DK202070204A1

DK202070204A1 - Compressor unit and method of stopping compressor unit

Info

Publication number: DK202070204A1
Application number: DKPA202070204A
Authority: DK
Inventors: Tezuka Satoshi; Nagura Kenji; Seyama Katsuhiro
Original assignee: Kobe Steel Ltd
Priority date: 2019-04-09
Filing date: 2020-04-02
Publication date: 2020-12-14
Also published as: NO20200362A1; CN111396285A; KR102142940B1; CA3075842C; CH716089A2; CA3075842A1; DK180716B1

Abstract

This application discloses a compressor unit that is installed in a ship and configured to collect a target gas that is a boil-off gas from an LNG storage tank of the ship and to supply at least a part of the target gas to a destination which demands the target gas. The compressor unit includes: a plurality of dampers provided between a plurality of compression stages to inhibit pressure fluctuation; a first seal part configured to seal between a piston and a cylinder part; and a second seal part surrounding a periphery of a piston rod, and configured to prevent the target gas sucked into the cylinder part from flowing toward the crank mechanism. All the first seal part and the second seal part are of an oilless type.

Description

DK 2020 70204 A1

COMPRESSOR UNIT AND METHOD OF STOPPING COMPRESSOR UNIT Technical Field

[0001] The present invention relates to a compressor unit that supplies a target gas, which is — aboil-off gas, from an LNG storage tank of a ship to a destination which demands the target gas. Background Art

[0002] Conventionally, as disclosed in JP-A-2011-517749, a compressor that increases a — pressure of a boil-off gas generated from a liquified natural gas (LNG) and supplies the boil- off gas to a destination which demands the target gas such as an engine has been developed.

[0003] In this connection, in a compressor used in an LNG ship, a lubrication type compressor is used (for example, paragraph 0021 of JP-A-2018-128039, paragraph 0114 of — JP-B-6371930).

[0004] Usually, an oil used in the compressor is discharged from the compressor in a state of being mixed in a boil-off gas, and then is separated and collected from the boil-off gas by an oil separator. However, in recent years, the demand for a clean boil-off gas has increased, — andithas been devised to capture an oil more reliably by using a charcoal filter in addition to the oil separator. Note that as disclosed in paragraph 0024 of US 2018/0066802 A, an oil slinger or oil wiper packing may be provided to prevent an oil from moving between a compression cylinder and a compression frame.

[0005] Meanwhile, as disclosed in paragraph 0019 of JP-A-2017-89595, a labyrinth piston reciprocating compressor that does not require a lubricant has also been developed. However, since the labyrinth seal method is generally non-contact between a piston and a cylinder, there is a problem that a gas in the compression chamber is more likely to leak as compared to a case in the piston ring seal method. This problem is particularly remarkable — when a high-pressure gas is compressed. Summary of Invention

[0006] An object of the present invention is to improve reliability of the compressor unit.

[0007] A compressor unit according to one aspect of the present invention is installed in a ship and configured to collect a target gas that is a boil-off gas from an LNG storage tank of the ship and to supply at least a part of the target gas to a destination which demands the target gas. The compressor unit includes: a plurality of compression stages configured to 1

DK 2020 70204 A1 sequentially increase a pressure of the target gas; a plurality of dampers provided between the plurality of compression stages to inhibit pressure fluctuation; and a crank mechanism configured to drive a piston of each of the compression stages. Each of the plurality of compression stages includes: the piston; a piston rod connected to the piston and configured to transmit power of the crank mechanism to the piston; a cylinder part configured to house the piston and form a compression chamber; a first seal part configured to seal between the piston and the cylinder part; a second seal part surrounding a periphery of the piston rod, and configured to prevent the target gas sucked into the cylinder part from flowing toward the crank mechanism; a wiper part surrounding the periphery of the piston rod at a position closer to the crank mechanism than the second seal part, and configured to inhibit entry of a lubricant in the crank mechanism into the cylinder part; and an oil slinger attached to the piston rod between the wiper part and the second seal part, and configured to further inhibit the entry of the lubricant into the cylinder part. All the first seal part and the second seal part are of an oilless type. In at least a final compression stage, the first seal part includes a piston ring group provided on an outer peripheral part of the piston and configured to seal between the piston and the cylinder part, the second seal part includes: a plurality of case parts arranged between the cylinder part and the piston rod; and a plurality of ring parts held by the plurality of case parts, and the first seal part and the second seal part of the at least final compression stage are of a contact type.

[0008] A compressor unit according to another aspect of the present invention is installed in a ship and configured to collect a target gas that is a boil-off gas from an LNG storage tank of the ship and to supply at least a part of the target gas to a destination which demands the target gas. The compressor unit includes: a plurality of compression stages configured to sequentially increase a pressure of the target gas; a plurality of dampers provided between the plurality of compression stages to inhibit pressure fluctuation; and a crank mechanism configured to drive a piston of each of the compression stages. Each of the plurality of compression stages from a first compression stage to an immediately preceding compression stage of a final compression stage includes: the piston; a piston rod connected to the piston — and configured to transmit power of the crank mechanism to the piston; a cylinder part configured to house the piston and form a compression chamber; a first seal part configured to seal between the piston and the cylinder part; a second seal part surrounding a periphery of the piston rod, and configured to prevent the target gas sucked into the cylinder part from flowing toward the crank mechanism; a wiper part surrounding the periphery of the piston rod ata position closer to the crank mechanism than the second seal part, and configured to inhibit entry of a lubricant in the crank mechanism into the cylinder part; and an oil slinger attached to the piston rod between the wiper part and the second seal part, and configured to further inhibit the entry of the lubricant into the cylinder part. The immediately preceding compression stage of the final compression stage and the final compression stage have tandem 2

DK 2020 70204 A1 structure in which the cylinder part of the final compression stage is provided on the cylinder part of the immediately preceding compression stage of the final compression stage. The piston in the immediately preceding compression stage of the final compression stage and the piston in the final compression stage smaller than the piston in the immediately preceding compression stage of the final compression stage in diameter are integrally configured. The final compression stage shares the piston rod, the second seal part, the wiper part, and the oil slinger with the immediately preceding compression stage of the final compression stage. In at least the final compression stage, the first seal part includes a piston ring group provided on an outer peripheral part of the piston and configured to seal between the piston and the cylinder part, and is configured as a contact type. In at least the immediately preceding compression stage of the final compression stage, the second seal part includes: a plurality of case parts arranged between the cylinder part and the piston rod; and a plurality of ring parts held by the plurality of case parts, and is configured as a contact type. All the first seal part and the second seal part are of an oilless type.

[0009] Regarding a method of stopping a compressor unit according to another aspect of the present invention, the compressor unit may include: a check valve provided in the discharge side flow path of the final compression stage; a decompression line connected to the discharge side flow path further downstream of the check valve; and an on-off valve provided in the discharge side flow path downstream of the decompression line. The method may include: closing the on-off valve; and reducing the pressure in the cylinder part of the final compression stage by opening the decompression line when the compressor unit stops.

[0010] Regarding a method of stopping a compressor unit according to another aspect of the — present invention, the compressor unit may include: a check valve provided in the discharge side flow path of the final compression stage; and a decompression line connected to the discharge side flow path between the final compression stage and the check valve. The method may include: reducing the pressure in the cylinder part of the final compression stage by opening the decompression line when the compressor unit stops.

[0011] The above-described technique can improve reliability of the compressor unit.

[0012] The object, feature, and advantage of the present invention will be more apparent from the following detailed description and the accompanying drawings.

Brief Description of Drawings

[0013] FIG. 1 is a schematic flow diagram of a compressor unit according to an embodiment of the present invention; 3

DK 2020 70204 A1 FIG. 2 is a schematic view of a compressor; FIG. 3 is a schematic cross-sectional view of a second seal part of the compressor; FIG. 4 is a schematic flow diagram of a part of another compressor unit; FIG. 5 is a schematic flow diagram of a part of another compressor unit; FIG. 6 is a schematic flow diagram of another compressor unit; FIG. 7 is a schematic flow diagram of another compressor unit; FIG. 8 is a schematic flow diagram of another compressor unit; FIG. 9 is a schematic cross-sectional view of the second seal part; FIG. 10 is a schematic plan view of a cylinder part of the compressor; FIG. 11 is a schematic longitudinal cross-sectional view of the cylinder part; FIG. 12 is a schematic longitudinal cross-sectional view of the cylinder part; FIG. 13 is a schematic plan view of another cylinder part; FIG. 14 is a schematic longitudinal cross-sectional view of the cylinder part; FIG. 15 is a schematic plan view of another cylinder part; FIG. 16 is a schematic cross-sectional view of the second seal part; FIG. 17 is a schematic view of a compression stage with tandem structure; FIG. 18 is a schematic view of the compression stage with tandem structure; FIG. 19 is a schematic view of the compression stage with tandem structure; FIG. 20 is a schematic view of two compression stages with double acting structure; FIG. 21 is a schematic flow diagram of another compressor unit; FIG. 22 is a schematic flow diagram of another compressor unit; and FIG. 23 is a schematic diagram of a horizontal compressor. Description of Embodiments

[0014] FIG. 1 is a schematic flow diagram of a compressor unit 100 according to an embodiment of the present invention. FIG. 2 is a schematic view of a compressor 500 constituting the compressor unit 100. The compressor unit 100 will be described with reference to FIGS. 1 and 2.

[0015] The compressor unit 100 is installed in a ship (not shown) including an LNG storage tank 101 in which a liquified natural gas (LNG) is stored. The compressor unit 100 is configured to collect a target gas that is a boil-off gas generated in the LNG storage tank 101. The compressor unit 100 is configured to increase a pressure of the collected target gas to — about 300 bar and to supply the pressurized target gas to a predetermined destination which demands the target gas (for example, a ship engine). In the following description, the terms “upstream” and “downstream” are used based on a flow direction of the target gas.

[0016] The compressor unit 100 includes a flow path 110 through which the target gas flows 4

DK 2020 70204 A1 toward the destination which demands the target gas, the compressor 500, a bypass line 411 configured to return the target gas to the upstream side, a plurality of dampers, and a plurality of coolers (see FIG. 1). In FIG. 1, the compressor unit 100 is shown as a device including components shown in a chain double-dashed line of FIG. 1 (this is similar in FIGS. 6 to 8).

— The compressor 500 includes a plurality of compression stages, a crank mechanism used as a common drive source for the plurality of compression stages, a crankcase 301 in which the crank mechanism is housed, and six cross guides 303 attached to the crankcase 301 (see FIG. 2). The plurality of compression stages includes a first compression stage 201, a second compression stage 202 that is a next stage of the first compression stage 201, a third compression stage 203 that is a next stage of the second compression stage 202, a fourth compression stage 204 that is a next stage of the third compression stage 203, and a fifth compression stage 205 that is a next stage of the fourth compression stage 204. The pressure of the target gas flowing through the flow path 110 is sequentially increased by the plurality of compression stages. The plurality of dampers are provided upstream and downstream of — the compression stages in order to inhibit pressure fluctuation in the target gas due to intermittent suction and discharge performed in conjunction with piston reciprocating motion in the respective compression stages 201 to 205. The plurality of coolers are provided to cool the target gas compressed in the plurality of compression stages.

[0017] An upstream end of the flow path 110 is connected to an upper part of the LNG storage tank 101 such that the boil-off gas generated in the LNG storage tank 101 flows in. A downstream end of the flow path 110 is connected to the destination which demands the target gas.

[0018] The flow path 110 includes a storage tank connection flow path 111, a stage connection flow path 113, and a demand destination connection flow path 114. The storage tank connection flow path 111 is connected to the LNG storage tank and guides the boil-off gas to the compressor unit 100. Since there are two first compression stages 201, the storage tank connection flow path 111 branches into branch parts 111A and 111B, and these branch — parts 111A and 111B are each connected to the first compression stage 201. The branch parts 111A and 111B are provided with dampers 261 and 262, respectively. The stage connection flow path 113 connects between the compression stages 201 to 205. In the stage connection flow path 113, a connection part with the first compression stages 201 branches into two branch parts 113A and 113B. Other parts of the stage connection flow path 113 are provided with the second to fifth compression stages 202 to 205, dampers 263 to 268, 271, 272, and a plurality of coolers 281 to 284. The demand destination connection flow path 114 is a flow path connecting the fifth compression stage 205 and the destination which demands the target gas, and a damper 273 and a cooler 285 are provided.

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[0019] The two first compression stages 201 are provided in two branch parts 111A, 111B so as to be parallel to each other. The second to fifth compression stages 202 to 205 are provided at intervals with one another in series in the stage connection flow path 113.

[0020] The crank mechanism is configured to change rotation of a crankshaft into linear reciprocating motion of a plurality of crossheads. The crankshaft is driven by a motor 302. The crossheads are used as connection regions with piston rods 213 of the first to fifth compression stages 201 to 205.

[0021] The crankshaft is connected to the motor 302 through a through hole formed in the crankcase 301. The crankcase 301 is configured to inhibit leakage of a lubricant used to lubricate the crank mechanism around the through hole, but does not have sealed structure (airtight structure). Therefore, the pressure in the internal space of the crankcase 301 is substantially equal to the atmospheric pressure.

[0022] The six cross guides 303 are arranged at intervals with one another in a horizontal direction, and protrude in a direction substantially perpendicular to the horizontal direction (more accurately, in the present embodiment, upward in a gravitational direction). In the cross guides 303, the above-described crossheads perform reciprocating motion.

[0023] In each cross guide 303, a blocking part 306 is provided. At the center of the blocking part 306, a through hole is formed to allow the piston rod 213 connecting the piston performing reciprocating motion in each of the compression stages 201 to 205 and the corresponding crosshead to pass therethrough.

[0024] An inert gas (for example, nitrogen) is supplied to the internal space of the cross guide 303 above the blocking part 306 in order to improve safety of the compressor unit 100. Supply pressure of the inert gas is substantially equal to the atmospheric pressure. Therefore, the pressure in the internal space of the cross guide 303 is substantially equal to the atmospheric pressure, in a similar manner to the pressure in the internal space of the crankcase 301.

[0025] The first to fifth compression stages 201 to 205 are constructed in line with positions of the cross guides 303 arranged in the horizontal direction. The first compression stage 201, the fourth compression stage 204, the fifth compression stage 205, the second compression stage 202, the third compression stage 203, and the first compression stage 201 are arranged in that order from the motor 302 side. The first to fifth compression stages 201 to 205 are connected by the flow path 110 so as to obtain pipe connection shown in FIG. 1. Note that FIG. 2 schematically shows arrangement of the first to fifth compression stages 201 to 205, 6

DK 2020 70204 A1 and actually, the first to fifth compression stages 201 to 205 are close to one another. Furthermore, the arrangement order of respective compression stages 201 to 205 is not limited to this.

[0026] The first compression stage 201 includes a cylinder part 211, a piston 212, the piston rod 213, a pair of suction valves 214, a pair of discharge valves 215, and a cylinder liner (not shown).

[0027] The cylinder part 211 includes a tube part 216 substantially coaxial with the cross guide 303, a rear head 217 attached to an opening end of the tube part 216 on a side of the crank mechanism, and a front head 218 that closes the other opening end of the tube part 216. At the central position of the rear head 217, the through hole and a recessed part substantially coaxial with the through hole are formed. The recessed part of the rear head 217 is open to the side of the crank mechanism.

[0028] The piston 212 is housed in a housing space of the cylinder part 211 surrounded by the tube part 216, the rear head 217, and the front head 218. In the cylinder part 211, compression chambers 221 and 222 for compressing the target gas are respectively formed between an end surface on the side of the crank mechanism of the piston 212 and the rear — head 217, and between an end surface on an opposite side of the crank mechanism of the piston 212 and the front head 218. In this way, the first compression stage 201 has double acting structure in which the compression chambers 221 and 222 are formed on both sides of the piston 212.

[0029] The pair of suction valves 214 is attached to suction ports formed at positions corresponding to the compression chambers 221 and 222. When the pressure of the target gas in the compression chambers 221 and 222 becomes equal to or less than the pressure upstream of the suction valves 214, the suction valves 214 allow the target gas to flow into the compression chambers 221 and 222.

[0030] The pair of discharge valves 215 is attached to discharge ports formed at positions corresponding to the compression chambers 221 and 222. When the pressure of the target gas in the compression chambers 221 and 222 becomes equal to or greater than the pressure downstream of the discharge valves 215, the discharge valves 215 allow the target gas to flow — out of the compression chambers 221 and 222.

[0031] The cylinder liner (not shown) is a cylindrical member attached to the inner peripheral surface of the cylinder part 211 in order to inhibit wear of the cylinder part 211, and includes cast iron or alloy steel. The cylinder liner can be replaced when worn by contact 7

DK 2020 70204 A1 with a first seal part described later. In the following description, the cylinder liner will be described as part of the cylinder part 211.

[0032] The piston rod 213 is connected to the end surface of the piston 212 on the side of the crank mechanism and the crosshead of the crank mechanism. The piston rod 213 passes through the rear head 217, extends to the crank mechanism in the cross guide 303, and is inserted into the through hole of the blocking part 306.

[0033] The first compression stage 201 includes a wiper part 231 and an oil slinger 232 in order to prevent the lubricant used to lubricate the crank mechanism from entering the compression chambers 221 and 222 through the outer peripheral part of the piston rod 213.

[0034] The wiper part 231 is a ring-shaped seal member surrounding a periphery of the piston rod 213. The wiper part 231 is fixed to the blocking part 306. The inner peripheral part of the wiper part 231 is in contact with the outer peripheral part of the piston rod 213.

[0035] The oil slinger 232 is a ring-shaped plate member. The oil slinger 232 is fixed to the piston rod 213 between the wiper part 231 and the rear head 217.

[0036] The first compression stage 201 includes a first seal part 241 and a second seal part

242. The first seal part 241 is provided to prevent circulation of the target gas between the compression chambers 221 and 222. The second seal part 242 is provided to prevent the target gas from leaking from the compression chamber 221 into the cross guide 303.

[0037] The first seal part 241 includes a plurality of piston rings 243 (piston ring group) attached to the outer peripheral part of the piston 212. That is, the first seal part 241 is a contact type seal member that seals between the piston 212 and the inner surface of the cylinder part 211 by the outer peripheral parts of the piston rings 243 coming into contact with the cylinder part 211 (more accurately, the cylinder liner not shown). Meanwhile, the first seal — part 241 is also an oilless type (in other words, non-lubricating) seal member with which the lubricant is not supplied to the piston rings 243. Note that a rider ring for preventing contact between the piston 212 and the inner surface of the cylinder part 211 is not shown.

[0038] In the first compression stage 201, each piston ring 243 is formed using a material — whose main component is polytetrafluoroethylene (PTFE) or modified PTFE. This is also similar in the second to fourth compression stages 202 to 204.

[0039] FIG. 3 shows a schematic cross section of the second seal part 242. As shown in FIGS. 2 and 3, the second seal part 242 is so-called rod packing and includes a plurality of 8

DK 2020 70204 A1 case parts 244, a plurality of ring parts 249, and a holding part 294. The case parts 244 and the ring parts 249 surround a periphery of the piston rod 213 disposed in the rear head 217.

[0040] The plurality of case parts 244 are housed in the recessed part between the rear head — 217 and the piston rod 213.

[0041] Each case part 244 includes a substantially circular bottom part 251 and a peripheral wall part 252 protruding from an outer edge of the bottom part 251 to the crank mechanism side. A through hole into which the piston rod 213 is inserted is formed at substantially the — center of the bottom part 251. The ring parts 249 are housed inside each case part 244.

[0042] The holding part 294 is located closer to the crank mechanism than the case parts

244. The holding part 294 is fixed to the rear head 217 with a bolt or the like (not shown).

[0043] The plurality of ring parts 249 are arranged along an axial direction of the piston rod

213. The inner peripheral parts of the ring parts 249 come into contact with the outer peripheral part of the piston rod 213. That is, the second seal part 242 seals between the piston rod 213 and the rear head 217 as a contact type seal member. Meanwhile, the second seal part 242 is also an oilless type (in other words, non-lubricating) seal member with which the lubricant is not supplied to the ring parts 249.

[0044] In the present embodiment, each ring part 249 is formed using a material whose main component is polytetrafluoroethylene (PTFE) or modified PTFE. This is also similar in the second to fourth compression stages 202 to 204.

[0045] The second to fourth compression stages 202 to 204 are substantially common to the first compression stage 201 except that a diameter of the piston 212 and an inner diameter of the cylinder part 211 are smaller than those of the first compression stage 201. That is, the first seal part 241 and the second seal part 242 of each of the second to fourth compression stages 202 to 204 are of a contact type and an oilless type. Also, the second to fourth compression stages 202 to 204 have double acting structure.

[0046] The diameter of the piston 212 and the inner diameter of the cylinder part 211 are smaller in the fifth compression stage 205 than in the first to fourth compression stages 201 to — 204. In the cylinder part 211 of the fifth compression stage 205, the compression chamber 222 is formed in a space on the opposite side of the crank mechanism with the piston 212 interposed, in a similar manner to the first compression stage 201.

[0047] Meanwhile, a pipe member 119 is connected to the space on the side of the crank 9

DK 2020 70204 A1 mechanism with the piston 212 interposed without the suction valve at a position where the suction valve is to be attached. The pipe member 119 is connected to the stage connection flow path 113 on the suction side of the fifth compression stage 205. As a result, the space on the side of the crank mechanism with the piston 212 of the cylinder part 211 interposed is always in communication with the stage connection flow path 113. That is, the space is a non- compression chamber 223 that is not used to compress the target gas. In this way, unlike the other compression stages 201 to 204, the fifth compression stage 205 has single acting structure in which only the space on one side of the piston 212 serves as the compression chamber 222. Note that the pipe member 119 may be connected to the demand destination connection flow path 114 on the discharge side of the fifth compression stage 205.

[0048] Since the fifth compression stage 205 receives the highest pressure among the second to fifth compression stages 202 to 205, the cylinder part 211 includes a forged material.

[0049] The fifth compression stage 205 includes the first seal part 241 and the second seal part 242. The first seal part 241 of the fifth compression stage 205 is a contact type seal member including the plurality of piston rings 243 (piston ring group) in a similar manner to the first compression stage 201, and seals between the piston 212 and the inner surface of the cylinder part 211. In addition, the first seal part 241 is also of an oilless type (that is, — structure in which no lubricant is supplied to the piston rings). Each piston ring 243 is formed using a material whose main component is at least one of polyimide (PT) and polyetheretherketone (PEEK), or a material whose main component is a mixture of one or both of these and PTFE or modified PTFE. By using such a main component material, the piston ring 243 has higher bending strength (Young's modulus) than a piston ring whose main component is only polytetrafluoroethylene (PTFE). Alternatively, the piston ring 243 may be formed using a material whose main component is another engineering plastic (for example, polyamide (PA)) with bending strength (Young's modulus) higher than a piston ring whose main component is only polytetrafluoroethylene (PTFE). Further alternatively, the piston ring 243 may be formed by molding carbon fibers. These alternative materials also have high sealing performance and high durability performance, in a similar manner to the piston ring 243 formed by using a material whose main component is at least one of polyimide (PI) and polyetheretherketone (PEEK), or a material whose main component is a mixture of one or both of these and PTFE or modified PTFE. This is similar in the ring parts 249 described later.

[0050] The second seal part 242 of the fifth compression stage 205 is a contact type seal member with which the inner peripheral parts of the ring parts 249 come into contact with the outer peripheral part of the piston rod 213 in a similar manner to the first compression stage

201. The second seal part 242 is also of an oilless type (that is, structure with which the 10

DK 2020 70204 A1 lubricant is not supplied to the ring parts 249).

[0051] Each ring part 249 is formed using a material whose main component is at least one of polyimide (PT) and polyetheretherketone (PEEK), in a similar manner to the piston rings

243. Alternatively, the ring part 249 may be formed using a material whose main component is another engineering plastic (for example, polyamide (PA)) with bending strength (Young's modulus) higher than polytetrafluoroethylene (PTFE). Further alternatively, the ring part 249 may be formed by molding carbon fibers. These alternative materials also have high sealing performance and high durability performance, in a similar manner to the ring part 249 — formed by using a material whose main component is at least one of polyimide (PI) and polyetheretherketone (PEEK).

[0052] The number of sets of the case parts 244 and the ring parts 249 of the second seal part 242 is larger in the fifth compression stage 205 than in the first compression stage 201.

— With this configuration, the axial direction length of the second seal part 242 is longer in the fifth compression stage 205 than in the first compression stage 201, and part of the second seal part 242 protrudes from the rear head 217 toward the crank mechanism. A seal region of the second seal part 242 is larger in the fifth compression stage 205 than in the first compression stage 201, making it possible to seal a higher-pressure target gas. The fifth compression stage 205 is similar to the first compression stage 201 in other structure.

[0053] In order to reduce imbalance of force, the total of weight of the piston 212 and the piston rod 213 and weight of the corresponding crosshead is substantially equal among the first to fifth compression stages 201 to 205. Note that the weight of the crosshead may be adjusted by adding a weight.

[0054] Each of the plurality of dampers is a pressure-resistant container provided on the flow path 110. The volume of these dampers is set large enough to reduce pressure fluctuation in the target gas that flows in. The dampers 261 and 262 are provided in the two branch parts 111A and 111B, respectively, and are close to the first compression stages 201. Fluctuation in the suction pressure of the two first compression stages 201 is inhibited.

[0055] Another damper 263 is provided at the downstream end of the branch parts 113A and 113B. The target gas compressed in the two first compression stages 201 flows into the — damper 263. The damper 263 is close to the first compression stages 201 and inhibits fluctuation in the discharge pressure of the first compression stages 201. Also, the damper 263 may be divided into two.

[0056] Another damper 264 is provided downstream of the damper 263. The damper 264 is 11

DK 2020 70204 A1 close to the second compression stage 202 and inhibits fluctuation in the suction pressure of the second compression stage 202. In this way, the two dampers 263 and 264 are provided in a flow path section between the first compression stage 201 and the second compression stage 202 in the stage connection flow path 113. A distance between the dampers 263 and 264 (distance along the stage connection flow path 113, the same hereinafter) is greater than a distance between the first compression stage 201 and the damper 263, and a distance between the second compression stage 202 and the damper 264. Also between other compression stages described below, two dampers are disposed to have a relationship similar to this distance relationship.

[0057] Dampers 265 and 266 are provided in a flow path section between the second compression stage 202 and the third compression stage 203. The damper 265 is close to the second compression stage 202, and fluctuation in discharge pressure of the second compression stage 202 is inhibited. The damper 266 is close to the third compression stage — 203, and fluctuation in suction pressure of the third compression stage 203 is inhibited.

[0058] Dampers 267 and 268 close to the third compression stage 203 and the fourth compression stage 204 respectively are provided in a flow path section between the third compression stage 203 and the fourth compression stage 204. The dampers 267 and 268 inhibit fluctuation in discharge pressure of the third compression stage 203 and suction pressure of the fourth compression stage 204. Dampers 271 and 272 respectively close to the compression stages 204 and 205 are provided in a flow path section between the fourth compression stage 204 and the fifth compression stage 205. Fluctuation in discharge pressure of the fourth compression stage 204 and suction pressure of the fifth compression — stage 205 are inhibited.

[0059] The remaining one damper 273 is disposed close to the fifth compression stage 205 in the demand destination connection flow path 114. The damper 273 inhibits fluctuation in discharge pressure of the fifth compression stage 205.

[0060] The plurality of coolers are provided in the stage connection flow path 113 and the demand destination connection flow path 114. Specifically, the cooler 281 is disposed in the flow path section between the dampers 263 and 264. Another cooler 282 is disposed in the flow path section between the dampers 265 and 266. Still another cooler 283 is disposed in the flow path section between the dampers 267 and 268. Still another cooler 284 is disposed in the flow path section between the dampers 271 and 272. The remaining cooler 285 is disposed downstream of the damper 273 in the demand destination connection flow path 114. The coolers 281 to 285 are provided to cool the target gas compressed by the first to fifth compression stages 201 to 205, respectively.

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[0061] The compressor unit 100 is configured to perform control for adjusting the pressure and flow rate of the target gas to be supplied to the destination which demands the target gas, and to perform control for decompressing the flow path 110 when the compressor 500 stops. Control-related regions used for such control will be described below.

[0062] In order to adjust the pressure and flow rate of the target gas to be supplied to the destination which demands the target gas, the compressor unit 100 includes the bypass line 411, a control valve 412, a pressure sensor 413, and a control unit 414. The bypass line 411 branches from between the cooler 284 and the damper 272 on the suction side of the fifth compression stage 205 in the stage connection flow path 113, and is connected to the storage tank connection flow path 111. That is, the bypass line 411 bypasses the first to fourth compression stages 201 to 204 and the dampers 261 to 268 and 271 to return the target gas upstream of the first compression stage 201. The control valve 412 is provided in the bypass line 411. The pressure sensor 413 is disposed between the cooler 284 and the damper 272, and detects the pressure of the target gas on the suction side of the fifth compression stage

205.

[0063] The pressure sensor 413 and the control valve 412 are electrically connected to the control unit 414. The control unit 414 controls the opening degree of the control valve 412 based on the pressure acquired by the pressure sensor 413. Note that the control unit 414 may be constructed as software or as a dedicated circuit.

[0064] The compressor unit 100 includes a decompression line 415, two on-off valves 416 and 417, and a check valve 418 for decompression control. The check valve 418 is provided ina discharge side flow path of the fifth compression stage 205 that is the final compression stage (that is, the demand destination connection flow path 114). The on-off valve 416 is provided downstream of the check valve 418. The opening degree of the on-off valve 416 is controlled in response to reception of a command signal from the control unit 414. The decompression line 415 branches from the demand destination connection flow path 114 downstream of the check valve 418 and upstream of the on-off valve 416. The tip of the decompression line 415 may be open to the atmosphere, or may be connected to a flare facility that burns the target gas released from the compressor unit 100 through the decompression line 415. The on-off valve 417 is provided in the decompression line 415. The opening degree of the on-off valve 417 is controlled in response to reception of a command signal from the control unit 414. When the compressor unit 100 is driven, the on- off valve 417 is normally closed.

[0065] An operation of the compressor unit 100 and a flow of the target gas will be described below.

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[0066] When the motor 302 operates, the crossheads in the crank mechanism perform reciprocating motion linearly. The power of the crossheads is transmitted to the pistons 212 of the first to fifth compression stages 201 to 205 via the piston rods 213 of the first to fifth compression stages 201 to 205. As a result, these pistons 212 also perform reciprocating motion linearly.

[0067] At this time, in each of the compression stages 201 to 205, the lubricant used in the crank mechanism is to move to the cylinder part 211 along the outer peripheral part of the piston rod 213. However, since the inner peripheral part of the wiper part 231 is in contact with the outer peripheral part of the piston rod 213, most of the lubricant that has flowed out of the crankcase 301 is scraped by the wiper part 231. With this configuration, entry of the lubricant into the cylinder part 211 is inhibited.

[0068] Furthermore, the oil slinger 232 is provided closer to the cylinder part 211 than the wiper part 231 on the piston rod 213. With this configuration, even when a very small amount of lubricant goes through the wiper part 231, the oil slinger 232 prevents entry of the lubricant.

[0069] In each of the first to fourth compression stages 201 to 204, suction and discharge of the target gas in the two compression chambers 221 and 222 are alternately repeated in connection with the reciprocating motion of the piston 212. In the fifth compression stage 205, suction and discharge of the target gas is performed in the compression chamber 222. The target gas discharged from the compression stages 201 to 205 is cooled by passing through the coolers 281 to 285, respectively.

[0070] While the compressor 500 is operating, the pressure sensor 413 detects suction pressure of the fifth compression stage 205. The detected pressure is output to the control unit

414. Based on the acquired pressure, the control unit 414 controls the opening degree of the control valve 412 such that the suction pressure of the fifth compression stage 205 becomes substantially constant. In the fifth compression stage 205, the pressure of the target gas of about 100 bar to 150 bar is increased by the first to fourth compression stages 201 to 204 is further increased to about 300 bar. Therefore, wear of the first seal part 241 is likely to proceed, and pressure fluctuation due to a decrease in the processing amount is likely to occur. Meanwhile, in the compressor unit 100, since the suction pressure of the fifth compression — stage 205 is controlled to be substantially constant by using the bypass line 411, a stable operation can be continued.

[0071] When the compressor 500 stops, an external signal requesting decompression processing for the compressor unit 100 is input into the control unit 414. The external signal 14

DK 2020 70204 A1 may be generated in response to an operation by an operator, or may be generated when a sensor monitoring the state of the compressor unit 100 detects an abnormality of the compressor unit 100. In response to reception of the external signal of an instrument downstream of the compressor unit 100, the control unit 414 generates a command signal for closing the on-off valve 416 and a command signal for opening the on-off valve 417. These command signals are output to the on-off valves 416 and 417. The on-off valve 416 closes in response to the command signal, whereas the on-off valve 417 opens in response to the command signal.

[0072] Since the on-off valve 417 is opened, the target gas in the fifth compression stage 205 is discharged through the decompression line 415. By providing the check valve 418 between the fifth compression stage 205 and the decompression line 415, a backward flow from the decompression line 415 to the fifth compression stage 205 is prevented. Furthermore, since the on-off valve 416 is closed, a backward flow of the target gas from the destination which demands the target gas is prevented. The target gas that has flowed into the decompression line 415 is released into the atmosphere or burned in the flare facility. Note that in the compressor unit 100, the target gas in the first to fourth compression stages 201 to 204 may also be decompressed by the decompression line 415. Moreover, another decompression line may be provided in the first to fourth compression stages 201 to 204.

[0073] The compressor unit 100 according to the present embodiment has been described above. Conventionally, as a compressor that supplies a boil-off gas to a destination which demands the target gas such as an engine in a ship, as shown in JP-A-2018-128039, a lubrication type compressor has been used, and the lubricant contained in the boil-off gas discharged from the compressor has been collected by a separator or the like. In contrast, in the compressor 500, since the first and second seal parts 241 and 242 are of an oilless type in all the compression stages 201 to 205, adulteration of oil into the target gas is prevented in the first place. Furthermore, the wiper part 231 and the oil slinger 232 prevent the lubricant used to lubricate the crank mechanism from entering the cylinder part 211, and the target gas can — be kept clean more reliably.

[0074] Furthermore, since the first and second seal parts 241 and 242 are of a contact type, sealing properties can be improved. In particular, since the fifth compression stage 205, which is the final compression stage, is in a high-pressure environment where the pressure of — the target gas of 100 bar to 150 bar is increased to 300 bar (or higher), the first and second seal parts 241 and 242 of the fifth compression stage 205 are preferably of a contact type, not a non-contact type such as a labyrinth seal.

[0075] In this way, the reliability of the compressor 500 can be improved by using oilless 15

DK 2020 70204 A1 type and contact type seal members for the first and second seal parts 241 and 242.

[0076] In the compressor 500, the single acting structure of the fifth compression stage 205 driven under the highest pressure environment can reduce the load on the second seal part 242, and the double acting structure of the other compression stages 201 to 204 can secure the processing amount of the target gas.

[0077] In the fifth compression stage 205, since the non-compression chamber 223 is provided between the compression chamber 222 and the second seal part 242, the load on the second seal part 242 can be further reduced. By compressing the target gas by the two first compression stages 201 arranged in parallel, the processing amount of the target gas can be further secured.

[0078] Unlike conventional techniques, the compressor 500 does not require lubrication of the seal part, and thus no incidental facilities for lubrication are required. As a result, layout in the compressor unit 100 can be simpler than that in the lubrication type compressor.

[0079] The internal pressure of the crankcase 301 to which the wiper part 231 is attached is substantially equal to the atmospheric pressure. An inert gas having a pressure substantially equal to the atmospheric pressure is supplied to the space on the piston 212 side of the wiper part 231 (that is, internal space of the cross guide 303). Therefore, the pressure difference between before and behind the wiper part 231 is substantially zero. With this configuration, deformation of the wiper part 231 due to the pressure difference can be inhibited, and thus the sealing performance of the wiper part 231 can be exhibited over a long period of time. In — addition, in all the first to fifth compression stages 201 to 205, since the pressure difference around the wiper part 231 is substantially zero, the wiper part 231 of the first to fifth compression stages 201 to 205 can be formed using a common member.

[0080] In the fifth compression stage 205, the piston ring 243 and the ring part 249 used for the first seal part 241 and the second seal part 242 are formed using a material whose main component is at least one of polyimide (PI) and polyetheretherketone (PEEK), or a material whose main component is a mixture of one or both of these and PTFE or modified PTFE. Since these materials are harder than materials whose main component is only PTFE, even in a high-pressure environment, the first seal part 241 and the second seal part 242 are not easily deformed, and can have excellent sealing performance over a long period of time.

[0081] By providing the dampers 261 to 268 and 271 to 273 near the suction side and discharge side of the first to fifth compression stages 201 to 205, the pressure fluctuation of the target gas is effectively inhibited. With this configuration, the vibration of the compressor 16

DK 2020 70204 A1 unit 100 due to the pressure fluctuation is inhibited.

[0082] A connection position of an upstream end of the bypass line 411 in the stage connection flow path 113 (upstream end in a flow direction in the bypass line 411) is between — the dampers 271 and 272. With this configuration, the bypass line 411 is less likely to be affected by the fluctuation in the discharge pressure of the fourth compression stage 204 and the suction pressure of the fifth compression stage 205 as compared to a case where the connection position of the upstream end of the bypass line 411 is located between the fourth compression stage 204 and the damper 271 or between the fifth compression stage 205 and the damper 272.

[0083] Meanwhile, a connection position of a downstream end of the bypass line 411 in the storage tank connection flow path 111 (downstream end in the flow direction in the bypass line 411) is located upstream of the dampers 261 and 262 on the suction side of the first compression stage 201. The bypass line 411 is less likely to be affected by the fluctuation in the suction pressure of the first compression stage 201 as compared to a case where the connection position of the downstream end of the bypass line 411 is located between the first compression stage 201 and the damper 261.

[0084] In the compressor unit 100 shown in FIG. 1, the decompression control may be performed by a control unit different from the control unit 414. As another method of decompression processing, the on-off valve 416 may be kept open in order to reduce the pressure of the destination which demands the target gas. Note that since the check valve 418 is provided upstream of the branch part of the decompression line 415 from the flow path — 110, the flow of the target gas from the destination which demands the target gas toward the compressor unit 100 is prevented.

[0085] FIG. 4 is a diagram showing another example of the bypass line. The upstream end of the bypass line 411 in the stage connection flow path 113 may branch from the flow path 110 between the damper 271 on the discharge side of the fourth compression stage 204 and the cooler 284.

[0086] FIG. 5 is a diagram showing still another example of the bypass line. The upstream end of the bypass line 411 may be directly connected to the damper 271 on the discharge side of the fourth compression stage 204.

[0087] FIG. 6 is a diagram showing still another example of the bypass line. In FIG. 6, two bypass lines 421 and 422 are used to control the pressure and flow rate of the target gas to be supplied to the destination which demands the target gas. Other configurations of a 17

DK 2020 70204 A1 compressor unit 100A are similar to the configuration of the compressor unit 100.

[0088] A connection position of the upstream end of the bypass line 421 in the stage connection flow path 113 (upstream end in the flow direction in the bypass line 421) is located between the damper 272 on the suction side of the fifth compression stage 205 and the cooler 284. Meanwhile, the connection position of the downstream end of the bypass line 421 in the stage connection flow path 113 (downstream end in the flow direction in the bypass line 421) is located between the damper 266 on the suction side of the third compression stage 203 and the cooler 282. The pressure sensor 413 is provided between the bypass line 421 and the damper 271 on the suction side of the fifth compression stage 205.

[0089] A connection position of the upstream end of the bypass line 422 in the stage connection flow path 113 is located between the damper 266 on the suction side of the third compression stage 203 and the cooler 282. Meanwhile, the connection position of the downstream end of the bypass line 422 in the storage tank connection flow path 111 is located upstream of the dampers 261 and 262 on the suction side of the first compression stages 201. A pressure sensor 419 is provided between the bypass line 422 and the damper 265 on the discharge side of the second compression stage 202.

[0090] A control valve 423 is attached to the bypass line 421. A control valve 424 is attached to the bypass line 422.

[0091] The opening degree of the control valve 423 is controlled by the control unit 414 based on the pressure acquired from the pressure sensor 413 such that the suction pressure of the fifth compression stage 205 is substantially constant. Meanwhile, the opening degree of the control valve 424 is controlled based on a detection value acquired from the pressure sensor 419 such that the suction pressure of the third compression stage 203 is substantially constant.

[0092] In the compressor unit 100A shown in FIG. 6, a very large pressure difference (about 300 bars) is generated between the suction side of the first compression stage 201 and the discharge side of the fifth compression stage 205. By using the two bypass lines 421 and 422, the pressure can be controlled in two steps, making it possible to inhibit the pressure fluctuation more effectively.

[0093] As described above, in the compressor units 100 and 100A, the first seal part 241 and the second seal part 242 of all of the first compression stage 201 to the fifth compression stage 205 are of an oilless type. Therefore, there is no possibility that the lubricant is mixed into the target gas flowing through the bypass line. Therefore, the connection positions of the 18

DK 2020 70204 A1 upstream end and the downstream end of the bypass lines, and the number of bypass lines can be arbitrarily set.

[0094] According to the above-described embodiment, the target gas is supplied to a single destination which demands the target gas. However, the target gas may be supplied to a plurality of destinations which demand the target gas. FIG. 7 shows a compressor unit 100B configured to supply the target gas to three destinations which demand the target gas. The compressor unit 100B will be described with reference to FIGS. 1 and 7.

[0095] “Demand destination 1” is connected to the flow path on the discharge side of the fifth compression stage 205 (demand destination connection flow path 114) shown in FIG. 7. The demand destination 1 is a ship engine. "Demand destination 2” is connected to a supply pipe 431 extending from the flow path section between the fourth compression stage 204 and the fifth compression stage 205 in the stage connection flow path 113. The demand destination 2 is a liquefaction device that re-liquefies the target gas. The liquefaction device is connected to the LNG storage tank 101 by using a pipe member (not shown) such that the re- liquefied target gas returns to the LNG storage tank 101. "Demand destination 3” is connected to a supply pipe 432 extending from the flow path section between the second compression stage 202 and the third compression stage 203 in the stage connection flow path

113. The demand destination 3 is a power generator mounted on a ship.

[0096] The structure used for processing the target gas supplied from the LNG storage tank 101 to the demand destination 1 is the same as the structure of the compressor unit 100 described with reference to FIG. 1.

[0097] The compressor unit 100B includes bypass lines 433, 434, and 435 in place of the bypass line 411 of the compressor unit 100.

[0098] The bypass line 433 bypasses the fifth compression stage 205 and the dampers 272 and 273 before and behind the fifth compression stage 205. The bypass line 434 bypasses the third and fourth compression stages 203 and 204, and the dampers 266 to 268 and 271 before and behind the third and fourth compression stages 203 and 204. The bypass line 435 bypasses the first and second compression stages 201 and 202, and the dampers 261 to 265.

[0099] Control valves 436, 437, and 438 are attached to the bypass lines 433, 434, and 435, respectively. The control valves 436, 437, and 438 are connected to the control unit 414.

[0100] The opening degree of the control valve 436 is controlled by the control unit 414 based on the detection value of the pressure sensor 413 such that the discharge pressure of the fifth compression stage 205 is constant. Similarly, the opening degree of the control valve 437 19

DK 2020 70204 A1 is controlled based on the detection value of the pressure sensor 441 such that the suction pressure of the fifth compression stage 205 is constant. The opening degree of the control valve 438 is controlled based on the detection value of the pressure sensor 442 such that the suction pressure of the third compression stage 203 is constant.

[0101] The compressor unit 100B includes the three bypass lines 433, 434, and 435 and the control valves 436, 437, and 438 provided in the bypass lines 433, 434, and 435 in order to make it possible to adjust the pressure of the target gas flowing into the three demand destinations 1 to 3, thereby allowing the flow rate and/or pressure suitable for the demand destinations to be obtained.

[0102] FIG. 8 is a diagram showing another example of the compressor unit. Å compressor unit 100C may include one damper, if pulsation of the flow path section between the respective compression stages 201 to 205 in the stage connection flow path 113 may be ignored. This allows the compressor unit 100C to be manufactured at a low price.

[0103] FIG. 9 is a view showing another example of the second seal part 242 of the fifth compression stage 205. In the holding part 294, a through hole 295 is formed through which a cooling fluid for cooling the ring part 249 and the like is supplied. In the present embodiment, the cooling fluid is water. The cooling fluid may be an antifreezing solution. The through hole 295 is formed at a position shifted in a radial direction from the through hole through which the piston rod 213 is inserted.

[0104] Except for the uppermost case part 244, a case cooling flow path 290 through which — the cooling fluid flows is formed in the case parts 244.

[0105] The case cooling flow path 290 includes ring-shaped grooves 291 formed on surfaces of the case parts 244 facing the compression chamber 221 side, and through holes 292 penetrating the case parts 244 in the axial direction so as to be connected to the ring-shaped — grooves 291. Formation positions of the through holes 292 in the radial direction correspond to a formation position of the through hole 295 in the holding part 294.

[0106] The ring-shaped groove 291 in the lowermost case part 244 communicates with a discharge path (shown by a broken line in FIG. 9).

[0107] When supplied to the through hole 295 in the holding part 294, the cooling fluid flows into the ring-shaped grooves 291 to cool the case parts 244 and is discharged through the discharge path. With this configuration, frictional heat generated between the ring parts 249 and the piston rod 213 is removed. As a result, the second seal part 242 can maintain 20

DK 2020 70204 A1 excellent sealing performance for a long period of time even if the lubricant is not supplied.

[0108] The structure of the second seal part 242 may be applied to the first to fourth compression stages 201 to 204. Note that in the second seal part 242 of FIG. 9, the ring- shaped groove 291 may be formed in the uppermost case part 244.

[0109] FIGS. 10 to 12 are views showing another example of the cylinder part 211 of the fifth compression stage 205. FIG. 10 is a schematic plan view of the cylinder part 211. FIG. 11 is a schematic cross-sectional view of the cylinder part 211 along line A-A of FIG. 10.

FIG. 12 is a schematic cross-sectional view of the cylinder part 211 along line B-B orthogonal to line A-A on an axis of the cylinder part 211. The cylinder part 211 will be described with reference to FIG. 2 and FIGS. 10 to 12.

[0110] The cylinder part 211 includes the front head 218, the tube part 216 in which the piston 212 is housed, two jackets 526 attached to the outer surface of the tube part 216, and the rear head 217 as in FIG. 3. As shown in FIG. 10, the tube part 216 has a substantially rectangular planar shape in plan view. The peripheral surfaces of the front head 218 and the tube part 216 include a pair of first surfaces 523 (left and right surfaces of FIG. 10) and a pair of second surfaces 524 (upper and lower surfaces of FIG. 10) substantially orthogonal to the first surfaces 523).

[0111] A plurality of first through holes 541 and a plurality of second through holes 542 penetrating the pair of first surfaces 523 are formed in the tube part 216. Both ends of each of the first through holes 541 and the second through holes 542 are opened on the pair of first surfaces 523. The first through holes 541 pass between the housing space where the piston 212 is housed and one of the second surfaces 524 (upper side in FIG. 10). The second through holes 542 are located on the opposite side of the first through holes 541 with the piston 212 interposed, and pass between the housing space where the piston 212 is housed and one of the second surfaces 524 (lower side in FIG. 10).

[0112] As shown in FIG. 11, an existence region of the plurality of first through holes 541 and the plurality of second through holes 542 overlaps with part of an existence region of the first seal part 241 (that is, the plurality of piston rings 243) in the radial direction.

[0113] As shown in FIG. 10, the cylinder part 211 includes the pair of jackets 526 fixed to the pair of first surfaces 523. Each of the jackets 526 includes a bottom wall part 527 disposed at a position spaced from the corresponding first surface 523, and peripheral wall parts 528 protruding from the outer peripheral edge of the bottom wall part 527 toward the corresponding first surface 523. The distal edge surfaces of the peripheral wall parts 528 are 21

DK 2020 70204 A1 in contact with the corresponding first surface 523. The contact regions between the peripheral wall parts 528 and the first surface 523 are sealed with a sealing material.

[0114] A flow path 529 surrounded by the first surface 523, the peripheral wall parts 528, and the bottom wall part 527 is formed in the cylinder part 211. The flow path 529 communicates with the first through holes 541 and the second through holes 542.

[0115] In the compressor 500, a cylinder cooling flow path part 540 is formed that surrounds the first seal part 241 (and the piston 212) in a circumferential direction by using the flow path 529, the plurality of first through holes 541, and the plurality of second through holes 542. A supply path (not shown) for supplying the cooling fluid to the flow path 529 is formed in one of the pair of jackets 526. RA discharge path (not shown) for discharging the cooling fluid after cooling the first seal part 241 is formed in the other jacket 526. When the compressor 500 is driven, the cooling fluid is supplied to the flow path 529 of one jacket 526 through the supply path, passes through the first through holes 541 and the second through holes 542, and then flows into the flow path 529 of the other jacket 526 and is discharged from the discharge path.

[0116] The cylinder cooling flow path part 540 cools the first seal part 241 over the entire circumference, whereby heat generated in the first seal part 241 can be efficiently removed. As a result, the first seal part 241 can maintain excellent sealing performance for a long period of time even when the lubricant is not supplied.

[0117] With the above-described configuration, by providing the first through holes 541 and the second through holes 542 directly in the tube part 216, the cooling fluid can be flowed to a position near the piston 212, and thus cooling efficiency can be further improved.

[0118] FIG. 13is a schematic plan view showing another example of the cylinder cooling flow path part 540 according to the fifth compression stage 205. FIG. 14 is a schematic longitudinal cross-sectional view of the cylinder part 211. The cylinder cooling flow path part 540 may be formed without using the jacket 526.

[0119] As shown in FIG. 13, the cylinder cooling flow path part 540 includes the plurality of first through holes 541, the plurality of second through holes 542, a plurality of third through holes 543, a plurality of fourth through holes 544, and a plurality of axial direction flow path parts 532. The plurality of first through holes 541 are formed to penetrate the pair of first surfaces 523. The plurality of second through holes 542 are located on the opposite side of the first through holes 541 with the piston 212 interposed, and penetrate the pair of first surfaces 523. The plurality of third through holes 543 are formed to penetrate the pair of 22

DK 2020 70204 A1 second surfaces 524. The plurality of fourth through holes 544 are located on the opposite side of the third through holes 543 with the piston 212 interposed, and penetrate the pair of second surfaces 524. Openings of the first to fourth through holes 541 to 544 are blocked by sealing members 533. In the cylinder cooling flow path part 540, a flow path surrounding the first seal part 241 (and the piston 212) is formed by the set of first to fourth through holes 541 to 544. As shown in FIG. 14, the flow path communicates with another flow path in the axial direction by the axial direction flow path parts 532. The cooling fluid flows through the entire cylinder cooling flow path part from a supply path (not shown) and is discharged from a discharge path (not shown). One end or both ends of the axial direction flow path part 532 penetrate an upper surface or lower surface of the cylinder part 211 and are sealed.

[0120] The cylinder part 211, which does not include the jacket 526, is smaller than the cylinder part 211 described with reference to FIG. 10 by the size of the jacket 526.

[0121] The cylinder cooling flow path part 540 shown in FIGS. 10 to 14 includes a ring- shaped continuous flow path so as to surround the piston 212. However, the piston 212 does not necessarily need to be surrounded by the ring-shaped continuous flow path, and the piston 212 may be surrounded by a plurality of independent flow paths. That is, an independent flow path corresponding to each of four outer surfaces (surfaces corresponding to the first surfaces — 523 and the second surfaces 524) of the substantially rectangular cylinder part may be formed. For example, as shown in FIG. 15, the cylinder cooling flow path part 540 may be formed by the two flow paths 529 formed by the two jackets 526, and the plurality of first through holes 541 and the plurality of second through holes 542 independent of the two flow paths 529.

[0122] The structure of the cylinder part 211 described with reference to FIGS. 10 to 15 may be applied to the compression stages 201 to 204 other than the fifth compression stage 205. Furthermore, in the cylinder part 211, the number of first to fourth through holes 541 to 544 may be one as long as the first seal part 241 can be sufficiently cooled.

[0123] FIG. 16 is a view showing another structure of the cylinder part 211 of the fifth compression stage 205. In the cylinder part 211, the rear head 217 may be omitted, and the second seal part 242 may block the opening end of the tube part 216 (that is, the second seal part 242 may also serve as the rear head 217). The cylinder part 211 of the other compression stages 201 to 204 may employ structure similar to the structure of FIG. 16.

[0124] FIG. 17 is a view showing another example of the compressor 500. In the compressor 500, a fifth compression stage 205E (final compression stage) and a fourth compression stage 204E (immediately preceding compression stage) may have tandem structure.

23

DK 2020 70204 A1

[0125] The fourth compression stage 204E is formed closer to the crank mechanism than the fifth compression stage 205E. The cylinder part 211 of the fourth compression stage 204E includes a tube part 511 extending in the axial direction of the piston rod 213, and an upper part 512 that closes an opening end of the tube part 511 on the opposite side of the crank mechanism. In the upper part 512, a through hole substantially coaxial with the tube part 511 is formed. An opening end of the tube part 511 on the side of the crank mechanism is closed by the rear head 217. The second seal part 242 is fixed to the rear head 217.

[0126] A piston 513 of the fourth compression stage 204E is connected to the piston rod

213. The plurality of piston rings 243 are attached to the outer peripheral part of the piston 513, and the piston rings 243 form the first seal part 241 of the fourth compression stage 204E.

[0127] In the cylinder part 211, the space on the opposite side of the crank mechanism with — the piston 513 interposed is used as a compression chamber 224a of the fourth compression stage 204E. The space on the crank mechanism side with the piston 513 interposed is a non- compression chamber 224b, and a pipe is connected to the non-compression chamber 224b so as to be opened to the flow path of the suction side of the fourth compression stage 204E. Note that the non-compression chamber may be connected to the discharge side.

[0128] The cylinder part 211 of the fifth compression stage 205E includes a tube part 514 and a front head 515. The tube part 514 is provided on the upper part 512 of the fourth compression stage 204E. The inner diameter of the tube part 514 of the fifth compression stage 205E is smaller than the inner diameter of the tube part 511 of the fourth compression — stage 204E.

[0129] A piston 516 of the fifth compression stage 205E is formed integrally with the piston 513 of the fourth compression stage 204E. The diameter of the piston 516 of the fifth compression stage 205E is smaller than the diameter of the piston 513 of the fourth — compression stage 204E. The plurality of piston rings 243 are attached to the outer peripheral part of the piston 516, and the piston rings 243 form the first seal part 241 of the fifth compression stage 205E.

[0130] In the cylinder part 211, the space on the opposite side of the crank mechanism with the piston 516 interposed is used as a compression chamber 225 of the fifth compression stage 205E.

[0131] Since the fourth compression stage 204E and the fifth compression stage 205E have tandem structure, the fifth compression stage 205E shares the piston rod 213, the second seal 24

DK 2020 70204 A1 part 242, the wiper part 231, and the oil slinger 232 with the fourth compression stage 204E. In other words, the piston rod 213, the second seal part 242, the wiper part 231, and the oil slinger 232 of the fourth compression stage 204E are used in common with the fifth compression stage 205E. That is, the piston rod 213 of the fourth compression stage 204E is — used to drive the piston of the fifth compression stage 205E. The second seal part 242 of the fourth compression stage 204E prevents the target gas in the cylinder part 211 of the fifth compression stage 205E from leaking to the crank mechanism side through the cylinder part 211 of the fourth compression stage 204E. The wiper part 231 and the oil slinger 232 of the fourth compression stage 204E prevent not only entry of the lubricant into the cylinder part 211 of the fourth compression stage 204E but also entry of the lubricant into the cylinder part 211 of the fifth compression stage 205E.

[0132] As described above, since the space between the piston 513 and the second seal part 242 of the fourth compression stage 204E is the non-compression chamber 224b, the load applied to the second seal part 242 is reduced.

[0133] FIG. 18is a view showing another example of the tandem structure of the fourth and fifth compression stages 204E and 205E. In the fourth compression stage 204E, the space on the opposite side of the crank mechanism with the piston 513 interposed is the non- compression chamber 224b, and the space on the side of the crank mechanism with the piston 513 interposed is used as a compression chamber 224c. Furthermore, as shown in FIG. 19, in the fourth compression stage 204E, the spaces on both sides of the piston 513 may be compression chambers 224d and 224e.

[0134] FIG. 20 is a view showing another example of the compressor 500. The fourth compression stage 204 and the fifth compression stage 205 may be implemented by one cylinder part 211. In the cylinder part 211, the suction valve 214 and the discharge valve 215 are provided forward and backward of the piston 212, respectively. In the cylinder part 211, the space on the opposite side of the crank mechanism with the piston 212 interposed is connected to the flow path on the discharge side of the third compression stage 203 in FIG. 1, and functions as a compression chamber 224f of the fourth compression stage 204.

[0135] Meanwhile, the space on the side of the crank mechanism in the cylinder part 211 with the piston 212 interposed is connected to the compression chamber 224f and functions as —acompression chamber 225a of the fifth compression stage 205. The two dampers 271 and 272 and the cooler 284 located between the dampers 271 and 272 are provided on the flow path connecting the compression chambers 224f and 225a.

[0136] In the compressor 500, the target gas is compressed in and discharged from the 25

DK 2020 70204 A1 compression chamber 224f of the fourth compression stage 204, and at the same time, the target gas is sucked into the compression chamber 225a of the fifth compression stage 205. The target gas is sucked into the compression chamber 224 of the fourth compression stage 204, and at the same time, the target gas is compressed in and discharged from the compression chamber 225a of the fifth compression stage 205. In the configuration shown in FIG. 20, the number of parts is reduced.

[0137] FIG. 21 is a diagram showing still another example of the compressor unit 100. As shown in FIG. 21, the on-off valve 416 of FIG. 1 may be omitted. In this case, in the demand destination connection flow path 214, the decompression line 415 is located upstream of the check valve 418. During the decompression processing, the check valve 418 prevents the backward flow of the target gas in the destination which demands the target gas (flow of the target gas toward the compressor unit 100). The decompression structure shown in FIG. 21 is more simplified than the decompression structure described with reference to FIG. 1 because the on-off valve 416 is not provided.

[0138] The embodiment disclosed this time is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and — scope of the claims and equivalents are therefore intended to be embraced therein.

[0139] In the above-described fifth compression stage 205, if main seal functions of the first seal part 241 are implemented by the contact between the piston rings 243 and the cylinder part 211, non-contact type seal structure such as labyrinth may be partially used as the first — seal part 241. This is also similar in the second seal part 242. This is also similar in the first seal part 241 and the second seal part 242 of the first to fourth compression stages 201 to 204. In addition, if the seal functions can be surely implemented, the first and second seal parts 241 and 242 may have seal structure of only non-contact type (for example, labyrinth seal) in all or part of the compression stages 201 to 204 except for the fifth compression stage 205.

[0140] The piston rings 243 of the first to fourth compression stages 201 to 204 may include the same material as the piston rings 243 of the fifth compression stage 205. This is also similar in the ring part 249 of the second seal part 242.

[0141] In the fifth compression stage 205 shown in FIG. 2, the space between the front head 218 and the piston 212 is used as the compression chamber 222, but the space between the rear head 217 and the piston 212 may be used as the compression chamber of the fifth compression stage 205.

26

DK 2020 70204 A1

[0142] According to the above-described embodiment, the compressor unit 100 may include the single first compression stage 201 as shown in FIG. 22.

[0143] The structure in which the two first compression stages 201 described with reference to FIG. 1 are connected in parallel may be applied to the second to fifth compression stages 202 to 205.

[0144] According to the above-described embodiment, a stepless capacity adjustment mechanism may be provided in the final compression stage instead of the bypass line. The capacity adjustment mechanism may be a suction valve unloader system, a clearance pocket system, or a speed control system. The capacity adjustment mechanism is controlled by the control unit 414 such that the pressure detected by the pressure sensor 413 falls within a predetermined control target range.

[0145] According to the above-described embodiment, in the compressor units 100 and 100A, the number of compression stages may be set at either of 3, 4, or 6 depending on the pressure to be discharged by the final compression stage.

[0146] According to the above-described embodiment, the structure similar to the structure of the compressor 500 may be applied to a horizontal compressor in which the piston 212 performs reciprocating motion in the horizontal direction (see FIG. 23).

[0147] A vaporizer described according to the above-described various embodiments mainly has the following characteristics.

[0148] A compressor unit according to one aspect of the above-described embodiment is installed in a ship and configured to collect a target gas that is a boil-off gas from an LNG storage tank of the ship and to supply at least a part of the target gas to a destination which demands the target gas. The compressor unit includes: a plurality of compression stages configured to sequentially increase a pressure of the target gas; a plurality of dampers provided between the plurality of compression stages to inhibit pressure fluctuation; and a crank mechanism configured to drive a piston of each of the compression stages. Each of the plurality of compression stages includes: the piston; a piston rod connected to the piston and configured to transmit power of the crank mechanism to the piston; a cylinder part configured to house the piston and form a compression chamber; a first seal part configured to seal between the piston and the cylinder part; a second seal part surrounding a periphery of the piston rod, and configured to prevent the target gas sucked into the cylinder part from flowing toward the crank mechanism; a wiper part surrounding the periphery of the piston rod at a position closer to the crank mechanism than the second seal part, and configured to inhibit 27

DK 2020 70204 A1 entry of a lubricant in the crank mechanism into the cylinder part; and an oil slinger attached to the piston rod between the wiper part and the second seal part, and configured to further inhibit the entry of the lubricant into the cylinder part. All the first seal part and the second seal part are of an oilless type. In at least a final compression stage, the first seal part includes a piston ring group provided on an outer peripheral part of the piston and configured to seal between the piston and the cylinder part, the second seal part includes: a plurality of case parts arranged between the cylinder part and the piston rod; and a plurality of ring parts held by the plurality of case parts, and the first seal part and the second seal part of the at least final compression stage are of a contact type.

[0149] With the above-described configuration, reliability of the compressor unit can be improved. That is, since the wiper part and the oil slinger are provided, it is inhibited that the lubricant in the crank mechanism enters the cylinder part and mixes with the target gas. Moreover, since all the first seal part and the second seal part are of an oilless type, the lubricant is prevented from mixing with the target gas. With only the oilless type seal parts, loads applied to the seal parts become excessively large. However, since the plurality of dampers to inhibit pressure fluctuation are provided between the plurality of compression stages, the seal parts are not exposed to large pressure fluctuation. Since the seal parts can maintain a shape that exerts seal functions even if the lubricant is not supplied, the compressor unit can confine the target gas in the compression chamber. Therefore, the target gas in the compression chamber can be compressed with high reliability. Since the first seal part and the second seal part of the at least final compression stage are of a contact type, in the compression stage including the contact type first seal part and the second seal part, sealing properties are maintained even in high-pressure environments. Therefore, gas leakage through — the seal parts is inhibited.

[0150] Regarding the above-described configuration, in the at least final compression stage, a case cooling flow path may be formed in the plurality of case parts. Water or an antifreezing solution may be used as the cooling fluid supplied to the case cooling flow path.

[0151] With the above-described configuration, the oilless type seal parts are used in an environment where heat is more likely to be generated than lubrication type seal parts. With the above-described configuration, the second seal part can be efficiently cooled by circulating the cooling fluid through the case cooling flow path.

[0152] Regarding the above-described configuration, in the final compression stage, the compression chamber may be only a space on a first side of the cylinder part with the piston interposed. A space on a second side of the cylinder part may be open to one of the suction side flow path of the final compression stage that is a stage connection flow path connecting 28

DK 2020 70204 A1 the final compression stage and the immediately preceding compression stage of the final compression stage, and a demand destination connection flow path.

[0153] With the above-described configuration, the compression chamber in the final compression stage is only the space on the first side of the cylinder part with the piston interposed, and the space on the second side of the cylinder part is open to one of the suction side flow path of the final compression stage that is the stage connection flow path connecting the final compression stage and the immediately preceding compression stage of the final compression stage, and the demand destination connection flow path. That is, the final compression stage has single acting structure. As compared with double acting, there is an effect that the number of high-pressure parts can be reduced, for example, a suction valve and a discharge valve disposed in the cylinder and controlling the flow of the gas into and from the compression chamber can be reduced to one chamber.

[0154] Regarding the above-described configuration, the space on the first side may be a space on an opposite side of the crank mechanism with the piston interposed. The space on the second side may be a space on a side of the crank mechanism.

[0155] With the above-described configuration, by using the space of the side of the crank — mechanism as a non-compression chamber, the load on the second seal part (rod packing) can be reduced.

[0156] Regarding the above-described configuration, tandem structure may be used in which the cylinder part of the final compression stage is provided on the cylinder part of an immediately preceding compression stage of the final compression stage. The piston in the immediately preceding compression stage of the final compression stage, and the piston in the final compression stage smaller than the piston in the immediately preceding compression stage in diameter may be integrally configured. In the final compression stage, only a space on an opposite side of the crank mechanism with the piston interposed may be the compression chamber.

[0157] With the above-described configuration, by using the space of the side of the crank mechanism as a non-compression chamber, the load on the second seal part (rod packing) can be reduced.

[0158] Regarding the above-described configuration, in one cylinder part, a space on a side of the crank mechanism with the piston interposed may be the compression chamber of the final compression stage. A space on an opposite side of the crank mechanism with the piston interposed may be the compression chamber of an immediately preceding compression stage 29

DK 2020 70204 A1 of the final compression stage.

[0159] With the above-described configuration, by forming the compression chambers of the final and immediately preceding compression stages in the spaces on both sides of one piston, itis possible to make the number of parts of the first seal part and the second seal part smaller and to make possibility of target gas leakage smaller as compared to a case of providing the compression chambers in separate cylinder parts.

[0160] Regarding the above-described configuration, in all the compression stages, the first seal part may include the piston ring group provided on the outer peripheral part of the piston and configured to seal between the piston and the cylinder part. The second seal part may include: the plurality of case parts arranged between the cylinder part and the piston rod; and the plurality of ring parts held by the plurality of case parts. The first seal part and the second seal part may be of a contact type.

[0161] With the above-described configuration, sealing properties can be improved more than a non-contact type seal (labyrinth seal).

[0162] Regarding the above-described configuration, a main component of a ring material of — the first seal part and/or the second seal part of the final compression stage may include one or both of PEEK and PI, or one or both of PEEK and PI may be mixed with PTFE.

[0163] With the above-described configuration, pressure resistance of the piston rings in the final compression stage can be improved.

[0164] A compressor unit according to another aspect of the above-described embodiment is installed in a ship and configured to collect a target gas that is a boil-off gas from an LNG storage tank of the ship and to supply at least a part of the target gas to a destination which demands the target gas. The compressor unit includes: a plurality of compression stages configured to sequentially increase a pressure of the target gas; a plurality of dampers provided between the plurality of compression stages to inhibit pressure fluctuation; and a crank mechanism configured to drive a piston of each of the compression stages. Each of the plurality of compression stages from a first compression stage to an immediately preceding compression stage of a final compression stage includes: the piston; a piston rod connected to the piston and configured to transmit power of the crank mechanism to the piston; a cylinder part configured to house the piston and form a compression chamber; a first seal part configured to seal between the piston and the cylinder part; a second seal part surrounding a periphery of the piston rod, and configured to prevent the target gas sucked into the cylinder part from flowing toward the crank mechanism; a wiper part surrounding the periphery of the 30

DK 2020 70204 A1 piston rod at a position closer to the crank mechanism than the second seal part, and configured to inhibit entry of a lubricant in the crank mechanism into the cylinder part; and an oil slinger attached to the piston rod between the wiper part and the second seal part, and configured to further inhibit the entry of the lubricant into the cylinder part. The immediately preceding compression stage of the final compression stage and the final compression stage have tandem structure in which the cylinder part of the final compression stage is provided on the cylinder part of the immediately preceding compression stage of the final compression stage. The piston in the immediately preceding compression stage of the final compression stage and the piston in the final compression stage smaller than the piston in the immediately preceding compression stage of the final compression stage in diameter are integrally configured. The final compression stage shares the piston rod, the second seal part, the wiper part, and the oil slinger with the immediately preceding compression stage of the final compression stage. In at least the final compression stage, the first seal part includes a piston ring group provided on an outer peripheral part of the piston and configured to seal between the piston and the cylinder part, and is configured as a contact type. In at least the immediately preceding compression stage of the final compression stage, the second seal part includes: a plurality of case parts arranged between the cylinder part and the piston rod; and a plurality of ring parts held by the plurality of case parts, and is configured as a contact type. All the first seal part and the second seal part are of an oilless type.

[0165] With the above-described configuration, reliability of the compressor unit can be improved. That is, since the wiper part and the oil slinger are provided, it is inhibited that the lubricant in the crank mechanism enters the cylinder part and mixes with the target gas. Moreover, since all the first seal part and the second seal part are of an oilless type, the lubricant is prevented from mixing with the target gas. With only the oilless type seal parts, loads applied to the seal parts become excessively large. However, since the plurality of dampers to inhibit pressure fluctuation are provided between the plurality of compression stages, the seal parts are not exposed to large pressure fluctuation. Since the seal parts can maintain a shape that exerts seal functions even if the lubricant is not supplied, the compressor unit can confine the target gas in the compression chamber. Therefore, the target gas in the compression chamber can be compressed with high reliability. Since the first seal part of the at least final compression stage and the second seal part of the immediately preceding compression stage of the at least final compression stage are of a contact type, in the compression stage including the contact type first seal part and the second seal part, sealing properties are maintained even in high-pressure environments, and gas leakage through the seal parts is inhibited.

[0166] Regarding the above-described configuration, in the final compression stage, only a space on an opposite side of the crank mechanism with the piston interposed may be the 31

DK 2020 70204 A1 compression chamber.

[0167] Regarding the above-described configuration, in the immediately preceding compression stage of the final compression stage, a space on an opposite side of the crank mechanism with the piston interposed may be a non-compression chamber, and a space on a side of the crank mechanism with the piston interposed may be used as the compression chamber.

[0168] Regarding the above-described configuration, in the at least final compression stage, — the cylinder part may include a cylinder cooling flow path part through which a cooling fluid flows to surround the piston. The cylinder cooling flow path part may include a through hole formed in the cylinder part.

[0169] The oilless type seal parts are used in an environment where heat is more likely to be — generated than lubrication type seal parts. With the above-described configuration, the first seal part can be efficiently cooled by supplying the cooling fluid to the cooling flow path part surrounding the cylinder part.

[0170] Regarding the above-described configuration, in the at least immediately preceding — compression stage of the final compression stage, a case cooling flow path may be formed in the plurality of case parts. Water or an antifreezing solution may be used as the cooling fluid supplied to the case cooling flow path.

[0171] With the above-described configuration, the oilless type seal parts are used in an environment where heat is more likely to be generated than lubrication type seal parts. With the above-described configuration, the second seal part can be efficiently cooled by circulating the cooling fluid through the case cooling flow path.

[0172] Regarding the above-described configuration, in all the compression stages, the first seal part may include the piston ring group provided on the outer peripheral part of the piston and configured to seal between the piston and the cylinder part, and may be of a contact type. In each of the compression stages from the first compression stage to the immediately preceding compression stage of the final compression stage, the second seal part may include: the plurality of case parts arranged between the cylinder part and the piston rod; and the — plurality of ring parts held by the plurality of case parts, and may be of a contact type.

[0173] With the above-described configuration, sealing properties can be improved more than a non-contact type seal (labyrinth seal). 32

DK 2020 70204 A1

[0174] Regarding the above-described configuration, a main component of a ring material of the first seal part of the final compression stage and/or the second seal part of the immediately preceding compression stage of the final compression stage may include one or both of PEEK and PI, or one or both of PEEK and PI may be mixed with PTFE.

[0175] With the above-described configuration, pressure resistance of the piston rings in the final compression stage can be improved.

[0176] Regarding the above-described configuration, a pressure difference between spaces before and behind the wiper part may be substantially zero in the crank mechanism.

[0177] With the above-described configuration, a load on the wiper part can be reduced.

[0178] Regarding the above-described configuration, the pressure in the spaces may be substantially equal to atmospheric pressure.

[0179] With the above-described configuration, in order to make the pressure in the spaces higher than the atmospheric pressure, sealed structure is required in the crankcase. However, the structure is not required for the atmospheric pressure, and the cost can be reduced.

[0180] Regarding the above-described configuration, the compressor unit may further include a bypass line bypassing the compression stages to return the target gas to an upstream side.

[0181] With the above-described configuration, by providing the bypass line, an operation can be performed under optimum operation conditions.

[0182] Regarding a method of stopping a compressor unit according to another aspect of the above-described embodiment, the compressor unit may further include: a check valve — provided in the discharge side flow path of the final compression stage; a decompression line connected to the discharge side flow path further downstream of the check valve; and an on- off valve provided in the discharge side flow path downstream of the decompression line. The method may include: closing the on-off valve; and reducing the pressure in the cylinder part of the final compression stage by opening the decompression line when the compressor unit stops.

[0183] With the above-described configuration, by closing the on-off valve, a backward flow of the gas from the destination which demands the target gas can be prevented during decompression, and by providing the check valve, a backward flow of the gas to the side of 33

DK 2020 70204 A1 the compressor unit can be also prevented. In addition, it is possible to perform decompression at a side of the destination which demands the target gas by opening the on-off valve as necessary at the time of release by the decompression line.

[0184] Regarding a method of stopping a compressor unit according to another aspect of the above-described embodiment, the compressor unit may further include: a check valve provided in the discharge side flow path of the final compression stage; and a decompression line connected to the discharge side flow path between the final compression stage and the check valve. The method may include: reducing the pressure in the cylinder part of the final compression stage by opening the decompression line when the compressor unit stops.

[0185] With the above-described configuration, a backward flow of the gas from a destination which demands the target gas can be prevented during decompression with a simple configuration.

[0186] The plurality of compression stages according to another aspect of the above- described embodiment are used in the compressor unit.

[0187] The technique of the above-described embodiment is suitably used for a compressor unit mounted on a ship.

34

Claims

DK 2020 70204 A1 Claims

1. A compressor unit that is installed in a ship and configured to collect a target gas that is a boil-off gas from an LNG storage tank of the ship and to supply at least a part of the target — gas to a destination which demands the target gas, the compressor unit comprising: a plurality of compression stages configured to sequentially increase a pressure of the target gas; a plurality of dampers provided between the plurality of compression stages to inhibit pressure fluctuation; and a crank mechanism configured to drive a piston of each of the compression stages, wherein each of the plurality of compression stages includes: the piston; a piston rod connected to the piston and configured to transmit power of the crank mechanism to the piston; a cylinder part configured to house the piston and form a compression chamber; a first seal part configured to seal between the piston and the cylinder part; a second seal part surrounding a periphery of the piston rod, and configured to prevent the target gas sucked into the cylinder part from flowing toward the crank mechanism; a wiper part surrounding the periphery of the piston rod at a position closer to the crank mechanism than the second seal part, and configured to inhibit entry of a lubricant in the crank mechanism into the cylinder part; and an oil slinger attached to the piston rod between the wiper part and the second seal part, and configured to further inhibit the entry of the lubricant into the cylinder part, all of the first seal part and the second seal part are of an oilless type, in at least a final compression stage, the first seal part includes a piston ring group provided on an outer peripheral part of the piston and configured to seal between the piston and the cylinder part, the second seal part includes: a plurality of case parts arranged between the cylinder — part and the piston rod; and a plurality of ring parts held by the plurality of case parts, and the first seal part and the second seal part of the at least final compression stage are of a contact type.

2. The compressor unit according to claim 1, wherein in the at least final compression stage, a case cooling flow path is formed in the plurality of case parts, and water or an antifreezing solution is used as a cooling fluid supplied to the case cooling flow path.

35

DK 2020 70204 A1

3. The compressor unit according to claim 1, wherein in the final compression stage, the compression chamber is only a space on a first side of the cylinder part with the piston interposed, and a space on a second side of the cylinder part is open to one of a suction side flow path of the final compression stage that is a stage connection flow path connecting the final compression stage and an immediately preceding compression stage of the final compression stage, and a demand destination connection flow path.

4. The compressor unit according to claim 3, wherein the space on the first side is a space on an opposite side of the crank mechanism with the piston interposed, and the space on the second side is a space on a side of the crank mechanism.

5. The compressor unit according to claim 1, wherein tandem structure is used in which the cylinder part of the final compression stage is provided on the cylinder part of an immediately preceding compression stage of the final compression stage, the piston in the immediately preceding compression stage of the final compression stage, and the piston in the final compression stage smaller than the piston in the immediately preceding compression stage in diameter are integrally configured, and in the final compression stage, only a space on an opposite side of the crank mechanism with the piston interposed is the compression chamber.

6. The compressor unit according to claim 1, wherein in one cylinder part, a space on a side of the crank mechanism with the piston interposed is the compression chamber of the final compression stage, and a space on an opposite side of the crank mechanism with the piston interposed is the compression chamber of an immediately preceding compression stage of the final compression stage.

7. The compressor unit according to any one of claims 1 to 6, wherein in all the compression stages, the first seal part includes the piston ring group provided on the outer peripheral part of the piston and configured to seal between the piston and the cylinder part, the second seal part includes: the plurality of case parts arranged between the cylinder part and the piston rod; and the plurality of ring parts held by the plurality of case parts, and the first seal part and the second seal part are of a contact type.

8. The compressor unit according to any one of claims 1 to 6, wherein a main component of a ring material of the first seal part and/or the second seal part of the final 36

DK 2020 70204 A1 compression stage includes one or both of PEEK and PI, or one or both of PEEK and PI are mixed with PTFE.

9. A compressor unit that is installed in a ship and configured to collect a target gas that is a boil-off gas from an LNG storage tank of the ship and to supply at least a part of the target gas to a destination which demands the target gas, the compressor unit comprising: a plurality of compression stages configured to sequentially increase a pressure of the target gas; a plurality of dampers provided between the plurality of compression stages to inhibit — pressure fluctuation; and a crank mechanism configured to drive a piston of each of the compression stages, wherein each of the plurality of compression stages from a first compression stage to an immediately preceding compression stage of a final compression stage includes: the piston; a piston rod connected to the piston and configured to transmit power of the crank mechanism to the piston; a cylinder part configured to house the piston and form a compression chamber; a first seal part configured to seal between the piston and the cylinder part; a second seal part surrounding a periphery of the piston rod, and configured to prevent the target gas sucked into the cylinder part from flowing toward the crank mechanism; a wiper part surrounding the periphery of the piston rod at a position closer to the crank mechanism than the second seal part, and configured to inhibit entry of a lubricant in the crank mechanism into the cylinder part; and an oil slinger attached to the piston rod between the wiper part and the second seal part, and configured to further inhibit the entry of the lubricant into the cylinder part, the immediately preceding compression stage of the final compression stage and the final compression stage have tandem structure in which the cylinder part of the final compression stage is provided on the cylinder part of the immediately preceding compression — stage of the final compression stage, the piston in the immediately preceding compression stage of the final compression stage and the piston in the final compression stage smaller than the piston in the immediately preceding compression stage of the final compression stage in diameter are integrally configured, the final compression stage shares the piston rod, the second seal part, the wiper part, and the oil slinger with the immediately preceding compression stage of the final compression stage, in at least the final compression stage, the first seal part includes a piston ring group provided on an outer peripheral part of 37

DK 2020 70204 A1 the piston and configured to seal between the piston and the cylinder part, and the first seal part is configured as a contact type, in the immediately preceding compression stage of the at least final compression stage, the second seal part includes: a plurality of case parts arranged between the cylinder part and the piston rod; and a plurality of ring parts held by the plurality of case parts, and the second seal part is configured as a contact type, and all the first seal part and the second seal part are of an oilless type.

10. The compressor unit according to claim 9, wherein in the final compression stage, only a space on an opposite side of the crank mechanism with the piston interposed is the compression chamber.

11. The compressor unit according to claim 10, wherein in the immediately preceding compression stage of the final compression stage, the space on the opposite side of the crank mechanism with the piston interposed is a non-compression chamber, and a space on a side of the crank mechanism with the piston interposed is used as the compression chamber.

12. The compressor unit according to claim 10, wherein in the immediately preceding compression stage of the final compression stage, the space on the opposite side of the crank mechanism with the piston interposed is the compression chamber, and a space on a side of the crank mechanism with the piston interposed is used as a non-compression chamber.

13. The compressor unit according to claim 1 or 9, wherein in the at least final compression stage, the cylinder part includes a cylinder cooling flow path part through which a cooling fluid flows to surround the piston, and the cylinder cooling flow path part includes a through hole formed in the cylinder part.

— 14. The compressor unit according to any one of claims 9 to 12, wherein in the immediately preceding compression stage of the at least final compression stage, a case cooling flow path is formed in the plurality of case parts, and water or an antifreezing solution is used as a cooling fluid supplied to the case cooling flow path.

15. The compressor unit according to any one of claims 9 to 12, wherein in all the compression stages, the first seal part includes the piston ring group provided on the outer peripheral part of the piston and configured to seal between the piston and the cylinder part, and the first seal 38

DK 2020 70204 A1 part is of a contact type, and in each of the compression stages from the first compression stage to the immediately preceding compression stage of the final compression stage, the second seal part includes: the plurality of case parts arranged between the cylinder part and the piston rod; and the plurality of ring parts held by the plurality of case parts, and the second seal part is of a contact type.

16. The compressor unit according to any one of claims 9 to 12, wherein a main component of a ring material of the first seal part of the final compression stage and/or the second seal part of the immediately preceding compression stage of the final compression stage includes one or both of PEEK and PI, or one or both of PEEK and PI are mixed with PTFE.

17. The compressor unit according to any one of claims 1 to 6 and 9 to 12, wherein a pressure difference between spaces before and behind the wiper part is substantially zero in the crank mechanism.

18. The compressor unit according to claim 17, wherein the pressure in the spaces is substantially equal to atmospheric pressure.

19. The compressor unit according to any one of claims 1 to 6 and 9 to 12, further comprising a bypass line bypassing the compression stages to return the target gas to an upstream side. —

20. A method of stopping a compressor unit, the compressor unit according to any one of claims 1 to 6 and 9 to 12 including: a check valve provided in a discharge side flow path of the final compression stage; a decompression line connected to the discharge side flow path further downstream of the check valve; and an on-off valve provided in the discharge side flow path downstream of the decompression line, the method comprising: closing the on-off valve; and reducing the pressure in the cylinder part of the final compression stage by opening the decompression line when the compressor unit stops.

21. A method of stopping a compressor unit, the compressor unit according to any one of claims 1 to 6 and 9 to 12 including: a check valve provided in a discharge side flow path of the final compression stage; and 39

DK 2020 70204 A1 a decompression line connected to the discharge side flow path between the final compression stage and the check valve, the method comprising: reducing the pressure in the cylinder part of the final compression stage by opening — the decompression line when the compressor unit stops.

22. The plurality of compression stages used in the compressor unit according to any one of claims 1 to 6 and 9 to 12. 40