Mass transfer into highly viscous liquid circulated forcibly in bubble column with draft tube

A propeller was set in inside the draft tube to promote liquid circulation in an airlift bubble column with an inner tube. The liquid was forced to flow upward in the draft tube and to flow down in the annulus by revolving the propeller. In the pressure drop throughout the circulation of highly viscous liquid in the internal airlift bubble column, the pressure drops at the walls of the draft tube and in the annulus were considerably higher than the other pressure drops. The averaged volumetric mass transfer coefficient in the whole bubble column was well estimated using the combination of previous dimensionless empirical equations. The additive liquid stream generated by the revolution of the propeller promoted gas holdup increase in the annulus and the increase of volumetric mass transfer coefficient.