Abstract
Some aluminium smelters in Norway occasionally experience hot cell sides and reduced current efficiency during the summer season. The increase in cell side temperatures is typically larger than what would be expected from modelling, where such changes are usually said to roughly follow the ambient temperature. The root cause of this phenomenon is not fully known, even though being subject to substantial research for years. In this paper we discuss different mechanisms that could contribute to such a behaviour. These contributions are theoretically evaluated and analysed in combination with results from targeted experiments and measurement campaigns. Furthermore, a detailed pot room model has been established looking at the effects of ventilation – cooling due to ventilation is probably the most difficult to measure and (perhaps) the easiest to model. The simulations confirm that the pot shell, if seen as isolated with no heat flux change, indeed follows the ambient temperature increase with some dependence on the initial conditions. Our results show that several different mechanisms contribute to higher cell side heat fluxes during summers, some more than others. However, the results also indicate that these mechanisms alone may not explain the observed operational behaviour. A new hypothesis is presented, suggesting that decreased current efficiency as the Anode-Cathode Distance (ACD) is squeezed might be another source for the temperature increase seen.