WO2009054726A1

WO2009054726A1 - Tank for transport and storage of liquid gas, with provisions for absorbing deformations due to temperature variations or internal loads

Info

Publication number: WO2009054726A1
Application number: PCT/NO2008/000372
Authority: WO
Inventors: Kåre SYVERTSEN; Arne Smedal
Original assignee: Sevan Marine Asa
Priority date: 2007-10-23
Filing date: 2008-10-20
Publication date: 2009-04-30
Also published as: WO2009054726A4; NO20075391L; NO329738B1

Abstract

Tank for transport and storage of cooled, liquid gas comprising a polygonal or circular-cylindric wall construction comprising one or several inner skin plates (2) abutting an outer insulation (3) and an outer wall structure (4) supporting the insulation. In the polygonal embodiment of the tank, the inner skin plates (2) in the area for knuckle lines between adjacent, plane parts of the skin plates (2) provided with an unsupported, curved plate part (2') with comparatively large radius of curvature, so that the curved plate part (2') by changing the radius of curvature will absorb the plate deformations due to temperature variations or internal loads in the tank (1).

Description

Tank for transport and storage of liquid gas, with provisions for absorbing deformations due to temperature variations or internal loads .

This invention relates to a tank for transport and storage of cool, liquid gas

(LNG, LPG etc.), comprising a polygonal or circular cylindric wall construction consisting of one or several internal skin plates abutting an outer insulation, and an outer wall structure supporting the insulation.

The technology today for transport and storage of cool, liquid gas is mainly based on three different constructions. In terms of tanks arranged in a ship these three types of construction can briefly described as follows:

- Spherical tanks of aluminum. The tanks are self-supporting and journalled in the ship hull on a "belly band".

- Membrane tanks consisting of thin plates of stainless steel abutting an insulation. Steel plates in this construction do not contribute to a strengthening element, but as a sealing against gas. The thin steel plates are arranged with a certain corrugation in order to absorb deformations due to temperature variations. In membrane tanks there will often be a membrane layer as there is a certain risk for puncturing of the thin membrane plates. - Self-supporting "conventional" tanks. These are tanks that can be built of stainless steel or aluminium. The concept is based on building a free-standing, self- supporting tanks arranged in spaces/tanks in the ship hull.

For all the relevant embodiments the tanks are isolated outside of the plates comprising the tank itself. The insulation must be sufficient to retain gas stored at temperatures down towards -17O⁰C without excessive heat transfer. This is important in order to reduce evaporation and preventing that the surrounding structures having too low temperatures.

A major object of the present invention is to provide a tank construction comprising internal skin plates having a designed and support that deformations due to temperature variations or internal loads can be absorbed without providing larges forces in the plates.

Another object for the invention is to provide a tank construction suitable for building of very large tanks, such as a diameter approximately 80 m and a height of 30- 40 m (approx. 200 000 m³). According to this invention a tank is provided comprising a polygonal wall construction of the above mentioned type characterized by the inner skin plates the area for buckling between adjacent, plane sections of the skin plates being equipped with a curved plate section with comparatively large radius of curvature, in order that the curved plate section by changing the radius of curvature absorbs the deformations of the plates due to temperature variations or internal loads in the tank.

According to this invention a tank is also provided comprising a circular cylindrical wall construction of the above mentioned type which is characterized by the inner skin plate being supported by a number of longitudinal, raised parts extending in the axial direction of the tank, the skin plates on each side of the respective raised parts have an unsupported, curved section with comparatively large radius of curvature so that the curved plate section by changing the radius of curvature will absorb plate deformations due to temperature variations or internal loads in the tank. Between the curved parts the skin plates will abut supporting panel/insulation blocks.

In a preferred embodiment of a tank according to the invention, the skin plates between the curved parts are equipped with a number of local bracings in the form of stays extending in the longitudinal direction of the tank. These stays are provided in order to keep the skin plates stable against the support panel.

The tank construction according to the invention is primary suitable for tanks used for transport and storage of gas on floating units, but the construction principle may also be used for storage tanks placed on land.

The invention will now be described further in connection with a number of embodiments and with reference to the drawings, where figure 1 illustrates a vertical, axial view in section of the centre of polygonal (see figure 2) according to the invention, figure 2 show a horizontal section through a central area of the tank according to figure 1, figure 3 shows a section of figure 2 with the detail A shown in enlarged scale, figure 4 shows a section of figure 1 with the detail B shown in enlarged scale, figure 5 shows an enlarged section of the detail B in figure 4 with the detail C shown in enlarged scale and where the curved skin plate is shown in two different functional positions, figure 6 shows a horizontal section through a tank with a circular cylindric profile with the detail D shown in enlarged scale, figure 7 shows the horizontal section of a similar tank as in figure 6, with the detail E shown in enlarged scale, figure 8 shows the detail E in figure 7 in a further enlarged scale, figure 9 shows an enlarged section through a first tank arrangement in a ship, with single rectangular tanks, figure 10 shows a vertical section according to line X-X in figure 9, figure 11 shows a horizontal section through another tank arrangement in a ship with rectangular tanks in an embodiment reducing the angle in the corners, figure 12 shows a vertical section according line XII-XII in figure 11, figure 13 shows a horizontal view through a third tank arrangement in a ship with polygonal tanks, figure 14 shows a vertical section according to the line XIV-XIV in figure 13, figure 15 shows a horizontal section through the fourth tank arrangement in a ship with longitudinal rectangular tanks, and figure 16 shows a vertical section according to the line XVI-XVI in figure 15.

In the various figure corresponding parts and elements are denoted with the preference number. In figures 1 and 2 there is shown a tank 1 designed according to the invention, as shown in detail in figure 3-5. In this embodiment the tank comprises a polygonal wall construction consisting of one or several internal skin plates 2 abutting an outer insulation 3 (insulation blocks), and an outer wall structure 4 supporting the insulation. The tank is an envisaged? in this case to be inbuilt in a floating vessel, e.g. a tanker, and surrounded by a number of ballast tanks 5. A ballast pump room 6 is arranged centrally under the tank, and above the ballast tanks there is a space 7 for various equipment, tanks etc.

Figure 3 shows a section of figure 2 where a detail A of a corner or a knuckle line of the side wall of the tank is shown in enlarged scale. As will appreciated?, one or the several skin plates 2 in the area for knuckle lines with adjacent, plane parts 2" of the skin plates comprise a unsupported, curved plate section 2' with relatively large radius of curvature. On each side of the curved part 2' the skin plates are supported by insulation blocks 3. The effect of this arrangement is that the curved plate part 2' by change in the radius of curvature will absorb plate deformations due to temperature variations or internal loads in the tank. The mentioned deformations will thus be absorbed without causing large forces in the skin plates.

Figure 4 shows a section of figure 1 wherein a detail B at the bottom of the tank is shown enlarged. As will appear, the tank is comprises with a sloping transition part 8 between the bottom and the wall, and the inner skin plates 2 are here comprised with two unsupported, curved plate parts 2' at each side of a central area of the transition part 8 where the skin plates are supported by the outer insulation 3. As will appreciated? The outer insulation will here comprise several converting? Knuckle lines and in these areas the inner skin plates must be equipped with a corner with a double curved face. Figure 5 shows an enlarged detail of the lower area of the detail B in figure 4 and shows the detail C in an enlarged scale. The figure shows the outer boundaries for the movement of the unsupported, curved plate part 2' of the inner skin plate under influence of pressure and temperature variations. As previously mentioned, the tank is suitable for storage of cooled, liquid gas and the curved plate part is then shown with a radius of curvature Rl at room temperature and empty tank, and a radius of curvature R2 with cooled tank. An area for partly abutment between the inner skin plate 2 and the outer insulation 3 is denoted L.

In the areas of the tank where the plane parts are large, the skin plates between the curved parts can comprise local stays extending in the longitudinal direction of the tank. These stays consist of longitudinal profiles welded to the skin plates at the inside (within the tank) or at the outside of these (in recessions made in the outer insulation). By arranging the profiles at the outside these may preferably be secured in insulation blocks, so that the tank faces are secured towards the insulation blocks. A such embodiment will provide an enhanced ability to resist pressure or suction (under pressure) which can arise due to high velocities from liquids ("sloshing" in the tank).

Figure 6 shows a horizontal section through a tank 10 with a circular cylindric section where the detail D is shown enlarged. The tank 10 has the same principle structure as the tank 1 in figures 1 and 2, but the skin plate(s) 2 here are supported by a number of peripheral, distinct, longitudinal raised parts 11 extending in the axial direction of the tank, the skin plate(s) on each side of the respective raised parts have an unsupported, curved part 2' with a comparatively large radius of curvature. Similarly as in the first embodiment it is achieved that the curved parts of plates by changing the radius of curvature will absorb the plate deformations due to pressure and temperature variations or internal loads in the tank. In the cylindric part between the raised parts the plate(s) will abut the outer insulation and not absorb forces, as all the tensional forces in the ring direction are cancelled by deformation of the curved parts of the skin plates at the raised parts.

The mentioned raised parts can be created in different ways and one preferred embodiment is shown in figure 7 which shows the detail E in an enlarged scale. In this embodiment the raised parts consist of vertical beams 12 with an inner flange 13 to which the ends of the unsupported, curved parts 2' of the skin plates 2 have been securely welded.

In figure 8 the detail E in figure 7 is shown in a further enlarged scale. The figure shows the curved parts 2' of the inner skin plates in two function positions, i.e. in a inner position for cooling of the tank, and an outer, contracted position after cooling.

In figures 9-16 some exemplary embodiments of tank arrangements in a ship are shown wherein different embodiments of tanks are used according to the invention. All tanks are structured in a similar way as previously mentioned, and comprise inner skin plates 2 arranged with unsupported deformation absorbing parts in the corners of the tank or at side faces of the tank, an inner insulation 3 surrounding the skin plates, and an outer wall structure 4 supporting the insulation. Further the outer walls and bottom of the tank are surrounded by ballast tanks 5. Figures 9 and 10 show an arrangement where a number of single, rectangular tanks 15 are arranged in series next to each other in a ship hull (not shown).

Figures 11 and 12 show a similar tank arrangement in a ship where a series of rectangular tanks 16 are arranged in an embodiment reducing the angle of the corners. Figures 13 and 14 show an arrangement where a number of polygonal tanks 17 also are arranged in a series next to each other in a ship hull.

Figures 15 and 16 show a tank arrangement where a large number of rectangular tanks are arranged in a series next to each other with the short sides of the tanks facing each other. As will appreciated, the longitudinal sides of the tanks are here equipped with a number of vertical extending raised parts 19 above which the inner skin plates 2 are provided with supporting and unsupporting areas in a similar way shown in figure 6, as will appear from the enlarged details F in the figure. Thus the mentioned forces and deformations of the longitudinal direction will be reduced. The thickness of the skin plates in the tank according to the invention will be chosen sufficient in order to obtain a robustness against local stress and to be able to carry the loads that the tank is subjected to. The bracing arrangements will preliminary be provided in order to stabilize the skin plates in the tank when the tank is empty or partly filled (no pressure of liquid which is pressing the plates towards the insulation blocks), or in order to ensure that the plates may endure loads due to liquid knocks (sloshing). Sloshing can cause local pressure loads which both plane and curved plate parts can be dimensioned against in a simple way. In addition, due to occasional high velocities of the liquid, a local under pressure can arise "suction" the plates out from the side. This type of loads represent a big problem for conventional LNG/LPG tanks of the membrane type.

In the proposed design the forces from any under pressure will be absorbed by the local bracing of the plane plate parts. If the stays are also provided in the tank, these will help to reduce the effect of sloshing.

The tank according to this invention will be built at normal temperature. By first filling with e.g. LNG the first part of the gas will function as a cooling medium. All gas filled in will evaporate until the operating temperature has been achieved. This means that all contraction of the skin plates and any braces in the tank will take place with an empty tank (no liquid pressure against the plates). When the tank is cooled it will be filled with e.g. LNG. By emptying the tank a small part of liquid gas will be retained in order to secure the tank is kept cool.

The above mentioned operation means that the tank all the time is kept cooled down, i.e. there will be no temperature variations in the operation phase. The temperature of the tank will be arised to room temperature only when needed during inspection, maintenance etc.

Claims

P a t e n t C l a i m s

1. Tank for transport and storage of cooled, liquid gas comprising a polygonal wall construction comprising one or several inner skin plates (2) abutting an outer insulation (3) and an outer wall structure (4) supporting the insulation, characterized by the inner skin plates (2) in the area for knuckle lines between adjacent, plane parts of the skin plates (2) designed with a curved plate part (2') with comparatively large radius of curvature, so that the curved plate part (2') by changing the radius of curvature will absorb the plate deformations due to temperature variations or internal loads in the tank (1).

2. Tank for transport and storage of cooled, liquid gas comprising a circular- cylindric wall construction consisting of one or several inner skin plates (2) abutting an outer insulation (3), and an outer wall structure (4) supporting the insulation, characterized by the inner skin plates (2) supporting a number of longitudinal raised parts (11) extending in the axial direction of the tank (10), wherein the skin plates (2) at each side of the respective raised parts (11) have an unsupported, curved part (2') with a comparatively large radius of curvature, so that the curved plate parts (2') by changing the radius of curvature absorbs plate deformations due to temperature variations or internal loads in the tank (10).

3. Tank according to claim 1 or 2, characterized by that the skin plates (2) between the curved parts (2') are equipped with a number of local bracings in the form of stays extending in the longitudinal direction of the tank (1).

4. Tank according to claim 3, characterized by the braces consisting of longitudinal profiles attached to the skin plates (2) on the inner or outer side of these.

5. Tank according to claim 1, characterized by the skin plates (2) in areas where several knuckle lines converge, e.g. in the interface between the bottom and the side wall of the tank according to claim 1 or 2, characterized by that the (1) is designed with a corner with dual curved face.

6. Tank according to claim 2, characterized by the raised parts consist of beams (12) with a inner flange (13) to which adjacent edges of the inner skin plates (2) are secured welded.