Development Of Portable Laser Remote Detector For Flammable And Toxic Gase

Methane（CH₄）and hydrogen sulfide（H₂S）are the most representative flammable and toxic gases in the oil and natural gas industry,respectively.Simultaneous non-contact remote measurement of these two gases is very important for danger warning and safe production.In response to the actual needs of CH₄ and H₂S leakage telemetry,this thesis developed a portable flammable and toxic gas telemeter prototype based on tunable diode laser absorption spectroscopy（TDLAS）technology.The main work and innovative results are as follows:（1）A prototype of a laser telemeter for simultaneous detection of CH₄ and H₂S is designed and developed.Aiming at the problems that traditional gas sensors can only achieve point measurement in contact mode with low sensitivity,based on TDLAS telemetry technology with non-cooperative target and the whilst a first harmonic normalized WMS-2f（WMS-2f/1f）method is adopted.A prototype design scheme of the mainframe plus probe gun is proposed based on the modular integration idea.And the feasibility of the scheme is verified by means of Tracepro optical path simulation and calculation of the received echo optical power under different non-cooperative targets.Through spectrum line optimization,the target spectrum lines of CH₄ and H₂S are determined to be 1653.73nm and 1578.13nm,respectively,and the best sinusoidal modulation currents are 27mA and 21.97mA,respectively,and the best tuning ranges are 50mA-145mA and 65mA-140mA,respectively.Time-division multiplexing of the two lasers based on optical fiber technology is employed achieve simultaneous detection of CH₄ and H₂S.（2）A method for noise suppression and concentration inversion was developed for TDLAS telemetry of non-cooperative targets.In order to improve the detection accuracy of the telemeter prototype,Butterworth filtering,Savitzky-Golay filtering and the combination of multiple sets of data averaging are used to increase the signal-to-noise ratio（SNR）of the WMS signal by 3.42 times without loss of spectral information.The Levenberg-Marquardt algorithm is used to perform non-linear least-squares fitting to achieve the calibration-free measurement of gas concentration.A parameter optimized adaptive Kalman filtering is utilized increases the measurement precision by2.01 times.（3）The performance of the telemeter prototype is evaluated and its effectiveness is verified.A prototype test platform is built to test and evaluate the warm-up time,accuracy,and sensitivity of the telemeter prototype.The results show that the preheating time is 30min,the measurement accuracy can reach 0.53%,and the sensitivity of CH₄and H₂S are 1.67ppm·m and 46.11ppm·m,repectivlely,with the integration time of 1s.A series of telemetry experiments is designed by using a transparent gas cell filled with standard gas to simulate CH₄ and H₂S gas leakage.WMS signals under different measurement distances and different non-cooperative targets are collected.The SNR of the 5m signal is 4.03 times that of the 20m,and the SNR with the aluminum plate is3.55 times that with the lacquered metal plate.The effectiveness of the telemeter prototype at a distance of 20m is proved through the concentration inversion.This prototype lays the foundation for the efficient inspection of harzad gas leaks in the oil and gas industry.