Automated dynamic control philosophy for sustainable energy savings on mine cooling systems

Abstract

Financial instability in the mining sector was identified as a significant reason for reduced production trends in South Africa. Coupled with increasing operational costs, the South African mining sector is confronted with a challenging financial situation. To remain financially competitive, on a global scale, mines are adopting significant socio-economic changes. Mineworkers require substantial cooling and ventilation to work in a safe and habitable environment. Deep-level mine cooling systems were identified as substantial energy-intensive consumers to supply such cooling. Mine cooling systems can make up to 28% of a mines total electricity consumption. Electricity cost-saving initiatives were studied, implemented and recognised as a viable solution to reduce end-use electrical energy consumption on mine cooling systems. Little attention has been directed, however, to the sustainability thereof. Literature reveals a need for a simple, practical and integrated solution to optimise deep-level mine cooling systems dynamically for sustainable cost savings. Therefore, an automated dynamic control strategy was presented to optimise the control of mine cooling systems to reduce operational costs and improve system sustainability. An integrated Energy Management System (EMS) was identified as a suitable controller for the implementation of this strategy. The EMS analysed the theoretical impact with the aid of a verified simulation model. The control strategy was implemented on a case study, Mine A, situated at a South African gold mining complex. An integrated dynamic temperature set point algorithm and ambient dry-bulb (DB) temperature prediction model was formulated, implemented and verified. The simulation results confirmed the accuracy of the automated dynamic control strategy with an average correlation error of 4%. The feasibility of the automated control strategy was investigated and validated to identify post-implementation cost savings. Implementation results showed a power demand reduction of 45.7%, or 1960 kW during the evening peak time-of-use period. This translated to an annual cost saving of R1.1 million and an operational efficiency improvement of 15%. The optimised dynamic control model, when compared to existing control practises, also attained a chiller coefficient of performance improvement and compressor power reduction of 7% and 4% respectively. An integrated performance monitoring daily report was established. Important KPIs were identified and included in the daily report. In addition to the implementation of automated cost saving measures, load shift savings were also reported for a period of 14 months; indicating the sustainable impact of this study. This strategy, demonstrated to be simple, showing significant performance improvements for South African mining industries.