MATHEMATICAL-MODELING OF ALUMINUM CELLS WITH PREBAKED ANODES .2. CURRENT DISTRIBUTION AND INFLUENCE OF SIDELEDGE

The current distribution at the electrodes in an industrial aluminium cell with prebaked anodes was calculated. The difference between the p rimary and secondary current distribution was determined for three dif ferent gaps between anodes or between anode and sidewall (2.5, 10 and 30 cm). The calculated current densities at the vertical sides of the anode were higher for the secondary current distribution than for the primary (almost double at the uppermost part of the anode), while the differences were much smaller at the cathode (6-20%). If the conductin g carbon sidelining is exposed to the electrolyte it will draw an aver age current density of 0.045 A cm(-2) for a 30 cm distance to the cath ode. If all this current leads to the formation of aluminium carbide w ith subsequent dissolution into the electrolyte, the sidelining will c orrode at a rate of 0.08 cm d(-1) of exposure. The influence of the sh ape and position of the ledge on the anode current distribution was st udied. When the distance between the ledge and anode was greater than 15 cm the shape of the sideledge does not affect the anode current den sities significantly, while the current density at the upper part of t he anode increases with increasing distance.