Septum and filtration properties of rigid and deformable particle suspensions

Suspensions of rigid polyethylene particles and deformable cross-linked dextran particles (Sephadex) were filtered on a planar septum by a constant applied pressure P. For both particle types the relation of Ruth, Montillon and Montanna (1933, Industrial and Engineering Chemistry, 25, 76-82) described the time dependence of the cumulative filtrate volume V over the whole range of concentration and applied pressure. The relation of Koenders and Wakeman (1996, Chemical Engineering Science, 51, 3897-3908; A.I.Ch.E. Journal, 43, 946-958; Transactions of the Institution of Chemical Engineers, 75, 309-320) described V(t) when the filtration was predominantly septum controlled. The fit of experimental data to the relation of Ruth et al. (1933) was used to obtain the suspension desorptivity S, the septum resistance R, and the dependence of S and R on the suspension concentration and the applied pressure P. The variation of S with P and the suspension concentration showed that the polyethylene cake was incompressible and that the Sephadex cake compressibility varied according to the magnitude of P, being very compressible for P > 3 kPa. For both suspensions the septum resistance R exceeded the unclogged or intrinsic septum resistance R-i. Measurements at a fixed P showed that R was independent of suspension concentration, but at a fixed concentration the excess resistance R - R-i increased approximately in proportion to P. To explain the variation of R with P and concentration, a qualitative model is proposed in terms of interparticle flocculation and the transmission of stress in the cake via particulate chains. (C) 2000 Elsevier Science Ltd. All rights reserved.