Hydrodynamics of a continuous mixer-settler system at high organic to aqueous phase ratios

Abstract

This study investigates separation efficiency and entrainment in a continuous settler at high continuous-to-dispersed phase ratios.

The effects of fluid properties (phase density, viscosity, and interfacial tension) and operating conditions (inlet phase ratio, droplet size, flow rate, and settling area) were examined using two liquid-liquid systems. The specific settling rate (SSR) was calculated based on the volumetric flow rate and the cross-sectional area of the settling zone. It was observed that an increase in droplet size from 150 microns to 200 microns resulted in a 15–30% change in separation efficiency. Increasing the SSR from 1 m³/hr/m² to 2 m³/hr/m² reduced the separation efficiency by 10% and 30% across the respective systems, also highlighting the effect of the respective system’s fluid properties. The high phase ratios were observed to directly affect both separation efficiency and entrainment due to the absence of a dispersion band. Systemic parameter sensitivity was greater at higher phase ratios (20:1 and 50:1) compared to lower phase ratios (10:1), due to reduced binary coalescence between droplets. The effect of the interfacial tension was observed through the Ohnesorge number. Finally, an empirical correlation was developed from the experimental data to predict the system's separation efficiency and entrainment.