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 systems, the understanding of this phenomenon and the ability to predict the limiting flux are essential for improving the design and operation of ultrafiltration processes. A new cell design, an annular cell fitted with a tangential 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 mainly axial flow. The cross-flow ultrafiltration of dilute suspensions of bentonite is studied under specific operating conditions in the three different configurations of filtration cells. The improvement of the permeation flux in the swirling cell, compared with that measured in the two other configurations, can reach 70% for a wall velocity gradient of 800 s⁻¹. This enhancement is highly linked to the removal of particles deposited at the membrane surface owing to the three-dimensional fluid flow involved in this particular cell. The bentonite deposit is compressible and characteristics of particles accumulation at the membrane surface are investigated.