Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Utilizing fused bath
Patent
1995-10-05
1997-12-02
Valentine, Donald R.
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Utilizing fused bath
204247, 373 89, C25C 322
Patent
active
056932111
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and an arrangement for closing and cooling of the top of an anode casing for a S.o slashed.derberganode in an electrolytic cell for production of aluminium.
The S.o slashed.derberganode which is used in electrolytic production cells for aluminium comprises a permanent anode casing made from cast iron or steel, which casing surrounds the selfbaking carbon anode. Unbaked carbonaceous electrode paste is charged at intervals to the top of the anode and the unbaked electrode paste is baked to a solid carbon anode by means of the heat generated by the current supply to anode and by means of heat from the molten electrolytic bath. A main feature of the S.o slashed.derberganode is thus that the baked anode is moved relatively to the permanent anode casing. Each electrolytic cell is normally equipped with one S.o slashed.derberganode.
The S.o slashed.derberganode is suspended by a large number of vertically arranged contact bolts normally made from steel, which also are used for conducting electric operating current to the anode. The lower ends of the contact bolts are baked into the anode. The contact bolts follow the downward movement of the anode until the lower ends reach a predetermined distance from the lower end of the anode. The contact bolts are then pulled out of the anode and placed in a higher position. By keeping the tip position of the contact bolts in different height positions in the anode, there will always be a sufficient number of bolts having such a tip position that a sufficient holding force is maintained and a good current connection between the bolts and the anode is secured.
The unbaked electrode paste which is charged to the top of the anode, evolves gases and volatile organic compounds during the baking process. Some of the gases and volatile compounds such as for example polyaromatic hydrocarbon compounds (PAH), are harmful to the health and it is therefore a wish to prevent these gases from escaping to the surroundings. Up till now it has been tried to reduce the outlet of gases from the top of the anode by using electrode pastes having a lowest possible content of volatile matter and by keeping the temperature on the top of the anode as low as possible. Even if the emission of gases from the top of the anode by these means has been reduced in the later years, it is not possible by the known technology to reduce emission of harmful gases from the anode top to an acceptable low level.
From Norwegian patent No. 172250 it is known to close the top of a S.o slashed.derberganode by means of at least one cover having openings for the contact bolts and where annular gaps between the contact bolts and the openings in the cover are sealed by means of sealing elements and where the gases which evolve during the baking of the electrode paste are collected and combusted. According to the Norwegian patent the cover comprises central cover plates having openings for the contact bolts and side cover plates arranged outside the central cover plates, said side cover plates being rotatably arranged. The annular gaps between the central cover plates and the contact bolts are according to Norwegian patent No. 172250 sealed by means of sealing elements which are gas tight arranged about each of the contact bolts and which sealing elements are freely floating on the central cover plates. In order to make it more easy to replace damaged central cover plates, the central cover plates are made in sections where each section comprises openings for at least two and preferably four contact bolts.
The arrangement according to Norwegian patent No. 172250 has been found to have the disadvantage that the cooling of the top of the anode becomes too small, which gives a too high temperature on the top of the anode. This effects the softening and baking of the anode paste, as a too high part of the binder in the unbaked anode paste which is charged to the top of the anode, is volatilized and is sucked off together with the gases evolved during baking.
DISCLOSUR
REFERENCES:
patent: 4002551 (1977-01-01), Duclaux et al.
patent: 4436607 (1984-03-01), Fischer
patent: 4608135 (1986-08-01), Brown
patent: 5128012 (1992-07-01), Olsen
Elkem Aluminium ANS
Valentine Donald R.
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