455255 Design of Taylor-Couette Disc Contactors

Tuesday, November 15, 2016: 8:30 AM
Mission II & III (Parc 55 San Francisco)
Annika Grafschafter, Enes Aksamija and Matthäus Siebenhofer, Institute of Chemical Engineering and Environmental Technology, Graz University of Technology, Graz, Austria

Many biorefinery processes suffer from poor economics. Target constituents do not show up in appropriate concentration for simple separation technologies. They rather have to be separated from side streams, low quality broths or multicomponent mixtures with low concentration but bad matrix properties. The gap between expectations and needs may be solved by combining simple solvent extraction with reactive separations. Liquid-liquid extraction is a leading technology to raise the economic feasibility of separation processes and provides access to combination of chemical reaction and separation in one reactor type. For application in reactive bioseparations the Taylor-Couette Disc Contactor (TCDC), a hydrodynamic hybrid of a Taylor-Couette Reactor and Rotating Disc Contactor (RDC), may offer advantageous operation features. This type of liquid-liquid contactor does not contain stator rings which provide dead zones for crud accumulation. Furthermore an increased shaft diameter improves the classical RDC design and tie-in a similar flow pattern compared to banded two phase flow of a Taylor-Couette Reactor. Increased rotor discs diameters form compartments during operation, stabilize the flow pattern and inhibit high axial dispersion. Compared with Taylor-Couette Reactors the active reactor volume is significantly increased which results in more stable banded Taylor-Couette vortexes even at higher flow rates.

In order to ensure economical and efficient operating points of any kind of reactor, they have to be designed appropriate for their application. For the design of continuously operating reactors, like the TCDC, the ideal plug flow reactor (PFR) and the continuously stirred tank reactor cascade (CSTR) model are applied. With these basic design concepts either the separation efficiency for a given column height, or the column height for continuous separation processes can be obtained. However, the initial points for these calculations is given by information about the hydrodynamic characteristics of the reactor. With given phase ratio and rotational speed the mean sauter diameter and dispersed-phase hold-up can be determined by empirical correlations. Hence the specific mass-transfer area in the column can be predicted and the reactor behavior is characterized.

For hydrodynamic characterization of the TCDC empirical correlations for drop size estimation and dispersed-phase hold-up, originally developed for RDC design are applied to predict drop size and hold-up in the TCDC. Based on experimental data of the mean sauter diameter and dispersed-phase hold-up at varying rotational speeds, the design rules are adjusted for the needs of TCDC design. Thus, it is possible to predict mass-transfer area in the TCDC with given flow rates and rotational speed.

In terms of modelling mass transfer, experiments confirm complete backmixing in each compartment, best approaching apparatus design with CSTR cascade model.

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See more of this Session: Extractive Separations Fundamentals and Design
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