A strategy to prioritise compressed air energy￾savings initiatives during production stoppages

Abstract

The cost of electricity in South Africa has increased significantly since 2007. Electricity tariffs increased by 165% over the past decade alone. This negatively affects the profitability of mines with electricity costs forming a large portion of the operational costs. The compressed air system, which is widely regarded as inefficient, is the largest consumer of electricity at a mine.

Energy-saving initiatives are a proven way of reducing electricity costs on the compressed air system of a mine. However, mines face challenges that affect the implementation of energy￾saving initiatives. One such challenge is production stoppages. Mines experiencing production stoppages may have limited time, capital and resources available to implement these initiatives.

Previous studies have primarily focused on prioritising and implementing energy-saving initiatives during a typical production period and did not consider production stoppages. The need exists for a strategy that assists mines during a production stoppage by prioritising and filtering energy￾saving initiatives.

To address the aforementioned need, a pre-existing prioritisation method was customised specifically for this scenario. By integrating it with a curated checklist of proven compressed air energy-saving initiatives from industry research, a user-friendly tool was created to streamline decision-making. Alongside this, a straightforward four-step energy-saving strategy was developed that integrates the prioritisation method to enable mines to effectively reduce compressed air demand and decrease electricity costs during production stoppages.

The developed strategy was applied to two case study production stoppages. The first case study tested the accuracy and benefit of the prioritisation method and compared it with industry knowledge and experience. This was done by comparing the results of the prioritisation method with the actual initiatives that were implemented, without a guided strategy, during the case study period.

The prioritisation method generated a list of four feasible energy-saving initiatives. These generated initiatives aligned with four out of the six initiatives that were implemented in reality. Unforeseen events resulted in the implementation of two initiatives which were not identified by the strategy. Therefore, the prioritisation method was found to be accurate in determining feasible energy-saving initiatives as well as prioritising these initiatives, except when faced with unforeseen events.

Additionally, results showed that an investigation period of five weeks could have been avoided if the prioritisation method had been used at the start of the case study production stoppage instead of relying on industry knowledge and experience. Usage of the method would have resulted in compressor set-point adjustments being made sooner and a potential saving of 500 MWh (14.3 MWh/day) could have been achieved. This is equivalent to a cost-saving potential of R410 000 with a daily saving of R14 000/day in the summer and R22 300/day in the winter.

The second case study tested the effectiveness of the developed strategy when fully implemented during a production stoppage. Four energy-saving initiatives were identified and successfully implemented according to priority as soon as the production stoppage began. Initiatives were fully reversed on the last day of the production stoppage and production restarted without delays. A total energy saving of 250 MWh (22.7 MWh/day) was achieved during eleven days, equivalent to a cost saving of R200 000 with a daily saving of R22 350/day in the summer and R35 400/day in the winter.

The overall strategy has proven to be an effective tool that may assist mines in reducing costs and saving time during production stoppages by prioritising and filtering energy-saving initiatives.