Understanding the mechanisms of bath carry-over with molten aluminium in smelters

Tapping of Hall-Heroult cells has always been associated with simultaneous uncontrolled aspiration of a significant amount of electrolytic bath with molten aluminium. The bath carried over with molten metal has numerous negative impacts on tapping tube blockage and crucible cleaning, as well as on downstream metal processing steps such as metal pretreatment and furnace operations and costs. Over the years, few studies have been done to understand die mechanisms responsible for bath aspiration during tapping. This paper presents the experimental work carried out at the Arvida Research and Development Centre using physical modelling to develop and understand the key parameters and mechanisms responsible for bath aspiration. The importance of integrating metal circulation patterns in the cell will be exemplified. Effects of key operating parameters such as tapping mass flow rate and tapping tube positioning will be presented. Correlation with industrial results will also be discussed.