Chinese Journal of Chemical Engineering ›› 2020, Vol. 28 ›› Issue (5): 1344-1356.doi: 10.1016/j.cjche.2020.02.026

• Process Systems Engineering and Process Safety • Previous Articles     Next Articles

Simultaneous synthesis of sub and above-ambient heat exchanger networks including expansion process based on an enhanced superstructure model

Yu Zhuang1,2, Rui Yang1, Lei Zhang1, Jian Du1, Shengqiang Shen2   

  1. 1 Institute of Process Systems Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian 116023, China;
    2 Key Laboratory of Liaoning Province for Desalination, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116023, China
  • Received:2019-11-28 Revised:2020-02-15 Online:2020-05-28 Published:2020-07-29
  • Contact: Jian Du
  • Supported by:
    The authors would like to gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (No. 21776035) and China Postdoctoral Science Foundation (No. 2019TQ0045).

Abstract: Synthesis of heat exchanger networks including expansion process is a complex task due to the involvement of both heat and work. A stream that expands through expanders can produce work and cold load, while expansion through valves barely affects heat integration. In addition, expansion through expanders at higher temperature produces more work, but consumes more hot utility. Therefore, there is a need to weigh work production and heat consumption. To this end, an enhanced stage-wise superstructure is proposed that involves synchronous optimization of expander/valve placement and heat integration for each pressure-change sub-stream in stages. A mixed-integer nonlinear programming (MINLP) model is established for synthesizing sub and aboveambient heat exchanger networks with multi-stream expansion, which explicitly considers the optimized selection of end-heaters and end-coolers to adjust temperature requirement. Our proposed method can commendably achieve the optimal selection of expanders and valves in a bid for minimizing exergy consumption and total annual cost. Four example studies are conducted with two distinct objective function (minimization of exergy consumption and total annual cost, respectively) to illustrate the feasibility and efficacy of the proposed method.

Key words: Superstructure, Heat exchanger networks, Expansion, Exergy, Economics, Mathematical modeling