Dephosphorisation in Bof Steelmaking

Phosphorus content in hot metal has been increasing in the last years at Huachipato Steel plant, as low phosphorus iron ore availability has been decreasing, which necessitates a study of the phosphorus slag-metal partition ratio in BOF furnaces for both high and low carbon steelmaking. Steel and slag samples were taken during high and low carbon processes to evaluate slag composition evolution. The study indicates that vanadium behaves similarly to phosphorus, with measured partition coefficients around 200 for high carbon and 400 for low carbon steels. Optical and scanning electron microscopy, along with energy dispersive spectroscopy (EDS), were used to analyze the presence of phosphorus and vanadium in slags. A mathematical correlation model was developed to predict the phosphorus content in steel post-blowing based on operational practices from 2007, considering factors such as phosphorus in the converter charge, temperature, carbon levels, and slag composition. The results reveal that the actual approach to equilibrium partition ratio is about 20% for high carbon and slightly over 30% for low carbon steels. These findings underscore the necessity for adjustments in operational practices to maintain acceptable phosphorus levels amidst rising hot metal phosphorus content.