CF4 gas detection method, system and equipment based on FTIR (Fourier transform infrared spectroscopy) and medium

Abstract

The invention discloses a CF4 gas detection method, system and equipment based on FTIR (Fourier Transform Infrared Spectroscopy) and a medium, and relates to the technical field of greenhouse gas detection. The method comprises the following steps: setting a standard concentration range, measuring gas concentration values and corresponding absorbance values under each standard concentration in an FTIR (Fourier Transform Infrared Spectroscopy) measurement system, and establishing a working fitting curve of absorbance and concentration; establishing a fitting objective function based on the working fitting curve; and carrying out iterative solution on the fitting objective function, determining optimal parameters, obtaining a final FTIR gas concentration calibration curve, and detecting the CF4 gas by using the FTIR gas concentration calibration curve. According to the invention, the accuracy and efficiency of monitoring can be improved, and on-line monitoring of CF4 gas is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of greenhouse gas detection, and particularly to a method, system, device and medium for detecting CF4 gas based on FTIR. Background Art

[0002] In the field of gas detection, traditional chemical methods have the advantages of direct measurement means and high measurement accuracy. However, they require pre-sampling of the gas to be measured, with cumbersome operations and no timeliness. Tetrafluoromethane (CF4) gas is one of the six greenhouse gases listed in the Kyoto Protocol and is also a greenhouse gas with a very strong global warming potential. According to the IPCC survey, the electrolytic aluminum industry is the main global source of CF4 gas emissions. Currently, the accounting method for perfluorocarbon gases generated by electrolytic aluminum mainly relies on the "Accounting Methods and Reporting Guidelines for Greenhouse Gas Emissions of Chinese Electrolytic Aluminum Enterprises (Trial)", and the measurement results have large errors and cannot achieve the purpose of real-time monitoring. Therefore, there is currently a lack of a real-time and effective detection method for CF4 gas. Summary of the Invention

[0003] The purpose of the present invention is to provide a method, system, device and medium for detecting CF4 gas based on FTIR, which can improve the accuracy and efficiency of monitoring and realize the on-line monitoring of CF4 gas.

[0004] To achieve the above purpose, the present invention provides the following solutions:

[0005] A method for detecting CF4 gas based on FTIR includes:

[0006] Setting a standard concentration range, measuring the gas concentration values and corresponding absorbance values at each standard concentration in the FTIR measurement system, and establishing a working fitting curve of absorbance and concentration;

[0007] Establishing a fitting objective function based on the working fitting curve;

[0008] Performing iterative solution on the fitting objective function to determine the optimal parameters, obtaining the final FTIR gas concentration calibration curve, and using the FTIR gas concentration calibration curve to detect CF4 gas.

[0009] Optionally, the setting of the standard concentration range, measuring the gas concentration values and corresponding absorbance values at each standard concentration in the FTIR measurement system, and establishing a working fitting curve of absorbance and concentration specifically includes:

[0010] Setting a standard concentration range;

[0011] Measure the gas concentration values at various standard concentrations in the FTIR measurement system, preprocess the measurement data, and determine the absorbance values corresponding to the gas concentration values according to the processed data;

[0012] Establish a working fitting curve of absorbance versus concentration based on the gas concentration values and the corresponding absorbance values.

[0013] Optionally, the preprocessing includes data smoothing, baseline correction, and normalization; wherein, the data smoothing uses a Savitzky-Golay filter; the baseline correction corrects the baseline drift by polynomial fitting of the baseline; the normalization uses an L2 normalization function.

[0014] Optionally, the fitting objective function is expressed as:

[0015]

[0016] where A measured,i is the absorbance value, A0 is the background absorbance, ∈(T,P) is the function of the molar extinction coefficient varying with temperature and pressure, k(T,P) is the correction factor, c i is the gas concentration, and l is the optical path length.

[0017] Optionally, the process of iteratively solving the fitting objective function includes:

[0018] Set the initial parameters p (0) , where p includes undetermined coefficients; the undetermined coefficients include the molar extinction coefficient ∈, the background absorbance A0, and the correction factor k(T,P);

[0019] Calculate the Jacobian matrix J and the residual r of the fitting objective function, and solve the fitting objective function:

[0020] p (k+1 ) = p (k) - (J T J) -1 J T r

[0021] Iteratively solve for the update amount Δp until the termination condition is met: p (k+1) = p (k) + Δp; where:

[0022] Δp = (J T J) -1 J T r

[0023] When ||Δp|| < ∈ or the maximum number of iterations is reached, the iteration stops, substitute the optimal undetermined coefficients into the objective function to obtain the calibration curve, and according to the actually measured absorbance value A measuredCalculating the gas concentration c through the calibration curve o .

[0024] The present invention also provides an FTIR-based CF4 gas detection system, including:

[0025] A data acquisition unit, configured to set a standard concentration range, measure the gas concentration values and the corresponding absorbance values at each standard concentration in the FTIR measurement system, and establish a working fitting curve of absorbance and concentration;

[0026] A target function establishment unit, configured to establish a fitting target function based on the working fitting curve;

[0027] An iterative optimization and gas detection unit, configured to perform iterative solution on the fitting target function, determine the optimal parameters, obtain the final FTIR gas concentration calibration curve, and detect CF4 gas by using the FTIR gas concentration calibration curve.

[0028] The present invention also provides an electronic device, including a memory and a processor, where the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the above-mentioned FTIR-based CF4 gas detection method.

[0029] The present invention also provides a computer-readable storage medium, which stores a computer program, and when the computer program is executed by a processor, it implements the above-mentioned FTIR-based CF4 gas detection method.

[0030] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0031] The present invention discloses an FTIR-based CF4 gas detection method, system, device and medium. The method includes setting a standard concentration range, measuring the gas concentration values and the corresponding absorbance values at each standard concentration in the FTIR measurement system, and establishing a working fitting curve of absorbance and concentration; establishing a fitting target function based on the working fitting curve; performing iterative solution on the fitting target function, determining the optimal parameters, obtaining the final FTIR gas concentration calibration curve, and detecting CF4 gas by using the FTIR gas concentration calibration curve. The present invention can improve the accuracy and efficiency of monitoring and realize the on-line monitoring of CF4 gas. Description of the Drawings

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 Schematic diagram of the CF4 gas detection method process in this embodiment;

[0034] Figure 2 Schematic diagram of the absorption spectra and absorption peaks of CF4 gas at different concentrations in this embodiment;

[0035] Figure 3 Linear fitting graph of the CF4 absorption peak value and concentration in this embodiment;

[0036] Figure 4 Fitted curve graph of absorbance-concentration of the data processed based on the above algorithm in this embodiment;

[0037] Figure 5 Schematic diagram of the absorbance data without algorithm processing in this embodiment;

[0038] Figure 6 Schematic diagram of the connection of the system device in this embodiment.

[0039] Reference numerals: 1, infrared light source; 2, interferometer; 3, sample cell; 4, IR detector; 5, computer; 6, dynamic gas calibrator; 7, CF4 standard gas; 8, N2 standard gas. Detailed implementation manners

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0041] The purpose of the present invention is to provide a CF4 gas detection method, system, device and medium based on FTIR, which can improve the accuracy and efficiency of monitoring and realize the online monitoring of CF4 gas.

[0042] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific implementation manners.

[0043] As Figure 1As shown in the figure, the present invention provides a method for detecting CF4 gas based on FTIR, which can overcome the deficiencies of the prior art in detecting CF4 gas. What the present invention aims to achieve is to introduce CF4 gas with different concentrations into the FTIR device to obtain the absorption spectra of CF4 gas with different concentrations, and establish a working fitting curve of absorbance and concentration through characteristic absorption peaks, so as to quickly detect the concentration of CF4 gas.

[0044] As a specific technical solution of the above concept, it mainly includes:

[0045] The CF4 standard gas and N2 are proportioned through a dynamic gas calibrator to obtain CF4 gas with different concentration gradients, which is introduced into the sample cell. A laser is generated by an infrared light source, and after passing through an interferometer, it is divided into two beams of light to form an optical path difference and interfere. The emitted interference light passes through the CF4 gas in the sample cell. Gas molecules will undergo vibrational energy level transitions and absorb the infrared light energy with the same vibration frequency as theirs, weakening the infrared light energy in several specific bands. The outgoing light beam carries the characteristic absorption information of the sample and is converted into an electrical signal by the IR detector and transmitted to the computer. Then, the Fourier transform algorithm is used to analyze the signal, and finally the absorption spectrum information of the sample is extracted.

[0046] Use FTIR technology to perform spectral analysis on CF4 gas with different concentrations, extract the characteristic peak values of its spectral lines, and construct a working curve between gas concentration and spectral peak values through linear fitting. To ensure data quality, first perform preprocessing steps such as smoothing, baseline correction, and normalization on the spectral data to reduce the influence of noise and baseline drift. After generating a working curve using the preprocessed spectral data, for CF4 gas with unknown concentration, its concentration can be accurately calculated by substituting the measured characteristic peak value into the working curve. This method significantly improves the accuracy of CF4 gas monitoring and realizes real-time online monitoring of greenhouse gas emissions during the electrolytic aluminum process.

[0047] The system device includes: infrared light source 1, interferometer 2, sample cell 3, IR detector 4, computer 5, dynamic gas calibrator 6, CF4 standard gas 7, and N2 standard gas 8.

[0048] Data preprocessing

[0049] In the Fourier transform infrared absorption spectroscopy (FTIR) measurement system, due to environmental noise interference in practical applications, it will cause large errors in the measurement results. Therefore, appropriate methods need to be used to preprocess the data before data processing. The specific steps include smoothing the data, baseline correction, and normalization to ensure the consistency and accuracy of the data. These steps significantly improve the quality of spectral data by reducing noise, correcting baseline drift, and scaling the data to the same scale, providing a more reliable basis for subsequent quantitative analysis and modeling.

[0050] To reduce noise, the Savitzky-Golay filter is used to smooth the data. The Savitzky-Golay filter smooths the data by performing polynomial fitting within a sliding window.

[0051]

[0052] Where: y i is the original spectral data point; y' i is the smoothed data point; k is half of the window size; c j are the coefficients of the Savitzky-Golay filter.

[0053] Subsequently, the baseline drift is corrected by fitting the baseline with a polynomial. The baseline correction steps are as follows: 1. Select an appropriate polynomial order n. 2. Fit the polynomial baseline using the least squares method. 3. Subtract the fitted baseline from the spectral data.

[0054]

[0055] Where: y baseline (x) is the fitted baseline; a i are the polynomial coefficients; x is the wavelength or frequency.

[0056] The corrected spectral data is:

[0057] y corrected (x) = y smoothed (x) - y baseline (x)

[0058] Finally, the purpose of using L2 normalization is to scale the spectral data to the same scale to eliminate the influence of the light source intensity change.

[0059]

[0060] Where: y normalized (x) is the normalized spectral data; N is the total number of spectral data points.

[0061] The preprocessed spectral data can significantly improve the signal-to-noise ratio and data consistency, enhance the identification of characteristic peaks, eliminate systematic errors, and thus improve the accuracy and efficiency of the analysis.

[0062] Establishment of the objective function: According to the Beer-Lambert law: A = ∈·c·l.

[0063] Where, ∈ is the molar extinction coefficient, c is the substance concentration, and l is the optical path length.

[0064] According to the actual situation, the temperature T, pressure P, and background absorbance A0 are introduced and extended to:

[0065]

[0066] Among them, ∈(T, P) represents the function of the molar absorption coefficient varying with temperature and pressure, k(T, P) is the correction factor, and A0 is the background absorbance.

[0067] Based on the above formula, the objective function of absorbance A and gas concentration c is established. Let the measured absorbance be A measured,i , and the theoretically calculated absorbance be A calculated,i , then the objective function is:

[0068]

[0069] The relative error δ i is defined as:

[0070]

[0071] Define the sum of squared total errors S as the objective function:

[0072]

[0073] The goal is to minimize the sum of squared total errors S to the minimum.

[0074] For the least squares fitting, in order to minimize the sum of squared errors, the Gauss - Newton iteration method is used for fitting:

[0075] 1. Initial parameter setting

[0076] Set the initial parameter p (0) , where p includes undetermined coefficients such as the molar absorption coefficient ∈, background absorbance A0, and correction factor k e .

[0077] 2. Iteration process

[0078] In each iteration step, update the parameter p: p (k+1) = p (k) - (J T J) -1 J T r

[0079] Among them, J is the Jacobian matrix and r is the residual vector.

[0080] The Jacobian matrix J:

[0081] Among them, r i is the i - th residual, and p j is the j - th parameter.

[0082] Residual vector r: r i = A measured,i - A calculated,i

[0083] Express the residual as:

[0084] Then calculate the Jacobian matrix:

[0085] The iteration stops when the condition is met.

[0086] Determination of the calibration curve: Determine the final FTIR gas concentration calibration curve through the optimal parameters obtained by iterative calculation. The calibration curve can be used to convert the measured absorbance into gas concentration.

[0087] Based on the above technical solutions, the following embodiments are provided.

[0088] High-purity nitrogen is used as the background gas in the experiment. After introducing high-purity nitrogen and purging for 5 minutes, when the instrument signal is stable, prepare to collect the background spectrum. First, test high-purity nitrogen. After the data is stable, test the gas to be measured, and store the test results in the computer. FTIR spectrometer test parameters: resolution 4 cm -1 ; Spectral acquisition range: 4500 cm -1 - 800 cm -1 .

[0089] Select 16 scans. Introduce CF4 standard gas for testing. Sequentially introduce the prepared CF4 gas into the gas cell of the FTIR and save the spectrum after stabilization. Since temperature and pressure have a great influence on the gas concentration, when establishing the working curve, the temperature and pressure of the standard gas for each concentration should be kept consistent, and at the same time, the temperature and pressure at this time should also be kept consistent with the temperature and pressure of the sample gas to be measured.

[0090] Experiment with different concentrations of CF4 gas to obtain the absorption spectrum of CF4 gas in the range of 1240 cm -1 ~ 1320 cm -1 as shown in Figure 2 It can be seen that there is an obvious absorption peak near 1280 cm -1 .

[0091] Select the absorption peak value near 1280 cm -1 for algorithm processing. As shown in Figure 3 the fitting formula of CF4 concentration and absorbance is obtained as: where R 2= 0.9878, the optimal molar absorptivity is 0.0039, the optimal correction factor is 0.7155, and the optimal background absorptivity is 0.0184.

[0092] Figure 4 For the data processed by the algorithm, the parameters of the target equation are A0 = 0.179128, epsilon = 4.820794, and k = 9.118819. The linear equation y = 0.476419x + 0.179128 is obtained by fitting with the patented method. The coefficient of determination R² reaches 0.999536, the mean square error MSE is 0.002514, and the mean absolute error MAE is 0.048669.

[0093] Figure 5 For the unprocessed data, the linear equation fitted by the patented method is y = 0.649824x - 0.808950, and the coefficient of determination R 2 is 0.981780, the mean square error MSE is 0.186954, and the mean absolute error MAE is 0.325714.

[0094] Comparing the coefficients of determination of the two groups of data, Figure 4 the coefficient of determination of the data processed by the algorithm is higher, indicating that its fitted curve has a stronger ability to explain the data. Comparing the mean square error and the mean absolute error, the error values of the data processed by the algorithm in Figure 4 are much smaller than Figure 5 the unprocessed data. It can be seen that using the algorithm to process the data greatly improves the accuracy of data fitting, and the effect is significantly improved compared with the data without using the algorithm.

[0095] Therefore, the present solution has the following beneficial effects:

[0096] (1) The FTIR technique can detect carbon tetrafluoride gas with high sensitivity and specificity. Since carbon tetrafluoride molecules have unique absorption peaks in the infrared spectral range, the FTIR device can accurately identify and measure carbon tetrafluoride while avoiding interference from other gas components. (2) The FTIR detection method can provide the ability to monitor and analyze carbon tetrafluoride gas in real time. Compared with traditional sample collection and laboratory analysis methods, the FTIR technique can complete the detection and analysis of gas samples within a few seconds, enabling timely response and accurate determination. (3) Compared with some other analytical methods, the FTIR detection method is a non-destructive analytical technique. This means that the sample does not need to be destructively processed or treated during the detection and analysis process, thus maintaining the integrity and original characteristics of the sample, reducing the complexity of experimental operations and the cost of sample processing. (4) The algorithm has strong noise reduction ability. It uses the Savitzky-Golay filter to smooth the data while maintaining data details; eliminates baseline drift through baseline correction to improve the accuracy of measurement data; L2 normalization enhances the robustness of the data and avoids systematic errors caused by changes in light source intensity; uses the Gauss-Newton iteration method for high-precision non-linear fitting, which can quickly find the optimal parameters to ensure the accuracy of the calibration curve; further optimizes the calibration curve by minimizing the sum of squared errors, significantly improving the accuracy of gas concentration measurement.

[0097] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other.

[0098] Specific examples are used in this article to elaborate on the principles and implementation manners of the present invention. The descriptions of the above embodiments are only used to help understand the core idea of the present invention; at the same time, for those of ordinary skill in the art, based on the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A CF4 gas detection method based on FTIR, characterized in that, Including: Set the standard concentration range, measure the gas concentration values and the corresponding absorbance values at each standard concentration in the FTIR measurement system, and establish a working fitting curve of absorbance vs. concentration; Based on the working fitting curve, establish a fitting objective function; Perform iterative solution on the fitting objective function to determine the optimal parameters, obtain the final FTIR gas concentration calibration curve, and use the FTIR gas concentration calibration curve to detect CF4 gas.

2. The CF4 gas detection method based on FTIR according to claim 1, wherein The step of setting the standard concentration range, measuring the gas concentration values and the corresponding absorbance values at each standard concentration in the FTIR measurement system, and establishing a working fitting curve of absorbance vs. concentration specifically includes: Set the standard concentration range; Measure the gas concentration values at each standard concentration in the FTIR measurement system, preprocess the measurement data, and determine the absorbance values corresponding to the gas concentration values according to the preprocessed data; Based on the gas concentration values and the corresponding absorbance values, establish a working fitting curve of absorbance vs. concentration.

3. The FTIR-based CF4 gas detection method according to claim 2, characterized in that, The preprocessing includes data smoothing, baseline correction, and normalization; among them, the data smoothing uses a Savitzky-Golay filter; the baseline correction corrects the baseline drift by polynomial fitting of the baseline; the normalization uses an L2 normalization function.

4. The FTIR-based CF4 gas detection method according to claim 1, wherein The fitting objective function is expressed as: Among them, A measured,i is the absorbance value, A0 is the background absorbance, ∈(T, P) is the function of the molar extinction coefficient varying with temperature and pressure, k(T, P) is the correction factor, c i is the gas concentration, and l is the optical path length.

5. The FTIR-based CF4 gas detection method according to claim 1, characterized in that The process of performing iterative solution on the fitting objective function includes: Set the initial parameter p (0) , where p includes undetermined coefficients; the undetermined coefficients include the molar absorptivity ∈, the background absorbance A0, and the correction factor k(T, P); Calculate the Jacobian matrix J and the residual r of the fitting objective function, and solve the fitting objective function: p (k+1 ) = p (k) -(J T J) -1 J T r Iteratively solve for the update amount Δp until the termination condition is satisfied: p (k+1) = p (k) + Δp; When ||Δp|| < ∈ or the maximum number of iterations is reached, the iteration stops. Substitute the optimal undetermined coefficients into the objective function to obtain the calibration curve, and calculate the gas concentration c based on the actually measured absorbance value A measured Calculate the gas concentration c through the calibration curve o .

6. A CF4 gas detection system based on FTIR, characterized in that, Including: A data acquisition unit for setting the standard concentration range, measuring the gas concentration values and the corresponding absorbance values at each standard concentration in the FTIR measurement system, and establishing a working fitting curve of absorbance vs. concentration; An objective function establishment unit for establishing a fitting objective function based on the working fitting curve; An iterative optimization and gas detection unit for performing iterative solution on the fitting objective function to determine the optimal parameters, obtaining the final FTIR gas concentration calibration curve, and using the FTIR gas concentration calibration curve to detect CF4 gas.

7. An electronic device, characterized in that, Including a memory and a processor, the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the FTIR-based CF4 gas detection method according to any one of claims 1-5.

8. A computer-readable storage medium, characterized in that, It stores a computer program, and when the computer program is executed by the processor, it implements the FTIR-based CF4 gas detection method according to any one of claims 1-5.

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