Detection Of Methane Concentration Based On Tunable Diode Laser Absorption Spectroscopy

With China's scientific and technological progress and social development,China's energy consumption is growing.The natural gas and coal occupy the main component in China's energy consumption structure and play a huge role in China's economic development.However,the accidents caused by the leakage of natural gas and coal gas have posed a significant threat to the life and property safety of the personnel concerned.The main components of natural gas and coal gas are methane,so it is very meaningful to be able to perform rapid on-line detection of methane gas concentration.The gas detection method based on tunable semiconductor laser absorption spectroscopy(TDLAS)is a relatively popular method for the detection of methane concentration because of its simple structure and fast response.In recent years,with the development of TDLAS technology,the research direction of gas detection has gradually developed from the concentration of gas in the laboratory to the on-line gas detection of open field.In this paper,the methane concentration detection system of simulated open field is built on the basis of gas pool,and the simulation and experimental tests related to the experiment are carried out.The main contents are as follows:(1)The methane concentration detection system was built,the methane concentration detection scheme was studied,and the noise of the system was analyzed in detail.(2)Based on the TracePro software,the simulation of the optical path of the detection system was carried out and the optical transmission characteristics of the system were analyzed.The diffusion of methane gas in the air was studied based on the Fluent software.The distribution of the velocity and concentration of methane gas The influence of the modulation parameters on the harmonic signal was analyzed,and the harmonic signal generation from the generation of the tuned signal to the phase-locked amplifier was studied.The influence of the modulation parameters on the harmonic signal was analyzed.Based on the principle of the lock-in amplifier,the design of the module was carried out.Finally,the harmonic signal obtained by Simulink-based lock-in amplifier and the real SR830 phase-locked amplifier on the output of the photoelectric detector was verified.And the accuracy of the lock-in amplifier was validataed.(3)The basic measurement of TDLAS methane concentration detection system and the influence of modulation parameters on the harmonic signal were carried out.The reflection angle,reflection distance and material type of the diffuse material on the effects of 2f and 2f/1f were completed.The 2f/1f signal has a great advantage over the traditional 2f signal about gas concentration detection method in the open field,and the minimum detection limit of the system was 27 ppm ·m.