CS202528B2 - Electrodes system - Google Patents

Abstract

1415305 Lead assembly for molten electrolyte furnaces ALUMINUM CO OF AMERICA 1 Sept 1972 [7 Sept 1971 (2)] 40591/72 Heading C7B A lead assembly for supplying current to an electrode or furnace chamber for use in the production of aluminium or aluminium chloride comprises a low resistance electrically conductive lead member of material which is susceptible to corrosive attack by chlorine at 550‹C having a fluid impervious electrically conductive sleeve member of material which is resistant to attack by chlorine at 550‹C, e.g. of graphite; with either (a) the sleeve extending around one end of the lead member, or (b) having a space extending between the lead member and the sleeve, which space is connected to means for introducing fluid thereto. As shown an electrode 14 is positioned abutting wall 12 of an aluminium molten electrolyte cell, and current is supplied thereto via corrosive lead member 16 provided with corrosion-resistant sleeve member 20; the lead member making a force-fit with the sleeve and the sleeve making a force-fit in a bore 18 in the electrode 14. The cell wall consists of a conductive shell 13 and an inner non- conductive lining 12; seal 32 serving to insulate the electrode from the conductive shell 13. Cooling fluid may be passed through passages 44 in the lead 16; and inert fluid may be passed under pressure through 28 to header space 21 and bores 30 between the lead and the sleeve.

Description

BACKGROUND OF THE INVENTION The present invention relates to an electrode system for conducting electrical current into or out of a chamber having a thermally insulating wall surrounding a high temperature corrosive environment, particularly for use in electrolytic cells for the production of metals, particularly aluminum. a resistor, one end of which is located in the chamber and is in electrical contact with the electrode, and the other end of which is outside the chamber, the electrical contact between the electrode and the wiring being made by an electrically conductive heat and corrosion resistant member disposed in said wall.

The benefits of using aluminum chloride as a raw material in the electrolytic reduction of aluminum have long been recognized, but the commercial implementation of this process has been hampered by the inability to solve many of the problems associated with this process.

One of the persistent serious problems was the problem of supplying and discharging the electrodes placed inside the electrolysers and furnaces used for the reduction process and the problem of the inlets and conductors that would withstand the corrosive composition components, i.e. the aluminum chloride and chlorine gas baths.

The electrodes in such an electrolyzer protrude in contact with the electrolyte bath to direct the bath current. Electrode leads are used to electrically connect electrodes to conductors and circuits outside the electrolysers.

However, the leads connected to the electrodes of the electrolyzer may be made of an electrically conductive metal, for example copper, but such leads are subject to corrosive disturbance of the bath and chlorine gas at the electrolyzer operating temperature, leading to their rapid destruction.

202528 2

Since the melting point of aluminum is about 660 ° C, electrolysers are used to produce aluminum from chloride, usually at temperatures of about 700 ° C. No known metal can withstand the corrosive action of chlorine at a temperature above about 550 ° C and have a longer service life than one or two days to a few weeks, depending on the metal used and on the durable temperatures.

The leads can be made of conductive non-metals, such as graphite, but if they are to be sized to carry the required current at low voltage drop, these leads are impractically large and carry excessive amounts of heat from the electrolyzer.

If the size of such leads is reduced in order to reduce heat loss and achieve practical dimensions, then these leads are not conductive enough, which means that their own electrical resistance creates undesirably large voltage drops along their length.

Thus, a solution to the problem of supplying and dissipating anode and cathode of electrolytic baths containing a corrosive environment would be to use conductive members that project into the electrodes that are made of a highly conductive material associated with low voltage drop exposed to attack by a corrosive environment such as is a highly conductive metal, but has been effectively protected against corrosive environments.

The invention solves this problem in that, in the aforementioned electrode assembly, the electrically conductive member is formed as a sleeve having a closed end and located within the electrode bore and a guide placed in the sleeve.

According to a preferred embodiment of the invention, an internal passageway extends through the conduit to the space connecting the longitudinally extending channels on the conduit surface.

The conduit is expediently provided with at least one cooling fluid channel.

According to a further embodiment of the invention, the outer diameter of at least a portion of the sleeve that extends into the electrode is provided with a bevel along its length which diminishes towards the electrode.

The main advantage of the invention is to provide an electrode assembly that is impermeable to the corrosive penetrating fluids present in the electrolytic reduction of aluminum from aluminum chloride dissolved in a molten halide bath, thereby greatly extending the working life of the electrolyzer. Another advantage of the present invention is the ability to detect and indicate the onset of failure of the electrode assembly due to the onset of corrosive fluid entering the cell wall after passing through the low-resistance conducting core in a timely manner.

The electrode assembly according to the invention will now be described by way of example with reference to the drawings.

Giant. 1 is a cross-sectional view of an electrode assembly constructed in accordance with the present invention.

Giant. 2 is a cross-sectional view of the electrode assembly of FIG. 1, taken along line II-II in FIG. 1.

Giant. 3 is an enlarged view of part of FIG.

In the drawings, a longitudinal sectional view of an electrode assembly 10 embedded in the wall of the illustrated aluminum aluminum electrolyser is shown. The wall of the electrolyzer, of which only a portion is drawn and which may form the top, side or other circumferential portion of the electrolyzer tub, consists of a relatively strong refractory and heat-insulating ♦ layer or wall 12 (shown only in part) and an outer metal sheath ДД, which has conductive properties and is preferably electrically grounded.

Such an electrolyzer wall is capable of storing a highly corrosive environment, such as is present in the electrolysis of aluminum chloride dissolved in a molten halide bath, such as a bath of one or more alkali metal halides, in the production of aluminum metal.

Corrosive fluids so direct, for example, molten bath components and chlorine gas evolving during electrolysis, are highly permeable and highly corrosive to metals, particularly at the high temperatures used in the operation of such electrolysers.

The electrode assembly shown. 10 comprises an electrode 14 which is located inside the electrolytic cells and exposed to the described environment and at least one low electric resistance conduit 69, preferably in the form of an elongated metal rod or rod passing through the cell wall 12, one end of which extends into the bore. 18 of the electrode 44, while the other end of the line 16 is located outside the electrolyzer to connect it to a power source. .

The metal rod forming the guide 16 is surrounded by an elongated sleeve 20 which is formed of an electrically conductive material, substantially impermeable, for example dense graphite, and. it is of such a size that it protrudes into the bore 18 of the electrode 14 and passes through the wall of the electrolysis cells. Particularly suitable for the purposes of the invention is a graphite sleeve coated with pyrolytic graphite.

For good electrical contact, the inner cross-sectional dimensions of the sleeve 20 and the outer cross-sectional dimensions of the guide 16 are selected such that the sleeve 20 and the guide 16 closely fit to each other, thereby achieving good electrical contact between the guide 16 and the sleeve 20.

In a similar manner, good electrical water conductivity is obtained between the electrode 14 and the sleeve by establishing a force contact between them. By selecting the dimensions for the sleeve 20 and the bore 8 of the electrode 14, to facilitate insertion and removal of the sleeve 20, a slight bevel may be provided on the outer cross-section of the sleeve 20 in such a mating relationship, the dimensions of which will decrease towards the electrode 14.

Preferably, the sleeve 20 extends over the entire portion of the line 36 which is disposed within the electrode 14 and is provided with a closed end. As shown in FIG. 1, the conduit 16 was completely enclosed therein. The sleeve 20 may also be provided with an open end and extend along the length of that portion of the conduit 16 which. As shown in FIG. 1, a space 21 is preferably provided between the end of the conduit 16 and the inner surface of the closed end of the sleeve 20.

The electrode 44 is as shown in FIG. 1 positioned so as to abut an interface on the inner surface of the insulating wall. 12 and may be of such size that it extends along this wall over a considerable distance. ...

In such a case, several electrode assemblies of the above type with a single electrode 64 are used. in order to reduce the resistance due to the shortening of the current path through the electrode 14 when the electric current is supplied to the electrode if it is an anode, and optionally when the current is removed from the electrode if it is a cathode. .

. As shown in FIG. 1, an electrically insulating sheath 22, which limits the opening through the wall of the electrolysers, concentrically surrounds that portion of the sleeve 40. which passes through the cell wall 12 and has a suitable dimension for receiving the sleeve 20. Between the two covers, i.e. the sleeve 20 and the insulating sheath 23, there is an elongated annular gap 24 the size of which. is exaggerated to illustrate. _in

A tight fit between the two covers is basically avoided since the grease of the insulating sheath 23 (preferably silicon oxinniride or quartz) cannot be easily machined to form such a fit, and the sleeve 20 has a somewhat greater expansion coefficient than the insulating sheath 23. It is. furthermore, it is desirable that the two covers sit freely on each other for the purpose. disassembly and assembly.

2Ó2528, · ’. 4

The insulating sheath 23 thus electrically insulates the conductive sleeve 20 and the conduit. 16 from the normally grounded metal sheath 13 of the electrolyser wall 12, but on the other hand they form an elongate partition for the flow of penetrating corrosive fluid in the form of an annular gap 24.

. In an electrolyzer in which a highly corrosive environment exists, the highly permeable and corrosive gaseous and liquid components tend to penetrate the electrode 14 due to its leakage and leak through its interface with the electrolyzer wall 12 and come into contact with the conductors. which are placed inside and which supply and divert current.

U arranged :! according to FIG. 1, therefore, in the absence of line protection. 16, such corrosive components tended to leak along the interface between the wall 12 and the electrode 14 and the electrode 14 apertures in contact with the conduit 16. '

According to the invention, it is guided by: Such a sleeve acts to prevent any bath or gas penetrating the electrode 14 or penetrating between the electrode 14 and the electrolytic wall 12 from reaching in any appreciable amount of conduction to the conduit 16, thereby extending considerably. increase its life.

For example, when using the sleeve 20 of the invention, the penetration of the corrosive components is reduced to such an extent that the guide 16 remains in a substantially good working condition for very long periods of time, even several years. In this way, the service life of the conduit 16 will correspond to the working periods between the normal shutdown of the aluminum production electrolyser for maintenance and repair, or even going well beyond those periods.

As a result, any maintenance that the protected conductor of the invention might require may be performed at a time when its electrolyser is normally stopped for the above purposes. The convergence of the graphite sleeve 20 described above also allows the entire electrode assembly 10 to be removed and the electrode assembly 10 removed. replaced before electrolysis ^.

According to a further embodiment of the invention, an inert liquid, preferably gas, that does not react chemically to the material of the line 16, the electrode 14 and the sleeve 20, and which is maintained around the corrosion line 16, can be adjusted to sufficient repulsion pressure to approach corrosive fluids, thereby avoiding contact with the fluid.

This, according to Vyyniasis, is achieved by introducing nitrogen gas or other inert gas from a remotely located pressure source 26 'through an internal passage 23 which extends over the entire length of the conduit 16 to the head space 21. To support the retention of the gas envelope, the outer surface the conduit 16 is provided with a plurality of small longitudinal channels 10 extending at least from the end of the conduit 16 to the adjacent wall 12 of the electrolyzer.

The gas located inside the ducts 30 diffuses and penetrates the interface between the inner surface of the sleeve 20 and the outer surface of the conduit 60, since even under normal tightness treatment these surfaces will still be sufficiently rough to admit a thin gas layer therebetween. \

As detailed in FIG. 2, the channels 10 are made small enough to prevent a greater reduction in the desired high degree of electrical contact between the sleeve 20 and the line 16. As mentioned above, the surfaces of the line 16 and the sleeve 20 will normally be sufficiently sufficiently roughness to allow gaseous fluid to enter between them, and this roughness or long-distance corrosion can be artificially increased to increase the hiding action. According to another embodiment, a guide 16 of a material that is artificially or naturally porous may be used.

Maintaining the gaseous coating at a desired pressure sufficient to repel any approaching corrosion fluids results in a pressure gradient that provides unidirectional flow of the wrapping gas away from the inlet and outward through the cracks of the electrode sleeve 20a, preferably at a minimum speed that is even approximately zero, so that little or no envelope gas is lost from the system. In this case, the sleeve 20 extends over the entire length of the guide V6 and is provided with a closed end so that the guide 16 is completely closed therein.

However, even in the case of a significant outward flow of the packaging fluid, such as may occur when a breakdown or breakthrough in the sleeve 20 and / or the electrode 14 occurs, the flow will be directed away from the line 16 and be such as to prevent corrosive fluid from entering the opening. As a result, the metal of the conduit 16 is protected against corrosive fluids.

As is evident, it is only necessary that the pressure of the envelope fluid be greater than the pressure existing within the working electrolyzer. This allows the use of low cost low pressure apparatus and connections for supplying packaging fluid to the electrode assembly, as well as allowing the use of inexpensive sealing assemblies at that end of the sleeve 2.0 that passes through the electrolyzer wall 12.

The described envelope gas also acts as an indicator or alarm device. for an indication of deteriorating conditions within the electrolyzer and an incipient electrode failure. Since the normal flow of inert envelope gas will be at a minimum, any appreciable increase in gas flow or pressure reduction resulting therefrom may be readily detectable, for example by a significant change in the pressure gauge 31 or flow meter 212 (or both) connected to the fluid system. as shown in FIG. 1, wherein the meters consistently show the system pressure and the envelope gas flow rate.

To accommodate the electrode assembly 10 in the electrolyzer wall and to form an effective seal between the housings 20 and 23 and the electrolyzer wall 12 and between the sleeve 20 and the guide 16, a removable concentration of the sealing assembly 32, Fig. 1, is used. The sealing assembly 32 consists, in particular, of a flange collar 36 disposed around the end of the sleeve 20 and secured to the metal housing 13 by suitable means, for example circumferentially spaced pins, fastened to the conductive housing 13 and passing through the adjacent part of the collar 36.

The collar 36 is insulated from the housing 13 and the studs by insulating sleeves 37 enclosing the studs in the collar 16 and an insulating pad 38 positioned between the collar and the housing, as well as insulating sleeves 38a located between the collar 36 and the stud heads.

An insulating stuffing material 39, for example an asbestos strand, is provided between the collar 36 and the adjacent portion of the sleeve 20; the stuffing material is preferably also located in the gap between the cell wall 12 and the insulating sheath 23 to seal the wall 12 around the sleeve 20.

At that end of the collar 36 which is facing away from the housing 13 and positioned around the conduit 16, the insulating insert 40 is held in place above the gland 39 by a rigid plate 41 secured to the collar 36 by bolts passing through the plate 41 to that portion of the collar 36. The part of the insulating insert D0 that lies between the inner edge of the plate 41 and the conduit effectively insulates both the conduit 16 and the collar 36 from the conduit 16 while securing the seal 39 at the end of the collar 20 and around the metal member.

Such a concentric seal arrangement suitably seals the electrolyzer wall 12 against leakage of liquids and gases around the insulating sheath 23 and seals the packaging fluid against leakage from that end of the sleeve 20 which is located outside the electrolyzer wall 12. In addition, the aforementioned sealing arrangement keeps the insulation provided by the insulating sheath 23 in place between the conductive sheath 12 of the electrolyzer and the sleeve 20 with its metallic conduit 16.

(. '

The part of the conduit 16 which passes through the cell wall 12. further, according to a preferred embodiment of the invention, it has a second inner channel or channels 44 (FIG. 1) for guiding the cooling fluid through the channel. Since the conduit 16 is highly conductive, the heat within its associated electrolyzer will be rapidly conveyed to all of its parts, including the mowing parts adjacent to the sealing kit 32. Passing the coolant through the channels 44 contributes to keeping this part of the conduit 16 ' the temperature is substantially uniform, so that its expansion and contraction is minimized in the area of the seal, if not even completely prevented. '

In this way, the sealing action of the seal is not adversely affected by changes in temperature inside and outside the electrolyzer. .

As mentioned above, corrosive fluids within the electrolyser can readily penetrate the interface between the electrode 10 and the cell wall and thus enter the annular gap 24 between the insulating sheet 23 and the sleeve 20.

If there were no obstructions, corrosive fluids would reach the seals located around the electrode or around the electrode assembly members adjacent to the electrolyzer conductive sheath 13, which would accumulate and partially solidify.

Such a partially solidified bath material and broken seals would provide a pathway for current flow between the electrode 14 and the conductive sheath 13. thereby reducing the efficiency of the electrode 14 in the operation of the electrolyzer and even shortening such a configuration.

The above-described cooling of the conduit 16 and thereby achieving a temperature reduction in the circumference of the insulating sheath 23 contributes to causing selectively placed solidification of the bath maaerial which is transferable to a solid state and penetrates into the annular gap 24 before it reaches the location The solid state material then serves as a barrier, which minimizes further penetration of the bath and maintains a high degree of electrical insulation between the sleeve 20 and guided by the abrasive sleeve.

Although the invention has been described above for carrying out a single layer or envelope of inert gaseous fluid around conduits 66, two or more substantially impermeable and concentrically located sleeves 20 arranged around conduits would be used. £ 6. . .

From the foregoing, it will be apparent to the coders that the invention has given a new and useful electrode system design in which the casing of chemically inert gaseous fluid is economically placed around a metal or other low-displacement, highly conductive material forming the conduit. interfering with the electrode in a consistent environment in which the metal induces a low voltage drop which is achievable with such joints from the resistive metal.

The electrode system according to the invention is particularly useful in the electrolytic reduction of aluminum from aluminum chloride dissolved in a bath of molten halogens, and although the invention does not in itself achieve such a reduction to the extent industrially most advantageous, it still constitutes a solution to one of the long-term problems. which have so far prevented progress in this area and thus contribute to making this reduction process a technical reality. .... ,,,,

However, the device according to the invention is extremely useful in a variety of electrolyses and constructions other than those used to reduce aluminum from aluminum chloride, such as electrically connected graphite resistive heating elements located inside the furnace chamber in the production of aluminum chloride from aluminum. chlorine gas, aluminum material and coal.

Claims (4)

SUBJECT OF THE INVENTION An electrode system 8 for conducting electrical current into or out of a chamber with a thermal insulating wall surrounding a high temperature corrosive environment, intended in particular for use in electrolytic cells for the production of metals, in particular aluminum, and having an electrode disposed therein a resistor, one end of which is located in the chamber and is in electrical contact with the electrode, and the other end of which is outside the chamber, the electrical contact between the electrode and the conduit being electrically conductive to the heat and corrosion bottom member disposed in said wall; characterized in that the electrically conductive member is formed as a sleeve (20) having a closed end and located inside the bore (18) of the electrode (14), and a guide (16) is disposed in the sleeve 420). 2. Electrode assembly according to claim 1, characterized in that it runs through the conduit (16) An internal passage (28) to the space (21) connecting the longitudinally extending channels (30) on the surface of the conduit (16). 3. Electrode assembly according to claim 1, characterized in that the conduit (161) is provided with at least one coolant channel (44). An electrode assembly according to any preceding claim, wherein the outer diameter of at least a portion of the sleeve (20) that extends into the electrode (14) is provided with a bevel along its length that diminishes towards the electrode (14).