Process Safety and Environmental Protection 9 0 ( 2 0 1 2 ) 349–356 Contents lists available at SciVerse ScienceDirect Process Safety and Environmental Protection journa l h o me p age: www.elsevier.com/locate/psep Simulation-based approach to design of inherently safer processes Arcady A. Kossoy * , Yury G. Akhmetshin ChemInform St. Petersburg (CISP) Ltd., PO Box 25, 131232 Saint-Petersburg, Russia a b s t r a c t Safety of chemical processes and plants is a matter of high priority. The design of an inherently safer process is one of very beneficial ways of achieving this goal. The paper describes the method of designing an inherently safer process for a chosen set of equipment and materials involved by applying non-linear optimization. The optimization is aimed at finding an operational mode, which guarantees safety of the process under normal conditions and provides maximal attainable safety in case of one typical accident scenario – cooling failure. Discussion covers problem statement, choice of the optimization criteria, appropriate methods for defining control variables. An important practical challenge is stability analysis of the optimized process mode with respect to permissible deviations of control parameters and variables from the estimated values. The original method for the stability analysis of a non-stationary process is proposed. It comprises simplified preliminary evaluation method followed by the more detailed numerical optimization-based analysis. Several examples illustrate application of the methods proposed. © 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Chemical process; Inherent safety; Non-linear optimization; Mathematical simulation; Stability analysis 1. Introduction The inherent safety concept introduced by Kletz (1976, 1998) is complex and multifaceted one, at that neither of the aspects is insignificant. This concept is most beneficial provided that it is applied starting from the early stages of a chemical process development and throughout its life. This feature has been intensively discussed (Crowl, 1996; Cave and Edwards, 1997; Hurme and Rahman, 2005; Lutz, 1997; Mannan et al., 2002; Shah et al., 2005 to cite a few). This paper is focused on one important facet – the choice of an operational mode that, for a chosen set of equipment and materials involved, can make the process inherently safer. This problem has been discussed in numerous articles, for instance (Howard, 1996; Regenass, 1984; Zaldivar et al., 1992). Majority of the methods proposed require separate con- sideration of every specific process and reaction. In some cases it allows obtaining convenient analytical expressions for the assessment and rating of reaction hazard but it does not give any general solution. It is because of the intrinsic ∗ Corresponding author. Tel.: +7 812 647 9252; fax: +7 812 647 9252. E-mail address: kossoy@cisp.spb.ru (A.A. Kossoy). Received 7 January 2012; Received in revised form 26 March 2012; Accepted 31 March 2012 complexity of a chemical process. In general case it represents non-stationary system (steady-state modes are only particu- lar cases). The problem becomes even more complicated due to essential non-linearity of the system which originates from strong exponential dependency of a reaction rate on temper- ature. Therefore the general solution can be attained only by using numerical simulation and nonlinear optimization meth- ods. Although this approach is widely used for process optimization, it is still rarely applied for designing inherently safer processes (see, e.g., Stoessel, 2008; The gOPT Dynamic Optimization Tool, 1996; Ubrich et al., 1999; Zaldivar et al., 1992). Nowadays mathematical optimization is more actively used for providing inherent security of a process (Uygun et al., 2004). The basic method applied in this area comes to reduc- tion of the nonlinear non-stationary optimization problem to the number of much simpler static ones. When the optimization-based approach is applied to the design of an inherently safer process the optimization is directed at finding of an operational mode which guarantees 0957-5820/$ – see front matter © 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.psep.2012.03.007