A CFD-DEM model for the simulation of direct reduction of iron-ore in fluidized beds

•Modelling of indirect reduction of iron ore in a polydisperse fluidized beds.•Heat, mass and momentum coupling between CFD and DEM.•Investigation of kinetic parameters and their effects on the reduction degree.•The rate determining step is seen to be the last stage of reduction. The aim of this work is the investigation of the indirect reduction of hematite in fluidized beds and the effects of different kinetic parameters on the reduction process at a numerical level, which are validated against experimental results. We utilize a CFD-DEM coupling method, where gas phase is represented by classic CFD and iron ores by DEM. Both phases are strongly coupled by heat and mass transfer. The particle reduction is modeled using unreacted shrinking core model taking into account the morphological changes of the ore. The model is validated and critical reaction parameters such as the activation energies, pre-exponenital factors and equilibrium constants are investigated. It sheds light on how much an influence the kinetic parameters have on the reduction degree and becomes evident that the rate determining step is reduction from wustite to iron. The model is then applied to a lab-scale fluidized bed reactor.