Study on mechanism of inducing coal spontaneous combustion and safe gas extraction volume under roof tunnel gas extraction

Based on the statistical analysis of roof tunnel gas extraction used in China,in order to coordinate the rela- tionship between roof tunnel gas extraction and coal spontaneous combustion,and to solve the problem of the coal spontaneous combustion induced by roof tunnel gas extraction,a case study was conducted in the Gengcun Mine,Chi- na. Firstly,though analyzing the measured data of roof tunnel gas composition and gob temperature,the occurrence of air leakage and coal spontaneous combustion were confirmed;Secondly,the air leakage passage and the constitute of air leakage power were identified by numerical calculation and theoretical analysis,and the mechanism of inducing coal spontaneous combustion under roof tunnel gas extraction was revealed;Thirdly,the concept of safe gas extraction volume was presented. According to the conservation of mass,using the ventilation air methane and the width of oxi- dized zone as constraint indices,the mathematical model of safe gas extraction volume was established. Through the model was tested,the mathematical model was verified and shown its validity and effectiveness.