Application of the rate-based approach to three-phase distillation columns

For more reliable modelling of multiphase separation equipments the nonequilibrium approach has been recently recognised as superior if compared with the traditional equilibrium stage concept. However, for general three phase (V-L-L) distillation processes in a tray column the interaction between two liquid phases, continuous and dispersed, must be modelled as equilibrium according to insufficient knowledge about transport phenomena at the liquid-liquid interface. On the other hand, for the mass and heat transfer between vapour phase and continuous liquid phase the rate-based (i.e. nonequilibrium) approach is more appropriate (Eckert, 1997). The combined model was implemented in the AspenTech SPEEDUP environment using the SPEEDUP problem oriented language together with user supplied FORTRAN routines, selected SPEEDUP unit modules and ASPEN PLUS physical property libraries (i.e. PROPERTIES PLUS). Comparison with results from the equilibrium model is provided in this contribution.