CHLORINE FLUXING FOR REMOVAL OF MAGNESIUM FROM MOLTEN ALUMINUM - PARTII - MATHEMATICAL-MODEL

This second part of a two-part article presents a mathematical model f or the ''chlorine fluxing'' of aluminum alloys, in particular, for the ''demagging'' of Al-Mg alloys such as those resulting from the recycl ing of used beverage cans. The model is based on the experimental resu lts described in Part I and, in conformity with those results, assumes that neither the reaction kinetics at the melt-bubble interface, nor mass transfer on the gas side of that interface, are rate determining. With the introduction of one correction factor (applied to the surfac e renewal model for mass transfer on the melt side of the melt-gas int erface), the model fitted the experimental data well, once measured va lues for the bubble size and rise velocity were introduced. The model was then used to predict the progress of demagging operations on an in dustrial scale. Computed results for these larger melts suggest that g ross emissions of chlorine/chlorides are avoidable in bringing the mag nesium content down to a critical value (which depends on operating ch aracteristics such as bubble size). A multiple-step strategy is sugges ted when a batch of alloy is to be brought to yet-lower magnesium leve ls. In that strategy, the chlorine content of the injected gas is redu ced as the processing of the batch proceeds. The predicted effects of other operating changes (deeper nozzle submergence, broad bubble size distribution, etc.) are reported.