Optimising energy recovery on mine dewatering systems

Abstract

Mines in South Africa face many challenges. Chief among these are rising production costs. This coupled with labour unrests and investor uncertainty means that mines are under significant strain. An excellent method to save costs on mines is through improved energy management, leading to better profitability. Mines are therefore continuously looking for innovative ways to reduce energy usage. Hydraulic energy recovery devices such as turbine pumps and three-chamber pipe feeder systems are often used to save energy. These devices use chilled water required for mining activities and underground cooling to aid in the resulting dewatering process. Hydraulic energy recovery devices do not entirely replace traditional pumps. It is therefore necessary to consider cost-saving initiatives on traditional pumping systems when controlling energy recovery devices. Previous studies show that typical cost-saving initiatives on these pumping systems are load management and water supply optimisation. Previous studies investigated the optimal integration of energy recovery devices into dewatering systems. However, these studies overlooked certain difficulties associated with controlling these systems. It was also found that certain technologies used in older studies were outdated. The study identified a need to develop an optimisation methodology to ensure maximum energy reduction through hydraulic energy recovery systems. The methodology must allow for additional cost savings through conventional load management and water supply optimisation. A methodology was proposed to optimally integrate hydraulic energy recovery devices into a mine dewatering system. The new process was verified through the simulation of a case study. The applicable methods were tested on the simulated case study and proved to be effective. The methodology was also tested on an alternative practical case study after being verified. The proposed methodology was used to develop a control strategy for the case study. The aim of the control strategy was to enhance the load management performance of the mine. It was shown that a load of 1.5 MW could be shifted from the Eskom evening peak and 2 MW from the morning peak. The result of these initiatives is a potential R1.7 million cost saving p.a. on the dewatering system of the practical case study if all the equipment remains available. The impact on the system electricity costs shows the effectiveness of the methodology.