Compressor unit

Abstract

The invention provides a compressor unit, a stopping method of the compressor unit and a plurality of compression sections for the compressor unit. A compressor unit is provided in a ship, collects a target gas, which is a boil-off gas, from a liquefied natural gas storage tank of the ship, and supplies at least a portion of the target gas to a consumer. The compressor unit includes: a plurality of dampers provided between a plurality of compression sections for suppressing pressure fluctuations; the first sealing part is used for sealing the piston and the air cylinder part; and a second seal part surrounding the piston rod and preventing the target gas sucked into the cylinder part from flowing to the crankshaft mechanism side. And all the first sealing parts and the second sealing parts are in a non-oil-supply type. Therefore, the reliability of the compressor unit can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a compressor unit that supplies a subject gas as a boil-off gas from an LNG storage tank of a ship to a demander, a stopping method of the compressor unit, and a plurality of compression stages for the compressor unit. BACKGROUND

[0002] Conventionally, as disclosed in Japanese Patent Publication Gazette No. 2011-517749, a compressor that boosts a boil-off gas generated from LNG (Liquified Natural Gas) and supplies it to a demander such as an engine has been developed.

[0003] The compressor used in an LNG ship adopts an oil-supplied compressor (for example, Japanese Patent Publication Gazette No. 2018-128038, paragraph 0021, Japanese Patent Gazette No. 6371930, paragraph 0114).

[0004] Generally, the oil used in the compressor is ejected from the compressor in a mixed state with the boil-off gas, separated from the boil-off gas by an oil separator, and recovered. However, in recent years, the demand for clean boil-off gas has increased, and oil is reliably captured by an activated carbon filter or the like in addition to the oil separator. In addition, as disclosed in paragraph 0024 of the specification of U.S. Patent Application Publication No. 2018 / 0066802, in order to prevent the movement of oil between the compression cylinder and the compression frame, an oil throw ring and an oil scraping ring are sometimes provided.

[0005] On the other hand, as disclosed in paragraph 0019 of Japanese Patent Publication Gazette No. 2017-89595, a labyrinth piston reciprocating compressor that does not require lubricating oil has also been developed. However, in general, the labyrinth seal type is a structure in which the piston and the cylinder are not in contact, and thus, compared to the piston ring seal type, there is a problem in that the gas in the compression chamber easily leaks. In particular, in the case of compressing high-pressure gas, this problem becomes significant. SUMMARY

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

[0007] One aspect of the present application relates to a compressor unit provided in a ship, recovering a target gas as boil-off gas from a liquefied natural gas storage tank of the ship, and supplying at least a part of the target gas to a demander. The compressor unit includes a plurality of compression stages sequentially boosting the target gas, a plurality of dampers provided between the plurality of compression stages for suppressing variation of pressure, and a crank mechanism driving pistons of the compression stages. The plurality of compression stages each has a piston, a piston rod connected to the piston to transmit power of the crank mechanism to the piston, a cylinder portion housing the piston to form a compression chamber, a first seal portion sealing between the piston and the cylinder portion, a second seal portion surrounding a periphery of the piston rod to prevent the target gas sucked into the cylinder portion from flowing toward the crank mechanism side, a wiping portion surrounding the periphery of the piston rod on the crank mechanism side with respect to the second seal portion to suppress lubricating oil in the crank mechanism from entering the cylinder portion side, and a slinger installed to the piston rod between the wiping portion and the second seal portion to further suppress the lubricating oil from entering the cylinder portion side. The first seal portion and the second seal portion are both oil-free. In at least a last compression stage, the first seal portion has a piston ring group provided at an outer peripheral portion of the piston to seal between the piston and the cylinder portion, and the second seal portion has a plurality of housing portions arranged between the cylinder portion and the piston rod and a plurality of ring portions held by the plurality of housing portions, and the first seal portion and the second seal portion of the at least last compression stage are contact type.

[0008] Another aspect of the present application relates to another compressor unit provided in a ship, recovering a target gas as boil-off gas from a liquefied natural gas storage tank of the ship, and supplying at least a part of the target gas to a demander. The compressor unit includes a plurality of compression stages sequentially increasing the pressure of the target gas, a plurality of dampers provided between the plurality of compression stages for suppressing the variation of the pressure, and a crank mechanism driving pistons of the compression stages. The compression stages from the first compression stage to the immediately preceding compression stage of the last compression stage each include a piston, a piston rod connected to the piston for transmitting the power of the crank mechanism to the piston, a cylinder portion housing the piston to form a compression chamber, a first seal portion sealing between the piston and the cylinder portion, a second seal portion surrounding the periphery of the piston rod to prevent the target gas sucked into the cylinder portion from flowing toward the crank mechanism, a wiping portion surrounding the periphery of the piston rod on the crank mechanism side with respect to the second seal portion to suppress the entry of lubricating oil in the crank mechanism into the cylinder portion side, and a slinger installed to the piston rod between the wiping portion and the second seal portion to further suppress the entry of the lubricating oil into the cylinder portion side. The immediately preceding compression stage of the last compression stage and the last compression stage have a tandem structure in which the cylinder portion of the last compression stage is provided on the cylinder portion of the immediately preceding compression stage of the last compression stage. The piston of the immediately preceding compression stage of the last compression stage and the piston of the last compression stage having a smaller diameter than the piston are integrally formed. The last compression stage and the immediately preceding compression stage of the last compression stage share the piston rod, the second seal portion, the wiping portion, and the slinger. In at least the last compression stage, the first seal portion has a piston ring group provided at the outer peripheral portion of the piston to seal between the piston and the cylinder portion, and is of a contact type. In at least the immediately preceding compression stage of the last compression stage, the second seal portion has a plurality of housing portions arranged between the cylinder portion and the piston rod and a plurality of ring portions held by the plurality of housing portions, and is of a contact type. Both the first seal portion and the second seal portion are of a non-oil fed type.

[0009] Still another aspect of the present application relates to a stopping method of a compressor unit. The compressor unit further includes a check valve provided in an injection side flow path of the last compression stage, a pressure reduction line connected to the injection side flow path at a portion located on a downstream side with respect to the check valve, and an on-off valve provided in the injection side flow path at a portion located on a downstream side with respect to the pressure reduction line. When the compressor unit is stopped, the pressure in the cylinder portion of the last compression stage is reduced by closing the on-off valve and opening the pressure reduction line.

[0010] Another aspect of the present application relates to another method for stopping a compressor unit. The compressor unit includes a last compression stage, a first compression stage, and a second compression stage. The first compression stage is disposed between the last compression stage and the second compression stage. The second compression stage is disposed between the first compression stage and a discharge side of the compressor unit. The method includes opening a pressure relief line connected to a flow path of the last compression stage, and reducing a pressure in a cylinder portion of the last compression stage.

[0011] Another aspect of the present application relates to a compressor unit including a plurality of compression stages.

[0012] According to the present application, it is possible to improve reliability of a compressor unit.

[0013] Objects, features, and advantages of the present application will become more apparent from the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a schematic flow path diagram of a compressor unit according to an embodiment of the present application.

[0015] Figure 2 is a schematic diagram of a compressor.

[0016] Figure 3 is a schematic sectional view of a second seal portion of a compressor.

[0017] Figure 4 is a schematic flow path diagram of a portion of another compressor unit.

[0018] Figure 5 is a schematic flow path diagram of a portion of another compressor unit.

[0019] Figure 6 is a schematic flow path diagram of another compressor unit.

[0020] Figure 7 is a schematic flow path diagram of another compressor unit.

[0021] Figure 8 is a schematic flow path diagram of another compressor unit.

[0022] Figure 9 is a schematic sectional view of a second seal portion.

[0023] Figure 10 is a schematic plan view of a cylinder portion of a compressor.

[0024] Figure 11 is a schematic longitudinal sectional view of a cylinder portion.

[0025] Figure 12 is a schematic longitudinal sectional view of a cylinder portion.

[0026] Figure 13is a schematic plan view of the other cylinder portion.

[0027] Figure 14 is a schematic longitudinal sectional view of the cylinder portion.

[0028] Figure 15 is a schematic plan view of the other cylinder portion.

[0029] Figure 16 is a schematic sectional view of the second seal portion.

[0030] Figure 17 is a schematic view of the compression section having a tandem structure.

[0031] Figure 18 is a schematic view of the compression section having a tandem structure.

[0032] Figure 19 is a schematic view of the compression section having a tandem structure.

[0033] Figure 20 is a schematic view of the two compression sections having a double motion structure.

[0034] Figure 21 is a schematic flow path view of the other compressor unit.

[0035] Figure 22 is a schematic flow path view of the other compressor unit.

[0036] Figure 23 is a schematic view of the horizontal type compressor. DETAILED DESCRIPTION

[0037] Figure 1 is a schematic flow path view of the compressor unit 100 to which the embodiment of the present application pertains. Figure 2 is a schematic view of the compressor 500 that constitutes the compressor unit 100. Reference is made to Figure 1 and Figure 2 to describe the compressor unit 100.

[0038] The compressor unit 100 is provided in a ship (not shown) having an LNG storage tank 101 in which LNG (Liquified Natural Gas) is stored. The compressor unit 100 recovers boil off gas, which is an object gas, that occurs in the LNG storage tank 101. The compressor unit 100 boosts the pressure of the recovered object gas to about 300 bar, and supplies the boosted object gas to a prescribed demander (for example, an engine of the ship). In the following description, the terms "upstream" and "downstream" are used with reference to the flow direction of the object gas.

[0039] The compressor unit 100 has a flow path 110 through which the target gas flows toward a demand side, a compressor 500, a bypass line 411 that returns the target gas to the upstream side, a plurality of dampers, and a plurality of coolers (see Figure 1 ). In Figure 1 , the compressor unit 100 is shown as a device including the constituent elements within the frame line shown by the two-dot chain line in Figure 1 (as is also the case in Figures 6 to 8 ). The compressor 500 has a plurality of compression stages, a crank mechanism used as a common drive source of the plurality of compression stages, a crankcase 301 that houses the crank mechanism, and six crosshead guides 303 installed in the crankcase 301 (see Figure 2 ). The plurality of compression stages include a first compression stage 201, a second compression stage 202 that is the next stage of the first compression stage 201, a third compression stage 203 that is the next stage of the second compression stage 202, a fourth compression stage 204 that is the next stage of the third compression stage 203, and a fifth compression stage 205 that is the next stage of the fourth compression stage 204. The target gas flowing through the flow path 110 is sequentially boosted by the plurality of compression stages. The plurality of dampers are provided upstream and downstream of the compression stages in order to suppress pressure fluctuations of the target gas caused by intermittent suction and discharge in conjunction with the reciprocating motion of the pistons in each of the compression stages 201 to 205. The plurality of coolers are provided in order to cool the target gas compressed in the plurality of compression stages.

[0040] The upstream end of the flow path 110 is connected to the upper portion of the LNG storage tank 101 in a manner that allows boil-off gas occurring in the LNG storage tank 101 to flow in. The downstream end of the flow path 110 is connected to the demand side.

[0041] The flow path 110 has a storage tank connection flow path 111, stage connection flow paths 113, and a demand side connection flow path 114. The storage tank connection flow path 111 is connected to the LNG storage tank 101 and guides boil-off gas to the compressor unit 100. Since there are two first compression stages 201, the storage tank connection flow path 111 is branched into branch portions 111A and 111B, which are connected to the first compression stages 201, respectively. Dampers 261 and 262 are provided in the branch portions 111A and 111B. The stage connection flow paths 113 connect between the compression stages 201 to 205. The connection portion to the first compression stage 201 is branched into two branch portions 113A and 113B. The second compression stage 202 to the fifth compression stage 205, dampers 263 to 268, 271, and 272, and the plurality of coolers 281 to 284 are provided in the other portions of the stage connection flow paths 113. The demand side connection flow path 114 is a flow path that connects the fifth compression stage 205 and the demand side, and dampers 273 and a cooler 285 are provided.

[0042] The two first compression stages 201 are connected to the two branch portions 111A, 111B in a manner of being arranged side by side. The second to fifth compression stages 202 to 205 are arranged in series in the segment connection flow path 113 at intervals from one another.

[0043] The crank mechanism converts the rotation of the crankshaft into the linear reciprocating motion of the plurality of crossheads. The crankshaft is driven by the motor 302. The crossheads are used as the connection points to the piston rods 213 of the first to fifth compression stages 201 to 205.

[0044] The crankshaft is connected to the motor 302 through the through hole formed in the crankcase 301. The crankcase 301 suppresses the leakage of the lubricating oil used for the lubrication of the crank mechanism around the through hole, but does not have airtight structure. Therefore, the pressure of the inside space of the crankcase 301 is substantially equal to the atmospheric pressure.

[0045] The six crosshead guides 303 are arranged at intervals from one another in the horizontal direction, and project toward a direction substantially orthogonal to the horizontal direction (more accurately, the upper side in the direction of gravity in the present embodiment). The crossheads reciprocate in the crosshead guides 303.

[0046] The occlusion portions 306 are provided in the respective crosshead guides 303. The through holes for the piston rods 213 to pass through are formed in the centers of the respective occlusion portions 306, the piston rods 213 being connected to the pistons reciprocating in the respective compression stages 201 to 205 and the crossheads corresponding thereto, respectively.

[0047] The inside space of the crosshead guide 303 on the upper side of the occlusion portion 306 is supplied with inert gas (for example, nitrogen) to improve the safety of the compressor unit 100. The supply pressure of the inert gas is substantially equal to the atmospheric pressure. Therefore, the pressure of the inside space of the crosshead guide 303 is also substantially equal to the atmospheric pressure, like the pressure of the inside space of the crankcase 301.

[0048] The first to fifth compression stages 201 to 205 are constructed in correspondence with the positions of the crosshead 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 this order from the motor 302. The first to fifth compression stages 201 to 205 are connected through the flow path 110 in a manner to obtain the piping connection as shown in FIG. 1. Figure 1 Figure 2 In the present embodiment, the arrangement of the first to fifth compression stages 201 to 205 is schematically shown, and in fact, the first to fifth compression stages 201 to 205 are in close contact. Furthermore, the arrangement order of the respective compression stages 201 to 205 is not limited thereto.​

[0049] The first compression section 201 has a cylinder portion 211, a piston 212, a piston rod 213, a pair of suction valves 214, a pair of discharge valves 215, and a cylinder liner (not shown).

[0050] The cylinder portion 211 includes a barrel portion 216 that is substantially coaxial with the cross head guide 303; a rear head 217 that is mounted to an open end of the barrel portion 216 on the side of the crank mechanism; and a front head 218 that closes the other open end of the barrel portion 216. A through hole and a recess that is substantially coaxial with the through hole are formed in a central position of the rear head 217. The recess of the rear head 217 is open to the side of the crank mechanism.

[0051] The piston 212 is housed in a housing space of the cylinder portion 211 that is surrounded by the barrel portion 216, the rear head 217, and the front head 218. In the cylinder portion 211, a compression chamber 221, 222 for compressing the target gas is formed between an end surface of the piston 212 on the side of the crank mechanism and the rear head 217, and between an end surface of the piston 212 on the side opposite to the crank mechanism and the front head 218. Thus, the first compression section 201 is a double acting structure in which the compression chambers 221, 222 are formed on both sides of the piston 212.

[0052] The pair of suction valves 214 are mounted to suction ports formed in positions corresponding to the compression chambers 221, 222. If the pressure of the target gas in the compression chambers 221, 222 is the same as or lower than the pressure on the upstream side of the suction valves 214, the suction valves 214 allow the target gas to flow into the compression chambers 221, 222.

[0053] The pair of discharge valves 215 are mounted to discharge ports formed in positions corresponding to the compression chambers 221, 222. If the pressure of the target gas in the compression chambers 221, 222 is the same as or higher than the pressure on the downstream side of the discharge valves 215, the discharge valves 215 allow the target gas to flow out from the compression chambers 221, 222.

[0054] The cylinder liner, which is not shown in the figure, is a cylindrical member that is installed to the inner peripheral surface of the cylinder portion 211 in order to suppress wear of the cylinder portion 211, and is formed of cast iron or alloy steel. The cylinder liner can be replaced in the case where it is worn due to contact with the first seal portion described later. In the following description, the cylinder liner is described as a part of the cylinder portion 211.

[0055] The piston rod 213 is connected to the end surface of the piston 212 on the side of the crank mechanism and to the cross head of the crank mechanism. The piston rod 213 penetrates the rear head 217, and extends to the side of the crank mechanism inside the cross head guide 303, and is inserted through the through hole of the obturator 306.

[0056] The first compression section 201 has a wiper 231 and an oil slinger 232 to prevent lubricating oil used for lubrication of the crank mechanism from entering the compression chambers 221, 222 through the outer peripheral portion of the piston rod 213.

[0057] The wiper 231 is a ring-shaped sealing member that surrounds the periphery of the piston rod 213. The wiper 231 is fixed to the obturator 306. The inner peripheral portion of the wiper 231 contacts the outer peripheral portion of the piston rod 213.

[0058] The oil slinger 232 is a ring-shaped plate member. The oil slinger 232 is fixed to the piston rod 213 between the wiper 231 and the rear cylinder head 217.

[0059] The first compression section 201 has a first seal 241 and a second seal 242. The first seal 241 is provided to prevent communication of the target gas between the compression chambers 221, 222. The second seal 242 is provided to prevent leakage of the target gas from the compression chamber 221 into the cross head guide 303.

[0060] The first seal 241 is composed of a plurality of piston rings 243 (piston ring group) installed on the outer peripheral portion of the piston 212. That is, the first seal 241 is a contact-type sealing member that seals between the piston 212 and the inner surface of the cylinder portion 211 by the outer peripheral portion of the piston ring 243 contacting the cylinder portion 211 (more accurately, a cylinder liner not shown in the figure). Further, the first seal 241 is a non-oil-fed (in other words, non-lubricated) sealing member that does not supply lubricating oil to the piston ring 243. In addition, a rider ring for preventing contact between the piston 212 and the inner surface of the cylinder portion 211 is not shown in the figure.

[0061] In the first compression section 201, the piston ring 243 is formed using a material in which PTFE (polytetrafluoroethylene) or modified PTFE is the main component. The same applies to the second to fourth compression sections 202 to 204.

[0062] A schematic cross-sectional view of the second seal 242 is shown in Figure 3 As shown in Figure 2 and Figure 3 The second seal 242 is a so-called rod seal that includes a plurality of housing portions 244, a plurality of ring portions 249, and a pressing portion 294. The housing portions 244 and the ring portions 249 surround the periphery of the piston rod 213 disposed inside the rear cylinder head 217.

[0063] The plurality of housing portions 244 are housed in recesses between the rear cylinder head 217 and the piston rod 213.

[0064] The housing portion 244 includes a substantially circular bottom portion 251 and a peripheral wall portion 252 protruding from the outer edge of the bottom portion 251 toward the crank mechanism side. A through-hole through which the piston rod 213 is inserted is formed in the substantially center of the bottom portion 251. The ring portion 249 is housed on the inner side of the housing portion 244.

[0065] The hold-down portion 294 is located on the crank mechanism side with respect to the housing portion 244. The hold-down portion 294 is fixed to the rear cylinder head 217 by a bolt or the like, which is not shown.

[0066] The plurality of ring portions 249 are arranged in the axial direction of the piston rod 213. The inner peripheral portion of the ring portion 249 contacts the outer peripheral portion of the piston rod 213. That is, the second seal portion 242 seals between the piston rod 213 and the rear cylinder head 217 as a contact-type seal member. Moreover, the second seal portion 242 is a seal member of the no-oil-supply type (in other words, the no-lubrication type) in which the ring portion 249 is not supplied with lubricating oil.

[0067] In the present embodiment, the ring portion 249 is formed using a material in which PTFE (polytetrafluoroethylene) or modified PTFE is the main component. The same applies to the second to fourth compression sections 202 to 204.

[0068] The second to fourth compression sections 202 to 204 are substantially the same as the first compression section 201 except that the diameter of the piston 212 and the inner diameter of the cylinder portion 211 are smaller than those of the first compression section 201. That is, in the second to fourth compression sections 202 to 204, each of the first seal portion 241 and the second seal portion 242 is of the contact type and the no-oil-supply type. Furthermore, the second to fourth compression sections 202 to 204 are double-acting structures.

[0069] In the fifth compression section 205, the diameter of the piston 212 and the inner diameter of the cylinder portion 211 are smaller than those of the first to fourth compression sections 201 to 204. In the cylinder portion 211 of the fifth compression section 205, as with the first compression section 201, a compression chamber 222 is formed in the space on the side opposite the crank mechanism with the piston 212 interposed therebetween.

[0070] On the other hand, in the space on the crank mechanism side with the piston 212 interposed therebetween, at a position at which the intake valve is installed, a pipe member 119 is connected without passing through the intake valve. The pipe member 119 is connected to the section connection flow path 113 on the intake side of the fifth compression section 205. As a result, the space on the crank mechanism side of the cylinder portion 211 with the piston 212 interposed therebetween becomes a state in which it is always communicated with the section connection flow path 113. That is, this space becomes a non-compression chamber 223 that cannot be used for compression of the target gas. Thus, the fifth compression section 205 is a single-acting structure in which only the space on one side of the piston 212 becomes a compression chamber 222, unlike the other first to fourth compression sections 201 to 204. In addition, the pipe member 119 is connected to the demand-side connection flow path 114 on the discharge side of the fifth compression section 205.

[0071] In the second to fifth compression stages 202 to 205, the fifth compression stage 205 is subjected to the highest pressure, and therefore, the cylinder portion 211 thereof is formed of a forged member.

[0072] The first seal portion 241 of the fifth compression stage 205, like the first compression stage 201, is a contact-type seal member constituted by a plurality of piston rings 243 (piston ring group) that seal between the piston 212 and the inner face of the cylinder portion 211. Further, the first seal portion 241 is also an oil-free type (i.e., a structure in which the piston rings are not supplied with lubricating oil). The piston rings 243 are formed using a material in which at least one of polyimide (PI) and polyether ether ketone (PEEK) is a main component or a material in which one or both of these is mixed with PTFE or modified PTFE is a main component. By using such a material having a main component, as compared with a piston ring in which only polytetrafluoroethylene (PTFE) is a main component, a large bending strength (Young's modulus) is obtained. Alternatively, the piston rings 243 can be formed using a material in which another engineering plastic (e.g., polyamide (PA)) having a large bending strength (Young's modulus) with respect to a piston ring in which only polytetrafluoroethylene (PTFE) is a main component is a main component. Further alternatively, the piston rings 243 can be formed by molding carbon fibers. These alternative materials, like the piston rings 243 formed using a material in which at least one of polyimide (PI) and polyether ether ketone (PEEK) is a main component or a material in which one or both of these is mixed with PTFE or modified PTFE is a main component, have high sealing function and high durability.

[0073] The second seal portion 242 of the fifth compression stage 205, like the first compression stage 201, is a contact-type seal member in which the inner peripheral portion of the ring portion 249 contacts the outer peripheral portion of the piston rod 213. The second seal portion 242 is an oil-free type (i.e., a structure in which the ring portion 249 is not supplied with lubricating oil).

[0074] The ring portion 249, like the piston rings 243, is formed using a material in which at least one of polyimide (PI) and polyether ether ketone (PEEK) is a main component. Alternatively, the ring portion 249 can be formed using a material in which another engineering plastic (e.g., polyamide (PA)) having a large bending strength (Young's modulus) with respect to polytetrafluoroethylene is a main component. Further alternatively, the ring portion 249 can be formed by molding carbon fibers. These alternative materials, like the ring portion 249 formed using a material in which at least one of polyimide (PI) and polyether ether ketone (PEEK) is a main component, have high sealing function and high durability.

[0075] In the fifth compression section 205, the number of the housing portions 244 of the second seal portions 242 and the number of the ring portions 249 are more than those of the first compression section 201. Accordingly, the axial length of the second seal portions 242 in the fifth compression section 205 is longer than that of the second seal portions 242 of the first compression section 201, and a part of the second seal portions 242 protrudes from the rear cylinder head 217 toward the crank mechanism side. In the fifth compression section 205, the seal area of the second seal portions 242 is larger than that of the first compression section 201, and thus, the second seal portions 242 can seal the target gas at a higher pressure. The other structures of the fifth compression section 205 are the same as those of the first compression section 201.

[0076] In the first to fifth compression sections 201 to 205, the total weight of the pistons 212 and the piston rods 213 and the corresponding cross heads is substantially equal in order to reduce the imbalance of forces. Alternatively, the weight of the cross heads can be adjusted by adding balance weights.

[0077] The plurality of dampers are pressure-resistant containers provided on the flow path 110. The volumes of the dampers are set to be large enough to reduce the pressure variation of the target gas flowing in. The dampers 261, 262 are provided in the two branch portions 111A, 111B, respectively, and are close to the first compression sections 201. The dampers 261, 262 suppress the suction pressure variation of the two first compression sections 201.

[0078] Another damper 263 is provided at the downstream end of the branch portions 113A, 113B. The target gas compressed by the two first compression sections 201 flows into the damper 263. The damper 263 is close to the first compression sections 201 and suppresses the discharge pressure variation of the first compression sections 201. Further, the damper 263 can also be two.

[0079] Still another damper 264 is provided on the downstream side of the damper 263. The damper 264 is close to the second compression section 202 and suppresses the suction pressure variation of the second compression section 202. Thus, the flow path section between the first compression section 201 and the second compression section 202 in the section connecting flow path 113 is provided with two dampers 263, 264. The distance between the dampers 263, 264 (the distance along the section connecting flow path 113. The same applies hereinafter) is larger than the distance between the first compression section 201 and the damper 263 and the distance between the second compression section 202 and the damper 264. Two dampers are arranged in the same relationship as this distance relationship between the other compression sections described below.

[0080] The flow path section between the second compression section 202 and the third compression section 203 is provided with dampers 265, 266. The damper 265 is close to the second compression section 202 and suppresses the discharge pressure variation of the second compression section 202. The damper 266 is close to the third compression section 203 and suppresses the suction pressure variation of the third compression section 203.

[0081] A damper 267, 268 is provided in the flow path section between the third compression stage 203 and the fourth compression stage 204, close to the third compression stage 203 and the fourth compression stage 204, respectively. The damper 267, 268 suppresses fluctuations in the discharge pressure of the third compression stage 203 and the suction pressure of the fourth compression stage 204. A damper 271, 272 is provided in the flow path section between the fourth compression stage 204 and the fifth compression stage 205, close to these compression stages 204, 205, respectively, to suppress fluctuations in the discharge pressure of the fourth compression stage 204 and the suction pressure of the fifth compression stage 205.

[0082] The remaining one of the dampers 273 is provided in the demand-side connecting flow path 114, close to the fifth compression stage 205. The damper 273 suppresses fluctuations in the discharge pressure of the fifth compression stage 205.

[0083] A plurality of coolers are provided in the stage connecting flow path 113 and the demand-side connecting flow path 114. Specifically, a cooler 281 is provided in the flow path section between the dampers 263, 264. Another cooler 282 is provided in the flow path section between the dampers 265, 266. Yet another cooler 283 is provided in the flow path section between the dampers 267, 268. Yet another cooler 284 is provided in the flow path section between the dampers 271, 272. The remaining cooler 285 is provided in the demand-side connecting flow path 114, on the downstream side of the damper 273. The coolers 281 to 285 are provided to cool the object gas compressed by the first compression stage 201 to the fifth compression stage 205, respectively.

[0084] The compressor unit 100 performs control for adjusting the pressure and flow rate of the object gas supplied to the demand side and control for depressurizing the flow path 110 when the compressor 500 is stopped. The control-related parts used for these controls are described below.

[0085] To adjust the pressure and flow rate of the object gas supplied to the demand side, the compressor unit 100 has a bypass line 411, a control valve 412, a pressure sensor 413, and a control section 414. The bypass line 411 branches from the stage connecting flow path 113 between the cooler 284 and the damper 272 on the suction side of the fifth compression stage 205, and is connected to the reservoir connecting flow path 111. That is, the bypass line 411 returns the object gas to the upstream side of the first compression stage 201, across the first compression stage 201 to the fourth compression stage 204 and the dampers 261 to 268, 271. The control valve 412 is provided in the bypass line 411. The pressure sensor 413 is provided between the cooler 284 and the damper 272, and detects the pressure of the object gas on the suction side of the fifth compression stage 205.

[0086] The pressure sensor 413 and the control valve 412 are electrically connected to the control section 414. The control section 414 controls the opening degree of the control valve 412 based on the pressure acquired by the pressure sensor 413. The control section 414 can be constructed as software or can be constructed with a dedicated circuit.

[0087] The compressor unit 100 has a pressure reduction line 415, two on-off valves 416, 417, and a check valve 418 for pressure reduction control. The check valve 418 is provided in the discharge side flow path of the last compression stage, i.e., the fifth compression stage 205 (i.e., the demand side connection flow path 114). The on-off valve 416 is provided on the downstream side with respect to the check valve 418. The opening degree of the on-off valve 416 is controlled in accordance with an instruction signal received from the control section 414. The pressure reduction line 415 branches from the demand side connection flow path 114 on the downstream side of the check valve 418 and on the upstream side of the on-off valve 416. The distal end of the pressure reduction line 415 can be open to the atmosphere or can be connected to a combustion device that combusts the object gas discharged from the compressor unit 100 through the pressure reduction line 415. The on-off valve 417 is provided in the pressure reduction line 415. The opening degree of the on-off valve 417 is controlled in accordance with an instruction signal received from the control section 414. The on-off valve 417 is normally closed during driving of the compressor unit 100.

[0088] The operation of the compressor unit 100 and the flow of the object gas will be described below.

[0089] If the motor 302 is operated, the cross head of the crank mechanism linearly reciprocates. The power of the cross head is transmitted to the pistons 212 of the first to fifth compression stages 201 to 205 through the piston rods 213 of the first to fifth compression stages 201 to 205. As a result, the pistons 212 also linearly reciprocate.

[0090] At this time, in each of the compression stages 201 to 205, the lubricating oil for the crank mechanism attempts to move toward the cylinder portion 211 along the outer peripheral portion of the piston rod 213. However, the inner peripheral portion of the wiper portion 231 contacts the outer peripheral portion of the piston rod 213, and thus most of the lubricating oil that attempts to flow out of the crank chamber 301 is scraped off by the wiper portion 231. Accordingly, the entry of the lubricating oil into the cylinder portion 211 is suppressed.

[0091] Further, an oil slinger 232 is provided in the piston rod 213 at a position on the cylinder portion 211 side with respect to the wiper portion 231. Accordingly, even if a very small amount of lubricating oil passes the wiper portion 231, the entry of the lubricating oil is prevented by the oil slinger 232.

[0092] In the first to fourth compression stages 201 to 204, the suction and discharge of the target gas in the two compression chambers 221, 222 are alternately repeated in conjunction with the reciprocating motion of the piston 212. In the fifth compression stage 205, the suction and discharge of the target gas in one compression chamber 222 are performed. The target gas discharged from each of the compression stages 201 to 205 is cooled by the coolers 281 to 285.

[0093] During the operation of the compressor 500, the pressure sensor 413 detects the suction pressure of the fifth compression stage 205. The detected pressure is output to the control section 414. The control section 414 controls the opening degree of the control valve 412 in such a manner that the suction pressure of the fifth compression stage 205 is substantially constant, based on the acquired pressure. In the fifth compression stage 205, the target gas boosted to 100 to 150 bar in the first to fourth compression stages 201 to 204 is further boosted to 300 bar or so, and thus the wear of the first seal section 241 is likely to become severe, and pressure fluctuation due to the reduction in the processing amount is likely to occur. In contrast, in the compressor unit 100, the bypass line 411 is controlled so as to make the suction pressure of the fifth compression stage 205 substantially constant, and thus stable operation can be continued.

[0094] At the time of the stop of the compressor 500, an external signal required for the decompression process of the compressor unit 100 is input to the control section 414. The external signal can be generated based on the operation of an operator, or can be generated when a sensor monitoring the state of the compressor unit 100 detects an abnormality in the compressor unit 100. The control section 414 generates an instruction signal for closing the on-off valve 416 and an instruction signal for opening the on-off valve 417, based on the received external signal of the device on the downstream side of the compressor unit 100. These instruction signals are output to the on-off valves 416, 417, respectively. The on-off valve 416 is closed based on the instruction signal, and the on-off valve 417 is opened based on the instruction signal.

[0095] The target gas in the fifth compression stage 205 is discharged through the decompression line 415 by the opening of the on-off valve 417. A check valve 418 is provided between the fifth compression stage 205 and the decompression line 415, and thus backflow from the decompression line 415 to the fifth compression stage 205 is prevented. Further, since the on-off valve 416 is closed, backflow of the target gas from the demand side is also prevented. The target gas flowing into the decompression line 415 is discharged to the atmosphere or burned in a combustion device. In addition, in the compressor unit 100, the target gas in the first to fourth compression stages 201 to 204 can also be decompressed by the decompression line 415. Further, another decompression line can be provided in the first to fourth compression stages 201 to 204.

[0096] The compressor unit 100 according to the present embodiment has been described above, but a compressor that supplies boil-off gas to a demander such as an engine in a ship has been disclosed in Japanese Patent Laid-Open No. 2018-128039, and a lubricating oil contained in boil-off gas emitted from an oil-supplied compressor is recovered by a separator or the like. In contrast, in the compressor 500, the first seal portion 241 and the second seal portion 242 are configured to be oil-free in all the compression stages 201 to 205, so that the oil is prevented from being mixed into the target gas. Further, the wiping portion 231 and the ring oil thrower 232 are used to prevent the lubricating oil for lubricating the crank mechanism from entering the cylinder portion 211, so that the target gas can be reliably and cleanly maintained.

[0097] Further, since the first seal portion 241 and the second seal portion 242 are of the contact type, the sealing performance can be improved. In particular, in the last compression stage, i.e., the fifth compression stage 205, since the target gas at 100 bar to 150 bar is pressurized to 300 bar (or more) in a high-pressure environment, the first seal portion 241 and the second seal portion 242 of the fifth compression stage 205 are preferably of the contact type, rather than the non-contact type such as a labyrinth seal.

[0098] Thus, in the compressor 500, the reliability can be improved by using the oil-free and contact-type seal member in the first seal portion 241 and the second seal portion 242.

[0099] In the compressor 500, the fifth compression stage 205 driven in the highest pressure environment is configured to be a single-acting structure, so that the load on the second seal portion 242 is reduced, and the other compression stages 201 to 204 are configured to be double-acting structures, so that the processing amount of the target gas can be ensured.

[0100] In the fifth compression stage 205, since the non-compression chamber 223 is provided between the compression chamber 222 and the second seal portion 242, the load on the second seal portion 242 can be further reduced. By using the two first compression stages 201 arranged in parallel to compress the target gas, the processing amount of the target gas can be further ensured.

[0101] In the compressor 500, since the seal portions do not need to be supplied with oil, unlike the conventional technology, the compressor unit 100 does not need the additional equipment for oil supply. As a result, compared with the oil-supplied compressor, the layout in the compressor unit 100 can be simplified.

[0102] The inner pressure of the crankcase 301 to which the wiping portion 231 is attached is substantially equal to the atmospheric pressure. The space on the piston 212 side of the wiping portion 231, that is, the inner space of the crosshead guide 303 is supplied with an inert gas at a pressure substantially equal to the atmospheric pressure. Therefore, the pressure difference before and after the wiping portion 231 is substantially zero. Accordingly, the deformation of the wiping portion 231 due to the pressure difference can be suppressed, so that the sealing performance of the wiping portion 231 can be exhibited for a long period of time. Further, the pressure difference around the wiping portion 231 is substantially zero in all of the first to fifth compression sections 201 to 205, so that the wiping portions 231 of the first to fifth compression sections 201 to 205 can be formed using the same member.

[0103] In the fifth compression section 205, the piston ring 243 and the ring portion 249 used for the first and second sealing portions 241 and 242 are formed using a material in which at least one of polyimide (PI) and polyether ether ketone (PEEK) is a main component or a material in which one or both of them is mixed with PTFE or modified PTFE as a main component. These materials are harder than a material in which only PTFE is a main component, so that the first and second sealing portions 241 and 242 are less likely to be deformed even in a high-pressure environment, and can have excellent sealing performance for a long period of time.

[0104] The dampers 261 to 268 and 271 to 273 are respectively provided near the suction side and the discharge side of the first to fifth compression sections 201 to 205, so that the pressure variation of the target gas is effectively suppressed. Accordingly, the vibration of the compressor unit 100 due to the pressure variation is suppressed.

[0105] The connection position of the upstream end of the bypass line 411 in the section connection flow path 113 (the end portion on the upstream side in the flow direction within the bypass line 411) is between the dampers 271 and 272. Accordingly, compared with the case where the connection position of the upstream end within the bypass line 411 is between the fourth compression section 204 and the damper 271 or between the fifth compression section 205 and the damper 272, the bypass line 411 is less likely to be affected by the discharge pressure variation of the fourth compression section 204 or the suction pressure variation of the fifth compression section 205.

[0106] Further, the connection position of the downstream end of the bypass line 411 in the reservoir connection flow path 111 (the end portion on the downstream side in the flow direction within the bypass line 411) is located on the upstream side with respect to the dampers 261 and 262 on the suction side of the first compression section 201. Compared with the case where the connection position of the downstream end of the bypass line 411 is between the first compression section 201 and the damper 261, the bypass line 411 is less likely to be affected by the suction pressure variation of the first compression section 201.

[0107] Figure 1In the compressor set 100 shown, pressure reduction control can be performed by a control section independent of the control section 414. As another method of pressure reduction processing, the open state of the on-off valve 416 can be maintained in order to reduce the pressure of the demand side. In addition, since the check valve 418 is provided upstream of the branch portion of the pressure reduction line 415 from the flow path 110, flow of the target gas from the demand side toward the compressor set 100 is prevented.

[0108] Figure 4 is a view showing another example of a bypass line. The upstream end of the bypass line 411 in the stage connection flow path 113 can also be branched from the flow path 110 between the damper 271 on the discharge side of the fourth compression stage 204 and the cooler 284.

[0109] Figure 5 is a view showing still another example of a bypass line. The upstream end of the bypass line 411 can also be directly connected to the damper 271 on the discharge side of the fourth compression stage 204.

[0110] Figure 6 is a view showing still another example of a bypass line. In Figure 6 , two bypass lines 421, 422 are used to control the pressure and flow rate of the target gas supplied to the demand side. The other structures of the compressor set 100A are the same as those of the compressor set 100.

[0111] The connection position of the upstream end of the bypass line 421 in the stage connection flow path 113 (the end portion on the upstream side of the flow direction within the bypass line 421) is between the damper 272 on the suction side of the fifth compression stage 205 and the cooler 284. In addition, the connection position of the downstream end of the bypass line 421 in the stage connection flow path 113 (the end portion on the downstream side of the flow direction within the bypass line 421) is 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.

[0112] The connection position of the upstream end of the bypass line 422 in the stage connection flow path 113 is between the damper 266 on the suction side of the third compression stage 203 and the cooler 282. In addition, the connection position of the downstream end of the bypass line 422 in the storage tank connection flow path 111 is on the upstream side of the dampers 261, 262 on the suction side of the first compression stage 201. The pressure sensor 419 is provided between the bypass line 422 and the damper 265 on the discharge side of the second compression stage 202.

[0113] The control valve 423 is installed in the bypass line 421. The control valve 424 is installed in the bypass line 422.

[0114] In the control section 414, the opening degree of the control valve 423 is controlled based on the pressure acquired from the pressure sensor 413 to make the suction pressure of the fifth compression section 205 substantially constant. Further, the opening degree of the control valve 424 is controlled based on the pressure acquired from the pressure sensor 419 to make the suction pressure of the third compression section 203 substantially constant.

[0115] Figure 6 In the compressor set 100A shown, a very large pressure difference (about 300 bar) occurs between the suction side of the first compression section 201 and the discharge side of the fifth compression section 205, but by using two bypass lines 421, 422, the pressure can be controlled in two stages, and thus, pressure fluctuation can be suppressed more effectively.

[0116] As explained above, in the compressor sets 100, 100A, all of the first seal sections 241 and the second seal sections 242 of the first to fifth compression sections 201 to 205 are oil-free. Therefore, there is no possibility that lubricating oil will mix into the object gas flowing in the bypass line. Therefore, the connection positions of the upstream end and the downstream end of the bypass line and the number of bypass lines can be arbitrarily set.

[0117] In the embodiment described, the object gas is supplied to a single demander. However, the object gas can also be supplied to a plurality of demanders. Figure 7 A compressor set 100B that supplies the object gas to three demanders is shown. Reference is made to Figure 1 and Figure 7 to describe the compressor set 100B.

[0118] In Figure 7 the discharge side of the fifth compression section 205 shown, a flow path (demander connection flow path 114) is connected to "demander 1". Demander 1 is an engine of a ship. A supply pipe 431 that extends in the section connection flow path 113 from the flow path section between the fourth compression section 204 and the fifth compression section 205 is connected to "demander 2". Demander 2 is a liquefaction device that reliquefies the object gas. The liquefaction device is connected to the LNG storage tank 101 using a pipe member not shown to return the reliquefied object gas to the LNG storage tank 101. A supply pipe 432 that extends in the section connection flow path 113 from the flow path section between the second compression section 202 and the third compression section 203 is connected to "demander 3". Demander 3 is a generator mounted on a ship.

[0119] The structure for processing the object gas supplied from the LNG storage tank 101 to demander 1 is the same as that of the compressor set 100 described with reference to Figure 1 .

[0120] The compressor set 100B has bypass lines 433, 434, 435 instead of the bypass line 411 of the compressor set 100.

[0121] The bypass line 433 passes through the fifth compression section 205 and the damper 272, 273 before and after the fifth compression section 205. The bypass line 434 passes through the third compression section 203 and the fourth compression section 204 and the dampers 266 to 268, 271 before and after the third and fourth compression sections 203, 204. The bypass line 435 passes through the first compression section 201 and the second compression section 202 and the dampers 261 to 265.

[0122] The control valves 436, 437, 438 are installed in the bypass lines 433, 434, 435, respectively. The control valves 436, 437, 438 are connected to the control unit 414.

[0123] 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 to make the discharge pressure of the fifth compression section 205 constant. Similarly, the opening degree of the control valve 437 is controlled based on the detection value of the pressure sensor 441 to make the suction pressure of the fifth compression section 205 constant. The opening degree of the control valve 438 is controlled based on the detection value of the pressure sensor 442 to make the suction pressure of the third compression section 203 constant.

[0124] The compressor unit 100B is able to adjust the pressure of the object gas flowing into the three demand sides 1 to 3 by having the three bypass lines 433, 434, 435 and the control valves 436, 437, 438 provided on the bypass lines 433, 434, 435, and is able to obtain the flow rate and / or the pressure suitable for the demand sides.

[0125] Figure 8 is a view showing another example of a compressor unit. In the compressor unit 100C, the dampers of the flow path sections between the compression sections 201 to 205 in the segment connection flow path 113 can be one in a case where the pulsation of the flow path sections can be ignored. Accordingly, the compressor unit 100C can be manufactured at a low cost.

[0126] Figure 9 is a view showing another example of the second seal portion 242 of the fifth compression section 205. The pressing portion 294 is formed with a through hole 295 through which a cooling fluid for cooling the ring portion 249 and the like is supplied. In the present embodiment, the cooling fluid is water. The cooling fluid can be an antifreeze solution. The through hole 295 is formed at a position deviated in the radial direction from the through hole through which the piston rod 213 is inserted.

[0127] The housing 244 is formed with a housing cooling flow path 290 through which the cooling fluid flows, in addition to the uppermost housing portion 244.

[0128] The housing cooling flow path 290 includes an annular groove 291 formed in the face of the housing portion 244 on the side toward the compression chamber 221, and a through-hole 292 that penetrates the housing portion 244 in the axial direction in a manner connected to the annular groove 291. The formation position of the through-hole 292 in the radial direction corresponds to the formation position of the through-hole 295 of the hold-down portion 294.

[0129] The annular groove 291 of the lowermost housing portion 244 communicates with the discharge path (indicated by a dashed line) of the cooling fluid. Figure 9

[0130] If the cooling fluid is supplied to the through-hole 295 of the hold-down portion 294, it flows into the annular groove 291 to cool the housing portion 244, and is discharged through the discharge path. Accordingly, the frictional heat generated between the ring portion 249 and the piston rod 213 is removed. As a result, the second seal portion 242 can maintain excellent sealing performance for a long period even if lubricating oil is not supplied.

[0131] The structure of this second seal portion 242 can also be applied to the first to fourth compression stages 201 to 204. In addition, in the second seal portion 242 of the Figure 9 uppermost housing portion 244, the annular groove 291 can be formed.

[0132] Figures 10 to 12 is a view that shows another example of the cylinder portion 211 of the fifth compression stage 205. Figure 10 is a schematic plan view of the cylinder portion 211. Figure 11 is a schematic cross-sectional view of the cylinder portion 211 along the A-A line thereof. Figure 10 is a schematic cross-sectional view of the cylinder portion 211 along the B-B line thereof that is perpendicular to the A-A line on the axis of the cylinder portion 211. Reference is made to Figure 12 , Figure 2 , Figures 10 to 12 for a description of the cylinder portion 211.

[0133] The cylinder portion 211 has a front cylinder head 218, a cylinder portion 216 in which the piston 212 is housed, two cylinder sleeves 526 installed on the outer side surface of the cylinder portion 216, and the same rear cylinder head 217 as the Figure 2 cylinder portion 216. As shown in Figure 10 , the cylinder portion 216 has a planar shape that is substantially rectangular in plan view. The peripheral surface of the front cylinder head 218 and the cylinder portion 216 includes a pair of first faces 523 (left and right faces) and a pair of second faces 524 (upper and lower faces) that are substantially perpendicular to the first faces 523. Figure 10 Figure 10

[0134] ​​​A plurality of first through holes 541 and a plurality of second through holes 542 are formed in the cylindrical portion 216, penetrating a pair of first surfaces 523. The two ends of the first through holes 541 and the second through holes 542 open at the pair of first surfaces 523. The first through holes 541 are connected to one of the receiving spaces of the piston 212. Figure 10 The second through hole 542 is located on the opposite side of the first through hole 541, separated by the piston 212, and is connected to the receiving space contained by the piston 212 by another ( Figure 10 (between the lower side) the second side 524.

[0135] like Figure 11 As shown, the areas where the plurality of first through holes 541 and the plurality of second through holes 542 exist overlap radially with a portion of the area where the first sealing portion 241 (i.e., the plurality of piston rings 243) exists.

[0136] like Figure 10 As shown, the cylinder section 211 has a pair of sleeves 526 fixed to a pair of first surfaces 523. Each sleeve 526 has a bottom wall portion 527 positioned away from the corresponding first surface 523 and a peripheral wall portion 528 protruding from the outer periphery of the bottom wall portion 527 toward the corresponding first surface 523. The distal edge of the peripheral wall portion 528 abuts against the corresponding first surface 523. The abutment portion between the peripheral wall portion 528 and the first surface 523 is sealed with a sealing material.

[0137] In cylinder section 211, a flow path 529 is formed, surrounded by a first surface 523, a peripheral wall section 528, and a bottom wall section 527. The flow path 529 communicates with a first through hole 541 and a second through hole 542.

[0138] In the compressor 500, a cylinder cooling flow path 540 is formed circumferentially surrounding the first seal 241 (and piston 212) by a flow path 529, a plurality of first through holes 541, and a plurality of second through holes 542. A supply path (not shown) is formed in one of a pair of sleeves 526 for supplying cooling fluid to the flow path 529. A discharge path (not shown) is formed in the other sleeve 526 for discharging the cooling fluid after cooling the first seal 241. When the compressor 500 is driven, cooling fluid is supplied to the flow path 529 of one of the sleeves 526 through the supply path, flows into the flow path 529 of the other sleeve 526 through the first through holes 541 and the second through holes 542, and is discharged through the discharge path.

[0139] By cooling the entire circumference of the first sealing portion 241 through the cylinder cooling flow path section 540, the heat generated in the first sealing portion 241 can be efficiently removed. As a result, the first sealing portion 241 can maintain excellent sealing performance for a long time even without the supply of lubricating oil.

[0140] According to the configuration, by directly providing the first through-hole 541 and the second through-hole 542 in the cylinder portion 216, the cooling fluid can be caused to flow to a position close to the piston 212, and thus the cooling efficiency can be further improved.

[0141] Figure 13 is a schematic plan view showing another example of the cylinder cooling flow path portion 540 involved in the fifth compression stage 205. Figure 14 is a schematic longitudinal sectional view of the cylinder portion 211. The cylinder cooling flow path portion 540 can also be formed without using the cylinder jacket 526.

[0142] As shown in Figure 13 , the cylinder cooling flow path portion 540 is provided with a plurality of first through-holes 541, a 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 flow path portions 532. The plurality of first through-holes 541 penetrate the pair of first faces 523. The plurality of second through-holes 542 are located on the opposite side of the first through-holes 541 across the piston 212, and penetrate the pair of first faces 523. The plurality of third through-holes 543 penetrate the pair of second faces 524. The plurality of fourth through-holes 544 are located on the opposite side of the third through-holes 543 across the piston 212, and penetrate the pair of second faces 524. The openings of the first through-holes 541 to the fourth through-holes 544 are plugged by the sealing member 533. In the cylinder cooling flow path portion 540, a flow path that surrounds the first seal portion 241 (and the piston 212) is formed by one set of the first through-holes 541 to the fourth through-holes 544. As shown in Figure 14 , the flow path is in communication with other flow paths in the axial direction through the axial flow path portions 532. The cooling fluid flows through the entire cylinder cooling flow path portion through a supply path not shown in the drawing, and is discharged through a discharge path not shown in the drawing. One end or both ends of the axial flow path portion 532 penetrate the upper face or the lower face of the cylinder portion 211, and are sealed.

[0143] The cylinder portion 211 does not have the cylinder jacket 526, and thus, as compared with the cylinder portion 211 described with reference to Figure 10 , is downsized.

[0144] Figures 10 to 14 The cylinder cooling flow path portion 540 shown in Figure 15As shown, the cylinder cooling flow path portion 540 can also be formed by the 2 flow paths 529 formed by the two cylinder sleeves 526 and the plurality of first through holes 541 and the plurality of second through holes 542 independent of the 2 flow paths 529.

[0145] Referring to Figures 10 to 15 The structure of the cylinder portion 211 described can be applied to the compression stages 201 to 204 other than the fifth compression stage 205. Further, in the cylinder portion 211, the number of the first through holes 541 to the fourth through holes 544 can also be one as long as the first seal portion 241 can be sufficiently cooled.

[0146] Figure 16 is a view showing other structures of the cylinder portion 211 of the fifth compression stage 205. In the cylinder portion 211, the rear cylinder head 217 can also be omitted and the second seal portion 242 can block the open end of the cylinder sleeve portion 216 (i.e., can function as the rear cylinder head 217). The cylinder portion 211 of the other compression stages 201 to 204 can also adopt the same structure as Figure 16 .

[0147] Figure 17 is a view showing another example of the compressor 500. In the compressor 500, the fifth compression stage 205E (the last compression stage) and the fourth compression stage 204E (the preceding compression stage) can also be in a tandem structure.

[0148] The fourth compression stage 204E is formed on the crank mechanism side with respect to the fifth compression stage 205E. The cylinder portion 211 of the fourth compression stage 204E has a cylinder sleeve portion 511 extending in the axial direction of the piston rod 213 and an upper portion 512 closing the open end of the cylinder sleeve portion 511 on the opposite side of the crank mechanism. The through hole substantially coaxial with the cylinder sleeve portion 511 is formed in the upper portion 512. The open end of the cylinder sleeve portion 511 on the crank mechanism side is closed by the rear cylinder head 217. The second seal portion 242 is fixed to the rear cylinder head 217.

[0149] The piston 513 of the fourth compression stage 204E is connected to the piston rod 213. The plurality of piston rings 243 is installed to the outer peripheral portion of the piston 513, and these piston rings 243 form the first seal portion 241 of the fourth compression stage 204E.

[0150] The space in the cylinder portion 211 on the opposite side of the crank mechanism across the piston 513 is used as the compression chamber 224a of the fourth compression stage 204E. The space on the crank mechanism side across the piston 513 is a non-compression chamber 224b, and a pipe is connected to the non-compression chamber 224b in a manner that the flow path is open to the suction side of the fourth compression stage 204E. Further, the non-compression chamber can be connected to the discharge side.

[0151] The cylinder portion 211 of the fifth compression section 205E has a cylinder portion 514 and a front cylinder head 515. The cylinder portion 514 is provided at the upper portion 512 of the fourth compression section 204E. The inner diameter of the cylinder portion 514 of the fifth compression section 205E is smaller than the inner diameter of the cylinder portion 511 of the fourth compression section 204E.

[0152] The piston 516 of the fifth compression section 205E is formed integrally with the piston 513 of the fourth compression section 204E. The diameter of the piston 516 of the fifth compression section 205E is smaller than the diameter of the piston 513 of the fourth compression section 204E. A plurality of piston rings 243 are attached to the outer peripheral portion of the piston 516, and these piston rings 243 form the first seal portion 241 of the fifth compression section 205E.

[0153] The space inside the cylinder portion 211 on the opposite side of the crank mechanism from the piston 516 is used as the compression chamber 225 of the fifth compression section 205E.

[0154] Since the fourth compression section 204E and the fifth compression section 205E are in a tandem structure, the piston rod 213, the second seal portion 242, the wiper portion 231, and the slinger 232 of the fifth compression section 205E are shared with the fourth compression section 204E. In other words, the piston rod 213, the second seal portion 242, the wiper portion 231, and the slinger 232 of the fourth compression section 204E are used in common for the fifth compression section 205E. That is, the piston rod 213 of the fourth compression section 204E is used to drive the piston of the fifth compression section 205E. The second seal portion 242 of the fourth compression section 204E prevents the target gas inside the cylinder portion 211 of the fifth compression section 205E from leaking to the side of the crank mechanism through the cylinder portion 211 of the fourth compression section 204E. The wiper portion 231 and the slinger 232 of the fourth compression section 204E not only prevent lubricating oil from flowing into the cylinder portion 211 of the fourth compression section 204E, but also prevent lubricating oil from flowing into the cylinder portion 211 of the fifth compression section 205E.

[0155] As described above, the space between the piston 513 and the second seal portion 242 of the fourth compression section 204E is the non-compression chamber 224b, and thus the load applied to the second seal portion 242 is reduced.

[0156] Figure 18 is a view showing another example of a tandem structure of the fourth compression section 204E and the fifth compression section 205E. In the fourth compression section 204E, the space on the opposite side of the crank mechanism from the piston 513 is provided as the non-compression chamber 224b, and the space on the side of the crank mechanism from the piston 513 is used as the compression chamber 224c. Further, as shown in Figure 19 In the fourth compression section 204E, the spaces on both sides of the piston 513 can also be provided as the compression chambers 224d, 224e.

[0157] Figure 20 is a view showing another example of the compressor 500. The fourth compression stage 204 and the fifth compression stage 205 can also be implemented by one cylinder section 211. In the cylinder section 211, an intake valve 214 and an exhaust valve 215 are provided on the front and rear sides of the piston 212, respectively. Spaces on the opposite sides of the crank mechanism from each other in the cylinder section 211 are connected to the compression chamber 224f of the fourth compression stage 204 and the compression chamber 225a of the fifth compression stage 205, respectively, via the piston 212. Figure 1 The flow path on the exhaust side of the third compression stage 203 of the

[0158] In addition, the space on the side of the crank mechanism from the piston 212 in the cylinder section 211 is connected to the compression chamber 224f, which functions as the compression chamber 225a of the fifth compression stage 205. Two dampers 271, 272 and a cooler 284 between the damper 271 and the damper 272 are provided in the flow path connecting the compression chamber 224f and the compression chamber 225a.

[0159] In the compressor 500, while the object gas is compressed and exhausted from the compression chamber 224f of the fourth compression stage 204, the object gas is sucked into the compression chamber 225a of the fifth compression stage 205. While the object gas is sucked into the compression chamber 224f of the fourth compression stage 204, the object gas is compressed and exhausted from the compression chamber 225a of the fifth compression stage 205. In the compressor 500, the object gas is compressed and exhausted from the compression chamber 225a of the fifth compression stage 205, and then the object gas is sucked into the compression chamber 224f of the fourth compression stage 204. Figure 20 In the structure shown in FIG. 8, the number of components is reduced.

[0160] Figure 21 is a view showing another example of the compressor unit 100. As shown in Figure 21 Figure 1 The on-off valve 416 of the structure shown in FIG. 7 can be omitted. At this time, the demand-side connection flow path 114 is located on the upstream side of the check valve 418. At the time of pressure reduction, the check valve 418 is used to prevent backflow of the object gas in the demand side (flow of the object gas toward the compressor unit 100). Figure 21 The pressure reduction structure shown in FIG. 8 does not provide the on-off valve 416, and accordingly, is simplified compared with the pressure reduction structure described with reference to FIG. 7. Figure 1

[0161] It should be understood that the embodiments disclosed herein are illustrative and not restrictive in all aspects. The scope of the present application is not represented by the description but by the claims, and includes all modifications equivalent in meaning and range to the claims.

[0162] ​​In the fifth compression section 205, as long as the primary sealing function of the first sealing part 241 is achieved through the contact between the piston ring 243 and the cylinder part 211, the first sealing part 241 can be used in some components with non-contact sealing structures such as labyrinth seals. The same applies to the second sealing part 242. The same applies to the first sealing part 241 and the second sealing part 242 in the first compression sections 201 to the fourth compression sections 204. Furthermore, as long as the sealing function can be reliably performed, the first sealing part 241 and the second sealing part 242 can also be non-contact sealing structures (e.g., labyrinth seals) in all or part of the compression sections 201 to 204 other than the fifth compression section 205.

[0163] The piston rings 243 of the first compression section 201 to the fourth compression section 204 can also be made of the same material as the piston rings 243 of the fifth compression section 205. The same applies to the ring portion 249 of the second sealing portion 242.

[0164] exist Figure 2 In the fifth compression section 205 shown, the space between the front cylinder head 218 and the piston 212 is used as a compression chamber 222. However, the space between the rear cylinder head 217 and the piston 212 can also be used as a compression chamber of the fifth compression section 205.

[0165] In the described embodiment, the compressor unit 100 may also have Figure 22 The single compressed segment 201 is shown.

[0166] Reference Figure 1 The structure described above, which connects two first compression sections 201 in parallel, can also be applied to the second compression sections 202 to the fifth compression sections 205.

[0167] In the described embodiment, a stageless capacity adjustment mechanism can be provided in the final compression section instead of a bypass route. The capacity adjustment mechanism can be a suction valve unloading mechanism, a clearance filling mechanism, or a speed control mechanism. The capacity adjustment mechanism is controlled by the control unit 414 such that the pressure detected by the pressure sensor 413 converges within a predetermined control target range.

[0168] In the described embodiment, the number of compression stages in compressor units 100 and 100A can be set to any number of 3, 4, or 6, depending on the pressure that the final compression stage should eject.

[0169] In the described embodiment, the same structure as compressor 500 can also be applied to a horizontally mounted compressor in which piston 212 reciprocates in the horizontal direction (see reference). Figure 23 ).

[0170] The application described in the various embodiments mainly has the following features.

[0171] One aspect of the embodiment described above is a compressor unit provided in a ship, recovering a target gas as boil-off gas from a liquefied natural gas storage tank of the ship, and supplying at least a part of the target gas to a demander. The compressor unit includes a plurality of compression stages sequentially increasing the pressure of the target gas, a plurality of dampers provided between the plurality of compression stages for suppressing variation in pressure, and a crank mechanism driving pistons of the compression stages. The plurality of compression stages each has a piston, a piston rod connected to the piston and transmitting power of the crank mechanism to the piston, a cylinder portion housing the piston and forming a compression chamber, a first seal portion sealing between the piston and the cylinder portion, a second seal portion surrounding a periphery of the piston rod to prevent the target gas sucked into the cylinder portion from flowing toward the crank mechanism, a wiping portion surrounding the periphery of the piston rod on the crank mechanism side with respect to the second seal portion to suppress lubricating oil in the crank mechanism from entering the cylinder portion side, and a slinger installed to the piston rod between the wiping portion and the second seal portion to further suppress the lubricating oil from entering the cylinder portion side. The first seal portion and the second seal portion are both oil-free. In at least a last compression stage, the first seal portion has a piston ring group provided at an outer peripheral portion of the piston to seal between the piston and the cylinder portion, and the second seal portion has a plurality of housing portions arranged between the cylinder portion and the piston rod and a plurality of ring portions held by the plurality of housing portions, and the first seal portion and the second seal portion of the at least last compression stage are contact type.

[0172] According to the above-described structure, the reliability of the compressor unit can be improved. That is, since the wiping portion and the slinger are provided, the lubricating oil in the crank mechanism is suppressed from entering the cylinder portion and mixing with the target gas. Also, since all of the first seal portions and the second seal portions are oil-free, the lubricating oil is prevented from mixing with the target gas. If these seal portions are made oil-free, the load applied to these seal portions becomes too large. However, since the plurality of dampers for suppressing variation in pressure are provided between the plurality of compression stages, these seal portions are not placed under large variation in pressure. These seal portions can maintain a shape to exhibit a sealing performance even if the lubricating oil is not supplied, and accordingly, the compressor unit can seal 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 portions and the second seal portions of the at least last compression stage are contact type, in the compression stages having the contact type first seal portions and second seal portions, the sealing performance can be maintained even in a high-pressure environment. Accordingly, the gas is suppressed from leaking through these seal portions.

[0173] In the structure, the housing cooling flow path can also be formed in the plurality of housing portions in the at least last compression stage. As the cooling fluid supplied to the housing cooling flow path, water or antifreeze can also be used.

[0174] According to the structure, the second seal portion can be cooled efficiently by circulating the cooling fluid in the housing cooling flow path.

[0175] In the structure, the compression chamber can also be located in the space on the side of the plurality of housing portions on the side opposite the plurality of housing portions in the last compression stage. The space on the side of the plurality of housing portions on the side opposite the plurality of housing portions in the last compression stage can also be open to the suction-side flow path of the last compression stage or the demand-side connection flow path that connects the last compression stage and the compression stage preceding the last compression stage.

[0176] According to the structure, the compression chamber in the last compression stage is located in the space on the side of the plurality of housing portions on the side opposite the plurality of housing portions, and the space on the side of the plurality of housing portions on the side opposite the plurality of housing portions is open to the suction-side flow path of the last compression stage or the demand-side connection flow path that connects the last compression stage and the compression stage preceding the last compression stage. That is, the last compression stage has a single-acting structure. As compared with a double-acting structure, the number of components for high pressure can be reduced by reducing the number of suction valves, discharge valves, and the like that are provided in the cylinder and control the input and output of the gas in the compression chamber.

[0177] In the structure, the space on the side opposite the plurality of housing portions can also be a space on the side opposite the plurality of housing portions with respect to the plurality of housing portions. The space on the side opposite the plurality of housing portions can also be a space on the side of the plurality of housing portions.

[0178] According to the structure, the load on the second seal portion (rod seal) can be reduced by providing the space on the side of the plurality of housing portions on the side opposite the plurality of housing portions as a non-compression chamber.

[0179] In the structure, the last compression stage can also have a tandem structure in which the plurality of housing portions of the compression stage preceding the last compression stage are provided on the plurality of housing portions of the last compression stage. The plurality of housing portions of the compression stage preceding the last compression stage and the plurality of housing portions of the last compression stage can also be integrally formed. The compression chamber can also be provided only in the space on the side opposite the plurality of housing portions with respect to the plurality of housing portions in the last compression stage.

[0180] According to the structure, the load on the second seal portion (rod seal) can be reduced by providing the space on the side of the plurality of housing portions on the side opposite the plurality of housing portions as a non-compression chamber.

[0181] In the structure, the space on the side of the crank mechanism from the piston in one cylinder section can be the compression chamber of the last compression section. The space on the opposite side of the crank mechanism from the piston can be the compression chamber of the preceding compression section of the last compression section.

[0182] According to the structure, by forming the compression chambers of the last and preceding compression sections in the spaces on both sides of one piston, the number of components of the first and second seal sections can be reduced, and the risk of leakage of the target gas can be reduced, compared with the case where the cylinder sections are provided separately.

[0183] In the structure, the first seal section can have a piston ring group that seals between the piston and the cylinder section at the outer peripheral portion of the piston in all compression sections. The second seal section can have a plurality of housing sections arranged between the cylinder section and the piston rod and a plurality of ring sections held by the plurality of housing sections. The first and second seal sections can be contact type.

[0184] According to the structure, the sealability can be further improved compared with non-contact type seal (labyrinth seal).

[0185] In the structure, the main component of the ring material of the first and / or second seal section of the last compression section can be one or both of polyether ether ketone or polyimide or a component in which one or both of them is mixed with polytetrafluoroethylene.

[0186] According to the structure, the pressure resistance of the piston ring in the last compression section can be improved.

[0187] Another aspect of the embodiment relates to a compressor unit provided in a ship, recovering a target gas as boil-off gas from a liquefied natural gas storage tank of the ship, and supplying at least a part of the target gas to a demander. The compressor unit includes a plurality of compression stages sequentially increasing the pressure of the target gas, a plurality of dampers provided between the plurality of compression stages for suppressing variation in the pressure, and a crank mechanism driving pistons of the compression stages. The compression stages from the first compression stage to the immediately preceding compression stage of the last compression stage among the plurality of compression stages each include a piston, a piston rod connected to the piston to transmit power of the crank mechanism to the piston, a cylinder portion housing the piston to form a compression chamber, a first seal portion sealing between the piston and the cylinder portion, a second seal portion surrounding a periphery of the piston rod to prevent the target gas sucked into the cylinder portion from flowing toward the crank mechanism side, a wiping portion surrounding the periphery of the piston rod on the crank mechanism side with respect to the second seal portion to suppress entry of lubricating oil in the crank mechanism into the cylinder portion side, and a slinger installed to the piston rod between the wiping portion and the second seal portion to further suppress entry of the lubricating oil into the cylinder portion side. The immediately preceding compression stage of the last compression stage and the last compression stage have a tandem structure in which the cylinder portion of the last compression stage is provided on the cylinder portion of the immediately preceding compression stage of the last compression stage. The piston of the immediately preceding compression stage of the last compression stage and the piston of the last compression stage having a diameter smaller than the piston are integrally formed. The last compression stage and the immediately preceding compression stage of the last compression stage share the piston rod, the second seal portion, the wiping portion, and the slinger. In at least the last compression stage, the first seal portion has a piston ring group provided at an outer peripheral portion of the piston to seal between the piston and the cylinder portion, and is of a contact type. In at least the immediately preceding compression stage of the last compression stage, the second seal portion has a plurality of housing portions arranged between the cylinder portion and the piston rod and a plurality of ring portions held by the plurality of housing portions, and is of a contact type. Both the first seal portion and the second seal portion are of a non-oil fed type.

[0188] According to the structure, it is possible to improve the reliability of the compressor unit. That is, since the wiping portion and the oil flinger are provided, it is possible to suppress the lubricating oil in the crank mechanism from entering the cylinder portion and mixing into the target gas. Also, all of the first seal portion and the second seal portion are oil-free, so it is possible to prevent the lubricating oil from mixing into the target gas. If these seal portions are simply made oil-free, the load applied to these seal portions becomes too large. However, since the plurality of dampers for suppressing pressure fluctuations are provided between the plurality of compression stages, these seal portions are not placed under large pressure fluctuations. These seal portions can maintain a shape that exhibits sealing performance even if lubricating oil is not supplied, and accordingly, the compressor unit can seal the target gas in the compression chamber. Therefore, it is possible to compress the target gas in the compression chamber with high reliability. The first seal portion of the last compression stage and the second seal portion of the compression stage preceding the last compression stage are contact type, so it is possible to maintain sealing performance even in a high-pressure environment in the compression stage having the contact type first seal portion and the second seal portion. Accordingly, it is possible to suppress leakage of the gas through these seal portions.

[0189] In the structure, in the last compression stage, only the space on the opposite side of the crank mechanism from the piston can be a compression chamber.

[0190] In the structure, in the compression stage preceding the last compression stage, the space on the opposite side of the crank mechanism from the piston can be a non-compression chamber, and the space on the crank mechanism side from the piston can be a compression chamber.

[0191] In the structure, in the compression stage preceding the last compression stage, the space on the opposite side of the crank mechanism from the piston can be a compression chamber, and the space on the crank mechanism side from the piston can be a non-compression chamber.

[0192] In the structure, in the at least last compression stage, the cylinder portion can have a cylinder cooling flow path portion through which a cooling fluid flows so as to surround the piston. The cylinder cooling flow path portion can include a through hole formed in the cylinder portion.

[0193] In the oil-free case, use is made in an environment in which heat is more likely to be generated than in the oil-supplied case. According to the structure, by supplying a cooling fluid to the cooling flow path portion that surrounds the cylinder portion, it is possible to efficiently cool the first seal portion.

[0194] In the structure, in the compression stage preceding the at least last compression stage, a housing cooling flow path can be formed in the plurality of housing portions. As the cooling fluid supplied to the housing cooling flow path, water or antifreeze can be used.

[0195] According to the structure, the second seal portion can be efficiently cooled by circulating the cooling fluid in the housing cooling flow path.

[0196] In the structure, the first seal portion can have a plurality of housing portions arranged between the cylinder portion and the piston rod and a plurality of ring portions held by the plurality of housing portions, and can be a contact type, in all of the compression stages.

[0197] According to the structure, the sealing performance can be further improved compared to a non-contact type seal (labyrinth seal).

[0198] In the structure, the main component of the ring material of the first seal portion of the last compression stage and / or the second seal portion of the compression stage preceding the last compression stage can be one or both of polyether ether ketone or polyimide or a component in which one or both of polyether ether ketone or polyimide is mixed with polytetrafluoroethylene.

[0199] According to the structure, the pressure resistance of the piston ring in the last compression stage can be improved.

[0200] In the structure, the pressure difference between the spaces before and after the wiping portion in the crankshaft mechanism can be zero.

[0201] According to the structure, the load on the wiping portion can be reduced.

[0202] In the structure, the pressure of the space can be substantially the same as the atmospheric pressure.

[0203] According to the structure, if it is desired to make the pressure of the space higher than the atmospheric pressure, a sealed structure needs to be provided in the crankcase, but if it is the atmospheric pressure, this structure is not needed, and the cost can be reduced.

[0204] In the structure, the compressor unit can further include a bypass line that returns the object gas to the upstream side across the compression stages.

[0205] According to the structure, by providing the bypass line, the operation can be performed in the most suitable operating condition.

[0206] The compressor unit stop method of the still another aspect of the embodiment is such that the compressor unit further includes a check valve provided in the discharge side flow path of the last compression stage, a pressure reduction line connected to the discharge side flow path at a position on a downstream side with respect to the check valve, and an open / close valve provided in the discharge side flow path at a position on a downstream side with respect to the pressure reduction line. At the time of stop of the compressor unit, the pressure in the cylinder portion of the last compression stage is reduced by closing the open / close valve and opening the pressure reduction line.

[0207] According to the method, the backflow of gas from the demand side at the time of pressure reduction is prevented by closing the open / close valve, and the backflow of gas to the compressor unit side is prevented by providing the check valve. Further, the pressure reduction on the demand side can be performed by opening the open / close valve as needed at the time of release of the pressure reduction line.

[0208] The compressor unit stop method of the still another aspect of the embodiment is such that the compressor unit further includes a check valve provided in the discharge side flow path of the last compression stage, and a pressure reduction line connected to the discharge side flow path between the last compression stage and the check valve. At the time of stop of the compressor unit, the pressure in the cylinder portion of the last compression stage is reduced by opening the pressure reduction line.

[0209] According to the method, the backflow of gas from the demand side at the time of pressure reduction can be prevented with a simple structure.

[0210] The plurality of compression stages of the still another aspect of the embodiment are used for the compressor unit.

[0211] Industrial applicability The technology of the embodiment is suitable for use in a compressor unit mounted on a ship.

Claims

1. A compressor unit, installed within a ship, recovers a target gas as an evaporation gas from the ship's liquefied natural gas storage tank and supplies at least a portion of the target gas to a demander, characterized in that... include: Multiple compression stages sequentially pressurize the target gas; Multiple shock absorbers are disposed between the multiple compression sections to suppress pressure fluctuations; as well as The crankshaft mechanism drives the pistons in each compression stage, among which... Each of the multiple compressed segments has: piston; A piston rod, connected to the piston, transmits the power of the crankshaft mechanism to the piston; The cylinder section houses the piston and forms a compression chamber; The first sealing part seals the space between the piston and the cylinder. The second sealing part surrounds the piston rod and prevents the target gas drawn into the cylinder from flowing towards the crankshaft mechanism side; A wiping portion, surrounding the piston rod on the crankshaft mechanism side relative to the second sealing portion, prevents lubricating oil from entering the cylinder section side of the crankshaft mechanism; and An oil slinger ring, installed on the piston rod between the wiping portion and the second sealing portion, further inhibits the lubricating oil from entering the cylinder side. Both the first and second sealing parts are oil-free. In at least the final compression phase, the first sealing portion has a group of piston rings disposed on the outer periphery of the piston to seal between the piston and the cylinder portion, and the second sealing portion has a plurality of housing portions disposed between the cylinder portion and the piston rod, and a plurality of ring portions held by the plurality of housing portions. The first and second seals of at least the last compression section are contact type. In the final compression section: the compression chamber, separated by the cylinder section, has the piston located only on one side of the space; and the space on the other side of the cylinder section is open to the suction-side flow path or the demand-side flow path of the final compression section, which serves as a connecting flow path between the final compression section and the preceding compression section. The preceding compression section of the final compression section is a double-action structure. In the compression section preceding the final compression section, the compression chambers are formed on both sides of the piston.

2. The compressor unit according to claim 1, characterized in that, In at least the final compression section, the cylinder section includes a cylinder cooling flow path section in which cooling fluid flows in a manner that surrounds the piston. The cylinder cooling flow path includes a through hole formed in the cylinder section.

3. The compressor unit according to claim 1, characterized in that, The space on one side is the space located on the opposite side of the crankshaft mechanism, separated by the piston, and the space on the other side is the space on the crankshaft mechanism side.

4. The compressor unit according to claim 1, characterized in that, In all compression sections, the first sealing portion has a group of piston rings disposed on the outer periphery of the piston to seal between the piston and the cylinder portion, and the second sealing portion has a plurality of housing portions disposed between the cylinder portion and the piston rod, and a plurality of ring portions held by the plurality of housing portions. The first sealing part and the second sealing part are contact type.

5. The compressor unit according to claim 1, characterized in that, Within the crankshaft mechanism, the pressure difference between the space before and after the wiping section is zero.

6. The compressor unit according to claim 5, characterized in that, The pressure in the space is essentially the same as atmospheric pressure.

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