The objective of this study is to examine the viability of extracting thermal energy produced from underground coal mine fires for electrical power generation. Underground coal mine fires present a high temperature heat source available at relatively shallow depths as compared to conventional geothermal resources. Several hundreds of burning underground coal mines are believed to exist worldwide. They may extend in plan area up to tens of square kilometers and are estimated to burn for up to tens of decades.

The performance of a closed-loop thermal energy extraction system, consisting of an array of vertical boreholes, is modeled using computer simulation. Geologic and thermal data for the model are taken from field studies of an actual underground coal mine fire in Wyoming, USA. Sensitivity and life cycle cost analyses are conducted to assess the feasibility of production of 1 MW of electrical power using a theoretical binary-cycle power plant. Simulation results show that the most sensitive parameters on the heat extraction rate are the average underground temperature and thermal conductivity. Based on model input assumptions, an average underground temperature of at least 190?C is required for a binary-cycle power plant to be economically feasible.

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