Synthesis and optimisation of energy integrated advanced distillation sequences

  • Qing Li

Student thesis: Master of Philosophy

Abstract

The synthesis of heat-integrated distillation sequences for energy-efficient separation of zeotropic multicomponent mixtures is complex due to the many interconnected design degrees of freedom. The synthesis must determine the basic separation configuration, including thermally coupled complex columns, column pressures, reflux ratios, feed conditions, condenser types and heat integration arrangements all simultaneously. The method most often used to address larger problems is to use short-cut distillation models to screen the large number of structural options and determine the best few potential designs, followed by more detailed examination of these designs using rigorous simulation. However, it is not clear whether short cut distillation models have the necessary accuracy for reliable screening, and whether heat integration must be included in the screening. To solve this generic problem, the novel contribution of this project is to explore the basis on which reliable screening can be carried out. A screening algorithm has been developed using optimisation of a superstructure for the sequence synthesis using short cut models, in conjunction with a transportation algorithm via an incidence matrix for the synthesis of the heat integration arrangement. The best few designs in terms of total operating cost from the screening are evaluated using rigorous simulations. The overall problem is solved by a decomposed simulation-based optimisation, achieved by a mixed-integer linear programming (MILP) formulation inside the Simulated Annealing (SA) algorithm. An industrial case study for the fractionation of natural gas liquids (NGLs) is used to evaluate the proposed approach. It has been found that separation problems of the type explored can be screened with confidence. The best sequences in terms of total operating costs identified by rigorous simulations can be pre-selected by the developed screening approach. Additionally, the non-heat-integrated designs using thermally coupled complex columns show much better performance than the corresponding designs using simple columns. However, once heat integration is included the difference between designs using complex columns and simple columns narrows significantly.
Date of Award31 Dec 2023
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRobin Smith (Supervisor) & Nan Zhang (Supervisor)

Keywords

  • Distillation sequencing
  • process synthesis
  • process optimisation
  • process design
  • energy integration

Cite this

'