KR100699163B1 - Reliquefaction apparatus of lng bog and reliquefaction method - Google Patents

Abstract

An apparatus and a method for reliquefying an LMG BOG is provided to constantly maintain the temperature of the BOG at an inlet of a condenser even when the amount of the generated BOG or a temperature change is generated by pre-cooling the BOG. An apparatus for reliquefying an LMG BOG includes compressors(70,71,72), a condenser and a nitrogen cycle unit. The nitrogen cycle unit includes a nitrogen cooling unit, a first nitrogen heat exchanger(60), and a first expansion unit. The nitrogen gas of an ultra-low temperature and pressure expanded in the first expansion unit loses heat in the condenser, and returns to a pressing cooling unit via the first nitrogen heat exchanger. The BOG compressed by the compressor exchanges heat with the first nitrogen heat exchanger to be pre-cooled. Some of the high pressure nitrogen gas introduced into the first nitrogen heat exchanger is expanded by a second expansion unit and is mixed with a lower pressure nitrogen gas passed through the condenser to be introduced into the first nitrogen heat exchanger and return to the nitrogen pressing cooling unit.

Description

Reliquefaction apparatus and method for reliquefaction of LNC tank {RELIQUEFACTION APPARATUS OF LNG BOG AND RELIQUEFACTION METHOD}

1 shows a schematic view of a reliquefaction apparatus of LNG BOG according to the prior art.

2 shows a schematic diagram of a reliquefaction apparatus of LNG BOG according to an embodiment of the present invention.

3 shows a flowchart of a reliquefaction method of LNG BOG according to an embodiment of the present invention.

[Description of Symbols for Main Parts of Drawing]

10: storage tank 11: safety valve

20: recirculation valve 30: thermostat

40, 41: BOG compressor 50: BOG condenser

60, 61: first and second nitrogen heat exchangers 70, 71, 72: nitrogen compressor

80, 81, 82: intermediate cooler 90: expansion turbine

91: expansion valve 92: gas-liquid separator

100: circulation pump 110: nitrogen buffer tank

200: coldbox

The present invention relates to a reliquefaction system of boil-off gas (BOG) generated from a storage tank of a carrier transporting cryogenic liquefied natural gas (LNG). It is about.

LNG is typically transported over long distances in a liquefied state. For example, an offshore tanker is used to transfer liquefied LNG to a second location where it is vaporized at the first location where LNG is liquefied and sent to a gas distribution system. Since LNG is liquefied at very low temperatures, that is, around -163 ° C at atmospheric pressure, LNG in storage tanks is continuously vaporized due to external heat transfer from the LNG carriers.When the pressure in the storage tanks exceeds the set safety pressure, BOG Is discharged to the outside through the safety valve. The discharged BOG is liquefied and returned to the storage tank or used as fuel for ships.

Since the conventional LNG carrier is a steam turbine propulsion method, BOG was burned in a boiler and used as a propulsion fuel of a ship. Recently, as the generation of BOG is reduced due to the insulation technology of storage tanks, it is difficult to secure the amount of BOG required for the propulsion of steam turbine vessels and ship propulsion by more efficient diesel engines is preferred. Accordingly, new technologies are required for the treatment of BOG and securing the stability of storage tanks.

In a reliquefaction apparatus, a cooling cycle comprises the steps of compressing a working fluid in a plurality of compressors, cooling the compressed working fluid by indirect heat exchange, expanding the working fluid, and expanding the expanded working fluid. Heating by indirect heat exchange with the compressed working fluid, and returning the heated working fluid to one of the compressors. The LNG vapor after the compression step is at least partially condensed by indirect heat exchange with the working fluid to be heated. One example of an apparatus for performing this cooling method is described in US Pat. No. 3,857,245.

According to US Pat. No. 3,857,245, the working fluid is derived from the LNG itself and is therefore operated by an open cooling cycle. Expansion of the working fluid is carried out by a valve to obtain partially condensed LNG. Partially condensed LNG is separated into a gaseous phase mixed with the liquid natural gas returned to the reservoir and the natural gas to be sent to the combustion burner. The working fluid is heated and cooled in the same heat exchanger so only one heat exchanger is used. The heat exchanger is located on the first skid-mounted platform and the working fluid compressor is mounted on the second skid-mounted platform.

At present, it is preferred to use incombustible gases as working fluids. Furthermore, in order to reduce the compression of the working fluid supplied from the outside, an expansion turbine is preferred over a valve for expanding the working fluid.

An example of an apparatus which improves these two advantages is described in WO98 / 43029. Two heat exchangers are used in the apparatus of this document, one of which is to warm the working fluid in the heat exchanger while partially condensing the compressed natural gas vapor, and the other is to cool the compressed working fluid. Moreover, the working fluid is compressed in two different compressors, one connected to the expansion turbine. Although not disclosed in WO98 / 43029, such a conventional device is installed in a board-shaped vessel, and a compressor and heat exchanger connected to an expansion turbine are located in the ship's cargo machinery room and the other compressor is located in the engine compartment. WO2005 / 047761 has a similar structure and this application is characterized by the precooling of BOG.

Korean Patent Laid-Open Publication Nos. 2001-0088406 and 2001-0089142 relate to an apparatus for use in a board type vessel for reliquefaction of compressed steam, and the components are manufactured and used in a pre-assembly. Referring to FIG. 1, which shows this reliquefaction apparatus, reliquefaction is performed in a closed cycle, where the working fluid is compressed in at least one compressor 122, 124, and 126 and the first heat exchanger 140. Is cooled in and expanded in turbine 128 and warmed in second heat exchanger 146, where the compressed steam is at least partially condensed. The apparatus comprises a first preassembly 172 comprising a second heat exchanger 146, and a second preheater on which the first heat exchanger 140, the compressors 122, 124 and 126, and the expansion turbine 128 are located. Assembly 182. Pre-assemblies 172 and 182 are located in respective platforms 170 and 180.

The reliquefaction apparatus as described above has been improved in terms of simplification of structure, ease of mounting on a ship, and reduction of heat loss, but there is still a need for improvement.

In particular, the conventional technique used a reverse Brayton cycle of nitrogen as a working fluid in a nitrogen cycle apparatus, which is a cold heat generating mechanism for BOG liquefaction, and has a disadvantage in that it cannot quickly cope with changes in the generation amount, temperature, etc. of the BOG depending on the ship's operating conditions. . In addition, when the nitrogen temperature is lowered too much by the expansion turbine, droplets generated by reaching the liquefaction point of nitrogen may damage the turbine blades. Therefore, new technologies are needed that can cope with the amount of BOG and temperature changes that occur.

Accordingly, the present invention is to solve the problem that can not be quickly dealt with when the generation amount, temperature, etc. of the BOG changes according to the operation conditions of the ship, the BOG generated in the storage tank during operation in the LNG carrier and outflow through the safety valve In a reliquefaction system in which the liquid is recovered into a storage tank after reliquefaction, the generated BOG is subjected to a precooling process by exchanging heat with an external working fluid at the front of the condenser, so that the BOG at the inlet of the condenser is changed even if there is a change in the amount or temperature An object of the present invention is to provide an LNG BOG reliquefaction apparatus and a method capable of maintaining a constant temperature within a set range.

Furthermore, the present invention provides a lower temperature by using an expansion valve as well as an expansion turbine in a reliquefaction system that reliquefies a BOG generated in a storage tank and flows out through a safety valve during operation in an LNG carrier. It is an object of the present invention to provide an LNG BOG reliquefaction apparatus and method for securing a stable pressure and temperature in a storage tank while eliminating LNG loss in any case.

In order to achieve the above object, the present invention provides a compressor for compressing evaporated vapor (BOG) generated in a storage tank of LNG; A condenser for at least partially condensing the evaporated vapor compressed by the compressor: a LNG BOG reliquefaction apparatus comprising a nitrogen cycle device for supplying cold heat to the condenser to return the BOG reliquefied by the condenser to the tank The nitrogen cycle apparatus comprises: nitrogen pressurizing means for pressurizing and cooling nitrogen; A first nitrogen heat exchanger for cooling the high pressure nitrogen gas passing through the nitrogen pressurized cooling means; And first expansion means for expanding the high pressure nitrogen gas passing through the first nitrogen heat exchanger to generate ultra low temperature nitrogen gas, wherein the ultra low temperature nitrogen gas expanded by the first expansion means receives cold heat from the condenser. It is configured to return to the nitrogen pressurized cooling means via the first nitrogen heat exchanger after being deprived, and the evaporated vapor compressed by the compressor is heat exchanged in the first nitrogen heat exchanger and precooled before being condensed.

Some of the high pressure nitrogen gas flowing into the first nitrogen heat exchanger from the nitrogen pressurized cooling means is expanded by the second expansion means, cooled to low temperature low pressure nitrogen gas, and then combined with the low pressure nitrogen gas passed through the condenser to form the first nitrogen heat exchanger. 1 is preferably introduced into the nitrogen heat exchanger and returned to the nitrogen pressurized cooling means.

In addition, a second nitrogen heat exchanger is further provided between the nitrogen pressurized cooling means and the first expansion means, and the high pressure nitrogen gas introduced into the second expansion means is primarily cooled in the second nitrogen heat exchanger. In addition, the first or second expansion means is preferably an expansion valve or an expansion turbine, the generator may be installed in the expansion turbine.

In addition, it is preferable to configure the condenser, the nitrogen heat exchanger, and the expansion means as one module.

In addition, it is preferable to supply the LNG from the reliquefied BOG or LNG tank to the BOG or the compressed BOG supplied to the compressor to cool the temperature of the BOG supplied to the condenser.

In yet another aspect, the present invention comprises the steps of compressing evaporative vapor (BOG) generated in the storage tank of LNG; Pressurizing and cooling the nitrogen gas which is a working fluid to provide cooling heat for condensing the compressed BOG, and expanding the pressurized nitrogen gas to generate cryogenic nitrogen gas; Heat exchange with the cryogenic nitrogen gas to at least partially condense the compressed BOG; In the BOG reliquefaction method comprising the step of returning the BOG liquefied by the condensation to the tank, the BOG generated in the LNG storage tank is subjected to a pre-cooling process in the first nitrogen heat exchanger in front of the BOG condenser Characterized in that.

In addition, a portion of the pressure-cooled nitrogen gas is expanded in a different path from the expansion to become a low-temperature gas, combined with the nitrogen gas whose temperature is increased by the condensation of the compressed BOG before the expansion step of the pressure-cooled nitrogen gas. It is preferable to precool by heat exchange between nitrogen gas.

In addition, it is preferable that the extraction amount of the portion of pressurized nitrogen gas extracted in another path for the precooling is adjustable.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. The temperature and pressure described below show one example, and the present invention is not limited to these numerical values.

2 is a schematic diagram of a LNG BOG reliquefaction apparatus according to the present invention. The device consists of a BOG cycle device, a nitrogen cycle device, and a cold box device that interfaces the two devices.

1) BOG cycle device

Natural gas is liquefied to cryogenic temperatures and stored in a tank at atmospheric pressure (1.013 bar). However, BOG is generated due to heat transfer from the outside during LNG transportation, which acts as a pressure increase factor of the storage tank 10. Therefore, in order to maintain the storage tank 10 at a constant atmospheric pressure level, when the storage tank pressure reaches about 1.03 bar, the safety valve 11 is opened and the BOG is discharged out of the storage tank 10 so that the two-stage BOG compressor 40 Re-liquefaction process is passed through (41).

The high temperature BOG discharged out of the storage tank 10 is sensed by the temperature sensor 12 and after being adjusted to a constant temperature through the temperature controller 30, the BOG compressor 40, 41 of the second stage It is preferable to flow in. BOG passed through the temperature controller 30 is maintained at 1.03 bar, superheated steam of -120 ℃.

Looking at the operation of the temperature controller 30 in more detail, it is possible to control the temperature by recycling and mixing the cryogenic LNG after the reliquefaction process to the hot BOG discharged from the storage tank 10, the control of the recycle amount is recycled This is performed by adjusting the opening degree of the valve 20. In addition, the temperature controller 30 may supply LNG from an LNG tank to a pump (not shown) as well as the reliquefied BOG. Temperature control usually operates only until the reliquefaction apparatus reaches a steady state, after which the recirculation valve 20 is closed and the cryogenic reliquefaction BOG is led to the storage tank 10.

The BOG passing through the temperature controller 30 is discharged in a superheated steam state of 3.6 bar and −41.98 ° C. after passing through two stages of the BOG compressors 40 and 41.

The BOG discharged from the two stage BOG compressors 40 and 41 passes through the first nitrogen heat exchanger 60 as a third path and is precooled to a superheated steam state of 3.3 bar and -134 ° C. At this time, the pre-cooling of the BOG is a mixture of low-temperature low-temperature low-temperature nitrogen gas discharged from the BOG condenser 50 to be described later in the first nitrogen heat exchanger 60 and the cryogenic nitrogen gas by the expansion turbine 90 Heat by nitrogen gas. Subsequently, the pre-cooled BOG is changed into a supercooled liquid state of 3.0 bar and -154.7 ° C. while passing through the BOG condenser 50 and then reintroduced into the storage tank 10 or recycled to the temperature controller 30. Detailed description of the BOG condenser 50 will be described in detail in the following cold box process. As such, even though the BOG is precooled by an external working fluid (nitrogen), there is an advantage in that the temperature of the BOG can be maintained within a predetermined range at the inlet of the BOG condenser 50 even if there is a change in the amount of BOG generation or temperature. In addition, when the BOG in the superheated steam discharged from the two-stage BOG compressors 40 and 41 flows into the BOG condenser, the temperature difference between the streams in the BOG condenser increases, causing problems in durability of the heat exchanger due to thermal stress. The BOG precooling process has an advantage of reducing the temperature difference between streams in the BOG condenser.

Through the BOG condenser 50, the entire BOG can be liquefied, but 70 to 99% is liquefied due to the influence of nitrogen, which is not easily liquefied completely. The gas-liquid mixture is separated from the gas and liquid in the gas-liquid separator 92 so that the liquid is re-introduced into the storage tank 10 by the circulation pump 100 or recycled to the temperature controller 30, the gas is generally external To be discharged.

The condensed BOG is reintroduced into the storage tank 10 by the circulation pump 100. The reflowing method of BOG into the storage tank 10 is a method of spraying through the spray head from the top of the tank or supplying to the bottom of the tank. When it enters the bottom of the tank, the nitrogen contained in the uncondensed gas contained in the condensed BOG is dissolved in the LNG to keep the nitrogen ratio in the gas phase low. Since nitrogen has a lower liquefaction point than methane, which is the main component of LNG, when the nitrogen content in the BOG is reduced, the load of the two-stage BOG compressor 40 or 41 or the BOG condenser 50 can be reduced.

2) Nitrogen cycle device

In the BOG condenser 50, BOG reliquefaction is performed by heat exchange with cryogenic nitrogen gas. The following description relates to a cycle apparatus for obtaining cryogenic nitrogen gas required for BOG reliquefaction.

Nitrogen gas at 14.3 bar and 36.08 ° C passes through three stages of nitrogen compressors 70, 71 and 72 and the intermediate coolers 80 and 81 and 82. Discharged. After the nitrogen gas is transferred to the cold box, the low pressure low temperature nitrogen returned through the BOG condenser 50 and the first nitrogen heat exchanger 60 and 57.7 bar through internal heat exchange in the second nitrogen heat exchanger 61. Cooled to -70 ° C.

At this time, some of the nitrogen gas cooled through the second nitrogen heat exchanger 61 passes through the expansion turbine 90, the temperature is lowered, the nitrogen is lowered temperature is returned to the nitrogen through the BOG condenser 50 Combined with and introduced into the first nitrogen heat exchanger (60), wherein the first nitrogen heat exchanger (60) is a high pressure through the internal heat exchange with the nitrogen gas of the high pressure partially cooled in the second nitrogen heat exchanger (61) It is preferable to further cool the nitrogen gas. By such cooling, the high pressure nitrogen has an effect of lowering the nitrogen temperature to the required set temperature at the inlet of the expansion valve 91. The high pressure nitrogen gas whose temperature is lowered in the first nitrogen heat exchanger 60 passes through the expansion valve 91 and finally changes to cryogenic gas required for BOG liquefaction of -162.6 ° C. The cryogenic nitrogen gas heats the BOG in the BOG condenser 50 to liquefy the BOG and the temperature rises.

Part of the high-pressure nitrogen gas to obtain a low-temperature nitrogen using an expansion turbine to flow into the first nitrogen heat exchanger 60, because the low-pressure nitrogen returned from the BOG condenser 50 is low in specific heat Since it is insufficient to cool the nitrogen, a portion of the nitrogen is lowered in advance using an expansion turbine, and the high pressure nitrogen gas is used to help cool the required temperature to the inlet of the expansion valve 91. After the remaining cold heat to cool the high pressure nitrogen in the second nitrogen heat exchanger 61 and the temperature rises to reach 14 bar, 36.08 ℃ to complete the nitrogen cycle. The nitrogen buffer tank 110 adjusts the mass flow rate of the nitrogen cycle in response to the variation of the BOG reliquefaction amount, that is, the variation of the cooling load of the nitrogen cycle. It may further comprise a source of supplemental working fluid (nitrogen) in case the amount of nitrogen is reduced.

3) Cold box device

The cold box includes a BOG condenser 50 for reliquefaction of BOG, first and second nitrogen heat exchangers 60 and 61 for internal heat exchange between the hot and cold portions of the nitrogen cycle and BOG precooling, and cryogenic nitrogen gas. The expansion valve 91 and the expansion turbine 90 for obtaining low temperature nitrogen required for internal heat exchange. Although not an essential component of the present invention, the generator G is connected to the expansion turbine 90 to produce electric power, and the auxiliary power source such as the BOG compressor 40, 41 or the nitrogen compressor 70, 71, 72, and the like. It is also possible to use.

By including the devices of the above process as a single module in the cold box 200, it is possible to shorten the connection pipe between the devices, which ensures the stable cryogenic nitrogen required for BOG reliquefaction. That is, the connection pipe between the inlet of the second nitrogen heat exchanger 61 and the expansion turbine 90 or the connection pipe between the inlet of the first nitrogen heat exchanger 60 and the expansion valve 91 is shortened, thereby expanding the expansion turbine 90 or the expansion valve. The cryogenic state of nitrogen at the outlet of expansion turbine 90 or expansion valve 91, which may be sensitive to the temperature of nitrogen at the inlet of 91, may be stabilized. In addition, since the connection pipe between the outlet of the expansion valve 91 and the BOG condenser 50 is shortened, it can be expected to minimize the temperature increase due to the nitrogen gas transfer.

In the present invention, in the configuration of the BOG reliquefaction apparatus, the cold box BOG condenser 50, the first and second nitrogen heat exchanger (60, 61) and expansion means (90, 91) in one cold box It is preferable to comprise 200, and to insulate them by one module. Insulation is generally performed using known insulators. By such a configuration, the cryogenic region of nitrogen gas can be stably managed, and the nitrogen heat exchanger can be easily designed and manufactured. In addition, the cold box may be manufactured in a preassembly to facilitate mounting on a ship.

When the generator G is connected to the expansion turbine 90, the power generated from the generator G is used as a power source of the BOG compressors 40, 41 or the nitrogen compressors 70, 71, 72. Can be.

Operation of the reliquefaction apparatus according to the configuration of the present invention is basically similar to the method known in the prior art by the step of compressing evaporated steam (BOG) generated in the storage tank of LNG; Pressurizing and cooling the nitrogen gas which is a working fluid to provide cooling heat for condensing the compressed BOG, and expanding the pressurized nitrogen gas to generate cryogenic nitrogen gas; Condensing at least a portion of the compressed BOG by heat exchange with the cryogenic nitrogen gas; And returning the BOG re-liquefied by the condensation to the tank, except that the BOG generated in the LNG storage tank is subjected to a pre-cooling process in a first nitrogen heat exchanger in front of the BOG condenser. Even if there is a temperature change, the temperature of the BOG at the inlet of the BOG condenser can be kept constant within the set range.

In addition, instead of expanding all of the pressurized nitrogen gas, a portion of the pressurized nitrogen gas is extracted and expanded in a path different from the expansion to generate a low temperature gas, and then combined with the nitrogen gas whose temperature is slightly increased by condensation of the compressed BOG. It may include the step of pre-cooling by heat exchange before the expansion of the pressure-cooled nitrogen gas.

Referring to this attached to Figure 3, in the storage tank of the cryogenic LNG carrier in the BOG reliquefaction method generated by the external heat transfer,

First, the circulation of BOG is a step in which the BOG discharged after opening the valve at the set pressure is maintained at 1.03bar and -120 ° C at a constant state of the two-stage compressor through the temperature controller (ST 10), and the BOG is the two-stage compressor. In the step of becoming a superheated state of high temperature and high pressure of 3.6 bar and -41.98 ° C. (ST 20), the precooling heat exchanger of the third path passes through the first nitrogen heat exchanger 60 to lower the temperature to 3.3 bar and −134 ° C. Step (ST 30), the pre-cooled BOG is re-liquefied into a subcooled liquid of 3.0 bar, -154.7 ℃ in a BOG condenser (ST 40), the step of recovering the re-liquefied BOG to a storage tank (ST 80),

Nitrogen gas circulation for cold heat supply for reliquefaction of the BOG, the pressure is raised to 58 bar, 40 ℃ after the nitrogen gas of 14.3 bar, 36.08 ℃ passes through the three-stage compressor and the intermediate cooler ( ST 90), the high pressure nitrogen is changed to a low temperature of 57.7 bar, -70 ° C through the low temperature nitrogen and the internal heat exchanger in the second nitrogen heat exchanger (ST 100), a portion of the high pressure nitrogen is expanded turbine Step of changing to a low temperature, low pressure gas of 15.2 bar, -129.3 ° C (ST 110), the cold nitrogen that is not sent to the expansion turbine combined with the nitrogen lowered in the expansion turbine in the first nitrogen heat exchanger (60) The internal heat exchange by the step 57.4 bar, -132 ℃ step (ST 120), the high pressure nitrogen passes through the expansion valve to 15.2 bar, -162.6 ℃ step (ST 130), low temperature low pressure nitrogen BOG condenser ( BOG reliquefaction at 50) followed by 14.9 bar, -145 ° C. Step to become a warm nitrogen gas (ST 140), the low temperature nitrogen gas passes through the first nitrogen heat exchanger (60) to change to a state of 14.6 bar, -86.42 ℃ (ST 150), the temperature is lowered by the expansion turbine Nitrogen is combined and passed through the second nitrogen heat exchanger (60) is characterized in that the step (ST 160) for changing the state to a high temperature of 14.3 bar, 36.08 ℃.

After the pre-cooled BOG is re-liquefied in the BOG condenser (ST 40), a step (ST 50) of separating the non-condensed gas contained in the re-liquefied BOG may be added, the re-liquefied BOG is a circulation pump ( It may be transferred to the storage tank 10 by the step (ST 60) is pressed by 100. Furthermore, a part of the reliquefaction BOG may be recycled through the temperature control valve 20 (ST 70) and supplied to the stage before or after the BOG is compressed (ST 20) to precool the BOG.

Pressure, temperature, etc. in each of the above steps is described by a specific number, but it is obvious that it can be changed depending on the amount of BOG, control method, and the like.

The present invention has the advantage of maintaining a constant temperature within the set range of the BOG at the inlet of the condenser, even if there is a change in the amount of BOG generation or temperature by passing the BOG pre-cooling process in front of the BOG condenser.

In addition, the present invention is a conventional art of the prior art that can damage the blade of the expansion turbine by a part of the nitrogen liquefied when lowering the temperature of the nitrogen using the expansion turbine in the BOG liquefaction system using the reverse braton cycle of nitrogen As a solution to the problem, the method extracts only a portion of pressurized nitrogen, expands it using an expansion turbine, and lowers the temperature of the nitrogen further through a expansion valve to lower the temperature of nitrogen without fear of droplet generation. There are advantages to it. In addition, it is possible to vary the operation of the nitrogen cycle by changing the amount of extracted nitrogen can easily cope with the dynamic change of the BOG.

In addition, the present invention can stably manage the pressure of the storage tank without the loss of LNG stored during operation of the LNG carrier. In particular, the introduction of a simple cold box module can reduce the size of the LNG reliquefaction apparatus, make stable management of the cryogenic region of nitrogen gas, and simplify the design and manufacture of the nitrogen heat exchanger. Specifically, since the connection pipe between the nitrogen heat exchanger and the expansion turbine inlet is shortened, the cryogenic state of the expansion turbine inlet or the outlet of the expansion turbine, which is sensitive to temperature, may be stabilized. In addition, since the connection pipe between the expansion valve outlet and the BOG condenser is shortened, it is possible to minimize the temperature rise issued during the cryogenic nitrogen gas transfer. Losses can also be prevented.

Claims (13)

A compressor for compressing evaporated vapor (BOG) generated in a storage tank of LNG; A condenser for condensing evaporated vapor compressed by the compressor; In the BOG reliquefaction apparatus consisting of a nitrogen cycle device for supplying cold heat to the condenser to return the BOG liquefied by the condenser to the tank, The nitrogen cycle apparatus comprises nitrogen pressurized cooling means for pressurizing and cooling nitrogen; A first nitrogen heat exchanger for cooling the high pressure nitrogen gas passing through the nitrogen pressurized cooling means; And first expansion means for expanding the high pressure nitrogen gas passing through the first nitrogen heat exchanger to generate ultra low temperature nitrogen gas, wherein the ultra low temperature nitrogen gas expanded by the first expansion means receives cold heat from the condenser. After being deprived, it is configured to return to the nitrogen pressurized cooling means via the first nitrogen heat exchanger, and the BOG compressed by the compressor is heat-exchanged in the first nitrogen heat exchanger and precooled before being condensed. Some of the high pressure nitrogen gas flowing into the first nitrogen heat exchanger from the nitrogen pressurized cooling means is expanded by the second expansion means, cooled to low temperature low pressure nitrogen gas, and then combined with the low pressure nitrogen gas passed through the condenser to form the first nitrogen heat exchanger. 1 LNG liquefied liquid regeneration apparatus, characterized in that flowing into the nitrogen heat exchanger and returned to the nitrogen pressure cooling means. delete The method of claim 1, wherein a second nitrogen heat exchanger is further provided between the nitrogen pressurized cooling means and the first expansion means, and the high pressure nitrogen gas flowing into the second expansion means is primarily cooled in the second nitrogen heat exchanger. LNG BOG reliquefaction apparatus. The reliquefaction apparatus of LNG BOG of Claim 3 whose said 1st or 2nd expansion means is an expansion valve or an expansion turbine. The apparatus of claim 4, wherein the expansion turbine is provided with a generator. The apparatus for reliquefying LNG BOG according to any one of claims 1, 3, 4, and 5, wherein the condenser, the nitrogen heat exchanger, and the expansion means are configured as one module. 7. The apparatus of claim 6, wherein the module is insulated. The apparatus of claim 6, wherein the module is made of a preassembly. The method according to any one of claims 1, 3, 4, and 5, wherein the BOG supplied to the compressor is supplied with LNG from the reliquefied BOG or LNG tank to cool the temperature of the BOG supplied to the condenser. Reliquefaction apparatus of LNG BOG characterized in that. The method according to any one of claims 1, 3, 4, and 5, wherein the BOG compressed by the compressor cools the temperature of the BOG supplied with the LNG from the reliquefied BOG or LNG tank and supplied to the condenser. LNG BOG reliquefaction apparatus, characterized in that the. Compressing evaporated vapor (BOG) generated in a storage tank of LNG; Pressurizing and cooling the nitrogen gas which is a working fluid to provide cooling heat for condensing the compressed BOG, and expanding the pressurized nitrogen gas to generate cryogenic nitrogen gas; Heat exchange with the cryogenic nitrogen gas to at least partially condense the compressed BOG; In the reliquefaction method of LNG BOG consisting of returning the BOG liquefied by the condensation to the tank, BOG generated in the LNG storage tank is subjected to a pre-cooling process in the first nitrogen heat exchanger in front of the BOG condenser, A portion of the pressurized cooled nitrogen gas is expanded in a path different from the expansion to become a low temperature gas, and is combined with the nitrogen gas whose temperature is increased by condensation of the compressed BOG, so that the nitrogen gas is before the expansion step of the pressurized cooled nitrogen gas. Reliquefaction method of LNG BOG characterized by precooling by heat exchange between. delete The method of claim 11, wherein the portion of the pressure-cooled nitrogen gas extracted for another pre-cooling for the pre-cooling the extraction amount is adjustable.

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