Correlation between self-ignition of a dust layer on a hot surface and in baskets in an oven

Abstract

Evaluation of self-ignition hazard of bulk materials requires experimental determination of self-ignition temperatures as a function of volume. There are two standardised methods: (1) determination of the self-ignition temperature of dust samples in oven and (2) measurement of the self-ignition temperature of a dust layer deposited on a hot surface. Sometimes, the sample behaviour during these tests makes the second method difficult to apply. The self-ignition phenomena in these two tests rely on the same principles. Their results are interpreted with the help of theoretical relations. The correlation described in this paper can be considered acceptable to deduce self-ignition temperature of a dust layer, based on results of self-ignition of the same dust in heating ovens, if the Biot number (alpha) can be estimated. Uncertainty on the correlation is near 30K. This uncertainty is on the same order of magnitude as the difference in the self-ignition temperature on a hot surface for thickness between 5 and 15 mm.

Determination of parameters used to prevent ignition of stored materials and to protect against explosions in food industries

“…If the temperature within the layer exceeded the plate temperature, it was understood that ignition had been produced, even if no flame was seen. The uncertainty of the results obtained is ±5 K. Alternative methods are being proposed [23].…”

Investigation of the propensity of sulfide concentrates to spontaneous combustion in storage

“…Mathematical models for depicting spontaneous heating of thermally unstable materials include Semenov's model, FrankKamenetskii's model, and Thomas' model (Janes et al, 2008;Nelson, Balakrishan, & Chen, 2003). When depletion of the reactant is neglected, the unsteady-state energy balance equation (Jones, Chiz, Koh, & Matthew, 1996;Malow & Krause, 2004) for selfheating of sulfide concentrates can be written as follows:…”

Self ignition of layers of powder mixtures: Effect of solid inertants

“…Two other fine chromel-alumel (K) thermocouples have been used. One placed within the dust sample, at the center of the layer about halfway up, in order to measure temperature inside the layer during the experiment, the other one at ambient temperature shielded from heat convection and radiation from the hot surface, to control the ambient temperature [35]. The maximum temperature reached by the powder during a test will sometimes be quoted.…”