WO1997019747A1

WO1997019747A1 - A device for entraining a gas into a liquid

Info

Publication number: WO1997019747A1
Application number: PCT/AU1996/000755
Authority: WO
Inventors: Erich Rudolf Hohne
Original assignee: Burns Philp Food Holdings Pty. Ltd.
Priority date: 1995-11-27
Filing date: 1996-11-25
Publication date: 1997-06-05
Also published as: AUPN683795A0

Abstract

An ejector device that can effectively entrain a gas, such as air or oxygen, into a liquid is described. The ejector comprises a liquid nozzle having a functionally elongate outlet bounded on each side by a gas nozzle also having a functionally elongate nozzle outlet. The nozzles are positioned, in use, such that gas will be entrained between the liquid stream exiting from the liquid nozzle outlet and a body of liquid in the container. A method for entraining a gas, such as air, at good volume capacity into a container, such as a yeast fermentation vessel, is also described.

Description

A Device for Entraining a Gas into a Liquid Field of the Invention

The present invention relates to a device for distributing a first fluid, such as a gas, into a second fluid, such as a liquid. In particular, the invention relates to an ejector device for entraining gas into a liquid stream and achieving an intensive mixing of the gas and liquid. Background of the Invention

The use of aeration and agitation is of great importance in aerobic waste treatment and industrial fermentation processes. Many different devices have been and are employed for the introduction and distribution of a gas, such as air, into a liquid.

The efficiency of gas distribution devices depends to a large extent on how finely the gas is distributed into the liquid. It is desirable, therefore, to have gas bubbles of small diameter which increases the available interfacial area between the gas and the liquid which in turn increases the rate of solution of gas into the liquid, which in the case of air is known as the oxygen transfer potential. The movement of the individual bubbles through the liquid and the movement on the surface of each bubble are also of importance. Agitation of the liquid which serves to create turbulence in the liquid is also beneficial. Such agitation serves to chop up a gas stream entering the liquid into small bubbles and also desirably delays the normal escape of the bubbles from the liquid thereby lengthening the time of contact between the gas and the liquid. Turbulence also imposes shear forces on the bubbles facilitating dissolution of the gas in the liquid.

While the efficiency of a gas distribution device is largely dependent on how finely a gas is distributed in the liquid and the amount of turbulence, it is also important that a sufficient volume of gas is introduced into the liquid to satisfy the gas consumption requirements of the industrial process. For example, in a yeast fermentation process a sufficient volume of air must be introduced to satisfy the oxygen consumption requirements of the growing yeast cells.

In the light of the above requirements, techniques for increasing the rate of gas absorption into a liquid have included two basic types of devices. firstly, those devices that each individually include a large number of gas outlets aiming for an advantageous physical gas distribution and. secondly, those with one or only a limited number of gas outlets that rely primarily on turbulent mixing derived from the conversion of kinetic energy. Known devices of the first type include gas spargers commonly used in the yeast fermentation industry in which air is pumped in through a plurality of perforated pipes, the perforations leading to the formation of fine air streams and subsequently bubbles.

Devices of the second type include conventional venturi-type nozzles. Conventional venturi-type nozzles create a low pressure zone with the aid of a high velocity liquid stream which is initially circular in cross- section. The gas is introduced into the low pressure zone and turbulently entrained into the liquid stream. While providing excellent gas distribution in a liquid, conventional venturi-type nozzles have a very low gas volume capacity. For example, the oxygen transfer capacity of a conventional venturi-type nozzle with an acceptable efficiency is only of the order of 1.0 - 1.5 kg of oxygen per device. Attempts have been made to scale-up venturi aerators beyond their typical nozzle outlet diameters of 2-8 mm, however, no significant improvements have been made. As a result, venturi-type nozzles have not found application in processes having a high gas demand as a prohibitive number of individual venturi-type nozzles would need to be employed.

The problem of venturi-type nozzles has been addressed to a limited extent by providing rotating venturi or ejector devices which are also an example of the second type of device. These devices still have a limited gas volume capacity and additionally have the disadvantages of expense, maintenance and difficulty of cleaning inherent in such moving systems.

Given the above, it would be desirable to have a device for distributing a gas into a liquid that combined the excellent distribution properties of a conventional venturi-type nozzle while having a high gas volume capacity. Summary of the Invention

According to a first aspect, the present invention consists in an ejector device for entraining a gas into a liquid comprising a liquid nozzle, having a functionally elongate liquid nozzle outlet, the liquid nozzle being bounded on at least one side by a gas nozzle having a functionally elongate gas nozzle outlet. The liquid and gas nozzles are preferably positioned in a container for the liquid such that, in use, gas exiting from the gas nozzle will be entrained between a liquid stream exiting the liquid nozzle and the liquid in the container. By functionally elongate, the liquid and gas nozzle outlets are taken to include a situation where the outlets each comprise a single opening or a situation where the outlets each comprise a plurality of openings that function together as if a single opening.

In a preferred embodiment, the liquid nozzle outlet is rectangular with the length to width ratio of the nozzle outlet being at least 5 :1, more preferably 10:1 and most preferably at least 100:1. The width of the liquid nozzle outlet is preferably 2-8 mm and more preferably 2-3 mm.

The velocity of the liquid stream is preferably at least three times, more preferably about four times, the velocity of the gas exiting the gas nozzle. Preferably, the velocity of the liquid stream is at least 15m s, more preferably at least 20m/s, while that of the gas is at least 3m/s, more preferably about 5 m/s.

The gas can be air and the oxygen transfer potential of the device, when the gas is air, is preferably at least 5, more preferably at least 50. most preferably at least 75 kilograms of oxygen/hour.

In one embodiment of the invention the elongate liquid nozzle is bounded on each side by a gas nozzle. The, or each, gas nozzle is preferably substantially the same length as the liquid nozzle. The. or each, gas nozzle outlet preferably has a width at least that of the liquid nozzle outlet, and preferably at least five times that width. The ejector device can be arranged so that the liquid stream exits the liquid nozzle in a substantially horizontal plane, a substantially vertical plane, or at an angle to the vertical plane. If the liquid nozzle is arranged so that the liquid stream exits in a substantially horizontal plane, and if there is only a single gas nozzle, it is preferred that the gas nozzle is positioned beneath the liquid nozzle. The liquid and gas nozzle outlets are each preferably linear. Alternatively, the outlets could be arcuate or even circular.

The ejector device may be constructed as a venturi to create a low pressure zone adjacent to the, or each, gas nozzle outlet. In this case it may be possible to rely upon gas being drawn into the liquid container by venturi action. It is however, more preferred to pump the gas through the gas nozzle.

Preferably, a mixing chamber of substantially rectangular cross- sectional shape is positioned over or proximate the nozzle outlets and adapted to facilitate mixing of the body of liquid in the container with the gas-entrained liquid exiting the nozzles.

In another aspect the present invention consists in a fermenter including at least one ejector device of the first aspect of the present invention. In one embodiment of this other aspect, the fermenter comprises a vessel for a liquid, the vessel having a base and a plurality of ejector devices according to the first aspect of the present invention being positioned adjacent the base such that the flow of gas into the vessel can rise through the liquid in the vessel. In a preferred embodiment of the further aspect, the gas is preferably air which enters the ejector devices through an air inlet means.

In a preferred embodiment, the liquid is preferably drawn out of the vessel and returned back through a liquid inlet means of the ejector devices. The liquid can be drawn from the vessel by an appropriate recirculating means.

Where the ejector devices in the fermenter operate on a venturi action, the flow of liquid through each ejector device entrains the air from the air inlet means into the liquid stream.

In yet a further aspect, the present invention consists in a method for entraining a gas into a liquid comprising ejecting a liquid stream through an ejector device according to the first aspect of the present invention such thai the gas exiting from the gas nozzle is entrained between the liquid stream exiting from the liquid nozzle and the liquid.

In a preferred embodiment of this further aspect, the gas is air which is aerating liquid in a yeast fermentation vessel.

Brief Description of the Drawings

Hereinafter given by way of example only, preferred embodiments of the invention are described with reference to the accompanying drawings, in which: Fig. 1 is a simplified cross-sectional view of an embodiment of the ejector device according to the present invention; Fig. la is a further cross-sectional view of the ejector device of Fig. 1 depicting the placement of a deflector at the outlet of the mixing chamber; Fig. 2 is a vertical cross-sectional view of one type of fermentation vessel having the ejector device of Fig. 1 located therein; Fig. 3 is a horizontal sectional view of the fermentation vessel of

Figure 2;

Fig. 4 is a vertical sectional view of the lower portion of another fermentation vessel having a plurality of the ejector devices of Fig. 1 located therein; and Fig. 5 is a horizontal sectional view of the fermentation vessel of Fig.

4. Preferred Modes of Carrying out the Invention

One embodiment of a typical yeast fermentation vessel which was modified by the applicant to allow testing of the present invention is generally depicted as 10 in Figs. 2 and 3. The vessel 10 is 6.0m in diameter and has a side wall 14 and a top 15, represents one of a number of different types of fermenter used by the applicant.

Regularly spaced proximate the lower end of the vessel 10 are a plurality of aeration tubes 11 disposed each side of a central air supply pipe 12, which in turn is fed from an air supply pipe 13 connected to a source of compressed air. The aeration tubes 11 each have a plurality of perforations through which air is bubbled into the vessel 10. The air bubbles serve to both aerate and agitate the yeast culture in the vessel 10 with the air serving to satisfy the oxygen consumption requirements of the yeast cells. The disposition of the aeration tubes 11 in the vessel 10 represents a typical aeration arrangement known in the prior art.

To allow insertion of ejectors according to the present invention into the vessel 10 for testing, the vessel 10 was modified by the removal of ten aeration tubes Ila, depicted in phantom in Fig. 3. In the place of the removed aeration tubes Ila, two ejector devices, generally depicted as 20, were mounted in a horizontal orientation in the vessel 10.

As is best depicted in Fig. 1, each ejector device 20 has a substantially cylindrical liquid chamber 21a surrounded by a substantially annular air chamber 28. Liquid is fed into the liquid chamber 21a from liquid supply pipe 21 (see Fig. 2) which in turn is attached to an outlet of a pump 23 which draws liquid from the vessel 10 through pipe 24. The air chamber 28 is fed by air-feeding pipe 22a (see Fig. 2) which interconnects through a T-joint 29 with an air supply pipe 22. The air supply pipe 22 is connected into and draws air from the air supply pipe 13 described above. The flow of liquid into the liquid chamber 21a moves through the opening 27 and out the rectangular liquid nozzle slot 23. The passage of the liquid through the liquid nozzle slot 23 draws and entrains air from air chamber 28 through the rectangular air nozzle outlets 31 and 32 which are located, respectively, above and below the liquid nozzle slot 23. The air- entrained liquid then enters a mixing chamber 25 of rectangular cross- section. The flow of liquid into the mixing chamber 25 from the ejector device 20 also draws liquid in the container 10 through the elongate openings 41 and 42 created by positioning the mixing chamber 25 proximate the liquid nozzle slot 23 and air nozzle outlets 31 and 32. The difference in velocity between the liquid stream exiting the liquid nozzle slot 23 (eg: approximately 20m/s) and the liquid moving through the elongate openings 41 and 42 (eg: approximately 5m/s) sets up a shear zone whereby strong turbulence is created and the desirable very small air bubbles are formed.

As depicted in Fig. la, a deflector 43, comprising a cylindrical pipe, can be positioned adjacent and extend the length of the outlet 44 of the mixing chamber 25 to slow the velocity of the air bubbles entering the liquid and further agitate the air-entrained liquid.

The liquid nozzle outlet 23 of each ejector device 20 is rectangular with the width of the nozzle being approximately 3 mm and the length being approximately 750 mm. In the embodiment depicted in Figs. 2 and 3, each ejector device 20 is oriented such that the air-entrained liquid enters the vessel 10 in a horizontal orientation.

Tests on the operation of the vessel 10 modified with the insertion of two ejector devices 20 have demonstrated that the oxygen transfer potential of the two ejector devices 20 is approximately equivalent to the potential of half the number of aeration tubes 11 originally employed in the vessel 10 before modification. In achieving this equivalent performance, the two ejector devices 20 only consumed 25-30 m'Vminute of air compared to 120- 135 m /minute of air consumed by the aeration tubes 11.

An example of a fermentation vessel specifically designed to use the ejector devices 20 according to the present invention is generally depicted as

50 in Figs. 4 and 5. The vessel 50 is 5.35m in diameter, 10m in height, and has a base 51 resting on a raised mound 63 above the ground 60. The vessel 50 also has a cylindrical sidewall 52 and a top which while not depicted in Figs. 4 and 5 would be similar to the top of the vessel 10 depicted in Figs. 2 and 3. Ten ejector devices 20 and associated mixing devices 25 are equally positioned about the base 51 on respective supports 53 in the vessel 50. Each ejector device 20 has its outlet nozzles disposed inwardly and at a slight upward angle to the base 51. While depicted ejector devices 20 have a slight upward angle, the ejector devices 20 could be positioned in the vessel 50 in a vertical orientation. If positioned in a vertical orientation, it would be preferred that a deflector 43, such as is depicted in Fig. la. be positioned above each outlet 44 of each mixing chamber 25 to break up the flow of air bubbles entering the liquid.

An air inlet pipe 54 extends between respective pairs of ejector devices 20. A liquid inlet pipe 55 is also connected to each ejector device 20 at the opposite end to the air inlet pipe 54 in each case. The air inlet pipe 54 is connected to the air chamber 28 of each ejector device 20. Similarly, the liquid inlet pipe 55 is connected to the liquid chamber 21a of each ejector device 20 connected thereto. The liquid inlet pipes 55 are connected through radiating pipes 56 to a central liquid supply line 57. The liquid supply line 57 is, in turn, connected to a pump 58, outside the vessel, that draws liquid from the vessel 50 below the ejector devices 20 through pipe 59.

Air is svipplied into the vessel from a source of compressed air through a central air inlet line 61 and then into radiating air svipply pipes 62 which, respectively, are connected through T-joints to the air supply pipes 54.

While the ejector devices are disposed at a slight upward angle to the horizontal, the ejector devices 20 could be placed in a vertical orientation should this be desired. In tall vessels and applications requiring a very large oxygen transfer, the vertical discharge of air-entrained liquid may be the preferred orientation for the nozzle outlets.

For the manufacture of baker's yeast, which is a typical application, the oxygen transfer potential of traditional air sparger devices is usually indicated by the amount of air required to grow a certain amount of yeast.

Other process conditions and the height of liquid above the sparger also have a large influence. The specific air consumption of a fermenter vessel which is 5.35m in diameter, 10 m in height, equipped with conventional sparger devices, and producing 23300 kg yeast 30% yeast solids is around 6.7m³ air/kg 30% solids yeast. In a fermenter of identical size and operating under the same operating conditions but having the ejector devices 20 as depicted in Figs. 4 and 5, it is anticipated that more than 30000 kg yeast 30% yeast solids can be produced with a reduced average air consumption of 3.0m^a air/kg solids yeast. This achievement of increased yield with lower air consumption requirements represents a considerable cost saving over the traditional techniqvies for yeast production.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. Λn ejector device for entraining a gas in to a liquid comprising a liquid nozzle, having a functionally elongate liquid nozzle outlet, the liquid nozzle being bounded on at least one side by a gas nozzle having a functionally elongate gas nozzle outlet.

2. The ejector device of claim 1 wherein the liquid and gas nozzles are positioned in a container for the liquid such that, in use, gas exiting from the gas nozzle will be entrained between a liquid stream exiting the liquid nozzle and the liquid in the container.

3. The ejector device of claim 2 further comprising a mixing chamber of substantially rectangular cross-section that is positioned over or proximate the liquid and gas nozzle outlets and adapted to facilitate mixing of the liquid in the container with the gas-entrained liquid exiling the nozzles.

4. The ejector device of claim 3 wherein a deflector is positioned adjacent an outlet of the mixing chamber.

5. The ejector device of claim 4 wherein the deflector comprises a cylindrical tube extending the length of the outlet of the mixing chamber.

6. The ejector device of any one of the preceding claims wherein the liquid and gas nozzle outlets are linear.

7. The ejector device of any one of claims 1-5 wherein the outlets are arcuate.

8. The ejector device of any one of claims 1-6 wherein the liquid nozzle outlet is rectangular.

9. The ejector device of claim 8 wherein the length to width ratio of the liquid nozzle outlet is at least 5:1, more preferably 10:1 and most preferably at least 100:1.

10. The ejector device of claims 8 or 9 wherein the width of the liquid nozzle outlet is between 2-8 mm and more preferably 2-3 mm.

11. The ejector device of any one of the preceding claims wherein the velocity of the liquid stream is preferably at least three times the velocity of the gas exiting the gas nozzle.

12. The ejector device of claim 11 wherein the velocity of the liquid stream is at least 15m/s, more preferably at least 20m/s.

13. The ejector device of claims 11 or 12 wherein the velocity of the gas is at least 3nι/s, more preferably at least 5 m s.

14. The ejector device of any one of the preceding claims wherein the liquid nozzle and gas nozzle are arranged so that both the liquid stream exits the liquid nozzle outlet and the gas exits the gas nozzle outlet in a substantially horizontal plane.

15. The ejector device of any one of claims 1-13 wherein the liquid nozzle and gas nozzle are arranged so that so that both the liquid stream exits the liquid nozzle outlet and the gas exits the gas nozzle outlet in a substantially vertical plane.

16. The ejector device of any one of claims 1-14 wherein only a single gas nozzle is positioned beneath the liquid nozzle.

17. The ejector device of any one of claims 1-15 wherein the elongate liquid nozzle outlet is bounded on each side by a gas nozzle outlet.

18. The ejector device of any one of the preceding claims wherein the length of the gas nozzle outlet is substantially the same as the length of the liquid nozzle outlet.

19. The ejector device of any one of the preceding claims wherein the width of the gas nozzle outlet is at least that of the liquid nozzle outlet, and preferably at least five times that width.

20. The ejector device of any one of the preceding claims wherein the ejector device is constructed as a venturi to create a low pressure zone adjacent to the gas nozzle outlet.

21. The ejector device of any one of the preceding claims wherein the gas is pumped through the gas nozzle.

22. The ejector device of any one of the preceding claims wherein the gas is air.

23. The ejector device of claim 22 wherein the oxygen transfer potential of the device is preferably at least 5, more preferably at least 50, most preferably at least 75 kilograms of oxygen/hour.

24. A fermenter having at least one ejector device as claimed in any one of claims 1-21.

25. The fermenter of claim 24 wherein the fermenter comprises a vessel for the liquid, the vessel having a base and a plurality of the ejector devices positioned adjacent the base.

26. The fermenter of claim 25 wherein ten of the ejector devices are equally spaced adjacent the base of the vessel.

27. The fermenter of any one of claims 24-26 wherein the gas is air and the air enters each of the ejector devices through an air inlet means.

28. The fermenter of any one of claims 24-27 wherein the liquid is drawn out of the vessel and returned back through a liquύd inlet means.

29. The fermenter of claim 28 wherein the liquid is drawn out of the vessel by a recirculating means.

30. The fermenter of claim 27 wherein if the ejector device operates on a venturi action, the flow of liquid through the device entrains the air from the air inlet means into the liquid stream.

31. A method for entraining a gas into a liquid comprising ejecting a liquid stream through an ejector device as claimed in any one of claims 1-21 in which the gas exiting from the gas nozzle is entrained between the liquid stream exiting from the liquid nozzle and the liquid.

32. The method of claim 31 wherein the gas is air which is aerating liquid in a yeast fermentation vessel.