271 CHEMICAL ENGINEERING TRANSACTIONS Volume 21, 2010 Editor J. J. Klemeš, H. L. Lam, P. S. Varbanov Copyright © 2010, AIDIC Servizi S.r.l., ISBN 978-88-95608-05-1 ISSN 1974-9791 DOI: 10.3303/CET1021046 Please cite this article as: Dkhil O., Elhajbelgacem A., Belghaieb J., Hajji N. and Labidi J., (2010), Energy optimization of a network of exchangers-reactors in a nitric acid production plant, Chemical Engineering Transactions, 21, 271-276 DOI: 10.3303/CET1021046 Energy optimization of a network of exchangers-reactors in a nitric acid production plant J. Belghaieb 1 , O. Dkhil 1 , A. Elhajbelgacem 1 , Nejib. Hajji 1 , Jalel Labidi* 2 1 Energy and Environment Research Unit, ENIG, Gabès, Tunisia 2 Dept. of Chemical and Environmental Engineering, University of the Basque Country Plaza Europa, 1, 20018, Donostia-San Sebastián, Spain jalel.labidi@ehu.es The aim of this work is to improve heat recovery in a nitric acid production plant using process integration. The studied plant produces 1340 tons of 58 % nitric acid per day and the necessary data is taken from its current operating state. Using collected data, the simulation of the process was conducted considering that the reactions continue to occur in pipes, which are regarded as adiabatic plug flow reactors and heat exchange is achieved in counter-current multitubular heat exchangers-reactors. The simulation results allowed to establish the exergy balance of the process and to identify the main zones of energy degradation. The analysis showed that the total exergy losses in the heat recovery exchanger network are about 20 MW and its overall exergetic efficiency is about 93 %. Energy degradation was found to be primarily localized in the water-cooled condenser of the low pressure reaction and in the gas-gas exchangers. Moreover, the application of pinch technology made it possible to estimate the pinch temperature and to determine the minimum consumption of hot and cold utilities. Finally, different solutions were suggested to minimize utility consumption in the studied plant. 1. Introduction Many industrial processes are basically processes of energy conversion. The considerable energy requirements of an industrial unit make it necessary to pay close attention to energy consumption and to the development of a convenient method for its estimation. Energy use can be determined effectively by considering both the first and the second law of thermodynamics, that is, by applying the concept of exergy. In this concept (Esciubba (2007), Ploumen (2001)), the quality of energy and its degradation in real processes is accounted for. The traditional approaches for energy optimization are useful for improving the efficiency of individual equipments. However, these methods remain insufficient to guide us in the optimization of the total configuration of the system. In fact, various thermodynamic systems show additional irreversibilities when they are interconnected. The reduction of such irreversibilities makes it possible to increase the overall efficiency thanks in particular to a better internal regeneration. Total optimization of such systems has been the object of many studies during the last years (Linnhoff, 1988; Yoda, 1995; Trivedi, 1994). This work lies within the scope of energy