Investigation of local mass transfer in a packed bed of pall rings using a limiting current technique

The mass-transfer coefficients at varied axial, radial, and angular positions in a packed bed of Pall rings were measured using the limiting current technique. The experimentation was carried out in a 0.30-m-diameter column with a bed height of 5.5 column diameters. Ferri-/ferrocyanide ions were used as the redox couple for the mass-transfer measurement. The local mass-transfer rate was found to be strongly dependent on the liquid feed distribution, especially at the top section of the packed bed. The local mass-transfer rate also varied significantly in the axial and radial directions in the packed bed. A maximum mass-transfer rate was observed at an axial distance of 1.5 column diameters (x/D = 1.5) when the multipoint liquid distributor was used while the highest transfer rate occurred at x/D = 2.5 for the single-point liquid distributor. However, for both types of liquid distributors the mass-transfer rate became steady at x/D > 4.5. The wall flow also reached steady-state x/D = 3.5. The average mass-transfer rate with the multipoint distributor was about 14% higher than that with the single-point distributor.