INFLUENCE OF COKE ASH ON BLAST FURNACE HEARTH BEHAVIOUR

Liquid iron in the ironmaking blast furnace picks up more than half of its carbon while percolating through the packed coke bed in the deadman and hearth of the blast furnace thus the conditions within the hearth have a direct impact on liquid drainage and hot metal quality. Consequently, the rate of carbon dissolution into liquid iron, and the factors contributing to the movement of liquids through the coke bed must be understood. Investigations using quenched coke dissolution techniques have demonstrated that a mineral layer was formed between the liquid iron and the coke matrix as coke dissolves into iron under conditions comparable to the lower zone of the blast furnace hearth. This layer was predominantly comprised of calcium aluminates and was observed to change both its composition and morphology with time and temperature. Based on these findings, and plant based observations of the Port Kembla blast furnaces, important phenomena such has hearth coke bed state (floating vs sitting) are able to be discussed in terms of a cleaning/fouling cycle contributed to by the formation of different calcium aluminates in the deadman, in turn influenced by the coke ash chemistry. Supporting arguments for each stage of the cycle are drawn from the fundamental research, plant based observation and detailed analysis of specific blast furnace events. Application of this knowledge to Port Kembla blast furnace operations has allowed identification of periods where there is elevated risk of compromised hearth conditions. Further work in this area is expected to identify techniques that will allow a floating deadman to be secured improving furnace stability, iron quality and reducing hearth wear