NZ202204A - Removing electrolysis bath residues from anodes by mechanised chipping - Google Patents

Description

Prterrty Data(s): ........

Complete Spaotfication Filed: !^m?? Class: Pubtioation Data: J16 AUG 19951 P.9. Journal, Nk NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION A PROCESS AND AN APPARATUS FOR THE REMOVAL BY CHIPPING OF ELECTROLYSIS BATH RESIDUES FROM PRECALCINED ANODES id We, ALUMINIUM PECHINEY, 2 8 rue de Bonnel, 694 3 3 Lyon, France, a French company, hereby declare the invention for which & / we pray that a patent may be granted to aox/us, and the method by which it is to be periormed, to be particularly described in and by the following statement:- 80A2-04 This invention relates to a process and apparatus for the removal by chipping of electrolysis bath residues from used precalcined anodes withdrawn from electrolysis cells for the production of aluminium by the Hall-Heroult process.

In electrolysis cells of the type in question, each anode unit comprises a moulded and precalcined carbon block comprising a certain number of closed cavities in which suspension and electrical connection means are sealed by casting a special molten cast iron or, in some cases, by means of a carbon-containing paste. These -means . are ...generally steel studs usually two to six in number, connected by flanges which are themselves welded to a suspension rod which is designed to lock onto the anode bar. A system of'this type is described, for example, in New Zealand Patent Specification No. 136312 and in United States Patent No. 4,119,505, both in the name of ALUMINIUM PECHINEY.

After an anode has been used, the entire anode unit is replaced. It comprises four recoverable and recyclable elements, namely: - the rod-flange assembly which will be resealed in a new precalcined anode, - the carbon residue or "butt" which, after suitable treatment, will be used as one of the constituents of the anode paste, - the electrolysis bath accumulated on the anode in the form of crusts wh'ich, after suitable treatment, will be reintroduced into the cells, - the sealing cast iron which will be re-used for sealing new anodes r The present invention is concerned with the separation of electrolysis bath crusts from the remainder of the anode system. .v .

This operation is normally carried out using more or less mechanised means in the form, of scrapers, picks, optionally vibrating power chisels, rakes, completed in some cases by the action of vibrating platforms which remove bath material detached from the anode unit.

Equipment of this type requires the continuous presence and intervention of operators under often hard conditions of heat, noise and dust difficult to contain.

The above-mentioned US Patent No. 4,119,505 describes an arrangement for breaking up crusts by pressure and impact which may be fitted to a service vehicle, for example of the semi-gantry type, and which acts on the cell itself when the used anode is withdrawn.

This arrangment.. is no longer compatible with current requirements regarding the collection of fluorine-containing effluents because that part of the cell being worked on has to be kept open to the atmosphere, which results in the release of fluorine-containing exhaust into the atmosphere from the cell, upsetting its thermal equilibrium.

In addition, the operating conditions of modern high-power cells, such as the 180,000 amp cells described in the following ALUMINIUM PECHINEY Patents: New Zealand Patent Specifications Nos. 180454, 182677, 183515 and 189577 and U^'S. Patent Specifications Nos. 4,169,034 and 4,200,513, which are fed with alumina at specific points rather than by the traditional crust-breakers, result in the formation of a solidified, very hard and extremely thick surface crust of electrolyte, which contributes towards rendering ineffective the means for removing the crusts from the anode butts by simple vibration or by lightweight pneuaatic tools.

The present invention relates to a process for the removal by chipping of electrolysis bath residues from used 'A t ' J ' £ £.03L3&{ anode units withdrawn from cells for the production of aluminium by the Hall-Heroult process, said units comprising a carbon residue or "butt" in which are sealed flanges welded to a suspension rod, characterised in that the used anode units are positioned on a frame designed to tilt about a horizontal axis, the frame is tilted to bring the suspension rod substantially to the horizontal, the electrolyte residues adhering to the flanges and to the carbon butt are broken by means of a tool which acts both by impact and by static thrust and the residues of the bath which fall by gravity are collected in a receiving means.

The breaking up of the electrolyte residues is preferably carried out in several successive stages and, between each stage, the used anode unit is rotated through a limited angle about an axis substantially coaxial with the axis of the suspension rod, each stage in the breaking up of the residues being carried out by combined displacements of the impact and static thrust tool along its vertical axis, parallel to its vertical axis and to the tilting axis of the frame and parallel to its vertical axis perpendicularly of the tilting axis of the frame.

The present invention also relates to an apparatus for carrying out the process, comprising: a frame comprising at least one support for a used anode unit, means for tilting the frame about a horizontal ..shaft, means for rotating the support, means for chipping the electrolyte residues, means for recovering the electrolyte residues.

Figures 1 to 4 show the various parts of the apparatus. Figure 1 illustrates the apparatus as a whole, the anode unit being shown in the receiving position (dotted lines) and in the chipping position (solid lines).

Figure 2 is a section through and Figure 3 a plan view of the means used to support, hold, three anode units arranged in-line. 2.02204 Figure 4 is a detailed view of'the locking mechanism for the suspension rod.

The apparatus comprises two separate parts which cooperate with one another to obtain the overall result, namely: the tilting support for the anode units and the chipping assembly: 1) The tilting support for the anode units: This support performs the following functions: it receives the used anode units arriving from the electrolysis shop with the supporting rod in the vertical position, - it positions and holds the anode units, - it tilts the anode units into the chipping position, it subjects the anode units to limited, successive rotations about an axis substantially coinciding with the axis of the suspension rod, it recovers the electrolysis bath;;residues.

The tilting support comprises a frame formed essentially by a beam (1) which is designed to rotate about its axis (2) on bearings (3, 3') under the power of a motor (not shown). The beam (1) supports on the one hand one or more (three in the embodiment illustrated) anode supports (5) equipped with guides (6) which position and centre the anode units and, on the other hand, an equal number of elements (7) for gripping and locking the suspension rods (8). In addition, each anode unit comprises sealing flanges (9) and a carbon butt (10). The maximum limits to which the electrolysis bath crusts to be removed are capable of growing are shown diagramma-tically by a dotted line on one of the anodes. Each anode support (5) is equipped with an individual motor (11) for rotating it about an axis (12) substantially coinciding with the axis of the anode rod (8).

The mechanism (7) by which the anode rods are locked onto the supporting arms (13) has certain original features: it comprises a fixed part (14) and a rotary part (15) made up of two identical elements (15a and . 15b) secured to the fixed part by bolts (16) with^a ' s. 6 clearance which, although reduced, is sufficient to -enable the part (15) to rotate about an axis which substantially corresponds to the axis (12) of the suspension rod. The two rotary elements (15a) and (15b) comprise a cutout (17) which corresponds to the cross-section of the suspension rod (8). The fixed part (14) is secured to the supporting arm (13) by a bolt (18) and a shock-absorbing block (19) of rubber or other elastomer. In addition, it rests on the supporting arm (13) through two rubber stops (20) which greatly reduce the transmission to the frame of the vibration caused by the chipping assembly.

By means of .this mechanism, each anode may be presented to the chipping assembly in the most favourable successive positions for ensuring the rapid and complete elimination of the electrolysis bath residues.

The beam (1) is rotated about its axis by means of jacks (21) . Normally, it is able to rotate through 90° so as to tilt the anodes into a position where the rod (8) is horizontal or forms only a relatively small angle of, for example, less than about 20° with the horizontal.

In the embodiment illustrated, the rotation takes place in such a way that the suspension rod is situated opposite the impact tool.

In the tilted position, the anodes are situated above means for recovering the bath crusts by gravity.

In the.embodiment illustrated, the recovery means comprises a grille (22) of which the mesh size allows through blocks of salt detached from the anode having a maximum size compatible with the following treatment installation. A hopper (not shown) may be positioned below this grille, feeding a conveyor belt which carries the electrolyte residues to recycling means known per se (magnetic removal of iron, crushing, grading, etc).

The recovery means may with, advantage be completed by a dust extractor which acts for example in 1' 202204 2OD30I 7 present between the anode supports and the grille. The pipe (2 3) is connected to an extractor equipped with suitable filters. 2) The chipping assembly: The chipping assembly performs the actual chipping function, i.e. the breaking up by impact and static thrust of the electrolysis bath crusts formed around the upper part of the anode butt.

Although it is possible in ■ theory to carry out the chipping operation by a pneumatic system, it has been found that the operation can be carried out more v quickly, more effectively and more completely by using a hydraulically controlled impact tool which applies.both a static thrust and an impact of which the amplitude and frequency are optimised for the particular conditions of the operation in question. A tool of the hydraulic "concrete breaker" type is perfectly suitable.

This tool (24), which is equipped with a suitable pick (25), is mounted on a pivotal arm (26) hinged at several points and controlled by hydraulic jacks (32) and (33) which enable all the necessary movements of the tool to be obtained while keeping its axis (34) substantially vertical.

In the ..embodiment illustrated, the arm moves the impact tool (24) by a distance of 0.5 metre in the horizontal direction and by a distance of 1.5 metres in the vertical direction.

In addition, the arm (26) and its control jacks (32, 33) are able to move together parallel to the beam (1) and to stop in any position relative to the anode supports.

By combining these three movements, the pick (25) is given access to the entire space in which the electrolysis bath residues may have accumulated on each anode unit.

The arm and the jacks are preferably integral with a cabin (35) designed to travel along rails (36) under the control of the machine operator. The cabin_(35j may be {■ sound-proofed and supplied with filtered air to provide the machine operator with satisfactory working conditions.

The use of this apparatus on used anode units taken from 180,000 amp electrolysis cells enables the electrolysis bath residues to be removed in less than 5 minutes under perfect conditions of hygiene and safety.

Claims (10)

WHAT WE CLAIM IS:

1. A process for the removal by chipping of electrolysis bath residues from used anode units withdrawn from electrolysis cells for the production of aluminium by the Hall-Heroulti process, said units comprising a carbon residue or "butt" in which are sealed flanges welded to a suspension rod, characterised in that the used anode units are positioned on a frame tilting about a horizontal axis, the frame is tilted to bring the suspension rod substantially to the horizontal, the electrolyte residues adhering to the flanges and to .the carbon butt are broken up under the action of a tool acting both by impact and by static thrust and the bath residues which fall by gravity are collected in receiving means.

2. A process as claimed in Claim 1, characterised in that the breaking-up of the electrolysis bath residues is carried out in several successive stages and in that, between each stage, the used anode unit is rotated through a limited angle about an axis substantially coinciding with the axis of the suspension rod.

3. A process as claimed in Claim 2, characterised in that each stage in the breaking up of the electrolysis bath residues is carried out by combined displacements of the impact and static thrust tool along its vertical axis, parallel to its vertical axis and to the tilting axis of the frame and parallel to its vertical axis perpendicularly of the tilting 'axis of the frame.

4. An apparatus for carrying out the process claimed in any of Claims 1 to 3, characterised in that it comprises: - a frame comprising at least one support for a used anode unit, - means for tilting the frame about a horizontal axis, - means for rotating the support, - means for chipping the electrolysis bath residues, - means for recovering the electrolysis bath residues^' £02^4

5. An apparatus as claimed in Claim 4, characterised in that the means for chipping the electrolysis bath residues comprise a pick fixed to a vibration and static thrust generator which has a substantially vertical axis and which is connected to means for displacing it along its vertical axis and parallel to that axis.

6. An apparatus as claimed in Claim 4, characterised in that the support for a used anode;unit'comprises means for locking the suspension rod comprising a fixed part and a rotary part made up of two identical elements secured to the fixed part by a plurality of bolts with a clearance sufficient to allow the rotary part to rotate about an axis which corresponds Substantially to the axis of the suspension rod, the two rotary elements comprising a cutout substantially corresponding to the cross-section of the suspension rod.

7. An apparatus as claimed in Claim 6, characterised in that the fixed part of the locking means is secured to the supporting arm by a bolt from which it is insulated by vibration-damping means.

8. An apparatus as claimed in Claim 6 or 7, characterised in that the fixed part of the locking means rests on the supporting arm through vibration-damping means.

9. A process as claimed in Claim 1, substantially as hereinbefore described with particular reference to the accompanying drawings.

10. An apparatus as claimed in Claim 4, substantially as hereinbefore described with particular reference to the accompanying drawings. ^ TV * 13 OCT3982 A- }> PARK « So If «fw km THe APtW!AHn