WO2016050374A1

WO2016050374A1 - Aeration system

Info

Publication number: WO2016050374A1
Application number: PCT/EP2015/063438
Authority: WO
Inventors: Bjørn Egil HEIMGÅRD; Yngve Solberg HJERTVIKREM
Original assignee: Heimgård Bjørn Egil; Hjertvikrem Yngve Solberg
Priority date: 2014-09-29
Filing date: 2015-06-16
Publication date: 2016-04-07
Also published as: NO20170630A1

Abstract

The present invention provides a fish farm seawater circulation and oxygenation system comprising a subsea arrangeable ejector device (1) comprising a pipe (2) and at least one ejector (3) arranged inside the pipe, the pipe (2) comprises a pipe inlet (4) and a pipe outlet (5); the ejector (3) comprises an ejector housing (6) having an ejector inlet (7) and an ejector outlet (8), and a nozzle (9) arranged inside the ejector housing, the nozzle is connectable by a conduit (10) to an air pump (11) for supply of pressurized air to the nozzle; such that seawater is sucked into the ejector inlet (7) and a mixture of air and seawater is ejected through the ejector outlet (8) and the pipe outlet (5), during use.

Description

AERATION SYSTEM

Field of the invention The present invention relates to a system for circulation and oxygenation of seawater in a fish farm.

Background In fish farms, particularly for farming salmonids such as salmon and steelhead, the seawater in which the fish is kept needs to be circulated and /or oxygenated to obtain favourable growth conditions.

In present fish farms, circulation of the seawater in the sea cages/pens is obtained by the natural movement of the seawater in a predominantly horizontal direction, and oxygenation is achieved either through the mentioned circulation of seawater or in some instances by use of an air hose lowered into the cage/pen for bobbling of air into the water. As a consequence, the condition of the seawater in the sea cages/pens is mostly decided by natural circumstances, i.e. the weather (wind, temperature etc.) at the site of the fish farm.

Norwegian patent application no. 892188 discloses a system for oxygenation and circulation of seawater in fish farms. The system makes use of a riser pipe, wherein air is bubbled into a lower part of the riser pipe to provide an air lift effect such that water is transported topside. The principle of air lift is not very efficient for circulation of seawater and a topside chamber is required to obtain a sufficient oxygenation of the water.

Presently there is no efficient method or system for controlling the amount of seawater circulation, oxygenation and/or temperature, in sea cages/pens. Thus, less than optimal growth conditions are usually the norm. The goal of the present invention is to provide a system and method which alleviates or avoids at least some of the disadvantages of the prior art.

Summary of the invention

The present invention provides fish farm seawater circulation and oxygenation system according to the appended claims, and as defined in following: In a first aspect, the present invention provides a fish farm seawater circulation and oxygenation system comprising a subsea arrangeable ejector device comprising a pipe and at least one ejector arranged inside the pipe,

the pipe comprises a pipe inlet and a pipe outlet;

- the ejector comprises an ejector housing having an ejector inlet and an

ejector outlet, and a nozzle arranged inside the ejector housing, the nozzle is connectable by a conduit to an air pump for supply of pressurized air to the nozzle;

such that seawater is sucked into the ejector inlet and a mixture of air and seawater is ejected through the ejector outlet and the pipe outlet, during use.

The seawater sucked into the ejector inlet during use is preferably, or most convenient, surrounding seawater provided through the pipe inlet, however, when/if required the pipe inlet may be fluidly connected, by for instance a hose, to seawater removed from the site of the first injector.

In one embodiment of the first aspect, the ejector outlet faces the pipe outlet.

In a further embodiment of the first aspect, the ejector housing is arranged at a distance from the inner surface of the pipe.

In a further embodiment of the first aspect, the system comprises an oxygen generator fluidly connected to the nozzle, such that the pressurized air may be enriched in oxygen during use.

In a further embodiment of the first aspect, the system comprises a heat exchanger arranged downstream of the air pump, such that the temperature of the pressurized air may be controlled. In a further embodiment of the first aspect, the system comprises at least one oxygen sensor able to communicate with, and/or control, the oxygen generator and/or the air pump, the oxygen sensor being arranged in a sea cage of a fish farm during use. In a further embodiment of the first aspect, the system comprises at least one temperature sensor able to communicate with, and/or control, the heat exchanger and/or the air pump, the temperature sensor being arranged in a sea cage of a fish farm during use. In a further embodiment of the first aspect, the system comprises an air shield system comprising a distributor unit, the distributor unit comprises a pipe having an inlet and multiple outlets spaced along the length of the pipe, wherein the pipe is arrangeable at the circumference of a sea cage of a fish farm, and the inlet is fluidly connected to an air source such that air is ejected through the multiple outlets at a circumference of a sea cage during use. In a further embodiment of the first aspect, the air shield system comprises an ejector and a seawater pump, the ejector having a first inlet, a second inlet and an outlet, the first inlet is fluidly connected to the seawater pump for supplying pressurized seawater to said inlet, the second inlet is fluidly connected to the air source, and the outlet is fluidly connected to the distributor unit, such that a mixture of seawater and air is ejected through the multiple outlets at a circumference of a sea cage of a fish farm, during use.

In a further embodiment of the first aspect, the pipe inlet is adapted to be arranged below, or in a lower part of, a sea cage of a fish farm, during use, preferably at least 5 meters below the sea surface.

In a second aspect, the present invention provides an ejector device for use in a system according to the first aspect, comprising a pipe and at least one ejector arranged inside the pipe;

- the pipe comprises a pipe inlet and a pipe outlet; and

the ejector comprises an ejector housing having an ejector inlet and an ejector outlet, and a nozzle arranged inside the ejector housing, the nozzle is connectable to an air pump for supply of pressurized air to the nozzle, wherein the ejector housing is arranged at a distance from the inner surface of the pipe and the ejector outlet faces the pipe outlet.

In a third aspect, the present invention provides for the use of a system according to the first aspect, or an ejector device according to the second aspect, in a fish farm. In an embodiment of the third aspect, the pipe inlet is arranged below, or in a lower part of, a sea cage of a fish farm, preferably at least 5 meters below the sea surface.

In a fourth aspect, the present invention provides a method of circulating and oxygenating seawater in a fish farm comprising the steps of: arranging an ejector device according to the second aspect below, or in a lower part of, a sea cage of the sea farm;

fluidly connecting the nozzle to an air pump; and

supplying air to the nozzle by use of the air pump such that a mixture of air and seawater is ejected through the pipe outlet. In the present disclosure the terms "lower part" and "upper part" of a sea cage is intended to mean the lower two thirds, and the upper one third of a sea cage, respectively. In the present disclosure, the term "ejector" is a device wherein a pressurized driving fluid, i.e. pressurized air, is injected via a nozzle arranged in an ejector housing comprising an ejector outlet and an ejector inlet. The ejector outlet and the ejector inlet are fluidly connected by a channel comprising a converging-diverging section (providing a Venturi-effect), and the nozzle is arranged facing the converging section. The principles behind such ejectors are well-known. The design of the ejector provides a low pressure zone in front of the converging-diverging section such that a liquid, i.e. sea water, is sucked into the ejector inlet when pressurized air is injected via the nozzle. A mixture of air and sea water is consequently ejected through the ejector outlet. As discovered by the applicant, the ejector provides both an excellent aeration effect of the sea water, as well as a significant pressure increase, such that the mixture of air and sea water is driven in a direction away from the ejector outlet.

Short description of the drawings

Fig. 1 shows a schematic drawing of fish farm seawater circulation and oxygenation system according to the invention.

Fig. 2 is a perspective view of an ejector device suitable for the system in fig. 1. Fig. 3 is a cross-sectional view of the ejector device in fig. 2.

Fig. 4 is a detailed cross-sectional view of the ejector arranged in the ejector device. Fig. 5 shows the comparative results of an ejector device according to the invention and a prior art solution. Detailed description of the invention

An embodiment of a fish farm seawater circulation and oxygenation system according to the invention is shown in fig. 1. The system is shown in combination with a fish farm sea cage, or sea pen, within which farmed fish is contained. Such common sea cages are well known to the skilled person and are commonly made of a mesh 35 or net framed with steel or plastic. The mesh/net 35 allows passage of sea water providing some exchange of the seawater inside the mesh, predominantly by the natural movement of the seawater in a horizontal direction. In use, the present system according to the invention comprises an ejector device 1 arranged below, or in a lower part 33 of, the sea cage. The ejector device comprises a pipe 2 and an ejector 3 arranged inside the pipe. Various types of ejectors 3 which may be used in the present system would be apparent to the skilled person based on the present disclosure. However, for illustrative purposes a schematic drawing of an ejector 3 suitable for use in the ejector device 1 is shown in figs. 3 and 4. The ejector comprises an ejector housing 6, having an inlet 7 and an outlet 8 (i.e. an ejector inlet 7 and an ejector outlet 8), and a nozzle 9 arranged within the ejector housing. The pipe 2 of the ejector device 1 has a pipe inlet 4 and a pipe outlet 5. The ejector outlet 8 of the ejector 3 is arranged in a direction towards the pipe outlet 5. Wire mesh 37 is arranged at the pipe inlet and the pipe outlet of the pipe 2. The mesh 37 prevents various objects present in the surroundings from entering the ejector device. Such objects may possibly disturb the operation of the ejector device. The diameter D of the pipe 2 will commonly be in the range of 300- 1000 mm, and the length between 0.5- 1.5 m, but other dimensions may be desired depending on the size and shape of the sea cage. The nozzle is connected to the air pump 11 by a hose 10 (i.e. a conduit). The air pump is able to provide pressurized air through the first inlet 2 of the ejector. An air flow meter 31 is arranged downstream of the air pump. As shown in figs. 3 and 4, the ejector housing has a converging-diverging section between the ejector inlet and the ejector outlet. In use, the pressurized air exiting the nozzle in front of the converging-diverging section will create a low pressure zone in a lower part of the ejector, i.e. in the converging part comprising the ejector inlet 7. Due to the low pressure zone, seawater will enter the ejector inlet 7. After entering the ejector inlet, the seawater is mixed with the pressurized air from the nozzle 9 and the seawater/air mixture ejected through the ejector outlet 8 and consequently through the pipe outlet 5. By this action, seawater is moved from below, outside of, or from a lower part 33 of, the sea cage to the sea cage, or to an upper part 34 of the sea cage. Thus, an efficient circulation and oxygenation of the seawater in the sea cage is obtained.

The ejector is arranged at a distance from the inner surface of the pipe. An annular space is formed, between the ejector housing and the inner surface of the pipe, connecting the pipe outlet with the pipe inlet. Consequently, seawater is also transported from the pipe inlet to the pipe outlet via the annular space (and into the sea cage) by help of the airlift effect in addition to the sea water being ejected from the ejector outlet.

The effect of the present ejector device 1 was compared to the effect of a device wherein the ejector 3 was replaced by a simple conduit for providing pressurized air into the lower part of the pipe 2. The latter solution is known in the prior art and is able to transport seawater from the pipe inlet to the pipe inlet by use of the airlift effect (i.e. an airlift pump). The results are given in fig. 5, and show clearly the advantageous effect of the present invention. In addition to providing a much more efficient water circulation, the present invention also provides a much more efficient oxygenation of the circulated water.

In addition to the improved circulation and oxygenation, a number of additional advantages are obtained by moving seawater in a vertical direction, i.e. exchang the seawater in the sea cage with seawater from below the sea cage.

A first additional advantage is that the temperature of the seawater in the sea cage may be controlled. In summer, the temperature in the upper part of the sea cage is higher than further down, and may in some cases become higher than recommended for optimal growth conditions. By exchanging the seawater in the upper part 34 of the sea cage with seawater from below, or from a lower part 33 of, the sea cage, the temperature may easily be lowered to a more optimal level. In winter, the opposite effect will occur, i.e. the temperature in the upper part of the sea cage becomes lower than further down, and will often be lower than desired for optimal growth conditions. By exchanging the seawater in the upper part of the sea cage with seawater from below, the temperature may easily be increased to a more optimal level. In the present embodiment, the system comprises multiple temperature sensors 15, 15' for monitoring the temperature in the upper and lower part of the sea cage, respectively. In addition, the system features a heat exchanger 13 able to heat and/or cool the pressurized air from the air pump 1 1 depending on the requirement for obtaining an optimal temperature of the sea water in the sea cage. The multiple temperature sensors 15,15' are preferably able to control/operate both the heat exchanger 13 and the air pump 11.

To provide additional oxygenation of the seawater in the sea cage, the embodied system also comprises an oxygen generator 12 fluidly connected to the nozzle of the ejector 3. By supplying oxygen to the pressurized air an increased oxygenation is obtained without increasing the rate of seawater passing through the ejector. The system is also equipped with multiple oxygen sensors 14,14' for monitoring the oxygen levels of the seawater in the sea cage and below. The multiple oxygen sensors 14, 14' are preferably able to control/operate both the oxygen generator 12 and the air pump 11. A second additional advantage concerns the possible prevention/alleviation of sea lice problems. Sea lice commonly reside in the upper few meters of the sea;

consequently it has been found that salmon held at 0-4 meters depth developed higher sea lice infestation than salmon held at 4-8 meters and 8- 12 meters depth (ref. Hevr0y et al., 2003. The effect of artificial light treatment and depth on the infestation of the sea louse Lepeophtheirus salmonis on Atlantic salmon (Salmo salar L.) culture. Aquaculture 220, 1-14). Based on this observation it has been proposed to use tarpaulin skirts (i.e. a skirt in a material not permeable to sea lice) around the sea cage to avoid or reduce the occurrence of sea lice infestation.

However, such skirts may seriously decrease the oxygen saturation levels available for the fish inside the sea cage (ref. Stien et al. Skirt around a salmon sea cage to reduce infestation of salmon lice resulted in low oxygen levels; Aquacultural Engineering, 51 (2012) 21-25). By use of the system according to the invention it is believed that the levels of sea lice present in the sea cage may be reduced without the use of a skirt since the seawater in the sea cage is replaced by seawater from below the sea cage, i.e. seawater from a depth wherein the levels of sea lice is low. Optionally, the system may advantageously also be combined with a tarpaulin skirt as described above, to prevent low levels of oxygen saturation.

The system of fig. 1 is also shown with an optional feature, i.e. an air shield system 16 (also called a bubble curtain). The air shield system comprises an ejector 21 (similar to the one described in connection with the ejector device 1) having a first inlet 23, a second inlet 24 and an outlet 25. The first inlet 23 is fluidly connected to a seawater pump 22 for supplying pressurized seawater to said first inlet. The second inlet 24 is fluidly connected to an air intake, and the outlet 25 is fluidly connected to a distributor unit 17. The distributor unit 17 comprises a pipe 18 (or tube) having an inlet 19 and multiple outlets 20, the multiple outlets are spaced along the length of the pipe, and the pipe may be arranged at the circumference of a fish farm sea cage, at a depth below or at a lower part of the sea cage. Additional features of the embodied air shield system are flow meters for air 26 and seawater 27, an oxygen sensor 32, as well as a coarse filter 28 for seawater arranged upstream of the seawater pump 13, a fine water filter 29 arranged downstream of the seawater pump, and an air filter 30. The air shield system will provide an additional preventive effect towards sea lice infestation, especially when combined with the circulation/oxygenation system according to the invention. If desired, the air shield system may also be used independent of the ejector device. In the prior art, air shields are obtained by having compressed air forced through a perforated tube, such that a rising curtain of air bubbles is formed. The air bubbles formed by this known method are quite large and not finely dispersed in the seawater when they rise to the surface. In contrast to the known methods of creating a bubble curtain, the present air shield system provides, due to the ejector 21 , an air curtain comprising both substantially smaller and more finely dispersed air bubbles, as well as a seawater stream rising in the same direction as the air bubbles. This provides for a much more efficient air curtain able to cover a large area at the circumference of a sea cage. The fish farm seawater circulation and oxygenation system according to the invention may also be used for dosage of any required fluids, solids or gas, such as medication, to the farmed fish. In that case, for instance medication may be injected by use of the ejector 3, preferably by providing the medication to the low pressure zone via the nozzle 9 or the ejector inlet 3, or by having a dedicated dosage line 36 in fluid connection to the low pressure zone via the ejector housing.

Claims

A fish farm seawater circulation and oxygenation system comprising a subsea arrangeable ejector device (1) comprising a pipe (2) and at least one ejector (3) arranged inside the pipe,

o the pipe (2) comprises a pipe inlet (4) and a pipe outlet (5); o the ejector (3) comprises an ejector housing (6) having an ejector inlet (7) and an ejector outlet (8), and a nozzle (9) arranged inside the ejector housing, the nozzle is connectable by a conduit (10) to an air pump (11) for supply of pressurized air to the nozzle;

such that seawater is sucked into the ejector inlet (7) and a mixture of air and seawater is ejected through the ejector outlet (8) and the pipe outlet (5), during use.

A system according to claim 1 , wherein the ejector outlet (8) faces the pipe outlet (5).

A system according to any of the preceding claims, wherein the ejector housing (6) is arranged at a distance from the inner surface of the pipe (2).

A system according to any of the preceding claims, comprising an oxygen generator (12) fluidly connected to the nozzle (9), such that the pressurized air may be enriched in oxygen during use.

A system according to any of the preceding claims, comprising a heat exchanger (13) arranged downstream of the air pump (1 1), such that the temperature of the pressurized air may be controlled.

A system according to claim 4, comprising at least one oxygen sensor (14, 14') able to communicate with, and/or control, the oxygen generator (12) and/or the air pump (11), the oxygen sensor being arranged in a sea cage of a fish farm during use.

A system according to any of the preceding claims, comprising at least one temperature sensor (15,15') able to communicate with, and/or control, the heat exchanger (13) and/or the air pump (1 1), the temperature sensor being arranged in a sea cage of a fish farm during use.

A system according to any of the preceding claims, having an air shield system (16) comprising a distributor unit (17), the distributor unit comprises a pipe (18) having an inlet (19) and multiple outlets (20) spaced along the length of the pipe, wherein the pipe is arrangeable at the circumference of a sea cage of a fish farm, and the inlet (19) is fluidly connected to an air source such that air is ejected through the multiple outlets (20) at a circumference of a sea cage during use.

9. A system according to claim 8, wherein the air shield system (16) comprises an ejector (21) and a seawater pump (22), the ejector having a first inlet (23), a second inlet (24) and an outlet (25), the first inlet is fluidly connected to the seawater pump (22) for supplying pressurized seawater to said inlet, the second inlet is fluidly connected to the air source, and the outlet is fluidly connected to the distributor unit, such that a mixture of seawater and air is ejected through the multiple outlets (20) at a circumference of a sea cage of a fish farm, during use.

10. A system according to any of the preceding claims, wherein the pipe inlet is adapted to be arranged below, or in a lower part (33) of, a sea cage of a fish farm, during use, preferably at least 5 meters below the sea surface.

11. An ejector device for use in a system according to any of the preceding

claims, comprising a pipe (2) and at least one ejector (3) arranged inside the pipe;

o the pipe (2) comprises a pipe inlet (4) and a pipe outlet (5); and o the ejector (3) comprises an ejector housing (6) having an ejector inlet (7) and an ejector outlet (8), and a nozzle (9) arranged inside the ejector housing, the nozzle is connectable to an air pump (11) for supply of pressurized air to the nozzle, wherein the ejector housing (6) is arranged at a distance from the inner surface of the pipe (2) and the ejector outlet (8) faces the pipe outlet (5).

12. Use of a system according to any of claims 1- 10, or an ejector device

according to claim 11 , in a fish farm.

13. Use according to claim 12, wherein the pipe inlet (4) is arranged below, or in a lower part (33) of, a sea cage of a fish farm, preferably at least 5 meters below the sea surface.

14. A method of circulating and oxygenating seawater in a fish farm comprising the steps of: arranging an ejector device (1) according to claim 1 1 below, or in a lower part of, a sea cage of the sea farm;

fluidly connecting the nozzle (8) to an air pump (11); and supplying air to the nozzle (8) by use of the air pump (11) such that a mixture of air and seawater is ejected through the pipe outlet (4).