Coal Preparation

New Dense Medium Cyclonic Separators

Coal Preparation » Gravity Separation

Published: July 96Project Number: C3006

Get ReportAuthor: Jon Davis | CRA Advanced Technology Development

Dense medium cyclone plant performance could be improved by ensuring that all particles are separated at an equivalent incremental ash. In practice, this means at an equal separation density.

The yield gain from such practice is estimated to be between 1 and 4%.

This project was established to determine whether there is an alternative dense medium cyclone design which would effect a separation at the constant cutpoint in all modules.


The criteria for an improved dense medium cyclone design were established to be:

  • Stable operation as a zero offset separator.
  • All feed particle sizes being separated at an equivalent cutpoint.

Following a review of the literature, the prospective existing alternative cyclonic separators were determined to be the three product dense medium cyclone, the long bodied cyclone, the Tri-Flo and the Larcodems separator. Of these, the long bodied and Tri-Flo separators are the focus of current ACARP studies and a Larcodems is installed in ACIRL's Maitland pilot plant and is available for commercial testing.


Testing of the three product cyclone indicated a number of capacity and efficiency issues which mean it is unlikely to find more than a few niche applications.

Tests of the Dynawhirlpool separator confirmed its poor separation efficiency on fine particles, but also confirmed that the device can be adjusted to operate as a zero-offset separator.

The most prospective alternate design was the direct-flow cylindrical cyclone designed by the Kutepov group in Moscow. This became the focus for further development and testing.

A direct flow cylindrical cyclone was constructed and tested in closed circuits. Significant and intrinsic design flaws were found, and explained, which made this device unsuitable for dense medium or hydrocyclone applications.

The cyclone design selected for testing was not successful; however the objective of optimising dense medium cyclone circuit performance remains an objective worth pursuing. The suitability of other devices such as the Tri-Flo and the Larcodems should be examined in the future.



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