Law Of Air Leakage In Goaf Of Shallow Seam In Ning Tiao Ta Mine And Its Application

Air leakage in goaf will promote the oxidation of residual coal in goaf,and may cause fire in serious cases.Shallow seam goaf is affected by both internal and external air leakage.The flow field in goaf may become more complex than that in common goaf,which increases the difficulty of fire prevention and extinguishing in goaf.In order to grasp the law of air leakage in goaf of shallow coal seam,firstly the characteristics of porous media in goaf,the flow pattern of mixed gas in goaf and the basic theorem and mathematical model of gas flow in goaf are given.Then the simulation method of air leakage flow field in shallow seam goaf is studied from three aspects:the distribution of porosity in caving zone,fracture zone and the setting of boundary conditions.In the caving zone,the negative exponential function is used to describe the distribution of porosity.For the coefficient a which represents the variation of porosity along the direction of goaf,and the coefficient b which represents the variation of porosity along the direction of roadway in working face,it is determined that a is-0.0223 and b is-0.08,by combining actual measurement with trial calculation.In the fractured zone,the method of combining the measured external air leakage with the trial calculation is given to determine the size of the porosity of the fractured zone.For the goaf under the influence of external air leakage,the method of setting pressure boundary conditions of the flow field in the goaf based on the calculation principle of mine ventilation network is given.Finally,according to the mathematical model of the gas flow in the goaf and the setting methods of these three aspects,the flow field of S1223 goaf in Ning Tiao Ta Mine is simulated when the external air leakage is 0,the external air leakage is 10m3/min,the external air leakage is 50m3/min(closest to the real external air leakage)and the external air leakage is 100m3/min.The simulation results show that the law of air leakage in show that the law of air leakage in shallow coal seam goaf is that the surface air leakage of 10m3/min has little influence on the flow field of goaf,which can be neglected,while the external air leakage of more than 50m3/min has a greater impact on the flow field of goaf,and the larger the surface air leakage,the greater the increase of the return cross wind speed in goaf.Based on the simulation results of goaf flow field with external air leakage of 50m3/min,the oxygen concentration distribution in S1223 goaf of Ning Tiao Ta Mine is further simulated The results show that the maximum oxidation temperature range is 0~260 m in the bottom plane of goaf.Combining with the flow field and oxygen concentration distribution law of S1223 goaf affected by 50m3/min air leakage,the risk of spontaneous combustion of residual coal in S1223 goaf of Ning Tiao Ta Mine is analyzed.It is found that the main influencing factor of spontaneous combustion of residual coal in Ning Tiao Ta Mine is the thickness of residual coal.In order to reduce the possibility of spontaneous combustion of residual coal in goaf,it is calculated that the minimum safe advancing speed should be 7.2m/d,so as to ensure the safe mining of S1223 working face in Ning Tiao Ta Mine,which is of great significance to the safe mining of Ning Tiao Ta Mine.