Hollow blade agitator for mass transfer in gas-liquid bioreactors

Power input and kLa values for a hollow blade turbine (H-turbine) and for a Rushton disc flat blade turbine (R-turbine) were measured in water (coalescent liquid) and 0.5 M Na2SO4 solution (noncoalescent liquid). The results show that a simple exchange of the R-turbine for the H-turbine, for the same impeller speed and gas flow rate, brings no improvement in kLa. The exchange of the turbines under the same gassed power level brings an insignificant decrease of kLa (ca 10%) in coalescent liquid, while in noncoalescent liquid both turbines give roughly the same kLa values at a power input lower than 1 kW/m3. For higher power inputs the kLa values of the H-turbine are significantly decreased (up to 60% at 5 kW/m3). When the ungassed power is kept constant, the exchange allows an increase in kLa by 30 to 60% in coalescent liquids. This increase is, however, realized at the expense of higher power demand (by 80 to 150%) of the H-turbine when aerated. In a noncoalescent liquid at low impeller speed (I) the exchange brings a substantial improvement of kLa (80 to 110%) at the expense of higher gassed power level (60-90%). At a higher impeller speed the power input of the H-turbine strongly increases (up to 140%) while the increase in kLa is only 60%. The exchange is then disadvantageous.