Effect of admixed silica on dispersibility of combustible dust clouds in a Godbert-Greenwald furnace

Dust dispersibility, the tendency of dust to form clouds that remain airborne, can be an important safety parameter in preventing dust explosion. One measure to moderate dust explosion hazards is adding solid inertants to combustible dust. In addition to being a solid inertant, noncombustible silica is sometimes used as an anti-caking agent or fluidization enhancement additive in powder systems, affecting particle interactions in dust clouds. In this study, six types of combustible dust were admixed with micro- and nano-sized silica to study the effect on dispersibility and ignition hazard in a Godbert-Greenwald (G-G) furnace. Both micro- and nano-silica increased dispersion for some dust types, by changing contact geometry between combustible particles, and thereby decreasing inter-particle forces. Only for polyethylene did addition of 1% micro-silica cause increased dispersibility resulting in enhanced ignition hazard, with minimum ignition temperature (MIT) slightly decreasing 10 °C. No reduced MIT values were found with 1% nano-silica. [Display omitted] •No particle breakage occurs in a G-G furnace•Actual particle size in dispersed dust clouds is larger than the primary particle size•Both micro- and nano-silica can increase dispersibility for some dust types•Addition of 1% micro-silica causes 10 °C decreases in MIT of polyethylene by increasing dispersion•No reduced MIT values are found by adding 1% nano-silica even with better dispersion