Application of a novel detection approach based on non-dispersive infrared theory to the in-situ analysis on indicator gases from underground coal fire

Coal mine fires, which can cause heavy casualties, environmental damages and a waste of coal resources, have become a worldwide problem. Aiming at overcoming the drawbacks, such as a low analysis efficiency, poor stability and large monitoring error, of the existing underground coal fire monitoring technology, a novel monitoring system based on non-dispersive infrared (NDIR) spectroscopy is developed. In this study, first, the measurement principle of NDIR sensor, the gas concentration calculation and its temperature compensation algorithms were expounded. Next, taking CO and CH4 as examples, the liner correlation coefficients of absorbance and the temperature correction factors of the two indicator gases were calculated, and then the errors of concentration measurement for CO, CO2, CH4 and C2H4 were further analyzed. The results disclose that the designed NDIR sensors can satisfy the requirements of industrial standards for monitoring the indicator gases for coal fire hazards. For the established NDIR-based monitoring system, the NDIR-based spectrum analyzer and its auxiliary equipment boast intrinsically safe and explosion-proof performances and can achieve real-time and in-situ detection of indicator gases when installed close to the coal fire risk area underground. Furthermore, a field application of the NDIR-based monitoring system in a coal mine shows that the NDIR-based spectrum analyzer has a permissible difference from the chromatography in measuring the concentrations of various indicator gases. Besides, the advantages of high accuracy, quick analysis and excellent security of the NDIR-based monitoring system have promoted its application in many coal mines.