Modeling of gas flow and temperature fields in underground coal fires

A two-dimensional model to simulate the flow and temperature fields in underground coal fires has been studied. The model is based on the theory of natural convection in porous media. A numerical solution procedure is used. Its predictions are compared with the limited field temperature data available. It is found from the model predictions that fractures or higher permeability are necessary to enhance natural convection. The air penetrates in the area behind the fire where many fractures of higher permeability occur due to subsidence. Air flows out from the hot area or cold area in front of the fire. In a shallow depth fire convection plays an important role, whereas in a deep fire convection velocities are smaller. Moreover, secondary combustion of volatiles produced from coal seam in the fracture or crack can markedly increase the convection. (C) 2001 Elsevier Science Ltd. All rights reserved.