Cold Flow Simulation in Underground Coal Gasification (UCG) Cavities

Abstract

Underground coal gasification (UCG), in the recent years, have gathered a significant amount of interest from the researchers because of its advantages over conventional mining and utilization techniques. It is one of the most promising and innovative technology where coal is gasified in-situ by injection of a suitable oxidant for the production of synthetic gas. The simultaneous occurrence of several phenomena such as complex flow patterns, chemical reactions, water influx, thermo-mechanical failure of the coal seam etc. make the mathematical modeling of the entire UCG process very abstruse and computationally challenging. The reaction between the oxidant and the coal in the deep underground seams leads to the formation of combustible gas and subsequently results in a cavity. As the gasification proceeds the cavity grows three dimensionally in a non-linear fashion. The cavity size strongly depends on several parameters like position and orientation of the inlet nozzle, coal properties etc. A comprehensive three-dimensional numerical study is conducted to understand the hydrodynamics within a given cavity size which would give us a relatively quick but reliable insights into the process. Five different cavity sizes are considered inside which the complete turbulent transport is simulated. Apart from the usual vertical and horizontal injection, the effect of inclined injection on the hydrodynamics is also reported here for the first time.