Three‐Dimensional Simulation of Hydrodynamics in a Rotating Disc Contactor using Computational Fluid Dynamics

Abstract

The 3D simulation of the hydrodynamic behavior of a rotating disc contactor (RDC) by means of computational fluid dynamics (CFD) was investigated for the n-butanol-succinic acid-water (BSW) system. For the two-phase liquid-liquid flow, the velocity distribution of the continuous phase and drop size distributions were determined using the k-x turbulence model in conjunction with the Eulerian-Eulerian approach and MUSIG model. In this system in which the holdup of the dispersed phase is low, the continuous phase velocity was computed by simultaneously solving the Navier-Stokes equations beside the different models of turbulence. The motions of the dispersed phase was calculated while considering buoyancy, drag and inertia forces, and equations related to the continuous and dispersed phases were coupled to each other by considering the momentum transfer on the interface and the effect of drop motions in turbulence. In this simulation, by considering drops' breakage, their path, the velocity profile, and also the velocity contour plot of the dispersed phase were obtained. A comparison of the holdup experimental values with the results predicted by CFD showed that the k-x model is the best descriptive model for the computation of holdup in a RDC. IntroductionLiquid-liquid extraction is an important separation process that is widely used in the chemical, biochemical, petrochemical, pharmaceutical, and food industries [1][2][3][4]. The rotating disc contactor (RDC) is one of the most important extraction columns, which was initially introduced by the Royal Dutch/ Shell Group [5]. RDC columns have extensively been used in the industry, particularly for liquid-liquid systems with low interfacial tension. The low interfacial tension means small drop sizes, thereby causing the efficiency of the RDC extractor to ameliorate.These columns consist of a set of distinct discs with equal horizontal intervals between the stators. The agitation provided by the discs mounted on the rotor shaft improves the performance of the RDC by breaking the dispersed phase droplets, hence increasing the interfacial area for mass transfer [4,6]. Drop sizes are controlled by the ratio of buoyancy to interfacial tension forces under the conditions of no agitation or low levels of turbulence (Re R N R D 2 R m c < 10000) 1) [7].Too high an agitation speed will exacerbate the axial mixing, thereby reducing the column performance. Axial mixing ends in concentration jumps all over the column so that this phenomenon causes operating lines to be closer to each other, the result of which is the decrease of concentration driving force and the need for more discs inside the column [2,8,9].Experimental investigations with agitated columns reveal that the drop size distributions of rising organic phase drops dispersed in a continuous aqueous phase are broad in the first stages, becoming narrower and shifting toward smaller drop sizes in the later stages of the column, until a final, steady-state distribution has been achieved; thus, providing evidence that dro...

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CFD simulations and particle image velocimetry measurements in an industrial scale rotating disc contactor

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