Thermal analysis of milling products and its implications in self-ignition

Abstract

Thermal degradation of soft wheat, durum wheat, and maize as well as native starch and maize dextrin used to make fireworks, under nitrogen atmosphere, was studied by differential scanning calorimetry and thermogravimetric analysis. The results indicate that bran-free products give rise to a decomposition via transglycosylation-volatilization. On the contrary, wheat products containing bran or ligno-cellulosic residues decompose via exothermic reaction of dehydration-charring. For each product, the curve is determined as a function of its physical form, i.e., flour, ground product, and grain. The comparison of the conversion calculated as a first-order kinetics and the experimental, exhibits a very low mean square error. On this basis, the pyrolysis was assumed to obey first-order kinetics. The kinetic results were then used to estimate the temperature of spontaneous combustion, when these products are stored in silos. In particular, Frank-Kamenetskii theory is applied to prove how the products, under particular conditions, can become extremely explosive.