WO2004067951A1

WO2004067951A1 - Arrangement at a wave power station ii

Info

Publication number: WO2004067951A1
Application number: PCT/NO2004/000009
Authority: WO
Inventors: Paul K. MØRCH
Original assignee: Moerch Paul K
Priority date: 2003-01-31
Filing date: 2004-01-15
Publication date: 2004-08-12
Also published as: NO20030491D0; NO20030491L

Abstract

An arrangement at a wave power station (1) of the type where the pressure head of the waves is used to drive a turbine (4) through flow, and where the water flows through a conical funnel (16), the largest diameter of which is at its lower end portion (20) and the smallest diameter of which is at the turbine (4), whereby the funnel (16) is designed to cause the mean velocity of the flowing water to be greater at the turbine (4) than at the lower end portion (20) of the funnel (16).

Description

ARRANGEMENT AT A WAVE POWER STATION II

This invention regards a wave power station designe , by means of turbines arranged in vertical tubes and rotatable in the horizontal plane, to utilise and convert the kinetic energy of ocean waves into electrical power.

Ocean waves arise from the conversion of part of the wind energy over oceans. The wave energy calculated per unit area is considerably greater than the solar and wind energy for the same area. The utilisation of wave energy from the sea therefore represents an almost inexhaustible renewable energy source, and is the only clean source of energy that has the potential to replace today's use of fossil fuels.

On the basis of the above, the last few decades have seen several proposals for utilisation of wave power. Large scale and full scale wave power stations have also been constructed in many forms, without any of the projects giving the desired results. Wave power stations based on the tapered channel principle appear to be simple and reliable. In a simplified manner, the system can be explained by the incoming waves being forced in between two tapering edges (wedge-shaped), whereby the maximum wave height is increased. At the narrowest end portion of the wedge there is a collecting basin provided at a level above the level of the sea. Wave crests that rise above this level flow over the edge of the basin, filling the basin. The height of fall of the water between the collecting basin and sea level is utilised in a conventional manner, by means of a low pressure turbine.

The reason why this type of wave power station has not gained extensive use is, among other things, the relatively low efficiency achieved. One of the reasons for this is that if an incoming wave does not quite make the edge of the basin, the water in this wave will return to the tapered channel where it may destroy an incoming wave that would have been of a sufficient size to get into the basin. Another reason is that when a really large wave occurs, which significantly exceeds the height of the basin, part of the energy of the wave will not be utilised because the water will fall to the relatively low, predetermined level of the basin. The two mentioned facts contribute towards an efficiency of approximately 15% for wave power stations based on the tapered channel principle.

Considerable expectations have been associated with wave power stations that operate according to the "oscillating air column" principle. In wave power stations of this type the vertical motion of the waves is brought into resonance with a column of air that causes the height fluctuations of the water surface inside the air container to be considerably larger than the wave height outside of the power station. Energy is extracted by the compressed air being led through a turbine.

In power stations of this type, the compressibility of the air causes great hysteresis in the air pressure, which leads to a significant reduction of the efficiency of the power station.

It has proven difficult to dimension wave power stations according to other prior art such as to give them sufficient strength to resist the forces that arise in environments of the type in question.

The object of the invention is to remedy the disadvantages of prior art.

The object is achieved in accordance with the characteristics given in the description below and in the appended claims .

A turbine unit according to the invention comprises a double turbine rotatable about a vertical axis, preferably arranged at sea level. The turbine casing is sealingly connected to an open-ended conical tube projecting down into the sea, where the diameter of the tube is at its smallest by the turbine casing and at its largest at the lower end portion. A similar cone projects upwards from the turbine casing, exhibiting its greatest diameter at the upper end portion. The upper end portion of the upper cone may be open or closed. The lower cone, the turbine casing and the upper cone form a funnel with an hour glass configuration, designed to lead water up and down, substantially in time with the wave height on the outside of the funnel. The conical geometry of the funnel causes the water velocity through the turbine casing to be greater than the mean water velocity at the lower portion of the lower cone, where the diameter is significantly greater.

The turbine, comprising two turbine wheels where the pitch of the turbine blades of one turbine is the opposite of the pitch of the blades of the other, is supported at and rotatably connected to a vertical rotatably supported shaft. The hub of the turbine wheels is equipped with a free- wheeling device, preferably in the form of a plurality of pawls that stop against complementary longitudinal grooves in the shaft. Thus the turbines are designed to drive the shaft when rotating in one direction, the working direction, while rotating freely in the opposite direction, the free-wheeling direction.

When the height of the wave surrounding the outside of the funnel is higher than the water surface inside the funnel, the static pressure difference causes water to flow in through the lower opening of the lower funnel and up through the turbine casing. The lower turbine is thereby caused to rotate in the working direction, rotating the shaft along with it. The upper turbine rotates freely on the shaft in the free-wheeling direction. When the surrounding wave falls, the water present in the upper funnel flows downwards, causing a reversal of the rotating direction of the turbines. In the case of a downward flowing water column, the upper turbine rotates in the working direction, rotating the shaft with it, while the lower turbine rotates freely on the shaft in the free-wheeling direction. Thus the shaft is caused to rotate in the same direction whether the water in the funnel is rising or falling.

The funnel with the associated turbine may be placed on a floating vessel, preferably of the type that exhibits relatively little in the way of heaving movement when in heavy seas. A vessel of the drilling platform type, where a significant portion of the buoyancy element is placed at a depth that ensures a negligible effect from surface waves on the vessel, is appropriate for the purpose. The desired freeboard may easily be adjusted by means of ballast.

Several turbines may be placed side by side and be connected to a common generator.

The wave power station according to the invention is also suitable for permanent installation at onshore sites where the conditions are otherwise favourable.

The upper portion of the funnel may be equipped with a pneumatic turbine, where this is designed to utilise the pressure and vacuum in the funnel that is created when the water flows in and out through the turbine. The planar geometry of the construction of the vessel may be significant with regard to how the waves reach the turbines located down-wave. The invention comprises any planar construction of the vessel. The following describes a non- limiting example of a preferred embodiment illustrated in the accompanying drawings, in which:

Figure 1 schematically shows a funnel with a turbine coupled up to a vessel;

Figure 2 schematically shows an enlargement of the funnel and the turbine of figure 1 with water flowing up through the funnel;

Figure 3 schematically shows an enlargement of the funnel and the turbine of figure 1 with water flowing down through the funnel;

Figure 4 schematically shows a plan view in which several turbines are connected to a common generator;

Figure 5 schematically shows a plan view of a turbine in which the free-wheeling device is shown encircling the shaft;

Figure 6 is an enlarged axial section of the hub of figure 5;

Figure 7 is a sectional view along VI-VI of the hub of figure Figure 8 is a sectional view of the funnel and the turbine with a pneumatic turbine arranged at the upper portion of the funnel;

Figure 9 is an enlarged cut-out showing the upper portion of the funnel equipped with a one-way valve;

Figure 10 shows the same as figure 9, but here the upper portion of the funnel is provided with through holes; and

Figure 11 is a side view of a relatively deep-draught vessel.

In the drawings, reference number 1 denotes a wave power o station comprising a funnel 2, a turbine 4, a shaft 6, the required transmission elements 8, a generator 10 and a vessel 12.

The funnel 2 is constituted by a turbine casing 14 surrounding the turbine 4, and a downward projecting conical s funnel tube 16 and an upward projecting funnel tube 18. The funnel tubes 16 and 18 each have their smallest diameter at their sealed connections to the turbine casing 14. The funnel tubes 16 and 18 have a significantly larger diameter at their respective opposite end portions 20 and 22. The downward o projecting end portion 20 of the lower funnel 16 is open, while the upper end portion 22 of the upper funnel may be open or closed, depending on the prevailing wave conditions. The turbine 4 is arranged concentrically in the turbine casing 14 and unidirectionally rotatably connected to the shaft 6. The shaft 6 is rotatably supported and connected via the transmission elements 8 to the generator 10. The turbine 4 comprises two turbine wheels 24, 26, where turbine wheel 24 is equipped with left-pitched blades while turbine wheel 26 is equipped with right-pitched blades .

The free-wheeling device of the turbine wheels 24, 26, see figure 5 and 7, comprise a plurality of pawls 30 rotatably supported in the hub 28. The shaft 6 is provided with axial grooves 32 designed to provide an abutment for the pawls 30 when the turbine wheel 24 rotates in the working direction.

The pawls 30 are rotated in a direction against the grooves 32 in the shaft 6 by a resilient element 34, preferably in the form of a spiral spring or a hydraulic piston.

When the surface of a wave 40 surrounding the funnel 2 is higher than the water surface inside the funnel 2, water flows in through the lower end portion 20 of the lower funnel 16 and up through the funnel 2, illustrated by means of arrows 36 in figure 2, where the mean water velocity is increased by the cross sectional area of the funnel 16 being smaller at the turbine casing 14. The water first flows through the lower turbine wheel 24, which is set rotating in the working direction. The pawls 30 are displaced in towards the grooves 32 in the shaft 6 by the springs 34, and the shaft 6 is drawn into the rotation. As mentioned, the turbine wheel 26 has blades with an opposite pitch, thus rotating in the free-wheeling direction.

When the water level outside the funnel 2 falls, the water present in the funnel 2 flows downwards, see arrows 38 in figure 3. The rotating direction of the turbine wheels 24, 26 is reversed and the upper turbine wheel 26 is rotated in the working direction, pulling the shaft 6 with it, while the lower turbine wheel 24 rotates in the free-wheeling direction.

o In order to give a more steady output to the generator 10 several turbines 4 may be connected. Figure 4 shows an example where each generator 10 is connected to four turbines 4. A further turbine 4 may be provided concentrically of the generator 10, in which case the generator 10 would be s connected to five turbines 4.

In an alternative embodiment, see figure 8, the upper end portion 22 of the funnel 2 is equipped with a pneumatic turbine 42 that communicates with the volume of air in the upper conical funnel tube 18. In principle, the pneumatic o turbine 42 is constructed as turbine 4, where two turbine blades with opposite pitch are unidirectionally rotatable about a shaft 6. When the water level in the upper funnel tube 18 rises, air flows out through the pneumatic turbine 42, thus providing energy for the pneumatic turbine 42. When 5 the water level in the upper funnel 18 tube falls, air is drawn down through the pneumatic turbine 42. In figure 8, the pneumatic turbine is arranged co-rotatingly with the turbine 4 about the shaft 6. The pneumatic turbine 42 may also have it own mounting (not shown).

In a further embodiment the upper conical funnel tube 18 is provided with a one-way valve 44, see figure 9. The one-way valve 44 is designed to prevent the build-up of a vacuum in the upper conical funnel tube 18 by opening when the pressure in the upper conical funnel tube 18 falls below the ambient pressure. Alternatively, the upper conical funnel tube 18 may be provided with through holes 46 to prevent a vacuum build- up, see figure 10. With this embodiment however, it will not be possible to utilise the pressure energy that builds up in the upper conical funnel tube 18 during the flow of water through the turbine 4 to force the water out again. By placing a significant part of the buoyancy elements 48 of the vessel 12 relatively deep in the sea, the heaving motion of the vessel caused by surface waves will be insignificant, see figure 11.

Claims

C l a i m s

1. An arrangement at a wave power station ( 1 ) of the type where the pressure head of the waves is used to drive a turbine (4) through flow, c h a r a c t e r i s e d

5 i n that the water is caused to flow through a conical funnel (16), the largest diameter of which is at its lower end portion (20) and the smallest diameter of which is at the turbine (4), whereby the funnel (16) is designed to cause the mean velocity of the flowing water o to be greater at the turbine ( 4 ) than at the lower end portion (20) of the funnel (16).

2. An arrangement in accordance with Claim 1 , c h a r a c t e r i s e d i n that the turbine (4) comprises at least two turbine wheels (24, 26) frees wheelingly supported at a turbine shaft ( 6 ) , of which at least one turbine wheel (24, 26) is right-pitched and at least one turbine wheel (24, 26) is left-pitched.

3. An arrangement in accordance with one or more of the preceding claims, c h a r a c t e r i s e d i n that o the free-wheeling device of the turbine wheels (24, 26) comprises a plurality of pawls (30).

4. An arrangement in accordance with one or more of the preceding claims, c h a r a c t e r i s e d i n that the upper portion (22) of the funnel (2) of the wave power station ( 1 ) is equipped with a pneumatic turbine (42).

5. An arrangement in accordance with one or more of claims 1 to 3, c h a r a c t e r i s e d i n that the funnel (2) is equipped with a one-way valve (44).

6. An arrangement in accordance with one or more of claims 1 to 3, c h a r a c t e r i s e d i n that the funnel (2) is provided with a through hole (46).

7. An arrangement in accordance with one or more of the preceding claims, c h a r a c t e r i s e d i n that the wave power station ( 1 ) is arranged on a submersible vessel ( 12) .

8. An arrangement in accordance with one or more of the preceding claims, c h a r a c t e r i s e d i n that the vessel (12) has a sufficiently deep draught to ensure that the heave motion caused by surface waves is negligible.