NO20200804A1 - Control method of compressor unit, compressor unit, and compression stage - Google Patents

Control method of compressor unit, compressor unit, and compression stage Download PDF

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Publication number
NO20200804A1
NO20200804A1 NO20200804A NO20200804A NO20200804A1 NO 20200804 A1 NO20200804 A1 NO 20200804A1 NO 20200804 A NO20200804 A NO 20200804A NO 20200804 A NO20200804 A NO 20200804A NO 20200804 A1 NO20200804 A1 NO 20200804A1
Authority
NO
Norway
Prior art keywords
pressure
flow path
target gas
bypass
storage tank
Prior art date
Application number
NO20200804A
Inventor
Satoshi Tezuka
Katsuhiro Seyama
Original Assignee
Kobe Steel Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kobe Steel Ltd filed Critical Kobe Steel Ltd
Publication of NO20200804A1 publication Critical patent/NO20200804A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C7/00—Methods or apparatus for discharging liquefied, solidified, or compressed gases from pressure vessels, not covered by another subclass
    • F17C7/02—Discharging liquefied gases
    • F17C7/04—Discharging liquefied gases with change of state, e.g. vaporisation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
    • F04B49/22—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00 by means of valves
    • F04B49/24—Bypassing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H21/00—Use of propulsion power plant or units on vessels
    • B63H21/12—Use of propulsion power plant or units on vessels the vessels being motor-driven
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B25/00—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby
    • B63B25/02—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods
    • B63B25/08—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid
    • B63B25/12—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid closed
    • B63B25/16—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid closed heat-insulated
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H21/00—Use of propulsion power plant or units on vessels
    • B63H21/12—Use of propulsion power plant or units on vessels the vessels being motor-driven
    • B63H21/14—Use of propulsion power plant or units on vessels the vessels being motor-driven relating to internal-combustion engines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H21/00—Use of propulsion power plant or units on vessels
    • B63H21/38—Apparatus or methods specially adapted for use on marine vessels, for handling power plant or unit liquids, e.g. lubricants, coolants, fuels or the like
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B63/00—Adaptations of engines for driving pumps, hand-held tools or electric generators; Portable combinations of engines with engine-driven devices
    • F02B63/04—Adaptations of engines for driving pumps, hand-held tools or electric generators; Portable combinations of engines with engine-driven devices for electric generators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C13/00—Details of vessels or of the filling or discharging of vessels
    • F17C13/02—Special adaptations of indicating, measuring, or monitoring equipment
    • F17C13/025—Special adaptations of indicating, measuring, or monitoring equipment having the pressure as the parameter
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C13/00—Details of vessels or of the filling or discharging of vessels
    • F17C13/04—Arrangement or mounting of valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2201/00—Vessel construction, in particular geometry, arrangement or size
    • F17C2201/01—Shape
    • F17C2201/0104—Shape cylindrical
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2205/00—Vessel construction, in particular mounting arrangements, attachments or identifications means
    • F17C2205/03—Fluid connections, filters, valves, closure means or other attachments
    • F17C2205/0302—Fittings, valves, filters, or components in connection with the gas storage device
    • F17C2205/0352—Pipes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2205/00—Vessel construction, in particular mounting arrangements, attachments or identifications means
    • F17C2205/03—Fluid connections, filters, valves, closure means or other attachments
    • F17C2205/0388—Arrangement of valves, regulators, filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2221/00—Handled fluid, in particular type of fluid
    • F17C2221/03—Mixtures
    • F17C2221/032—Hydrocarbons
    • F17C2221/033—Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
    • F17C2223/0146—Two-phase
    • F17C2223/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2223/0161—Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/01—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the phase
    • F17C2225/0146—Two-phase
    • F17C2225/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2225/0161—Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/03—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the pressure level
    • F17C2225/036—Very high pressure, i.e. above 80 bars
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/01—Propulsion of the fluid
    • F17C2227/0128—Propulsion of the fluid with pumps or compressors
    • F17C2227/0157—Compressors
    • F17C2227/0164—Compressors with specified compressor type, e.g. piston or impulsive type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/01—Propulsion of the fluid
    • F17C2227/0128—Propulsion of the fluid with pumps or compressors
    • F17C2227/0171—Arrangement
    • F17C2227/0185—Arrangement comprising several pumps or compressors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/03—Heat exchange with the fluid
    • F17C2227/0337—Heat exchange with the fluid by cooling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
    • F17C2250/04—Indicating or measuring of parameters as input values
    • F17C2250/0404—Parameters indicated or measured
    • F17C2250/043—Pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
    • F17C2250/06—Controlling or regulating of parameters as output values
    • F17C2250/0689—Methods for controlling or regulating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2260/00—Purposes of gas storage and gas handling
    • F17C2260/02—Improving properties related to fluid or fluid transfer
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00—Effects achieved by gas storage or gas handling
    • F17C2265/03—Treating the boil-off
    • F17C2265/032—Treating the boil-off by recovery
    • F17C2265/037—Treating the boil-off by recovery with pressurising
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00—Effects achieved by gas storage or gas handling
    • F17C2265/05—Regasification
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2270/00—Applications
    • F17C2270/01—Applications for fluid transport or storage
    • F17C2270/0102—Applications for fluid transport or storage on or in the water
    • F17C2270/0105—Ships
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/30—Use of alternative fuels, e.g. biofuels
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T70/00—Maritime or waterways transport
    • Y02T70/50—Measures to reduce greenhouse gas emissions related to the propulsion system
    • Y02T70/5218—Less carbon-intensive fuels, e.g. natural gas, biofuels

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • Ocean & Marine Engineering (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)
  • Control Of Positive-Displacement Pumps (AREA)
  • Control Of Multiple Motors (AREA)

Description

CONTROL METHOD OF COMPRESSOR UNIT, COMPRESSOR UNIT, AND COMPRESSION
STAGE
Technical Field
[0001]
The present invention relates to a control method of a compressor unit that supplies a target gas that is a boil off gas from an LNG storage tank of a ship to a demand destination, and a compressor unit.
Background Art
[0002]
Conventionally, there has been developed a compressor unit that increases the pressure of a boil off gas (hereinafter, referred to as "target gas") generated from a liquefied natural gas (LNG) and supplies the boil off gas to a demand destination such as an engine or a generator (see JP 6371930 B 1, JP 2011-517749 A, and JP 2018-128039 A). In order to prevent the pressure on a discharge side of a compression stage in the compressor unit from excessively increasing, the compressor unit includes a bypass line for returning the target gas upstream (see JP 6371930 B 1 and JP 2011-517749 A). Generally, when the pressure on the discharge side of the compression stage exceeds a predetermined threshold, a bypass valve disposed in the bypass line is opened and a high pressure target gas returns upstream. As a result, the pressure on the discharge side of the compression stage decreases, and the load on the compression stage is reduced.
[0003]
Meanwhile, the amount of the target gas generated in an LNG storage tank storing LNG may decrease due to various factors. If the pressure of the target gas in a storage tank connection flow path connected to the LNG storage tank excessively decreases, the load on a first compression stage in the compressor unit may excessively increase. As described above, even if the pressure on the discharge side of the compression stage is controlled so as not to be excessively increased as in the related art described above, an increase in load on the compression stage cannot be avoided in some cases.
Summary of Invention
[0004]
An object of the present invention is to provide a technique of supplying a target gas to a demand destination without excessively increasing the load on a compression stage of a compressor unit even with a small amount of a target gas generated.
[0005]
A control method according to one aspect of the present invention is used to control a compressor unit that is installed in a ship and compresses a target gas that is a boil off gas generated in an LNG storage tank of the ship. The compressor unit includes a plurality of compression stages that sequentially increase a pressure of the target gas, a bypass line that extends from one end connected toa storage tank connection flow path connecting a first compression stage to the LNG storage tank to bypass apart of the plurality of compression stages, anda bypass val ve that is disposed in the bypass line. Another end of the bypass line is connected to a flow path section between compression stages adjacent to each other. The compressor unit further includes another bypass line whose one end is connected to the flow path section and whose another end is located on a downstream side of the flow path section to bypass one or two or more compression stages, and another bypass valve disposed in the other bypass line. The control method includes, at a time of driving the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low-pressure state, opening the bypass valve and retuming the target gas to the storage tank connection flow path through the bypass line to reduce a pressure of the target gas in the flow path section and increase a pressure of the target gas in the storage tank connection flow path. The control method also includes, when it is determined that the target gas in the flow path section is in a predetermined low-pressure state, opening the other bypass valve and retuming the target gas to the flow path section through the other bypass line to reduce a pressure ofthe target gas in a flow path where the other end of the other bypass line is located and increase a pressure of the target gas in the flow path section. A low-pressure-side threshold in a case where it is determined that the target gas in the flow path section is in the predetermined lowpressure state is larger than a low-pressure-side threshold in a case where it is determined that the target gas in the storage tank connection flow path is in the predetermined low-pressure state.
[0006]
A control method according to another aspect of the present invention is used to control a compressor unit that is installed in a ship and compresses a target gas that is a boil off gas generated in an LNG storage tank of the ship. The compressor unit includes a plurality of compression stages that sequentially increase a pressure of the target gas, a bypass line that extends from one end connected toa storage tank connection flow path connecting a first compression stage to the LNG storage tank to bypass apart of the plurality of compression stages, anda bypass val ve that is disposed in the bypass line. Another end of the bypass line is connected to a flow path section between the compression stages adjacent to each other. The control method includes, at a time of driving the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low-pressure state, opening the bypass valve and retuming the target gas to the storage tank connection flow path through the bypass line, when it is determined to be out of the low-pressure state, closing the bypass val ve, and determining whether or not the target gas in the flow path section is in a predetermined high-pressure state, and when the target gas becomes in the high-pressure state which is caused by a decrease in temperature of the target gas in the storage tank connection flow path, opening the bypass valve.
[0007]
A compressor unit according to another aspect of the present invention is used for the control method described above. The compressor unit includes the plural ity of compression stages, a drive unit that drives the plurality of compression stages, the bypass line, the bypass valve, the other bypass line, the other bypass val ve, a pressure sensor that detects a pressure of a target gas in the storage tank connection flow path, another pressure sensor that detects a pressure of the target gas in the flow path section, and a control unit that campares a pressure value acquired by the pressure sensor with the low-pressure-side threshold of the target gas in the storage tank connection flow path, and when it is determined that the target gas in the storage tank connection flow path is in the low-pressure state, executes control to open the bypass val ve, and that campares a pressure value acquired by the other pressure sensor with the low-pressure-side threshold of the target gas in the flow path section, and when it is determined that the target gas in the flow path section is in a predetermined low-pressure state, executes control to open the other bypass valve.
[0008]
A compressor unit according to another aspect of the present invention is used for the control method described above. The compressor unit includes the plurality of compression stages, a drive unit that drives the plurality of compression stages, the bypass line, the bypass val ve, a pressure sensor that detects a pressure of a target gas in the storage tank connection flow path, another pressure sensor that detects a pressure of the target gas in the flow path section, and a control unit that, when it is determined, based on a pressure acquired by the pressure sensor, that the target gas in the storage tank connection flow path is in the low-pressure state, executes control to open the bypass val ve, and when it is determined to be out of the low-pressure state, executes control to close the bypass valve, and that, when it is determined, based on a pressure acquired by the other pressure sensor, that the target gas becomes in a predetermined high-pressure state which is caused by a decrease in temperature of the target gas in the storage tank connection flow path, executes control to open the bypass valve.
[0009]
A plurality of compression stages according to another aspect of the present invention are used in the compressor unit described above.
[0010]
The technique described above can supply the target gas to a demand destination without excessively increasing a load on the compression stage of the compressor unit even with a small amount of the target gas generated.
[0011]
The purposes, features and advantages of the compressor unit described above will become more apparent from the following detailed description and the accompanying drawings.
Brief Description of Drawings
[0012]
FIG. 1 isa schematic f!ow diagram of a compressor unit;
FIG. 2 isa schematic flowchart illustrating a control method of a bypass val ve in the compressor unit;
FIG. 3 isa schematic flowchart illustrating a control method of the bypass val ve in the compressor unit; and
FIG. 4 isa schematic flow diagram of a compressor unit.
Description of Embodiments
[0013]
FIG. 1 isa schematic flow diagram of a compressor unit 100. The compressor unit 100 will be described with reference to FIG. 1.
[0014]
The compressor unit 100 is installed in a ship (not illustrated) that has an LNG storage tank 101 storing a liquefied natural gas (LNG). The compressor unit 100 is configured to sucka target gas that isa boil off gas generated in the LNG storage tank 101 and compress the sucked target gas. Specifically, the compressor unit 100 is configured to increase the pressure of the target gas to about 300 barG (30 MPaG) and supply the target gas whose pressure has been increased toa demand destination. In the following description, the terms "upstream" and "downstream" are used based on the flow direction of the target gas.
[0015]
The compressor unit 100 is a reciprocating compression mechanism, and includes a flow path 110 in which the target gas flows to the demand destination, a plurality of compression stages 201 to 205 that sequentially increase the pressure of the target gas, a plurality of coolers 281 to 284, anda drive unit (not illustrated). The drive unit includes a drive source (motor, engine, or the like) and a crank mechanism that transmits the power of the drive source to the first to fifth compression stages 201 to 205. In FIG. 1, the compressor unit 100 is illustrated as a device that includes components illustrated within a two-dot chain line frame.
[0016]
The upstream end of the flow path 110 is connected to an upper part of the LN G storage tank 101 so as to allow a boil off gas generated in the LN G storage tank 101 to en ter the flow path 110. A downstream end of the flow path 110 is connected to the demand destination. The flow path 110 includes a storage tank connection flow path 111, a stage connection flow path 113, and a demand destination connection flow path 114.
[0017]
The storage tank connection flow path 111 is connected to the LNG storage tank 101 and guides the boil off gas to the first compression stage 201 of the compressor unit 100. The compressor unit 100 incl udes two first compression stages 201, and thus the storage tank connection flow path 111 includes a main pipe 111 C extending from the LNG storage tank 101 and branch parts 111 A, 111 B branching from the main pipe 111 C. These branch parts 111 A, 111 B are connected to the first compression stages 201, respectively. That is, the two first compression stages 201 are respectively connected to the two branch parts 11 lA, 111B so as to be in parallel to each other. The compressor unit 100 may include a single first compression stage 201.
[0018]
The stage connection flow path 113 is constituted by a plurality of flow paths connecting the first to fifth compression stages 201 to 205 so as to allow the target gas to flow from one compression stage to the next compression stage. On an upstream side of the stage connection flow path 113, connection parts with the first compression stages 201 are branch parts 113A, 113B, respectively. The second to fifth compression stages 202 to 205 are disposed in other parts of the stage connection flow path 113. The second to fifth compression stages 202 to 205 are serially arranged so as to sequentially increase the pressure of the target gas compressed in the first compression stage 201.
[0019]
The demand destination connection flow path 114 is a flow path connecting the fifth compression stage 205 to the demand destination.
[0020]
The crank mechanism includes a crosshead connected toa piston rod of each of the first to fifth compression stages 201 to 205. The crank mechanism is configured to change a rotation of a crankshaft to a reciprocating movement of the crosshead for the purpose of reciprocating the pi ston rod and a piston connected to a distal end of the pi ston rod.
[0021]
The coolers 281 to 284 are disposed in the stage connection flow path 113 and the demand destination connection flow path 114 in order to cool the target gas compressed in the second to fifth compression stages 202 to 205. The coolers 281 to 284 are configured to exchange heat with cooling water having a temperature lower than that of the target gas.
[0022]
The cooler 281 is attached in a flow path section between the second compression stage 202 and the third compression stage 203 in the stage connection flow path 113. The cool er 282 is attached in a flow path section between the third compression stage 203 and the fourth compression stage 204 in the stage connection flow path 113. The cooler 283 is attached in a flow path section between the fourth compression stage 204 and the fifth compression stage 205 in the stage connection flow path 113. The cooler 284 is attached in the demand destination connection flow path 114.
[0023]
The compressor unit 100 is configured to execute control to ad just the pressure of the target gas in the storage tank connection flow path 111, the stage connection flow path 113, and the demand destination connection flow path 114. Control-related parts used for pressure control will be described below.
[0024]
The compressor unit 100 includes bypass lines 411 to 413, bypass valves 421 to 423, pressure sensors 431 to 434, anda control unit 414.
[0025]
The bypass line 411 is connected to the storage tank connection flow path 111 and the stage connection flow path 113 so as to bypass the first compression stage 201 and the second compression stage 202. One end of the bypass line 411 is connected to the main pipe 111 C of the storage tank connection flow path 111. The other end of the bypass line 411 is connected to the stage connection flow path 113 between the cool er 281 and the third compression stage 203.
[0026]
The bypass line 412 is configured to bypass the third compression stage 203. One end of the bypass line 412 is connected to a flow path section between the cooler 281 and the third compression stage 203 in the stage connection flow path 113 (that is, flow path section to which other end of the bypass line 411 is connected). The other end of the bypass line 412 is connected to a flow path section between the cooler 282 and the fourth compression stage 204 in the stage connection flow path 113.
[0027]
The bypass line 413 is configured to bypass the fourth compression stage 204 and the fifth compression stage 205. One end ofthe bypass line 413 is connected to the flow path section between the cooler 282 and the fourth compression stage 204 in the stage connection flow path 113. The other end of the bypass line 413 is connected to the demand destination connection flow path 114 on a downstream side of the cooler 284.
[0028]
The bypass valves 421 to 423 are attached to the bypass lines 411 to 413, respectively. The bypass valves 421 to 423 are electrically connected to the control unit 414. The bypass valves 421 to 423 are configured such that the opening rate of these bypass valves can be adjusted under the control ofthe control unit 414.
[0029]
The pressure sensor 431 is attached to the main pipe 111 C of the storage tank connection flow path 111. The pressure sensor 431 is configured to detect the pressure of the target gas in the storage tank connection flow path 111 ( that is, pressure of target gas generated in LN G stora ge tank 101) and generate a detection signal indicating a detected pressure (hereinafter, referred to as "detected pressure").
[0030]
The pressure sensor 432 is attached to the flow path section between the cooler 281 and the third compression stage 203 in the stage connection flow path 113. The pressure sensor 432 is configured to detect the pressure of the target gas in the flow path section between the cool er 281 and the third compression stage 203, and generate a detection signal indicating a detected pressure. The detected pressure acquired by the pressure sensor 432 indicates the pressure of the target gas sucked into the third compression stage 203.
[0031]
The pressure sensor 433 is attached to the flow path section between the cooler 282 and the fourth compression stage 204 in the stage connection flow path 113. The pressure sensor 433 is configured to detect the pressure of the target gas in the flow path section between the cooler 282 and the fourth compression stage 204, and generate a detection signal indicating a detected pressure. The detected pressure acquired by the pressure sensor 433 indicates the pressure of the target gas sucked into the fourth compression stage 204.
[0032]
The pressure sensor 434 is attached to the demand destination connection flow path 114. The pressure sensor 434 is configured to detect the pressure of the target gas in the demand destination connection flow path 114 and generate a detection signal indicating a detected pressure.
[0033)
The control unit 414 is electrically connected to the bypass valves 421 to 423 and the pressure sensors 431 to 434. The control unit 414 is configured to receive detection signals from the pressure sensors 431 to 434 and determine the opening rate of the bypass valves 421 to 423 based on the detection signals received. The control unit 414 may be configured as software or a dedicated circuit.
[0034]
An operation of the compressor unit 100 and a flow of a target gas will be described below with reference to FIGS. 1 to 3. FIG. 2 and FIG. 3 are schematic flowcharts illustrating a control method ofthe bypass valve 421. FIG. 2 illustrates a control method for eliminating a predetermined low-pressure state in the storage tank connection flow path 111. FIG. 3 illustrates a control method for eliminating a predetermined high-pressure state between the second compression stage 202 and the third compression stage 203 in the stage connection flow path 113.
[0035]
When the compressor unit 100 is driven, the target gas is repeatedly sucked and discharged in the first to fifth compression stages 201 to 205. The target gas discharged from the second to fifth compression stages 202 to 205 passes through the coolers 281 to 284 to be cooled. After a compression process in the first to fifth compression stages 201 to 205 and a cooling process in the coolers 281 to 284, the target gas is supplied to a demand destination. During these processes, the pressure of the target gas in the flow path 110 is acquired by the pressure sensors 431 to 434.
Normally, when the suction pressure and the discharge pressure in each of the first to fifth compression stages 201 to 205 are within anormal range, the bypass valves 421 to 423 are closed. However, when the suction pressure and the discharge pressure deviate from the normal range, the control unit 414 controls the bypass valves 421 to 423 based on pressures detected by the pressure sensors 431 to 431 and adjust the pressure of the target gas in the flow path 110.
[0036]
Opening rate control of the bypass val ve 421 will be described first. While the compressor unit 100 is driven, the amount of a target gas generated in the LNG storage tank 101 may decrease due to various factors. Consequently, the pressure of the target gas in the storage tank connection flow path 111 decreases. The bypass val ve 421 for eliminating a low-pressure state of the storage tank connection flow path 111 is controlled as illustrated in FIG. 2.
[0037]
While the compressor unit 100 is driven, the pressure sensor 431 detects the pressure of the target gas in the storage tank connection flow path 111. The control unit 414 compares a pressure acquired by the pressure sensor 431 with a predetermined low-pressure-side threshold (step S 110). When it is determined that the pressure of the target gas in the storage tank connection flow path 111 is lower than the low-pressure-side threshold, that is, when it is determined that the target gas is in a low-pressure state, the control unit 414 opens the bypass valve 421 (step S120). Ifthe pressure detected by the pressure sensor 431 is not lower than the low-pressure-side threshold, the bypass valve 421 is kept closed. The low-pressure-side threshold is, for example, about O barG (0 MPaG). When the load on the first compression stage 201 is in an acceptable range even if a low-pressure target gas is sucked, the low-pressure-side threshold may be less than O barG.
[0038]
As the bypass valve 421 is opened, the high-pressure target gas compressed in the first compression stage 201 and the second compression stage 202 flows into the storage tank connection flow path 111 through the bypass line 411. As a result, the pressure of the target gas in the flow path section between the second compression stage 202 and the third compression stage 203 decreases, and the pressure of the target gas in the storage tank connection flow path 111 increases.
[0039]
The control unit 414 continuously or intermittently compares the pressure detected by the pressure sensor 431 with the low-pressure-side threshold after the bypass valve 421 is opened (step S 130). lf the pressure detected by the pressure sensor 431 is lower than the low-pressure-side threshold, the bypass valve 421 is kept opened (step S120). The process loop of steps S120 and S 130 is continued until the pressure detected by the pressure sensor 431 is higher than or equal to the low-pressure-side threshold. When the pressure detected by the pressure sensor 431 becomes higher than or equal to the low-pressure-side threshold, the bypass val ve 421 is closed (step S 140).
[0040]
While the bypass valve 421 isopen (step S120), the opening rate ofthe bypass valve 421 is sequentially adjusted based on the comparison of the low-pressure-side threshold with the pressure detected by the pressure sensor 431. Specifically, in the control unit 414, the opening rate ofbypass val ve 421 is increased according to the magnitude of the difference between the detected pressure and the low-pressure-side threshold. Consequently, when the pressure of the storage tank connection flow path 111 is excessively low, the amount of the target gas retuming to the storage tank connection flow path 111 through the bypass line 411 increases, and thus the pressure in the storage tank connection flow path 111 can be quickly recovered. Further, when the pressure of the storage tank connection flow path 111 approaches the low-pressure-side threshold, the opening rate is reduced, and thus it is possible to prevent the target gas from unnecessarily retuming to the storage tank connection flow path 111.
[0041]
Next, control executed when the target gas between the second compression stage 202 and the third compression stage 203 in the stage connection flow path 113 is in a high-pressure state will be described with reference to FIG. 3. In the compressor unit 100, for example, when the temperature of the target gas in the storage tank connection flow path 111 decreases, the throughput ofthe compressor unit 100 may be excessive.
[0042]
While the compressor unit 100 is driven, the pressure sensor 432 detects the pressure ofthe target gas in the flow path section between the second compression stage 202 and the third compression stage 203. The control unit 414 compares a pressure acquired by the pressure sensor 432 with a predetermined high-pressure-side threshold (step S210). When it is determined that the pressure of the target gas is higher than the high-pressure-side threshold, that is, when it is determined that the target gas is in a high-pressure state, the control unit 414 opens the bypass valve 421 (step S220). If the pressure detected by the pressure sensor 432 is lower than or equal to the high-pressure-side threshold, the bypass valve 421 is kept closed. The high-pressure-side threshold is set to, for example, 11 barG.
[0043]
As the bypass valve 421 is opened, the high-pressure target gas compressed in the first compression stage 201 and the second compression stage 202 flows into the storage tank connection flow path 111 through the bypass line 411. As a result, the pressure of the target gas in the flow path section between the second compression stage 202 and the third compression stage 203 decreases, and the pressure of the target gas in the storage tank connection flow path 111 increases.
[0044]
The control unit 414 continuously or intermittently compares the pressure detected by the pressure sensor 432 with the high-pressure-side threshold after the bypass valve 421 is opened (step S230). If the pressure detected by the pressure sensor 432 is higher than the high-pressure-side threshold, the bypass val ve 421 is kept opened (step S220). The process loop of steps S220 and S230 is continued until the pressure detected by the pressure sensor 432 is lower than or equal to the high-pressure-side threshold. When the pressure detected by the pressure sensor 432 is lower than or equal to the high-pressure-side threshold, the bypass valve 421 is closed (step S240).
[0045]
While the bypass val ve 421 isopen (step S220), the opening rate of the bypass valve 421 is sequentially adjusted based on the comparison of the high-pressure-side threshold with the pressure detected by the pressure sensor 432. Specifically, in the control unit 414, the opening rate of bypass val ve 421 is increased according to the magnitude of the difference between the detected pressure and the high-pressure-side threshold. Consequently, when the pressure of the target gas in the flow path section between the second compression stage 202 and the third compression stage 203 is excessively high, the amount of the target gas retuming to the storage tank connection flow path 111 through the bypass line 411 increases, and thus the pressure in the flow path section can be quickly reduced. Further, when the pressure in the flow path section approaches the high-pressure-side threshold, the opening rate is reduced, and thus it is possible to prevent the target gas from unnecessarily retuming to the storage tank connection flow path 111.
[0046)
As described above, in the compressor unit 100, the pressure of the target gas at both ends of the bypass line 411 is acquired by the pressure sensors 431, 432. When the target gas is in a lowpressure state at the end of the bypass line 411 located in a low-pressure side flow path (storage tank connection flow path 111) and when the target gas is in a high-pressure state at the end of the bypass line 411 located in a high-pressure side flow path (flow path section between second and third compression stages 202 and 203 ), the opening rate of the bypass val ve 421 is controlled.
[0047)
Next, opening rate control of the bypass valves 422,423 will be described. Opening control similar to the opening rate control of the bypass val ve 421 is executed on the bypass valves 422,423. Regarding the opening rate control ofthe bypass valve 422, the control unit 414 acquires pressures on a suction side and a discharge side of the third compression stage 203 which the bypass line 412 bypasses (pressures detected by pressure sensors 432,433). When the pressure detected by the pressure sensor 432 is lower than the predetermined low-pressure-side threshold, that is, when the target gas is in a low-pressure state, or when the pressure detected by the pressure sensor 433 is higher than the predetermined high-pressure-side threshold, that is, when the target gas is in a high-pressure state, the control unit 414 opens the bypass valve 422. The low-pressureside threshold and the high-pressure-side threshold set in the bypass valve 422 are respectively larger than the low-pressure-side threshold and the high-pressure-side threshold set in the bypass valve 421.
[0048)
Regarding the opening rate control ofthe bypass valve 423, the control unit 414 acquires a pressure on a suction side of the fourth compression stage 204 and a pressure on a discharge side of the fifth compression stage 205 which the bypass line 413 bypasses (pressures detected by pressure sensors 433, 434). When the pressure detected by the pressure sensor 433 is lower than the predetermined low-pressure-side threshold or when the pressure detected by the pressure sensor 434 is higher than the predetermined high-pressure-side threshold, the control unit 414 opens the bypass valve 423. The low-pressure-side threshold and the high-pressure-side threshold set in the bypass valve 423 are respectively larger than the low-pressure-side threshold and the high-pressure-side threshold set in the bypass valve 422.
[0049)
The embodiment of the present invention has been described above. If the target gas in the storage tank connection flow path 111 is in a low-pressure state, the bypass valve 421 is opened to prevent an excessive load on the first and second compression stages 201, 202. Further, if the target gas in the flow path section between the second and third compression stages 202 and 203 is in a low-pressure state, the bypass valve 422 is opened to prevent an excessive load on the third compression stage 203. Similarly, if the target gas in the flow path section between the third and fourth compression stages 203 and 204 is in a low-pressure state, the bypass valve 423 is opened to prevent an excessive load on the fourth and fifth compression stages 204, 205.
[0050]
In addition, when the target gas is in a high-pressure state in the flow path section between the second and third compression stages 202 and 203, the bypass valve 421 is opened. An excessive load on the first and second compression stages 201, 202 is thus reduced. Similarly, if the target gas is in a high-pressure state in the flow path section between the third and fourth compression stages 203 and 204, the bypass valve 422 is opened to prevent an excessive load on the third compression stage 203. lf the target gas is in a high-pressure state in the demand destination connection flow path 114, the bypass valve 423 is opened to prevent an excessive load on the fourth and fifth compression stages 204, 205.
[0051]
The disclosed embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined not by the description above but by the claims, and is intended to include all modifications within the scope and meaning equivalent to the claims.
[0052]
In the embodiment described above, when the amount of the target gas generated in the LN G storage tank 101 decreases, the pressure detected by the pressure sensor 431 also decreases, so that the difference between the pressures detected by the pressure sensors 431 and 432 increases. At step S 110 in FIG. 2, altematively, the difference between the pressure detected by the pressure sensor 431 and the pressure detected by the pressure sensor 432 may be calculated, and the lowpressure state may be determined based on whether or not the magnitude of the difference calculated exceeds a predetermined upper limit value of a pressure difference. When it is determined that the target gas in the storage tank connection flow path 111 is in a low-pressure state, step S120 in FIG. 2 is performed and the bypass valve 421 is opened.
[0053]
In the embodiment described above, when it is determined whether or not the target gas is out of the low-pressure state (step S 120), a value larger than the low-pressure-side threshold may be used as a determination value. When it is determined whether or not the target gas is out of the high-pressure state (step S220), a value smaller than the high-pressure-side threshold may be used as a determination value.
[0054]
In the embodiment described above, the opening rate of the bypass val ve 421 may be adjusted based on the ratio of the pressure detected by the pressure sensor 431 (or pressure sensor 432) and the low-pressure-side threshold ( or high-pressure-side threshold). This description is applicable to the bypass valves 422, 423. When precise opening rate control is not required, the bypass valves 421 to 423 may be controlled by two values, that is, a fully closed state anda fully opened state. This description is applicable to the bypass valves 422, 423.
[0055]
In the present embodiment, as illustrated in FIG. 4, the bypass line 411 may be connected to the flow path 110 (that is, storage tank connection flow path 111 and demand destination connection flow path 114) so as to bypass the first to fifth compression stages 201 to 205.
Altematively, a bypass line may be disposed in each of the compression stages 201 to 205. As described above, the bypass line may be appropriately changed.
[0056)
Regarding the embodiment described above, the number of compression stages to be used may be less than five (for example, three), or may be more than five (for example, six).
[0057]
The control method of a bypass val ve according to the embodiment described above may be applied to other screw or turbo compressors. In this case, power may be transmitted to a compression stage using a gear mechanism instead of a crank mechanism in a compressor unit. Power may be transmitted directly from a drive source to the compression stage.
[0058]
The embodiments described above mainly includes a compressor unit having the following configuration.
[0059]
A control method according to one aspect of the embodiment described above is used to control a compressor unit that is installed in a ship and compresses a target gas that is a boil off gas generated in an LNG storage tank of the ship. The compressor unit includes a plurality of compression stages that sequentially increase a pressure of the target gas, a bypass line that extends from one end connected to a storage tank connection flow path connecting a first compression stage to the LNG storage tank to bypass apart of the plurality of compression stages, and a bypass val ve that is disposed in the bypass line. Another end of the bypass line is connected to a flow path section between compression stages adjacent to each other. The compressor unit further includes another bypass line whose one end is connected to the flow path section and whose another end is located on a downstream side of the flow path section to bypass one or two or more compression stages, and another bypass valve disposed in the other bypass line. The control method includes, at a time of driving the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low-pressure state, opening the bypass valve and retuming the target gas to the storage tank connection flow path through the bypass line to reduce a pressure of the target gas in the flow path section and increase a pressure of the target gas in the storage tank connection flow path. The control method also includes, when it is determined that the target gas in the flow path section is in a predetermined low-pressure state, opening the other bypass valve and retuming the target gas to the flow path section through the other bypass line to reduce a pressure of the target gas in a flow path where the other end of the other bypass line is located and increase a pressure of the target gas in the flow path section. A low-pressure-side threshold in a case where it is determined that the target gas in the flow path section is in the predetermined lowpressure state is larger than a low-pressure-side threshold in a case where it is determined that the target gas in the storage tank connection flow path is in the predetermined low-pressure state.
[0060]
According to the configuration described above, when the bypass valve is opened, a part of the target gas retums to the storage tank connection flow path through the bypass line, and the pressure of the target gas in the storage tank connection flow path increases. As a result, it is possible to prevent the pressure in the storage tank connection flow path from excessively decreasing and reduce an excessive load on the compression stage which the bypass line bypasses.
[0061]
In the configuration described above, opening rate of the bypass val ve is adjusted based on a result of comparison between a preset value and a pressure of the target gas in the storage tank connection flow path. Opening rate of the other bypass val ve is adjusted based on a result of comparison between a preset value and a pressure of the target gas in the flow path section.
[0062]
According to the configuration described above, the opening rate of the bypass val ve is adjusted based on the result of comparison between the preset value and the pressure of the target gas in the storage tank connection flow path, and thus the amount of the target gas retuming to the storage tank connection flow path through the bypass line can be adjusted.
[0063]
A control method according to another aspect of the embodiment described above is used to control a compressor unit that is installed in a ship and compresses a target gas that isa boil off gas generated in an LNG storage tank of the ship. The compressor unit includes a plurality of compression stages that sequentially increase a pressure of the target gas, a bypass line that extends from one end connected to a storage tank connection flow path connecting a first compression stage to the LNG storage tank to bypass apart of the plurality of compression stages, and a bypass val ve that is disposed in the bypass line. Another end of the bypass line is connected to a flow path section between the compression stages adjacent to each other. The control method includes, at a time of driving the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low-pressure state, opening the bypass valve and retuming the target gas to the storage tank connection flow path through the bypass line, when it is determined to be out of the low-pressure state, closing the bypass val ve, and determining whether or not the target gas in the flow path section is in a predetermined high-pressure state, and when the target gas becomes in the high-pressure state which is caused by a decrease in temperature of the target gas in the storage tank connection flow path, opening the bypass valve.
[0064]
According to the configuration described above, it is possible to prevent the pressure of the target gas in a flow path on a downstream side of the storage tank connection flow path from excessively increasing and reduce an excessive load on the compression stage which the bypass line bypasses.
[0065]
In the configuration described above, opening rate of the bypass val ve in a case where it is determined to be in the predetermined low-pressure state is adjusted based on a result of comparison between a preset value and a pressure of the target gas in the storage tank connection flow path. Opening rate of the bypass valve in a case where it is determined to be in the predetermined high-pressure state is adjusted based on a result of comparison between a preset value anda pressure of the target gas in the flow path section.
[0066]
A compressor unit according to another aspect of the embodiment described above is used for the control method described above. The compressor unit includes the plurality of compression stages, a drive unit that drives the plurality of compression stages, the bypass line, the bypass val ve, the other bypass line, the other bypass val ve, a pressure sensor that detects a pressure of a target gas in the storage tank connection flow path, another pressure sensor that detects a pressure of the target gas in the flow path section, and a control unit that campares a pressure value acquired by the pressure sensor with the low-pressure-side threshold of the target gas in the storage tank connection flow path, and when it is determined that the target gas in the storage tank connection flow path is in the low-pressure state, executes control to open the bypass val ve, and that campares a pressure value acquired by the other pressure sensor with the low-pressure-side threshold of the target gas in the flow path section, and when it is determined that the target gas in the flow path section is in a predetermined low-pressure state, executes control to open the other bypass valve.
[0067]
A compressor unit according to another aspect of the embodiment described above is used for the control method described above. The compressor unit includes the plurality of compression stages, a drive unit that drives the plurality of compression stages, the bypass line, the bypass val ve, a pressure sensor that detects a pressure of a target gas in the storage tank connection flow path, another pressure sensor that detects a pressure of the target gas in the flow path section, anda control unit that, when it is determined, based on a pressure acquired by the pressure sensor, that the target gas in the storage tank connection flow path is in the low-pressure state, executes control to open the bypass val ve, and when it is determined to be out of the low-pressure state, executes control to close the bypass valve, and that, when it is determined, based on a pressure acquired by the other pressure sensor, that the target gas becomes in a predetermined high-pressure state which is caused by a decrease in temperature of the target gas in the storage tank connection flow path, executes control to open the bypass valve.
[0068]
A plurality of compression stages according to another aspect of the embodiment described above are used in the compressor unit described above.
[0069]
The technique described in the above embodiment is applicable to a compressor unit mounted on a ship.

Claims (7)

Claims
1. A control method of a compressor unit that is installed in a ship and compresses a target gas that isa boil off gas generated in an LNG storage tank of the ship,
the compressor unit including:
a plurality of compression stages that sequentially increase a pressure of the target gas; a bypass line that extends from orre end connected to a storage tank connection flow path connecting a first compression stage to the LNG storage tank to bypass a part of the plurality of compression stages; and
a bypass valve that is disposed in the bypass line,
another end of the bypass line being connected to a flow path section between compression stages adjacent to each other,
the compressor unit further including:
another bypass line whose orre end is connected to the flow path section and whose another end is located on a downstream side of the flow path section to bypass orre or two or more compression stages; and
another bypass valve disposed in the other bypass line,
the control method comprising:
at a time of driving the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low-pressure state, opening the bypass valve and returning the target gas to the storage tank connection flow path through the bypass line to reduce a pressure ofthe target gas in the flow path section and increase a pressure of the target gas in the storage tank connection flow path; and
when it is determined that the target gas in the flow path section is in a predetermined lowpressure state, opening the other bypass valve and retuming the target gas to the flow path section through the other bypass line to reduce a pressure of the target gas in a flow path where the other end of the other bypass line is located and increase a pressure of the target gas in the flow path section, wherein
a low-pressure-side threshold in a case where it is determined that the target gas in the flow path section is in the predetermined low-pressure state is larger than a low-pressure-side threshold in a case where it is determined that the target gas in the storage tank connection flow path is in the predetermined low-pressure state.
2. The control method according to claim 1, wherein
opening rate of the bypass val ve is adjusted based on a result of comparison between a preset value and a pressure of the target gas in the storage tank connection flow path, and opening rate of the other bypass val ve is adjusted based on a result of comparison between a preset value and a pressure of the target gas in the flow path section.
3. A control method of a compressor unit that is installed in a ship and compresses a target gas that isa boil off gas generated in an LNG storage tank of the ship,
the compressor unit including:
a plurality of compression stages that sequentially increase a pressure of the target gas; a bypass line that extends from one end connected to a storage tank connection flow path connecting a first compression stage to the LNG storage tank to bypass a part of the plurality of compression stages; and
a bypass valve that is disposed in the bypass line,
another end of the bypass line being connected to a flow path section between the compression stages adjacent to each other,
the control method comprising:
at a time of driving the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low-pressure state, opening the bypass val ve and retuming the target gas to the storage tank connection flow path through the bypass line;
when it is determined to be out of the low-pressure state, closing the bypass val ve; and determining whether or not the target gas in the flow path section is in a predetermined high-pressure state, and when the target gas becomes in the high-pressure state which is caused by a decrease in temperature of the target gas in the storage tank connection flow path, opening the bypass val ve.
4. The control method according to claim 3, wherein
opening rate of the bypass val ve in a case where it is determined to be in the predeterrnined low-pressure state is adjusted based on a result of comparison between a preset value anda pressure of the target gas in the storage tank connection flow path, and
opening rate of the bypass val ve in a case where it is determined to be in the predetermined high-pressure state is adjusted based on a result of comparison between a preset value anda pressure of the target gas in the flow path section.
5. A compressor unit used for the control method according to claim 1 or 2, the compressor unit comprising:
the plurality of compression stages;
a drive unit that drives the plurality of compression stages;
the bypass line;
the bypass valve;
the other bypass line;
the other bypass valve;
a pressure sensor that detects a pressure of a target gas in the storage tank connection flow path;
another pressure sensor that detects a pressure of the target gas in the flow path section; and
a control unit that compares a pressure value acquired by the pressure sensor with the lowpressure-side threshold of the target gas in the storage tank connection flow path, and when it is determined that the target gas in the storage tank connection flow path is in the low-pressure state, executes control to open the bypass valve, and that compares a pressure value acquired by the other pressure sensor with the low-pressure-side threshold of the target gas in the flow path section, and when it is determined that the target gas in the flow path section is in a predetermined low-pressure state, executes control to open the other bypass val ve.
6. A compressor unit used for the control method according to claim 3 or 4, the compressor unit comprising:
the plurality of compression stages;
a drive unit that drives the plurality of compression stages;
the bypass line;
the bypass valve;
a pressure sensor that detects a pressure of a target gas in the storage tank connection flow path;
another pressure sensor that detects a pressure of the target gas in the flow path section; and
a control unit that, when it is determined, based on a pressure acquired by the pressure sensor, that the target gas in the storage tank connection flow path is in the low-pressure state, executes control to open the bypass val ve, and when it is determined to be out of the low-pressure state, executes control to close the bypass valve, and when it is determined, based on a pressure acquired by the other pressure sensor, that the target gas becomes in a predetermined high-pressure state which is caused by a decrease in temperature of the target gas in the storage tank connection flow path, executes control to open the bypass valve.
7. The plurality of compression stages used in the compressor unit according to claim 5.
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