Gas Movement Law Of Overlying And Underlying Coal-Rock Under Mining Conditions And Gas Drainage Control

Coal occupies a dominant position in China’s energy consumption structure.Among the accidents probably occur in the high gas outburst coal mines,such as flood,fire and roof accidents and other disasters,the gas accident is the most serious accident,which causes great loss of property and life and produces harmful effect.At the same time,as a clean energy,gas’ exploitation and utilization also have broad prospects under the background of promoting the development and utilization of new energy in China.Therefore,prevention and control of gas disaster are the most important part in coal mine safety production.Gas drainage is the most effective way to control gas in coal mine enterprises.At present,gas drainage takes into account both mine gas control and gas utilization,which is an important measure for coal mine production safety,energy saving and environmental protection.The coal seams in China have a wide range of coal seam development,and all the major mining areas have development.A series of effective gas control methods have been explored by scientific researchers after years of theoretical,experimental and field studies.However,considering the Karst landform,an special conditions,in Guizhou,coal seam conditions are complex,development of structure,fault and karst and unstable coal seam,which make mining and gas treatment extremely hard,especially in near distance coal seam group.In the mining process of close coal seams,since the overlying and underlying coal rock and mining between the layers are very close,gas volume,discharges to the working face and gob is large,it is extremely easy to cause the upper corner gas accumulation and overrun and affect production,at the same time,the process of coal roadway in strip gas drainage is relatively difficult,which have seriously affected the coal mine pumping and mining and excavating balance.This dissertation studies on the gas flow pattern and gas comprehensive management during excavation and mining in the coal and rock near mass at 9# coal seam Longfeng coal mine of Lin Dong Coal Mining Bureau.It has theoretically analyzed the stress distribution and deformation law of overlying and underlying coal and rock mass influenced by mining.Meanwhile,the gas occurrence characteristics,flow patterns of diffusion and seepage are analyzed.Combined with distribution and mining condition at the 9# coal seam Longfeng coal——the first mining layer and outburst coal seam,it located in the middle of coal seam group and collected more gas emission in space mining—— theoretical analysis and numerical simulation are conducted about the unaffected 9# first mining coal seam outburst pre pumping method of mining,and through theoretical analysis and numerical simulation of 9# coal seam overlying and underlying coal rock mass deformation and gas flow law,zoning collection law,proposed legislative body drainage gas control method the dragon and mine 9# coal seam pumping of theoretical analysis and numerical simulation study.The radius of influence parameters,establishes the comprehensive gas control Longfeng coal mine 9# coal mining drainage system,so as to solve the overlying and underlying coal rock to 9# coal mining space flood control gas dilemma caused by the structure,and more than 30 units of mine in mining 9# coal seam has good reference and promotion.The main coal mines in Guizhou province are high gas outburst mines,the main coal seam gas content is higher in each district,the gas pressure is bigger and the coal and gas outburst dynamic phenomenon is widespread;At the same time,since U-type ventilation is the main mode in each mine,the gas accumulation is serious,which seriously affects the safety production of the mine.In the process of close distance coal seam mining,the gas emission is large and all kinds of disasters occur frequently.The safety accidents caused by gas accidents are very serious.Since the construction of Longfeng mine,more than 20 coal and gas outburst accidents have occurred during the mining process and the frequent gas overrun has greatly restricted the safety production of the mine.Longfeng coal mine consists of 9 to 15 layers of coal seam(line),with high quality anthracite as its main coal seam,4#,5#,9# and 13# coal,which belong to close distance outburst coal seam group,and each seam has high gas.In this dissertation,the sources of gas in the working face are calculated,of which about 73.5% come from the upper adjacent layer and about 26.5% come from the lower adjacent layer.Study on regional migration rule of pressure relief gas,the effective drainage radius and drainage borehole bottom position are deeply studied and a more reasonable drainage way was determine,taking into account that the key factors of gas drainage standards,eliminating outburst and gas control in the same times.Based on theory of mining condition in coal mining face under the overlying and underlying coal body pressure relief gas flow patterns,Analyses were conducted on the occurrence regularity of coal seam gas in general,it is given that the pore fracture system of different gas flow patterns and mathematical expression and coupling law of diffusion equation-gas migration flow.According to the condition of mining working face under the overlying coal rock zones,expounded the height of "three zones" development and the "three zones" in the law of gas migration,deformation distribution,stress and plastic zone distribution of coal and rock,and gas gathering above the working face of the "O" ring.Through theoretical analysis,9# coal seam Longfeng coal mine calculated the mining fractured area and height of 9# in overlying "three zone" of the calculation,analysis of migration and accumulation of gas in the pressure relief gas zones in goaf and the "three zones".At the same time,the theoretical analysis of the stress distribution,deformation and plastic zone distribution of underlying coal rock mass,further analysis of the underlying coal mining rock movement law of gas and gas accumulation area,finally,determined the focus of comprehensive gas control and drainage utilization.According to the above theoretical analysis,the numerical simulation of stress distribution,deformation and plastic zone distribution was produced by FLAC3 D version 5.0 in 9# coal seam mining face.Studied on the damage and fracture of the mining areas of mining the coal and rocks during excavation,provided important theoretical support for the mining method of gas pressure relief gas flow and selection the corresponding smoke.The numerical results obtained overlying and underlying coal mining process with the stress distribution and the deformation of coal and rock mass and the development of plastic zone.The "three zone" height,stress distribution and plastic zone,produced by simulation results,are basically same with theoretical analysis.Based on theoretical analysis and numerical simulation results and the actual conditions of Longfeng coal mine,obtained the 9# coal seam of Longfeng coal mine overlying and underlying coal rock mass deformation and fracture development,through FLUENT numerical simulation,law of the overlying and underlying coal rock mass flow and pressure relief gas accumulation as follow: During 9# coal mining,coal emission is large.Since the close-range between 9# coal with 4# coal and 5# coal,emission is maximum contribution in 9# coal,4# coal and 5# coal from a large number of pressure relief gas into the first excavation space,and the formation of a gas accumulation area in coal near 5#;A large amount of gas released from 4# coal and 5# coal first flows into the mining space,and a gas accumulation area is formed around the 5# coal;1# and 2# coal seams are far away from 9# coal,and are in the upper part of fracture zone,with a small amount of cracks and less gas emission,compared with 4# and 5# coal,it has certain hysteresis,and has little effect on the mining space,but because of the gas floating,another gas accumulation area will be formed near the 1# coal seam.The emission rate of 10#,11# and 13# seams in the underlying coal seams is about 26.5% of the adjacent strata,and the mining pressure relief gas moves upward to the 9# coal mining space with the development of the separation fissures and vertical fractures in the lower part.According to gas flow law and accumulation condition of 9# coal 5912 mining face in Longfeng mine,buried pipe drainage and high drilling along the groove is arranged in the air return,solved a lot of gas coal face gas accumulation area,numerical simulation confirmed the results the effectiveness of the drainage method.According to dynamic characteristics of gas migration,demand of gas drainage and actual situation of mining field in excavation and mining of 9# coal seam of Longfeng coal mine.Three dimensional drainage system was proposed,which contains bedding boreholes to solve pre-drainage gas in working face,gas drainage by pressure relief pipe and high position borehole gas drainage.Namely,High position drilling is adopted to carry out gas drainage for drainage area of 5# coal gas accumulation area in gob,and inclined boreholes are arranged for gas drainage in 1# coal gas accumulation area,the comprehensive gas drainage idea of gas drainage from closed gob after mining.From above,it has been studied that the key position of gas drainage treatment,however,in order to ensure the best gas drainage effect,it is necessary to further research on the effective radius of gas drainage.Based on the gas pre-drainage standard,through theoretical analysis and numerical simulation,studied on the drilling pressure,drilling hole diameter,length,hole spacing and drainage effect of mining time on drainage effect,optimizing drilling drainage parameters.The effect of stereoscopic drainage and eliminating in 5912 excavation face demonstrates that,facing of comprehensive treatment of gas drainage in multi gas source in close distance outburst coal seam of mining face,it can effectively liberate the gas accumulation in the upper corner of the coal seam and frequent gas over run,it also speeds up the mining speed and solves the restriction relation of "pumping,digging and mining".When the 9# coal is mined in other coal mines of this tectonic unit,the comprehensive gas control experience can be used for reference.