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(452f) Operating Condition Optimization on Mass Transfer in Aerated Stirred Tank Fermentors

Authors: 
Becker, L., Siemens PLM
Aglave, R., Siemens PLM Software
Eppinger, T., Siemens PLM Software
Oxygen is a critical
component of aerobic fermentations and is sparingly soluble in
aqueous solutions. Due to the slow mass transfer of oxygen from the
bubbles into the liquid the rate of cell metabolism depends on the
rate of oxygen supply from the gas phase. Mass transfer across
gas-liquid interfaces plays also a vital role in many other reaction
systems. The mass transfer is a function of the gas-liquid surface
area which is increased with high agitation rates. The shear rates
are increased resulting in bubble brake-up. With the agitation rate
the power consumption is increased as well. Micro-organisms, such as
yeast, are damageable and thus limit the shear rates, too.

Traditionally dimensionless
correlations are used to improve the design of production scale
stirred tank fermenters. These aid incorporating many important
design variables of the materials and geometry. However, design
methodologies available for stirred tank fermenters are insufficient
and many times contain errors. By making assumptions on the system
correlations often omit important influences on the mass transfer.
Using computational fluid dynamics enables us to make fewer
assumptions on the geometry and physics resulting in a better insight
into the system. This enables the engineer to make meaningful
decisions with fewer constraints.

In the current state of
industrial engineering a typical vessel is going to be operated
yielding various products. Therefore the tank geometry is not
designed from scratch but instead has to be used with little
alternations. In these or similar scenarios the operating conditions
- such as agitation rate or mass flow rates - are a mayor leverage
increasing the performance.

In this work the
performance of a stirred tank fermenter is going to be optimized
using CFD simulations in combination with design explorations.
STAR-CCM+ as a finite volume based physics solver and HEEDS exploring
the design space are the tools used. After validating the simulation
a Pareto front optimization with power consumption vs. mass transfer
rate will be presented.

References:

Aglave,
R., & Eppinger, T. (2016, December). Influence of Bubble Size
Distribution in Gas-Liquid Flows. In 
High
Performance Computing Workshops. 
IEEE.

Doran,
P. M. (1995). 
Bioprocess
engineering principles
.
Academic press.

Sorenson,
K. L. (2010). 
Comparative
studies on oxygen mass transfer for the design and development of a
single-use fermenteor
.
Utah State University.

Davis,
R. Z. (2009). 
Design
and scale-up of production scale stirred tank fermenteors
.
Utah State University.