Power demand and mass transfer capability of mechanically agitated gas-liquid contactors and their relationship to air-lift fermenters

Analysis of established correlations for power uptake, gassed power uptake and overall volumetric mass transfer coefficient (k_La) shows that when operating at constant impeller speed small increases in gas superficial velocity will result in both an increase in k_La) and a decrease in the total power input to the vessel. This is confirmed experimentally. At or near flooding, increasing the superficial velocity will continue to increase k_La still further, but with no further decrease in the agitator power uptake, total power input will increase.The transition region tends to lie on the corresponding k_La vs power input relation for an air-sparged situation (i.e. no mechanical agitation).A given mass transfer capability (k_La) value will be achieved at the same power/unit volume with both air sparged vessels and mechanically agitated vessels providing the gas superficial velocity is greater than 25 mm/sec.