Investigation on the potential hazard zone of gas explosion in the goaf under longwall top caving coal mining condition

In the present work, the potential hazards in mining goafs of multicomponent gas explosions coupled with coal spontaneous combustion were systematically analyzed using both an experimental and numerical method. Programmed heating experiments show that many kinds of combustible gaseous products (CH4, CO, C2H6 and C2H4) are released during the coal oxidation process undersimulated mining goaf conditions. The generation rate of each gas increases significantly after 200 degrees C and reaches a peak value at about 400 degrees C similar to 500 degrees C. According to these results, a new model for the determination of the dynamic explosion limits of multi-component combustible gases in the goaf was proposed and validated to quantitatively determine the explosion hazard. Based on the dynamic explosion limits, the gases and temperature distributions in the goaf, the determination method for the potential explosion hazard in the goaf was proposed. As a typical working face in the Dafosi coal mine in China, the research results indicated that air leakages into the goaf influence the explosion hazard zones, but the hazard zones are always limited within the range of 50 m from the working face. To quantitatively analyze the risk of a gas explosion in the goaf zone, one index was defined to evaluate the explosion potential. With the mining forward, the risk index would be greatly increased after 30 days until to 50 days. After that, the risk in the deep zone would stabilize. The higher the amount of air, the higher explosion potential in the goaf.