Case study: Energy savings for a deep-mine water reticulation system Jan Vosloo, Leon Liebenberg ⇑ , Douglas Velleman Center for Research and Continuing Engineering Development, North-West University (Pretoria Campus), and Consultants to TEMM Intl. (Pty) Ltd. and HVAC (Pty) Ltd., Suite No. 93, Private Bag X30, Lynnwood Ridge 0040, South Africa article info Article history: Received 14 July 2011 Received in revised form 10 October 2011 Accepted 14 October 2011 Available online 3 December 2011 Keywords: Load-shift Demand-side management Deep mines Water reticulation abstract In deep level mining, water reticulation systems are one of the major consumers of electricity. The refrig- eration plants, together with the underground water supply and dewatering systems are integrated to form one complete water reticulation system. This integrated water reticulation system extracts hot water from the mine, cools it down and returns the cold water to the various underground mining levels. As much as 42% of the total energy consumption on a typical deep level gold mine can be ascribed to the water reticulation system. Reducing the overall water demand and therefore electricity costs will depend on climatic conditions, operating strategy, water reservoir capacity, and electricity tariff rates. In this paper, a method is presented to determine the optimum water reticulation strategy for different electric- ity tariffs. This model minimises the total operating cost of the water reticulation system by a trade-off between the cost involved in providing effective pump control and the savings achieved under a specified electricity tariff. A case study of a typical deep mining operation shows that a reduction of 65% during peak demand and 2% overall electricity reduction is possible by adopting this new control strategy. The corresponding savings in operating cost is 13%. Techniques were developed to integrate, simulate, optimise and control all components of the water reticulation system. This will allow for a quick assessment of the effect of individual components on the complete system. By integrating all these components into a single system, the operation of each component can be assessed and optimally controlled without adversely affecting other operations of the system. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction In an era of high energy costs, coupled with increasing concerns regarding sustainability, improving the efficiency of water and en- ergy use is an important goal for the mining industry [1]. Water reticulation systems can consume up to 42% of a deep mine’s total electricity usage [2]. In addition, up to 30% of a typical deep-level mine’s electricity cost can be attributed to power used during peak hours [3]. The amount of water consumed by the mine can how- ever be reduced by optimally controlling the water demand and by reducing water wastage, i.e., ‘load management’ or ‘demand- side management’. Time-of-Use (ToU) pricing structures were implemented by the South African electricity utility Eskom as one of the important ap- proaches to demand-side management (DSM). Their purpose was to persuade, by introducing a three-section ToU tariff structure (viz. peak, standard, and off-peak periods), large industrial consum- ers in particular, to shift their electrical loads [2,4–7]. Load-shifting implies that the water-pumping periods should be scheduled in such a way that pumping is avoided during the expensive peak periods, (07:00–10:00 and 18:00–20:00), and shifted to the cheap- er off-peak periods. Under the load-shifting method, electric power to all the pumps is always available, but the delivery rate may vary with ToU [8]. The kind of loads most frequently associated with load-shifting procedures are those which deliver energy services whose quality is not substantially affected by supply interruptions of short dura- tion [9]. With deep-mines, such typical water reticulation loads are those associated with some form of water storage. The identification and selection of a suitable power curtailment strategy is a complex task, considering the multiple, incommensu- rate, and potentially conflicting objectives. These objectives might include the minimising of maximum power demand, maximising profits, minimising losses, and minimising adverse effects to the customer [10]. The selection of adequate load-shifting actions to be implemented over sets of loads, grouped according to some cri- teria, is therefore a multi-objective optimisation problem. This paper reports on the development and testing of an inte- grated and automated load-shifting modelling and real-time con- trol strategy on a deep mine water reticulation system, while at the same time taking into consideration the mine’s production schedule and safety requirements. The emphasis of this paper is 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.10.024 ⇑ Corresponding author. Tel.: +27 (0)12 809 0995. E-mail address: LLiebenberg@researchtoolbox.com (L. Liebenberg). Applied Energy 92 (2012) 328–335 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy