JP2013184504A - Ship, sea floating type equipment, and method for storing liquefied natural gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ship having an LNG tank, sea floating type equipment, and a method for storing liquefied natural gas, where the tank has a small number of tank structural members and has a shorter weld length required for construction than an independent rectangular tank, and furthermore, has a thinner board thickness and has a small number of weld management portions than a pressure tank, and moreover, the tank can be reduced in weight and manufacturing costs, and is also not much inferior in the volumetric efficiency for a rectangular hull cross-sectional shape to the independent rectangular tank.SOLUTION: In a ship 1 for carrying liquefied natural gas and sea floating type equipment for generating, storing and shipping the liquefied natural gas, a cargo space 2 for storing the liquefied natural gas is formed of a twin-barrel cylindrical tank 10 having a center-line bulkhead and being not a pressure vessel, and a drip pan 40 is provided for serving as a partial secondary barrier which receives the liquefied natural gas leaked from the tank 10 at a lower part of the cylindrical part of the tank 10.

Description

  The present invention relates to a ship for transporting liquefied natural gas (LNG), an offshore floating facility for producing, storing and unloading liquefied natural gas, and a liquefied natural gas storage method.

  In ships called LNG carriers that transport conventional liquefied natural gas (hereinafter referred to as LNG), the International Maritime Organization (IMO) has established standards for LNG tanks that store liquefied natural gas. According to the rules of steel ships of classification societies such as the Maritime Association (NK), the storage temperature of LNG is very low (LPG is minus 45 ° C, LNG is minus 163 ° C). LNG tanks such as membranes, independent secondary tank type A with full secondary barrier, independent secondary tank type B with partial secondary barrier, independent independent tank type C without secondary barrier (pressure vessel ) One of the tanks is to be adopted. Here, the design vapor pressure P of the independent tank type C must be set to a value equal to or higher than the value given by the following equation (1) as a pressure vessel.

P = 0,2 + A · C (ρ _r ) ^1.5 (MPa) (1)
Here, A = 0.00185 (σ _m / Δσ _A ) ²
σ _m : Designed primary film stress
Δσ _A : Allowable dynamic membrane stress (both amplitudes at the expression probability Q = 10 ⁻⁸ level)
55 N / mm ² : ferrite-pearlite, martensite and
Austenitic steel
25 N / mm ² : Aluminum alloy (5083-0)
C: Larger value determined from the tank dimensions shown below
h, 0.75b or 0.45L
h: Tank height (in the depth direction of the ship) (m)
b: Width of tank (ship width direction) (m)
L: Length of tank (length direction of ship) (m)
ρ _r : Specific gravity of cargo at design temperature (in the case of fresh water: ρ _r = 1)

  In addition, the above-mentioned secondary barrier, for example, can store leaked liquid cargo (LNG) for 15 days in consideration of the load frequency distribution specified in the rules, except for specific routes, in the Steel Ship Rules of the Japan Classification Society, and It is necessary to prevent the temperature of the hull structure from becoming lower than the dangerous temperature when leaking from the primary barrier, and the mechanism of the primary barrier destruction does not cause the secondary barrier destruction. The mechanism of the destruction of the secondary barrier does not cause the destruction of the primary barrier, and moreover, the function must be satisfied even at a static lateral inclination angle of 30 degrees.

  In addition, when a partial secondary barrier is required, the installation range of the partial secondary barrier is determined based on the leak corresponding to the magnitude of the fracture obtained by applying the load frequency distribution specified in the rule after the first leak is discovered. In any case, the inner bottom plate at the bottom of the tank needs to be protected from leaked cargo, and outside the range of the partial secondary barrier, the leaked cargo in the compartment between the primary barrier and the secondary barrier It is said that equipment that leads to

  On the other hand, with the development of offshore gas fields far from the land, the floating LNG production storage and offloading facility that can produce, store and load LNG on the ocean Body equipment is in the spotlight. This offshore floating facility is called "LNG FPSO", "Floating LNG", "FLNG", etc., but it moves to the offshore gas field, and the gas mined by berthing on the offshore of the gas field is LNG Are temporarily stored and shipped to the LNG carrier. By using this offshore floating facility, it will be possible to produce natural gas from offshore gas fields, which have been difficult to develop until now, and to use associated gas generated during offshore oil field production.

  In designing and constructing this offshore floating facility, the technology of the LNG carrier is applied. However, the requirements for LNG tanks in offshore floating facilities are different from those for LNG carriers in the following respects. The first point is that a large deck area can be secured because the LNG production plant is mounted on the upper deck of the floating body. Second, because LNG is produced and stored on the ocean as needed, the amount of LNG stored gradually increases from one shipment to the next, so it can be almost fully loaded like an LNG carrier. In other words, it is necessary to make the LNG tank mountable at an arbitrary liquid level, and it is necessary to consider that the impact pressure due to sloshing acts on the tank wall. The third point is that since maintenance is not possible at the dock as in the case of an LNG carrier, since it is still moored at the gas field site, ease of maintenance and long-term reliability at sea is required.

  As an LNG tank that satisfies all of these requirements, an independent rectangular tank with a track record of construction is known for LNG carriers, but in this independent rectangular tank, a cylindrical tank or a spherical tank supports the LNG load by the membrane force of the curved plate. On the other hand, since the LNG load is supported by a flat plate reinforced by a very large number of stiffeners, the number of members and the weld length are longer than those of other tanks, resulting in an increase in manufacturing cost. Therefore, the development of an inexpensive LNG tank system for offshore floating type facilities is required instead.

  As one of the LNG tanks that are candidates for the LNG carrier and the offshore floating type equipment, a twin-cylinder tank having two parallel cylindrical shapes that intersect each other is proposed as a type C independent tank (for example, Patent Document 1). However, since this LNG tank needs to satisfy the condition of the pressure vessel, which is a type C condition, when attempting to increase the capacity of the tank, the plate thickness increases remarkably from the viewpoint of strength, and the weight, manufacturing man-hours and Since the manufacturing cost increases, there is a problem that it is difficult to adopt this method for an actual large tank.

JP 2009-517272 A

  The present invention has been made in view of the above-described situation, and its object is to reduce the number of tank structural members and the welding length required for construction compared to an independent rectangular tank, and to compare it with a pressure tank. The LNG tank is thin and has a small number of welding management points, is lightweight, can be manufactured at low cost, and has a volume efficiency for a rectangular hull cross-sectional shape that is not inferior to that of an independent rectangular tank. An object of the present invention is to provide a marine vessel, an offshore floating facility, and a liquefied natural gas storage method.

  In order to achieve the above object, a ship according to the present invention is a ship that transports liquefied natural gas, wherein the cargo hold for storing the liquefied natural gas is a twin-trunk cylindrical tank having a centerline partition wall, and a pressure vessel A drip pan as a partial secondary barrier for receiving the liquefied natural gas leaked from the tank is provided at the bottom of the cylindrical portion of the tank.

  In order to achieve the above object, an offshore floating facility according to the present invention is an offshore floating facility that produces, stores, and loads liquefied natural gas. A drip pan as a partial secondary barrier for receiving the liquefied natural gas leaked from the tank is provided at the bottom of the cylindrical portion of the tank. Configure.

  The liquefied natural gas storage method of the present invention for achieving the above object is a liquefied natural gas storage method in a ship that transports liquefied natural gas or an offshore floating facility that produces, stores, and loads liquefied natural gas. And a tank with a center line provided with a drip pan as a partial secondary barrier for receiving the liquefied natural gas leaked to the lower part of the cylindrical portion of the tank. And storing the liquefied natural gas.

  According to these configurations and methods, it is not necessary to satisfy the condition of the pressure vessel, which is a type C condition, and therefore it is not necessary to increase the plate thickness from the viewpoint of strength even if the capacity of the tank is increased. Furthermore, compared with an independent square tank, there are few tank structural members, the welding length required for construction is short, and also a plate | board thickness is thin compared with a pressure tank, and there are few welding management locations. Therefore, an increase in weight, manufacturing man-hours, and manufacturing costs can be suppressed, and the volumetric efficiency with respect to the rectangular hull cross-sectional shape is relatively large, which is not significantly inferior to the volumetric efficiency of the independent rectangular tank.

  According to the ship, offshore floating type equipment, and liquefied natural gas storage method of the present invention, compared with an independent rectangular tank, there are fewer tank structural members, a weld length required for construction is short, and compared with a pressure tank. It is possible to reduce the manufacturing cost by reducing the plate thickness and the number of welding management points, and reducing the manufacturing cost. Furthermore, the volume efficiency for the rectangular hull cross-sectional shape is not much inferior to that of the independent rectangular tank. It is possible to provide an upper floating type facility and a liquefied natural gas storage method.

It is side sectional drawing which shows the structure of the ship of embodiment which concerns on this invention. It is YY sectional drawing of FIG. It is XX sectional drawing of FIG. It is a sectional side view which shows the structure of a tank. It is X1-X1 sectional drawing of FIG. It is X2-X2 sectional drawing of FIG. It is an enlarged view of the fix support part of FIG. It is an enlarged view of the sliding support part of FIG. It is a partial enlarged view which shows the arrangement | positioning relationship between a tank and a drip pan. It is a side view which shows the structure of the offshore floating body type equipment of embodiment which concerns on this invention. It is a top view of FIG. It is a figure which shows the tank in the cargo hold of X4-X4 sectional drawing of FIG.

  Hereinafter, a ship, an offshore floating facility, and a liquefied natural gas storage method according to embodiments of the present invention will be described with reference to the drawings. The ship to which the present invention is applied is a ship that carries liquefied natural gas (LNG).

  As shown in FIGS. 1 to 3, a ship 1 according to an embodiment of the present invention includes a cargo hold 2 that stores liquefied natural gas, a ship bottom plate 3, a ship side outer plate 4, an upper deck 5, and a transverse bulkhead 6. Form in the enclosed. The double bottom 3a is provided between the bottom plate 2a and the bottom plate 3 of the cargo hold 2 of the cargo hold 2, and the ship side outer plate 4 side is also made into a double structure so that even if the bottom plate 3 is damaged due to grounding or collision. It is configured to prevent the cargo hold 2 from being flooded.

  As shown in FIGS. 4 to 6, the cargo hold 2 is equipped with a tank 10 that is a double-trunk cylindrical tank having a centerline partition wall 13 and is not a pressure vessel as a tank for storing LNG. And configure. The tank 10 includes a body plate shell 11, an end plate shell 12, a centerline partition wall 13, two front and rear support rings 14, a water control partition wall 15, and the like. A connecting pipe 16 is provided to keep the left and right tanks at the same pressure. The body plate shell 11 is provided with a ring stiffener 11a and a dome 11b as a reinforcing material, and a pump dome 11c, and the center line partition wall 13 is provided with a stiffener (not shown).

  Of these structural members, most of the body plate shell 11 and the end plate shell 12 can be applied with a design calculation formula based on a thin film theory. This thickness is determined by the yield strength criteria for static and dynamic internal pressure loads when cargo is loaded. However, the transition part (knuckle part) 18 from the shell plate part shell 11 to the end plate part shell 12 shown in FIG. 4 or the crossing part of the body plate part shell 11 or the end plate part shell 12 and the center line partition wall 13 shown in FIG. A local bending stress is generated at the Y joint portion 17. Therefore, dimension determination by thin film theory may not be appropriate, and in such places, the plate thickness is determined based on direct strength analysis using a finite element method (FEM). In addition, a ring stiffener 11 a having a flat cross section is disposed on the inner surface of the shell plate shell 11 so as to satisfy the buckling strength standard against the external pressure when the tank 10 is empty.

The design vapor pressure of the tank 10 is about 0.025 MPa because it is a type B tank, and is about 1/15 or less than the design vapor pressure of the type C that needs to be a pressure vessel. Even if the capacity is increased, the increase in plate thickness can be suppressed. As a result, it is about 7 to more than 8 times the maximum tank capacity (5400m ³ ) in an LPG ship equipped with a catamaran cylindrical tank with a centerline bulkhead, which is a type C pressure vessel. A capacity tank can be realized.

  The plate thickness of the center line partition wall 13 is determined so as to satisfy the yield strength standard in the same manner as the body plate shell 11 and the end plate shell 12 by the balance of the film force at the Y joint portion 17. Since the function of a watertight bulkhead is required for lifting and restoring performance in an emergency, stiffeners are arranged vertically and horizontally to withstand the hydraulic pressure when only one tank is fully loaded.

  The support ring 14 has a T-shaped trans-ring structure that matches the tank support structure of the hull. The ring structure of the support ring 14 is an important member and has a complicated distribution of supporting reaction force and structural response. Therefore, based on the stress obtained from the direct strength analysis using the finite element method model, the overall rigidity and partial dimensions are determined so as to satisfy the yield / buckling strength criteria.

  In addition, since the storage amount of the tank 10 gradually increases according to the production amount from one shipment to the next, it cannot be almost fully loaded like an LNG carrier. It can be installed with. Therefore, in consideration of sloshing, a water control partition wall 15 having a communication hole 15a as shown in FIG.

  On the tank 10, a pump dome 11c is installed immediately above a sump 11d provided for discharging LNG. In the LNG ship, since the ship has an aft trim (an inclined posture with the bow side up), the sump 11d is installed behind the tank 10 in the captain direction. On the other hand, the offshore floating facility (FLNG) basically assumes an even trim (horizontal posture), so the sump 11d is installed in the center of the tank 10.

  As shown in FIGS. 4 and 5, supports 21 and 22 that support the tank 10 are provided as the tank support structure 20. The supports 21 and 22 are provided at two positions in the front and rear of the cargo hold 2 on which the tank 10 is mounted, and the support (fixed support) 21 fixed to the hull is the rear side (or front side) as shown in FIG. ), A support (sliding support) 22 slidable with respect to the hull is installed on the front side (or rear side) as shown in FIG. The front-rear position is determined in consideration of the overall bending of the tank structure and the structural arrangement of the cargo hold 2 and the double bottom 3a.

  This tank support structure 20 transmits the total weight acting on the tank 10 and the inertial force due to shaking to the ship side skin 4 and the cargo hold 2 and the double bottom 3a, and at the top, prevents the cargo hold 2 from floating when it is flooded. In order to provide the structure 25, a trans-ring structure that extends substantially outside the tank 10 except for the upper deck 5 is adopted.

  Further, as shown in FIG. 9, a reinforced laminated wood 23 serving as a heat insulating material and a buffer material is disposed between the tank 10 and the tank support structure 20. The installation range of the reinforced laminated wood 23 is determined so that an excessive reaction force is not generated at the end of the installation range even at a large inclination with reference to a support reaction force distribution by direct strength analysis using a finite element method model. . Further, as shown in FIGS. 7 and 8, when the tank 10 is mounted on the tank support structure 20, the gap between the reinforced laminated wood 23 and the tank support structure 20 is filled with a filling resin 24 to close the gap. The range of the reinforced laminated wood 23 is set up to a position (horizontal position) right next to the center in the vertical direction of the tank 10 so as to cover the lower side of the tank 10 as shown by an arc-shaped thick line portion in FIG. Is done.

  Further, the tank support structure 20 causes the heat shrinkage of the tank 10 to be caused by sliding between the lower base of the support 22 and the reinforced laminated wood 23 in the circumferential direction, as shown in FIG. It is designed to absorb and avoid excessive thermal stress. In addition, for the longitudinal acceleration at the time of collision required by the International Maritime Organization (IMO) standards, the rigidity of the structures of the supports 21 and 22 and the double bottom 3a so that they can be supported by the fixed support 21 at the rear. To decide.

  Further, as shown in FIG. 9, a drip pan 40 as a partial secondary barrier that receives the liquefied natural gas L leaked from the tank 10 is provided at the lower portion of the cylindrical portion of the tank 10. Moreover, the heat insulation structure 26 is comprised from the polymer-type heat insulating material represented by the polyurethane.

  As shown in FIGS. 10 to 12, the offshore floating type facility 1 </ b> A according to the embodiment of the present invention is formed with substantially the same structure as the hull structure of the ship 1 according to the embodiment of the present invention. A tank 10A having the same structure as that of the tank 10 of the ship 1 according to the present invention for storing, that is, a double-trunk cylindrical tank having a centerline partition wall and not a pressure vessel is mounted in the cargo hold 2A. And configure.

  Unlike the ship 1, this offshore levitation equipment 1A has a machine room equipped with utility equipment for supplying utilities such as electric power and steam necessary for LNG production as a floating body equipment under the upper deck 5A. The bow machine room 51 and the stern machine room 52 are provided at the bow part and the stern part, respectively.

  In addition to the cargo hold 2A equipped with a tank 10A for storing produced LNG until shipment, as a floating body facility, although not shown, a condensate tank for storing condensate separated from natural gas, a change in the storage amount of the tank 10A The ballast tank and the like for adjusting the attitude of the offshore floating type equipment 1A are formed.

  Further, on the upper deck 5A, a liquefaction that removes and liquefies impurities such as acid gas contained in the natural gas mined from the one point mooring external turret 53, natural gas mining device 54, and gas field. A natural gas production facility 55, a living facility 56, a helicopter deck 57, and the like are provided.

  The offshore floating facility 1A can effectively use the limited space of the offshore floating facility 1A by adopting the tank 10A having a larger capacity than the LNG carrier of the prior art, thereby reducing the number of tanks. I am doing so. Further, in the offshore floating facility 1A, the amount of water injected into the ballast tanks appropriately distributed is adjusted, and the attitude of the offshore floating facility 1A is adjusted according to the change in the storage amount of the tank 10A. There is no generation of trim like a ship, and it can maintain a horizontal state at all times.

  And the liquefied natural gas storage method of embodiment of this invention is the liquefied natural gas storage method in the ship 1 which conveys liquefied natural gas, or the offshore floating-type equipment 1A which produces, stores and unloads liquefied natural gas. And a central cylinder 13 having a drip pan 40 as a partial secondary barrier for receiving a leaked LNG at the lower part of the cylindrical portion of the tank 10 or 10A. LNG is stored in the mold tanks 10 and 10A.

  According to these configurations and methods, the tanks 10 and 10A loaded with liquefied natural gas need not satisfy the conditions of the pressure vessel, which is a type C condition. From the above viewpoint, it is not necessary to significantly increase the plate thickness. Furthermore, compared with an independent square tank, there are few tank structural members, the welding length required for construction is short, and also a plate | board thickness is thin compared with a pressure tank, and there are few welding management locations. Therefore, an increase in weight, manufacturing man-hours, and manufacturing costs can be suppressed, and the volumetric efficiency with respect to the rectangular hull cross-sectional shape is relatively large, which is not significantly inferior to the volumetric efficiency of the independent rectangular tank.

  According to the ship, offshore floating type equipment, and liquefied natural gas storage method of the present invention, compared with an independent rectangular tank, there are fewer tank structural members, a weld length required for construction is short, and compared with a pressure tank. This is a liquefied natural gas tank that has a small plate thickness, requires fewer welding management points, is lightweight, can be manufactured at low cost, and is not significantly inferior to an independent rectangular tank in terms of volumetric efficiency for a rectangular hull cross-sectional shape. Can be provided as a ship for transporting liquefied natural gas, an offshore floating facility, and a liquefied natural gas storage method.

DESCRIPTION OF SYMBOLS 1 Ship 1A Offshore floating type equipment 2, 2A Cargo hold 10, 10A Tank 11 Shell plate shell 12 End plate shell 13 Centerline partition 14 Support ring 15 Water control partition 16 Connection pipe 17 Y joint 18 Transition part (knuckle part)
20 Tank support structure 21 Support (fix support)
22 Support (sliding support)
23 Reinforced laminated wood 24 Filling resin 25 Lifting prevention structure 40 Drip pan

Claims (3)

  In a ship carrying liquefied natural gas, the cargo hold for storing the liquefied natural gas is composed of a double-trunk cylindrical tank having a centerline partition wall and a tank that is not a pressure vessel, and the cylindrical portion of the tank A ship provided with a drip pan as a partial secondary barrier for receiving the liquefied natural gas leaked from the tank at a lower part.   In offshore floating facilities that produce, store and ship liquefied natural gas, the cargo hold for storing the liquefied natural gas is composed of a double-trunk cylindrical tank having a centerline partition and a tank that is not a pressure vessel And a drip pan as a partial secondary barrier for receiving the liquefied natural gas leaked from the tank is provided below the cylindrical portion of the tank.   In a liquefied natural gas storage method in a ship that transports liquefied natural gas or an offshore floating facility that produces, stores, and unloads liquefied natural gas, it is constituted by a tank that is not a pressure vessel, and a cylindrical portion of the tank The liquefied natural gas storage is characterized in that the liquefied natural gas is stored in a twin-cylinder cylindrical tank having a centerline partition wall provided with a drip pan as a partial secondary barrier for receiving the liquefied natural gas leaked to the lower part of the tank Method.

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