Numerical investigation of nonisothermal reduction of hematite using Syngas: the shaft scale study

A mathematical model is developed to investigate the reduction process of hematite in the reduction zone of the Midrex shaft furnace as a moving bed reactor. It is described as a counter-current moving bed cylindrical reactor in which hematite pellets are reduced by a gaseous mixture of hydrogen, water vapour, carbon dioxide and carbon monoxide, namely Syngas. It is laterally injected into the bed at the lower part close to the bottom. Governing equations, including continuity, momentum, energy and mass equations, are derived based on the conceptual model for both gas and solid phases in the cylindrical coordinate system. A three interface unreacted shrinking core model (USCM) is applied to describe the reduction process in the pellet scale at the hematite–magnetite, magnetite–wustite and wustite–iron interfaces. The concluded equations are solved numerically based on the finite volume method. The model predictions are validated by a comparison with the operating data of the Gilmore Midrex plant. It was seen that the model can reproduce the operating data satisfactorily. Finally, the distribution of process variables in the bed is exhaustively explained.