BACKGROUND OF THE INVENTION

THIS invention relates to the aeration of a liquid. More specifically, the invention relates to an aerator for the oxygenation of a liquid during water purification or water aeration.

Various different types of aerators for oxygenating a liquid are known. For example, conventional surface aerators include an impeller or the like which is rotated below the liquid surface so as to draw atmospheric air into the liquid. The most commonly used surface aerators are slow, vertical-shaft turbine aerators which generally operate at peripheral speeds in the range of 4m/s to 6m/s. These aerators take water in through a base, with or without a central draft tube, and throw the water radially. High-speed, vertical-shaft surface aerators and horizontal-shaft surface aerators are also known. With high-speed, vertical-shaft aerators, the impeller, which usually is housed within a tube, is driven directly by a motor without intermediary reduction gearing, and consequently these aerators tend to have relatively small diameter impellers. Horizontal-shaft aerators may be mounted lengthwise or crosswise, and generally are designed to operate at relatively low specific powers.

For all types of surface aerators, it is desirable to improve or increase the oxygenation of the liquid. It is an object of the present invention to provide an alternative aerator which includes an effective rotor and impeller arrangement for efficiently oxygenating a liquid.

SUMMARY OF THF. INIVFNTIΩN

According to the invention there is provided an aerator for the oxygenation of a liquid during water purification or water aeration, the aerator comprising: a standpipe; an air inlet for allowing air into the standpipe; a disperser depending from the standpipe; a rotor located at least partly within the disperser, the rotor defining a plurality of radially extending rotor blades; drive means for rotating the rotor; and an impeller comprising: a hub, and a plurality of spoke formations extending radially from the hub, wherein some of the spoke formations are aligned with the rotor blades and some of the spoke formations are aligned with gaps between the rotor blades, and wherein the diameter defined by the impeller is larger than the diameter defined by the rotor.

In a preferred embodiment of the invention, the impeller is formed integrally with the rotor.

In a particularly preferred arrangement, each spoke formation includes a first deflecting formation connected to the hub, and a second deflecting formation extending from the first deflecting formation. In this embodiment, the second deflecting formation may include an upper portion and a lower portion, wherein the upper portion defines two opposed surfaces which slope outwardly and downwardly from an upper edge of the second deflecting formation, and the lower portion defines two opposed surfaces which slope outwardly and upwardly from a lower edge of the second deflecting formation.

Typically, each second deflecting formation, in use, extends above the upper surfaces of the rotor blades approximately the same amount as it extends below these surfaces.

The disperser may include a generally annular disperser body defining a plurality of dispersing apertures. In one embodiment of the invention, the disperser includes guide formations projecting from the disperser body for directing air and liquid flowing out of the disperser, through the dispersing apertures, in radial directions so as to effect radial flow from the disperser body. Ideally, the disperser is of the type described in South African patent 2004/6846.

The draft tube may include a funnel shaped entrance at a lower end thereof, in which case, the funnel shaped entrance may define a plurality of inlet apertures in a side wall thereof. The draft tube typically is connected to a lower region of the disperser.

Preferably, the aerator includes a support for supporting the standpipe above or at least partially within a liquid.

In one embodiment, the support is connected to a fixed structure. Alternatively, the support may be connected to floats for floating the aerator on the liquid surface.

The air inlet typically includes an inlet chamber and a conduit leading from the inlet chamber to the standpipe.

In one arrangement, the drive means for rotating the rotor comprises an electric motor connected to a drive shaft for the rotor via a belt and pulley arrangement.

BRIEF DESCRIPTION QF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a cross-sectional view of an aerator for oxygenating a liquid in accordance with one embodiment of the present invention;

Figure 2 shows a perspective view of a rotor and impeller arrangement for the aerator of Figure 1 ; and

Figure 3 shows a top view of the rotor and impeller arrangement of Figure 2. DETAII F∏ ∏FS∏RIPTION DF THt= INVFNTIDN

Figure 1 of the drawings illustrates an aerator 10 according to one embodiment of the present invention. The aerator in this embodiment is designed for the treatment of domestic waste water in the form of sewage effluent which has a specific oxygen demand. It will be appreciated that, with suitable modifications, the aerator of the invention could also be used in various other applications, for example in the treatment of industrial effluent such as waste water from distilleries or from plants for producing comestibles, pharmaceuticals or cosmetics. The aerator could also be used to oxygenate water in reservoirs or dams to sustain underwater life forms such as fish.

The aerator 10 includes a standpipe 12 which is suspended from a support in the form of a steel frame 14. The frame 14 is mounted to a fixed structure (not illustrated) such as a concrete side wall of an aeration tank (also not illustrated). A disperser 16 depends from the standpipe 12, as shown. The disperser includes a generally annular body 18 defining a plurality of substantially rectangular dispersing apertures 20. In this embodiment of the invention, the disperser 16 is a disperser of the type described in South African patent 2004/6846, the entire contents of which is incorporated herein by reference. As can be seen, the disperser 16 also includes guides 22 which project outwardly from the disperser body 18 for directing water and air, passing through the dispersing apertures 20, in a radial direction from the disperser body 18. Each guide 22 includes an upper wall 24, a pair of opposed side walls 26 and a lower wall 28 which extend outwardly from the disperser body 18, around the dispersing apertures 20. Disperser formations in the form of ribs 30 are located between adjacent, circumferentially spaced- apart dispersing apertures 20, for directing air and liquid within the disperser 16 through the dispersing apertures 20.

An integral rotor and impeller arrangement 32 is fixed to a drive shaft 34 so as to be located within the disperser 16, as shown. With reference also to Figures 2 and 3 of the drawings, the rotor and impeller arrangement 32 includes a rotor 36 which defines eight rotor blades 38, and an impeller 40 which defines a hub 41 and sixteen spoke formations 42 extending radially from the hub. As can be seen, eight of the spoke formations 42 are aligned with the eight rotor blades 38, and the remaining eight spoke formations are aligned with the gaps between the rotor blades. Furthermore, the diameter defined by the impeller 40 is seen to be larger than the diameter defined by the rotor 36.

Each spoke formation 42 includes a first deflecting formation in the form of a blade 44 and a second deflecting formation 46 which is connected to the blade 44 so as to extend radially outwardly from the blade. The second deflecting formations 46 each include an upper portion 50 which defines a pair of opposed surfaces 52 extending downwardly and outwardly from an upper edge 54 thereof, and a lower portion 56 which defines a pair of opposed surfaces 58 extending upwardly and outwardly from a lower edge 60 thereof. In a preferred arrangement, each second deflecting formation 46 extends above the upper surfaces of the rotor blades 38 approximately the same amount as it extends below these surfaces.

In this embodiment of the invention, the rotor blades 38 and the spoke formations 42 are solid and are cast as a single unit from an abrasive resistant material such as a high-density polyurethane which may or may not be reinforced, for example with steel. However, it will be appreciated that the impeller and the rotor could be formed separately so as to be connectable, independently of one another, to the drive shaft 34.

The rotor 36 is driven by an electric motor 62 which is mounted to the support frame 14 by a motor mounting designated generally with the reference numeral 64. The electric motor 62 is connected to the drive shaft 34 via a pair of pulleys 66 and 68, and a drive belt 70. As can be seen, the drive shaft 34 is mounted to the support frame 14 by means of bearings 72 and 74 and a bearing support 76.

An air inlet 78 allows air to be sucked into the standpipe 12 for oxygenation within the aerator 10. The air inlet 78 includes an entrance chamber 80, and a conduit 82 leading from the chamber 80 to the standpipe 12.

Below the disperser 16, a draft tube 84 allows liquid to be drawn upwardly into the disperser for aeration. The draft tube 84 includes an annular body 86, and a funnel shaped entrance portion 88 which defines a plurality of apertures 90.

In practice, the aerator 10 is mounted on the support frame 14 within an aeration chamber or tank (not illustrated) for aerating a liquid in the tank during a water purification process. In this embodiment of the invention, the liquid is sewage effluent. The support frame 14 is arranged to hold the disperser 16 within the tank so that the draft tube entrance 88 is raised slightly off the bottom of the tank, say by 200mm, and the impeller 40 is submerged in the liquid, typically by no more than 1 m.

Air bubbles are introduced into the sewage effluent by generating a vortex within the standpipe 12, which extends below the surface of the sewage effluent. The vortex is generated as a consequence of rotation of the rotor 36 and the impeller 40 within the sewage effluent, and creates a vacuum in the area 92 above the sewage effluent. The vacuum draws atmospheric air into the standpipe 12 via the air inlet 78, and this air is drawn into the sewage effluent to create air bubbles as the air and effluent is forced through the dispersing apertures 20 by the rotor 36. In this way, the sewage effluent is oxygenated, as required.

The specific configuration of the rotor 36 and the impeller 40, and in particular the feature of larger diameter spoke formations than rotor blades, is important for the creation of an effective vortex and hence effective oxygenation.

It should be appreciated that the invention is not limited to the oxygenation of sewage effluent and that it could also be used in various other applications, such as, for example, in the oxygenation of industrial waste water requiring treatment prior to disposal. The aerator of the invention could also be used to aerate water in dams or reservoirs to sustain underwater life forms such as fish. It will also be appreciated that the invention is not limited to the specific embodiment described above and that the aerator could assume various different forms. For example, instead of being fixed within an aeration tank, the aerator could be connected to floats for floating the aerator on a liquid surface. In this case, the aerator could be used to aerate water in a dam or a reservoir. Furthermore, the disperser could assume various other configurations, for example, the disperser need not include the ribs 30 or the guides 22, and could instead simply include an annular body and a plurality of dispersing apertures. It will also be understood that in some embodiments of the invention, for example in cases where the aerator is floated on a water surface in a dam or a reservoir, the draft tube 84 need not be included. Alternatively, the draft tube could have various other configurations and need not include the funnel shaped entrance 88.