Novel solutions for compressed air demand management on deep-level mines

Abstract

Mining makes a significant contribution to South Africa’s economy (7.3% of the gross domestic product) and provides direct employment to more than 450 000 people. The bulk of South Africa’s mineral wealth lies in deep-level platinum and gold mining. However, this industry is struggling to stay profitable. High operational costs have been identified as one of the major factors influencing profitability. One approach to improve the profit margins of deep-level mines is decreasing electricity costs. Industrial compressed air systems are major consumers of electricity on deep-level mines. It has been estimated that 40 to 80% of the generated compressed air is wasted through leaks, thus indicating that there is significant scope for improvement. Existing compressor electricity cost saving strategies focus on controlling the supply of compressed air which is limited to end-user requirements. Studies on underground leak reduction are limited. There is a need for methods to reduce deep-level mine compressor power consumption through the management of underground wastages. Benchmarking models have successfully been used to identify scope for electricity savings on mine compressed air systems. Existing methods are not designed to indicate scope for underground wastage management. A novel benchmarking model has been developed to prioritise shafts based on the scope for underground demand reduction. This benchmarking model was able to improve resource utilisation by up to 57% when compared to existing benchmarking models. Studies involving underground compressed air leak audits mostly rely on impractical comprehensive audits of an entire shaft. Leak auditing methodologies used in the potable water distribution industry were modified to be applied to mine compressed air networks. When this method was applied to a deep-level mining shaft, it reduced the auditing time by approximately 65%. An annual cost saving of R620-million is possible when the flow reduction achieved is extrapolated over 25 deep-level mines. The estimated annual resource cost to maintain this saving is R34.6-million. The methods developed in this study were combined into one integrated method to reduce underground leaks and achieve electricity cost savings on the compressors. However, existing electricity savings quantification methods were found to be unable to accurately quantify the savings achieved on deep-level compressed air systems. A novel savings quantification method was developed based on the parameters used in the new benchmarking model. The new method was tested on various scenarios and found to quantify the savings equally or better than existing methods and in less time. In one scenario, the new quantification method improved the quantification accuracy by up to 83%, amounting to an estimated annual savings difference of R14.5-million.