Page 454 - Dust Explosions in the Process Industries

ignition of Dust Clouds and Dust Deposits 42 7

200 300 400 500 600 700 800
MIN. IGNITION TEMPERATURE I"C1

Figure 5.23 Correlation between minimum ignition temperature ofdust clouds (BAM furnace) and
minimum equivalent electric spark ignition energy for various scratch and grinding ignition sources
(From Muller, 1989).

from the specific ones used in the experiments of Ritter and Muller. However, their
approach is an interesting attempt at resolving a very complex matter.
Dahn and Reyes (1987), using a 20 liter explosion vessel, studied ignition of transient
dust clouds by grinding sparks generatedby forcing a metal rod against a rotating grind-
ing wheel located within the vessel. A striking feature, shown in Table 5.7, is the nega-
tive result obtained with the two aluminumrods. This is in accordancewith the discussion
in Section 1.1.4.5 in Chapter 1.

5.4.3
SPARKS, HOT SPOTS, AND FLASHES FROM SINGLE
ACCIDENTAL IMPACTS

Pedersen and Eckhoff (1987) studied the ignition of clouds of corn starch and grain dust
in air by sparks, hot spots, and thermite flashes from single accidental impacts,using the
apparatusdescribedin Section 7.12.2 in Chapter 7 and illustratedin Figures 7.40 and 7.41.
They investigated impacts of net energies up to 20 J and tangential velocities of approach
from 10ds to 25 m/s. Table 7.2 in Chapter 7 gives someresults from ignition with titanium