FIELD OF INVENTION
The present invention generally relates to control systems, and, more particularly, to a a process for controlling smelting of aluminium in an aluminium smelting cell.
BACKGROUND
Aluminium is one of the metals which is excessively used these days owing to its capability of being put to diverse uses. Some of the most prominent uses of aluminium include, but are not limited to, in automobiles, utensils, food packaging, casings of electronic equipment, transmission lines and the like. Few reasons why aluminium is used so widely is its low density, passivity to corrosion, ductility and malleability. However, aluminium is generally not available in its elemental form in the environment. Bauxite is the common form in which aluminium is found in the nature and aluminium is separated from bauxite by using electrolytic reduction. Particularly, Hall-Heroult smelting process is conventionally used for separating aluminium from bauxite into its components, i.e. aluminium and oxygen. Fig. 1 illustrates the electrolytic cell, commonly called "pot", that is conventionally used to implement the Hall-Heroult process. As shown, the pot 100 includes a steel shell 105 in which carbon cathode lining 110 is provided. The carbon cathode includes steel bars 115 embedded therein for carrying current out of the pot 100. Further, the pot 100 includes one or more carbon anodes 120 and a molten bath 125 containing sodium hexafluoroaluminate (Na3AlF6), alumina and aluminium flouride. A number of pots are placed in series such that direct current is passed through the anodes to the cathode through the cryolite bath and subsequently to anode of adjacent pot.
Consequent to passage of electric current, liquid aluminium gets deposited at the cathode while oxygen in the alumina combines with carbon from the anodes to produce carbon-di¬oxide and as a result the anode constantly depletes as the electrolytic reaction proceeds. Also, additional alumina is fed, at regular intervals, into the pots from hoppers operated by actuators so as to maintain the desired concentration of the molten bath. The concentration of alumina is critical to the process since should the concentration fall to

about 1.5 to 2%, a phenomenon called "anode effect" occurs. Particularly, during the anode effect, the normal electrolytic reactions fail to occur and as a result gases like CO, CF4 and C2F6 are produced. These gases form bubbles that adhere to the anode bottom, thereby creating an electrically insulating layer. Consequently, the electrical resistance of the pot increases and the normal voltage rises by up to 10 to 15 times of normal level of 4 to 5 volts, thereby affecting the performance of the pot and efficiency thereof.
It is thus essential that anode effect be avoided so as to maintain the efficiency of the entire process. It will thus be evident that there is a requirement to maintain the appropriate concentration of alumina in the bath so as to avoid any anode effects. This is carried out by selecting an appropriate feed strategy of alumina. Generally, the feed strategy is based on measurement of pot voltage and current at appropriate intervals so as to determine the interval of feeds. However, such conventional feed strategies are not capable of controlling the amount of alumina fed based on appreciation of real time situation and thus at times more amount of alumina than what is actually needed is added. A harmful effect of adding excess amount of alumina could be that the pots become mucky.
Accordingly, there persists a need for a process for controlling an aluminium smelting cell that effectively avoids anode effect.
Further, there persists a need for a process for controlling an aluminium smelting cell that controls the amount of alumina fed on a real time basis.
Furthermore, there exists a need for a process for controlling an aluminium smelting cell that effectively avoids wastage of alumina, thereby enhancing the throughput.
Moreover, there exists a need for a control system that effectively avoids anode effect by controlling, on a real time basis, the amount of alumina fed to the cell.

OBJECTS OF THE INVENTION:
In view of the foregoing disadvantages inherent in the prior art, the general purpose of the present invention is to provide a process for smelting of aluminium in an aluminium smelting cell that obviates the above and other disadvantages from existing art.
Accordingly, an object of the present invention is to provide a process for controlling smelting of aluminium in a smelting cell such that the process effectively avoids anode effects based on real-time control over the quantity of alumina being fed to the cell.
Another object of the present invention is to a control system for controlling smelting of aluminium that effectively avoids anode effects based on real-time control over the alumina being fed to the cell.
These and other objects and advantages of the invention will be clear from the ensuing description.
SUMMARY:
In light of the above objects, one aspect of the present invention relates to a process for smelting of aluminium in an aluminium smelting cell. The process comprises determining value of voltage and current at first pre-determined intervals and noise value in the current and voltage pertaining to the smelting cell at second pre¬determined intervals. The process further comprises computing a raw resistance value from the determined value of voltage and current, average noise value from the determined noise value, and a smooth resistance value based on the raw resistance value. The process also comprises determining number of dumps of alumina to be

added to the smelting cell by selecting an appropriate alumina dumping strategy from a noise feed dump strategy, a fast feed dump strategy and a high volt dump feed strategy based on at least one of the computed value of raw resistance, smooth resistance value and average noise. Finally, the process comprises controlling voltage of the smelting cell by raising or lowering anode in the alumina smelting cell based on comparison of smooth resistance value and the control resistance value at third pre-determined intervals.
In another embodiment of the present invention, the first pre-determined interval ranges between 10 millisecond (ms) to 500 ms.
In yet another embodiment of the present invention, the first pre-determined interval is 100 milliseconds (ms).
In still another embodiment of the present invention, computing the raw resistance value comprises computing a change in raw resistance (dR) value by determining raw resistance at every 3 second interval and computing a rate of change of raw resistance (dR/dT) therefrom.
In still another embodiment of the present invention, the second pre-determined interval ranges between 1 to 6 minutes.
In still another embodiment of the present invention, the second pre-determined interval is 3 minutes.
In still another embodiment of the present invention, computing the average noise value comprises computing the average of noise values for three minutes preceding the instant when the average noise is to be computed.

In still another embodiment of the present invention, selecting the noise feed strategy as the alumina feed strategy comprises determining the number of dumps of alumina as one and selecting time interval between consecutive dumps to one of 20 minutes and actual time interval of alumina dumps determined based on dumps of last 24 hours when the average noise value is determined to be greater than 0.05 Volts and the determined noise value is greater than 0.05 V, and concluding the noise feed strategy when the computed average noise value is less than 0.05 V.
In still another embodiment of the present invention, selecting the fast feed strategy as the alumina feed strategy comprises computing deviation in computed value of raw resistance with respect to the control resistance value, and selecting the number of dumps of alumina from a pre-determined set of dump values, when the average noise value lies between 0.05 Volts and 0.1 Volts, the deviation in the computed value of raw resistance with respect to the control value is at least 0.05 V and the computed value of the rate of change of raw resistance is determined to be positive for at least ten consecutive 3 second intervals the set of dump values being based on time duration between consecutive fast feed dumps and number fast feed dumps in preceding eight hours. The fast feed dumps conclude when deviation between the smooth resistance value and the control value is less than 0.01 V.
In still another embodiment of the present invention, selecting the fast feed strategy as the alumina feed strategy comprises computing deviation in computed value of raw resistance with respect to the control resistance value, and selecting the number of dumps of alumina from a pre-determined set of dump values, when the average noise value lies is less than 0.05 Volts, the deviation in the computed value of raw resistance with respect to the control value is at least 0.05 V and the computed value of the rate of change of raw resistance is determined to be positive for at least two consecutive 3 second intervals, the set of dump values being based on time duration between

consecutive fast feed dumps and number fast feed dumps in preceding eight hours. The fast feed dumps conclude when deviation between the smooth resistance value and the control resistance value is less than 0.01 V.
In still another embodiment of the present invention, selecting the high volt feed strategy as the alumina feed strategy comprises computing deviation in the computed value of raw resistance with respect to a control value, and selecting the number of dumps as 4 when the deviation in the computed value of raw resistance with respect to the control value is greater than 1 V
In still another embodiment of the present invention, the third pre-determined interval ranges between 12 seconds to 60 second.
In still another embodiment of the present invention, the anode is raised when the smooth resistance value is determined to be less than the control resistance value.
In still another embodiment of the present invention, the anode is lowered when the smooth resistance value is determined to be greater than the control resistance value.
Another aspect of the present invention relates to a system for smelting of aluminium comprising an aluminium smelting cell having a pot, cathode and anode, a means for determining value of voltage and current pertaining to the smelting cell at first pre¬determined intervals and noise value in the determined current and voltage at second pre-determined intervals and a controller communicably coupled to the means for receiving the determined value of cell voltage, current and noise value. The controller is adapted to compute a raw resistance value from the determined value of voltage and current, average noise value from the determined noise value and a smooth resistance value based on the raw resistance value. The at least one of the the computed value of

raw resistance, average noise and smooth resistance is used by the controller for determining number of dumps of alumina to be added to the smelting cell by selecting an appropriate alumina dumping strategy from a noise feed dump strategy, a fast feed dump strategy and a high volt dump feed strategy. Also, the controller is adapted to compare the smooth resistance value and the control resistance value at third pre¬determined intervals for controlling voltage of aluminium smelting cell by raising or lowering the anode. The system also includes a plurality of actuators coupled to the controller for raising or lower the anode and for dumping alumina in the smelting cell based on the selected alumina feeding strategy.
In another embodiment of the present invention, the controller is a programmable logic controller.
In another embodiment of the present invention, the controller is a microprocessor.
These aspects together with other aspects of the present invention, along with the various features of novelty that characterize the present invention, are pointed out with particularity in the claims annexed hereto and form a part of this present invention. For a better understanding of the present invention, its operating advantages, and the specific objects attained by its uses, reference should be made to the accompanying drawing and descriptive matter in which there is illustrated an exemplary embodiment of the present invention.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS:
The advantages and features of the present invention will become better understood with reference to the following detailed description and claims taken in conjunction with the accompanying drawings, in which:

Fig. 1 illustrates a view of a typical smelting cell, as known in the art.
Fig. 2 illustrates a process for controlling smelting in a smelting cell, in accordance with an embodiment of the present invention.
Fig. 3 illustrates a block diagram of a control system for controlling smelting in a smelting cell, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF INVENTION WITH REFERENCE TO DRAWINGS:
The exemplary embodiments described herein detail for illustrative purposes are subject to many variations in structure and design. It should be emphasized, however, that the present invention is not limited to a particular process and system for controlling smelting of aluminium as described. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.
The terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Further, the terms "first," "second," and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another.
Fig. 2 illustrates a flow diagram for a process 200 for smelting of aluminium in an aluminium smelting cell. The process 200 is implemented in a control system 500 for a smelting cell 300, as shown in Fig. 3, and thus the process 200 will be explained in conjunction with Fig. 3. The process commences at 202 with the smelting cell 300 set up such that a carbon anode 305 (Fig. 3) is held in position within the a 310 containing the

electrolyte bath 315 in which the alumina is to be added in a manner such that the concentration of alumina is maintained at an optimum level. At the same time the quantity of alumina added should be as per the requirement and such that addition of any excess quantity than what is required, is avoided. As shown in Fig. 3, the smelting cell 300 includes actuator 320 coupled to the anode 305 so as to raise or lower the anode 305 from the pot 310, when required. Also, the cell 300 includes hopper and actuator assembly 325 that are adapted to add a pre-determined quantity of alumina to the electrolytic bath 315 when required. The operation of the actuator 320 and hopper and actuator assembly 325 will be controlled based on the process 200, as will be explained in the ensuing description.
Referring to Fig. 2 again, the process 200 includes determining a value of voltage and current in the cell 300, and noise in the current and voltage pertaining to the smelting cell 300, at 204. Particularly, the control system 500 includes a means 505 (Fig. 3) that is adapted to determine the voltage, current and noise value pertaining to each of the pots. More particularly, the means 505 determines the current and voltage through the pot 310 regularly at first predetermined intervals and the noise value in the said current and voltage at second predetermined intervals. In an embodiment of the present, the first predetermined interval ranges between 10 millisecond (ms) to 500 ms. In yet another embodiment, the first predetermined time interval is preferably 100 millisecond (ms). Thus, after every first pre-determined interval, the means 505 determines the value of the pot current and the pot voltage. In one embodiment of the present invention, the means 505 could be a digital multimeter adapted to measure voltage and current and noise meter adapted to measure noise. In another embodiment, the means 505 could comprises separate digital voltmeter and digital ampere-meter for measurement of the voltage and current respectively, and noise meter for measurement of noise in the voltage and current, In yet another embodiment of the present invention, the means 505 may include analog input modules.

Furthermore, in an embodiment of the present invention, the second pre-determined interval ranges between 1 to 6 minutes. In yet another embodiment of the present invention, the second pre-determined time interval is preferably 3 minutes. Thus, the noise in the measured voltage and current is determined after every second predetermined interval by the means 505.
Further, the means 505 is coupled to a controller 510, as shown in Fig. 3. In an embodiment of the present invention, the means 505 may be implemented within a controller 510 of the control system 500. In an embodiment of the present invention, the controller 510 may be a programmable logic controller. In yet another embodiment of the present invention, the controller 510 may be a microprocessor, such as an Intel processor, running at 1.1 Gigahertz (GHz) and adapted to support fan less configuration with low power requirement, universal serial bus ports, software programmable timer function with interval setting features, having up to 10 analog input channels each having capability with 1 millivolt resolution at 100 millisecond intervals and having a main memory of up to 2 Gigabytes. As shown in Fig. 3, the controller 510 is also coupled to actuator 320 and the hopper and actuator assembly 325 so as to selectively operate the same for raising or lowering the anode 305 and dumping alumina in the pot, respectively. The control system 500 may also include various buzzers/alarms coupled to the controller 510 so as to give appropriate warning signals, when required.
Referring back to Fig. 3, the present invention further envisages that upon determining the value of voltage, current and noise, the process 200 includes, at 206, the step of computing a raw resistance value, an average noise value from the determined noise value and smooth resistance value based on the computed raw resistance value. In this regard, the controller 510 determines the raw resistance value from the determined value of voltage and current based on the following equation:
(Equation Removed)
where, BACKEMF is a constant value representative of back electromotive force (EMF) developed in the cell.
The step of computing raw resistance value further includes computation of a change in raw resistance (dR) value at every 3 second interval and thereby computing a rate of change of raw resistance value, i.e. dR/dT .
Furthermore, smooth resistance is computed at every 6 sec interval by two stage filtering of computed Raw Resistance by using the following equations:
Stage-I Resistance is computed every 1.5 seconds by following formula:
(Formula Removed)
where RR and last value of RR represent the value of raw resistance at the end and beginning of the 1.5 seconds interval. In this respect, iResGain! is a constant and has a value 0.2, in one embodiment of the present invention
Stage-II Resistance is computed every 6.0 seconds by following formula:
(Formula Removed)
where RR1 and last value of RR1 represent the value of raw resistance computed at the end and beginning of the 6 seconds interval.
Stage-III (Smooth) Resistance is computed every 6.0 seconds by following formula:
(Formula Removed)
In this respect, iResGain_2 is a constant and has a value 0.2609, in one embodiment of the present invention.
Further, the average noise is computed by using noise values determined for second pre¬determined intervals preceding the instant when the average noise is to be computed. In an embodiment of the present invention, the average noise is computed by using noise values determined for three minutes preceding the instant when the average noise is to be computed. Thus, for the described embodiment, the computation of the average noise is based on the following equation:
(Equation Removed)
Where NV=Noise Value (calculated in Noise) is taken in 3 seconds samples.
Referring back to Fig. 2, the process 200 at 208 includes determining, based on the computed values of at least one of the raw resistance, smooth resistance and average noise, number of dumps of alumina to be provided to the smelting cell 300 by selecting an appropriate dump strategy selected from a noise feed dump strategy, a fast feed dump strategy and a high volt dump feed strategy. Particularly, the present invention envisages use of different feed strategies as per the requirement, thereby controlling the amount of alumina being added to the cell 300 as per the real-time requirement and thus avoiding any wastage of alumina, as will be evident from the following paragraphs. In an embodiment of the present invention, each dump includes a charge of 4 kilograms of alumina.
The various feed strategies would now be explained. Particularly, to determine which feed strategy to be used, the process 200, at 208, includes determining whether the computed average noise value is greater than 0.05 Volts (V) as well as the noise value is greater than 0.05 V. Upon determining the computed average noise value to be greater than 0.05 Volts (V) and noise value to be greater than 0.05 V, the controller 510 selects the noise feed strategy in which a single dump of alumina is given at a pre-determined noise feed interval. This pre-determined noise feed interval is calculated based on actual time interval of alumina dumps in the last 24 hours of operation of the cell. In an embodiment of the present invention, the actual time interval as determined from last 24
hours of operation may be ranging between 12 to 20 minutes. In the event such a data is not available, the controller 510 gives a dump at every 20 minutes. Particularly, when the controller 510 determines that the average noise value is greater than 0.05 Volts (V) and noise value is greater than 0.05 V, it gives appropriate signals at every pre-determined noise feed interval to the hopper and actuator assembly 325 so as to feed one dump of alumina into the pot. The noise feed strategy concludes when the average noise value becomes less than 0.05 V or in the event the fast feed strategy commences.
Particularly, it is to be noted that the controller 510, during the noise feed strategy, continually determines the value of rate of change of raw resistance (dR/dT) and a difference between the computed raw resistance value and a control resistance value. In this respect, the control resistance is a constant value derived by summation of base resistance, temporary resistance, noise control resistance and anode set resistance. Particularly, the base control resistance is a constant resistance required for running a particular pot and hence is dependent upon individual pot characteristics (such as drops, pot life, lining type and the like. The typical range for the base control resistance is between 4.10 volts to 5.0 volts (V). Also, temporary resistance is an additional resistance required to run the pot and it depends upon conditions of pot (such as temperature, noise, age etc. The value of temporary resistance ranges between 0.20 V to 2 V.
In addition, the noise control resistance is a resistance value automatically added by the controller to control an unstable pot and it depends upon the noise in the pot. Further, its value typically ranges between 0.05 V to 0.30 V. Moreover, anode set resistance is an additional resistance required during new anode setting and depends upon the characteristics of anode. Its typical value ranges between 0.15 V to 0.45 V
Further, as stated, the controller 510 determines the difference between the computed raw resistance value and control resistance value, and dR/dT during the continuation of noise feed strategy to take decision regarding commencing the fast feed strategy. In an embodiment of the present invention, this determination is carried out every three second.
Particularly, the controller 510 is adapted to check the value of dR/dT every 3 seconds. The present invention envisages that if the difference between the computed raw resistance and control resistance is at least 0.05 volts, dR/dT is computed to be positive for at least ten consecutive 3 second intervals and computed average noise value lies between 0.05 V to 0.1 V, the controller 510 commences the fast feed strategy. More particularly, in the fast feed strategy, the controller 510 selects the number of dumps from a pre-determined set of dumps which may be stored in a memory (not shown) coupled to the controller 510. The set of dump values includes a set of values determined based on the time duration between consecutive feed dumps and number of dumps in the preceding eight hours. The set of dump values are represented in the form of a look-up table which includes different values of dumps as per track time which is calculated as:
Track time= samples of time between consecutive fast feed dumps for preceding 8
hours/number of fast feed dumps in preceding eight hours (6)
The look up table depicting the values of dumps as per different track times under different working condition of the pot (i.e. non-working, low stub or anode set conditions) is as follows:
(Table Removed)
Specifically, the controller 510 calculates actual track time as per equation (6) and selects a value of number of dumps to be given during the fast feed strategy from the look up table as per the working condition of the pot.

In this regard, it is to be noted that controller 510 determines the difference between the computed raw resistance value and control resistance value in terms of voltage by multiplying the difference with constant line current across each of the pots and hence the difference has been expressed in volts. Throughout the description, the difference between resistance values will be expressed in terms of volts.
Further, the controller 510 concludes fast feed dump when the value of smooth resistance and control resistance value is less than 0.01 V. In an embodiment of the present invention, this comparison of smooth resistance and control resistance is carried out every 1 to 6 seconds. Preferably, the comparison is carried out every 3 seconds This control philosophy in the present invention helps in avoiding anode effect over the known systems since in the conventional systems, the decision to terminate feed is carried out at larger intervals of 1 minute which gives rise to anode effect.
Furthermore, the controller 510 may commence fast feed strategy even when the average noise is determined to be less than 0.05 V at step 208 of the process 200. Particularly, upon determining that the computed average noise is less than 0.05V, the controller checks if the deviation in computed value of raw resistance and control value is at least 0.05 volts and computed value of dR/dT is positive for at least two consecutive 3 second intervals . In the event, the deviation in computed value of raw resistance and control value is at least 0.05 volts and computed value of dR/dT is positive for at least two consecutive 3 second intervals, fast feed strategy commences with the number of dumps being decided based on the pre-determined set of dumps having a set of values determined based on the time duration between consecutive feed dumps and number of dumps in the preceding eight hours. More particularly, the controller 510 computes a track time according to equation (6) and picks up a value of number of dumps corresponding to the track time from the look up table, as explained hereinbefore.
Further, the controller 510 concludes fast feed dump when the value of smooth resistance and control resistance value is less than 0.01 V. In an embodiment of the present

invention, this comparison of smooth resistance and control resistance is carried out every 1 to 6 seconds. Preferably, the comparison is carried out every 3 seconds and this helps in avoiding anode effect over the known prior arts wherein the decision to terminate feed was carried out at intervals of 1 minute. Thus, the present invention provides control over short intervals and thus avoids anode effect effectively.
Furthermore, in the event the deviation in computed value of raw resistance with respect to the control resistance value exceeds 1 V, the controller 510 selects the high volt feed strategy in which the 4 dumps are given. The high volt feed concludes after 4 dumps.
Referring back to Fig. 2, the process 200 also includes, at 210, controlling the voltage of the smelting cell 300 by raising or lowering the anode 305. Particularly, this control is carried out based on a comparison of smooth resistance and control resistance at third pre-determined intervals in addition to the normal automatic voltage control procedure that takes place every 3 minutes in a conventional cell. In this respect, the present invention envisages that the comparison between the control resistance and the smooth resistance is carried out at every third pre-determined interval. In an embodiment of the present invention, the third pre-determined interval ranges between 12 to 60 seconds. In a preferable embodiment, the third pre-determined time interval is 24 seconds. In particular, the present invention envisages that the controller 510, at every third pre¬determined time interval, determines whether the smooth resistance is less than the control resistance. In the event, the smooth resistance is less than the control resistance, the controller 305 gives an appropriate signal to the actuator 320 of the anode 305 to raise the anode 305 from the pot 310. Alternatively, if the smooth resistance is greater than the control resistance, the controller 305 gives an appropriate signal to the actuator 320 to lower the anode 305 into the pot 310. Further, the present invention envisages that the anode movement is limited to 0.4 seconds. The present invention further envisages that the comparison between the smooth resistance and the control resistance, at step 210, is carried out every 18 seconds during tapping and every 42 second during anode effect termination.

Consequent to the raising or lowering of the anode 305, the resistance of the cell changes and as a result the voltage of the cell 300 may be controlled.
The process 200 concludes at 212 with the liquid aluminium being being deposited at the cathode. The liquid aluminium is removed by using any conventional process, such as using a siphon.
Thus, in this manner, the present invention envisages an improved process of smelting in the aluminium smelting cell 300. The present invention also envisages a unique control system 510 that helps in a real time control of the smelting process, thereby effectively avoiding anode effects. In the process, described herein, the decision regarding feeding is taken every 3 seconds unlike the conventional systems where this decision is made every 1 minute. Consequently, the anode effect in the present invention is reduced as compared to the prior arts. Besides, the present invention utilizes the concept of determining consecutive positive dR/dT so as to decide regarding the feeding decision and this provides a better decision making procedure for detecting alumina concentration over the conventional arts. In addition, the present invention envisages that the decision regarding termination of fast feed takes place every 3 seconds as compared to time period of 1 minute in the conventional systems which resulted in overfeeding of alumina and consequent wastage of alumina. Also, the present invention, includes an additional step of controlling the anode movement at every 24 seconds interval besides the normal movement at every 3 minute interval in conventional arts. The beneficial effect achieved in the present invention is that the system achieves an efficiency of 94.5% as compared to conventional systems where the efficiency is 93%.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that

various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.

We claim:
1. A process for controlling smelting of aluminium in an aluminium smelting cell,
the process comprising:
determining value of voltage and current pertaining to the smelting cell at first pre¬determined intervals and noise value in the current and voltage at second pre-determined intervals;
computing a raw resistance value from the determined value of voltage and current, average noise value from the determined noise value, and a smooth resistance value based on the raw resistance value;
determining number of dumps of aluminium to be added to the smelting cell by selecting an appropriate alumina dumping strategy from a noise feed dump strategy, a fast feed dump strategy and a high volt dump feed strategy based on at least one of the computed value of raw resistance, smooth resistance value and average noise; and controlling voltage of the smelting cell by raising or lowering anode in the aluminium smelting cell based on comparison of smooth resistance value and the control resistance value at third pre-determined intervals.
2. The process as claimed in claim 1, wherein the first pre-determined interval ranges between 10 millisecond (ms) to 500 ms.
3. The process as claimed in claim 1, wherein the first pre-determined interval is 100 milliseconds (ms).
4. The process as claimed in any of claims 2 and 3, wherein computing the raw resistance value comprises computing a change in raw resistance (dR) value by determining raw resistance at every 3 second interval intervals and computing a rate of change of raw resistance (dR/dT) therefrom.
5. The process as claimed in claim 1, wherein the second pre-determined interval ranges between 1 to 6 minutes.

6. The process as claimed in any of claims 1, wherein the second pre-determined interval is 3 minutes.
7. The process as claimed in any of the preceding claims, wherein computing the average noise value comprises computing the average of noise values for three minutes preceding the instant when the average noise is to be computed.
8. The process as claimed in any of the claims 1 to 7, wherein selecting the noise feed strategy as the alumina feed strategy comprises:
determining the number of dumps of alumina as one and selecting time interval between consecutive dumps to one of 20 minutes and actual time interval of alumina dumps determined based on dumps of last 24 hours when the average noise value is determined to be greater than 0.05 Volts and the determined noise value is greater than 0.05 V; and concluding the noise feed strategy when the computed average noise value is less than 0.05 V.
9. The process as claimed in any of the claims 1 to 7, wherein selecting the fast feed
strategy as the alumina feed strategy comprises
computing deviation in computed raw resistance value with respect to the control
resistance value; and
selecting the number of dumps of alumina from a pre-determined set of dump values,
when the average noise value lies between 0.05 Volts and 0.1 Volts, the deviation in the
computed raw resistance value with respect to the control resistance value is at least 0.05
V and the computed value of the rate of change of raw resistance (dR/dT) is determined
to be positive for at least ten consecutive 3 second intervals the set of dump values being
based on time duration between consecutive fast feed dumps and number fast feed dumps
in preceding eight hours; and
concluding the fast feed dumps when deviation between the smooth resistance value and
the control resistance value is less than 0.01 V.

10. The process as claimed in any of the claims 1 to 7, wherein selecting the fast feed
strategy as the alumina feed strategy comprises
computing deviation in computed value of raw resistance with respect to the control
resistance value; and
selecting the number of dumps of alumina from a pre-determined set of dump values,
when the average noise value lies is less than 0.05 Volts, the deviation in the computed
value of raw resistance with respect to the control resistance value is at least 0.05 V and
the computed value of the rate of change of raw resistance (dR/dT) is determined to be
positive for at least two consecutive 3 second intervals, the set of dump values being
based on time duration between consecutive fast feed dumps and number fast feed dumps
in preceding eight hours; and
concluding the fast feed dumps when deviation between the smooth resistance value and
the control resistance value is less than 0.01 V.
11. The process as claimed in any of the claims 1 to 7, wherein selecting the high volt
feed strategy as the alumina feed strategy comprises
computing deviation in the computed raw resistance value with respect to a control resistance value; and
selecting the number of dumps as 4 when the deviation in the computed raw resistance value with respect to the control resistance value is greater than 1 V.
12. The process as claimed in claim 1, wherein the third pre-determined interval ranges between 12 seconds to 60 second.
13. The process as claimed in claim 12, wherein the anode is raised when the smooth resistance value is determined to be less than the control resistance value.
14. The process as claimed in claim 12, wherein the anode is lowered when the
smooth resistance value is determined to be greater than the control resistance value.

15. A system for smelting of aluminium comprising:
an aluminium smelting cell having a pot, cathode and anode;
a means for determining value of voltage and current pertaining to the smelting cell at first pre-determined intervals and noise value in the determined current and voltage at second pre-determined intervals;
a controller communicably coupled to the means for receiving the determined value of cell voltage, current and noise value and to compute a raw resistance value from the determined value of voltage and current, average noise value from the determined noise value and a smooth resistance value based on the raw resistance value, at least one of the the computed raw resistance value, average noise value and smooth resistance value being used for determining number of dumps of alumina to be added to the smelting cell by selecting an appropriate alumina dumping strategy from a noise feed dump strategy, a fast feed dump strategy and a high volt dump feed strategy, the controller being adapted to compare the smooth resistance value and the control resistance value at third pre¬determined intervals to raise or lower the anode for controlling voltage of the aluminium smelting cell; and
a plurality of actuators coupled to the controller to raise or lower the anode and to dump alumina in the smelting cell based on the alumina feeding strategy.
16. The system as claimed in claim 15, wherein the controller is a programmable
logic controller.
17. The system as claimed in claim 15, wherein the controller is a microprocessor.