Heat and mass integration to consolidate distillation columns in a multicomponent distillation configuration can lead to a number of new energy efficient and cost-effective configurations. In this work, a powerful and simple-to-use fact about heat and mass integration is identified. The newly developed heat and mass integrated configurations, which we call as HMP configurations, involve first introducing thermal couplings to all intermediate transfer streams, followed by consolidating columns associated with a lighter pure product reboiler and a heavier pure product condenser. A systematic method of enumerating all HMP configurations is introduced. The energy savings of HMP configurations is compared with the well-known fully thermally coupled (FTC) configurations. HMP configurations can have very similar and sometimes even the same minimum total vapor duty requirement as the FTC configuration is demonstrated, while using far less number of column sections, intermediate transfer streams, and thermal couplings than the FTC configurations. Figure 3. (a) A configuration derived from the configuration in Figure 2c by introducing thermal couplings at all submixtures; (b) A HMP configuration that is thermodynamically equivalent to the configuration in Figure 3a.Note that the thermal coupling at submixture DEF of Figure 7a is converted into a liquid-only transfer stream19 in Figure 7b, indicated by the curved arrow.Figure 9. (a) One possible operable dividing wall column drawn from the FTC configuration of Figure 8a using the methodology of Madenoor Ramapriya et al. 24,25 Notice that this dividing wall column uses three dividing walls and nine intermediate transfer streams; (b) one possible operable dividing wall column version synthesized from the HMP configuration of Figure 8b; (c) one possible operable dividing wall column version synthesized from the HMP configuration of Figure 8c. Notice that both dividing wall columns of Figures 8b, c use only 2 dividing walls and 5 intermediate transfer streams.
The operating cost of a multicomponent distillation system comprises two major aspects: the overall heat duty requirement and the temperature levels at which the heat duties are generated and rejected. The second aspect, often measured by the thermodynamic efficiency of the distillation system, can be quantified by its total exergy loss. In this article, we introduce a global optimization framework for determining the minimum total exergy loss required to distill any ideal or near-ideal multicomponent mixture using a sequence of columns. Desired configurations identified by this new framework tend to use milder-temperature reboilers and condensers and are thus attractive for applications such as heat pump assisted distillation. Through a case study of shale gas separations, we demonstrate the effectiveness of this framework and present various useful physical insights for designing energy efficient distillation systems.
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