Underground storage system for fluid storage

Abstract

The invention relates to an underground storage system (1) for fluid storage, comprising a recess (2) having a bottom (3), a support element (4) comprising at least one opening (7) suitable for receiving an assembly element (18), at least one tank (10) having a longitudinal axis (l), a lower end (14) and an upper end (12), a first closure means (16) suitable for closing the tank (10) at its lower end (14), and a second closure means (17) suitable for closing the tank (10) at its upper end (12), the upper end (12) being suitable for being assembled to the support element (4) via the assembly element (18) so that the tank (10) is suspended inside the recess (2) and an axial clearance (G) suitable for absorbing an axial thermal expansion of the tank (10) remains between the first closure means (16) and the bottom (3).

Description

Description Title of the invention: Underground storage system for fluid storage technical field [1] The invention relates to the field of underground storage, particularly for the storage of fluids. More specifically, the invention relates to the field of underground storage systems for the storage of gases, for example, for the storage of hydrogen or oxygen. Even more specifically, the invention relates to the field of high-pressure fluid storage. "High pressures" is understood to mean pressures ranging from 100 bar to 1200 bar, and more specifically from 200 bar to 500 bar. [2]The invention also relates to an underground storage method for the storage of fluids. Technological background [3]One of the emerging technologies for reducing the carbon footprint of industries is the use of hydrogen generated by renewable processes, such as wind or solar power. The electricity produced by these renewable processes can be used by an electrolyzer to produce hydrogen and oxygen, notably from the electrolysis of water. [4] This large quantity of hydrogen, produced by electrolysis, must be compressed and stored so that it can then be used on demand to continuously power either vehicles, such as trucks or cars, or to supply the electricity grid during peak consumption periods. In this case, to produce this electricity, the hydrogen can power either a turbine or hydrogen fuel cells. As for oxygen, it may be advantageous to store it for use in fields such as agriculture or for medical purposes. [5]Some gases, such as hydrogen, are known to be difficult to contain. For example, their low density requires storage at high pressure, Their small molecule size and low viscosity make them prone to leaks. Therefore, they must be stored in a perfectly sealed system capable of storing large quantities of gas while meeting strict safety standards, particularly to minimize the risk of leaks. Underground storage is also advantageous for consumers and industrial users because it significantly reduces the surface area required for these storage facilities. [6]Such underground fluid storage systems are generally installed at depths of between 10 meters and 50 meters. These storage systems can be installed in terrains of different geological natures, for example solid rocks such as granite or basalt, or any other type of underground geological structure. [7] In this regard, the prior art described in US patent 10837601: a device comprising a unit fixed in a single underground borehole, the unit comprising a plurality of separate containers fixed by means of at least one retaining device, each container of the plurality of separate containers having at least one plug comprising an inlet hole, an outlet hole, and a central hole, the central hole being positioned eccentrically with respect to a radial center of a top surface of the plug, the unit being fixed in the single underground borehole by cement extending continuously between the plurality of containers to surround the unit and make contact with a lateral wall of the underground borehole. Furthermore, the unit is fixed to an anchoring element near the bottom of the underground borehole.The drawback of such a system is that, to hold the containers in place in the underground borehole, they are secured in cement and attached at the bottom to the anchoring element. This makes maintenance operations complex, particularly when it is necessary to remove a container from the unit for replacement, as the cement and the anchoring element prevent such removal. However, this type of operation may be necessary, especially in the event of a leak, for inspection, or maintenance. Consequently, the maintenance and safety of such a system are not optimal. Furthermore, securing the containers in cement in this way results in significant compressive stress on the container walls, which increases the risk of leakage. Summary [8] To overcome the above drawbacks, a first objective of the invention is to facilitate maintenance operations on an underground fluid storage system, such as for gases. Furthermore, a second objective of the invention is to enable the storage of large quantities of fluids at high pressures while complying with strict safety standards. Finally, a third objective of the invention is to allow the underground storage of several different fluids, at different pressures, in a single device, within a single storage system. [9]Thus, the invention provides an underground storage system for the storage of fluids, said storage system comprising: - a recess suitable for construction in a plot of land, said recess having a bottom, - a support element comprising at least one opening suitable for receiving an assembly element, - at least one reservoir, said reservoir having a longitudinal axis (1), a lower end and an upper end, - a first closing means suitable for closing the tank at its lower end, and a second closing means suitable for closing the tank at its upper end, said upper end being suitable for being assembled to the support element via the assembly element so that the tank is suspended inside the recess and an axial clearance suitable for absorbing an axial thermal expansion of said tank remains between the first closing means of the tank and the bottom of the recess.

[0010] Thanks to these features, the tank's integrity is not compromised by mechanical stresses related to its axial thermal expansion during fluid injection and withdrawal operations. Indeed, the axial clearance prevents axial thermal expansion from compressing the tank against the bottom of the recess during such operations. Repeated applications of such stresses weaken the tank's seal, particularly at the closure mechanism. [1 l]Furthermore, unlike prior art devices, such a system eliminates the need for cement to secure the tank. The tank is therefore only fixed to the support element. The tank is thus suspended in a fluid. any imperfection originating from the environment in which the system is placed. For example, the tank may be suspended in air or water from surrounding rock formations. Therefore, removing a tank from the system is both possible and simple.

[0012] According to one embodiment, the tank is suspended in a substantially vertical manner.

[0013] According to one embodiment, the reservoir is composed of at least one metal tube, said metal tube having at least one termination having at least one threaded portion.

[0014] According to one embodiment, the metal tube has two terminations, each of said two terminations having at least one threaded portion.

[0015] In one embodiment, the tank consists of at least two metal tubes joined by screws to form a column of tubes. The connection between two metal tubes can be made by an integral connection or by means of a connecting piece, such as a sleeve.

[0016] According to one embodiment, the axial play satisfies the following inequality: [Math 1] Where: G is the length of the axial clearance expressed in meters, L represents the length of a reservoir (10) expressed in meters, P represents the geothermal gradient expressed in degrees Celsius per meter, a represents the coefficient of thermal expansion of the metal expressed in Celsius 1 .

[0017] The geothermal gradient P varies depending on the geological formation in which the storage system is placed. Thus, P is such that 0.02° / m < p < 2° / m. 'a' represents the coefficient of thermal expansion of the metal expressed in degrees Celsius. 1 The coefficient of thermal expansion, a, varies depending on the type of metal used in the tubes to form a tank. Thus, a is such that 8*10' 6 °C' 1 < a < 18*10' 6 °C' 1 .

[0018] Using threaded tubes to construct the tank facilitates assembly and disassembly. This is particularly advantageous when a tube needs to be replaced. Maintenance and servicing of the tank are therefore simplified, and system safety is increased.

[0019] According to one embodiment, the reservoir consists of a single tube.

[0020] In one embodiment, the tubes used to construct a reservoir are metallic tubes, preferably threaded metallic tubes. For example, these could be titanium metal tubes, or steel tubes of the type used in the oil and gas industry, particularly the tubes used to construct oil and / or gas production wells.

[0021] In one embodiment, the first and / or second closing means is adapted to close the tank by screwing. In this case, the thread of said closing means may be male or female. In addition to the thread, the first and / or second closing means may also include a metal bearing surface. The presence of a metal bearing surface contributes to improving the sealing of the closure, which is particularly advantageous for gas storage, especially for hydrogen storage, a gas particularly prone to leakage.

[0022] According to one embodiment, the first closing means and / or the second closing means is a weld.

[0023] Screw-type closures are preferred to welds because they do not significantly alter the tank wall thickness at the point of closure. Therefore, with screw-type closures, the tank's mechanical properties at the closure remain unchanged. Furthermore, in the case of hydrogen storage, they prevent potential hydrogen corrosion problems that can occur with welds.

[0024] According to one embodiment, the support element comprises an upper surface 54 and a lower surface 56.

[0025] In one embodiment, the support element is placed on the ground or fixed to a concrete or cement slab, said slab being poured onto the ground surface. The support element may be fixed to the concrete or cement slab by any means known to a person skilled in the art.

[0026] According to one embodiment, the support element is a circular cylindrical plate or an angular geometric shape.

[0027] According to one embodiment, the support element has at least a surface area between 0.2 m 2 and 10 m 2 , preferably between 0.7 m 2 And

[0028] According to one embodiment, the support element can be a metal plate.

[0029] According to one embodiment, at least one opening is a through hole made in a thickness of the support element.

[0030] According to one embodiment, at least one opening in the support element is a circular opening.

[0031] According to one embodiment, the assembly element is fixed to the upper end of the tank.

[0032] According to one embodiment, the assembly element is welded or screwed to the upper end of the tank.

[0033] According to one embodiment, the assembly element is tubular and has a collar, said collar being able to rest on a surface of the support element so that when the assembly element is fixed to the upper end of the tank, said tank is suspended from the support element by means of the assembly element.

[0034] According to one embodiment, the system comprises a plurality of tanks, each tank having a longitudinal axis 1, a lower end and an upper end, said upper end of each tank being able to be assembled to the support element via an assembly element so that each tank is suspended inside the recess.

[0035] Such a system, comprising multiple tanks, allows for tanks of varying lengths within the same storage system. This is particularly advantageous for avoiding unnecessarily high loads on the support structure. Furthermore, the length of a tank can be adjusted to facilitate pressure increases or decreases as needed, depending on the fluid's storage conditions. Thus, different fluids can be stored within the same system.

[0036] According to one embodiment, each tank is connected to its own fluid supply and fluid withdrawal circuit so that when the storage system includes a plurality of tanks, said tanks can be independent of each other.

[0037] Thanks to these characteristics, it is possible to store larger quantities of fluid. In particular, for the same depth of the excavation, it is possible to to store a large quantity of gas at very high pressures in a plurality of tanks. Furthermore, with such a system it is possible to store different fluids, each fluid being able to be stored under conditions, including temperature and pressure conditions, that are specific to the fluid and its intended use.

[0038] In one embodiment, each tank can be equipped with sensors, such as pressure gauges, thermometers, leak detectors, or humidity sensors. This allows for monitoring the pressure and detecting leaks in each tank. This is advantageous both for system safety and when the tanks do not all store the same fluid. These sensors can also be placed directly within the recess.

[0039] According to one embodiment, the system comprises a single reservoir.

[0040] According to one embodiment, the length L of a reservoir is between 1 meter and 3000 meters, preferably between 10 meters and 2500 meters, even more preferably between 20 meters and 500 meters.

[0041] According to one embodiment, the storage system comprises between 1 and 26 tanks, preferably between 1 and 14 tanks, even more preferably between 1 and 6 tanks.

[0042] According to one embodiment, the excavation has a depth of between 10 meters and 2500 meters, preferably between 20 meters and 500 meters, said depth being measured between the ground surface and the bottom of the excavation.

[0043] According to one embodiment, the excavation includes at least one lining.

[0044] Depending on the method of construction, the tanking is made of concrete, cement, or steel.

[0045] In one embodiment, the tanking is a tanking tube. The tanking tube can be cemented.

[0046] In one embodiment, the ground consists of solid rock, such as granite or basalt. The advantage of constructing the storage system in ground composed of solid rock is that it eliminates the need for lining, thus simplifying system installation. Conversely, lining is necessary when the system is constructed in soft ground.

[0047] Depending on one embodiment, the hollowing can be carried out by drilling or by excavation.

[0048] According to one embodiment, the recess has an average diameter of between 0.5 meters and 4.5 meters, preferably between 1 meter and 3 meters.

[0049] Another object of the invention relates to an underground storage method for the storage of fluids, said method comprising the following steps: - to create a recess (2) in a plot of land (40), said recess (2) having a bottom (3), - provide a support element (4) comprising at least one opening (7) suitable for receiving an assembly element (18), - provide at least one tank (10), said tank (10) having a longitudinal axis (1), a lower end (14) and an upper end (12), - provide a first closing means (16) suitable for closing said reservoir (10) at its lower end (14), and a second closing means (17) suitable for closing the reservoir (10) at its upper end (12), - assemble said upper end (12) to the support element (4) via the assembly element (18) so that the tank (10) is suspended inside the recess (2) and an axial clearance (G) capable of absorbing an axial thermal expansion of said tank (10) remains between the first closing means (16) of the tank (10) and the bottom (3) of the recess (2). Definitions

[0050] The "lower end" of the tank refers to the end of the tank that is located near the bottom of the excavation. This "lower end" is defined in contrast to the "upper end" of the tank, which is located near the support element and therefore the ground surface.

[0051] The term "axial clearance" refers to a length extending along the longitudinal axis 1 of the tank, measured between the first tank closure and the bottom of the recess. It should be noted that a tank may not be perfectly vertical. In this case, the longitudinal axis 1 of the tank is at an angle to the vertical in the (x; y) coordinate system. This angle has a maximum value of 15°. In this case, the axial clearance G is measured by orthogonal projection onto the vertical axis through a point on the first closure closest to the bottom of the recess. In other words, the clearance axial always corresponds to the shortest distance, measured between the bottom of the recess and the first closing means.

[0052] A "threaded metal tube" is defined as a tube comprising at least one end with at least one threaded portion, suitable for assembly with another threaded metal tube comprising at least one end with at least one additional threaded portion. The thread may be male or female.

[0053] The term "bottom of the excavation" refers to the surface at the bottom of the excavation. Thus, when the excavation is lined and the lining is cemented, the term "bottom of the excavation" designates the surface of the cement layer at the bottom of the excavation. When the lining is not cemented, the term "bottom of the excavation" simply refers to the surface of the ground at the bottom of the excavation. Brief description of the figures

[0054] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of several particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings.

[0055] It should be understood, however, that the present application is not limited to the specific arrangements, structures, features, embodiments, and appearance indicated. The drawings are not drawn to scale and are not intended to limit the scope of the claims to the embodiments depicted in those drawings.

[0056] Therefore, it must be understood that when features mentioned in the claims are followed by references, such references are included solely for the purpose of improving the understanding of the claims and do not in any way limit their scope.

[0057] Figure 1 is a schematic cross-sectional view of a storage system according to one embodiment of the invention.

[0058] Figure 2 is an isolated three-dimensional diagram of the support element of the storage system illustrated in Figure 1.

[0059] Figure 3 is an isolated three-dimensional diagram of an alternative support element that can be used in one embodiment of the invention.

[0060] Figure 4 is a three-dimensional diagram of an assembly element that can be used in the storage system illustrated in Figure 1. Description of the implementation methods

[0061] Figure 1 illustrates a cross-sectional view of a storage system 1 according to an embodiment of the invention, in a coordinate system (x; y). The x-axis of the coordinate system (x; y) is a horizontal axis, and the y-axis of the coordinate system (x; y) is a vertical axis.

[0062] The storage system 1 includes a recess 2 made in a terrain 40, a support element 4 placed on a surface of a soil S of the terrain 40, and six tanks 10 suspended from the support element 4 in the recess 2 (only four tanks are visible in Figure 1).

[0063] The recess 2 has a bottom 3 and includes a casing 30. The recess 2 can be obtained by drilling or excavation, and has a depth of 500, measured between the surface of the ground S and the bottom 3. The recess 2 is of substantially circular cylindrical shape and has an average diameter of 4 meters.

[0064] The lining is made of cement and extends vertically from the surface of the ground S to the bottom 3 of the excavation 2.

[0065] As shown in Figures 1 and 2, the support element 4 is a circular cylindrical plate having a central body 50 and a flange 52, said flange 52 having a lower surface 56 resting on the ground S. The central body 50 has a first thickness E that can be between 10 mm and 500 mm. The flange 52 has a second thickness e that can be between 5 mm and 200 mm. In the embodiment illustrated in Figures 1 and 2, the support element 4 is a metal plate in which the first thickness E is equal to 250 mm, and the second thickness e is equal to 100 mm.

[0066] The support element 4 further comprises an upper surface 54, said upper surface 54 being opposite the lower surface 56 of the collar 52, and said upper surface 54 having an area equal to 8.6 m² 2

[0067] As illustrated in Figure 2, the support element 4 also includes six openings 7. The openings 7 are through holes, provided in the first thickness E of the body 50 of the support element 4. According to Figure 3, which illustrates a support element 4 that can be used in an embodiment according to the invention, the support element 4 includes fourteen openings 7 provided in the first thickness E of the body 50.

[0068] Each tank 10 is suspended from the support element 4 by means of an assembly element 18. Thus, for each tank 10 of the storage system 1, an axial clearance G remains between, on the one hand, the first means of Closure 16, which closes the tank 10 at its lower end 14, and on the other hand, the bottom 3 of the recess 2. This axial clearance G serves to absorb the axial thermal expansion of the tank 10, which occurs particularly during filling and emptying operations. Thus, for each tank 10, the dimensions of the axial clearance G, and in particular its length, depend directly on the surrounding conditions of the storage system 1, especially the temperature and pressure conditions, and the capacity of the tank 10 to expand when subjected to variations in temperature and pressure, particularly during filling and emptying operations. Therefore, the axial clearance G of any tank 10 in the storage system 1 satisfies the following inequality: [Math 1] Where: G is the axial clearance length expressed in meters. L represents the length of a reservoir 10 expressed in meters. P represents the geothermal gradient expressed in degrees Celsius per meter. The geothermal gradient P varies depending on the geological formation in which the storage system 1 is placed. Thus, P is such that 0.02° / m < p < 2° / m. a represents the coefficient of thermal expansion of the metal expressed in degrees Celsius. 1 The coefficient of thermal expansion, α, varies depending on the type of metal used to make the tubes that form a tank 10. Thus, α is such that 8*10' 6 °C' 1 < a < 18*10' 6 °C' 1 .

[0069] The tanks 10 are tubular, of circular section, and each has a longitudinal axis (1), a lower end 14 and an upper end 12.

[0070] Each tank is closed at its lower end 14 by a first closing means 16, and each tank 10 is closed at its upper end 12 by a second closing means 17. In the embodiment illustrated in Figure 1, the lower end 14 and the upper end 12 of each tank 10 are threaded ends, and the first closing means 16 and the second closing means 17 also have a thread, said thread being complementary to the thread of the lower end 14 and upper end 12. Thus, the lower end 14 is sealed by screwing it with the first closing means 16, and the upper end 12 is sealed by screwing it with the second closing means 17.

[0071] The second closing means 17 is equipped with sensors 19, which are pressure gauges, thermometers, and leak detectors. Of course, the first closing means 16 can also contain pressure gauges, thermometers, and leak detectors. Other types of sensors can be used depending on the intended purpose.

[0072] Each reservoir 10 can be composed of a plurality of tubes A. In the embodiment illustrated in Figure 1, the reservoirs 10 are composed of several threaded tubes A. Thus, the tubes A are assembled by screwing them together to form a column C of tubes A. Therefore, an assembly consisting of a column C, closed at its ends 12 and 14 by closure means 16 and 17, forms a reservoir 10. A reservoir 10 can also be composed of a single tube A, closed at its ends 12 and 14 by closure means 16 and 17.

[0073] Each tank 10 is assembled to an assembly element 18. Each assembly element 18 is inserted into an opening 7 and is retained by a collar 62 which butts against the upper surface 54 of the support element 4. Each assembly element 18 is therefore suspended from the support element 4. In this way, each tank 10 is suspended from the support element 4 by means of the assembly element 18 to which it is assembled.

[0074] As illustrated in Figure 4, an assembly element 18 is a tubular metal part, of circular cross-section, which includes a tubular body 60 and a collar 62.

[0075] The body 60 of the assembly element 18 is fixed to the upper end 12 of a tank 10, preferably by screwing. Welding may be used in an alternative embodiment. The body 60 of the assembly element 18 has a male or female thread (not shown) complementary to the thread of the upper end 12 of the tank 10 to which the assembly element 18 is assembled. The flange 62 comprises an upper surface 64 and a lower surface 66.

[0076] In the embodiment illustrated in Figure 1, the tubular body 60 of each assembly element 18 is inserted into an opening 7 in the support element 4. Each assembly element 18 rests on the support element 4 via its lower surface 66, which abuts against the upper surface 54 of the support element 4. Furthermore, each assembly element 18 is assembled to a tank 10 by screwing at the upper end 12 of said tank 10.

[0077] The collar 62 of the assembly element 18 therefore allows the latter to rest on the upper surface 54 of the support element 4. Thus, the assembly element 18 does not need to be fixed to the support element 4, for example by welding or screwing, which simplifies the assembly of the storage system 1, in particular for suspending the tanks 10.

Claims

Demands

1. Underground storage system (1) for the storage of fluids, said storage system (1) comprising: - a recess (2) constructed in a plot of land (40), said recess (2) having a bottom (3), - a support element (4) comprising at least one opening (7), - an assembly element (18) inserted into the opening (7) of the support element (4), - at least one tank (10), said tank (10) having a longitudinal axis (1), a lower end (14) closed by a first closing means (16), and an upper end (12) closed by a second closing means (17), said upper end (12) being assembled to the support element (4) by means of the assembly element (18) so that the tank (10) is suspended inside the recess (2) and an axial clearance (G) capable of absorbing an axial thermal expansion of said tank (10) remains between the first closing means (16) of the tank (10) and the bottom (3) of the recess (2).

2. Storage system (1) according to claim 1, characterized in that the tank (10) is composed of at least one metal tube (A), said metal tube (A) having at least one termination having at least one threaded portion.

3. Storage system (1) according to claim 2, characterized in that the tank (10) is composed of at least two metal tubes (A) assembled by screwing, so as to form a column of tubes (C).

4. Storage system (1) according to any one of the preceding claims, characterized in that the axial clearance (G) satisfies the following inequality: [Math 1] Where: G is the length of the axial clearance expressed in meters, L represents the length of a reservoir (10) expressed in meters, P represents the geothermal gradient expressed in degrees Celsius per meter, a represents the coefficient of thermal expansion of the metal expressed in meters per degree Celsius.

5. Storage system (1) according to any one of the preceding claims, characterized in that the first closing means (16) and / or the second closing means (17) is suitable for closing the tank by screwing.

6. Storage system (1) according to any one of the preceding claims, characterized in that said system (1) comprises a plurality of tanks (10), each tank (10) having a longitudinal axis (1), a lower end (14) and an upper end (12), said upper end (12) of each tank (10) being able to be assembled to the support element (4) by means of an assembly element (18) so that each tank (10) is suspended inside the recess (2).

7. Storage system (1) according to any one of the preceding claims, characterized in that the recess (2) comprises at least one casing (30).

8. Storage system (1) according to claim 7, characterized in that the casing (30) is made of concrete, cement, or steel.

9. An underground storage method for the storage of fluids, said method comprising the following steps: constructing a recess (2) in a ground (40), said recess (2) having a base (3), provide a support element (4) comprising at least one opening (7) suitable for receiving an assembly element (18), provide at least one tank (10), said tank (10) having a longitudinal axis (1), a lower end (14) and an upper end (12), provide a first closing means (16) suitable for closing said tank (10) at its lower end (14), and a second closing means (17) suitable for closing the tank (10) at its upper end (12), assemble said upper end (12) to the support element (4) via the assembly element (18) so that the tank (10) is suspended inside the recess (2) and an axial clearance (G) suitable for absorbing axial thermal expansion of said tank (10) remains between the first closing means (16) of the tank (10) and the bottom (3) of the recess (2).

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