Determination of Spontaneous Ignition Behaviour of Calcium Stearate Dust Accumulation

The self-ignition of combustible dusts depends on their chemical composition, on the properties of the substances in the composition, on the granulometry and geometry of the mass of the material and, last but not least, on the ambient temperature. Self-ignition is a complex process that takes place in three successive or simultaneous stages of development. These stages influence each other and are the following: self-heating, evaporation of moisture, and self-ignition itself. The underlying cause of self-heating (or possibly self-ignition) is that molecules on the surface of combustible dust particles are subjected to exothermic reactions with oxygen in the air transported in the free volume between particles, even at normal temperatures. Any amount of heat released will then cause an increase in temperature in the reactive dust-air system, thus accelerating the reaction of other dust molecules with oxygen. Calcium stearate is a carboxylate of calcium, classified as a calcium soap. It is a component of some lubricants, surfactants, as well as many foodstuffs. Due to its large utilization, it was considered important to analyze the flammability properties at bulk depositing to ensure proper safety regulations to avoid unwanted events such as fires or explosions. This paper aims to describe/present the self-ignition behaviour of combustible dust as a function of volume by evaporation tests under constant temperature conditions. The obtained results showed the maximum quantity that can be stored in bulk and the time until an ignition could take place, so that protective measures can be taken to avoid incidents (fires, explosions).