Study On The Combined Anti-fire Technology Of Net In The Final Mining Stage Of Fully Mechanized Caving Face Prone To Spontaneous Combustion

Spontaneous coal combustion is one of the main natural disasters faced by the coal industry in China.The spontaneous combustion of coal in more than 90% of goaf is caused by geological structure,abnormal mining and stopping and removal of mining frame and other factors,which lead to the slowing and stagnation of mining speed.Especially at the end of mining frame stage,the mining on the working face is completely stagnant,and the dangerous area of spontaneous combustion in goaf is prone to spontaneous combustion because of long-term stable air leakage and oxygen supply.In view of the plight of "face firing" during stop-mining and shelf-removal of fully mechanized caving face in Baiguangou Coal Mine,Xu Mine Group,Gansu Province,this thesis proposes to adopt combined plugging of net cloth to seal off the whole working face and reduce air leakage in goaf during the laying stage of final mining shelf-laying.The distribution characteristics of location,area,temperature field and gas field of spontaneous combustion danger area under various sealing conditions are compared and analyzed.The evolution characteristics of the spontaneous combustion danger zone in goaf under the combined plugging of the whole working surface mesh are studied,and the influence law of different nitrogen injection parameters on the spontaneous combustion danger zone in goaf under the combined working surface mesh is analyzed.On this basis,combined with the similar experiment of the goaf physical platform,the distribution and flow characteristics of the temperature field and gas field in the abnormal oxidation zone of goaf under the action of mesh are further verified and mastered.The research results show that the combined fire prevention technology of net layout at the final collecting rack stage can effectively control air leakage in the goaf and reduce the area and distance from the working face of the goaf spontaneous combustion danger area,and the shrinkage effect of nitrogen injection inert goaf spontaneous combustion danger area is significant.The results of the project provide a theoretical basis for the implementation of the technology of air leakage and fire prevention combined with mesh and cloth,and provide safety and technical guarantee for the final collection rack of fully mechanized caving face.Detailed research conclusions are as follows:(1)Using numerical simulation method,the location,area,temperature field and gas field distribution characteristics of spontaneous combustion danger area in different plugging conditions were compared and analyzed,and the distribution characteristics of spontaneous combustion danger area in goaf under the combined plugging of the whole working surface network were mastered.The results show that the spontaneous combustion danger area of the goaf is closer to the working face,and the area of the spontaneous combustion danger area of the goaf decreases by 47%.The high temperature area and CO flow field in the goaf move to the return air side.Compared with the two channels,the goaf spontaneous combustion danger area is closer to the working face,and the coal spontaneous combustion area decreases by 70%.The high temperature area and CO flow field in the goaf shrink;Compared with the two plugging,the spontaneous combustion risk of goaf under the combined plugging of the whole working surface network is lower.(2)The influence law of the combined plugging of nitrogen in two channels and the whole working surface on the danger area of spontaneous combustion in goaf was compared and analyzed,the best nitrogen injection scheme under different plugging conditions was obtained,and the shrinkage effect of the combined plugging of nitrogen in the combined plugging of net and cloth on the danger area of spontaneous combustion in goaf was clarified.The results show that nitrogen injection should be used at both inlet and return air sides under two blocking channels,and the best nitrogen injection effect can be obtained when the nitrogen injection amount is higher than800m3/h.However,the best nitrogen injection effect can be obtained when the nitrogen injection amount is 600m3/h at 20 m behind the inlet air side under the combined blocking of the whole working surface mesh.Nitrogen injection at the air inlet side is 600m3/h.Compared with the shrinkage rate of the spontaneous combustion danger area in the goaf blocked by two channels,the shrinkage rate of the spontaneous combustion danger area in the goaf blocked by the whole working surface network is 9.51%,and the shrinkage effect is more significant.(3)Based on the goaf similar experiment platform,the variation rule of spontaneous combustion danger zone in goaf under different plugging was obtained and further verified.Without plugging,the oxidation zone position at the inlet side is about 40cm～90cm away from the working face,the oxidation zone position at the return side is about 40cm～90m,and the oxidation zone area is 4927cm2.On the inlet and return air side,the oxidation zone moved forward by 10 cm,the width decreased by about 20%,and the area of the oxidation zone decreased by 16%.Under the sealing of the whole working face,the oxidation zone on the inlet side moves forward by 20 cm,the width of the oxidation zone on the return side moves forward by 40 cm,and the width of the oxidation zone decreases by about 64% and the area of the oxidation zone decreases by 55%.Compared with the two blocks,the spontaneous combustion danger area of the goaf under the combined plugging of the whole working face network is smaller and closer to the working face.There are 82 figures,7 tables and 89 references in this article.