Exergy analysis of multistage cascade low temperature refrigeration systems used in olefin plants M. Mafi, S.M. Mousavi Naeynian, M. Amidpour* Department of Mechanical Engineering, K.N. Toosi University of Technology, Tehran, Iran article info Article history: Received 9 July 2007 Received in revised form 17 March 2008 Accepted 13 May 2008 Published online 28 May 2008 Keywords: Process Manufacturing Hydrocarbon Survey Exergy Refrigeration system Cascade system Propylene Ethylene Efficiency Low temperature abstract This paper provides an exergy analysis for multistage cascade low temperature refrigera- tion systems used in olefin plants. The equations of exergy destruction and exergetic efficiency for the main system components such as heat exchangers, compressors and expansion valves are developed. The relations for total exergy destruction in the system and the system overall exergetic efficiency are obtained. Also, an expression for minimum work requirement for the refrigeration systems of olefin plants is developed. It shows that the minimum work depends only on the properties of incoming and outgoing process streams cooled or heated with refrigeration system and the ambient temperature. Using actual work input values, the exergetic efficiency of the low temperature cascade refriger- ation system of a typical olefin plant is determined to be 30.88% indicating a great potential for improvements. The novelty of this paper includes the suggestions for increasing efficiencies, along with discussion about the reasons for deviation from reversible processes. ª 2008 Elsevier Ltd and IIR. All rights reserved. Analyse exerge ´ tique des syste ` mes frigorifiques en cascade a ` basse tempe ´ rature utilise ´ s dans les installations de production d’ole ´ fines Mots cle ´s : Proce ´de ´ ; Fabrication ; Hydrocarbure ; Enque ˆte ; Exergie ; Syste ` me frigorifique ; Syste `me en cascade ; Propyle `ne ; E ´ thyle `ne ; Efficacite ´ ; Basse tempe ´ rature * Corresponding author. Department of Mechanical Engineering, K.N. Toosi University of Technology, No. 15, Pardis Street, Mollasadra Avenue, Vanak Square, Tehran 1999143344, Iran. Tel.: þ98 21 88677272; fax: þ98 21 88677273. E-mail address: amidpour@kntu.ac.ir (M. Amidpour). www.iifiir.org available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ijrefrig 0140-7007/$ – see front matter ª 2008 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2008.05.008 international journal of refrigeration 32 (2009) 279–294