Iron and aluminum powder explosibility in 20-L and 1-[formula omitted] chambers

Abstract

Metallic dusts with low values for maximum pressure Pmax and volume-normalized maximum rate of pressure rise KSt as determined in bench-scale apparatus have been labeled as “marginally explosible.” These dusts pose unique challenges because they may be shown to be explosible using standardized bench-scale apparatus, yet they may not be found to be explosible using larger standardized test chambers. Furthermore, some metallic powders produce higher KSt values with increasing test scale.Results and preliminary analysis stemming from a comprehensive experimental campaign involving selected iron and aluminum powders of varying specific surface area are presented.Fine-, medium-, and coarse-particle size iron powder with Siwek 20-L KSt values less than 45 bar⋅m/s were also found to be explosible in the Fike 1-m3 vessel. The coarse iron was only found to be non-explosible with the sub-75 μm fraction removed. The fine, medium, and coarse iron powders produced lower maximum rates of pressure rise across all concentrations in the 20-L chamber compared to the 1-m3 vessel. Fine-, medium-, and coarse-particle aluminum powders were also tested. The coarse aluminum powder could be exploded under the corresponding experimental conditions of 20-L chamber but not under the corresponding experimental conditions of 1-m3 chamber. The volume-normalized maximum rate of pressure rise for the finest aluminum powder was found to be overdriven in the 20-L vessel using an ignition energy of 10 kJ compared to tests performed with the same ignition energy in the 1-m3 vessel. An ignition energy of 5 kJ was found to be more appropriate for testing fine aluminum in the 20-L sphere. In contrast, the medium-particle size aluminum produced a KSt value substantially higher in the 1-m3 vessel compared to the 20-L chamber.