DE1558751A1 - Furnace tank for the smelting electrolysis of aluminum - Google Patents

Description

Furnace tank for the smelting electrolysis of aluminum. The invention concerns the improvement of the refractory inner lining that the molten Electrolyte bath and the metal it contains, in furnaces for aluminum production by fused-salt electrolysis of alumina in cryolite. In particular, the invention relates to an improved Cryolite tank in ovens of the type mentioned.

So far (see US Pat. No. 3,093,570 and French Pat. No. 1,353,565) some materials made of a mixture of aluminum oxide and cryolite with a content of at least 20 % and preferably more than 40% aluminum oxide have been used for the lining of the soil and / or the walls of traditional furnaces for the reduction of alumina to avoid the well-known disadvantages of coal-lined tanks (rapid disruption or deterioration of the side walls, swelling, deformation and swelling of the floor, etc.). According to a proposal, which does not belong to the known state of the art, a refractory material made of practically pure cryolite (natural or synthetic) is used for the lining of the floor and / or the walls of traditional or multi-cell furnaces; this achieves certain advantages over the above-mentioned mixture of aluminum oxide and cryolite. It has now been found that it is possible to considerably improve the properties of the above-mentioned refractory materials from a mixture of cryolite and alumina or cryolite alone for the construction of such oven trays. The invention is of particular importance for the construction of multi-cell furnaces where, as a result of the use of bipolar electrodes, the side walls should be much higher than in traditional ovens. Indeed, it has been found that when a certain percentage of coals (more or less diapered) are incorporated into the refractory mass of cryolite or a mixture of cryolite and alumina, the properties of this refractory material are improved to make it suitable for the construction of To make inner tubs in single-cell or multi-cell furnaces more suitable for aluminum melting. It has been found, in particular, surprisingly, that the stability of large vertical walls can be considerably improved by the invention, not only for walls made of cryolite alone, but also for walls made of cryolite-alumina mixtures which are otherwise not used for such structures would be suitable.

The drawing shows a typical multi-cell aluminum furnace. This particular furnace is a furnace of Halsbandart. The structural details of this furnace can be found in U.S. Patent 3,178,363. The furnace of the invention is similar to that shown in Figure 6 of US Pat. No. 3,178,363, the appropriate parts of which are incorporated by reference.

The tub 1 containing the bath consists of carbonaceous material and is lined with a refractory layer 2 on its entire inner surface. The tub b is protected on the outside by an insulating jacket 3, which provides thermal insulation. The bipolar electrodes 4 are permanently suspended from support rods 7 which are fastened to longitudinal beams 17. The rods are attached to the beams 17 by collars or rings 19. Each beam 7 is electrically isolated from its suspension beam by an insulator 20. The beams 17 are also electrically isolated from the rest of the furnace by insulators (not shown). The connecting rods 28 for the supply of electricity to the collar oven also serve to suspend the monopolar electrodes 4 '. The consumable anode part 5 of each electrode is charged from the upper part through a shaft not shown in the drawing. Both the bipolar electrodes 4 and the monopolar end electrodes 4 'are encased with a fire-resistant protective coating which is inert to the bath and the electrolysis. The refractory frame comprises the side covers 6, the backing covers 22 and the top covers 43. The middle refractory longitudinal wall 12 is provided with vertical pockets or containers 13 for receiving the metal produced. The metal produced in any one of the cells is conveyed to the corresponding container 13 through individual recesses 25, which are of suitable dimensions and are arranged on the bottom of the tub to accommodate the bath circulation, and preferably have a sloping bottom. The containers 13 are connected by a channel 29 to the recess 25 with an inclined bottom . An overflow 33 is designed to overflow the molten aluminum into a collecting container 31 which is provided for each row of cells. The term "coal grit" is used here to refer to any carbonaceous material with grains of any size, for example metallurgical coke grits, as used at the beginning of traditional furnaces as a layer acting as a thermal resistance between anode and cathode. In the drawing, the refractory layer which is to be formed by the material according to the invention, namely cryolite or a cryolite-alumina mixture containing coal powder, is denoted by the reference number 2 and can be in the form of prefabricated shaped pieces.

To produce the molded pieces according to the invention, it is sufficient to have an empty mold or casting shell (made of carbon, silicon nitride-bonded silicon carbide, as it is sold under the trade name "Refrax" by Carborundum, metal or another suitable material) having the desired shape Filling carbonaceous semolina of the desired quality, size and properties. (The correct selection of these parameters will be apparent to a person skilled in the art; this selection is based, for example, on the electrical conductivity according to which it is or is not required for the respective type of furnace). If necessary, this coal grit can be mixed with a certain percentage of solid cryolite and / or aluminum oxide, which has preferably been preheated to a temperature above 900 °. Molten and essentially pure cryolite or molten cryolite with a high content of aluminum oxide (10-20 yd Aluminum oxide and more) is then poured into the mold. This molten or molten material fills the free joints in the coal powder.

The method of making the materials according to the invention can be varied further.

For example, the resin mold or shape to produce a more economical material to be filled not only with carbonaceous meal and alumina, but also with a solid cryolite bath with a large percentage of dissolved therein alumina, so that the resultant in the mold after the casting compound has a sufficiently Contains a high percentage of aluminum oxide. Pouring can be further facilitated by subjecting the mold to a vacuum.

In this way, the risk of lump formation, which is impenetrable for the further flow of the molten cryolite in the mold, between the solid particles filling this mold is avoided.

The tub or the molded pieces (e.g. building blocks or plates) or the tub parts cast in this way can easily be welded together by simply heating the tub once the individual pieces have been put together. The welding of the aforementioned building blocks or panels in place can be facilitated by a thin layer of pulverized in the welds or distributed molten Kryolithmaterials.

In this way, joints (the ones in every construction always represent weak points) through simple adhesion of the individual pieces avoided the neighbors when they are hot. If no such treatment should immediately lead to a perfect weld, you don't need anything to do anything other than wait for the furnace to begin carefully, where these junctions are finally turned off.

Once these tubs are put together in place. are, they can be easily exposed to the outside with the usual fire-proof and heat-insulating Material to be completed, welding with the outer layers through a layer of pulverized carbon paste is obtained. In many cases they are however, these refractory and heat-insulating materials are superfluous and the external ones Metal tub alone (crucible shell) is sufficient.

The above-described cryolite materials prefabricated in this way have high melting points and are subject to chemical or electrochemical attacks Not subject to bathing. After all, material made from cryolite alone is in the sense of the Subject of the invention is preferable to such with an alumina content. the In one embodiment, the invention was made using prefabricated fittings from cryolite described; it goes without saying that the scope of the invention is not limited to such an embodiment, but also includes its variants and Equivalents.

For example, a further method of construction of a furnace pan according to the invention consists in introducing a shaped body (e.g. made of coal) into the metal shell, which can be lined with a heat-insulating material and forms the outer part of the furnace pan, so that there is a clear distance between the body and leaving the inner walls and / or the bottom of the lined shell. Thereafter, the molten cryolite or the cryolite-alumina mixture containing carbon grits dispersed therein is poured into the clearance to fill it. Measure allows the cryolite materials to solidify, whereupon the body is removed.

All percentages are by weight.

Claims (12)

P atentan sp r ü che 1. oven tray made of a refractory material, consisting of substantially pure natural or synthetic cryolite or cryolite Aluminiumoxydmischungen is formed, labeled in for receiving the molten electrolyte bath and aluminum in single-cell or Mehrzellenöfen for molten salt electrolysis for the production of aluminum, characterized -draws that the refractory cryolite mass contains a certain amount of coal powder dispersed therein. 2. Oven pan according to .Anspruch 1, thereby G e k e n n n z e i c h -n e t that the tub is made of at least one prefabricated Form piece consists. 3. Prefabricated fittings according to claim 2, made of substantially pure., - natural or synthetic cryolite with a content of dispersed therein Coal semolina. Prefabricated molded pieces according to Claim 2, made from cryolite-aluminum oxide mixtures with a content of coal meal dispersed therein. . 5. Prefabricated fittings according to claim 4 of mixtures of cryolite and alumina which are at least about 20% Ä1203 included. 6. Method of manufacturing the fittings according to claim 3, characterized in that molten, essentially pure natural or synthetic cryolite in a coal powder Containing casting shell or mold pours the molten cryolite by cooling can solidify and then the molding is removed from the casting shell or mold. 7. A method for the production of fittings according to claim 4 or 5, characterized g e does not indicate that one can use a molten solution of cryolite with a Aluminum oxide content, preferably more than 20% aluminum oxide, in a coal powder containing pouring shell or mold pours the molten cryolite solution through Allow to solidify and then remove the molding from the casting shell or mold. B. NNZ process for the preparation of shaped articles according to claim 3 or 4, characterized g e k e s iehnet by pouring molten, substantially pure, natural or synthetic cryolite in a Gußsehale or shape that not only with carbon semolina, but also with at least one Materials such as aluminum oxide, which may have been preheated to more than 9000C, cryolite in natural or synthetic form, solid solutions of cryolite enriched with A1203, or solid electrolyte baths. 9. Method according to claim 7, characterized in that the coal grit containing casting shell also at least one of the materials such as aluminum oxide, which is optionally preheated to more than 900 ° C, natural or synthetic Cryolite, solid solutions of cryolite enriched with A1203, solid electrolyte baths contains. 10. A method for the construction of the furnace pan according to claim 2, characterized g e k Note that you can put in place the various pieces that are form the inner pan of cryolite material by heating the composite and closed tub welded by conventional means so that the individual Fittings of the inner cryolite pan are welded to those that are immediately are adjacent. 11. The method according to claim 10, characterized in that welding is facilitated on the spot by distributing or spreading a thin layer of powdered or molten cryolite material in en welds. 12. The method for the construction of a furnace pan according to claim 1, wherein this pan is contained in a metal shell lined with heat-insulating material, characterized in that this pan is built up on the spot by inserting a molded body into the lined shell (for example from Coal) introduces , with a clear distance between the ifidrper and the inner walls and / or the bottom of the lined shell , molten cryolite or cryolite-aluminum oxide mixtures with. a content of coal powder dispersed therein is poured into the clearance to fill it, and the molten material is allowed to solidify, whereupon the body is removed.