Heat Exchanger Network Modification for Waste Heat Utilisation under Varying Feed Conditions

Abstract

Waste heat streams are often neglected due to their comparatively low temperatures. However, they can still be utilised by retrofitting existing heat exchanger networks (HEN). Traditionally Pinch Analysis has been used to set heat recovery targets and these can be used as indicators for the retrofit. However, when an existing HEN contains a number of non-optimally placed heat exchangers, major topology modifications may be needed. As a result it may be more economic to achieve heat recovery smaller than the Pinch targets. In some cases exploiting or constructing utility-exchanger heat paths may be too costly and waste heat utilisation for added value side-product should be considered. In this paper the problems in retrofitting a HEN for utilities usage reduction are discussed. Additionally, HEN modification analysis is performed aiming at generating hot water as the value-added product. As the operating conditions vary, the modified network should also be flexible. These issues are addressed by a procedure development presented in this work, where different arrangements of HEN for modification are evaluated. The developed methodology is applied to a case study.