Simulation Analysis And Experimental Research Of Methane Telemetry Based On TDLAS-WMS

Natural gas contains 85 % methane,which can easily cause explosions when the methane concentration in the air is between 5 % and 15 %.The use of natural gas is ubiquitous in daily life,such as using natural gas for cooking in households and using it as a fuel instead of other energy sources for heating and dissolution in industrial parks.In recent years,detecting natural gas leaks has become an important research topic.In the field of gas detection,Tunable Diode Laser Absorption Spectroscopy(TDLAS)has developed rapidly due to its high detection accuracy,fast response speed,and low price.Especially after the proposal of Wavelength Modulation Spectroscopy(WMS),TDLAS-WMS has become the mainstream architecture for remote sensing system design.Currently,there are problems with large errors and low accuracy in the remote sensing systems for methane gas detection on the market.Therefore,this thesis designs a methane remote sensing simulation system based on TDLAS-WMS and optimizes the working parameters of the remote sensing system to improve its accuracy and reduce errors.A methane remote sensing simulation system was established using MATLAB’s Simulink module,which mainly consists of a laser output module,simulated external environment module,and harmonic detection module.The simulation used wavelength modulation and normalized second harmonic techniques to simulate each module and used the ratio of the peak value of the second harmonic to the fundamental harmonic as the detection signal.The simulation analyzed the effects of different frequencies of sine waves,modulation coefficient m,and the frequency ratio of sine waves and sawtooth waves on the normalized second harmonic signal.The results showed that m=2.2 was the optimal modulation coefficient,and the frequency of sine waves had little effect on the second harmonic signal but had no effect on the normalized second harmonic signal.The value of the normalized second harmonic signal was the largest when the frequency ratio of sine waves and sawtooth waves was 6000:1.In the methane integration concentration range of 0ppm·m～2000 ppm·m,the linear regression least squares method was used to fit and calibrate the measurement concentration-detection signal data,and concentration inversion and error analysis were performed.The results showed that the error range of concentration inversion using normalized second harmonic signal was-3.57 %～4.06 %.Based on the simulation results,the parameters of the remote sensing equipment were adjusted,and the error range of the equipment for concentration inversion was-4.68 %～2.45 %,which significantly improved compared to the measurement error of 10 %～20 % of the laser methane remote sensing instrument currently on the market.The stability and detection limit of the experimental system were evaluated using the Allan variance analysis method.The detection limit of the telemetry system is 37.85 ppm·m when the integration time was 5 s.When the optimal integration time was 345 s,the corresponding detection limit was 6.27 ppm·m.The results of optimizing the working parameters of the remote sensing system through the simulation system have important guiding significance for improving the accuracy and reducing the measurement error of the laser methane remote sensing system.Figure [57] table [7] reference [71]...