Numerical
investigation on dispersion phenomena in packed bed reactors with low tube-to-particle
diameter ratio
Nico
Jurtz1, Gregor
Wehinger1, Thomas Eppinger2, Matthias Kraume1
1Chair Chemical and Process
Engineering, TU Berlin, Berlin, Germany;
2CD-adapco, Nuremberg, Germany;
Abstract
Packed bed reactors (PBR) are widely used in
the chemical and process industry. They play a key role in the heterogeneous
catalysis or in novel process concepts like the chemical looping. A quantity to
characterize the mass transfer in PBR’s is the dispersion coefficient. But correlation
to determine the dispersion coefficient fail for reactors with a low
tube-to-particle diameter ratio due to local wall effects that play an
important role (Delgado, 2006).
The flow field of that special reactor
configuration can be determined by the use of spatially resolved
CFD-simulations using the DEM-CFD coupled approach from (Eppinger, 2011). Based
on the calculated flow field a numerical residence time analysis is conducted
using the Lagrangian parcel approach. Compared to other passive scalar based
approaches this method is beneficial in terms of accuracy and calculation time.
The dispersion coefficient can subsequently be calculated based on the simulated
residence time distribution function (RTD).
Validation studies show that the presented
method allows an accurate and efficient prediction of the RTD. Further
simulations show the effect of diameter ratio, Reynolds number and particle
shape on the RTD and the dispersion coefficient. Effects like channeling,
stagnant zones and back mixing will be detected by analyzing the shape of the RTD
and localized by evaluating the calculated flow field.
References
Delgado, J., 2006. A
critical review of dispersion in packed beds. Heat Mass Transfer 42, 279-310
Eppinger, T., Seidler, K.,
Kraume, M., 2011. DEM-CFD simulations of fixed bed reac-tors with small tube to
particle diameter ratios. Chem. Eng. J. 166, 324-331.
