A new minimum cost model for water reticulation systems on deep mines

Thesis (Ph.D. (Electrical and Electronic Engineering))--North-West University, Potchefstroom Campus, 2009.In the past, electricity in South Africa was taken for granted. This situation suddenly changed in January 2008, when the electricity supply system threatened to collapse. Energy efficiency was suddenly brought to the fore when steep tariff increases and consumption penalties were enforced on consumers. The mining sector is affected most severely. The expected tariff increments, together with consumption penalties, will drastically increase production costs. A number of mines will be forced to reduce production or even close in order to avoid these high costs. This will have a negative effect on the South African economy that relies heavily on mining to earn foreign exchange. In deep level mining, water reticulation is one of the primary consumers of electricity. The refrigeration plants, together with the underground water supply and underground dewatering systems are integrated to form a complete water reticulation system. This system uses up to 41.9% of the total energy consumption on a typical gold mine. It is used to extract hot water from the mine, refrigerate it and distribute the cold water back to underground mining levels. Work has been done on individual elements of dewatering and refrigeration systems to reduce electricity costs. However, no results could be found of an integrated control solution for all aspects of mine water reticulation. In this study novel techniques were developed to integrate, simulate, optimise and control all elements involved in the water reticulation system. This enables quick assessment of the effect of individual components on the complete system. By integrating all elements into a single system, components can now be optimally controlled without adversely affecting other parts of the system. These techniques were applied on Kopanang and Tshepong water reticulation systems. The results concluded that over and above conventional demand side management (DSM) initiatives, additional savings could be realised. An additional outcome was to develop generic models to evaluate and optimise any deep level mine dewatering system. These models were applied on a number of mine dewatering systems. By using these new techniques on only two mines, the average load was reduced by 2.3 MW, which realises annual savings of more than R 3-million (2008 tariffs). The new models should be applied on all deep level mines to optimise energy consumption on their water reticulation systems. The mining sector can save more than R 20-million annually at 2008 tariffs. It is also suggested that this application be applied to other sectors, such as large water distribution installations.Doctora