WO2005113328A1

WO2005113328A1 - Single-compartment liquefied natural gas carrier

Info

Publication number: WO2005113328A1
Application number: PCT/US2005/011716
Authority: WO
Inventors: Brett W. Wilson; Ronald R. Bowen
Original assignee: Exxonmobil Upstream Research Company
Priority date: 2004-05-14
Filing date: 2005-04-06
Publication date: 2005-12-01

Abstract

A marine vessel is provided, the marine vessel having a containment structure for containing fluid therein. The containment structure has a single cargo hold forming the entire fluid-carrying cargo area for the marine vessel, and is undivided by bulkheads. The containment structure also includes an array of tanks within the single cargo hold for containing the fluid. The array of tanks is configured in such a manner and preferably occupies a volume within the cargo hold such that, should flooding of the cargo hold occur, the marine vessel will not capsize or founder. The individual tanks are preferably adapted for carrying natural gas in any of the following states: compressed (CNG), liquefied (LNG), and pressurized liquefied (PLNG). Preferably, the cargo hold of the containment structure is entirely beyond a distance from the hull of the ship required by the IGC code for side damage extents.

Description

SINGLE-COMPARTMENT LIQUEFIED NATURAL GAS CARRIER

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application 60/571 ,282, filed May 14, 2004.

BACKGROUND

Field of the Inventions

[0002] Embodiments of the present invention generally relate to the transportation of large fluid volumes in a marine vessel. More particularly, embodiments of the present invention relate to an integrated design of a fluid containment system and marine transport vessel. An improved hull arrangement is offered for reducing complexity and/or expense for marine transport vessels carrying large fluid volumes in multiple, independent tanks.

Description of Related Art

[0003] Clean burning natural gas has become the fuel of choice in many industrial and consumer markets around the industrialized world. Natural gas sources are often located in remote locations relative to the commercial markets desiring the gas. The natural gas is oftentimes transported across oceans using large-volume marine vessels. To maximize gas volumes for transportation, the gas may be taken through a liquefaction process. The liquefied natural gas, or "LNG", is formed by chilling very light hydrocarbons, e.g., gases containing methane to approximately -160° C, where it is stored at ambient pressure in special, cryogenic tanks disposed on large ships for marine transportation. Additionally, LNG may be liquefied at an increased pressure and warmer temperature, above -160° C, in which case it is known as Pressurized LNG (PLNG). [0004] LNG vessels include a hull configured to hold the cryogenic tanks. These vessels may be required by international regulations such as the International Gas Code to have double hulls consisting of a double bottom and double sides. The double hull provides a measure of protection to the cargo in the event of damage to the ship. In this respect, the outer hull can be damaged but seawater will not contact the tanks on board unless the inner hull is also penetrated.

[0005] Various types of tanks are known for containing LNG. These include insulated prismatic membrane tanks, moss sphere tanks and other types of tanks. For PLNG, the tanks must not only maintain cryogenic temperatures, but must contain pressure as well. PLNG tanks may consist of upright bottles configured in arrays within a marine vessel's cargo hold region. These multiple arrays of tanks are placed in separate compartments, or "cold boxes" within the cargo hold. The tanks are bottle-shaped or cylindrical in configuration, and are typically in an equally spaced relation within the cargo holds. The cold boxes, in turn, are positioned linearly along the hull of the vessel, and are insulated to maintain the bottles or other tank arrangement at a desired temperature. The multiple cold boxes are needed to provide adequate compartmentalization for the marine vessel in the event a cold box or boxes is/are penetrated as a result of damage to the marine vessel. This compartmentalization prevents flooding from spreading from damaged compartments to other portions of the ship (which would then capsize or founder the ship).

[0006] Where PLNG or LNG is stored in upright bottles for marine transportation, arrays of the bottles will be placed in separate cold boxes. Typically, four or five separate cold boxes may be employed fore and aft along approximately the middle two-thirds of the ship. The outer boundary of the cold boxes typically will be integral with the inner hull of a double hulled vessel. The cold boxes are separated by transverse watertight bulkheads in a back-to-back or double fashion, transverse to the longitudinal axis of the ship. This paired bulkhead arrangement is referred to as a "cofferdam." Cofferdams are located between cold boxes so as to enable heating of the ship steel in the bulkheads to prevent the steel from reaching cryogenic temperatures and fracturing.

[0007] The use of multiple cold boxes and attendant cofferdams results in high costs for insulation of the various interior surfaces of each cold box. For example, each cold box interior surface, i.e., top, bottom, port and starboard sides, along with forward and aft sides - must be insulated to ensure that the cargo remains cryogenic and that the ship's hull steel is not exposed to excessively cold temperatures that could lead to brittle fracture. Additionally, the small distance between the adjacent cofferdam bulkheads requires that some form of active heating (cofferdam ventilation or heat tracing of the bulkheads) be installed. Additional background can be found in DE 195 33 066 to Gloystein, "Entwicklungstendenzen im Gastankerbau aus der besonderen Sicht internationaler Vorschriften" by M. Bockenhauer in Jahrbuch Der Schiffbautechnischen Gesellschaft, vol. 68 (1974) pages 97-118, U.S. 3,863,460 to Straile et al., DE 31 43 457 to Thiele, and FR 1 452 058 to Les Conduites Immergees.

SUMMARY

[0008] A marine vessel is provided. The marine vessel has a containment structure for containing fluid therein. The containment structure has a single cargo hold forming the entire fluid-carrying cargo area for the marine vessel, and is undivided by bulkheads. The containment structure also includes an array of tanks within the single cargo hold for containing the fluid. The array of tanks is preferably configured in such a manner and preferably occupies a volume within the cargo hold such that, should flooding of the cargo hold occur, the marine vessel will not capsize or founder. The individual tanks of the containment structure are preferably adapted for carrying natural gas in any of the following states: compressed (CNG), liquefied (LNG), and pressurized liquefied (PLNG). [0009] In the preferred embodiment, the cargo hold of the containment structure has side boundaries that are beyond a distance from an outer side shell of the double hull required by the IGC code for side damage extent boundaries. In addition, the cargo hold has a bottom that is beyond a distance from an outer bottom shell of the double hull required by the IGC code for bottom damage extent. In one aspect, the cargo hold has side boundaries that reside a distance from an outer side shell of a double hull that is at least the lesser of one-fifth of the beam of the ship, or 11.5 meters, and the cargo hold has a bottom boundary that resides beyond a distance from an outer bottom shell of a double hull that is at least the lesser of 1/15th the beam of the ship, or 2 meters;

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 presents a plan view of the main deck of a fluid transportation vessel. Visible in this view is the top of a containment structure, in one embodiment. Individual tanks within the containment structure are seen.

[0011] Figure 2 is a side view of the vessel of Figure 1. Visible in this view is a side of the containment structure of Figure 1. Individual tanks within the containment structure are again seen.

DETAILED DESCRIPTION

Definitions

[0012] The following words and phrases are specifically defined for purposes of the descriptions and claims herein. To the extend that a term has not been defined, it should be given its broadest definition that persons in the pertinent art have given that term as reflected in printed publications, dictionaries and/or issued patents.

[0013] "Marine vessel" means a floating vessel configured to transport volumes of commodities such as LNG or PLNG. [0014] "Cargo hold" means an enclosure having walls in which cargo is carried. The cargo hold may be integral to the hull of the vessel, or may be separable.

[0015] "Tank" means any container for holding a volume of fluid, such as LNG or PLNG. One non-limiting example is a cylindrical bottle. Another non- limiting example is one or more fluid containers in fluid communication with one another.

[0016] "Independent tank" means a single container forming its own tank, and not in fluid communication with other containers.

[0017] "IGC Code" means the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk."

[0018] "Beam" means the width of a vessel from starboard to port at any given cross-sectional location. In the context of a double hull ship, beam is measured from the outer surface of the outer shell of the hull.

[0019] In the context of a double hull ship, the term "hull" means any outer side shell or bottom shell.

[0020] "Array" refers to any collection of tanks, i.e., two or more tanks.

[0021] "Containment volume" means the total volume that an individual tank can contain.

Description of Specific Embodiments

[0022] The following provides a description of specific embodiments of the present invention:

[0023] A marine vessel is provided, with the marine vessel having a containment structure for containing fluid therein. The containment structure comprises a single cargo hold forming the entire fluid-carrying cargo area for the marine vessel. The single cargo hold is undivided by bulkheads. In addition, the containment structure comprises an array of tanks within the single cargo hold. Each of the tanks in the array of tanks contains a portion of the fluid. In one embodiment, the array of tanks is configured in such a manner and occupies a volume within the cargo hold such that, should flooding of the cargo hold occur, the marine vessel will not capsize or founder. In one arrangement, each of the tanks in the array of tanks is designed to have a geometry selected from the group consisting of: spherical, ovoid, and cylindrical.

[0024] The cargo hold may include an insulated floor common to each of the tanks, insulated side walls forming lateral boundaries for the cargo hold, and an insulated top also common to each of the tanks. In addition, the cargo hold preferably has side boundaries that are beyond a distance from an outer side shell of a double hull ship arrangement as required by the IGC code for side damage extent. In one arrangement, the cargo hold has side boundaries that reside a distance from an outer side shell of the double hull that is at least the lesser of one-fifth of the beam of the ship, or 11.5 meters, and the cargo hold has a bottom boundary that resides beyond a distance from an outer bottom shell of the double hull that is at least the lesser of 1/15th the beam of the ship, or 2 meters.

Description of Embodiments Shown in the Drawings

[0025] The following provides a description of specific embodiments shown in the drawings:

[0026] Figure 1 presents a plan view of a marine vessel 50 for holding a containment structure 100. The main deck 20 of the vessel 50 is seen. The vessel 50 includes a forward end 54, an aft end 52, and starboard 58 and port 56 sides. The illustrative vessel 50 is self propelled, though the claimed containment structures are not limited to use on self-propelled ships. In this respect, the claimed containment structures have utility on floating stations, such as a floating production, storage and offloading vessel ("FPSO"). [0027] Additional components of the illustrative vessel 50 are more clearly seen in Figure 2. Figure 2 provides a side view of the vessel 50 of Figure 1. The vessel 50 has an engine room 60. The vessel 50 also has a rudder 64, an engine exhaust stack 62, a reliquefaction facility 66, and a bridge / house 68. The illustrative vessel 50 has a double hull 70. An exterior 72 and an interior 74 hull are each visible in Figure 2. The double hull arrangement 70 means that the vessel has an outer bottom and inner bottom arrangement, and an outer side and inner side shell arrangement for the bottom and sides of the ship 50, respectively.

[0028] The vessel 50 is configured to transport fluids over a large marine body such as the ocean (not shown). Examples of such fluids include various hydrocarbons. Examples of hydrocarbons include lighter hydrocarbons such as methane and ethane. Such lighter hydrocarbons may be maintained in the vessel 50 under pressure. In addition or alternatively, such lighter hydrocarbons may be maintained in a refrigerated state, a heated state, or an ambient or other thermal condition. In one example, the hydrocarbon is a liquefied natural gas, or "LNG." In another example, the hydrocarbon is a pressurized liquefied natural gas, or "PLNG." In another example, the hydrocarbon is a compressed natural gas, or "CNG."

[0029] Also visible in Figure 1 and Figure 2 is a containment structure 100 for containing fluids. In Figure 1 , a top of the containment structure 100, in one embodiment, is seen, while Figure 2 provides a side view of the containment structure 100 of Figure 1. The containment structure 100 first comprises an arrangement of individual tanks 120. The tanks 120 are preferably disposed in an array of columns and rows, though other array arrangements may be employed. The independent tanks 120 are preferably cylindrical in shape, though other shapes may be employed, such as spherical, ovoid, or bottle-shaped. The various tanks 120 are held within a shared, single cargo hold 110 undivided by bulkheads. Where the tanks 120 are for holding LNG or PLNG, the single cargo hold 110 serves as a "cold box," and provides insulation for the various tanks 120. Thus, a tank design is provided wherein fluids, preferably PLNG, may be stored within independent containers or "tanks" 120 inside of a single large compartment 110. Multiple cofferdams separating separate compartments are not needed.

[0030] The tanks may define individual containers, e.g., bottle-shaped containers, or may define more than one container in fluid communication. In either arrangement, an array of tanks is provided within the single cargo hold. Preferably, the array of tanks is configured in such a manner and occupies such a volume within the cargo hold that, should flooding of the cargo hold occur, the marine vessel will not capsize or founder. In one embodiment the array of tanks is attached to the single cargo hold. In one embodiment the array of tanks is permanently attached to the single cargo hold.

[0031] Features of the cargo hold 110 are shown in Figure 2. The cargo hold 110 has a top 118 that extends over the various tanks 120. In addition, the cargo hold 110 has a floor 116 that extends under the various tanks 120. Thus, both the top 118 and bottom 116 of the cargo hold 110 are considered "common" to the tanks 120. In one embodiment, the floor 116 and top 118 of the cargo hold 110 are insulated, providing a cold box. Any insulation technique for a cold box as is known in the art may be employed. However, the cargo hold 110 preferably forms the entire fluid-carrying cargo area for the vessel 50, meaning that the vessel 50 does not reserve additional cargo area or subdivision for carrying other fluids.

[0032] Those of ordinary skill in the art will understand that a multiple- cargo-hold (or, in the case of LNG ships, multiple-tank) arrangement is largely dictated by international design regulations, e.g., regulations promulgated by the International Marine Organization. These regulations require that the ship be able to float and maintain a measure of residual statical stability in the event of damage to the side or bottom of the ship's hull, that is, when a collision results in the unlikely penetration through the double hull of a tanker or other ship and into its cargo hold region. Where the cargo containers are entirely contained or encompassed within the structural prism that is inside the side damage and bottom damage extents required by the IGC Code for damage stability, no subdividing bulkheads or cofferdams are required. This results in a substantively greater degree of protection of the cargo containers from collision (the containers are located farther inboard) and from grounding (the containers are above the damage zone, but also, the containment bottom area exposed to damage is reduced).

[0033] The cargo hold 110 shown in Figures 1 and 2 has side walls 130 that together define a boundary for the containment structure 100. The side walls 130 may optionally be insulated as well for forming the "cold box." In one arrangement, the boundary formed by the side walls 130 is configured to reside not only inside of the ship's hull 70, but also within the parameters for flooding damage, i.e., "extent of side damage" as specified by the IGC Code as it may from time to time be amended. In one arrangement, the cargo hold has a bottom boundary that entirely resides within the parameters for flooding damage, i.e., "extent of bottom damage," specified by the IGC Code as it may from time to time be amended. In one known version, the IGC Code provides that liquid-cargo-carrying vessels must segregate cargo holds along the length of the ship, and employ a cofferdam arrangement to ensure stability during flooding if the side boundary of any cargo hold is less than one-fifth of the beam of the vessel, or if the bottom boundary of any cargo hold is less than two meters from the hull of the vessel.

[0034] It is noted that while the cargo containers in a liquid-container ship are commonly placed inside of a double hull, the liquid containers remain relatively close to the side of the ship. Ship design regulations provided in the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk ("IGC Code" require the use of bulkheads when liquid cargo is within a certain distance of the side and bottom hulls. In this way, in the event that a collision occurs resulting in a loss of fluid integrity of the hull and its contents, only a portion of the vessel receives seawater. Furthermore, the ship must be designed so that in the event of such a calamity, the entire vessel remains afloat and upright. [0035] It is also noted that the "extent of side damage" is taken from the design waterline throughout the length of the ship. Typically, marine vessels will have a hull that tapers significantly inward at the front of the ship to allow for a more streamlined and fuel-efficient design. For the illustrative ship arrangement in Figure 2, the single cold box 110 should taper inwards at the forward end 54 of the ship 50. A tapered configuration is shown at 114 in Figure 1. Using the disclosed containment structure design 100, the cargo hold 110 can extend for a majority of the ship's length, thereby avoiding the requirement of the IGC Code for transverse bulkheads for subdivision. By eliminating the intermediate transverse bulkheads and cofferdams, the cold box insulation area is reduced significantly, with attendant ship cost savings

[0036] Currently, the IGC Code requires (1) a side damage penetration extent of the lesser of 1/5th the beam, or 11.5 meters from the outer side shell, and (2) a bottom damage penetration extent that is the lesser of 1/15th the beam, or 2 meters from the ship's outer bottom. In one known PLNG ship, the hull of the ship is 30.0 meters in depth, while the height of the double bottom, that is, between the exterior hull of the ship and the bottom of the known containment structure, is 3.0 meters. The beam of the hull is 55 meters, while the width of the containment structure is 47 meters. This means that the distance from the outer side shells to the containment structure is only 4.0 meters. Thus, in the above described PLNG ship, the side damage must be taken as extending beyond the four meters from the side hull and into the containment structure. While the extent of bottom damage is acceptable, IGC regulations will require that the containment structure be subdivided by multiple cofferdams.

[0037] To avoid this requirement, a single-container cargo-hold arrangement, in one embodiment, is offered herein. In one arrangement, the cargo hold 110 of the disclosed containment structure 100 is 31.0 meters in width, while the beam of the ship 50 remains 55 meters. This provides a clearance of 12.0 meters on each side of the containment structure 110. Thus, a side damage penetration extent of greater than 11.5 meters or 1/5th of the vessel beam is provided. At the same time, the floor 116 of the containment structure 110 remains configured to provide the needed penetration extent of the lesser of at least 1/15th the beam, or 2 meters from the ship's bottom. By reducing the width of the containment structure 100 relative to the ship beam, the need for multiple cofferdams is avoided and a single containment structure may be utilized and the marine vessel design still satisfy the IGC code. In this instance, the cargo hold is entirely within a structural prism that is inside the side and bottom damage extents imposed by the IGC code for damage stability.

[0038] It should be noted that the containment system 100 is not limited to the individual tank size, nor the ship size described above. Other sizes of ships, carrying smaller or larger amounts of cargo than that depicted in Figures 1 and 2, may be used. Additionally, other shapes and dimensions of containers may also be incorporated into ship configurations that would then represent alternative embodiments. Further, a vessel having the above described fluid containment system may carry not only gas, but hydrocarbon fluids including full-wellstream from oil field production.

Claims

Claims:What is claimed is:

1. A marine vessel having a double hull, the marine vessel having a containment structure for containing fluid therein, the containment structure comprising: a single cargo hold forming the entire fluid-carrying cargo area for the marine vessel, the single cargo hold being undivided by bulkheads and having side boundaries that are beyond a distance from an outer side shell of the double hull required by the IGC code for side damage extent; and an array of tanks within the single cargo hold for containing the fluid.

2. The marine vessel of claim 1 , wherein the array of tanks is configured in such a manner and occupies a volume within the cargo hold such that, should flooding of the cargo hold occur, the marine vessel will not capsize or founder.

3. The marine vessel of claim 1 , wherein at least some individual tanks of the array of tanks have a containment volume of at least 100 cubic meters.

4. The marine vessel of claim 1 , wherein each of the tanks in the array of tanks is adapted for carrying fluid in both a liquid state and a gaseous state.

5. The marine vessel of claim 1 , wherein each of the tanks in the array of tanks is adapted for carrying hydrocarbon fluid in both a liquid state and a gaseous state.

6. The marine vessel of claim 1 , wherein each of the tanks in the array of tanks is adapted for carrying natural gas in any of the following states: compressed (CNG), liquefied (LNG), and pressurized liquefied (PLNG).

7. The marine vessel of claim 1 , wherein: each of the tanks in the array of tanks is adapted for carrying liquefied natural gas at least atmospheric pressure; and each of the tanks in the array of tanks is designed to have a geometry selected from the group consisting of: spherical, ovoid, and cylindrical.

8. The marine vessel of claim 1 , wherein: each of the tanks in the array of tanks is adapted for carrying liquefied natural gas under pressure; each of the tanks in the array of tanks is designed to have a geometry selected from the group consisting of: spherical, ovoid, and cylindrical; and the cargo hold comprises: an insulated floor common to each of the tanks; insulated side walls forming lateral boundaries for the cargo hold; and an insulated top also common to each of the tanks.

9. The marine vessel of claim 1 , wherein: the cargo hold has a bottom that is beyond a distance from an outer bottom shell of the double hull required by the IGC code for bottom damage extent.

10. The marine vessel of claim 1 , wherein the cargo hold has side boundaries that reside beyond a distance from a side hull of the vessel that is at least the lesser of one-fifth of the beam of the marine vessel, or 11.5 meters.

11. The marine vessel containment structure of claim 1 , wherein the cargo hold has a bottom boundary that resides beyond a distance from a bottom hull of the vessel that is at least the lesser of 1/15th the beam of the ship, or 2 meters.

12. The marine vessel of claim 1 , wherein: the cargo hold has side boundaries that reside a distance from an outer side shell of the double hull that is at least the lesser of one-fifth of the beam of the ship, or 11.5 meters; the cargo hold has a bottom boundary that resides beyond a distance from an outer bottom shell of the double hull that is at least the lesser of 1/15th the beam of the ship, or 2 meters; and the cargo hold has a front end that tapers in response to the shape of the hull of the marine vessel.

13. The marine vessel of claim 1 , wherein: the cargo hold has side boundaries that reside a distance from an outer side shell of the double hull that is at least the lesser of one-fifth of the beam of the ship, or 11.5 meters; the cargo hold has a bottom boundary that resides beyond a distance from an outer bottom shell of the double hull that is at least the lesser of 1/15th the beam of the ship, or 2 meters; and the array of tanks is configured in such a manner and occupies a volume within the cargo hold such that, should flooding of the cargo hold occur, the marine vessel will not capsize or founder.

14. The marine vessel of claim 1 , wherein each of the tanks in the array of tanks is an independent tank having a diameter of approximately 10 meters.

15. The marine vessel of claim 1 , wherein the array of tanks is attached to the single cargo hold.

16. The marine vessel of claim 1 , wherein the array of tanks is permanently attached to the single cargo hold.