| Mine fire is one of the main disasters faced by coal mining,especially in the mining of extra-thick coal seam group,using the top-down coal mining method,due to the overlying rock layer is affected by multiple mining,easy to produce a large number of mining fissures,forming a complex wind leakage and oxygen supply channel,water along the fissures into the void area,and at the same time,the"water vapor replacement"phenomenon generated by water exploration and release will also cause secondary or multiple oxidations of waterlogged coal and increase the amount of wind leakage.At the same time,the phenomenon of"water vapor replacement"produced by water exploration and release will also cause secondary or multiple oxidations of waterlogged coal and intensify the amount of air leakage,which will increase the natural danger of the mining void area of extra-thick coal seam stratification,and has serious harm to the physical and mental health of underground coal mine workers and the safety production of enterprises.The research on the evolution of the fracture field in the seam mining of extra-thick coal seams in China is not perfect,and the effect of spontaneous combustion prevention technology in the mining area is not satisfactory.In this dissertation,the research on the dynamic evolution and quantitative evolution law of fracture field of extra-thick coal seam stratified mining,the difference between spontaneous combustion characteristics of raw coal and dipping air-dried secondary oxidized coal,and the determination of the natural danger zone of coal is carried out,and the comprehensive spontaneous combustion prevention and control technology of extra-thick coal seam stratified mining is constructed on this basis,which is of great use and theoretical value to ensure the safe and efficient recovery of extra-thick coal seam stratified mining mines.Using similar simulation experiments,the dynamic evolution law of stress field and fracture field of single upper seam mining and both upper and lower seam mining of extra-thick coal seam is studied based on the fugacity conditions and mining method of 172307 working face of Lingquan mine,revealing the dynamic evolution process of roof fracture,the number of cycles to pressure,step,the highest off-seam fracture,stress distribution characteristics and overburden rock The change law of"three belts"with the distance of working face,etc.,and the key area of fire prevention and extinguishing were determined.PFC2D software was used to construct a two-dimensional model of the direction and tendency of mining of extra-thick coal seams,and to obtain the dynamic and quantitative evolution law of overburden collapse,top and bottom fissures,and the dynamic data set of porosity distribution in the mining void area.The number of mining fissures shows a segmental growth trend in the process of mining a single upper stratum and both upper and lower stratum;through the dynamic data set of porosity distribution in the PFC2Dmining area,based on the bottom plate stress and overburden fissure zoning characteristics,we proposed to compile the porosity and permeability zoning by dividing into three areas along the coal seam strike direction and two areas along the coal seam tendency direction and fitted the mathematical model of porosity and permeability in the mining area.The surface morphology,pore structure,and main functional groups of raw coal and waterlogged air-dried secondary oxidized coal were studied by scanning electron microscope,automatic specific surface area,porosity analyzer,and Fourier infrared spectrometer,and the structural differences between raw coal and waterlogged air-dried secondary oxidized coal were obtained;the signature gas release pattern,oxygen consumption rate and combustion characteristics parameters of raw coal and waterlogged air-dried secondary oxidized coal were investigated by using programmed temperature rise and thermal analysis devices.The natural hazard,natural signature gas,and critical oxygen concentration of spontaneous combustion of raw coal and water-immersed air-dried secondary oxidized coal were investigated by using programmed temperature rise and thermal analysis devices,and the increase in the natural hazard of water-immersed air-dried secondary oxidized coal was mainly due to the change in the pore structure.Using CFD simulation software,the distribution models of oxygen consumption rate,exothermic intensity,spontaneous combustion critical oxygen concentration and porosity and permeability of the coal body are combined to obtain the natural hazard area of seam mining of extra-thick coal seams under a steady-state;on this basis,the natural hazard area of seam mining of extra-thick coal seams under different advancing speed conditions is established by moving coordinate system,and the minimum advancing speed is determined by combining the change law of oxygen concentration field and temperature field is 3.6m/d.Based on the results of the dynamic evolution law of fracture field,coal spontaneous combustion characteristics and natural ignition law of extra-thick seam mining,the three-in-one integrated fire prevention and control technology system of"inerting and cooling,covering and oxygen isolation,plugging and wind control"was proposed for extra-thick seam mining.Through field industrial tests,a series of measures such as liquid nitrogen injection,spraying inhibitor,grouting and slurry spraying can effectively prevent and control the spontaneous combustion of coal relics in the mining area of extra-thick coal seam stratification.There are 108maps,23tables and 233references in the dissertation. |
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