An extended superstructure modeling method for simultaneous synthesis of direct work exchanger networks

Work integration is a significantly promising strategy to achieve notable reduction in energy consumption. Work recovery has been performed by graphical integrating method and transhipment model in open literatures, but the economic performance is ignored. To overcome the limitations, this paper proposes an extended superstructure-based optimization model for simultaneous synthesis of direct work exchanger networks (WEN), which aims at the optimal trade-off between capital investment and operational expenditure. The operational expense involves electricity generated by expanders and electricity consumed by compressors. The developed stage-wise superstructure, which is different from that of heat exchanger networks (HEN), should consider utility compressors/expanders as well as valves in parallel at each stage of the superstructure, and utility compressors in series for lowpressure streams prior to entering the superstructure. The direct WEN superstructure is formulated as a mixed-integer nonlinear programming (MINLP) model with the objective of minimizing total annual cost (TAC). Three example studies are conducted to assess the efficacy of the proposed model. The results indicate better direct WEN configurations can be obtained with considerable savings in TAC, in which the minimum pressure difference sensitivity study is conducted to further confirm the effectiveness and importance for the effect of pressure manipulation on output. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.