KR20230023114A - Boil-Off Gas Reliquefaction System and Method for Ship - Google Patents

Abstract

Disclosed are a system and a method for reliquefying boil-off gas of a ship, which can increase re-liquefaction performance by effectively cooling boil-off gas to be re-liquefied while controlling boil-off gas temperature within an appropriate range required by a compressor. According to the present invention, the system for reliquefying boil-off gas of a ship comprises: a compressor for compressing boil-off gas generated from liquefied gas stored in a storage tank provided on the ship; a heat exchanger cooling the compressed gas compressed by the compressor; a refrigerant circulation line through which refrigerant supplied to the heat exchanger circulates; a temperature elevating line connected from the storage tank to the compressor; and a heater provided on the temperature elevating line. The heater heats the boil-off gas to an appropriate input temperature of the compressor.

Description

Boil-Off Gas Reliquefaction System and Method for Ship}

The present invention relates to a re-liquefaction system and method for re-liquefying boil-off gas (BOG) generated from liquefied gas stored in a storage tank of a ship and recovering it 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 a 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. These compressors are provided in accordance with the fuel supply conditions required by the engine, but also require the temperature of boil-off gas introduced into the compressor to be in an appropriate range to prevent damage to the device.

The present invention is to propose a system capable of increasing re-liquefaction performance by effectively cooling boil-off gas to be re-liquefied while controlling boil-off gas temperature within an appropriate range required by the compressor.

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

a heat exchanger cooling the compressed gas compressed by the compressor;

a refrigerant circulation line through which the refrigerant supplied to the heat exchanger circulates;

Ga line connected from the storage tank to the compressor; and

Including: a heater provided in the ga-line,

The heater provides a boil-off gas re-liquefaction system of a ship, characterized in that for heating the boil-off gas to an appropriate input temperature of the compressor.

Preferably, a gas supply line connected from the storage tank to the compressor via the heat exchanger; And a gas supply valve provided on the gas supply line to control the flow rate of boil-off gas to be introduced into the compressor via the heat exchanger: After heat exchange with the compressed gas, it may be introduced into the compressor.

Preferably, a bypass valve provided in the heating line to control the flow rate of the boil-off gas to be introduced into the compressor via the heater is further included, and the boil-off gas generated in the storage tank is heated by heat exchange through the heat exchanger Introduced to the compressor, but when the re-liquefaction system is not operated or the load of the re-liquefaction system is low, all or part of the evaporation gas generated in the storage tank bypasses the heat exchanger and heats in the heater through the heating and can be introduced into the compressor.

Preferably, a refrigerant compression unit provided in the refrigerant circulation line and compressing the refrigerant discharged after heat exchange in the heat exchanger; And a refrigerant expansion device provided in the refrigerant circulation line and supplying the refrigerant to the heat exchanger by expanding and cooling the refrigerant. The refrigerant may be expanded and cooled in the expansion device and supplied as a cold heat source to the heat exchanger.

Preferably, in the heat exchanger, the compressed gas compressed in the compressor, the refrigerant expanded and cooled in the refrigerant expansion device, the uncompressed boil-off gas to be introduced from the storage tank to the compressor along the gas supply line, and the refrigerant compression Four streams of refrigerant compressed in the section can be heat exchanged.

Preferably, the refrigerant compression unit may be connected to the refrigerant expansion device and receive expansion energy of the refrigerant from the refrigerant expansion device to compress the refrigerant.

Preferably, the compressor compresses the boil-off gas with the fuel supply pressure of the propulsion engine provided in the ship, but the propulsion engine can receive the compressed boil-off gas at 10 to 20 bara.

Preferably, a pressure reducing device for receiving the compressed gas cooled by heat exchange in the heat exchanger and reducing the pressure; and a gas-liquid separator for gas-liquid separation by receiving the reduced boil-off gas from the pressure reducing device, wherein the flash gas separated in the gas-liquid separator joins the uncompressed boil-off gas stream at the front end of the heat exchanger, and the gas-liquid separator The liquefied gas separated from may be recovered to the storage tank.

According to another aspect of the present invention, the boil-off gas generated from the onboard storage tank is compressed with a compressor, cooled by heat exchange in a heat exchanger supplied with a refrigerant circulating along the refrigerant circulation line, and re-liquefied,

The boil-off gas generated from the storage tank is heated to an appropriate input temperature of the compressor through a heater, and there is provided a method of re-liquefying boil-off gas of the ship, characterized in that it can be introduced into the compressor.

The boil-off gas generated in the storage tank is heated by heat exchange through the heat exchanger and introduced to the compressor. When the re-liquefaction system is not operated or the load of the re-liquefaction system is low, the boil-off gas generated in the storage tank is transferred to the heat exchanger. Bypassing the machine, it may be heated in the heater through the heating line and introduced into the compressor.

The refrigerant circulating in the refrigerant circulation line is compressed in the refrigerant compression unit, cooled through the heat exchanger, expanded and cooled in the refrigerant expansion device, and supplied as a cold heat source to the heat exchanger, and the refrigerant compression unit is connected to the refrigerant expansion device, The refrigerant may be compressed by receiving expansion energy of the refrigerant from the refrigerant expansion device.

The compressor compresses the boil-off gas with the fuel supply pressure of the propulsion engine provided in the ship, but the propulsion engine can receive the compressed boil-off gas at 10 to 20 bara.

In the present invention, the cryogenic uncompressed evaporation gas generated from the storage tank is introduced into the compressor through the heat exchanger, used as a cooling heat source of the heat exchanger together with the refrigerant in the refrigerant circulation line, and the cryogenic evaporation gas at the proper input temperature required by the compressor. so that it can be supplied to the compressor. Furthermore, a heating line is provided in which the boil-off gas from the storage tank bypasses the heat exchanger and can be directly supplied to the compressor, and a heater is provided in the heating line so that the re-liquefaction system is not operated or the load of the re-liquefaction system is low. Even at this time, the boil-off gas is heated to an appropriate input temperature so that it can be supplied to the compressor.

In this way, by using the cooling heat of the boil-off gas itself and the cooling heat of the refrigerant cycle to increase the cooling efficiency of the heat exchanger, in order to increase the re-liquefaction rate, additional facilities for compressing the boil-off gas to be re-liquefied to high pressure, such as a boost compressor, are installed and operated. CAPEX and OPEX can be reduced. Regardless of the operation and load of the re-liquefaction system, boil-off gas can be supplied at an appropriate input temperature, preventing damage to the compressor and enabling stable operation.

In addition, since only the residual boil-off gas is re-liquefied after fuel consumption, the load of the refrigerant cycle can be adjusted according to the amount of residual boil-off gas, thereby reducing fuel consumption.

1 schematically shows a boil-off gas re-liquefaction system of a ship according to an 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 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.

1 schematically shows a boil-off gas re-liquefaction system of a ship according to an embodiment of the present invention.

Compressors (100a, 100b) for re-liquefying the boil-off gas generated in the storage tank in which the liquefied gas is stored provided on the ship as shown in FIG. 1, receiving and compressing the boil-off gas generated in the storage tank (T), It includes a heat exchanger 200 that receives all or part of the boil-off gas compressed by the compressor and cools it by heat exchange with the uncompressed boil-off gas and the refrigerant to be introduced into the compressor. To this end, a gas supply line (GL) is connected from the storage tank (T) to the compressors (100a, 100b) via a heat exchanger, and a re-liquefaction line (RL) for re-liquefying the boil-off gas at the rear end of the compressor and supplying it to the storage tank is each is provided.

In addition, a refrigerant circulation line (CL) in which the refrigerant supplied to the heat exchanger 200 circulates is provided, and the refrigerant circulation line is provided with a refrigerant expansion device 650 in which the refrigerant supplied to the heat exchanger is expanded and cooled, and after heat exchange in the heat exchanger. A refrigerant compression unit 600 for compressing the discharged refrigerant is provided.

The refrigerant compression unit 600 is provided as a compander compressor and is axially connected to the refrigerant expansion device 650 to receive expansion energy of the refrigerant and drive the compander compressor. The refrigerant compression unit may be driven by a motor, and the motor may be connected to the refrigerant expansion device 650 to receive expansion energy of the refrigerant and compress the refrigerant while the motor is driven.

The refrigerant compressed in the refrigerant compression unit 600 is introduced into the heat exchanger 200, cooled, supplied to the refrigerant expansion device 650 along the refrigerant circulation line CL, expanded and cooled, and returned to the heat exchanger 200. supplied as a refrigerant.

Accordingly, in the heat exchanger 200 in this embodiment, all or part of the compressed boil-off gas, the uncompressed boil-off gas to be introduced into the compressor, the refrigerant expanded and cooled in the refrigerant expansion device, and the refrigerant compressed in the refrigerant compression unit are 4 The branch streams exchange heat.

As the refrigerant supplied to the heat exchanger while circulating in the refrigerant circulation line CL, for example, nitrogen (N ₂ ) may be used. In the case of supplying compressed refrigerant to a heat exchanger, cooling it with the cooling heat of the refrigerant itself, expanding it, supplying it to the heat exchanger, and cooling it by exchanging heat with the boil-off gas, the main component is methane to cool the boil-off gas to the liquefaction temperature. Due to the difference in heat capacity between boil-off gas and nitrogen, a large amount of nitrogen refrigerant is required, resulting in the use of most of the cooling heat of the refrigerant cycle for cooling the nitrogen refrigerant itself, and increased capacity of devices that compress and expand the refrigerant, There is a problem of causing an increase in power consumption. In order to solve this problem, in the present embodiment, the cryogenic uncompressed boil-off gas generated from the storage tank is configured to be introduced to the compressor through the heat exchanger, thereby reducing the refrigerant flow rate required in the refrigerant cycle, and accordingly, a device for compressing and expanding the refrigerant. Reduces capacity and power consumption, reducing installation and operating costs.

In the system of this embodiment, looking at the process of treating the boil-off gas generated from the liquefied gas in the storage tank, the boil-off gas generated in the storage tank T is introduced into the compressors 100a and 100b via the heat exchanger 200 .

In the compressor (100a, 100b) to compress the boil-off gas, for example, the boil-off gas can be compressed by the fuel supply pressure of the main engine or propulsion engine of the ship. For example, if a DF engine is provided, it can be compressed to 5.5 barg, to 15 barg if an X-DF engine is provided, and to 300 barg if an ME-GI engine is provided. The compressed boil-off gas may be supplied as fuel to the propulsion engine E1 and the power generation engine E2 of the ship, and the remaining boil-off gas after fuel supply may be re-liquefied.

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 propulsion engine and power generation engine, and the remaining amount of compressed gas is It can be re-liquefied through the re-liquefaction line (RL).

The boil-off gas compressed by the compressor is introduced into the heat exchanger 200 along the reliquefaction line RL and cooled. The boil-off gas to be compressed and re-liquefied and the refrigerant compressed in the refrigerant compression unit form the hot stream of the heat exchanger, and the uncompressed boil-off gas and the refrigerant cooled by expansion in the refrigerant expansion device form the cold stream.

In the heat exchanger 200, four streams are heat-exchanged, and the hot stream is cooled by heat exchange with the cold stream. The heat exchanger may be provided with, for example, a brazed aluminum heat exchanger (BAHE).

The introduction and discharge positions of each stream in the heat exchanger can be different so that the heat exchange between the hot stream and the cold stream is more effective and the compressed gas to be re-liquefied can be cooled.

The nitrogen refrigerant introduced into the heat exchanger after expansion cooling in the cold stream of the heat exchanger has a temperature of around -167 ℃, for example, if the pressure is around 10 bar, and is higher than the uncompressed evaporation gas around -50 ℃, which is another cold stream of the heat exchanger. The temperature is low. Therefore, when introduced together in the heat exchanger, all of the cold heat of the nitrogen refrigerant is not used for cooling the compressed gas to be re-liquefied, and some of the cold heat can be absorbed by other flows. It is introduced downstream so that it passes through all of the heat exchanger, and the uncompressed boil-off gas flow (GL) having a high temperature in the cold stream is introduced into the middle part of the heat exchanger.

Therefore, the compressed gas of the re-liquefaction line passes through the high-temperature region of the heat exchanger and the low-temperature region and is sequentially cooled. is supplied and cooled, and in the low-temperature region, it is sequentially cooled by exchanging heat with one cold stream and the refrigerant of the refrigerant circulation line immediately after being introduced into the heat exchanger.

By exchanging heat in this way, the compressed gas to be re-liquefied can be cooled more effectively to increase the re-liquefaction rate, and damage to the device can be prevented by preventing thermal fatigue of the heat exchanger.

On the other hand, the boil-off gas cooled by heat exchange in the heat exchanger is introduced into the decompression device 400 of the reliquefaction line and reduced in pressure, and the boil-off gas reduced in the decompression device is introduced into the gas-liquid separator 500.

The decompression device 400 may be composed of an expander that depressurizes the compressed and cooled boil-off gas or an expansion valve such as a Joule-Thomson valve. Through decompression, the evaporation gas is cooled by adiabatic expansion or isentropic expansion.

The evaporation gas depressurized and additionally cooled in the pressure reducing device is introduced into the gas-liquid separator 500, and the liquid separated in the gas-liquid separator is supplied to the storage tank T along the reliquefaction line RL and stored again. However, since flash gas (a gas) and liquefied gas (a liquid) may not be phase-separated 100% even though the gas-liquid separator passes through the gas-liquid separator in the present embodiments, the separated liquid or liquefied gas may include unseparated flash gas.

The flash gas separated in the gas-liquid separator is supplied from the top of the gas-liquid separator to the uncompressed boil-off gas flow in front of the heat exchanger and heater through the flash gas line FL, and may be introduced into the compressor via the heat exchanger or heater.

The system of this embodiment increases the cooling efficiency of the heat exchanger by using the cooling heat of the boil-off gas itself and the cooling heat of the refrigerant cycle, so as to increase the re-liquefaction rate. CAPEX and OPEX can be saved because it can be installed and operated.

On the other hand, boil-off gas generated in the storage tank (T) is discharged from the storage tank at a cryogenic temperature in the range of -140 ° C to -100 ° C depending on the tank operation, the type of compressor provided for engine fuel supply Depending on the method, the evaporation gas introduced may be required to be within a certain temperature range. In particular, a compressor for fuel supply of a medium-pressure engine such as an X-DF engine may be installed as a room temperature compressor. The low-temperature evaporation gas generated in the tank passes through the heat exchanger and can be sufficiently heated and introduced to the compressor. Even if it passes through the steamer, the evaporation gas is not sufficiently heated to the proper input temperature required by the compressor.

In order to solve this problem, in the system of this embodiment, a heating line (BL) that can be directly introduced into the compressors 100a and 100b bypassing the heat exchanger 200 in the storage tank T is provided, and the evaporation A heater 300 capable of heating gas was provided.

A gas supply valve (GV) is provided in the gas supply line (GL) to control the flow rate of boil-off gas to be introduced into the compressors (100a, 100b) via the heat exchanger (200), and the heater (300) is provided in the heating line (BL) A bypass valve (BV) is provided to adjust the flow rate of the boil-off gas to be introduced into the compressors 100a and 100b via.

When the re-liquefaction system is operated, the boil-off gas generated in the storage tank (T) is heated by heat exchange through the heat exchanger 200 and introduced into the compressors 100a and 100b, but the re-liquefaction system is not operated or the re-liquefaction system is loaded When the load is low, all or part of the boil-off gas generated in the storage tank bypasses the heat exchanger and is heated in the heater 300 through the heating line BL to be introduced into the compressors 100a and 100b.

By controlling the opening and closing of the gas supply valve (GV) and the bypass valve (BV), the flow rate of boil-off gas introduced to the compressor through the heat exchanger and the heater is adjusted, so that the re-liquefaction system is not operating or the re-liquefaction system is Even when the load is low, the compressor can supply boil-off gas at the proper input temperature required. In this way, boil-off gas can be supplied at an appropriate input temperature regardless of the operation and load of the re-liquefaction system, preventing damage to the compressor and stably operating it.

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
GL: gas supply line
BL: Gaonline
CL: refrigerant circulation line
100a, 100b: compressor
200: heat exchanger
300: heater
400: decompression device
500: gas-liquid separator
600: refrigerant compression unit
650: refrigerant expansion device

Claims (12)

A compressor for compressing boil-off gas generated from liquefied gas stored in a storage tank provided on the ship;
a heat exchanger cooling the compressed gas compressed by the compressor;
a refrigerant circulation line through which the refrigerant supplied to the heat exchanger circulates;
Ga line connected from the storage tank to the compressor; and
Including: a heater provided in the ga-line,
The heater boil-off gas re-liquefaction system of the ship, characterized in that for heating the boil-off gas to an appropriate input temperature of the compressor. According to claim 1,
a gas supply line connected from the storage tank to the compressor via the heat exchanger; and
Further comprising: a gas supply valve provided in the gas supply line to control the flow rate of boil-off gas to be introduced into the compressor via the heat exchanger;
Boiled gas generated in the storage tank is introduced into the compressor after heat exchange with the compressed gas in the heat exchanger through the gas supply line. According to claim 2,
Further comprising: a bypass valve provided in the ga-line to control the flow rate of boil-off gas to be introduced into the compressor via the heater;
The evaporated gas generated in the storage tank is heated by heat exchange through the heat exchanger and introduced into the compressor,
When the re-liquefaction system is not operated or the load of the re-liquefaction system is low, all or part of the boil-off gas generated in the storage tank bypasses the heat exchanger and is heated in the heater through the gauging line and introduced into the compressor Boiled gas re-liquefaction system of a ship, characterized in that. According to claim 3,
a refrigerant compression unit provided in the refrigerant circulation line and compressing the refrigerant discharged after heat exchange in the heat exchanger; and
Further comprising a refrigerant expansion device provided in the refrigerant circulation line and supplying the refrigerant to the heat exchanger by expanding and cooling the refrigerant,
The refrigerant in the refrigerant circulation line is compressed in the refrigerant compression unit, cooled through the heat exchanger, expanded and cooled in the refrigerant expansion device, and supplied as a cold heat source to the heat exchanger. According to claim 4,
In the heat exchanger, compressed gas compressed in the compressor, refrigerant expanded and cooled in the refrigerant expansion device, uncompressed evaporation gas to be introduced from the storage tank to the compressor along the gas supply line, and compressed in the refrigerant compression unit A system for reliquefying boil-off gas of a ship, characterized in that four flows of refrigerant are heat-exchanged. According to claim 4,
The refrigerant compression unit is connected to the refrigerant expansion device and receives the expansion energy of the refrigerant from the refrigerant expansion device to compress the refrigerant. According to claim 6,
The compressor compresses the boil-off gas with the fuel supply pressure of the propulsion engine provided on the ship,
The ship's boil-off gas re-liquefaction system, characterized in that the propulsion engine is supplied with boil-off gas compressed to 10 to 20 bara. According to any one of claims 1 to 7,
a decompression device for receiving the compressed gas cooled by heat exchange in the heat exchanger and reducing the pressure; and
Further comprising: a gas-liquid separator for gas-liquid separation by receiving the reduced boil-off gas from the pressure reducing device,
The flash gas separated in the gas-liquid separator joins the uncompressed boil-off gas flow in front of the heat exchanger, and the liquefied gas separated in the gas-liquid separator is recovered to the storage tank. . The boil-off gas generated from the onboard storage tank is compressed with a compressor, cooled by heat exchange in the heat exchanger supplied with the refrigerant circulating along the refrigerant circulation line, and re-liquefied,
Boiled gas generated from the storage tank is heated to an appropriate input temperature of the compressor through a heater and can be introduced into the compressor. According to claim 9,
The evaporated gas generated in the storage tank is heated by heat exchange through the heat exchanger and introduced into the compressor,
When the re-liquefaction system is not operated or the load of the re-liquefaction system is low, the boil-off gas generated in the storage tank bypasses the heat exchanger and is heated by the heater through the heating line and introduced into the compressor. A method for re-liquefying evaporation gas of ships. According to claim 10,
The refrigerant circulating in the refrigerant circulation line is compressed in the refrigerant compression unit, cooled through the heat exchanger, expanded and cooled in the refrigerant expansion device, and supplied to the heat exchanger as a cold heat source,
The refrigerant compression unit is connected to the refrigerant expansion device, the ship's boil-off gas re-liquefying method, characterized in that for compressing the refrigerant by receiving the expansion energy of the refrigerant from the refrigerant expansion device. According to claim 11,
The compressor compresses the boil-off gas with the fuel supply pressure of the propulsion engine provided on the ship,
The propulsion engine is a method of re-liquefying boil-off gas of a ship, characterized in that supplied with boil-off gas compressed to 10 to 20 bara.

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