Gas holdup in a trayed cold-flow bubble column

An experimental study was performed to investigate the effect of sieve tray s on the time-averaged gas holdup profiles and the overall gas holdup in a cold-flow bubble column that was scaled-down from a commercial unit. gamma -ray computed tomography (CT) was used to scan the column at several axial locations in the presence and absence of trays from which the local variati on of the gas holdup was extracted. The overall gas holdup was also determi ned using the same configuration by comparing the expanded and static liqui d heights. Air and water were used as the gas-liquid system. The superficia l gas and liquid velocities were selected to span the range of the commerci al system using gas spargers having multiple lateral distributors that were also scaled-down from the commercial design. To investigate the impact of sparger hole density on the local and overall gas holdup, two difference sp arger designs were used in which the hole density per lateral was varied. T he gas hole velocity was maintained constant at ca. 245 m/s, which approach ed that used in the commercial reactor. It is shown that the local gas hold up determined by CT is generally higher in the tray down corner region and exhibits an asymmetric pattern when trays are present. The use of increased sparger hole density at a constant gas superficial velocity leads to steep er gradient in the gas holdup near the column centerline and a higher overa ll gas holdup. These findings suggest that the performance of bubble column reactors for various applications is sensitive to both sparger and tray de sign. (C) 2001 Elsevier Science Ltd. All rights reserved.