The effect of size and shape of annular centrifugal contactors upon hydrodynamics and mass transfer using HNO3-TBP/OK

Abstract

Annular centrifugal contactors (ACCs) are process intensification equipment for liquid-liquid extraction (also known as solvent extraction) that use centrifugal force that 200x greater than traditional gravity settling (Baker et al., 2022a). The size and throughput of ACCs have been denoted by their increasing rotor diameter (RD), from 10 mm up to 1330 mm. In this work a multiscale ACC platform has been commissioned, (consisting of 10, 25, 40 mm RD ACCs), to collect the physical liquid-holdup and mass transfer across several sizes to inform future computation modelling flowsheets of liquid-liquid extraction (LLE).Experimental studies have been performed with nitric acid with tributyl phosphate in odourless kerosene (TBP/OK) relevant to the development of advanced PUREX processes for recovery of actinides from spent fuel. Hydrodynamic trials determined the minimum Relative Centrifugal Force (RCF) required to separate extreme solvent/aqueous (S/A) feed ratios and total throughputs across the three sizes of ACC. The novel 'stepped stop' method has provided understanding of the actual liquid holdups within the two distinctly different regions (mixing annulus and separating rotor) ACC during operation to provide accurate residence times. These values were subsequently used to calculate the mass transfer and stage efficiency of aqueous nitric acid with tributyl phosphate in odourless kerosene. The smallest contactor was determined to be distinct and likely under-predicting performance of larger contactors. Ultimately the geometry and the aspect ratio supersedes using rotor diameter for defining scale-up of annular centrifugal contactors.