Effect of Dust Dispersion and Morphology on Dust Deflagration Hazard

Abstract

Dust explosions have led to numerous fatalities, injuries and property loss. Standards (ASTM, ISO etc.) mention a 20 L or a 1 m^3 apparatus to measure explosion parameters. These standards assume the dust particle size distribution remains unaltered post-dispersion in these apparatus. Recent studies have shown that dispersion in the standard 20 L apparatus, widely used for dust explosion properties measurement, leads to significant particle breakage. Reduction in particle size distribution due to dispersion can lead to erroneous risk assessment due to association of explosion parameters with pre-dispersion particle size distribution. This research investigates various factors that affect dust particle size reduction during dispersion and studies the effect of dust particle shape on minimum ignition energy (MIE). First, we explored the role of outlet valve, dispersion nozzle, cloud turbulence, and dust concentration on particle breakage. Also, the behavior of nanomaterial post-dispersion was analyzed. Results show significant particle breakage occurs due to outlet valve, nozzle, and cloud turbulence. An inverse relation between dust concentration and particle breakage was found. Nanomaterial de-agglomerates post-dispersion generating large surface area, thereby increasing explosion hazard. Second, we analyzed particle breakage due to dispersion in the MIE apparatus. Results show that MIE apparatus does not cause particle breakage but it alters the size distribution of electrostatic dusts significantly, which can affect ignition energy measurement of electrostatic dusts. Third, consequence of particle breakage due to dispersion on MIE was studied. Results show significant reduction in the MIE value of the dust post-dispersion, highlighting increased risk. Fourth, dependence of size reduction due to dust dispersion on different materials was studied. A sigmoidal correlation between particle breakage due to dispersion and the mechanical properties (brittleness index) of materials was established allowing process industries to identify dusts susceptible to breakage during explosion testing. Finally, we examined the effect of particle morphology on MIE of dusts. By testing spherical and irregular shaped material with similar size distribution, we demonstrated that morphology significantly impacts the MIE of dusts and should be included as a factor in risk assessment. This research will result in improved ASTM testing standards and accurate risk assessment for better safety measures.