Page 495 - Dust Explosions in the Process Industries

462 Dust Explosions in the Process Industries

analysiswas also extended to two and three vessels coupled by ducting. Good agreement
with experiments was demonstrated.
Lunn et al. (1988) and Lunn (1989) applied the Heinrich-Kowall theory for extending
the nomograph method for vent sizing to the region of low maximumexplosion pressures.

6.5.4
THEORY BY RUST

Rust (1979) based his theory on considerations very similar to those of Heinrich and
Kowall, using maximum rates of pressure rise from closed-bombtests for assessing an
average burning velocity in the vented explosion via the cube root law. The weakest point
in Rust’s theory, as in all theories of this category, is the assessment of the burning
velocity of the dust cloud.

6.5.5
THEORY BY NOMURA AND TANAKA

The process studied theoretically by Nomura and Tanaka (1980), being identical with
that considered by Yao (1974) for gases, is illustrated in Figure 6.24. They envisaged
a boundary surface x-xsufficiently close to the vent for essentially all the gas in the
vessel being to the left of the surface and sufficiently apart from the vent for the gas
velocity through the surface to be negligible. They then formulated a macroscopic
energy balance equation for the flow system describing the venting process, assuming
that all the pressure and heat energy was located to the left of the x-xline in Figure 6.24
and all the kinetic energy to the right.

Figure 6.24 Conceptual model of explosion vent-
ing (From Nomura and Tanaka, 1980).

Although the approach taken by Nomura and Tanaka is somewhat different from those
of Heinrich and Kowall and Rust, the basic features are similar and in accordance with
what has been said in Section 6.5.1. It may appear as if Nomura and Tanaka were unaware