Advantages and risks in increasing cyclone length

A.C. Hoffmann, M. de Groot, W. Peng, University of Groningen, Department of Chemical Engineering,
Nijenborgh 4, 9747 AG Groningen, The Netherlands,

H.W.A. Dries and J. Kater, Shell Global Solutions International B.V., PO Box 38000;
1030 BN Amsterdam, The Netherlands

Abstract
The effect of cyclone length on separation efficiency and pressure drop has been investigated experimentally by varying the length of the cylindrical segment of a cylinder-on-cone cyclone, and theoretically. The experimental results span cyclone lengths from 2.65 to 6.15 diameters. They show a marked improvement in cyclone performance with increasing length until 5.5 cyclone diameters; beyond this length the separation efficiency was dramatically reduced. Experimental data are shown to agree well with the predictions of a range of models and CFD simulations. This is helpful to assess the benefit of prolonging a given cyclone. The physical mechanisms behind the observed trends are elucidated. The dramatic fall in separation performance for the longest length is shown to be caused by the ‘natural turning’ phenomenon.

Topical Headings: 2. Particle Technology and Fluidization or 3. Separations or 9. Energy and Environmental Engineering.

Key Words: Cyclone, Separation performance, model prediction, CFD, natural turning length.