Simultaneous synthesis of flexible heat exchanger networks for unequal multi-period operations

The synthesis of heat exchanger networks has received significant attention in the last four decades due to the rising cost of fossil based energy sources and their attendant greenhouse gas emissions potential. However, most of the methods presented in the literature for heat exchanger network synthesis (HENS) have assumed that plants' process stream parameters, such as supply/target temperatures and stream flowrates, are fixed, hence having a single period of operation. In reality, process parameters vary within certain ranges due to changes in environmental conditions, changes in product quality demand, plant start-ups/shut-downs, and other disturbances which may upset the system. This implies that plants need to be designed to accommodate the aforementioned potential variations in operating parameters. This paper presents a new 3-step approach for the synthesis of flexible heat exchanger networks for multi-period operations with unequal period durations. The first step entails optimising a representative single period network of the multi-period problem. The solution to the representative network is then used to initialise the multi period network in the second step. In the third step, the resulting network from the second step is redesigned/evaluated to handle unforeseen changes in lengths of periods. The solutions obtained from the newly presented method compare favourably with those in the literature. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.