Harmony Gold’s Tshepong mine in the Free State has retrofitted its 25-year old chillers with York equipment. The initiative, which saw the replacement of major components and a switch to the use of an ozone friendly refrigerant, has improved performance of the chillers significantly. This has increased energy efficiencies and assisted the mine to reliably reach the needed cooling capacity, which has delivered improved working conditions and increased productivity.
Tshepong is one of Harmony’s largest operations; it has a single vertical shaft extending to a depth of 2,161 metres. The mine undertakes conventional undercut mining, where ore is transported to the Harmony 1 plant, 23 kilometres away. The mine employs approximately 5,000 people. The three chillers at the Tshepong surface plant deliver 10.2 MW of cooling each, supplying 300 litres per second of water at three degrees Celsius to cool the underground workings of the shaft.
Tom Smith, chief operating officer at Harmony Gold South Africa explains, “Our 25-year old chillers were nearing end of life and we faced a number of challenges. The equipment was not functioning efficiently, parts were hard to get, and we were experiencing a lot of breakdowns. With insufficient cooling in the mine, working conditions are not optimal, affecting workers’ outputs and impacting production schedules.”
Johnson Controls proposed overhauling the existing chillers, stripping out the failing components and replacing them with newer technology that would improve performance and help the mining operation achieve specified cooling requirements. As the chillers were running on refrigerant R22, an a hydrochlorofluorocarbon (HCFC) refrigerant that is in the process of being phased out due to its ozone depletion potential, Johnson Controls also proposed the use of the more eco-friendly R134a refrigerant.
The job entailed the removal of the existing drivetrain (compressor, speed increaser and motor) on each chiller. These were replaced with a new compressor with an integral speed increaser and a two-pole motor designed for the new R134a refrigerant. Refrigerant pipework had to be altered to accommodate the new compressor and the system had to be cleaned and all traces of mineral oil removed.
“We are very pleased with the outcome. The retrofit has improved cooling performance measurably – and it has made a major difference to the teams working underground, improving working conditions and productivity. In addition, with more efficient motors we are achieving energy savings. Due to some of the plants being switched off during winter the actual impact will only be realised in summer. Calculated savings are 8,884 MWh and calculated saving per plant 336.2 MWh per month,” Smith says.
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