Numerical simulation of geothermal energy transfer beneath exothermic waste rock piles

Abstract

The installation of a ground coupled heat pump system can be expensive because it requires the drilling of boreholes to install ground heat exchangers. The cost of a system can be reduced by decreasing the total heat exchanger length or the number of boreholes, which depends, among other factors, on the ambient subsurface temperature. Systems designed according to heating loads therefore require fewer heat exchangers for higher subsurface temperatures. At open pit mines, where waste rock is accumulated in piles, exothermic oxidation of sulfide minerals within the piles can increase subsurface temperatures. To investigate the potential reduction in borehole length resulting from increased subsurface temperatures, heat transfer associated to a vertical ground heat exchanger installed beneath a waste pile was simulated with a numerical model. The physical characteristics of the pile are based on those of the South Dump waste rock pile of the Doyon Mine in Abitibi, Québec, Canada. Optimization of the heating loads assigned to the exchanger shows that the borehole length required for a given building can be reduced by 15% to 46%, depending on the location of the system relative to the waste rock pile.

Acknowledgments

Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) and additional student scholarships from the Fonds québecois de la recherche sur la nature et les technologies (FQRNT); the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE); the Canadian Foundation for Geotechnique (CFG); and the Canadian Institute of Mining-Thetford Mines Branch (CIM-TM). The contribution of anonymous reviewers to the improvement of the original manuscript is further acknowledged.

Jasmin Raymond, PGEO, PhD, Student Member ASHARAE, is Post-doctoral Fellow. René Therrien, PE, PhD, is Professor. Louis Gosselin, PE, PPhys, PhD, Member ASHRAE, is Professor. René Lefebvre, PhD, is Professor.