FORM - 2
THE PATENTS ACT, 1970
(39 of 1970)

COMPLETE SPECIFICATION
Section 10

HINDALCO INDUSTRIES LIMITED, an Indian company, registered under' the Companies Act, 1956, having its registered Office at Century Bhavan, Dr. Annie Besant Road, Mumbai - 400 025, India;
GRANTED
21-10-2004
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:-

The subject invention relates to a method and device for feeding controlled powdery material specifically alumina feed to the hopper of the electrolytic cell in the manufacturing aluminum, more specifically from a single source thereof to a plurality of discharge points, more specifically the transfer of fine grained alumina to a plurality of aluminum reduction cells in a potline.
Specifically, the subject invention relates to an improved method and device for providing a continuous supply of alumina to the hopper of electrolytic cells.
More specifically, the subject invention relates to an improved process for feeding controlled powdery material specifically alumina feed to the hopper of the electrolytic cell in the manufacture of aluminum.
The embodiment of the invention resides in a system for feeding controlled powdery material specifically alumina feed to the hopper of the electrolytic cell in the manufacture of aluminum.
In reduction plant the aluminum is produced by electrolyzing alumina in reduction cell or pots. This is achieved by dissolving alumina in cryolite bath and passing high intensity current through carbon electrodes. Aluminum thus produced by the process of electrolysis, gets deposited on cathode and is tapped periodically in molten form.
The electrochemical reactions involved are as follows:
AIA > 2AI+3+3CH
2Alt3+6e > 2AI at cathode
30-2 > 3/202 + 6e 1
3/2 02 + 3/2 C > 3/202 | at anode

The regular/constant feed of alumina in electrolyte or cryolite bath is must for the smooth operations of pots. Any minor variation/shortage of alumina in

bath will have adverse effect on pot operation leading to the higher consumption of energy, bath material and loss of production. The resistance of bath varies inversely in parabolic form with respect of Alumina contents in the bath. If the alumina percentage in bath drops down to less than 2%, the voltage of pot increases by many-folds in a matter of seconds and could be as high as 100 volts or even more against normal operating requirement of 4.4. to 4.5 volts.
Hence, it is highly desirable that alumina feeding devices are never starved of alumina at any moment of time
Alumina is universally produced by the Hall -Heroult process wherein alumina is electrolytically reduced to aluminum metal in a fused fluoride salt electrolyte. Aluminum plants employing this process generally have a number of reduction cells connected in series and either positioned side by side as with prebake cells or end to end as with Soderberg cells.
In the operation of aluminum reduction cells , small discrete quantities of alumina are fed to electrolyte in each reduction cell to replenish the dissolved alumina which is consumed in making the metal. If the alumina concentration in the fused electrolyte bath goes too low , an anode effect occurs where the resistance of the cell increases dramatically. Usually, alumina is fed at periodic intervals in small quantities to avoid mucking up the cells where undissolved alumina settles to the cathode metal interface and thereby interfaces with the electrolytic process.
In most commercial aluminum plants , alumina is fed to the reduction cells either from a feed hopper permanently fixed to the cell superstructure or from a feed hopper mounted on a wheeled or tracked vehicle which moves from cell to cell. In the former instance , the feed hopper on the cell is filled with alumina from a bucket carried by an overhead crane.

As discussed earlier, conventionally, the Pot Tending Cranes are deployed to fill the alumina into the hoppers , consuming around 30-35% of the time. These cranes have to perform number of other jobs besides feeding of Alumina and are thus heavily loaded.
In the process of revival of pot lines after interruption, the pot-tending cranes have to carry out a number of additional emergency jobs like changing of burn (melted stubs), stub out carbon and attending wild pots. This restricts crane availability for filling pots hoppers with alumina, which creates further abnormal conditions leading to a chronic situation which ultimately damages the pot lining and close down the pot.
The biggest disadvantage found with the use of pot-tending cranes is that they have a major impact on design of pot rooms, limiting the number of pots and production capacity per pot line, which affects the capital cost of the production plant considerably. The methods presently in use for hopper filling have not been satisfactory because they are inefficient, time consuming, expensive and moreover generate much dust in the pot room due to the frequent transfer of alumina from container to container.
Other methods of feeding alumina to the reduction cell have been suggested wherein alumina is transported pneumatically or in some other fluidized form, such as with air activated gravity conveyors. However, such methods have not been found successful due to the difficulty in controlling the feeding of small quantities of alumina which is necessary for efficient operation of reduction cell.
The aluminum smelting process is highly sensitive to thermal balance, electro-magnetic movement of metal & bath, quantum of heat dissipated at various points, bath chemistry, anode size and shape, alumina granulometry, physical and chemical characteristics and alumina concentration in the bath. With any disturbance in the optimum conditions, the sensitive balance of

various complexities is disturbed leading to the drop in efficiency, increase in power consumption and operating conditions becoming hostile resulting in the closing down of the pot itself.
These systems are generally not capable of continuously distributing alumina powder into a plurality of streams having controlled quantity and then conveying alumina to different parts of an electrolytic cell.
The pneumatic conveying system has also been used conventionally, where the alumina is conveyed by high pressure air at high velocity. The high velocity creates alumina particle attrition, which results in the creation of muck in the pots as fine alumina does not get dissolved easily. In such pneumatic system, plugging at the point feeders also increases because of increased fines. Moreover, it results in the increase in electrical resistance of the bath leading to high anode effects,high power consumption high bath temperature, burn-off , loose nuts and the like ultimately affecting the pot operation.
Considering the draw backs involved in the high pressure conveying system, a system was also evolved using medium pressure. In this system, a special hardware was used using pneumatic impulse valves for each pot line. The alumina hopper level sensing devices along with number of pressure vessels were placed at various locations. In this system, an air compressor with special air mechanism and computer controlled system to monitor the demand and supply requirements for various pots in line were installed. In this system, though the particle breakdown found to be lower then the conventional pneumatic conveying systems but still it was higher then what is required ideally. Moreover, the capital intensive installation, high operating and maintenance cost are also not desirable.
Another system tried for such alumina conveying is the use of air assisted gravity conveying system, where air assisted gravity conveying system have

to have 5-6 degrees gradient from feed to discharge point for easy movements of solid particles. In case of free flowing particles this gradient can further be reduced to a maximum of 3-4 degrees. In this system, to feed alumina to the last pot, the feed end of air assisted slide will have to be raised by 20 meters from the discharge point of pot hoppers. The effective material height of the alumina silo is reduced on account of angle of repose. Moreover, the main air slide which feeds the pot air slide running at 90 degrees will have to be provided with a gradient which will foul with power collector and gantries of Pot Tending Cranes.
However, even this system was found to be technically not feasible.
Hence, for moving alumina by horizontal air slides, conventionally two types of pressures are used. The low air pressure is used for aerating/fluidisation of alumina and high pressure for moving the alumina forward up to the last pot. The high pressure creates attrition and disturbs pot operation.
A conveying channel known as air slide is also used conventionally, which works on fluidization principle and flow occurs due to gravity (i.e. in inclined position). These conveying apparatus are found not to be suitable due to space limitation and more air consumption.
To overcome the drawbacks involved in the available systems, many apparatuses have been proposed which are intended to permit a regular feed of alumina to an electrolysis tank . One such apparatus as described in French Pat. No. FR-A-2099434 which provides for feed of alumina to an electrolysis cell and comprises a tank for storing of alumina, below which there is a measuring device for controlling the amount of alumina which issues from the tank. It also provides means for the fluidized transportation of the alumina, which is also known as air cushion conveyor means being disposed between the measuring device and the cell to be supplied with

alumina. However, such an arrangement suffers from major disadvantages in regard to industrial utilization thereof.
To overcome the above referenced problems of the conveyance of alumina from storage silo to electrolytic cell , the conveyor system of subject invention has been invented.
The system of subject invention comprises a storage silo for storing aiumlna powder and horizontal conveying channels.
Accordingly, the subject invention relates to a process for feeding
controlled powdery material specifically alumina feed to the hopper of the electrolytic cell in the manufacture of aluminum comprising :-
feeding alumina from the storage silo to main horizontal conveying channel

supplying air to the main horizontal conveying channel at a desired
pressure to cause alumina powder to flow in semi-hydrostatic condition to fill the upper plenum of the said main horizontal conveying channel;
balancing the said pressure by releasing the air from the dedusters

connected to the said main horizontal conveying channel to enable the column
of alumina to be filled in the said dedusters;
discharging the alumina from the said column in the said dedusters to the small horizontal conveying channels .through discharge chutes of the said main horizontal conveying channel;
supplying the air to the small horizontal conveying channel divided in three segments, at a desired pressure to create the pressure gradient to

enable the alumina to move and discharge in the hopper of the said -
electrolytic cell
automatically controlling the supply of the alumina as per the requirement by the formation of alumina powder cone inside the said hopper of the electrolytic cell

The embodiment of the invention resides in , a device, for feeding controlled
powdery material specifically alumina feed to the hopper of the electrolytic cell
in the manufacture of aluminum, comprising :-

main horizontal conveying channel ." to receive the powdery material
specifically alumina from the storage silo provided with means to create the
air and pressure gradient in the said main horizontal conveyor channel for the
movement of alumina
plurality of dedusters to create column of alumina in the said main
horizontal conveying channel
small horizontal conveying channels being supplied the alumina from

the said main horizontal conveying channel by means of discharge chutes
a plurality of fans to provide air to the said main horizontal conveying channel and said small horizontal conveying channels
point feeders and hopper gates provided in the hopper of the said electrolytic cell for the supply of required amount of alumina in the said hopper
a clamp provided at the said point feeders of the said hopper for the opening and closing of the said outlet
a duct connecting the said dust collecting system to the said hopper for the release of air and dust and
a breather is provided in the said hopper for the release of air in the said dust collecting system enabling the alumina to move.

Accordingly, the present Invention relates to
a device for feeding controlled powdery material specifically alumina feed to the hopper of t he electrolytic cell in the manufacture of aluminum comprising:-
main horizontal conveying apparatus to receive the powdery material specifically alumina from the storage silo provided with means to create the air and pressure gradient in the main horizontal conveyor channel for the movement of alumina;
plurality of dedusters to create column of alumina in the said main horizontal conveying channel;
small horizontal conveying channels being supplied with the alumina from the said main horizontal conveying channel by means of discharge chutes ;
a plurality of fans provided in the horizontal conveying channel to provide air to the said main horizontal conveying channel1'and said small horizontal conveying channels;
point feeders and hopper gates provided in the hopper of the said electrolytic cell for the supply of required amount of alumina in the said hopper;
a clamp provided at the outlet of the said small horizontal conveying channels for the opening and closing of the said outlet;
a dust duct connecting the said dust collecting system to the said hopper for the supply of alumina; and
a breather for the release of air in the said dust collec¬ting device to enable the alumina to move.

The subject invention can best be described with reference to the accompanying drawings, however the same should not be construed to restrict the scope of the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 relates to a flow diagram of horizontal conveying channels;
Figure 2 relates to the detailed diagram of electrolyte cell hopper connected to horizontal conveying channels.
DETAILED DESCRIPTION OF THE INVENTION
The main horizontal conveying channels (2) has lower plenum (3) for flow of air and upper plenum (4) for flow of aerated alumina. The upper plenum and the lower plenum are separated by a porous membrane (5). The property of the porous membrane (5) selected is such that air passes from the lower plenum (3) to upper plenum (4) but alumina is not allowed to pass from upper plenum to lower plenum (3). Pipes (6) and centrifugal fan (7) are used for supplying air to the main horizontal conveying channel (2). The air thus provided creates a pressure P. This pressure P and predetermined number of dedusters (8) cause semi hydrostatic flow condition in the alumina powder. The aerated alumina fills the upper plenum (4) of the main horizontal conveying channel.
Air is released through the dedusters (8) and column of alumina is created in all the dedusters (8). The column of alumina thus created balances the pressure P.
The alumina from the main horizontal conveying channel (2) goes to small horizontal conveying channels (11) (as shown in figure 2) via discharge chute (9). Each electrolytic cell has one small horizontal conveying channels

(11). This conveying channel is also having upper plenum (4) for alumina, lower plenum (3) for air and porous membrane (5) in between. Air for this conveying channel is fed by a separate centrifugal fan (10). The difference between the main horizontal conveying channel (2) and small horizontal conveying channel (11) is that the main horizontal conveying channel has been provided with dedusters (8) whereas small horizontal conveying channels (11) are not provided with dedusters (8). Small horizontal conveying channel (11) is made up of three segment (12). The purpose of having three segment is to create pressure gradient between the first and the last segment and also for electrical insulation (15). Out let (13) of the small horizontal conveying channel discharges alumina to the electrolytic cell hopper (16) as and when required. These hoppers are covered (14) and clamped tightly.
Automatic alumina feeding system works on the principle of semi hydrostatic flow characteristic of powdery materials. The air at pressure P flows from lower plenum (3) to upper plenum (4) through the porous membrane (5). This air causes aeration of powder coming out of the storage silo (1). The condition .of powder becomes semi-fluid and starts flowing due to pressure gradient towards empty side. Provision of dedusters (8) at different distances, increases the flow rate. The upper plenum (4) of horizontal conveying system is always full of alumina having air in between the particles and is in equilibrium and balanced condition.
The dedusters (8) used, are of rectangular section and inclined to the axis of the horizontal conveying channels but it can be of any shape circular, elliptical and the like and can be installed vertical also. The size & number of dedusters depends upon the flow rate of powder, size & conveying distance of horizontal conveying channels.
The pressure in the present system is maintained at 80 to 130m bar and flow is 11 to 15 X 10"3 m3/m2 sec. The feed rate of alumina is 6 to 25 Tons/Hour.

The horizontal conveying channel (11) used for feeding alumina to the
electrolyte cell hoppers do not have dedusters. Further they are made of the
three segment. Air distribution in these three segments is at different rate to
establish quick and smooth flow of alumina to the storage hopper (16). These
conveying channels are also having insulation joints (15) to insulate DC circuit
of electrolyte cell from the earth. Electrolyte cell hopper (16) is having 4 hours
storage capacity of alumina. These hoppers are covered having one
emergency feed point and are tightened by specially designed clamps for
quick opening and closing. Point feeders (18) at hopper gates (22) are
provided inside the hopper (16) for feeding measured amount of alumina to
electrolytic cell. A special type of breather (19) is fitted inside hopper to
release the air in the-dust collecting device (20) through a duct (21).
The automatic stopping and starting of alumina is achieved inside the hopper by cone formation (17) of powder by virtue of its angle of repose. The cone formed under the discharge chutes (13) of conveying channel stops the powder flow automatically. This takes place when a particular pressure difference between the first and last segment is set, that is ranging from 8 to 15 m bar.
This system has been experimented on alumina powder, but is suitable for all types of powdery material, which gets aerated when air is supplied. This system is a closed system and can supply a powdery material from a storage tank through a horizontal conveying channel to another storage bin automatically that is feed on demand basis without use of any control valve. Different size and shape of deduster (8) can be used for releasing air. Supply ofair can be done either from one fan or from more than one fan.
The subject application is a statement of invention and it is obvious that various modifications and improvements can be made to the present invention without departing from the spirit of the claimed invention.

WE CLAIM:
1. A device for feeding controlled powdery material specifically alumina feed to the hopper (16) of the electrolytic cell in the manufacture of aluminum comprising:-
main horizontal conveying apparatus (2) to receive the powdery material specifically alumina from the storage silo provided with means to create the air and pressure gradient in the main horizontal conveyor channel (2) for the movement of alumina;
plurality of dedusters (8) to create column of alumina in the said main horizontal conveying channel (2);
small horizontal conveying channels (11) being supplied with the alumina from the said main horizontal conveying channel (2) by means of discharge chutes (9);
a plurality of fans (7) to provide air to the said main horizontal conveying channel and said small horizontal conveying channels (11);
point feeders and hopper (16) gates provided in the hopper (16) of the said electrolytic cell for the supply of required amount of alumina in the said hopper (16);
a clamp provided at the outlet of the said small horizontal conveying channels (11) for the opening and closing of the said outlet;
a dust duct connecting the said dust collecting system to the said hopper (16) for the supply of alumina; and

a breather for the release of air in the said dust collecting device to enable the alumina to move.
2. A device as claimed in claim 1, wherein the said main horizontal conveying channel (2) and said small horizontal conveying channel(11) are divided in two plenums, upper plenum (4) for flow of aerated alumina, and lower plenum (3), for flow of air membrane provided between the two plenum allowing the passage of air from upper plenum (4) to lower plenum (3).
3. A device as claimed in claim 1, wherein said main horizontal conveyor channel (2) provided with fans for the supply of air to the said main horizontal conveyor channel (2) and said small conveyor channel (11).
4. A device as claimed in claim 1, wherein the small horizontal conveying channel (11) comprises three segments to create pressure gradient between the first and last segment.
5. A process for feeding controlled powdery material specifically alumina feed to the hopper (16) of the electrolytic cell in the manufacture of aluminum by the device as claimed in claim 1 comprising:-
feeding alumina from the storage silo to main horizontal conveying channel (2) at a feed rate 6 to 25 ton/hour;
supplying air to the main horizontal conveying channel (2) at a desired pressure to cause alumina powder to flow in semi - hydrostatic condition to fill the upper plenum (4) of the said main horizontal conveying channel (2);
balancing the said pressure by releasing the air from the dedusters (8) connected to the said main horizontal conveying channel (2) to enable the column of alumina to be filled in the said dedusters (8);

discharging the alumina from the said column in the said dedusters to the small horizontal conveying channels (11) through discharge chutes (9) of the said main horizontal conveying channel;
supplying the air to the small horizontal conveying channel (11) divided in three segments, at a pressure as herein described to create the pressure gradient to enable the alumina to move and discharge in the hopper (8) of the said electrolytic cell;
automatically controlling the supply of the alumina enabling the formation of alumina powder cone inside the said hopper (16) of the electrolytic cell.
6. A process as claimed in claim 5, wherein the said pressure in the main horizontal conveying channel (2) is due to the columns of alumina created in the said dedusters.
7. A process as claimed in claim 5, wherein the supply of the air to the main horizontal conveying channel (2) and to the small horizontal conveying channels (11) is provided by means of pipes (6) and centrifugal fans.
8. A process as claimed in claim 5, wherein the pressure is maintained at 80 to 130 mbar and the flow of alumina is maintained at 11 to 15 x 103m2 sec.
9. A process as claimed in claim 5, wherein the pressure gradient and the electric insulation is provided in the small horizontal conveying channel (11) by dividing the said conveying channel in the three segments.
10. A process as claimed in claim 9, wherein the air distribution in the each segments of the said small horizontal conveying channel (11) is at different rate for the quick and smooth flow of alumina to the storage hopper.

11. A process as claimed in claim 9, wherein the pressure difference between the said first and said last segment of the said small conveying channel is between 8 and 15 millibar.
12. A process as claimed in claim 5, wherein the automatic supply of alumina to the hopper is controlled due to formation of cone in the hopper (16).
13. A device for feeding controlled powdery material specifically alumina feed to the hopper (16) of the electrolytic cell in the manufacture of aluminum, substantially as hereinbefore described with reference to the accompanying drawings.
14. A process for the feeding controlled powdery material specifically alumina feed to the hopper (16) of the electrolytic cell in the manufacture of aluminium, substantially as herein before described with reference to the accompanying drawings.
Dated this 2nd day of May, 2000.
(RAMESH C. DHAWAN)
OF LALL LAHIRI & SALHOTRA
AGENT FOR THE APPLICANTS