EP4658468A1

EP4658468A1 - A method for recycling a composite structure with a metal containing member

Info

Publication number: EP4658468A1
Application number: EP24703910.0A
Authority: EP
Inventors: Troels Bach NIELSEN; Aksel PETERSEN
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2023-01-31
Filing date: 2024-01-31
Publication date: 2025-12-10
Also published as: CN120584021A; WO2024160324A1

Abstract

A method for recycling a composite structure (6, 6a) is disclosed The composite structure (6, 6a) comprises a metal containing member (11), such as a metal mesh, arranged at or near a surface of the composite structure (6, 6a). A release agent (12) is applied to the surface of the composite structure (6, 6a), the applied release agent (12) softening the surface of the composite structure (6, 6a). The metal containing member (11) is mechanically removed from the composite structure (6, 6a), and the composite structure (6, 6a) is subsequently processed for at least partly recycling of the material of the composite structure (6, 6a).

Description

A METHOD FOR. RECYCLING A COMPOSITE STRUCTURE WITH A METAL

CONTAINING MEMBER

FIELD OF THE INVENTION

The present invention relates to a method for recycling a composite structure, such as an epoxy composite structure, where the composite structure comprises a metal containing member arranged at or near a surface of the composite structure. The composite structure may, e.g., be in the form of a wind turbine blade or a part of a wind turbine blade.

BACKGROUND OF THE INVENTION

At the end of their lifetime, composite structures, such as wind turbine blades, need to be disposed of. This could, e.g., involve depositing the composite structure in a landfill, possibly after cutting the composite structure into smaller parts. In order to reduce the environmental impact, there is a desire to at least partly recycle composite structures. However, due to the composite nature of these structures, it is difficult to separate the structures into their original constituent parts, and this renders appropriate recycling of material difficult, or even impossible. For instance, the composite structures may comprise fibres arranged in a matrix of a cured resin, e.g. an epoxy based resin. Once cured, it is not possible to mechanically separate the fibres from the resin.

One previous approach for recycling composite structures, such as epoxy composite structures, is to subject the composite structure to shredding or grinding, and subsequently performing a separation process on the shredded or grinded material, in order to mechanically separate the fibres from the resin material. However, the fibres as well as the resin material retrieved in this manner are often contaminated, i.e. the fibres are contaminated by resin material and the resin material is contaminated by fibres. Accordingly, the retrieved fibres as well as the retrieved resin material is unsuitable for recycling for high quality products. Another approach for recycling composite structures is to remelt the fibre material applied for the composite structure, with the purpose of using the remelted material for producing new fibres which can be used for new composite structures, or for other purposes. Such remelting may, e.g., be preceded by a processing step in which the composite structure is subjected to pyrolysis, solvolysis or another kind of process which results in granulation of the composite material.

Some composite structures may comprise one or more metal containing members. Such members could, e.g., be in the form of bolts, screws, bushings, etc., which it may be possible to remove from the composite structure. Furthermore, the composite structure may be provided with electrical wires, conductive tapes or strips, metal meshes, etc. For instance, a lightning protection system for a wind turbine blade may include such electrically conductive members. Metal containing members of this kind may be embedded in the composite structure in a manner which does not allow for readily removing the members from the composite structure during end of life processing.

Thus, if a composite structure which comprises embedded metal containing members is cut and/or shredded, and subsequently subjected to, e.g., pyrolysis or solvolysis, the resulting product will contain residues of metal material. This renders glass fibre material of the partly processed composite product unsuitable for remelting, since such metal residues may form alloys with metallic parts of the melting oven, and this may lead to degradation or failure of the recycling production line.

DESCRIPTION OF THE INVENTION

It is an object of embodiments of the invention to provide a method for recycling a composite structure with a metal containing member which allows for remelting of fibre material of the composite structure. The invention provides a method for recycling a composite structure, the composite structure comprising a metal containing member arranged at or near a surface of the composite structure, the method comprising the steps of:

- applying a release agent to the surface of the composite structure, the applied release agent softening the surface of the composite structure,

- mechanically removing the metal containing member from the composite structure, and

- processing the composite structure for at least partly recycling of the material of the composite structure.

Thus, the invention relates to a method for recycling a composite structure. In the present context the term 'composite structure' should be interpreted to mean a structure which is made from a composite material, i.e. a material which comprises suitable fibres embedded in a matrix of cured resin.

The composite structure comprises a metal containing member which is arranged at or near a surface of the composite structure. The metal containing member may be embedded in the composite structure at or near the surface thereof, in which case it is not possible, or it is at least difficult and inconvenient, to mechanically remove the metal containing member from the composite structure. The metal containing member may, e.g., be in the form of a metal containing layer, such as a metal mesh or sheet. As an alternative, the metal containing member may be or comprise one or more strips, one or more tapes, one or more wires, such as electrical wires, one or more bushings or similar objects, etc.

In the present context the term 'at or near a surface' should be interpreted to mean that the metal containing member forms an outer boundary of the composite structure, or that only a thin layer separates the metal containing member from such a boundary. Such a thin layer may, e.g., be a coating or only a single layer of fibre material with resin in a multi-layered composite structure. Thus, the metal containing member is accessible without cutting the composite structure, and access may be gained to the metal containing member from the surface. The surface may be regarded as an outer surface of the composite structure. However, in the case that the composite structure is of a kind which also defines one or more interior surfaces, the metal containing member may be at or near such an interior surface. An interior surface is, e.g., defined by a wind turbine blade, which will normally comprise a shell defining a hollow interior. A surface facing the hollow interior may be regarded as an interior surface.

In the method according to the invention, a release agent is initially applied to the surface of the composite structure, i.e. the release agent is applied to a part of the composite structure which is close to the position where the metal containing member is arranged. The applied release agent softens the outer surface of the composite structure. This should be interpreted to mean that the texture of the surface changes in such a manner that it is possible to gain access to the metal containing member which is arranged at or near the surface. For instance, the release agent may cause at least part of the material of the outer surface to dissolve or swell, thereby causing at least partly disintegration or degradation of the part of the composite structure which is near the surface. Thus, the release agent may, e.g., be a swelling agent. The release agent preferably causes softening of the cured resin of the composite structure, such as partly or fully disintegration or degradation of the cured resin.

Next, the metal containing member is mechanically removed from the composite structure. The softening of the surface of the composite structure caused by the applied release agent causes the metal containing member to be released from the composite structure, notably from the matrix of cured resin, possibly in combination with mechanical action. Accordingly, following the softening of the surface of the composite structure, the metal containing member is readily accessible for mechanical removal in one piece. This allows the metal containing member to be removed completely from the composite structure, without leaving any metal containing residues.

Finally, the composite structure is processed for at least partly recycling of the material of the composite structure. Since the metal containing member was removed completely, it is ensured that the processed composite material is completely free of metal residues, regardless of how the composite structure is processed. This renders the processed composite material suitable for a wide range of recycling options, including remelting of fibre material, without risking damage to the processing equipment.

In the present context, the term 'recycling' should be interpreted to cover reuse of certain parts of the composite material, such as fibre mats which may be retrieved in one piece from the composite material or the metal containing member, as well as to cover recycling of various constituent materials of the composite material, e.g. remelting of fibres, and using the retrieved material in other contexts.

The step of processing the composite structure may comprise cutting and/or shredding the composite structure. According to this embodiment, once the metal containing member has been removed from the composite structure, the composite structure, without the metal containing member, is processed into smaller pieces, e.g. by cutting the composite structure into manageably sized pieces. The smaller pieces may subsequently be shredded, or even grinded, to form a granular or granular-like product. As an alternative, the composite structure may be shredded directly without cutting it into smaller pieces. The smaller pieces of the granular or granular-like product may then undergo one or more further processing steps in order to at least partly recycle the composite material or the constituent parts of the composite material.

The step of processing the composite structure may comprise subjecting the composite structure to pyrolysis or solvolysis. In the present context, the term 'pyrolysis' should be interpreted to mean a thermochemical process in which the material is exposed to high temperatures, and in the absence of oxygen, undergoes chemical and physical separation into different molecules. In the present context, the term 'solvolysis' should be interpreted to mean a chemical reaction of a solvent and a solute which results in the formation of new compounds. Accordingly, pyrolysis as well as solvolysis results in the constituent materials of the composite structure being separated from each other. The pyrolysis or solvolysis may, e.g., take place after shredding or grinding of the composite structure. Alternatively, pyrolysis or solvolysis may be performed on the intact composite structure, or on smaller, manageable pieces of the composite structure.

The composite structure may comprise glass fibres, and the step of processing the composite structure may comprise remelting of the glass fibres. According to this embodiment, glass fibre material is retrieved from the processed composite structure, and the remelted material may be used for a variety of purposes. For instance, new glass fibres may be produced from the remelted material. However, the remelted material may alternatively be applied for other purposes.

Remelting the glass fibres may be particularly relevant in the case that the fibres are damaged or worn, in which case the retrieved fibres may be unsuitable for direct reuse in high quality products. The remelting may, e.g., take place after pyrolysis or solvolysis.

When remelting glass fibres of the composite structure, it is particularly important that any metal is completely removed from the composite structure before the remelting is performed, because in the case that the material being remelted contains metal residues there is a risk that alloys are formed between metal residues and parts of the glass melting setup, and this may cause damage to the equipment.

The step of mechanically removing the metal containing member may comprise mechanically separating the metal containing member from the composite structure. According to this embodiment, the metal containing member is removed from the composite structure in one piece, and with no or only a limited amount of other materials of the composite structure being removed along therewith. Thus, all metal is efficiently removed from the composite structure, and essentially all of the rest of the material of the composite structure remains and is processed for recycling.

For instance, the step of mechanically removing the metal containing member may comprise gripping a portion of the metal containing member and pulling the metal containing member away from the composite structure. For instance, a corner, an end, or an edge of the metal containing member may be gripped by means of a suitable tool, and the metal containing member may then be retrieved by pulling it away from or out of the composite structure, using the tool.

As an alternative, the metal containing member may be mechanically removed from the composite structure by rolling off the metal containing member, by pushing the metal containing member, or in any other suitable way.

The metal containing member may be in the form of a metal mesh. In the present context the term 'mesh' should be interpreted to mean a sheet-like structure which is not solid, but rather comprises a plurality of through-going holes. The mesh may, e.g., be formed from a plurality of threads or wires arranged along at least two non-parallel directions and crossing each other in a plurality of contact points.

Such a metal mesh may, e.g., be applied as part of lightning protection in a wind turbine blade. In this case the metal mesh conducts electrical current originating from a lightning strike along the wind turbine blade, e.g. from the tip of the wind turbine blade and towards a suitable conductor connected to the root end of the wind turbine blade.

The step of applying a release agent to the surface of the composite structure may comprise spraying or smearing the release agent onto the surface of the composite structure. According to this embodiment, the release agent is applied to the surface of the composite structure but will not necessarily reach inner parts of the composite structure, such as layers arranged below the outermost parts of the composite structure. Thus, the surface and the region of the composite structure which is arranged immediately adjacent to the surface are affected by the release agent, but regions of the composite structure arranged further down, such as a core region of the composite structure, are not affected, and therefore the composite material of these regions remain substantially intact. Thus, the metal containing member can be removed from the composite structure, essentially without affecting the remaining material of the composite structure, and therefore the material which is subsequently processed for recycling purposes has a predictable structure and composition. Furthermore, applying the release agent by spraying or smearing is an easy manner of applying the release agent, which results in minimal waste of release agent.

As an alternative, the release agent may be applied in another manner, e.g. by submerging the composite structure in a vessel containing the release agent.

The method may further comprise the step of covering the surface of the composite structure with a patch or a pouch, before, during or after the step of applying a release agent to the surface of the composite structure. According to this embodiment, once the release agent has been applied to the surface of the composite structure, the surface, with the release agent applied thereto, is covered, e.g. with a patch or a pouch. This prevents the release agent from running off or evaporating before it has had the time to soften the surface of the composite structure sufficiently to release the metal containing member.

As an alternative, the composite structure may be positioned in a pouch, a bag or a similar item, and the release agent may subsequently be supplied to the pouch or bag, in order to bring the surface of the composite structure into contact with the release agent. This allows the composite structure to be submerged in release agent, covering the entire surface of the composite structure, with a minimal amount of release agent. This embodiment is particularly relevant in the case that the release agent is a liquid.

As another alternative, the release agent may be of a kind which sticks to the surface of the composite structure. In this case the release agent may, e.g., be a foam, a gelation, or a similar material. As an alternative, the release agent may be mounted on of form part of an adhesive patch, e.g. in the form of a depot layer which releases the release agent gradually. In this case the step of applying the release agent to the surface of the composite structure may comprise mounting or positioning one or more such patches on the surface of the composite structure. In any event, applying a release agent which sticks to the surface of the composite structure ensures that the release agent remains in contact with the surface of the composite structure for a sufficiently long period of time to ensure that the surface is softened sufficient to allow for removal of the metal containing member.

Use of covering the surface before, during or after applying the release agent further allows for reducing or preventing loss to the environment during the softening and facilitate recovering of the release agent after the softening is completed.

The method may further comprise the step of reusing the removed metal containing member. This is possible because the metal containing member is removed from the composite structure in one piece, as described above. According to this embodiment, the removed and retrieved metal containing member is directly reused, as it is, in a new composite structure or in another suitable structure. This reduces the environmental footprint of the new structure because it is not necessary to spend energy for forming a new metal containing member. Furthermore, the need for virgin material resources for manufacturing the new structure is reduced, because the material of the retrieved metal containing member is reused.

The composite structure may be an epoxy composite structure. According to this embodiment, the resin of the composite structure is an epoxy resin. Alternatively, another kind of resin may be applied.

The composite structure may comprise an epoxy based coating arranged over the metal containing member. According to this embodiment, the softening of the surface of the composite structure may encompass softening the coating in order to make the metal containing member available to be mechanically removed.

The epoxy of the epoxy composite structure or epoxy based coating may be an amine cured epoxy-based resin. It was found by the inventors of the present invention that such epoxy composite structures or epoxy based coatings were particularly advantageous in being readily softened by release agent comprising consisting of formic acid, and preferably more than 50 wt-% formic acid. The release agent may comprise acid. According to this embodiment, the resin is preferably of a kind which is acid breakable, in the sense that the resin comprises polymer, e.g. epoxy polymer, which is capable of swelling upon exposure to an acid containing release agent to mechanically break some of the chemical bonds, or which is capable of chemically disassemble into monomers and/or oligomers.

The release agent may, e.g., comprise formic acid. Formic acid is readily available at low cost. Furthermore, formic acid is considered safe to humans as well as with regard to the environment. Finally, the inventors of the present invention have found that formic acid is an efficient release agent with respect to epoxy resins applied in some relevant epoxy composite structures, such as certain wind turbines blades. Accordingly, formic acid is a suitable, safe, and cost effective choice for the release agent.

As an alternative, the release agent may comprise other suitable kinds of acid, such as acetic acid.

The method may further comprise the step of chemically and/or mechanically cleaning the metal containing member. According to this embodiment, residues from the original composite structure, such as residues of the matrix of resin, are removed from the retrieved metal containing member, in order to put it into a shape which is more suitable for reuse. Chemical cleaning of the metal containing member may, e.g., include applying a solvent, a release agent or the like to the retrieved metal containing member. This may, e.g., cause resin particles, such as epoxy particles, being stuck to the surface of the metal containing member to chemically break and/or be released from the surface. Mechanical cleaning of the metal containing member may, e.g., include washing, e.g. by applying water, and possibly surfactant or soap, rubbing, rolling, bending, compressing, applying a pressurized fluid, e.g. water or air, etc. Such mechanical cleaning may, e.g., cause resin particles, such as epoxy particles, being stuck to the surface of the metal containing member to mechanically break and/or be mechanically released from the surface. 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 perspective view of a wind turbine,

Figs. 2-4 illustrate a wind turbine blade being processed in accordance with a method according to an embodiment of the invention, and

Fig. 5 illustrates method steps of a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a wind turbine 1 comprising a tower 2 and a nacelle 3 mounted on top of the tower 2. A rotor 4 with a hub 5 carrying three wind turbine blades 6 is mounted rotatably on the nacelle 3. Accordingly, wind acting on the wind turbine blades 6 causes the rotor 4 to rotate, and the mechanical energy is transformed into electrical energy by means of a generator (not shown), in a manner which is known per se.

When the wind turbine 1, or one or more components of the wind turbine 1, has reached its end of life, it will be decommissioned. To this end, it is desirable to recycle the material of the various components to the greatest possible extent. In particular, the material of the wind turbine blades 6, which is often a composite material, may advantageously be fully or partly recycled, e.g. by applying a method according to an embodiment of the invention.

Fig. 2 is a perspective view of a composite structure in the form of a wind turbine blade 6. The wind turbine blade 6 extends in a longitudinal direction between a root end 7 and a tip end 8. A reinforcing web 9 extends along the longitudinal direction inside the wind turbine blade 6 between a pressure side and a suction side. The wind turbine blade 6 of Fig. 2 has been demounted from a wind turbine, and the composite material of the wind turbine blade 6 is about to be at least partly recycled by means of a method according to an embodiment of the invention. This will be described in further detail below.

Fig. 3 illustrates the wind turbine blade 6 of Fig. 2 in the process of being cut into smaller parts 6a, the cutting step being illustrated by saw blades 10. The smaller parts 6a are easier to manage than the entire wind turbine blade 6, and each of the smaller parts 6a constitutes a composite structure in the sense of the claimed invention. It should, however, be mentioned that the cutting step illustrated in Fig. 3 is optional, and that the method steps described below could, alternatively, be performed on the intact wind turbine blade 6, as it is illustrated in Fig. 2. The cutting step may alternatively be conducted after the process described below to facilitate transportation of the composite, recycling, or reuse.

Fig. 4 illustrates the wind turbine blade 6 of Fig. 2. A release agent has been applied to the outer surface of the wind turbine blade 6, and this has caused softening of the region near the surface of the wind turbine blade 6, to an extent which allows a metal containing member 11, in the form of a metal mesh, to be mechanically removed from the wind turbine blade 6. In Fig. 4 the metal containing member 11 is in the process of being removed from the wind turbine blade 6.

Thus, the metal containing member 11 is removed from the wind turbine blade 6 in one piece. This ensures that no metal is left in the wind turbine blade 6. Furthermore, this allows the metal containing member 11 to be reused directly as it is, or the metal to be recycled.

Once the metal containing member 11 has been removed from the wind turbine blade 6, the composite material of the wind turbine blade 6 can be processed for recycling. This could, e.g., include subjecting the wind turbine blade 6 to pyrolysis or solvolysis and subsequent remelting of the fibres of the composite material. Since the metal has been completely removed from the wind turbine blade 6 before such recycling processing is performed, the processing can be performed without risking damage to the processing equipment due to the formation of alloys between metal residues in the composite material and metal parts of the equipment.

Fig. 5 illustrates method steps according to an embodiment of the invention. A wind turbine blade 6, e.g. of the kind illustrated in Figs. 2-4, is initially cut into smaller parts 6a, e.g. in the manner illustrated in Fig. 3. The wind turbine blade 6 is made from a composite material, i.e. it comprises suitable fibres, e.g. glass fibres, embedded in a matrix of cured resin, e.g. epoxy resin. The fibres may be provided in the form of fibre mats, or they may be loose fibres. The wind turbine blade 6 is further of a kind which comprises a metal containing member, in the form of a metal mesh 11, arranged near an outer surface of the wind turbine blade 6. The metal mesh 11 may, e.g., form part of a lightning protection system for the wind turbine blade 6. Thus, each of the smaller parts 6a constitutes a composite structure which comprises a metal containing member 11.

The composite structures 6a are submerged in a release agent 12 accommodated in a vessel 13. The release agent 12 may comprise acid, such as formic acid, and it acts on the composite structures 6a in such a manner that the surfaces of the composite structures 6a soften, but the interior parts of the composite structures 6a may not be affected by the release agent 12. More particularly, the release agent 12 may cause swelling of polymers of the resin of the composite structures 6a, and this may cause the cured resin to disintegrate into swelled particles, e.g. swelled epoxy particles. This releases the metal containing members 11 from the matrix of resin, thus allowing the metal containing members 11 to be mechanically removed from the respective composite structures 6a in one piece. The retrieved metal containing members 11 may subsequently be recycled, e.g. by reusing the retrieved metal containing members 11 as they are, or by appropriately recycling the material of the metal containing members 11.

The composite structures 6a are further retrieved from the vessel 13. Since the metal containing members 11 have been removed in one piece, these retrieved composite structures 6a contain no metal residues. The retrieved composite structures 6a are processed in order to recycle the material of the composite structures 6a. In the embodiment illustrated in Fig. 5, this processing includes subjecting the composite structures 6a to pyrolysis, thereby obtaining pyrolyzed material 14, and subsequently remelting the fibres of the composite material in a melting oven 15. Since the retrieved composite structures 6a contain no metal residues, these process steps can be performed without risking damage to the processing equipment, including the melting oven 15.

Claims

1. A method for recycling a composite structure (6, 6a), the composite structure (6, 6a) comprising a metal containing member (11) arranged at or near a surface of the composite structure (6, 6a), the method comprising the steps of:

- applying a release agent (12) to the surface of the composite structure (6, 6a), the applied release agent (12) softening the surface of the composite structure (6, 6a),

- mechanically removing the metal containing member (11) from the composite structure (6, 6a), and

- processing the composite structure (6, 6a) for at least partly recycling of the material of the composite structure (6, 6a).

2. The method according to claim 1, wherein the step of processing the composite structure (6, 6a) comprises cutting and/or shredding the composite structure (6, 6a).

3. The method according to claim 1 or 2, wherein the step of processing the composite structure (6, 6a) comprises subjecting the composite structure (6, 6a) to pyrolysis or solvolysis.

4. The method according to any of the preceding claims, wherein the composite structure (6, 6a) comprises glass fibres, and wherein the step of processing the composite structure (6, 6a) comprises remelting of the glass fibres.

5. The method according to any of the preceding claims, wherein the step of mechanically removing the metal containing member (11) comprises mechanically separating the metal containing member (11) from the composite structure (6, 6a).

6. The method according to claim 5, wherein the step of mechanically removing the metal containing member (11) comprises gripping a portion of the metal containing member (11) and pulling the metal containing member (11) away from the composite structure (6, 6a).

7. The method according to any of the preceding claims, wherein the metal containing member (11) is in the form of a metal mesh.

8. The method according to any of the preceding claims, wherein the step of applying a release agent (12) to the surface of the composite structure (6, 6a) comprises spraying or smearing the release agent (12) onto the surface of the composite structure (6, 6a).

9. The method according to any of the preceding claims, further comprising the step of covering the surface of the composite structure (6, 6a) with a patch or a pouch, before, during or after the step of applying a release agent (12) to the surface of the composite structure (6, 6a).

10. The method according to any of the preceding claims, further comprising the step of reusing the removed metal containing member (11).

11. The method according to any of the preceding claims, wherein the composite structure (6, 6a) is an epoxy composite structure.

12. The method according to any of the preceding claims, wherein the composite structure (6, 6a) comprises an epoxy based coating arranged over the metal containing member (11).

13. The method according to any of the preceding claims, wherein the release agent (12) comprises acid.

14. The method according to any of the preceding claims, further comprising the step of chemically and/or mechanically cleaning the metal containing member