(467a) Modeling the Residence Time Distribution In a Batch Fermentor: Comparison of CFD Prediction with Experiment | AIChE

(467a) Modeling the Residence Time Distribution In a Batch Fermentor: Comparison of CFD Prediction with Experiment

Authors 

Lencastre Fernandes, R. - Presenter, Technical University of Denmark
Dutta, A. - Presenter, University of Ghent
Heins, A. - Presenter, Technical University of Denmark
Eliasson Lantz, A. - Presenter, Technical University of Denmark
Nopens, I. - Presenter, Ghent University
Gernaey, K. V. - Presenter, Technical University of Denmark


Continuous
stirred tank reactors (CSTR) are ubiquitously used as fermenters in the biotechnological
production of enzymes, pharmaceuticals, metabolites, antibodies, etc. They are
also used in the bioprocess industry for the production of bio-ethanol, bio-hydrogen
and even in mammalian cell culture. In most cases, a scale-up of these processes
is necessary to yield commercial success and viability. As with most scaling-up
operations, mixing is also a crucial parameter in a biological process and is
often not ideal when operating at industrial scale. Poor mixing in a CSTR may be
caused by gas by-passing and back-mixing phenomena leading to the formation of dead
zones where, in the case of a bioreactor, cells will experience a limited supply
of nutrients and oxygen. In large-scale bioreactors gradients of e.g.
substrate, oxygen and pH arise as a result of non-ideal mixing, resulting in a spatially
heterogeneous extracellular environment. This fact has been suggested to be the
main reason behind lower product yields, but higher cell viability, in comparison
to lab scale cultivation (Enfors et al., 2001) 

Understanding bioreactor hydrodynamics in general, and
non-ideal mixing in particular, is a key problem to understand the inherent bioprocess.
The Residence Time Distribution (RTD) is one such way to characterize the
non-ideal mixing in a CSTR (Choi et al., 2004). To
estimate the RTD, a glucose tracer study has been performed experimentally in a
Sartorius CPlus¨ batch bioreactor, having
a working capacity of 10 litres, and the results were
compared using Computational Fluid Dynamics (CFD) simulations. Several cases
with varying impeller speed have been considered to study the effect of mixing
phenomena on the RTD. The mean and variance of the distribution are analyzed for
the extent of the deviation of the reactor behavior from its ideal state.
Furthermore, the sensitivity of the sliding mesh is tested by varying the
position of the interface zone. This would eventually contribute to building an
optimized model of the bioreactor, and will be used for integration with
biological models aiming at improving performance prediction in the cases of
poorly-mixed reactors.

Reference

[1]
Enfors, S.O., Jahic, M., Rozkov, A., Xu, B., Hecker, M., J?rgen, B. et al. (2001). Physiological
responses to mixing in large scale bioreactors. J. Biotechnol., 85, 175-185.

[2] Choi, B.S., Wan, B., Philyaw, S.,
Dhanasekharan, K., Ring, T.A. (2004). Residence Time Distribution in a stirred
tank: comparison of CFD predictions with experiment. Ind. Eng. Chem. Res., 43,
6548-6556.