Multi-channel methane dissipation monitoring method and device based on laser spectrum absorption

Abstract

The invention provides a multichannel methane dissipation monitoring method and device based on laser spectrum absorption, and belongs to the technical field of methane monitoring, and the method comprises the steps: obtaining the specific absorption wavelength of methane to laser, and determining the wavelength of a laser light source based on the wavelength; determining the monitoring frequency; modulating the wavelength of the laser; performing multi-channel photoelectric signal conversion, performing amplification and noise reduction on a multi-channel electric signal obtained after conversion, and extracting second harmonics of a multi-channel methane gas absorption signal; the extracted second harmonic is subjected to noise reduction through LabVIEW, monitored second harmonic data and standard data obtained after noise reduction are called through MATLAB, iterative fitting is conducted on the second harmonic data and the standard data, a fitting coefficient is obtained, and the multi-channel methane gas concentration is obtained through inversion based on an inversion model. According to the invention, methane concentration data of a plurality of dissipation surfaces are obtained through multiple channels, large-range continuous methane concentration monitoring of the plurality of dissipation surfaces is realized, and the accuracy, reliability and continuity of methane concentration monitoring are improved.

Description

Technical Field

[0001] This invention relates to the field of methane gas monitoring technology, and in particular to a multi-channel methane emission monitoring method and device based on laser spectral absorption. Background Technology

[0002] Methane, as an important energy source, is used in various aspects of social development. However, methane goes through multiple stages from production and transportation to utilization, and each stage carries the risk of leakage. Methane leaks and emissions not only impact the environment and contribute to climate change but also waste resources and increase costs. Therefore, methane monitoring is essential. By monitoring methane emissions, we can better understand the use and depletion of methane, promptly identify leaks and emission problems, and take corresponding measures for maintenance and improvement, reducing resource waste, improving energy efficiency, and controlling costs.

[0003] Currently, monitoring of methane leaks and emissions typically employs single-point monitoring technology. This technology focuses on monitoring methane emissions at a single point, making it unable to monitor methane concentration changes over a large area in real time. This is particularly true for monitoring large regions or mobile sources, limiting its coverage and real-time performance, and failing to provide a comprehensive picture of methane concentration distribution. Furthermore, when the methane leak is small, single-point monitoring may miss some leaks and has a large margin of error, potentially leading to undetected methane leaks. Summary of the Invention

[0004] To address the above issues and to comprehensively and in real-time reflect the methane concentration changes within a large-area emission region while reducing the probability of missed detection, this invention provides a multi-channel methane emission monitoring method and device based on laser spectral absorption. By determining multiple monitoring points within a large area and performing multi-channel methane emission monitoring based on laser spectral absorption technology, methane concentration data from multiple emission surfaces can be acquired through multiple channels, effectively compensating for the shortcomings of single-point methane monitoring and improving the accuracy and reliability of methane monitoring.

[0005] On one hand, this invention application provides a multi-channel methane emission monitoring method based on laser spectral absorption, the method comprising: Obtain the specific absorption wavelength of methane to laser light, and determine the laser source wavelength based on the specific absorption wavelength; Multiple monitoring points are set up and the monitoring frequency is determined. The methane emission from multiple channels is monitored in real time according to the monitoring frequency. The laser wavelength is modulated by a set sine wave; Multi-channel photoelectric signal conversion: The modulated laser light is absorbed at multiple points in the methane gas region and the resulting multi-channel optical signal is converted into a multi-channel electrical signal by a photodetector. The multi-channel electrical signal obtained after conversion is amplified by a preamplifier, and the amplified multi-channel electrical signal is denoised by a low-pass filter circuit. The second harmonic of the multi-channel methane gas absorption signal in the multi-channel electrical signal is extracted by a lock-in amplifier. The second harmonic of the extracted multi-channel methane gas absorption signal is denoised using LabVIEW. MATLAB is then used to call the denoised second harmonic data and standard data obtained from monitoring, and the second harmonic data and standard data are iteratively fitted to obtain the fitting coefficients. Based on the inversion model, the multi-channel methane gas concentration is inverted.

[0006] As a further improvement of this invention, obtaining the specific absorption wavelength of methane for laser light and determining the laser source based on the wavelength includes: The specific absorption wavelength of methane molecules is obtained based on the absorption characteristics of methane molecules in the near-infrared band and the absorption parameters of methane in the HITRAN database. Then, the wavelength of the laser source is determined based on the obtained absorption wavelength.

[0007] As a further improvement of this invention, obtaining the specific absorption wavelength of methane for laser light and determining the laser source based on the wavelength includes using a laser source with a wavelength of 1650 nm.

[0008] As a further improvement of this invention, the modulation of the laser wavelength by a set sine wave includes using a sine wave with a frequency of f=10KHz and a peak-to-peak value of 110mV to modulate the laser wavelength.

[0009] As a further improvement of this invention, the second harmonic of the extracted multi-channel methane gas absorption signal is denoised using LabVIEW. MATLAB is used to call the denoised second harmonic data and standard data obtained from monitoring, and iterative fitting is performed on the second harmonic data and standard data to obtain fitting coefficients. The multi-channel methane gas concentration is inverted based on the inversion model. After denoising the second harmonic in LabVIEW, the denoised second harmonic data is dynamically stored.

[0010] As a further improvement of this invention application, before iteratively fitting the second harmonic data and the standard data, the second harmonic data and the standard data are subjected to the same depth processing using MATLAB.

[0011] As a further improvement of this invention, obtaining the specific absorption wavelength of methane for laser light and determining the wavelength of the laser source based on the wavelength includes using a DFB tunable laser source.

[0012] On the other hand, this invention application provides a multi-channel methane emission monitoring device based on laser spectral absorption, including a multi-channel fiber optic methane monitor, multiple laser monitoring probes, and fiber optic cables. Each laser monitoring probe is connected to the methane monitor via a fiber optic cable. The multi-channel fiber optic methane monitor is connected to an analysis and processing module. The multi-channel fiber optic methane monitor extracts the second harmonic of the multi-channel methane gas absorption signal. The analysis and processing module is used to perform noise reduction on the second harmonic of the multi-channel methane gas absorption signal using LabVIEW and MATLAB data processing.

[0013] As a further improvement of this invention, the analysis and processing module includes a mobile workstation, a PC, a terminal server, or a cloud server.

[0014] As a further improvement of this invention, the laser monitoring probe includes at least three probes.

[0015] This invention application provides a multi-channel methane emission monitoring method and device based on laser spectral absorption. By acquiring methane concentration data from multiple emission surfaces through multiple channels, it achieves continuous methane concentration monitoring over a wide range of multiple emission surfaces, thereby improving the accuracy, reliability, and continuity of methane concentration monitoring. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a multi-channel methane emission monitoring method based on laser spectral absorption, according to an embodiment of this invention.

[0017] Figure 2 This is a schematic diagram of the structure of a multi-channel methane emission monitoring device based on laser spectral absorption, according to an embodiment of this invention.

[0018] Figure 3 This is another specific flowchart of the multi-channel methane emission monitoring method based on laser spectral absorption, which is an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached diagram: 1. Multi-channel fiber optic methane monitor; 2. Laser monitoring probe; 3. Fiber optic cable. Detailed Implementation

[0020] The following describes specific embodiments and appendices. Figure 1-3 The invention application is described in detail so that those skilled in the art can more fully understand the purpose, features and effects of the invention application.

[0021] Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In the event of any discrepancy between the definition of a term in this application and its commonly understood meaning by one of ordinary skill in the art, the definition stated in this application shall prevail.

[0022] This invention application provides a multi-channel methane emission monitoring method and device based on laser spectral absorption, which improves existing methane emission monitoring methods, thereby achieving multi-point monitoring of methane emission over a large area and improving the efficiency and reliability of methane emission monitoring.

[0023] Example 1 As a specific embodiment of this invention, this embodiment provides a multi-channel methane emission monitoring method based on laser spectral absorption, referring to... Figure 1 , Figure 2 Multiple laser monitoring probes are connected to a multi-channel fiber optic methane monitor via cables. The specific steps are as follows: S01. Obtain the specific absorption wavelength of methane to laser light, and determine the laser source wavelength based on the specific absorption wavelength. The specific absorption wavelength is obtained based on the absorption characteristics of methane molecules to laser wavelengths. Specifically, the specific absorption wavelength of methane molecules is obtained based on the absorption characteristics of methane molecules in the near-infrared band and the absorption parameters of methane in the HITRAN database. Then, the wavelength of the laser source is determined based on the obtained absorption wavelength.

[0024] Furthermore, a DFB tunable laser source with an emission wavelength of 1650 nm was employed. Using methane absorption parameters from the HITRAN database, the absorption wavelength of methane could be accurately determined. Comparing the absorption coefficients of methane to different wavelengths of laser light, it was found that methane gas exhibits optimal absorption of monochromatic light at a wavelength of approximately 1650 nm. Therefore, the emission wavelength of the laser source was determined to be 1650 nm. DFB lasers possess advantages such as narrow linewidth, high power, and tunability, making them suitable for gas detection. By adjusting the output wavelength of the laser, it can be ensured that the laser source matches the optimal absorption wavelength of methane, thereby improving detection sensitivity and accuracy.

[0025] S02, laser wavelength modulation, lock-in amplifier extracts second harmonic. A sine wave is set, the laser is wavelength modulated, and the second harmonic of the multi-channel methane gas absorption signal is extracted by a lock-in amplifier.

[0026] Furthermore, by adjusting the frequency and amplitude of the sine wave pair, the modulation effect is optimized, enabling the absorption signal of methane gas to be effectively extracted. The lock-in amplifier can extract the second harmonic synchronized with the modulation signal from the received signal based on the frequency and amplitude of the modulation signal, and then filter and amplify the received signal to eliminate noise and interference.

[0027] S03. Analyze and process the second harmonic of the extracted multi-channel methane absorption signal to obtain methane concentration information. This invention discloses a multi-channel methane emission monitoring method based on laser spectral absorption, which enables real-time monitoring of methane concentration over a large area of ​​emission surface within a fixed volume and over a continuous time period. This allows monitoring personnel to promptly understand the concentration distribution of methane after emission, avoiding missed detections due to single-point monitoring and ensuring the comprehensiveness and accuracy of methane monitoring. Simultaneous monitoring of multiple points significantly improves monitoring efficiency. Furthermore, the multi-channel methane emission monitoring method has good scalability, allowing for the addition or removal of monitoring points as needed, facilitating flexible adjustment of the monitoring range.

[0028] Example 2 As a specific embodiment of this invention, this embodiment provides a multi-channel methane emission monitoring device based on laser spectral absorption. The methane emission monitoring method based on laser spectral absorption of this embodiment is used for methane emission monitoring, with reference to... Figure 2 It includes a multi-channel fiber optic methane monitor and multiple laser monitoring probes 2, wherein the laser monitoring probes 2 and the multi-channel fiber optic methane monitor 1 are connected by fiber optic cables 3.

[0029] At the laser monitoring probe 2, the laser beam emitted by the multi-channel fiber optic methane monitor 1 passes through the environment containing methane gas. The methane molecules in the environment will absorb part of the light energy. The laser beam after the light energy is attenuated is received and returned to the multi-channel fiber optic methane monitor 1 for further processing to extract the second harmonic of the multi-channel methane gas absorption signal.

[0030] Furthermore, the multi-channel fiber optic methane monitor 1 is connected to an analysis and processing module for analyzing and processing the second harmonic of the multi-channel methane absorption signal extracted by the multi-channel fiber optic methane monitor 1 to obtain methane concentration information. The analysis and processing module includes, but is not limited to, a mobile workstation, PC, terminal server, or cloud server.

[0031] Preferably, the analysis and processing module uses a PC, which allows for more flexible multi-channel methane emission monitoring at the work site and timely feedback of monitoring results. The analysis and processing module can acquire the second harmonic of the multi-channel methane absorption signal extracted by the multi-channel fiber optic methane monitor 1 in real time, thereby ensuring efficient analysis and acquisition of multi-channel methane gas concentration.

[0032] The multi-channel methane emission monitoring device based on laser spectral absorption proposed in this invention can simultaneously acquire methane concentration data from multiple locations through multi-point detection, thereby providing more comprehensive and accurate information. This helps to gain a deeper understanding of methane leakage or emission. The multi-channel online monitoring can reflect the changes in methane concentration at each location in real time and dynamically, which helps to detect problems in a timely manner and take corresponding measures.

[0033] Example 3 As a specific embodiment of this invention, this embodiment takes the methane emission monitoring of a storage tank at a joint station as an example to further illustrate this invention. In this embodiment, a rotating bracket and five laser monitoring probes are installed on the top of the storage tank, centered on the breather valve. All laser monitoring probes are connected to a multi-channel fiber optic methane monitor via fiber optic cables, and the multi-channel fiber optic methane monitor is connected to a PC. Continuous monitoring is performed at the five locations for 30 days. (Refer to...) Figure 3 The specific monitoring methods are as follows.

[0034] S010. Obtain the specific absorption wavelength of methane to laser light, and determine the laser source wavelength based on the specific absorption wavelength. According to the HITRAN database, methane gas has the best absorption effect on monochromatic light with a wavelength of around 1650nm, so a DFB tunable laser source with an emission wavelength of 1650nm is used to emit laser light.

[0035] S020. Determine the monitoring frequency and conduct real-time monitoring of methane emissions through multiple channels. In this example, the sampling frequency for each set of methane concentration monitoring and environmental monitoring data is set to 120 times / hour.

[0036] S030. Modulate the laser wavelength. A sine wave is used to modulate the wavelength of the laser. In this example, a sine wave with a frequency of f=10kHz and a peak-to-peak value of 110mV is used to modulate the wavelength of the laser.

[0037] S040, Multi-channel photoelectric signal conversion After the laser passes through multiple points in the methane gas region, it is absorbed to obtain a multi-channel optical signal, which is then converted into a multi-channel electrical signal by a photodetector.

[0038] S050, multi-channel electrical signal amplification, extraction of the second harmonic of methane gas absorption signal. First, the converted multi-channel electrical signal is amplified by a preamplifier, and then noise from the environment and the instrument itself is removed by a low-pass filter circuit. Finally, the second harmonic of the methane gas absorption signal is extracted by a lock-in amplifier.

[0039] S060. Analyze and process the second harmonic of the extracted multi-channel methane absorption signal to obtain methane concentration information. The extracted second harmonic of the multi-channel methane absorption signal is imported into the PC. First, the second harmonic is further denoised using LabVIEW to remove unwanted noise components and enhance the quality of the second harmonic signal.

[0040] LabVIEW has a wealth of built-in signal processing functions and tools, including filter design, wavelet analysis, and spectrum analysis, which provide robust support for noise reduction. Monitoring personnel can directly call these functions without having to write complex algorithms from scratch.

[0041] Furthermore, the monitoring personnel determined the function suitable for second harmonic noise reduction of the multi-channel methane absorption signal by comparing the processing results of different signal processing tools in LabVIEW, so as to obtain the optimal second harmonic signal after noise reduction.

[0042] After denoising the second harmonic within LabVIEW, the denoised second harmonic data is dynamically stored.

[0043] Standard data is pre-saved. MATLAB is used to call up the noise-reduced second harmonic data and standard data obtained from monitoring. The fitting coefficient 'a' is obtained by iteratively fitting the second harmonic data and standard data, and then the multi-channel methane gas concentration is inverted based on the inversion model. Thus, methane emission concentration monitoring data from five monitoring points on the top of a storage tank at a certain joint station are simultaneously obtained and can be continuously monitored.

[0044] Based on the monitoring results, the degree of methane emission at each location can be determined, and the locations can be sorted according to the degree of emission to obtain the concentration distribution of methane emission. This helps monitoring personnel to more accurately and comprehensively grasp the emission trend of methane at the top of the storage tank.

[0045] Furthermore, before iteratively fitting the second harmonic data and the standard data, MATLAB was used to perform the same depth processing on the second harmonic data and the standard data.

[0046] The order of the above steps is not a limitation of this invention application, and those skilled in the art can adjust the order of the steps according to the specific circumstances.

[0047] This invention application combines fiber optic technology to simultaneously obtain the absorption characteristics of methane molecules at multiple venting surfaces in multiple channels. After the laser beam passes through the methane vent, it is received by a photodetector and converted into an electrical signal. The obtained electrical signal is then amplified, filtered, and digitized to obtain methane concentration data in multiple channels over a wide range, thus realizing the monitoring of methane concentration at multiple venting surfaces.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A multi-channel methane emission monitoring method based on laser spectral absorption, characterized in that, The method includes: Obtain the specific absorption wavelength of methane to laser light, and determine the laser source wavelength based on the specific absorption wavelength; Multiple monitoring points are set up and the monitoring frequency is determined. The methane emission from multiple channels is monitored in real time according to the monitoring frequency. The laser wavelength is modulated by a set sine wave; Multi-channel photoelectric signal conversion: The modulated laser light is absorbed at multiple points in the methane gas region and the resulting multi-channel optical signal is converted into a multi-channel electrical signal by a photodetector. The multi-channel electrical signal obtained after conversion is amplified by a preamplifier, and the amplified multi-channel electrical signal is denoised by a low-pass filter circuit. The second harmonic of the multi-channel methane gas absorption signal in the multi-channel electrical signal is extracted by a lock-in amplifier. The second harmonic of the extracted multi-channel methane gas absorption signal is denoised using LabVIEW. MATLAB is then used to call the denoised second harmonic data and standard data obtained from monitoring, and the second harmonic data and standard data are iteratively fitted to obtain the fitting coefficients. Based on the inversion model, the multi-channel methane gas concentration is inverted.

2. The multi-channel methane emission monitoring method based on laser spectral absorption according to claim 1, characterized in that, The step of obtaining the specific absorption wavelength of methane to laser light and determining the laser source based on the wavelength includes: The specific absorption wavelength of methane molecules is obtained based on the absorption characteristics of methane molecules in the near-infrared band and the absorption parameters of methane in the HITRAN database. Then, the wavelength of the laser source is determined based on the obtained absorption wavelength.

3. The multi-channel methane emission monitoring method based on laser spectral absorption according to claim 2, characterized in that, The process of obtaining the specific absorption wavelength of methane for laser light and determining the laser source based on the wavelength includes using a laser source with a wavelength of 1650 nm.

4. The multi-channel methane emission monitoring method based on laser spectral absorption according to claim 1, characterized in that, The modulation of the laser wavelength by the set sine wave includes using a sine wave with a frequency of f=10KHz and a peak-to-peak value of 110mV to modulate the laser wavelength.

5. The multi-channel methane emission monitoring method based on laser spectral absorption according to claim 1, characterized in that, The second harmonic of the extracted multi-channel methane gas absorption signal is denoised using LabVIEW. MATLAB is used to call the denoised second harmonic data and standard data obtained from monitoring, and iterative fitting is performed on the second harmonic data and standard data to obtain fitting coefficients. The multi-channel methane gas concentration is inverted based on the inversion model. After denoising the second harmonic in LabVIEW, the denoised second harmonic data is dynamically stored.

6. The multi-channel methane emission monitoring method based on laser spectral absorption according to claim 5, characterized in that, Before iteratively fitting the second harmonic data and the standard data, MATLAB was used to perform the same depth processing on the second harmonic data and the standard data.

7. The multi-channel methane emission monitoring method based on laser spectral absorption according to claim 1, characterized in that, The process of obtaining the specific absorption wavelength of methane for laser light and determining the laser source wavelength based on the wavelength includes using a DFB tunable laser source.

8. A multi-channel methane emission monitoring device based on laser spectral absorption, characterized in that, The system includes a multi-channel fiber optic methane monitor (1), multiple laser monitoring probes (2), and fiber optic cables (3). Each laser monitoring probe (2) is connected to the methane monitor (1) via fiber optic cables (3). The multi-channel fiber optic methane monitor (1) is connected to an analysis and processing module. The system uses the multi-channel methane emission monitoring method based on laser spectral absorption as described in any one of claims 1-7 for monitoring. The multi-channel fiber optic methane monitor (1) extracts the second harmonic of the multi-channel methane gas absorption signal. The analysis and processing module is used by LabVIEW to perform noise reduction on the second harmonic of the multi-channel methane gas absorption signal and MATLAB data processing.

9. The multi-channel methane emission monitoring device based on laser spectral absorption according to claim 8, characterized in that, The analysis and processing module includes a mobile workstation, PC, terminal server, or cloud server.

10. The multi-channel methane emission monitoring device based on laser spectral absorption according to claim 8, characterized in that, The laser monitoring probe (2) includes at least three.

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