Carbon as in situ energy source in induration of hematite pellets and its effect on pellet properties

Fuel consumption during high temperature induration is one of the principal reasons for the cost
intensiveness of the iron ore pelletisation process. While magnetite ore is oxidised to hematite
during induration at high temperature and provides internal heat energy to the pellet, there is
hardly any internal heat generation. Furthermore, magnetite is prone to form diffusion bonds at
950–1200uC, whereas with hematite ore, the diffusion bonding is much less at that low
temperature and so requires very high temperature of induration (around 1300uC or above) and
hence consumes more energy. In this study, the external heat energy in pellets has been supplied
by adding coke fines as a source of carbon which is oxidised to CO or CO2 producing in situ heat
to the pellets and also reduces a part of the hematite to magnetite during induration. These help in
bond formation and lowering the external energy requirement. The study has been carried out
with varying carbon percentage (0–5%) and the effect of carbon and its optimisation level has
been determined. Up to 2% carbon has been found to be optimum to improve cold crushing
strength, porosity, reducibility and decrease the reduction degradation index of pellets, as well as
reduce the requirement of induration furnace temperature by 80uC and considerably decrease
fuel consumption. However, excess addition of carbon increases the porosity markedly and
reduces pellet strength.