KR20110026867A - Floating structure with a transfer pipe line - Google Patents

Abstract

PURPOSE: A floating structure with a transfer pipe line is provided to consecutively transfer Liquefied natural Gas between storage tanks even during loading or unloading. CONSTITUTION: A floating structure with a transfer pipe line comprises a loading pipe line(L3), an unloading pipe line(L2), and a transfer pipe line(L10). The loading and unloading pipe lines connect storage tanks and load and unload LNG in the storage tanks. The transfer pipe line transfers LNG stored in one storage tank to the other storage tank regardless of the loading and unloading pipe lines. The transfer pipe line is composed of transfer charging lines(11) and transfer discharging lines(12).

Description

FLOATING STRUCTURE WITH A TRANSFER PIPE LINE

The present invention relates to a floating structure having a storage tank capable of storing liquefied natural gas (Liquefied Natural Gas; LNG), and more particularly, between the storage tanks separately from a ship loading pipe for loading and unloading LNG. The present invention relates to a floating structure having a transfer pipe connecting therein to continuously transfer LNG between storage tanks even during a loading or unloading operation.

Natural gas is transported in a gaseous state through onshore or offshore gas piping, or to a distant consumer while stored in an LNG carrier in the form of liquefied liquefied natural gas (LNG). 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 carriers for loading LNG into the sea and loading and unloading LNG to land requirements include LNG storage tanks (commonly referred to as cargo holds) that can withstand the cryogenic temperatures of liquefied natural gas. LNG storage tanks installed inside LNG carriers can be classified into independent type and membrane type depending on whether the load of cargo directly affects the insulation.

Independent tank type storage tanks are either SPB type or Moss type storage tanks. These types of storage tanks use a large amount of non-ferrous metal as the main material, which greatly increases the manufacturing cost of the storage tanks. Currently, LNG storage tanks are the most frequently used membrane storage tanks. Membrane storage tanks are relatively inexpensive and have been proven in LNG storage tanks for a long time without causing any safety problems. .

Membrane type storage tanks are further divided into GTT NO 96 type and Mark III type, which are described in US Pat. Nos. 5,269,247, 5,501,359, and the like.

The GTT NO 96 type storage tank includes a primary sealing wall and a secondary sealing wall made of Invar steel (36% Ni) having a thickness of 0.5 to 0.7 mm, a plywood box and a perlite. The primary heat insulation wall and the secondary heat insulation wall which consist of) are alternately laminated on the inner surface of a ship body.

In the case of the GTT NO 96 type, the primary sealing wall and the secondary sealing wall have almost the same degree of liquid tightness and strength, so that when the primary sealing wall 10 is leaked, the cargo is secured only by the secondary sealing wall for a considerable period of time. It can support. Also, the sealing wall of GTT NO 96 type is easy to weld than the Mark III type membrane because the membrane is straight type, so the automation rate is high, but the overall welding length is longer than Mark III type. In addition, in the case of GTT NO 96, a double couple is used to support an insulation box (that is, an insulation wall).

Meanwhile, the Mark III type storage tank includes a primary sealing wall made of a 1.2 mm thick stainless steel membrane, a secondary sealing wall made of a triplex, a polyurethane foam, and the like. The primary heat insulating wall and the secondary heat insulating wall formed are alternately provided on the inner surface of the hull.

In the case of Mark III type, the sealing wall has corrugated wrinkles, and shrinkage by the cryogenic LNG is absorbed by the corrugated wrinkles so that a large stress is not generated in the membrane. Mark Ⅲ type heat dissipation system is not easy to reinforce due to its internal structure, and its feature of preventing LNG leakage is weaker than that of GTT NO 96 type secondary sealing wall due to the characteristics of secondary sealing wall.

The membrane-type liquefied natural gas storage tank may be more vulnerable to a sloshing problem because it is difficult to install a reinforcing member inside. Sloshing refers to a phenomenon in which a liquid substance, ie, LNG, flows in a storage tank when a vessel moves in various sea conditions, and the wall surface of the storage tank is severely impacted by sloshing.

Since the sloshing phenomenon inevitably occurs during the operation of the ship or mooring the floating structure, it is necessary to design the storage tank structure to have sufficient strength to withstand the impact force due to the sloshing.

Accordingly, a membrane type storage tank has been proposed in which upper and lower chamfers are inclined at approximately 45 degree angles on the upper and lower sides of the tank to withstand the impact force due to sloshing. In the case of a conventional storage tank having a chamfer, the problem due to the sloshing phenomenon can be solved to some extent, but this alone has a limit in dealing with the impact force due to the gradually increasing storage tank or sloshing during intermediate loading.

In particular, as the demand for floating structures such as LNG Floating, Production, Storage and Offloading (FPSO) or LNG Floating Storage and Regasification Unit (FSRU) has been increasing recently, even in LNG storage tanks installed in such floating structures, It was required to solve the problem.

The LNG FPSO is a floating structure used to directly produce and liquefy natural gas extracted from a gas well and store it in an LNG storage tank and, if necessary, to transfer LNG stored in the LNG storage tank to an LNG carrier. In addition, the LNG FSRU is a floating structure that stores LNG unloaded from LNG carriers in offshore lands in LNG storage tanks, and then vaporizes LNG as needed to supply land demand.

When the LNG is in an intermediate loading state where the LNG is partially loaded at approximately 10 to 90% of the height of the storage tank, the load due to sloshing becomes large. The load due to sloshing acts even more when the LNG is in an intermediate load with approximately 20 to 50% of the storage tank's height, and the intermediate load with the LNG partially loaded to about 25 to 30% of the storage tank's height. It works best when in a loaded state. Therefore, in the case of LNG carriers, in order to avoid such a partially loaded state, the LNG carriers were artificially filled in the storage tank or operated in a completely empty state.

However, floating structures such as LNG FPSOs and LNG FSRUs are used in a floating state while being anchored at a predetermined position on the sea, and are influenced by external variables such as production in gas fields, demands from customers, and supply of LNG to LNG carriers. Since the loading amount of the LNG storage tank is changed, there is a problem that it is not possible to arbitrarily adjust the amount of LNG to be stored, so that the intermediate loading state in which the impact force due to sloshing acts the most cannot be avoided. Therefore, there is a demand for reinforcement or operation methods in preparation for intermediate loading.

On the other hand, as shown in Figure 1, in the case of the conventional LNG carrier 1, the main line (L1) for connecting the plurality of storage tanks 3 installed in the hull with each other is provided, this main line (L1) Unloading line (L2) and loading line (L3) connected to the (not shown in Figure 1, but the unloading line (L2) and shipping line (L3) is provided separately, but the loading and unloading operation is performed using one line) May be loaded into the storage tanks 3 or all the LNG stored in the storage tanks 3 are unloaded. When unloading, the unloading pump 3a installed in the storage tank 3 is used. The regasification apparatus 5 may be installed in the unloading line L2.

In the case of a conventional LNG carrier, all the LNG contained in the LNG carrier is unloaded through the main line L1, the unloading line L2 and the shipping line L3, and then docked or docked. Inspection or maintenance work can be carried out within.

However, in the case of floating structures such as LNG FPSO or LNG FSRU, which must be used while mooring at a certain location on the sea, it is virtually impossible to move the location or unload all of the LNG for maintenance of the storage tank. Accordingly, only the storage tanks for which maintenance is required among the plurality of storage tanks installed in the hull of the floating structure should be emptied and the maintenance work on the storage tanks should be performed.

However, in the case of floating structures such as LNG FPSO or LNG FSRU, since the loading and unloading operation of LNG is continuously performed, the main line L1 installed to connect the respective storage tanks 3 to each other is provided. There is a problem in that LNG cannot be transferred between storage tanks.

As a result, if LNG is to be transferred from one storage tank to another during the loading or loading process, the loading or loading operation is stopped again after stopping the loading or loading operation and completing the cargo transfer through the common main line. I had to.

The present invention for solving these problems, the storage tanks even during the loading or unloading operation by installing a transfer pipe for connecting between the storage tanks separately from the cargo loading pipe for loading and unloading LNG It is to provide a floating structure that can continuously transfer LNG between.

According to an aspect of the present invention for achieving the above object, a floating structure having a plurality of storage tanks for storing liquefied gas and used in a floating state at sea, by connecting a plurality of the storage tanks the storage tank A lading pipeline for loading or unloading liquefied gas in the container; A conveying pipeline for connecting the plurality of storage tanks separately from the ship loading pipeline to transfer the liquefied gas contained in one of the plurality of storage tanks to another storage tank; There is provided a floating structure comprising a.

The transfer pipeline preferably includes a transfer filling line for receiving liquefied gas from another storage tank, and a transfer discharge line for supplying liquefied gas to the another storage tank.

A transfer pump may be installed at the end of the transfer discharge line. Alternatively, an end of the transfer discharge line may be connected to a unloading pump for unloading the liquefied gas contained in the storage tank through the main pipeline.

The transfer pipeline may extend outside of the plurality of storage tanks. Alternatively, the transfer pipeline may extend in a plurality of the storage tanks.

The storage tank is preferably a membrane tank or a stand-alone tank.

The storage tank is preferably arranged in one row or two or more rows in the hull of the floating structure.

When the storage tank is arranged in two or more rows, the hull of the floating structure is installed along the longitudinal cofferdam and the width direction of the floating structure installed along the longitudinal direction of the floating structure. It is preferably partitioned by the widthwise cofferdam.

The floating structure is preferably any one selected from the LNG carrier, LNG RV, LNG FPSO and LNG FSRU.

According to the present invention as described above, there is provided a floating structure provided with a transfer pipe for connecting between the storage tanks separately from the ship loading pipe for loading and unloading LNG.

According to the floating structure of the present invention, LNG can be continuously transferred between storage tanks through a transfer pipe even during a loading or unloading operation, and the unloading or loading operation can be continuously performed without being interrupted. Can be.

In addition, according to the floating structure of the present invention, LNG can be transferred between the storage tanks so as to minimize the time that the storage tank is exposed to the intermediate loading state during the loading or unloading operation.

Hereinafter, a floating structure according to a preferred embodiment of the present invention will be described in detail with reference to the drawings.

In the present specification, the floating structure is a concept including both a structure and a vessel used while floating in an ocean where a flow occurs while having a storage tank for storing a liquid cargo loaded at a cryogenic state such as LNG, for example This includes both LNG carriers and LNG Regasification Vessels (RVs), as well as offshore structures such as LNG Floating, Production, Storage and Offloading (FPSO) or LNG Floating Storage and Regasification Units (FSRUs).

FIG. 2 shows a schematic side view of a floating structure provided with a pipeline dedicated to transfer between storage tanks, according to a first embodiment of the invention, and FIG. 3 shows a storage according to a second embodiment of the invention. A schematic side view of a floating structure with a dedicated pipeline for transfer between tanks is shown.

As shown in the figure, the floating structure 10 according to the first and second embodiments of the present invention, even during the loading or unloading of the liquid cargo, such as LNG, the cargo transfer between the storage tank (3) A pipeline dedicated to transfer (hereinafter referred to as a 'transfer pipeline') L10 or L20 is provided so as to be possible. The conveying pipeline L10 or L20 of the present invention is a pipeline which is independent of the main pipeline L1 jointly connected to all the storage tanks 3 installed in the floating structure 10. Apart from the line L1 it is jointly connected to all storage tanks 3 installed in the floating structure 10.

According to the present invention, as the storage tank 3 installed in the floating structure 10, a membrane type tank may be employed or a standalone tank may be employed. In addition, the storage tanks 3 may be arranged in one row or two or more rows along the longitudinal direction in the hull of the floating structure 10.

When the storage tank is arranged in two or more rows, the inner space of the hull is divided longitudinally and horizontally by the widthwise bulkhead structure installed along the width direction of the hull and the longitudinal bulkhead structure installed along the longitudinal direction of the hull. Storage tanks are arranged in each partitioned space. As the partition structure, a cofferdam or the like may be utilized. The cofferdam is, for example, a grid-like structure in which a void space is provided inside, similar to a transverse cofferdam installed in front of and behind a membrane-type storage tank in a conventional LNG carrier.

By arranging the storage tanks in two rows, the amount of liquid cargo stored in one storage space is reduced, and as the width of the storage tank is reduced, the natural period of motion of the liquid cargo moves away from the natural period of motion of the floating structure. The magnitude of the motion of the cargo can be reduced. Accordingly, the impact force due to sloshing applied to the storage tanks arranged in two rows can be drastically reduced.

As shown in FIG. 2, the floating structure according to the first embodiment of the present invention has a main line L1 connecting the respective storage tanks 3 to each other as in the related art, and this main line L1. LNG may be loaded into the storage tanks 3 or unloaded LNG stored in the storage tanks 3 through a loading line L2 and a shipping line L3 connected to the storage tanks 3.

At the time of unloading, the unloading pump 3a installed in the storage tank 3 is used, and the regasification apparatus 5 may be installed at the unloading line L2. Although the loading line L2 and the loading line L3 are illustrated as being separately provided, loading and unloading operations may be performed using one line. An example of a floating structure that carries out loading and unloading operations through one pipeline includes, for example, an LNG carrier.

The main pipeline L1 is divided into two lines inside the storage tank 3. These two lines are a filling line for supplying LNG to the general membrane tank at shipment and a discharging line for discharging LNG from the general membrane tank at unloading. Only one line may be installed inside the storage tank so that the filling line can serve as the discharge line as needed in the design. A discharge pump 3a may be installed in the discharge line for discharging LNG when unloading.

According to the first embodiment, each of the storage tanks 3 is connected to each other separately from the main line L1, so that LNG contained in any one of the plurality of storage tanks is stored in another. A pipeline dedicated to transfer (i.e., a transfer pipeline) L10 that can be transferred to the storage tank 3 is provided.

The conveying pipeline L10 may extend along the longitudinal direction of the hull from the outside of the storage tanks 3 and may branch and extend into the respective storage tanks 3. Like the main pipeline L1 described above, the transfer pipeline L10 may be divided into two lines inside the storage tank 3. These two lines are a transfer filling line 11 for receiving LNG from another storage tank and a transfer discharge line 12 for supplying LNG to another storage tank. The transfer pump 15 may be installed at the end of the transfer discharge line 12.

As described above, according to the first embodiment of the present invention, the LNG contained in one storage tank 3 is transferred to the transfer pump 15, the transfer discharge line 12, the transfer pipeline L10, and the transfer filling line 11. Through this, it is possible to transfer to another storage tank (3).

Although not shown, the main pipeline L1 and the transfer pipeline L10 are provided with devices such as valves or spools for opening and closing respective pipelines so as to control the transfer direction of LNG.

The regasification apparatus 5 is connected to the unloading pipeline L2, which may be installed on a floating structure such as, for example, an LNG RV or an LNG FSRU, or, for example, with an LNG carrier. Likewise, it may be used to be installed outside the floating structure. The natural gas regasified by the regasification apparatus 5 can continue to be supplied to each customer.

3, a floating structure according to a second preferred embodiment of the present invention will be described.

As shown in FIG. 3, the floating structure according to the second embodiment of the present invention has a main line L1 connecting the respective storage tanks 3 to each other like the first embodiment described above. The LNG may be loaded into the storage tanks 3 or the LNG stored in the storage tanks 3 through the unloading line L2 and the shipping line L3 connected to the main line L1. At the time of unloading, the unloading pump 3a installed in the storage tank 3 is used, and the regasification apparatus 5 may be installed at the unloading line L2.

In FIG. 3 for explaining the floating structure according to the second embodiment, the same components as those in the above-described first embodiment are assigned the same member numbers, and detailed description thereof will be omitted.

According to the second embodiment, each of the storage tanks 3 is connected to each other separately from the main line L1, so that the LNG contained in any one of the plurality of storage tanks is further replaced. A pipeline dedicated to the transfer (i.e., the transfer pipeline) L20, which can be transferred to the storage tank 3, is installed.

Unlike the conveying pipeline L10 of the first embodiment described above extending outside the storage tanks 3, the conveying pipeline L20 of the second embodiment has a length of the hull inside the storage tanks 3. It can extend along the direction. The conveying pipeline L20 of the second embodiment may have two lines branching inside the storage tank 3. These two lines are a transfer filling line 28 for receiving LNG from another storage tank and a transfer discharge line 27 for supplying LNG to another storage tank. The distal end of the transfer discharge line 27 may be connected to the unloading pump 3a installed inside the storage tank 3.

As described above, according to the second embodiment of the present invention, the LNG contained in one storage tank 3 is unloaded from the unloading pump 3a, the transfer discharge line 27, the transfer pipeline L20, and the transfer filling line 28. Through this, it is possible to transfer to another storage tank (3).

Although not shown, the main pipeline L1 and the transfer pipeline L20 are provided with a device such as a valve or a spool for opening and closing the respective pipelines so as to control the transfer direction of the LNG.

The regasification apparatus 5 is connected to the unloading pipeline L2, which may be installed on a floating structure such as, for example, an LNG RV or an LNG FSRU, or, for example, with an LNG carrier. Likewise, it may be used to be installed outside the floating structure. The natural gas regasified by the regasification apparatus 5 can continue to be supplied to each customer.

The floating structure according to the first embodiment of the present invention is provided with a conveying pipeline L10 extending from the outside of the storage tank 3, and the floating structure according to the second embodiment of the present invention is provided with the storage tank 3. ), A conveying pipeline L20 is installed, which extends in the interior thereof. As such, according to the present invention, the conveying pipeline may extend outside or inside the storage tank 3.

Further, in the floating structure according to the first embodiment of the present invention, a separate transfer pump 15 is provided at the end of the transfer discharge line 12 of the transfer pipe line L10, and according to the second embodiment of the present invention. According to the floating structure, the discharging discharge line 27 end of the conveying pipeline L20 is installed to be connected to the existing discharging pump 3a, but the discharging discharging line 12 of the first embodiment is the conventional discharging pump It may be installed to be connected to (3a), or may be modified so that a separate transfer pump 15 is installed at the end of the transfer discharge line 27 of the second embodiment.

In addition, when the storage tanks 3 are arranged in two or more rows in the floating structure, a plurality of transport pipelines L10 or L20 may be arranged in the longitudinal direction of the hull along the storage tanks, Branch lines branching from the pipeline may be configured to be connected to the respective storage tanks.

As described above, the floating structure according to the present invention has been described with reference to the illustrated drawings, but the present invention is not limited to the embodiments and drawings described above, and in the technical field to which the present invention belongs within the claims. Of course, various modifications and variations can be made by those skilled in the art.

1 is a schematic side view of a floating structure according to the prior art,

2 is a schematic side view of a floating structure provided with a pipeline dedicated to transfer between storage tanks, according to a first embodiment of the invention, and

3 is a schematic side view of a floating structure provided with a pipeline dedicated to transfer between storage tanks, according to a second embodiment of the invention.

Description of the Related Art

3: general membrane tank 3a: unloading pump

5: regasification device 10: floating structure

11, 28: transfer filling line 12, 27: transfer discharge line

15: transfer pump L1: main pipeline

L2: unloading pipeline L3: shipping pipeline

L10, L20: conveying pipeline

Claims (10)

A floating structure having a plurality of storage tanks for storing liquefied gas and used in a floating state at sea, A ship of lading for connecting a plurality of said storage tanks to load or unload liquefied gas in said storage tanks; A conveying pipeline for connecting the plurality of storage tanks separately from the ship loading pipeline to transfer the liquefied gas contained in one of the plurality of storage tanks to another storage tank; Floating structure comprising a. The method according to claim 1, The transfer pipeline, the floating structure comprising a transfer filling line for receiving the liquefied gas from the another storage tank, and a transfer discharge line for supplying the liquefied gas to the another storage tank. The method according to claim 2, Floating structure, characterized in that the transfer pump is installed at the end of the transfer discharge line. The method according to claim 2, And a distal end of the transfer discharge line is connected to an unloading pump for unloading liquefied gas contained in the storage tank through the main pipeline. The method according to claim 1, The conveying pipeline, the floating structure characterized in that extending from the outside of the plurality of storage tanks. The method according to claim 1, The conveying pipeline is a floating structure, characterized in that extending in the plurality of the storage tank. The method according to claim 1, The storage tank is a floating structure, characterized in that the membrane tank or the independent tank. The method according to claim 1, The storage tank is a floating structure, characterized in that arranged in a plurality of rows or more than one row or two rows inside the hull of the floating structure. The method according to claim 8, When the storage tank is arranged in two or more rows, the hull of the floating structure is installed along the longitudinal cofferdam and the width direction of the floating structure installed along the longitudinal direction of the floating structure. A floating structure, which is partitioned by a widthwise cofferdam. The method according to claim 1, The floating structure is a floating structure, characterized in that any one selected from the LNG carrier, LNG RV, LNG FPSO and LNG FSRU.

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