System assessment of recycling of steel slag in converter steelmaking

Aimed to utilize useful components and reduce the environmental impacts, the present study investigated the recycling of steel slag in converter steelmaking. A mathematical model based on the regular solution model was firstly developed to calculate the activities of calcium oxide and ferrous oxide and the substitution ratio of steel slag. The dephosphorization experiments were conducted in an induction furnace. In addition, theoretical analysis of the detailed heat expenditure items of dephosphorization agent was carried out. The heat enthalpy of unit mass slag was measured by differential scanning calorimetry. The results of dephosphorization experiments indicate that there is a sharp drop in phosphorus content in hot metal at the initial stage of dephosphorization. It was found that the optimal proportion of steel slag in dephosphorization agent is 20%. The heat enthalpy of unit mass slag No.1 and No.2 are 1164 kJ/kg and 1131 kJ/kg, respectively. The cooling capacity of steel slags are lower than the reference dephosphorization agent. One ton of reference dephosphorization agent made of 42% lime, 50% scale and 8% soda, could reduce the temperature of 80 ton of hot metals by up to 83.60 °C. The corresponding temperature drop by using No.1 and No.2 steel slags are 56.01 and 55.99 °C, respectively. For each increase of 5% substitution ratio with No.1 slag, the temperature drop of hot metal increases by 5.80 °C; for each increase of 5% substitution ratio with No.2 slag, the temperature drop of hot metal increases by 2.70 °C. The main factor that influences the temperature drop is the slag amount.