FIELD OF TKE INVENTION
The present invention relates to a process for automatic termination of anode effect in an electrolytic
reduction pot. The process for automatic termination of anode effect includes the steps of anode effect
breaking and feeding (AEB), anode lowering, anode raising and adjustment of the pot voltage. Anode I
lowering and raising is done with help of an anode motor. The said sequence of steps is implemented in
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a chip present inside an electronic pot control (EPC) system. I
I
Backcround of the invention
I Aluminum is produced by electrolj~sis of Alumina dissolved in a molten bath of cryolite held in
electrolytic cell. An electrolytic cell consists an anode, cathode and an electrolyte - medium for
carrying out electrolysis consisting mainly of cryolite in which the alumina (aluminum oxide) is
I
I dissolved.
In an electrolytic cell, when direct current is passed from anode to cathode through molten electrolyte,
alumina dissolved in electrolyte is dissociated into Aluminum and Oxygen. Aluminum being positively
I charged goes to cathode and oxygen being negatively charged goes to anode. Aluminum continues to
deposit on cathode, which is tapped out periodically. Oxygen reacts with anode carbon forming C02
and CO, which ultimately goes out of cell aradio communication resourcess pot gases. The consumed
anodes are replaced in certain sequences periodically with new anodes to continue the process.
The process continues through the entire life of electrolyte cell with periodic metal tapping, anode
charging and feeding of alumina in the electrolyte.
Alumina is fed into the pots by making hole in the crust with the help of breaker at two places and
subsequently, feeding the alumina into the hole by Alumina feeders. The content of Alumina in the
electrolyte is kept within control band by microprocessor fitted on each individual pot. Most of the
time microprocessor keeps alumina concentration within the desired band. But due to some accidental
reasons, anode effect occurs, which needs to be terminated immediately, in order to minimize losses.
In industrial cells, anode effect'occurs when Alumina content of the bath becomes too low to sustain
normal elec~olysisT. he cell voltage then aThe graph shown in Figd indicates the characteristic of cell
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resistance druptly rises to 20 to 50 V. The reason for high voltage during anode effect is due to
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blockage of gas bubble at anode bottom, as at low alumina concentration electrolyte loses the wetting
Aluminum reduction plants varies within wide limit depending apon cell design, cell control and
property to
feeding praktice for alumina. The frequency of anode effect has been reduced with the introduction of
wet and wash off the gas bubbles. The frequency with which mode effect occurs in
I point feeding system. For point fed,prebake cells, the frequency is normally 0.1 per pot day but lower
figures havt also been achieved.
(greenhousC gases), increased energy consumption, increased cell emissions, sidewall attack and
increased bath temperature. Equally importad is the duration of anode effect. With manual feeding, it
The anode
can last several minutes, while with automatic feeding it can be brought down to less than 1 minute.
effect is considered a detrimental event since it leads to emission of CF4 and C2F6
Once the anode effect has occurred in a cell, a fair amount of alumina is added. In addition, it is
necessary to stir the electrolyte to remove gas bubbles.
.Related Art
Reference can be made to a US patent number 4,417,958, in which anode effect is extinguished after a
short time if, immediately after it appears, fine granular salts are introduced together with an injection
medium through a suitable channel into the electrolyte and under the anodes.
Reference can be made to another US patent number 6,866,767, in which instead of adding the full
amount of alumina required following each crust breaking, as is traditional, the standard dose of
alumina is now split into two smaller doses. Thus, a major proportion, e.g. about 50 to 90% by weight,
of the theoretically required alumina to sustain the electrolysis between crust breakings is added
following a crust breaking. The electrical resistance of the electrolyte is monitored between crust
breakings, and if the resistance begins to rapidly increase indicating the approach of an anode effect,
I the anodes are activated into a pumping action thereby breaking the crust adjacent the anodes, allowing
I
alumina to flow into the molten electrolyte, and also creating a stirring action within the molten
electrolyte. This lowers the resistance such that any anode effect is avoided until the next full crust
breaking.
Reference can be made to a patent number CN1807692, in which there is a nitrogen blanking effect for
quenching anode in the production of electrolyzing aluminum, which is characterized by making'
nitrogen pass through preheated steel pipe; getting through anode bottom-hand; passing through air
current stirring aluminum water and electrolyte; destroying a layer of unspace gas film which forms on
anode surface; escaping gas; achieving blanking effect. The method possesses the advantages of
a economic, environment protection and safety, which adapts for all prebaked-anode electrolyzing
aiurninurn manufacturers.
Reference ,may be made to another patent number CN1724714 wherein, is described a method: to
automatically control and extinguishing the anode effect of electro-bath by compressed gas. A
compressed gas channel is set, and a gas jet device is set on the truss of the aluminum output end of
electro-bath and connection to the compressed gas channel. The pressure of the compressed gas is over
0.2mPa, and the content of vapor is lower than 0.01%. effect detecting and predicting program is stored
in automatic control program of t!e electro-bath and taking judge or predict according to the wave of
t.@e electro-bath voltage when anode effect happens. When the electro-bath voltage is lower than the
I voltage preference, the judge effect would be extinguished, the air valve would be close by electro-bath
controlling box instruction executive branch, and the executive branch returns to original state. The
advantage is high success ratio of automaticdly controlling extinguishing effect and can effectively
decrease effect coefficient 0.1O.radio communication resources
Most of the processes described above use an external chemical or agent for termination of anode
effect: None of those processes include a method in which anode effect is automatically terminated by
raising and lowering of anode with the help of an anode motor, without using any external gas or
compressed air.
The main object of the present invention is to provide a process for the automatic termination of anode
effect in an electrolytic reduction cefi.
Another object of the present invention is to provide a process for the automatic termination of anode
effect by automatic identification of the anode effect occurrence.
Yet another object of the present invention is to provide a process for the automatic termination of
anode effect by automatic breaking of crust and feeding of alumina.
A further object of the present invention is to provide a process for the automatic termination of anode
effect by automatically lowering and raising the anodes, in steps.
Another object of the present invention is to provide a process for the automatic termination of anode
effect to save the energy, to improve the .production efficiency, to reduce generation of greenhouse
gases, to preserve natural resource and to minimize engagement of labour.
radio conimunication resourcesSTATEMENT 9F THE INVENTION
According to the present invention, there is provided a process for automatic termination of anode
I
I effect, in an electrolytic reduction pot comprising plurality of anodes immersed in molten alumina bath
, the said process comprising,the steps of:
iv.
v.
vi.
vii.
. . .
Vlll.
ix.
X.
xi.
xii.
xiii.
continuously monitoring of pot voltage and current values;
comparing the voItage values with a predetermined value;
identification of occurrence of anode effect, when voltage value goes above the
predetermined value and stays at such values for at least a predetermined time;
m&ng opening in the solidified crust on ihe surface of the alumina bath adjacent the
said anodes,
feeding alumina into the pot through said opening in the crust,
repeating step (iv) and (v);
waiting for stabilization of the pot voltage aftsr alumina addition in step (vi),
lowering of said anodes in predeteipined stages with intermediate short pause;
waiting for stabilization of the pot voltage;
repeating step (ii);
repeating steps from (viii) to (x), until voltage value is below the predetermined
voltage;
identification of termination of anode effect , when voltage value falls below the
predetermined voltage and stays at such value for at least a predetermined time;
raising the said anodes to original position of said anodes upon identification of
termination af anode effect.
According to another aspect of the invention, there is provided a system for automatic termination of
anode effect for an elecirolytic reduction pot, wherein the said system comprises:
at least one zhode, at least one cathode and a power supply connected to said pot;
an electronic pot controller (EPCj connected to said pot;
a pot voltage sensor for monitoring the said pot voltage and current values;
a means for comparing the predetermined value of voltage applied to said electronic pot
controller to identify the occurrence and tennination of anode effect;
a crust breaker for making opening in the crust after identification of occurrence of anode
effect under the control of said electronic controller;
an alumina feeder for feeding alumina into the said pot through said opening in the crust;
an anode motor for lowering and raising the said anodes under the control of said electronic pot
controller;
a central pot line computer for storing the data captured by said electronic pot controller;
a signal distributor for providing communication between said central pot line computer and
said electronic pot controller and
an audio amplifier for announcing the various status and faultconditions of the said electronic
pot controller.
BRIEF DESCmION OF ACCOMPANYING DFUWlNGS
I Figure lis a cross section view of a prior art an electrolytic reduction cell.
Figure 2 indicates the entire assembly of Electronic pot control panel, along with the input and output.
I Figure 3 indicates a number of electrolytic cells connected in series along with a bus bar configuration
for passage of current, and constitutes a pot line, spread over in two rooms.
Figure 4 indicates the electronic pot control system.
Figure 5 is a timing dia,gam showing steps in a process for automatic termination of anode effect.
Figure 6 is a graph, indicating the influence of alumina concentration on resistance of the electrolyte.
DETAIL DESCRIPTION WITH EFERENCE TO DMWINGS
Figure 1 shows an aluminum reduction cell 100 comprising electrolytic cell (I), cathode block (2),
silicon carbide side lining (3), which is thermally insulated by refractory material Calcium Silicate
Board (4), Dense Firebricks (5) and diatherm 23 insulation bricks (6). Aluminum is produced by
electrolysis of Alumina dissolved in a molten bath of cryolite (7) held in electrolytic cell (1). Anelectrolytic
cell (1) consists an anode (8) - a positive terminal which' is made of calcined petroleum
coke and coal tar pitch, cathode (2) -a negative terminal which is made of anthracitelgraphite carbon
blocks in which steel collector bars are embedded to make electrical connection and electrolyte -
medium for ca,lying out electrolysis consisting mainly of cryolite. Aluminum fluoride and Calcium
1 fluoride in which Alumina is dissolved for electrolysis. E!ectrolytic cells (1) are rectangular steel cells
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in which cathode cavity is constructed to hold molten electrolyte (7) for electrolysis. Bottom of the
electrolytic cell (1) in constructed with prebake carbon blocks providing proper heat insulation and
refractory barrier underneath, while sidewalls are made of silicon carbide brick (3) with proper heat
i I I '
backup. Carbon anodes (8) suspended .from an anode bus (1.0) as conduct current into the cell (1.). The
metal of molten aluminium (9) forms an integral part of cathode. Anode rods (8) carry the current
1 from the anode bus (10) through steel stubs cast with iron into holes in the tops of the anodes. The
voltage is applied ,between anode bus bar (10) and'cathode bus bar (1 1) resulting in a large current flow
between them. Current is conducted out of the cell (1) through steel collector bars (19) to the cathode
bus (1 1) and on to the next cell. The magnitude of the current is typically over 85000 amp. The
electrical current passing through the electrolyte (7) converts alumina into its aluminium and oxygen
components by electrolysis. The aluminium drops to the cathode bottom (2) forming the metal pad (9),
while oxygen combines with carbon from anodes (8) and escapes as carbon dioxide gas. As alumina is
consumed, more alumina is added, as programmed. The carbon oxide is vented away by an overlying
duct (not shown here).
Figure 2 indicates the entire assembly of Electronic pot control (EPC) panel, along with the input and
output. The automatic anode effectresistance of electrolyte termination system is a part of Electronic
Pot Control (EPC) System, which comprises the integrated Logic for automatic termination of anode
effect, in EPROM Chip (31), along kith other components as DC Timer (39), AC Timer (40), Pot
voltage protection (PVPM) Module (36), AE Module (24), Communication card (34), C?U Card (33 ),
Display Card (38), 110 Card (35). As in any control system, it has a set of "inputs" and a set of
"outputs" and the system (200) processes the inputs (201) to generate the outputs (202). This depends
I on the logic encoded inside the EPROM (3 I), which forms a part of the EPC panel (20). The EPROM
' chip serves as the semiconductor memory to store the functional 6r control logic of the entire EPC
system (200). It contains the logical program of all the scheduled & unscheduled process operation
in different sub-routines. These subroutines are called for interrupt based execution by the main
program. This Anode Effect Termination(AET) logic is one of these subroutines with immediate
priority. All the inputs (21,22,23 & 24) are interfaced with the CPU card (33) through the UO card
(35). Inputs (21, 22, 23 & 24) can be a pot voyage from pot (21), pot line current from SD (22), set
point from central PC (23) and anode beam position from proximity switch (24). The proximity switch
(24) is meant for sensing the pulse based Anode position and is mounted besides the cam attached to
the gear box o/p shaft. Similarly all the outputs (26,27,28,29) coming out from the EPC (20) are
connected internally to the CPU card (33) through the I/O card (35). The Outputs (26,27,28,29) can be
an air solenoid (26), crust breaker solenoid (27), feeder solenoid (28) 2nd fluidization solenoid (29).
The other sub systems of the EPC pane1 are Display ca?d (38), which has a number of LED based
status indications, key board (41), which contains 2 number of keys that can be used to send commands
to the EPC (20) by the operator. Push button switches (42) are used for operation in manual mode.
There are various protection sub systems like the DC timer (39), AC timer (40) and the PVPM.module
(36). PVPM (Pot voltage protection Module) (36) is a hardware protection device against anode
movement. It is a comparator based circuit which prohibits against anode lowering if the pot voltage
is less than 3.5 V and against anode raising if the pot voltage is greater than 7.5 V. It provides
protection asainst short circuit and open circuit of pot These hard wares ensure safety of the pot even
if the program (31) goes wrong and behaves erratically. The AE module (37) is a hardware unit which
is connected to the AE lamp (30) and is responsible for its switching during an Anode Effect (AE)
condition. The AE Module (37) is functionally meant for Anode effect detection and generating
the alarm for derting the operator. AE detection is carried out by comparing the pot voltage of
that pot to a predetermined set voltage i.e SV (hardware set) in the module. ?'he moment Actual pot
voltage exceeds the said set value, it actuates annunciation. This sub systems acts to draw the attention
of the operator to that particular pot by visual means. It works as a stand-by system to the voice based
audio annunciation system (45,46), which announces the various status and fault conditions of the EPC
system throughout the pot room by means of a recorded voice. The central line computer PC (43) and
6
the multiplexing device, Signal Distributor SD' (44) is kept in the control room away from the pot line.
' Various process parameters (23) can be set in the PC (43) and can be downloaded to individual
EPCresistance of electrolyte (20) if it is a "Single pot parameter" and to all the EPCs (20) connected to
the PC (43) if it is a "Group parameter". Similarly, each EPC (20) captures data continuousl; from the
pot and sends them to the PC (43), which stores them all for future analysis. For this communication to
happen, the communication card (34) acts as the intermediate link between the CPU card (33) and the
SD (44). The data bus (47) runs through out the pot room in a loop and combines all EPCs (20) into
- one control system. This is the data transfer backbone of the entire EPC system. The Power Supply
System (32) caters to all the power supply n~edosf the P C(2 0).
Figure 3 indicates a number of electrolytic cells connected in series along with a bus bar configuration
forpassage of current, and constitxtes a pot line, spread over in two rooms. In order to regulate the
aluminium reduction process, it is necessay to control the electrical power in the reduction cell (100).
Typically, electrical current (56) is applied to a line of multiple cells arranged in series. Direct current
enters at oce end of one room from rectifier station and travels through the pots connected in series one
after the other in the entire room, and then to the other room through cross-over bus bar (51) and
further travels back to rectifier station through pots of the other room. EPC system (200) is further
connected to the following components of the system: Pot line current sensor (50), Cell Volta, ~e sensor
(52), anode motor (48), Alumina feeder(54) and Crust breaker (55). Anode motor (48) is the motor
used for raising and lowering the anodes.
Figure 4 indicates the electronic pot control system. Each pot cell (1) is connected with one EPC (20)
and this EPC (20) is responsible for the control of that particular pot. The EPC (20) controls as per the
logic programmed, in its EPROM (31) memory. These EPCs are in turn connected with the Central
pot line computer (43) (PC) through a multiplexing device called signal Distributor (SD) (44). The PC
(43) and SD (44) are kept in the control room away from the pot line. Various process parameters can
I be set in the PC (43) and can be downloaded to individual EPC (20) if it is a "Single pot parameter"
and to all the EPCs connected to the PC (43) if it is a "Group parameter". Similarly, each EPC (20)
captures data continuously from the pot and sends them to the PC (43), which stores them all for future
analysis. The pot cell units are connected with rectifier acting as electrical energy source (25).
Figure 5 represents a timing diagram showing the sequence of various operations performed by the
EPC to terminate anode effect. The anode effect termination (AET) process in an aluminium
electrolyte cell automatically consists of four steps: AE breaking and feeding (AEB) (12') anode
lowering (13'), anode raising (14') and adjusting the pot voltage. The,said timing diagram (20') showsthe
sequences of various operations performed by the EPC (15) on the onset of an anode effect in a pot
if AET logic is enabled in that particular pot (through single pot parameter no. 30 (described below))
and if all the necessary conditions for starting the AET logic is met.. For implementation of pis logic,
following changes have been done:
a) EPC Timer Setting:
DC Timer (25) : Set at 8 (8 x 0.8 = 6.4 seconds)
AC Timer (26) : Set at 7 (7 seconds)
I b) The Pot Voltage Protection Module (PVPM) (36), for hardware protection of anode movement
corresponding to pot voltage, should be by passed. The same protection is made available in the
I software and is not applicable when AET iogic is ON. (No anode movement below 3.5 volts and above
7.0 volts).
I Group parameter no. 27 I Total duration of second AET &ode lowering, unit in seconds, default: 191i
c) Parameter Settings:
I I I sec.
Group parameter no. 29
i Single pot parameter no. / AET software enables swirch, default is 0 (off). Set the value at 255 to,1
Total duration of first AET anode lowering, unit in seconds, default: 18
sec.
1 Group parameter no. 29 /Total duration of first AET anode lowering, unit in seconds, default: 18 I
I
i I
! / sec.
I
I
/ switch ON.
The EPC (20) continuously tdces measurement of the pot voltage. As soon as the pot voltage goes
above 8 Volts and stays there for at least-30 seconds, it is said to be under anode effect (AE). Soon
after occurrencs of AE (l'), the EPC initiates AEB (Anode Effect Breaking) sequence (12'), wherein
there is two cycles of crust breaking (2', 4') and feeding (3', 5'j by crust breaker (55) and point feeders.
Due to this operation, the pot gets a definite amount of alumina into the pot, which increases the
concentration of free alumina in the pot. This helps in adjusting the alumina concentration in the pot of
,the desired level. Thereafter it waits (6') for some time - 10 seconds for the pot voltage to stabilize.
Then EPC (20) initiates the lowering (7') of the anode by activating the downward movement of the
anode motor (48) by 18 secs (as mentioned in group parameter no. 29). This is done in four stages with
intermediate short pause and not at one stietch to avoid the tripping of the AC and DC timers (25,26)
and ultimately movement of the anode motor (48). These timers are hardware timer elements in the
EPC (20) and protect the pot against any movement either in upward or downward direction on
continuously and hence prevent an open circuit or short circuit condition in the pot line. Mter this
operatioc, the trapped gases normally escape out of the pot through the feeding holes. It has been
observed that in 90-95% of the cases during this cycle the anode effect gets terminated. After lowering
sequence, EPC waits (8') and determines whether the anode effect has been terminated successfully or
not. If it has been terminated successfully, EPC gives co&and to the anode motor for raising (1 1') the
anode by equal amount as it was lowered in the lowering (7') cycle. This is also carried out in four
stages.
But, in case AE still persists after the first lowering (7') cycle, the EPC initiates another'cycle of
lowering (9') of the anode by 19 secs (as mentioned in group parameter no. 27). This second lowering
cycle is also in four stages similar to the first lowering cycle. Then EPC waits (10') and determines
whether the mode effect has been terminated successfully or not. If it has been terminated successfully,
EPC gives command to the anode motor for raising (1 1') the anode by equal amount as it was lowered
combinedly in the first and second lowering (7', 9') cycles. This is carried out in eight stages.
After the raising (1 1') operation, the final operation in the voltage adjustment phase, which has not
been shown in the timing sequence (20') as because by then the anode effect has been terminated
automatically, and EPC works to bring the pot voltages to its normal working level. This phue is like
any other period in the operation of the pot by EPC. However, this phase assumes importance as
I
: sometimes it so happens that the pot voltage remains low after the A . is terminated and the EPC has to
give command to the anode motor (48) to raise the anode.
,I
1 While the AET logic is operating, the red LED light marked as "AEB" on the EPC panel will be
steadily on. If the AET logic cannot terminate the AE or if AET logic is interrupted by some other.
reasons, the red AEB light on the EPC will go off and the audio annunciation system will announce the
I operator to terminate the anode effect manually. Therefore as soon as an AE occurs, the operator must
come soon to the pot and monitor the AET process. He should intervene with a bamboo only if the
I AEB light goes off and gets a message from the annunciation system for AET failure and shall never
insert bamboo or move anode when AEB light is ON, as this will interrupt the AET logic.
I I I 14 I Alumina feeding two times 112sec. 1
The automatic anode effect termination sequence (20') is shown in the table below:
I I
!
1 Step I, Action
I Compulsory Loop I 1 I Normal breaking 16 sec.
1
I 12 ~luminfae eding two times 1 12 sec.
I 1 3 / Normal breaking
I
6 sec.
i
(Step l~ction I I
I I i / 5 1 wait ! 10sec. 1
I I I
1 5 j Lower anodes in 4 stage (as per setting the parameter no. 29) / 18 sec. 1
LOO^ 0 19 1 Lower anode in 4 stages (as per setting in parameter no. 27)- / 19 sec. 1
I j10 I ~ a i t /10sec. 1
1
I I
1 1 1 1 If AE is still on, declare an AET failure
I I Wait O s e c 1
I I 1 12 /Raise anode (= Total lower) 118 + i 19 1 I I 1 I I I
I 1 1 sec.
I i 1 13 I Adjust pot voltage as per set voltage value I I I
I I I
I Ii 8 ! Check if AE out. If yes, jump to step 12 I I
The AET logic will not be started if any of the following conditions below are true:
(a) If AET logic has not been enabled by means of a software switch (i.e. if pot parameter no. 30 is not
set at 255).
(b) If pot line cnrrent is fluctuating or less than 10 kA below the set value.
(c) Within one hour after DC power outage.
(d) During and 5 minutes after tapping.
(e) Less than half an hour after last AE in the pot.
(g) If there is any fault in the EPC indicated by a fault no.
(h) If EPC is in manual mode.
(i) Less than half an hour after initialization of EPC parameter.
Cj) If ARC control is in disabled (off) condition.
When an AE occurs, and EPC is in AUTO mode, even if AET logic does not start for some reasons or
the other as mentioned above, the anode effect Breaking and Feeding will still function, but anode
lowering and raising will not happen.
During course of AET in operation, it can zlso be interrupted when any of the following conditions
occur:
a) If the EPC is switched to Manual Mode.
b) If AET logic is disabled through software switch (parameter no. 30).
c) If any EPC fault occurs.
d) Pot line current goes below 10 kA of set value or starts fluctuating.
Whenever AE occurs, operator must go near the pot, break the hole, prepare bamboo and monitor the
running of the anode motor and movement of the anode bus bar. The operator should observe whether
any liquid bath (electrolyte) overflow is there. If there is too much bath overflow during anode
lowering, operator should press manual button to interrupt AET logic. Once AET logic is interrupted
manually or by EPC, operator should lull AE manually by inserting a bamboo only if the AEB light
goes off. If the anodes are at a lower position, and bath is full to the level of deck plate, operator should
I I raise the anode first and then insert the bamboo otherwise bath will spill out. 1 Figure 6 is a ,oraph, indicating the influence of alumina concentration on resistance of the electrolyte.
I I I
The graph shown in Fig-6 indicates the characteristic of cell resistance w.r.t concentration of Alumina
I I in the cell. This in turn depicts that higher voltage (higher Resistance at same stipulated current) in the
I -
I cell is the result of starvation of Alumina in the cell. This is the cause of the AE. The more the
starvation period continues, it affects the process in two ways 1. The cell voltage remains at higher
voltage resulting Energy loss due to unnecessary higher voltage in the cell. 2. Less consumption of
I Alumina results in less production. Therefore effectiveness of AET logic is critical against saving in
terms of the said losses.

We Claim:
1) A process for automatic termination of anode effect, in an electrolytic reduction pot
.comprising plurality.of anodes immersed in molten alumina bath , the said process comprising '
the steps of: . .
i. continuously monitoring of pot voltage and current values;
. . 1 . 11. comparing the voltage values with a predeiermined value;
I
iii. identification of occurrence of anode effect, when voltage value goes above the
predetermined value and stays at such values for at least a predetermined time;
iv. making opening in the solidified crust on the surface of the alumina bath adjacent the said
anodes, resistance of electrolyte
v. feeding alumina into the pot through said opening in the crust,
I: .
vi. repeating step (iv) and (v);
vii. waiting for stabilization of the pot voltage after alumina addition in step (vi),
...
vm. lowering of said anodes in stages with intermediate short pause;
ix. waiting for stabilization of the pot voltage;
x. repeating step (ii);
xi. repeating steps from (viii) to (x), until voltage value is below the predetermined voltage;
xii. identificzition of termination of anode effect , when voltage value falls below the
predetermined voltage and stays at such value for at least a predetermined time;
. . . xi11 . raising the said anodes to original position of said anodes upon identification of
termination of anode effect.
2) The process for automatic termination of anode effect as claimed in claim 1, wherein said
predetermined voltage value is 8 volts and predetermined time value is 30 sec.
3) The process for automatic termination of anode effect as claimed in claim 1, wherein said
lowering of anodes is done preferably in four stages.
4) The process for automatic termination of anode effect as claimed in claim 1, wherein said
lowering of the anodes is repeated preferably two times at short intervals.
5) A system for automatic termination of anode effect in an electrolytic reduction pot, wherein
the said system comprises:
at least one anode, at least one cathode and a power supply connected to said pot;
an electronic pot controller (EPC) connected to said pot;
a pot voltage sensor for monitoring the said pot voltage and current values;
a means for comparing the predetermined value of voltage applied to said electronic pot
controller to identify the occurrence and termination of anode effect;
a crust breaker for making opening in the crust after identification of occurrence of anode
effect under the control of said electronic controller;
an alumina feeder for feeding alumina into the said pot through said opening in the crust;
an anode motor for lowering and raising the said anodes under the control of said electronic pot
controller;
a central pot line computer for storing the data captured by said electronic pot controller;
a signal distributor for providing communication between said central pot line computer and
said electronic pot controller and
an audio amplifier for announcing the various status and fault conditions of the said electronic ,
pot controller .
6) A system for automatic termination of anode effect in an electrolytic reduction pot as claimed
in claim 5, wherein said electronic pot controller comprises:
a logically pro,mmrnable erasable programmed read only memory (EPROM) chip,
a central'processing unit (CPU) card by which all the inputs of said electronic pot controller are - interfaced through a inputfoutput (VO) card ;
a display card with a plurality of light emitting diodes (LED) for indicating the status of anode
effect;
a key board having a-plurality of keys to send commands to s ~eldect ronic pot controller;
push button switches for manual operations of the system;
DC timer, AC timer for the safety of said pot,
I
anode effect (AE) module and a pot voltage protection module (PWM).
7) The system as claimed in claim 5 wherein said electronic pot controller is configured to capture ,
data continuously from the pot and transfer to the said central pot line computer for future
analysis.
8) The system as claimed in claim 6 wherein said inputs of said electronic pot controller comprise
pot voltage from pot, pot line current from said signal distributor, set point from central pot line
computer and anode beam from proximity switch.
9) The system as claimed in claim 6 wherein said EPROM chip is a semiconductor memory to
store the functional and control logic of said electronic pot controller.
I
10) The system as claimed in claim 6 wherein said PVPM module is configured to disallow anode
lowering when pot voltage value goes above the predetermined value and anode-raising when
pot voltage value goes below the predetermined value.
11) The system as claimed in claim 10 wherein said PVPM module disallows anode lowering when
pot voltage value goes above the predetermined value of 7.5 volts and anode raising when pot
voltage goes below the predetermined value of 3.5 volts.
12) The system as claimed in claim 6 wherein said AE module is configured to switch on or switch
off power supply to AE lamp on incidence or termination of anode effect.
13) A process for automatic termination of anode effect substantially as hereinbefore described with
reference to the accompanying drawings.
14) A system for automatic termination of anode effect substantially as hereinbefore described with
reference to the accompanying drawings.