Use of mine ventilation exhaust as combustion air in gas-fired turbo-electric generators

Methane liberated in coal mines is a potential safety hazard because it is explosive at relatively low concentrations (5-15%) in air. To manage methane, underground mines are ventilated with large quantities of air, and in some cases the gas is also drained with gob wells, and predrained with vertical and horizontal wells. The ventilation air is used to dilute methane emissions to levels well below the explosive limit, and the diluted stream is discharged to the atmosphere. Unfortunately, this waste stream may contain as much as 60% of the total gas energy that was originally in the coal. Also, methane is considered by some to be 24.5 times more detrimental than CO₂ in contributing to the greenhouse effect. The volume of the waste stream, the high electric power demands of a mine, and the greenhouse effect of methane provide a strong incentive for converting the waste-methane chemical energy to the electrical or mechanical equivalent. A preliminary economic assessment of a proposed test-turbine installation at the Jim Walter Resources No. 5 Mine, shows that such a project makes good sense economically, even without considering the emission-reduction benefits. This unit could produce enough power to drive a ventilation fan, provide a profitable rate of return, and produce a 2% reduction in emissions. A market study indicates that there is the potential to generate 706 to 816 MW of power from mine ventilation gas in the United States