A multi-lobe cargo tank for transporting and / or storage of liquified gases.

Abstract

A multi-lobe cargo tank for transporting and / or storage of liquified pressurized gases, wherein the tank comprises four part-cylindrical main lobes (L1..L4), with corresponding first part-cylindrical sector outer shell (12a..12d) and parallel main lobe axes (a1..a4), wherein said four main lobes (L1..L4) are arranged in a first lobe pair (L1-L2) and a second lobe pair (L3-L4), wherein said first lobe pair (L1-L2) and said second lobe pair (L3-L4) are separated by two intermediate cylindrical lobes (L5, L6), arranged in an intermediate lobe pair (L5-L6), each with a second part- cylindrical sector outer shell (12i5, 12i6) and an intermediate main lobe axes (a5..a6), wherein said tank further comprises first and second end covers (13a, 13b), wherein said first and second end covers (13a, 13b), each comprising two outwardly end cover pairs, comprises a quarter-part spherical shell portion (14a1-14a4) and a two pair of 45-degree cut, radially directed cylindrical pipe portion (15a1 - 15a4).

Description

[0001] A multi-lobe cargo tank for transporting and / or storage of liquified gases. Field of the invention

[0002] The present invention relates to a cryogenic marine transport tank for liquefied gases. The liquefied gases may be LNG, LPG, CO2.

[0003] Background of the invention

[0004] The present invention relates to the field of transporting and I or storage of cryogenic liquified gases in a tank, more specifically in a multi-lobe cargo tank. Pipelines may provide a possible transport for short runs, but the for long distances the capital cost will be prohibitively high, so an alternative transport of captured CO2 from a CO2 source to a facility of usage or long-term isolation of captured CO2 is needed.

[0005] Disclosure of background art

[0006] The applicant has been working with development 4-lobe cargo tank and holds a Norwegian patent no. 348169 within this field for storage and transportation of captured Carbon Dioxide (CO2), please see Fig. 1A-1. US4459929 describes a multi-lobe tank which comprises, top, bottom and two opposed side walls 1 to 4 each consisting of parallel, part-cylindrical lobes 11 which are connected and tied together by tie-plates 13, 14 and elongated armed insert elements 16, 17, and 17a. Each one of the other two opposed side walls 5, 6 comprises at least two part-lobes 11c which present straight edges to which the common straight end edges of a series of two-way corner transition pieces 12c and part-transition 12d pieces are joined, and in that the end of each part-lobe 11c has a respective part-transition piece 12d joined thereto to present a curved edge to which a part-spherical three-way corner 12b is joined to close-off the side wall 5 or 6. The transition and parttransition pieces 12c, 12d, are joined via elongate curved insert elements 12e in which there is a smooth transition from being of generally "Y" cross-section at one end to "T" cross-section at the other end.

[0007] Wall thickness and weight problem

[0008] A good reason for having a 4-lobe tank is that the tank wall thickness required for a pressurized tank increases proportionally with the radius of the tank. The 4-lobe tank may have a wall thickness of about 60 mm for a 7.5 m radius for storing liquid CO2 at 8 Bar and -54 Deg. C. For lobe radii beyond 7.5 m the tools and methods for shaping thicker tank walls, both the cylindrical lobe walls and particularly parts of the end covers would be prohibitively difficult and expensive, and the welding of thick plates would be particularly difficult. Arranging one big 4-lobe tank across the beam of a ship would require a too wide tank. Arranging several 4-lobe tanks along the cargo hold would not provide the height required , please see below.

[0009] Weld line support problem

[0010] The common straight end edges where the series of two-way corner transition pieces 12c and part-transition 12d pieces are joined, i.e. welded, is straight. The joining line has no backing support to any reinforcing rib, , it does not meet the parallel! internal tie plates 13. That welding line represents a weakness in a high-pressure or cryogenic tank against internal pressure, sloshing, and cycles of thermal contraction and expansion. Moreover, the complex shapes of each of the two-way corner transition pieces 12c and part-transition pieces 12d are circular at the partcircular edge which meets a part-cylindrical lobe 11, 11a, and straight at their opposite straight edge meeting the straight edge of part-lobe 11c of side wall 5, and the same situation at the opposite side wall 6. These back unnsupported welding lines is vulnerable to the thermal and mechanical and fluid loads incurred.

[0011] The complex shape transition pieces 12c, 12d, are difficult to shape and weld, and the problems are cumulative with regard to welding precision and weld reliability through thermal cycling during loading and unloading and internal sloshing and ship roll and pitch, particularly.

[0012] Orientation and height of cargo problem

[0013] Liquid CO2 has a density of 1.17 and LNG has a density of between 0.41 and 0.5, less than half of the density of water. So a cargo tank in a ship designed for full load of LNG will have a rather low volume capacity of liquid CO2 utilizing only between 35% and 43% of the tank. The tank of US4459929 has a low height and large footprint and a series of tanks arranged in the cargo space would have little capacity compared to the beam width and length of the cargo space of the ship.

[0014] Bottom support problem

[0015] The tank of US4459929 is supported under the lobe-parallel elongated armed insert elements 17a directly welded to the tank lobes 11. The lower face of the support beam is mounted on a further horizontal web plate 27 which is supported above the floor 28 of the hold via a girder construction 29. This incurs a linear load to the welds between the elongate elements 17a and the tank lobes, particularly when the prior art tank is loaded and arranged in a ship subject to heave, pitch and roll. Unloading problems

[0016] The tank of US4459929 is provided with a multitude of lobes at the bottom of the flatly oriented tank.This is a disadvantage with respect to unloading as each lobe requires a separate drain in each lower lobe.

[0017] Objects of the present invention

[0018] An object of the present invention is to increase the cargo volume for lobed cryogenic cargo tanks for cryogenic gasses in liquified state such as LNG, LPG, and CO2, particularly for ship tanks, without significantly increase of the shell thickness or the bulkhead thickness. Weight and production costs are some factors that have encourage the development of multi-lobed cargo tanks, especially transportation of liquified gasses at sea onboard ship as eg. very large crude carriers (VLLC’s).

[0019] Another object of the present invention is to provide a cryogenic gas tank which may utilize the cargo hold volume better than the background art for different liguified gasses such as LNG and CO2.

[0020] Another object of the present invention is to provide a cryogenic multi-lobe tank that is more easily assembled than the tanks of the prior art.

[0021] Another object of the present invention is to provide a cryogenic multi-lobe tank that is less subject to point or line load under cryogenic gas loaded condition, both with regard to heave, pitch, roll, and sloshing.

[0022] Another object of the present invention is to provide a cryogenic tank ship which may be utilized for better transport economy and also to provide one significant small part of a solution to the global warming problem.

[0023] Summary of the invention

[0024] The invention is defined by the attached independent claim 1 which is a multi-lobe cargo tank for transporting and / or storage of liquified gases.

[0025] Further inventive embodiments of the invention are set out in the dependent claims.

[0026] Six-lobe cryogenic cargo tanks have rectangular aspect when seen along the lobe axes, and may be better oriented and arrangement of the tank in the cargo space utilization in a tank ship without increasing the tank wall thickness, particularly when the cargo volume increases. Further advantages of the invention are described toward the end of the description of the invention and its embodiments.

[0027] Description of the drawing figures

[0028] Embodiments of the present invention will now be described, by way of example, with reference to the following Figures.

[0029] The enclosed Figures illustrates the lobe-strip concept. Fig. 1B , Fig. 1C and and Fig.

[0030] 2A show the different embodiments of a tank of the invention. Fig. 1C illustrates an embodiment with its lobe axes in a vertical position. Figs. 1C , Fig. 3B, and Fig. 4 show embodiments with their lobe axes in a horizontal position.

[0031] There may be be more than one lobe-strip L7, L8 inserted.

[0032] For orientation and cross section view of the web frames BH, which may also be called or stringers / srames, are named BH-A, BH-B and BH-C. The web frames have large apertures e.g. illustrated in Fig. 3B, wherein the web frames in addition to having large apertures, extend far into the tank, and extend also beyond the shell. Also where web frames cross, e.g. the web frame BH-C extend internally to either sides of web frames BH-B and BH-A, BH-A.

[0033] In Fig. 1A-a the two axial-parallel web frames BH-A , BH-A and transverse frames BH-C are shown in a 4 lobed tank of the prior art. The 4-lobe tank has two types of web frame BH-A (axial-parallel) and BH-C (axis-transverse).

[0034] Fig. 1 A-b a prior art tank disclosed in US4459929 is shown flat lying in isometric view, and in section view arranged on a tank compartment substrate.

[0035] In Fig. 1 B similar lobes are arranged, but with amiddle stage section of lobe-strips L5 and L6 inserted between such two sets of lower lobe pairs L1 , L2 and upper lobe pair L3, L4. .

[0036] Fig. 1 A-a and Fig. 1 B show the two halves that will have similar design as the the design of the prior art 4-lobe tank when it comes to items 12a, 12b, 12c, 12d, 14a1, 14a2, 14a3, 14a4, and 15a1, 15a2, 15a3, 15a4. Fig. 1 B illustrates an embodiment of the six-lobe tank, with vertically arranged lobe axes and central web frame BH-B, and vertically arranged first and second web frames BH-A and BH-A, and with horizontally arranged lobe-transverse web frames BH-C.

[0037] Turning the embodiment of Figure 1 B 90 deg and you will have the horizontal position of the tank shown in Fig. 1C.

[0038] Fig. 1C illustrate an embodiment with horizontally arranged lobe axes, and vertically arranged central web frame BH-B and also vertically arranged lobe-transverse web frames BH-C, and horizontally arranged lobe frames BH-A.

[0039] Fig. 2A illustrates an embodiment of the present invention with the central web frame BH-B arranged in a vertical position with the end covers to the bottom and to the top. That embodiment's web frames BH-C’s are indicated as horizontal lines.

[0040] Fig. 2A shows the tank web frames BH-A and BH-B in vertical position. The two vertical lines on each side of the lobe-strip in BH-B illustration are then two intermediate web frames (BH-A). In an embodiment, onboard a ship, the tank would have been turned 90 deg around it’s centre so that the centre web frame BH-B is pointing forward-aft as in Fig. 1C and Fig. 4, or it could have its current position shown in Fig. 2 but installed foremost or aft in the cargo section.

[0041] Fig. 2B illustrates the background art 4-lobe with the web frames BH-A arranged vertically and the lobe-transverse web frames BH-C arranged horizontally.

[0042] Fig. 3A illustrates a 4-lobe cargo tank in a VLCC type vessel and ordinary deck elevation.

[0043] Fig. 3A shows a 4-lobe tank of the background art in vertical position.

[0044] Fig. 3B illustrates the tank of the invention in horizontal position with its lobe axes arranged along the central beam (20) indicating the cross section of section web frames BH-C. The deck level compared to a VLCC type vessel has, due to the inserted lobe pair L5, L6 and the orientation of the tank standing on its shorter side, been elevated to give more cargo volume for the cryogenic six-lobe tank in the height. Such a tank according to the invention with intermediate lobes inserts L5 and L6 has two lobe-parallel web frames BH-A, BH-A in parallel and one lobe-parallel centre web frame BH-B that will follow the curve about the end covers 13a, 13b of the inserted lobe-strip shell of the inserted lobe section L5, L6, and the section web frames BH-C that will follow the shape of the inserted lobe strips shell cylindrical portions. The tank illustrated in Fig. 3B has the first lobe pair L1 , L2 at the bottom, the intermediate lobe pair L5, L6 in the middle, and the second lobe pair L3, L4 at the top, and the lobe axes parallel with the main beam, which provides an advantageous aspect ratio of the tank. The tank may be filled to the top with light cryogenic gas such as LNG Methane, and, depending on stability considerations and roll, alternatively be filled to a lower level such as to near the upper horizontal perforated bulkhead web frame BH-A with heavier cryogenic liquid C02, please see Fig. 3B.

[0045] Fig. 3B illustrates the six-lobe tank of the present invention with its main web frame BH-B in a center plane parallel position, here arranged to the starboard side of the center plane, (which advantageously requires a higher central beam for the ship which provides increased longitudinal bending moment resistance of the ship).

[0046] The embodiment illustrated in fig. 3B solves most of all of the problems mentioned above and has most or all of the significant advantages mentioned towards the end of the description.

[0047] Fig. 4 illustrates the invention with three laterally arranged pairs of six-lobe cryogenic tanks arranged each pair in separate cargo sections about the central beam 20, in a number of 3 such pairs, 6 such tanks. The number of pairs along the cargo hold may be less than six or more, e.g. 8 such pairs. The length of such a tank may be 50 metres and the volume of such a tank may be 28000 m3 each, and the dead weight of the tank 4000 tons. The ship cargo section illustrated is 60 m beam width.

[0048] Reference numeral table

[0049] 1 A multi-lobe cargo tank

[0050] 2 4-lobe cargo tank Prior art

[0051] L1-L4 Four part-cylindrical main lobes

[0052] L1-L2 First lobe pair

[0053]

[0054] L3-L4 Second lobe pair L5-L6 Intermediate lobe pair

[0055] L5, L6 Intermadiate cylindrical lobes

[0056] a1 - a4 Parallel main lobe axes

[0057] a5-a6 Intermediate main lobe axes

[0058] 12a..12d First part-cylindrical sector outer shell

[0059] 12i5, 12i6 Second part-cylindrical sector outer shell

[0060] 14a1-14a4 quarter-part spherical shell portion

[0061] 15a1 - 15a4

[0062] 16a - 16b

[0063] 18 tank shell contact support below lower

[0064] lobes L1 and L2.

[0065] 17a, 17b anti-flotation brackets on tank web

[0066] frames / cargo hold web frames.

[0067] 20, 20' Central beam of ship, parallel lateral

[0068] beams of ship

[0069] 21 apertures or perforations in bulkhead

[0070] plates

[0071] 22 cryogenic tank cargo section

[0072] 23 oil tank cargo section

[0073]

[0074] Description of embodiments of the invention

[0075] The present invention provides a multi lobe tank for transporting and / or storage of liquified gases, - wherein the tank comprises four part-cylindrical main lobes, with corresponding first part-cylindrical sector outer shell and parallel main lobe axes, - wherein said four main lobes are arranged in a first lobe pair and a second lobe pair,

[0076] - wherein said first lobe pair and said second lobe pair are separated by two intermediate cylindrical lobes, arranged in an intermediate lobe pair, each with a second part-cylindrical sector outer shell and an intermediate main lobe axes, - wherein said tank further comprises first and second end covers,

[0077] - wherein said first and second end covers, each comprising:

[0078] - two outwardly end cover pairs, comprises;

[0079] - a quarter-part spherical shell portion and a two pair of 45-degree cut radially directed cylindrical pipe portion, each arranged with an axis transverse to each corresponding main lobe axis, arranged for said first lobe pair and said second lobe pair, and

[0080] - an intermediate end cover pair, comprises;

[0081] - a number of curved lobe-strips, for said intermediate pair of cylindrical lobes, and arranged between said quarter spherical shell portion and said 45-degree cut radially directed cylindrical pipe portion for said first lobe pair and said quarter spherical shell portion and said 45-degree cut radially directed cylindrical pipe portion for said second lobe pair.

[0082] In an embodiment of the invention said multi-lobe cargo tank further comprises; - at least two intermediate (or transverse) web frames BH-A, wherein one is arranged between said first lobe pair L1 , L2 and said intermediate pair of cylindrical lobes L5, L6 and one is arranged between said second lobe pair L3, L4 and said intermediate pair of cylindrical lobes L5, L6.

[0083] In an embodiment of the invention said at least two intermediate web frames are arranged through said multi-lobe cargo tank. Said intermediate web frames are aligned in such way that said lobe pairs can be welded directly to the intermediate web frames.

[0084] In an embodiment of the invention said multi-lobe cargo tank comprises;

[0085] - a center (or longitudinal) web frame BH-B, arranged to between the lobes L1 , L5, L4 and lobes L2, L6, L3 in the lobe pairs L1-L2, L3-L4, L5-L6. Such that said center web frame BH-B is arranged through center of said first lobe pair L1 ,L2, said intermediate lobe pair L5, L6 and said second lobe pair L3, L4.

[0086] In an embodiment of the invention said center web frame BH-B is arranged through said multi-lobe cargo tank 1 shell.

[0087] In an embodiment of the invention said multi-lobe cargo tank has a number of curved lobe-strips 16e, f, g, h, that are curved with a first radius Ri equal to a spherical radius Rs for said cylindrical lobe shell 12i6 or 12i5, please see Fig. 3B, or said quarter spherical shell portion 14a1-14a4.

[0088] In an embodiment the so-called 45-degree cut or triangular, radially directed cylindrical pipe portions 15a1 ... 15a4 are arranged with each their axis which is transverse to each crossing of a BH-A and BH-B web frame crossing, i.e. perpendicular to a corresponding main lobe axis. The 45-degree cut radially directed cylindrical pipe portions 15a1 ... 15a4 may be formed either by cutting them out of a pipe as illustrated or by forming triangular plates and bending them about a single axis to a radius R.

[0089] In an embodiment the central web frame BH-B has an arch portion BH-B3 spanning between the two crossing web frames BH-A, BH-A, This arch portion starts out where the crossing web frames BH-A, BH-A are "flat", perpendicular to the lobe axes, thus there are no dips in the radial direction where the lobes meet at the BH-B / BH-A crossings.

[0090] In an embodiment of the invention, a number of curved lobe-strips (16a.... 16d), (16e, .... h) are arranged for constituing the shell of the end cover for said intermediate pair of cylindrical lobes (L5, L6). Each lobe strip preferably have the same curve radius as the cylindrical fifth or sixth side lobe or intermediate lobe shell 12i5 , 12i6, and are joined side by side between the intermediate lobe shell transition web frame BH-C and the arch web frame section BH-B3 at the ultimate end of the tank, and this arrangement is made also at the opposite end cover. Please see Fig.

[0091] 1B and Fig. 1C. Each strip (16a, ...) may be formed by cutting its outline from a flat plate and bending it mono-axially to the desired radius, or cutting it with its outline and forming it with a spherical required radius, of which the first may be the simpler.

[0092] The quarter-spherical shell portions (14a1- 14a4) may be manufactured a similar way.

[0093] In an embodiment of the invention said multi-lobe cargo tank radius’ Ri, Rs are larger than 5 meters or in a preferred embodiment larger than 6 meters or in an even more preferred embodiment larger than 7 meters, e.g. 7.5 metres.

[0094] In the invention said multi-lobe cargo tank 1 comprises;

[0095] - one or more sectional perforated web frames BH-C, arranged perpendicular on said intermediate web frames BH-A and / or said center web frame BH-B. The sectional web frames BH-C are arranged perpendicular to the lobe axes through said multi-lobe cargo tank 1.

[0096] All web frames may comprise perforated or large aperture bulkhead plates such as illustrated in Fig. 2A and Fig. 3B to allow distribution of liquid and to prevent sloshing. In an embodiment of the invention a shell joint angle <t>, please see Fig. 3B, to said web frames BH-A, BH-B or BH-C, and also the corresponding end cover section shell is larger than 60 degrees. The web frame cross section may be similar to a "Y" with the stem extending at either sides, i.e. externally and internally relative to the flanges crossing.

[0097] In an embodiment of the invention the shell thickness of the first part-cylindrical shell plates, the second part-cylindrical shell plates, and the first and second end covers is 40 - 60 mm for a cylindrical or spherical radius of 7.5 meters.

[0098] In an embodiment of the invention the steel quality of the tank must satisfy cryogenic conditions down to liquid CO2 under 8 barg pressure, and most preferably steel quality which may be cycle between CO2 and LNG.

[0099] In an embodiment of the invention, said vertically arranged web frames (BH-C) are provided with tank anti-flotation brackets (17a) corresponding with cargo hold antiflotation brackets (17b), please see Fig. 3B.

[0100] In an embodiment of the invention the multi-lobe cargo tank (1 ) is supported by tank shell support material (18), please see Fig. 3B, wherin tank shell contact support material (18) is arranged below lower lobes (L1) and (L2).

[0101] In an embodiment of the invention, shell support 18 in can be arranged in tank cradles 19, also under the entire arc of BH-B. This may be arranged slidingly in order not to transfer stresses from the flexing hull to the tank, and this is advantageous in order not to strain the cryogenic tanks. In an embodiment of the invention when arranged in a ship, the cradles may be arranged under as few areas as two cradles arranged adjacent near either ends in order not to create several stress transfer zones in the tank.

[0102] Apertures in central web frame BH-B is illustrated. Corresponding apertures in web frames BH-A and BH-C are also present.

[0103] The invention comprises a cryogenic cargo tanker comprising one or more of said cryogenic multi-lobe ship tanks (1 ) of any of the preceding claims. In an embodiment of the invention the cryogenic carto tanker is arranged such that the one or more tanks are arranged with said lobe axes parallel to a central beam (20) of the ship, or generally with said lobe axes parallel to a longitudinal axis of the ship. In this way one may utilize long tanks axially.

[0104] In an embodiment of the invention the tanks (1 ) are arranged to either sides of a central beam (20), please see Fig. 4.

[0105] In an embodiment of the invention the tanks (1 ) are arranged for carrying LNG one way, and CO2 another way. This is a significant advantage because then one may carry LNG from a gas producing petroleum well across the sea to an LNG receiving power plant or other LNG consuming industry, and CO2 from the related combustion or consumption of LNG may be captured in a CO2 capture plant, compressed and liquefied to liquid CO2 and returned in the same or a similar ship back to sequestering of CO2 in a well for pressure support for increasing production such as tail produsction of oil or gas, or simply for permanent storage of CO2 in an "abandoned" petroleum well.

[0106] Oil and cryogenic gas may hardly be transported in the same tanks. In an embodiment of the invention, in the cryogenic cargo tanker of the inventionthe tanks (1) are arranged along a centerline of the ship between parallel lateral main beams (20'), wherein cargo tank sections (23) are arranged at the starboard and port sides of tank cargo sections (22) between said lateral main beams (20').

[0107] In an embodiment of the invention the tanks (1 ) are arranged for carrying CO2 one way and the lateral cargo tank sections are arranged for carrying oil another way. This is another significant advantage because then one may carry oil from a gas producing petroleum well across the sea to an oil receiving power plant or other oil consuming industry, and CO2 from the related combustion or consumption of oil may be captured in a CO2 capture plant, compressed and liquefied to liquid CO2 and returned in the same or a similar ship back to sequestering of CO2 in a well for pressure support for increasing production such as tail produsction of oil or gas, or simply for permanent storage of CO2 in an "abandoned" petroleum well.

[0108] The radii of said cylindrical lobes (L1 , ... L6) may be 3 to 9 metres, preferably 4.5 to 8 metres, or most preferably 5 to 7.5 metres. The axial length along said central web frame (BH-B) is 15 to 70 metres, preferably 25 to 60 metres, and most preferably 40 to 55 metres.

[0109] Advantages of the invention

[0110] Weld support advantages

[0111] The main welding lines of the cylindrical lobes of the present invention are supported by the higher and lower web frames BH-A, BHA, and the vertically and longitudinally arranged web frame BH-B. The end cover bulb of the end covers represented by the L5 / L6 web frame part of web frame BH-B providesa more spherical-shaped end cover thus with reduced tension in the web frame and tank wall compared to the straight-line shaped end covers 5 and 6 of the background art US4459929.

[0112] The central web frame BH-B's arch portion BH-B3 spanning between the two crossing web frames BH-A, BH-A, together with the curved lobe-strips (16a.... 16d), (16e, .... h) are arranged for constituing the shell of the end cover for said intermediate pair of cylindrical lobes (L5, L6). make the end covers of the tank convex and less susceptible to thermal stresses due to all forces then will be tensile forces not bending moments. Further, while the shape of the tank is complex each component may generally be made with a fixed radius, not a variable radius from one end to the other such as the complex shaped parts of the cited US-patent.

[0113] This arch portion starts out where the crossing web frames BH-A, BH-A are "flat", perpendicular to the lobe axes, thus there are no dips in the radial direction where the lobes meet at the BH-B / BH-A crossings.

[0114] In an embodiment of the invention, a number of curved lobe-strips (16a.... 16d), (16e, .... h) are arranged for constituing the shell of the end cover for said intermediate pair of cylindrical lobes (L5, L6). Each lobe strip preferably have the same curve radius as the cylindrical fifth or sixth side lobe or intermediate lobe shell 12i5 , 12i6, and are joined side by side between the intermediate lobe shell transition web frame BH-C and the arch web frame section BH-B3 at the ultimate end of the tank, and this arrangement is made also at the opposite end cover. Please see Fig.

[0115] 1B and Fig. 1C.

[0116] bottom support advantage bottom support in the form of shell support 18 in arranged in tank cradles 19, directly under the lower lobes in the present invention instead of only under the lobe parallel elongated armed insert elements of the prior art, incurs no transition bending moment forces between the liquid cargo via the weld of the lobe wall plate to the web frame beam flange on either sides of the stem of the Y-similar cross-section of the web frame. Moreover, the direct bottom support under the lobes of the present invention provides a much more distributed load than the line concentrated load of the prior art. This relates particularly to heave and pitch load variation but also to roll load both vertically and laterally: an even distribution under the bottom lobes induces less point loads from the tank to the cargo hold structure.

[0117] Orientation and height of cargo advantage

[0118] The present invention provides an advantageous solution to the problem related to the significant density density difference between liquid CO2 with a density of 1.17 and LNG with a density of between 0.41 and 0.5. The present six-lobe tanks arranged with their lobe axes parallel with the main axis of the ship and with two lobes L3 and L4 at the bottom and intermediate lobes L5 and L6 stacked in the middle and lobes L1 and L2 stacked on the top, the footprint of a full LNG design load will have an advantageous narrower footprint laterally and will, loaded with liquid CO2 up to 43% of the tank, carry more CO2 than the corresponding capacity of the US4459929 flat-lying tank.Thus the present invention tank will have a larger CO2 carrying capacity building in the height, better utilizing to the beam width and length of the cargo space of the ship. A ship with such tanks would also have better roll characteristics without unneccessarily sacrificing stability, due to the low density of the relatively highly placed centre of the LNG load. When carrying CO2 the centre of gravity of the CO2 load will be much lower and contribute to a faster roll frequency but would still be dampened significantly by the apertures of the tank-internal deeply extending web frames preventing sloshing.

[0119] Flotation risk prevention

[0120] The background art has a risk of tank flotation in case of water intrusion into its cargo hold. The present invention has advantageous anti-flotation brackets (17a, 17b) arranged between the web frames BH-C and the ship's web frames contribute to avoid tank flotation and deck and structural damage in case of leakage in a tank compartment.

[0121] Unloading advantages The tank of the present invention is provided with only two lobes at the bottom of the vertically stacked horizontal and ship- longitudinaly lobe axes oriented tank.This is an advantage with respect to unloading as the two lower lobes requires only two liquid drains, one in each lower lobe.

[0122] Circular economy advantages

[0123] The advantages of enabling a ship of transporting LNG one way (see Fig. 4) and C02 another way, e.g. the return sailing path, or transporting oil one way (see Fig.

[0124] 5) and C02 another way, e.g. the return sailing path, will enable utilizing the ship's carrying capacity both ways and avoid "dead transfer". This may be utilized in a tour / retour sailing or in a triangle route.

Claims

Claims1. A multi-lobe cargo tank (1 ) for transporting and / or storage of liquified gases, - wherein the tank comprises four part-cylindrical main lobes (L1.. L4), with correspondingfirst part-cylindrical sector outer shell (12a..12d) and parallel main lobe axes (a1..a4),- wherein said four main lobes (L1 ,.L4) are arranged ina first lobe pair (L1-L2) anda second lobe pair (L3-L4),- wherein said first lobe pair (L1-L2) and said second lobe pair (L3-L4) are separated bytwo intermediate cylindrical lobes (L5, L6), arranged in an intermediate lobe pair (L5-L6),each with a second part-cylindrical sector outer shell (12i5, 12i6) and an intermediate main lobe axes (a5..a6),- wherein said tank further comprisesfirst and second end covers (13a, 13b).

2. The multi-lobe cargo tank (1) according to claim 1 , comprising- a central lobe-parallel web frame BH-B arranged between and spanning said first pair of main lobes L1, L2, between said intermediate lobes L5, L6, and said second pair of lobes L3, L4, and said end covers (13a, 13b)- a second lobe-parallel web frame BH-A arranged between and spanning said first pair of lobes (L1 , L2) and said pair of intermediate lobes (L5, L6), and- another second lobe-parallel web frame BH-A arranged between and spanning said pair of intermediate lobes (L5, L6) and said second pair of main lobes (L3, L4), - a third set of lobe-transverse web frames (BH-C) spanning all cylindrical lobes (L1 , L2, L3, L4, L5, L6, arranged between said first end cover and said second end cover (13b),- said central web-frame (BH-B) comprising an arch portion (BH-B3) extending beyond crossings between said central web frame (BHB) and second web frames (BH-A, BH-A), respectively.

3. The multi-lobe cargo tank (1 ) of claim 1 or 2,- wherein said first and second end covers (13a, 13b), each comprises; - two outwardly end cover pairs closing said first and second lobe pairs (L1 , L2) and said third and fourth lobe pairs (L3, L4), respectively, comprising;- two quarter-part spherical shell portions (14a1-14a4) and - two triangular cylindrical pipe portions (15a1 - 15a4) arranged with their top point adjacent to a crossing of adjacent web frames BH-B and web frame BH-A, and - a number of curved lobe-strips (16a....), for said intermediate pair of cylindrical lobes (L5, L6) arranged between said centralweb-frame's (BH-B) arch portion (BH-B3), said end cover adjacent transverse web frame (BH-C), and between said second web frames (BH-A, BH-A).

4. The multi-lobe cargo tank (1) according to any of the preceding claims, wherein one or more of said web frames (BH-A), (BH-B), and (BH-C) are arranged through the shell of said multi-lobe cargo tank (1).

5. The multi-lobe cargo tank (1) according to any of the preceding claims , wherein said center web frame (BH-B) , said second web frames (BH-A, BH-A) and said transverse web frames (BH-C) are arranged through said multi-lobe cargo tank (1) comprising apertures (21) in bulkhead plates or perforated bulkheads.

6. The multi-lobe cargo tank (1) according to any of the preceding claims, wherein said number of curved lobe-strips (16....x) are curved with a first radius (Ri) equal to a spherical radius (Rs) for said quarter spherical shell portion (14a1-14a4).

7. The multi-lobe cargo tank (1) according to claim 6, wherein said radius’ (Ri, Rs) are larger than 5 meters or in a preferred embodiment larger than 6 meters or in an even more preferred embodiment larger than 7 meters.

8. The multi-lobe cargo tank (1) according to any of the preceding claims, wherein said vertically arranged web frames (BH-C) are provided with tank anti-flotation brackets (17a) corresponding with cargo hold anti-flotation brackets (17b).

9. The multi-lobe cargo tank (1) according to one of the preceding claims, wherein a joint angle (<t>) between said shell plates and said web frames (BH-A, BH-B or BH-C) and in the corresponding end cover sections is larger than 60 degrees.

10. The multi-lobe cargo tank (1) according to any of the preceding claims, wherin tank shell contact support material (17) is arranged below lower lobes (L1) and (L2).

11. The multi-lobe cargo tank (1) according to any of the preceding claims, wherein the radii of said cylindrical lobes (L1 , ... L6) are 3 to 9 metres, preferably 4.5 to 8 metres, or most preferably 5 to 7.5 metres.

12. The multi-lobe cargo tank (1) according to any of the preceding claims, wherein the axial length along said central web frame (BH-B) is 15 to 70 metres, preferably 25 to 60 metres, and most preferably 40 to 55 metres.

13. The multi-lobe cargo tank (1) according to any of the preceding claims, arranged for cryogenic cargo of LNG.

14. The multi-lobe cargo tank (1) according to any of the preceding claims, arranged for cryogenic cargo of CO2 under pressure of about 8 Bar.

15. The multi-lobe cargo tank (1) according to any of the preceding claims, comprising shell support 18 arranged in tank cradles 19.

16. A cryogenic cargo tanker comprising one or more of said cryogenic multi-lobe ship tanks (1 ) of any of the preceding claims.

17. The cryogenic carto tanker of claim 16, wherein said one or more tanks are arranged with said lobe axes parallel to a central beam (20) of the ship, or generally with said lobe axes parallel to a longitudinal axis of the ship.

18. The cryogenic cargo tanker of claim 16 or 17, wherein said tanks (1 ) are arranged to either sides of a central beam (20).

19. The cryogenic cargo tanker of claim 18, wherein said tanks (1) are arranged for carrying LNG one way, and CO2 another way.

20. The cryogenic cargo tanker of claim 16 wherein said tanks (1) are arranged along a center line of the ship between parallel lateral main beams (20'), wherein cargo tank sections (23) are arranged at the starboard and port sides of tank cargo sections (22) between said lateral main beams (20').21 : The cryogenic cargo tanker of claim 16, wherein said tanks are arranged for carrying CO2 one way and the lateral cargo tank sections 23 are arranged for carrying oil another way.

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