SYNTHESIS AND ANALYSIS OF RESILIENT HEAT EXCHANGER NETWORKS

Simple and reliable methods to synthesize the most efficient Heat Exchanger Network {lcub}HEN{rcub} to heat and cool process streams between stated temperature bounds have become available recently. Marselle et al. (1982) have introduced a more realistic problem formulation, the "resilient heat exchanger network problem", which requires an energy efficient design that can cope with the uncertainties in an industrial environment, where variations in flowrates and temperatures are inevitable. They suggested a heuristic synthesis procedure and pointed out its limitations.; In this study, a rigorous analysis of the problem is presented. Examples are included to demonstrate that the HEN's designed on the basis of intuitively possible heuristics are not only inefficient but are often inoperable.; Some fundamental properties of optimal resilient HEN's are proven first. A rigorous non-linear optimization problem is formulated to test network resilience for specified ranges of inlet temperature and flowrate variations. Using reasonable assumptions, this computationally difficult problem is modified into simpler formulations for a variety of common industrial situations. An evolutionary synthesis technique is presented to generate resilient HEN. The method is easy to use and has intuitive appeal.; This study also addresses the problem of analyzing network resilience. A Resilience Index {lcub}RI{rcub} is defined to quantify the ability of a HEN to cope with inlet and target temperature variations. A simple physical approach and a more accurate numerical algorithm for the calculation of the RI are presented. This new analysis technique can be used for existing networks to detect bottlenecks or at the design stage to guide the selection between alternatives according to the criteria of resilience.; An interactive software package of RESHEX has been developed for synthesis and analysis of HEN's. The program incorporates the recent techniques for utility and area targeting, automatized synthesis of energy efficient HEN's and the analysis formulations developed in this thesis. The Transhipment problem formulation (Papoulias and Grossmann, 1983) for HEN synthesis is modified to allow the designer to directly influence the stream splits and the number of exchangers in a network structure. An analysis option is available to investigate the effect of modifications in a network on its area requirement and the energy efficiency.; Finally, the usefulness of the program is demonstrated by a case study conducted to revamp an industrial feed preheat train. Alternate designs are proposed with different levels of energy savings and investment requirements.