Page 469 - Dust Explosions in the Process Industries

436 Dust Explosions in the Process Industries

The silo was one of a complex of severalpartly condemned bolted steel plate silos that
were made availablefor dust explosionexperiments. Pneumatic injectionof dust through
a 200 mm 0 pipeline was used for generating explosible dust clouds in the silo. With
wheat grain dust, about 300 kg of dust was blown into the silo per experiment.With corn
starch the quantity was somewhatless, about 200 kg. A larger quantity was required for
the wheat grain dust because dispersion was not complete due to fibrous particles, and
lumps settled to the silo bottom before all the dust had been injected. The ignition point
was close to the silo bottom. In all experiments but one, dust injection was terminated
a few seconds before ignition, allowing the dust cloud to become comparatively quies-
cent. The experimentalresults for wheat grain dust as well as corn starch explosions are
shown in Figure 6.3, together with predictions based on some of the vent sizing meth-
ods discussed or mentioned in Section 6.I.
The vent cover used in the experimentswas a sheet of plastic with a low static opening
pressure, on the order of 0.01-0.02 bar(g). The final, exceptional corn starch explosion,

0 5 10 15
VENT AREA OF 500 m3 SILO [m']

Figure 6.3 Results from vented corn starch and wheat grain dust explosions in a 500 m3silo cell in
Norway. Comparison is made with predicted Pred/ventarea correlations by various vent sizing meth-
ods in current use. Pred means the maximum pressure in the vented enclosure during the explosion
(From Eckhoff and Fuhre, 1984, with adjustments by Eckhoff, 1990j.