Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
  • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
  • C25C3/16—Electric current supply devices, e.g. bus bars

Definitions

• the present invention relates to a cathode assembly for an aluminum electrolytic cell.
• Such electrolysis cells are used for the electrolytic production of aluminum, which is usually carried out industrially by the Hall-Heroult process.
• a melt composed of alumina and cryolite is electrolyzed.
• the cryolite, Na 3 [AIF 6 ] serves to lower the melting point from 2,045 ° C. for pure aluminum oxide to approximately 950 ° C. for a mixture containing cryolite, aluminum oxide and additives such as aluminum fluoride and calcium fluoride.
• the electrolysis cell used in this method has a bottom composed of a plurality of adjacent cathode blocks forming the cathode.
• the cathode blocks are usually composed of a carbonaceous material.
• 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.
• the gaps between the individual walls delimiting the grooves of the cathode blocks and the busbars are often poured with cast iron in order to electrically and mechanically connect the busbars to the cathode blocks through the cast iron busbars produced thereby.
• the aluminum formed is deposited below the electrolyte layer due to its greater density compared to that of the electrolyte, ie as an intermediate layer between the upper side of the cathode blocks and the electrolyte layer.
• the aluminum oxide dissolved in the cryolite melt is split by the flow of electrical current into aluminum and oxygen.
• the layer of molten aluminum is the actual cathode because aluminum ions are reduced to elemental aluminum on its surface. Nevertheless, the term cathode will not be understood below to mean the cathode from an electrochemical point of view, ie the layer of molten aluminum, but rather the component forming the electrolytic cell bottom and composed of one or more cathode blocks.
• a major disadvantage of the Hall-Heroult process is that it is very energy intensive. To produce 1 kg of aluminum about 12 to 15 kWh of electrical energy is needed, which accounts for up to 40% of the manufacturing cost. In order to reduce the manufacturing costs, it is therefore desirable to reduce the specific energy consumption in this process as much as possible.
• cathode blocks are used recently, which in the operation of the electrolytic cell to the molten aluminum and the electrolyte side facing is profiled by one or more recesses and / or elevations.
• Such cathode blocks whose tops each have between 1 and 8 and preferably 2 elevations with a height of 50 to 200 mm, are disclosed, for example, in EP 2 133 446 A1.
• the cathode blocks are composed of anthracite, synthetic graphite, mixtures of anthracite and synthetic graphite or of graphitized carbon.
• the surface profiling serves the purpose that to reduce movement of the molten aluminum caused by the electromagnetic interaction present in the electrolysis and thereby to achieve less corrugation and bulging of the aluminum layer.
• the reduced wave formation is intended to avoid short circuits and unwanted reoxidation of the aluminum formed, which may otherwise occur if the distance between the molten aluminum layer and the anode is set too low.
• the distance between the molten aluminum and the anode can be reduced, so that the ohmic losses occurring in the intervening layer of cryolite-containing melt and thus the specific energy consumption can be reduced with this arrangement.
• the wave formation in the molten aluminum can only be reduced to some extent, so that there is still a relatively high specific energy consumption of the assembly during the electrolysis operation.
• equalization of the current density distribution takes place from the inhomogeneous current density distribution in the cathode block, which means that current vectors occur in the aluminum layer, away from the long side ends of the cathode block to the center of the cathode block Cathode blocks out and thus oriented in the horizontal direction.
• These horizontally directed current vectors in the aluminum melt caused by the uneven current density distribution in the cathode block cause increased electromagnetic interactions on the aluminum material, which in turn contribute to increased wave formation and thus counteract the purpose of surface profiling.
• the inhomogeneous current density distribution in the surface profiled cathode block leads to a reduced service life of the cathode block, since the inhomogeneous current density distribution causes very high current densities in certain areas of the cathode block, which in turn causes increased wear of the cathode block by electrochemical reactions in these areas.
• WO 2007/1 18510 A2 has proposed a cathode assembly having a cathode block in which the groove provided in the cathode block for receiving a bus bar has a depth varying over its length, wherein the depth of the groove, viewed in the longitudinal direction of the cathode block, increases from the edge regions to the center of the cathode block.
• the busbar is encased in a conventional manner with cast iron, this enclosure is done by pouring liquid cast iron in the space between the groove and the busbar.
• the energy efficiency of the cathode blocks described in this document is comparatively low and therefore in need of improvement.
• the object of the present invention is therefore to provide a cathode assembly which, when used in a fused-salt electrolysis in an electrolytic cell, causes an increased energy efficiency and at the same time, even if it is constructed on the basis of graphite, an increased wear resistance over the Melting flux electrolysis prevailing abrasive, chemical and thermal conditions.
• this object is achieved by a cathode arrangement for an aluminum electrolysis cell having at least one cathode block based on carbon and / or graphite, which has an at least partially profiled surface and at least one groove, wherein in the at least one Groove is provided at least one bus bar, and wherein the at least one groove has a varying depth over its length.
• providing a variable depth groove in a surface profiled cathode block minimizes waviness in the molten aluminum, and therefore the distance between the molten aluminum layer and the anode can be further reduced, thereby providing a electrolysis operation higher energy efficiency can be achieved.
• the present invention provides a cathode assembly having improved energy efficiency in electrolysis operation and increased wear resistance. It is of particular advantage in this case that the advantageous effects can be achieved by technically simple and cost-implementable measures.
• the total ground voltage measured between the end of the power supply bar and the cathode block surface can be kept approximately constant, which is the case in other constructions, such as that described in WO 02/068723 A1. not the case.
• a cathode arrangement is understood to mean a cathode block having at least one groove, wherein in each of the at least one groove at least one conductor rail possibly having a cast iron envelope is accommodated.
• this term refers to an arrangement of several, each having at least one groove having cathode blocks, wherein in each of the at least one groove at least one possibly a cast iron casing having bus bar is added.
• the at least one groove, with respect to the longitudinal direction, in its center has a greater depth than at its two longitudinal ends.
• the cathode arrangement according to the invention may have at least one groove for receiving in each case at least one bus bar, wherein preferably each slot has a depth varying over its length.
• the cathode arrangement according to the invention is particularly suitable for the use of conventional groove and / or busbar cross-sections.
• the groove and / or the busbar may have a substantially rectangular cross-section in a conventional manner.
• the busbar may in particular also consist of steel in a conventional manner.
• the cathode block has an at least partially profiled surface.
• a profiled surface is understood here to mean a surface which has at least one depression and / or elevation extending in the transverse direction, in the longitudinal direction or in any other direction, for example in a direction extending at an acute or obtuse angle to the longitudinal direction, of the cathode block wherein the indentation, as distinct from a surface roughness, seen transversely to the cathode block surface, has at least a depth or height of 0.05 mm and preferably of 0.5 mm.
• the at least one depression of the cathode block will be limited in practice by two side walls and a bottom wall.
• the bottom wall of the at least one recess of the cathode block viewed in the height direction of the cathode block, at least substantially exactly above the at least one bus bar, wherein the bottom wall of the at least one depression the busbar over at least 60%, preferably over at least 80% and especially preferably covers 100% of the width of the bus bar measured in the transverse direction of the cathode block.
• the at least one recess and the at least a busbar in this embodiment viewed in the height direction of the cathode block, so arranged opposite to each other, that the bottom wall of the recess completely or at least largely covers the busbar.
• the busbar comprises a cast iron envelope
• the at least one depression preferably covers the busbar, including the width of the surrounding cast iron envelope, at least 60%, preferably at least 80% and particularly preferably 100%.
• the at least one depression it is possible for the at least one depression to extend only over part of the length of the cathode block.
• the depth and / or width of the at least one recess varies over the length of the cathode block.
• the geometry of the recess can vary over the length of the cathode block.
• a depression of the cathode block extends over a part or essentially the entire length of the cathode block at least approximately parallel to the conductor rail.
• the at least one depression and / or elevation, seen in the transverse direction of the cathode block can have any desired geometry.
• the at least one recess or elevation, seen in the transverse direction of the cathode block convex, concave or polygonal, such as trapezoidal, triangular, rectangular or square, may be formed.
• the surface profiling comprises at least one depression, the ratio of depth to width of the at least one depression being 1: 3 to 1: 1 and preferably 1: 2 to 1: 1.
• the depth of the at least one recess is 10 to 90 mm, preferably 40 to 90 mm and particularly preferably 60 to 80 mm, for example about 70 mm.
• the width of the at least one recess is 100 to 200 mm, more preferably 120 to 180 mm and most preferably 140 to 160 mm, such as about 150 mm.
• the surface profiling comprises at least one projection
• the height of the at least one elevation is 10 to 150 mm, preferably 40 to 90 mm and particularly preferably 60 to 80 mm, for example about 70 mm.
• the width of the at least one protrusion is 50 to 150 mm, more preferably 55 to 100 mm and most preferably 60 to 90 mm, such as about 75 mm.
• the at least one elevation viewed in the longitudinal direction of the cathode block, extends only in regions.
• the at least one protrusion extend the entire length of the cathode block to achieve the effect of reducing or completely reducing waviness of the molten aluminum.
• the height and / or width of the at least one bump varies over the length of the cathode block.
• the geometry of the survey can vary over the length of the cathode block.
• the ratio of the width of the at least one recess to the width of the at least one projection is preferably 4: 1 to 1: 1, such as about 2: 1.
• the present invention is not limited. Good results are obtained, for example, when the cathode block has in its transverse direction 1 to 3 wells and preferably 2 wells.
• the cathode block contained in the cathode assembly is composed of carbon and / or graphite, i. the cathode block contains amorphous carbon, graphite or a mixture of amorphous carbon, graphitized carbon and / or graphitic carbon.
• the cathode block may optionally contain carbonized and / or graphitized binder, such as pitch, in particular coal tar and / or petroleum pitch. If pitch is mentioned below, it means all pitches known to those skilled in the art.
• the cathode block of the cathode arrangement according to the invention contains as carbon exclusively graphitic and / or graphitized carbon or a mixture of graphitic carbon with amorphous carbon. If a mixture of graphitic or graphitized carbon and amorphous carbon is used, this mixture contains preferably 10 to 99 wt .-%, particularly preferably 30 to 95 wt .-% and most preferably 60 to 90 wt .-% graphitic or graphitized carbon. If graphitic carbon is included in the mixture, it may be both natural graphite and synthetic graphite.
• the starting material for amorphous carbon is preferably anthracite, which is then used at a temperature of 800 and 2200 ° C. and especially preferred. kart between 1 .200 and 2,000 ° C is calcined.
• the preparation is carried out so that a mixture of particulate anthracite and coal tar pitch as a binder is brought into a mold and this is then compacted into a green body before the green body by a heat treatment at a temperature of, for example, 1, 000 to 1, 300 ° C is carbonized.
• cathode block for a cathode assembly of an aluminum electrolytic cell based on carbon and / or graphite, which has an at least partially profiled surface and at least one groove for receiving a busbar, wherein the groove has a varying depth over its length having.
• a cathode block can be advantageously used as part of the previously described cathode arrangement.
• the cathode block may be based on amorphous carbon, graphitic carbon, graphitized carbon or any mixture of the above carbons, with graphitic carbon and in particular graphitized carbon being particularly preferred.
• FIG. 1 shows a schematic cross section of a section of a
• Aluminum electrolytic cell comprising a cathode assembly according to an embodiment of the present invention
• FIG. 2 shows a longitudinal section of the cathode arrangement of the aluminum electrolysis cell shown in FIGS. 3A to 3E each show a schematic cross section of the surface profiling of a cathode block according to other embodiments of the present invention.
• FIG. 1 shows a cross-section of a section of an aluminum electrolysis cell 10 with a cathode arrangement 12, which at the same time forms the bottom of a trough for aluminum melt 14 produced during operation of the electrolysis cell 10 and for a cryolite-aluminum oxide located above the aluminum melt 14 Melt 16 forms.
• the cryolite-alumina melt 16 is an anode 18 of the electrolytic cell 10 in contact.
• the trough formed by the lower part of the aluminum electrolytic cell 10 is limited by a lining of carbon and / or graphite, not shown in FIG. 1.
• the cathode arrangement 12 comprises a plurality of cathode blocks 20, 20 ', 20 ", which are connected to one another via a ramming mass 24, 24' inserted into a ramming mass gap 22, 22 'arranged between the cathode blocks 20, 20', 20".
• the anode 18 includes a plurality of anode blocks 26, 26 ', with the anode blocks 26, 26' being each about twice as wide and about half as long as the cathode blocks 20, 20 ', 20 ", with the anode blocks 26, 26' being such arranged above the cathode blocks 20, 20 ', 20 "such that one anode block 26, 26' in width covers two adjacent cathode blocks 20, 20 ', 20" and one cathode block 20, 20', 20 "in length two adjacent anode blocks 26, 26 'covers.
• Each cathode block 20, 20 ', 20 has a profiled surface, wherein in each cathode block 20, 20', 20" two in cross-section substantially rectangular recesses 34, 34 'are provided, which are separated by a survey 36.
• Each recess 34, 34 ' is bounded by a bottom wall 33, 33' and two side walls 35, 35 '.
• the bottom walls 33, 33 ' are parallel to the transverse direction of the cathode block 20'.
• the width of the depressions 34, 34 ' is 150 mm in each case and the depth of the depressions 34, 34' is 70 mm in each case
• the elevation 36 has a width of 75 mm and a height of 70 mm. Both the corners in the two recesses 34, 34 'and the corners of the elevation 36 are each rounded off with a radius of 20 mm.
• each cathode block 20, 20 ', 20 "on its underside in each case two grooves 38, 38', each having a rectangular, namely substantially rectangular cross-section, wherein in each groove 38, 38 'in each case a busbar 40, 40' made of steel a likewise rectangular or substantially rectangular cross-section is added.
• the gap between the busbar 40, 40 'and the groove 38, 38' is in each case cast with cast iron 44, 44 '.
• the recesses 34, 34 ' seen in the height direction of the cathode block 20', are exactly above the respective associated busbar 40, 40 ', so that the bottom walls 33, 33' cover the respective busbars 40, 40 'including the surrounding cast iron sheath 44, 44' over their full width.
• the energy efficiency of the electrolysis operation is further increased because a good electrical conductive path between the busbar and the molten aluminum layer is provided, along which the electric current only a minimum distance in the electrically relatively poorly conductive cathode block must cover.
• the current efficiency of the cathode arrangement is further increased.
• the cross section of the cathode assembly 10 is shown at one longitudinal end of the cathode block 20, 20 ', 20 "in Fig. 1.
• the depth of the grooves 38, 38" of the cathode block 20, 20', 20 varies over the length of the grooves 38, 38 ".
• the groove cross-section in the region of the center of the groove 38, 38 " is indicated by a dashed line 46, 46 'in Fig. 1.
• the width 48 of each groove 38, 38 ' is substantially constant over the entire groove length and is about 15 cm, whereas the width 50 of the cathode blocks 20, 20', 20 "is about 65 cm is.
• FIG. 2 shows a longitudinal section of the cathode block 20, 20 ', 20 “shown in FIG. 1.
• the groove 38, 38' viewed in its longitudinal section runs to the center of the cathode block 20, 20 '. 20 "in the shape of a triangle, thereby ensuring a substantially uniform electrical vertical current density over the entire cathode length.
• the bus bar 40, 40 ' which is not shown in FIG.
• busbar 40, 40 'could which has a substantially constant distance from the groove bottom and in particular in its longitudinal section to the triangular course of the groove 38, 38' is adjusted.
• both the grooves 38, 38 'and depressions 34, 34' are applied to the top of the cathode blocks 20, 20 ', 20 "during the molding process, such as by vibration molding and / or stamping.
• FIGS. 3A to 3E show examples of different configurations of the depressions 34, 34 'and the elevations 36 of the surface profiling of the cathode blocks 20, 20', 20 ", namely, in cross section, rectangular with rounded corners (not shown) (FIG. Fig. 3A), substantially undulating (Fig. 3B), triangular (Fig. 3C), convex (Fig. 3D) and sinusoidal (Fig. 3E), with the rectangular and wavy surface profilings of Figs. 3A and 3B respectively by a bottom wall 33, 33 'and two side walls 35, 35' limited recesses 34, 34 'have.

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• Organic Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)

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• 2011
  • 2011-02-11 DE DE102011004010A patent/DE102011004010A1/de not_active Withdrawn
• 2012
  • 2012-02-06 CN CN2012800086355A patent/CN103403227A/zh active Pending
  • 2012-02-06 CA CA2826328A patent/CA2826328A1/fr not_active Abandoned
  • 2012-02-06 EP EP12702044.4A patent/EP2673397A1/fr not_active Withdrawn
  • 2012-02-06 WO PCT/EP2012/051965 patent/WO2012107403A1/fr active Application Filing
  • 2012-02-06 RU RU2013141552/02A patent/RU2013141552A/ru not_active Application Discontinuation

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