Page 459 - Dust Explosions in the Process Industries

426 Dust Explosions in the Process industries

20 - EXPERIMENTS BY
GRAY ET AL. (19811
,=7
15 -
\
I
W
a: -
3
y 10
Wa: COOL FLAMES
a SLOW
5-
01 ‘ I I I
450 500 550 600 650
25 1 I
MATHEMATICAL
- MODEL BY
20 - 0
HARRISON AND
&- CAlRNlE (19881
E
- - 0 -
KEY:
2 15
WLL 0 SLOW OXIDATION
-
10 - 0 A OSCILLATORY
IGNITIONS
W
a:Q
0 OSCILLATORY
5- COOL FLAMES
0‘ ‘ I I I X STEAOY-STATE
COMBUSTION (GLOW)
450 500 550 600 650
VESSEL TEMPERATURE IKI
Figure 5.26 Comparison of experimentally observed and numerically predicted ignition diagrams
for acetaldehyde/air in a continuously stirred 0.5 liter glass bulb (From Harrison and Cairnie, 1988).
Tyler concluded that there was no theoretical model by which data from Godbert-
Greenwald furnace tests could be transformed to minimum ignition temperatures in the
more-complex practical situations in industry. He suggested that stirred reactor ignition
experiments,as performed successfullyfor combustiblegas mixtures,could provide a more
fundamentalunderstandingof dust cloud ignition processes. Such experimentsmay yield
appropriateactivation energies for the ignition processes, which may be used to scalemin-
imum ignition temperatures more reliably. The study of ignition of acetaldehyde/airmix-
tures, by Harrison and Cairnie (1988) and Harrison et al. (1988), taking this approach, is
an excellent example of its potential. Figure 5.26 shows a comparison of experimentally
determined and theoreticallypredicted ignition diagrams for the acetaldehyde/airsystem.

REFERENCES

Aakre, M. (1980, April) “Maaling av laagaste gnistenergi for tenning av pulverlag.” Report No.
790705-1. Bergen, Norway: Chr. Michelsen Institute.
Adomeit,P., and K. Henriksen.(1988) “ZeitlicherVerlauf der Entflammungeines brennbaren Schiittguts
an einer heissen Oberflache.” Staub-Reinhalt.LL@48, pp. 371-377.
Allen, J., and H. F. Calcote. (1981) “Grain Dust Ignition by Friction Sparks.” Report SMS-81-049.
Washington DC: National Grain and Feed Association.