NO345742B1

NO345742B1 - Electrodes for use in sea water, an arrangement of such electrodes and an electric fence comprising the arrangement

Info

Publication number: NO345742B1
Application number: NO20190807A
Authority: NO
Inventors: Rune Eritzland
Original assignee: Sfd Innovation As
Priority date: 2019-06-27
Filing date: 2019-06-27
Publication date: 2021-07-12
Also published as: WO2020263106A1; NO20190807A1

Description

ELECTRODES FOR USE IN SEA WATER, AN ARRANGEMENT OF SUCH ELECTRODES AND AN ELECTRIC FENCE COMPRISING THE ARRANGEMENT

Introduction

The present invention relates to an electrode adapted for being operated in a corrosive environment. More particularly, the electrode is adapted to be operated in sea water. The invention also relates to an electrode arrangement for inflicting injury on pelagic larva in sea water. The arrangement comprises electrodes according to the invention, where at least a first electrode and a second electrode are configured to be arranged in parallel and separated by a spacing. The electrodes are adapted to be provided with different electric polarity for conducting a pulsating electric current through the spacing.

The present invention further relates to an electric fence provided with the electrode arrangement and a fish cage provided with the electrical fence.

Prior art

Farming fish in closed enclosures such as net cages means that an artificially large biomass will be present within a restricted volume. This gives good conditions for fish parasites and in particular for parasites that have only one host in the course of their life cycle. Crustacean fish parasites in the subclass Copepoda, the so-called copepods, are examples of such parasites.

In the farming of salmonoids, in particular salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss), ectoparasite attacks by the copepods of the family Caligidae, in particular Lepeophtheirus salmonis, salmon louse, Caligus elongatus, so-called sea louse, and C. rogercresseyi, are a great problem. Like other crustaceans, these ectoparasites grow by moulting, and they go through several stages altogether in the course of their life cycles. From the egg, a free-swimming nauplius I larva is released first. In L. salmonis, it is 0.5 mm long and the sizes below refer to salmon lice. The nauplius I grows into a nauplius II larva, 0.6 mm long, which in turn grows into a copepodid 0.7 mm long. It is the copepodid that constitutes the infectious stage as the copepodid attaches to a host. The first three stages can last several weeks and the duration is dependent on the water temperature. By low water temperatures the larvae grow slowly. In this period, the small larvae have a limited ability to move actively in the water and will, in the main, drift with the water current. Thereby they are dispersed over a large area.

There are several known methods of removing lice from farmed fish without bringing the fish out of the net cage in which they are normally kept. These methods may be divided into bath treatment, treatment with active substances mixed into the feed and the use of cleaner fish. In addition, there are methods which bring the fish out of the net cage, including treating with fresh water, hot water and by flushing. Bath treatments and bringing fish out of the net cage by pumping is stressful to the fish. Stressed fish have reduced appetite which causes less growth. This is an economic loss. The handling of the fish also causes some mortalities of the fish.

Thus, there is a need for alternatives to today's methods of controlling crustacean parasites in fish farming, or at least supplementary methods. In particular, there is a need for alternatives that do not include the use of chemicals, and do not involve physically handling of the fish.

One such alternative is based on the use of an electrode arrangement and pulsating electrical current with alternating polarity. An example of such electrode arrangement is disclosed in WO 2014/054951 A1. This method is a preventive method as the infectious stage of the parasites are killed or injured before settling on a host.

A problem with the electrode arrangement is that the marine environment subjects the electrodes to extensive corrosion, requiring frequent replacements of the electrodes, during which time the fence is inactive.

Patent application US 2017/0113957 discloses a system for purifying wastewater. The system comprises a rod-shaped or a tube-shaped inner electrode and a sleeve-shaped outer electrode. An annulus is formed between the inner electrode and the outer electrode. The outer electrode is formed with a plurality of apertures. Patent document US 5439567 discloses an apparatus for treatment of a fluid. The apparatus comprises a perforated first electrode and an inner, coaxially disposed second electrode. An annulus is formed between the first electrode and the second electrode.

Summary of the invention

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. This object is achieved through features, which are specified in the description below and in the claims that follow. In particular, an object of the invention is to provide an electrode with improved resistance towards corrosion. The improved electrode is used in an electrode arrangement for inflicting injury on pelagic larva in sea water with improved operational reliability and with reduced operational cost.

By injury to a pelagic larva is meant, in what follows, that irreversible or reversible injury is inflicted on the larva, having a disturbing or destructive effect on the further life cycle of the larva. Such injury may be disturbing or destructive to the larva's infection capacity relative to a host, ability to attach to a surface or ability to grow. By injury is also meant lethal injury. Reversible injury includes a temporary paralysation as well.

In a first aspect the invention relates more particularly to an electrode for use in sea water, the electrode comprises a conductor core forming a surface and an insulator jacket which surrounds the conductor core. The insulator jacket comprises a plurality of perforations for exposing portions of the surface of the conductor core to the sea water.

By means of providing the insulator jacket with perforations, portions of the electrode core is contacted with the sea water, while other portions of the electrode core are protected from the corrosive environment. Accordingly, the electrode core is subjected to reduced corrosion exposure, while being in direct contact with the sea water.

According to an embodiment of the invention, the electrode core may comprise one of carbon, graphite and titanium. Carbon, graphite and titanium have all the advantage of relatively good corrosion resistance in sea water.

According to an embodiment of the invention, the insulator jacket may comprise a glass reinforced polymer. The glass reinforced polymer has the advantage of providing insulation of the electrode core with high form stability. According to further embodiments of the invention, such glass reinforced polymer may comprise a polymer chosen from a group comprising an epoxy resin, polyethylene terephthalate (PET), polyvinyl chloride (PVC) and polyurethane (PUR).

According to an embodiment of the invention, the electrodes may be formed as rods. Preferably, the electrodes may be formed as straight rods. A plurality of rods may abut head to tail within the insulator jacket. I.e. the insulator jacket may be longer than one individual rod.

According to an embodiment of the invention, the perforations may be dispersed in a row in the insulating jacket parallel to an elongated axis of the electrodes.

In a second aspect the invention relates more particularly to an electrode arrangement comprising

- at least a first electrode and a second electrode configured to be arranged in parallel and separated by a spacing, wherein the electrodes are adapted to be provided with different electric polarity for conducting a pulsating electric current through the spacing. The arrangement is characterised in that the electrodes comprise a conductor core forming a surface, and an insulator jacket which surrounds the conductor core, wherein the insulator jacket comprises a plurality of perforations for exposing portions of said surface of the conductor core to the sea water.

The at least two elongated electrodes are to be submerged in the water at a fish farm for inflicting injury on pelagic larva by means of providing a pulsating electric current with changing polarity to the electrodes. Thereby, electric current is conducted through the water at the spacing between the electrodes.

According to an embodiment of the invention, the perforations may be dispersed along a row in the insulating jacket parallel to an elongated axis of the electrodes, and the at least first electrode and the at least adjacent second electrode may be configured to be oriented so that said rows of perforations may be facing each other. By orienting the perforations at the insulator jacket of the respective electrode so that the rows of perforations of neighbouring electrodes are facing each other, the conduction of the electric current through the spacing is facilitated.

According to an embodiment of the invention, the at least first electrode and the at least second electrode may be configured to be positioned so that the perforations along the row of the at least first electrode are aligned with the perforations along the row of the at least second electrode.

According to an embodiment of the invention, the electrode arrangement may comprise spacers configured to hold the electrodes at said spacing. The spacers may for example be cord in which one of the electrodes are hanging from the other electrical electrode. Preferably, the spacers may be of an electric insulating material. According to an alternative embodiment, the spacers may be solid bars holding the electrodes spaced apart on a predetermined distance.

According to an embodiment of the invention, the electrodes may comprise a length in the range of 3 – 10 meters, preferably 4 – 8 meters, more preferably 5 – 7 meters, for example 6 meter.

According to an embodiment of the invention, said spacing may be in the range of 0.5 – 1.5 meter. Preferably the range may be 0.8 – 1.2 meter, more preferably the range may be 0.9 – 1.1 meter.

According to an embodiment of the invention, the arrangement comprises a plurality of first electrodes configured to be connected so that they have a same first polarity and a plurality of second electrodes configured to be connected so that they have a same second polarity different from the first polarity, wherein the first electrodes and second electrodes are alternately arranged. This means that each electrode has an adjacent electrode with an opposite polarity.

According to an embodiment of the invention, the arrangement comprises a first group comprising of a first set of electrodes and a second set of electrodes, and a second group comprising of a first set of electrodes and a second set of electrodes, wherein the arrangement comprises connection elements for connecting the first group with the second group, such that the first set of electrodes are connected together with aligned longitudinal axis, and the second set of electrodes are connected together with aligned longitudinal axis.

The above object is further achieved by means of an electric fence for inflicting injury on pelagic larva in sea water. The fence comprises an electrode arrangement according to any of above embodiments and a pulse generator configured to provide a pulsating electric current, wherein the at least two electrodes are connected to the pulse generator so that a pulsating electric current is conducted through the spacing.

The above object is further achieved by means of a fish cage comprising the electric fence according to the above embodiment, a support structure holding the electrode arrangement and an electric power source connected to the pulse generator.

According to an embodiment of the invention, the support structure comprises a buoyancy element.

By a buoyancy element is meant a single buoyancy body or a compound buoyancy body which is lighter than water. The buoyancy body may be filled with air or a material which is lighter than water. The buoyancy body may be a rigid or flexible tubular body. The buoyancy body may be made up of several connected buoyancy bodies. The buoyancy body may also be composed of, in the main, ball-shaped buoys that are connected into a chain.

By a net cage is meant, in what follows, a defined enclosure for fish. At the top, along its outer side, the net cage is provided with floating means which keep the net cage in place in a water column. The net cage is provided with side walls and a bottom consisting of a netting, usually a seine. From the floating means, a wall may extend upwards to prevent fish in the net cage from jumping out of the net cage. The net cage may be provided with a net over the net cage to prevent access by birds. In the water surface, a net cage may have a circular shape, a square shape or some other appropriate shape. A net cage is moored to the seabed by anchoring means of a kind known per se. A net cage may lie by itself or be connected to other net cages through a shared mooring system. The net cages may be connected to a floating stage. Net cages may be of different sizes. Known within the art are, for example, circular net cages with a circumference of approximately 120 metres and with a diameter of approximately 40 metres.

According to an embodiment of the invention the fish cage may be provided with a number of hoisting mechanisms which mau be positioned on the support structure, the hoisting mechanism may be provided with a plurality of winding drums formed with different operating radii, and each winding drum may be connected to a separate spacer. The spacer may be a flexible spacer such as a rope, wire or cable.

The above object is further achieved by means of use of an electrode arrangement according to any of above embodiments.

Brief description of the drawings

In the following is described examples of preferred embodiments illustrated in the accompanying drawings, wherein:

Figure 1 discloses an electrical fence comprising an electrode arrangement according to an embodiment of the invention;

Figure 2 discloses in a larger scale an example of an electrode according to the invention;

Figure 3 discloses in a different scale a fish cage and an electrode arrangement according to a further embodiment of the invention; and

Figure 4 discloses in a larger scale schematically a hoisting mechanism for the electrode arrangement.

Detailed description of the invention

In the drawings, the reference numeral 1 indicates a fish cage of a fish farm. The fish cage 1 comprises an electrode arrangement 10 for inflicting injury on pelagic larva in sea water 9 according to an embodiment of the invention. The electrode arrangement 10 comprises at least a first elongated electrode 12a and a second elongated electrode 12b arranged in parallel and separated by a spacing D.

The electrode 12, 12a, 12b according to the invention, is shown in more detail in figure 2. The electrode 12, 12a ,12b comprises a conductor 30 and an insulator jacket 32. The insulator jacket 32 surrounds a surface 31 of the conductor 30. The insulator jacket 32 comprises preferably mainly a glass reinforced polymer, such as glass reinforced with an epoxy resin, also termed fibreglass, or the insulator jacket 32 comprises a polymer such as polyethylene terephthalate (PET), polyvinyl chloride (PVC) or polyurethane (PUR). The glass reinforced polymer, such as glass reinforced epoxy, has the advantage of providing insulation of the conductor 30 with high form stability. The insulator jacket 32 protects the surface 31 of the conductor 30 from corrosion.

The insulator jacket 32 is tube shaped and forming a first end portion and a second end portion. The first end portion is adapted for joining with a second end portion of a neighbouring insulator jacket 32. The first end portion may be a female end portion and the second end portion may be a male end portion. The first end portion and / or the second end portion may be provided with locking means for keeping the insulator jackets 32 together. The length of the insulator jacket 32 is adapted to the purpose.

The insulator jacket 32 comprises a plurality of through holes or perforations 34. The perforations 34 may be formed by drilling or by milling. Referring to figure 1, the perforations 34 of the electrode 12, 12a, 12b are distributed in a row along the insulating jacket 32.

The conductor 30 may comprise a metal. Preferably a conductor 30 of metal comprises titan. In an alternative embodiment the conductor 30 comprises carbon. In a further alternative embodiment, the conductor 30 comprises graphite.

A conductor 30 of titan comprises a titan rod. Titan is a metal of low flexibility which means that each rod is stiff. Each titan rod may be three to five meters of length. A length of about four meters is suitable for the purpose. The internal diameter of the insulator jacket 32 is somewhat larger than the external diameter of the conductor 30. A titan rod is positioned within the tube-shaped insulator jacket 32 by displacing the titan rod into the insulator jacket 32. The insulator jacket 32 may be twice the length of the titan rod. A first titan rod and a second titan rod are positioned head to tail within the insulator jacket 32. The first titan rod abuts the second titan rod head to tail within the insulator jacket 32. When the electrode 12, 12a, 12b is submerged in sea water, sea water will penetrate and fill the space between the conductor 30 and the insulator jacket 32. Sea water will in addition fill any space between the first titan rod and the second titan rod. The sea water between the first titan rod and the second titan rod provides electrical connection between the two rods.

A conductor 30 of carbon comprises a carbon rod. A conductor 30 of graphite comprises a graphite rod. Both carbon and graphite are brittle materials. The length of a carbon rod or a graphite rod may be from 1 meter to 1.5 meter for the purpose of the invention. Several carbon rods or graphite rods are displaced into the tube-shaped insulator jacket 32 such that they abuts each other inside the insulator jacket 32. Sea water will fill any gaps or spaces between the carbon rods or the graphite rods as explained previously for rods of titan.

An electrical fence 6 as shown in figure 3, comprises several connected electrodes 12, 12a, 12b. Two and two electrodes 12, 12a, 12b are electrically connected at their ends with a connecting element 50. The pulse generator 20 and the electric power source 22 are not disclosed in figure 3. It shall be understood that the purpose of figure 3 is to illustrate the principle of the electrode arrangement 10 of the invention. Other numbers of electrical electrodes 12a, 12b may be used.

The connecting element 50 is provided with a first branch 51 and a second branch 52. The first branch 51 is provided with a fitting that connects to a male end portion of the insulator jacket 32. The second branch 52 is provided with a fitting that connects to a female end portion of the insulator jacket 32. The connecting element 50 is in electrical connection with the conductor 30.

The connecting elements 50 are in electrical contact with the pulse generator 20 and the electric power source 22.

The electrode arrangement 10 further comprises spacers 14 for holding the electrodes 12a, 12b at said spacing D. The spacers 14 are for example a rope in which one of the electrical electrodes 12a, 12b are hanging from the other electrode 12. In an alternative embodiment, the spacers 14 are solid bars holding the electrical electrodes 12a, 12b spaced apart at a predetermined distance. The spacing D is preferably in the range of 0.5 – 1.5 meter, preferably 0.8 – 1.2 meter, more preferably 0.9 – 1.1 meter.

The fish cage 1 comprises a support structure 15 comprising a buoyancy element 16 for providing buoyancy. The elongated electrodes 12 are connected to the buoyancy element 16 so that the electrodes 12 are hanging submerged in sea water 9 from the buoyancy element 16.

The invention is further illustrated in relation to an electric fence 6 for inflicting injury on pelagic larva in sea water. The electrical fence 6 comprises the electrode arrangement 10 and a pulse generator 20 adapted to be connected to an electric power source 22 and to the electrodes 12a, 12b via the connecting elements 50, see figure 3. The pulse generator 20 is configured to provide a pulsating electric current to the electrodes 12a, 12b. Thereby, electric current is conducted through the sea water 9 in the spacing D between the electrodes 12a, 12b. The conduction of the electric current through the spacing D has the effect of inflicting injury on pelagic larva in sea water 9, wherein the amount of active crustacean parasites flowing into the fish cage 1 is reduced.

The insulator jacket 32 comprises a plurality of through holes or perforations 34. Each perforation 34 exposes a portion 310 of the surface 31 to the sea water 9. Thereby an electrical current flows through the spacing D from one electrode 12 to the neighbouring electrode 12.

Referring to figure 1, the perforations 34 of the first electrode 12a are distributed in a row along the insulating jacket 32 parallel to an elongated axis of the electrode 12a. The perforations 34 of the second electrode 12b are distributed correspondingly. The two electrodes 12 are oriented so that the perforations 34 in the first electrode 12a are facing corresponding perforations 34 in the second electrode 12b. In figure 1, the second electrode 12b is provided with two rows of perforations 34, one row directed towards the first electrode 12a above and one row is directed towards the first electrode 12a below. Thereby, the efficiency of the electrode arrangement 10 is improved. Preferably, the first electrode 12a and the second electrode 12b are positioned so that the perforations 34 along the row of the first electrode 12 are aligned with the perforations 34 along the row of the second electrode 12b.

Figure 3 discloses an electrode arrangement 10 of a fish cage 1 according to a further embodiment of the invention. The fish cage 1 comprises an enclosure 7. The enclosure 7 is formed by a net. In the disclosed embodiment, the electrode arrangement 10 is arranged at an upper part close to the surface 99 of the water 9 and not covering the full depth of the enclosure 7. Pelagic larva is predominantly present in water 9 close to the surface 99. The electrode arrangement 10 is accordingly effective in reducing pelagic larva even if it is not fully enclosing enclosure 7.

The conductor 30 may comprise a metal. Preferably the conductor 30 is formed of titan. Preferably the conductor 30 comprises one titan rod. Titan is a metal of low flexibility which means that each rod is stiff. Each electrode 12, 12a, 12b may be three to five meters of length. A length of about four meters is suitable for the purpose. An electrical fence 6 is longer than four meters. Two and two electrodes 12, 12a, 12b are electrically connected at their ends with a connecting element 50 as shown in figure 3. The pulse generator 20 and the electric power source 22 are also not disclosed in figure 3. It shall be understood that the purpose of figure 3 is to illustrate the principle of the electrode arrangement 10 of the invention. Other numbers of electrical electrodes 12a, 12b may be used.

In one embodiment the spacer 14 comprises a rope or a wire. The fence 6 is lowered into the sea water 9 and raised from the sea 9 by a hoisting mechanism 8. A number of hoisting mechanisms 8 may be positioned on the support structure 15. In one embodiment the hoisting mechanism comprises a motor 82, a shaft 84 and several winding drums 86, 87, 88 that are fixed to the shaft 84. The winding drums 86, 87, 88 are formed with different operating radii. Each winding drum 86, 87, 88 is connected to a separate spacer 14. Due to the different operating radii, the winding drums 86, 87, 88 feed out spacers 14 of different lengths for each turn. Turning in the opposite direction the winding drums 86, 87, 88 rewind the spacers 14 of different lengths for each turn. Figure 4 shows three winding drums 86, 87, 88. The number of winding drums 86, 87, 88 are adapted to the number of electrodes 12, 12a, 12b. As an example, the electrode arrangement 10 shown in figure 3 requires six winding drums 86, 87, 88.

At the start with most of the spacers 14 winded on the winding drums 86, 87, 88, the electrodes 12, 12a, 12b are all close to the water surface 99. When the motor 82 is activated, the different spacers 14 are fed out at different speed such that the lowermost electrode 120 descends most while the uppermost electrode 129 descends least. The operating radii of the winding drums 86, 87, 88 are matched to keep the vertical distance between each row of electrodes 12, 12a, 12b equal. The vertical distance as such increases with increasing descending distance, and vice versa when the electrodes 12, 12a, 12b are elevated in the water 9.

The pulse generator 20 and the electric power source 22 are adapted to deliver electrical current at a suitable ampere adapted to the vertical distance between the electrodes 12, 12a, 12b.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

C l a i m s

1. An electrode (12) for use in sea water (9), the electrode (12) comprises a conductor core (30) forming a surface (31) and an insulator jacket (32) which surrounds the conductor core (30), c h a r a c t e r i s e d i n that the insulator jacket (32) comprises a plurality of perforations (34) for exposing portions (310) of the surface (31) of the conductor core (30) to the sea water (9).

2. An electrode (12) according to claim 1, wherein the conductor core (30) comprises one of graphite, carbon and titanium.

3. An electrode (12) according to any one of the previous claims, wherein the insulator jacket (32) comprises a glass reinforced polymer.

4. An electrode (12) according to claim 3, wherein the glass reinforced polymer comprises a polymer chosen from a group comprising an epoxy resin, polyethylene terephthalate (PET), polyvinyl chloride (PVC) and polyurethane (PUR).

5. An electrode (12) according to any one of the previous claims, wherein the electrodes (12a, 12b) are formed as rods.

6. An electrode (12) according to claim 5, wherein a plurality of rods abut head to tail within the insulator jacket (32).

7. An electrode (12) according to any one of the previous claims, wherein the perforations (34) are dispersed in a row in the insulating jacket (32) parallel to an elongated axis of the electrodes (12a, 12b).

8. An electrode arrangement (10) for inflicting injury on pelagic larva in sea water (9), the arrangement (10) comprises

- at least a first electrode (12, 12a) and a second electrode (12, 12b) configured to be arranged in parallel and separated by a spacing (D), wherein the electrodes (12a, 12b) are adapted to be provided with different electric polarity for conducting a pulsating electric current through the spacing (D),

c h a r a c t e r i s e d i n that

the electrodes (12a, 12b) comprise a conductor core (30) forming a surface (31) and an insulator jacket (32) which surrounds the conductor core (30), said insulator jacket (32) comprises a plurality of perforations (34) for exposing portions

9. The electrode arrangement (10) according to claim 8, wherein the perforations (34) are dispersed in a row in the insulating jacket (32) parallel to an elongated axis of the electrodes (12a, 12b), wherein the at least first electrode (12a) and the at least adjacent second electrode (12b) are configured to be oriented so that said rows of perforations are facing each other.

10. The electrode arrangement (10) according to any of claims 9 or 10, wherein the electrode arrangement (10) comprises spacers (14) configured to hold the electrodes (12a, 12b) at said spacing (D).

11. The electrode arrangement (10) according to claim 10, wherein said spacing (D) is in the range of 0.5 – 1.5 meter.

12. The electrode arrangement (10) according to any one of the claims 8 to 11, wherein the electrode arrangement (10) comprises a plurality of first electrodes (12a) configured to be connected so that they have a same first polarity and a plurality of second electrodes (12b) configured to be connected so that they have a same second polarity different from the first polarity, wherein the first electrodes (12a) and the second electrodes (12b) are alternately arranged.

13. An electric fence (6) for inflicting injury on pelagic larva in sea water (9), wherein the fence (6) comprises an electrode arrangement (10) according to any one of claim 7 to 11, and a pulse generator (20) configured to provide a pulsating electric current, wherein the at least two electrodes (12a, 12b) are connected to the pulse generator (20) so that a pulsating electric current is conducted through the spacing (D).

14. A fish cage (1) comprising the electric fence (6) according to claim 13, a support structure (15) holding the electrode arrangement (10) and an electric power source (22) connected to the pulse generator (20).

15. The fish cage (1) according to claim 14, wherein the support structure (15) comprises a buoyancy element (16).

16. The fish cage according to claims 14 or 15, wherein a number of hoisting mechanisms (8) are positioned on the support structure (15), the hoisting mechanism (8) is provided with a plurality of winding drums (86, 87, 88) formed with different operating radii, and each winding drum (86, 87, 88) is connected to a separate spacer (14).