A review of options for cooling ultra deep mines in Northern Ontario and Quebec

MEMO 2014
The definition of ultra deep mines adopted in this study was one where the autocompression mine ventilation air temperature at intake to a mine levels is exceeded by the virgin rock temperature (VRTs) at the same depth. Under these conditions, significant new heat loads (in the >10 MWR range), arise from broken ore and rock and these are in addition to those expected from strata heat, electric and diesel powered equipment and curing processes. At shallower depths where autocompression temperatures exceeded VRTs, broken rock may have acted as a heat sink and cooled ventilation air, especially if the rock was wetted down.

As well as producing estimates of required refrigeration duties necessary to bring expected mine air temperatures to acceptable levels, mine climate simulations for these new deeper conditions also produced some counter intuitive results. The most important of these was that the substitution of diesel mining equipment with electrical equipment produces far lower energy and cost savings, associated with lower ventilation system duties, than previously anticipated. Air flow rates do not fall substantially because they have to be maintained to dilute the heat (rather than to dilute air borne contaminants). The magnitude of waste heat transferred to mine ventilation air by diesel powered mining equipment fleets is in the multi-megawatt range, and this heat acts similarly to strata heat in that it promotes Natural Ventilation Energy. When a diesel fleet is replaced with an electric fleet, this contribution to NVE is lost, and the duty on main and/or surface fans must increase to maintain the same air flows.

The top three ultra deep mine cooling concepts that were identified as being the most promising options for the region were: i) ice stopes (as exemplified by those at Stobie mine, but equipped with a springtime air bypass), ii) lake cooling (as exemplified by the system installed at Cornell University) and iii) hydraulic air compressors (as exemplified by the system that operated at Ragged Chutes, Cobalt, Ontario). The discounted cost of refrigeration kWh supplied using existing shallow stopes reengineered as ice stopes was found to be one sixth of that of cooling with mechanical refrigeration plant.
Keywords: Mine ventilation,Ice stopes,Mine refigeration,Deep mine cooling,Ultra deep mines
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