Invariant rectifying-stripping curves for targeting minimum energy and feed location in distillation

Invariant rectifying-stripping (IRS) curves are proposed that are independe nt of the feed location and operating reflux of the distillation column for a given separation problem. IRS curves represent the enthalpy surpluses an d deficits in the rectifying and stripping sections, respectively, as a fun ction of temperature for all possible values of reflux and reboil. The IRS curves provide a new representation on the temperature-enthalpy diagram to set distillation column targets prior to detailed design for minimum energy requirement, feed location, feed preconditioning, and side-exchanger loads . The application of the proposed concepts to two binary distillation examp les (one featuring a tangent pinch) and a multicomponent distillation examp le illustrates the usefulness of the IRS curves in properly locating the fe ed, determining the minimum utility requirements, and reducing the tedium o f repeated simulations. The IRS curves are rigorously invariant and provide the absolute minimum utility requirements for binary systems (ideal as wel l as non-ideal); however, they are near-invariant and predict the near-mini mum utility requirements for multicomponent systems (where the pseudo-binar y concept of a light and heavy key is employed). (C) 1999 Elsevier Science Ltd. All rights reserved.