Method of controlling aluminum reduction cell with prebaked anodes

Abstract

In the method of controlling an aluminum reduction cell with prebaked anodes an area of reduced alumina concentration is defined in the cell by measuring the present electrical current values in at least one anode of the cell independently of other anodes. Upon detection of the electric current reduction in this anode, the rate of alumina feeding is increased into a bath of the cell at the area of reduced alumina concentration.

Description

FIELD OF THE INVENTION [0001] This invention relates to aluminum production by electrolysis of alumina. More particularly, the invention relates to control processes for electrolytic cells utilizing prebaked anodes and improving the respective control of alumina feeding systems. BACKGROUND OF THE INVENTION [0002] In the conventional operation of electrolytic cells in which alumina, Al2O3 is reduced to aluminum, Al, the alumina is added to the cell on a prescribed time schedule. In recent years, operation of aluminum production cells and control of the alumina concentration in the electrolytic bath have been significantly and progressively automated. This automation is necessary to obtain the desired high current efficiency operational process flow of the cell. [0003] An essential factor affecting process flow of an aluminum electrolytic cell, which produces aluminum by the electrolysis of alumina dissolved in molten cryolite, is the rate of introduction of the alumina into the bath....

AI Technical Summary

Benefits of technology

[0011] The method of the invention can be utilized to control processes in the aluminum reduction cells with prebaked anodes, so as to improve the quality of controlling the alumina feeding systems. The method consists of the steps of measuring present electric current, comparing the value of the present electrical current with the predetermined values thereof, and maintaining such present values within preset limits by regulating the amount of alumina charged into the cell. Further, in the method of the invention, an area of reduced alumina concentration is identified in the cell by measuring the existing, present electrical current values. The area of reduced alumina concentration can be also identified by reviewing the rate of increase of the back EMF value at each anode independently of other anodes in the cell. Then, a control a signal is generated by the control system to a specific feeder of the alumina feeding system to raise alumina concentration in the area of reduced alumina concentration to predetermined levels.

[0013] It is a further object of the invention to eliminate unplanned anode effects and alumina aggregation of the cathode bottom and to ultimately improve performance of the aluminum reduction process.

Problems solved by technology

Operating with high sludge accumulations eventually results in decreased metal production.

On the other hand, operating with a deficiency of alumina or with too little alumina being consistently added to the bath requires extra energy.

An alumina deficiency causes the occurrence of the ‘anodic effect’ or ‘racing’ phenomenon, which causes an abrupt increase in the voltage at the terminals of the cell, which can go from 4 to 30 or 40 volts, and which has repercussions on the entire production process.

Such control systems must allow no deviation because both repetitive occurrences of anode effects and excessive sludge interfering with the cathode operation are technologically unacceptable.

The disadvantage of the above discussed method is that the control algorithm is too undeveloped resulting in low quality stabilization of the thermal energy and the electrochemical conditions of the process.

A substantial drawback of this method is that of depending upon Ucell=f (CAl), which is a function nonlinear in nature over (minimum) the range of CAl=3.5-4.5%.

Operational experience suggests that the use of the above-discussed prior art method does not always bring positive results.

Images