No abstract

Physical properties of molten slag such as viscosity, density and surface tension have a significant influence on the slag splashing process in an oxygen steelmaking converter. Particularly, viscosity determines the shear forces that rule droplets formation. Besides, stirring of the molten slag bath strongly depends on this property. In this work, the influence of viscosity on the efficiency of slag splashing is explored by means of transient Computational Fluid Dynamics simulations. Several values of viscosity are employed in the computer experiments. In order to quantify the splashing efficiency as function of slag viscosity, an average slag fraction on the converter walls is defined and calculated. CFD results are compared with those of an empirical expression, and at least qualitative agreement is found.

Steelmakers worldwide agree that the most efficient and cost-effective solution in BOF steelmaking is to desulfurize the hot metal between the blast furnace and converter. Various methods are currently in use, among which the Kanbara Reactor (KR, using only lime as a reagent), Magnesium mono-injection (MMI, using only magnesium; also known as the Ukraina-Desmag process) and co-injection (using magnesium and lime/CaC 2) are leading. These three hot metal desulfurization methods are compared based on metallurgy, efficiency, costs and overall performance. Both available data from literature and experience from Danieli Corus engineers is used for this study. The KR process is able to reach low sulfur concentrations (> 10 ppm) in hot metal and has lower reagent costs. However, due to higher Fe-loss and heavy wear the KR process has the highest operational costs. The Magnesium mono-injection process is very fast due to the use of the reactive magnesium as reagent. Major problems with resulfurization (sulfur levels below 50 ppm cannot be reached) and the violence of the process made that this process could never get a firm foothold in the western steel industry. The co-injection process with magnesium and lime proves to be able to combine the best of both worlds. It can reach low sulfur concentrations and desulfurize fast. Co-injection is also the most flexible and cost effective.

The way in which slag density influences the slag splashing phenomenon in an oxygen steelmaking converter is numerically analyzed in this work. Several values of the density of the slag are considered, and their effect on the global mass balance and slag average volume fraction on the sidewalls of the converter is studied using isothermal, two-dimensional transient computational fluid dynamics simulations. Diameter of the slag drops is determined from the slag density and the impact velocity of the nitrogen jet. Besides, the effect of the nitrogen jet Mach number on the slag splashing is simulated and discussed. A qualitative comparison between the computer simulations and results from the literature is made.

An improved mathematical model to describe the decarburization process in basic oxygen furnaces for steelmaking is presented in this work. This model takes into account those factors or parameters that determine the bath-oxygen impact area, such as the cavity depth, the lance height, the number of nozzles and the nozzles diameter. In the thermal issue, the model includes the targeted carbon content and temperature. The model is numerically solved, and is validated using reported data plant. The oxygen flow rate and the lance height are varied in the numerical simulations to study their effect on the carbon content and decarburization rate.