FLOW CHARACTERISTICS OF BUBBLE-COLUMN WITH PACKED PERFORATED DRAFT TUBE

To improve bubble column performance, a bubble column with packed perforated draft tube was proposed. Net rings having relatively small flow resistance were used as packings and the dimensions of the perforated draft tube and the net ring were varied. The flow pattern was observed, and the gas holdup, gas-liquid interfacial area and liquid mixing time were measured. By packing the net rings in the perforated draft tube, ''bubble subdivision by packings'' occurred in addition to ''bubble subdivision by perforated wall''. The draft tube diameter, pore diameter, fractional free area and opening of net ring had the optimum values for the gas holdup and gas-liquid interfacial area. When the optimum draft tube diameter was used, the gas holdup and gas-liquid interfacial area were almost equal to those of the packed bubble column. The liquid mixing time was much shorter than those of standard and packed bubble columns. The COD removal was almost equal to that of the packed bubble column, and the present column was expected to be applied to a waste water treatment.