MODELING THE VIABILITY OF UNDERGROUND COAL FIRES AS A HEAT SOURCE FOR ELECTRICAL POWER GENERATION

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. At various underground temperatures, a two-variable optimization scheme is used to determine minimum borehole depth and mass flow rate required to yield a fluid temperature of 100oC entering a theoretical binary-cycle power plant. Geologic and thermal data for the model are taken from field studies of an actual underground coal mine fire in Wyoming, USA. Life-cycle cost analyses are conducted to assess the feasibility of production of 100 kWe to 1000 kWe. Simulation results show that, under certain conditions, the concept is economically comparable to other alternative power generation technologies. 1