Distribution law of gas and change rule of "three zones" in the goaf of fully mechanized top-coal caving working face under the continuous nitrogen injection

During the mining of the fully mechanized top-coal caving working face 8202 in Tashan Mine of Datong Coalmine Group,the nitrogen was injected continuously into the buried pipelines in the goaf to prevent from the spontaneous combustion of the missed coal in the goaf.At the same time,the concentration of oxygen and carbon monoxide before and after nitrogen injection was measured by the buried beam tubes in every measuring point,combining with the theory of the spontaneous combustion of missed coal in the goaf,the distribution change of "three zones" of coal spontaneous combustion in the goaf was got.The results show that in the continuous nitrogen injecting into the goaf,the concentration of oxygen decline significantly as the goaf depth increase,at last stabilize at 5% or so,and the concentration of carbon monoxide stay below 50×10-6 as the goaf depth increase.More nitrogen injection,more decline of concentration of oxygen and carbon monoxide.With much air-supplying and air-leaking volume in the working face,the width of heat dissipation zone was impacted little.After the nitrogen injection,the oxidation zone shorten about 60 m and the suffocation zone move ahead 70 m around.