EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

Treatment of hot metal in a Basic Oxygen Furnace (BOF) is a highly exothermic, complex, oxidising-refining process in order to remove hot metal impurities (mainly carbon and phosphorus) from iron and to achieve an optimal end temperature for further treatment of the crude steel. End-point control of the BOF process is in general based on static charge calculations and observation of decarburisation via off-gas analysis or in-blow sublance measurements of steel temperature and carbon content. On-line information on dephosphorisation behaviour is not available. The objective of the research project BOFdePhos, funded by the European RFCS programme, is the development of a comprehensive dynamic model for on-line monitoring and control of the BOF process behaviour with focus on dephosphorisation. For that purpose extensive investigations on thermodynamics and kinetics regarding the main aspects of dephosphorisation were made. This includes the development of a thermodynamic database covering the dephosphorisation reaction, as well as the performance of various laboratory experiments revealing valuable information about the main contact area for dephosphorisation reactions (e.g. slag foam structure, slag viscosity, droplets behaviour in the foam) and the rate of lime dissolution in slag. The results of these investigations, together with the results of CFD model calculations of flow fields and mixing behaviour in steel and slag, defined the basis for set-up of multi-zone reaction models which were used for detailed simulations of the dephosphorisation process in the BOF converter in order to derive appropriate submodels to be applied within on-line process models. Necessary BOF process data for validation of the model calculations were provided from the Tata Steel converters in Port Talbot and IJmuiden. Furthermore, a new sensor technology measuring the oxygen activity in the slag as well as the slag height and bath level and allowing also for in-situ slag samplings has been developed and successfully tested within this project. These new measurements provide additional information to the enhanced on-line models for an optimised dynamic end-point control of the BOF process.