KR20210111924A - Boil-Off Gas Treatment System and Method for Ship - Google Patents

Abstract

Disclosed are a boil-off gas treatment system for a ship and a method thereof which can effectively cool boil-off gas to increase reliquefaction performance and treat the boil-off gas. According to the present invention, the boil-off gas treatment system for a ship comprises: a boil-off gas supply line connected from a storage tank provided on a ship to a main engine; a compressor provided on the boil-off gas supply line, and receiving boil-off gas created from liquefied gas stored in the storage tank to compress the boil-off gas; a reliquefaction line branching from the boil-off gas supply line at the rear end of the compressor to be connected to the storage tank, and re-liquefying compression gas compressed by the compressor; a first heat exchanger provided on the reliquefaction line and receiving the compression gas to cool the compression gas by heat exchange with uncompressed boil-off gas to be supplied to the compressor; a branch line branching from the reliquefaction line at the front end of the first heat exchanger, and merging with the reliquefaction line at the rear end of the first heat exchanger; a second heat exchanger provided on the branch line and receiving compression gas branching to the branch line to cool the compression gas; a first decompression device provided downstream of the merging point of the branch line in the reliquefaction line, and decompressing compression gas cooled through the first or the second heat exchanger; a gas-liquid separator provided on the reliquefaction line and receiving boil-off gas decompressed by the first decompression device to separate gas and liquid; and a fuel supply line supplying gas separated by the gas-liquid separator to a generation engine in the ship through the second heat exchanger.

Description

Boil-Off Gas Treatment System and Method for Ship

The present invention relates to a system and method for treating BOG on a ship, and more particularly, by supplying BOG generated from a storage tank as fuel for a main engine and a power generation engine on board, and re-liquefying BOG that is not supplied as fuel. It relates to a system and method for treating boil-off gas of a ship stored in a storage tank.

In recent years, the consumption of liquefied gas such as liquefied natural gas (LNG) is rapidly increasing worldwide. The liquefied gas obtained by liquefying the gas at a low temperature has the advantage of increasing the storage and transport efficiency because the volume is very small compared to the gas. In addition, since liquefied gas including liquefied natural gas can remove or reduce air pollutants during the liquefaction process, it can be viewed as an eco-friendly fuel that emits less air pollutants during combustion.

Liquefied natural gas is a colorless and transparent liquid that can be obtained by cooling and liquefying natural gas containing methane to about -163°C, and has a volume of about 1/600 compared to natural gas. Accordingly, 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 -163 ℃ atmospheric pressure, liquefied natural gas is sensitive to temperature changes and evaporates easily. For this reason, the storage tank that stores the liquefied natural gas is insulated, but external heat is continuously transferred to the storage tank. -Off Gas, BOG) occurs.

BOG is a type of loss and is an important problem in transport efficiency. In addition, when the boil-off gas is accumulated 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 BOG generated in the storage tank are being studied. Recently, for the treatment of BOG, a method of re-liquefying BOG and returning it to the storage tank, and turning BOG into fuel such as engines of ships, etc. A method of using it as an energy source of a consumer is being used.

As a method for re-liquefying BOG, a method of re-liquefying BOG by heat exchange with a refrigerant by having a refrigeration cycle using a separate refrigerant, a method of re-liquefying BOG itself as a refrigerant without a separate refrigerant, etc. There is this.

Meanwhile, among engines generally used in ships, there are gas fuel engines such as DF engines, X-DF engines, and ME-GI engines as engines capable of using natural gas as fuel.

The DF engine (DFDE, DFGE) is composed of 4 strokes, and adopts an Otto Cycle that 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. are doing

The X-DF engine is composed of two strokes, uses about 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 of around 300 barg is directly injected into the combustion chamber near the top dead center of the piston.

1 schematically shows a conventional BOG treatment system for ships.

As shown in FIG. 1 , in the conventional BOG treatment system for ships, when the main engine ME and the power generation engine GE are provided, the BOG discharged from the storage tank T is compressed in the compressor 10 and It is supplied as the 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 in the middle and supplied as the fuel of the power generation engine (GE).

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

BOG cooled in the heat exchanger 20 is decompressed by the decompression device 30 and partially reliquefied, and the reliquefied liquefied gas and BOG remaining in a 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 stored again, and the gaseous BOG separated by the gas-liquid separator 40 joins the BOG discharged from the storage tank T. and is introduced into the heat exchanger 20 as a refrigerant.

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

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

According to one aspect of the present invention for solving the above problems, the boil-off gas supply line connected to the main engine from the storage tank provided on the ship;

a compressor provided in the boil-off gas supply line to receive and compress the boil-off gas generated from the liquefied gas stored in the storage tank;

a reliquefaction line branched from the boil-off gas supply line at the rear end of the compressor and connected to the storage tank, and re-liquefying the compressed gas compressed in the compressor;

a first heat exchanger provided in the reliquefaction line to receive the compressed gas and cool it through heat exchange with the uncompressed BOG to be supplied to the compressor;

a branch line branched from the reliquefaction line at the front end of the first heat exchanger and joined to the reliquefaction line at the rear end of the first heat exchanger;

a second heat exchanger provided in the branch line to receive and cool the compressed gas branched to the branch line;

a first pressure reducing device provided downstream of the junction of the branch lines in the reliquefaction line and decompressing the cooled compressed gas through the first or second heat exchanger;

a gas-liquid separator provided in the reliquefaction line to receive the boil-off gas depressurized in the first decompression device and separate the gas-liquid; and

A fuel supply line for supplying the gas separated in the gas-liquid separator to the onboard power generation engine through the second heat exchanger is provided.

Preferably, in the reliquefaction line, a fuel replenishment line is branched between the junction of the branch lines and the first pressure reducing device and connected to the front end of the second heat exchanger of the fuel supply line; and a second pressure reducing device provided in the fuel replenishment line and decompressing the compressed gas cooled through the first or second heat exchanger.

Preferably, a refrigerant replenishment line for supplying the gas separated in the gas-liquid separator to the front end of the first heat exchanger of the boil-off gas supply line; a fuel supply valve provided in the fuel supply line; and a pressure control valve provided in the refrigerant replenishment line.

Preferably, the reliquefaction line may further include a water level control valve provided downstream of the gas-liquid separator to control the flow rate of the liquid supplied from the gas-liquid separator to the storage tank.

Preferably, in the reliquefaction line, a first valve provided at a downstream branch point of the branch line; And a second valve provided upstream of the second heat exchanger in the branch line: It is possible to distribute the flow rate of the compressed gas supplied to the first and second heat exchangers by the first and second valves. have.

Preferably, the compressor is a multi-stage compressor that receives BOG and compresses it to the fuel supply pressure of the main engine, and the BOG compressed through some stages of the compressor may be supplied to the power generation engine.

According to another aspect of the present invention, the boil-off gas generated from the storage tank in which the liquefied gas is stored in the ship is compressed to the fuel supply pressure of the main engine in the ship with a compressor,

Among the gas compressed in the compressor, the compressed gas not supplied as fuel of the main engine is divided into two flows, cooled in the first heat exchanger and the second heat exchanger, and the pressure is reduced to gas-liquid separation in the gas-liquid separator, and the separated liquid is separated from the liquid in the gas-liquid separator. Re-storage in a storage tank,

The first heat exchanger cools the compressed gas by heat exchange with the uncompressed boil-off gas to be introduced into the compressor,

The second heat exchanger cools the compressed gas by heat exchange with the gas separated in the gas-liquid separator,

The gas heat-exchanged with the compressed gas in the second heat exchanger provides a method for treating BOG of a ship, characterized in that it is supplied to an onboard power generation engine.

Preferably, the compressed gas cooled in the first and second heat exchangers may be branched and reduced pressure to be supplied to the power generation engine through the second heat exchanger.

Preferably, the second heat exchanger cools the compressed gas through heat exchange with the gas separated in the gas-liquid separator when the ship is anchored, low-speed operation, or when there is a lot of gas separated in the gas-liquid separator, and the high-speed operation of the ship or the gas-liquid separator When the separated gas is small, the compressed gas may be cooled by heat exchange with a two-phase low-temperature fluid that has been decompressed by branching the compressed gas cooled in the first and second heat exchangers.

Preferably, the gas separated in the gas-liquid separator may be joined to the flow of uncompressed BOG in front of the first heat exchanger.

Preferably, the compressor is a multi-stage compressor that receives BOG and compresses it to the fuel supply pressure of the main engine, and the BOG compressed through some stages of the compressor may be supplied to the power generation engine.

In the system of the present invention, the heat exchanger for cooling the compressed gas to be reliquefied is composed of a first heat exchanger using uncompressed boil-off gas as a refrigerant and a second heat exchanger using the gas separated in the gas-liquid separator as a refrigerant, and the compressed gas to be reliquefied divided and cooled.

By dividing the first and second heat exchangers in this way, the design and operation of each heat exchanger is simplified, and the flow rate of compressed gas to be reliquefied, gas flow rate separated from the gas-liquid separator, fuel requirements of the power generation engine, maintenance, etc. Therefore, each heat exchanger can be operated independently. In particular, since the low-temperature fluid flowing into the second heat exchanger becomes a single-phase or two-phase fluid depending on the operating conditions of the ship, it may be advantageous in terms of design and operation of the heat exchanger to divide the first and second heat exchangers when configuring the heat exchanger. .

In addition, since only two fluid flows are heat exchanged in each heat exchanger, the heat exchange efficiency can be increased to effectively cool the compressed gas to be reliquefied, and the gas separated from the gas-liquid separator is supplied to the power generation engine to remove nitrogen remaining in the reliquefaction system. By reducing it, the process can be stabilized and the reliquefaction performance can be improved.

BOG that cannot be consumed due to fuel supply and re-liquefaction must be burned out in the GCU, etc. By improving the re-liquefaction performance, it is possible to reduce the amount of BOG to be combusted to prevent energy waste and to reduce carbon dioxide emissions generated during combustion. In addition, it is possible to secure the safety of the vessel by effectively treating the boil-off gas.

1 schematically shows a conventional BOG treatment system.
Figure 2 schematically shows a BOG treatment system of a ship according to a basic embodiment of the present invention.
3 schematically shows a BOG treatment system for a ship according to a preferred 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 illustrating 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 signs to the elements of each drawing, it should be noted that only the same elements are indicated by the same reference signs as possible even if they are indicated on different drawings.

Hereinafter, the ship in the present invention includes liquefied gas and any type of engine that can use BOG generated from liquefied gas as fuel for propulsion or power generation engines, or using liquefied gas or BOG as fuel for inboard engines. ships with self-propelled capabilities such as LNG carriers, liquefied petroleum gas carriers, and LNG RVs (Regasification Vessels), as well as LNG FPSO (Floating Production Storage Offloading) and LNG FSRU (Floating Storage Regasification). Unit) may include offshore structures that do not have propulsion capabilities but are floating in 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 boil-off gas in a stored state, and can be used as a fuel for engines and the like. Such liquefied gas is, for example, liquefied petrochemicals such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), Liquefied Ethylene Gas, Liquefied Propylene Gas, etc. It may be gas. However, in the embodiments to be described later, an example in which LNG, which is one of representative liquefied gases, is applied will be described.

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

2 schematically shows a BOG treatment system for a ship according to a basic embodiment of the present invention.

As shown in FIG. 2 , the system of this basic embodiment compresses the boil-off gas discharged from the storage tank T in the compressor 10 in a ship equipped with a main engine ME and a power generation engine GE. It is a system that supplies the fuel of the main engine, cools and depressurizes the compressed gas that is not supplied as fuel through a heat exchanger and a pressure reducing valve 30 , separates the gas-liquid in the gas-liquid separator 40 , and recovers it to the storage tank.

The heat exchanger 20A cools the uncompressed boil-off gas to be supplied to the compressor as a refrigerant and the compressed gas to be reliquefied by heat exchange. BOG cooled in the heat exchanger 20 is reduced in pressure by the pressure reducing valve 30 and a part is reliquefied, and the reliquefied liquefied gas and BOG remaining in a gaseous state are supplied to the gas-liquid separator 40 and phase separated. .

At this time, the first line L1 for supplying the gas and flash gas separated in the gas-liquid separator to the power generation engine through the heat exchanger 20A is configured to additionally secure the refrigerant of the heat exchanger.

Part of the compressed gas cooled through the heat exchanger is reduced by the JT valve 50, and a second line (L2) is additionally configured to merge into the front end of the heat exchanger of the first line (L2), and is supplied to the power generation engine through the heat exchanger. can

In this way, the flash gas is supplied to the power generation engine through the heat exchanger 20A through the first line L1, and when the amount of flash gas is small or the nitrogen content in the flash gas is high and the amount of heat is low to be supplied as fuel, etc. By depressurizing a portion of the compressed gas cooled through the second line (L2) and supplying it to the power generation engine through the heat exchanger again, the refrigerant in the heat exchanger can be additionally secured to effectively cool the compressed gas to be reliquefied. have.

However, when exchanging three streams of uncompressed BOG, compressed gas to be reliquefied, and fuel gas to be supplied to a power generation engine in one heat exchanger as described above, the operating pressures of the uncompressed BOG and the fuel gas flow are different from each other in the heat exchanger. Design difficulties arise. In particular, when the flash gas separated from the gas-liquid separator is not supplied as fuel for the power generation engine, the operating pressure of the gas-liquid separator is around 3 to 8 barg. can Embodiments to be described later are configured to solve these problems to facilitate the design and operation of the heat exchanger.

3 schematically shows a BOG treatment system for a ship according to a preferred embodiment of the present invention.

As shown in Figure 3, the system of this embodiment is provided in the boil-off gas supply line (GL) connected to the main engine (ME) from the storage tank (T) provided on the ship, the boil-off gas supply line and stored in the storage tank The compressor 100 receives and compresses the boil-off gas generated from the liquefied gas, and is branched from the boil-off gas supply line at the rear end of the compressor and connected to the storage tank, and among the compressed gas compressed in the compressor, the compressed gas that is not supplied as fuel is re-liquefied. It includes a reliquefaction line (RL) to liquefy.

The reliquefaction line (RL) is provided with a first heat exchanger 200 that receives compressed gas and cools it through heat exchange with uncompressed BOG to be supplied to the compressor, and is branched from the reliquefaction line at the front end of the first heat exchanger. 1 A branch line BL is provided at the rear end of the heat exchanger to join the reliquefaction line. The branch line is provided with a second heat exchanger 250 for cooling by receiving the compressed gas branched into the branch line.

A first pressure reducing device 300 for depressurizing the compressed gas cooled through the first or second heat exchangers 200 and 250 is provided downstream of the junction of the branch lines in the reliquefaction line, and the first pressure reducing device is downstream of the first pressure reducing device. 1 A gas-liquid separator 400 for gas-liquid separation by receiving the boil-off gas decompressed in the decompression device is provided.

In addition, a fuel supply line FL for supplying the gas separated in the gas-liquid separator 400 to the onboard power generation engine GE through the second heat exchanger 250 is provided.

That is, in this embodiment, the heat exchanger for cooling the compressed gas to be reliquefied is a first heat exchanger 200 using uncompressed boil-off gas as a refrigerant, and a second heat exchanger 250 using the gas separated in the gas-liquid separator as a refrigerant. By configuring, the compressed gas to be reliquefied branched to the reliquefaction line after compression in the compressor is divided into two flows, the first heat exchanger 200 of the reliquefaction line RL and the second heat exchanger of the branch line BL ( 250) and cooled.

The first heat exchanger 200 cools the compressed gas by exchanging heat with the uncompressed boil-off gas of the boil-off gas supply line GL to be introduced into the compressor, and the second heat exchanger 250 is separated from the gas-liquid separator and the fuel supply line ( The compressed gas is cooled by heat exchange with the fuel gas to be supplied to the power generation engine along FL).

In the second heat exchanger 250 , the process operation conditions may be changed from the low-temperature gas introduced into the second heat exchanger 250 to the two-phase low-temperature fluid through the second pressure reducing device according to the operating conditions. In this case, as shown in FIG. 2 , when a single three-phase heat exchanger is applied, it may be difficult to design and operate a heat exchanger under a given process condition. Therefore, in this embodiment, each heat exchanger is configured separately to recover cold heat from the low-temperature fluid.

In the reliquefaction line, a first valve (V1) is provided downstream of the branch point of the branch line, and a second valve (V2) is provided upstream of the second heat exchanger in the branch line, respectively. 2 It is possible to control the flow rate of compressed gas passing through the heat exchanger.

By dividing the first and second heat exchangers in this way, the design and operation of each heat exchanger is simplified, and the flow rate of compressed gas to be reliquefied, gas flow rate separated from the gas-liquid separator, fuel requirements of the power generation engine, maintenance, etc. Therefore, each heat exchanger can be operated independently. In addition, since only two fluid streams exchange heat in each heat exchanger, efficient heat exchange can be achieved.

A fuel replenishment line branched between the junction of the branch line BL and the first pressure reducing device 300 in the reliquefaction line RL and connected to the front end of the second heat exchanger 250 of the fuel supply line FL SL is provided, and a second pressure reducing device 500 for decompressing the compressed gas cooled through the first or second heat exchanger is provided in the fuel replenishment line.

The second pressure reducing device 500 may be an expander or a Joule Thompson valve for decompressing the boil-off gas, and the boil-off gas is cooled by adiabatic expansion or isentropic expansion through decompression.

A refrigerant replenishment line (CL) is provided for supplying the gas separated in the gas-liquid separator to the front end of the first heat exchanger of the BOG supply line, a pressure control valve (PCV) is provided in the refrigerant replenishment line, and a fuel supply valve ( FV) are provided respectively.

A water level control valve (LCV) is provided downstream of the gas-liquid separator in the reliquefaction line (RL) to control the flow rate of the liquid supplied from the gas-liquid separator to the storage tank.

The internal pressure can be controlled by discharging the flash gas from the gas-liquid separator through the pressure control valve (PCV) of the refrigerant replenishment line, and the condensate separated from the gas-liquid separator, that is, liquefied gas, is reliquefied by adjusting the water level control valve (LCV). The liquid level of the gas-liquid separator can be maintained by sending it to the storage tank through the line.

Looking at the BOG treatment method in this embodiment as a whole, BOG generated in the storage tank T is introduced into the compressor 100 and compressed. BOG in the compressor is compressed by the fuel supply pressure of the onboard main engine (ME), and the BOG compressed in the compressor is supplied to the main engine.

The compressor 100 may compress the boil-off gas to the fuel supply pressure of the main engine, for example, 15 barg if the X-DF engine is provided, and 300 barg if the ME-GI engine is provided. The compressor 100 may be provided as a multi-stage compressor in which a plurality of compressors and an intermediate cooler are alternately disposed and sequentially pass through them to compress the boil-off gas to the fuel supply pressure of the main engine, and the number of compressors and intermediate coolers constituting the multi-stage compressor can be changed according to the fuel supply pressure of the main engine.

BOG compressed through some stages of the multi-stage compressor may be supplied to a power generation engine (GE) that is supplied with a lower pressure fuel than the main engine.

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

According to ship regulations, a compressor that supplies fuel to an engine must be designed for redundancy in preparation for an emergency.

Downstream of the compressor 100, the reliquefaction line (RL) is branched from the boil-off gas supply line (GL) and is connected to the storage tank (T), and BOG that is not supplied as fuel of the main engine is branched into the reliquefaction line After reliquefaction, it is re-stored in the storage tank (T).

In the reliquefaction line (RL), a first heat exchanger 200 for cooling the compressed BOG by heat exchange with the uncompressed BOG of the BOG supply line, and a first pressure reducing device for decompressing the cooled BOG through the first heat exchanger. (300), a gas-liquid separator 400 for gas-liquid separation of the boil-off gas decompressed in the first decompression device is sequentially provided.

Through the branch line BL branching from the reliquefaction line at the front end of the first heat exchanger, the compressed gas to be reliquefied is branched into two flows, and the first heat exchanger 200 of the reliquefaction line and the second heat exchange of the branch line After cooling in the group 250, they are rejoined and introduced into the first pressure reducing device.

The first pressure reducing device 300 may be configured as an expander for reducing the compressed boil-off gas or an expansion valve such as a Joule-Thomson valve. Through decompression, the boil-off gas is adiabatically expanded and further cooled.

The boil-off gas further cooled through the first pressure reducing device is introduced into the gas-liquid separator 400, and the liquid separated in the gas-liquid separator is returned to the storage tank T along the reliquefaction line RL, and the separated gas, that is, The flash gas is used as a refrigerant in the second heat exchanger 250 along the fuel supply line FL and then supplied to the power generation engine.

By supplying the gas separated in the gas-liquid separator to the power generation engine through the second heat exchanger 250, the refrigerant of the second heat exchanger can be secured. In addition, when going through the reliquefaction system, nitrogen (N ₂ ), which is more volatile than methane and hydrocarbon components, is unliquefied and remains in a gaseous state or is volatilized as flash gas, and methane is mainly left in the condensate. After gas-liquid separation in the gas-liquid separator, nitrogen By supplying the gas with many components to the power generation engine through the second heat exchanger, nitrogen remaining in the reliquefaction system is reduced, thereby stabilizing the process and improving the reliquefaction performance.

That is, if nitrogen is contained in a large amount, energy is consumed for the compression activity of unnecessary gas, so energy loss occurs as much as the content of nitrogen in the capacity of the compressor. (C1) achieves a thermodynamically stabilized equilibrium state, and the energy loss of the compressor can be reduced.

On the other hand, if the amount of branched gas or flash gas in the gas-liquid separator is small, or when the amount of heat when supplied as fuel is low due to the high nitrogen content in the flash gas, downstream of the junction of the reliquefaction line (RL) and the branch line (BL). A part of the compressed gas cooled through the fuel replenishment line SL branched from the Compressed gas can be extracted from the middle stage and supplied to the power generation engine along with flash gas.

Even when there is little or no gas to be reliquefied, such as during high-speed operation of a ship, the compressed gas through some stages of the multi-stage compressor can be directly supplied to the power generation engine.

The amount of BOG supplied to the power generation engine through the second heat exchanger 250 through the fuel supply line FL and the fuel replenishment line SL may vary depending on the load of the power generation engine, the configuration of the compressor, and the like.

The present invention is not limited to the above embodiments, and it is apparent to those of ordinary skill in the art that the present invention can be implemented with various modifications or variations without departing from the technical gist of the present invention. did it

T: storage tank
ME: main engine
GE: power generation engine
GL: BOG supply line
RL: Reliquefaction line
BL: branch line
FL: fuel supply line
SL: refueling line
100: compressor
200: first heat exchanger
250: second heat exchanger
300: first pressure reducing device
400: gas-liquid separator
500: second pressure reducing device

Claims (11)

BOG supply line connected to the main engine from the storage tank provided on the ship;
a compressor provided in the boil-off gas supply line to receive and compress the boil-off gas generated from the liquefied gas stored in the storage tank;
a reliquefaction line branched from the boil-off gas supply line at the rear end of the compressor and connected to the storage tank, and re-liquefying the compressed gas compressed in the compressor;
a first heat exchanger provided in the reliquefaction line to receive the compressed gas and cool it through heat exchange with the uncompressed BOG to be supplied to the compressor;
a branch line branched from the reliquefaction line at the front end of the first heat exchanger and joined to the reliquefaction line at the rear end of the first heat exchanger;
a second heat exchanger provided in the branch line to receive and cool the compressed gas branched to the branch line;
a first pressure reducing device provided downstream of the junction of the branch lines in the reliquefaction line and decompressing the cooled compressed gas through the first or second heat exchanger;
a gas-liquid separator provided in the reliquefaction line to receive the boil-off gas depressurized in the first decompression device and separate the gas-liquid; and
and a fuel supply line for supplying the gas separated in the gas-liquid separator to the onboard power generation engine through the second heat exchanger. The method of claim 1,
a fuel replenishment line branched between the junction of the branch line and the first pressure reducing device in the reliquefaction line and connected to the front end of the second heat exchanger of the fuel supply line; and
A second decompression device provided in the fuel replenishment line to decompress the compressed gas cooled through the first or second heat exchanger: BOG treatment system of a ship further comprising: 3. The method of claim 2,
a refrigerant replenishment line for supplying the gas separated in the gas-liquid separator to the front end of the first heat exchanger of the boil-off gas supply line;
a fuel supply valve provided in the fuel supply line; and
A pressure control valve provided in the refrigerant replenishment line: BOG treatment system of a vessel further comprising: 4. The method of claim 3,
and a water level control valve provided downstream of the gas-liquid separator in the reliquefaction line to control the flow rate of the liquid supplied from the gas-liquid separator to the storage tank. 5. The method according to any one of claims 1 to 4,
a first valve provided at a downstream branch point of the branch line in the reliquefaction line; and
A second valve provided upstream of the second heat exchanger in the branch line: further comprising,
BOG treatment system of a vessel capable of distributing a flow rate of compressed gas supplied to the first and second heat exchangers by the first and second valves. 6. The method of claim 5,
The compressor is a multi-stage compressor that receives boil-off gas and compresses it to the fuel supply pressure of the main engine,
BOG treatment system for ships, characterized in that the BOG compressed through some stages of the compressor can be supplied to the power generation engine. The boil-off gas generated from the storage tank where the liquefied gas is stored in the ship is compressed by the compressor to the fuel supply pressure of the ship's main engine,
Of the gas compressed in the compressor, the compressed gas not supplied as the fuel of the main engine is divided into two flows, cooled in the first heat exchanger and the second heat exchanger, and the pressure is reduced to gas-liquid separation in the gas-liquid separator, and the separated liquid is separated from the liquid in the gas-liquid separator. Re-storage in a storage tank,
The first heat exchanger cools the compressed gas by heat exchange with the uncompressed boil-off gas to be introduced into the compressor,
The second heat exchanger cools the compressed gas by heat exchange with the gas separated in the gas-liquid separator,
The gas heat-exchanged with the compressed gas in the second heat exchanger is a method for treating BOG of a ship, characterized in that it is supplied to an onboard power generation engine. 8. The method of claim 7,
BOG treatment method of a ship, characterized in that the compressed gas cooled in the first and second heat exchangers is branched and decompressed, and supplied to the power generation engine through the second heat exchanger. The method of claim 8, wherein in the second heat exchanger,
When the vessel is moored, the compressed gas is cooled by heat exchange with the gas separated in the gas-liquid separator when there is a lot of gas separated in the gas-liquid separator during low-speed operation or when there is a lot of gas separated in the gas-liquid separator. BOG treatment method for a ship, characterized in that the compressed gas is cooled by heat exchange with a two-phase low-temperature fluid that has been decompressed by branching the compressed gas cooled in the first and second heat exchangers. 9. The method of claim 8,
The gas separated in the gas-liquid separator is a BOG treatment method for a ship, characterized in that it can be joined into the uncompressed BOG flow at the front end of the first heat exchanger. 11. In claim 10,
The compressor is a multi-stage compressor that receives boil-off gas and compresses it to the fuel supply pressure of the main engine,
BOG treatment method of a ship, characterized in that the BOG compressed through some stages of the compressor can be supplied to the power generation engine.

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