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Poster Presentation 3-46
Foam Formation in a Mechanically Stirred Vessel
F. Delvignea, M. Bruxelmaneb and P. Thonarta
aFaculté des Sciences Agronomiques de Gembloux Centre Wallon de Biologie Industrielle Passages des Deportes 2, 5030 Gembloux, Belgium
bFaculté Polytechnique de Mons. Laboratoire de génie chimique et biochimique, Belgium
Telephone: 081-62-2272; E-mail: delvignef@fsagx.ac.be
This study relates to the foam phenomena induced by gas flow and stirrer speed in aerated and mechanically stirred tank bioreactors. Foaming solution selected to represent culture media contained Tween®40 and distilled water and the impeller used was a standard TD6 Rushton turbine. The volumes considered were 6 and 300 liters.
We define a foaming capacity which reflects the evolution of the height of the foam in the headspace of the vessel. Visual evaluation of this parameter has permitted us to highlight a transition zone below which the foaming capacity (FC) of the system increases drastically. This zone corresponds to the loading point of the impeller. For the TD6 Rushton impeller, the minimum foaming capacity was found for the lowest combination of N-G and the compromise for maximum mass transfer to minimum foaming capacity corresponds to the loading point. Correlations can be found between the foam capacity and respectively the power dissipated (Pg), the gas superficial velocity (Gs), the pumping time (tp) and the Froude number (Fr). Pg proved to be an important parameter because it combines the action of the gas flow rate and the action of the stirring velocity. We obtained a correlation: FC = a (Pg/V)a Gsb, which is identical to that which represents the evolution of volumetric mass transfer coefficient in stirred vessel.
The scale-up is difficult to establish due to intervening wall effects in the small-scale vessel. Indeed, these effects act directly on foam ascension in the vessel.
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