Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Involving measuring – analyzing – or testing during synthesis
Reexamination Certificate
1999-10-12
2001-02-06
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Involving measuring, analyzing, or testing during synthesis
C205S389000
Reexamination Certificate
active
06183620
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for controlling the AlF
3
content in cryolite melts for aluminum reduction, wherein the temperature of the melt is measured.
A process of this type is known from U.S. Pat. 4,668,350. In the process disclosed therein, a known relation between the bath temperature and the bath composition (NaF:AlF
3
) is used. From this relation a target temperature of the bath is calculated as a function of a target composition (NaF:AlF
3
). The temperature of the bath is measured and AlF
3
is added, if the bath temperature is higher than the target temperature. Of course, the bath temperature is also influenced by a series of other factors.
BRIEF DESCRIPTION OF THE INVENTION
An object of the invention is to provide a very exact process that makes it possible to operate the aluminum reduction at as low a temperature as possible, and therefore as energy-saving as possible.
This object is achieved according to the invention in that the liquidus temperature of the cryolite melt is measured, the measured liquidus temperature is compared to a first target value, and AlF
3
is added to the bath if the measured liquidus temperature is higher than the first target value. If the measured liquidus temperature is lower than the first target value, the measured liquidus temperature is compared with a second target value that is lower than the first target value, and NaF or Na
2
CO
3
is added to the bath if the measured liquidus temperature is lower than the second target value.
Since the liquidus temperature of a melt allows very exact conclusions about the proportion of individual components of the melt, the process according to the invention offers the possibility of caring out the aluminum reduction process in as energy-favorable a manner as possible and thus as economically as possible. The invention also explicitly includes the reverse comparison between a target value and the measured value of the liquidus temperature, namely that the measured liquidus temperature is first compared with the second target value, and NaF or Na
2
CO
3
is added to the bath if the measured liquidus temperature is lower than this second target value. If the measured liquidus temperature is higher than the second target value, the measured liquidus temperature is compared to the first target value, which is greater than the second target value, and AlF
3
is added to the bath if the measured liquidus temperature is higher than this first target value. If, for example, the measured liquidus temperature is lower than the second target value, a comparison with the first, higher target value is of course superfluous. If the measured liquidus temperature lies between the two target values, no addition of a component influencing the liquidus temperature occurs.
REFERENCES:
patent: 4045309 (1977-08-01), Andersen
patent: 4668350 (1987-05-01), Desclaux et al.
patent: 4867851 (1989-09-01), Basquin et al.
patent: 5094728 (1992-03-01), Entner
patent: 0 195 142 A1 (1986-09-01), None
patent: 0 455 590 A1 (1991-11-01), None
patent: 0 703 026 A1 (1996-03-01), None
Akin Gump Strauss Hauer & Feld L.L.P.
Heraeus Electro-Nite International N.V.
Valentine Donald R.
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