Modern Mining February 2019

PRODUCT News

Cavex® hydrocyclones improve plant efficiencies

The successful performance of Weir Minerals’ Cavex® hydro- cyclones at a diamond mine in South Africa’s Northern Cape Province has proved

The customer required a solution that could offer at least six months of wear-life, and a probable error of separation (Ep) of no greater than 0,08 at a cut density of 3,1 tonnes per cubic metre (t/m 3 ). Tracer tests were used to monitor the efficiency of the separation achieved by the Cavex® hydrocyclones to ensure all of these requirements were met. “Ep values achieved were 0,042 for the 4 mm tracer tests and 0,035 for the 8 mm tracer tests, which were below the set max- imum target of 0,08 from the mine,” Zimba said. “This highlighted the benefits and improved efficiencies of the Cavex laminar spiral feed inlet.” The lower the Ep, the more efficient the separation; it is defined as half the differ- ence between the density at which 75 % is recovered to sinks, and that at which 25 % is recovered to sinks. “The customer’s tracer tests on the Cavex hydrocyclones showed that cut points of 3,08 t/m 3 were achieved for both the 4 mm and 8 mm tracers,” Zimba said. “This was within the performance levels of 3,1 t/m 3 that the customer had specified.” Initially, the hydrocyclones were commissioned to treat only fines at the dia- mond plant – the minus 8+1 mm material. Later, however, the mine decided to run a combined DMS, after which the full DMS ficult access road to the mining operation, made it essential for us to custom-design the substation and transformers to with- stand the rough journey,” says Trafo Power Solutions MD David Claassen. According to Claassen, the com- plete solution was manufactured in a fast-track project that took only 12 weeks. This included the in-house design of venti- lation and airflow systems to deal with the extreme heat and humidity levels of over 90 %, as well as lighting and small power equipment. He highlights the suitability of dry-type transformers to the climatic conditions at the mine, especially their ability to remain cool with only minimal movement of air across the windings. Where necessary, extremely high ambient temperatures may require the employment of forced air options in the design.

size range of minus 20+1 mm was treated through all the fines DMS hydrocyclones. The unique design of the laminar spiral inlet geometry delivers sharper separation and maximises capacity while delivering a longer wear-life than conventional involute or tangential feed inlet designs. By providing a natural flow path into the hydrocyclone body, the design allows the feed stream to blend smoothly with the rotating slurry inside the chamber, reducing turbulence and improving separation efficiency. “Combining our cone and spigot com- ponents in the hard metal range is an important contribution to the reduction in turbulence,” Zimba explained. “Another vital factor is the Cavex inlet design with 360 deg scroll; this design was proven through extensive computational fluid dynamics (CFD) analysis as well as our mul- tiple installations to date.” Weir Minerals also conducts ongoing research and development on methods to minimise turbulence on assembled casted components. The Cavex® hydrocyclones are designed with a variety of inlet sizes to accommodate a wide top size at specified medium-to-ore ratios. The inlet sizes range from 0,2 to 0,33 as a function of the hydro- cyclone diameter. Rajen Govender, Weir Minerals Africa, tel (+27 11) 929-2701, e-mail: rajen.govender@mail.weir “The cast resin design of dry-type trans- formers improves their efficiency and hence their heat losses, so cooling requirements are reduced,” he says. “Their efficiency also means they consume less energy, which in this application saves on diesel costs.” Among the advantages of dry-type transformers are that they require almost no maintenance and can last up to 25 years without much attention. Oil-filled transformers, on the other hand, need regular maintenance and sampling of oil if they are to operate safely and consis- tently. In a remote location like Bisie mine, this advantage delivers particular benefits to the user. Dry-type transformers can also be installed indoors, without the need for their own civils infrastructure such as bund walls and structures as there is no oil posing

t he t e c hno l og y ’s applicability in dense medium separation (DMS) plants treat- ing diamondiferous

material.

In her presentation to the Southern African Institute of Mining and Metallurgy (SAIMM) diamond conference in Johan­ nesburg in 2018, Weir Minerals Africa’s Senior Process Engineer, Boitumelo Zimba, said the hydrocyclones improved plant effi- ciencies and produced 40 % more tonnage than the mine’s target. “As the Cavex hydrocyclone is tried and tested in hard rock mining and coal classification, the Cavex 360 deg lam- inar spiral inlet profile was used as a basis for the development of a dense medium cyclone,” Zimba said. “Individual casting patterns were developed and produced in order to fabricate the Cavex dense medium hard chrome cyclone with the exact laminar spiral feed chamber that exists when moulded out of rubber.”

Dry-type transformers delivered to tin project One of the world’s highest grade known tin deposits is being developed in the DRC and dry-type transformers from specialist sup- plier Trafo Power Solutions are now integral to powering this effort.

Two 3 000 kVA, 400 V/11 kV cast resin transformers – housed in 6 m contain- ers – were recently delivered to Alphamin Resources’ remote Bisie mine site in North Kivu province. They will step up the sup- ply from the operation’s diesel-powered generator plant from 400 V to 11 kV. Trafo Power Solutions also supplied two 100 kVA, 400 V/400 V Dyn11 dry-type lighting trans- formers for outdoor applications. Bisie is located about 180 km north‑west of Goma, in the Walikale Territory – some 60 km from the town of Walikale and 32 km from the national route linking Walikale with Kisangani. “The mine’s remote position, and the dif-

safety or environmental risks. Trafo Power Solutions, tel (+27 11) 325-4007, website: www.trafo.co.za

46  MODERN MINING  February 2019