AN ANALYSIS OF THE EFFECT OF RHEOLOGY ON LOCAL GAS HOLD-UP - THE CASEOF THYLOSIN PRODUCTION

The industrial production of the antibiotic Thylosin based on the cult ivation of filamentous Streptomyces fradiae, is considered as an examp le of an analysis of possible oxygen deficiency caused by a growth-ind uced rise of apparent viscosity. The time-course of broth theology and its power law pseudoplastic behaviour are illustrated. The stirred ve ssel hydrodynamics is represented by mass balances derived on the basi s of the 'network-of-zones' concept developed previously. The axisymme trical stirred bed is divided into backmixed cells interrelated by liq uid fluxes carrying a content of gas. Bubble size, liquid circulation I-ate, bubble rise velocity and gas flow rate are the model parameters . The effects of theology are introduced in the model by relationships known to describe bubble motion due to buoyancy and due to liquid cir culation, both depending on apparent viscosity. By this means, the loc al gas hold-up distribution patterns are obtained and related to theol ogy numerically. Zones of non-uniform gas distribution are identified and related to viscosity variation. Referring to the sample fermentati on, the results are intended to form the basis of a reasonable process policy.