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 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
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
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.