Hydrodynamics and axial mixing in a packed gas-liquid column

Abstract

The objective of this study was to investigate the pilot-plant gas absorption packed column hydrodynamics, as well as axial mixing in the system air-water. The pressure drop and the gas phase holdup data were determined in dependence on the flow rates of gas and liquid phases. The influence of superficial velocities of liquid and gas phases on the liquid axial dispersion in a gas-liquid packed bed column (ID 15 cm) consisting of Raschig rings (15x15x2 mm) were investigated. The pressure drop was measured with a U-type manometer, connected to the bottom and the top of the working part of the column. The gas phase holdup data in the air-water two-phase system was calculated as a ratio of the gas phase volume to the total volume of the two-phase system. Axial dispersion in the water phase has been determined by examining of the distribution of residence times of a salt tracer (NaCl) in the packed bed. The tracer was injected in the liquid flow above the packed bed; samples of liquid were simultaneously taken from two sites at 1 m distance along the bed. Salt concentrations in the samples were determined by conductivity measurements. The mean residence time and the axial dispersion number were calculated by the moment method. The axial dispersion increases with an increase of liquid flow velocities and decrease of superficial air velocities.