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Title: The preliminary design of heat-integrated multicomponent distillation sequences through generation of flowsheet superstructures
Author: Leeson, Duncan
ISNI:       0000 0004 7659 1513
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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Given that in 2012 distillation was estimated to consume roughly 3% of energy globally, managing the heating and cooling duties of these processes is essential. Currently, many process design strategies involve designing the separation system before energy integration is considered, leading to suboptimal solutions. In this thesis, a model for the preliminary design of a distillation sequence is presented as a MILP, using only basic thermodynamic data from feed components. The model has been developed based on a reduced superstructure with temperatures calculated via a discrete grid. Process streams from elsewhere in the plant are also considered concurrently, and consideration of these often changes the optimal sequence. The examples suggest cost reductions of over 30% when ancillary streams are not considered when compared to a basic heuristical approach, and up to 50% when a small number of additional process streams are included. The model was then further developed to include multieffect distillation, where separators are considered as a system of two parallel columns. Including the opportunity for multieffect distillation led to changes in the optimal sequence, with associated costs reduced by up to a further 30% compared to the previous iteration of the model. The model has been demonstrated on two industrial case studies; crude oil refining and platformate separation. Both examples demonstrate the flexibility of the model to deal with complex industrial problems, with the crude example showing optimise under an uncertain feedstock, while the platformate demonstrates the importance of including as much information about the process as possible to find the optimal result. As a preliminary design tool, the model should be used as initialisation for detailed process design. This has been investigated, with the distribution between multieffect columns made continuous. This led to further cost reductions with a short solution time, due to the initialisation offered by the linear models.
Supervisor: Shah, Nilay ; Fennell, Paul ; Mac Dowell, Niall Sponsor: Shell International Ltd ; Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral