Two-step hybrid approach for the synthesis of multi-period heat exchanger networks with detailed exchanger design

• New method for designing multi-period heat exchanger networks is proposed.
• Detailed exchanger designs used to determine correction factors for MINLP step.
• Correction factors used to stir optimization towards realistic exchanger designs.
• Effects of changes in flow-rates on heat transfer coefficients is considered.
• Optimal solution is determined based on solution obtained from detailed design.

In this study a novel methodology for multi-period heat exchanger network synthesis is presented. The new synthesis method aims to systematically generate many candidate networks and, through the use of more detailed individual heat exchanger designs and their evaluation over all periods, guide the network optimisation to more realistic designs. This is done by using the multi-period mixed integer non-linear programming (MINLP) stage-wise superstructure (SWS) model and modifying it to include correction factors. These correction factors enable the MINLP optimisation of the overall cost of the designed network, which uses only shortcut models of the individual exchangers, to be guided by more detailed models of the individual heat exchangers that comprise the network. The designs obtained at the topology optimisation stage thus more accurately represent an actual network. The correction factors take into account aspects of the real design, such as TEMA standards, FT correction factors, number of shells, and changes in overall heat transfer coefficients. Each exchanger is designed to function over all periods of operation, and if this is not possible, extra exchangers are designed for the periods that cannot be satisfied. The methodology is applied to a case study that demonstrates the benefits of the proposed approach.