MechChem Africa July-August 2021

Warman ® mill circuit pumps: a global flagship Following over 80 years of continual development and innovation, Weir Minerals’ Warman ® Mill Circuit (MC) slurry pumps are the company’s global flagship product for the mining sector. Product manager for pumps, Marnus Koorts, outlines some of the modern features driving this success.

“M ill circuit pumps are often described as the beating heart of amine’s minerals extraction circuit. They sit alongside every grindingmill, pumping newly ground mineral slurries up into the cyclones, which separate the coarse and the finemate - rial, sending coarse particles back for further milling and the fines on for minerals extrac - tion,” begins Koorts “Slurry pump wear rates are directly re - lated to the volume and size of the particles. Larger pieces of rock from a primary mill impactingon thepump’s throat bush, impeller and volute liner cause muchmore rapid wear than the micron-sized fine abrasive particles being pumpedout of the endof themill circuit by the tailings pumps,” Koorts explains. A typical centrifugal pump on the tailings endof amill circuit, he suggests, might last for many months before wear components such as the liner, throat bushor impeller couldneed replacing, while amill circuit pump can have a wear life of months, and possibly only weeks, if the installation is not optimised. “The problem, of course, is if the primary mill’s circuit pump stops, thewholemill circuit must stop and minerals extraction, often for the entire mine, comes to a standstill. This immediately impacts production, with direct

ofmaterial fromthe high pressure outlet side of the pump back to the inlet side. “This gap, therefore, directly affects the pump’s efficiency: the less fluid that recircu - lates, thebetter the efficiency. As the impeller and the throatbush wear, however, the gap widens and more and more of the slurry is able to recirculate. By adjusting the throat bush gap back to the minimum specified, we are able to reduce recirculation and routinely restore pump efficiency to its best possible,” Koorts explains. The electricity costs of driving a large multi-kilowatt motor on mill pumps far outweigh the initial investment costs, so if a couple of percentage points of the pump efficiency can be recovered by minimising recirculation – on a 1.6 kW or larger motor, for example – this quickly justifies the invest - ment onaWarman ® pumpwith this capability. Pointing to a second innovation on the throat inlet, he highlights the small pre-swirl vanes that guide the material flow through the eye of the impeller, which prevents direct impacts of large particles onto the impeller blades. Deepexpellingvaneshavealsobeenadded on the high pressure side of the throatbush to reduce the formation of eddies. This mini- mises turbulence, prevents the formation of

consequences for the income stream of the entire operation,” he points out. “Our value offering at Weir Minerals is to produce mill circuit pumps that are not only reliable, but also have the maximum possible life between wear component changeouts,” Koorts tells MechChem Africa. Weir Minerals reported an R&D investment of 1.3%of total global sales in its 2020Annual Report. According toKoorts: “Ahigh percent - age of that spend goes to advancing our flag - shipWarman ® MC pumps. We have, over the years, developeda long listof ground-breaking innovations that areunique tous.We invented the adjustable throatbush, for example, and we have been advancing that technology ahead of our competitors for many years,” he continues. Explaininghowthisworks, he says thatma- terial from the sump of the grinding mill goes into the pump at the throat and is propelled by centrifugal forces through the impeller to the outer volute of the pump casing. The throat bush sits around the inlet side of the pump creating a small gap between the rotat- ing impeller and the casing. It is important to minimise this gap, as itminimises recirculation The Warman ® MC: the industry benchmark

Left: A Warman MC slurry pump under test during developmental stages at one of Weir Minerals’ numerous test facilities. Right: A Warman MCU 350 slurry pump being assembled at the Weir Minerals facility in Alrode.

4 ¦ MechChem Africa • July-August 2021