The application of localized vapour compression technology in deep mine cooling: Presenting the underground Air Cooling Unit (ACU). (SAEEC2011)

Underground mining operations are some of the major energy consumers in South Africa. The intensity of energy usage is further linked to the depth at which mining takes place; the deeper the level at which ore is extracted, the higher the energy requirements become to perform actual mining and keep the environment within health and safety limits for workers. The mining industry and its consultants therefore invest a lot of time in optimizing energy requirements and to develop new energy efficient alternatives for certain mining and support processes as mines are getting ever deeper. M-Tech Industrial has developed a mobile Air Cooling Unit (ACU) for localized cooling purposes in deep mines, based on the operational principles of a heat pump vapour compression cycle. The technology holds several advantages over conventional cooling technology in mines. The major advantage is the fact that heat can be extracted from the air and pumped via the vapour compression cycle into water as heat sink. The ACU can utilise water at temperatures of up to 45°C as heat sink as opposed to chilled water only. The higher amount of heat contained in the water means that much less water is required underground for cooling purposes. The energy saving is therefore realized primarily in a reduction in the amount of water that needs to be displaced (pumped) from underground back to surface where the existing refrigeration plant is installed. A further reduction in energy requirement is realized by a reduction in refrigeration plant load. This paper will discuss in brief the basic operation of the ACU and how it is integrated into the mining environment. An energy balance analysis based on a model mine is then provided to illustrate the energy savings potential of the ACU concept on cooling processes at the mine. Lastly a parametric analysis is provided that illustrates the increasing economic viability of utilizing the ACU concept with an increase in depth of mining operations below- surface.