KR20100131698A - Marine floating structure for liquefied gas storage having cofferdam - Google Patents

Abstract

PURPOSE: A marine floating structure for liquefied-gas storage having a cofferdam is provided to enhance the space utilization of a ship since the cofferdam plays a role as a water ballast tank. CONSTITUTION: A marine floating structure for liquefied-gas storage comprises a cofferdam(20), which plays a role as a water ballast tank(30), an inner barrier(21) and a heating unit. The inner barrier divides the cofferdam into an internal part(22) and an external part(24). A water flow structure is formed between the internal part and the external part. The heating unit is installed on the external part. The water flow structure comprises a water flow hole, which is formed on the lower part of the barrier. The cofferdam is separated from an external ballast tank by an external barrier and an opening, which has a larger size than the water flow hole, is formed on the lower part of the external barrier to enable the water to flow between the external ballast tank and the external part.

Description

MARINE FLOATING STRUCTURE FOR LIQUEFIED GAS STORAGE HAVING COFFERDAM}

The present invention relates to a liquefied gas storage offshore floating structure, and to an improved structure of a cofferdam and an improved arrangement of heating means used for the cofferdam. As used herein, the term 'sea floating structure' is meant to include both an offshore floating plant and a ship with a propulsion function that is floating at sea.

Natural gas is transported in gaseous form through onshore or offshore gas piping, or liquefied in the form of liquefied natural gas (LNG) or liquefied petroleum gas (LPG), followed by LNG carriers or LPG. It is transported to a remote consumer while stored in a transport. Liquefied natural gas is obtained by cooling natural gas to cryogenic temperature (approximately -163 ℃), and its volume is reduced to about 1/600 than natural gas in gas state, so it is very suitable for long distance transportation through sea.

LNG transporter for loading and unloading LNG to land requirements by operating the sea with LNG, or LNG RV (Regasification) that reloads LNG after unloading the sea with LNG for recharging the stored LNG The vessel includes a storage tank (commonly referred to as a cargo hold) that can withstand the cryogenic temperatures of liquefied natural gas.

Recently, there is a growing demand for offshore floating structures such as LNG Floating, Production, Storage and Offloading (FPSO) or LNG Floating Storage and Regasification Units (FSRUs), which are being installed on LNG carriers or LNG RVs. Storage tanks are included.

LNG FPSO is an offshore floating structure used to liquefy the produced natural gas directly from the sea and store it in a storage tank and, if necessary, to transport LNG stored in the storage tank to an LNG carrier. The LNG FSRU is an offshore floating structure that stores LNG unloaded from LNG carriers in storage tanks at sea far from the land, and then vaporizes LNG as needed to supply it to land demand.

As described above, a storage tank for storing LNG in a cryogenic state is installed in an offshore structure such as an LNG carrier, an LNG RV, an LNG FPSO, or an LNG FSRU that transports or stores a liquid cargo such as LNG.

These storage tanks can be classified into Independent Type and Membrane Type, depending on whether the load directly affects the insulation. Membrane type storage tanks are generally divided into GT NO 96 type and TGZ Mark III type, and standalone storage tanks are divided into MOSS type and IHI-SPB type.

The GT and TGZ tank structures described above are described in U.S. Patent Nos. 6,035,795, 6,378,722, 5,586,513 and U.S. Patent Publication Nos. 2003-0000949 and the like, and Korean Patent Publication Nos. 10-2000-0011347 and 10-2000. -0011346 and the like. In addition, the structure of the stand-alone storage tank is described in Korean Patent Nos. 10-15063 and 10-305513.

In general, a membrane tank is used as a storage tank for storing LNG. A liquefied gas storage offshore floating structure with this is known, in which liquefied gas storage tanks arranged inside the hull are arranged along the length of the hull, and a cofferdam is located between neighboring liquefied gas storage tanks. The cooper dam separates and insulates the liquefied gas storage tanks. In general, the cofferdam is a grid-like structure in which a void space is provided therein, and is configured to partition the internal space of the floating structure to install a membrane storage tank in each compartment. Although the bulkhead of the cofferdam is not in direct contact with the LNG, the LNG contained in the liquefied gas storage tank is at a cryogenic temperature of about -163 ° C. Thus, the cold air of LNG can make the steel plate constituting the bulkhead extremely low and vulnerable. . In addition, since the cofferdam is a closed space, heat is not supplied from the outside so that the internal temperature may drop to about -60 ° C. Therefore, there is a need to heat the cofferdam to maintain a certain temperature or more.

On the other hand, conventionally, techniques for heating the cofferdam by spraying seawater to the cofferdam or by installing a heating coil in the entire cofferdam have been proposed. However, such prior art was not economical due to the overall installation of the heating coil or the complicated seawater injection structure. In addition, the cofferdam has been pointed out as a major factor that hinders ship space efficiency.

Accordingly, the technical problem of the present invention is that the cofferdam can serve as a part of the water ballast tank, thereby increasing the space utilization of the ship, and reducing the size of the means such as the heating coil or the installation area of the heating means. It is also to provide a liquefied gas storage offshore floating structure useful.

The liquefied gas storage marine floating structure according to an aspect of the present invention includes a cofferdam that serves as a water ballast tank, and divides the cofferdam into an inner part and an outer part, and separates seawater between the inner part and the outer part. It includes an inner partition formed with a water passage structure for passing through, and the heating means provided in the outer part.

Preferably, the water passage structure includes a water hole formed in the lower portion of the partition wall.

More preferably, the cofferdam is separated and partitioned from the outer ballast tank by an outer partition wall, and an opening having a size larger than that of the through hole is provided at the lower side of the outer partition wall for water flow between the outer ballast tank and the outer part. Is formed.

Preferably, the heating means is a heating coil disposed over both side portions of the outer part and the upper portion of the outer part, the lowest height of both sides of the heating coil is higher than the opening and lower than the draft line.

Preferably, the bottom of the outer part and the inner part is the same, and the outer part surrounds both sides and the top of the inner part.

Preferably, at least one through hole is formed in the upper portion of the partition wall to allow ventilation between the inner part and the outer part.

Preferably, the cofferdam is located between adjacent liquefied gas storage tanks in the longitudinal direction.

Preferably, the cofferdam may be positioned between adjacent liquefied gas storage tanks in a width direction by a two-row or multi-row arrangement of liquefied gas storage tanks.

Preferably, the heating means uses one selected from seawater, freshwater and antifreeze as the heat exchange medium.

Preferably, the inner part of the cofferdam may be provided with one or more wash bulks that allow partial passage in the longitudinal direction in order to reduce the effect of sloshing generated in a partially filled state.

According to the present invention, the cofferdam may serve as a water ballast tank, thereby increasing space utilization of the ship. By the cofferdam being divided into the inner part and the outer part and the heating means being limitedly installed in the outer part, it is possible to reduce the installation area of the heating means, in particular the heating coil, and to reduce the maintenance cost of the heating means. In addition, since the cofferdam is heated by the sea water and the heating means, the liquefied gas stored in the liquefied gas storage tank opposite the cofferdam partition wall, in particular, the LNG temperature can prevent the temperature of the hull structure from dropping. Furthermore, the present invention has the effect of preventing the ballast water of the polar operating vessel from freezing.

Hereinafter, a liquefied gas storage marine floating structure according to an embodiment of the present invention including an improved structure of the cofferdam and a structure for heating the cofferdam.

1 is a cross-sectional view showing a liquefied gas storage marine floating structure according to an embodiment of the present invention. The liquefied gas storage marine floating structure shown in FIG. 1 may be a vessel having liquefied gas storage tanks or a marine floating liquefied gas production / storage / treatment facility. Such facilities include, for example, FPSOs having the ability to produce, store, and unload LNG, or FSRUs having the ability to regasify LNG.

As shown in FIG. 1, the liquefied gas storage marine floating structure includes a plurality of liquefied gas storage tanks 10 in the hull 1, and the liquefied gas storage tanks 10 are a membrane type suitable for storing LNG. It is preferable. The liquefied gas storage tanks 10 are arranged in a row along the longitudinal direction. The cofferdam 20 is located between the neighboring liquefied gas storage tanks 10. Each of the liquefied gas storage tanks 10 arranged in one row along the longitudinal direction by the plurality of cofferdams 20 is separated from the neighboring liquefied gas storage tank 10.

As already mentioned in the description of the background art, LNG is in a cryogenic state of approximately -163 ° C. Therefore, due to the cold air of LNG, the walls of the cofferdam 20 must be made of low temperature steel that is resistant to low temperatures. In addition, since the cofferdam 20 is a closed space, since heat is not supplied from the outside, the internal temperature may drop to about -60 ° C. Therefore, it is necessary to keep the cofferdam 20 at a predetermined temperature or more.

FIG. 2 is a cross-sectional view taken along the line I-I of FIG. 1, showing a copper dam 20 serving as a water ballast tank and an efficient structure capable of heating the copper dam 20 to an appropriate temperature.

Referring to FIG. 2, the cofferdam 20 also serves as a water ballast tank, and an outer water ballast tank 30 defined by the wall 31 of the hull is disposed outside thereof. In the present invention, since the cofferdam also serves as a water ballast tank, the water ballast tank on the existing hull side is defined as an 'outer water ballast tank' in order to distinguish it from the cofferdam.

In this embodiment, the cofferdam 20 is divided and partitioned into an inner inner part 22 and an outer part 24 surrounding the inner part 22 by an inner partition wall 21. The inner part 22 and the outer part 24 share the same bottom wall 201 of the cofferdam 20. The inner partition wall 21 is formed entirely on the remaining portion except for the bottom wall 201, whereby the outer part 24 has a structure that entirely surrounds both sides and the upper portion of the inner part 22. . In addition, it is preferable that the upper corners on both sides of the inner partition wall 21 be formed in a chamfer or round shape.

The cofferdam 20 is separated from the external water ballast tank 30 by an external partition 25. In addition, the water ballast tank 30 surrounds the lower and both sides of the cofferdam 20. The cofferdam 20 has a structure that can freely pass through the external water ballast tank 30 so as to serve as a water ballast tank. In addition, the inner part 22 and the outer part 24 of the cofferdam 20 has a structure capable of free passage and free passage.

The freely passable structure between the cofferdam 20 and the water ballast tank 30, and the freely passable and freely ventable structure between the inner part 22 and the outer part 24 of the cofferdam 20 As described below.

In order to freely pass water between the inner part 22 and the outer part 24 of the cofferdam 20, a through hole 212 serving as a passage for seawater is formed on both lower sides of the inner partition wall 21 therebetween. . Accordingly, the inner part 22 and the outer part 24 are at the time of ballasting, that is, when seawater enters the cofferdam 20 from the outer water ballast tank 30, the height of the seawater is increased by the inner part ( Both the 22 and the outer part 24 are maintained at an arbitrary level from the bottom wall 201. Alternatively, a valve may be used instead of the through hole 212.

Accordingly, the lower region of the cofferdam 20 may be heated using seawater in the inner part 22 and the outer part 24. By heating by the sea water, it is possible to prevent the lower region temperature of the cofferdam 20 from excessively falling by the LNG of the liquefied gas storage tank 10 (see FIG. 1) opposite to the cofferdam. At this time, the position of the water supply hole 212 is preferably located as close as possible to the bottom wall 201 of the cofferdam 20, through which, it is possible to smoothly pass through.

A plurality of through holes 214 are formed in the upper portion of the inner partition wall 21 to smoothly vent and pass water between the inner part 22 and the outer part 24. The positions of the through holes 214 may be determined at upper centers of the inner partition walls 21 and upper corners of the upper partition walls 21, respectively. The through holes 214 may help the water flow more smoothly by freely entering and exiting the air when water is required between the inner part 22 and the outer part 24.

In addition, for free passage between the external water ballast tank 30 and the cofferdam 20, water passage openings 252 are formed in the lower portion of the external partition wall 25. The water passage openings 252 have a larger size than the water passage 212 of the inner partition wall 21 for smoother free water passage. In addition, the water passage opening 252 is preferably formed on the inclined surface at both corners of the lower bottom of the outer partition wall (25). During ballasting, the seawater of the external water ballast tank 30 is continuously passed through the opening 252 and the aforementioned water hole 212 to the outer part 24 and the inner part 22 of the cofferdam 20. Enter).

Heating means 40 for heating the upper region of the cofferdam 20 far away from the seawater is provided with a heating coil 40 through which a heat exchange medium flows in the outer part 24 of the cofferdam 20. As the heat exchange medium, various kinds of heat exchange fluids that can be obtained in an offshore floating structure such as sea water, fresh water, antifreeze, or cooling water such as an engine may be used. Although a heating coil 40 as described above may be most preferably used, it is also possible to heat the outer part 24 of the cofferdam 20 by direct injection of other heating means, such as water (especially seawater). Can be considered. For example, heating means for heating the outer part 24 with thermal energy obtainable in other ways, such as electric heating, may also be considered.

In this embodiment, the heating coil 40 is limited to the outer part 24 for economical efficiency and to minimize the installation area. This is possible by having the area in which the cofferdam 20 is heated by sea water. Of course, it is determined differently from the region where the heating coil 40 is installed and the region heated by the sea water. In addition, the heights of the two lowest points 41 and 41 of the heating coil 40 are set higher than the water passage opening 252 formed in the outer partition 25 and lower than the draft line L. More preferably, the heights of the lowest points 41 and 41 on both sides of the heating coil 40 are determined to be a position away from the water line L by a certain height Hd, and in this embodiment, the height is about 2 m. The two compartments, which are separated into the outer part 24 and the inner part 22, have no problem with the flow of free water and aeration when seawater ballasting, but by restricting the flow of fluid between the two compartments, Can be heated.

The inner part 22 of the cofferdam 20 may be provided with one or more wash bulks that allow partial passage in the longitudinal direction in order to reduce the effect of sloshing generated in a partially filled state.

Hereinafter, a liquefied gas storage marine floating structure according to another embodiment of the present invention.

3 is a plan sectional view showing a liquefied gas storage marine floating structure according to another embodiment of the present invention, Figure 4 is a cross-sectional view taken along II-II of FIG.

Referring to FIG. 3, a plurality of liquefied gas storage tanks 10 are provided in the hull 1, and the liquefied gas storage tanks 10 are arranged in two rows along the length direction. By such a two-row arrangement, in the present embodiment, unlike the previous embodiment in which the lateral cofferdam 20 existed only between neighboring liquefied gas storage tanks 10, 10 in the longitudinal direction, in the present embodiment, in the width direction The longitudinal longitudinal cofferdam 50 exists between neighboring liquefied gas storage tanks 10 and 10. The structure and shape of the lateral cofferdam 20 is substantially the same as in the previous embodiment, and therefore only the structure of the longitudinal cofferdam 50 is shown in FIG. 4.

As shown in FIG. 4, the longitudinal cofferdam 50 of the present embodiment can serve as a water ballast tank, and is divided into an inner part 52 and an outer part 54 by an inner partition 51. do. Between the inner part 52 and the outer part 54, the water can be freely flown by a through hole 512 formed in the inner partition 51. In addition, the upper portion of the inner partition 51 is formed through the free passage, further, through the free passage 514 for free passage. The outer part 54 is freely connected to the external water ballast tank 30, for this connection of the outer bulkhead 55 of the longitudinal cofferdam 50 defining the outer part 54. An opening or passage (not shown) may be formed in the vicinity of the lower portion, which is in communication with the outer part 54 and smaller in size than the water hole. A heating coil 40 is disposed on both side portions of the outer part 54 and an upper portion of the outer part 54, and a lowest point of the heating coil 40 is a water passage opening formed under the outer partition wall 55. (Not shown) and between the waterline (or level).

The inner part 52 of the cofferdam 50 may be provided with one or more wash bulks that allow partial passage in the longitudinal direction in order to reduce the effect of sloshing generated in a partially filled state. .

As described above, the present invention has been described with reference to the illustrated drawings, but the present invention is not limited to the above-described embodiments and drawings, and has a general knowledge in the technical field to which the present invention belongs within the claims. Of course, various modifications and variations can be made by them.

1 is a cross-sectional view showing a liquefied gas storage marine floating structure according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line I-I of FIG. 1, showing an improved structure of the cofferdam. FIG.

3 is a cross-sectional view showing liquefied gas storage marine floating structures according to another embodiment of the present invention.

Sectional view taken along II-II of FIG. 3 of FIG. 4.

Claims (10)

A liquefied gas storage offshore floating structure having a cofferdam that also serves as a water ballast tank, An inner partition wall dividing the cofferdam into an inner part and an outer part and having a water passage structure configured to allow seawater to flow between the inner part and the outer part; Liquefied gas storage marine floating structure comprising a heating means installed in the outer part. The liquefied gas storage marine floating structure of claim 1, wherein the water flow structure includes a water hole formed in a lower portion of the partition wall. The method according to claim 2, wherein the cofferdam is separated from the outer ballast tank by an outer partition wall, the opening having a size larger than the through hole for the water flow between the outer ballast tank and the outer part, the lower side of the outer partition wall Liquefied gas storage marine floating structure, characterized in that formed in. 4. The liquefied gas according to claim 3, wherein the heating means is a heating coil disposed over both side portions of the outer part and the upper part of the outer part, and the lowest point height of both sides of the heating coil is higher than the opening and lower than the draft line. Storage maritime floating structures. The liquefied gas storage marine floating structure of claim 1, wherein a bottom of the outer part and the inner part is the same, and the outer part surrounds both sides and an upper part of the inner part. The liquefied gas storage marine floating structure of claim 1, wherein at least one through hole is formed at an upper portion of the partition wall to allow aeration between the inner part and the outer part. The liquefied gas storage marine floating structure according to claim 1, wherein the cofferdam is positioned between neighboring liquefied gas storage tanks in a longitudinal direction. The liquefied gas storage marine floating structure according to claim 1, wherein the cofferdam is positioned between adjacent liquefied gas storage tanks in a width direction by two-row or multi-row arrangement of liquefied gas storage tanks. The liquefied gas storage marine floating structure of claim 1, wherein at least one water barrier bulkhead is installed in an inner part of the cofferdam in a longitudinal direction. The liquefied gas storage marine floating structure according to claim 1, wherein the heating means uses one selected from seawater, freshwater, and antifreeze as a heat exchange medium.

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