KR102384712B1 - Boil-Off Gas Reliquefaction System - Google Patents

Abstract

A vessel BOG reliquefaction system is disclosed.
The vessel BOG reliquefaction system includes: a multi-stage compressor for compressing BOG; a heat exchanger cooling the boil-off gas compressed by the multi-stage compressor by heat exchange using the boil-off gas before being compressed by the multi-stage compressor as a refrigerant; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; and a bypass line for supplying boil-off gas to the multi-stage compressor by bypassing the heat exchanger.

Description

Boil-Off Gas Reliquefaction System {Boil-Off Gas Reliquefaction System}

The present invention relates to a system and method for re-liquefying BOG generated in a storage tank using BOG itself as a refrigerant.

Natural gas is usually liquefied and transported over long distances in the state of liquefied natural gas (LNG). Liquefied natural gas is obtained by cooling natural gas to a cryogenic temperature near atmospheric pressure -163°C, and its volume is significantly reduced compared to that in gaseous state, so it is very suitable for long-distance transportation by sea.

Even if the liquefied natural gas storage tank is insulated, there is a limit to completely blocking external heat, and the liquefied natural gas is continuously vaporized in the storage tank by the heat transferred into the liquefied natural gas. The liquefied natural gas vaporized inside the storage tank is called boil-off gas (BOG).

When the pressure of the storage tank becomes higher than the set pressure due to the generation of boil-off gas, the boil-off gas is discharged to the outside of the storage tank. BOG discharged to the outside of the storage tank is used as fuel for the engine or is reliquefied and returned to the storage tank.

In general, the BOG reliquefaction apparatus has a refrigeration cycle, and the BOG is reliquefied by cooling the BOG by the refrigerating cycle. A partial re-liquefaction system (PRS) is used to heat exchange with a cooling fluid in order to cool the BOG.

1 is a schematic configuration diagram of a conventional partial reliquefaction system.

Referring to FIG. 1 , the conventional partial reliquefaction system compresses the boil-off gas discharged from the storage tank T in multiple stages by a multi-stage compressor 200, and then compresses the boil-off gas compressed by the multi-stage compressor 200. , in the heat exchanger 100, the boil-off gas discharged from the storage tank (T) is cooled by heat exchange with a refrigerant.

The fluid cooled by the heat exchanger 100 is expanded by the pressure reducing device 300 to partially or fully reliquefied, and the liquefied natural gas reliquefied by the gas-liquid separator 400 and the gaseous BOG are separated. .

Even if the re-liquefaction system is configured to handle all BOG generated during operation, there may be cases where BOG must be burned out because more BOG is generated than usual, such as when liquefied natural gas is shipped to a storage tank. can

An object of the present invention is to provide a ship including a reliquefaction system that can be prepared even when a large amount of boil-off gas is generated, which is not normal operation in a normal state.

In particular, when BOG generated from a liquefied natural gas (LNG) storage tank is pressurized and then BOG itself is used as a refrigerant without a separate refrigerant and heat exchanges with each other to reliquefy BOG, the reliquefaction efficiency is improved. For this purpose, it is necessary to compress the boil-off gas at a high pressure, and to compress the boil-off gas to a high pressure, an oil supply type cylinder compressor must be used.

Lubrication oil is mixed with boil-off gas compressed by the oil-supply cylinder compressor. The inventors of the present invention have discovered that, while the compressed BOG is cooled in the heat exchanger, the lubricating oil mixed with the compressed BOG is condensed or solidified before BOG, thereby blocking the flow path of the heat exchanger. In particular, in the case of a narrow flow path (e.g., a microchannel type flow path), PCHE (Printed Circuit Heat Exchanger, also called DCHE), the flow path of the heat exchanger is blocked by condensed or solidified lubricant more frequently. do.

Therefore, the inventors of the present invention, in order to prevent or alleviate the phenomenon that the condensed or solidified lubricating oil clogs the flow path of the heat exchanger, develop various techniques for separating the oil mixed with the compressed BOG.

The present invention is a system that can alleviate or improve the phenomenon that the condensed or solidified lubricating oil clogs the flow path of the heat exchanger, and can remove the condensed or solidified lubricating oil blocking the flow path of the heat exchanger in a simple and economical way and to propose a method.

According to one aspect of the present invention for achieving the above object, a multi-stage compressor for compressing boil-off gas; a heat exchanger cooling the boil-off gas compressed by the multi-stage compressor by heat exchange using the boil-off gas before being compressed by the multi-stage compressor as a refrigerant; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; and a bypass line for supplying boil-off gas to the multi-stage compressor by bypassing the heat exchanger. Including, a boil-off gas reliquefaction system for ships is provided.

when the heat exchanger cannot be used; and when there is no need to reliquefy the boil-off gas; In any one or more cases, the boil-off gas may be supplied to the multi-stage compressor by bypassing the heat exchanger along the bypass line.

The multi-stage compressor may include one or more oil-fed cylinders, and when the flow path of the heat exchanger is partially or completely blocked by the condensed or solidified lubricating oil, the boil-off gas is bypassed along the bypass line to bypass the heat exchanger. It can be supplied with a multi-stage compressor.

when the boil-off gas discharged from the storage tank can be used as a refrigerant in the heat exchanger, and the pressure of the boil-off gas supplied to the multi-stage compressor does not satisfy the suction pressure condition required by the multi-stage compressor; and when it is necessary to control the internal pressure of the storage tank to a low range; In one or more of the cases, some or all of the boil-off gas may be bypassed along the bypass line by the heat exchanger to satisfy the suction pressure condition required by the compressor.

The compressor may compress the boil-off gas to 150 to 350 bar.

The compressor may compress the boil-off gas to 80 to 250 bar.

The heat exchanger may include a microchannel type flow path.

The heat exchanger may be PCHE.

According to another aspect of the present invention for achieving the above object, 1) the boil-off gas is compressed by a multi-stage compressor; 2) cooling the boil-off gas compressed by the multi-stage compressor by heat exchange by a heat exchanger using the boil-off gas before being compressed by the multi-stage compressor as a refrigerant; and 3) depressurizing the fluid cooled by the heat exchanger by a decompression device, wherein the boil-off gas reliquefaction method for ships can be supplied to the multi-stage compressor by bypassing the heat exchanger by a bypass line. provided

when the heat exchanger cannot be used; and when there is no need to reliquefy the boil-off gas; In any one or more cases, the boil-off gas may be supplied to the multi-stage compressor by bypassing the heat exchanger along the bypass line.

The multi-stage compressor may include one or more oil-fed cylinders, and when the flow path of the heat exchanger is partially or completely blocked by the condensed or solidified lubricating oil, the boil-off gas is bypassed along the bypass line to bypass the heat exchanger. It can be supplied with a multi-stage compressor.

When the performance of the heat exchanger falls below 60 to 80% of the normal case, it may be determined that it is 'time to remove the condensed or solidified lubricant'.

a temperature difference between the front end of the low-temperature flow path and the rear end of the high-temperature flow path of the heat exchanger (hereinafter referred to as 'temperature difference of low-temperature flow'); a temperature difference between the rear end of the low-temperature flow path and the front end of the high-temperature flow path of the heat exchanger (hereinafter referred to as 'temperature difference of high-temperature flow'); and a pressure difference between the front and rear ends of the high-temperature flow path (hereinafter referred to as 'pressure difference in the high-temperature flow path'); By one or more of, the 'time to remove the condensed or solidified lubricating oil' can be determined.

The smaller of the 'temperature difference of the low-temperature flow' and the 'temperature difference of the high-temperature flow' is greater than the first set value and lasts for more than a 'set time', or the 'pressure difference in the high-temperature flow path' is set to the second setting than when it is normal If the value is greater than or equal to 'a certain period of time' or longer, it may be determined that the 'time point at which the condensed or solidified lubricating oil should be removed'.

BOG may circulate through the bypass line, the multi-stage compressor, the high-temperature flow path of the heat exchanger, and the pressure reducing device until the heat exchanger is normalized.

The circulation process may be continued until it is determined that the temperature of the high-temperature flow path of the heat exchanger is as high as the temperature of the boil-off gas sent to the high-temperature flow path of the heat exchanger after being compressed by the multi-stage compressor.

The engine can be run while removing condensed or solidified lubricant.

when the boil-off gas discharged from the storage tank can be used as a refrigerant in the heat exchanger, and the pressure of the boil-off gas supplied to the multi-stage compressor does not satisfy the suction pressure condition required by the multi-stage compressor; and when it is necessary to control the internal pressure of the storage tank to a low range; In one or more of the cases, some or all of the boil-off gas may be bypassed along the bypass line by the heat exchanger to satisfy the suction pressure condition required by the compressor.

The compressor may compress the boil-off gas to 150 to 350 bar.

The compressor may compress the boil-off gas to 80 to 250 bar.

The heat exchanger may include a microchannel type flow path.

The heat exchanger may be PCHE.

According to another aspect of the present invention for achieving the above object, the step of compressing the boil-off gas by a multi-stage compressor; cooling the boil-off gas compressed by the multi-stage compressor by heat exchange by a heat exchanger using the boil-off gas before being compressed by the multi-stage compressor as a refrigerant; and depressurizing the fluid cooled by the heat exchanger by a pressure reducing device; in a method for re-liquefying BOG in a system for re-liquefying BOG, including: A method of starting a BOG reliquefaction system for ships is provided, which bypasses the heat exchanger by a bypass line and supplies it to the multi-stage compressor.

According to another aspect of the present invention for achieving the above object, a multi-stage compressor for compressing boil-off gas; a heat exchanger cooling the boil-off gas compressed by the multi-stage compressor by heat exchange using the boil-off gas before being compressed by the multi-stage compressor as a refrigerant; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; and a bypass line for supplying the boil-off gas to the multi-stage compressor by bypassing the heat exchanger, and supplying the boil-off gas to the multi-stage compressor by bypassing the heat exchanger by the bypass line when starting or restarting the boil-off gas re-liquefaction. A boil-off gas reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, the BOG is compressed by a compressor, the compressed BOG is heat-exchanged with the BOG before being compressed in a heat exchanger to cool, and the fluid cooled by heat exchange is reduced pressure. In the method for discharging lubricating oil in a system for re-liquefying BOG by decompression by an apparatus, BOG used as a refrigerant in the heat exchanger is supplied to the heat exchanger along a first supply line, and from the heat exchanger to the refrigerant Used BOG is supplied to the compressor along a second supply line, and BOG before being used as a refrigerant in the heat exchanger may be supplied to the compressor by bypassing the heat exchanger along a bypass line, and on the bypass line A bypass valve for controlling the flow rate and opening/closing of the fluid is installed, a first valve for controlling the flow rate and opening/closing of the fluid is installed at a front end of the heat exchanger on the first supply line, and a rear end of the heat exchanger on the second supply line is provided with a second valve for controlling the flow rate and opening/closing of the fluid, the compressor includes at least one oil-supply cylinder, 2) opening the bypass valve and closing the first valve and the second valve; 3) compressing the boil-off gas before being used as a refrigerant in the heat exchanger by the compressor through the bypass line; and 4) sending some or all of the boil-off gas compressed by the compressor to the heat exchanger, including, by melting or coagulating the lubricating oil condensed or solidified by the boil-off gas compressed by the compressor and increased in temperature, or lowering the viscosity There is provided a method for draining a lubricant, characterized in that it is drained.

The method of discharging the lubricant may further include the step of 1) determining whether to remove the condensed or solidified lubricant, which is performed before step 2).

During reliquefaction of BOG, the reliquefied liquefied gas and BOG remaining in a gaseous state are separated by a gas-liquid separator, and the reliquefied liquefied gas separated by the gas-liquid separator is separated by the gas-liquid separator along a fifth supply line. The boil-off gas in the gaseous state separated by the gas-liquid separator may be discharged from the gas-liquid separator along a sixth supply line, and the method for discharging the lubricating oil includes: 5) the boil-off gas passing through the heat exchanger to the gas-liquid sending to a separator; and 6) discharging the lubricating oil collected in the gas-liquid separator.

The boil-off gas sent to the gas-liquid separator in step 5) may be sent to the bypass line along the sixth supply line to undergo the compression process in step 3).

Steps 3) to 5) may be repeated until the temperature of the high-temperature flow path of the heat exchanger is as high as the temperature of the boil-off gas sent to the heat exchanger after being compressed by the compressor.

In step 4), the BOG compressed by the compressor may be used as a fuel of the engine, and the remaining BOG remaining after being used in the engine may be sent to the heat exchanger.

In step 1), when the performance of the heat exchanger falls below 60 to 80% of the normal case, it can be determined that it is time to discharge the condensed or solidified lubricant.

In step 1), the temperature difference between the temperature of the BOG used as a refrigerant in the heat exchanger at the front end of the heat exchanger and the BOG cooled by the heat exchanger after being compressed by the compressor (hereinafter, ‘low temperature flow’) a condition in which the temperature difference of ') is greater than or equal to the first set value for a certain period of time or longer; The temperature difference between the temperature of the boil-off gas used as a refrigerant in the heat exchanger and the boil-off gas sent to the heat exchanger after being compressed by the compressor (hereinafter referred to as 'temperature difference of high temperature flow') is equal to or greater than the first set value condition in which the state persists for more than a certain period of time; and a pressure difference between the pressure at the front end of the heat exchanger of the boil-off gas compressed by the compressor and sent to the heat exchanger, and the pressure difference at the rear end of the heat exchanger of the boil-off gas cooled by the heat exchanger (hereinafter, 'pressure in the high temperature flow path') 'difference') is the second set value or more, and the condition continues for a certain period of time or longer; If one or more of these are satisfied, it can be determined that it is time to discharge the condensed or solidified lubricant.

In step 1), the temperature difference between the temperature at the front end of the heat exchanger of the boil-off gas used as a refrigerant in the heat exchanger and the temperature difference of the boil-off gas cooled by the heat exchanger after being compressed by the compressor (hereinafter, 'low temperature flow' temperature difference'); and a temperature difference between the temperature of the boil-off gas used as a refrigerant in the heat exchanger and the boil-off gas that is compressed by the compressor and sent to the heat exchanger (hereinafter referred to as 'temperature difference of high temperature flow'); The state in which the smaller of the values is greater than or equal to the first set value continues for a certain period of time or longer, or the pressure at the front end of the heat exchanger of the boil-off gas that is compressed by the compressor and sent to the heat exchanger, and the boil-off gas cooled by the heat exchanger If the pressure difference at the rear end of the heat exchanger (hereinafter referred to as 'pressure difference in the high-temperature flow path') is equal to or greater than the second set value for more than a certain period of time, it is determined that it is 'time to discharge the condensed or solidified lubricant'. can

An alarm may sound to indicate the time when the condensed or solidified lubricant should be drained.

The first set value may be 35°C.

The second set value may be twice the normal case.

The second set value may be 2 bar (200 kPa).

The predetermined time may be 1 hour.

When the boil-off gas is reliquefied, the liquefied gas separated by the gas-liquid separator may be supplied to a storage tank along the fifth supply line, and an eighth valve for controlling the flow rate and opening/closing of the fluid is provided on the fifth supply line. may be installed, and the eighth valve may be closed during steps 2) to 6).

When it is determined that the heat exchanger is normalized, the first valve and the second valve are opened and the bypass valve is closed, and then the boil-off gas may be reliquefied.

The compressor may compress the boil-off gas to 150 to 350 bar.

The compressor may compress the boil-off gas to 80 to 250 bar.

The heat exchanger may include a microchannel type flow path.

The heat exchanger may be PCHE.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger for cooling the boil-off gas compressed by the compressor by heat-exchanging the boil-off gas discharged from the storage tank with a refrigerant; a first valve installed on a first supply line for supplying boil-off gas to be used as a refrigerant in the heat exchanger to the heat exchanger to control the flow rate and opening/closing of the fluid; a second valve installed on a second supply line for supplying boil-off gas used as a refrigerant in the heat exchanger to the compressor to control the flow rate and opening/closing of the fluid; a bypass line for supplying boil-off gas to the compressor by bypassing the heat exchanger; and a decompression device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger, wherein the compressor includes at least one oil-supply cylinder, and the bypass line is located in front of the first valve. There is provided a boil-off gas reliquefaction system that branches from the first supply line and joins the second supply line at the rear end of the second valve.

The BOG reliquefaction system may further include a gas-liquid separator installed at the rear end of the pressure reducing device to separate the reliquefied liquefied gas and the BOG remaining in a gaseous state.

BOG in a gaseous state separated by the gas-liquid separator may be discharged along a sixth supply line and then merged with BOG to be used as a refrigerant in the heat exchanger to be used as a refrigerant in the heat exchanger, wherein the sixth supply line is It may be joined to the first supply line in front of the first valve.

The compressor may compress the boil-off gas to 150 to 350 bar.

The compressor may compress the boil-off gas to 80 to 250 bar.

The heat exchanger may include a microchannel type flow path.

The heat exchanger may be PCHE.

According to another aspect of the present invention for achieving the above object, the BOG is compressed by a compressor, the compressed BOG is heat-exchanged with the BOG before being compressed in a heat exchanger to cool, and the fluid cooled by heat exchange is reduced pressure. In the method for discharging lubricating oil in a system for reliquefying boil-off gas by decompression by a device, the compressor includes at least one oil-supplying cylinder, and after bypassing the heat exchanger through a bypass line for boil-off gas to the compressor compressed by the compressor, supplying the BOG compressed by the compressor to the engine, and supplying the remaining BOG after supplying the engine to the heat exchanger, condensed or solidified by the BOG compressed by the compressor and increased in temperature There is provided a lubricating oil discharging method, characterized in that dissolving or lowering the viscosity of the lubricating oil is discharged.

According to another aspect of the present invention for achieving the above object, in the method of discharging lubricating oil in a system for reliquefying BOG using BOG itself as a refrigerant, when reliquefying BOG, the heat exchanger is stored The boil-off gas discharged from the tank is used as a refrigerant to heat exchange the boil-off gas compressed by a compressor to cool it, and the compressor includes at least one oil-supply cylinder, and is installed to bypass the heat exchanger to maintain the heat exchanger A lubricating oil discharging method is provided, in which the condensed or solidified lubricating oil is melted or the viscosity is lowered and discharged by a bypass line used at the time of discharge.

According to another aspect of the present invention for achieving the above object, there is provided a fuel supply method, characterized in that fuel is supplied to the engine while discharging the condensed or solidified lubricating oil by melting or lowering the viscosity.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger for cooling the boil-off gas compressed by the compressor by heat-exchanging the boil-off gas before being compressed by the compressor with a refrigerant; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; and a gas-liquid separator installed at the rear end of the pressure reducing device to separate the reliquefied liquefied gas and the boil-off gas remaining in a gaseous state, wherein the compressor includes at least one oil-supplying cylinder, and the gas-liquid separator includes: A lubricating oil discharge line for discharging the lubricating oil collected inside the gas-liquid separator is connected, the boil-off gas reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, in the method of discharging the lubricating oil in the system for re-liquefying the boil-off gas using the boil-off gas itself as a refrigerant, the lubricant oil collected in the gas-liquid separator is discharged through a lubricant discharge line. A method for discharging lubricating oil is provided, characterized in that the lubricating oil discharge line is installed separately from a fifth supply line for discharging the reliquefied liquefied gas from the gas-liquid separator when the boil-off gas is reliquefied through the gas-liquid separator. .

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger cooling the boil-off gas compressed by the compressor by heat exchange using the boil-off gas before being compressed by the compressor as a refrigerant; and a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger, wherein a first temperature sensor installed at a front end of the low-temperature flow path of the heat exchanger and installed at a rear end of the high-temperature flow path of the heat exchanger a fourth temperature sensor to be; a second temperature sensor installed at a rear end of the low-temperature flow path of the heat exchanger and a third temperature sensor installed at a front end of the high-temperature flow path of the heat exchanger; and a first pressure sensor installed at a front end of the high temperature flow path of the heat exchanger and a second pressure sensor installed at a rear end of the high temperature flow path of the heat exchanger. Including one or more of, the compressor is provided with at least one oil-fueled cylinder, BOG reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger cooling the boil-off gas compressed by the compressor by heat exchange using the boil-off gas before being compressed by the compressor as a refrigerant; and a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger, wherein a first temperature sensor installed at a front end of the low-temperature flow path of the heat exchanger and installed at a rear end of the high-temperature flow path of the heat exchanger a fourth temperature sensor to be; a second temperature sensor installed at a rear end of the low-temperature flow path of the heat exchanger and a third temperature sensor installed at a front end of the high-temperature flow path of the heat exchanger; and a differential pressure sensor for measuring the pressure difference between the front end and the rear end of the high temperature flow path of the heat exchanger. Including one or more of, the compressor is provided with at least one oil-fueled cylinder, BOG reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, the BOG is compressed by a compressor, the compressed BOG is heat-exchanged with the BOG before being compressed in a heat exchanger to cool, and the fluid cooled by heat exchange is reduced pressure. In the BOG reliquefaction system decompressed by the device, the compressor includes at least one oil-fed cylinder, and an alarm sounds when detecting abnormality in the performance of the heat exchanger, the BOG reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, in the method for discharging lubricating oil in a system for re-liquefying BOG using BOG itself as a refrigerant, evaporation in the heat exchanger when BOG is reliquefied The gas itself cools the boil-off gas as a refrigerant, and the temperature difference between the temperature measured by the first temperature sensor installed at the front end of the low-temperature flow path of the heat exchanger and the temperature measured by the fourth temperature sensor installed at the rear end of the high-temperature flow path of the heat exchanger, and a smaller value of the difference between the temperature measured by the second temperature sensor installed at the rear end of the low temperature flow path of the heat exchanger and the temperature difference measured by the third temperature sensor installed at the front end of the high temperature flow path of the heat exchanger. or a pressure difference between the pressure measured by the first pressure sensor installed at the front end of the high temperature flow path of the heat exchanger and the pressure difference measured by the second pressure sensor installed at the rear end of the high temperature flow path of the heat exchanger; A lubricating oil draining method is provided for determining whether it is necessary to drain the lubricating oil.

According to another aspect of the present invention for achieving the above object, in the method for discharging lubricating oil in a system for re-liquefying BOG using BOG itself as a refrigerant, evaporation in the heat exchanger when BOG is reliquefied The gas itself cools the boil-off gas as a refrigerant, and the temperature difference between the temperature measured by the first temperature sensor installed at the front end of the low-temperature flow path of the heat exchanger and the temperature measured by the fourth temperature sensor installed at the rear end of the high-temperature flow path of the heat exchanger, and a smaller value of the difference between the temperature measured by the second temperature sensor installed at the rear end of the low temperature flow path of the heat exchanger and the temperature difference measured by the third temperature sensor installed at the front end of the high temperature flow path of the heat exchanger. or a pressure difference measured by a differential pressure sensor measuring the pressure difference between the front and rear ends with the high-temperature oil of the heat exchanger as an index, determining whether it is necessary to discharge the condensed or solidified lubricant, a lubricant discharge method is provided do.

According to another aspect of the present invention for achieving the above object, the BOG is compressed by a compressor, the compressed BOG is heat-exchanged with the BOG before being compressed in a heat exchanger to cool, and the fluid cooled by heat exchange is reduced pressure. In the method for discharging the lubricating oil in a system for re-liquefying BOG by decompression by a device, the compressor includes at least one oil-supplying cylinder, and in the front end of the heat exchanger of BOG used as a refrigerant in the heat exchanger a condition in which the temperature difference between the temperature of the BOG and the boil-off gas cooled by the heat exchanger after being compressed by the compressor (hereinafter, referred to as 'temperature difference of low temperature flow') is equal to or greater than the first set value for a predetermined period of time or longer; The temperature difference between the temperature of the boil-off gas used as a refrigerant in the heat exchanger and the boil-off gas sent to the heat exchanger after being compressed by the compressor (hereinafter referred to as 'temperature difference of high temperature flow') is equal to or greater than the first set value condition in which the state persists for more than a certain period of time; and a pressure difference between the pressure at the front end of the heat exchanger of the boil-off gas compressed by the compressor and sent to the heat exchanger, and the pressure difference at the rear end of the heat exchanger of the boil-off gas cooled by the heat exchanger (hereinafter, 'pressure in the high temperature flow path') 'difference') is the second set value or more, and the condition continues for a certain period of time or longer; When one or more of these are satisfied, a method for discharging lubricant is provided, which is determined as 'the point at which the condensed or solidified lubricant should be discharged'.

According to another aspect of the present invention for achieving the above object, the BOG is compressed by a compressor, the compressed BOG is heat-exchanged with the BOG before being compressed in a heat exchanger to cool, and the fluid cooled by heat exchange is reduced pressure. In the method for discharging the lubricating oil in a system for re-liquefying BOG by decompression by a device, the compressor includes at least one oil-supplying cylinder, and in the front end of the heat exchanger of BOG used as a refrigerant in the heat exchanger a temperature difference between the temperature of the BOG and the BOG cooled by the heat exchanger after being compressed by the compressor (hereinafter referred to as 'temperature difference of low temperature flow'); and a temperature difference between the temperature of the boil-off gas used as a refrigerant in the heat exchanger and the boil-off gas that is compressed by the compressor and sent to the heat exchanger (hereinafter referred to as 'temperature difference of high temperature flow'); The state in which the smaller of the values is greater than or equal to the first set value continues for a certain period of time or longer, or the pressure at the front end of the heat exchanger of the boil-off gas that is compressed by the compressor and sent to the heat exchanger, and the boil-off gas cooled by the heat exchanger When the pressure difference at the rear end of the heat exchanger (hereinafter referred to as 'pressure difference in the high-temperature flow path') is equal to or greater than the second set value, it is determined that it is 'time to discharge the condensed or solidified lubricating oil' , a lubricating oil draining method is provided.

According to another aspect of the present invention for achieving the above object, in a method for discharging lubricating oil in a system for re-liquefying BOG using BOG itself as a refrigerant, at least one of a temperature difference and a pressure difference of equipment A method for discharging lubricating oil is provided, which is characterized in that the 'time point at which the condensed or solidified lubricating oil should be discharged' is identified as an index and the 'time point at which the condensed or coagulated lubricating oil should be discharged' is notified by an alarm.

According to another aspect of the present invention for achieving the above object, a compressor for compressing BOG, and heat exchange for cooling the BOG by using the BOG as a refrigerant before the BOG compressed by the compressor is compressed by the compressor as a refrigerant. In the boil-off gas reliquefaction system comprising a group and a pressure reducing device for decompressing the fluid cooled by the heat exchanger, it is installed at one or more of the front and rear ends of the heat exchanger to detect whether the heat exchanger is clogged by lubricating oil detection means; and an alarm informing that the heat exchanger detected by the sensing means is clogged by lubricating oil.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger cooling the boil-off gas compressed by the compressor by heat exchange using the boil-off gas before being compressed by the compressor as a refrigerant; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; and a second oil filter installed at a rear end of the pressure reducing device, wherein the compressor includes at least one oil-supplying cylinder, and the second oil filter is for cryogenic use.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger cooling the boil-off gas compressed by the compressor by heat exchange using the boil-off gas before being compressed by the compressor as a refrigerant; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; a gas-liquid separator installed at the rear end of the decompression device to separate the reliquefied liquefied gas and the boil-off gas remaining in a gaseous state; and a second oil filter installed on a fifth supply line through which the liquefied gas separated by the gas-liquid separator is discharged, wherein the compressor includes at least one oil-supplying cylinder, and the second oil filter is cryogenic Yongin, BOG reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger cooling the boil-off gas compressed by the compressor by heat exchange using the boil-off gas before being compressed by the compressor as a refrigerant; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; a gas-liquid separator installed at the rear end of the decompression device to separate the reliquefied liquefied gas and the boil-off gas remaining in a gaseous state; and a second oil filter installed on a sixth supply line through which the boil-off gas in the gaseous state separated by the gas-liquid separator is discharged, wherein the compressor includes at least one oil-supply cylinder, and the second oil The filter is for cryogenic use, BOG reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger cooling the boil-off gas compressed by the compressor by heat exchange using the boil-off gas before being compressed by the compressor as a refrigerant; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; a bypass line for supplying boil-off gas to be used as a refrigerant in the heat exchanger to the compressor by bypassing the heat exchanger at a front end of the heat exchanger; and a bypass valve installed on the bypass line to control the flow rate and opening/closing of the fluid, wherein when the pressure of the boil-off gas supplied to the compressor is lower than the suction pressure condition required by the compressor, the bypass valve is Characterized in that part or all of the open, boil-off gas reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, the BOG is compressed by a compressor, the compressed BOG is heat-exchanged with the BOG before being compressed in a heat exchanger to cool, and the fluid cooled by heat exchange is reduced pressure. In the method of supplying fuel to an engine of a system for re-liquefying boil-off gas by decompression by a device, when the pressure of the boil-off gas supplied to the compressor is lower than the suction pressure condition required by the compressor, it is to be supplied to the compressor A fuel supply method is provided for supplying a part or all of the boil-off gas to the compressor by bypassing the heat exchanger.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger for cooling the boil-off gas compressed by the compressor by heat-exchanging the boil-off gas before being compressed by the compressor with a refrigerant; a bypass line for supplying boil-off gas to the compressor by bypassing the heat exchanger; a second valve installed on a second supply line for sending boil-off gas used as a refrigerant in the heat exchanger to the compressor to control the flow rate and opening/closing of the fluid; and a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger, wherein the compressor includes at least one oil-supply cylinder, and the bypass line is located at the rear end of the second valve. There is provided a boil-off gas reliquefaction system, which is joined to the second supply line.

According to another aspect of the present invention for achieving the above object, the BOG is compressed by a compressor, the compressed BOG is heat-exchanged with the BOG before being compressed in a heat exchanger to cool, and the fluid cooled by heat exchange is reduced pressure. A method for discharging lubricating oil in a system for re-liquefying BOG by decompression by a device, wherein the compressor includes at least one oil-supplying cylinder, and a method for sending BOG used as a refrigerant in the heat exchanger to the compressor. 2 A second valve is installed on the supply line to control the flow rate and opening/closing of the fluid, and after bypassing the heat exchanger through the bypass line, the boil-off gas is compressed by the compressor, and the excess boil-off gas remaining after supplying the engine to the engine is removed. It is supplied to a heat exchanger to melt and discharge the lubricating oil compressed by the compressor and condensed by the boil-off gas having a higher temperature, and the bypass line joins the second supply line at the rear end of the second valve, the lubricating oil discharging method provided

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger for cooling the boil-off gas compressed by the compressor by heat-exchanging the boil-off gas before being compressed by the compressor with a refrigerant; a bypass line for supplying boil-off gas to the compressor by bypassing the heat exchanger; a first valve installed on a first supply line for supplying boil-off gas to be used as a refrigerant in the heat exchanger to the heat exchanger to control the flow rate and opening/closing of the fluid; and a decompression device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger, wherein the compressor includes at least one oil-supply cylinder, and the bypass line is located in front of the first valve. Branched from the first supply line, the boil-off gas reliquefaction system is provided.

According to another aspect of the present invention for achieving the above object, a compressor for compressing boil-off gas; a heat exchanger for cooling the BOG compressed by the compressor by heat-exchanging the BOG before being compressed by the compressor with a refrigerant; a bypass line in which the boil-off gas to be used as a refrigerant in the heat exchanger is branched from a first supply line supplied to the first heat exchanger, and bypasses the heat exchanger to supply the boil-off gas to the compressor; a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger; and a gas-liquid separator installed at the rear end of the decompression device to separate the reliquefied liquefied gas and the boil-off gas remaining in the gaseous state, wherein the compressor includes at least one oil-supplying cylinder, and by the gas-liquid separator BOG in a gaseous state is discharged from the gas-liquid separator along a sixth supply line, and the sixth supply line is joined to the first supply line in front of the branching point of the bypass line, BOG reliquefaction system this is provided

According to the present invention, even when the amount of BOG discharged from the storage tank exceeds the amount that can be reliquefied using BOG itself as a refrigerant, BOG can be treated.

In addition, according to an embodiment of the present invention, the cooling heat of the boil-off gas sent to the gas combustion unit (GCU) can be used to re-liquefy the boil-off gas, thereby reducing the amount of the boil-off gas sent to the gas combustion device. , the amount of boil-off gas to be reliquefied can be increased. Therefore, even when the amount of BOG generated is particularly higher than usual, the amount of BOG burned and thrown away by the gas combustion device can be reduced, and the liquefied natural gas transported by the ship can be preserved as much as possible.

According to the present invention, it is possible to remove the condensed or solidified lubricating oil in the heat exchanger simply and economically only with the existing equipment, without the need to additionally install additional equipment or supply a separate fluid for lubricating oil removal.

According to the present invention, by driving the engine while removing the internal condensed or solidified lubricating oil, it is possible to maintain the heat exchanger while continuing the operation of the engine. In addition, it is possible to remove the condensed or solidified lubricating oil by utilizing the surplus boil-off gas remaining after being used in the engine. In addition, there is an advantage that the lubricating oil mixed with the boil-off gas can be burned by the engine.

According to the present invention, using the improved gas-liquid separator, there is an advantage that the lubricating oil having a lowered viscosity or melted collected in the gas-liquid separator can be efficiently discharged.

According to the present invention, a cryogenic oil filter is installed in at least one of the rear end of the decompression device, the fifth supply line through which liquefied gas is discharged from the gas-liquid separator, and the sixth supply line through which the boil-off gas is discharged from the gas-liquid separator. It has the advantage of being able to effectively remove the mixed lubricant.

According to the present invention, it is possible to simply and economically satisfy the suction pressure condition required by the compressor, maintain the reliquefaction performance, and satisfy the fuel consumption required by the engine, without the need to install additional equipment. can

1 is a schematic configuration diagram of a conventional partial reliquefaction system.
2 is a schematic diagram of a BOG reliquefaction system included in a ship according to a first preferred embodiment of the present invention.
3 is a schematic diagram of a boil-off gas reliquefaction system included in a ship according to a second preferred embodiment of the present invention.
4 is a schematic diagram of a BOG reliquefaction system included in a ship according to a third preferred embodiment of the present invention.
5 is a schematic diagram of a BOG reliquefaction system according to a fourth preferred embodiment of the present invention.
6 is a schematic diagram of a boil-off gas reliquefaction system according to a fifth preferred embodiment of the present invention.
7 is an enlarged view of a gas-liquid separator according to an embodiment of the present invention.
8 is an enlarged view of a second oil filter according to an embodiment of the present invention.
9 is an enlarged view of a second oil filter according to another embodiment of the present invention.
10 is a schematic diagram of a BOG reliquefaction system according to a sixth preferred embodiment of the present invention.
11 is an enlarged view of a pressure reducing device according to an embodiment of the present invention.
12 is an enlarged view of a pressure reducing device according to another embodiment of the present invention.
13 is an enlarged view of a heat exchanger and a gas-liquid separator according to an embodiment of the present invention.
14 and 15 are graphs showing the amount of reliquefaction according to the BOG pressure in a partial re-liquefaction system (PRS).
16 is a plan view of the filter element shown in FIGS. 8 and 9 .

Hereinafter, the configuration and operation of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. The ship of the present invention can be applied and applied in various ways to a ship equipped with an engine using natural gas as a fuel, a ship including a liquefied gas storage tank, or an offshore structure. In addition, the following examples may be modified in various other forms, and the scope of the present invention is not limited to the following examples.

In the following examples, the case of liquefied natural gas will be described as an example, but the present invention may be applied to various liquefied gases, and the following examples may be modified in various other forms, and the scope of the present invention is limited to the following examples it's not going to be

In the following examples, the fluid flowing through each flow path may be in a gaseous state, a gas-liquid mixed state, a liquid state, or a supercritical fluid state, depending on the operating conditions of the system.

2 is a schematic diagram of a BOG reliquefaction system included in a ship according to a first preferred embodiment of the present invention.

Referring to FIG. 2 , the BOG reliquefaction system included in the ship of this embodiment includes a multi-stage compressor 200 , a heat exchanger 100 , a pressure reducing device 300 , and a first discharge line L1 .

The storage tank (T) is equipped with a sealing and insulating barrier to store liquefied gas such as liquefied natural gas in a cryogenic state, but it cannot completely block the heat transmitted from the outside, and the evaporation of the liquefied gas continues in the tank. In order to prevent an excessive increase in tank pressure due to such boil-off gas, and to maintain the internal pressure at an appropriate level, the boil-off gas inside the storage tank (T) is discharged.

A first control valve 510 for controlling the flow rate and opening/closing of the boil-off gas may be installed on the line through which the boil-off gas is discharged from the storage tank T.

The multi-stage compressor 200 of this embodiment includes a plurality of compression cylinders 210, 220, 230, 240, 250 and a plurality of coolers 810, 820, 830, 840, 850, and from the storage tank T The discharged BOG is compressed in multiple stages. A plurality of coolers (810, 820, 830, 840, 850) of this embodiment is a plurality of compression cylinders (210, 220, 230, 240, 250) at the rear end of a plurality of compression cylinders (210, 220, 230, 240, 250) It is installed alternately with the compression cylinders (210, 220, 230, 240, 250) to cool the boil-off gas that has risen in temperature as well as the pressure compressed by the compression cylinders (210, 220, 230, 240, 250).

BOG compressed by the multi-stage compressor 200 of this embodiment may be partially sent to the main engine propelling the ship, and the remaining BOG not required by the main engine is a heat exchanger 100 to undergo a re-liquefaction process. can be sent to

The main engine may be a ME-GI engine. The ME-GI engine consists of two strokes, and a diesel cycle in which high-pressure natural gas having a pressure of about 300 bar is directly injected into the combustion chamber near the top dead center of the piston. is adopting

It is known that the ME-GI engine uses natural gas of approximately 150 to 400 bar, preferably approximately 150 to 350 bar, more preferably approximately 300 bar as fuel.

The multi-stage compressor 200 of this embodiment may compress BOG to a pressure required by the main engine, and when the main engine is a ME-GI engine, it may compress BOG to a pressure of approximately 150 to 350 bar. .

In the present invention, instead of the ME-GI engine as the main engine, an X-DF engine or a DF engine using boil-off gas at a pressure of about 6 to 20 bar as fuel may be used. Since the boil-off gas is low pressure, it can be re-liquefied by additionally pressurizing the boil-off gas compressed to be supplied to the main engine. The pressure of the boil-off gas additionally pressurized for re-liquefaction may be about 80 to 250 bar.

BOG, which has passed through only some of the compression cylinders 210 and 220 included in the multi-stage compressor 200 of this embodiment, may be partially branched and sent to the generator. The generator of this embodiment may require natural gas of a pressure of about 6.5 bar, and the boil-off gas compressed to about 6.5 bar by some of the compression cylinders 210 and 220 included in the multi-stage compressor 200 of this embodiment is a generator can be sent to On the line through which BOG is sent from the multi-stage compressor 200 to the generator, a third control valve 530 for controlling the flow rate and opening/closing of BOG may be installed.

The heat exchanger 100 of this embodiment cools by heat-exchanging some or all of the BOG compressed by the multi-stage compressor 200 with the BOG discharged from the storage tank T.

When the heat exchanger 100 of this embodiment is being maintained or the heat exchanger 100 is broken, etc., when the heat exchanger 100 cannot be used, the boil-off gas discharged from the storage tank T is ) through the heat exchanger 100 can be bypassed. A third shutoff valve 630 for opening and closing the bypass line L3 is installed in the bypass line L3 of this embodiment. The third shut-off valve 630 is normally closed and is opened when it is necessary to use the bypass line L3.

The bypass line L3 may be utilized as follows.

1) When the heat exchanger cannot be used

Basically, the bypass line L3 is used when the heat exchanger 100 is broken or the heat exchanger 100 cannot be used, such as when maintenance is required. For example, when some or all of the BOG compressed by the multi-stage compressor 200 is sent to the main engine, if the heat exchanger 100 cannot be used, re-liquefying the surplus BOG that has not been used in the main engine is given up. Then, the boil-off gas discharged from the storage tank T is directly supplied to the multi-stage compressor 200 by bypassing the heat exchanger 100 along the bypass line L3, and then compressed by the multi-stage compressor 200. is supplied to the main engine, and the surplus BOG can be sent to a gas combustion device for incineration.

2) Removal of condensed or solidified lubricant

As an example of using the bypass line L3 for maintenance of the heat exchanger 100, when the flow path of the heat exchanger 100 is blocked by the condensed or solidified lubricating oil, the condensed or solidified using the bypass line L3 and removing the lubricant.

A plurality of cylinders 210, 220, 230, 240, 250 included in the multi-stage compressor 200, some operate in an oil-free lubricated method, and the rest operate in an oil-lubricated method. can In particular, when the BOG compressed by the multi-stage compressor 200 is compressed to 80 bar or more, preferably 100 bar or more, for use as a fuel of the main engine or for re-liquefaction efficiency, the multi-stage compressor 200 ) will include a cylinder of oil lubrication type to compress the boil-off gas to high pressure.

In the existing technology, in order to compress the boil-off gas to 100 bar or more, it is necessary to supply lubricating oil for lubrication and cooling to the reciprocating type multi-stage compressor 200 , for example, to the piston sealing portion.

Lubricating oil is supplied to the oil-lubricated cylinder, and at the current level of technology, some of the lubricant is mixed with the boil-off gas that has passed through the oil-lubricated cylinder. The lubricating oil mixed with the boil-off gas is condensed or solidified before the boil-off gas in the heat exchanger 100 and is accumulated in the flow path of the heat exchanger 100. Since the amount is increased, the inventors of the present invention have found that it is necessary to remove the condensed or solidified lubricating oil inside the heat exchanger 100 after a certain period of time.

In particular, the heat exchanger 100 of this embodiment is preferably a PCHE (Printed Circuit Heat Exchanger, also referred to as DCHE) in consideration of the pressure and/or flow rate of the boil-off gas to be reliquefied, the reliquefaction efficiency, and the like. As the flow path is narrow (microchannel type flow path) and curved, the flow path can be easily clogged by the condensed or solidified lubricating oil. PCHE (DCHE) is produced by companies such as Kobelko and Alfalval.

When the flow path of the heat exchanger 100 is blocked by the condensed or solidified lubricating oil, the cooling efficiency of the heat exchanger 100 is reduced. Therefore, when the performance of the heat exchanger 100 falls below a certain value compared to the normal case, it can be estimated that the lubricating oil condensed or solidified inside the heat exchanger 100 has accumulated to some extent or more, for example, of the heat exchanger 100 . When the performance drops to about 50 to 90% or less, preferably about 60 to 80% or less, and more preferably about 70% or less of the normal case, it is determined that the lubricating oil condensed or solidified inside the heat exchanger 100 should be removed can do.

"About 50 to 90% or less" in the normal case is meant to include all of about 50% or less, about 60% or less, about 70% or less, about 80% or less, and about 90% or less, and "about 60 to 80% or less' is meant to include all of about 60% or less, about 70% or less, and about 80% or less.

Whether the performance of the heat exchanger 100 has deteriorated is determined by the temperature difference of the low-temperature fluid supplied to or discharged from the heat exchanger 100 (that is, the temperature difference between the front end of the low-temperature flow path and the rear end of the high-temperature flow path of the heat exchanger 100) Hereinafter, it is referred to as 'the temperature difference of the low temperature flow'), the temperature difference between the high temperature fluid supplied to or discharged from the heat exchanger 100 (that is, the rear end of the low temperature flow path and the front end of the high temperature flow path of the heat exchanger 100 ) of the temperature difference, hereinafter referred to as 'temperature difference of high temperature flow'), and the pressure difference between the front and rear ends of the high temperature flow path of the heat exchanger 100 (hereinafter referred to as 'pressure difference of the high temperature flow path'), etc. It can be determined whether the old lubricant needs to be removed.

The low-temperature flow path of the heat exchanger 100 is a flow path through which BOG discharged from the storage tank T is supplied, and the high-temperature flow path of the heat exchanger 100 is a flow path through which BOG compressed by the multi-stage compressor 200 is supplied. it is euro

The boil-off gas discharged from the storage tank (T) does not contain an oil component or exists at a very insignificant level, and the point at which the boil-off gas is mixed with lubricating oil is when the boil-off gas is compressed by the multi-stage compressor (200). After using the boil-off gas discharged from T) as a refrigerant, condensed or solidified lubricating oil hardly accumulates in the low-temperature flow path of the heat exchanger 100 that is sent to the multi-stage compressor 200, and the boil-off gas compressed by the multi-stage compressor 200 is After cooling, the condensed or solidified lubricating oil is accumulated in the high-temperature flow path of the heat exchanger 100 sent to the pressure reducing device 300 .

Therefore, since the flow path is blocked by the condensed or solidified lubricating oil and the pressure difference between the front and rear ends of the heat exchanger 100 increases rapidly in the high temperature flow path, the pressure applied to the high temperature flow path of the heat exchanger 100 is measured to condense or solidify. It is desirable to determine whether the old lubricant should be removed.

Determining whether to remove the condensed or solidified lubricating oil by the pressure difference between the front and rear ends of the heat exchanger 100 is particularly applicable to the heat exchanger 100 of this embodiment, in which the PCHE in which the flow path is narrow and curved can be applied. Considering that, it can be usefully used.

More specifically, whether the performance of the heat exchanger 100 has deteriorated is determined whether the smaller of the 'temperature difference of the low-temperature flow' and the 'temperature difference of the high-temperature flow' is greater than the first set value and continues for more than 'a certain period of time', If the 'pressure difference in the high temperature flow path' continues for more than a 'predetermined time' longer than the second set value compared to the normal case, it may be determined that it is time to remove the condensed or solidified lubricating oil.

The first setpoint may be approximately 20 to 50°C, preferably approximately 30 to 40°C, more preferably approximately 35°C, and the second setpoint may be approximately 1 to 5 bar, preferably approximately 1.5 to 3 bar , more preferably about 2 bar (200 kPa), and the 'constant time' may be about 1 hour.

If it is determined that it is time to remove the condensed or solidified lubricating oil, the condensed or solidified lubricating oil removal process is performed using the bypass line (L3).

BOG discharged from the storage tank T is sent to the multi-stage compressor 200 through the bypass line L3 and is no longer sent to the heat exchanger 100 . Accordingly, the refrigerant is not supplied to the heat exchanger 100 .

BOG discharged from the storage tank (T) is sent to the multi-stage compressor (200) after bypassing the heat exchanger (100) through the bypass line (L3). The boil-off gas sent to the multi-stage compressor 200 is compressed by the multi-stage compressor 200 and not only the pressure but also the temperature is increased, and the temperature of the boil-off gas compressed to about 300 bar by the multi-stage compressor 200 is about 40 to 45 ° C. becomes

If the boil-off gas, which has been compressed by the multi-stage compressor 200, and whose temperature has increased, continues to be sent to the heat exchanger 100, the low-temperature boil-off gas discharged from the storage tank T used as a refrigerant in the heat exchanger 100 is converted into a heat exchanger ( 100) is not supplied, and only the high-temperature BOG is continuously supplied to the heat exchanger 100, so the temperature of the high-temperature flow path of the heat exchanger 100 through which the BOG compressed by the multi-stage compressor 200 passes is gradually decreased. goes up

When the temperature of the high-temperature flow path of the heat exchanger 100 is above the temperature at which the lubricating oil is condensed or solidified, the condensed or solidified lubricating oil accumulated inside the heat exchanger 100 is gradually melted or the viscosity is lowered, and the melt or the viscosity is lowered. The lubricating oil is mixed with the boil-off gas and exits the heat exchanger 100 .

As the temperature of the high-temperature flow path of the heat exchanger 100 rises, the condensed or solidified lubricating oil accumulated in the heat exchanger 100 melts or increases in viscosity, and is mixed with the boil-off gas and sent to the gas-liquid separator 400 . In the process of removing the condensed or solidified lubricating oil inside the heat exchanger 100 by using the bypass line L3, re-liquefaction of the boil-off gas is not performed, so the re-liquefied liquefied gas does not collect in the gas-liquid separator 400, and the gas The boil-off gas in the state and the lubricating oil with melted or lowered viscosity are collected.

BOG in a gaseous state collected in the gas-liquid separator 400 is discharged from the gas-liquid separator 400 and is again sent to the multi-stage compressor 200 along the bypass line L3.

When using the bypass line (L3) to remove the condensed or solidified lubricating oil, the boil-off gas is discharged from the bypass line (L3), the multi-stage compressor (200), and the heat exchanger (100) until the heat exchanger (100) is normalized. The flow path, the pressure reducing device 300 and the gas-liquid separator 400 are circulated, and in the circulation process, the high temperature flow path of the heat exchanger 100 is compressed by the multi-stage compressor 200 after the temperature of the high temperature flow path of the heat exchanger 100 is compressed. It continues until it is determined that the temperature of the boil-off gas sent to the furnace has risen. However, as a rule of thumb, the cycle may continue until it is determined that sufficient time has elapsed.

When it is determined that most of the lubricating oil that has been condensed or solidified with the inside of the heat exchanger 100 is collected in the gas-liquid separator 400 (that is, it is determined that the heat exchanger 100 is normalized), it is compressed by the multi-stage compressor 200 Blocks the flow of boil-off gas into the heat exchanger 100 , and discharges the melted or reduced viscosity lubricating oil collected in the gas-liquid separator 400 .

In order to rapidly discharge the melted or reduced viscosity lubricating oil collected in the gas-liquid separator 400 , nitrogen may be injected (nitrogen purging) into the gas-liquid separator 400 to discharge the lubricating oil. The pressure of nitrogen injected into the gas-liquid separator 400 during nitrogen purging may be about 5 to 7 bar.

Through the above-described process, not only the condensed or solidified lubricating oil inside the heat exchanger 100, but also the condensed or coagulated lubricating oil accumulated in pipes, valves, instruments, and various equipment may be removed.

In the present invention, it is possible to drive the engine (main engine and / or engine for power generation) while removing the condensed or solidified lubricating oil inside the heat exchanger 100, the condensed or solidified lubricating oil inside the heat exchanger 100 If the engine is driven during removal, since the heat exchanger 100 can be maintained while the engine operation is continued, the vessel can be propelled and power generation can be generated even during the maintenance of the heat exchanger 100, and the surplus BOG remaining after being used in the engine It has the advantage of being able to remove condensed or solidified lubricating oil by using

In addition, if the engine is driven while the condensed or solidified lubricating oil inside the heat exchanger 100 is removed, the lubricating oil compressed by the multi-stage compressor 200 and mixed with the boil-off gas can be burned by the engine. That is, the engine is not only used for its original purpose for propulsion or power generation of a ship, but also serves to remove oil mixed with boil-off gas.

3) When it is not necessary to reliquefy the boil-off gas

In addition, when there is no need to re-liquefy the BOG because there is almost no surplus BOG, such as in the ship's ballast state, all BOG discharged from the storage tank T is sent to the bypass line L3, and the BOG is heat exchanged. It bypasses the unit 100 so that it can be sent directly to the multi-stage compressor 200 . BOG compressed in the multi-stage compressor 200 is used as fuel for the main engine. When it is determined that it is not necessary to re-liquefy the BOG because there is almost no surplus BOG, the third shut-off valve 630 may be controlled to automatically open.

The inventors of the present invention have discovered that, when the boil-off gas is supplied to the engine through the heat exchanger 100 having a narrow flow path according to the present invention, the pressure drop of the boil-off gas occurs a lot by the heat exchanger 100 . When there is no need for re-liquefaction, as described above, by bypassing the heat exchanger 100 and compressing the boil-off gas, fuel can be smoothly supplied to the engine.

4) BOG re-liquefaction start or restart

The bypass line L3 can be used even when the boil-off gas is not reliquefied but the amount of boil-off gas is increased to re-liquefy the boil-off gas.

If the BOG is not reliquefied but the BOG is reliquefied due to an increase in the amount of BOG (that is, when re-liquefying BOG is started or restarted), the BOG discharged from the storage tank (T) is transferred to the bypass line (L3) All of the BOG bypasses the heat exchanger 100 and is directly supplied to the multi-stage compressor 200, and the BOG compressed by the multi-stage compressor 200 is sent to the high-temperature flow path of the heat exchanger 100. can Part of the boil-off gas compressed by the multi-stage compressor 200 may be sent to the main engine.

Through the above-described process, if the temperature of the high-temperature flow path of the heat exchanger 100 is increased at the time of starting or restarting the BOG reliquefaction, the heat exchanger 100, other equipment, piping, etc. may remain in the previous BOG reliquefaction process, It has the advantage of being able to start reliquefying BOG after removing condensed or solidified lubricating oil or other residues or impurities.

The residue may include lubricating oil mixed with the boil-off gas compressed by the compressor and then sent to the heat exchanger at the time of re-liquefaction of the boil-off gas, and the boil-off gas compressed by the compressor.

If the BOG re-liquefaction is started or restarted, the low-temperature BOG discharged from the storage tank T is directly transferred to the heat exchanger 100 without using the bypass line L3 to increase the temperature of the high-temperature flow path of the heat exchanger 100. When supplied to the heat exchanger 100 , since the low-temperature BOG discharged from the storage tank T is supplied to the low-temperature flow path of the heat exchanger 100 in a state in which the high-temperature BOG is not yet supplied to the high-temperature flow path of the heat exchanger 100 , the heat exchanger Lubricating oil that has not yet been condensed or solidified remaining in 100 may also be condensed or solidified by lowering the temperature of the heat exchanger 100 .

While continuing the process of increasing the temperature of the heat exchanger 100 high-temperature flow path using the bypass line L3, after a certain amount of time (that is, when it is determined that the condensed or solidified lubricant or other impurities are almost removed. The duration can be determined by experience, and it may take about 1 minute to 30 minutes, preferably about 3 minutes to 10 minutes, more preferably about 2 minutes to 5 minutes.), The first valve 510 and the second valve 520 are slowly opened and the third shut-off valve 630 is slowly closed to start re-liquefaction of BOG. As time passes, the first valve 510 and the second valve 520 are fully opened and the third shut-off valve 630 is completely closed, and all of the boil-off gas discharged from the storage tank T is removed from the heat exchanger 100 . It is used as a refrigerant to reliquefy the boil-off gas.

5) To satisfy the suction pressure condition of the multi-stage compressor

In addition, the bypass line L3 may be utilized to satisfy the suction pressure condition of the multi-stage compressor 200 when the pressure inside the storage tank T is low.

When the amount of BOG generated is small because the amount of liquefied gas inside the storage tank (T) is small, or when the amount of BOG supplied to the engine for propulsion of the vessel is large due to the speed of the ship, the storage tank (T) ), when the internal pressure is low, the multi-stage compressor 200 may not satisfy the suction pressure condition at the front end of the multi-stage compressor 200 required.

In particular, when PCHE (DCHE) is applied to the heat exchanger 100 , the PCHE has a narrow flow path, and when the boil-off gas discharged from the storage tank T passes through the PCHE, the width of the pressure drop is large.

Conventionally, when the suction pressure condition required by the multi-stage compressor 200 is not satisfied, part or all of the boil-off gas is recirculated by a recirculation line installed inside the multi-stage compressor 200 to protect the multi-stage compressor 200.

However, if the suction pressure condition of the multi-stage compressor 200 is satisfied in a manner of recirculating the boil-off gas, the amount of boil-off gas compressed by the multi-stage compressor 200 is eventually reduced, so that the reliquefaction performance is reduced and , the engine may not be able to meet the required fuel consumption. In particular, if the fuel consumption required by the engine is not satisfied, the operation of the vessel is greatly disturbed. Therefore, even when the internal pressure of the storage tank T is low, the engine is A method capable of satisfying the required fuel consumption was urgently required.

According to the present invention, without the installation of additional equipment, by utilizing the bypass line (L3) that has been previously installed for maintenance and repair of the heat exchanger 100, even when the internal pressure of the storage tank (T) is low, multi-stage It is possible to satisfy the suction pressure condition required by the multi-stage compressor 200 without reducing the amount of boil-off gas compressed by the compressor 100 .

According to the present invention, when the internal pressure of the storage tank (T) is below a certain value, the third shut-off valve (630) is opened to partially or all of the boil-off gas discharged from the storage tank (T) through the bypass line (L3). By bypassing the heat exchanger 100 through the direct transfer to the multi-stage compressor (200).

According to how insufficient the pressure of the storage tank T is compared to the suction pressure condition required by the multi-stage compressor 200, the amount of boil-off gas sent to the bypass line L3 can be adjusted. That is, all of the boil-off gas discharged from the storage tank (T) may be sent to the bypass line (L3) by completely opening the third shut-off valve (630), and only partially open the third shut-off valve (630), the storage tank (T) Only a part of the boil-off gas discharged from the evaporator may be sent to the bypass line L3 and the rest may be sent to the heat exchanger 100 . As the amount of BOG bypassing the heat exchanger 100 through the bypass line L3 increases, the pressure drop of BOG decreases.

If the BOG discharged from the storage tank T bypasses the heat exchanger 100 and is sent directly to the multi-stage compressor 200, the pressure drop can be minimized, but the cooling heat of BOG is used for re-liquefaction of BOG. Therefore, in consideration of the internal pressure of the storage tank (T), the fuel consumption required by the engine, the amount of boil-off gas to be reliquefied, whether to use the bypass line (L3) to reduce the pressure drop, and the storage tank It is decided how much of the boil-off gas discharged from (T) to be sent to the bypass line (L3).

For example, when the internal pressure of the storage tank (T) is less than or equal to a predetermined value, and the vessel is operated at a predetermined speed or more, it may be determined to be advantageous to reduce the pressure drop by using the bypass line (L3). Specifically, it can be determined that it is advantageous to reduce the pressure drop by using the bypass line (L3) when the internal pressure of the storage tank (T) is 1.09 bar or less and the speed of the vessel is 17 knots or more.

In addition, even if all of the boil-off gas discharged from the storage tank T is sent to the multi-stage compressor 200 through the bypass line L3, it may not be possible to satisfy the suction pressure condition required by the multi-stage compressor 200, in this case In this case, it is possible to satisfy the suction pressure condition by using a recirculation line installed inside the heat exchanger 100 .

That is, when the pressure of the storage tank T is lowered and the suction pressure condition required by the multi-stage compressor 200 cannot be satisfied, the multi-stage compressor 200 is protected by using a recirculation line in the prior art, whereas in the present invention, the According to this, the suction pressure condition of the multi-stage compressor 200 is satisfied by using the primary bypass line L3, and all the boil-off gas discharged from the storage tank T is transferred to the multi-stage compressor 200 through the bypass line L3. Even if sent, the recirculation line is used as a secondary when the suction pressure condition required by the multi-stage compressor 200 cannot be satisfied.

In order to meet the suction pressure condition of the multi-stage compressor 200 through the recirculation line secondly after using the bypass line L3 as the first, the third shutoff valve 630 is opened than the pressure value, which is the condition for using the recirculation line. The phosphorus pressure value can be set higher.

The condition of using the recirculation line and the condition that the third shut-off valve 630 is opened, it is preferable to use the shear pressure of the multi-stage compressor 200 as a factor, but the internal pressure of the storage tank T may be used as a factor.

The shear pressure of the multi-stage compressor 200 may be measured by a first pressure sensor (not shown) installed at the front end of the multi-stage compressor 200, and the internal pressure of the storage tank T is measured by a second pressure sensor (not shown). can be measured.

The third shut-off valve 630 is preferably a valve with a faster reaction rate than a normal case so that the opening degree can be quickly adjusted according to the pressure change of the storage tank T.

6) When it is necessary to control the internal pressure of the storage tank to a low range

In addition, when it is necessary to control the internal pressure of the storage tank (T) to a low range, the bypass line (L3) is installed to satisfy the suction pressure condition of the multi-stage compressor (200) even if the pressure of the storage tank (T) is lowered. can be used

The decompression device 300 of this embodiment expands the boil-off gas cooled by the heat exchanger 100 after being compressed by the multi-stage compressor 200 . BOG, which has undergone a compression process by the multi-stage compressor 200 , a cooling process by the heat exchanger 100 , and an expansion process by the decompression device 300 , is partially or completely reliquefied. The pressure reducing device 300 of this embodiment may be an expansion valve such as a Joule-Thompson valve, or an expander.

The first discharge line L1 of this embodiment branches from the line through which the boil-off gas discharged from the storage tank T is sent to the heat exchanger 100, and some or all of the boil-off gas discharged from the storage tank T is sent to the gas burner.

According to the BOG reliquefaction system included in the ship of this embodiment, part or all of BOG generated in the storage tank T by the first discharge line L1 can be sent to the gas combustion device to be burned, so the storage tank It can also be prepared for cases where BOG is generated more than usual, such as when liquefied natural gas is shipped to (T).

On the first discharge line L1 of this embodiment, a first shut-off valve 610 for opening and closing the first discharge line L1 is installed, and a blower 700 that sucks boil-off gas and sends it to a gas combustion device is provided. It may be installed at the rear end of the first shut-off valve 610 .

The BOG reliquefaction system included in the ship of this embodiment is installed at the rear end of the decompression device 300 , and passes through the multi-stage compressor 200 , the heat exchanger 100 , and the decompression device 300 , and is liquefied natural. It may further include a gas-liquid separator 400 for separating the gas and the boil-off gas remaining in the gaseous state.

The liquefied natural gas separated by the gas-liquid separator 400 of this embodiment is sent to the storage tank T, and the boil-off gas separated by the gas-liquid separator 400 of this embodiment is the boil-off gas discharged from the storage tank T and may be sent to the heat exchanger 100 .

The point at which the boil-off gas separated by the gas-liquid separator 400 of this embodiment joins with the boil-off gas discharged from the storage tank T is between the branching point of the first discharge line L1 and the heat exchanger 100 . can be That is, on the line through which the boil-off gas discharged from the storage tank T is sent to the heat exchanger 100 , the junction of the branch point of the first discharge line L1 and the boil-off gas separated by the gas-liquid separator 400 evaporates. It may be located sequentially in the flow direction of the gas.

2 shows that the boil-off gas separated by the gas-liquid separator 400 is joined between the branching point of the first discharge line L1 and the heat exchanger 100, but in the gas-liquid separator 400 of this embodiment The boil-off gas separated by the may be merged between the branching point of the storage tank T and the first discharge line L1. That is, on the line through which the BOG discharged from the storage tank T is sent to the heat exchanger 100 , the junction of the BOG separated by the gas-liquid separator 400 and the branching point of the first discharge line L1 are BOG can be located sequentially in the flow direction of

When the junction of the boil-off gas separated by the gas-liquid separator 400 of this embodiment is between the branch point of the first discharge line L1 and the heat exchanger 100, a part of the boil-off gas discharged from the storage tank T or All of them are sent to the gas combustion device by the first discharge line L1 , and all of the boil-off gas separated by the gas-liquid separator 400 is sent to the heat exchanger 100 .

A second control valve 520 for controlling the flow rate and opening/closing of the boil-off gas may be installed on the line through which the gaseous boil-off gas is discharged from the gas-liquid separator 400 of the present embodiment.

3 is a schematic diagram of a boil-off gas reliquefaction system included in a ship according to a second preferred embodiment of the present invention.

The BOG reliquefaction system included in the ship of the second embodiment shown in FIG. 3 has a second discharge line L2, compared to the BOG reliquefaction system included in the ship of the first embodiment shown in FIG. 2 . Differences exist in that they are included, and below, the differences will be mainly described. Detailed description of the same members as those of the boil-off gas reliquefaction system included in the ship of the first embodiment described above will be omitted.

Referring to FIG. 3 , the BOG reliquefaction system included in the ship of this embodiment, like the first embodiment, includes a multi-stage compressor 200 , a heat exchanger 100 , a pressure reducing device 300 , and a first discharge line. (L1).

A first control valve 510 for controlling the flow rate and opening/closing of the boil-off gas may be installed on the line through which the boil-off gas is discharged from the storage tank T, as in the first embodiment.

The multi-stage compressor 200 of this embodiment, like the first embodiment, includes a plurality of compression cylinders (210, 220, 230, 240, 250) and a plurality of coolers (810, 820, 830, 840, 850) and , the boil-off gas discharged from the storage tank (T) is compressed in multiple stages.

BOG compressed by the multi-stage compressor 200 of this embodiment, like the first embodiment, may be partially sent to the main engine propelling the vessel, and the remaining BOG not required by the main engine is reliquefied. It may be sent to the heat exchanger 100 for passing.

The main engine, like the first embodiment, may be a ME-GI engine.

The multi-stage compressor 200 of this embodiment, like the first embodiment, can compress the BOG to a pressure required by the main engine, and when the main engine is an ME-GI engine, BOG at a pressure of about 300 bar can be compressed.

BOG, which has passed through only some of the compression cylinders 210 and 220 included in the multi-stage compressor 200 of this embodiment, may be partially branched and sent to the generator, as in the first embodiment. The generator of this embodiment, like the first embodiment, may require natural gas at a pressure of about 6.5 bar, and is about 6.5 by some of the compression cylinders 210 and 220 included in the multi-stage compressor 200 of this embodiment. BOG compressed to bar can be sent to the generator. On the line through which the boil-off gas is sent from the multi-stage compressor 200 to the generator, as in the first embodiment, a third control valve 530 for controlling the flow rate and opening/closing of the boil-off gas may be installed.

The heat exchanger 100 of this embodiment, like the first embodiment, heats some or all of the boil-off gas compressed by the multi-stage compressor 200 with the boil-off gas discharged from the storage tank T to cool it.

When the heat exchanger 100 of this embodiment is being maintained or the heat exchanger 100 is out of order, etc., when the heat exchanger 100 cannot be used, as in the first embodiment, the discharge from the storage tank T BOG may bypass the heat exchanger 100 through the bypass line L3. A third shutoff valve 630 for opening and closing the bypass line L3 is installed in the bypass line L3 of the present embodiment, as in the first embodiment.

In addition, similarly to the first embodiment, the bypass line L3 of this embodiment is 1) when the heat exchanger 100 is broken or the heat exchanger 100 cannot be used, such as when maintenance is required, 2) heat exchange When the flow path of the machine 100 is blocked by condensed or solidified lubricating oil, in order to remove the condensed or solidified lubricating oil, 3) there is almost no surplus BOG and there is no need to reliquefy the BOG, 4) BOG In the case of re-liquefying BOG because the amount of BOG increases without re-liquefying the BOG (that is, when starting or restarting BOG re-liquefaction), 5) When the pressure inside the storage tank (T) is low, the multi-stage compressor 200 ) to satisfy the suction pressure condition of 6) when the internal pressure of the storage tank T needs to be controlled to a low range, the suction pressure condition of the multi-stage compressor 200 is satisfied even if the pressure of the storage tank T is lowered. It can be used to make it possible.

The decompression device 300 of this embodiment expands the boil-off gas cooled by the heat exchanger 100 after being compressed by the multi-stage compressor 200 , like the first embodiment. BOG, which has undergone a compression process by the multi-stage compressor 200, a cooling process by the heat exchanger 100, and an expansion process by the decompression device 300, is partially or completely reliquefied, as in the first embodiment. . The pressure reducing device 300 of this embodiment may be an expansion valve such as a Joule-Thompson valve, or an expander.

The first discharge line L1 of this embodiment branches from the line through which the boil-off gas discharged from the storage tank T is sent to the heat exchanger 100, as in the first embodiment, and is discharged from the storage tank T Some or all of the boil-off gas produced is sent to the gas combustion device.

On the first discharge line L1 of this embodiment, as in the first embodiment, a first shut-off valve 610 for opening and closing the first discharge line L1 is installed, and the boil-off gas is sucked and sent to the gas combustion device A blower (Blower, 700) may be installed at the rear end of the first shut-off valve (610).

However, the BOG reliquefaction system included in the ship of this embodiment branches from the line through which BOG is sent from the heat exchanger 100 to the multi-stage compressor 200 and merges with the first discharge line L1, the second It may further include a discharge line (L2). A second shut-off valve 620 for opening and closing the second discharge line L2 is installed on the second discharge line L2.

In this embodiment, the first discharge line (L1) is, when the heat exchanger 100 is being maintained or the heat exchanger 100 is broken, etc., when the heat exchanger 100 cannot be used, the heat exchanger 100 ) is used to send BOG from the storage tank (T) to the gas combustion device, and there is no need to send BOG generated in the storage tank (T) to the gas combustion device in a state where the heat exchanger 100 can be used. If there is, use the second discharge line (L2).

In addition, in this embodiment, although the case including both the first discharge line (L1) and the second discharge line (L2) has been described, the present invention, the first branched between the storage tank (T) and the heat exchanger (100) The second discharge line L2 branched between the heat exchanger 100 and the multi-stage compressor 200 without including the first discharge line L1 may be configured to be directly connected to the gas combustion device.

According to the first embodiment shown in FIG. 2 , since the boil-off gas sent to the gas combustion device after being discharged from the storage tank T is branched from the front end of the heat exchanger 100, after being discharged from the storage tank T, the multi-stage Only boil-off gas sent to the compressor 200 is used as the refrigerant of the heat exchanger 100 .

However, according to this embodiment, since the boil-off gas is sent to the gas combustion device through the second discharge line L2 branched from the rear end of the heat exchanger 100, it is discharged from the storage tank T and then sent to the gas combustion device. BOG and BOG discharged from the storage tank (T) and sent to the multi-stage compressor (200) are all used as the refrigerant of the heat exchanger (100).

Accordingly, according to the present embodiment, the cooling efficiency by the heat exchanger 100 can be increased compared to that of the first embodiment. When the cooling efficiency by the heat exchanger 100 increases, the flow rate of re-liquefied BOG increases, and the surplus BOG is reliquefied or sent to a gas combustion device for processing. the flow rate is reduced.

Unlike the first embodiment, the heat exchanger 100 of this embodiment is designed to have a larger capacity than that of the first embodiment because it must also accommodate the flow rate of boil-off gas sent to the gas combustion apparatus.

The point at which the second discharge line L2 of this embodiment joins is preferably the first discharge line L1 at the rear end of the first shut-off valve 610, and when the present embodiment includes the blower 700, the first The point where the two discharge lines (L2) are joined is preferably between the first shut-off valve (610) and the blower (700).

According to the BOG reliquefaction system included in the ship of this embodiment, a part or all of BOG generated in the storage tank T by the first discharge line L1 or the second discharge line L2 is converted into a gas combustion device. Since it can be sent to the evaporator and burned, it can be prepared for cases in which BOG is generated more than usual, such as when liquefied natural gas is shipped to the storage tank (T).

The boil-off gas reliquefaction system included in the ship of this embodiment, like the first embodiment, is installed at the rear end of the pressure reducing device 300 , and includes a multi-stage compressor 200 , a heat exchanger 100 , and a pressure reducing device 300 . It may further include a gas-liquid separator 400 that separates the liquefied natural gas and the boil-off gas remaining in a gaseous state while passing through.

Like the first embodiment, the liquefied natural gas separated by the gas-liquid separator 400 of this embodiment is sent to the storage tank T, and the boil-off gas separated by the gas-liquid separator 400 of this embodiment is stored in a storage tank ( It may be combined with the boil-off gas discharged from T) and sent to the heat exchanger 100 .

The point at which the boil-off gas separated by the gas-liquid separator 400 of this embodiment joins with the boil-off gas discharged from the storage tank T is, like the first embodiment, a branching point of the first discharge line L1 and the heat exchanger 100 . In addition, the boil-off gas separated by the gas-liquid separator 400 of the present embodiment may be merged between the branching point of the storage tank T and the first discharge line L1, as in the first embodiment.

When the junction of the boil-off gas separated by the gas-liquid separator 400 of this embodiment is between the branch point of the first discharge line L1 and the heat exchanger 100, as in the first embodiment, from the storage tank T Only a part or all of the discharged BOG is sent to the gas combustion device by the first discharge line L1 , and all BOG separated by the gas-liquid separator 400 is sent to the heat exchanger 100 .

A second control valve 520 for controlling the flow rate and opening/closing of the boil-off gas may be installed on the line through which the gaseous boil-off gas is discharged from the gas-liquid separator 400 of the present embodiment, as in the first embodiment.

4 is a schematic diagram of a BOG reliquefaction system included in a ship according to a third preferred embodiment of the present invention.

The BOG reliquefaction system included in the ship of the third embodiment shown in FIG. 4 includes a first discharge line L1, compared to the BOG reliquefaction system included in the ship of the first embodiment shown in FIG. 2 . There is a difference in that it further includes the second discharge line L2 without doing so, and below, the difference will be mainly described. Detailed description of the same members as those of the boil-off gas reliquefaction system included in the ship of the first embodiment described above will be omitted.

Referring to FIG. 4 , the BOG reliquefaction system included in the ship of this embodiment includes a multi-stage compressor 200 , a heat exchanger 100 , and a pressure reducing device 300 , like the first embodiment. However, the BOG reliquefaction system included in the ship of this embodiment, unlike the first embodiment, does not include the first discharge line (L1), but includes the second discharge line (L2).

A first control valve 510 for controlling the flow rate and opening/closing of the boil-off gas may be installed on the line through which the boil-off gas is discharged from the storage tank T, as in the first embodiment.

The multi-stage compressor 200 of this embodiment, like the first embodiment, includes a plurality of compression cylinders (210, 220, 230, 240, 250) and a plurality of coolers (810, 820, 830, 840, 850) and , the boil-off gas discharged from the storage tank (T) is compressed in multiple stages.

BOG compressed by the multi-stage compressor 200 of this embodiment, like the first embodiment, may be partially sent to the main engine propelling the vessel, and the remaining BOG not required by the main engine is reliquefied. It may be sent to the heat exchanger 100 for passing.

The main engine, like the first embodiment, may be a ME-GI engine.

The multi-stage compressor 200 of this embodiment, like the first embodiment, can compress the BOG to a pressure required by the main engine, and when the main engine is an ME-GI engine, BOG at a pressure of about 300 bar can be compressed.

BOG, which has passed through only some of the compression cylinders 210 and 220 included in the multi-stage compressor 200 of this embodiment, may be partially branched and sent to the generator, as in the first embodiment. The generator of this embodiment, like the first embodiment, may require natural gas at a pressure of about 6.5 bar, and is about 6.5 by some of the compression cylinders 210 and 220 included in the multi-stage compressor 200 of this embodiment. BOG compressed to bar can be sent to the generator. On the line through which the boil-off gas is sent from the multi-stage compressor 200 to the generator, as in the first embodiment, a third control valve 530 for controlling the flow rate and opening/closing of the boil-off gas may be installed.

The heat exchanger 100 of this embodiment, like the first embodiment, heats some or all of the boil-off gas compressed by the multi-stage compressor 200 with the boil-off gas discharged from the storage tank T to cool it.

The decompression device 300 of this embodiment expands the boil-off gas cooled by the heat exchanger 100 after being compressed by the multi-stage compressor 200 , like the first embodiment. BOG, which has undergone a compression process by the multi-stage compressor 200, a cooling process by the heat exchanger 100, and an expansion process by the decompression device 300, is partially or completely reliquefied, as in the first embodiment. . The pressure reducing device 300 of this embodiment may be an expansion valve such as a Joule-Thompson valve, or an expander.

The second discharge line L2 of this embodiment branches from the line through which the boil-off gas is sent from the heat exchanger 100 to the multi-stage compressor 200, is discharged from the storage tank T, and then the refrigerant in the heat exchanger 100 Some or all of the boil-off gas used in the furnace is sent to the gas combustion device.

On the second discharge line (L2) of this embodiment, a second shut-off valve 620 for opening and closing the second discharge line (L2) is installed, and a blower (Blower, 700) that sucks the boil-off gas and sends it to the gas combustion device. It may be installed at the rear end of the second shut-off valve 620 .

In this embodiment, when the heat exchanger 100 is being maintained or the heat exchanger 100 is broken, etc., when the heat exchanger 100 cannot be used, the boil-off gas discharged from the storage tank T is transferred to the bypass line. When it is necessary to bypass the heat exchanger 100 through (L3) and send the boil-off gas generated in the storage tank T to the gas combustion device in a state in which the heat exchanger 100 can be used, the storage tank After the boil-off gas discharged from (T) is used as a refrigerant in the heat exchanger 100, it is sent to the gas combustion device along the second discharge line (L2). A third shutoff valve 630 for opening and closing the bypass line L3 is installed in the bypass line L3 of the present embodiment, as in the first embodiment.

According to the first embodiment shown in FIG. 2 , since the boil-off gas sent to the gas combustion device after being discharged from the storage tank T is branched from the front end of the heat exchanger 100, after being discharged from the storage tank T, the multi-stage Only boil-off gas sent to the compressor 200 is used as the refrigerant of the heat exchanger 100 .

However, according to this embodiment, since the boil-off gas is sent to the gas combustion device through the second discharge line L2 branched from the rear end of the heat exchanger 100, it is discharged from the storage tank T and then sent to the gas combustion device. BOG and BOG discharged from the storage tank (T) and sent to the multi-stage compressor (200) are all used as the refrigerant of the heat exchanger (100).

Therefore, according to the present embodiment, the cooling efficiency by the heat exchanger 100 can be increased compared to that of the first embodiment. When the cooling efficiency by the heat exchanger 100 increases, the flow rate of re-liquefied BOG increases, and the surplus BOG is reliquefied or sent to a gas combustion device for processing. the flow rate is reduced.

Unlike the first embodiment, the heat exchanger 100 of this embodiment is designed to have a larger capacity than that of the first embodiment because it must also accommodate the flow rate of boil-off gas sent to the gas combustion apparatus.

According to the BOG reliquefaction system included in the ship of this embodiment, some or all of BOG generated in the storage tank T by the second discharge line L2 can be sent to the gas combustion device to be burned, so the storage tank It can also be prepared for cases where BOG is generated more than usual, such as when liquefied natural gas is shipped to (T).

In addition, similarly to the first embodiment, the bypass line L3 of this embodiment is 1) when the heat exchanger 100 is broken or the heat exchanger 100 cannot be used, such as when maintenance is required, 2) heat exchange When the flow path of the machine 100 is blocked by condensed or solidified lubricating oil, in order to remove the condensed or solidified lubricating oil, 3) there is almost no surplus BOG and there is no need to reliquefy the BOG, 4) BOG In the case of re-liquefying BOG because the amount of BOG increases without re-liquefying the BOG (that is, when starting or restarting BOG re-liquefaction), 5) When the pressure inside the storage tank (T) is low, the multi-stage compressor 200 ) to satisfy the suction pressure condition of 6) when the internal pressure of the storage tank T needs to be controlled to a low range, the suction pressure condition of the multi-stage compressor 200 is satisfied even if the pressure of the storage tank T is lowered. It can be used to make it possible.

The boil-off gas reliquefaction system included in the ship of this embodiment, like the first embodiment, is installed at the rear end of the pressure reducing device 300 , and includes a multi-stage compressor 200 , a heat exchanger 100 , and a pressure reducing device 300 . It may further include a gas-liquid separator 400 that separates the liquefied natural gas and the boil-off gas remaining in a gaseous state while passing through.

Like the first embodiment, the liquefied natural gas separated by the gas-liquid separator 400 of this embodiment is sent to the storage tank T, and the boil-off gas separated by the gas-liquid separator 400 of this embodiment is stored in a storage tank ( It may be combined with the boil-off gas discharged from T) and sent to the heat exchanger 100 .

A second control valve 520 for controlling the flow rate and opening/closing of the boil-off gas may be installed on the line through which the gaseous boil-off gas is discharged from the gas-liquid separator 400 of the present embodiment, as in the first embodiment.

5 is a schematic diagram of a BOG reliquefaction system according to a fourth preferred embodiment of the present invention.

Referring to FIG. 5 , the BOG reliquefaction system of this embodiment includes a heat exchanger 100 , a first valve 510 , a second valve 520 , a first temperature sensor 810 , and a second temperature sensor 820 . ), compressor 200, third temperature sensor 830, fourth temperature sensor 840, first pressure sensor 910, second pressure sensor 920, pressure reducing device 600, bypass line (BL) , and a bypass valve 590 .

The heat exchanger 100 heats the BOG compressed by the compressor 200 by using the BOG discharged from the storage tank T as a refrigerant to cool it. BOG used as a refrigerant in the heat exchanger 100 after being discharged from the storage tank T is sent to the compressor 200, and BOG compressed by the compressor 200 is discharged from the storage tank T It is cooled by the heat exchanger 100 using boil-off gas as a refrigerant.

BOG discharged from the storage tank T is sent to the heat exchanger 100 along the first supply line L1 to be used as a refrigerant, and BOG used as a refrigerant in the heat exchanger 100 is transferred to the second supply line L2 ) along with the compressor 200 . Part or all of the boil-off gas compressed by the compressor 200 is sent to the heat exchanger 100 along the third supply line L3 to be cooled, and the fluid cooled in the heat exchanger 100 is transferred to the fourth supply line L4 ) is sent to the decompression device 600 .

The first valve 510 is installed on the first supply line L1 to control the flow rate and opening/closing of the fluid, and the second valve 520 is installed on the second supply line L2 to control the flow rate and opening/closing of the fluid. adjust the

The first temperature sensor 810 is installed at the front end of the heat exchanger 100 on the first supply line L1 , and measures the temperature of boil-off gas discharged from the storage tank T and supplied to the heat exchanger 100 . The first temperature sensor 810 is preferably installed in front of the heat exchanger 100 so as to measure the temperature of the boil-off gas immediately before being supplied to the heat exchanger 100 .

In the present invention, the front end includes the upstream meaning, and the rear end includes the downstream meaning.

The second temperature sensor 820 is installed at the rear end of the heat exchanger 100 on the second supply line L2, and after being discharged from the storage tank T, measures the temperature of the boil-off gas used as a refrigerant in the heat exchanger 100. measure The second temperature sensor 820 is preferably installed immediately after the heat exchanger 100 so as to measure the temperature of the boil-off gas immediately after being used as a refrigerant in the heat exchanger 100 .

The compressor 200 compresses the boil-off gas used as a refrigerant in the heat exchanger 100 after being discharged from the storage tank T. BOG compressed by the compressor 200 may be supplied as fuel of the high-pressure engine, and the remaining BOG remaining after being supplied as fuel of the high-pressure engine may be sent to the heat exchanger 100 to undergo a re-liquefaction process.

On the fuel supply line SL for sending the boil-off gas compressed by the compressor 200 to the high-pressure engine, a sixth valve 560 for controlling the flow rate and opening/closing of the fluid may be installed.

The sixth valve 560 serves as a safety device for completely blocking the supply of boil-off gas sent to the high-pressure engine when the gas mode operation of the high-pressure engine is stopped. The gas mode refers to a mode in which the engine is operated using natural gas as a fuel, and when the boil-off gas to be used as fuel is insufficient, the engine is switched to the fuel oil mode and fuel oil is used as the fuel of the engine.

In addition, on the line for sending the remaining BOG among the BOG compressed by the compressor 200 as fuel of the high-pressure engine to the heat exchanger 100, a seventh valve 570 for controlling the flow rate and opening/closing of the fluid. can be installed.

When the boil-off gas compressed by the compressor 200 is sent to the high-pressure engine, the compressor 200 may compress the boil-off gas to a pressure required by the high-pressure engine. The high-pressure engine may be a ME-GI engine using high-pressure boil-off gas as fuel.

It is known that the ME-GI engine uses natural gas of approximately 150 to 400 bar, preferably approximately 150 to 350 bar, more preferably approximately 300 bar as fuel. The compressor 200 of the present invention can compress the boil-off gas to approximately 150 to 350 bar so that the compressed boil-off gas can be supplied to the ME-GI engine.

In the present invention, instead of the ME-GI engine as the main engine, an X-DF engine or a DF engine using boil-off gas at a pressure of about 6 to 20 bar as fuel may be used. Since BOG is at a low pressure, it can be re-liquefied by additionally pressurizing BOG compressed to be supplied to the main engine. The pressure of the boil-off gas additionally pressurized for re-liquefaction may be approximately 80 to 250 bar.

14 and 15 are graphs showing the amount of reliquefaction according to the BOG pressure in a partial re-liquefaction system (PRS). The reliquefaction target BOG refers to BOG that is cooled and reliquefied, and was named to distinguish it from BOG used as a refrigerant.

14 and 15 , it can be seen that the reliquefaction amount shows the maximum value when the pressure of the boil-off gas is around 150 to 170 bar, and there is little change in the amount of reliquefaction between 150 and 300 bar. Therefore, when the ME-GI engine using boil-off gas at a pressure of about 150 to 350 bar (mainly 300 bar) as a fuel is a high-pressure engine, the re-liquefaction system is facilitated so that a high re-liquefaction amount is maintained while supplying fuel to the high-pressure engine. It has the advantage of being able to control it.

The compressor 200 includes a plurality of cylinders 210, 220, 230, 240, 250 and a plurality of coolers 211, 221, 231, 241, 251). The coolers 211 , 221 , 231 , 241 , and 251 are compressed by the cylinders 210 , 220 , 230 , 240 and 250 and cool the boil-off gas whose temperature as well as pressure has increased.

When the compressor 200 includes a plurality of cylinders 210, 220, 230, 240, and 250, the boil-off gas supplied to the compressor 200 is generated by the plurality of cylinders 210, 220, 230, 240, and 250. compressed in multiple stages. Each of the cylinders 210 , 220 , 230 , 240 , and 250 may have the meaning of each compression stage of the compressor 200 .

In addition, the compressor 200, a first recirculation line (RC1) for sending some or all of the boil-off gas that has passed through the first cylinder 210 and the first cooler 211 to the front end of the first cylinder 210; a second recirculation line (RC2) for sending some or all of the boil-off gas that has passed through the second cylinder 220 and the second cooler 221 to the front end of the second cylinder 220; a third recirculation line (RC3) for sending some or all of the boil-off gas that has passed through the third cylinder 230 and the third cooler 231 to the front end of the third cylinder 230; And the fourth cylinder 240, the fourth cooler 241, the fifth cylinder 250, and the fourth recirculation that sends some or all of the boil-off gas that has passed through the fifth cooler 251 to the front end of the fourth cylinder 240 It may include a line RC4.

In addition, a first recirculation valve 541 for controlling the flow rate and opening/closing of the fluid is installed on the first recirculation line RC1, and a second recirculation valve 541 for controlling the flow rate and opening/closing of the fluid on the second recirculation line RC2 ( 542) is installed, a third recirculation valve 543 for controlling the flow rate and opening/closing of the fluid is installed on the third recirculation line RC3, and a third recirculation valve 543 for controlling the flow rate and opening/closing of the fluid is installed on the fourth recirculation line RC4 4 A recirculation valve 544 may be installed.

The recirculation lines RC1, RC2, RC3, and RC4 recirculate some or all of the boil-off gas when the suction pressure condition required by the compressor 200 is not satisfied because the internal pressure of the storage tank T is low. ) to protect When the recirculation lines RC1, RC2, RC3, and RC4 are not used, the recirculation valves 541, 542, 543, 544 are closed, and the suction pressure conditions required by the compressor 200 are not satisfied, so the recirculation lines RC1, RC2 , RC3, RC4) open the recirculation valves 541, 542, 543, 544 if necessary to use.

In FIG. 5 , the case in which the boil-off gas has passed through all of the plurality of cylinders 210 , 220 , 230 , 240 and 250 included in the compressor 200 is sent to the heat exchanger 100 , but a plurality of BOG that has passed through some of the cylinders 210 , 220 , 230 , 240 and 250 may be branched from the middle of the compressor 200 and sent to the heat exchanger 100 .

In addition, BOG that has passed through some of the plurality of cylinders 210, 220, 230, 240, 250 may be branched in the middle of the compressor 200 and sent to a low-pressure engine to be used as fuel, and the surplus BOG is It can also be sent to a Gas Combustion Unit (GCU) for combustion.

The low-pressure engine may be a DF engine (eg, DFDE) using boil-off gas at a pressure of about 6 to 10 bar as a fuel.

A plurality of cylinders (210, 220, 230, 240, 250) included in the compressor 200, some operate in an oil-free lubricated (oil-free lubricated) manner and the rest may operate in an oil lubricated (oil lubricated) manner. there is. In particular, when the boil-off gas compressed by the compressor 200 is compressed to 80 bar or more, preferably 100 bar or more, in order to use the boil-off gas as a fuel for a high-pressure engine or for re-liquefaction efficiency, the compressor 200 is In order to compress the boil-off gas to a high pressure, it will include a lubrication type cylinder.

In the existing technology, in order to compress the boil-off gas to 100 bar or more, it is necessary to supply lubricating oil for lubrication and cooling to the reciprocating type compressor 200 , for example, to the piston sealing portion.

Lubricating oil is supplied to the oil-lubricated cylinder, and at the current level of technology, some of the lubricant is mixed with the boil-off gas that has passed through the oil-lubricated cylinder. The inventors of the present invention have discovered that the boil-off gas is compressed and the lubricating oil mixed with the boil-off gas is condensed or solidified before the boil-off gas in the heat exchanger 100 to block the flow path of the heat exchanger 100 .

The boil-off gas reliquefaction system of this embodiment may further include an oil separator 300 and a first oil filter 410 installed between the compressor 200 and the heat exchanger 100 to separate oil mixed with the boil-off gas. there is.

The oil separator 300 mainly separates lubricating oil in a liquid state, and the first oil filter 410 separates lubricating oil in a vapor state or mist (droplet) state. Since the oil separator 300 separates lubricating oil with larger particles than the first oil filter 410 , the oil separator 300 is installed at the front end of the first oil filter 410 to evaporate compressed by the compressor 200 . It is preferable that the gas passes through the oil separator 300 and the first oil filter 410 sequentially and then is sent to the heat exchanger 100 .

5 illustrates a case in which both the oil separator 300 and the first oil filter 410 are included. It may contain only one. However, it is preferable to use both the oil separator 300 and the first oil filter 410 .

5 shows a case in which the first oil filter 410 is installed on the second supply line L2 at the rear end of the compressor 200 , but the first oil filter 410 is installed at the front end of the heat exchanger 100 . It may be installed on the third supply line (L3) of the plurality, may be installed in parallel.

The boil-off gas reliquefaction system of this embodiment includes at least one of the oil separator 300 and the first oil filter 410, and the compressor 200 of this embodiment includes a cylinder of a non-oil lubrication type and a cylinder of an oil lubrication type. In this case, the boil-off gas that has passed through the oil-lubricated cylinder is configured to be sent to the oil separator 300 and/or the first oil filter 410, and the boil-off gas that has passed through only the oil-free lubrication type cylinder is transferred to the oil separator 300 ) or it may be configured to be sent directly to the heat exchanger 100 without passing through the oil filter 410 .

For example, the compressor 200 of this embodiment includes five cylinders 210 , 220 , 230 , 240 , 250 , and the front three cylinders 210 , 220 , 230 are oil-free lubrication and the rear end two cylinders 240 , 250) may be an oil supply lubrication method. In the case of branching the boil-off gas at the third stage or less, the boil-off gas is sent directly to the heat exchanger 100 without passing through the oil separator 300 or the first oil filter 410 . In the case of branching the boil-off gas at four or more stages, the boil-off gas may be configured to be sent to the first heat exchanger 100 after passing through the oil separator 300 and/or the first oil filter 410 .

The first oil filter 410 may be a coalescer type oil filter.

A non-return valve 550 may be installed on the fuel supply line SL between the compressor 200 and the high-pressure engine. The non-return valve 550 serves to prevent the boil-off gas from flowing back and damaging the compressor when the high-pressure engine is stopped.

When the boil-off gas reliquefaction system of this embodiment includes the oil separator 300 and/or the first oil filter 410 , the reverse flowed boil-off gas flows to the oil separator 300 and/or the first oil filter 410 . To prevent flow, the non-return valve 550 is preferably installed at the rear end of the oil separator 300 and/or the first oil filter 410 .

In addition, even when the expansion valve 600 is abruptly closed, etc., the boil-off gas may reverse flow and damage the compressor 200 . Therefore, the non-return valve 550 has the third supply line L3 connected to the fuel supply line SL. ), it is preferable to be installed at the front end of the branching point.

The third temperature sensor 830 is installed at the front end of the heat exchanger 100 on the third supply line L3 and measures the temperature of boil-off gas sent to the heat exchanger 100 after being compressed by the compressor 200 . do. The third temperature sensor 830 is preferably installed in front of the heat exchanger 100 so as to measure the temperature of the boil-off gas immediately before being supplied to the heat exchanger 100 .

The fourth temperature sensor 840 is installed at the rear end of the heat exchanger 100 on the fourth supply line L4 and measures the temperature of the boil-off gas cooled by the heat exchanger 100 after being compressed by the compressor 200 . measure The fourth temperature sensor 840 is preferably installed immediately after the heat exchanger 100 so as to measure the temperature of the boil-off gas immediately after being cooled by the heat exchanger 100 .

The first pressure sensor 910 is installed at the front end of the heat exchanger 100 on the third supply line L3 and measures the pressure of boil-off gas sent to the heat exchanger 100 after being compressed by the compressor 200 . do. The first pressure sensor 910 is preferably installed in front of the heat exchanger 100 so as to measure the pressure of the boil-off gas immediately before being supplied to the heat exchanger 100 .

The second pressure sensor 920 is installed at the rear end of the heat exchanger 100 on the fourth supply line L4 to measure the pressure of the boil-off gas cooled by the heat exchanger 100 after being compressed by the compressor 200 . measure The second pressure sensor 920 is preferably installed immediately after the heat exchanger 100 so as to measure the pressure of the boil-off gas immediately after being cooled by the heat exchanger 100 .

As shown in FIG. 5, it is preferable that the first to fourth temperature sensors 810 to 840, the first pressure sensor 910, and the second pressure sensor 920 are all installed, but the present embodiment is limited thereto. not, only the first temperature sensor 810 and the fourth temperature sensor 840 (hereinafter, referred to as a 'first pair') are installed, or the second temperature sensor 820 and the third temperature sensor Only 830 (hereinafter, referred to as a 'second pair') is installed, or only the first pressure sensor 910 and the second pressure sensor 920 (hereinafter referred to as a 'third pair') are installed, or Only two of the first to third pairs may be installed.

The pressure reducing device 600 is installed at the rear end of the heat exchanger 100 , and decompresses the boil-off gas cooled by the heat exchanger 100 after being compressed by the compressor 200 . BOG, which has undergone a compression process by the compressor 200 , a cooling process by the heat exchanger 100 , and a pressure reduction process by the decompression device 600 , is partially or completely reliquefied. The pressure reducing device 600 may be an expansion valve such as a Joule-Thomson valve or an expander depending on the configuration of the system.

The BOG reliquefaction system of this embodiment is installed at the rear end of the decompression device 600 , passes through the compressor 200 , the heat exchanger 100 , and the decompression device 600 , and reliquefied liquefied natural gas, a gaseous state It may further include a gas-liquid separator 700 for separating the remaining boil-off gas.

The liquefied gas separated by the gas-liquid separator 700 is sent to the storage tank T along the fifth supply line L5, and the boil-off gas separated by the gas-liquid separator 700 passes through the sixth supply line L6. Accordingly, it may be sent to the heat exchanger 100 after being merged with the boil-off gas discharged from the storage tank (T).

5 shows that the boil-off gas separated by the gas-liquid separator 700 is sent to the heat exchanger 100 after being merged with the boil-off gas discharged from the storage tank T, but the present invention is not limited thereto. The unit 100 is composed of three flow paths, and the boil-off gas separated in the gas-liquid separator 700 may be used as a refrigerant in the heat exchanger 100 along a separate flow path.

In addition, it is also possible to directly send the fluid that is decompressed by the decompression device 600 without including the gas-liquid separator 700 and partially or entirely reliquefied to the storage tank T.

An eighth valve 581 for opening and closing the flow rate of the fluid may be installed on the fifth supply line L5. The level of the liquefied gas inside the gas-liquid separator 700 is adjusted by the eighth valve 581 .

A ninth valve 582 for controlling the flow rate and opening/closing of the fluid may be installed on the sixth supply line L6. The pressure inside the gas-liquid separator 700 is adjusted by the ninth valve 582 .

7 is an enlarged view of the gas-liquid separator according to an embodiment of the present invention. As shown in FIG. 7 , the gas-liquid separator 700 includes at least one water level sensor 940 for measuring the level of the internal liquefied gas. can be

The boil-off gas reliquefaction system of this embodiment is installed between the darkening device 600 and the gas-liquid separator 700 and includes a second oil filter 420 that filters oil mixed with the fluid depressurized by the decompression device 600 . may include

5 and 7 , the second oil filter 420 may be installed on the fourth supply line L4 between the pressure reducing device 600 and the gas-liquid separator 700 (position A in FIG. 7 ). ), may be installed on the fifth supply line L5 through which the reliquefied liquefied gas is discharged from the gas-liquid separator 700 (position B in FIG. 7 ), and BOG in a gaseous state is discharged from the gas-liquid separator 700 . It may also be installed on the sixth supply line L6 (position C in FIG. 7). FIG. 5 illustrates a case in which the second oil filter 420 is installed at position A of FIG. 7 .

BOG in the gaseous state separated by the gas-liquid separator 700 may be supplied to the low-temperature flow path of the heat exchanger 100 by being combined with the BOG discharged from the storage tank T, and lubricating oil in the gas-liquid separator 700 may be Since they are collected, the possibility that a small amount of lubricating oil is mixed in the boil-off gas in the gaseous state separated by the gas-liquid separator 700 cannot be excluded.

The inventors of the present invention, when lubricating oil is mixed with the boil-off gas in the gaseous state separated by the gas-liquid separator 700 and sent to the low-temperature flow path of the heat exchanger 100, the lubricating oil is compressed by the compressor 200 and mixed with the boil-off gas It was found that a more difficult situation may occur than in the case of being supplied to the high-temperature flow path of the heat exchanger 100 .

Since the fluid used as a refrigerant in the heat exchanger 100 is supplied to the low-temperature flow path of the heat exchanger 100, cryogenic boil-off gas is supplied throughout the system operation, and high enough to melt the condensed or solidified oil. No fluid with temperature is supplied. Therefore, it is very difficult to remove the condensed or solidified oil accumulated in the low-temperature flow path of the heat exchanger 100 .

In order to minimize the possibility that lubricating oil is mixed with the boil-off gas in the gaseous state separated by the gas-liquid separator 700 and sent to the low-temperature flow path of the heat exchanger 100, the second oil filter 420 is moved to the A position or C position in FIG. can be installed on

When the second oil filter 420 is installed at the position C in FIG. 7 , most of the lubricating oil melted or having a lower viscosity is collected in a liquid state in the gas-liquid separator 700 , and is discharged along the sixth supply line L6 . Since the amount of lubricating oil in the state is small, filtering efficiency is high, and it is advantageous that the second oil filter 420 does not need to be replaced relatively frequently.

When the second oil filter 420 is installed at the position B in FIG. 7 , it is possible to block the lubricating oil flowing into the storage tank T, thereby preventing contamination of the liquefied gas stored in the storage tank T. There is this.

The first oil filter 410 is installed at the rear end of the compressor 200, and since the boil-off gas compressed by the compressor 200 is approximately 40 to 45° C., there is no need to use an oil filter for cryogenic temperatures. However, the temperature of the fluid decompressed by the decompression device 600 is about -160 to -150° C. so that at least a part of the boil-off gas can be re-liquefied, and the liquefied gas and boil-off gas separated by the gas-liquid separator 700 . Since the temperature of is also approximately -160 to -150 ℃, the second oil filter 420 is installed at any position A, B, and C in FIG. 7, it must be designed for cryogenic use.

In addition, since most of the lubricating oil mixed with the boil-off gas of about 40 to 45° C. compressed by the compressor 200 is in a liquid state or a mist state, the oil separator 300 is suitable for separating the lubricating oil in a liquid state. is designed, and the first oil filter 410 is designed to be suitable for separating lubricating oil in a mist state (a part of lubricating oil in a vapor state may be included).

On the other hand, the lubricating oil mixed with the cryogenic fluid, the fluid decompressed by the pressure reducing device 600 , the boil-off gas separated by the gas-liquid separator 700 , and the liquefied gas separated by the gas-liquid separator 700 , is below the pour point. of the solid (or solidified) state, the second oil filter 420 is designed to be suitable for separating the lubricating oil in the solid (or solidified) state.

8 is an enlarged view of a second oil filter according to an embodiment of the present invention, and FIG. 9 is an enlarged view of a second oil filter according to another embodiment of the present invention.

8 and 9, the second oil filter 420 may have the structure shown in FIG. 8 (hereinafter referred to as a 'lower discharge type') or the structure shown in FIG. It is called 'top discharge type'). In FIGS. 8 and 9 , a dotted line indicates a fluid flow direction.

8 and 9 , the second oil filter 420 includes a fixing plate 425 and a filter element 421 , and the second oil filter 420 has an inlet pipe 422 and an outlet pipe 423 . , and an oil discharge pipe 424 are connected.

The filter element 421 is installed on the fixing plate 425 to separate the lubricating oil mixed with the fluid flowing in through the inlet pipe 422 .

16 is a plan view of the filter element 421 shown in FIGS. 8 and 9. Referring to FIG. 16, the filter element 421 may have a hollow (Z space in FIG. 16) cylindrical shape, and a mesh (Mesh). ) may have a form in which multi-level layers of different sizes are stacked on top of each other. The fluid flowing in through the inlet pipe 422 passes through the multi-stage layers included in the filter element 421 and the lubricant is filtered. The filter element 421 may separate the lubricating oil by a physical adsorption method.

The fluid (evaporated gas, liquefied gas, or gas-liquid mixed fluid) filtered by the filter element 421 is discharged along the discharge pipe 423, and the lubricant filtered by the filter element 421 is an oil discharge pipe 424 ) is discharged along with

The material of the components used in the second oil filter 420 is made of a material that can withstand cryogenic temperatures so as to separate the lubricating oil mixed with the cryogenic fluid. The filter element 421 may be made of a metal material that can withstand cryogenic temperatures, and specifically, the filter element 421 may be made of SUS material.

Referring to FIG. 8 , in the 'lower discharge type' oil filter, the fluid supplied through the inlet pipe 422 connected to the upper part of the oil filter passes through the filter element 421, and then the space formed under the fixing plate 425. (X in FIG. 8), it is discharged through the discharge pipe 423 connected to the lower part of the oil filter.

In the 'bottom discharge type' oil filter, the fixing plate 425 is installed under the oil filter, the filter element 421 is installed on the upper surface of the fixing plate 425, and the filter element 421 is based on the fixing plate 425. The discharge pipe 423 is connected to the opposite side.

In addition, the 'bottom discharge type' oil filter is supplied so that the fluid introduced through the supply pipe 422 can be filtered by the upper part of the filter element 421 (that is, the entire filter element can be used to the maximum). It is preferable that the pipe 422 is connected higher than the upper end of the filter element 421 .

The supply pipe 422 and the discharge pipe 423 are preferably installed on opposite sides (left and right with respect to the filter element 421 in FIG. 8) in view of the flow of fluid, and the lubricating oil filtered by the filter element 421 is gathered at the lower part of the filter element 421 , so the oil discharge pipe 424 is preferably connected to the lower side of the filter element 421 .

In the case of the 'lower discharge type' oil filter, the oil discharge pipe 424 may be connected directly above the fixing plate 425 .

As shown in (a) of FIG. 8, when a fluid having a plurality of liquid components (for example, a volume ratio of 90% liquid and 10% gas) is supplied to the 'bottom discharge type' oil filter, the liquid component has a density is large, so an appropriate flow from top to bottom occurs and the filtering effect is excellent.

However, as shown in (b) of FIG. 8, when a fluid having a large number of gas components (for example, a volume ratio of 10% liquid and 90% gas) is supplied to the 'bottom discharge type' oil filter, the density decreases Since small gaseous components stay on the upper part of the oil filter, the flow of the fluid deteriorates and the filtering effect is reduced.

Referring to FIG. 9 , in the 'upper discharge type' oil filter, the fluid supplied through the inlet pipe 422 connected to the lower part of the oil filter passes through the filter element 421, and then the space formed above the fixing plate 425. It is discharged through the discharge pipe 423 connected to the upper part of the oil filter after passing (Y in FIG. 9).

The 'upper discharge type' oil filter has a fixed plate 425 installed above the oil filter, a filter element 421 installed on the lower surface of the fixed plate 425, and a filter element 421 based on the fixed plate 425. The discharge pipe 423 is connected to the opposite side.

In addition, the 'upper discharge type' oil filter is supplied so that the fluid introduced through the supply pipe 422 can be filtered by the lower part of the filter element 421 (that is, the entire filter element can be used as much as possible). It is preferable that the pipe 422 is connected further below the lower end of the filter element 421 .

The supply pipe 422 and the discharge pipe 423 are preferably installed on opposite sides (left and right with respect to the filter element 421 in FIG. 9) in view of the flow of fluid, and the lubricating oil filtered by the filter element 421 is gathered at the lower part of the filter element 421 , so the oil discharge pipe 424 is preferably connected to the lower side of the filter element 421 .

Referring to FIG. 9 , in the 'upper discharge type' oil filter, the fluid supplied along the pipe 422 connected to the lower part of the oil filter passes through the filter element 421, and then the pipe 423 connected to the upper part of the oil filter is connected. discharged according to The lubricating oil filtered by the filter element 421 is discharged to the outside along a separate pipe 424 .

As shown in (a) of FIG. 9, when a fluid having a large number of gas components (for example, a volume ratio of 10% liquid and 90% gas) is supplied to the 'upper discharge type' oil filter, the gas component has a density Since is small, an appropriate flow from bottom to top occurs and the filtering effect is excellent.

However, as shown in (b) of FIG. 9, when a fluid having a large number of liquid components (for example, a volume ratio of 90% liquid and 10% gas) is supplied to the 'top discharge type' oil filter, the density decreases Because large liquid components stay at the bottom of the oil filter, the flow of the fluid deteriorates and the filtering effect is reduced.

Therefore, when the second oil filter 420 is installed at the position B in FIG. 7 , it is preferable to apply the second oil filter 420 of the 'bottom discharge type' shown in FIG. 8, and C in FIG. When the second oil filter 420 is installed at the location, it is preferable to apply the second oil filter 420 of the 'upper discharge type' shown in FIG. 9 .

When the second oil filter 420 is installed at the position A in FIG. 7 , the fluid decompressed by the pressure reducing device 600 is in a gas-liquid mixed state (100% reliquefaction is possible in theory), but the gas component in the volume ratio Since the ratio of is higher, it is preferable to apply the second oil filter 420 of the 'top discharge type' shown in FIG. 9 .

The bypass line (BL) of the present invention branches from the first supply line (L1) of the front end of the heat exchanger (100), bypasses the heat exchanger (100), and then the second end of the heat exchanger (100) It joins the supply line (L2).

In general, the bypass line bypassing the heat exchanger is installed inside the heat exchanger to form an integral body with the heat exchanger. When the bypass line is installed inside the heat exchanger, when the valves installed at the front and/or rear ends of the heat exchanger are closed, fluid is not supplied to the heat exchanger and fluid is not supplied to the bypass line at the same time.

However, in the present invention, the bypass line BL is installed outside the heat exchanger 100 separately from the heat exchanger 100 , and the first valve 510 and/or the heat exchanger 100 installed at the front end of the heat exchanger 100 . ) The bypass line BL branches from the first supply line L1 in front of the first valve 510 so that boil-off gas can be supplied to the bypass line BL even when the second valve 520 installed at the rear end is closed. and merged into the second supply line L2 at the rear end of the second valve 520 .

A bypass valve 590 is installed on the bypass line BL, and the bypass valve 590 is normally closed and is opened when the bypass line BL needs to be used.

Basically, the bypass line BL is used when the heat exchanger 100 cannot be used, such as when the heat exchanger 100 breaks down or maintenance is required. For example, when the BOG reliquefaction system of this embodiment sends some or all of the BOG compressed by the compressor 200 to the high-pressure engine, if the heat exchanger 100 cannot be used, it cannot be used in the high-pressure engine. After giving up re-liquefying the surplus BOG and supplying the BOG discharged from the storage tank T to the compressor 200 by bypassing the heat exchanger 100 along the bypass line BL, the compressor 200 The BOG compressed by the BOG is supplied to the high-pressure engine, and the surplus BOG can be sent to the GCU for incineration.

As an example of using the bypass line BL for maintenance of the heat exchanger 100, when the flow path of the heat exchanger 100 is blocked by the condensed or solidified lubricating oil, the condensed or solidified using the bypass line BL and removing the lubricant.

In addition, when there is no need to re-liquefy BOG because there is almost no surplus BOG, such as in the ship's ballast state, all BOG discharged from the storage tank T is sent to the bypass line BL, and BOG is heat exchanged. It bypasses the machine 100 so that it can be sent directly to the compressor 200 . BOG compressed in the compressor 200 is used as a fuel for a high-pressure engine. When it is determined that there is little surplus BOG and there is no need to reliquefy BOG, the bypass valve 590 may be controlled to automatically open.

The inventors of the present invention have discovered that, when the boil-off gas is supplied to the engine through the heat exchanger having a narrow flow path according to the present invention, the pressure drop of the boil-off gas occurs a lot by the heat exchanger. When there is no need for re-liquefaction, fuel can be smoothly supplied to the engine by bypassing the heat exchanger and compressing the boil-off gas as described above.

In addition, the bypass line BL can be used even when the BOG is not reliquefied and the BOG is reliquefied due to an increase in the amount of BOG.

If the BOG is not reliquefied but the BOG is reliquefied due to an increase in the amount of BOG (that is, when starting or restarting BOG re-liquefaction), the BOG discharged from the storage tank T is transferred to the bypass line BL. All of the BOG bypasses the heat exchanger 100 and is directly supplied to the compressor 200, and the BOG compressed by the compressor 200 can be sent to the high-temperature flow path of the heat exchanger 100. . A portion of the boil-off gas compressed by the compressor 200 may be sent to the high-pressure engine.

Through the above-described process, if the temperature of the high-temperature flow path of the heat exchanger 100 is increased at the time of starting or restarting the BOG reliquefaction, the heat exchanger 100, other equipment, piping, etc. may remain in the previous BOG reliquefaction process, It has the advantage of being able to start reliquefying BOG after removing condensed or solidified lubricating oil or other residues or impurities.

The residue may include lubricating oil mixed with the boil-off gas compressed by the compressor and then sent to the heat exchanger at the time of re-liquefaction of the boil-off gas, and the boil-off gas compressed by the compressor.

If the BOG re-liquefaction is started or restarted, the low-temperature BOG discharged from the storage tank T is directly transferred to the heat exchanger 100 without using the bypass line BL to increase the temperature of the high-temperature flow path of the heat exchanger 100. When supplied to the heat exchanger 100 , since the low-temperature BOG discharged from the storage tank T is supplied to the low-temperature flow path of the heat exchanger 100 in a state in which the high-temperature BOG is not yet supplied to the high-temperature flow path of the heat exchanger 100 , the heat exchanger Lubricating oil that has not yet been condensed or solidified remaining in 100 may also be condensed or solidified by lowering the temperature of the heat exchanger 100 .

While continuing the process of increasing the temperature of the heat exchanger 100 high-temperature flow path using the bypass line BL, after a certain amount of time (that is, when it is determined that the condensed or solidified lubricant or other impurities are almost removed. The duration can be determined by experience, and it may take about 1 minute to 30 minutes, preferably about 3 minutes to 10 minutes, more preferably about 2 minutes to 5 minutes.), The first valve 510 and the second valve 520 are slowly opened and the bypass valve 590 is slowly closed to start reliquefying the boil-off gas. As time passes, the first valve 510 and the second valve 520 are fully opened and the bypass valve 590 is completely closed, and all of the BOG discharged from the storage tank T is BOG in the heat exchanger 100 . It is used as a refrigerant to reliquefy

In addition, the bypass line BL may be utilized to satisfy the suction pressure condition of the compressor 200 when the pressure inside the storage tank T is low.

In addition, when it is necessary to control the internal pressure of the storage tank T to a low range, the bypass line BL can be used to satisfy the suction pressure condition of the compressor 200 even if the pressure of the storage tank T is lowered. can

By using the bypass line (BL) to remove the condensed or solidified lubricant and when the pressure inside the storage tank (T) is low, the bypass line (BL) is used to satisfy the suction pressure condition of the compressor (200) A more detailed look at the case is as follows.

1. When the bypass line (BL) is used to remove condensed or solidified lubricant

A predetermined lubricating oil is mixed with the boil-off gas that has passed through the oil supply lubrication type cylinder of the compressor 200, and the lubricating oil mixed with the boil-off gas is condensed or solidified before the boil-off gas in the heat exchanger 100, and the flow path of the heat exchanger 100 Since the amount of condensed or solidified lubricating oil accumulated in the flow path of the heat exchanger 100 increases as time passes, it is necessary to remove the condensed or solidified lubricating oil inside the heat exchanger 100 after a certain period of time. The inventors of the present invention have found that

In particular, the heat exchanger 100 of this embodiment is preferably a PCHE (Printed Circuit Heat Exchanger, also referred to as DCHE) in consideration of the pressure and/or flow rate of the boil-off gas to be reliquefied, the reliquefaction efficiency, and the like. As the flow path is narrow (microchannel type flow path) and curved, the flow path can be easily clogged by the condensed or solidified lubricating oil. PCHE (DCHE) is produced by companies such as Kobelko and Alfalval.

Condensed or solidified lubricant can be removed through the following steps.

1) determining whether to remove the condensed or solidified lubricant

2) opening the bypass valve 590 and closing the first valve 510 and the second valve 520

3) step in which the boil-off gas discharged from the storage tank (T) passes through the bypass line (BL) and is compressed by the compressor (200)

4) sending a part or all of the boil-off gas of high temperature compressed by the compressor 200 to the heat exchanger 100

5) sending the boil-off gas that has passed through the heat exchanger 100 to the gas-liquid separator 700

6) discharging the lubricating oil collected in the gas-liquid separator 700

7) Checking that the heat exchanger 100 is normalized

1) determining whether to remove the condensed or solidified lubricant

When the flow path of the heat exchanger 100 is blocked by the condensed or solidified lubricating oil, the cooling efficiency of the heat exchanger 100 decreases. Therefore, when the performance of the heat exchanger 100 falls below a certain value compared to the normal case, it can be estimated that the lubricating oil condensed or solidified inside the heat exchanger 100 has accumulated to a certain extent or more, for example, of the heat exchanger 100 . When the performance drops to about 50 to 90% or less, preferably about 60 to 80% or less, more preferably about 70% or less of the normal case, it is determined that the lubricating oil condensed or solidified inside the heat exchanger 100 should be removed can do.

"About 50 to 90% or less" in the normal case is meant to include all of about 50% or less, about 60% or less, about 70% or less, about 80% or less, and about 90% or less, and "about 60 to 80% or less' is meant to include all of about 60% or less, about 70% or less, and about 80% or less.

When the performance of the heat exchanger 100 decreases, the temperature difference between the low-temperature BOG L1 supplied to the heat exchanger 100 and the low-temperature BOG discharged from the heat exchanger 100 increases, and the heat exchanger 100 . The temperature difference between the high-temperature boil-off gas (L2) discharged from the and the high-temperature boil-off gas (L3) supplied to the heat exchanger 100 also increases. In addition, when the flow path of the heat exchanger 100 is blocked by the condensed or solidified lubricating oil, the flow path of the heat exchanger 100 is narrowed, and thus the pressure difference between the front end L3 and the rear end L4 of the heat exchanger 100 increases. will do

Accordingly, the temperature difference 810 and 840 of the low-temperature fluid supplied to or discharged from the heat exchanger 100 and the temperature difference 820 between the high-temperature fluid supplied to the heat exchanger 100 or discharged from the heat exchanger 100 . , 830), it is possible to determine whether to remove the condensed or solidified lubricating oil by the pressure difference 910 and 920 applied to the high-temperature flow path of the heat exchanger 100 or the like.

Specifically, the temperature of the boil-off gas discharged from the storage tank T and sent to the heat exchanger 100 measured by the first temperature sensor 810 and the compressor 200 measured by the fourth temperature sensor 840 are The temperature difference (meaning an absolute value) of the boil-off gas cooled by the heat exchanger 100 after being compressed by the If the abnormality continues, it may be determined that heat exchange is not performed properly in the heat exchanger 100 .

For example, if the 'temperature difference of the low temperature flow' is 20 to 50 ° C or higher, preferably 30 to 40 ° C or higher, more preferably approximately 35 ° C or higher, for 1 hour or longer, condensed or solidified lubricating oil It can be judged that it is the time to discharge.

When the heat exchanger 100 operates normally, the boil-off gas compressed to about 300 bar by the compressor 200 becomes about 40 to 45° C., and about -160 to -140° C. discharged from the storage tank T. The boil-off gas may be slightly increased in temperature while being transferred to the heat exchanger 100 to be about -150 to -110°C, preferably about -120°C.

The BOG reliquefaction system of this embodiment includes a gas-liquid separator 700, and the BOG separated by the gas-liquid separator 700 is merged with BOG discharged from the storage tank T, and the heat exchanger 100 ), the temperature of the BOG supplied to the heat exchanger 100 is lower than when only BOG discharged from the storage tank T is sent to the heat exchanger 100, and by the gas-liquid separator 700 As the amount of the BOG in the separated gas state increases, the temperature of the BOG supplied to the heat exchanger 100 may be further lowered.

The boil-off gas of about 40 to 45° C. supplied to the heat exchanger 100 along the third supply line L3 is cooled by the heat exchanger 100 to become about -130 to -110° C., and in a normal case, ' The temperature difference' of the cold stream is preferably approximately 2-3°C.

In addition, the temperature of the boil-off gas used as a refrigerant in the heat exchanger 100 after being discharged from the storage tank T measured by the second temperature sensor 820 and the compressor 200 measured by the third temperature sensor 830 ), the temperature difference (meaning an absolute value) of the boil-off gas sent to the heat exchanger 100 after being compressed by the If the abnormality continues, it may be determined that heat exchange is not performed properly in the heat exchanger 100 .

If the 'temperature difference of the hot flow' is 20 to 50 ° C or higher, preferably 30 to 40 ° C or higher, more preferably approximately 35 ° C or higher, for 1 hour or longer, it is necessary to discharge the condensed or solidified lubricating oil. time can be judged.

When the heat exchanger 100 operates normally, after being discharged from the storage tank T, the temperature is slightly increased while being transferred to the heat exchanger 100 of approximately -150 to -110°C (preferably approximately -120°C) BOG, after being used as a refrigerant in the heat exchanger 100, may be approximately -80 to 40°C depending on the speed of the ship, and BOG of approximately -80 to 40°C used as a refrigerant in the heat exchanger 100 is compressed in the compressor 200 to approximately 40 to 45 °C.

In addition, the pressure of the boil-off gas sent to the heat exchanger 100 after being compressed by the compressor 200 measured by the first pressure sensor 910 and the heat exchanger 100 measured by the second pressure sensor 920 ), when the pressure difference (hereinafter, referred to as 'pressure difference in the high-temperature flow path') of the boil-off gas cooled by can be judged that

The boil-off gas discharged from the storage tank (T) does not contain an oil component or exists at a very insignificant level, and the point at which the boil-off gas is mixed with lubricating oil is when the boil-off gas is compressed by the compressor ( 200 ). ) After using the BOG discharged from the refrigerant as a refrigerant, condensed or solidified lubricating oil hardly accumulates in the low-temperature flow path of the heat exchanger 100 that is sent to the compressor 200, and after cooling the BOG compressed by the compressor 200 Condensed or solidified lubricating oil is accumulated in the high-temperature flow path of the heat exchanger 100 sent to the pressure reducing device 600 .

Therefore, since the flow path is blocked by the condensed or solidified lubricant oil and the pressure difference between the front and rear ends of the heat exchanger 100 increases rapidly in the high temperature flow path, the pressure applied to the high temperature flow path of the heat exchanger 100 is measured to condense or solidify. Determine whether the old lubricant needs to be removed.

Determining whether to remove the condensed or solidified lubricating oil by the pressure difference between the front and rear ends of the heat exchanger 100 is particularly applicable to the heat exchanger 100 of this embodiment, in which the PCHE in which the flow path is narrow and curved can be applied. Considering that, it can be usefully used.

For example, when the 'pressure difference in the high temperature flow path' is more than doubled compared to the normal case and the state continues for more than 1 hour, it may be determined that it is time to discharge the condensed or solidified lubricating oil.

When the heat exchanger 100 operates normally, the boil-off gas compressed by the compressor 200 passes through the heat exchanger 100 and the pressure does not drop significantly even if it is cooled, and is approximately 0.5 to 2.5 bar, preferably approximately 0.7 to A pressure drop of the order of 1.5 bar, more preferably approximately 1 bar, occurs. Condensation occurs when the 'pressure difference in the high-temperature flow path' remains at a certain pressure or more, for example, 1 to 5 bar or more, preferably 1.5 to 3 bar or more, and more preferably about 2 bar (200 kPa) or more for 1 hour or more. Alternatively, it can be determined that it is time to discharge the solidified lubricant.

As described above, it may be determined whether the condensed or solidified lubricant should be removed using any one of the 'temperature difference of the low temperature flow', the 'temperature difference of the high temperature flow', and the 'pressure difference of the high temperature flow path' as an index. However, to increase reliability, use at least two of 'temperature difference of low temperature flow', 'temperature difference of high temperature flow', and 'pressure difference of hot flow path' as indicators to determine whether condensed or solidified lubricant should be removed It is preferable to do

For example, the smaller of the 'temperature difference of the low temperature flow' and the 'temperature difference of the high temperature flow' lasts for more than 1 hour at 35℃ or more, or the 'pressure difference in the high temperature flow path' is more than twice the normal value or 200 If it continues for more than 1 hour in a state of kPa or more, it can be determined that it is time to remove the condensed or solidified lubricant.

The first temperature sensor 810, the second temperature sensor 820, the third temperature sensor 830, the fourth temperature sensor 840, the first pressure sensor 910, and the second pressure sensor 920 are, It can be seen as a kind of detection means for detecting whether the heat exchanger 100 is clogged by lubricating oil.

In addition, the BOG reliquefaction system of the present invention includes a first temperature sensor 810 , a second temperature sensor 820 , a third temperature sensor 830 , a fourth temperature sensor 840 , and a first pressure sensor 910 . ), and a control device (not shown) for determining whether the heat exchanger 100 is clogged with lubricant based on a value detected by one or more of the second pressure sensor 920 . The control device may be viewed as a kind of determination means for determining whether the heat exchanger 100 is clogged by lubricating oil.

2) opening the bypass valve 590 and closing the first valve 510 and the second valve 520

By determining whether to remove the condensed or solidified lubricating oil in the first step, if it is decided to remove the condensed or solidified lubricating oil inside the heat exchanger 100, the bypass valve 590 installed on the bypass line BL opens, and the first valve 510 installed on the first supply line L1 and the second valve 520 installed on the second supply line L2 are closed.

When the bypass valve 590 is opened and the first valve 510 and the second valve 520 are closed, the boil-off gas discharged from the storage tank T passes the bypass line BL and is sent to the compressor 200 and is no longer heat exchanged. It is not sent to the device 100. Accordingly, the refrigerant is not supplied to the heat exchanger 100 .

3) step in which the boil-off gas discharged from the storage tank (T) passes through the bypass line (BL) and is compressed by the compressor (200)

BOG discharged from the storage tank T bypasses the heat exchanger 100 through the bypass line BL and then is sent to the compressor 200 . The BOG sent to the compressor 200 is compressed by the compressor 200 and not only the pressure but also the temperature is increased, and the temperature of the BOG compressed to about 300 bar by the compressor 200 is about 40 to 45°C.

4) sending a part or all of the boil-off gas of high temperature compressed by the compressor 200 to the heat exchanger 100

If the boil-off gas, which has been compressed by the compressor 200, is continuously sent to the heat exchanger 100, the low-temperature boil-off gas discharged from the storage tank T used as a refrigerant in the heat exchanger 100 is transferred to the heat exchanger 100. ), and only the high-temperature BOG is continuously supplied to the heat exchanger 100, the temperature of the high-temperature flow path of the heat exchanger 100 through which the BOG compressed by the compressor 200 passes is gradually increased.

When the temperature of the high-temperature flow path of the heat exchanger 100 is above the temperature at which the lubricating oil is condensed or solidified, the condensed or solidified lubricating oil accumulated inside the heat exchanger 100 is gradually melted or the viscosity is lowered, and the melt or the viscosity is lowered. The lubricating oil is mixed with the boil-off gas and exits the heat exchanger 100 .

When using the bypass line (BL) to remove the condensed or solidified lubricating oil, the boil-off gas flows through the bypass line (BL), the compressor (200), and the high temperature flow path of the heat exchanger (100) until the heat exchanger (100) is normalized. , the pressure reducing device 600 and the gas-liquid separator 700 are circulated.

In addition, when removing the condensed or solidified lubricating oil by using the bypass line BL, it is discharged from the storage tank T and the bypass line BL, the compressor 200, the high temperature flow path of the heat exchanger 100, and reduced pressure The boil-off gas that has passed through the device 600 may be sent to a tank or other recovery device installed separately from the storage tank T in a state in which melted or lowered lubricating oil and boil-off gas are mixed. The boil-off gas inside the tank or other recovery device installed separately from the storage tank T is sent back to the bypass line BL, so that the condensed or solidified lubricant removal process can be continued.

When the fluid in which melted or reduced viscosity lubricating oil and boil-off gas are mixed is sent to a tank installed separately from the storage tank T or another recovery device, even if the gas-liquid separator 700 is installed at the rear end of the pressure reducing device 600, the gas-liquid separator Since 700 serves the same role as the existing BOG reliquefaction system, and lubricating oil with melted or lowered viscosity is not collected inside the gas-liquid separator 700 (the lubricating oil with melted or lowered viscosity is stored in the storage tank (T) and Since it is collected in a separately installed tank or other recovery device), it is not necessary to include the improved gas-liquid separator 700 to discharge the lubricating oil, thereby reducing costs.

5) sending the boil-off gas that has passed through the heat exchanger 100 to the gas-liquid separator 700

As the temperature of the high-temperature flow path of the heat exchanger 100 rises, the condensed or solidified lubricating oil accumulated in the heat exchanger 100 melts or increases in viscosity, and is mixed with the boil-off gas and sent to the gas-liquid separator 700 . In the process of removing the condensed or solidified lubricating oil inside the heat exchanger 100 by using the bypass line BL, re-liquefaction of the boil-off gas is not made, so the re-liquefied liquefied gas does not collect in the gas-liquid separator 700, and the gas The boil-off gas in the state and the lubricating oil with melted or lowered viscosity are collected.

BOG in a gaseous state collected in the gas-liquid separator 700 is discharged from the gas-liquid separator 700 along the sixth supply line L6 and is sent back to the compressor 200 along the bypass line BL. Since the first valve 510 was closed in the second step, the BOG in the gaseous state separated by the gas-liquid separator 700 is merged with the BOG discharged from the storage tank T, and the compressor follows the bypass line BL. 200 is supplied, and is not supplied to the low-temperature flow path of the heat exchanger 100 .

Therefore, supplying the boil-off gas in the gaseous state separated by the gas-liquid separator 700 to the bypass line BL with the first valve 510 closed causes the lubricating oil partially included in the boil-off gas to be removed from the heat exchanger ((100) ) is prevented from being supplied to the low-temperature flow path, thereby preventing clogging of the low-temperature flow path of the heat exchanger 100 .

The gas-liquid boil-off gas collected in the gas-liquid separator 700 is discharged from the gas-liquid separator 700 along the sixth supply line L6 and is sent back to the compressor 200 along the bypass line BL. It continues until it is determined that the temperature of the high-temperature flow path of the unit 100 is as high as the temperature of the boil-off gas sent to the high-temperature flow path of the heat exchanger 100 after being compressed by the compressor 200 . However, as a rule of thumb, the cycle may continue until it is determined that sufficient time has elapsed.

While the condensed or solidified lubricating oil inside the heat exchanger 100 is removed using the bypass line BL, the eighth valve 581 is closed so that the lubricating oil collected in the gas-liquid separator 700 flows through the fifth supply line L5. It should not be sent to the storage tank (T). When lubricating oil is introduced into the storage tank (T), the purity of the liquefied gas stored in the storage tank (T) may be lowered, and thus the value of the liquefied gas may fall.

6) discharging the lubricating oil collected in the gas-liquid separator 700

The melted or reduced viscosity lubricating oil discharged from the heat exchanger 100 is collected inside the gas-liquid separator 700. In order to treat the lubricating oil collected inside the gas-liquid separator 700, in this embodiment, the conventionally used gas-liquid oil A gas-liquid separator 700 in which the separator 700 is improved may be used.

13 is an enlarged view of a heat exchanger and a gas-liquid separator according to an embodiment of the present invention. For the convenience of description, illustration of some devices is omitted.

13, in the gas-liquid separator 700, in addition to the fifth supply line L5 for sending the liquefied gas separated by the gas-liquid separator 700 to the storage tank T, the lubricating oil collected in the gas-liquid separator 700 is supplied A lubricant discharge line (OL) for discharging is additionally installed. The lubricating oil discharge line OL is connected to the lower end of the gas-liquid separator 700 so that the oil collected in the lower part of the gas-liquid separator 700 can be effectively discharged, and the end of the fifth supply line L5 is connected to the lubricating oil discharge line OL. It is positioned higher in the gas-liquid separator 700 than the lower end of the gas-liquid separator 700 . It is preferable to position the end of the fifth supply line L5 higher than the level of the lubricating oil when the amount of lubricating oil collected in the gas-liquid separator 700 is maximized so that the fifth supply line L5 is not blocked by the lubricating oil. .

A third valve 530 for controlling the flow rate and opening/closing of the fluid may be installed on the lubricant discharge line OL, and a plurality of third valves 530 may be installed.

Since the lubricating oil collected in the gas-liquid separator 700 cannot be naturally discharged or it may take a lot of time to discharge, the lubricating oil inside the gas-liquid separator 700 may be discharged through nitrogen purging. When nitrogen of about 5 to 7 bar is supplied to the gas-liquid separator 700 , the pressure in the gas-liquid separator 700 increases, so that the oil can be quickly discharged.

In order to discharge the lubricating oil in the gas-liquid separator 700 by nitrogen purging, a nitrogen supply line NL may be installed to join the third supply line L3 at the front end of the heat exchanger 100 . If necessary, a plurality of nitrogen supply lines may be installed at different locations.

A nitrogen valve 583 for controlling the flow rate and opening/closing of the fluid is installed on the nitrogen supply line (NL), and the nitrogen valve 583 is maintained in a closed state in normal times when the nitrogen supply line (NL) is not used, and nitrogen purging When it is necessary to use the nitrogen line (NL), such as when supplying nitrogen to the gas-liquid separator 700 for this purpose, the nitrogen valve 583 is opened. A plurality of nitrogen valves 583 may be installed.

Nitrogen purging may be performed by directly injecting nitrogen into the gas-liquid separator 700, but if a nitrogen supply line for use in another purpose is already installed, the lubricating oil in the gas-liquid separator 700 by utilizing the installed nitrogen supply line It is preferable to discharge

All of the BOG discharged from the storage tank T is sent to the bypass line BL to be compressed by the compressor 200, and the BOG compressed by the compressor 200 is sent to the high-temperature flow path of the heat exchanger 100, After passing through the high-temperature flow path of the heat exchanger 100, the boil-off gas decompressed in the pressure reducing device 600 is sent to the gas-liquid separator 700, and the boil-off gas discharged from the gas-liquid separator 700 is sent back to the bypass line BL. Continuing the process, when it is determined that most of the lubricating oil condensed or solidified inside the heat exchanger 100 is collected in the gas-liquid separator 700 (that is, it is determined that the heat exchanger 100 is normalized), the compressor 200 Blocks the inflow of the boil-off gas compressed by the heat exchanger 100 into the heat exchanger 100, and opens the nitrogen valve 583 to perform nitrogen purging.

7) Checking that the heat exchanger 100 is normalized

When it is determined that the heat exchanger 100 is normalized again because the condensed or solidified lubricant oil inside the heat exchanger 100 is discharged, and the process of discharging the lubricant inside the gas-liquid separator 700 is also completed, the first valve 510 and The second valve 520 is opened, the bypass valve 590 is closed, and then the BOG reliquefaction system is normally operated again. When the BOG reliquefaction system operates normally, BOG discharged from the storage tank T is used as a refrigerant in the heat exchanger 100 , and BOG used as a refrigerant in the heat exchanger 100 is generated by the compressor 200 . A part or all of it is reliquefied through a compression process, a cooling process by the heat exchanger 100 , and a pressure reduction process by the decompression device 600 .

The determination that the heat exchanger 100 is normalized again is similar to when finding out whether to remove the condensed or solidified lubricant, 'temperature difference of low temperature flow', 'temperature difference of high temperature flow', and 'pressure difference of high temperature flow path' One or more values of ' can be used as indicators.

Through the above-described process, not only the condensed or solidified lubricating oil inside the heat exchanger 100, but also the condensed or coagulated lubricating oil accumulated in pipes, valves, instruments, and various equipment may be removed.

Conventionally, during the above-described step of removing the condensed or solidified lubricating oil inside the heat exchanger 100 from the heat exchanger 100 using the bypass line BL, a high-pressure engine and/or a low-pressure engine (hereinafter, ' engine') can be driven. When servicing a part of the equipment included in the fuel supply system or the reliquefaction system, it is common not to drive the engine because fuel cannot be supplied to the engine or the surplus BOG cannot be reliquefied.

However, as in the present invention, if the engine is driven while the condensed or solidified lubricating oil inside the heat exchanger 100 is removed, since the heat exchanger 100 can be maintained while the engine operation is continued, the heat exchanger 100 ), it has the advantage of being able to propel the ship and generate electricity, and remove the condensed or solidified lubricating oil by utilizing the surplus boil-off gas remaining after being used in the engine.

In addition, if the engine is driven while the condensed or solidified lubricating oil inside the heat exchanger 100 is removed, the lubricating oil compressed by the compressor 200 and mixed with the boil-off gas can be burned by the engine. That is, the engine is not only used for its original purpose for propulsion or power generation of a ship, but also serves to remove oil mixed with boil-off gas.

On the other hand, the process of finding out whether the condensed or solidified lubricating oil should be removed by the alarm may include ① an alarm activation step and/or ② an alarm generating step.

10 is a schematic diagram of a BOG reliquefaction system according to a sixth preferred embodiment of the present invention, FIG. 11 is an enlarged view of a pressure reducing device according to an embodiment of the present invention, and FIG. 12 is another embodiment of the present invention It is an enlarged view of the decompression device according to

As shown in FIG. 10 , two compressors 200 and 210 of the present invention may be installed in parallel. The two compressors 200 and 210 may have the same specification, and when one of the compressors fails, the other may serve as redundancy. For the convenience of description, illustration of other devices is omitted.

Referring to FIG. 10, when two compressors 200 and 210 are installed in parallel, the boil-off gas discharged from the storage tank T is sent to the second compressor 210 through the seventh supply line L22, BOG compressed by the second compressor 210 is partially sent to the high-pressure engine along the fuel supply line SL, and the surplus BOG is sent to the heat exchanger 100 through the eighth supply line L33. A reliquefaction process may be performed. A tenth valve 571 for controlling the flow rate and opening/closing of the fluid may be installed on the eighth supply line L33.

In addition, as shown in FIG. 11, two pressure reducing devices 600, 610 may be installed in parallel, and as shown in FIG. 12, two pairs of pressure reducing devices 600 and 610 installed in series are They can also be installed in parallel.

Referring to FIG. 11 , two pressure reducing devices 600 and 610 installed in parallel may serve as the other one of the pressure reducing devices 600 and 610 in case of failure, and the two pressure reducing devices 600 and 610 installed in parallel may serve as redundancy. ) An isolation valve 620 may be installed at each of the front and rear ends.

Referring to FIG. 12 , two pressure reducing devices 600 are connected in series, and two pairs of pressure reducing devices 600 and 610 connected in series are installed in parallel. In some cases, two pressure reducing devices 600 are connected in series for decompression stability depending on the manufacturer. When any one of the two pairs of pressure reducing devices installed in parallel (600, 610) fails, the other pair may serve as redundancy.

An isolation valve 620 may be installed at the front and rear ends of each of the two pairs of pressure reducing devices 600 and 610 installed in parallel. The isolation valve 620 shown in FIGS. 11 and 12 isolates the pressure reducing devices 600 and 610 when maintenance of the pressure reducing devices 600 and 610 is required, such as when the pressure reducing devices 600 and 610 are out of order. It is used for isolation.

① Alarm activation stage

When the boil-off gas reliquefaction system of the present invention includes one compressor 200 and one pressure reducing device 600 as shown in FIG. 5, the opening rate of the pressure reducing device 600 is equal to or greater than the set value, When the seventh valve 570 is open, the second valve 520 is open, and the level of the liquefied gas inside the gas-liquid separator 700 is normal, the alarm is activated.

When the BOG reliquefaction system of the present invention includes one compressor 200 as shown in FIG. 5 and includes two pressure reducing devices 600 and 610 connected in parallel as shown in FIG. , the opening rate of the first pressure reducing device 600 or the second pressure reducing device 610 is equal to or greater than the set value, the seventh valve 570 is open, the second valve 520 is open, and the gas-liquid separator ( 700) When the level of the internal liquefied gas is normal (referred to as the 'first alarm activation condition'), the alarm is activated.

The boil-off gas reliquefaction system of the present invention includes a single compressor 200 as shown in FIG. 5, and includes two pairs of pressure reducing devices 600 and 610 installed in parallel as shown in FIG. In this case, the opening rate of any one of the two first pressure reducing devices 600 installed in series or any one of the two second pressure reducing devices 610 installed in series is equal to or greater than the set value, and the seventh valve 570 is opened. state, the second valve 520 is open, and the level of the liquefied gas inside the gas-liquid separator 700 is normal (referred to as a 'second alarm activation condition'), the alarm is activated.

When the BOG reliquefaction system of the present invention includes two compressors 200 and 210 installed in parallel as shown in FIG. 10 and includes a single pressure reducing device 600 as shown in FIG. , the opening rate of the pressure reducing device 600 is equal to or greater than the set value, the seventh valve 570 or the tenth valve 571 is in an open state, the second valve 520 is in an open state, and the gas-liquid separator 700 is in an open state. When the level of the liquefied gas is normal (referred to as the 'third alarm activation condition'), the alarm is activated.

The BOG reliquefaction system of the present invention includes two compressors 200 and 210 installed in parallel as shown in FIG. 10, and two pressure reducing devices 600 and 610 connected in parallel as shown in FIG. ), the opening rate of the first pressure reducing device 600 or the second pressure reducing device 610 is equal to or greater than the set value, the seventh valve 570 or the tenth valve 571 is open, and the second When the valve 520 is open and the level of the liquefied gas inside the gas-liquid separator 700 is normal (referred to as a 'fourth alarm activation condition'), an alarm is activated.

The BOG reliquefaction system of the present invention includes two compressors 200 and 210 installed in parallel as shown in FIG. 10, and two pairs of pressure reducing devices 600 installed in parallel as shown in FIG. 610), any one of the two first pressure reducing devices 600 installed in series or the opening rate of any one of the two second pressure reducing devices 610 installed in series is equal to or greater than the set value, and the seventh valve 570 or the tenth valve 571 is open, the second valve 520 is open, and the level of liquefied gas inside the gas-liquid separator 700 is normal (referred to as a 'fifth alarm activation condition'). ), the alarm is activated.

In the 'first to fifth alarm activation conditions' described above, the set value of the opening rate of the first pressure reducing device 600 or the second pressure reducing device 610 may be 2%, and the liquefied gas inside the gas-liquid separator 700 is When the water level of is normal, it means that the re-liquefied liquefied gas inside the gas-liquid separator 700 is checked and it can be determined that the re-liquefied process is being performed normally.

② Alarm generation stage

The condition in which the 'temperature difference of the low temperature flow' is greater than or equal to the set value and continues for a certain period of time or longer, the condition that the 'temperature difference of the high temperature flow' is greater than the set value for more than a certain period of time, and the 'pressure difference in the high temperature flow path' are set When any one of the conditions that lasts for more than a certain period of time is satisfied with more than a value, an alarm may be sounded to notify the time when the condensed or solidified lubricating oil should be removed.

In addition, in order to increase reliability, the condition in which the 'temperature difference of the low temperature flow' is greater than or equal to the set value for a certain period of time When two or more of the conditions in which the 'pressure difference' is greater than the set value and lasting for a certain period of time are satisfied, an alarm may sound to notify the time when condensed or solidified lubricating oil should be removed.

In addition, the smaller of 'temperature difference of low temperature flow' and 'temperature difference of high temperature flow' is greater than or equal to the set value and continues for a certain period of time (or condition), or 'pressure difference in high temperature flow' is greater than or equal to the set value If it continues for more than a certain period of time, an alarm can sound to notify you when it is necessary to remove the condensed or solidified lubricant.

In the present invention, abnormal performance of the heat exchanger, generation of an alarm, etc. may be determined by appropriate control means. As the control means for determining the performance abnormality of the heat exchanger, the occurrence of an alarm, etc., the control means used in the boil-off gas reliquefaction system of the present invention, preferably a vessel to which the boil-off gas reliquefaction system of the present invention is applied, or Control means used in offshore structures may be used, and separately installed control means may be used to determine abnormal performance of heat exchangers, occurrence of alarms, and the like.

In addition, utilization of the bypass line, discharge of lubricating oil, fuel supply of the engine, starting or restarting of the boil-off gas reliquefaction system, opening and closing of various valves for these, etc. may be automatically or manually controlled by the control means.

2. When using the bypass line (BL) to satisfy the suction pressure condition of the compressor (200) when the pressure inside the storage tank (T) is low

When the amount of BOG generated is small because the amount of liquefied gas inside the storage tank (T) is small, or when the amount of BOG supplied to the engine for propulsion of the vessel is large due to the speed of the ship, the storage tank (T) ), when the internal pressure of the compressor 200 is low, the suction pressure condition in the front end of the compressor 200 required by the compressor 200 may not be satisfied.

In particular, when PCHE (DCHE) is applied to the heat exchanger 100 , the PCHE has a narrow flow path, and when the boil-off gas discharged from the storage tank T passes through the PCHE, the width of the pressure drop is large.

Conventionally, when the compressor 200 does not satisfy the required suction pressure condition, the recirculation valves 541 , 542 , 543 , 544 are opened and some or all of the BOG is opened by the recirculation lines RC1 , RC2 , RC3 , and RC4 . was recirculated to protect the compressor 200 .

However, if the suction pressure condition of the compressor 200 is satisfied by recirculating the boil-off gas, the amount of the boil-off gas compressed by the compressor 200 is eventually reduced, so that the reliquefaction performance is reduced, and the engine It may not be possible to meet this required fuel consumption. In particular, if the fuel consumption required by the engine is not satisfied, the operation of the vessel is greatly disturbed. Therefore, even when the internal pressure of the storage tank T is low, the engine is There is an urgent need for a method to satisfy the fuel consumption.

According to the present invention, without the installation of additional equipment, by utilizing the bypass line BL that has been previously installed for maintenance and repair of the heat exchanger 100, even when the internal pressure of the storage tank T is low, the compressor It is possible to satisfy the suction pressure condition required by the compressor 200 without reducing the amount of boil-off gas compressed by ( 100 ).

According to the present invention, when the internal pressure of the storage tank (T) is below a certain value, the bypass valve 590 is opened to heat exchange some or all of the BOG discharged from the storage tank (T) through the bypass line (BL). The device 100 is bypassed and sent directly to the compressor 200 .

According to how insufficient the pressure of the storage tank T is compared to the suction pressure condition required by the compressor 200, the amount of boil-off gas sent to the bypass line BL can be adjusted. That is, by opening the bypass valve 590 and closing the first valve 510 and the second valve 520, all of the boil-off gas discharged from the storage tank T may be sent to the bypass line BL, and the bypass valve ( 590), the first valve 510, and the second valve 520 are all partially opened to send only a part of the boil-off gas discharged from the storage tank T to the bypass line BL and the rest to the heat exchanger 100. may be As the amount of BOG bypassing the heat exchanger 100 through the bypass line BL increases, the pressure drop of BOG decreases.

If the BOG discharged from the storage tank T bypasses the heat exchanger 100 and is sent directly to the compressor 200, the pressure drop can be minimized, but the cooling heat of BOG can be used for re-liquefaction of BOG. Therefore, in consideration of the internal pressure of the storage tank (T), the fuel consumption required by the engine, the amount of boil-off gas to be reliquefied, whether to use the bypass line (BL) to reduce the pressure drop, and the storage tank ( It is decided how much of the boil-off gas discharged from T) is sent to the bypass line (BL).

For example, when the internal pressure of the storage tank T is less than or equal to a predetermined value, and the vessel is operated at a predetermined speed or more, it may be determined to be advantageous to reduce the pressure drop by using the bypass line BL. Specifically, it can be determined that it is advantageous to reduce the pressure drop by using the bypass line BL when the internal pressure of the storage tank T is 1.09 bar or less and the speed of the vessel is 17 knots or more.

In addition, even if all of the boil-off gas discharged from the storage tank T is sent to the compressor 200 through the bypass line BL, it may not be possible to satisfy the suction pressure condition required by the compressor 200. In this case, recirculation Use lines RC1, RC2, RC3, RC4 to satisfy the suction pressure condition.

That is, when the pressure of the storage tank T is lowered and the suction pressure condition required by the compressor 200 cannot be satisfied, in the related art, the compressor 200 is directly operated using the recirculation lines RC1, RC2, RC3, and RC4. On the other hand, according to the present invention, the suction pressure condition of the compressor 200 is satisfied by first utilizing the bypass line BL, and all the boil-off gas discharged from the storage tank T is discharged through the bypass line BL. Even if sent to the compressor 200, when the suction pressure condition required by the compressor 200 cannot be satisfied, the recirculation lines RC1, RC2, RC3, and RC4 are used secondarily.

In order to match the suction pressure condition of the compressor 200 through the secondary recirculation lines RC1, RC2, RC3, RC4 after using the bypass line BL in the first direction, the recirculation valves 541, 542, 543, 544 are A pressure value that is a condition for opening the bypass valve 590 is set higher than a pressure value that is an open condition.

For the conditions in which the recirculation valves 541, 542, 543, 544 are opened and the bypass valve 590 is opened, it is preferable to use the shear pressure of the compressor 200 as a factor, but the internal pressure of the storage tank T as a factor can also be used

The shear pressure of the compressor 200 may be measured by a third pressure sensor (not shown) installed at the front end of the compressor 200, and the internal pressure of the storage tank T may be measured by a fourth pressure sensor (not shown). can

On the other hand, the sixth supply line (L6) for discharging the gaseous boil-off gas separated by the gas-liquid separator 700, the first supply at the rear end of the point where the bypass line (BL) branches from the first supply line (L1) When joined to the line L1, a portion of the boil-off gas discharged from the storage tank T while preventing the pressure drop to some extent is used as a refrigerant in the heat exchanger 100, the bypass valve 590, the first valve When the system is operated with both the 510 and the second valve 520 open, the boil-off gas in the gaseous state separated by the gas-liquid separator 700 may be directly sent to the bypass line BL.

The temperature of the boil-off gas in the gaseous state separated by the gas-liquid separator 700 is lower than the temperature of the boil-off gas discharged from the storage tank T and supplied to the heat exchanger 100, When the gaseous BOG is sent directly to the bypass line BL, the cooling efficiency of the heat exchanger 100 may decrease, and at least a portion of the gaseous BOG separated by the gas-liquid separator 700 is 100) is preferably supplied.

However, if the amount of BOG generated in the storage tank T is less than the amount of BOG required as fuel by the engine, it may not be necessary to reliquefy BOG, but there is no need to reliquefy BOG. If there is no need to supply a refrigerant to the heat exchanger 100, all of the boil-off gas in the gaseous state separated by the gas-liquid separator 700 can be sent to the bypass line BL.

Therefore, in the present invention, the sixth supply line (L6), the bypass line (BL) is merged into the first supply line (L1) in front of the branching point from the first supply line (L1). When the sixth supply line (L6) is merged into the first supply line (L1) at the front end of the branching point of the bypass line (BL), the boil-off gas discharged from the storage tank (T) and the gas separated by the gas-liquid separator (700) After the boil-off gas of the bypass line BL is first joined at the front end of the branch point, it is sent to the bypass line BL and the heat exchanger 100 according to the opening rates of the bypass valve 590 and the first valve 510, respectively. Since the flow rate of the boil-off gas is determined, it is easy to control the system, and it is possible to prevent the case where the boil-off gas in the gaseous state separated by the gas-liquid separator 700 is directly sent to the bypass line BL.

The bypass valve 590 is preferably a valve with a faster reaction rate than a normal case so that the opening degree can be quickly adjusted according to the pressure change of the storage tank T.

6 is a schematic diagram of a boil-off gas reliquefaction system according to a fifth preferred embodiment of the present invention.

The BOG reliquefaction system of the fifth embodiment shown in FIG. 6 has a differential pressure instead of the first pressure sensor 910 and the second pressure sensor 920, compared to the BOG reliquefaction system of the fourth embodiment shown in FIG. 5 . There is a difference in that the sensor 930 is installed, and below, the difference will be mainly described. Detailed description of the same members as those of the boil-off gas reliquefaction system of the fourth embodiment described above will be omitted.

The BOG reliquefaction system of this embodiment, unlike the fourth embodiment, instead of the first pressure sensor 910 and the second pressure sensor 920, the third supply line (L3) of the front end of the heat exchanger 100 (L3) and a differential pressure sensor 930 for measuring the pressure difference between the pressure of the heat exchanger 100 and the pressure of the fourth supply line L4 at the rear end of the heat exchanger 100 .

The 'pressure difference in the high temperature flow path' can be detected by the differential pressure sensor 930, and as in the fourth embodiment, among the 'pressure difference of the high temperature flow path', the 'temperature difference of the low temperature flow', and the 'temperature difference of the high temperature flow' One or more can be used as an indicator to determine whether to remove condensed or solidified lubricant.

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

T : storage tank L1, L2 : discharge line
L3: bypass line 100: heat exchanger
200: multi-stage compressor
210, 220, 230, 240, 250: compression cylinder 300: pressure reducing device
400: gas-liquid separator 510, 520, 530: control valve
610, 620, 630: shut-off valve 700: blower
810, 820, 830, 840, 850 : cooler
BL : bypass line
SL : Fuel supply line OL : Lubricating oil discharge line
NL: nitrogen supply line 100: heat exchanger
200, 210: Compressor 300: Oil separator
410, 420: oil filter 550: non-return valve
590: bypass valve 583: nitrogen valve
600, 610: pressure reducing device 620: isolation valve
700: gas-liquid separator 910, 920: pressure sensor
930: differential pressure sensor 940: water level sensor
810, 820, 830, 840: temperature sensor
L1, L2, L3, L4, L5, L6, L7, L8: supply line
RC1, RC2, RC3, RC4 : Recirculation line
541, 542, 543, 544: recirculation valve
210, 220, 230, 240, 250: cylinder
211, 221, 231, 241, 251: cooler
510, 520, 530, 560, 570, 571, 581, 582: valve

Claims (9)

A compressor comprising at least one oil-supply type cylinder and compressing boil-off gas; and
Including; a heat exchanger for cooling the boil-off gas compressed by the compressor;
The boil-off gas compressed by the compressor includes lubricating oil, and the boil-off gas containing the lubricating oil is introduced into the heat exchanger so that the lubricating oil is condensed or solidified in the reliquefaction process,
a pressure reducing device installed at the rear end of the heat exchanger to depressurize the fluid cooled by the heat exchanger;
A cryogenic filter installed at the rear end of the pressure reducing device, the second oil filter separating the lubricating oil in a solid state; and
In order to cool the compressed BOG, the refrigerant supplied to the low-temperature flow path of the heat exchanger bypasses the heat exchanger, and the refrigerant is not supplied to the low-temperature flow path of the heat exchanger by the compressor only in the high-temperature flow path of the heat exchanger. BOG reliquefaction system comprising a; a bypass line for dissolving or lowering the viscosity of the condensed or solidified lubricating oil in the heat exchanger by supplying the compressed BOG. The method according to claim 1,
Part of the boil-off gas compressed by the compressor is supplied to the engine,
BOG is supplied to the engine and the remaining BOG is sent to the heat exchanger, BOG reliquefaction system. The method according to claim 1,
The refrigerant is uncompressed BOG to be supplied to the compressor, and the uncompressed BOG is supplied to the compressor after cooling heat is recovered in the heat exchanger. The method according to claim 1,
A gas-liquid separator installed at the rear end of the pressure reducing device to separate the reliquefied liquefied gas and the boil-off gas remaining in a gaseous state;
The lubricating oil discharged from the heat exchanger is collected in the gas-liquid separator, BOG reliquefaction system. 5. The method according to claim 4,
a fifth supply line connected to supply the liquefied gas separated by the gas-liquid separator to the storage tank; and
A lubricating oil discharging line provided separately from the fifth supply line and discharging the lubricating oil collected in the gas-liquid separator; including a boil-off gas reliquefaction system. 6. The method of claim 5,
The second oil filter is installed on the fifth supply line, BOG reliquefaction system. 6. The method of claim 5,
A sixth supply line through which boil-off gas in a gaseous state separated by the gas-liquid separator is discharged; further comprising,
The second oil filter is installed on the sixth supply line, BOG reliquefaction system. 6. The method of claim 5,
The second oil filter is installed between the pressure reducing device and the gas-liquid separator, the boil-off gas reliquefaction system. The method according to claim 1,
The heat exchanger includes a microchannel type flow path, BOG reliquefaction system.

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