Page 562 - Dust Explosions in the Process Industries

Assessment of lgnitability 529

generated with the same dusts in larger vessels, such as the 1m3IS0 vessel and various
20 liter vessels. This occurs even though the pressures measured in the Hartmann bomb
are not corrected for the increased initial pressure due to the dust dispersion air.
The measurement of maximum constant-volumepressures generated by dust explo-
sions in closed bombs is fairly straightforward.Apart from the wall-cooling effects in
small bombs, the results do not depend much on the details of the experiment as long as
the dust cloud is reasonably well dispersed and the average nominal dust concentration
is varied systematicallyto identify the worst case.

7.14.2.2
The 1 m3Standard ISOVessel
Side and top views of this apparatus are illustrated in Figure 7.54.
A container of approximately 5 liters capacity and capable of being pressurized with
air to 20 bar is attached to the explosion chamber. The container is fitted with a 19 mm
!B opening valve of 10 ms opening time. The container is connected to the explosion
chamber via a 19 mm Iz!perforated semicircular spray pipe. The diameter of the holes
in the pipe should be in the range 4-6 mm. The number of holes is chosen such that their
total cross-sectional area is approximately 300 m2.
The ignition source is a pyrotechnicalignitor with a total energy of 10kJand arranged
to fire after a fixed delay of 0.6 s after onset of dust injection. The mass of the pyrotech-
nical ignition source is 2.4 g, and it consists of 40% zirconium, 30%barium nitrate, and

10 KJ CHEMICAL IGNITOR

cFLUSHING AIR

DUST CONTAiNER
\
\ ,PRESSURE SENSOR

t -FLUSHING AIR

PRESSUR
SEhiSDR

TOP VIEW

Figure 7.54 The 7 m3 closed vessel specified by the International Standards Organization (7985a)
to determine maximum explosion pressures and maximum rates ofpressure rise of dust clouds in air
(From Verein deutscher Ingenieure, 7 988).