DE1041262B - Furnace for the electrolytic aluminum production - Google Patents

Description

GERMAN

It is a known fact that in the liquid aluminum bath and in the cryolite bath of furnaces for Electrolytic aluminum-generating electromagnetic forces occur which affect normal operation can have a disruptive effect. These forces come about because the electric current in the liquid Aluminum and in the cryolite bath is influenced by the magnetic fields generated by the strong Direct currents are caused in the various parts of the furnace. To the harmful electromagnetic To reduce forces in the weld pool, one has after a not previously published proposal tries to increase the strength of the magnetic field by a favorable arrangement of the power supply to the Oven reduce. In this way, however, one can never entirely avoid the fact that some of them are quite strong magnetic fields arise in the furnace.

In detailed investigations of the magnetic fields occurring in aluminum furnaces, it was found that that vertical components of the magnetic field are always present in the weld pool. According to the laws of Electromagnetism call these vertical components of the magnetic field horizontally directed forces in those parts of the weld pool in which horizontal flow components occur.

It has now been found that horizontal flow components in the cryolite bath are not noticeable It happens, however, that in liquid aluminum there are sometimes very strong horizontal current components

Furnace for electrolytic
Aluminum production

Applicant:
Elektrokemisk A / S, Oslo

Representative: Dr. G. W. Lotterhos

and Dr.-Ing. H. W. Lotterhos, patent attorneys,

Frankfurt / M., Lichtensteinstr. 3

Claimed priority:
Norway April 16, 1953

Johan Wleügel, Röa, Oslo (Norway),
has been named as the inventor

The drop along the cathode bars consequently leads to a greater voltage drop due to the carbon lining and therefore a greater current density in the parts near the furnace sides than in the central parts of the lining.

According to the invention, the horizontal

may occur. It can therefore _flow components in the transverse direction of the furnace in the liquid aluminum

minium, sometimes very strong electromagnetic forces in the horizontal direction appear, caused by vertical components of the magnetic field.

In the construction of the furnace floor it is generally 35
my usual, the cathode bars of the
Insert the long sides of the furnace. The cathode bars are usually straight and will
inserted horizontally so that the coal lining
above the cathode bar in the entire width 40 is almost the same. Calculations have proven

liquid aluminum is significantly reduced by the fact that the cathode bars have a z. B. from the Curved shape as can be seen in the drawing. This will increase the thickness of the coal lining in the Sew the sides of the furnace larger than the central parts of the same, and by adjusting the curvature the cathode bar and thereby the thickness of the carbon lining can be achieved that the Current density in all parts of the coal lining

of the furnace is the same. It has now been found that with such a floor construction in the liquid Aluminum large horizontal flow components in the cross direction of the furnace can arise.

The investigations have shown that this is the cause of these horizontal current components lies in the fact that the resulting voltage drop from the middle of the furnace towards the sides of the furnace leads to that the current density in the coal lining

sen that the cathode bars should have a curvature that is approximately a parabola around a to achieve even power distribution.

Experience has shown that the electrical resistance 45 is the coal lining in an old furnace floor bigger than in a new one because the lining is gradually being impregnated by the cryolite bath. In one In the new furnace floor, the voltage drop through the same is 0.25 to 0.30 volts, while it is in the old one the parts that are initially on the oven sides, greater than 50 oven floors can be 0.7 to 0.9 volts. Calculated

is than in the middle parts of the same. The liquid aluminum does namely because of the good electrical Conductivity of the metal from an almost equipotential part of the system, and the stresses show that the above, to achieve a uniform current distribution in the furnace bottom required curvature of the cathode bar must be made less when the resistance in

«O9 65IV37O

the coal feed increases. It is therefore advantageous to replace the cathode bars with a new furnace floor to bend less and with an old oven floor more than theoretically in both cases Corresponds to the correct value. This results in weak horizontal current components in the first operating period arise in the direction of the long sides of the furnace, which, however, stop completely after a while, while later weak horizontal stream components running transversely in the direction of the furnace center appear. These horizontal flow components in the liquid aluminum are in the transverse direction of the furnace in any case, by far smaller than with the usual oven floor construction with straight and horizontal ones Cathode bars.

You can also use a slightly different type of furnace pan when using curved cathode bars Give shape than that provided for straight cathode bars. Such a shape of the furnace pan is shown in the accompanying drawing.

The drawing shows schematically a cross section through a furnace half, the center line of which is indicated by CC. 1 is the furnace pan and 2 is the insulating layer that z. B. can consist of asbestos. 3 is the coal lining and 4 is the anode, which is immersed in the liquid cryolite bath 5. Under the cryolite is the liquid aluminum 6. 7 is a cathode bar which is curved according to the invention. As a result, the coal lining near the sides of the furnace is thicker than in the central parts of the furnace.

8 denotes the curvature of the cathode bars in known furnace floors, and 9 is the corresponding theoretical curve for the furnace floors according to the invention.

As stated above, in practice it is advantageous to use a curvature that is between these two curvatures.

It is not necessary to use an insulating stocking that is often used in common floor constructions to provide the cathode bars, thereby avoiding the difficulties associated with obtaining a satisfactory electrical insulation are connected. Also with regard to thermal insulation and mechanical strength, a furnace pan according to the figure offers great advantages compared to Oven pans of the usual type.

Claims (2)

Patent claims: 1. Furnace for electrolytic aluminum production with inserted laterally above the floor Cathode bars, characterized in that the cathode bars are curved so that the height the coal lining above the cathode bars near the furnace sides is greater than in the central parts of the furnace. 2. Furnace according to claim 1, characterized in that the cathode bars in a new coal lining less and with an old coal lining more curved than in both cases to achieve a complete uniform power distribution is required. For this purpose 1 sheet of drawings © «09 65 & / 370 10.58: