WO2003074957A1

WO2003074957A1 - Method and apparatus for handling of used electrolyte containers

Info

Publication number: WO2003074957A1
Application number: PCT/NO2003/000072
Authority: WO
Inventors: Paul Hovda
Original assignee: Sunnhordland Mekaniske Verksted A.S.
Priority date: 2002-03-01
Filing date: 2003-02-28
Publication date: 2003-09-12
Also published as: IS7734A; NO318056B1; EA200500370A1; NO20021023L; NO20021023D0; AU2003208677A1

Abstract

There is disclosed a method for handling of a used potshell employed during the smelting processes, for removing of contents in it, where the contents consist of insulation bricks, bottom carbon blocks, bus bars or similar, that are embedded in tamping paste, remains of raw material from the smelting process, plus residues of any smelted metal. The method is characterised by carrying out the following stages: a) loose matter is removed from the potshell by digging out and vacuum cleaning b) bus bars, such as cathode bus bars, are split into smaller lengths, such as by sawing, and removed to separate waste storage facilities, and optionally bus bars and bottom carbon blocks are sawn up simultaneously and removed together, c) the bottom carbon blocks are sawn up into sections between adjoining blocks, and removed, d) removal of tamping paste, and e) removal of insulating bricks. An apparatus (the product) for carrying out the method, and an application thereof, is also disclosed.

Description

METHOD AND APPARATUS FOR HANDLING OF USED ELECTROLYTE CONTAINERS

The present invention concerns a method and an apparatus for removing the contents of potshells used during the melting processes. Reference is also made to a specially selected area of use.

The method according to the invention is specially connected with the dismantling of cathode potshells that are used in an electrolytic cell in an aluminium plants, for the production of molten metallic aluminium.

There is now a growing demand for waste material extracted from a pot shell to be re-circulated and recycled to the fullest extent, so that this can contribute financially to the process. The statutory constraints and concessions that international smelting plants are subject to, make this branch of industry continually aware of the need to improve its processes and to recover materials from the process. The invention concerns this dismantling process and also the quality assurance of the dismantling process of spent cathode potshells/ovens from smelting plants that produce crude aluminium. The apparatus and tools have been adapted to the following types of smelting plant:

smelting plants where potshells are dismantled /re-lined inside the electrolysis halls smelting plants where the potshells are disconnected, transported outside, dismantled and re-lined at separate facilities .

A cathode potshell for an aluminium electrolytic cell consists of a robust steel shell that is lined internally from the base up with: Several layers of insulating brick, Bottom carbon blocks with cast-in bus bars, Side-wall carbon blocks, and

Tamping paste between bottom- and side-wall carbon blocks.

The upper layer of the bottom carbon blocks thus forms the bottom of the oven/cell.

All primary plants have different lifetime periods of their furnaces/cells, for instance a plant with an annual production of 100,000 tonnes needs to dismantle and re-line about 50 furnaces a year.

With the cell in operation, the molten aluminium is separating (by electrolysis) as a lower stratum, while the raw material, cryolite, with dissolved aluminium oxide and other additives (fluorides) are added from the upper level and forms a so- called "bath". The upper anode is in contact with the bath layer.

When replacing a potshell, all the loose matter in the bottom must be removed. The loose material appears as a mixture of the rest of the bath, carbon material, solidified lumps and flakes of aluminium, and hard or brittle lumps of cryolite. Additionally, there are carbon blocks and the refractory materials remaining, either complete, i.e. in their original shape, or in more or less pulverized form. It is thus an extremely heterogeneous and complex material that shall be removed from the oven container.

The plants use different means of performing the process, that roughly consists of disconnecting the furnace from the electrical supply and cooling it down before dismantling starts. The dismantling process consists of the following activities : vacuum cleaning of loose material removal of bottom layer of residue (remains of solidified metal) excavating bottom carbon blocks/cathode bus bars. Since the bus bars are embedded in the bottom carbon blocks, it will be cut up in large pieces in one action, removal of insulation layer/fire bricks in the bottom

Tools used for this process are so-called "ploughs" or similar production machinery fitted with hydraulic tools, hammers or shovels .

Most plants have outsourced this to local contractors.

The dismantling process is characterised in that it is noisy due to the use of hydraulic hammers, and lot of dust is produced in the area, thus the work is preferably effected outdoors .

In practice, the used material from the ovens is not sorted/fractionated optimally for a re-use purpose.

The dismantling process mainly employs two methods.

1. With dry dismantling, the cathode potshell is left to cool down in air before dismantling starts.

2. With so-called wet dismantling, water is added to the potshell while the contents are still warm.

The problem with the wet method is that a fluid phase is introduced that complicates any eventual separation process. The substance that is more pulverised is sticky and difficult to handle, and also gives off more or less toxic gases such as ammonia, when water is added to it.

The dry dismantling process offers more advantages, despite the problem of dust. The sorting process is far simpler with dry material. It is preferred that the largest amount of waste should be recycled back into the process. This concerns, in particular, the white materials such as solidified metal, oxides, cryolite and similar. However, the cathode bus steel bars may also be used, since such waste is often delivered to scrap dealers. The carbon material, such as the remains of the tamping substance and cathode carbon, are generally stored at local depots.

Aluminium is characteristically a green, light metal that has a steadily increasing scope of applications in industry and for consumer goods. Further, it has been normal to recirculate the residual metals of aluminium by feeding them back to the process by re-smelting.

The actual process of producing prime aluminium is being widely adapted in an ongoing attempt to use more environmentally friendly processes.

By means of the method and apparatus according to this invention, an attempt is made to eliminate the foregoing environmental drawbacks with current methods of demolishing oven containers. This also means that a method is sought that can sort out the fractions in the dismantled matter, so that large parts - preferably all fractions - of this material can be recycled or constitute a saleable product for other areas of use.

A further aim of this invention is that the entire dismantling process shall be a closed activity, thus avoiding the previous noise and dust disturbance.

Another aim of the invention is to promote a method that is more amenable and which eliminates the problems of noise, dust and effluent in the surroundings. It is an aim of the invention is to produce a new method and apparatus for handling of potshells that shall imply quality assurance of the complete process, since the aim is for the dismantling process and sorting of waste to be conducted in an environmentally more favourable manner

In addition, such a dismantling process must, logistically, be seen in connection with the course of events (routes) that a potshell undergoes in one circulation, i.e. from its construction stage, placed in store, transported to hall for use, withdrawal from oven (such as after 3-5 years) and then back to the dismantling process, i.e. in a kind of circulation .

The method according to the invention is characterised by the features presented in the characterising clause of claim 1. The embodiments of the method which are preferred in particular, are stated in the dependent claims 1-6.

The apparatus (product) is characterised by the features presented in the characterising clause of claim 7. The embodiments of the apparatus which are preferred in particular, are stated in the dependent claims 7-12.

According to the invention (of claim 13) the apparatus (tools) and method are employed for handling and demolishing/sorting of spent cathode potshells/ovens from aluminium plants.

The invention shall now be explained further by referring to the accompanying figures, of which:

Figure 1 shows a flow chart of each stage that the potshell passes through from its disconnection from and connection to a new furnace, assembled and connected up and put into operation again. Figure 2 is an overview of a facility (building) where the dismantling process takes place, plus what tools/main appliances shall be used. Dismantling inside the electrolysis halls includes the mobile tools and covers that secure the process.

Figure 3 shows a section and structure of a cathode potshell/furnace. In addition, it illustrates the tool frame on top of the potshell frame using a vacuum cleaner for removing oxides and other loose material. Each tool included in the process can be collected from a tool store connected to the tool frame. The whole process is controlled by an operator in a closed control cabin. The operator is thus fully protected from ingress of noise, gas and dust.

Figure 4 shows cutting tools for use in splitting up the bottom carbon blocks and cathode steel bus bars.

Figure 5 shows how the operator removes the split up sections of bottom carbon blocks including cathode steel bus bars ready for processing, sorting and packing in container. The blocks are removed by means of a gripping tool (a claw) .

After the bottom- and side-wall carbon blocks have been removed, the tool/claw is used for digging out the insulating bricks. This material is ground up and stored in a so called big bag. The potshell is vacuumed in its bottom and is then ready for onward transport to the facility for control, mechanical repair and re-lining.

As mentioned in the introduction, the complete potshell is removed from its site in the furnace and is replaced with a previously re-lined potshell that is installed. The furnace can thus be re-started quickly and come on stream.

Figure 1 shows how a spent potshell is removed from its position in the electrolysis hall 22, and transported via a series of facilities (highly generalised outline) where it is cleaned and prepared for re-lining and transported back to the electrolysis hall for connection to the production in hall 22.

The potshell to be dismantled is indicated with 10 and is collected in the electrolysis hall 22 for transport to a cooling area with a specially designed wagon marked with 12.

The cooling area/holding stage, marked 14, is fitted with a rail-mounted crane or wagon. The spent potshell is transported onwards to the cleaning facility with sorting plant for used materials .

The potshell enters the holding stage 14. In an adjoining side hall 16 the dismantling apparatus according to the invention is arranged, and here the potshell is cleaned of waste matter as explained in the foregoing. The actual digging out thus takes place in a protected separate area and with subsequent sorting at source, where remains of firebricks, carbon and steel are removed and sent to sorting and recycling to be optimally re-used, as previously mentioned.

After the cleaning in hall 16 the potshell 10 is sent back to the line via the holding stage 14, and then on to a facility 18 for mechanical repair and any alignment of the potshell 10. The potshell 10 is then sent to a facility 20 where it is re- lined. This means that it is made ready for re-use in an electrolysis cell.

Next, the potshell 10 is put on a wagon 12 returning it to the electrolysis hall for connection and operation. At the bottom left of the figure there is a sketch of a potshell that has been removed from the production oven.

Figure 2 shows a hall 24 where the dismantling process takes place under cover in a closed system. The shell 10 enters the system on wagon 12 to the cooling area/holding stage 25 from where a crane system 26 collects the shell 10 from the holding stage 25 and takes it forward to the entrance to the dismantling facility 28.

The holding stage 25 and dismantling unit 28 are separated by a wall with a entrance that can be opened, in order to prevent noise, dust and gases from affecting the working environment in the rest of the hall 24 and the surroundings.

The actual dismantling unit 28, see figure 3, comprises a tool rig 30 that is mounted up on the oven frame and stabilised for effecting the dismantling. Built into the rig is a trussed frame with guides for lengthwise 32 and transverse movements for presenting service tools in the two horizontal directions.

The rail system 32,34 for lengthwise and transverse feed with holder 36 tool 38 (shown here vacuum cleaning) are arranged such that the potshell 10 is positioned between the feet of the frames and under the rail system. The tool thus has full access to all parts of the contents in the bottom of potshell 10. In one corner of the rig 30 there is an operator cabin 42 from where an operator can monitor and control the dismantling process .

The transverse movement of the holder 36 (see figure 3) is done by means of it being mounted on a traverser carriage 36 that can be moved across in a travelling crane that is resting on legs, one on either side, and which can move on wheels on a rail, i.e. wheels run between an upper 32a and a lower 32b rail on either side of the oven container to enable movement along the potshell.

The holder (traversing carriage) 36 is encased and comprises a remote-controlled engine for operating the driving wheels for making traverse movements, and any drive gear for the lengthwise movement. The carriage also contains devices for connecting different tools. The actual tool can be arranged and removed from the carriage by means of a separate collecting device such as a hydraulic derrick, since the tool not in immediate use can be temporarily placed in a holding area, which is not detailed.

Figure 3 shows the rig 30 mounted on the top of the oven and the first phase of vacuum cleaning is underway. The tool carriage 36 is fitted with a vacuum cleaner 38 underneath it. The vacuum cleaner hose 40 leads to an external suction unit that is not shown here.

It is most practical if the tool carriage 36 is designed for rapid changing of different dismantling tools for other operations, i.e. for mounting of scrapers, punching hammers, grab devices, claws, saw units (circular saw, angle grinder) and the like to loosen and retrieve large fragments from the potshell. The actual tool can be arranged and removed from the carriage by means of a separate collecting device, since the tool not in immediate use can be temporarily placed in a holding area, (not shown) .

Figures 3 and 4 indicate the base lining 35 of firebrick, the overlaying bottom carbon block 33 and the bus bars 39 that lie embedded in the tamping paste.

Figure 4 shows a tool carriage 36 fitted with cutting/sawing equipment 44 (with necessary motor) for operating a saw blade 44 used for cutting\dividing the bottom carbon block 33 and cathode steel bus bars 39.

Figure 5 shows a carriage with a hydraulic driven crane 46, with grips 48 used for collecting segments of the bottom carbon block 33 and cathode steel bus bars 39 from the potshell 10. The figure shows a rail traversing crane that can move across the area and which is thus used for lifting the actual potshell off (and onto) the wagon 12.

In this description it is shown that the complete operation can be conducted by means of a single rig 30 with tool carriage 36, where the holder 36 is replaced according to what operation is required for servicing the material down below in the potshell. Since such material can be highly heterogeneous, i.e. if materials vary distinctly in size, from pulverised form to large blocks/slabs, the need for special tools varies from one potshell to the other.

According to an alternative method, a series of such rigs may be arranged consecutively, where each rig has a fixed special tool in one holder. The potshell is then transported from one facility to the next where the shell is consecutively given the proper treatment for each station as needed in the particular case.

It is thus not necessary for each facility to have its own operator cabin (42 on the figures) . Instead, a single centrally placed operator cabin or control room can be used, from which the operator can remotely control all phases of the process. A more detailed control and monitoring of conditions down in the potshell can be done by means of video cameras.

According to alternative practices, the potshell can be raised up on its edge during dismantling, or turned upside down so that loose fragments fall off for further treatment. The tooling of the apparatus can easily be adapted to such positions of the potshell.

The invention presented here presents a fresh and more environmentally friendly method and apparatus for handling the waste material that is taken out or dismantled from used potshell. This eradicates the previous disadvantages of such shell dismantling, since the process can now be fully closed off, so that no noise or dust is emitted to the surroundings. With the invention each operator carrying out or monitoring the dismantling process is fully protected from noise, dust and any harmful gases.

Claims

C L A I S.

1. Method for handling of a used potshell utilized in smelting processes, for removing its contents, where the contents consist of insulating brick, bottom carbon blocks, bus bars or similar that are embedded in the tamping paste, remains of raw material from the smelting process, plus residues of any smelted metal, characterised by carrying out the following steps: a) loose matter is removed from the potshell by digging out and vacuum cleaning b) conductor rails, such as cathode rails, are cut into smaller lengths, such as by sawing, and are removed to separate waste storage, c) the bottom carbon blocks are divided by sawing in the sections between adjoining blocks, and are removed, optionally the bus bars and bottom carbon blocks are sawn up simultaneously and removed together, d) removal of tamping paste, and e) removal of insulating bricks.

2. Method according to claim 1, characterised by the potshell being handled at a facility by means of a handling machine/a rig that can move along the potshell and which contains a holder for mounting different tools for handling the material in the potshell, said tools comprising:

-a digging implement for the initial detaching, digging out and removal of the loose matter, -a suction device for removing of dust,

-a sawing device, such as a circular saw, for segmenting conducting bus bars and cathode carbon blocks, -gripping device, such as a gripping claw, for removing parts of the conductor rail, bottom carbon blocks, and other large, solid and block shaped parts of the material, and

- a place for an operator for manual control of the process .

3. Method according to claim 1-2, characterised by the use of a carriage that can be moved along and across the potshell, and arranged for simple replacement of the said tools.

4. Method according to claim 1-2, characterised by the use of a carriage fitted with tools, since the carriage is replaceable, in that a holder with the necessary tool can be arranged.

5. Method according to claim 1-4, characterised in that the longitudinal movement occurs by means of the holder being mounted on a traversing carriage that can move along a girder

(as in a travelling crane) , where the beam is supported on two legs on either side, and which is moveable on a rail one on each side of the potshell to provide the movement along it.

6. Method according to any of the preceding claims, characterised by one of the actual tools is arranged and removed from the holder by means of a separate collecting device, such as a hydraulic driven derrick, in that the tool not in immediate use can be temporarily placed in a holding area for different tools.

7. Apparatus for handling of a spent potshell employed during the smelting processes, for removing of contents in it, where the contents comprising insulation bricks, blocks of bottom carbon material, bus bars (such as cathode steel bus bars) or similar that are embedded in tamping paste, remains of raw material from the melting process, and residues of any melted metal, characterised by: an facility for handling the potshell comprising a handling machine/ a rig that can move along the potshell and which includes a holder for mounting different tools that handle the material in the potshell, in that the tools comprise : - a digging implement for the initial detaching, digging out and removal of the loose matter,

- a suction device for removing of dust, - a sawing device, such as a circular saw, for segmenting bus bars and cathode carbon blocks,

- a gripping device, such as a mechanical claw, for removing parts of the conducting bus bars, blocks of bottom carbon material, and other large, solid and block- shaped parts of the material, and

- a location for an operator for manual control of the process .

8. Apparatus according to claim 7, characterised by a holder that can move in longitudinal and transverse direction of the potshell, and is arranged for easy replacement of the said tools .

9. Apparatus according to any of claims 7-8, characterised by_ a holder fitted with a tool, in that the holder is replaceable, so that a holder with the required tool can be arranged

10. Apparatus according to claims 7-9, characterised by the longitudinal movement being achieved by means of the holder being mounted on a traversing carriage that can be moved along a girder (as in a travelling cane) , where the beam is supported on two legs, one on either side, and which is moveable on a rail on each side of the potshell to provide the movement along it.

11. Apparatus according to the foregoing claim 7-10, characterised in that the actual tool is arranged and is removed from the holder by means of a separate collecting device, such as a hydraulic driven derrick, in that the tools not in immediate use, are temporarily placed in a holding area for the different tools.

12. Apparatus according to any of the preceding claims 7-11, characterised by a number of rigs arranged in a series in which each rig is fitted with a fixed special tool in a holder, in that the potshell is moved from one facility to the next where the shell is consecutively given the proper treatment needed in the particular case.

13. Application of the apparatus and method for handling cathode potshells used in the electrolysis hall in an aluminium plants, and which shall be taken out of operation, shall be cleaned (dismantled) , repaired, re-lined and re-used in the electrolysis.

14. Application according to claim 13, for recycling of waste from the potshell.