Page 108 - Dust Explosions in the Process Industries

Dust Explosions: An Overview 8 7

COMPRESSED AIR [6 bar lg)l

n

CYLINDER/PISTON SYSTEM I
EXPLOSION --- 4

$-
PRESSURE DETECTOR

Figure 1 39 Active fast-closing, compressed-gas-driven valve system for blocking the opening
between the process unit where the primary explosion occurs and the duct or pipe. Nitrogen is injected
into the duct or pipe simultaneously with the valve being closed, to obtain additional protection.
PRESSURIZED
CONTAINER FOR
EXTINGUISHING AGENT
INFRARED FAST-OPENING VALVE
FLAME DETECTOR ----------- (EXPLOSIVE CHARGE OPERATED)
\ ,NOZZLE
.___ 0

/ I \
/ / \
IGNITION SOURCE FLAME FRONT DISPERSION OF EXTINGUISHING MEDIUM

Figure 1.90 A system for interrupting dust explosions in ducts by fast automatic injection ofan extin-
guishing agent ahead of the flame.
1.4.5
EX P LOS IO N - P R E S S U RE- R ES I STA N T E Q U I PM E N T

1.4.5.1
Background

If a dust cloud becomes ignited somewhere in the plant, a local primary dust explosion
occurs. As discussed in Sections 1.4.6 and 1.4.7, the maximum explosion pressure in such
a primary explosion can be effectively reduced to tolerable levels. However, in some