Modelling the reduction of an iron ore-coal composite pellet with conduction and convection in an axisymmetric temperature field

A mathematical model of the coal-based direct reduction process of iron ore in a pellet composed of coal and iron ore mixture is investigated using a finite-control volume method. Heat transfer by conduction in the solid, convection by gaseous media inside, and radiation from the surroundings of the pellet are included in the model. The pellet is assumed to be spherical initially and the temperature around the pellet is taken to be symmetric about an axis passing through the centre. The parameters of the process, such as thermal conductivity, specific heats, and heats of the reaction, are all temperature dependent. The shrinkage/swelling of the pellet is also considered. We find that the effect of convection on the temperature and on the overall average reduction is small. However, the effect on the local concentration of the reaction components is significant. We predict that a uniform surrounding temperature field around the pellet yields a better average reduction.