FR2750889A1 - Device for injection of water into gas for use in fish farms - Google Patents

Abstract

Process for injecting gas into a flowing liquid comprises injecting it into a diffusion device (5) and emitting it though a perforated, elastic diffusion membrane (17) made of rubber, around which the gas moves in a spiral direction, so that it contacts a liquid stream. Also claimed is a device for carrying out the above process comprising a gas injection chamber (4) containing a cylindrical gas diffuser (5). An injection tube is provided and the diffusion device has perforations which allow the diffusion of very small bubbles. A component (3',8) gives the liquid stream a rotating movement.

Description

 The present invention relates to a method and a device for injecting a gas into a liquid, mainly air and / or oxygen in water, it is necessary to oxygenate the water used in particular in the field fish farming or for example in breeding tanks etc.

 There are narrow operational margins in intensive fish farming in fishponds (closed farming systems for hatching and fish farming); thus, all the elements of production must be adjusted in relation to each other to have the best possible environment and the best welfare of the fish. The quality of the environment created depends on several factors which, to a large extent, are linked.

In a closed farming system, there is a complex interaction between the following factors
- temperature
- the luminosity
- the density of the biomass
- the oxygen content
- water flow
- waste concentration
- food supply
- flow configuration and flow speed
The pattern of fish behavior in the biological environment is determined by these factors.

 The best possible water quality in the tanks is obtained by a correctly adjusted water flow and optimal flow configurations giving a regular diffusion of oxygen and food and the fastest possible elimination of waste through the out of the well.

 Objects installed in the tank have a negative impact on the flow configuration and the hydraulic configuration of the tank and reduce the water quality. If the object is used to disperse a gas in the water, it creates an upward flow in the water which further increases the negative effect. The impact depends on the size of the bubbles and the amount of gas used.

 The present invention will have a minimal negative impact on the hydraulics and the environment of the tank, since the gas which has not been diffused in the inlet device will be emitted with the water in the tank in the form of extremely small bubbles with correspondingly low upward force. The pores of the tube with fluid and gas emission slots, positioned vertically and distributed evenly along the depth of the water on the bottom of the tank, inject water and gas bubbles into the tank. approximately equal proportion and with the same dispensing pressure. This results in optimal hydraulics of the tank and an optimal environment in the tank.

 The prior art in fish farming involves the use of a hollow sintered body made of metal to oxygenate the total water flow. In such installations, this is carried out in connection with the injection of water under pressure by injecting oxygen into a sintered body made of metal, under a water pressure of 1 to 4 bars. The use of sintered bodies made of metal to disperse oxygen is not very effective since the gas bubbles produced in the flow of water are not small enough; therefore, the contact surface between gas and water is small. The use of sintered bodies made of metal in salt water often results in salt deposits in the sintered body made of metal with the result of reducing or stopping the dispersion of oxygen.

 German patent application No. 2 120 875 describes a method and a device for injecting a gas into a fluid, in which the gas is injected into a diffusion device in a downstream flow of liquid. 'downstream has a speed greater than the speed of ascent of the bubbles; the gas bubbles therefore follow the downstream flow of the liquid, to be emitted, for example at the bottom of the tank.

 U.S. Patent No. 5,138,595 describes the use of a perforated membrane to diffuse, for example a gas into a liquid. From FIGS. 8 to 10 of the patent, it appears that elastic membranes are arranged on the outside of the necessary device, the liquid to be treated dispersing through the device shown, then flowing upwards towards the outside of the device. made upward force caused by the presence of gas bubbles in the surrounding liquid.

 The embodiment shown in Figure 15 of the patent varies somewhat from what is described above in that the necessary device has an inner perforated membrane which extends inwardly from the downstream flow some cash.

 U.S. Patent No. 5,234,632 shows a device for injecting a gas into a liquid by pushing a gas through a perforated membrane that surrounds a pipe. It is suggested that an advantage of this device is that the pipe is opened so that liquid can enter the pipe, thereby canceling the upward force in the pipe. An opening is arranged at one end in order to avoid the formation of dead zones having no exchange of liquid.

 The document EP-A-546 335 represents a device which basically corresponds to that of the US patent No. 5,138,595 mentioned above.

 U.S. Patent No. 4,717,515 shows a device for injecting gas into a liquid by emitting the gas through a porous wall, and causing the liquid to be preferably swept laminarly through the wall for the purpose to remove the gas bubbles in the nascent state.

 British Patent No. 1,362,789 is known a device for injecting gas into a liquid, in which the liquid is injected into the upper part of a vertical pipe in which is placed another coaxial pipe to supply the gas. bottom of the coaxial pipe is expanded and gives the shape of a "torpedo", so the liquid flowing down into the space between the outer pipe and the coaxial pipe causes a tubular flow downstream. lower part of the expanded pipe is provided with a conically formed wire mesh through which the injected gas is pushed in the form of bubbles transported by the downstream flow, said flow being released from the lower outlet open the liquid injection pipe near the bottom of the tank, so the liquid flow rate decreases when the gas is injected.

 Also for this latter device, the speed downstream of the liquid flow will be greater than the speed of ascent of the bubbles formed; the bubbles will thus be transported downstream by the flow of liquid.

 The present device is linked to the device described in said British Patent No. 1,362,789 in the sense that in a preferred embodiment the gas injection pipe is arranged coaxially inside a gas injection enclosure, and in that the correct gas injection device is designed as a "torpedo", giving the injected water a speed gradient as it passes between the "torpedo" and the gas injection enclosure. The gas bubbles formed are transported by the flow of water downstream to the outlet opening of the gas injection enclosure.

 The present device varies from what is known by the British patent mentioned above, in the sense that the injected gas is not emitted through a trellis of wires, but through a diffuser having the form of a membrane constituted of an elastic material, such as rubber, arranged around a gas diffusion / channeling device which constitutes the central part of the "torpedo". Thus, the gas is injected when the speed of the liquid is at its maximum, a characteristic which contributes to the dispersion of the bubbles in the flow of liquid.

 The rubber membrane is perforated with a multiplicity of openings which are made in the rubber using suitable needles.

 When not exposed to an internal gas pressure, the elastic nature of the membrane causes it to shrink, sealingly sealing the perforations so that liquids cannot permeate it, so that, for example, salt water cannot pass through or plug the perforations as is the case with sintered metal.

 Due to the multiplicity of perforations in the elastic membrane and the high speed of the water on the membrane, a gas / oxygen supplied to the outer surface of the membrane is separated from said membrane in the form of gas bubbles. microscopic in size which is necessary in order to obtain a high degree of surface contact between the liquid and the gas and therefore good absorption of the gas in the liquid. The rate of ascent of the microscopic gas bubbles is low; therefore, the contact period and the contact surface between the gas and the liquid is considerable, and this results in better absorption.

The present invention will now be described with reference to the accompanying drawings, in which
FIG. 1 is a schematic view of a first device according to the present invention,
FIG. 2 is a schematic view of a diffusion device according to the present invention,
FIG. 3 is a view on a larger scale of a detail concerning the gas injection enclosure represented diagrammatically in FIG. 1,
FIG. 4 represents the outline of the device in which the liquid inlet is arranged tangentially in order to give the liquid a rotary movement,
FIG. 5 is a cross-sectional view of a rubber membrane used in the diffuser,
FIG. 6 is a top view, partially in cross section, of the central part,
FIG. 7 represents the central part provided with tracks of the profile for channeling the gas / oxygen, the membrane being arranged around said part,
- Figure 8 shows the results obtained in the experiments concerned.

 Referring to Figure 1, an embodiment 1 according to the present invention is shown. Embodiment 1 is shown in the preferred orientation, that is, vertical; however, it is obvious that the longitudinal axis of embodiment 1 can form any angle with the vertical axis if the vertical orientation is not possible or is not practical. The embodiment will be described and explained below with reference to the preferred vertical orientation. Embodiment 1 consists of a gas injection pipe 2, a liquid injection pipe 3 for injecting water or a liquid to be enriched with gas, which is in communication with an enclosure d gas injection 4 in which is arranged a diffuser 5. Preferably, the gas injection enclosure is located in a slotted pipe 6 provided with slits 7 to release the liquid saturated with gas.

 Referring to Figure 2, the diffuser according to the present invention is shown in more detail.

 The diffuser 5 consists of an upper conical part 9, a central part 10 provided with a diffusion membrane 17 and a lower conical part 11. The gas injection pipe 2 is preferably centered using a rotary and centering fin 8 which rotates the downstream flow so that the downstream liquid flow rotates around the central part 10 provided with the diffusion membrane 17 when the liquid is transported to downstream through the gas injection enclosure 4.

 Figure 3 shows in more detail the gas injection enclosure 4, provided with a rotating and centering fin 12, as well as a recycling device 13, the purpose of which will be described later.

 FIG. 4 represents the injection pipe 3 arranged tangentially in order to give the liquid a rotary movement. This tangential arrangement of the injection pipe 3 can be used in addition to the rotary and centering fin 8, or in its place.

 Figure 5 is a cross section of the elastic, perforated membrane. At its upper end, the membrane has an upper rim 18, and a lower rim 18 ', arranged around the upper and lower part of the central part 10 to close them in a leaktight manner.

 Figure 6 is a cross section of the central portion 10 made of a suitable solid material, arranged with two end pieces 19 and 19 ', and having an opening 14 for arranging the injection pipe 2 for the gas. In the lower part of the central part, an opening 14 'is arranged to adapt the lower conical part 11, in which the gas injection pipe 2 is fixed. Through openings to release the gas injected through the central part 10 are indicated by the reference numeral 15.

 Figure 7 is a side view of the central part 10. Around the outer perimeter of the central part 10, a spiral-shaped slot 16 is wound which will channel the gas emitted through the openings 15 (Figure 6), so that said gas largely passes through the spiral-shaped slot 16 when the diffusion membrane (shown diagrammatically in FIG. 5) is arranged as a seal around the central part 10.

 The diffusion membrane has a large number of perforations ranging from 10 to 50 perforations per cm2, from which the injected gas is separated in the form of microscopic bubbles when gas / oxygen is injected through the injection pipe gas 2. When the gas injection is cut, the perforations are sealed, thereby preventing, for example, salt water from penetrating through said perforations and clogging them due to the deposit of salt .

 Below, the mode of operation of the new device will be explained in more detail, with reference to Figure 1.

 Liquid / water is injected through the pipe 3, flows down through the gas injection enclosure 4 and exits through the openings 7. When the water / liquid passes through the rotary vane and centering 8 (FIG. 2) and / or is injected tangentially, the water is put into rotary movement, rotating around the difflision device 5. At the level of the rotary and centering fin 12, the rotary movement of the The water is amplified and the water mainly flows through the slotted pipe 6 and exits through the openings 7.

 By maintaining the rotary movement or even increasing the speed of rotation, the flow of water is caused in the slotted pipe 6 to behave approximately as a flow of liquid in a hydrocyclone; that is, a slight phase of liquid and microscopic bubbles which is concentrated and flows downstream along a central line through embodiment 1. Most of the In any case, microscopic bubbles are brought down to the bottom of the slotted pipe before the water flow changes direction, rises and then leaves through the openings 7. In this way, the gas bubbles are kept longer in embodiment 1 and the absorption of gas in the liquid is improved. Naturally, this absorption continues when the microscopic bubbles and the liquid saturated with gas leave the device through the openings 7.

 The slotted pipe 6 having openings 7 is advantageous, since the direction of the outgoing gas can be established so as to obtain a desirable configuration of movement in the surrounding liquid, for example a circular movement in a circular well. The slotted pipe 6 having openings 7 thus represents a preferred embodiment of the present device.

 In other applications, for example for injecting gas into a liquid flowing out of a pipe, the lower end of the slotted pipe can be opened, or the slotted pipe can be completely eliminated so that the gas is only injected through the diffusion device installed in the gas injection enclosure 4. The high efficiency of the gas injection results in adequate gas saturation in the liquid flow.

 The dimensions of the gas injection enclosure 4 and the diameter of the diffusion device 5 are preferably such that the speed of the water along the membrane is 2 to 10 times greater than the average speed towards the downstream beyond the diffusion device 5. The flow speed along the membrane is preferably at least 1 m / s.

 When gas / oxygen is injected into the injection pipe 2, the injected gas / oxygen is pushed through the membrane of the diffusion device 5 and is separated in the form of microscopic bubbles. Due to the high speed of the water, they are transported downward through the gas injection enclosure 4, and the water saturated with gas is supplied to the slotted pipe 6 and emitted through the openings 7.

 Any larger gas bubble caused by the coalescence of microscopic bubbles rising through the gas injection enclosure 4 is extracted through recycling openings 13 (see also Figure 3) due to the lower pressure existing in the gas injection enclosure 4 caused by the high speed of the liquid, and is dispersed in the flow of liquid at high speed and emitted through the slotted pipe 6.

 The usefulness of the new device was tested in a commercial fish farming installation in octagonal breeding tanks with a height of 3.5 m and a tank volume of 321 m3. The water in the tank was enriched with oxygen using a device as shown in Figure 1.

 The oxygen injection device was installed in September 1995 in two of the facility's 14 breeding tanks (tanks 9 and 10). The installation was adapted to the existing supply pipes (pipes to slots).

The testing process involved measurements in tank # 9 at regular intervals over a period of approximately 1.5 months to establish the following
- Oxygen level in raw water (inlet water)
- Oxygen dosage (injected oxygen)
- Oxygen level in the outlet water (outlet tank)
- Water flow
- Water temperature
- Speed of spinning in the tank / speed of swimming of the fish
- Salinity
- pH
- Total gas pressure saturation in raw water
- CO2 in the tank and in the outlet water
- Ammonia in the tank and in the outlet water
- Biomass density (kg of biomass per m3 of water)
- Average weight of biomass (average weight of fish)
- Quantity of nourishing materials, kg.

Oxygen consumption compared to the revised oxygen consumption tables for salmon published in 1994 by SINTEF, Foundation for
Scientific and Industrial Research of Nonvegian University for Science and
Technology (mg of O2 per min. Per kg of fish), which take into account temperature, salinity, average weight and swimming speed.

 The oxygen consumption tables give average values over 24 hours, regardless of variations over the 24 hour period caused by the diet. The consumption in 2 is at its maximum at the time of feeding and during the following three or four hours.

 The oxygen yield (injected oxygen / oxygen used) for tank no. 9 is calculated for corresponding oxygen values of the raw water and the outlet water in the tank and outside The measurements were taken approximately one hour after feeding and the values of the tables for the oxygen consumption of the fish are not adjusted to the increased consumption.

As a result, the actual yield is somewhat higher than indicated by the appended results.

 Figure 8 shows that yields in the range of 91 to 94 percent were obtained using the new device, compared to yields of 48 to 59 percent for existing gas injection devices (for tanks Nos. 8 and 12).

 The results indicate that it is advantageous to inject gas having a maximum oxygen purity, preferably greater than 99.5% by volume of O 2.

 The present device is clearly more effective than any other device commonly used.

 Another use of the diffusion device 5 in fish farming is for injecting carbon dioxide as a gas with the intention of stunning the fish before killing it.

 Particular attention is paid to the use of the present process and device in the oxygen enrichment of water for fish farming; However, there are obviously other applications of the present invention, for example in the treatment industries for enriching liquids with gases, for example in the manufacture of chemical pulps, in water purification plants, in chlorination. / ozonation of water etc., or for chemical reactions in which a gas must react with a component present in a liquid, for example the oxidation of hydrogen sulfide to elemental sulfur.

 Although the diffusion device comprising the central part provided with the diffusion membrane is shown provided with an upper conical part 9 and a lower conical part 11, these latter parts may have other geometrical configurations than those represented on the Figure 2; they can for example be rounded or have other shapes which are suitable for the desired flow configuration for the liquid. The central part 10, which is designed to support the diffusion membrane as well as to disperse the injected gas, is shown in the embodiment as consisting of a cylinder having a spiral-shaped slot intended to ensure a regular gas discharge per unit area of the diffusion membrane when said membrane is arranged vertically in the gas injection enclosure 4, with the aim of compensating for the difference in hydraulic pressure existing between the upper and lower part of the diffusion membrane.

 If the diffusion membrane is to be arranged in a horizontal pipe through which a liquid flow is brought, the central part can be designed as a pipe with perforations or as a rigid mesh with an appropriate mesh width, the effect of pressure equalization obtained by a central part provided with spiral-shaped slots wound on the external surface is not necessary.

 All elements of the new device can be made from a suitable plastic, metal, metal alloy or combinations thereof. Those skilled in the art will be able to select the material which is best suited to the application. The diffusion membrane must be made from an elastic material, preferably an elastic rubber material, selected from a suitable plastic or rubber.

Claims (14)

 1. Method for injecting gas into a flowing liquid, said gas being injected into a diffusion device (5) after which the flow of liquid enriched in gas is brought to a consumption location when the gas injected into the device diffusion is emitted through an elastic diffusion membrane (17) made of rubber provided with a multiplicity of perforations,  characterized in that the injected liquid is caused to rotate in a spiral movement around the diffusion membrane (17).  2. Method according to claim 1, characterized in that the speed of the liquid is maintained at a minimum of 1 m / s along the membrane (17).  3. Method according to claim 1, characterized in that the injected liquid is water, and that the gas injection preferably contains at least 99.5% by volume of O2.  4. Device for implementing the method according to claim 1 for injecting gas into a flowing liquid, said device comprising a gas injection enclosure (4), in which is arranged a longitudinal gas diffusion device (5 ), preferably having a cylindrical shape, characterized in that an injection pipe (2) is provided for injecting gas into the diffusion device (5), that the diffusion device (5) comprises an elastic membrane rubber diffusion (17), said membrane being provided with a multiplicity of perforations to emit very fine bubbles, and upstream of said diffusion device, a device (3 ′, 8) is arranged to give the flow of liquid a rotational movement.  5. Device according to claim 4, characterized in that the device (3 ') consists of an injection pipe (4) mounted tangentially on the gas injection enclosure (3).  6. Device according to claim 4, characterized in that the device (8) comprises a rotation and centering fin.  7. Device according to any one of claims 4 to 6, characterized in that it comprises downstream of the diffusion device (5), a rotary and centering fin (12) to maintain the speed of rotation of the water .  8. Device according to any one of claims 4 to 7, characterized in that the gas injection enclosure (4) is in hydraulic communication with a slotted pipe (6) mounted downstream, provided with emission openings (7) for the gas-enriched liquid, and in that said gas injection enclosure (4) near the upper end of the slotted pipe (6) is provided with at least one opening (13) communicating with said slotted pipe (6).  9. Diffusion device (5) used in the device according to any one of claims 4 to 8, comprising a membrane, perforated, elastic, rubber, preferably cylindrical, characterized in that it comprises a device for dispersing gas (10) comprising a hollow cylindrical element (20), provided with an opening (14) for receiving a gas injection pipe (2) for injecting gas towards the internal part of the element (20), thus that outlet openings (15) arranged at the other end of the element (20) for emitting gas towards the diffusion membrane (17) arranged around said element (20) and said enveloping diffusion membrane (17).  10. Diffusion device according to claim 9, characterized in that the external surface of the element (20) is provided with at least one channel (16) for dispersing the gas between said element (20) and said diffusion membrane (17).  11. Diffusion device according to claim 9, characterized in that the channels (16) are hollowed out on the external surface of the element (20), extending in the form of a spiral from one end of said element towards the other.  12. Diffusion device according to claim 9 or 11, characterized in that the element (20) constitutes a sealed central part situated between a preferably conical part (9), part (9) through which the injection pipe gas is supplied, and a second conical part (11).  13. Use of the device according to any one of claims 4 to 8 for enriching with oxygen the water sent to a tank for breeding aquatic animals.  14. Use of the device according to any one of claims 4 to 8 for the treatment of aquatic animals in a breeding tank by enriching the water injected into the breeding tank using a different gas oxygen.