Abstract
The Dividing Wall Column (DWC) accommodates fully thermally coupled distillation sections for high purity separation of three or more products in a single unit. Compared to conventional distillation sequences, there are significant potentials for savings in energy, capital cost, and space. The technology has been in industrial use from before 1990 with large number of reported applications. However, even in recent literature, difficulties in design and operation are still listed as obstacles. Thus, there is a need for easily available assessment tools and methods such that the environmentally sustainable DWC technology will be applied wherever applicable. The Vmin-diagram and related methodology and knowledge is one such tool. In this paper we briefly explain the concept and on how the Vmin-diagram can be used to assess separation tasks and also to suggest simplifications to the internal configuration of a distillation system for a certain separation task or similar classes. The original papers presenting the Vmin-diagram made use of simplifying assumptions like constant molar flows, constant relative volatilities, and infinite number of stages. This opened for refined use of the Underwood equations to deduce the exact analytical expressions that can explain the complex column behavior and the minimum energy operating conditions. This may mislead some readers to get the impression that the concept is only valid for these kinds of ideal assumptions. But this is not so. The key properties that determine minimum energy and product distribution are valid also for real mixtures. In this paper it will be focused on how the Vmin-diagram concept can be used to assess separations that are candidates for 3- or 4 product DWC and show examples on how it can be used in the case of latter to arrive at some simplified and more practical structures for industrial implementation.