(374e) A Method for Minimization of Total Exergy Loss over the Complete Search Space of Regular Distillation Configurations

Exergy of a stream is its potential to do work when it is brought to the reference conditions via a reversible path. And it is a good metric to account for the temperature level at which heat is used or rejected in a distillation column. The thermodynamic efficiency of a distillation configuration can be derived through exergy analysis. Thus, performing exergy analysis, in conjunction with minimization of total heat duty, will help us identify distillation configurations with low energy requirement and high thermodynamic efficiency. Such configurations are particularly valuable for cryogenic as well as natural gas liquids (NGL) separations.

Here, we present a global optimization algorithm based on Underwood's equations that minimizes the total exergy loss of any regular-column distillation configuration (i.e. distillation sequence separating n components using n-1 columns) which separates any ideal or near-ideal multicomponent mixture. This objective function tends to favor configurations that use high temperature condensers and low temperature reboilers, relative to other configurations with similar vapor duties. For the first time, a global optimization based rank-list of the complete search space of regular-column configurations based on minimizing total exergy loss is synthesized. The identification of configurations that simultaneously have low vapor duty and high thermodynamic efficiency provides industrial practitioners with strong candidates for heat pump assisted multicomponent distillation.