Study on the Spontaneous Combustion Characteristics and Prevention Technology of Coal Seam in Overlying Close Goaf

The short-distance coal seam group refers to the coal seams which has obvious mining influence on the adjacent coal seam during mining process. In the process of short-distance coal seam mining, there are a large number of cracks around the stope due to the mining stress, resulting in serious air leakage and high risk of spontaneous combustion. To mining the working face under the condition of overlying close goaf in Xutuan Coal Mine in Huaibei Mining area, the distribution of spontaneous combustion dangerous area in goaf was studied systematically with the help of engineering test, laboratory research and numerical simulation. Results show that a "Gamma" distribution of high oxygen concentration area was found above the roadway of the goaf due to the effect of air leakage and coal seam space, the high spontaneous combustion risk area is close to the return airway. A three-dimensional distribution of the high spontaneous combustion risk area was formed in the composite goaf after mining in the lower coal seam face, the spontaneous combustion risk of the upper position is higher than that of the lower position. Besides, based on the pyrolysis-room temperature oxidation experiments of coal sample, it is considered that the inert environment and high temperature promote the production of active groups in coal and thus enhanced the oxidation ability of coal, mechanism of spontaneous combustion of residual coal in the overlying goaf was further revealed. Accordingly, the comprehensive fire prevention and fire extinguishing measures of nitrogen injection, leakage plugging and inhibitor injection are put forward. With the method of numerical simulation, it was found that nitrogen injection at the position of 50 m in the goaf can effectively reduce the spontaneous combustion risk in the compound goaf, and the injection of TEMPO inhibitor was put forward based on the secondary oxidation characteristics of residual coal. The research conclusion can provide theoretical guidance for the fire prevention technology of coal seam mining in the overlying close goaf.