Condicionamento de escórias em forno elétrico a arco para otimização das condições de espumação da escória e refino do aço

Abstract

Currently the greatest challenge for the steel industry is to increase the production in a sustainable way in order to be competitive with the Asian and also the subsidized products in the global market, while causing the least possible environmental impact due to their activities. Hence, the smelting shops, steel-producing unit in mini-mills (Electric Mills), employ significant effort to improve the electric arc furnace efficiency, which is responsible for melting and carrying out the first stages of the steel refining. The appropriate formulation and conditioning of the electric arc furnace slag enhance its foaming, achieving its maximal volume without increasing flux additions, and consequently decreasing the thermal losses, steel impurities, process time, energy and refractory consumption. In the present study, the process information of six different electric steel plants was collected. A mass balance coupled with thermodynamic models was created for each plant in order to determine the lowest cost flux recipe, given the steel impurity restrictions, MgO saturation and slag viscosity, both prone to foaming. Magnesia rich material was used as the MgO source, because of its refractoriness oxide characteristics, such as high melting point and lower solubility. Due to these properties, a small addition of the MgO-rich material, calculated by using mass balance and thermodynamic models, allows the slag to maintain its viscosity and saturation required for foaming. Furthermore, each formulation and recipe in particular was tested in their respective plant. The experimental results showed a considerable improvement in furnace thermal efficiency, electrical energy savings, process time, refractory wear and steel quality. The latter is related to improvements in the final slag composition properties, which was also assessed by using thermodynamic calculations. The calculations showed a positive relation between the CaO activity and MgO content in the slag, increasing its desulfurization capacity, as well as a strong relation among the precipitated MgO amount and the effective viscosity (considering solid and liquid phases) of the slag, all of them correlated and basicity dependent.