GB2043790A - Power Generation from Tidal Energy - Google Patents

Abstract

An annular float (14) which rises and fails with the tide drives a piston (16) reciprocable in a chamber (15) to pump liquid continuously to drive a turbine (33). The float (14) is ballasted with seawater to assist its descent and the ballast is discharged to assist its ascent. Liquid which is temporarily surplus is stored in chamber 26 and used to drive the turbine during slack. water. Chamber 26 communicates with chamber 27 which contains air compressed by turbine-driven pumps. <IMAGE>

Description

SPECIFICATION Power Generation from Marine Energy This invention concerns the generation of power from marine energy.

The increasing scarcity and cost of fossil fuels is making the need for the development of alternative sources of energy to meet mankind's requirements in the coming centuries increasingly urgent.

Considerable attention has been given to the possibilities of harnessing naturally occurring sources of energy such as the sun and wind. The supply of these sources is, however, generally uncertain on account of ciimatic factors and more and more interest is developing in the possibility of harnessing wave and tidal energy which are always present notwithstanding seasonal variations.

According to the present invention, there is provided apparatus for the generation of power from marine energy comprising a float located in the sea, and which is of such buoyancy and such mass that it is capable of pumping liquid to drive a turbine both when the tide is rising and when the tide is falling.

The invention will be further apparent from the following description with reference to the single figure of the accompanying drawing which shows, by way of example only, a vertical crosssection through one form of apparatus embodying the invention.

Referring now to the drawing it will be seen that the apparatus comprises a tower-like structure generally indicated at 10 extending upwardly from a concrete base 11 secured to the seabed by piles 12.

The structure 10 is surrounded by an annular float 1 4 which will be described in greater detail hereinafter.

The lowermost part of the structure 1 0 houses a cylindrical chamber 1 5 in which is mounted a piston 1 6 connected by piston rods 1 7 to a web 1 8 connected to the float 1 4 by means of a rotatable joint indicated at 19. The upper part of the structure 10 is mounted on legs 20 which extend upwardly from the lowermost part and through apertures 21 formed in the web 18 and contains a low pressure liquid reservoir 22, a manifold chamber 23 for high pressure liquid, a turbine housing 24, a compressor housing 25, a high pressure liquid store 26 and a high pressure compressed air tank 27.

It will be understood that as the float 14 rises and falls with the rise and fall of the tide, the piston 1 6 will be reciprocated within the chamber 1 5. A ball valve 28 mounted in the piston 16 connects the part of the chamber 15 on high pressure side of the piston 1 6 with channels 29 in the piston rods 1 7 which telescopically engage conduits 30 extending downwardly from the manifold chamber 23. Thus high pressure liquid is pumped continuously to the chamber 23.

Pipes 31 deliver high pressure liquid from the chamber 23 via pressure governors 32 to drive a turbine 33 located in the housing 24, excess high pressure liquid being passed through a pipe 34 from the chamber 23 to the store 26. Liquid which has passed over the turbine 33 falls through a channel 35 into the reservoir 22 for return through a pipe 36 and ball valve 37 or 38 to the part of the chamber 1 5 on the low pressure side of the piston 1 6.

Various measures may b6adopted to ensure that the turbine 33 can be driven at full power continuously despite the variations in tidal flow.

Firstly, as the tide approaches the turn and become slack, the part of the chamber 1 5 on the low pressure side of the piston 1 6 may be pressurised by connecting it with the chamber 23 (which is in communication with the store 26) to assist in completing the stroke of the piston 16, a pipe 39 and mechanically controlled valves 40 and 41 being provided for this purpose.

Secondly, by proper management of the ballasting of the float 1 4 with seawater it can be ensured that movement of the float lags behind that of the tide enabling the piston 1 6 to execute strokes of greater length that the difference between the levels of the sea at high tide and low tide.

Finally, during the period when the float 1 4 is reversing its direction of travel, the turbine 33 may be driven by liquid from the store 26 which can be fed to the chamber 23 through the pipe 34. Such liquid is returned to the store 26 from the reservoir 22 by means of a pump 42, pipe 43 and valve 44 to any necessary extent having regard to feed of liquid through pipe 34 as a result of wave action on the float 14. The pressure of the liquid in the store 26 is maintained by the pressure of the compressed air in the tank 27 which communicates with the store 26 by means of feed and return pressure valves 45 and 46.

High pressure compressed air is supplied to the tank 27 from compressors in the housing 25 which are driven by. power derived from the turbine 33 or from the electrical distribution grid during "off-peak" or low-demand periods.

With regard to ballasting of the float 14, it should be noted that there is always advantage to be gained by admitting sea water to the float 14, as ballast, at any time when that water travels downwardly as a result of both weighting of the float thereby and the ebb of the tide through a distance which exceeds that over which the water must be lifted for discharge as is possible as a result of the fall of the tide.

Referring again to the drawing, it will be seen that the float 14 comprises four compartments constituting a primary ballast tank 50, a secondary ballast tank 51, a low-pressure compressed air tank 52 (which is supplied with compressed air from theCompressors contained within the housing 25 during low-demand periods as aforesaid or by wind-driven mechanism-not shown-mounted on the roof of the float 14 or top of the structure 1 0) and rapid discharge tank 53.

We now describe the ballasting of the float 14 with seawater from the time that it reaches its highest point. At this point ballast intake valves 54 and 55 open in the primary and secondary ballast tanks 50 and 51 respectively to allow the ingress of seawater. The primary ballast tank 50 fills very rapidly to build up pressure on the piston 16 to reduce the tidal inertia and therefore the duration of the change-over period. The secondary ballast tank 51, however, is arranged to fill up at a rate which governs the rate of descent of the float 14 and becomes completely full as the float completes its descent.

During descent of the float 14, seawater from the primary ballast tank 50 is blown up intro the rapid discharge tank 53 through pipes 56 (only one of which is shown in the drawing) by means of compressed air from the tank 52 which is fed to the primary ballast tank 50 through a valve 57 and pipe 58. During this operation vent valves 48 which normally establish a connection between the tank 50 and atmosphere, through pipes 49, are closed as are the valves 54.

At completion of the descent of the float 14 vent valves 59 connecting the secondary ballast tank 51 with atmosphere close and valves 60 connecting the compressed air tank 52 with the secondary ballast tank 51 open to commence discharge of sea water from the tank 51 through discharge pipes 61 and flap valves 62. Also at completion of the descent of the float 1 4 gravity discharge valves 63 open to permit rapid discharge of seawater from the tank 53 thus reversing thrust on the piston 1 6 and again reducing the duration of the change-over period.

As the float 1 4 ascends, seawater is continuously discharged from the tank 51 such that the rate of rise of the float is constant and, of course, faster than that of the tide. Completion of discharge from the tank 51 coincides with the full ascent of the float 14 and is so arranged that the sudden loss of pressure through the pipes 61 causes the valves 60 to shut.

It is suggested that the completion of the ascent should coincide with the build-up of tidal activity as the ebb starts and that conversely the completion of the descent should coincide with the build-up of tidal pressure as the flood commences. In the case of a neap tide this could be quite some time after high and low water respectively. In consequence, piston thrust reversals and change-over periods can be achieved as quickly as is possible.

Calculations have shown that 13.5 megawatts can be generated by a unit as described above located in some 60 metres of water and with a float diameter of some 1 50 metres operating a piston some 30 metres in diameter and with a stroke of some 30 metres.

Although the capital costs of providing power by means of apparatus as described herein is undoubtedly greater than that required by conventional or nuclear power stations, it must be remembered that this apparatus will have ionger life, requires no energy input in the form of fuel and can operate largely unmanned.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art being possible without departing from the scope thereof, as defined by the appended claims.

Thus, for example, although the turbine will normally be arranged to drive an alternator for the generation of electrical energy it may provide mechanical energy for direct use in irrigation or similar schemes.

Claims (10)

Claims

1. Apparatus for the generation of power from marine energy comprising a float located in the sea, and which is of such buoyancy and such mass that it is capable of pumping liquid to drive a turbine both when the tide is rising and when the tide is falling.

2. Apparatus according to claim 1 wherein said float is ballasted with seawater to assist its descent and wherein the seawater ballast is discharged to assist its ascent.

3. Apparatus according to either claim 1 or claim 2 wherein said float is mechanically connected with a piston which is reciprocable in a cylinder and which is equipped with a valve whereby liquid on the high-pressure side thereof is displaced to drive said turbine.

4. Apparatus according to claim 3 including also a store for liquid at high pressure, which receives liquid from the high pressure side of said piston not required to drive said turbine.

5. Apparatus according to claim 4 wherein the pressure of liquid in said high pressure store is maintained by a supply of compressed air.

6. Apparatus according to claim 5 wherein said supply of compressed air is derived from compressors which are driven by power derived from said turbine.

7. Apparatus according to any one of claims 2 to 6 inclusive wherein said float comprises primary ballast tanks and secondary ballast tanks, the arrangement being such that seawater ballast is admitted to both said ballast tanks when the float is at its high point, such that the primary ballast tank fills rapidly and such that the secondary ballast tank fills gradually as the float makes its descent.

8. Apparatus according to claim 7 including a discharge tank and a compressed air tank, the compressed air being used to displace seawater from the primary ballast tank to the discharge tank to permit rapid discharge thereof when the float reaches its bottom point.

9. Apparatus according to claim 8 wherein seawater ballast from the secondary ballast tank is discharged gradually as the float makes its ascent by means of compressed air derived from said compressed air tank.

10. Apparatus substantially as described herein with reference to and as illustrated by the single figure of the accompanying drawing.