Reduction Kinetics of Iron Ore-Graphite Composite Pellets in a Packed-Bed Reactor under Inert and Reactive Atmospheres

Abstract

The rate of reduction of iron ore-graphite composite pellets in a packed-bed reactor under controlled atmosphere (inert and reducing) has been studied through experiments and modeling exercises. A customized high-mass, high-temperature thermogravimetric setup was constructed to carry out reduction experiments in a packed-bed reactor. A very low overall apparent activation energy estimated from experimental data indicates that the packed-bed reduction is unlikely to be chemical kinetics controlled. A kinetic model has been developed to calculate the temporal evolution of various phases of iron oxides and metallic iron. The rate-dependent parameters of the kinetic model are estimated from experimental data by applying an optimization tool. The predicted phases at various degrees of reduction were verified by X-ray diffraction and metallographic investigation, and a reasonable agreement between the results has been observed. It is observed that both the rate and the extent of metallic-iron production increase under reactive atmosphere. In addition, a simplified thermal model has been developed to ascertain the role of heat transfer on the kinetics of the reduction process under inert atmosphere. The reduction kinetics of the packed bed under reactive atmosphere, on the other hand, is not controlled by heat transfer and might possibly be controlled by CO-gas mass transfer through the pellets.