NO328739B1 - Tank for storage of LNG or other cryogenic fluids - Google Patents

Abstract

A tank (1) for storing LNG or other cryogenic fluids, comprising an inner tank (2) having a bottom (2a), an inner side wall (2b) extending upwardly to an insulating roof (2f), an outer tank (2) 3) having a bottom (3a), an exterior sidewall (3b) extending upwardly around the inner tank to level above it, an exterior gas-tight cladding (3c) on or in the exterior sidewall, and an exterior roof structure (3d) above the inner tank, insulating material (4) between the inner and the outer tank, and at least one feed (5) for filling and emptying. The tank is characterized in that the sidewall (3b) of the outer tank (3) is molded in concrete as a homogeneous unit with sufficient integrated annular strength at an upper end so that the outer roof structure (3d) can be arranged directly on the outer sidewall. Further thoughts are also described.

Description

Field of the invention

The present invention relates to the storage of LNG, i.e. liquefied natural gas, and other cryogenic liquids. More specifically, the invention relates to large tanks for storing LNG or other cryogenic liquids.

Prior art and the background of the invention

To store LNG, tanks are required that can withstand operating temperatures lower than

-161 °C, which is the boiling point at atmospheric pressure for methane, the main component in LNG. Normal operating temperature for an LNG tank is -163 °C.

LNG is today usually stored in double-walled tanks at atmospheric pressure. The inner tank serves to keep the LNG content contained, while the outer tank holds insulation material in place, protects the inner tank and the insulation against external influences, and provides increased safety in the event of a leak in the inner tank. For small to medium-sized tanks, it is neither unusual for pressure tanks nor insulation provided by arranging a vacuum between the tank walls, which designs are inappropriate for large tanks because the walls have to be built disproportionately strong. To limit the wall thickness, circular tank cross-sections are most common. Generally, the outer tank is designed to keep the LNG or gas contained if a leak occurs in the inner tank, especially if the tank is located in a place with poor ventilation or in a populated area. For import and export terminals for LNG, the tanks can have a size of up to approx. 160,000 m<3>, or even 200,000 m<3>, which can result in a tank diameter of approx. 70 m and a tank height of approx. 60 m.

For large LNG tanks, mainly two types of construction are used. The first type of construction is a cylindrical, self-standing tank where the inner tank is built of suitable steel and the outer tank is built of steel or reinforced/prestressed concrete. The second type of construction is a membrane tank where a thin metal membrane, e.g. 1.2 mm thick, is installed inside a cylindrical concrete structure which is again built either below or above ground level. An insulation layer is placed between the stainless steel metal membrane and the load-bearing concrete structure.

In patent publication US 3,319,431, which deals with a double-walled cryogenic tank, the problems associated with temperature expansion are described, which problems are significantly reduced by having the inner and outer tank have more equal thermal expansion, by thermal insulation being arranged outside the outer tank, so that the temperature becomes more equal for the two tanks that make up the double wall structure.

In patent publication NO 314814, a tank for storing cryogenic fluids is described, comprising a tank (11) with a bottom part (12), a vertical wall part (14) and preferably an upper boundary (15), which tank (11) is equipped with a fluid-tight barrier (26) which prevents the stored fluids from penetrating out of the tank (11), said fluid-tight barrier (26) preferably being formed of thin joined metal plates, which tank is characterized by said vertical wall part (14) comprising a inner structural bearing part (24), an outer structured bearing part (25) and that the fluid-tight barrier (26) is arranged between said inner (24) and outer (25) structural bearing part, which structurally bearing wall parts (24, 25) and the intermediate fluid-tight barrier (26) together constitute a compact, structurally integrated and fluid-tight wall section (14). The inner structurally supporting part (24) is made of multiaxial tension-reinforced concrete, just like the outer structurally supporting part (25). The fluid-tight barrier (26) is made of a ductile material, such as Ni-steel. As mentioned, the vertical wall part of the tank forms a compact, structurally integrated and fluid-tight wall part, which is achieved, among other things, by the lower end of the vertical wall part being finished by a horizontal metal plate (27) as well as an inner (29) and an outer (28 ) vertical steel plate extending along the inner and outer periphery of the vertical wall (14), which vertical steel plates (28, 29) are welded to said horizontal steel plate (27). Thus, it is not possible to achieve independent contraction or expansion of wall elements in the vertical wall section, without tensions arising that act on the other wall elements. This poses a problem that can lead to cracking during repeated filling and emptying of such a tank. There is a need for a tank without the aforementioned problem.

Summary of the invention

The above-mentioned need is met by providing a tank for the storage of LNG or other cryogenic fluids, comprising

an inner tank with a bottom, an inner side wall that extends upwards to an insulating roof, if any,

an outer tank with a bottom, an outer side wall extending upwards around the inner tank to a level above it, an outer gas-tight cladding on or in the outer side wall, and an outer roof structure over the inner tank,

insulating material between the inner and the outer tank, and

at least one passage for filling and emptying,

characterized by that

the inner tank has side walls consisting of an inner concrete wall, an intermediate low-temperature ductile dense layer and an outer prestressed concrete wall, where the side walls act as one unit during operation, but where the inner side wall can contract freely during cooling and the outer side wall can expand freely upon increased temperature, as said side walls are freely stored and the outer side wall is suitably prestressed.

The invention also provides a more general tank for the storage of LNG or other cryogenic fluids, comprising side walls that extend upwards and consist of an inner concrete wall, an intermediate low-temperature ductile dense layer and an outer prestressed concrete wall, characterized by the fact that the side walls during operation act as one unit, but where the inner concrete wall can contract freely during cooling and the outer prestressed concrete wall can expand freely at increased temperature, the inner concrete wall with the intermediate low-temperature ductile dense layer arranged thereon, and the outer prestressed concrete wall, is freely stored in an upper and a lower end. Tanks for cryogenic fluids mean tanks designed to be able to store fluids at -40°C or colder, or more generally tanks that are exposed to large temperature variations so that the problem mentioned at the outset is relevant.

In this way, the initially mentioned problems with cracking are avoided.

The concrete side walls of the tank are advantageously slip-cast, to minimize cost and construction time.

The tank advantageously includes at least one earthquake support between the outer and inner side walls, to increase safety against leakage.

Drawings

The invention is illustrated with three drawings, of which

Figure 1 illustrates a tank according to the present invention, where half the tank is shown in section, Figure 2 illustrates the transition between inner tank, roof and outer tank, for the tank illustrated in Figure 1, and Figure 3 illustrates the transition between side wall and bottom for the tank illustrated in

Figure 1.

Detailed description

Reference is made to Figure 1 where a tank 1 according to the invention for storing LNG or other cryogenic fluids is illustrated. The tank 1 comprises an inner tank 2 with a bottom 2a, inner side walls 2b which extend upwards and consist of an inner concrete wall 2c, an intermediate low-temperature ductile dense metal layer 2d, an outer prestressed concrete wall 2e, and an insulating roof 2f.

Furthermore, the tank 1 comprises an outer tank 3 with a bottom 3a, an outer side wall 3b which extends upwards around the inner tank 2 to a level above it, an outer gas-tight steel cladding 3c on the inside of the outer side wall, and an outer roof structure 3d above it inner tank. Insulation material 4 is arranged between the inner tank 2 and the outer tank 3. Furthermore, at least one passage 5 for filling and emptying is arranged, which is not illustrated in detail, but consists of import and export pipes, pumps and cables. During the implementation, there are also facilities for access by personnel.

The tank side wall 3b in the outer tank 3 is cast in concrete as one homogeneous unit, preferably without joints, with sufficient ring strength at an upper end so that the outer roof structure 3d can be arranged directly on the outer side wall. The side wall 3b in the outer tank 3 is advantageously designed with increased wall thickness at the upper end, and advantageously also at a lower end so that sufficient ring stiffness to withstand assumed stresses in an earthquake is achieved.

The extended wall thickness, with resulting increased ring stiffness and ring strength at the upper end and the lower end of the side wall 3b in the outer tank 3, can be seen clearly in Figure 1. However, reference is made to Figure 2, where it is more clearly evident how the upper end of the outer side wall 3b is designed with extended wall thickness at the upper end, so that the outer roof structure 3d can be arranged directly on the outer side wall. Correspondingly increased wall thickness and increased ring stiffness are also found at the lower end of the side wall 3b. The side walls extend upwards from the periphery of the bottom parts, typically vertically, but they can be arranged at an angle. With the concept that the outer roof structure can be arranged directly on the outer side wall, it is meant that no further structural arrangements are necessary to be able to build the outer roof directly on the outer side wall. This means concretely that there is no reinforcing ring beam at the upper end of the outer side wall. This saves considerable work and costs.

With the tank according to the present invention, concrete side walls 2c, 2e, 3b are preferably slip-cast. Slip casting is advantageous in that the time for casting can be significantly reduced compared to casting with climbing formwork.

The tank according to the present invention preferably comprises at least one earthquake support 6 between the outer and inner side walls. Earthquake supports are illustrated on

Figures 1, 2 and 3. The earthquake supports are advantageously arranged as two sets of earthquake supports, with six earthquake supports in each set, one set of earthquake supports being arranged at a low level and one set at a higher level, as can be seen from Figure 1. The earthquake supports advantageously contain pitch which, when hot, is poured into a space between the side walls and is solidified as a support after filling the inner tank. The basin can be melted to empty out, should this be relevant. Thus, pipes for filling are arranged, and advantageously a device for melting, such as heating cables, as well as a pipe for emptying the brook. The earthquake support itself can advantageously be constructed as a wooden structure which is arranged between the inner and outer side walls, with devices for filling and possibly devices for melting the stream and emptying.

Reference is also made to Figure 3 where a section of the lower part of the tank is illustrated, at the transition between the bottom and side walls. More specifically, bottom 2a in the inner tank and bottom 3a in the outer tank are illustrated, both of which are made of low-temperature ductile metal. It is also clear how the space between the bottom layers is layered with two layers of insulating blocks, 7a, 7b, as small blocks, preferably of insulating concrete, are arranged in an upper layer 7a, and larger blocks 7b, preferably of insulating concrete, are arranged in a lower layer, with overlying, intermediate and underlying sliding layer 8, preferably sliding layer of smooth plywood. The purpose of said advantageous construction is to allow temperature-induced expansion and compression, without tension formations and cracking. Furthermore, a support ring 9 and a support ring 10 are illustrated, the support ring 10 being arranged under the inner side wall and made of compressive perlite concrete. In detail B, it is illustrated how the bottom of the outer tank and the gas-tight cladding in the form of low-temperature ductile metal cladding on the inside of the outer tank's side wall are designed with a rounded transition between said elements, and a yielding material 3g, for example mineral wool, is arranged on the inside of the transition, the attachment of the low-temperature ductile metal to the substrate near the transition is smooth, and the transition is essentially on the outside of the insulation on the relatively warm side of the tank wall, so that the transition can withstand strain without cracking. In case of leakage of LNG to the outer tank, the transition will contract against the yielding material so that undue stress build-up is avoided.

The tank according to the present invention advantageously has an inner wall construction that is quite similar to the wall construction for the tank according to NO 314814, however, the inner wall construction is not joined as one integrated unit, so that undesirable stress build-up and cracking during cooling/filling and emptying is avoided, as it large temperature changes occur. The inner part of the inner wall can contract when filling, so that undesirable tension formation is avoided. When the tank is full or empty, however, the inner wall structure acts as one integrated unit, as the outer part of the inner side wall is suitably prestressed.

Figure 3 illustrates in more detail how the transition between bottom and inner side wall is advantageously arranged. More specifically, it is clear how the inner tank has side walls that act as one unit during operation, but where the inner vertical side wall 2c can contract freely during filling and the outer vertical side wall 2e in the inner tank can expand freely at increased temperature, as the lower end of the inner concrete wall 2c and the lower end of the outer prestressed concrete wall 2e are both equipped with Teflon-coated foot plates 11 which can slide freely on an underlying Teflon-coated plate 12 arranged on the support ring 10. Teflon can be replaced with other means that provide low friction, for example molybdenum disulphide-based coatings . A similar arrangement can advantageously also be found at the upper end of the side wall in the inner tank, which can be seen in Fig. 2. The transition between the inner bottom 2a and the base plate on the inner concrete wall 2c contains a torus 13 which can absorb temperature-induced strain.

Both the foot plates 11 and the underlying Teflon-coated plate 12 are advantageously made of low-temperature ductile steel, preferably of the high-strength type.

Claims (4)

1. Tank (1) for storage of LNG or other cryogenic fluids, comprehensive an inner tank (2) with a bottom (2a), an inner side wall (2b) which extends upwards to an optional insulating roof (2f), an outer tank (3) with a bottom (3 a), an outer side wall (3b) extending upwards around the inner tank to a level above it, an outer gas-tight lining (3 c) on or in the outer side wall, and a outer roof construction (3d) over the inner tank, insulating material (4) between the inner and the outer tank, and at least one passage (5) for filling and emptying, characterized by that the inner tank has side walls (2b) consisting of an inner concrete wall (2c), an intermediate low-temperature ductile dense layer (2d) and an outer prestressed concrete wall (2e), where the side walls act as one unit during operation, but where the inner side wall ( 2c) can contract freely during cooling and the outer side wall (2e) can expand freely at increased temperature, as said side walls are freely stored and the outer side wall (2e) is suitably prestressed. 2. Tank (1) for storage of LNG or other cryogenic fluids, extensive side walls (2b) which extend upwards and consist of an inner concrete wall (2c), an intermediate low-temperature ductile dense layer (2d) and an outer prestressed concrete wall (2e), characterized in that the side walls act as one unit during operation, but where the inner concrete wall (2c) can contract freely during cooling and the outer prestressed concrete wall can expand freely at increased temperature, the inner concrete wall (2c) with the intermediate low-temperature ductile dense layer (2d) arranged thereon, and the outer prestressed concrete wall (2e), are freely stored at an upper and a lower end. 3. Tank according to claim 1 or 2, characterized in that it comprises a foot plate (11) under the inner concrete wall (2c) and a foot plate (11) under the prestressed concrete wall (2e), an underlying plate (12) under the foot plates, which plates (11, 12) are made of low temperature ductile steel. 4. Tank according to claim 3, characterized in that a smooth coating is arranged on the footplates (11) and the underlying plate (12).