US2825690A - Self-baked annular anode for melting furnaces - Google Patents

Description

March 4, 1958 L. FERRAND fi fi SELF-BAKED ANNULAR ANODE FOR MELTiNG FURNACES Filed Feb. 3, 1956 I I I 1 1 I I United States Patent-O 'ance with Soderbergsprocess as known upzto the present, and making it possible to use large-diameter annular anodesawhile making it also possible to. design a furnace for use :in aluminum-production which is absolutely continuous in its" operation from the double point '-of view of metal tapping and-alumina supply.

A way" of achievingsuch an anode .will berdescribed hereinafter.

The description is concernedprincipally with the anode Patented Mar. 4, 1958 carbon pastetfillingiheiintervals'l -l :betweenthe several elementsaof the. structure; the metal framework :thus :pro- 2,825,690 -vided;being1 rigidlyconnected with the;furnacea metal framework which-howeverisysupported independently of :SELF-BAKED ANNULARTANODE FOR MELTING 52: thersubstructure.

FURNACES t uThevardal= chinlney 111 is perforated :over: the :.-second l 1 third-sof itsvheight-awith: vents :through .whichthe tar Loms Ferrand Pans France wapours-zrresulting from the: self-baking of, theitcarbon Application February 3,-19 ,-S Flo-5635393 m-:-:pastefilling can sber'suckediwith zelectrolytic: gasesstby the v i a s V eaction rof'zaavacnumzcreated: in stride-chimney; .Depend- Clmmspnonty apphcahon France April 181951 iHg-zfl'OXRZthi COVfiIs 18 .WhiChi is'csecured in fillidr'tight fi claims. (Cl; 2041-4228) manner-rte itheraxialxchimney; llsis asheat recuperatori22 -:-composed:;'ofvertical. tubes and designed .to recover. the :sehsible'eheatdnkthe cgas'esefrom zithfiifikCtITOlYtitPTOCfiSS, My invention relatestoaself-baked :anode'for use in u-exclusiue2of :the iheatzrayszemanatingzfrom theifree surthCJCOIIfiIILIOUSTKHd: automaticioperation of' ifurnaces for :fa'ce:17 of rthe;:rne'lt;; owingito:the pr'ovision ofa polished Y P 0f 'metalsimoiablysof'ialumistainlessssteel refiectorfifi' witht'zazparabolic:generatrixfby -num,by the :dry process tandzis' intendedtto'remedy the rwhicha saidzsrays: are reflected '%'.back.'-:onto:said'fsurface; inconveniences. inherent to self-baking anodes in accord- :;said parabolict-refiectonbeing-:secured to the .tube bundle in such a manner that its focus 3liiszsuhstantiallycoin- "cidentm'ith' tlm freei SUIfHCfiIOf the melt 17.

1 r; The:ivariouszasectoreshapedeor;:prismatic: block sets 'thus J; constituted; which i are :xassumed ato "be: three in number :?inithe examp lezillustrated; and :reach layer of these blocks asuspended' frornaaz separate ringrwith the aidofsivertistructureitself, the way in which it is built and the carrying ont of the electrolytic'process; exclusive of the means by 'Whichdh'ehnode is suspendedand the current distributed,"which means*are well-known and need not be 7 are atttachedzeach'atolone ofithreerings 40,141' 542 rigid rrespeetively with :radial larms .43; 244-1and .45'sat :theeends 'coflwhichitheaintensit'y 0f the :cnrrent fed -thereto can -be 1 represented in any great detail.

Figure 1 illustrates an embodiment of an electrolytic furnace in half-elevational and half-sectional views.

1 Figure 2 illustrates the same furnace with theone half in top plan view and the other ha-lf in a horizontal secascertained by thezmeasurementrof the voltage drop be- :tween two equidistantpoititseSG-Jand 5-1.: The. ends of fed-thereto; and-consequently to'=set the current :density for each layer at 'any desired valueiand toensurent-hat Figure 3 diagrammatically represents the three-thermo- 1 ele'ctndcouples adapted'to govern the temperature, and

th'eway in which they are connected difire'ntially. --Il1'e smallestcircles in the left half of Fig. 2"represents suspension or distribution studs which are-'notsho'wn in Fig? l in order' to make itmore easily readable.

The-furnaceillustrated, which isintended more-specifically for the electrolytic production of aluminum, is compjrisedprimarilyof a'sub'structurerestedon the ground and compo'sed in its-turn of-a sheet metal shell L afirst heat-insulating kieselguh'r lining 2; a second refractory lining-3; an inner amorphous'carbonlining4 sp'ace'dfrom the latter with a view to making it fluid-tight with the aid-of str'ongly' tampedcarbon paste s; and delimiting an inn'cr elaboration chamber 6 having suitably" shaped si'cl'e =wall's -ada pted to contain the-molten salt mixture serving' in theelaborationof the metal and on the bottom '-of'whicli "rests the metal layer 7"which covers thenonconductive carbon sole-which-is integral with the carbon lining 4; I

The metal layer 7 which provides'the 'liquid'cath'o'de is conductivelys connected with the steel negative polepieces SthrQugh-ClianneIs 9 provided in a well-known manner Within the refractory lining 3.

" "According to my invention; the fnrnacesuperstruct ure "providing theanode u'nitis comprised of-afixedcylindritahshellldmade of suitably reinforced steel;a-vertical axial stainless steel chimney 11 arranged'concentric with said shell; cylindrical metal partitions '12 arranged likewise concentric with said chimney and spaced at' distimes from one'another which increase from the outside towards the centre, radial bracing webs 13 between each; pairof the aforesaid partitions and agglomeratedv in the axial chimney than'at-IG in the peripherai region. According to inyin'ventihn, in -order-' toptovidefor the supply' ofalumina where an"anode-of-the kinddescribed is used; supply hoppers "21 are provided at the periphery of the anode mass which communicatewith dischargetubesiii issuing at 49 under the burntportion 14b-'of the block The-alumina falls freely-through tubes 20 only of the block I near the-casing -10'as a 'result' of thedifierence in-the pressures prevailing-"in the tubes 20 and "in the supply hoppers -21 'thereabove' and is entrained into-the-melt-by"-means of the gas bubbles which are let' thereintmafa rate ';orfrequency which depends'onthe gas pressure; Itisobvious thafasthe outer casing '10 is fixed; th'e'itubes'w rigidtherewith' are alsofixedl These tubesha'vetheir lower-ends flush 'with theloweredges ofgthe' casings 10, 11; lzalong a easily.

plastic material (see fine-squared portion 14a) is progressively baked as the temperature increases towards the bath, until the carbon becomes solid (see larger squares 14b) and becomes anintegral part of the rods .15 "by adhering strongly thereto, so that when thesero ds are pulled or pushed it is possible to move the carbonated masses I, II, III upwards or' downwards. It is evident;

that these carbonated masses of layer I, by sliding in most 'centage of dissolved alumina in the melt shall decrease towards the centre from a maximum which corresponds to the lowest melting point of the melt, in order to prevent the same from coagulating in the peripheral region, down M to a minimum which is close to zero in the central region, which together with the higher temperature'prevailing' in the said central region favours the obtainment of a high conductivity of the melt in the said region, as

required in view of the larger interpolar distance of the central annular mass.

The alumina is led into the said hoppers 21 pneumatically through a manifold 33 while a pressure is maintained in said hoppers through a manifold 34 connected with the delivery side of the exhauster through a pressurev regulator, which means that a certain yet very small amount of the gases from the electrolysis is, recycled. The gases of electrolysis raise at the contact with the faces14c of the anodes and are withdrawn by the action the surface of the bath 17 and are cooled prior to being exhausted at 48 by circulating in the direction of the dotted arrows around the recuperator 22 cooled by 'a fluid streaming through the conduit 47 and ,leaving through conduit 35 in the direction of the full line arrows.

In adjusting the current densities through the .various annular concentric anode masses it is necessary to account for the differences that may exist between the temperature of the interpolar layer of the melt and the temperatures on the one hand of the bottom metal layer providing the cathode and the top-layer of the melt within the axial chimney.

With this end in view, according to my invention, an

intermediate thermo-couple t immersed through the protective alumina layer in the melt 6' and located just.

' asaaeso said pole pieces 8, so that't shall at all times. be less than t by ten odd degrees centigrade, t t is adjusted g in such a manner that t;; shall at all times be higher than 2 by about to 40 degrees depending on the value assigned to 1 and this, by suitably setting the current intensities 1 I l 'of' each layer I, II, III so that a the best physico-chemical conditions (density, conduc-v tivity, viscosity of the melt) adapted to'eo'ntribute' to the obtaining of the highest efiiciencyof the electrolysis.

What I claim is: 1. In a cell for the electrolytic production of metals 4 'and more particularly'of aluminum, said cell comprising a carbon pan adapted to'contain a salt melt and a subjacent body of metal constituting one pole of the cell; a wall structure surrounding said pan, and at least one negative cathode contact fixedly secured within a cavity filled of the'same metal in said wall structure beyond the outer periphery of said pan, and in communication with said pan, the improved means comprising a self: baked annular anode arranged to dip into thesalt melt contained in said cell, a fixed cylindrical metal casing surrounding said annular anode, a vertical cylindrical chimneyarranged coaxially within the innermost anode,

cylindrical metal partitions arranged between said casing and said chimney'and coaxial with, them at increasingly of a vacuum created in the chimney; they escapefrom J wider-radial spacing intervals starting from the'outside,

radial metal partitions dividing said anode into a plu- -'rality of-coaxial uniformly thick sector-shaped prismatic decreases from the outside to the inside.

above the'liquid metal surface 7 is provided which is adapted to influence the temperature regulator RGT in dependency on the temperature of the meltin the interpolar region, together with two 'further thermocouples t and t ofwhich the former is immersed down to the bottom of one of the cavities 9 and gives the:

a thick line while that portion which is made of the.

other metalbeing represented by a'thin line;

7 In addition to the recording temperature 2 on a sepairate chart in order to supervise the operation of the.

temperature regulator depending on the value of" I assigned thereto, the difierences r z and l -i may be recorded by an additional apparatus of high sensitiveness by means of which .'the said temperature dif ferences can be ascertained directly and controlled more Following the of the cooling watenthroughf coils 58 embedded in the V V adjustment of i ,t .bysuitably acting upon the coolingof the pole pieces 8 which is' effected" in a manner'known per se byyarying the rate of flow chimney.

chambers filled with a block of sintered carbon'paste successively raw then cooked from thetopf to thebottom, meansfor; maintaining the prismatic blocks of each annular layer at the same level, the basic level-of each layer concerned being adjusted to a progressively increasingheight from the outside to the inside, according} to a modified adjustment of each annular layer 2. In a cell according to claim l,.wherein' the vertical cylindrical chimney is perforated in the middle third of its height with vents through which the gases proceeding from the baking of the carbon paste can be sucked together with those proceeding from the electrolytic process by the action of a vacuum 'created in said 4.111s cell according to claim 1, cylindrical discharge.

tubes rigid with said fixed cylindrical metal casing and arranged at the periphery of the anode segments in the outer. annular layer which can slide freely on said tubes,

7 supply hoppers at the tops of said tubes and communicatingtherewith through calibrated'orifices, a manifold for the intake of fluidified alumina, a manifold for 'the. removal: of theexcess conveying gas, both of which manifolds communicate with the'saidsupply hoppers.

' 5. Inacellaccording to claim 1, a fluid-tightcover for the chimney, a heat recuperator depending from said cover, a reflector witha parabolic generatn'x secured to said=recuperator having its focus coinciding with the free, r ac of the melt and an exhauster connected with said chimney; V a

inlthe'u'pper portion of thefmelt within thev chimney, a temperature regulator actuated by said fsecond'thennm which according to claim '1, .coaxial metal rings couple, apparatus responsive to the voltage drop between References Cited in the file of this patent two equidistant points on the current inputs leading to UNITED STATES PATENTS each annular layer and consequently to control the 1 current density through each annular layer. 2560,85; Ferrand July 195.1 5 2,593,741 Ferrand Apr. 22, 1952 FOREIGN PATENTS 328.178 Italy July 31, 1935

Claims (1)

1. IN A CELL FOR THE ELECTROLYTIC PRODUCTION OF METALS AND MORE PARTICULARLY OF ALUMINUM, SAID CELL COMPRISING A CARBON PAN ADAPTED TO CONTAIN A SALT MELT AND A SUBJACENT BODY OF METAL CONSTITUTING ONE POLE OF THE CELL, A WALL STRUCTURE SURROUNDING SAID PAN, AND AT LEAST ONE NEGATIVE CATHODE CONTACT FIXEDLY SECURED WITHIN A CAVITY FILLED OF THE SAME METAL IN SAID STRUCTURE BEYOND THE OUTER PERIPHERY OF SAID PAN, AND IN COMMUNICATION WITH SAID PAN, THE IMPROVED MEANS COMPRISING A SELFBAKED ANNULAR ANODE ARRANGED TO DIP INTO THE SALT MELT CONTAINED IN SAID CELL, A FIXED XYLINDRICAL METAL CASING SURROUNDING SAID ANNULAR ANODE, A CERTICAL CYLINDRICAL CHIMNEY ARRANGED COAXIALLY WITHIN THE INNERMOST ANODE, CYLINDRICAL METAL PARTITIONS ARRANGED BETWEEN SAID CASING AND SAID CHIMNEY AND COAXIAL WITH THEM AT INCREASINGLY WIDER RADIAL SPACING INTERVALS STARTING FROM THE OUTSIDE, RADIAL METAL PARTITIONS DIVIDING SAID ANODE INTO A PLURALITY OF COAXIAL UNIFORMLY THICK SECTOR-SHAPED PRISMATIC CHAMBERS FILLED WITH A BLOCK OF SINTERED CARBON PASTE SUCCESSIVELY RAW THEN COOKED FROM THE TOP TO THE BOTTOM, MEANS FOR MAINTAINING THE PRISMATIC BLOCKS OF EACH ANNULAR LAYER AT THE SAME LEVEL, THE BASIC LEVEL OF EACH LAYER CONCERNED BEING ADJUSTED TO A PROGRESSIVELY INCREASING HEIGHT FROM THE OUTSIDE TO THE INSIDE, ACCORDING TO A MODIFIED ADJUSTMENT OF EACH ANNULAR LAYER WHICH DECREASES FROM THE OUTSIDE TO THE INSIDE.

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