The objective of this work was to develop a process model for the CAS-OB (Composition Adjustment by Sealed argon bubbling-Oxygen Blowing). The CAS-OB is designed to homogenize and control the steel composition and temperature before the casting. In the heating mode (OB) studied here, a refractory bell is lowered and submerged 30 cm below the liquid steel surface of the ladle and under this well-defined sealed volume, oxygen gas is injected to oxidize solid aluminum particles that are fed and molten at the surface. Under consideration were the melting of the solid aluminum particles, the oxidation of pure molten aluminum, and the oxidation of dissolved species, in this case Al, Mn, C and Si, and the solvent Fe. We also considered the formation and oxidation of steel droplets formed in the blowing when they pass through and react with the surface slag and also the reaction of pure aluminum on the top of the slag layer. Based on our simulations, only 30-40% of the chemical energy can be used to heat up the steel. A fraction of 0.8-0.85 of the O2 can be utilized in the process; these values correspond to those obtained in previous work. The main part of the heating energy comes from the oxidation of the fed Al. FeO is primarily an intermediate product of the reactions. The model was tested against industrial trials for steel temperature and compositions of slag and steel, and it succeeded in capturing correct trends and absolute accuracy within the analyzing accuracy.
During ladle stirring, a gas is injected into the steel bath to generate a mixing of the liquid steel. The optimal process control requires a reliable measurement of the stirring intensity, for which the induced ladle wall vibrations have proved to be a potential indicator. An experimental cold water ladle with two eccentric nozzles and eight mono-axial accelerometers was thus investigated to measure the vibrations. The effect of the sensors' positions with respect to the gas plugs on the vibration intensity was analyzed, and experimental data on several points of the ladle were collected for future numerical simulations. It is shown that the vibration root-mean-square values depend not only on process parameters, such as gas flow rate, water, and oil heights, but also on the radial and axial positions of the sensors. The vibration intensity is clearly higher, close to the gas plumes, than in the opposite side. If one of the nozzles is clogged, the vibration intensity close to the clogged nozzle drops drastically (À 36 to À 59%), while the vibrations close to the normal operating nozzle are hardly affected. Based on these results, guidelines are provided for an optimized vibration-based stirring.
In the production of steel, the CAS-OB process is used for composition adjustment, temperature control and removal of various dissolved impurities. In this work we have studied the CAS-OB process with CFD and focused on the behavior of the slag layer, which is produced on the top of molten steel. Dynamic mesh adaption has been applied to resolve the slag layer boundary in a detailed way. As a result the time dependent evolution of the slag layer is presented. The chosen approach to describe the process offers an effective and promising way to study this complex system. In the future this model will be validated against experimental data.
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