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A new lime-slaking facility, which will help a mine water treatment plant achieve significant cost savings, has been equipped with a stainless steel Grundfos booster pump to reliably handle the corrosive permeate.
Located in the Mpumalanga coal fields, a recently completed lime slaker forms part of a mine water treatment plant designed and operated by water reclamation and desalination specialist, Nafasi Water.
The facility – or reactor – combines calcium oxide with water on site, replacing the traditional delivery method of transporting the heavier calcium hydroxide powder. According to Ashton Drummond, chief strategy officer at Nafasi Water, this allows for a substantial reduction in transport costs.
“The savings achieved by slaking lime on site are significant, adding up over time to ensure an attractive payback period for the investment in the lime slaking reactor,” says Drummond. “The calcium oxide is added to a mixing tank, which is temperature controlled to ensure the optimal conversion to calcium hydroxide.”
The calcium hydroxide is an important element in the functioning of Nafasi Water’s treatment plants, where the company applies its proprietary HiPRO™ technology (Hi recovery Precipitating Reverse Osmosis) around South Africa.
“HiPRO™ allows high water recovery from complex mine-impacted waters,” he says. “Depending on the feed quality and product quality requirements, water recovery of between 98% and 99.5% can be achieved. At times, the only liquid to leave the plant is the moisture in dewatered sludges,” he says.
The plant treats mine-impacted water so that it is clean enough to be discharged back into the river system, in accordance with environmental regulations. The water quality is so high it is also made available to the local municipality, providing drinking water for the community.
The requirement for stainless steel in the two Grundfos end-suction pumps supplied to the project – one for duty and one for standby – is due to the corrosive nature of the reverse osmosis (RO) permeate being pumped. Stripped of mineral content, the water tends to leach aggressively. The pump transfers this water into the lime slaker, where it is mixed with the powdered lime in exact quantities and at the precise temperature.
According to Raymond Makgoga, associate sales engineer at Grundfos, the pump delivers 50 m3 per hour at a pressure of about 4.5 bar. To enhance the efficiency of the pump, it is fitted with an IE3 WEG motor rated at
15 kW. In this application, the pump is expected to meet a discharge head of 51 m. Makgoga also highlights that the WEG motor was able to accommodate the plant’s requirement of a 525 V power connection.
“We regard strength and efficiency as the hallmarks of our newly developed Grundfos end-suction pump range, which includes the NB close-coupled and NK long-coupled configuration,” he says. “These powerful single stage pumps are designed to work hard in the most demanding industrial environments, where only the fittest pumps will survive in the long run.”
He highlights that all Grundfos NB/NK stainless steel end-suction pumps are excellent solutions for industrial applications where pumping of aggressive media is required.
Among the features, he says, are optimised hydraulics in the housing and impeller, as well as loose flanges for easy installation. The stainless steel shafts mean improved corrosion resistance with no sticking elements, while the heavy duty bearing brackets ensure correct lubrication for long pump lifetime.
Drummond says the relationship between Nafasi Water and Grundfos goes back many years, and its water treatment plants today make extensive use of Grundfos pumps. “When we issue our requirements for pump packages to the market, we generally find that Grundfos is exceptionally competitive, while offering technically compliant solutions to a wide range of needs,” he says.
Makgoga notes that Grundfos was also recently able to provide two multi-stage centrifugal pumps with control drives to a Nafasi Water treatment plant in the Springs area of Gauteng.
The benefits of Nafasi Water plants to the local communities extend beyond the supply of clean water, notes Drummond. “Nafasi Water prioritises the upskilling of local residents in our plant operations, which has allowed some employees to enter the company as operators and develop their careers to become managers at these plants,” he says.
The HiPRO™ process has been recognised over the years both locally and internationally for its contribution to water quality and environmental management. It was awarded a gold medal by the South African Institute for Engineers and a Greening Future Award by the Mail & Guardian newspaper. It also earned recognition in the sustainability category of Nedbank Capital’s Green Mining Awards.
Further afield, HiPRO™ was named by the United Nations Framework Convention on Climate Change (UNFCCC) as one its Lighthouse Projects in the Momentum for Change awards at COP17.
