Abstract

In this work a nonequilibrium stage model for cross flow distillation columns is developed. Concentration gradients on trays are integrated analytically for simple flow patterns on the basis of an overall rate approach. Empirical mixing corrections for bulk and interface concentrations and the assumption of constant interface properties of other nonequilibrium stage (NEQ) models are completely avoided. Simulations were carried out for two distillation cases of non-ideal mixtures. The importance of flow modelling on separation is shown and compared with mass transfer cross effects. Calculated separations for distillation trays, over a wide range of operating conditions, suggest that the proposed model provides a better approximation of concentration profiles, compared with the multicomponent efficiency (MEF) and the NEQ stage model. It is also shown that the efficiency-based model may predict incorrect mass transfer directions for trace components; this behaviour is caused by neglecting the convective contribution in the calculation of multicomponent mass transfer rates. (C) 2000 Elsevier Science Ltd. All rights reserved.