Flooding limit in countercurrent gas-liquid structured packed beds-Prediction from a linear stability analysis of an Eulerian two-fluid model

Countercurrent flooding limits in gas-liquid structured packed bed columns were studied using a stability analysis of the solutions of a transient two-zone two-fluid hydrodynamic model around a uniform state. The model is based on the volume-average mass and momentum balance equations and the double-slit drag closures. The source terms in momentum balance equations refer to the total phase interaction and mechanical dispersion forces and the closure expression relating the gas and liquid pressures is given by capillary dispersion and gravity. The model predicts very well the flooding limits for air-water countercurrent flow through various Mellapak structured packings. The incidence on the column-limited flooding point of packing geometry (porosity and specific surface area), fluid throughputs and properties (viscosity, gas and liquid densities) and liquid spreading characteristics was discussed from the perspective of model simulated trends. Gravity was unveiled as the most important factor in the stabilization force which contributes to the attenuation of liquid waves inducing a tendency to make the flow more uniform. Its contribution was factored in using a modified capillary pressure model. Beside gravity, this formulation indicated that the stabilizing role of capillary forces could not be disregarded, particularly for lower values of the gravity scaling factor in liquid-rich regions at relatively high liquid flow rates.