Demand side management on an intricate multi-shaft pumping system from a single point of control

Abstract

Eskom, the sole supplier of electricity in South Africa is facing an energy crisis. This is due to the steady increase in demand for electricity in South Africa. Low electricity prices in South Africa have helped the energy intensive industries of South Africa to be more competitive. Unfortunately this has resulted in poor energy efficiency practices and has hampered incentives to save energy. To address this problem, Eskom initiated a Demand Side Management (DSM) programme. DSM is beneficial to both Eskom and the client. However, due to the high cost of implementing such projects, it is feasible to implement it only on sites where the load shift potential is high enough for Eskom to benefit. The mining industry has been targeted for DSM programmes. This is due to the existence of a large mining sector in South Africa and to its energy intensive nature. Most mining operations require large amounts of water which is used to cool the underground environment and so ensure productivity and the safety of the workers. Due to the large amounts of water needed for mining, the electricity usage of these pumping systems is very high. If the use of this electricity can be optimised by implementing DSM principles, this will result in the long term savings of costs for the mines involved. The majority of pumping systems found on mines are single shaft systems. Individually these systems have a very high DSM potential. However, if multiple shaft systems can be used for DSM, the benefits will be far greater. Furthermore, combining several sites with an interconnected water pumping system will increase the potential for DSM and enable sites where individually the potential is too low to be feasible for a DSM project to raise their potential. This will result in more sites where DSM projects can be implemented and more clients who can benefit from the DSM programme. The purpose of this study is to investigate and implement a DSM project on an intricate multi-shaft mine pumping system which will be controlled from a single point. The project required a detailed investigation of the pumping systems on each shaft and how the water system is interlinked between the shafts. This project was carried out on Beatrix Mine Shafts 1, 2 and 3. The pumping systems were analysed and simulated according to the specific constraints and requirements that were specified by the mine. During the investigation and implementation of this project, possible efficiency improvements on certain pump stations were discovered and implemented. The improvements enabled both an increase in water flow to the surface and a decrease in power consumption. Due to this load reduction, the savings achieved were higher than those found in most load shifting projects. Moreover, additional infrastructures were installed to ensure communication between pumping systems. Once the simulation and optimisation of the control system was completed, the pumping system network was automated. The load shift resulted in a ± 3.5 MW shift in the morning peak demand period and a ± 6.0 MW shift in the evening peak demand period. This load shift has resulted in an average cost saving of R 80 000 per month during summer tariff period, and R 300 000 per month during winter tariff period. This saving result was calculated by taking load reduction into account. This project has shown that a DSM project can be implemented successfully, given the necessary historical data and expertise, on a pumping system that is interconnected between multiple shafts.