Effect of electrochemical changes on the heat balance in aluminium smeltins cells

Abstract The dual operating problems of anode effect and sludging, in smelting cells, highlight the central concept of this paper, that is, the electrochemical parameters which determine the rate and efficiency of the electrolysis also control the overall cell heat balance. An additional constraint is present since the material balance, and the necessity of maintaining it through bulk feeding, exerts a strong influence on those same electrochemical parameters. Low concentrations of alumina in the bath result in excessive polarization and anode effect. Overfeeding gives rise to sludging and voltage instability. Even during stable operation the conductivity, decomposition voltage and polarization potentials respond to the electrochemical depletion of the alumina. These interactions place severe limits on the controllability of the batch fed smelting cell so that its operation is essentially dynamic. New technology now emphasizes the concept of continuous or 'point feeding' of the alumina.