NO20210744A1

NO20210744A1 - Compressor unit

Info

Publication number: NO20210744A1
Application number: NO20210744A
Authority: NO
Inventors: Satoshi Tezuka
Original assignee: Kobe Steel, Ltd
Priority date: 2020-06-29
Filing date: 2021-06-09
Publication date: 2021-12-30
Also published as: JP6759482B1; KR102342035B1; CN112983789A; JP2022010692A; GR1010122B

Description

DESCRIPTION

Title of Invention:

COMPRESSOR UNIT

Technical Field

[0001] The present invention relates to a compressor unit for supplying a target gas which is a boil-off gas from an LNG storage tank provided in a ship to a demand destination.

Background Art

[0002] Evaporated gas compressor units have been developed for increasing a pressure of an evaporated gas to be supplied to an engine or the like (see Japanese Unexamined Patent Publication No. 2018-534206). The evaporated gas compressor unit disclosed in Japanese Unexamined Patent Publication No. 2018-534206 includes a main compression part and a preliminary compression part arranged in parallel to the main compression part. The main compression part has five compressors. The preliminary compression part has as many compressors as the main compression part, or more compressors than the main compression part. The evaporated gas compressed by the main compression part and the preliminary compression part is supplied to an ME-GI engine. In the configuration where the main compression part and the preliminary compression part are connected in series, a part of the evaporated gas having passed through a part of the compressors of the main compression part and a part of the evaporated gas having passed through a part of the compressors of the preliminary compression part can be branched and sent to a DFGE (hereinafter, referred to as “sub-demand destination”).

[0003] By the way, the gas to be supplied to the sub-demand destination via a branch line as described above flows through a gas conveying passage, the gas having a pressure which is higher than a pressure of the gas actually required by the sub-demand destination, and then the pressure of the gas is decreased immediately before the gas flows into the sub-demand destination. Therefore, a pipe extending from a reciprocating compressor to the sub-demand destination and an instrumentation device disposed therebetween need to be resistive to a high pressure. This results in an increase in the cost of the pipe and the instrumentation device. When a plurality of reciprocating compressors is used to supply the gas to the sub-demand destination, the cost of pipes and instrumentation devices further increases.

Summary of Invention

[0004] The present invention has an object to prevent an increase in a pressure of a target gas in a flow path from a plurality of reciprocating compressors to a demand destination.

[0005] A compressor unit according to one aspect of the present invention is for use in a ship for compressing a target gas which is a boil-off gas suctioned from an LNG storage tank provided in the ship. The compressor unit includes: a first reciprocating compressor having a plurality of compression stages for compressing a target gas and supplying the target gas to a demand destination; a second reciprocating compressor having a plurality of compression stages and parallelly connected with the first reciprocating compressor, the second reciprocating compressor being configured to compress a target gas and supplying the target gas to the demand destination; and a controller. The first reciprocating compressor includes: a first branch line branching off from a stage connection passage connecting one compression stage and a subsequent compression stage with each other, the first branch line being connected to a gas conveying passage for conveying a target gas to another demand destination; a first check valve provided on the first branch line for preventing a target gas from flowing back from the gas conveying passage to the stage connection passage; a first pressure adjustment valve provided on the first branch line for adjusting at an upstream side of the first check valve a pressure of a target gas to be supplied to the gas conveying passage; a first discharge pressure detector for detecting a pressure of a target gas on a discharge side of the one compression stage; and a first supply pressure detector for detecting a pressure of a target gas at a downstream side of the first pressure adjustment valve. The second reciprocating compressor includes: a second branch line branching off from a stage connection passage connecting one compression pressure stage and a subsequent compression stage with each other, the second branch line being connected to the gas conveying passage for conveying a target gas to another demand destination; a second check valve provided on the second branch line for preventing a target gas from flowing back from the gas conveying passage to the stage connection passage of the second reciprocating compressor; a second pressure adjustment valve provided on the second branch line for adjusting at an upstream side of the second check valve a pressure of a target gas to be supplied to the gas conveying passage; a second discharge pressure detector for detecting a pressure of a target gas on a discharge side of the one compression stage of the second reciprocating compressor; and a second supply pressure detector for detecting a pressure of a target gas at a downstream side of the second pressure adjustment valve. The controller is configured to determine whether a detected pressure obtained by each of the first discharge pressure detector and the second discharge pressure detector is in a predetermined range, and adjust an opening degree of each of the first pressure adjustment valve and the second pressure adjustment valve so that a detected pressure obtained by each of the first supply pressure detector and the second supply pressure detector approaches a pressure value required by the other demand destination when the detected pressure is in the predetermined range.

[0006] The above-described compressor unit can prevent an increase in a pressure of a target gas in a flow path from the plurality of reciprocating compressors to a demand destination.

[0007] The object, features, and advantages of the present invention will be further clarified by the following detailed description and the accompanying drawings.

Brief Description of Drawings

[0008] Fig. 1 is a schematic diagram of a compressor unit.

Fig. 2 is a schematic diagram of a part of the compressor unit.

Fig. 3 is a schematic diagram of a part of the compressor unit.

Fig. 4 is a flowchart schematically showing a control of supplying a target gas from a first reciprocating compressor of the compressor unit to a sub-demand destination.

Fig. 5 is a flowchart schematically showing a supply stop control of stopping the supply of the target gas to the sub-demand destination.

Description of Embodiments

[0009] Fig. 1 a schematic view of a compressor unit 100. Each of Figs. 2 and 3 is a schematic diagram of a part of the compressor unit 100. The compressor unit 100 will be described with reference to Figs.1 to 3.

[0010] The compressor unit 100 is provided in an unillustrated ship including an LNG storage tank 101 which stores an LNG (liquefied natural gas). The compressor unit 100 is configured to suction a target gas which is a boil-off gas that occurs in the LNG storage tank 101, and compress the suctioned target gas. The compressor unit 100 is further configured to supply the compressed target gas to a main demand destination 501 (for example, an engine) and a sub-demand destination 502 (for example, a power generator, an engine, or the like). Hereinafter, the terms “upstream” and “downstream” are used in the following description on the basis of a flowing direction of the target gas.

[0011] The compressor unit 100 includes a first reciprocating compressor 300, a second reciprocating compressor 400 parallelly connected with the first reciprocating compressor 300, and a controller 420 for controlling the first reciprocating compressor 300 and the second reciprocating compressor 400. The first reciprocating compressor 300 has the same structure as the second reciprocating compressor 400.

[0012] The first reciprocating compressor 300 includes a flow path 110 for allowing the target gas to flow to the main demand destination 501, first to sixth compression stages 201 to 206 for sequentially increasing the pressure of the target gas, a plurality of coolers 281 to 285, and an unillustrated driving part. The driving part has a driving source (a motor, an engine, or the like), and a crank mechanism for transmitting a driving force from the driving source to each of the first compression stage 201 to the sixth compression stage 206.

[0013] The flow path 110 is provided with two first compression stages 201, and the second compression stage 202 to the sixth compression stage 206 one by one.

[0014] The flow path 110 connects the LNG storage tank 101 and the main demand destination 501 with each other so that the boil-off gas which has occurred in the LNG storage tank 101 can be supplied to the main demand destination 501. The flow path 110 includes a storage tank connection passage 111, a plurality of stage connection passages 115 to 119, and a demand destination supply passage 114.

[0015] The storage tank connection passage 111 has an upstream end connected to the LNG storage tank 101, and a downstream end connected to the first compression storages 201 of the compressor unit 100. In detail, the storage tank connection passage 111 has a main section 121 extending from a top portion of the LNG storage tank 101, and sub-sections 122, 123 bifurcating from the main section 121 at a downstream end thereof and respectively connected to the two first compression stages 201. In other words, the two first compression stages 201 are connected to the storage tank connection passage 111 in parallel to each other.

[0016] The stage connection passages 115 to 119 are arranged in such a manner as to allow the target gas to flow from one compression stage to a subsequent compression stage. The stage connection passage 115 is configured to allow the target gas to flow from the two first compression stages 201 to the second compression stage 202. In detail, the stage connection passage 115 has a main section 124 extending from the second compression stage 202 toward the first compression stages 201, and sub-sections 125, 126 bifurcating from the main section 124 at an upstream end thereof and respectively connected to the two first compression stages 201. The stage connection passage 116 connects the second compression stage 202 and the third compression stage 203 with each other. The stage connection passage 117 connects the third compression stage 203 and the fourth compression stage 204 with each other. The stage connection passage 118 connects the fourth compression stage 204 and the fifth compression stage 205 with each other. The stage connection passage 119 connects the fifth compression stage 205 and the sixth compression stage 206 with each other.

[0017] The demand destination supply passage 114 connects the sixth compression stage 206 to the main demand destination 501.

[0018] The coolers 281 to 285 are configured to cause heat exchange between the target gas and a coolant having a lower temperature than the target gas. The cooler 281 is provided on the stage connection passage 116 for cooling the target gas discharged from the second compression stage 202. The cooler 282 is provided on the stage connection passage 117 for cooling the target gas discharged from the third compression stage 203. The cooler 283 is provided on the stage connection passage 118 for cooling the target gas discharged from the fourth compression stage 204. The cooler 284 is provided on the stage connection passage 119 for cooling the target gas discharged from the fifth compression stage 205. The cooler 285 is provided on the demand destination supply passage 114 for cooling the target gas discharged from the sixth compression stage 206.

[0019] The compressor unit 100 includes bypass lines 411 to 414 for adjusting the pressure of the target gas in the flow path 110. The bypass lines 411 to 413 are configured to return the target gas upstream from branch points 311 to 313 on the corresponding stage connection passages 116, 117, 119. The branch points 311 to 313 are respectively provided downstream of the coolers 281, 282, 284.

[0020] The bypass line 411 is connected to the main section 121 of the storage tank connection passage 111 with bypassing the first compression stages 201 and the second compression stage 202. The bypass line 412 is connected to the stage connection passage 116 at a connection point 315 provided downstream of the branch point 311 and upstream of the third compression stage 203 with bypassing the third compression stage 203. The bypass line 413 is connected to the stage connection passage 117 at a position downstream of the branch point 312 and upstream of the fourth compression stage 204 with bypassing the fourth compression stage 204 and the fifth compression stage 205. The bypass line 414 is configured to return the target gas upstream from the branch point 314 provided downstream of the cooler 285 in the demand destination supply passage 114. The bypass line 414 is connected to the stage connection passage 119 at a position downstream of the branch point 313 and upstream of the sixth compression stage 206 with bypassing the sixth compression stage 206.

[0021] Bypass valves 421 to 424 are respectively attached to the bypass lines 411 to 414.

[0022] Pressure sensors 431 to 434 are disposed in the flow path 110 in correspondence to the bypass lines 411 to 414. The pressure sensor 431 is attached to the stage connection passage 116 at a position downstream of the cooler 281 and upstream of the branch point 311, the pressure sensor 431 being configured to detect a discharge pressure from the second compression stage 202. The pressure sensor 432 is attached to the stage connection passage 117 at a position downstream of the cooler 282 and upstream of the branch point 312, the pressure sensor 432 being configured to detect a discharge pressure from the third compression stage 203. The pressure sensor 433 is attached to the stage connection passage 119 at a position downstream of the cooler 284 and upstream of the branch point 311, the pressure sensor 433 being configured to detect a discharge pressure from the fifth compression stage 205. The pressure sensor 434 is attached to the demand destination supply passage 114 at a position downstream of the cooler 285 and upstream of the branch point 314, the pressure sensor 434 being configured to detect a discharge pressure from the sixth compression stage 206.

[0023] As shown in Fig. 2, the first reciprocating compressor 300 includes a first branch line 320 for supplying the target gas to the sub-demand destination 502 (for example, a power generator, an engine, a gas combustion apparatus). The first branch line 320 branches off from the stage connection passage 116 which connects the second compression stage 202 and the third compression stage 203 with each other. In detail, the first branch line 320 branches off from the stage connection passage 116 between the branch point 311 of the bypass line 411 from the stage connection passage 116 and the connection point 315 of the bypass line 412 to the stage connection passage 116.

[0024] The first branch line 320 has a downstream end connected to a gas conveying passage 102 extending from the sub-demand destination 502. The first reciprocating compressor 300 can supply the gas discharged from the second compression stage 202 to the sub-demand destination 502, the gas having a discharge pressure which is closest to and larger than a pressure required by the sub-demand destination 502.

[0025] The first branch line 320 is provided with a first on-off valve 321, a first pressure adjustment valve 322, a pressure sensor 324, and a first check valve 323 in this order toward the gas conveying passage 102. The first check valve 323 prevents the target gas from flowing back from the gas conveying passage 102. The first pressure adjustment valve 322 adjusts at an upstream side of the first check valve 323 the pressure of the target gas to be supplied to the gas conveying passage 102. The pressure sensor 324 detects the pressure of the target gas at a downstream side of the first pressure adjustment valve 322 (in detail, the pressure sensor 324 detects the pressure between the first pressure adjustment valve 322 and the first check valve 323).

[0026] The second reciprocating compressor 400 includes a flow path 110 having an upstream end connected to the main section 121 of the storage tank connection passage 111 of the first reciprocating compressor 300. The flow path 110 of the second reciprocating compressor 400 has a downstream end connected to the demand destination supply passage 114 of the first reciprocating compressor 300.

[0027] As shown in Fig. 3, the second reciprocating compressor 400 is configured to supply the target gas to the sub-demand destination 502 in cooperation with the first reciprocating compressor 300. The second reciprocating compressor 400 includes a second branch line 330, a second on-off valve 331, a second pressure adjustment valve 332, a pressure sensor 334, and a second check valve 333, which are similar to the first branch line 320, the first on-off valve 321, the first pressure adjustment valve 322, the pressure sensor 324, and the first check valve 323 of the first reciprocating compressor 300. The second branch line 330 is provided with the second on-off valve 331, the second pressure adjustment valve 332, the pressure sensor 334, and the second check valve 333 in this order toward the gas conveying passage 102. The remaining configuration of the second reciprocating compressor 400 is equivalent to that of the first reciprocating compressor 300. In the compressor unit 100, since the first reciprocating compressor 300 and the second reciprocating compressor 400 have the same structure, common parts utilization is encouraged therebetween.

[0028] The controller 420 shown in Fig. 1 acquires information indicating a detected pressure obtained by each of the pressure sensors 431 to 434, 324, 334 of each of the first reciprocating compressor 300 and the second reciprocating compressor 400. Although not shown in Fig. 1, in fact, the controller 420 and the pressure sensors 431 to 434, 324, 334 are electrically connected with each other. Moreover, the controller 420 is electrically connected to the bypass valves 421 to 424, the first on-off valve 321, the second on-off valve 331, the first pressure adjustment valve 322, and the second pressure adjustment valve 332.

[0029] The controller 420 is configured to adjust an opening degree of each of the bypass valves 421 to 424 on the basis of the detected pressure obtained by each of the pressure sensors 431 to 434 to keep a constant pressure balance among the storage tank connection passage 111, the stage connection passages 115 to 119, and the demand destination supply passage 114 of the first reciprocating compressor 300. The controller 420 is further configured to control the first on-off valve 321 and the first pressure adjustment valve 322 on the basis of the detected pressure obtained by each of the pressure sensor 431 and the pressure sensor 324 in order to supply the gas at a constant pressure from the first reciprocating compressor 300 to the sub-demand destination 502. Hereinafter, the pressure sensor 431 of the first reciprocating compressor 300 is called “first discharge pressure detector 431A”, and the pressure sensor 324 of the first reciprocating compressor 300 is called “first supply pressure detector 324”.

[0030] Similarly, the controller 420 adjusts an opening degree of each of the bypass valves 421 to 424 on the basis of the pressure sensors 431 to 434 to keep a constant pressure balance among the flow passage 111, the flow passages 115 to 119, and the flow passage 114 of the second reciprocating compressor 400. The controller 420 is further configured to control the second on-off valve 331 and the second pressure adjustment valve 332 on the basis of the detected pressure obtained by each of the pressure sensors 431, 324 in order to supply the gas at a constant pressure to the sub-demand destination 502. Hereinafter, the pressure sensor 431 of the second reciprocating compressor 400 is called “second discharge pressure detector 431B”, and the pressure sensor 334 of the second reciprocating compressor 400 is called “second supply pressure detector 334”.

[0031] Next, operations of the first reciprocating compressor 300 will be described below. When the first reciprocating compressor 300 is driven, the target gas is sequentially compressed in the first compression stages 201 to the sixth compression stage 206. The target gas discharged respectively from the second compression stage 202 to the sixth compression stage 206 is cooled while passing through the coolers 281 to 285. The target gas having a high pressure after discharged from the sixth compression stage 206 is supplied to the main demand destination 501 through the demand destination supply passage 114.

[0032] During the drive of the first reciprocating compressor 300, each of the first discharge pressure detector 431A and the pressure sensors 432 to 434 detects the pressure of the target gas at a corresponding position in the flow path 110. When a value of the detected pressure obtained by each of the first discharge pressure detector 431A and the pressure sensors 432 to 434 is in a predetermined normal range, the bypass valves 421 to 424 are kept closed. When the value of the detected pressure obtained by each of the first discharge pressure detector 431A and the pressure sensors 432 to 434 deviates from the normal range, the controller 420 adjusts the opening degree of each of the bypass valves 421 to 424 so that the value of the detected pressure obtained by each of the first discharge pressure detector 431A and the pressure sensors 432 to 434 can be returned to the normal range. The above-described operations are applicable to the second reciprocating compressor 400.

[0033] By the way, the first reciprocating compressor 300 supplies the target gas to the sub-demand destination 502 while supplying the target gas to the main demand destination 501. Fig. 4 shows a flow of supply of the target gas from the first reciprocating compressor 300 to the sub-demand destination 502. However, it is not necessary to always supply the target gas to the sub-demand destination 502 while supplying the target gas to the main demand destination 501.

[0034] The controller 420 keeps the first on-off valve 321 closed when the first reciprocating compressor 300 is started to operate (step S110). To confirm the pressure of the target gas at an upstream side (hereinafter, may be referred to as “primary side”) of the first pressure adjustment valve 322, the controller 420 refers to a detected pressure obtained by the first discharge pressure detector 431A (hereinafter, may be referred to as “detected pressure at the primary side”). The controller 420 determines whether the detected pressure at the primary side is in a predetermined range that is set in advance (step S120), and keeps the first on-off valve 321 closed when the detected pressure at the primary side is not in the predetermined range (No in step S120). The controller 420 opens the first on-off valve 321 when the detected pressure at the primary side falls in the predetermined range (step S130).

[0035] The controller 420 acquires a detected pressure obtained by the first supply pressure detector 324 (hereinafter, referred to as “detected pressure at a secondary side”) at a downstream side (hereinafter referred to as the “secondary side”) of the first supply pressure detector 324. Then, the controller 420 adjusts the opening degree of the first pressure adjustment valve 322 on the basis of the detected pressure at the secondary side so that the pressure of the target gas can become a pressure required by the sub-demand destination 502 (step S140).

[0036] The controller 420 executes a control of closing the first on-off valve 321 when the detected pressure at the primary side deviates from the predetermined range (step S110). By stopping the supply of the target gas to the sub-demand destination 502, the pressure balance among the flow passage 111, the flow passages 115 to 119, and the flow passage 114 of the first reciprocating compressor 300 is stabilized. In the meantime, the second reciprocating compressor 400 may continue supplying the target gas to the sub-demand destination 502. Thereafter, the detected pressure at the primary side is continuously detected (step S120). Further, the first reciprocating compressor 300 resumes the supply of the target gas to the sub-demand destination 502 when the detected pressure falls in the predetermined range again (steps S130, S140).

[0037] In the first reciprocating compressor 300, when the controller 420 receives an input of a stop signal (step S210), the controller 420 executes a control of decreasing the opening degree of the first pressure adjustment valve 322 (step S220). As a result, the detected pressure at the secondary side of the first pressure adjustment valve 322 gradually decreases. When the detected pressure at the secondary side falls below a predetermined threshold (step S230), the controller 420 closes the first on-off valve 321 (step S240). In the first reciprocating compressor 300, the first on-off valve 321 is closed after the opening degree of the first pressure adjustment valve 322 is decreased to suppress the gas flow to the secondary side. Accordingly, a rapid change in the pressure at the primary side is prevented.

[0038] The second reciprocating compressor 400 also supplies the target gas to the sub-demand destination 502 through similar steps to those shown in Fig.4. In short, the second on-off valve 331 between the second discharge pressure detector 431B and the second pressure adjustment valve 332 is kept closed by the controller 420 when the second reciprocating compressor 400 is started to operate (step S110). The controller 420 determines it on the basis of the detected pressure obtained by the second discharge pressure detector 431B whether the pressure at the primary side (an upstream side) of the second pressure adjustment valve 332 is in a predetermined range that is set in advance (step S120). The controller 420 opens the second on-off valve 331 when the detected pressure at the primary side falls in the predetermined range (step S130).

[0039] After the second on-off valve 331 is opened, the controller 420 adjusts the opening degree of the second pressure adjustment valve 332 on the basis of the detected pressure obtained by the second supply pressure detector 334 so that the pressure of the target gas at the secondary side of the second pressure adjustment valve 332 can become the pressure required by the sub-demand destination 502 (step S140).

[0040] In the second reciprocating compressor 400, the controller 420 executes a control of closing the second on-off valve 331 when the detected pressure at the primary side of the second pressure adjustment valve 332 deviates from the predetermined range, like the first reciprocating compressor 300 (step S110). This control results in stopping the supply of the target gas from the second reciprocating compressor 400 to the sub-demand destination 502. In the meantime, the first reciprocating compressor 300 may continue supplying the target gas to the sub-demand destination 502. Thereafter, the second reciprocating compressor 400 resumes the supply of the target gas to the sub-demand destination 502 when the detected pressure at the primary side falls in the predetermined range again (steps S120, S130, S140).

[0041] In the second reciprocating compressor 400, when the controller 420 receives an input of a stop signal (step S210), the controller 420 executes a control of decreasing the opening degree of the second pressure adjustment valve 332 (step S220). When the detected pressure at the secondary side falls below a predetermined threshold (step S230), the second on-off valve 331 is closed (step S240). In the second reciprocating compressor 400, the second on-off valve 331 is closed after the opening degree of the second pressure adjustment valve 332 is decreased. Accordingly, a rapid change in the pressure at the primary side is prevented.

[0042] The embodiment of the present invention is described heretofore. The pressure of the target gas decreases at the downstream side of each of the first pressure adjustment valve 322 and the second pressure adjustment valve 332 in the corresponding line. Therefore, a pipe constituting the gas conveying passage 102 and an instrumentation device to be attached to the gas conveying passage 102 do not need to be resistive to a high pressure. As a result, a cost reduction in the pipe and the instrumentation device is achieved. However, a pipe connecting the first pressure adjustment valve 322 and the first check valve 323 with each other, and a pipe connecting the second pressure adjustment valve 332 and the second check valve 333 with each other may be resistive to a high pressure.

[0043] Since the first check valve 323 is provided for the first reciprocating compressor, a negative influence onto the upstream side of the first check valve 323 even if the pressure abnormally rises at the downstream side of the first check valve 323. The first on-off valve 321 is closed when the detected pressure at the primary side of the first pressure adjustment valve 322 deviates from the predetermined range, and thus can prevent an outflow of the target gas toward the sub-demand destination 502 under an unstable state of the gas pressure at the upstream side of the first pressure adjustment valve 322. The second reciprocating compressor 400 attains the same effect.

[0044] The first reciprocating compressor 300 includes the first branch line 320 at the downstream side of the second compression stage of which discharge pressure is the smallest among the second to the sixth compression stages 202 to 206, discharge pressures of the second to the second compression stages 202 to 206 being larger than the pressure required by the sub-demand destination 502. Consequently, it is possible to prevent the pressure at the primary side of the first pressure adjustment valve 322 from unnecessarily increasing, and thus the pressure at the secondary side thereof can be easily adjusted. The second reciprocating compressor 400 attains the same effect.

[0045] The above-described embodiment merely shows an example in all the aspects, and thus should not be limited. The scope of the invention should be defined by the scope of claims, not the description of the above-described embodiments, and further cover meanings equivalent to those readable in the scope of claims and all the changes falling within the scope of the claims.

[0046] Regarding the embodiment, the first reciprocating compressor 300 may have a single first compression stage 201. The first reciprocating compressor 300 may have less than five compression stages. The second reciprocating compressor 400 may have the same structure.

[0047] The compressor unit described in connection with the various embodiment mainly has the following features.

[0048] A compressor unit according to one aspect of the above-described embodiment is for use in a ship for compressing a target gas which is a boil-off gas suctioned from an LNG storage tank provided in the ship. The compressor unit includes: a first reciprocating compressor having a plurality of compression stages for compressing a target gas and supplying the target gas to a demand destination; a second reciprocating compressor having a plurality of compression stages and parallelly connected with the first reciprocating compressor, the second reciprocating compressor being configured to compress a target gas and supplying the target gas to the demand destination; and a controller. The first reciprocating compressor includes: a first branch line branching off from a stage connection passage connecting one compression stage and a subsequent compression stage with each other, the first branch line being connected to a gas conveying passage for conveying a target gas to another demand destination; a first check valve provided on the first branch line for preventing a target gas from flowing back from the gas conveying passage to the stage connection passage; a first pressure adjustment valve provided on the first branch line for adjusting at an upstream side of the first check valve a pressure of a target gas to be supplied to the gas conveying passage; a first discharge pressure detector for detecting a pressure of a target gas on a discharge side of the one compression stage; and a first supply pressure detector for detecting a pressure of a target gas at a downstream side of the first pressure adjustment valve. The second reciprocating compressor includes: a second branch line branching off from a stage connection passage connecting one compression pressure stage and a subsequent compression stage with each other, the second branch line being connected to the gas conveying passage for conveying a target gas to the other demand destination; a second check valve provided on the second branch line for preventing a target gas from flowing back from the gas conveying passage to the stage connection passage of the second reciprocating compressor; a second pressure adjustment valve provided on the second branch line for adjusting at an upstream side of the second check valve a pressure of a target gas to be supplied to the gas conveying passage; a second discharge pressure detector for detecting a pressure of a target gas on a discharge side of the one compression stage of the second reciprocating compressor; and a second supply pressure detector for detecting a pressure of a target gas at a downstream side of the second pressure adjustment valve. The controller determines whether a detected pressure obtained by each of the first discharge pressure detector and the second discharge pressure detector is in a predetermined range, and adjusts an opening degree of each of the first pressure adjustment valve and the second pressure adjustment valve so that a detected pressure obtained by each of the first supply pressure detector and the second supply pressure detector approaches a pressure value required by the other demand destination when the detected pressure is in the predetermined range.

[0049] In this configuration, the pressure of the target gas decreases at the downstream side of each of the first pressure adjustment valve and the second pressure adjustment valve. Hence, a pipe constituting a flow passage for conveying the gas to the other demand destination and an instrumentation device to be attached to the flow passage do not need to be resistive to a high pressure. As a result, a cost reduction in the pipe and the instrumentation device is achieved.

[0050] With this configuration, the first reciprocating compressor may include a first on-off valve for opening and closing the first branch line between the first discharge pressure detector and the first pressure adjustment valve. The second reciprocating compressor may include a second on-off valve for opening and closing the second branch line between the second discharge pressure detector and the second pressure adjustment valve. The controller may open the first on-off valve and the second on-off valve when the detected pressure falls in the predetermined range.

[0051] In this configuration, the target gas is supplied to the other demand destination after confirmation of the state where the pressure at the upstream side of each of the first pressure adjustment valve and the second pressure adjustment valve is in the predetermined range.

[0052] With this configuration, the controller may decrease the opening degree of each of the first pressure adjustment valve and the second pressure adjustment valve in accordance with an instruction of stopping supply of a target gas to the other demand destination, and closes the first on-off valve and the second on-off valve when the detected pressure obtained by each of the first supply pressure detector and the second supply pressure detector falls below a predetermine threshold.

[0053] In this configuration, the controller can prevent a rapid pressure increase in the stage connection passage of each of the first reciprocating compressor and the second reciprocating compressor by decreasing the opening degree of each of the first pressure adjustment valve and the second pressure adjustment valve before closing the first on-off valve and the second on-off valve.

[0054] With this configuration, the stage connection passage may be provided on a discharge side of a compression stage of the plurality of compression stages, the compression stage being configured to discharge a target gas having a pressure which is closest to and larger than the pressure value required by the other demand destination.

[0055] In this configuration, a pressure at a primary side of each of the first pressure adjustment valve and the second pressure adjustment valve can be kept low. Accordingly, the pressure is easily controlled.

[0056] With this configuration, the first reciprocating compressor may have as many compression stages as the second reciprocating compressor.

[0057] The technologies described in the embodiment are preferably applicable a compressor unit for use in a ship.

This application is based on Japanese Patent application No.2020-111390 filed in Japan Patent Office on June 29, 2020, the contents of which are hereby incorporated by reference.

Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.

Claims

1. A compressor unit (100) for use in a ship for compressing a target gas which is a boil-off gas suctioned from an LNG storage tank (101) provided in the ship, the compressor unit (100) comprising:

a first reciprocating compressor (300) having a plurality of compression stages (201-205) for compressing a target gas and supplying the target gas to a demand destination (501);

a second reciprocating compressor (400) having a plurality of compression stages (201-205) and parallelly connected with the first reciprocating compressor (300), the second reciprocating compressor (400) being configured to compress a target gas and supplying the target gas to the demand destination (501); and

a controller (420), wherein

the first reciprocating compressor (300) includes:

a first branch line (320) branching off from a stage connection passage (116) connecting one compression stage (202) and a subsequent compression stage (203) with each other, the first branch line (320) being connected to a gas conveying passage (102) for conveying a target gas to another demand destination (502);

a first check valve (323) provided on the first branch line (320) for preventing a target gas from flowing back from the gas conveying passage (102) to the stage connection passage (116);

a first pressure adjustment valve (322) provided on the first branch line (320) for adjusting at an upstream side of the first check valve (323) a pressure of a target gas to be supplied to the gas conveying passage (102);

a first discharge pressure detector (431A) for detecting a pressure of a target gas on a discharge side of the one compression stage (202); and

a first supply pressure detector (324) for detecting a pressure of a target gas at a downstream side of the first pressure adjustment valve (322),

the second reciprocating compressor (400) includes:

a second branch line (330) branching off from a stage connection passage (116) connecting one compression pressure stage (202) and a subsequent compression stage (203) with each other, the second branch line (330) being connected to the gas conveying passage (102) for conveying a target gas to another demand destination (502);

a second check valve (333) provided on the second branch line (330) for preventing a target gas from flowing back from the gas conveying passage (102) to the stage connection passage (116) of the second reciprocating compressor (400);

a second pressure adjustment valve (332) provided on the second branch line (330) for adjusting at an upstream side of the second check valve (333) a pressure of a target gas to be supplied to the gas conveying passage (102);

a second discharge pressure detector (431B) for detecting a pressure of a target gas on a discharge side of the one compression stage (202) of the second reciprocating compressor (400); and

a second supply pressure detector (334) for detecting a pressure of a target gas at a downstream side of the second pressure adjustment valve (332), and

the controller (420) is configured to determine whether a detected pressure obtained by each of the first discharge pressure detector (431A) and the second discharge pressure detector (431B) is in a predetermined range, and adjust an opening degree of each of the first pressure adjustment valve (322) and the second pressure adjustment valve (332) so that a detected pressure obtained by each of the first supply pressure detector (324) and the second supply pressure detector (334) approaches a pressure value required by the other demand destination (502) when the detected pressure is in the predetermined range.

2. The compressor unit (100) according to claim 1, wherein

the first reciprocating compressor (300) includes a first on-off valve (321) for opening and closing the first branch line (320) between the first discharge pressure detector (431A) and the first pressure adjustment valve (322),

the second reciprocating compressor (400) includes a second on-off valve (331) for opening and closing the second branch line (330) between the second discharge pressure detector (431B) and the second pressure adjustment valve (332), and

the controller (420) is configured to open the first on-off valve (321) and the second on-off valve (331) when the detected pressure falls in the predetermined range.

3. The compressor unit (100) according to claim 2, wherein

the controller (420) is configured to decrease the opening degree of each of the first pressure adjustment valve (322) and the second pressure adjustment valve (332) in accordance with an instruction of stopping supply of a target gas to the other demand destination (502), and close the first on-off valve (321) and the second on-off valve (331) when the detected pressure obtained by each of the first supply pressure detector (324) and the second supply pressure detector (334) falls below a predetermine threshold.

4. The compressor unit (100) according to any one of claims 1 to 3, wherein the stage connection passage (116) is provided on a discharge side of a compression stage (202) of the plurality of compression stages (201-205), the compression stage (202) being configured to discharge a target gas having a pressure which is closest to and larger than the pressure value required by the other demand destination (502).

5. The compressor unit (100) according to claim 4, wherein

the first reciprocating compressor (300) has as many compression stages (201-205) as the second reciprocating compressor (400).