Synthesis and optimization of NGL separation as a complex energy-integrated distillation sequence

Abstract

The synthesis of heat-integrated distillation sequences for energy-efficient separation of zeotropic multicomponent mixtures is complex due to the many interconnected design degrees of freedom. This paper explores the basis on which reliable screening can be carried out. To solve this problem, a screening algorithm has been developed using optimization of a superstructure for the sequence synthesis using shortcut models, in conjunction with a transportation algorithm for the synthesis of the heat integration arrangement. Different approaches for the inclusion of heat integration are explored and compared. Then the best few designs from this screening are evaluated using rigorous simulations. A case study for the separation of NGL is used to compare options. It has been found that separation problems of the type explored can be screened reliably using shortcut distillation models in conjunction with the synthesis of heat exchanger network designs. Unintegrated designs using thermally coupled complex columns show much better performance than the corresponding designs using simple columns. However, once heat integration is included the difference between designs using complex columns and simple columns narrows significantly.