Refrigeration and Cooling Concepts for Ultra-deep Platinum Mining

At present, the cooling of all the hot underground operations at Impala is achieved by providing refrigerated air from surface. However, the depth of a number of planned projects will approach 2 000 m below surface and other future proposed operations will extend to even deeper levels. Obviously these depths will approach the horizon where acceptable underground conditions can no longer be achieved by providing only refrigerated air from surface. At the deeper mining levels supplementary means of providing cooling will have to be implemented. The objective of this paper is to provide a review of the ‘supplementary’ refrigeration technology for the ‘ultradeep’ planned operations and suggest strategic recommendations in this regard. This paper includes a generic examination of the most cost-effective provision of cooling at depth and gives a summary of the strategic way forward for the future deep shafts and reviews the potential technologies to be applied. Impala’s operations have evolved through a number of generations in which the mining has become increasingly deeper and more ventilation and refrigeration has been applied. The cooling of all the second and third generation operations is achieved by providing refrigerated air from surface. In addition, all service water is cooled atmospherically in cooling towers on surface. Basically, the approach has been to provide more and more air and to make it colder as the depth has increased. For the more recent deeper projects this has included the use of a dedicated fridge shaft. Detailed trade-off studies indicated that this was a better approach to the alternatives of either making the main shafts bigger or introducing air cooling underground. However, as operations get deeper and deeper, the concept of surface bulk air cooling becomes less and less positionally efficient until ultimately the depth is reached where it becomes cost-effective to start introducing supplementary underground air cooling rather than more and more surface air cooling (even in dedicated fridge shafts).