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.
This study demonstrates the efficacy
of a short-cut method such
as the Global Minimization Algorithm (GMA),
,
that
uses assumptions of ideal mixtures, constant molar overflow (CMO)
and pinched columns, in pruning the search-space of distillation column
configurations for zeotropic multicomponent separation, to provide
a small subset of attractive configurations with low minimum heat
duties. The short-cut method, due to its simplifying assumptions,
is computationally efficient, yet reliable in identifying the small
subset of useful configurations for further detailed process evaluation.
This two-tier approach allows expedient search of the configuration
space containing hundreds to thousands of candidate configurations
for a given application.
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