CN115420062B - Marine nitrogen liquefaction system and method - Google Patents

Marine nitrogen liquefaction system and method Download PDF

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Publication number
CN115420062B
CN115420062B CN202211032083.3A CN202211032083A CN115420062B CN 115420062 B CN115420062 B CN 115420062B CN 202211032083 A CN202211032083 A CN 202211032083A CN 115420062 B CN115420062 B CN 115420062B
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nitrogen
pipeline
pressure
communicated
circulating
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CN115420062A (en
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余楠
童雪梅
张益诚
王俊新
陶文灿
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China Ship Development and Design Centre
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China Ship Development and Design Centre
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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
    • F25J1/0012—Primary atmospheric gases, e.g. air
    • F25J1/0015—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
    • F25J1/003—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
    • F25J1/0275—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
    • 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
    • F25J1/0278—Unit being stationary, e.g. on floating barge or fixed platform
    • 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
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Ocean & Marine Engineering (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

The invention discloses a marine nitrogen liquefaction system which comprises a nitrogen circulating compressor, a nitrogen storage tank, a main heat exchanger, a turbine expander, a liquefier, a nitrogen production device and a liquid nitrogen storage tank, wherein an inlet and an outlet of the nitrogen circulating compressor are communicated with a circulating pipeline; the nitrogen storage tank is arranged on a first pipeline, and two ends of the first pipeline are respectively communicated with the circulating pipeline; the circulating pipeline is communicated with one end of a second pipeline, the second pipeline is communicated with a first fluid channel of the main heat exchanger, the other end of the second pipeline is communicated with an inlet of the turbine expander, and an outlet of the turbine expander is communicated with the circulating pipeline through a third pipeline. The beneficial effects of the invention are as follows: the invention consists of two parts, namely nitrogen circulation and nitrogen liquefaction, which are operated independently and are not interfered with each other, so that the reliability, operability, maintainability and safety of the device in ship application are improved.

Description

Marine nitrogen liquefaction system and method
Technical Field
The invention relates to the technical field of nitrogen liquefaction, in particular to a marine nitrogen liquefaction system and method.
Background
The ship needs a large amount of nitrogen resources and is used in the fields of controlled atmosphere preservation, gas inhibition, pneumatic control and the like. The domestic ships generally adopt technologies such as pressure swing adsorption and membrane separation, and air is used as a raw material to prepare nitrogen on site of the ship, the nitrogen is compressed to be more than 15MPa and then is filled into a steel cylinder group, but the nitrogen stored in the steel cylinder occupies more weight and space resources. Because the density of liquid nitrogen is far higher than that of nitrogen, the volume and weight of the storage equipment are obviously lower than those of the steel cylinder group, and a large amount of weight and space resources can be saved.
Cryogenic media are required for nitrogen liquefaction, and common methods for achieving cryogenic temperatures in industry include phase-change refrigeration and gas adiabatic expansion refrigeration. The phase-change refrigeration is refrigeration by absorbing heat from the outside when liquid such as freon, ammonia and the like is gasified. The application range of each refrigeration medium is different, and the temperature is reduced step by a multi-stage cascade technology, so that the low temperature below-170 ℃ can be obtained. However, the device of the technology has complex composition, and the circulating refrigeration medium adopts flammable and explosive substances such as ethylene, methane and the like, so that the device is not suitable for ships.
The gas adiabatic expansion refrigeration is to utilize the throttling and decompression of high-pressure gas in an expander to refrigerate, and the temperature is gradually reduced to the nitrogen liquefaction temperature through gas circulation refrigeration. In the gas industrial production, a low-pressure expander refrigeration process and a medium-pressure expander refrigeration process are mostly adopted according to different liquefied gas amounts. The nitrogen gas of the product enters the cold box and is divided into two paths, part of the nitrogen gas is expanded and refrigerated by an expander, and the other nitrogen gas is liquefied. The whole flow nitrogen in the liquefaction cycle is in a gas state, no liquid nitrogen is generated, and the method is particularly suitable for occasions needing to liquefy the nitrogen on offshore platforms or ships. For example, chinese patent nos. 201820684683.0 and 201821012130.7 disclose a boil-off gas (BOG) reliquefaction device for a ship, wherein the boil-off gas is liquefied by using the boil-off gas itself as a refrigerant, a liquid working medium is present in the device, and the refrigeration cycle and the liquefaction cycle are not independent of each other.
However, the conventional marine gas liquefaction device may have liquid refrigerant, which is adversely affected by the conditions of offshore tilting and swinging, and has a low gas liquefaction rate, so that the complete liquefaction of nitrogen cannot be realized. Moreover, the traditional land nitrogen liquefaction device has complex equipment composition, limited space on an offshore platform and a ship, and can not be directly applied to the land nitrogen liquefaction device.
Disclosure of Invention
The invention aims to provide a safe and reliable nitrogen liquefaction system and method for a ship, aiming at the defects of the prior art.
The invention adopts the technical scheme that: the marine nitrogen liquefaction system comprises a nitrogen circulating compressor, a nitrogen storage tank, a main heat exchanger, a turbine expander, a liquefier, a nitrogen production device and a liquid nitrogen storage tank, wherein an inlet and an outlet of the nitrogen circulating compressor are communicated with a circulating pipeline; the nitrogen storage tank is arranged on a first pipeline, and two ends of the first pipeline are respectively communicated with the circulating pipeline; the circulating pipeline is communicated with one end of a second pipeline, the second pipeline is communicated with a first fluid channel of the main heat exchanger, the other end of the second pipeline is communicated with an inlet of the turbine expander, and an outlet of the turbine expander is communicated with the circulating pipeline through a third pipeline; the third pipeline is provided with a liquefier and is communicated with the second fluid channel of the main heat exchanger; the inlet of the nitrogen making device is communicated with the raw material gas supply pipeline, the outlet of the nitrogen making device is communicated with one end of a fourth pipeline, and the fourth pipeline sequentially passes through the third fluid channel of the main heat exchanger and the liquefier along the fluid flow direction and then is communicated with the inlet of the liquid nitrogen storage tank.
According to the scheme, the marine nitrogen liquefaction system further comprises a fifth pipeline and a nitrogen cooler, one end of the fifth pipeline is connected with the circulating pipeline, and the other end of the fifth pipeline is communicated with the inside of the turbine expander to provide lubricating nitrogen for the bearing operation of the turbine expander; the braking end of the turbine expander is connected with the nitrogen cooler through a pipeline, and the nitrogen cooler is connected with the braking end of the turbine expander through a return pipeline; after the brake nitrogen 104 is warmed up through the expander brake end, it is cooled down to room temperature in the nitrogen cooler and re-enters the expander brake end.
According to the scheme, the marine nitrogen liquefaction system further comprises a bearing gas storage tank, and the bearing gas storage tank is arranged on the fifth pipeline.
According to the scheme, the return pipeline is communicated with the circulating pipeline.
According to the scheme, the main heat exchanger, the liquefier and the turboexpander can be arranged in the cold box.
According to the above scheme, the valves are arranged on the first pipeline, the circulating pipeline, the second pipeline, the fourth pipeline and the fifth pipeline.
The invention also provides a pressure regulating method based on the marine nitrogen liquefaction system, which comprises the following steps: after the nitrogen circulating compressor is started, the valve V2 and the valve V3 are opened, and high-purity nitrogen in the nitrogen storage tank enters the nitrogen circulating compressor, so that the pressure of the high-pressure nitrogen is gradually increased; the high-pressure nitrogen passes through a valve V3 and returns to the inlet of the nitrogen recycle compressor; after the inlet and outlet pressure of the nitrogen circulating compressor is stable, closing a valve V3, and opening a valve V4 to enable the circulated high-pressure nitrogen to fully enter the cold box; during the nitrogen liquefaction process, when the inlet pressure of the nitrogen recycle compressor is reduced, the valve V3 is opened, and when the inlet pressure of the nitrogen recycle compressor is increased, the valve V3 is closed; valve V2 opens when the nitrogen recycle compressor outlet pressure decreases and valve V1 opens when the nitrogen recycle compressor outlet pressure increases.
The invention also provides a marine nitrogen liquefaction method based on the system, which comprises the following steps: the low-pressure nitrogen is compressed to a set pressure in a nitrogen recycle compressor; the compressed high-pressure nitrogen is cooled to a set temperature in a main heat exchanger to become low-temperature high-pressure nitrogen; the high-temperature and high-pressure nitrogen enters a turbine expander, the pressure is reduced to 0.1-0.2 MPa, and the temperature is reduced to-196 ℃ to-180 ℃; the cooled low-pressure nitrogen is sequentially returned to the liquefier and the main heat exchanger to provide cold energy for cooling and liquefying the nitrogen prepared by the nitrogen preparation device; the nitrogen gas prepared by the nitrogen making device is cooled to a set temperature in the main heat exchanger and the liquefier 7 in sequence, and condensed into liquid nitrogen.
According to the scheme, the low-pressure nitrogen is compressed to 0.4-1.2 MPa in the nitrogen recycle compressor.
According to the scheme, the high-pressure nitrogen is cooled to-150 ℃ to-120 ℃ in the main heat exchanger.
The beneficial effects of the invention are as follows: the invention consists of two parts, namely nitrogen circulation and nitrogen liquefaction, which are operated relatively independently and are not interfered with each other, so that the reliability, operability, maintainability and safety of the device in ship application are improved; the refrigerating part adopts high-purity nitrogen as a refrigerant medium, and the pressure stability, safety and reliability of a nitrogen circulation airtight space can be ensured by arranging the nitrogen storage tank and the plurality of control valves; the whole flow nitrogen in the refrigeration cycle is in a gas state, and no liquid nitrogen is generated; the device has simple composition and structure, high liquefaction rate of products and capability of resisting the inclined and swaying working conditions under the offshore platform and marine environment.
Drawings
FIG. 1 is a flow chart of an embodiment of the present invention.
Wherein: 1. a nitrogen recycle compressor; 2. a nitrogen storage tank; 3. a bearing gas storage tank; 4. a nitrogen cooler; 5. a main heat exchanger; 6. a turbine expander; 7. a liquefier; 8. a nitrogen making device; 9. a liquid nitrogen storage tank; 10. a cold box; 11. a circulation line; 12. a first pipeline; 13. a second pipeline; 14. a third pipeline; 15. a fourth pipeline; 16. a return line; 17. a fifth pipeline; 101. compressing and circulating nitrogen; 102. low pressure recycle nitrogen; 103. bearing gas of the expander; 104. braking nitrogen; 201. nitrogen gas; 202. liquid nitrogen; V1-V5 are valves.
Detailed Description
For a better understanding of the present invention, the present invention is further described below with reference to the drawings and specific examples.
The marine nitrogen liquefaction system shown in fig. 1 comprises a nitrogen circulating compressor 1, a nitrogen storage tank 2, a main heat exchanger 5, a turbo expander 6, a liquefier 7, a nitrogen production device 8 and a liquid nitrogen storage tank 9, wherein an inlet and an outlet of the nitrogen circulating compressor 1 are communicated with a circulating pipeline 11; the nitrogen storage tank 2 is arranged on the first pipeline 12, and two ends of the first pipeline 12 are respectively communicated with the circulating pipeline 11; the circulating pipeline 11 is communicated with one end of a second pipeline 13, the second pipeline 13 is communicated with the first fluid channel of the main heat exchanger 5, the other end of the second pipeline 13 is communicated with the inlet of the turbine expander 6, and the outlet of the turbine expander 6 is communicated with the circulating pipeline 11 through a third pipeline 14; the third pipeline 14 is provided with a liquefier 7, and the third pipeline 14 is communicated with the second fluid channel of the main heat exchanger 5; the inlet of the nitrogen making device 8 is communicated with a raw material gas supply pipeline, the outlet of the nitrogen making device 8 is communicated with one end of a fourth pipeline 15, and the fourth pipeline 15 sequentially passes through the third fluid channel of the main heat exchanger 5 and the liquefier 7 along the fluid flow direction and then is communicated with the inlet of the liquid nitrogen storage tank 9.
Preferably, the marine nitrogen liquefaction system further comprises a fifth pipeline 17 and a nitrogen cooler 4, one end of the fifth pipeline 17 is connected with the circulating pipeline 11, and the other end of the fifth pipeline 17 is communicated with the interior of the turbine expander 6 to provide lubricating nitrogen for bearing operation of the turbine expander 6; the braking end of the turbine expander 6 is connected with the nitrogen cooler 4 through a pipeline, and the nitrogen cooler 4 is connected with the braking end of the turbine expander 6 through a return pipeline 16; after the brake nitrogen 104 is heated up through the brake end of the turbo expander 6, the temperature is lowered in the nitrogen cooler 4, and the brake nitrogen is re-introduced into the brake end of the turbo expander 6.
Preferably, the marine nitrogen liquefaction system further comprises a bearing gas storage tank 3, and the bearing gas storage tank 3 is mounted on the fifth pipeline 17.
Preferably, the return line 16 communicates with the recirculation line 11.
Preferably, the main heat exchanger 5, the liquefier 7, the turboexpander 6 and other low-temperature components can be arranged in the cold box 10 for uniform heat preservation.
In the invention, valves are respectively arranged on the pipelines; specifically, valves disposed on the first pipe 12, the circulation pipe 11, the second pipe 13, the fourth pipe 15, and the fifth pipe 17 are shown by the marks V1 to V5 in fig. 1. The nitrogen liquefaction process adopts high-purity nitrogen as a refrigeration cycle medium and is stored in the nitrogen storage tank 2 at ordinary times. In order to ensure stable system pressure, 4 valves are arranged at the inlet and the outlet of the nitrogen circulating compressor 1, and the opening of the valves is regulated according to pressure change. After the nitrogen recycle compressor 1 is started, the valve V2 and the valve V3 are opened, and high-purity nitrogen in the nitrogen storage tank 2 enters the nitrogen recycle compressor 1, so that the pressure of the high-pressure nitrogen 102 is gradually increased. The high pressure nitrogen 102 passes through valve V3 and is returned to the inlet of the nitrogen recycle compressor 1. After the inlet and outlet pressure of the nitrogen circulating compressor 1 is stable, the valve V3 is closed, and the valve V4 is opened, so that the circulated high-pressure nitrogen 102 completely enters the cold box 10. During the liquefaction of nitrogen 201, valve V3 is opened when the inlet pressure of nitrogen recycle compressor 1 is reduced, and valve V3 is closed when the inlet pressure of nitrogen recycle compressor 1 is increased; when the outlet pressure of the nitrogen recycle compressor 1 is reduced, the valve V2 is opened, and when the outlet pressure of the nitrogen recycle compressor 1 is increased, the valve V1 is opened. Through the above process, the pressure stability of the inlet and outlet of the nitrogen recycle compressor 1 can be ensured.
A marine nitrogen liquefaction method based on the system, which comprises the following steps: the low-pressure nitrogen 101 is compressed to a set pressure (which may be 0.4 to 1.2 MPa) in the nitrogen recycle compressor 1; the compressed high-pressure nitrogen 102 is cooled to a set temperature (which can be-150 ℃ to-120 ℃) in the main heat exchanger 5 to become low-temperature high-pressure nitrogen 102; the high-temperature and high-pressure nitrogen 102 enters a turbine expander 6, the pressure is reduced to 0.1-0.2 MPa, and the temperature is reduced to-196 ℃ to-180 ℃; the cooled low-pressure nitrogen 101 sequentially returns to the liquefier 7 and the main heat exchanger 5 to provide cold energy for cooling and liquefying the nitrogen 201 prepared by the nitrogen preparation device 8; the nitrogen 201 produced by the nitrogen producing device 8 is cooled to a set temperature (which may be-150 ℃ to-120 ℃) in the main heat exchanger 5, cooled to a set temperature (which may be-180 ℃ to-160 ℃) in the liquefier 7, and condensed into liquid nitrogen 202.
Examples: see fig. 1.
The nitrogen liquefaction process and the refrigeration process are independently operated.
The nitrogen circulating compressor 1 is started, low-pressure nitrogen 101 is compressed to 0.4-1.2 MPa in the nitrogen circulating compressor 1, compressed high-pressure nitrogen 102 enters the cold box 10, and the main heat exchanger 5 is cooled to-150 ℃ to-120 ℃ by the returned low-temperature compressed circulating nitrogen 101; the high-temperature and high-pressure nitrogen 102 enters the turbo expander 6 to be expanded, decompressed and cooled (the temperature is lower than the boiling point of the high-pressure nitrogen), the pressure is reduced to about 0.1-0.2 MPa, the temperature is reduced to about-196 ℃ to-180 ℃, and the energy in the decompression process of the compressed nitrogen 101 is transmitted to the pressurizing end at the other side of the turbo expander 6 through the main shaft; the cooled low-pressure nitrogen 101 returns to the liquefier 7 and the main heat exchanger 5 in turn to provide cooling capacity for cooling and liquefying the nitrogen 201. After the rewarming, the low-pressure nitrogen gas 101 is returned to the nitrogen gas circulation compressor 1, and the refrigeration cycle is performed again.
Part of high-pressure nitrogen 102 enters the bearing gas storage tank 3 through the one-way valve V5 and then is used as an expander bearing gas 103 to be directly connected with the turbine expander 6, so as to provide lubricating nitrogen for the bearing operation of the turbine expander 6; the braking end of the turbo expander 6 is directly connected with the nitrogen recycle compressor 1, and the braking nitrogen 104 is cooled to normal temperature in the nitrogen cooler 4 after being heated by the braking end of the turbo expander 6, and reenters the braking end of the turbo expander 6.
The nitrogen 201 prepared by the nitrogen making device 8 is cooled to-150 ℃ to-120 ℃ by the low-pressure nitrogen 101 in the main heat exchanger 5, cooled to about-180 ℃ to-160 ℃ by the low-pressure nitrogen 101 in the liquefier 7, completely condensed into liquid nitrogen 202, and then sent into the liquid nitrogen storage tank 9.
The nitrogen liquefaction process adopts high-purity nitrogen as a refrigeration cycle medium and is stored in the nitrogen storage tank 2 at ordinary times. In order to ensure stable system pressure, 4 valves are arranged at the inlet and the outlet of the nitrogen circulating compressor 1, and the opening of the valves is regulated according to pressure change. After the nitrogen recycle compressor 1 is started, the valves V2 and V3 are slowly opened, and high-purity nitrogen in the nitrogen storage tank 2 enters the nitrogen recycle compressor 1, so that the pressure of the high-pressure nitrogen 102 is gradually increased. The high-pressure nitrogen passes through a valve V3 and returns to the inlet of the nitrogen recycle compressor 1. After the inlet and outlet pressure of the nitrogen circulating compressor 1 is stable, V3 is slowly closed, V4 is slowly opened, and the circulated high-pressure nitrogen 102 completely enters the cold box 10. In the nitrogen liquefaction process, when the inlet pressure of the nitrogen recycle compressor 1 is reduced, the valve V3 is slightly opened, and when the inlet pressure of the nitrogen recycle compressor 1 is increased, the valve V3 is slightly closed; when the outlet pressure of the nitrogen recycle compressor 1 is reduced, the valve V2 is slightly opened, and when the outlet pressure of the nitrogen recycle compressor 1 is increased, the valve V1 is slightly opened. Through the above process, the pressure stability of the inlet and outlet of the nitrogen recycle compressor 1 can be ensured.
The invention separates the refrigeration of the expander and the liquefaction of nitrogen, and the refrigeration and the liquefaction of nitrogen are respectively and independently operated. The inlet of the nitrogen circulating compressor 1 is provided with a nitrogen storage tank 2, and a stable air source is provided for the refrigeration cycle of the turbine expander 6. The whole process gas in the liquefaction cycle is in a gaseous state and no liquid state is generated, so that the device has strong capability of adapting to the ship tilting and swinging environment, has simple device composition and structure, and is suitable for occasions needing to liquefy nitrogen on offshore platforms or ships.
Finally, it should be noted that the foregoing is merely a preferred embodiment of the present invention, and the present invention is not limited thereto, and although the present invention has been described in detail with reference to the embodiment, it will be apparent to those skilled in the art that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features thereof, but any modifications, equivalents, improvements or changes thereof may be made without departing from the spirit and principle of the present invention.

Claims (9)

1. The marine nitrogen liquefaction system is characterized by comprising a nitrogen circulating compressor, a nitrogen storage tank, a main heat exchanger, a turbine expander, a liquefier, a nitrogen production device and a liquid nitrogen storage tank, wherein an inlet and an outlet of the nitrogen circulating compressor are communicated with a circulating pipeline; the nitrogen storage tank is arranged on a first pipeline, and two ends of the first pipeline are respectively communicated with the circulating pipeline; the circulating pipeline is communicated with one end of a second pipeline, the second pipeline is communicated with a first fluid channel of the main heat exchanger, the other end of the second pipeline is communicated with an inlet of the turbine expander, and an outlet of the turbine expander is communicated with the circulating pipeline through a third pipeline; the third pipeline is provided with a liquefier and is communicated with the second fluid channel of the main heat exchanger; the inlet of the nitrogen making device is communicated with the raw material gas supply pipeline, the outlet of the nitrogen making device is communicated with one end of a fourth pipeline, and the fourth pipeline sequentially passes through the third fluid channel of the main heat exchanger and the liquefier along the fluid flow direction and then is communicated with the inlet of the liquid nitrogen storage tank; the marine nitrogen liquefaction system further comprises a fifth pipeline and a nitrogen cooler, one end of the fifth pipeline is connected with the circulating pipeline, and the other end of the fifth pipeline is communicated with the interior of the turbine expander to provide lubricating nitrogen for the bearing operation of the turbine expander; the braking end of the turbine expander is connected with the nitrogen cooler through a pipeline, and the nitrogen cooler is connected with the braking end of the turbine expander through a return pipeline.
2. The marine nitrogen liquefaction system of claim 1, further comprising a bearing gas storage tank mounted on the fifth pipeline.
3. The marine nitrogen liquefaction system of claim 2, wherein the return line is in communication with the circulation line.
4. The marine nitrogen liquefaction system of claim 2, wherein the main heat exchanger, liquefier, and turboexpander are each mountable within a cold box.
5. The marine nitrogen liquefaction system of claim 2, wherein the valves are disposed on the first line, the circulation line, the second line, the fourth line, and the fifth line.
6. A method of pressure regulation based on a marine nitrogen liquefaction system according to claim 5, characterized in that the method is: after the nitrogen circulating compressor is started, a valve (V2) and a valve (V3) are opened, and high-purity nitrogen in the nitrogen storage tank enters the nitrogen circulating compressor, so that the pressure of the high-pressure nitrogen is gradually increased; the high-pressure nitrogen passes through a valve (V3) and returns to the inlet of the nitrogen recycle compressor; after the inlet and outlet pressure of the nitrogen circulating compressor is stable, closing a valve (V3), and opening a valve (V4) to enable the circulated high-pressure nitrogen to completely enter the cold box; during the nitrogen liquefaction process, when the inlet pressure of the nitrogen recycle compressor is reduced, the valve (V3) is opened, and when the inlet pressure of the nitrogen recycle compressor is increased, the valve (V3) is closed; the valve (V2) opens when the nitrogen recycle compressor outlet pressure decreases and the valve (V1) opens when the nitrogen recycle compressor outlet pressure increases.
7. A marine nitrogen liquefaction process based on the system of claim 5, characterized in that it comprises: the low-pressure nitrogen is compressed to a set pressure in a nitrogen recycle compressor; the compressed high-pressure nitrogen is cooled to a set temperature in a main heat exchanger to become low-temperature high-pressure nitrogen; the high-temperature and high-pressure nitrogen enters a turbine expander, the pressure is reduced to 0.1-0.2 MPa, and the temperature is reduced to-196 ℃ to-180 ℃; the cooled low-pressure nitrogen is sequentially returned to the liquefier and the main heat exchanger to provide cold energy for cooling and liquefying the nitrogen prepared by the nitrogen preparation device; the nitrogen gas prepared by the nitrogen preparation device is cooled to a set temperature in the main heat exchanger and the liquefier (7) in sequence, and condensed into liquid nitrogen.
8. The marine nitrogen liquefaction process according to claim 7, wherein the low pressure nitrogen is compressed to 0.4 to 1.2MPa in a nitrogen recycle compressor.
9. The marine nitrogen liquefaction process of claim 7, wherein the high pressure nitrogen is cooled to-150 ℃ to-120 ℃ in the main heat exchanger.
CN202211032083.3A 2022-08-26 2022-08-26 Marine nitrogen liquefaction system and method Active CN115420062B (en)

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