| China produces tremendous coal and coal spontaneous combustion has been disturbing underground mining operations,which causes most fire accidents in mine sites.It is a standing procedure to deal with the fire emergency that seal ignition area with water until fire is extinguished.The coal gets hydrated due to water immersion.During the drainage,dewatering of the hydrated coal corresponds to a water saturation-air dry process.As to pore structure evolution and characteristics of spontaneous combustion in this situation,they are lack of study.Therefore,for safely unsealing,drainage and improving fire fighting in coal mine goaf,it is important that research spontaneous combustion in water saturation-air dry process.This thesis is based on regional geology and real mining operation of Maying mine,combining with literature review,experiments,theoretical analysis and numerical calculation.First,through measurement of moisture content,specific surface area,true density test,moisture content and change of pore structure,the changing regulation of the moisture content and the pore structure in water saturation-air dry process were obtained,concluding that secondary porosity is generated during the process.Then,spontaneous combustion characteristics of raw coal and hydrated coal was inferred through experiment and temperature programmed chromatography oxygen test in different particle size and drying time,obtaining the patterns of oxygen absorption and indicating gas evolution affected by particle size,drying time and temperature.As indicator,the detected gases include CO,CO2,CH4,C2H4,C2H6,C3H8.Finally,thermo gravimetric analysis was conducted on the coal samples in different particle size and moisture content by TG-DSC test,showing that there are 5 characteristic temperature T1-T5 in the test:T1 adsorption temperature,T2 dewatering temperature,T3 oxygen adsorption temperature,T4 ignition temperature,T5 burning-down temperature.Correspondingly,the spontaneous combustion can be divided into 5 stages,namely adsorption weight stage(T0-T1),desiccation weightlessness stage(T1-T2),oxygen weight stage(T2-T3),oxidative decomposition stage(T3-T4),combustion stage(T4-T5).The regulation that how saturated-air drying process affects the activation energy was obtained by calculating it at the 5 stages.Based on that,a model was developed for calculating spontaneous combustion time affected by size and moisture content.According to a series of theory related to porous medium,combined with flow field,thermal field and gas concentration distribution of the mining goaf,the mathematical model was developed for simulating hydrated coal spontaneously combusting in water saturation-air dry process.A set of data from 9104 working face was put into the model as initial conditions,and the process was simulated at different coal moisture content.The results show how water content and drying time affects the maximum oxygen consumption,CO generation,average concentration of CO,the maximum temperature,heating rate.It also pointed that,to 9104 working face,the critical moisture content is 14%.The results are not universal,however,the methods can be applied widely.By studying on coal seam geological condition,hydrogeological condition and recent mining operation of 9104 working face,drill holes were properly done when excavating air-return gate to release water and "three zones" were monitored at the same time.After mining flood,the oxidation zone is 1.4?2.9 times,average 2.45 times,as wide as before.It can be concluded that secondary pores are generated because of contractile force in water saturation-air dry process,which makes enlarged broken area,increased tunnels for air flowing and more specific surface.Those cause more adsorption of oxygen and thus increase probability of coal spontaneous combustion.Therefore,in mining goaf,the hydrated coal is more likely to spontaneous combust when drying after immersion,which should be highly noticed. |
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