Limit parameter changes and hazardous area determination of residual coal spontaneous combustion in compound goaf

Secondary oxidation of residual coal is easy to occur in the upper layer when the layered fully mechanized mining is used in the extra-thick coal seam, which makes it more difficult to prevent and control coal spontaneous combustion.In order to accurately determine the hazardous area of spontaneous combustion in upper and lower stratified goaf in ZF1801 working face of Xiagou Coal Mine, the spontaneous combustion limit parameters of 4^# coal seam were analyzed through programmed heating experiment, and the hazardous area of residual coal spontaneous combustion in goaf was analyzed according to the gas monitoring data. The results show that the oxygen consumption rate and exothermic intensity of 4^# coal seam change with temperature both in accordance with Gaussian Function relationship; with the increase of residual coal thickness, the lower limit of oxygen concentration gradually decreases, while the upper limit of air leakage intensity gradually increases; when the residual coal thickness is constant and the temperature reaches 90 ℃, the limit parameters of the two are the lowest; the hazardous area of residual coal spontaneous combustion is 20 m to 125 m on the return air side of lower stratified goaf` in ZF1801 working face and its width is 105 m, while it is 0 m to 40 m on side of upper layered return air roadway and inlet air roadway and its width is 40 m; when the advancing speed of the working face is lower than 2.34 m/d and its mining is stopped for more than 28 days, there is a danger of spontaneous combustion in the goaf. The results can provide reference for the determination of spontaneous combustion hazardous area in goaf during the final mining period in lower layered fully mechanized working face.