Scale-up of Bioprocesses
Table 11.7. Reactor properties of the modeled reactor
Stirrenvessel diameter
Number of impellers
Stirrer rate
2.6 s'1
Baffle diameter/vessel diameter
Number of baffles
Liquid volume
varying - up
to 25 m3
The microbial (oxygen consuming) reaction in the reactor is not given in the paper, but it is described by
Monod type kinetics. The dissolved oxygen concentration was measured in the reactor by a movable
oxygen electrode, which allowed measurement at different axial positions. Furthermore, the overall
oxygen transfer rate was calculated. The measurement showed (as could be expected) that the oxygen
concentration was not constant throughout the reactor space. Futhermore, the oxygen transfer rate was
overestimated using a single correlation for k,a of the type given by Eq. 1
or 2.
Coalescing case
Non-coalescing case
Figure 11.12. Schematic representation of compartments in the model by Oosterhuis and Kossen, 1983
To better model the oxygen transfer rate, the reactor was divided into one or two well mixed-regions close
to the impellers and one or two bubble regions (i.e. regions which behave like bubble columns) one
located in the top part of the reactor and the other located in the region between the turbines as shown in
Fig. 11.12. For a coalescing medium, i.e. for the case where the time for coalescence was lower than the
circulation time, only one well-mixed region and one bubble region was used. For the case of a non-
coalescing medium, however, the time for coalescence to occur was expected to be larger than the
circulation time, and two mixed regions and two bubble regions were used. The main reason for making
this compartment division was that the oxygen transfer rate could be expected to be higher in the well-
mixed region close to the impellers and somewhat lower in the bubble region, and two different
correlations should be used for the gas-liquid mass transfer to the well-mixed and bubble regions
respectively (Fig. 11.13),
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