EP0609146A1 - Underground reservoirs having a sole leak-proof tank for holding for example a liquefied gas, and the arrangement of such reservoirs - Google Patents

Abstract

The present invention relates to an underground reservoir having a single (sole) leakproof (leaktight) container, such as especially a liquefied cryogenic gas. This reservoir which is of the type comprising an external container (2) made of concrete buried in the ground, a rigid structure with a base slab (4) and possibly a covering dome (3) as well as a leaktight heat-insulating jacket (5) which inside the structure delimits a filling space for the fluid, is characterised in that the external container (2) has the form of a substantially leaktight thick wall, this container (2) as well as the covering dome (3) being formed integrally with each other and, together with the base slab (4) constituting the rigidifying structure of the reservoir. The invention applies to a holding tank, for example for a port terminal, for filling with liquid natural gas. <IMAGE>

Description

The present invention relates to an underground tank with a single sealed enclosure, for the confinement of any fluid, such as in particular a liquefied cryogenic gas. More particularly, the invention relates to a liquid natural gas confinement tank, for example for a port loading terminal.

It has already been proposed, mainly in the case of installations located on relatively soft soil, to at least partially bury a storage tank or "storage" of a fluid, such as for example a liquid fuel. Such a solution makes it possible, compared with conventional "aerial" tanks, to reduce the surface area on the ground and to limit the impact on the environment of the installation, while offering a high level of security.

There is in particular a type of buried tank comprising an external concrete enclosure buried in the ground and provided to allow the excavation in the latter of a cavity of corresponding shape. A rigid structure is provided in the external enclosure. This structure, which is made of reinforced concrete or metal, includes a bottom slab and a covering dome. A sealed envelope of thermal insulation is fixed inside the rigid structure, and delimits in the latter a space where the fluid to be "stored" or stored can be confined. In general, the rigid structure is constituted by a second internal enclosure of reinforced concrete, in which the bottom slab which is formed by a poured slab, is embedded.

Such a tank comprising an external enclosure and an internal enclosure is tedious to produce and proves to be complex and costly.

In addition, in the case of coastal or submerged installations, the water contained in the ground can exert considerable forces on the rigid structure of conventional buried tanks, and in particular on their bottom slabs or rafts since the external enclosure does not allow the interior of the tank to be properly insulated against water infiltration. Thus, with a conventional underground tank with a capacity of the order of 100,000 m³, it is common for the raft to be subjected, under the effect of the water contained in the soil, to a lifting effort of the order of 40 t / m². So, to guarantee the stability and the holding of the tank, the combined action of the mass of the latter and the friction essentially between the slab, the concrete enclosures and the ground, must roughly correspond to that of a mass of 100,000 t.

In addition, conventional underground tanks must be provided during their construction with water pumping devices under their raft at high flow rate, to allow the dryness of the excavation.

Also, the present invention aims to overcome in particular the drawbacks of the prior art set out above, and to propose a buried tank whose structure is both simple, resistant and inexpensive.

To this end, the invention relates to a reservoir for the confinement of any fluid, such as in particular a liquefied cryogenic gas, and of the type comprising an external enclosure made of molded concrete buried in the ground, a rigid structure with a bottom slab, and possibly a covering dome as well as a waterproof envelope and thermal insulation which delimits the interior of the structure a loading space for the fluid, characterized in that the external enclosure has the form of a thick and substantially sealed wall, this enclosure as well as the covering dome being made of material and constituting with the bottom slab, the rigid structure of the tank.

It will be noted here that advantageously, the base of the above-mentioned external enclosure extends at least as far as near a substantially impermeable layer of the ground.

According to another characteristic of the invention, the bottom slab has the form of a reinforced concrete slab, freely resting on the one hand on one or more stops integral with the external enclosure, and on the other hand on a system drainage.

It will also be specified here that the reinforced concrete slab preferably has a thickness less than that of the external enclosure.

Preferably, the aforementioned insulation envelope comprises a waterproof metal membrane, fixed inside the external enclosure and on the bottom slab, by means of a thermal insulation layer.

In this case, the insulation layer may advantageously comprise at least one thickness of rigid stress distribution panels, thus that at least one thickness of plastic foam panels, these panels may be impermeable and hermetically connected to each other by watertight connections so as to constitute a layer of continuous and hermetic insulation.

According to one embodiment of the invention, the above-mentioned insulation layer is fixed to the concrete using a preferably continuous thickness of adhesive material.

In addition, the aforementioned envelope comprises a tight steel dome hermetically fixed by its periphery to the metal membrane and constituting an internal coating for the covering dome, as well as a suspended aluminum roof and covered with an insulation layer. thermal, which is interposed between the waterproof membrane and the dome, in order to maintain the latter at approximately room temperature.

According to yet another characteristic, the covering dome, and possibly the aforementioned waterproof dome, rest on the external enclosure of the tank by means of a crowning beam of corresponding shape.

The invention also relates to an arrangement of buried tanks as described above, and arranged inside a substantially sealed wall, buried and closed, for example cylindrical, and whose base extends at least up to 'near the above-mentioned substantially impermeable layer of the ground.

The invention will be better understood and other characteristics, and advantages thereof will appear more clearly in the detailed description which follows and refers to the appended schematic drawings, given only by way of example, in which.

Figure 1 is a cutaway view of a buried tank according to one embodiment of the invention.

FIG. 2 is a view in vertical section along a diameter of the reservoir in FIG. 1.

FIG. 3 is an enlarged view of the detail designated at III in FIG. 2.

FIG. 4 is an enlarged view of the detail designated at IV in FIG. 2.

Figure 5 shows a vertical sectional view of an arrangement of buried tanks according to the invention.

In the figures, the general reference numeral 1 designates a buried tank. Here, the tanks 1 are provided for the confinement of liquid natural gas. However, many other types of fluids can also be stored or "stored" in such a tank.

Each tank 1 is a buried tank of the so-called "membrane" type. More specifically, the tank 1 comprises an external concrete enclosure 2, which is at least partially buried in the ground, itself designated by the reference S in the figures. The enclosure 2 which is roughly cylindrical, delimits in the soil S an excavation or cavity of corresponding shape.

The buried tank 1 has a rigid structure, that is to say a structure guaranteeing the stability and the holding of the tank 1 under the effect of the stresses which may be applied to it. The rigid structure here is provided with a covering dome 3, disposed above the enclosure 2 and projecting from the ground S. However, it can be envisaged that the tanks 1 do not have a covering dome. The rigid structure of the tank 1 also has a bottom slab 4, placed opposite the dome 3 or the top of the tank 1, and the shape of which corresponds substantially to that of the cavity defined by the external enclosure 2. We see on the Figures that the covering dome 3 as well as the bottom slab 4 are poured and reinforced concrete structures.

We also note in the figures an envelope 5 which delimits inside the cavity defined by the external enclosure 2 as well as by the dome 3 and the slab 4, a space for loading and confining the fluid to be stored. The envelope 5 is sealed and also has the function of thermally isolating the fluid stored in the tank 1, the concrete structural elements 2, 4 and possibly 3.

In accordance with the invention, the external enclosure 2 has the form of a thick and substantially sealed wall, with which the covering dome 3 is advantageously made of one piece, so that they constitute, with the bottom slab 4, the rigid structure of the corresponding tank 1.

It is already understood that, since the external enclosure 2 is waterproof and has sufficient thickness and rigidity to withstand the internal and external stresses which are applied to the reservoir 1, the erection of this tank is simplified and its production requires less material.

Thanks to its rigid structure, it is possible, and often advantageous, to provide for the external enclosure 2 to extend deep into the ground as close to a substantially impermeable layer SI thereof, so that infiltration d water inside the cavity defined by the reservoir 1 are greatly minimized. Obviously, it is also possible that the enclosure 2 projects positively inside the naturally impermeable layer SI of the ground. Thus, the forces produced by the water contained in the soil S and having a tendency to raise the slab 4, are greatly reduced. Also, thanks to the limitation of the external forces applied to the tank 1, and above all by the fact that the external enclosure 2 and the rigid structure are integrated with each other, the tank 1 is of simpler constitution and requires much less material for its manufacture, than equivalent tanks of the prior art.

In the same vein, since the infiltration of water into the tank 1 is minimized, and therefore that the lifting efforts of the slab 4 are extremely reduced compared to the known tanks, the thickness (and therefore the mass) of this bottom slab 4 can also be minimized. As seen in the example of FIGS. 1 and 2, the bottom slab 4 even has a thickness less than that of the external enclosure 2.

Consequently, with a reservoir 1 according to the invention, with a fluid capacity of the order of 100,000 m³, the thickness of the external enclosure 2 can be of the order of 2.20 m and that of the bottom slab only about 1 m. However, it is known that for an equivalent tank of the prior art, the thickness of the external enclosure and of the rigid vertical structure is more than 3 m, while the bottom slab can reach 7 m in height.

Now, this bottom slab 4 will be described in more detail. In the figures, this has the form of a reinforced concrete slab which rests freely on the one hand against one or more stops integral with the enclosure 2, and on the other hand on a drainage system 6.

Here, the periphery of the bottom raft 4 is supported without embedding on a stop 24 in the form of an annular console, integrated into the enclosure 2. Such an arrangement of the raft without embedding in the vertical walls of the tank 1 is completely different from the prior art.

For its part, the drainage system 6 essentially comprises a second slab consisting of porous aggregates arranged on the bottom of the cavity excavated in the soil S. Thus, when water infiltrates inside the enclosure 2, it is drained through the second raft 6 to delivery pumps (not shown). As illustrated in FIG. 2, these pumps deliver into one or more wells P formed in the soil S near the reservoir 1, by means of conduits 66 produced through the enclosure 2.

It should also be emphasized here that, according to the illustrated embodiment, the tank 1 is provided with a device for keeping frost-free of its concrete elements. This device comprises on the one hand conduits 64 (FIG. 2) for circulation of a hot fluid, such as for example water, provided under the bottom slab 4, that is to say inside the second slab 6, and on the other hand conventional electric heating cables 28 (FIG. 2), arranged in galvanized steel tubes, themselves embedded in the concrete of the external enclosure 2 substantially up to the level of the slab 4.

Another major difference between the invention and the known reservoirs concerns the actual structure of the external enclosure 2. In fact, in addition to the fact that it is load-bearing and waterproof, the enclosure 2 is made of reinforced concrete and molded directly in soil S.

More precisely, this enclosure 2 is produced by digging in the ground S a trench of corresponding shape, then by molding a concrete of suitable composition in the trench, after having placed there reinforcement cages as well as the heating cables 28. Such a wall can, for example, be obtained using equipment of the type designated by the name "Hydrofraise" and developed by the Soletanche Company. This type of equipment makes it possible to manufacture concrete walls from 70 to 80 m deep, under conditions and with very precise dimensional tolerances (approximately 1 per 1000).

Then, a coating or sealing facing is applied to the internal or excavation face of the enclosure 2, for example by spraying concrete onto a wire mesh itself fixed by anchoring on this enclosure. The facing, the thickness of which according to the example mentioned above is of the order of 0.15 m makes it possible to obtain a smoother surface condition of the excavation face. Essentially, the surface finish thus obtained must allow good attachment of the casing 5 to the concrete, as will be better explained below.

At the top of the external enclosure 2, a beam of corresponding shape 32 is provided. It is clear from FIGS. 1 and 2 that this so-called crowning beam is integrated both into the enclosure 2 and into the covering dome 3, which allows a good transmission of forces inside the concrete structure, as well as a reinforcement of the external enclosure 2. Here, the annular crowning beam 32 illustrated has a cross section greater than that of the enclosure 2, and is made of prestressed and reinforced concrete. More specifically, after the erection of the enclosure 2 of molded concrete, reinforcements and prestressing cables are made integral and anchored in the latter then, concrete is poured into a formwork corresponding to the crowning beam that l 'we wish to obtain. Following this, the cables are stretched to adequately prestress the concrete thus poured.

It is from the crowning beam 32 that the covering dome 3 is made, in the case where such a dome is provided for the tank 1. In this case, the covering dome 3 is anchored at the top of the enclosure 2 via the beam 32. A metal dome 35, called to form part of the envelope 5, by forming an internal coating of the dome 3 is made from a lattice of metal beams on which are welded sheet metal plates. After manufacture, the dome 35 which defines a sealed surface corresponding to the dome 3, is made integral with the beam 32. After removal and fixing of an appropriate reinforcement on the dome 35, concrete is poured until the dome 3 is obtained. According to the above example, the thickness of the concrete of this covering dome 3 varies from 0.5 to 1.0 m from its center to its periphery. It is at this peripheral that the concrete of the dome 3 is connected to that of the beam 32. It goes without saying that the dome 35 remains within the tank 1 after pouring the concrete, and is therefore fixed to the dome 3, which itself came out of the box with beam 32 and thick enclosure 2.

As indicated above, the metal dome 35 is integral with the dome 3 and forms part of the sealed and insulating envelope 5. Here, the envelope 5 comprises a metallic membrane which is welded to a shoulder 352, itself integral of the periphery of the dome 35. This welding is obviously continuous and hermetic, so that this membrane and the dome constitute a sealed containment enclosure.

In FIGS. 3 and 4 respectively, the metal membrane of the enclosure 5 is designated at 54 and 52. It can also be seen that the envelope 5 comprises a layer of thermal insulation 55. The membrane consists of sheets of stainless steel austenitic with a thickness of the order of 1.2 mm, welded together in a leaktight manner and is fixed to the concrete by means of layer 55. These sheets which form a containment pocket, are ribbed to resist deformations linked to the mechanical and thermal stresses applied to them by the fluid stored in the tank 1.

Referring now to Figures 3 and 4, the structure and the implementation of the thermal insulation layer of the casing 5 will be described in detail.

It appears from the drawings that the insulation layer 55 is formed by one or more thicknesses of rigid panels 57, for example of plywood, as well as by at least one thickness of foam panels made of plastic material 56, preferably waterproof. . Here, the layer 55 comprises, starting from the concrete wall a series of foam panels 56, sandwiched between two plywood thicknesses 57. The panels 57 have the function of distributing the stresses applied to the insulating layer 55 , and therefore allow a better positioning thereof on the concrete walls. As for them, the insulating panels 56 are for example constituted by blocks of closed cell foam, based on polyurethane (PU) or polyvinyl chloride (PVC).

Similarly, the foam panels 56 can be waterproof and hermetically connected to each other by leaktight connections, in order to constitute an additional layer of insulation, continuous and hermetic.

One of the faces of the panels 57 facing the concrete is bonded to the latter, for example using a layer of suitable adhesive material. It is conceivable that the layer of adhesive material is continuous and impermeable, so that it contributes to the sealing of the reservoir 1.

It is possible to compensate with the adhesive material for surface defects in the concrete and to avoid the presence of pockets between the concrete and the insulation layer 55.

On the other hand, it can be seen in FIGS. 1, 2 and 5 that a suspended roof 36, which is fixed by means of tie rods or of cables 37 to the dome 35 and therefore to the dome 3, is interposed between the latter and the external enclosure 2. This roof 36 is constituted by a lattice of aluminum beams, itself covered with a layer of insulation 365 , for example in glass wool. Near the shoulder 352 described above, the suspended roof 36 comes into contact at its periphery with the insulation envelope 5, of which it is a part. It is then understood that this suspended roof 36 as well as its layer of glass wool 365 makes it possible to thermally isolate the fluid contained in the tank 1, the dome 3 and its dome 35, so as to maintain these elements at approximately room temperature. .

The reference numeral 70 designates in the figures pipes for loading and unloading the fluid to be stored in the reservoir 1. These pipes 70 which are of conventional type will not be described in more detail here.

Referring now to Figure 5, we see an arrangement of tanks 1 roughly similar to those just described. These tanks 1 are buried in an area of the ground S which is itself enclosed in a substantially sealed wall, buried and closed 20. Advantageously, the wall 20 is produced by molding in a trench in the ground, of a waterproof and deformable material, such as for example a plastic concrete or a sealing grout. For example, four tanks 1 arranged in a square could be confined inside a buried wall 20 of cylindrical or parallelepiped shape. Here, this wall 20 has a thickness at most equal to that of the external enclosures 2 of the corresponding reservoirs 1, and its base projects deeper than the latter into the ground. Preferably, the wall 20 extends up to the interior of the substantially impermeable layer SI. Such an enclosure or buried wall 20 which is substantially sealed, therefore makes it possible to minimize the infiltration of water into the area where the reservoirs 1 are located, so that the height and above all the thickness of the latter can be considerably reduced . The reference numeral 201 designates in FIG. 5 a system for pumping the water contained inside the wall 20. It is understood that such a system 201 has the function of evacuating out of the wall 20, so that its level is constantly maintained below the level of the rafts 4 of the tanks 1 surrounded by this wall 20. Since the infiltration of water into the ground where the tanks 1 are buried is minimized by the presence of the waterproof wall 20, the pumping system 201 of the arrangement of FIG. 5, can be very simple, which makes this arrangement particularly economical.

Obviously, the invention is in no way limited to the illustrated embodiments, but includes all the equivalents of the technical means described as well as their combinations, if these are carried out according to the spirit.

Claims (11)

Tank for the containment of any fluid, such as in particular a liquefied gas, and of the type comprising a concrete enclosure (2) buried in the ground (S), a rigid structure with a bottom slab (4) and essentially a covering dome (3) as well as a sealed envelope of thermal insulation (5) which delimits inside the structure a loading space for the fluid, the external enclosure having the form of a thick and substantially wall waterproof, characterized in that this enclosure (2) as well as the covering dome (3) are integrally formed with one another and constitute, together with the bottom slab (4), said rigid structure of the tank (1) , and that the base of the above-mentioned external enclosure (2) extends at least to a layer (SI) substantially impermeable to water, of the ground (S). Tank according to claim 1, characterized in that it comprises a drainage system (6) comprising a second slab consisting of porous aggregates disposed on the bottom of the cavity excavated in the ground (S) and the aforementioned slab (4) and provided with a device for evacuating the water penetrated into the second raft (6) towards the outside, using the delivery pumps and wells (P) formed in the ground (S) near the tank (1), by means of conduits (66) produced through the enclosure (2). Tank according to claim 1 or 2, characterized in that the bottom slab (4) has the shape of a reinforced concrete slab, resting freely on the one hand on one or more stops (24) integral with the external enclosure (2), and on the other hand on the drainage system (6). Tank according to one of claims 1 to 3, characterized in that the reinforced concrete slab or slab (4) has a thickness less than that of the corresponding external enclosure (2). Tank according to one of claims 1 to 4, characterized in that the aforementioned insulation envelope (5) comprises a waterproof metallic membrane (52; 54) fixed inside the external enclosure (2) and on the bottom slab (4) by means of a thermal insulation layer (55). Tank according to claim 5, characterized in that the above-mentioned insulation layer (55) comprises at least one thickness of rigid panels (57) for stress distribution, as well as at least one thickness of foam plastic panels. Tank according to claim 6, characterized in that the aforementioned foam panels (56) are impermeable and hermetically connected to each other by leaktight connections, in order to constitute a layer of continuous and hermetic insulation. Tank according to claim 7, characterized in that the above-mentioned insulation layer (55) is fixed to the concrete with a preferably continuous thickness of adhesive material. Tank according to one of Claims 4 to 8, characterized in that the aforementioned envelope further comprises a sealed dome (35) of steel hermetically fixed by its periphery to the metal membrane and constituting an internal coating for the covering dome, as well as an aluminum suspended roof (36) and covered with a layer of thermal insulation (365) which is interposed between the waterproof membrane and the dome in order to maintain the latter at approximately room temperature. Tank according to one of Claims 1 to 9, characterized in that the above-mentioned dome (3) and possibly the above-mentioned waterproof dome (35) rest on the external enclosure (2) of the tank (1) via a crowning beam (32) of corresponding shape. Tank arrangement (1) according to one of claims 1 to 10, characterized in that said tanks (1) are arranged inside a substantially sealed, buried and closed wall (20), and the base of which s 'extends at least near the substantially impermeable layer (SI) of the ground (S).

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