Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a cell for fused-salt
- electrolysis and is particular to a cell for fused-salt elec-
trolysis for reducing alumina in the presence of cryolite to
metallic aluminum, comprising an insulated tank, which has
a carbon bottom, two rows of anode rods, which are disposed
on opposite sides of an anode carrier, which is arranged in
the longitudinal center plane, an exhaust gas-collecting duct
extending at the longitudinal center between the two rows of
anode rods, and two covers, which are downwardly inclined from
the outside of respective rows of anode rods to respective
longitudinal edges of the tank and which are provided each at
its outer longitudinal edge and at each of its transverse edges
with a skirt than extends as far as to the respective edge of
the tank.
The exhaust gases formed in the electrochemical
process of recovering aluminum from alumina contain fluorine,
which is a product of the reaction of the cryolite in the elec-
trolytic cell, and finely divided carbon, which released by the
carbon anodes. For ecological reasons, it is essential to
reduce particularly the fluorine content in the exhaust gases
to the utmost minimum before such gases are discharged into
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the atmosphere so that the environment is not adversely affected.
It is known for this purpose to purify the exhaust
air which escapes from the buildings which contain plants for
fused-salt electrolysis - this air contains the exhaust gases -
and then to discharge the air in an ecologically innocuous
state. To this end the natural chimney action in the building
is utilized to move the air in the buildings, which contains
the exhaust gases from the electrolysis, to mechanical means,
such as blowers, purifiers or the like, which are mounted on
the roofs and serve to discharge the emissions. The purifiers
consist essentially of liquid-wetted filters, between which
a mist is maintained so that dust particles an gaseous
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constituents are retained by the filters and by the liquid
particles and the purified air is discharged into the
atmosphere.
Whereas the mechanical means which are available at
present can handle and purify all air in the buildings, they
do not decisively improve the conditions within the building
from the aspect of work hygiene.
To ~aintain the concentration of the noxious exhaust
gases which escape from the cells for fused-salt electrolysis
- 10 within tolerable limits, it is known to provide the cells for
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fused-salt electrolysis with a cover. This cover consists of
a collecting duct, which extends longitudinally between the
rows of anode rods and which is provided at its outer periphery
- with two cover plates, which are downwardly inclined toward the
longitudinal side of the tank. The anode rods extend through
~ the cover plates and those edge portions of the cover plates
; which are near the longitudinal sides of the tank closely
embrace the anode blocks so that an uncovered surface of the
eleotrolytic cell remains exposed between the inside periphery
of the tank and the outside edge of the cover plates and permits
o~ an access to the interior of the cell whereas the exhaust
gases from the cell can be sucked off only from a relatively
small part thereof.
It is known to eliminate this disadvantage by the use
of a cell for fused-salt electrolysis in which the cover plates
are mounted on a tube which is longitudinally bisected and -
which engages the upper portion of the periphery of the
cylindrical exhaust gas-collecting duct. Hinged plates are
mounted at the outside edges of the cover plates and rest on
the longitudinal edges of the tank. The rate at which exhaust
gases escape into the air in the building is much reduced by
this arrangement.
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On the other hand, the arrangement has the - ~
disadvantage that these means muat be entirely removed a ;
remplacement of the anode.
; For this reason it has been proposed (Opened German
Specification 2,251,898) so to design to cover that the same
must be opened only when it is desired to charge the cell and
to remove the molten aluminum. This object is accomplished in
that the cover covers the anodes on their vertically extending
sides, transverse walls intended to rest on the ends of the
tank are mounted on the cover, and the anodes consist of
continuous anodes. This arrangement i not highly suitable
where so-called manipulators are to be used, which can, e.g.,
automatically break up the slag crust, and feed the alumina to
the cell, -Besides, the arrangement requires the use of
continuous anodes.
It is an object of the invention to provide a cell
for fused-salt electrolysis with covers which are so designed
that the electrolytic cell can be operated in a simple manner
by a manipulator, the molten material can be removed without
obatruction, the anodes can be replaced without special
difficulties, and particularly tight covers are also provided.
This object i~ accomplished in that each cover is
hinged adjacent to its longitudinal edge adjacent to the anodes
and at least at its corner portions to a support which extends
along the row of anode rods, a carrying arm is firmly secured
to each end portion of the support, the carrying arm is pivoted
at its other end to the anode carrier and is connected by an
operating linkage to a piston rod of a cylinder of a first
- hydraulic or pneumatic actuator. A cylinder of a second
hydraulic or pneumatic actuator is pivoted to the support at
least adjacent to the middle thereof, and the piston rod of
the last-mentioned actuator engages the cover.
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Because the entire anode carrier descends slowly as
the anodes are consumed, the fixation of the bearing bracket to
the anode carrier ensures that there will be no relative
movement between the anode carrier and the cover so that the
struc,ture is very tight.
The second actuator is operable to impart a sufficient
upward pivotal movement to the cover when it is desired to
' charge the cell for fused-salt electrolysis and to remove the
molten aluminum.
1 As above mentioned each carrying arm is engaged by
; an operating linkage, which is connected to the piston rod of
a first pneumatic actuator having a cylinder secured to the
, anode carrier. When it is desired to replace the anodes, this
arrangement may be used to impart a further pivotal movement to
the previously raised cover so that the anodes can be rendered
accessible in a simple manner.
The cover may be suitably secured by means of a plu-
rality of brackets to the preferably tubular support. The
,~ piston rod of'the actuator which is disposed adjacent to the
middle of the support and serve~ to move the cover may be con-
nected to such bracket.
According to a special feature of the invention,
U-shaped anode rod seals are disposed on that side of the
support which faces the exhaust gas-collecting duct, which
extends as far as to the anode rods, and these seals embrace
the anode rods and positively engage the same so that the ~' -
seals can adjust themselves to the instantaneous position of
the anode, rods, which is not exactly fixed. ~,
Each anode rod seal consists of a sliding element,
which'positively embraces the anode rod and which is horizontal-
ly slidably ~ounted in a guide whic,h is mounted on a baseplate.
The apparatusaccording to theinventionisshownbywayof
exampleonthedrawingand willbe explained more fully hereinafter.
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Fig. 1 is a front elevation showing the cover in
closed position.
Fig. 2 is a side elevation showing the cover in
closed position.
Fig. 3 shows a slidable anode rod seal.
Fig. 4 is a side elevation showing the anode rod
seal.
An anode carrier 3 carrying anode rods 2 is disposed
over the cell 1 for fused-salt electrolysis and extends in the
longitudinal center plane of said cell. A rectangular exhaust
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gas-collecting duct 4 is disposed between the two rows of anodes.
A covers plate 5 is downwardly inclined from each row of anode
rods to the longitudinal edge of the electrolytic cell 1.
Skirts 6 of asbestos are mounted on the longitudinal edge and
the end edges of each cover 5 and rest on the longitudinal
edge and the end edges of the electrolytic cell 1 and prevent
an escape of exhaust gases adjacent to these edges. Brackets
7 are secured to cover 5 at that longitudinal edge thereof
which is near the anodes and serve to hinge the respective
covers 5 to a support tube 8. Carrying arms are secured to
respective end portions of the support tube 8. ~he other end
of each carrying arm is pivoted to a bearing bracket 10, which
is mounted on the anode carrier 3. A composite operating
linkage 11 is connected to the carrying arm 9 and to the piston
rod of a pneumatic actuator, the cylinder 12 of which i9 mounted
on the anode carrier 3. An abutment 14 is mounted in the middle
of the ~upport tube 8. ~he end of the cylinder 13 of a pneumatic
actuator is pivoted to the abutment 14. Ihe piston rod of said
actuator is pivoted to a bracket 7, which is mounted on the
cover 5. Pivotal movements I and II, respectively, are imparted
to the cover by the actuators comprising the cylinders 1~ and 12.
lhe arrangement according to the invention permits of
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a control of each eover in such a manner that the pneurnatic
actuator comprising the cylinder13 is operated to impart an
upward pivotal movement to the cover 5 when it is desired to
perform general operations in the cell, such as breaking
erusts, eharging alumina, ladling molten metal and checking
the cells. For a replacement of anodes, a further upward
pivotal movement, beyond the vertical position, is imparted
to the previously raised cover 5 about the pivotal axis of
the carrying arm 9.
Figs. 3 and 4 show the seals between the anode rods
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and the cover. ~he anode rod 2 is positively embraced by a
horizontally slidable element 15, whieh is slidably mounted in -
a guide 16 on a baseplate 17. lhe baseplate is secured to
the supporting tube 8 and direetly engages the anode earrier 3.
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