The Study Of The Influence Of High Level Borehole Extraction To Goaf Spontaneous Combustion

Tens of millions of coal resources are lost because of coal spontaneous combustion and coal seam gas every year, it become the important factors which restrict the development of the world’s coal production. To prevent gas accumulation and explode,use the the high level borehole to drainage of coal seam gas, but in the process of drainage, the goaf air leakage will be increased inevitably, the distribution of goaf spontaneous combustion “three zones” will be affected, and the normal judge of residual coal spontaneous combustion in goaf will be more difficult. Therefore, combination with the practical situation of Xuan Dong Mine Ⅲ3303 mining face in this paper, use the numerical simulation method to study the residual coal spontaneous combustion in goaf in the condition of high level borehole.Through analyzing the coal spontaneous combustion theory, coupling theory of the goaf gas drainage and spontaneous combustion is understood. Gas migration rule is put forward under the condition of high level borehole on the basis of seepage theory and gas drainage. The Ⅲ3303 mining face takes “the hole of coal seam+low smoke lane+roof hole” comprehensive extraction method. Based on the actual data of goaf, the goaf gas concentration field and velocity fieldz are described, 303 working face goaf spontaneous combustion 3d model is set up. According to the simulation results, mined-out area is divided into “three zones” distribution by FLUENT software simulate. Reasonable and effective prevention measures are put forward on the goaf spontaneous combustion.Through analysis, as working distance increases, namely the deeper mined-out area,the goaf air leakage wind speed decreases, and the gas concentration increases, the oxygen concentration decreased. Before the high level borehole drainage gas, the goaf air leakage intensity of return air side is higher than in the wind and the gas concentration and oxygen concentration in the return air side was significantly higher in the wind side caused by the inadequate return air side roof caving and small wind resistance from the mining face the same depth. Air leakage is serious in the process of high level borehole,and the gas concentrations decreased. What is more, under the action of negative pressure of suction, return air side of the gas concentration was decreased due to the drilling in the return air side. At close range of mining coal face, the oxygen concentration is 20~21%,the oxygen concentration reduced to8%~13% into the wind side in 25m~40m range.Oxygen concentration is diminished distribution centered around drainage hole in return air side. Adopts double index partition method, Mined-out area of “three zones” is divided front and back the high level borehole drainage. As a whole, the increase in the oxidation zone of the goaf caused by process of high level borehole gas drilling, that is,the danger area of spontaneous combustion in goaf is increasing. The overall width of the cooling zone is larger, the overall width of the choke zone is reduced. The results of the numerical simulation of spontaneous combustion “three zones” and the results of the actual field sampling are little difference, which verifies the correctness of FLUENT numerical simulation.