AU710845B2 - Device for mixing gas in a liquid - Google Patents

Description

WO 97/32661 PCT/N096/00047 DEVICE FOR MIXING GAS IN A LIQUID The present invention concerns a device for adding a gas to a liquid, particularly for use in connection with fish rearing tanks and in cleaning technique, as stated in the introductory part of Claim 1. The invention is particularly directed to use in rearing tanks.

Adding gas to a liquid may be done for many reasons, such as to add anaesthetic gas when slaughtering fish in rearing tanks, for floatation basins in cleaning plants, adding oxygen to biofilters or for oxygenating the water in a rearing tank (tanks and large ponds). Such tasks may today be performed with different equipment, such as diffusors, ejector pumps, 0 2 -columns, pond airing and deep shaft systems.

Especially in land-based fish farming, many different devices for reducing water consumption have lately emerged, such as a bridge filter with diffusor. In order to maintain the correct hydraulic relationship in the tanks, large amounts of energy are necessary when using the mammoth pump principle (blowing in air for moving the water). Creating optimal hydraulic in a large tank by means of this technology is practically impossible.

US 4 844 843 discloses a device for adding gas to a liquid, at the same time as they are mixed. The device comprises an elongated tube for supply of liquid and gas, and a stirring mechanism inthe form of a motor driven propeller arranged by the outlet of the tube, for providing the liquid and the gas to be well mixed and that the mixture is driven out in the liquid reservoir. If increasing the gas supply to the liquid reservoir is desirable, the speed of the propeller is increased. However, an increase in the amount of gas added to the liquid in this known device, will have the side effect of changing the current relationship. By increasing the speed of the propeller to supply more gas to the liquid, also the current in the reservoir will also increase.

It is thus an object of present invention to provide a device for adding a gas to a liquid, where the amount of gas and the basin hydraulics (the current speed) can be controlled independently of each other. The jet should be controlled as to amount, pressure and direction, and thus give optimum tank hydraulics in different operating situations.

The object of the invention is achieved with features as stated in the characterizing part of Claim 1. Further features are clear from the accompanying dependent claims.

WO 97/32661 PCT/N096/00047 2 In the following the invention should be described further by means of an example of embodiments and with reference to the enclosed drawings, where Fig. 1 shows a longitudinal section view of a first, preferred embodiment of the present invention, Fig. 2 shows a longitudinal section view of the venturi pipe and the nozzle pipe from the embodiment of Fig. 1, and Fig. 3 shows a longitudinal section view of a second embodiment of the present invention.

In Fig. I is shown a device according to the present invention, generally denoted 1.

The device 1 comprises a pump 2 having a motor 3 connected to an operation shaft 4. At the outer end of the operating shaft 4 is connected a pump vane 5. The operating shaft 4 is arranged within a cylindrical housing 6, which in operation is partly submerged in water as shown in the drawing with an imagined water line. In the house 6 is a first inlet opening 8 for air situated over the water line, and under the water line is situated a second inlet opening 9 for water.

In the centre of housing 6, surrounding the operation axle 4, is provided a gas tube 7, which is best illustrated in Fig. 2. The gas tube 4 is at its upper end provided with an inlet opening for air and is at its lower end terminated in a nozzle 11, having openings 12 distributed around the circumference of the nozzle 11. The nozzle 11 with the openings 12 is surrounded with a venturi 13 connected to a pump housing 14. The gas tube 7 can be controlled in the longitudinal direction of housing 6, by means of a controlling means 15. The controlling means 15 comprises an adjustment bracket 16 connected to housing 6, and which contains a mounting bracket 18. The mounting bracket 18 is connected to a block 20 situated within housing 6. Block 20 is mounted to an upper holding plate 21 connected to the glass tube 7, and movable relative to housing 6. By loosening the holding screw 19 and rotating an adjustment screw 17, the upper holding plate 21 can move the glass tube 7, as the holding screw 19 slides in a slit (not shown) on the wall of the housing 6. Thus, the glass tube can be moved up and down in the housing 6, as it slides in a lower holding plate 22, mounted to the inner wall of the housing 6.

Peripherally on the pump vane 5 is situated ajet tube 23, which is bent 90,-to eltend the substantial of its length parallel with the housing 6. The jet tube 23 can also be WO 97/32661 PCT/N096/00047 3 positioned in other ways, for example when rearing flat fish, the jet tube 23 should be situated horizontally along the bottom of the rearing tank. Jet orifices 24 are situated along the jet tube 23, in its longitudinal direction. Preferably, the jet orifices have closure/controlling means (not shown), so that they can be individually closed, or controlled, respectively. At the end of the jet tube 23, which is above the water surface, is situated a pressure controller 25, which functions as a pressure indicator and alarm transmitter.

During operation, the motor 3 will drive the operating axle 4 and thus the pump vane into rotation. Water will be drawn in from the second inlet opening 9 into the pump housing, and ejected out through the jet orifices 24 of the jet tube 23. Additionally, air that a conventional pump would have rejected as false air, is drawn in through the first inlet opening 8, and sucked through the openings 12 of the nozzle 11 of the nozzle tube 7.

The air from the nozzle openings 12 is mixed into the water, in the form of bubbles.

These bubbles are expanded in the underpressure created through the venturi 13. When water has passed the venturi 13, the pump vane will, by whipping, cause the bubbles to divide in a plurality of smaller bubbles, that will be better distributed in the water leaving the jet tube 23.

If the position of the jet tube 7 is changed in relation to the venturi 13, larger, resp.

smaller amounts of water/air will be drawn in and mixed in the pump vane 14. This effect is achieved by the venturi effect is changed and the cross section of the water inlet is changed and thus the water velocity in the venturi and the amount of water in the pump housing 14 is thereby reduced. If changing the flow velocity in the tank is desirable, this may be achieved by changing the velocity of the pump vane 5. This can also be achieved by changing the cross section of the water inlet via the position of the nozzle 11 in the venturi 13. The effect of mixed gas and/or the flow velocity can be increased or decreased, by changing the cross section of the opening and number of jet openings 24 that is open on the jet tube 23. This enables the same pump to be used over a large range to give better agitation, for fish of different size (of rearing tanks), and by flotation of particles of different size (by cleaning plants).

In fig. 3 is shown a second example of an embodiment of the present invention. Here, air from the inlet opening 8 is not only sucked in by the pump vane 5, but also pumped WO 97/32661 PCT/N096/00047 4 in by a multiple step pump 27. In addition, the device is provided with a float 26, to ensure correct operation level in the liquid.

Controlling the position of the nozzle 11 in relation to the venturi 13, and the velocity of the pump vane 5 can also be controlled automatically. This can be performed by means of electrical and/or hydraulic means, based on the background of desired flow velocity flow relations and 0 2 -concentration.

A person skilled in the art will also see that other embodiments are possible within the scope of the invention. For example, the motor can be constructed horizontal and situated below the water surface, having a short axle to the pump vane. In such an embodiment the thermal energy of the motor is supplied to the water of the tank.

Claims (7)

1. A device for adding a gas to a liquid, including an elongated housing that is submersible in the liquid, said housing having a first inlet opening for gas, and a second inlet opening for liquid, a gas tube is situated in the housing, which at its first end communicates with the first inlet opening for gas, and an axle that at its first end is connected to a motor, and at its second end is provided with a pump vane, and a mixture of gas and liquid is discharged out in the vicinity of the pump vane, characterized by the gas tube at its second end is equipped with a nozzle with nozzle openings, wherein the nozzle is situated in a venturi, and that the gas tube is controllable in the longitudinal direction by means of controlling means, so that the position of the nozzle in relation to the venturi can be changed.

2. Device according to Claim 1, characterized by a gas pump is situated in the housing, which pumps gas in the gas tube.

3. Device according to Claim 1 or 2, to' characterized by the controlling means includes an adjustment screw that by rotation is adapted to move the t gas tube and a holding screw adapted for holding the gas tube in desired position, adjusted by the adjustment e* screw.

4. Device according to any one of Claims 1 to 3, characterized by a jet tube is arranged outside the pump e vane, which is equipped with jet openings. t 30

5. Device according to any one of Claims 1 to 4, characterized by the size of the jet openings can be controlled individually.

6. Device according to any one of Claims 1 to 0: characterized by the jet openings is arranged for 0* 35 individually closure, and opening, respectively.

7. A device for adding a gas to a liquid substantially as herein described with reference to the Figures.