THERMAL MANAGEMENT OF ALUMINIUM CELL BATH CRUST

Abstract

When a consumed carbon anode in an aluminium electrolysis cell is replaced, the solid crust covering the anode and the bath is removed and transported in hopper cars to a cooling area where it remains for a period of one to four days, or more, to cool from a temperature of approximately 900°C to an acceptable temperature for autogenous milling, gas cleaning, product classification, and recycle to the process. This article addresses the possibility of processing the hot crust material more rapidly by using a separate or combined crushing/heat exchange system. Results of mechanical and thermal tests are presented and discussed. Mechanical tests demonstrated that it requires much less force to crush hot crust than cold crust samples. The thermal tests consisted of submitting both a single block and a bed of particles of the crust material to heating and cooling cycles to determine the convective heat transfer coefficient and the thermal diffusivity. The values obtained for the heat transfer coefficients were similar to those predicted by correlations, while the thermal diffusivity was larger than expected. Based on the results, a number of strategies to manage the crust material were proposed and analyzed from the perspectives of the plant conditions. Some of these options are briefly discussed and simulated. The results of the simulations indicate that in order to significantly reduce the cooling time, the size of the crust pieces should be reduced prior to cooling.