Finding optimal multicomponent distillation flowsheets

A general approach to the synthesis of the complete set of distillation flowsheets for multicomponent zeotropic mixtures is considered, which includes construction of generalized separation graphs and an analysis of all intermediate fractions. The approach is applied to the distillation of particular zeotropic four-component mixtures of different compositions. An optimal distillation flowsheet is obtained for each of the 60 cases examined. The dynamic programming conception is inapplicable to mixtures consisting of a few components, because some of the columns of the optimal flowsheet may function in a nonoptimal way, which is in agreement with the optimization theory for large systems.