US3573179A - Method and apparatus for the control of electrolytic refining cells - Google Patents

Method and apparatus for the control of electrolytic refining cells Download PDF

Info

Publication number
US3573179A
US3573179A US519109A US3573179DA US3573179A US 3573179 A US3573179 A US 3573179A US 519109 A US519109 A US 519109A US 3573179D A US3573179D A US 3573179DA US 3573179 A US3573179 A US 3573179A
Authority
US
United States
Prior art keywords
pot
resistance
block
value
anode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US519109A
Other languages
English (en)
Inventor
George P Dirth
Terrence K Mcmahon
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
International Business Machines Corp
Original Assignee
International Business Machines Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by International Business Machines Corp filed Critical International Business Machines Corp
Application granted granted Critical
Publication of US3573179A publication Critical patent/US3573179A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • 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

Definitions

  • This invention relates to a control system and particularly to a control system for an electrolytic refining operation such as the process which provides aluminum by the electrolytic reduction of aluminum oxide dissolved in molten cryolite.
  • Each pot includes a carbon anode which is immersed into a bath of molten cryolite having aluminum oxide dissolved therein, and a container of heat insulating material surrounding a conductive cathode pan having a plurality of conductors imbedded in the bottom thereof.
  • a typical commercial operation would consist of 120 to 140 such pots connected in series with sufiicient voltage impressed across the line so that the voltage drop across each pot is from 4 /2 to 5 volts, and the resulting line current between 50 and 100 kiloamperes.
  • the first is the Soderberg anode in which an open ended steel shell is loaded with carbon paste. As the lower portion of the anode is depleted, more paste is added. The heat liberated during the refining operation bakes the paste as it sinks toward the reaction zone. The heat from the pot substitutes for the baking furnace.
  • the Niagara anode is a baked block carbon anode which is prepared in the special furnace. The Niagara anodes are replaced as they become depleted.
  • a crust of frozen cryolite forms over the reaction bath. This crust must be broken in order to enter fresh aluminum oxide (alumina). The presence of this crust necessitates that feeding be done in discrete batches rather than on a continuous basis. The crust also renders it extremely difficult to determine just how much alumina goes into the cryolite solution after the pot is fed.
  • the concentration In the operation of a cell it is necessary to maintain the alumina concentration within definite limits, usually considered to be two percent to eight percent by weight. At the upper limit a sludge of alumina forms at the cathode, thereby reducing current efficiency. In this condition the pot is said to be sick.
  • the bath When the concentration reaches the lower limit, the bath itself begins to reduce causing a gas film to form about the anodes. The increased resistance caused by the film results in a sharp increase in the pot voltage drop and a corresponding drop in the line current.
  • the pot voltage drop will increase from five to ice about thirty volts.
  • the anode effect is in general a less serious commercial problem than overfeeding. Industrial practice is to operate in the lower part of the feasible concentration range to avoid the sick pot condition.
  • Still another object of our invention is to provide a means for determining the operating point of a refining cell which is not upset by a change in the anode position.
  • control of the individual pot is based upon the slope or trend of the bath resistance profile instead of actual measured resistances.
  • the total line current is measured as well as the IR drop across the individual pots. From these values, the individual bath resistance values may be computed. These values are accumulated over a period of time, for example 5 minutes, and the average rate of change or slope of the resistance curve is determined. When this slope or trend reaches a predetermined value, additional alumina should be added to that particular cell.
  • the anodecathode distance which substantially aifects the absolute value bath resistance, may determine the offset in the absolute value of the resistance profile, but does not materially affect its shape.
  • the absolute value of resistance may be used to control the anode cathode distance as in conventional controllers.
  • current efiiciency may be calculated by the system by recording the ore consumption of the pot. This may be achieved by determining the average current flow through the pot and the amount of aluminum produced by the individual pot. The former value is easily maintained by data logging equipment, but the latter must be estimated by some indirect means such as the weight of charge of alumina over a long period of time.
  • FIG. 1 is a pictorial schematic diagram of a control system embodying our invention.
  • FIG. 2 is a graph illustrating the variation in A1 concentration with time for a typical pot.
  • FIG. 3 is a graph illustrating the change in pot resistance for the same pot as FIG. 2.
  • FIG. 4 shows the various components which make up the pot resistance.
  • FIGS. 5a, 5b and 5c are data flow diagrams for a computer program used in the system of FIG. 1.
  • the line to be controlled includes a string of series connected pots 1, having anode elements 2, a conductive cathode pan 3, having rods 4 imbedded therein, and an insulating shell 5.
  • Each pot normally contains a pool 6 of molten aluminum at the bottom of a bath 7 of cryolite and dissolved alumina. Loss of heat from the surface of the bath causes a crust 8 to form.
  • Each pot has an anode positioning device 10 shown in schematic form as a motor 11 and associated reduction gears 12.
  • the position of anode 2 relative to the upper surface of molten aluminum pool 6 may be adjusted by means of motor 11.
  • Each pot 1 has associated therewith feed indicating means shown as light 15.
  • light 15 would be connected directly across the cell.
  • light 15 is not connected across the pot, but is controlled by other means.
  • the pots are series connected, each of the intermediate pots having a bus from the anode 2 to the preceding cathode rods 4.
  • the end pots are connected to a suitable source of direct current represented by terminals ⁇ 16 and 17. Assuming a line of 140 pots, the DC. source voltage would lie between 600 and 700 volts. The current through the line would lie between 50 and 100 kiloamperes.
  • the line current is measured by means of magnetic amplifier Ztl, having control winding 21 connected across a current shunt 22.
  • Output winding 23 is energized from an AC. source connected to terminals 24.
  • the output 23 is connected to rectifier 25 to develop a DC. voltage across load resistor 26 which is proportional to the DC. current flowing in the pot line.
  • each pot is measured by means of a magnetic amplifier 30 having a control winding 31 connected across the pot to be energized by the voltage drop across the pot.
  • Output winding 33 is energized from an AC. source connected to terminals 34.
  • Rectifier 35 is connected to output winding 33 to provide a D.C. signal across load resistor 36 which is proportional to the voltage drop across the associated pot.
  • the signal voltages developed across load resistors 26 and 36a36n are scanned by multiplexer or signal transfer means 40 under control of a computer or central processing unit 41 and converted into digital form by analog to digital converter 42. The resulting digital values are utilized by central processing unit 41 to determine the proper time for feeding the pots.
  • An output printer 43 allows the operator to monitor the process variables.
  • FIGS. 2 and 3 illustrate the change in alumina concentration and pot resistance as a function of time for a typical pot.
  • the pot is fed at time 0.
  • the concentration of alumina beings to rise immediately, increasing to a maximum of approximately 7% after 45 minutes.
  • FIG. 4 is an analysis of the resistance profile. The most significant component in the period immediately after feeding is the resistance due to dissolved alumina (A1 0 concentration. The slope of the total resistance closely parallels the contribution of the alumina concentration until three hours have passed.
  • a typical anode movement produces a resistance change that makes the rapid rise in resistance prior to the anode effect more difiicult to detect.
  • the curves of FIG. 4 are idealized in that the noise which exists on the pot line has been removed.
  • the presence of noise complicates the problem of detecting an impending anode effect and requires that some form of filtering be used to condition the signal.
  • rectangles are used to designate computer manipulation of data such as calculating and recognizing time signals.
  • the circles are used to indicate computer operations where certain counters or terms are set to predetermined values.
  • a diamond shape indicates that a test is performed and the program may take either of two paths depending on the result of the test.
  • the control operation begins with a time signal as indicated in block 101.
  • the first occurrence of the recur rent 72 second time signal operates to set a first, or K, counter to the value of l as shown in block 102.
  • This counter will normally be a register within computer 41 and is used to keep track of the number of times the pot resistance values have been determined.
  • Block 103 indicates that the pot line current is read. In the embodiment of FIG. 1, this operation would involve computer instructions which cause multiplexer 40 to connect the output of magnetic amplifier 20 to analog to digital converter 42. The resulting digital value is transferred to central processing unit 41 where it is stored for future use.
  • Block 104 indicates that a second, or I, counter is set to the value of 1.
  • This counter is similar to K counter mentioned previously and will normally be a register within the computer.
  • the register could be discrete hardware or simply a location in storage which is handled like a register.
  • the I counter is used to keep track of the particular pot which is being scanned. The use of the I counter for this purpose allows certain program steps to be modified and used over and over for all pots without the necessity for repeating the storage for all instructions for every pot.
  • block 105 specifies that the voltage across the specified pot will be read. Similar to the previously described operation for reading the line current, this operation involves a signal from central processing unit 41 to multiplexer 40 which connects the output of magnetic amplifier 30a to analog to digital converted 42. The digital value representing the voltage across cell a is then placed in the storage associated with central processing unit 41.
  • a check of the status of the I counter is made as shown by block 106.
  • the No output from block 106 is followed and the branch to block 107 is made. This branch indicates that all pots in the line have not been serviced and the I counter must be incremented to read the next pot.
  • the operation of block 107 adds 1 to the value in the I counter and returns the sequence to the input of block 105 where the next pot voltage is read.
  • the loop comprising blocks 105, 106 and 107 is repeated until the I counter reaches 140 indicating that all pot voltages have been read and the values are in the storage of central processing unit 41.
  • the exit from the loop is made through the Yes output of block 106 to block 108 which causes the pot line current to be read again and the value placed in storage.
  • the value representing the first read line current (block 103) is substracted from the second reading of line current (block 108) to determine what change occurred during the period in which the pot voltages were read.
  • the change in current, as determined in the step of block 109, is compared against a permissible limit in block 110 to determine whether the accumulated data may be processed further. Since the resistance value for each pot is to be calculated by dividing the line current by the pot voltage, a wide fluctuation in line current While reading pot voltages would make the calculation meaningless. Where pot voltages cannot be read in a very short period it may be necessary to reduce the number of pots read in one pass and break the line into three or four segments of 35 to 50 pots each.
  • the Yes signal from block 110 indicates a limit violation and the branch is made to the input of block 104. All the pot voltages are again read through blocks 105-107, and the line current read at block 108 and compared, in blocks 109, 110, to the value obtained in the previous reading in block 108. Assuming that the limit for change in line current is not violated, the No output of block 110 leads to block 111 which operates to set the I counter to 1 in preparation for calculation of resistance values for the individual pots.
  • the resistance calculation designated by block 112 takes the form of where R is the pot resistance, E is the measured voltage across the pot, I is the measured line current and CEMF is the counter electromotive force of the pot.
  • the CEMF is initially set to a theoretical value but is later modified by data obtained from the measured values.
  • block 113 After the resistance value for the pot designated by the I counter has been calculated in block 112, block 113 operates to substract the present value from the last calculated value. The change in resistance is tested against a limit in block 114. In the event that the change is greater than the limit, the Yes signal of block 114 is followed to the block 115. This block increments or decrements the CEMF value and recalculates the previously calculated resistance values until they come within the limit established by block 114.
  • This manipulation of the CEMF provides for accommodation of anode movements without affecting calculations of the change in pot resistance due to variations in dissolved alumina concentration. All preceding calculations since the last anode effect are normalized to the new anode position by recalculating with an adjusted CEMF. The increments must be small enough to enable satisfaction of the limit test.
  • the No signal from block 114 is followed to block 116 which tests the value in the I counter. If the I counter value is less than 140, the No signal from block 116 is followed to block 117 which increments the I counter and re-enters the loop including blocks 112116 for calculation of another pot resistance.
  • the existence of 140 in the I counter provides an exit by the Yes signal from block 116 to the test of the K counter indicated by block 118.
  • the K counter operates to keep track of the number of times the pot voltages have been measured and the individual resistance values calculated.
  • four readings are taken at 72 second intervals. The purpose of taking more than one reading is to achieve a measure of filtering of the input data.
  • the K counter value will be less than four and the No signal from block 118 will lead to block 119 to increment the K counter.
  • the operation would await the next 72 second signal as shown in block 120. At the occurrence of the next 72 second signal an entry to block 103 would occur and a scan and calculation routine would follow.
  • the K counter stands at 4. This results in an exit from block 118 according to the Yes signal leading to block 121.
  • the I counter is reset to 1 by this block preparatory to the final calculations of the resistance profile.
  • block 124 specifies a calculation of the value designated Trend j. This value is equal to the difference between the average E calculated at block 123 and the composite resistance value calculated the previous run, RHj 1.
  • the sign of Trend i may be either positive or negative depending on whether the pot resistance is increasing or decreasing. Since the resistance tends to decrease after a feed operation the existence of a negative sign for the value of Trend j is indicative of a high alumina concentration and no danger of an anode effect exists.
  • Block 125 senses the sign of Trend 1'. When the value is less than zero, indicating a negative sign, the Yes signal leads to block 126 which resets the value of Trend j to zero. If this reset operation did not occur, an accumulation of negative values would occur, complicating the detection of an impending anode effect.
  • Block 127 prevents Trend i from accumulating a positive value sufficient to signal a feed operation during the one hour period while the fed alumina is going into solution by testing to see whether a feed has been signaled within the past hour. If a feed has occurred, the Yes signal leads to block 126 where T is set to zero just as it was for negative values of T If a feed has not been signaled within the past hour, the No signal exits from block 127 to block 128 where the Trend calculation is completed.
  • Additional calculations are performed in block 12? as a step in calculating the new value for the filtered resistance of the pot RI-I
  • the step set forth in block 129 calculates .3 of the difference between E which is the raw average resistance of block 123 and RH which is the calculated filtered resistance for the preceding 288 second period.
  • the next step in the calculation provides for a preliminary calculation of the new RI-l by adding the result of block 129 to the value of RH This manner of combination provides a filtering action since only .3 of the change between the raw average and the last calculated value is used to modify the calculated value.
  • Block 131 calculates the value of .l of the total trend T which was calculated at block 128.
  • the value T is added to the preliminary value of RI-I obtained in block 130 to give the final value of RH Having completed the calculations associated with evaluation of the resistance trend a test is made at block 133 to determine whether or not the previously obtained value of T block 128, is in excess of an established limit for the particular pot. If there is no violation, the No signal exits to block 134 which tests the I counter to see whether all pots have been considered. If the I counter value is less than 140, the No signal exits to block 135, which increments the I counter and re-enters the loop at the input to black 122. If the I counter stands at 140, all pots have been serviced and the Yes signal exits to block 136 which provides for re-entry of the routine upon receipt of the first 72 second signal as shown at block 101.
  • exit from block 133 is according to the Yes signal leading to block 137 which gain tests to see whether one hour has elapsed since the last feed was signaled. If the No signal is present, indicating that a feed was signaled within the last hour, exit occurs to block 134 and no further action is taken on the particular pot.
  • exit from block 137 occurs through the Yes signal leading to block 138.
  • An indicator which signals the necessity for a feed operation is activated by the operation set out in block 138.
  • central processing unit 41 would signal multiplexer 40 to turn on the light over the pot which needs feeding. The operator turns the light off when he feeds the pot.
  • the operation of block 138 is such that a record of the time when the light is turned on is retained. The assumption is made that feeding occurs within a few minutes from this time.
  • the foregoing system contemplates the use of a digital computer for performance of the required calculations but the same calculations could be performed by other means.
  • the necessary measurements of line current and pot voltage may be taken with existing or conventional meters designed for the appropriate current and voltages involved.
  • the calculations on this data may be done by means of a desk calculator or even by hand if necessary. It will be recognized that the speed of data acquisition and the ensuing calculations will determine the number of pots which can be handled in a group.
  • the method of controlling the alumina content of said bath by signalling a feed operation to feed additional alumina into said bath prior to the occurrence of an anode effect therein comprising the steps of:
  • step 1 comprises the steps of:
  • a method according to claim 2 wherein said development of signals representing the value of total pot resistance from said measured values in step C comprises the steps of:
  • E is the measured voltage value
  • I is the measured current value
  • CEMF is a value for the counter-electromotive force of the cell
  • determination of said time rate of change of said total pot resistance of step 2 comprises the steps of:
  • a method according to claim 4 including the additional steps of:
  • apparatus for controlling the alumina content of each of said cells by signalling feed operations to feed additional alumina into individual ones of said cells prior to the occurrence of an anode effect therein comprising:
  • feed indicator means each associated with one of said cells, for indicating that a feed operation is required for the associated cell
  • control means including a digital computer arranged to comprise:
  • a system according to claim 6 having analog to digital converter means operable in accordance with said control means for converting the analog output of said sensors to digital form for transfer to said computer.

Landscapes

  • 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)
US519109A 1965-12-14 1965-12-14 Method and apparatus for the control of electrolytic refining cells Expired - Lifetime US3573179A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US51910965A 1965-12-14 1965-12-14

Publications (1)

Publication Number Publication Date
US3573179A true US3573179A (en) 1971-03-30

Family

ID=24066870

Family Applications (1)

Application Number Title Priority Date Filing Date
US519109A Expired - Lifetime US3573179A (en) 1965-12-14 1965-12-14 Method and apparatus for the control of electrolytic refining cells

Country Status (2)

Country Link
US (1) US3573179A (cs)
NL (1) NL6617456A (cs)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3625842A (en) * 1968-05-24 1971-12-07 Kaiser Aluminium Chem Corp Alumina feed control
US3627666A (en) * 1967-11-06 1971-12-14 Pechiney Apparatus for automatically regulating the anode gap in electrolysis cells
US3660256A (en) * 1967-12-07 1972-05-02 Gen Electric Method and apparatus for aluminum potline control
JPS4989697A (cs) * 1972-12-27 1974-08-27
US3847761A (en) * 1972-04-06 1974-11-12 Aluminum Co Of America Bath control
US3878070A (en) * 1972-10-18 1975-04-15 Southwire Co Apparatus for and method of producing metal
US3888747A (en) * 1972-10-18 1975-06-10 Nat Southwire Aluminum Method of and apparatus for producing metal
US4008142A (en) * 1973-07-25 1977-02-15 Siemens Aktiengesellschaft Apparatus for operating the furnaces of an electrolysis plant
US4024034A (en) * 1973-07-25 1977-05-17 Siemens Aktiengesellschaft Method for operating the furnaces of an electrolysis plant
US4638441A (en) * 1984-01-18 1987-01-20 R.F.J. Associates Limited Data acquisition system for the computer control of aluminum smelters
US4654130A (en) * 1986-05-15 1987-03-31 Reynolds Metals Company Method for improved alumina control in aluminum electrolytic cells employing point feeders
EP0386899A3 (en) * 1989-02-24 1991-02-06 Comalco Aluminium, Ltd. Process for controlling aluminium smelting cells
US20050106426A1 (en) * 2003-09-12 2005-05-19 Daimlerchrysler Ag Method of monitoring a fuel cell unit
US20100065435A1 (en) * 2006-12-19 2010-03-18 Michael Schneller Aluminum production process control

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3627666A (en) * 1967-11-06 1971-12-14 Pechiney Apparatus for automatically regulating the anode gap in electrolysis cells
US3660256A (en) * 1967-12-07 1972-05-02 Gen Electric Method and apparatus for aluminum potline control
US3625842A (en) * 1968-05-24 1971-12-07 Kaiser Aluminium Chem Corp Alumina feed control
US3847761A (en) * 1972-04-06 1974-11-12 Aluminum Co Of America Bath control
US3878070A (en) * 1972-10-18 1975-04-15 Southwire Co Apparatus for and method of producing metal
US3888747A (en) * 1972-10-18 1975-06-10 Nat Southwire Aluminum Method of and apparatus for producing metal
JPS4989697A (cs) * 1972-12-27 1974-08-27
US4024034A (en) * 1973-07-25 1977-05-17 Siemens Aktiengesellschaft Method for operating the furnaces of an electrolysis plant
US4008142A (en) * 1973-07-25 1977-02-15 Siemens Aktiengesellschaft Apparatus for operating the furnaces of an electrolysis plant
US4638441A (en) * 1984-01-18 1987-01-20 R.F.J. Associates Limited Data acquisition system for the computer control of aluminum smelters
US4654130A (en) * 1986-05-15 1987-03-31 Reynolds Metals Company Method for improved alumina control in aluminum electrolytic cells employing point feeders
EP0386899A3 (en) * 1989-02-24 1991-02-06 Comalco Aluminium, Ltd. Process for controlling aluminium smelting cells
US5089093A (en) * 1989-02-24 1992-02-18 Comalco Aluminum Ltd. Process for controlling aluminum smelting cells
EP0671488A2 (en) 1989-02-24 1995-09-13 Comalco Aluminium, Ltd. Process for controlling aluminium smelting cells
US20050106426A1 (en) * 2003-09-12 2005-05-19 Daimlerchrysler Ag Method of monitoring a fuel cell unit
US7124040B2 (en) * 2003-09-12 2006-10-17 Daimlerchrysler Ag Method of monitoring a fuel cell unit
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

Also Published As

Publication number Publication date
NL6617456A (cs) 1967-06-15

Similar Documents

Publication Publication Date Title
US3573179A (en) Method and apparatus for the control of electrolytic refining cells
CA1165356A (en) Method and apparatus for controlling electrode drive speed in a consumable electrode furnace
US3660256A (en) Method and apparatus for aluminum potline control
Bearne The development of aluminum reduction cell process control
AU588861B2 (en) Method of controlling the alumina feed into reduction cells for producing aluminium
US3629079A (en) Alumina feed control
CA1109824A (en) Method of controlling feed of alumina to an aluminum electrolytic cell
US3625842A (en) Alumina feed control
US3434945A (en) Terminal voltage regulation in electrolytic aluminum production
US3888747A (en) Method of and apparatus for producing metal
US3622475A (en) Reduction cell control system
US4425201A (en) Method for improved alumina control in aluminum electrolytic cells
US4654129A (en) Process for accurately maintaining a low alumina content in an electrolytic smelting cell for the production of aluminum
US20070095672A1 (en) Method of controlling aluminum reduction cell with prebaked anodes
US7175749B2 (en) Method and device for detecting anode effects of an electrolytic cell for aluminum production
US4654130A (en) Method for improved alumina control in aluminum electrolytic cells employing point feeders
US3455795A (en) Apparatus and method for the operation of cells for the igneous electrolysis of alumina
US3345273A (en) Method of and apparatus for indicating anode positions
US3380897A (en) Method of determining ore concentration
US3871984A (en) Transmission of pot line control signals
US3578569A (en) Anode polarization detector
EP0195143B1 (en) Controlling aluminium reduction cell operation
RU2023058C1 (ru) Способ управления процессом электролитического получения алюминия в электролизере
US3491002A (en) Adjusting anode blocks in an electrolytic cell
US3875030A (en) Detection of grounded anodes