Abstract
For a bubble column with draft tube sparging gas into the annulus, the effects of equipment dimensions and liquid properties on the circulation flow rates of liquid and gas are experimentally studied. The gas circulation flow rate is estimated by comparing gas holdup in the downcomer with that in a gas-liquid cocurrent downflow bubble column.
The liquid circulation flow rate becomes higher as the distance between the upper end of draft tube and the liquid surface at aeration lengthens, and it remains unchanged when the distance is beyond double the column diameter. It increases with increasing draft tube diameter and with increasing bubble size. The gas circulation flow rate is strongly governed by the liquid circulation flow rate. The driving force for gas circulation is the difference between the descending velocity of liquid and the rising velocity of bubble swarm in the downcomer. Based on the energy balance, an empirical equation of the loss coefficient in the zone above the upper end of the draft tube is obtained. The circulation flow rates of liquid and gas calculated by using the energy balance and correlations, agree with the measured data within an error of ±30%.
