Power savings by impeller replacements for main fan stations in the South African gold mining industry

Fans in deep level mines consume significant amounts of energy, usually between 1 and 4MWe per fan. When these are overdesigned, as is often the case, energy is wasted and an opportunity exists for energy efficiency interventions. Typically, savings of 1MWe in a three-fan configuration can be achieved. This paper presents the theoretical viability of the replacement of main fan station impellers to ensure more efficient fan operation. The new impellers will be designed to be more aerodynamically efficient and reduce the shaft load on the motor at the current operating point. The result is reduced electrical energy consumption and a reduction in the electrical costs of the fan station. Impeller replacements are feasible on mines where fans operate below their design point. The majority of underground gold mines were designed for a larger pressure drop and lower volume flow than is presently being encountered. This paper will focus on the challenges that are faced in order to arrive at a suitable impeller with improved efficiency. The aim is to design an impeller with lower pressure head and higher volume flow capability, shifting the best efficiency point to a slightly higher volume flow. This requires the manipulation of impeller design parameters such as blade width, blade tip exit angle, impeller outer and eye diameter and blade number. Various parameters that influence the choke and surge margins, such as the use of splitter vanes and inlet eye shape; were also identified.