A New Approach to Evaluate BOF Phosphorus Refining Performance

09 Sep 2011

Li Zushu, Mariana Adderley; Tata Steel RD&T Swinden Technology Centre, United Kingdom
James Morgan, Keith Bain, Johan van Boggelen; Tata Steel RD&T Teesside Technology Centre, United Kingdom

The increased requirements for tighter steel specifications, in particular low phosphorus levels, combined with possible high phosphorus hot metal compound the difficulty of steelmaking phosphorus control in Tata Steel Europe. Investigations are being carried out to improve phosphorus refining performance in BOF vessels. The phosphorus refining performance in BOF vessels at Tata Steel Europe is evaluated by comparing the actual phosphorus partition with the equilibrium value. Various models are already available for calculating the equilibrium phosphorus partition, most of which were designed to produce a better fit to particular laboratory and or plant data by adding correction factors. In this study, a new method is devised which looked at the materials charged into the vessel, the turndown bath analysis and the turndown temperature, and considered the mass of the elements present at a theoretical equilibrium using the thermodynamic software MTDATA. A Gibbs free energy minimum of the system was created showing which phases are present at the refining temperatures such as liquid metal, monoxides (e.g. free lime), liquid slag and possible di-calcium silicate (2CaO·SiO2). The theoretical equilibrium phosphorus partition is then calculated by summing the masses of all the phases present and the phosphorus present in these phases. It was found that the phosphorus partition in BOF vessels at three Tata Steel Europe BOS plants was in the range of 15-40% of the theoretical equilibrium value calculated by MTDATA. Based on the results generated from the new approach, measures to improve vessel phosphorus refining performance have been discussed by correlating the phosphorus partition with various parameters such as bath temperature, basicity and FeO content in the slag and the performance of bath agitation system.

Paper presented at EOSC 2011 - The 6th European Oxygen Steelmaking Conference, Stockholm, Sweden, September 7-9, 2011