WO2014091023A1

WO2014091023A1 - Side-wall block for a wall in an electrolytic cell for reducing aluminum

Info

Publication number: WO2014091023A1
Application number: PCT/EP2013/076624
Authority: WO
Inventors: Frank Hiltmann; Janusz Tomala; Ghazanfar Abbas; Thomas Frommelt; Rainer Schmitt; Markus Pfeffer
Original assignee: Sgl Carbon Se
Priority date: 2012-12-13
Filing date: 2013-12-13
Publication date: 2014-06-19
Also published as: CA2893476A1; EP2931945A1; CN104854264B; RU2668615C2; RU2015127998A; UA118098C2; JP2016505714A; CN104854264A; CA2893476C; JP6457397B2

Abstract

The invention relates to a side-wall block for a wall in an electrolytic cell, in particular for producing aluminum, a method for producing such a side-wall block, use of such a side-wall block, and an electrolytic cell having such a side-wall block. The side-wall block (28) is a layered body, comprising a layer having a higher thermal conductivity and a layer having a lower thermal conductivity, wherein the difference in the thermal conductivity is at least 5 W/(m·K).

Description

SIDE STONE FOR A WALL IN AN ELECTROLYZE CELL

TO REDUCE ALUMINUM

The present invention relates to a side brick for a wall in an electrolysis cell, in particular for the production of aluminum, a method for producing such a side brick and a use of such a side brick and an electrolytic cell with such a side brick.

Electrolysis cells are used for the electrolytic production of aluminum, which is usually carried out industrially by the Hall-Heroult process. In the Hall-Heroult process, a melt composed of alumina and cryolite, preferably about 15 to 20% alumina and about 85 to 80% cryolite, is electrolyzed. The cryolite, Na 3 [AIF ₆ ], serves to lower the melting point from 2,045 ° C. for pure alumina to about 960 ° C. for a mixture containing cryolite, alumina and additives such as aluminum fluoride and calcium fluoride, so that the Molten electrolysis can be carried out at a reduced temperature of about 960 ° C. The electrolytic cell used in this method has a bottom which is composed of a plurality of, for example, 24, adjacent to one another, the cathode forming cathode blocks. Between the adjacent cathode blocks, a joint is formed in each case. The arrangement of the cathode block and possibly filled gap is generally referred to as the cathode bottom. The cathode bottom is surrounded by a wall formed of several side bricks, which forms, together with the cathode bottom, an inner tub which receives the aluminum layer and the melt layer and which is surrounded by an outer steel tub. The joints or interstices between adjacent cathode blocks and between the cathode blocks and the side stones are usually made of ramming mass Carbon and / or carbon containing material, such as anthracite or graphite, and a binder, such as coal tar pitch, filled. This serves to seal against molten constituents and to compensate for mechanical stresses which occur, for example, due to the expansion of the cathode block during the heating during the commissioning of the electrolysis cell. In order to withstand the thermal and chemical conditions prevailing in the operation of the electrolytic cell, the cathode blocks are usually composed of a unitary carbonaceous material and the sidestones of a unitary carbon or silicon carbide containing material. In each case, grooves are provided on the lower sides of the cathode blocks, in each of which at least one bus bar is arranged, through which the current supplied via the anodes is removed from the electrolysis cell. Below the cathode bottom, ie, between the cathode blocks and the bottom of the cathode-receiving steel trough, there is usually provided a lining of a refractory material which thermally insulates the bottom of the steel trough from the cathode bottom.

About 3 to 5 cm above the layer of molten aluminum located on the top of the cathode is arranged an anode formed of individual anode blocks, wherein between the anode and the surface of the aluminum, the melt containing alumina and cryolite is located. During the electrolysis carried out at about 960 ° C., the aluminum formed is deposited below the melt layer due to its greater density compared to that of the melt, ie as an intermediate layer between the upper side of the cathode blocks and the melt layer. During electrolysis, the aluminum oxide dissolved in the cryolite melt is split by the flow of electrical current into aluminum and oxygen. Electrochemically, the layer of molten aluminum is the actual cathode because aluminum ions are reduced to elemental aluminum on its surface. Nonetheless, the term cathode will not be used hereinafter to refer to the cathode from an electrochemical point of view, ie the layer of molten aluminum understood, but the cathode bottom forming, composed of one or more cathode blocks component. Modern electrolysis cells are operated at high electrolysis currents of, for example, up to 600 kA to ensure high productivity of the electrolysis cell. These high currents lead to increased heat generation during the electrolysis process. Due to the high heat generation, it turns out to be difficult to adjust the heat dissipation from the electrolyte cell so that everywhere in the electrolysis cell, the thermal conditions are achieved, optimally in terms of stability and efficiency of the electrolysis and in terms of the life of the electrolytic cell are, for example, the energy efficiency of the electrolysis is reduced by excessive thermal energy losses in areas of high heat generation of the electrolysis cell. Thus, the unfavorable thermal conditions in the electrolysis cell affect the reliability and economy of the electrolysis operation and the service life of the electrolysis cell.

Although the removal of surplus heat produced in the electrolysis cell, ie heat not required for the maintenance of the melting process, can be adjusted via the bottom of the steel tub through the refractory lining arranged between the cathode bottom and the steel tub, which usually consists of refractory bricks or plates, which are inserted in the steel tub and stacked on each other in the area of the bottom of the steel tub. However, for the temperature conditions in the region of the layer of liquid aluminum and the melt layer, in which the electrolysis takes place, the heat release over the relatively thin formed lateral wall of the formed by the cathode bottom and the side stones inner tub plays an essential role. The heat flows in this lateral wall are particularly relevant for the thermal conditions in the electrolytic cell, since the lateral wall is usually It may be in contact with various constituents and media in the electrolysis cell, ie in particular with the layer of liquid aluminum, the liquid melt layer arranged thereon, a layer of solidified melt or crust above the liquid melt layer and the gaseous atmosphere developing during the electrolysis cell with the various elements contained within.

The amounts of thermal energy generated must be partially removed in a defined manner, but at the same time too high heat losses, which mean energy losses and thus affect the efficiency of the electrolysis process must be avoided.

In the area of the relatively thin sidewalls, in known electrolysis cells, due to the vertical construction of the sidewalls and the constructive requirements resulting therefrom, no additional lining of stacked refractory bricks is provided, as in the region of the bottom of the steel tub, so that the adaptation of the heat output over the Side walls is not possible in the same simple manner as in the floor area. Uniform sidewalls, which usually consist of a material containing carbon or silicon carbide, are homogeneous with respect to the heat conduction properties perpendicular to the sidewall plane and allow only limited control of the heat flows and the course of the isotherms in the sidewall during operation. The gap between such a sidewall and a cathode block is usually filled with ramming mass of carbon and / or carbonaceous material such as anthracite or graphite, and a binder such as coal tar. This joint is often manually or semi-automatically tamped, whereby stamping errors can occur, which can lead to damage to the joint or, in the worst case, even to premature failure of the entire electrolysis cell. This damage often only occurs during commissioning or during operation of the electrolysis cell. The risk of the occurrence of the injury is the larger the wider or thicker the corresponding joint is. A wider or thicker joint also means a higher workload and a higher burden on the environment and the staff responsible for the electrolysis cell, as are harmful substances in conventional ramming masses. It is known to replace some or all of the ramming mass needed between the sidestones and cathode blocks with an inclined layer of pregrenated carbon or graphite. If only part of this ramming mass is replaced, the thickness of the ramming mass joint is reduced by more than 50% to 99%, preferably more than 75% to 99%, particularly preferably more than 90% to 99%. It is also possible that this layer does not fill the entire volume of the original tamping layer, for example to create room for an enlargement of the anode surface. Usually, a thin, vertical circumferential ramming compound of, for example, 50 mm thickness is maintained. With this inclined layer vertically arranged side stones can be connected, for example, silicon nitride bonded silicon carbide. Such a construction comprising a side brick and a sloping layer is hereinafter referred to as "composite side brick." A composite side brick in which the silicon nitride bonded silicon carbide is bonded to the inclined layer is already used in modern electrolysis cells In addition, the application of the adhesive material requires an additional work step The side stones of such a composite side stone consist of a uniform material and thus allow no differentiation with respect to the thermal conductivity in the side stone itself. the adhesive joint can have an influence on the heat flow in the electrolysis cell. Since the glue joint itself is very thin, irregularities in the cause the corresponding local heat flow. Carbonation of the adhesive matrix as during cell start-up may result in a reduction in its adhesion, which may weaken the bond between the oblique prebaked carbon or graphite layer and the vertical sidestring. If there is a failure of this connection, that is, that the above inclined layer and the vertical side stone are no longer connected to each other, the heat flow is degraded in an undefined manner and the necessary heat dissipation can not be sufficiently ensured. This can lead to overheating of the electrolysis cell, and in the worst case to their premature failure, ie the lifetime or life of the electrolysis cell is reduced. The use of adhesive material can also take place between the individual side stones, which form the side wall, in the form of a thin adhesive layer.

DE3506200 discloses sidestones for the wall of an electrolytic cell which are a layered composite comprising an inner layer of a carbonaceous material and an outer layer of a hard ceramic material, these two layers being intimately interconnected. This allows a virtually unhindered heat flow from the inside to the outside. However, the resistance to wear, especially abrasive and / or corrosive wear is not sufficient when using such side stones. With the known electrolysis cells, therefore, no optimal process conditions can be achieved, in particular during operation with high electrolysis currents, whereby the achievable stability and economic efficiency of the electrolysis process are limited and the service life of the electrolysis cell is impaired. Therefore, it is an object of the invention to provide a side brick for the wall of an electrolytic cell, which ensures optimal process conditions and a correspondingly high efficiency and stability during the electrolysis operation and a long service life of the electrolysis cell when used in the electrolytic cell. In particular, the Seitenstein should adjust the heat output through the side wall of the electrolysis cell such that prevail during the electrolysis optimal thermal conditions in the electrolytic cell and thermal losses during operation, caused by an unfavorable heat and temperature distribution, are largely avoided. The operating temperature of the cell during electrolysis is between 920 ° C and 1000 ° C, preferably between 950 ° C and 980 ° C. Furthermore, this side brick should have increased resistance to abrasive and / or corrosive wear, in particular to abrasive wear. This side brick should also be able to be produced, for example, without the use of adhesive (s). Furthermore, this side brick, if it is designed as a composites side brick, also allow that the ramming mass between the side wall and the cathode block can be omitted partially or completely. According to the invention this object is achieved by a side brick for a wall in an electrolytic cell, in particular for the production of aluminum, which is a laminated body and a layer having a lower thermal conductivity and a layer having a higher thermal conductivity, wherein the difference between lower and higher thermal conductivity at least 5 W / nrrK, measured at a temperature between 920 ° C to 1000 ° C, preferably between 950 ° C and 980 ° C, and wherein at least one of the layers with silicon (powder), an oxide ceramic material or a non- oxide material is doped. This laminate can be made without the use of adhesive (s), as explained later. The design of the side stone may also indicate the use of adhesive (s) between see the individual side stones, which form the side wall, are omitted. Due to the shape of this composite body can - as also stated later - be dispensed with partially or completely on the ramming mass to fill the gap between side brick and cathode block.

It has been recognized that the configuration of a side brick for an electrolytic cell with layers with different thermal conductivity, wherein at least one of the layers with silicon (powder), an oxide ceramic material or a non-oxidic material is doped, a very easy to be accomplished and at the same time highly efficient adaptation of the thermal conditions in the electrolytic cell in their operation allows such that the stability and efficiency of the electrolysis and the life of the electrolysis cell can be optimized. In addition, the resistance to wear, in particular abrasive and / or corrosive wear is increased. If adhesive material is used between the individual side stones, the design of this side stone makes it possible to dispense entirely with this adhesive material. Furthermore, it was recognized that, in addition to this adaptation of the thermal conditions, it is also possible to partially or completely dispense with the ramming mass for filling the joint between side brick and cathode block by means of a special shaping of these side bricks.

In the following, when the term "side stone" is used, this term may also encompass the above-mentioned composite side stones As described below, a composite side stone has a special shape.

The terms "lower" and "higher" thermal conductivity mean that the respective layer which has this thermal conductivity has a "lower" or "higher" thermal conductivity compared to the respective other layer. In particular, the one layer consists of a material with a lower thermal conductivity and the other layer of a material with a higher thermal conductivity, wherein the two materials are different from each other. If the laminated body comprises more than two layers, all the layers may have mutually different thermal conductivities, or at least two layers may have the same thermal conductivity and / or at least two groups of layers may be provided which each have the same thermal conductivity. For more than two layers it is sufficient if between at least two of the layers a thermal conductivity difference of at least 5 W / nrrK - measured at a temperature between 920 ° C to 1000 ° C, preferably between 950 ° C and 980 ° C - exists. In particular, the thermal conductivities of the layers differ in at least one direction of the side stone, which is preferably a direction that is in particular perpendicular to the side wall formed by the side stones. The difference between lower and higher thermal conductivity - measured at a temperature between 920 ° C to 1000 ° C, preferably between 950 ° C and 980 ° C - can be between 5 W / nrrK and 80 W / nrrK, preferably between 5 and 70 W / nrrK, more preferably between 8 W / nrrK and 60 W / nrrK, and most preferably between 10 W / nrrK and 50 W / nrrK.

Through the different layers of the side stone with different thermal conductivity, the heat conduction and Abgäbe over the side stones and the course of the isotherms in the side wall can be adjusted specifically. Since the side stones are in some areas directly in contact with the layer of liquid aluminum and the melt layer in which the electrolysis takes place, thereby the local, for the stability and efficiency of the electrolysis particularly important temperature conditions can be influenced directly and with high efficiency, so that for the operation of the electrolysis cell optimal thermal conditions can be guaranteed. For example, different thermal conductivities can be provided in the areas of the side stone that are used of the side stone in the electrolysis cell come into contact with the various media of the electrolysis cell. Likewise, several layers with different thermal conductivities can follow one another along the heat flow direction through the sidestones to adjust the heat flow in said direction. The resulting optimization of the thermal conditions in the electrolysis cell leads to a considerable increase in the stability and efficiency of the electrolysis process and the service life of the electrolysis cell. The stability and efficiency of the electrolysis process and the service life of the electrolysis cell are also increased by doping at least one of the layers with silicon (powder), an oxidic ceramic material or a non-oxidic material.

The side stones according to the invention, which also comprise composite side stones, can preferably be built into an electrolytic cell in a conventional manner, which corresponds to known side stones with homogeneous thermal conductivity, in each case with respect to a defined spatial direction, and used there for lining the lateral wall of the steel trough. without the changes of the electrolysis cell that are relevant to the construction being necessary or disadvantages that have to be taken into account, the lateral wall of the electrolytic cell, in particular in a known manner, can be made relatively thin. The side stones can be produced with little effort and with excellent mechanical stability and in particular very good cohesion between the various layers by the side bricks are burned in one piece from a single coherent green body in which different, the layers to be produced corresponding green mixtures are contained, the Base body can correspond to a single side brick or several side stones can be separated from the fired body. In the production of a composite side stone, the desired polygonal shape can be worked out, for example, from such a fired green body over the entire length of the green body at first before then individual composite sidestones are cut off like a disk. The preferred polygonal forms will be discussed later. During a finishing process, grouting, elevations, recesses and roughening can be added to a composite side stone. Here again it should be noted that the cohesion between the different

Layers of the side stones according to the invention without the use of adhesive (s) is achieved.

Advantageous embodiments of the invention are described in the subclaims, the description and the figures.

In the following description, when reference is made to one or more layers of the side stone formed as a layered body, it refers to layers having different thermal conductivity, in particular each having a thermal conductivity that differs from the thermal conductivity of at least one other layer of the side stone by 5 W / nrrK or more - measured at a temperature between 920 ° C to 1000 ° C, preferably between 950 ° C and 980 ° C - differs. The particular two layers can follow one another in a predetermined direction, which may correspond to a relevant for the thermal conditions in the electrolysis cell heat flow direction and may be given for example by the thickness direction of the side stone. As a result of the resulting variation in the thermal conductivity over the thickness of the side stone, the total heat flow through the side stone in this direction can be regulated in such a way that a desired isothermal course in the side stone is ensured. However, the layers can also follow one another eg in the height direction of the side stone which does not comprise composite side stone, wherein in particular the height regions of the side stone covered by the different layers when used in an electrolysis cell with different media of the electric lysezelle - such as liquid aluminum, liquid or solidified

Melt, gas phase - can be in contact. As a result of the resulting variation in the thermal conductivity over the height of the side stone, the heat dissipation can be adapted to the heat generation taking place in the respective medium and the respective desired thermal conditions and additionally to the chemical requirements of the individual media.

The inventively desired adaptation of the thermal conditions in an electrolytic cell during their operation can already be realized if the side brick has exactly two layers with different thermal conductivity. Such a layer structure also has a high stability and can be produced with little effort and high reliability and reproducibility. In principle, however, the number of different layers of the side stone is not limited to exactly two. Instead, the side brick may also comprise a higher number of layers, for example at least three, four, five, six or more different layers. As a result, an even more differentiated local coordination of the heat conduction behavior of the side stone to the thermal conditions in the electrolysis cell can be achieved. Preferably, the side brick comprises two to four layers, more preferably two to three layers, most preferably two layers. If, in addition to the desired adaptation of the thermal conditions in an electrolytic cell during operation, a partial or complete replacement of the ramming mass between cathode block and side brick is intended, ie a composite sidestone is used, then this composite sidestone may also have a higher number of layers, for example at least three , four, five, six or more different layers. Preferably, the composite side brick comprises two to four layers, more preferably two to three layers, most preferably two layers. The layers can follow one another in a predetermined direction, which in particular can correspond to a thickness or height direction of the side stone, so that a variation of the thermal conductivity of the side stone in the thickness direction or the height direction of the side stone is achieved. The side stone may also have successive layers in different directions, so that a variation of the thermal conductivity of the side stone in different directions is achieved. For example, a plurality of layers of side stone following one another in a first direction may form a first layer sequence and a plurality of other layers following one another in the first direction form a second layer sequence, wherein the two layer sequences preferably in a second direction different from the first direction and in particular perpendicular to the first direction Following each other, which would be like a checkerboard pattern. According to an advantageous embodiment, the laminated body has an alternating sequence of a layer with a lower thermal conductivity and a layer with a higher thermal conductivity. This alternating sequence can take place in a predetermined direction, which corresponds in particular to the thickness or height direction. However, it may also be that an alternating sequence of a layer with a lower thermal conductivity and a layer with a higher thermal conductivity in a first direction, and an alternating sequence in a direction different from the first direction, in particular to the first direction perpendicular second direction. In this case, a particularly favorable heat conduction behavior is achieved when an outer layer of the laminated body represents a layer with a lower thermal conductivity and the other outer layer is a layer with a higher thermal conductivity. This effectively and directly adjusts the heat absorption, distribution and discharge across the outer surfaces of the side stone formed by the outer layers of the side stone. It is preferred that in this case the outer layer of the laminated body, which in contact with the liquid Aluminum and / or the liquid melt layer, is a layer having a lower thermal conductivity, and that the other outer layer of the laminated body, which is in contact with the cathode bottom and / or the tub is a layer having a higher thermal conductivity. The direction in which the thermal conductivities differ is the direction which is perpendicular to the sidewall formed by the sidestones.

In principle, the layers and / or the side stone may have any suitable shape. It should be understood that the shape is critically dependent on the intended use of the side stone, i. the adaptation of the thermal conditions in an electrolytic cell in their operation alone or the combination of this adjustment with the partial or complete replacement of the ramming mass between the cathode block and side stone. A particularly advantageous embodiment with regard to the heat conduction behavior and the manufacturability of the side stone is that the layers of the side stone have a block shape, in particular a cuboid shape, and are connected to one another via contact surfaces, in particular their base surfaces or via their side surfaces. Such layers can be produced particularly easily and allow the targeted adaptation and variation of the thermal conductivity along the main directions of a preferably block-shaped, in particular cuboid, side stone.

Preferably, the side brick is block-shaped, in particular cuboid. The thickness direction of one or more layers of the side stone may in each case coincide with the thickness direction of the side stone, so that the orientation of the layers is matched to the orientation of the side stone and the corresponding main heat conduction directions in the side stone. Layers interconnected by their bases can accordingly follow one another in the thickness direction of the side stone and over their side surfaces interconnected layers can follow one another in the height direction of the side stone.

For the purposes of the invention, a block is understood to mean a body having six rectangular surfaces, eight rectangular corners and twelve edges, each of which has at least four equal lengths and are parallel to one another. If the block represents a cuboid, four edges are the same length and parallel to each other. But it is also possible that eight of the twelve edges are the same length, in each case four edges are parallel to each other or all edges are the same length, with each four edges are parallel to each other here.

If the side stone is used as a composite side brick in the electrolysis cell, an advantageous embodiment of the side brick is that at least one layer of the side brick has a block shape, in particular a cuboid shape, and at least one layer of the side brick has a polygonal shape. These layers are connected to each other via contact surfaces, in particular their base surfaces; the base of the layer having a block shape hereby has either a partial or complete contact with the base of the layer having a polygonal shape. At a complete contact of the bases both layers have the same height; lies a partial one

Before contact, the layer having a polygonal shape has a height which is 30% to less than 100%, preferably 40% to 80%, more preferably 50% to 75%, of the height of the layer having a block shape. Such layers can also be produced very easily and allow on the one hand a targeted adaptation and variation of the thermal conductivity along the main directions of the side stone, on the other hand is made possible with such a side stone, the partial or complete replacement of the ramming mass between side brick and cathode block. At least one layer of the composite sidestone has a polygonal shape. For the purposes of the invention, a polygon is understood to mean a polygon which may preferably contain three to six corners, particularly preferably three to five corners. As a polygon with four corners, for example, a rectangle, square or trapezoid understood. These polygons may be in regular or irregular form. In the context of the invention, a regular polygon is understood to be a polygon in which all sides have the same length and all internal angles are the same size. Due to the different polygonal shapes, the composite side stones can be adapted to the desired electrolysis cell design; For example, more space for anodes can be created by the corresponding design of a composite side stone, ie the design of a layer in polygonal shape. Larger anode surfaces allow higher current and thus higher productivity. In addition, the shape of the composite side stone can be adapted to the shape of the original circumferential ramming gap joint. Furthermore, these polygons can be present with normal and / or rounded corners. A normal corner is the point at which two sides of the corresponding polygon meet. A rounded corner is understood as meaning a corner which has a concave curvature running inwards without an angular change in this curved area. Rounded corners have the advantage, compared to sharp corners, that a more even distribution of forces occurs at the rounded corners. This more uniform distribution of forces causes a reduction in the stresses occurring, and thus a reduced formation of cracks and / or defects at these points of the composite side stone. Preferably, the polygon contains only normal corners, or one corner of the polygon is rounded, and the other corners represent normal corners.

The thickness direction of one or more layers of the composite side stone can in each case coincide with the thickness direction of the side stone, so that the Orientation of the layers to the alignment of the side stone and the corresponding main heat conduction directions in the side stone is adjusted. The layers connected to one another via their base surfaces can accordingly follow one another in the thickness direction of the composite side stone.

The side brick, including the composite side stone, may in principle have a flat design with a relatively small thickness and in particular a significantly greater height and width, wherein the side stone may have a greater height than width. The thickness of the side stone may, for example, be between 50 and 700 mm when the layers are joined together over their bases, and depends on the type of use. If the side stone is used only to adapt the thermal conditions in an electrolysis cell, the thickness is preferably between 60 and 250 mm, more preferably between 80 and 150 mm, very particularly preferably between 90 and 110 mm. If, on the other hand, a composite sidestone is used in the electrolysis cell, the thickness is preferably between 150 and 600 mm, particularly preferably between 200 and 350 mm, very particularly preferably between 225 and 300 mm. The ratio of the thicknesses of, in particular, two layers may be for example at most 1: 3, preferably at most 1: 2 and particularly preferably 1: 1.

The width of the side stone, including the composite side stone, can be arbitrarily adapted to the length of the side wall of the electrolysis cell, that is, it can occupy either the entire length of this side wall or it is only a part of the length of the side wall. The length of a side wall may be, for example, either 3500 mm to 4000 mm or 10000 to 15000 mm. If the length of the side wall is 10,000 to 15,000 mm, the width of the side stone may be that length or the side wall may be covered with, for example, 2 to 3 side stones having a length of 5,000 mm. If the width of the side stone occupies the entire length of the side wall of the electrolysis cell, on the one hand can be dispensed with such a side stone on the adhesive material may be used for the joints between the individual side bricks, on the other hand requires the simpler installation of this side stone time savings. In the case where the width of the side stone according to the invention is only a part of the length of the side wall, then at least two side stones according to the invention are used. In the context of the invention it is possible to use sidestones according to the invention with different widths, ie the width of a single side stone can be adjusted as required. If the width of the side stone according to the invention, including the composite side stone, occupies only a part of the length of the side wall, it may be between 300 and 600 mm, preferably between 400 and 600 mm, particularly preferably between 450 and 550 mm. The height of the side stone, including the composite side stone, may for example be between 500 and 900 mm, preferably between 600 and 800 mm, particularly preferably between 600 and 750 mm. In the case of a composite sidestone, the length of the layer is here taken as a block having a block shape.

According to an exemplary embodiment, the side brick, which does not comprise a composite side brick, comprises two layers which are successive in the thickness direction of the side brick, in particular partially or completely interconnected over their base surface, each of 30% -70%, preferably 50%, of the thickness of the Cover the side stone and thus cover the entire thickness of the side stone. It should be understood that the percentages of the individual layer thicknesses - also below - always together make up 100%. One layer can extend over the entire height of the side stone. Likewise, the side brick, which does not comprise a composite side brick, two successive in the height direction of the side stone, in particular connected over their side surfaces layers each covering 30% - 70%, preferably 50%, the height of the side stone and thus the entire height of Cover the side stone. A layer may extend over the entire thickness of the side stone.

According to an advantageous embodiment, one or more and in particular all layers of the side brick, which represents no composite Seitenstein, each having a thickness of 25 to 125 mm, preferably 30 to 100 mm, more preferably 40 to 75 mm and most preferably 45 to 55 mm up. This is particularly preferred when the side brick has two layers which are connected to one another via their base surfaces and follow one another in the thickness direction and in particular make up 30-70%, preferably 50%, of the thickness of the side stone. The layers can each extend over the entire height of the side stone.

According to a further preferred embodiment, one or more and in particular all layers of the side stone, which does not comprise a composite side stone, when these layers are interconnected via their side surfaces and follow one another in the height direction, have a height of 150 to 450 mm, preferably 200 to 400 mm, more preferably from 250 to 350 mm, and most preferably from 280 to 320 mm. This is particularly preferred if this side brick has two layers which are connected to one another via their side surfaces and follow one another in the vertical direction and in each case extend in particular over 30% -70%, preferably 50%, of the height of the side stone. The layers can each extend over the entire thickness of the side stone. The ratio of the heights of, in particular, two layers can be, for example, at most 1: 3, preferably at most 1: 2 and particularly preferably 1: 1. According to an exemplary embodiment for a composite side brick, this side brick has two layers which follow one another in the thickness direction of the side brick, in particular partially or completely interconnected over their base surface, each covering 30% -70%, preferably 50%, of the thickness of the side brick and thus cover the entire thickness of the side stone. It should be understood that the percentages of the individual layer thicknesses - also below - always together make up 100%. A layer may extend partially or completely over the entire height of the side stone. It may be that the layer having a polygonal shape either extends completely over the entire height of the layer having a parallelepiped shape or extends from 30% to less than 100%, preferably from 40% to 80%, particularly preferably 50% to 75%, above the height of the layer having a cuboid shape.

According to a further advantageous embodiment, one or more - and in particular all - layers of the composite side stone each have a thickness of 75 to 250 mm, preferably 100 to 175 mm, and particularly preferably 1 10 to 150 mm. This is particularly preferred when the composite side brick has two layers which are partially or completely connected to one another via their base surfaces and follow one another in the thickness direction and in particular each make up 30-70%, preferably 50%, of the thickness of the composite side stone. With complete contact of the base surfaces, the layers each extend over the entire height of the composite side stone; if, on the other hand, there is partial contact of the bases, then the layer having a polygonal shape extends from 30% to below 100%, preferably from 40 to 80%, particularly preferably from 50% to 75%, over the height of the layer having a cuboid shape , According to a further embodiment, one or more rectangular layers, and in particular all parallelepiped layers of the composite side stone, have a height of 500 to 900 mm, preferably of 650 to 850 mm, particularly preferably of 700 to 800 mm and one or more, and in particular All polygonal layers have a height of 150 to less than 900 mm, preferably from 200 to 720 mm, most preferably from 250 to 675 mm.

The side brick can be in contact with various constituents or media of the electrolysis cell over its height, in particular with the layer of liquid aluminum, the melt layer, possibly a crust of solidified melt arranged on the melt layer and with a developing one during operation of the electrolysis cell gaseous atmosphere with the various substances contained therein. In its lower part, the side stone may be in communication with the cathode bottom and / or a ramming mass, which is used to establish a tight connection between the cathode bottom and the

Seitenstein can be provided. The side stone may, as described above, have several successive layers with different thermal conductivities in its height direction, and preferably those height regions of the side stone in which the side stone comes into contact with different media are formed by different layers of the side stone. As a result, the heat absorption and dissipation via the side stone is adapted to the respective thermal conditions and requirements in the different media. As a result of this adaptation, the side stones are less stressed overall, which leads to greater wear resistance.

Alternatively or additionally, the side brick may have several layers in the thickness direction of the side stone with different heat conductivities. As a result, the heat conduction of the side stone in a heat Flow direction can be varied, which is perpendicular to the side of the side stone limiting the inside of the tub.

A preferred embodiment for the use of side stone in an electrolytic cell in thermal, mechanical and chemical stability of the side stone is that at least one layer, preferably all layers, of a material selected from the group consisting of carbon, graphitic carbon, graphitized carbon or silicon carbide or any mixtures thereof or containing such material. These materials are particularly suitable for withstanding the conditions encountered in the use of the side stone in an electrolytic cell and the resulting contact of the side brick with the layer of liquid aluminum and the melt layer. Furthermore, the choice of suitable material compositions makes it possible to adapt the heat conductivity of the side brick in a favorable range of values. The thermal conductivity of one or more and in particular all layers of the side stone can - measured at a temperature between 920 ° C and 1000 ° C, preferably between 950 ° C and 980 ° C - for example between 4 and 120 W / nrrK, in particular between 4 and 100 W / nrrK, preferably between 5 and 80 W / nrrK, more preferably between 8 and 50 W / nrrK be.

A particularly high wear resistance of the side stone and thus a particularly long service life of an electrolysis cell equipped with the side stone is achieved if the carbon is anthracite, preferably electrically calcined anthracite, and the silicon carbide is silicon nitride bonded silicon carbide.

Even further improvement in the thermal and mechanical properties of the side stone can be achieved if the production of the side stone comprises a pitch impregnation step followed by carbonization. Here, the whole side stone or at least one layer of the side stone can be subjected to impregnation as described above.

At least one of the layers may comprise silicon (powder), an oxide ceramic material, such as, for example, aluminum oxide or titanium dioxide, or a non-oxidic ceramic material, which preferably comprises at least one metal from groups 4 to 6 and at least one element the 13th or 14th group of the Periodic Table of the Elements is composed of doped. Doping is here understood to mean the addition into the green mixture, the individual proportion of one or more dopants in the green mixture being 3 to 15% by weight, preferably 5 to 10% by weight. Preference is given to powdery particles having a diameter of less than 200 μιτι, more preferably used under 63 μιτι. Among these non-oxide materials are, in particular, metal carbides, borides, metal nitrides and metal carbonitrides with a metal of the 4th to 6th group, such as titanium, zirconium, vanadium, niobium, tantalum, chromium or tungsten, preferably titanium is used. It is also possible, any mixtures of oxidic ceramic materials, any mixtures of non-oxide ceramic materials, any mixtures of oxidic ceramic materials and non-oxide ceramic materials, any mixtures of oxidic ceramic materials and silicon (powder), any mixtures of non -oxidic ceramic materials and silicon (powder) or any mixtures of oxidic ceramic materials, non-oxidic ceramic materials and (silicon) powder to use. As preferred non-oxide materials, titanium diboride or titanium carbide may be mentioned. If silicon (powder) is used, it converts to silicon carbide during the firing process. It is also possible to use a precursor for the production of silicon nitride-bonded silicon carbide using a mixture of silicon carbide and silicon powder. Here, the combustion process must be carried out under controlled nitrogen content of the fuel gas at up to 1400 ° C, in order to convert the silicon to the actual binder gas. phase to ensure silicon nitride. In general, the heat treatment is carried out by firing as in conventional ceramic materials, ie the firing temperature is adapted to the ceramic material used. It may therefore be that in the production of the composite, the different requirements for the combustion processes of the individual materials used, must be considered. In particular, this layer is the layer which, during operation, makes contact with the surrounding steel trough and is thus exposed to an increased risk of oxidative wear. Preferably, the side stone is made monolithic, so that the layers of the side stone are integrally and materially connected to each other. Such a compound is distinguished from a glued or mechanical connection by increased stability. The side stone can form a composite of the individual layers. This results in a thermally, mechanically and chemically very high resistance of the side stone and thus a particularly long service life of an equipped with the side stone electrolytic cell. In particular, the side stone may be obtained in one piece from a green block, which may accordingly contain a plurality of different green mixtures forming the starting materials for the different layers of the side stone of the various layers of the finished side stone. The side stone may be obtainable by firing the green block, wherein in particular carbonization and / or graphitization of the green material of the green block may take place. For example, the thermal conductivity of the side stone at a temperature between 920 ° C and 1000 ° C according to DIN 51936 can be measured. In this case, a pulsed laser is used in measurements that exceed temperatures above 400 ° C. Within a layer, the side brick may have at least substantially homogeneous thermal conductivity. Between a layer having a lower thermal conductivity and a layer having a higher Having thermal conductivity, a transition region may be formed in which the thermal conductivity, for example at least substantially continuously, decreases from the higher to the lower value. Such a transition region, which can be made relatively small compared to the total extent of the layers, can be regarded as part of the two layers.

The invention further provides a process for the preparation of a side stone according to the invention as described herein which comprises the steps:

a) providing a mixture for the layer with the lower thermal conductivity, a mixture for the layer with the higher thermal conductivity, and optionally one or more mixtures for at least one further layer,

b) forming a green block with layer structure of the mixtures according to step a) and

c) firing the green block according to step b) at a temperature of 800 to 1400 ° C, preferably 1000 to 1300 ° C.

By producing the side stone by firing a green block with various green mixtures forming the starting materials for the layers, a uniform side stone with a high stability and a cohesive and monolithic cohesion between the individual layers of the side stone is achieved. Forming the green block according to step b) may include that the green

Mixtures are placed in a mold. In this case, several layers of the green mixtures can be formed in the mold according to the layer structure of the finished side stone. The production of the layer structure can be accomplished in a simple manner such that the layers of the green mixtures follow one another in an opening direction of the mold. In a particularly simple way The layers can be introduced into the mold in such a way that they are oriented substantially horizontally, preferably horizontally, and preferably follow one another in the vertical direction. Forming the green block according to step b) may further include vibratory shaping and / or block pressing of the green material. This can be done with or without vacuum. As a result, existing voids within the material can be completely or partially eliminated, so that everywhere a desired bulk density is uniformly achieved. In addition, a particularly high homogeneity in terms of bulk density can be achieved if the formation of the green block comprises pressurizing or compressing the green material in order to compact the material.

Particularly suitable as materials for the green mixtures are all green materials which can be fired to one of the preferred materials mentioned above with respect to the finished side stone. For example, at least one green mixture may contain a material selected from the group consisting of a carbonaceous material, such as carbon black. Anthracite, a graphitic or graphitizable material, e.g. synthetic graphite and pitch, or any mixture of these materials. Further, a particular carbonaceous binder such as binder pitch may be included in the mixture. The targeted composition of the material of the individual layers of the green block makes it possible to set the thermal conductivity of the various layers of the resulting side brick in a targeted manner.

When a green mixture comprises a carbonaceous material, it is preferable to carbonize the green mixture material during firing of the green block. Furthermore, graphitization of the material can take place as a further step d). For this purpose, the carbonized or green shaped body to temperatures of more than 2000 ° C and preferably more than 2200 ° C are heated. In order to further improve the thermal and mechanical properties of the side stone, a further step e) may be provided after step c) of firing and / or after a possibly provided step d) of graphitizing, which comprises impregnating the fired green block and optionally graphitized green block Bad luck covers.

Preferably, the method described above first produces a base body with a plurality of layers, from which several side stones having the desired dimensions are cut out in a step following the method steps described above, in particular by a cutting operation. This also applies to the production of a composite stone. Another object of the invention is a side stone, which is obtainable by the method described herein. When used in an electrolysis cell, the side stone causes an optimization of the thermal conditions in the electrolysis cell during the electrolysis operation and also has a high mechanical stability and a very strong cohesion between the various layers of the side stone. Depending on the width of the side stones can be dispensed with the adhesive material between the side stones. If a composite side stone is used, it is also possible to dispense, in part or in full, with the ramming mass between the side brick and the cathode block.

The use of the side stone according to the present invention for lining the side walls in an electrolytic cell constitutes a further independent subject matter of the present invention. Within the scope of the invention it is also possible that for the lining of the side wall both at least one side stone, which is used to adapt the thermal is used, is combined with at least one Kompositseitenstein. The number of side stones or composite side stones used here can be adjusted as needed. Another object of the invention is an electrolytic cell, in particular for the production of aluminum, which comprises a cathode, an anode and a wall, wherein at least a portion of the wall is formed by a side stone according to the present invention. This side stone can also be a composite side stone as described. The advantages and preferred embodiments described herein with respect to sunstone, its manufacture and use, and in particular its use in an electrolytic cell, when used appropriately, are advantages and preferred embodiments of the electrolytic cell of the present invention. The at least one side brick preferably forms a lateral wall of a well the layer of liquid aluminum and the melt layer are included. The side brick can thereby line a lateral wall of an outer steel tub of the electrolysis cell, which surrounds the inner tub formed by the side brick. As mentioned above, the amount of thermal energy generated in an electrolytic cell must be partly removed on the one hand, on the other hand, however, too high heat losses must be avoided in order to ensure a specific temperature distribution in the electrolysis cell. In addition to the previously described side stones or composite side stones according to the invention and the refractory lining, which is located between the cathode and the steel trough, the cathode also has an influence on the thermal management in the electrolysis cell. If too much heat is removed from the electrolysis cell, the cryolite solidifies in the melt in excess and may extend to the cathode surface. As a consequence, the cathodic current flow is disturbed, resulting in an inhomogeneous current distribution along the cathode. denoberfläche, and thus leads to an increased electrical resistance and thus to reduced energy efficiency of the electrolytic cell. The thermal management from the cathode to the underlying refractory lining can be adjusted well, whereas the thermal management from the cathode to the sidewalls is much more difficult to adjust. Usually, the cathode blocks that form the cathode are made of a uniform material, ie, these homogeneous cathode blocks have the same thermal conductivity, so that these cathode blocks are poorly or not at all able to support optimal thermal management in the electrolysis cell. This is especially true for the setting of thermal management from the cathode to the sidewalls.

WO 02/064860 describes cathode blocks which, viewed in the direction of the cathode longitudinal side, have different layers which have different electrical resistances, i. For the production of the cathode blocks, different materials (having different specific electrical resistances) are used in layers in the direction of the cathode longitudinal side. With these cathode blocks, the flow of current through the cell should be approximated to the ideal current flow even without expensive guidance of power rails.

Cathode blocks having different layers toward the cathode longitudinal side due to the use of different materials also have different thermal conductivities within the cathode block. Such cathode blocks can also be advantageously used to reduce the heat losses caused by the cathode, in particular in the direction of the cathode longitudinal side, ie towards the side walls. As a result, the course of the heat flow can also be controlled in the individual cathode blocks, and thus the cathode as a whole. Advantageously, the respective cathode block comprises in the direction of the cathode longitudinal axis. at least three layers, preferably three layers to seven layers, more preferably three layers to five layers, most preferably three layers. In this case, there are layers with a higher thermal conductivity and layers with a lower thermal conductivity, it being understood that in adjacent layers, one layer has a higher thermal conductivity compared to the other layer. The difference between the thermal conductivity between a higher thermal conductivity layer and a lower thermal conductivity is at least 10%, based on the lower thermal conductivity material, in the temperature range of 920 to 1000 ° C measured in the direction of the longitudinal axis of the cathode block. The cathode block may comprise at least two layers which have the same thermal conductivity, ie which consist of the same material. This may be the two outer or marginal layers of the cathode block. With such a cathode block, it is possible to selectively control the heat flow in this cathode block by selecting the number of layers, the order of the layers and the selection of the thermal conductivity values of each one of the layers. In the event that a lower heat outflow from the electrolysis cell is desired, a cathode block can be used which has, for example, three layers. The two outer layers, ie the two layers, which are in direct thermal contact with the side wall of the electrolytic cell or via the ramming mass, represent layers with a lower thermal conductivity, whereas the third, middle layer is present as a layer with a higher thermal conductivity. If, on the other hand, a higher heat output from the electrolysis cell is desired, then in a cathode block there are three layers, the two outer layers, those having a higher thermal conductivity compared to the third, middle layer.

The length of a cathode block is normally 2,500 - 3,500 mm. The length of a single layer mentioned above - viewed in the cathode longitudinal direction - depends on the desired heat flow in the cathode block and can be selected as a function of this heat flow. Furthermore, this length of a single layer depends on the number of layers in the cathode block. For example, if there are seven layers, a single layer will have a length of 300-600 mm. If only three layers are used, the outer or marginal layers are 400 to 600 mm long and the inner layer has a length of 1700 to 2300 mm. Regardless of the number of layers, the outer or marginal layers of the cathode block have a length of 400 to 600 mm, preferably 500 mm.

The individual layers of said cathode blocks are composed of carbon, i. made of a material containing carbon. With regard to the thermal conductivity, it has proved to be advantageous if the cathode block is composed of a material which is at least 50% by weight, preferably at least 80% by weight, particularly preferably at least 90% by weight, very particularly preferably at least 95 wt .-% and most preferably at least 99 wt .-% carbon. Said carbon may be selected from the group consisting of amorphous carbons, graphitic carbons, graphitized carbons and any mixtures of two or more of the aforementioned carbons.

For the preparation of these cathode blocks, the same method as for the above-described invention sidestones can be used. Therefore, for the preparation of the cathode blocks, reference is made to the corresponding above statements for the method for producing the side stones according to the invention. It is also true for the production of the cathode blocks that firing a green block with various green mixtures forming the starting materials for the layers achieves a uniform cathode block having a high stability and a cohesive cohesion between the individual layers of the resulting monolithic cathode block.

Particularly suitable materials for the green mixtures in the production of cathode blocks are all green materials which can be fired to one of the preferred materials mentioned above with respect to the finished cathode block. For example, at least one green mixture may contain a material selected from the group consisting of a carbonaceous material, such as carbon black. Anthracite, a graphitic or graphitizable material, e.g. synthetic graphite and pitch, or any mixture of these materials. Further, a particular carbonaceous binder such as binder pitch may be included in the mixture. The targeted composition of the material of the individual layers of the green block allows the heat conductivity of the various layers of the resulting cathode block to be adjusted in a targeted manner.

The shape of the layers in a cathode block may be different. In addition to layers which occupy the complete height H of the cathode block, there may also be layers which occupy only a part of this height H, as shown by way of example in FIGS. 10 and 11. This shaping of the layers can be done depending on the desired heat flow in the cathode block, i. With this shaping, in addition to the selection of the materials of the layers, and thus the thermal conductivity values, this heat flow can be controlled in a targeted manner.

By combining the side stones according to the invention with the abovementioned cathode blocks in an electrolysis cell, that is to say both the sidestones according to the invention and the cathode blocks described above can be used together in an electrolytic cell, the thermal conditions in an electrolytic cell even more targeted - as by the sidestones invention alone - control. As a result, the process conditions can be optimized in an electrolysis cell, whereby the achievable stability and efficiency of the electrolysis process improves and the life of the electrolysis cell is increased. It should be understood that any of these sidewall embodiments may be combined with any of the cathode block embodiments. Hereinafter, the present invention will be described by way of example with reference to advantageous embodiments with reference to the accompanying drawings. Show it:

1 shows an electrolytic cell according to an embodiment of the invention in a sectional perspective view.

2 shows a side brick according to an embodiment of the invention in a perspective view;

3 shows a side brick according to a further embodiment of the invention in a perspective view;

4 shows a base body, from which several side stones according to a

Embodiment of the invention are separable, in perspective view;

Fig. 5 shows a further basic body, from which a plurality of side stones are detachable according to an embodiment of the invention, in perspective view. 6 shows various embodiments of a composite side stone, in cross section;

FIG. 7 shows a basic body from which a plurality of composite side bricks can be separated out according to an embodiment of the invention, as well as a separated composite side brick, in a perspective illustration; FIG.

8 shows a further basic body, from which a plurality of composite sidestones can be separated out according to an embodiment of the invention, in a perspective representation;

9 shows a further base body, from which a plurality of composite side stones are detachable according to an embodiment of the invention, in cross-section.

10 is a cathode block in a perspective view and,

FIG. 11 shows cathode blocks having different shapes of the layers. FIG.

Fig. 1 shows an electrolytic cell for the production of aluminum according to an embodiment of the invention in a partially sectioned perspective view. The electrolysis cell comprises a cathode which is composed of a plurality of cathode blocks 12 forming a cathode bottom. On top of the cathode is a layer 14 of liquid aluminum and thereon a liquid melt layer 16 and above the liquid melt layer 16 a layer or crust 18 of solidified melt is arranged. Above the melt layer 16, an anode is arranged, which consists of a plurality of immersed into the melt layer 16 anode blocks 20. During operation of the electrolytic cell, electrical power is supplied via the anode blocks 20 and passed through the melt layer 16 and the liquid aluminum layer 14 to the cathode blocks 12. The current is dissipated via the cathode blocks 12 and via the busbars 22 inserted at the bottom thereof into corresponding slots of the cathode blocks 12. In the melt layer 16, the electrolysis takes place, which leads to the elimination of elemental aluminum from the melt, which accumulates at the top of the cathode bottom to form the layer 16 of liquid aluminum.

The electrolysis cell has a steel sump 24 serving as an outer casing, in the bottom region of which several plates 26 of a refractory material stacked on top of one another are thermally insulated from the bottom of the steel sump 24.

The lateral walls of the steel tub 24 are lined with a plurality of cuboidal side stones 28. The side bricks 28 form the side walls of an inner tub, in which the layer 14 of liquid aluminum, the liquid

Melt layer 16 and the solidified melt layer 18 are received and whose bottom is formed by the cathode bottom 12 formed by the cathode bottom. The joints formed between a cathode block 12 and a side brick 28 are sealed by a ramming compound 30. Such a ramming mass may also be provided for sealing the joints between the cathode blocks 12 and for sealing the joints between the side bricks 28.

As shown in Fig. 1, the side bricks 28 are formed substantially cuboid and stand upright in the steel tub 24, so that the height direction the side stones 28 is parallel to the vertical. The sides of the sidestones 28 delimiting the tub interior are thereby formed by their base surfaces 32 parallel to the height direction and the width direction of the side bricks 28 and the side bricks 28 are connected to one another via their side surfaces 34 parallel to the height direction and the width direction. The side bricks 28 stand, as shown in Fig. 1, in different areas of their height with different components or media of the electrolytic cell in contact, namely with the ramming mass 30, possibly the layer 14 of liquid aluminum, the liquid melt layer 16 and solidified melt layer 18.

During the electrolysis operation, significant amounts of thermal energy are generated in the electrolytic cell. Usually about one third of this thermal energy is absorbed by the sidestones 28 and discharged to the outside. The main heat flow direction corresponds to the thickness direction of the side stones 28. Approximately 15% of the thermal energy is absorbed via the cathode bottom or the ingot.

The sidestones 28 of the electrolysis cell shown in Fig. 1 each have at least one layer with a lower thermal conductivity and a layer with a higher thermal conductivity, wherein the difference between lower and higher thermal conductivity is at least 5 W / nrrK. Thereby, the heat absorption and dissipation over the side wall formed by the sidestones 28 adapted so that set optimal thermal conditions in the electrolytic cell in their operation, thereby improving the stability, reliability and efficiency of the electrolysis and increases the service life of the electrolysis cell becomes.

2 and 3 each show a side brick 28 according to an embodiment of the invention, which is incorporated, for example, in the electrolytic cell shown in FIG. can be set. The side bricks 28 each have a relatively small thickness d and a width b and a height h which is greater than the width b.

The side brick 28 shown in FIG. 2 has two cuboidal layers 36, 38, wherein the layer 36 has a lower and the layer 38 has a higher thermal conductivity. The layers 36, 38 are connected to each other via their parallel to the height direction and the width direction base surfaces 40, 42, each forming a contact surface, follow each other in the thickness direction of the side stone 28 and each extend over about half of the thickness d of the side stone 28th This allows the heat flows in the thickness direction and the isothermal layers within the sidestones 28 to be adjusted to optimize the thermal operating conditions in the electrolysis cell during operation. The side brick 28 shown in FIG. 3 likewise has two cuboidal layers 36, 38, wherein the layer 36 has a lower and the layer 38 has a higher thermal conductivity. The layers 36, 38 are connected to one another via their side surfaces 44, 46, which are parallel to the width direction and the thickness direction and each form a contact surface, follow one another in the height direction of the side stone 28 and each extend over approximately half the height h of FIG Side stone 28. Based on the installation situation in the electrolytic cell, the upper half of the height is preferably formed by the layer 36 with the lower thermal conductivity. As a result, the heat conduction via the side brick 28 can be adapted to the various constituents or media of the electrolysis cell and the thermal conditions present therein in the respective height range, thereby optimizing the thermal conditions prevailing in the electrolysis cell during electrolysis become. In the case described above, the heat is due to the good thermal contact between the lower half of Height comprising the layer 38 with the higher thermal conductivity and the cathode, which takes place via the ramming mass 30, is dissipated.

In another thermal design of the electrolytic cell, a reverse arrangement of the layers with respect to their thermal conductivity may be useful.

4 shows a main body 48, which has been produced as an intermediate product of a method according to the invention for producing a side brick. The main body 48 is cuboidal and consists of a cuboidal layer 36 having a lower thermal conductivity and a cuboidal layer 38 having a higher thermal conductivity, which are interconnected via their base surfaces. By means of a cutting process, it is possible to cut off from the base body 48 a plurality of side stones forming slices which have two layers 36, 38 with different thermal conductivity.

For this purpose, the main body 48, as indicated in Fig. 4 by dashed lines, cut along several cutting planes, which extend perpendicular to the running between the two layers 36, 38 interface. FIG. 5 shows a further main body 48, which substantially corresponds to the main body shown in FIG. 4. However, the main body 48 comprises two layers 36 with a lower thermal conductivity and a layer 38 arranged therebetween with a higher thermal conductivity, which are interconnected via their base surfaces. As shown in Fig. 5, the base 48 for cutting the sidestones is not only cut in several planes perpendicular to the interfaces between the layers 36, 38, but additionally in a median plane of the layer 38 parallel to these interfaces, so that the resulting Side stones each have two layers 36, 38 with different thermal conductivity. This manufacturing process has a higher economy. 6 shows cross sections of various embodiments of a composite side brick 29 according to the invention, which can be used, for example, in the electrolytic cell shown in FIG.

All the composite side stones listed in FIG. 6 have a cuboidal layer 36 and a polygonal layer 38, wherein the layer 36 has a lower thermal conductivity and the layer 38 has a higher thermal conductivity. The layers 36, 38 are connected to one another via their base surfaces 40, 42, which each form a contact surface, parallel to the height direction and the width direction, follow one another in the thickness direction of the composite side brick 29 and extend in each case over 30% -70%, preferably 50%, the thickness d of the composite side stone 29. The base surfaces 40, 42 may in this case have a partial or complete contact with each other. By means of these different configurations of the composite side stones, on the one hand the heat flows in the thickness direction and the isothermal layers within the composite side brick 29 can be adjusted so that the thermal operating conditions in the electrolysis cell are optimized during operation, on the other hand it is also possible to use such a composite side brick 29 partially or completely dispense with the ramming mass between this composite Seitenstein 29 and the cathode block.

In Fig. 6a), the layer 38 has a trapezoidal shape, in Fig. 6b), the layer 38 has a triangular shape and in Fig. 6c), the layer 38 has a shape of an irregular pentagon with a rounded corner. In these embodiments, the base surfaces 40, 42 in complete contact. The base surfaces 40, 42, however, have only a partial contact in FIGS. 6d) and 6e), wherein in FIG. 6d) the layer 38 is a rectangle having a rounded corner and in FIG. 6e) the layer 38 is in the form of a has irregular pentagons with a rounded corner. In another thermal design of the electrolytic cell, a reverse arrangement of the layers may be useful in terms of their thermal conductivity.

FIG. 7 shows a main body 48, which has been produced as an intermediate product of a method according to the invention for producing a composite side brick 29. This main body 48 is cuboid and consists of a cuboidal layer 36 having a lower thermal conductivity and a cuboidal layer 38 having a higher thermal conductivity, which are interconnected via their base surfaces. These layers represent horizontal layers. The layer 36 is machined so that this layer assumes the desired polygonal shape over the entire length of the base 48. In a next step, discs of the desired width are then cut off from this base body 48. It is thus possible to exploit the grain orientation which occurs in the production of the base body and thus different properties occurring in the horizontal or vertical direction, such as the thermal conductivity, and to adjust it in the side stone by selecting the base areas accordingly during machining of the base body.

FIG. 8 shows a main body 48, which has been produced as an intermediate product of a method according to the invention for producing a composite side brick 29. This main body 48 is cuboidal and consists of two cuboidal layers 36 having a lower thermal conductivity and a cuboidal layer 38 having a higher thermal conductivity, which are interconnected via their base surfaces. These layers represent vertical layers, with the layers 36 representing the two outer layers. Here, a plurality of disks can be cut off from the main body 48, the two outer layers 36 and an inner layer 38 with different chen Wärmeleitfähigkeiten have. In a next step, the layer 38 is cut so that two blocks are obtained, from which in a further step the layer 38 is cut so that the desired polygonal shape is obtained. Alternatively, it is first possible to divide it into two halves in the longitudinal direction, to work out the polygon and then, if necessary, to cut slices of the desired length.

It is possible here, by the orientation of the layers in the production of the corresponding base body - either in horizontal or in vertical form - to influence various properties, such as the thermal conductivity, for example. The reason for this is the different grain orientation during the shaping process and the resulting directional dependence of the physical properties. FIG. 9 likewise shows a main body 48, which has been produced as an intermediate product of a method according to the invention for producing a composite side stone 29. This main body 48 is cuboid and, like the main body 48 in FIG. 8, consists of two parallelepipedal layers 36 with a lower thermal conductivity and a cuboidal layer 38 with a higher thermal conductivity, which are interconnected via their bases. These layers represent vertical layers, with the layers 36 representing the two outer layers. Here, too, a plurality of disks can be cut off from the main body 48, which have two outer layers 36 and an inner layer 38 with different thermal conductivities. In a next step, by suitable cutting from such a single cut piece, two composite sidestones 29 having the same shape can be cut out. The advantage of this method lies in the order of processing, which requires that hardly any material loss occurs. 10 shows a cathode block 12 comprising three layers, wherein the two outer layers consist of the same material A and the middle layer consists of the material B. The individual layers go here over the complete height of the cathode block.

Fig. 1 a) and b) show different forms of the layers in a cathode block 12, wherein in these cathode blocks in each case two materials, ie material A and material B, is used. In this case, the two layers of the material A take only a part of the height H and the length L of the cathode block.

EXAMPLES

Exemplary Embodiment 1 A side brick is made from a mixture A containing 58% by weight (% by weight) of electrically calcined anthracite, 9% by weight of synthetic graphite, 17% by weight of binder pitch, 8% by weight of silicon and 8% by weight. % Alumina, and a blend B containing 77% by weight of synthetic graphite and 23% by weight of binder pitch. For this purpose, a vibrating mold for producing a green block is filled with the two mixtures in such a way that two successive layers of mixture A and mixture B follow one another in the green block in the height direction of the sidestones to be produced. The height of the layers in the Rüttelform is taking into account a target density, which results from a subsequent filling on the following densification of the green block, chosen so that after compaction both layers each extend over half the height of the green block. This is followed by burning of the green block in a ring furnace at 1200 ° C to produce a body.

Thereafter, slices having a thickness of 10 cm are cut off from the fired and preprocessed base body, which can be further processed in a subsequent step and impregnated, for example, with a pitch. An exemplary finished side brick has a width of 475 mm, a height of 640 mm and a thickness of 100 mm, based on the installation situation of the side stone in the electrolytic cell in which this is vertically arranged along its height direction, the upper 320 mm Seitensteinhöhe from the mixture A resulting material A and the lower 320 mm from the mixture B resulting material B are formed.

In this case, the material A has a thermal conductivity of approximately 8 W / nRrK measured at room temperature in one direction of the side stone, while the Material B in the same direction of the side stone, in the grain orientation of the materials A and B, has a thermal conductivity of about 45 W / nrrK.

The thermal conductivity at room temperature can be measured according to ISO 12987, in a given direction, in the case of pressurization of the starting material during the production of the side-brick, e.g. perpendicular or parallel to the direction of pressurization, i. against or in the grain orientation.

The thermal conductivity measured at a temperature between 920 ° C to 1000 ° C is about 9 W / nrrK for material A and about 37 W / nrrK for material B. The measurement of the thermal conductivity can be done here in grain alignment according to DIN 51936 using a pulsed laser.

Embodiment 2:

A composite sidestone is made from a mixture A containing 58% by weight of electrically calcined anthracite, 9% by weight of synthetic graphite, 17% by weight of binder pitch, 8% by weight of silicon and 8% by weight of alumina, and a mixture B containing 65% by weight of synthetic graphite, 5% by weight of alumina, 10% by weight of silicon powder and 20% by weight of binder pitch. For this purpose, a vibrating mold for producing a green block is filled with the two mixtures so that successive layers of mixture A and mixture B follow one another in the green block in the height direction of the combo stones to be produced. The height of the layers in the Rüttelform is taking into account a target density, which results from a subsequent filling on the following densification of the green block, chosen so that after compaction both layers each extend over half the height of the green block. This is followed by burning of the green block in a ring furnace at 1300 ° C for producing a base body. Thereafter, the layer containing material A is processed so that it assumes the desired polygonal shape over the entire length of the green block. In a next step, then slices of a thickness of 50 cm are cut off from this basic body. An exemplary finished composite stone has a width of 500 mm, a height of 700 mm and a thickness of 250 mm.

The material A has a thermal conductivity of about 8 W / nrrK measured at room temperature in one direction of the side brick, while the material B in the same direction of the side stone, in the grain orientation of the materials A and B, has a thermal conductivity of about 45 W / nrrK , The thermal conductivity at room temperature can be measured according to ISO 12987, in a particular direction, in the case of pressurization of the starting material during the production of the side brick, e.g. perpendicular or parallel to the direction of pressurization, i. against or in the grain orientation.

The thermal conductivity measured at a temperature between 920 ° C to 1000 ° C is about 9 W / nrrK for material A and about 37 W / nrrK for material B.

Embodiment 3

A cathode block as shown in Fig. 10 is prepared by filling in a vibrating mold, the height of which is considered as a finished height of the green body, first with a mixture A, then with a mixture B and then again with a mixture A.

The mixture A is composed as follows:

57% by weight anthracite

24 wt .-% graphite and

- 19 wt .-% binder pitch. Further, the mixture B is composed as follows:

80 wt .-% graphite and

20% by weight binder pitch. The height of the layers in the Rüttelform is taking into account a target density, which results from a subsequent filling on the following densification of the green block, chosen so that after compaction both layers each extend over half the height of the green block. This is followed by burning of the green block in a ring furnace at 1200 ° C to produce a body. The material A has a thermal conductivity of about 15 W / nrrK measured at room temperature in one direction of the cathode block, while the material B has a heat conductivity of about 40 W / nrrK in the same direction of the cathode block, in grain alignment of the materials A and B , The thermal conductivity at room temperature can be measured according to ISO 12987, in a certain direction, in the case of pressurization of the starting material during manufacture of the cathode block, eg perpendicular or parallel to the direction of pressurization, ie against or in the grain orientation. A cathode block thus produced may have a width of 420 mm, a height of 400 mm and a length of 3100 mm, and may be used for the production of a cathode bottom having, for example, 24 cathode blocks. Such cathode blocks can be used together with the side stones according to the invention in an electrolysis cell. LIST OF REFERENCE NUMBERS

12 cathode block

14 layer of liquid aluminum

16 layer of liquid melt

18 layer of solidified melt

20 anode block

22 busbar

24 steel tub

26 refractory plate

28 side stone

29 composite side stone

30 ramming mass

32 base area

34 side surface

36 layer with lower thermal conductivity

38 layer with higher thermal conductivity

40, 42 floor space

44, 46 side surface

48 main body b width

h height

d thickness

H height of the cathode block

L length of the cathode block

Claims

claims:

Seitenstein for a wall in an electrolytic cell, in particular for the production of aluminum, wherein

the side brick (28) is a laminated body,

comprising a layer (36) having a lower thermal conductivity and a layer (38) having a higher thermal conductivity, the difference between lower and higher thermal conductivity being at least 5 W / nrrK, measured at a temperature between 920 ° C and 1000 ° C,

By doing so, that is

at least one of the layers (36, 38) is doped with silicon (powder), an oxidic ceramic material or a non-oxidic material.

Side stone according to claim 1,

By doing so, that is

the laminated body has an alternating sequence of a layer (36) with a lower thermal conductivity and a layer (38) with a higher thermal conductivity.

Side stone according to claim 2,

By doing so, that is

an outer layer of the laminated body is a layer (36) having a lower thermal conductivity and the other outer layer is a layer (38) having a higher thermal conductivity.

Side stone according to one of claims 1 to 3,

characterized in that the layers (36, 38) have a block shape, in particular a cuboid shape, and are connected to one another via contact surfaces, in particular their base surfaces (40, 42) or via their side surfaces (44, 46).

Side stone according to one of claims 1 to 3,

By doing so, that is

one of the layers (36, 38) has a block shape, in particular a cuboid shape, and the other layer (36, 38) has a polygonal shape, the two layers being connected to one another via contact surfaces, in particular their base surface (40, 42).

Side stone according to claim 5,

By doing so, that is

the layer (36, 38) having a polygonal shape represents a polygon having three to six corners.

Side stone according to one of claims 1 to 6,

By doing so, that

when the layers (36, 38) are connected to one another via their base surfaces (40, 42), the thickness of the layered body is 50 to 700 mm.

Side stone according to claim 4,

By doing so, that is

when the layers (36, 38) are interconnected via their side surfaces (44, 46), the height of the layers is 150 to 450 mm.

Side stone according to one of claims 1 to 8,

By doing so, that is

at least one layer (36, 38) of a material selected from the

Group consisting of carbon, graphitic carbon, graphitic carbon or silicon carbide or any mixtures thereof or contains such a material.

10. Seitenstein according to one of claims 1 to 9,

By doing so, that is

the difference between lower thermal conductivity and higher thermal conductivity is 5 to 80 W / nrrK, preferably 5 to 70 W / nrrK, more preferably 8 to 60 W / nrrK, and most preferably between 10 W / nrrK and 50 W / nrrK.

1 1. Method for producing a side brick (28) according to one of Claims 1 to 10, comprising the following steps:

a) providing a mixture for the layer (36) having the lower thermal conductivity, a mixture for the layer (38) having the higher thermal conductivity, and optionally one or more mixtures for at least one further layer,

b) forming a green block having a layer structure from the mixtures according to step a)

c) firing the green block according to step b) at a temperature of 1100 to 1400 ° C, preferably 1200 ° C.

12. The method according to claim 1 1,

By doing so, that is

the forming according to step b) comprises a vibration shaping.

13. Use of a side brick (28) according to any one of claims 1 to 12 for lining the side walls in an electrolytic cell.

14. electrolytic cell, in particular for the production of aluminum, which comprises a cathode (12) and an anode (20) and a lateral wall, where at least a portion of the wall is formed by a side brick (28) according to at least one of claims 1 to 11.

An electrolytic cell according to claim 14, wherein said cathode is formed of cathode blocks constituting a laminated body comprising layers having a lower thermal conductivity and layers having a higher thermal conductivity.