CN113266999A - Absorption refrigeration combined BOG reliquefaction system of LNG ship and use method thereof - Google Patents

Absorption refrigeration combined BOG reliquefaction system of LNG ship and use method thereof Download PDF

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CN113266999A
CN113266999A CN202110594091.6A CN202110594091A CN113266999A CN 113266999 A CN113266999 A CN 113266999A CN 202110594091 A CN202110594091 A CN 202110594091A CN 113266999 A CN113266999 A CN 113266999A
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stage
heat exchanger
gas
natural gas
nitrogen
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巨永林
殷靓
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Shanghai Jiaotong University
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Shanghai Jiaotong University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F25J1/0025—Boil-off gases "BOG" from storages
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
    • F25J3/0209—Natural gas or substitute natural gas
    • F25J3/0214—Liquefied natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/005—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by expansion of a gaseous refrigerant stream with extraction of work
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/007—Primary atmospheric gases, mixtures thereof
    • F25J1/0072—Nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0203—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle
    • F25J1/0204—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle as a single flow SCR cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0262—Details of the cold heat exchange system
    • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
    • F25J1/0265—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
    • F25J1/0268—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer using a dedicated refrigeration means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
    • F25J1/0277—Offshore use, e.g. during shipping
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/30—Compression of the feed stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2260/00—Coupling of processes or apparatus to other units; Integrated schemes
    • F25J2260/30—Integration in an installation using renewable energy
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • F25J2270/906—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration by heat driven absorption chillers

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Ocean & Marine Engineering (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

The invention provides a BOG reliquefaction system of an LNG ship combined with absorption refrigeration and a using method thereof.A liquefied natural gas evaporation gas pressurization module is sequentially connected with a first-stage heat exchanger, a second-stage heat exchanger, a third-stage heat exchanger, a natural gas throttle valve and a liquefied natural gas separator; the liquid phase outlet of the liquefied natural gas separator is connected with the liquefied natural gas storage module; the nitrogen compression module is sequentially connected with the second-stage heat exchanger, the ammonia gas heat exchanger and the inlet of the tee pipe fitting; one outlet of the tee pipe fitting is sequentially connected with the first-stage refrigerant throttling device and the inlet of the first-stage mixer; the other outlet of the tee pipe fitting is connected with a third-stage heat exchanger, a second-stage refrigerant throttling device and an inlet of a first-stage mixer in sequence; the outlet of the first-stage mixer is sequentially connected with the third-stage heat exchanger, the second-stage heat exchanger and the nitrogen compression module. The liquefaction process has low energy consumption and strong adaptability to different gas sources.

Description

Absorption refrigeration combined BOG reliquefaction system of LNG ship and use method thereof
Technical Field
The invention relates to the technical field of chemical engineering and low-temperature engineering, in particular to a BOG reliquefaction system of an LNG ship combined with absorption refrigeration and a using method thereof.
Background
Natural gas has been used as a clean energy source in large scale all over the world, the demand of China for the natural gas is increased year by year, and the market pattern of supply and demand shortage enables China to become a large natural gas import country, wherein the import amount of liquefied natural gas accounts for more than 50% of the total import amount. Natural gas is typically transported in gaseous form by pipeline or in liquid form by rail, road or ship, but lng carriers are typically chosen for long-distance cross-sea transport.
For an LNG ship, LNG is generally stored in a low-temperature storage tank with high thermal insulation at minus 164 ℃, but due to the influence of a series of objective factors such as ship body shaking and heat leakage of the storage tank, part of the LNG is heated and evaporated to generate boil-off gas. With the continuous production of boil-off gas, the pressure in the storage tank is gradually increased, which may cause danger if the part of the boil-off gas is not processed in time. There are generally three types of vapor treatment: firstly, the evaporation gas is combusted and discharged through an exhaust valve, which is obviously not beneficial to environmental protection and causes economic loss; secondly, the boil-off gas is sent into a gas turbine to provide power for the gas turbine, but when the liquefied natural gas carrier stops at a port and the like, the produced boil-off gas needs to be additionally treated; thirdly, the boil-off gas is re-liquefied by a re-liquefying system and returned to the liquefied natural gas storage tank. It is therefore necessary for lng carriers to be equipped with reliquefaction devices.
The traditional liquefied natural gas carrier boil-off gas reliquefaction system mainly comprises a nitrogen inverted brayton reliquefaction system, a Claude reliquefaction system, a Kapitza reliquefaction system, a mixed refrigerant reliquefaction system and a direct reliquefaction system (a partial reliquefaction system). However, with the progress of science and technology, the adoption of a new refrigeration technology and the reasonable utilization of solar energy, waste heat and the like to replace the traditional mode will reduce the energy consumption and become the inevitable trend of future development.
Publication No. CN1808027A discloses an operating system for an lng carrier for subcooling liquefaction of boil-off gas, the operating system comprising a boil-off gas compressor, a cryogenic heat exchanger connected to a refrigeration system, a first check valve and a first pressure control valve installed on a pipeline between an lng phase separator and a gas combustion unit, and a second check valve and a second pressure control valve installed in parallel on a parallel pipeline connected to the aforementioned pipeline. The parallel piping is connected to the piping between the boil-off gas compressor and the cryogenic heat exchanger to supply the boil-off gas to the upper vapor zone of the liquefied natural gas phase separator. Thus, the pressure and liquid level of the liquefied natural gas phase separator are stably controlled. The power consumption is effectively reduced and economic benefits are obtained by stably operating the pressure and liquid level of the lng phase separator. Said invention has more energy consumption.
Disclosure of Invention
In view of the defects in the prior art, the invention aims to provide a BOG reliquefaction system of an LNG ship combined with absorption refrigeration and a using method thereof.
The BOG reliquefaction system of the LNG ship combined with the absorption refrigeration, provided by the invention, comprises a liquefied natural gas evaporation gas pressurization module, a liquefied cold box module, a nitrogen compression module, an absorption refrigeration module and a liquefied natural gas storage module;
the liquefied cold box module comprises a first-stage heat exchanger, a second-stage heat exchanger, a third-stage heat exchanger, a natural gas throttle valve, a liquefied natural gas separator, an ammonia gas heat exchanger, a three-way pipe fitting, a first-stage refrigerant throttling device, a first-stage mixer and a second-stage refrigerant throttling device;
the liquefied natural gas evaporation gas pressurization module is sequentially connected with the first-stage heat exchanger, the second-stage heat exchanger, the third-stage heat exchanger, the natural gas throttling valve and the liquefied natural gas separator;
the liquid phase outlet of the liquefied natural gas separator is connected with the liquefied natural gas storage module;
the nitrogen compression module is sequentially connected with the second-stage heat exchanger, the ammonia gas heat exchanger and the inlet of the tee pipe fitting;
one outlet of the three-way pipe fitting is sequentially connected with the first-stage refrigerant throttling device and the inlet of the first-stage mixer; the other outlet of the three-way pipe fitting is sequentially connected with the third-stage heat exchanger, the second-stage refrigerant throttling device and the inlet of the first-stage mixer;
and the outlet of the first-stage mixer is sequentially connected with the third-stage heat exchanger, the second-stage heat exchanger and the nitrogen compression module.
Preferably, the liquefied natural gas boil-off gas pressurizing module comprises a boil-off gas first-stage compressor, a boil-off gas first-stage cooler, a boil-off gas second-stage compressor, a boil-off gas second-stage water cooler, a boil-off gas third-stage compressor and a boil-off gas third-stage water cooler which are sequentially connected;
the evaporation gas third-stage water cooler is connected with the second-stage heat exchanger, and the evaporation gas first-stage compressor is connected with the first-stage heat exchanger.
Preferably, the first stage refrigerant throttling device and the second stage refrigerant throttling device are throttle valves or expansion machines.
Preferably, the nitrogen compression module comprises a first-stage nitrogen compressor, a first-stage nitrogen cooler, a second-stage nitrogen compressor, a second-stage nitrogen cooler, a third-stage nitrogen compressor and a third-stage nitrogen cooler which are connected in sequence;
the first-stage nitrogen compressor is connected with the second-stage heat exchanger, and the third-stage nitrogen cooler is connected with the second-stage heat exchanger.
Preferably, the absorption refrigeration module comprises a first-stage water cooler, an ammonia solution pump, a fourth-stage heat exchanger, a rectifying tower, a second-stage water cooler, a concentrated ammonia solution throttling valve, a second-stage mixer, a dilute ammonia solution throttling valve and a third-stage water cooler;
the first-stage water cooler is sequentially connected with the ammonia solution pump, the fourth-stage heat exchanger and the rectifying tower;
the outlet of the top of the rectifying tower is sequentially connected with the second-stage water cooler, the concentrated ammonia solution throttle valve, the ammonia gas heat exchanger and the inlet of the second-stage mixer;
the bottom outlet of the rectifying tower is connected with the fourth-stage heat exchanger, the dilute ammonia solution throttling valve and the inlet of the second-stage mixer;
the outlet of the second-stage mixer is connected with the first-stage water cooler; and the third-stage water cooler is connected with the fourth-stage heat exchanger.
Preferably, the first-stage heat exchanger, the second-stage heat exchanger and the third-stage heat exchanger are all multi-flow heat exchangers, and the heat exchangers are plate-fin heat exchangers or wound-tube heat exchangers.
The invention also provides a use method of the BOG reliquefaction system of the LNG carrier based on the combined absorption refrigeration, which comprises the following steps:
the method comprises the following steps: the raw material evaporated gas is discharged from the liquefied natural gas storage tank, is compressed and cooled by the liquefied natural gas evaporated gas pressurizing module after being released by the first-stage heat exchanger, sequentially enters the second-stage heat exchanger, the first-stage heat exchanger and the third-stage heat exchanger for cooling and liquefaction, is throttled and depressurized by the natural gas throttle valve to the liquefied natural gas storage pressure, enters the liquefied natural gas separator, and enters the liquefied natural gas storage module after being obtained from the bottom;
step two: the nitrogen raw material enters a second-stage heat exchanger and an ammonia gas heat exchanger for heat exchange and cooling after being pressurized and cooled by the nitrogen compression module, and is divided into two flows after passing through a tee pipe: one stream is throttled and cooled by a first-stage refrigerant throttling device, the other stream passes through a third-stage heat exchanger and a second-stage refrigerant throttling device in sequence and then enters the third-stage heat exchanger to provide cold energy for the third-stage heat exchanger and the second-stage heat exchanger, the two streams are mixed by a first-stage mixer and then provide cold energy for the third-stage heat exchanger and the second-stage heat exchanger, and nitrogen which is discharged after the cold energy is provided by the second-stage heat exchanger returns to a nitrogen compression module to complete refrigeration cycle;
step three: the ammonia solution is pumped out by the ammonia solution pump and then is heated by the fourth-stage heat exchanger and then enters the rectifying tower for rectification, the concentrated ammonia solution coming out from the top of the rectifying tower is cooled by the second-stage water cooler and then is throttled and depressurized by the concentrated ammonia solution throttle valve, latent heat is released by the ammonia gas heat exchanger and then enters the inlet end of the second-stage mixer, the dilute ammonia solution coming out from the bottom of the rectifying tower is throttled and depressurized by the dilute ammonia solution throttle valve after being subjected to heat exchange and cooling by the fourth-stage heat exchanger, and two streams of fluid are cooled by the first-stage water cooler after being mixed by the second-stage mixer and then return to the inlet end of the ammonia solution pump again to complete circulation.
Preferably, in the step one, when the evaporation gas pressure of the raw material liquefied natural gas is higher than 3.8MPa, the liquefied natural gas evaporation gas pressurizing module is not started.
Preferably, in the first step, the storage pressure of the liquefied natural gas is 0.14 MPa.
Preferably, the heat required by the absorption refrigeration module is from solar energy, waste heat or industrial waste heat.
Compared with the prior art, the invention has the following beneficial effects:
1. the process for reliquefying the evaporated gas of the nitrogen expansion liquefied natural gas carrier combined with the absorption refrigeration disclosed by the invention explores the feasibility of combining with a new technology, and is low in energy consumption;
2. according to the invention, through simulation calculation of HYSYS software widely adopted in the oil and gas industry, the liquefaction process is low in energy consumption and strong in adaptability to different gas sources, and is a reliquefaction process of a reliquefaction device for the boil-off gas of a nitrogen expansion liquefied natural gas carrier, which is relatively suitable for combining absorption refrigeration;
3. the liquefaction process flow of the invention has low energy consumption and stronger adaptability to different gas sources, and simultaneously provides possibility for the combination of the traditional on-board boil-off gas reliquefaction flow and the novel refrigeration technology.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
fig. 1 is a process flow diagram of the BOG reliquefaction system of the LNG carrier in combination with absorption refrigeration according to the present invention.
The figures show that:
1. a boil-off gas first stage compressor; 2. a boil-off gas first stage cooler; 3. a boil-off gas second stage compressor; 4. a second stage water cooler for the boil-off gas; 5. a third stage compressor for boil-off gas; 6. a third-stage water cooler for the evaporated gas; 7. a second stage heat exchanger; 8. a first stage heat exchanger; 9. a third stage heat exchanger; 10. a natural gas throttle valve; 11. a liquefied natural gas separator; 12. a first stage nitrogen compressor; 13. a first stage nitrogen cooler; 14. a second stage nitrogen compressor; 15. a second stage nitrogen cooler; 16. a third stage nitrogen compressor; 17. a third stage nitrogen cooler; 18. an ammonia gas heat exchanger; 19. a tee pipe fitting; 20. a first stage refrigerant throttling device; 21. a first stage mixer; 22. a second stage refrigerant throttling device; 23. a first stage water cooler; 24. an ammonia solution pump; 25. a fourth stage heat exchanger; 26. a rectifying tower; 27. a second stage water cooler; 28. a concentrated ammonia solution throttle valve; 29. a second stage mixer; 30. a dilute ammonia solution throttle valve; 31. a third stage water cooler; 32. a liquefied natural gas storage module; 33. the liquefied natural gas evaporation gas pressurization module; 34. a liquefaction cold box module; 35. a nitrogen compression module; 36. absorption refrigeration module.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
The BOG reliquefaction system of the LNG ship combined with the absorption refrigeration, provided by the invention, comprises a liquefied natural gas boil-off gas pressurization module 33, a liquefied cold box module 34, a nitrogen compression module 35, an absorption refrigeration module 36 and a liquefied natural gas storage module 32.
The liquefied cold box module 34 comprises a first-stage heat exchanger 8, a second-stage heat exchanger 7, a third-stage heat exchanger 9, a natural gas throttle valve 10, a liquefied natural gas separator 11, an ammonia gas heat exchanger 18, a tee pipe fitting 19, a first-stage refrigerant throttling device 20, a first-stage mixer 21 and a second-stage refrigerant throttling device 22.
The liquefied natural gas evaporation gas pressurizing module 33 is sequentially connected with the first-stage heat exchanger 8, the second-stage heat exchanger 7, the third-stage heat exchanger 9, the natural gas throttle valve 10 and the liquefied natural gas separator 11. The liquid phase outlet of the liquefied natural gas separator 11 is connected with the liquefied natural gas storage module 32. The nitrogen compression module 35 is connected with the second-stage heat exchanger 7, the ammonia gas heat exchanger 18 and the inlet of the tee pipe fitting 19 in sequence. One outlet of the tee pipe 19 is connected with a first-stage refrigerant throttling device 20 and an inlet of a first-stage mixer 21 in sequence. The other outlet of the tee pipe 19 is connected with the third-stage heat exchanger 9, the second-stage refrigerant throttling device 22 and the inlet of the first-stage mixer 21 in sequence. The outlet of the first-stage mixer 21 is connected with the third-stage heat exchanger 9, the second-stage heat exchanger 7 and the nitrogen compression module 35 in sequence. The first-stage heat exchanger 8, the second-stage heat exchanger 7 and the third-stage heat exchanger 9 are all multi-flow heat exchangers, and the heat exchangers are plate-fin heat exchangers or wound-tube heat exchangers. The first stage refrigerant restriction 20 and the second stage refrigerant restriction 22 are throttle valves or expanders.
The absorption refrigeration module 36 includes a first-stage water cooler 23, an ammonia solution pump 24, a fourth-stage heat exchanger 25, a rectifying tower 26, a second-stage water cooler 27, a concentrated ammonia solution throttle valve 28, a second-stage mixer 29, a dilute ammonia solution throttle valve 30, and a third-stage water cooler 31. The first-stage water cooler is connected with the ammonia solution pump 24, the fourth-stage heat exchanger 25 and the rectifying tower 26 in sequence, the outlet of the top of the rectifying tower 26 is connected with the second-stage water cooler 27, the concentrated ammonia solution throttle valve 28, the ammonia gas heat exchanger 18 and the inlet of the second-stage mixer 29 in sequence, the outlet of the bottom of the rectifying tower 26 is connected with the fourth-stage heat exchanger 25, the dilute ammonia solution throttle valve 30 and the inlet of the second-stage mixer 29, the outlet of the second-stage mixer 29 is connected with the first-stage water cooler 23, and the third-stage water cooler 31 is connected with the fourth-stage heat exchanger 25.
The nitrogen compression module 35 includes a first-stage nitrogen compressor 12, a first-stage nitrogen cooler 13, a second-stage nitrogen compressor 14, a second-stage nitrogen cooler 15, a third-stage nitrogen compressor 16, and a third-stage nitrogen cooler 17, which are connected in sequence. The first stage nitrogen compressor 12 is connected to the second stage heat exchanger 7, and the third stage nitrogen cooler 17 is connected to the second stage heat exchanger 7.
The liquefied natural gas boil-off gas pressurizing module 33 comprises a first stage compressor 1 of the boil-off gas, a first stage cooler 2 of the boil-off gas, a second stage compressor 3 of the boil-off gas, a second stage water cooler 4 of the boil-off gas, a third stage compressor 5 of the boil-off gas and a third stage water cooler 6 of the boil-off gas which are connected in sequence. The third-stage water cooler 6 of the evaporated gas is connected with the second-stage heat exchanger 7, and the first-stage compressor 1 of the evaporated gas is connected with the first-stage heat exchanger 8.
The system comprises a liquefied natural gas evaporation gas re-liquefaction loop, a nitrogen refrigeration circulation loop and an absorption refrigeration circulation loop:
the specific structure of the liquefied natural gas boil-off gas reliquefaction circuit is as follows: the system comprises an evaporated gas first-stage compressor 1, an evaporated gas first-stage cooler 2, an evaporated gas second-stage compressor 3, an evaporated gas second-stage water cooler 4, an evaporated gas third-stage compressor 5, an evaporated gas third-stage water cooler 6, a first-stage heat exchanger 8, a second-stage heat exchanger 7, a third-stage heat exchanger 9, a natural gas throttle valve 10 and a liquefied natural gas separator 11 which are sequentially connected;
the nitrogen refrigeration cycle specifically comprises: a first-stage nitrogen compressor 12, a first-stage nitrogen cooler 13, a second-stage nitrogen compressor 14, a second-stage nitrogen cooler 15, a third-stage nitrogen compressor 16, a third-stage nitrogen cooler 17, a second-stage heat exchanger 7, an ammonia gas heat exchanger 18 and a tee pipe 19;
the absorption refrigeration cycle specifically has a configuration in which: a first-stage water cooler 23, an ammonia solution pump 24, a fourth-stage heat exchanger 25, a rectifying tower 26, a second-stage water cooler 27, a concentrated ammonia solution throttle valve 28, an ammonia gas heat exchanger 18, a second-stage mixer 29, a dilute ammonia solution throttle valve 30 and a third-stage water cooler 31.
As a preferred technical scheme, the system can also optionally comprise a nitrogen storage unit, an instrument control unit, an instrument wind and PSA nitrogen generation module and a generator module. The generator module is used for providing electric energy for the reliquefaction process when a power supply system is not available.
The invention also provides a use method of the BOG reliquefaction system of the LNG carrier combined with the absorption refrigeration, which comprises the following steps:
the method comprises the following steps: the raw material evaporation gas is discharged from the liquefied natural gas storage tank, is compressed and cooled by the liquefied natural gas evaporation gas pressurizing module 33 after being released cold energy by the first-stage heat exchanger 8, sequentially enters the second-stage heat exchanger 7, the first-stage heat exchanger 8 and the third-stage heat exchanger 9 for cooling and liquefaction, is throttled and depressurized by the natural gas throttle valve 10 to liquefied natural gas storage pressure, enters the liquefied natural gas separator 11, and is subjected to liquefied natural gas product obtained from the bottom and enters the liquefied natural gas storage module 32;
step two: the nitrogen raw material enters the second-stage heat exchanger 7 and the ammonia gas heat exchanger 18 for heat exchange and cooling after being pressurized and cooled by the nitrogen compression module 35, and is divided into two flows after passing through the tee pipe fitting 19: one stream is throttled and cooled by a first-stage refrigerant throttling device 20, the other stream passes through a third-stage heat exchanger 9 and a second-stage refrigerant throttling device 22 in sequence and then enters the third-stage heat exchanger 9 to provide cold energy for the third-stage heat exchanger, the two streams are mixed by a first-stage mixer 21 to provide cold energy for the third-stage heat exchanger 9 and a second-stage heat exchanger 7, and nitrogen which is discharged after the cold energy is provided by the second-stage heat exchanger 7 returns to a nitrogen compression module 35 to complete refrigeration cycle;
step three: the ammonia solution is pumped out by the ammonia solution pump 24, then is heated by the fourth-stage heat exchanger 25, and enters the rectifying tower 26 for rectification, the concentrated ammonia solution from the top of the rectifying tower 26 is cooled by the second-stage water cooler 27, is throttled and reduced in pressure by the concentrated ammonia solution throttle valve 28, releases latent heat by the ammonia gas heat exchanger 18, enters the inlet end of the second-stage mixer 29, the dilute ammonia solution from the bottom of the rectifying tower 26 is cooled by the fourth-stage heat exchanger 25, is throttled and reduced in pressure by the dilute ammonia solution throttle valve 30, is mixed by the second-stage mixer 29, is cooled by the first-stage water cooler 23, and returns to the inlet end of the ammonia solution pump 24 again to complete circulation.
In the first step, when the evaporation gas pressure of the raw material liquefied natural gas is higher than 3.8MPa, the liquefied natural gas evaporation gas pressurization module 33 is not started. The liquefied natural gas storage pressure is 0.14 MPa.
The heat required by the absorption refrigeration module 36 is from solar energy, waste heat, or industrial waste heat.
The method for reliquefying the boil-off gas by using the nitrogen expansion liquefied natural gas carrier boil-off gas reliquefaction system combined with the absorption refrigeration is concretely seen in the following embodiments:
example 1
The molar components of the evaporated gas of the liquefied natural gas are 95 percent of CH4 and 2 percent of C2H6 and 3 percent of N2, the pressure is 0.14MPa, the temperature is-125 ℃, and the flow rate is 350 kg/H; the nitrogen flow was 2000 kg/h. The specific steps of the nitrogen expansion liquefied natural gas carrier boil-off gas reliquefaction process combined with absorption refrigeration are as follows:
1. the raw material of the liquefied natural gas evaporation gas is heated to-35 ℃ by the cold energy released by the primary heat exchanger 8;
2. the evaporated gas heated in the step 1 is compressed to 3.8MPa by a three-stage compressor (an evaporated gas first-stage compressor 1, an evaporated gas second-stage compressor 3 and an evaporated gas third-stage compressor 5) and is cooled to 30 ℃ by a cooler (an evaporated gas first-stage cooler 2, an evaporated gas second-stage water cooler 4 and an evaporated gas third-stage water cooler 6);
3. the evaporated gas in the step 2 is cooled to-19 ℃ through a second-stage heat exchanger 7, cooled to-81 ℃ through a first-stage heat exchanger 8, and cooled to-136 ℃ through a third-stage heat exchanger 9;
4. the high-pressure low-temperature liquefied natural gas obtained in the step (3) passes through a natural gas throttle valve 10, is throttled and depressurized to 0.14MPa, enters a liquefied natural gas separator 11, is obtained from the bottom, and is input into a liquefied natural gas storage tank;
5. the nitrogen raw material is pressurized to 2.47MPa by a first-stage nitrogen compressor 12, a second-stage nitrogen compressor 14 and a third-stage nitrogen compressor 16, and then is cooled to 30 ℃ by a first-stage nitrogen cooler 13, a first-stage nitrogen cooler 15 and a first-stage nitrogen cooler 17;
6. the nitrogen cooled in the step 5 is cooled to-26 ℃ through a second-stage heat exchanger 7 and an ammonia gas heat exchanger 18;
7. the nitrogen cooled in the step 6 is divided into two parts by a tee pipe 19, and one part is throttled, cooled and depressurized to 0.18MPa by a first-stage refrigerant throttling device 20; one strand of the refrigerant passes through the third heat exchanger 9 to be cooled to-78 ℃, the pressure of the second-stage refrigerant throttling device 22 is reduced to 0.18MPa, and the refrigerant enters the third heat exchanger 9 to provide cold for the refrigerant and is heated to-117 ℃;
8. the two streams from step 7 are mixed by a first mixer 21;
9. the nitrogen mixed in the step 8 provides cold energy for the third-stage heat exchanger 9 and the second-stage heat exchanger 7, and the nitrogen returns to the first-stage nitrogen compressor 12 after being reheated to 25 ℃ to complete the refrigeration cycle;
10. pumping the ammonia solution by an ammonia solution pump 24 to increase the pressure to 1.3 MPa;
11. the ammonia solution boosted in the step 10 is heated to 123 ℃ through a fourth-stage heat exchanger 25;
12. the ammonia solution heated in the step 11 enters a rectifying tower 26 for rectification, the concentrated ammonia solution from the top of the rectifying tower 26 is cooled to 30 ℃ by a second-stage water cooler 27, throttled and reduced in pressure to 0.12MPa by a concentrated ammonia solution throttle valve 28, and enters the inlet end of a second-stage mixer 29 after latent heat is released by an ammonia gas heat exchanger 18; the dilute ammonia solution from the bottom of the rectifying tower 26 exchanges heat through a fourth-stage heat exchanger 25 and is cooled to 38 ℃, and the dilute ammonia solution is throttled and reduced in pressure to 0.12MPa through a dilute ammonia solution throttle valve 30;
13. the two streams exiting step 12 are mixed by second stage mixer 29
14. The ammonia solution mixed in step 13 is cooled to 30 ℃ by the first-stage water cooler 23, and then returns to the inlet end of the ammonia solution pump 24 again to complete circulation.
Through simulation calculation, the unit energy consumption of the process for reliquefying the evaporated gas of the nitrogen expansion liquefied natural gas ship combined with the absorption refrigeration is 0.7878 kWh/kgLNG.
Example 2
The molar component of the evaporated gas of the liquefied natural gas is 93 percent of CH4+2 percent of C2H6+5 percent of N2, the pressure is 0.16MPa, the temperature is-120 ℃, the flow rate is 350kg/H, and the flow rate of nitrogen is 2030 kg/H. The specific steps of the nitrogen expansion liquefied natural gas carrier boil-off gas reliquefaction process combined with absorption refrigeration are as follows:
1. the raw material of the liquefied natural gas evaporation gas is heated to-35 ℃ by the cold energy released by the primary heat exchanger 8;
2. the evaporated gas heated in the step 1 is compressed to 3.8MPa by a three-stage compressor (an evaporated gas first-stage compressor 1, an evaporated gas second-stage compressor 3 and an evaporated gas third-stage compressor 5) and is cooled to 30 ℃ by a cooler (an evaporated gas first-stage cooler 2, an evaporated gas second-stage water cooler 4 and an evaporated gas third-stage water cooler 6);
3. the evaporated gas in the step 2 is cooled to-19 ℃ through a second-stage heat exchanger 7, cooled to-79 ℃ through a first-stage heat exchanger 8, and cooled to-139 ℃ through a third-stage heat exchanger 9;
4. the high-pressure low-temperature liquefied natural gas obtained in the step (3) passes through a natural gas throttle valve 10, is throttled and depressurized to 0.14MPa, enters a liquefied natural gas separator 11, is obtained from the bottom, and is input into a liquefied natural gas storage tank;
5. the nitrogen raw material is pressurized to 2.47MPa by a first-stage nitrogen compressor 12, a second-stage nitrogen compressor 14 and a third-stage nitrogen compressor 16, and then is cooled to 30 ℃ by a first-stage nitrogen cooler 13, a first-stage nitrogen cooler 15 and a first-stage nitrogen cooler 17;
6. the nitrogen cooled in the step 5 is cooled to-26 ℃ through a second-stage heat exchanger 7 and an ammonia gas heat exchanger 18;
7. the nitrogen cooled in the step 6 is divided into two parts by a tee pipe 19, and one part is throttled, cooled and depressurized to 0.18MPa by a first-stage refrigerant throttling device 20; one strand of the refrigerant passes through the third heat exchanger 9 to be cooled to-78 ℃, the pressure of the second-stage refrigerant throttling device 22 is reduced to 0.18MPa, and the refrigerant enters the third heat exchanger 9 to provide cold for the refrigerant and is heated to-117 ℃;
8. the two streams from step 7 are mixed by a first mixer 21;
9. the nitrogen mixed in the step 8 provides cold energy for the third-stage heat exchanger 9 and the second-stage heat exchanger 7, and the nitrogen returns to the first-stage nitrogen compressor 12 after being reheated to 25 ℃ to complete the refrigeration cycle;
10. pumping the ammonia solution by an ammonia solution pump 24 to increase the pressure to 1.3 MPa;
11. the ammonia solution boosted in the step 10 is heated to 123 ℃ through a fourth-stage heat exchanger 25;
12. the ammonia solution heated in the step 11 enters a rectifying tower 26 for rectification, the concentrated ammonia solution from the top of the rectifying tower 26 is cooled to 30 ℃ by a second-stage water cooler 27, throttled and reduced in pressure to 0.12MPa by a concentrated ammonia solution throttle valve 28, and enters the inlet end of a second-stage mixer 29 after latent heat is released by an ammonia gas heat exchanger 18; the dilute ammonia solution from the bottom of the rectifying tower 26 exchanges heat through a fourth-stage heat exchanger 25 and is cooled to 38 ℃, and the dilute ammonia solution is throttled and reduced in pressure to 0.12MPa through a dilute ammonia solution throttle valve 30;
13. the two streams exiting step 12 are mixed by second stage mixer 29
14. The ammonia solution mixed in step 13 is cooled to 30 ℃ by the first-stage water cooler 23, and then returns to the inlet end of the ammonia solution pump 24 again to complete circulation.
Through simulation calculation, the unit energy consumption of the boil-off gas reliquefaction process of the nitrogen expansion liquefied natural gas carrier combined with absorption refrigeration is 0.7844 kWh/kgLNG.
Example 3
The molar component of the evaporated gas of the liquefied natural gas is 80 percent of CH4, 5 percent of C2H6 and 15 percent of N2, the pressure is 0.2MPa, the temperature is-100 ℃, the flow rate is 350kg/H, and the flow rate of nitrogen is 2100 kg/H. The specific steps of the nitrogen expansion liquefied natural gas carrier boil-off gas reliquefaction process combined with absorption refrigeration are as follows:
1. the raw material of the liquefied natural gas evaporation gas is heated to-35 ℃ by the cold energy released by the primary heat exchanger 8;
2. the evaporated gas heated in the step 1 is compressed to 3.8MPa by a three-stage compressor (an evaporated gas first-stage compressor 1, an evaporated gas second-stage compressor 3 and an evaporated gas third-stage compressor 5) and is cooled to 30 ℃ by a cooler (an evaporated gas first-stage cooler 2, an evaporated gas second-stage water cooler 4 and an evaporated gas third-stage water cooler 6);
3. the evaporated gas in the step 2 is cooled to-19 ℃ through a second-stage heat exchanger 7, cooled to-68 ℃ through a first-stage heat exchanger 8, and cooled to-154 ℃ through a third-stage heat exchanger 9;
4. the high-pressure low-temperature liquefied natural gas obtained in the step (3) passes through a natural gas throttle valve 10, is throttled and depressurized to 0.14MPa, enters a liquefied natural gas separator 11, is obtained from the bottom, and is input into a liquefied natural gas storage tank;
5. the nitrogen raw material is pressurized to 2.47MPa by a first-stage nitrogen compressor 12, a second-stage nitrogen compressor 14 and a third-stage nitrogen compressor 16, and then is cooled to 30 ℃ by a first-stage nitrogen cooler 13, a first-stage nitrogen cooler 15 and a first-stage nitrogen cooler 17;
6. the nitrogen cooled in the step 5 is cooled to-26 ℃ through a second-stage heat exchanger 7 and an ammonia gas heat exchanger 18;
7. the nitrogen cooled in the step 6 is divided into two parts by a tee pipe 19, and one part is throttled, cooled and depressurized to 0.18MPa by a first-stage refrigerant throttling device 20; one strand of the refrigerant passes through the third heat exchanger 9 to be cooled to-78 ℃, the pressure of the second-stage refrigerant throttling device 22 is reduced to 0.18MPa, and the refrigerant enters the third heat exchanger 9 to provide cold for the refrigerant and is heated to-117 ℃;
8. the two streams from step 7 are mixed by a first mixer 21;
9. the nitrogen mixed in the step 8 provides cold energy for the third-stage heat exchanger 9 and the second-stage heat exchanger 7, and the nitrogen returns to the first-stage nitrogen compressor 12 after being reheated to 25 ℃ to complete the refrigeration cycle;
10. pumping the ammonia solution by an ammonia solution pump 24 to increase the pressure to 1.3 MPa;
11. the ammonia solution boosted in the step 10 is heated to 123 ℃ through a fourth-stage heat exchanger 25;
12. the ammonia solution heated in the step 11 enters a rectifying tower 26 for rectification, the concentrated ammonia solution from the top of the rectifying tower 26 is cooled to 30 ℃ by a second-stage water cooler 27, throttled and reduced in pressure to 0.12MPa by a concentrated ammonia solution throttle valve 28, and enters the inlet end of a second-stage mixer 29 after latent heat is released by an ammonia gas heat exchanger 18; the dilute ammonia solution from the bottom of the rectifying tower 26 exchanges heat through a fourth-stage heat exchanger 25 and is cooled to 38 ℃, and the dilute ammonia solution is throttled and reduced in pressure to 0.12MPa through a dilute ammonia solution throttle valve 30;
13. the two streams exiting step 12 are mixed by second stage mixer 29
14. The ammonia solution mixed in step 13 is cooled to 30 ℃ by the first-stage water cooler 23, and then returns to the inlet end of the ammonia solution pump 24 again to complete circulation.
Through simulation calculation, the unit energy consumption of the boil-off gas reliquefaction process of the nitrogen expansion liquefied natural gas carrier combined with absorption refrigeration is 0.7867 kWh/kgLNG.
Aiming at different components of the evaporated gas of the liquefied natural gas, the nitrogen flow also needs to be correspondingly adjusted when necessary, so that the process energy consumption is lowest. Comparing example 1, example 2 and example 3, it can be found that the re-liquefaction process of the boil-off gas of the nitrogen expansion liquefied natural gas ship combined with the absorption refrigeration has better adaptability to the boil-off gas of different gas sources, most process parameters do not need to be adjusted, and only the nitrogen flow rate needs to be adjusted according to the components of the boil-off gas.
Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, units provided by the present invention as pure computer readable program code, the system and its various devices, modules, units provided by the present invention can be fully implemented by logically programming method steps in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system and various devices, modules and units thereof provided by the invention can be regarded as a hardware component, and the devices, modules and units included in the system for realizing various functions can also be regarded as structures in the hardware component; means, modules, units for performing the various functions may also be regarded as structures within both software modules and hardware components for performing the method.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims (10)

1. The BOG reliquefaction system of the LNG carrier combined with the absorption refrigeration is characterized by comprising a liquefied natural gas evaporation gas pressurization module (33), a liquefied cold box module (34), a nitrogen compression module (35), an absorption refrigeration module (36) and a liquefied natural gas storage module (32);
the liquefied cold box module (34) comprises a first-stage heat exchanger (8), a second-stage heat exchanger (7), a third-stage heat exchanger (9), a natural gas throttling valve (10), a liquefied natural gas separator (11), an ammonia gas heat exchanger (18), a three-way pipe fitting (19), a first-stage refrigerant throttling device (20), a first-stage mixer (21) and a second-stage refrigerant throttling device (22);
the liquefied natural gas evaporation gas pressurization module (33) is sequentially connected with the first-stage heat exchanger (8), the second-stage heat exchanger (7), the third-stage heat exchanger (9), the natural gas throttling valve (10) and the liquefied natural gas separator (11);
the liquid phase outlet of the liquefied natural gas separator (11) is connected with the liquefied natural gas storage module (32);
the nitrogen compression module (35) is sequentially connected with the second-stage heat exchanger (7), the ammonia gas heat exchanger (18) and the inlet of the tee pipe fitting (19);
one outlet of the tee pipe (19) is connected with the first-stage refrigerant throttling device (20) and the inlet of the first-stage mixer (21) in sequence; the other outlet of the tee pipe (19) is connected with the third-stage heat exchanger (9), the second-stage refrigerant throttling device (22) and the inlet of the first-stage mixer (21) in sequence;
and the outlet of the first-stage mixer (21) is sequentially connected with the third-stage heat exchanger (9), the second-stage heat exchanger (7) and the nitrogen compression module (35).
2. The BOG reliquefaction system of the LNG carrier combined with the absorption refrigeration as claimed in claim 1, wherein the liquefied natural gas boil-off gas pressurizing module (33) comprises a boil-off gas first stage compressor (1), a boil-off gas first stage cooler (2), a boil-off gas second stage compressor (3), a boil-off gas second stage water cooler (4), a boil-off gas third stage compressor (5) and a boil-off gas third stage water cooler (6) which are connected in sequence;
the evaporation gas third-stage water cooler (6) is connected with the second-stage heat exchanger (7), and the evaporation gas first-stage compressor (1) is connected with the first-stage heat exchanger (8).
3. The BOG reliquefaction system in combination with absorption refrigeration of LNG carrier according to claim 1, characterized in that the first stage refrigerant throttling device (20), the second stage refrigerant throttling device (22) are throttle valves or expanders.
4. The BOG reliquefaction system of the LNG carrier combined with the absorption refrigeration as claimed in claim 1, wherein the nitrogen compression module (35) comprises a first stage nitrogen compressor (12), a first stage nitrogen cooler (13), a second stage nitrogen compressor (14), a second stage nitrogen cooler (15), a third stage nitrogen compressor (16) and a third stage nitrogen cooler (17) connected in series;
the first-stage nitrogen compressor (12) is connected with the second-stage heat exchanger (7), and the third-stage nitrogen cooler (17) is connected with the second-stage heat exchanger (7).
5. The LNG carrier BOG reliquefaction system in combination with absorption refrigeration according to claim 1, wherein the absorption refrigeration module (36) includes a first-stage water cooler (23), an ammonia solution pump (24), a fourth-stage heat exchanger (25), a rectifying tower (26), a second-stage water cooler (27), a concentrated ammonia solution throttle valve (28), a second-stage mixer (29), a dilute ammonia solution throttle valve (30), and a third-stage water cooler (31);
the first-stage water cooler is connected with the ammonia solution pump (24), the fourth-stage heat exchanger (25) and the rectifying tower (26) in sequence;
the outlet of the top of the rectifying tower (26) is sequentially connected with the inlets of the second-stage water cooler (27), the concentrated ammonia solution throttle valve (28), the ammonia gas heat exchanger (18) and the second-stage mixer (29);
the bottom outlet of the rectifying tower (26) is connected with the fourth-stage heat exchanger (25), the dilute ammonia solution throttling valve (30) and the inlet of the second-stage mixer (29);
the outlet of the second-stage mixer (29) is connected with the first-stage water cooler (23); the third-stage water cooler (31) is connected with the fourth-stage heat exchanger (25).
6. The BOG reliquefaction system in combination with absorption refrigeration for LNG carriers according to claim 1, characterized in that the first stage heat exchanger (8), the second stage heat exchanger (7) and the third stage heat exchanger (9) are all multi-flow heat exchangers in the form of plate fin heat exchangers or wound tube heat exchangers.
7. A method for using the BOG reliquefaction system of the LNG carrier combined with the absorption refrigeration as claimed in any one of claims 1 to 6, comprising the following steps:
the method comprises the following steps: the raw material evaporation gas is discharged from the liquefied natural gas storage tank, is compressed and cooled by the liquefied natural gas evaporation gas pressurizing module (33) after the cold energy is released by the first-stage heat exchanger (8), sequentially enters the second-stage heat exchanger (7), the first-stage heat exchanger (8) and the third-stage heat exchanger (9) for cooling and liquefaction, is throttled and depressurized by the natural gas throttling valve (10) to the liquefied natural gas storage pressure, enters the liquefied natural gas separator (11), and is subjected to liquefied natural gas product obtained from the bottom and enters the liquefied natural gas storage module (32);
step two: the nitrogen raw material enters a second-stage heat exchanger (7) and an ammonia gas heat exchanger (18) for heat exchange and cooling after being pressurized and cooled by the nitrogen compression module (35), and is divided into two streams of fluid after passing through a tee pipe fitting (19): one stream is throttled and cooled by a first-stage refrigerant throttling device (20), the other stream sequentially passes through a third-stage heat exchanger (9) and a second-stage refrigerant throttling device (22) and then enters the third-stage heat exchanger (9) to provide cold energy for the third-stage heat exchanger, the two streams are mixed by a first-stage mixer (21) to provide cold energy for the third-stage heat exchanger (9) and a second-stage heat exchanger (7), and nitrogen which is discharged after the cold energy is provided by the second-stage heat exchanger (7) returns to a nitrogen compression module (35) to complete refrigeration cycle;
step three: ammonia solution is pumped out by the ammonia solution pump (24), then is heated by the fourth-stage heat exchanger (25), and then enters the rectifying tower (26) for rectification, then is cooled by the second-stage water cooler (27), then is throttled and depressurized by the concentrated ammonia solution throttle valve (28), and enters the inlet end of the second-stage mixer (29) after latent heat is released by the ammonia heat exchanger (18), and then is throttled and depressurized by the dilute ammonia solution throttle valve (30), after being heat-exchanged and cooled by the fourth-stage heat exchanger (25), the dilute ammonia solution coming out from the bottom of the rectifying tower (26) is mixed by the second-stage mixer (29), then is cooled by the first-stage water cooler (23), and then returns to the inlet end of the ammonia solution pump (24) again to complete circulation.
8. The method of reliquefying boil-off gas of claim 7, wherein in step one, the LNG boil-off gas pressurization module (33) is not activated when the raw LNG boil-off gas pressure is higher than 3.8 MPa.
9. The method of reliquefying boil-off gas of claim 7, wherein in step one, the liquefied natural gas storage pressure is 0.14 MPa.
10. The method of reliquefying boil-off gas of claim 7, wherein the heat required by the absorption refrigeration module (36) is from solar energy, waste heat or industrial waste heat.
CN202110594091.6A 2021-05-28 2021-05-28 Absorption refrigeration combined BOG reliquefaction system of LNG ship and use method thereof Pending CN113266999A (en)

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