US2856343A - Electrolytic cell - Google Patents

Description

Oct. 14, 1958 R. H. COLEMAN ETAL 2,856,343

ELECTROLYTIC CELL Filed, Aug. 31. 1956 3 Sheets-Sheet 1 SR /9 VT W 4 FIGURE ROBERT H.COLEMAN BEYMON BLANCHARD WAYNE J.JOK|LEHTO INVENTOR.

Bmgmdw Oct. 14, 1958 Filed Aug. 51, 1956 5 FIGURE u R. H. COLEMAN ET AL 2,856,343

ELECTROLYTIC CELL 5 Sheets-Sheet 2 ROBERT H. COLEMAN BEYMON B LANCHAR D WAYNE J. JOKILEH TO INVENTOR.

Oct. 14, 1958 R. H. COLEMAN ETAL 2,856,343

ELECTROLYTIC CELL 5 Sheets-Sheet 3 Filed Aug. 31, 1956 ROBERT H. COLEMAN BEYMON BLANCHARD WAYNE J. JOKI LEH TO INVENTOR.

BYMM

ELECTROLYTIC C-ELL Application August 31, 1956, Serial No. 607,473

7 Claims. Cl. 204-243) This invention relates to an improved electrolytic cell for fused salt electrolysis and, more particularly, to cells adapted for electrolysis of a molten salt to produce an alkali metal. Still more particularly, the invention relates to such cells, adapted for electrolysis of a fused salt such as sodium chloride under conditions to produce sodium, of improved construction and design whereby during operation of the cell damage to the anode or anodes is substantially prevented or obviated and the sidewall support and bottom seal structure are considerably strengthened and improved to prevent bath leakage from the cell.

In certain types of modern electrolytic cells for electrolysis of fused salts, disadvantages are encountered as, by reason of temperature gradients that occur, thermal stresses are set up that result in compression in theb'ase portion of the cell whereby fracturing of the anodes (e. g., graphite) occurs. In illustration, certain cells of modern type comprise a horizontally disposed base plate having an anode-receiving socket in which an anode is vertically placed and which extends into an electrolysis zone. At the periphery of the base plate, an upstanding flange is attached perpendicular to the plane of the base plate. Between this flange and the shell, which has a smaller diameter than the base plate, there is an annular space which is filled with a refractory insulating seal. Additionally, such cells are provided with a layer of refractory, insulating cement covering the base plate and of a thickness suflicient to completely surround and tightly embrace the anode or anodes at a height above the anode-receiving socket or sockets. Although cells of such design are normally adequate, they are subject to objection in that, during operation, expansion of components of the cell base structure occur. Since the forces that result therefrom are opposed by the flange at the periphery of the base plate, to which the flange is rigidly attached as by welding, compressive forces are created which cause crushing of the graphite anode disposed in the anode-receiving socket in the base plate. Obviously, occurrence of anode fracturing is objectionable as it results in a high voltage drop across the cell which lowers power efflciency, disturbs the thermal balance, and eventually necessitates pumping out and complete rebuilding of the cell. Such premature pumping, before the cell has served a useful life, results in serious loss of sodium production and materially increases operating costs.

Moreover, in cells as aforedescribed other disadvantages are encountered for the following reasons:

(1) The insulating refractory joint directly under the steel shell between bricks which serve as points of support for the shell is very weak and therefore easily penetrated by the molten electrolyte.

(2) An uneven foundation is provided for the sidewall bricks since in "the construction of the cell the first course of bricks must be laid on an intermediate layer of the refractory cement bottom material. A second sealing layer of this same refractory insulating cement Unitfd States tent must then be poured after these bricks are in position. This weakens the bottom structure of the cell since the bond between the two layers of refractory cement as well as the bond between the partially dried refractory cement and brick are inherently of lower strength and therefore subject to rapid penetration by the molten electrolyte.

(3) Moreover, in those cells wherein the top surface of the refractory insulating seal in the space between the shell and flange is at a level substantially higher than the layer of refractory material covering the base plate, the additional height of insulating refractory material retains the heat energy at the base of the cell and sufficient base cooling is therefore not obtained which again promotes seepage of molten electrolyte through the refractory in the cell bottom.

Such penetration of the bottom refractory and lower sidewalls by the cell bath is extremely detrimental to cell operation since short circuits develop through the penetrated portion of the refractory whereby the steel shell on the sidewall of the cell no longer remains electrically neutral, and becomes anodic. In addition, a further hazard may result due to seepage of the molten electrolyte from the cell to the copper bus bars located beneath or to personnel working underneath.

It is the primary object of this invention to provide an electrolysis cell of improved construction to obviate or substantially minimize objectionable features of electrolysis cells as aforedescribed. It is still another object of this invention to provide a fused salt electrolysis cell of improved construction to prevent undesired fracturing of anodes during operation of the cell. It is still a further object of this invention to provide a fused salt electrolysis cell of improved design whereby, in addition to prevention of fracturing of the anode or anodes, improved cell bottom and sidewall construction are obtained thereby preventing undesired seepage of cell bath through the lower portion of the cell. These and other advantages that result from the improved electrolytic cell embodied herein will be apparent from the following more detailed description thereof.

Generally speaking, the fused salt electrolysis cell comprises a metal base plate insulated from ground, an anode-receiving socket set in said base plate, an anode (e. g., graphite) set in said socket and extending into the electrolysis zone of said cell, a layer of refractory, insulating material covering said base plate of a thickness sufiicient to surround and embrace said anode at a height above said socket, cell side walls constructed of a refractory-lined metal shell, the bottom portion of said side walls being spaced from said base plate, a metal cathode located in the electrolysis zone and an electrical connection extending through a side wall of said cell, a flange attached to said base plate extending upwardly to a height above the bottom of said cell andspaced away from said shell, a refractory insulating seal in the space between said shell and flange, and a compressible heat resistant material in between the lower inner wall portion of said flange and refractory material in the space between said shell and flange.

In a specific embodiment, a fused salt electrolysis cell as embodied herein comprises a horizontally disposed steel base plate forming the cell bottom and insulated from ground, said plate extending laterally beyond the side walls and spaced below the lower edge of the shell as hereinafter described, an anode receiving socket formed in the said base plate in which a graphite anode is disposed to extend upwardly to the electrolysis zone, a layer of refractory insulating material covering the base plate and extending upward to completely surround and tightly embrace said 'anode at a height above said socket, cell side walls of a diameter smaller than the base plate and consisting of a steel shell, compressible heat resistant innerlining material and refractory brick wall reposing on a complete mortared course of refractory bricks laid on the said base plate, an upstanding steel flange, spaced from and concentric with the shell, at the periphery of the base plate, said flange extending upward above the bottom edge of the shell to a height no higher than thelevel of the top surface of the refractory material that covers the anode sockets and forms the cell bottom lining, and a layer of compressible heat resistant dielectrical material separating said flange from the shell and side wall supporting refractory bricks. In the electrolysis zone a steel cathode supported by arms extending through the side walls for electrical connections is disposed in a manner to completely surround the anode in conventional manner.

In order to more fully describe the invention, reference is made to the accompanying drawings which, in Fig. I, partly in vertical section and partly in elevation, shows an embodiment of the invention with Fig. II being an exploded view of the lower left hand portion of Fig. l; and Fig. III being an alternate embodiment of the invention over that shown in Fig. II. In all of the figures, the same reference numerals have been used to designate similar elements. It should be understood, however, that such embodiments have been utilized for purposes of illustration and not limitation.

In the drawings, in which Fig. I and II, illustrate the lower portion of a fused salt electrolytic cell, there is shown a cell cylindrical in shape having a centrally located vertical, graphite anode 2 surrounded by an annular steel cathode 3 which is supported by two arms 4. The anode is supported by base plate 5 which is a circular steel plate horizontally placed and having therein a socket 6 for the anode. At its periphery, plate 5 is provided with an upstanding flange 7. Plate 5 is insulated from ground by insulators 24 and is supported by beams 25. Anode 2 is centered in socket 6 by any suitable means such as the projection 8 on the interior bottom wall of socket 6 and set screws 9.

The side walls of the cell are formed first of a cylindrical steel shell 10 which is open at top and bottom and provided with two openings for cathode arms 4. The diameter of shell 10 is smaller than that of plate 5 so that when the shell and anode are concentrically placed there is an annular space between shell 10 and flange 7. A complete row of mortar joined refractory bricks 11 is laid on plate 5 to support shell 10 and refractory brick lining 15, and a layer of compressible, thermally stable,

dielectrical material 12, such as asbestos, is placed upon the inside of said shell 10, in between the shell and the refractory lining. Between flange 7 and the shell support brick 11, a layer 13 of compressible, thermally stable, dielectrical material is installed to a height not substantially greater than that of the shell support brick. A refractory, insulating cement 14 is then placed in the annular space between the upstanding flange 7 and shell 10. Compressive layer 13 must not extend substantially higher than support brick 11, since upstanding flange 7 must exert retaining force on refractory seal cement 14 and shell 10.

On the inside of the cell, after the first upright course of side wall brick 15 is laid, the layer of refractory cement 14 may be poured and rammed tight, in one single operation, in sufficient thickness to cover the top of the anode socket 6. Following this operation, shell 10 lined with compressible material 12 as shown, may be bricked up in the conventional manner with suitable refractory brick 15. During the bricking operation, cathode 3 is installed. In order to expedite the installation, with the cathode arms 4 projecting through the sides of the cell, shell 10 is preferably formed in two halves which are subsequently fastened by conventional means, such as flanges 16 and bolts 17 after the cathodes are in place.

Cathode arms 4 are sealed by refractory insulating cement 18, held in place by flanges 19 or other suitable means. The cell may be completed by installing the remaining conventional elements (not shown) such as a collector ring and domesupport assembly, diaphragm, gas collecting dome, riser pipe and the like in the usual manner, none of these being a part of this invention. Electrical connections are made in the usual manner, for example, to anode 2 by means of bus bars 20 and bolts 21 and to cathode arms 4 by bus bars 22 and bolts 23.

If desired, the cell may be provided with cooling means, and for example, by providing a cooling jacket for anode socket 6.

The distance between flange 7 and shell 10 may be varied considerably but the distance in combination with the thickness of refractory insulating cement and compressible refractory material 13 must be such that plate 5 is electrically insulated from shell 10.

The height of flange 7 and the insulating seal therein are kept at substantially the same or lower level than the top of refractory cement 14 such that suficient cooling of cell bath occurs to decrease seepage of molten salt electrolyte through the refractory lining 15 of shell 10 in the lower portion of the cell.

The compressible, thermally stable, preferably dielectrical material, such as compressible material 13 and, compressible material 12, should be resistant to temperatures of at least 300 C. Such compressible materials may suitably consist of asbestos in the form of mats or sheets, molded forms of asbestos, mica bonded to asbestos, quartz paper, ceramic paper or other suitable thermally and preferably electrically resistant materials having a, physical form which permits a substantial degree of compression. Layers of such compressible materials having a total thickness of approximately 4; to inches have been found to be suitable, depending on the compressibility of the particular material used and the coefi'icient of expansion of the refractory cement.

The present invention provides a means for absorbing and neutralizing the stresses imposed upon shell 10 and flange 7 by reason of expansion of plate 5 and refractory cement 14 during ope-ration of the cell. It has been found that, in the absence of use of such a compressible material in the manner disclosed herein, the thermal stresses are eventually translated to compressive forces acting upon anode 2 causing the latter to break resulting in a considerable decrease in power efliciency of the cell, dangerous bath leakage through the bottom and eventual premature pump-out of the cell. Moreover, the improvement of the seal directly under the shell, the improved foundation provided for the sidewall brick, the more uniform, non-stratified single pouring of the refractory cement bottom and the additional cooling provided by the lowered flange height all contribute to more positive, controlled sealing of the bath within the cell.

In Figure III a still further embodiment is shown which incorporates the same principles of construction in an alternate way. In this case, shell 10 has been offset at the bottom by welding a continuous formed angle to the lower periphery of the shell 10 which rests on support brick 11. The first course of sidewall brick is laid on the offset angle of the shell against insulating and compressive material 12, compressive and dielectrical material 13 is placed against the inside of the angle and then the refractory cement bottom 14 is poured in one continuous layer.

Although, in the specific embodiment utilized for illustrative purposes a cell of circular construction has been employed, other modes of construction may be used inpossible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is desired therefore that only such limitations be imposed on the appended claims as are stated therein.

What is claimed is:

1. A fused salt electrolysis cell comprising a horizontally disposed metal base plate, an anode-receiving socket set in said plate and extending below the bottom thereof, an anode set in said socket and extending upward into a zone of electrolysis, a metal cathode in said zone surrounding said anode, a refractory-lined metal shell having a smaller cross-section than said plate, said cathode being supported in said zone by cathode-supporting means extending through an opening in said metal shell, the lower edge of said shell being spaced above the top of said plate and supported by a refractory material support for said shell on said plate, a refractory material covering said base plate and extending upward to completely surround and tightly embrace said anode at a height above said socket, an upstanding flange at the periphery of said base plate and extending above the bottom of said shell, a refractory insulating seal in the annular space between said flange and lower part of said shell and a compressible heat-resistant material in between the inner side wall of said flange and the refractory material support for said shell, said compressible heat-resistant material being more compressible than said refractory insulating seal in the annular space between said flange and lower part of said shell.

2. A cell, as defined in claim 1, wherein the compressible heat-resistant material is disposed in between the inner wall of said flange at a portion thereof not substantially above the refractory support for said shell.

3. A cell, as defined in claim 1, wherein the refractory insulating seal in the annular space between said flange and lower part of said shell fills said annular space to a height not substantially higher than the upper surface of the refractory covering the base plate and surrounding the anode.

4. A fused salt electrolysis cell comprising .a horizontally disposed substantially circular metal base plate, an anode-receiving socket set in said plate and extending below the bottom thereof, an anode set in said socket and extending upward into a zone of electrolysis, a metal cathode in said zone surrounding said anode, a refractory lined metal shell having a smaller diameter than said plate, said cathode being supported in said Zone by cathode-supporting means extending through an opening in said shell, the lower edge of said shell being spaced above the top of said plate and supported by refractory brick disposed in between said plate and said lower edge of said shell, a refractory material covering said plate and extending upward to completely surround and tightly embrace said anode at a height above said socket, an up standing flange at the periphery of said plate and extending above the bottom of said shell, a refractory insulating seal in the annular space between said flange and lower part of said shell, and a compressible heat-resistant material disposed in between the inner side wall of said flange and the refractory brick support for said shell, said compressible heat-resistant material being more compressible than said refractory insulating seal in the annular space between said flange and lower part of said shell.

5. A cell, as defined in claim 4, in which a compressible heat-resistant material lining is disposed in the inner wall surface of said shell in between said shell and the refractory lining for said shell.

6. A cell, as defined in claim 4, in which the lower edge of the shell is supported by a complete mortared course of refractory brick.

7. An electrolysis cell, as defined in claim. 1, wherein the compressible heat-resistant material is asbestos.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A FUSED SALT ELECTROLYSIS CELL COMPRISING A HORIZONTALLY DISPOSED METAL BASE PLATE, AN ANODE-RECEIVING SOCKET SET IN SAID PLATE AND EXTENDING BELOW THE BOTTOM THEREOF, AN ANODE SET IN SAID SOCKET AND EXTENDING UPWARD INTO A ZONE OF ELECTROLYSIS, A METAL CATHODE IN SAID ZONE SURROUNDING SAID ANODE, A REFRACTORY-LINED METAL SHELL HAVING A SMALLER CROSS-SECTION THAN SAID PLATE, SAID CATHODE BEING SUPPORTED IN SAID ZONE BY CATHODE-SUPPORTING MEANS EXTENDING THROUGH AN OPENING IN SAID METAL SHELL, THE LOWER EDGE OF SAID SHELL BEING SPACED ABOVE THE TOP OF SAID PLATE AND SUPPORTED BY A REFRACTORY MATERIAL SUPPORT FOR SAID SHELL ON SAID PLATE, A REFRACTORY MATERIAL CONVERING SAID BASE PLATE AND EXTENDING UPWARD TO COMPLETELY SURROUND AND TIGHTLY EMBRACE SAID ANODE AT A HEIGHT ABOVE SAID SOCKET, AN UPSTANDING FLANGE AT THE PERIPHERY OF SAID BASE AND EXTENDING ABOVE THE BOTTOM OF SAID

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