Modeling Cathode Cooling Due to Power Interruption

Extended electrical power interruptions often result in the shutdown and restart of aluminum cells in potlines. Cooling cells to ambient temperature causes irreversible and non-repairable damage to the carbon cathode lining, ultimately leading to numerous, often deep, cooling cracks on the surface of cathode blocks as well as in the seams between blocks, which shortens potlife. It has been proposed that these cracks occur because the strain set up by thermal gradients in the cooling cathode lining exceeds the strain capacity of the cathode; however, there has been no supporting evidence for this hypothesis until now. New ANSYS® based thermal cooling models were developed, including a 2D full cell slice model, a 3D full side slice model, and a 3D full cell quarter model, to determine cathode cooling rates, the differences in temperature gradients, and the resultant stress from cooling cathodes over a period of 24 to 48 hours. The results indicate that significant temperature gradients and corresponding stresses develop during cooling, causing cracking of the cathode blocks. It was found that reducing the aluminum metal level in cells during cooling reduces the level of stress and thus mitigates, if not eliminates, the cathode surface cracks.