Energy recovery from incoming high pressure cold water in deep level mines

The mining industry in South Africa, being responsible for 18% of electricity demand, is seriously looking at alternative, more energy effective processes, without reducing output. Deep level mines require large volumes of cold water at the underground production levels. The energy consumed by these pumping installations constitutes approximately 14% of the mine's overall demand. Normally, water is refrigerated on surface and sent down the mine to depths of more than 3000m below surface. The pressure of this water at a specific production level can be up to 10 times higher than that which is required for work at that level and this excess pressure is then dissipated to the required working pressure by means of Pressure Reduction Valve (PRV) stations. If the potential energy of the pressure of the incoming cold water can be utilised, instead of being dissipated, significant energy savings can be achieved. Two such technologies exist in the mining industry and are described in this paper: The Three Chamber Pump System (3CPS) and the Pump-as-a-Turbine (PaT) system. A case study of such an installation is presented, which shows that electricity savings of between 15%-25% on the mine pumping system can be achieved. Making use of the Eskom IDM funding programme, the payback period can be reduced from about 6 years to less than 3 years.