Abstract
This paper presents the development of a mathematical model to describe the direct reduction of iron oxides in a shaft furnace. The concept of the shrinking core model was adopted. A pellet model was developed for the direct reduced iron using three consecutive reaction schemes, while the furnace was modelled as a one-dimensional steady state moving bed reactor. The combined pellet-reactor model was used to determine the profiles of compositions and temperature of gas and solid. The resulting boundary value problem was solved using the orthogonal collocation method. Validation of the model against data from a local iron/steel plant showed satisfactory results. A sensitivity analysis was carried out for the effects of key operating parameters, such as bustle gas temperature, ratio of gas/solid feedrates and reductant/oxidant ratio. Useful profiles were compiled to illustrate the results of the sensitivity analysis. These results may serve as guidelines for further optimisation studies of the unit.