(339a) Hydraulics of Taylor-Couette Disc Contactors

Annika Grafschafter, Matthäus Siebenhofer

A global and sustainable implementation of renewable bioresources has become a high priority target nowadays. Downstream processing in the biobased industry often faces highly dilute mixtures making product isolation a challenge. In separation and isolation of value added products from highly dilute aqueous feed, liquid-liquid extraction has established as a basic unit operation. The Taylor-Couette Disc Contactor (TCDC) [1, 2] is a stirred liquid-liquid extraction column with a simple design of internals and thus suitable for applications in bioseparations. The internals of the TCDC are similar to the Rotating Disc Contactor (RDC), but without stator rings and with increased shaft and disc diameter. Without stator rings, crud accumulation and fouling along the active mixing zone of the column is avoided, making the TCDC particularly suitable for harsh operation conditions. The increase of the shaft diameter up to an optimum ratio of D/D_Sh = 0.5 prevents formations of hydrodynamic dead zones along the shaft and does induce banded two-phase flow as observed in Taylor-Couette reactors. Compared to Taylor-Couette reactors, the TCDC provides a much higher hydraulic capacity beyond 30 m³ m^-2 h^-1.

For successful design and operation performance of extraction columns, the comprehensive knowledge of hydraulics is needed. Therefore, data of the dispersed phase holdup (φ), drop size distribution (DSD) and residence time distribution (RTD) were determined in a 0.1 m and 0.3 m diameter pilot plant scale TCDC. For hydrodynamic characterization, the effect of the hydraulic load, rate of rotation and phase ratio was investigated. The minimum rate of rotation necessary for formation of fully developed toroidal vortexes in a single compartment can be predicted for specified hydraulic load. The influence of the hydraulic load on DSD is nearly negligible. The effect of the phase ratio on φ at low hydraulic load is insignificant but at high hydraulic load, the phase ratio has a strong impact on φ. Analysis of the RTD of the continuous phase suggests application of the tank-in-series model. The number of corresponding vessels in series was deduced from the maximum of the exit age distribution [3]. For given rate of rotation, the number of corresponding vessels in series increases with increasing hydraulic load. A reversed trend was observed for fixed hydraulic load and varying rate of rotation. Increasing rate of rotation contributes to backmixing. Summing up the operation experience in pilot scale Taylor-Couette Disc Contactors provide high load performance and flexibility in operation. Due to the simple design principle, it can withstand harsh operation conditions, even significant solids load in the feed.

[1] E. Aksamija, C. Weinländer, R. Sarzio, M. Siebenhofer, Sep. Sci. Technol. 2015, 50 (18), 2844–2852. DOI: 10.1080/01496395.2015.1085406

[2] A. Grafschafter, M. Siebenhofer, Chemie-Ingenieur-Technik 2017, 89 (4), DOI: 10.1002/cite.201600142

[3] O. Levenspiel, Chemical Reaction Engineering, Wiley, 1999.