Study on coal spontaneous combustion prediction and control technology during withdrawal period of super long fully-mechanized mining face

In order to control the long-mechanized coal spontaneous combustion in the gob of No.9303 ultra-long fully-mechanized mining face in Jining No.2 coal mine caused by the long shelf-removal cycle, the large amount of residual coal in the gob and the existence of air leakage, etc., the combined monitoring method was used to study the integrated prevention and control technology suitable for coal spontaneous combustion prediction and prevention during the period of super long working face removal based on mathematical modeling, temperature-programming test and in-situ monitoring. According to the existing research on the prediction of CO in upper corner during mining and the on-site conditions, the mathematical model of CO concentration in upper corner during the stoppage and withdrawal of the support was deduced.The generation of CO and C2H4 during the oxidation and temperature rise of the gob was obtained by the programmed temperature chromatographic analysis test. According to the theory of coal spontaneous combustion risk area, the distribution of "three zones" in gob was observed on the spot. Through the mathematical model of CO prediction in upper corner, the monitoring data of gob beam tube and the calculation of working face parameters, the predicted concentration of CO in upper corner was obtained, and the risk of spontaneous combustion of residual coal in gob was judged.Finally, combined with the prediction results, the characteristics of working face ignition and the experience in coal spontaneous combustion prevention and control, the prevention and control measures such as leakage reduction, inerting and cooling were put forward. The results show that the critical temperature of the residual coal oxidation temperature is 60～80 ℃, the drycracking temperature is 110～130 ℃,and the index gas of residual coal oxidation temperature in gob increases exponentially with the change of temperature.The predicted concentration ranges of CO in the upper corner corresponding to the three characteristic temperatures of normal temperature, critical temperature and dry crack temperature are respectively:36.30×10-6,(410.02～1 758.05)×10-6,(12 264.33～38 197.95)×10-6.By comparing the predicted concentration of CO in the upper corner with the field monitoring value, the degree of spontaneous combustion of coal in the gob during the stoppage and removal of mining was successfully predicted. The corresponding prevention and control measures proposed successfully eliminated the hidden dangers of spontaneous combustion of coal and ensured the smooth progress of removing the support frame.