Analysing the impact of pre-cooling on mine refrigeration systems

Abstract

Globally the mining sector is facing a harsh economic climate, with sharp increases in production costs and decreased productivity. In South Africa the situation is worsened by the continuous increase in labour and electricity costs. The South African mining sector consumes close to 15% of the total electricity supply, which contributes to 30% of their operational costs. Refrigeration systems are one of the largest energy consumers on mines, accounting for 28% of a mines total power usage. As development expands deeper underground the cooling requirements increases. There is a clear need to improve the efficiency of the existing refrigeration system infrastructure. The main focus of most studies lies on the energy intensive refrigeration plants; however, they form only a small part of the mine cooling system. Pre-cooling plays a vital role in the efficiency of the cooling system. There is also a lack of maintenance on cooling towers, creating the possibility to investigate the impact that Pre-cooling towers have on the whole cooling system. This dissertation investigates the effect Pre-cooling towers have on mine refrigeration systems. Specifically, how deteriorated pre-cooling negatively effects the performance of refrigeration system compared to the optimal operating conditions. This was done by identifying ineffective pre-cooling, developing an optimised solution and implementing the solution on mine refrigeration systems. Implementation of the proposed solution resulted in an observed increase in the pre-cooling efficiency. The improvement in efficiency can lead to a reduction in the operation cost of the refrigeration system. It must however be noted that mines which exceed their cooling capacity will not experience a reduction in their refrigeration system’s operational costs. They will, however, experience an increase in their cooling ability. The case study showed a reduction of 6.7°C on the chill dams. The energy savings and operational improvements are subjected to external factors such as the ambient conditions and water usage. It can therefore be concluded that, through improving the efficiency of the cooling towers, the overall performance of a mine’s refrigeration system can be improved along with an associated reduction in the operational costs. The focus after optimisation must however be on continued maintenance of the pre-cooling towers in order to derive a sustainable benefit