Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Utilizing fused bath
Reexamination Certificate
1999-12-07
2001-11-20
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Utilizing fused bath
C205S392000, C204S245000
Reexamination Certificate
active
06319388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of managing the operation of a plant for the production of aluminium by igneous electrolysis. It also relates to the plant for implementing this method.
It relates more particularly to the management of the tools needed to operate such a plant, and especially to the lifting tools, handling tools, etc. conventionally employed in plants of the type in question.
2. Description of the Related Art
It is known that the production of aluminium by igneous electrolysis employs an alumina electrolysis reaction in a bath of molten cyrolite according to the reaction:
Al
2
O
3
+2e+Na
3
[AlF
6
]→2Al +3O
2
+3C→3CO
2
+F alumina cryolite
This reaction uses a molten bath comprising a mixture of cryolite and alumina, the temperature of which is generally greater than 800° C. On account of the energy used and in order to limit the losses inherent in the start-up phases as far as possible, aluminium production plants employing this technology generally operate continuously with a series of aluminium tanks, the number and size of which depend, on the one hand, on the available amperage of the direct current supplying the tanks and, on the other hand, on the desired production quantity.
Moreover, plants are frequently organized in such a way that they have a number of tanks in series, mounted parallel to each other and installed within the same building or in separate buildings placed symmetrically with respect to a central passageway which is intended, in particular, to allow handling of the ladles containing a bath of molten cryolite for the electrolysis tanks, the beams for lifting the anode frames and other movements of the tank accessories, and which is more particularly intended for the handling of crucibles for tapping off the molten aluminium obtained by electrolysis.
Such series of electrolysis tanks may extend over relatively large distances, which may typically be as much as one kilometre, and, without this constituting a standard, a number of plants include two parallel series comprising 288 tanks, each of the series being served by eight identical complex machines which carry all the tools needed for the operation of said plant and which secure: the change of the anodes, which process includes:
the pricking of the surface crust forming on the
upper surface of each of the tanks, that is to say
the breaking of this crust,
the collecting of all or some of the pieces coming
from the breaking of said crust,
the actual pulling-out of the spent anodes,
the fitting of fresh anodes;
the lifting of the anode frames, this being necessary due to the wear of the said anodes over time;
the operations of removing excess material from the bath of molten cryolite and of tapping off the molten aluminium obtained;
and finally, the ancillary maintenance operations and corrective actions during operation.
Within plants known at the present time, the operating principle of which is illustrated diagrammatically with regard to
FIG. 1
, these machines (
5
) operate in a “slidewise” to-and-fro movement.
FIG. 1
therefore shows four successive zones (
11
) representing four movements of each of the two machines (
5
) illustrated in this figure.
As indicated above, each of said machines (
5
) is capable of carrying out all the tasks corresponding to the functions needed for the correct operation of the plant. More specifically, a machine (
5
) carries out, during a first movement over a zone (
11
) of tanks to which it is assigned, one and the same defined task, so that it repeats this task at each tank. Said machine is then moved to the starting tank of the zone (
11
) in question so as to carry out a second task, different from the first, and the cycle is thus repeated for the various tasks necessary for the operation of the plant.
Thus, for the plant described above having 288 tanks, eight machines thus carry out the forward-and-return movements, and therefore the slidewise operation, in order for these various tasks to be accomplished.
Although, from the standpoint of the actual technical result, the mode of operation of this type of plant is satisfactory, it is accompanied, however, by drawbacks of a functional or structural nature which are recalled below.
Firstly, the tools of each machine have an insufficient utilization factor, consequently entailing an increased requirement in terms of machines. Moreover, because of their multitask function, these machines necessarily mean that the elements of which they are composed are overdesigned so as to be able to accomplish the tasks requiring high levels of technical performance and characteristics.
Next, this mode of operation leads to a complexity in the technical organization of the machines which is unfavourable to automation of the functions. This complexity of organization also results in the use of heavy and bulky machines, increasing the cost of manufacturing the machines, but also the more general civil engineering costs associated with the size of the buildings and of the factories in which such plants are mounted.
Finally, such an organization means that there have to be more operators, since it is necessary for someone to be in the cabin to control the machine and for someone to be on the ground to carry out the attendant manual operations, which furthermore involve safety problems.
In other words, the use of multifunctional or multitask machines limits the number of tanks capable of being treated by the same machine, given the operating process employed, in fact additionally increasing the operating costs of the plant in question.
This increase in the costs is therefore firstly inherent in the low utilization factor of the too numerous elementary functions for one and the same machine. It therefore concerns three main elements impacting the engineering of this type of plant, namely:
the handling equipment;
the mode of managing the plant;
the design and engineering of the plant.
The so-called “slidewise” operation associated with such universal machines therefore involves, apart from the overall costs of very substantial and very heavy equipment, also very high running costs.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to optimize the equipment, starting by increasing their productivity and, as a corollary, decreasing both the operating costs and the costs of constructing the plants of the type in question.
The invention therefore relates firstly to a method of managing the operation of a plant for the production of aluminium by igneous electrolysis, of the type having two electrolysis tankrooms, that is to say two series of mutually parallel and symmetrical tanks with respect to a central passageway in which the handling of a ladle for pouring molten cryolite and of a liquid-aluminium tapping ladle are in particular carried out, and in which the two electrolysis tankrooms are supplied with electricity in series.
This method consists in carrying out the various handling operations at each of the tanks, necessary for the operation of the plant, in a closed loop, the members needed for said operation being moved over all the tanks of the electrolysis tankrooms in continuous cycles always in the same direction.
Thus, said members are moved in the first tankroom in a defined direction as far as the end of said tankroom, are then transferred to the adjacent end of the parallel tankroom, hereafter called the second tankroom, are then moved in said second tankroom in the opposite direction with respect to the direction of movement adopted in said first tankroom and finally are transferred to said first tankroom, in order thus to repeat the various cycles necessary for the operation of the plant.
Thus, each of these members carries out a smaller number of operations than in the scope of the plants of the prior art, these operations being repeated from one tank to another, the members circulating constantly in the same direction as far as the end of the tankrooms, where they are transferred to the
Huon Serge
Piron Gerard
ACIS
Gorgos Kathryn
Knobbe Martens Olson & Bear LLP
Parsons Thomas H
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