Holistic evaluation of surface cooling plant configurations for different seasons at deep mines

Abstract

The mining sector consumes a large portion of South Africa’s electricity. Deep mining contributes to 15% of the total electricity consumption in South Africa. Mining electricity costs in South Africa have increased by 655% over the last 18 years. The increase in mining electricity costs is 3.6 times more compared to the increase of inflation for the 2021/22 year in South Africa. The electricity costs for a typical deep gold mine account for 18% of all the operating costs. Cooling systems in deep mines consume more than 20% of the electricity used on the mine and it is a big factor to be considered. Annual reports of deep gold mining companies state that rising mining costs will harm attempts to increase financial margins and growth funding on gold-producing operations with low margins (nearing the end of their operating lives). This may result in increased debt and a loss in the profitability of deep gold mines. The increase in mining electricity cost and the unreliability thereof are in the top 10 risks as identified by gold mining companies and opportunities to mitigate the risk are needed. Deep mines are influenced by electricity cost increases because deeper mines require more cooling. Research shows that electricity reductions in cooling systems of deep mines are possible. Surface cooling systems and cooling plant configurations of deep mines can typically become integrated and complex, as more cooling is required to go deeper. Changes made to complex and integrated cooling systems can affect the underground conditions of deep mines. A holistic evaluation was done on a complex and integrated cooling system with plant configurations for different seasons. An integrated, phased electricity saving approach was developed for a deep mine cooling system, maintaining the underground conditions. The electricity saving strategy of deep mine cooling systems will lead to electricity cost reductions in different seasons. The holistic evaluation entails five different steps to reach the desired outcome. This includes investigation and understanding, simulations, calibration and verification, simulated strategies and implementation and

validation. The different phases of the electricity saving strategies on integrated and complex cooling systems were evaluated and implemented and led to electricity cost reductions. Due to the complexity of the cooling systems of case study Mine A and the uncertainty of the effect on underground conditions, a phased electricity saving approach was developed. The second phase of the implemented electricity savings strategy led to a power reduction of 1.44 MW, resulting in a ZAR 1.73 million cost saving for one winter month and ZAR 5.18 million per annum. More electricity savings can be achieved if the ventilation system of the case study Mine A can be resolved. The phased electricity saving strategy that was developed through holistically evaluating surface cooling systems and plant configurations of a deep mine can ensure that an electricity reduction is achieved, while also maintaining underground conditions. This will lead to better service delivery on the deep mine cooling systems and lower electricity costs in different seasons. Due to the increase in mining electricity costs, the phased energy saving strategy that was developed for complex and integrated deep mine cooling systems will relieve the pressure on the increased debt and loss in profitability for deep gold mines.