Development Of Near-infrared Methane Isotope Sensor System

As the main green energy source,methane has become more prominent in human production and life,and it is gradually reducing the proportion of traditional fossil energy sources.At the same time,as an explosive and flammable harmful gas,methane has also brought some production safety accidents,environmental pollution and global climate warming.Therefore,real-time online and accurate detection of methane gas concentration is particularly important.In addition,the carbon isotope abundance of methane also has widespread applications in coal seam genetic analysis,human health monitoring and energy extraction,so based on the principle of infrared laser absorption spectroscopy,this paper has developed a near-infrared methane isotope sensor to realize the real-time online detection of methane concentration and its carbon isotope abundance.This paper first selects the methane isotope absorption line based on the selection principle of the isotope absorption line.Then the overall structure of the sensor system is designed,including the optical part,the electrical part and the gas part.According to the wavelength range of the selected absorption line,the working current range and working temperature of the laser are determined.Subsequently,the hardware part of the sensor was designed,including the pressure control module and the auxiliary gas pretreatment module.The overall structure of the pressure control module and the performance parameters of each component were given.The three sub-circuits of the control circuit board(main control circuit,acquisition execution circuit,and power supply circuit)are mainly designed,and their operating theories are described comprehensively.Moreover,two auxiliary gas pretreatment modules were designed,namely the gas-liquid separation module and the dust removal and dehumidification module.Finally,the software part of the sensor is designed,including the upper computer monitoring with processing platform and pressure control circuit software.The software flow and implementation program of the four sub-modules of the upper computer monitoring with processing platform(acquisition card control module,signal generation module,signal processing module,monitoring display module)were introduced.At the same time,the working principle of linear regression algorithm was described.In addition,three subprograms(initialization program,ADC acquisition program,PID dynamic adjustment program)of the pressure control software were written.After completing the design and integration of the sensor,the detection performance of the sensor was tested using 5000 ppmv standard methane gas.In order to verify the advantages of the linear regression algorithm,the traditional absorbance maximum ratio method was introduced for comparison.The mean values of ¹²CH₄ and¹³CH₄ concentrations obtained by linear regression algorithm for consecutive 30minutes are 4975.49 ppmv and 51.63 ppmv,respectively,and the standard deviation 1?is 17.7 ppmv and 0.11 ppmv,respectively.For the carbon isotope abundance,the continuous 30 minutes mean and standard deviation 1?obtained using the linear regression algorithm are-46.52‰and 3.67‰,respectively,while the results obtained using the maximum absorbance ratio are 16.33‰and 9.62‰,respectively.The results obtained by the linear regression algorithm are more consistent with the natural theoretical values,and the stability is higher,which proves that the linear regression algorithm has advantages.The ideal detection limit of the sensor isotope abundance is0.91‰using the Allan variance calculation.Finally,the performance of the pressure control module was tested.The stabilization time was about 282 s,and the 250 s average pressure and standard deviation 1?were 100.04 Torr and 0.14 Torr,respectively.The experiment proves that the developed near-infrared methane isotope sensor is practical and can be combined with auxiliary gas pretreatment module for field application.The main innovative points of this thesis:In response to the demand for simultaneous detection of methane concentration and its carbon isotope abundance,a methane isotope sensor based on infrared laser absorption spectroscopy was developed.The linear regression algorithm was used to improve the accuracy and stability of the detection results.The pressure control module was independently developed,realizing the gas pressure control.The sensor upper computer monitoring with processing platform was designed.