Influence of nut coke on iron ore sinter reducibility under simulated blast furnace conditions

One of the most important factors to increase the economic efficiency of the blast furnace process is to reduced coke losses (undersieve product known as nut coke). In recent years there has been increased interest in mixing nut coke in the sinter layers. In order to clarify the influence of nut coke on sinter reducibility, sinter and sinter-nut coke mixtures were isothermally reduced with 30%CO-70%N-2 at 1173-1523 K using a muffle furnace supported by an on-line gas analyser. Reflected light microscopy, scanning electron microscopy and X-ray technique were used to characterise the microstructure and the different phases developed in the original and reduced sinter. Sinter reduced without nut coke participation exhibited reduction retardation at elevated temperatures (> 1373 K) while the presence of nut coke prevented such phenomena. The rate controlling mechanism of sinter and sinter-nut coke mixture was predicted from the correlation between apparent activation energy calculations, mathematical modelling derived from gas-solid reaction model and microstructure examination.