Convection mechanisms for geothermal heat exchangers in a vertical mine shaft

Transactions of the Society for Mining, Metallurgy, and Exploration , 2013, Vol. 334, No. 1, pp. 506-509

Thornton, R.; Wahl, N.; Blackketter, D.M.

This paper evaluated using a water-filled abandoned mine (Orphan Boy) as a heat source for a 240-kW closed-loop heat pump with the goal of heating a 2,000-m² building. The mine has a 245-m vertical shaft connected to a large stope by three horizontal cross-cut shafts. There is 1,250 x 10⁶ L of water at a consistent temperature of 24-26° C that is available mostly in the stope. The only heat exchanger placement option is in the vertical shaft. Therefore, the focus was to model heat exchanger placement in the vertical shaft to determine the extent to which the systems will induce thermal currents between the stope and vertical shaft. Modeling of thermal currents, temperature profiles and heat contribution from the ground was done using finite difference and computational fluid dynamics. An optimal configuration was determined showing sufficient water movement and heat transfer will occur with a low water temperature in the shaft above 20° C. This project supports a U.S. Department of Energy (DOE) grant that will implement the full-scale system.