Abnormal Swelling during Reduction of Binder Bonded Iron Ore Pellets with CO-CO₂ Gas Mixtures

Abstract

Abnormal swelling during reduction of iron ore pellets with CO-CO₂ gas mixtures was investigated in the temperature range of 700 to 1000°C.
Influence of addition of gaseous sulfur COS at low partial pressures to inlet gas mixtures, CO₂/(CO+CO₂) in inlet gas and temperature as well as kinds of binders such as Portland cement, bentonite and lime on swelling were examined.
When the ratio P_COS/P_CO in inlet reducing gas was lower in 10⁻² than the equilibrium ratio between iron and iron sulfide, abnormal swelling of pellets was observed for non cement bonded pellets, in particular, giving maximum around 900°C. Cement bonded pellets provided moderate abnormal swelling independently of adding gaseous sulfur to inlet gas mixtures. Their swelling seemed to be caused by gasification of sulfur species present in cement. These results supported our previous findings that the existence of sulfur is essential to the abnormal swelling and the swelling is mostly accompanied with the formation of fibrous irons.
The results are discussed along with previous researches and gas chromatography of sulfur species in exit gas to evaluate the sulfur activity in gas near the reaction front inside cement bonded pellets.