A control system for the efficient operation of bulk air coolers on a mine

Abstract

Eskom provides 98% of South Africa’s ever increasing electricity demand. The mining sector is a vital contributor to the economy, but also consumes vast amounts of electricity. This sector is responsible for almost 15% of the country’s electricity usage. Mines heavily depend on the supply of cold water and air. Refrigeration systems are therefore constantly operational and can account for 25% of a mine’s electricity costs. The need therefore exists to investigate possible energy savings initiatives. Refrigeration systems are typically used to lower the temperature of water and air. Bulk Air Coolers (BACs) are used to produce cold air. The aim of this study is to investigate possible electricity cost savings in a mine refrigeration system. This can be achieved by enabling equipment to dynamically adapt to changes in their environment. Electricity usage reduction has the greatest financial impact if it occurs during Eskom peak periods. Time-dependent schedules of operation are therefore used to achieve this objective. Due to the lack of such a controller in the mining industry, the focus of this study is a BAC control system. A BAC controller would be able to follow guidelines that could lead to electricity cost savings. It was therefore developed and incorporated in the Real-time Energy Management System (REMS). The BAC controller combines various inputs and constraints to determine the output. An electricity usage reduction during the Eskom evening peak period was consequently achieved. The BAC controller was implemented on three sites. Electrical energy usage during the evening peak period was reduced via the load shifting method. This aids Eskom in their effort to reduce the peak period demand. Air temperature and dam levels were closely monitored during the peak period. If any preset condition was violated, the load shifting was abandoned for that day. It was shown that a total power reduction of 7 MW is possible between the three sites. The electricity savings occurred in the evening peak period. A calculation was made to determine the possible annual savings by using the achieved daily cost savings. The winter months were not included in the calculation. An annual cost saving of R1 166 694.41 is therefore possible without having to reduce output quantities.