WO2011107799A2

WO2011107799A2 - Improved tidal stream turbine

Info

Publication number: WO2011107799A2
Application number: PCT/GB2011/050415
Authority: WO
Inventors: Matthew French; Robert W Rust; James Cassidy
Original assignee: Silvine Corporation
Priority date: 2010-03-02
Filing date: 2011-03-02
Publication date: 2011-09-09
Also published as: GB201003463D0; WO2011107799A3

Abstract

The invention relates to a tidal stream turbine (10) arranged to be located underwater in a tidal stream flow to generate a hydraulic head. The turbine comprises a nacelle (12) pivotally coupled to a support such that the nacelle (12) can rotate about a substantially vertical pivot axis A; a rotor (22) having a plurality of circumferentially spaced blades (26) radially extending from a hub (24); a plurality of circumferentially spaced guide vanes (30) radially extending from the nacelle (12) and positioned upstream of the rotor; and a pump (34) arranged to be driven by the rotor (22) and having a water inlet (40) and a water outlet (42). In use the tidal stream causes the rotor (22) to rotate, thereby driving the pump (34) which draws in water through the water inlet (40), increases the hydraulic head of the water, and delivers the water from the outlet (42).

Description

IMPROVED TIDAL STREAM TURBINE

The invention relates to a tidal stream turbine that is arranged to generate a hydraulic head from a tidal stream. This invention also relates to an installation for generating electricity from a tidal stream using a tidal stream turbine.

There are currently a number of known ways of generating electricity from natural resources. For example, it is known to generate electricity from the sun using solar panels, from the wind using wind turbines, and from flowing water using hydro turbines.

One type of hydro turbine is a tidal stream turbine which is used to generate electricity from tidal streams. Tidal stream turbines generally comprise a rotor which is driven by the tidal stream and which mechanically drives an electrical generator, thereby generating electricity. Since the electricity is generated underwater, it is important to ensure that the electronic components of the generator are housed in a watertight casing. Providing a watertight casing can be both complicated and expensive.

Further, a large number of tidal stream turbines must be used in order to generate sufficient electrical power. It is therefore necessary to combine the electrical output of the individual turbines before feeding the electrical power to the main grid. This may require complicated and expensive circuitry.

It is therefore desirable to provide an improved tidal stream turbine that can be used to generate electricity.

According to an aspect of the invention there is provided a tidal stream turbine arranged to be located underwater in a tidal stream flow to generate a hydraulic head, comprising: a nacelle coupled to a support post and rotatable about a substantially vertical pivot axis; a rotor having a plurality of circumferentially spaced rotor blades radially extending from a hub which is rotationally mounted to the nacelle such that the rotor can rotate about a substantially horizontal rotor axis; a plurality of circumferentially spaced guide vanes radially extending from the nacelle and positioned upstream of the rotor; and a pump arranged to be driven by the rotor and having a water inlet and a water outlet; wherein in use the tidal stream flow causes the rotor to rotate, thereby driving the pump which draws in water through the water inlet, increases the hydraulic head of the water, and delivers the water from the water outlet. The nacelle may be pivotably coupled to the support post, the support post may comprise an upper portion attached to the nacelle and a lower portion attached to a support frame with the upper and lower portions rotatable with respect to one another, or the entire support post may be rotatable with respect to a support frame.

The rotor blades may be impulse blades, or primarily impulse blades, arranged to change the direction of the tidal stream flow. This may mean that the primary purpose, or function, of the blades is to change the direction of the tidal stream flow, thereby generating a torque. It should be appreciated that the blades may or may not be purely impulse blades. For example, the blades could be purely impulse blades, or the blades could be a combination of both impulse blades and reaction blades, thereby generating torque due to both impulse and reaction, but with impulse being the major contributor to the generation of torque. The guide vanes may be arranged to change the direction of the tidal stream flow. This may change the direction of the tidal stream flow before it reaches the rotor so that there is a greater directional change of the tidal stream flow across the rotor.

The nacelle may be freely rotatable about the pivot axis. This would allow the nacelle to fully rotate by any angle, without angular restriction.

The support post may comprise a fluid conduit which is arranged to convey water from the water outlet through the support post. The support post may comprise a hollow support member which forms at least part of the fluid conduit. This would remove the need for separate fluid conduits to convey the pressurised water which would allow full rotation of the nacelle. The turbine may further comprise a fluid-tight swivel joint which allows the nacelle to pivot and allows the support post to covey water from the water outlet. The fluid-tight swivel joint would prevent the leakage of pressurised fluid from the fluid conduit whilst still allowing the nacelle to freely rotate. The swivel joint may be disposed at any position between the nacelle and a support base or frame arranged to be mounted to the seabed. The swivel joint may be between the nacelle and the support post, or may be between upper and lower portions of the support post, or may be between the support post and a support base or frame. The hub may be mounted to the nacelle behind the vertical pivot axis and the horizontal rotor axis may intersect the vertical pivot axis. This would allow the tidal stream turbine to align with the tidal stream flow direction. The water inlet may be located in front of the rotor. The water inlet may be located at the front of the nacelle.

The pump may be located in the nacelle. The rotor may be located towards the rear of the nacelle.

According to a second aspect of the invention there is provided a tidal stream turbine arranged to be located underwater in a tidal stream flow to generate a hydraulic head, comprising: a nacelle coupled to a support post and rotatable about a substantially vertical pivot axis; a rotor having a plurality of circumferentially spaced rotor blades radially extending from a hub which is rotationally mounted to the nacelle such that the rotor can rotate about a substantially horizontal rotor axis; and a pump arranged to be driven by the rotor and having a water inlet and a water outlet; wherein the support post comprises a fluid conduit which is arranged to convey water from the water outlet through the support post; and wherein in use the tidal stream flow causes the rotor to rotate, thereby driving the pump which draws in water through the water inlet, increases the hydraulic head of the water, and delivers the water from the water outlet through the fluid conduit. The support post may comprise a hollow support member which forms at least part of the fluid conduit. The tidal stream turbine may further comprise a fluid-tight swivel joint which allows the nacelle to pivot and allows the support post to covey water from the water outlet. The tidal stream turbine may further comprise a plurality of circumferentially spaced guide vanes radially extending from the nacelle and positioned upstream of the rotor. The guide vanes may be arranged to change the direction of the tidal stream flow.

The rotor blades may be impulse blades arranged to change the direction of the tidal stream flow. The nacelle may be freely rotatable about the pivot axis. The hub may be mounted to the nacelle behind the vertical pivot axis and the horizontal rotor axis may intersect the vertical pivot axis. The water inlet may be located in front of the rotor. The water inlet may be located at the front of the nacelle. The pump may be located in the nacelle. The rotor may be located towards the rear of the nacelle.

The invention also relates to an installation for generating electricity from a tidal stream, comprising: a tidal stream turbine in accordance with any statement herein located underwater in a tidal stream and supported on the seabed by the support; a delivery duct in fluid communication with the water outlet of the pump of the tidal stream turbine and arranged to deliver water to the shore; a generator arranged to generate electricity using the water delivered by the delivery duct to the shore. The delivery duct may be in fluid communication with the water outlet of the pump through a fluid conduit, at least part of which may be formed by a hollow support which is arranged to support the nacelle.

In one arrangement there is a plurality of tidal stream turbines and the delivery duct is in fluid communication with the water outlet of the pump of each tidal stream turbine. According to a further aspect of the invention there is provided a tidal stream turbine arranged to be located underwater in a tidal stream and to generate a hydraulic head, the turbine comprising: a nacelle pivotally coupled to a support such that the nacelle can rotate about a substantially vertical pivot axis; a rotor having a plurality of circumferentially spaced blades radially extending from a hub which is rotationally mounted to the nacelle behind the vertical pivot axis such that the rotor can rotate about a substantially horizontal rotor axis that intersects the vertical pivot axis; and a pump arranged to be driven by the rotor and having a water inlet and a water outlet; wherein in use the tidal stream causes the rotor to rotate, thereby driving the pump which draws in water through the water inlet, increases the hydraulic head of the water, and delivers the water from the outlet.

It will be appreciated that, in operation, the nacelle will rotate about the vertical pivot axis in response to tidal flow past it, so as to align the nacelle with the tidal stream with the hub positioned behind the vertical pivot axis, i.e. downstream of the vertical pivot axis with respect to the tidal flow direction. Thus, in this specification, references to the positions of components in front or behind other components relate to the tidal flow direction when the nacelle is rotated into alignment with the tidal stream.

According to another aspect of the invention there is provided a tidal stream turbine arranged to be located underwater in a tidal stream and to generate a hydraulic head, the turbine comprising: a nacelle pivotally coupled to a support such that the nacelle can rotate about a substantially vertical pivot axis; a rotor having a plurality of circumferentially spaced blades radially extending from a hub which is rotationally mounted to the nacelle such that the rotor can rotate about a substantially horizontal rotor axis; and a pump arranged to be driven by the rotor and having a water inlet located in front of the rotor and a water outlet; wherein in use the tidal stream causes the rotor to rotate, thereby driving the pump which draws in water through the water inlet, increases the hydraulic head of the water, and delivers the water from the outlet. According to a yet another aspect of the invention there is provided a tidal stream turbine arranged to be located underwater in a tidal stream and to generate a hydraulic head, the turbine comprising: a nacelle pivotally coupled to a support such that the nacelle can rotate about a substantially vertical pivot axis; a rotor having a plurality of circumferentially spaced blades radially extending from a hub which is rotationally mounted to the nacelle such that the rotor can rotate about a substantially horizontal rotor axis; a stator positioned in front of the rotor, the stator having a plurality of circumferentially spaced vanes radially extending from the nacelle; and a pump arranged to be driven by the rotor and having a water inlet and a water outlet; wherein in use the tidal stream causes the rotor to rotate, thereby driving the pump which draws in water through the water inlet, increases the hydraulic head of the water, and delivers the water from the outlet.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

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

Figure 1 schematically shows an installation for generating electricity from a tidal stream using tidal stream turbines; Figure 2 schematically shows a tidal stream turbine; and

Figure 3 schematically shows the flow path through the stator guide vanes and the rotor blades of the tidal stream turbine of Figure 2.

Figure 1 schematically shows an installation 1 for generating electricity from a tidal stream. The installation 1 comprises a plurality of tidal stream turbines 10 located underwater in a tidal stream, and an electricity generation plant 100 located onshore. With reference to Figure 2, each turbine 10 comprises a nacelle 12 which is arranged to be supported on the seabed by a substantially vertical support post 14 attached to a support frame 16. The support post 14 is guyed by four guy rods 20 which brace the support post 14 against the nacelle and rotor drag. The turbine 10 is installed underwater by anchoring the support frame 16 to bedrock or the seabed with rock anchors 18 or piles, for example. In other embodiments the frame plate 16 may be piled and mud matted. The support post 14 holds the nacelle 12 between about 10- 20m above the seabed. This keeps the nacelle 12 clear of the seabed boundary layer and the associated seabed debris included in this area of the tidal flow. The support post 14 is provided with a nacelle fluid-tight swivel joint 23 which allows the nacelle 12 to freely pivot or rotate about a substantially vertical axis A. The vertical axis A passes through the centre of the nacelle 12 and the nacelle 12 is capable of full 360° rotation. The support post 14 is also provided with a hinge joint 23 which allows the nacelle 12 to be pivoted about a horizontal axis out of the tidal stream for maintenance purposes.

The turbine 10 is an axial flow impulse turbine and comprises a rotor 22 and a stator 28 that are attached to the nacelle 12 towards the rear with the rotor 22 located behind the stator 28. The rotor 22 comprises a hub 24 and a plurality of blades 26 that are circumferentially spaced and radially extend from the hub 24. The hub 24 is rotationally mounted to the nacelle 12 such that the rotor 22 can rotate about a substantially horizontal rotor axis B. The rotor axis B is substantially coincident with the longitudinal axis of the nacelle 12 and intersects the vertical pivot axis A. The stator 28 comprises a plurality of guide vanes 30 that are circumferentially spaced and radially extend from the nacelle 12. The guide vanes 30 are fixed with respect to the nacelle 12 and may extend directly from the nacelle 12 or may extend from a hub that is fixed to the nacelle 12. The rotor 22 and the stator 28 are located behind the vertical pivot axis A of the nacelle 12.

Inside the nacelle 12 there is located a torque converter 32 and a pump 34. The torque converter 32 is connected to the hub 24 of the rotor 22 by a first shaft 36 and the pump 34 is connected to the torque converter 32 by a second shaft 38. The torque converter 32 may be mechanical or hydraulic with a speed ratio of 150:1 , for example. In this embodiment the pump 34 is a multi-stage mixed flow pump. The pump 34 has a water inlet 40 that is located in the front of the nacelle 12 and a water outlet 42 that is in fluid communication with an outlet pipe (or fluid conduit) 44 that passes down the centre of the support post 14. In this particular embodiment the support post 14 is hollow and forms the fluid conduit 44 and therefore both supports the nacelle 12 and acts as a fluid line. The fluid-tight swivel joint 23 prevents the leakage of pressurised water from the fluid conduit 44 whilst allowing the nacelle 12 to freely rotate by any angle about the support post 14. The rotor 22 is arranged to drive the pump 34 through the torque converter 32 such that water is drawn in through the water inlet 40 and pumped out, or discharged, through the water outlet 42. The pump 34 increases the hydraulic head of the water and generates a pressure of between 35-40 barg (3.5-4MPa). In use, the tidal stream turbine 10 is located underwater in a tidal stream, between 20- 60 metres below sea level, and is anchored to the seabed. The turbine 10 self-aligns with the flow direction of the tidal stream F. The drag force on the rotor/stator 22, 28 caused by the tidal stream causes the nacelle 12 to pivot about the vertical pivot axis A until the rotor and stator 22, 28 are aligned with the flow direction of the tidal stream and are behind the pivot axis A so that the drag force is minimised. When the turbine 10 is aligned with the tidal stream (i.e. when the plane of the rotor is at right angles to the tidal stream), the flow direction of the tidal stream F is substantially parallel to the axis of the nacelle and the rotor and stator 22, 28 which are behind the pivot axis A. As the flow direction of the tidal stream changes, the nacelle 12 pivots about the vertical axis A until the rotational axis B of the rotor 22 is aligned with the flow direction F. This self-alignment feature is achieved by locating the rotor and stator 22, 28, which create large drag forces, behind the vertical pivot axis A.

With reference to Figure 3, the tidal stream passes through the guide vanes 30 of the stator 28 which change the direction of the flow such that the flow is at the optimal angle with respect to the blades 26 of the rotor 22 when the rotor is rotating at its design speed. The flow through the blades 26 of the rotor 22 causes the rotor to rotate about the rotational axis B. The stator guide vanes 30 change the direction of the flow to ensure the optimum change in direction across the rotor blades 26 which maximises the power output of the tidal stream turbine 10. As can be seen from Figure 3, the rotor blades 26 are purely impulse blades 26 as they have a substantially constant and a relatively small thickness.

The stator guide vanes 30 also provide a number of other benefits. The rotor 22 generates a torque on the nacelle 12 about a substantially horizontal axis as a result of the torque required to drive the torque converter 32 and the pump 34. This torsional force tends to rotate the nacelle 12 about a horizontal axis and therefore induces torque and stresses in the support post 14 and the connection between the nacelle 12 and the support post 14. However, the arrangement of the guide vanes 30 generates a torque on the nacelle 12 about a horizontal axis that is in the opposite direction to that generated by the rotor 22. Therefore, the net torsional force on the nacelle 12 is reduced.

Although the drag created by the rotor 22 tends to align the tidal stream turbine with the tidal stream flow direction, it is slightly offset from the flow direction due to gyroscopic effects. However, the additional drag created by the stator 28 reduces the gyroscopic effect and therefore the tidal stream turbine is more closely aligned with the tidal stream flow direction. The stator guide vanes 30 also prevent large debris from coming into contact with the rotor 22 and causing potential damage.

As the rotor 22 rotates it drives the pump 34 which draws in seawater through the water inlet 40 located at the front of the nacelle 12. The pump 34 increases the hydraulic head of the water and the water that exits the pump 34 through the water outlet 42 has a pressure of between 35-40 barg. This pressurised water flows down the fluid conduit 44, which is formed by the interior of the support post 14 of the tidal stream turbine 10. Using the hollow support post 14 having a fluid-tight swivel joint 23 to convey the pressurised water delivered by the pump 34 allows the nacelle 12 to freely rotate about the support post 14 with no angular limitation or stops.

Although it has been described that the swivel joint 23 could be provided between an upper end of the support post 14 and the nacelle 12 or at any position between the nacelle 12 and the frame 16 so that the nacelle 12 can freely rotate. In this particular embodiment the diameter of the rotor 22 is 6m and the blades 26 are designed such that the rotor 22 rotates at a speed between about 6-16 rpm. The torque converter 32 increases this rotational speed to about 900-1800 rpm and drives the pump 34 at this speed. The tidal stream turbine 10 generates approximately 210kW of hydraulic power at a tidal stream speed of 4 knots, and 5MW of hydraulic power at a tidal stream speed of 12 knots.

Providing the pump water inlet 40 at the front of the nacelle has a number of advantages. Firstly, the velocity of the water is at its maximum and therefore the water is at a higher static pressure when entering the pump eye which results in a higher hydraulic head at the water outlet 42. Secondly, the velocity pressure increase due to the higher pump inlet pressure which helps to prevent cavitation of the pump impellors. This is particularly beneficial as the pump is required to work over a wide range of flow rates. As shown in Figure 1 , the electricity generation installation 1 comprises a plurality of tidal stream turbines 10 that are each located underwater in a tidal stream and anchored to the seabed. There may be approximately 150 tidal stream turbines per square mile (2.59 km2). The outlet pipe 44 of each tidal stream turbine 10 is connected to a common delivery duct 90 that takes the water pumped by the tidal stream turbines 10 to shore. The pressure in the delivery duct 90 is maintained at 30 barg by a control valve 92. If the water pressure being delivered by the tidal stream turbines 10 is greater than 30 barg then the control valve 92 automatically opens and returns a proportion of the water to the sea. The outlet pipe 44 of each tidal stream turbine 10 is provided with a non-return valve 46 which ensures that each turbine 44 only delivers pressurised water to the delivery duct 90 once it has overcome the backpressure. Onshore, the hydraulic head of the water is used to generate electricity using the electricity generation plant 100. In this particular embodiment the pressurised water is used to drive a Pelton wheel 102 which in turn drives a generator 104 in order to generate electricity. The electricity generated is fed through a switch gear 106 and then a transformer 108 before being fed to the main power grid. The water used to drive the Pelton wheel 102 is returned to the sea via a spillway.

Generating the electricity onshore using the hydraulic head of the water means that it is not necessary to have any electronics located subsea. The results in an installation which is less complicated than known prior art systems.

As will be readily apparent to one skilled in the art, the hydraulic head generated by the tidal stream turbines 10 may be used to generate electricity by other suitable methods onshore. For example, the water may be pumped by the tidal stream turbines 10 to a reservoir which is above sea-level where it can be stored, before subsequently being allowed to flow back to the sea via a water powered electrical generator.

Although it has been described that the tidal stream turbine is located in the sea, as will be readily apparent to one skilled in the art, the tidal stream turbine could be located in any suitable location where there is a natural flow of water.

Claims

CLAIMS:

1 . A tidal stream turbine arranged to be located underwater in a tidal stream flow to generate a hydraulic head, comprising:

a nacelle coupled to a support post and rotatable about a substantially vertical pivot axis;

a rotor having a plurality of circumferentially spaced rotor blades radially extending from a hub which is rotationally mounted to the nacelle such that the rotor can rotate about a substantially horizontal rotor axis;

a plurality of circumferentially spaced guide vanes radially extending from the nacelle and positioned upstream of the rotor; and

a pump arranged to be driven by the rotor and having a water inlet and a water outlet;

wherein in use the tidal stream flow causes the rotor to rotate, thereby driving the pump which draws in water through the water inlet, increases the hydraulic head of the water, and delivers the water from the water outlet.

2. A tidal stream turbine according to claim 1 , wherein the rotor blades are impulse blades arranged to change the direction of the tidal stream flow.

3. A tidal stream turbine according to claim 1 or 2, wherein the guide vanes are arranged to change the direction of the tidal stream flow.

4. A tidal stream turbine according to any preceding claim, wherein the nacelle is freely rotatable about the pivot axis.

5. A tidal stream turbine according to any preceding claim, wherein the support post comprises a fluid conduit which is arranged to convey water from the water outlet.

6. A tidal stream turbine according to claim 5, wherein the support post comprises a hollow support member which forms at least part of the fluid conduit.

7. A tidal stream turbine according to any preceding claim, further comprising a fluid-tight swivel joint which allows the nacelle to pivot and allows the support post to covey water from the water outlet.

8. A tidal stream turbine according to any preceding claim, wherein the hub is mounted to the nacelle behind the vertical pivot axis and the horizontal rotor axis intersects the vertical pivot axis.

9. A tidal stream turbine according to any preceding claim, wherein the water inlet is located in front of the rotor.

10. A tidal stream turbine according to claim 9, wherein the water inlet is located at the front of the nacelle.

1 1 . A tidal stream turbine according to any preceding claim, wherein the pump is located in the nacelle.

12. A tidal stream turbine according to any preceding claim, wherein the rotor is located towards the rear of the nacelle.

13. A tidal stream turbine arranged to be located underwater in a tidal stream flow to generate a hydraulic head, comprising:

a rotor having a plurality of circumferentially spaced rotor blades radially extending from a hub which is rotationally mounted to the nacelle such that the rotor can rotate about a substantially horizontal rotor axis; and

wherein the support post comprises a fluid conduit which is arranged to convey water from the water outlet; and

wherein in use the tidal stream flow causes the rotor to rotate, thereby driving the pump which draws in water through the water inlet, increases the hydraulic head of the water, and delivers the water from the water outlet through the fluid conduit.

14. A tidal stream turbine according to claim 13, wherein the support post comprises a hollow support member which forms at least part of the fluid conduit.

15. A tidal stream turbine according to claim 13 or 14, further comprising a fluid-tight swivel joint which allows the nacelle to pivot and allows the support post to covey water from the water outlet.

16. A tidal stream turbine according to any of claims 13-15, further comprising a plurality of circumferentially spaced guide vanes radially extending from the nacelle and positioned upstream of the rotor.

17. A tidal stream turbine according to claim 16, wherein the guide vanes are arranged to change the direction of the tidal stream flow.

18. A tidal stream turbine according to any of claims 13-17, wherein the rotor blades are impulse blades arranged to change the direction of the tidal stream flow.

19. A tidal stream turbine according to any of claims 13-18, wherein the nacelle is freely rotatable about the pivot axis.

20. A tidal stream turbine according to any of claims 13-19, wherein the hub is mounted to the nacelle behind the vertical pivot axis and the horizontal rotor axis intersects the vertical pivot axis.

21 . A tidal stream turbine according to any of claims 13-20, wherein the water inlet is located in front of the rotor.

22. A tidal stream turbine according to claim 21 , wherein the water inlet is located at the front of the nacelle.

23. A tidal stream turbine according to any of claims 13-22, wherein the pump is located in the nacelle.

24. A tidal stream turbine according to any of claims 13-23, wherein the rotor is located towards the rear of the nacelle.

25. An installation for generating electricity from a tidal stream, comprising:

a tidal stream turbine in accordance with any of claims 1 -24 located underwater in a tidal stream and supported on the seabed by the support; a delivery duct in fluid communication with the water outlet of the pump of the tidal stream turbine and arranged to deliver water to the shore;

a generator arranged to generate electricity using the water delivered by the delivery duct to the shore.

26. An installation according to claim 25, wherein the delivery duct is in fluid communication with the water outlet of the pump through a fluid conduit formed by the support.

27. An installation according to claim 25 or 26, wherein there are a plurality of tidal stream turbines and the delivery duct is in fluid communication with the water outlet of the pump of each tidal stream turbine.