The Numerical Simulation Research Of Oxygen Concentration Under The Condition Of Nitrogen Injection

The goaf oxygen concentration field under different ventilation modes and different nitrogen injection schemes was studied by using the method of numerical sinulation.The mathematical model of the working face and goaf has been established based on fluid mechanics and the basic theory of porous media. It involves computational fluid dynamics method for numerical simulation the concentration distribution of oxygen. The nitrogen injection parameters were optimized by quantitative simulation.This paper analyzed the porosity distribution and gas flow resistance, based on analog simulation and theory analysis, employing the algorithm of test to confirmed the goaf caving coal and rock permeability, porosity and viscosity parameters.The whole area was divided into "three zones" according to different oxygen concentration. And the study of characteristics of spontaneous "three zones" under U、U+L and Y-type ventilation led to the conclusions as follows:.(1)Under U-type ventilation,the spontaneous combustion zone shrinking and moves closer to the working face as nitrogen injection increases. When the injection reaches180.12m3/h, it proves to be the minimum volume to prevent spontaneous combustion. Nitrogen injection position range from10to30m, the zone is smaller, about25m-35m, and the safety mining speed is lower than the normal speed. When position is at10m, the spontaneous combustion zone is about25m.(2)Spontaneous zone is different as the nitrogen injection changes under U+L ventilation. When nitrogen injection position is30m to working face, the spontaneous zone turns to be31m, and safety mining speed is1.9m/d. With the increase of nitrogen injection volume, Mining area inlet side of the spontaneous combustion zone width shrinkage significantly, and the return air side of the spontaneous combustion zone width with a little change. When nitrogen injection hole position distance30m to working face, the best nitrogen injection volume is180.12m3/h;(3) The width of spontaneous zone is82m with no nitrogen injection volume with Y type ventilation, the safety mining speed is about3.6m/d. Nitrogen injection volume is295.92m3/h, in order to prevent the Y-type from spontaneous combustion, mined-out area of reasonable nitrogen injection locations from20m to30m, spontaneous combustion zone is smaller from29m to32m.The best nitrogen injection locations is20m.the spontaneous zone is about29m.