WO2006046872A1

WO2006046872A1 - Tank for storage of lng or other cryogenic fluids

Info

Publication number: WO2006046872A1
Application number: PCT/NO2005/000402
Authority: WO
Inventors: Otto Skovholt; Bjørn SJETNAN; Trond Johansen; Terje Myrhaug; Steinar Johansen
Original assignee: Concryo As; Ncc Construction As
Priority date: 2004-10-25
Filing date: 2005-10-25
Publication date: 2006-05-04
Also published as: NO20044586L; WO2006062411A1; WO2006046873A1; NO328739B1; NO20044586D0; WO2006046874A1

Abstract

A tank (1) for storage of LNG or other cryogenic fluids, comprising: an inner tank (2) having a bottom (2a), an inner side wall (2b) extending upwards to an optional insulating roof (2f); an outer tank (3) having a bottom (3a), an outer side wall (3b) extending upwards around the inner tank to a level above said inner tank, an outer gas tight lining (3c) on or in the outer side wall, and an outer roof construction (3d) above said inner tank; insulating material (4) between said inner tank and said outer tank; and at least one feedthrough (5) for filling and draining, distinguished in that the inner tank has side walls (2b) consisting of an inner concrete wall (2c), an intermediate low temperature ductile tight layer (2d), and an outer prestressed concrete wall (2e), which side walls act as one unit in operation, but wherein the inner side wall (2e) can contract freely during cooling and the outer side wall ( 2e) can expand freely at increased temperature, as said side walls are supported freely and the outer side wall (2e) is adaptedly prestressed.

Description

TANK FOR STORAGE OF LNG OR OTHER CRYOGENIC FLUIDS

Field of invention

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

Prior art and background of the invention

Storage of LNG requires tanks withstanding operating temperatures lower than -161 ⁰C, which is the boiling point at atmospheric pressure of methane, the main component of LNG. A normal operating temperature of an LNG tank is -163 ⁰C.

Today, LNG is usually stored in double-walled tanks at atmospheric pressure. The inner tank serves to keep the LNG content enclosed, whereas the outer tank keeps the insulating material in position, protects the inner tank and the insulation against external influence, and provides increased security in case of leakage in the inner tank. For small to medium size tanks it is not unusual to use pressure tanks or isolation provided by arranging a vacuum between the tank walls. Such arrangements are inadequate for large tanks because the walls must be made unduly solid. In order to limit the wall thickness a circular cross section of the tank is the most usual. The outer tank is usually constructed to keep LNG or gas enclosed if a leakage should occur in the inner tank, especially if the tank is situated at a location having bad ventilation or in a populated area. The tanks of LNG import and export terminals may have sizes of up to about 160,000 m³, or even 200,000 m³, which may necessitate a tank diameter of about 70 m and a tank height of about 60 m.

For large LNG tanks, mainly two types of constructions are used. The first type of construction is a cylindrical, self-standing tank of which the inner tank is made of a suitable steel and the outer tank is built of steel or reinforced/prestressed concrete. The second type of construction is a membrane tank in which a thin metal membrane, for instance of a thickness of 1.2 mm, is installed in a cylindrical concrete structure which is built either below or above the ground level. An insulating layer is positioned between the metallic membrane of stainless steel and the load-bearing concrete structure.

Patent Publication US 3,319,431, dealing with a double- walled cryogenic tank, describes the problems connected with temperature expansion, which problems are substantially reduced by the inner tank and the outer tank having a more equal thermal expansion, due to the fact that temperature isolation is arranged outside the outer tank, which makes the temperature more equal in the two tanks constituting the double wall structure. Patent publication NO 314,814 teaches a tank for storage of cryogenic fluids, comprising a tank (11) having a bottom part (12), a vertical wall part (14), and preferably an upper delimitation (15), which tank (11) is equipped with a fluid tight barrier (26) preventing the stored fluids from seeping out from the tank (11), said fluid tight barrier (26) being preferably made of thin, joined metal plates; said tank being distinguished by said vertical wall part (14) comprising an inner structurally bearing part (24), an outer structurally bearing part (25), and said fluid tight barrier (26) being arranged between said inner (24) and outer (25) structurally bearing parts, said structurally bearing wall parts (24, 25) constituting, together with the intermediate fluid tight barrier (26), a compact, structurally integrated and fluid tight wall part (14). The inner structurally bearing part (24) is made of multi-axially prestressed concrete, and likewise the outer structurally bearing 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 i.a. by the lower end of the vertical wall part being terminated 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 part without tensions occurring, which tensions are acting on the remaining wall elements. This represents a problem which may lead to cracking by repeated filling and draining of a such tank. There is a demand for a tank that is not encumbered by said problem.

Summary of the invention The above-mentioned demand is met by providing a tank for storage of LNG and other cryogenic fluids, comprising an inner tank having a bottom, an inner side wall extending upwards to an optional insulating roof, an outer tank having a bottom, an outer side wall extending upwards around the inner tank to a level above said inner tank, an outer gas tight lining on or in the outer side wall, and an outer roof construction above said inner tank, insulating material between said inner tank and said outer tank, and at least one feedthrough for filling and draining, distinguished in that the inner tank has side walls consisting of an inner concrete wall, an intermediate low temperature ductile tight layer, and an outer prestressed concrete wall, which side walls act as one unit in operation, but wherein the inner side wall can contract freely during cooling and the outer side wall can expand freely at increased temperature, as said side walls are supported freely and the outer side wall is adaptedly prestressed. The invention also provides a more general tank for storage of LNG or other cryogenic fluids, comprising side walls extending upwards and consisting of an inner concrete wall, an intermediate low temperature ductile tight layer and an outer prestressed concrete wall, distinguished in that the side walls act as one unit when in operation, but wherein the inner concrete wall can contract freely during cooling and the outer prestressed concrete wall can expand freely at increased temperature, as said inner concrete wall having the intermediate low temperature ductile tight layer arranged thereon and the outer prestressed concrete wall, are supported freely at an upper end and at a lower end. With tanks for cryogenic fluids are meant tanks designed for storage of fluids at -40 ⁰C or lower temperature, or more general, tanks exposed to large temperature variations, so that the problems mentioned above are relevant.

Thus, the above-mentioned cracking problems are avoided.

The side walls of the tank, made of concrete, are preferably slip formed so as to minimize costs and building period. The tank preferably comprises at least one earth quake support between the outer and inner side wall in order to improve the security against leakage.

Drawings

The invention is illustrated by three drawings, of which: Figure 1 illustrates a tank according to the invention, in half section,

Figure 2 illustrates the transition between inner tank, roof and outer tank, for the tank of Figure I₅ and

Figure 3 illustrates the transition between the side wall and bottom of the tank, for the tank of Figure 1.

Detailed description

Reference is made to Figure I₅ illustrating a tank 1 according to the invention for storage of LNG or other cryogenic fluids. The tank 1 comprises an inner tank 2 having a bottom 2a, inner side walls 2b extending upwards and consisting of an inner concrete wall 2c, an intermediate low temperature ductile tight metal lining 2d, an outer wall 2e of prestressed concrete, and an insulating roof 2f.

The tank 1 further comprises an outer tank 3 having a bottom 3 a, an outer side wall 3b extending upwards around the inner tank 2 to a level above said inner tank, an outer gas tight steel lining 3 c on the inner side of the outer wall, and an outer roof construction 3d above the inner tank. An insulating material 4 is arranged between the inner tank 2 and the outer tank 3. Also, at least one feedthrough 5 is arranged for filling and draining, which feedthrough is not shown in detail, but consists of inlet and outlet pipes, pumps and cables. Means for access of personnel are provided at the feedthrough locality. The side wall 3b of the outer tank 3 is formed in concrete as a homogenous unit, preferably without joints, and with a sufficient ring strength at an upper end, so that the outer roof construction 3d can be arranged directly on the outer side wall. The side wall 3b of the outer tank 3 is preferably formed with an enlarged wall thickness at the upper end, and preferably even at a lower end, so as to achieve a sufficient ring rigidity to resist expected impact in case of an earth quake.

The enlarged wall thickness, with the resulting increased ring rigidity and ring strength at the upper end and the lower end of the side wall 3b of the outer tank 3, is clearly seen in Figure 1. Reference is made, however, to Figure 2, from which it appears more clearly how the upper end of the outer side wall 3d has been formed with an enlarged wall thickness, for the outer wall construction 3d to be arranged directly on the outer side wall. Similarly, enlarged wall thickness and increased ring rigidity is also found at the lower end of the side wall 3b. The side walls are extending upwards from the periphery of the bottom parts, typically vertically, but they may also be arranged inclined. The conception of arranging the outer wall construction directly on the outer side wall implies that additional construction arrangements are not required for building the outer roof directly on the outer side wall. In clear terms, this means that there is no reinforcing ring beam at the upper end of the outer side wall. Thus, considerable work and considerable costs are saved. In the tank of the present invention side walls of concrete 2c, 2e, 3b are preferably slip formed. Slip forming is advantageous because the casting time can be considerably reduced as compared to casting using climbing formwork.

The tank of the present invention preferably comprises at least one earthquake support 6 between the outer and the inner side wall. Earthquake supports are illustrated in Figures 1, 2, and 3. The earthquake supports are advantageously arranged as two sets of earthquake supports, each set having six earthquake supports, one set of earthquake supports being arranged at a low level and one set at a higher level, as indicated in Figure 1. The earthquake supports advantageously comprise pitch having been introduced in a hot state into an intermediate space between the side walls and having been solidified so as to provide support after filling of the inner tank. The pitch may be melted for draining, if needed. Thus, filling lines are provided and advantageously also means for melting, such as heating cables, as well as a line for draining of the pitch. The earthquake support per se may advantageously be a wood construction arranged between the inner wall and the outer wall, having means for filling and optionally means for melting of the pitch and draining thereof.

Reference is made to Figure 3, wherein a section of the lower part of the tank is shown, at the transition between the bottom and the side walls. More precisely, the bottom 2a of the inner tank and the bottom 3 a of the outer tank are shown, which are both made of a low temperature ductile metal. It is also shown how the space between the bottom layers is stratified with two layers of isolating blocks 7a, 7b, with small blocks, preferably made of isolating concrete, arranged in an upper layer 7a, and larger blocks, preferably made of isolating concrete, being arranged in a lower layer 7b, with overlaying, intermediate and underlying slip layers 8, preferably slip layers of low friction plywood. The purpose of said advantageous construction is to allow temperature induced expansion and compression, without stress formation and cracking. Furthermore, a support ring 9 is shown, and also a bearing ring 10, said bearing ring 10 being arranged below the inner side wall and being made of a pressure resistant perlite concrete. At detail B, it is shown how the bottom of the outer tank and the gas tight lining in the form of a low temperature ductile metal lining on the inner side of the side wall of the outer tank is shaped with a rounded transition between said elements and a yielding material 3g, for instance mineral wool, is arranged at the inside of said transition, the fastening of the low temperature ductile metal against the support near said transition is slip able, and the transition is situated mainly on the outside of the isolation on the relatively hot side of the tank wall, so said transition can resist stretching without cracking. In case of leakage of LNG to the outer tank, the transition will contract against the yielding material, whereby excessive stress build-up is avoided.

The tank of the present invention has advantageously an inner wall construction fairly similar to the wall construction of the tank according to NO 314,814, however, said inner wall construction is not joined as one integrated unit, thereby avoiding undesired stress build-up and cracking upon cooling/filling and draining, when large temperature changes occur. The inner part of the inner wall may contract during filling, whereby undesired stress is avoided. However, when the tank is full or empty, the inner wall construction acts as an integrated unit, because the outer part of the inner side wall is adaptedly prestressed.

Figure 3 shows in more detail how the transition between bottom and inner side wall advantageously is arranged. More precisely, it is shown how the inner tank has side walls acting as one unit during operation, allowing the inner vertical side wall 2c to contract freely during filling and allowing the outer vertical side wall 2e of the inner tank to 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 both are provided with teflon lined footings 11 which can slide freely on an underlying teflon lined plate 12 arranged on the support ring 10. Teflon may be replaced by other means providing low friction, for instance molybdenum disulphide based coatings. A similar arrangement is advantageously also provided at the upper end of the side wall of the inner tank, as shown in Figure 2. The transition between the inner bottom 2a and the footing on the inner concrete wall 2c contains a torus 13 capable of absorbing temperature induced strain.

The base plates 11 and the underlying Teflon lined plate are preferably made of low temperature ductile steel, preferably of high tensile type.

Claims

5 1. A tank (1) for storage of LNG or other cryogenic fluids, comprising an inner tank (2) having a bottom (2a), an inner side wall (2b) extending upwards to an optional insulating roof (2f), an outer tank (3) having a bottom (3a), an outer side wall (3b) extending upwards around the inner tank to a level above said inner tank, an outer gas tight lining (3c) on or o in the outer side wall, and an outer roof construction (3d) above said inner tank, insulating material (4) between said inner tank and said outer tank, and at least one feedthrough (5) for filling and draining, characterized in that the inner tank has side walls (2b) consisting of an inner concrete wall (2c), an s intermediate low temperature ductile tight layer (2d), and an outer prestressed concrete wall (2e), which side walls act as one unit in operation, but wherein the inner side wall (2e) can contract freely during cooling and the outer side wall ( 2c) can expand freely at increased temperature, as said side walls are supported freely and the outer side wall (2e) is adaptedly prestressed. 0

2. A tank (1) for storage of LNG or other cryogenic fluids, comprising side walls (2b) extending upwards and consisting of an inner concrete wall (2c), an intermediate low temperature ductile tight layer (2d) and an outer prestressed concrete wall (2e), 5 characterized in that the side walls act as one unit when in operation, but wherein the inner concrete wall (2c) can contract freely during cooling and the outer prestressed concrete wall can expand freely at increased temperature, as said inner concrete wall (2c) having the intermediate low temperature ductile tight layer (2d) arranged thereon and the outer prestressed concrete wall (2e), are supported freely at an o upper end and at a lower end.

3. The tank of claim 1 or 2, characterized in that it comprises a footing (11) below the inner concrete wall (2c), a footing (11) below the prestressed concrete wall (2e) and an underlying plate (12) 5 below the footings, said plates (11,12) being made of low temperature ductile steel.

4. The tank of claim 3, characterized in that a low friction coating is arranged on the footings (11) and the underlying plate (12).