Page 517 - Dust Explosions in the Process Industries

484 Dust Explosions in the Process Industries

I

OUST SAMPLE

Figure 7.8 Dust disperser for FMRC settling
velocity apparatus (From Ural, 1989a).

Figure 7.9 The FMRC liftoff apparatus for assessing the dispersibility of thin dust layers (From Ural,
1989a).
radial flow velocity of the air increases with decreasing distance from the plate center.
When the airflow has been properly adjusted to the dust layer in question, the particles
inside a circle of diameter smaller than 380 mm is lifted off the plate by the airflow,
whereas the particles outside this circle remain in the dust layer. As long as this critical
circle for liftoff can be reasonably well identified, a corresponding average critical air
velocity for liftoff can also be identified. As would be expected from powder-mechani-
cal considerations(see Chapter 3), the critical average linear air velocity for liftoff is not
constant for a given cohesive dust but depends on the degree of compaction of the dust
layer. Figure 7.10 gives a set of results for maize starch layers generated by three dif-
ferent compaction methods.