Research Of Temperature Distribution Of Coal Deposits At The Mining Scale

It is necessary to research on the temperature distribution law in coal bed for resolving high temperature thermal damage effectively and preventing spontaneous combustion of coal in goaf. In this paper, a simulation study and experiment research of the temperature distribution law in coal bed has been made which provides theoretical bases for underground cooling measures and appropriate ventilation strategy.Firstly, based on the volume average theory of porous media, a three-dimensional coupled mathematical model of the coal bed was built by analyzing heat transfer mechanism of the stope. The volume average theory and Darcy-Forchheimer empirical formula were combined in the derivation of the momentum equation and a uniform flow equation of mined-out area and work face was established. On heat transfer aspect, by deeply analysis the heat source in coal mine bed, author presents a more actual internal heat form and temperature field boundary conditions, and calculation scale expanded from work face and mined-out area to the place of surrounding rock which temperature close to the original rock. In porosity simulation aspect, based on the original two dimensional porosity continuous distribution model, a three-dimensional porosity model has been developed so that to improve the reliability of numerical simulation results.The proposed mathematical model was discrete under control volume integration method. Among them, general variables use ordinary grid and momentum equations use staggered grid. Besides, coupling between velocity and pressure use SIMPLE algorithm treatment and convection terms use power format. Source terms use local linearization assumption. The second and third boundary conditions use additional source term method. In order to solve the model, alternating direction linear iterative method was used, and sub-relaxation approach has also been given. Finally, author programs three-dimensional solution to resolve the discrete model numerically by FORTRAN programming language to obtain numerical simulation of coal bed flow field,temperature field and oxygen concentration field.Secondly, in order to verify stope temperature distribution during underground mining, a reduced scale test rig was constructed to mimic the heat transport phenomena within the coal mine stope. Based on the governing equations of the flow and temperature field in the stope, the dimensionless correlations ofδr2χr/ur2=δr3dnr2/ur=χr/pfr and xr/urTr=1/qr were proposed to reproduce the phenomena in the actual stope. Reasonable values for independence variables were suggested and scale numbers for heat sources to yield similar temperature distribution were also derived. Meanwhile, the measured temperature distribution is compared with the numerical simulation data in the spontaneous oxidation zone of the goaf. It is shown that the trend of temperature distribution presents a regular pattern both theoretically and empirically that keeps agreement with the numerical simulation results and that the heat transfer in the mine stope can be reasonably reproduced in the established model.Finally, the author analyzes and validates three-dimensional temperature field model of coal bed that presented in this paper through measuring the temperature field of Linnan Coal Mine 11 coal seam. The process of air flow and heat transfer in Linnan Coal Mine 11 coal seam 1019 working face and goaf is simulated using the model proposed. Actual stope parameters are considered and the regular pattern of flow field and temperature field distribution is given. Results of simulation and measurement are compared and analyzed. The results shows that temperature peaks of every cross section appear at stope centerline in the side of the tailgate, and the temperature of air return area in goaf is higher than that of air inlet area because of the influence of coal oxidation exotherm and palisades high temperature in goaf which results that the whole air return area in goaf formed local high temperature area. Although with few errors, the temperature distribution trend of actual value measured by thermocouple sensor consisted with the simulation curve. Results of temperature field simulated by the model can reflect the law of temperature field distribution in stope. The prediction of the coal bed temperature field distribution by the model can provide strong basis for forecasting coal spontaneous combustion in goaf and formulating ventilation strategies of work face in engineering projects practically.