US3400062A - Method of controlling aluminum content during aluminumg electrolysis - Google Patents

Method of controlling aluminum content during aluminumg electrolysis Download PDF

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US3400062A
US3400062A US459601A US45960165A US3400062A US 3400062 A US3400062 A US 3400062A US 459601 A US459601 A US 459601A US 45960165 A US45960165 A US 45960165A US 3400062 A US3400062 A US 3400062A
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Prior art keywords
anode
sensing
pilot
alumina
during
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US459601A
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Guy D Bruno
Cheldelin Neal
Wells Nathaniel
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Howmet Aerospace Inc
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Aluminum Company of America
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Priority to NL130687D priority Critical patent/NL130687C/xx
Application filed by Aluminum Company of America filed Critical Aluminum Company of America
Priority to US459601A priority patent/US3400062A/en
Priority to NL6607293A priority patent/NL6607293A/xx
Priority to NO163188A priority patent/NO121071B/no
Priority to BR179961/66A priority patent/BR6679961D0/pt
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/20—Automatic control or regulation of cells
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts

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  • This invention relates to the art of fused salt electrolysis, and, more particularly, to the control of the metallic compound or solute constituent of a fused electrolyte in an electrolytic cell producing molten metal, Iwith reference to maintaining the concentration of the 4solute within closely prescribed lirnts.
  • the invention is directed to improved method and control means for the electrolytic production of aluminum.
  • yAs is well known, commercial production of aluminum is by electrolysisrof molten cryolite-alumina salts in high amperage electrolytic cells of either the pre-baked anode or the continuous, self-baking Soderberg anode type.
  • electrolysisrof molten cryolite-alumina salts in high amperage electrolytic cells of either the pre-baked anode or the continuous, self-baking Soderberg anode type.
  • a multiplicity of like cells are arranged in what is called a potline, in series electrically, and direct current of the order of fifty thousand to one hundred thousand amperes, 'and more, is used in the cells, depending upon their size, with a voltage drop of generally between 4 and 6 volts across each cell.
  • the anode effect is known as an ano'dic spark or arc discharge, and is characteristic of the electrolysis of molten salts' and especially of the electrolysis of cryolite-alumina salts. It is stopped an-d normal electrolysis restored by the expedient of breaking the yfrozen top crust ofbath and adding and stirring alumina into the bath.
  • the invention further provides in fused bath electrolysis of alumina-cryolite compounds a method of operation which controls the alumina content of the bath within closely prescribed limits so as to secure continuous normal electrolytic action and improved efficiency.
  • Another object of the invention includes the provision of novel method and means for eliminating the occurrence of anode effect in a molten salt bath electrolytic cell susceptible thereto; ⁇ for sensing and controlling the concentration of the solute constituent of such molten salt bath so as to keep the solute concentration within closely prescribed percentage limits; and especially for avoiding the decrease in the efficiency of electrolysis, as exemplified by the increase in power consumption and reduction in production from an aluminum reduction cell due to the large increase in cell voltage as a result of depletion of dissolved alumina in the electrolyte of the cell to a critical concentration or the inefficiency of the process when the cell has an excess of alumina or is sick.
  • a further object of the invention is to provide for the electrolytic reduction of aluminum under a pilot anode method of alumina control to secure continuous electrolysis with improved efficiency, and additionally to provide new and improved mode of pilot anode operation to minimize consumption of the pilot anode.
  • Still another object is to provide for pilot anode sensing periodically of the dissolved alumina concentration in a fused cryolite electrolytic bath at predetermined periods and for responsively thereto selecting the rate of alumina feed to the bath accordingly as more is needed to be added either at a normal or slow rate or at an accelerated or fast rate to keep the concentration within prescribed limits between successive periods.
  • FIG. 1 is a diagrammatic representation of a multiple prebaked anode type of aluminum reduction electrolytic cell or furnace equipped with a pilot anode and an automatic alumina or ore feeder, and schematically showing electrical power supply to the cell and the pilot anode;v
  • FIG. 2 is a schematic, across-the-line circuit diagram of a control system for controlling the operation of the pilot anode and, in turn, the operation of the cell in accordance with the present invention
  • FIG. 3 is a circuit detail of another form of regulated ore feed which may be used
  • FIG. 4 is a view similar to FIGS. 1 and 2 combined, but showing a separate or external power supply for the pilot anodeand a modified and simplified control system for the pilot anode in the practice of the invention under pilot anode control, and
  • FIG. 5 is a timing diagram of the program timer employed in the control system of FIG. 4.
  • an aluminum reduction electrolytic cell is operated with tight control about a preselected percentage content of the alumina in solution in the electrolyte under a pilot anode control program consisting essentially of a standby phase and a sensing phase.
  • a pilot anode is provided which is immersed or dipped into the electrolyte of the cell to a given immersion depth.
  • the pilot anode is maintained on continuous anode effect, which condition has been discovered to be essential in order to minimize consumption thereof and thus make the pilot anode control practical and reliable.
  • alumina is added to the electrolyte or bath at the slow or the fast feed rate depending on the selection made at the immediately preceding sensing phase.
  • the anode effect on the pilot anode is eliminated preferably by reversing the current flow through it. Then forward current calculated to give a specific contol current density on the pilot anode is applied thereto, this current density exceeding that on the working anode or anodes of the cell. Accordingly, an anode effect will or will not be induced on the pilot anode depending on the percentage of alumina in solution in the electrolyte.
  • the rate of alumina feed is selected to be the slow rate and, at the end of the sensing phase, the current density on the pilot anode is increased to such value as to induce an anode effect thereon for the next standby period.
  • the rate of alumina feed is selected to be the fast rate and, at the end of the sensing phase, the current density is again increased to assure maintenance of the anode effect during the next standby stage.
  • slow feed rate means a rate calculated to deliver less alumina than the cell will consume by electrolysis during a standby stage
  • fast feed rate means a rate calculated to deliver more alumina than the cell can consume during such stage.
  • numeral 1 denotes a conventional aluminum reduction cell or pot which may ⁇ be connected in series with like cells 1', 1 in a potline and supplied with direct current power from a source (not shown).
  • Numeral 2 denotes the carbon cathode lining of the cell, 3 the molten aluminum pool cathode, 4 the molten electrolyte or bath consisting essentially of dissolved aluminum oxide or alumina and cryolite, .along with such additives as are customarily employed in a commercial Hall bath, and 5 the carbon anodes which dip into the bath and are periodically adjusted vertically to the proper working distance with respect to the top of the cathode.
  • the top crust normally present is indicated at 6.
  • alumina may be added to the bath by operation of a feeder 7 of any conventional type.
  • the one shown includes an air-cylinder operated crust-breaking plugger 8, controlled by solenoid operated valve 9, and measuring means 10 having inlet and outlet valve means operatively connected to the plugger for discharging a measured quantity of alumina each time the plugger is actuated.
  • electrolysis proceeds with the current flowing through the electrolyte from the anode to the cathode, thereby decomposing the aluminum oxide into metallic aluminum with evolution of gases at the anode which eventually escape from the cell.
  • the alumina in solution is used up in direct propor tion to the production of metal and more must be introduced into the bath without overfeeding it, so as to avoid development of a sick cell. Due to the prevalent variable conditions, it has been found not possible to feed the alumina precisely in accord with the consumption rate so underfeeding is the rule with sulferance of anode effects and all of the attendant disadvantages and adverse effects.
  • electrolysis is carried out with continuous control of the alumina in solution within a narrow range of a preselected percentage level, such as 41/2 percent, for example, by pilot anode sensing of the alumina concentration of the bath at regular time intervals and selecting one of two alumina feed rates in accord with the results of each sensing operation.
  • apilot anode 12 suitably of carbon or graphite, or other suitable conductive material, is adjustably and insulatedly mounted at the pot 1 with its lower end dipped into the bath.
  • the current density is a function of the extent it is immersed or dipped into the bath, it is desired to set it to a given immersion depth, a depth of about 4 inches having been found to be quite satisfactory.
  • this may be varied within limits, as also may the size and shape of the pilot anode.
  • it should be as small as possible, such as between 1A in. and 2 in., so that the surface area wetted by the bath is limited, thereby reducing its current requirements and operating power cost.
  • Power for the pilot anode may be taken or shunted from the potline bus several pots upstream from pot 1, as at tap 13, to make available a voltage between l2 and 20 volts across the pilot anode-cathode circuit of'pot 1.
  • This forward current supply is arranged as a dual or variable voltage source for the pilot anode by means of a voltage dropping ballast resistor 14 having high voltage tap A and low voltage tap B, both adjustable and preset for impressing preselected high and low voltages on the pilot anode for the purposes hereafter described. Selection of the voltage taps is by means of contacts CRZ in circuit lines 1A and 1B of FIG. 1, while contactor CR in line 1A is operable to open and close the circuit between contacts CRZ and the pilot anode.
  • Contaetor CR is normally energized, its energizing circuit extending from power tap 13 through voltage adjusting resistor 15 in line 2B, normally closed contacts CR1 in line 2A, its operating coil to tap 16 of the cathode bus of pot 1.
  • the pilot anode is adapted to be shunted directly to tap 16 to place it at cathode potential for reverse current flow through it by means of contactor RC whose contact controls the reverse current circuit, this RC contactor being controlled by normally open contact CR1 in line 2B. It is to be noted that by means of the contacts CR1 in the lines 2A and 2B, only contactor CR or contactor RC can be energized at any one time.
  • the pilot anode is adapted for connection to tap 16 through a sensing circuit that includes normally open contact CRS and normally closed contact TR7 in line 1A and a sensor relay CR4, which senses and is responsive to the voltage on the pilot anode when the sensing circuit is closed as hereafter described.
  • the electrolysis is carried out under a pilot anode control program sequence which comprises the following three steps or conditions, each of preselected duration:
  • Standby stage or period- This stage is of multiple minutes duration, during which a first or high voltage is impressed on the pilot anode and it is on anode effect, whereby its rate of consumption is minimized, it is kept at operating temperature and in a condition ready to be used for sensing.
  • said first or high voltage means a voltage which causes the resultant current flow to provide a current density on the pilot anode, in amps./ sq. in. of bath wetted area thereof, suflicient to induce and maintain an anode effect thereon. This voltage is always greater than the low or sensing voltage herebelow described.
  • the duration of the standby period regulates the frequency of sensing the level of dissolved alumina in the bath.
  • the time chosen may suitably be within a multiple minutes range which provides at least 2 to 4 sensing periods per hour.
  • Reverse current stage The current direction through the pilot anode is reversed in order to eliminate the anode effect which lhas been maintained thereon during the standby stage.
  • the time interval for this stage may suitably be about 8 to 10 seconds for example.
  • Sensing stage- At this stage, a second or low voltage, preselected in dependence on the level of alumina control desired and derived through tap B, is impressed on the pilot anode to cause the resultant current through it in the forward direction to provide a given control current -density thereon in order to determine the alumina content of the bath by whether or not an anode effect appears on such anode.
  • the sensing current density on the pilot anode is selected to correspond to a desired dissolved alumina concentration so that when the concentration declines to the predetermined control value, an anode effect is induced on the pilot anode.
  • the sensor associated with the pilot anode circuit is rendered effective to detect if an anode effect has appeared or ⁇ not and responsively to select the fast or the slow feed rate for the standby stage which follows.
  • the time interval for the sensing stage is preferably made quite brief, within the range of between about 10 and 20 seconds, in order to minimize the pilot anode consumption which occurs when it is working as a sensing electrode.
  • the voltage on the pilot anode is switched from the low to the high voltage tap of the supply in order to assure inducing an anode effect thereon, or to maintain it if one is present, for the succeeding standby stage, and the cycle repeats.
  • Stages 2 and 3 constitute a sensing cycle.
  • control 6 relay CR12. in line 3 has four sets of contacts to be found in lines 3 5-16-17, respectively, a line under a numeral indicating that the referenced contact in that line is normally closed.
  • the high volta-ge of between 14-16 volts is impressed on the pilot anode 12 and its current density is suddenly raised to a value suicient to induce an anode effect thereon, which then persists until eliminated.
  • the duration of the standby stage is controlled by a conventional synchronous motor driven reset timer TM3 in line 18, set to provide a 20 minute timing period. It is now timing, as also are conventional synchronous motor driven repeat cycle timers TM1 and TMZ in lines 20 and 19 which run continuously and serve as Slow feed and fast feed timers, respectively, for the ore feeder 7 (FIG. 1). They are set for 120 seconds and 60 seconds timing periods, respectively.
  • timer TMI is controlling the ore feeder 7 by periodically operating the feeder solenoid S1 in line 16, and also shown in FIG. l, for ore feeding at the slow feed rate during this standby stage. Also, all of the components in the respective circuit lines 1 through 15 are de-energized.
  • control contact TM3- in line 1 closes. Thereby, control relay CR3 in line 1 energizes or picks up and locks in through its contact CR3 and series contact TR2 in line 3 so that it will remain energized throughout the remainder of the program sequence.
  • Control relay CR3 closes its contact CR3 in line 1A to close a point in the sensing circuit and it also closes its contact CR3 in line 13 to energize the following: adjustable pneumatic time delay relays TR1 and TR7 in lines 11 and 12, control relay CRI in line 13, control contactor CR2 in line 14, and clutch coil TMS in line 10 of the reset timer TMS.
  • This timer is reset to its time set point by energization of its clutch coil and it runs toward "zero for timing, but it does not start timing until its clutch coil is de-energized.
  • Timing relay TR1 is set for 10 seconds before its contact in line 13 opens and it regulates the duration of the reverse current stage.
  • Timing relay TR7 immediately opens its contact TR7 in line 1A to open the sensing circuit to prevent the sensing relay CR4 from being exposed to transient surges when reverse current is removed and forward sensing current is supplied to the
  • Cont-rol contactor CRZ switches the forward current supply circuit from high voltage tap A to low voltage tap B by operation of its contacts in lines 1A and 1B, and remains energized to the end of the sensing cycle.
  • Control relay CRI operates its contacts in lines 2A and 2B thereby de-energizing contactor CR to open the forward current circuit and energizing contactor RC to close the reverse current circuit which shorts the pilot anode to the cathode tap 16 for the duration of the reverse current stage. Opening the forward current circuit by contactor CR prevents shorting the forward current power supply during the reverse current stage.
  • Relay CRI stays energized during the second timing period of timing relay TR1 and its contact in line 15 opens to prevent operation of timing relays TRS and TR2 at this time. At its contact CRl in line 5, it opens a point in the locking circuit of relay CR12 in line 32. This relay serves as an ore feed rate selector.
  • selector relay CR12 When energized, it selects the fast feed rate by closing its contact in line 17 and renders the slow feed rate ineffective by opening its contact in line 16. This lets the fast feed timer TM2 control the ore feeder solenoid in line 16. Conversely when de-energized, it selects slow feed by its contact in line 16 to let the Slow feed timer TM1 control the ore feeder solenoid and locks out fast feed by its contact in line 17. In order to remain on fast feed during a standby period, selector relay CR12 locks in through its normally open contact in series with normally closed contact CR1 in line 5. Hence, whenever relay CR1 is energized and opens its contact in line 5, as above mentioned, selector relay CR12 will be de-energized or reset, thereby preparing it to be responsive to the following sensing stage and to return ore feed to the slow rate.
  • pilot anode may be raised clear of the bath briefly and then reimmersed in order to eliminate the anode effect thereon.
  • the anode effect may be eliminated by simply going to zero current, particularly when a pilot anode of a small size, within the lower half of the size range, is being used.
  • timing relay TR1 When timing relay TR1 times out, it ends the reverse current stage and starts the sensing stage by opening its contact in line 13 to de-energize relays TR7 and CRI.
  • the contacts of relay CRI return to normal position.
  • its contact in line 5 closes to allow selector relay CR12 to lock-in if it is actuated to select fast feed during sensing;
  • its contact in line 2B opens to de-energize contactor RC, thus opening the reverse current circuit;
  • its contact in line 2A closes to energize contactor CR, thus re-establishing the forward current circuit to impress the low sensing voltage from tap B on the pilot anode, and its contact in line 15 closes to start adjustable pneumatic timing relays TR2 and TR3 (connected in parallel in line 15) timing out.
  • TR2 controls the duration of the sensing stage and is set for l0 seconds.
  • TR3 determines when the sensors contact CR4 in line 3 is effective on the feed rate selector CR12 and is set for 7 seconds.
  • the pilot anode is working under the impressed low voltage of about 8 volts and a current of about 200 amperes, giving a control current density which will result in an anode effect thereon if the alumina concentration in the ⁇ bath has reached the critical density-concentration level, as heretofore described.
  • the sensor CR4 (FIG. l) responds to the increased voltage to sense the anode effect if it occurs.
  • timing relay TR7 After elapse of the 5 seconds afforded by timing relay TR7, which time allows the anode voltage and current to stabilize, its contact in line 1A closes to expose the sensor CR4 to the anode voltage.
  • Sensor CR4 energizes if the anode voltage has increased due to the presence of an anode effect and closes its contact CR4 in line 3, otherwise it remains de-energized (no anode effect) and its contact stays open.
  • the alumina concentration of the bath is measured as to whether it is above or below the preselected percentage level or control point and responsively thereto selection is made of the fast or slow feed rate for the next standby period.
  • the actual concentration level may be suflciently above the critical level with respect to the control current density as not to result in fast feed selection, so that it may go somewhat below the selected control level during the next standby stage; but, in such case, the fast feed will be selected at the sensing stage which follows. This condition is minimized by using shorter standby periods and more frequent sensing.
  • the sensing cycle ends at time-out of timing relay TR2 and opening of its contact TR2 in line 3. This opens the locking circuit of relay CR3 and it de-energizes. Responsively thereto, the sensing circuit is opened to de-energize sensor CR4 so its contact in line 3 opens if it had been closed, timing relays TR1, TR2 and TR3 are reset, contactor CR2 is de-energized and its contacts in lines 1A and 1B switches the forward current circuit from tap B to tap A. This impresses the high voltage on the pilot anode to induce an anode effect thereon if none is present, or to maintain it if one had developed during sensing. Also, the clutch coil of the reset timer TM3 is de-energized and the timer starts to run from its time set point toward zero for timing the standby stage of the program sequence which now repeats.
  • electrolysis proceeds without depletion of the alumina in solution in the electrolyte to the critical anode effect producing level because of the periodic sensing of the concentration level and change in ore feed rate in accord with the outcome of such sensing, thereby maintaining adequate alumina in the bath for continuous normal electrolysis.
  • the ore may be fed to the reduction cell by use of a motor driven screw type of feeder 20, an example of which is shown and described in U.S. Patent 2,713,024, and the feed rate controlled by adjustment of motor speed by means of a suitable motor speed controller 21, the specific nature of which is well known to those skilled in such art, and the selector relay CR12 used to activate controller 20 selectively for the desired fast and slow feed rates.
  • a motor driven screw type of feeder 20 an example of which is shown and described in U.S. Patent 2,713,024
  • a pilot anode controlled reduction cell which duplicates that of FIG. 1 is shown, but a separate variable voltage rectified power supply is employed for the standby and sensing stages of the program sequence in lieu of using shunted potline power. It is designed to provide for instant change in voltage and sudden rise of current on the pilot anode when anode effect is to be induced thereon at the end of a sensing stage.
  • three phase AC power at 440 volts, 60 cycles, for example, is supplied through a fused disconnect switch (not shown) to a variable three phase autotransformer TX1.
  • This transformer boosts the voltage applied to step-down transformer TX2 during the standby stage and it allows varying of the magnitude of the sensing current to the pilot anode during the sensing stage.
  • Transformer TX2 reduces the voltage to the appropriate level for operating the pilot anode.
  • Its respective primary phase windings has two sets of input taps to provide the desired high and low voltage outputs from its secondary windings.
  • One set of taps Lo is connected to the low voltage output sliders of transformerTXl through contacts LV1, 2 and 3, respectively (line 2) to give the adjustable low voltage for sensing, while the other set of taps Hi is connected to the high voltage output ends of transformer TX1 through contacts HV1, 2 and 3, respectively (line 3) to give the high voltage for the standby stage.
  • transformer TX2 The secondary windings of transformer TX2 are connected to a three phase full wave bridge rectifier, the diodes of which (lines S, 6 and 7) rectify the three phase AC voltage to DC voltage, the positive side of the DC output circuit being connected to the pilot anode 12 and the negative side to the cathode tap 16 of the cell 1. Fuses in series with the diodes serve to protect the diodes against short circuit currents.
  • an adjustable rheostat R1 of low ohmic value across which ⁇ is connected, through contact PT-3, a full wave rectifier bridge 25, and a voltage responsive sensor relay CR4 is connected to the output side of rectifier 25.
  • capacitor 26 Shunted across relay CR4 is capacitor 26 which filters the rectified current to eliminate possibility of relay chatter at pick-up.
  • Resistance R1 provides a voltage drop in direct proportion to the current flow through it and this voltage, rectified, is applied to sensor CR4 to determine whether or not an anode effect appears on the pilot anode during sensing, contact PT-3 regulating when such voltage is impressed on the sensor during the sensing stage.
  • Use of a DC sensing relay provides sensitive and positive relay action under the low voltage sensing conditions.
  • CR12 in line 20 identifies the ore feed rate selector and TM1 and TM2 in lines 23 and 22 the timers which effect operation of the ore feeder at the fast or slow rate depending upon which set of contacts CR12 in lines 13 and 14 is closed.
  • Selector relay CR12 is normally energized for the slow feed'rate and de-energized for the fast feed rate.
  • HV in line 15 identifies the contactor whose contacts -in line 3 supplies high voltage power to the taps Hi of transformer TX2, while LV in line 18 identities the contactor whose contacts in line 2 supplies low voltage power to the taps Lo of transformer TX2.
  • CRS in ⁇ line'17 identifies the contactor or relay whose contact vin line 8 shorts the pilot anode to the pot cathode to give reverse current.
  • TX3 in line 16 identifies a step-down transformer which supplies through bridge rectifier 27 the voltage to operate contactor CRS which preferably has a DC operating coil, so TX3 can be considered the same as CRSs coil.
  • PT in line 24 identifies a conventional synchronous motor driven, repeat cycle program timer, or cam timer, having three sets of cam-operated contacts, PT-1 on cam 1, PT-2A and PT-ZB on cam 2 and PT-3 on cam 3, which programmed in sequence and durationl of operation in accordance with the program shown in the timing diagram of FIG. 5. It co-ordinates the action of all of the other components of the control system. It may be selected to provide a desired total cycle time, the cycle time being of 30 seconds duration, as shown in FIG. 5. In the circuit diagram, the cam-operated contacts are shown in normal position when on rise of the cams.
  • SR in line 12 identifies a well known rotary stepping relay which times the length of the standby stage. It has a DC operating coil, supplied through bridge rectifier 28, and two sets of cam-operated contacts, SR-IA, SR-lB and SR-lC on cam 1 and SR-2 on cam 2, and selfinterrupting contact SR. It has 36 steps per revolution and advances one step upon de-energization of its coil after having been energized by closure of contact PT-1 (line 12). Hence, it completes one cycle responsively to cam timer PT completing 36 cycles or revolutions, thus providing a standby period of 18 minutes duration.
  • contact SR-2 (line 11) opens, this being the home position to which the stepping relay will run whenever pushbutton switch PB-l in line 11 is depressed.
  • contacts SR-1A, SR-1B and SR-1C operate, these contacts being shown in the positions they have during the standby stage.
  • cam timer PT The program or cam timer PT, of course, is running and during each cycle its cam 2 and cam 3 contacts are operated without any effect since the circuits in which they are located are dead. At time 0, however, its cam 1 contact PT-l in line 12 closes to energize the stepping relay SR, and at time 3K1 opens to de-energize this relay and it advances one step. This continues for each cycle of the cam t-imer PT until the stepping relay reaches step 3, thus ending the standby cycle and starting the sensing cycle.
  • contact SR-1A in line 15 opens to deenergize HV Which removes the high voltage power from transformer TX2 and also to disable the ore feeder so as to prevent agitation of the bath during sensing, thereby guarding against possible variation of the pilot anode area exposed to the bath which in turn would affect the sensing current density.
  • Contact SR-lB in line 20 opens with no effect since it is paralleled by PT-2B in line 18 which is closed at this time.
  • Contact SR-1C in line 16 closes to connect the left side of transformer TX3 and contactor LV to one side of the power supply line. Since contact PT-ZA in line 16 is open at this time, the transformer is not energized.
  • contactor LV in line 18 energizes through closed contact PT-2B when the HV interlock clears, thus switching in the low voltage supply prior to reverse current flow through the pilot anode. This is a matter of switching convenience in the program sequence and may be omitted, if desired.
  • contact PT-2B in line 18 opens to deenergize contactor LV thereby disabling the external power supply, and to reset selector relay CR12 if it had been energized.
  • Contact PT-ZA in line 16 closes to energize transformer TX3 and contactor CRS in line 17 picksup to close its contact in line 8, thereby connecting the pilot anode to the pot cathode for the reverse current flow through it to eliminate the anode effect thereon.
  • contact PT-2A in line 16 opens to terminate the reverse current flow; shortly thereafter contact PT-2B closes to energize contactor LV and thus start the sensing stage.
  • These contacts are set for PT-ZA to open before PT-ZB closes and thus provide an interval of about 2./3 of a second before supplying the forward sensing current to the pilot anode. With no forward current supplied to the pilot anode for this brief interval after termination of the reverse current flow, enough of a gas film builds up at the anode to limit the initial forward current surge.
  • Pick-up of contactor LV closes its contacts in line 2 thus feeding transformer TX2 from the low voltage taps of transformer TX1 and impressing'the preselected low voltage on the pilot anode for the sensing current flow through it during the sensing stage.
  • the value of this current is preselected to give ⁇ a current density on' the pilot anode in accordance with 'the' preselected alumina percentage control level 'desired in'the'bathAs heretofore described, ananode effect will'y or will notbe inducedl on the'l pilot anode depending on the density-concentration relationship existing at the time '0f sensing.
  • SR-lC in line 16 opens to drop out relay LV which removes the low voltage power from transformer TX2.
  • SR-lA in line closes to enable ore feeding at the rate selected by CR12 and to pick-up HV after the interlock LV in line 15 clears.
  • Pick-up of HV, at its contacts in line 3 applies the boosted voltage from TX1 to the high voltage taps Hi of TX2 and thus impresses the high standby voltage on the pilot anode.
  • the initial current surge through the pilot anode is adequate to induce an anode effect thereon with alumina concentrations up to about 7.25 percent, thus insuring its inducement at the start of the standby period if none had developed during sensing.
  • the same sequence occurs and the high standby voltage maintains the anode effect.
  • Contact SR-IB in line 20 closes at this time to keep CR12 locked-in during the standby period if it had been energized during sensing. Then throughout the standby period, the system remains in the condition described, the stepping relay advancing one step for each cycle of the timer PT until it reaches step 3, whereupon sensing of the alumina concentration is repeated.
  • the pushbutton switch PBI enables an operator to go through the sensing cycle at will.
  • the stepping relay advances to home position 2 and opens its contact SR-2 in line 11.
  • timer PT takes over in order to step relay SR to step 3 in the normal fashion.
  • the sensing cycle may not be initiated, except at the beginning.
  • said metallic compound comprises aluminum oxide.
  • a control system for a molten metal producing reduction cell having an anode, a cathode and a fused electrolyte bath into which ore constituting a metallic compound to be reduced by electrolysis is fed and dissolved, the improvement comprising:
  • said second voltage causing the resultant current to give a selected control current density on said pilot anode which will result in an anode effect thereon during said sensing stage in case the ore concentration in said bath has decreased to the critical percentage level with respect to said control current density;
  • a normally open circuit including a control switch connecting said pilot anode to said cell cathode for reverse current ow through said pilot anode to eliminate the anode effect thereon at a time interposed between said standby stage and said sensing stage;
  • Feeder means selectively operable to feed ore into said bath at an underfeed rate and at an overfeed rate during said standby stage;
  • a selector device for selecting the rate of ore feeding by said feeder means
  • said second voltage causing the resultant current to provide a selected control current density on said pilot anode for the occurrence of an anode effect thereon during said sensing stage at a percentage level of said solute constituent in said bath greater than said critical percentage level;
  • Means including a control switch for making said pilot anode cathodic with respect to said bath for reverse current flow through said pilot anode to eliminate the anode effect thereon at a time interposed between said standby stage and said sensing stage;
  • a sensor relay operable responsively to the occurrence of an anode effect on said pilot anode during said sensing stage
  • Variable voltage transformer means energizable from an AC source and including rectifying means connected to said pilot anode and to said cell cathode to provide direct current energy to power said pilot anode;
  • a first control switch controlling said transformer means for energizing said pilot anode at a current density sufficient to establish and maintain it on anode effect during a standby stage of a selected time duration;
  • a second control switch controlling said transformer means for energizing said pilot anode for a sensing stage of from about 10 to 30 seconds duration at a control current density selected in accordance with a preselected -alumina percentage level to be maintained in said bath, whereby depletion of the alumina content of said bath to said percentage level is indicated by an :anode effect appearing on said pilot anode during said sensing stage;
  • a normally open circuit including a third control switch for making said pilot anode cathodic with respect to said bath for reverse current flow through said pilot anode to eliminate the anode effect thereon iat a time interposed between said standby stage and said sensing stage;
  • Timing means for effecting operation of said control switches in a program sequence consisting of said standby stage, said reverse current flow and said sensing stage in the order named, and for actuating said first and second control switches to open position prior to said reverse current flow through said pilot anode;
  • said transformer means comprises a variable three phase autotransformer having low voltage Output sliders, and energizable lfrom a three phase AC power supply circuit, and a three phase step-down transformer havingprirnary phase windings each provided with high andlow voltage input taps and secondary output windings', and said rectifying means Vcomprises a lthree vphase full wave bridge' rectifier connected to said secondary output windings to provide direct current energy to power said pilot anode;v
  • a control system as in claim 15 wherein the sensor means comprises a DC relay, and said relay is connected through a full wave rectifier bridge and a normally Open switch across aresistance of low ohmic value, and said resistance is connected in the low voltage supply circuit to said low voltage input tap ofvone phase of said primary phase windings to provide a 'voltage ydrop in direct proportion to the current flow through said' resistance, said voltage drop being less than the pick-up voltage of said relay when an anode effect is present on said pilot anode during said sensing stage, and means controlled by -said timing means foriactuating said normally open switch to closedposition andthereby renderrsaid relay effective for sensing during said sensing stage.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
US459601A 1965-05-28 1965-05-28 Method of controlling aluminum content during aluminumg electrolysis Expired - Lifetime US3400062A (en)

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NL130687D NL130687C (fr) 1965-05-28
US459601A US3400062A (en) 1965-05-28 1965-05-28 Method of controlling aluminum content during aluminumg electrolysis
NL6607293A NL6607293A (fr) 1965-05-28 1966-05-26
NO163188A NO121071B (fr) 1965-05-28 1966-05-26
BR179961/66A BR6679961D0 (pt) 1965-05-28 1966-05-27 Aperfeicoamentos relativos a producao de metal por eletrolise

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Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3539461A (en) * 1967-10-19 1970-11-10 Kaiser Aluminium Chem Corp Anode effect termination
US3539456A (en) * 1968-06-25 1970-11-10 Aluminum Co Of America Electrolytic cell solute determining apparatus and method
US3629079A (en) * 1968-02-23 1971-12-21 Kaiser Aluminium Chem Corp Alumina feed control
US3660256A (en) * 1967-12-07 1972-05-02 Gen Electric Method and apparatus for aluminum potline control
US3674674A (en) * 1968-12-27 1972-07-04 Delfzijl Aluminium Apparatus for controlling electrode adjustment during aluminum oxide reduction
US3847761A (en) * 1972-04-06 1974-11-12 Aluminum Co Of America Bath control
US4098651A (en) * 1973-12-20 1978-07-04 Swiss Aluminium Ltd. Continuous measurement of electrolyte parameters in a cell for the electrolysis of a molten charge
US4654130A (en) * 1986-05-15 1987-03-31 Reynolds Metals Company Method for improved alumina control in aluminum electrolytic cells employing point feeders
DE4428743A1 (de) * 1994-08-13 1996-02-22 Georg Prof Dr Mueller Verfahren und Vorrichtung zur Messung und Steuerung bzw. Regelung der Sauerstoffkonzentration in Siliciumschmelzen
US20030173210A1 (en) * 2000-08-15 2003-09-18 Parker Hannifin Ab Pneumatic actuator system
US20100065435A1 (en) * 2006-12-19 2010-03-18 Michael Schneller Aluminum production process control
US8753564B2 (en) 2011-06-13 2014-06-17 Mac Valves, Inc. Piston rod and cylinder seal device for aluminum bath crust breaker
US8906291B2 (en) 2011-06-13 2014-12-09 Mac Valves, Inc. Piston rod and cylinder seal device for aluminum bath crust breaker
US8910562B2 (en) 2011-06-13 2014-12-16 Mac Valves, Inc. Pneumatic system for controlling aluminum bath crust breaker
US8932515B2 (en) 2011-06-13 2015-01-13 La-Z-Boy Incorporated Crust breaker aluminum bath detection system
WO2018202959A1 (fr) 2017-05-03 2018-11-08 Laurent Michard Procédé de pilotage d'une cuve d'électrolyse de l'aluminium
WO2023111640A1 (fr) * 2021-12-15 2023-06-22 Arcelormittal Appareil d'électrolyse pour la production de fer avec un dispositif d'alimentation en oxyde de fer amélioré

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1193683B (de) * 1963-08-30 1965-05-26 Alusuisse Verfahren und Vorrichtung zur automatischen Regelung der Klemmenspannung bei einer Anlage zur Herstellung von Aluminium durch Schmelz-flusselektrolyse
US3294656A (en) * 1961-10-17 1966-12-27 Alusuisse Method of producing aluminium
US3317413A (en) * 1963-09-23 1967-05-02 Pechiney Cie De Produits Control of alumina content during igneous electrolysis

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3294656A (en) * 1961-10-17 1966-12-27 Alusuisse Method of producing aluminium
DE1193683B (de) * 1963-08-30 1965-05-26 Alusuisse Verfahren und Vorrichtung zur automatischen Regelung der Klemmenspannung bei einer Anlage zur Herstellung von Aluminium durch Schmelz-flusselektrolyse
US3317413A (en) * 1963-09-23 1967-05-02 Pechiney Cie De Produits Control of alumina content during igneous electrolysis

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3539461A (en) * 1967-10-19 1970-11-10 Kaiser Aluminium Chem Corp Anode effect termination
US3660256A (en) * 1967-12-07 1972-05-02 Gen Electric Method and apparatus for aluminum potline control
US3629079A (en) * 1968-02-23 1971-12-21 Kaiser Aluminium Chem Corp Alumina feed control
US3539456A (en) * 1968-06-25 1970-11-10 Aluminum Co Of America Electrolytic cell solute determining apparatus and method
US3674674A (en) * 1968-12-27 1972-07-04 Delfzijl Aluminium Apparatus for controlling electrode adjustment during aluminum oxide reduction
US3847761A (en) * 1972-04-06 1974-11-12 Aluminum Co Of America Bath control
US4098651A (en) * 1973-12-20 1978-07-04 Swiss Aluminium Ltd. Continuous measurement of electrolyte parameters in a cell for the electrolysis of a molten charge
US4654130A (en) * 1986-05-15 1987-03-31 Reynolds Metals Company Method for improved alumina control in aluminum electrolytic cells employing point feeders
DE4428743A1 (de) * 1994-08-13 1996-02-22 Georg Prof Dr Mueller Verfahren und Vorrichtung zur Messung und Steuerung bzw. Regelung der Sauerstoffkonzentration in Siliciumschmelzen
US20030173210A1 (en) * 2000-08-15 2003-09-18 Parker Hannifin Ab Pneumatic actuator system
US6776081B2 (en) * 2000-08-15 2004-08-17 Parker Hannifin Ab Pneumatic actuator system
US20100065435A1 (en) * 2006-12-19 2010-03-18 Michael Schneller Aluminum production process control
US8052859B2 (en) 2006-12-19 2011-11-08 Michael Schneller Aluminum production process control
US8753564B2 (en) 2011-06-13 2014-06-17 Mac Valves, Inc. Piston rod and cylinder seal device for aluminum bath crust breaker
US8906291B2 (en) 2011-06-13 2014-12-09 Mac Valves, Inc. Piston rod and cylinder seal device for aluminum bath crust breaker
US8910562B2 (en) 2011-06-13 2014-12-16 Mac Valves, Inc. Pneumatic system for controlling aluminum bath crust breaker
US8932515B2 (en) 2011-06-13 2015-01-13 La-Z-Boy Incorporated Crust breaker aluminum bath detection system
WO2018202959A1 (fr) 2017-05-03 2018-11-08 Laurent Michard Procédé de pilotage d'une cuve d'électrolyse de l'aluminium
WO2023111640A1 (fr) * 2021-12-15 2023-06-22 Arcelormittal Appareil d'électrolyse pour la production de fer avec un dispositif d'alimentation en oxyde de fer amélioré

Also Published As

Publication number Publication date
NO121071B (fr) 1971-01-11
NL130687C (fr)
BR6679961D0 (pt) 1973-04-26
NL6607293A (fr) 1966-11-29

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