Note: Descriptions are shown in the official language in which they were submitted.
~ ~77442
Process for changing aluminum reduction cells and production
unit for carrying out said process
The invention relates to a process for changing the pots
llof transverse cells for fused salt electrolytic production
5 1l of aluminum, which are connected in series such that -the
llelectric current from the cathode bar ends of one cell is
¦¦conducted via risers to the long side of the anode beam of
¦ the subsequent cell, and relates too to a production unit
,lfor carrying out the said process.
,,,1
' Aluminum is produced from aluminum oxide by the fused salt
electrolytic process in which the said oxide is dissolved
in a fluoride melt comprised for the greater part of cryol-
¦ite. The cathodically deposited aluminum collects under the
i fluoride melt on the carbon floor of the cell, the surface
1 of the liquid aluminum itself forming the cathode. Dipping
into the melt from above are anodes which, in conventional
I processes, are made of amorphous carbon. As a result of
the electrolytic decomposition of the aluminum oxide, oxygen
l forms at the carbon anodes and combines with the carbon
~ there to form CO2 and CO. The electrolytic process takes
¦ place in the temperature range of around 940 - 970C.
During the course of production, the electroly-te becomes
deplete in aluminum oxide. At a lower concentration of
z _
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1 1 ~ 77~2
,
l to 2 wt.% aluminum oxide in the electrolyte the anode
effect occurs whereby the voltage increases from e.g. 4 - 5 V
to 30 V and more. Then at the latest the crust of solidified
,electrolyte must be broken open and the aluminum oxide con- ¦
'centration raised by adding fresh alumina.
~I
Old aluminum cells have the cathode pot built in to the
llpot room floor, usually in a pit. The lifetime of the cathode
¦ lining under normal production conditions i5 on average
il4 ~ 6 years, possibly slightly longer. After this the cathode
llining must be repaired or replaced. The metal conductor
,parts of the pot or other parts can likewise make repair or
¦replacement of the pot necessary. Repairing the pots in situ
lasts altogether about 3 - 4 weeks, during which time the
cell does not produce aluminum.
1,
'~Proposed in Swiss patent 341 003 is an arrangement which
allows the pot to be lowered into another room and trans-
ported away. This pot features parts projecting out at two
¦ sides and is mounted on a`supporting metallic frame.
The British Patents No. 929 822 and 396 658 propose a pot
room concept using a reinforced concrete supporting struct-
¦ ure which is suitable for accommodating fused salt aluminum
reduction cells. The pot room is divided up into indlvidual
¦ blocks which are electrically insulated from each other
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and with respect to the earth and superstructure both in
the horizontal and in the vertical directions~ Some 5 - l~/o
cells have to be kept in reserve, which of course represents
a further unproductive expenditure.
In view of the long distance to be transported
under the other cells and the relatively high cost of the
foundations for the raised pot room, it has been proposed
in British Patent Specification 2,013,244, published August
8, 1979, K. Rolfsen et al, to move the cathode pots out
and in the pot room transverse to the row of cells and at
approximately the same height as the level of operation.
The pot is mounted on foundations i.e., it has a cellar
space provided below it. Before the pot is removed, the
transport wagon is pushed under the cell and the pot raised
from the foundations. Compared with other pot room concepts,
the proposal in the aforementioned British Patent
Specification substantially improves work place safety.
A number of disadvantages however still remains
- As can be seen from Figure 1 of the afore-mentioned
British Patent Specification cellaring is still required,
which is relatively expensive. The cellar work is there-
fore not eliminated, but simply reduced. Numerous busbars
have to be separated and further work necessary in order
to remove the cell.
- Before going into se~vice a new pot must be delivered
with a transport wagon and a jacking system used to
lower the pot onto the foundations. At that stage of
installation - especially in the case of modern high
powered cells - stressing can cause cracks in the
cathode, which drastically reduce thè lifetime of the
pot.
~ 177~4Z
The invention seeks to develop a process for
changing the pots of transverse cells for fused salt electro-
lytic production of aluminum, which enables electrolytic cells
to be changed in a minimum of time and providing optimum
work-place hygiene, without the cells being damaged by
stressiny. It is a further object to develop an
economically operating production unit for carrying out the
said process in an optimum manner~
In accordance with one aspect of the invention there
is provided a process for changing transverse cells for fused
salt electrolytic production of aluminum, which are connected
in series in a pot room such that the electric current from
the cathode bar ends of one cell is conducted via risers to
the long side of the anode beam of the subsequent cell which
comprises bridging the risers using a short circuiting device,
separating and disconnecting transverse cells including said
risers, moving the disconnected cell to be changed in the
longitudinal direction of the cell on rollers such that the
cell remains at the same level, wherein said cell is moved
through an appropriately sized closeable opening in one wall
of the pot room, providing a transporter adjacent said pot
room which has a running surface at the level of the pot room
and transporting said cell on said transporter for repair.
In accordance with another aspect of the invention
there is provided a production unit for transverse cells for
fused salt electrolytic production of aluminum, which are
connected in series in a pot room such that the electric cur-
rent from the cathode bar ends of one cell is conducted via
risers to the long side of the anode beam of the subsequent
cell which comprises at least one ground level concrete base
slab in said pot room, a lower concrete slab adjacent said
I ~7744~
upper slab, a plurality of said cells on said upper slab
connected so that said cells can be coupled and uncoupled,
roller means on said cells for longitudinallY displacing
said cells, a closeable opening in the wall of the pot room
adjoining said lower slab, beams embedded in said upper slab
corresponding to the location of said rollers leading to said
closeable opening, transporter means on said lower slab com-
municating with said beams for transporting said cells and
having running surfaces at the same level as the running
surfaces of said beams.
With respect to the process, the invention in
particular has the following features:
- The risers are bridged using a short circuiting device,
- the risers are separated and disconnected along with the
releasable feed, exhaust, compressed air and electrical
control lines,
- the cell to be changed is moved out of the row of cells in
the longitudinal direction of the cell ~n at least four
rollers on the self-supporting steel shell and such that
the cell remains at the same level and
- is moved through an appropriately sized closeable opening
1 ~ ~77442
in one long wall oE the pot room onto a low transporter
which has a running surface at the level of the pot room
along the length of which it can be moved,
l¦- the whole cell is transported for repair into the work-
5 I shop, and
- in a similar manner a new cell is inserted into the row,
the risers connected, all the cell facilities linked up
again and the short circuiting bridge removed.
¦ If an overaged or malfunctioning cell has to be removed from
llthe pot room, care must be taken that the electric circuit
formed by the cells connected in series is not broken by
the removal of a cell. The risers leading to and from the
cell in question must therefore be bridged by means of a
I short circuiting device. This is done preferably by arrang-
ling a heavy section busbar over the cell at the same time
ensuring that the contact resistance between the busbar and
! the riser is kept as small as possible.
The suhsequent separation of the risers is useully done by
l sawing, loosening bolts or with an oxy-acetylene burner, as
i a result of which the necessary play required to remove the
I cell is provided. ~fter disconnecting the supply lines etc.
the whole cell i.e.
I - the complete cathode pot with cathode bars,
!- the anode superstructure with the rest of the risers, and
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- the day's supply silo on the cell and the crust breaker,
are removed.
iAccording to the process of the invention there is therefore ¦
¦no cellaring work necessary; the cell can be removed quickly
¦and separated from the infra-structure in only a few steps.
~Not only is it possible to repair the cathode part of the
cell, but also the anode superstructure and all anode com-
ponents can be attended to in the repair shop. This is im
~ portant especially in the case of long, transverse cells
¦ which are not easily accessable.
Also from the economic standpoint the quick change ~
of cells is important as the loss in production can be kept
to a minimum.
The transporter which can be moved along the pot room is
also suitable for transporting at least one tapping crucible
which can be moved up to the end of the cell. Usefully the
foundry is conceived such that the full crucible can be
moved from the transporter at ground level to the casting
furnace~
With respect to the device for carrying out the process the
object is achieved as described in claim 2.
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The investment costs for the pot room or rooms can be sub-
stantially lowered, as the construction work only requires
levelling of the ground and a small amount of earth to be
removed for the lower concrete slab; furthermore no cellar-
'ling is necessary. An upper concrete slab for the pot roomjcan join on to one side of -the lower concrete slab. If,
however, two pot rooms are planned, then upper concre-te slabs
can be provided on both sides of the lower concrete slab.
IlIn the latter case the transporter can be used for both
sides.
The pot room covering the upper concrete slab is of light
construction as the crane runways have only relatively
! modest loads to support e.g. when lifting anodes or crust
Ibreakers.
Usefully the reduction cells are arranged asymmetric, close
to the wall remote from the lower concrete slab~ A broad
inspection gangway is therefore available the whole length
of the pot room in the same direction as the lower concrete
slab.
The invention can in principle be realised with every kind
¦¦of cell, provided the steel shell is self-supporting. De-
pendiny on the weight of the cell - which in present day
Il cell designs can be up to 250 t - four to eight rollers
¦¦ are provided for each cell.
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As a rule these rollers must -turn slowly about 100 times
every 4 - 6 years i~e. the normal service of a cell. Con-
sequently in practice it is only the s-tatic loading which
~lis important as the rollers do not move while the cell is
'lin service. The number and type of roller are determined
l¦from the permissible static load.
,il
j! A cell which has to be changed is preferably removed from
'lthe row of cells using a pulling facility mounted on the
transporter. A pully wheel attached to a hook on the rear
jwall of the pot room is employed when pulling the new cell
into place. The cell must only feature a ring, lug or the
like at each end in order that it can be pulled into or out
of place with the cable of the pulling mechanism.
I! The transporter is preferably in the form of a railway veh-
i icle as this allows greater load to be transported with
less resistance to rolling movement. A vehicle with rubber
tyres, not running on rails, has the disadvantage that the
height of loading i.e. the height of the running surface
I can not be kept constant so readily.
The invention is explained in greater detail in the follow-
¦ling description of an exemplified embodiment and with the
help of schema-ic dr~wings viz,
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~ 17~442
~Figure 1: A perspective view of a pot room open at one end.
Figure 2: A plan view of another uni-t for producing primary
aluminum.
ll
IiFigure 3: A vertical section through a roller.
Il
I~A pot room 10 covers over an upper concrete foundation slab
~12. Slightly lower, normally 30 - 50 cm lower, is a lower
concrete slab 14. Joining on to the other long side of this
latter slab 14 is another upper concrete slab 12 which is
¦also covered by a pot room not shown here.
.,
I The whole unit for producing primary aluminum is therefore
symmetrical with respect to the longitudinal axis of the
Illower concrete slab 14. According to another version, this
¦llower concrete slab 14 can also be roofed over.
Heavy duty I-beams 16 are embedled in the upper concrete
Islabs 12 over the whole width. The spacing between these
¦¦ pairs o beams corresponds to the spacing of rollers support-
ing the cells 18. The running surface of the I-beams is at
the same level as the pot room floor or a few millimetres
lower.
~ The upper concrete slab 12 is cast directly onto the levelle~
Il ground in the pot room, which represents considerable cost
! savings.
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';
For simplicity the cathode busbars surrounding the cathoae
'pot 20 have been omitted here; these can be led around the
cell and/or under the cell, and are connected to the anode
Ibeam of the next cell via risers 22. Only the cathode bar
ends 2g are indicated here. The anode superstructure 26 of
¦the cell 18 is not shown in detail; to be seen however are
the anode rods 28 and the hooding 30 at the sides.
If a cell 18 has to be removed, the door 32 is raised and
llthe cell pulled out onto a transporter 34 by means of a cabl
,'drive which is mounted on the right of the transporter but
is not shown here.
The loading surfaces 36 of the transporter 34 are at exactly
¦ the same level as the running surface 38 (figure 3) of the
i steel I-beams 16 in the upper concrete slab i2.
1 The cell transporter 34 runs on four rails 40 mounted as
double normal gauge rails in the lower concrete slab 14.
Reinforcement 42 is provided below the rails 40in the slab
1l4. ~.
l Figure 2 shows electrolytic cells 18 for producing aluminum
~ in a pot room 10. In the figure a cell is shown on the
rail-bound transporter 34, ready to be moved to the cell
epair and maintenance shop 46 The concrete base 44 is at
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¦ the same level as the upper concrete slab 12 in the pot
room. The floor of the repair shop 46 also features I-beams
16. In the workshop 46 the anode and cathode parts of the
cell are separated and overhau].ed.
1l The foundry 48 at the facing long side of the lower concrete
slab 14 also features a concrete flooring 50 at the same
! level and with I-beams 16 embedded in it. A crucible 52,
¦which can be moved on rollers of the same type as the cells
,18, can be drawn via I-beams 16 onto the transporter 34
and moved to the end 54 of any of the cells 18.
Finally, the production unit can also have a cell storage
space which can likewise be reached using the transporter 34.
,
The roller shown in detail in figure 3 resting on the runninc
sur~ace 3a of the I-beam 16 ~eatures:
- A reinforced outer ring 56, which is the roller running
surface, is 50 - 80 mm wide and has an outer diameter of
100 - 150 mm;
- a heavy duty roller bearing with small rollers 58 which
Il are arranged like a ball bearing held in the working pos- ¦
20 11 ition by a cage 60;
!~ - an inner ring 62, and
- a threaded axle 64 held in place by a locking bolt 66.
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A supply line 68 for lubricant leads to the heav~ duty bear-
ing which employs a high temperature grease such as e.g.
graphite or molybdenum sulphide.
'The axle 64 is mounted in a bearing block 70 which is, in
1i turn, bolted to a section 74 reinforcing the floor 72 of the
reduction cell.
The inner ring 62 and axle 64 are securely mounted in the
Ibearing block 70. On moving the reduction cell therefore
llthe inner ring 62 and axle 64 do not move, but the outer
Iring 56 supported by the smaller rollers 58 turns.
Il
Bolted to the lower flange of the reinforcing section 74
and to the bearing block 70 are guard plates 76 which are
lldismountable and extend almost down to the running surface
1l38. Immediately inside the guard plates 76 flat sections 78
~ prevent the running surface 38 from becoming excessively
¦dirty due to accumulation of electrolyte material, aluminum
~or alumina. The effectiveness of the guard plates can be
subs-tantially increased by having guard plates 76 extending
he full length of the cell.
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