BE1029706B1 - ENERGY STORAGE AND FRESHWATER PRODUCTION DEVICE - Google Patents

Abstract

The present invention relates to a device for storing energy in the form of compressed air under the surface of a body of water. The device comprises a screw in the form of an internal helical thread and integral with a tube. Driven in rotation by a motor, the screw is configured to drive discrete volumes of air separated from each other by a continuum of water from an atmosphere towards a bottom of the body of water, thus compressing the discrete volumes of air which are then stored in a submerged tank. The inner surface of the tube includes a structured portion configured to lift and transfer a volume of water from the continuum of water to the discrete volumes of air with each rotation of the tube, which falls by gravity back into the discrete volumes of air as drops, thereby cooling discrete volumes of air as they are compressed, and reducing the work required to compress the air.

Description

ENERGY STORAGE AND FRESHWATER PRODUCTION DEVICE

FIELD OF THE INVENTION

The present invention relates to an energy storage device in the form of compressed air. The device is of the type comprising a reservoir submerged at the bottom of a body of water configured to store a reserve of compressed air under the surface of the body of water, and a screw in the form of an internal and integral helical thread from a tube. The tube and the screw are driven in rotation by a motor, the rotation of the tube and the screw driving discrete volumes of air from an upstream opening of the tube partially emerged above the surface of a body of water towards a downstream opening of the tube anchored to the bottom of the body of water and in fluid communication with the submerged reservoir. Discrete volumes of air are compressed as they travel deeper down the screw towards the downstream opening of the tube. The energy storage device of the present invention is more efficient than known devices because a portion of the inner surface of the tube is structured and configured to lift and entrain a volume of water from the water continuum to the discrete volumes of air with each rotation of the tube. The entrained volume of water falls by gravity into the discrete volumes of air in the form of drops. By heating up and evaporating at least partially on contact with discrete volumes of compressed air, the drops cool the discrete volumes of air. The cooling of the air during its compression decreases the thermodynamic work of air compression. In addition to the droplets, the film of water that adheres to the inner walls also participates in the process of evaporation and cooling.

TECHNOLOGICAL BACKGROUND

[0002] For ecological reasons made spectacularly evident by the phenomena associated with global warming, it becomes essential to considerably reduce the emissions of CO 2 and other greenhouse gases. A solution to this problem lies in the use of renewable energies such as wind, photovoltaic, hydraulic or geothermal energies, for example.

[0003] Nevertheless, the development of renewable energies encounters numerous obstacles. In particular, the development of hydraulic and geothermal energies is limited by the availability of favorable sites for their production, and the development of wind and photovoltaic energies suffers from the unpredictability of production due to the intermittency of their production depending on weather situation. Wind and photovoltaic energy are thus unavailable in the absence of wind or solar radiation, respectively. This intermittency of certain sources of renewable energy, otherwise widely available, has highlighted the need to develop solutions for the storage of energy in order to absorb the surpluses of production generated when the weather conditions are favorable or the demand for energy is low, and to supply the surpluses thus stored when the weather conditions are unfavorable or when the demand for energy is high, for example.

[0004] In documents US2012/0119510 and BE1024212, an energy storage device in the form of compressed air in a body of water is described. This comprises a helical duct configured to, when rotated, draw and compress air from an atmosphere above the surface of the body of water towards the bottom of the water. Air enters the duct through an opening in the duct in contact with the atmosphere and exits the duct through an opening in fluid communication with a reservoir submerged below the surface of the body of water. In the tank, a certain amount of energy can therefore be stored in the form of compressed air. The compressed air can then be brought back to the surface of the body of water by means of a pipe in order to be directly consumed, or transformed into another form of energy by means of a turbine, for example. In some embodiments, the compressed air can be brought back to the surface of the body of water by going back through the helical conduit. The compressed air then drives the helical conduit in rotation and is decompressed as it approaches the surface of the body of water. In this case, coupling the rotating helical conduit with an alternator makes it possible to generate electricity.

[0005] When the air is compressed, its temperature rises. The work required by the compression is thus increased. At the end of compression, the air arriving in the submerged tank can therefore reach significant temperatures. The air stored in the tank is then cooled by heat transfer to the surrounding water, which generates energy losses. The cycle of compression and decompression of the air, first lowering it to the bottom of the body of water, then raising it to the surface to recover the energy thus stored, leads to severe losses due mainly to thermodynamic phenomena. linked to the heating of the air during its compression and its cooling during decompression. Figure 5 illustrates a cycle of air volume (V) versus depth (h) which is proportional to pressure (p). The solid line indicates the cycle of compression (A) and decompression (C) in systems as described in BE1024212. It can be seen that during the storage of compressed and heated air, it cools to reach equilibrium with the ambient temperature at the bottom of the water body and thus dissipates part of the compression work. Consequently, the volume of air recovered after decompression is only around 55% of the volume of air initially injected into the device.

[0006] In the document US2012/0119510, the helical duct is in the form of an Archimedes' screw composed of a shaft along which extends a helical thread, the Archimedes' screw being internal and integral from a pipe. As a solution to the previous problem of air heating as the compression progresses, the document US2012/0119510 proposes a hollow shaft of the Archimedes screw to increase the circulation of water from the body of water by contact with the air volumes during compression of the air volumes along the screw, thereby increasing heat transfers between the air volumes and the water surrounding the device and cooling the air volumes.

[0007] In several embodiments, the shaft of the screw device of US2012/0119510 may have a hollow core which defines a cavity allowing the circulation of water along the Archimedes screw. During compression, cold water from the depths of the water body can be brought up against the stable water stratification using a pump.

Cold water can move from the bottom end of the screw device to the top end of the screw device via the cavity to improve cooling. Similarly, hot water from the surface of the water and/or a thermal reservoir can be drawn from the high end to the low end to improve the heating of the air during its decompression during the ascent of the air to the surface by means of the device as described above. This additional cooling and heating during compression and decompression, respectively, increases the efficiency of the screw device and the yield of the energy storage. This solution makes it possible to bring the compressed air into contact with colder water during compression, for example, but requires a system comprising a pump to ensure the circulation of water within the cavity of the shaft. of the screw. In addition, the water-air interface allowing the heat exchange between the air being compressed and the water remains limited. Finally, the quantity of heat exchanged varies with the speed of rotation of the device. For example, when the power consumed by the device to compress air increases, the speed of rotation of the Archimedes screw increases, which has the effect of reducing the duration of the air compression and therefore the transfer associated heat and cooling.

[0008] There therefore remains a need for an energy storage device in the form of compressed air under the surface of a body of water in which the heat exchanges between the air and

Calf of the body of water are improved. Preferably, the dependence of heat transfer on the power consumed to compress the air will be decreased. Preferably, this increase in heat exchange will not require additional machinery such as a pump to be implemented, thus simplifying the energy storage device. The present invention proposes a solution allowing an increase in heat transfer between the compressed air and the surrounding water in an innovative and simple way.

SUMMARY OF THE INVENTION

The device according to the present invention relates to an energy storage device in the form of compressed air comprising:

- a tube extending along a longitudinal axis (Z) normal to a cross section of the tube with a tube length (Lt) measured along the longitudinal axis (Z) and separating an upstream opening and an opening downstream of the tube, - a screw internal to the tube, in the form of a helical thread extending along and centered on the longitudinal axis (Z),

e Comprising an outer radial end of the screw joined continuously and rigidly and hermetically to an interior surface of the tube along a length of the screw, and e defining a continuous helical fluid passage inside the tube between the upstream opening and the downstream opening,

- An anchor configured to anchor the downstream opening to the bottom of a body of water at a depth (H),

- a motor, preferably an electric motor, configured to rotate the tube and the screw around the longitudinal axis (Z),

- a floating device configured to keep at least part of the emerged upstream opening above a surface of the body of water when the downstream opening is anchored to the bottom of the body of water, so that:

e the at least partially emerged upstream opening is at a distance (L) from a vertical of the downstream opening measured along a horizontal axis normal to the vertical, so that a ratio (L / H) of the distance (L) to the depth (H) is less than 1.75,

e during the rotation of the tube and the screw driven by the motor around the longitudinal axis (Z), discrete volumes of air separated from each other by a continuum of water from the body of water are driven by the screw rotating from one atmosphere from the upstream opening to the downstream opening, compressing the discrete volumes of air as the discrete volumes of air move towards the downstream opening, - a submerged tank configured for storing a reserve of compressed air, the submerged tank being in fluid communication with the downstream opening of the tube and anchored to the bottom of the body of water so that the discrete volumes of air reaching the downstream opening can fill the tank immersed, which is preferably a bladder tank comprising a flexible wall,

The device according to the present invention is characterized in that the inner surface of the tube comprises a structured part of the tube representing at least 20% of an area of the inner surface of the tube and configured to lift and drive a volume of water from the continuum of water towards the discrete volumes of air with each rotation of the tube, which falls by gravity into the discrete volumes of air in the form of drops, the at least partial evaporation of which cools the discrete volumes of air as they are compressed.

In a preferred variant, the device according to the invention further comprises a distilled water collection device configured to, - collect distilled water obtained by condensation of the compressed air reserve during its cooling in the tank submerged and for - evacuating the distilled water thus collected towards the surface of the body of water, through a distilled water evacuation conduit, the distilled water collection device preferably comprising a receptacle in fluid communication with the distilled water drain.

In a preferred variant, the structured part of the tube of the device according to the invention comprises one or more striations of the tube formed by a number of ridges of the tube, in which a ridge of the tube has, - a depth of ridge of the tube measured along a radial direction normal to the longitudinal axis (Z) comprised between 1 and 5 mm, preferably between 2 and 4 mm, and - a groove width of the tube measured in a tangential direction orthogonal to a directrix of the streak, between 1 and 5 mm, preferably between 2 and 4 mm, the striations of the tube covering at least 30% of an area of the structured part of the tube.

In a preferred variant, a surface of the screw of the device according to the invention comprises a structured part of the screw representing at least 5% of an area of the surface of the screw and able to transfer, with each rotation of the tube, a second volume of water from the continuum of water towards the discrete volumes of air, which falls by gravity into the discrete volumes of air in the form of drops, the at least partial evaporation of which thus further cools the volumes air during the compression of the latter.

In a preferred variant of the device according to the invention comprising a structured part of the screw, the structured part of the screw comprises grooves of the screw formed by a number of grooves of the screw, a groove of the screw having a screw groove depth measured in a direction normal to the surface of the screw between 1 and 5 mm, preferably between 2 and 4 mm, and a screw groove width measured in a direction tangential to the surface of the screw and orthogonal to a directrix of the groove of the screw comprised between 1 and 5 mm, preferably between 2 and 4 mm, the grooves of the screw covering at least 30% of an area of the structured part of the screw.

In a preferred variant of the device according to the invention comprising striations, the structured part comprises a first striation and a second striation, each of the first and second striations is formed by a number of substantially parallel striations between them, and in which at least one selection of the stripes of the first stripe intersects with at least one selection of the stripes of the second stripe.

In an advantageous embodiment, the motor of the device according to the invention is electric and is further configured to act as a generator and to generate electrical energy when a rotor of the motor is driven in rotation by the tube and the screw in rotation around the longitudinal axis (Z), the rotation of the tube and of the screw being driven by a rise by an interior of the tube towards the surface of the body of water of compressed air introduced into the tube from the submerged tank.

In an advantageous embodiment of the device according to the invention comprising an electric motor configured to act as a generator, the structured part of the tube is configured to drive a volume of water from the continuum of water to the discrete volumes of air with each rotation of the tube, which falls by gravity into the discrete volumes of air in the form of drops, thus heating the discrete volumes of air as they are decompressed.

In a preferred variant, the device according to the invention further comprises a guide shaft extending along the longitudinal axis (Z).

In a preferred variant of the device according to the invention comprising a guide shaft, the device further comprises a gap surrounding a side surface of the shaft and separating the screw from the guide shaft over an entire length of the guide shaft, a width of the gap normal to the side surface of the shaft preferably being between 1 mm and 10 cm.

In a preferred variant, the tube length (Lt) of the device according to the invention is between 10 m and 300 m, preferably between 20 m and 200 m, preferably between 50 m and 150 m.

In a preferred variant of the device according to the invention, a nominal speed of rotation of the tube driven by the motor is between 1 revolution / min and 600 revolution / min, preferably between 10 revolution / min and 240 revolution / min , preferably between 30 rpm and 120 rpm, preferably between 50 rpm and 80 rpm.

In an advantageous embodiment of the device according to the invention, the tube has a circular section with an internal diameter of between 5 cm and 10 m, preferably between 10 cm and 5 m, preferably between 20 cm and 2 m. .

BRIEF DESCRIPTION OF FIGURES

These aspects as well as other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, reference being made to the drawings of the figures, in which:

Fig.1 shows a partial longitudinal sectional view of a storage device according to the invention.

Fig.2 shows a sectional view of a first embodiment of the submerged tank included in the storage device according to the invention.

Fig.3 shows a sectional view of a second embodiment of the submerged tank included in the storage device according to the invention, comprising an alternative distilled water harvesting device.

Fig.4 represents a storage device according to the invention in which the floating device is represented, as well as a pipe allowing the injection of compressed air from the submerged tank to the tube.

Fig.5 represents a graph of the volume of air according to the depth reached by the air under the surface of a body of water, in order to compare the effect of the adiabatic and isothermal compression and decompression of the air on the yield of a cycle also including intermediate isobaric cooling and heating.

Fig.6 represents examples of structures forming the structured part of the tube and/or of the screw of the storage device according to the invention.

Fig.7 represents a section of the tube and the screw of a device according to the invention in operation and at several angular positions around the longitudinal axis (Z), thus showing the contribution of drops of water in the volumes discrete air through the structured part of the rotating tube.

FIG.8 represents an overview of a device according to the present invention.

FIG.9(a) to 9(d) represent different variants of screws in the form of helical threads according to the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Air compression device: tube (2)

As shown in Figures 1 and 8, an energy storage device in the form of compressed air according to the present invention comprises a tube (2) extending along a longitudinal axis Z, which n is not necessarily straight, over a length of tube (Lt) separating an upstream opening (2u) from a downstream opening (2d) of the tube. Preferably, the tube length (Lt) is between 10 m and 300 m, preferably between 20 m and 200 m, preferably between 50 m and 150 m. The longitudinal axis (Z) is normal to a cross section of the tube (2), which is the intersection between a plane normal to the longitudinal axis (Z) and the tube (2). The cross section of the tube (2) preferably has rotational symmetry about the longitudinal axis (Z). Preferably, the internal diameter of the tube, that is to say the distance separating the longitudinal axis (Z) from an internal surface of the tube (2s), decreases between the upstream opening (2u) and the opening downstream (2d) so that the internal diameter of the tube at the level of the downstream opening (2d) is smaller than the internal diameter of the tube at the level of the upstream opening (2u). Preferably, the internal diameter of the tube is between 5 cm and 10 m, preferably between 10 cm and 5 m, preferably between 20 cm and 2 m.

[0025] The longitudinal axis (Z) is preferably rectilinear by design. However, and as illustrated in Figure 8, depending on the dimensions, the relative weight of the device in relation to the water, and the forces to which it is subjected, in particular currents, the longitudinal axis (Z) may have a curvature associated with the absorption of the forces linked to the force of gravity or to the sea currents exerted on the device according to the invention when the latter is installed in a body of water.

Screw (3) inside the tube

The device according to the invention also comprises a screw (3) internal to the tube (2). The screw has a shape of a helical thread extending along the longitudinal axis (Z) over a length of the screw (3) measured along the longitudinal axis (Z). As shown in Figures 9(a) to 9(d), a helical thread is defined here as an object obtained by rotating a profile (2p) along a helix around an axis of the helix. A rectangular profile (2p) is illustrated in Figures 9(a) to 9(d), but it is clear that the profile (2p) can have any other geometry suitable for obtaining a screw (3). The helix defines an outer radial end (3e) of the screw. The profile is closed so that the air comprised in a discrete volume (7) of air housed in a pitch of the screw cannot pass through it to reach an adjacent pitch. The screw pitch (dp) is preferably, but not necessarily, constant. For example, for a screw helical thread pitch of 8m, an outer radius of the screw measured from the longitudinal axis (Z) to the outer radial end (3rd) can be 10m and an inner radius of the screw defining a central channel measured from the longitudinal axis to the nearest point of the screw can be between 0 m (no central channel) to 5 m. These values can be reduced linearly with depth while maintaining the same ratio between them.

[0027] The screw comprises an outer radial end (3rd) of the screw (3) (defining the helix defined above) joined in a continuous and rigid and hermetic manner to the inner surface of the tube (25) over the entire length of the screw (3). The outer radial end (3rd) of the screw (3) is the part of the screw (3) farthest from the longitudinal axis (Z). The hermetic connection between the screw (3) and the tube (2) prevents the passage of air between the outer radial end (3e) of the screw (3) and the inner surface of the tube (2s). Finally, the screw (3) is joined rigidly to the tube (2) and is therefore rigidly secured to the tube (2). The screw (3) internal to the tube (2) thus defines a continuous helical fluid passage inside the tube (2) connecting the upstream opening (2u) and the downstream opening (2d). The seal between the outer radial end (3rd) of the screw (3) and the inner surface (2s) of the tube (2) is formed by any means known to those skilled in the art. For example, the joint can be formed by welding, brazing, gluing, melting, overmolding, etc. Preferably, the screw in the form of the helical thread is coaxial with the longitudinal axis (Z). Regardless of whether the helical thread is coaxial or not with the longitudinal axis (Z), when the tube enters into rotation around the longitudinal axis (Z), the screw is rotated around the same longitudinal axis (Z) by the seal formed between the outer radial end (3e) of the screw (3) and the inner surface (2s) of the tube (2).

Axial geometry of the screw (3) with or without guide shaft (16)

[0028] As illustrated in Figures 1, 9(c) and 9(d), the device according to the invention may further comprise a guide shaft (16), of preferably circular section, and extending along the longitudinal axis (Z) over a length at least equal to the length of the screw (3). Preferably, the screw (3) surrounds the guide shaft (16) over the entire length of the screw (3). As illustrated in Figure 9 (c), the guide shaft (16) can be coupled to the screw (3) rigidly or through bearings (see Figure 1) allowing rotation of the screw relative to the guide shaft. In the latter case, the bearings are preferably - evenly distributed along the guide shaft (16), and a gap (17) surrounds a side surface of the shaft (16s) except at the location of the bearings . As shown in Figure 1, the gap separates the screw (3) from the shaft (16) along the entire length of the shaft. Preferably, a width of the gap measured in a direction normal to the side surface of the shaft (16s) between the screw (3) and the shaft (16) is between 1 mm and 10 cm. This variation is illustrated in Figure 9(d), in which the device includes a space between the shaft (16) and the helical thread, defining a continuous passage allowing the continuum of water (12c) to flow independently of the screw (2). As discussed above, the guide shaft can be rigidly coupled to the screw (2) or mobile in rotation along the longitudinal axis (Z) via bearings.

A guide shaft has the advantage of considerably increasing the tensile strength of the system formed by the tube (2) and the screw (3). This can be particularly advantageous in the case where the tube is formed of modules assembled to one another. A guide shaft (16) makes it possible to substantially increase the tensile strength of the tube. Preferably, the guide shaft (16) is cylindrical or conical in shape, and coaxial with the longitudinal axis (Z).

Alternatively, illustrated in Figures 4, 9 (a) and 9 (b), the device according to the invention may not include a guide shaft (16) coaxial with the longitudinal axis (Z) . If the profile (2p) does not extend to the longitudinal axis (Z) as shown in Figure 9(b), a helical passage is formed defining an inner end of the helical thread allowing the continuum of water ( 12c) to flow freely along the longitudinal axis (Z). On the other hand, as illustrated in Figure 9(a), if the profile (2p) extends to the longitudinal axis (Z), no passage is defined and the water continuum (12c), as discrete volumes (7) of air, must flow along the surface of the helical thread.

[0031] Preferably, the screw (3), the tube (2), and preferably the guide shaft are made from materials resistant to water corrosion, and to seawater corrosion. especially. Preferably, the screw (3) and the tube (2) comprise one or any combination of the following materials: aluminum, stainless steel, composite material comprising glass fibers. The materials of the screw (3), the tube (2), and the guide shaft (16) can be identical or different.

Anchor (4)

The device according to the invention further comprises an anchor (4) configured to anchor the downstream opening (2d) to the bottom of a body of water at a depth (H) below a surface of the body of water (13). The surface of the body of water (13) is the surface separating the body of water of an atmosphere from the body of water overhanging it. The depth (H) separating the surface of the body of water (13) from the downstream opening (2d) is measured in the vertical direction at the location of the downstream opening (2d). The depth (H) can vary according to the position of the device (1), this being able for example to evolve with the direction of the sea currents and/or the tides in the case of a device installed at sea. shown in Figure 1, the anchor comprises a part firmly attached to a bottom of the body of water and connected to the tube (2), for example through the guide shaft (16), by a cable, thus preventing the downstream opening (2d) to float to the surface of the body of water (13). The anchor (4) of the device according to the invention can be fixed at the location of the screw (3) and / or the tube (2) and / or the guide shaft

(16). Alternatively or concomitantly, the anchor (4) can also comprise a bearing, a ball joint, piles, or a rigid structure intended to maintain the downstream opening (2d) in a fixed position, or any combination of these elements. The anchor can be firmly attached to the bottom of the body of water and / or include a large mass in order to retain the downstream opening (2d) of the device under water. Preferably, the anchor (4) is configured to allow precession of the longitudinal axis (Z) around a vertical axis. Finally, the device according to the invention can comprise several anchors, the anchors being attached to the other parts of the device in one or more places.

Engine (5)

The device according to the invention further comprises a motor (5), preferably an electric motor, configured to drive the tube (2) and the screw (3) in rotation around the longitudinal axis (Z) in the direction causing the descent of the fluids carried in the screw. The motor (5) is preferably powered by renewable energy of wind or photovoltaic origin for example. Preferably, a nominal speed of rotation of the tube (2) is between 1 revolution / min and 600 revolution / min, preferably between 10 revolution / min and 240 revolution / min, preferably between 30 revolution / min and 120 revolution / min, preferably between 50 rpm and 80 rpm.

The motor (5), comprising a stator and a rotor configured to rotate relative to the stator, can be coupled in different ways to the other components of the device according to the invention, or to components not forming part of the invention. , in order to produce the rotational drive of the tube (2) and of the screw (3) around the longitudinal axis (Z). In a variant of the device comprising a guide shaft (16) rigidly coupled to the screw (3) and to the tube (2), the rotor can be coupled directly to the guide shaft (16) as illustrated in

Figure 8. The stator must be fixed relative to the rotor to prevent rotation of the motor rather than the tube (2) and screw (3). As shown in Figure 8, the stator can be attached by a plurality of buoys, preferably at least three buoys, which are anchored to the bottom of the body of water. If the device is close to a shore, it may be possible to secure the stator to the shore.

In a variant comprising a guide shaft (16) coupled to the screw (3) by bearings allowing rotation of the screw relative to the guide shaft, the motor stator (5) is rigidly fixed to the guide shaft (16) and, as illustrated in Figure 1, the rotor is coupled to an outer surface of the tube and rotates the tube (2) through a coupling means, such as for example a gear comprising a first toothed wheel firmly coupled to the rotor of the motor and a second toothed wheel firmly coupled to an outer surface of the tube (2), or by a system of transmission belts. To prevent the guide shaft (16) from rotating rather than the tube (2) and the screw (3), the transmission shaft can be anchored to the bottom of the body of water so as to prevent it from rotating around the longitudinal axis (Z). Preferably, the guide shaft (16) is anchored to the bottom of the body of water, leaving it freedom of rotation around the vertical axis and any horizontal axis, perpendicular to the vertical axis and parallel to the surface. of the body of water.

In another variant of the device independent of the presence or absence of a guide shaft (16) illustrated in Figure 4, the motor rotor is coupled to the outer surface of the tube (2) through a coupling means, such as for example a gear comprising a first toothed wheel solidly coupled to the rotor of the motor and a second toothed wheel solidly coupled to the outer surface of the tube (2), or by a system of transmission belts. The stator must be fixed relative to the rotor to prevent rotation of the motor rather than the tube (2) and the screw (3). As illustrated in Figure 4, the stator can be fixed by a plurality of buoys (6), preferably at least three buoys, which are anchored to the bottom of the body of water. If the device is close to a shore, it may be possible to secure the stator to the shore. In order to stiffen the system, the stator can be coupled to the outer surface of the tube via a bearing allowing the rotation of the tube relative to the stator (see Figure 4).

The floating device (6) illustrated in Figures 4 and 8, makes it possible to maintain the motor stator (5) in a substantially immobile position in a terrestrial reference, and to prevent the motor stator (5) from rotating around [axis of the rotor or the motor (5) to move around the longitudinal axis (Z) because of the resistance opposed by the tube (2) to rotate around the longitudinal axis (Z).

[0038] Preferably, the motor is electric and powered through an electric cable. For example, the electric cable can pass through the guide shaft (16) and reach an electricity production site by being placed on the bottom of the body of water as shown in Fig.

Figure 1 by the dashed line. Preferably, the motor can deliver a power of between 100 kW and 100 MW, preferably between 1 MW and 10 MW.

Floating device (6)

The device according to the invention comprises a floating device (6) configured to, on the one hand, fix the stator of the motor (5) with respect to its rotor, in order to ensure that the motor actually drives the rotation of the tube and the screw and not the rotation of the stator (see discussion in the previous section) and, on the other hand, to maintain at least a part of the upstream opening (2u) emerged above a surface of the plane d water (13) when the downstream opening (2d) is anchored to the bottom of the body of water. The anchoring of the downstream opening (2d) to the bottom of the body of water is such that: - the upstream opening (2u) at least partially emerged is at a distance (L) from a vertical of the downstream opening (2d) measured along a horizontal axis normal to the vertical, such that a ratio (W/H) of distance (L) to depth (H) is less than 1.75,

- during the rotation of the tube (2) driven by the motor (5) around the longitudinal axis (Z), discrete volumes (7) of air separated from each other by a continuum of water from the plane of water are drawn from the atmosphere at the location of the upstream opening (2u) towards the downstream opening (2d), compressing the discrete volumes (7) of air when the discrete volumes (7) of air move towards the downstream opening (2d).

The floating device (6) may include several buoys to fix the motor stator (5). For the tube (2), the device comprises one or more ballasts to compensate for the flotation created by the air entrained in the tube. It can be anchored to the bottom of the water, as shown in

Figure 8. It can be attached solidly, or through a bearing or a ball joint, to the tube (2) or to the screw (3).

Air compression

When the device according to the invention operates, the tube (2) and in particular the downstream opening (2d) are therefore maintained by means of the anchor (4) and the floating device (6) under the surface of the body of water (13), except for at least a portion of the upstream opening (2u). The upstream opening (2u) is at least partially emerged above the surface of the body of water (13) in order to allow the entry of air from the atmosphere situated above the body of water towards the inside of the tube (2). In working order, the longitudinal axis (Z) is therefore inclined in such a way that the ratio (L/H) is less than 1.75. Preferably, the longitudinal axis (Z) is not perfectly vertical (i.e., L/H > 0) and L/H preferably at least equal to 0.1, preferably at least equal to 0.2. The motor (5) is actuated to activate the rotation of the tube (2) and the screw (3) around the longitudinal axis (Z). The energy consumed by the motor is the energy that the device of the present invention seeks to store in the form of compressed air. Part of this energy can be recovered at leisure in a second step by decompressing the air thus compressed.

[0042] Depending on the ratio (L / H), the dimensions of the screw, and the dimensions of the tube (2) in particular, each rotation of the tube and the screw allows a discrete volume (7) of air from the atmosphere above the body of water to enter via the upstream opening (2u). Each discrete volume (7) of air is enclosed in the tube (2) in one pitch of the screw and moves one screw pitch with each rotation of the screw (3) around the longitudinal axis (Z) . In the device according to the invention shown in Figure 1, approximately 30% of the upstream opening (2u) is emerged, and the discrete volume of air (7) formed at each rotation of the tube (2) is contained in a screw pitch defined between a surface of the screw (3s), the inner surface of the tube (2s), and a contact surface of the discrete volume of air (7) with the continuum of water (12c). In particular, the surface of the screw (3s) and the inner surface of the tube (2s) prevent the discrete volume of air (7) from rising towards the surface of the water, and entrain the discrete volume of air (7 ) towards the downstream opening (2d) of the tube and the bottom of the body of water.

[0043] With each rotation of the tube (2) of the device according to the invention around the longitudinal axis (Z), the discrete volumes of air (7) trapped at each screw pitch are thus driven towards the screw pitch following until reaching the downstream opening by the rotation of the tube (2). The discrete volumes of air are separated from each other by a continuum of water from the body of water.

When the device according to the invention is in operation, it therefore contains a continuum of water, that is to say a certain quantity of water such that there is a path within the continuous helical fluidic passage located at the inside the tube which crosses the latter over the entire length of the tube (Lt), from the downstream opening (2d) towards the upstream opening (2u), the path being entirely immersed in the certain quantity of water and therefore not passing through the discrete volumes of air (7).

The discrete volumes (7) of air are therefore spaced out at each thread pitch along the screw (3) and the tube (2) in positions corresponding to each turn of the screw. The pressure of the discrete volume (7) of air in a given screw pitch is substantially equal to the pressure of the water continuum (12c) in this same screw pitch, which is itself in equilibrium with the pressure of the water of the body of water at a depth identical to that of the discrete volume (7) of air. As the upstream (2u) and downstream (2d) openings of the tube (2) are separated from each other by a vertical distance (H), the transfer by rotation of the screw (3) of a discrete volume (7) of air from a first screw pitch to a second screw pitch adjacent and downstream of the first, by a distance equal to the height (dx) of the screw pitch, causes a corresponding descent equal to the product of the height (dx) of the thread and the cosine of the angle formed with the vertical by the longitudinal axis (Z) between the first and the second thread. As the water pressure increases by approximately 1 bar every 10 m, the pressure of the discrete volumes (7) of air can rapidly increase with the rotation of the screw (3) and the descent of a screw thread following discrete volumes (7) of air towards the downstream opening (2d) of the tube, located at a depth (H) relative to the upstream opening (2u).

Submerged tank (9)

The device according to the invention comprises a submerged tank (9) configured to store energy in the form of a reserve of compressed air. The reservoir is therefore entirely contained below the surface of the water body. According to the invention, the submerged tank is in fluid communication with the downstream opening (2d) of the tube (2) and is configured to receive the previously compressed air reaching the downstream opening (2d) and escaping from the tube ( 2) through it. In the embodiments of the invention shown in Figures 1 to 4 and 8, the submerged tank is a flexible bladder retained at the bottom of the body of water by anchors (4) through cables. Alternatively or together, the tank (9) can be attached to the guide shaft (16) which is itself anchored to the bottom of the body of water as shown in Figure 1.

In the embodiments illustrated in Figures 4 and 8, the submerged tank (9) is anchored directly to the bottom of the body of water by means of a tank anchor. Similar to the anchoring (4) of the downstream opening (2d) of the tube (2), the anchoring of the reservoir may comprise, alternatively or concomitantly, a bearing, a ball joint, piles, a rigid structure, a cable, a mass of concrete or metal, or any combination thereof. As shown in Figures 3 and 8, the tank can also be prevented from rising to the surface of the water body by means of several anchors. Submerged tanks adapted to the present invention, the wall of the tank (9p) of which is flexible are available on the market in the field of energy storage in the form of underwater compressed air (UW-CAES) from several businesses. For example Hydrostor or

Thin Red Line Aerospace offer such tanks.

Preferably, the submerged tank (9) has a maximum capacity of compressed air that can be stored between 100 m° and 10000 m°, preferably between 1000 and 5000 m°.

Preferably, the compressed air is stored in the tank at a pressure (P) of between 3 and 50 bar, preferably between 8 and 20 bar, corresponding to immersion depths (H) of approximately 80 to 200 m . Preferably, the submerged tank (9) has a maximum energy storage capacity of between 30 and 1700 MWh, preferably between 100 and 1000 MWh.

In Figure 1 (the dimensions are not to scale), the submerged tank (9) comprises an opening of the submerged tank (21) overhanging the downstream opening (2d) of the tube and configured so that the compressed air escaping from the downstream opening (2d) in the body of water and rising vertically in the body of water enters the submerged tank through the tank opening (21). As shown in Figure 1, the fluid communication between the submerged tank (9) and the downstream opening (2d) is unidirectional and therefore does not allow compressed air to be reinjected from the submerged tank (9) inside the tube ( 2). The compressed air discharge duct (20) from the submerged tank (9) as shown in

Figure 1 allows the compressed air stored in the tank to be evacuated to a place of consumption located on the surface of the body of water. The place of consumption can for example include a turbine in which the energy of the compressed air is transformed into mechanical energy. An alternator coupled in rotation with the turbine can transform the mechanical energy thus produced into electrical energy. The evacuation of compressed air directly through the compressed air evacuation pipe (20) of the submerged tank (9) towards a turbine located on the surface of the body of water, however, has the defect that the air decompressing at the level of the outlet cools abruptly and follows the adiabatic curve (C) represented by the continuous curve in Figure 5. The air temperature at the outlet of the turbine can be lower than -100°C depending on the pressure (P) of storage .

In an alternative variant, shown in Figure 4, the compressed air can be reintroduced into the tube (2) by a compressed air discharge conduit (20) from the submerged tank (9) to the tube ( 2). The compressed air wants to rise to the surface and must therefore cause the screw (3) to rotate around the longitudinal axis (Z). Contrary to the compression process discussed above, the discrete volumes (7) of air pass with each rotation of the screw from one step to the next, until reaching the upstream opening (2u). The motor (5) is configured in generator mode, the rotation of the rotor driven by the rotation of the screw (3) and the tube (2) makes it possible to supply electrical energy and thus to recover (part of) the energy supplied by the engine to store the compressed air in the tank. It is clear that it is not essential for the generator and the motor (5) to be combined, and two separate units can be envisaged, but the use of a single unit combining the two functions of motor and generator seems interesting.

In the tank, the air is stored at a pressure substantially equal to the pressure of

Calf from the body of water surrounding the reservoir. In the reservoir in the form of a flexible bladder as shown in Figure 1, the compressed air overhangs and is in direct contact with the water of the body of water through an air / water interface of the reservoir. The air pressure within the submerged tank (9) is therefore equal to the water pressure at a depth equal to that of the air / water interface of the tank, which is at a depth of approximately (H), either at a pressure (P) of approximately,

P [bar] = (H [m] / 10 [m / bar]) + Pa [bar], with Pa designating the atmospheric pressure at the level of the water body; in general, Pa = 1 bar.

Adiabatic or isothermal compression

[0050] In the absence of heat exchange, the air heats up during its compression adiabatically and can reach high temperatures. For example, a quantity of atmospheric air compressed from a pressure of 1 bar and a temperature of 20°C in order to reach a pressure of 11 bar, i.e. the pressure reached at a depth of 100 m under water, can exceed 400°C in temperature. Such temperatures induce stresses on the materials used to make the tube (2), the screw (3), as well as the submerged tank (9), among others. In addition, as indicated above, this rise in the temperature of the air during compression generates additional work to compress the air, this additional work being lost during the cooling of the air in the submerged tank (9) .

[0051] Figure 5 shows a thermodynamic cycle of the air volume as a function of the pressure (P) or equivalently, of the depth in the body of water during a compression phase (A) of a volume (V7) of a discrete volume (7) of air, storage (B) of the compressed air in the tank (9) at the bottom of the body of water, and decompression (C) of the stored air . The solid line indicates the adiabatic cycle (i.e., without heat exchange with the outside). The continuous curve segment (A) characterizes the work done to compress a volume (V / V7 = 100%) of air from an initial pressure, Pa = 1 bar to a pressure (P) reached at a depth (H) . The work (WW) is the area under the compression curve included in a volume segment (dV) (ie, W=[pdV). Pressure is approximately related to depth by the expression mentioned above, p [bar] = (h [m] / 10 [m / bar]) + 1 [bar], where Pa:= 1 bar.

We see at the depth (H) (or at the pressure (P)), that during the storage of the compressed air in the tank at the bottom of the body of water, the air loses the heat accumulated during the compression by dispersing it in the water surrounding the tank. The heating energy of the air is thus lost and cannot be recovered during decompression. This cooling of the stored air results in a decrease in the volume visible in the segment (B) of the solid line which descends vertically indicating a decrease in volume without modification of the pressure, since the air remains at the depth (H) .

[0053] An adiabatic decompression follows the segment (C) of the continuous curve in the direction of the arrow. During adiabatic decompression, air cools as it expands. The work (VW) recovered is the area of the surface under the decompression curve included in a volume segment (dV) (ie. W= f p dV). It can be seen that the hysteresis of the adiabatic compression and decompression cycle defined by the continuous curve is characterized by severe energy losses.

In practice, purely adiabatic compression is impossible. The heat exchanges during the compression of the air are not zero because the air of the discrete volumes (7) can transmit its heat to the water of the body of water surrounding the tube through the wall of the tube, and / or to the water continuum (12c) inside the tube. However, it is clear that a solution making it possible to increase the heat transfer from the air of the discrete volumes (7) to the water of the body of water during compression reduces the compression energy to be supplied to the device. according to the invention. Similarly, a solution to increase the heat transfer from the water of the body of water to the air of the discrete volumes (7) during decompression would increase the energy recovered. A system characterized by perfect heat transfers, making it possible to maintain a constant temperature is called isothermal and is represented in Figure 5 by dotted curves. By comparing the dotted and solid curves of the

Figure 5, it can be seen that the area of a hysteresis of an isothermal cycle is significantly lower than that of an adiabatic cycle. The present invention proposes a solution for obtaining a more efficient compression/decompression cycle, deviating from an adiabatic cycle and approaching an isothermal cycle. The proposed solution includes the provision of a structure (8) to a part of the inner surface of the tube (2)

Structured part of the tube (8)

The device according to the invention proposes a solution for increasing the heat transfer between the discrete volumes (7) of air and the water of the water continuum (12c) present in the tube (2). In particular, the inner surface of the tube (2s) comprises a structured portion of the tube (8) configured to lift and transfer a volume of water from the continuum of water (12c) to the discrete volumes (7) of air at each rotation of the tube (2). The volume of water carried by the structure falls by gravity into the discrete volumes of air in the form of drops (129), thus cooling the discrete volumes (7) of air as they are compressed.

The level of cooling increases with the proportion of the volume of drops (12g) being vaporized (12v) during the fall of these through the discrete volumes (7) of air because the latent heat of the water drops consumes much heat energy drawn from the discrete volumes (7) of air.

[0056] Figure 7 shows several views in section normal to the longitudinal axis (Z) of the tube of the device (2) according to the invention in operation, at different stages of the transfer of water from the continuum by the structured walls of the tube in discrete volumes (7) of air followed by the fall and evaporation (12v) of this water in the form of drops (12g). Four cavities are shown on the inner surface of the tube, representing four cross-sectional ridges. The ridges are configured to draw water from the continuum as the tube rotates (clockwise in Figure 7). During operation of the device according to the invention, at least a portion of the structured part of the tube (8) is in contact with the discrete volumes (7) of air and plunges into the continuum of water with the rotation of the tube ( 2), thereby being brought into contact therewith as shown in Figure 7(a). As the tube (2) rotates, the structured part of the tube (8) emerges from the water continuum as shown in Figure 7(b). The ridges of the structured part are configured as pockets that each collect a part of the water volume in the form of small volumes of water, taking it out of the water continuum during the rotation of the tube (2). The ridges each carry with them the small volumes of water from the water continuum to positions overhanging the discrete volume of air as shown in Figure 7(c). By effect of gravity, the small volumes of water are detached from the structured part of the tube (8) as illustrated in Figure 7(d). They fall in the form of drops (12g), like rain, towards the water continuum by crossing the discrete volume (7) of air.

The drops passing through the discrete volume of air thus offer a large exchange surface between the continuum and the air of the discrete volumes and makes it possible to vaporize a large volume (12v) of water with the corresponding calorific energy consumption, reducing thus substantially the temperature of the corresponding discrete volume of air. In addition, the heat transfer between the drops falling in the air and this air is improved thanks to the friction of the air against the drops which move within it. This solution is advantageous compared to that proposed in US2012/0119510 discussed in the "technological background" section above because at the area of the water / air interface between the water continuum (12c) and the discrete volumes of air already described, we add here the area of the interface between the drops (12g) and the discrete volumes of air, which is substantially greater than the first area. Consequently, the heat exchange is substantially higher with the device of the present invention than with that of US2012/0119510. In a preferred embodiment of the present invention, the structured parts of the tube (8) and preferably of the screw are such that, in addition to promoting the formation and fall of drops of water which evaporate on contact with the volumes discrete amounts of air heated during compression, also allow the formation of a film of water which adheres to the surfaces and also increases the water/air interface and the heat exchange between the two phases. In addition to the structured surface, the surfaces of the tube and the screw may include a surface treatment or a hydrophilic coating layer promoting the adhesion of water to said surfaces.

The air heated during compression is therefore cooled by water and water vapor from the water continuum, the temperature of which is lower than that of the air being compressed. As the discrete volumes (7) of air are compressed, heat is thus transferred from the air to the water drops and the water continuum. By falling back into the water continuum, the drops thus heated (if not completely vaporized) increase the temperature of the water continuum. A portion of water in the water continuum can thus exceed the evaporation temperature and thus increase the partial vapor pressure in the discrete volumes (7) of air. The volume of water evaporated from drops (12g) of small dimensions (and offering a very large interface area with the air) is much greater than the volume evaporated from the interface between the continuum of water and discrete volumes of air. The heat absorbed by the water continuum (12c) by transfer through its interface with the air and by the fall of the non-volatilized drops is transferred from the water continuum to the water of the body of water surrounding the — device which acts as a reservoir or thermal damper. Preferably, the device according to the invention is installed in a body of water with a thermal inertia such as a difference in temperature of the water of the body of water before and after having received a heat input associated with the compression of a quantity of air equivalent to the complete filling of the submerged tank (9) is less than 50°C, preferably less than 10°C, preferably less than 1°C. Heat is transferred from the water continuum to the water in the body of water surrounding the device by heat conduction through the walls of the tube and/or by flow or exchange between the water in the water continuum and the water from the body of water outside the tube (2). In the latter case, the exchange of water between the continuum and the outside of the tube is for example carried out by circulation of water from the continuum along the helical fluid passage from the upstream opening (2u) to the downstream opening (2d) or vice versa.

According to the invention, the structured part of the tube (8) covers at least 20% of an area of the inner surface of the tube (2s). The structured part of the tube (8) preferably covers between 30 and 100% of the area of the inner surface of the tube (2s), preferably between 50 and 70% of the area of the inner surface of the tube (2s) . It can be distributed regularly or irregularly along the tube, and comprise several distinct parts. For example, the structured part of the tube (8) can cover a part of the inner surface of the tube which is continuous from the upstream opening (2u) to the downstream opening (2d). In another example, the structured part of the tube (8) occupies only a portion of the length of the tube adjacent to the downstream opening (2d) of the tube (2). In another example, the structured part of the tube (8) comprises different sub-parts distinct and separated from each other, located at regular distance intervals along the tube (2), to modulate the volume of water transported by the streaks at each rotation as well as the volume of the small volumes of water embarked in each streak.

Examples of structured parts of the tube (8) are shown in Figure 6. For each of them, top, cross-sectional and perspective views are shown, from left to right in Figure 6. The structured part of the tube (8) according to the invention comprises structurings configured to carry, retain, and release water from the continuum towards the discrete volumes (7) of air, by the effect of gravity preferably combined with the capillarity effect, as the tube (2) rotates.

In a first embodiment of the structured part of the tube (8) according to the invention represented in Figures 6(a-a) to 6(a-c), this comprises two striations (18), the striations of one striation being parallel to each other and crossing the streaks of the other striation at an angle greater than zero and preferably substantially at a right angle, visible at the intersection of the directrix of the streaks (Sx). In the case illustrated in Figure 6(a-a), the ridges of the striations (18) occupy the area shown shaded (dotted) and have a ridge width (Sw). If the ridges are separated by a distance equal to Sw, then the ridges would cover 75% of the structured part of the tube (8). Figure 6(a-b) is a cross-sectional view of the ridges, in which a section of a ridge is of a triangular shape and the depth of one of the ridges (Sd) is measured along the direction normal to the inner surface of the tube (2s) not covered by a ridge and adjacent to the ridge. Figure 6(a-c) represents a perspective view of the structured part of the tube of Figures 6(a-a) and 6(a-b), in which the two families of grooves are represented.

In a second embodiment of the structured part of the tube (8) according to the invention shown in Figures 6(b-a) to 6(b-c), this comprises two striations (18), the striations of a striation being parallel to each other and crossing the striation of the other striation according to a preferably right angle measured at the intersection of the directrix of the striation (Sx). In the case illustrated in Figure 6(b-a), the ridges of the striations (18) have a ridge width (Sw). If the ridges are separated by a distance equal to Sw, then the ridges would cover 75% of the structured part of the tube (8). Figure 6(b-b) is a cross-sectional view of the ridges, in which a section of a ridge is of a curved shape, preferably semi-circular or semi-elliptical, and the depth of one of the ridges (Sd) is measured along the direction normal to the inner surface of the tube (2s) not covered by a ridge and adjacent to the ridge. There

Figure 6(b-c) represents a perspective view of the structured part of the tube of Figures 6(b-a) and 6(b-b), in which the two families of grooves are represented.

In a third embodiment of the structured part of the tube (8) according to the invention represented in Figures 6(c-a) to 6(c-c), the latter comprises a plurality of cavities distributed in a regular manner on the structured part of the tube (8). Cavities can be hemispherical, polygonal, square, etc. In the case illustrated in Figure 6(c-a), hemispherical, conical, and square cavities occupy the area shown in dotted lines. In the case of hemispherical or conical cavities, these are separated by a distance equal to twice the maximum diameter of a cavity. The hemispherical or conical cavities therefore cover on average 8.7% of the structured part of the tube (8) in this example. Figure 6(c-b) is a sectional view of the cavities, in which a section of a hemispherical cavity is of a semicircular shape, a section of a conical cavity is of a triangular shape, and a section of a square (or polygonal) cavity is square. The cavities have a cavity depth (Sd) measured along the direction normal to the inner surface of the tube (2s) not covered by a cavity and adjacent to the cavity. Figure 6(c-c) shows a perspective view of the structured part of the tube of Figures 6(c-a) and 6(c-b).

In a fourth embodiment of the structured part of the tube (8) according to the invention represented in Figures 6(d-a) to 6(d-c), the latter comprises a striation (18) composed of parallel streaks between they. In the case illustrated in Figure 6(d-a), the streaks of the striations (18) occupy the area shown in dotted lines. They can be separated by a distance equal, for example, to three times the width of a stripe (Sw). The ridges thus cover % of the structured part of the tube (8). Figure 6(d-b) is a cross-sectional view of the ridges, in which a section of a ridge is of a semi-circular, triangular or square shape. Any other profile is possible. The depth of one of the ridges (Sd) is measured along the direction normal to the inner surface of the tube (2s) not covered by a ridge and adjacent to the ridge.

Figure 6(d-c) shows a perspective view of the ridges of the structured portion of the tube 25 of Figures 6(d-a) and 6(d-b).

The structured part of the tube (8) may comprise grooves or grooves or ridges as shown in Figures 6(a-a), 6(b-a) and 6(d-a), cavities as shown in

Figure 6(c-a), or recesses, or grooves. Preferably, the structured part of the tube (8) comprises one or more striations of the tube (18) comprising a number of ridges of the tube able to take away a volume of water from the water continuum (12c) in the form of small volumes of water, towards the corresponding discrete volumes (7) of air by the combined effect of gravity and capillarity. Preferably, a groove of the tube has, - a groove depth of the tube (Sd) measured along a radial direction normal to the longitudinal axis (Z) comprised between 1 and 5 mm, preferably between 2 and 4 mm , and - a groove width of the tube (Sw) measured in a tangential direction orthogonal to a directrix of the groove (Sx), between 1 and 5 mm, preferably between 2 and 4 mm.

[0065] The striations of the tube (18) cover at least 10%, preferably at least 30% of an area of the structured part of the tube (8). Preferably, the striations cover a fraction of the area of the structured part of the tube (8) comprised between 40 and 90%, preferably between 50 and 80%.

Preferably, the structured part of the tube (8) comprises at least a first groove of the tube (18) crossing a second groove of the tube (18), each being formed by a number of grooves, as shown in Figures 1 , 6(a-a) and 6 (b-a). The ridges belonging to the same ridge of the tube (18) are substantially parallel to each other, and at least a selection of the ridges of the first ridge of the tube intersects with at least a selection of the ridges of the second ridge of the tube.

Structured part of the screw (10)

Preferably, the device according to the invention also comprises a structured part of the screw (10) covering at least 5% of an area of the surface of the screw (3s). Similar to the structured part of the tube (8), the structured part of the screw (10) is configured to transfer, with each rotation of the tube (2), a second volume of water from the continuum of water to the volumes discrete volumes (7) of air, which falls by gravity into the discrete volumes (7) of air in the form of drops and thus further cools the discrete volumes (7) of air during their compression.

As discussed for the structured part of the inner surface of the tube (2), the structured part of the screw (1) can also comprise cavities, hollows or grooves as described in Figure 6, of the same or different shape from those of the structured part of the tube (8).

[0068] Preferably, the structured portion of the screw (10) includes screw ridges formed by a number of screw ridges. A screw groove has a screw groove depth measured along a direction normal to the screw surface (2s) of between 1 and 5 mm, preferably between 2 and 4 mm, and a screw groove width measured in a direction tangential to the surface of the screw (3s) and orthogonal to a directrix of the groove of the screw (18) comprised between 1 and 5 mm, preferably between 2 and 4 mm. Preferably, the ridges of the striations of the screw cover at least 30% of an area of the structured part of the screw (10).

Preferably, the structured part of the screw (10) comprises at least two striations of the screw, each of the striations of the screw comprising a number of striations of the screw substantially parallel to each other, at least a selection of the striations of the screw of the first screw ridge crossing at least a selection of the screw ridges of the second screw ridge.

Electricity generator

According to an advantageous embodiment of the invention, the operation of the device (1) is reversible, that is to say that the motor (5) is electric and configured to operate in generator mode in order to generate a electrical energy when a rotor of the motor is coupled and driven in rotation by the tube (2) in rotation around the longitudinal axis (Z). During operation of the device in generator mode, the tube (2) is rotated around the longitudinal axis (Z) in a direction opposite to that associated with the compression of the discrete volumes (7) of air. The rotation of the tube is activated by the compressed air transferred from the reservoir (9) to the inside of the tube (2) near the downstream opening (2d). As the tube comprises a continuum of water (12c), a discrete volume (7) of compressed air must, in order to rise to the surface of the body of water, activate the rotation of the screw (3) (and therefore of the tube ) to pass successively from one thread to the next, until reaching the upstream opening (2u). The discrete volumes (7) of air coming from the submerged tank (9) are decompressed by the rotation of the tube (2), as they rise step by step towards the upstream opening (2u) by each rotation the screw (3) and the tube (2).

To recover the stored energy, the compressed air from the submerged tank (9) is reinjected into the screw in order to be decompressed by going up along the screw (3) and thus causing the rotation of the screw ( 3) and the tube (2) which also drives the rotation of the rotor of the motor (5) which operates in generator mode. In the embodiment of the invention shown in Figure 4, during compression, the compressed air leaves the tube through the downstream opening (2d) of the screw and enters the flexible bladder. Going up towards the top of the flexible bladder, the air escaping from the downstream opening decompresses slightly, depending on the difference in depth between the downstream outlet (2d) of the tube and the air-water interface in the submerged tank (9). The air entering the flexible bladder therefore has a lower pressure than that of the downstream opening (2d) and cannot be reinjected into the downstream opening (2d) without undergoing additional compression. To overcome this lack of reversibility of the circulation of compressed air between the submerged tank (9) and the downstream opening (2d), and to avoid the implementation of additional compression means, an air evacuation duct tablet can be installed to allow fluid communication between the submerged tank and the inside of the tube (2), as shown in Figure 4.

Preferably, a compressed air outlet orifice from the compressed air tank (9) to the compressed air discharge duct is positioned at an upper end of the submerged tank, that is to say at a location of the tank closest to the surface of the water body, in order to be able to empty all the compressed air stored in the submerged tank and fully exploit its capacity. As the submerged tank is emptied of air, the air/water interface of the tank rises inside the submerged tank until it reaches the upper end of the submerged tank when all of the air tablet has been evacuated from it. In order to be able to inject all of the compressed air from the submerged tank into the tube (2) and to recover a maximum of energy by decompression of the compressed air, a compressed air inlet orifice of the conduit evacuation of compressed air towards the inside of the tube (2) is preferably positioned in the vicinity of the downstream opening (2d) in order to optimize the recovery of energy during the decompression of the compressed air coming from the reservoir, and at a depth less than the upper end of the reservoir. It is preferable to optimize the position of the tube inlet (2). It is therefore necessary to maximize the depth of the upper end of the tank, which must necessarily be deeper than the inlet, in the absence of a means of compressing the air. For this reason, it is preferable to limit the height of the tank above the downstream opening of the tube (2). For a given tank volume, this means that it is better to expand the tank dimensions laterally.

The compressed air exhaust duct may include a controllable valve configured to open or close the compressed air exhaust duct and to control the flow of compressed air reinjected from the submerged tank into the tube (2 ).

Preferably, the device according to the invention is therefore reversible and configured to generate electrical energy by decompressing the compressed air stored in the submerged tank (9), by causing it to rise along the screw (3) by discrete volumes (7) of air causing the tube (2) to rotate around the longitudinal axis (Z). The tube (2) coupled in rotation with the rotor of the electricity generator driving the rotor of the generator in rotation, the generator then producing electrical energy which can be consumed. In the device according to the invention, the presence of the structured parts of the tube (8) and preferably of the screw (10) increase the work extracted during the decompression of the discrete volumes (7) of air in the tube by heating the air in decompression phase.

Indeed, the temperature of the discrete volumes (7) of air during decompression and rising from the vicinity of the downstream opening (2d) towards the upstream opening (2u) decreases with the pressure. In the case of air decompression during which the heat exchanges between the discrete volumes (7) and the water continuum are weak, the decompression is close to an adiabatic decompression represented in Figure 5, segment ( C) of the continuous curve, and the temperature of the discrete volumes of air can drop to temperatures below 0°C and to temperatures of the order of -100°C and below depending on the rate of decompression. As during the compression of the discrete volumes (7) of air, the structured parts of the tube (8) and preferably of the screw (10) in the device according to the invention are configured to transfer with each rotation of the tube (2) a volume of water collected in the continuum of water (12c) towards the discrete volumes (7) of air, the volume of water falling by gravity into the discrete volumes (7) of corresponding air in the form of drops ( 12g), thus heating the discrete volumes (7) of air during the decompression of the latter. The discrete volumes (7) of air are thus reheated during decompression, increasing the work that can be extracted from decompressing the air, thus approximating an isothermal cycle.

In Figure 5, a compression-decompression cycle of a discrete volume of air by a device according to the invention is represented by the dashed curve marked "INV". By comparing the segments (C) of the continuous curve representing an adiabatic cycle and of the dotted curve representing an isothermal cycle that those skilled in the art would like to achieve, it can be seen that the cycle according to the invention is clearly detached from the adiabatic cycle and approaches the isothermal cycle (without however reaching it). Thanks to the better heat exchange between the air and the surrounding water, the energy that can be supplied by the device by the decompression of a given quantity of compressed air from the submerged tank (9) is therefore greater than that obtained by a device according to the prior art, as described in BE1024212 and even in US2012/0119510. The increase in heat exchange between the water in the continuum and the discrete volumes of air optimizes the recovery of the energy stored in the form of compressed air in the submerged tank (9). In addition, it decreases the stresses on the materials in contact with the discrete volumes of air by significantly increasing the sub-zero temperature of the discrete volumes of air with which these materials are in contact.

During the decompression of the discrete volumes (7) of air, the heat exchanges between them and the water continuum induces a decrease in the temperature of the water continuum. Preferably, the device according to the invention is then configured to allow a transfer of heat from the water of the body of water outside the tube (2) towards the continuum of water in order to limit the decrease in temperature of the continuum of water, this decrease in temperature negatively impacting the transfer of heat between the continuum of water and the discrete volumes (7) of air. The water in the body of water outside the tube (2) then acts as a heat reservoir. It suffices to allow a flow of water allowing the entry of water from the body of water into the tube through one of the openings upstream or downstream of the tube to form the continuum of water (12c) and allowing the exit of the water continuum through the other of the upstream or downstream openings of the tube, in order to ensure continuous renewal of the water of the water continuum (12c) and thus to maintain its temperature substantially constant.

[0075] Figure 5 is an example of a graph representing the evolution of the normalized volume, (V / V7), of a discrete volume (7) of given air of initial volume (V7) according to its depth under the surface of the water body, h (m)/. The depth (h) is directly proportional to the pressure of the discrete volume (7) of air by the relation, p [bar] = (h [m] / 10 [m / bar]) + 1 [bar]. The cycle comprises four phases (A), (B), (C), (D) indicated in Figure 5 and traversed in the direction indicated by the arrows, during which the state variables which are the temperature, the volume V / V7, and the pressure proportional to the depth under water h (m) of the discrete volume of air vary. As indicated above, the solid curve represents an adiabatic cycle (i.e., without heat exchange with the outside), the dotted curve represents an isothermal cycle, which the person skilled in the art would like to achieve, and the dashed curve represents a compression cycle. - decompression with a device according to the present invention. The evolution of a discrete volume (7) of air during the different phases (A), (B), (C), (D) of a compression-decompression cycle is discussed. (A) Compression in which the volume of air decreases with increasing depth h(m) and pressure (p) at which it is located. During a first stage of compression, between approximately 0 and 15 m depth, the temperature gradient between the discrete volume of air and the continuum of water are negligible and therefore the heat exchanges are weak and the pressure and the air temperature rise almost adiabatically following the continuous curve of an adiabatic cycle.

Between about 15 m and 50 m depth, the temperature of the air volume increases relative to that of the water temperature of the continuum. Without a cooling source, the compression continues adiabatically along the continuous curve. In order to increase the thermal exchanges between the discrete volume of air and the continuum of water the drops (12g) falling from the structured part of the inner surface of the tube through the discrete volume of air. Thanks to this cooling, the dashed curve of the cycle according to the invention detaches itself from the adiabatic cycle and tends towards the isothermal cycle, without however reaching it. Considering that the work (W) necessary to compress the discrete volume of air is the integral under the curve included in a segment defined by two volume values (W= [P dV), one can visualize the saving of work obtained by a device according to the invention with respect to an adiabatic cycle. (B) Cooling of the discrete volume of air stored in the submerged tank (9). The decrease in temperature of the discrete volume (7) of air is the result of heat exchange with the water in the body of water, in a substantially isobaric manner. The volume of air stored in this way decreases with temperature. At the start of this cooling phase, the adiabatically compressed air has a higher temperature and volume than the isothermal compressed air, and the air compressed with the device of the present invention has a volume between adiabatic and isothermal compressions. In all cases, the compressed air finally reaches the same volume corresponding to the temperature and pressure prevailing in the tank (9).

This loss of heat translates into a loss of stored energy that cannot be recovered. (C) Discrete air volume decompression, in which air volume increases with decreasing depth h(m) at which it is located. During a first stage of decompression (between approximately 50 m and 35 m in Figure 5), the heat exchanges between the discrete volume of air and the continuum of water are negligible because the temperature gradient between the air and water is not important. The air pressure and temperature decrease almost adiabatically following the continuous curve in Figure 5. When the temperature gradient between cold air and

Warmer calf increases with the decompression level (between about 35 m and 0 m depth in Figure 5), the contact between the drops (12g) falling from the ridged part of the inner surface of the tube and the air of the volume discrete air heats the air cooled by the decompression, and the curve treated according to the present invention detaches from the continuous adiabatic curve and approaches, without joining it, the dotted curve of an isothermal cycle. The volume corresponding to isothermal decompression is higher than for adiabatic decompression, and the work extracted from air decompression is therefore higher in the isothermal case. The device according to the invention makes it possible to recover the energy at a level substantially higher than an adiabatic cycle, and the volume of the discrete volume of air at the end of decompression, that is to say when the latter escapes in the atmosphere above the body of water through the upstream opening (2u) at the end of the decompression, approaches the theoretical 90% of the initial volume of the discrete volume of air. (D) Heating of the discrete volume of air, during which the temperature of the decompressed air increases in an isobaric way by heat exchange with the air of the atmosphere of the body of water until reaching the temperature of this one , equal to the initial temperature of the discrete volume of air at the start of the cycle. This energy stored in the discrete volume of air cannot be recovered.

The adiabatic and isothermal cycles represented in FIG. 5 are obtained under very strong hypotheses which are difficult to obtain in a device of the type of that of the present invention. For example, the cycle comprising only adiabatic compressions and decompressions (continuous curve) is obtained under the assumption that the volumes of air are perfectly thermally insulated, and the isothermal cycle (dotted curve) is obtained under the assumption that the exchanges of heat between the discrete volumes of air and the continuum of water are perfect so that the temperature of the discrete volumes of air does not vary. In practice, in a device of the type of the device of the present invention, a cycle traversed by a discrete volume of air is neither completely adiabatic nor completely isothermal.

The objective, however, is to push it towards an isothermal cycle. As illustrated in the

Figure 5, the device makes it possible to approach an isothermal cycle considerably, thus notably improving the efficiency of the energy storage device compared to an adiabatic system or close to it of the prior art.

On the graph of Figure 5, the losses or dissipations associated with the work of compression and decompression of the discrete volume (7) of given air are proportional to the interior area of the hysteresis cycles represented, and therefore lower in the isothermal case (dotted curve) with respect to the adiabatic case (continuous curve) and the invention is indeed between the two extremes, relatively close to the isothermal hysteresis. A storage efficiency is defined as a ratio of an energy or mechanical work extracted from the device during the decompression of a given quantity of air on an energy or mechanical work supplied to the device during the compression of this same given quantity of air. 'air.

In the preferable case of a device according to the invention configured to be reversible in order to be able to compress and decompress the air, the heat exchanges between the air and the continuum of water make it possible to bring the cycle thus traversed closer to an isothermal type cycle and to move it away from an adiabatic type cycle, thus reducing the hysteresis area associated with the cycle and therefore the losses associated with the storage of energy in the form of compressed air. Consequently, the efficiency of the energy storage is improved in the device according to the invention compared to that of the devices of the prior art.

Device for collecting (11) distilled water (12)

[0079] During the compression of the discrete volumes (7) of air, these heat up and enter the submerged tank (9) at a temperature higher than that of the water in the body of water surrounding the submerged tank. The air thus compressed contains a certain partial pressure of water vapor, the water vapor being derived from the partial pressure of water vapor in the atmosphere above the body of water in the vicinity of the opening upstream (2u), and an evaporation of the drops (12g) from the continuum of heated water vaporized during the compression of the air. During storage, the compressed air in the submerged tank (9) cools by transmitting its heat to the water surrounding the tank until it reaches the temperature of

Calf from the body of water surrounding the submerged tank. During this process, the saturation vapor pressure of the water in the stored compressed air decreases with temperature, causing condensation of the water vapor inside the submerged tank (9) forming distilled water ( 120).

Preferably, the submerged tank (9) of the device according to the invention comprises a device (11) for collecting distilled water (12d) configured to collect distilled water (12d) obtained by condensation of the compressed air reserve. during its cooling in the submerged tank (9), as shown in Figures 2 and 3. The distilled water collection device (11) is further configured to discharge the distilled water thus collected towards the surface of the body of water (13), through a distilled water discharge conduit (14), and preferably includes a receptacle (15) in fluid communication with the distilled water discharge conduit (14).

In Figure 2, the distilled water collection device (11) is internal to the submerged tank (9), and the water vapor which condenses on contact with the compressed air with an inner surface of the tank ( 9s) cooled by the water of the body of water in contact with the wall of the tank (Op) forms drops flowing by the effect of gravity towards the opening of the tank (21). A receptacle (15) similar in shape to a gutter overhanging the opening of the tank (21) is configured to collect the drops of distilled water flowing along the wall. The wall of the reservoir (9p) comprises an orifice capable of ensuring fluid communication between the receptacle (15) and the distilled water discharge pipe (14).

In another embodiment of the distilled water collection device (11) according to the invention shown in section in Figure 3, the latter comprises a flexible cover configured to bring the drops of condensed distilled water to the contact of the inner surface of the reservoir (9s) towards the receptacle (15). The receptacle (15) and the flexible cover have a symmetry of revolution, and the receptacle is configured to float at the air/water interface of the tank by means of a buoy having the shape of a torus. Distilled water (12) is discharged from the receptacle (15) to the surface of the body of water via the distilled water discharge conduit (14) in fluid communication with the receptacle (15). Such a distilled water collection device (11) is configured to operate at different compressed air filling levels of the tank (9) thanks to the buoy. The receptacle (15) fixed to the buoy is configured to rise and fall inside the submerged tank (9) following the level of the air/water interface of the tank, itself depending on the level of filling with compressed air of the reservoir (9). The flexible cover is attached to the buoy and also adapts to variations in the level of the air / water interface of the tank thanks to its flexibility.

[0083] Preferably, the distilled water discharge conduit (14) of the distilled water collection device (11) according to the invention comprises a valve configured to allow a user to control the flow rate of distilled water flowing through the distilled water discharge pipe (14).

REF [DERNTON 6 Floating device LI 8 [Partestucturêedutbe 9 [Résenorimme

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Claims (13)

1. Energy storage device (1) comprising: - a tube (2) extending along a longitudinal axis (Z) normal to a cross section of the tube with a tube length (Lt) measured along of the longitudinal axis (Z) and separating an upstream opening (2u) and a downstream opening (2d) of the tube (2), - a screw (3) internal to the tube (2), in the form of a helical thread extending along and centered on the longitudinal axis (Z), e Comprising an outer radial end (3e) of the screw (3) joined continuously and rigidly and tightly to an inner surface of the tube (2s) on an entire length of the screw, and e defining a continuous helical fluid passage inside the tube (2) between the upstream opening (2u) and the downstream opening (2d), - an anchor (4) configured to anchor the downstream opening (2d) at the bottom of a body of water at a depth (H), - a motor (5), preferably an electric motor, configured to rotate the tube (2) and the screw ( 3) around the longitudinal axis (Z), - a floating device (6) configured to keep at least part of the upstream opening (2u) emerged above a surface (13) of the body of water (12) when the downstream opening (2d) is anchored to the bottom of the body of water (12), so that: e the at least partially emerged upstream opening (2u) is at a distance (L) of a vertical of the downstream opening (2d) measured along a horizontal axis normal to the vertical, such that a ratio (L / H) of distance (L) to depth (H) is less than 1.75, e during the rotation of the tube (2) and the screw (3) driven by the motor (5) around the longitudinal axis (Z), discrete volumes (7) of air separated from each other by a continuum of water (12c) of the body of water are driven by the rotating screw from one atmosphere of the upstream opening (2u) towards the downstream opening (2d), compressing the discrete volumes (7) of air at the as the discrete volumes (7) of air move towards the downstream opening (2d), - a submerged tank (9) configured to store a reserve of compressed air, the submerged tank (9) being in fluid communication with the downstream opening (2d) of the tube (2) and anchored to the bottom of the body of water so that the discrete volumes (7) of air reaching the downstream opening (2d) can fill the submerged tank ( 9), which is preferably a bladder tank comprising a flexible wall (9p), characterized in that the inner surface of the tube (2s) comprises a structured part of the tube (8) representing at least 20% of an area of the inner surface of the tube (2s) and configured to lift and entrain a volume of water from the continuum of water towards the discrete volumes (7) of air with each rotation of the tube (2), which falls by gravity into the discrete volumes of air in the form of drops (12g), the at least partial evaporation of which cools the discrete volumes (7) of air as they are compressed. 2. Device according to claim 1, further comprising a device for collecting distilled water (11) configured to, - collect distilled water (12) obtained by condensation of the reserve of compressed air during its cooling in the tank immersed (9) and for - evacuating the distilled water thus collected towards the surface of the body of water (13), through a distilled water evacuation pipe (14), the distilled water collection device ( 11) preferably comprising a receptacle (15) in fluid communication with the distilled water discharge pipe (14). 3. Device according to claim 1 or 2, in which the structured part of the tube (8) comprises one or more ridges of the tube (18) formed by a number of ridges of the tube, in which a ridge of the tube has, - a depth of the groove of the tube measured along a radial direction normal to the longitudinal axis (Z) comprised between 1 and 5 mm, preferably between 2 and 4 mm, and - a width of the groove of the tube measured in a tangential direction orthogonal to a directrix of the streak, comprised between 1 and 5 mm, preferably between 2 and 4 mm, the striations of the tube (18) covering at least 30% of an area of the structured part of the tube (8). 4. Device according to any of the preceding claims, wherein a surface of the screw (3s) comprises a structured part of the screw (10) representing at least 5% of an area of the surface of the screw (3s). and capable of transferring, on each rotation of the tube (2), a second volume of water from the continuum of water to the discrete volumes (7) of air, which falls by gravity into the discrete volumes (7) of air in the form of drops (12g), of which The at least partial evaporation thus further cools the discrete volumes (7) of air during the compression of the latter. The device of claim 4, wherein the structured portion of the screw (10) comprises screw ridges formed by a number of screw ridges, one screw ridge having a screw ridge depth measured in a direction normal to the surface of the screw (25) comprised between 1 and 5 mm, preferably between 2 and 4 mm, and a groove width of the screw measured in a direction tangential to the surface of the screw (3s) and orthogonal to a director of the groove of the screw (18) of between 1 and 5 mm, preferably between 2 and 4 mm, the grooves of the screw covering at least 30% of an area of the structured part of the screw ( 10). 6. Device according to any one of claims 3 or 5, wherein the structured part comprises a first striation and a second striation, each of the first and second striations is formed by a number of streaks substantially parallel to each other, and in which at at least one selection of the stripes of the first stripe intersects with at least one selection of the stripes of the second stripe. 7. Device according to any one of the preceding claims, in which the motor (5) is electric and is further configured to act as a generator and to generate electrical energy when a rotor of the motor is rotated by the tube. (2) and the screw (3) in rotation around the longitudinal axis (Z), the rotation of the tube (2) and of the screw being driven by a rise by an interior of the tube (2) towards the surface of the plane of compressed air water introduced into the tube from the submerged tank. 8. Device according to claim 7, in which the structured part of the tube (8) is configured to drive a volume of water from the continuum of water towards the discrete volumes (7) of air with each rotation of the tube (2) , which falls by gravity into the discrete volumes of air in the form of drops (12g), thus heating the discrete volumes (7) of air as they are decompressed. 9. Device according to any one of the preceding claims, further comprising a guide shaft (16) extending along the longitudinal axis (2). 10. Device according to claim 9, further comprising a gap (17) surrounding a side surface of the shaft (16s) and separating the screw (3) from the guide shaft (16) over an entire length of the shaft, a width of the gap normal to the side surface of the shaft (16s) preferably being between 1 mm and 10 cm. 11. Device according to any one of the preceding claims, in which the tube length (Lt) is between 10 m and 300 m, preferably between 20 m and 200 m, preferably between 50 m and 150 m. 12. Device according to any one of the preceding claims, in which a nominal speed of rotation of the tube (2) driven by the motor (5) is between 1 revolution / min and 600 revolution / min, preferably between 10 revolution / min and 240 rpm, preferably between 30 rpm and 120 rpm, preferably between 50 rpm and 80 rpm. 13. Device according to any one of the preceding claims, in which the tube (2) has a circular section with an internal diameter of between 5 cm and 10 m, preferably between 10 cm and 5 m, preferably between 20 cm and 2 Mr.