Work

Tracking Evolution of Reactive Species in Pellets During HyDR through combined X-ray and Neutron Imaging

Year: 2026

Type: preprint

Abstract: Steel production emits 3.6 Gtyr −1 of CO 2 , and the majority of these emissions come from a single step: ironmaking. Hydrogen-based direct reduction (HyDR) offers a lowemission alternative, producing H 2 O instead of CO 2 when operated with green H 2 . Though conceptualized in the 1930s, market adoption of HyDR remains limited due to reactor failures from sticking of iron-ore pellets. The sticking phenomenon is rooted in rate-limiting kinetics, where transport of reactive species competes with surface reaction to become the dominant process. We combine X-ray and neutron imaging to simultaneously resolve microscale pore network evolution and the spatial distribution of reactive species in two iron ore pellets, one non-fractured and one fractured, across three stages of reduction. We detect a consistent accumulation of hydrogenous species on the surface and interior of both pellets across all timepoints. Pellet pores > 10 2 µm, do not contribute to this accumulation, marking regions of efficient mass transport. Within the pellet interior, hydrogenous species are spotted in the pellet matrix and at pore boundaries. Isolated pore boundaries have up to 3× higher enrichment of hydrogenous species than the largest connected pore cluster, marking them as regions of poor mass transport. By quantifying permeability, diffusivity, and tortuosity, we show that improved bulk transport with reduction progress does not mitigate local trapping. Our findings connect hydrogenous species retention to pore network evolution and mass transport behavior. Insights from this study provide a basis for microstructural design strategies that could boost transport of reactive species and improve HyDR reactor performance.

Source: ChemRxiv

DOI: 10.26434/chemrxiv.15008637/v1