UNDERGROUND STORAGE SYSTEM FOR LIQUID STORAGE

Description

Technical field

[0001] The invention relates to the field of underground storage, in particular for the storage of fluids. More particularly, the invention relates to the field of underground storage systems for the storage of gases, for example for the storage of hydrogen or for the storage of oxygen. Even more particularly, the invention relates to the field of the storage of fluids at high pressures. By "high pressures" is meant pressures which may be between 100 bar and 1200 bar, more particularly between 200 bar and 500 bar.

[0002] The invention also relates to an underground storage method for storing fluids. Technological background

[0003] One emerging technology to reduce 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 in an electrolyzer to produce hydrogen and oxygen, particularly through water electrolysis.

[0004] 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. In this case, to produce this electricity, the hydrogen can power either a turbine or hydrogen fuel cells. As for oxygen, it may be interesting to store it for use in a field such as agriculture or for medical purposes.

[0005] Some gases, such as hydrogen, are known to be difficult to contain. For example, their low density requires high-pressure storage, and their small molecules and low viscosity make them prone to leaks. Therefore, they must be stored in a perfectly sealed device capable of storing large quantities of gas while meeting strict safety standards, particularly to minimize the risk of leaks. Underground storage is also attractive to consumers and manufacturers because it very effectively reduces the space used above ground for these storage facilities.

[0006] Such underground fluid storage systems are typically installed at depths between 10 meters and 50 meters. These storage systems can be installed in terrains of various geological types, for example, solid rocks such as granite or basalt, or any other type of underground geological structure.

[0007] In this regard, the prior art described in US patent 10837601: a device comprising a unit secured in a single subterranean borehole, the unit comprising a plurality of separate containers secured via at least one retainer, 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 relative to a radial center of a top surface of the plug, the unit being secured in the single subterranean borehole by cement extending continuously between the plurality of containers to surround the unit and contact a sidewall of the subterranean borehole. Further, the unit is secured to an anchor member proximate the bottom of the subterranean borehole.The disadvantage of such a device is that, to keep the containers in place in the underground borehole, said containers are fixed in cement and attached from below to the anchoring element, which makes maintenance operations complex, especially when it is necessary to extract a container from the unit to change it, the cement and the anchoring element prevent such extraction. However, this type of operation may be necessary, especially in the event of a leak, for a control or maintenance operation. The maintenance and safety of such a device are therefore not optimal. In addition, maintaining the containers in cement in this way causes significant compression work on the container walls, which increases the risk of leakage. CN202915039U describes a high-pressure underground gas storage system. Summary

[0008] In order to overcome the above drawbacks, a first aim of the invention is to facilitate maintenance operations on an underground storage system for fluids, such as gases. Furthermore, a second aim of the invention is to enable large quantities of fluids to be stored at high pressures while complying with strict safety standards. Finally, a third aim of the invention is to enable the underground storage of several different fluids, at different pressures, in a single device, within a single storage system.

[0009] Thus, the invention provides an underground storage system for storing fluids in accordance with independent claim 1.

[0010] Thanks to these characteristics, the integrity of the tank is not compromised by mechanical stresses linked to the axial thermal expansion of the tank during fluid injection and sampling operations. Indeed, the axial clearance prevents, during such operations, axial thermal expansion from causing the compression of the tank against the bottom of the recess. Such stresses applied repeatedly weaken the tightness of the tank, particularly at the level of the closure means.

[0011] Furthermore, unlike prior art devices, such a system eliminates the need for cement to secure the tank. The tank is therefore only secured to the support element. The tank is therefore suspended in any fluid from the environment in which the system is placed. For example, the tank is suspended in air or water from the surrounding rock formations. It is therefore possible and simple to remove a tank from the system.

[0012] According to one embodiment, the tank is suspended substantially vertically.

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

[0014] According to one embodiment, the metal tube has two ends, each of said two ends being provided with at least one threaded portion.

[0015] According to one embodiment, the tank is composed of at least two metal tubes assembled by screwing, so as to form a column of tubes. The assembly between two metal tubes can be done by an integral connection or by means of a connecting piece, such as a sleeve.

[0016] According to one embodiment, the axial play respects the following inequality: G ≥ L 2 ∗ β ∗ α + 20 ∗ α ∗ 80 ∗ 1 − e − 0.11 ∗ L Where: G is the length of the axial clearance expressed in meters, L represents the length of a reservoir (10) expressed in meters, β represents the geothermal gradient expressed in degrees Celsius per meter, α represents the coefficient of thermal expansion of the metal expressed in Celsius -1< .

[0017] The geothermal gradient β varies depending on the geological formation in which the storage system is placed. Thus β is such that 0.02° / m≤ β≤2° / m. α 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 that makes up the tubes used to form a reservoir. Thus, α is such that 8*10 -6< °C -1< ≤ α ≤ 18*10 -6< °C -1< .

[0018] Using threaded pipes to make the tank easier to assemble and disassemble. This is particularly beneficial when a pipe needs to be replaced. This makes tank maintenance and upkeep easier, and system safety is increased.

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

[0020] According to one embodiment, the tubes used to make a tank are metal tubes, preferably threaded metal tubes. For example, they may be titanium metal tubes, or steel tubes of the type used in the gas and oil industry, in particular the tubes used to make gas and / or oil production wells.

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

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

[0023] Closures capable of screwing the tank shut are preferred over welds, as screwed closures do not significantly alter the tank wall thickness at the closure. Thus, with screwed closures, the mechanical properties of the tank at the closure are unchanged. Furthermore, in the case of hydrogen storage, they avoid potential problems of hydrogen corrosion, which can occur on a weld.

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

[0025] According to one embodiment, the support element is placed on the ground or fixed to a concrete or cement plate, said plate being cast on the surface of the ground. The fixing of the support element to the concrete or cement plate can be done by any means known to those 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 one surface area of ​​between 0.2 m 2 and 10 m 2, preferably between 0.7 m 2 and 4 m 2.

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

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

[0030] According to one embodiment, the at least one opening of 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 l, a lower end and an upper end, said upper end of each tank being adapted to be assembled to the support element by means of an assembly element so that each tank is suspended inside the recess.

[0035] Such a system, which comprises a plurality of tanks, allows for tanks of different lengths to be used within the same storage system. This is particularly advantageous in order to avoid suspending an unnecessarily high load from the support element. In addition, the length of a tank can be adapted to facilitate the necessary increase or decrease in pressure depending on the storage conditions of the fluid. Thus, different fluids can be stored in the same system.

[0036] According to one embodiment, each tank is connected to a fluid supply and to a fluid sampling circuit which are specific to it so that when the storage system comprises 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 recess, it is possible to store a large quantity of gas at very high pressures in a plurality of tanks. In addition, with such a system it is possible to store different fluids, each fluid being able to be stored under conditions, in particular temperature and pressure conditions, which are specific to the fluid and the use for which the fluid is intended.

[0038] According to one embodiment, each tank can be equipped with sensors, such as pressure gauges, thermometers, leak detectors or humidity detectors. In this way, it is possible to monitor the pressure as well as the presence of leaks in each tank. This is advantageous, on the one hand for the safety of the system, and on the other hand when the tanks do not all store the same fluid. These sensors can also be placed directly in the recess.

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

[0040] According to one embodiment, the length L of a tank 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 recess has a depth of between 10 meters and 2500 meters, preferably between 20 meters and 500 meters, said depth being measured between the surface of the ground and the bottom of the recess.

[0043] According to one embodiment, the recess comprises at least one casing.

[0044] According to one embodiment, the casing is made of concrete, cement, or steel.

[0045] According to one embodiment, the casing is a casing tube. The casing tube may be cemented.

[0046] In one embodiment, the ground is composed of solid rock, such as granite or basalt. The advantage of building the storage system in a ground composed of solid rock is that it is possible to do without casing, which simplifies the installation of the system. However, casing is necessary when the system is built in soft ground.

[0047] According to one embodiment, the recess can be made 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 storing fluids in accordance with independent claim 9. Definitions

[0050] The term "lower end" of the tank means the end of the tank that is located near the bottom of the recess. This "lower end" is defined in contrast to the so-called "upper end" of the tank, which is located near the support element and therefore the ground surface.

[0051] "Axial clearance" means a length, which extends along the longitudinal axis l of the tank, measured between the first closing means of the tank and the bottom of the recess. Note that the position of a tank may not be perfectly vertical. In this case, the longitudinal axis l of the tank has an angle with respect to the vertical in the (x; y) reference frame. This angle has a maximum value of 15°. In this case, the measurement of the axial clearance G is done by orthogonal projection on the vertical axis passing through a point of the first closing means located closest to the bottom of the recess. In other words, the axial clearance always corresponds to the shortest distance, measured between the bottom of the recess and the first closing means.

[0052] The term "threaded metal tube" means a tube comprising at least one termination having at least one threaded portion, capable of being assembled to a threaded metal tube comprising at least one termination having at least one complementary threaded portion. The thread may be male or female.

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

[0054] The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes, with reference to the accompanying drawings.

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

[0056] Therefore, it is to be understood that where features recited in the claims are followed by references, such references are included solely to enhance the understanding of the claims and in no way limit the scope thereof. There Figure 1 is a diagram of a sectional view of a storage system according to one embodiment of the invention. Figure 2 is an isolated three-dimensional diagram of the support element of the storage system illustrated in Figure 1 . There Figure 3 is an isolated three-dimensional diagram of an alternative support element that may be used in one embodiment of the invention. Figure 4 is a three-dimensional diagram of an assembly element that can be used in the storage system shown in Figure 1 . Description of the embodiments

[0057] There Figure 1illustrates a sectional view of a storage system 1 according to an embodiment of the invention, in a reference frame (x; y). The x axis of the reference frame (x; y) is a horizontal axis, and the y axis of the reference frame (x; y) is a vertical axis.

[0058] The storage system 1 comprises a recess 2 made in a ground 40, a support element 4 placed on a surface of a ground S of the ground 40, and six tanks 10 suspended from the support element 4 in the recess 2 (only four tanks are visible on the Figure 1 ).

[0059] 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.

[0060] The casing is made of cement and extends vertically from the surface of the ground S to the bottom 3 of the recess 2.

[0061] As shown on the figures 1 And 2 , the support element 4 is a circular cylindrical plate having a central body 50 and a collar 52, said collar 52 having a lower surface 56 resting on the ground S. The central body 50 has a first thickness E which can be between 10 mm and 500 mm. The collar 52 has a second thickness e which 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.

[0062] 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 m 2 < .

[0063] As illustrated in the Figure 2 , the support element 4 also comprises six openings 7. The openings 7 are through holes, arranged in the first thickness E of the body 50 of the support element 4. According to the Figure 3 , which illustrates a support element 4 which can be used in an embodiment according to the invention, the support element 4 comprises fourteen openings 7 arranged in the first thickness E of the body 50.

[0064] 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 closing means 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 has the function of absorbing an axial thermal expansion of the tank 10, which occurs in particular during filling and emptying operations. Thus, for each tank 10, the dimensioning of the axial clearance G, and in particular its length, depends directly on the surrounding conditions of the storage system 1, in particular the temperature and pressure conditions, and the capacity of the tank 10 to elongate when it is subjected to variations in temperature and pressure, in particular during filling and emptying operations.Thus, the axial clearance G of any tank 10 of the storage system 1 meets the following inequality: . G ≥ L 2 ∗ β ∗ α + 20 ∗ α ∗ 80 ∗ 1 − e − 0.11 ∗ L Where: G is the length of the axial clearance expressed in meters. L represents the length of a reservoir 10 expressed in meters. β represents the geothermal gradient expressed in degrees Celsius per meter. The geothermal gradient β varies according to the geological formation in which the storage system 1 is placed. Thus β is such that 0.02° / m≤ β≤2° / m. α represents the coefficient of thermal expansion of the metal expressed in degrees Celsius -1< . The coefficient of thermal expansion α varies according to the type of metal that makes up the tubes used to form a reservoir 10. Thus, α is such that 8* 10 -6< °C -1< ≤ α ≤ 18*10 -6< °C -1< .

[0065] The tanks 10 are tubular, of circular section, and each have a longitudinal axis (l), a lower end 14 and an upper end 12.

[0066] 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 reservoir 10 are threaded ends, and the first closure means 16 and the second closure means 17 also have a thread, said thread being complementary to the thread of the lower 14 and upper 12 ends. Thus, the lower end 14 is closed in a sealed manner by screwing with the first closure means 16, and the upper end 12 is closed in a sealed manner by screwing with the second closure means 17.

[0067] The second closure means 17 is equipped with sensors 19 which are pressure gauges, thermometers and leak detectors. Of course, the first closure means 16 can also contain pressure gauges, thermometers and leak detectors. Other types of sensors can be used depending on the objective that has been set.

[0068] Each reservoir 10 may be composed of a plurality of tubes A. In the embodiment illustrated in Figure 1 , the tanks 10 are composed of several threaded tubes A. Thus, the tubes A are assembled by screwing so as to form a column C of tubes A. Thus, an assembly composed of a column C, closed at its ends 12 and 14 by closing means 16 and 17, forms a tank 10. A tank 10 can also be composed of a single tube A, closed at its ends 12 and 14 by closing means 16 and 17.

[0069] Each reservoir 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 abuts 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 reservoir 10 is suspended from the support element 4 by means of the assembly element 18 to which it is assembled.

[0070] As illustrated in the Figure 4 , an assembly element 18 is a tubular metal part, of circular section, which comprises a tubular body 60 and a collar 62.

[0071] The body 60 of the assembly element 18 is fixed to the upper end 12 of a tank 10, preferably by screwing. It is possible to use welding 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 said assembly element 18 is assembled. The collar 62 comprises an upper surface 64 and a lower surface 66.

[0072] In the embodiment illustrated in the Figure 1, the tubular body 60 of each assembly element 18 is inserted into an opening 7 of the support element 4. Each assembly element 18 rests on the support element 4 by means of 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 reservoir 10 by screwing to the upper end 12 of said reservoir 10.

[0073] 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 by screwing, which simplifies the assembly of the storage system 1, in particular for suspending the tanks 10.

Claims

1. Underground storage system (1) for storing fluids, said storage system (1) comprising: - a hole (2) made in a ground (40), said hole (2) having a bottom (3), - a support element (4) comprising at least one opening (7), - a joining element (18) inserted in the opening (7) of the support element (4), - at least one reservoir (10), said reservoir (10) having a longitudinal axis (l), a bottom end (14) closed by a first closure means (16), and a top end (12) closed by a second closure means (17), the joining element (18) being attached to the top end (12), and said top end (12) being joined to the support element (4) via the joining element (18) such that the reservoir (10) is hung inside the hole (2) and such that an axial clearance (G) able to absorb axial thermal expansion of said reservoir (10) remains between the first closure means (16) of the reservoir (10) and the bottom (3) of the hole (2).

2. Storage system (1) according to Claim 1, characterized in that the reservoir (10) is composed of at least one metal tube (A), said metal tube (A) having at least one end provided with at least one threaded portion.

3. Storage system (1) according to Claim 2, characterized in that the reservoir (10) is composed of at least two metal tubes (A) screwed to each other, 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: G ≥ L 2 ∗ β ∗ α + 20 ∗ α ∗ 80 ∗ 1 − e − 0.11 ∗ L in which: G is the length of the axial clearance expressed in metres, L represents the length of a reservoir (10) expressed in metres, β represents the geothermal gradient expressed in degrees Celsius per metre, and α represents the coefficient of thermal expansion of the metal expressed in metres per degree Celsius.

5. Storage system (1) according to any one of the preceding claims, characterized in that the first closure means (16) and / or the second closure means (17) is able to close the reservoir by screw-fastening.

6. Storage system (1) according to any one of the preceding claims, characterized in that said system (1) comprises a plurality of reservoirs (10), each reservoir (10) having a longitudinal axis (l), a bottom end (14) and a top end (12), said top end (12) of each reservoir (10) being able to be joined to the support element (4) via a joining element (18) such that each reservoir (10) is hung inside the hole (2).

7. Storage system (1) according to any one of the preceding claims, characterized in that the hole (2) has 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. Underground storage method for storing fluids, said method comprising the following steps: making a hole (2) in a ground (40), said hole (2) having a bottom (3), providing a support element (4) comprising at least one opening (7) able to receive a joining element (18), providing at least one reservoir (10), said reservoir (10) having a longitudinal axis (l), a bottom end (14) and a top end (12), providing a first closure means (16) able to close said reservoir (10) at its bottom end (14), and a second closure means (17) able to close the reservoir (10) at its top end (12), joining said top end (12) to the support element (4) via the joining element (18), and insert the reservoir (10) and the joining element (18) in the opening (7) such that the reservoir (10) is hung inside the hole (2) and such that an axial clearance (G) able to absorb axial thermal expansion of said reservoir (10) remains between the first closure means (16) of the reservoir (10) and the bottom (3) of the hole (2).