A Novel Design Criterion for Alumina Feeders in Aluminium Electrolysis Cells

The theoretical possibility of agglomeration-free alumina feeding in aluminium reduction cells is addressed. The treatment is based on calculated times for dissolution of alumina particles and their terminal velocity in the bath. It was found that the dissolution rate from a few hundred grams of alumina kept in dispersion is sufficient to supply the entire cell. To derive a criterion for dispersion as single particles and avoiding agglomeration, two types of consideration were made; I) The volume fraction of solid alumina sinking through the bath at a rate corresponding to the consumption must be considerably below unity, or 2) Particles landing on the bath surface must have time to sink away before they are hit by succeeding particles. The two considerations end up with very similar mathematical expressions. Based on the
derived criteria, normal point feeding produces agglomerates, while continuous feeding to the same surface area may produce single particles.