Page 471 - Dust Explosions in the Process Industries

438 Dust Explosions in the Process Industries

length-to-diameterratio of four of the 500 m3silos may be too small to make Radandt’s
constants for “silos” applicable.
Both the Swedishand the Norwegian vent sizing methods are comparativelyliberal, sug-
gesting Predvalues that are in fact lower than the experimentalmaximum values.An argu-
ment in defense of such a liberal approach is that vent sizing involves risk-analytical
considerations rather than being a fully deterministic problem (see Section 6.6). In the
500 m3 silo explosion experiments, researchers attempted to create a worst-case situa-
tion in terms of both dust concentration and location of the ignition point.

6.2.2
EXPERIMENTS IN SLENDER SILOS OF LID = 6

Sizing of vents for large, slender silos of the kind frequentlyused in the grain, feedstuffs,
and food industries remains a controversial subject. However, during the 1980s, valu-
able information has been gained through large-scale experiments.Two experimentalpro-
grams were run in parallel, one in Norway, reported by Eckhoff, Fuhre, and Pedersen
(1987) and Eckhoff et al. (1988), and one in Switzerland and the Federal Republic of
Gemany, reported by Radandt (1985,1989) and Bartknecht (1987). Both silos had LID
values close to 6, but the volume of the Norwegian silo was 236 m3,whereas that of the
Swiss-German one was only 20 m3.A cross section of the Norwegian silo is shown in
Figure 6.6, and a picture of the experimental site in Figure 6.7.

STRONG STEEL GRID SUPPORTING
STEEL COVER PLATES
HIGHEST IGNITION POINT
DUST INLET
PIPE, TOP
PRESSURE PROBE 1INJECTION
DUST CONCENTRATION t
PROBE
DUST CONCENTRATIO
PROBE
INTERMEDIATE IGNITION
POINT

DUST CONCENTRATIO
PROBE
DUST CONCENTRATIO
PROBE
PRESSURE PROB
INTERMEDIATE I
POINT
DUST CONCENTRATI
PROBE
DUST CONCENTRATI
PROBE
PRESSURE PROBE
-
LOWEST IGNITION POINT 0 P
1
2
3
DUST INLET, METERS Figure 6.6 236 m3silo in Norway for dust
BOTTOM INJECTION explosion experiments, L/D = 6 (From Eckhoff
et ai., 1987).