| The study on the prevention and control of coal spontaneous combustion is beneficial to the "green" mining and utilization of low-grade coal in northwest China and the safe and efficient exploitation of coal resources in northwest China.The physical and chemical changes,energy accumulation and migration and fluid-solid interaction of the goaf residual coal spontaneous combustion are the mine disasters caused by self-acceleration and concealed fire source.The principle of coal fire prevention involves many subjects.The simulation software can be used to simulate the temperature field and gas concentration field in the process of coal spontaneous combustion,so as to intuitively understand their changing rules and provide a basis for finding hidden source of coal in underground.Based on the spontaneous combustion experiment of coal,the temperature and gas changes in the reaction process of loose coal with oxygen at low temperature were explored.Combined with the thermal property experiment,the heat transfer and heat conduction characteristics of loose coal were revealed.The spontaneous combustion process of coal was presented by the simulation software to study the change rules of coal spontaneous combustion temperature field and gas field.The thermal conductivity and specific heat capacity of loose coal are analyzed by comparing the experimental results of different gas intake,thickness and thermal physical properties of coal samples.It is concluded that the thermal diffusivity decreases and the specific heat capacity increases with the increase of the air intake of the same coal sample,while the thermal conductivity increases,but the variation is small.The higher the degree of metamorphism of coal sample,the faster the decrease of thermal diffusivity.At the same time,the greater the change of thermal diffusivity.According to the coal spontaneous combustion experiment,the function equation of simulation parameters is selected.Low temperature oxidation exothermic of loose coal is not only the heat source of its heating,but also the heat source in simulation.The variation of gas distribution and temperature distribution during the whole heating process was studied by means of coal spontaneous combustion experiment.The results show that the maximum temperature point has strong mobility when the coal temperature exceeds the critical temperature.The maximum temperature point only takes one tenth of the ignition period to move more than one third of the original distance from the intake side.At the same time,it is found that the temperature decreases obviously at 65cm away from the intake side when the temperature is higher than 85 ?.According to the characteristics of coal spontaneous combustion experimental device,the geometric model of experimental furnace is established and meshed.The gas flow in the furnace is determined as laminar flow.Based on the actual oxygen concentration and temperature of coal,the parameters such as oxygen consumption rate and heat release intensity are modified.The mathematical model of coal spontaneous combustion is established.The results show that the coupling method is correct and feasible.Through Fluent simulation,the temperature field,the concentration field of O2,the concentration field of CO,the distribution law of the concentration field of CO2 in the furnace and the simulation results under high temperature conditions are obtained.It is found that the distribution of CO2 and CO in the previous experimental furnace is similar,and the distribution of CO is different when the coal temperature is higher.The main manifestation is that the distribution of CO2 concentration is less than that of CO concentration;in the later stage of the experiment,the volume proportion of high temperature points in the experimental furnace is small.It shows that the range of high temperature point of spontaneous combustion of residual coal in goaf is small.Hidden and movable high temperature point is the difficulty of mine fire prevention and extinguishing. |
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