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Abstract
Gaseous reduction by hydrogen was performed for three types of hematite pellets, two from industry and one prepared in the laboratory. The reduction mechanisms of the pellets were studied based on the morphologies of the partially reduced samples. Two mechanisms were found, the mechanisms of the two types of industrial pellets being very similar. The degree of reduction was followed as a function of time for each type of pellets. On the basis of the reaction mechanism of the industrial pellets, a mathematical model was developed. As a pioneer effort, the model combined the computational fluid dynamics approach for the flow and mass transfer in the gas phase with model of gas diffusion in the solid phase as well as the description of the chemical reaction at the reaction sites. The calculation results agreed well with the experimentally obtained reduction curves. The present work also emphasized the importance of evaluation of the reduction mechanisms and the properties of different types of iron ore pellets prior to developing a process model. While the present approach has established a good foundation for the dynamic modeling of the shaft reactor, more efforts are required to accomplish a realistic process model.
Highlights
THE rising interests in application of direct-reduced iron (DRI) have given the researchers new challenges in this area
Experiments were conducted to study the mechanisms of reduction of different hematite pellets by hydrogen gas
A model was developed to couple mass transfer in the gas phase, gas diffusion in the solid and the chemical reaction at the reaction front to describe the isothermal reduction of single iron oxide pellets
Summary
THE rising interests in application of direct-reduced iron (DRI) have given the researchers new challenges in this area. An important factor in production of DRI in industrial practice, such as MIDREX or HYL processes, is the dynamic control of the process in the reactors. This dynamic control along with optimization of the process is essential to ensure both smooth process operation and the quality of the products, for example the metallization degree and cementite fraction in the reduced pellets. The chemical potentials of the gaseous species and the temperature vary at different positions in the reactor. The chemical potentials of the species can differ inside each pellet at a given position. An efficient dynamic control of the process and the quality of the products demands a realistic process model
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