EP3884082A1

EP3884082A1 - A method and equipment for storing and transporting hot gas emitting components

Info

Publication number: EP3884082A1
Application number: EP19802079.4A
Authority: EP
Inventors: Are DYRØY; Morten Karlsen; Albert BERVELING; Tore ØREN
Original assignee: Norsk Hydro ASA
Current assignee: Norsk Hydro ASA
Priority date: 2018-11-20
Filing date: 2019-10-18
Publication date: 2021-09-29
Also published as: NO20181483A1; CA3115400A1; AU2019382674B2; AU2019382674A1; NZ774532A; WO2020104119A1; ZA202102663B; BR112021007370A2; EA202191405A1

Abstract

A method and equipment for storing and transporting hot gas emitting components taken out of an electrolysis cell for aluminium production, the cell being of Hall-Héroult type with prebaked anodes, the components comprise at least one of; spent anode/s, bath material, anode covering material, the equipment comprises a top open closeable container that is closeable by means of lid(s), and further means for allowing a fluoride adsorbing material to be poured onto said component/s that have been brought into a central chamber ( C ) of the container. The equipment comprises further at least one fluidising air slide(s) arranged at the outside of the container where material is readily available for said air slide(s) as pre-stored material in compartment(s) in the equipment or readily available by external supply of material during the covering operation. The air slide(s) distribute the fluoride adsorbing material, by fluidisation of the material, through one or more inlet openings (O) in on or more side wall(s) (2) of the container, further into the central chamber (C) and finally covering said component(s) with material.

Description

A method and equipment for storing and transporting hot gas emitting components

The present invention concerns a method and equipment for storing and transporting hot gas emitting components such as anode butts from a pre-baked electrolysis cell system. The equipment comprises as a main component a closable, transportable storage container. In addition to the hot consumed anodes (anode butts), other emissive materials such as anode cover material and bath material have to be removed from cells in operation, in particular during anode change or other maintenance operations. The invention also includes use of the equipment for transportation of new anodes to the cells.

In connection with the operation of a modern electrolysis system for the production of aluminium, there are extensive requirements for the transportation of various materials to the cells, for example oxide, fluoride, anodes, etc. Moreover, operation involves the removal of consumed anodes, crusts and other material from the cells in addition to the metal produced.

Some of this transportation is crane-based, i.e. the objects are handled by means of one or more cranes that can serve the cells in the electrolysis hall in connection with specific operations. Another part of the transportation is performed by means of wheeled vehicles. In particular, closed boxes for anode butt transport is commonly transported by means of wheeled vehicles. The vehicles can be driven by an operator or automatic guided vehicles has also been proposed.

One problem with electrolysis cell systems that are built so that the cells are arranged in two parallel rows with a row of supporting columns in the space between the rows is that it can be difficult to manoeuvre the vehicles in an effective manner in the system. When, for example, consumed anodes and other material are removed from an electrolysis cell, it is important that it can be transported fast either out of the hall or to a temporary store so that the hall atmosphere is not impaired on account of unnecessary delay in removing the stated anodes or material, which will emit gases after removal from the cell. If a temporary store is used, it is important that this is arranged so that the operation of the rest of the electrolysis cell system is affected as little as possible, while the distance over which hot material is transported is limited to a minimum.

DE 4344036A1 shows a method and an arrangement for changing anodes in connection with aluminium melting electrolysis with heat recovery. The arrangement comprises transport containers that are designed to hold consumed anodes and bath material. The transport containers in which consumed anodes/bath material are placed are transported to a chamber in a heat exchanger system. The residual heat from the material in the stated containers is utilised to preheat new anodes. A filter device is arranged for preventing fluoride gas to escape from the container.

DE 4221882 A1 concerns a transport device for hot residual anodes. The transport device comprises a closed container in which consumed anodes are inserted. To limit emissions of contaminated gases such as fluoride into the hall atmosphere during transportation out of the hall, the container is fitted with a filter that can be made of alumina to chemically bind fluoride in the gas in order to retain such gases. The container comprises swivelling lids to allow anodes to be inserted/removed.

EP 0838540 shows a temporary store for used anodes and bath material that consists of a container that is connected to an opening in the superstructure of an electrolysis cell.

US 6,161 ,307 discloses a fluid bed system for cooling hot spent anode butts. The butts are brought to an elongated fluidised bed cooling chamber comprising particles of alumina and conveyor means for transporting a hot, spent anode butt through the fluidised bed. Since the hot anode buttes emerging from the potlines are at that point emitting fluorides at a very rapid rate, it is important to bring them to the fluidised bed as soon as possible and the hot anode butts may be transported in a closed mobile carrier, that is typically a self-contained, free-standing, moveable box. It is adapted to reducing the contact between the hot anode butt and moist atmospheric air before the butt has cooled sufficiently to avoid the generation of HF, and fluoride emissions during the transportation may be further minimized by covering the hot butts with alumina. The hot anode butts have a crust of solidified bath which is attached to the top of each butt.

EP2507413B1 discloses a process for changing used anode and a support and system for temporarily storing such a used anode where the butt having pieces of bath cover onto it, is placed on a support and a smothering powder such as alumina is poured onto the spent anode to limit the fluorinated gas emission. The support can be associated functionally with a tank that is pre-filled with powder and that is opened when a spent anode is on the support such that the powder flows towards the spent anode by gravity forces. In one other embodiment, the powder can be poured onto the spent anode by means of a commonly available overhead travelling crane equipped with a powder discharge conduit to cover the anode with powder. Such equipment is commonly used for covering new anodes replacing a spent one in a cell.

EP2710170B1 discloses a method and device for processing anode butts by covering said butts with alumina being able to adsorb fluoride, where the butt is immersed into alumina that is fluidised to facilitate immersion so that the butt is covered by static alumina until the end of its transport to a anode butt station for further processing of the butt. The device comprises a tray containing non-fluidised alumina in sufficient quantities to cover the anode butt and means of fluidisation of this alumina. The bottom of the tray can be made of a material able to retain alumina above it while forming a plenum chamber for fluidised gas below it and having sufficient porosity to fulfil the function of a fluidisation fabric.

Applicant’s own W003/042618 discloses a method and an arrangement for the operation of an electrolysis cell system, comprising a hall with electrolysis cells that use anodes of the pre-bake type for the production of aluminium, comprising temporary storage of consumed anodes and other material that are removed from the cells in closable storage arrangements arranged in the hall, where the storage arrangements are connected to an extraction system, the storage arrangements are arranged at a distance from the cells so that the operations performed on the cells are not obstructed by the storage arrangements, and the storage arrangements are also designed to be connected to an extraction system placed at a distance from the cells.

One challenge with this solution is to avoid air-burn of the carbon based material in the butts, due to the surrounding air being sucked into the storage arrangement. Air burn is unwanted as it involves loss of recyclable material and prolongation of the cooling period due to the combustion taking place.

This may be remedied at least partly by covering said butts by pouring alumina powder onto it and to limit the contact between the butts and oxygen containing gas. However, to be able to apply the alumina powder at least one or more lids have to be opened and there is a high risk of first puncturing the underpressurized system inside the storage arrangement and secondly that at least some of the alumina powder which may contain some air due to previous fluidisation, will be expanding as it hits the hot butts and that a gas containing both alumina powder and fluoride may leak out of the storage arrangement during this operation and end up in the ambient air.

This can be avoided by the present method and equipment where alumina or similar fluoride adsorbing material is brought to cover the anode butts and other hot, gas emitting components while the container itself is closed, i.e. with the lids or similar closure means shut. In an embodiment, the container may be connected to a suction system and be underpressurized at least during this operation. It can either be connected to a cell and be underpressurised by the cell’s gas extraction system, or to a separate gas extraction system. Still further, the equipment comprises a system for distribution of the fluoride adsorbing material inside the container that allows the material to flow in a gentle manner and to cover the hot emissive components without heavy dusting. These and further advantages can be achieved with the invention as defined in the accompanying claims.

The present invention will be described in further detail in the following by means of examples and figures, where:

Figure 1 shows in perspective an equipment according to the present invention, where the lids of a container are in open position and with two anodes therein,

Figure 2 shows in perspective an equipment according to the present invention, where the lids of a container are shut and with two anodes therein,

Figure 3 shows in top view an equipment with the lids shut, and an indication of the cross-sectional views A-A and B-B in Fig. 4 and 5 respectively,

Figure 4 shows a cross-sectional view of the equipment along line A-A in Fig. 3, and with no anodes therein

Figure 5 shows a cross-sectional view of the equipment along line B-B in Fig. 3, and with no anodes therein,

Figure 6 shows a cross sectional view of the equipment along line A-A in Fig. 3, and with two anode butts therein,

Figure 7 shows an enlarged portion E of the encircled area in Fig. 6,

Figure 8 shows the principles of operating the fluidising elements or air slides of Fig. Figure 9 shows the principles of operating the fluidising elements of Fig. 7.

In Figure 1 there is disclosed in perspective an equipment 1 according to the present invention, where lids 3, 4 of a container 2 are in open position and with two partly shown anodes stored therein. The rods 5, 6 of the anodes are supported by a frame structure 7 having brackets 8, 9.

In Figure 2, the equipment is rotated 90 degrees anti-clockwise and the lids 3, 4 are shut. Figure 3 shows in top view the equipment 1 where the frame 7 has been removed and with the lids 3, 4 shut, and an indication of the cross-sectional views A-A and B-B shown in Fig. 4 and 5 respectively. It can be seen closable openings 10, 1 1 , 12 communicating with compartments surrounding the container for filling fluoride adsorbing powder such as alumina into the container 2, which shall be explained later. Further, the lids have seals 13, 14 that can be soft lip seals that close accurately the opening between a slot in the lids and the anode rods 5, 6.

Figure 4 shows a cross-sectional view through the equipment 1 along line A-A as disclosed in Fig. 3, where there are compartments 23, 24 for receiving and storing a fluoride adsorbing powder, such as alumina, that can be filled via the closable openings 10, 1 1 , 12. See also Fig. 3 where two additional compartments are indicated at position 27 and 28. In the receiving compartments 23, 24 there are further arranged fluidising elements 25, 26 for fluidising the material during the filling operation, to be able to distribute the material to all available spaces in the compartments. Compartments 23’, 24’ are not filled during this filling operation, just partly due to the material’s angle of repose. During the operation of covering the butts with powder, materials can be transported via and from these compartments 23’, 24’ and into the chamber C of the container via one or more openings O in the walls of the container 2 by activating fluidising elements 25”, 26” together with the elements 25, 26 and 25’, 26’ (see also Fig. 7). Together, these fludising elements serves as onboard air slides for transporting the material from its storage to the chamber C.

The equipment 1 can be provided with tanks for pressurized fluidising gas 15, 16. Tank 16 is for the purpose of explanation not cross-sectioned and reference 17 is a coupling for filling pressurised gas accessible from the outside of the container. In case pressurised air is accessible at the loading/unloading point, it is not necessary to provide the equipment with tanks for pressurised gas, just a gas filling joint will be sufficient.

Similarly, Figure 5 shows a cross-sectional view through the equipment 1 along line B-B as disclosed in Fig. 3, where the compartments 27, 28 for receiving and storing a fluoride adsorbing powder such as alumina that can be filled via at least one closable opening 10, 1 1 , 12. In the receiving compartments 27, 28 there are further arranged fluidising elements 29, 30 for fluidising the material during the filling operation, to be able to distribute the material to all available space in the compartments. Compartments 27’, 28’ are not filled during this filling operation. Materials can be transported via and from these compartments 27’, 28’ and into the chamber C via openings O’ in the walls of the container 2 by activating fluidising elements 29’, 30’ similar to that explained in Fig. 4 and 7. Tanks 18, 19 with pressurised fluidising gas are provided in the equipment outside the container walls. The gas can be controlled by one or more valves and transported via pipes 18’ to the fluidising elements. The release of gas can be done manually or controlled by a PLC. A sensor registering the presence of a butt and possibly the closure of the lids can be used to control the activation of fluidising gas and filling of powder into the chamber C.

Figure 6 shows a cross sectional view of the equipment 1 along line A-A in Fig. 3, and with two anodes therein, having anode rods 5, 6, anode yokes 5’, 6’ and anode carbon blocks 5”, 6”. The anodes are supported by the frame 7, and further main components of the equipment 1 such as container 2, compartments 23, 23’; 24,24’, tank 15, coupling 17, central chamber C are shown. Figure 7 shows an enlarged portion E of the encircled area in Fig. 6 and there are shown compartment 23 for receiving and storing a fluoride adsorbing powder such as alumina that can be filled via the closable openings. In the receiving compartment 23 there is further arranged fluidising element 25 for fluidising the material during the filling operation, to be able to distribute the material to all available spaces in the compartments. Compartment 23’ is not filled during this filling operation, i.e. the dividing wall D will serve as a lock similar to a water lock. Materials can be transported via and from compartment 23’ and into the chamber C via opening O in the wall of the container 2 by activating fluidising elements 25, 25’ together with the fluidising element 25”. Piping 18’ and tank 15 are also shown, as well as anode rod 5, anode yoke 6’ and anode carbon block 6” in part.

Fig 8 and 9 shows one embodiment of operating the fluidising elements of Fig. 7, where Fig. 8 relates to filling material in the compartment 23 of the box during activating the fluidising element 25 and 25’ to enhance distribution of material M via onboard air slides to the various compartments. The piping 18” and supply of air is arranged so that the fluidising elements 25’ and 25” can be operated separately.

In Fig. 9 the material content of the compartment 23 is to be directed to the central chamber C. Materials M can be transported from compartment 23 via compartment 23’ and into the chamber C via opening O in the wall of the container 2 by activating fluidising elements 25, 25’ and 25” simultaneously, that have a function as onboard air slides.

The opening O must be arranged at a level that secures complete covering of the butts in the chamber C. To obtain this, the angle of repose of the material must be accounted for as well as varying heights of the butts and also varying presence of anode covering material ACM at the top of the butts.

The method relates to storing and transporting hot gas emitting components from an electrolysis cell for aluminium production, the cell being of Hall-Heroult type with prebaked anodes, the components comprise at least one of; spent anode(s), bath material, anode covering material. In addition, new anodes can be transported in the equipment. However, these need not to be covered by an adsorbing material. According to the method, component(s) are removed from the electrolysis cell and placed in a central chamber ( C ) of a top open closeable container provided with lid(s) that can be the closed immediately after placing the component(s) in the container to limit gas emissions to ambient air. Then said component(s) are covered with a layer of a fluoride absorbing material that can be alumina. The lid(s) can be shut automatically or manually and to operate the equipment, a PLC can be integrated in the equipment and also remotely controlled by manual trigging of actions.

The fluoride adsorbing material can be poured into the central chamber of the container by at least one feeding hole arranged in the top of the container where the feeding hole is closed after the filling operation.

Alternatively, the container is provided with compartments at its outside, said compartments having onboard air slides for distribution of the fluoride adsorbing material into the central chamber ( C ) where the hot gas emitting component(s) is placed. The transport is carried out by fluidising the material, which then flows by gravity into the chamber( C ) through one or more openings O in the wall(s) of the container 2. The fluoride adsorbing material is readily available for said air slides as pre-stored material in compartments of the equipment or readily available by external filling during the covering operation.

The fluoride adsorbing material can be alumina that is branched off the ordinary alumina transport to the cells and discharged by a filling hose or the similar, or can be alumina carried in a reservoir on a crane or a vehicle, said reservoir having a discharge hose. During filling of fluoride adsorbing material, the central chamber ( C ) of the container can be subjected to an underpressure by means of a gas extraction system, that could be the gas extraction system of a cell where the central chamber is connected to this system via one hose or the like.

Generally, the equipment comprises a top open closeable container that is closeable by means of lid(s), and further comprising means for allowing a fluoride adsorbing material to be poured onto said component(s) that have been brought into a central chamber ( C ) of the container. The equipment can further comprise compartments with fluidising air slides arranged onboard at the outside of the container’s walls 2, where material is readily available for said air slides as pre-stored material in compartment(s) in the equipment or readily available by external supply of material during the covering operation. The air slides distribute the fluoride adsorbing material by fluidisation of the material, through one or more inlet openings (O) in the side walls of the container 2, further into the central chamber (C) and finally covering said component(s) with material.

The container can have air slides and corresponding inlet openings arranged along one, two, three or all its sides, which in a preferred embodiment is four side walls.

The compartments for pre-storing material are arranged in the equipment, along at least one side of the container wall 2.

The equipment may comprise tank(s) for pressurised fluidising gas, where the tank(s) can be pre-filled by a coupling accessible from the outside of the equipment, or it can have accessible coupling/s for supplying pressurized air.

The container can be thermally insulated, by appropriate materials. The insulation can be arranged at the inside or the outside of the container’s walls. A Programmable Logic Controller can be included in the equipment for controlling operations such as closing the lids, pouring action of fluoride adsorbing material by controlling valves between the tanks for pressurised fluidising gas and the fluidising elements, etc.

After use, the equipment can be turned up-side down for removal of the fluoride adsorbing material and other fragments of material.

Claims

1. A method for storing and transporting hot gas emitting components from an electrolysis cell for aluminium production, the cell being of Hall-Heroult type with prebaked anodes, the components comprise at least one of; spent anode(s), bath material, anode covering material, wherein the method comprises removal of said component/s from the electrolysis cell and placing it in a central chamber ( C ) of a top open closeable container provided with lid(s) that can be closed,

characterised in that

the lid(s) are closed immediately after placing the component(s) in the container to limit gas emissions to ambient air, followed by covering said component(s) with a layer of a fluoride adsorbing material that can be alumina.

2. A method in accordance with claim 1 ,

characterised in that

the lid(s) can be shut automatically or manually.

3. A method in accordance with claim 1 ,

characterised in that

the fluoride adsorbing material is poured into the central chamber of the container by at least one feeding hole arranged in the top of the container where the feeding hole is closed after the filling operation.

4. A method in accordance with claim 1 ,

characterised in that

the container is provided at its outside with onboard air slides for distribution of the fluoride adsorbing material into the central chamber ( C ) where the hot gas emitting component/s is placed, the transport is carried out by fluidising the material, which then flows by gravity into the chamber( C ) through one or more openings in the wall(s) of the container.

5. A method in accordance with claim 4,

characterised in that

the fluoride adsorbing material is readily available for said air slides as pre-stored material in compartments of the equipment or readily available by external filling during the covering operation.

6. A method in accordance with claim 3 or 5,

characterised in that

the fluoride adsorbing material is alumina that is branched off the ordinary alumina transport to the cells and discharge by a filling hose or the similar, or can be alumina carried in a reservoir on a crane or a vehicle, said reservoir having a discharge hose.

7. A method in accordance with claim 1 ,

characterised in that

the central chamber ( C ) of the container during filling of fluoride adsorbing material is subjected to an underpressure by means of a gas extraction system.

8. A method in accordance with claim 7,

characterised in that

the gas extraction is performed by connecting the central chamber ( C ) of the container to the gas extraction system of an electrolysis cell via a hose or the similar.

9. An equipment for storing and transporting hot gas emitting components taken out of an electrolysis cell for aluminium production, the cell being of Hall-Heroult type with prebaked anodes, the components comprise at least one of; spent anode/s, bath material, anode covering material, the equipment comprises a top open closeable container that is closeable by means of lid(s), and further comprising means for allowing a fluoride adsorbing material to be poured onto said component(s) that have been brought into a central chamber ( C ) of the container, characterised in that

the equipment further comprises at least one fluidising air slide(s) arranged at the outside of the container where material is readily available for said air slide(s) as pre-stored material in compartment(s) in the equipment or readily available by external supply of material during the covering operation, and that the air slide(s) distribute the fluoride adsorbing material by fluidisation of the material, through one or more inlet openings (O) in a side wall(s) of the container, further into the central chamber (C) and finally covering said component(s) with material.

10. An equipment in accordance with claim 9,

characterised in that

the container has air slides and corresponding inlet openings arranged along more than one side and up to all its sides.

11. An equipment in accordance with claim 9,

characterised in that

the compartment(s) for pre-storing material are arranged along at least one side of the container and may comprise all sides.

12. An equipment in accordance with claim 9,

characterised in that

the equipment comprises tank(s) for pressurised fluidising gas, where the tank(s) can be pre-filled by a coupling accessible from the outside of the equipment.

13. An equipment in accordance with claim 9, characterised in that

the container is thermally insulated.

14. An equipment in accordance with claim 9,

characterised in that

a PLC controller is included in the equipment for controlling operations such as closing the lids, pouring action of fluoride adsorbing material, etc.

15. An equipment in accordance with claim 9,

characterised in that

the equipment comprises externally available coupling(s) for supply of pressurised fluidising gas.