Simultaneous optimization approach for heat exchanger network retrofit with process changes

This paper addresses the problem of a heat exchanger network (HEN) retrofit considering process changes. Traditionally it is a common practice to fix process conditions before a HEN is retrofitted. However, it has been realiz ed that there exists strong interactions between HENs and processes, and it should simultaneously consider the changes to process conditions (e.g. flo w rates, temperatures) and the HEN retrofit. In this paper, new insights fo r process changes and their impacts an HEN retrofit have been-developed and the T-H diagram is used to represent the interactions. On the basis of the newly developed understanding, a systematic method has been developed to d eal with process changes and HEN topological changes in a simultaneous way. To demonstrate this, a short-cut crude distillation model has been built u p that relates stream temperatures and flow rates to process conditions. Th is model has been combined with the model for HEN topological changes propo sed by Zhu and Asante,(1) which forms a complete model for optimizing the t radeoff between HEN retrofit and process changes. The case study shows sign ificant cost savings by considering process changes and HEN modifications s imultaneously.