Influence of scale on the inerting of dust explosions

Experiments were performed to compare intermediate-scale (1-m3) and laboratory-scale (20-L) inerting results. In general, laboratory-scale inerting levels were higher than intermediate-scale values. This can be attributed to the use of a strong ignition source to initiate the inerting experiments, which may have overdriven the explosions in the smaller test vessel. Previously reported agreement between the smaller test vessel and full-scale experiments may be due to overdriving in the 20-L chamber, leading to high inerting levels similar to those encountered in full-scale tests due to flame acceleration. Use of weaker ignition sources in the laboratory-scale chamber did produce inerting levels similar to those observed in the intermediate-scale vessel.; A new flammability limit parameter has been defined by J. Going, K. Chatrathi, P. Amyotte and A. G. Dastidar as the Minimum Inerting Concentration (MIC; in units of mass concentration, i.e. g/m3). This is the concentration of inertant required to prevent a dust explosion regardless of fuel concentration. Previous experimental work at Fike Corporation (Blue Springs, MO) in a 1-m 3 spherical chamber has shown this flammability limit to exist for coal dust when inerting with monoammonium phosphate, sodium bicarbonate and lime stone. The MIC also existed for cornstarch powder when inerting with sodium bicarbonate. In the current work, inerting experiments on a larger variety of dusts were performed in a spherical 1-m3 chamber and a 20-L Siwek chamber using identical materials. The results show that an MIC can be determined for some materials in both chambers.; Calculated adiabatic flame temperatures (CAFT), along with a selected limit flame temperature for combustion propagation, have been used in determining the flammability envelope for hydrocarbon gases. The current work discusses the use of this methodology to determine the flammability of solid fuel/oxidizer/inertant mixtures based upon previous work by other researchers. Their model has been modified to allow for comparisons between inerting levels determined in a 20-L chamber and a 1-m3 chamber. The results indicate that the 20-L and 1-m3 models can be used to predict the experimental inerting levels of the 1-m3 chamber, with limitations. Ultimately, the utility of this modified CAFT and limit flame temperature model as a predictive/screening tool for inerting level and minimum inerting concentration determination has been demonstrated to perform well at low fuel dust concentrations.