Coolant strategies for BOF steelmaking

Thermal balance of basic oxygen furnace (BOF) steelmaking is controlled primarily by the scrap added as coolant. In the present steel scenario, insufficient availability and high cost of prime scrap has led us to explore the possibilities to use alternative coolants. Until now, choice of alternative coolants used in converter is determined by availability, price and operational strategies of the shop. These coolants have varying cooling effects and significantly influence the blowing parameters and turn-down performance. With the aim to reduce cost and dependence on prime scrap, various alternative coolants, such as iron ore lumps, pig iron, iron ore pellets, direct reduced iron and lime have been experimented with in 130 t converters under different conditions. The heat absorption behaviour and melting rate of these coolants were significantly different and found to be dependent on physical properties and addition patterns. Each coolant was individually compared for its effect on turn-down chemistry, tap temperature, slag condition and refractory wear pattern. Use of some of these coolants had beneficial effect of forming foamy slag and improved the dephosphorisation. Combined use of these coolants has helped in minimising the prime scrap requirement. This paper describes the utility of blow patterns, optimisation of coolant mix and addition strategies contrived for the synergic use of alternative coolants.