Mechanical Technology June 2016

⎪ Pump systems, pipes, valves and seals ⎪

Fit-for-purpose slurry pumping and lowest TCOs Using the flagship MD range of slurry pumps as an example, Metso’s Europe, Middle East and Africa director for mining flow control, Steve Sedgwick talks about Metso’s approach to slurry pump design and the key features that enable the company to offer the lowest possible total costs of ownership.

S lurry pumps include various types of heavy-duty centrifugal pumps used for the hydraulic transportation of solids. “Slurry pumping involves a varied portfolio, depending on the media being pumped, but slurry pumps are almost always de- signed and chosen based on their wear performance,” begins Sedgwick. The Metso slurry pump range covers the pumping of any type of materials, primarily ground rock, including large particles using dredge pumps that can handle particles of over 150 mm. “The typical discharge from the mill in a minerals processing application is in the 100 µ m to 250 µ m average particle size range, combined with large rocks and a steel content caused by mining activity and broken mill balls (scats), which are all pumped as very dense slurries that cause high wear rates on the pump’s internal components,” he explains “Metso can offer the full range of duties and wear lining options, from

Metso’s slurry pump selection chart and its pump selector software, Pumpdim, use the aspect ratio as the primary variable in organising its range for different slurry requirements.

rubber-lined to high chrome white cast iron, but to get the best value, the pump has to be well suited to the slurry it is pumping,” he adds. Showing a summary diagram of the slurry pump range, Sedgwick says

the internal impeller diameter at the eye of the impeller – OD/ID. Our flagship MD pump is designed to meet these extremely abrasive Category 4 needs,” he tells MechTech . The aspect ratio is a simple number that sets the basic design limitation for any centrifugal pump subjected to wear. If the aspect ratio is large, then the size of the pump has to be made larger to accom- modate the larger impeller. This allows the impeller to rotate at a slower speed for the duty required, and it increases the impeller vane length and thickness, which slows its deterioration rate. But the larger size is associated with higher costs. “A Category 4 MD pump might have an impeller with an OD of 600 mm and an ID of 200 mm. A Category 3 with an aspect ratio of 2.5 that can produce the same duty only needs an impeller with a 500 mm OD for the same inlet size. So a pump capable of producing the same flow and head has an impeller, a volute and a frame size that are all physically smaller by some 25%,

that Metso’s approach to han- dling the diversity of differ- ent slurry types starts with the American Hydraulic

Institute’s wear cat- egory classification. “For a Category 4 slurry, for example, we recommend an impeller aspect ratio of 3. This is the ratio between the pump’s outside diameter and

Designed from its inception for mill circuit applications, the Metso

MD series MDM hard metal and MDR rubber lined slurry pumps offer sustained performance with maximum time between mill

shutdowns.

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Mechanical Technology — June 2016