Solid‑liquid separation is carried out in many industries and plays a crucial role in the overall process efficiency or can be a bottleneck for product specifications. The dewatering characteristics of solid‑liquid mixtures, so called suspensions, have to be determined to compare filtration equipment performance or to design new equipment.
A variety of frameworks exist nowadays, the most common of which is the conventional filtration theory developed by Ruth, Tiller & Shirato utilising the specific filter resistance α(p) and the filter cake porosity ε(p). The conventional theory considers the applied pressure as the explicit factor for filtration and describes the process on a macro‑scale level. This results in conventional theory using average values to describe filtration processes. The averaging approach is fine for incompressible materials where the filtration parameters do not change with increasing pressure. For compressible materials, a theoretical framework with a local description has to be used. The compressional rheology framework developed by Buscall & White uses the local solids volume fraction f as the explicit parameter, and implicitly the solids pressure given by the compressive yield stress Py(f) and the rate given by the hindered settling function R(f). Using the solids concentration as the explicit parameter allows transferring material characteristics to different devices and more reliable scale up.
As well as the theoretical framework, the characterisation itself poses another hurdle. In this paper both the conventional filtration and the compressional rheology theory are presented. Furthermore, characterisation techniques such as the Nutsche cell, the Compression‑Permeability Cell and a piston‑driven filtration rig are compared using calcium carbonate of different degrees of compressibility. This will highlight the differences between the theories and characterisation techniques alike, leading to recommendations for good practice...
Session: L3 - Cake Filtration - Modelling, Simulation, Characterization
Day: 13 March 2018
Time: 16:45 - 18:00 h