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WO1992003219A1 - Aeration apparatus with diffuser - Google Patents

Aeration apparatus with diffuser Download PDF

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Publication number
WO1992003219A1
WO1992003219A1 PCT/AU1991/000398 AU9100398W WO9203219A1 WO 1992003219 A1 WO1992003219 A1 WO 1992003219A1 AU 9100398 W AU9100398 W AU 9100398W WO 9203219 A1 WO9203219 A1 WO 9203219A1
Authority
WO
WIPO (PCT)
Prior art keywords
conduit
plate
liquid
diffuser
bubbles
Prior art date
Application number
PCT/AU1991/000398
Other languages
French (fr)
Inventor
Graeme John Jameson
Original Assignee
The University Of Newcastle Research Associates Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The University Of Newcastle Research Associates Limited filed Critical The University Of Newcastle Research Associates Limited
Publication of WO1992003219A1 publication Critical patent/WO1992003219A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/23—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids
    • B01F23/232—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids using flow-mixing means for introducing the gases, e.g. baffles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/14—Flotation machines
    • B03D1/1431—Dissolved air flotation machines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/23—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids
    • B01F23/231—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids by bubbling
    • B01F23/23105—Arrangement or manipulation of the gas bubbling devices
    • B01F23/2312—Diffusers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/23—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids
    • B01F23/232—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids using flow-mixing means for introducing the gases, e.g. baffles
    • B01F23/2323—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids using flow-mixing means for introducing the gases, e.g. baffles by circulating the flow in guiding constructions or conduits
    • B01F23/23231—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids using flow-mixing means for introducing the gases, e.g. baffles by circulating the flow in guiding constructions or conduits being at least partially immersed in the liquid, e.g. in a closed circuit
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/23—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids
    • B01F23/234—Surface aerating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/23—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids
    • B01F23/234—Surface aerating
    • B01F23/2341—Surface aerating by cascading, spraying or projecting a liquid into a gaseous atmosphere
    • B01F23/23413—Surface aerating by cascading, spraying or projecting a liquid into a gaseous atmosphere using nozzles for projecting the liquid into the gas atmosphere
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/40—Mixing liquids with liquids; Emulsifying
    • B01F23/45—Mixing liquids with liquids; Emulsifying using flow mixing
    • B01F23/454—Mixing liquids with liquids; Emulsifying using flow mixing by injecting a mixture of liquid and gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
    • B01F25/20—Jet mixers, i.e. mixers using high-speed fluid streams
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
    • B01F25/40—Static mixers
    • B01F25/42—Static mixers in which the mixing is affected by moving the components jointly in changing directions, e.g. in tubes provided with baffles or obstructions
    • B01F25/43—Mixing tubes, e.g. wherein the material is moved in a radial or partly reversed direction
    • B01F25/433—Mixing tubes wherein the shape of the tube influences the mixing, e.g. mixing tubes with varying cross-section or provided with inwardly extending profiles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
    • B01F25/40—Static mixers
    • B01F25/42—Static mixers in which the mixing is affected by moving the components jointly in changing directions, e.g. in tubes provided with baffles or obstructions
    • B01F25/43—Mixing tubes, e.g. wherein the material is moved in a radial or partly reversed direction
    • B01F25/433—Mixing tubes wherein the shape of the tube influences the mixing, e.g. mixing tubes with varying cross-section or provided with inwardly extending profiles
    • B01F25/4335—Mixers with a converging-diverging cross-section
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
    • B01F25/40—Static mixers
    • B01F25/42—Static mixers in which the mixing is affected by moving the components jointly in changing directions, e.g. in tubes provided with baffles or obstructions
    • B01F25/43—Mixing tubes, e.g. wherein the material is moved in a radial or partly reversed direction
    • B01F25/433—Mixing tubes wherein the shape of the tube influences the mixing, e.g. mixing tubes with varying cross-section or provided with inwardly extending profiles
    • B01F25/4337—Mixers with a diverging-converging cross-section
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/74—Treatment of water, waste water, or sewage by oxidation with air
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F2101/00—Mixing characterised by the nature of the mixed materials or by the application field
    • B01F2101/305—Treatment of water, waste water or sewage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/23—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids

Definitions

  • the gas-liquid mixture which forms in the pipe can have a voidage of up to 60 percent by volume approximately, and behaves as a homogeneous fluid whose density is much less than the liquid in which the pipe is immersed. Accordingly, in the absence of any special
  • the present invention aims to prevent the formation of the plume, by mounting a shield or diffuser outside the vertical pipe, which has the effect of breaking up the dense foam which issues from the pipe exit, and allowing the gas bubbles to rise
  • the present invention provides apparatus , for aerating liquids wherein a dense dispersion of bubbles
  • a substantially vertical conduit adapted to be immersed in use in a body of liquid
  • a diffuser extending outwardly from the exterior of the conduit and positioned to be immersed in the body of liquid, the diffuser being arranged to disperse bubbles issuing from the lower end of the conduit outwardly away from the conduit as the bubbles rise in the body of liquid.
  • the diffuser comprises a plate surrounding the conduit and extending outwardly and upwardly from a predetermined position on the exterior of the conduit.
  • the plate is provided with a plurality of holes therethrough sized to allow a predetermined flow rate of bubbles through each hole.
  • a gap is provided between the inner periphery of the plate and the exterior of the conduit and a diverting ring is positioned on the exterior of the conduit below the gap, arranged to divert upwardly moving bubbles outwardly away from the conduit and away from the gap between the conduit and the plate.
  • Figure la is a diagrammatic cross-sectional elevation through a basic form of aeration apparatus with diffuser according to the invention
  • Figure lb is a view similar to Figure la showing the behaviour of a bouyant plume of dense foam in the absence of a- diffuser
  • Figure lc is a sectional plan view of the diffuser incorporated in the apparatus of Figure la;
  • Figure 2a is a cross-sectional elevation through the lower part of the conduit forming part of the apparatus of Figure la showing an alternative embodiment of the diffuser;
  • Figure 2b is a plan view of the diffuser shown in Figure 2a.
  • Figure 3a and Figure 3b are diagrammatic cross-sectional elevations of alternative forms of diffuser.
  • the invention relates to any form of aeration apparatus in which a dense dispersion of bubbles is emitted from the lower end (5) of a downwardly extending conduit or pipe (3) immersed in a body of water (4) , in the form of the invention shown in Figure la, liquid enters through an entry pipe (1) and a nozzle assembly (22) which terminates in an orifice (2) which faces essentially vertically downwards.
  • the nozzle is mounted in the top of a conduit or pipe (3) which is essentially vertical.
  • the liquid issues from the orifice (2) in the form of a high-speed jet (8) which can move downwardly through the pipe (3) .
  • the vertical pipe is mounted by way of support means (not shown) so that its lower end is submerged in a reservoir of liquid (4) having a surface (9) .
  • the liquid may or may not be identical in all respects to the liquid entering through the entry pipe (1) .
  • the liquid levels in the reservoir and inside the vertical pipe (3) are the same.
  • the high-speed liquid jet is first established by the orifice (2), it travels downwards through the pipe (3) and plunges into the liquid, entraining gas which is inside the pipe and carrying it out of the lower extremity (5) , to rise in the reservoir (4) in the form of fine bubbles.
  • the vertical pipe (3) fills rapidly with a dense foam of bubbles dispersed in the feed liquid, and the pressure in the head space of the pipe drops below the ambient pressure outside the pipe. Accordingly, new gas is drawn into the pipe through the air entry (6) and may be regulated by valve (7) .
  • the gas-liquid mixture which forms in the vertical pipe (3) has a voidage of up to 60 percent by volume approximately, and behaves as a homogeneous fluid whose density is much less than the liquid in the reservoir (4) . Accordingly, in the absence of any special precautions, it tends to rise as a buoyant plume, hugging the outer wall of the pipe (3) and rising rapidly to the surface (9) , as shown in Figure lb. Consequently, the bubbles in the plume do not mix with the liquid in the reservoir, and the possibility of contact with this liquid is lost.
  • the bubble diffuser can conveniently be made from a plate in the form of a frustum of a cone, inverted so that the open end is uppermost.
  • the cone is perforated with a multiplicity of holes (11) as shown in the alternative view, Figure lc.
  • the buoyant plume issuing from the exit (5) of the vertical pipe (3) ,rises and spreads over the underside of the diffuser (10) , to pass through the individual holes (11) in the diffuser (10) .
  • the bubbles of gas rise individually through the liquid in the reservoir (4) .
  • the diameter of the conical diffuser (10) shown in Figure lc should be in the range 1.5 to 10 times the outer diameter of the pipe (3) , with good practical results being found when the cone diameter is 2 to 3 times the pipe diameter.
  • the half-angle of the cone from which the frustum is formed is conveniently in the range 30 to 60 .
  • the diameter of the holes (11) can be in the range 1 to 30 mm, and the holes should be distributed evenly over the conical surface to give an open area in the range 1 to 15% of the area of the surface.
  • the diffuser it is not necessary for the diffuser to be in the shape of a cone. Other shapes will perform as well, providing the elevation of the underside of the diffuser above the exit (5) of the vertical pipe (3) , always increases as the radial distance from the axis of the pipe increases. If the underside of the diffuser surface is at any stage horizontal or tending to dip downwards as radial distance from the vertical pipe increases, there will be a tendency for the bubbles to collect in this area and coalesce, and thereby form less surface area per unit of gas volume, which will reduce the efficiency of any contacting operation between the gas and the liquid.
  • An alternative form of the diffuser is shown in
  • FIGs 2a and 2b where the diffuser (12) takes the shape of part of a circular dish, with holes (13) perforating the dish.
  • the radius of curvature of the dish can conveniently be in the range 2 to 20 times the diameter of the vertical pipe (3)
  • the diameter of the diffuser (12) shown in Figure 2b should be in the range 1.5 to 20 times the outer diameter of the pipe (3) , with good practical results being found when the diffuser diameter is 2 to 3 times the pipe diameter.
  • the diameter of the holes (13) can be in the range 1 to 30 mm, and the holes can conveniently be distributed evenly over the surface to give a total area of the perforations in the range 1 to 20% of the area of the diffuser surface.
  • a difficulty which can arise with the diffuser arrangements as shown in Figures la and 2a is that solid matter which may have been suspended in the liquid in the reservoir, may tend to settle on the upper face of the diffuser (10) or (12) and build up into a thick layer which may block the holes (11) or (13) .
  • This possibility can be avoided by mounting the diffuser (10) or (12) so that an annular gap (15) exists between the diffuser and the pipe wall (3) .
  • the conical diffuser is advantageous in this application because it will provide a surface of constant angle to the horizontal, down which any solids which may have deposited on the upper surface may slide toward the axis of the cone.
  • the half-angle of the cone, of which the diffuser is a frustum, should be such that the solids will slide toward the axis and hence fall through the annular gap (15) .
  • a diverting ring (14) or (16) in conjunction with the annular space (15) .
  • the purpose of the diverting ring is to prevent the dense foam rising from the open end (5) of the pipe (3) , from entering the annular gap (15) and thereby evading the diffuser (10) or (12) .
  • the ring is mounted on the outer wall of the vertical pipe (3) , and can conveniently be of triangular section (14) as shown in Figure 3a or of semi-circular section as in Figure 3b at (16) .
  • the invention has been described with reference to the aeration of wastewaters, it is also suitable for the flotation of mineral particles so as to remove the valuable minerals from unwanted waste matter, by contacting them with fine bubbles in a suspension of the mineral in water, so that the particles which it is desired to remove have been rendered non-wetting by the liquid while the particles which are to remain in the liquid are rendered wettable by the liquid.
  • the valuable particles then adhere to the surface of the fine bubbles and rise with them to the surface of the liquid, from which they may be removed as a froth.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Dispersion Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Chemistry (AREA)
  • Biotechnology (AREA)
  • Aeration Devices For Treatment Of Activated Polluted Sludge (AREA)
  • Physical Water Treatments (AREA)

Abstract

Aeration apparatus in which a dense dispersion of bubbles is generated within a conduit or tube (3) having its lower end (5) immersed in a body of liquid (4) is provided with a diffuser plate (10) extending outwardly and upwardly from the outer periphery of the conduit (3), and immersed in the liquid (4). The diffuser plate (10) is typically conical or dish shaped and has a number of holes therethrough permitting bubbles to be released from the underside of the diffuser plate in an even dispersion through the holes into the body of liquid (4). Embodiments are also described wherein a gap is provided between the diffuser plate and the outer periphery of the conduit (3), allowing solids accumulating on the top surface of the plate to be dispersed through the gap.

Description

"AERATION APPARATUS WITH DIFFUSER" TECHNICAL FIELD This invention relates to an aeration apparatus which may be used in many diverse fields including the aeration
5 of water or other liquids in waste water treatment and pollution control, the separation of oil from water, or the separation of minerals in suspension by the so-called flotation method.
BACKGROUND ART
10 Various types of aeration apparatus are known where a dense dispersion of bubbles in a liquid is emitted from the lower end of a downwardly extending pipe or column and allowed to rise, either in a large body of liquid or within a cell or column.
15 The gas-liquid mixture which forms in the pipe can have a voidage of up to 60 percent by volume approximately, and behaves as a homogeneous fluid whose density is much less than the liquid in which the pipe is immersed. Accordingly, in the absence of any special
20 precautions, it tends to rise as a buoyant plume, hugging the outer wall of the pipe and rising rapidly to the surface of the liquid in which the pipe is immersed. Consequently, the bubbles in the plume do not mix well with the liquid and the possibility of optimising contact
25 with this liquid is lost. The present invention aims to prevent the formation of the plume, by mounting a shield or diffuser outside the vertical pipe, which has the effect of breaking up the dense foam which issues from the pipe exit, and allowing the gas bubbles to rise
30 individually in the liquid in the reservoir rather than as a plume.
DISCLOSURE OF INVENTION
* Accordingly the present invention provides apparatus , for aerating liquids wherein a dense dispersion of bubbles
• 35 is emitted from the lower end of a substantially vertical conduit adapted to be immersed in use in a body of liquid, characterised by the provision of a diffuser extending outwardly from the exterior of the conduit and positioned to be immersed in the body of liquid, the diffuser being arranged to disperse bubbles issuing from the lower end of the conduit outwardly away from the conduit as the bubbles rise in the body of liquid. Preferably the diffuser comprises a plate surrounding the conduit and extending outwardly and upwardly from a predetermined position on the exterior of the conduit.
Preferably the plate is provided with a plurality of holes therethrough sized to allow a predetermined flow rate of bubbles through each hole..
Preferably a gap is provided between the inner periphery of the plate and the exterior of the conduit and a diverting ring is positioned on the exterior of the conduit below the gap, arranged to divert upwardly moving bubbles outwardly away from the conduit and away from the gap between the conduit and the plate.
BRIEF DESCRIPTION OF DRAWINGS Notwithstanding any other forms that may fall within its scope, one preferred form of the invention and variations thereof will now be described with reference to the* accompanying drawings, in which:
Figure la is a diagrammatic cross-sectional elevation through a basic form of aeration apparatus with diffuser according to the invention; Figure lb is a view similar to Figure la showing the behaviour of a bouyant plume of dense foam in the absence of a- diffuser;
Figure lc is a sectional plan view of the diffuser incorporated in the apparatus of Figure la; Figure 2a is a cross-sectional elevation through the lower part of the conduit forming part of the apparatus of Figure la showing an alternative embodiment of the diffuser;
Figure 2b is a plan view of the diffuser shown in Figure 2a; and
Figure 3a and Figure 3b are diagrammatic cross-sectional elevations of alternative forms of diffuser. MODES FOR CARRYING OUT THE INVENTION Although the invention relates to any form of aeration apparatus in which a dense dispersion of bubbles is emitted from the lower end (5) of a downwardly extending conduit or pipe (3) immersed in a body of water (4) , in the form of the invention shown in Figure la, liquid enters through an entry pipe (1) and a nozzle assembly (22) which terminates in an orifice (2) which faces essentially vertically downwards. The nozzle is mounted in the top of a conduit or pipe (3) which is essentially vertical. In operation, the liquid issues from the orifice (2) in the form of a high-speed jet (8) which can move downwardly through the pipe (3) .
The vertical pipe is mounted by way of support means (not shown) so that its lower end is submerged in a reservoir of liquid (4) having a surface (9) . The liquid may or may not be identical in all respects to the liquid entering through the entry pipe (1) .
Initially, the liquid levels in the reservoir and inside the vertical pipe (3) are the same. When the high-speed liquid jet is first established by the orifice (2), it travels downwards through the pipe (3) and plunges into the liquid, entraining gas which is inside the pipe and carrying it out of the lower extremity (5) , to rise in the reservoir (4) in the form of fine bubbles. The vertical pipe (3) fills rapidly with a dense foam of bubbles dispersed in the feed liquid, and the pressure in the head space of the pipe drops below the ambient pressure outside the pipe. Accordingly, new gas is drawn into the pipe through the air entry (6) and may be regulated by valve (7) .
The gas-liquid mixture which forms in the vertical pipe (3) has a voidage of up to 60 percent by volume approximately, and behaves as a homogeneous fluid whose density is much less than the liquid in the reservoir (4) . Accordingly, in the absence of any special precautions, it tends to rise as a buoyant plume, hugging the outer wall of the pipe (3) and rising rapidly to the surface (9) , as shown in Figure lb. Consequently, the bubbles in the plume do not mix with the liquid in the reservoir, and the possibility of contact with this liquid is lost. To prevent the formation of the plume, it has been found advantageous to mount a shield or diffuser (10) outside the vertical pipe (3) , which has the effect of breaking up the dense foam which issues from the pipe exit (5) , and allowing the gas bubbles to rise individually in the liquid in the reservoir (4) rather than as a plume. The bubble diffuser can conveniently be made from a plate in the form of a frustum of a cone, inverted so that the open end is uppermost. The cone is perforated with a multiplicity of holes (11) as shown in the alternative view, Figure lc. In operation, the buoyant plume issuing from the exit (5) of the vertical pipe (3) ,rises and spreads over the underside of the diffuser (10) , to pass through the individual holes (11) in the diffuser (10) . After passing through the individual holes (11) , the bubbles of gas rise individually through the liquid in the reservoir (4) .
The diameter of the conical diffuser (10) shown in Figure lc should be in the range 1.5 to 10 times the outer diameter of the pipe (3) , with good practical results being found when the cone diameter is 2 to 3 times the pipe diameter. The half-angle of the cone from which the frustum is formed is conveniently in the range 30 to 60 . The diameter of the holes (11) can be in the range 1 to 30 mm, and the holes should be distributed evenly over the conical surface to give an open area in the range 1 to 15% of the area of the surface.
It is not necessary for the diffuser to be in the shape of a cone. Other shapes will perform as well, providing the elevation of the underside of the diffuser above the exit (5) of the vertical pipe (3) , always increases as the radial distance from the axis of the pipe increases. If the underside of the diffuser surface is at any stage horizontal or tending to dip downwards as radial distance from the vertical pipe increases, there will be a tendency for the bubbles to collect in this area and coalesce, and thereby form less surface area per unit of gas volume, which will reduce the efficiency of any contacting operation between the gas and the liquid. An alternative form of the diffuser is shown in
Figures 2a and 2b, where the diffuser (12) takes the shape of part of a circular dish, with holes (13) perforating the dish. The radius of curvature of the dish can conveniently be in the range 2 to 20 times the diameter of the vertical pipe (3) , and the diameter of the diffuser (12) shown in Figure 2b should be in the range 1.5 to 20 times the outer diameter of the pipe (3) , with good practical results being found when the diffuser diameter is 2 to 3 times the pipe diameter. The diameter of the holes (13) can be in the range 1 to 30 mm, and the holes can conveniently be distributed evenly over the surface to give a total area of the perforations in the range 1 to 20% of the area of the diffuser surface.
A difficulty which can arise with the diffuser arrangements as shown in Figures la and 2a is that solid matter which may have been suspended in the liquid in the reservoir, may tend to settle on the upper face of the diffuser (10) or (12) and build up into a thick layer which may block the holes (11) or (13) . This possibility can be avoided by mounting the diffuser (10) or (12) so that an annular gap (15) exists between the diffuser and the pipe wall (3) . The conical diffuser is advantageous in this application because it will provide a surface of constant angle to the horizontal, down which any solids which may have deposited on the upper surface may slide toward the axis of the cone. The half-angle of the cone, of which the diffuser is a frustum, should be such that the solids will slide toward the axis and hence fall through the annular gap (15) . It is advantageous to use a diverting ring (14) or (16) in conjunction with the annular space (15) . The purpose of the diverting ring is to prevent the dense foam rising from the open end (5) of the pipe (3) , from entering the annular gap (15) and thereby evading the diffuser (10) or (12) . The ring is mounted on the outer wall of the vertical pipe (3) , and can conveniently be of triangular section (14) as shown in Figure 3a or of semi-circular section as in Figure 3b at (16) .
Although the invention has been described with reference to the aeration of wastewaters, it is also suitable for the flotation of mineral particles so as to remove the valuable minerals from unwanted waste matter, by contacting them with fine bubbles in a suspension of the mineral in water, so that the particles which it is desired to remove have been rendered non-wetting by the liquid while the particles which are to remain in the liquid are rendered wettable by the liquid. The valuable particles then adhere to the surface of the fine bubbles and rise with them to the surface of the liquid, from which they may be removed as a froth.

Claims

CLAIMS : -
1. Apparatus for aerating liquids wherein a dense dispersion of bubbles is emitted from the lower end of a substantially vertical conduit adapted to be immersed in use in a body of liquid, characterised by the provision of a diffuser extending outwardly from the exterior of the conduit and positioned to be immersed in the body of liquid, the diffuser being arranged to disperse bubbles issuing from the lower end of the conduit outwardly away from the conduit as the bubbles rise in the body of liquid.
2. Apparatus as claimed in claim 1 wherein the diffuser comprises a plate surrounding the conduit and extending outwardly and upwardly from a predetermined position on the exterior of the conduit.
3. Apparatus as claimed in claim 2 wherein the plate is substantially circular in plan view having a diameter between 1.5 and 10 times the outer diameter of the conduit.
4. Apparatus as claimed in claim 3 wherein the diameter of the plate is between 2 and 3 times the outer diameter of the conduit.
5. Apparatus as claimed in any one of claims to 4 wherein the plate is shaped to the frustrum of a cone having a half angle between 30° and 60°.
6. Apparatus as claimed in any one of claims 2 to 4 wherein the plate is dish shaped, having a radius of curvature between 2 and 20 times the outer diameter of the conduit.
7. Apparatus as claimed in any one of claims 2 to 6 wherein the plate is provided with a plurality of holes therethrough sized to allow a predetermined flow rate of bubbles through each hole.
8. Apparatus as claimed in claim 7 wherein the holes have a diameter between 1mm and 30mm.
9. Apparatus as claimed in either claim 7 or claim 8 wherein the total area of the holes is between 1% and 20% of the surface area of the plate.
10. Apparatus as claimed in any one of claims 2 to 9 wherein a gap is provided between the inner periphery of the plate and the exterior of the conduit.
11. Apparatus as claimed in claim 10 wherein a diverting ring is positioned on the exterior of the conduit below the gap, arranged to divert upwardly moving bubbles outwardly away from the conduit and away from the gap between the conduit and the plate.
PCT/AU1991/000398 1990-08-27 1991-08-27 Aeration apparatus with diffuser WO1992003219A1 (en)

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PCT/AU1991/000398 WO1992003219A1 (en) 1990-08-27 1991-08-27 Aeration apparatus with diffuser
PCT/AU1991/000397 WO1992003218A1 (en) 1990-08-27 1991-08-27 Aeration of liquids

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KR (1) KR930702065A (en)
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ZA (2) ZA916774B (en)

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GB2582980A (en) * 2019-04-12 2020-10-14 Colin Howard Stanwell Smith Improvements to sewage treatment plants

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MX9100829A (en) 1992-04-01
JPH06500260A (en) 1994-01-13
CA2090619A1 (en) 1992-02-28
ZA916775B (en) 1992-05-27
WO1992003220A1 (en) 1992-03-05
EP0546033A4 (en) 1994-02-02
KR930702065A (en) 1993-09-08
CN1060453A (en) 1992-04-22
EP0546033A1 (en) 1993-06-16
MX9100830A (en) 1992-04-01
ZA916774B (en) 1992-05-27
WO1992003218A1 (en) 1992-03-05

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