Online monitoring system of index gases concentration applied to coal sponta-neous combustion

Coal resources, as the main fossil energy, play an important role in the national economic development.The high-efficiency and high-productivity of coal mines is the development trend of China's coal industry in the future.The main problem affecting the high-efficiency and high-productivity mining of coal mines is coal mine safety, and coal spontaneous combustion in goaf is one of the major disasters in coal mines.Real-time monitoring of gases concentration, the main index of coal goaf, is of great significance for preventing and controlling coal spontaneous combustion.A set of high integrated real-time on-line monitoring system for multi index gases is designed based on Tunable Diode Laser Absorption Spectroscopy(TDLAS) and multiplexing phase lock technology.The system makes use of the “fingerprint” absorption spectrum characteristics of different gas molecules and the narrow linewidth and fast tuning characteristics of Distributed Feed Back(DFB) laser.Fast detection of gas con-centration by detecting an isolated absorption line of the target gas, and in the system circuit design, multi-channel scanning signal and sinusoidal modulation signal without phase error are used.In this system, a lock-in amplifier is used to realize the real-time on-line detection of six kinds of index gas concentrations, such as CH₄,CO₂,O₂,CO,C₂H₂ and C₂H₄,through time-sharing and automatic channel switching.The detection limits of the system to six kinds of index gases are tested in laboratory, which are 9.9×10^-4,4.73×10^-4,0.12%,7.2×10^-7,1.3×10^-6 and 1.28×10^-5.The experiment shows that the system has good stability and low detection limit.In the cooperative coal mine, through the under-mine beam tube pumping system, the gas sample of the intake and return air roadway of the goaf is directly connected to the underground gas monitoring system, and the real-time gas concentration field test is completed.The test results show that the system can provide effective data guarantee for coal mine safe production and early warning, meet the requirements of coal mine safety detection standards, promote the establishment of coal spontaneous combustion characteristic information index system and the determination of classification early warning method, so as to realize the recognition and early warning of hidden fire source danger degree of coal spontaneous combustion.