Thermodynamic analysis of slagging and dephosphorization for small particle limestone

In order to explore the optimal process conditions for slagging and steelmaking by injecting limestone powder into the converter, a thermodynamic analysis was conducted on the slagging and dephosphorization effect of small particle limestone based on the basic experiment of slagging and dephosphorization. Using univariate experimental method, the effects of limestone particle size, reaction temperature, slag basicity, and FeO content on the slagging and dephosphorization of limestone were investigated, and the optimal parameters were obtained. The experimental results show that the limestone particles with average particle size of 0.84 mm has the best slagging and dephosphorization effect, and either too large or too small particles can cause decrease in dephosphorization rate. The optimal slagging and dephosphorization effect is achieved at experimental temperature of 1 400 ℃. When the temperature is lower than 1 400 ℃, the slagging is insufficient and the speed is slow, while temperature is higher than 1 400 ℃, there is a phenomenon of phosphorus return. The dephosphorization rate of molten iron increases with the increase of basicity. When the slag basicity R=3.5, the slag is in good condition and the dephosphorization effect is the best. When the basicity is too high, the slag viscosity is high and the amount of foam slag is large, which is easy to overflow. The dephosphorization rate of molten iron increases with the increase of FeO content in the slag. When the FeO mass fraction is 20%, the slag state is optimal. When the FeO mass fraction reaches 30%, slag overflow phenomenon will occur during the reaction process. Under the best process conditions obtained from the experiment, the dephosphorization speed of limestone in the early stage of the slagging and dephosphorization process is fast, the foam slag is in good condition, there are many types of solid solution phases in the slag, and the endpoint dephosphorization rate reaches over 85%. The phosphorus content in steel can be reduced to below 0.02%, which can complete the dephosphorization task and provide research foundation for industrial application of converter injection limestone powder smelting.