Not Applicable
The present disclosure relates to a system for the support of tanks for liquids in vessels. More particularly the disclosure relates to a system for bearing or support of vertical forces on tanks for liquids in vessels at the base of the tanks and for horizontal forces at few places so that the bearing of forces that arise are transferred in an advantageous manner to the construction of the vessel.
It is advantageous that the capacities of a ship are exploited in the most efficient way while safety is maintained. The design and therefore the fastening of tanks thereto are influenced by the liquid that is to be transported. This is influenced by the environment that the liquid requires. Liquids that are to be transported may be, for example, foodstuffs that require cooling in order to maintain quality, while other liquids require an over- or under-pressure. An energy carrier such as a liquefied natural gas (LNG) transport vessel requires a tank having a storage temperature of around −160° C. at atmospheric pressure. For carbon dioxide (CO2) transportation, a requirement is, for staying fluent, a temperature of −60° C. in addition to a pressure of about 600 kPa. When transporting other liquids, other conditions apply. Together with dimensions and weight of such tanks, this lay the foundation for even minor improvements may result in large economic profit and competitive advantages.
In the art is known to use hardwood to transfer support forces from a tank to hull as pure pressure via hardwood layers or synthetic materials with similar properties. It is essential that the materials in these layers have very good temperature insulating properties and that they can endure the pressure that they are subjected to.
Hardwood is a suitable material for this purpose, but there are many synthetic alternatives. The products DEHONIT® and PERMALI, which are trademarks of the German company “Deutshe Holzveredlung Schmeing” are examples of products for such use.
Tanks intended for transport of liquids with boats are often formed as spheres, cylinders or prisms. U.S. Reissue Pat. No. RE 29424 describes supporting of tanks having a cylinder shaped cross section that rest on a skirt with opposite sides firmly fastened to a hull of a ship, claim 1. The '030 reissue patent describes another form of support, where a number of support units along a horizontal circumference of the tank is put into opposite positioned sleeves.
Vessels may also comprise high vertical cylinder shaped tanks. High tanks may be advantageous for transporting liquids because it will then have better opportunity to adapt the amount of liquid that may be transported with a given hull of a vessel. In addition there are of course other technical problems to addressed as a consequence of using such high tanks. An example of such consequences may be conditions regarding the stability of the vessel. Another and important example is the vertical and horizontal support of such high tanks.
International (PCT) Application Publication No. WO 2010/020431 describes a device for storing a self supporting vertical tank for LNG. It comprises a support arrangement that enables a horizontal relative motion between the tank and the foundation. In this way the tank may contract and expand according to the temperature of the tank without unwanted tension to appear.
The foregoing International Application also describes an arrangement with vertical support faces that are distributed evenly around the tank in two heights. In this way the tank is supported when horizontal forces are applied and pitching is prevented.
A disadvantage with self supporting big and high vertical tanks is that they result in large local load because it is not straightforward to distribute the load. Normally the load is either applied to a ring on the bottom of a ship or to the sidewalls of the hull of the ship. This is described in the '431 PCT publication.
There are mainly two different versions of cryogenic tank design for transport of LNG that are being used today. One is a self supporting tank while the other is a so called membrane type. The most common self supporting type is the Moss tank with a design owned by the Norwegian company Moss Maritime and is a spherical tank. One advantage with self supporting tanks like the Moss tank is that they are robust. One disadvantage is that they are not very efficient in that much space is wasted in the hull with spherical tanks.
The French company Gaz Transport & Technigaz (GTT) own some important designs of membrane type tanks. A membrane tank has a layer of corrugated metal that can maintain its proportions in a wide temperature range so that the tank can fill out the space inside a hull and thus rest on the inner bottom and on the walls of the hull. This results in a very efficient utilization of the space in a ship. Disadvantages of membrane tanks today are that they have a history of leakage and they are not as robust as self supporting tanks. Maintenance on membrane tanks therefore has to be done at frequent intervals and this adds to the cost of running such ships.
A system for support of a cargo tank in a vessel according to one aspect include a cargo tank having a generally flat and generally flexible base. The system includes support elements substantially evenly distributed underneath the base of the tank. Each support element comprises an insulation layer transferring pressure generally evenly distributed from the contents of the tank, through the bottom structure of the vessel and on to water pressure exerted on an outer bottom of the vessel. The cargo tank comprises at least two pairs of tank pressure faces fastened to a tank shell, wherein at least one pair of the tank pressure faces is arranged transversely and wherein at least one pair of the tank pressure faces is arranged longitudinally in the vessel. An insulation layer is arranged proximate to each of the tank pressure faces.
A corresponding hull pressure face is arranged proximate to each of the insulation layers on the other side of each of the insulation layers. Each hull pressure face is fastened to a ship side or to a bulkhead, wherein each tank pressure face and each corresponding hull pressure face is aligned so that an orthogonal line of force is directed generally tangentially to a middle of the tank shell so that the insulation layers can transfer pressure without transferring substantial bending moment from the support loads to the cargo tank structure or to the bottom of the vessel and, at the same time, thermally insulate between the cargo tank and the vessel.
A support system for different shapes of load tanks in vessels like carrier ships and storage ships is described. Without this being a limitation on the scope of the present disclosure, described embodiments are particularly suited for cooled liquids, e.g., liquid natural gas (LNG).
One important advantage of a system according to the present disclosure for vertical high tanks may be that vertical pressure comprising large static components is supported separately from horizontal pressure, mainly induced by dynamic movement of the vessel.
An important feature for tanks for storing, for example, LNG, is that there is substantially no metallic contact between loaded tanks and the structure of the vessel. This may be important when the liquid that is to be transported has a temperature which is lower than common steel in ships may endure without degrading some of the material properties of such steel. The liquid that is to be transported may, for instance, be LNG having a typical storage temperature of about −160° C. Another typical liquid that may be transported is carbon dioxide (CO2) having a typical storage temperature of −60° C. at a pressure of 600 kPa. All support forces from tank to the hull of the vessel are generally transferred as pure pressure straight through hardwood layers or synthetic materials having similar properties. It is important that the material in these layers have suitable temperature insulating properties and that they are able to withstand the pressure they are to be subjected to. Hardwood is a well suited material for this purpose, but there are synthetic materials available as well.
In a first example embodiment, the vessel is a ship equipped with number of cylinder shaped tanks being arranged vertically. A support system for cylinder shaped cargo tanks designed for cooled liquid gas in transport ships and storage ships is presented.
The base of the vertical tank 4, 40 is generally flat and may be generally flexible. Underneath this base may be disposed a number of generally evenly distributed support elements. The pressure from the contents of the tank may be substantially evenly distributed to the support elements and further through the bottom structure of the vessel 41 and then to the water pressure on the outer bottom 10 of the vessel. In this way there no substantial bending moment is transferred from a tank to the structure of the vessel. If the tank bottom had a rigid construction, this would be difficult to achieve. Common self-supporting tanks known in the art prior to the present disclosure normally have support frames covering only part of the tank, e.g., in a ring underneath and covering the outer part of the base of the tank.
The reference number in the drawings named “support point pair” 8 is a word structure shown in
The number of support point pairs 8 in the planes 2 and 3 shown in the drawings may be minimized to two in each plane, but in some cases three or more may be more suitable. In principle, the least number of support points that are necessary to support horizontal movements of a vertical tank is four, preferably angularly separated by about 90 degrees, distributed in two planes. In this first embodiment, the construction is preferably carried out horizontal support point pairs 8. In
Support point pairs 8 in this present embodiment address only horizontal forces while all vertical forces are transferred through the construction below plane 1. The support point pairs 8 are designed to be as long as required to accept a construction where a center in the reaction force from the ship is generally tangential to the middle of the tank shell 23. This results in that no torque is applied into the tank shell 23, but that the force goes tangentially directly into the tank shell 23 as pressure. This provides a substantially even distribution of stress in the tank shell 23.
Overturning or tipping is counteracted by the support point pairs 8 in plane 3 taking on more force than those in plane 2.
The construction has enough flexibility in the insulation layers 26, 15, to transfer substantially all forces, including forces from deformation, e.g. initiated by temperature variations and the moving of the ship 41, without undesirable stress being imparted upon the cargo tank(s) 4, 40 or the ship. The cargo tank(s) may expand or shrink freely in the radial direction without imparting to the corresponding support point pair 8 any additional force. This is particularly important when expecting substantial temperature variations as for, e.g., LNG.
When the cargo tank 4, 40 has applied thereto a horizontal transverse load 30 in the starboard direction as in
Similarly, a horizontal side load 34 applied to the tank 4, 40 will be substantially supported by the support point pair 8 at the longitudinal bulkhead. The reaction load 35 will in this example result in a torque 37 applied to the tank 4, 40 which is supported by a secondary reaction load 36 in the support point pair 8 arranged at the transverse bulkhead 5.
Support point pair 8 in plane 3 may in such cases absorb substantially the whole load, and the support point pairs 8 in plane 2 will only contribute in extreme cases in which the whole of the tank is influenced to slide or move horizontally. If the support in plane 1 prevents the tank from sliding or moving horizontally, one omit arranging the support in plane 2.
Forces directed upward may appear if damage occurs and water gets into the hold outside a tank 4, 40. If the tank is exposed to water on the outside and the tank is not sufficiently filled so that it does not float, additional support point pairs 8 may be added to prevent the tank 4, 40 from floating inside the hold. This is not shown in the figures relating to this first embodiment, but reference is made to the following embodiments where this is described.
In a second example embodiment, the vessel is a ship equipped with a number of cylinder shaped tanks that are placed horizontally. The embodiment is a simple support system for lying cylinder shaped cargo tanks designed for cooled liquids in gas and storage ships. The cooled liquid may for instance be LNG.
In the present embodiment a construction with support point quads 9 is used in addition to the construction with support point pairs 8 as described earlier herein.
In
Support point pairs 8 may also be arranged on the fore and/or aft end surfaces of cargo tanks. This is not shown in the drawings or described further in the embodiments. The different support point pairs 8 in one vessel may not be designed equally, but may be adapted to different requirements.
The construction may be designed with flexibility and tolerances to handle all loads, including loads resulting from deformations, that may be initiated, e.g., by temperature variations and the movement of the vessel, without undesirable strain being transferred onto the cargo tank 4, 40, 104 or ship 41, 141. The cargo tank may in principle expand or shrink freely in its radial or axial direction without adding any additional strain to any of the support point pairs 8 or support point quads 9. This is important when the tanks may be large temperature variations as with e.g. LNG.
When the cargo tank 104 has a horizontal transverse load 130 applied toward starboard as in
The horizontal transverse reaction load 131 in turn apply a rotating torque 133 to the tank resulting in a secondary reaction load 132 from the ship supported at the upper part of the support point pair arranged at the port side. Part of the applied horizontal transverse load 130 will be supported by vertical reaction forces 128 and will provide a larger load on the starboard side than on the port side of the vessel.
While vertical tanks may have a flexible base, horizontal tanks are generally completely self supporting. Both horizontal and vertical applied forces acting on big tanks 4, 40, 104 should be applied as close to the tank shell 23 as possible, preferably by letting the forces act along the middle of the shell 23, so that bending forces are not transferred into the tank. This may be obtained in the present example through the construction of the support point pair 8 and the support point quad 9, allowing the forces to act along the center line 27 of the support point pair and quad 8, 9 tangential to the center line of the tank 4, 40, 140. The length of the hull support pair 24, the hull support quad 124, the tank support pair 25 and the tank support quad 125 may vary to a large extent depending on the shape of the tank. It may even be split in separate halves for long designs, including long horizontal tanks.
Support points in the present description is to imply a limited area for support and not a literal point.
While the invention has been described with reference to a limited number of embodiments, those skilled in the art will readily devise other embodiments which do not exceed the scope of the present invention. Accordingly, the invention shall be limited in scope only by the attached claims.
This is a continuation of International Application No. PCT/NO2011/000177 filed on Jun. 20, 2011. Priority is claimed from Norwegian Patent Application No. 20100881 filed on Jun. 18, 2010 and Norwegian Patent Application No. 20101555 filed on Nov. 4, 2010. All of the foregoing applications are incorporated herein by reference in their entirety.
Number | Name | Date | Kind |
---|---|---|---|
3071094 | Leroux | Jan 1963 | A |
3583352 | Alleaume | Jun 1971 | A |
20120055920 | Rekstad | Mar 2012 | A1 |
Number | Date | Country |
---|---|---|
2010020431 | Feb 2010 | WO |
Entry |
---|
International Search Report, International Application No. PCT/NO2011/000177. |
International Preliminary Report of Patentability, International Application No. PCT/NO2011/000177. |
Number | Date | Country | |
---|---|---|---|
20130092073 A1 | Apr 2013 | US |
Number | Date | Country | |
---|---|---|---|
Parent | PCT/NO2011/000177 | Jun 2010 | US |
Child | 13705612 | US |