A simplified CFD for three-dimensional analysis of fluid mixing, mass transfer and bioreaction in a fermenter equipped with triple novel geometry impellers

A Three-dimensional networks-of-zones model has been developed to describe the performance of a novel geometry Narcissus (NS)impeller when used for gas-liquid mixing in a triple impeller bioreactor. The networks-of-zones can be simply adapted from an earlier version based upon the Rushton turbine. The adaptation is achieved by a conformal stretching of the zone volumes. This accommodates the complex up-down liquid flow pattern by a simple adjustment of the zone volumes matrix, whilst the underlying mass and component balances on every zone stay unchanged. Some results are presented for a pilot-scale Tylosin fermenter. Spatially complex fields in three-dimensions are visualized by solid-body graphics for gas hold-up, bubble phase oxygen, liquid-phase dissolved oxygen, nitrate nutrient and bioreaction rates for a 3 × 2 × (10 × 10)× 60 configuration comprising 36,000 zones. The triple NS impeller produces locally higher levels of dissolved oxygen than are achieved by triple Rushton turbines. In both cases, the behaviour predicted is completely different from that obtained by an oversimplified plug (gas)-backmixed (liquid)bioreactor model.