| China will still use coal as the main energy source for a long period of time,but coal spontaneous combustion disasters occur frequently in the process of coal mining,which seriously affects the normal production of the coal industry.However,the coal-bearing strata represented by the Shendong mining area in my country generally have the characteristics of shallow coal seam burial and close coal seam spacing.During the mining process,it is easy to form a composite goaf that is interconnected between the surface and the goaf.The mining process brings a higher risk of coal spontaneous combustion.In order to obtain the evolution of the spontaneous combustion risk area in the goaf caused by the development of surface fissures in the shallow coal seam group during mining.This paper takes the goaf of shallow buried coal seam group in Ningtiaota Coal Mine as the research object.Using a research method that combines theoretical analysis and numerical simulation,based on the development law of surface fissures,air leakage mechanism and gas migration model in mined-out coal seams in shallow buried and short distances as support,Simulated the evolution of the spontaneous combustion risk area of the composite goaf under different mining conditions in the lower coal seam of the shallow-buried coal seam group,And according to the obtained law,further research was carried out on the fire-fighting technology mainly based on surface fissure sealing and surface injection of liquid CO2 technology.The results show that:By studying the change of oxygen concentration in the composite goaf at different advancing distances,it is found that when there is no overlying goaf,there are obvious changes in the "three zones" of spontaneous combustion in the goaf within 300m of the working face advance,however,after the working face has advanced over 300m,the spontaneous combustion "three zones" in the goaf have little change.When there is an overlying goaf,the oxidation zones on the inlet and return air sides of the upper and lower gobs advance with the working face,the oxygen concentration in the back of the goaf gradually forms a symmetrical distribution that gradually decreases from both sides of the gob to the middle.By changing the advancing speed of different working faces,it is found that the overall oxygen concentration of the upper and lower goafs decreases continuously with the increase of the advancing speed,the width of the oxidation zone on both sides of the overlying goaf is reduced by about 38m,the width of the oxidation zone on the inlet side of the lower goaf is reduced by about 236m,and the width of the return side is reduced by about 477m.The effect of plugging surface fissures to inert goaf can be measured by the maximum air leakage on the surface,when the surface air leakage is 0.5m3/s and below,the oxygen concentration of the lower coal seam goaf can be reduced to less than 8%in the rear area about 287m from the air inlet side and about 64m from the return air side to the working face.When the flow rate of liquid CO2 perfused on the ground is larger,the scope of the inerting goaf will be larger,and less perfusion time is required,liquid CO2 perfusion flow is more suitable for 1000m3/h,when combined with multi-point liquid CO2 perfusion,the 8 injection points use the least injection time and have better inerting effect on the overlying goaf. |
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