SE193563C1 - - Google Patents

Description

Priority given from 8 June 1955 (Itallen) This invention relates to the production of aluminum genora electrolysis, air and salt malt, i.e. from alumina lost in a bath of narrow salts. More particularly, the invention relates to an improvement of the furnaces and methods of producing aluminum, as described in British Patent 800,092.

It is an object of this invention to facilitate a reduction of the work, the installation costs and the operating costs, especially the power consumption, as well as to facilitate the operation and to increase the capacity in comparison not only with ordinary methods and ovens, which are currently in use, but above in comparison with methods and furnaces soin proposed in the above-mentioned patent.

The invention also intends to enable the treatment of aluminas, SOTO: are less pure than or cheaper than the ordinary Bayeral alumina, while at the same time obtaining aluminum of higher quality as a result of a certain sorting, thereby obtaining, e.g. the raluminum products of varying degrees of purity are formed in successive cells in the furnace, such a product is extracted separately, Iran separates the others.

The invention also aims to provide the possibility of interverts, from operation with a number of different cells, as described in British Patent Specification 800 092, to operation with the cells connected to each other and, conversely, from the possibility of effecting a circulation from cell to cell , which harmonizes with the lure circulation in the habit cell, which also takes place in a closed circuit (secondary circulation), without the generation of counter-hours and without the bubbles of anode gas being forced to Raja long paths, as occurs in a natal furnace of ordinary kind, with horizontal electrode surfaces, are connected to thereby effect circulation of the salt malt from oven to oven.

The invention relates to the life of reducing or eliminating temperature variations in the individual cells and to preventing varine losses to a considerable extent, as far as possible in furnaces which have been Hilda before the advent of the furnace according to British patent 800 092, especially when working with a noranalt sludge furnace and makes the anatomy of alumina and in some cases ave, in the draining of the formed metal independent of the normal operation of the individual electrolytic cells, so that maiming and possibly also bottling need not require that the furnace is opened and the furnace can be operated normally without crusting and without anode effects.

These advantages are achieved by the invention, which relates to a multicellular suction for melt electrolysis in general and in particular for the production of aluminum with different cells, provided partly with bipolar intermediate electrodes, which are electrolytically consumable and intended to be regularly (periodically) restored to the consumed surfaces and aro stationary and Eiretradeswise inclined, the cathode side of these electrodes preferably being smoothed out of graphite and the consumable anode side of electrode carbon, partly with two part electrodes, the latter equipped with current-carrying metal nipples connected to, current rails and with separate collection chambers under the electrolysis chambers. at 40 c: 4 2— - of which the cells communicate with each other through wires at such levels that & malt electrolyte can flow from one cell to another, since the cells are divided into at least two groups arranged in two. rows on opposite sides of a longitudinal cradle of refractory and insulating material, and that circulating and lifting devices are arranged between said groups, so that the electrolyte can circulate through the electrolytic spaces in a closed circuit.

The invention also relates to a salt in the production of aluminum by electrolysis from alumina load in a bath of narrow salts in the above-described multicellular furnace with different series-connected electrolytic cells with hypoldar jug, characterized in that the electrolyte is caused to aerate within the furnace in one. closed circuit through the double row of separate cells, while an electrical strain was passed through the cells in series, that alumina is sewn to the electrolyte continuously or intermittently, that the formed aluminum metal is drained individually from each cell.

In the same furnace, within a single sheath of sheet metal clad with insulating and refractory material, two or more cell systems can be arranged, preferably electrically parallel to each other and preferably arranged with the lifting devices next to each other and separated by a transverse cradle of the same material and with the same function as the longitudinal diaphragm.

In an oven with a stub circuit as described above, the cells can be thanked with a roof of removable bricks of heat-insulating, refractory, preferably porous and light materials, which lamp themselves to allow passage of the electrolytic gases and / or if necessary are provided with a slide for facilitating of the passage of these gases. The ovens can also have removable outer lids of refractory and heat-insulating material.

If said bricks and outer lids are deposited over or near a cell which is used to renew the anode surface, this causes heat loss and local increase in the viscosity or solidification of the melt, thereby stopping its circulation to the frail cell during the renewal operation. When the bricks and the outer lids are returned to their place, the local internal temperature can rise again, whereby the bath is melted or its viscosity is reduced so that circulation of the hair ferments the cell with it, the renewed anode can automatically bathe again.

Furthermore, means can be provided for individual regulation or shut-off of the wires, which are arranged in solid blocks arranged on the electrodes, for circulation of the bath xnelLan adjacent cells, which means are preferably made of plugs controllably arranged hal in the black for shut-off of the wires. The plugs are arranged to be installed at different levels and are accessible for installation from above, preferably from a stable above the removable bricks.

Circulation through difference in water level requires one. first cell with maximum level, and one last cell with minimum level. These are arranged according to the invention means for lifting the bath, preferably arranged in connection with a pair of closed duck chambers the interior of the oven, where the bath is lifted from the last bile with the lowest Alvan to it. first cell with the highest level.

In the furnace according to the invention it is important that said duct chambers and conduits, which connect the branches of the cell system, the bath circulation are arranged only in inner cradles in the electrolysis furnace, i.e. not only inside a particular apparatus installation, but in an inner Z011 surrounded by electrolytic cells, and Even drain pockets each communicating with one of the storage cores are thus arranged, namely in the longitudinal cradle between the two branches of the branching cell system.

It is also convenient to arrange in each cell a permanent electrical contact between the cathode and the metal in the collecting chamber. For this purpose, it is lame to force the carbon cathode against one or more carbon rods, which extend as far as the bottom of the collection chamber, so that the occurrence of one is compromised. fixed electrical connection between the cathode surface and the aluminum metal.

The consumption of alumina during the electrolysis was suitably replaced at one or more feedlots in the cell system, preferably outside the cells or the electrolysis rooms. At these feeding stalls, e.g. a separate chamber arranged between the cells, alumina, for example, is caused to fall from above by means of a feeding device continuously on the day below the existing surface type in the bath, which, thus continuously renewed, is caused to circulate on suitable salt and kept at a higher temperature. the following is referred to as "critical temperature". The term "critical temperature" refers to the temperature at which a particular bath of narrow salts becomes so viscous that it binds the circulation in the furnace of this invention. This "critical temperature" is, of course, always higher than the solidification temperature of the bath in question. It Or edge aft it does not Or an.Edligt to prevent staining of the bath surface, in ordinary furnaces (tendency to form surface crusts or crusts), where it in ordinary ovens Or inevitably aft to use a certain mechanical work for the introduction of alumina into the baths.

The aluminum metal formed in the individual cells is drained from the draining pockets, which may be arranged in the furnace cradle between the two branches of the system, where this Aram has reached, elevated and practically uniform temperature. It has not previously been possible to arrange drainage pockets in warm inner cradles, which cradles have no or almost no temperature gradient and operate at practically stable temperatures uniform and higher than the critical temperature for the bath and the metal. On the other hand, the idea is not to provide drain pockets for aluminum, which are based on the principle of communicating Icarl and arranged .1 outer walls of ordinary furnaces for aluminum electrolysis at horizontal bath layers. However, it has never been possible to use such drain pockets in practice, which in ordinary furnaces could only be built in external furnace walls, even though their use was hindered by the occurrence of one. more or less sharp heat gradient depending on the thermal conductivity of the material used in the manufacture of the outer rocks, and their respective thicknesses. Even if the insulation is improved, the constructive requirements for ordinary furnaces have in practice never provided operation in a relatively contrived and calm manner, such external drain pockets, which had a tendency to become clogged, for example by local solidification of the bath or metal. These imperfections have increased in ordinary furnaces Tried horizontal bath layers through unavoidable functional irregular bits of the cathode bottom. Finally, in ordinary furnaces for electrolysis of aluminum, internal partitions of inert refractory material have never been proposed for obvious reasons.

This invention did not merely involve a pre-bathing with respect to the processes and devices described in British Patent No. 800,092 and a considerable technical advance over the types of processes and furnaces provided with Tried horizontally abutting electrode surfaces currently in use. In addition to the well-known proposals to prevent in a series of liquids a certain number of electrolytic furnaces for electrolysis in salt malt on such salt, that the bath is passed in a closed circuit through, a certain number of furnaces of ordinary construction, for example according to U.S. Pat. In this patent it is proposed that Tn.ata a smelt, rich in alumina, to a first furnace in a series and to bring the bath, which has a low A1203 content, when it leaves the last furnace in the series, back to its original composition before .it is re-introduced into the first furnace in the series. To this end, the almninium oxide found in a cheap bauxite ore saint is loosened, with suitable subsequent treatments the contaminants and the slag from the A1203 salunda enriched bath. However, the realization of this proposal in practice would inevitably lead to irregularities and require the overcoming of obstacles which in practice could not be overcome and which were essentially overcome. the need to keep the fluorinated bath (which is very chemically active) at elevated temperatures of about 950 to 1000 ° C at the usual place in the circuit and therefore also in the connecting parts outside the furnaces. Otherwise the viscosity will impede circulation, before the solidification of the bath at 850-950 ° C can even interrupt it. It is sufficient to state only: the length of the circuit in which the bath must pass the genor (usually an individual oven is several meters long, the hot transferring surfaces become quite large) and this also applies to the water level which is required to promote circulation of badet frau., the first to the last oven in the series); .operations for initiating and stopping the water circuit saint de for installation of mangden bad sum shall be led aro much answer, etc .; de manga yttre banor, soul ma.ste bringas. Over the so-called critical temperature of the bath at the start-up and at that temperature during the electrolysis and during interruptions in the process; the relation that the internal (secondary) circulation in the individual ordinary furnaces Andras on an irrational through influence of the unidirectional circulation from one furnace to another, and the relation that the installation of the electrode spacing between the carbon anode and the cathode metal and the draining of the metal in the individual furnaces in the circuit be answered to also implement Tried hansyn to the requirements (examplein constant temperature and flow rate) on the bath flowing genoin the, individual furnaces in the circuit; the stoma volumes and quantities flowing baths in the circuit in relation to the production of aluminum per day.

A partial circulation of the bath Moan furnace (of the type with bipolar electrodes) is described in Swiss patent 293 187, where, however, the circulation is not closed. The mom furnace and above all the electrolysis bath consists of aluminum chloride, which does not consume the electrode (as in the case of alumina) during, the electrolysis, but develops chlorine at the anode, for which reason the furnace .according to the Swiss patent, the liana must be hermetically sealed. It lamps, for operation at 700 ° C and could not be used in the electrolysis of alumina in fluorinated smelters with carbon anodes consumed.

In the mentioned patents there is no proposal on the design and operating principles which are applied according to this invention.

One. embodiment of a furnace, its mode of operation and the electrolysis carried out therein, all in accordance with this invention, will be described by way of example and not intended to limit the invention dArtlll, in connection with the accompanying drawings.a.

Pa. In the drawings, Fig. 1 is a plan view of a twin oven according to the invention, which comprises two cell systems, each system comprising two groups of electrolytic cells in series (the cells are shown in the upper row untapped, ii. the lower row to hoger fully roofed and in the lower row to the left without the outer lid but with a brick roof gap). Fig. 2a is a longitudinal section of the lower right branch or cell group at the furnace of Fig. 1, and the section is taken along the line B-B in Figs. 4, 5, 6 and 7. Fig. 2b is a longitudinal section of the oven. , hogra cell group according to Fig. 1 (but provided with a lid) and the section taken along the lines C – C in Figs. 4, 5, 6 and 7. Fig. 3 shows on a larger scale a part of Fig. 2a. Fig. 4 is a cross-section along the line E-E in Figs. 2a and 2b. Fig. 5 is a cross-section along the line F — F in Figs. 2a and 2b. Fig. 6 Or a cross section along the line A — A pa. Figs. 2a and 2b. Fig. 7 Or a cross section along the line D — D p5. Figs. 2a and 2b.

The furnace in the form of a cell system with callers arranged in rows according to this invention can be designed (seen in plan) in different configurations, for example in the form of a rectangle or in a U-shape or S-shape. If a rectangular long and narrow space is accessible Or a particularly suitable shape it with two systems of electrolysis or of rectangular shape with the lifting devices weld towards each other or with independent bath circuits electrically parallel but housed in a single rectangular Denim embodiment is shown in Fig. 1, where the single-line arrows 1 schematically indicate the path of the current, while the double-line arrows 2 schematically indicate the direction of flow (circulation) of the electrolysis head. A metal casing 3 contains a cell housing 4 of layers of refractory electrical and non-insulating material, the four branches 5 ', 5 "and 6', 6" of cell groups, which branches, as indicated in pairs, form the two independent systems of callers, which, however, placed in a twin oven.

The two longitudinal branches of each cell system have common Ifingsgaende intermediate walls 7 and 8, and the two cell systems have in common a dva.rgfiende Inellanvagg 9.

At the top of the cells an insulation arranged by different insulating layers, which are removable, for example by outer lid 10 and by bricks 11 covered thereon. Each longitudinal spruce of the furnace consists of a certain number of elementary cells (Figs. 2a, 2b and 3). Intermediate chamber or feeding stall 12 with. feeders 13 for supplying alumina may be interposed between certain cells.

The cells Oro designed as described in the Hriti patent 800 092 with part electrodes 14 (anodes) and 15 (cathodes) provided with metal nipples (for example of iron) 16 which conduct the electric current, and with bipolar intermediate electrodes 17, anode installation layer 18, electrolytic chambers (the cells themselves 1g for the bath 20, and lower chambers 21 for collecting the aluminum metal 22, each provided with a drain outlet 23. The cell electrodes and the drain chambers are enclosed by a housing 24 of material which resists attack by the bath and the metal, impermeable, electrically insulating. and which shapes the bath temperature. It's one. decided and important advantage of the cells in the furnace according to this invention, that the electrode carbon is thanked over its entire width by solid blocks 25 of such an inert, insulating, resistant and impermeable material, which blocks form heads, in which wires 26 are arranged for communication from cell to cell, through which the bath 20 circulates and which form only an external bypass for the electric current. These lines are located at a 15th level of the gas collection channels 27, which Oro arranged at the top of the cells. The blocks 25 carry the above-mentioned removable bricks 11, which suitably consist of porous material which allows the removal of electrolytic gases, the removal of which may be arranged slid (not shown in the drawings) in these bricks. The gases are discharged through outlet 28. In these blocks 25 are arranged - vertical hall 29 with adjustable plugs 30 intended for all restricting the channels in the lines 26. These plugs are shown in Figs. 2a, 2b and 3 in a raised layer. The A-drain openings 23 communicate with an equal starting number of pockets 31 (Fig. 4) in the intermediate wall 7, 8. Outer drain openings 47 are also arranged with plugs 48 (Fig. 4). The electrode carbon in the individual cells tilt to the same degree but. preferably in different directions in the two branches of one and the same cell system, as shown in Figs. 2a and 2b.

One of the two spirits in each cell system consists essentially of two selectively insulated and closed chambers 32, 33, of which the chambers 32 have their bottom at a higher level than the chamber 33 (Fig. 6). The two chambers communicate with each other through a line 34. These two duck chambers communicate in their Tried the two adjacent first and last cells 35 and 36, respectively, in the two branches of the cell system. The other spirit may be arranged on the same salt, or the two ducklings may be extruded, provided that the levels of the two duck cells in this spirit are at the same height or almost the same height, in which case these two duck cells may be directly connected. with each other, for example through a wire 37 shown in Fig. 7. In order not to complicate the drawing more than necessary, the fixed electrical contacts (for example carbon rods), which as stated above are arranged between the graphite electrode and the metal in the lower collecting chamber, have not been shown. in habit cell.

The materials which may otherwise be such as are already used in ordinary furnaces for the metal casing and for the refractory and heat-insulating layers of the cell housing (e.g. refractory bricks, such as laths, porOs refractory bricks, powdered alumina) or form the longitudinal the anellan cradles and the outer lids, while the inner layer in direct contact with the narrow electrolysis bath and with the formed liquid metal consists of air, a non-attackable and add porous material with respect to the bath and the metal, preferably of a solid material as before. smelted or sintered at very high temperatures, for example corundum, aluminum nitride, magnesium oxide, which is pre-smelted on an electric scale. The material to be used for the solid blocks 25 should be a single electrical conductor but analogously coiled. good heat conductor. Electrosmalt magnesium oxide (MgO) or corundum (A1203) have been used successfully. The bricks 11, which form the roof of the cells, may for example consist of materials containing magnesium oxide and / or asbestos, ie. of material which slides a good thermal insulator, which emits 1000 ° C, preferably porOst or fibrous and that. These bricks are composed so that they will. the gas layer Over the bath at such a temperature that solidification at the yin of hatred. avoided. The electrodes are, by themselves, electrolytically tangible carbonaceous material on the anode side and air graphite on the cathode side, and the metal nipples are usually air jam or steel on the edge itself.

The operation of the furnace according to the invention proceeds in the following manner: The electrolytic current is passed through the furnace circuit In the following direction: second anode / high voltage bipolar electrode / bath / bipolar electrode / badian cathode. It can be taken through a metal conductor to which the sour heist electrode koi in the furnace, which will act only as an end anode, and be taken out of the furnace Iran part indistinguishable .the preceding electrode carbon, which km-species to act exclusively as a duck cathode and originally isolated from. end anode.

Both the inlet and the outlet for the current are made through metal nipples distributed in the end electrode carbon and which are suitably located at a great distance from the active electrode surface. This can be achieved by arranging ay nipples or connecting nipples on whichever is suitable, set, for example in a plane perpendicular to said surface, as stated for example in British patent 800 092 and as shown to the right in Figs. 2a and 21) or by arranged parallel to said surface, the path shown to the left in Figs. 2a and 2b and in Fig. 3.

The simplest way to connect the furnace to the supply rails is to select, as a pair of connection electrode coils, the two electrodes (be one or another and the other a cathode), which are coated at the head of the cell system and provide it with suitable metal conductors. the circuit Or as Saill is indicated in Fig. 1. Another lamp connection is obtained by opening the chain of cells, preferably at half the distance between the spirits of the furnace, by dividing a bipolar electrode carbon (an intermediate wall) in an anode carbon. 14 'and a cathode carbon 15' each provided with nipples as shown in the middle parts of Figs. 2a and 2b, although in this case, contrary to what is shown in the drawings, the two electrodes are of course Oro electrically insulated Iran each other.

As radon is introduced, the electrolytic current gemarn cell system preferably passes in a direction opposite to the bath circulation. As amen already speciesforts, the current passes through the hypolar coal and salunda Iran from one cell to another. Only a very small part of the stream passes with the bathing stream through the lines 26.

In the furnace according to the invention, the bath in fact - always within the furnace - circulates through all the cells until it returns to the output cell, from which, the water flows through the whole cell system, and so on. The bath stream from the usual cell to the next can form new conduits arranged in the inner side cradles of the furnace, but preferably through the inner grooves which separate the individual cells, namely through conduits 26, sludge passing through the upper parts of the inner cradles, which are provided in the blocks 25 of suitable material (Fig. 3).

The velocity air the secondary circulation ie. The circulation of the air bath within each cell should be as low as possible in order not to prevent the use of aluminum. A. On the other hand, the rate of main circulation of the bath should be sufficient to ensure a satisfactory supply of alumina to the cell located furthest from the respective feed stalls, unless separate mating to each individual cell is used.

The secondary bath circulation in each cell should take place preferably. 'hags kated.en and up along the anode.

The problems that arise when it comes to: the circulation of the bath in the closed furnaces in a closed circuit is mainly due to the necessity of holding the bath in each part of the circuit at a temperature (higher on the critical temperature at which it loses its flowability), which Or equal to or near the optimum operating temperatures, which may be those, yid which, electrolytic cells are operated If & present. At this temperature, the bath is easily flowing and the degree of flow to be stored is surprisingly dull, and consequently the circulation overcomes ay, in reality, insignificant pressure losses. It is, however, appropriate to limit as much as possible the possibility of bypassing the current through the bath between the two parts or which are under the full voltage of the furnace. 6 - British Patent No. 800 092 states that the upper part of the transverse partition between two adjacent callers is therein coated with a special material which is not attacked by the bath and is not oxidizable.

Instead of limiting the use of this material to only one coating, according to this invention the upper part of the cradles, which are partially immersed in the bath and inactive for electrolysis, can suitably consist of a solid block of said material, which rests on the bipolar piston wall underneath and there is suitably attached to the side cradles in the furnace as already mentioned, or of a carbon block completely and the hall covered with the said material.

In the upper inactive part of the cradle formed on this salt, the conduits 26 are arranged to ensure substantially parallel streamlined flow of the bath. Through these conduits, the bath flows in the required amount and a very small difference in water level is made between the two adjacent cells. It is possible that Ora each of the two branches of the cell system in the furnace is slightly inclined in the direction of the bathing stream. The bath fluid, which leaves the wires, enters the individual cells in connection with the cathode surface. Only a portion of this bath stream flows down the tangent cathode, while at the exposed anode surface Midas one. oppatgd.ende strom, which is promoted by the evolution of gases and by temperature. This ascending current is combined with the main current, which enters the outlet channels.

In Fig. 7 it can be seen that the channels which open into the cradles (horizontal blocks) at the top of the part electrodes in the two. the outer cells of the free spirit of the furnace, are connected to each other by a conduit 37, which passes through the longitudinal cradle, which separates the two branches of the cell system of the furnace. At the opposite Auden of the cell system Aro are arranged lifting devices 32, 33, which are described in the following and shown in Fig. 6.

The bath circulation through the lines described above requires that the temperature therein should decrease somewhat in comparison with the temperature of the bath in the anode zone at least as long as the main circulation is to be maintained. However, it is required that such a baduiva difference between the different cells be maintained as is necessary to ensure the desired flow, regardless of the moderate variations in the mean level which occur in the furnace during operation. This can be achieved by closing the gas chambers 36 above the electrolyte in the cells by means of the bricks of insulating porous material, as described above and resting on the upper parts of the transverse cradles between each pair of cells and preferably having such proportions that the free surface is held at a higher temperature The solidification temperature for the bath, whereby the possibility of crust formation is avoided. Without thermal insulation, the baths would solidify at the top and no electrolyte could flow through the channels 26 from one cell to the other. As already stated, the gas discharge from the individual cells occurs through the porosity of the bricks and, if necessary, through a suitably dimensioned hall. The bricks only need to be removed when the anode surface is renewed. They can be thanked or partially filled with alumina. At the other end of the furnace, the one in which the above-mentioned transverse conduit 37 Or is arranged, means are provided for providing the required level difference for effecting the bath circulation in the whole circuit. In this case, it may also be appropriate to provide the feed of alumina. By extending the side cradles of the furnace, it is possible to obtain at the Duck Cells two adjacent duck chambers, for example as wide as the cells, with vertical or inclined cradles, and said, deep enough to allow intermittent operation of the bath submersion or to accommodate the lifting device. These cradles in these ducks can be higher than those in the cells.

The thermal insulation should be such that it is s5.- kerstalles, that the temperature has bathed The above-mentioned duck chamber can be held Over the »critical. >> point as stated above.

This is facilitated by the fact that the heat which develops in the duck cells is greater due to the transition resistance at the iron-carbon contact. The insulation will be Miter if two chains of Geller are arranged, ie. a twin furnace, in a single symmetrical arrangement on & Want set, that the respective hand chambers are located next to each other, at which arrangement it may be convenient to group the stables for feeding alumina into the duck cells instead of halfway along the cell rows, as shown in fig. 1, 2a and 2b. A small extra heat-cold Mr duck carts and feeding stalls can be arranged above.

Atmin pA. a stall of the circuit, preferably at one end of the furnace, It is necessary to lift the bath, possibly by manually actuated means, but preferably by pneumatic devices, in such a way that the bath obtains a sufficient level difference for it to be able to flow into the. cell, ddr bath located. at his highest Diva. The return of the bath to the first cell in one branch of the furnace from the last cell in another branch, which cells are located next to each other, can preferably be effected without direct flow between the cells in order to avoid an orbit of electricity. , as already stated, the voltage drop between these two cells dr maximum, ie. , the total voltage drop in the furnace. It is possibly advantageous to use lifting systems which break the continuity of the bath. The passage of the bath through the chambers can suitably take place, for example, as described below in connection with Fig. 6.

Each of the duck chambers was connected to the adjacent cell by means of longitudinal conduits 39, 40. The bath was located in the duct chamber 33 adjacent to the duct anode at a level slightly lower than the level in the adjacent cell, while the the second duck chamber 32 must have laths at a higher level (for example a few decimetres higher), with the aid of forced movement of the desired amount of bath. An awkward set to ensure the lifting of the bath from one chamber to another Sr following. The chamber 33 with lower ntva communicates with the adjacent cell by means of one or more channels 39 provided with a small stop valve (for example a ball valve 41, of intangible refractory material with a specific weight, which is lower than the specific weight of the bath, whereby the ball for example Sr of carbon coated with electrosmalt magnesium or alumina) which valve serves to allow only tightening of the bath frail the last cell in the right duck chamber and prevent re-straining The upper part of each chamber is closed and is further insulated by a carefully fitting lid 10. We The two duck canoes communicate with each other through at least one channel 34. The person who is not occupied by the bath in the lower level duck chamber 83 is alternatively caused to communicate through a line 44 with a tank (not shown in the drawing) containing an inert gas, ( for example, electrolytic gas) as Mlles at sufficient tuck to lift the liquid from the bearing to the right duck chamber. By regulating the magnitude and frequency of pressure changes and the length of periods of overpressure and atinosar pressure in the camaraderie. 33 the interanitated transfer to the desired bath capacity from the said chamber to the chamber 32, amen to the sealing of the ball valve 41, which acts as an obstacle to backflow, is not perfect. Chamber 32 Sr provided with a gas outlet valve 45.

At the second free sound of the furnace (Fig. 7), the transition of the bath from one duck cell to the other takes place through at least one sufficiently long conduit 37, which passes through the partition 42, which divides the two branches of the furnace. The transverse section and the length of the conduit or conduits 37 are such that the electric current is thereby limited to a small percentage, for example 2-3%, of that which passes through the furnace and passes between the duck cells. Similar limitations apply to the conduits 26 between which are two adjacent cells in the same branch of the furnace.

The required alumina oxide can be fed continuously or intermittently, through one or more chambers or tanks or openings inserted into the cell row in such a way that the bath can flow through it. These feed stalls can be arranged, for example, at the edges of the furnace or in the intermediate layers (12 and 13, Figs. 2a and 2b). Anode effects are avoided. Therefore, there is no longer any need, as in ordinary furnaces, to frequently break the bath crust, nor is it required that each elemental cell be fed directly with alumina as in British Patent 800092.

From the feed stall 12, which is fed to the feed device 13, the alumina passes to the main bath circuit, which is caused to flow under Figs. 2a and 2b under a wedge wall 38 to an adjacent chamber and then to the nearest adjacent electrolytic cell to the feed stall.

The draining of the metal formed during the electrolysis takes place in the furnace according to the invention, preferably by vertical pockets arranged one for each cell in the lure refractory brickwork between the two branches of the furnace as shown in Fig. 4. Each cell is in its lower part provided with an outlet channel 23, which after a short horizontal part communicates with a vertical pocket 31, which extends as far as the upper edge of the cell. The liquid aluminum metal fills this side channel and rises in the pocket 31 to a level which is a few centimeters lower than the level in the cell in the melt, which has a lower specific weight of the metal. These drain pockets, which are arranged in the inner longitudinal wall of the furnace, are located at a sufficiently high temperature to prevent not only the solidification of the metal but also the solidification of any part of the bath which may be present. The pockets 31 are closed at the top by a lid 46, which are very thick to provide thermal insulation.

The metal is drained with the help of a suction tube, which is periodically immersed in the metal from above the edge of the sun. Devices are also provided to enable side draining, for example for complete recovery of the furnace through drain outlet 47 with refractory plugs 48, as shown in Fig. 4.

The anad surface is suitably renewed amedelbaat after draining from the respective cell and preferably after previous shut-off in the current. British Patent 800,092 and amen British Patent 802,959 disclose methods by which it is possible to carry out renewal or supplementation of anode carbon (consumed by electrolysis) either by lowering the bath level in the cell, until the entire surface of the old the anode is exposed and subsequent application to the surface of one or more discs of the anode material is coated with a binder layer, or alternatively if, for example, one works with a full cell by tilting only the new piece or pieces of anode carbon against the old anodema. In the said patent it is also mentioned the relation that the increase of the voltage drop, which occurs in the salunda Aterstallda anode, can be reduced to a bradel of 1 volt.

From an operational point of view, it is important and distinctive of this invention that the following suitable procedure for draining and renewing the anode surface in the individual cells can be carried out at suitable times during furnace operation as indicated by the control devices (instruments for grating the levels, strength and voltages), thermocouples and voltages. , which for the sake of simplicity and since they do not form part of the invention are not shown in the drawings. In a cell as shown in Fig. 3 the recoverable or recovered thickness 18 of the anode layer which is largely consumed, the electric current is generally shut off, the outer cover 10 is removed to allow access to the underlying brick 11 in the cell in question and up avldgsnas awn this brick. The cooling induced on this salt can only be sufficient to cause the bath to solidify in the adjacent lines 26, thereby. the circulation is interrupted. Otherwise, and in vertical Ml 29 pulls provided with plugs 30, the interruption of circulation can be effected or promoted by lowering these plugs 30 by throttling the conduits. Then the cover 46 (Fig. 4) is removed to the drain pocket 31, which communicates with this cell, and by suction the formed metal and a certain excess, ie. The amount of metal required to cause the bath level to sink in the cell below the level of the insulating material stage 24 ', on which the bipolar electrode and in particular the replaceable anode part 18 rests. The new anode part is then inserted and applied to the surface of the unused part of the electrode. Named new anode part, Tara can either one. compact carbon sheet (or consisting of a number of elements) is generally coated on the surface with binder (e.g. containing carbon monoxide and with a high melting point) to be brought into engagement with the base electrode carbon. A part of the extracted liquid is re-introduced through the draining fig, namely as much as is required to cause the bath level to rise again in the cell, whose anode has just been renewed, at a time which lies between the levels of the baths in the two adjacent cells. The porous brick 11 is then restored and the electric current is disconnected. Finally, the oven lid 10 is restored after or before lifting the plugs 30.

Quantitative example. As an example, quantitatively, one of the many possible embodiments of this invention is described quantitatively.

The furnace in this example is of the single cell system type (ie it is not of the twin type soul shown in Fig. 1). It consists of hell and the hall of 28 elementary cells divided into two branches, one (fig. 2a) with 12 (branch a) and the other (fig. 2b) with 16 or (branch b). The two branches of the divided cell system are separated by a single Mugsgaencle septum. Dc tvd duck chambers for lifting the bath Oro placed between the sixth and seventh cell emanating from the left branch a. The duck anode in the sixth cell and the duck cathode in the seventh cell of the branch a Oro connected by busbars for supply of electricity. There are two stables for feeding alugnium oxide, one of the usual branches. It for branch a Or inserted between the ninth and tenth cells, it gets the other branch b pi fern cells distance frail the opposite spirits of the furnace. The inclination towards the vertical plane of the electrode plane. Or + 30 ° for the cells in branch a and -30 ° for the cells in the other branch. The spacing between two electrode carbon blocks in each cell (which is usually less than 15 cm and preferably 4 and 12 cm) is in some cases between 4 and 8 cm. The thickness of the intermediate transverse partitions (usually less than 30 cm) in the present example varies periodically from 22 to 26 cm and the length of the channels in the solid blocks which form the heads of the bipolar electrodes (usually less than 15 cm). Or in this example about 18 cm, while the bypassed electric current Or less On 2%. The nasal blocks and inner cradles of the cells, the chambers ° eh. the pockets In contact with the bath and the metal Oro lined with electrosmalt A1203. The permanent part of the intermediate bipolar electrodes Or of graphite. The replaceable anode part Or of electrode carbon. Its initial thickness Or 4 cm. The volume of the bath periodically reaches in each of said electrolysis rooms a maximum of about 50 liters without increasing the volume of it. the pocket-shaped part is included in the smoking. The volume of the metal collection chamber below bon Tara starre On. the above-mentioned Tartlet for it to be possible to bring about periodic renewal (restoration) of the used anode in saraband with drainage as described above. In this example, the lower chamber is 1/3 larger than the maximum volume absorbed by the bath in the electrolytic cell. Each electrolytic chamber (or element or cell) has a horizontal dimension in the transverse direction, which is 86 cm and a depth (in the vertical direction) of active surface of about 60 cm with a projection on the vertical plane of the active anode and cathode surfaces of 4800 cm2. This project "s" Or of course less On the effective - —9 surfaces> S >> (S = s x cos a, .ddr a is the angle of inclination of the .electrode surfaces in relation to the vertical plume). When the furnace is operated with 2500 amperes, the current density at the electrode (Unford to a projection on the normal vertical plane) ° Inclination 0.5 amperes / cm2, This furnace of, for example, about 250 kW and which works with voltages other than 100 volts has a capacity of about one half a ton of aluminum per day. If O. is required. it is possible to obtain one tonne of aluminum per day or more by Wining the dirnensions and / or the number of elements (elementary cells) and / or the number of cell systems (for example in a twin furnace). The circulation of the bath usually requires a flow preferably ranging from Iran, 30 to 150 cm 3 per second, in the example from 50 to 100 cm 3 per second. The bath circulates in a direction opposite to the electric current. It was. The alumina feedstocks together introduce from 11 to 13 grams of alumina per second into the cell system, also depending on the flow of the bath and other operating factors. Drainage, n of the number, can usually be carried out every four days for each cell. In this example, seven cells are drained every day. Each drained cell gives a net amount of 65-70 kg of metal '. The draining is carried out simply by sucking metal from the draining pockets, which are arranged in the hot intermediate cradle in the oven. The plug closing the top of the respective tubes is pulled out and the drain pipe is temporarily inserted from above for tapping by suction of metal. In the process according to this invention and in particular in the above example, the temperatures and compositions of the cryolite bath may be the variable ones. It is possible, for example, to work with an alumina content in the bath of, for example, about 5% in the cell which is located. Anxiety from the alumina feedstock and with a content of, for example. about 11i the cell, .som befin, ner sig naranast naninda inmatningsstalle. the above example is the speed of the wires 10-20 mm / sec. and in the main circulation in the cells 1-2 mm / sec.

To feed alumina, it is not necessary to open the lids in the individual cells. This is only required if anode renewal in the individual cells is cold performed. Anode renewal in the example in question takes place sasoni described above as an operation after one. bottling operation, i.e. after each period of four days or a multiple thereof thereof either on the salt described in British Patent 800,092 or in the manner described in British Patent 802,959.

However, it is possible according to the present invention to work on the following salt. The lids 10 are opened, not only on the cell to be restored, but, if necessary, the lids on the two lower cells are also removed, the heat-insulating bricks 11 are removed, the upper conduits 26 are closed by means of the plugs 30 between the adjacent cells and the electric current. . Drainage is then carried out by sucking up the metal from it. in this case: the opening pocket until the bath drops to the level dies step 24 ', on which the anode, somaterstallas rests, which step thus remains exposed. The plate or strips of recovery carbon (pre-coated with binder on the contact surface) are placed on the old anode and the excess metal, which has been removed from the pocket, namely the excess of the current cell capacity, hiles back in the pocket, so that the bath rises again From the lower number collection core to the cell and ater essentially meets this. Then the electrical current Ater and the cell are closed kers-1511d.

After a certain time, the heat level is automatically restored to the connecting channels, so that the plugs 30, which are immersed, are no longer loaded by solidified bath but can easily be lifted and fixed in the raised bed. It is desirable that the cross section and the average length of the connecting lines. 26 between two adjacent cells limo such that the desired bath flow (e.g. 50 to 100 cm 3 per second) is obtained without. need to resort to newspaper-level differences or very large .flow rates. It is advisable to keep the speed of the main circuit in the channels below 50 nun / sec. In the secondary circuits between the anode and the cathode of a single cell, it is black to measure the relative velocities, which are wholly or partly dependent on the velocities of the main circuit. The bath level difference required to ensure circulation throughout the series of cells is very large in view of the considerable flowability of fluoride baths. The order of magnitude of this level difference dr .only a few decimetres for the whole oven. This, of course, simplifies the problem of raising the bath intermittently, from the sixth cell (the one with the lowest level) up to the seventh cell (the cell riled the highest level) in the branch "a".

The. the direction of the electric current is opposite to the direction of the main circulation in the bath. The circulation takes place from the cathode surface to the anode surface of the air. subsequent bipolar electrode. The matte level differences which exist in the furnace according to the invention allow easy transition from furnace operation with two separate multicellular furnaces, were at all the plugs 30 in the channels 26 drawn lowered and the lifting device stationary, to the furnace operation with closed circulation through the cell system. Nd.r the individual cells have achieved it. normal temperature for lull operation, the plugs can in fact be easily raised and the lifting device ■ can be started, whereby the main circulation of the bath is started through all the individual cells in the oven. The consumption of materials (carbon and fluorine compounds), as well as the work required, are lower or in the usual case not higher than in industrial furnaces with horizontal layers and adjustable electrode spacing, as soon as possible. Energy consumption is as much as 30 to 50% lower. 2iven construction costs are considerable stocks for the same production.

The furnace according to this invention entails considerable advantages even in addition to the multicellular furnace according to British patent 800 092, for example greater possibility of effectively insulating the upper part and the insides of the furnace and a consequent reduction of the electric power to be converted into heat, larger capacity, less work , simplified anode renewal, bottling without extraction of bath and without direct contact with the bath, improved heat equalization of the bath between the different cells, less propensity to form crusts, possibility of using less pure aluminas and formation of high quality metal by the above-mentioned sorting, which obviously can be obtained at the circulation. of the bath through the cells In series of separate drains according to this invention.

The furnace according to this invention can be advantageously used for other electrolysis processes in smelters, and its field of application is not limited to the production of metallic aluminum from its oxide. In these cases, the aluminum compound used (other than A1.02), the electrolysis bath (other than Surveillance fluorides) and the product (other than metallic Al) can be varied.

It should be noted that for the sake of clarity, no bath has been shown in the drawings in lines 26, 34 and 37.

It is obvious that the construction kit allows furnaces according to this invention and the forming edge for their operation to be modified or varied beyond what is described above without departing from the scope of the invention.

Claims (11)

Patent claim: Multicellular furnace for smelt electrolysis in general and in particular for the production of aluminum with different callers, provided partly with bipolar intermediate electrodes (17), which are electrolytically consumable and intended to be regularly (periodically) restored to the consumed surfaces and are vertically stationary and preferably the cathode side (5 ') of these electrodes preferably being ay grant and the consumable anode side (4') being electrode carbon, partly with two. part electrodes (14, 15), the latter equipped with current-carrying metal nipples (16) connected to current supply rails saint with separate collection chambers (21) below the electrolysis chambers (19), can be drawn .clarav, that the cells communicate with each other through wires (12, 26, 37) at such levels that small electrolyte (20) can flow frail from one to the other, that the cells are distributed in at least two. groups (5 ', 5 ", 6', 6") arranged in two. radar on opposite sides of a longsgie, nd cradle (7, 8) ay refractory and insulating material, and that circulation and lifting devices (32, 33, 34, 44) are arranged between said groups, so that the electrolyte can circulate through the electrolytic spaces in a closed cycle. Furnace according to claim 1, Unsubscribed from the fact that in a housing (3) of sheet metal lined with marine and electrically insulating refractory materials (4) are arranged at least two double rows of ay caller (5 'and 5 "; 6' ° eh 6 "), which radars are preferably electrically connected in parallel and preferably arranged sued their spirits provided with lifting devices against each other and separated by a transverse cradle (9) of refractory and electrically insulating material. Furnace according to claim 1, characterized in that the longitudinal cradle (7, 8) is straight and that the cell rows (5 ', 5 "and 6', 6") are parallel. 4. An oven according to any one of claims 31-3, characterized therefrom, depending on the slopes of the electrodes (14, 15, 17) and, therefore, the electrolytic spaces (19) being opposite in the two. side by side, the rows of each double row (double row 5 ', 5 "; double row 6', 6") ay caller, which slope preferably carried the same absolute value, and with deviations from the vertical plane ay between inclination 15 ° and inclination 45 ° . 5. A furnace according to any one of claims 1-4, characterized in that its cells are filled with an ink-removable brick (11) of heat-insulating, refractory, preferably porous and light material, which lamp itself to allow passage of electrolytic gases, and / or provided with the necessary or necessary hall (28) to facilitate the passage of gases. Furnace according to claim 5, characterized in that all the webs have removable outer lids (10) of heat-insulating material over the tile roof (11), 7. A furnace according to any one of the claims 16, characterized in that the conduits (26) connecting the cells in the furnace for directing the flow of the electrolyte from one cell to the other are arranged in solid blocks (25) coated over the electrodes and consisting of or are coated with materials which are impermeable and permanently snot - —11 attack of the sanitary bath, electrically join conductive and add heat insulating. 2. A furnace according to claim 6, characterized by means for installing or closing individual conduits (26) for bath circulation between adjacent cells, which means. Preferably, plugs (30) are slidable in slides (28) arranged in the solid blocks or spacers of said conduits (26), which plugs are arranged to be fastened at different levels and to be installed from a stable over the cells. Furnace according to any one of claims 18, characterized in that the chambers (21) below the electrolytic spaces for collecting the aluminumite metal (22) each have at least one third larger volume than the maximum volume obtained by the bath (20) between the electrodes in the respective individual the cells. Furnace according to any one of claims 1 to 9, characterized by at least one device for adding alumina, not including a feeding device (13) for dosing the alumina connected to a closed chamber (12) which provides communication for electrolyte (20) between two. narbelagna caller. 5. A furnace, according to claim 10, characterized in that the triating device Ar is arranged to supply alumina to the surface of the electrolyte gramming in the chamber (12), which has at least one between the sieve outlet and the feeding device. transverse partition (38) preferably conceals the upper part of the chamber (12) to a level below the surface of the electrolyte head. Furnace according to any one of claims 1-11, characterized by a pair of duck cores (32, 33) separate for lifting the electrolyte Iran cell (36) with the lowest level to adieu. (35) with the highest level in the closed bath cycle. 7. An oven according to claim 12, characterized in that said pair of chambers (32, 33) are arranged radially two successive cells (36, 35) in the closed bath cycle, one of the chambers (33) having a laid coated bath, and the second chamber (32) has a highly coated bottom, and the two. the chambers are in inboard communication and communicate with the respective adjacent cells. 8. A furnace according to claim 13, characterized in that the chamber (33) with the dedicated hood is divided by a vertical partition (43), which projects from the roof almost to the hood, in e.g. departments, of which the larger department communicates with it. adjacent the cell and in its upper part is provided with an opening (44), connected to external devices for introducing inert gases at high pressure, preferably at regular time intervals, so that in the compartment a temporary moderate overpressure is achieved, and the lower compartment communicating with its chamber (32) with it. hog coated bottom. 9. A furnace according to claim 13 or 14, characterized in that the chamber (32) with the Magt helagna hottnen dr forseold tined an outlet valve (15) and is, dimensioned pa. thus, it is possible to maiming the electrolyte. to the n.arbed cell (35) with the highest level practically continuous, also cm joke with constant flow, while the introduction of electrolyte from the chamber (33) with the la'.gt coated bottom to the chamber (32) with the highly coated the bottom occurs at regular time intervals. 10. A furnace according to any of the patent claims 13-15, characterized in that the chamber (33) has laid the coated batter in communication with the adjacent cell (36) at least one. line (39) provided with a simple ball valve (11), whose ball is of refractory material as a joke is attacked by the bath and more easily on the bath, for example by carbon coated with .electrosmalt MgO, which valve is closed automatically by the effect of increased pressure the chamber. (33) with the load on the bottom, said that in the first place the backflow of hadvatska to the cell (36) is prevented and in the second place the diversion of the slightly compressed gas from the chamber with the coated bath against the cell. 11. A furnace according to any one of claims 1-16, characterized in that in the inner longitudinal cradle (7, 8) Indian the adjacent cell rows are arranged shafts (31) in a number corresponding to the number of calls and each communicating at its hotspot. with the respective individual collection chamber (21) for the sanitary aluminum metal (22) produced in the cells, which shafts are closed with lids (16), which are insulating and are removable to allow the metal (22) to be removed by suction. Ngn according to patent claim 17, Urine drawn by side drain outlet (47) above & by said shaft (31) for complete emptying of one or more callers or of the whole furnace. Furnace according to any one of claims 1-18, characterized in that the cradles are in contact with the narrow electrolyte (20) and with the narrow metal (22) and also cladding of the drain shaft (31), of the intermediate chambers for feeding of alumina, of the duck cores (32, 33) for lifting the hat and of the hare connecting wires (26), are made of layers of, refractory material ailed to add electrical leakage form and to add porosity as well as resistance to attack by the bathing parts and the liquid metal . 12— - 14. In the production of aluminum by electrolysis of alumina lost in a bath of = Alta salts in a multicellular furnace with separate series-connected electrolytic cells with bipolar electrodes according to claims 1 to 19, which may be caused by the electrolyte being circulated within the furnace during the electrolysis in a closed circuit through the double row of separate cells, while an electric current is passed through the cells in series, that alumina is fed to the electrolyte continuously or intermittently and that the formed aluminum metal is drained individually from each cell. 11. ll. 15. The kit according to claim 20, characterized in that the circulation of the electrolyte in a closed circuit through the cells is effected by lifting electrolyte at substantially regular time intervals from a cell with low bath level to a nearby bath with high bath, level, said circulation partly is independent of and partly combined with secondary movements of the electrolyte due to the electrolysis, whereby the electrolyte sinks along the cathode and rises along the anode in a single cell, so that the bath flow in the individual cells interacts with the bath circulation throughout the furnace. 16. A salt according to claim 21, characterized in that the lifting of the electrolyte is carried out between two on-board communicating adjacent chambers, the first of which has a laid coated bottom and communicates with a saintly arranged near cell with the lowest level and the second has a The highly coated bottom thus communicates with the cell with the highest level in the closed circuit of cells, by means of the pressure action, by using substantially regular time intervals inert gas in the first chamber that the electrolyte of a laid overpressure is pressed down therein and displaced to it. the second chamber and Iran this chamber is diverted to the adjacent cell riled the highest level, thereby preventing backflow of electrolyte to the cell with the lowest level in the appropriate manner. 17. According to patent claim 22, + Bray, it is noted that the inert gas used for said displacement is the sum of gas evolved during the electrolysis. 18. according to any one of claims 20-23, characterized in that the assumption of alumina is carried out in one or more places in the circuit of cells by causing suitably matched amounts of alumina to fall on a free surface of the electrolyte, preferably while circulating, and that the electrolyte is caused to flow a certain distance, preferably in a labyrinth, to the Iran feed stall until it enters the first cell or stall. 19. According to any one of claims 20-24, characterized in that tapping one of the formed metal is performed periodically by. separate shafts, each communicating with the metal produced in the cell in question, and coated between the adjacent rows of cells, so that the number is kept at a higher temperature than the operating temperature critical for aluminum or preferably for the other. The cryolite bath 20. Set according to the patent claim 20, Urinated according to the fact that electrode electrode atoms higher than 0.2 amperes / can, preferably ay about 0.5 amperes / m 2, anyandas, which become the projection of the electrode surfaces pO. 21. According to patent claim 20, characterized in that the circulation velocity of the electrolyte between the cells is less than 50 microns / sec, preferably less than 20 minutes per second, and the circulation velocity from electrode to electrode is usually less than 5 man / sec. ., preferably less than 2 nun / sec 22. Set according to patent claim 20, it may be noted, dfiray, that the maximum level difference between the highest and the lowest individual baths in the cells of the furnace in the closed cycle and during normal operation Wiles does not exceed a few decimetres, while the circulation rate of the electrolyte between the cells does not exceed a few deciliters per second. 23. according to claim 20, characterized in that the speed of the secondary circulation ay the bath in the outer space between the electrodes in each individual cell is kept such that normal separation of aluminum mid cathode and accumulation of aluminum metal below this space between the electrodes joke is prevented, genoin that strointathete, n is coordinated with the width of the space between the electrodes and the depth of the cell. 24. A kit according to claim 20, characterized in that the bath is caused to circulate through the cells in a closed circuit in a direction opposite to the anode / badicatode direction. 25. was intended to replace the spent anode in an oven according to claims 1-19, characterized in that the bath is removed in the area adjacent to this cell, provided that the passage of the electrolyte to the oda Iran cell is limited or prevented by the cooling of the electrolyte thereby occurring, that The electrolytic current is preferably interrupted by draining by removing from the shaft connected to the cell a metal volume equal to the volume of the metal formed since the previous draining, that the replacement of spent anode is then carried out by placing a disc against the old anode. or elements sum to form a wafer of anode replacement material, so that the bath level is caused to rise in the cell until the space between the electrodes is filled again, that the electric current is connected, and where appropriate the Ater area is connected so that the temperature can rise ph again, whereby the circulation of, electrolyte through the cell Aterstalles. 26. A salt according to claim 31, in which the electrolytic stream is broken, characterized in that a volume of metal in excess of the amount formed since the previous tapping is taken out during the tapping, and of such. size that the bath level is immersed in the electricity until the electrolytic space between the electrodes is completely empty, and that said disc or element of anode replacement material is applied to the old anode, possibly after coating its pallor surface with a binder containing the carbonate, after which it is hailed back to the drain shaft. previously extracted metal surplus. A salt according to claim 31 or 32, characterized in that in order to promote or bring about said interruption in the electrolysis current from and to the cell channels connecting this cell and the adjacent cells are throttled for the time that the anode assembly lasts. 28. A kit according to claim 31, 32 or 33, characterized in that the anode arrangement is carried out by applying to the consumed electrodes discs or elements of anode replacement material of uniform thickness at such time intervals that the electrode position is between 2 and 15 cm, preferably between , n 4 and 12 cm. Request Publications: Patent Application Iran Iran 254311, 293187; Germany 399 693, 477 425.