Fluid dynamics and mass transfer in bubble columns with and without packing

Doktorsavhandling, 2004

Bubble columns are used in the chemical industry to perform gas – liquid reactions, like oxidation, hydrogenation and fermentation. The objective of the present thesis was mainly to study the fluid dynamics of semi batch packed bubble columns at both atmospheric and pressurized conditions. Some mass transfer studies have also been performed in a non-isothermal bubble column without packing. The study shows an upward liquid flow in the centre of a semi batch packed bubble column and a downward flow along the wall. As a result of this the one-dimensional dispersion model does not give a good description of the conditions inside the bed. It was also observed that the change in flow regime from bubble flow to pulsation flow affects the hydrodynamics. The pulses increases the radial dispersion and as a consequence, a minimum value of the dispersion coefficient was observed at the transition point. Also the frictional pressure drop is affected, a maximum point is observed in the transition region. The pressure influence both the gas holdup and the one dimensional dispersion coefficient in a packed bubble column. The gas holdup and the dispersion coefficient increases at increasing pressure. LDA measurements demonstrate that the axial time-averaged liquid velocity is lower in packed bubble columns compared to published results for bubble columns without packing. The time averaged liquid velocity and the RMS value of the liquid depends on the packing size. The results of the kLa measurements were in line with published data in the literature. However, the literature shows a large scatter in the volumetric mass transfer data (sulphite oxidation method). The ratio kla/εG is constant and is of the same order (0.5) for a non-coalescing sodium sulphite solution as for a stronger coalescing system, such as air - water in the heterogeneous regime.