Oxygen‐transfer rates and efficiencies in one‐ and two‐stage airlift towers

The primary consideration in fermentor design is the supply of oxygen to the growing microorganisms. The oxygen‐transfer characteristics of a two‐stage splitcylinder airlift tower were compared to those of a similar single‐stage airlift tower of equal liquid volume using a sodium sulfite–air system. At superficial gas velocities, from 720 to 1200 cm/min, no difference in K L a was apparent. The K L a was significantly larger in the two‐stage tower for a gas velocity between 1200 and 2728 cm/min. At 2728 cm/min a K L a of 25.2 min −1 was achieved in the two‐stage system, and at 2262 cm/min the two‐stage tower had a 54% larger K L a than the single stage. A comparison of dispersion‐volume based K L a showed a 27% larger value at a gas velocity of 2262 cm/min. The performance ratios for the two‐stage tower were larger than those for the single‐stage tower at oxygen‐transfer rates greater than 180 mmol/liter hr. A comparison of the data with literature values is presented.