Heat exchanger network synthesis/retrofit using MINLP stage-wise superstructure with non-isothermal mixing

Abstract

To enhance the energy recovery through heat integration, heat exchanger network (HEN) synthesis has been introduced for industrial processes. The design of an optimal-cost HEN is a challenging research topic in recently decade. This work modifies a mixed-integer nonlinear programming (MINLP) stage-wise model by commercial optimization software; GAMS, for simultaneous synthesis where the main objective is to minimize total annual cost composing of capital and operational expenses. The proposed model overcomes the area trade-off restriction caused by the assumption of isothermal mixing and allows any split stream flow through multiple exchangers in series as well as bypass stage before mixing non-isothermally for simultaneous synthesis. Dealing with the MINLP case, the initialization strategy is developed to find feasible starting point for the optimization problem resulting in better HENs compared to published results from the literatures. In addition, the retrofit of HENs is done by applying retrofit constraints to HENS model.