WO2021219345A1

WO2021219345A1 - System and method for supplying gas bubbles into fluid

Info

Publication number: WO2021219345A1
Application number: PCT/EP2021/059301
Authority: WO
Inventors: Ingar Kjøstolfsen; Bård-Inge Hansen
Original assignee: Nippon Gases Norge As
Priority date: 2020-04-30
Filing date: 2021-04-09
Publication date: 2021-11-04
Also published as: NO345652B1; EP4142483A1

Abstract

The invention discloses a system (1) and a method for operating such system for supplying gas bubbles (500) into a fluid (300). The system comprises a longitudinal cylindrical fluid pipe (200) for the fluid (300) to pass therethrough, a turbulence inducing device (400) arranged within the longitudinal cylindrical fluid pipe (200) for generating a turbulent flow of the fluid (300) and a gas supplying device (100). The gas supply device comprises an outer surface (102) and an inner surface (104) enclosing a toroid shaped chamber (101),a gas inlet (106) configured to feed gas into the toroid shaped chamber (101) and a membrane (110) arranged at the inner surface (104), the membrane (110) being configured to allow gas to pass from the toroid shaped chamber (101) into the flow of fluid (300) as gas bubbles (500). The gas supplying device (100) is arranged upstream relative to the turbulence inducing device (400) such that the turbulent flow of fluid (300) passes a cross-sectional area (600) enclosed by the membrane (110) when passing the turbulence inducing device or immediately after exiting the turbulence inducing device (400).

Description

Title

System and method for supplying gas bubbles into fluid.

Technical Field The present invention relates to a system for supplying gas bubbles into a fluid as defined in the preamble of claim 1 and a method for using such device.

Background and prior art

Without limiting the scope of the present invention, the background will be described with reference to aquaculture. Oxygen is a major contributing factor in aquaculture alongside water and feed. The oxygen content of the water should be above 80% saturation in relation to air to maintain adequate fish welfare and fish growth. In intensive fish farming, the oxygen supplied naturally from the water source is usually not sufficient to maintain the requirement for good fish welfare. Therefore, extra oxygen must be added and dissolved in the water.

The development in aquaculture is directed towards land-based installations and closed containment aquaculture installations. In land-based installations seawater is pumped into the installations, and a part of the water is often reused. In closed containment aquaculture installations, which are floating in the sea, seawater is pumped into the installation from great depths. In both cases an oxygen supply is needed.

The solubility of oxygen in water is small because the surface tension of the water must be broken for sufficient gas absorption. Different solutions for dissolving gas in water are known. W02003024578A1 discloses a solution for supplying oxygen to water which include diffuser hoses within the fish tank which give little utilization of added oxygen. Typically, 25% of the added amount of oxygen is absorbed by the water.

W02006133113A2 involves adding oxygen to the water under pressure immediately before the water is fed to the fish using oxygen cones. Other publications use columns or the like which typically have a high degree of gas utilization, being about 90%. However, these solutions have a large energy demand as the water is pumped up to 3-5 bar overpressure.

US 2018/0050312 A1 discloses a method for dissolving oxygen into water by employing a microporous membrane. A pipe section is disclosed having a throat section comprising a membrane through which gas passes into the throat section. The throat section has a narrower diameter than the remaining part of the pipe and has a cone shaped inlet and outlet. Hence a laminar flow of liquid passes the membrane to sweep off the gas bubbles from the membrane surface for dissolving the gas into the liquid. Hence, a specific configuration of the fluid pipe is required.

WO 86/05123 discloses a system for feeding gas into liquid. The system involves a water pipe having an impeller arranged therein for creating turbulence to the liquid. Downstream the impeller the liquid is guided by baffles before passing through a gas feeding device within the pipe for introducing gas into the liquid. By matching the impeller blades and the guide baffles with each other the turbulent motion of the liquid is converted into kinetic energy of the flow which is directed parallel to the tube axis. By adjusting the impeller and the baffles so that the direction of the liquid flow leaving the impeller blade is approximately parallel to the tangent of the baffle intake edge, there is achieved a method for attenuating turbulence which is important for increasing the solubility of gas in the liquid of the system.

RU 2382673 discloses a method of a small dimensioned, such as laboratory sized system, for supplying gas bubbles into a liquid. The invention relates to the optimalization of the linear fluid velocity of the liquid passing the membrane such that a high degree of dissolved gas bubbles in the liquid is obtained without increasing the gas pressure. The change in the fluid velocity is used to change the size of the gas bubbles due to the change in turbulence of the fluid. Higher turbulence causes less gas to be dissolved in the liquid since the gas pressure is constant. This optimalization teaches to limit the linear fluid velocity for obtaining a high degree of dissolved gas for a determined gas pressure.

Hence, it is an object of the present invention to mitigate the disadvantages known from prior art.

It is also an object of the present invention to provide a simplified system when compared to prior art.

Further, it is an object of the present invention to provide a gas supplying device having a high degree of gas utilization, preferably above 90%.

Another object of the present invention is to utilize existing conventional fluid pipes and instruments already present in the fluid pipes, such as pumps, providing an energy efficient gas supply to fluid.

Summary

The present invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the invention.

The present invention relates to a system and a method for supplying gas bubbles into a turbulent flow of fluid for dissolving the gas bubbles in the fluid. The system comprises a longitudinal cylindrical fluid pipe for fluid to pass therethrough and a turbulence inducing device arranged therewithin for generating a turbulent flow of fluid.

The system further comprises a gas supplying device for supplying gas to the turbulent flow of fluid. The gas supplying device comprises an outer surface and an inner surface, wherein the inner surface has a smaller cross sectional area than the outer surface. The outer and inner surfaces enclose, at least partly, a toroid shaped chamber.

More specifically the toroid shaped chamber may be enclosed by parallel inner and outer axial surfaces oriented along an axial direction, and by two parallel radial surfaces oriented perpendicular to the inner and outer surfaces. In this exemplary design, the toroid shaped chamber has a rectangular cross-section circumventing an axial center axis. The axial direction is parallel to the longitudinal direction of the longitudinal cylindrical fluid pipe.

The gas supplying device further comprises a gas inlet allowing gas to be fed into the toroid shaped chamber and a membrane arranged at the inner surface. The membrane is configured to allow gas to pass from the toroid shaped chamber into a flow of turbulent fluid as gas bubbles. Hence, the gas entering the flow of turbulent fluid may only pass through the membrane.

The gas supplying device is arranged upstream relative to the turbulence inducing device such that the turbulent flow of fluid passes a cross-sectional area enclosed by the membrane when passing the turbulence inducing device or immediately after exiting the turbulence inducing device.

In an example aspect of the inventive system the gas supplying device is arranged proximate to or adjoining the turbulence inducing device. “Proximate to” should be interpreted as being arranged as close as possible without shearing a boundary, while “adjoining” should be interpreted as arranged such that the gas supplying device and the turbulence inducing device have a common boundary.

The turbulence inducing device may for example be a propeller pump such as an axial flow pump, an injection pump or a submersible mixer. The submersible mixer may comprise a jet ring for increasing the mixer efficiency and reducing energy consumption.

The membrane may be made of a corrosion and wear resistant material. The material may be selected from at least one of a polymer-based material such as polyurethane or polyethylene; a ceramic-based material such as alumina (AI2O3) and zirconium oxide (ZrC ); a steel-based material such as stainless steel; and a nickel-based material such as nickel alloys comprising alloying elements of at least one of copper, molybdenum, chromium, iron and tungsten.

In a preferred aspect, the membrane is made of a steel-based material or nickel- based material, and in an even more preferred aspect of a nickel -based material.

In an example aspect of the invention the membrane comprises pores having a pore size of any one of 0.1 to 10 pm, or preferably 0.3 to 5 pm or even more preferably 0.4 to 1 pm, for example 0.5 pm.

The longitudinal cylindrical fluid pipe comprises an inlet at a first end and an outlet at the opposite second end. The fluid passes inside the inner surface of the longitudinal cylindrical fluid pipe from the first end towards the second end. In a preferred example aspect, the longitudinal cylindrical fluid pipe has constant or close to constant inner diameter through the whole length of longitudinal cylindrical fluid pipe comprising the turbulence inducing device and the gas supplying device.

The longitudinal cylindrical fluid pipe may be submerged in water during use.

During operation of the system the gas pressure within the toroid shaped chamber should be high enough to move the gas from the toroid shaped chamber through the membrane and into the turbulent flow of fluid exiting the turbulence inducing device within the longitudinal cylindrical fluid pipe. Hence the gas pressure within the toroid shaped chamber should be higher than the counter pressure of the fluid passing the cross-sectional area enclosed by the membrane for the gas to pass through the membrane from the toroid shaped chamber.

The gas passes into the turbulent flow of fluid in the form of gas bubbles attaching themselves to an outer surface of the membrane which corresponds to the inner surface of the gas supplying device, hence facing the fluid. The turbulent flow of fluid pushes on the gas bubbles arranged at the outer surface of the membrane by shear forces. The gas bubbles are hence disengaged therefrom as the gas dissolves into the fluid. Hence, it is an important feature of the present invention that the turbulent flow of fluid passes the cross-sectional area enclosed by the membrane when passing the turbulence inducing device or immediately after exiting from the turbulence inducing device, as high turbulence of the flow of fluid is required to disengage and dissolve the gas bubbles into the fluid.

If the gas bubbles are not disengaged from the outer surface of the membrane, the gas bubbles will grow in size until they self-disengage from the surface. After such self-disengagement, the gas bubbles will start moving along an inner wall/surface of the longitudinal cylindrical fluid pipe in an upstream direction until they exit the longitudinal cylindrical fluid pipe. These gas bubbles are hence not dissolved into the fluid. Such growth of gas bubbles should therefore be avoided to keep the gas loss at a minimum.

If the gas pressure within the toroid shaped chamber is lower than the counter pressure of the fluid passing the cross-sectional area enclosed by the membrane, the fluid may be allowed to enter into the toroid shaped chamber causing interruption to the system. Further, fluid passing through the membrane may comprise particles which may clog the pores of the membrane. In such undesired situations, maintenance of the membrane must be performed before the system can continue to operate.

To minimize the risk of fluid entering the toroid shaped chamber, the gas supplying device may in an advantageous aspect comprise a plurality of gas inlets. In an example aspect the toroid shaped chamber may comprise at least a first and a second gas inlet allowing gas to be fed into the toroid shaped chamber, for example by connecting a gas container with pressurized gas in gas communication with the gas inlet(s). If the first gas inlet fails to allow the needed gas pressure to enter the toroid shaped chamber, the second gas inlet can be activated to take over the gas supply. The required gas pressure is thereby maintained.

In an example aspect of the invention, the gas supplying device may comprises a pressure sensor configured to detect the gas pressure inside said toroid shaped chamber. The pressure sensor may be configured to transmit via a transmitter the detected pressure to a controller configured to control the gas pressure in the toroid shaped chamber. The gas pressure within the toroid shaped chamber may consequently be adjusted to optimize operation efficiency.

Further, the pressure sensor may comprise another transmitter sending signals to said controller, optionally to a second controller configured to detect an anomalous pressure within the toroid shaped chamber. Upon such pressure readings, the pressure can be adjusted, manually or automatically, thereby ensuring that the pressure is always above a predetermined value prohibiting fluid within the longitudinal cylindrical fluid pipe from entering into the toroid shaped chamber.

In an example aspect any pressure loss sensed by the pressure sensor approaching below the counter pressure of the fluid will be registered by the pressure sensor which will transmit signals thereof to the control device. The control device will ensure that for example the feeding rate of gas into the gas supplying device is increased sufficiently to maintain the gas pressure within the toroid shaped chamber above the hydrostatic pressure of the fluid.

In a further example aspect of the system, the toroid shaped chamber may comprise a plurality of individual compartments comprising individual gas inlets wherein the compartments are not in gas communication with each other. Dividing the toroid shaped chamber into a plurality of compartments having their own gas inlet(s) and respective gas supply may for example be advantageous if the gas supply to one of the compartments fails. While fixing the broken gas supply, gas can still be fed into the fluid through the remaining compartments such that a complete shutdown of the system can be avoided.

Further, if the longitudinal cylindrical fluid pipe is arranged horizontally during use, the counter pressure of the fluid passing the cross-sectional area enclosed by the membrane will be different along the circumference of the membrane due to gravity forces acting on the fluid. The gravity forces influence the counter pressure of the fluid such that the counter pressure of the fluid is at its highest at a lowest gravity area of the membrane and is at its lowest at the opposite part arranged at an upper gravity area of the membrane. In such an aspect it may be advantageous that the toroid shaped chamber is divided into a plurality of individual compartments, wherein each compartment comprises an individual gas pressure and an individual gas inlet. Consequently, each of the individual compartments can have an adjusted gas pressure such that each compartment comprises a gas pressure being equal to or above the hydrostatic pressure of the fluid passing the individual compartments.

According to an example aspect of the system, the gas supplying device may be designed as a pipe segment of the longitudinal cylindrical fluid pipe circumventing the radial diameter of the longitudinal cylindrical fluid pipe. The inner surface of the gas supplying device may be arranged flush with the inner surface of the longitudinal cylindrical fluid pipe such that the fluid flow is not interrupted after exiting the turbulence inducing device. An interruption in the turbulent flow after exiting the turbulence inducing device may cause a reduction in the velocity of the flow of fluid and hence more energy may be needed to drive the turbulence inducing device at a higher speed to compensate for the velocity loss. The inner surface of the gas supplying device may for example have a shape that corresponds to the shape of the inner diameter of the longitudinal cylindrical fluid pipe.

For example, if the longitudinal cylindrical fluid pipe is straight, meaning that the inner diameter of the longitudinal cylindrical fluid pipe is a constant throughout at least the part of the longitudinal cylindrical fluid pipe comprising the turbulence inducing device, then the diameter of the inner surface of the gas supplying device will be equal to the diameter of the inner surface of the longitudinal cylindrical fluid pipe.

If the circumference of the inner surface of the longitudinal cylindrical fluid pipe has a continuously increasing diameter, i.e. the diameter is increasing in the direction of the fluid flow, then the circumference of the inner surface of the toroid shaped chamber will have a corresponding continuous increasing diameter such that the inner surface of the toroid shaped chamber is flush with the inner surface of the longitudinal cylindrical fluid pipe. If the circumference of the inner surface of the longitudinal cylindrical fluid pipe has a continuous decreasing diameter, i.e. the diameter is decreasing in the direction of the fluid flow, then the circumference of the inner surface of the toroid shaped chamber will have a corresponding continuous decreasing diameter such that the inner surface of the toroid shaped chamber is flush with the inner surface of the longitudinal cylindrical fluid pipe.

Further, a radial extension of the gas supplying device may be larger than the radial extension of the longitudinal cylindrical fluid pipe, wherein the radial extension is relative to the longitudinal cylindrical fluid pipes longitudinal center axis. In this aspect the gas inlet may be arranged at the radial extension of the gas supplying device extending beyond the radial extension of the longitudinal cylindrical fluid pipe.

The gas supplying device may be attached to the longitudinal cylindrical fluid pipe by welding or by bolts extending from the outer surface of the gas supplying device into the outer surface of the fluid pipe.

In another example aspect of the invention, the gas supplying device may be arranged within the longitudinal cylindrical fluid pipe. The gas supplying device may in this aspect be adjoining the turbulence inducing device in the longitudinal direction of the longitudinal cylindrical fluid pipe and arranged such that the inner surface of the gas supplying device is arranged flush with the inner diameter of the turbulence inducing device at least where the turbulence inducing device is adjoining the gas supplying device.

In this aspect the gas supplying device may be fixed to the turbulence inducing device by brackets or by welding.

In another further aspect the turbulence inducing device and the gas supplying device may be arranged inside an installation container placed inside the longitudinal cylindrical fluid pipe. The installation container may comprise at least a first compartment cell containing the turbulence inducing device and a second compartment cell containing the gas supplying device. Hence, the second compartment cell is arranged upstream the first compartment cell and the first and second compartment cells are in fluid communication with each other and the longitudinal cylindrical fluid pipe.

A person skilled in the art will understand that the system may comprise a plurality of turbulence inducing devices arranged in series downstream the gas supplying device ensuring enough shear force generated by the turbulent flow of fluid to cause the surface tension of the gas bubbles to break. It is also provided a method for supplying gas bubbles into a fluid by use of a system according to any one of the aspects described above, wherein the method involves introducing a gas into the gas inlet of the gas supplying device, introducing a flow of fluid into the longitudinal cylindrical fluid pipe, adjusting the gas pressure within the toroid shaped chamber generating an overpressure relative to a pressure within the flow of fluid, routing the flow of fluid through the turbulence inducing device generating a turbulent flow characteristic within the flow of the fluid, routing the flow of fluid through a cross-section of the longitudinal cylindrical fluid pipe enclosed by the membrane, and allowing the gas entering from the gas inlet to pass from the toroid shaped chamber via the membrane into the fluid as gas bubbles.

The fluid may be a liquid, preferably a water-based liquid such as sea-water, brackish water, fresh water, potable water, tunnel water, wastewater, process water etc.

The gas may be oxygen, carbon dioxide or an inert gas.

In a first example aspect of the method, the gas may be oxygen and the fluid may be a water-based liquid such as sea water, brackish water, fresh water or waste water. For example, the system of the present invention may be used to add oxygen to seawater before the water is supplied to a fish tank

In a second example aspect the gas is CO2 and the fluid may be water-based liquid, such as waste water, potable water, process water or tunnel water. For example, the system of the present invention may be used to add CCfi-gas to basic water such as waste water or tunnel water for pH-regulation.

In a third example aspect the gas may be an inert gas such as nitrogen or argon and the fluid is a water-based liquid such as sea water, potable water, wastewater, fresh water. For example, the system of the present invention may be used to add inert gas to a water-based liquid for 02-stripping. The system of the present invention may be used in systems requiring a high degree of fluid flow through the pipe, such as between 1000 to 100 000 liters fluid per minute. Further, the inner diameter of the pipe can be up to at least 1000 mm.

In the context of the application the term “circular” should be interpreted to include any cross-sectional shapes which are common for longitudinal cylindrical fluid pipes. Most longitudinal cylindrical fluid pipes comprise a merely circular cross- section. However, the term may also include cross sections having an oval shape, irregular circular shape etc. Further the cross-sectional shape may comprise an increasing or decreasing diameter in the direction of the fluid flow.

In the context of the application the term “pore size” should be interpreted as the distance between two opposite walls of the pore, e.g. the diameter of cylindrical pores.

In the following description, numerous specific details are introduced to provide a thorough understanding of different embodiments of the system. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details, or with other components, systems, etc. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.

Brief description of the drawings

These and other characteristics of the invention will be clear from the following description of embodiments, given as non-restrictive examples, with reference to the attached drawings wherein:

FIG. 1A is a perspective view of a fist example embodiment of the invention wherein the gas supplying device is designed as a pipe segment of the longitudinal cylindrical fluid pipe.

FIG. IB is a cross-sectional open view of the first example embodiment shown in FIG. 1A.

FIG. 2A is an open view of a second example embodiment of the invention wherein the gas supplying device is connected to an upstream end of the pump within the longitudinal cylindrical fluid pipe.

FIG. 2B is a perspective view of a pump comprising a jet ring to be connected to the gas supplying device with brackets.

FIG. 2C is a cross-sectional view of the second example embodiment shown in FIG. 2A.

FIG. 3A is an open view of a third example embodiment of the invention wherein the gas supplying device is connected to an upstream end of the pump within the longitudinal cylindrical fluid pipe.

FIG. 3B is a cross-sectional view of the third example embodiment shown in FIG. 3 A.

FIG. 4A is a perspective view of a fourth example embodiment of the invention wherein a pumps and a gas supplying device are to be arranged inside an installation container. FIG. 4B is a top view of the fourth example wherein the pump is arranged inside the installation chamber.

FIG. 5A is cross-sectional view of a gas supplying device comprising one compartment.

FIG. 5B is cross-sectional view of a gas supplying device comprising two compartments.

FIG. 5C is cross-sectional view of a gas supplying device comprising four compartments.

FIG. 6 is a perspective view of a gas supplying device.

In the drawings, like reference numerals have been used to indicate like parts, elements or features unless otherwise explicitly stated or implicitly understood from the context.

Detailed description of the invention

For reasons of convenience, the description below considers that the terms

“upwards” or “upstream” correspond to an axial longitudinal direction (z) that is generally parallel to the central axis of the longitudinal cylindrical fluid pipe 200 and that extends from the first end towards the second end corresponding to the main direction of the fluid therein, whereas the terms “downwards” or “downstream” correspond to the opposite direction.

FIGS. 1A and IB illustrate a fist example embodiment of system 1.

In FIG. 1A the system 1 comprises a longitudinal cylindrical fluid pipe 200 and a gas supplying device 100 integrated as a pipe segment of the fluid pipe 200. The gas supply device 100 has a toroid shaped chamber 101. Gas is supplied into the toroid shaped chamber 101 via gas inlet 106 being connected to a gas cylinder or the like (not shown). The drawing illustrates how the radial extension of the gas supplying device 100 can be larger than the radial extension of the fluid pipe 200 and how the gas inlet 106 can be arranged at the radial extension 112 of the gas supplying device 100 since the radial extension 112 extends beyond the radial extension of the fluid pipe 200. The direction of the radial extension 112 can be seen as being perpendicular to the longitudinal direction of the fluid pipe 200.

Even if only one gas inlet 106 is shown, there may be a multiple of gas inlets arranged for supplying gas into the toroid shaped chamber 101.

FIG. IB shows the same first example embodiment as FIG. 1A. The open arrow within the fluid pipe 200 indicate a direction of the laminar flow of fluid 300 downstream the turbulence inducing device 400 while the small closed arrows indicate the turbulent flow of fluid 300 after exiting the turbulence inducing device 400 before and/or after dissolving gas into the fluid 300.

A membrane 110 of the gas supplying device 100 is shown introducing gas bubbles 500 onto the inner surface of the gas supplying device 100. The gas supplying device 100 is arranged upstream the turbulence inducing device 400. In this embodiment the gas supplying device 100 is arranged proximate the turbulence inducing device 400, hence being arranged as close as possible to the turbulence inducing device 400 without physically shearing a boundary. Hence the turbulent flow of fluid 300 exiting the turbulence inducing device 400 passes the cross- sectional area enclosed by the inner surface 104 of the gas supplying device 100/membrane 110 of the gas supplying device 100 when passing the turbulence inducing device or immediately after exiting the turbulence inducing device 400. The membrane 110 can be seen as having an inner surface facing inside the toroid shaped chamber 101 and an outer surface facing the flow of fluid 300.

The inner surface 104 of the gas supplying device 100 with respect to the radial direction is shown being arranged flush with the inner surface 206 of the fluid pipe 200

The turbulence inducing device 400 is illustrated as a pump 400 with impeller blades 402 (the motor not shown). However, a person skilled in the art will understand that the turbulence inducing device 400 can be any device causing a high degree of turbulence enabling the gas bubbles 500 to dissolve into the fluid 300.

FIGS. 2A and 2B illustrate a second example embodiment of system 1.

The system 1 is different from the system 1 in FIGS. 1A and IB in that the gas supplying device 100 is arranged inside the fluid pipe 200.

The gas supplying device 100 at its downstream end 130 is contacting an upstream end 420 of the turbulence inducing device/pump 400 shearing a boundary.

FIG. 2C illustrates how the gas supplying device 100 can be attached to the pump 400 comprising a jet ring 406 by using brackets 800. A major part of pump passage 410 (see FIG. 2A), through which the fluid 300 travels, is shown as being conically shaped with a decreasing diameter in the direction of the flow of fluid 300. The upstream area of the pump passage 410 comprises a jet ring 406. The jet ring 406 has an inner surface 407 facing the flow of fluid which is oriented parallel with the central axis of the fluid pipe 200. The inner surface 104 of the gas supplying device 100 is also oriented parallel with the central axis of the fluid pipe 200 such that the inner surface 407 of the jet ring 406 of the pump 400 is arranged flush with the inner surface 104 of the gas supplying device 100. This is illustrated in FIG. 2B. The brackets 800 fixes the gas supplying device 100 to the jet ring 406 of the pump 400.

Hence, as shown in FIG. 2B, laminar flow of fluid 300 (indicated by the open arrow) is passed through the turbulence inducing device 400 in which the laminar flow is converted into a turbulent flow of fluid 300 indicated by small closed arrows. When passing the turbulence inducing device or immediately after exiting the turbulence inducing device 400 the flow of fluid enters the cross-sectional area 600 enclosed by the inner surface 104/membrane 110 of the gas supplying device 100. The turbulent flow of fluid 300 then dissolves the gas bubbles 500 arranged on the inner surface 104 of the gas supplying device 100.

Even if not shown, gas is supplied into the toroid shaped chamber of the gas supplying device 100 via at least one gas inlet which is passed through a hole in the fluid pipe 200.

FIGS. 3A and 3B illustrate a third example embodiment of system 1 which is similar to the second example embodiment shown in FIGS. 2 A and 2B, but where the whole length of the pump passage 410 in the axial direction is oriented parallel with the central axis of the fluid pipe 200. The gas supplying device 100 is attached to the pump 400 at the upstream end of the pump passage 410 by brackets 800.

FIGS. 4 A and 4B illustrate a fourth example embodiment of system 1 where the turbulence inducing device/pump 400 and the gas supplying device 100 is arranged inside an installation container 700. The installation container 700 has a first cell/cassette compartment 702 comprising the pump 400 and a second cell/cassette compartment 704 comprising the gas supplying device 100. The first and second compartment cells 702,704 keep the pump 400 and gas supply 100 in place respectively.

FIG. 4 A illustrates how a pump 400 can be inserted into the first cell 702, while FIG. 4B illustrate the pump 400 and gas supplying device 100 after they have been arranged within the first and second cells 702, 704 respectively.

Even if the depicted installation container 700 only comprises two cells 702,704, a person skilled in the art will understand that such an installation container may comprise more cells for inter alia arranging a plurality of pumps 400 to the system 1

The gas supplying device 100 can be sealed within the second cell 704 by O-rings.

Common for all of the above described embodiments is that the fluid 300 enters via the first end 202 of the fluid pipe 200. The fluid 300 may have a laminar flow as indicated by the big open arrow in FIGS. 1-3 and as a dashed arrow in FIG. 4. The flow of fluid 300 is then forced into the pump 400 which may comprise a pump passage 410 (see FIG. 2A and 3A). When the fluid 300 is passing the impeller blades 402 of the pump 400, the flow of fluid 300 begins to rotate/swirl with the impeller blades 402 (see FIGS. IB and 2C) and the magnitude of the velocity of the flow of fluid 300 increases, establishing a turbulent flow of fluid 300. In other words, the kinetic energy of flow of fluid 300 entering the pump 400 is converted into pressure by exerting an angular momentum to the flow of fluid 300 traveling through the pump 400, hence producing a turbulent flow of fluid 300.

The turbulent flow of fluid 300 may for example have a velocity from 3 to 10 m/s when entering the cross-sectional area 600 enclosed by the membrane 110 contributing to a swift disengagement of gas bubbles 500 from the surface of the membrane 110 facing the flow of fluid 300. Such swift disengagement prevents the gas bubbles 500 from growing, and hence gas bubbles 500 having a large diffusion area are disengaged providing an efficient solubility of the gas bubbles 500 into the fluid 300.

The above described jet ring 406 arranged on the pump 400 in the second example embodiment (see FIG. 2C) increases the velocity of the flow of fluid 300, accompanied with rotational movement.

The rotational movement of the flow of fluid 300 is sustained when the flow of fluid 300 enters the cross-sectional area 600 enclosed by the inner surface 104/membrane 110. As explained above in connection with FIGS. 1-4, the turbulent flow of fluid 300 interacts with the gas bubbles 500 exiting through the membrane 110 of the gas supplying device 100. Shear forces from the turbulent flow of fluid 300 will dissolve the gas bubbles 500 exiting through the membrane 110 and a gas enriched fluid 300 will be obtained.

The fluid 300 enriched with gas will then exit the fluid pipe 200 at the second end 204.

FIGS 5A, 5B and 5C are cross-sectional views of different configurations of the gas supplying device 100 taken in the plane indicated as A-A in FIG. 3 A.

Fig 5 A shows a first example configuration of the gas supplying device 100 wherein the toroid shaped chamber 101 has one single compartment 120 having a gas pressure Pi. Further, the gas supplying device 100 has one gas inlet 106 allowing gas to be fed into the compartment 101. The gas pressure is equal to or higher than the counterpressure of the fluid passing the cross-sectional area 600, thereby preventing fluid from entering into the compartment 120.

Fig 5B shows a second example configuration of the gas supplying device 100 wherein the toroid shaped chamber comprises a first and a second compartment 120,121. The first compartment has a first gas inlet 106, while the second compartment has a second gas inlet 107. The first compartment 120 has a first gas pressure Pi which is controlled through the first gas inlet 106 and the second compartment 121 has a second gas pressure P2 controlled through the second gas inlet 107. The first gas pressure Pi and the second gas pressure P2 may be the same or different depending on the counterpressure of the fluid passing the first and second compartments 120,121 through the cross-sectional area 600 enclosed by the membrane 110. Both gas pressures Pi,P2 should be equal to or higher than the counterpressure of the fluid passing the cross-sectional area 600, thereby preventing fluid from entering into the compartments 120,121. If the fluid pipe is vertically arranged, both the first and second pressures Pi,P2 can be equal. If the fluid pipe is horizontally arranged, the first and the second gas pressures Pi,P2 may be different as the gravity force exerted on the fluid will result in a different counterpressure from the fluid passing the first and second compartment 120,121.

Fig 5C shows a third example configuration of the gas supplying device 100 wherein the toroid shaped chamber comprises a first, second, third, fourth, fifth and sixth compartment 120, 121,121’, 122, 122’, 123. The first compartment 120 has a first gas pressure Pi, the second and third compartments 121,121’ have a second gas pressure P2, the fourth and fifth compartments 122,122’ have a third gas pressure P3 and the sixth compartment 123 has a fourth gas pressure P4. The first compartment 120 has a first gas inlet allowing control of the first gas pressure Pi, the second and third compartments have a second and third gas inlet 107,107’ respectively allowing control of the second gas pressure P2, the fourth and fifth compartments have a fourth and fifth gas inlet 108,108’ respectively allowing control of the third gas pressure P3, and the sixth compartment has a sixth gas inlet 109 allowing control of the fourth gas pressure P4.

Hence, the shown second gas pressure P2 is identical or near identical within the second and third chambers 121,121’, and the shown third gas pressure P3 is identical or near identical within the fourth and fifth chambers 122,122’, but may all be regulated to be different.

The first, second, third and fourth gas pressures Pi,P2,P₃,P4 should be equal to or higher than the counterpressure of the fluid passing the cross-sectional area 600, thereby preventing fluid from entering into the compartments 120, 121,121’, 122, 122’, 123. If the fluid pipe is vertically arranged, the compartments 120, 121,121’, 122, 122 ’,123 may have the same gas pressure Pi,P2,P₃,P4. If the fluid pipe is horizontally arranged, the four gas pressures Pi,P2,P₃,P4 may be different as the gravity force exerted on the fluid will result in a different counterpressure from the fluid passing the different compartments 120, 121,121’, 122, 122 ’,123, however being equal for the second and third chamber 121,121’, and equal for the fourth and fifth chamber 122,122’. Further, all the compartments 120, 121,121’, 122, 122’, 123 can be equipped with pressure sensors for controlling the pressure therewithin, even if not shown.

FIG. 6 is a perspective view of the gas supplying device 100 having a toroid shaped chamber 101 enclosed by the outer surface 102, the inner surface 104 and the two radial surfaces 112,114 being perpendicularly oriented to the inner and outer surfaces 102,104. Hence, the toroid shaped chamber 101 has a rectangular cross section taken in the plane indicated as B-B.

The toroid shaped chamber 101 comprises a first and a second gas inlet 106,107 for controlling the gas pressure within the toroid shaped chamber 101. Even if not shown in any of the above disclosed embodiments and configurations, the toroid shaped chamber of the gas supplying device may comprises a pressure sensor having a transmitter which sends signals to a controller. The controller detects any anomality in pressure within the toroid shaped chamber. Such anomalous pressures can be accompanied by pressure adjustments ensuring that the pressure is always equal to or higher than the counter pressure of the fluid within the fluid pipe. The fluid may consequently be prohibited from entering into the toroid shaped chamber.

Claims

1. A system (1) for supplying gas bubbles (500) into a fluid (300), wherein the system (1) comprises a longitudinal cylindrical fluid pipe (200) for the fluid (300) to pass therethrough, a turbulence inducing device (400) arranged within the longitudinal cylindrical fluid pipe (200) for generating a turbulent flow of the fluid (300) and a gas supplying device (100) comprising an outer surface (102), an inner surface (104) having a cross sectional area smaller than the outer surface (102), wherein the outer and inner surfaces (102,104) encloses a toroid shaped chamber (101) a gas inlet (106) configured to feed gas into the toroid shaped chamber (101) and a membrane (110) arranged at the inner surface (104), the membrane (110) being configured to allow gas to pass from the toroid shaped chamber (101) into the flow of fluid (300) as gas bubbles (500), wherein the gas supplying device (100) is arranged upstream relative to the turbulence inducing device (400) such that the turbulent flow of fluid (300) passes a cross-sectional area (600) enclosed by the membrane (110) when passing the turbulence inducing device (400) or immediately after exiting the turbulence inducing device (400). 2. The system (1) according to claim 1, wherein the membrane (110) comprises a pore size of any one of 0.1 to 10 pm or 0.3 to 5 pm or 0.4 to 1 pm or 0.5 pm.

3. The system (1) according to claim 1 or 2, wherein the membrane (110) comprises a material selected from at least one of a polymer-based material, a ceramic-based material, steel-based material and nickel-based material. 4. The system (1) according to any one of the preceding claims, wherein the gas supplying device (100) comprises at least two gas inlets (106,107,108,109) configured to allow gas into the toroid shaped chamber (101).

5. The system (1) according to claim 4, wherein the toroid shaped chamber (101) is divided into a plurality of compartments (120,121,122,123), wherein the at least two gas inlets (106,107,108,109) are configured to allow gas into each of the compartments (120,121,122,123).

6. The system (1) according to any one of the preceding claims, wherein the gas supplying device (100) comprises a pressure sensor configured to detect a pressure inside said toroid shaped chamber (101).

7. The system (1) according to claim 6, wherein the pressure sensor is configured to transmit the detected pressure to a control device, wherein the control device is configured to control the gas pressure within the toroid shaped chamber (101).

8. The system according to any one of the preceding claims, wherein the gas supplying device (100) is designed as a pipe segment of the longitudinal cylindrical fluid pipe (200) circumventing the radial diameter of the longitudinal cylindrical fluid pipe (200).

9. The system according to claim 8, wherein the inner surface (104) of the gas supplying device (100) is arranged flush with the inner surface (202) of the longitudinal cylindrical fluid pipe (200).

10. The system (1) according to claim 8 or 9, wherein a radial extension of the gas supplying device (100) is larger than the radial extension of the longitudinal cylindrical fluid pipe (200), and wherein the gas inlet (106,107,108,109) is arranged at the radial extension (112) of the gas supplying device (100) extending beyond the radial extension of the longitudinal cylindrical fluid pipe (200).

11. The system (1) according to any one of claims 8 to 10, wherein the gas supplying device (100) is attached to the longitudinal cylindrical fluid pipe (200) by bolts extending from the outer surface of the gas supplying device (100) into the outer surface of the longitudinal cylindrical fluid pipe (200).

12. The system (1) according to any one of claims 1 to 7, wherein the gas supplying device (100) is adjoining the turbulence inducing device (400) in the longitudinal direction of the longitudinal cylindrical fluid pipe (200) and circumventing the diameter of the turbulence inducing device (400) in the radial direction.

13. The system (1) according to claim 12, wherein the gas supplying device (100) is fixed to the turbulence inducing device (400) by brackets.

14. The system (1) according to any one of claims 1 to 7, wherein the turbulence inducing device (400) and the gas supplying device (100) is arranged inside an installation container (700) placed inside the longitudinal cylindrical fluid pipe (200), wherein the installation container (700) comprises at least a first cell (702) containing the turbulence inducing device (400) and a second cell (704) containing the gas supplying device (100), wherein the second cell (704) is arranged upstream the first cell (702) and wherein the first and second cell (702,704) are in fluid communication with each other and the longitudinal cylindrical fluid pipe (200).

15. A method for supplying gas bubbles (500) into a fluid (300) by use of a system (1) comprising a longitudinal cylindrical longitudinal cylindrical fluid pipe (200), a turbulence inducing device (400) arranged within the longitudinal cylindrical fluid pipe (200) for generating a turbulent flow of the fluid (300) and a gas supplying device (100) comprising an outer surface (102), an inner surface (104) having a cross sectional area smaller than the outer surface (102), wherein the outer and inner surfaces (102,104) encloses a toroid shaped chamber (101), a gas inlet (106) configured to allow gas communication into the toroid shaped chamber (101) and a membrane (110) arranged on the inner surface (104), the membrane (110) being configured to allow gas to pass from the toroid shaped chamber (101) into the fluid (300) as gas bubbles (500), wherein the gas supplying device (100) is arranged adjoining and upstream the turbulence inducing device (400) such that the turbulent flow of fluid (300) passes a cross-sectional area (600) enclosed by the membrane (110) when passing the turbulence inducing device (400) or immediately after exiting the turbulence inducing device (400), wherein the method involves the following steps: a) introducing a gas into the gas inlet (106) of the gas supplying device (100), b) introducing a flow of fluid (300) into the longitudinal cylindrical fluid pipe

(200), c) adjusting the gas pressure within the toroid shaped chamber (101) generating an overpressure relative to a pressure within the flow of fluid (300), d) routing the flow of fluid (300) through the turbulence inducing device (400) generating a turbulent flow characteristic within the flow of the fluid (300) e) routing the flow of fluid (300) through a cross-section (600) of the longitudinal cylindrical fluid pipe (200) enclosed by the membrane (110), and e) allowing the gas entering from the gas inlet (106) to pass from the toroid shaped chamber (101) via the membrane (110) into the fluid (300) as gas bubbles (500).

16. The method according to claim 15, wherein the gas is oxygen and the fluid is a water-based liquid such as sea water, brackish water, fresh water or waste water.

17. The method according to claim 15, wherein the gas is CO2 and the fluid is water-based liquid, such as waste water, potable water, process water or tunnel water.

18. The method according to claim 15, wherein the gas is an inert gas such as nitrogen or argon and the fluid is a water-based liquid such as sea water, wastewater, potable water or fresh water.