Optimal synthesis of heat exchanger networks for multi-period operations involving single and multiple utilities

The synthesis of heat exchanger networks in chemical plants is vital for energy saving. Most papers presented on this subject have focused on processes having single periods of operation. However, in reality, chemical processes may be multi-period in nature due to changes in environmental conditions, requirements for start-ups and shut-downs, etc. In cases like this, there may be variations in operating parameters such as supply and target temperatures, and flow rates. Further, such processes may involve multiple hot/cold utilities. For processes of this nature, it is imperative to use a mathematical based approach so as to adequately handle the multidimensional nature of the problem However, solving such models may be difficult except a systematic approach is adopted. In this paper, a modified version of the stage-wise superstructure of Yee and Grussman (1990) is adapted to the synthesis of heat exchanger networks having multiple periods of operations. A new set of solution approaches, which involves solving multi-period MINLP models in a two-step approach is presented. The newly developed method is applied to three examples, out of which two were taken from the literature. In the two examples taken from the literature, the solutions obtained from this study performed better than those presented in the literature. (C) 2014 Elsevier Ltd. All rights reserved.