Simulation of iron oxides reduction under hydrogen using CFD-DEM

The steel industry produces residues containing iron oxides from which iron can be recovered via reduction. However, traditional methods use fossil gases and produce CO 2 as a by-product. To improve the environmental neutrality of the process, reduction under hydrogen generates water as a by-product. To understand this complex and novel process, we develop a simulation methodology coupling three methods. We use computational fluid dynamics to model the physics of the gas phase. The dynamics of the particles in which iron oxides are processed is modeled using the discrete-element method. Finally, the conversion process of the particles is modeled using the unreacted shrinking core model. The three methods are coupled and exchange information to achieve a realistic simulation of the reduction under hydrogen. The fitted model is used to study the progression of the reduction under different operating conditions. A parametric study under different gas temperatures and pressures shows that the conversion is faster for higher values of both parameters for the first stages of the process. However, for longer processing times the conversion slows down, and higher pressures may result in lower conversion, in accordance with experimental results in literature. The kinetic parameters of the model are fitted to the initial and final composition of the briquettes processed under industrial conditions whose operating parameters were unavailable. Thus, they are effective kinetic parameters valid for the materials used in this study. The uncertainty associated with the unknown operating conditions implies that the quantitative predictions should be treated with corresponding caution.