Understanding Scale-Up of High-Current Electrodes

A simple and generic model for the heat distribution in electrodes for primary metal production has been investigated. The equations have been analyzed focusing on understanding the scale-up of electrodes under both direct current (DC) and alternating current (AC) conditions. The analysis provides a theoretical foundation for Westly’s empirical scale-up rule. For graphite and small carbon electrodes, the current-carrying capacity is limited by the ohmic heating, which controls the lateral heat flux and the temperature at the electrode periphery. For these electrodes, the current capacity is higher for DC than for AC. For large carbon or Søderberg electrodes, the electrode current must be limited to avoid large thermal stresses and subsequent breakages, especially in connection with shutdowns or considerable current fluctuations. Thermally, the current capacity is then limited by the maximum temperature difference between the center and the periphery. For this case, AC electrodes can carry more current than DC.