Storage system and method for storing fluids comprising means for reducing risks

Abstract

This is an underground storage system (1) for storing fluids. It comprises a cavity (2) formed in the ground (3), said cavity (2) having a bottom (7), a support element (4) comprising at least one opening (9), an assembly element (6) inserted into the opening (9) of the support element (4), the assembly element (6) comprising ventilation vents to allow the fluid contained in the tank (5) to escape in the event of a leak, and at least one tank (5), said tank (5) having a longitudinal axis, a lower end (11) closed by a first closing means (10), and an upper end (12) closed by a second closing means (13).

Description

[0001] DESCRIPTION

[0002] TITLE: STORAGE SYSTEM AND METHOD FOR THE

[0003] STORAGE OF FLUIDS INCLUDING MEANS OF

[0004] RISK REDUCTION

[0005] Technical field

[0006] The present invention relates to underground storage and in particular the storage of fluids, for example hydrogen or oxygen. More particularly, the invention relates to the field of reducing the risks of a fluid storage system and, in particular, of a high-pressure fluid storage system, which may be between 100 bar and 1200 bar, more particularly between 200 bar and 500 bar.

[0007] The invention also relates to a method for underground storage of fluids.

[0008] Technological background

[0009] The risks of such a system are mainly related to explosion and / or fire caused by a leak of the fluid contained in the tanks. Indeed, an explosive fluid such as hydrogen is very easily flammable and instantly causes a strong detonation. This type of incident leads to structural damage and / or potentially fatal human injuries.

[0010] The solutions provided today concern in particular the reduction of risks in the event of a fluid leak and propose, for example, a pressure relief valve which opens if a quantity of fluid is released into the cavity, to direct the fluid into a pipe and evacuate it.

[0011] However, this type of installation is unreliable because the drainage system pipes are prone to clogging. Likewise, over time, the valve may no longer function effectively. This requires maintenance and, if necessary, component replacement. Furthermore, since the fluid is not directly diluted in air, an increase in pressure is likely to cause an explosion and subsequent damage to the drainage system.

[0012] Statement of the invention

[0013] The invention therefore aims to overcome the aforementioned drawbacks by proposing an effective solution which is not subject to mechanical constraints leading to additional maintenance operations.

[0014] The subject of the invention is an underground storage system for storing fluids comprising a recess arranged in a ground, said recess having a bottom, a support element comprising at least one opening, an assembly element inserted into the opening of the support element, the assembly element comprising ventilation vents to allow the fluid contained in the tank to escape in the event of a leak, at least one tank, said tank having a longitudinal axis, a lower end closed by a first closing means, and an upper end closed by a second closing means.The upper end is assembled to the support element by means of the assembly element so that the tank is suspended inside the recess and that an axial clearance capable of absorbing axial thermal expansion of said tank remains between the first means for closing the tank and the bottom of the recess.

[0015] Advantageously, the support element separates an upper cavity from a lower cavity, said upper cavity being open and comprising a first diameter greater than a second diameter of the lower cavity. Thus, the tank is entirely buried below ground level, including the second closure means which closes the upper end of the tank. Such a configuration of the storage system makes it possible to guide a deflagration occurring in the recess and thus to reduce the deflagration angle in the event of an explosion.

[0016] Advantageously, the lower cavity is filled with an explosion-proof fluid and / or solid. Thus, since the lower cavity is already filled, it cannot be filled with oxygen. The amount of oxygen in the lower cavity is therefore zero or negligible. Consequently, in the event of a tank leak, the risk of explosion is considerably reduced, if not zero.

[0017] According to one embodiment, the explosion-proof fluid and / or solid comprises antibacterial agents and / or anticorrosion agents.

[0018] Advantageously, the upper end of the tank includes a lifting cap system when handling the tank, and a system for connecting the valves and pipes when storing and distributing the fluid contained in the tank.

[0019] Advantageously, the tank comprises at least one metal tube, said metal tube having at least one termination provided with at least one threaded portion.

[0020] The tank consists of at least two metal tubes assembled by screwing, so as to form a column of tubes.

[0021] Advantageously, the axial clearance capable of absorbing axial thermal expansion of the tank complies with the following inequality:

[0022] Where: G is the length of the axial clearance expressed in meters, L represents the length of a reservoir 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.

[0023] According to one embodiment, the storage system comprises a plurality of tanks, each tank having a longitudinal axis, a lower end and an upper end, said upper end of each tank being assembled to the support element by means of an assembly element such that each tank is suspended inside the recess.

[0024] Optionally, the first closing means and / or the second closing means is capable of closing the tank by screwing.

[0025] Advantageously, the recess comprises at least one casing, said casing being made of concrete, cement, or steel.

[0026] The invention also relates to an underground storage method for storing fluids via a storage system as described above. The method comprises at least the following steps: providing a recess in a ground, said recess having a bottom, providing a support element comprising at least one opening capable of receiving an assembly element, the assembly element comprising ventilation vents to allow the fluid contained in the tank to escape in the event of a leak, providing at least one tank, said tank having a longitudinal axis, a lower end and an upper end, providing a first closing means capable of closing said tank at its lower end, and a second closing means capable of closing the tank at its upper end,assembly of said upper end to the support element by means of the assembly element so that the tank is suspended inside the recess, and that an axial clearance capable of absorbing axial thermal expansion of said tank remains between the first means for closing the tank and the bottom of the recess.,

[0027] Definitions The term "lower end" of the tank means the end of the tank which 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.

[0028] "Axial clearance" means a length, which extends along the longitudinal axis of the tank, measured between the first means of closing 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 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 is done by orthogonal projection on the vertical axis passing through a point of the first means of closing 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 means of closing.

[0029] 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.

[0030] The term "bottom of the recess" means 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 designates the surface of the layer of cement at the bottom of the recess. When the lining is not cemented, the term "bottom of the recess" simply designates the surface of the ground at the bottom of the recess.

[0031] Brief description of the drawings

[0032] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

[0033] - [Fig. 1] is a schematic view of the general structure of an underground storage system;

[0034] - [Fig. 2] is a schematic view representing the assembly element of an underground storage system;

[0035] - [Fig. 3] is a schematic view showing the ventilation vents present on the assembly element of an underground storage system;

[0036] - [Fig. 4] is a schematic view of a support element separating a lower cavity from an upper cavity in an underground storage system;

[0037] - [Fig. 5A] is a schematic view of a tank in an underground storage system including a lifting cap system; and

[0038] - [Fig. 5B] is a schematic view of a tank in an underground storage system including a connection system.

[0039] Detailed description

[0040] Figure 1 illustrates a sectional view of a storage system 1 according to one embodiment of the invention. As illustrated, the system is placed in a (x; y) frame in which the x axis of the (x; y) frame is a horizontal axis, and the y axis of the (x; y) frame is a vertical axis.

[0041] The storage system 1 comprises a recess 2 made in a ground 3, a support element 4 placed on a ground surface S of the ground 3, six tanks 5 suspended from the support element 4 in the recess 2 (only four tanks 5 being visible in FIG. 1) and an assembly element 6 which comprises ventilation vents to allow the fluid contained in the tank 5 to escape in the event of a leak. In various embodiments, the storage system 1 generally comprises at least one tank 5. The recess 2 has a bottom 7 and comprises a casing 8. The recess 2 can be obtained by drilling or by excavation. The recess 2 is of substantially circular cylindrical shape and has an average diameter of 4 meters. The casing 8 is made of cement and extends vertically from the surface of the ground S to the bottom 7 of the recess 2.

[0042] The support element 4 is a circular cylindrical plate which separates the storage system 1 into an upper cavity C1 and a lower cavity C2. The support element 4 has a central body and a collar, said collar having a lower surface resting on the ground S. The central body has a first thickness and the collar has a second thickness. The support element 4 further comprises an upper surface, said upper surface being opposite the lower surface of the collar.

[0043] The support element 4 also comprises one or more openings 9. The openings 9 are through holes, arranged in the first thickness of the body of the support element 4. In the illustrated embodiment, the support element comprises six openings

[0044] Each tank 5 is suspended from the support element 4 by means of an assembly element 6. Thus, for each tank 5 of the storage system 1, an axial clearance G remains between, on the one hand, the first closing means 10 which closes the tank 5 at its lower end 11 and, on the other hand, the bottom 7 of the recess 2. This axial clearance G has the function of absorbing an axial thermal expansion of the tank 5, which occurs in particular during filling and emptying operations. Thus, for each tank 5, 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 5 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 5 of the storage system 1 meets the following inequality:.

[0045] [Math 1]

[0046] Where: G is the length of the axial clearance expressed in meters. L represents the length of a reservoir 5 expressed in meters. P represents the geothermal gradient expressed in degrees Celsius per meter. The geothermal gradient P varies according to 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 a varies according to the type of metal that makes up the tubes used to form a reservoir 5. Thus, a is such that 8 * 10-6 °C- 1 < a < 18 * 10-6 °C- 1.

[0047] The tanks 5 are tubular, of circular section, and each have a longitudinal axis, a lower end 11 and an upper end 12.

[0048] Each tank 5 is closed at its lower end 11 by a first closing means 10, and each tank 5 is closed at its upper end 12 by a second closing means 13. In the embodiment illustrated in FIG. 1, the lower end 11 and the upper end 12 of each tank 5 are threaded ends, and the first closing means 10 and the second closing means 13 also have a thread, said thread being complementary to the thread of the lower end 11 and upper end 12. Thus, the lower end 11 is closed in a sealed manner by screwing with the first closing means 10, and the upper end 12 is closed in a sealed manner by screwing with the second closing means 13.

[0049] The second closing means 13 is equipped with sensors 14 such as pressure gauges, thermometers and leak detectors. Of course, the first closing means 10 can also contain pressure gauges, thermometers and leak detectors. Other types of sensors can be used depending on the nature of the parameters to be controlled.

[0050] Each tank 5 may comprise a plurality of tubes A. In the embodiment illustrated in FIG. 1, the tanks 5 comprise several threaded tubes A. Thus, the tubes A are assembled by screwing so as to form a column C of tubes A. Thus, each tank 5 is formed by an assembly which comprises a column C, closed at its ends 11, 12 by closing means 10, 13. A tank 5 may also be composed of a single tube A, closed at its ends 11, 12 by closing means 10, 13.

[0051] Each tank 5 is assembled to an assembly element 6 visible in Figure 2. Each assembly element 6 is inserted into an opening 9 and is retained by a collar 15 which abuts against the upper surface of the support element 4. Each assembly element 6 is therefore suspended from the support element 4. In this way, each tank 5 is suspended from the support element 4 by means of the assembly element 6 to which it is assembled.

[0052] For example, an assembly element 6 is a tubular metal part, of circular section, which comprises a tubular body 16, a collar 15 and ventilation vents 17.

[0053] The body 16 of the assembly element 6 is fixed to the upper end 12 of a tank 5, preferably by screwing. The body 16 of the assembly element 6 comprises a male or female thread (not shown) complementary to the thread of the upper end 12 of the tank 5 to which said assembly element 6 is assembled. The collar 15 comprises an upper surface 18 and a lower surface 19, the air vents 17 passing through these two surfaces 18, 19. It is possible, as a variant, to fix the body 16 of the assembly element 6 by welding. In another variant, the body 16 of the assembly element 6 comprises a male thread complementary to a female thread of the opening 9 of the support element 4, thus the assembly element 6 is screwed into the opening 9.

[0054] In the embodiment illustrated in Figure 1, the tubular body 16 of each assembly element 6 is inserted into an opening 9 of the support element 4. Each assembly element 6 rests on the support element 4 via its lower surface 19 bearing against the upper surface of the support element 4. Furthermore, each assembly element 6 is assembled to a tank 5 by screwing to the upper end 12 of said tank 5. The collar 15 therefore allows the assembly element 6 to rest on the upper surface of the support element 4. Thus, the assembly element 6 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 5.

[0055] Figure 3 illustrates a tank 5 suspended from the support element 4 via the assembly element 6. Indeed, the assembly comprising the assembly element 6 fixed to the upper end 12 of the tank 5 is inserted into the opening 9 and rests on the upper face of the support element 4. In this configuration, the opening 9 has a larger diameter than the outside diameter of the assembly element 6. There is therefore a radial space between the support element 4 and the assembly element 6.

[0056] If there is no means of ventilation in such a storage system 1 and a leak occurs, the released fluid accumulates in the recess and builds up pressure before creating an explosion, and / or a detonation, and / or a fire. In order to minimize these risks, ventilation vents 17 create an air circulation passage between the upper cavity C1 and the lower cavity C2. The storage system 1 is thus not airtight, which allows the fluid released from the reservoirs 5 to easily escape to the outside of the storage system and the recess, in the event of a leak. The ventilation vents 17 are holes passing through the collar of the assembly element 6. The ventilation vents can be, for example, the holes of a ventilation grid, circular and / or rectangular holes. Of course, air vents can have other shapes not described in this document.

[0057] The total ventilation surface is expressed according to the following relationships:

[0058] [Math 2]

[0059] A = Nvent * Avent

[0060] A < Agap * 0.9 In which A denotes the total ventilation surface, Nvent is the number of ventilation vents 17 greater than or equal to 1, Avent is the surface area of ​​a ventilation vent 17, Agap is the total surface area of ​​the radial space which is located between the support element 4 and the assembly element 6, and which is calculated according to the following equation:

[0061] [Math 3]

[0062] Agap = — (d9 2 — d6 2 )

[0063] Where Gap is the width of the radial gap, which is calculated using the following equation:

[0064] [Math 4]

[0065] Gap = (d.9 — d6) / 2

[0066] Where d9 is the diameter of the opening 9, and d6 is the outside diameter of the assembly element 6.

[0067] The support element 4 separates the upper cavity C1 from the lower cavity C2. According to an embodiment shown in FIG. 4, the upper cavity C1 is open and comprises a first diameter DI greater than a second diameter D2 of the lower cavity C2.

[0068] In the event of a deflagration, this configuration helps guide the explosion and reduce the induced pressure of the deflagration.

[0069] Indeed, if there is a leak of fluid in the storage system 1 and the latter increases in pressure before it can be properly evacuated through the air vents 17, an explosion may occur. Such an explosion causes structural damage and / or potentially fatal human damage. In order to reduce the scope of the deflagration, once the fluid is outside the recess 2, an upper cavity C1 is created, this cavity having a larger diameter than that of a lower cavity C2 into which the fluid is released.

[0070] In the example illustrated in Figure 4, the upper cavity C l drives the overpressure gas flow towards the outside of the storage system 1 according to a conical shape of solid angle a and whose apex coincides with the bottom of the upper cavity C l , which corresponds to the support element 4. The surrounding structures are then avoided. The angle a is determined as a function of the depth d of the upper cavity C l . If there is no upper cavity C l , the angle a is equal to 90°, and the explosion risks damaging the surrounding structures. Preferably, the depth of the upper cavity C l is at least one meter.

[0071] Another means for reducing the risks of explosion and / or fire in the storage system 1 is to at least partially fill the recess 2, in particular to at least partially fill the lower cavity C2, with a material comprising at least one explosion-proof fluid and / or at least one explosion-proof solid.

[0072] In the event of a leak from the reservoir 5, filling the lower cavity C2 makes it possible to direct the released fluid to the support element 4, in order to avoid an increase in the pressure in the lower cavity C2. The released fluid is thus rapidly diluted in the upper cavity C1 via the air vents 17 and the risks of explosion and fire are avoided. Filling the lower cavity C2 also makes it possible to reduce or eliminate its oxygen content to avoid detonations in the event of a leak of a flammable fluid.

[0073] The explosion-proof material is a liquid and / or a solid, for example, demineralized water, fresh water, salt water, sand, brine, or oil. It may also contain antibacterial agents such as chlorine, an antibacterial filter, or hydrogen peroxide and anti-corrosion agents.

[0074] This material must not induce pressure on the lower cavity C2 and on the tanks 5.

[0075] The volume of the material is characterized by the following equation: [Math 5]

[0076] Vm = Vc2 - VR

[0077] Where Vm is the volume of the material, Vc2 is the volume of the lower cavity C2, VR is the volume of the reservoirs contained in the lower cavity C2.

[0078] The volume of the lower cavity C2 is calculated according to the following equation:

[0079] [Math 6]

[0080] Where rc2 denotes the radius of the lower cavity C2, and hc2 is the height of the lower cavity C2.

[0081] The volume of the tanks 5 is calculated according to the following equation:

[0082] Where rR is the radius of a tank 5 , hR denotes the height of a tank 5 , NR denotes the number of tanks 5 contained in the storage system 1.

[0083] The pressure of the material is characterized by this equation:

[0084] [Math 8]

[0085] Pm = hc2 * VMm * g

[0086] Where Pm is the pressure of the material, VMm denotes the density of the material and g is the intensity of Earth's gravity.

[0087] Figures 5a and 5b illustrate the closure means 13 of the upper end 12 of a reservoir 5. The upper part of the closure means 13 comprises a machined male or female junction to allow the connection of valves and pipes for the distribution of the fluid contained in the reservoir 5.

[0088] According to an embodiment illustrated in Figure 5a, a thread is machined on the outer diameter of the upper part of the closure means 13, in order to ensure the installation of a lifting plug 20. This embodiment is substantially used when handling the tank 5 typically during maintenance phases, for example if components are to be replaced. The lifting plug 20 comprises a body 22 and a lifting means 24. The body 22 has a first female threaded housing 23 assembled by screwing to the male junction of the upper part of the closure means 13. The body 22 further comprises a second housing 25 axially opposite the first housing 23. The second housing 25 is configured to receive and fix the lifting means 24. The lifting means 24 is inserted and fixed in the second housing 25 by screwing. According to the embodiment illustrated in Figure 5a, the lifting means 24 is a lifting ring.According to another embodiment illustrated in Figure 5b, a thread is machined on the inside diameter of the upper part of the closing means 13, in order to ensure the installation of a connection system 21. This connection system makes it possible to connect the valves and pipes of the tank 5 to external machines, making it possible to manage the distribution of the fluid contained in the tank 5.

[0089] This system is advantageous in that it allows the use of several necessary tips depending on the operations carried out on the storage system 1. The installation of a lifting cap 20 makes it possible in particular to avoid the risks of injury or damage to the structures when handling the tank 5. In addition, the internal thread and the external thread made on the upper part of the same closure means 13 prevent the lifting cap 20 and the connection system 21 from being fixed at the same time on the same tank 5. Such a configuration requires the operator to empty the tank 5 before removing the connection system 21 and fixing the lifting cap 20 in order to handle the tank 5, for example for maintenance. This prevents the operator from handling a full tank. A storage system with such characteristics therefore presents fewer risks.

[0090] Storage system 1 is used to store any type of fluid, especially explosive gases. The fluid can be hydrogen, oxygen, methane, nitrogen, ammonia, preferably, the fluid is hydrogen.

[0091] The invention also relates to an underground storage method for storing fluids using a storage system 1 as described above.

[0092] According to this method, during a first step, a recess 2 is made in a terrain 3, said recess 2 having a bottom 7.

[0093] In the next step of the method, a support element 4 is provided comprising at least one opening 9 capable of receiving an assembly element 6, the assembly element 6 comprising ventilation vents 17 to allow the fluid contained in the reservoir 5 to escape in the event of a leak.

[0094] Then, in the following step, at least one reservoir 5 is provided, said reservoir 5 having a longitudinal axis, a lower end 11 and an upper end 12, then a first closing means 10 capable of closing said reservoir 5 at its lower end 11, and a second closing means 13 capable of closing the reservoir 5 at its upper end 12.

[0095] Said upper end 12 is then assembled to the support element 4 by means of the assembly element 6 so that the reservoir 5 is suspended inside the recess 2, and an axial clearance G capable of absorbing axial thermal expansion of said reservoir 5 remains between the first closure means 10 of the reservoir 5 and the bottom 7 of the recess 2.

Claims

CLAIMS 1. Underground storage system (1) for storing fluids, characterized in that said system (1) comprises: a recess (2) arranged in a ground (3), said recess (2) having a bottom (7), a support element (4) comprising at least one opening (9), an assembly element (6) inserted into the opening (9) of the support element (4), the assembly element (6) comprising ventilation vents (17) to allow the fluid contained in the reservoir (5) to escape in the event of a leak, at least one reservoir (5), said reservoir (5) having a longitudinal axis, a lower end (11) closed by a first closure means (10), and an upper end (12) closed by a second closure means (13),said upper end (12) being assembled to the support element (4) by means of the assembly element (6) so that the tank (5) is suspended inside the recess (2) and that an axial clearance (G) capable of absorbing an axial thermal expansion of said tank (5) remains between the first closing means (10) of the tank (5) and the bottom (7) of the recess (2)., 2. Storage system (1) according to claim 1, wherein the support element (4) separates an upper cavity (Cl) from a lower cavity (C2), said upper cavity (Cl) being open and comprising a first diameter (Dl) greater than a second diameter (D2) of the lower cavity (C2).

3. Storage system (1) according to claim 2, wherein the lower cavity (C2) is filled with an explosion-proof fluid and / or solid.

4. Storage system (1) according to claim 3, wherein the explosion-proof fluid and / or solid comprises antibacterial agents and / or anti-corrosion agents.

5. Storage system (1) according to any one of claims 1 to 4, wherein the upper end (12) of the tank (5) comprises a lifting cap system (20) when handling the tank (5), and a connection system (21) of the valves and pipes when storing and distributing the fluid contained in the tank (5).

6. Storage system (1) according to any one of claims 1 to 5, wherein the reservoir (5) comprises at least one metal tube (A), said metal tube (A) having at least one termination provided with at least one threaded portion.

7. Storage system (1) according to any one of claims 1 to 6, in which the tank (5) comprises at least two metal tubes (A) assembled by screwing, so as to form a column of tubes (C).

8. Storage system (1) according to any one of claims 1 to 7, wherein the first closing means (10) and / or the second closing means (13) is capable of closing the reservoir (5) by screwing.

9. Storage system (1) according to any one of claims 1 to 8, which comprises a plurality of tanks (5), each tank (5) having a longitudinal axis, a lower end (11) and an upper end (12), said upper end (12) of each tank (5) being assembled to the support element (4) by means of an assembly element (6) so that each tank (5) is suspended inside the recess (2).

10. Underground storage method for storing fluids via a storage system (1) according to any one of claims 1 to 9, characterized in that it comprises at least the following steps: arranging a recess (2) in a ground (3), said recess (2) having a bottom (7), providing a support element (4) comprising at least one opening (9) capable of receiving an assembly element (6), the assembly element (6) comprising ventilation vents (17) for allowing the fluid contained in the reservoir (5) to escape in the event of a leak, providing at least one reservoir (5), said reservoir (5) having a longitudinal axis, a lower end (11) and an upper end (12), providing a first closing means (10) capable of closing said reservoir (5) at its lower end (11), and a second closing means (13) capable of closing the reservoir (5) at its upper end (12), - assembling said upper end (12) to the support element (4) by means of the assembly element (6) so that the reservoir (5) is suspended inside the recess (2), and that an axial clearance (G) capable of absorbing an axial thermal expansion of said reservoir (5) remains between the first closing means (10) of the reservoir (5) and the bottom (7) of the recess (2).

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