Chapter 18 - Heat exchanger network synthesis

Abstract

This chapter focuses on sequential and simultaneous approaches used in heat exchanger network (HEN) synthesis. Sequential methods can be performed by insight-based techniques that do not use optimization at all or to a limited extent as an auxiliary tool. Insight-based techniques usually are not reliable tools to attack larger-scale problems, although they are quite efficient for solving smaller ones and also provide an understanding of optimization models. Pinch-technology-based approaches to design heat exchanger networks are widely used in industry, and they are simple and employ graphical tools that visualize solution algorithms, thus providing insight and greater understanding. They also give the designer control of the design procedure. The final pinch design method (PDM) allows calculation of network structure and basic parameters of heat exchangers and splitters. As the PDM employs some heuristic elements, due to inherent simplifications hidden in PT concepts, a second design stage is often necessary. It provides the targets and the optimum HRATvalue calculated by supertargeting, which is then applied in the design. To deal with a HEN synthesis problem in a systematic manner, a superstructure concept is often employed as the most rigorous and general technique. This concept has found a wide application in simultaneous design methods for various systems. First a superstructure is created, and then an optimal structure is calculated by optimization. The superstructure concept can be also applied to the design of a HEN with known HLD, that is, a sequential procedure for HEN synthesis. A superstructure, in general, must involve all possible structures of the HEN and as matches and their loads are fixed by HLD the superstructure can be substantially reduced.