WO2015055258A1

WO2015055258A1 - Aqua farming

Info

Publication number: WO2015055258A1
Application number: PCT/EP2013/071899
Authority: WO
Inventors: Wei He
Original assignee: Statoil Petroleum As
Priority date: 2013-10-18
Filing date: 2013-10-18
Publication date: 2015-04-23

Abstract

An offshore support structure arranged to support a substantial load above the water surface, the structure comprising a frame (21, 22) located in use substantially below the water surface, and a net extending around the frame such that fish can be farmed within the frame.

Description

Aqua farming

TECHNICAL FIELD The invention relates to the field of aqua farming and fish cages. BACKGROUND

Demand for fish is generally increasing due to higher consumption by individual consumers and a growing population of consumers. Many traditional fisheries are reaching maximum sustainable production levels. Traditional fisheries include inshore protected production sites. Examples of problems associated with inshore production sites are pollution of the environment by the production sites and limitations to available space. Production can be moved to more exposed offshore production sites to address some of these problems. Offshore production sites have the advantages of more space, a reduced environmental impact and access to higher water quality.

At an offshore production site, the fish may be contained in a submersible fish cage. An example of a fish cage is shown in Fig. 1 . The fish cage includes a buoyancy ring (1 ) which can float on the sea surface and a net (2) which extends downwards from the buoyancy ring towards anchors (3). This type of fish cage is expensive and complicated to operate and maintain. The fish cage also moves with the water flow due to the generally flexible structure of the cage and strong motion under severe weather conditions may cause damage to fish. Any holes in the nets due to the motion may cause fish to escape which in turn may cause genetic pollution of wild fish.

SUMMARY

According to a first aspect of the invention is herein disclosed an offshore support structure arranged to support a substantial load above the water surface, the structure comprising a frame located in use substantially below the water surface, and a net extending around the frame such that fish can be farmed within the frame. The support structure may comprise a plurality of legs arranged to rest on the seabed and to extend from the seabed to the water surface and the plurality of legs may be connected to each other by beams. The frame may be a jacket foundation for a wind turbine and said substantial load may be the load from the wind turbine. Alternatively, the substantial load may be at least one of: navigation lights, an oil platform, a gas platform, a power station, a meteorological mast. At least one fish net may be arranged around the circumference of the legs. The fish cage may extend along the height of the support structure under water. The structure may comprise four nets, wherein each net is attached to one of the four sides of the jacket foundation. The support structure may be arranged to carry at least one of: a fish feeding system, a fish vaccination system, a fish disease treatment system, a cleaning system, a fish harvesting system. A cover may be provided for temporarily closing the jacket foundation from the water surrounding the jacket foundation to substantially prevent medicament provided within the fish cage from leaving the fish cage. The offshore support structure according to the first aspect may further comprise a system for collecting fish waste and for injecting collected fish waste into the sea bed.

According to a second aspect of the invention, there is provided a wind farm comprising a plurality of support structures according to the first aspect of the invention.

According to a third aspect of the invention, there is provided a fish net adapted to be attached to the offshore support structure according to any one of the preceding claims for aqua-farming.

According to a fourth aspect of the invention, there is provided a method of retrofitting an offshore wind turbine jacket foundation with a fish net to create an offshore fish cage for aqua-farming.

BRIEF DESCRIPTION OF DRAWINGS

Some embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 illustrates a fish cage. Figure 2 illustrates schematically a jacket foundation. Figure 3 illustrates schematically a jacket foundation.

Figure 4 illustrates schematically a wind turbine and jacket foundation with a fish cage.

DETAILED DESCRIPTION

Herein disclosed is a fish cage which has a rigid support structure. The rigid support structure extends from the sea bed to above the water surface and can bear a load such as a wind turbine. The support structure may have a plurality of legs extending from the sea bed to the water surface and the legs may be connected to each other by beams. In particular, the support structure may be a jacket foundation arranged to carry a wind turbine. A net can be arranged around the legs of the jacket foundation to form a cage and the net may extend from the seabed to the sea surface. A single net or a plurality of nets may be used to form a cage. The net may be retrofitted around the jacket foundation of a wind turbine in situ, or the jacket foundation and net may be manufactured together before the wind turbine is placed.

The offshore rigid support structure may support a substantial load other than a wind turbine. Examples of other devices are navigation lights, an oil platform, a gas platform, a power station, a meteorological mast. In an offshore wind farm, a power station is provided for each group of 10 to 15 wind turbines and the power station may also be supported by a jacket foundation. A large number of fish cages can be created by arranging a net around each available jacket foundation in an offshore wind farm or another production site.

The nets may be folded up in containers which are attached to the jacket foundation and the nets may be unfolded for use. The nets may be attached to the jacket foundation by way of horizontal or vertical tracks along which the nets can move for opening and closing the nets in the way of curtains. The strong foundation of the wind turbine jacket foundation provides a rigid foundation for a fish cage. The jacket foundation can withstand severe weather conditions and will substantially be at rest. The jacket foundation is arranged to bear the load of the wind turbine due to the weight of the wind turbine itself and due to the force of the wind onto the wind turbine. The additional load onto the jacket foundation due to the fish nets is small when compared to the load due to the weight of the wind turbine and the force of the wind onto the wind turbine. The fish nets attached to the jacket foundation will move much less than the net of a conventional submergible fish cage which reduces damage due to motion of the cage. The risk of fish escape is lower due to the lower risk of cage damage.

The jacket foundation may be used to support other functions related to fish production. Examples of systems which may be attached to the jacket foundation are: a fish feeding system, a fish vaccination system, a fish disease treatment system, a cleaning system, a fish harvesting system. An example of fish disease which could be treated is salmon lice. Examples of cleaning systems are a dead fish catcher, over-feed spill and fish waste removers. The fish waste may be injected into the sea bed for storage to avoid pollution of the surrounding waters and to avoid the need to transport to an onshore location. These systems reduce the environmental impact due to pollution. The jacket foundation may also be used to support further functions relating to the fish cage, such as submerging and raising the fish net.

The fish cage may also include a cover for closing off the fish cage from the seawater surrounding the fish cage during disease treatment or during vaccination. The fish cage may be isolated from the surrounding sea water for the duration required to administer medicaments to the fish, for example for a duration of 10 hours. The jacket foundation provides a rigid and convenient support for the cover. Portions of the fish cage extending above the water surface during normal use may be submerged during extreme weather conditions to prevent the fish cage from being damaged. The lowering and raising of a portion of the fish cage can be done along the rigid structure of the jacket foundation. The installation and maintenance of the fish cage can be combined with the installation and maintenance of the wind turbine jacket foundation and the cage and wind turbine can share access facilities. It may not be cost effective to build a rigid foundation with the strength of a jacket foundation for the sole purpose of a foundation for a fish cage, but the presence of a wind turbine jacket foundation avoids the need for a separate fish cage foundation. A jacket foundation used for a fish cage provides environmental benefits because of the combination of aquaculture with offshore wind farms.

Figure 2 illustrates a jacket foundation with an integrated fish cage. The jacket foundation has four legs (21 ) generally arranged, respectively, at four corners of a square in the transverse direction. In a specific example, the distance between the legs along a side of the square is substantially 27m near the bottom of the jacket foundation. The size of the jacket in transverse direction reduces towards the top, where the distance between the legs along a side of the square is substantially 25m. The height of the foundation is substantially 40m. Adjacent legs are connected to each other by beams (22), whereby the legs and beams are connected by way of K-joints and X-joints. Fish nets cover the outside of the jacket foundation such that fish which are inside the jacket foundation cannot escape. The top of the cage may be open if the fish nets on the outside of the jacket foundation extend above the water surface. The bottom of the cage may be formed by the seabed or a closed surface from the jacket foundation.

The volume of a fish cage with the dimensions of the above exemplary jacket foundation is 27053m³. A large number of fish cages can be created with the jacket foundations in a typical offshore wind farm which has a large number of wind turbines. A 1000 MW offshore wind farm with 100 units of 10 MW wind turbines can accordingly house 100 fish cages.

Figure 3 illustrates a jacket foundation with an integrated fish cage which is similar to the one illustrated in Figure 2, but the width of the foundation in the horizontal plane does not reduce towards the top of the foundation. The height of the jacket foundation is 66 m. Since the water depth is 40 m, the portion of the jacket up to 40 m from the sea bed can be used for fish farming. This jacket foundation would provide an internal space of 25000 m³, and 1000 of these fish cages would be able to contain 50000 tonnes of fish at a given time for a typical fish density of 20kg/m³. Figure 4 illustrates a wind turbine resting on a jacket foundation whereby a fish cage is provided within the jacket foundation. By way of example, the weight of a 10 MW wind turbine is around 1200 tonnes and the weight of the jacket foundation is around 1000 tonnes. The weight and rigidity of the foundation provides a rigid support structure for the fish cage. Such a jacket foundation does not require significant alterations to its overall structure to be suitable to bear the additional load of the fish cage. By way of comparison, a conventional fish cage with a 12 meter circumference and a depth of 25m is around 20 tonnes without ballast weight and an anchoring system.

Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS:

1 . An offshore support structure arranged to support a substantial load above the water surface, the structure comprising

a frame located in use substantially below the water surface, and

a net extending around the frame such that fish can be farmed within the frame.

2. The offshore support structure according to claim 1 , wherein the support structure comprises a plurality of legs arranged to rest on the seabed and to extend from the seabed to the water surface.

3. The offshore support structure according to claim 2, wherein the plurality of legs are connected to each other by beams.

4. The offshore support structure according to any one of the preceding claims, wherein the frame is a jacket foundation for a wind turbine and wherein said substantial load is the load from the wind turbine.

5. The offshore support structure of any one of claims 1 to 3, wherein the substantial load is at least one of: navigation lights, an oil platform, a gas platform, a power station, a meteorological mast.

6. The offshore support structure according to any one of claims 2 or 3, wherein the at least one fish net is arranged around the circumference of the legs.

7. The offshore support structure according to any one of the preceding claims, wherein the fish cage extends along the height of the support structure under water.

8. The offshore support structure according to claim 4, comprising four nets, wherein each net is attached to one of the four sides of the jacket foundation.

9. The offshore support structure according to any one of the preceding claims, wherein the support structure is arranged to carry at least one of: a fish feeding system, a fish vaccination system, a fish disease treatment system, a cleaning system, a fish harvesting system.

10. The offshore support structure according to claim 9, further comprising a cover for temporarily closing the jacket foundation from the water surrounding the jacket foundation to substantially prevent medicament provided within the fish cage from leaving the fish cage.

1 1 . The offshore support structure according to any one of the preceding claims, further comprising a system for collecting fish waste and for injecting collected fish waste into the sea bed.

12. A wind farm comprising a plurality of support structures according to any one of the preceding claims.

13. A fish net adapted to be attached to the offshore support structure according to any one of the preceding claims for aqua-farming.

14. A method of retrofitting an offshore wind turbine jacket foundation with a fish net to create an offshore fish cage for aqua-farming.