KR102033538B1 - Boil-Off Gas Reliquefaction System and Method for Ship - Google Patents

Abstract

Disclosed are a boil-off gas reliquefying system and method for a ship. The boil-off gas reliquefying system for the ship according to the present invention comprises: a compressor receiving boil-off gas, generated from a liquefied gas stored in a storage tank arranged in a ship, to compress the boil-off gas to a fuel supply pressure of the main engine arranged in the ship; a heat exchanger receiving a portion of the gas compressed by the compressor to cool the compressed gas by exchanging heat with a non-compressed boil-off gas to be supplied from the storage tank to the compressor; a reliquefying unit receiving the compressed gas cooled by the heat exchanger to additionally cool and reliquefy the compressed gas; a compander compressor receiving another portion of the gas compressed by the compressor, additionally compressing the received gas and introducing the gas into the heat exchanger; and a compander expander receiving the compressed gas cooled through the heat exchanger after being additionally compressed by the compander compressor and expanding and cooling the compressed gas, wherein the compander compressor is connected to the compander expander to additionally compress the compressed gas by the expansion energy of the compressed gas, and the compressed gas expanded and cooled by the compander expander is joined with the flow of non-compressed boil-off gas supplied to the heat exchanger to be supplied as a coolant of the heat exchanger. The present invention can more effectively cool the boil-off gas to enhance the reliquefying rate.

Description

Boil-Off Gas Reliquefaction System and Method for Ship

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

Recently, the consumption of liquefied gas such as liquefied natural gas (Liquefied Natural Gas, LNG) is increasing worldwide. Liquefied gas liquefied gas at low temperature has the advantage that the storage and transport efficiency can be improved because the volume is very small compared to the gas. In addition, liquefied gas, including liquefied natural gas can remove or reduce air pollutants during the liquefaction process, it can be seen as an environmentally friendly fuel with less emissions of air pollutants during combustion.

Liquefied natural gas is a colorless and transparent liquid obtained by liquefying natural gas containing methane as a main component at about -163 ℃ and having a volume of about 1/600 compared to natural gas. Therefore, when liquefied and transported natural gas can be transported very efficiently.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -162 ℃ at normal pressure, liquefied natural gas is sensitive to temperature changes and easily evaporated. As a result, the storage tank storing the liquefied natural gas is insulated. However, since the external heat is continuously transferred to the storage tank, the natural gas is continuously vaporized in the storage tank during the transport of the liquefied natural gas. -Off Gas, BOG) occurs.

Boil-off gas is a kind of loss and is an important problem in transportation efficiency. In addition, when boil-off gas is accumulated in the storage tank, the internal pressure of the tank may be excessively increased, and there is also a risk that the tank may be damaged. Accordingly, various methods for treating the boil-off gas generated in the storage tank have been studied. In recent years, for the treatment of the boil-off gas, a method of re-liquefying the boil-off gas to return to the storage tank, and returning the boil-off gas to a fuel such as an engine of a ship The method used as an energy source of a consumer is used.

As a method for reliquefaction of the boil-off gas, a refrigeration cycle using a separate refrigerant is provided to re-liquefy the boil-off gas by exchanging it with the refrigerant, a method of re-liquefying the boil-off gas itself as a refrigerant without a separate refrigerant, and the like. There is this.

On the other hand, among the engines generally used in ships as a fuel that can use natural gas as a fuel gas engines such as DFDE, X-DF engine, ME-GI engine.

DFDE is composed of four strokes and adopts the Otto Cycle, which injects natural gas with a relatively low pressure of about 5.5 bar into the combustion air inlet and compresses the piston as it rises.

The X-DF engine consists of two strokes, uses about 16 bar of natural gas as fuel, and employs an auto cycle.

The ME-GI engine is composed of two strokes and employs a diesel cycle that directly injects high pressure natural gas near 300 bar into the combustion chamber near the top dead center of the piston.

The present applicant is a method of reliquefaction of the boil-off gas by using the boil-off gas itself as a refrigerant without a separate refrigerant, and after cooling the boil-off gas compressed by the compressor by heat-exchanging with the boil-off gas before being compressed by the compressor, Invented a method of expanding to re-liquefy a portion of the boil-off gas, such a system is called PRS (Partial Re-liquefaction System).

When there is a large amount of liquefied gas inside the storage tank and the amount of boil-off gas is generated, when the vessel is anchored or when the vessel is operated at a low speed and there is a small amount of boil-off gas used in the engine. However, the PRS alone may not satisfy the required amount of reliquefaction, and the present inventors have invented a technique of improving the PRS to reliquefy more of the boil-off gas.

As an improved technology of PRS, a system that can further cool the boil-off gas by the refrigerant cycle using the boil-off gas itself as a refrigerant is called MRS (Methane Refrigeration System).

The present invention further intends to propose a system that can enhance the reliquefaction performance by cooling the boil-off gas to be effectively reliquefied without additionally providing a refrigerant heat exchanger like MRS.

According to an aspect of the present invention for solving the above problems is a compressor for receiving the boil-off gas generated from the liquefied gas stored in the storage tank of the vessel to compress the fuel supply pressure of the main engine provided in the vessel;

A heat exchanger receiving a portion of the compressed gas compressed by the compressor and cooling the uncompressed evaporated gas to be supplied to the compressor from the storage tank by heat exchange;

A reliquefaction unit receiving the compressed gas cooled by the heat exchanger and further cooling the reliquefaction unit;

A compander compressor which receives another part of the compressed gas compressed by the compressor and further compresses and introduces the compressed gas into the heat exchanger; And

And a compander expander for expanding and cooling the compressed gas supplied through the heat exchanger after the additional compression in the compander compressor.

The compander compressor is connected to the compander expander to further compress the compressed gas by the expansion energy of the compressed gas,

The compressed gas expanded and cooled in the compander expander is joined to the uncompressed boil-off gas supplied from the storage tank to the heat exchanger and supplied to the refrigerant of the heat exchanger. A system is provided.

Preferably, the reliquefaction unit, a pressure reduction device for receiving the compressed gas cooled by the heat exchanger to reduce the pressure to cool; And a gas-liquid separator for receiving the compressed gas cooled by the decompression device and separating the gas-liquid, wherein the liquid separated in the gas-liquid separator is supplied to the storage tank, and the separated gas is introduced into the heat exchanger from the storage tank. It can be joined to the uncompressed evaporated gas.

Preferably, the system comprises a boosting compressor provided between the compressor and the heat exchanger to receive the compressed gas to be reliquefied through the heat exchanger and the reliquefaction unit after compression, and further compress and introduce the compressed gas into the heat exchanger; And a cooler provided between the compander compressor and the heat exchanger to cool the compressed gas and introduce the compressed gas into the heat exchanger.

The compressor, the main compressor for compressing the boil-off gas to the fuel supply pressure of the main engine; And a redundancy compressor provided in parallel with the main compressor.

Preferably, in the system, only one of the main compressor and the redundancy compressor can be driven or driven simultaneously.

According to another aspect of the invention, the evaporation gas supply line is provided to the main engine of the vessel from a storage tank provided in the vessel for storing liquefied gas;

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

Downstream of the compressor, branched from the boil-off gas supply line and connected to the storage tank, the compressed gas remaining as fuel of the main engine is cooled and reliquefied by heat exchange with uncompressed boil-off gas to be supplied to the compressor. A reliquefaction line for restoring to a storage tank;

A heat exchanger provided in the reliquefaction line to cool the compressed gas by heat exchange with the uncompressed evaporated gas to be supplied from the storage tank to the compressor along the boil-off gas supply line;

A refrigerant refill line branched from the boil-off gas supply line downstream of the compressor and connected to the front end of the heat exchanger of the boil-off gas supply line; And

A compressor provided in the refrigerant supplementing line and compressed by the compressor and branched to the refrigerant supplementing line to further compress and introduce the compressed gas into the heat exchanger, and expand and cool the compressed gas cooled through the heat exchanger. ,

The compander provides a boil-off gas reliquefaction system, characterized in that for further compressing the compressed gas by the expansion energy of the compressed gas.

Preferably, the compander includes: a compander compressor which is compressed by the compressor and receives the compressed gas branched to the refrigerant replenishment line to further compress and introduce the compressed gas into the heat exchanger; And a compander expander configured to receive the compressed gas cooled through a heat exchanger after expansion of the compander compressor, and expand and cool the compressed gas, wherein the compander compressor is connected to the compander expander and the shaft to expand the compressed gas. It can be driven by receiving energy.

Preferably, the reliquefaction line, the pressure reduction device for receiving the compressed gas cooled by the heat exchanger to reduce the pressure to cool; And a gas-liquid separator for receiving the compressed gas cooled by the decompression device and separating the gas-liquid, wherein the liquid separated in the gas-liquid separator is supplied to the storage tank along the reliquefaction line, and the separated gas is supplied from the storage tank. The uncompressed evaporated gas introduced into the heat exchanger may be joined.

Preferably, the system comprises: a boosting compressor provided upstream of the heat exchanger in the reliquefaction line to receive the compressed gas to be reliquefied through the heat exchanger after compression and to further compress and introduce the compressed gas into the heat exchanger; And a cooler provided between the compander compressor and the heat exchanger in the refrigerant supplement line to cool the compressed gas to be introduced into the heat exchanger.

Preferably, the compressor, the main compressor for compressing the boil-off gas to the fuel supply pressure of the main engine; And a redundancy compressor provided in parallel with the main compressor.

Preferably, in the system, the boil-off gas supply line is branched in front of the main compressor and the redundancy compressor and joined after the main compressor and the redundancy compressor, and in the boil-off gas supply line, the rear end of the main compressor, the redundancy compressor and A first valve provided between the confluence points of the first valves; A second valve provided between the rear end of the redundancy compressor and the confluence point in the boil-off gas supply line; And a third valve provided upstream of the compander compressor in the refrigerant supplement line.

Preferably a system is provided with a linkage line connecting the rear end of the main compressor and the redundancy compressor upstream of the confluence point of the boil-off gas supply line, from the linkage line to a rear end of the third valve of the refrigerant refill line. A fourth valve provided with a connection line and provided between the main compressor and a branch point of the connection line in the interlocking line; And a fifth valve provided between the redundancy compressor and the branch point of the connection line in the interlocking line.

According to another aspect of the present invention, by compressing the boil-off gas generated from the storage tank provided in the vessel for storing the liquefied gas to the fuel supply pressure of the main engine in the compressor,

A part of the compressed gas is branched downstream of the compressor, the uncompressed evaporated gas to be supplied to the compressor and the heat exchanger are cooled by heat exchange in a heat exchanger to be re-liquefied, and then stored in the storage tank.

The uncompressed evaporated gas to be supplied to the compressor from the storage tank by branching the part of the compressed gas compressed by the compressor and further compressing it in a compander to be introduced into the heat exchanger to be cooled, and expanding and cooling the cooled compressed gas. Provided is a method of treating a boil-off gas of a ship, characterized in that to be supplied to the refrigerant of the heat exchanger.

Preferably, the compander may further compress the compressed gas by the expansion energy of the compressed gas.

In the system of the present invention, a portion of the compressed boil-off gas may be compressed, cooled, and expanded to be supplied upstream of the heat exchanger, thereby increasing the flow rate of the refrigerant introduced into the heat exchanger.

In this way, by increasing the refrigerant flow rate of the heat exchanger, it is possible to more effectively cool the boil-off gas to be reliquefied to increase the reliquefaction rate.

In addition, by applying the expander to use the expansion energy of the compressed gas to further compress the boil-off gas to be supplemented with the refrigerant, it is possible to reduce the use of power consumed to further compress the boil-off gas, and to increase the energy efficiency of the vessel have.

Meanwhile, since the boil-off gas to be reliquefied is further compressed by the boosting compressor, and the boil-off gas to be supplemented with the refrigerant is further compressed by the expansion energy of the compressed gas by the compander, the compressor compresses the boil-off gas by the fuel supply pressure of the main engine in the ship. It can be designed to reduce the motor size and reduce the power required by the compressor.

1 is a schematic diagram of a boil-off gas reliquefaction system according to a first embodiment of the present invention.
2 is a schematic diagram of a boil-off gas reliquefaction system according to a second embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, the configuration and operation of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Here, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are denoted by the same reference numerals as much as possible even if displayed on different drawings.

In the present invention, the vessel is equipped with an engine capable of using liquefied gas and evaporated gas generated from liquefied gas as a fuel of a propulsion or power generation engine, or all kinds of using liquefied gas or evaporated gas as fuel for an onboard engine. Vessels, including LNG carriers, liquid hydrogen carriers, and self-propelled vessels such as LNG Regasification Vessels, LNG Floating Production Storage Offloading (FPSO), and LNG Floating Storage Regasification Unit (FSRU). It may also include offshore structures that are not propelling but are floating on the sea.

In addition, in the present invention, the liquefied gas may include all kinds of liquefied gas that can be transported by liquefying the gas at a low temperature, generate evaporated gas in a stored state, and be used as a fuel such as an engine. Such liquefied gas is, for example, liquefied petrochemical such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), Liquefied Ethylene Gas, Liquefied Propylene Gas, etc. It may be a gas. However, in the following embodiment, it will be described with an example that LPG which is one of the representative liquefied gas is applied.

Meanwhile, the fluid flowing through each line of the embodiments may be in any one of a liquid state, a gas-liquid mixed state, a gas state, and a supercritical fluid state according to operating conditions of the system.

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

As shown in Figures 1 and 2, the system of the first and second embodiments, the evaporation gas supply line (GL) connected to the main engine of the vessel from the storage tank (T) provided in the vessel to store the liquefied gas Compressor 100, which is provided in the boil-off gas supply line and receives the boil-off gas generated from the liquefied gas and compresses it to the fuel supply pressure of the main engine, branched from the boil-off gas supply line downstream of the compressor, is connected to the storage tank, The reliquefaction line (RL) which cools, reliquefies and re-stores the uncompressed evaporated gas to be supplied to the compressor and heat exchange with the uncompressed evaporated gas to be supplied to the compressor, and re-stores it as a storage tank, It comprises a heat exchanger 200 for cooling by the heat exchange with the uncompressed evaporated gas to be supplied to the compressor from the storage tank along the boil-off gas supply line.

The system of the first and second embodiments further comprises a refrigerant supplement line (CL) which is branched from the boil-off gas supply line downstream of the compressor and connected to the front end of the heat exchanger of the boil-off gas supply line, The compressed gas branched into the refrigerant supplementing line is further compressed to be introduced into the heat exchanger, and a compander 400 for expanding and cooling the compressed gas cooled through the heat exchanger may be configured to increase the flow rate of the refrigerant introduced into the heat exchanger. It was configured to be. In this way, by increasing the flow rate of the refrigerant (cold BOG) of the heat exchanger, it is possible to more efficiently cool the evaporated gas to be reliquefied to increase the reliquefaction rate.

In this embodiment, the compander further compresses the compressed gas by the expansion energy of the compressed gas, thereby reducing power consumption for further compression of the compressed gas.

The compander 400 is compressed by the compressor and supplied with a compressed gas branched to the refrigerant supplement line, and further compressed to be introduced into the heat exchanger, and the compressor is cooled through the heat exchanger after the additional compression in the compressor. The compressor includes a compander expander 420 for expanding and cooling the compressed gas, and the compander compressor is connected to the shaft of the compander expander so as to be driven by receiving the expansion energy of the compressed gas.

A cooler 450 may be provided between the compander compressor and the heat exchanger in the refrigerant supplement line CL to cool the compressed gas to be introduced into the heat exchanger 200.

On the other hand, the heat exchanger may be provided as a PCHE (Printed Circuit Heat Exchanger) type. The evaporated gas to be introduced into the heat exchanger may be introduced into the heat exchanger after removing the lubricating oil mixed through the oil filter (not shown).

Meanwhile, a reliquefaction unit is provided in the reliquefaction line RL, and the reliquefaction unit receives a compressed gas cooled by a heat exchanger to depressurize and cool it, and receives a compressed gas cooled by a decompression device. A gas-liquid separator 320 for separating is provided.

The decompression device 310 may be configured as an expansion valve such as an expander or Joule-Thomson valve for adiabatic expansion and cooling of the compressed and cooled boil-off gas.

The boil-off gas compressed, cooled, and expanded-cooled through a compressor, a heat exchanger, and a decompression device is re-liquefied in whole or in part to be introduced into the gas-liquid separator 320. It is possible to dissolve the liquefied natural gas stored in the storage tank by directing the additional cooled evaporated gas directly to the storage tank without decomposing the gas-liquid separator and depressurizing the pressure reducing device.

The liquid separated in the gas-liquid separator is supplied to and stored in the storage tank along the reliquefaction line (RL), and the separated gas is joined to the boil-off gas supply line (GL) together with the uncompressed evaporated gas introduced into the heat exchanger from the storage tank. The refrigerant may be supplied to the heat exchanger.

Upstream of the heat exchanger in the reliquefaction line is provided with a boosting compressor 500 for receiving a compressed gas to be reliquefied through the heat exchanger after compression to further compress and introduce into the heat exchanger.

For methane, the main component of LNG, the critical point is about -80 ° C and 55 bar. When reliquefaction of the boil-off gas generated in LNG, the higher the compression pressure of the boil-off gas, the higher the re-liquefaction rate, and the maximum amount of re-liquefaction when compressed to around 150 to 170 bar, but a large change in the re-liquefaction amount between 150 to 300 bar Found none. Therefore, in order to effectively reliquefy the boil-off gas, it is preferable to compress it to 100 bar or more, preferably 150 bar to 300 bar. However, if the main engine powered by the boil-off gas does not need such a high-pressure fuel, compressing all the boil-off gas to high pressure only for reliquefaction is very power consuming and wastes energy. It costs a lot. Therefore, the present invention allows the compressor to compress only the fuel supply pressure of the main engine, and to further compress the boil-off gas to be reliquefied and the boil-off gas to be replenished by the boosting compressor 500 and the compander compressor 410, respectively. .

Through this, the compressor 100 can be designed to compress the boil-off gas by the fuel supply pressure of the ship's main engine to reduce the motor size, reduce the installation cost, and reduce the operating cost by reducing the power required by the compressor.

For example, if the X-DF engine is adopted as the main engine, the compressor compresses the evaporated gas by about 16 bar and the booster compressor further compresses the compressed gas to 100 bar or more, preferably 150 bar to 170 bar. Can be.

The compressor 100 includes a main compressor 100a for compressing boil-off gas to the fuel supply pressure of the main engine, and a redundancy compressor 100b provided in parallel with the main compressor.

Compressors that supply fuel to the engine should have a redundancy design in case of emergency. Redundancy design is a replacement for another when one cannot be used due to failure, maintenance, etc. Designed to be used. To this end, in the present embodiments, the compressor is designed as a main compressor and a redundancy compressor.

The boil-off gas supply line GL is branched in front of the main compressor and the redundant compressor and then joined at the rear of the main compressor and the redundant compressor to supply the boil-off gas to the main compressor and the redundant compressor.

In the boil-off gas supply line, a first valve V1 is provided between the rear end of the main compressor and the confluence point of the redundancy compressor, and a second valve V2 is provided between the rear end of the redundancy compressor and the confluence point, respectively. A third valve V3 is provided upstream of the compander compressor in the line.

In addition to the above-described system, the system of the second embodiment shown in FIG. 2 provides an interlocking line NL for connecting the rear end of the main compressor and the redundancy compressor upstream of the confluence point of the boil-off gas supply line. The connection line (NLa) is connected to the rear end of the third valve of the refrigerant refill line from.

A fourth valve V4 is provided between the main compressor and the branch point of the connection line in the interlocking line, and a fifth valve V5 is provided between the redundancy compressor and the branch point of the connection line in the interlocking line.

In this way, the interlocking line and the connecting line may be provided, and the main compressor and the redundancy compressor may be used for supplying fuel, re-liquefying the boil-off gas, and refilling the refrigerant through opening and closing of the first to fifth valves. It can increase elasticity and increase utilization.

For example, when the second, third and fourth valves are blocked and the first and fifth valves are opened, the main compressor can supply fuel and reliquefaction evaporative gas, and the redundancy compressor can be driven to refill the refrigerant.

In case of failure or maintenance of the main compressor, the first and fourth valves may be shut off and the second, third and fifth valves may be opened to supply fuel, reliquefaction evaporative gas supply, and refrigerant replenishment.

In addition, it can be operated in various ways by opening and closing the valve according to various system conditions.

The present invention is not limited to the above embodiments, and various modifications or changes may be made without departing from the technical scope of the present invention, which will be apparent to those of ordinary skill in the art. It is.

T: storage tank
GL: Evaporative Gas Supply Line
RL: Reliquefaction Line
CL: Refrigerant Filling Line
NL: interlocking line
NLa: connection line
V1, V2, V3, V4, V5: first to fifth valves
100: compressor
100a: main compressor
100b: redundancy compressor
300: reliquefaction unit
310: decompression device
320: gas-liquid separator
400: compander
410: compander compressor
420: compander inflator
450: cooler
500: boosting compressor

Claims (14)

Compressor for receiving the boil-off gas generated from the liquefied gas stored in the storage tank provided in the vessel to compress the fuel supply pressure of the main engine provided in the vessel;
A heat exchanger that receives a portion of the compressed gas compressed by the compressor and cools the uncompressed evaporated gas to be supplied to the compressor from the storage tank by heat exchange;
A reliquefaction unit receiving the compressed gas cooled by the heat exchanger and further cooling the reliquefaction unit;
A compander compressor which receives another part of the compressed gas compressed by the compressor and further compresses and introduces the compressed gas into the heat exchanger; And
And a compander expander for expanding and cooling the compressed gas supplied through the heat exchanger after the additional compression in the compander compressor.
The compander compressor is connected to the compander expander to further compress the compressed gas by the expansion energy of the compressed gas,
The compressed gas expanded and cooled in the compander expander is joined to a flow of the uncompressed evaporated gas supplied from the storage tank to the heat exchanger and supplied to the refrigerant of the heat exchanger. system. The method of claim 1, wherein the reliquefaction unit
A decompression device for cooling by receiving the compressed gas cooled by the heat exchanger under reduced pressure; And
And a gas-liquid separator for receiving the compressed gas cooled by the decompression device and separating the gas-liquid.
The liquid separated in the gas-liquid separator is supplied to the storage tank, and the separated gas is joined to the uncompressed boil-off gas introduced into the heat exchanger from the storage tank. The method of claim 2,
A boosting compressor provided between the compressor and the heat exchanger to receive and further compress the compressed gas to be reliquefied through the heat exchanger and the reliquefaction unit after compression, and introduce the compressed gas into the heat exchanger; And
And a cooler provided between the compander compressor and the heat exchanger to cool the compressed gas and introduce the compressed gas to the heat exchanger. The method of claim 2,
The compressor, the main compressor for compressing the boil-off gas to the fuel supply pressure of the main engine; And a redundancy compressor provided in parallel with the main compressor. The method of claim 4, wherein
The main compressor and the redundancy compressor is driven only one, or can be driven simultaneously characterized in that the boil-off gas reliquefaction system of the ship. An evaporative gas supply line connected to a main engine of the vessel from a storage tank provided on the vessel and storing liquefied gas;
A compressor provided in the boil-off gas supply line and receiving the boil-off gas generated from the liquefied gas and compressing the boil-off gas to a fuel supply pressure of the main engine;
Downstream of the compressor, branched from the boil-off gas supply line and connected to the storage tank, the compressed gas remaining as a fuel of the main engine is cooled and reliquefied by heat exchange with uncompressed boil-off gas to be supplied to the compressor. Reliquefaction line for restoring to storage tank;
A heat exchanger provided in the reliquefaction line to cool the compressed gas by heat exchange with the uncompressed boil-off gas to be supplied from the storage tank to the compressor along the boil-off gas supply line;
A refrigerant refill line branched from the boil-off gas supply line downstream of the compressor and connected to the front end of the heat exchanger of the boil-off gas supply line; And
A compressor provided in the refrigerant supplementing line and compressed by the compressor and branched to the refrigerant supplementing line to further compress and introduce the compressed gas into the heat exchanger, and expand and cool the compressed gas cooled through a heat exchanger. ,
And the compander further compresses the compressed gas by the expansion energy of the compressed gas. The method of claim 6, wherein the compander
A compander compressor, which is compressed by the compressor and receives the compressed gas branched to the refrigerant supplementing line, and further compresses and introduces the compressed gas into the heat exchanger; And
And a expander expander configured to receive the compressed gas cooled through the heat exchanger after the additional compression in the expander compressor to expand and cool the compressed gas.
And the compander compressor is connected to the compander expander and the shaft to be driven by receiving the expansion energy of the compressed gas. 8. The reliquefaction line of claim 7 wherein
A decompression device for cooling by receiving the compressed gas cooled by the heat exchanger under reduced pressure;
A gas-liquid separator for receiving the compressed gas cooled by the decompression device and separating the gas-liquid;
The liquid separated in the gas-liquid separator is supplied to the storage tank along the reliquefaction line, and the separated gas is joined to the uncompressed boil-off gas introduced from the storage tank to the heat exchanger. Reliquefaction System. The method of claim 8,
A boosting compressor provided upstream of the heat exchanger in the reliquefaction line to receive the compressed gas to be reliquefied through the heat exchanger after compression and to further compress and introduce the compressed gas into the heat exchanger; And
And a cooler provided between the compander compressor and the heat exchanger in the refrigerant supplement line to cool the compressed gas and introduce the compressed gas into the heat exchanger. The method of claim 9,
The compressor, the main compressor for compressing the boil-off gas to the fuel supply pressure of the main engine; And a redundancy compressor provided in parallel with the main compressor. The method of claim 10,
The boil-off gas supply line is branched in front of the main compressor and the redundancy compressor, and then joined at the rear end of the main compressor and the redundancy compressor,
A first valve provided between the rear end of the main compressor and a confluence point of the redundancy compressor in the boil-off gas supply line;
A second valve provided between the rear end of the redundancy compressor and the confluence point in the boil-off gas supply line;
And a third valve provided upstream of the compander compressor in the refrigerant supplement line. The method of claim 11,
An interlocking line is provided to connect a rear end of the main compressor and the redundancy compressor upstream of the confluence point of the boil-off gas supply line.
A connection line is provided from the interlocking line to a rear end of the third valve of the refrigerant supplementing line.
A fourth valve provided between the main compressor and a branch point of the connection line in the interlock line; And
And a fifth valve provided between the redundancy compressor and the branch point of the connection line in the interlocking line. Compresses the evaporated gas generated from the storage tank provided in the vessel to store the liquefied gas in the compressor to the fuel supply pressure of the main engine of the vessel,
A portion of the compressed gas is branched downstream of the compressor to cool and reliquefy the uncompressed boil-off gas to be supplied to the compressor and the heat exchanger in a heat exchanger, and re-store it in the storage tank.
The uncompressed evaporated gas to be supplied to the compressor from the storage tank by branching the part of the compressed gas compressed by the compressor and further compressing the compressed gas by introducing it into the heat exchanger and cooling the expanded compressed gas. And to supply the refrigerant to the refrigerant of the heat exchanger. The method of claim 13,
And the compander further compresses the compressed gas by the expansion energy of the compressed gas.

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