Shortcut method for the design of extraction columns for multi-component mixture separations

Shortcut methods are valuable tools for the fast evaluation of different units and flowsheets in separation process design. In this paper, a systematic method for the estimation of the minimum solvent flow rate required in counter-current extraction columns is presented. A key element is the identification of a mode of operation under saddle-pinch control, characterizing multi-component extractive separations. The criterion defining this mode leads to a new shortcut method, which provides both, a systematic calculation of all pinch points and a criterion for minimum solvent flow rate estimation. It requires low computational effort, it is robust and does not need any specific initialization. Furthermore, the shortcut method is fully algorithmic and thus, at least in principle, applicable to any number of components. Its features are highlighted by means of an example of an extractive separation of a four component mixture.