Conceptual insights to debottleneck the Network Pinch in heat- integrated crude oil distillation systems without topology modifications Mamdouh A. Gadalla a,⇑ , Omar Y. Abdelaziz b,c , Fatma H. Ashour c a Department of Chemical Engineering, The British University in Egypt, El-Shorouk City, Cairo 11837, Egypt b Department of Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden c Department of Chemical Engineering, Cairo University, Giza 12613, Egypt article info Article history: Received 9 April 2016 Received in revised form 3 August 2016 Accepted 7 August 2016 Keywords: Network Pinch Energy efficiency Retrofit Heat exchanger network Crude distillation unit Process integration abstract Heat exchanger network pinch sets the limitations of heat recovery for existing network topologies. Improving the heat recovery within a pinched-network is independent of the areas of individual exchang- ers present in the network, rather the topology of the network must be altered. Such a change in the topology can be very capital intensive and in many cases seems not easy to implement. This research aims to overcome the Network Pinch through proposing process operation changes, avoiding network topology alterations; hence, debottlenecks the heat-integrated systems towards further energy savings beyond the maximum heat recovery limitations. A new graphical representation is recently proposed to simulate existing preheat trains/networks with all energy equipment. The recent graphical represen- tation is employed in this work to identify the pinching matches that limit heat recovery. Therefore, such graphs are key tools to identify potential process changes by which the Network Pinch is overcome. New graphs are constructed involving hot stream temperatures against cold stream temperatures. Existing exchangers are described by straight lines, with slopes related to flows of process streams and heat capacities. Exchanger matches touching the line where hot outlet stream temperature equals cold inlet stream temperature are pinching matches; this condition corresponds to absolute maximum heat recovery (DT = 0). Potential process changes within a distillation unit are identified to relax the Network Pinch and further heat recovery is maximised. The slope of such an exchanger match is decreased or the location of the pinching match is altered keeping the same slope. These changes are translated into process changes within the crude oil distillation unit. Accordingly, the process changes are determined based on which match is pinched besides its location within the network. An illustrative example shows that process changes overcome the Network Pinch and energy recovery is increased by 14% beyond the maximum level achieved for the existing process conditions. Capital investments imposed are minor compared with substantial energy cost savings. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction One major obstacle in industrial processes and chemical plants, including refineries, is the energy intensive feature. Typically, in energy-integrated crude distillation systems, large amounts of fuel oil, natural gas, or in some cases part of the crude oil processed are burned in the fired heater to provide the energy required for crude fractionation. Heat exchanger networks (HENs) are essential in the chemical plants to minimise external utility consumption through recovering process heat available at no operating costs. Indeed, lit- erature is rich in addressing HEN synthesis problems, however, there is markedly less contributions on HEN retrofitting which is based on revamping the existing preheat trains [1,2]. Crude distillation units (CDUs) are of major energy consump- tion in refining industries. Energy of crude oil products and other process hot streams is recovered in preheat trains to reduce exter- nal utility requirements (fuel and flue gas consumption). Energy recovery in preheat trains maximises crude temperatures prior to entering the fired heaters. Maximum energy recovery in crude pre- heat trains is limited by the physical design of the exchanger net- work and together with the given process conditions. Revamping preheat trains once implies maximising the energy recovery in the network and reducing the external fuel consumption. Exchan- ger networks characterised with this condition are known as pinched networks or Network Pinch is taking place. Modifying http://dx.doi.org/10.1016/j.enconman.2016.08.011 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: Mamdouh.Gadalla@bue.edu.eg (M.A. Gadalla). Energy Conversion and Management 126 (2016) 329–341 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman