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HYDROCYCLONES 28 E&MJ; • FEBRUARY 2018 www.e-mj.com Although simple in concept, the hydrocy- clone fulfils an essential role in both classi- fication and purification across a wide range of industries. Mineral processing is no ex- ception, with cyclones often being an inte- gral part of closed-circuit grinding systems. The centrifugal force applied to parti- cles being spun within a cyclone is many times greater than gravity, allowing the device to achieve a much better separa- tion efficiency based on either (or both) particle size and density. Larger or more dense particles are directed toward the underflow, while finer or lighter material reports upward to the overflow. The better design of the cyclone, and the less wear there is internally, the less opportunity there is for larger particles to be misdi- rected to the overflow, or for slimes to sink into the underflow. In a typical closed-cir- cuit grinding system, the consequences of either situation can have a significant impact on operating economics. Critical considerations include the rel- ative sizes of the inlet and overflow spools, the apex spigot and the vortex finder, while finer separations will be made pos- sible by reducing the overall cyclone di - ameter. The skill comes in achieving the optimum relationships between each of these variables, together with others such as the required flow rates, flow pressures and feed consistency. Metso's New Designs Ben Klein, global product manager for hydrocyclones at Metso, told E&MJ; that the company has recently developed a new line of classification equipment to complement its existing product offering. In developing both the MHC Series hydro- cyclone and the Metso UltraFine Screen, Metso can now provide the optimum tech- nology for a given application, Klein said. "Both products have been tested extensively and offer significant advan- tages over previously available technol- ogies," he said. "These advancements have the potential to deliver long-term benefits in improving classification ef- ficiency while considering capital costs and operating costs." Klein continued by explaining that when evaluating hydrocyclones and fine screens, it is important to recognize the impact the classification equipment technology has on the capital expense, operating expenses and overall plant per- formance. With respect to classifier selec- tion, one must target several key objec- tives, including: • Selecting equipment that improves overall plant performance, through im- proved grinding circuit performance and improved recovery of valuable minerals; • Selecting equipment that will provide acceptable availability and mainten- ance costs; and • Reducing the capital costs, including the direct capital costs of the classifier as well as indirect cost implications such as the resulting mill selection, building costs, slurry-transport equipment costs, and indirect cost factors influenced by the classification equipment. Overall, a comprehensive review of these elements, including application and site-specific details, must be com- pleted during equipment selection to provide the lowest total cost of ownership, he counseled. Metso reported that the internal geo- metry of its MHC Series hydrocyclone is optimized to promote smooth flow from the inlet through the entire hydrocyclone, minimizing turbulence and increasing throughput. The low turbulence has the A Simple Spin on Classification In use as an essential classification and dewatering tool for the best part of 90 years, today hydrocyclones play a key role in maintaining concentrator flow. E&MJ; looks at the technology fundamentals and how equipment optimization is still in progress. By Simon Walker, European Editor Installing a large Metso hydrocyclone. The company's MHC Series cyclones are designed internally to achieve smooth flow with less turbulence and higher throughput as a result. Depending on the throughput required, hydrocyclones can be mounted in various ways, including in clusters that minimize the footprint required. (Photo: Metso)