Gas-liquid mass transfer in dual impeller bioreactor

Abstract

The gas-liquid mass transfer coefficient K L a in a fermenter is known to be a strong function of mode of energy dissipation and physicochemical properties of the liquid media. Four impeller combinations of lower and upper impellers, namely disc turbine-disc turbine, disc turbine-pitched blade downflow turbine, pitched blade downflow turbine-pitched blade downflow turbine, and pitched blade downflow turbine-pitched blade upflow turbine (first mentioned is the lower impeller) have been tested in a laboratory bioreactor for their fractional gas hold-up and gas-liquid mass transfer performance. The liquid phase physico-chemical properties have been varied using solutions of electrolytes, aqueous solutions of sodium salts of carboxymethyl cellulose and simulated fermentation media. Correlations have been developed for the prediction of the fractional gas hold-up and gas-liquid mass transfer coefficient for liquids with different physico-chemical properties. It has been observed that the impeller combination of disc turbine-pitched blade downflow turbine gave highest values of fractional gas hold-up and of gas-liquid mass transfer coefficient using the least power.