On the scale-up criteria for bubble columns

It is generally admitted that experimental data obtained in “laboratory-scale” bubble columns are representative of “industrial-scale” reactors if the well-known three “Wilkinson et al. scale-up criteria” are satisfied: (a) the diameter of the bubble column is larger than 0.15 m, (b) the sparger openings are larger than 1-2 mm and (c) the aspect ratio is larger than 5. In this paper, we contribute to the existing discussion and we have experimentally studied the combined effect of the aspect ratio (within the range of 1-15) and the sparger design (considering both “coarse” and “fine” spargers) on the gas holdup in a large-diameter and large-scale gas-liquid bubble column. The bubble column has been operated both in the batch mode and in the counter-current mode. Filtered air has been used as the gaseous phase in all the experiments, while the liquid phase has included deionized water and different aqueous solutions of organic (i.e., ethanol) and inorganic (i.e., sodium chloride, NaCl) active agents. It is found that the “Wilkinson et al. scale-up criteria” are valid for the air-water case in the batch mode for “very-coarse” spargers. Conversely, they are no more valid when considering different liquid velocity, and/or aqueous solutions of active agents, and other sparger openings.