Recovering, and repurposing, otherwise wasted low-grade thermal energy contained within process water streams


Dr John Scott (Laurentian), Mr Greg Ross (Northern Ontario School of Medicine), Mr Ian Ross (Laurentian)

The mining and mineral processing industry contains many opportunities for heat recovery using heat pumps that could be capitalized upon to increase plant wide energy efficiency, decrease costs and reduce CO2 emissions. A facility can be rapidly analyzed for feasibility of heat pump assisted recovery of cooling water waste heat using models we have developed. To demonstrate this a variety of nickel smelter process cooling water flows of very low grade (10-25 °C) were examined for applicability to heat pump assisted space heating of associated office and laboratory facilities. The methodology presented is straightforward and robust, and suitable for use at any facility with "untapped" process cooling water flows. Our analysis highlights that onsite process cooling water can offer the potential for simultaneous cost and emissions reductions if recovered by an open-loop heat pump system. Modelling of the smelter process flows indicated that retrofitting a heat pump system could lead to a 19% reduction in space heating costs and a 62% decrease in CO2 emissions. Furthermore, the removal of thermal energy in the cooling water streams results in a cooler return flow that could further improve the efficiency of the process cooling.