Research And Application Of Gases Monitoring Method In Coal Mine Based On Laser Absorption Spectroscopy

The high-productivity and high-efficiency of coal mine is the development trend of China’s coal industry.The main problem affecting the high-productivity and highefficiency mining of coal mine is coal mine safety.Coal spontaneous fire is one of the major disasters of coal mine.TDLAS(Tunable Diode Laser Absorption Spectroscopy)technology with the advantages of high sensitivity,reliability and automation is applied to the monitoring of indicator gas concentration of spontaneous combustion in coal mine.It can provide scientific basis for the early prediction and prevention of coal spontaneous combustion.The related research work is about how to improve the measurement range and accuracy of TDLAS gas detection system and how to realize the remote real-time monitoring of gases concentration of CH4,CO2,O2 CO,C2H2 and C2H4 in multiple areas of underground coal mine under harsh environment,mainly including the following aspects.(1)By analyzing the causes of measurement errors of mixed gases in terms of spectral parameters and concentration inversion process,the concept of separation degree between adjacent spectral lines is defined,and the influence degree between adjacent spectral lines is given,which mainly depends on the center interval of two spectral lines,the spectral line broadening and the ratio of two gas concentrations,and the larger the ratio,the larger the error.A regression prediction model based on the PLS(Partial Least Squares)principle,which combines principal component analysis,canonical correlation analysis and multivariate linear regression analysis,is proposed to invert the concentration of mixed gases with spectral interference.Tested with gases at different concentration ratios of CH4 and CO,the results show that when the ratio of CH4 to CO increases,the relative error of inversion of CO concentration increases rapidly by LS(Least Squares)method,and when the ratio is greater than 2,the relative error of inversion of CO concentration is greater than 10%,while PLS algorithm can satisfy the ratio within 100,and its inversion error of CO concentration can still be guaranteed within 10%.The results shows that compared with the traditional LS algorithm,the regression prediction model based on PLS principle has the advantages of automatic extraction of absorption spectral line characteristics,strong antiinterference and accurate regression prediction results.It can effectively solve the problem of overlapping interference of CH4 absorption spectral lines in the calculation of CO concentration.(2)By choosing an appropriate absorbance threshold,combining the advantages of DAS(Direct Absorption Spectroscopy)and WMS(Wavelength Modulation Spectroscopy),the laser can detect the direct absorption signal and the second harmonic signal within one cycle of current driving signal by adopting the time division multiplexing technology,a self-calibrated full range gas detection system has been designed.The measurement range experiments of CH4 gas were carried out in the laboratory.The absolute error of measurement value is only 0.006%and 0.02%when CH4 was detected at 0.025%and 0.25%,the relative error of detection result is less than 6%when the concentration of CH4 is more than 0.8%,and the measurement result has good linearity.The relative errors corrected by the temperature correction algorithm of empirical data are all within 1.5%for the CH4 concentration measured in the environment of-40℃～60℃.The results show that the wide temperature full range gas detection scheme can effectively overcome the problem of large measurement error of indicator gas caused by coal spontaneous fire in coal mine resulting in large change of ambient temperature.(3)Aiming at the difficulties of remote real-time monitoring of multi indicator gases in multi areas of coal mine.An on-line monitoring system for multi indicator gases concentration of CH4,CO2,O2,CO,C2H2 and C2H4 at multi areas of coal mine is designed by using a phase-locked amplifier and time-sharing and automatic channel switching.The real-time gas concentration monitoring tests were completed in cooperative coal mine by using the system.The results show that the effective data guarantee for coal mine safe production and early warning can be provided by the system,and the system can meet the requirements of coal mine safety detection standards.The research work in this dissertation provides an effective solution for the application of laser absorption spectroscopy technology in the measurement range and accuracy of coal mine underground natural ignition index gases,and lays a solid foundation for determining the quantitative relationship between coal spontaneous combustion multi-component index gases and characteristic temperature,the establishment of coal spontaneous combustion characteristic information index system and the determination of hierarchical early warning method,as well as the identification and early warning of hidden fire source of coal spontaneous combustion.