JP2018128038A - Boil-off gas recovery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boil-off gas recovery system that can restrain performance deterioration of a heat exchanger in a reliquefying system for boil-off gas.SOLUTION: A boil-off gas recovery system 1 comprises: a tank 2 that stores liquefied gas 100; a reciprocating compressor 3 to which poly-α-olefin lubricating oil is supplied, and that compresses boil-off gas 100A generated by evaporation of a portion of the liquefied gas 100 in the tank 2; a separator 14 that separates the poly-α-olefin lubricating oil included in the boil-off gas discharged from the compressor 3; and a reliquefying system 9 that comprises a heat exchanger that cools the boil-off gas from which the poly-α-olefin lubricating oil has been separated by the separator 14, by exchanging heat with the boil-off gas to be supplied to the compressor 3 from the tank 2, and that returns the liquefied boil-off gas to the tank 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a boil-off gas recovery system.

  In a liquefied natural gas carrier, boil-off gas is generated when the liquefied natural gas stored in the tank is vaporized by heat entering from the outside during marine transportation. This boil-off gas is effectively used as fuel for the engine, steam boiler or generator in the ship, and surplus gas is returned to the tank after being reliquefied. As described above, as a technique for re-liquefying the boil-off gas generated in the tank and returning it to the tank, a boil-off gas recovery system described in Patent Document 1 below is known.

  As shown in FIG. 7, the boil-off gas recovery system disclosed in Patent Document 1 below compresses boil-off gas generated in the tank 11 with an oil supply type compressor 15, and a part of the compressed boil-off gas is a heat exchanger. The liquid is liquefied again through cooling by 14 and expansion by the expansion valve 17, and then returned to the tank 11. Here, the boil-off gas discharged from the compressor 15 may be mixed with lubricating oil used in the compressor 15. For this reason, in the boil-off gas recovery system of Patent Document 1 below, a filter for removing oil contained in the boil-off gas is arranged in the second pipe 16.

JP2015-158263A

  The boil-off gas recovery system of Patent Document 1 is configured to remove oil contained in the boil-off gas with a filter. However, vaporous oil may pass through the filter. For this reason, it is difficult to sufficiently remove the vapor-like oil. For this reason, the oil component that has passed through the filter solidifies and precipitates in the flow channel of the heat exchanger 14, thereby narrowing the flow channel, and as a result, there is a problem that the heat exchange performance is significantly reduced.

  This invention is made | formed in view of the said subject, The objective is to provide the boil-off gas collection | recovery system which can suppress the performance fall of the heat exchanger in the reliquefaction system of boil-off gas.

  The boil-off gas recovery system according to one aspect of the present invention is generated by evaporation of a part of the liquefied gas in the tank while the tank storing the liquefied gas and the poly-α-olefin-based lubricating oil are supplied. A reciprocating compressor that compresses boil-off gas, an oil separator that separates the poly-α-olefin-based lubricant contained in the boil-off gas discharged from the compressor, and the poly separator by the oil separator. A heat exchanger that cools the boil-off gas from which the α-olefin-based lubricating oil has been separated by heat exchange with the boil-off gas supplied from the tank to the compressor, and the liquefied boil-off gas is A reliquefaction system that returns to the tank.

  The boil-off gas recovery system includes a compressor to which poly-α-olefin-based lubricating oil is supplied. The poly-α-olefin-based lubricating oil has a significantly lower vapor pressure than the mineral oil-based lubricating oil generally used in reciprocating compressors. For this reason, the amount of vapor-like oil contained in the boil-off gas discharged from the compressor can be greatly reduced compared to a boil-off gas recovery system equipped with a reciprocating compressor using mineral oil-based lubricating oil. It becomes possible. Therefore, by separating the mist or liquid oil contained in the boil-off gas after compression by the oil separator, the amount of oil flowing into the heat exchanger in the reliquefaction system can be greatly reduced. Therefore, since the precipitation of oil in the flow path of the heat exchanger is suppressed, it is possible to suppress the performance deterioration of the heat exchanger.

  The boil-off gas recovery system may further include a reuse system that returns the poly-α-olefin-based lubricating oil separated by the oil separator to the compressor.

  According to this configuration, the cost can be reduced by reusing the poly-α-olefin-based lubricating oil. In particular, since poly-α-olefin-based lubricating oil is expensive, the effect of cost reduction by providing a reuse system is remarkable.

  As is apparent from the above description, according to the present invention, it is possible to provide a boil-off gas recovery system capable of suppressing the performance deterioration of the heat exchanger in the boil-off gas reliquefaction system.

It is a figure showing typically composition of a boil off gas recovery system concerning Embodiment 1 of the present invention. It is a figure which shows typically the structure of the reliquefaction system provided in the said boil-off gas collection | recovery system. It is a figure which shows typically the structure of the reuse system provided in the said boil-off gas collection | recovery system. It is a figure which shows typically the structure of the boil off gas recovery system which concerns on other embodiment of this invention. It is a figure which shows typically the structure of the boil off gas recovery system which concerns on other embodiment of this invention. It is a figure which shows typically the structure of the boil off gas recovery system which concerns on other embodiment of this invention. It is a figure which shows typically the structure of the boil off gas collection | recovery system in a prior art example.

  Hereinafter, a boil-off gas recovery system according to an embodiment of the present invention will be described in detail based on the drawings.

(Embodiment 1)
First, a boil-off gas recovery system 1 according to Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram illustrating a boil-off gas recovery system 1 according to the first embodiment. FIG. 2 is a schematic configuration diagram showing the reliquefaction system 9 in the boil-off gas recovery system 1 according to the first embodiment. FIG. 3 is a schematic configuration diagram showing a reuse system 50 in the boil-off gas recovery system 1 according to the first embodiment.

<Overall configuration of boil-off gas recovery system>
The boil-off gas recovery system 1 is installed in a ship that carries liquefied gas such as liquefied natural gas. As shown in FIG. 1, the boil-off gas recovery system 1 includes a tank 2, a compressor group 3, a cooler 51, a separator 14 (oil separator), a reliquefaction system 9, and a reuse system 50. Are mainly provided with pipes for connecting the constituent elements to each other and various control valves provided in the respective pipes.

  The tank 2 stores liquefied gas 100 such as liquefied natural gas. The liquefied natural gas is stored in the tank 2 at a temperature of about −160 ° C. In the tank 2, the boil-off gas 100 </ b> A is generated by evaporating a part of the liquefied gas 100 due to heat intrusion from the outside. In addition, the tank 2 is not limited to what stores liquefied natural gas, For example, you may store other types of liquefied gas 100, such as liquefied petroleum gas.

  The compressor group 3 is connected to the tank 2 via the first pipe 4. The boil-off gas 100A generated in the tank 2 passes through the first pipe 4 and is supplied to the compressor group 3. The compressor group 3 includes an oil-free compressor 3a that does not require lubricating oil, and an oil-supplying compressor 3b that requires lubricating oil. The oil-free and oil-provided compressors 3 a and 3 b compress the boil-off gas 100 </ b> A generated by evaporation of a part of the liquefied gas 100 in the tank 2. The oil supply type compressor 3b is arrange | positioned in the back | latter stage of the oilless type compressor 3a. The oil-free compressor 3a may be omitted.

  The oil-free compressor 3a has two compression stages 3aa. The oil supply type compressor 3b has three compression stages 3bb. The number of compression stages can be set according to the type of the liquefied gas 100 so that the boil-off gas can be increased to a pressure necessary for reliquefaction. Therefore, the number of compression stages is not limited to the five stages in the present embodiment, but may be four stages or less, or may be six stages or more.

  Each of the oil-free and oil-provided compressors 3a and 3b is a reciprocating compressor (reciprocating compressor). That is, the compressors 3a and 3b are configured to increase the pressure of the boil-off gas sucked into the cylinder through the suction port by the reciprocating motion of the piston and to discharge the boosted boil-off gas from the discharge port. A cylinder valve is provided at each of the suction port and the discharge port.

  A poly-α-olefin (PAO) -based lubricating oil is supplied to the oil supply type compressor 3b. The poly-α-olefin-based lubricating oil has a narrow molecular weight distribution and a much lower vapor pressure than the mineral oil-based lubricating oil generally used in reciprocating compressors. That is, the poly-α-olefin-based lubricating oil has significantly fewer vapor components than the mineral oil-based lubricating oil. Lubricating oil used in the compressor 3b can be mixed into the boil-off gas discharged from the oil supply type compressor 3b. However, by using a poly-α-olefin-based lubricating oil with a small amount of vapor components, the amount of vapor-like oil contained in the boil-off gas discharged from the oil supply type compressor 3b can be greatly reduced.

  The poly-α-olefin-based lubricating oil contains a base oil made of poly-α-olefin or a hydride thereof, and various additives. The poly-α-olefin is an oligomer or polymer obtained by polymerizing a linear α-olefin having a double bond at the terminal (α position) as a raw material. Poly-α-olefins are synthetic lubricating oils characterized by a high viscosity index and a low pour point.

  As a monomer used for polymerization of poly-α-olefin, for example, an α-olefin having 3 to 20 carbon atoms can be used, and an α-olefin having 8 to 12 carbon atoms can be used. Is preferred. Specifically, as α-olefin, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1- Examples include pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nanodecene, and 1-eicocene. In particular, an α-olefin selected from the group consisting of 1-octene, 1-decene and 1-dodecene is preferable, and 1-decene is more preferable from the viewpoint of the balance of viscosity index, low temperature fluidity and low evaporation.

  The cooler 51 cools the boil-off gas compressed by the compressors 3a and 3b, and is disposed at the subsequent stage of the compressors 3a and 3b. The cooler 51 cools the boil-off gas by heat exchange using seawater, for example. By cooling with the cooler 51, the temperature of the boil-off gas supplied to the engine 6 or the like can be adjusted to a predetermined temperature. At this time, the vapor-like oil contained in the boil-off gas can be condensed.

  The separator 14 separates the liquid (mist-like) poly-α-olefin-based lubricating oil contained in the boil-off gas discharged from the compressor 3 b and is disposed at the rear stage of the cooler 51. The separator 14 is connected to the compressor 3 b through the second pipe 5. A cooler 51 is provided in the middle of the second pipe 5. As shown in FIG. 1, the separator 14 includes a main body portion 25 having a cylindrical shape, and a small diameter portion 26 having a cylindrical shape smaller in diameter than the main body portion 25 and disposed in the main body portion 25. ing. The outer surface of the small diameter portion 26 is configured in a mesh shape.

  The boil-off gas cooled by the cooler 51 passes through the second pipe 5 and flows into the small diameter portion 26 from the upper end side of the small diameter portion 26 of the separator 14. Then, as shown by a broken line in FIG. 1, the boil-off gas flows in the small diameter portion 26 from the upper end toward the lower end, and then passes through the mesh on the outer surface of the small diameter portion 26. At this time, the mist-like lubricating oil contained in the boil-off gas does not pass through the mesh and accumulates at the bottom of the small diameter portion 26. The boil-off gas passes through the mesh of the small diameter portion 26 and then flows out of the separator 14 from a gas outlet provided on the side surface of the main body portion 25. Thus, by using the mesh structure of the small diameter portion 26, the lubricating oil contained in the boil-off gas can be separated. The oil accumulated at the bottom of the small diameter portion 26 hangs down to the bottom of the main body portion 25 through the mesh hole (reference numeral 101 in FIG. 1). Further, the separator 14 is provided with a level sensor 24 that detects whether or not the liquid level of the oil component 101 accumulated at the bottom of the main body 25 exceeds a predetermined reference height.

  One end of a gas outlet pipe 5 </ b> A is connected to the gas outlet of the separator 14. As shown in FIG. 1, the gas outlet pipe 5A is branched into three at the first portion 5AA. Each branch pipe is connected to the engine 6, the gas combustion device 7, and the generator 8. As a result, the boil-off gas from which the liquid oil has been removed by the separator 14 can be supplied to the engine 6, the gas combustion device 7, and the generator 8. Each branch pipe may be provided with a control valve (not shown). By controlling the opening and closing of these control valves, the amount of boil-off gas supplied to the engine 6, the gas combustion device 7 and the generator 8 can be adjusted.

  The engine 6 generates a propulsion force of the ship by burning the supplied boil-off gas. The generator 8 generates electric power necessary for driving various devices of the ship by generating electric power using the supplied boil-off gas as fuel. When the amount of boil-off gas generated exceeds the amount required as fuel for the engine 6 and the generator 8, the gas combustion device 7 burns excess boil-off gas and safely processes it.

<Reliquefaction system>
Next, the reliquefaction system 9 provided in the boil-off gas recovery system 1 will be described with reference mainly to FIG. 1 and FIG. The reliquefaction system 9 cools and expands the boil-off gas whose pressure has been increased by the compressors 3a and 3b and reliquefies it. The reliquefaction system 9 includes a third pipe 10, a heat exchanger 16, a fourth pipe 17, an expansion valve 18, a gas-liquid separator 19, a fifth pipe 21, and a sixth pipe 20. Have.

  The third pipe 10 has one end connected to the second part 5AB located upstream of the first part 5AA in the gas outlet pipe 5A and the other end connected to the heat exchanger 16. . Thus, the boil-off gas from which the liquid oil component has been separated by the separator 14 passes through the gas outlet pipe 5A, flows into the third pipe 10 from the second portion 5AB, and is supplied to the heat exchanger 16. As shown in FIG. 1, a first control valve 29 is provided in the third pipe 10, and the amount of boil-off gas flowing into the third pipe 10 from the gas outlet pipe 5A by controlling the opening and closing of this valve. Can be adjusted.

  The heat exchanger 16 cools the boil-off gas to a liquefiable temperature (for example, −100 ° C.). As shown in FIG. 2, the heat exchanger 16 has a liquid oil component (poly-α-olefin-based lubricating oil) by the low temperature side passage 16 a through which the boil-off gas sent from the tank 2 to the compressor 3 passes and the separator 14. And a high temperature side passage 16b through which the separated boil-off gas passes.

  The heat exchanger 16 is a boil-off gas (boil-off gas that passes through the low-temperature side passage 16a) supplied from the tank 2 to the compressor 3 and a boil-off gas from which liquid oil is separated by the separator 14 (through the high-temperature side passage 16b). Heat exchange with the boil-off gas). By this heat exchange, the boil-off gas passing through the high temperature side passage 16b is cooled. At this time, a part of the boil-off gas may be liquefied. Further, the boil-off gas passing through the low temperature side passage 16a is heated from −160 ° C. to −50 ° C., for example.

  As shown in FIG. 2, the 1st piping 4 is connected to the entrance and exit of the low temperature side channel | path 16a. The other end of the third pipe 10 is connected to the inlet of the high temperature side passage 16b. One end of the fourth pipe 17 is connected to the outlet of the high temperature side passage 16b.

  The fourth pipe 17 has one end connected to the heat exchanger 16 and the other end connected to the gas-liquid separator 19. The expansion valve 18 expands the boil-off gas cooled in the heat exchanger 16 to reduce the pressure, and is provided in the fourth pipe 17. A part of the boil-off gas is liquefied by the expansion valve 18.

  The gas-liquid separator 19 separates the boil-off gas partially liquefied by the heat exchanger 16 and the expansion valve 18 into a liquid component and a gas component. One end of the fifth pipe 21 and one end of the sixth pipe 20 are connected to the gas-liquid separator 19.

  The sixth pipe 20 has one end connected to the bottom of the gas-liquid separator 19 and the other end connected to the tank 2. Thereby, the liquid component of the boil-off gas separated in the gas-liquid separator 19 can be returned to the tank 2 via the sixth pipe 20.

  The fifth pipe 21 connects the gas-liquid separator 19 and the first pipe 4 to each other, and connects the gas-liquid separator 19 and the gas combustion device 7 to each other. More specifically, the fifth pipe 21 branches into two branch pipes 21A and 21B at the first portion 21AA. One branch pipe 21 </ b> A is connected to the first pipe 4 on the outlet side of the heat exchanger 16, and the other branch pipe 21 </ b> B is connected to the gas combustion device 7. Thereby, the gas component of the boil-off gas separated in the gas-liquid separator 19 can be caused to flow into the first pipe 4 and the gas combustion device 7 via the fifth pipe 21.

  As shown in FIG. 2, each branch pipe 21A, 21B is provided with a second control valve 31 and a third control valve 30, respectively. With these valves, the opening degree of the boil-off gas flow path in each of the branch pipes 21A and 21B can be adjusted. Thereby, the amount of boil-off gas flowing into the first pipe 4 side and the amount flowing into the gas combustion device 7 side can be adjusted.

<Reuse system>
Next, the reuse system 50 provided in the boil-off gas recovery system 1 will be described with reference mainly to FIGS. The reuse system 50 returns the liquid lubricating oil (poly-α-olefin-based lubricating oil) separated from the boil-off gas by the separator 14 to the oil-feeding compressor 3b. As shown in FIG. 3, the reuse system 50 includes a first oil pipe 52, a fourth control valve 52A, a strainer 53, an oil tank 54, an oil supply source 55, a second oil pipe 57, an oil The pump 56, the lubricator 55, and a plurality of (three in this embodiment) third oil pipes 55A, 55B, and 55C are mainly included.

  The first oil pipe 52 has one end connected to the bottom of the main body 25 in the separator 14 and the other end connected to the top of the oil tank 54. The first oil pipe 52 is provided with a fourth control valve 52A and a strainer 53. As shown in FIG. 3, the strainer 53 is provided downstream of the fourth control valve 52A.

  By opening the fourth control valve 52A, the lubricating oil accumulated at the bottom of the separator 14 (main body portion 25) can be caused to flow into the first oil pipe 52. The fourth control valve 52A may be configured to open when the level sensor 24 detects that the liquid level of the oil component 101 exceeds a predetermined reference height. Further, by allowing the lubricating oil to pass through the strainer 53, foreign matters contained in the lubricating oil can be removed.

  The oil tank 54 stores the lubricating oil from which foreign matter has been removed by the strainer 53. An oil supply source 55 for supplying unused poly-α-olefin-based lubricating oil is connected to the oil tank 54. Thereby, the amount of lubricating oil in the oil tank 54 can be adjusted by adding unused lubricating oil from the oil supply source 55 to the lubricating oil recovered by the separator 14.

  The second oil pipe 57 has one end connected to the lower part of the oil tank 54 and the other end connected to the inlet of the lubricator 55. An oil pump 56 is provided in the middle of the second oil pipe 57. By operating the oil pump 56, the lubricating oil stored in the oil tank 54 can be supplied to the lubricator 55 via the second oil pipe 57.

  The lubricator 55 supplies lubricating oil to the oil supply type compressor 3b. The lubricator 55 is configured to be operated by a motor 55D. The oiling device 55 has a plurality of (three in this embodiment) outlets, and one ends of third oil pipes 55A, 55B, and 55C are connected to the outlets. The other ends of the third oil pipes 55A, 55B, and 55C are connected to the compression stage 3bb, respectively. The number of outlets and the number of third oil pipes in the lubricator 55 are the same as the number of compression stages in the oil supply type compressor 3b. Accordingly, the lubricating oil can be supplied from the lubricator 55 to the oil supply type compressor 3b through the third oil pipes 55A, 55B, and 55C. In this way, the poly-α-olefin-based lubricating oil recovered by the separator 14 can be returned to the oil-feeding compressor 3b and reused as the piston lubricating oil.

<Effect>
Next, a characteristic configuration and operational effects of the boil-off gas recovery system 1 according to Embodiment 1 will be described.

  The boil-off gas recovery system 1 includes a tank 2 that stores a liquefied gas 100, a poly-α-olefin-based lubricating oil, and a boil-off gas 100A generated by evaporation of a part of the liquefied gas 100 in the tank 2. A reciprocating compressor 3b that compresses the oil, a separator 14 (oil separator) that separates mist-like poly-α-olefin-based lubricating oil contained in the boil-off gas discharged from the compressor 3b, and a separator 14 A liquefied boil-off gas having a heat exchanger 16 that cools the boil-off gas from which the mist-like poly-α-olefin-based lubricating oil has been separated by heat exchange with the boil-off gas supplied from the tank 2 to the compressor 3. And a reliquefaction system 9 for returning the water to the tank 2.

  The boil-off gas recovery system 1 includes a compressor 3b to which a poly-α-olefin-based lubricating oil is supplied. The poly-α-olefin-based lubricating oil has a much lower vapor pressure than the mineral oil-based lubricating oil generally used in reciprocating compressors. For this reason, compared with the boil-off gas recovery system provided with the reciprocating compressor in which mineral oil type lubricating oil is used, the quantity of the vapor-like oil content contained in the boil-off gas discharged from the compressor 3b is reduced significantly. Can do. Therefore, by separating the mist or liquid oil contained in the boil-off gas after compression by the separator 14, the amount of oil flowing into the heat exchanger 16 of the reliquefaction system 9 can be greatly reduced. Therefore, since the precipitation of oil in the flow path of the heat exchanger 16 is suppressed, it is possible to suppress the performance deterioration of the heat exchanger 16.

  Further, according to the boil-off gas recovery system 1, oil precipitation in the fourth pipe 17 located on the downstream side of the heat exchanger 16 can also be suppressed. If the oil component solidifies and precipitates in the fourth pipe 17, the oil component that is in a liquid state at room temperature may flow downstream along with the boil-off gas and mix into the tank 2 when the system is restarted. There is sex. On the other hand, according to the boil-off gas recovery system 1, the oil content in the fourth pipe 17 can also be suppressed, so that the oil content in the tank 2 can also be prevented.

  The boil-off gas recovery system 1 includes a reuse system 50 that returns the poly-α-olefin-based lubricating oil separated by the separator 14 to the compressor 3b. Costs can be reduced by reusing the poly-α-olefin-based lubricating oil by the reuse system 50. In particular, since the poly-α-olefin-based lubricating oil is expensive, the effect of cost reduction by providing the reuse system 50 is remarkable.

(Other embodiments)
Finally, other embodiments of the present invention will be described.

  In the first embodiment, the case where the boil-off gas recovery system 1 includes the lubricating oil reuse system 50 has been described. However, the present invention is not limited to this. As shown in FIG. 4, a boil-off gas recovery system 1 </ b> A in which a lubricating oil reuse system is omitted may be used.

  In the boil-off gas recovery system 1 according to the first embodiment, the cooler 51 may be omitted.

  In the first embodiment, as an example of the oil separator, the case where the lubricant oil is separated from the boil-off gas using the separator 14 having the small-diameter portion 26 whose outer surface is configured in a mesh shape has been described. It is also possible to separate the lubricating oil. For example, an oil separator using a baffle plate or an oil separator by centrifugation may be used.

  In the first embodiment, the configuration in which the boil-off gas after passing through the final compression stage 3bb is guided to the reliquefaction system 9 has been described, but the present invention is not limited to this. As shown in FIG. 5, the 3rd piping 10 in the reliquefaction system 9 may be connected between compression stages 3bb in the oil supply type compressor 3b. In this case, the cooler 51 and the separator 14 are also disposed between the compression stages 3bb. Thereby, the boil-off gas extracted from the middle stage of the compressor 3b can be guided to the reliquefaction system 9.

  In the first embodiment, the case where the third oil pipes 55A, 55B, and 55C for returning the lubricating oil separated from the boil-off gas is directly connected to the oil supply type compressor 3b is described, but the present invention is not limited to this. As shown in FIG. 6, each of the third oil pipes 55A, 55B, 55C may be connected between the compression stages 3aa, 3bb. According to this configuration, the power required to pump the lubricating oil can be made smaller than when the third oil pipes 55A, 55B, and 55C are directly connected to the oil supply type compressor 3b.

  Like the reuse system 50 in the first embodiment, the configuration is not limited to the configuration in which the lubricating oil recovered by the separator 14 and the unused lubricating oil are mixed and then supplied to the oil supply type compressor 3b. The structure which supplies separately the lubricating oil and unused lubricating oil to the compressor 3b may be sufficient. Alternatively, the lubricating device 55 may be omitted, and the lubricating oil may be directly supplied from the oil tank 54 to the oil supply type compressor 3b by the oil pump 56.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Boil-off gas recovery system 2 Tank 3a, 3b Compressor 9 Reliquefaction system 14 Separator (oil separator)
16 Heat exchanger 50 Reuse system 100 Liquefied gas 100A Boil-off gas

Claims (2)

A tank storing liquefied gas;
A reciprocating compressor that compresses boil-off gas generated by evaporation of a part of the liquefied gas in the tank, while being supplied with poly-α-olefin-based lubricating oil;
An oil separator for separating the poly-α-olefin-based lubricating oil contained in the boil-off gas discharged from the compressor;
A heat exchanger that cools the boil-off gas from which the poly-α-olefin-based lubricating oil has been separated by the oil separator by heat exchange with the boil-off gas supplied from the tank to the compressor; A boil-off gas recovery system comprising: a re-liquefaction system that returns the liquefied boil-off gas to the tank.   2. The boil-off gas recovery system according to claim 1, further comprising a reuse system that returns the poly-α-olefin-based lubricating oil separated by the oil separator to the compressor.

Images