European Meeting on Chemical Industry and Environment edition:6 location:Mechelen, Belgium date:May 17-19, 2010
A possible method to avoid explosions from occurring inside industrial process plants in which mixtures of a combustible gas and air are present is working outside the flammable range of these mixtures. To this end, the flammability limits must be known at the process conditions. The determination of these limits might seem straightforward. However, going through the literature reveals the richness of the subject. First, the published flammability limit data were obtained using nearly as many different experimental methods as there were studies. To complicate matters even further, significant differences exist between the results of different studies. Normally, standardisation is expected to reduce these discrepancies. Nevertheless, it was found by various authors that even the results obtained with the two methods adopted by the European standard EN 1839 differ significantly. Next, a number of empirical laws are in widespread use, such as the modified law of Burgess and Wheeler to calculate the temperature dependence of the flammability limits and Le Chatelier's mixing rule to calculate the flammability limits of a combustible mixture based upon the flammability limits of the composing combustibles. Finally, a variety of numerical methods exists to calculate estimates for the flammability limits.
The aim of this paper is to present a review of some of the existing methods to determine the flammability limits. First, the discrepancy between the experimental results obtained with the two methods adopted by EN 1839 will be explained and some new flammability criteria will be presented that might eliminate this discrepancy. Next, the value of the modified law of Burgess and Wheeler and of Le Chatelier’s mixing rule will be discussed. Finally, the potential of calculating the flammability limits by using numerical methods will be explored.