Electrical energy cost improvement of platinum concentrator blower systems

Abstract

This research addresses the critical need for electrical energy efficiency within the South African platinum mining industry, where processing plants account for approximately 19% of total electricity consumption. Despite the sector's economic significance, rising Eskom tariffs and declining production have placed operations under severe financial pressure. While demand-side management initiatives have historically focused on mining shafts and cooling systems, auxiliary blower systems in concentrator plants have remained largely underexplored. These systems often operate as significant base-load consumers with substantial inherent inefficiencies, primarily due to a lack of structured methodologies for aligning air supply with the dynamic requirements of continuous flotation processes. Consequently, this study develops and validates a systematic four-phase methodology comprising data acquisition, analysis, simulation modelling, and implementation, to identify and capture electricity cost-saving opportunities in these systems. The methodology was applied across four distinct case studies encompassing both positive displacement and centrifugal blower configurations. Comprehensive analysis revealed that historical blower operation was characterised by significant oversupply, with air production consistently exceeding flotation cell demand by 20-50%. This resulted in excess air being vented to atmosphere through blow-off valves whilst maintaining full energy consumption, representing substantial electrical energy wastage. According to various literature reviews conducted, the blow-off valve position serves as a valuable indicator of system oversupply, though direct quantification of wasted air volume remained constrained by the absence of accurate compressed air flow instrumentation.Simulation using Process Toolbox software achieved calibration accuracy within 5% of actual system performance, enabling safe evaluation of operational scenarios without causing a disruption in production. Empirical validation proved to be a critical component of this study. In Case Study A and B, initial theoretical calculations proved inadequate, as subsequent testing revealed that additional blowers were required to maintain the pressure setpoint. This discrepancy was primarily due to system leaks and the degradation of key components, highlighting the necessity of experimental verification to account for real-world conditions that theory alone cannot predict. Case Study C yielded the highest absolute savings through the discovery that several installed motors differed from their nameplate specifications by up to 75 kW. This discrepancy, identified during the system audit, allowed for the development of a revised, improved sequencing strategy based on actual motor power ratings rather than theoretical data. By prioritising the operation of smaller, more efficient units, the plant successfully reduced energy consumption while meeting all process requirements. Case Study D demonstrated that by restoring the surge control protection to manufacturer specifications, both system stability and efficiency were significantly improved within the centrifugal blower systems. The methodology achieved combined energy cost savings exceeding R4 million across the four case studies annually, ranging from R160 000 to R2 million per site. These energy cost savings were realised through reduced blower utilisation, improved sequencing based on motor efficiency, pressure setpoint optimisation, and restoration of manufacturer design specifications. Ultimately, the findings validate that systematic optimisation can mitigate the prevalent air oversupply in platinum concentrators without compromising production stability or recovery. The study establishes a structured framework for identifying inefficiencies that is transferable to broader minerals-processing applications, including gold and copper flotation. Future opportunities identified include the integration of automated control systems with variable frequency drives and the expansion of the methodology to encompass demand-side flotation air optimisation.