Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
  • C25C7/02—Electrodes; Connections thereof
• • 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 electrolysis cell, a cathode block for such a cathode assembly, and a method of manufacturing such a cathode assembly.
• 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 cathode assemblies used in the Hall-Heroult method is their relatively low wear resistance, which manifests itself by a removal of the cathode block surfaces during the electrolysis.
• the removal of the cathode block surfaces due to an inhomogeneous current distribution within the cathode blocks is not uniform over the length of the cathode blocks, but to an increased extent at the cathode block ends, so that the surfaces of the cathode blocks change after a certain electrolysis time to a W-shaped profile. Due to the uneven removal of the cathode block surfaces, the service life of the cathode blocks is limited by the places with the largest removal.
• WO 2007/1 18510 A2 proposes a cathode block whose groove, which is intended to receive a conductor rail, has a greater depth in the middle, relative to the cathode block length, than at the cathode block ends.
• Another disadvantage of the cathode arrangement used in the Hall-Heroult process is its comparatively high electrical resistance.
• One of several reasons for the comparatively high electrical resistance is that the contact resistance between the bus bars and the cathode blocks of the cathode is comparatively high, and this contact resistance also increases with increasing service life of the cathode.
• the graphite foil reduces the electrical contact resistance between the busbar or the surrounding layer of solidified cast iron and the cathode block due to their good two-sided positive locking
• the graphite foil due to their elasticity in particular reduces the increase of this contact resistance with increasing operating time of the cathode, because the graphite foil filling gaps formed between the walls of the cathode block and the bus bar during the creeping of the steel of the bus bar and the carbon of the cathode block.
• graphite foils have a smooth and very lubricious surface.
• graphite foil is not or only to a very limited extent connectable with cast iron, so that a pouring of the gap between busbar and graphite foil with liquid cast iron and a subsequent hardening or solidification of the cast iron not to a compound of graphite foil with the cast iron, but only a cladding of the busbar with cast iron leads.
• a cathode arrangement for an aluminum electrolysis cell having at least one cathode block based on carbon and / or graphite, which has at least one groove lined at least in regions with a graphite foil, wherein at least one bus bar is provided in the at least one groove, which at least partially has a casing made of cast iron, wherein in the at least one groove bounding wall of the cathode block at least one recess is provided and engages the casing of cast iron at least partially into the at least one recess.
• This solution is based on the recognition that a precisely fitting and in the direction perpendicular to the longitudinal direction of the cathode block displacement positive connection of a busbar with a graphite foil lined groove having cathode block is achieved if provided in at least one groove defining wall of the cathode block at least one recess is introduced and at least partially covered with cast iron busbar so in the groove that the casing of cast iron engages at least partially into the recess.
• the cathode assembly according to the invention has the advantage of improved current transfer between the bus bar and the cathode block and thus improved energy efficiency due to the electrical and mechanical properties of graphite foil with the lining of the groove with graphite foil, while avoiding the associated with the high lubricity of graphite Disadvantage of an uncontrolled mobility of the busbar in the groove in the direction perpendicular to the longitudinal direction of the cathode block and a concomitant possible impairment of the electrical connection between the busbar and the cathode block during prolonged operation of the electrolysis cell.
• the present invention makes it possible to use the lubricious properties of the graphite foil specifically to selectively ensure a longitudinal displacement of the busbar in the groove, especially in movements caused by temperature changes during startup.
• the cathode arrangement according to the invention with the advantages described above can be produced with extremely little effort and without expensive additional process steps.
• the proposed mechanical connection between the busbar and the cathode block can be achieved simply by filling a depression of the cathode block at least partially with the cast iron in the course of the already required potting of the busbar with the cast iron.
• a very intimate contact between the busbar, the casing of cast iron, the graphite foil and the cathode block is achieved, which contributes to a particularly low electrical contact resistance between the busbar and the cathode block.
• the graphite foil absorbs the mechanical pressure occurring during the operation of the cathode arrangement perpendicular to the film plane.
• a recess is defined as a recess, in contrast to a mere surface roughness, which has a depth of at least 0.05 mm, and preferably 0.5 mm, relative to the surface of the wall delimiting the groove.
• a graphite foil in the sense of the present invention does not only mean thin graphite sheet, but in particular also a partially compressed preform or a flexible sheet of expanded graphite.
• 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 casing of cast iron can be in direct contact, at least in the region of the depression, with the graphite foil or with the cathode block itself. Although this is preferred according to the present invention, this is not mandatory.
• the casing of cast iron at least partially engages in the at least one recess, so at least partially fills the cavity formed by the at least one recess.
• the portion of the cast-iron casing, which engages in the at least one depression is designed to be complementary to the depression. In this way, a particularly good form-locking engagement of the cast iron casing in the depression and thus a particularly effective mechanical attachment of the cast iron casing and the associated busbar to the cathode block can be achieved.
• the at least one recess engaging portion of the envelope and possibly the sheathed busbar at least 70%, preferably at least 80%, especially preferably at least 90%, most preferably at least 95% and most preferably 100% of the well fills.
• each of the at least one recess extends continuously over at least 20%, preferably over at least 40%, more preferably over at least 60%, most preferably over at least 80% and most preferably at least approximately over the entire length of the groove.
• a possible slipping out of the busbar can be prevented from the groove during assembly.
• the recess extends over a considerable part of the groove length as described above, good slidability of the bus bar in the longitudinal direction of the groove can be ensured while still reliably preventing unwanted displacement of the bus bar parallel to the depth direction of the groove.
• the cathode block can also have a multiplicity of depressions which follow one another in the longitudinal direction of the groove and which are separated from one another by depression-free sections of the groove. This embodiment is particularly especially advantageous if a longitudinal displacement of the busbar in the cathode block is not desired.
• the at least one depression preferably has a depth of 2 mm to 40 mm, more preferably 5 mm to 30 mm and most preferably 10 mm to 20 mm.
• the at least one recess preferably has an opening width of 2 mm to 40 mm, particularly preferably 5 mm to 30 mm and very particularly preferably 10 mm to 20 mm, based on the height of the cathode block.
• the at least one depression in cross-section preferably has an area of 1.5 mm 2 to 1.600 mm 2 , particularly preferably 10 mm 2 to 900 mm 2 and very particularly preferably 40 mm 2 to 400 mm 2 , These values are particularly preferred for wells with a polygonal and especially with a rectangular cross-section. If the at least one depression has a curved cross section, such as a substantially semicircular cross section, the at least one depression in cross section preferably has an area of 1.5 mm 2 to 630 mm 2 , particularly preferably 10 mm 2 to 350 mm 2 and most preferably from 40 mm 2 to 160 mm 2 .
• the at least one recess can have any polygonal or curved cross section.
• Good results in terms of a good positive engagement of the cast iron casing in the at least one depression and at the same time with regard to a reliable and unproblematic Brownier- the recess with cast iron during the casting are achieved in particular if the at least one depression has an at least substantially semicircular, triangular, rectangular or trapezoidal cross-section.
• the at least one recess extends substantially perpendicularly into the wall of the cathode block delimiting the groove. In this way, a particularly reliable fixing effect in the depth direction of the groove is effected.
• the at least one depression viewed in the depth direction of the groove, is delimited at each of its ends by a transitional area between the depression and an adjoining portion of the groove wall.
• the angle between the adjacent portion of the groove wall and the wall of the depression, viewed from the cathode block inner side is preferably 90 degrees to 160 degrees, more preferably 90 degrees to 135 degrees, and most preferably 100 degrees to 120 Degree.
• the radius of curvature of the transition region is preferably at most 50 mm, more preferably at most 20 mm and most preferably at most 5 mm.
• the groove bounding wall comprises a bottom wall and two side walls, each side wall each having at least one, preferably a recess extending perpendicularly to the surface of the respective side wall.
• a two-sided mounting of the busbar is achieved in the groove, whereby the busbar is particularly effective in the desired position can be fixed.
• a plurality of, for example per side wall at least 1, at least 2, at least 3 or at least 4 recesses may be provided, in each of which the enclosure the busbar made of cast iron engages at least in sections.
• the depth and / or the volume of the individual depressions is lower, the more depressions are provided in the groove.
• the at least one recess has over its length an at least substantially constant distance to the bottom wall of the groove and extends parallel to this.
• a displaceability of the busbar is ensured parallel to the groove bottom.
• each of the at least one recess is at least partially and preferably fully lined with the graphite foil, wherein of course preferably also the remaining areas of the groove are fully lined with the graphite foil.
• a displaceability of the busbar in the longitudinal direction of the at least one depression and thus in the longitudinal direction of the cathode block as described above can be ensured if a majority of the surface and preferably at least approximately the entire surface of the wall delimiting the groove Graphite foil is lined.
• the graphite foil can be pressed by the sheathing of the busbar made of cast iron against the boundary of the recess to cause both a particularly good electrical contact and a particularly effective positive locking. This effect is particularly useful when heating the electrolysis cell for commissioning, since the specific thermal expansion of steel or iron is about three times the specific thermal expansion of conventional cathode materials.
• the lining of the at least one recess of the groove with the graphite foil can be achieved in the manufacture of the cathode assembly in a simple manner that the graphite foil is inserted into the groove so that it fills the depression, and then the cast iron is poured into the groove in that the graphite foil is pressed into the depression and in particular pressed directly there against the cathode block material delimiting the depression.
• the at least one groove has a varying depth along its length or the length of the cathode block, it being particularly preferred that these be based on the Longitudinal direction, in its center has a greater depth than at its two longitudinal ends.
• the practically unique cross-sectional shape for the groove is rectangular, and therefore the effect of the present invention, namely reliable avoidance of the bus bar falling out of the slot opening, is particularly pronounced here.
• the cathode block has a groove of varying depth
• the at least one recess of the cathode block is preferably formed to have a substantially constant distance from the bottom of the groove over the length of the groove so as to have If necessary, to move the busbar along the longitudinal direction of the cathode block.
• the cathode arrangement according to the invention is also particularly suitable for the use of conventional groove and / or busbar geometries.
• the groove and / or the busbar may have a substantially rectangular cross-section in a conventional manner. This is particularly preferred when the groove has a depth varying in the longitudinal direction.
• the busbar may in particular also consist of steel in a conventional manner.
• the graphite foil lining the groove at least in regions contains expanded graphite and in particular preferably compressed expanded graphite, which is particularly preferably binder-free.
• the graphite foil lining the groove at least regionally consists of expanded graphite and particularly preferably compressed binder-free expanded graphite.
• the film may in principle also be formed by a substantially plate-shaped preform which contains expanded graphite and thereby has sufficient elasticity to be elastically deformed so as to permit the above-described filling of the recess by the cast iron envelope and thereby into the recess between the cast iron and the wall bounding the groove.
• the graphite content of the graphite foil is at least 60%, more preferably at least 70%, particularly preferably at least 80%, particularly preferably at least 90% and very particularly preferably at least approximately 100%.
• the graphite foil has a thickness between 0.2 mm and 3 mm, preferably between 0.2 mm and 1 mm and particularly preferably between 0.3 mm and 0.5 mm.
• the graphite foil can be inserted or glued into the groove.
• An adhesion of the graphite foil into the groove is particularly preferred if the graphite foil is pressed against the surface of the depression only comparatively little or if even the slightest displacement of the graphite foil in the longitudinal direction of the cathode block is to be avoided.
• the cathode block has one or two grooves for receiving in each case at least one bus bar.
• a groove of the cathode block can accommodate exactly one busbar, but in particular also two busbars which are inserted into different longitudinal sections of the slot.
• the busbars can be arranged opposite one another on the front side.
• Another object of the present invention is a cathode block for a cathode assembly of an aluminum electrolytic cell based on carbon and / or graphite, which has at least one groove for receiving a bus bar, wherein provided in the at least one groove defining wall of the cathode block at least one recess is.
• a cathode block can be used with advantage 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.
• the present invention relates to a method for producing a cathode arrangement for an aluminum electrolysis cell, which comprises the following steps:
• the graphite foil located in the groove Due to the static pressure of the cast iron column, the graphite foil located in the groove is forced into the at least one depression, where it is pressed against the cathode block defining the at least one depression, in particular. In this way, it is particularly easy to produce a cathode arrangement with a recess which is partially or completely lined by the graphite foil and has a particularly low electrical contact resistance between the conductor rail and the cathode block.
• the different thermal expansion tions of steel or iron and cathode material reaches a particularly intimate contact.
• the graphite foil can be inserted and / or glued into place prior to insertion of the busbar.
• a loose insertion of the graphite foil in the groove may be sufficient as a prefixing, since the graphite foil is preferably pressed by the cast iron during casting onto the at least one wall of the cathode block delimiting the groove.
• a carbonaceous or graphite-containing starting material or a mixture of several such materials can be brought into a mold and then compacted to form a green body.
• the starting materials are preferably present in particulate or granular form.
• the green body can be heated while carbonized and optionally graphitized.
• both carbonized cathode blocks which are understood to mean those cathode blocks which have been subjected to a temperature treatment of up to a maximum of 1, 500 ° C. and preferably between 800 and 1 200 ° C.
• cathode blocks which are understood as those cathode blocks, which have been subjected to a temperature treatment of more than 2,000 ° C and preferably between 2,300 and 2,700 ° C in their preparation and have a high proportion of graphitic carbon.
• cathode blocks based on graphitic carbon can be used, that is, those which have not been graphitized, but have been added with graphite as the starting material.
• carbonized cathode blocks for example, a mixture of calcined anthracite, graphite and hard coal and / or Petroleumpech is used, whereas graphitic cathode blocks, for example from a mixture containing graphite and coal and / or petroleum pitch.
• graphite refers here to both natural and synthetic graphite.
• the starting material containing carbon and / or graphite is introduced into a mold which has a projection which is complementary to the at least one recess.
• the at least one recess can be produced by subsequently removing and / or displacing cathode block material of the at least one wall of the cathode block delimiting the groove.
• the recess can be subsequently introduced by a milling process, wherein a milling head used for introducing the depression preferably has a cross section corresponding to the recess.
• Another object of the present invention is a cathode assembly, which is obtainable by a method as described above.
• FIG. 1 is a cross-sectional view of a portion of an aluminum electrolytic cell having a cathode assembly according to an embodiment of the present invention
• Fig. 2 is a longitudinal section of the cathode assembly shown in Fig. 1
• 3a-d are exemplary cross-sections of depressions, which are provided in a groove of a cathode block according to the invention.
• FIG. 1 shows in cross-section 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 an aluminum melt 14 produced during operation of the electrolysis cell 10 and for a cryolite present above the aluminum melt 14.
• Alumina melt 16 forms. With the cryolite-alumina melt 16 is an anode 18 in contact. Laterally, 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, which are each connected to one another via a ramming mass 24 inserted into a ramming mass gap 22 arranged between the cathode blocks 20.
• a cathode block 20 in this case comprises two grooves 26 arranged on its underside and having a rectangular, namely substantially rectangular cross section, wherein in each groove 26 in each case a bus bar 28 made of steel with likewise rectangular cross section is accommodated.
• Each of the groove 26 delimiting wall 32, 34 is lined by a dashed lines in Fig. 1 graphite foil 30 shown.
• the grooves 26 are each bounded by two side walls 32 and a bottom wall 34 of the cathode block 20, wherein in each of the side walls 32 is provided a substantially perpendicular in the side wall 32 extending recess 36 having an approximately semicircular cross-section.
• Each recess 36 is bounded by an upper and a lower transition region 37 of the cathode block 20, respectively.
• the transition regions 37 are in the present Embodiment angularly formed at an angle ⁇ between the adjacent portion of the groove wall and the wall of the recess of 90 degrees.
• the gap between the busbar 28 and the lined with the graphite foil 30 groove 26 is in each case cast with cast iron 38, so that the graphite foil 30 is fixed between the cast iron 38 and the cathode block 20.
• the graphite foil 30 is pressed by the cast iron 38 against the respective groove 26 bounding walls 32, 34.
• the recesses 36 are each lined by the graphite foil 30, wherein the cast iron 38 form-fittingly fills the lined depressions 36 and presses the graphite foil 30 against the cathode block 20 delimiting the depression 36. In this way, over the entire cross section of the groove 26, a low electrical contact resistance between the bus bar 28 and the cathode block 20 is ensured.
• the cast iron 38 forms a sheath 39 for the busbar 28 and communicates with the busbar 28 in material connection.
• the received in the wells 36 cast iron 38 forms with the recess 36 delimiting material of the cathode block 20 each have a positive connection, which prevents movement of the connected to the cast iron 38 busbar 28 in the direction of the arrow 40. An unwanted movement of the bus bar 28 in the depth direction of the groove 26 or even falling out of the bus bar 28 from the groove 26 are prevented.
• the cross section of the cathode assembly 10 is shown concretely at a longitudinal end of the cathode block 20.
• the depth of the grooves 26 of the cathode block 20 varies over the length of the grooves 26.
• the groove cross section in the region of the center of the groove 26 is indicated in Fig. 1 by a dashed line 42.
• the difference between the groove depth at the longitudinal ends of the groove 26 and in the middle of the groove 26 in the present embodiment is about 10 cm.
• the width 44 of each groove 26 is over the entire groove length in Essentially constant and is about 15 cm, whereas the width 46 of the cathode blocks 20 is about 65 cm each.
• a plurality of anodes 18 and a plurality of cathode blocks 20 are arranged one above the other so that each anode 18 covers two juxtaposed cathode blocks 20 and covers in length half of a cathode block 20, wherein each two juxtaposed anodes 18 the length of a Cover cathode block 20.
• FIG. 2 shows the cathode block 20 shown in FIG. 1 in longitudinal section.
• the groove 26 viewed in its longitudinal section extends towards the center of the cathode block 20 in the shape of a triangle, thereby ensuring a substantially uniform electrical vertical current density over the entire cathode length.
• the recesses 36 extend as indicated in FIG. 2 by a dashed line parallel to the groove bottom 34 and have over the length of the groove 26 at a constant distance from the groove bottom 34.
• bus bar 28 is bar-shaped in the present exemplary embodiment and has a rectangular longitudinal section, so that between the bus bar and the groove bottom 34 there is an intermediate space becoming larger towards the center of the groove 26 which may be filled either by cast iron 38 or by additional metal plates connected to the bus bar 28.
• a bus bar 28 could be used, which is adapted in its longitudinal section to the triangular course of the groove 26.
• FIGS. 3a to d show exemplary depressions 36, which are provided in a groove of a cathode block 20 according to the invention, in cross-section.
• the depressions 36 each have a substantially semicircular cross section (FIG. 3 a), a substantially trapezoidal cross section (FIG. 3b) or a substantially triangular cross section (Fig. 3c).
• the angle ⁇ of the transition regions 37 between the wall of the recess 36 and the adjacent portion of the groove wall 32, viewed from the inside of the cathode block 20, is approximately 90 degrees in FIG. 3a, approximately 120 degrees in FIG Fig. 3c about 125 degrees.
• FIG. 3 d shows an embodiment in which a plurality of recesses 36 with a triangular cross-section as shown in FIG. 3 c are arranged consecutively in the depth direction of the groove 26 in order to effect a particularly reliable support of an inserted bus bar 28.
• the transition regions 48 between two adjoining recesses 36 have between the walls of two adjacent recesses 36, seen from the inside of the cathode block 20, an angle ß of about 70 degrees.
• 3 a to d each extend perpendicularly into the side wall 32 of the cathode block 20 delimiting the groove 26 so that they form a fixation with cast iron received in the depressions 36 which is effective in the depth direction of the groove 26 and prevents unwanted movement of the bus bar 28 parallel to the depth direction of the groove 26 after casting the bus bar 28 with cast iron 38.

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• Electrolytic Production Of Metals (AREA)

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• 2011
  • 2011-02-11 DE DE201110004009 patent/DE102011004009A1/de not_active Withdrawn
• 2012
  • 2012-02-06 WO PCT/EP2012/051979 patent/WO2012107412A2/fr active Application Filing
  • 2012-02-06 CN CN2012800086302A patent/CN103429792A/zh active Pending
  • 2012-02-06 EP EP12702548.4A patent/EP2673400A2/fr not_active Withdrawn
  • 2012-02-06 CA CA 2825785 patent/CA2825785A1/fr not_active Abandoned
  • 2012-02-06 RU RU2013141549/02A patent/RU2013141549A/ru not_active Application Discontinuation
  • 2012-02-06 AU AU2012215568A patent/AU2012215568A1/en not_active Abandoned
  • 2012-02-06 BR BR112013020197A patent/BR112013020197A2/pt not_active Application Discontinuation
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