Design and Optimization of Intensified Non-sharp Distillation Configurations

Abstract

Abstract For an N-component mixture, a separation sequence with only sharp splits needs the minimum number of N-1 simple columns with 2(N-1) heat exchangers to achieve N pure products. As the number of columns and heat exchangers are the dominant criteria to evaluate a distillation configuration, traditional distillation configurations with only sharp splits have been the preferred alternatives. However, sharp split separations present intrinsic thermodynamic inefficiencies, and one way to reduce these inefficiencies is by means of non-sharp splits. This refers to the possibility of obtaining one product in more than one stream. Moreover, the increasing in both the number of columns and heat exchangers due to the non-sharp splits can be reduced by combining the individual columns and by introducing thermal couplings. In this work, the non-sharp distillation sequence for the separation of a four component mixture of hydrocarbons is considered. Using the aforementioned method, different alternative sequences were designed by the rigorous method with Aspen PlusV8.0, going from 4 to 3 and to 2 columns; then optimized by minimizing the total annual cost by means of a platform consisting in Aspen PlusV8.0 (rigorous simulation) and Visual Basic (stochastic optimizer Differential Evolution), to finally compare the sequences. Moreover, the synthesis methodology used allows deriving two types of intensified systems, the systems with less column sections or the systems with dividing wall columns.