WO2019245385A1

WO2019245385A1 - An arrangement at floating net cage

Info

Publication number: WO2019245385A1
Application number: PCT/NO2019/050132
Authority: WO
Inventors: Sven Jørgen STRØMMEN
Original assignee: Fjord Miljo As
Current assignee: Fjord Miljo As
Priority date: 2018-06-21
Filing date: 2019-06-21
Publication date: 2019-12-26
Anticipated expiration: 2020-12-21
Also published as: NO20190779A1; NO346320B1

Abstract

A pressure equalization arrangement for a floating net cage comprises at least a partial liquid barrier and has one or more intake openings in the liquid barrier and is provided with a filter device allowing osmotic pressure equalization. The filter device may be a mechanical filter or a membrane gauze, such as a plankton gauze. The net cage may be a semi-closed net cage with a lice skirt or a completely closed net cage.

Description

Arrangement at floating net cage

Field of the invention

The invention relates to floating arrangements for farming and storage of marine organisms. More specifically, the invention relates to a pressure equalization

arrangement for a floating net cage as indicated in the preamble of claim 1.

Background of the invention

Floating arrangements for farming and storage of marine organisms, such as fish, are well known. These arrangements may be net cages or other floating structures and may be open, closed or semi-closed. Closed arrangements are characterized by containers with dense walls (fixed or flexible) preventing passage of water. Water must therefore be pumped in and out of the arrangement. One example of a closed arrangement is discussed in Norwegian patent No. 332341 Bl, wherein a net cage structure is described for fish farming, comprising a closed net cage fastened to a float collar at least partly immersed in the water, as well as at least an inlet line for supply of fresh water and an outlet in a lower part of the net cage bottom portion for discharge of water and waste from the net cage via a drain line. Another example is discussed in Norwegian patent No. 342403 Bl, describing a floating dense net cage apparatus for farming of marine organisms, wherein the apparatus comprises a closed net cage with water-impermeable walls for establishing a main water reservoir, wherein the walls are fastened to a floating collar with at least one intake pipeline for supply of fresh water and with at least one outlet pipeline for discharge of water and waste from the net cage.

Semi-closed arrangements are characterized by one part of the circumference of the container being lined with or covered by a dense wall preventing passage of water, the remaining parts of the container having a net or seine allowing passage of water. The dense wall portion is typically placed at the upper portion of the arrangement, the purpose being to form a barrier against lice and other parasites (therefore often referred to as a "lice skirt"). One example of a semi-closed arrangement is mentioned in

Norwegian patent No. 341377, describing a farming net cage for fish farming, comprising a float collar floating at the water surface, a seine fastened to the float collar for housing the farmed fish, and wherein the seine is also attached to a bottom ring down in the water, as well as a skirt surrounding the seine and extending down in the water to an area over the bottom ring. Several flow setters are placed upright in the seine, and the flow setter comprises an elongate vertical suction pipe having a lower inlet for suction of water and an upper, substantially horizontal outlet for distributing the water in the upper water body of the seine and for setting the water body into rotation.

With various methods for shielding against salmon lice, a preventive effect with up to 80% reduction of salmon lice is well documented. Deeper shielding gives a better protection against lice, but also involves bigger challenges regarding the environment in the net cage. Poor environment, inter alia, means that oxygen consumption in the skirt volume is higher than the supply, such that the level is lower than the fish need to maintain normal activity, that there is accumulation of algae and jellyfish, which may adversely affect the fish, with accumulation of plankton and other organisms, such as bait, which may give the fish illnesses and other problems. It has also been experienced that cleaner fish feed on the bait instead of on the lice of the salmon. The environment in a net cage (specially a farming net cage) is crucial for production results, fish welfare and health. One of the most important environmental factors is oxygen. Swimming activity and processes associated with feed uptake depend on sufficient oxygen supply to the fish tissue. The levels must be kept well above the levels required by a full-fed salmon also at the highest temperatures experienced in open net cage production for ensuring good fish welfare and good growth. Generally, a poor environment may reduce the immune system of the fish and make the fish vulnerable to illnesses and increase the mortality in the production. Experience from tests with snorkel net cages shows substantially better preventive effect with a deeper snorkel (deeper swimming),

Prior art aiming at improved environment by using shielding against lice consists of replacement of the water within the skirt volume. Examples of such prior art include Norwegian patent application No. 20161871 and Norwegian patent application No. 20162033. Other prior art comprises pumping out the surface water in the net cage. These methods have in common that the surface water is displaced to the benefit of water deeper down in the water column.

Arrangements according to prior art make it possible to achieve a considerable preventive effect by deep shielding while creating an optimal environment in the seine for growth. The fish may then show signs of wellbeing through increased activity in the net cage volume and behave as if there was no skirt/shielding around the net cage. The extensive replacement of the water allows use of deep skirts. However, if the replacement of water is sufficiently efficient, modifications of the function of the skirts will also be necessary. Depending on the location of the site, natural sudden changes in the environment may also occur.

Closed net cage solutions are known for separating the fish from parasites and other pathogens in the sea while obtaining a more stable production. Some have a dense, flexible gauze while others have hard materials such as concrete, steel and glass fiber. Examples of closed solutions are as mentioned above described in Norwegian patent Nos. 332341 Bl and 342403 Bl. It is known that there is also a risk of damage associated with closed farming solutions and thereby also risk of escape. There may also be a risk for the fish in case of pump failure or by holes on the plant and the tank running empty of water. In normal operation of a closed plant, the energy costs will represent a cost factor which does not exist with an open net cage solution. In closed and semi-closed farming plants at sea, the characteristics of the water may be different inside and outside the plant. Especially, the water may have a different salt content (salinity), which gives the water different levels of density. In semi-closed plants water being pumped up from the deep has a higher density than the water at the surface when this has a higher incorporation of fresh water. Water with low salinity will seek equalization with water having a higher salinity. This may cause pressure differences that may represent a risk factor for equipment and escape of fish when the difference becomes large. Therefore there is a need to equalize the pressure differences and thereby the forces acting on the wall. In closed plants these forces may be compensated for by sufficient buoyancy. However, if the closed unit is damaged it may empty itself. Therefore there is a need for a solution allowing equalization of the difference between the characteristics of the water outside and inside of a closed or semi-closed arrangement (e.g. a net cage).

Prior art also comprises Norwegian patent application No. 20120327 Al, describing water being brought into a net cage from a larger depth in the water column. Such water may have a higher salt content than the water at the surface and this places higher demands on the buoyancy body keeping the closed net cage floating. A floating net cage may also be subject to strong water currents, which may lead to unwanted organisms entering the net cage. To remedy these problems a slot system in a wall portion of a semi-open type net cage or a closed type net cage has been developed. The slots may be placed at different depths, e.g. below the level where salmon lice, jellyfish and algae occur, or in the upper portion of the wall to allow water rich in oxygen to flow into the net cage if the water supply from deeper water layers should fail.

Prior art also comprises Norwegian patent application No. 20150884 Al, describing a closed tank for fish farming, wherein the container is provided with a liquid-tight hull and with a water supply system and a drain system for water. The water supply system comprises a number of essentially vertical inlet tubes which also constitute a supporting part of the container.

Prior art also comprises Norwegian patent application No. 20111326 Al, describing a floating, cylindrical and closed tank consisting of panels made of watertight fiber glass laminate materials and internal buoyancy foam-based materials. The panels form the walls and the bottom of the tank. The top of the tank is open to the air but is protected against predators via a thick mesh top network. The tank is supplemented with water via a plurality of intakes and a pump integrated in the tank wall.

Prior art also comprises Norwegian patent application No. 20110254 Al, describing a closed net cage fastened to a float collar partly immersed in the water. Fresh water is supplied via an intake pipe to the net cage via one or more water sprinklers.

Prior art also comprises Norwegian patent application No. 160753 B, describing a floating, watertight and circular net cage with a float collar. The net cage is provided with adjustable nozzles for supply of fresh water ensuring rotation of the water volume. Pollution and impure water is carried away under controlled conditions. Prior art also comprises Norwegian patent application No. 19922866 B, describing a method of supplying water to a closed net cage for fish farming. The method involves sea water being pumped preferably from deeper sea layers in a suitable supply pipe and led into a closed net cage so that water body of the net cage is set in a rotating movement. The supply pipe has mounted thereto an inlet grid to prevent fish from outside to enter the net cage.

The prior art lice skirts that are used around net cages to protect and form a barrier against lice, are predominantly impervious sheets of various materials that are placed around the net cages and extend from the water surface and to a distance of about 5 to 10 meters into the water, thereby creating a“closed cage” in the upper few meters from the water surface. This is a semi-variant of a fully enclosed cage. Some sheets are water-permeable to some extent, others are not. After some time in seawater, the sheets are covered with fouling, whereby the water-permeability is reduced and for all practical purposes become impervious. When the permeability is not maintained, pressure differences will develop between the skirt inside and outside. This is because various compositions and concentrations of salinity and temperature in periods may occur in the water columns inside the skirt and outside the skirt. Using systems for pumping water from other depths in the skirt volume, the effect from salinity and temperature differences will be augmented. Summary of the invention

The invention is disclosed and characterized in the independent claim, whilst the dependent claims describe other characteristics of the invention.

A pressure equalization arrangement for a floating net cage is provided, comprising at least a partial liquid barrier, characterized by one or more intake openings formed in the liquid barrier and provided with a fluid-permeable filter device allowing osmotic pressure equalization whilst not allowing passage of larger particles or objects.

In one embodiment, the intake opening is an opening in the liquid barrier, and the filter device is placed in the opening.

In another embodiment, the intake opening comprises a fluid channel fastened to the liquid barrier and in fluid communication with the inside of the net cage, and the fluid projects from the liquid barrier; and a portion of the fluid channel is provided with a filter device. The filter device may be removable, and in one embodiment, at least one portion of the fluid channel is movable relative to the net cage.

The filter device may be a mechanical filter or a membrane gauze. The membrane gauze may have openings (mesh width or pore size) with a size between 50 and 600 pm. In one embodiment, the openings of the membrane gauze have a size between 250 and 350 pm. In another embodiment, the openings of the membrane gauze have a size of 300 pm.

It is also provided a control unit for a floating net cage, comprising a liquid barrier, characterized by one or more intake openings formed in an upper region of the liquid barrier and fumshed with a fluid-permeable membrane gauze which allows osmotic pressure equalization but blocks the passage of larger particles or objects, and where the liquid barrier comprises two sheets that are interconnected in an upper portion and not connected in a lower portion, whereby the two sheets may be entered onto an upper part of an eksisting liquid barrier. At least one of the sheets may in a lower region be furnished with weights or a weight rope.

The net cage may be a semi-closed net cage, and the liquid barrier may be a lice skirt. In another embodiment, the net cage may be a fully closed net cage completely enclosed by the liquid barrier, and the liquid barrier is the wall of the net cage. The arrangement according to the invention provides a suitable modification of the function of the lice skirts and also represents an energy-efficient, sustainable and environment-friendly solution. The arrangement according to the invention also provides a solution which will have an emergency function at closed plants, and which may be utilized in reduction of energy consumption at closed plants at sea. The arrangement according to the invention makes it possible to offset the osmotic pressure between the water inside the net cage and the water at the outside of the net cage, in a semi-closed and in a closed net cage. Furthermore, the arrangement according to the invention utilizes the osmotic pressure difference to reduce energy consumption in floating, closed and semi-closed farming plants. The arrangement according to the invention gives reduced operating expenses and a lower energy consumption by optimizing pump operation to obtain target parameters.

By means of the arrangement according to the invention, it is possible to control the oxygen level in the water in the net cage, to control the water temperature in the net cage, to control the salinity level and to reduce the risk of damage to equipment as well as to reduce the risk of escape by using a skirt. The arrangement according to the invention may act as a natural "battery" in case of power failure in that the valves/inlets will take in water as long as there is an osmotic pressure difference between the water inside the net cage and the water outside. This gives time for an emergency function. Furthermore, the arrangement of the invention may also have an emergency function in closed farming plants by preventing collapse in case of damage (e.g. holes in the wall) to the plant. In case of damage, plants according to prior art will empty themselves for water due to high density of the water that has been pumped in. However, the arrangement according to the invention will in such a situation supply water to the net cage (i.e. into the plant/net cage) until the osmotic pressure in the water inside the plant/net cage is equal, or essentially equal, to the osmotic pressure in the water outside the plant/net cage and thereby prevent emptying of the net cage volume. The arrangement according to the invention will also have an emergency function in case of shutdown (e.g. pump failure). In such a situation the arrangement according to the invention will supply water until the osmotic pressure difference is equalized, which gives valuable time to get the system up and running again.

Brief description of the drawings

The aforementioned and other characteristics of the invention will be further explained in the following description of embodiments, presented as non-limiting examples and with reference to the accompanying drawings, wherein:

Figure 1 is a perspective view of a semi-closed net cage according to a first embodiment of the invention;

Figure 2 is a perspective view of a semi-closed net cage according to a second embodiment of the invention; Figures 3 and 4 are perspective views of an embodiment of the invention, wherein Figure 4 shows a membrane gauze with an intake portion mounted thereto, and Figure 3 shows the membrane gauze demounted from the intake portion;

Figures 5 and 6 are perspective views showing a section of a net cage furnished with an alternative embodiment of the invention, in an assembly phase;

Figure 7 is a perspective view of the alternative embodiment shown in figures 5 and 6, in an assembled state on a net cage; and

Figure 8 is another (side) perspective view of the alternative embodiment shown in figures 5-7. Detailed description of embodiments of the invention

The following description may use expressions as "horizontal", "vertical", "lateral", "hack and forth", "up and down", "upper", "lower", "inner", "outer", "forward", "rear", etc. These expressions essentially refer to the perspectives and locations showed in the drawings and related to a normal use of the invention. The expressions are used only to facilitate the comprehension of the description and should not he limiting.

Figure 1 shows a first embodiment of the invention in use on a semi-closed net cage 1. The semi-closed net cage 1 comprises a float ring 3 supporting a seine bag 2 and is shown floating at the surface S of a water body W. The seine bag is of a basically known type (note that the lower part of the seine bag is not shown in Figures 1 and 2). Arrangements for bringing water from larger depths and up to the upper level of the net cage, as described above, are not shown as such arrangements are well known. The net cage 1 is provided with a fluid-tight barrier in the form of a lice skirt 5, suspended in the float ring and extending in a distance down the water body. The lice skirt prevents, as is well known, water from passing between the inside of the net cage (IN) and the water at the outside of the net cage (OUT) and acts as such as a liquid barrier. Such lice skirts are well known and do not need to be further described herein.

In the illustrated embodiment the liquid barrier (the lice skirt) 5 comprises three openings 4, each having a gauze lOa sewn into it. The invention shall not be limited to this number of openings in the lice skirt; there may be more or fewer. The gauze lOa is a fine-meshed, fluid-permeable membrane gauze allowing passage of liquid through an osmotic pressure difference, but stopping particles, plankton, lice and other parasites and larger objects. The membrane gauze lOa may have openings (i.e. pore size or mesh width) of a size between 50 and 600 pm, preferably between 250 and 350 pm. In one embodiment, the size of the openings is 300 pm. In the farming industry, the membrane gauze is often referred to as a "plankton gauze". The membrane gauze provides balancing of the difference in salinity in the water inside the net cage (IN) and the water outside the net cage (OUT). It is advantageous, but not a condition, that a plurality of openings 4 with a membrane gauze lOa sewn into them are placed symmetrically around the periphery of the lice skirt 5. Although the net cage 1 is shown floating with the float ring 3 at the water surface S, the invention shall not be limited to such a use, but shall also include net cage solutions completely immersed beneath the water surface.

Figure 2 shows a second embodiment of the invention in use on a semi-closed net cage 1 of basically the same type as showed in Figure 1. However, in this second

embodiment the openings (reference number 4 in Figure 1) are replaced by a plurality of intake valves 6. Figure 2 shows two intake valves 6, however, the invention shall not be limited to this number; there may be more or fewer. It is advantageous, but not a condition, that a plurality of intake valves 6 are placed symmetrically around the periphery of the lice skirt 5.

The intake valve 6 will now be described in more detail with reference to Figures 3 and 4. A fluid channel 8 is fastened to the liquid barrier (the lice skirt) 5 by means of conventional fastening means, such as a through bracket 7 and bolts 11. The fluid channel 8 may be a rigid tube, but is preferably a flexible tube or a hose being movable up and down in the water body, independently of the position of the net cage in the water body. The fluid channel may be fabricated in plastic or metal or combinations of such materials. The fluid channel 8 may have its own buoyancy means (not shown) and be maintained in the desired position by means of mooring lines 12 which may be fastened to the float ring 3 or other supporting structures. The fluid channel has preferably a certain negative buoyancy. An intake portion 9 of the fluid channel 8 is provided with openings allowing passage of water, and the fluid channel thereby creates a channel between the inside of the net cage (IN), at the inside of the lice skirt 5, and the outside of the net cage (OUT), at the outside of the lice skirt 5. Although the figure shows that the intake portion 9 is provided with perforations, it is to be understood that other openings in the tube or hose 8 are possible. The intake portion 9 is in the illustrated embodiment provided with a membrane gauze lOb. The membrane gauze 1 Ob is a fine- meshed, fluid-permeable membrane gauze allowing passage of liquid through an osmotic pressure difference, but stopping particles, plankton, lice and other parasites and larger objects. The membrane gauze lOab may have openings (i.e. pore size or mesh width) of a size between 50 and 600 pm, preferably between 250 and 350 pm. In one embodiment, the size of the openings is 300 pm. The membrane gauze is in the farming industry referred to as a "plankton gauze" and provides balancing of the difference in salinity in the water inside the net cage (IN) and the water outside the net cage (OUT). In the embodiment shown in Figure 3, the membrane gauze is designed as a cylinder that can be thread over the water intake portion 9 and replaced as part of normal maintenance and care. Although not shown, an automatic cleaning of the membrane gauze lOb while it is mounted to the intake portion is also conceivable.

An advantage of being able to move the flexible tube or hose 8 up and down in the body of water, is that the intake 9 with its mambrane gauze lOb may be placed at that depth in the body of water where the difference in salinity between the water inside and outside the net cage is the greatest.

The fluid intake portion 9 and the membrane gauze 10b may have other shapes than those illustrated in the figures, e.g. the shape of a cylinder, a globe or a cube. A central principle is that the intake portion 9 with the membrane gauze 10b provides a larger surface for water intake than the diameter of the fluid channel 8.

The invention is described above with reference to a semi-closed net cage with a liquid barrier in the form of a lice skirt. However, it should be understood that the invention may also be used on a fully closed net cage. In such a case, the liquid barrier may be the actual tub wall in the net cage. It should also be understood that a mechanical filter may replace the membrane gauze lOa, lOb, although this is seen as a less gentle and more complicated and maintenance intensive solution.

An alternative embodiment of the invention is illustrated in figures 5-8. This

embodiment comprises a control unit 20 having a membrane gauze lOc, corresponding to the membrane gauze described above with reference to figure 1. Reference number 22 in figure 8 denotes connection lugs. The membrane gauze lOc is assembled in a skirt/liquid barrier having similar properties as the skirt 5 which is described above, but this unit comprises two sheets 25a, 25b having an impervious sheet (e.g. a PVC sheet) that are connected in an upper portion and not connected in the lower portion. This enables the control unit 20 to be entered onto the upper part of the existing skirt sheets from above. The skirt sheet 5 may be lowered down to below the water surface in that region in which the control unit is to be assembled. The two split sheets 25a,b may be furnished with weights or steel ropes 21 (see figure 8) along the edges and in the middle in order for it to maintain its shape and bear against the skirt sheets 5 on both sides (see figure 7). One of the split sheets (25a or 25b) may also comprise magnets (not shown), placed such that steel weights (not shown) on the opposite split sheet (25b or 25a) is pulled towards the magnets. The sheets will thus be pinched firmly to the intermediate portion of the skirt sheet. The embodiment with a filter (membrane gauze) lOc and connected (sewn on) split sheets 25a,b is in the plane bearing against the skirt sheet 5 shaped such that it conforms to a natural arc that forms when the skirt sheet is 5 lowered below the water surface between two or more supports on the float ring 3. The weights will force the skirt sheet below the water surface such that the filter becomes submerged and starts letting water into the volume inside the net cage. The skirt sheet may during production be adapted with openings suitable for the applicable solution. One variant for adaptation of the skirt sheet is that a portion of the top of the skirt sheet is removed to allow assembly of this embodiment. The control unit 20 makes it possible to let filtered water in across the sheets in closed or semi-closed net cages. The control unit may be retro-fitted onto existing lice skirts.

Claims

Patent claims

1. A pressure equalization arrangement for a floating net cage (1) comprising at least a partial liquid barrier (5), characterized in that

one or more intake openings (4; 6) formed in the liquid barrier (5) and provided with a fluid-permeable filter device (lOa; lOb) allowing osmotic pressure equalization whilst not permitting passage of larger particles or objects.

2. A pressure equalization arrangement according to claim 1, wherein the intake opening (4) is an opening in the liquid barrier, and the filter device (lOa) is placed in the opening.

3. A pressure equalization arrangement according to claim 1, wherein the intake opening (6) comprises a fluid channel (8) fastened to the liquid barrier and in fluid communication with de inside of the net cage (IN), and wherein the fluid channel (8) projects from the liquid barrier; wherein a portion (9) of the fluid channel (8) is provided with a filter device (10b).

4. A pressure equalization arrangement according to claim 3, wherein the filter device (10b) is removable.

5. A pressure equalization arrangement according to any one of claims 3-4, wherein at least one portion of the fluid channel is movable in relation to the net cage.

6. A pressure equalization arrangement according to any one of claims 1-5, wherein the filter device is a mechanical filter

7. A pressure equalization arrangement according to any one of claims 1-5, wherein the filter device is a membrane gauze (10a; 10b).

8. A pressure equalization arrangement according to claim 7, wherein the membrane gauze (10a; 10b) has a pore size between 50 and 600 pm.

9. A pressure equalization arrangement according to claim 8, wherein the membrane gauze (10a; 10b) has a pore size between 250 and 350 pm.

10. A pressure equalization arrangement according to claim 9, wherein the membrane gauze (10a; 10b) has a pore size of 300 pm.

11. A pressure equalization arrangement according to any one of claims 1-10, wherein the net cage (1) is a semi-closed net cage, and the liquid barrier (5) is a lice skirt.

12. A pressure equalization arrangement according to any one of claims 1-10, wherein the net cage (1) is a completely closed net cage completely enclosed by the liquid barrier, and wherein the liquid barrier is the wall of the net cage.

13. A control unit (20) for a floating net cage (1), comprising a liquid barrier

(25a, b), characterized by one or more intake openings formed in an upper region of the liquid barrier and furnshed with a fluid-permeable membrane gauze (lOc) which allows osmotic pressure equalization but blocks the passage of larger particles or objects, and where the liquid barrier comprises two sheets (25a, 25b) that are interconnected in an upper portion and not connected in a lower portion, whereby the two sheets may be entered onto an upper part of an eksisting liquid barrier (5).

14. The control unit according to claim 13, where at least one of the sheets (25a,b) in a lower region is furnished with weight or a weight rope (21).