CN113653629A

CN113653629A - Compressor unit and compressor unit control program

Info

Publication number: CN113653629A
Application number: CN202111044228.7A
Authority: CN
Inventors: 胁田康平; 新谷浩司
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2021-01-06
Filing date: 2021-09-07
Publication date: 2021-11-16
Anticipated expiration: 2041-09-07
Also published as: KR102355150B1; CN113653629B; JP2022106106A; GR20210100621A; NO20211183A1; GR1010277B; JP6850403B1

Abstract

The invention provides a compressor unit and a compressor unit control program. The compressor unit includes a first reciprocating compressor, a second reciprocating compressor connected in parallel with the first reciprocating compressor, and a control part. The first reciprocating compressor includes a first check valve, a first pressure sensor, a first bypass flow path, and a first bypass valve. The second reciprocating compressor includes a second check valve, a second pressure sensor, a second bypass flow path, and a second bypass valve. The control unit controls the opening degree of the first bypass valve such that the pressure detected by the first pressure sensor becomes a first set value, and controls the opening degree of the second bypass valve such that the pressure detected by the second pressure sensor becomes a second set value lower than the first set value. Accordingly, the gas supply amount from the compressor can be easily made to coincide with the gas demand amount of the demand side.

Description

Compressor unit and compressor unit control program

Technical Field

The present invention relates to a compressor unit and a compressor unit control program.

Background

Conventionally, a compressor unit for compressing a boil-off gas generated by vaporization of a liquefied gas in a storage tank in a liquefied natural gas carrier or the like is known. Such a compressor unit has a structure in which a plurality of compressors of a plurality of stages are arranged in parallel. In this compressor unit, the gas discharged from each compressor is supplied to a demand source such as an engine.

Such techniques are disclosed in Japanese patent application publication Nos. 2018-518415, 2018-534206, and 2019-11735. Japanese patent laid-open publication No. 2018-518415 discloses a boil-off gas compressor mounted on an LNG ship or the like, in which a reciprocating compressor and a centrifugal compressor are provided in parallel. Japanese patent laid-open publication No. 2018-534206 discloses a boil-off gas treatment system for an LNG carrier, which includes a main compression unit and a backup compression unit that is used instead of the main compression unit when the main compression unit is not used. Japanese laid-open patent publication No. 2019-11735 discloses that 2 gas compressors are arranged in parallel in an LNG carrier, and one of the compressors is used as a spare compressor, as in japanese laid-open patent publication No. 2018-534206.

In the case where gas is supplied to a demand side from the boil-off gas compressor disclosed in japanese patent laid-open publication No. 2018-518415, the sum of the gas handling amounts (gas supply amounts) of the compressors provided in parallel needs to satisfy the gas demand amount of the demand side. Here, if the required gas amount of the demand side varies, the total gas supply amount from the compressors does not match the required gas amount, and as a result, the discharge pressure of each compressor varies. Specifically, the discharge pressure decreases when the required amount of gas increases, and the discharge pressure increases when the required amount of gas decreases.

In contrast, a technique is conceivable in which the supply amount of gas from the compressor is made to match the varied required amount of gas by controlling each compressor so that the discharge pressure is maintained at a predetermined set pressure. However, when the set values (target values) of the discharge pressures of the compressors are made to be the same, the gas throughput of both the compressors needs to be adjusted based on the pressure information on the discharge side (demand side), which makes the control complicated. That is, when the pressure control accuracy is deteriorated, it may be difficult to match the gas supply amount from the compressor with the gas demand amount of the demand side.

Disclosure of Invention

The purpose of the present invention is to provide a compressor unit and a compressor unit control program that make it possible to easily match the amount of gas supplied from a compressor to the amount of gas required by a customer.

A compressor unit according to an aspect of the present invention is a compressor unit that is installed in a ship and compresses a target gas, which is a boil-off gas, sucked from a liquefied natural gas storage tank of the ship. This compressor unit includes: a first reciprocating compressor having a plurality of compression stages for compressing the target gas to be supplied to a demand side; a second reciprocating compressor having a plurality of compression stages and connected in parallel to the first reciprocating compressor in such a manner as to compress the target gas and supply the compressed target gas to the demand side; and a control part controlling driving of the first reciprocating compressor and the second reciprocating compressor. The first reciprocating compressor includes: a first check valve disposed at a downstream position from the final compression stage; a first pressure sensor disposed between the final compression section and the first check valve; a first bypass flow path bypassing at least the final compression section; and a first bypass valve provided in the first bypass flow path. The second reciprocating compressor includes: a second check valve disposed at a downstream position from the final compression stage; a second pressure sensor disposed between the final compression section and the second check valve; a second bypass flow path bypassing at least the final compression section; and a second bypass valve provided in the second bypass flow path. The compressor unit is configured such that the target gas discharged from the second reciprocating compressor and the target gas discharged from the first reciprocating compressor merge at a flow path downstream of the first check valve and the second check valve. The control unit includes an opening degree control unit that controls an opening degree of the first bypass valve such that a pressure detected by the first pressure sensor becomes a first set value, and controls an opening degree of the second bypass valve such that a pressure detected by the second pressure sensor becomes a second set value lower than the first set value.

Another aspect of the present invention relates to a compressor unit control program for controlling an operation of the compressor unit, the compressor unit control program causing a computer constituting the control unit to function as an opening degree control unit and to be stored in a storage medium of the computer, wherein the opening degree control unit controls an opening degree of the first bypass valve such that a detected pressure of the first pressure sensor becomes the first set value, and controls an opening degree of the second bypass valve such that a detected pressure of the second pressure sensor becomes the second set value.

According to the present invention, the amount of gas supplied from the compressor can be easily matched with the amount of gas required by the demand side.

Drawings

Fig. 1 is a schematic diagram of a compressor unit according to an embodiment.

Fig. 2 is a functional block diagram of the control unit in the first embodiment.

Fig. 3 is a flowchart for explaining the opening degree control of the first bypass valve.

Fig. 4 is a flowchart for explaining the opening degree control of the second bypass valve.

Fig. 5 is a functional block diagram of a control unit in the second embodiment.

Detailed Description

(first embodiment)

Hereinafter, a compressor unit and a compressor unit control program according to an embodiment will be described in detail with reference to the drawings. Fig. 1 is a schematic diagram of a compressor train 100.

The compressor train 100 is installed in a ship (not shown) having an LNG storage tank 101 for storing LNG (Liquefied Natural Gas). The compressor unit 100 sucks a target gas (boil off gas) generated in the LNG storage tank 101 and compresses the sucked target gas. The compressor unit 100 supplies the compressed target gas to a demand side 501 (for example, an engine). In the following description, terms "upstream" and "downstream" are used with reference to the flow direction of the target gas.

The compressor unit 100 includes: a first reciprocating compressor 300 compressing and supplying the object gas to the demander 501; a second reciprocating compressor 400 connected in parallel with the first reciprocating compressor 300 in such a manner as to compress and supply the object gas to the demand side 501; and a control part 420 controlling driving of the first reciprocating compressor 300 and the second reciprocating compressor 400. The first reciprocating compressor 300 and the second reciprocating compressor 400 are substantially the same configuration.

The compressor unit 100 includes a flow path 102 for circulating a target gas, which is a boil-off gas generated in the LNG storage tank 101, toward the demand side 501. The flow path 102 connects the LNG storage tank 101 and the demand side 501 to each other so that the target gas can be supplied to the demand side 501. The flow path 102 includes a first flow path 110 for allowing the target gas to flow to the first reciprocating compressor 300 and a second flow path 210 connected to the first flow path 110 for allowing the target gas to flow to the second reciprocating compressor 400. The second flow path 210 branches from the first flow path 110 at a location between the LNG storage tank 101 and a first compression stage 201 (described later) in the first flow path 110, and is connected to the first flow path 110 at a location downstream of a sixth compression stage 206 (final compression stage), described later.

The first reciprocating compressor 300 includes: a first compression stage 201 to a sixth compression stage 206 for sequentially increasing the pressure of the target gas; a plurality of coolers 281-285; and a driving unit (not shown). The drive unit includes a drive source (a motor, an engine, and the like) and a crank mechanism that transmits power of the drive source to the first compression stage 201 to the sixth compression stage 206.

The first compression stage 201 is provided with 2 in the first channel 110, and the second compression stage 202 to the sixth compression stage 206 are provided with 1 in each of the first channel 110. The configuration is not limited to the configuration in which 2 first compression stages 201 are provided in parallel with each other. It is also possible to have a structure in which 1 first compression stage 201 is provided.

The first flow path 110 includes a storage tank connection flow path 111, a plurality of stage connection flow paths 115 to 119, and a demand side supply flow path 114.

The storage tank connection line 111 has an upstream end connected to the LNG storage tank 101 and a downstream end connected to the first compression stage 201 of the compressor train 100. Specifically, the storage tank connection passage 111 includes a main pipe 121 extending from an upper portion of the LNG storage tank 101, and

branch pipes

122 and 123 branching into two branches at a downstream end of the main pipe 121 and connected to the 2 first compression stages 201. That is, the 2 first compression stages 201 are connected to the storage tank connection passage 111 in parallel with each other.

The stage connecting channels 115-119 are arranged so that the target gas flows from 1 compression stage to the next compression stage. The stage connection flow path 115 flows the target gas from the 2 first compression stages 201 to the second compression stage 202. That is, the stage connecting passage 115 includes a main pipe 124 extending from the second compression stage 202 toward the first compression stage 201, and

branch pipes

125 and 126 branching into two at an upstream end of the main pipe 124 and connected to 2 first compression stages 201. The stage connecting flow path 116 connects the second compression stage 202 and the third compression stage 203 to each other. The stage connecting flow path 117 connects the third compression stage 203 and the fourth compression stage 204 to each other. The stage connecting flow path 118 interconnects the fourth compression stage 204 and the fifth compression stage 205. The stage connecting flow path 119 connects the fifth compression stage 205 and the sixth compression stage 206 to each other.

The consumer supply flow path 114 is a flow path connecting the sixth compression stage 206 to the consumer 501.

The coolers 281 to 285 exchange heat between the target gas and cooling water having a lower temperature than the target gas. The cooler 281 is provided in the stage connecting flow path 116 so as to cool the target gas discharged from the second compression stage 202. The cooler 282 is provided in the stage connecting passage 117 so as to cool the target gas discharged from the third compression stage 203. The cooler 283 is provided in the stage connecting passage 118 so as to cool the target gas discharged from the fourth compression stage 204. The cooler 284 is provided in the stage connecting flow path 119 so as to cool the target gas discharged from the fifth compression stage 205. The cooler 285 is provided in the demand side supply passage 114 so as to cool the target gas discharged from the sixth compression stage 206.

The compressor unit 100 (first reciprocating compressor 300) has bypass flow paths 411 to 413, 414A for adjusting the pressure of the target gas in the first flow path 110. The bypass channels 411 to 413 return at least a part of the target gas from the branch parts 311 to 313 on the

segment connecting channels

116, 117, and 119 to the upstream side. The branching portions 311 to 313 are located downstream of the

coolers

281, 282, 284.

The bypass passage 411 bypasses the first compression stage 201 and the second compression stage 202 and is connected to the main pipe 121 of the reserve tank connection passage 111. The bypass flow path 412 bypasses the third compression stage 203, and is connected to the stage connection flow path 116 at a connection portion 315 on the downstream side of the branch portion 311 and on the upstream side of the third compression stage 203. The bypass passage 413 bypasses the fourth compression stage 204 and the fifth compression stage 205, and is connected to the stage connection passage 117 on the downstream side of the branch portion 312 and on the upstream side of the fourth compression stage 204. The bypass passage 414A (first bypass passage) returns at least a part of the target gas from the branch portion 314 of the demand-side supply passage 114 located on the downstream side of the cooler 285 to the upstream side. That is, the bypass passage 414A is a first bypass passage that bypasses at least the final compression stage. The bypass passage 414A bypasses the sixth compression stage 206 (final compression stage), and is connected to the stage connection passage 119 on the downstream side of the branch portion 313 and on the upstream side of the sixth compression stage 206.

Bypass valves

421A, 422A, 423A, 424A are respectively attached to the bypass flow passages 411 to 413, 414A. The bypass valve 424A provided in the bypass passage 414A corresponds to a first bypass valve provided in a first bypass passage that bypasses at least the final compression stage.

Pressure sensors 431 to 433 and 434A are disposed in the first flow path 110 corresponding to the bypass flow paths 411 to 413 and 414A. The pressure sensor 431 is attached to the stage connection flow path 116 on the downstream side of the cooler 281 and on the upstream side of the branching portion 311 so as to detect the discharge pressure, which is the pressure of the gas discharged from the second compression stage 202. The pressure sensor 432 is attached to the stage connection flow path 117 on the downstream side of the cooler 282 and on the upstream side of the branching portion 312 so as to detect the discharge pressure, which is the pressure of the gas discharged from the third compression stage 203. The pressure sensor 433 is attached to the stage connection flow path 119 on the downstream side of the cooler 284 and on the upstream side of the branch portion 313 so as to detect the discharge pressure, which is the pressure of the gas discharged from the fifth compression stage 205. Since the pressure sensor 434A (first pressure sensor) is used to detect the pressure of the gas discharged from the sixth compression stage 206, that is, the discharge pressure, and to control the demand-side supply pressure, it is installed on the demand-side supply flow path 114 on the downstream side of the cooler 285 and on the downstream side of the branch portion 314.

A first check valve 451 is disposed in the first flow path 110 downstream of the sixth compression stage 206. Specifically, the first check valve 451 is provided downstream of the branch portion 314 in the demand side supply flow path 114, and prevents the reverse flow of the target gas from the demand side 501 to the sixth compression stage 206 and from the second reciprocating compressor 400.

In the following description, a portion of the demand-side supply flow path 114 that is located upstream of the first check valve 451 (a portion on the first reciprocating compressor 300 side) is referred to as a "first compressor-side flow path portion 114A". A portion of the demand-side supply flow path 114 that is located downstream of the first check valve 451 is referred to as a "first demand-side flow path portion 114D". A portion of the demand-side supply flow path 114 of the second flow path 210 that is located upstream of the second check valve 452 (a portion on the second reciprocating compressor 400 side) to be described later is referred to as a "second compressor-side flow path portion 114B". A portion of the demand-side supply flow path 114 of the second flow path 210 that is located downstream of the second check valve 452 is referred to as a "second demand-side flow path portion 114C". The second demand side passage portion 114C is connected to the first demand side passage portion 114D. The pressure sensor 434A is provided between the branch portion 314 and the first check valve 451 at the first compressor-side flow path portion 114A.

As shown in fig. 1, the upstream end of the second flow path 210 is connected to the main pipe 121 of the reserve tank connection flow path 111 in the first flow path 110. The downstream end of the second channel 210 is connected to the demand side supply channel 114 in the first channel 110. That is, the object gas discharged from the second reciprocating compressor 400 through the second demand side flow path portion 114C and the object gas discharged from the first reciprocating compressor 300 through the first demand side flow path portion 114D are merged at the merging point 13.

The second reciprocating compressor 400 has the same structure as the first reciprocating compressor 300 (the number of compression stages is the same). In fig. 1, substantially the same symbols are attached to corresponding structures between the second reciprocating compressor 400 and the first reciprocating compressor 300. That is, the second reciprocating compressor 400 includes first to sixth compression stages 201 to 206. A bypass passage 411 for bypassing the first and second compression stages 201 and 202, a bypass passage 412 for bypassing the third compression stage 203, and a bypass passage 413 for bypassing the fourth and fifth compression stages 204 and 205 are provided. Bypass

valves

421B, 422B, 423B are respectively attached to the bypass flow passages 411 to 413. A second bypass passage 414B bypassing the sixth compression stage 206 is provided. A second bypass valve 424B is attached to the second bypass passage 414B. The second bypass flow path 414B is a bypass flow path that bypasses at least the final compression stage.

Also, the second reciprocating compressor 400 includes a second check valve 452 and a second pressure sensor 434B disposed downstream compared to the sixth compression stage 206. The second check valve 452 is provided downstream of the branch portion 314 in the demand side supply flow path 114 of the second flow path 210, and prevents the reverse flow of the target gas from the first reciprocating compressor 300 side. The second pressure sensor 434B is provided between the sixth compression stage 206 and the second check valve 452, that is, the second compressor-side flow passage portion 114B of the second flow passage 210.

In the compressor unit 100, since the first reciprocating compressor 300 and the second reciprocating compressor 400 have substantially the same structure, the components used in each can be commonly used.

As shown in fig. 2, the control unit 420 includes a detection pressure receiving unit 461, a determination unit 463, an opening degree control unit 464, and a storage unit 466.

The detected pressure receiving unit 461 receives data indicating the detected pressure of the first pressure sensor 434A and the detected pressure of the second pressure sensor 434B, respectively.

The set value of the discharge pressure of the sixth compression stage 206 of the second reciprocating compressor 400 (hereinafter, referred to as "second set value") is a value lower than the set value of the discharge pressure of the sixth compression stage 206 of the first reciprocating compressor 300 (hereinafter, referred to as "first set value"). The first set value is set to the same value as the required pressure of the demand side 501. In the present embodiment, the second set value is set to a value of 99% or more and less than 100% of the first set value. In the following description, the first set value is 30MPa, and the second set value is 29.9 MPa. The second set value may be set to another value of 29.7MPa or more and less than 30 MPa.

The judgment section 463 compares the pressure detected by the first pressure sensor 434A with the first set value to judge the magnitude relationship therebetween, and compares the pressure detected by the second pressure sensor 434B with the second set value to judge the magnitude relationship therebetween. The determination unit 463 outputs information of each determination result to the opening degree control unit 464.

The opening degree control portion 464 controls the opening degree of the first bypass valve 424A such that the pressure detected by the first pressure sensor 434A becomes the first set value, and controls the opening degree of the second bypass valve 424B such that the pressure detected by the second pressure sensor 434B becomes the second set value. The opening degree control unit 464 transmits an opening degree change signal (an opening degree increase signal or an opening degree decrease signal) to the first bypass valve 424A and the second bypass valve 424B based on the information of the determination result output from the determination unit 463. Details of this control will be described later.

The storage 466 stores a program for controlling the operation of the compressor unit 100. The compressor unit control program causes the computer constituting the control unit 420 to function as the detected pressure receiving unit 461, the determining unit 463, and the opening degree control unit 464. That is, the functions of the detected pressure receiving Unit 461, the determining Unit 463, and the opening degree control Unit 464 are obtained by reading and executing a program stored in the storage Unit 466 by a Computer (CPU) constituting the control Unit 420. The storage part 466 is formed using a storage medium such as various storage devices, and a compressor unit control program is stored in the storage medium.

The control unit 420 may control the opening degree of the bypass valve 421A based on the detected pressure of the pressure sensor 431 of the first reciprocating compressor 300 by the same functional configuration as described above. Similarly, the control unit 420 may control the opening degrees of the

bypass valves

422A and 423A based on the detected pressures of the pressure sensors 432 and 433, respectively. The same applies to the control of the bypass valves 421B to 423B of the second reciprocating compressor 400.

The control unit 420 may be formed of a plurality of controllers provided corresponding to the bypass valves 421A to 424A and 421B to 424B, respectively. In this case, each controller has functions corresponding to the detection pressure receiving unit 461, the determination unit 463, the opening degree control unit 464, and the storage unit 466.

Hereinafter, the opening degree control of the first bypass valve 424A and the second bypass valve 424B by the opening degree control portion 464 will be described based on the flowcharts of fig. 3 and 4. Fig. 3 is a flowchart for explaining the opening degree control of the first bypass valve 424A, and fig. 4 is a flowchart for explaining the opening degree control of the second bypass valve 424B.

First, the opening degree control of the first bypass valve 424A is explained based on fig. 3. First, the first pressure sensor 434A detects the gas pressure in the first compressor-side flow path portion 114A, and transmits data indicating the detected pressure to the detected pressure receiving portion 461 (step S10). Next, the determination unit 463 compares the detection pressure of the first pressure sensor 434A (hereinafter, may be referred to as a first detection pressure) with the first set value, and determines whether or not the first detection pressure is greater than the first set value (step S20).

When the first detected pressure is higher than the first set value (yes in step S20), the opening degree control unit 464 receives information of the determination result from the determination unit 463, and increases the opening degree of the first bypass valve 424A (step S30). Accordingly, the flow rate of the target gas flowing from the branch portion 314 into the first bypass passage 414A increases, and therefore the pressure detected in the first compressor-side passage portion 114A gradually decreases. On the other hand, when the first detected pressure is equal to or lower than the first set value (no in step S20), the opening degree control section 464 proceeds to step S40 without increasing the opening degree of the first bypass valve 424A.

In step S40, the determination unit 463 compares the first detection pressure with the first set value, and determines whether or not the first detection pressure is smaller than the first set value. When the first detected pressure is lower than the first set value (yes in step S40), the opening degree control unit 464 receives information of the determination result from the determination unit 463, and decreases the opening degree of the first bypass valve 424A (step S50). Accordingly, the flow rate of the target gas flowing from the branch portion 314 into the first bypass passage 414A decreases, and therefore the pressure detected in the first compressor-side passage portion 114A gradually increases. On the other hand, when the first detected pressure is equal to the first set value (no in step S40), the opening degree controller 464 does not increase or decrease the opening degree of the first bypass valve 424A, and returns to step S10. By repeating the above steps S10 to S50, the first detected pressure detected at the first compressor-side flow path portion 114A approaches the first set value (e.g., 30 MPa).

Fig. 4 shows a flow of the opening degree control of the second bypass valve 424B. This control flow is the same as the control flow of fig. 3 except for the point where the second pressure sensor 434B is used instead of the first pressure sensor 434A, the point where the second set value is used instead of the first set value, and the point where the opening degree of the second bypass valve 424B is controlled instead of the first bypass valve 424A. Therefore, detailed description of the control flow of the second bypass valve 424B is omitted. By repeating steps S11 to S51 in fig. 4, the pressure detected by the second pressure sensor 434B in the second compressor-side flow path portion 114B approaches the second set value (for example, 29.9 MPa).

As described above, the second reciprocating compressor 400 is controlled so that the pressure of the target gas in the second compressor-side flow passage section 114B becomes the second set value, and the first reciprocating compressor 300 is controlled so that the pressure of the target gas in the first compressor-side flow passage section 114A becomes the first set value.

In the compressor unit 100, when the pressure of the target gas in the first compressor side flow passage section 114A and the second compressor side flow passage section 114B is higher than the pressure of the target gas in the first demand side flow passage section 114D and the second demand side flow passage section 114C, the target gas is supplied from the two

compressors

300 and 400 to the demand direction 501, respectively.

As described above, the first set value of the discharge pressure of the first reciprocating compressor 300 is a value greater than the second set value of the discharge pressure of the second reciprocating compressor 400. Accordingly, the opening degree of the first bypass valve 424A of the first reciprocating compressor 300 is smaller than the opening degree of the second bypass valve 424B of the second reciprocating compressor 400. As a result, the amount of the target gas supplied from the first reciprocating compressor 300 to the demand side 501 is larger than the amount supplied from the second reciprocating compressor 400.

On the other hand, when the required amount of the gas from the demand side 501 decreases, the consumption amount of the target gas decreases, and therefore, the pressures in the first demand side flow path portion 114D and the second demand side flow path portion 114C increase. Then, if the pressure exceeds the second set value, the second reciprocating compressor 400 is in a state where the target gas is not supplied to the downstream side of the second check valve 452. Therefore, the target gas is supplied to the demand side 501 only by using the first reciprocating compressor 300.

As described above, by setting the second set value to be lower than the first set value, when the required amount of the gas of the demand side 501 varies, the target gas can be supplied to the demand side 501 in an amount corresponding to the required amount of the demand side 501 without performing control for adjusting the flow rate balance of the two

compressors

300 and 400 every time.

Sometimes the equipment of the demand side 501 is load-disconnected due to tripping or the like. At this time, the controller 420 forcibly increases the opening degrees of the bypass valves 421A to 424A and 421B to 424B of all the compression stages 201 to 206 so that the entire amount of the target gas discharged from the two

compressors

300 and 400 does not flow into the second demand-side flow path portion 114C. At this time, the amount of the target gas discharged from the first reciprocating compressor 300 is greater than the amount of the target gas discharged from the second reciprocating compressor 400, and therefore, the opening degree of the bypass valves 421A to 424A in the first reciprocating compressor 300 is increased to a greater extent than the opening degree of the bypass valves 421B to 424B in the second reciprocating compressor 400. This prevents the target gas from being supplied from the two

compressors

300 and 400 to the demand side 501 in the load-disconnected state. The width of increase in the opening degrees of the bypass valves 421A to 424A and 421B to 424B may be corrected in consideration of the characteristics of the respective bypass valves.

Although the first embodiment of the present invention has been described above, in the case where 2

reciprocating compressors

300 and 400 are used in combination to operate, it is conceivable to perform discharge pressure control in which the set values of the discharge pressures in the final compression stages are the same as a comparative example of the first embodiment. However, in such discharge pressure control, it is necessary to control the opening degrees of the first bypass valve 424A and the second bypass valve 424B to be always the same, and therefore, when the pressure fluctuation of the demand side 501 occurs, it is necessary to change the opening degrees of both the bypass valves by the same amount in accordance with the fluctuation. Therefore, the discharge pressure control of the compressor unit 100 becomes complicated.

In contrast, in the compressor unit 100 according to the present embodiment, the respective set values are set so that there is a difference between the set values of the discharge pressure in the sixth compression stage 206, that is, the final compression stage. Accordingly, when the required amount of gas of the demand side 501 varies, the state in which the target gas is supplied from the two

compressors

300 and 400 is switched to the state in which the target gas is supplied only from the first reciprocating compressor 300. That is, even without the discharge pressure control according to the comparative example, the target gas of an amount corresponding to the required amount of the demand side 501 can be easily supplied to the demand side 501.

(second embodiment)

A compressor unit and a compressor unit control program according to a second embodiment will be described below with reference to fig. 5. Since the second embodiment is basically the same as the first embodiment, only the differences from the first embodiment will be described here.

As shown in fig. 5, the control unit 420 of the second embodiment further includes a set value determining unit 462 and a required pressure receiving unit 465. The required pressure receiving unit 465 receives data indicating the required pressure of the target gas from the demand side 501. The set value determining unit 462 determines the first set value and the second set value based on the required pressure of the target gas received by the required pressure receiving unit 465. For example, when the required pressure of the demand side 501 is 30MPa, the set value determining unit 462 sets the first set value to 30MPa, which is the same as the required pressure, and sets the second set value to a value of 29.7MPa or more and less than 30 MPa.

The set value determination unit 462 changes the first set value and the second set value while maintaining the difference between the first set value and the second set value, based on the change in the demand pressure from the demand side 501. For example, if the required pressure is changed from 30MPa to 25MPa, data indicating the changed required pressure is input from the demand side 501 to the required pressure receiving unit 465. Based on the input data, the set value determination unit 462 changes the first set value from 30MPa to 25MPa, and changes the second set value to a value of 24.75MPa or more and less than 25 MPa.

The compressor unit control program according to the second embodiment causes the computer constituting the control unit 420 to function also as a set value determination unit 462 and a requested pressure receiving unit 465. That is, the CPU reads and executes the program stored in the storage unit 466, thereby obtaining the functions of the set value determining unit 462 and the required pressure receiving unit 465.

As described above, in the second embodiment, when the first set value and the second set value are changed in response to a change in the demand pressure of the demand side 501, the difference between the two set values is maintained. In this case, the operation of the compressor that can easily cope with the gas demand of the demand side 501 can be realized.

(third embodiment)

Next, a compressor unit 100 according to a third embodiment will be described. The second set value of the second reciprocating compressor 400 may be set to a value of 93% (28 MPa) or more and less than 99% (29.7 MPa) of the first set value of the first reciprocating compressor 300. At this time, when the compressor unit 100 is operated, the target gas is normally supplied only from the first reciprocating compressor 300 to the demand side 501 without being supplied from the second reciprocating compressor 400 to the demand side 501.

On the other hand, if the gas demand from the demand side 501 increases, the increased gas demand exceeds the maximum gas handling capacity (maximum gas supply capacity) of the first reciprocating compressor 300, and even if the first bypass valve 424A is fully closed, the gas supply capacity to the demand side 501 becomes insufficient. As a result, the amount of the target gas decreases in the first demand side flow path portion 114D and the second demand side flow path portion 114C, and the pressure gradually decreases.

Then, if the pressures of the first demand side flow path portion 114D and the second demand side flow path portion 114C decrease to the second set value, the object gas compressed by the second reciprocating compressor 400 flows from the merging point 13 into the first demand side flow path portion 114D and is supplied to the demand side 501. Thus, the shortage of the gas treatment amount of the first reciprocating compressor 300 can be supplemented with the gas treatment amount of the second reciprocating compressor 400, and the increased gas demand from the demand side 501 can be satisfied.

The embodiments disclosed herein are illustrative in all respects and should not be construed as being limiting. The scope of the present invention is defined by the claims rather than the description above, and includes all modifications equivalent in meaning and scope to the claims. Therefore, the following embodiments are also included in the scope of the present invention.

In the above-described embodiment, the case where the pressure of the target gas is controlled only by the bypass mechanism (bypass flow path and bypass valve) has been described, but the present invention is not limited to this. As the control of the processing amount and the pressure of the target gas, for example, a known control such as an unloading control may be combined with the control using the bypass mechanism.

In the above embodiment, the case where both the first reciprocating compressor 300 and the second reciprocating compressor 400 have 6 compression stages has been described, but the number of compression stages may be 5 stages or less, or 7 stages or more. In addition, the number of stages of the compression stages of the first and second

reciprocating compressors

300 and 400 may also be different from each other.

The demand source 501 is not limited to the engine, and may be other ship equipment such as a generator.

In the embodiment, the bypass flow path 414A (first bypass flow path) bypasses only the final compression stage, but instead, the bypass flow path 414A may bypass the final compression stage and 1 or more compression stages ahead thereof. Further, the second bypass flow path 414B bypasses only the final compression stage, but instead, the second bypass flow path 414B may bypass the final compression stage and 1 or more compression stages ahead thereof.

Here, the embodiments are summarized.

(1) The compressor unit according to the above embodiment is a compressor unit that is installed in a ship and compresses a target gas, which is a boil-off gas, sucked from a liquefied natural gas storage tank of the ship. This compressor unit includes: a first reciprocating compressor having a plurality of compression stages for compressing the target gas to be supplied to a demand side; a second reciprocating compressor having a plurality of compression stages and connected in parallel to the first reciprocating compressor in such a manner as to compress the target gas and supply the compressed target gas to the demand side; and a control part controlling driving of the first reciprocating compressor and the second reciprocating compressor. The first reciprocating compressor includes: a first check valve disposed at a downstream position from the final compression stage; a first pressure sensor disposed between the final compression section and the first check valve; a first bypass flow path bypassing at least the final compression section; and a first bypass valve provided in the first bypass flow path. The second reciprocating compressor includes: a second check valve disposed at a downstream position from the final compression stage; a second pressure sensor disposed between the final compression section and the second check valve; a second bypass flow path bypassing at least the final compression section; and a second bypass valve provided in the second bypass flow path. The compressor unit is configured such that the target gas discharged from the second reciprocating compressor and the target gas discharged from the first reciprocating compressor merge at a flow path downstream of the first check valve and the second check valve. The control unit includes an opening degree control unit that controls an opening degree of the first bypass valve such that a pressure detected by the first pressure sensor becomes a first set value, and controls an opening degree of the second bypass valve such that a pressure detected by the second pressure sensor becomes a second set value lower than the first set value.

In the compressor unit, the discharge pressure of the first reciprocating compressor is controlled to a first set value, and the discharge pressure of the second reciprocating compressor is controlled to a second set value lower than the first set value. When 2 reciprocating compressors are used in combination to operate, it is conceivable as a comparative example of the present invention to perform discharge pressure control in which the set values of the discharge pressures of the respective final compression stages are the same. However, in such discharge pressure control, the opening degrees of the first bypass valve and the second bypass valve need to be always the same, and therefore, when a pressure fluctuation of the demand side occurs, the opening degrees of the two bypass valves need to be changed by the same amount to follow the fluctuation. Therefore, the discharge pressure control of the compressor unit becomes complicated. In contrast, in the above embodiment, the set values of the discharge pressure in the final compression stage are different from each other. Therefore, when the required amount of gas on the demand side varies, the state of the gas to be supplied from the two reciprocating compressors is switched to the state of the gas to be supplied only from the first reciprocating compressor. That is, even without the discharge pressure control according to the comparative example, the target gas can be easily supplied to the demand side in an amount corresponding to the demand amount of the demand side.

(2) In the compressor train, the second set value may be a value that is 99% or more and less than 100% of the first set value.

According to this configuration, since the second set value is a value slightly smaller than the first set value, the discharge pressure of the first reciprocating compressor immediately reaches the second set value when the gas supply amount from the first reciprocating compressor is insufficient. Therefore, when the gas treatment amount from the first reciprocating compressor is insufficient, the gas supply from the second reciprocating compressor to the demand side can be promptly started.

(3) In the compressor unit, the control unit may further include: a required pressure receiving unit that receives a required pressure of the target gas from the demand side; and a set value determination unit configured to determine the first set value and the second set value based on the requested pressure received by the requested pressure receiving unit. The set value determination unit may change the first set value and the second set value while maintaining the difference between the first set value and the second set value based on a change in the required pressure.

According to this configuration, when the first set value and the second set value are changed in response to a change in the demand pressure of the demand side, the difference between the two set values is maintained, and therefore, when the gas supply amount from the first reciprocating compressor is insufficient as before the change of the set value, the gas supply from the second reciprocating compressor to the demand side can be promptly started.

(4) The first reciprocating compressor and the second reciprocating compressor may also have the same number of the compression stages in the compressor string.

(5) In the compressor unit, when the load on the demand side is off, the control unit may forcibly increase the opening degree of the first bypass valve such that the entire amount of the target gas discharged from the first reciprocating compressor is returned from the flow passage on the downstream side of the final compression stage of the first reciprocating compressor, and forcibly increase the opening degree of the second bypass valve such that the entire amount of the target gas discharged from the second reciprocating compressor is returned from the flow passage on the downstream side of the final compression stage of the second reciprocating compressor, wherein the increase width of the opening degree of the first bypass valve is larger than the increase width of the opening degree of the second bypass valve.

According to this configuration, it is possible to prevent the target gas from being supplied from the first reciprocating compressor and the second reciprocating compressor to the demand side in the load disconnected state.

(6) A compressor unit control program according to the embodiment is a program for controlling an operation of the compressor unit, the program causing a computer constituting the control unit to function as an opening degree control unit that controls an opening degree of the first bypass valve so that a pressure detected by the first pressure sensor becomes the first set value and controls an opening degree of the second bypass valve so that a pressure detected by the second pressure sensor becomes the second set value, and the program being stored in a storage medium of the computer.

By operating the computer using this program, the target gas is normally supplied only from the first reciprocating compressor to the demand side, and therefore, unlike the case where the gas is always supplied from 2 compressors to the demand side, deterioration in the accuracy of the pressure control can be suppressed.

As is clear from the above description, the gas supply amount from the compressor can be easily made to correspond to the gas demand amount of the demand side.

The present application is based on Japanese patent application No. 2021-000851 filed to the office on 6/1/2021, the contents of which are incorporated herein by reference.

In order to describe the present invention, the present invention has been described properly and sufficiently by the embodiments with reference to the drawings in the above description, but it should be understood that the modifications and/or improvements of the embodiments can be easily made by those skilled in the art. Therefore, a modified embodiment or an improved embodiment that a person skilled in the art carries out may be interpreted as being included in the scope of claims as long as the modified embodiment or the improved embodiment does not depart from the scope of claims described in the claims.

Claims

1. A compressor unit provided in a ship and configured to compress a target gas, which is a boil-off gas sucked from a liquefied natural gas storage tank of the ship, the compressor unit comprising:

a first reciprocating compressor having a plurality of compression stages for compressing the target gas to be supplied to a demand side;

a second reciprocating compressor having a plurality of compression stages and connected in parallel to the first reciprocating compressor in such a manner as to compress the target gas and supply the compressed target gas to the demand side; and

a control part controlling driving of the first reciprocating compressor and the second reciprocating compressor, wherein,

the first reciprocating compressor includes:

a first check valve disposed at a downstream position from the final compression stage;

a first pressure sensor disposed between the final compression section and the first check valve;

a first bypass flow path bypassing at least the final compression section; and

a first bypass valve provided in the first bypass flow path,

the second reciprocating compressor includes:

a second check valve disposed at a downstream position from the final compression stage;

a second pressure sensor disposed between the final compression section and the second check valve;

a second bypass flow path bypassing at least the final compression section; and

a second bypass valve provided in the second bypass flow path,

the target gas discharged from the second reciprocating compressor and the target gas discharged from the first reciprocating compressor are merged at a flow path on the downstream side of the first check valve and the second check valve,

the control unit includes an opening degree control unit that controls an opening degree of the first bypass valve such that a pressure detected by the first pressure sensor becomes a first set value, and controls an opening degree of the second bypass valve such that a pressure detected by the second pressure sensor becomes a second set value lower than the first set value.

2. The compressor rack of claim 1,

the second set value is a value that is 99% or more and less than 100% of the first set value.

3. Compressor train according to claim 1 or 2,

the control unit further includes:

a required pressure receiving unit that receives a required pressure of the target gas from the demand side; and

a set value determining unit configured to determine the first set value and the second set value based on the requested pressure received by the requested pressure receiving unit,

the set value determination unit changes the first set value and the second set value while maintaining a difference between the first set value and the second set value, based on a change in the required pressure.

4. Compressor train according to claim 1 or 2,

the first reciprocating compressor and the second reciprocating compressor have the same number of the compression sections.

5. Compressor train according to claim 1 or 2,

the control section, in a case where the load of the demand side is disconnected,

forcibly increasing an opening degree of the first bypass valve to return a total amount of the target gas discharged from the first reciprocating compressor from a flow path on a downstream side of the final compression stage of the first reciprocating compressor,

forcibly increasing an opening degree of the second bypass valve to return a total amount of the target gas discharged from the second reciprocating compressor from a flow path on a downstream side of the final compression stage of the second reciprocating compressor,

the magnitude of increase in the opening degree of the first bypass valve is larger than the magnitude of increase in the opening degree of the second bypass valve.

6. A program for controlling a compressor unit, characterized in that,

for controlling the operation of the compressor package of claim 1,

the compressor unit control program is for causing a computer constituting the control unit to function as an opening degree control unit and to be stored in a storage medium of the computer, wherein,

the opening degree control unit controls the opening degree of the first bypass valve such that the pressure detected by the first pressure sensor becomes the first set value, and controls the opening degree of the second bypass valve such that the pressure detected by the second pressure sensor becomes the second set value.