(401a) Modeling of Taylor-Couette Disc Contactors

Annika Grafschafter and Matthaeus Siebenhofer

The Taylor-Couette Disc Contactor (TCDC) is a liquid-liquid extraction column [1]. From the hydrodynamic point of view, it is a hybrid of a classical Rotating Disc Contactor (RDC) and a Taylor-Couette Reactor. The TCDC design is based on RDC design, but without stator rings and an increased shaft diameter. The flow pattern in the single compartment is induced by centrifugal force, counteracted by friction of the continuous phase. It compares well to banded two phase flow of a Taylor-Couette reactor. The modeling of two-phase flow in chemical process applications is not an extraordinary task when it is possible to predict the specific mass transfer area and the hydraulic operation range. Two-phase contactors can be appropriately designed by accurate prediction of the hydrodynamic characteristics, e.g. the mean sauter diameter and dispersed-phase hold-up, giving access to the basic design of the plug flow reactor (PFR) and the continuously stirred tank reactor (CSTR) cascade. For the design of stirred liquid-liquid extractions columns literature recommends application of the PFR model. To consider axial back mixing, the classical HTU-NTU concept as deduced from the PFR model, is extended with a height of dispersion unit (HDU-value) with the aid of axial dispersion coefficients [2]. However, the axial dispersion coefficient of both phases is difficult to determine.

Due to the formation of toroidal vortexes (banded two phase flow), each compartment of the TCDC rather corresponds to two ideal stirred tank reactors in series with ideal mixing, suggesting CSTR cascade design.

Modeling of hydraulics, including the prediction of the stirring speed, the drop size distribution and mean sauter diameter as well as hold up, flooding and the specific power demand as well as the residence time distribution of the continuous phase [1] and the disperse phase [3] in the single compartment and the column has been validated with experiments. Mass transfer experiments with the systems n-butanol-undecane-water and acetic acid-Cyanex 923-water have confirmed that the concentration profile along the column height and the separation efficiency can be precisely modeled with CSTR cascade design

[1] Aksamija E., (2015), Der Taylor-Couette Disc Contactor; ein vereinfachtes und optimiertes Design von Drehscheibenextraktoren, PhD Thesis, University of Technology Graz

[2] Mersmann A., Kind M., Stichlmaier J., (2005), Thermische Verfahrenstechnik, Springer-Verlag Berlin Heidelberg, p.382 â?? 383

[3] Sarzio R., (2015), Experimentelle Validierung der CFD-Simulationen mehrphasigen Strömung

in der RDC Kolonne, Master Thesis, University of Technology Graz