KR102276357B1 - Boil-Off Gas Treatment System and Method for Ship - Google Patents

Abstract

A system and method for treating BOG on a ship are disclosed. The system for treating BOG of a ship of the present invention is provided in a ship provided with a main engine and a power generation engine receiving a lower pressure fuel than the main engine, receiving BOG generated from a storage tank in which the liquefied gas is stored and provided in the ship. a compressor that compresses the fuel supply pressure of the main engine; a precooler for receiving all or part of the compressed gas from the compressor and cooling it through heat exchange with a refrigerant; a heat exchanger for receiving the compressed gas cooled by the precooler and exchanging heat with the uncompressed BOG to be supplied to the compressor; an expansion means for receiving the compressed gas cooled from the heat exchanger and reducing the pressure; and a refrigerant heat exchanger that receives the uncompressed boil-off gas heat-exchanged with the compressed gas from the heat exchanger and heat-exchanges with the refrigerant to be supplied to the precooler, wherein some of the compressed gas decompressed by the expansion means is It is characterized in that it can be supplied to the power generation engine through the 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, BOG generated from a storage tank is supplied as fuel for a main engine and a power generation engine on board, and BOG that is not supplied as fuel is BOG itself. It relates to a system and method for treating BOG of a ship for reliquefying it with the cooling heat of the ship and storing it 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 since external heat is continuously transferred to the storage tank, the liquefied natural gas is continuously naturally vaporized in the storage tank during the process of transporting the liquefied natural gas, resulting in boil-off gas (Boil). -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 12 to 15 barg of natural gas as a 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, in a ship provided with a main engine and a power generation engine receiving a lower pressure fuel than the main engine,

a compressor provided on a ship and receiving boil-off gas generated from a storage tank in which liquefied gas is stored and compressing it to the fuel supply pressure of the main engine;

a precooler for receiving all or part of the compressed gas from the compressor and cooling it through heat exchange with a refrigerant;

a heat exchanger for receiving the compressed gas cooled by the precooler and exchanging heat with the uncompressed BOG to be supplied to the compressor;

an expansion means for receiving the compressed gas cooled from the heat exchanger and reducing the pressure; and

and a refrigerant heat exchanger that receives the uncompressed boil-off gas heat-exchanged with the compressed gas from the heat exchanger and heat-exchanges with the refrigerant to be supplied to the precooler; and

A portion of the compressed gas decompressed by the expansion means is provided with a BOG treatment system for a ship, characterized in that it can be supplied to the power generation engine through the heat exchanger.

Preferably, the expansion means includes: a first pressure reducing valve for receiving a portion of the compressed gas cooled from the heat exchanger and reducing the pressure; and a second pressure reducing valve that receives another part of the compressed gas cooled from the heat exchanger and reduces the pressure to the fuel supply pressure of the power generation engine, wherein the compressed gas pressure-reduced by the second pressure reducing valve is supplied to the heat exchanger. It may be supplied to the power generation engine through the

Preferably, the method further includes a gas-liquid separator for receiving the boil-off gas pressure-reduced from the first pressure reducing valve and separating the gas-liquid gas, wherein the gas separated in the gas-liquid separator is the uncompressed boil-off gas to be introduced from the storage tank to the heat exchanger. The liquid joined to the flow and separated in the gas-liquid separator may be supplied to the storage tank.

Preferably, a refrigerant compressor for compressing the refrigerant discharged from the precooler; and a refrigerant condenser for cooling the refrigerant compressed in the refrigerant compressor, wherein the refrigerant compressed and cooled through the refrigerant compressor and the refrigerant condenser is introduced into the refrigerant heat exchanger, cooled further, and then introduced into the precooler, , the refrigerant may circulate in a refrigerant circulation line of a closed loop.

Preferably, a heater for heating the boil-off gas, which has been depressurized and heat-exchanged through the second pressure reducing valve and the heat exchanger, according to the fuel supply conditions of the power generation engine; may further include.

Preferably, the precooler may be supplied with liquefied gas from the storage tank as a refrigerant through the refrigerant heat exchanger, and the liquefied gas used as a refrigerant in the refrigerant heat exchanger may be supplied to the power generation engine.

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

a boil-off gas supply line connected to the main engine from a storage tank for storing liquefied gas provided in the ship;

a compressor provided in the boil-off gas supply line to receive the boil-off gas generated from the liquefied gas and compress it to the fuel supply pressure of the main engine;

Downstream of the compressor, branched from the BOG supply line and connected to the storage tank, the BOG that is not supplied as fuel of the main engine is cooled and reliquefied through heat exchange with uncompressed BOG to be supplied to the compressor. line;

a heat exchanger provided in the reliquefaction line to receive the compressed gas compressed from the compressor and cool it through heat exchange;

a precooler provided at a front end of the heat exchanger in the reliquefaction line to precool the compressed gas to be introduced into the heat exchanger;

a refrigerant heat exchanger receiving the uncompressed boil-off gas heat-exchanged with the compressed gas from the heat exchanger and exchanging heat with the refrigerant to be supplied to the precooler; and

A branch line branching from the reliquefaction line at the rear end of the heat exchanger to depressurize the compressed gas and supplying it to the power generation engine through the heat exchanger is provided.

Preferably, a refrigerant circulation line in which the refrigerant for cooling the compressed gas in the precooler circulates; a refrigerant compressor provided in the refrigerant circulation line to compress the refrigerant discharged from the precooler; and a refrigerant condenser provided in the refrigerant circulation line and cooling the refrigerant compressed by the refrigerant compressor, wherein the refrigerant compressed and cooled through the refrigerant compressor and the refrigerant condenser is introduced into the refrigerant heat exchanger for further cooling After being cooled, it may be introduced into the precooler.

Preferably, a first pressure reducing valve provided in the reliquefaction line and receiving a portion of the compressed gas cooled from the heat exchanger to reduce pressure; a second pressure reducing valve provided in the branch line and receiving another part of the compressed gas cooled from the heat exchanger to reduce the pressure to the fuel supply pressure of the power generation engine; and a gas-liquid separator for receiving the boil-off gas pressure-reduced from the first pressure reducing valve and separating the gas-liquid, wherein the liquid separated in the gas-liquid separator is restored to the storage tank, and the gas is introduced into the heat exchanger. It may be joined to the flow of uncompressed boil-off gas in the gas supply line.

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 BOG compressed in the compressor, BOG not supplied as fuel of the main engine is pre-cooled by heat exchange with a refrigerant in a precooler, and cooled by heat exchange with uncompressed BOG to be introduced into the compressor in a heat exchanger, and reduced pressure. It is further cooled to re-liquefy and stored again in the storage tank,

A portion of the boil-off gas cooled at the rear end of the heat exchanger is branched and decompressed and supplied to a power generation engine receiving fuel at a lower pressure than that of the main engine through the heat exchanger,

In the heat exchanger, the BOG compressed and pre-cooled by the compressor is cooled by heat exchange with the BOG compressed to be supplied to the compressor and the BOG decompressed to be supplied to the power generation engine and uncompressed BOG to be introduced into the compressor;

The refrigerant supplied to the precooler is cooled by heat exchange in the downstream of the heat exchanger with the uncompressed BOG to be supplied to the compressor after heat exchange in the heat exchanger.

Preferably, the refrigerant is compressed, cooled, and condensed after passing through the precooler, and the condensed refrigerant is further cooled by heat exchange with the uncompressed BOG and then introduced into the precooler, so that the refrigerant circulates along the refrigerant circulation line. can

Preferably, the boil-off gas cooled through the precooler and heat exchanger after being compressed in the compressor is further cooled under reduced pressure and then gas-liquid separated, the liquid is supplied to the storage tank and re-stored, and the separated flash gas is It may be joined to the flow of the uncompressed BOG to be introduced from the storage tank to the heat exchanger.

In the system of the present invention, it is possible to increase the cooling performance of the heat exchanger by additionally securing the refrigerant in the heat exchanger by reducing a portion of the boil-off gas to be reliquefied and supplying it to the power generation engine through the heat exchanger. The flash gas separated from the reliquefaction gas can also be used as a refrigerant for cooling the gas to be reliquefied, so that the gas to be reliquefied can be effectively cooled.

In addition, before cooling the gas to be reliquefied in the main heat exchanger, it is precooled in the precooler and then transferred to the heat exchanger to be cooled in stages, so that the gas to be reliquefied can be cooled more effectively and reliquefaction efficiency can be increased.

In particular, the uncompressed BOG discharged from the heat exchanger is used for cooling the refrigerant supplied to the precooler again, so that the cooling heat of the uncompressed BOG can be additionally utilized. By cooling the refrigerant in this way, the amount of work required for refrigerant compression in the refrigerant cycle can be reduced, thereby reducing the size of the equipment.

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 is a schematic diagram of a conventional BOG treatment system.
2 is a schematic diagram of a BOG treatment system for a ship according to a first embodiment of the present invention.
3 is a schematic diagram of a BOG treatment system for a ship according to a second embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the 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 the boil-off gas generated from the liquefied gas as a fuel for an engine for propulsion or power generation, or uses liquefied gas or boil-off gas as a fuel for an onboard engine. 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.

FIG. 2 schematically shows a BOG treatment system for a ship according to a first embodiment of the present invention, and FIG. 3 schematically shows a BOG treatment system for a ship according to a second exemplary embodiment of the present invention.

As shown in FIGS. 2 to 3 , the BOG treatment system of the first to second embodiments is provided for a ship and is for supplying or re-liquefying BOG generated from a storage tank in which liquefied gas is stored as fuel for processing. , a boil-off gas supply line (GL) connected from the storage tank to the onboard main engine (ME) is provided, and the boil-off gas supply line receives the boil-off gas generated from the liquefied gas stored in the storage tank and converts it to the fuel supply pressure of the main engine. Compressor 100 for compression is provided.

BOG generated in the storage tank T is introduced into the compressor 100 and compressed. The compressor 100 may be provided as a multi-stage compressor in which a plurality of compressors and 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.

The compressor compresses the boil-off gas to the fuel supply pressure to the main engine, for example, 5.5 barg when a DF engine is provided, 12 to 15 barg when an X-DF engine is provided, and 300 barg when a ME-GI engine is provided can be compressed with The number of compressors and intercoolers constituting the multi-stage compressor can be changed according to the fuel supply pressure of the main engine.

A fuel supply line (SL) is provided from the middle stage of the multi-stage compressor to the onboard power generation engine (GE), and the BOG compressed through a part of the compressor of the multi-stage compressor can be supplied to the power generation engine having a lower fuel supply pressure than that of the main engine. .

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

According to ship regulations, the compressor that supplies fuel to the engine must be designed for redundancy in preparation for emergency situations. It is designed to be usable. For this purpose, although only one set of compressors is shown in the drawings of the present embodiments, a plurality of compressors may be provided.

On the other hand, a reliquefaction line (RL) branched from the boil-off gas supply line (GL) and connected to the storage tank is provided downstream of the compressor 100, and the compressed gas not supplied as fuel of the main engine is cooled and reliquefied and stored. Re-storage in tank (T).

A precooler 200 and a heat exchanger 300 are sequentially provided in the reliquefaction line RL to cool the compressed gas to be reliquefied by being compressed in the compressor.

In particular, in the present embodiments, the precooler 200 is provided at the front end of the heat exchanger 300 in the reliquefaction line RL, and the precooler 200 compresses the compressed gas branched into the reliquefaction line after compression in the compressor. It is supplied and pre-cooled by heat exchange with the refrigerant, and the heat exchanger 300 receives the compressed gas cooled through the pre-cooler and further cools it through heat exchange with the uncompressed BOG to be supplied to the compressor.

There is a difference in the refrigerant supplied to the precooler 200 in the systems of the first and second embodiments, and a separate refrigerant cycle in which the refrigerant circulates may be configured to supply the refrigerant to the precooler (see the first embodiment of FIG. 2 ). For example, it may be configured to receive boil-off gas or liquefied gas generated from the storage tank and use it as a refrigerant (the second embodiment of FIG. 3 ).

First, in the first embodiment shown in FIG. 2 , a refrigerant circulation line CLa of a closed loop through which the refrigerant circulates is provided to supply the refrigerant to the precooler. The refrigerant circulation line (CLa) is characterized in that the refrigerant heat exchanger 400 for cooling the refrigerant in the refrigerant circulation line by heat exchange with uncompressed BOG to be supplied to the compressor after heat exchange in the heat exchanger is provided.

A refrigerant compressor 410 for compressing the refrigerant discharged from the precooler 200 and a refrigerant condenser 420 for cooling the refrigerant compressed in the refrigerant compressor are provided in the refrigerant circulation line CLa.

The refrigerant compressed and cooled through the refrigerant compressor 410 and the refrigerant condenser 420 is introduced into the refrigerant heat exchanger 400, is further cooled, and then introduced into the precooler 200, heat exchanged with the compressed gas in the precooler, and again By being introduced into the refrigerant compressor, it forms a closed loop refrigerant cycle.

As a result of modeling a system consisting of a refrigerant heat exchanger that additionally cools the refrigerant with the cooling heat of uncompressed BOG, it is found that the work of the refrigerant compressor in the refrigerant cycle is reduced by 36% compared to the case of compressing and condensing without configuring the refrigerant heat exchanger. Confirmed.

Therefore, as in this embodiment, by configuring the refrigerant heat exchanger to cool the refrigerant circulating in the refrigerant cycle with the cooling heat of uncompressed BOG to be introduced into the compressor after passing through the heat exchanger, the amount of work required for refrigerant compression in the refrigerant cycle is reduced, the refrigerant It is possible to reduce the size and size of compression equipment and piping included in the cycle and reduce costs.

As the refrigerant of the refrigerant circulation line, a refrigerant having a boiling point of -30 ° C or less may be used, for example, a mixed refrigerant such as SMR (Single Mixed Refrigerant) or C3MR (Propane-precooled Mixed Refrigerant), nitrogen may be used.

The gas to be reliquefied is pre-cooled in the pre-cooler 200 and then introduced into the heat exchanger 300 to be cooled again by the uncompressed BOG. As such, since pre-cooling in the precooler is followed by secondary cooling in the main heat exchanger, the BOG to be reliquefied can be cooled more effectively, thereby improving the reliquefaction performance.

Meanwhile, the heat exchanger 300 may be provided as a Printed Circuit Heat Exchanger (PCHE) or a Direct Contact Type Heat Exchanger (DCHE). BOG 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 the compression process.

In the first and second embodiments, a branch line (BL) branching from the reliquefaction line (RL) is provided at the rear end of the heat exchanger 300, and after compression, the cooled compressed gas is reduced through the heat exchanger. It is sent to the heat exchanger 300 to recover cooling heat from the heat exchanger, and then supplies it to the power generation engine (GE).

Thus, in the heat exchanger 300 in the system of the present embodiments, the compressed gas of the reliquefaction line (RL) pre-cooled after compression, the boil-off gas of the branch line (BL) decompressed after branching to supply to the power generation engine, the compressor Three streams of uncompressed boil-off gas of the boil-off gas supply line (GL) to be supplied are heat-exchanged.

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

At the rear end of the heat exchanger 300 , an expansion means for decompressing the boil-off gas cooled through the precooler and the heat exchanger is provided.

The expansion means may be provided, for example, as an expansion valve such as an expander or a Joule-Thomson valve for decompressing the compressed BOG, and the BOG is cooled by isentropic expansion or adiabatic expansion through decompression.

In particular, in the present embodiments, the expansion means consists of two types, a first pressure reducing valve 500 provided in the reliquefaction line RL and a second pressure reducing valve 550 provided in the branch line BL, and the first BOG that has been decompressed in the pressure reducing valve 500 and cooled is reliquefied along the reliquefaction line and stored in a storage tank, and the BOG is decompressed in the second pressure reducing valve 550 and cooled down in the heat exchanger along the branch line again. After recovering the cooling heat, it is supplied as fuel for the power generation engine that is supplied with fuel at a lower pressure than the main engine.

For example, the gas to be cooled and reliquefied under reduced pressure is reduced to about 4 barA through the first pressure reducing valve 500, and the gas to be supplied as fuel of the power generation engine through the heat exchanger after cooling is reduced in consideration of the pressure reduction during heat exchange. The pressure can be reduced to about 6.5 barA through the second pressure reducing valve 550 .

A heater 700 for heating fuel to be supplied to the power generation engine is additionally provided in the branch line BL, and the boil-off gas heated through the heat exchanger is additionally heated in accordance with the fuel supply conditions of the power generation engine and supplied to the power generation engine. .

The amount of BOG supplied to the power generation engine through the branch line may vary depending on the load of the power generation engine and the configuration of the compressor.

As such, in the present embodiments, the cooling heat of the boil-off gas to be supplied to the power generation engine through the branch line connected to the power generation engine through the heat exchanger can also be used for reliquefaction, so that the reliquefaction performance is improved by cooling the gas to be reliquefied more effectively. can be raised In addition, the boil-off gas to be supplied to the power generation engine is heated through the heat exchanger, so that the thermal energy of the system can be effectively utilized.

On the other hand, BOG cooled by the precooler 300 and the heat exchanger 200 in the reliquefaction line RL, and further cooled by reduced pressure through the first pressure reducing valve 500, is passed through the gas-liquid separator 600 to the gas-liquid are separated

The liquid separated in the gas-liquid separator 600, that is, the liquefied gas is re-stored in the storage tank along the re-liquefaction line RL.

The flash gas line (FL) is connected from the gas-liquid separator to the BOG supply line (GL) at the front of the heat exchanger, and the gas separated in the gas-liquid separator, that is, the flash gas, joins the flow of uncompressed BOG to be introduced from the storage tank to the heat exchanger. and can be supplied to the heat exchanger as a refrigerant.

The system of the second embodiment shown in FIG. 3 is configured to use the liquefied gas of the storage tank as a refrigerant in the precooler 200, and for this purpose, a refrigerant supply line connected from the storage tank T to the precooler 200 ( CLb) is prepared.

The liquefied gas may be supplied as a refrigerant to the precooler from the storage tank along the refrigerant supply line CLb.

The refrigerant supply line CLb is connected from the storage tank T to the rear end of the heat exchanger 200 of the branch line BL through the refrigerant heat exchanger 400 and the precooler 200 . After heat exchange with the uncompressed boil-off gas discharged from the heat exchanger in the refrigerant heat exchanger 400, the liquefied gas heat-exchanged with the compressed gas in the precooler 200 joins the branch line to be supplied as fuel of the power generation engine (GE). can

Since the gas to be reliquefied is precooled in the precooler with the cooling heat of the liquefied gas to be supplied to the power generation engine and then cooled again in the heat exchanger, it can be cooled more effectively to increase the reliquefaction rate. In addition, the fuel to be supplied to the power generation engine can be vaporized by absorbing thermal energy from the high-temperature compressed gas in the precooler, so that energy efficiency can be improved by effectively utilizing the thermal energy of the system.

As in the first embodiment, the compressed gas cooled through the precooler 200 and the heat exchanger 300 passes through the first pressure reducing valve 500 and the gas-liquid separator 600 along the reliquefaction line RL. .

After additional cooling under reduced pressure, the gas-liquid gas is separated into flash gas and liquefied gas in the gas-liquid separator, and the separated flash gas joins the flow of uncompressed BOG to be introduced from the storage tank to the heat exchanger through the flash gas line (FL) and enters the heat exchanger. The refrigerant is supplied, and the liquefied gas is supplied to the storage tank.

As described above, in the present embodiments, BOG generated from a storage tank in which liquefied gas is stored is compressed by a compressor to the fuel supply pressure of the onboard main engine, and the BOG compressed in the compressor is not supplied as fuel of the main engine. The uncompressed BOG is pre-cooled by heat exchange with the refrigerant in the precooler, cooled by heat exchange with the uncompressed BOG to be introduced into the compressor in the heat exchanger, and further cooled under reduced pressure to separate gas-liquid and then stored again in the storage tank. In particular, after heat exchange in the heat exchanger, the uncompressed BOG to be supplied to the compressor is heat-exchanged with the refrigerant to be supplied to the precooler, and a part of the BOG cooled at the rear end of the heat exchanger is branched to reduce pressure, and to be supplied to the power generation engine through the heat exchanger, In the heat exchanger, the BOG compressed and pre-cooled in the compressor is cooled by heat exchange with the BOG compressed to be supplied to the uncompressed BOG to be introduced into the compressor and the power generation engine.

By cooling the gas to be reliquefied sequentially through the precooler and heat exchanger, the reliquefaction performance can be effectively cooled, and the amount of gas burned in the GCU can be reduced or eliminated by preventing energy loss, thereby reducing carbon dioxide emissions.

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
CLa: Refrigerant circulation line
CLb: Refrigerant supply line
FL: flash gas line
SL: fuel supply line
100: compressor
200: precooler
300: heat exchanger
400: refrigerant heat exchanger
410: refrigerant compressor
420: refrigerant condenser
500: first pressure reducing valve
550: second pressure reducing valve
600: gas-liquid separator
700: heater

Claims (12)

In a ship provided with a main engine and a power generation engine supplied with fuel at a lower pressure than the main engine,
a compressor provided in the ship and receiving boil-off gas generated from a storage tank in which liquefied gas is stored and compressing it to the fuel supply pressure of the main engine;
a precooler for receiving all or part of the compressed gas from the compressor and cooling it through heat exchange with a refrigerant;
a heat exchanger for receiving the compressed gas cooled by the precooler and exchanging heat with the uncompressed BOG to be supplied to the compressor;
an expansion means for receiving the compressed gas cooled from the heat exchanger and reducing the pressure; and
and a refrigerant heat exchanger that receives the uncompressed boil-off gas heat-exchanged with the compressed gas from the heat exchanger and heat-exchanges with the refrigerant to be supplied to the precooler; and
A portion of the compressed gas decompressed by the expansion means may be supplied to the power generation engine through the heat exchanger. According to claim 1, wherein the expansion means
a first pressure reducing valve receiving a portion of the compressed gas cooled from the heat exchanger and reducing the pressure; and
a second pressure reducing valve for receiving another part of the compressed gas cooled from the heat exchanger and reducing the pressure to the fuel supply pressure of the power generation engine;
The BOG treatment system of a ship, characterized in that the compressed gas pressure-reduced by the second pressure reducing valve is supplied to the power generation engine through the heat exchanger. 3. The method of claim 2,
Further comprising; a gas-liquid separator for receiving the boil-off gas pressure-reduced from the first pressure reducing valve and separating the gas-liquid;
The gas separated in the gas-liquid separator joins the flow of the uncompressed BOG to be introduced from the storage tank to the heat exchanger, and the liquid separated in the gas-liquid separator is supplied to the storage tank. system. 4. The method of claim 3,
a refrigerant compressor for compressing the refrigerant discharged from the precooler; and
Further comprising; a refrigerant condenser for cooling the refrigerant compressed in the refrigerant compressor;
The refrigerant compressed and cooled through the refrigerant compressor and refrigerant condenser is introduced into the refrigerant heat exchanger, cooled further, and then introduced into the precooler, and the refrigerant circulates in a closed loop refrigerant circulation line. gas processing system. 5. The method of claim 4,
and a heater for heating the boil-off gas that has been depressurized and heat-exchanged through the second pressure reducing valve and the heat exchanger according to the fuel supply conditions of the power generation engine. 4. The method of claim 3,
In the precooler, liquefied gas from the storage tank is supplied as a refrigerant through the refrigerant heat exchanger,
The liquefied gas used as a refrigerant in the refrigerant heat exchanger may be supplied to the power generation engine. In a ship provided with a main engine and a power generation engine supplied with fuel at a lower pressure than the main engine,
a boil-off gas supply line connected to the main engine from a storage tank for storing liquefied gas provided in the ship;
a compressor provided in the boil-off gas supply line to receive the boil-off gas generated from the liquefied gas and compress it to the fuel supply pressure of the main engine;
Reliquefaction for cooling and re-liquefying the BOG branched from the BOG supply line downstream of the compressor and connected to the storage tank, and cooling and reliquefying BOG which is not supplied as fuel of the main engine through heat exchange with uncompressed BOG to be supplied to the compressor. line;
a heat exchanger provided in the reliquefaction line to receive the compressed gas compressed from the compressor and cool it through heat exchange;
a precooler provided at a front end of the heat exchanger in the reliquefaction line to precool the compressed gas to be introduced into the heat exchanger;
a refrigerant heat exchanger receiving the uncompressed boil-off gas heat-exchanged with the compressed gas from the heat exchanger and exchanging heat with the refrigerant to be supplied to the precooler; and
BOG treatment system of a vessel including a; branch line branching from the reliquefaction line at the rear end of the heat exchanger to depressurize the compressed gas and supplying it to the power generation engine through the heat exchanger. 8. The method of claim 7,
a refrigerant circulation line through which a refrigerant for cooling the compressed gas in the precooler circulates;
a refrigerant compressor provided in the refrigerant circulation line to compress the refrigerant discharged from the precooler; and
Further comprising; a refrigerant condenser provided in the refrigerant circulation line to cool the refrigerant compressed in the refrigerant compressor;
The refrigerant compressed and cooled through the refrigerant compressor and refrigerant condenser is introduced into the refrigerant heat exchanger, cooled further, and then introduced into the precooler. 8. The method of claim 7,
a first pressure reducing valve provided in the reliquefaction line and receiving a portion of the compressed gas cooled from the heat exchanger to reduce pressure;
a second pressure reducing valve provided in the branch line and receiving another part of the compressed gas cooled from the heat exchanger to reduce the pressure to the fuel supply pressure of the power generation engine; and
It further includes; a gas-liquid separator for receiving the boil-off gas pressure-reduced from the first pressure reducing valve and separating the gas-liquid;
The liquid separated in the gas-liquid separator is re-stored in the storage tank, and the gas is joined to the uncompressed BOG flow of the BOG supply line to be introduced into the heat exchanger. 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,
Among the BOG compressed in the compressor, BOG not supplied as fuel of the main engine is pre-cooled by heat exchange with a refrigerant in a precooler, and cooled by heat exchange with uncompressed BOG to be introduced into the compressor in a heat exchanger, and reduced pressure. It is further cooled to re-liquefy and stored again in the storage tank,
A portion of the boil-off gas cooled at the rear end of the heat exchanger is branched and decompressed and supplied to a power generation engine receiving fuel at a lower pressure than that of the main engine through the heat exchanger,
In the heat exchanger, the BOG compressed and pre-cooled in the compressor is cooled by heat exchange with the BOG compressed to be supplied to the compressor and the BOG decompressed to be supplied to the power generation engine,
The refrigerant supplied to the precooler is cooled by heat exchange in the downstream of the heat exchanger with the uncompressed BOG to be supplied to the compressor after heat exchange in the heat exchanger. 11. The method of claim 10,
The refrigerant is compressed, cooled, and condensed after passing through the precooler, and the condensed refrigerant is further cooled by heat exchange with the uncompressed BOG and then introduced into the precooler,
The refrigerant is a boil-off gas treatment method of a ship, characterized in that circulating along the refrigerant circulation line. 12. The method of claim 11,
After compression in the compressor, the boil-off gas cooled through the precooler and heat exchanger is further cooled under reduced pressure and then gas-liquid separated, the liquid is supplied to the storage tank and stored again, and the separated flash gas is removed from the storage tank. BOG treatment method of a ship, characterized in that it joins the flow of the uncompressed BOG to be introduced into the heat exchanger.

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