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Mathematical and physical models of water deoxidation in a batch aluminum degassing reactor using the rotor-injector technique were developed. The mathematical model was successfully validated against measured degassing kinetics. The physical model was employed to perform a process analysis using a two-level factorial experimental design to determine the influence of gas flow rate, impeller angular velocity, and gas injection points on gas consumption efficiency and degassing kinetics. A combination of higher rotor speeds and gas flow rates results in fast degassing kinetics. However, moderate gas flow rates are recommended to save gas.

An experimental study of the gas-liquid dynamics in a water model of an aluminum ladle was conducted. The rotor degassing performance was evaluated for two commercial rotor-injector devices compared to a new rotor design. In this work, the influence of the turbulent properties of the flow fields on the bubble size distribution is analyzed for a better understanding of its impact on the degassing efficiency in aluminum refinement operations. The degassing process was analyzed by two different methods: (a) a high-speed camera was used to obtain the bubble size distribution into the container; and (b) the particle image velocimetry technique (PIV) was employed to obtain the liquid flow properties. It was found that the rotor geometry plays an important role on the average size and distribution of the bubbles. The energy dissipation rate contours show significant differences for the distinct rotors tested. These hydrodynamic states and bubbles distribution dominate the kinetic and efficiency of the degassing processes. It was shown that the new rotor configuration enhances the degassing kinetics, due to a more suitable bubble dispersion compared to the commercial rotors tested.

A mathematical model is developed to describe deoxidation of water in a physical model of a batch aluminum degassing reactor equipped with the rotor-injector technique, assuming that deoxidation kinetics of water is similar to dehydrogenization of liquid aluminum. Degassing kinetics is described by using mass transport and mass balance principles by assuming that degassing kinetics can be characterized by a mass transfer coefficient, which depends on the process variables. The transport coefficient and the average bubble diameter are estimated with correlations reported in the literature for similar gas-injection systems. The water physical model helped to validate the mathematical model and to perform a process analysis by varying: 1) Gas flow rate (20 and 40 l/min); and 2) Impeller’s angular velocity (290 and 573 rpm). Results from the model agree well with measurements of deoxidation kinetics at low impeller rotating speeds. At high rotating speeds the model is still valid but less reliable because it does not take into account the formation of the vortex at the free surface. Nevertheless, the model provides predictions of the influence of every operating parameter and it can be used as a good approximation for real systems.