second harmonic signals of two adjacent absorption lines of H 2 O to determine which absorption line has the highest value of the second harmonic signal and the left and right bottom values that can be substituted into the calculation formula to calculate the humidity of the waste gas.

[0168] In this embodiment, through precise mathematical formulas for calculation, this method can provide accurate O 2 concentration and waste gas humidity measurement results. Combining parameters such as temperature, pressure, optical path, and spectral line intensity, this method reduces measurement errors and improves the reliability of data.

[0169] In one embodiment, determine the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of H 2 O and the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of O 2 and select the maximum value from the amplitudes of the four second harmonic signals;

[0170] Obtain the frequency shift of the center frequency of the absorption spectral line corresponding to the maximum value Δυ , and determine the waste gas flow velocity V of the chimney duct according to the frequency shift Δυ ; the calculation formula for the waste gas flow velocity V is:

[0171]

[0172] where is the center frequency of the absorption spectral line, φ is the incident angle when the laser with the characteristic wavelength emitted by the first laser and the second laser is combined into one path by the coupler and then incident on the other side of the chimney duct.

[0173] Specifically, the flow velocity measurement is based on the Doppler effect. The lasers emitted by 2 lasers are collimated and then enter the coupler. After combining the 2 paths of lasers into one path, and then through the beam splitter, the light energy is divided in a ratio of 1:1, and the light rays are at an angle φ incident on the other side of the chimney duct. The optical signals attenuated by absorption of the measured gas are respectively received by the first photodetector 1 and the second photodetector 2, and signal processing is performed through the signal processing circuit.

[0174] Furthermore, compare the amplitudes of the second harmonic signals of the four absorption spectral lines corresponding to H 2 O and O 2 two gases, and select one absorption spectral line with the largest amplitude of the second harmonic signal for subsequent calculation, that is, perform flow velocity calculation.

[0175] The second harmonic signals corresponding to the absorption of 2 beams of light will shift, that is, the center frequency of the absorption spectral line will shift, and the frequency shift is Δυ , and the waste gas flow velocity formula is used to calculate V :

[0176]

[0177] where c is the speed of light, c = 3×1010 cm / s, and the frequency shift is Δυ , is the central frequency of the absorption line φ is the incident angle when the laser with characteristic wavelengths emitted by the first laser and the second laser is combined into one path by the coupler and then incident on the other side of the chimney duct

[0178] In this embodiment, the frequency shift of the absorption line is used to determine the flow rate, providing a high-precision flow rate measurement method, especially suitable for high-speed gas flows. This method does not require physical contact with the exhaust gas, reducing the wear and maintenance requirements of the measuring equipment, lowering the maintenance cost, and also reducing the potential safety hazards during the measurement process. And using this method can provide real-time flow rate data, which helps to adjust relevant parameters in a timely manner and optimize the combustion efficiency

[0179] Based on the same inventive concept, the embodiment of the present application also provides a device for implementing the above-mentioned exhaust gas detection applied to a chimney duct, as Figure 7 shown, an exhaust gas detection device applied to a chimney duct, the device includes:

[0180] A signal generation circuit that generates a low-frequency triangular wave and a high-frequency sine wave in different time periods

[0181] A laser, including a first laser and a second laser, the low-frequency triangular wave superimposed on the high-frequency sine wave drives the first laser and the second laser in different time periods, and the laser with characteristic wavelengths emitted by the first laser and the second laser are both used to pass through the exhaust gas in the chimney duct. The laser with characteristic wavelengths emitted by one of the first laser and the second laser can cover two adjacent absorption lines of H 2 O, and the laser with characteristic wavelengths emitted by the other can cover two adjacent absorption lines of O 2

[0182] A photodetector that receives the laser passing through the exhaust gas in the chimney duct

[0183] A signal processing circuit that performs the above series of steps based on the laser passing through the exhaust gas in the chimney duct

[0184] Specifically, the signal generation circuit 1 generates a driving signal for controlling the operation of the laser in different time periods, and the driving signal is a signal generated by superimposing a low-frequency triangular wave on a high-frequency sine wave. The laser 2 and the laser 5, the laser with characteristic wavelengths emitted by each laser are both used to pass through the exhaust gas in the chimney duct. The laser with characteristic wavelengths emitted by one of the first laser and the second laser can cover two adjacent absorption lines of H 2 O, and the laser with characteristic wavelengths emitted by the other can cover two adjacent absorption lines of O 2 ​Two adjacent absorption spectral lines. The first temperature control circuit 3 and the second temperature control circuit 4 are used to control and maintain the operating temperature of the laser, ensuring the stability of the laser and the accuracy of the measurement. The first collimator 6 and the second collimator 7 are used to adjust the direction and shape of the light beam, ensuring that the laser can accurately pass through the waste gas in the chimney pipe. The coupler 8 is used to combine the light beams of the two lasers into one path for measuring the absorption spectral lines of H 2 O and O 2 absorption spectral lines. The beam splitter 9 divides the combined light beam into two paths again for separately measuring the absorption spectral lines of H 2 O and O 2 absorption spectral lines. The chimney pipe 10 is the passage for waste gas emission. The laser beam passes through the waste gas in the pipe to measure the absorption spectral lines of the waste gas. The first photodetector 11 and the second photodetector 12 are used to receive the laser after passing through the waste gas, and the detectors convert the optical signal into an electrical signal for subsequent processing. The signal processing circuit 13 receives the output signal of the photodetector and performs data processing. The display screen 14 is used to display the measurement results for the operator to monitor. Wherein the air flow is the waste gas flow in the chimney pipe.

[0185] In this embodiment, by using this waste gas parameter detection device based on the absorption spectroscopy technology, the waste gas parameters in the chimney pipe, including temperature, pressure, flow rate, humidity and oxygen concentration, can be monitored in real time and accurately. This non-contact measurement reduces physical wear, extends the equipment life, and reduces the cost of maintaining the equipment.

[0186] It should be noted that, as Figure 8 shown, for a method and device for measuring waste gas parameters based on the absorption spectroscopy technology provided in this application, for monitoring the temperature, pressure, flow rate, humidity and oxygen concentration in the waste gas in the chimney by this method and device, the specific steps are as follows:

[0187] Step 801: Drive and modulate two lasers in a time-division manner by superimposing a low-frequency triangular wave and a sine wave. The laser beams with characteristic wavelengths emitted by the two lasers can respectively cover the absorption spectral lines of H 2 O and two absorption spectral lines;

[0188] Step 802: Obtain the H 2 O, O 2 Compare the amplitudes of the second harmonic signals of two adjacent absorption spectral lines of the two gases to obtain the spectral line intensity ratio r, and obtain the temperature value T through polynomial fitting;

[0189] Step 803: Calculate the pressure through the broadening mechanism of the gas line shape function. From σ g , σ v value, obtain the full width at half maximum of collision broadening σ l value, according toσ l The function relationship with pressure P to obtain the pressure value;

[0190] Step 804: Calculate the sample gas flow velocity based on the Doppler effect V ;

[0191] Step 805: Obtain the sample gas temperature T and pressure P calculated above, substitute them into the derived concentration calculation formula, and respectively obtain the humidity and oxygen concentration values.

[0192] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0193] The above embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for detecting exhaust gas from a chimney pipe, characterized in that: The method comprises: Obtaining the ratio of the second harmonic signal amplitudes of two adjacent absorption lines of H2O and the ratio of the second harmonic signal amplitudes of two adjacent absorption lines of O2; driving the first laser and the second laser in time periods by superimposing a low-frequency triangular wave with a high-frequency sine wave, the characteristic wavelength lasers emitted by the first laser and the second laser are both used for the exhaust gas passing through the chimney pipe, and the characteristic wavelength laser emitted by one of the first laser and the second laser can cover the two adjacent absorption lines of H2O, and the characteristic wavelength laser emitted by the other laser can cover the two adjacent absorption lines of O2; Determine the line intensity ratio of the two adjacent absorption lines of H2O based on the ratio of the second harmonic signal amplitudes of the two adjacent absorption lines of H2O, and determine the line intensity ratio of the two adjacent absorption lines of O2 based on the ratio of the second harmonic signal amplitudes of the two adjacent absorption lines of O2; Obtaining the fitting correlation coefficient between the line intensity ratio of the two adjacent absorption lines of O2 and the temperature and the fitting correlation coefficient between the line intensity ratio of the two adjacent absorption lines of H2O and the temperature, taking the gas corresponding to the largest fitting correlation coefficient as the reference gas, and determining the exhaust gas temperature value of the chimney pipe based on the line intensity ratio of the two adjacent absorption lines of the reference gas; According to the exhaust gas temperature value and the second harmonic signals of two adjacent absorption lines of the reference gas, the exhaust gas pressure value of the chimney pipe is determined by the broadening mechanism of the gas linear function, and the concentration value of O2 and the humidity value of the exhaust gas are determined based on the exhaust gas temperature value of the chimney pipe and the exhaust gas pressure value of the chimney pipe; Obtaining a fitting correlation coefficient between the line intensity ratio of two adjacent absorption lines of O2 and temperature and a fitting correlation coefficient between the line intensity ratio of two adjacent absorption lines of H2O and temperature, and taking a gas corresponding to a largest fitting correlation coefficient as a reference gas, including: determining a target temperature range according to the line intensity ratio of two adjacent absorption lines of O2 and / or the line intensity ratio of two adjacent absorption lines of H2O; obtaining a fitting correlation coefficient corresponding to O2 and a fitting correlation coefficient corresponding to H2O in the target temperature range, and taking a gas corresponding to a largest fitting correlation coefficient as a reference gas; Wherein, determining the target temperature interval according to the spectral line intensity ratio of the two adjacent absorption lines of O2 and / or the spectral line intensity ratio of the two adjacent absorption lines of H2O includes: obtaining a polynomial function; the polynomial function is a monotonic function, and the temperature and the spectral line intensity ratio are a monotonic function relationship, which can be fitted through data points in a preset database to obtain the polynomial coefficients of the polynomial function, and the data points include different temperatures and the corresponding spectral line intensities or spectral line intensity ratios at different temperatures; based on the monotonic function relationship between the temperature and the spectral line intensity ratio, selecting a candidate temperature interval that matches the spectral line intensity ratio of the two adjacent absorption lines of O2 and / or the spectral line intensity ratio of the two adjacent absorption lines of H2O from multiple candidate temperature intervals as the target temperature interval.

2. The exhaust gas detection method according to claim 1, characterized in that: Determining the exhaust gas temperature value of the chimney pipe based on the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas includes: Substituting the spectral line intensity ratio of two adjacent absorption spectral lines of the reference gas into a polynomial function with known polynomial coefficients to obtain the exhaust gas temperature value of the chimney pipe; The polynomial function is: , a, b, c, d, e are the polynomial fitting coefficients; The calculation method for the intensity ratio of two adjacent absorption lines of the reference gas is: ； r is the intensity ratio of two adjacent absorption lines of the reference gas, S(T) is the intensity of the absorption line, K 21 , K 22 are the harmonic signal calibration coefficients of the first and second absorption lines of the reference gas, It is the ratio of the second harmonic signal amplitudes of two adjacent absorption lines of the reference gas.

3. The exhaust gas detection method according to claim 1, characterized in that: According to the exhaust gas temperature value and the second harmonic signals of two adjacent absorption spectral lines of the reference gas, the exhaust gas pressure value of the chimney pipe is determined through the broadening mechanism of the gas linear function, including: Substitute the exhaust gas temperature value into the half-maximum full width calculation formula of Doppler broadening to obtain the half-maximum full width of Doppler broadening σ g ; According to the second harmonic signals of two adjacent absorption lines of the reference gas, the half-height value Get the full width at half maximum of the comprehensive stretch σ v ;in, is the left foot value of the second harmonic signal of one of the two adjacent absorption lines of the reference gas, is the right foot value of the second harmonic signal of the absorption spectrum line, is the maximum value of the second harmonic signal of the absorption spectrum line; Based on the full width at half maximum of the Doppler broadening σ g and the half-maximum width of the comprehensive broadening σ v , determine the full width at half maximum of collision broadening σ l ; Full width at half maximum according to collision broadening σ l The functional relationship between pressure and pressure is used to obtain the pressure value.

4. The exhaust gas detection method according to claim 3, characterized in that: Based on the full width at half maximum of the Doppler broadening σ g and the half-maximum width of the comprehensive broadening σ v Determine the full width at half maximum of collision broadening σ l The calculation formula is as follows: ； Full width at half maximum according to collision broadening σ l The calculation formula of the pressure value is as follows: ； in, P is the pressure value, T is the exhaust gas temperature, T 0 is the reference temperature, n 1 、n 2.

1.

2.

1. 2 are the temperature correlation coefficient, air broadening coefficient and self-broadening coefficient corresponding to the second harmonic signals of two adjacent gas absorption lines of the reference gas.

5. The exhaust gas detection method according to claim 1, characterized in that: Obtain the second harmonic signals of two adjacent absorption lines of H2O and O2 respectively, including: A triangular wave driving signal is formed by superimposing a low-frequency triangular wave on a high-frequency sine wave. Second harmonic signal acquisition is performed at both the rising and falling edges of the triangular wave driving signal to obtain the second harmonic signals of two adjacent absorption lines of H2O and O2 respectively; wherein the triangular wave driving signal drives the first laser or the second laser in each half cycle.

6. The exhaust gas detection method according to claim 1, characterized in that: Determining the concentration value of O2 and the humidity value of the exhaust gas based on the exhaust gas temperature value of the chimney pipe and the exhaust gas pressure value of the chimney pipe includes: Substitute the exhaust gas temperature value of the chimney pipe and the exhaust gas pressure value of the chimney pipe into the concentration calculation formula to obtain the concentration value of O2 and the humidity value of the exhaust gas; wherein the concentration calculation formula is: ； in, is the concentration value, y Represents gas type O2 or H2O, It is the left foot value of the second harmonic signal of one of the two adjacent absorption lines of O2 or H2O. is the right foot value of the second harmonic signal of the absorption spectrum line, is the highest value of the second harmonic signal of the absorption spectrum line, and the concentration of H2O is equal to the humidity value of the exhaust gas. L represents the optical path, b 0. K y are the zero point absorption coefficient and the calibration coefficient, respectively. v c The center frequency of the first laser or the second laser output ,S(T) is the spectral line intensity of the gas, and S(T) Related to the exhaust gas temperature value of the chimney duct.

7. The exhaust gas detection method according to claim 1, characterized in that: The method further comprises: Determine the amplitudes of the second harmonic signals of two adjacent absorption lines of H2O and the amplitudes of the second harmonic signals of two adjacent absorption lines of O2, and select the maximum value from the amplitudes of the four second harmonic signals; Obtain the frequency shift of the center frequency of the absorption spectrum line corresponding to the maximum value △υ , according to the frequency shift △υ Determine the exhaust gas flow rate of the chimney duct V ; Exhaust gas flow rate V The calculation formula is: ； in, is the center frequency of the absorption line, φ It is the incident angle of the laser beams with characteristic wavelengths emitted by the first laser and the second laser after being combined by the coupler and incident on the other side of the chimney pipe.

8. An exhaust gas detection device applied to a chimney pipe, characterized in that: The device comprises: The signal generating circuit generates low-frequency triangle waves and high-frequency sine waves in different time periods; The laser comprises a first laser and a second laser, wherein the low-frequency triangular wave superimposed on the high-frequency sine wave drives the first laser and the second laser in time periods, the characteristic wavelength lasers emitted by the first laser and the second laser are both used for exhaust gas passing through the chimney pipe, and the characteristic wavelength laser emitted by one of the first laser and the second laser can cover two adjacent absorption lines of H2O, and the characteristic wavelength laser emitted by the other laser can cover two adjacent absorption lines of O2; a photodetector to receive laser light from exhaust gas passing through the chimney duct; A signal processing circuit executes the exhaust gas detection method for a chimney pipe according to any one of claims 1 to 7 based on the laser of the exhaust gas passing through the chimney pipe.

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