Improvement of the performance of the ultrafiltration of bentonite suspensions using a swirling decaying annular flow: comparison with tangential plane and axial annular flows

The limiting flux induces a performance limitation of ultrafiltration syste ms, the understanding of this phenomenon and the ability to predict the lim iting flux are essential for improving the design and operation of ultrafil tration processes. A new cell design, an annular cell fitted with a tangent ial inlet, which induces a swirling decaying flow, is tested. Performances of this ultrafiltration unit configuration are compared with two other more classical geometries: a simple plane unit and an annular cell involving ma inly axial flow. The cross-flow ultrafiltration of dilute suspensions of be ntonite is studied under specific operating conditions in the three differe nt configurations of filtration cells. The improvement of the permeation fl ux in the swirling cell, compared with that measured in the two other confi gurations, can reach 70% for a wall velocity gradient of 800 s(-1). This en hancement is highly linked to the removal of particles deposited at the mem brane surface owing to the three-dimensional fluid flow involved in this pa rticular cell. The bentonite deposit is compressible and characteristics of particles accumulation at the membrane surface are investigated. (C) 2001 Elsevier Science B.V.. All rights reserved.