A FLUID DYNAMIC STUDY USING A SIMULATED VISCOUS, SHEAR THINNING BROTHOF THE RETROFITTING OF LARGE AGITATED BIOREACTORS

Studies were conducted(1) in 19-m(3) fermenters (14-m(3) working volum e) using four Rushton turbines, four Prochem Maxflo Ts, and three Ligh tnin' A315s and the results in water have been reported earlier. Here, a 1.7 wt/vol% Xanthan solution has been used as the working fluid, si mulating viscous broths to give Reynolds numbers (Re) between 1800 and 4500. As predicted from small-scale studies, the power numbers at the se values of Re were similar to those in water. The K factor (the rati o of power draw under aerated conditions compared to non-aerated) was the same as in water at the higher values of Re, but at the lower valu es it fell more rapidly with increasing aeration rate and to a lower v alue than in water. At all times, K was higher than with Rushton turbi nes. Vibration characteristics were also measured. Under aerated condi tions, the fermenters vibrated with an amplitude 75% to 100% less than in water due to viscous damping. With increasing air flow, the amplit ude increased steadily due to the presence of very large and rapidly r ising bubbles in such fluids to give values 2.5 to 3 times those in wa ter. Nevertheless, these mechanical problems can be overcome, allowing such agitators to be used successfully in high viscosity mycelial fer mentations. (C) 1996 John Wiley & Sons, Inc.