An integrated 3D model for underground coal gasification

Underground coal gasification has received renewed interest in both Western and Eastern Europe because of the vast amounts of otherwise unminable coal deposits that occur on the European continent. A field test is currently being held in Spain, and other countries have also shown interest in this method of utilizing coal resources. In this study we have developed a model to combine reactive heat and mass transport together with thermomechanical failure behavior. In the model, we use multigrid methods to solve the flow equations in the entire domain. This is combined with thermo-mechanical failure properties of both coal and rock overlying the coal formation. With this approach, a 3D picture of the development of an underground coal gasifier is obtained, and the influence of well-layout and the sensitivity of the process to other model parameters can be investigated in detail, with high computational efficiency. The model consists of two modules : The first module solves the flow equations in the entire flow domain. The second module selects a block of coal for gasification and a block of coal and/or rock for thermo-mechanically induced spalling. Other features such as ash content, the possibility of including heterogeneities, and natural convection-driven cavity gasification are also incorporated in the model.