Method for installation and maintenance of floating wind turbines

Abstract

Present invention relates to a method for maintaining and installation of offshore wind turbines, comprising the following steps: - positioning a floating service vessel (8) with a crane (10) above a semi- submerged sub-structure (2) of a floating wind turbine (1), said sub-structure (2) comprising a number of mainly vertical pontoons or columns (3, 4, 5) interconnected by tubular beams (6), - providing contact between the tubular beams (6) and an interface arrangement (14) on the service vessel, and - lifting the service vessel (8) above the water surface.

Description

METHOD FOR INSTALLATION AND MAINTENANCE OF FLOATING WIND TURBINES.Technical Field

[0001] Present invention relates to a method for installing and maintenance of floating wind turbines. More specifically, present invention relates to installing and maintenance of wind turbines in an offshore environment, where the wind turbines are placed on a semi-submersible foundation floating on a body of water.Background Art

[0002] Wind turbines for use offshore, comprises a tower which forms the support for the wind turbine. This tower can either be placed on the sea bottom if the water depth is not too large, or on a floating sub-structure if the water depth is large. When mounting and maintaining the wind turbines, this are most frequently done by using a floating service vessel with a crane to perform the necessary installation or maintenance operations. One severe problem with this solution, is that operations like these only can be performed in relatively calm sea, due to the relative movements between the service vessel and the wind turbine. Further, use of large floating vessels for installation and maintenance of wind turbines offshore is an expensive operation. One alternative solution could be to tow the floating wind turbine to shore and perform the installation by the quayside, but this is also an expensive and time-consuming operation.

[0003] One known solution to avoid this problem can be found in Norwegian patent NO 346593. This invention mitigates the problem by using a portable crane which is being lifted with a ship crane placed on a service vessel onto a floating sub-structure supporting the wind turbine.

[0004] US 20110017659A1 teaches a device and a method for assembling and servicing a wind turbine, where the tower of the wind turbine is supported by the seabed and a jack-up offshore platform with a crane for assembling and servicing a wind turbine. The legs of the jack-up platform are also supported by the seabed. This solution can only be used in relatively shallow waters.

[0005] US 8701579B2 describes an offshore wind turbine installation vessel, where the turbine shall be installed on a foundation that is installed on the seabed prior to the installation of wind turbine on the foundation. A crane used for the installationoperation is provided on the installation vessel. This solution does not take into account the relative movements between the foundation and installation vessel due to the effect of waves.

[0006] US10302068 B2 describes use of a jack-up platform with a crane for installation and maintenance of an offshore wind turbine. The platform is an offshore platform that was previously used in hydrocarbon production. This solution can only be used in shallow waters and does not take into account any relative movement due to wave action if the wind turbine sub-structure is floating in the water surface.

[0007] US 11168666A1 describes a jack-up platform for facilitating installation of offshore wind-turbines, which has a receiving space that comprises a centralizing system configured to centralize a received floating barge in the receiving space.

[0008] WO 2017204656 A1 describes a method providing a vessel that has a broad submerged hull and a narrow tower that extends upwards from the submerged hull. A submerged portion of the vessel is arranged in an attachable utility unit.

[0009] US2012183359 A1 describes a method for installing a water-submersible platform. The method includes lowering the platform in the water from a vessel positioned above the platform, while spuds connecting the vessel to the platform stabilize the platform during lowering. It is also disclosed an assembly of the vessel and platform, and a vessel that is used to connect to the platform.

[0010] WO 2022045896 A1 discloses an installation vessel for offshore structures, for example wind turbines. The vessel has a loading deck and upper edge of each two longitudinally extending hull side walls that are configured to be located above the water line.

[0011] DE 19741988 shows a wind turbine where a crane is temporarily attached to the tower of the wind turbine. The crane is capable of moving up and down along the tower.

[0012] DE 19647515 shows a similar crane that is capable of installing further tower sections om top of the tower section to which the crane is attached.

[0013] US 20180282134 also shows a crane which is attached to the tower of a wind turbine, said crane is capable of moving up and down along the tower of the wind turbine. The crane is adapted to replace the blades of the wind turbine.

[0014] DE 102012002720 A1 also describes a crane that is attached to the tower structure of a wind turbine.

[0015] US 9.120.652 describes a wind turbine where a small service crane is arranged inside the nacelle. A hatch is opened through which the crane can emerge when there is a need for the service crane.

[0016] GB 2558242A shows a larger service crane arranged on top of the nacelle.

[0017] In all these known solutions, the crane is fixed or removably arranged either on the tower of the wind turbine or on the semi-submersible sub-structure of the wind turbine.Summary of invention

[0018] Present invention relates to a method for maintaining and installation of offshore wind turbines, comprising the following steps:- positioning a floating service vessel with a crane above a semi-submerged substructure of a floating wind turbine, said sub-structure comprising a number of mainly vertical pontoons or columns interconnected by tubular beams,- providing contact between the tubular beams and an interface arrangement on the service vessel, and- lifting the service vessel above the water surface.

[0019] The interface arrangement is preferably legs protruding from the service vessel, said legs are each provided with an interface arrangement to make contact with the tubular beams.

[0020] In one preferred embodiment, the legs are of a jack-up type where the legs can be moved up and down.

[0021] In another preferred embodiment, the legs are not movable.

[0022] Preferably, the floating service vessel is raised above the sea surface by either i) extending the legs and raise the service vessel out of the water; or ii) de-ballasting the semi-submerged sub-structure and raise the sub-structure until the service vessel is above the sea surface.

[0023] In a preferred embodiment, the legs are stools or cradles.Brief description of drawings

[0024] Figure 1 shows a first step of a method according to present invention for placing a floating crane vessel on a semi-submersible sub-structure of a wind turbine;

[0025] Figure 2 shows a second step of the method where the legs of the floating crane vessel is in contact with the sub-structure;

[0026] Figure 3 shows the final step of the method where legs the floating crane vessel has been extended to bring the crane vessel above the sea level.

[0027] Figure 4 shows the situation where the floating vessel is supported by the sin-structure and the crane is raised for operation.

[0028] Figure 5 shows a first step of the method according to a second embodiment of the invention, where the crane vessel is placed above the sub-structure; and

[0029] Figure 6 shows the final step of the method according to Fig. 5, where the semi-submersible sub-structure has been de-ballasted and thereby raising the crane vessel above the water level.Detailed description of the invention

[0030] Figure 1 depicts the first step of the method according to present invention. Figurel also shows an exemplary semi-submersible sub-structure (2) for an offshore wind turbine unit (1). The sub-structure (2) is partially submerged, and the top of the tubular beams (6) is approximately 10 meters below the sea surface. The substructure (2) comprises a number of approximately vertically oriented pontoons or pillars (3, 4, 5) connected to each other by tubular beams (6). The cross-section of the pontoons or pillars (3, 4, 5) can be circular, square, rectangular or polygonal. The pontoons or pillars (3, 4, 5) and / or tubular beams (6) are hollow and provide the necessary buoyancy for the sub-structure. The sub-structure in Fig.1 has been shown with a triangular design with three pontoons or pillars (3, 4, 5) but the design can also have a square, rectangular, or polygonal design. Further, the sub-structure (2) is connected to one or more upwardly extending towers (7) which support and carries the nacelle of the wind turbine. During normal operation, the sub-structure (2) is submerged below the sea surface. The sub-structure (2) has a ballasting system to raise or lower the sub-structure (2) in relation to the water surface by pumping water in or out from the pontoons (3, 4, 5) and / or the tubular beams (6).

[0031] Further Fig. 1 depicts the first step of positioning a service vessel (8) in position above the sub-structure. This vessel can for example be a barge which is towed by a tug (9), or the service vessel (8) can have engines to move the vessel. The service vessel (8) comprises a crane (10) and a number of legs (13). In one preferred embodiment, the legs (13) can be of a jack-up type, where the legs can be moved up and down. In a second preferred embodiment, the legs (13) having a fixed length and cannot be extended or retracted. This second embodiment will be described further with reference to Figs. 5 and 6. Further, the service vessel (8) can comprise support structures such as cradles (11) to support wind turbine blades (12) to be installed or replaced.

[0032] Figure 2 shows the situation where the service vessel (8) has been positioned in a floating condition above the sub-structure (2). The legs (13) have been partially extended such that a lower part of the legs (13) is in contact with the tubular beams (6). The lower part of each leg (13) has a support structure or interface arrangement (14) with a shape complementary to the exterior part of the tubular beam (6).

[0033] Figure 3 shows the situation where the legs (13) of the service vessel (8) have been fully extended and have lifted the service vessel (8) a distance above the sea surface. In this position, the service vessel (8) is unaffected by waves and there will not be any relative movement between the service vessel (8) and the substructure (2) resulting in that the operation of the crane (10) can be performed even at relatively large wave heights.

[0034] In the fully extended position of the legs (13) , the length of upper parts of the legs (13) are such that the upper parts of the legs (13) protruding upwards from the deck of the service vessel (8) will not interfere with the operation of the crane (10).

[0035] Figure 4 shows the situation in Fig.3 where the legs (13) has been fully extended and the service vessel (8) has been raised above the sea surface. The crane (10) on the service vessel (8) has been raised and is ready for operation.

[0036] Figure 5 shows second preferred embodiment of the invention, where the service vessel (8) is placed above the sub-structure (2). In this embodiment, the legs (13) on the service vessel (8) are not lowered, but instead the sub-structure (2) is deballasted until the lower part of the legs (13) is in contact with the tubular beams (8).Instead of legs (13) the service vessel (8) can have other types of the sub-structure (2) is then further de-ballasted, and the sub-structure (2) will then lift the service vessel (8) above the water surface. As an alternative to the legs (13) shown in Fig. 5 and 6, it is possible to have other types of interface arrangements such as stools or cradles that can make connection with the tubular beams (6).

[0037] List of reference numerals1 floating wind turbine unit2 floating semi-submersible sub-structure 3, 4, 5 pontoons / columns6 tubular beams7 wind turbine tower8 crane vessel9 tug 10 crane11 support structure / cradle12 turbine blade13 jack-up legs14 Interface arrangement

Claims

Claims1. Method for maintaining and installation of offshore wind turbines, comprising the following steps:5 - positioning a floating service vessel (8) with a crane (10) above a semi- submerged sub-structure (2) of a floating wind turbine (1), said sub-structure(2) comprising a number of mainly vertical pontoons or columns (3, 4, 5) interconnected by tubular beams (6),- providing contact between the tubular beams (6) and an interface10 arrangement (14) on the service vessel, and- lifting the service vessel (8) above the water surface.

2. The method according to claim 1 , where the interface arrangement is legs (13) protruding from the service vessel (8), said legs (13) are each provided with an interface arrangement (14) to make contact with the tubular beams (6).

3. The method according to claim 1 or 2, where the legs (13) are of a jack-up type where the legs (13) can be moved up and down.

4. The method according to claim 1 or 2, where the legs (13) are not movable.

5. The method according to any one of the preceding claims, where the floating service vessel (8) is raised above the sea surface by either20 i) extending the legs (13) and raise the service vessel out of the water; or ii) de-ballasting the semi-submerged sub-structure (2) and raise the sub- structure (2) until the service vessel (8) is above the sea surface.The method according to claim 4, where the legs (13) are stools or cradles.

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