Process for accurately maintaining a low alumina content in an e

Details Process for accurately maintaining a low alumina content in an e Process for accurately maintaining a low alumina content in an e

1986-05-05

1987-03-31

Williams, Howard S.

Chemistry: electrical and wave energy

Processes and products

C25C 306

Patent

active

046541292

ABSTRACT:
A process is disclosed for accurately maintaining a low alumina content of between 1 and 4.5% in a cell for the production of aluminum by electrolysis in the Hall-Heroult process. According to the invention, a control parameter P=-1/D(dR.sub.1 /dt), is determined, wherein D is the variation in the alumina content of the electrolytic bath in % weight per hour, R.sub.1 is the internal resistance of the cell, and t is the time. A series of operations is then carried out in a repeated cycle, starting with the cell being fed alumina at a nominal rate which is substantially equal to the quantity consumed by electrolysis. At periodic intervals, an over-supply of alumina is added in order to enrich the bath, and the over-supply is continued for a preset time during which dR.sub.1 dt is negative. The feed rate is then reduced to less than the nominal feed rate, during which time dR.sub.1 dt passes through zero to become positive and the regulation parameter P, the value of which tends to rise, is measured often. The successive values of P are compared with a required preset value Po. As soon as P equals Po, the feed rate is returned to the nominal feed rate and a new cycle is recommenced.

REFERENCES:
patent: 3629079 (1971-12-01), Bristol
patent: 4431491 (1984-02-01), Bonny et al.

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