ON THE DEGASSING KINETICS IN A LADLE EQUIPPED WITH A ROTATING IMPELLER ASSISTED THROUGH PHYSICAL MODELING

A full scale water physical model of an aluminum degassing crucible was used to analyze the kinetics and removal efficiency of dissolved oxygen from water by N2 injection, similar to hydrogen removal from liquid aluminum. Different process parameters were studied, such as impeller design (two impellers designs were used, named “B” and “C”), rotation velocity, and gas flow rate, to understand the effects of these variables on the degasification kinetics. Oxygen removal from water follows a first order kinetics mathematically represented by an exponential decay. The slope parameter “a” was used to characterize degassing kinetics, which corresponds to a global mass transfer coefficient used as an operational kinetic parameter. Results show that as rotation velocity, gas flow rate and geometry complexity are increased, oxygen removal kinetics increases. Nevertheless, the main contribution of this work is the introduction of a novel gas injection design, consisting in gas injection through a pipe placed below the impeller instead of the conventional injection through the impeller. This novel technique was tested and compared to the traditional technique, and it was found that under similar operating conditions the novel technique yields an important increase on “a” values up to 45% for commercial impellers (impellers “B” and “C”). Hydrodynamics of the system was also modified considerably with the introduction of this novel technique: vortex size was decreased and bubble distribution improves. These changes are related to the pump up capacity for each impeller.