Modeling cathode cooling due to power interruption

Abstract

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, and ultimately causes the formation of numerous, often deep, cooling cracks on the surface of cathode blocks and in the seams between blocks and ultimately shorten potlife. It had been proposed that these cracks are caused because the strain setup by thermal gradients in the cooling cathode lining exceeds the strain capacity of the cathode, but heretofore there has been no supporting evidence to support this hypothesis. New ANSYS® based thermal cooling models, (2D+ full cell slice model, 3D full side slice model and a 3D full cell quarter) were developed to determine the cathode cooling rates, the differences in the temperature gradients and the resultant stress from cooling cathodes for 24 to 48 hours. The results indicate significant temperature gradients and corresponding stress develop during cooling to cause cracking of the cathode blocks. Reducing the aluminum metal level in cells during cooling was found to reduce the level of stress and thus reduce, if not eliminate the cathode surface cracks.