Abstract
Flow and mass transfer characteristics of an external-loop airlift column with a tapered riser were investigated. In a certain range of gas flow rate, solid particles were sustained in the tapered section in the riser. We investigated the lower and upper limit of the liquid circulation velocity for this region. For the liquid velocity lower than the lower limit, solid particles settled at the bottom of lower connecting tube, and for the liquid velocity higher than the upper limit, solid particles were circulated accompanied by liquid flow. In the intermediate region, solid particles were sustained in the tapered section in the riser. The effects of the solid particles sustained in the tapered section on gas holdup, liquid circulation velocity, and oxygen transfer rate were discussed.
