Chemical Engineering Science 59 (2004) 5233–5239 www.elsevier.com/locate/ces CFDmodellingofstirredtankchemicalreactors:homogeneousand heterogeneousreactionsystems Leszek Rudniak, Piotr M. Machniewski,Aleksandra Milewska, Eugeniusz Molga ∗ Faculty of Chemical and Process Engineering, Warsaw University of Technology, ul. Warynskiego 1, 00-645 Warsaw, Poland Received 2 March 2004 Available online 28 October 2004 Abstract The presented work is a part of studies carried out to develop a practical method to prevent runaway events in chemical reactors. The use of computational fluid dynamics (CFD) techniques is proposed here to indicate in advance the local hot-spots in the reaction mixture, so as to elaborate an efficient and sensitive method for early warning detection of runaway. The CFD method has been chosen to support, elaborated by Bosch et al. (Comput. Chem. Eng. 28 (2004) 527), the on-line runaway detection method in batch reactors, which is based on the divergence criterion. Series of CFD simulations have been executed for two exothermic reactions, being the esterification reaction of the 2-butanol and the propionic anhydrite catalysed by the sulphuric acid (homogeneous system) and the hydrolysis of the propionic anhydrite catalysed by the sulphuric acid (heterogeneous system). For both the considered reactions the results of calculations have been verified with the results of experimental measurements performed in a bench scale RC1 Mettler-Toledo reaction calorimeter. The elaborated conclusions can be further employed in the parametric sensitivity analysis (Comput. Chem. Eng. 28 (2004) 527; Am. Inst. Chem. Eng. J. 45 (1999) 2429) to indicate a number of temperature sensors and their location inside the reactor, which will help to apply efficiently the divergence criterion method.  2004 Elsevier Ltd. All rights reserved. Keywords: Computational fluid dynamics; Chemical reactors; Modelling; Multiphase reactions; Thermal runaway; Reactor safety 1. Introduction In a chemical reactor carrying out the exothermic reac- tion, when the rate of heat generation by chemical reaction exceeds the rate of heat removal by cooling, the reaction accelerates and, if no countermeasures are taken, the loss of temperature control (thermal runaway) may occur. The most important part of each early warning detection sys- tem is a proper and robust criterion to distinguish between a dangerous situation and a non-dangerous one (Bosch et al., 2004). The new general criterion to define runaway limits in chemical reactors, recently developed and tested, is based on the divergence of the system by applying state space recon- struction techniques (Strozzi et al., 1999; Zbilut et al., 2002; Bosch et al., 2004). This early warning detection method ∗ Corresponding author. Tel.: +48226606293; fax: +48228251440. E-mail address: molga@ichip.pw.edu.pl (E. Molga). 0009-2509/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2004.09.014 employs multi-point temperature measurements, so for its efficient and safe application to predict runaways, the most important aspect is a study of runaway detection as a func- tion of location and number of temperature sensors installed inside the reactor. In this work the use of computational fluid dynamics (CFD) techniques is proposed to support the mentioned early warning detection method. With CFD simulations the local and instantaneous values of liquid velocity, reactant con- centrations and reactor temperature can be determined. The results of CFD simulations are essential to indicate in ad- vance the local non-uniformities of temperature appearing in the reactor and to estimate the possibility of the global thermal runaway propagation in the reactor from appearing “hot-spots”. Furthermore, the CFD technique helps to indi- cate a location and number of temperature sensors, which is particularly important for the processes performed in indus- trial reactors.