Reconfiguring mine water reticulation systems for cost savings

Abstract

Rising electricity costs in South Africa force companies, including gold mines, to minimise their energy consumption (EC). More than 30% of the total energy demand for deep-level mines is consumed by the water reticulation system (WRS). Energy intensive centrifugal pumps are housed in the dewatering system of the WRS. Significant energy and cost savings can be realised by decreasing the amount of water transferred through the dewatering system. To achieve this, cold-water supply or demand needs to be decreased. Water supply optimisation is a typical demand-side management (DSM) initiative that reduces EC of the dewatering system, by minimising cold-water supply to underground services. However, it only reduces water supply within the blasting shift, which is typically 6‒8 hours per day. Load shifting (LS) is a DSM initiative that optimises the time-of-use operating schedule on dewatering pumps. Note that a decrease in water supply to underground tertiary air-cooling systems increases the LS performance of dewatering pumps. For a decrease in water demand for the entire day, the WRS can be reconfigured. This entails removing chilled water cars and replacing them with strategically placed centralised bulk air-coolers. This results in increased energy and cost savings over the entire duration of a day. A methodology was developed to accurately evaluate energy and cost savings of the dewatering system for a reconfigured WRS. Actual data obtained from the mine was verified through calculations and simulations. This data was then used as inputs to evaluate EC of the dewatering system for the original and reconfigured WRS. The methodology was applied on a reconfigured WRS of a gold mine in South Africa. The predicted energy-efficiency and cost saving was 49.1 GWh and R31.8 million per annum, respectively.