| Goaf is an area where coal spontaneous combustion occurs frequently.Due to the complexity of the goaf,the coal spontaneous combustion heat source in the goaf is concealed.The study on the gas and temperature variation characteristics in the goaf caused by coal spontaneous combustion is the basis for analyzing and determining the location of coal spontaneous combustion heat source in goaf and carrying out effective prevention and control.In this paper,the goaf of 1301 working face in Longgu Coal Mine is taken as the research object.With the help of FLAC3 D numerical simulation software,the vertical stress and plastic failure change law of overburden rock during coal seam mining are analyzed.By analyzing the characteristics of the stress distribution on the strike and dip direction of the goaf,a goaf spatial distribution model suitable for this study object was developed;Using the programmed temperature experiment and theoretical derivation,the formulas for the oxygen consumption rate and CO generation rate suitable for spontaneous combustion of the coal in the goaf are established;On the basis of the above research,a numerical simulation model of the distribution of the gas-heat field of the coal spontaneous combustion hidden heat source in the goaf is developed,and variation law of gas and temperature field in the goaf with hidden heat source is simulated.The results show that:(1)Using FLAC3 D simulation software,the dynamic changes of vertical stress and plastic failure of overlying strata during coal seam mining were simulated and studied;According to the characteristics of plastic failure of the overburden rock after the coal seam mining is completed,the height of the caving zone is delimited to 15.05 m and the height of the fractured zone is delimited to 28.3m;Based on the characteristics of stress changes in the floor of the goaf,hyperbolic tangent function was used to establish a three-dimensional distribution model of porosity and permeability.(2)Programmatic temperature experiments were used to study the parameters of coal spontaneous combustion,and the formulas of oxygen consumption rate and CO generation rate of coal samples are established through theoretical derivation and regression analysis.Considering the effects of oxygen concentration,residual coal particle size,and residual coal thickness on the degree of oxidation of coal samples,the formulas were revised to obtain the formulas for oxygen consumption rate and CO generation rate of residual coal applicable to the actual goaf.(3)Comprehensively considering the spatial distribution characteristics of the goaf,residual coal consumption of oxygen,residual coal gas emission and other factors,a numerical simulation model of gas-heat field distribution of coal spontaneous combustion hidden heat source was established.The steady-state simulation method is used to simulate the gas field distribution in the goaf.The three zones of spontaneous combustion in the goaf were divided according to the oxygen concentration: the width of the spontaneous combustion zone on the inlet side of the goaf is 57 m,the width of the spontaneous combustion zone in the middle of the goaf is 46.4m,and the width of the spontaneous combustion zone on the return side of the goaf is 52 m.According to the results of the division of three zones in goaf,several possible heat source points are set in the spontaneous combustion zone,and the distribution characteristics of gas-heat field in goaf under different heat source conditions are studied.(4)Based on the steady-state simulation results of the gas field in the goaf,the distribution characteristics of the gas and temperature fields in the goaf in the presence of a hidden heat source were simulated.The results show that the migration of the disaster gas CO is mainly affected by the combined effects of ventilation wind pressure and diffusion.The heat transfer process of the heat source in the goaf is similar to the CO diffusion process in the early stage.Convection heat transfer is the main method of heat transfer.Due to the enhanced heat conduction between the broken coals and rocks,there is a certain difference between the heat transfer process and the CO diffusion process in the later stage.At the same time,the number of hidden heat source points in the goaf is increased,and the distribution of CO and temperature on the accessible boundary of the goaf is systematically studied when the heat source is located at different locations.And the research results are helpful to guide the analysis of heat source location. |
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