The link between operational practices and specific energy consumption in metal ore milling plants – Ontario experiences

•Although energy consumption in mills is most efficient at design capacity, they are not always operated in this manner.•Top-down/bottom-up energy assessment reduces uncertainty in audit.•Demand savings and energy savings yield cost savings illustrated with the Ontario industrial tariffs. An energy audit was conducted on a base metal milling facility where a top-down, bottom-up approach was presented to balance data measurements and estimates. The relation between throughput and specific electricity consumption, presented as a part-load efficiency curve for a milling operation, was established from the audit data. Unsurprisingly, the most efficient use of electricity occurred when the mill was operating at design capacity, but a survey of 14 metal mills operating in Ontario showed that 12 were operated under design capacity during 2012. For base metal flotation mills, 16–36% electricity cost savings could be realized by modification to the operating schedule, which would ensure that these facilities operated at design capacity even if plant operation was intermittent. With the Ontario electricity tariff arrangements, additional cost savings from strategic scheduling could reduce demand during coincident peak hours, which could provide financial benefit to these milling facilities.