The integrated effect of DSM on mine chilled water systems

Abstract

The national electricity utility in South Africa, Eskom, is currently under pressure to supply the increasing demand for electricity on a national level. To address this problem in the short term, Eskom partially funds load management and energy efficiency projects. In the meantime, Eskom is also increasing their generation capacity through the erection of new power stations. To finance these capital projects, sharp tariff increases, higher than inflation, are levied, resulting in higher operating expenditures for the consumers. These increased tariffs are especially affecting industrial institutions. Large industries are therefore willing participants in the partially Eskom funded electricity savings programme that hold benefits for both parties. One of these large industries is the Mining Sector. This sector is an energy intensive group and consumes up to 15% of Eskom’s total output. The refrigeration and pumping systems used in the sectors are two of the major electricity consumers. As part of Eskom’s Demand Side Management (DSM) initiative, an electrical energy savings project was implemented in the deep mines’ chilled water systems. The cooling system is optimally controlled to ensure less underground water usage. This ensures that less water is pumped out by the de-watering system, reducing electrical energy usage. A variety of components, such as refrigeration and energy recovery depend on chilled water to function properly. Every relevant component was simulated and the verification of results was done through correlations with process data obtained from the mine. The simulation results showed acceptable error margins that would not influence accuracy. Two sites where a water supply optimisations project was implemented were selected as case studies. In both case studies, thermal results of the refrigeration and cooling system showed a reduction in cooling effectiveness. In case study A, the energy recovery components showed negative results. All of the results were converted to electrical energy costs to enable comparison. Constraints were evident during deep mine water supply optimisation. These were determined and the thermal effects were simulated. This study enabled basic quantifications of environmental impact and also determining project cost savings. The studies showed that positive and negative effects can be brought on in the mining systems with the reduction in chilled water use. In some cases the cooling system components showed a decrease in cooling effectiveness, but exhibited electrical energy savings. This impact was during periods where no personnel were underground in the working area. In conclusion the study also showed that cost savings resulting from the reduced chilled water are substantially higher than negative financial losses seen on the other components.