The effects of hot metal temperature, oxygen gas flow rate from a top lance and argon gas flow rate from an injection lance on iron oxide formation and dephosphorization rates in hot metal were investigated with 3 kg- and 200 kg-scale furnaces. The results were summarized as follows.
1) Iron oxide formation rate increased with lower hot metal temperature, higher oxygen gas flow rate and lower argon gas flow rate.
2) A kinetic model was developed to estimate the iron oxide formation on hot metal, and a mathematical model for hot metal dephosphorization has been made based on the aforementioned model of iron oxide formation and the coupled reaction model.
3) Dephosphorization and the formation rate of iron oxide in 200 kg-scale tests agreed well with those were obtained by the mathematical model.
4) Oxygen activity at slag/metal interface obtained by the mathematical model agreed with the equilibrium oxygen activity with FeO in slag.
5) In the early stage of dephosphorization, the gas flow rate of the bottom blowing need to be lower in order to enhance the iron oxide formation. In the late stage of dephosphorization, that needs to be higher in order to enhance the mass transfer of phosphorus in hot metal.
6) Industrial hot metal dephosphorization tests were carried out with a 350 t-scale top and bottom converter. The conditions of top blowing oxygen and bottom blowing nitrogen have been improved by adopting the mathematical model in order to increase the iron oxide content in slag. It has been possible to increase dephosphorization efficiency without fluor spar at lower hot metal temperature (below 1300°C) by improving the blowing conditions.
