Variable-speed retrofit of a legacy slurry pumping duty: Measured energy reduction with proxy-based operability assessment

Legacy ore beneficiation plants often operate slurry pumps at fixed speed despite variable sump inflow and slurry conditions, which can increase electricity demand and complicate level control. This study evaluates a variable-speed retrofit in which a variable frequency drive was integrated with level feedback and proportional–integral control for a legacy slurry pumping duty. Measured average operating power decreased from 25.6 kW before retrofit to 11.6 kW after implementation, documenting a substantial reduction in electrical demand under the observed operating regime. Because hydraulic-duty data were unavailable for both periods, this result is not presented as a duty-normalised specific-energy reduction. Process interpretation was supported by a bounded proxy framework based on a flowsheet-consistent solids band over 177 days. The proxy analysis linked solids variability to derived slurry density behaviour and operability implications. Overall, the study documents measured electrical-demand reduction and provides a framework for discussing retrofit performance where plant instrumentation is limited.