In Situ Evolution of the Frozen Layer Under Cold Anode

Hall-Héroult electrolysis cell based on prebaked anode technology is continuously disturbed by anode change operations. Insertion of a cold anode in a cell will freeze a layer of molten cryolite under it and thus greatly affects, among others, the thermal balance and electrical distribution. To better understand the evolution of the frozen layer and its impact on the cell performance an experimental campaign has been performed on sixteen anodes having between 15 min and 6 h of operation. The selected anodes were instrumented to keep track of the temperature and voltage drop evolutions while the frozen layer thicknesses were estimated by image analysis after the anodes were removed from the cell after the designated time. Results show that the frozen layer completely disappeared after three hours of operation and before the anode reaches a thermoelectrically steady state.