Page 107 - Dust Explosions in the Process Industries

80 Dust Explosions in the Process Industries

Figure 1.87 Compressed-gas-driven, fast-closing
slide valve actuated by a fast solenoid (Courtesy of
IRS, Darmstadt, Germany).

described successful performance of a fast-closing (30 ms) compressed-gas-operated flap
valve, illustrated in Figure 1.88. Figure 1.89 illustrates an active (pressure sensor) fast-
closing compressed-gas-driven valve that blocks the duct at the entrance rather than fur-
ther downstream.

Figure 1.88 A compressed-gas-driven, fast-closing
flap valve.

The.last active isolation method of dust explosions in ducts and pipes to be men-
tioned is interruption by fast automatic injection of extinguishing chemicals ahead of
the flame. The system is illustrated in Figure 1.90. This is a special application of the
automatic explosion suppression technique, which is described in Section 1.4.7.
Bartknecht (1978, 1987) and Gillis (1987) discussed this special application and gave
some data for the design of adequate performance by such systems. Important param-
eters are the type of dust, initial turbulence in primary explosion, duct diameter, dis-
tance from vessel where primary explosion occurs, method used for detecting the onset
of the primary explosion, and type, quantity, and rate of release of the extinguishing
agent.