Abstract
This project focuses on the importance of solvent content in prewetted powders to assess their impact on ignition sensitivity and explosion severity. Various mixtures were studied, including magnesium stearate-ethanol and wheat middlings-eucalyptus oil. The mixtures were prepared by liquid granulation and then mixed in a chaotic stirrer. Their minimum ignition energy (MIE) and explosion severity were determined using a modified Hartmann tube and a 20L explosion sphere, respectively. A statistical approach was used to model the impact of variations in fuel concentration, solvent content, and ignition energy through a Box-Behnken experimental design, confirming that adding ‘a few drops’ of a flammable liquid to a powder can significantly alter its explosive behaviour, either positively or negatively, depending on the powder’s flammability. The most influential parameter is the global fuel equivalence ratio (of both powder and solvent). Adding a small amount of solvent often tends to increase the explosion severity of mixtures, but as the proportion of liquid increases, the resulting change in particle size (agglomeration) and energy loss due to fragmentation notably moderates the mixtures’ reactivity. From a thermodynamic point of view, the vaporization of the liquid does not seem to impact the maximum explosion pressure significantly. Admixtures of prewetted powder must be subject to a thorough risk assessment. In particular, a change in explosivity class (St) must lead to a change in the vent sizing procedure and a modification of safety measures.
