Sustainable DSM on deep mine refrigeration systems : a novel approach

Abstract

The supply and demand of energy have become a world wide concern. It is predicted that world energy usage could increase from 15TW, to 21TW by 2020. In South Africa the peak demand for electrical energy has already outrun the supply. Eskom produces 96% of South Africa's electricity requirements and has launched a Demand Side Management (DSM) program. Its primary target is that of reducing electrical load during the peak demand period. South African mines are the main "culprits" regarding the intensive use of electricity. Large refrigeration plants supply chilled water which is used to cool deep underground working areas. If these cooling systems could be controlled to operate more intelligently it could help Eskom with its problems during peak supply (from 18:00 to 20:00). To investigate the potential for Demand Side Management (DSM) in these systems, integrated simulation is required. It has to predict these systems' responses to DSM control strategies and its effect on critical underground conditions. Mathematical models of refrigeration equipment were therefore simplified and integrated into software for simulation purposes. The accuracy of the predictions of the software was verified on the refrigeration system of Kopanang Gold Mine near Orkney in the Free Sate. New control algorithms were developed to control a refrigeration system for load shift purposes. These algorithms were also combined into a new global control philosophy which can be applied to any refrigeration system to establish a load shift potential. A unique investigation protocol was developed which can also be used to investigate any refrigeration system for a DSM potential. The only way to sustainably and effectively realise a DSM potential in a refrigeration system, via optimised control, is through the implementation of an Energy Management System (EMS). A Real-Time Energy Management System (REMS) was developed to be applied as a fully automated control software solution. It communicates with a Supervisory Control and Data Acquisition system (SCADA) which in turn controls plant automation infrastructure. Refrigeration systems in South African mines were investigated and four systems were identified and submitted to Eskom DSM for approval. All four proposals were approved with the required DSM target of 17MW to be removed from the Eskom evening peak period. Eskom DSM supplied all capital funding for the required plant automation infrastructure. The Real-time Energy Management System (REMS) was installed on the refrigeration systems of Kopanang and Tshepong Gold Mines. The REMS system realised a DSM potential of 3.6MW on Kopanang, and 4.0MW on Tshepong without compromising requirements for plant equipment, process, maintenance or mine health and safety constraints. Automated and optimised control of mine refrigeration systems is an effective, sustainable and cost effective option for Eskom DSM. The REMS system not only realises the much needed control of the evening peak energy capacity Eskom needs, but also realises electricity cost savings for the mines involved, by effective operation of these systems during cheaper tariff periods. The REMS system at Kopanang Gold Mine has been operating automatically for more than 20 months, realising cost savings in excess of R2-million for the mine over this period. The projected cost savings for Tshepong Gold Mine are approximately R500-thousand per annum. The methodologies and strategies developed in this study can be utilised to quickly and effectively investigate the untapped 60MW worth of DSM potential in the refrigeration systems of South African mines.