Quantifying the effects of system constraints on the electricity cost of dewatering pumps

Abstract

Eskom embarked on a capacity expansion programme in 2005. The capacity expansion programme is being funded by above-inflation electricity tariff increases, which put large electricity consumers such as mines under financial pressure. The implementation of demand side management (DSM) initiatives has become an important measure to offset the impact of above-inflation electricity tariff increases in the mining industry. Mine dewatering pumps consume approximately 15% of the total electricity used at gold mines. The implementation of DSM initiatives on dewatering pumps can result in significant cost savings. Unfortunately, various constraints may negatively affect the cost savings generated by DSM initiatives on mine dewatering pumps. The system constraints include low pump efficiencies, low pump availability, low water storage capacity and high water inflow. The aim of this research is to quantify the effects of these system constraints on the electricity cost of dewatering pumps. Simulations were done to determine the cumulative cost effect of reducing the impact of the system constraints. The constraints to the electricity costs of the dewatering system were changed individually to quantify effects of each of the constraints. The effect of these changes were also added together to obtain a cumulative cost saving. It was found that cumulative savings of R21.57 million per annum are possible if an improvement strategy to reduce the impact of the system constraints could be implemented. The possible savings were also compared with the savings achieved when manual load shifting was done on the same mine. This manual load-shifting attempt was done by doing daily load shifting by stopping and starting pumps according to load-shifting possibilities. A brief overview was also given of a mine of which the mine dewatering system was being maintained properly. This study concluded by summarising the outcomes and making recommendations towards future studies.