Page 116 - Dust Explosions in the Process Industries

Dust Explosions: An Overview 89

Figure 1.99 Damaged cyclone after a dust explo-
sion. The vent cover was too strong to open before
the cyclone itself ruptured (From Department of
Employment and Productivity, 1970).

Figure 1 .I 00 Epoxy-coated explosion vent panel: (left) mounted on vent, (right) after having relieved
an explosion (Courtesy of Fike Corporation, Blue Springs, MO, United States).

Such panels are manufactured in a wide range of sizes and shapes, and coatings may
be provided that allow permanent contact with various types of chemically aggressive
atmospheres. Often, a backing film of Teflon is used as environmental protection, to pre-
vent the vent panel from contaminating the product inside the enclosure that is equipped
with the vent. However, the upper working temperature limit of Teflon is about 230°C.
Brazier (1988) described special panels designed for service temperatures up to 450°C.
Figure 1.101 shows a bursting panel design originally developed for bucket elevators
but that may have wider applications. It consists of the bursting panel itself, which is a
0.04 mm thick aluminum foil of P,,, 0.1 bar(g), supported by a 0.5 mm metal gauze and
a second 0.5 mm metal gauze for further cooling of the combustion gases (“flame
arrester”). Additional layers of metal gauze may be added as required for adequate cool-
ing. The combustion gases should be cooled to the extent that unburned discharged dust
and dust that may be whirled up in the building are not ignited. In an explosion, the explo-
sion detection panel is blown out and operates a proximity switch that triggers whatever
preprogrammed automatic actions that should be taken (closing of the plant or valves,
automatic suppression, and so forth).