Biocoal is a fossil- free reductant in metallurgical processes. Due to the increasing use, risks associated with self-heating needs to be better understood. In this work, the apparent activation energy and reaction kinetics of a commercial biocoal were investigated using isothermal calorimetry, differential scanning calorimetry, thermogravimetric analysis, and basket heating tests, including the crossing‑point method. The derived kinetic parameters were subsequently used to estimate critical storage volumes at 50 °C using both the Frank-Kamenetskii theory and a numerical model based on a global apparent reaction‑rate expression. The results demonstrate that the activation energy depends strongly on temperature and reaction progress, exhibiting distinct kinetic regimes. At temperatures relevant for self‑heating, activation energies obtained from isothermal calorimetry and the crossing‑point method were substantially lower than the 87–90 kJ mol −1 assumed in the N.4 test method for goods classification. As a consequence, the UN N.4 test for classification of goods classified the biocoal as non‑self‑heating, while both Frank-Kamenetskii theory and the numerical model predicted thermal runaway for container‑scale storage volumes. The study highlights that reliance on the fixed activation‑energy assumption in the N.4 procedure may lead to false‑negative classifications. Recommendations for improved testing strategies are proposed, including multi‑temperature calorimetric measurements, clearer definitions of the crossing‑point temperature, and consideration of extent of reaction-dependent reaction rates. The findings support recent regulatory actions to classify biocoal as self‑heating for maritime transport and underscore the need for revised standards to ensure its safe handling and storage.
Dahlbom et al. (Thu,) studied this question.