WO2019045628A1

WO2019045628A1 - A system for providing a flow to a fluid

Info

Publication number: WO2019045628A1
Application number: PCT/SE2018/050869
Authority: WO
Inventors: Joel SAFRANI; Ulf ARBÈUS; Mattias ANTONSSON
Original assignee: Wallenius Water Innovation Ab
Priority date: 2017-09-04
Filing date: 2018-08-30
Publication date: 2019-03-07
Also published as: SE1751065A1; SE541852C2

Abstract

A system and a method for providing a flow to a fluid in a tank and a tank comprising such a system. Said system comprising: -at least one fluid guiding arrangement (5; 5'; 5'') which when provided in a tank comprising a fluid is configured for receiving fluid from the tank into an inlet (15; 5'; 15'') of the fluid guiding arrangement and guiding fluid from the inlet (15; 5'; 15'') of the fluid guiding arrangement to an outlet (17; 17'; 17'') of the fluid guiding arrangement, which inlet and outlet during use of the system are provided below a fluid surface (6) in the tank, wherein said fluid guiding arrangement (5; 5'; 5'') further is configured such that the fluid being guided from 10 the inlet to the outlet will be guided such that it passes a middle section fluid passage (11; 11'; 11'') of the fluid guiding arrangement (5; 5'; 5'') which during use is positioned at a greater distance above a bottom (4; 4'') of the tank than both the inlet and the outlet and which middle section fluid passage comprises at least one gas outlet (13; 13'; 13'') for removing gas out from the fluid guiding 1 arrangement; and -at least one gas providing device (25) configured for providing gas into the fluid guiding arrangement (5; 5'; 5'') through the inlet (15; 15'; 15''), wherein the system (1; 1') comprises a rotation device (205) configured for allowing the system to rotate such that the outlet (17; 17') of the system rotates in a plane 20 parallel to a bottom (4) of a tank when the system is provided in the tank such that the fluid can be delivered from the outlet (17; 17') of the fluid guiding arrangement (5; 5') in different directions.

Description

A system for providing a flow to a fluid

TECHN ICAL FI ELD OF TH E I NVENTION

The present invention relates to a system and method for providing a flow to a fluid in a tank and to a tank comprising such a system.

RELATED ART

The mixing or flowing of fluids is needed in many different technical fields and by different reasons. For example both in sewage treatment systems and in aquaculture systems it is often suitable to keep a suspension in a tank, i.e. avoid material to sediment to a bottom in the tank. Mixing the content in the tank is one method to avoid material to sediment to the bottom of the tank. I n an aquaculture system food and excrements from the fishes may sediment to the bottom of the tank and this may cause problems with the water quality, e.g. anoxic conditions. The environment in both aquaculture systems and sewage treatment systems put high demands on the mixing systems used therein. Corrosion may be a problem. I n aquaculture, mixing is normally accomplished by aerating or by the water main stream creating a flow in a certain direction. Back draws are sedimentation at the bottom of the tank and specifically with the latter one requiring high velocities. Within wastewater, aeration and/or submersible mixers, agitators or jet mixers accomplish mixing that all are depending on electricity and are built by many components that is a potential risk of failure. None of the mixers solves the problem of sedimentation at the bottom of the tank/basin.

SUMMARY OF THE I NVENTION

An object of the invention is to provide an effective and robust system and method for providing a flow to a fluid.

This is achieved by a system, a tank and a method according to the independent claims. According to one aspect of the invention a system is provided for providing a flow to a fluid in a tank, said system comprising: at least one fluid guiding arrangement which when provided in a tank comprising a fluid is configured for receiving fluid from the tank into an inlet of the fluid guiding arrangement and guiding fluid from the inlet of the fluid guiding arrangement to an outlet of the fluid guiding arrangement, which inlet and outlet during use of the system are provided below a fluid surface in the tank, wherein said fluid guiding arrangement further is configured such that the fluid being guided from the inlet to the outlet will be guided such that it passes a middle section fluid passage of the fluid guiding arrangement which during use is positioned at a greater distance above a bottom of the tank than both the inlet and the outlet and which middle section fluid passage comprises at least one gas outlet for removing gas out from the fluid guiding arrangement; and

at least one gas providing device configured for providing gas into the fluid guiding arrangement through the inlet, wherein the system comprises a rotation device configured for allowing the system to rotate such that the outlet of the system rotates in a plane parallel to a bottom of a tank when the system is provided in the tank such that the fluid can be delivered from the outlet of the fluid guiding arrangement in different directions. Hereby a simple and robust system for providing a flow to a fluid is achieved. This system comprises only few components compared to conventionally used mixing systems. This is advantageous because the system will have a long life time and will require less

maintenance. In the system according to the invention there are no moving parts and no impellers which would need sealing to work in a fluid and which may be destroyed by corrosion. Furthermore the system according to the invention will be more efficient than conventional mixers. Furthermore the system according to the invention can be produced from cheap materials which are resistant to the fluid in the tank. Thanks to the rotation device the outflow from one system can be provided in different directions and hereby reach different parts of a tank. According to another aspect of the invention a tank comprising such a system is provided.

Hereby a tank is provided which comprises a simple and robust system for providing a flow to a fluid in the tank as described above.

According to another aspect of the invention a method is provided for providing a flow to a fluid in a tank, said method comprising the steps of: providing gas into an inlet of a fluid guiding arrangement of a system provided in the tank for providing a flow to the fluid in the tank, said inlet being provided below a fluid surface in the tank and being open for receiving fluid from the tank; guiding fluid mixed with the gas from the inlet in a direction from a bottom of the tank towards the fluid surface in the tank through a first fluid passage of the fluid guiding arrangement to a middle section fluid passage of the fluid guiding arrangement;

releasing gas through the middle section fluid passage, said middle section fluid passage being connected to said first fluid passage and to a second fluid passage; - guiding fluid received from the middle section fluid passage in a direction

towards the bottom of the tank through the second fluid passage of the fluid guiding arrangement to an outlet of the fluid guiding arrangement;

delivering the fluid out from the outlet

rotating the system (1; 1') such that the outlet (17; 17') of the system rotates in a plane parallel to a bottom of the tank such that the fluid can be delivered from the outlet of the system in different directions.

Hereby a simple and robust method for providing a flow to a fluid is provided.

In one embodiment of the invention said fluid guiding arrangement further comprises a first fluid passage having a first end and a second end and a second fluid passage having a first end and a second end, and wherein said middle section fluid passage of the fluid guiding arrangement connects the second end of the first fluid passage with the second end of the second fluid passage such that during use of the system in a tank comprising a fluid both the first end of the first fluid passage and the first end of the second fluid passage are provided below the middle section fluid passage in the tank, and wherein said inlet is provided at the first end of the first fluid passage for receiving fluid into the first fluid passage and said outlet is provided at the first end of the second fluid passage for delivering fluid out from the second fluid passage, said outlet being in fluid communication with said inlet via said second fluid passage, said middle section fluid passage and said first fluid passage. I n one embodiment of the invention said second fluid passage substantially encircles said first fluid passage. I n another embodiment of the invention the first fluid passage, the second fluid passage and the middle section fluid passage are embodied as a bent pipe. Both these embodiments are standalone units which can be positioned inside a tank in a wanted position. I n one embodiment of the invention the outlet of the fluid guiding arrangement is configured for being positioned and directed during use in a tank com prising a fluid such that fluid is injected out from the outlet substantially along a bottom surface of the tank. Hereby content in the tank can be mixed conveniently and furthermore a bottom of the tank can be kept clean and sedimentation to the bottom is avoided. I n one embodiment of the invention the middle section fluid passage comprises a gas cavity closed from above by an upper closure and the gas outlet comprises a vertical pipe or a vertical pipe with slots protruding through the upper closure. Herby the system is fully submersible and can be used in all types of tanks having different depths.

Further embodiments are described in the dependent claims.

BRI EF DESCRI PTION OF TH E I NVENTION

Figure 1 is a cross sectional side view of a tank comprising a system according to one embodiment of the invention.

Figure 2a is a cross sectional side view of a system according to another embodiment of the invention.

Figure 2b is a perspective side view of the same system as shown in Figure 2a. Figures 2c-2d show schematically an example of a brake arrangement. Figure 3a is a top view of a tank according to one embodiment of the invention where a number of systems as shown in Figures 1 or 2 are provided along one of the side walls.

Figure 3b is a top view of a tank according to another embodiment of the invention comprising a system as shown in Figure 1 or 2 where the system is provided with a transferring device.

Figure 3c is a top view of a tank according to another embodiment of the invention comprising a system as shown in Figure 1 or 2 where the system is provided with a rotation device.

Figures 4a-4b show schematically two different examples of gas outlets according to different embodiments of the invention.

Figure 5a is a cross sectional side view of a tank comprising a system according to one embodiment of the invention.

Figure 5b is a top view of the same tank and system as shown in Figure 5a.

Figure 6 is a cross sectional side view of a tank comprising a system according to another embodiment of the invention.

Figure 7a is a schematic cross sectional top view of an inlet of a system according to one embodiment of the invention.

Figure 7b shows schematically how gas and fluid is mixed inside a first fluid passage of a system according to one embodiment of the invention. Figure 8 is a flow chart of a method according to one embodiment of the invention.

DETAI LED DESCRI PTION OF THE EMBODIMENTS

According to the invention a system and a method for providing a flow to a fluid in a tank is provided. This could be in order to mix the content in the tank and/or in order to keep a suspension in the tank and/or in order to avoid sedimentation in the tank. It could also be for the purpose to transport fluid in a tank. Furthermore according to the invention a tank comprising such a system is provided. The tank can for example be an aquaculture tank or a sewage treatment tank. The tank can for example be a Recirculating Aquaculture System, RAS, tank and the system for providing a flow to a fluid in the tank according to the invention can then be separated from the RAS circulation. The system according to the invention comprises at least one fluid guiding arrangement and at least one gas providing device. The gas providing device is configured for providing gas into the fluid guiding arrangement through an inlet of the fluid guiding arrangement. When the system is provided in a tank comprising a fluid it is configured for guiding fluid from an inlet of the fluid guiding arrangement to an outlet of the fluid guiding arrangement. Both the inlet and the outlet are during use provided below the fluid surface in the tank. Said fluid guiding arrangement is further configured such that the fluid being guided from the inlet to the outlet will be guided such that it passes a middle section fluid passage which during use is positioned at a greater distance above a bottom of the tank than both the inlet and the outlet and which middle section fluid passage comprises at least one gas outlet. Gas can be removed out from the fluid guiding arrangement through the gas outlet.

The fluid guiding arrangement comprises a first fluid passage having a first end and a second end and a second fluid passage having a first end and a second end. The second ends of the first and second fluid passages are connected via a middle section fluid passage such that during use of the system in a tank comprising a fluid both the first end of the first fluid passage and the first end of the second fluid passage are provided below the middle section fluid passage in the tank. I.e. both the first and second fluid passages extend from their first ends to their second ends in a direction essentially from a bottom of the tank to a fluid surface in the tank. However the first ends of the first and second fluid passages do not need to be provided at the same level in the tank and they do not need to be provided close to a bottom of the tank. Said middle section fluid passage can during use of the system in a tank in some embodiments of the invention be provided both below the fluid surface in the tank, at the fluid surface or above the fluid surface. The middle section fluid passage comprises at least one gas outlet. An inlet is provided at the first end of the first fluid passage for receiving fluid into the first fluid passage and an outlet is provided at the first end of the second fluid passage for delivering fluid out from the second fluid passage. The outlet is in fluid communication with said inlet via said second fluid passage, said middle section fluid passage and said first fluid passage.

Hereby the gas providing device will provide gas into the fluid guiding arrangement through the inlet. Fluid from the surroundings of the inlet will also flow into the inlet of the fluid guiding arrangement. The gas and the fluid will mix inside the first fluid passage and will due to its lower density compared to the pure fluid raise inside the first fluid passage towards the fluid surface in the tank. This is the same principle as used in air lift pumps. However in the system according to this invention a second fluid passage is provided for guiding the fluid back down again in the tank. Gas will be released through the gas outlet of the middle section fluid passage. The fluid is guided back towards a bottom of the tank to be release through an outlet of the fluid guiding arrangement which outlet can be provided close to the bottom of the tank if the purpose is to keep a bottom of the tank clean. However the outlet can also be provided above the bottom of the tank. The flow of the gas into the inlet of the fluid guiding arrangement, the length of the first fluid passage, i.e. at which depth in the tank the inlet and the gas providing device are provided and the dimensions of the fluid guiding arrangement are factors that will affect the flow of the fluid out from the outlet of the fluid guiding arrangement. A high flow of the fluid out from the outlet will improve mixing efficiency and for example a bottom of the tank can be kept clean or a flow can be provided in an aquaculture raceway tank. Different embodiments of the system according to the invention will now be described with reference to the drawings.

Figure 1 is a cross sectional side view of a tank 3 comprising a system 1 according to one embodiment of the invention. The system 1 comprises a fluid guiding arrangement 5 and a gas providing device 25. In this embodiment the system 1 is a stand-alone unit which can be positioned in a tank in different positions and at different levels within the tank. In the embodiment shown in Figure 1 the gas providing device is 25 is provided close to a bottom 4 of the tank. However other positions are also possible. The whole system 1 can be positioned higher up in the tank as long as the gas providing device 25 is provided below a fluid surface 6 in the tank. In some embodiments of the invention the whole system 1 can be fully submersible below the fluid surface in the tank. This is an advantage because then the same type of system can be provided to tanks of different sizes and still be provided at the same level, for example close to a bottom of a tank. The design of a middle section fluid passage 11 and 13 gas outlet are then adapted for being fully submersible as will be further described below in relation to Figures 4a-b. The fluid guiding arrangement 5 comprises in this embodiment a first fluid passage 7 having a first end 7a and a second end 7b. An inlet 15 of the fluid guiding arrangement 5 is provided at the first end 7a of the first fluid passage 7 and the gas providing device 25 is positioned such that gas is provided into this inlet 15. The first fluid passage 7 has an elongated extension between its first and second ends essentially along an axis A which extends between the bottom 4 of the tank 3 and a fluid surface 6 in the tank. Suitably this axis A is provided along the shortest way between the bottom of the tank and the fluid surface, i.e. in a vertical direction often along one of the outer walls 8 of the tank 3, however the first fluid passage 7 could as well be provided with a slight inclination towards a tank outer wall 8.

The fluid guiding arrangement 5 comprises further a second fluid passage 9 having a first end 9a and a second end 9b. An outlet 17 of the fluid guiding arrangement 5 is provided at the first end 9a of the second fluid passage 9. A middle section fluid passage 11 connects the second end 7b of the first fluid passage 7 with the second end 9b of the second fluid passage 9. The outlet 17 is in fluid communication with the inlet 15 via the second fluid passage 9, the middle section fluid passage 11 and the first fluid passage 7. The second fluid passage 9 has an elongated extension between its first and second ends. In this embodiment the elongated extension of the second fluid passage 9 extends along essentially the same axis A as the extension of the first fluid passage 7. However, in another embodiment the second fluid passage 9 could be extended in a slightly different direction. The middle section fluid passage 11 connects the first and second fluid passages 7, 9 such that a bent configuration like a hair pin is provided. In this embodiment of the invention the fluid guiding arrangement 5 is provided as a bent tube. The middle section fluid passage 11 comprises a gas outlet 13. When the system 1 is provided in a fluid in a tank 3 the middle section fluid passage 11 will be provided above the rest of the system 1, i.e. be the part of the system 1 provided at the largest distance from a bottom 4 of the tank 3. The middle part fluid passage 11 can be provided close to a fluid surface 6 in the tank 3 however this is not necessary. The system will work appropriately even if the whole system is submerged below the fluid surface 6 and also if the system is provided at a higher level in the tank. However at least the inlet 15 needs to be provided below the fluid surface 6. The system 1 can as described above be provided in different positions in a tank comprising a fluid and at different levels within the tank. However the orientation of the system 1 within the tank needs to be such that the inlet 15 and the outlet 17 are provided below the middle part fluid passage 11 in the tank, i.e. closer to a bottom 4 of the tank 3 than the middle part fluid passage 11. The efficiency of the system, i.e. the power of the fluid flow out from the outlet 17 is as described above dependent on the length of the first fluid passage 7 and the position of the inlet below the fluid surface 6, i.e. at what distance below a fluid surface the inlet 15 is positioned. It is also dependent on the amount and flow of gas provided into the inlet 15, i.e. dependent on the ratio between air and fluid in the first fluid passage 7. The efficiency is dependent also on the air-release efficiency before being directed downwards. If air is not 100% released, air bubbles will obstruct and reduced the water flow.

The outlet 17 is in this embodiment provided as a bent configuration of the first end 9a of the second fluid passage 9. The outlet direction is provided such that a flow out from the system 1 is provided in a wanted direction. Furthermore the dimensions of the outlet can be adapted for providing a more focused flow out from the outlet 17 reaching a longer distance in the tank. In this embodiment of the invention the system is positioned and the outlet 17 is designed such that a flow of fluid out from the system 1 is provided right above a bottom 4 of the tank 3. This is suitable if the tank for example is an aquaculture tank and a reason for providing a flow to the content in the tank is to keep a bottom clean from food and excrements. One or more systems 1 as the one shown in Figure 1 can be provided in the tank 3 such that the flow out form the outlet/s 17 can reach the whole tank as will be described below in relation to Figures 3a-c. In this embodiment of the invention the whole fluid guiding arrangement 5 is provided as a bent pipe. The dimensions of the pipe, such as diameter and form of the pipe and radius of the bend, i.e. the bend where a middle section fluid passage 11 connects the first and second fluid passages 7, 9 are suitably chosen such that the fluid flow through the fluid guiding arrangement is as lossless as possible. The bend of the pipe, i.e. the connection between the first and second fluid passages 7, 9 can in one embodiment of the invention have a larger radius than what is shown in Figure 1. A larger radius may improve the preserving of flow through the fluid guiding arrangement 5 and may facilitate the releasing of gas from the system through the gas outlet 13. The design of the gas outlet 13 in the middle section fluid passage 11 will affect the fluid flow through the system. The gas needs to be removed out from the fluid guiding arrangement 5 before the fluid is guided back downwards through the second fluid passage 9. Different examples of gas outlets 13 will be further described in relation to Figures 4a-4b.

The gas providing device 25 should be positioned and dimensioned in relation to the inlet 15 of the fluid guiding arrangement 5 such that gas is provided from a gas providing device gas outlet 26 into the fluid guiding arrangement 5 together with fluid from the surroundings of the inlet 15. The gas and the fluid are mixed inside the first fluid passage 7. The gas providing device gas outlet 26 can be a fine bubble diffusor. Hereby the mixing of gas and fluid will be efficient. However also a coarse bubble diffusor could be used. Dimensions and positions of the gas providing device 25 are further described in relation to Figure 7.

Figure 2a shows schematically a cross sectional side view of a system 1' according to another embodiment of the invention. Figure 2b is a perspective view of the same system 1' as shown in Figure 2a. The system comprises a fluid guiding arrangement 5' and a gas providing device 25. Also in this embodiment the system 1' is a stand-alone unit which can be positioned in a tank in different positions and at different levels within the tank. The system 1' according to this embodiment can be provided fully submersed below a fluid surface in the tank. Hereby a middle section fluid passage 11' and its gas outlet 13' are adapted for allowing submersion of the system below the surface which will be further described in relation to Figures 4a-4b.

The fluid guiding arrangement 5' comprises a first fluid passage 7' having a first end 7a' and a second end 7b', a second fluid passage 9' having a first end 9a' and a second end 9b' and a middle section fluid passage 11' connecting them as also described above in relation to the embodiment shown in Figure 1. An inlet 15' is provided at the first end 7a' of the first fluid passage 7' and an outlet 17' is provided at the first end 9a' of the second fluid passage 9'. When the system 1' is used in a tank comprising a fluid both the first and second fluid passages 7', 9' extend substantially along an axis A which extends between a bottom of the tank and a fluid surface in the tank, suitably in a vertical direction. A difference in this embodiment is however that the second fluid passage 9' substantially encircles the first fluid passage 7', i.e. the second fluid passage 9' is a tube and the first fluid passage 7' is another tube provided inside the tube of the second fluid passage 9'. The tubes can in one embodiment of the invention have a circular cross section, i.e. be cylinders where the first fluid passage 7' has a smaller radius than the second fluid passage 9'. However other geometries of the cross sections are also possible. The outlet 17' can be provided all around the outer circumference of the first end 9a' of the second fluid passage 9' for delivery of fluid out from the system in all directions or as shown in Figures 2a-2b only in one direction. The outlet 17' can be just an opening somewhere around the circumference in the first end 9a' of the second fluid passage 9' or it can be a built on funnel for focusing and directing the flow out from the system as shown in Figures 2a-2b.

The system 1' can be mounted to the tank in different ways. If rotation of the system 1' in the tank is wanted one possible way of mounting is as shown in Figure 2b where the system 1' is mounted to a shaft 41. The shaft 41 is mounted in the tank in a vertical direction from the bottom of the tank to the fluid surface. The shaft is in this embodiment of the invention mounted rigidly to the tank and the system 1' is mounted to the shaft such that it can rotate around the shaft 41. In the embodiment shown in Figure 2b the system 1' is mounted to the shaft 41 by two bearings 42a, 42b. The number of bearings could however be varied. Hereby the system 1' can be rotated inside a tank for directing the outflow of fluid from the outlet 17' in different directions. The system 1' could be rotated by an electric motor. However another possibility is to let the system 1' rotate by its own by the forces created by the fluid flow out from the system 1'. In case of such a rotation a brake mechanism 43 would suitably be provided to the shaft 41 in order to control the rotational speed. A brake mechanism could for example be a friction brake, an electric motor brake, a paddle or an hydraulic brake. An example of such an hydraulic brake mechanism is shown and described further in Figures 2c-2d.

Figure 2c shows the brake mechanism 43 provided to the system 1' in Figure 2b in greater detail. This is only one example of a brake mechanism which can be used together with the system 1' according to the invention. This example brake mechanism comprises a first gearwheel 45 which is provided around the shaft 41 such that it is fixedly connected to the shaft 41. The brake mechanism 43 comprises furthermore a second gearwheel 47 which has a smaller diameter than the first gearwheel 45 and which is mounted in gearwheel engaging contact with the first gearwheel 45. The second gear wheel 47 is also mounted to a peristaltic pump device housing 48 of a peristaltic pump device 49. The peristaltic pump device housing 48 is in turn connected to one of the bearings 42a by which the system 1' is mounted to the shaft 41. Hereby the peristaltic pump device 49 and its housing 48 will rotate together with the system 1' around the shaft 41. The rotation of the peristaltic pump device housing 48 also induces rotation of the second gear wheel 47 and by its engaging contact with the first gearwheel 45 the second gearwheel 47 will not only rotate around the shaft 41 but will also rotate around its center axis. The second gearwheel 47 is furthermore connected to a tube compression part 51 provided inside the peristaltic pump device housing 48. Hereby the rotation of the second gearwheel 47 around its center axis will induce the rotation of the tube compression part 51 of the peristaltic pump device 49. The peristaltic pump device 49 is shown in cross section in Figure 2d. The tube compression part 51 comprises in this embodiment a triangle where corners 51a, 51b, 51c of the triangle alternate to compress a tube 53 of the peristaltic pump device 49 when the triangle rotates together with the second gear wheel 47. However the geometry and number of corners of the tube compression 51 part can differ. The tube 53 of the peristaltic pump device 49 comprises a fluid and is short cut, i.e. connected in a loop around the tube compression part 51. Hereby a counter force will be provided from the peristaltic pump device 49 to the system 1' when it rotates. This type of hydraulic brake mechanism is suitable because it can provide a progressive brake power.

In Figure 3a it can be seen that a number of systems 1, 1' as the ones described in relation to Figures 1 and 2 can be provided along one side wall 21 of the tank 3, 3'. Hereby a fluid flow from the systems 1, 1' can reach the whole bottom 4, 4' of the tank 3, 3'. Figure 3b is a top view of a tank 103 according to another embodiment of the invention. The system 1, 1' can be the same as shown in Figure 1 or Figure 2 but the system 1, 1' is here provided with a transferring device 105. The transferring device 105 can be a motor connected to wheels on the system 1, 1' or for transferring the system 1; 1' along a rail inside the tank. The transferring device 105 can be configured to transfer the system 1, 1' in any suitable way, such as for example along a side wall 121 in the tank 103 or along any other path in the tank 103. If the tank is of another form than rectangular the transferring path will be adopted according to that form. In one embodiment of the invention the whole bottom of the tank should be reached by the flow from the outlet 17, 17' of the system 1, 1' and the transferring path will be designed for achieving that.

Figure 3c is a top view of a tank 203 according to another embodiment of the invention. The system 1, 1' can be the same as shown in Figure 1 or 2 and is in this embodiment provided with a rotation device 205. The rotation device 205 could be a shaft 41, possibly together with an electric motor and/or a brake 43 as the one described above in relation to Figures 2a-2d but the system 1; 1' could also be mounted to the tank in another way, for example directly to the bottom without a vertical shaft. In this embodiment the tank 203 is cylindrical however a system 1, 1' comprising a rotation device 205 could also be used in a rectangular tank. The system 1, 1' is here provided in the middle of the tank 203 and by rotating the system 1, 1' and thus the outlet 17, 17' of the system the whole bottom of the tank can be reached by the flow out from the outlet. The rotation device 205 can comprise a motor for providing the rotation but it can also be a mounting of the system in the tank allowing the system 1 to rotate by the forces created by the fluid flow out from the outlet 17, 17' of the system 1, 1' as described above in relation to Figure 2b.

Figures 4a-4b show schematically two different examples of gas outlets 13; 13' according to different embodiments of the invention. These gas outlets 13; 13' can be provided in any of the systems 1; 1' as described above in relation to Figures 1 and 2. The middle section fluid passage 11; 11' will comprise a gas cavity 60 in its upper part (referring to directions of the drawings and directions in the tank when the system 1; 1' is used in a tank). The size of the gas cavity 60 will change during use of the system depending on the flow of gas from the gas providing device 25 into the inlet 15; 15' of the fluid guiding arrangement 5; 5'. In Figure 4a three different fluid levels within the middle section fluid passage 11; 11' of the fluid guiding arrangement 5; 5' of the system 1; 1' are illustrated. HO corresponds to the fluid level when the gas providing device 25 is not operating, HQmin corresponds to the fluid level when the gas providing device 25 provides gas into the inlet 15; 15' of the system 1; 1' at a minimum gas flow and HQmax corresponds to the fluid level when the gas providing device 25 provides gas into the inlet 15; 15' at a maximum gas flow. These different fluid levels are only illustrative and they show that there will always be a gas cavity 60 within the system 1; 1'. A gas outlet 13; 13' is provided in the middle section fluid passage 11; 11'. In Figure 4a a gas outlet 13; 13' is provided as a vertical pipe 61 protruding through an upper closure 62 provided to the middle section fluid passage 11; 11'. The vertical pipe 61 protrudes through the gas cavity 60 and possibly also further down in to the fluid as shown in Figure 4a. The vertical pipe 61 comprises in this embodiment slots 63 around its periphery for allowing gas to enter the inside of the pipe and escape upwards out from the system 1; 1'. In Figure 4b another embodiment of a gas outlet 13; 13' is shown. In this embodiment a shorter vertical pipe 65 is provided protruding through the upper closure 62 and ending with an open lower inlet 66 within the gas cavity 60. Hereby gas can escape into the open lower inlet 66 of the shorter vertical pipe 65 and escape out from the system 1; 1'. These are only two examples of gas outlets 13; 13' which can be provided in the system 1; 1' according to the invention. Another possible gas outlet 13; 13' could comprise a pipe with a floating ball acting as a valve for allowing controlled escape of gas out from the fluid guiding arrangement 5; 5' of the system 1; 1'. By providing a gas outlet 13; 13' and a gas cavity 60 as described above to a system 1; 1' according to the invention it will be possible to submerse the system 1; 1' completely below a fluid surface in a tank. This can be suitable if the same type of system is used in different types and sizes of tanks.

Figure 5a is a cross sectional side view of a tank 3" comprising a system 1" according to another embodiment of the invention. Figure 5b is a top view of the same tank 3" and system 1" as shown in Figure 5a. In this embodiment of the invention the system 1" for providing a flow to the fluid in the tank 3" is a stationary installation in the tank 3". The system 1" is provided along an outer side wall 31 of a tank 3" and a fluid guiding

arrangement 5" of the system 1" comprises a bottom slit inner side wall 33 provided inside and parallel to the outer side wall 31 of the tank 3" with an open slit 34 provided between the bottom slit inner side wall 33 and a bottom 4" of the tank 3". Said open slit 34 defines an outlet 17" of the fluid guiding arrangement 5". The fluid guiding arrangement 5" comprises further an intermediate inner side wall 37 provided between the bottom slit inner side wall 33 and the outer side wall 31. A second fluid passage 9" of the fluid guiding arrangement 5" is provided between the bottom slit inner side wall 33 and the intermediate inner side wall 37 and a first fluid passage 7" of the fluid guiding arrangement 5" is provided between the intermediate inner side wall 37 and the outer side wall 31. As can be seen in Figure 5b the bottom slit inner side wall 33 and the intermediate inner side wall 37 are provided along the whole length of the outer side wall 31. The intermediate inner side wall 37 is lower than both the outer side wall 31 and the bottom slit inner side wall 33 and a middle section fluid passage 11" of the fluid guiding arrangement 5" is hereby provided above the level of the intermediate inner side wall 37 and between the bottom slit inner side wall 33 and the outer side wall 31. This middle section fluid passage 11" has in this embodiment an open upper surface, i.e. a gas outlet 13" is provided in the form of a fluid surface in the tank. Hereby gas can be released when the fluid passes through the middle section fluid passage 11" on its way from the first fluid passage 7" to the second fluid passage 9". A gas providing device 25 is provided between the intermediate inner side wall 37 and the outer side wall 31. In this embodiment the gas providing device 25 is provided close to the bottom 4" of the tank 3" and gas is provided into the first fluid passage 7". In this embodiment a tube 141 is also provided between the intermediate inner side wall 37 and the outer side wall 31. Such a tube 141 may improve the efficiency of the system but is not necessary. The first fluid passage 7" is defined by this tube 141 and an inlet 15" to the fluid guiding arrangement 5" is an inlet to the tube 141. An outlet of the tube 141 is connected to the middle section fluid passage 11". The gas providing device 25 is positioned such that gas is provided into the inlet of the tube 141. Furthermore, in this embodiment a sealing 43 is provided around the tube 141 sealing towards the intermediate inner side wall 37 and the outer side wall 31. Such a sealing 43 will ensure that the fluid is guided correctly through the middle section fluid passage 11" and to the second fluid passage 9".

In this tank 3" fluid need to be redirected to the volume between the intermediate inner side wall 37 and the outer side wall 31. Such a fluid redirection system is not shown in these views.

As can be seen in Figure 5b a number of tubes 141 can be provided side by side along the outer side wall and between the outer side wall 31 and the intermediate inner side wall 37. Hereby a fluid flow along the bottom 4" of the tank 3" can be provided such that the fluid flow reaches the whole bottom 4". Either one gas providing device 25 can be provided for each tube 141. Alternatively a gas providing device 25 could be provided with a transferring device. Such a gas providing device 25 can be transferred along the outer side wall 31 of the tank 3" and used for all of the tubes 141. Figure 6 is a cross sectional side view of a tank 403 comprising a system 401 for providing a flow to a fluid in the tank 403 according to another embodiment of the invention. The system 401 is almost identical with the system 1 as described in relation to Figure la and the parts are given the same numbering and will not be described again. The only difference is that the first fluid passage 7 is longer than the second fluid passage 9. In this embodiment of the invention the tank 403 comprises a recessed part 404 for housing the at least one gas providing device 25, the inlet 15 and parts of the first fluid passage 7 of the system 401 for providing a flow to a fluid in the tank. Hereby the first fluid passage 7 can be made longer and because of the increased pressure from the fluid at a bottom 405 of the recessed part 404 of the tank 403 this will provide a more efficient system 401, i.e. a better flow of fluid can be provided from the outlet 17 of the fluid guiding arrangement 5 of the system 401. With such an arrangement as described in relation to Figure 6 it is also possible to transport a fluid between two different tanks.

Figure 7a is a schematic cross sectional top view of an inlet 15; 15' of a system 1; 1' according to one embodiment of the invention. A gas providing device gas outlet 26 can be seen centered within the inlet 15; 15'. This centered position and the size relation between the diameter of the gas providing device gas outlet 26 and the diameter of the inlet 15; 15' and a distance between the inlet 15; 15' and the gas providing device gas outlet 26 are important factors for achieving a god mixing effect of the gas and the fluid inside the first fluid passage 7; 7'. Another factor is the type of diffusor that is used for providing the gas. One suitable diffusor can be a fine bubble diffusor. Figure 7b is a schematic cross sectional side view of a part of the first fluid passage 7; 7' and a gas providing device gas outlet 26 of the same system 1; 1' as shown in Figure 7a. Figure 7b shows schematically how gas and fluid is mixed inside the first fluid passage 7; 7' of a system 1; according to one embodiment of the invention. It can be seen that a fully developed mixing between gas and fluid is achieved at a distance L from the inlet 15, 15'. This is due to drag. The distance L depends on diffusor type, dimensions of the inlet 15, 15', gas flow and distance between 26 and inlet 15, 15'. Dimensions of the inlet 15, 15' must be adapted to these circumstances to achieve as high efficiency as possible. Figure 8 is a flow chart of a method according to one embodiment of the invention. The steps of the method are described in order below: SI: Providing gas into an inlet 15; 15'; 15" of a fluid guiding arrangement 5; 5'; 5" of a system 1; 1'; 1" provided in a tank 3; 3" for providing a flow to the fluid in the tank. Said inlet 15; 15'; 15" being provided below a fluid surface in the tank and being open for receiving fluid from the tank. S3: Guiding fluid mixed with the gas from the inlet 15; 15'; 15" in a direction from a bottom 4; 4" of the tank towards a fluid surface 6 in the tank through a first fluid passage 7; 7'; 7" of the fluid guiding arrangement 5; 5'; 5" to a middle section fluid passage 11; 11'; 11" of the fluid guiding arrangement.

S5: Releasing gas through the middle section fluid passage 11; 11'; 11". Said middle section fluid passage is connected to said first fluid passage 7; 7'; 7" and to a second fluid passage 9; 9'; 9".

S7: Guiding fluid received from the middle section fluid passage 11; 11'; 11" in a direction towards the bottom of the tank through the second fluid passage of the fluid guiding arrangement to an outlet 17; 17'; 17" of the fluid guiding arrangement. S9: Delivering the fluid out from the outlet.

In one embodiment of the invention the delivering of the fluid from the outlet is provided essentially along a bottom of the tank.

In one embodiment of the invention the providing of gas into an inlet of a fluid guiding arrangement comprises providing fine bubbles of the gas at a suitable flow such that a mixing ratio between gas and fluid in the first fluid passage of the fluid guiding arrangement is typically between 1:5 and 1:15.

In one embodiment of the invention the method further comprises the step of rotating the system for providing a flow to the fluid such that the outlet of the system rotates in a plane parallel to a bottom of the tank such that the fluid can be delivered from the outlet of the fluid guiding arrangement in different directions.

In one embodiment of the invention the method further comprises providing a controlled brake power to the rotation of the system such that a controlled rotation of the system is achieved when the system is mounted in the tank such that it can rotate by the forces provided from the flow of fluid out from the outlet.

In one embodiment of the invention the method further comprises the step of transferring the system for providing a flow to the fluid along one or more paths in the tank.

Claims

A system (1; 1'; 1"; 401) for providing a flow to a fluid in a tank (3; 3"; 103; 203; 403), said system comprising:

at least one fluid guiding arrangement (5; 5'; 5") which when provided in a tank comprising a fluid is configured for receiving fluid from the tank into an inlet (15; 15'; 15") of the fluid guiding arrangement and guiding fluid from the inlet (15; 15'; 15") of the fluid guiding arrangement to an outlet (17; 17'; 17") of the fluid guiding arrangement, which inlet and outlet during use of the system are provided below a fluid surface (6) in the tank, wherein said fluid guiding arrangement (5; 5'; 5") further is configured such that the fluid being guided from the inlet to the outlet will be guided such that it passes a middle section fluid passage (11; 11'; 11") of the fluid guiding arrangement (5; 5'; 5") which during use is positioned at a greater distance above a bottom (4; 4") of the tank than both the inlet and the outlet and which middle section fluid passage comprises at least one gas outlet (13; 13'; 13") for removing gas out from the fluid guiding arrangement; and

at least one gas providing device (25) configured for providing gas into the fluid guiding arrangement (5; 5'; 5") through the inlet (15; 15'; 15"), wherein the system (1; 1') comprises a rotation device (205) configured for allowing the system to rotate such that the outlet (17; 17') of the system rotates in a plane parallel to a bottom (4) of a tank when the system is provided in the tank such that the fluid can be delivered from the outlet (17; 17') of the fluid guiding arrangement (5; 5') in different directions.

A system according to claim 1 wherein said fluid guiding arrangement (5; 5'; 5") further comprises a first fluid passage (7; 7'; 7") having a first end (7a; 7a') and a second end (7b; 7b') and a second fluid passage (9; 9'; 9") having a first end (9a; 9a') and a second end (9b; 9b'), and wherein said middle section fluid passage (11; 11'; 11") of the fluid guiding arrangement connects the second end (7b; 7b') of the first fluid passage (7; 7'; 7") with the second end (9b; 9b') of the second fluid passage (9; 9'; 9") such that during use of the system in a tank comprising a fluid both the first end (7a; 7a') of the first fluid passage (7; 7'; 7") and the first end (9a; 9a') of the second fluid passage (9; 9'; 9") are provided below the middle section fluid passage (11; 11'; 11") in the tank, and wherein said inlet (15; 15'; 15") is provided at the first end (7a; 7a') of the first fluid passage (7; 7'; 7") for receiving fluid into the first fluid passage (7; 7'; 7") and said outlet (17; 17'; 17") is provided at the first end (9a; 9a') of the second fluid passage (9; 9'; 9") for delivering fluid out from the second fluid passage (9; 9'; 9"), said outlet (17; 17'; 17") being in fluid communication with said inlet (15; 15'; 15") via said second fluid passage (9; 9'; 9"), said middle section fluid passage (11; 11'; 11") and said first fluid passage (7; 7'; 7").

A system according to claim 2, wherein said second fluid passage (9') substantially encircles said first fluid passage {!').

A system according to claim 2, wherein the first fluid passage (7), the second fluid passage (9) and the middle section fluid passage (11) are embodied as a bent pipe.

A system according to any one of the claims 2-4, wherein said first fluid passage (7; 7'; 7") has an elongated extension between the first and second ends (7a, 7b; 7a', 7b') essentially along an axis A and said second fluid passage (9; 9'; 9") has an elongated extension between said first and second ends (9a, 9b; 9a', 9b') essentially along the same axis A.

A system according to claim 5, wherein the system is configured for being provided in the fluid to be flowed such that the axis A is substantially vertical and such that the middle section fluid passage (11; 11'; 11") is provided at a greater distance from a bottom of the tank than the rest of the system.

7. A system according to any one of the preceding claims, wherein the outlet (17; 17'; 17") of the fluid guiding arrangement (5; 5'; 5") is configured for being positioned and directed during use in a tank comprising a fluid such that fluid is injected out from the outlet (17; 17'; 17") substantially along a bottom surface of the tank.

8. A system according to any one of the preceding claims, wherein the rotation device (205) comprises a shaft (41) which is vertically mounted in the tank and to which shaft the system is mounted such that the system can rotate from the forces provided by the flow of fluid out from the outlet (17').

9. A system according to claim 8, wherein said rotation device further comprises a brake mechanism (43) connected to the shaft (41), said brake mechanism providing a controlled brake power to the rotation of the system.

10. A system according to claim 9, wherein said brake mechanism (43) comprises a

peristaltic pump device (49) providing a hydraulic brake power to the shaft (41).

11. A system according to any one of the preceding claims, wherein the system (1; 1') comprises a transferring device (105) configured for transferring the system along one or more paths in the tank.

12. A system according to any one of the preceding claims, wherein the middle section fluid passage (11; 11') comprises a gas cavity (60) closed from above by an upper closure (62) and the gas outlet (13; 13') comprises a vertical pipe (65) or a vertical pipe (61) with slots (63) protruding through the upper closure.

13. A system according to any one of the preceding claims, wherein the at least one gas providing device (25) comprises a diffusor providing fine bubbles.

14. A system according to any one of the preceding claims, wherein a gas providing device gas outlet (26) of the at least one gas providing device (25) has a dimension corresponding to the dimension of the inlet (15; 15') and is positioned such that gas is provided symmetrically into the first fluid passage (7; 7').

15. A tank comprising a system for providing a flow to a fluid in the tank according to any one of the claims 1-14.

16. A tank according to claim 15, wherein the tank is an aquaculture tank or a sewage treatment tank.

17. A tank according to claim 16, wherein the tank is a Recirculating aquaculture system, RAS, tank and the system for providing a flow to a fluid in the tank is separated from the RAS circulation.

18. A method for providing a flow to a fluid in a tank (3; 3"), said method comprising the steps of:

providing gas (SI) into an inlet (15; 15'; 15") of a fluid guiding arrangement (5; 5'; 5") of a system (1; 1'; 1") provided in the tank for providing a flow to the fluid in the tank (3; 3"), said inlet (15; 15'; 15") being provided below a fluid surface (6) in the tank and being open for receiving fluid from the tank;

guiding (S3) fluid mixed with the gas from the inlet (15; 15'; 15") in a direction from a bottom (4; 4") of the tank towards the fluid surface in the tank through a first fluid passage (7; 7'; 7") of the fluid guiding arrangement (5; 5'; 5") to a middle section fluid passage (11; 11'; 11") of the fluid guiding arrangement; releasing gas (S5) through the middle section fluid passage (11; 11'; 11"), said middle section fluid passage being connected to said first fluid passage (7; 7'; 7") and to a second fluid passage (9; 9'; 9"); guiding (S7) fluid received from the middle section fluid passage in a direction towards the bottom of the tank through the second fluid passage of the fluid guiding arrangement to an outlet (17; 17'; 17") of the fluid guiding arrangement; delivering (S9) the fluid out from the outlet

19. A method according to claim 18, wherein the delivering of the fluid from the outlet (17; 17'; 17") is provided essentially along a bottom of the tank.

20. A method according to any one of the claims 18-19, wherein the providing of gas (SI) into the inlet of the fluid guiding arrangement comprises providing fine bubbles of the gas at a suitable flow such that a mixing ratio between gas and fluid in the first fluid passage of the fluid guiding arrangement is between 1:5 and 1:15.

21. A method according to any one of the claims 18-20, comprising providing a

controlled brake power to the rotation of the system such that a controlled rotation of the system is achieved when the system is mounted in the tank such that it can rotate by the forces provided from the flow of fluid out from the outlet.

22. A method according to any one of the claims 18-21, further comprising the step of transferring the system for providing a flow to the fluid along one or more paths in the tank.