Flow characteristics of bubble column with perforated draft tube. Effects of equipment dimensions and gas dispersion

The effects of equipment dimensions and gas dispersion on the flow characteristics of a bubble column with perforated draft tube were experimentally examined. Gas was dispersed into the inner section of the draft tube or into the annular section between the column and the draft tube. Under various combinations of column diameter and diameter and length of the draft tube, the flow pattern was observed and the liquid mixing time, gas holdup and specific gas-liquid interfacial area were measured.In either gas dispersion, gas and liquid radially flowed through holes in the draft tube, and large bubbles were subdivided into small ones. Gas dispersion into the inner section was more effective in shortening the liquid mixing time. The liquid mixing time was shortened by increasing the ratio of height/column diameter, and was most shortened at a diameter ratio of draft tube/column of about 0.6. Gas dispersion into the annular section was effective in increasing the gas holdup and the interfacial area. The interfacial area was also increased by decreasing the characteristic length of the gas dispersion section.