JP2018128039A - 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 3b to which 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 first separator 14 that separates the lubricating oil included in the boil-off gas discharged from the compressor 3b; an activated carbon filter 70 that adsorbs the lubricating oil included in the boil-off gas that has passed through the first separator 14; and a reliquefying system 9 that comprises a heat exchanger that cools the boil-off gas that has passed through the activated carbon filter 70, by exchanging heat with the boil-off gas to be supplied to the compressor 3b 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.

  In the boil-off gas recovery system of Patent Document 1 below, as shown in FIG. 9, the boil-off gas generated in the tank 11 is compressed by a refueling compressor 15, and a part of the compressed boil-off gas is 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, with this filter, it may be difficult to sufficiently remove the oil contained in the boil-off gas. 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 decreases.

  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.

  A boil-off gas recovery system according to an aspect of the present invention includes a tank that stores liquefied gas, and a reciprocating operation that compresses boil-off gas generated by evaporation of a part of the liquefied gas in the tank while being supplied with lubricating oil. A dynamic compressor, an oil separator that separates the lubricating oil contained in the boil-off gas discharged from the compressor, and the lubricating oil contained in the boil-off gas that has passed through the oil separator is adsorbed An adsorption filter; and a heat exchanger that cools the boil-off gas that has passed through the adsorption filter by heat exchange with the boil-off gas supplied from the tank to the compressor, and the liquefied boil-off gas is contained in the tank And a re-liquefaction system. The adsorption filter is preferably an activated carbon filter.

  In the boil-off gas recovery system, after the lubricating oil contained in the boil-off gas discharged from the compressor is separated by the oil separator, the lubricating oil contained in the boil-off gas can be further adsorbed by the adsorption filter. Thus, the amount of the lubricating oil contained in the boil-off gas can be greatly reduced by the two-stage operation of separating the lubricating oil by the oil separator and adsorbing the lubricating oil by the adsorption filter. For this reason, the inflow amount of the oil component to the heat exchanger in the reliquefaction system can be significantly 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. In particular, the activated carbon filter is preferable because of its high ability to adsorb lubricating oil.

  The boil-off gas recovery system may further include monitoring means for monitoring whether or not the lubricating oil is contained in the boil-off gas that has passed through the adsorption filter.

  According to this configuration, it can be confirmed whether or not the lubricating oil contained in the boil-off gas is sufficiently removed by the oil separator and the adsorption filter.

  The boil-off gas recovery system includes a differential pressure gauge that detects a pressure difference before and after the adsorption filter, and an alarm that generates an alarm when the pressure difference detected by the differential pressure gauge exceeds a predetermined reference value. May be further included.

  According to this configuration, since the arrival of the lifetime of the adsorption filter can be recognized by an alarm, the adsorption filter can be replaced quickly.

  The boil-off gas recovery system includes a level sensor that detects whether or not the liquid level of the lubricating oil in the oil separator exceeds a predetermined reference height, and the liquid level is the reference height. It may further comprise deriving means for deriving the lubricating oil to the outside of the oil separator when exceeding the limit, and a drain tank for storing the lubricating oil derived by the deriving means.

  According to this configuration, since the lubricating oil can be led out of the oil separator at the timing when the liquid level of the lubricating oil exceeds the reference height, maintenance management of the oil separator is easy.

  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 activated carbon filter in the said boil-off gas collection | recovery system. It is a figure which shows typically the structure of the reliquefaction system 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 Embodiment 2 of this invention. It is a figure which shows typically the structure of the boil off gas collection | recovery system which concerns on the modification of the said Embodiment 2. FIG. It is a figure which shows typically the structure of the boil off gas recovery system which concerns on Embodiment 3 of this invention. It is a figure which shows typically the structure of the boil off gas recovery system which concerns on Embodiment 4 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 illustrating the activated carbon filter 70 (adsorption filter) in the boil-off gas recovery system 1 according to the first embodiment. FIG. 3 is a schematic configuration diagram showing the reliquefaction system 9 in the boil-off gas recovery system 1 according to the first embodiment.

  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 first separator 14 (oil separator), an activated carbon filter 70 (adsorption filter), and a reliquefaction. The system 9 is mainly provided with a pipe for connecting these components to each other, and various control valves provided in each pipe.

  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 is supplied with 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 check valve is provided at each of the suction port and the discharge port.

  The cooler 51 cools the boil-off gas compressed by the compressors 3 a and 3 b, and is disposed at the rear stage of the compressor group 3. 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. The boil-off gas discharged from the compressor 3b can be mixed with lubricating oil used in the compressor 3b. On the other hand, the vapor-like lubricating oil (oil component) contained in the boil-off gas can be condensed by cooling in the cooler 51.

  The first separator 14 separates liquid or mist-like lubricating oil (lubricating oil used in the oil-feeding compressor 3b) contained in the boil-off gas discharged from the compressor 3b. Is arranged. The first separator 14 is connected to the compressor 3 b via the second pipe 5. A cooler 51 is provided in the middle of the second pipe 5. As shown in FIG. 1, the first 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. Have. 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 first 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 liquid or 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 flows out of the first separator 14 from a gas outlet provided on the side surface of the main body 25 after passing through the mesh of the small diameter portion 26. 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).

  The boil-off gas recovery system 1 stores a level sensor 24 provided in the first separator 14, a derivation means 80 for deriving the lubricating oil outside the first separator 14, and the lubricating oil derived by the derivation means 80. And a drain tank 90.

  The level sensor 24 detects whether or not the liquid level of the lubricating oil in the first separator 14 (main body part 25) exceeds a predetermined reference height. Specifically, the level sensor 24 has a pair of electrodes, and is configured such that when the liquid level of the lubricating oil reaches a reference height, the gap between the pair of electrodes is filled with the lubricating oil. At this time, the electrical resistance between the pair of electrodes changes. The level sensor 24 detects that the level of the lubricating oil in the first separator 14 exceeds a predetermined reference height by detecting the change in the electrical resistance.

  The deriving means 80 derives the lubricating oil out of the first separator 14 when the level of the lubricating oil in the first separator 14 exceeds the reference height. The derivation means 80 includes a drain pipe 82, a drain valve 81 provided in the drain pipe 82, and a control unit 83 that controls opening and closing of the drain valve 81.

  As shown in FIG. 1, the drain pipe 82 has one end connected to the bottom of the first separator 14 (main body portion 25) and the other end connected to the top of the drain tank 90. The control unit 83 receives from the level sensor 24 a detection signal indicating that the level of the lubricating oil in the first separator 14 has exceeded the reference height. The control unit 83 receives the detection signal and performs control to open the drain valve 81. Thereby, when the liquid level of the lubricating oil in the first separator 14 exceeds the reference height, the lubricating oil can be guided from the first separator 14 to the drain tank 90 via the drain pipe 82.

  The activated carbon filter 70 adsorbs lubricating oil contained in the boil-off gas that has passed through the first separator 14, and is disposed at the subsequent stage of the first separator 14. The activated carbon filter 70 is connected to the first separator 14 by a third pipe 70A. Thereby, the boil-off gas that has passed through the first separator 14 can be caused to flow into the activated carbon filter 70 via the third pipe 70A.

  FIG. 2 is a longitudinal sectional view showing a detailed configuration of the activated carbon filter 70. As shown in FIG. 2, the activated carbon filter 70 mainly includes a casing 71, a lid 73, an activated carbon cartridge 72, and fastening members 74 and 75. In the present embodiment, the activated carbon filter 70 is arranged in a posture (vertically placed) along the vertical direction. However, the attitude | position which arrange | positions the activated carbon filter 70 is not limited to this, You may arrange | position with the attitude | position (horizontal placement) along a horizontal direction.

  The casing 71 has a cylindrical shape that can accommodate the activated carbon cartridge 72 therein, and the upper end side is open. A gas inflow port 71 </ b> A for allowing the boil-off gas to flow into the casing 71 is provided substantially at the center of the bottom 71 </ b> C of the casing 71. The lid 73 has a disk shape substantially the same diameter as the casing 71, and is fixed to the upper end of the casing 71 by fastening members 74 and 75. A gas outlet 73A for allowing the boil-off gas to flow out to the outside is provided at the approximate center of the lid 73.

  The activated carbon cartridge 72 is accommodated in the casing 71 and can be taken out from the casing 71. Specifically, after removing the fastening members 74 and 75 and removing the lid 73 from the casing 71, the activated carbon cartridge 72 can be taken out from the upper end opening of the casing 71. In this way, the replacement work of the activated carbon cartridge 72 can be performed.

  The activated carbon cartridge 72 has a large number of particulate activated carbon particles 72A and an accommodating portion 72B that accommodates the activated carbon particles 72A. The activated carbon particles 72A can adsorb liquid or mist-like lubricating oil contained in the boil-off gas. As shown in FIG. 2, a space 71 </ b> B is provided between the activated carbon cartridge 72 and the bottom 71 </ b> C of the casing 71. By providing the space 71 </ b> B, the boil-off gas that has flowed into the casing 71 can flow into the entire activated carbon cartridge 72.

  The boil-off gas that has passed through the first separator 14 flows into the casing 71 from the gas inlet 71A. Then, the boil-off gas spreads in the radial direction in the space 71B and then passes through the activated carbon cartridge 72 as indicated by broken line arrows in FIG. At this time, the liquid or mist-like lubricating oil contained in the boil-off gas (the lubricating oil that could not be completely separated by the first separator 14) can be adsorbed on the activated carbon particles 72A. The boil-off gas passes through the activated carbon cartridge 72 and then flows out from the gas outlet 73A. Thus, by performing the operation of separating the lubricating oil by the first separator 14 and the operation of adsorbing the lubricating oil by the activated carbon filter 70, the amount of the lubricating oil contained in the boil-off gas can be significantly reduced.

  As shown in FIG. 1, the boil-off gas recovery system 1 further includes a differential pressure gauge 76 and an alarm generation unit 77. The differential pressure gauge 76 detects a pressure difference before and after the activated carbon filter 70. The alarm generation unit 77 generates an alarm when the pressure difference detected by the differential pressure gauge 76 exceeds a predetermined reference value. For example, the alarm generation unit 77 may be an audio type or a lighting type. Thereby, the pressure of the boil-off gas flowing into the activated carbon filter 70 (pressure of the boil-off gas upstream of the activated carbon filter 70) and the pressure of the boil-off gas flowing out of the activated carbon filter 70 (pressure of the boil-off gas downstream of the activated carbon filter 70). The alarm generation unit 77 can inform the operator that the time for replacement of the activated carbon cartridge 72 has come.

  One end of a gas outlet pipe 5A is connected to the gas outlet 73A of the activated carbon filter 70. 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. Thus, the boil-off gas that has passed through the activated carbon filter 70 can be supplied to the engine 6, the gas combustion device 7, and the generator 8, respectively.

  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.

  Next, the reliquefaction system 9 provided in the boil-off gas recovery system 1 will be described with reference mainly to FIGS. 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 fourth pipe 10, a heat exchanger 16, a fifth pipe 17, an expansion valve 18, a gas-liquid separator 19, a sixth pipe 21, and a seventh pipe 20. Have.

  The fourth 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 that has passed through the activated carbon filter 70 passes through the gas outlet pipe 5A, flows into the fourth pipe 10 from the second portion 5AB, and is supplied to the heat exchanger 16. As shown in FIG. 1, the fourth pipe 10 is provided with a first control valve 29. By controlling the opening and closing of the first control valve 29, the amount of boil-off gas flowing into the fourth pipe 10 from the gas outlet pipe 5A can be adjusted.

  The heat exchanger 16 cools the boil-off gas to a liquefiable temperature (for example, −100 ° C.). As shown in FIG. 3, the heat exchanger 16 includes a low-temperature side passage 16a through which boil-off gas sent from the tank 2 to the compressors 3a and 3b passes, and a high-temperature side passage 16b through which boil-off gas that has passed through the activated carbon filter 70 passes. And have.

  The heat exchanger 16 includes a boil-off gas (boil-off gas that passes through the low-temperature side passage 16a) supplied from the tank 2 to the compressors 3a and 3b, and a boil-off gas that passes through the activated carbon filter 70 (boil-off through the high-temperature side passage 16b). Heat exchange with 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. 3, the 1st piping 4 is connected to the entrance / exit of the low temperature side channel | path 16a. The other end of the fourth pipe 10 is connected to the inlet of the high temperature side passage 16b. One end of the fifth pipe 17 is connected to the outlet of the high temperature side passage 16b.

  The fifth 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 middle of the fifth pipe 17. A part of the boil-off gas is liquefied by the expansion valve 18.

  The gas-liquid separator 19 separates a partially liquefied boil-off gas into a liquid component and a gas component. One end of the sixth pipe 21 and one end of the seventh pipe 20 are connected to the gas-liquid separator 19.

  The seventh 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 seventh pipe 20.

  The sixth 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. Specifically, the sixth pipe 21 branches into two branch pipes 21A and 21B in the first part 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 sixth pipe 21.

  As shown in FIG. 3, 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.

  Here, the 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, a compressor 3b that is supplied with lubricating oil and compresses the boil-off gas, and a first separator 14 that separates lubricating oil contained in the boil-off gas discharged from the compressor 3b. And an activated carbon filter 70 that adsorbs lubricating oil contained in the boil-off gas that has passed through the first separator 14, and a heat exchanger 16 that cools the boil-off gas that has passed through the activated carbon filter 70. And a reliquefaction system 9 for returning to

  In the boil-off gas recovery system 1, after the lubricating oil contained in the boil-off gas discharged from the compressor 3 b is separated by the first separator 14, the lubricating oil contained in the boil-off gas can be further adsorbed on the activated carbon filter 70. it can. As described above, the amount of the lubricating oil contained in the boil-off gas can be greatly reduced by the two-stage operation of the separation of the lubricating oil by the first separator 14 and the adsorption of the lubricating oil by the activated carbon filter 70. Specifically, the concentration of the lubricating oil in the boil-off gas can be reduced to 0.5 ppm or less by the first separator 14 and further reduced to 0.1 ppm or less by the activated carbon filter 70. For this reason, the amount of oil flowing into the heat exchanger 16 in 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.

  The boil-off gas recovery system 1 includes a differential pressure gauge 76 that detects a pressure difference before and after the activated carbon filter 70, and an alarm generation unit 77 that generates an alarm when the pressure difference exceeds a predetermined reference value. I have. Thereby, since the arrival of the life of the activated carbon filter 70 can be recognized by an alarm, the replacement work of the activated carbon cartridge 72 can be performed quickly.

  The boil-off gas recovery system 1 includes a level sensor 24 that detects whether or not the liquid level height of the lubricating oil in the first separator 14 exceeds a predetermined reference height, and the liquid level height is the reference level. Deriving means 80 for deriving the lubricating oil out of the first separator 14 when exceeding the height, and a drain tank 90 for storing the lubricating oil derived by the deriving means 80 are provided. Accordingly, since the lubricating oil can be led out of the first separator 14 at a timing when the liquid level of the lubricating oil exceeds the reference height, maintenance management of the first separator 14 is easy.

(Embodiment 2)
Next, a boil-off gas recovery system 1A according to Embodiment 2 of the present invention will be described with reference to FIG. The boil-off gas recovery system 1A according to the second embodiment has basically the same configuration as the boil-off gas recovery system 1 according to the first embodiment, but the boil-off gas that has passed through the activated carbon filter 70 contains lubricating oil. It is different in that it further comprises monitoring means for monitoring whether or not it is. Only differences from the first embodiment will be described below. In FIG. 4, the configurations of the cooler 51 and the first separator 14 disposed between the compressor 3b and the activated carbon filter 70 are omitted.

  As shown in FIG. 4, the boil-off gas recovery system 1 </ b> A according to the second embodiment includes a monitoring unit 65. The monitoring unit 65 includes a second separator 60 disposed at the subsequent stage of the activated carbon filter 70, and a control unit 63 that controls the operation of the compressors 3a and 3b.

  More specifically, the boil-off gas recovery system 1A has a gas branch pipe 61 having one end connected to the third part 5AC upstream of the second part 5AB in the gas outlet pipe 5A. The other end of the gas branch pipe 61 is connected to the inlet of the second separator 60. Thereby, the boil-off gas that has passed through the activated carbon filter 70 can be supplied from the third portion 5AC to the gas branch pipe 61 and supplied to the second separator 60. The gas branch pipe 61 is provided with a fourth control valve 62. By controlling the opening and closing of the fourth control valve 62, the amount of boil-off gas flowing from the gas outlet pipe 5A into the gas branch pipe 61 can be adjusted.

  The second separator 60 has the same configuration as the first separator 14 described in the first embodiment. Therefore, according to the second separator 60, if the first separator 14 and the activated carbon filter 70 do not function sufficiently and the boil-off gas that has passed through the activated carbon filter 70 still contains liquid or mist-like lubricating oil, Can be separated. Therefore, whether or not a large amount of lubricating oil is contained in the boil-off gas flowing downstream of the activated carbon filter 70 depends on the amount of lubricating oil separated by the second separator 60 (the amount of lubricating oil accumulated at the bottom of the main body 25). Can be confirmed. That is, it can be confirmed whether or not the lubricating oil contained in the boil-off gas is sufficiently removed by the first separator 14 and the activated carbon filter 70 in the previous stage of the second separator 60.

  Similar to the first separator 14, the second separator 60 is provided with the level sensor 24. When the level sensor 24 detects that the level of the lubricating oil in the second separator 60 exceeds a predetermined reference height, a detection signal is transmitted to the control unit 63. In response to the detection signal, the control unit 63 performs control to stop the operations of the compressors 3a and 3b. That is, when the amount of lubricating oil separated by the second separator 60 reaches a predetermined amount, the control unit 63 stops the operations of the compressors 3a and 3b. Thereby, even when the lubricating oil in the boil-off gas is not sufficiently removed by the first separator 14 and the activated carbon filter 70 due to some cause (failure), the boil-off gas containing a large amount of the lubricating oil is reliquefied by the reliquefaction system 9. It can be prevented from flowing to the side.

  As shown in FIG. 4, the boil-off gas recovery system 1 </ b> A includes an eighth pipe 64 having one end connected to the gas outlet of the second separator 60 and the other end connected to the first pipe 4. Yes. Thereby, the boil-off gas which flowed out from the 2nd separator 60 can be returned to the front of the compressor 3a.

  Further, the gas branch pipe 61 may be omitted, and the second separator 60 may be disposed in the middle of the gas outlet pipe 5A as shown in FIG. Moreover, the monitoring means 65 may not be provided with the control part 63, and may be comprised only by the 2nd separator 60. FIG. In this case, the worker periodically checks the amount of the lubricating oil separated by the second separator 60, and when the separated amount of the lubricating oil exceeds a predetermined amount, the worker operates the compressors 3a and 3b. Stop manually.

(Embodiment 3)
Next, a boil-off gas recovery system 1B according to Embodiment 3 of the present invention will be described with reference to FIG. The boil-off gas recovery system 1B according to the third embodiment has basically the same configuration as the boil-off gas recovery system 1 according to the first embodiment, except that a plurality of first separators 14 and a plurality of activated carbon filters 70 are provided. Are different in that they are arranged in parallel. Hereinafter, only differences from the first embodiment will be described in detail.

  As shown in FIG. 6, a plurality (two in the present embodiment) of the first separators 14 are provided and arranged in parallel. Specifically, the second pipe 5 branches into two separator upstream pipes 131 and 132 at the site 5E. Each separator upstream pipe 131, 132 is connected to the inlet of the first separator 14. The third pipe 70 </ b> A has two separator downstream pipes 133 and 134 connected to the outlet of the first separator 14. The two separator downstream pipes 133 and 134 merge at the site 5F.

  The boil-off gas recovery system 1B includes separator switching means 110 that switches the supply of boil-off gas to the plurality of first separators 14. The separator switching means 110 includes on-off valves 111 and 112 provided before and after (upstream and downstream) of one first separator 14 (upper side in FIG. 6) and the other first separator 14 (lower side in FIG. 6). Open / close valves 113 and 114 provided in front of and behind. Separator switching means 110 may further include a controller for controlling these on-off valves 111-114.

  By controlling the on-off valves 111 to 114, the supply of boil-off gas to the plurality of first separators 14 can be switched. Specifically, the boil-off gas can be supplied only to the lower first separator 14 in FIG. 6 by closing the on-off valves 111 and 112 and opening the on-off valves 113 and 114. During this time, maintenance and inspection of the upper first separator 14 in FIG. 6 can be performed. On the other hand, the boil-off gas can be supplied only to the upper first separator 14 in FIG. 6 by opening the on-off valves 111 and 112 and closing the on-off valves 113 and 114.

  As shown in FIG. 6, the activated carbon filter 70 is provided in a plurality (two in the present embodiment) in the same manner as the first separator 14 and is arranged in parallel. Specifically, the third pipe 70A is branched into two filter upstream pipes 135 and 136 at the part 5G. The two filter upstream pipes 135 and 136 are connected to the inlet of the activated carbon filter 70. The gas outlet pipe 5 </ b> A has two filter downstream pipes 137 and 138 connected to the outlet of the activated carbon filter 70. The two filter downstream pipes 137 and 138 join at the part 5H.

  The boil-off gas recovery system 1 </ b> B has filter switching means 120 that switches supply of boil-off gas to the plurality of activated carbon filters 70. The filter switching means 120 includes open / close valves 121 and 122 provided before and after one activated carbon filter 70 (upper side in FIG. 6) and open / close valves provided before and after the other activated carbon filter 70 (lower side in FIG. 6). 123, 124. The filter switching means 120 may further include a controller that controls these on-off valves 121 to 124.

  By controlling the on-off valves 121 to 124, the supply of boil-off gas to the plurality of activated carbon filters 70 can be switched. Specifically, the boil-off gas can be supplied only to the lower activated carbon filter 70 in FIG. 6 by closing the on-off valves 121 and 122 and opening the on-off valves 123 and 124. In the meantime, the activated carbon cartridge 72 can be replaced with the activated carbon filter 70 on the upper side in FIG. On the other hand, the boil-off gas can be supplied only to the upper activated carbon filter 70 in FIG. 6 by opening the on-off valves 121 and 122 and closing the on-off valves 123 and 124.

  As described above, in the boil-off gas recovery system 1B according to the third embodiment, the plurality of first separators 14 and the plurality of activated carbon filters 70 are arranged in parallel, and means for switching the supply of boil-off gas to these is provided. ing. Thus, maintenance and inspection of the first separator 14 and replacement work of the activated carbon cartridge 72 can be performed while continuing the operation of the boil-off gas recovery system 1B.

  In the third embodiment, the case where two each of the first separator 14 and the activated carbon filter 70 are provided has been described, but three or more may be arranged in parallel. Only one of the first separator 14 and the activated carbon filter 70 may be arranged in parallel.

(Embodiment 4)
Next, a boil-off gas recovery system 1C according to Embodiment 4 of the present invention will be described with reference to FIG. The boil-off gas recovery system 1C according to the fourth embodiment has basically the same configuration as that of the boil-off gas recovery system 1 according to the first embodiment, except that a plurality of first separators 14 and a plurality of activated carbon filters 70 are provided. Are different in that they are arranged in series. Hereinafter, only differences from the first embodiment will be described in detail.

  As shown in FIG. 7, a plurality (two in the present embodiment) of the first separators 14 are provided and arranged in series. Moreover, the activated carbon filter 70 is provided with two or more (two in this embodiment), and is arrange | positioned in series. Thereby, the boil-off gas discharged from the compressor 3b can be passed through the first separators 14. Further, the boil-off gas that has passed through the first separator 14 can be passed through the plurality of activated carbon filters 70. Thereby, it becomes possible to further reduce the amount of lubricating oil contained in the boil-off gas.

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

  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. 8, the 4th 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, the first separator 14 and the activated carbon filter 70 are also arranged 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 gas inlet 71A is provided at the lower part of the activated carbon filter 70 and the gas outlet 73A is provided at the upper part of the activated carbon filter 70 has been described, but the present invention is not limited to this. A gas outlet may be provided at the lower part of the activated carbon filter 70, and a gas inlet may be provided at the upper part of the activated carbon filter 70.

  In the first to fourth embodiments, the differential pressure gauge 76 and the alarm generation unit 77 may be omitted. Further, the level sensor 24, the derivation means 80, and the drain tank 90 may be omitted.

  In the said Embodiment 1-4, although the activated carbon filter 70 was demonstrated as an example of the adsorption filter in this invention, it is not limited to this. For example, an adsorption filter composed of a porous material such as zeolite may be used.

  In the boil-off gas recovery system according to Embodiments 1 to 4, the cooler 51 may be omitted.

  In the above embodiment, the first separator 14 having the small-diameter portion 26 whose outer surface is configured in a mesh shape has been described as an example of the oil separator in the present invention, but the lubricating oil may be separated by another oil separator. Is possible. For example, an oil separator using a baffle plate or an oil separator by centrifugation may be used. The same applies to the second separator 60 included in the monitoring means in the present invention.

  In the first embodiment, a pipe that connects an arbitrary part in the third pipe 70A and the first part 5AA in the gas outlet pipe 5A may be provided. Thus, the boil-off gas that has passed through the first separator 14 can be directly supplied to the engine 6, the gas combustion device 7, and the generator 8, bypassing the activated carbon filter 70. The piping is provided with a control valve.

  In the first embodiment, the case where the cooler 51 is disposed only at the subsequent stage of the fifth compression stage 3bb has been described. However, the cooler 51 may be disposed at the subsequent stage of each compression stage 3aa, 3bb.

  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, 1A, 1B, 1C Boil-off gas recovery system 2 Tank 3a, 3b Compressor 9 Reliquefaction system 14 First separator (oil separator)
16 Heat exchanger 24 Level sensor 65 Monitoring means 70 Activated carbon filter 76 Differential pressure gauge 77 Alarm generating part 80 Deriving means 90 Drain tank 100 Liquefied gas 100A Boil-off gas

Claims (5)

A tank storing liquefied gas;
A reciprocating compressor that compresses boil-off gas generated by evaporation of a portion of the liquefied gas in the tank, as well as being supplied with lubricating oil;
An oil separator that separates the lubricating oil contained in the boil-off gas discharged from the compressor;
An adsorption filter for adsorbing the lubricating oil contained in the boil-off gas that has passed through the oil separator;
Re-liquefaction having a heat exchanger that cools the boil-off gas that has passed through the adsorption filter by heat exchange with the boil-off gas supplied from the tank to the compressor, and returns the liquefied boil-off gas to the tank And a boil-off gas recovery system.   The boil-off gas recovery system according to claim 1, further comprising monitoring means for monitoring whether or not the lubricating oil is contained in the boil-off gas that has passed through the adsorption filter. A differential pressure gauge for detecting a pressure difference before and after the adsorption filter;
The boil-off gas according to claim 1, further comprising: an alarm generation unit that generates an alarm when the pressure difference detected by the differential pressure gauge exceeds a predetermined reference value. Collection system. A level sensor that detects whether or not the liquid level of the lubricating oil in the oil separator exceeds a predetermined reference height;
Deriving means for deriving the lubricating oil out of the oil separator when the liquid level height exceeds the reference height;
The boil-off gas recovery system according to any one of claims 1 to 3, further comprising a drain tank that stores the lubricating oil derived by the deriving means.   The boil-off gas recovery system according to any one of claims 1 to 4, wherein the adsorption filter is an activated carbon filter.

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