CA1152979A - Gas diffusion apparatus - Google Patents
Gas diffusion apparatusInfo
- Publication number
- CA1152979A CA1152979A CA000345544A CA345544A CA1152979A CA 1152979 A CA1152979 A CA 1152979A CA 000345544 A CA000345544 A CA 000345544A CA 345544 A CA345544 A CA 345544A CA 1152979 A CA1152979 A CA 1152979A
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- Canada
- Prior art keywords
- diffusion elements
- diffusion
- gas
- faces
- header pipe
- Prior art date
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- Aeration Devices For Treatment Of Activated Polluted Sludge (AREA)
Abstract
Abstract of the Disclosure Combination of a diffusion element useful for sewage aeration, an element holder, a seal and a peripheral retaining means. The diffusion element has upper and side faces which are both gas permeable at pressures normally encountered in sewage aeration, when in contact with a liquid medium. The diffusion element is supported by the element holder and the seal is an elastomeric ring positioned at the periphery of the upper face of the diffusion element, preferably abutting a topmost portion of the peripheral side face.
The peripheral retaining means is preferably a positioning ring affixed to the element holder and adjusted to retain the elastomeric sealing ring or uniformly press it into sealing engagement with the diffusion element to block the emission of aeration bubbles from its peripheral side face into the liquid medium. The elastomeric ring and retaining means are positioned and shaped to provide substantially all of the gas permeable area of the upper face of the element with free access to surrounding liquid to avoid the formation of air pockets at the surface of the air discharge face.
The peripheral retaining means is preferably a positioning ring affixed to the element holder and adjusted to retain the elastomeric sealing ring or uniformly press it into sealing engagement with the diffusion element to block the emission of aeration bubbles from its peripheral side face into the liquid medium. The elastomeric ring and retaining means are positioned and shaped to provide substantially all of the gas permeable area of the upper face of the element with free access to surrounding liquid to avoid the formation of air pockets at the surface of the air discharge face.
Description
The invention relates to equipment useful as a sewage aera-tion system, ozonator, recarbonation system or the like and, more par-ticularly, to such a system including a sealing means for sealing the permeable sides of a diffusion element to block the flow of bubbles therefrom and for avoiding the formation of gas pockets at the gas diffusion surface of the diffusion element.
It is known in the art to block the flow of bubbles fram the vertical or near vertical sides of a diffusion element by either applying a relatively expensive impermeable coating to the sides or compressing a peripheral region of the gas diffusion face of the dif-fusion element to render the sides of the diffusion element impermeable.
Such means have been employed to avoid the undesirable merging of bubbles that occurs when bubbles are emitted by the vertical faces of a porous diffusion element.
During manufacture, the peripheral portions of the diffu-sion elements disclosed in United States patent No. 4,046,845 issued September 6, 1977 to Veeder are subjected to sufficient extra compres-sion to render them imperme~ble and thus block the flow of bubbles frcm the vertical sides of the elements. However, it has been found that the compressive stress necessary to produce these impermeable peripheral regions can result in areas of reduced permeability in more centrally located portions of the gas diffusion face of the dif- -fusion element. These areas of reduced permeability may produce an uneven distribution of hubbles across the upper surface of the diffu-~! .
sion element and thereby reduce the mass transfer efficiency of a unit volume of gas.
~ In addition, some aeration systems in the prior art have -1 .
utilized sealing means, clamping members and/or holders that extend in spaced but closely adjacent relationship to some por-tion of the gas diffusion surface of a diffusion element. It has been determined that such extending members may form crevices adjacent the surface of the associated diffusion element, ; - 2 -: 1~ 5Z979 in which gas pockets form. The bubbles which enter such crevices tend to empty the crevices of liquid. Thus the effect of surface tension on the adjoining portion of the gas diffusion surface is reduced, whereby such portion manifests less resistance to the discharge of gas. Thus, more gas is released over these areas of reduced surface tension effect than elsewhere on the gas discharge surface and the resulting uneven distribution of bubbles reduces the mass transfer efficiency of the system.
Accordingly, it is an object of the invention to provide a simple and relatively inexpensive means for sealing the sides of a diffusion element to prevent the lateral release of bubbles and to avoid the ~ormation of gas pockets adjacent the gas diffusion surface of the element.
Another object of the invention is to provide a sealing means that may be used in combination with a pre-stressed, partially gas permeable peripheral region of a diffusion element to block the flow of bubbles from the sides of the dissuion element.
These and other objects of the invention will become apparent from a review of the detailed specification which ollows and a consideration of the accompanying drawings in which like characters identify identical apparatus.
BRIEF SUr~MARY OF THE INVENTION
According to the invention, a wastewater aeration system comprises: a tank; a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe`; a plurality of plenums secured to said header pipe at spaced locatIons along said header pipe in communi-cation with said gas outlet openings; porous diffusion elements secured to said plenums for receiving pressurized gas and re-leasing bubbles in a liquid, said diffuser elements having:
` - 3 -~4.
~ ~ s~9 (1) gas input faces for receiving said pressurized gas;
It is known in the art to block the flow of bubbles fram the vertical or near vertical sides of a diffusion element by either applying a relatively expensive impermeable coating to the sides or compressing a peripheral region of the gas diffusion face of the dif-fusion element to render the sides of the diffusion element impermeable.
Such means have been employed to avoid the undesirable merging of bubbles that occurs when bubbles are emitted by the vertical faces of a porous diffusion element.
During manufacture, the peripheral portions of the diffu-sion elements disclosed in United States patent No. 4,046,845 issued September 6, 1977 to Veeder are subjected to sufficient extra compres-sion to render them imperme~ble and thus block the flow of bubbles frcm the vertical sides of the elements. However, it has been found that the compressive stress necessary to produce these impermeable peripheral regions can result in areas of reduced permeability in more centrally located portions of the gas diffusion face of the dif- -fusion element. These areas of reduced permeability may produce an uneven distribution of hubbles across the upper surface of the diffu-~! .
sion element and thereby reduce the mass transfer efficiency of a unit volume of gas.
~ In addition, some aeration systems in the prior art have -1 .
utilized sealing means, clamping members and/or holders that extend in spaced but closely adjacent relationship to some por-tion of the gas diffusion surface of a diffusion element. It has been determined that such extending members may form crevices adjacent the surface of the associated diffusion element, ; - 2 -: 1~ 5Z979 in which gas pockets form. The bubbles which enter such crevices tend to empty the crevices of liquid. Thus the effect of surface tension on the adjoining portion of the gas diffusion surface is reduced, whereby such portion manifests less resistance to the discharge of gas. Thus, more gas is released over these areas of reduced surface tension effect than elsewhere on the gas discharge surface and the resulting uneven distribution of bubbles reduces the mass transfer efficiency of the system.
Accordingly, it is an object of the invention to provide a simple and relatively inexpensive means for sealing the sides of a diffusion element to prevent the lateral release of bubbles and to avoid the ~ormation of gas pockets adjacent the gas diffusion surface of the element.
Another object of the invention is to provide a sealing means that may be used in combination with a pre-stressed, partially gas permeable peripheral region of a diffusion element to block the flow of bubbles from the sides of the dissuion element.
These and other objects of the invention will become apparent from a review of the detailed specification which ollows and a consideration of the accompanying drawings in which like characters identify identical apparatus.
BRIEF SUr~MARY OF THE INVENTION
According to the invention, a wastewater aeration system comprises: a tank; a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe`; a plurality of plenums secured to said header pipe at spaced locatIons along said header pipe in communi-cation with said gas outlet openings; porous diffusion elements secured to said plenums for receiving pressurized gas and re-leasing bubbles in a liquid, said diffuser elements having:
` - 3 -~4.
~ ~ s~9 (1) gas input faces for receiving said pressurized gas;
(2) upwardly facing gas discharge faces for contacting said liquid and releasing said bubbles into said liquid in an upward direction;
(3) side faces at least semi- permeable to gas, said side faces extencling around the peripheries of said gas discharge faces; and
(4) said discharge faces and said side faces defining edges at their intersection; and elastomeric sealing means abutting but not attached to said elements and extending along said edges abutting at least a topmost portion of said side faces for sealing a portion of said diffusion elements adjacent the edges and for preventing the lateral emission of bubbles from said side faces.
BR~EF DESCRIPTION OF THE DRAWINGS
Figure l~is a fragmsntary v-iew of a ~ewage aeration tank comprising air supply main, downcomer pipe, distribution pipes, header pipes and diffusers.
Figure 2 is a perspective view of a section of header pipe and diffusers of Figure 1.
Figure 3 is a vertical transverse cross section of the header pipe and one of the diffusers of Figure 2 taken on section line 3-3 of Figure 2.
Figure 4 is a longitudinal cross section of the diffuser and pipe of Figure 3, the component part of the diffuser being exploded for clarity.
` Figure 5 is an enlarged portion of Figure 4 showing portions of the wall of the header pipe and the lower wall of .j .
the plenum, along with the details of the air flow regulator me~ber which is in communication and connected with .. ~
. ~ , . . .~
f 1~529'~9 f the air outlet and inlet openings in said pipe and lower wall. This figure also shows an optional chec~ valve member on the air flow regulator me~ber.
Figure 6 is a plan view of the plenum of Figure 4.
Figure 7 is an enlarged portion of Figure 3 showing the peripheral edge of the diffusion element in transverse cross section, along with portions of the plenum, retaining means and sealing means.
Figures 8 to 12 show the same portion of the apparatus as Figure 7, but with varying modifications to the diffusion element, retaining means and sealing means.
Description of Preferred and ~ 7 ~ Various OtheriFmbodiments ~ -t~S~ tt~t~-S~
' The above mentioned figures and the following text describe preferrea embodiments of the invention and Yarious others which may be used. It should however be understood that the various embodiments disclosed herein are given only by way of example and that the invention may be embodied in many forms other than those actually disclosed herein.
For example, Figure 1 discloses one of many possible arrangements of ~, .
~ the air distribution piping of a sewage aeration system. In Figure l, sewage Is ~- aeration tank 1 includes bottom 2 with side and end walls 3 and 4 to , contain a body of sewage which is to be aerated. Compr¢ssorS ~not shown) feed air to an air main 8 which generally is supported above the level of liquid in the tank, and which feeds into a downcomer pipe 9 extending vertically from air '~ main 8 to a horizontally disposed distributor pipe 10 supported substantially :
horizontally a short distance above bottom 2. Parallel rows of air header plpes ll, also supported horizontally a short distance ahove bottom 2, are fed by distributor pipe 10. The spacing, in a hori~ontal plane, of air headers 11 and diffusers 12 is determined on the basis of criteria l;nown to persons skilled in the art.
l~ Figure 2 shows in perspective~a broken out and enlarged portion of one `~, 30 oE the air headers 11 with its diffusers 12. Ileader pipes of any material may be used, including for instance, metallic, resin-lined metallic, and rigid resin pipe, including reinforced or unreinforced thermoplastic and thermoset resin pipe. If one chooses a pipe having a load bearing ~Jall of polyneric `
.. . .
1~52~379 f matorial, which is preferred, it should have a tensile strength of about 2000 to about 60,000 psi, a flexural modulus of about 4 x 104 to about 4 x 106 psi and a stiffness of about 10 to about 1000 psi, by AS~ D-2412. ~Jhatever pipe is used, the pipe material is chosen with due regard to its resistance .o corrosion, weather, collapse and impact. Suitable provision (not shown) should be made for expansion and contraction where necessary.
The plenum is of polymeric material, may be reinforced and preferably has the physical properties described above in connection with the preferred pipe. The plenum may be fashioned by any appropriate forming process, such as for instance, injection molding, lay up and spray up techniques.
As shown in~Eigures ~ and 4~r.header~pipe~ has air~ outlet~pen~ngs formed at longitudinally spaced intervals along its top center line to feed air into the respective plenums 14 of diffusers 12. Each plenum 14 may or may not include lower wall means 15. All or at least a substantial portion of such lower wall means, when provided, is circular in transverse cross section and conforms to the outer surface 16 of pipe 11. Lower wall l5 may be held in .. . .
close fitting engagement with pipe 11 in a Yariety of ways, including various mechanical arrangements such as clamps or straps but preerably by bonding to the pipe. In general, any bonding technique may be employed, such as for instance, adhesive bonding; but if the pipe is of polymeric material, w'nich is prefexred, the attachment may also be made by solvent or thermal (including sonic~ welding. The latter is of considerable advantage in terms of ease and economy of construction. Depending on the type of attaclment means employed, the plenum may be sealed to the pipe by the same means ùsed in attachment, or l 25 by diffrrent means. Thus one may provide an elastomeric seal between the !: plcnum lower wall15 and pipe outer surface 16 or the seal may be provided by the welding or adhesive referred to above.
From the standpoint of structural integrity, especially when using ~ :1 both polymeric pipe and a plenum of polymeric material, it is beneficial that lower wall means 15 be held in close fitting engagement with a substantial portion of the length of the pipe outer surface 16 (as shown in Figure 4) - 6 - ~
, , - ' ' ~15Z979 and with the transverse cross section of the pipe. PreEerably, lower wall 15 conforms and enages with the transverse cross section of the pipe through an arc of at least about 20, more preferably about 45 or more degrees and most preferably about 70 or more degrees, at least in the mid portion 17 (Figurc 4) of the lower wall means. In the illustrative and preferred embodiment shown in Figures 3 and 4 the arc is about 90.
As shown in Figures 3 and 4, lower wall ~eans 15 includes an air inlet opening 22, around which there may be provided a small upstanding boss 23 (Figure 3) on the inner surface of plenum lower wall means 15. Air outlet opening 13 and air inlet opening 22 are maintained in registry with one another. ~ }~ S, ~.7.~ *,~ s~ ~o~ q~*
According to the invention,the system may be proYided with an air flow regulator member, one possible example of which is indicated by reference numeral 24. According to a pre~erred embodiment, a combined bonded assembly is formed by the pipe, by lower wall means 15 and by the air flow regulator member or a sleeve member 25 in which the air flo~ regulator ~ember is mounted. Thus~ for instance~ all of these parts may be simultaneously adhesively bonded or welded, with considerable savings in manufacturing steps and costs. The air fiow regulator member 24 will be discussed in greater detail , below. The lower wall means 15 may be of any desired shape as viewed in ~ ~ .
horizontal plan view. It may for instance have a square, rectangular, circular or oval outline, the latter being preferred. Air inlet opening 22 and regulator ;~ ~ 2b~ are both preferably within this outline as viewed in plan view.
~ A wide variety of gas flow regulator means may be ~ployed in the inven-.j :
-~ ~ tion, including those with varying pressure response characteristics. For instance ~ one may employ regulators which respond exponentially to changes in pressure, such as for instance fixed orifices, or those which respond in a morc linear fashion, such as for instance passages with large ratios of length to cross sectional area. Orifices which change their cross section in response to ; pressure changes are also contemplated, including those which can perfonm a 3n valving function and those which are capDble only of uni-directional flow.
~ ~ .
'~ . - . - ' ,: -' ~'' ' ~ ,' `
l~SZ~9 Examples appear in Figures 3, 4 and 5, Figure 5 shows the regulator 24 of Figures 3 and 4 enlarged and in longitudinal cross section. In this embodiment, the regulator is a plug member having a central void to communicate through the open bottom of sleeve 25 with the interior of pipe 11. Extending laterally fro~ recess 32 are a pair of hori~ontal orifices 33 communicating with the interior of plenum 14.
As sho~m in Figures 3 and 4 these orifices 33 are in direct open communication with the interior of plenum 14. However, if the outer ends of orifices 33 are covered by an elastic band 34 as shown inFigure 5, the orifices have a uni-,~dlrectional flow characteristic, i.e. they function as check valves. The uni~
directional flow charactèristicAof the ~egulator-tends--~br`maintain pressu~e~S~-~within plenum 14, thus discouraging backflow of liquid from the exterior o~
the diffuser through the diffusion element 35 into the plenum when pressure in the ~ain inadvertently falls below the hydrostatic pressure of the depth of diffuser placement, or is interrupted. This reduces the difficulties of start-ing up the system when pressure is restored. Backflow of sewage-laden water through diffusion element 35 or regulator 24 tends to plug these components, leading to possible complete plugging or non-uniform distribution of air flow .
through the element and/or system when the flow of air under pressure is restored.
The foregoing Figures 3, 4 and 5 disclose but a few of the possible alternatiYe forms of regulators which may be mounted within the transverse cross sectional area of the plenum, of the header pipe or of both of them. How-ever, the various flow regulator devices depicted herein have the common characteristic that each of them is included in a member which terminates ~` ; beneath the diffuser element 35. Persons skilled in the art will readily furnish a variety of alternative regulator devices, mounted in various fashions, which ; ~ corrcspond to the foregoing.
As shown in Figures 3 through 6, side ~all means 26 is connected ~ ~ 30 with the periphery of lower wall means 15. Preferably, the side wall ~eans is ;~ connected with the entire periphery of the lower wall means, and is inclined : - 8 -- : -' up~ardly and outwardly from the lower wall means. Diffusion element supporting means, spaced upwardly and out~ardly from the lower wall means, are provideA
on said side wall means. Such supporting means may for instance include a horizon-tal annular shelf 27 ith inner and outer diameters respectively smaller and larger than the diameter of the lower edge of the diffusion element 35, to be described in greater detail below. Shelf 27 may, if desired, be part of a step in side wall means 26, the rising portion of which step comprises a cylin-drical generally upright wall 21. The diffusion element supporting means may be in any desired position on side wall means 26, but is preferably at (in, on or near) the extreme upward and outward projection of ~7all means 26 Preferably also wall means 26 i5 of a conical shape.
According to one of the preferred alternative forms of the invention, disclosed in Pigures 3-4, the plenum includes an integral generally upstanding wall 28 which, when viewed in plan view, surrounds the diffusion element supporting means, e.g. annular horizontal shelf 27. ~1hen provided, which is preferred, upstanding wall 28 has a height which is about equal co the height of the diffusion element 35. Thus, according to this preferred alterna-tive, the height of wall 28 ls about equal to or slightly greater or less than the height of the diffuser element. Wall 28 has an inner surface 29, also generally upstanding, an upper edge 30 and threaded outer surface 31. The shelf 27 and generally upstanding wall 28 therefore can, in the preferred embod-~ iment, provide a socket to receive diffusion element 35, in which substantially `~ the entire height of diffusionelement 35 is recessed as shown in Figure 3 and in the enlargement in Figure 7.
::
~ 25 Irrespective of the particular form of support arrangement adopted, ~ .
it is preferred that the element be so supported that all portions thereof which emit air to the surrounding l;.quid may have ready access to replacement water, to ' ~
maintain such emitting portions in contact with water and subject to the influence of surface tension. Thus, it is preferred to avoid a situation in which a side surface oE the element is adjacent to a crevice which can be swept clear and kept clear of water by the air discharged from the side surface. The _ g _ ' ~ ~ .
~s2g79 air ~nanating frcm the element adjacent said crevices is subject to far less surface tension effect, causing air to be preferentially routed to that por-tion of the element and thus correspondingly impairing the uniformity of distribution of flow from the element. However, if the supporting means and other associated structure are so shaped and positioned that any ex~osed portion of the element capable of emitting air to the liquid has ready access to replacement liquid, so that the surface is not swept and kept clear of water, the aforementioned distribution difficulty can be avoided. Alterna-tively, a portion of the diffusion element which would otherwise discharge air into a crevice of the type described a~ove can be sealed by appropriately positioning a seal of lesser height than the element, by applying an imperme-able coating to the surface, or by sufficiently campressing such sides or any portion thereof having access to water so as to render same substantially impermeable. However, the preferred diffuser elements include sides which are porous, at least semi-permeable, free of adherent material preventing bubble emission, and "vertical" (including near vertical, e.g. within about 20 of vertical). Still more preferably such vertical or near vertical edges are covered by the combined structure of the plenum, sealing means and retain-ing means. According to a particularly preferred e~bodiment, described in greater detail below, the sealing means is of lesser height than the diffuser element, but is positioned at an upper edge defined by the intersection of said vertical or near vertical sides and an upward facing portion of the upper gas discharge surface of the element.
~; A wide variety of diffusion elements may be employed, made of varying materials in varying configurations. The elements may, for instance, be formed of organic or inorganic materials in partlculate and/or fibrous forms. An exemplary organic material is particles of fusible polymeric material as disc]osed in United States patent 3,970,731 issued July 20, 1976 to Oksman. Exemplary of inorganic materials are metal and ceramic powders, including for example, alumina, silica, mullite, and vari-ous clays. The finely divided materials are generally shaped and compacted under pressure and, if necessary, heated or fired to fully develop the S15~79 necessary coherency. sonding with organic or inorganic binders is contemplated and the finely divided particles and/or fibers may be bound together by organic adhesive bonds, ceramic or fusion bonding or sintering.
Among the applicable shapes are those which appear round, oval, square, rectangular, polygonal and irregular in plan view, and those which appear substantially horizontal in transverse cross section, including those which are truly flat and those which are only generally horizontal, in the sense of including non-planar surfaces but extending in a generally horizontal direction from one edge to the other. The elements may have plain, vertical or inclined edges, with or without steps and the edge portions may include bevels, rounded portions, grooves and the like.
In general, the applicable elements preferably have active gas discharge surfaces which are free of bubble emitting macro openings, such as those shown for instance in U.S. Patent 3,970,731 issued July 20, 1976 to Oksman. Preferably the element is such that it will emit fine bubbles from random locations throughout the gas discharge surface. Preferably the gas transmission surfaces of the element are free of air transmitting macro holes longer than 0.3T wherein T is the average thickness of the element weighted on an area basis, or are free of macro holes. A macro hole is an intention-ally produced hole substantially larger than the pore size normally producedby compaction of the particulate material. It is beneficial if substantially all gas paths through the body of the element to its gas discharge surface, as installed in the plenum or other holder, are about the same length. More-over, it is preferred to employ a diffusion element having a bubble release pressure in the range of about 2 to about 20, preferably about 3 to about 15 ~ and more preferably a~out 4 to about 10 inches of water gauge. The optimum ; bubble release pressure is considered to be about 7 inches. ~he values given are for bubble re]ease pressure in water of new elements as manufactured, i.e. prior to use. A technique for determining bubble releast pressure and other preferred characteristics for the diffusion elements used in the present inven-tion are disclosed in Canadian application Serial No. 345,502 of Lloyd Ewing et al entitled M FFUSION ELEMENT. It is also preferred to fabricate the element '~
.
l~S;i~979 of hydrophilic materials, i.e. materials which are hydrophilic in the element as manufactured and prior to use. Also, preferably, the element is one whose sides, including for example peripheral vertical edges and vertical or near vertical surfaces of steps near the periphery of the ~lements are porous, at least semi-permeable and free of adherent material preventing bubble emission. A "semi-permeable" side of a diffusion element will emit air or other gas in significant quantities under normal operating conditions, e.g. aerating pressure and water depth (assuming such emission were not blocked by sealing means or otherwise), but has a bubble release pressure at least about l/20th greater than the average bubble release pressure of the normal gas discharge surface of the element, said average being weighted on an area basis. The preferred elements have a specific permeability when new of about 6 to about 200 SCFM at 2 inches of water gauge. One may choose a diffusion element having any one or all of the above preferred characteristics, it being understood however, that that portion of the volume of the element which is beneath the gas discharge surface will be free of through-holes other than pores.
The most preferred diffusion element is a ceramic plate of circular outline having a stepped edge, depicted in Figures 3 and 4, and includes circular central flat area 70, annular beveled edge 71, annular flat surface 72, outer annular beveled surface 73 and horizontal annular surface 74, whose respective outer diameters are 4.5, 6.5, 7.6, 8.7 and 9.25 inches respectively. Surface 70 lies 0.070 inch below surface 72. Beveled surface 73 is at angle of inclination of 25 relative to the horizontal and its common edge with ~152~9 vertical side surface 75 has a 1/16th inch radius as viewed in transverse cross section. The respective overall heights of horizontal annular surface 74, the top edge of vertical side surface 75 and horizontal flat surface 72 are 0.5, 0.741 and 1.000 inch respectively.
The plate is formed from a mix containing particles of alumina with mean transverse and longitudinal dimensions of 0.020 and 0.032 inch respectively, and 20 parts by weight of ceramic bonding agent, per hundred parts by weight of alumina particles. The mix is compacted in a press having a ram with a planar surface and a cylindrical die cavity having a bottom wall with a shape corresponding to the upper surface of diffuser element 35.
The sides of the die cavity and the ram correspond in diameter with the peripheral edge 76 of diffuser element 35, the height of the die cavity from its bottom surface to its upper edge being 1.5 inches. The mix is poured into the cavity in excess, is struck off level with the top of the die and is compressed to the dimensions previously given under a pressure of approximately 900 psi. The resultant compact, after removal from the press, is fired in a kiln at a temperature sufficient to fuse the bonding agent and is then gradually cooled. The resultant product is a coherent porous ceramic diffuser element having a specific permeability of 25 SCFM - 3 SCFM.
The diffuser element, whether of the above described preferred type or not, is supported by and preferably nests within the plenum on the diffusion element supporting means. A sealing means is provided adjacent the periphery of the diffusion element for preventing -12a -, . ~ .
~52979 leakage of air past the periphery of the element. Such sealing means may be fabricated from a wide variety of materials in a wide variety of forms. For example, one may employ various plastics and rubber elastomers. The sealing means may be one or more members of circular, flat or other cross-section, including special profiles matched to the shape of the diffusion element and/or its supporting means. The requisite shapes can be produced by any suitable forming process, such as for instance extrusion, casting and other molding techniques.
The invention contemplates sealing means which are not adherent or attached to the element. Those elements which are neither adherent or attached to the element. Those elements which are neither adherent nor attached to the element, which are preferred in the present invention are preferably held against the element by the structure of the plenum, by the structure of the retaining means described in greater detail below, by the structure of the diffusion element itself, or preferably by a combination of the ~ 20 foregoing. Disposition of the sealing means adjacent the ; periphery of the diffusion element discharge surface includes placement inside or outside the outline of the periphery of the element as viewed in plan view and at varying elevations alongside and/or above the element. The preferred position for the sealing means is :
- 13 ~
~L~52979 at the upper edge of a side surface of the el~ment. The sealing means may overlap said edge or may be located adjacent the edge, such as for example just above or belcw it. Several embodiments are described in greater detail in connection with Figures 7 through 12.
In the particularly preferred embodiment disclosed in Figures 3, 4 and 7 herein, a polyisoprene O-ring 80, having a Shore A Durometer hardness of ab~ut 40+3, nests in an annular step formed about the upper portion of the peripheral surface of diffusion element 35. The diameter "D" of the cross section of O-ring 80 preferably slightly exceeds the spacing between inner surface 29 of plenum side wall means 26 and opposed, facing vertical or near vertical side 75 of element 35, but the height of vertical or near verti-cal surface 75 is substantially smaller than "D", e.g. about 0.5 to 0.8D.
The retaining means employed in the invention, located at the peri-phery of the diffusion element for securing it to the plenum, can also take a wide variety of forms. m us, the invention contemplates retaining means which secure the element by direct or indirect contact about its entire periphery or at spaced points about its periphery. This is in contrast to the center bolt arrangement shown for instance in U.S. patent 4,046,845 issued September 6, 1977 to Veeder and V.S. patent 3,532,272 issued October 20 6, 1970 to Branton.
Attachment of the diffuser element by central or other fasteners which extend through holes in the element, the boundaries of which lie within the active diffusion surface, produce detrimental effects, the pre-diction of which would not be obvious.
In much of the prior art, sealing between element and plenum is accomplished through vertically loaded elastc~eric gaskets. The required loading to effect adequate seal of the porous diffuser element may be high, e.g. 50 pounds/lineal inch of seal. Greater strength and rigidity of the diffuser and plenum are required to distribute these forces about the peri-phery than in the preferred embodiments of this invention wherein con-tinuous peripheral clamping or retaining is employed.
11~i2979 Further, fasteners extending through the element into the plenum typically require holes with clearance. Unless the interiors of the holes are sealed in their entireties, free passage of air is provided in these clearances that promotes excessive flow from the diffuser element in the vicinity of the fastener. Enlarging the sealed area under the lower horizontal surface of the retaining means, to lengthen the path of air from the clearance zone to the diffuser surface, does not correct this deficiency, since the reduction in unit flow (flux) in the vicinity of the fastener resulting from the additional sealed area at the surface, similarly reduces the frictional pressure drop in that region, and the problem of non-uniform distribution persists.
The detrimental effects of the type fastener above described may be overcome by the use of the peripheral clamping or retaining methods employed in our invention.
Among the applicable retaining means are, for example, those including clips, clamps and rings which clamp or merely restrain, secured to the plenum by bolts, hooks, threads and ~ other fastening means.
; However, the preferred retaining means of the present invention shown in Figures 3, 4, 7 and 9 through 12 is an internally threaded retaining ring 84 including a ~ 25 cylindrical member 85 having external gripping lugs 87 and internal threads 86 matching external threads 31 in side wall means 28 of the plenum. Cylindrical member 85 has attached to it above the threads 86 a flange 88 which extends inwardly over generally upstanding wall 28 of the plenum and at least partly across the top of sealing means 80. According to a ; :
1~s2~7s preferred embodiment, the said flange 88 leaves the upper inner quadrant of the cross section of the O-ring 80 uncovered (shown in greater detail in Figure 7) while clamping the O-ring with sufficient force to press it in tight engagement with at least the uppermost portion of vertical side portion 75 closely adjacent the edge 89 between side 75 and the upwardly facing adjacent surface 73, thereby avoiding formation of a crevice at the side of the diffusion element which would be susceptible to expulsion of the liquid in the crevice by the gas flowing through it.
Figures 8 through 11 show alternative but less preferred embodiments of the combination of plenum, diffusion element, sealing means and retaining means which may nevertheless be used successfully in the invention.
Each of these various embodiments has in common a plenum side wall means 26, annular horizontal shelf 27, and generally upstanding wall means 28 which is about of equal height with the diffuser element and which faces the opposed peripheral surface or surfaces of the diffusion element which is indicated by reference numerals 35 and 35A through 35E.
For example, in Figure 8, generally upstanding wall means 28 i5 provided with peripheral flange 90 and circumferentially spaced bolt holes 91 through which extend bolts 93 to clamp a plurality of circumferentially spaced clips 92 against the respective upper surfaces of flange 90 and diffusion element ~; 35A. An elastomeric band or hoop member 95 serves as sealing means. For example, the hoop or band may have an unstretched inside diameter of about 85% of the outside diameter of diffuser element 35A, and is of slightly greater width than ~lSZ~79 the vertical thickness of the diffuser element. When stretched and placed around diffusion element 35A, the extra width of the band forms an inturned upper edge 97, an inturned lower edge 98 and a cylindrical center portion 96, which respectively enclose the upper and lower edges 99 and 100 of the element. Inturned lower edge 98, bearing against annular horizontal shelf 27, seals the interior of the plenum from the vertical space between upstanding wall 28 and element 35A. Cylindrical portion 96 of the elastomeric band prevents air from passing peripherally out of diffusion element 35A into the crevice between itself and upstanding wall means 28. This is an example of retaining means which engages only the element and not the sealing means, and does not contact the entire periphery of the element.
The embodiment of Figure 9 includes an elastomeric ring 101 of rectangular cross section that is nested in an annular step formed about the upper portion of the peripheral surface of diffusion element 35B. The cross section of the rectangular ring 101 is preferably dimensioned to slightly exceed both the spacing between the inner surface 29 of the plenum side wall means 26 and opposed vertical facing side 102 of element 35B, and the height of the vertical side 102 of the annular step. The retaining means for the rectangular ring 101 may generally be the same as was described for the embodiment of Figure 7.
~' The embodiment of Figure 10 utilizes an elastomeric sealing ring 103 of circular cross-section to seal the upper portion of the peripheral edge of diffuser element 35C. The ~15Z~79 generally upstanding wall means 28 has formed in its upper portion an annular shelf 107. This shelf has an elevation such that the underside of annular flange 104 of the retaining means, extending inwardly above the wall
BR~EF DESCRIPTION OF THE DRAWINGS
Figure l~is a fragmsntary v-iew of a ~ewage aeration tank comprising air supply main, downcomer pipe, distribution pipes, header pipes and diffusers.
Figure 2 is a perspective view of a section of header pipe and diffusers of Figure 1.
Figure 3 is a vertical transverse cross section of the header pipe and one of the diffusers of Figure 2 taken on section line 3-3 of Figure 2.
Figure 4 is a longitudinal cross section of the diffuser and pipe of Figure 3, the component part of the diffuser being exploded for clarity.
` Figure 5 is an enlarged portion of Figure 4 showing portions of the wall of the header pipe and the lower wall of .j .
the plenum, along with the details of the air flow regulator me~ber which is in communication and connected with .. ~
. ~ , . . .~
f 1~529'~9 f the air outlet and inlet openings in said pipe and lower wall. This figure also shows an optional chec~ valve member on the air flow regulator me~ber.
Figure 6 is a plan view of the plenum of Figure 4.
Figure 7 is an enlarged portion of Figure 3 showing the peripheral edge of the diffusion element in transverse cross section, along with portions of the plenum, retaining means and sealing means.
Figures 8 to 12 show the same portion of the apparatus as Figure 7, but with varying modifications to the diffusion element, retaining means and sealing means.
Description of Preferred and ~ 7 ~ Various OtheriFmbodiments ~ -t~S~ tt~t~-S~
' The above mentioned figures and the following text describe preferrea embodiments of the invention and Yarious others which may be used. It should however be understood that the various embodiments disclosed herein are given only by way of example and that the invention may be embodied in many forms other than those actually disclosed herein.
For example, Figure 1 discloses one of many possible arrangements of ~, .
~ the air distribution piping of a sewage aeration system. In Figure l, sewage Is ~- aeration tank 1 includes bottom 2 with side and end walls 3 and 4 to , contain a body of sewage which is to be aerated. Compr¢ssorS ~not shown) feed air to an air main 8 which generally is supported above the level of liquid in the tank, and which feeds into a downcomer pipe 9 extending vertically from air '~ main 8 to a horizontally disposed distributor pipe 10 supported substantially :
horizontally a short distance above bottom 2. Parallel rows of air header plpes ll, also supported horizontally a short distance ahove bottom 2, are fed by distributor pipe 10. The spacing, in a hori~ontal plane, of air headers 11 and diffusers 12 is determined on the basis of criteria l;nown to persons skilled in the art.
l~ Figure 2 shows in perspective~a broken out and enlarged portion of one `~, 30 oE the air headers 11 with its diffusers 12. Ileader pipes of any material may be used, including for instance, metallic, resin-lined metallic, and rigid resin pipe, including reinforced or unreinforced thermoplastic and thermoset resin pipe. If one chooses a pipe having a load bearing ~Jall of polyneric `
.. . .
1~52~379 f matorial, which is preferred, it should have a tensile strength of about 2000 to about 60,000 psi, a flexural modulus of about 4 x 104 to about 4 x 106 psi and a stiffness of about 10 to about 1000 psi, by AS~ D-2412. ~Jhatever pipe is used, the pipe material is chosen with due regard to its resistance .o corrosion, weather, collapse and impact. Suitable provision (not shown) should be made for expansion and contraction where necessary.
The plenum is of polymeric material, may be reinforced and preferably has the physical properties described above in connection with the preferred pipe. The plenum may be fashioned by any appropriate forming process, such as for instance, injection molding, lay up and spray up techniques.
As shown in~Eigures ~ and 4~r.header~pipe~ has air~ outlet~pen~ngs formed at longitudinally spaced intervals along its top center line to feed air into the respective plenums 14 of diffusers 12. Each plenum 14 may or may not include lower wall means 15. All or at least a substantial portion of such lower wall means, when provided, is circular in transverse cross section and conforms to the outer surface 16 of pipe 11. Lower wall l5 may be held in .. . .
close fitting engagement with pipe 11 in a Yariety of ways, including various mechanical arrangements such as clamps or straps but preerably by bonding to the pipe. In general, any bonding technique may be employed, such as for instance, adhesive bonding; but if the pipe is of polymeric material, w'nich is prefexred, the attachment may also be made by solvent or thermal (including sonic~ welding. The latter is of considerable advantage in terms of ease and economy of construction. Depending on the type of attaclment means employed, the plenum may be sealed to the pipe by the same means ùsed in attachment, or l 25 by diffrrent means. Thus one may provide an elastomeric seal between the !: plcnum lower wall15 and pipe outer surface 16 or the seal may be provided by the welding or adhesive referred to above.
From the standpoint of structural integrity, especially when using ~ :1 both polymeric pipe and a plenum of polymeric material, it is beneficial that lower wall means 15 be held in close fitting engagement with a substantial portion of the length of the pipe outer surface 16 (as shown in Figure 4) - 6 - ~
, , - ' ' ~15Z979 and with the transverse cross section of the pipe. PreEerably, lower wall 15 conforms and enages with the transverse cross section of the pipe through an arc of at least about 20, more preferably about 45 or more degrees and most preferably about 70 or more degrees, at least in the mid portion 17 (Figurc 4) of the lower wall means. In the illustrative and preferred embodiment shown in Figures 3 and 4 the arc is about 90.
As shown in Figures 3 and 4, lower wall ~eans 15 includes an air inlet opening 22, around which there may be provided a small upstanding boss 23 (Figure 3) on the inner surface of plenum lower wall means 15. Air outlet opening 13 and air inlet opening 22 are maintained in registry with one another. ~ }~ S, ~.7.~ *,~ s~ ~o~ q~*
According to the invention,the system may be proYided with an air flow regulator member, one possible example of which is indicated by reference numeral 24. According to a pre~erred embodiment, a combined bonded assembly is formed by the pipe, by lower wall means 15 and by the air flow regulator member or a sleeve member 25 in which the air flo~ regulator ~ember is mounted. Thus~ for instance~ all of these parts may be simultaneously adhesively bonded or welded, with considerable savings in manufacturing steps and costs. The air fiow regulator member 24 will be discussed in greater detail , below. The lower wall means 15 may be of any desired shape as viewed in ~ ~ .
horizontal plan view. It may for instance have a square, rectangular, circular or oval outline, the latter being preferred. Air inlet opening 22 and regulator ;~ ~ 2b~ are both preferably within this outline as viewed in plan view.
~ A wide variety of gas flow regulator means may be ~ployed in the inven-.j :
-~ ~ tion, including those with varying pressure response characteristics. For instance ~ one may employ regulators which respond exponentially to changes in pressure, such as for instance fixed orifices, or those which respond in a morc linear fashion, such as for instance passages with large ratios of length to cross sectional area. Orifices which change their cross section in response to ; pressure changes are also contemplated, including those which can perfonm a 3n valving function and those which are capDble only of uni-directional flow.
~ ~ .
'~ . - . - ' ,: -' ~'' ' ~ ,' `
l~SZ~9 Examples appear in Figures 3, 4 and 5, Figure 5 shows the regulator 24 of Figures 3 and 4 enlarged and in longitudinal cross section. In this embodiment, the regulator is a plug member having a central void to communicate through the open bottom of sleeve 25 with the interior of pipe 11. Extending laterally fro~ recess 32 are a pair of hori~ontal orifices 33 communicating with the interior of plenum 14.
As sho~m in Figures 3 and 4 these orifices 33 are in direct open communication with the interior of plenum 14. However, if the outer ends of orifices 33 are covered by an elastic band 34 as shown inFigure 5, the orifices have a uni-,~dlrectional flow characteristic, i.e. they function as check valves. The uni~
directional flow charactèristicAof the ~egulator-tends--~br`maintain pressu~e~S~-~within plenum 14, thus discouraging backflow of liquid from the exterior o~
the diffuser through the diffusion element 35 into the plenum when pressure in the ~ain inadvertently falls below the hydrostatic pressure of the depth of diffuser placement, or is interrupted. This reduces the difficulties of start-ing up the system when pressure is restored. Backflow of sewage-laden water through diffusion element 35 or regulator 24 tends to plug these components, leading to possible complete plugging or non-uniform distribution of air flow .
through the element and/or system when the flow of air under pressure is restored.
The foregoing Figures 3, 4 and 5 disclose but a few of the possible alternatiYe forms of regulators which may be mounted within the transverse cross sectional area of the plenum, of the header pipe or of both of them. How-ever, the various flow regulator devices depicted herein have the common characteristic that each of them is included in a member which terminates ~` ; beneath the diffuser element 35. Persons skilled in the art will readily furnish a variety of alternative regulator devices, mounted in various fashions, which ; ~ corrcspond to the foregoing.
As shown in Figures 3 through 6, side ~all means 26 is connected ~ ~ 30 with the periphery of lower wall means 15. Preferably, the side wall ~eans is ;~ connected with the entire periphery of the lower wall means, and is inclined : - 8 -- : -' up~ardly and outwardly from the lower wall means. Diffusion element supporting means, spaced upwardly and out~ardly from the lower wall means, are provideA
on said side wall means. Such supporting means may for instance include a horizon-tal annular shelf 27 ith inner and outer diameters respectively smaller and larger than the diameter of the lower edge of the diffusion element 35, to be described in greater detail below. Shelf 27 may, if desired, be part of a step in side wall means 26, the rising portion of which step comprises a cylin-drical generally upright wall 21. The diffusion element supporting means may be in any desired position on side wall means 26, but is preferably at (in, on or near) the extreme upward and outward projection of ~7all means 26 Preferably also wall means 26 i5 of a conical shape.
According to one of the preferred alternative forms of the invention, disclosed in Pigures 3-4, the plenum includes an integral generally upstanding wall 28 which, when viewed in plan view, surrounds the diffusion element supporting means, e.g. annular horizontal shelf 27. ~1hen provided, which is preferred, upstanding wall 28 has a height which is about equal co the height of the diffusion element 35. Thus, according to this preferred alterna-tive, the height of wall 28 ls about equal to or slightly greater or less than the height of the diffuser element. Wall 28 has an inner surface 29, also generally upstanding, an upper edge 30 and threaded outer surface 31. The shelf 27 and generally upstanding wall 28 therefore can, in the preferred embod-~ iment, provide a socket to receive diffusion element 35, in which substantially `~ the entire height of diffusionelement 35 is recessed as shown in Figure 3 and in the enlargement in Figure 7.
::
~ 25 Irrespective of the particular form of support arrangement adopted, ~ .
it is preferred that the element be so supported that all portions thereof which emit air to the surrounding l;.quid may have ready access to replacement water, to ' ~
maintain such emitting portions in contact with water and subject to the influence of surface tension. Thus, it is preferred to avoid a situation in which a side surface oE the element is adjacent to a crevice which can be swept clear and kept clear of water by the air discharged from the side surface. The _ g _ ' ~ ~ .
~s2g79 air ~nanating frcm the element adjacent said crevices is subject to far less surface tension effect, causing air to be preferentially routed to that por-tion of the element and thus correspondingly impairing the uniformity of distribution of flow from the element. However, if the supporting means and other associated structure are so shaped and positioned that any ex~osed portion of the element capable of emitting air to the liquid has ready access to replacement liquid, so that the surface is not swept and kept clear of water, the aforementioned distribution difficulty can be avoided. Alterna-tively, a portion of the diffusion element which would otherwise discharge air into a crevice of the type described a~ove can be sealed by appropriately positioning a seal of lesser height than the element, by applying an imperme-able coating to the surface, or by sufficiently campressing such sides or any portion thereof having access to water so as to render same substantially impermeable. However, the preferred diffuser elements include sides which are porous, at least semi-permeable, free of adherent material preventing bubble emission, and "vertical" (including near vertical, e.g. within about 20 of vertical). Still more preferably such vertical or near vertical edges are covered by the combined structure of the plenum, sealing means and retain-ing means. According to a particularly preferred e~bodiment, described in greater detail below, the sealing means is of lesser height than the diffuser element, but is positioned at an upper edge defined by the intersection of said vertical or near vertical sides and an upward facing portion of the upper gas discharge surface of the element.
~; A wide variety of diffusion elements may be employed, made of varying materials in varying configurations. The elements may, for instance, be formed of organic or inorganic materials in partlculate and/or fibrous forms. An exemplary organic material is particles of fusible polymeric material as disc]osed in United States patent 3,970,731 issued July 20, 1976 to Oksman. Exemplary of inorganic materials are metal and ceramic powders, including for example, alumina, silica, mullite, and vari-ous clays. The finely divided materials are generally shaped and compacted under pressure and, if necessary, heated or fired to fully develop the S15~79 necessary coherency. sonding with organic or inorganic binders is contemplated and the finely divided particles and/or fibers may be bound together by organic adhesive bonds, ceramic or fusion bonding or sintering.
Among the applicable shapes are those which appear round, oval, square, rectangular, polygonal and irregular in plan view, and those which appear substantially horizontal in transverse cross section, including those which are truly flat and those which are only generally horizontal, in the sense of including non-planar surfaces but extending in a generally horizontal direction from one edge to the other. The elements may have plain, vertical or inclined edges, with or without steps and the edge portions may include bevels, rounded portions, grooves and the like.
In general, the applicable elements preferably have active gas discharge surfaces which are free of bubble emitting macro openings, such as those shown for instance in U.S. Patent 3,970,731 issued July 20, 1976 to Oksman. Preferably the element is such that it will emit fine bubbles from random locations throughout the gas discharge surface. Preferably the gas transmission surfaces of the element are free of air transmitting macro holes longer than 0.3T wherein T is the average thickness of the element weighted on an area basis, or are free of macro holes. A macro hole is an intention-ally produced hole substantially larger than the pore size normally producedby compaction of the particulate material. It is beneficial if substantially all gas paths through the body of the element to its gas discharge surface, as installed in the plenum or other holder, are about the same length. More-over, it is preferred to employ a diffusion element having a bubble release pressure in the range of about 2 to about 20, preferably about 3 to about 15 ~ and more preferably a~out 4 to about 10 inches of water gauge. The optimum ; bubble release pressure is considered to be about 7 inches. ~he values given are for bubble re]ease pressure in water of new elements as manufactured, i.e. prior to use. A technique for determining bubble releast pressure and other preferred characteristics for the diffusion elements used in the present inven-tion are disclosed in Canadian application Serial No. 345,502 of Lloyd Ewing et al entitled M FFUSION ELEMENT. It is also preferred to fabricate the element '~
.
l~S;i~979 of hydrophilic materials, i.e. materials which are hydrophilic in the element as manufactured and prior to use. Also, preferably, the element is one whose sides, including for example peripheral vertical edges and vertical or near vertical surfaces of steps near the periphery of the ~lements are porous, at least semi-permeable and free of adherent material preventing bubble emission. A "semi-permeable" side of a diffusion element will emit air or other gas in significant quantities under normal operating conditions, e.g. aerating pressure and water depth (assuming such emission were not blocked by sealing means or otherwise), but has a bubble release pressure at least about l/20th greater than the average bubble release pressure of the normal gas discharge surface of the element, said average being weighted on an area basis. The preferred elements have a specific permeability when new of about 6 to about 200 SCFM at 2 inches of water gauge. One may choose a diffusion element having any one or all of the above preferred characteristics, it being understood however, that that portion of the volume of the element which is beneath the gas discharge surface will be free of through-holes other than pores.
The most preferred diffusion element is a ceramic plate of circular outline having a stepped edge, depicted in Figures 3 and 4, and includes circular central flat area 70, annular beveled edge 71, annular flat surface 72, outer annular beveled surface 73 and horizontal annular surface 74, whose respective outer diameters are 4.5, 6.5, 7.6, 8.7 and 9.25 inches respectively. Surface 70 lies 0.070 inch below surface 72. Beveled surface 73 is at angle of inclination of 25 relative to the horizontal and its common edge with ~152~9 vertical side surface 75 has a 1/16th inch radius as viewed in transverse cross section. The respective overall heights of horizontal annular surface 74, the top edge of vertical side surface 75 and horizontal flat surface 72 are 0.5, 0.741 and 1.000 inch respectively.
The plate is formed from a mix containing particles of alumina with mean transverse and longitudinal dimensions of 0.020 and 0.032 inch respectively, and 20 parts by weight of ceramic bonding agent, per hundred parts by weight of alumina particles. The mix is compacted in a press having a ram with a planar surface and a cylindrical die cavity having a bottom wall with a shape corresponding to the upper surface of diffuser element 35.
The sides of the die cavity and the ram correspond in diameter with the peripheral edge 76 of diffuser element 35, the height of the die cavity from its bottom surface to its upper edge being 1.5 inches. The mix is poured into the cavity in excess, is struck off level with the top of the die and is compressed to the dimensions previously given under a pressure of approximately 900 psi. The resultant compact, after removal from the press, is fired in a kiln at a temperature sufficient to fuse the bonding agent and is then gradually cooled. The resultant product is a coherent porous ceramic diffuser element having a specific permeability of 25 SCFM - 3 SCFM.
The diffuser element, whether of the above described preferred type or not, is supported by and preferably nests within the plenum on the diffusion element supporting means. A sealing means is provided adjacent the periphery of the diffusion element for preventing -12a -, . ~ .
~52979 leakage of air past the periphery of the element. Such sealing means may be fabricated from a wide variety of materials in a wide variety of forms. For example, one may employ various plastics and rubber elastomers. The sealing means may be one or more members of circular, flat or other cross-section, including special profiles matched to the shape of the diffusion element and/or its supporting means. The requisite shapes can be produced by any suitable forming process, such as for instance extrusion, casting and other molding techniques.
The invention contemplates sealing means which are not adherent or attached to the element. Those elements which are neither adherent or attached to the element. Those elements which are neither adherent nor attached to the element, which are preferred in the present invention are preferably held against the element by the structure of the plenum, by the structure of the retaining means described in greater detail below, by the structure of the diffusion element itself, or preferably by a combination of the ~ 20 foregoing. Disposition of the sealing means adjacent the ; periphery of the diffusion element discharge surface includes placement inside or outside the outline of the periphery of the element as viewed in plan view and at varying elevations alongside and/or above the element. The preferred position for the sealing means is :
- 13 ~
~L~52979 at the upper edge of a side surface of the el~ment. The sealing means may overlap said edge or may be located adjacent the edge, such as for example just above or belcw it. Several embodiments are described in greater detail in connection with Figures 7 through 12.
In the particularly preferred embodiment disclosed in Figures 3, 4 and 7 herein, a polyisoprene O-ring 80, having a Shore A Durometer hardness of ab~ut 40+3, nests in an annular step formed about the upper portion of the peripheral surface of diffusion element 35. The diameter "D" of the cross section of O-ring 80 preferably slightly exceeds the spacing between inner surface 29 of plenum side wall means 26 and opposed, facing vertical or near vertical side 75 of element 35, but the height of vertical or near verti-cal surface 75 is substantially smaller than "D", e.g. about 0.5 to 0.8D.
The retaining means employed in the invention, located at the peri-phery of the diffusion element for securing it to the plenum, can also take a wide variety of forms. m us, the invention contemplates retaining means which secure the element by direct or indirect contact about its entire periphery or at spaced points about its periphery. This is in contrast to the center bolt arrangement shown for instance in U.S. patent 4,046,845 issued September 6, 1977 to Veeder and V.S. patent 3,532,272 issued October 20 6, 1970 to Branton.
Attachment of the diffuser element by central or other fasteners which extend through holes in the element, the boundaries of which lie within the active diffusion surface, produce detrimental effects, the pre-diction of which would not be obvious.
In much of the prior art, sealing between element and plenum is accomplished through vertically loaded elastc~eric gaskets. The required loading to effect adequate seal of the porous diffuser element may be high, e.g. 50 pounds/lineal inch of seal. Greater strength and rigidity of the diffuser and plenum are required to distribute these forces about the peri-phery than in the preferred embodiments of this invention wherein con-tinuous peripheral clamping or retaining is employed.
11~i2979 Further, fasteners extending through the element into the plenum typically require holes with clearance. Unless the interiors of the holes are sealed in their entireties, free passage of air is provided in these clearances that promotes excessive flow from the diffuser element in the vicinity of the fastener. Enlarging the sealed area under the lower horizontal surface of the retaining means, to lengthen the path of air from the clearance zone to the diffuser surface, does not correct this deficiency, since the reduction in unit flow (flux) in the vicinity of the fastener resulting from the additional sealed area at the surface, similarly reduces the frictional pressure drop in that region, and the problem of non-uniform distribution persists.
The detrimental effects of the type fastener above described may be overcome by the use of the peripheral clamping or retaining methods employed in our invention.
Among the applicable retaining means are, for example, those including clips, clamps and rings which clamp or merely restrain, secured to the plenum by bolts, hooks, threads and ~ other fastening means.
; However, the preferred retaining means of the present invention shown in Figures 3, 4, 7 and 9 through 12 is an internally threaded retaining ring 84 including a ~ 25 cylindrical member 85 having external gripping lugs 87 and internal threads 86 matching external threads 31 in side wall means 28 of the plenum. Cylindrical member 85 has attached to it above the threads 86 a flange 88 which extends inwardly over generally upstanding wall 28 of the plenum and at least partly across the top of sealing means 80. According to a ; :
1~s2~7s preferred embodiment, the said flange 88 leaves the upper inner quadrant of the cross section of the O-ring 80 uncovered (shown in greater detail in Figure 7) while clamping the O-ring with sufficient force to press it in tight engagement with at least the uppermost portion of vertical side portion 75 closely adjacent the edge 89 between side 75 and the upwardly facing adjacent surface 73, thereby avoiding formation of a crevice at the side of the diffusion element which would be susceptible to expulsion of the liquid in the crevice by the gas flowing through it.
Figures 8 through 11 show alternative but less preferred embodiments of the combination of plenum, diffusion element, sealing means and retaining means which may nevertheless be used successfully in the invention.
Each of these various embodiments has in common a plenum side wall means 26, annular horizontal shelf 27, and generally upstanding wall means 28 which is about of equal height with the diffuser element and which faces the opposed peripheral surface or surfaces of the diffusion element which is indicated by reference numerals 35 and 35A through 35E.
For example, in Figure 8, generally upstanding wall means 28 i5 provided with peripheral flange 90 and circumferentially spaced bolt holes 91 through which extend bolts 93 to clamp a plurality of circumferentially spaced clips 92 against the respective upper surfaces of flange 90 and diffusion element ~; 35A. An elastomeric band or hoop member 95 serves as sealing means. For example, the hoop or band may have an unstretched inside diameter of about 85% of the outside diameter of diffuser element 35A, and is of slightly greater width than ~lSZ~79 the vertical thickness of the diffuser element. When stretched and placed around diffusion element 35A, the extra width of the band forms an inturned upper edge 97, an inturned lower edge 98 and a cylindrical center portion 96, which respectively enclose the upper and lower edges 99 and 100 of the element. Inturned lower edge 98, bearing against annular horizontal shelf 27, seals the interior of the plenum from the vertical space between upstanding wall 28 and element 35A. Cylindrical portion 96 of the elastomeric band prevents air from passing peripherally out of diffusion element 35A into the crevice between itself and upstanding wall means 28. This is an example of retaining means which engages only the element and not the sealing means, and does not contact the entire periphery of the element.
The embodiment of Figure 9 includes an elastomeric ring 101 of rectangular cross section that is nested in an annular step formed about the upper portion of the peripheral surface of diffusion element 35B. The cross section of the rectangular ring 101 is preferably dimensioned to slightly exceed both the spacing between the inner surface 29 of the plenum side wall means 26 and opposed vertical facing side 102 of element 35B, and the height of the vertical side 102 of the annular step. The retaining means for the rectangular ring 101 may generally be the same as was described for the embodiment of Figure 7.
~' The embodiment of Figure 10 utilizes an elastomeric sealing ring 103 of circular cross-section to seal the upper portion of the peripheral edge of diffuser element 35C. The ~15Z~79 generally upstanding wall means 28 has formed in its upper portion an annular shelf 107. This shelf has an elevation such that the underside of annular flange 104 of the retaining means, extending inwardly above the wall
5 means 28 and ring 103, will not clamp the bottom surface of ring 103 against the horizontal surface of shelf 107, even when the retaining means is screwed down as far as possible on the holder. The retaining means and its short dependent lip 105 assist in the sealing function by keeping the ring 103 and element 35C in place, but sealing pressure is provided by horizontal compression of ring 103 between the upper portion of upstanding wall means 28 and the upper portion of the side of the element, at and just below the edge marking the line of demarcation between the side and upper surfaces of the element. An interference fit between the wall means 28, ring 103 and the side of element 35C causes the desired compression.
The embodiment of Figure 11 includes an elastomeric hoop 18 of generally c-shaped cross section. The inner side 109 of elastomeric hoop 108 is shaped to abut the uppermost portion of a diffusion element 35D having an outwardly slanting peripheral edge 110. The outer side 111 of elastomeric hoop 108 is shaped to abut the topmost portion of the inner surface of wall means 28. The hoop 108 is held in sealing contact with the uppermost portion of diffusion element 35D
by a retaining means having an annular flange 112 extending `~ inwardly over upstanding wall 28 of the plenum and the top of hoop 108. The annular flange 112 tends to urge hoop 108 downwardly to wedge hoop 108 in sealing contact between the slanting peripheral edge 110 of diffusion element 35D and the upstanding wall means 28. .
~.~SZ979 In the embodiment of Figure 12 the side of the diffuser element 35E has a tapered peripheral edge 113 dimensioned so that a topmost portion of the peripheral edge 113 extends outwardly over an annular shoulder 114 of upstanding wall means 28. A sealing ring 115 of triangular cross section rests upon annular shoulder 114 and is held in a sealing position by the abutting surface of the extending topmost portion of the peripheral edge 113.
The diffuser element 35E and triangular sealing ring 115 are held in place by an internally threaded clamping ring 116 having threads 117 that engage corresponding outwardly facing threads 118 of upstanding wall means 28.
The clamping ring 116 has an annular flange 119 with an inner surface 120 of about the same diameter as the top surface of diffuser element 35E. Lugs 121 are situated at spaced points around the inner surface 120 of the clamping ring 116 and extend a short distance inwardly over the top surface of diffuser element 35E to hold the diffuser element 35E in : place. Thus, the diffuser element 35E is clamped only at its periphery, and only at spaced positions along the periphery.
The diffuser element 35E is supported in the plenum by the abutting surfaces of the triangular sealing ring 115 and the topmost portion of the peripheral edge 113. However, it should be appreciated that an additional means of support, such as an annular shoulder, could be provided to contact the bottom surface 122 of diffuser element 35E to provide additional support for diffuser element 35E in the plenum.
Figures 7 and 9 through 12 show sealing rings that are substantially smaller than the height of their respective diffusion elements. Each of the sealing rings is positioned '. ' :
1~ 5~79 adjacent the edge or intersection between the permeable or semi-permeable side and the upper gas discharge surfaces of a diffusion element, in an abutting relation to an uppermost portion of the diffuser side surface. Such positioning of the sealing ring serves to block direct flow of air from the side of the diffusion element to the liquid. The positionîng and sealing engagement of the sealing ring also avoids the formation of air-trapping crevices that would otherwise disturb the uniform emission of aeration bubbles at the gas discharge surface of the diffusion element. However, it should be noted that similar benefits (with some reduction of available air discharge area) can be obtained by positioning the sealing ring upon the upper gas discharge surface of the element adjacent to and radially inwardly of the above-mentioned edge or intersection.
A particularly beneficial result is obtained when a sealing means is positioned at the above-mentioned edge or intersection, and the pores extending to the side of the diffusion element are covered, such as for example by the band member 95 of Figure 8, or are reduced in permeability, such as for example by using the semi-permeable stepped side configuration that is shown in Figure 7. ~hese and other ~ possible arrangements can prevent or offset any tendency which ;~ may exilst for air to short-circuit from the space between upstanding wall means 28 and the element through the side of tbe element to its upper discharge surface.
In the stepped configuration, the particulate material of the diffusion element beneath horizontal annular surface 74 and adjacent peripheral surface 76 has been subjected to sufficient reduction in apparent volumetric :
~15Z~9 compression ratio to reduce its permeability, as compared to the upwardly facing gas discharge surfaces 72 and 73, i.e. it is semi-permeable as defined above. In addition, the surface in the vicinity of the vertical side surface 75 has been rendered semi-permeable in a similar fashion during formation of beveled surface 73. The limited reduction in apparent volumetric compression ratio results in a controlled reduction in effective pore diameter, the effect of which is an increase in fric*ional resistance to specific fluid flow as well as an increase in bubble release pressure, both of which serve to compensate for the reduction in specific flow resistance provided by the clearance passage. Uniformity of gas discharge across the diffusion surface may thus be promoted. Of course, it should be understood that if the peripheral surface ~6 were subjected to sufficient compressive stress in the manufacturing process to render it impermeable, such compressive stress can adversely affect permeability of the element radially inward of its peripheral zone, thus promoting non-uniform -- and therefore less efficient -- gas discharge. Therefore, it is preferable to apply only enough compressive stress in the manufacturing process to reduce but not destroy the permeability of the sides of the element.
The property of reduced permeability relative to the upwardly facing gas discharge surfaces is beneficial when combined with the sealing means at the above described edge.
The combination tends to reduce both the crevice difficuties described above and dlfficulties with short circuiting of air from the plenum to the element gas discharge surface along air flow paths of differing length. For this reaRon, the combination of a side of reduced permeability and a sealing ~5Z9~79 means at the above described edge represents a preferred embodiment of the present invention.
The invention was conceived and has been illustrated herein in the context of the waste-water and sewage aeration art. However, experience with the invention has suggested that it can be applied to gas diffusion processes in general, including sewage treatment processes involving substantiallypure oxygen, or oxygen- or ozone-enriched air, or non-sewage treatment processes involving a wide variety of gases and liquids.
Th~ foregoing are but a few of the many ways in which the present invention may be embodied. The above embodiments are offered for purposes of illustration and not limitation. Accordingly, it is intended to protect all subject matter defined by the accompanying claims and all equivalents thereof.
The embodiment of Figure 11 includes an elastomeric hoop 18 of generally c-shaped cross section. The inner side 109 of elastomeric hoop 108 is shaped to abut the uppermost portion of a diffusion element 35D having an outwardly slanting peripheral edge 110. The outer side 111 of elastomeric hoop 108 is shaped to abut the topmost portion of the inner surface of wall means 28. The hoop 108 is held in sealing contact with the uppermost portion of diffusion element 35D
by a retaining means having an annular flange 112 extending `~ inwardly over upstanding wall 28 of the plenum and the top of hoop 108. The annular flange 112 tends to urge hoop 108 downwardly to wedge hoop 108 in sealing contact between the slanting peripheral edge 110 of diffusion element 35D and the upstanding wall means 28. .
~.~SZ979 In the embodiment of Figure 12 the side of the diffuser element 35E has a tapered peripheral edge 113 dimensioned so that a topmost portion of the peripheral edge 113 extends outwardly over an annular shoulder 114 of upstanding wall means 28. A sealing ring 115 of triangular cross section rests upon annular shoulder 114 and is held in a sealing position by the abutting surface of the extending topmost portion of the peripheral edge 113.
The diffuser element 35E and triangular sealing ring 115 are held in place by an internally threaded clamping ring 116 having threads 117 that engage corresponding outwardly facing threads 118 of upstanding wall means 28.
The clamping ring 116 has an annular flange 119 with an inner surface 120 of about the same diameter as the top surface of diffuser element 35E. Lugs 121 are situated at spaced points around the inner surface 120 of the clamping ring 116 and extend a short distance inwardly over the top surface of diffuser element 35E to hold the diffuser element 35E in : place. Thus, the diffuser element 35E is clamped only at its periphery, and only at spaced positions along the periphery.
The diffuser element 35E is supported in the plenum by the abutting surfaces of the triangular sealing ring 115 and the topmost portion of the peripheral edge 113. However, it should be appreciated that an additional means of support, such as an annular shoulder, could be provided to contact the bottom surface 122 of diffuser element 35E to provide additional support for diffuser element 35E in the plenum.
Figures 7 and 9 through 12 show sealing rings that are substantially smaller than the height of their respective diffusion elements. Each of the sealing rings is positioned '. ' :
1~ 5~79 adjacent the edge or intersection between the permeable or semi-permeable side and the upper gas discharge surfaces of a diffusion element, in an abutting relation to an uppermost portion of the diffuser side surface. Such positioning of the sealing ring serves to block direct flow of air from the side of the diffusion element to the liquid. The positionîng and sealing engagement of the sealing ring also avoids the formation of air-trapping crevices that would otherwise disturb the uniform emission of aeration bubbles at the gas discharge surface of the diffusion element. However, it should be noted that similar benefits (with some reduction of available air discharge area) can be obtained by positioning the sealing ring upon the upper gas discharge surface of the element adjacent to and radially inwardly of the above-mentioned edge or intersection.
A particularly beneficial result is obtained when a sealing means is positioned at the above-mentioned edge or intersection, and the pores extending to the side of the diffusion element are covered, such as for example by the band member 95 of Figure 8, or are reduced in permeability, such as for example by using the semi-permeable stepped side configuration that is shown in Figure 7. ~hese and other ~ possible arrangements can prevent or offset any tendency which ;~ may exilst for air to short-circuit from the space between upstanding wall means 28 and the element through the side of tbe element to its upper discharge surface.
In the stepped configuration, the particulate material of the diffusion element beneath horizontal annular surface 74 and adjacent peripheral surface 76 has been subjected to sufficient reduction in apparent volumetric :
~15Z~9 compression ratio to reduce its permeability, as compared to the upwardly facing gas discharge surfaces 72 and 73, i.e. it is semi-permeable as defined above. In addition, the surface in the vicinity of the vertical side surface 75 has been rendered semi-permeable in a similar fashion during formation of beveled surface 73. The limited reduction in apparent volumetric compression ratio results in a controlled reduction in effective pore diameter, the effect of which is an increase in fric*ional resistance to specific fluid flow as well as an increase in bubble release pressure, both of which serve to compensate for the reduction in specific flow resistance provided by the clearance passage. Uniformity of gas discharge across the diffusion surface may thus be promoted. Of course, it should be understood that if the peripheral surface ~6 were subjected to sufficient compressive stress in the manufacturing process to render it impermeable, such compressive stress can adversely affect permeability of the element radially inward of its peripheral zone, thus promoting non-uniform -- and therefore less efficient -- gas discharge. Therefore, it is preferable to apply only enough compressive stress in the manufacturing process to reduce but not destroy the permeability of the sides of the element.
The property of reduced permeability relative to the upwardly facing gas discharge surfaces is beneficial when combined with the sealing means at the above described edge.
The combination tends to reduce both the crevice difficuties described above and dlfficulties with short circuiting of air from the plenum to the element gas discharge surface along air flow paths of differing length. For this reaRon, the combination of a side of reduced permeability and a sealing ~5Z9~79 means at the above described edge represents a preferred embodiment of the present invention.
The invention was conceived and has been illustrated herein in the context of the waste-water and sewage aeration art. However, experience with the invention has suggested that it can be applied to gas diffusion processes in general, including sewage treatment processes involving substantiallypure oxygen, or oxygen- or ozone-enriched air, or non-sewage treatment processes involving a wide variety of gases and liquids.
Th~ foregoing are but a few of the many ways in which the present invention may be embodied. The above embodiments are offered for purposes of illustration and not limitation. Accordingly, it is intended to protect all subject matter defined by the accompanying claims and all equivalents thereof.
Claims (17)
1. A wastewater aeration system comprising:
a tank;
a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe;
a plurality of plenums secured to said header pipe at spaced locations along said header pipe in communication with said gas outlet openings;
porous diffusion elements secured to said plenums for receiving pressurized gas and releasing bubbles in a liquid, said diffuser elements having:
(1) gas input faces for receiving said pressurized gas;
(2) upwardly facing gas discharge faces for contacting said liquid and releasing said bubbles into said liquid in an upward direction;
(3) side faces at least semi-permeable to gas, said side faces extending around the peripheries of said gas discharge faces; and (4) said discharge faces and said side faces defining edges at their intersection; and elastomeric sealing means abutting but not attached to said elements and extending along said edges abutting at least a top most portion of said side faces for sealing a portion of said diffusion elements adjacent the edges and preventing bubbles from being emitted from said side faces and passing into said tank.
a tank;
a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe;
a plurality of plenums secured to said header pipe at spaced locations along said header pipe in communication with said gas outlet openings;
porous diffusion elements secured to said plenums for receiving pressurized gas and releasing bubbles in a liquid, said diffuser elements having:
(1) gas input faces for receiving said pressurized gas;
(2) upwardly facing gas discharge faces for contacting said liquid and releasing said bubbles into said liquid in an upward direction;
(3) side faces at least semi-permeable to gas, said side faces extending around the peripheries of said gas discharge faces; and (4) said discharge faces and said side faces defining edges at their intersection; and elastomeric sealing means abutting but not attached to said elements and extending along said edges abutting at least a top most portion of said side faces for sealing a portion of said diffusion elements adjacent the edges and preventing bubbles from being emitted from said side faces and passing into said tank.
2. A wastewater aeration system according to claim 1 wherein the gas discharge faces of said diffusion elements are broken only by uniformly sized pores.
3. A wastewater aeration system according to claim 1 wherein said diffusion elements include means for emitting bubbles randomly over the surface of said gas discharge faces.
4. A wastewater aeration system according to claim 1 wherein said diffusion elements include gas transmission surfaces and a plurality of associated gas passages, said elements being substantially free of macro holes in said surfaces that are more than 3/10 of the average thickness T of said diffusion elements weighted on an area bases.
5. A wastewater aeration system according to claim 1 wherein said diffusion elements include means for defining gas diffusion passages therethrough substantially all of which are of substantially the same length.
6. A wastewater aeration system according to claim 1 wherein said diffusion elements include means for releasing said bubbles at a bubble release pressure in the range of about two to about twenty inches of water gauge.
7. A wastewater aeration system according to claim 1 wherein the material of said diffusion elements is hydrophilic prior to use in the system.
8. A wastewater aeration system according to claim 1 wherein the gas discharge faces of said diffusion elements are substantially flat.
9. A wastewater aeration system according to claim 1 including means for positioning said elastomeric sealing means in sealing engagement with said side faces of said diffusion elements, said upper side edges defining a line of demarcation between said side faces and the peripheries of said upwardly facing gas discharge faces.
10. A wastewater aeration system according to claim 1 further comprising regulator means for regulating the flow of said pressurized gas input faces of said diffusion elements.
11. A wastewater aeration system according to claim 1 including means for supplying all gas discharge portions of the gas discharge faces of said diffusion elements with replacement liquid to maintain a uniform surface tension effect over the gas discharge faces of said diffusion elements.
12. A wastewater aeration system according to claim 1 further comprising:
holder means for supporting said diffusion elements, said holder means having upwardly directed side wall means adjacent to the side faces of said diffusion elements; and retaining means positioned along the peripheries of the diffusion elements and said elastomeric sealing means.
holder means for supporting said diffusion elements, said holder means having upwardly directed side wall means adjacent to the side faces of said diffusion elements; and retaining means positioned along the peripheries of the diffusion elements and said elastomeric sealing means.
13. A wastewater aeration system according to claim 12 wherein said retaining means is clamping means for pressing said elastomeric sealing means and diffusion elements into engagement.
14. A wastewater aeration system comprising:
a tank;
a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe;
a plurality of plenums secured to said header pipe at spaced locations along said header pipe in communication with said gas outlet openings;
porous diffusion elements in each of said plenums for receiving pressurized air and discharging corresponding aeration bubbles in water, said diffusion elements having (1) air input faces for receiving said pressurized air, (2) upwardly facing air discharge faces for contacting said water and for discharging said bubbles against the surface tension effect of said water to release said aeration bubbles in an upward direction, said air discharge faces having a bubble release pressure in the range of about two to about twenty inches of water gauge, and (3) side faces extending around the peripheries of said air discharge faces, said side faces being at least semi-permeable to air and free of air-blocking adherent material; and an elastomeric sealing means distinct from and not bonded to said diffusion elements, said sealing means abutting at least a top most portion of said side faces and extending around the peripheries of said air discharge faces to sealably engage said side faces and prevent bubbles from being emitted from said side faces and passing into said tank.
a tank;
a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe;
a plurality of plenums secured to said header pipe at spaced locations along said header pipe in communication with said gas outlet openings;
porous diffusion elements in each of said plenums for receiving pressurized air and discharging corresponding aeration bubbles in water, said diffusion elements having (1) air input faces for receiving said pressurized air, (2) upwardly facing air discharge faces for contacting said water and for discharging said bubbles against the surface tension effect of said water to release said aeration bubbles in an upward direction, said air discharge faces having a bubble release pressure in the range of about two to about twenty inches of water gauge, and (3) side faces extending around the peripheries of said air discharge faces, said side faces being at least semi-permeable to air and free of air-blocking adherent material; and an elastomeric sealing means distinct from and not bonded to said diffusion elements, said sealing means abutting at least a top most portion of said side faces and extending around the peripheries of said air discharge faces to sealably engage said side faces and prevent bubbles from being emitted from said side faces and passing into said tank.
15. A waste water aeration system comprising:
a tank;
a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe;
a plurality of plenums secured to said header pipe at spaced locations along said header pipe in communciation with said gas outlet openings;
diffusion elements in said plenums, said diffusion elements being free of through holes other than gas diffusion pores and having:
(1) porous sides, at least a portion of said sides being at least semi-permeable in water, (2) porous downturned lower gas input surfaces and porous upturned upper gas discharge surfaces, and (3) upper edges of said sides, comprising a line of demarcation between said side and said upper surfaces; and elastomeric sealing members distinct from and not bonded to said diffusion elements, positioned in sealing engagement with said diffusion elements, abutting at least a top most portion of said porous sides, and extending along the peripheries of said upper surfaces to prevent bubbles from being emitted from said sides and passing into said tank.
a tank;
a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe;
a plurality of plenums secured to said header pipe at spaced locations along said header pipe in communciation with said gas outlet openings;
diffusion elements in said plenums, said diffusion elements being free of through holes other than gas diffusion pores and having:
(1) porous sides, at least a portion of said sides being at least semi-permeable in water, (2) porous downturned lower gas input surfaces and porous upturned upper gas discharge surfaces, and (3) upper edges of said sides, comprising a line of demarcation between said side and said upper surfaces; and elastomeric sealing members distinct from and not bonded to said diffusion elements, positioned in sealing engagement with said diffusion elements, abutting at least a top most portion of said porous sides, and extending along the peripheries of said upper surfaces to prevent bubbles from being emitted from said sides and passing into said tank.
16. A wastewater aeration system according to claim 15, comprising diffusion element holders including upwardly extending inner wall means closely adjacent to the sides of said diffusion elements, and positioning rings extending along the peripheries of the diffusion elements for holding said elements and sealing members in place in said holders.
17. A wastewater aeration system comprising:
a tank;
a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe;
a plurality of plenums secured to said header pipe at spaced locations along said header pipe in communication with said gas outlet openings;
diffusion elements in said plenums, said diffusion elements being free of through holes other than gas diffusion pores and having:
(1) porous sides, at least a portion of said sides being at least semi-permeable in water, (2) porous upturned upper gas discharge surfaces and porous down-turned lower gas input surfaces, the surfaces having no macro holes therein, and having pores which are substantially all of substantially equal length extending between said upper and lower surfaces , and (3) upper side edges on said sides, comprising lines of demarcation between said side and said upper surfaces; and elastomeric sealing members distinct from and not bonded to said diffusion elements positioned in sealing engagement with said diffusion elements, abutting at least a top most postion of said porous sides, and extending along the peripheries of said upper surfaces to prevent bubbles from being emitted from said sides and passing into said tank.
a tank;
a header pipe disposed within said tank and having gas outlet openings at spaced locations along the length of said header pipe;
a plurality of plenums secured to said header pipe at spaced locations along said header pipe in communication with said gas outlet openings;
diffusion elements in said plenums, said diffusion elements being free of through holes other than gas diffusion pores and having:
(1) porous sides, at least a portion of said sides being at least semi-permeable in water, (2) porous upturned upper gas discharge surfaces and porous down-turned lower gas input surfaces, the surfaces having no macro holes therein, and having pores which are substantially all of substantially equal length extending between said upper and lower surfaces , and (3) upper side edges on said sides, comprising lines of demarcation between said side and said upper surfaces; and elastomeric sealing members distinct from and not bonded to said diffusion elements positioned in sealing engagement with said diffusion elements, abutting at least a top most postion of said porous sides, and extending along the peripheries of said upper surfaces to prevent bubbles from being emitted from said sides and passing into said tank.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1158679A | 1979-02-12 | 1979-02-12 | |
| US011586 | 1979-02-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1152979A true CA1152979A (en) | 1983-08-30 |
Family
ID=21751067
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000345544A Expired CA1152979A (en) | 1979-02-12 | 1980-02-12 | Gas diffusion apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1152979A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113471123A (en) * | 2021-07-06 | 2021-10-01 | 华海清科股份有限公司 | Vertical rotary wafer processing equipment and ventilation system applying same |
-
1980
- 1980-02-12 CA CA000345544A patent/CA1152979A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113471123A (en) * | 2021-07-06 | 2021-10-01 | 华海清科股份有限公司 | Vertical rotary wafer processing equipment and ventilation system applying same |
| CN113471123B (en) * | 2021-07-06 | 2023-08-25 | 华海清科股份有限公司 | Wafer vertical rotation processing equipment and ventilation system applied by same |
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