Exclusion of gas sparger influence on mass transfer in bubble columns

Gas phase CO₂ concentration profiles were measured in two sizes of bubble columns with different gas spargers and with the liquid phase (tap water) entrance or exit (cocurrent or countercurrent flow) at a certain height above the gas distributor. The region of high turbulence intensity near the sparger was locally separated from the region of high mass transfer rates in such columns. A modified back flow cell model was applied to describe the experimental data. The k_L-values obtained from fitting the profiles agreed for both columns and, in addition, did not differ for cocurrent and countercurrent flow. This is in remarkable contrast to previous findings(10,11). The large influence of the gas sparger on the k_L-values even in tall bubble columns was thus demonstrated. It is thought that this may probably be one of the reasons why correlations for prediction of k_L differ so significantly.