Study On The Spontaneous Combustion Characteristics And Prevention Of Close-Distance Coal Seam Group Mining In Xutuan Coal Mine

Spontaneous combustion of residual coal in goaf is one of main disasters affecting coal mine safety production.In the process of close distance coal seam mining,due to the small distance between coal seams,the upper and lower goafs interconnected due to the influence of coal seam mining.The air flow penetrates into the overlying goaf through cracks and induces the oxidation and heating of residual coal to cause coal spontaneous combustion.In addition,once the spontaneous combustion disaster occurs,the toxic and harmful gases will flow between the upper and lower goafs,which makes it difficult to accurately determine the location of the spontaneous combustion and brings a serious burden to the mine fire prevention and control work.In this paper,the close-distance coal seam mining in Xutuan Coal Mine of Huaibei Mining Area is taken as the research object.Based on the elastic-plastic theory and the empirical formula of rock strat a collapse,the failure of coal seam roof and floor during the close-distance coal seam mining is analyzed,and the air leakage in the air leakage area is measured by the comprehensive method of“barometer+tracer gas”.It’s found that there is positive pressure air leakage in the inlet roadway and the working face,and the air leakage is 33 m³/min and 93 m³/min respectively,and the closer the inlet roadway is to the working face,the more serious the air leakage is outward.The low-temperature oxidation experiment and thermal analysis experiment were used to compare the gas products and characteristic temperature changes during the secondary oxidation process of the 7₁ coal in Xutuan Coal Mine and the coal samples with different pre-oxidation degrees.After pre-oxidation treatment,the gas products C₂H₄and C₃H₈ in the secondary oxidation process of 7₁ coal are significantly earlier than the initial oxidation temperature of raw coal,and the characteristics temperature is also significantly earlier than the initial oxidation of raw coal,especially for the dry cracking temperature,the maximum advance was 23.56℃.In addition,based on the theoretical calculation of the KAS method,the ignition activation energy of 7₁ during the secondary oxidation process is significantly lower than that of the primary oxidation.The secondary oxidation activation energy of the pre-oxidized coal at 160℃is 33.82KJ/mol lower than that of the raw coal.From multiple angles,the risk of spontaneous combustion of 7₁ coal in Xutuan Coal Mine is significantly increased during the secondary oxidation process.The gas composition and temperature change at different coal seam spacing positions in the overlying goaf were monitored by drilling.It was found that the smaller the coal seam spacing and the closer the coal seam spacing is,the more serious the influence of roadway air leakage is.At the same time,the method of combining engineering test with numerical simulation is adopted,and the distribution range of spontaneous combustion risk area in composite goaf is divided according to the oxygen concentration as the main index.The measured range of spontaneous combustion zone near the inlet side in the lower part of the composite goaf is 43.2 m–94.9 m,and that near the return side is 18 m–54.1 m.The maximum width of spontaneous combustion zone in the upper part of the composite goaf is 46.55 m by simulation analysis.In addition,the secondary oxidation of residual coal is induced in the upper part of the composite goaf due to the infiltration of airflow in the lower coal seam goaf,and its spontaneous combustion risk is the strongest.The upper part of the composite goaf is mostly in the range of oxygen concentration suitable for coal spontaneous combustion,which is blocked by rock in the process of air infiltration.Compared with the lower coal seam goaf spontaneous combustion risk area,the range is increased and the forward characteristics are obvious.Based on the investigation results of spontaneous combustion of residual coal in close coal seam mining of Xutuan Coal Mine,the comprehensive fire prevention and extinguishing measure of“strengthening monitoring,plugging nitrogen injection and high-level intubation grouting”were put forward.Meanwhile,Fluent numerical simulation is used to analyze the influence of different nitrogen injection positions on the distribution of spontaneous combustion risk areas in the compound goaf,and combined with the actual nitrogen injection in the mine,it is proposed that the nitrogen injection port is 30 m deep in the goaf,and the nitrogen injection interval is 30 m.It can play the best fire-fighting effect on the compound goaf.There are 37 figures,8 tables and 90 references in this paper.