Cost-effective compressor control to reduce oversupply of compressed air

Mine compressed air systems are energy intensive with the potential for optimisation and electricity cost savings. However, funding for energy saving initiatives has reduced significantly since 2013. A need therefore exists, for cost-effective energy management strategies that can be implemented in short timeframes. Upgrading existing throttle control systems on compressors is expensive. Existing compressor control is typically done using guide vanes or butterfly valves. Available cost-effective methods, such as stop-start control, have negative effects on compressors. This study focuses on identifying and implementing a cost-effective strategy by utilising a combination of available throttle control strategies and existing infrastructure. This reduces the implementation cost of conventional optimisation methods, while avoiding the damaging effects of frequent stopping and starting. Previous studies showed that surge margins of compressors can be shifted to allow a reduced flow through the compressor, without activating the surge protection. A strategy was developed to overwrite an inefficient guide vane control by converting an existing square open/close butterfly valve into a variable throttle control. An actuator and positioner were installed on the existing open/close valve to enable variable throttle control. The improved throttle control endorsed further reduction in flow, compared to that of the existing guide vane control. The strategy was implemented on a mine as a case study. An average savings of 650kWh per weekday was realised. This equates to a potential cost saving of R3.4 million annually. This method can be applied to similar compressors in other industries.