GB2534227A

GB2534227A - Lifting system

Info

Publication number: GB2534227A
Application number: GB1500862.6A
Authority: GB
Inventors: Colclough Robert; Sargent Nicholas; Twibell Timothy
Original assignee: Marine Current Turbines Ltd
Current assignee: Marine Current Turbines Ltd
Priority date: 2015-01-19
Filing date: 2015-01-19
Publication date: 2016-07-20
Also published as: GB201500862D0

Abstract

A lifting system for installing and retrieving equipment e.g. tidal turbines on a surface piercing structure 1 comprises a lifting mechanism such as a winch 6 mounted to a topside structure. The system further comprises a lifting frame 8 which moves on guides on the tower 1. The lifting frame 8 has releasable couplings (14, 15, 16, figures 1-5) to connect to a piece of equipment such as a crossbeam 11. Flexible supports such as chains 7 couple the frame to winch 6. The lifting mechanism and frame are stored out of the water when not engaged in installing and retrieval, which reduces corrosion and possible damage from water action.

Description

LIFTING SYSTEM

This invention relates to a lifting system for subsea equipment, in particular for power trains of tidal turbines mounted on a surface piercing structure.

In a surface piercing tidal turbine, the drive trains are mounted below the sea surface in normal use, on a crossbeam, but need to be retrieved at intervals for maintenance and repair. The current arrangements in use, for example on the SeaGen system deployed in Strangford Lough use a lift leg system. The lift legs are permanently attached to the tidal turbine crossbeam and are therefore subjected to ocean loading most of their life. They are pulled up by a hydraulic system located on the top of the structure when access is required. Lift legs are expensive fabrications, and are not suited well to survival in large waves, due to high bending stresses.

This problem is not addressed by subsea turbines which are mounted directly to the sea bed on a structure which is not surface piercing, as installing and retrieving the turbine requires a support vessel and crane, which are only on site for a minimum period when required. For fully submerged systems, retrieval of the powertrain to a suitable lifting ship or barge usually requires the intervention of a diver or use of a remotely operated vehicle to locate the turbine and connect lifting cables, or chains, from the vessel to the powertrain/drivetrain.

In accordance with a first aspect of the present invention, a lifting system for installing and retrieving equipment on a surface piercing structure comprises a lifting mechanism for mounting to a topside structure of the surface piercing structure, the lifting mechanism comprising a source of lift power and a source of mechanical advantage; a lifting frame comprising one or more releasable couplings to connect a piece of equipment to the frame and one or more guides adapted to move on guide rails on the surface piercing structure; and flexible supports coupling the frame to the lifting mechanism; wherein the lifting mechanism and frame are stored out of the water when not engaged in installing and retrieval.

Preferably, the source of mechanical advantage comprises a winch.

Where available, the source of lift power may be from a diesel generator, electrical machine, or compressed air supply, but preferably, the source of lift power comprises a hydraulic unit.

Preferably, the releasable couplings further comprise a remotely controlled actuator for releasably fixing the couplings to the equipment; Preferably, the remotely controlled actuator comprises a pin.

In use, the pin cooperates with aligned holes in the equipment and the frame.

Preferably, the remotely controlled actuator is a hydraulic or compressed air powered actuator.

The actuator may be mounted on the connecting frame, but preferably, the actuator is mounted on the equipment.

This has the advantage that the control lines to the actuator can be protected in a rigid duct, mounted to the crossbeam.

In accordance with a second aspect of the present invention, a method of installing and retrieving equipment on a surface piercing structure comprises releasably connecting a lifting frame to a piece of equipment, coupling one or more guides of the lifting frame to guide rails on the surface piercing structure; engaging a source of mechanical advantage with the frame through flexible supports; and moving the frame and equipment from a first position to a second position on the surface piercing structure; wherein, when the frame and equipment move from a first position above the surface of the water to a second position below the surface of the water, the connection between the frame and the equipment is released at the second position and the frame and flexible supports returned to the first position.

Preferably, the equipment is required to move from a second position, below the surface of the water to a first position above the surface of the water, the frame is lowered on its flexible supports to the second position and connected to the equipment.

Preferably, the connection between the frame and the equipment is made at the second position and the equipment, frame and flexible supports returned to the first position.

Preferably, the releasable connection of the lifting frame to the equipment is made by operating a hydraulic, or compressed air, actuator on the equipment.

An example of a lifting system and method according to the present invention 30 will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic diagram showing the drivetrain installed and a lifting system according to the present invention positioned above the sea surface; Figure 2 is a schematic diagram showing the lifting system of the present invention, below the sea surface with the drivetrain, ready for retrieval; and, Figure 3 is a schematic diagram showing the drivetrain and lifting system retrieved and above the sea surface.

Figure 4 illustrates part of the lifting system of the present invention in more detail; Figure 5 is an alternative view illustrating part of the lifting system of the present invention in more detail; and, Figure 6 is a perspective view of the overall system of the present invention.

Figs. 1 to 3 illustrate how the system of the present invention operates, Fig.4 and Fig.5 show more detail of the connections between the lifting frame and the crossbeam and Fig. 6 is a detailed view of the system of the present invention. The invention is described with respect to a surface piercing tidal turbine, but is also suitable for use in other applications where subsea equipment must be retrieved, such as installing J-tubes for underwater cables or servicing and maintenance in oil and gas production.

A surface piercing structure, or tower, 1 supports a crossbeam 2 and a lifting system 3. Tidal turbine drivetrains (not shown) are mounted on the crossbeam. The lifting system is mounted on a topside structure 4 and when not in use, is out of the water. A power unit 5, typically a hydraulic power unit, on the topside structure 4 provides power to winches 6, which are connected, by flexible support members 7, such as chains, or wire rope, to a lifting frame 8. In this example, a duct 9 protects hydraulic lines 10 connected to a crossbeam interface 11, situated below the sea surface 12 when in use.

The crossbeam 2 is located on splines at the base of the tower 1 and guide rails 13 on the tower are used as a guide for the lifting frame 8 to be lowered from the top of the tower to the crossbeam. The top of the lifting frame 8 is connected to the chain 7 or wire rope and the trolley can be raised or lowered using the winch 6 on the topside structure 4.

Where chain is used, the size of chain links required to support the weight of the turbine power train on the crossbeam is very large and if left in place after the turbine has been lowered to its operational position at the base of the structure, there is a high likelihood of damage being caused by the chain moving about in the current. If the chain is kept in place underwater, then it needs adjustable tensioning, to prevent the chain causing damage when not in use. This adds cost and complication. In addition, corrosion in the splash zone of highly aerated water is a major issue, which is typically addressed by making the chain links even larger to allow for corrosion over a predetermined timescale, again adding cost and increasing the damage the chain can do if left unconstrained. By storing the chain out of the water and only immersing it when it is being used, the corrosion is reduced, so the increase in chain size required to cope with corrosion is also less than that for chain left permanently underwater and the chain is not in a position to cause damage, so the tensioning is not required.

After installing the drivetrains, by connecting the crossbeam on which they are mounted, to the lifting frame and lowering the crossbeam into position beneath the surface 12, the lifting frame 8 and chain 7 are disconnected from the crossbeam and turbine drivetrain and recovered to a position above the surface 12 to minimise damage and corrosion, as shown in Fig. 1. The connecting mechanism is illustrated in more detail in Figs. 4 and 5. Holes 14, 15 in the lifting frame and crossbeam interface respectively are aligned and fastened with a pin 16 to enable the crossbeam and drivetrain to be secured for lowering and once the drivetrain is in place, the pin is removed and the lifting frame 8 separates from the crossbeam interface 11.

Alternatively, a retractable pin on one of the lifting frame or the equipment may cooperate with a recess on the other of the lifting frame or the equipment. Clearly, other types of fixing are possible, still within the scope of the inventions, such as a sprung hook and eye type connection, with an actuator to release the lifting frame from the crossbeam when the crossbeam is in position, or other suitable couplings.

Unlike the existing surface piercing structures for tidal turbines, the system of the present invention is able to retrieve the subsea tidal turbine drivetrains and lift them clear of the sea surface using a system that in normal conditions lives above the water surface on top of a surface piercing structure and so is better protected from corrosion and less able to cause damage to other parts.

In order to retrieve the drivetrain, the lifting frame needs to be correctly positioned and aligned to reconnect with the crossbeam. For example, guide rails 13 on the structure 1, normally used to keep the crossbeam 2 in alignment on the tower, may be used to guide the lifting frame 8 into contact with the crossbeam interface 11, although other guide mechanisms may be installed and used to position the frame. The guide rails 13 on the tower prevent the lifting frame moving excessively and ensure alignment of lifting holes on the trolley and the crossbeam. The lifting frame 8 is lowered on its chains by the winches 6 and the lifting holes 14 on the lifting frame are aligned with the lifting holes 15 in the crossbeam interface 11. At this point a pin 16 is inserted through the holes 14, 15, so that the crossbeam and lifting frame are connected. The sliding pins can be situated on the crossbeam and remain underwater with it, or be mounted on the lifting frame. The example shown has the pins 16 on the crossbeam interface 11. . The pins are remotely controlled, for example by a hydraulic actuator, or an electrical actuator, or pneumatic actuator and when located on the crossbeam, hydraulic lines 10 are taken down to the crossbeam 2 from the topside structure 4, typically in a rigid duct that protects the hydraulic lines from ocean loading, such as a steel duct, although other suitable materials may be used. In this case, the hydraulic lines may need to be disconnected at the end on the topside structure, before the crossbeam is raised. If the pins are mounted on the lifting frame, then a connection with the topside structure, to provide control and actuate the pins, is required, for example by a hydraulic power pack....

The crossbeam is lifted using the winches 6 and hydraulic power unit 5 on the topside structure until it is clear of the water surface and maintenance operations can proceed. For relatively small loads, electric winches can be used. Once the repair or maintenance has been completed, the lifting frame and crossbeam are lowered again until the crossbeam rests on the splines. The pins are then retracted and the lifting frame is raised again, so that it is clear of the water surface, where it stays until it is needed next. The present invention makes efficient use of existing equipment on a surface piercing tower, with relatively few additional parts being required, as well as preventing damage and corrosion. In operation, the surface of the tower and the guiderails on the tower guide the lifting frame into position on the crossbeam quickly and efficiently. There is no need for a diver or ROV to connect a guideline for the lifting cables, so the whole operation can be carried out relatively quickly and cheaply, in comparison to other subsea retrieval methods involving a diver, or ROV.

The invention may also be applied to other lifting and lowering operations, such as for J-tubes which control the radius of an underwater cable and support it in a current, or for raising an offshore wind turbine into position near the top of its support structure.

Claims

CLAIMS1. A lifting system for installing and retrieving equipment on a surface piercing structure, the system comprising a lifting mechanism for mounting to a topside structure of the surface piercing structure, the lifting mechanism comprising a source of lift power and a source of mechanical advantage; a lifting frame comprising one or more releasable couplings to connect a piece of equipment to the frame and one or more guide members adapted to move on guides on the surface piercing structure; and flexible supports coupling the frame to the lifting mechanism; wherein the lifting mechanism and frame are stored out of the water when not engaged in installing and retrieval.
2. A system according to claim 1, wherein the source of mechanical advantage comprises a winch.
3. A system according to claim 1 or claim 2, wherein the source of lift power comprises a hydraulic unit.
4. A system according to any preceding claim, wherein the releasable couplings further comprise a remotely controlled actuator for releasably fixing the couplings to the equipment;
5. A system according to claim 4, wherein the remotely controlled actuator comprises a pin.
6. A system according to claim 4 or claim 5, wherein the remotely controlled actuator is a hydraulic or compressed air powered actuator.
7. A system according to any of claims 4 to 6, wherein the actuator is mounted on the equipment.
8. A method of installing and retrieving equipment on a surface piercing structure, the method comprising releasably connecting a lifting frame to a piece of equipment, coupling one or more guide members of the lifting frame to guides on the surface piercing structure; engaging a source of mechanical advantage with the frame through flexible supports; and moving the frame and equipment from a first position to a second position on the surface piercing structure; wherein, when the frame and equipment move from a first position above the surface of the water to a second position below the surface of the water, the connection between the frame and the equipment is released at the second position and the frame and flexible supports returned to the first position.
9. A method according to claim 8, wherein, when the equipment is required to move from a second position, below the surface of the water to a first position above the surface of the water, the frame is lowered on its flexible supports to the second position and connected to the equipment.
10. A method according to claim 8 or claim 9, wherein the connection between the frame and the equipment is made at the second position and the equipment, frame and flexible supports returned to the first position.
11. A method according to any of claims 8 to 10, wherein the releasable connection of the lifting frame to the equipment is made by operating a hydraulic, or compressed air, actuator on the equipment.