Physical and Numerical Modelling of Multiphase Flow in a Slag Stabilization Process
Basic Oxygen Furnace (BOF) steelmaking process is one of the main steelmaking processes, during which slag is produced as a by-product. It was reported that approximately 10 million tons of BOF slag is produced annually in Europe. This BOF slag is conventionally disposed through landfilling/dumping, leading to land occupation, environmental impact and a waste of material resource. To avoid that, many efforts have been attempted to reuse the BOF slag. However, the application of the BOF slag is restricted by its volume swelling during natural aging due to the presence of free lime. In order to stabilize BOF slag and to modify slag composition for its high-added value applications, the silica-rich additives/slag modifiers are injected into molten BOF slag with oxygen as carrier gas. Several key issues need to be addressed during this process. 1) metal recovery. A poor metal recovery was found after the FEhS process. This is probably attributed to the breakage of large metallic droplets into fine ones which cannot sediment fast enough to the bottom of the slag pot and hence trap in the slag; 2) mixing behavior. A good mixing is closely related to the gas-liquid slag two-phase flow, therefore, the flow characteristics of this two-phase flow needs to be clearly understood. It is also very important to understand the migration behavior of the additive particle; 3) fluidity of the slag phase. Slag fluidity is of significant importance to the industrial operation. It is greatly influenced by the slag viscosity. The injected slag modifiers (e.g., SiO2 or Al2O3) can alter the slag viscosity by changing the slag structure, therefore improving the slag fluidity. This process closely relates to the dissolution behavior of the slag modifiers.
However, it is very difficult to perform in-situ experiments to understand the metallic droplet behavior (i.e., coalescence and breakage) and the mixing behavior of slag additives/modifier in the slag stabilization process due to the opaque, the high operating temperature and the gas-liquid-solid multiphase coexistence. Therefore, the modelling approaches developed in this work is very beneficial for parametric studies and can expand the industrial operators’ insight into the flow characteristics, leading to optimizing the stabilization process.