KR20230060560A - Boil-off Gas Treatment System And Method For Ship - Google Patents

Abstract

A system and a method for treating boil-off gas of a ship are disclosed. The system for treating boil-off gas of a ship of the present invention comprises: a compressor that receives and compresses boil-off gas generated from liquefied gas stored in a storage tank of a ship; a cooling part that receives and cools the compressed gas compressed by the compressor; a separator for separating gas and liquid from the reliquefied gas cooled in the cooling part; a fuel supply line that supplies liquefied gas from the storage tank to a propulsion engine in the ship; a compression pump provided in the fuel supply line to compress the liquefied gas with the fuel supply pressure of the propulsion engine; and a liquid line that supplies the reliquefied gas separated in the separator to a front end of the compression pump of the fuel supply line, thereby capable of reliquefying more boil-off gas.

Description

Boil-off Gas Treatment System And Method For Ship}

The present invention relates to a system and method for treating boil-off gas of a ship, and more particularly, to supply boil-off gas (BOG) generated from liquefied gas stored in an onboard storage tank as fuel for a power generation engine and to supply it as fuel. It relates to a system and method for treating boil-off gas of a ship that re-liquefies boil-off gas that has not been re-liquefied and supplied to a propulsion engine or recovered to a storage tank.

Recently, consumption of liquefied gas such as liquefied natural gas (LNG) is rapidly increasing worldwide. Since liquefied gas obtained by liquefying gas at a low temperature has a very small volume compared to gas, it has the advantage of increasing storage and transfer efficiency. In addition, liquefied gas, including liquefied natural gas, can remove or reduce air pollutants during the liquefaction process, so it can be seen as an eco-friendly fuel with less air pollutant emissions during combustion.

Liquefied natural gas is a colorless and transparent liquid obtained by liquefying natural gas whose main component is methane by cooling it to about -163 ° C, and has a volume of about 1/600 compared to natural gas. Therefore, when the natural gas is liquefied and transported, it can be transported very efficiently.

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

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

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

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 is composed of 4 strokes, and adopts an Otto Cycle in which natural gas having a relatively low pressure of about 5.5 barg is injected into the combustion air inlet and compressed while the piston rises.

The X-DF engine is composed of two strokes, uses about 15 barg of natural gas as fuel, and adopts an Otto cycle.

The ME-GI engine consists 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.

The present applicant uses the boil-off gas itself as a refrigerant without a separate refrigerant to re-liquefy the boil-off gas. After cooling the boil-off gas compressed by the compressor by exchanging heat with the boil-off gas before being compressed by the compressor, A method of re-liquefying a part of the boil-off gas by expanding it has been invented, and such a system is called a PRS (Partial Re-liquefaction System).

When the amount of boil-off gas is large due to the large amount of liquefied gas inside the storage tank, when the amount of boil-off gas to be re-liquefied is large, such as when the ship is anchored or operated at low speed and the boil-off gas used in the engine is small , PRS alone may not satisfy the required amount of re-liquefaction, so the present applicant invented a technique for improving PRS to re-liquefy more boil-off gas.

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

A mixed refrigerant or a separate refrigerant such as nitrogen may be used to cool the boil-off gas to be re-liquefied.

On the other hand, in a ship equipped with an engine capable of using boil-off gas as fuel, a compressor for supplying fuel to the engine can be used to re-liquefy the boil-off gas.

1, in a ship equipped with a propulsion engine and power generation engines E1 and E2 receiving boil-off gas and liquefied gas generated from LNG as fuel, the boil-off gas compressed through the fuel supply compressor 10 is supplied to the power generation engine E2 A boil-off gas treatment system for supplying fuel and re-liquefying compressed gas not supplied as fuel through a re-liquefying unit 20 including a heat exchanger and recovering it to a storage tank is schematically illustrated.

In this way, as fuel for the propulsion engine, liquefied gas in the storage tank may be transferred from the storage tank by a pump, compressed with a high-pressure pump, and then supplied through a carburetor according to fuel supply conditions of the engine.

The present invention intends to propose a method for smoothly supplying fuel to a propulsion engine and a power generation engine while processing boil-off gas generated from a storage tank and reducing operating costs through efficient system operation.

According to one aspect of the present invention for solving the above problems, a compressor for receiving and compressing the boil-off gas generated from the liquefied gas stored in the storage tank of the ship;

a cooling unit receiving and cooling the compressed gas compressed by the compressor;

a separator for gas-liquid separation of the re-liquefied gas cooled in the cooling unit;

A fuel supply line through which liquefied gas is supplied from the storage tank to the inboard propulsion engine;

a compression pump provided in the fuel supply line to compress liquefied gas with fuel supply pressure of the propulsion engine; and

There is provided a boil-off gas treatment system of a ship including a liquid line for supplying the re-liquefied gas separated in the separator to the front end of the compression pump of the fuel supply line.

Preferably, a first control valve provided between the cooling unit and the separator to adjust the pressure of the re-liquefied gas to be introduced into the separator; a second control valve provided in the liquid line; a recovery line branched off from the liquid line downstream of the second control valve and connected to the storage tank; a fourth control valve provided in the recovery line; and a shut-off valve provided downstream of the branching point of the recovery line in the liquid line.

a pressure sensor provided in the fuel supply line to sense the pressure at the front end of the compression pump; and a temperature sensor provided in the fuel supply line and sensing a temperature at a front end of the compression pump.

When the pressure detected by the pressure sensor is higher than the set value, the fourth control valve may be opened to send a part of the re-liquefied gas separated from the separator to the storage tank through the recovery line to lower the pressure at the front end of the compression pump.

Further comprising a transfer pump provided in the storage tank and transferring liquefied gas to the fuel supply line, wherein the amount of re-liquefied gas supplied from the separator to the fuel supply line through the liquid line is smaller than the fuel demand of the propulsion engine. In this case, it is possible to supply liquefied gas from the storage tank to the compression pump through the transfer pump by an insufficient amount.

Preferably, a cooling unit bypass line supplying the compressed gas compressed in the compressor to the separator by bypassing the cooling unit; and a fifth control valve provided in the cooling unit bypass line, wherein the pressure sensor and the temperature sensor sense the pressure and temperature of the liquefied gas at the front end of the compression pump to obtain effective suction at the front end of the compression pump due to a supercooled state. When the head (NPSH) is not satisfied, the pressure of the liquefied gas separated from the separator may be increased by opening the fifth control valve, bypassing the cooling part from the compressor, and injecting compressed gas into the separator.

Preferably, a separator bypass line connected from the front end of the first control valve to the rear end of the second control valve of the liquid line; and a sixth control valve provided in the separator bypass line.

Preferably, when the pressure and temperature of the liquefied gas are sensed by the pressure sensor and the temperature sensor and the supercooled state of the re-liquefied gas is stably maintained enough to satisfy the effective suction head of the compression pump, the first control valve is closed and A sixth control valve may be opened to supply re-liquefied gas from the cooling unit to the compression pump by bypassing the separator.

Preferably, a gas supply line connected from the storage tank to the compressor via the cooling unit; a flash gas line supplying the separated gas from the separator to the gas supply line; and a third control valve provided in the flash gas line, wherein the gas supply line is connected to an onboard power generation engine, and the compressor can compress boil-off gas with fuel supply pressure of the power generation engine.

Preferably, a bypass line connected to the compressor by bypassing the cooling unit from the storage tank; and a preheater provided in the bypass line and heating the boil-off gas.

Preferably, a re-liquefaction line is connected from the rear end of the compressor to the separator via the cooling unit, and the cooling unit cools and re-liquefies the compressed gas by heat exchange with the refrigerant circulating in the refrigerant circulation line. can

According to another aspect of the present invention, the boil-off gas generated from the liquefied gas stored in the storage tank of the ship is compressed with a compressor, and the re-liquefied gas cooled through the cooling unit is gas-liquid separated in the separator,

There is provided a method for treating boil-off gas of a ship, characterized in that the re-liquefied gas separated from the separator is supplied to the propulsion engine by supplying the re-liquefied gas to the front end of the compression pump of the fuel supply line through which the liquefied gas is supplied to the ship's propulsion engine.

Preferably, the pressure at the front end of the compression pump is sensed and when the detected pressure is higher than a set value, a part of the re-liquefied gas separated from the separator is sent to the storage tank to lower the pressure at the front end of the compression pump and supplied from the separator to the fuel supply line. When the amount of re-liquefied gas is less than the fuel demand of the propulsion engine, the insufficient amount of liquefied gas may be pumped from the storage tank and supplied to the compression pump.

Preferably, when the pressure and temperature of the liquefied gas at the front of the compression pump are detected and the effective suction head (NPSH) at the front of the compression pump is not satisfied due to the supercooled state, the compressed gas is bypassed from the compressor to the cooling unit The pressure of the liquefied gas separated from the separator may be increased by injecting into the separator.

Preferably, when the supercooled state of the re-liquefied gas is stably maintained enough to satisfy the effective suction head of the compression pump by detecting the pressure and temperature of the liquefied gas at the front end of the compression pump, the separator is bypassed from the cooling unit to Liquefied gas can be directly supplied to the compression pump.

Preferably, the compressor compresses the boil-off gas with the fuel supply pressure of the onboard power generation engine, and in the cooling unit, the uncompressed boil-off gas to be supplied from the storage tank to the compressor and the refrigerant circulating in the refrigerant circulation line exchange heat with the compressor. The compressed gas can be cooled and re-liquefied.

In the present invention, the boil-off gas is re-liquefied and sent directly to the front end of the compression pump of the propulsion engine so that it can be supplied as fuel to the propulsion engine, thereby shortening the length of the pipe for supplying fuel and preventing the additional operation of the transfer pump provided in the storage tank. It can reduce electrical energy consumption.

Accordingly, in the past, cool-down was required from the storage tank to the front end of the compression pump prior to fuel supply to the propulsion engine. occurrence can be reduced.

In addition, by configuring a cooling unit bypass line and a control valve that can bypass the cooling unit and introduce the compressed gas into the separator, the re-liquefied gas is not smoothly discharged from the separator due to the decrease in separator pressure due to the supercooled re-liquefied gas. It is possible to prevent cavitation and prevent damage to the device by solving and meeting the effective suction head of the front end of the compression pump.

1 schematically shows an example of a conventional boil-off gas treatment system.
2 schematically illustrates a boil-off gas treatment system according to an embodiment of the present invention.
3 to 5 schematically illustrate a method of operating the system of the embodiment shown in FIG. 2 according to ship operating conditions.

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 a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In adding reference numerals to the components of each drawing, it should be noted that the same components are marked with the same numerals as much as possible, even if they are displayed on different drawings.

Hereinafter, in the ship of the present invention, all types of engines that can use liquefied gas and boil-off gas generated from liquefied gas as fuel for engines for propulsion or power generation are installed or use liquefied gas or boil-off gas as fuel for inboard engines. of ships, typically LNG carriers, liquid hydrogen carriers, ships with self-propelled capabilities such as LNG RVs (Regasification Vessel), LNG FPSOs (Floating Production Storage Offloading), LNG FSRUs (Floating Storage Regasification Units) ) may also include offshore structures that do not have propulsion capability but are floating on the sea.

In addition, in the present invention, the liquefied gas can include all types 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. 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. may be gas. However, in an embodiment 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 mixture state, a gas state, and a supercritical fluid state according to operating conditions of the system.

FIG. 2 schematically shows a boil-off gas treatment system according to an embodiment of the present invention, and FIGS. 3 to 5 schematically show a method of operating the system according to a ship operating state.

As shown in FIG. 2, the system of this embodiment is provided on the ship to process boil-off gas generated from the storage tank in which liquefied gas is stored, and a compressor for receiving and compressing boil-off gas generated from the storage tank T ( 100A, 100B), and a cooling unit 200 that receives and cools all or part of the boil-off gas compressed by the compressor.

Compressors (100A, 100B) to compress the boil-off gas, for example, can compress the boil-off gas to the fuel supply pressure of the power generation engine of the ship. The compressor compresses the boil-off gas with the fuel supply pressure of the power generation engine to supply fuel to the power generation engine E2, and sends the remaining boil-off gas to the re-liquefaction line to be re-liquefied. The compressor can compress the boil-off gas to 5 to 10 bara, for example, if a DF GE engine is provided.

According to ship regulations, a compressor that supplies fuel with an engine must be designed for redundancy in case of an emergency. This means that it is designed to be usable. To this end, the compressor is composed of a main compressor (100A) and a redundancy compressor (100B), and in normal operation, the main compressor, that is, one compressor is operated to supply fuel to the power generation engine from it, and the remaining amount of compressed gas is supplied to the re-liquefaction line ( RL) to re-liquefy.

Fuel supply to the propulsion engine is a compression pump (400A, 400B) that pumps liquefied gas from the transfer pump (P) provided in the storage tank (T) and pressurizes it to the fuel supply pressure of the propulsion engine along the fuel supply line (FSL) And it can be supplied to the propulsion engine through the vaporizer 500 for heating the pressurized liquefied gas according to the fuel supply temperature.

A pressure sensor (PT) and a temperature sensor (TT1) are provided in the fuel supply line to detect pressure and temperature at the front end of the compression pump.

A liquefied gas branch line connected to the power generation engine from the fuel supply line downstream of the vaporizer may be branched, and the pressure and temperature of the liquefied gas may be adjusted and supplied to the power generation engine E2.

The compressed gas supplied to the reliquefaction line RL after being compressed by the compressors 100A and 100B is cooled through the cooling unit 200 . The cooling unit may include a heat exchanger that cools the compressed gas compressed by the compressor, the uncompressed boil-off gas to be introduced into the compressor, and the refrigerant through heat exchange. To this end, a gas supply line (GL) is connected from the storage tank (T) to the compressor (100A, 100B) via the cooling unit, and a re-liquefaction line (RL) connected to the cooling unit for re-liquefaction of boil-off gas at the rear end of the compressor. provided In addition, a bypass line (BL) capable of supplying evaporation gas from the storage tank to the compressor by bypassing the cooling unit is connected, and a preheater 250 for heating the evaporation gas is provided in the bypass line. When the re-liquefaction system is not in operation or at the beginning of operation of the re-liquefaction system, the boil-off gas from the storage tank can be directly supplied to the compressor through the bypass line without passing through the heat exchanger of the cooling unit.

In the heat exchanger of the cooling unit, a refrigerant circulating through a refrigerant circulation line (not shown) may be supplied to supply cold heat. As such, the refrigerant circulating through the refrigerant circulation line and supplied to the heat exchanger is, for example, nitrogen (N ₂ ). can be used

In the system of this embodiment, a separator 300 for gas-liquid separation of the re-liquefied gas cooled in the cooling unit, and a liquid line for supplying the re-liquefied gas separated from the separator to the front end of the compression pumps 400A and 400B of the fuel supply line ( LL) is provided.

A first control valve (CV1) for adjusting the pressure of the re-liquefied gas to be introduced into the separator is provided between the cooling unit and the separator, and a second control valve (CV2) is provided in the liquid line, respectively.

The gas separated from the separator 300 is supplied to the gas supply line GL through the flash gas line FL, and joins the flow of uncompressed boil-off gas from the storage tank. A third control valve (CV3) is provided in the flash gas line.

On the other hand, at the downstream of the second control valve (CV2), the liquid line (LL) is branched into two flows, one flow is connected to the front end of the compression pump of the fuel supply line (LLa), and the other flow is branched from the liquid line and stored It is connected to the tank (LLb). As such, a fourth control valve CV4 is provided in the recovery line LLb branched from the liquid line and connected to the storage tank, and a shut-off valve IV is provided downstream of the branching point of the recovery line from the liquid line.

A cooling unit bypass line (CBL) is provided in which compressed gas compressed by the compressor bypasses the cooling unit and is supplied to the separator, and a fifth control valve (CV5) for opening and closing the cooling unit bypass line is provided in the cooling unit bypass line. When the re-liquefied gas introduced into the separator through the cooling unit is supercooled, the separator pressure is lowered, and as a result, the re-liquefied gas separated from the separator is not smoothly discharged to the liquid line or recovery line, or the supply of the super-cooled re-liquefied gas The effective suction head of the front end of the compression pump may not be satisfied. In the system of this embodiment, when the re-liquefied gas is supercooled, a part of the compressed gas compressed in the compressors 100A and 100B bypasses the cooling unit 200 and is directly introduced into the separator 300. A cooling unit bypass line (CBL) ) was formed.

In addition, the system of this embodiment has a separator bypass line (SBL) connected from the front end of the first control valve (CV1) to the rear end of the second control valve (CV2) of the liquid line (LL), and a sixth control provided on the separator bypass line. Includes valve CV6. When the re-liquefied gas passing through the cooling unit satisfies the effective suction head of the compression pump and stably maintains a supercooled state, the compression pumps (400A, 400B) of the fuel supply line (FSL) directly from the cooling unit 200 without passing through the separator A separator bypass line (SBL) was constructed to supply re-liquefied gas to the front end.

Next, with reference to FIGS. 3 to 5, the operation method of the system according to the present embodiment according to the ship operation state will be schematically reviewed.

First, FIGS. 3 and 4 relate to the driving method of the present embodiment when the propulsion engine and the power generation engine are operated by ship navigation.

As shown in FIG. 3, the boil-off gas of the storage tank T is compressed in the compressor 100A through the heat exchanger of the cooling unit 200 through the gas supply line GL and supplied to the power generation engine E2, The compressed gas not supplied to the power generation engine is re-liquefied through the heat exchanger of the cooling unit 200 along the re-liquefying line RL, and then introduced into the separator 300 through the first control valve CV1. The re-liquefied gas separated from the separator passes through the second control valve (CV2) and the shutoff valve (IV) through the liquid line (LL) and is supplied to the front end of the compression pump (400A) of the fuel supply line (FSL). .

If the re-liquid amount is greater than the fuel demand of the propulsion engine, the pressure at the front end of the compression pump rises. can be maintained as The pressure sensor (PT) detects the pressure at the front end of the compression pump (400A) and compares it with the set value. It is sent to the storage tank (T) through and controlled to lower the front pressure of the compression pump.

Conversely, if the amount of re-liquefied gas supplied from the separator to the fuel supply line through the liquid line is less than the fuel demand of the propulsion engine, pumping the liquefied gas from the storage tank (T) through the transfer pump (P) as much as the insufficient amount Supplement is supplied by the compression pump (400A).

While the pressure sensor (PT) and temperature sensor (TT1) detect the pressure and temperature of the liquefied gas at the front of the compression pump, the subcooling state of the re-liquefied gas lowers the separator pressure, resulting in effective suction at the front of the compression pump When the head (NPSH) is not satisfied, the fifth control valve (CV5) of the cooling unit bypass line (CBL) is opened to inject some of the compressed gas from the compressor (100A) into the separator (300) bypassing the cooling unit (200). It increases the pressure of the re-liquefied gas separated from the separator and adjusts the effective suction head of the compression pump.

When the state of the re-liquefied gas maintains a stable supercooled state sufficient to satisfy the effective suction head of the compression pump, as shown in FIG. 4, the first control valve (CV1) at the inlet of the separator 300 is closed and the separator bypass line (SBL) By opening the sixth control valve (CV6) of the cooling unit 200, the re-liquefied gas can be directly supplied to the front end of the compression pump (400A). At this time, while the pressure sensor PT detects the pressure at the front end of the compression pump and the amount of re-liquid exceeds the fuel demand of the propulsion engine, if the pressure at the front end of the compression pump rises, the fourth control valve (CV4) is opened as described above to release some of the re-liquefied gas. It is recovered to the storage tank through the recovery line (LLb), and conversely, if the amount of ash is less than the fuel demand of the propulsion engine, the liquefied gas from the storage tank is supplied supplementally to the compression pump through the transfer pump (P).

Meanwhile, in an anchoring state of the ship, there is no fuel consumption required by the propulsion engine. 5 schematically shows the driving method of this embodiment in such a mooring state.

As shown in FIG. 5, in the anchored state, the shutoff valve (IV) of the liquid line (LLa) connected to the fuel supply line (FSL) is closed, and the second control valve (CV2) and the fourth control valve (CV4) are opened. The entire amount of re-liquefied gas that has passed through the cooling unit 200 and the separator 300 is recovered to the storage tank T through the recovery line LLb.

Even in this case, if the re-liquefied gas is not smoothly discharged from the separator because the separator pressure is lowered due to supercooling of the re-liquefied gas, as described above, the fifth control valve (CV5) is opened to direct some of the compressed gas to the separator by bypassing the cooling unit. By injecting, the separator pressure can be increased and the re-liquefied gas can be smoothly discharged into the storage tank.

As described above, in this embodiment, the re-liquefied gas is sent directly to the front end of the compression pump of the propulsion engine so that it can be supplied as fuel to the propulsion engine, thereby shortening the length of the pipe for fuel supply and reducing the additional operation of the transfer pump, thereby reducing the electric energy Consumption is reduced, and only the shortened fuel supply path can be cooled down prior to fuel supply to the propulsion engine, reducing additional BOG caused by pipe cool-down.

In addition, it solves the problem that the re-liquefied gas is not smoothly discharged from the separator due to the pressure drop in the separator due to the supercooled re-liquefied gas, and the cavitation of the compression pump is easily controlled to satisfy the effective suction head of the front end of the compression pump. ) and damage to the device.

It is obvious to those skilled in the art that the present invention is not limited to the above embodiments and can be variously modified or modified without departing from the technical gist of the present invention. it did

T: storage tank
P: transfer pump
GL: gas supply line
FSL: 1st fuel supply line
RL: reliquefaction line
LL: Liquidline
100A, 100B: Compressor
200: cooling unit
300: separator
400A, 400B: compression pump
500: carburetor
CV1, CV2, CV3, CV4, CV4, CV5, CV6: first to sixth control valves

Claims (16)

A compressor for receiving and compressing boil-off gas generated from liquefied gas stored in a storage tank of a ship;
a cooling unit receiving and cooling the compressed gas compressed by the compressor;
a separator for gas-liquid separation of the re-liquefied gas cooled in the cooling unit;
A fuel supply line through which liquefied gas is supplied from the storage tank to the inboard propulsion engine;
a compression pump provided in the fuel supply line to compress liquefied gas with fuel supply pressure of the propulsion engine; and
A liquid line for supplying the re-liquefied gas separated in the separator to the front end of the compression pump of the fuel supply line: Ship boil-off gas treatment system comprising a. According to claim 1,
a first control valve disposed between the cooling unit and the separator and regulating the pressure of the re-liquefied gas to be introduced into the separator;
a second control valve provided in the liquid line;
a recovery line branched off from the liquid line downstream of the second control valve and connected to the storage tank;
a fourth control valve provided in the return line; and
A shut-off valve provided downstream of the branching point of the recovery line in the liquid line: Ship's boil-off gas treatment system further comprising a. According to claim 2,
a pressure sensor provided in the fuel supply line to sense the pressure at the front end of the compression pump; and
Ship's boil-off gas treatment system further comprising: a temperature sensor provided in the fuel supply line to detect the temperature at the front end of the compression pump. According to claim 3,
When the pressure detected by the pressure sensor is higher than the set value, the fourth control valve is opened to send some of the re-liquefied gas separated from the separator to the storage tank through the recovery line to lower the pressure at the front end of the compression pump. gas handling system. According to claim 3,
Further comprising a transfer pump provided in the storage tank and transferring liquefied gas to the fuel supply line,
When the amount of re-liquefied gas supplied from the separator to the fuel supply line through the liquid line is less than the fuel demand of the propulsion engine, supplying liquefied gas from the storage tank to the compression pump through the transfer pump by the insufficient amount Ship's evaporation gas treatment system, characterized in that. According to claim 3,
a cooling unit bypass line supplying the compressed gas compressed by the compressor to the separator by bypassing the cooling unit; and
A fifth control valve provided in the cooling unit bypass line;
When the pressure sensor and the temperature sensor detect the pressure and temperature of the liquefied gas at the front of the compression pump and the effective suction head (NPSH) at the front of the compression pump is not satisfied due to the supercooled state, the fifth control valve is opened to open the compressor The boil-off gas treatment system of a ship, characterized in that by bypassing the cooling unit and injecting compressed gas into the separator to increase the pressure of the liquefied gas separated from the separator. According to claim 6,
a separator bypass line connected from the front end of the first control valve to the rear end of the second control valve of the liquid line; and
A sixth control valve provided in the separator bypass line: The ship's boil-off gas treatment system further comprising a. According to claim 7,
When the pressure and temperature of the liquefied gas are sensed by the pressure sensor and the temperature sensor and the supercooled state of the re-liquefied gas is stably maintained enough to satisfy the effective suction head of the compression pump, the first control valve is closed and the sixth control valve The boil-off gas treatment system of a ship, characterized in that it is possible to supply re-liquefied gas to the compression pump by bypassing the separator from the cooling unit by opening the. According to claim 7,
a gas supply line connected from the storage tank to the compressor via the cooling unit;
a flash gas line supplying the separated gas from the separator to the gas supply line; and
Further comprising a third control valve provided in the flash gas line,
The gas supply line is connected to the onboard power generation engine, and the compressor compresses the boil-off gas with the fuel supply pressure of the power generation engine. According to claim 9,
a bypass line connected to the compressor by bypassing the cooling unit from the storage tank; and
Ship's boil-off gas treatment system further comprising: a preheater provided in the bypass line and heating the boil-off gas. According to any one of claims 1 to 10,
A re-liquefaction line connected from the rear end of the compressor to the separator through the cooling unit;
The cooling unit cools and re-liquefies the compressed gas by heat exchange with the refrigerant circulating in the refrigerant circulation line. The evaporation gas generated from the liquefied gas stored in the ship's storage tank is compressed with a compressor, and the re-liquefied gas cooled through the cooling unit is separated from the gas-liquid in the separator,
A method for treating boil-off gas of a ship, characterized in that the re-liquefied gas separated from the separator is supplied to the propulsion engine by supplying the re-liquefied gas to the front end of the compression pump of the fuel supply line through which the liquefied gas is supplied to the ship's propulsion engine. According to claim 12,
The pressure at the front of the compression pump is detected and when the detected pressure is higher than the set value, a part of the re-liquefied gas separated from the separator is sent to the storage tank to lower the pressure at the front of the compression pump,
When the amount of re-liquefied gas supplied from the separator to the fuel supply line is less than the fuel demand of the propulsion engine, liquefied gas is pumped from the storage tank by an insufficient amount and supplied to the compression pump. gas treatment method. According to claim 13,
When the effective suction head (NPSH) of the compression pump is not satisfied due to the supercooled state by detecting the pressure and temperature of the liquefied gas at the front of the compression pump, bypassing the cooling unit from the compressor and injecting the compressed gas into the separator A method for treating boil-off gas of a ship, characterized in that for increasing the pressure of the liquefied gas separated from the separator. According to claim 14,
When the supercooled state of the re-liquefied gas is stably maintained enough to satisfy the effective suction head of the compression pump by detecting the pressure and temperature of the liquefied gas at the front end of the compression pump, the re-liquefied gas is directly bypassed from the cooling unit by bypassing the separator A method for treating boil-off gas of a ship, characterized in that it can be supplied by the compression pump. According to any one of claims 12 to 15,
The compressor compresses the boil-off gas with the fuel supply pressure of the onboard power generation engine,
The cooling unit cools and re-liquefies the compressed gas in the compressor by heat exchange with the refrigerant circulating in the refrigerant circulation line and the uncompressed boil-off gas to be supplied from the storage tank to the compressor.

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