Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02909228 2015-10-08
DESCRIPTION
LNG SHIP
Technical Field
[0001]
The present invention relates to a liquefied natural gas (LNG)
ship.
Background Art
[0002]
It has been increasing LNG demand as clean energy every year since
the amount of exhausted nitrogen oxides or sulfurous acid gas in combustion
is small. The LNG is liquefaction material obtained by cooling a natural
gas to about -162 C. Then, a tank of a LNG carrier transporting the LNG
on the sea has a structure in which a cryogenic material is used so as
to withstand a wide temperature change and thermal shrinkage and thermal
stress caused by a temperature difference are taken into consideration.
Further, since the LNG carrier is used to transport a large amount of
LNG at a high speed, the LNG carrier generally has a speed of about 20
knots, and its capacity exceeding 200,000 m3 is now planned due to the
tendency of an increase in size of a hull.
[0003]
In an existing LNG carrier, a LNG tank mounted thereon is generally
divided into two types. One is a moss spherical tank type and the other
is a membrane type (for example, see USPN 5697312 and USPN 7137345).
[0004]
In the moss spherical tank type, a spherical tank made of aluminum
alloy is fixed into a hold through a skirt-shaped support structure
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extending downward from the equatorial portion thereof. In the tank,
both the weight of the liquid cargo loaded therein and the dynamic force
acting on the liquid cargo due to the rolling of ship are directly put
on the tank itself, and are transmitted to the hull through the skirt.
Of course, a heat insulating material of the tank is provided on the
outer surface of the tank.
[0005]
Meanwhile, in the membrane type tank, a heat insulating material
is provided inside a double hull structure of a hull and a top surface
thereof is liquid-tightly covered by a membrane. In this type tank, the
liquid pressure of LNG is transmitted to the hull structure through the
heat insulating material. As the membrane, stainless steel or nickel
alloy (invar) having a small thermal expansion coefficient is used.
[0006]
Incidentally, since the hold is formed in a substantially box shape,
a useless space is inevitably formed around the spherical tank when the
moss spherical tank is applied in the hold. For this reason, the moss
spherical tank has a disadvantage in that the tank volume is small compared
with the size of the hull of both types.
[0007]
Meanwhile, since the membrane type tank can be made in a shape
along the hold, a large tank space is obtained, and hence volumetric
efficiency is satisfactory. On the contrary, when the membrane type tank
encounters heavy weather in a half load condition, a sloshing phenomenon
occurs in which a large pressure is applied (attacked) to the inner wall
of the tank due to the harmony of the shaking of the hull and the shaking
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of the LNG liquid level. That is, the liquid cargo inside the tank is
violently ruffled due to the shaking of the hull, and hence the membrane
or the heat insulating material is damaged due to the impact. In the
spherical tank, since the tank wall is curved, the impact can be smoothly
disappeared. Further, since the heat insulating material is provided
outside the tank, the sloshing substantially does not cause any problem.
Accordingly, in the membrane type tank, there is always a need of full
or almost full load condition so that the LNG in the cargo is not ruffled.
[0008]
The moss type and the membrane type are mainly used in the cargo
tank of the LNG ship, but these types have merits and demerits as described
above. For the use of the LNG ship, it is important to select the ship
type based on the enough consideration of the advantages anddisadvantages .
Here, an independent prismatic tank is developed as an ideal LNG cargo
tank in many ship builders in Japan based on the advantages and
disadvantages. As an example thereof, a SPB tank manufactured by IHI
Corporation is known.
Citation List
Patent Literatures
[0009]
Patent Literature 1: USPN 5697312
Patent Literature 2: USPN 7137345
Summary of Invention
Technical Problem
[0010]
Unlike the spherical tank, the independent prismatic tank is of
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an ideal type without any disadvantage in which the tank volume is small
compared with the size of the hull of both types.
However, the material of the used plate is limited to a material
in which a strength property is exhibited in a cryogenic region, and
stainless steel and aluminum are mainly used as the material. For this
reason, the independent prismatic tank cannot compete with the moss type
and the membrane type from the viewpoint of building cost, and hence
only several ships are built.
[0011]
The LNG is a liquid, and the behavior of the free surface inside
the tank causes a large influence. Particularly, the membrane type should
avoid the sloshing of the liquid level in the tank of the LNG ship caused
by waves due to the tank structure.
[0012]
An object of the invention is to obtain an economical hull structure
by employing an independent prismatic tank having a large tank volume
with respect to a ship size and reducing material cost.
[0013]
Another obj ect of the invention is to obtain a hull structure capable
of accurately handling sloshing in a tank liquid level.
[0014]
The other objects will be proved by the following description.
Solution to Problem
[0015]
The invention solves the above-described problems as below.
[0016]
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<Invention of claim 1>
A LNG ship having a structure in which a substantially prismatic
tank is installed inside a hold while not being integrated with a hull
structure material,
wherein a tank bottom surface is provided with inclined surfaces
formed at the left and right sides of a center line direction of the
ship as a boundary so that each angle intersecting a horizontal line
becomes equal to or smaller than 4.00, and
support bodies integrated with the hull structure material are
arranged so as to correspond to the inclined surfaces and the tank is
put on the support bodies.
[0017]
(Operation and Effect)
In the structure in which the tank is installed inside the hold
while not being integrated with the hull structure (for example, the
double hull structure) material (without any welding structure), there
is an economical advantage in that a high-cost material is not needed.
Further, since the tank has a substantially prismatic shape , the volumetric
efficiency of the tank is larger than that of the spherical tank.
Meanwhile, the tank bottom surface is provided with the inclined
surfaces formed at the left and right sides of the center line direction
of the ship as the boundary so that each angle intersecting the horizontal
line becomes equal to or smaller than about 4.0 , the support bodies
integrated with the hull structure material are arranged so as to
correspond to at least the inclined surfaces, and the tank is put on
the support bodies.
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There is a possibility that the sideslip of the tank may occur
with the thermal deformation of the hull caused by a change in LNG amount
inside the tank and the like. The thermal deformation sideslip is
suppressed or prevented by friction resistance between the tank bottom
surface and the support bodies having inclined top surfaces.
It is possible to simply select a tank structure in accordance
with a structure material of an oil tanker or a LPG tanker. Precisely,
unlike the membrane type, it is unnecessary to use a particular structure
for protection against sloshing phenomenon. Thus, economic efficiency
is improved in the selection of the material and the structure of the
tank.
[0018]
<Invention of claim 2>
The LNG ship according to claim 1, wherein a flat surface is formed
at a center portion of the tank bottom surface, a receiving body integrated
with the hull structure material is provided so as to correspond to the
flat surface, and the flat surface is installed on the receiving body.
[0019]
(Operation and Effect)
Although the flat surface may not be provided in the tank bottom
surface, if the flat surface of the tank is installed on the receiving
body and the main load of the tank is supported by the receiving body,
there is an advantage in strength design of the tank.
[0020]
<Invention of claim 3>
The LNG ship according to claim 1 or 2, wherein the support bodies
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are arranged at the left and right sides of the center line direction
of the ship as the boundary so as to be located at a plurality of positions
separated from each other in a ship width direction.
[0021]
(Operation and Effect)
When the support bodies are arranged at the left and right sides
at the plurality of positions separated from each other in the ship width
direction, the sideslip of the tank occurs smoothly and the weight
decreases.
[0022]
<Invention of claim 4>
The LNG ship according to claim 1 or 2, wherein the support bodies
are arranged at the left and right sides of the center line direction
of the ship as the boundary so as to be located at a plurality of positions
separated from each other in a ship width direction and are provided
along a ship longitudinal direction.
[0023]
(Operation and Effect)
When the support bodies are arranged along the ship longitudinal
direction, the tank can be stably supported.
[0024]
<Invention of claim 5>
The LNG ship according to claim 1 or 2, wherein the support bodies
are arranged at the left and right sides of the center line direction
of the ship as the boundary so as to be located at a plurality of positions
in a zigzag pattern.
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[0025]
(Operation and Effect)
The support bodies can be arranged at the left and right sides
of the center line direction of the ship as the boundary so as to be
located at the plurality of positions in the zigzag pattern.
[0026]
<Invention of claim 6>
The LNG shipaccording to claiml, wherein a keyportion is integrally
formed with a center upper portion of the tank in a protruding manner
and anchor point chocks are provided in the hull structure material so
as to be located at front and rear sides in the center line direction
of the ship corresponding to the key portion.
[0027]
(Operation and Effect)
In order to set the center upper portion of the tank as a thermal
deformation center of the tank for forward and backward direction, the
anchor point chock having a width in the ship width direction is provided
in the hull so as to suppress the movement of the tank for forward and
backward direction as small as possible, and this point is set as the
thermal deformation center. Thus, it is possible to minimize stress in
a LNG pipe connected between tanks and an expansion joint connected between
a tank and a pipe outside of the tank.
[0028]
<Invention of claim 7>
The LNG ship according to claim 1 , wherein a material of the prismatic
tank is selected from aluminum alloy, 9% nickel steel, and stainless
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steel.
[0029]
<Invention of claim 8>
The LNG ship according to claim 1, wherein the LNG ship includes
a LNG carrier, FLNG, FSRU, and SRV.
[0030]
(Operation and Effect)
The term of the "LNG ship" of the invention is widely used as a
ship including a LNG carrier, FLNG, FSRU, and SRV.
Advantageous Effects of Invention
[0031]
As described above, according to the invention, it is possible
to obtain the economical hull structure by employing the independent
prismatic tank having the large tank volume with respect to the ship
size and reducing the material cost.
Further, it is possible to suppress or prevent the sideslip or
the lateral movement of the tank caused by the waves by friction resistance
between the inclined surfaces of the tank bottom surface and the support
bodies having the inclined top surfaces.
Brief Description of Drawings
[0032]
Fig. 1 is a front view of a LNG ship.
Fig. 2 is a plane view of the LNG ship.
Fig. 3 is a cross-sectional view of the LNG ship.
Fig. 4 is a view taken along the line 4-4.
Fig. 5 is a partial plane view of another arrangement example of
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support bodies.
Fig. 6 is a cross-sectional view of another shape example of a
tank.
Fig. 7 is a cross-sectional view of still another shape example
of a tank.
Description of Embodiments
[0033]
Hereinafter, an embodiment of the invention will be described with
reference to the accompanying drawings.
[0034]
As illustrated in Figs. 1 and 2, a LNG tanker has a structure in
which a bow area 10, a tank space 12, an engine room 14, and a stern
area 16 are connected in this order from the front side, and an accommodation
area 18 and a steering room 20 are provided above the engine room. The
tank space 12 is divided into a plurality of sections by transfer bulkheads
22. Reference sign 23 denotes a bulkhead provided for the bow area 10.
[0035]
The invention relates to a LNG ship in which each independent tank
30 having a substantially prismatic shape is installed inside a hold
while not being integrated with hull (double hull) structure materials
32 and 33.
Further, the bottom surface of the independent prismatic tank 30
is provided with inclined surfaces 30A provided at the left and right
sides of the center line direction of the ship as the boundary so that
each angle 0 intersecting a horizontal line H becomes equal to or smaller
than 4.0 . Then, support bodies 34, 34 ... integrated with the hull structure
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material 33 are arranged so as to correspond to the inclined surfaces
30A and 30A, and the tank 30 is put on the support bodies 34, 34 ....
[0036]
Further, a center portion of the bottom surface of the tank 30
is provided with a flat surface 30B. Then, a receiving body 35 integrated
with the hull structure material 33 is provided so as to correspond to
the flat surface 30B, and the flat surface 30B is installed on the receiving
body 35. The support bodies 34, 34 ... are arranged along a ship longitudinal
direction.
[0037]
In the invention, since a structure is employed in which the tank
30 is provided as the independent prismatic tank and is installed inside
the hold while not being integrated with the hull structures (for example,
the double hull structures) 32 and 33 (without any welding structure) ,
there is an economical advantage in that a high-cost material is not
needed. Further, since the tank 30 has the substantially prismatic shape,
the volumetric efficiency of the tank 30 is larger than that of the spherical
tank.
[0038]
The bottom surface of the prismatic tank 30 is provided with the
inclined surfaces 30A formed at the left and right sides of the center
line direction of the ship as the boundary so that each angle 0 intersecting
the horizontal line H becomes equal to or smaller than 4.0 , the support
bodies 34, 34 ... integrated with the hull structure material 33 are arranged
so as to correspond to the inclined surfaces 30A and 30A, and the tank
30 is put on the support bodies 34, 34 .... Thus, there is possibility
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that sideslip of the tank 30 may occur with thermal deformation of the
hull caused by a change in LNG amount inside the tank. This thermal
deformation sideslip is suppressed or prevented by friction resistance
between the bottom surface 30A of the tank 30 and the support bodies
34 having inclined top surfaces.
[0039]
The inclination angle 0 intersecting the horizontal line H of the
bottom surface 30A of the tank 30 is not limited. However, when the
inclination angle 0 is set to be large, there is a possibility that the
liquid cargo amount may decrease and an extreme sideslip may occur.
Accordingly, it is desirable that the inclination angle 0 be equal to
or smaller than 4.0 and be 0.5 to 2.5 .
[0040]
Meanwhile, it is desirable to employ a structure in which a key
portion 40 is integrally formed with a center upper portion of the tank
30 in a protruding manner and anchor point chocks 41 and 41 are provided
in the hull structure material so as to be located at the front and rear
sides in the center line direction of the ship corresponding to the key
portion 40. Thus, it is possible to restrict the thermal deformation
sideslip of the tank for forward and back direction.
[0041]
Although not illustrated in the drawings, a heat insulatingmaterial
can be provided on the outer surface of the tank 30.
[0042]
In the above-described example, the support bodies 34, 34 ... are
arranged along the ship longitudinal direction, but can be arranged
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appropriately. For example, as illustrated in Fig. 5, the support bodies
can be arranged in a zigzag pattern.
[0043]
The "substantially prismatic independent tank" of the invention
may be a prismatic shape in the cross-section as a whole, and does not
need to be a precise prismatic shape. For example, as illustrated in
Fig. 6, it is possible that a tank 30C includes chamfered corners 30a
and round corners 30b and inclined top surfaces 30c.
[0044]
Further, as illustrated in Fig. 7, it is possible that a tank 30D
includes a small tank 30d at an upper portion and a main tank 30e at
a lower portion.
[0045]
As a material of the tank 30, aluminum alloy, 9% nickel steel,
stainless steel, or the like can be used.
[0046]
The above-described embodiments can be used in combination.
Industrial Applicability
[0047]
The invention can be applied to a LNG carrier and in addition,
the invention can be applied also to a FLNG (LNG-FPSO (Floating Production,
Storage and Off-loading system)), FSRU, and SRV, which require handling
of sloshing phenomenon in the same manner as the LNG carrier.
[0048]
In the FLNG (LNG-FPSO), impurities of natural gas from a marine
gas field are removed and the natural gas is liquefied to produce LNG
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so that the LNG is stored on a ship or a barge having a LNG storage capacity.
Then, the LNG is shipped off to a LNG ship for carrying the LNG. As compared
with a case where a liquefied natural gas plant is constructed on the
land, this system has the following advantages: a pipeline from the marine
gas field to the land can be reduced; an environmental load can be reduced
because development on the coast is not required; and workers can be
comparatively easily secured because the LNG-FPSO is constructed in a
country or a region different from those in which a gas field is developed
and is towed to the site.
[0049]
The LNG ship of the present invention includes a re-gasification
unit and the examples of the re-gasification unit are an FSRU (Floating
Storage and Re-gasification Unit) and SRV (Shuttle and Re-gasification
Vessel) . The FSRU is mounted with a re-gasification unit and fixes a
ship having an LNG storage capacity on the sea and receives LNG from
the other LNG ship. The natural gas re-gasified by the FSRU is sent out
to a pipeline on the land. The SRV does not transfer LNG from the other
LNG ship but transports LNG loaded in at a liquefaction base to a demand
area, re-gasifies the LNG on the deck, and sends out the re-gasified
natural gas to a pipeline on the land.
Reference Signs List
[0050]
10: bow area, 12: tank space, 14: engine room, 16: stern area,
18: accommodation area, 20: steering room, 30, 30A to 30D: independent
prismatic tank, 30A: inclined surface, 30B: flat surface, 32, 33: hull
structure material, 34: support body, 35: receiving body, 0: inclination
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angle
