THE INFLUENCE OF VESSEL HEIGHT AND TOP-SECTION SIZE ON THE HYDRODYNAMIC CHARACTERISTICS OF AIRLIFT FERMENTERS

Fermentations of the yeast Saccharomyces cerevisiae were carried out i n a 90 to 250-L working volume concentric tube airlift fermentor. Meas urements of liquid circulation velocity, gas hold-up, and liquid mixin g were made under varying conditions of gas flowrate, vessel height, a nd top-section size. Both liquid circulation velocity and mixing time increased with vessel height. Liquid velocity varied approximately in proportion to the square root of column height, supporting a theoretic ally based relationship. The effect of vessel height on gas hold-up wa s negligible. The height of the top-section had a significant effect o n liquid mixing. Mixing time decreased with increasing size of the top -section up to a critical height. As the top-section was expanded beyo nd this height, little improvement in mixing was seen. This indicated the presence of a two-zone flow pattern in the top-section. Liquid vel ocity and gas hold-up were essentially independent of top-section heig ht. (C) 1994 John Wile & Sons Inc.