EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

Outokumpu Stainless Tornio Work is an integrated steel plant, which features production of molten ferrochrome at the same site. The refining of the molten ferrochrome is conducted in an ferrochrome converter, which is essentially a modified argon-oxygen decarburisation (AOD) converter. The process control of the ferrochrome converter is based on composition samples and temperature measurements. As the composition analysis takes several minutes, the process model has to determine the blowing scheme without accurate a priori knowledge of the composition of the metal bath. From the perspective of process control, the most important element at the initial stage of blowing is silicon, the content of which has a considerable effect on the energy balance. In the field of steelmaking, disposable emf sensors have several applications as fast and convenient measurement system, which supports conventional composition measurements. Nevertheless, the application of disposable emf sensors in ferrochrome refining has not been studied exhaustively. The objective of this work was to study the application of emf sensors for the measurement of silicon content in refined ferrochrome melts. The employed measuring equipment included a Multi-Lab III central unit, Celox HM-Si probes and additional equipment manufactured by Heraeus Electro-Nite. Because the emf signal is a measure of the oxygen activity, it is an indirect measure of the content of species with highest affinity. In order to determine whether silicon has the highest oxygen affinity, theoretical emf values were calculated for the selected elements (Si, C, Cr and Ti) in the molten ferrochrome. Based on the obtained results it was possible to discard part of the elements in further considerations. The sensitivity of the computational emf value of silicon with respect to temperature and composition was then studied in more detail. Preliminary results suggest that disposable emf sensors can be employed for measurement of the silicon content of ferrochrome in the studied period of refining.