FR2514790A1 - Cleaning spent anodes obtd. in mfg. aluminium by electrolysis - in jig where hydraulic chisels are used to knock electrolyte residues off carbon anode stumps - Google Patents

Abstract

In mfg. Al by the Hall-Heroult process, spent anodes, i.e. carbon stumps, are obtd., which are attached by lugs to anode suspension bars. The spent anodes are covered with electrolyte residue. To reclaim both the spent anodes or stumps, and the residue, the latter is knocked off the stumps by percussion chisels or picks. In the pref. cleaning jig, the stumps are located on supports while their suspension bars are vertical. The supports are then swivelled through an arc of 90 deg. so the stumps can be cleaned by hydraulic chisels. The electrolyte residue removed from the stumps falls through a grid into a collector bin. All the parts of the spent anodes are reclaimed and re-used.

Description

METHOD AND DEVICE FOR Lt} .LItsINATION BY STITCHING
ELECfRflLYSE BATH JZESIDllS ON PRE-COOKED ANODES
The present invention relates to a process and an apparatus for the removal by pricking of the residues of electrolysis bath on spent prebaked anodes, removed from the electrolysis tanks for the production of aluminum by the Hall-Héroult process.

In these tanks, each anode element comprises a carbon block, molded and precooked comprising a certain number of closed cavities in which are sealed, by casting a special cast iron, or sometimes by means of a carbon paste, suspension means and electrical connection. These means are generally steel rods two to six in the most frequent cases - connected by lugs themselves welded to a suspension rod which comes to lock on the anode bar. Such a system is described, for example, in French patent no. 1,519,475 (= US. 3,351,546) and in French patent no. 2,350,407 (= US. 4,119,505), one and the another in the name of ALWfINIW1 PECHINEY.

When an anode is worn out, the entire anode element is replaced, which includes four recoverable and recyclable elements - the rod-lug assembly, which will be resealed in a precooked anode.
new, - the carbon residue or "cigarette butt" which will be, after treatment agreed
ble, used as one of the constituents of the anode paste, - the electrolysis bath, accumulated on the anode in the form of crusts
and which will, after suitable treatment, be reintroduced into the tanks, - the sealing cast iron which will be used to seal the new
old anodes.

The invention relates to the separation of the crusts of the electrolysis bath from the rest of the anode system.

This operation is usually done with more or less mechanized means using scrapers, jackhammers, vibrating or non-vibrating chisels, harrows, sometimes supplemented by the action of vibrating tables ensuring the evacuation of the bath detached from the element. anodic.

Such equipment requires the continuous presence and action of operators in often painful conditions of whining, noise and difficult to collect dust.

In the French patent FR. 2,350,407 already cited, a device for breaking crusts by pushing and percussion, which can be adapted to a service machine, of the semi-portal type for example, and which operates on the tank itself, at the time removal of the spent anode.

This device is no longer compatible with the factual requirements on the capture of fluorinated effluents, because it obliges to keep open the open part of the tank on which one operates, which leads to the release into the atmosphere, fluorinated emissions from the tank, and disturbs its thermal balance.

In addition, the operating conditions of modern high-power tanks, such as the 180,000 amp tanks described in the ALUMINUM PECHINEY patents: FR. 2,324,761 (= US 4,049,518), FR.

2,333,060 (= US 4,072,597), FR. 2,343,826 (= US 4,090,930), FR. 2 423554 (= US.4 210 514), FR. 2,425,482 (= US.4 16n 034), PR. 7,427,760 (= US.

4,200,513), and the supply of alumina of which is now carried out and no longer by traditional crust breakers, leads to the formation of a superficial crust of fixed electrolyte which is very solid and thicker. important, which contributes to making ineffective the means of eliminating crusts on anode butts by simple vibration or by light pneumatic tools.

The object of the invention is a process for removing, by stitching, residues of the electrolysis bath on the spent anode elements removed from the tanks for the production of aluminum by the lIall-! Kroult process, said elements comprising a carbon residue, called "butt" in which are sealed lugs welded to a suspension rod, pl-océée according to which one positions the anodic worn elements on a chassis rocking around a horizontal axis, one rocks the chassis so bring the suspension rods substantially horizontally, break the electrolyte residues adhering to the legs and the carbon butt, under the action of a tool acting both by percussion and static thrust and collect the residue from the bath which fall, by gravity, into a means of reception.

Preferably, the breaking of the electrolyte residues is carried out in several successive stages and, between each stage, there is a limited rotation of the spent anode element around an axis substantially coincident with the axis of the suspension rod. , each stage of breaking of the residues being effected by combined displacements of the percussion and static thrust tool along its vertical axis, parallel to its vertical axis and to the tilting axis of the casts, and parallel to its vertical axis , perpendicular to the chassis tilt axis.

Another object of the invention is a device for implementing the method comprising - a chassis with at least one worn anode element support, - a means for tilting the chassis around a horizontal axis, - a means for rotation of the support, - a means for pricking the electrolyte residues, - a means for recovering the electrolyte residues.

Figures 1 to 4 show the different parts of the device.

Figure 1 shows the entire device where the anode element is shown in the receiving position (dotted lines) and in the stitching position (solid lines).

Figure 2 shows in section, and Figure 3 in plan, the support device, immobilization, tilting and rotation, designed for three spent anode elements arranged in line.

Figure 4 shows the detail of the locking device of the suspension rod.

The apparatus comprises two distinct parts which cooperate to obtain the overall result: the tilting support of anode elements and the stitching device 10 / - The tilting support of anode elements
It performs the following functions - reception of spent anode elements arriving from the electrical room
trolysis, with the support rod in a vertical position, - positioning and immobilization of the anode elements, - tilting of the anode elements in the stitching position, - limited and successive rotations of the anode elements around a
axis substantially coinciding with the axis of the suspension rod, - recovery of electrolysis bath residues.

The tilting support comprises a frame, essentially foxne by a beam (1) which can rotate around its axis (2) on the bearings (3) (3 '), thanks to a motor not shown. The beam (1) supports, on the one hand, one or more (three in the case shown) anode supports (5), provided with guides (6) which ensure the positioning and centering of the anode elements and, on the other hand, an equal number of devices (7) for gripping and locking the suspension rods (8). Each anode element further comprises the sealing lugs (9) and the carbon negot (10). On one of the anodes, there is shown schematically by a dotted line the lignites of the bulk that.

can reach the maximum of the crusts of electrolysis bath to be eliminated. Each anode support (5) is provided with an individual motorized rotation means (11), around a sensiblenent axis (12) coincident with the axis of the anode rod (8).

The locking device (7) of the anode rods on the support arms (13) has certain original features: it comprises a fixed part (14) and a rotary part (15), formed of two identical elements (15a and 15b), tightened on the fixed part by the bolts (16), with a reduced clearance that is sufficient for. ensure its rotation about an axis which corresponds substantially to the axis (12) of the suspension rod. The two rotary elements (15a) and (15b) have a cutout (17) which corresponds to the cross section of the suspension rod (8). The fixed part (14) is secured to the support arm (13) by a bolt (18) and a rubber or other elastomer damper block (19). In addition, it comes to bear on the support arm (13). by two rubber stops (20) which greatly reduce the transmission to the chassis of vibrations caused by the stitching device.

Thanks to this device, each anode can be presented to the stitching device in the most favorable successive positions to ensure rapid and total elimination of the electrolysis bath residues.

The chassis beam (1) is rotated about its axis under the effect of the jacks (21). It can normally rotate 90 "so as to tilt the anodes to a position where the rod (8) is horizontal or forms with the horizontal only a relatively limited angle, less than about 200 (value given without limitation) .

In the case shown, the rotation is carried out so that the suspension rod is on the side of the percussion device.

In the tilted position, the anodes are placed above a device for recovering bath crusts by gravity.

In the case shown, the recovery device comprises a grid (22) whose mesh size allows the passage of blocks of salt detached from the anode, of a maximum dimension compatible with the treatment tallation ions which follows. . Below this grid, a hopper (not shown) can be placed feeding a conveyor belt which transports the electrolyte residues to recycling devices which are known in themselves (magnetic removal, grinding, calibration, etc. ..).

The device can advantageously be supplemented by a dust vacuum cleaner which acts, for example, in the space situated between the anode supports and the grid. The pipe (23) is connected to a vacuum cleaner fitted with suitable filters.

20 / - The stitching device
It provides the actual stitching function, that is to say the case by percussion and static thrust of the crusts of the electrolysis bath which coat the upper part of the anode butt.

Although it is theoretically possible to operate the stitching by a pneumatic device, it has been found that the operation was simultaneously faster, more efficient and more complete if a percussion tool with hydraulic control was used, which provides both a static thrust and a percussion whose amplitude and frequency are optimized for the particular conditions of this operation.

A hydraulic "hrise-concrete" type tool is ideal.

This tool (24) provided with a suitable chisel (25) is mounted on an articulated arm (26) provided with a plurality of articulations and controlled by the hydraulic cylinders (32) and (33) which make it possible to obtain all the tool movements while constantly maintaining its axis (34) substantially vertical.

In the case shown, the arm moves the percussion tool (24) in the horizontal direction, with an amplitude of 0.5 m and, in the vertical direction, of 1.5 m.

In addition, the assembly of the arm (26) and its control jacks (32) (33) can move parallel to the chassis beam (1), and position itself at any location relative to the anode supports .

By combination of these three movements, the chisel (25) can access the entire volume in which, on each anode element, electrolysis bath residues may have accumulated.

Preferably, the arm and the jacks are integral with a cabin (35) movable on rails (36) on the initiative of the operator. The cabin (35) can be soundproofed and supplied with filtered air to ensure satisfactory working conditions for the operator.

The implementation of this device, on spent anode elements coming from electrolysis tanks at 180,000 amperes, makes it possible to ensure the elimination of the residues of electrolysis bath in a time of less than five minutes under perfect conditions of health and safety.

Claims (8)

10 / - Method of elimination by stitching, of electrolysis bath residues on the spent anode elements removed from the tanks for the production of aluminum by the Hall-Héroult process, said elements comprising a carbon residue, known as a "butt" in which are lugs welded to a suspension rod, characterized in that the worn anode elements are positioned on a chassis rocking about a horizontal axis, the chassis is tilted so as to bring the suspension rods substantially to horizontally, the electrolyte residues adhering to the legs and the carbon butt are broken under the action of a tool acting both by percussion and static thrust and the bath residues which fall by gravity are collected in a medium reception. 20 / - Method of elimination according to claim 1, characterized in that the electrolysis bath residue is broken up in several successive stages and that, between each stage, there is a limited rotation of the anode element worn around an axis substantially coincident with the axis of the suspension rod. 30 / - Method of elimination according to claim 2, characterized in that each stage of breaking of the electrolysis bath residues is carried out by combined displacements of the percussion tool and of static thrust along its vertical axis, parallel to its axis vertical and to the chassis tilt axis, and parallel to its vertical axis, perpendicular to the chassis tilt axis. 40 / - Device for implementing the method according to any one of claims I to 3, characterized in that it comprises - a chassis with at least one worn anode element support, - a means for tilting the chassis around a horizontal axis, - a means of rotation of the support, - a means of stitching the residues of electrolysis bath, - a means of recovering residues of electrolysis bath. 50 / - Device according to claim 4, characterized in that the means for tapping the residues of electrolysis bath comprises a chuck attached to a generator of vibration and static thrust of substantially vertical axis, and connected to displacement means along its vertical axis and parallel to this axis. 60 / - Device according to claim 4, characterized in that the worn anode element support comprises a locking means of the suspension rod (12), comprising a fixed part (14), a rotary part (15) formed of two identical elements (15a) and (15b) tightened on the fixed part by a plurality of bolts (16) with sufficient play to ensure its rotation about an axis which corresponds substantially to the axis (12) of the rod suspension, the two rotary elements (15a) and (15b) comprising a cutout (17) corresponding substantially to the cross section of the suspension rod (8). 70 / - Device according to claim 6, characterized in that the fixed part (14) is subject to the support arm (13) by a bolt (18) from which it is isolated by a vibration damping means. 80 / - Device according to claim 6 or 7, characterized in that the fixed part (14) of the locking means is supported on the support arm (13) by means of means (20) for damping vibrations.