Effect of feed on optimal thermodynamic performance of a distillation column

Invariant rectifying-stripping (IRS) curves are presented for thermodynamic analysis of distillation column. The IRS curves are invariant to the column configuration (i.e., feed location and total number of stages) and therefore, they are useful to set quantitative targets such as minimum energy requirement (minimum condenser and reboiler duties), appropriate feed location, proper feed preconditioning, scope for side-condensers/reboilers, as well as thermo-economic optimization of distillation column. In this paper, the relation between the IRS curves and exergy loss in an adiabatic distillation column is established through a simple graphical representation. A general methodology is put forward to analyze the optimal thermodynamic performance of a distillation column. Effects of feed composition, thermal condition of the feed, relative volatility of components, and sharpness of separation on the thermodynamic efficiency of a distillation column are presented in this study. The methodology, described in this paper, is equally applicable to real systems, with or without tangent pinch. A general principle for feed preheating and side-exchanging is also developed. (C) 2002 Elsevier Science B.V. All rights reserved.