Floating Structure

Abstract

The floating structure (1) comprises a floating member (2) including a peripheral wall (3) in which a pressure reservoir (11) for storing compressed gas is provided, and a compressor (4) for supplying the compressed gas to the pressure reservoir. The compressor is a liquid piston gas compressor (4) including two containers (5, 6) for containing a liquid and a gas to be compressed above the liquid, and a pump (7) for transferring the liquid between the containers (5, 6). At least the containers (5, 6) are located within the peripheral wall (3) of the floating member (2) and are provided with respective closable inlets (9) for receiving gas from outside the floating member (2) and respective closable outlets (12) through which the containers (5, 6) communicate with the compression container (11) for transferring compressed gas from the containers (5, 6) to the pressure reservoir (11) under operating conditions.

Description

[Technical field]

[0001] The present invention relates to a floating structure comprising a buoyant member including a peripheral wall within which is provided a pressure reservoir for storing compressed gas, and a compressor for supplying compressed gas to the pressure reservoir. [Background technology]

[0002] Such floating structures are well known in the prior art. In known floating structures, a compressor compresses a gas, for example ambient air, and is driven by an electric motor connected to a renewable energy source, such as a set of PV panels. When the demand for electricity is low, surplus electricity from the renewable energy source can be supplied to the electric motor to drive the compressor and supply compressed gas to the pressure reservoir. Thus, the surplus energy is stored in the form of compressed gas. When the available renewable energy becomes low, for example at night in the case of PV panels, the compressed gas can be converted into electricity, for example by expanding it over a turbine coupled to a generator. Summary of the Invention [Problem to be solved by the invention]

[0003] It is an object of the present invention to provide a floating structure with relatively high efficiency of energy storage in the form of compressed gas. [Means for solving the problem]

[0004] This object is achieved by means of a floating structure according to the invention, in which the compressor is a liquid piston gas compressor comprising two containers for containing a liquid and a gas to be compressed above the liquid, and a pump for transferring the liquid between the containers, at least the containers being located within the peripheral wall of the buoyant member and at least the containers being provided with respective closable inlets for receiving gas from outside the buoyant member and closable outlets, through which the containers communicate with a pressure reservoir to transfer compressed gas from the containers to the pressure reservoir under operating conditions.

[0005] The advantage of the floating structure according to the invention is that the liquid piston gas compressor maintains the temperature of the compressed gas at a relatively low level during compression due to the heat transfer from the compressed gas to the liquid in the container, which results in a relatively high efficiency energy conversion from electrical energy to the stored compressed gas. Furthermore, since the container is located inside the peripheral wall of the buoyant member, it provides the opportunity to simply cool the liquid in the container and / or the compressed air in the pressure reservoir by using water placed in it. Furthermore, since both the pressure reservoir and the container of the liquid piston gas compressor are located inside the peripheral wall, the distance between the pressure reservoir and the container can be minimized, thus minimizing the pipe length and resulting in a relatively low flow loss.

[0006] Under operating conditions, when compressed gas is supplied to the pressure reservoir, when the liquid level in a container drops, the inlet of the corresponding container may be opened and the outlet of the container may be closed, and when the liquid level in the container rises, the outlet may be opened and the inlet may be closed.

[0007] In a particular embodiment, the buoyant member is located above the lower side, the container is located at the lower part of the buoyant member and the pressure reservoir is located at the upper part of the buoyant member when the floating structure is in an operational state in which at least the lower side of the buoyant member is submerged in water. In the operational state, the container is close to the water covering the peripheral walls of the buoyant member, facilitating cooling of the liquid in the container. The low position of the container may have an advantageous effect on the stability of the buoyant member, since it creates a relatively low center of gravity.

[0008] The pump may be located within the peripheral wall of the buoyancy member, which means that piping between each of the reservoirs and the pump can be minimised.

[0009] The pump may be located within one of the containers, for example so that it is submerged in the liquid under operating conditions.

[0010] The pump may be driven by an electric motor.

[0011] In a particular embodiment, under operating conditions, the electric motor is electrically connected to a power source, preferably a source of collected renewable energy, such as a number of PV panels or wind turbines, through an electric circuit, so as to operate the pump with electrical energy from the power source, preferably provided on the floating structure. In case of a renewable energy source, this provides an opportunity to store surplus electricity generated by the renewable energy source in the form of compressed gas.

[0012] In one embodiment, the liquid piston gas compressor can be operated in reverse and the electric motor can be operated as a generator, whereby the expanded gas from the pressure reservoir drives a pump and a generator to generate electrical energy. In this case, the pump can be a reversible thimble pump. There can be a separate turbine and generator arranged in parallel to the pump and driven by the liquid to convert the expanded gas from the pressure reservoir into electrical energy. It is also conceivable to feed the compressed gas to an expansion device such as a gas turbine, which is coupled to a generator for converting the energy from the compressed gas into electrical power.

[0013] In a preferred embodiment, at least a portion of the peripheral wall forms an envelope wall of the pressure reservoir, since the peripheral wall is used to provide buoyancy and to seal the pressure reservoir.

[0014] The pressure reservoir may be configured such that its allowable working pressure is at least 14 bar, although it is also contemplated that the allowable working pressure of the pressure reservoir is at least 20 bar, 30 bar or 40 bar.

[0015] Preferably the gas is air, since air can be easily supplied to the compressor from the ambient air surrounding the buoyancy member.

[0016] At least a portion of the outer wall of at least one of the containers may be formed by a portion of the peripheral wall of the buoyancy member, in which case the peripheral wall is used to provide buoyancy and to form the outer wall of at least one of the containers, and when the portion of the peripheral wall coinciding with at least a portion of the outer wall of at least one of the containers is immersed in water, the liquid may be efficiently cooled by the water under operating conditions.

[0017] One of the containers may at least partially surround the other of the containers. For example, the containers may be arranged concentrically with respect to each other, and the outer wall of the outer container may coincide with a portion of the peripheral wall of the buoyancy member. When the peripheral wall at the level of the container and the wall of the inner container have a circumference, this configuration minimizes the volumetric loss of the containers when the dimensions of the peripheral wall change due to contraction and expansion.

[0018] The liquid in the vessel may be water. The liquid in the vessel may be seawater, although preferably the water is less corrosive than seawater. Nevertheless, alternative liquids other than water are contemplated.

[0019] In a particular embodiment, the floating structure comprises a frame to which the floating member is attached, the frame extending in a main plane, the projected contour of the peripheral wall of the floating member on the main plane having a size in a first direction less than six times its size in a second direction perpendicular to the first direction, for example less than five, four or three times its size in the second direction, or the size in the first direction is substantially equal to its size in the second direction. In the latter case, the floating member may be cylindrical with a centerline extending perpendicular to the main plane.

[0020] In one embodiment, the buoyancy member has an upper side located above a lower side of the buoyancy member when the floating body structure is in an operational state, and the distance between the upper side and the lower side is greater than three times the largest dimension of the perimeter wall in the horizontal direction, although it is conceivable that the distance is greater than four, five, six, eight or ten times the largest dimension of the perimeter wall in the horizontal direction. For example, the buoyancy member may have a cylindrical side wall including a vertical centerline and a length to diameter ratio that is, for example, greater than three, four, five, six, eight or ten times.

[0021] The frame may be a platform extending in a major plane.

[0022] The frame may have the same shape and may be part of a larger floating structure that includes multiple interconnected frames that are moveable relative to each other.

[0023] In operation, the buoyancy member may be fully immersed in water.

[0024] The peripheral wall of the flotation members may comprise tapered circumferential walls such that a plurality of identical flotation members may be nested within one another during transport. For example, tapered flotation members may be closed at their smallest side and open at their widest side before being transported to the offshore site such that they nevertheless fit together, while the tapered flotation members are separated from one another and the widest side of the flotation members is closed after arrival at the offshore site where the flotation members will be installed.

[0025] More generally, the peripheral wall of the buoyancy member in a non-final state may be in a state such that multiple identical buoyancy members in a final state may be nested within one another in their non-final states.

[0026] The buoyant member may be a first buoyant member, while a second buoyant member may be attached to the frame at a distance from the first buoyant member. The second buoyant member may be identical to the first buoyant member. It is also possible that the pressure reservoirs of the first and second buoyant members communicate with each other. It is further conceivable that only the first buoyant member is provided with a container for the liquid piston compressor, while the second buoyant member is not provided with a container but houses a pressure reservoir.

[0027] In a preferred embodiment, the frame has an equilateral shape when viewed from above and includes three flotation members.

[0028] The first and second levitation members may be configured to be operated in anti-phase when identical to each other. This means that the first and second levitation members are operated alternately to average the power to the electric motors of the respective liquid piston gas compressors. Similarly, the conversion of compressed gas to electrical power may also be controlled in anti-phase.

[0029] The invention will now be described by way of example with reference to highly schematic drawings which show embodiments of the invention. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a cross-sectional view of one embodiment of a floating structure according to the present invention. [Diagram 2] FIG. 2 is a view similar to FIG. 1, showing an alternative embodiment. [Diagram 3] FIG. 2 is a view similar to FIG. 1, showing another alternative embodiment. [Figure 4] FIG. 13 is a side partial cross-sectional view of yet another alternative embodiment of a floating body structure according to the present invention. [Diagram 5] FIG. 13 is a perspective partial cross-sectional view of yet another alternative embodiment of a floating body structure according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Figure 1 shows an embodiment of a floating structure 1 according to the invention in an operating state. The floating structure 1 comprises an elongated floating member 2 including a peripheral wall 3 in the form of a cylindrical tank with a closed upper side and a closed lower side. Figure 1 shows that the lower side of the floating member 2 is located below the water level W. The floating member 2 has a vertical orientation when floating in the water. The height of the floating member 2 is greater than its diameter, preferably greater than three times its diameter.

[0032] The floating structure 1 is provided with a liquid piston gas compressor 4 for converting electrical energy into compressed gas that can be stored by the floating member 1. The liquid piston gas compressor 4 has a first vessel 5, a second vessel 6, a pump 7 and an electric motor 8 for driving the pump 7. The first and second vessels 5, 6 contain a liquid, for example water, which can be pumped between the first vessel 5 and the second vessel 6 by the pump 7. The floating structure 1 is also provided with a controller (not shown) for pumping water from the first vessel 5 to the second vessel 6 and in the opposite direction. The hatched areas in the first and second vessels 5, 6 in FIG. 1 indicate that the actual water level in the first vessel 5 is lower than the actual water level in the second vessel 6. Above the water in the first and second vessels 5, 6 there are respective compression chambers 5a, 6a containing air that is compressed by the water in the first and second vessels 5, 6.

[0033] Under the operating conditions of the liquid piston gas compressor 4, air is drawn from the outside of the floating member 2 into one of the first and second containers 5, 6, in which the water level is lowered through the corresponding closable inlet 9 and one of the air tubes 10. At the same time, air is compressed in the compression chamber 5a, 6a of the other of the first and second containers 5, 6, in which the water level is raised. The compression chambers 5a, 6a of the first and second containers 5, 6 communicate with the pressure reservoir 11 through their respective closable outlets 12. The closable inlet 9 and outlet 12 are also controlled by the controller. The inlet 9 of the first container 5 and the outlet 12 of the second container 6 may be simultaneously opened when water is pumped from the first container 5 to the second container 6, while the inlet 9 of the second container 6 and the outlet 12 of the first container 5 are closed. This means that compressed gas is transferred from the compression chamber 6a of the second vessel 6 to the pressure reservoir 11. Similarly, the inlet 9 of the second vessel 6 and the outlet 12 of the first vessel 5 may be simultaneously opened when water is pumped from the second vessel 6 to the first vessel 5, while the inlet 9 of the first vessel 5 and the outlet 12 of the second vessel 6 are closed. In this case, compressed air is transferred from the compression chamber 5a of the first vessel 5 to the pressure reservoir 11.

[0034] The liquid piston gas compressor 4 can be made relatively compact, since under operating conditions the water is repeatedly alternated between the first vessel 5 and the second vessel 6. This can be achieved by operating the pump 7 in the reverse direction, but it is also possible to apply known change-over valves for alternating the flow direction between the first vessel 5 and the second vessel 6.

[0035] 1 shows that the majority of the envelope wall of the pressure reservoir 11 coincides with the peripheral wall 3 of the flotation member 2. This may minimise thermal resistance between the pressure reservoir 11 and the air and / or water surrounding the flotation member 2. The peripheral wall 3 may be made of steel, although alternative materials capable of withstanding high pressures are contemplated. Indeed, the pressure reservoir 11 may be designed to tolerate a working pressure of at least 14 bar.

[0036] Inside the pressure reservoir 11 is a ladder 13 which allows an operator to inspect or repair components at the bottom of the buoyancy member 2 .

[0037] In the embodiment shown in Figure 1, the pump 7 is located inside the first vessel 5, but it may be located in a different location as shown in Figure 2. In the embodiment shown in Figure 2, features corresponding to features in the embodiment shown in Figure 1 have the same reference numbers. Figure 2 shows that the pump 7 and the electric motor 8 are located above and outside the surrounding wall. This means that a relatively long water pipe 14 is required between the pump 7 and the first and second vessels 5, 6, but the pump 7 and the electric motor 8 are easily reachable by an operator.

[0038] In the embodiment shown in Figures 1 and 2, the first and second vessels 5, 6 are arranged concentrically with respect to each other. The second vessel 6 partially surrounds the first vessel 5. Furthermore, the second vessel 6 has a circumferential outer wall that coincides with the peripheral wall 3 of the buoyancy member 2. Since the circumferential outer wall of the second vessel 6 is immersed in the surrounding water, efficient heat transfer between the surrounding water and the water and air within the second vessel 6 may be achieved.

[0039] Figure 3 shows another alternative embodiment in which the first container 5 and the second container 6 have a different configuration. In the embodiment shown in Figure 3, features corresponding to features in the embodiment shown in Figure 2 have the same reference numbers. In this case, the first and second containers 5, 6 are separated by a partition 15. Many alternative configurations are possible.

[0040] Figure 4 shows an alternative embodiment of the floating structure 1 in which a wind turbine 16 is mounted on the floating member 2 shown in Figure 1. The liquid piston compressor 4 functions similarly as described above with respect to the embodiment shown in Figure 1. The wind turbine 16 forms a source of electricity collected from renewable energy and is electrically connected to the electric motor 8 through an electric circuit (not shown) to operate the pump 7 by the electric energy from the wind turbine 16. If the electric energy generated from the wind turbine 16 cannot be used for other electrical consumers, this electric energy can be converted into compressed air and stored in the pressure reservoir 11.

[0041] FIG. 5 shows another alternative embodiment of the floating structure 1. In this case, the floating structure 1 comprises a triangular frame 17 that extends in a horizontal main plane and may be part of a larger floating structure comprising a number of similar frames movably connected to each other. A number of PV panels 18 are attached to the upper side of the frame 17, and the three floating members 2 shown in FIG. 1 are attached to the lower side of the frame 17. As in the embodiment including the wind turbine 16, the PV panels 18 form a source of power harvested from renewable energy electrically connected to the electric motors 8 of the liquid piston gas compressors 4 of the three floating members 2. In this embodiment, each of the floating members 2 is provided with a liquid piston gas compressor 4, but it is also conceivable that only one of the floating members has a liquid piston gas compressor 4, while the other two are provided with a pressure reservoir 11 solely for receiving compressed gas from the single liquid piston gas compressor 4.

[0042] The peripheral wall 3 of each of the buoyancy members 2 is cylindrical between its upper and lower sides, so that the projected contour on the main plane of the peripheral wall has a size in a first direction equal to the size in a second direction perpendicular to the first direction. In alternative embodiments, the size in the first direction may be three or four times smaller than the size in the second direction. In the embodiment shown in Figure 5, the height of each of the buoyancy members 2, i.e. the height in the direction perpendicular to the main plane, is greater than three times the diameter of the projected contour on the main plane.

[0043] It is conceivable to apply a combination of alternative (renewable) energy sources, for example PV panels and one or more wind turbines, wave energy generators, etc.

[0044] Above we have described how electricity can be converted to compressed air and stored, but to recover electrical energy from the compressed air in the pressure reservoir 11, the liquid piston gas compressor 4 only needs to be able to operate in the reverse direction. The electric motor 8 can be operated as a generator, whereby the expanding gas from the pressure reservoir 11 drives the pump 7, e.g. as a turbine, and a generator, to generate electrical energy and supply it to the electrical circuit. This can be done under no wind conditions in the case of the wind turbine 16, or at night in the case of the PV panels 18.

[0045] The invention is not limited to the embodiments shown and described above, which may be varied in different ways within the scope of the claims and their technical equivalents. [Explanation of symbols]

[0046] 1 Floating structure 2 Floating members 3. Perimeter Wall 4. Liquid piston gas compressor 5. First Container 5a Compression chamber 6 Second Container 6a Compression chamber 7. Pump 8 Electric Motor 9 Closable inlet 10 Air Pipe 11 Pressure Reservoir 12 Closable outlet 13. Ladder 15 Bulkhead 16 Wind Turbine 17 Frame 18 PV panels

Claims

1. A floating structure (1) comprising a floating member (2) including a peripheral wall (3) in which a pressure reservoir (11) for storing compressed gas is provided, and a compressor (4) for supplying compressed gas to said pressure reservoir, said compressor being a liquid piston gas compressor (4) including two vessels (5, 6) for containing a liquid and a gas to be compressed above said liquid, and a pump (7) for transferring liquid between said vessels (5, 6), at least said vessels (5, 6) being A floating structure (1), characterized in that at least the containers (5, 6) located within the peripheral wall (3) of the floating member (2) are provided with respective closable inlets (9) for receiving gas from outside the floating member (2) and respective closable outlets (12), through which the containers (5, 6) communicate with the compression container (11) to transfer compressed gas from the containers (5, 6) to the pressure reservoir (11) under operating conditions.

2. The floating structure (1) of claim 1, wherein when the floating structure (1) is in an operating state in which at least the lower side of the floating member is immersed in water, the upper side of the floating member (2) is located above the lower side, the containers (5, 6) are located at the lower part of the floating member (2), and the pressure reservoir (11) is located at the upper part of the floating member (2).

3. 3. The floating structure (1) according to claim 1 or 2, wherein the pump (7) is located within the peripheral wall (3) of the buoyant member (2).

4. 4. The floating structure (1) according to claim 3, wherein the pump (7) is located inside one of the vessels (5, 6).

5. 5. The floating structure (1) according to any one of claims 1 to 4, wherein the pump (7) is driven by an electric motor (8).

6. The floating structure (1) according to claim 5, wherein under operating conditions, the electric motor (8) is electrically connected to a power source (16, 18) via an electric circuit, preferably collected from renewable energy, such as a plurality of PV panels (18) or a wind turbine (16), so as to operate the pump (7) with electrical energy from the power source (16, 18), the power source (16, 18) being preferably provided on the floating structure (1).

7. 7. The floating structure (1) according to claim 5 or 6, wherein the liquid piston gas compressor (4) is operable in a reverse direction and the electric motor (8) is operable as a generator, whereby the expanding gas from the pressure reservoir (11) drives the pump (7) and the generator to produce electrical energy.

8. 8. The floating structure (1) according to any one of claims 1 to 7, wherein at least a part of the peripheral wall (3) forms an envelope wall of the pressure reservoir (11).

9. 9. The floating structure (1) according to any one of claims 1 to 8, wherein the pressure reservoir is configured such that its allowable working pressure is at least 14 bar.

10. The floating structure (1) according to any one of claims 1 to 9, wherein the gas is air.

11. 11. A floating structure (1) according to any one of claims 1 to 10, wherein at least a part of the outer wall of at least one of the containers (5, 6) is formed by a part of the peripheral wall (3) of the buoyancy member (2).

12. 12. The floating structure (1) according to claim 11, wherein one of the vessels (6) at least partially surrounds the other of the vessels (5).

13. 13. The floating structure according to claim 1, wherein the liquid is water.

14. 14. The floating structure (1) according to any one of claims 1 to 13, comprising a frame (17) to which the buoyant member (2) is attached, the frame (17) extending in a main plane, and a projected outline of the peripheral wall (3) of the buoyant member (2) on the main plane has a size in a first direction that is smaller than six times its size in a second direction perpendicular to the first direction, for example, the size in the first direction being smaller than five, four or three times its size in the second direction, or the size in the first direction being substantially equal to its size in the second direction.

15. The floating structure (1) according to any one of claims 1 to 14, wherein when the floating structure (1) is in an operating state, an upper side of the floating member (2) is located above a lower side of the floating member (2), and the distance between the upper side and the lower side is greater than three times the largest size of the surrounding wall (3) in the horizontal direction.

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