Mass Transfer into Highly Viscous Liquid Circulated Forcibly in Bubble Column with Draft Tube

To promote liquid circulation in an airlift bubble column with an inner draft tube, a propeller was set in inside the draft tube. By revolving the propeller, the liquid is forced to flow upward in the draft tube and to flow down in the annulus. For a bubble column of constant diameter and a highly viscous liquid, the effects of the diameter of the draft tube and the revolution rate of the propeller on gas holdup, liquid circulation rate and volumetric mass transfer coefficient were investigated experimentally. 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 much larger than the other pressure drops. By the combination of previous dimensionless empirical equations, the averaged volumetric mass transfer coefficient in the whole bubble column was estimated relatively well. The additive liquid stream generated by the revolution of the propeller promoted the increase of gas holdup in the annulus and the increase of volumetric mass transfer coefficient.