Device and Method for Generating Gas Bubbles in a Liquid

Abstract

The invention relates to a device for generating gas bubbles in a liquid in a container, including at least one rotatable hollow shaft arranged horizontally in at least one container; at least one gassing disc arranged vertically on the at least one hollow shaft; and at least one feed line for supplying at least one compressed gas to the interior of the at least one hollow shaft, said compressed gas being brought into the feed line and hollow shaft directly, without a liquid carrier.

Claims

1. A device for generating gas bubbles in a liquid in a container, wherein at least one rotatable hollow shaft is arranged horizontally in at least one container, wherein the at least one hollow shaft comprises at least one first hollow shaft with a diameter d.sub.3a and a second hollow shaft with a diameter d.sub.3b, and wherein d.sub.3a<d.sub.3b, such that the first hollow shaft is arranged inside the second hollow shaft; at least one gassing disc is arranged vertically on the at least one hollow shaft; and there is at least one feed line for supplying at least one compressed gas to the interior of the at least one rotatable hollow shaft, wherein the compressed gas is directly introduced into the feed line and the hollow shaft without a liquid carrier.

2. The device as claimed in claim 1, wherein the at least one first rotatable hollow shaft is composed of a gas-permeable material.

3. The device as claimed in claim 1, comprising at least two rotatable hollow shafts arranged parallel and horizontally offset with respect to each other, each of which has at least one gassing disc.

4. The device as claimed in claim 1, wherein at least two gassing discs are arranged on the at least one rotatable hollow shaft.

5. The device as claimed in claim 1, wherein between 10 and 100 gassing discs are arranged on the at least one rotatable hollow shaft.

6. The device as claimed in claim 1, wherein the at least one hollow shaft is rotatable at a rotation speed of between 10 and 250 rpm.

7. The device as claimed in claim 1, wherein the at least one compressed gas is selected from a group composed of air, CO.sub.2, N.sub.2, ozone, methane, or natural gas.

8. The device as claimed in claim 1, wherein a gas pressure in the at least one rotatable hollow shaft is between 1 and 5 bar.

9. The device as claimed in claim 1, wherein a ceramic gassing disc with an average pore size of between 0.05 m and 10 m is used as a gassing disc.

10. The device as claimed in claim 1, wherein at least one device for generating a pulse of the compressed gas is provided in the at least one feed line.

11. The device as claimed in claim 10, wherein the at least one device for generating a pulse in the compressed gas generates a pulse of the compressed gas with a frequency of between 5 and 15 Hz.

12. The device as claimed in claim 10, wherein the at least one device for generating a pulse is a fluidic oscillator, an automatic valve and/or a displacement compressor.

13. A method for generating gas bubbles in a liquid in a container using at least one device as claimed in claim 1, wherein the method comprises: introduction of a compressed gas into at least one feed line, wherein the compressed gas is directly brought into the at least one feed line without a liquid carrier; introduction of the compressed gas into the interior of the at least one horizontally arranged rotatable hollow shaft; wherein the at least one hollow shaft rotates at a rotation speed of between 10 and 250 rpm, and introduction of the compressed gas through at least one gassing disc vertically arranged on the horizontally rotating hollow shaft into the liquid with the production of gas bubbles.

14. The method as claimed in claim 13, wherein the bubbles produced in the liquid have a bubble size of between 1 m and 200 m.

15. The method as claimed in claims 13, wherein the gas flowing in the at least one feed line is subjected to pulsation at a frequency of between 5 and 15 Hz using at least one device for generating a pulse arranged in the at least one feed line.

16. A system for purification of a liquid comprising at least one container with a device for producing bubbles as claimed in claim 1, and at least one container in the form of a flotation cell for accommodating the liquid mixed with the bubbles having at least one filtration unit for separating components contained in the liquid.

17. A method for water purification using a system as claimed in claim 16, wherein the liquid comprises water.

18. The device of claim 1, wherein the at least one feed line is configured to supply the at least one compressed gas to the interior of the first hollow shaft.

19. The device of claim 7, wherein the gas-permeable material comprises a perforated material.

20. The device of claim 4, wherein at least three gassing discs are arranged on the at least one rotatable hollow shaft.

Description

[0058] The invention is explained in further detail below with reference to the figures by means of examples in the drawings. The figures are as follows:

[0059] FIG. 1A shows a first schematic side view of a device for producing gas bubbles in a liquid according to an embodiment,

[0060] FIG. 1B shows a second schematic side view of a device for producing gas bubbles in a liquid according to an embodiment,

[0061] FIG. 2A shows a schematic view of two hollow shafts arranged parallel and offset with respect to each other with a plurality of gassing discs according to a second embodiment;

[0062] FIG. 2B shows a schematic side view of the rotating gassing discs, and

[0063] FIG. 3 shows a schematic side view of a system for purification of a liquid comprising a device for producing gas bubbles.

[0064] The general structure of a first embodiment of the device according to the invention for producing gas bubbles is shown in FIG. 1A.

[0065] The side view of FIG. 1A shows a device 1 with a feed line 2 for feeding the compressed gas and a hollow shaft 3 through which the compressed gas is further introduced into the gassing discs 4.

[0066] In the embodiment shown in FIG. 1A, four circular gassing discs of a ceramic material are arranged on the hollow shaft. The ceramic discs are composed of aluminum oxide and have an outer diameter of 152 mm and an inner diameter of 25.5 mm. The membrane surface area is 0.036 m.sup.2, and the pore size of the gassing discs is in the range of 2 m. The gas is introduced from the hollow shaft 3 into a hollow cavity of the ceramic disc 4 and penetrates from the inside of the hollow cavity through the pores of the ceramic material into the liquid to be purified, which is provided around and above the hollow shaft having the gassing discs, forming microbubbles with a bubble size of approx. 45 to 50 m. The gassing discs 4 are arranged on the hollow shaft by means of stainless steel or plastic fastening elements. The distance of the gassing discs from one another can be set as desired.

[0067] At the end of the hollow shaft 3 opposite the gas feed line 2, a suitable device for moving the hollow shaft is provided. This device can be provided in the form of a motor that transfers the corresponding rotary movement via a plurality of gears to the hollow shaft.

[0068] The embodiment shown in FIG. 1B illustrates the structure of the hollow shaft 3. The latter is composed of two hollow shafts 3a, 3b lying inside one another: a hollow shaft of smaller diameter 3a that is arranged inside a second hollow shaft of larger diameter 3b. This principle makes it possible to achieve a highly uniform and symmetrical distribution of pressure inside the hollow shaft 3b of larger diameter. The ceramic discs 4 are thus symmetrically supplied with gas, and uniform bubble production in the medium to be gassed is achieved. The shafts 3a, 3b can be produced from metallic or nonmetallic materials.

[0069] The ceramic discs 4 are clamped onto the shaft in at least one clamping area, and at the same time sealed via this clamping using seals composed of any desired materials. Each of the at least one clamping areas is delimited by two end pieces 6.

[0070] Connecting pieces 5, which are composed of metallic or non-metallic materials and may be of varying dimensions, are used as spacers between the ceramic discs 4. It is essential that the entire apparatus composed of hollow shafts 3a, b, end pieces 6, connecting pieces 5, and ceramic discs 4 must rotate.

[0071] The drive 7 for rotational movement of the shaft can be located directly on the shaft, but can also be driven via various mechanical force deflection means, such as bevel gears or 90 reduction gearboxes. The drive 7 of the shaft can therefore be positioned on the one hand in a medium to be gassed, but on the other also outside of the medium to be gassed. However, the drive 7 can also be provided via any known type of drive (such as an electrical, hydraulic, or pneumatic drive).

[0072] The shaft 3a, b can be supported at least two positions, with various types of bearings being suitable for use, such as ball bearings, grooved ball bearings, needle bearings, and roller bearings. Gas introduction 2 into the rotating shaft must take place via at least one seal. The latter can be positioned inside or outside of the medium to be gassed. The drive 7 and gas introduction 2 into the shaft can be configured in any desired position on the shaft.

[0073] The view of FIG. 2A shows two hollow shafts, each having four gassing discs, which are arranged parallel and offset with respect to one another. The gassing discs on each of the hollow shafts move in the same direction and engage with one another because of the offset horizontal arrangement (FIG. 2B). Such an arrangement of two parallel hollow shafts with the corresponding gassing discs allows the production of a large number of gas microbubbles and thus a high surface area of gas bubbles available for the attachment of foreign matter such as, for example, organic components. Accordingly, a high specific surface area is available to which the hydrophobic solid particles from the liquid to be purified can attach themselves, thus allowing separation of the organic foreign matter from the liquid to be purified by means of flotation.

[0074] As described above in detail, the present device for producing gas bubbles can also comprise at least one fluidic oscillator that is provided in one of the gas feed lines 2. A gas bubble diameter of 45 to 50 m is ensured by producing oscillation of the gas at approx. 9 to 10 Hz. Accordingly, a bubble size of between 45 and 50 m is ensured in combination with the gassing discs arranged on the hollow shaft.

[0075] FIG. 4, in turn, shows a schematic view of a system 20 for purification of a liquid, more particularly water, which comprises at least one of the above embodiments of a device for producing gas bubbles. The side view of the system 20 in FIG. 4 shows a flocculation unit 10 into which the water to be purified and the flocculating agent have been introduced. After mixing of the water to be purified with the flocculating agent, for example using a stirrer, the mixture can be introduced from the flocculation unit 10 via a dividing wall into a further separate section or container 20, in which at least one hollow shaft 20a with four gassing discs according to the embodiment of FIG. 1 is provided.

[0076] In the present experimental method, wastewater that has been mixed with humic substances is used. In this case, the entire content of organic substances in the wastewater is simulated by humic substances, which also occur in nature due to normal biological decay. For flocculation of the humic substances contained in the water, iron and aluminum-containing substances containing trivalent ions are primarily suitable as precipitants. In the present case, an FeCl.sub.3 solution is used as a flocculating agent. After addition of the flocculating agent using a static mixer, flocculation of the humic acids contained in the wastewater takes place in the flocculation unit 10 by means of the flocculating agent FeCl.sub.3.

[0077] After passing through the flocculation unit 10, the wastewater mixed with FeCl.sub.3 from the flocculation unit 10 is introduced into the container 20 containing the gassing device composed of a hollow shaft with four gassing discs at a flow rate of 400-700 l/hr.

[0078] Air is injected via the gassing device 20a in the container 20, thus causing the direct formation of microbubbles in the introduced water mixed with a flocculating agent. The gassing discs or gassing plates of the gassing device rotate in the same direction at a rotation speed of 180 rpm, resulting in a phase shift of 180. The microbubbles formed attach themselves to the flakes to form flake-air bubble agglomerates, which are introduced in the further course of the method into the flotation cell 30 provided downstream. Due to attachment of the microbubbles to the flocculated organic components, the agglomerates thus formed rise in the flotation cell in the direction of the surface of the liquid present in the flotation cell 30 and form a solid layer on the surface of the water that is mechanically separated, for example using scrapers. The pre-purified water is located in the flotation cell 30 below this solid layer. The water pre-purified in this manner is withdrawn using a suitable pump by the filtration unit 40 arranged in the flotation cell 30 and is available for further treatment, such as, for example, further desalination processes. In order to prevent fouling of the surface of the filtration unit 40, air can be directly fed onto the surface of the filtration unit 40 via perforated hoses, thus mechanically removing deposits on the surface of the filtration unit 40.