Anode mounting arrangement for a fluorine cell

Abstract: An anode mounting arrangement within an anode compartment of a fluorine cell is described, the arrangement comprising an anode portion (40) having flexible hanger means (42) connected thereto, said flexible hanger means being connected to a wall (26) of said anode compartment so as to allow movement between said anode and the walls (22) of said anode compartment; and electrically insulating guide members (46) interposed between said anode and said walls.

Description: The present invention relates to an anode mounting arrangement within an anode compartment of a fluorine cell, particularly, though not exclusively, to an on-demand type of fluorine cell for the production of fluorine gas. A problem which arises is that generally known as stud-fires and stud-leaks. Known cells have their anode hangers passing through the cell lid and insulated therefrom by plastics material seals. A considerable amount of heat can be generated during operation of a fluorine cell due to the passage of electrical current and the resultant resistance heating. This problem can also be exacerbated by the above noted problem of poor electrical contact between the anode and anode connector or hanger. Such heating greatly increases the chances of a runaway reaction between the seal material, often a fluoroelastomer rubber, and the generated fluorine, thus causing a fluorine leak. In extreme cases, the seal and the metal of the electrical connection stud actually burn in the stream of fluorine gas producing a stud-fire. A further problem with known fluorine cells is that of ensuring accurate vertical alignment of the anode within the anode compartment so as to guarantee even separation of anode and cathode and, in the extreme case, that no electrical contact whatsoever is made with the surrounding cell walls which may constitute the cell cathode. A consequential problem of the inaccuracy of anode mounting with known cells is that fluorine bubbles sometimes find their way into the hydrogen side of the cell and results in a violent reaction during recombination of the fluorine and hydrogen. EP 0534 081 describes an anode mounting arrangement having a metal sleeve for hanging an anode. It is an object of the invention to provide an improved means of securing the anode within the cell. It is another object of the present invention to provide a cell construction such that the stud-leaks and stud-fires are obviated. According to the present invention there is provided an anode mounting arrangement within an anode compartment of a fluorine cell, the arrangement comprising an anode portion having flexible hanger means connected thereto, said flexible hanger means being connected to a wall of said anode compartment so as to allow movement between said anode and the walls of said anode compartment and electrically insulating guide members interposed between said anode and said walls. According to a feature of the present invention, the flexible hanger means may be connected to an inner surface of the anode compartment by a method such as, for example, welding whereby no through-hole is produced in the wall of the anode compartment, an electrical connection stud being connected by suitable means such as, for example, welding on the anode compartment outer surface. This arrangement obviates the occurrence of stud-leaks and stud-fires since there is no need to provide sealing means at this point and neither is there a hole through which fluorine can leak at the anode attachment point. The flexible anode hanger may comprise a metal rod such as a mild steel material. However, any other suitable metal may be used. The term "flexible" is used to denote the ability of the anode to deflect so as to be able to accommodate any movement or dimensional inaccuracies between the carbon portion and the insulating guide members. The electrically insulating guide members may preferably comprise wholly or partially fluoro-plastics materials, for example, such that the anode with the flexible hanger member becomes self aligning within the anode compartment of the fluorine cell. Alternatively, ceramic materials such as alumina for example may be employed, provided that such ceramic guides are positioned such that they do not become wetted by the liquid electrolyte. Such guide members may be attached to the wall or walls of the anode compartment. Alternatively, the guide members may be attached to the anode member itself, to cathode plates or to the base of the cell. The best position may be dependant upon the internal geometry of each particular cell. The anode compartment may be rectangular in cross section, in which case the guide members may be attached preferably, to each wall. The anode compartment may alternatively be substantially circular in cross section, in which case, the guide member may be either circular or may comprise two or more arc-shaped segments. Guide members may be situated at one axial position and be of relatively long axial length or may be placed at two axial levels and be, for example, relatively shorter in axial length. The guide members have been found to maintain electrical insulation between the anode and anode compartment wall. A particular advantage of the mounting structure of the present invention is that it has been found possible to allow the electrolyte to freeze without damage being caused to the anode by contraction effects. The flexible hanger means allows some movement of the anode relative to the anode compartment walls such that shrinkage of the electrolyte during freezing may be automatically compensated; and, the insulation members prevent any possible contact between the anode itself and the anode compartment walls. In order that the present invention may be more fully understood, examples will now be described by way of illustration only with reference to the accompanying drawings, of which: Figure 1 shows a cross section through a schematic diagram of a fluorine cell including the anode mounting arrangement according to the present invention; Figure 2 shows a cross section through the anode compartment of Figure 1 along the line 3-3; and Figure 3 shows a cross section through the anode of Figure 2 along the line 4-4. Referring now to the drawings and where the same features are denoted by common reference numerals. In Figure 1 a cross section through a schematic diagram of a fluorine cell including an anode mounting arrangement according to the present invention is shown generally at 10. The cell comprises a cell container 12 of mild steel construction, the cell container being cathodic. The cell container is provided with an electrical resistance heating jacket 14 for melting the electrolyte 16 within the cell. To the top of the cell container is fixed a sealing plate 18 which is insulated from the cathodic cell container by an insulating and sealing member 20. An electrically neutral skirt member 22 made of, in this case, Monel (Trade mark) metal depends from the plate 18 and also extends upwardly therefrom to a flange member 24. A sealing lid member 26 is fixed to the flange 24 but is insulated therefrom by a sealing and insulating member 28, the lid 26 being anodic. The skirt member 22 extends downwardly and has its end 30 immersed in the electrolyte 16 so as to form two distinct chambers above the level 32 of the electrolyte; a cathode compartment or hydrogen chamber 34 and an anode compartment or fluorine gas chamber 36 which are separated from each other by the skirt member 22 and the electrolyte surface 32. Within the anode compartment. 36 is an anode, shown generally at 40, and suspended from the sealing lid 26 by a flexible anode hanger 42 in the form of a mild steel rod which is welded 44 to the underside of the lid 26. The anode extends below the end 30 of the skirt member 22. Attached to the wall on the anode compartment 36 side of the skirt 22 are anode guide blocks 46 of fluoro-plastics material which maintain the anode 40 substantially central within the anode compartment 36 and prevent contact of the anode 40 with the skirt 22. On the outer surface of the lid member is welded 48 an anode connector stud 50, thus, there is no through-hole provided in the lid member 26. In the upper portion of the fluorine chamber 36 is an outlet conduit 52 having a valve 54. Similarly, in the upper portion of the cathode compartment is a conduit 56 having a valve 58. Continuity sensor probes 60, 62 are provided to detect minimum and maximum heights of the electrolyte level 32, respectively. The probes are connected to a device 66 which starts and stops electrolysis in response to signals from the probes by providing a power supply indicated at 68,70 to the anode and cathode of the cell. A PTFE base layer 72, is fixed to the inner floor of the cell container 12 to prevent the generation of hydrogen gas beneath the anode compartment 36.

Claims: An anode mounting arrangement within an anode compartment (36) of a fluorine cell (10), the arrangement comprising an anode portion (40) having flexible hanger means (42) connected thereto, said flexible hanger means (42) being connected to a wall (26) of said anode compartment (36) so as to allow movement between said anode (40) and the walls (22) of said anode compartment (36) ; and electrically insulating guide members (46) interposed between said anode (40) and said walls (22). An anode mounting arrangement according to claim 1 wherein the flexible hanger means (42) is connected to an inner surface of the anode compartment (36) by a method whereby no through hole is produced in the wall of the anode compartment (36). An anode mounting arrangement according to claim 2 wherein the connection method is welding. An anode mounting arrangement according to any one preceding claim from 1 to 3 wherein the electrically insulating guide members (46) comprise fluoro-plastics materials. An anode mounting arrangement according to any one of preceding claims 1 to 4 wherein the guide members (46) are attached to the wall or walls (22) of the anode compartment (36). A fluorine cell having an anode mounting arrangement according to any one of preceding claims 1 to 5.

Inventors: HEARNE MARTIN PETER, HODGSON GRAHAM, HEARNE, MARTIN PETER, HODGSON, GRAHAM, Hearne, Martin Peter, BNFLElectrogas, Hodgson, Graham, c/o Fluorogas Limited
Applicants: BRITISH NUCLEAR FUELS PLC
Application year: 1995
Main classification: C25B9
IPC codes: C25B15, C25B1, C25B11, C25B9