Simulating operational improvements on mine compressed air systems

Abstract

As the operational costs of deep-level mines increase and gold ore grades decrease, profitability in the South African gold mining sector is becoming a challenge. Electricity tariff increases moreover contribute to the rising cost of mining operations. Compressed air supply systems are the most significant energy users in a mine; and they contribute to approximately 20% of the total power usage. Research has shown that these compressed air networks are systemically inefficient. Hence, improving the efficiency of these systems would result in a significant reduction in energy costs. Previous studies have revealed the usefulness of simulations to improve deep-level mining systems. However, these studies did not follow a structured methodology for producing compressed air simulations and they used simplified compressed air models that reduced the simulation precision and testable scenarios. Recent developments in software allow for simpler and speedier development of complex system simulation models. In this study, a simulation methodology was developed and investigations were conducted in respect of compressed air systems. A compressed air system was subsequently modelled in software to recreate the system operation accurately. Finally, a proposed means of improvement was simulated, analysed and quantified to enhance energy savings and service delivery. Two case studies were evaluated. For each case study, various scenarios were simulated. In Case Study 1, two air network intervention scenarios were tested on a compressed air system. The results showed that energy cost savings of R0.91m could be achieved. The simulation results were very similar to tests later performed on the physical systems. The results of Case Study 2 showed that by reducing air usage at refuge bays, an average power reduction of 1 megawatt (MW) could be achieved. The improvement in efficiency would potentially lead to R5.2m in annual energy cost savings. In addition, a significant improvement of 15 kPa in system pressure during the drilling period was identified. Other scenarios showed annual energy cost savings of up to R2.5m. An additional analysis was performed to assess the use of periodically repeated simulations. The results demonstrated that operational changes in a system could be identified through repeated simulations. It would therefore be possible to use this information for further improvement and cost savings. The study showed that a simulation is a valuable tool for identifying improvements in compressed air systems. By utilising a structured methodology to develop detailed compressed air simulations, inefficiencies and opportunities for operational improvements could be successfully identified