Duanmu, Fanyi; (2024) Advances in Fluid Separation: Design and Optimisation of Dividing Wall Columns and Simulated Moving Beds. Doctoral thesis (Ph.D), UCL (University College London).

Text Fanyi DUANMU - PhD Thesis.pdf - Accepted Version Access restricted to UCL open access staff until 1 March 2025. Download (10MB)

Abstract

This thesis explores the design and optimisation challenges in large-scale (distillation) and small-scale (chromatography) separation techniques. Dividing wall columns (DWC) and simulated moving beds (SMB) are considered in this work for distillation and chromatography, respectively, due to their high complexity and wide applications. By developing innovative and efficient shortcut methods, superstructure models, and optimisation strategies, this research aims to address and overcome the complexities associated with the modelling and optimisation of these advanced separation systems. The thesis begins with a proposed combined sequential stochastic-deterministic optimisation approach along with speed-up approaches (e.g., dynamic bounds). The stochastic optimisation with loose convergence tolerance is applied first to obtain the preliminary design, which will act as the initial design in the deterministic optimisation for the local search. The proposed approaches are tested on complex chemical processes, which can improve the quality of the optimal designs while reducing the CPU time. The work then delves into DWCs. The thesis proposes a shortcut design method for complex distillation structures, such as the reduced vapour transfer DWCs, using a simple optimisation procedure without the need for iterative manual calculations. The proposed shortcut method greatly reduces the risk of initialisation failure or convergence issues for simulation and optimisation tasks. The study continues with designing and optimising more process-intensified DWCs, including the heat-integrated DWCs and novel hybrid reactive DWCs, to enhance energy efficiency and extend the applications of DWCs. Moving to the realm of chromatography, the thesis presents a novel superstructure model that allows simultaneous optimisation of the type of SMB (standard SMB and Varicol) and column design (e.g., the number of columns, switch actions, switch time, flow rates, and column dimensions). A thorough comparison with the conventional approach of optimising each possible structure reveals that the proposed superstructure is robust and more time-efficient.

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