Steady-State Model for Estimating Gas Production from Underground Coal Gasification

A pseudo-one-dimensional channel model has been developed to estimate gas production from underground coal gasification. The model incorporates a zero-dimensional steady-state cavity growth submodel and models mass transfer from the bulk gas to the coal wall using a correlation for natural convection. Simulations with the model reveal that the gas calorific value is sensitive to coal reactivity and the exposed reactive surface area per unit volume in the channel. A comparison of model results with several small-scale field trials conducted at Centralia in the U.S.A. show that the model can make good predictions of the gas production and composition under a range of different operating conditions, including operation with air and steam/oxygen mixtures. Further work is required to determine whether the model formulation is also suitable for simulating large-scale underground coal gasification field trials.