Study On Prevention And Control Technology System For Spontaneous Combustion In Shallow And Close Distance Coal Seam Group Of Suan Cigou Coal Mine

In the shallow and close distance coal seam group mining,due to the upper and lower coal seam mining repeatedly,not only the goaf of close distance coal seams will be connected through the cracks,but also the surface of the earth and the upper old goaf.It will lead more source and passage of air leakage and make a complex air leakage line.Therefore,once the spontaneous combustion of coal happened in goaf,toxic and harmful gases will flow between multilayer goafs.It is difficult to determine the location of fire,and make fire management more difficult.In addition,surface air leakage into the upper old goaf,which will bring the accumulated toxic and harmful gases in old goaf to the working face.As a result,it will impose great danger to the safety of the workers.Therefore,studying on the crack of overlying strata under this mining condition and the air leakage pattern in the goaf,and working out reasonable fire prevention measurements will be significant for preventing the spontaneous fire of residual coal in the goaf.In this paper,Suan Cigou Coal Mine is taken as the research object.According to the coal seam in this coal mine is shallow buried and the space between each coal seam is small which can easily lead the goaf and the surface connected and also between goafs.Based on this kind of mining condition,UDEC numerical simulation software is used to study the development and evolution of fractures in the upper and lower coal seam.The results show that after the mining of upper shallow coal seam,the fractures in the overlying strata are not connected with the surface.When the lower coal seam is mined from open-off cut to 60 m,the upper and lower goaf areas are connected through the cracks.When the coal seam is mined to 90 m,the overlying rock fracture of the upper goaf is connected with the surface due to the influence of the repeated mining activities.Based on the fractures connectivity condition in the mining process of shallow and close distance coal seams in Suan Cigou Coal Mine,the numerical model is established to study goaf air leakage.The Fluent numerical simulation software was used to simulate the air leakage in the mined out area when the ground surface was connected with the goaf.The simulation results indicate that when the air from the surface leaks into the upper old goaf,the air at intake entry of the face at the bottom will also leak into the upper old goaf through the roof fractures.It results in a complex distribution of oxygen concentration in the upper old goaf with local oxygen concentration exceeding 7%,and has high risks of spontaneous combustion.The air which is from the surface and bottom goaf in the upper goaf will flow into return entry at the bottom,increasing the width of the oxidation zone.Through the study on the air leakage in goaf of Suan Cigou Coal Mine,it is known that there are many air leakage sources in the mine.The poisonous and harmful gas in the upper goaf will flow into the working face easily.Therefore,it is difficult to obtain an ideal control effect only by using conventional measures such as inert gas injection,plugging and sealing.So,spontaneous fire prevention and control technology system is established by using the local dynamic balance control technology as the main method for multiple goafs in different layers,it can regulate and control the pressure difference in goaf by cooperating with a variety of conventional fire prevention measures.By using this method,the air leakage in the goaf is lessened,the oxygen concentration is greatly decreased,and the risk of coal spontaneous combustion and the possibility of toxic and harmful gas entering into the working face are effectively reduced.