NO20162006A1

NO20162006A1 - A suspension arrangement for anode beams in cells of Hall-Héroult type for the electrolytic production of aluminum and a method for stabilizing the operation of such cells

Info

Publication number: NO20162006A1
Application number: NO20162006A
Authority: NO
Inventors: Elmar Wedershoven; Markus Fechner; Morten Liane
Original assignee: Norsk Hydro As
Priority date: 2016-12-15
Filing date: 2016-12-15
Publication date: 2018-06-18
Also published as: EP3555346A1; WO2018108604A1; EA036249B1; EP3555346B1; EA201991433A1; CA3043981A1; CA3043981C

Abstract

A suspensjon arrangement for anode beams in cells of Hall-Héroult type for the electrolyticproduction of aluminium including an anode superstructure comprising an elongated generally horizontally disposed anode beam supporting anodes and a suspensjon arrangement for supporting said anode beam from said anode superstructure for movement relative thereto. It includes jacks spaced at positions along the longitudinal center line of said anode beam and supporting said anode beam from said anode superstructure for selectively lifting or lowering said anode beam vertically relative to said anode superstructure, and for selectively lifting or lowering either of the two opposite longitudinal ends of said anode beam relative to the other end thereof. It further includes torsional means mounted on said anode beam and said anode superstructure for preventing said anode beam from rotating about the longitudinal axis thereof. It also has guide means mounted on said anode beam and said anode superstructure for cooperative engagement for preventing said anode beam from moving sideways in opposite horizontal directions transverse to said longitudinal axis. The anode beam is divided into two anode bar sections A, B, aligned one after the other in the longitudinal direction of the cell, where each anode bar section is provided with two jacks and have torsional means arranged at or near the ends of each of said anode bar section. The invention also relates toa method for stabilizing the operation of an electrolytic cell of Hall- Héroult type for aluminium production, by use of the suspensjon arrangement.A suspension arrangement for anode beam cells in Hall-Héroult type for the electrolytic production of aluminum including an anode superstructure comprising an elongated generally horizontally disposed anode beam supporting anodes and a suspension arrangement for supporting said anode beam from said anode superstructure for movement relative thereto. It includes jacks spaced at positions along the longitudinal center line of said anode beam and supporting said anode beam from said anode superstructure for selectively lifting or lowering said anode beam vertically relative to said anode superstructure, and for selectively lifting or lowering either of the two opposite longitudinal ends of said anode beam relative to the other end thereof. It further includes torsional means mounted on said anode beam and said anode superstructure to prevent said anode beam from rotating about its longitudinal axis. It also has guide means mounted on said anode beam and said anode superstructure for cooperative engagement to prevent said anode beam from moving sideways in opposite horizontal directions transverse to said longitudinal axis. The anode beam is divided into two anode bar sections A, B, aligned one after the other in the longitudinal direction of the cell, where each anode bar section is provided with two jacks and has torsional means arranged at or near the ends of each said anode bar section. The invention also relates to a method for stabilizing the operation of an Hall-Héroult type electrolytic cell for aluminum production, using the suspension arrangement.

Description

The present invention relates to a suspension arrangement for anode beams in cells for t electrolytic production of aluminum. The cell being of the Hall-Héroult type, commonly wit carbon based anodes. A cell for producing aluminum by electrolysis of this type includes a flat steel shell with a lining on the inside. The main part of the lining is of a electronicall conducting material that forms the cathode. The anode, which is also commonly made of carbon materials, usually in the form of several carbon blocks or elements, are fixedly held by anode hangers. The anode hangers are securely attached to an anode beam, providing a firm mechanical as well as electrical connection with the anode beam. Such carbon blocks are usually referred to as anode carbon bodies. The invention also relates to a method for stabilizing the operation of an electrolytic cell of Hall-Héroult type for aluminium productio by use of the said suspension arrangement.

During the electrolytic process the carbon bodies are consumed at their lower ends by the precipitated gases, and to be able to keep a constant distance between the anode and the cathode (anode-cathode-distance, abbreviated ACD), the anode beam and the anode carbon bodies have to be simultaneously lowered. The anode beam is provided with vertical regulating means, and when the anode beam has reached the lowermost regulating level all the anode hangers are removed from the anode beam and temporarily attached to a so called "crossing bar". The anode beam is then raised to its uppermost positions, whereafter all the anode hangers are reattached to the anode beam in its new position.

In cells operating today, for instance a 250K ampere cell, the weight of the anode suspension arrangement may be about 35 tons and the length of the anode beam about meters. Obviously, with such dimensions, the anode suspension arrangement is a large and expensive construction. The vertical regulating means for the anode beam has to b so constructed that the anode beam may be raised or lowered by parallel movement, or tilted to either end in its longitudinal direction to achieve an inclined position.

The known types of suspension arrangements may roughly be divided into three differen groups.

A: Four separate jack devices, of which two at a time are driven by the same motor, are each mounted at one of the end corners of the anode beam. The jack devices are placed on or suspended by separate construction elements which either stand at the short end o the electrolytic cell or on a self-supported anode superstructure. (If one, instead of tw motors are used, it is not possible to tilt the anode beam.)

B: Separate jack devices are each driven by a motor. The jack devices are mounted on a hall floor on the center line of the electrolytic cell, at the short end of the cell, providing upward movement of the anode beam.

C: One single jack device with a motor is mounted at one of the anode superstructure ends. The jack device controls two mechanisms (one on each side of the anode superstructure, and each attached to one of the beams of which the anode beam is made) and functions as follows: when the jack is moved upwards or downwards, the anode beam is subject to a sheer vertical movement (it is not possible to tilt the anode beam).

These existing arrangements have several disadvantages.

Arrangement A fulfils several functional demands, but when the electrolytic cells are very long, the mechanical load on the anode beam is unfavorable, which again results in the anode beam being too heavy if deformation stability is to be held within reasonable limits.

Arrangement B is encumbered with the same disadvantage as arrangement A and also must be provided with a sideway support for the anode beam.

Arrangement C provides a favorable location of the suspension points between the anod beam and the mechanisms, so that the mechanical dimensioning of the anode beam may be optimized, but lacks the possibility of tilting the anode beam which is commonly used in connection with the terminations (killing) of anode effect.

EP 0256848 B1 discloses a suspension arrangement for an anode beam in a cell for electrolytic production of aluminum includes two jacks disposed along the center line of the anode beam, between an anode superstructure and the anode beam. The anode beam is movable in the vertical direction by such jacks which are separately driven, or driven by one common motor. To prevent the anode beam from rotating around its longitudinal axis, there is disposed a torsion device between the anode beam and the anode superstructure. The anode beam is provided with side supporting structure which prevents the anode beam from moving sideways.

This solution represents a stable construction that also allow the anode beam to be tilted. However in larger cells, i.e. above 300kA, the load to be carried by the anode beam will require heavy dimensions of the beam and the jack system to represent the required stability.

CN 2471795 Y discloses an anode beam system with an anode beam divided in two bars.

An electrical connection is arranged between the two opposing bar ends. Each anode bar is controlled by one motor that drives two jacks arranged towards the ends of the anode bars. This arrangement allows that the anode bar can be lifted and lowered, but not tilted. No indications of individual control of each of the anode bars is given.

OBJECT OF THE INVENTION

It is the object of the present invention to provide an anode arrangement for larger cells, i. above 300kA, wherein it is possible to obtain a stable suspension for the anode beam and the jack devices, at the same time as the possibility of lifting lowering groups of anodes independently of other groups. Further, the solution involving a divided or split anode beam with the described jacking and suspension system, brings a lot of new opportunities with regard to controlling and manipulating the anode-cathode-distance, both globally and locally in an electrolysis cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal side view, partly in section, of a divided anode beam with an anode suspension arrangement according to the present invention,

FIG. 3 is a principal view of the same, where the divided bar is in a certain position,

FIG. 4 is a principal view of the same, where the divided bar is in a certain position,

FIG. 5 is a principal view of the same, where the divided bar is in a certain position,

FIG. 6 is a principal view of the same, where the divided bar is in a certain position,

FIG. 7 is a principal view of the same, where the divided bar is in a certain position,

FIG. 8 is a principal view of the same, where the divided bar is in a certain position.

DETAILED DESCRIPTION OF THE INVENTION

As shown in Fig. 1, anode bar section A and anode bar section B will together represent one anode beam arranged in the longitudinal direction of the cell. A similar beam structure is hidden behind it and forms together a frame construction which constitutes two parallel, divided beams (only one shown) formed from aluminum, and which is disposed above an electrolytic cell (not shown) in the longitudinal direction thereof. The two anode bar section A, B are connected to a set of two parallel anode bar sections by means of cross bars (not shown) preferably at the ends of the bar sections, and depending on the length of said bar sections, at one or more points spaced along the longitudinal direction of the bar sections This is similar to the example as shown in FIG. 2, of EP 0256848 B1. In that Fig. the beams 10, 11, are provided with four cross bars 12.

The anode bar sections A, B are electrically connected via a flexible conductor lead 4.

Anode carbon bodies are connected to the said anode beams in two parallel rows by means of anode hangers (not shown). As the lower ends of the carbons are consumed during th electrolytic process, the consumed carbon is replaced by lowering the anode beams. A suspension arrangement moves the anode beams in the vertical direction and transfers the forces acting on the anode beams to a self-supported steel construction, the

so-called anode superstructure 1, which either is supported by the cathode shell, or independently of this, on a separate building-construction.

The anode suspension arrangement comprises four jack devices J1, J2, J3, J4, which at their lower ends are rotatably attached to, at positions between the anode bar sections A, B transversely disposed cross shafts 5, 6, 7, 8, and at their upper ends are connected to the anode superstructure 1. The shafts 5, 6, 7, 8, are disposed between the anode bars A, B (only one divided beam shown due to the parallel alignment) with such distance between one another and the beams that the forces acting on the jack devices are essentially equal, and the strain and stress forces in the beams, i.e. the divided anode beams are the lowest possible. Accordingly, the jack devices J1, J2, J3, J4 are arranged in the vertical symmetry plane between the anode beams or anode bar sections A, B.

The jack devices J1, J2, J3, J4 are separately driven, and provide a vertical, parallel movement as well as tilting movement of the anode bar sections A, B. The activation of the jack devices can be controlled by a pot controller, where in case certain deviations is observed on the cell, a pre-programmed activation pattern of the jacks can be run. Such preprogrammed activity can for instance be linked to anodic effects occurring on one or more anodes.

To prevent the anode bar sections from rotating round its longitudinal axis, the ends of the anode bar sections A, B are provided with torsional devices L1, L2, L3, L4. The torsional devices each include two arm members a1, a2 (only one set explained here) which are linked to one another. The lower ends of arms a2 are rotatably attached to the respective bar section A, while the free ends of arms a1 are fixedly attached to the ends of a respective torsion shaft a3 which is rotatably disposed on the anode superstructure 2.

The functioning of the torsional devices is as follows. When the anode bar sections tends to be twisted around its longitudinal axis, the arms a2 on one side of the bar section will push the arms a1 on the same side which results in a rotation of the torsion shaft a3. This rotation will, however, be prevented by the corresponding arms (not shown) on the oth side in the parallel anode bar section, whereby the anode bar section is kept in its same horizontal position with respect to its axis.

To be able to withstand the side forces acting on the anode bar sections, there is disposed a mechanical guiding or supporting arrangement between the anode bar sections and th anode superstructure. Such arrangement may include rollers which are rotatably disposed on the anode bar section, for example at each corner thereof, and which can roll against a roll guide on the anode superstructure 1. Or, such arrangement may include guide shoes mounted on the anode bar section and which can slide along vertical guideways on the anode superstructure.

The details of the anode suspension arrangement, comprising jacks, torsional devices and the mechanical guiding or supporting arrangement between the anode bar sections and th anode superstructure can be based upon the constructional design as that shown in th Applicant’s own EP 0256848 B1.

In Fig. 1 and the following Figures the symb-o--l-- O--O outside the anode beam’s ends indicates a neutral position of the anode beam.

As shown in Fig. 2 there is schematic given an initial position of the anode bar sections A and B. By adjusting the jacks J1, J2 to respective positions P1, P2 and the jacks J3, J4 to positions P3, P4, the anode bar sections A, B are illustrated at A’, B’ respectively.

As shown in Fig. 3 there is schematic given an initial position of the anode bar sections A and B. By adjusting the jacks J1, J2 to respective positions P1, P2 and the jacks J3, J4 to positions P3, P4, the anode bar sections A, B are illustrated at A’, B’ respectively.

As shown in Fig. 4 there is schematic given an initial position of the anode bar sections and B. By adjusting the jacks J1, J2 to respective positions P1, P2 and the jacks J3, J4 to positions P3, P4, the anode bar sections A, B are illustrated at A’, B’ respectively.

As shown in Fig. 5 there is schematic given an initial position of the anode bar sections and B. By adjusting the jacks J1, J2 to respective positions P1, P2 and the jacks J3, J4 to positions P3, P4, the anode bar sections A, B are illustrated at A’, B’ respectively.

As shown in Fig. 6 there is schematic given an initial position of the anode bar sections A and B. By adjusting the jacks J1, J2 to respective positions P1, P2 and the jacks J3, J4 to positions P3, P4, the anode bar sections A, B are illustrated at A’, B’ respectively.

As shown in Fig. 7 there is schematic given an initial position of the anode bar sections and B. By adjusting the jacks J1, J2 to respective positions P1, P2 and the jacks J3, J4 to positions P3, P4, the anode bar sections A, B are illustrated at A’, B’ respectively.

As shown in Fig. 8 there is schematic given an initial position of the anode bar sections and B. By adjusting the jacks J1, J2 to respective positions P1, P2 and the jacks J3, J4 to positions P3, P4, the anode bar sections A, B are illustrated at A’, B’ respectively.

It should be understood that each of the anode bar sections A and B, independently of each other and as far as the flexible conductor lead 4 allows it, can be lifted, lowered and tilted clockwise and counter clockwise.

Experienced advantages with the functionality of a split or divided anode beam according to the present invention can be summarized as follows:

Metal pad curvature in the cell will flatten out if the amperage in the cell is reduced, resulting in an individual changed anode - cathode distance (ACD) per anode along the anode beam, i.e. the anodes at the ends of the cell will get a reduced ACD compared to steady state operation, whilst the anodes in the middle of the cell will get an increased ACD. This individual change of ACD will result in increased current pick-up at the ends, and reduced current pick-up in the middle of the cell, causing MHD (magneto hydro dynamic) instability in the cell, and at severe situations the end anodes will be immersed into the metal and taking such a high current load that the bimetallic weld connecting the anode rod to the anode yoke melts/ breaks because of the high heat generation in the weld. By lowering th middle ends, and lifting the outer ends of the two anode beams, the individual ACD might be kept more or less constant at amperage reductions. This option for controlling the tw beams is illustrated in figure 7. However, the metal pad curvature is not symmetrical in the cell, so it will not be possible to obtain an almost constant ACD at all anodes. A more precise beam tilting to adapt the individual ACDs would have been tilting the anode beams as described, but more in the tapping end than in the duct end of the cell, i.e. a mirrored tilting of the beams illustrated in figure 6 and 7. In addition to compensation for metal pad curvature (1), the use of the split beam / four motor configuration helps compensate f uneven current distribution during start-up and early operation. It also reduces the need for adjusting anode height with Pot Tending Machine (PTM) during the start-up/ early operation.

Anode effect (AE) quenching. To create a higher, turbulent bath flow to force alumina ric bath into the ACD area, and to create an angled surface / underside of the butt to help gas escape from the surface during, and/or to temporarily short-circuit end anodes on each anode beam into the metal, different combinations of beam movements under an anode effect will be favorable for the quenching. Such typical position combinations are given figures 2 and 4.

Quenching anode effect only at a few anodes in the cell. Different tilting of one - or in som cases both - anode beam sections to add alumina rich bath locally to the anodes with an anode effect, and/or to reduce the amperage pull on these anodes, is an option to quenc a local anode effect, and hence to avoid/reduce CFx gas emission, and/or to avoid an anode effect on the entire cell. Typical anode beam movement will be as given in figure 3, bu more sophisticated beam movements and combinations of movements might be introduced, provided information about the exact position of the local anode effect(s). However, this option depends on a system that monitors the current pick-up per anode, for example individual anode current measurement (IACM).

Preferably, distributed alumina feeding should be combined with the described beam movements to gain a reduced duration of local anode effects.

Anode deviations. At situations with known anode failures at individual anode(s), different beam tilting combinations might temporarily be used to lower the local current pick-up on these anodes until permanent, corrective actions are taken (for example until the pot tendin machine (PTM) is available). A beam movement - or combinations of movement of both beam sections - to increase the ACD at the anode with deviation will be dependent of where these anodes are positioned.

Claims

1. A suspension arrangement for anode beams in cells of Hall-Héroult type for electrolytic production of aluminum including an anode superstructure, an elon generally horizontally disposed anode beam supporting anodes, and a sus arrangement for supporting said anode beam from said anode superstruct movement relative thereto, including jacks spaced at positions along the longit center line of said anode beam and supporting said anode beam from said superstructure, for selectively lifting or lowering said anode beam vertically rela to said anode superstructure and for selectively lifting or lowering either of th opposite longitudinal ends of said anode beam relative to the other end t further including torsional means, mounted on said anode beam and said superstructure, for preventing said anode beam from rotating about the longit axis thereof, and guide means mounted on said anode beam and said superstructure for cooperative engagement for preventing said anode bea moving sideways in opposite horizontal directions transverse to said longitu axis,

c h a r a c t e r i s e d in t h a t

the anode beam is divided into two anode bar sections (A, B) aligned one aft other in the longitudinal direction of the cell, where each anode bar secti provided with two jacks and have torsional means arranged at or near the e each of said anode bar section.

2. A suspension arrangement according to claim 1,

c h a r a c t e r i s e d in t h a t

said torsional means comprises, adjacent each said end of said anode bar se a torsion shaft rotatably mounted on said anode superstructure, a pair of first members rigidly attached at first ends thereof to respective ends of said torsi shaft, and a pair of second arm members linked at first ends thereof to second of respective said first arm members, second ends of said second arm membe being rotatably attached to respective sides of said anode bar section.

3. A suspension arrangement according to claim 1

c h a r a c t e r i s e d in t h a t

said guide means comprise vertically extending guideways on said an superstructure, and guide shoes mounted on said anode bar and vertically sl engaging said guideways

4. A suspension arrangement according to claim 1

c h a r a c t e r i s e d i n t h a t

said guide means comprise vertically extending guides on said an superstructure, and rollers mounted on said anode bar and vertically rolli engaging said guides.

5. A suspension arrangement according to claim 1

c h a r a c t e r i s e d in t h a t

each anode bar section (A, B) can be tilted to an angular position independ the other.

6. A suspension arrangement according to claim 1,

c h a r a c t e r i s e d in t h a t

each anode bar section (A, B) can be raised / lowered independently of the o

7. A method for stabilizing the operation of an electrolytic cell of Hall-Héroult type aluminium production, by use of the suspension arrangement of claims 1 - 6 , c h a r a c t e r i s e d in t h a t

the divided anode beam to be aligned in a position where it can adapt to a in anode - cathode distance due to a change of metal pad curvature in the c

8. A method for stabilizing the operation of an electrolytic cell of Hall-Héroult type aluminium production, by use of the suspension arrangement of claims 1 - 6 , c h a r a c t e r i s e d in t h a t

the divided anode beam can be aligned in a position where it can compens uneven current distribution during start-up and early operation of the cell.

9. A method for stabilizing the operation of an electrolytic cell of Hall-Héroult type aluminium production, by use of the suspension arrangement of claims 1 - 6 , c h a r a c t e r i s e d in t h a t

it is applied to quench anode effect by creating a high, turbulent bath flow to alumina rich bath into the ACD area, and to create a tilted underside of the a to help gas escape from the lower surface thereof.

10. A method for stabilizing the operation of an electrolytic cell of Hall-Héroult typ aluminium production, by use of the suspension arrangement of claims 1 - 6 , c h a r a c t e r i s e d in t h a t

it is applied in situations with known failures at individual anode(s), where diff beam tilting combinations can temporarily be used to lower the local current pic on the actual anodes until permanent, corrective actions are taken.