Numerical Assessment on Effects of Longitudinal Slots and Its Application in Aluminium Reduction Cells

The effects of longitudinal slots on gas evolution and bubble-driven flow in Hall–Héroult cells by a computational fluid dynamics (CFD) model have been investigated. A similar flow pattern in the anode-to-cathode distance (ACD) or spacing was shown between unslotted and slotted cases, but more complex local flow and gas evolution behavior beneath the anodes are derived from the slots. The gas accumulates in the slots/anode gaps and is released from these paths, and over 50% of gas bubbles escape from the slot tops in the slotted case. The design of the current applied slots in smelters was optimized based on CFD simulations, and it was shown that a trisected slotted design along the width direction produced the minimum ‘gas holdup’ in the ACD regions. The effects of the slot-inclined direction on bath flow and gas holdup were further investigated to quantitatively evaluate the easily made mis-operation in the anode change process during commercial production. Based on the findings of this analysis, using the horizontal slot design instead of the current typical inclined slot design is recommended, as it avoids the issue of operator error while still providing a similar benefit to the inclined slots. At the end of this paper, an industrial application of slotted anodes is discussed as an example to indicate that the slotted anode technology should be carefully applied, especially for smelters with poor quality anodes.