CN110487023B - Method for producing liquid nitrogen by utilizing LNG cold energy - Google Patents
Method for producing liquid nitrogen by utilizing LNG cold energy Download PDFInfo
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- CN110487023B CN110487023B CN201910739821.XA CN201910739821A CN110487023B CN 110487023 B CN110487023 B CN 110487023B CN 201910739821 A CN201910739821 A CN 201910739821A CN 110487023 B CN110487023 B CN 110487023B
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 239
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 118
- 239000007788 liquid Substances 0.000 title claims abstract description 73
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 15
- 238000003303 reheating Methods 0.000 claims abstract description 11
- 238000001816 cooling Methods 0.000 claims abstract description 10
- 239000013526 supercooled liquid Substances 0.000 claims abstract description 9
- 238000004064 recycling Methods 0.000 claims abstract description 5
- 238000005265 energy consumption Methods 0.000 claims description 8
- 238000005057 refrigeration Methods 0.000 claims description 5
- 230000008859 change Effects 0.000 claims description 4
- 239000000047 product Substances 0.000 claims description 4
- 230000006835 compression Effects 0.000 claims description 2
- 238000007906 compression Methods 0.000 claims description 2
- 239000013589 supplement Substances 0.000 claims description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 14
- 238000000034 method Methods 0.000 description 11
- 239000003345 natural gas Substances 0.000 description 6
- 238000000926 separation method Methods 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 4
- 229910001873 dinitrogen Inorganic materials 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000012263 liquid product Substances 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010612 desalination reaction Methods 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000008676 import Effects 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
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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
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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
- F25J1/003—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
- F25J1/0032—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 the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
- F25J1/0035—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 the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by gas expansion with extraction of work
- F25J1/0037—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 the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by gas expansion with extraction of work of a return stream
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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
- F25J1/003—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
- F25J1/0032—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 the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
- F25J1/0045—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 the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by vaporising a liquid return stream
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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
- F25J1/02—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
- F25J1/0221—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 the cold stored in an external cryogenic component in an open refrigeration loop
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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
- F25J1/02—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
- F25J1/0221—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 the cold stored in an external cryogenic component in an open refrigeration loop
- F25J1/0224—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 the cold stored in an external cryogenic component in an open refrigeration loop in combination with an internal quasi-closed refrigeration loop
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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
- F25J1/02—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.
- F25J1/0285—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings
- F25J1/0288—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders
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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
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/62—Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
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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
- F25J2270/00—Refrigeration techniques used
- F25J2270/04—Internal refrigeration with work-producing gas expansion loop
- F25J2270/06—Internal refrigeration with work-producing gas expansion loop with multiple gas expansion loops
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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
- F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
- F25J2290/34—Details about subcooling of liquids
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Separation By Low-Temperature Treatments (AREA)
- Filling Or Discharging Of Gas Storage Vessels (AREA)
Abstract
A method for producing liquid nitrogen by utilizing LNG cold energy, which comprises the following steps: LNG is compressed by a liquid pump and then is sent to a heat exchanger to exchange heat with nitrogen, and after reheating to a lower temperature, the LNG is sent to a BOG compressor to be pressurized and finally sent to an NG pipe network, and nitrogen from the pipe network or a circulating compressor is divided into two streams: one is firstly subjected to supercharging cooling through a supercharging end of an expander, then enters a main heat exchanger to be cooled to a certain temperature, is pumped out to the expander to be expanded, and the expanded nitrogen is subjected to reheating to normal temperature, then enters the supercharging end of the expander again to be subjected to supercharging cooling, is returned to the main heat exchanger in a liquefier to be cooled, is pumped into the expander to be expanded after being reduced to a certain temperature, and the expanded low-pressure nitrogen is returned to the heat exchanger to be reheated, and is directly discharged or is sent into a nitrogen circulation compressor to be circulated after being discharged from a cold box; one strand of liquid nitrogen is directly sent into a heat exchanger to exchange heat with LNG, cooled to a target temperature and condensed into liquid nitrogen, and the liquid nitrogen is divided into two parts: one liquid nitrogen is throttled to low pressure and then sent into a subcooler to subcool the liquid nitrogen, and the evaporated low-pressure liquid nitrogen is reheated by a main heat exchanger and is discharged or recycled by a recycle nitrogen compressor for recycling; and secondly, directly throttling the supercooled liquid nitrogen and sending the supercooled liquid nitrogen into a liquid nitrogen storage tank.
Description
Technical Field
The invention relates to a method for producing liquid nitrogen by utilizing LNG cold energy, which is mainly suitable for liquefying air and liquid nitrogen to produce liquid products such as liquid nitrogen and the like, and belongs to the technical field of low-temperature air separation.
Background
With the implementation of national energy structure adjustment and energy conservation and emission reduction policies, the adoption of more efficient and clean energy to replace traditional energy has been greatly developed. Natural gas is used as one of clean energy sources, and has the advantages of high energy density, convenient use, less pollution and larger consumption. According to the economic development trend of the country and related laws and policies, the natural gas demand potential of the country will be further expanded in the future. Through the development of more than ten years, the domestic natural gas supply forms a multi-gas source supply pattern at present, a relatively complete LNG industrial chain is basically formed, the development is very rapid in the aspect of LNG receiving stations in recent years, the import quantity of LNG is rapidly increased, and the annual growth is 52%.
Natural gas changes from a gaseous state to a liquid state, LNG, when cooled to about one 162 ℃ at atmospheric pressure. LNG is colorless transparent liquid, the main component is methane, the volume of the LNG is about l/625 of the volume of standard gaseous natural gas with the same quality, the density is 450kg/nf, and the LNG has the characteristics of high energy storage rate, small occupied area and investment saving. The LNG contains 30% of high-grade cold energy, and along with the continuous expansion of the scale of the LNG, the full utilization of the cold energy contained in the LNG has great economic value and social significance.
At present, the cold energy utilization of the LNG at home and abroad mainly depends on air separation, light hydrocarbon separation, low-temperature power generation, sea water desalination, carbon dioxide trapping, low-temperature crushing of waste rubber, refrigeration and the like. The LNG cold energy and the cold energy quality of the low-temperature air separation technology are the closest, and are the accepted better modes, for example, the reasonable utilization can greatly reduce the production energy consumption of liquid products (liquid nitrogen and the like) of the air separation device, and can greatly reduce the cost of the liquid nitrogen, liquid oxygen and the like.
Patent ZL200810121860.5 proposes a liquid nitrogen production device and method consisting of a low-temperature nitrogen circulator, a nitrogen turbine compressor, a natural gas heat exchanger, a high-temperature booster turbo expander, a low-temperature booster turbo expander, a vapor-liquid separator and a liquid nitrogen subcooler, wherein the electric consumption for producing 1kg of liquid nitrogen is only 0.24kwh. Although the method and the device have higher LNG cold energy utilization efficiency, the technology is far from mature due to the adoption of a low-temperature air inlet mode by a compressor, a supercharger and the like, and the equipment cost is extremely high.
Patent ZL201410616943.7 provides a recycle LNG cold energy's nitrogen liquefaction system, and this system adopts a nitrogen gas recycle compressor to aim at providing a simple structure, and cold energy utilization is high, can reduce nitrogen gas compressor pressure grade and heat exchanger pressure grade, practices thrift the nitrogen gas liquefaction system of energy consumption. The system has simple equipment and mature and reliable technology, but has low LNG cold energy utilization rate in practical application.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for producing liquid nitrogen by utilizing LNG cold energy, which has mature technology, low equipment cost and extremely high LNG cold energy utilization rate.
The invention aims at being completed through the following technical scheme, and discloses a method for producing liquid nitrogen by utilizing LNG cold energy, which comprises the following steps: LNG is compressed by a liquid pump and then is sent to a heat exchanger to exchange heat with nitrogen, and after reheating to a lower temperature, the LNG is sent to a BOG compressor to be pressurized and finally sent to an NG pipe network, and nitrogen from the pipe network or a circulating compressor is divided into two streams: one is firstly subjected to supercharging cooling through a supercharging end of an expander, then enters a main heat exchanger to be cooled to a certain temperature, is pumped out to the expander to be expanded, and the expanded nitrogen is subjected to reheating to normal temperature, then enters the supercharging end of the expander again to be subjected to supercharging cooling, is returned to the main heat exchanger in a liquefier to be cooled, is pumped into the expander to be expanded after being reduced to a certain temperature, and the expanded low-pressure nitrogen is returned to the heat exchanger to be reheated, and is directly discharged or is sent into a nitrogen circulation compressor to be circulated after being discharged from a cold box; one strand of liquid nitrogen is directly sent into a heat exchanger to exchange heat with LNG, cooled to a target temperature and condensed into liquid nitrogen, and the liquid nitrogen is divided into two parts: one liquid nitrogen is throttled to low pressure and then sent into a subcooler to subcool the liquid nitrogen, and the evaporated low-pressure liquid nitrogen is reheated by a main heat exchanger and is discharged or recycled by a recycle nitrogen compressor for recycling; and secondly, directly throttling the supercooled liquid nitrogen and sending the supercooled liquid nitrogen into a liquid nitrogen storage tank.
The invention compresses the low-temperature NG by using the low-temperature BOG compressor, ensures the cold energy quality of LNG and greatly obtains the power consumption of the BOG compressor.
The invention utilizes the supercharging expansion series connection of the high-temperature expansion machine and the low-temperature expansion machine, so that the heat exchange temperature difference of the heat exchanger reasonably improves the LNG cold energy utilization efficiency to the maximum extent, and can adapt to the capability of LNG component change, thereby greatly improving the variable working condition efficiency;
the invention uses the conventional nitrogen compressor as the circulating compressor, avoids the use of a low-temperature nitrogen centrifugal compressor which is expensive and has poor reliability, greatly reduces the equipment investment and greatly improves the reliability;
in the method for producing liquid nitrogen by utilizing LNG cold energy, the unit energy consumption of the liquid nitrogen obtained by the production is preferably 0.3kwh/Nm3, and is more than 50% lower than that of the liquid nitrogen produced by a conventional liquefying device; the method of the invention not only greatly reduces the unit energy consumption of liquid nitrogen, but also can greatly reduce the equipment investment and improve the equipment reliability.
Drawings
Fig. 1 is a schematic flow chart of the invention for producing liquid nitrogen by using LNG.
Detailed Description
The invention will be described in detail with reference to specific examples, wherein the method for producing liquid nitrogen by using LNG cold energy is as follows: LNG is compressed by a liquid pump and then is sent to a heat exchanger to exchange heat with nitrogen, and after reheating to a lower temperature, the LNG is sent to a BOG compressor to be pressurized and finally sent to an NG pipe network, and nitrogen from the pipe network or a circulating compressor is divided into two streams: one is firstly subjected to supercharging cooling through a supercharging end of an expander, then enters a main heat exchanger to be cooled to a certain temperature, is pumped out to the expander to be expanded, and the expanded nitrogen is subjected to reheating to normal temperature, then enters the supercharging end of the expander again to be subjected to supercharging cooling, is returned to the main heat exchanger in a liquefier to be cooled, is pumped into the expander to be expanded after being reduced to a certain temperature, and the expanded low-pressure nitrogen is returned to the heat exchanger to be reheated, and is directly discharged or is sent into a nitrogen circulation compressor to be circulated after being discharged from a cold box; one strand of liquid nitrogen is directly sent into a heat exchanger to exchange heat with LNG, cooled to a target temperature and condensed into liquid nitrogen, and the liquid nitrogen is divided into two parts: one liquid nitrogen is throttled to low pressure and then sent into a subcooler to subcool the liquid nitrogen, and the evaporated low-pressure liquid nitrogen is reheated by a main heat exchanger and is discharged or recycled by a recycle nitrogen compressor for recycling; and secondly, directly throttling the supercooled liquid nitrogen and sending the supercooled liquid nitrogen into a liquid nitrogen storage tank.
The invention is provided with a low-temperature BOG compressor, the LNG pump is compressed and then sent to a main heat exchanger in a liquefaction cold box for reheating, and the LNG pump is sent to the BOG compressor for compression after being reheated to the low temperature ranging from 0 ℃ to 130 ℃ and finally sent to an NG pipe network; when the LNG flow is larger and the refrigeration capacity is more, the temperature of the NG fed into the BOG compressor is reduced so as to reduce the consumption of the BOG compressor, and meanwhile, the loads of the nitrogen compressor and the expander are reduced so as to reduce the unit energy consumption of liquid nitrogen.
The invention is provided with a conventional product nitrogen compressor and a high-low temperature expander, the processes of the expander are serial pressurizing, expanding, pressurizing and expanding, the load adjustment of each unit is determined according to whether the LNG cold quantity is sufficient or not, if the LNG cold quantity caused by the flow or component change is sufficient, the load of each unit can be properly reduced to reduce the unit energy consumption of liquid nitrogen, otherwise, the load of each unit is increased to supplement the cold quantity of liquid nitrogen products.
In the method, the inlet temperature range of the low-temperature BOG compressor is 20 to 130 ℃ below zero, the optimal value is 40 ℃ below zero, and the low-temperature BOG compressor is matched according to the cooling capacity of LNG; the inlet pressure is in the range of 1-3bar, preferably 1.6bar; the exhaust pressure is matched according to the terminal gas consumption condition;
in the method, the exhaust pressure of the circulating nitrogen compressor ranges from 24 bar to 30bar, the optimal value is 27bar, and the inlet pressure and the exhaust quantity are matched according to the LNG cold energy and the liquid yield;
in the method, the pressure, the temperature and the flow of each stage of the high-low temperature expander are matched according to the LNG cold energy and the liquid yield;
in the method, when the LNG components and the flow are changed, parameters of the expander and the nitrogen compressor are adjusted to be matched, and when the change is large, the expander can be opened and closed to carry out public adjustment.
Examples: fig. 1 shows a method for producing liquid nitrogen by using LNG cold energy according to the present invention, the method is: LNG is compressed to 1.6bar through a liquid pump P1, then is sent to a heat exchanger to exchange heat with nitrogen, is reheated to a lower temperature of about-40 ℃, is sent to a BOG compressor to be pressurized, and finally is sent to an NG pipe network. Nitrogen from the pipe network or recycle compressor at a pressure of 27bar is split into two streams: one 01 is pressurized and cooled through the pressurizing end of the expander, then enters the main heat exchanger to be cooled to a certain temperature and is pumped out to the expander to be expanded, the expanded nitrogen is reheated to normal temperature and then enters the pressurizing end of the expander again to be pressurized and cooled, and is returned to the main heat exchanger in the liquefier to be cooled, after the temperature is reduced to a certain temperature, the nitrogen is pumped into the expander to be expanded, the expanded low-pressure nitrogen is returned to the heat exchanger to be reheated, and the nitrogen is directly discharged or sent into the nitrogen circulation compressor to be circulated after exiting the cold box; directly sending the first stream 02 into a heat exchanger to exchange heat with LNG, cooling to a target temperature, condensing into liquid nitrogen, and dividing the liquid nitrogen into two parts: one 04 liquid nitrogen is throttled to low pressure and then sent into a subcooler to subcool the liquid nitrogen, and the evaporated low-pressure liquid nitrogen is reheated by a main heat exchanger and is discharged or recycled by a recycle nitrogen compressor for recycling; and secondly, directly throttling the supercooled liquid nitrogen to be sent into a liquid nitrogen storage tank.
In the method, if the LNG flow changes and the refrigeration capacity is sufficient, the inlet temperature of the low-temperature BOG compressor is properly reduced, otherwise, the inlet temperature of the BOG compressor is properly increased; if the LNG component is changed and the refrigeration capacity is sufficient, the load of the nitrogen compressor and the expansion unit can be reduced appropriately, otherwise, the corresponding load needs to be increased.
In the method, the inlet temperature of the circulating nitrogen compressor is normal temperature, and the inlet temperature must be ensured to be above 0 ℃ to ensure the safety of the device; the outlet pressure of the nitrogen compressor can be properly adjusted; if the working condition changes greatly, the high-temperature expansion machine and the low-temperature expansion machine can be properly started and stopped to adapt to the working condition changes.
Claims (3)
1. A method for producing liquid nitrogen by utilizing LNG cold energy, which is characterized by comprising the following steps: LNG is compressed by a liquid pump and then is sent to a heat exchanger to exchange heat with nitrogen, and after reheating, the LNG is sent to a BOG compressor to be pressurized and finally sent to an NG pipe network, and nitrogen from the pipe network or a circulating compressor is divided into two streams: one is firstly subjected to supercharging cooling through a supercharging end of an expander, then enters a main heat exchanger to be cooled to a certain temperature, is pumped out to the expander to be expanded, and the expanded nitrogen is subjected to reheating to normal temperature, then enters the supercharging end of the expander again to be subjected to supercharging cooling, is returned to the main heat exchanger in a liquefier to be cooled, is pumped into the expander to be expanded after being reduced to a certain temperature, and the expanded low-pressure nitrogen is returned to the heat exchanger to be reheated, and is directly discharged or is sent into a nitrogen circulation compressor to be circulated after being discharged from a cold box; one strand of liquid nitrogen is directly sent into a heat exchanger to exchange heat with LNG, cooled to a target temperature and condensed into liquid nitrogen, and the liquid nitrogen is divided into two parts: one liquid nitrogen is throttled to low pressure and then sent into a subcooler to subcool the liquid nitrogen, and the evaporated low-pressure liquid nitrogen is reheated by a main heat exchanger and is discharged or recycled by a recycle nitrogen compressor for recycling; and secondly, directly throttling the supercooled liquid nitrogen and sending the supercooled liquid nitrogen into a liquid nitrogen storage tank.
2. The method for producing liquid nitrogen by utilizing LNG cold energy according to claim 1, wherein: the LNG pump is compressed and then sent to the main heat exchanger in the liquefaction cold box for reheating, and after reheating, sent to the BOG compressor for compression and finally sent to the NG pipe network; when the LNG flow is larger and the refrigeration capacity is more, the temperature of the NG fed into the BOG compressor is reduced so as to reduce the consumption of the BOG compressor, and meanwhile, the loads of the nitrogen compressor and the expander are reduced so as to reduce the unit energy consumption of liquid nitrogen.
3. The method for producing liquid nitrogen by using LNG cold energy according to claim 1 or 2, wherein: the nitrogen compressor and the high-low temperature expander of the conventional product are configured, the flow of the expander is serial pressurization, expansion, pressurization and expansion, the load adjustment of each unit is determined according to whether the LNG cold quantity is sufficient or not, if the LNG cold quantity caused by the change of flow or components is sufficient, the load of each unit is properly reduced, so that the unit energy consumption of liquid nitrogen is reduced, otherwise, the load of each unit is increased to supplement the cold quantity of the liquid nitrogen product due to the insufficient LNG cold quantity.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910739821.XA CN110487023B (en) | 2019-08-12 | 2019-08-12 | Method for producing liquid nitrogen by utilizing LNG cold energy |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910739821.XA CN110487023B (en) | 2019-08-12 | 2019-08-12 | Method for producing liquid nitrogen by utilizing LNG cold energy |
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| Publication Number | Publication Date |
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| CN110487023A CN110487023A (en) | 2019-11-22 |
| CN110487023B true CN110487023B (en) | 2024-02-23 |
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| CN201910739821.XA Active CN110487023B (en) | 2019-08-12 | 2019-08-12 | Method for producing liquid nitrogen by utilizing LNG cold energy |
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| CN115751838B (en) * | 2022-11-02 | 2024-01-02 | 广东粤豫科技有限公司 | Energy-saving external liquefaction system and energy-saving nitrogen and oxygen external liquefier device |
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| US5139547A (en) * | 1991-04-26 | 1992-08-18 | Air Products And Chemicals, Inc. | Production of liquid nitrogen using liquefied natural gas as sole refrigerant |
| FR2805034A1 (en) * | 2000-02-11 | 2001-08-17 | Air Liquide | Nitrogen liquefaction process involves compressing nitrogen to supercritical pressure, cooling by heat exchange with flow of liquefied natural gas in primary exchanger, expanded to specific pressure and liquefying |
| AU2009100992A4 (en) * | 2009-09-30 | 2009-11-05 | Jayaram, Narsimhan Mr | LPG / LNG floating production unit, using a novel direct injected, single nitrogen expanded refrigeration cycle |
| CN101614464A (en) * | 2008-06-23 | 2009-12-30 | 杭州福斯达实业集团有限公司 | Method for liquefying natural gas through double-expansion of high-temperature and low-temperature nitrogen gas |
| CN106288650A (en) * | 2015-06-26 | 2017-01-04 | 上海恩图能源科技有限公司 | Nitrogen at room reclaims LNG cold energy technique |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US20140352353A1 (en) * | 2013-05-28 | 2014-12-04 | Robert S. Wissolik | Natural Gas Liquefaction System for Producing LNG and Merchant Gas Products |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5139547A (en) * | 1991-04-26 | 1992-08-18 | Air Products And Chemicals, Inc. | Production of liquid nitrogen using liquefied natural gas as sole refrigerant |
| FR2805034A1 (en) * | 2000-02-11 | 2001-08-17 | Air Liquide | Nitrogen liquefaction process involves compressing nitrogen to supercritical pressure, cooling by heat exchange with flow of liquefied natural gas in primary exchanger, expanded to specific pressure and liquefying |
| CN101614464A (en) * | 2008-06-23 | 2009-12-30 | 杭州福斯达实业集团有限公司 | Method for liquefying natural gas through double-expansion of high-temperature and low-temperature nitrogen gas |
| AU2009100992A4 (en) * | 2009-09-30 | 2009-11-05 | Jayaram, Narsimhan Mr | LPG / LNG floating production unit, using a novel direct injected, single nitrogen expanded refrigeration cycle |
| CN106288650A (en) * | 2015-06-26 | 2017-01-04 | 上海恩图能源科技有限公司 | Nitrogen at room reclaims LNG cold energy technique |
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