Effect of Particle Size Distribution and Inerting Mechanism on Explosion Severity of Organic/mineral Mixtures

Abstract

The animal feed industry mixes cereals, vitamins, amino acids, and mineral powders to produce a solid mixture called “Premix”. The mitigation of premix explosions is challenging due to the diversity of composition, particle size, and nature of the mixed products. Therefore, determining their explosion safety parameters requires many standardised tests and a time-consuming process. However, it is possible to reduce the extensive use of experimental characterisation by better understanding the physicochemical mechanisms involved. In this context, this project aims to study the influence of Particle Size Distribution (PSD) and the mineral chemical nature on the explosion severity of organic and mineral powder mixtures commonly used for premix manufacturing. Cornflour was mixed with four minerals (sodium chloride, sodium bicarbonate, calcium carbonate, and magnesium oxide) chosen based on their industrial applications and inerting mechanisms (scavenging of radicals, inert gas generation, and heat sink). The powders were sieved to obtain samples with distinct particle size ranges. PSD was analysed ex-situ and in-situ to study the fragmentation behaviour of the products. The explosion tests method was based on the standard ISO/IEC 80079-20-2 using the 20L sphere. The results indicated that due to physical and chemical effects, NaHCO₃ is the most efficient inerting agent. Moreover, its initial PSD did not affect the inhibition performance due to its brittleness and the explosibility test pressure gradient, leading to possible inerting overestimation. NaCl reduced the deflagration index (K_St) less efficiently due to the incomplete decomposition into scavenging agents of free radicals, essential for flame propagation. The unsuitable addition of purely thermal inhibitors (CaCO₃, MgO) could increase the mixture’s K_St due to a dispersibility improvement, dust cloud PSD reduction and radiation effects. The mineral nature selection during product design could then significantly impact the inherent safety in the premix industry.