IE86143B1 - A floating multistage air compressor with turbine - Google Patents

Abstract

There is provided a floating generator (10) which incorporates a turbine (12) and a plurality of open-bottomed air tanks (1 to 6) in a row along a longitudinal axis. The first air tank (1) of the row communicates with the atmosphere via a non-return inlet valve (11) and the last air tank (6) of the row communicates with the atmosphere via the turbine (12). The upper part of each air tank communicates with the next tank in the row via one-way valve means (21 to 61) so that air can pass in one direction only from the first air tank 91) to the last air tank (6). Buoyancy compartments and ballast compartments are provided along each side of the row, substantially symmetrical with respect to the longitudinal axis. In use, air is drawn into the first air tank (1) due to a pressure differential caused by wave action and air is compress cumulatively through the series of tanks until the compress air expands to atmospheric pressure via the turbine to produce power. <Figure 1>

Description

A FLOATING MULTISTAGE AIR COMPRESSOR WITH TURBINE BACKGROUND OF THE INVENTION There is today, enormous interest in renewable sources of energy, to try and combat climate change associated with the continuing use of carbon based fuels. Such fuels are finite resources, and there now seems to be the political will to develop alternative sources of energy that are not carbon based. By developing renewable sources of energy particularly for electrical power production, the hope is that carbon emissions will be reduced; and that is furthermore carbon based fuels can be reserved for those uses where alternative fuels would be impracticable, for instance, aircraft, agriculture, road transport, etc.

This invention relates to power production by converting the energy of water waves using a floating device. There are quite a number of floating devices that are being developed. A brief mention of the main types and their shortcomings will now be addressed. 1. Wave Bobbing buoys There are a number of these, and some even have direct conversion to electrical power without using intermediate working fluids in hydraulic or pneumatic systems. Whilst some may be sound in principle and operation, their actual potential for meaningful power production tends to be limited. 2. Floating Articulated Hulls e.g. the Pelamis Device This system is now well developed and is capable of producing respectable amounts of power. However the system relies on using hydraulic rams to resist the relative motion between the articulated hulls, and converting this to electrical power via a hydraulic system which of necessity has to be complex. This is designed for continuous use, but even so the forces involved at the rams are enormous with rapid variation and change of direction. It is 861 43 punishing for the hydraulics, and it is difficult to imagine the system being able to cope over extended periods without supervision and intervention. 3. Oscillating Water Columns - Floating Devices In these devices air is in direct communication with water, usually in io open bottomed tanks or chambers such that changes in water pressure cause the air within to be compressed when under the influence of a wave, or the air pressure within to be reduced when under the influence of a trough. Air which has been compressed is then expanded via a power turbine to the uncompressed state, that is it can be released to atmosphere, or to a tank or is chamber that in the uncompressed state.

Most of these only make use of the pressure difference attainable from a series of one wave to trough events, as would be brought about by water waves travelling past the device. Consequently there has to be a certain minimum wave height (say 2M.) for there to be any meaningful pressure difference for turbine function. Even then the turbine has to be of a type that can usefully exploit large air volumes being expanded over a small pressure difference. The air conditions forthcoming from such single stage compression make it difficult for any turbine to work efficiently.

The purpose of this invention is to use the oscillating water column principle more effectively, by multiplying the air pressure consequent on a single wave to trough event and cumulatively compressing the air through a series of compression tanks or chambers. This higher air pressure then enables a turbine to operate more efficiently using lower air volumes to better effect. Also the purpose is to allow a generator using the oscillating water column principle to work in waves of smaller height than would otherwise be possible. A yet further purpose is to provide a generator which is simple In build and operation with few moving parts. Such moving parts as are employed can be designed for long service life and can be repaired, serviced or replaced with relative ease.

THE INVENTION - BROAD ASPECTS AND PRINCIPLES According to the present invention there is provided a floating generating vessel as set out in claim 1, with optional preferred features set out in the attached dependent claims. io The floating generator is moored and is comprised of a single and contiguous row of open bottomed air tanks, substantially of the same size and geometry forming a rigid structure, such that water can flow freely into or out of the same thus raising or lowering the air pressure in each tank, along each side of said structure substantially in symmetry, an arrangement of side tanks is consisting of buoyancy compartments in combination with ballast tanks is fastened and integral therewith, this being to provide buoyancy for the generator at a chosen freeboard and trim, also to provide the generator with adequate lateral stability and to provide downward forces to oppose and balance upwards forces caused by air pressure internally within the air tank array. For pressure to exist within the tanks, it can only do so by coexisting with restraint forces. In the floating situation the provision of this essential requirement is difficult. This invention provides a solution.

Non-return valve means are provided to connect the upper part of any tank to a tank adjacent to it, to allow air to pass from tank to tank substantially in one direction only from the first tank through to the final tank. At one end, the first tank is fitted with an inlet non- return valve or valves which allow air to pass substantially only in the inwards direction from the atmosphere. At the other end of the generator, the final tank is fitted with a power turbine or turbines through which air can pass only in the outward direction to atmosphere.

For practical reasons of economy and ease of construction, it may be advantageous for the non-return valves connecting the upper parts of adjacent tanks to be fitted at or near the top of the dividing bulkhead walls. The direct connection thus provided also has the advantage that energy losses will tend to be minimised. The generator’s freeboard and trim should be chosen such that in the calm sea conditions, adequate reserve of buoyancy is provided and also to ensure that the non-return valves are clear of the water by an established distance. Generally the option, where nonreturn valves are incorporated at or near the top of the bulkhead walls is the preferred arrangement, but this does not exclude alternatives. For the purposes of description in what follows, the preferred arrangement has been adopted.

In operation in conditions of sufficient wave height, when the first tank is under the influence of a trough water flows out rapidly creating vacuum conditions causing air to be inspired into that tank via the inlet non-return valve(s). The air cannot then escape to atmosphere, except possibly is minimally by leakage past the inlet non-return valve(s). When the first tank is subsequently under the influence of a wave, water enters rapidly and compresses the air. Over this period of compression, if the pressure attained happens to exceed that in the second tank, then air can and will pass into that tank via the buikhead non-return valve(s). The passage of this air is dependent on the wave to trough disposition ruling at the time. The second tank is continuously being pressurised and depressurised by the inflow and outflow of water consequent on wave action. Again during the period when the second tank is being pressurised, if the pressure attained happens to exceed that in the third tank, then air can and will pass into the third tank via the bulkhead non-return vaive(s) as wave to trough disposition allows over the time scale of pressurisation of the second tank. The third tank is continuously being pressurised and depressurised by wave action in the same manner as the first and second tanks. In the same manner as described for the preceding tanks, under the right conditions air can and will pass through the buikhead non-return valve(s) into the forth tank. This process of air being compressed and forced to pass from tank to tank continues along the contiguous row of tanks to the final tank, where the air can expanded back to atmospheric pressure through a turbine to produce mechanical power.

The aim is to bring about a mean air pressure increase from tank to tank along the row with the highest pressure being attained in the final tank. Such would not be possible without the simultaneous provision of restraint forces to match or balance the upward forces generated by a rising of the pressure within the tanks. In this arrangement this provision is met by a rising of the generator out of the water at a small angle such that at the first tank station the generator’s freeboard remains much the same, but at the final tank station the generator’s freeboard is measurably increased, in the calm condition when waves of significant height are absent, the arrangement of buoyancy compartments along each side keep the generator afloat at a chosen freeboard and trim. With regard to the ballast tanks, it is arranged that in the calm condition at the chosen freeboard and trim, these will be full or partially full of water and the majority of the volume of these will be below the is water line. Ballast water within the side tanks that is submerged is buoyancy neutral whereas ballast water above the water line is negative in its effect on the generator’s buoyancy. Increasing air pressure from tank to tank along the length replaces the role of the buoyancy compartments correspondingly as they emerge from the water thus providing increasing restraint forces.

Similarly as ballast water volume emerges from the water, a corresponding weight loading is applied to the generator to restrain and allow pressure increases to develop. Since the mean pressure increase is stepped from tank to tank, the emergence of buoyancy and ballast increases along the length towards the final tank resulting in the generator assuming an angle to the water line ruling at the calm condition.

Depending on conditions, wave action will be able to support a certain air flow through the turbine to produce mechanical power, exploiting the then existing corresponding pressure difference between the final tank and atmosphere. Pressure difference and flow rate are interdependent, but power production is essentially the product of the two; thus for given wave conditions there will be an optimal air flow rate. The aim is to achieve this flow rate by turbine control. Pressure difference and volume flow rate are easily able to be measured. Whatever pressure regime exists in the tanks, this always kept in being by the restraint forces provided by the emergence of buoyancy and ballast water volume from the water progressively along the length.

In order to achieve a cumulative pressure rise from tank to tank along with the restraint on which such depends, few tank configurations are suitable. However a contiguous single row system as described offers a simple solution, but this does result in a long device. A long generating vessel as aforesaid will work in a confused sea with no set direction, but will do so in an opportunistic way with air being compressed from tank to tank randomly, as and when favourable pressure differences occur. The generator works better and more effectively in sea waves set in direction and of reasonably regular wave length. The generator’s orientation with respect to the direction of the waves then becomes an important factor. In very general terms, the generator is may advantageously be moored so that its longitudinal axis is aligned, within certain limits, with the direction of advance of the waves. Mooring provision which is capable of adjustment to achieve such alignment then becomes an important requirement.

Waves are formed by the action of wind on the sea surface over reasonably large distances. Consequently they tend to be then set in a certain direction and to become reasonably regular in size, height and length. In order to take advantage of such waves, the generator may be moored with its longitudinal axis disposed generally in the direction of advance of the waves with the first or inlet air tank heading into the oncoming waves. In this context, this generally means a sector which spans an arc of approximately 45° either side of the direction of advance of the waves. Mooring means are provided to orientate the generator as aforesaid and particularly the aim is to keep the generator aligned so that the tank bulkheads are as far as practicable parallel with the lines of advancing waves, that is to say perpendicular to the direction of their advance. In this context, as far as practicable means within up to about 16° either side of the desired direction. The generator may be constructed with the tank bulkheads, (1) at 90° to the longitudinal axis of the generator; or (2) with the bulkheads at an angle between 90° and about 45° thereto. The tanks will normally be straight sided and thus the tanks will be rectangular in shape for (1), or may be shaped like a parallelogram for {2). The purpose of providing bulkheads set at an angle, is to make the generator suitable for being disposed at an angle of up to about 45° to the direction of advance of the waves. Angled bulkheads could be set either one way or the other with respect to the 90° case. When angled and once constructed, one side of the generator normally has to be that facing the advancing waves; that is to say the generator can only be angled one way. The angle of inclination of io the generator’s longitudinal axis could, if need be, exceed the “about 45°” stated above.

When the generator is disposed and orientated with its longitudinal axis at an angle to the direction of advance of the waves, its length spans and affects a much broader band of waves to extract energy therefrom, is Furthermore as the angle of orientation in the design is increased from 0° to 45°, the tanks receive waves which are increasingly energetically fresh. For instance at a 30° angle waves may have to pass through approx 3 tanks before leaving the generator, or only approx 2 tanks for the 45° case; whereas in the 0° case waves would have to pass through and along the whole the whole tank array. In the 0° case, only the leading tanks would experience fresh waves and the rest would experience waves of depleted energy.

The cost of the generator is principally that related to the price of constructional material in finished form, almost certainly this would be the weight of finished steel or other suitable material used for construction. For generators of approximately the same size and therefore cost, the angled generator is more cost effective in terms energy extraction per unit cost and may thus be preferred. The optimum angle or range of angles will need to be determined by development and operational experience. It must be noted that a chosen angle for orientation of necessity involves building the generator with bulkheads set at an angle which is complementary to this chosen angle; that is to say for example, a chosen 30° angle of orientation wouid mean setting the bulkheads at 60° to the longitudinal axis of the generator. The angled generator could be constructed with rectangular tanks with each displaced sideways in stepped form, so that the axis joining the centres of the tank array is the longitudinal axis of the generator, which wouid then be orientated so that the bulkheads are as far as practicable aligned in parallel with the line of advancing wave fronts. It would be difficult to fit the side buoyancy compartments and ballast tanks to such a structure. The preferred arrangement is for the generator to be straight sided, and for the air tanks to be of parallelogram shape at the appropriate angle. The side buoyancy compartments and ballast tanks can then be made to be an integral part of the structure with ease.

When orientated and consequently constructed in any of the ways described, the generator works effectively and rhythmically whenever the average wave length exceeds twice the distance between tank centres. Under these conditions, a tank becoming pressured by a moving wave, will tend to is have a tank down -stream of it that is experiencing a trough and thus air wilt be forced to migrate thereto via the non-return valve. In any specific design, tank spacing is thus an important consideration in relation to wave lengths that are expected to prevail in the location that the generator is to be deployed.

The foregoing describes the broad aspects, the principles and the thrust of the invention. Within the scope of this, many variations are possible including the number of air tanks, the size and geometry ofthe tanks, and the configuration of buoyancy and ballast provision with appropriate dimensions to achieve the objectives as disclosed. There is the matter of balance between air tank size and number with corresponding upward air pressure forces to be restrained by redistribution of buoyancy and ballast water contribution; all dependent on dimensions allocated to the same and the ratios between them. There is the question of the non-return valves, their type, size, their position and manner of incorporation into the generator, their reliability and service life etc. Then there is the question of the chosen freeboard and trim in the calm condition. This has already been referred to but values need to be established; again this is a matter of experience and development. To some extent such is dependent on the position and manner of incorporation of the non-return valves. If there is need for extra ballast other than by water within ballast tanks then such could be provided by dense concrete low down in the structure, or by gravel or rock materials within certain tanks etc. There are all manner of possibilities. Whilst such matters may be attended to some extent initially by design; pilot schemes, experimentation and operational experience will have a major input into generators of optimal commercial form. In common with any new technology, this is normal and is part of an expected development process.

With regard to the turbine, it is well known that generally, this energy convertor works more efficiently using higher rather than lower pressures. This generator compresses atmospheric air in stages cumulatively before expanding it through the turbine. It is able to provide the turbine with much better air conditions than would result from exploiting the air pressure consequent on one wave alone. The generator may therefore able to make use of smaller waves than would otherwise be the case.

The main components and what is required of them will now be discussed.

The Turbine The turbine will in most cases be used to drive an electrical generator to supply power to a grid network. Many types of electrical generators and systems are now available. Some of these do not require the turbine to run at synchronous grid speed; thus the turbine speed can vary and this allows much greater flexibility for the turbine design and selection. In spite of these developments with regard to electrical generation, it may be advantageous to smooth out pressure fluctuations caused by wave action in the final air tank. This may be achieved by providing a dry air delivery tank in which pressurised air is stored before admission to the turbine.

Non- return valves The design and performance of these are of crucial importance. They should be of simple and robust construction with a long expected service life. They must be capable of passing large volumes of air over short time periods (up to just a few seconds). Leakage backwards is acceptable so long as it is small in comparison with the main air flow in the desired direction. Reliability of operation is paramount. The vaives must be accessible for maintenance or replacement, and in this regard the bulkhead non-return vaives would be best deck-mounted and just sealed into each bulkhead. The valves will open when a small differential pressure exists in the desired direction. It might be necessary to have the opening pressure adjustable. The valves will tend to be of large sectional area, and may be provided as non-return gates, which in the shut position are housed within a faired in aperture with peripheral clearance.

Side- tanks The dimensions and geometry of these is a matter of detailed design is which may be altered /adjusted to take advantage of pilot schemes and operational experience. However guiding principles are as in (a) & (b) as follows:-(a) Buoyancy Compartments With respect to each side, these should provide in substantially equal measure sufficient buoyancy to keep the generator afloat at a chosen freeboard and trim, and that is supporting the weight of the structure and components plus the weight of any form of ballast carried on board. The compartments should be subdivided to enhance watertight integrity in common with normal marine practice. The geometry and water plane areas etc. will need to be chosen to give the generator desired response characteristics to waves. Furthermore the compartments should provide adequate reserve of buoyancy to maintain seaworthiness and to compensate for any inward leakage or other fault conditions. Again this is a matter of geometry and water plane areas. (b) Ballast Tanks Usually these are completely filled with water. In the calm condition the major part of their volume will be submerged. These should be of sufficient volumetric capacity to be able to provide adequate restraint forces as submerged vofume emerges from the water. Again the size and geometry is a matter for detailed design. Water plane area is ali important here in terms of downward force provided per metre of emergence. As the air pressure is intended to develop along the generator's length, generally water plane area will need to increase also, perhaps in a number of step increases. The ballast tanks fulfil another function in that they provide inertial mass. The effect of this is to impair or deaden the generator’s response movement to waves, and this then allows wave action to compress the air within the tanks more effectively.

Other Ballast Provision An intended build up of air pressure within the tanks may well require is restraint force provision which exceeds that which is practicable by side tank ballast alone. Further water ballast may be provided by adding a water tank at the trailing end of the air tank array sandwiched between side tank or protruding alone in part or in whole there from. This tank may be completely filled with water and submerged completely or partially in the calm condition.

When generating in a wave regime, emergence of water volume relating to this tank would provide increasing restraint forces in like manner to the side ballast tanks. Water volume in this ballast tank that is above the calm condition water line, will require additional side buoyancy compartment volume to compensate.

If lateral stability becomes an issue in the generating mode with considerable water ballast now removed from immersion, additional ballast of a heavy material such as dense concrete could be incorporated low down in the structure, as a ballast keel for instance. This would then require more buoyancy compartment volume to compensate to maintain desired freeboard and trim in the calm condition.

Air Tanks The air tanks can be described as air on water tanks. They are free flood at their lower ends with the minimum of restriction, so that as far as practicably possible air pressure equals external water pressure contemporaneously.

The number of contiguous tanks can range from a minimum two to any number which is practicable. The maximum number is usually determined by considerations of length and the requirements for structural integrity. Then there is the consideration of the maximum practicable air pressure that is to be achieved and the consequences. For example, if the final tank target pressure is 4 M. water pressure (W.G.), then the whole structure will have to have sufficient depth to accommodate a corresponding water level in that tank and that structural depth has then to be at least 4M. below sea level. This requirement reduces towards the first tank where the maximum pressure attained may be say 1.5M. W.G. Generally a final tank pressure of around 3M is W.G. can be regarded as being attainable with 6 to 8 tanks. This may be taken as a sensible starting point in the development process.

Generally the tanks will be constructed with sides which are substantially vertical. It may be advantageous to reduce the water plane area gradually from the first tank through to the final tank. This may be able to be done without detriment to the effectiveness of the compression process, by reducing this area approximately in inverse proportion to the expected pressure increases on the absolute scale. Thus the ratio would then be 10M.

W.G.(atmospheric) to 13 M. W.G. (final tank), or 10/13 i.e. approx.75%, The progressive area reductions, in whatever ratios are actually chosen, lead to corresponding reductions upward forces and therefore the restraint requirement. A direct consequence is that buoyancy and ballast tank volumes, and their water plane areas can be reduced. The requirement for extra ballast at the generator’s trailing end can also be reduced.

Mooring Arrangements and Generator Location Mooring the generator and the manner of providing arrangements to effect alignment and orientation, as required by the invention, are for specialists in that field and are beyond the scope of this disclosure. However in practice the requirement may not be that onerous. The generator is likely to be located near a coast in water which is quite shallow, where oncoming waves have developed over open water and their shape has become more pronounced by reason of a shelving sea bed. Offshore winds will have little distance to form waves of size enough to be of interest. Thus that 180*sector is of no interest. Furthermore the generator may be located in a bay or inlet between headlands. This would again restrict the extent of the sector which is workable and for which adjustment of orientation needs to be provided.

Profile, Seaworthiness and Ability to Survive The generator may be built with a streamlined profile so as to offer the least resistance to wind and waves, thereby minimising the loading on the moorings. To this end deck mounted items such as the turbo-generator is housing may be of rounded streamlined form. The decks over air tanks and side tanks may with advantage be gently curved so as to be rapidly self draining without restriction. In rough conditions waves may swill over rather than be ridden over as is the more conventional approach.

In the survival mode, the generator would be shut down and would assume the non-generating low profile attitude. To ensure this the first tank would be vented continuously to atmosphere so that air could not be in any way pressurised, and the turbine would be bypassed to allow the final tank to be vented to atmosphere continuously. The mooring system could with advantage bring the generator’s axis in line with the direction of advancing waves i.e. head on to the sea.

As a last resort, in extraordinary storm conditions or just prior to the onset of the same, the generator could be deliberately sunk by remote initiation of arrangements to scuttle. The generator could then be refloated later. This may be viewed as being preferable to the generator breaking adrift and being wrecked completely by being washed ashore, or damaging or sinking other vessels by collision. In view of the generator’s ability to multiply the effects of wave pressure, it should not normally be necessary to choose a location with risk of extreme conditions.

DESCRIPTION OF THE DRAWINGS Embodiments of this invention will now be described by way of example only by reference to the accompanying schematic drawings which are as follows:-10 Figures 1 to 7 relate to a first embodiment of the invention where the air on water tanks are rectangular in shape, and where the bulkhead walls dividing the tanks are set at right angles to the longitudinal axis of the generator.

Figure 1 shows a front view of the generator with essential components is numbered.

Figure 2 shows a view of the generator in section with essential components numbered.

Figure 3 shows a plan view with electrical generator/alternator coupled to the turbine with essential components numbered.

Figure 4 shows a further view of the generator in section with essential components numbered.

Figure 5 shows a centreline sectional front view on C-C of figure 3 of the same generator floating at a chosen draft and trim in calm conditions.

Figure 6 shows a centreline sectional front view on C-C of figure 3 of the same generator depicted in random sea conditions and extracting energy therefrom seized at a typical moment in time.

Figure 7 shows the same generator as shown in Figure 6, but seized at another typical moment in time.

Figure 8 shows a skeletal plan view of the generator with the dividing bulkheads between air on water tanks set at 90° to the longitudinal axis of the generator, and with the generator aligned optimally to waves advancing down the page.

Figure 9 shows a skeletal plan view of the generator with the dividing bulkhead walls between air on water tanks set at 60° to the longitudinal axis of the generator, and with the generator aligned optimally at 30° to waves advancing down the page.

Figure 10 shows a skeletal plan view of the generator with the dividing bulkhead walls between air on water tanks set at 45° to the longitudinal axis of the generator, and with the generator aligned optimally at 45° to waves advancing down the page.

Figure 11 shows a plan view of the generator in section at the water io plane in calm conditions with water plane area reducing from the first tank through to the final tank.

N. B. With regard to figures 7, 8 and 9 optimal alignment means within approx. 15° either side of the ideal target direction for orientation. The scale and geometry relating to figures 8, 9 and 10 are slightly different to those in is figures 1 to 7 and 11.

DETAILED DESCRIPTION Figures 1 to 4 show a first embodiment of the invention with component 20 parts identified by numbering.

A floating generating vessel 10 comprises six adjoining air tanks in a contiguous row or array along almost its entire length and has a deck 10a, These air tanks are numbered 1 to 6 and are open bottomed so that air contained therein communicates directly with water, usually sea water, so that air pressure within equals water pressure, and changes in water pressure cause almost immediate corresponding changes in air pressure. To emphasise this, the openings at the tank bottoms are denoted by 8.

A further tank 7 is a ballast tank which has a closed bottom and which is normally filled with water at least up to the expected water line level in the calm condition, but this tank may be filled above this level. At least one, preferably vertical, longitudinal dividing wall 70 is fitted to prevent large scale and rapid lateral movement of water within; this being to enhance transverse stability of the generator 10. In figure 2 just one such wall 70 is shown. In order to further improve transverse stability, particularly when generating with ballast tankz7 lifted further out of the water, additional heavy ballast such as concrete could be located at the bottom of tank 7 or could be added externally.

Along each side of the generator 10, buoyancy compartments 14 & 16 are fitted as an integral part of the whole structure symmetrically with respect to the longitudinal axis of the vessel 10. These compartments 14, 16 are io sub-divided in accordance with accepted marine practice, and some of the capacity may contain variable water ballast for adjustment of water line, trim and angle of heel.

Along each side of the generator 10, ballast tanks 16 & 20 are fitted as an integral part of the whole structure symmetrically with respect to the is longitudinal axis of the vessel 10. These tanks 18,20 are sub-divided in accordance with accepted marine practice. These tanks 18,20 may be filled completely with water which is usually the case, or if necessary only partially; again to provide capacity for adjustments.

The first air tank 1 is fitted with a deck mounted non-return valve 11 20 which allows air to pass from the atmosphere only inwards in to air tank 1. At or near the top of the bulkhead walls 22 between tank 1 and tank 2, tanks 2 and 3, tanks 3 and 4, tanks 4 and 5, and tanks 5 and 6 are fitted with nonreturn valves 21, 31, 41, 51 and 61 to allow the passage of air only in one direction from air tank 1 through to the last air tank 6 whenever there is a favourable pressure difference across a valve. The non-return valves open when a predetermined differential pressure is reached, and provision may be made for the value of this pressure to be adjustable. These non-return valves may advantageously be deck mounted.

An additional air tank.9 may be incorporated to increase the volumetric capacity of air tank 6 via aperture 15. The purpose of the additional capacity so provided is to smooth out pressure fluctuations consequent upon wave action in air tank 6. Aperture 15 may if necessary be fitted with a non-return valve so as to allow air to pass from tank 6 to tank 9. This may improve pressure stability in tank 9.

A turbine 12 is connected to air tank 6 or to additional tank 9 if fitted.

Compressed air is expanded in turbine 12 to atmosphere to produce usable mechanical power. The turbine 12 and air tank 6(/9) may with advantage be fitted with an air flow meter and pressure gauge respectively; these are not shown. Usually turbine 12 is coupled to an alternator or other electrical generator 19. The generating vessel 10 is shown floating in calm conditions at a water line denoted by W/L and in this configuration the longitudinal axis of io the generator is substantially horizontal as is the general lengthways dimension of the deck 10a.

Again with reference to figures 1 to 4 of this embodiment, it can be seen that at about the mid-point of tank 5 the width of both buoyancy compartments and ballast tanks increase. Furthermore the horizontal dividing is deck 17 between buoyancy and ballast compartments/tanks is lowered; as seen particularly by reference to figures 2 and 4. This is to provide additional buoyancy to compensate for the additional weight of steel or other constructional material (including solid ballast if fitted) at this end plus the added weight for machinery along with additional air tank 9. Additionally, ballast tank 7 will usually be filled to a water level above the generator’s water line in the calm non-generating mode. Water volume in ballast tank 7 that is above the water line also needs extra buoyancy volume to compensate. Such is provided by the increase in the capacity of buoyancy compartment 16.

The foregoing states the general principles for design which then need to be incorporated in design details necessary to build the generator. With regard to buoyancy compartment and ballast tank provision, these would include dimensions, geometry with position of both vertical and horizontal dividing walls. It is imperative in the design that as already mentioned, flexibility for adjustments to both buoyancy and ballast be built in to the design. Such is necessary to adjust the generators freeboard, trim and angle of heel etc. The forces attendant upon air pressures acting on large areas will need to be catered for. There will also be large structural loadings on the generating vessel 10, particularly at the turbine end where water displacement buoyancy is replaced by air pressure forces when generating.

Ballast water volume that is immersed is buoyancy neutral. However such water provides inertial mass which may be beneficial, in that the generator vessel’s response movement to waves may be impaired thus enabling wave action in the air tanks 1 to 6 to be more positive in pressurising the air within.

Prior to generation, the generating vessel 10 will need to be set up floating in calm conditions and be made to assume the desired io freeboard/draft, trim and with no meaningful angle of heel. The desired or chosen freeboard and trim will have been established by the design and development process previously mentioned in the general section. This can be done by adjustment of water ballast within the buoyancy compartments 14 and 16, but could if need be, involve some adjustment of the amount of is water contained in the ballast tanks 18 and 20. If needed solid ballast could also be incorporated in the structure and the amount of this could be adjusted. Figure 5 shows the generating vessel 10 set up after adjustments as above described with the deck 10a substantially horizontal.

Figure 6 shows the generating vessel 10 floating in water waves 20 compressing atmospheric air in stages, and producing usable mechanical energy by expanding the compressed air back to atmospheric pressure via the turbine 12. Although difficult to depict by a simple drawing, the wave regime is intended to be shown as being random with the waves having no set pattern. The generating vessel 10 is moored in a fixed position, but is receiving waves in a random and unpredictable way. However, the generator 10 still compresses atmospheric air, albeit in an opportunistic and irregular way as already described above in the section headed “Broad aspects and principles”.

Figure 6 shows the situation seized at a particular time; the air in tank 1 is compressed by a wave and air is being forced into tank 2 via the bulkhead non-return valve 21. Further along the air in tank 3 is compressed and air is being forced into tank 4 via the bulkhead non-return valve 41, although the flow rate is waning by reason of the wave starting to affect that tank. Tank 5 is predominantly under the influence of a trough and is effectively dormant.

Tank 6 is pressurised by the wave shown at that station but the effect is smoothed by reason of the additional volume of air tank 9. Air is being expanded to atmospheric pressure in turbine 12 to produce mechanical power.

At another typical instant in time as depicted in Figure 7, different tanks are pressurised by wave action. Air tanks 1, 3 and 5 are under trough conditions allowing air to be drawn into tank 1 from the atmosphere via nonio return valve 11, and air to be forced from tank 2 to tank 3 and from tank 4 to tank 5 via non-return valves 31 and 51 respectively. The result is that air will be forced to migrate along the tank array through the relevant non-return valves gaining pressure in doing so. Depending on wave energy in terms of height, frequency and disposition - all difficult to quantify - a sustainable air is flow at a useful pressure difference for turbine operation should be forthcoming. As previously explained, air flow rate and pressure difference across the turbine 12 are interdependent but they can be optimised for power production. Again increasing air pressure along the tank array is kept in being by restraint forces, visible in degree by angle the generator 10 assumes compared with its trim in the calm condition.

The generating vessel 10, of necessity to provide cumulative compression with restraint forces both of which are interdependent, requires length. A lengthy generating vessel, the subject of the foregoing description is able to work more effectively in a wave regime which is reasonably regular and set in direction. The vessel is then orientated with its longitudinal axis in the general direction of advance of the waves. The principles, method of operation and requirements are detailed earlier under Broad Aspects and Principles” Figure 8 shows the generator 10 aligned with its longitudinal axis parallel with the direction of advance of waves and with air tank bulkheads 22 set at 90° to that axis. Waves are advancing down the page and wave crests are depicted at 90° to that axis i.e. parallel with the tank bulkheads 22. The wave length is almost 3 times the distance between tank centres. In this situation at any time, a tank under wave pressure always tends to have a tank with resting pressure (trough conditions) ahead of it. Air is thus forced to migrate from tank to tank along the array gaining pressure as it does so. The process becomes rhythmic, predictable and more effective.

The width of sea waves from which energy is being extracted is indeterminate, but is pictorially approximately represented by distance “d” between lines A and B. This distance is not much more than the width of the generating vessel 10. Furthermore as the waves travel down the generator 10, they become energy depleted such that air tanks 4, 5 and 6 are not contributing nearly as much as the leading air tanks.

Figure 9 shows an example of the generator 10 with its longitudinal axis set at an angle to the direction of advance of waves. In this case that is angle is 30° and the tank bulkheads 22 are set at 60° to that axis. Waves are advancing down the page and wave crests are depicted at an angle of 60° to the axis of the generator 10 i.e. parallel with tank bulkheads 22. The wave length is about 3 times the distance between tank centres. Air is forced to migrate from tank to tank along the array gaining pressure as it does so; the same reasons for this apply as stated in the previous paragraph relating to figure 8.

The bulkhead wall 23 between air tank 6 and ballast tank 7 is set at an angle. This is a matter of practicality. Both tanks are vertical walled and thus the centre of force for air pressure in tank 6, and the centre of gravity for ballast tank 7, can be regarded as acting through the centroid of those areas. By inspection it can be seen that the centroids of both areas are approximately equidistant from the longitudinal axis of the generator. Thus when generating with the whole generating vessel 10 at an angle, the upward air force in air tank 6 and the downward gravitational force of the water in ballast tank 7 have minimal effect in producing a heeling moment. This means that heeling moments relating to both tanks are to all intents self-cancelling.

From figure 9, it can easily be seen that the width of wave band from which energy is being extracted as depicted by the distance “d” between lines A and B has greatly increased compared to the figure 8 situation. A wave has to pass through approx. 3 tanks before emerging from the leeward side. The generator 10 experiences waves that have not been energy depleted.

Figure 10 shows the 45° case, which except for the different angles that apply is essentially the same as for the 30° case as in figure 8. The same arguments apply with respect to ratio between wavelength and distance between tank centres. The same arguments apply regarding the geometry of air tank 6 and ballast tank 7. io The wave band width affected by energy extraction has again increased as can be seen by reference to distance “d” between lines A and B. Furthermore a wave has to pass through just approx. 2 tanks before emerging from the leeward side. The generator 10 experiences only waves which are fresh and energetic. is As mentioned previously under the section devoted to air tanks in Broad Aspects and Principles”, it may be advantageous to reduce the air tank water plane area progressively from tank to tank. Figure 11 is intended to illustrate this, and also give some idea of how this results in a reduction of the restraint that has to be provided. In Figure 11 the water plane area of air tank 6 is about 75% that of air tank 1 whilst the side walls 24 of the vessel 10 are substantially parallel to each other and to the longitudinal axis of the vessel . However any reasonable ratio could be chosen after some detailed design analysis. The area reductions from the first tank through to the final tank may also be effected by keeping the tanks rectangular in shape and reducing their width from tank to tank. Any method of effecting such area reductions may also be designed for application to generators with bulkheads which are angled as aforementioned in this description.

The foregoing describes examples of how the principles of this disclosure may be put into practical effect. There may be variations and other ways in terms of apparatus and method, of using the principles and broad aspects of this invention as enunciated and these would therefore be included within its scope Of particular relevance is the manner of achieving multistage air compression in various situations. For such to be possible employing a floating vessel where air pressure tanks communicate with water, directly or indirectly, air pressure cannot exist without the coexistence of restraint forces to oppose proportionately those caused by air pressure within. A solution to this problem is disclosed herein and constitutes a major part of this invention. The intention of this disclosure is to include within its scope any invention which may set forth different apparatus and method, but which employs the same or similar means of providing balancing forces, to oppose those consequent on air pressure thereby making it possible for such air pressure to exist.

Claims (10)

1. 5 Claims

1. A floating generating vessel comprising: a turbine, a plurality of contiguous, open-bottomed air tanks in a io row along a longitudinal axis, the first air tank of the row communicating with the atmosphere via a non-return inlet valve such that air can flow into the first tank from the atmosphere, the last air tank of the row communicating with the atmosphere through the turbine, and an upper part of is each air tank communicating with the upper part of the next air tank in the row via one-way valve means such that air can pass in one direction only from the first air tank to the last air tank, an arrangement of buoyancy compartments provided 20 along each side of the row of air tanks, substantially symmetrical with respect to the longitudinal axis, an arrangement of ballast compartments provided along each side of the row of air tanks, substantially symmetrical with respect to the longitudinal axis, 25 wherein atmospheric air can be drawn into the first air tank by a pressure differential caused by wave action and can be compressed cumulatively through the series of one-way valve means to the last air tank by said wave action where the compressed air expands to atmospheric pressure via the 30 turbine to produce power.

2. A floating generating vessel as claimed in claim 1 wherein an additional ballast tank is provided adjacent the final air tank.

3. 5 3. A floating generating vessel as claimed in claim 2 wherein the additional ballast tank provides a water compartment disposed along the longitudinal axis at a location remote from the first air tank, io 4. A floating generating vessel as claimed in claim 3 wherein the additional ballast tank is provided with additional buoyancy compartments along each side of the water compartment, substantially symmetrical with respect to the longitudinal axis and is provided with additional ballast is compartments along each side of the water compartment substantially symmetrical with respect to the longitudinal axis. 5. A floating generating vessel as claimed in claim 3 or claim 4 20 wherein the water compartment incorporates one or more substantially vertical, lengthways extending walls to improve transverse stability.

4. 6. A floating generating vessel as claimed in any one of claims 25 1 to 5 wherein the ballast and buoyancy compartments are wider and of greater water plane area towards the last air tank.

5. 7. A floating generating vessel as claimed in claim 6 wherein 30 the sides of the vessel are parallel relative to the lengthwise axis and the water plane area of the tanks is reduced from the first air tank to the last air tank.

6. 8. A floating generating vessel as claimed in claim 7 wherein 35 the air tank area reductions are effected by a tapering of their width inwardly from the first air tank to the last air tank.

7. 9. A floating generating vessel as claimed in any one of claims 1 to 8 wherein a substantially vertical bulkhead is provided between each two adjoining air tanks, the one way valves being provided in said bulkheads at an uppermost location io therein.

8. 10. A floating generating vessel as claimed in claim 9 wherein each bulkhead is angled relative to the longitudinal axis of the vessel.

9. 11. A floating generating vessel as claimed in any one of claims 1 to 10 wherein an additional air storage vessel is provided between the last air tank of the row and the turbine in order to smooth out pressure fluctuations.

10. 12. A floating generating vessel as claimed in claim 11 wherein the last air tank communicates with the air storage vessel via a further non-return valve. 25 13. A floating generating vessel as claimed in any one of claims 1 to 12 wherein the levels of ballast and/or buoyancy provided by the ballast/buoyancy compartments can be varied. 30 14. A floating generating vessel as claimed in any one of claims 1 to 13 wherein mooring means are provided for positioning the vessel, said mooring means enabling the direction of the longitudinal axis to be adjusted.