A method for breaking up the crusts are formed in the case of charging of aluminum melt flux electrolysis cells

摘要

In a process for the fused salt electrolysis of alumina reduction to a predetermined level of the alumina content of the bath is detected by a pilot anode, of small base area relative to the total anode, which is subjected to pulses of current whereby the density of the current through the base area is higher than that through the bath anode surface under normal running conditions, the voltage of the pilot anode being measured during the impulse and the impulse being repeated until the measured voltage exceeds a predetermined threshold corresponding to the required level and the applied current density. Pulse durations and repetition times are exemplified. The pilot anode is in mechanical contact with the remainder of the tank anode system but electrically insulated therefrom and is arranged to be connected in a manner producing across its base, the tank anode current density at times other than during the application of a measuring impulse. The detection of a minimum desired alumina level may be used to control alumina replenishment which may be achieved by breaking the bath crust by horizontal anode movement. The content may be kept between desired limits by successively and alternately applying currents producing two differing but predetermined based densities which control the replenishment which is terminated at the higher level indication. The replenishment may be made in small quantities at close time intervals at a rate exceeding the mean consumption rate. The arrangement may be applied individually to the tanks of a group and the successive application of impulses may be automatically controlled, the voltages being measured between the rod of a pilot anode and the positive frame of the following tank. Regulation of the inter-polar distance between electrodes may be achieved in response to the simultaneous determination of tank internal resistance. The impulse may be from a separate direct current source or may be from a circuit in parallel with the main source and the pilot anode may be an insulated insert in a bore within an anode or may be one anode of a group of prebaked anodes. The switching may be achieved by pneumatically operated rocking conductor bars. The measured voltages may be used to operate warning lights.