MechChem Africa September-October 2021

Lime slaker plant cuts water treatment costs 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. L ocated in theMpumalanga coal fields, a recently completed lime slaker forms part of a mine water treat- ment plant designed and operated by water reclamationanddesalination specialist, Nafasi Water.

The facility – or reactor – combines calci- umoxidewithwater on site, replacing the tra- ditional delivery method of transporting the heavier calciumhydroxidepowder. 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 proprietaryHiPRO™technology (Hi recov- ery Precipitating Reverse Osmosis) around South Africa. “HiPRO™allows highwater 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. Thewater quality is so high it is also made available to the local municipality, providing drinkingwater for the community. The requirement for stainless steel in the twoGrundfos end-suction pumps supplied to the project –one for duty andone for standby – is due to the corrosive nature of the re- verse 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, associ- ate sales engineer at Grundfos, the pump delivers 50m 3 per hour at a pressure of about 4.5bar. Toenhance theefficiencyof thepump, it is fitted with an IE3 WEG motor rated at 15kW. In this application, the pump is expect-

A view from the top of Nafasi’s lime slaker plant showcasing the water tank, Grundfos booster pumps, calcium hydroxide storage unit and reactor.

Grundfos booster pumps for pumping water from the permeate water tank to the slaker tank and for backwash.

ed tomeet adischargeheadof 51m.Makgoga also highlights that theWEGmotor 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 con- figuration,” he says. “These powerful single stage pumps are designed to work hard in

themost 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 applica- tions where pumping of aggressive media is required. Among the features, he says, areoptimised hydraulics in the housing and impeller, aswell

10 ¦ MechChem Africa • September-October 2021