WO1992008050A1

WO1992008050A1 - Liquid treatment apparatus

Info

Publication number: WO1992008050A1
Application number: PCT/GB1991/001953
Authority: WO
Inventors: Neale Thomas
Original assignee: Flow Research Evaluation Diagnostics Limited
Priority date: 1990-11-06
Filing date: 1991-11-06
Publication date: 1992-05-14
Also published as: AU8871291A

Abstract

A vertical axis wind turbine (or VAWT) has a rotor (3) which carries vertical aerofoil blades (7) at the outer ends of arms (5). The blades are free to pivot within limits (8) about vertical axes near their leading edges and diametrically opposite blades (7) are linked (9) so that they move substantially in unison, at least at low speeds. In the preferred application, the VAWT is mounted over a sewage treatment tank (1) and is coupled to a co-axial rotor (10) carrying stirring devices which, in use, are immersed in the liquid or slurry. These stirring devices comprise sub-rotors (14, 21) with paddles (16, 17) that sweep just above the base of the tank (1) and just below surface level (L), stirring up sediment and drawing in air bubbles respectively. These sub-rotors counter-rotate with respect to the main stirrer rotor (10), being driven by a coupling (20) to the VAWT, with a further coupling (22) between the sub-rotors and a fixed member (23) drawing the main rotor (10) around.

Description

LIQUID TREATMENT APPARATUS

This invention relates to liquid treatment apparatus.

It has been proposed to create turbulence in liquid by means of a wind driven rotor driving an agitator directly, such as in GB-A-2220583A. US-4030859 and US-4292540 are also of interest. But the effect of these devices is somewhat limited, with a rather small agitator or impeller rigidly mounted on a vertical drive shaft. It is one aim of this invention to provide a much more effective arrangement, capable of a much greater spread of turbulence, and in particular to use vertical axis wind turbines, known as VA Ts. These consist of an annular array of aerofoil blades set vertically on a common rotor, the power usually being taken from a vertical co-axial shaft coupled to or rigid with the rotor.

The normal practice in a VAWT is to fix the blades to the rotor. However, this produces a fluctuating torque at the output shaft which is particularly detrimental if, for example, it is being used to generate electricity.

It has been proposed to allow the blades to pivot independently between limits either side of a median position tangential to the path of the blades, and this is described in GB-B-2156442. But the arrangement there is only seen as an auxiliary to normal powered rotation, and it is not very efficient.

It is a further aim of this invention to reduce torque fluctuation substantially, and to provide a simple, robust VAWT, with a low cut-in speed and good torque recovery, and with an automatic cut-out at high speeds.

A particular application will be the treatment of waste water or slurry, where the rotor can carry immersed elements to stir up and aerate the liquid and thus promote microbiological activity.

But it can have many other different applications, and the object is to use a VAWT to perform certain mechanical operations directly, rather than, for example, generating electricity, which is then used to energise motors, pumps and so on. That obviously introduces substantial losses before the work is actually done.

According to one aspect of the present invention there is- provided liquid treatment apparatus comprising a VAWT, a liquid container, a rotor coupled to the VAWT, and stirring means carried by the rotor and adapted to agitate, liquid in the container when the VAWT drives the rotor, characterised in that the stirring means comprise subsidiary rotors linked to the VAWT to be driven thereby.

Preferably the subsidiary rotors will counter- rotate with respect to the main rotor, but there may be circumstances where rotation in the same direction is appropriate. The subsidiary rotors preferably have angled blades adapted to raise solid matter from the bottom of the container and/or to disturb the upper surface of the liquid by the turbulence they create. Because of the different median in which the VAWT and the stirring means rotate, it is advantageous to have step-down gearing from the VAWT to both the rotor and to the subsidiary rotors.

In more detail, the blades will have an angle of incidence to the liquid as they are swept through it, and in one preferred form there is a set of such blades on each subsidiary rotor near the bottom of the container with a positive angle of incidence tending to give lift. But they will be shaped to accentuate turbulence, and this will cause solid matter settling on the bottom of the container to be agitated and thrown up into the main body of the liquid.

Another set of such blades may be provided on each subsidiary rotor near the top, to sweep through the liquid just below the surface. These will have a negative angle of incidence, and will also be shaped to promote turbulence. Just disturbance of the surface layer may be sufficient, but for some purposes they may be designed to create and draw air bubbles down into the body of liquid, to promote aerobic treatment. For simplicity and cheapness, such blades will generally be fixed to their respective subsidiary rotors, although provision can be made for adjusting them, either in height or depth, or in their angles of incidence.

These subsidiary rotors will turn somewhat in the manner of the planets of an epicyclic gear and they may be directly driven by the VAWT. They may also be coupled to a static member so that their rotation by the VAWT causes the coupling to the static member to rotate the main rotor. According to another aspect of the present invention there is provided a VAWT in which each aerofoil blade is free to pivot within limits about a respective vertical axis, blades being linked so that they pivot substantially in unison.

Generally there will be one or more pairs of diametrically opposed blades, and the linkage is then conveniently between opposite blades of each pair. It may simply be a rigid horizontal link between corresponding points offset from the pivot axes. However, the linkage will preferably incorporate means which maintain pivoting in unison at low speeds but which allow the blades at least limited independence at high speeds. Conveniently, this may take the form of a spring which behaves as a substantially rigid member at low speeds but which is distortable by centrifugal forces at high speeds.

The limits will generally be defined by stops, but those limiting the trailing-edge-out position of the blades may have a progressive characteristic which confines the associated blades to median positions at low speeds but which shift under the influence of centrifugal forces to allow the trailing edges to move outwardly of the median positions.

With this arrangement, the incidence of each blade adjusts automatically under aerodynamic loading to achieve a higher proportion of unidirectional torque than can be attained with fixed blades, or even with independently swinging blades as in GB-B-2156442. It has been found that the attainable tip speed can be increased by a factor of about two, so that power may be increased by a factor of about eight. It is believed that the reason is that the links or tie-rods take up the centrifugal force and therefore overcome the problem of premature limitation of turbine speed when all the blades are deflected.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic plan view of part of a

VAWT, and

Figure 2 is a side elevation, partly in section, of the VAWT mounted over a sewage treatment tank and driving an agitator or stirrer assembly. A cylindrical tank 1 with its axis vertical contains sewage to a level L. A bridge 2 carries a VAWT rotor 3 co-axially over the tank. This has a shaft 4 journalled to the centre of the bridge 2 and four horizontal, equispaced arms 5 radiating from it. There could be more or less, but generally four will be the most convenient. At the outer end of each arm 5 there is an upstanding rod 6 and sleeved over these rods near their leading edges are aerofoil blades 7. At the foot of each blade 7 the associated arm 5 carries two stops 8 between which the blade 7 is free to move. Its median position is tangential to the imaginary cylinder through the rods 6.

The blades 7 of each diametrically opposed pair are linked by a horizontal tie 9 coupled to corresponding points near the trailing edge. The length of this tie is such that both blades can simultaneously adopt their median positions, but during operation they will move to either side of them as indicated by the broken lines. The tie 9 may be a rigid link so that the two opposed blades will always move in unison, one 'out' and the other 'in'. However, preferably there will be a modification of this, for example by having a stiff spring 9A (Figure l) interposed in the link. The stiffness will be such that, at low speeds, the link will still act like a rigid bar. However, as speed increases and centrifugal forces begin to have an effect, the trailing edge portions of the blades will tend to fly outwards. This will stretch the spring and so both blades can simultaneously abut their outer stops 8. Another way of allowing opposite blades a degree of independence is to have a lost motion device incorporated in the tie.

The stops 8 are shown as fixed fingers. However, they may be made adjustable and in one preferred arrangement the outer stops may be compressible buffers. Initially they will be extended and provide stops engaging the blades when the latter are substantially tangential to their cylinder of revolution. But when the blades are forced to swing, these buffers progressively retract as speed increases until they reach full compression at about 10° of blade pivot.

The bridge 2 also indirectly carries on its underside a stirrer rotor 10, above the level L. This has a boss 11 journalled on the VAWT shaft 4 which extends below the bridge and from it two diametrically opposed booms radiate. At their ends the booms 12 have bearings to carry short vertical shafts 13 and at the lower ends of these, below the booms 12 but still above the level L, there are four-armed spiders 14. Rods 15 depend from the ends of the horizontal spider arms and at the upper end of each rod 15, so that it will just be immersed below level L, is an inclined paddle 16. At the lower end of each rod 15 another inclined paddle 17 is carried. Each paddle 17 has a positive angle of incidence to the liquid as it is swept through it, its leading edge being further from the bottom than its trailing edge. These trailing edges may be formed other than straight to promote turbulence; for example they may have notches. The paddles 16, however, have a negative angle of incidence but their trailing edges, just below the surface L, may also have notches or other formations to promote turbulence there. Alternatively the paddles may take the form of cambered blades. It will be understood that for some purposes only the upper paddles 16 may be required, while for others just the lower paddles 17 will suffice. Also it may be appropriate occasionally to have intermediate paddles on the rods 15.

Above the boss 11 of the stirrer rotor 10, the shaft 4 has a co-axial multi-grooved drum 18 fixedly mounted on it and at their upper ends, level with the drum 18, the shafts 13 each have a pulley 19 of greater diameter than the drum. Belts 20 are entrained round these pulleys and the drum. Above the pulleys 19, each shaft 13 carries a further, smaller pulley 21 and about these are entrained belts 22 which engage around a multi-grooved drum 23 fixed to the bridge 2 and through which the shaft 4 co-axially extends. It will be understood that there could be more booms 10, for example three or four in an equispaced arrangement, each carrying a stirrer assembly with belt (or chain) drive.

It has been found experimentally that the VAWT rotor 3 will begin to turn in very light winds, of the order of 2 metres per second or even less. The blades 7 assume positions dictated by the wind and rest against one or other of the stops 8. As the rotor turns, and the wind comes on the opposite sides of the blades, so they flip over until arrested by the other stop 8, this movement being kept in unison by the ties 9 to a degree determined by the speed and the influence of the spring 9A.

The drum 18 rotates with the VAWT and the belts 20 drive the pulleys 19, rotating the spiders 14 at a slower speed than the VAWT. A step down of about 3:1 is generally satisfactory. The pulleys 21 rotate with the pulleys 19 and the belts 22 are therefore worked around the drum 23. This causes the stirrer rotor 10 to rotate, again at a stepped down speed. There is therefore a kind of planetary motion by the paddle devices, which rotate in the opposite direction to the rotor 10. Rotation in the same direction can easily be achieved by twisting the belts. The relatively small paddles 16 and 17 induce complex swirl in the body of liquid, and effectively promote particle dispersion and aeration throughout. Solid matter accumulated at the base of the tank 1 is disturbed by the paddles 17 and the turbulence they cause disperses the matter upwards. At the same time, the paddles 16 sweeping just below surface level L disturb the surface layer and may pull air bubbles into the liquid, to promote aerobic treatment.

As he wind speed increases, so obviously will the rotor 3 turn faster. This may be checked by automatic braking devices. But one consequence will be that the blades 7 switch over progressively later until the point is reached when the centrifugal effect will keep them pinned to the outer stops 8 with the spring 9A extended, thus reducing the efficiency of the turbine.

This application to sewage treatment is just one example of how the VAWT may be used. Similar apparatus to that described can be used for mixing and/or aerating liquid or viscous materials in many different fields. It will also be understood that the VAWT can provide drive for many different devices, not necessarily for mixing, and can be used to generate electricity.

Claims

1. Liquid treatment apparatus comprising a VAWT, a liquid container, a rotor coupled to the VAWT, and stirring means carried by the rotor and adapted to agitate liquid in the container when the VAWT drives the rotor, characterised in that the stirring means comprise subsidiary rotors linked to the VAWT to be driven thereby.

2. Liquid treatment apparatus as claimed in claim 1, wherein the subsidiary rotors counter-rotate with respect to the main rotor.

3. Liquid treatment apparatus as claimed in claim 1 or 2, wherein the stirring means have angled blades adapted to raise solid matter from the bottom of the container and/or to disturb the upper surface of the liquid by the turbulence they create.

4. Liquid treatment apparatus as claimed in claim 1, 2 or 3, wherein there is step-down gearing from the VAWT to the rotor.

5. Liquid treatment apparatus as claimed in any preceding claim, wherein there is step-down gearing from the

VAWT to the subsidiary rotors.

6. Liquid treatment apparatus as claimed in any preceding claim, wherein the subsidiary rotors are directly driven by the VAWT and are also coupled to a static member so that their rotation by the VAWT causes the coupling to the static member to rotate the main rotor.

7. A VAWT in which each aerofoil blade is free to pivot within limits about a respective vertical axis, blades being linked so that they pivot substantially in unison.

8. A VAWT as claimed in claim 7, wherein there is at least one pair of diametrically opposed blades and the linkage is between opposite blades of the or each pair.

9. A VAWT as claimed in claim 8, wherein the linkage is a rigid horizontal link between corresponding points offset from the pivot axes.

10. A VAWT as claimed in claim 7, 8 or 9, wherein the linkage incorporates means which maintain pivoting in unison at low speeds but which allow the blades at least limited independence at high speeds.

11. A VAWT as claimed in claim 10, wherein said means include a spring which behaves as a substantially rigid member at low speeds but which is distortable by centrifugal forces at high speeds.

12. A VAWT as claimed in any one of claims 7 to 11, wherein the limits are defined by stops, those limiting the trailing-edge-out position of the blades having a progressive characteristic which confines the associated blades to median positions at low speeds but which shift under the influence of centrifugal forces to allow the trailing edges to move outwardly of the median positions.

13. Liquid treatment apparatus as claimed in any one of claims 1 to 6, wherein the VAWT is as claimed in any one of claims 7 to 12.

14. Liquid treatment apparatus comprising a liquid container, a main rotor, drive means for the rotor, and stirring means carried by the rotor, the stirring means including a plurality of subsidiary rotors with blades that follow a planetary motion adjacent the base of the container and/or the surface of liquid in the container, as the main rotor rotates.

15. Liquid treatment apparatus as claimed in claim 14, wherein the blades are angled to raise solid matter from the bottom of the container and/or to disturb the upper surface of the liquid by the turbulence they create.

16. Liquid treatment apparatus as claimed in claim 14 or 15, wherein the subsidiary rotors are driven to counter-rotate with respect to the main rotor.

17. Liquid treatment apparatus as claimed in claim 14,.15 or 16, wherein the drive means comprise a VAWT as claimed in any one of claims 7 to 12.