Closed-loop bulk air conditioning: A renewable energy-based system for deep mines in arctic regions

Abstract

With depletion of shallow deposits, the number of underground mines expected to reach more than 3 km depth during their lifetime is growing. Although surface cooling plants are mostly effective in mine air-conditioning, usually secondary cooling units are needed below 2 km depth. This need emerges due to the elevated thermal impacts caused by auto-compression of mine air as well as heat emissions from strata and mine machinery. As a result, in cold climates, like Canada, ultra-deep mines need their secondary underground cooling plants running year-round while the intake air must be heated to protect the sensitive machinery and liners from freezing during the winter season. To cool mine air, horizontal bulk-air-conditioners with direct spray cooling systems are commonly used due to their high performance. Conventionally, sprayed water in bulk-air-coolers are mechanically circulated and refrigerated in coupled refrigeration plants. This set up can be transformed to a natural cooling/heating process by resurfacing the warm underground bulk-air-cooler spray water for mine air heating on the surface and re-sinking the chilled water for cooling in the underground bulk air coolers. This could significantly cut-down the fossil-fuel consumption in burners for mine air pre-conditioning and refrigeration cost when applicable. This paper presents an anonymous real-life example to study the feasibility of the proposed idea for an ultra-deep Canadian mine.