DE1131418B - Arrangement of power supplies to suppress the magnetic effects in electrolysis furnaces with high current for the production of aluminum - Google Patents

Description

Electrolysis furnaces with an amperage of 100 000 A and more used, in which the influence of magnetic fields to level fluctuations and Movements of the surface of the liquid aluminum accumulated at the bottom of the furnace tub.

The movement of the surface can take place statically, so that the metal mirror remains stationary. However, it can also result in more or less rapid movements of the metal, which the Significantly reduce the yield from electrolysis.

The high-amperage electrolytic furnaces are usually in the shape of an elongated rectangle, one pair of sides is significantly longer than the other. In the following description these will be Magnetic field and the strength of the current in any point of the liquid metal defined by the projection these values on three coordinate axes, the zero point of which is the center of the crucible bottom of the Electrolytic furnace is. The x-axis runs parallel to the long side of the furnace, the j-axis runs in the same horizontal plane perpendicular to the x-axis, d. H. parallel to the narrow sides of the rectangle; the The z-axis is perpendicular to this plane (see Fig. 1).

Let B be the value of the magnetic field at a certain point and Bx, By and Bz the projections of B onto the x, y and z axes.

J is the value for the current density and Jx, Jy and Jz are the projections from / onto the x, y and z axes, respectively.

The static changes in the liquid level at the level of the molten metal are proportional the products

arrangement

of power supplies to suppress the magnetic effects in electrolysis furnaces

with high amperage for the production of aluminum

Applicant:

PECHINEY Compagnie de Produite Chimiques et Electrometallurgiques, Paris

Representative: Dr.-Ing. F. Wuesthoff, Dipl.-Ing. G. Pulse and Dipl.-Chem. Dr. rer. nat. E. Frhr. v. Pechmann, patent attorneys, Munich 9, Schweigerstr. 2

Claimed priority: France of February 28, 1956 (No. 709 429)

Jacques Bocquentin, Ricuperoux, Isere, and Jean Givry, L'Argentiere,

Hautes-Alpes (France) have been named as inventors

Bz · Jx and Bz ■ Jy

from the vertical component of the field and the horizontal components of the current density.

It has been proposed to suppress the horizontal longitudinal components Jx by calculating the conductors going from one furnace to the next in order to distribute the current well in the bottom of the furnace.

It has also been proposed to reduce or suppress the transverse currents Jy by placing slopes of solid fluoride around all of the liquid metal so as to obtain a cathode surface which was substantially the same as the anode surface. In this way, good electrolysis yields are obtained, even if magnetic fields are still present. Nevertheless, the more the magnetic fields are reduced, the better the electrolytic furnace works and the more stable it is, if the current is occasionally expanded, that is, if the component Jy is not equal to zero.

It has been proposed to reduce the strength of the magnetic field B by dividing the conductors located on the outside of the furnace into as large a number of smaller conductors as possible, which are arranged in tracks at a certain distance from the metal. A significant improvement is obtained, but these arrangements sometimes interfere with the operator's work.

Finally, it has been proposed to suppress the magnetic fields by removing the conductors at a great distance from the liquid metal, always alternately in such a way that through neighboring conductors the current flows in the opposite direction. A disadvantage here was the considerable Investments for the conductors and extremely high power losses.

It is the object of the invention to provide a simple arrangement for supplying power to electrolytic furnaces

209 609/359

to show, through which the magnetic effect in the center of the tub is completely suppressed.

To achieve this object, the invention proposes that the means for supplying the current to the anodes of the furnace and the side conductors are arranged such that the side conductors see at the intersection of a third degree curve passing through the center of the tub and being independent on the type of supply of the current to the supply rails, with a circle, the radius of which depends on the type of current supply mentioned, the circle and the third-degree curve being determined by the following formulas:
Circle:
(«- V ₂ ) b (c ² + (F) + (« - V ₂ ) d (a * + b *) = 0, third-degree curve:

d {b * - α ² ) (d ² + c *) + b (d ^z - c ² ) (α ² + b ² ) = 0, in which α is the distance between two distributors assigned to the anode system and one perpendicular to the furnace Central axis, b the vertical distance of a line through the central points of the distributors opposite the furnace center, c the distance between the side conductor and the above central axis, d the vertical distance between the furnace center and a line through the central points of the lateral conductors and the current distribution coefficient on the means both ends of the manifold. This avoids the disadvantages associated with the previously known arrangements, and the result is a satisfactory and uniform operation of the oven, even if several ovens are set up lengthways, ie if the long sides of a rectangular oven are the extension of the long sides of the in Form the sense of the current passage of the existing and the following furnace.

The lateral conductors are preferably divided into as large a number of parallel individual conductors as possible divided, which are arranged around a center line for which the position defined in claim 1 is applicable. To take into account the magnetic shielding effect caused by the furnace pan surrounding metal jacket is exercised, the side conductors on the mentioned in claim 1 Third degree curve located closer to the vertical axis passing through the center of the furnace pan be.

The invention is explained in more detail by means of schematic drawings of exemplary embodiments.

Fig. 1 is a perspective view of the liquid metal at the bottom of the electrolytic furnace.

Fig. 2 shows a row of cells in a longitudinal arrangement, successively from a current of the same intensity are flowed through.

Fig. 3 is a cross section through the crucible 1 of the cell. The power supply devices 2, 2 form the distribution system that receives the electricity from the previous furnace and it distributed over the anode system of the cell. 3, 3 are (in a middle position) the lateral conductors, which are arranged parallel to the longitudinal sides of the cell. Figure 4 is a top plan view of the cell of Figure 3. Here 3 ', 3' are the ends of the side conductors which take in the current coming from the previous furnace; they are connected to the distribution system 2, 2. The feed devices 2 ίο are each via the conductor ends 3 'only by one Powered by the end of it.

Fig. 5 shows two consecutive in the longitudinal direction arranged cells in side view, the distribution system 2, as in Fig. 4, only from one Is fed with electricity from the end,

Fig. 6 shows two cells according to Fig. 5, but with the distribution system 2 from both ends is fed with electricity. The one through the conductor 3 'out The current fed to the previous furnace is divided into two parts, one parallel to 3 Head 4 leads to the other end of the distribution system 2. In this case the conductors 3 of Figs the middle position of the ladder system 3 and 4 of FIG. 6. These conductors 3 and 4 can be used as tracks be arranged by ladders of smaller dimensions, as previously suggested.

Similar to FIG. 3, FIG. 7 shows a cross section through the electrolysis furnace, with curves 5, 6, 7 and 10 are drawn, the intersection points 8, 9 and 11 for the arrangement of the conductors according to the invention are decisive.

The longitudinal arrangement of the electrolytic furnace is very often used because it is space-saving and work relieved, but particularly strong magnetic effects can occur.

In the electrolytic furnace according to the invention, the magnetic effects in the center O of the tank of the electrolytic furnace are in fact zero. Such effects still exist on the rest of the furnace surface, but they are very weak in the vicinity of the center O , and in practice their strength shows a certain symmetry with regard to this point, which leads to sufficient stability when the electrolysis furnace is working.

The vertical component Bz of the field created by the horizontal conductors in the vicinity of the cell is zero for reasons of symmetry.

The transverse component Jy of the current density is also zero in the center of the furnace for reasons of symmetry, as is Jx. There are therefore no magnetic effects of static origin.

The effects of dynamic origin depend on the

Size of a rotation vector R ab, which can be calculated with the help of the values for the components Bx, By, Bz and for the current densities Jx, Jy, Jz and their partial derivatives.

Expressed mathematically, the following equations apply to the projections of the vector R onto the x , y and z axes:

JxX - JjX

Ry = Bx

dJx dx

dJy dx

dJx dJx

^ - + Bz

Rz = Bx -

dJz

+ By

+ By

dy

dJy ~ dy ~

dJz

_r dBx _T dBx Jx - Jy-

Bz-

+ Bz

-Jx

Jx

dx

dBy dx

dBz

-Jy

-Jy

dy dBy

dBz dy

Jz dBx Jz dz T- dBy dz dBz

dz

At the center O of the cell, Bx , like its partial derivative, is zero; - -j - as well as - ^ -

and -—- are zero if the above

Precautions were taken to ensure the distribution of the current in the tank bottom. Only the vertical current component is present

Jz, because Jx = Jy- 0. The derivative

—J - ^ -, namely the dz

Change in the vertical component of the field according to the height of the liquid metal is also zero.

The derivative - -, -, namely the change in the vertical component of the current density in the transverse sense, is equal to zero, since Jz is practically constant in a very large area around the center O.

In the center O of the tub, the components Ry and Rz of the rotation vector are therefore equal to zero, and it remains:

_n dJy _T dBy Ry = By -y- - Jz - ^ -. dy dz

In the center of the tub, the metal can rotate about an axis parallel to the j-axis. To avoid this, Ry must be zero; however, the vertical component of the current density Jz cannot be zero,

just as little as - ~, the term for the change

dy

the horizontal, transverse component of the current density in the transverse sense. The elimination of the magnetic effects in the center of the tub, which is the subject of the invention, can therefore only be achieved by removing the transverse component By of the magnetic field and the by ~ - ~

makes the expressed change of the same along the vertical equal to zero.

For the purpose of calculating the component By , the distance between the parts of the distribution system 2, 2 from the z-axis (see FIG. 3) is called α , while the vertical distance of a line through the middle points of the conductor 2 relative to the center O of the tub is included b is designated. The distance of the conductor 3 from the z-axis is designated as c , and the perpendicular distance between O and a line through the central points of the conductor 3 is designated as d.

oil means the current intensity arriving from the side of the preceding furnace in the distribution system 2 (FIG. 4) and (1 - «I) the current intensity with which the distribution system is supplied from the opposite side (case of FIG. 6). In the case of FIG. 5, «= 1.

The field present at point O is calculated from the current flowing through conductors 2 and 3, as if they were conductors of indefinite length through which the current flowed in reality in the conductors in the Level YOZ flows. Experience teaches that in this way one gets a sufficient approximation in practice.

You get:

2 1 (oi Head 2.2 21 («
9 T (nt Head 3.3 rf C ² ) ² By
dBy i / l ^b ^ dz b * -a ² - »Μ ( ^C + ^{/ a)} (a ² + Ö ² ) ^{2 / a)} (^

To make By and - - ^ - equal to zero at the same time,

dz

one must therefore fulfill two conditions, namely: («- V ₂ ) b (c ² + </ ² ) + (« - V ₂ ) d (α ² + έ ² ) = 0

α ² + Z> ² ) ² = 0.

{<% - V ₂ ) (b ² - α ² ) (</ ² + c ² ) ²

+ («~ V2) (c ^a -

In these equations the factor «can be eliminated so that one obtains:

d (b * - α ² ) (d ^z + c ² ) + b {d * - c ² ) (α ² + b ² ) = 0,

whereby the above second equation can be replaced.

Given α and b, ie the position of the conductors of the distribution system 2, 2 ', which is generally determined by the construction and working conditions of the furnace, it can be seen that the third equation represents a curve of the third degree which is independent of the power distribution in the distribution system («).

The first equation corresponds to a circle whose radius varies with α. The distance α is generally small. If it is set equal to zero, FIG. 7 is obtained, in which 5 represents the third-degree curve on which the conductors 3, 3 must always be located. is the circle that corresponds to a value for κ = 1, where the current is only supplied on one side. The radius of the circle 6 is equal to b / 2. 7 is the circle with a radius of 5 b / 2 corresponding to a value for α of Ve. The middle position of the conductors 3 must therefore correspond to point 8 if the current is supplied to the distribution system 2, 2 from one side only, and point 9 if the distribution system is supplied with current from both ends; two thirds of the current flow through the end closer to the preceding tub and one third through the other end.

The arrangement of the lines is therefore defined by the following table:

55 c / bd / b

0.5
0.35

«= 2/3

1.7 0.7

It is assumed here that the distance b of the distribution system 2, 2 from the tub bottom is known. This is the most common case, but it can also be assumed that one of the dimensions c or d is known, giving a solution to the above equations which does not exceed the scope of the invention.

The above position for the side ladder represents the middle point of the ladder, which is in a possible

large number of parallel conductors arranged in tracks and arranged around this center line could be.

The calculations were carried out without the magnetic shielding effect of the iron container, the that surrounds and contains the tub of the electrolytic furnace. Because this container has the same elements of symmetry like the tub, it can weaken the magnetic fields considerably, however do not change their direction.

It is difficult to accurately assess the importance of the shielding effect; but if one assumes that the field generated by the conductors 3, 3 is weakened by half, which certainly means an upper limit, then one finds that it is sufficient if one wants to be sure that no magnetic effects occur at point O. to arrange the conductors 3 on the curve 5 (Fig. 7), namely at the intersection with the circle 10 (radius 7 & / 6), ie at point 11. <x is then equal to 0.8, ie that 80% of the total Amperage must be fed to the end of the distribution system 2, which is on the side of the preceding tub, and 20% ^a * i the other end.

The following examples illustrate the invention without restrict them.

example 1

An electrolysis furnace with 100,000 A, arranged lengthwise, with 2 of the distribution bars Ends (Fig. 6) are supplied with current, showed a poor distribution of the magnetic fields:

On the side facing the previous oven the field was weak, in the center it was stronger and very large strong at the end facing the following furnace. The molten metal at the bottom of the furnace pan was one Subjected to rotation, and its surface showed irregular level fluctuations, the maximum Reached 5 cm.

The course of the stove was very unstable, the bathroom froze on the tub walls on that side of the Tub where the field was weak, narrowing the active zone, and on the other hand it was impossible to the solid fluoride slopes on the opposite side, d. H. at that of the following Cell facing side, maintain.

If the conductors 3, 3 were arranged according to the invention, the magnetic effects in the center O of the trough were equal to zero. In relation to the point O, they were on the whole symmetrical. The fluctuations in the surface area of the liquid metal virtually disappeared and regular slopes of solidified fluoride could be maintained on all sides of the tub. The operation of the furnace is much more stable and the energy consumption is reduced by 800 kWh / t aluminum.

Example 2

A 50,000 amp electrolytic furnace equipped with baked anodes and arranged lengthwise was used. The distribution bars 2,2 were only supplied with power from one side (Fig. 5), the conductors 3, 3 (d = 0) arranged at the level of the tank bottom generated magnetic fields with a very strong horizontal component By on the side of the preceding furnace, which was half the value of the former near the point O and zero on the opposite side. However, the fields had a very strong vertical component Bz . The operation of the oven was very unstable and all the phenomena described in Example 1 were observed.

After changing the position of the conductors 3, 3 according to the invention (point 8 of FIG. 7), an improvement was made achieved which corresponded to that described above. The course of the electrolysis was very stable, and the The yield was increased by more than 3%, so that it rose from over 87% of the theoretical yield.

Claims (3)

PATENT CLAIMS: 1. Arrangement of power supplies to suppress the magnetic effects in the center of the tub of electrolytic furnaces with high amperage for the production of aluminum, characterized in that the supply devices (2) for the current to the anodes of the furnace and the lateral conductors (3) are arranged in this way are that the lateral conductors (3) at the intersection (8 or 9 or 11) of a curve of the third degree (S), which passes through the center (O) of the tub and is independent of the type of supply of the current the supply rails (2), with a circle (6 or 7 or 10), the radius of which depends on the type of power supply mentioned, the circle and the third-degree curve being determined by the following formulas: Circle: (oc- = 0, Third degree curve: d (O ² - α ² ) (d ^z + c ² ) + b (d * - c ² ) (a ^a + Z> ² ) = 0, in which α is the distance between two distributors assigned to the anode system and one perpendicular to the furnace standing central axis, b the vertical distance of a line through the middle points of the distributor opposite the furnace center, c the distance of the lateral conductor from the above central axis, d the vertical distance between the furnace center and a line through the central points of the lateral conductors and the current distribution coefficient the two ends of the distributor means 2. Arrangement according to claim 1, characterized in that the lateral conductors (3) in a the largest possible number of parallel individual conductors are divided, which are arranged around a center line are, for which the position defined in claim 1 applies. 3. Arrangement according to claim 1, characterized in that for the purpose of taking into account the magnetic shielding effect which is exerted by the metal jacket surrounding the trough of the furnace, the lateral conductors (3) on the third-degree curve mentioned in claim 1 (S) closer to the through the center (O) of the furnace pan vertical axis (7) are arranged. Documents considered: French Patent No. 1 110 685. Older patents considered: German patents No. 1 010 744.1041 262.1 049 108, 192. 1 sheet of drawings © 209 609/359 6.62