Design Of Methane Remote Sensing System Based On TDLAS

With the introduction of China’s carbon peaking and carbon neutrality goals,the demand for natural gas as a clean energy source in industrial production and daily life is increasing,so a large number of natural gas transportation and storage facilities have been built.However,the occurrence of gas leaks can cause significant damage to people’s lives and property and national interests.Therefore,a fast detection speed,wide monitoring range and intrinsically safe method is needed to realize the remote sensing of methane gas leakage.Tunable Diode Laser Absorption Spectroscopy(TDLAS)technology has the advantages of high accuracy,good real-time performance and high resolution,and has attracted the attention of domestic and foreign researchers in the field of gas remote sensing.Based on Direct Absorption Spectroscopy(DAS)technology,DAS based gas remote sensing system is a costeffective product because of its simple structure,low cost,and ideal gas detection sensitivity.There is a shortage of reflected echo signals using angular reflectors in telemetry systems,so the telemetry system designed in this paper has a telescope transceiver module with a large receiving surface,which can realize the collection of diffuse reflected luminous power from rough reflective surfaces.Then combined with the embedded design using STM32L151RET6 as MCU,after the display of the Qt-based development of the PC software.Online monitoring of CH4 column concentration in the open optical circuit was realized.The main contents of this article are as follows:1.Learned about optical and non-optical detection methods in gas detection,introduced several common gas remote sensing detection methods,including Differential Optical Absorption Spectroscopy Technology,Differential Absorption Lidar Technology,Fourier Transform Infrared Spectroscopy Technology and Tunable Diode Laser Absorption Spectroscopy Technology,as well as informed about the development status of gas remote sensing systems at home and abroad.2.Introduced infrared spectrum absorption theory,including the mechanism of light and gas molecule interaction,Beer Lambert’s law,and absorption line intensity and line shape function.Introduced the implementation theory of direct absorption spectrometry and wavelength modulation spectrometry in TDLAS technique.The relationship between the reflected luminous power and the distance from the reflecting surface is analyzed.These theories are introduced to build the foundation for the development of CH4 remote sensing system.3.Introduced the hardware design of gas remote sensing system,including the optical module system design and electrical module system design.The optical module system design mainly included the research and construction of laser collimation unit and telescopic receiver unit structure,and completed the optical transceiver system design of gas remote sensing with a receiving surface diameter of 200mm.The electrical module system design mainly includes the laser control circuit of the signal generation module,the preamplifier and signal processing circuit of the signal detection module,and the hardware circuit of the embedded module,meanwhile,the type and performance parameters of the main electronic devices are introduced and analyzed.The hardware foundation was built for the software demodulation of CH4 column density later.4.The software of the gas telemetry system is designed,including the STM32-based embedded software and the Qt-based PC software.The embedded software realized the functions of reflected luminous power acquisition,signal digital filtering and absorption spectrum calculation.The PC software realizes the functions of transmission spectrum map,CH4 absorption spectrum map,presentation of fitted column density and communication with the slave computer.The software system displays CH4 column density to help users monitor CH4 leakage.5.Experimental analysis of the methane remote sensing system.It was conducted the calibration experiment of remote sensing distance and reflected light power.The experimental data showed that there is a good linear relationship(R2=0.9969)between the reflected luminous power and the inverse of the square of the distance in the range of 9～19.8m from the diffuse reflecting surface,and the experiment also demonstrated that the system still has a high signalto-noise ratio at a distance of 28.8m from the diffuse reflecting surface.Based on the experimental data,the relationship between the column density and the output value of the system was fitted and a set of well mapped parameters(R2=0.99957)was obtained.Finally,a 24-hour long-term stability test was performed for a constant column concentration gas mass.It was verified that this system has a sensitivity of 100 ppm-m for gas detection and can operate for a long time.In summary,the CH4 remote sensing system designed in this article was able to detect methane concentration at a distance of 10m from the rough reflective surface for a long time with a detection sensitivity of 100ppm·m,and the farthest detection distance is 28.8m.