US20140157824A1 - Method for improved thermal performing refrigeration cycle - Google Patents
Method for improved thermal performing refrigeration cycle Download PDFInfo
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- US20140157824A1 US20140157824A1 US13/707,132 US201213707132A US2014157824A1 US 20140157824 A1 US20140157824 A1 US 20140157824A1 US 201213707132 A US201213707132 A US 201213707132A US 2014157824 A1 US2014157824 A1 US 2014157824A1
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- nitrogen
- refrigeration cycle
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- 238000005057 refrigeration Methods 0.000 title claims abstract description 54
- 238000000034 method Methods 0.000 title claims description 22
- 239000003507 refrigerant Substances 0.000 claims abstract description 41
- 239000007788 liquid Substances 0.000 claims abstract description 29
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 169
- 229910052757 nitrogen Inorganic materials 0.000 claims description 74
- 239000007789 gas Substances 0.000 claims description 47
- 238000001816 cooling Methods 0.000 claims description 10
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical group C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 10
- 239000003345 natural gas Substances 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 3
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims description 2
- 238000011144 upstream manufacturing Methods 0.000 abstract description 2
- 230000005611 electricity Effects 0.000 abstract 1
- 239000012530 fluid Substances 0.000 description 8
- 230000008569 process Effects 0.000 description 6
- 239000006200 vaporizer Substances 0.000 description 5
- 238000004891 communication Methods 0.000 description 4
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
- 238000010926 purge Methods 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 230000000153 supplemental effect Effects 0.000 description 1
- 230000008016 vaporization Effects 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
Images
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
- F25J1/0022—Hydrocarbons, e.g. natural gas
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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
- F25J1/0047—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
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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
- F25J1/006—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
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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
- F25J1/0203—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
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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
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0244—Operation; Control and regulation; Instrumentation
- F25J1/0245—Different modes, i.e. 'runs', of operation; Process control
- F25J1/0249—Controlling refrigerant inventory, i.e. composition or quantity
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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
- F25J2210/42—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
- F25J2270/00—Refrigeration techniques used
- F25J2270/14—External refrigeration with work-producing gas expansion loop
- F25J2270/16—External refrigeration with work-producing gas expansion loop with mutliple gas expansion loops of the same refrigerant
Definitions
- the present invention relates to a method and device for improving the thermal performance of a nitrogen refrigeration cycle.
- Gas liquefaction is a known process used to liquefy gases and commonly employs a nitrogen refrigeration cycle to provide the necessary refrigeration.
- the nitrogen refrigeration cycle in its most basic terms, includes the following steps: nitrogen gas is compressed, cooled, and then expanded in a turbo booster. During this expansion, the temperature of the gas drops and the expanding gas moves the turbine, which in turn performs work on the compressor of the turbo booster. The cold gas is then used to provide the necessary cooling to liquefy the target stream.
- FIG. 1 represents typical nitrogen refrigeration cycle 1 that is useful for providing the necessary refrigeration to liquefy the target gas.
- Nitrogen gas 2 is partially compressed in turbo booster 10 (which is a combination of compressor 20 and turbine 30 in which the turning of turbine 30 helps to turn compressor 20 ) and then further compressed in high pressure compressor 40 and then partially cooled in a heat exchanger 50 . Cooled compressed nitrogen 41 then exits the heat exchanger 50 and is expanded in turbine 30 of the turbo booster 10 . Expanded refrigerant 32 is then used to provide refrigeration for a gas stream (not shown). During this set up, nitrogen is lost in the turbo booster 10 and high pressure compressor 40 . These losses are made up by the introduction of gaseous nitrogen from LIN tank 60 .
- Liquid nitrogen 62 is withdrawn from LIN tank 60 and vaporized in ambient vaporizer 64 .
- ambient vaporizer 64 is supplemented with an electric heater which requires at least some utility cost or other type of vaporizer such as steam sparged water bath, natural gas fired water bath, electric, etc . . . Therefore, methods known heretofore may require additional utility cost.
- a first portion 66 is used to provide the makeup losses for high pressure compressor 40 and turbo booster 10 by injecting first portion 66 into the warm end of heat exchanger 50 .
- a second portion can be used as utility nitrogen for other users (e.g., instrument, purge/utility gas for both this plant or another nearby plant).
- the present invention is directed to a device and a method that satisfies at least one of these needs.
- Certain embodiments of the present invention relate to the use of an improved refrigeration cycle as part of a liquefaction process, in which makeup refrigerant is introduced on the cool side of the heat exchanger as opposed to the warm side of the heat exchanger.
- the method for producing a liquefied gas stream from an inlet gas feed stream can include the steps of:
- introducing a liquid refrigerant makeup stream into the refrigeration cycle by adding the liquid refrigerant makeup stream to the expanded refrigerant prior to heat exchange contact with the inlet gas feed stream to provide for makeup losses in the refrigeration cycle and to provide additional refrigeration to the refrigeration cycle.
- the inlet gas feed stream to be liquefied is natural gas.
- the refrigeration cycle is a nitrogen refrigeration cycle and the liquid refrigerant makeup stream originates from a liquid nitrogen tank containing liquid nitrogen.
- the expanded refrigerant is nitrogen.
- the expanded refrigerant is expanded in a device selected from the group consisting of an expansion valve, a turbo-expander, and a liquid (or dense fluid) expander.
- the method can further includes the steps of withdrawing a utility nitrogen stream from the nitrogen vapor stream subsequent to heat exchange contact with the inlet gas feed stream, and introducing the utility nitrogen stream to a second user for use as utility nitrogen.
- the method producing a liquefied gas stream from an inlet gas feed stream can include the steps of:
- the nitrogen refrigeration cycle can include the steps of: expanding a nitrogen stream to a cold nitrogen vapor stream, cooling at least a portion of the inlet feed gas stream by heat exchange contact with the cold nitrogen vapor stream, compressing the cold nitrogen vapor stream to form a compressed nitrogen vapor stream, and cooling at least a portion of the compressed nitrogen vapor stream by heat exchange contact with the cold nitrogen vapor stream.
- an apparatus for producing a liquefied gas stream from an inlet gas feed stream can include a heat exchanger, a refrigeration cycle, and a makeup liquid refrigerant tank.
- the heat exchanger has a cold side and a warm side and is configured to receive the inlet gas feed stream and to produce the liquefied gas stream.
- the refrigeration cycle is configured to provide refrigeration to the heat exchanger.
- the refrigeration cycle further includes a compressor and an expander, wherein the compressor is configured to compress a refrigerant to a compression pressure, wherein the expander is configured to receive the compressed refrigerant and expand the compressed refrigerant to an expanded pressure to produce a cold refrigerant at an outlet of the expander, and wherein the outlet of the expander is in fluid communication with the cold side of the heat exchanger.
- the makeup liquid refrigerant tank is configured to introduce a makeup liquid refrigerant with the cold refrigerant prior to heat exchange with the inlet gas feed stream.
- the makeup liquid refrigerant tank is in fluid communication with the refrigeration cycle at a point downstream the outlet of the expander and upstream the cold side of the heat exchanger.
- the expander is a device selected from the group consisting of an expansion valve, a turbo-expander, and a liquid/dense fluid expander.
- the apparatus can further include a utility nitrogen withdrawal line configured to withdraw a nitrogen stream from the refrigeration cycle at a point downstream the warm side of the heat exchanger and introduce the nitrogen stream to a second user for use as utility nitrogen.
- Certain embodiments of the present invention advantageously do not require supplemental energy for the vaporization of the make up fluid.
- FIG. 1 shows a refrigeration cycle in accordance with the prior art.
- FIG. 2 shows a refrigeration cycle in accordance with an embodiment of the invention.
- FIG. 3 shows a liquefaction process in accordance with the prior art.
- FIG. 4 shows a liquefaction process in accordance with an embodiment of the invention.
- Nitrogen refrigeration cycle 1 of FIG. 2 is largely similar to nitrogen refrigeration cycle 1 of FIG. 1 , with the exception of the makeup nitrogen.
- LIN tank 60 is in fluid communication with the cold side of the heat exchanger.
- liquid nitrogen 62 travels from LIN tank 60 and is combined with gaseous nitrogen 32 where liquid nitrogen 62 vaporizes.
- the flow rate of liquid nitrogen 62 is about 1% of the flow rate of expanded refrigerant 32 , thereby allowing liquid nitrogen 62 to vaporize when combining with expanded refrigerant 32 before going through heat exchanger 50 .
- a small amount of second portion 68 can be withdrawn on the warm side of heat exchanger 50 in order to provide a makeup stream for nearby utilities.
- FIG. 3 represents another example as known in the prior art while FIG. 4 represents another embodiment of the present invention. These figures are used to show the comparative advantages of embodiments of the present invention.
- Compressed nitrogen 42 exits high pressure compressor 40 and is split into two portions.
- First portion 44 is compressed in first turbo-booster 15 and then further compressed in second turbo-booster 25 .
- Fully compressed nitrogen 27 is cooled in heat exchanger 50 and then expanded in second turbo-booster 25 to provide expanded first portion 34 .
- Expanded first portion 34 is introduced into the cool side of heat exchanger 50 where it provides refrigeration to feed gas 48 in order to produce liquid feed 52 .
- Feed gas 48 can be any gas that is desirable to liquefy, for example, natural gas.
- Expanded first portion 34 exits heat exchanger 50 and is recompressed in high pressure compressor 40 to start the cycle over again.
- second portion 46 enters heat exchanger 50 and is only partially cooled before being expanded in first turbo-booster 15 to reduce both its pressure and temperature. Expanded second portion 36 is introduced to heat exchanger 50 to provide additional cooling before it combines with expanded first portion 34 on its way back to high pressure compressor 40 .
- first turbo-booster 15 As in FIG. 1 , nitrogen is lost in first turbo-booster 15 , second turbo-booster 25 , and high pressure compressor 40 . These losses are made up by the introduction of gaseous nitrogen 66 from LIN tank 60 . Liquid nitrogen 62 is withdrawn from LIN tank 60 and vaporized in ambient vaporizer 64 . A first portion 66 is used to provide the makeup losses for high pressure compressor 40 and turbo booster 10 by injecting first portion 66 into the warm end of heat exchanger 50 . A second portion 68 can be used as utility nitrogen for other users (e.g., for makeup losses for a nearby air separation plant) or as instrument gas and/or purge gas for this plant and/or another nearby facility.
- Nitrogen refrigeration cycle 3 of FIG. 4 is largely similar to nitrogen refrigeration cycle 3 of FIG. 3 , with the exception of the makeup nitrogen.
- LIN tank 60 is in fluid communication with the cold side of the heat exchanger 50 .
- liquid nitrogen 62 travels from LIN tank 60 and is combined with expanded refrigerant 34 , where it vaporizes.
- FIG. 4 % Change Nitrogen flow leaving High 22613 20797 8% Pressure Compressor (Nm 3 /hr) Loss if First Turbo-booster 68 68 — (Nm 3 /hr) Loss in Second Turbo-booster 68 68 — (Nm 3 /hr) Loss in High Pressure 102 102 — Compressor (Nm 3 /hr) Utility Usage (kW) 1213 1112 8% Total Make-up LIN (Nm 3 /hr) 338 338 — LIN added to Recycle (Nm 3 /hr) 238 238 — LIN sent to Utilities (Nm 3 /hr) 100 100 —
- embodiments of the present invention can achieve approximately an 8% improvement over methods and apparatus of the prior art. This is extremely beneficial as embodiments of the present invention can provide a cost savings on both the capital cost because of the reduced size of the refrigeration cycle equipment and on the energy required to run the high pressure compressor.
- Optional or optionally means that the subsequently described event or circumstances may or may not occur.
- the description includes instances where the event or circumstance occurs and instances where it does not occur.
- Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
Abstract
Description
- The present invention relates to a method and device for improving the thermal performance of a nitrogen refrigeration cycle.
- Gas liquefaction is a known process used to liquefy gases and commonly employs a nitrogen refrigeration cycle to provide the necessary refrigeration. The nitrogen refrigeration cycle, in its most basic terms, includes the following steps: nitrogen gas is compressed, cooled, and then expanded in a turbo booster. During this expansion, the temperature of the gas drops and the expanding gas moves the turbine, which in turn performs work on the compressor of the turbo booster. The cold gas is then used to provide the necessary cooling to liquefy the target stream.
- One problem with refrigeration cycles is that there are refrigerant losses. The mechanical equipment used in the process contains seals, which have gas losses to the atmosphere that must be made up. Although mechanical designs are available which recover a portion of these seal gas losses back to a low pressure stream within the refrigeration cycle, this does not completely eliminate the losses and can incur additional capital cost. One solution to this problem is shown in
FIG. 1 . -
FIG. 1 represents typicalnitrogen refrigeration cycle 1 that is useful for providing the necessary refrigeration to liquefy the target gas.Nitrogen gas 2 is partially compressed in turbo booster 10 (which is a combination ofcompressor 20 andturbine 30 in which the turning ofturbine 30 helps to turn compressor 20) and then further compressed inhigh pressure compressor 40 and then partially cooled in aheat exchanger 50. Cooled compressednitrogen 41 then exits theheat exchanger 50 and is expanded inturbine 30 of theturbo booster 10. Expandedrefrigerant 32 is then used to provide refrigeration for a gas stream (not shown). During this set up, nitrogen is lost in theturbo booster 10 andhigh pressure compressor 40. These losses are made up by the introduction of gaseous nitrogen fromLIN tank 60.Liquid nitrogen 62 is withdrawn fromLIN tank 60 and vaporized inambient vaporizer 64. Often, particularly in cold environments,ambient vaporizer 64 is supplemented with an electric heater which requires at least some utility cost or other type of vaporizer such as steam sparged water bath, natural gas fired water bath, electric, etc . . . Therefore, methods known heretofore may require additional utility cost. Afirst portion 66 is used to provide the makeup losses forhigh pressure compressor 40 andturbo booster 10 by injectingfirst portion 66 into the warm end ofheat exchanger 50. A second portion can be used as utility nitrogen for other users (e.g., instrument, purge/utility gas for both this plant or another nearby plant). - However, there is a need for an improved refrigeration cycle that requires less power and/or makeup fluid.
- The present invention is directed to a device and a method that satisfies at least one of these needs. Certain embodiments of the present invention relate to the use of an improved refrigeration cycle as part of a liquefaction process, in which makeup refrigerant is introduced on the cool side of the heat exchanger as opposed to the warm side of the heat exchanger.
- In one embodiment, the method for producing a liquefied gas stream from an inlet gas feed stream can include the steps of:
- cooling at least a portion of the inlet gas feed stream by heat exchange contact with an expanded refrigerant to produce the liquefied gas stream, wherein the expanded refrigerant is circulated in a refrigeration cycle; and
- introducing a liquid refrigerant makeup stream into the refrigeration cycle by adding the liquid refrigerant makeup stream to the expanded refrigerant prior to heat exchange contact with the inlet gas feed stream to provide for makeup losses in the refrigeration cycle and to provide additional refrigeration to the refrigeration cycle.
- In another embodiment, the inlet gas feed stream to be liquefied is natural gas. In another embodiment, the refrigeration cycle is a nitrogen refrigeration cycle and the liquid refrigerant makeup stream originates from a liquid nitrogen tank containing liquid nitrogen. In another embodiment, the expanded refrigerant is nitrogen. In another embodiment, the expanded refrigerant is expanded in a device selected from the group consisting of an expansion valve, a turbo-expander, and a liquid (or dense fluid) expander. In another embodiment, the method can further includes the steps of withdrawing a utility nitrogen stream from the nitrogen vapor stream subsequent to heat exchange contact with the inlet gas feed stream, and introducing the utility nitrogen stream to a second user for use as utility nitrogen.
- In another embodiment, the method producing a liquefied gas stream from an inlet gas feed stream can include the steps of:
- cooling at least a portion of the inlet gas feed stream by heat exchange contact with a nitrogen refrigeration cycle to produce the liquefied gas stream; and
- adding a liquid refrigerant makeup stream into the expanded refrigerant prior to heat exchange contact with the inlet gas feed stream to provide for makeup losses in the nitrogen refrigeration cycle and to provide additional refrigeration to the nitrogen refrigeration cycle. In one embodiment, the nitrogen refrigeration cycle can include the steps of: expanding a nitrogen stream to a cold nitrogen vapor stream, cooling at least a portion of the inlet feed gas stream by heat exchange contact with the cold nitrogen vapor stream, compressing the cold nitrogen vapor stream to form a compressed nitrogen vapor stream, and cooling at least a portion of the compressed nitrogen vapor stream by heat exchange contact with the cold nitrogen vapor stream.
- In another aspect of the invention, an apparatus for producing a liquefied gas stream from an inlet gas feed stream is provided. In one embodiment, the apparatus can include a heat exchanger, a refrigeration cycle, and a makeup liquid refrigerant tank. In one embodiment, the heat exchanger has a cold side and a warm side and is configured to receive the inlet gas feed stream and to produce the liquefied gas stream. In one embodiment, the refrigeration cycle is configured to provide refrigeration to the heat exchanger. Preferably, the refrigeration cycle further includes a compressor and an expander, wherein the compressor is configured to compress a refrigerant to a compression pressure, wherein the expander is configured to receive the compressed refrigerant and expand the compressed refrigerant to an expanded pressure to produce a cold refrigerant at an outlet of the expander, and wherein the outlet of the expander is in fluid communication with the cold side of the heat exchanger. In one embodiment, the makeup liquid refrigerant tank is configured to introduce a makeup liquid refrigerant with the cold refrigerant prior to heat exchange with the inlet gas feed stream.
- In another embodiment, the makeup liquid refrigerant tank is in fluid communication with the refrigeration cycle at a point downstream the outlet of the expander and upstream the cold side of the heat exchanger. In another embodiment, the expander is a device selected from the group consisting of an expansion valve, a turbo-expander, and a liquid/dense fluid expander. In an additional embodiment, the apparatus can further include a utility nitrogen withdrawal line configured to withdraw a nitrogen stream from the refrigeration cycle at a point downstream the warm side of the heat exchanger and introduce the nitrogen stream to a second user for use as utility nitrogen.
- Certain embodiments of the present invention advantageously do not require supplemental energy for the vaporization of the make up fluid.
- These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.
-
FIG. 1 shows a refrigeration cycle in accordance with the prior art. -
FIG. 2 shows a refrigeration cycle in accordance with an embodiment of the invention. -
FIG. 3 shows a liquefaction process in accordance with the prior art. -
FIG. 4 shows a liquefaction process in accordance with an embodiment of the invention. - While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims.
- Now turning to
FIG. 2 .Nitrogen refrigeration cycle 1 ofFIG. 2 is largely similar tonitrogen refrigeration cycle 1 ofFIG. 1 , with the exception of the makeup nitrogen. InFIG. 2 ,LIN tank 60 is in fluid communication with the cold side of the heat exchanger. As such,liquid nitrogen 62 travels fromLIN tank 60 and is combined withgaseous nitrogen 32 whereliquid nitrogen 62 vaporizes. In one embodiment, the flow rate ofliquid nitrogen 62 is about 1% of the flow rate of expandedrefrigerant 32, thereby allowingliquid nitrogen 62 to vaporize when combining with expandedrefrigerant 32 before going throughheat exchanger 50. A small amount ofsecond portion 68 can be withdrawn on the warm side ofheat exchanger 50 in order to provide a makeup stream for nearby utilities. By combiningliquid nitrogen 62 on the cold side ofheat exchanger 50, additional refrigeration is provided tonitrogen refrigeration cycle 1, whereas the prior art loses this refrigeration inambient vaporizer 64, which often must be supplemented with electric power (utility cost) in the form of an electric trim heater. -
FIG. 3 represents another example as known in the prior art whileFIG. 4 represents another embodiment of the present invention. These figures are used to show the comparative advantages of embodiments of the present invention. - Now turning to
FIG. 3 .Compressed nitrogen 42 exitshigh pressure compressor 40 and is split into two portions.First portion 44 is compressed in first turbo-booster 15 and then further compressed in second turbo-booster 25. Fully compressednitrogen 27 is cooled inheat exchanger 50 and then expanded in second turbo-booster 25 to provide expandedfirst portion 34. Expandedfirst portion 34 is introduced into the cool side ofheat exchanger 50 where it provides refrigeration to feedgas 48 in order to produceliquid feed 52.Feed gas 48 can be any gas that is desirable to liquefy, for example, natural gas. Expandedfirst portion 34exits heat exchanger 50 and is recompressed inhigh pressure compressor 40 to start the cycle over again. During the same cycle,second portion 46 entersheat exchanger 50 and is only partially cooled before being expanded in first turbo-booster 15 to reduce both its pressure and temperature. Expandedsecond portion 36 is introduced toheat exchanger 50 to provide additional cooling before it combines with expandedfirst portion 34 on its way back tohigh pressure compressor 40. - As in
FIG. 1 , nitrogen is lost in first turbo-booster 15, second turbo-booster 25, andhigh pressure compressor 40. These losses are made up by the introduction ofgaseous nitrogen 66 fromLIN tank 60.Liquid nitrogen 62 is withdrawn fromLIN tank 60 and vaporized inambient vaporizer 64. Afirst portion 66 is used to provide the makeup losses forhigh pressure compressor 40 andturbo booster 10 by injectingfirst portion 66 into the warm end ofheat exchanger 50. Asecond portion 68 can be used as utility nitrogen for other users (e.g., for makeup losses for a nearby air separation plant) or as instrument gas and/or purge gas for this plant and/or another nearby facility. - Now turning to
FIG. 4 .Nitrogen refrigeration cycle 3 ofFIG. 4 is largely similar tonitrogen refrigeration cycle 3 ofFIG. 3 , with the exception of the makeup nitrogen. InFIG. 4 ,LIN tank 60 is in fluid communication with the cold side of theheat exchanger 50. As such,liquid nitrogen 62 travels fromLIN tank 60 and is combined with expandedrefrigerant 34, where it vaporizes. - Simulations were run for the processes shown in
FIG. 3 andFIG. 4 for liquefying a natural gas stream having a flow rate of 3,265 Nm3/hr. The results can be found in Table I below: -
TABLE I Simulation Results FIG. 3 FIG. 4 % Change Nitrogen flow leaving High 22613 20797 8% Pressure Compressor (Nm3/hr) Loss if First Turbo- booster 68 68 — (Nm3/hr) Loss in Second Turbo- booster 68 68 — (Nm3/hr) Loss in High Pressure 102 102 — Compressor (Nm3/hr) Utility Usage (kW) 1213 1112 8% Total Make-up LIN (Nm3/hr) 338 338 — LIN added to Recycle (Nm3/hr) 238 238 — LIN sent to Utilities (Nm3/hr) 100 100 — - As is clearly shown in Table I, embodiments of the present invention can achieve approximately an 8% improvement over methods and apparatus of the prior art. This is extremely beneficial as embodiments of the present invention can provide a cost savings on both the capital cost because of the reduced size of the refrigeration cycle equipment and on the energy required to run the high pressure compressor.
- While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, language referring to order, such as first and second, should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps or devices can be combined into a single step/device.
- The singular forms “a”, “an”, and “the” include plural referents, unless the context clearly dictates otherwise.
- Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
- Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
Claims (9)
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