A New Approach to Generate Flexible Multiperiod Heat Exchanger Network Designs with Timesharing Mechanisms

Abstract

Seasonal changes in demands, supplies, and also in the operating conditions of a chemical process may call for different system structures to optimize the performance of its heat exchanger network (HEN). To produce a multiperiod HEN design, the traditional approach is to solve a single mathematical program that minimizes the total annual cost (TAC). This objective function, that is, TAC, is usually the sum of the annualized capital costs and annual utility costs determined according to given durations of all periods in a year. As a result, the conventional designs are often suboptimal, since the period lengths may have to be adjusted in response to the unexpected disturbances during actual operations. A new design approach is taken in the present study to circumvent the aforementioned drawback. In particular, a single-period model is first constructed and solved to produce the optimal design for each period individually. A timesharing strategy is then applied to integrate all such single-period designs so as to reduce the overall capital investment as much as possible while still keeping the utility consumption rates in every period at the minimum levels. In addition to their economic benefits, the new designs should be considered to be more flexible, since they are optimal despite unforeseen changes in the operation schedule. Finally, the numerical results of extensive case studies are also reported in this paper to demonstrate the effectiveness of the proposed approach.