Study Of The Fluid Flow In An Underground Coal Gasification Cavity Model

Underground coal gasification technology,which is an environmentally friendly cleaning mining of deep coal resources,has attracted increasing attention under challenges of environmental pollution,sharp reduction of shallow coal and large deposit of deep coal.The physical and chemical processes in coal combustion involves jet,diffusion,heat transfer and chemical reactions,and the regimes are complex and diverse.Accordingly,the study of underground coal gasification technology is of value in industrial application and of significance in the field of fluid mechanics and heat transfer.Firstly,in the thesis,a simplified two dimensional numerical model describing the flow and thermodynamic progress in a gasification cavity was established based on the characteristics of the flow and chemical reaction of the combustion zone in underground coal gasification.The rectangular and water-drop cavities have an inlet at the bottom wall,an outlet at the left wall,an adiabatic bottom wall and isothermal top and side walls.Coal gas exists at the high-temperature wall surface and diffuses into the cavity.Secondly,SST k-ω turbulence model,P1 radiation model and ED combustion model were selected after the optimization tests of turbulence,radiation and chemical reaction model.Furthermore,a number of numerical cases for different Res and Les were obtained.The numerical results show that for Re = 100～423 and Le = 14,the jet flow is dominant in the gasification cavity.The distribution of the jet flow is uniform,and the vortex is distinct.The chemical reaction is sufficient,and the high-temperature combustion zone with weak radiation heat transfer is located in the middle of the gasification cavity.For Re = 50 and Le = 0.5～1,mass diffusion is dominant in the cavity.The distribution of the jet flow is nonuniform,the vortex is generated in the right region of the cavity due to mass diffusion.The chemical reaction is sufficient,and the hightemperature combustion zone with strong radiation heat transfer almost occupies the entire gasification cavity.For Re = 50 and Le = 5～14,the jet flow and mass diffusion are equivelent.The jet flow and high-temperature combustion zone may shrink and stretch with the weak radiation heat transfer,and the vortex size is periodic.The flow is periodic in the fully-developed stage.The fluctuation is mainly that the jet and hightemperature combustion zone shrink and stretch with time.The fluid flow and combustion in the water-drop gasification cavity are more complex for the same Re and Le.The simplified two dimensional numerical model of the flow and thermodynamic process in the underground coal gasification cavity and numerical results will be able to support for a further study of the complex dynamics process of underground coal gasification.