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Mines are getting deeper with every year that passes – 30 m deeper, if industry reports are correct.

With increased depth, comes increased ventilation and cooling needs, a fact Howden knows well from its experience of working with the deepest mines in South Africa.

Originally founded in 1854 by James Howden in Scotland as a marine engineering firm, Howden made an entry into South Africa in the 1950s seeking to cater to the demands of the mining and power industries. By the 1960s, it was helping equip the country’s deep gold mines with all the ventilation and cooling products they needed to extract ore safely and productively from kilometres below surface.

“Initially mines used only ventilation as a method of cooling, but, as mining depth increased, mechanical refrigeration was required to counteract the increasing heat loads in mines,” Theuns Wasserman: Team Leader – Howden SA’s Mine Cooling and Compressor Division, told IM.

This saw many deep gold mines in South Africa install Freon™ centrifugal chillers above and below ground to provide the necessary cooling for personnel and machines underground.

While an improvement on the status quo, the heat rejection system for underground machines proved problematic, with the machines’ cooling capacity limited by the temperature and amount of reject air available, according to Wasserman. At the same time, the water quality of the mines resulted in high fouling on the piping shell and tube heat exchangers employed on these early centrifugal chillers.

This resulted in the machines being limited to cooled water temperatures of 6-8°C, he said.

To rectify this, mines started to pump chilled air from surface to underground. While this boosted cooling capacity, the required infrastructure took up space in the shaft and the process was both energy- and opex-intensive.