WO1993012043A1

WO1993012043A1 - Low pressure process for entraining gas into liquid solution

Info

Publication number: WO1993012043A1
Application number: PCT/US1992/010726
Authority: WO
Inventors: Daniel G. Noyes
Original assignee: U.S. Water Technologies, Inc.
Priority date: 1991-12-09
Filing date: 1992-12-09
Publication date: 1993-06-24
Also published as: AU3276493A

Abstract

The invention is a method for entraining gas in a liquid solution and an apparatus for practicing the method. In the method of theinvention, gas is introduced into a liquid solution being pumped through a conduit at the point of lowest absolute pressure in the system upstream of the pumping means. The gas is introduced into the liquid as bubbles or gas pockets with as small a diameter as is mechanically possible at the narrowest point of a venturi in the conduit and the increasing liquid pressure in the system downstream of the ventury is utilized to compress the bubbles still further. The bubbles or pockets of gas are prevented from coalescing as they pass through the pumping means and exit the apparatus by the pumping means itself. The apparatus comprises a conduit having a passageway therethrough in which a ventury is formed. An annular chamber is provided in the body of the conduit at the narrowest point of the venturi where the gas is introduced into the liquid. The gas is introduced upstream of a pumping means, which utilizes a shear force to prevent the bubbles from coalescing as the liquid exits the apparatus through the pumping means.________

Description

LOW PRESSURE PROCESS FOR ENTRAINING GAS INTO LIQUID SOLUTION

Background of the Invention

Field of the Invention

This invention pertains to a method and apparatus for entraining gases into a liquid solution. More specifically, the invention is a method and apparatus for entraining gases such as chlorine into wastewater to facilitate wastewater treatment.

Description of the Prior Art

It has long been known that entrainment of gas into wastewater facilitates wastewater treatment by either introducing and mixing chemicals or stimulating aerobic activity and therefore contaminant breakdown. The current approach is to circulate the wastewater in a containment tank and through an entrainment apparatus placed in the tank. The entrainment apparatus generally consists of a pump and a means for aspirating the gas into the liquid solution at some point downstream of the pump.

The principle of operation in this approach derives from Bernoulli's Principle, wherein the pressure exerted by a fluid is inversely proportional to the velocity of fluid flow. Thus, the liquid is pumped through a venturi in the entrainment apparatus where the velocity of the fluid is greater and the relative pressure of the fluid is lowered. When the liquid solution exits the entrainment apparatus and returns to the circulating wastewater in the tank, velocity decreases markedly and the pressure exerted rises. As an extension of Bernoulli's Principle, fluid passing through a venturi will reach its point of highest velocity, and hence lowest pressure, at the narrowest point in the venturi. This technique has also been used in the prior art to add an additional pressure zone so that there is a first pressure zone at the neck of the venturi downstream from the pump, a second pressure zone between the venturi exit and the circulating wastewater, and a third pressure zone in the wastewater circulating in the tank.

The manipulation of fluid flow to control pressure and enhance gas transfer efficiency in the entrainment process as practiced in the prior art nevertheless contains many deficiencies. The primary deficiency arises from introduction of the gas downstream of the pump because of the increase in absolute pressure downstream of the pump that inherently arises from the pump's use. .Therefore, although introduction downstream of the pump benefits from a lower relative pressure, the effective absolute pressure is much higher and the entrainment process much less efficient.

It is therefore a feature of this invention to provide an improved process and apparatus wherein the gas is introduced into the liquid solution upstream of the pumping means and therefore at the point of lowest absolute pressure.

It is also a feature of this invention to provide an improved process and apparatus wherein the gas is introduced into the liquid solution at the narrowest point of a venturi upstream of the pump to further lower the absolute pressure at which the gas is introduced.

It is a still further feature of this invention to provide an improved process and apparatus wherein the gas is introduced in the form of bubbles that are as small as mechanically possible at the point of lowest absolute pressure in the system.

It is a still further feature of this invention to provide an improved process and apparatus that utilizes recovering fluid pressure downstream of the venturi to facilitate entrainment. __.τnτn»rγ of the Invention The invention is a method for entraining gas in a liquid solution and an apparatus for practicing the method. In the method of the invention, gas is introduced into a liquid solution being pumped through a conduit at the point of lowest absolute pressure in the system upstream of the pumping means. The gas is introduced into the liquid as bubbles or gas pockets with as small a diameter as is mechanically possible at the narrowest point of a venturi in the conduit and the increasing liquid pressure in the system downstream of the venturi is utilized to compress the bubbles still further. The bubbles or pockets of gas are prevented from coalescing as they pass through the pumping means and exit the apparatus by the pumping means itself. The apparatus comprises a conduit having a passageway therethrough in which a venturi is formed. An annular chamber is provided in the body of the conduit at the narrowest point of the venturi where the gas is introduced into the liquid. The gas is introduced upstream of a pumping means, which utilizes a shear force to prevent the bubbles from coalescing as the liquid exits the apparatus through the pumping means.

A Brief Description of the Drawings A more particular description of the invention briefly summarized above can be had by reference of the exemplary preferred embodiments illustrated in the drawings of this specification so that the manner in which the above cited features, as well as others that which will become apparent, are obtained and can be understood in detail. The drawings nevertheless illustrate only typical, preferred embodiments of the invention and are not to be considered limiting of its scope as the invention will admit to other equally effective embodiments.

In the drawings;

Figure 1 is a side view of the apparatus of the invention in one embodiment;

Figure 2 is a partial cut-away of the apparatus in Figure 1;

Figure 3 illustrates the deployment of the apparatus of Figures 1-2 in a tank holding wastewater for treatment;

Figure 4 illustrates the operation of the apparatus in

Figures 1-2 in the environment illustrated in Figure 3; Figure 5 is an end view of the preferred pumping means of the apparatus of the invention;

Figure 6 is a longitudinal, cross-sectional view of pumping means of Figure 5 along line 6-6 of Figure 5;

Figure 7 is a longitudinal view of the pumping means of Figure 5;

Figure 8 is a second end view of the pumping means of Figure 5;

Figure 9 is an end view of an alternative embodiment of the pumping means of Figure 5; Figure 10 is a side view and partial cut-away of the embodiment of Figure 9 along line 9-9 of Figure 9; and

Figure 11 is a side view and partial cutaway view of a second alternative embodiment of the pumping means of Figure 5.

Description of the Preferred Embodiment

The apparatus of the invention, generally denoted 10, is illustrated in Figures 1-2. Apparatus 10 in Figure 1 generally comprises conduit 12 having entry 7 and vacuum tube 14, conduit 12 being fixedly mounted to motor 16 as is shown. Motor 16 is operated by electrical power provided via cord 19, is transported and maneuvered with handle 18, and may be any one of several well known in the art to be suitable for this type of application. Motor 16 in the preferred embodiment is manufactured by Ebara and sold to the general public as Model No. 50EY3U6.4.

As shown in the cross-sectional view of the apparatus in Figure 2, conduit 12 has passageway 27 therethrough in which venturi 25 is formed by interior wall 23 of conduit 12. Annular chamber 28 is formed in interior wall 23 of conduit 12 and is fluidly connected to passageway 27 at the narrowest point of venturi 25 via plurality of aspirating openings 29. Each of plurality of aspirating openings 29 is as small as is mechanically possible and in the preferred embodiment, each opening is 0.075 inches in diameter. It is furthermore desirable that as many such openings as is mechanically possible be used. Annular chamber 28 is also fluidly connected to a source of gas via vacuum tube 14.

Pumping means 26 comprising body 22 and impeller 24 in the embodiment of Figures 1-4 is an axial flow centrifugal pump and is powered via cord 19 and an electric motor housed in body 16. Conduit 12 is fixedly mounted to body 16 by legs 53 extending from flange 55 of conduit 12, which legs are in turn bolted to flange 57 of body 16. Conduit 12 is mounted to body 16 so that pumping means 22 is mounted at least partially in passageway 27 of conduit 12 to draw fluid in the direction of arrow 15 at entry 17 to passageway 27 and past venturi 25.

Figure 3 illustrates the apparatus as it is deployed to practice the method of the invention. Apparatus 10 is suspended in wastewater 32 held in containment tank 30 by supporting cables 34 and 36. Power cord 19 runs from apparatus 10 to a power source not shown. Vacuum tube 14 is connected to extension 38 which runs to the surface of wastewater 32 to provide a fluid connection with the ambient atmosphere.

The operation of apparatus 10 as deployed in Figure 3 is illustrated in Figure 4. Wastewater 32 is drawn into conduit 12 through entry 17 at point 40 by pumping means

22. Wastewater 32 then flows through venturi 25 at point

42. Gas from the ambient atmosphere is drawn through extension 38 and vacuum tube 14 into annular chamber 28 (shown in Figure 2) by the flow of wastewater 32 through venturi 25 and is aspirated into wastewater 32 through plurality of aspirating openings 29 (also shown in Figure

2) at point 42, the narrowest point of venturi 25. As passageway 17 through conduit 12 widens downstream of point 42 the recovering liquid pressure resulting from decreased fluid flow operates on the bubbles or gas pockets aspirated into wastewater 32 at point 42 to compress them.

The compressed bubbles then pass through pumping means 22 at point 44. Pumping means 22 is especially designed to impart a shearing force to the bubbles in wastewater 32 as is discussed both above and below. This shearing force operates to prevent the bubbles from coalescing to form larger gas pockets and further compresses the bubbles. Wastewater 32 then exits conduit 12 as shown in Figure 4 to return to the general circulating body of wastewater 32 held in tank 30 at point 46.

The overall effect of the operation of apparatus 10 is to create a general circulating effect in wastewater 32 held in tank 30 shown in Figure 3. The fluid flow velocity at point 46 is nevertheless much lower than at any point in conduit 12 and, hence, the fluid pressure much higher. Wastewater 32 therefor flows from a zone of high pressure at point 46 to progressively lesser zones of pressure at points 40, 42, and 44, before returning to point 46 and the higher pressure. Gas bubbles introduced at point 42 are therefore acted upon by progressively increasing pressures to facilitate entrainment of the gas into the liquid to produce a super-saturated solution.

The embodiment of pumping means 22 preferred over that shown in Figures 1-4 is illustrated in Figures 5-8. However, pumping means 22 may be any means for imparting kinetic energy to wastewater 32 as it passes through apparatus 10, such as the axial flow centrifugal pump (i.e., pumping means 22) of Figures 1-4. Pumping means 22 should also impart a shearing force to prevent the bubbles from coalescing and to compress their size. In its preferred embodiment (shown in Figures 5-8) , however, pumping means 22 comprises body 52 having recess 54 therein. In the wall of recess 54 is formed helical screw 56. Pumping means 22 is fixedly mounted to the rotating shaft (not shown) of the electric motor housed in body 16

(shown in Figures 1-4) by nut 60 as the end of the shaft extends through aperture 80 in one end of pumping means 22.

Body 52 is thereby rotated at a controlled speed in a manner well known to those in the art and helical screw 56 in recess 54 imparts kinetic energy to the liquid flowing therethrough. A shearing force is also imparted to prevent bubbles from coalescing and to compress them. Slot 70 is cut in the wall of body 52 and recess 54 to fluidly connect recess 54 with the environment external to body 52 so that liquid pumped through recess 54 can exit.

Because impeller 24 is a helical screw in the preferred embodiment, pumping means 26 is fully reversible without loss of pumping efficiency simply by rotating body 22 in a counter-clockwise direction provided that motor 16 is fully reversible. Furthermore, the pumping characteristics of pumping means 26 can be variable without changing the revolutions per minute of the rotatable shaft of motor 16 because the amount of kinetic energy imparted by a helical screw (or segmented helical screw or inclined paddle) is dependent on the proportion of the screw that operates on the passing fluid.

Thus, the pumping characteristics of pumping means 26 may be varied by changing the point in recess at which pumping means 26 meets the fluid being pumped. Also, because impeller 24 is formed in the walls of the recess rather than being embodied in a conventional impeller, pumping means 26 is relatively impervious to clogging and has vastly improved solids handling capabilities. Pump 10 consequently also more efficiently handles fluids having high viscosity, which is the converse of most kinetic pumps.

Other variations will become readily apparent to those in the art having the benefits of the teachings herein, such as is shown in Figures 9-11. An embodiment of pumping means 26 extrapolating the above teachings to achieve higher pumping efficiencies is illustrated in Figures 9-10, with arrows in Figure 10 illustrating fluid flow through pump 110, the extrapolation of pumping means 26. Figures 9-10 show an embodiment of pump 110 in which body 112 rotates in a clockwise direction within jacket 140 which in turn rotates in a counterclockwise direction within housing 145 and to which fluid is delivered via fluid bearing conduit 150. The means for rotating jacket 140 and housing 145 is not shown, but powered means 132 may be easily modified by those of ordinary skill in the art to rotate both body 112 and jacket 140 in their respective directions.

As is most easily seen in Figure 10, jacket 140 has means for imparting kinetic energy 142 formed in its interior wall and means for imparting kinetic energy 144 formed in its exterior wall. Having an imparting means formed in both the exterior wall and the interior wall greatly increases the pumping efficiency attributable to jacket 140. Fluid consequently flows through pump 110 after exiting fluid bearing conduit 150, passing through recess 113 of body 112, through slots 116a-b into the recess of body 140, exiting the recess of body 140 into the recess of housing 145, and out of housing 145. Figure 11 illustrates how these principles may be extrapolated beyond the embodiment of Figures 9-10, with arrows illustrating fluid flow through pump 110. In Figure 11, body 112 has means for imparting kinetic energy 152 formed in its exterior surface and housing 145 has means for imparting kinetic energy 154 formed in the wall of its recess and slots 148a-b through which the fluid being pumped exits the recess of housing 145. Body 112, in this embodiment, does not have slots 116a-b but is instead open on the end opposite fluid bearing conduit 150 to allow egress of the fluid being pumped. Furthermore, housing 145 rotates in a clockwise direction, as does body 112, while jacket 140 rotates in a counterclockwise direction.

The pumping efficiency of the pump 110, is dependent upon the amount of rotating means for imparting kinetic energy with which the fluid interacts as well as the design of the imparting means. Thus, teachings of the invention can be still further extrapolated to achieve higher pumping efficiencies by rotating body 112, jacket 140, and housing 145 within still more layers of housings having imparting means formed in the interior and exterior walls. However, complexities in manufacturing and assembly practically constrain such extrapolation to some degree.

Furthermore, helical screw 156 of pumping means 26, or pump 110, may also be replaced by a segmented helical screw or an inclined paddle and still perform satisfactorily. It is also anticipated that gas permeable membrane technology will someday be sufficiently advanced that such a membrane may be used to replace plurality of aspirating openings 29 in the preferred embodiment. It will also be recognized that the present invention can be generalized to entrain most gases into most liquids and not only for entraining ambient atmosphere into wastewater and that pump 110 may find applications other than for pumping wastewater in an entrainment process. These and other such modifications and variations on the preferred embodiment are to be considered within the scope and spirit of the invention disclosed and claimed herein.

Claims

WHAT IS CLAIMED IS;

1. A method for entraining a gas in a liquid solution comprising the steps of: pumping a liquid through a conduit having a passageway therethrough, the conduit having means for pumping situated at least partly in the passageway downstream of a venturi in the passageway; introducing the gas into the liquid as bubbles at the narrowest point of the venturi; utilizing the recovering liquid pressure to reduce the size of the bubbles introduced at the narrowest point of the venturi; and preventing the bubbles from coalescing as they pass through the pumping means.

2. The method of claim 1, wherein the step of preventing the bubbles from coalescing is performed by the pumping means.

3. The method of claim 1, wherein the bubbles have a diameter of 0.075 inches when introduced.

4. The method of claim 1, including increasing the liquid pressure downstream from the pumping means to further facilitate entrainment of the bubbles into the liquid.

5. An apparatus for entraining a gas in a liquid solution comprising: a conduit having a passageway including a venturi therethrough; means for introducing the gas into the liquid as bubbles at the narrowest point of the venturi; means for providing gas to the gas introducing means; and means for pumping liquid through said conduit positioned partly in said conduit downstream of the venturi.

6. The apparatus of claim 5, wherein said gas introducing means comprises an annular chamber in said conduit, the annular chamber being in fluid communication with the passageway via a plurality of spaced apart openings in the wall of the conduit at the narrowest point of the venturi.

7. The apparatus of claim 5 and claim 6, wherein the gas providing means is a vacuum tube between the gas introducing means and a source of gas.

8. The apparatus of claim 5, wherein the pumping means prevents coalescence of bubbles introduced into the liquid.

9. The apparatus of claim 5 wherein the pumping means facilitates compression of the introduced bubbles into the liquid.

10. The method of claim 1 and claim 2, wherein the pumping means comprises: a powered means having a rotatable shaft; and a body having a recess in which a means for imparting kinetic energy is formed and at least one opening in the wall of the body to permit the liquid pumped through the recess by the imparting means to exit the recess, said body being mounted to the rotatable shaft of said powered means.

11. The pumping means of claim 10 wherein the imparting means is at least one of a helical screw, a segmented helical screw, and an inclined paddle.

12. The apparatus of claim 5, claim 8, and claim 9, wherein the pumping means comprises: a powered means having a rotatable shaft; and a body having a recess in which a means for imparting kinetic energy is formed and at least one opening in the wall of the body to permit the liquid pumped through the recess by the imparting means to exit the recess, said body being mounted to the rotatable shaft of said powered means.

13. The pumping means of claim 12 wherein the imparting means is at least one of a helical screw, a segmented helical screw, and an inclined paddle.

14. An apparatus for entraining a gas in a liquid solution comprising: a conduit having a passageway therethrough, the passageway including a venturi, and having an annular chamber in fluid communication with the passageway via a plurality of spaced apart openings in the wall of the conduit at the narrowest point of the venturi; a vacuum tube in fluid communication with the annular chamber; a pump located at least partly in the passageway of said conduit downstream of the venturi, said pump comprising: a powered means having a rotatable shaft; and a body having a recess in which a means for imparting kinetic energy is formed and at least one opening slot in the wall of the body to permit liquid pumped through the recess by the imparting means to exit the recess, said body being mounted to the rotatable shaft of said powered means.

15. A kinetic pump comprising: a powered means having a rotatable shaft; and a body having a recess in which a means for imparting kinetic energy is formed and at least one opening slot in the wall of the body to permit fluid pumped through the recess by the imparting means to exit the recess, said body being mounted to the rotatable shaft of said powered means.

16. The kinetic pump of claim 15 wherein said pump body also has a means for imparting kinetic energy formed in the exterior surface of said pump body to impart additional pumping force to the fluid exiting the recess.

17. A kinetic pump comprised of a means for imparting kinetic energy formed in the wall of a recess in a rotatable body, the body having an opening to permit fluid pumped through the recess by the imparting means to exit the recess.

18. The kinetic pump of claim 17, wherein said pump body also has a means for imparting kinetic energy formed in the exterior surface of εaid pump body to impart additional pumping force to the fluid exiting the recess.

19. The apparatus of claims 15, 16, 17, and 18, wherein the imparting means is at least one of a helical screw, a segmented helical screw, and an inclined paddle.

20. The pump of claims 15, 16, 17, and 18, wherein said pump body rotates within a jacket having an opening to permit the fluid to exit the jacket, the inner wall of the jacket having a means for imparting kinetic energy formed therein to impart additional pumping force to the fluid exiting the recess.

21. The pump of claim 20, wherein the jacket rotates.

22. The pump of claim 20, wherein the imparting means formed in the inner wall of the jacket is at least one of a helical screw, a segmented helical screw, and an inclined paddle.

23. The pump of claim 20, wherein the jacket rotates within a housing.

24. The pump of claim 22, wherein a means for imparting kinetic energy is formed in the exterior surface of the jacket to impart additional pumping force to the fluid exiting the recess.

25. The apparatus of claim 23, wherein the imparting means formed in the exterior surface of the jacket is at least one of a helical screw, a segmented helical screw, and an inclined paddle.