CHEMICAL ENGINEERING TRANSACTIONS VOL. 29, 2012 A publication of The Italian Association of Chemical Engineering Online at: www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Hon Loong Lam, Jiří Jaromír Klemeš Copyright © 2012, AIDIC Servizi S.r.l., ISBN 978-88-95608-20-4; ISSN 1974-9791 DOI: 10.3303/CET1229022 Please cite this article as: Prashant K. and Perry S. J., (2012), Optimal selection of steam mains in total site utility systems, Chemical Engineering Transactions, 29, 127-132 127 Optimal Selection of Steam Mains in Total Site Utility Systems Kumar Prashant, Simon J Perry* Centre for Process Integration, School of Chemical Engineering and Analytical Science, The University of Manchester, Sackville Street, Manchester, M13 9PL, UK simon.perry@manchester.ac.uk This paper examines the optimal location (pressure) and the number of steam levels required to meet the external heating and cooling demands of individual site processes. The model developed makes use of Mixed Integer Linear Programming (MILP) techniques, implemented in a Visual Basic/Excel environment and linked to existing simulation software in order to extract the appropriate data for the total site. The model makes use of various methods of calculating shaftwork produced from the expansion of steam from simple single stage turbines operating between the steam levels involved. The shaftwork targeting methods include the TH model (Raissi, 1994), simple isentropic expansion, Willans’ line methods, and methods developed recently by Ghannadzadeh et al (2012) . Different models of shaftwork calculation are required depending on the nature of the data available. Results from various case studies are validated by comparison with simulation, and show that the optimal location of a fixed number of steam levels can significantly change depending on the method of shaftwork calculation used. Similarly the number of steam levels has an influence on the overall site heat recovery through the steam mains and the steam needed to be supplied by the boiler. This new approach to the selection of the appropriate and optimal pressure of the steam mains across total sites can also be applied to existing total sites in order to improve operational performance. The procedure can also be applied in the total site context to examine improvements in waste heat utilisation and consequently in distributed energy systems. 1. Introduction Total Site technology was developed initially by Dhole and Linnhoff (1993) and later expanded by Raissi (1994) and Klemes et al. (1997), as an extension of Process Integration/Pinch technology developed by Linnhoff et al (1982). Total Site technology extends Process Integration techniques from single processes to multiple processes which make up chemical processing sites. The graphical tools developed, supporting the technology, are based on extracting the heating and cooling demands of individual processes which are not met by process heat recovery, and have to be met by external heating and cooling utilities. These tools include the Site Profiles, the Site Composites, and the Site Utility Grand Composite curves (SUGCC). In using these graphical tools, targets can be set for the steam used and generated by the site processes at particular pressures (levels), heat recovery across the site through steam use and generation, the steam required to be produced by the boiler, and the shaftwork produced by steam turbines in relation to site cogeneration. The steam used and generated at different pressure levels, the heat recovery through the steam levels, steam demand from the boiler, and shaftwork produced depends however on the number and pressure of the steam levels involved, which previously has been performed in a relatively ad-hoc manner dependent on existing practices.