Packed Bed Liquid Phase Dispersion in Pulsed Gas-Liquid Downflow

Abstract

A theoretical analysis of a pulsed gas-liquid downward flow through a packed bed showed that the axial dispersion of the liquid-phase observed in such flows is mainly caused by the difference in velocity and rapid mixing between fast-moving liquid slugs and slow-moving liquid films. This chromatographic behavior was described by a model which considers the liquid phase as consisting of two continuous phases flowing cocurrently at different velocities with continuous material exchange between the two streams. The liquid dispersion in the column may be characterized by a single mixing parameter. Impulse response experiments, in good accord with the model, showed that liquid dispersion decreases with increasing liquid flow rate because of improving mixing, attains a constant asymptotic value at high gas velocities, and is generally smaller in pulsed flow than in the gas-continuous (trickle) flow regime. Additional advantages of pulsed flow operation in catalytic reactors are increased wetting of the pellets, enhanced transport coefficients, and improved flow uniformity through the bed.