Inefficient cooling towers contribute to a high level of wasted energy, which accounts for a significant portion of a deep-level mines’ production costs, says South Africa-based Industrial Cooling Towers (ICT) GM Henk Oosthuizen.
Mines must ensure that all operational machinery is sufficiently cooled, as more efficient machinery will reduce electricity costs drastically, he says.
“Deep-level mining’s greatest challenge is high temperatures, whether it be from under- ground ambient conditions or the high amount of heat gain produced by operational machinery. High temperatures do not only destroy machinery but also render it less effi- cient, while machinery that is kept at its minimum operational temperature will have a much longer life span,” states Oosthuizen.
The applications for ICT’s cooling towers for deep-level mines range from precooling service water, cooling the condenser circuit of fridge plant units, compressor cooling and cooling machinery that uses water as a coolant.
The towers cool process water used to regulate the operating temperature of machinery, by means of evaporation. Water heated during machine cooling is cooled down by being pumped through the tower. Once the water reaches an optimal temperature, it recirculates to the machinery at a constant rate in a rapid, repetitive process.
“The cooler the temperature at which a machine operates, the more efficient it becomes. For example, compressed air supplied to underground operations at high temperatures loses pressure as it cools. The colder the compressed air, the longer it retains its pressure. Therefore, the colder the temperature at which compressors operate, the more efficient they become,” explains Oosthuizen.
Product Development and Projects
To improve its product offering, ICT has developed a fill media, to keep the water in suspension for a longer time, that is better suited to dirty water applications. This fill media does not clog the cooling tower as easily as other types of fill media as it has bigger strategically placed holes.
The company also recently partnered with energy service company HVAC International, which has completed a turnkey project for State-owned power utility Eskom, which funded a cost and power saving initiative for miner Harmony Gold’s Kusasalethu mine, near Carletonville.
“Instead of using fridge plant units to cool down water for the mine’s operations, we have installed cooling towers to precool the water before it reaches the fridge plant, as cooling towers consume much less energy than fridge plants,” explains Oosthuizen.
He says the challenge with deep-level-mine cooling is that mining conditions become hotter the deeper one mines, owing to higher virgin rock temperatures.
Higher volumes of chilled water at increasingly lower temperatures are then required for cooling, which means that compressors have to operate at higher levels to pump compressed air to where it is used – sometimes 3 000 m deep and 3 000 m horizontally to the actual mining operations, Oosthuizen explains.
The mine water stays in circulation and is reused. Over time, the total dissolved solids (TDS) and the suspended solids (SS) inside the process water increase. The TDS and SS then begin to clog the cooling tower media and the extremes of the low- and high-pH levels can also cause the fill media, as well as the heat exchangers on the machinery, to foul up.
To prevent this, Oosthuizen recommends the installation of cooling towers that are big enough in relation to the size of the mining operation and are serviced regularly. If these guidelines are not adhered to, the cooling towers could become inefficient.
“Correct water treatment is necessary to ensure that the cooled water stays within acceptable parameters and to ensure that the fill media inside the cooling towers consist of material that can withstand the harsh conditions of mining water,” he advises.