WO2017160007A1 - Device for partially re-liquefying boil-off gas of liquefied natural gas for ship - Google Patents

Abstract

The present invention relates to a device for partially re-liquefying boil-off gas of liquefied natural gas for a ship, wherein the device compresses boil-off gas (BOG) generated in an LNG storage tank (100) for a ship, re-liquefies the compressed boil-off gas, and stores the re-liquefied boil-off gas. The present invention provides the configuration of a device for partially re-liquefying boil-off gas of liquefied natural gas for a ship, the device comprising: a storage tank (100) for storing LNG; a first heat exchanger (170) for exchanging heat using low-temperature heat of the low-temperature BOG boil-off gas discharged from the storage tank (100); a compressor (130) for compressing boil-off gas introduced through the first heat exchanger (170) into high-pressure gas at 250-300 bar; a branch portion (210) comprising a second channel (200) for transferring the high-pressure gas discharged from the compressor (130) to the first heat exchanger (170) and a first channel (190) for transferring the same to a precooler (120); a precooler (120) for cooling the high-pressure gas discharged through the first channel (190) to a state of -25 to 30ºC and 300 bar; a second heat exchanger (180) for additionally cooling the high-pressure gas discharged through the precooler (120) using flash gas at -162ºC; a pressure-reducing/expanding valve (140) for merging compressed gases cooled through the second heat exchanger (180) of the first channel (190) and the first heat exchanger (170) of the second channel (200) and pressure-reducing the same to an atmospheric state, thereby expanding the same; and a liquid/gas separator (160) for separating the boil-off gas that has been pressure-reduced by the pressure-reducing/expanding valve (140) into a saturated liquid and a saturated gas, transferring the flash gas to the second heat exchanger (180), and transferring the saturated liquid to the storage tank (100). The liquefaction process using the partial re-liquefaction device according to an embodiment of the present invention is a method for re-liquefying a larger amount of BOG, and the method substantially reduces the cost of the partial re-liquefaction device and provides an efficient system that reduces energy consumption.

Description

Evaporative gas partial reliquefaction apparatus of liquefied natural gas for ship

The present invention relates to a boil-off gas (BOG) partial reliquefaction apparatus generated in a storage tank of a carrier transporting cryogenic liquefied natural gas (LNG), in particular a BOG portion mounted on a vessel It relates to a reliquefaction apparatus.

In the present invention, LNG is evaporated by heat inflow during transportation in a tank of a LNG carrier, or vaporized from an LNG storage tank such as a vaporized gas of a bunkering vessel of an offshore LNG vessel, and a vessel operating natural gas as a fuel. In the configuration of the partial reliquefaction of the gas boil-off-gas (Boil-off-gas) that is continuously generated, More specifically, the compression unit for compressing the low-temperature evaporated gas discharged from the storage tank; A precooling unit branching the compressed gas into a high-pressure compressed gas stream and cooling a portion of the compressed gas by using a general refrigerating device; A first cooling unit and a second cooling unit which reduce the temperature by separating the cooled gas from the BOG evaporation gas and the flash gas; A pressure reducing expansion valve for lowering the pressure after the cooled compressed gas is coalesced; It consists of a liquid separator that separates cryogenic liquids and gases produced after expansion. Here, the flash gas obtained after passing through the reduced pressure expansion valve provides a low temperature in the second cooling heat exchanger, and is sucked or discharged to the compressor 130. In addition, the general refrigeration unit is composed of a compressor 130, a condenser, expansion valve, evaporator.

The liquefaction process using the boil-off gas partial liquefaction apparatus according to an embodiment of the present invention is a method of partial liquefaction of a larger amount of BOG to significantly reduce the cost of the reliquefaction apparatus, and to configure an effective partial liquefaction apparatus that reduces energy waste. Can provide.

LNG is typically transported over long distances in a liquefied state. 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 LNG carriers.When the pressure in the storage tanks exceeds the set safety pressure, BOG Is discharged to the outside through safety valves or used as boiler fuel for ships. Or, it is liquefied using a reliquefaction unit and returned to the storage tank. As such, the recent trend is attempting to increase the liquid transport volume by partially reliquefying it.

Recently, natural gas, a clean energy source, is increasing in use worldwide, and for its trade, liquefied natural gas (“LNG”), which has liquefied natural gas at -162 ° C, is transported by carrier. In addition, in order to prevent pollution of the port, LNG is used as fuel for ships such as cafes and coastal ships, and transportation for use of this LNG fuel, fuel tank filling and storage system for ships are being promoted.

Even though the tanks for transporting LNG or bunkering vessels are properly insulated, 0.15% of LNG is vaporized daily by external heat inflow, and thus boil-off-gas (BOG) of -100 ℃ to -130 ℃ is produced. It occurs continuously, and especially during the filling process, a large amount of BOG is generated. For long-distance LNG transport ship 20 man m is the ^3-level of 4 to 5000 tons LNG is vaporized during the 20 days the average flight period of the BOG generation of 5 to 6Ton per hour.

Recently, ME-GI engine, which is a mixed gas of natural gas and light oil, has been developed to efficiently use evaporated BOG, and this engine compresses the vaporized BOG to a high pressure of 250 to 300 bar and uses it as a fuel for ships. Typically, the liquefaction of cryogenic gases, such as natural gas, consists of Linde cycle compression-cooling-expansion, and the higher the pressure, the higher the reliquefaction yield. The engine is already equipped with a high-pressure compressor to be able to apply the BOG reliquefaction process. In the case of offshore LNG fuel propulsion vessels, the high-pressure natural gas ME-GI engine is also used, thereby enabling the reliquefaction of BOG using this compressor.

In the reliquefaction process using the ME-GI engine compressor, there are a partial reliquefaction system (PRS) and a complete reliquefaction system in which the BOG evaporated is cooled, expanded under reduced pressure, and only partially reliquefied.

1 and 2 is a view schematically showing an embodiment of a conventional partial reliquefaction apparatus (PRS) of the LNG transport vessel.

According to one embodiment of the prior art, the BOG of -100 to -130 ℃ generated in the storage tank is supplied to the compressor through a heat exchanger through the discharge pipe is compressed to 250 to 300 bar, the compressed evaporated gas is returned to the heat exchanger- After cooling about 90 to -115 ° C, the enthalpy expansion process is reduced to atmospheric pressure through the expansion valve, and theoretically, about 35% to 45% of the BOG is liquefied and returned to the storage tank.

In related patents, there are patents such as Korean Patent Publication Nos. 10-2013-0127270, 10-2013-0131946, 10-2013-0147915, 10-2014-0033792, and the like. However, in all these methods, the actual yield of BOG reliquefaction is reduced by about 20 to 30% due to deterioration of heat exchanger efficiency and external heat inflow, and thus, continuous technical improvement is required to increase reliquefaction amount.

1 and 2, the partial reliquefaction system of Figure 1 is to apply the triple heat exchanger in using the cold heat of the BOG and flash gas, the re-liquefaction yield is largely influenced by the heat exchange efficiency, and effective according to the load fluctuation It is difficult to obtain heat exchange, and there is a disadvantage that the price of the cryogenic heat exchanger is high. In this process, the maximum theoretical reliquefaction rate is around 45% based on the use of BOG and flash gas temperature up to 10 ° C. If the heat exchange efficiency is 90%, the liquefaction rate drops sharply to 29%. I can't.

2 is a process in which the vaporized flash gas is coalesced with the BOG generated in the tank, and the liquefaction rate is greatly reduced by increasing the concentration of nitrogen gas which is not liquefied among the components of the flash gas with an increase in operating time. . The theoretical maximum reliquefaction rate of this process is 40%.

That is, the above methods all reduce the actual yield of BOG reliquefaction by about 10 to 15% due to a decrease in heat exchanger efficiency and external heat inflow, so there is a need for continuous improvement of technology to increase the amount of reliquefaction. .

On the other hand, Figure 3 is a view schematically showing the BOG complete reliquefaction apparatus of the conventional LNG transport vessel.

The reliquefaction apparatus shown in FIG. 3 includes Hamworthy's reliquefaction apparatus and TGE reliquefaction apparatus using a multi-stage refrigeration cycle as a method of completely reliquefying all the BOGs generated. This process consists of a cryogenic nitrogen refrigeration cycle, which includes a storage tank in which nitrogen gas is stored, a nitrogen gas compressor-expander that expands and cools the nitrogen gas supplied from the tank, and a nitrogen gas supplied from the compander. And a cold box heat exchanger for liquefying BOG boil-off gas supplied from the compressor. Since the refrigeration system is composed of a cryogenic nitrogen refrigeration cycle, the size of the installation is large, so the installation area is large, and the apparatus cost is large.

These related patents include WO 2009/136793, WO 2011/078669, US2014 / 0102133 (2014, 4,17), and Korean Patent Publication No. 2001-0089142.

Therefore, the present invention is designed to improve the problems of the BOG partial reliquefaction process and the complete reliquefaction process, by precooling the compressed boil-off gas using a refrigerating device to further lower the temperature before expansion, the nozzle and the expansion device The present invention relates to a configuration of a partial reliquefaction apparatus that applies an expansion valve to improve reliquefaction rate.

Accordingly, the present invention is designed to ameliorate the problems of these BOG partial reliquefaction processes. The present invention significantly improves heat exchange efficiency by branching the compressed BOG gas stream by separating the cold heat of the BOG and the cold heat of the flash gas, and precooling the branched compressed boil-off gas with a freezer to further lower the temperature before expansion. It is a technique that greatly expands the reliquefaction rate to 55% to 60% or more by expanding with a reduced pressure expansion valve.

The present invention was created to improve the prior art as described above, in the process of re-liquefying the BOG evaporated from the storage tank of the LNG transport vessel, LNG filled bunkering vessel, LNG fuel propulsion vessel, the use of cold heat separation and pre-cooling By applying the method, it provides a configuration that greatly improves the reliquefaction rate of BOG to around 60%, thereby effectively treating ships' BOG to provide saving of natural gas and securing safety.

The present invention is to compress the low-temperature evaporated gas BOG discharged from the LNG storage tank to branch the high-pressure compressed gas flow to increase the heat exchange efficiency by separating the cold heat of the BOG and the cold heat of flash gas, general R134a, ammonia freezer It relates to a configuration of a partial reliquefaction apparatus characterized by improving the BOG reliquefaction rate by pre-cooling using such.

According to an aspect of the present invention, in the cooling heat exchanger provided with two or more high-pressure BOG of 250 to 300 bar by the cooling process of the BOG boil-off gas and flash gas retained, and pre-cooled branched high-pressure BOG with a freezer Through the process, the amount of reliquefaction is greatly increased by increasing the supercooling rate.

In addition, the refrigerating device may be ammonia freezer having a large latent heat, or one or more freezing devices such as R508 and R23 having a lower temperature may be applied to the configuration of the device.

The cooling heat exchanger may be composed of one or more according to the capacity, the flow of the branched flow path of the compressed gas may be composed of two or more branched flows.

Compresses boil-off-gas (BOG) generated in a marine LNG storage tank 100 according to an embodiment of the present invention, reliquefies the compressed boil-off gas, and stores the re-liquefied boil-off gas. An apparatus for partial liquefaction of boil-off liquefied natural gas, comprising: a storage tank (100) storing LNG; A first heat exchanger (170) for exchanging heat by using cold heat of a low temperature -130 ° C BOG boil-off gas discharged from the storage tank (100); A compressor (130) for compressing the evaporated gas introduced through the first heat exchanger (170) into a high pressure gas of 250 to 300 bar; Branching portion consisting of a second flow path 200 for transferring the high pressure gas discharged to the compressor 130 to the first heat exchanger 170, and a first flow path 190 for transferring to the precooler 120 ( 210; A precooler (120) for cooling the high pressure gas discharged to the first flow passage (190) to -25 to -30 ° C at 300 bar; A second heat exchanger 180 for further cooling the high pressure gas discharged through the precooler 120 using a flash gas of −162 ° C .; Pressure-expanding expansion for decompressing and expanding the compressed gas cooled through the second heat exchanger 180 of the first flow passage 190 and the first heat exchanger 170 of the second flow passage 200 at atmospheric pressure. A valve 140; The vaporized gas decompressed by the reduced pressure expansion valve 140 is separated into a saturated liquid and a saturated gas, a flash gas is transferred to the second heat exchanger 180, and a saturated liquid is a liquid to be transferred to the storage tank 100. It provides a configuration of the partial reliquefaction apparatus of the boil-off liquefied natural gas for ships configured to include a separator (160).

Meanwhile, the first heat exchanger 170 cools the compressed high pressure compressed gas introduced through the second flow passage 200 by using the cold heat of the evaporated gas of −130 ° C. discharged from the storage tank 100. It is characterized by.

The precooler 120 cools the high-pressure compressed gas discharged through the compressor 130 to −25 to −30 ° C., and the freezer 110 may be any one of an ammonia freezer, an R134a freezer, and an R508 freezer. It is characterized in that one is used selectively.

On the other hand, the second heat exchanger 180 is introduced through the precooler 120 through the first passage 190 by using a flash gas of -162 ℃ discharged from the liquid separator 160. It is characterized in that the compressed gas is cooled through a heat exchange process.

In addition, the pressure of the high pressure compressed gas of 300 bar state through the pressure-expansion expansion valve 140 to the saturated liquid state and the saturated gas state of the atmospheric pressure state, and then the liquid gas through the liquid separator 160 is stored in the storage To the tank 100, the flash gas in the gas state is characterized in that separated and transported to the second heat exchanger (180) side.

According to the partial reliquefaction apparatus of the boil-off liquefied natural gas of the present invention, the compressor 130, by branching the flow of gas compressed at high pressure to separate the cold heat of the BOG and the cold heat of the flash gas, ammonia freezer The present invention relates to an apparatus for improving the BOG reliquefaction rate by 10% to 20% over conventional partial reliquefaction systems by precooling using.

In addition, this is to provide a configuration of a reliquefaction apparatus that can more effectively process the BOG of ships to secure the safety of natural gas, energy saving and minimize the cost of the partial reliquefaction apparatus.

1 is a view showing a partial reliquefaction apparatus of BOG which is LNG boil-off gas according to the prior art.

2 is a view showing another embodiment of a partial reliquefaction apparatus of BOG which is LNG boil-off gas according to the prior art.

3 is a view showing an embodiment of a complete reliquefaction apparatus of BOG which is LNG boil-off gas according to the prior art.

4 is a block diagram of a partial boil-off gas liquefaction apparatus of liquefied natural gas for ship according to an embodiment of the present invention.

[Description of the code]

100. Storage Tank 110. Freezer

120: precooler 130. compressor

140. Pressure reducing valve 160. Liquid separator

170. First heat exchanger 180. Second heat exchanger

190. The first euro 200. The second euro

       210. Branch

The present invention has been made in order to solve the above problems, in the reliquefaction of the BOG vaporized in the LNG storage tank 100 of the LNG transport vessel or a vessel operated by LNG fuel is compressed at high pressure in the compressor 130 of the vessel BOG gas is branched to separate and suck BOG cold heat and flash gas cold heat, and a part of the compressed discharge gas is precooled using a general refrigerating device, and a combination of a reduced pressure expansion valve 140 and the like is used to improve the reliquefaction rate. It relates to the configuration of a partial reliquefaction apparatus.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 4 is a block diagram of the partial liquefaction apparatus of the boil-off gas of liquefied natural gas for a representative road according to an embodiment of the present invention.

Looking at, compressing the boil-off-gas (BOG: boil-off-gas) generated in the marine LNG storage tank 100 according to an embodiment of the present invention, re-liquefied the compressed boil-off gas, the re-liquefied boil-off gas An apparatus for partial liquefaction of a boil-off liquefied natural gas for ship, comprising: a storage tank (100) storing LNG; A first heat exchanger 170 for exchanging heat by using cold heat of a low temperature boil-off gas discharged from the storage tank 100; A compressor (130) for compressing the evaporated gas introduced through the first heat exchanger (170) into a high pressure gas of 250 to 300 bar; Branching portion consisting of a second flow path 200 for transferring the high pressure gas discharged to the compressor 130 to the first heat exchanger 170, and a first flow path 190 for transferring to the precooler 120 ( 210; A precooler (120) for cooling the high pressure gas discharged to the first flow passage (190) to -25 to -30 ° C at 300 bar; A second heat exchanger 180 for further cooling the high pressure gas discharged through the precooler 120 using a flash gas of −162 ° C .; After coalescing the compressed gas cooled through the second heat exchanger 180 of the first flow passage 190 and the first heat exchanger 170 of the second flow passage 200, it expands by depressurizing to atmospheric pressure. Pressure reducing expansion valve 140 to be made; The evaporated gas decompressed by the pressure reducing expansion valve 140 is separated into a saturated liquid and a saturated gas, and the flash gas is transferred to the second heat exchanger 180, and the saturated liquid is transferred to the storage tank 100. It provides a configuration of the partial liquefaction apparatus of the boil-off liquefied natural gas for ships comprising a liquid separator (160).

On the other hand, the first heat exchanger 170, the compressed high-pressure compressed gas flowing through the second passage 200 by using the cold heat of -130 ℃ BOG boil-off gas discharged from the storage tank 100 It is characterized by cooling.

The precooler 120 cools the high pressure compressed gas discharged through the compressor 130 to −25 to −30 ° C., and the freezer 110 used may include an ammonia freezer, an R134a freezer, and an R508 freezer. It is possible to selectively use any one of the commonly used refrigerators.

On the other hand, the second heat exchanger 180, by using the flash gas of -162 ℃ discharged from the liquid separator 160, characterized in that for cooling the compressed gas flowing through the first flow passage (190). do.

In addition, the pressure of the high pressure compressed gas of 300 bar state through the pressure-expansion expansion valve 140 to the saturated liquid state and the saturated gas state of the atmospheric pressure state, and then the liquid gas through the liquid separator 160 is stored in the storage To the tank 100, the flash gas in the gas state is characterized in that separated and transported to the second heat exchanger (180) side.

In detail, as shown in FIG. 4, the BOG partial reliquefaction apparatus includes an LNG storage tank 100, a refrigerator 110, a precooler 120, a compressor 130, and a reduced pressure expansion valve of a vessel in which LNG is stored. 140, the liquid separator 160, the first heat exchanger 170, the second heat exchanger 180 is provided.

First, referring to FIG. 4, the BOG partial reliquefaction process according to an exemplary embodiment of the present invention, the BOG gas discharged from the storage tank 100 passes through one point in a state of about −130 ° C. 1 atm. After being introduced into the first heat exchanger 170, while passing through the compressor 130, it is compressed and discharged into a high pressure gas of 300 bar of approximately 30 ℃.

At this time, the high pressure gas discharged to the compressor 130 is branched to the first flow passage 190 and the second flow passage 200 in the branch 210 and transferred. At this time, the ratio of the high pressure gas branched from the branch 210 to the first passage 190 and the second passage 200 is generally divided into a ratio of 6: 4, but according to the adjustment of the system configuration. At the level of those skilled in the art, the ratio is an adjustable part.

At this time, the second flow path 200 is introduced into the first heat exchanger 170, the high-pressure gas is introduced through the heat exchange with BOG gas of -130 ℃ in the first heat exchanger 170, -124.5 ℃ Pass 300 "at 300 bar.

Meanwhile, the gas branched into the first flow passage 190 flows into the precooler 120, and the high pressure gas that has undergone the precooling process in the precooler 120 is identified as 300 bar at −25 ° C. at the 5 ′ point. do. At this time, the refrigerator 110 constituting the precooler 120 is generally applied to the configuration of a general freezer used in the market, as an embodiment that any one of the ammonia freezer, R134a freezer and R508 freezer is selectively used. It is possible.

Next, the pre-cooled high pressure gas in a state of 300 bar at -25 ° C in the precooler 120 flows into the second heat exchanger 180. At this time, the high-pressure gas that is secondarily cooled in the second heat exchanger 180 passes through the 6 'point at about -66 ° C and 300 bar.

The high pressure gas cooled in each of the first flow passage 190 and the second flow passage 200 is joined again at six points and flows into the decompression expansion valve 140. Through the reduced pressure expansion valve 140 to the atmospheric pressure expansion through the reduced pressure, 1 bar -161.7 ℃ state of the liquid and gas in the mixed state is passed through 7 points.

The liquid LNG passes through the seven points and the liquid gas is separated from the liquid separator 160 to be transferred to the storage tank 100 side, and the flash gas is transferred to the second heat exchanger 180. After transported to the side and used in the second cooling process, it is used as fuel of the boiler.

Through the above process, when the liquefied gas partial reliquefaction apparatus of liquefied natural gas for ships according to an embodiment of the present invention, the system for building a high efficiency of the re-liquefaction of BOG gas up to 55 to 60% You can build

Meanwhile, the high pressure BOG gas (methane gas 90%, nitrogen gas 3%) of 250 to 300 bar discharged from the compressor 130 is separated into two flow paths. The high pressure gas flow of the first flow passage 190 is pre-cooled to -25 to 30 ℃ by the precooler 120 which is the evaporator of the refrigerating device.

In this case, as the refrigerating apparatus that can be applied to the precooler 120, all the refrigerating apparatuses used in general land such as ammonia, R134a, and R508 freezers may be applied. On the other hand, the pre-cooled high-pressure evaporated gas is further cooled by a flash gas of -162 ℃ which is a saturated gas discharged from the liquid separator 160 in the second heat exchanger (180).

On the other hand, the high pressure gas of the second flow path 200 is cooled after heat exchange in the second heat exchanger 170 and BOG of -130 ℃ vaporized from the storage tank 100 and the high pressure gas of the first flow passage 190 and To join. The cooled gas is expanded to atmospheric pressure in the reduced pressure expansion valve 140 to obtain a saturated liquid and a saturated gas, respectively.

The liquid and gas are separated in the liquid separator 160, the liquefied LNG is injected into the tank 100 and stored again, and the separated flash gas is separated to the second heat exchanger 180 side. It is used to provide cooling heat. At this time, the liquid and gas composition of the liquid separator 160, the liquid is 100% pure methane, the flash gas is a portion of the methane gas and the total amount of nitrogen that is not liquefied.

On the other hand, when the flash gas having a high nitrogen content which is not liquefied is coalesced with BOG, it causes a lower liquefaction rate. Therefore, the flash gas is used to remove the condensation heat of the condenser (not shown) of the refrigerator 110 after undergoing a heat exchange process using the retained cooling heat, or discharged outside the process to be used as a boiler fuel or a compressor as necessary. Can flow into the 130.

At this time, if the low temperature of the flash gas is used to remove the heat of condensation of the refrigerator 110, the condensation temperature is significantly lowered, thereby reducing the power consumption of the compressor 130 of the refrigerating device.

 The precooler 120 may be composed of one or a plurality of refrigerators 110, heat exchangers, depending on the capacity, and formed by forming a plurality of branches of more than two flow paths in order to maximize the low temperature by process. It is possible to do

This can be applied when reliquefying the BOG of large long-haul LNG carriers, LNG bunkering offshore or vessels fueled by LNG.

As described above, in the present embodiment, instead of the conventional partial reliquefaction process having a low reliquefaction yield, the compressed gas is branched. The use of cold heat greatly improves the heat exchange efficiency, and the reliquefaction rate of BOG generated by the application of refrigeration precooling equipment can be expected to increase significantly from 55 to 60% from the existing 40 to 50% level.

As mentioned above, although embodiment of this invention was described, the person of ordinary skill in the pertinent art can add, change, delete or add a component within the range which does not deviate from the idea of this invention described in a claim. The present invention may be modified and changed in various ways. This will also be included within the scope of the invention.

Claims (4)

1. Evaporation of boil-off-gas (BOG) generated in the LNG storage tank 100 for ships, reliquefaction of the compressed boil-off gas and storage of the re-liquefied boil-off gas In the gas partial reliquefaction apparatus,

   A storage tank 100 in which LNG is stored;

   A first heat exchanger 170 for exchanging heat by using cold heat of a low temperature BOG boil-off gas discharged from the storage tank 100;

   A compressor (130) for compressing the evaporated gas introduced through the first heat exchanger (170) into a high pressure gas of 250 to 300 bar;

   Branching portion consisting of a second flow path 200 for transferring the high pressure gas discharged to the compressor 130 to the first heat exchanger 170, and a first flow path 190 for transferring to the precooler 120 ( 210;

   A precooler (120) for cooling the high pressure gas discharged to the first flow passage (190) to -25 to -30 ° C at 300 bar;

   A second heat exchanger 180 for further cooling the high pressure gas discharged through the precooler 120 using a flash gas of −162 ° C .;

   After coalescing the compressed gas cooled through the second heat exchanger 180 of the first flow passage 190 and the first heat exchanger 170 of the second flow passage 200, it expands by depressurizing to atmospheric pressure. Pressure reducing expansion valve 140 to be made;

   The evaporated gas decompressed by the pressure reducing expansion valve 140 is separated into a saturated liquid and a saturated gas, and the flash gas is transferred to the second heat exchanger 180, and the saturated liquid is transferred to the storage tank 100. Evaporation gas partial reliquefaction apparatus of the liquefied natural gas for ships comprising a liquid separator (160).
2. The method of claim 1,

   The first heat exchanger 170,

   Cooling the compressed high pressure compressed gas introduced through the second flow passage 200 by using the cold heat of the -130 ℃ BOG gas discharged from the storage tank 100,

   The second heat exchanger 180,

   Evaporative gas partial reliquefaction apparatus of liquefied natural gas for ships, characterized in that for cooling the compressed gas flowing through the first passage 190 by using a flash gas of -162 ℃ discharged from the liquid separator 160 .
3. The method of claim 1,

   The precooler 120,

   The high pressure compressed gas discharged through the compressor 130 is cooled to −25 to −30 ° C., and the refrigerant 110 used may be any one of an ammonia freezer, an R134a freezer, and an R508 freezer. Evaporative gas partial reliquefaction apparatus of liquefied natural gas for ships.
4. The method of claim 1,

   After depressurizing the high-pressure compressed gas of 300 bar state to the saturated liquid state and the saturated gas state of the atmospheric pressure state through the reduced pressure expansion valve 140, and the liquid gas through the liquid separator 160 is the storage tank ( 100), the gaseous flash gas is part of the liquefied natural gas for ship boil-off gas reliquefaction apparatus, characterized in that separated and transported to the second heat exchanger (180) side.

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