Study On Temperature Propagation Characteristics Of Migration Process In Coal Fire Combustion Center

There are different degrees of underground coal seam combustion in all coal-producing countries in the world,which seriously threatens the lives of local residents and the safe production of coal mines.Studying the temperature field distribution characteristics of the coal fire combustion center migration process will help to deepen the understanding and research on the evolution mechanism of coal field fire area.The method of experimental research and numerical simulation was adopted.The physical and mechanical properties of coal and rock mass,was investigated and the similarity Criterion was used to detennine equivalent materials and their ratio for dynamic evolution of coalfield Fire.Simultaneously,the laser flash apparatus LFA457 were adopted to heat transfer characteristics of coal,respectively.Then a physical similarity simulation experiment device and numerical simulation for coalfield fire were built to explore the variation of temperature.The following conclusions are obtained:Similar Material Specimens was used to investigate the variation of uniaxial compressive strength,elastic modulus,and thermal conductivity.We found that the compressive strength and thermal conductivity could be adjusted in a large range by changing the sand-binder ratio,and those could be adjusted in a small range by changing the proportion of cements.Determine the ratio of similar simulation experiments applicable to coal field fire dynamic evolution.With the increase of temperature between 30 and 210 ?,the thermal diffusivity of coal sample gradually decreased,specific heat capacity gradually enhanced,and thermal conductivity gradually increased.When the temperature exceeded 210 ?,the thermal diffusivity of coal sample gradually increased,the increasing tendency of specific heat capacity tended to steady,and thermal conductivity gradually rapidly increased.Furthermore,with the elevating temperature,the thermal diffusivity of rock stratum gradually decreased and then tended to steady,specific heat capacity gradually enhanced and then tended to steady,and thermal conductivity gradually firstly inclined and secondly raised.Moreover,in fixed temperature,the largest thermal diffusivity,specific heat capacity,and thermal conductivity was sandy mudstone,siltstone,and sandy mudstone respectively.The evolution law of the movement of the high temperature point was obtained by monitoring of each temperature measuring point in the model.In the natural development phase,The highest temperatures in the coal seams of the No.1,No.2,No.3,No.4 and No.5 measuring point was reached 472.9 ?,419.6 ?,386.7 ?,357.8 ? and 141.3 ? at 48 h,108 h,168 h,204 h and 300 h,respectively.The time to reach the maximum temperature of 139.1 ?(No.33),128.5 ?(No.34)and 125.7 ?(No.35)in the overlying strata 1 and 81.6 ?(No.61),71.9 ?(No.62),69.3 ?(No.63)in the overlying strata 2 were 84 h,168 h,216 h,96 h,168 h and 216 h,respectively.The high temperature point of the coalfield fire moves along with the depth of the same level of coal seam,and the temperature of the high temperature point decreases gradually.Compared with the corresponding coal seam temperature,the overlying strata showing hysteresis has a lower maximum temperature and a longer time to reach the maximum temperature.Mathematical model is established based on similar simulation experiment device to investigate the variation of temperature for experiment device,and the evolution process of temperature field in different stage is analyzed.Those results showed that the high temperature source point moves to the intake side at first.The high temperature fire source moves to deep coal seam after coal is completely burned,and finally it cools down as time goes on.Temperature field in high temperature zone of coal seam is elliptical shape,and coal combustion consumes a lot of oxygen,which leads to the decrease of overall oxygen concentration in coal seam.Oxygen concentration in the goaf increases as the high temperature fire source moves deep into the coal seam.However,the oxygen concentration on the right side of the combustion zone is further reduced.