Shortcut Distillation Model for Heat Integration

Abstract

Distillation is a common process unit that requires substantial energy input. The energy input can be reduced by applying heat integration methods to the distillation system. A shortcut distillation model that does not require rigorous stage-by-stage calculation is proposed here to reduce computational difficulty. As traditional shortcut models utilizing the constant molar overflow (CMO) assumption are not sufficiently accurate for the study, the shortcut model used in this study utilizes a non-CMO assumption. A relation is derived from approximate material and energy balances to predict the change in liquid and vapour flows throughout the column. Coupled with material and energy balances over sub-sections and the entire column, the model can fully specify a distillation column. The model can be used for energy targeting in conjunction with heat integration models to simultaneously optimize the process. A case study was carried out on an air separation unit (ASU). Results of the case study showed that the energy required is 197 Wh per kg of pure O2 produced. The results obtained are encouraging with close agreement when compared to an ASPEN simulation as the differences are below 2 %. However, the heat integration results of the MHEX from both the model and the ASPEN simulation showed a minimum temperature approach (DTmin) of almost 0. This is probably due to the usage of the ideal method where enthalpy calculation depends only on temperature.