Systematic CFD–DEM Analysis of Pure-Hydrogen Moving-Bed Direct Reduction: Effects of Temperature, Pressure, and Gas/Solid Flow Rates on Reduction Kinetics, Spatial Uniformity and Energy Efficiency

Pure-hydrogen direct reduction is a promising route for low-carbon ironmaking, yet the coupled effects of gas–solid flow, heat transfer, and operating parameters in hydrogen shaft furnaces remain unclear. In this study, a three-dimensional CFD–DEM model coupled with gas–solid reactions have been developed to simulate iron ore pellet reduction in a laboratory-scale moving-bed shaft furnace under a pure hydrogen atmosphere. The model resolves particle motion, gas transport, heat transfer, and multi-step reduction kinetics, and incorporates hydrogen recycling, recompression, and top-gas heat recovery for energy consumption evaluation. The effects of reduction gas temperature, operating pressure, gas flow rate, and solid discharge rate on reduction behavior, spatial uniformity, and energy performance are systematically analyzed. The results show that increasing gas temperature markedly enhances reduction kinetics and metallization degree, while higher pressure and gas flow improve radial reduction uniformity with diminishing returns due to increased compression work or reduced gas residence time. The solid discharge rate governs particle residence time and imposes a fundamental trade-off between metallization degree, energy consumption, and productivity. These findings provide quantitative insights and practical guidance for optimizing pure-hydrogen shaft furnace reduction processes.