Simulation of the Fluid Dynamics of Solvent Extraction Columns from Single Droplet Parameters

Abstract

A droplet population balance model is used to simulate the hydrodynamic behaviour of solvent extraction columns. This model describes the axial change of local column hold-up and local droplet size distributions caused by basic phenomena such as droplet rise, axial dispersion, and droplet break-up and coalescence. In order to reduce the effort invested in experimental scale-up, single droplet experiments were performed in small-scale laboratory devices. A Rotating Disc Contactor (RDC) with 5 compartments was used for this purpose. The single droplet movement is investigated by using a light source to reproduce the three dimensional particle trajectories on a two-dimensional screen. The resulting pictures are analysed by digital image processing. The experiments were performed for different droplet sizes under different agitation and throughput conditions. Droplet rise is found to slow down with increasing agitation whereas higher continuous phase throughput shows only a weak influence on the relative rising velocity. Simultaneously the axial dispersion coefficient decreases at higher agitation and continuous phase flow rates. Based on these single droplet parameters, the population balance equation is solved numerically for a RDC column using a Galerkin method.