Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Patent
1998-09-25
2000-12-12
Krynski, William
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
428402, 4283202, 428323, 428325, 427180, 427212, 427220, 427215, B32B 1502, B32B 1702, B32B 1900
Patent
active
061596035
DESCRIPTION:
BRIEF SUMMARY
A method for the use of material containing carbon in the electrolytic production of aluminium The present invention concerns a method for the use of material containing carbon as a packing material, anode mass or collar mass in the electrolytic production of aluminium.
At aluminium works throughout the world, large quantities of fine-grained material containing carbon, or carbon dust, are produced annually as a result of breakdown during handling and transportation, cleaning of anode remnants (butts) and collection in filters when cleaning air and waste gases.
Approximately 5-10% fine carbon dust is produced from the quantity of coke purchased annually. The majority of this dust cannot today be recycled or used. This is because the dust is difficult to handle and partly because the contaminants in the dust make it unsuitable for recycling in anodes. Today, the dust is dumped. In the future it will probably become more expensive to dump it and the legislation governing the dumping of waste will probably become stricter. Therefore, it is not possible to base plans on the continued dumping of large quantities of carbon dust.
It is desirable to be able to use the current carbon by-products as raw materials. If the dust were reused, the result would be better carbon production economy as well as better resource management. At the same time, the environment would be spared major negative impacts.
A great deal of the dust comes from crushing butts from the electrolysis process. The butts contain contaminants from the electrolysis bath which it is undesirable to return to, for example, the anode mass for prebaked anodes in the form of dust. If butts are recycled for anodes, they must be carefully cleaned before use, i.e. that part of the butts which contains too many contaminants from the bath must be removed. The bath contains large quantities of sodium (Na), which makes this material not very suitable for recycling in aluminium production. It has been shown that if the anode mass has too high a content of sodium when burned, the bath components can diffuse out from the anode in the baking process and change the physical properties of the fireproof stone in the cassette walls so that the furnace is broken down over time. Furthermore, the quality of the anodes will be reduced if they contain bath components. The bath contains large quantities of sodium (Na) and if the bath residues in the anode are exposed to moisture during production and storage, the reaction with sodium (Na) may lead to severe expansion which may, in extreme cases, divide an anode in two. The greatest problem with bath residues in anodes, however, is that sodium is a catalyst for the air and CO.sub.2 reactivity of the anodes.
When burning anodes, a packing material is used to support the carbon bodies in the furnace chamber in order to avoid shape deviations. The packing material will also absorb volatile components which are liberated from the carbon during burning and be sacrificial material in connection with oxidation on account of the surplus oxygen in the furnace.
Coke, or packing coke, is today the most widespread packing material in connection with calcination of anodes for use in the aluminium industry. Coke can, for example, be produced in connection with the distillation of crude oil (petroleum coke).
Norwegion Patent No. 77.619 states that mixtures of coke ballast and bauxite powder, graphite, anthracite and clay soil can be used as a filling powder when burning carbon bodies. A further indication of weight ratios, etc. is also given.
A disadvantage of using coke as the packing material, possibly mixed with other materials as stated above, is that it results in the consumption of valuable raw materials.
Carbon dust cannot directly replace packing coke as the dust does not support the carbon and does not either maintain its position as well as larger grains of coke.
In order to protect the nipples on the anode hanger for an anode in an electrolysis cell, collar mass is used around the lower ends of the nipples on the top of the anod
REFERENCES:
patent: 3932244 (1976-01-01), Mikkelsen
patent: 4483840 (1984-11-01), Delhay et al.
patent: 5145570 (1992-09-01), Jusufbegovic
patent: 5578174 (1996-11-01), Sekhar
Fykse Nils
Kippernes Bergitte Husa
Linga Hogne
Madslien Bodil
Solli Lene Navestad
Krynski William
Norsk Hydro ASA
Shewareged B.
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