Coal-char/Slag Interactions during Pulverised Coal Injection in a Blast Furnace: Reaction Kinetics and Wetting Investigations

Abstract

The kinetics of reactions taking place in the slag/carbon interfacial region was investigated at 1 500°C for a range of carbonaceous materials, namely synthetic graphite, natural graphite and two coal-chars. Two blast furnace slags, one rich in iron oxide and other rich in silica were used in this study. Slag/carbon reactions were studied in a horizontal tube resistance furnace in argon atmosphere, using the sessile drop approach. The volumes of CO and CO₂ evolved were obtained from an analysis of off-gases with the help of a mass spectrometer. These reactivity studies were supplemented with wettability measurements on these systems. With iron oxide rich slag 1, all carbonaceous materials showed non-wetting behaviour without much improvement with time. With silica rich slag 2, natural graphite and coal-chars showed dynamic wetting after some time. Synthetic graphite however continues to remain non-wetting. Reduction of iron oxide was a predominant reaction with slag 1 and reached completion for all carbon substrates. Reduction of silica, main reaction with slag 2, was however partial with considerable amounts of unreduced silica remaining behind even after 1 800 s of contact. Overall reaction rates in the initial stages of contact were quite similar for both graphites whereas both coal-chars showed relatively high reaction rates. These results point towards the important roles played by the chemical composition of slags and carbonaceous materials in reduction reactions.