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MEI Online: Sizing & Classification: Latest News: November 15th 2001

:: New Invention Will Replace Industrial Screens & Mixers?  

A new invention by Australian scientists is poised to revolutionise the use of separator screens used in a large number of industrial applications, from recycling to mining.

The inventors of the Rotary Classifier, Drs Guy Metcalfe and Dr Kurt Liffman of CSIRO Thermal & Fluids Engineering say, "We believe that the fast, accurate particle classification possible with the Rotary Classifier makes it worth up to $100 million in the Australian market alone".

Dr Metcalfe says, "The Rotary Classifier overcomes the major problems of 'blinding' (where material jams the holes of the screen, effectively reducing the screen's operating surface), and constant wear-and-tear on screens from abrasive granular material". "Both of these factors contribute to significant operating costs for maintenance, downtime and replacement."

Dr Metcalfe says, "The Rotary Classifier is more than just a separator screen. It has been designed to separate different materials, classify particles into groups by size or density, or it can be a highly effective mixer for different density materials such as wood and plastic which are inclined to layer rather than be evenly distributed during blending".

The secret of the just patented CSIRO Rotary Classifier is based on an observation that granular materials tumbled in a rotating vessel, segregate spontaneously depending on their size and density. In essence, the vessel tumbles the particulate material, producing continuous or discrete avalanches in the surface. This action moves particles of smaller size or higher density towards the centre of the material and particles of larger size, or lower density, radially outward from the centre. Extraction of particulate material occurs at selected radial locations.

The device comprises a rotary longitudinal tube with a fixed endplate functioning as an output for the device, with holes for extracting particles from the tube. The holes are placed at different radial positions (or differently configured endplates are used) depending on the desired sizes of particulate material to be extracted. One, or several sized fractions can be removed simultaneously. Dr Metcalfe says, "Successful trials of the Rotary Classifier have been conducted on materials such as salt and building sand, which showed very fast and accurate separation into the particle size required. Classification of the salt was complete after three revolutions at 2 rpm. These are extraordinarily good results and highlight the speed and cost savings just on the operating side, even before wear and tear and production downtime is taken into account."

The advantages offered by the Rotary Classifier are also available to a wide range of industries.

The classification of iron ore is one potential market. Other industrial applications where the Rotary Classifier can provide improved screening and mixing are:

  • Coal/ash separation - For separating coal from silicates at power stations.
  • Copper wire recycling - Separating the copper from the insulation.
  • Brick and concrete recycling - For removing contaminants such as steel, plastic, timber and organics prior to use.
  • Mineral sands reduction - This is an application for running the Classifier in a mode where it mixes instead of separates, to solve the problem of undesirable segregation in the heating kilns used in the reduction process to produce, for example, titanium.
    Based on CSIRO research, if coal is ground to a particular size, dependent on the density difference between coal and titanium oxide, all the particles will mix well and the reduction will proceed more effectively.
  • Composite building products - made from wood chips and shredded, recycled plastic flakes.

Dr Metcalfe says, "Now that we have proved the Rotary Classifier, CSIRO Australia is looking for commercial partners who are in the industrial market and are interested in further development of the technology".

The invention of the Rotary Classifier follows another unique product recently unveiled by CSIRO Thermal & Fluids Engineering that has added a new dimension to the world of industrial mixing. The CSIRO Rotated Arc Mixer (RAM) also involved the work of Dr Metcalfe and is a unique new mixing technology, which does away with the need for impellers in mixing vessels.




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