Improved control of clear water underground pumping system for demand side management at an interconnected South African goldmine
Abstract
Deep level clear water pumping at gold mines accounts for nearly 30 % of a mine’s total electricity consumption. Demand side management (DSM) initiatives for various deep level water pumping systems have been implemented throughout South Africa for more than a decade which contributed to the reduction of the demand for the national electrical utility, Eskom. Therefore many DSM load shifting projects at South African mines have been implemented, but most of the solutions were on single shaft pumping systems.
To date, no successful fully automated load shifting project has been implemented on an intricate interconnected underground gold mine pumping system with several shafts. This paper presents work done to optimise an automated pumping control system on a mine and comparing it to manual load shifting results.
The mine studied consisted of three shafts and pump stations at six interlinked levels. Total power demand peaks at 16 MW on weekdays. A simulation of the mine’s pumping system has been done by iterating pumping times to find optimal dam levels throughout the day in order to increase electricity cost savings in Eskom peak times. Data was collected from the mine in order to generate an effective water and energy balance to validate the simulation. The simulation consisted of a control strategy which focused on each level individually without inputs from other levels. The simulation model had a 91% accuracy for the maximum amount of load that can be shifted. Previous studies indicated that an automated load shifting system resulted in more electricity cost saving for mines.
This paper illustrates that with semi-automated load shifting a higher electricity cost saving potential is possible than with manual load shifting. Semi-automated load shifting had a 78% increased cost saving in summer and a 5.5% increase in winter when compared to manual load shifting results. The evening peak load shifting amount for semi-automated load shifting increased by 38% in summer and 0.11% in winter when compared to manual load shifting. The most efficient point to operate the mine’s pumping system, in order to gain the maximum possible electricity cost saving with load shifting has been indicated by a controller.
Increased electricity cost savings for the mine also means that pressure will be relieved on Eskom’s distribution system due to a reduction in peak demand electricity usage
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