Optimisation of heat exchanger networks involving isothermal and non-isothermal mixing by global and local solvers

Abstract

Abstract The synthesis of heat exchanger networks (HENs) has been an active research field over the last four decades (Klemes and Kravanja, 2013). Systematic methods based on pinch analysis, mathematical programming or their combinations have been successfully applied within this research field in order to reduce utility consumption and achieve sustainability within chemical processes. The HEN synthesis problems including isothermal (Yee and Grossmann, 1990) and non-isothermal (Bjork and Westerlund, 2002) mixing are formulated as Mixed-Integer Non-Linear Programming (MINLP) models. These problems are NP hard problems (Furman and Sahinidis, 2001), and combinatorial complexity, model size, number of non-convexities and hence, computational burden, increase dramatically by the number of hot and cold streams and stages. On the other hand, the computational speeds of computers and optimisation algorithms have been improved over the last two decades by several (6-7) orders of magnitude, which enable the solving of larger problems than those solved in past as well as solving smaller problems closer to global optima. This paper firstly presents an overview of the literature and problems of different complexities in order to show that over the recent period the medium and larger HEN synthesis problems have been successfully solved with local optimisation solvers, and that the obtained results are closer to their global optima. Also, a role of our research was to explore the possibilities of some currently available global and local optimisation solvers for solving the HEN synthesis problems of different complexities including isothermal and non-isothermal mixing. The obtained results of this work are in good agreements with the literature results, and in some cases the improved solutions have been identified.