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Modeling Cavity Growth in Underground Coal Gasification

A. Sarraf Shirazi, J. Mmbaga, and R. Gupta
University of Alberta
Edmonton, AB

Underground coal gasification (UCG) has received renewed interest due to its potential for utilization of the vast amounts of coals available in deep underground seams and the current drive towards clean coal utilization. UCG process involves the reaction between air/steam and coal in deep underground seams to form a combustible gas which is brought to surface via a production well and used as a fuel or chemical feedstock.

This paper presents a model for the growth of cavity with the chemical reactions, which is crucial for determining the duration and extent of the reaction process for a given injection point. COMSOL Multiphysics is used to model the combined effects of fluid flow in porous media, mass transfer of species, heat transfer, and reaction kinetics. Growth of the cavity is tracked by changing the porosity/permeability with reactions.

Cavity shape, growth rate, and temperature profile are presented and compared to literature values and recent field trials.