Rapid screening of design alternatives for nonideal multiproduct distillation processes

Abstract

The determination of the minimum energy demand using shortcut methods based on the well-known Underwood method has become a widely used tool for rating the economic incentive towards the usage of complex heat integrated column configurations for the separation of multicomponent mixtures into three or more products. However, available methods are only valid for ideal mixtures. Fast and reliable methods for the assessment of the minimum energy demand of the separation of nonideal zeotropic and azeotropic multicomponent mixtures in thermally coupled columns are still missing. The method introduced here addresses the case of complex column configurations with and without heat integration. It is based on the decomposition of the process into sequences of simple columns. The minimum energy demand of each column is determined using the rectification body method (RBM). Application of the suggested design method allows rapid screening of the different process alternatives by ranking their overall energy demand, exergy consumption or utility cost. The influence of the appearance of multiple steady states for azeotropic mixtures on the design decision is also discussed. The method is illustrated with a nonideal zeotropic and two azeotropic multicomponent separation examples.