Optimal mine water management to improve ambient conditions

Abstract

The local mining industry in South Africa is experiencing a decline in gold production. This is due to unique production challenges faced by the industry. One of the major concerns is the production cost associated with the deepening of mines to retrieve the resources. This comes with added operational costs which forces the mines to increase production to maximise profit. This might lead to the closing down of marginal mines. The increase in mining depth makes it difficult to maintain acceptable underground environmental conditions for the mine workers. Optimal production and productivity from the mine workers are enhanced by optimal underground conditions. The cost of maintaining good environmental conditions is affected by the increase in depth. This encourages deep-level mines to implement cost saving initiatives and underground cooling initiatives by optimising current systems and using the current infrastructure effectively. One area offering large optimisation potential is addressing the inefficiencies of the cooling systems of deep-level gold mines. These inefficiencies include low cooling duties supplied by the cooling systems and high outlet temperatures on tertiary cooling systems. The cooling systems use water as a primary cooling medium. The mismanagement of chill water used by the cooling systems adds to the inefficiencies of the cooling systems. Lower service delivery from the cooling systems results in an increase in underground temperatures. High underground temperatures reduce miners’ productivity and production because miners are less productive in high temperatures. The water mismanagement adds additional constraints to the system as unnecessary energy is used to remove the water from underground. This in turn results in additional costs which can be better utilised elsewhere. Different cooling systems are utilized underground. Because less research has been done on tertiary cooling systems, there is more scope for research on these systems. It was evident that a need existed to optimise the water management of tertiary cooling systems in order to improve underground conditions and reduce energy use in Mine A. A methodology was then developed to identify, evaluate and solve the inefficiencies found on the tertiary cooling systems. This method involved a step-by-step approach which incorporated a root cause analysis and a reconfiguration strategy to optimise water management on tertiary cooling systems. An investigation performed on Mine A showed that poor water management and inefficient pipeline configurations contributed to high water usage during the off-peak times when system pressures increase. The average duty of the tertiary cooling system was found to be 177kW compared to the design duty of 500kW per cooling car. The average outlet wet-bulb temperatures on the cooling cars appeared to be 28,5°C, which is more than the recommended outlet temperature of 26°C. The developed methodology was applied, and inefficiencies were identified. A new configuration was then developed which involved the installation of flow regulating valves and the optimasation of the system by maximizing the flow through the cooling cars. Simulations showed that the suggested configuration could lead to an overall decrease of 3,5°C in wet-bulb temperatures and an increase of 4,4 MW in cooling duty across mine A. The simulation on the installation of pressure regulating valves showed an overall saving of 18 ℓ/s in water usage. A suggestion was also made to remove unnecessary components on the system. This showed an expected saving of R640 000 p.a.