Optimising load management on a deep-level Mine's refrigeration systems through maintenance and operational improvements

With the decline in productivity in the mining industry it is crucial to reduce operational costs while still maintaining safe underground working conditions. A load shifting project was implemented on the refrigeration system of Mineshaft A as part of a demand side management (DSM) initiative. The DSM project over-performed by 0.5 MW, but an increase in service water temperature was measured over the Eskom evening peak periods. The chill dam temperature increased with more than 10 °C during load shifting. It was thus proposed that the surface refrigeration system of Mineshaft A be optimised in order to retain the energy savings, while improving service delivery. After an in-depth investigation it was found that both the pre-cooling towers and the control philosophy used to incorporate load shifting were very inefficient. It was thus proposed that the pre-cooling tower fans be repaired and the control philosophy be optimised by matching the evaporator flow rate of the fridge plants with the warm water flow rate into the surface hot dams. This resulted in lower pre-cool dam temperatures and, along with the optimised control philosophy, the chill dam temperature improved by a daily average of 3.9 °C. This improvement was realised even with the presence of a broken fridge plant in the surface refrigeration system of Mineshaft A. The load shift performance also increased with an average of 1 MW, realising an additional annual cost saving of R 375 000.