Research On Spectrum Detection Technology Of Methane Carbon Isotope In Natural Gas

Methane carbon isotope detection has been widely used in food safety,geological exploration,astrophysics and other fields.In recent years,many domestic research institutions have found that methane carbon isotope in natural gas is closely related to many physical phenomena,so the research on methane carbon isotope detection in natural gas has important practical application value.Compared with other detection technologies,tunable diode laser absorption spectroscopy(TDLAS)technology has the characteristics of high sensitivity,high resolution and easy field application.Therefore,the research on methane carbon isotope detection based on TDLAS technology is one of the main trends at present.Up to now,the research on methane carbon isotope detection at home and abroad is concentrated in the mid infrared band,which requires strict detection environment,constant temperature and low pressure,so it is difficult to be applied in the field.Therefore,it is of great significance to research the detection system of methane carbon isotope in natural gas based on near infrared with high sensitivity,stability,reliability and simple structure.Through in-depth investigation and analysis of domestic and foreign research progress of spectral detection technology of methane carbon isotope in natural gas,and comparison with its technical scheme,the TDLAS technology based detection of methane carbon isotope in natural gas has been carried out.The principle of TDLAS technology,isotope detection and other related theories have been studied in detail.By selecting the target absorption line of methane carbon isotope with the same low energy level,the influence of temperature on the measurement results is reduced,and the laser and detector are selected according to the absorption line.Through the research on the design of power module,laser driving circuit,preamplifier,low-pass filter,temperature and pressure detection circuit,the hardware part of methane carbon isotope detection system is developed,in order to avoid the influence of interference absorption peak on carbon isotope measurement results,a two-stage current driven laser is proposed;The multi peak Gaussian fitting program is written by using MATLAB,the pressure broadening and absorption spectrum drift are integrated into the function model,and the development of methane carbon isotope detection system software system is completed.Subsequently,methane carbon isotope detection experiments were carried out,including pressure sensitivity,temperature sensitivity and long-term stability experiments.The experimental results show that the relative precision standard deviation of temperature sensitivity experimental results is increased from 16.95 ‰ to 2.88 ‰ by selecting the target absorption line of methane carbon isotope with the same low energy level;The relative precision standard deviation of pressure sensitivity experimental results is increased from 31.1‰ to 1.4 ‰ by adding the pressure compensation algorithm;By using Allan analysis of variance long-term stability experimental data,when the integration time is 135 s,the theoretical detection limit is 0.1453 ‰.To sum up,in view of the lack of research on methane carbon isotope in the near infrared band at home and abroad,and the strict requirements of experimental conditions(pressure and temperature)in the experimental process,a methane carbon isotope detection system based on TDLAS technology is designed.By selecting the appropriate absorption spectrum and laser source,and taking the dependence of experimental results on temperature and pressure into account in the multi peak Gaussian fitting model,the anti-interference and universality of the detection system are improved,which provides a new technical solution for the detection of methane carbon isotope in natural gas.