Page 118 - Dust Explosions in the Process Industries

Dust Explosions: An Overview 9 7

Figure 1.1 02 Four hinged explosion doors of 0.8 m2 each, with energy dissipation buffers, mounted
on inlet hopper to a twin-rotor hammer mill for grinding household waste and bulky refuse: Pred =
1 .O bar(@ (Courtesy of T. Pinkwasser, Buhler, Switzerland).

is to prevent secondary air being sucked into the enclosure after the primary explosion
has terminated, giving rise to secondary explosions and fires. The reversible vent covers
include counterbalanced hinged doors and spring-loaded, axially traversing vent covers.
One type of reversible hinged explosion vent cover is shown schematically in Figure 1.104.
The bafile plate is spring-loaded and acts as a shock absorber when hit by the vent cover.
Additional shock absorption is provided by the air cushion formed between the vent cover
and baffle plate during impact. The adjustable prestressing device sets the static opening
pressure, Pstat, of the vent cover to the desired level. Figure 1.105 shows the type of dust
explosion vent illustrated in Figure 1.104 installed in the roof of a silo. Kappeler (1 978) dis-
cussed the successful use of reversible hinged explosion doors on dust filter enclosures.
One problem that can arise when using reversible explosion covers is implosion due
to the internal underpressure that follows the cooling of the gases inside the enclosure,
when sealed just after the explosion. Wiemann, Bauer, and Moller (1989) showed