KR102203737B1 - Boil-Off Gas Treatment System and Method for Ship - Google Patents

Abstract

A system and method for treating boil-off gas of a ship are disclosed. The boil-off gas treatment system of a ship of the present invention is provided with a main engine and a power generation engine receiving fuel at a lower pressure than the main engine, and evaporation connected to the main engine from a storage tank provided in the ship to store liquefied gas. Gas supply line; A compressor provided in the boil-off gas supply line and receiving boil-off gas generated from the liquefied gas and compressing it at a fuel supply pressure of the main engine; The boil-off gas is branched from the boil-off gas supply line downstream of the compressor and is connected to the storage tank, and the boil-off gas not supplied as fuel of the main engine is cooled by heat exchange with the uncompressed boil-off gas to be supplied to the compressor. A reliquefaction line for restoring into a storage tank; A heat exchanger provided in the reliquefaction line, receiving compressed gas compressed by the compressor, and cooling through heat exchange with uncompressed boil-off gas to be supplied to the compressor along the boil-off gas supply line; A branch line branched from the reliquefaction line at a rear end of the heat exchanger to depressurize the compressed gas and supply it to the power generation engine; And a refrigerant supplement line branched from the branch line and connected to a front end of the heat exchanger of the boil-off gas supply line.

Description

Boil-Off Gas Treatment System and Method for Ship}

The present invention relates to a boil-off gas treatment system and method for re-liquefying boil-off gas (BOG) generated from liquefied gas stored in a ship with cold heat of the boil-off gas itself.

In recent years, the consumption of liquefied natural gas (LNG) and other liquefied gases is increasing rapidly around the world. The liquefied gas obtained by liquefying the gas at a low temperature has an advantage of increasing storage and transfer efficiency because the volume is very small compared to the gas. In addition, liquefied gases, including liquefied natural gas, can remove or reduce air pollutants during the liquefaction process, and thus can be regarded as eco-friendly fuels with little emission of air pollutants during combustion.

Liquefied natural gas is a colorless and transparent liquid obtained by liquefying natural gas containing methane as its main component by cooling it to about -162°C, and has a volume of about 1/600 compared to natural gas. Therefore, when the natural gas is liquefied and transported, it can be transported very efficiently.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -162°C at normal pressure, liquefied natural gas is sensitive to temperature changes and is easily evaporated. For this reason, the storage tank storing liquefied natural gas is insulated, but external heat is continuously transmitted to the storage tank. -Off Gas, BOG) occurs.

Boil-off gas is a kind of loss and is an important problem in transport efficiency. In addition, if the boil-off gas accumulates in the storage tank, the internal pressure of the tank may increase excessively, and in severe cases, there is a risk of damage to the tank. Therefore, various methods for treating the boil-off gas generated in the storage tank have been studied. Recently, for the treatment of the boil-off gas, a method of re-liquefying the boil-off gas and returning it to the storage tank, and the boil-off gas as fuel such as a ship's engine. The method of using it as an energy source of the customer is being used.

As a method for re-liquefying the boil-off gas, a method of reliquefying the boil-off gas by heat exchange with the refrigerant by providing a refrigeration cycle using a separate refrigerant, a method of re-liquefying the boil-off gas itself as a refrigerant without a separate refrigerant, etc. There is this.

Meanwhile, among engines generally used in ships, gas-fueled engines such as DFDE, X-DF engine, and ME-GI engine are used as engines that can use natural gas as fuel.

DFDE is composed of four strokes, and adopts an Otto Cycle in which natural gas with a relatively low pressure of 5.5 barg is injected into the inlet of the combustion air, and the piston rises to compress it.

The X-DF engine consists of two strokes, uses 15 barg of natural gas as fuel, and adopts an auto cycle.

The ME-GI engine is composed of two strokes, and adopts a diesel cycle in which high-pressure natural gas near 300 barg is injected directly into the combustion chamber near the top dead center of the piston.

1 schematically shows a conventional boil-off gas treatment system for ships.

In the conventional boil-off gas treatment system for ships as shown in FIG. 1, when the main engine ME and the power generation engine GE are provided, the boil-off gas discharged from the storage tank T is compressed by the compressor 10 It is supplied as fuel of the main engine, and when the fuel supply pressure of the power generation engine is lower than that of the main engine, the boil-off gas that has undergone a partial compression process of the compressor 10 is branched from the middle and supplied as fuel of the power generation engine GE.

Among the boil-off gas supplied to the compressor 10, the remaining boil-off gas is supplied as fuel for the main engine and power generation engine, and the remaining boil-off gas is supplied to the heat exchanger 20, and is cooled through heat exchange with the boil-off gas discharged from the storage tank T. .

The boil-off gas cooled in the heat exchanger 20 is depressurized by the decompression device 30 and partially re-liquefied, and the re-liquefied liquefied gas and the boil-off gas remaining in a gaseous state are supplied to the gas-liquid separator 40 and phase separated. .

The liquefied gas separated by the gas-liquid separator 40 is supplied to the storage tank T and stored again, and the gaseous evaporative gas separated by the gas-liquid separator 40 joins the boil-off gas discharged from the storage tank T. It is introduced into the heat exchanger 20 as a refrigerant.

In this way, the boil-off gas is reliquefied by using the boil-off gas itself as a refrigerant without a separate refrigerant. The boil-off gas compressed by the compressor is heat-exchanged with the boil-off gas before being compressed by the compressor to cool it, and then expand it by a JT valve. The present applicant named a system for re-liquefying a part of the boil-off gas by making it a PRS (Partial Re-liquefaction System).

The present invention further improves the PRS to more effectively cool the boil-off gas to increase the reliquefaction performance and to propose a system capable of treating the boil-off gas.

According to an aspect of the present invention for solving the above-described problem, in a ship provided with a main engine and a power generation engine receiving fuel at a lower pressure than the main engine,

A boil-off gas supply line connected to the main engine from a storage tank provided on the ship to store liquefied gas;

A compressor provided in the boil-off gas supply line and receiving boil-off gas generated from the liquefied gas and compressing it at a fuel supply pressure of the main engine;

The boil-off gas is branched from the boil-off gas supply line downstream of the compressor and is connected to the storage tank, and the boil-off gas not supplied as fuel of the main engine is cooled by heat exchange with the uncompressed boil-off gas to be supplied to the compressor. A reliquefaction line for restoring into a storage tank;

A heat exchanger provided in the reliquefaction line, receiving compressed gas compressed by the compressor, and cooling through heat exchange with uncompressed boil-off gas to be supplied to the compressor along the boil-off gas supply line;

A branch line branched from the reliquefaction line at a rear end of the heat exchanger to depressurize the compressed gas and supply it to the power generation engine; And

A refrigerant supplement line branched from the branch line and connected to a front end of the heat exchanger of the boil-off gas supply line is provided.

Preferably, the system may further include a first expansion device provided in the branch line and branched at a rear end of the heat exchanger to decompress the compressed gas to be supplied to the power generation engine and supply it to the heat exchanger.

Preferably, the system may further include a second expansion device provided in the refrigerant supplement line to decompress the branched compressed gas and supply it to the uncompressed boil-off gas flow in front of the heat exchanger.

Preferably, the refrigerant supplement line is branched at a rear end of the first expansion device of the branch line, and the second expansion device further depressurizes the compressed gas depressurized by the first expansion device and supplies it to the front end of the heat exchanger. I can.

Preferably, the refrigerant supplement line is branched at a front end of the first expansion device of the branch line, and the second expansion device decompresses the compressed gas cooled in the heat exchanger and supplies it to the front end of the heat exchanger.

Preferably, in the reliquefaction line, a pressure reducing device for further cooling by depressurizing the compressed gas cooled in the heat exchanger; And a gas-liquid separator for gas-liquid separation by receiving the compressed gas depressurized by the decompression device.

Preferably, the system further comprises a flash gas line connected from the gas-liquid separator to a front end of the heat exchanger of the boil-off gas supply line, wherein the flash gas separated from the gas-liquid separator is transferred to the heat exchanger through the flash gas line. It may be joined to the uncompressed boil-off gas to be introduced.

According to another aspect of the present invention, in a ship provided with a main engine and a power generation engine receiving fuel at a lower pressure than the main engine,

Compressing the boil-off gas generated from the storage tank storing the liquefied gas in the ship with a compressor at the fuel supply pressure of the main engine,

Among the boil-off gas compressed by the compressor, the boil-off gas that is not supplied to the fuel of the main engine is cooled by heat exchange in a heat exchanger with the uncompressed boil-off gas to be introduced into the compressor, further cooled under reduced pressure, and reliquefied to the storage tank. Save again,

A part of the boil-off gas cooled at the rear end of the heat exchanger is branched and decompressed, and supplied to the power generation engine through the heat exchanger, while reducing the branched boil-off gas to join the flow of the uncompressed boil-off gas and introduced into the heat exchanger. There is provided a method for treating boil-off gas of a ship, characterized in that the refrigerant to be replenished can be supplemented.

Preferably, the boil-off gas branched from the rear end of the heat exchanger and supplied to the power generation engine is reduced by a first expansion device and supplied to the power generation engine through the heat exchanger, and the evaporation to be joined to the uncompressed boil-off gas flow The gas may be branched to the rear end of the first expansion device, further decompressed through the second expansion device, and then supplemented with a refrigerant to be introduced into the heat exchanger.

Preferably, the boil-off gas branched from the rear end of the heat exchanger and supplied to the power generation engine is reduced by a first expansion device and supplied to the power generation engine through the heat exchanger, and the evaporation to be joined to the uncompressed boil-off gas flow The gas may be branched at the front end of the first expansion device, depressurized by the second expansion device, and supplemented with a refrigerant to be introduced into the heat exchanger.

Preferably, the boil-off gas is compressed in the compressor, then cooled by heat exchange in the heat exchanger, further cooled under reduced pressure, reliquefied and re-stored in the storage tank, and flash gas generated from the re-liquefied liquefied gas May be separated and joined to the uncompressed evaporation gas to be introduced into the heat exchanger and supplied to the refrigerant of the heat exchanger.

In the system of the present invention, the evaporated gas to be reliquefied after being cooled in a heat exchanger is branched, depressurized, and supplied to the onboard power generation engine through a heat exchanger, and a part of the branched evaporated gas is decompressed and replenished with refrigerant upstream of the heat exchanger. It can improve the cooling performance and increase the reliquefaction performance. In addition, flash gas generated from the re-liquefied gas can also be supplied as a refrigerant flow upstream of the heat exchanger to increase the amount of refrigerant introduced into the heat exchanger, thereby improving the cooling performance of the heat exchanger.

In this way, the cooling heat of the boil-off gas to be supplied to the power generation engine is used in the heat exchanger, and the re-liquefied gas is effectively cooled by increasing the refrigerant of the heat exchanger through the reduced boil-off gas and flash gas, and the boil-off gas to be supplied to the power generation engine. Can be heated, increasing the energy efficiency of the system and improving the reliquefaction performance of the boil-off gas, and effectively treating the boil-off gas to secure the safety of the ship.

1 is a schematic diagram of a conventional boil-off gas treatment system.
Figure 2 is a schematic diagram of the boil-off gas treatment system of the ship according to the first embodiment of the present invention.
3 is a schematic diagram of a boil-off gas treatment system for a ship according to a second embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the object achieved by the implementation of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, the configuration and operation of a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Here, in adding reference numerals to elements of each drawing, it should be noted that only the same elements are marked with the same numerals as possible, even if they are indicated on different drawings.

Hereinafter, the ship in the present invention is all types of engines that can use liquefied gas and boil-off gas generated from liquefied gas as fuel for propulsion or power generation engines, or use liquefied gas or boil-off gas as fuel for onboard engines. These ships include LNG carriers, liquefied petroleum gas carriers, and ships with self-propelled capabilities such as LNG RV (Regasification Vessel), LNG Floating Production Storage Offloading (FPSO), and LNG Floating Storage Regasification (FSRU). It does not have propulsion capability like the unit), but may include offshore structures that are floating on the sea.

In addition, in the present invention, the liquefied gas may be transported by liquefying the gas at a low temperature, generating boil-off gas in a stored state, and may include all kinds of liquefied gas that can be used as fuel such as an engine. These liquefied gases are, for example, liquefied petrochemicals such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), Liquefied Ethylene Gas, and Liquefied Propylene Gas. It can be gas. However, in the embodiments to be described later, LPG, which is one of the representative liquefied gases, is applied as an example.

Meanwhile, the fluid flowing through each line of the present embodiments may be in any one of a liquid state, a gas-liquid mixture state, a gas state, and a supercritical fluid state, depending on the operating conditions of the system.

FIG. 2 schematically shows the boil-off gas treatment system of the ship according to the first embodiment of the present invention, and FIG. 3 schematically shows the boil-off gas treatment system of the ship according to the second embodiment of the present invention.

As shown in Figures 2 and 3, the boil-off gas treatment system of the present embodiments is provided on a ship with a main engine (ME) and a power generation engine (GE) receiving fuel at a lower pressure than the main engine. A compressor that is provided in the boil-off gas supply line (GL) connected to the main engine from the storage tank (T) that stores gas, and the boil-off gas supply line to receive boil-off gas generated from the liquefied gas and compress it to the fuel supply pressure of the main engine. (100), branched from the boil-off gas supply line at the downstream of the compressor and connected to the storage tank, and the boil-off gas that is not supplied as fuel of the main engine is cooled by heat exchange with the uncompressed boil-off gas to be supplied to the compressor and reliquefied to store tank It is a system that includes a reliquefaction line (RL) for restoring into the furnace.

The reliquefaction line RL is provided with a heat exchanger 200 that receives compressed gas compressed by a compressor and cools it through heat exchange with uncompressed boil-off gas to be supplied to the compressor along the boil-off gas supply line, and at the rear end of the heat exchanger. A branch line BL branching from the reliquefaction line to depressurize the compressed gas and supplying it to the power generation engine, and refrigerant supplement lines CLa and CLb branched from the branch line and connected to the front end of the heat exchanger of the boil-off gas supply line are provided.

In the first and second embodiments, the boil-off gas generated in the storage tank T is introduced into the compressor 100 and compressed. The compressor 100 may be provided as a multi-stage compressor in which a plurality of compressors and intermediate coolers are alternately arranged, and through these in sequence, compressing the boil-off gas to the fuel supply pressure of the main engine.

The compressor compresses the boil-off gas to the fuel supply pressure to the main engine, for example, 5.5 barg if a DF engine is provided, 15 barg if an X-DF engine is provided, and 300 barg if a ME-GI engine is provided. can do. The number of compressors and intermediate coolers constituting the multistage compressor can be changed according to the fuel supply pressure of the main engine.

According to ship regulations, the compressor that supplies fuel to the engine must be designed with redundancy in case of an emergency. Redundancy design means that when one cannot be used for reasons such as failure or maintenance, the other is replaced. It means designing to be usable. To this end, although only one set of compressors is shown in the drawings of the present embodiments, a plurality of compressors may be provided.

At the downstream of the compressor, the reliquefaction line (RL) is branched from the boil-off gas supply line and is connected to the storage tank, and the boil-off gas not supplied as fuel of the main engine is branched to the reliquefaction line and is re-liquefied and then re-stored into the storage tank. .

A heat exchanger 200 is provided in the reliquefaction line to cool all or part of the boil-off gas compressed by the compressor by heat exchange with the uncompressed boil-off gas to be supplied from the storage tank to the compressor.

Meanwhile, the heat exchanger may be provided with a printed circuit heat exchanger (PCHE) or a direct contact type heat exchanger (DCHE). The boil-off gas to be introduced into the heat exchanger may be introduced into the heat exchanger after removing the lubricating oil mixed in the compression process through an oil filter (not shown).

In the system of the present embodiments, a branch line BL branched from the reliquefaction line is provided to reduce the boil-off gas compressed by the compressor and cooled in the heat exchanger to be supplied to the power generation engine (GE) receiving lower pressure fuel than the main engine. do. In particular, the evaporation gas reduced in the branch line BL is configured to be supplied to the power generation engine GE through the heat exchanger 200.

Thus, in the heat exchanger 200 in the system of the first and second embodiments, the compressed boil-off gas to be re-liquefied in the re-liquefaction line RL, and the boil-off gas of the branch line BL depressurized to supply to the power generation engine , Three flows of uncompressed boil-off gas from the boil-off gas supply line GL to be supplied to the compressor are heat-exchanged.

For example, the main engine is a ME-GI engine, and the power generation engine that receives lower pressure fuel is DFGE (Dual Fuel Generator Engine) or TFGE (Triple Fuel Generator Engine), and a medium-pressure engine that receives fuel with lower pressure than ME-GI engine. It can be composed of.

The evaporated gas branched to the branch line and decompressed may be heat-exchanged with the compressed gas to be reliquefied through a heat exchanger, heated, and then further heated in a heater (not shown) to be supplied to the power generation engine.

The amount of boil-off gas supplied to the power generation engine through the branch line may be about 600 to 1000 kg/h, but this may vary depending on the load of the power generation engine, and may also vary according to the configuration of the compressor.

The branch line BL is provided by branching from the reliquefaction line at the rear end of the heat exchanger, and refrigerant supplement lines CLa and CLb connected from the branch line to the front end of the heat exchanger of the boil-off gas supply line are provided. The branch line is provided with a first expansion device 300 for supplying the compressed gas to the heat exchanger by decompressing the compressed gas that is branched from the rear end of the heat exchanger and supplied to the power generation engine.

The refrigerant supplement line is provided with a second expansion device for decompressing the branched compressed gas and supplying the uncompressed evaporated gas flow at the front end of the heat exchanger. In the first and second embodiments, the branch point of the refrigerant supplement line is different from the branch line. It is composed.

As shown in FIG. 2, in the first embodiment, the refrigerant supplement line CLa is branched at the rear end of the first expansion device 300 of the branch line BL. In the first embodiment, the second expansion device 350 further depressurizes the compressed gas depressurized in the first expansion device and supplies it to the front end of the heat exchanger, whereby the flow of uncompressed evaporative gas introduced into the heat exchanger merges, so that the flow rate of the refrigerant is Can increase.

In the second embodiment of FIG. 3, the refrigerant supplement line CLb is branched at the front end of the first expansion device 300 of the branch line BL. In the second embodiment, the second expansion device 350 is a heat exchanger. The compressed gas cooled in can be decompressed and supplied to the front end of the heat exchanger.

The first and second expansion devices 300 and 350 may be configured as expansion valves such as an expander or a Joule-Thomson valve for decompressing the compressed boil-off gas. Through decompression, the boil-off gas is adiabatically expanded and cooled.

In the present embodiments, in order to supply the power generation engine with fuel at a lower pressure than the main engine, the evaporative gas reduced through the first expansion device is used in the heat exchanger so that the cold heat of the evaporated gas that has been reduced and cooled can be used for reliquefaction. Then, it is supplied to the power generation engine.

In addition, among the boil-off gas branched through the branch line BL, the boil-off gas not supplied to the power generation engine is branched from the rear end (first embodiment) or front end (second embodiment) of the first expansion device, and the second expansion device As a result, the boil-off gas supply line is expanded to the pressure at the inlet side of the heat exchanger and decompressed, and supplied to the front end of the heat exchanger of the boil-off gas supply line GL. As described above, the cooling performance of the heat exchanger can be improved by increasing the amount of the uncompressed boil-off gas flow (Cold BOG) of the boil-off gas supply line used as the refrigerant of the heat exchanger through the refrigerant supplement lines CLa and CLb.

In particular, the amount of compressed gas flow (Hot BOG) in the reliquefaction line in the heat exchanger is large, making it difficult to sufficiently cool by cold heat of the uncompressed boil-off gas flow (Cold BOG) in the boil-off gas supply line. In an operating section in which the low-pressure cold-heat ratio is relatively high, the refrigerant refrigerant of the heat exchanger can be replenished through the refrigerant supplement line and the second expansion device, thereby improving the cooling performance and the re-liquid performance of the heat exchanger.

On the other hand, the reliquefaction line RL is provided with a decompression device 400 for further cooling by decompressing the compressed gas cooled in the heat exchanger, and a gas-liquid separator 500 for gas-liquid separation by receiving the compressed gas depressurized by the decompression device.

The pressure reducing device 400 may be configured as an expander or an expansion valve such as a Joule-Thomson valve for reducing the compressed boil-off gas.

The liquid separated by the gas-liquid separator 500, that is, the liquefied gas is re-stored in a storage tank along the re-liquefaction line RL.

The flash gas line FL is connected from the gas-liquid separator to the front end of the heat exchanger of the boil-off gas supply line. Through the flash gas line, the gas separated by the gas-liquid separator, that is, the flash gas may be introduced into the heat exchanger as a refrigerant by joining the uncompressed evaporated gas to be introduced into the heat exchanger.

As described above, in the present embodiments, in a ship equipped with a main engine and a power generation engine receiving fuel at a lower pressure than the main engine, the boil-off gas generated from the storage tank in which the liquefied gas is stored is used as a compressor to the fuel supply pressure of the main engine. The compressed boil-off gas, which is not supplied as fuel of the main engine, is cooled by heat exchange with the uncompressed boil-off gas to be introduced into the compressor, and is further cooled under reduced pressure and reliquefied and stored in a storage tank while heat exchange. Part of the evaporated gas cooled at the rear end of the machine is branched and decompressed. After using cold heat through a heat exchanger again, it is supplied to the power generation engine, and the branched evaporated gas is decompressed to join the flow of uncompressed evaporation gas to refrigerant introduced into the heat exchanger. Make it possible to supplement.

Through this, it is possible to more effectively cool the gas to be reliquefied by using the cold heat of the boil-off gas to be supplied to the power generation engine, and to supplement the refrigerant introduced into the heat exchanger to increase the cooling performance of the heat exchanger and to increase the re-liquefaction rate of the boil-off gas.

It is obvious to those of ordinary skill in the art that the present invention is not limited to the above embodiments, and can be implemented with various modifications or variations within the scope of the technical gist of the present invention. I did it.

T: storage tank
ME: main engine
GE: Power generation engine
GL: Boil-off gas supply line
RL: Reliquefaction line
BL: branch line
CL: refrigerant supplement line
FL: flash gas line
100: compressor
200: heat exchanger
300: first expansion device
350: second expansion device
400: pressure reducing device
500: gas-liquid separator

Claims (11)

In a ship equipped with a main engine and a power generation engine that receives fuel at a lower pressure than the main engine,
A boil-off gas supply line connected to the main engine from a storage tank provided on the ship to store liquefied gas;
A compressor provided in the boil-off gas supply line and receiving boil-off gas generated from the liquefied gas and compressing it at a fuel supply pressure of the main engine;
The boil-off gas is branched from the boil-off gas supply line downstream of the compressor and is connected to the storage tank, and the boil-off gas not supplied to the main engine is cooled by heat exchange with the uncompressed boil-off gas to be supplied to the compressor and re-liquefied. A reliquefaction line for restoring into a storage tank;
A heat exchanger provided in the reliquefaction line, receiving compressed gas compressed by the compressor, and cooling through heat exchange with uncompressed boil-off gas to be supplied to the compressor along the boil-off gas supply line;
A branch line branching from the reliquefaction line at a rear end of the heat exchanger to depressurize the compressed gas and supply it to the power generation engine; And
Including; a refrigerant supplement line branched from the branch line and connected to a front end of the heat exchanger of the boil-off gas supply line,
A decompression device for additionally cooling the compressed gas cooled in the heat exchanger to the reliquefaction line; And a gas-liquid separator for gas-liquid separation by receiving the compressed gas depressurized by the decompression device,
The branch line is branched from the reliquefaction line between the heat exchanger and the decompression device. The method of claim 1,
A first expansion device provided in the branch line and branched at a rear end of the heat exchanger to decompress the compressed gas to be supplied to the power generation engine and supply it to the heat exchanger. The method of claim 2,
A second expansion device provided in the refrigerant supplement line and decompressing the branched compressed gas to supply the uncompressed boil-off gas flow at the front end of the heat exchanger. The method of claim 3,
The refrigerant supplement line is branched at a rear end of the first expansion device of the branch line, and the second expansion device further depressurizes the compressed gas depressurized by the first expansion device and supplies it to a front end of the heat exchanger. The boil-off gas treatment system of the ship. The method of claim 3,
The refrigerant supplement line is branched at a front end of the first expansion device of the branch line, and the second expansion device depressurizes the compressed gas cooled in the heat exchanger and supplies it to the front end of the heat exchanger. Gas treatment system. delete The method according to claim 4 or 5,
A flash gas line connected from the gas-liquid separator to the front end of the heat exchanger of the boil-off gas supply line; further comprising,
The flash gas separated by the gas-liquid separator is combined with the uncompressed boil-off gas to be introduced into the heat exchanger through the flash gas line. In a ship equipped with a main engine and a power generation engine that receives fuel at a lower pressure than the main engine,
Compressing the boil-off gas generated from the storage tank storing the liquefied gas in the ship with a compressor at the fuel supply pressure of the main engine,
Among the boil-off gas compressed by the compressor, the boil-off gas that is not supplied to the fuel of the main engine is cooled by heat exchange in a heat exchanger with the uncompressed boil-off gas to be introduced into the compressor, further cooled under reduced pressure, and reliquefied to the storage tank. Save again,
The boil-off gas is compressed in the compressor, then cooled by heat exchange in the heat exchanger, further cooled under reduced pressure, reliquefied and re-stored in the storage tank, and flash gas generated from the reliquefied liquefied gas is separated and the It is joined to the uncompressed evaporation gas to be introduced into the heat exchanger and supplied to the refrigerant of the heat exchanger,
A part of the boil-off gas cooled at the rear end of the heat exchanger is branched and decompressed, and supplied to the power generation engine through the heat exchanger, while reducing the branched boil-off gas to join the flow of the uncompressed boil-off gas and introduced into the heat exchanger. Boil-off gas treatment method of a ship, characterized in that the refrigerant to be replenished. The method of claim 8,
The boil-off gas to be branched from the rear end of the heat exchanger and supplied to the power generation engine is reduced by a first expansion device and supplied to the power generation engine through the heat exchanger,
The boil-off gas to be joined to the uncompressed boil-off gas flow is branched to the rear end of the first expansion device, is further depressurized through a second expansion device, and is then supplemented with refrigerant to be introduced into the heat exchanger. Processing method. The method of claim 8,
The boil-off gas to be branched from the rear end of the heat exchanger and supplied to the power generation engine is reduced by a first expansion device and supplied to the power generation engine through the heat exchanger,
The boil-off gas to be joined to the flow of the uncompressed boil-off gas is branched from the front end of the first expansion device, depressurized by a second expansion device, and supplemented with a refrigerant to be introduced into the heat exchanger. . delete

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