DE2712465A1 - GENERATION OF SMALL GAS BUBBLES IN A LIQUID - Google Patents

Description

Patent attorney

Dipl. Ing.

National Research N 11 P 10

_t _ March 12, 1977

Development Corporation

London / England

Creation of small gas bubbles in a liquid

The invention relates to the generation of small gas bubbles in liquids, and in particular to the generation of particularly small bubbles which are required in some industrial processes, for example flourishing of small or very fragile objects such as flakes or loose aggregations of very finely divided substances. Such processes require gas bubbles with diameters of the order of magnitude

LU

25-100 migraines. Larger bubbles like those with conventional ones Ventilation methods are achievable, have not proven themselves in such methods; the reason for this is obvious to see in the fact that large air bubbles in water, i.e. the liquid most commonly used, rise so quickly, that the contact time is too short for many particles to accumulate on the bubbles, and because many of those collected and captured Particles are "washed off" again by the rapid relative movement between the bubble and the liquid.

A particular method of application for the present invention is the treatment of waste water and fermentation fluids, and generally those gas / liquid systems in which there is as large a surface as possible between the liquid and the Gas based on the volume of the gas wants to have.

D-4000 Düsseldorf 1 ■ Bahnstrasse 62 ■ Telephone 0211/356338 - 2 -

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This not only includes absorption systems, which will be discussed later, but also systems that in which gas dissolved in liquids is to be released, for example by using a suitable inert gas, such as blowing nitrogen or air through liquid.

There are known methods for generating gas bubbles of suitable size for all of these indicated applications; the best-known processes all have considerable technical disadvantages, in particular a high energy requirement.

The invention relates to an arrangement of the type indicated in the preamble of claim 1 and solves that indicated above Task by applying the features of the labeling part of claim 1. Particularly useful configurations of the invention are described in subclaims.

In the following, the invention is explained using exemplary embodiments with reference to the drawing. In the drawing show:

1 shows an axial section through a rotor with two blades;

FIG. 2 shows a plan view of the rotor according to FIG. 1;

3 shows a section along the line III-III in FIG

on a larger scale and with an assigned graphic representation;

Fig. 4 is a section through another embodiment of a rotor blade s;

Figure 5 is a section along the line V-V in Figure 6;

FIG. 6 shows a plan view of a two-bladed rotor according to FIG. 5;

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7 shows a top view of a further rotor

Figures 8 and 9 are sections along the lines VIII-VIII and IX-IX in Figure 7;

10 shows a plan view of a further two-bladed rotor;

Figures 11 and 12 sections along lines XI-XI and XII-XII in Fig. 10;

13 shows an axial partial section through a further two-leaf Rotor;

14 shows a schematic side view of a system for generating small air bubbles;

15 shows a schematic side view of another installation;

16 shows a sectioned side view of a part of another installation.

FIG. 1 shows a two-bladed rotor 1 with a hollow shaft 2 which is driven by the motor 3 indicated schematically. The bushing 4 in the center of the shaft is supplied with compressed air from the compressed air source shown schematically at 5; In another version, air can also be drawn in directly from the atmosphere without pumps. Two rotor blades 6 and 7 are attached to the lower end of the shaft and protrude radially from the shaft. Each blade has an inner radially extending one Implementation 8, which is in communication with the bore 4 of the shaft 2. The leadthroughs 8 stand with outlet openings 9 the outer surfaces of the blades 6 and 7 in connection; see figure When the rotor is in a standing liquid according to the direction of the ax 10 in FIG. 2 is moved, forms the openings 9

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gas escaping into the liquid forms a thin film 11 (see Figure 3), which runs over the rear portion of the leaf surface and is continuously thinner, and finally dissolves in the area of the rear edge of the sheet into a multitude of tiny bubbles. The lower half FIG. 3 shows a graph of the fluid pressure near the blade area above the blade of FIG front (right) to back when the sheet moves to the right in the liquid in relation to FIG. 3. In Figure 3 a section through the leaf is shown. The X-axis shows the pressure value 0 within the liquid, but relatively far from the leaf. You can see from the graph that the pressure is on the relatively blunt nose of the streamlined profile is above ambient pressure. Going back from the nose 12 of the profile, falls the pressure very quickly below ambient pressure and reaches a minimum value at the abscissa 13, which is thickest Part of the profile. Further from the minimum at 13 the pressure rises again until it reaches the ambient pressure at the abscissa value 14 achieved. As shown, the sheet has a sharp edge at the abscissa value 15, instead of which the Pressure is again typically above ambient pressure. It can be seen in particular from FIG. 3 that the outlet openings located just downstream of the abscissa 13, so that the holes release air into the liquid, thereby changing the above-mentioned Gas film extending from the holes 9 to the rear, over an area over which the pressure is constantly increasing Environmental value increases.

Experience has shown that the ever thinning gas film dissolves at the point of the profile in gas bubbles 16 at which the ambient pressure is reached again.

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The size of the gas bubbles 16 generated in this way depends on the thickness of the gas film immediately before it Dissolving into individual bubbles; this parameter can be changed or influenced by various technical features will. For example, a spoiler 17 according to FIG. 4 can be in the rear area of the area over which the gas flows Blade surface are attached, the tip 18 of which lies approximately in the abscissa where the value 14 is indicated in FIG. The overall streamlined cut surface of the blade should be "disturbed" as little as possible.

Surface-active additives can also be added, which reduce the surface tension between liquid and gas and thereby make the interface between liquid and gas more unstable, resulting in smaller gas bubbles permit.

Another possibility is to change the pressure inside the sheet: the lower this pressure, the thinner the gas film becomes and the bubbles that arise from the gas film become smaller.

In the embodiment shown in Figures 5 and 6, the hollow shaft 2 carries hollow arms 19 and on these are blades 20, which are essentially the same in shape as the blades 6 and 7 of FIG. 1, but are attached to the arms 19 in this way are set so that the longitudinal axes of the blades and thus also the cavities present therein run parallel to the shaft 2 and not at right angles as in the previously described exemplary embodiment.

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The outlets 21 indicated in FIG. 6 lie either on the inner and / or outer (shown) curved ones Work surfaces of the leaves.

The blades, which are streamlined and teardrop-shaped in profile, not only support the formation of a thin one Gas films and thus the generation of the smallest bubbles, but also minimize the energy required for Rotation of the rotor in liquid is required. When you consider the essential pressure distribution over the work surfaces If the blades do not change as a result, then the blades of the rotors shown in FIGS. 1 and 5 can also be used tend to permit not only the necessary introduction of the gas into the liquid but also a pumping action exercise on the liquid.

Of course, the invention also includes the kinematic reversal of the process described, after which the Relative movement between the liquid and the leaves is brought about by the fact that the leaves are arranged in a stationary manner but the liquid is moved accordingly.

In a system in which the blades rotate horizontally about a vertical axis according to FIG. 1, the speed at one point on the sheet is directly proportional to the distance from the axis of rotation greater, which at all the pressure conditions occur on the surface of the leaves. The pressure P on the surface of a sheet with distance R from the axis has the size

1 2 2

ρ = P _o - - K pw r

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Where K is a constant, typically 1, ρ the pressure in the area of the axis of rotation and w the frequency of rotation.

It is advantageous if the pressure at each of the holes 9 shown in FIG. 1 is constant because each of these holes is connected to the atmosphere via the feedthroughs 8, and because only some of the holes give off air, if not the Pressure at all holes is at or below atmospheric pressure. The same consideration also applies if a slot is used instead of several adjacent holes.

To improve the effectiveness, the shape of the leaf can vary from one point to the next on a radius change, which changes the coefficient K in the equation. An important variable that can be changed is the ratio of the thickness T of the blade to the size c, i.e. the profile depth, which values are shown in FIGS. 8 and 9 are specified.

In a sheet according to Figure 7 with 2 slots 30 (instead of several holes) close to the leading edge of the sheet was the depth of the profile c 31 mm and the thickness T increased with radial distance from the W _e He 31 of 0.005 m on at B 0.003 m at A. At a speed of 600 rpm and an immersion depth of 0.25 m in water, the air left the slot as a uniform thin film which turned into fine bubbles in the area of the rear edge of the profile.

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A comparable interpretation of the dimensions can be made with such sheets are made, which are arranged vertically according to Figure 5 to the increasing from top to bottom to compensate hydrostatic pressure. In this case, the ratio T / c must become larger Depth get bigger.

Another way of compensating for pressure changes over the length of a sheet is to change the relative pressure Position of the holes or slots along the depth of the blade, i.e. a change from item 30 in the figures 8 or 9 on the drawing horizontally.

It can be seen from the pressure distribution in FIG. 3 that, starting from the leading edge of the sheet towards the rear, the liquid pressure close to the surface of the blade from its value in the area of the nose of the profile to a minimum in the area the trailing edge falls off. The absolute value of these pressure changes for a blade of constant cross-section depends on the square of the relative speed between the leaf and the liquid. With one rotated horizontally around an axis Blade this speed increases with the radius, so that with constant values of T and C over the length of the sheet a constant gas pressure can be achieved by changing the position of the corresponding holes or the Slots changes. As shown in Figures 10-12, the slot or hole 32 is further forward in Relocated towards the nose 33, where the sheet itself moves faster (relative to the liquid). According to Figures 5 and 6 vertically extending blades, an equivalent method can be applied to the ascending hydrostatic Compensate for pressure.

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In this case, the holes or the slots are placed with increasing depth below the liquid level further away from the nose 33 to the rear.

Another way of compensating for the increasing speed over the length of a sheet, which is rotated about a vertical axis consists in curving the longitudinal axis of the sheet so that According to Figure 13, the ends of the leaves are deeper in the water than the parts near the axis. In Figure 13 is the vertical drive shaft denoted by 35; it knows the gas supply 37. The leaves are labeled 34 and have passages 37 and 38 for feeding slots 36 in the outer ends of the blades. on In this way, the increasing hydrostatic pressure can change the dynamic pressure along the length counteract the leaves. The blade should have a parabolic shape for optimal operation. These Shape can be obtained according to the equation

2g V 0

where r is the radius of the inner end of each slot 36 and h is the increase in depth of the blade for points at radius r beyond r
and g is the acceleration due to gravity.

at the radius r beyond r · w is the frequency of rotation

In some applications it may be necessary to have a continuous flow of small bubbles into a large volume of liquid introduced, e.g. flopping or when venting a large container.

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In such a case, one can provide a system in which the liquid is rotated by a corresponding The vessel containing the ventilation leaves flows, and then into the large container. For example, according to FIG be provided for aeration of a liquid to be biologically clarified in a continuous process, the to flow raw liquid through a conduit 41 into an aeration tank 40. The line 41 goes into a reservoir 42, in which ventilation blades 43 work on a shaft 44. By a pump 45 is Liquid drawn off from the main vessel 40 and - depending on the position of an adjustable valve 47 either discharged via a line 46 or back into the tank 40; For details, see Figure 14. Another valve 48 allows liquid that has not yet been aerated to be introduced into the container 40 past the line 41. The liquid receives by the pump such a speed that that of the leaves 43 generated bubbles reach down to the bottom of the container 40 via a sink tube 49, which the lower end of the reservoir 42 forms. In this way, favorable flotation properties or a good supply are obtained of oxygen or other gas to or from the liquid.

If necessary, the shaft 44 of the blades 43 can be extended so that the bubbles close to the bottom of the tank 40 develop. In such a case, the pump 45 and the lowering tube 49 can be dispensed with, if necessary. Alternatively can one also make the shaft 44 longer and let a propeller run inside the tube 49, which then does the function the pump 45 takes over.

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In a further treatment system according to FIG. 15, 50 represents a volume of a liquid which in a container 51 is located. A pump 52 pumps the liquid around by sucking it through the suction pipe 53 which opens relatively close below the surface of the liquid. The pump delivers into the line 54, from which the liquid passes through a diffuser 55 back into the tank, the diffuser is attached relatively close to the floor 51. Within the line 54 is a ventilation sheet of the type described Kind, which is arranged in a stationary manner, with the necessary relative movement between the liquid and sheet is reached by the movement of the liquid. The necessary air reaches slots 57 and 58 on the opposite major sides of the sheet 56 by a center connection 59 between the slots, which in turn is in communication with the atmosphere outside the pipe 54 via a suction pipe 60. Care must be taken that air bubbles forming at the mouths of the slots 57 and 58 are also present of the liquid 54 move downward into the liquid 50 through the diffuser 55. So that no air bubbles get in move in the opposite direction, i.e. climb upwards, care must be taken to ensure that the downwards The speed of the liquid is greater than the rate of ascent of air bubbles within the lines below the ventilation device is. The sheet 56 can also be placed in the horizontally extending part of the conduit will.

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In systems of the type shown in Figure 15 there is air not only brought into the liquid by the venturi effect through the sheet 56, but also through a suction effect due to the hydrostatic conditions corresponding to the height of the sheet 56 above the Liquid 50 level in the container. These two effects together can be large enough to ensure that the slots 57 and 58 give off air when the inlet 60 is only in communication as shown with the ambient air, and not under increased pressure. Care must also be taken that the height of the inlet 60 above the level of the liquid 50 is so great that the liquid with the required Speed goes through the diffuser. If this is not achieved at first, then it may be necessary to give up the air with pressure at 60.

It should be pointed out here that FIG. 15 is a simplified representation compared to FIG. 14, with In Figure 15 some components and details have been omitted, e.g. the means in connection with the Valve 47.

An arrangement according to FIG. 15 was made with 14 sheets in parallel arrangement instead of a single sheet in

2 operated a downwardly leading line with a cross-section of 0.01 m. The liquid flow rate (water) was 4.42 10 m / s, the air intake was 8.8 χ 10 m / s and the height of the leaves above the liquid level was about 1 m.

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In this way, vesicles with an average diameter of about 0.001 µm were generated. The pressure drop across the leaves was in magnitude

3 2

Order of 7x10 N / m.

Of course, you need in systems of the type shown schematically in Figures 14 and 15 Skimmer or the like for removing relatively solid objects floating on the liquid.

In some applications, especially if there are putrefactive substances in the liquid to be processed, it can be appropriate to choose the means for adjusting the liquid velocity so that they are parallel to Liquid movement are proceeding or are suspended. In the illustration according to FIG. 16, the sheet 56 is replaced according to Figure 15 by a correspondingly designed body 61, which allows the liquid to flow faster, as it flows past the upstream end of the body and then slows down as the fluid moves approaches the rear edge of the body and flows away from it. If the line 62 is a cylindrical Has cross-section, then you can design the body 61 as a rotationally symmetrical mandrel, of course other shapes with regard to the shape of the cross-section of the conduit are possible, e.g. rectangular, in particular but square. Air is introduced through an inlet 63 and connections 64 as indicated by the parts with the reference numerals 60, 57 and 58 in Figure 15, or indeed through holes or slots 65 in the wall of conduit 62.

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This last-mentioned case of the entry of the air through the openings 65 in the wall represents an embodiment which differs entirely from the exemplary embodiments of the invention described in that the gas penetrates through openings which are arranged in components near the surface of the "leaf" are, and not through the inside of the sheet.

In this latter embodiment of the invention, the "sheet" can also be solid and not have any internal openings or openings Have bushings.

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Claims (15)

Patent attorney AEL Dipl. Ing. Patent attorney MICHAELKORN 2712465 National Research N 11 P. _. . _ March 12, 1977 Development Corporation London / England Claims Device for generating small gas bubbles in liquids with a streamlined-drop-shaped body ("sheet") with a streamlined cross section, tapering to a point at least at one end, a liquid container and means for generating a relative movement between the sheet and the liquid, characterized in that the sheet is mounted in relation to the liquid flowing past that the tapering end (in profile) is downstream, so that a variable pressure is set over at least one surface of the sheet against which the flow is flowing, which is below the ambient pressure in the liquid, and that at one Place of the flowed area in front of the downstream end a gas outlet is arranged so that the gas runs as a thin film downstream of the opening over the surface of the sheet and merges into small bubbles in the area of its downstream end. 2. Apparatus according to claim 1, characterized by a rotor to which the blade is attached to the Generating at least a part of the relative movement between the liquid and the sheet rotates. 3. Apparatus according to claim 1, characterized by means for forcing the liquid past the sheet so as to to generate at least part of the relative movement between the liquid and the sheet. 709840/0847 D-4000 Düsseldorf 1 Bahnstrasse 62 Phone 0211/356338 - 2 - ORIGINAL INSPECTED N 11 P 2712A65 4. Apparatus according to claim 2, characterized by a plurality of blades on a rotor. 5. Apparatus according to claim 4, characterized in that the blades are struck at an angle on the rotor in order to exert a pumping effect on the liquid when the rotor is rotating. 6. Apparatus according to claim 4, characterized in that the blades themselves are in communication with a gas supply, and that the gas outlets are formed on the surfaces of the blades themselves. 7. Apparatus according to claim 6, characterized in that the rotor shaft is arranged vertically, that the blades protrude in their longitudinal extension substantially radially from the rotor, and that the ratio of thickness to depth of the blades decreases with increasing distance s / on of the rotor shaft. 8. Apparatus according to claim 4, characterized in that the rotor shaft is vertical that the blades themselves with their longitudinal extension also run vertically, so that the ratio of thickness / depth of each sheet with the depth of immersion of the sheet in the liquid increases. 9. Apparatus according to claim 4, characterized in that the blades protrude radially from the rotor, that discharge openings over the length of the leaves are provided, and that the relative positions of the outlet openings over the length of the blades change as the distance between the holes and the rotor axis increases. 10. The device according to claim 4, characterized in that the rotor shaft is arranged vertically, and the blades are curved in their longitudinal extent at the base of the rotor in radial planes, the tips of the blades are axially displaced with respect to the base downward so that they Immerse deeper in the liquid than the foot point. 11. The device according to claim 6, characterized in that that the outlets are located on the blade surfaces close downstream from the point at which in use the pressure of the liquid on the sheet is the smallest, and that the pressure of the liquid towards the surface in downstream direction steadily increases. 709840/0847 - # - N 11 P 12. The device according to claim 3, characterized in that the sheet is fixedly arranged in a conduit for flowing liquid, that the gas outlet is formed in the sheet surface, and that the gas reaches the outlet through openings in the suspension of the sheet and in the Blade itself are formed. 13. The apparatus according to claim 3, characterized in that the sheet is fixedly arranged in a conduit with liquid driven past, and that the gas outlets are formed in the wall of the conduit near the point on the sheet surface at which a sub-ambient pressure is established . 14. The device according to claim 1, characterized in that that the cross-sectional shape of the blade at the upstream end, (12; Figure 4) is relatively blunt. 15. Plant for the treatment of a liquid with gas in a treatment tank, characterized by means for feeding the liquid to be treated into the vessel by an apparatus according to claim 1, means for drawing off of liquid from the boiler and means for changing the proportions of those amounts withdrawn Liquid that is either dispensed from the container or fed back into the container. 709840/0847