On droplets size distribution in a pulsed column. Part I: In-situ measurements and corresponding CFD-PBE simulations

The pulsed column is one of the most used contactors in solvent extraction processes, especially in the nuclear fuel treatment industry and for hydrometallurgical applications. The optimisation of solvent extraction operations needs a thorough understanding of the diphasic flow's properties inside the apparatus, especially that of the dispersed phase. For the first time, in-situ measurements of the drop size distribution (DSD) were achieved in a small diameter pulsed column (lab scale), by using the SOPAT-VF light reflectance video probe on two water-in-oil (W/O) systems exhibiting low and high viscosities of the oil phase. Separate effects of the pulse amplitude and frequency on the DSD and the phase hold-up were evidenced for both O/W systems, despite their different viscosity levels. This technique allowed very precise measurements of droplet-diameters in quite a confined space, three orders of magnitude, which is remarkable. Experimental findings allowed the validation of a computational fluid dynamics (CFD)-population balance equation (PBE) coupled model and the improvement of breakage and coalescence kernel parameters. Rupture and coalescence mechanisms were correctly captured. The dependence of emulsion's properties on the column hydrodynamics could then be illustrated over one period of the pulsed flow. Incidence of higher levels of pulsation intensity, hardly achievable experimentally, and separate investigation of the effects of viscosity and surface tension are presented. (C) 2016 Elsevier B.V. All rights reserved.