A Thermodynamic Study of Eliminating Fluorspar Applications in the AOD Process

Sammanfattning

This study aims to eliminate fluorspar usage by finding alternative flux materials and to test Al2O3 as a potential substitute. An industrial AOD trial was performed in 304 stainless steel production at Outokumpu, Avesta to establish the reference states. Thermodynamic calculations were conducted to evaluate the properties of the slags and to find the optimal slag compositions during the reduction and desulphurization stages. The results show an that increasing Al2O3 content in reduction slag will increase the liquid fraction of the slag and help with desulphurization while increasing the viscosity and the equilibrium Al content in the steel. During desulphurization stage, an increasing Al2O3 content in the slag leads to a poorer desulphurization. However, adding a appropriate amount of Al2O3 can help increase the liquid fraction of the slag and lower the melting temperature, which provides excellent kinetic conditions. Fluorspar can be completely replaced by the optimal slags, leading to an annual reduction of approximately 3765 tons in fluorspar consumption and a cost saving of around 2.05 million USD per year. The optimized slag compositions provide valuable reference for fluorine-free slag design in AOD process and may help to improve the refining efficiency and reduce the refractory wear in stainless steel production.