Ulrich Meier

Modelling filtration with superimposed sedimentation

Abstract Filtration at moderate rates is often superimposed by sedimentation. This work shows that classical cake filtration equations can be complemented by an additional sedimentation term to model cake filtration measurements with significant sedimentation. Algorithms are derived for zone as well as clarifying sedimentation. In contrast to the classical filtration theory not the absolute values but the differentials of cake height and filtrate volume are set into a proportional relation. The resulting set of equations can be solved numerically. If the porosity is expressed as a function of the cake height and the Carman–Kozeny relation is employed, the model may be extended to compressible cakes. Experiments with the system ‘lactose in ethanol’ justify the model. Experimental data can be fitted much better with the new model than with equations of the classical filtration theory alone. In contrast with other filtration models that include sedimentation, no additional parameters need to be introduced, and the physical meaning of constants such as cake resistance, specific cake volume and, settling velocity is maintained.

Influences of physicochemical parameters on the separation of colloidal organics

The impact of physico-chemical parameters on solid-liquid separation of a micronized lactose-in-ethanol suspension is investigated by means of Fraunhofer diffraction, focused beam reflectance measurement (FBRM), electrokinetic sonic amplitude (ESA), sedimentation and filtration experiments. Lactose-in-ethanol dispersions are quite unstable, with a strong particle agglomeration and sedimentation tendency. Only diluted suspensions show a significant impact of physico-chemical parameters such as pH. ESA titrations show the surface properties of lactose to change strongly when acids and bases are added. High base concentrations were found to accelerate cake filtration, while high acid concentrations slow it down.