DESCRIPTION

RE-LIQUEFACTION APPARATUS INSTALLED IN LIQUEFIED GAS CARRIER

Technical Field

The present invention is related to a re-liquefaction apparatus installed in a liquefied gas carrier which carries combustible liquefied gas such as liquefied petroleum gas (LPG) and liquefied natural gas (LNG), the liquefied gas carrier, and a method of building the liquefied gas carrier.

Background Art
Referring to FIG. 1, a conventional LPG carrier 101 will be described. The LPG carrier 101 is provided with a plurality of LPG tanks 102 which store LPG gas, and a plurality of re- liquefaction apparatuses 106 which re-liquefy boil-off gas of the LPG gas. The LPG tanks 102 are provided under a deck. The re-liquefaction apparatus 106 is provided with a compressor 161 which compresses the boil-off gas, a condenser 162 connected with the compressor 161, an expansion valve 163 connected with the condenser 162 and a motor 181 for driving the compressor 161.

The plurality of compressors 161 for the plurality of re-liquefaction apparatuses 106 are arranged in a gas compressor room 103 provided onto the deck. The plurality of motors 181 for the plurality of re-liquefaction apparatuses 106 are arranged in a motor room 104 provided onto the deck. The gas compressor room 103 and the motor room 104 are partitioned by a partition 105. The motor 181 and the compressor 161 are connected by an intermediate shaft 183 which passes through the partition 105. A partition seal 184 is provided to seal a gap between the partition 105 and the intermediate shaft 183.

The motor 181 which may be an ignition source and the compressor 161 which treats combustible LPG gas receive the following restriction from the viewpoint on the safety.
It is necessary to provide the partition 105 between the motor 181 and the compressor 161 and to arrange the motor 181 and the compressor 161 in separate rooms, i.e. the motor room 104 and the gas compressor room 103.

To connect the motor 181 and the compressor 161 through the partition 105, a special partition passing-through device like the intermediate shaft 183 and the partition seal 184 is required. Because the motor room 104 must be a safe room into which the LPG gas does not invade, an arrangement position of a ventilation fan in the motor room 104 is limited and a place where the motor room 104 is arranged is limited.

Because it is required that the partition 105 is provided between the motor 181 and the compressor 161, the re-liquefaction apparatus 106 can not be freely arranged in the inboard. Because it is necessary to install the motor 181, the compressor 161 and the intermediate shaft 183 in a narrow space of the inboard, more work hours are necessary, comparing a case where the re-liquefaction apparatus 106 assembled in the factory is installed in the inboard.

It is necessary to prepare a flexible joint such as an elastic rubber coupling for the intermediate shaft 183 so as to facilitate an axis adjustment between the motor 181 and the compressor 161.
JP H09-221098A discloses a conventional LPG carrier. JP 2009-204080A discloses a conventional LNG carrier.

An example that the explosion-proof type motor is applied to any ship does not exist as far as the inventor of the present application knows.

Citation List
[Patent Literature 1] JP HG9-221098A [Patent Literature 2] JP 2009-204080A Summary of the Invention An object of the present invention is to provide a re-liquefaction apparatus which is installed in a liquefied gas carrier and which has a high degree of freedom of the inboard arrangement, the liquefied gas carrier, and a method of building the re-liquefaction apparatus.
The re-liquefaction apparatus, which is installed in the liquefied gas carrier, in the first viewpoint of the present invention is provided with a compressor which compresses boil-off gas of combustible liquefied gas, and an explosion-proof type motor which drives the compressor.

By using the explosion-proof type motor, even if any explosion happens inside the explosion-proof type motor, a container of the explosion-proof type motor is not destroyed. Also, it is prevented that any spark rushes out of the container to ignite the combustible gas. Therefore, it is not necessary to arrange the explosion-proof type motor and the compressor in the separate rooms partitioned with the partition. Therefore, the degree of freedom of the I inboard arrangement of the re-liquefaction apparatus increases.

It is desirable that the above re-liquefaction apparatus is further provided with a base sheet on which the compressor and the explosion-proof type ) motor are installed. It is desirable that the above re-liquefaction apparatus is further provided with a gas leakage detector and a shut-off valve which shuts off the supply of the boil-off gas to the compressor when the gas leakage detector detects a leakage of the liquefied gas.

It is desirable that the above re-liquefaction apparatus is further provided with a temperature sensor which detects a motor temperature of the explosion-proof type motor, and a warning unit which generates a warning when the motor temperature is higher than a first reference temperature.

It is desirable that the above re-liquefaction apparatus is further provided with a motor control unit which stops the explosion-proof type motor when the motor temperature is higher than a second reference temperature.

It is desirable that the above re-liquefaction apparatus is further provided with a temperature sensor which detects a motor temperature of the explosion-proof type motor, and a motor control unit which stops the explosion-proof type motor when the motor temperature is higher than a reference temperature.

The above re-liquefaction apparatus may be provided with a motor covered with an explosion-proof box instead of the explosion-proof type motor. By covering the neighborhood of the motor by the explosion-proof box, even if the motor explodes. the explosion-proof box is not destroyed and it can be prevented that any spark rushes out of the explosion-proof box to ignite the
combustible gas. Therefore, it is not necessary to arrange the motor and the compressor in
separate rooms partitioned with a partition. Therefore, the degree of freedom of the inboard arrangement by the re-liquefaction apparatus increases . Desirably, cooling fins are provided for the I explosion-proof box.

The liquefied gas in a second viewpoint of the present invention is provided with a plurality of tanks which store combustible liquefied gas; and a plurality of re-liquefaction apparatuses which re- ) liquefy boil-off gas of liquefied gas. Each of the plurality of re-liquefaction apparatuses is provided with a compressor which compresses the boil-off gas; and an explosion-proof type motor which.drives the compressor. )

It is desirable that the liquefied gas carrier is further provided with a spare re-liquefaction apparatus; and a pipe system which switches a state between a state that the spare re-liquefaction apparatus is not connected with any of the plurality 5 of tanks and a state that the spare re- liquefaction apparatus is connected with an optional one of the plurality of tanks. he plurality of re-liquefaction apparatuses are connected with the plurality of tanks, respectively. The spare re-liquefaction apparatus is provided with a compressor which compresses the boil-off gas; and an explosion-proof type motor which drives the compressor.

Desirably, the plurality of tanks contain a first tank and a second tank which are adjacent to each other. The plurality of re-liquefaction apparatuses contain a first re-liquefaction apparatus and a second re-liquefaction apparatus. The liquefied gas carrier is further provided with a BOG mother pipe which connects the first tank and the second tank; and an RLG mother pipe which connects the first tank and the second tank.

A first valve or a first spool piece is provided for the BOG mother pipe. The BOG mother pipe is provided with a BOG mother pipe first tank side part connecting the first valve or the first spool piece and the first tank; and a BOG mother pipe second tank side part connecting the first valve or the first spool piece and the second tank. A second valve or a second spool piece is provided for the RLG mother pipe.

The RLG mother pipe is provided with an RLG mother pipe first tank side part connecting the second valve or the second spool piece and the first tank; and an RLG mother pipe second tank side part connecting the second valve or the second spool piece and the second tank. Each of the plurality of re-liquefaction apparatuses is provided with a BOG pipe which supplies the boil-off gas to the compressor; and an RLG pipe which returns re-liquefaction gas to which the boil-off gas is re-liquefied. The BOG pipe of the first re-liquefaction apparatus is connected with the BOG mother pipe first tank side part.

The BOG pipe of the second re-liquefaction apparatus is connected with the BOG mother pipe second tank side part. The RLG pipe of the first re-liquefaction apparatus is connected with the RLG mother pipe first tank side-part. The RLG pipe of the second re-liquefaction apparatus is connected with the RLG mother pipe second tank side part.
It is desirable that the liquefied gas carrier is further provided with a BOG mother pipe; a group of valves or spool pieces provided for the BOG mother pipe such that the BOG mother pipe is separated to a plurality of BOG mother pipe parts; an RLG mother pipe; a group of valves or spool pieces provided for the RLG mother pipe such that the RLG mother pipe is separated to a plurality of RLG mother pipe parts; a plurality of tank side BOG pipes which connect the plurality of tanks with the plurality of BOG mother pipe parts, respectively; and a plurality of tank side RLG pipes which connect the plurality of tank with the plurality of RLG mother pipe parts, respectively.

A valve or a spool piece is provided for each of the plurality of tank side BOG pipes, and a valve or a spool piece is provided for each of the plurality of tank side RLG pipes. Each of the plurality of re-liquefaction apparatuses is provided with a re-liquefaction apparatus side BOG pipe which supplies the boil-off gas to the compressor; and a re-liquefaction apparatus side RLG pipe which returns re-liquefaction gas to which the boil-off gas is re-liquefied.

The plurality of re-liquefaction apparatuses are connected with the plurality of BOG mother pipe parts through the re-liquefaction apparatus side BOG pipes, respectively.. The plurality of re-liquefaction apparatuses are connected with the plurality of RLG mother pipe parts through the re-liquefaction apparatus side RLG pipes, respectively.Desirably, the plurality of re-liquefaction apparatuses are provided for the plurality of tanks, respectively.

Each of the plurality of re-liquefaction apparatuses may be provided with a motor covered with an explosion-proof box instead of the explosion-proof type motor. Each of the spare re-liquefaction apparatus and the plurality of re-liquefaction apparatuses comprises a motor covered with an explosion-proof box instead of the explosion-proof type motor.

A method of building a liquefied gas carrier in a third viewpoint of the present invention includes: assembling a re-liquefaction apparatus which re-liquefies boil-off gas of combustible liquefied gas; and installing the re-liquefaction apparatus in a hull or a hull block.

The assembling a re-liquefaction apparatus includes: installing a compressor which compress the boil-off gas, and an explosion-proof type motor on a base sheet; and connecting the compressor and the explosion-proof type motor.

It is desirable that the assembling a re-liquefaction apparatus includes: installing a compressor which compress the boil-off gas, and an explosion-proof type motor on a base sheet; installing the compressor which compresses the boil-off gas, the motor, and an explosion-proof box which covers the motor, on the base sheet, in place of connecting the compressor and the explosion-proof type motor; and connecting the compressor and the motor.

According to the present invention, the re-liquefaction apparatus which is installed in the liquefied gas carrier with a high degree of freedom of inboard arrangement of the re-liquefaction apparatus, the liquefied gas carrier and a method of building the re-liquefaction apparatus are provided.

Brief Description of the Drawings The above object, the other objects, the effect and the features of the present invention would be made clear from the description in the embodiments in conjunction with the attached drawings:

FIG. 1 is a schematic diagram showing a conventional LPG carrier;

FIG. 2 is a schematic diagram showing a re-liquefaction apparatus according to a first embodiment of the present invention;

FIG. 3 is a schematic diagram showing of the re-liquefaction apparatus according to a modification of the first embodiment;

FIG. 4 is a schematic diagram showing the re-liquefaction apparatus according to a second embodiment of the present invention;

FIG. 5 is a schematic diagram showing the re-liquefaction apparatus according to a third embodiment of the present invention;

FIG. 6 is a diagram showing a part of the re-liquefaction apparatus according to a modification of the third embodiment;

FIG. 7 is a schematic diagram showing a liquefied gas carrier according to a fourth embodiment of the present invention;

FIG. 8 is a schematic diagram showing the liquefied gas carrier according to a fifth embodiment of the present invention;

FIG. 9 is a schematic diagram showing the liquefied gas carrier according to a sixth embodiment of the present invention;

FIG. 10 is a schematic diagram showing the liquefied gas carrier according to a seventh embodiment of the present invention;

FIG. 11 is a schematic diagram showing a re-liquefaction apparatus centralized arrangement area of the liquefied gas carrier according to the seventh embodiment; I

FIG. 12 is a schematic diagram showing the re-liquefaction apparatus centralized arrangement area according to a first modification of the seventh embodiment;

FIG. 13 is a schematic diagram showing the re-'■) liquefaction apparatus centralized arrangement area according to a second modification of the seventh embodiment;

FIG. 14 is a schematic diagram showing the re-liquefaction apparatus centralized arrangement area ) according to a third modification the seventh embodiment;

FIG. 15 is a schematic diagram showing the re-liquefaction apparatus centralized arrangement area according to a fourth modification of the seventh 5 embodiment; and
FIG. 16 is a schematic diagram showing the re-liquefaction apparatus centralized arrangement area according to a fifth modification of the seventh embodiment.

Description of Embodiments
Referring to the attached drawings, embodiments of a re-liquefaction apparatus, a liquefied gas carrier in which the re-liquefaction apparatus is installed, and a method of building the liquefied gas carrier according to the present invention will be described below.

[First Embodiment]
Referring to FIG. 2, the re-liquefaction apparatus 6 according to a first embodiment of the present invention will be described. The re-liquefaction apparatus 6,is installed in the liquefied gas carrier which carries combustible liquefied gas such as LPG gas and LNG gas and re-liquefies the boil-off gas of the liquefied gas.

The re-liquefaction apparatus 6 is provided with a base sheet 60, a compressor 61 which compresses the boil-off gas, a condenser 52 connected with the compressor 61, an expansion valve 63 connected with the condenser 62, a boil-off gas (BOG) pipe 64 to supply the boil-off gas to the compressor 61 from a tank, a RLG pipe 65 to return to the tank, the re-liquefaction gas obtained by the re-liquefying the boil-off gas, an explosion- proof type motor 66 which drives the compressor 61, and a spacer 67 to connect the explosion-proof type motor 66 and the compressor 61.

The spacer 67 is provided for a distance adjustment between the explosion-proof type motor 66 and the compressor 61.
The compressor 61, the condenser 62, the expansion valve 63 and the explosion-proof type motor 66 are installed on the base sheet 60, such that the re-liquefaction apparatus 6 is formed as a unit.

According to the present embodiment, even if an explosion happens inside the motor 66, the container of the explosion-proof type motor 66 is not destroyed so that it can be prevented that a spark rushes out of the container to ignite the combustible gas, because the explosion-proof type motor 66 is used. Therefore, it is not necessary to arrange the explosion-proof type motor 66 and the compressor 61 in the separate rooms partitioned with a partition.

Because no partition is provided between the explosion-proof type motor 66 and the compressor 61, an intermediate shaft and a special partition passing-through device such as partition seal are not required, and the explosion-proof type motor 66 and the compressor 61 can be connected without using a I flexible joint such as an elastic rubber coupling.

Because it is not necessary to arrange the explosion-proof type motor 66 and the compressor 61 in separate rooms which are partitioned with the partition, the degree of freedom of the inboard arrangement of the re-liquefaction apparatus 6 increases. Because the re-liquefaction apparatus 6 can be arranged in a free space, the inboard space can be used effectively.

Because it is not necessary to arrange the explosion-proof type motor 66 and the compressor 61 in the separate rooms partitioned with the partition, the explosion-proof type motor 66 and the compressor 61 can be arranged nearby. Therefore, the re-liquefaction apparatus 6 can be operated under the centralized control. The check and maintenance of the re-liquefaction apparatus 6 become easy.

The design change when changing a model of the explosion-proof type motor 66 can be minimized by connecting the explosion-proof type motor 66 and the compressor 61 through the spacer 67.
However, when the distance between the explosion-proof type motor 66 and the compressor 61 is determined in advance, the explosion-proof type motor 66 and the compressor 61 may be directly connected without the spacer 67, as shown in FIG. 3.

The re-liquefaction apparatus 6 may not be provided with the expansion valve 63 and may not be provided with the expansion valve 63 and the condenser 62.

Because it is not necessary to arrange the explosion-proof type motor 66 and the compressor 61 in the separate rooms partitioned with the partition, a method of building the liquefied gas carrier according to the first embodiment will be described below.

The method of building the liquefied gas carrier according to the first embodiment is provided with a step of assembling the re-liquefaction apparatus 6 and a step of installing the re-liquefaction apparatus 6 in a hull 10 (to be described later).

The step of assembling the re-liquefaction apparatus 6 is executed in an outboard area like a factory. The step of assembling the re-liquefaction apparatus 6 is provided with a step of installing the compressor 61 and the explosion-proof type motor 66 on the base sheet 60, a step of connecting the compressor 61 and the explosion-proof type motor 66 such that the explosion-proof type motor 66 can drive the compressor 61.

In the step of connecting the compressor 61 and the explosion-proof type motor 66, the
explosion-proof type motor 66 and the compressor 61 are connected through the spacer 67 or without the spacer 67.

According to the method of building the liquefied gas carrier according to the present embodiment, it is sufficient to carry the explosion-proof type motor 66 and the compressor 61 into the hull 10 together with the base sheet 60 and to install them, and it is not necessary to adjust an axis wick between the explosioa-proof type motor 66 and the compressor 61 in hull 10. Therefore, the work in the hull 10 can be reduced and the building cost of the liquefied gas carrier is reduced.

Instead of the step of installing the re-liquefaction apparatus 6 in the hull 10, if the step of installing the re-liquefaction apparatus 6 in a hull block and the step of assembling the hull 10 from the hull blocks are executed, the building cost of the liquefied gas carrier is more reduced.

[Second Embodiment] Referring to FIG. 4, the re-liquefaction apparatus 6 according to a second embodiment of the present invention will be described. In the re-liquefaction apparatus 6 according to the present embodiment, a gas leakage detector 71, a shutoff valve 72, a temperature sensor 73, a warning unit 74 and a motor control unit 75 are added to the re-liquefaction apparatus 6 according to the first embodiment.

The shutoff valve 72 is provided for the BOG pipe 64. The shutoff valve 72 shuts off the supply of the boil-off gas to the compressor 61 when the gas leakage detector 71 detects the leakage of liquefied gas .

The temperature sensor 73 detects the surface temperature or winding temperature of the explosion-proof type motor 66 as the motor temperature. The warning unit 74 generates a warning when the motor temperature is higher than a first reference temperature, to inform abnormality to sailors. The motor control unit 75 stops the explosion-proof type motor 66 automatically when the motor temperature is higher than a second reference temperature. Here, it is preferable that the second reference temperature is higher than the first reference temperature.

By shutting-off the supply of the boil-off gas to the compressor 61 based on the detection of the gas leakage, generating the warning based on the motor temperature and stopping the explosion-proof type motor 66 based on the motor temperature, the reliability to the gas explosion prevention is improved.

It should be noted that optional one or two of the shut-off of the supply of the boil-off gas to the com.pressor 61 based on the detection of the gas leakage, the generation of the alarm based on the motor temperature and the stop of the explosion-proof type motor 66 based on the motor temperature may be executed.

[Third Embodiment]
Referring to FIG. 5, the re-liquefaction apparatus 6 according to a third embodiraent of the present invention will be described. The re-liquefaction apparatus 6 according to the present embodiment is provided with a motor 81 covered by an explosion-proof box instead of the explosion-proof type motor 65, and an intermediate shaft 83 and the partition seal 84 instead of the spacer 67. The explosion-proof box covers the motor 81 individually. That is, the explosion-proof box 82 covers only one motor 81.

The motor 81 and the compressor 61 are connected by the intermediate shaft 83 which passes through the explosion-proof box 82. The intermediate shaft 83 is provided with a flexible joint like the elastic rubber coupling. The partition seal 84 is provided to seal a gap between the intermediate shaft 83 and the explosion-proof box 82.

According to the present embodiment, even if the motor 81 explodes, the explosion-proof box 82 is not destroyed so that it is prevented that a spark rushes out of the explosion-proof box 82 to ignite the combustible gas by covering the neighborhood of the motor 81 by the explosion-proof box 82. Therefore, it is not necessary to arrange the motor 81 and the compressor 61 in the separate rooms partitioned with the partition. Therefore, the degree of freedom of the inboard arrangement of the re-liquefaction apparatus 6 increases.

Because it is not necessary to arrange the motor 81 and the compressor 61 in the separate rooms partitioned with the partition, the motor 81 and the compressor 61 can be arranged nearby. Therefore, the re-liquefaction apparatus 6 can be operated under the centralized control.

The check and maintenance of the re-liquefaction apparatus 6 become easy.According to the present embodiment, the length of the intermediate shaft 83 can be made shorter than the intermediate shaft 183 passing through the partition 105.

It is desirable to provide cooling fins 85 for the explosion-proof box 82, as shown in FIG. 6. The cooling fins 85 radiate the heat generated while the motor 81 is operating, into air efficiently to prevent the temperature of the motor 81 from rising.

Because it is not necessary to arrange the motor 81 and the compressor 61 in the separate rooms partitioned with the partition, the method of building the liquefied gas carriers according to the third embodiment to be described below becomes possible.

The method of building the liquefied gas carrier according to the third embodiment is provided with the step of assembling the re-liquefaction apparatus 6 and the step of installing the re-liquefaction apparatus 6 in the hull 10 (to be described later) .

The step of assembling the re-liquefaction apparatus 6 is executed in an outboard area like the factory. The step of assembling the re-liquefaction apparatus 6 is provided with a step of installing the compressor 61, the motor 81 and the explosion-proof box 82 covering the motor 81, on .the base sheet-60, and a step of connecting the compressor 61 and the motor 81 such that the motor 81 can drive the compressor 61. In the step of connecting the compressor 61 and the motor 81, the motor 81 and the compressor 61 are connected through the intermediate shaft 83.

According to the method of building the liquefied gas carrier according to the present embodiment, it is sufficient to carry the motor 81, the explosion-proof box 82 and the compressor 61 into the hull 10 together with the base sheet 60 and to install them, and it is not necessary to adjust an axis center between the motor 81 and the compressor 61 in the hull 10, Therefore, it is possible to reduce a work in the hull 10 so that the building cost of the liquefied gas carrier can be reduced.

Instead of the step of installing the re-liquefaction apparatus 6 in the hull 10, if the step of installing the re-liquefaction apparatus 6 in a hull block (not shown) and the step of assembling the hull 10 from hull blocks are executed, the building cost of the liquefied gas carrier can be more reduced.

[Fourth Embodiment]
Referring to FIG. 1, the liquefied gas carrier 1 according to a fourth embodiment of the present invention will be described. The liquefied gas carrier 1 is provided with the hull 10, a plurality of tanks 2-1 to 2-N which store the liquefied gas, a plurality of re-liquefaction apparatuses 6-1 to 6-N which re-liquefy the boil-off gas of liquefied gas, a re-liquefaction apparatus 6-{N+l) and a pipe system 3. The tanks 2-1 to 2-N, the re-liquefaction apparatuses 6-1 to 6-N and the re-liquefaction apparatus 6-{N+l) are installed in the hull 10.

The hull 10 is provided with a bow 11, a stern 12 and a deck 13. The tanks 2-1 to 2-N are provided under the deck 13 and are arranged along the longitudinal direction of the hull 10 (a direction from the bow to the stern) . The plurality of re-liquefaction apparatuses 6-1 to 6-N and the re-liquefaction apparatus 6-(N+l) are provided on the deck 13. The re-liquefaction apparatus 6-(N+l) functions as a spare re-liquefaction apparatus. Each of the plurality of re-liquefaction apparatuses 6-1 to 6-N and the re-liquefaction apparatus 6-(N+l) is the re-liquefaction apparatus 6 in any of the above embodiments. Therefore, the plurality of re-liquefaction apparatuses 6-1 to 6-N and the re-liquefaction apparatus 6-(N+l) can be freely arranged in the hull 10.

The re-liquefaction apparatuses 6-1 to. 6-N are connected with the tanks 2-1 to 2-N, respectively. The re-liquefaction apparatuses, 6-1 to 6-N re-liquefy the boil-off gases from the tanks 2-1 to 2-N, to produce the re-liquefaction gases, and return the re-liquefaction gases to the tanks 2-1 to 2-N, respectively.

The re-liquefaction apparatuses 6-1 to 6-N are distributedly arranged and provided for the tanks 2-1 to 2-N, respectively. That is, the re-liquefaction apparatuses 6-1 to 6-N are arranged on or above the tanks 2-1 to 2-N, respectively.

The pipe system 3 is configured to switch between a state that the spare re-liquefaction apparatus 5-{N+l) is connected with neither of the tanks 2-1 to 2-N and a state that being connected with an optional one of the tanks 2-1 to 2-N. More specifically, the pipe system 3 is provided with a BOG mother pipe 31, a RLG mother pipe 32, a plurality of BOG pipes 33-1 to 33-N and a plurality of RLG pipes 34-1 to 34-N. The BOG mother pipe 31 and the RLG mother pipe 32 extend to the longitudinal direction of the hull 10.

A valve or a spool piece 40 is provided for each of the BOG pipes 33-1 to 33-N. A valve or a spool piece 40 is provided for each of the RLG pipes 34-1 to 34-N. The BOG mother pipe 31 is connected with the tanks 2-1 to 2-N through the BOG pipes 33-1 to 33-N, respectively. The RLG mother pipe 32 is connected with the tanks 2-1 to 2-N through the RLG pipes 34-1 to 34-N, respectively.

The BOG-pipe 64 and the RLG pipe 65 of the spare re-liquefaction apparatus 6-{N+l) are connected with the BOG mother pipe 31 and the RLG mother pipe 32, respectively.
When the re-liquefaction apparatus 6-L of the re-liquefaction apparatuses 6-1 to 6-N has failed, the pipe system 3 is switched to the state that the spare re-liquefaction apparatus 6-(N+l) is connected with the tank 2-L.

At this time, the boil-off gas is supplied to the spare re-liquefaction apparatus 6-(N+1) through the BOG pipe 33-L and the BOG mother pipe 31 from the tank 2-L. The spare re-liquefaction apparatus 6-(N+l) re-liquefies the boil-off gas to produce the re-liquefaction gas, and the re-liquefaction gas is returned to the tank 2-L through the RLG mother pipe 32 and the RLG pipe 34-L from the I spare re-liquefaction apparatus 6-(N+l).
[Fifth Embodiment] Referring to FIG. 8, the liquefied gas carrier 1 according to a fifth embodiment of the present J invention will be described. The liquefied gas carrier 1 according to the present embodiment is same as the liquefied gas carrier 1 according to the fourth embodiment except for the following points.

In the pipe system 3 according to the present embodiment, the BOG mother pipe 31 connects the tank 2-1 and the tank 2-2 and the RLG mother pipe 32 connects the' tank 2-1 and the tank 2-2. A valve or spool piece 40 is provided for the BOG mother pipe 31.

The BOG mother pipe 31 contains the BOG mother pipe part 31-1 which connects the valve or spool piece 40 and the tank 2-1, and a BOG mother pipe part 31-2 which connects the valve or spool piece 40 and the tank 2-2. The valve or spool piece 40 is provided for the RLG mother pipe 32.

The RLG mother pipe 32 contains a RLG mother pipe part 32-1 which connects the valve or spool piece 40 and the tank 2-1, and a RLG mother pipe part 32-2 which connects the valve or spool piece 40 and the tank 2-1.

The BOG pipe 64 of the re-liquefaction apparatus 2-1 is connected with the BOG mother pipe part 31-1. The BOG pipe 64 of the re-liquefaction apparatus 2-2 is connected with the BOG mother pipe part 31-2 . The RLG pipe 65 of the re-liquefaction apparatus 2-1 is connected with the RLG mother pipe part 32-1. The RLG pipe 65 of the re-liquefaction apparatus 2-2 is connected with the RLG mother pipe part 32-2.

According to the present embodiment, when both of the re-liquefaction apparatuses 2-1 and 2-2 operate normally, the valve or spool piece 40 provided for the BOG mother pipe 31 is in a close condition, and the valve or spool piece 40 provided for the RLG mother pipe 32 is in the close condition. At this time, the re-liquefaction apparatus 2-1 re-liquefies the boil-off gas from the tank 2-1 and returns the re-liquefaction gas to the tank 2-1.

The re-liquefaction apparatus 2-2 re-liquefies the boil-off gas from the tank 2-2 and returns the re-liquefaction gas to the tank 2-2. When the one of the re-liquefaction apparatuses 2-1 and 2-2 fails, the valve or spool piece 40 provided for the BOG mother pipe 31 becomes an open condition and the valve or spool piece 40 provided for the RLG mother pipe 32 becomes an open condition. Then, the other re-liquefies the boil-off gas from the re-liquefaction tanks 2-1 and 2-2 and returns the re-liquefaction gas to the re-liquefaction tanks 2-1 and 2-2.

[Sixth Embodiment] Referring to FIG. 9, the liquefied gas carrier 1 according to a sixth embodiment of the present invention will be described. The liquefied gas carrier 1 according to the present embodiment is the same as the liquefied gas carrier 1 according to the fourth embodiment except for the following points.

In the pipe system 3 according to the present embodiment, a group of valves or spool pieces 40 is
provided for the BOG mother pipe 31 such that the BOG mother pipe 31 is divided into a plurality of BOG mother pipe parts 31-1 to 31-N. The group of valves or spool pieces 40 is provided for the RLG mother pipe 32 such that the RLG mother pipe 32 is divided into a plurality of RLG mother pipe parts 32-1 to 32-N. The BOG pipes 33-1 to 33-N connect the tanks 2-1 to 2-N with the BOG mother pipe parts 31-1 to 31-N, respectively.

The RLG pipes 34-1 to 34-N connect the tank 2-1 to 2-N with the RLG mother pipe parts 32-1 to 32-N, respectively. The valve or spool piece 40 is provided for each of the BOG pipes 33-1 to 33-N. The valve or spool piece 40 is provided for each of the RLG pipes 34-1 to 34-N. The re-liquefaction apparatuses 6-1 to 6-N are connected with the BOG mother pipe parts 31-1 to 31-N through the BOG pipes 64, respectively.

The re-liquefaction apparatuses 6-1 to 6-N are connected with the RLG mother pipe parts 32-1 to 32-N through the RLG pipes 65, respectively. In the present embodiment, the spare re-liquefaction apparatus 6-(N+l) is not provided.

According to the present embodiment, it is possible to connect an optional tank of the tanks 2-1 to 2-N with an optional re-liquefaction apparatus of the re-liquefaction apparatuses 6-1 to 6-N. Also, according to the present embodiment, because the mother pipe is divided into many pipe parts.compatibility is increased.

[Seventh Embodiment] Referring to FIG. 10, the liquefied gas carrier 1 according to a seventh embodiment of the present invention will be described. The liquefied gas carrier 1 according to the present embodiment is the same as the liquefied gas carrier 1 according to either of the fourth and sixth embodiments except for the following points. According to the present embodiment, the re-liquefaction apparatus is centered and arranged.

In the present embodiment, the re-liquefaction apparatuses 6-1 to 6-N are arranged in a centralized arrangement area 5 for the re-liquefaction apparatuses are provided onto a deck 13. It should be noted that when the liquefied gas carrier 1 according to the present embodiment corresponds to the liquefied gas carrier 1 according to the fourth embodiment, the re-liquefaction apparatuses 6-1 to 6-(N+l) are arranged in the centralized arrangement area 5. Hereinafter, a case where the re-liquefaction apparatuses 6-1 to 6-N are intensively arranged in the centralized arrangement area 5 will be described.

However, a case where the re-liquefaction apparatuses 6-1 to 6-(N+l) are intensively arranged in the re-liquefaction apparatus centralized arrangement area 5 is the same as the above case.
Referring to FIG. 11, the re-liquefaction apparatuses 6-1 to 6-N are arranged in one line in a lateral direction in the re-liquefaction apparatus centralized arrangement area 5. That is, the re-liquefaction apparatuses 6-1 to 6-N are arranged along one straight line extending in the lateral direction of the hull 10.

It should be noted that in each of the re-liquefaction apparatuses 6-1 to 6-N, the motor 66 or 81 may be arranged on the front side (the side of bow 11) and the compressor 61 may be arranged on the rear side (the side of stern 12) .

The motor 66 or 81 may be arranged on the rear side and the compressor 61 may be arranged on the front side. Whether the motor 66 or 81 is arranged on the front side or the rear side may be unified among the re-liquefaction apparatuses 6-1 to 6-N and may not be unified. The re-liquefaction apparatus centralized arrangement area 5 can be made compact by arranging one of the motors 66 or 81 on the front side and the other on the rear side for the neighboring re-liquefaction apparatuses.

This is the same in FIG. 12 to FIG. 16 to be described First Modification of Seventh Embodiment Referring to FIG. 12, the re-liquefaction apparatuses 6-1 to 6-N are arranged in the lateral direction of the hull in the re-liquefaction apparatus centralized arrangement area 5 according to a first modification of the seventh embodiment, but the neighboring re-liquefaction apparatuses are arranged to shift in the front and rear direction.

Second Modification of Seventh Embodiment Referring to FIG. 13, in the re-liquefaction apparatus centralized arrangement area 5 according to a second modification of the seventh embodiment, the re-liquefaction apparatuses 6-1 to 6-N are arranged in one line in the lateral direction of the hull on either side of the BOG mother pipe 31 and the RLG mother pipe 32.

The re-liquefaction apparatuses 6-1 to 6-N may be arranged such that the re-liquefaction apparatuses are shifted in the front and rear direction, and the re-liquefaction apparatuses are not shifted.

Third Modification of Seventh Embodiment Referring to FIG. 14, the re-liquefaction apparatuses 6-1 to 6-N are arranged in two lines in the lateral direction of the hull in the re-liquefaction apparatus centralized arrangement area 5 according to a third modification of the seventh embodiment. That is, the re-liquefaction apparatuses 6-1 to 6-N are arranged in two straight linesextending in the lateral direction of the hull 10 ,

Fourth Modification of Seventh Embodiinent Referring to FIG. 15, the re-liquefaction apparatuses 5-1 to 6-N are arranged in multiple lines in the lateral direction of the hull in the re-liquefaction apparatus centralized arrangement area 5 according to a fourth modification of the seventh embodiment. That is, the re-liquefaction apparatuses 6-1 to 6-N are arranged in three or more straight lines extending in the lateral direction of the hull 10.

Fifth Modification of Seventh Embodiment Referring to FIG. 16, the re-liquefaction apparatuses 6-1 to 6-N are arranged in one line in a vertical direction of the hull in the re-liquefaction apparatus centralized arrangement area 5 according to a fifth modification of the seventh embodiment. The re-liquefaction apparatuses 6-1 to 6-N are arranged in one straight line extending in the longitudinal direction of the hull 10. It should be noted that the re-liquefaction apparatuses 6-1 to 6-N may be arranged in plural lines in the vertical direction.
With reference to the embodiments, the present invention has been described, but the present invention is not limited to the above embodiments.

Various modifications can be made to the above embodiments. The above embodiments may be combined with each other. This patent application claims a priority based on Japan Patent Application No. JP 2010-026448 filed on February 9, 2010. The disclosure thereof is incorporated herein by reference.

CLAIMS

1. A re-liquefaction apparatus, which is installed into a liquefied gas carrier, comprising:

a compressor which compresses boil-off gas of combustible liquefied gas; and
an explosion-proof type motor which drives said compressor.

2. The re-liquefaction apparatus according to claim 1, further comprising:

a base sheet on which said compressor and said explosion-proof type motor are installed.

3. The re-liquefaction apparatus according to claim 1 or 2, further comprising:

a gas leakage detector; and a shut-off valve configured to shut off supply of the boil-off gas to said compressor when said gas leakage detector detects leakage of the liquefied gas.

4. The re-liquefaction apparatus according to any of claims 1 to 3, further comprising:
a temperature sensor configured to detect a m.otor temperature of said explosion-proof type motor; and a warning unit configured to generate a warning when the motor temperature is higher than a first reference temperature.

5. The re-liquefaction apparatus according to claim 4, further comprising:

a motor control unit configured to stop said explosion-proof type motor when the motor temperature is higher than a second reference temperature.

6. The re-liquefaction apparatus according to any of claims 1 to 3, further comprising:
a temperature sensor configured to detect a motor temperature of said explosion-proof type motor; and
a motor control unit configured to stop said explosion-proof type motor when the motor temperature is higher than a reference temperature.

7. The re-liquefaction-apparatus according to any of claims 1 to 6, wherein a motor covered by an explosion-proof box is used instead of said explosion-proof type motor.

8 . The re-liquefaction apparatus according to claim 7, wherein said explosion-proof box comprises cooling fins.

9. A liquefied gas carrier comprising: JO -a plurality of tanks which store combustible liquefied gas; and a plurality of re-liquefaction apparatuses which re-liquefy boil-off gas of the liquefied gas, wherein each of said plurality of re-liquefaction apparatuses comprises:
a compressor which compresses the boil-off gas; and an explosion-proof type motor which drives said compressor.

10. The liquefied gas carrier according to claim 9, further comprising: a spare re-liquefaction apparatus; and a pipe system which switches between a state that said spare re-liquefaction apparatus is not connected with any of said plurality of tanks and a state that said spare re-liquefaction apparatus is connected with an optional one of said plurality of tanks, wherein said plurality of re-liquefaction apparatuses are connected with said plurality of tanks, respectively, andwherein said spare re-liquefaction apparatus comprises: a compressor which compresses the boil-off gas; and an explosion-proof type motor which drives said compres sor.

11. The liquefied gas carrier according to claim 9, wherein said plurality of tanks contain a first tank and a second tank which are adjacent to each other, and said plurality of re-liquefaction apparatuses contain a first re-liquefaction apparatus and a second re-liquefaction apparatus,
wherein said liquefied gas carrier further comprises:

a BOG mother pipe which connects said first tank and said second tank; and
an RLG mother pipe which connects said first tank and said second tank,
wherein a first valve or a first spool piece is provided for said BOG mother pipe,
wherein said BOG mother pipe comprises:

a BOG mother pipe first tank side part connecting said.first valve or said first spool piece and said first tank; and

a BOG mother pipe second tank side part connecting said first valve or said first spool piece and said second tank, wherein a second valve or a second spool piece is provided for said RLG mother pipe, wherein said RLG mother pipe comprises:

an RLG mother pipe first tank side part connecting said second valve or said second spool piece and said first tank; and

an RLG mother pipe second tank side part connecting said second valve or said second spool piece and said second tank, wherein each of said plurality of re-liquefaction apparatuses comprises:

a BOG pipe which supplies the boil-off gas to said compressor; and an RLG pipe which returns re-liquefaction gas to which the boil-off gas is re-liquefied, and wherein said BOG pipe of said first re-liquefaction apparatus is connected with said BOG mother pipe first tank side part, said BOG pipe of said second re-liquefaction apparatus is connected with said BOG mother pipe second tank side part, said RLG pipe of said first re-liquefaction apparatus is connected with said RLG mother pipe first tank side part, and said RLG pipe of said second re-liquefaction apparatus is connected with said RLG mother pipe second tank side part.

12. The liquefied gas carrier according to claim 9, further comprising:

a BOG mother pipe;

a group of valves or spool pieces provided for said BOG mother pipe such that said BOG mother pipe is separated to a plurality of BOG mother pipe parts; an RLG mother pipe;
a group of valves or spool pieces provided for said RLG mother pipe such that said RLG mother pipe is separated to a plurality of RLG mother pipe parts;

a plurality of tank side BOG pipes which connect said plurality of tanks with said plurality of BOG mother pipe parts, respectively; and

a plurality of tank side RLG pipes which connect said plurality of tank with said plurality of RLG mother pipe parts, respectively, wherein a valve or a spool piece is provided for each of said plurality of tank side BOG pipes, and a valve or a spool piece is provided for each of said plurality of tank side RLG pipes, wherein each of said plurality of re-liquefaction apparatuses comprises:

a re-liquefaction apparatus side BOG pipe which supplies the boil-off gas to said compressor; and

a re-liquefaction apparatus side RLG pipe which returns re-liquefaction gas to which the boil-off gas is re-liquefied, and wherein said plurality of re-liquefaction apparatuses are connected with said plurality of BOG mother pipe parts through said re-liquefaction apparatus side BOG pipes, respectively, and said plurality of re-liquefaction apparatuses are connected with said plurality of RLG mother pipe parts through said re-liquefaction apparatus side RLG pipes, respectively.

13. The liquefied gas carrier according to any of claims 9 to 12, wherein said plurality of re-liquefaction apparatuses are provided for said plurality of tanks, respectively.

14. The liquefied gas carrier according to any of claims 9 to 13, wherein each of said plurality of re-liquefaction apparatuses comprises a motor covered with an explosion-proof box instead of said explosion-proof type motor.

15. The liquefied gas carrier according to claim 10, wherein each of said spare re-liquefaction apparatus and said plurality of re-liquefaction apparatuses comprises a motor covered with an explosion-proof box instead of said explosion-proof type motor.

16. A method of building a liquefied gas carrier, comprising: assembling a re-liquefaction apparatus which re-liquefies boil-off gas of combustible liquefied gas; and installing said re-liquefaction apparatus in a hull or a hull block, wherein said assembling a re-liquefaction apparatus comprises: installing a compressor which compress the boil-off gas, and an explosion-proof type motor on a base sheet; and connecting said compressor and said explosion-proof type motor.

17. The method of building a liquefied gas carrier according to claim 16, wherein said assembling a re-liquefaction apparatus comprises: installing a compressor which compress the boil-off gas, and an explosion-proof type motor on a basesheet; installing said compressor which compresses the boil-off gas, said motor, and an explosion-proof box which covers said motor, on said base sheet, instead of connecting said compressor and said explosion-proof type motor; and
connecting said compressor and said motor.