The synthesis of the functionally distinct thermally coupled distillation configurations for quaternary mixtures is presented. The concept of the intended individual splits has been presented to formulate a distinct separation sequence, with which a functionally distinct thermally coupled configuration can be generated for a multicomponent distillation. Twentytwo functionally distinct thermally coupled distillation configurations for quaternary mixtures have been identified. They include the possible thermally coupled configurations in the available superstructures for quaternary distillations. Moreover, some new feasible thermally coupled configurations have been found which are not included in the known superstructures. These functionally distinct thermally coupled configurations constitute a unique space with which the other possible thermally coupled schemes can be generated. It provides a more complete search space of the possible alternatives to synthesize the global optimum distillation systems for quaternary separations.

This paper presents the synthesis of heat-integrated thermally coupled distillation systems for multicomponent separations. The synthesized new distillation systems employ the thermal coupling and heat-integration principles simultaneously. As a consequence, they have the potential to significantly reduce both the energy and capital costs to a bigger magnitude than the traditional simple column configurations as well as the systems employing either heat integration or thermal coupling alone. First, a subspace of the possible heat-integrated partially coupled (HIPC) configurations with sharp splits has been identified for a multicomponent distillation. A formula is derived to calculate the number of possible HIPC configurations for any n-component mixture. A simple procedure is given to obtain the practical HIPC configurations for an n-component mixture. Then, the possible thermodynamically equivalent structures of the identified HIPC configurations are presented. The other possible heat-integrated thermally coupled distillation systems involving sloppy splits for an n-component mixture are also discussed. These heat-integrated thermally coupled distillation systems constitute a specific search space to look for the optimal distillation systems for multicomponent separations.

A thermodynamically equivalent structure (TES) is the distinct feature of a thermally coupled configuration. This paper presents the synthesis and optimal design of thermodynamically equivalent thermally coupled systems for multicomponent distillations. First, the original thermally coupled configurations (OTCs) for traditional distillation configurations with sharp splits are generated. Then, generation of all of the possible TESs for the OTCs is presented. Two rules are developed for synthesizing the possible TESs for any OTC involving both sharp and sloppy splits. Formulas are derived to calculate the number of TESs for an n-component mixture. It is observed that there exist intrinsic uneven distributions of vapor and liquid flows between columns of the OTCs. The TESs provide the opportunities to redistribute the vapor and liquid flows between columns and thus improve column equipment designs of an OTC. Heuristics and a simple procedure have been approached to find an optimal TES.

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