Reduction cell control system

Claim 2

The method of claim 1 in which the cell has adjustably spaced electrodes, including the step of: periodically adjusting the electrode spacing of said cell, thereby changing the value of cell resistance at a particular bath alumina concentration; and, wherein said sensing of a function of bath alumina concentration comprises monitoring the cell resistance during the interval between successive adjustments of the electrode spacing.

Claim 3

The method of claim 1 wherein said low rate of feed is substantially zero.

Claim 4

The method of claim 4 wherein said regulating of the rate of feeding alumina into the bath includes operating the cell alternately with and without feeding, and initiating further feeding at said high rate of feed in response to changes in cell resistance during said interval between successive adjustments of electrode spacing.

Claim 6

The method of claim 6 in which the cell has adjustably spaced electrodes, including the step of: periodically adjusting the electrode spacing of said cell, thereby changing the value of cell resistance at a particular bath alumina concentration; and wherein said sensing of a function of bath alumina concentration comprises monitoring the cell resistance during the interval between successive adjustments of the electrode spacing.

Claim 7

The method of claim 7 wherein said sensing further comprises producing a feed control signal for indicating changes in cell resistance during said interval; and wherein said regulating includes operating the cell alternately with and without feeding, said low rate of feed being substantially zero, and changing from operation without feeding to operation at said high rate of feed in response to said feed control signal.

Claim 8

In the operation of an electrolytic cell for the production of aluminum wherein alumina dissolved in a molten salt bath is reduced to aluminum metal by passing electric current through said bath between adjustably spaced electrodes, the cell resistance being affected by the spacing of such electrodes and by variations in bath alumina concentration, the method which comprises: periodically adjusting the cell''s electrode spacing thereby changing the value of cell resistance at a particular alumina concentration of the bath; monitoring the cell resistance during the interval between successive adjustments of the electrode spacing, said monitoring being effective to detect the occurrence of a transition from decreasing to increasing resistance of the cell, each such transition indicating that the cell is tending toward either an overfed condition or an underfed condition, but, when it occurs during operation of the cell without feeding, indicating a tendency toward an underfed condition; producing a feed control signal for indicating the occurrence of said transition from decreasing to increasing cell resistance when it occurs during operation of the cell without feeding; and, feeding alumina into the bath in response to said signal as electrolysis proceeds, continuing the operation of said cell following said feeding, and initiating further feeding upon a recurrence of said signal.

Claim 9

The method of claim 9 wherein said monitoring of cell resistance includes generating output signals proportional to cell resistance; and, producing said feed control signal in response to said output signals which indicate a transition from decreasing to increasing resistance of the cell when said transition occurs during operation of the cell without feeding.

Claim 10

The method of claim 10 wherein said output signals are proportional to (E-k/I); E being the voltage across said cell, I being the line current passing through said cell, and k being a predetermined constant voltage.

Claim 11

The method of claim 9 including the step of regulating said feeding of alumina into the bath to maintain the cell resistance substantially constant during the period between successive adjustments of the electrode spacing.

Claim 12

The method of claim 9 which includes discontinuing said feeding of alumina into said bath prior to the occurrence of increasing resistance of the cell during feeding.

Claim 13

The method of claim 9 wherein said continuing operation of the cell proceeds without feeding.

Claim 14

The method of claim 9 wherein said feeding proceeds to the extent that subsequent operation of the cell without feeding results in decreasing cell resistance.

Claim 15

In operation of an electrolytic cell for the production of aluminum metal by passing electric current through said bath between adjustably spaced electrodes, the cell resistance being affected by the spacing of such and by variations in bath alumina concentration, the method which comprises: periodically adjusting the cell''s electrode spacing, thereby changing the value of cell resistance at a particular alumina concentration of the bath; producing a feed control signal for indicating changes in cell resistance during the interval between successive adjustments of the electrode spacing; feeding alumina into the bath in response to said feed control signal; and, regulating said feeding to counteract said changes in cell resistance, thereby maintaining the cell resistance substantially constant over the period between said adjustments of the electrode spacing.

Claim 16

The method of claim 16 wherein said regulating includes feeding alumina into the bath and alternately discontinuing said feeding or reducing the rate of feeding to prevent overfeeding and to avoid upset conditions of the cell due to excessive feeding.

Claim 17

The method of claim 17 in which said feeding and adjusting of the electrode spacing are effective to mainTain the cell resistance substantially constant over the period between successive tapping generations to remove accumulated aluminum.

Claim 18

The method of claim 15 wherein said feed control signal is provided for indicating the occurrence of a transition from decreasing to increasing resistance of the cell during a period of operation without feeding.

Claim 19

In the operation of an electrolytic cell for the production of aluminum wherein alumina dissolved in a molten salt bath is reduced to aluminum metal by passing electric current through said bath between adjustably spaced electrodes, the cell resistance being affected by the spacing of such electrodes and by variations in bath alumina concentration, the method which comprises: periodically adjusting the cell''s electrode spacing thereby changing the value of cell resistance at a particular alumina concentration of the bath; and, feeding alumina into the bath, monitoring the cell resistance as operation of the cell proceeds, and regulating subsequent feeding to counteract changes in cell resistance during the interval between successive adjustments of the electrode spacing.

Claim 20

The method of claim 20 in which periodic adjustments of the electrode spacing are made at substantially the same bath alumina concentration.

Claim 21

The method of claim 20 including the step of: selecting a predetermined value of cell resistance corresponding to the desired A-C distance for operation of the cell at a particular bath alumina concentration; and, wherein said adjusting of the electrode spacing is effective to maintain the cell resistance close to said predetermined value as operation of the cell proceeds.

Claim 22

The method of claim 20 wherein the cell has a cathode and a plurality of prebaked carbon anodes; and in which said regulating includes operating the cell alternately without feeding or at reduced feeding to prevent overfeeding and to avoid upset conditions of the cell and increased cell resistance due to excessive feeding.

Claim 23

The method of claim 23 including the steps of: operating the cell under stable conditions at substantially constant electrode spacing; and, varying the bath alumina concentration to find an optimum concentration providing substantially minimum cell resistance; and, wherein said regulating of subsequent feeding is effective to maintain the bath alumina concentration close to said optimum concentration as operation of the cell proceeds.

Claim 24

The method of claim 20 which includes conducting said monitoring of the cell resistance following a feeding operation effective to achieve increased bath alumina concentration such that continued operation of the cell following said feeding results in decreasing bath alumina concentration over a period of decreasing cell resistance; producing a feed control signal for indicating the occurrence of a transition from decreasing to increasing resistance of the cell as operation of the cell proceeds at substantially constant electrode spacing; and, initiating further feeding in response to said signal.

Claim 25

In the operation of an electrolytic cell for the production of aluminum wherein alumina dissolved in a molten salt bath is reduced to aluminum metal by passing electric current through said bath between adjustably spaced electrodes, the cell resistance being affected by the spacing of such electrodes and by variations in bath alumina concentration, the method which comprises: feeding alumina into the bath to achieve increased bath alumina concentration such that continued operation of the cell following said feeding in decreasing bath alumina concentration over a period of decreasing cell resistance; monitoring cell resistance as operation of the cell proceeds at substantially constant electrode spacing; producing a feed control signal for indicating the occurrence of a transition from decreasing to increasing resistance of the cell; and, initiating further feeding in response to said signal.

Claim 26

Apparatus for the production of aluminum comprising: a. an electrolytic cell for reducing alumina dissolved in a molten salt bath, including adjustably spaced electrodes for passing electric current through said bath; b. control means for producing a feed control signal responsive to changes in cell resistance during a period in which the anode-cathode spacing of the cell remains substantially constant; and, c. feeder means for introducing alumina into the bath in response to said feed control signal.

Claim 27

Apparatus according to claim 27 wherein said control means include means providing output signals proportional to (E-k)/I; E being the voltage across and I the line current passing through the cell, and k being a predetermined constant voltage.

Claim 28

Apparatus for the production of aluminum, comprising: a. An electrolytic cell for reducing alumina dissolved in a molten salt bath, including adjustably spaced electrodes for passing electric current through said bath; b. control means for detecting changes in cell resistance, and for generating a feed control signal responsive to said changes during a period in which the electrode spacing remains substantially constant; and c. feeder means for introducing alumina into the bath in accordance with said feed control signal.

Claim 29

Apparatus according to claim 29 wherein said control means are operative to actuate said feeder means upon detecting the occurrence of a transition from decreasing to increasing resistance of the cell.

Claim 30

Apparatus for the production of aluminum, comprising: a. an electrolytic cell for reducing alumina dissolved in a molten salt bath, including adjustably spaced electrodes for passing electric current through said bath; b. means for adjusting the cell''s electrode spacing in response to a position control signal; c. means for introducing alumina into the bath in response to a feed control signal; and d. control means responsive to changes in cell resistance for producing said position control signal, and for producing a feed control signal responsive to changes in cell resistance during a period in which the anode-cathode spacing of the cell remains substantially constant.