Simultaneous Optimization Approach for Heat Exchanger Network Retrofit with Process Changes

Abstract

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 realized that there exists strong interactions between HENs and processes, and it should simultaneously consider the changes to process conditions (e.g. flow rates, temperatures) and the HEN retrofit. In this paper, new insights for process changes and their impacts on 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 deal with process changes and HEN topological changes in a simultaneous way. To demonstrate this, a short-cut crude distillation model has been built up that relates stream temperatures and flow rates to process conditions. This model has been combined with the model for HEN topological changes proposed by Zhu and Asante, which forms a complete model for optimizing the tradeoff between HEN retrofit and process changes. The case study shows significant cost savings by considering process changes and HEN modifications simultaneously.