Reduction of Pellets-Nut Coke Mixture under Simulating Blast Furnace Conditions

In recent years an intensive work has been carried out to decrease the coke losses of the blast furnace through mixing small-sized coke called "nut coke" in the iron ore burden layers. In order to clarify the influence of nut coke on the pellets reducibility, industrial iron ore pellets were reduced with and without nut coke participation under different temperatures and atmospheres. Isothermal and non-isothermal reduction tests under simulating blast furnace conditions were performed using an experimental laboratory rig. Furthermore, reflected light microscopy, scanning electron microscopy and X-ray technique were applied to characterize the microstructure and different phases developed in the origin and reduced pellets. Pellets reduced isothermally without nut coke participation exhibited reduction retardation (RR) at elevated temperature (>= 1373K) whereas the presence of nut coke had a positive effect of preventing such phenomena. The non-isothermal reduction of pellets showed that, as the amount of nut coke in pellets bed increased, the reducibility of pellets increased, too. The rate controlling mechanism of pellets and pellets-nut coke mixtures was predicted from the correlation between apparent activation energy calculations and microstructure examination.