FLOW DYNAMICS IN A DRAFT-TUBE BUBBLE COLUMN USING VARIOUS LIQUIDS

Gas hold-up and liquid circulation rates in a draft-tube bubble column (0.22 m diameter, 851 capacity) fitted with various diameter draft-tubes are measured for water and aqueous solutions of ethanol, glycerol and carboxymethylcellulose (CMC), respectively. The data are analyzed in terms of a development of the simple energy balance incorporating flow contraction coefficients to quantify deviations from ideal flow. Ethanol and glycerol enhance the entrainment of gas bubbles into the downcomer compared with pure water and inhibit liquid circulation. In CMC solutions, however, large coalesced bubbles are easily disengaged at the top of the column with little entrainment into the downcomer and promote the highest liquid circulation rate. Bubble column geometry, i.e. draft-tube diameter, affects both bubble entrainment and the flow contraction coefficients, and interacts with the fluid properties to affect both gas hold-up and liquid circulation.