Patent ID: 8123928
Filing Date: 2012-02-28
Classification: C25C

Abstract:
1. A process for shutting down an operating electrolytic cell for the production of aluminium, the electrolytic cell having a cathode block, a depth of molten aluminium layer covering the cathode block, and a depth of molten electrolytic bath covering the molten aluminium layer, a plurality of anodes disposed for vertical movement into and out of the electrolytic cell to vary an anode-cathode distance separating a bottom surface of the anodes from a top surface of the molten aluminium layer, electrolysis electric power being applied to the anodes to reduce alumina fed to the electrolytic cell and produce aluminium metal on the cathode block, the process comprising: a) gradually moving downwardly the anodes from an operating position where the bottom surfaces of the anodes are immersed in the electrolytic bath to a cooling position where the bottom surfaces are immersed in the molten aluminium layer; b) allowing the electrolytic cell to cool and moving up and down the anodes periodically on a short distance to break a peripheral crust of solidifying electrolytic bath forming at a periphery of the electrolytic cell during the cooling step; c) after the electrolytic bath is completely solidified into a cohesive mass, raising the anodes to create a space between a bottom surface of the solidified electrolytic bath and a top surface of molten aluminium layer; and d) allowing the electrolytic cell to cool until the aluminium layer solidifies.