US3722836A

US3722836A - Gas diffuser

Info

Publication number: US3722836A
Authority: US
Inventors: E Savage; D Heaney
Original assignee: Dravo Corp
Current assignee: TETRA RESOURCES Inc A CORP OF; TETRA RESOURCES Inc A CORP OF DELAWARE
Priority date: 1970-06-24
Filing date: 1970-06-24
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27
Also published as: FR2078319A5; GB1281630A

Abstract

A gas diffuser for admitting gas into a body of liquid is disclosed. The diffuser includes an elongated body with a chamber extending inwardly from an open face thereof and a resilient strip covering the chamber and secured to the body so as to flex at its ends under the urging of the pressure of gas in the chamber. The body includes a pair of cavities adjacent its end walls. The cavities act as resonance chambers causing the gas therein to resonate with the strip as the gas stream flows across the cavities. In addition, the strip is tapered from an intermediate portion thereof to its ends.

Description

United States Patent Savage et al.

I451 Mar. 27, 1973 [54] GAS DIFFUSER 2,532,554 12 1950 Jocck .261 1 3 137 882 6/1964 Blanchard ....26l/DIG. 44 [75] Inventors: Elton S. Savage, Wexford; Donald F.

y, Pittsburgh, both of Pa. 3,278,165 10/1966 Gaffney ...259/DlG. 44

[73] Assignee: Dravo Corporation, Pittsburgh, Pa. Primary Examiner-Tim R. Miles Filed: June 24, 1970 Attorney-Parmelee, Utxler 8L Welsh [21 Appl. No.: 49,369 [57] ABSTRACT A gas diffuser for admitting gas into a body of liquid is Cl 261/64 disclosed. The diffuser includes an elongated body 43 with a chamber extending inwardly from an open face [51] Int. Cl. ..B01f 3/04 th of a d a ilient tri covering the chamber and Field of sealdl 261/124, 1, 64 64 114 secured to the body so as to flex at its ends under the VT; 43, 44 urging of the pressure of gas in the chamber. The body includes a pair of cavities adjacent its end walls. The [56] References Cited cavities act as resonance chambers causing the gas therein to resonate with the strip as the gas stream UNlTED STATES PATENTS flows across the cavities. In addition, the strip is 3,182,978 5/1965 Reilly ..26l/l24 tap r d from an intermediate portion thereof to its 2,113,615 4/1938 Farmer ends. 3,l23,305 3/1964 Eisenkraft ..289/DlG. 44

17 Claims, 5 Drawing Figures Patented March 27, 1973 INVENTORS ELTON S. SAVAGE and DONALD F. HEANEY their Attorneys GAS DIFFUSER This invention is for an improvement in a diffuser of the general type disclosed in U.S. Pat. No. 3,182,978 assigned to our assignee, and will be described herein by way of example, but without limitation, for the aeration of sewage.

The diffusion of gas into a liquid containing solids, particularly where the operation may be intermittent, as in the aeration of sewage, requires that the air or gas be released near the bottom of a tank of several feet in depth so that the gas, such as the air in sewage treatment, will bubble up through an effective depth of liquid before it reaches the surface and thereby provide oxygen necessary for the chemical and biological reactions occurring in the tank. It has also been found that oxygen transfer is improved when the gas is released as abundant small bubbles, which of course expand as they rise because of decreasing hydrostatic pressure toward the surface, therebyincreasing the area of contact with the liquid in a greater ratio than than the expansion of a single large bubble, and also where high local turbulence is provided at the air discharge openings.

Various types of diffuser nozzles have been used having a plurality of small holes or slits through which the compressed air or other gas is released into the liquid in which the nozzle is immersed. However, a difficulty arises from the clogging of these openings where there are solids in the liquid. This is especially so if there is a period of agitation followed by a period where settling of the solids takes place. In such cases, when the supply of air or other gas to the nozzle is stopped, the hydrostatic pressure at the bottom of the tank tends to force the liquid into the nozzle and seek its own level in the air supply pipe to the diffuser, or at least a level where a condition of equilibrium is established between the liquid pressure and the air trapped in the supply pipe. In either case, this back flow, or suction draws fibers and other solids in the liquid into the small holes or slits, clogging them, or the solids even enter the diffuser and block the discharge holes or slits when air pressure is again applied to the nozzles.

In US. Pat. No. 3,182,978 there is shown a diffuser body in which there is a chamber into which the air or gas under pressure is supplied. A resilient strip forms a closure for one face of this chamber. When air under pressure is supplied to the chamber, it flexes the strip and is discharged into the treatment tanks. The vibration of the strip agitates and dislodges sediment which may be on or in the diffuser, and also provides mechanical agitation of the surrounding liquid. When the supply of air under pressure is stopped, the strip is pressed against a seat on the diffuser body to exclude or restrict backflow into the chamber, and exclude any material influx of solids, and the diffuser is therefore non-clogging at all times.

The present invention improves the performance of the earlier device, providing a more uniform discharge of smaller bubbles and also causes high local turbulence around the discharge openings. To this end there is provided a distributor body of generally rectangular shape having an elongated air chamber over which is resilient cover strip as in the earlier structure shown in said patent, but in addition thereto there is a resonance cavity or pulse chamber so arranged as to cause the air stream passing over it to resonate with the strip and create a higher amplitude and/or rate of vibration of the spring. By virtue of this action we feel that the bubbles of air discharging from the diffuser are sheared to reduce their size, and, also, high local turbulence is caused at the discharge openings. We also find that increased oxygen transfer is enhanced by tapering the flexible strip in thickness, the thickness decreasing, and its resilience increasing toward the free end of the cover strip.

Other details and advantages of this invention will become apparent as the following description of a preferred embodiment thereof proceeds.

In the accompanying drawings we have shown a preferred embodiment of this invention in which:

FIG. 1 is a schematic view showing in vertical transverse section a sewage treating tank with a pair of diffusers embodying the present invention therein;

FIG. 2 is a longitudinal section view through the diffuser of this invention;

FIG. 3 is a transverse section through the diffuser looking along the line III-III of FIG. 2;

FIG. 4 is an inverted perspective view of the diffuser;

and

FIG. 5 is a perspective view of the resilient strip forming part of the invention showing the taper thereof.

Referring now to the drawings, 10 designates a tank, usually several feet in depth, such as the aeration tank for treating sewage. It is in this tank that one or more of the diffusers, designated generally as 12, is located relatively close to the bottom so as to be several feet below the liquid level of the sewage and the solids which are distributed therethrough. The diffusers 12 are used to discharge air into the tank to rise through the liquid and escape at the surface. The air serves to transfer oxygen to the liquid, i.e. aerate the liquid, and to agitate the tank contents. The oxygen is necessary for the chemical and biological processes utilized for treating the sewage.

Each diffuser 12 includes an elongated body 14 of generally rectangular shape, preferably of plastic, corrosion-resistant aluminum, or other material resistant to the contents of the tank, and of generally inverted U- shape in transverse section, with a top wall 16 that has a connector 17 into which an air supply pipe 18 is connected. It has spaced parallel side walls 20 and end wall portions 22. The side walls are shouldered throughout their lengths providing on the inner edges an inverted ledge 24. The end walls 22 terminate flush with the 7 level of these shoulders. This structure provides an elongated chamber 26 with the face 28 of the body opening downward.

In each end wall portion 22 of the body there is a cavity 30 which is elongated transversely of the body to substantially the full width of the chamber 26, but the width of which is quite small compared to the overall length of the chamber, and each cavity is separated from the main chamber 26 by a relatively narrow transverse partition, as shown. Each end portion is preferably of a height greater than the remainder of the body 12, so that the cavities 30 are deeper than the chamber 26.

There is a thin flat strip 34 formed from a resilient material, such as stainless steel, providing a closure over the open face 28 of the chamber 26. This strip 34 rests on ledges 24 between the vertical shoulders at the bottom edges of the side walls and its ends bear against and seat against the edges of the end walls 22 of the body. The strip 34 is tapered from a central portion 34a thereof to the ends thereof. The degree of taper is selected in accordance with the maximum thickness of the strip 34 and the strength characteristics of the material used for the strip. The strip 34 is clamped in place at the longitudinal center of the diffuser by a strip retainer 36, this retainer having a thick intermediate section 36a to fit between the shoulders of side walls 20 and bear against the strip 34 at the central portion 34a thereof. Retainer 36 also has ears 36b at each end which overlap the bottom faces of the side walls of the diffuser. Machine screws or bolts 38 pass through the ears 36b and are screwed into the side walls of the diffuser body and hold the retainer 36 in position to clamp the strip 34 flat against the ledges or seat areas 24 and end walls 22.

Thus, while the strip 34 isimmovably clamped in place between its ends, its ends are free to flex as air pressure builds up in the air chamber 26. As the ends flex away from the seats, air escapes and the strip springs back against its seat on the ledges 24 and the edges of the end walls 22. This flexing of the ends is in the nature of an oscillating valving action producing, when the diffuser is immersed in liquid and adequate air supplied thereto, a fairly regular and uniform succession of bubbles at each end of the diffuser, but without backflow of liquids into the diffuser.

The flexing action of the strip may be roughly compared to that of a reed in an organ or wind instrument, with the escaping air flowing across the lip of each cavity, or analogous to the blowing of air from ones lips across the top of a bottle, the cavities providing much the same kind of a resonant function. This, we feel, increases the amplitude, rate and/or energy level of vibration of strip 34 which causes the strip to shear the air to produce smaller size bubbles, and also causes an increase in the local turbulence at the discharge ends of the diffuser. The result is an increase in oxygen transfer in the tank. The decrease in thickness of the strip 34 from its mid portion 34a toward its free ends desirably supplements the effectiveness of this result. Maximum vibration of the strip 34 may be obtained by sizing the taper thereof to conform with the size of cavities 30 whereby the strip will vibrate at the resonate frequency of the air cavities. It should be noted, however, that improved oxygen transfer has been found to result by using a flat strip in conjunction with the air cavities.

The dimensions are not critical, but we have found that with a body about 7 inches in length and less than 2 inches in width, a stainless steel strip 34 having a thickness of about 0.032 inch at the central portion 34a and tapering to 0.0305 inch at the ends will be quite satisfactory and withstand the hydrostatic pressure in the liquid in which it is immersed. With the foregoing dimensions, we have found that cavities of a depth ranging between about one-fourth to one-half the length of the free-flexing portion of the strip 34 are satisfactory, but this is not critical.

A preferred shape and location of cavity is shown, but cavities may have other shapes and more than one cavity may be provided at each end of the body. In fact, one or more cavities may even be provided in the top of the air chamber so long as they provide resonance as the flow of air passes over them. We have also found that the cavity may be vented to the surrounding environment, assuming that the vent is so restricted to retain in the cavity, during operation, a pocket of air that will pulse with the vibration of the strip 34. The exact effect these cavities have on the action of the strip is not understood and for this reason we say that either or any combination of the amplitude, or energy level, or rate of vibration of the strip is increased.

In addition to the modifications just specified, a flat strip 34 may be used in the described diffuser; a tapered strip 34 may be used without any cavities 30 in the diffuser; or the strip 34 formed from a resilient nonmetallic material. Even other changes and modifications may be made in this invention within the contemplation of the following claims.

We claim:

1. A diffuser comprising a body having a chamber therein with means for supplying gas under pressure thereto, one face of said chamber comprising a resilient closure member fixed at one point to the body and having edge portions seated on the body, said closure member being arranged to vibrate in a direction normal to its surface under pressure of gas in the chamber to release gas from the chamber, the body having a cavity therein which is in communication with the chamber when the closure is vibrating and said cavity located such that gas passing through the chamber passes over the cavity causing the gas in the cavity to resonate with the strip.

2. A diffuser as defined in claim 1 in which said cavity is positioned in the edge of the body under the edge portion against which the closure seats.

3. A diffuser as defined in claim 1 in which said body and the chamber therein is generally of rectangular shape with said closure extending in the direction of the length of the body, the cavity being located adjacent one end of the chamber.

4. A diffuser as defined in claim 1 in which said body and the chamber therein is generally of rectangular shape with the resilient closure comprising a strip extending lengthwise over the chamber and fixed to the body midway between its ends with the sides and ends of the strip seating on the sides and ends of the body, the body having a resonance cavity therein adjacent to each end of the body and over which the strip extends.

5. A diffuser as defined in claim 1 in which said resilient closure tapers from maximum thickness adjacent the point where it is fixed to the body to minimum thickness at the edge most remote from said point.

6. A diffuser as defined in claim 4 in which said strip tapers in thickness lengthwise from a maximum midway between its ends toward both ends.

7. In a gas diffuser including an elongated body having side and end walls and an open face defining a chamber therein, an elongated resilient strip covering the chamber, and a retainer extending across the strip for securing the strip to the body to allow the ends of the strip to flex away from the body under the urging of the pressure of gas in the chamber, the improvement therewith comprising:

said body having at least one resonance cavity therein located such that gas passing through the chamber passes over the cavity causing gas in the cavity to resonate with the strip.

8. The improvement as set forth in claim 7 wherein said resonance cavity extends from the chamber towards the closed end of the body.

9. The improvement as set forth in claim 7 wherein said resonance cavity extends laterally of the chamber.

10. The improvement as set forth in claim 7 wherein said resonance cavity is adjacent an end wall of the body.

11. The improvement as set forth in claim 7 wherein said body has a pair of resonance cavities, each of which extends transversely of the body from the chamber to adjacent the closed face, and each of the cavities is adjacent an end wall of the body.

12. In a gas diffuser including an elongated body having side and end walls and an open face defining a chamber therein, an elongated resilient strip covering the chamber, and a retainer extending across the strip for securing the strip to the body to allow the ends of the the strip to flex away from the body under the urging of the pressure of gas in the chamber, the improvement therewith comprising:

said body having at least one resonance cavity therein located such that gas passing through the chamber passes over the cavity causing gas in the cavity to resonate with the strip;

said strip being tapered from an intermediate portion thereof to at least one of the ends thereof.

13. The improvement as set forth in claim 12 wherein said body has a pair of resonance cavities, each of which extends transversely of the body from the chamber to adjacent the closed face of the body, and

each of the cavities is adjacent an end wall of the body; and said strip is tapered from an intermediate portion thereof to both ends thereof.

14. The improvement as set forth in claim 13 wherein the taper characteristics of the strip and the size of the resonance cavities are such that the strip will vibrate at the resonate frequency of the cavities.

15. A gas diffuser for admitting gas to a fluid, comprising:

an elongated body having side and end walls, a

closed face, and an open face;

a chamber in aid body extending from and including the open face of the body;

a resilient strip secured at one point of its length to said body covering the open face of the body, the portion of the strip beyond the point of connection being free to flex outwardly under the urging of the pressure of gas in said chamber;

said body having at least one resonance cavity therein located such that gas passing through said chamber passes over the cavity causing gas in the cavity to resonate with the strip; and

gas inlet connection means on said body for admitting gas into said chamber.

16. The diffuser valve as set forth in claim 15 wherein said resonance cavity extends transversely to said chamber towards the closed end of said body and is disposed between an end wall of said body and said gas inlet means; said strip is secured to said body at a point where said strip will flex above said cavity.

17. The diffuser valve as set forth in claim 15 wherein said strip is tapered from an intermediate point thereof towards an end t her eof

Claims

7. In a gas diffuser including an elongated body having side and end walls and an open face defining a chamber therein, an elongated resilient strip covering the chamber, and a retainer extending across the strip for securing the strip to the body to allow the ends of the strip to flex away from the body under the urging of the pressure of gas in the chamber, the improvement therewith comprising: said body having at least one resonance cavity therein located such that gas passing through the chamber passes over the cavity causing gas in the cavity to resonate with the strip.

12. In a gas diffuser including an elongated body having side and end walls and an open face defining a chamber therein, an elongated resilient strip covering the chamber, and a retainer extending across the strip for securing the strip to the body to allow the ends of the the strip to flex away from the body under the urging of the pressure of gas in the chamber, the improvement therewith comprising: said body having at least one resonance cavity therein located such that gas passing through the chamber passes over the cavity causing gas in the cavity to resonate with the strip; said strip being tapered from an intermediate portion thereof to at least one of the ends thereof.

13. The improvement as set forth in claim 12 wherein said body has a pair of resonance cavities, each of which extends transversely of the body from the chamber to adjacent the closed face of the body, and each of the cavities is adjacent an end wall of the body; and said strip is tapered from an intermediate portion thereof to both ends thereof.

15. A gas diffuser for admitting gas to a fluid, comprising: an elongated body having side and end walls, a closed face, and an open face; a chamber in aid body extending from and including the open face of the body; a resilient strip secured at one point of its length to said body covering the open face of the body, the portion of the strip beyond the point of connection being free to flex outwardly under the urging of the pressure of gas in said chamber; said body having at least one resonance cavity therein located such that gas passing through said chamber passes over the cavity causing gas in the cavity to resonate with the strip; and gas inlet connection means on said body for admitting gas into said chamber.

17. The diffuser valve as set forth in claim 15 wherein said strip is tapered from an intermediate point thereof towards an end thereof.