Predicting the Liquid Phase Mass Transfer Resistance of Structured Packings

Published correlations for estimating the liquid phase mass transfer coefficients of structured packings are compared using experimental evidence on the efficiency of Montz-Pak B1-250MN and B1-500MN structured packings as measured in total reflux distillation tests using the chlorobenzene/ethylbenzene system at two operating pressures. Large differences are found between different correlations with respect to both the absolute values of mass transfer coefficients and the fraction of liquid phase based resistance and their trends with respect to increasing vapor and liquid loads. A new Delft Model liquid side mass transfer coefficient correlation that incorporates a more appropriate definition of the liquid film exposure length is presented which now generates lower values. The revised liquid film model, combined with an enhanced turbulent vapor phase mass transfer coefficient, leads to doubling the fractional liquid phase resistance with respect to that based on penetration theory assuming equal contact times. This effect results in predicting efficiencies which are slightly more conservative and agree reasonably well with experimental HETP data presented in this paper. Key words: distillation, structured packings, mass transfer, liquid phase resistance