KR102657771B1 - 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 for a ship according to the present invention includes a boil-off gas supply line connected from a storage tank storing liquefied gas in a ship to the main engine of the ship; A compressor provided in the boil-off gas supply line to compress the boil-off gas generated in the storage tank; A reliquefaction line branched from the boil-off gas supply line downstream of the compressor and connected to the storage tank, re-liquefies the boil-off gas that is not supplied as fuel for the main engine and stores it back in the storage tank; a heat exchanger provided in the reliquefaction line and cooling the compressed gas compressed in the compressor by heat exchange with uncompressed boil-off gas to be supplied to the compressor; A post-cooler that receives the compressed gas cooled by the heat exchanger and further cools it; And a branch line branched from the reliquefaction line at the front of the heat exchanger and connected to a power generation engine that receives lower pressure fuel than the main engine, wherein the boil-off gas branched from the branch line is decompressed and then transferred to the post-cooler. and are sequentially supplied to the power generation engine through a heat exchanger, and the flash gas and unliquefied gas generated from the reliquefied gas in the reliquefaction line pass through the postcooler and join the uncompressed boil-off gas flow at the front of the heat exchanger. It is characterized by being

Description

Boil-Off Gas Treatment System and Method for Ship {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; Boil-Off Gas) generated from liquefied gas stored in a ship using the cold heat of the boil-off gas itself.

Recently, the consumption of liquefied gas such as liquefied natural gas (LNG) is rapidly increasing worldwide. Liquefied gas, which is made by liquefying gas at low temperature, has a much smaller volume than gas, so it has the advantage of increasing storage and transportation efficiency. In addition, liquefied gas, including liquefied natural gas, can remove or reduce air pollutants during the liquefaction process, so it can be viewed as an eco-friendly fuel with low 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 by cooling it to about -162°C, and has a volume of about 1/600 of that of natural gas. Therefore, when natural gas is liquefied and transported, it can be transported very efficiently.

However, the liquefaction temperature of natural gas is extremely low at -162°C at normal pressure, so liquefied natural gas is sensitive to temperature changes and easily evaporates. For this reason, storage tanks that store liquefied natural gas are insulated, but external heat is continuously transferred to the storage tank, so during the transportation of liquefied natural gas, liquefied natural gas is continuously naturally vaporized within the storage tank, producing boil-off gas (boil). -Off Gas, BOG) occurs.

Evaporation gas is a type of loss and is an important issue in transportation efficiency. In addition, if evaporation gas accumulates in the storage tank, the pressure inside the tank may increase excessively, and in severe cases, there is a risk of tank damage. Therefore, various methods are being studied to treat boil-off gas generated within the storage tank. Recently, for the treatment of boil-off gas, a method of re-liquefying the boil-off gas and returning it to the storage tank, using the boil-off gas as fuel for ship engines, etc. Methods such as using it as an energy source for consumers are being used.

Methods for re-liquefying the boil-off gas include a method of re-liquefying the boil-off gas by heat-exchanging it with a refrigerant using a refrigeration cycle using a separate refrigerant, and a method of re-liquefying the boil-off gas itself as a refrigerant without a separate refrigerant. There is.

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

DFDE consists of a 4-stroke cycle and adopts the Otto Cycle, which injects natural gas with a relatively low pressure of about 5.5 barg into the combustion air inlet and compresses it as the piston rises.

The X-DF engine consists of a two-stroke engine, uses natural gas of about 15 barg as fuel, and adopts the Otto cycle.

The ME-GI engine consists of two strokes and adopts the diesel cycle, which injects high-pressure natural gas around 300 barg directly into the combustion chamber near the top dead center of the piston.

Figure 1 schematically shows a conventional marine boil-off gas treatment system.

As shown in Figure 1, in a conventional marine boil-off gas treatment system, when a main engine (ME) and a power generation engine (GE) are provided, the boil-off gas discharged from the storage tank (T) is compressed in the compressor (10). It is supplied as fuel for 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 in the compressor 10 is branched in the middle and supplied as fuel for the power generation engine (GE).

Among the evaporative gases supplied to the compressor 10, the surplus evaporative gases remaining after being supplied as fuel for the main engine and the power generation engine are supplied to the heat exchanger 20 and cooled through heat exchange with the evaporative gases discharged from the storage tank (T). .

The boil-off gas cooled in the heat exchanger (20) is decompressed by the pressure reducing device (30) and a part of it is re-liquefied, and the re-liquefied liquefied gas and the boil-off gas remaining in the gaseous state are supplied to the gas-liquid separator (40) and phase separated. .

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

In this way, the boil-off gas itself is used as a refrigerant without a separate refrigerant to re-liquefy the boil-off gas. The boil-off gas compressed by the compressor is cooled by heat exchange with the boil-off gas before being compressed by the compressor, and then expanded by a J-T valve, etc. The applicant named the system for re-liquefying part of the boil-off gas as PRS (Partial Re-liquefaction System).

The present invention goes further and proposes a system that improves the PRS to more effectively cool the boil-off gas, improve reliquefaction performance, and process the boil-off gas.

According to one aspect of the present invention for solving the above-described problem, a boil-off gas supply line connected from a storage tank storing liquefied gas in a ship to the main engine of the ship;

A compressor provided in the boil-off gas supply line to compress the boil-off gas generated in the storage tank;

A reliquefaction line branched from the boil-off gas supply line downstream of the compressor and connected to the storage tank, re-liquefies the boil-off gas that is not supplied as fuel for the main engine and stores it back in the storage tank;

a heat exchanger provided in the reliquefaction line and cooling the compressed gas compressed in the compressor by heat exchange with uncompressed boil-off gas to be supplied to the compressor;

A post-cooler that receives the compressed gas cooled by the heat exchanger and further cools it; and

It includes a branch line branched from the reliquefaction line at the front end of the heat exchanger and connected to a power generation engine that receives lower pressure fuel than the main engine,

The boil-off gas branched from the branch line is depressurized and then sequentially passed through the post-cooler and heat exchanger before being supplied to the power generation engine,

A ship's boil-off gas processing system is provided, wherein the flash gas and unliquefied gas generated from the re-liquefied gas in the re-liquefaction line pass through the post-cooler and join the uncompressed boil-off gas flow at the front of the heat exchanger. do.

Preferably, an expansion means provided in the branch line to depressurize the compressed boil-off gas; an additional line branching from the reliquefaction line at a rear end of the post-cooler and connected to a front end of the expansion means of the branch line; a first valve provided upstream of a confluence point of the additional line in the branch line; and a second valve provided in the additional line.

Preferably, when operating the ship, the first valve is closed and the second valve is opened to branch off the boil-off gas at the rear end of the after-cooler through the additional line and supply it to the power generation engine.

Preferably, a decompression device provided in the re-liquefaction line, receives the boil-off gas cooled by heat exchange in the heat exchanger and the post-cooler, depressurizes it, and provides additional cooling; And it may further include a gas-liquid separator that receives the additionally cooled boil-off gas from the pressure reducing device in the re-liquefaction line and separates gas-liquid.

Preferably, it further includes a flash gas line connected from the top of the gas-liquid separator to the front end of the heat exchanger of the boil-off gas supply line through the post-cooler, and the liquid separated in the gas-liquid separator is connected to the reliquefaction line. Accordingly, the flash gas and unliquefied gas separated in the gas-liquid separator are supplied to the storage tank, exchange heat in a post-cooler along the flash gas line, and then join the uncompressed boil-off gas flow at the front of the heat exchanger.

Preferably, in the heat exchanger, the compressed gas branched along the re-liquefaction line, the uncompressed boil-off gas to be supplied to the compressor along the boil-off gas supply line, and the power generation along the branch line after decompression in the expansion means. The three streams of evaporative gas to be supplied to the engine exchange heat,

In the post-cooler, three streams are used: compressed gas from the reliquefaction line cooled in the heat exchanger, boil-off gas to be supplied to the power generation engine after decompression in the expansion means, and flash gas from the flash gas line separated from the gas-liquid separator. This heat can be exchanged.

Preferably, a heater provided in the branch line to heat the liquefied gas to be supplied to the power generation engine may further include.

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

The boil-off gas generated from the storage tank where the liquefied gas is stored is compressed by a compressor to the fuel supply pressure of the main engine,

Among the boil-off gases compressed in the compressor, the boil-off gas that is not supplied as fuel for the main engine is cooled by heat exchange in a heat exchanger with the uncompressed boil-off gas to be introduced into the compressor, and is further cooled and re-liquefied in a post-cooler to be stored in the storage tank. However, the flash gas generated from the re-liquefied liquefied gas is separated and joins the uncompressed boil-off gas to be introduced into the heat exchanger through the post-cooler,

A portion of the compressed boil-off gas is branched and decompressed at the front of the heat exchanger and supplied to the power generation engine,

A method of treating boil-off gas of a ship is provided, wherein the boil-off gas depressurized to be supplied to the power generation engine is supplied to the power generation engine through the after-cooler and heat exchanger in sequence.

Preferably, when operating the ship, the boil-off gas compressed and cooled at the rear end of the after-cooler can be branched, decompressed, and supplied to the power generation engine through an after-cooler and a heat exchanger.

Preferably, the boil-off gas cooled through the heat exchanger and the post-cooler is further cooled under reduced pressure, re-liquefied, and stored again in the storage tank, and the flash gas generated from the re-liquefied liquefied gas is separated and stored in the storage tank. It can join the uncompressed boil-off gas introduced into the heat exchanger from.

In the system of the present invention, a post-cooler is configured, and a portion of the compressed boil-off gas to be re-liquefied is decompressed and supplied to the power generation engine through the post-cooler and a heat exchanger, thereby effectively cooling the re-liquefied boil-off gas to improve re-liquefaction performance. The flash gas separated from the reliquefied gas is joined to the uncompressed boil-off gas flow introduced into the heat exchanger, allowing the flash gas to be additionally supplied as a refrigerant from the heat exchanger.

In addition, the extraction point of gas to be supplied to the power generation engine can be selected depending on the operating conditions of the ship, such as when the ship is in operation or at anchor, allowing the system to be operated more efficiently and flexibly.

In this way, by using the cold heat of the boil-off gas to be supplied to the power generation engine and the cold heat of the flash gas, the gas to be reliquefied can be effectively cooled, while the boil-off gas to be supplied to the power generation engine can be heated, and the system can be operated flexibly according to the operating situation. Through this, the energy efficiency of the system can be increased, the re-liquefaction performance of boil-off gas can be improved, and the safety of the ship can be ensured by effectively processing boil-off gas.

1 is a schematic diagram of a conventional boil-off gas treatment system.
Figure 2 is a schematic diagram of a ship's boil-off gas treatment system according to an embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the objectives achieved by practicing 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 structure and operation of a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Here, in adding reference numerals to components in each drawing, it should be noted that identical components are indicated with the same reference numerals as much as possible, even if they are shown in different drawings.

Hereinafter, the ship in the present invention is any type installed with an engine that can use liquefied gas and boil-off gas generated from the liquefied gas as fuel for propulsion or power generation engines, or uses liquefied gas or boil-off gas as fuel for the ship's engines. of ships, including ships with self-propelled capabilities such as LNG carriers, liquid petroleum gas carriers, and LNG RVs (Regasification Vessels), as well as LNG FPSOs (Floating Production Storage Offloading) and LNG FSRUs (Floating Storage Regasification). Unit) may also include offshore structures that do not have propulsion capabilities but are floating in the sea.

In addition, the liquefied gas in the present invention may include all types of liquefied gas that can be transported by liquefying gas at low temperature, generate boil-off gas in a stored state, and can be used as fuel for engines, etc. 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 could be gas. However, in the examples described later, the application of LNG, one of the representative liquefied gases, will be described 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.

Figure 2 schematically shows a ship's boil-off gas treatment system according to an embodiment of the present invention.

As shown in Figure 2, the system of this embodiment is applied to a ship equipped with a main engine (ME) and a power generation engine (GE) supplied with fuel at a lower pressure than the main engine, and a storage tank (T) where liquefied gas is stored. A boil-off gas supply line (GL) is connected to the main engine of the ship, and a compressor 100 is provided in the boil-off gas supply line to compress the boil-off gas generated in the storage tank to the fuel supply pressure of the main engine.

The boil-off gas generated in the storage tank (T) is introduced into the compressor 100 along the boil-off gas supply line and compressed. The compressor 100 may be configured as a multi-stage compressor in which a plurality of compressors and an intercooler are alternately arranged and sequentially compress the boil-off gas to the fuel supply pressure of the main engine.

The compressor compresses the evaporative gas to the fuel supply pressure of the main engine, for example, 5.5 barg for a DF engine, 15 barg for an X-DF engine, and 300 barg for a ME-GI engine. can do. The number of compressors and intercoolers that make up the multi-stage compressor can be changed depending on the fuel supply pressure of the main engine.

According to ship regulations, compressors that supply fuel to engines must be designed with redundancy in preparation for emergency situations. Redundancy design means that when one compressor cannot be used due to breakdown, maintenance, etc., the compressor that supplies fuel to the engine must be designed with redundancy in place of the other compressor. This means designing it so that it can be used. For this purpose, only one set of compressors is shown in the drawing of this embodiment, but a plurality of compressors may be provided.

Downstream of the compressor 100, the re-liquefaction line (RL) branches off from the boil-off gas supply line (GL) and connects to the storage tank, and re-liquefies the boil-off gas that is not supplied as fuel for the main engine and stores it in the storage tank. . The reliquefaction line (RL) includes a heat exchanger (200) that cools the compressed gas compressed in the compressor by heat exchange with the uncompressed boil-off gas to be supplied to the compressor, and a post-cooler (200) that receives the compressed gas cooled in the heat exchanger and further cools it ( 300) is prepared.

In the heat exchanger 200, all or part of the boil-off gas compressed in the compressor is cooled by heat exchange with uncompressed boil-off gas to be supplied to the compressor from the storage tank.

The heat exchanger can be provided as a Printed Circuit Heat Exchanger (PCHE) or 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 passing through an oil filter (not shown) to remove lubricating oil mixed in during the compression process.

The evaporation gas cooled in the heat exchanger is further cooled through heat exchange in the post-cooler 300. Gas to be supplied to the power generation engine and flash gas are used as refrigerants to cool the boil-off gas to be reliquefied in the post-cooler, which will be described later.

Meanwhile, the re-liquefaction line RL is provided with a re-liquefaction unit 400 that additionally cools and re-liquefies the cooled boil-off gas through a heat exchanger and a post-cooler. The reliquefaction unit includes a decompression device (410) that receives the boil-off gas cooled by heat exchange from the heat exchanger and the post-cooler, decompresses it, and further cools it, and a gas-liquid separator (420) that receives the additionally cooled boil-off gas from the decompression device and separates gas and liquid. It can be included.

The pressure reducing device 410 may be composed of an expansion valve such as an expander or Joule-Thompson valve that depressurizes the compressed boil-off gas, and the boil-off gas is isentropically expanded or adiabatically expanded through decompression and cooled.

The boil-off gas that has been compressed, cooled, and expansion-cooled through the compressor 100, heat exchanger 200, post-cooler 300, and pressure reduction device 410 is re-liquefied in whole or in part and introduced into the gas-liquid separator 420.

At the top of the gas-liquid separator, a flash gas line (FL) is provided that connects to the front end of the heat exchanger of the boil-off gas supply line through the post-cooler.

The liquid separated from the gas-liquid separator is supplied to the storage tank (T) along the re-liquefaction line (RL), and the flash gas and unliquefied gas separated from the gas-liquid separator are supplied to the post-cooler (300) along the flash gas line (FL). After being used as a refrigerant, it may join the uncompressed boil-off gas flow at the front of the heat exchanger and be introduced as a refrigerant into the heat exchanger.

In this embodiment, in particular, fuel is supplied to the power generation engine (GE), which receives lower pressure fuel than the main engine through a branch line (BL) branched from the reliquefaction line at the front of the heat exchanger, and the boil-off gas branched from the branch line The pressure is reduced through the expansion means 500 provided in the branch line, and then sequentially passed through the post-cooler 300 and the heat exchanger 200 and supplied to the power generation engine (GE).

In this way, the boil-off gas branched out to be supplied to the power generation engine is decompressed and supplied to the power generation engine through a post-cooler and heat exchanger, and the flash gas separated from the gas-liquid separator is also supplied to the front of the heat exchanger through a post-cooler, thereby forming a heat exchanger ( In 200), there are three streams of compressed gas to be branched and re-liquefied along the re-liquefaction line, uncompressed boil-off gas to be supplied to the compressor along the boil-off gas supply line, and boil-off gas to be supplied to the power generation engine along the branch line after decompression in the expansion means. This heat is exchanged, and in the post-cooler 300, there are three flows: compressed gas from the re-liquefaction line cooled in the heat exchanger, boil-off gas to be supplied to the power generation engine after decompression in the expansion means, and flash gas from the flash gas line separated from the gas-liquid separator. Heat can be exchanged.

Since the boil-off gas to be supplied to the power generation engine is branched at the front of the heat exchanger, the flow rate of boil-off gas to be cooled in the heat exchanger (boil-off gas to be re-liquefied, hot BOG) is reduced, allowing for more effective cooling of the boil-off gas to be re-liquefied. .

In addition, by configuring an additional post-cooler and using the cold heat of the boil-off gas to be supplied to the power generation engine and the cold heat of the flash gas to cool the boil-off gas to be re-liquefied, the gas to be re-liquefied is cooled more effectively, improving the re-liquefaction performance. It can be increased, and the boil-off gas to be supplied to the power generation engine can be heated, allowing efficient use of heat energy in the system.

For example, the main engine is the ME-GI engine, and the power generation engine supplied with lower-pressure fuel is the DFGE (Dual Fuel Generator Engine) or TFGE (Triple Fuel Generator Engine), and the medium-pressure engine supplied with lower-pressure fuel than the ME-GI engine. It can be configured as:

The branch line (BL) is additionally provided with a heater 600 that heats the liquefied gas to be supplied to the power generation engine, and the boil-off gas heated through the aftercooler and heat exchanger is additionally heated according to the fuel supply conditions of the power generation engine. can be supplied.

The amount of boil-off gas supplied to the power generation engine through the branch line may vary depending on the load of the power generation engine, compressor configuration, etc.

Meanwhile, in the system of this embodiment, an additional line (AL) is additionally provided that branches off from the reliquefaction line at the rear end of the post-cooler and connects to the front end of the expansion means of the branch line, and an additional line (AL) is provided upstream of the confluence point of the additional line in the branch line. One valve (V1) may be provided in the additional line, and a second valve (V2) may be provided in each additional line.

Accordingly, the opening/closing and opening degrees of the first and second valves are adjusted according to the ship's operating conditions to enable fuel to be supplied to the power generation engine from the front end of the heat exchanger or the rear end of the post-cooler.

For example, when the ship is docked, the first valve (V1) is opened and the second valve (V2) is closed, the boil-off gas is branched at the front of the heat exchanger through the branch line (BL), and the pressure is reduced by the expansion means (500). , the boil-off gas cooled by reduced pressure is supplied to the power generation engine (GE) through the post-cooler 300 and the heat exchanger 200, and when the ship is in operation, the first valve (V1) is closed and the second valve (V2) is opened. By opening the additional line (AL), the boil-off gas can be branched at the rear of the post-cooler, decompressed, and then supplied to the power generation engine through the post-cooler and heat exchanger.

When a ship is anchored, there is no or little boil-off gas supplied as fuel for the main engine, so the amount of boil-off gas to be re-liquefied through the re-liquefaction line increases. Therefore, if the boil-off gas flow (Hot BOG) in the reliquefaction line increases relative to the uncompressed boil-off gas flow (Cold BOG) in the boil-off gas supply line used as a refrigerant in the heat exchanger, it is possible to effectively cool the boil-off gas to be reliquefied. Therefore, in this case, the amount of hot BOG passing through the heat exchanger can be reduced by opening the first valve to branch off the boil-off gas at the front of the heat exchanger in the reliquefaction line and supply it to the power generation engine through the branch line.

Under ship operating conditions, there is a lot of boil-off gas supplied as fuel for the main engine, so the amount of boil-off gas to be reliquefied is relatively small. As the amount of cold BOG in the heat exchanger increases, the amount of hot BOG decreases. Therefore, in this case, the hot BOG can be sufficiently cooled by the cold heat of the uncompressed boil-off gas Cold BOG, so the boil-off gas can be branched through an additional line at the rear of the post-cooler and supplied to the power generation engine by closing the first valve and opening the second valve. there is.

In this way, the extraction point of the gas to be supplied to the power generation engine can be selected depending on the ship's operating conditions, allowing the system to be operated more efficiently and flexibly.

It is obvious to those skilled in the art that the present invention is not limited to the above-mentioned embodiments, and that it can be implemented with various modifications or variations without departing from the technical gist of the present invention. It was done.

T: storage tank
ME: main engine
GE: Power generation engine
GL: Evaporative gas supply line
RL: Reliquefaction line
BL: branch line
AL: Additional line
FL: Flash gas line
100: Compressor
200: heat exchanger
300: Post-cooler
400: Reliquefaction unit
410: Pressure reducing device
420: Gas-liquid separator
500: expansion means
600: heater
V1: first valve
V2: Second valve

Claims (10)

A boil-off gas supply line connected from a storage tank storing liquefied gas in a ship to the main engine of the ship;
A compressor provided in the boil-off gas supply line to compress the boil-off gas generated in the storage tank;
A reliquefaction line branched from the boil-off gas supply line downstream of the compressor and connected to the storage tank, re-liquefies the boil-off gas that is not supplied as fuel for the main engine and stores it back in the storage tank;
a heat exchanger provided in the reliquefaction line and cooling the compressed gas compressed in the compressor by heat exchange with uncompressed boil-off gas to be supplied to the compressor;
A post-cooler that receives the compressed gas cooled by the heat exchanger and further cools it; and
It includes a branch line branched from the reliquefaction line at the front end of the heat exchanger and connected to a power generation engine that receives lower pressure fuel than the main engine,
The boil-off gas branched from the branch line is depressurized and then sequentially passed through the post-cooler and heat exchanger before being supplied to the power generation engine,
A ship's boil-off gas treatment system, wherein flash gas and un-liquefied gas generated from the re-liquefied gas in the re-liquefaction line pass through the post-cooler and join the uncompressed boil-off gas flow in front of the heat exchanger. According to clause 1,
Expansion means provided in the branch line to depressurize the compressed boil-off gas;
an additional line branching from the reliquefaction line at a rear end of the post-cooler and connected to a front end of the expansion means of the branch line;
a first valve provided upstream of a confluence point of the additional line in the branch line; and
A ship's boil-off gas treatment system further comprising a second valve provided in the additional line. According to clause 2,
When operating the ship, the first valve is closed and the second valve is opened to branch off the boil-off gas at the rear end of the after-cooler through the additional line and supply it to the power generation engine. According to clause 2,
A decompression device provided in the reliquefaction line to receive the boil-off gas cooled by heat exchange in the heat exchanger and the post-cooler, depressurize it, and provide additional cooling; and
A gas-liquid separator that receives the additionally cooled boil-off gas from the pressure reducing device in the re-liquefaction line and separates gas-liquid. According to clause 4,
It further includes a flash gas line connected from the top of the gas-liquid separator to the front end of the heat exchanger of the boil-off gas supply line through the post-cooler,
The liquid separated in the gas-liquid separator is supplied to the storage tank along the re-liquefaction line, and the flash gas and unliquefied gas separated in the gas-liquid separator are heat exchanged in the post-cooler along the flash gas line and then transferred to the heat exchanger. A ship's boil-off gas treatment system, characterized in that it joins the uncompressed boil-off gas flow of the front end. According to clause 5,
In the heat exchanger, the compressed gas branched along the re-liquefaction line, the uncompressed boil-off gas to be supplied to the compressor along the boil-off gas supply line, and the uncompressed boil-off gas to be supplied to the power generation engine along the branch line after decompression in the expansion means. The three streams of boil-off gas exchange heat,
In the post-cooler, three streams are used: compressed gas from the reliquefaction line cooled in the heat exchanger, boil-off gas to be supplied to the power generation engine after decompression in the expansion means, and flash gas from the flash gas line separated from the gas-liquid separator. A ship's boil-off gas treatment system characterized by heat exchange. According to clause 5,
A heater provided in the branch line to heat the liquefied gas to be supplied to the power generation engine. In a ship equipped with a main engine and a power generation engine supplied with fuel at a lower pressure than the main engine,
The boil-off gas generated from the storage tank where the liquefied gas is stored is compressed by a compressor to the fuel supply pressure of the main engine,
Among the boil-off gases compressed in the compressor, the boil-off gas that is not supplied as fuel for the main engine is cooled by heat exchange in a heat exchanger with the uncompressed boil-off gas to be introduced into the compressor, and is further cooled and re-liquefied in a post-cooler to be stored in the storage tank. However, the flash gas generated from the re-liquefied liquefied gas is separated and joins the uncompressed boil-off gas to be introduced into the heat exchanger through the post-cooler,
A portion of the compressed boil-off gas is branched and decompressed at the front of the heat exchanger and supplied to the power generation engine,
The boil-off gas depressurized to be supplied to the power generation engine is supplied to the power generation engine through the after-cooler and heat exchanger in sequence. According to clause 8,
When operating the ship, the boil-off gas compressed and cooled at the rear end of the after-cooler is branched, decompressed, and supplied to the power generation engine through an after-cooler and a heat exchanger. According to clause 9,
The boil-off gas cooled through the heat exchanger and the post-cooler is further cooled under reduced pressure, reliquefied, and stored in the storage tank.
A method of treating boil-off gas on a ship, characterized in that flash gas generated from the re-liquefied liquefied gas is separated and joined with uncompressed boil-off gas introduced from the storage tank to the heat exchanger.

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