Predicting the onset of defluidization in hydrogen metallurgy fluidized beds: A CFD-DEM study with a modified sintering force model

As a vital pathway for decarbonizing the steel industry, hydrogen-based fluidized-bed ironmaking offers high efficiency by directly utilizing iron ore fines. However, the inherently large specific surface area of fines makes them exceptionally susceptible to adhesion-induced defluidization. Simulating defluidization is traditionally hindered by the extreme timescale mismatch between hour-scale reduction kinetics and millisecond-scale granular hydrodynamics. The present work establishes a practical computational fluid dynamic–discrete element method (CFD–DEM) coupling framework, decoupling reduction from hydrodynamics via a state-mapping strategy. To capture the intrinsic nonlinear acceleration of solid-state diffusion, the conventional sintering force model is modified by introducing a sigmoidal temperature correction. Crucially, the framework is quantitatively validated against high-temperature experiments, accurately predicting the critical iron content triggering defluidization across 873–1073 K and resolving the severe overestimations inherent in the conventional sintering force model. Comprehensive particle-scale analyses, encompassing interparticle force competition, contact duration statistics, and transient flow structures, reveal the micromechanics of agglomeration. We elucidate that defluidization is governed by the synergistic coupling of temperature and iron content: temperature acts as a temporal accelerator compressing the characteristic sintering timescale, while iron content serves as a spatial determinant providing topological connectivity. This coupled interplay triggers a percolation-driven phase transition, where transient cohesive clusters abruptly merge into a system-spanning rigid skeleton. Building upon the mechanistic understanding, a high-resolution regime map is constructed to delineate the nonlinear operational boundary, establishing a validated engineering blueprint to proactively avert bed defluidization and optimize the industrial operation of hydrogen metallurgy technologies.