Integrated analysis of iron dust explosions in a 20-L sphere: Mass and heat balance analysis combined with gas–particle dispersion modelling

The transition to hydrogen-based metallurgy and iron-based energy carriers introduces explosion hazards associated with fine iron dust. However, standardised 20-L tests may not capture the true iron explosion severity, as Pₘₐₓ occurs at ≥1500 g/m³, exceeding the vessel’s oxygen capacity (~660–990 g/m³). To resolve this discrepancy, oxygen consumption after the explosion was quantified, allowing a comparison between stoichiometric and pressure-based heat release. The results show that both pressure and oxygen consumption increase between 500 and 1000 g/m³ and then plateau at ≥1500 g/m³ (~3.8 bar, 92–99%), indicating oxygen-limited conditions. The calculated stoichiometric heat release exceeds the pressure-derived heat release. This quantifies significant heat losses in the 20-L apparatus. Despite oxygen depletion, pressure-based heat release continues to increase approximately linearly. This suggests that only a fraction of the nominal dust mass participates in the process, which explains why no significant heat sink effect is observed. CFD simulations further support this assumption by revealing incomplete dust injection with material being trapped in the valve. The overpressure–concentration model developed in this study, which is based on measured oxygen consumption, demonstrates higher values (around 5.6 bar) and a shift in the maximum overpressure to around 1000 g/m³, as well as a decline at higher loadings. These results provide an upper-bound (worst-case) estimate of explosion severity that is not captured by standard 20-L measurements. Together, these findings demonstrate that standard 20-L sphere measurements do not accurately reflect the true Pₘₐₓ for iron-based dusts, highlighting the need for improved dispersion systems and revised testing methodologies.