Economic optimization of heat exchanger network synthesis (HENS) using a combinatorial approach

In this paper a method for automatic synthesis of heat exchanger networks (HENs) is described. The method, named COMBINET, is based on combinatorial procedures. No pinch rules are used. The main idea is to find good HENs from an economic point of view. Networks are optimised with respect to maximum net present value (NPV) of savings. The procedure however is well suited for optimising energy recovery, minimising heat exchanger area, minimising number of matches, etc. Networks are designed by combining heat exchangers, that have been optimised individually with respect to economics. When dealing with large stream problems, only the economically most important heat exchangers are combined. The claim is: When dealing with a large number of possible stream matches one need only investigate a small part of the combinations in order to find good and practical solutions. COMBINET exhibits some similarity with a method presented by Victorov, V.K., (1995), 'New Combinatorial Method for Synthesis of HENs,' Trans IChemE, Vol. 73, Part A, pp. 915-918, and the differences will be discussed in the paper. Eight additional cases from the open literature, which all have the data necessary for carrying out an economically optimisation, have been investigated and the results derived by applying different optimisation methods are reported. In five of the eight cases COMBINET has shown better results than reported in the originally references, and in the remaining three cases COMBINET has shown equally good results. COMBINET is easy to apply to any case that can be described by data for streams and economics. The method, incorporated in a PC-program, will then automatically find the optimal network subjected to the prescribed conditions. This method is therefore believed to be a practical tool for heat exchanger network synthesis.