Investigation on the Modes of Consumption of Residual Char by the Slag Phase during Pulverised Coal Injection in Blast Furnace

摘要

One of the factors limiting the maximum rate of coal injection in the blast furnace is the accumulation of unburnt char. If the amount of unburnt char entering the blast furnace could be consumed, it could enable higher PCI rates. The interaction of unburnt char with slag, hot metal and the gaseous phases could have a significant influence on char assimilation. This work examines the interaction of a low iron oxide and a high iron oxide bearing slag with different carbonaceous substrates, including three graphites and six chars. Experiments were conducted in a high temperature tube furnace at 1500°C and 1400°C in an argon atmosphere, and the slag/carbon/gas interactions were studied in-situ.The results showed that there are different modes of consumption of the carbonaceous materials possible, depending on the slag composition and the ash content and composition of the carbonaceous substrates. The main mode of consumption of the carbonaceous material through interaction with slag is the consumption of carbon in the reduction of iron oxide and silica in the slag. The kinetics of these reduction reactions could dictate the consumption rate of carbon in a char present in the blast furnace during coal injection. When interacting with the high FeO slag, the amount of carbon likely to be consumed is larger as compared to the low FeO slag. When interacting with the low FeO slag, the assimilation of some ash components in the char into the slag phase could also result in the consumption of char during coal injection. Apart from these, consumption of both, the carbon and the ash in the char, could result from in-situ reduction of the oxides in the ash by carbon. The consumption of carbon will be more at temperatures above 1500°C when both iron oxide and silica are reduced. At lower temperatures, only iron oxide is reduced, and therefore the consumption of carbon will be relatively less.