WO2022126282A1 - Lng process using feedstock as primary refrigerant - Google Patents
Lng process using feedstock as primary refrigerant Download PDFInfo
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- WO2022126282A1 WO2022126282A1 PCT/CA2021/051842 CA2021051842W WO2022126282A1 WO 2022126282 A1 WO2022126282 A1 WO 2022126282A1 CA 2021051842 W CA2021051842 W CA 2021051842W WO 2022126282 A1 WO2022126282 A1 WO 2022126282A1
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- WIPO (PCT)
- Prior art keywords
- chilling
- feedstock
- gas
- temperature
- turbo
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims abstract description 178
- 230000008569 process Effects 0.000 title claims abstract description 164
- 239000003507 refrigerant Substances 0.000 title claims abstract description 55
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 173
- 239000003949 liquefied natural gas Substances 0.000 claims abstract description 102
- 239000003345 natural gas Substances 0.000 claims abstract description 18
- 239000007789 gas Substances 0.000 claims description 113
- 239000000203 mixture Substances 0.000 claims description 25
- 230000001143 conditioned effect Effects 0.000 claims description 23
- 239000007788 liquid Substances 0.000 claims description 23
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 claims description 20
- 238000000605 extraction Methods 0.000 claims description 16
- 239000001294 propane Substances 0.000 claims description 10
- 238000012384 transportation and delivery Methods 0.000 claims description 10
- 238000011144 upstream manufacturing Methods 0.000 claims description 9
- NNPPMTNAJDCUHE-UHFFFAOYSA-N isobutane Chemical compound CC(C)C NNPPMTNAJDCUHE-UHFFFAOYSA-N 0.000 claims description 8
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 claims description 6
- 239000002253 acid Substances 0.000 claims description 6
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 claims description 6
- 229910052753 mercury Inorganic materials 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 239000004215 Carbon black (E152) Substances 0.000 claims description 5
- 229930195733 hydrocarbon Natural products 0.000 claims description 5
- 150000002430 hydrocarbons Chemical class 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 4
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 claims description 4
- 238000009833 condensation Methods 0.000 claims description 3
- 230000005494 condensation Effects 0.000 claims description 3
- 238000007599 discharging Methods 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 abstract description 10
- 230000007704 transition Effects 0.000 abstract description 8
- 230000009467 reduction Effects 0.000 description 24
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 22
- 230000006835 compression Effects 0.000 description 21
- 238000007906 compression Methods 0.000 description 21
- 239000012071 phase Substances 0.000 description 21
- 238000012545 processing Methods 0.000 description 21
- 239000000470 constituent Substances 0.000 description 16
- 239000003570 air Substances 0.000 description 15
- 238000001816 cooling Methods 0.000 description 14
- 238000012546 transfer Methods 0.000 description 14
- 229910002092 carbon dioxide Inorganic materials 0.000 description 11
- 230000006872 improvement Effects 0.000 description 10
- 238000005057 refrigeration Methods 0.000 description 9
- 238000013459 approach Methods 0.000 description 8
- 230000000694 effects Effects 0.000 description 8
- 239000000446 fuel Substances 0.000 description 8
- 238000003860 storage Methods 0.000 description 8
- 230000008859 change Effects 0.000 description 7
- 238000010586 diagram Methods 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 238000011084 recovery Methods 0.000 description 6
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 5
- 239000005977 Ethylene Substances 0.000 description 5
- 230000008901 benefit Effects 0.000 description 5
- 238000011161 development Methods 0.000 description 5
- 230000018109 developmental process Effects 0.000 description 5
- 238000010587 phase diagram Methods 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 230000003750 conditioning effect Effects 0.000 description 4
- 239000012530 fluid Substances 0.000 description 4
- 239000002737 fuel gas Substances 0.000 description 4
- 238000009434 installation Methods 0.000 description 4
- 239000007791 liquid phase Substances 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 239000000284 extract Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
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- 238000007781 pre-processing Methods 0.000 description 2
- 230000002028 premature Effects 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- OFBQJSOFQDEBGM-UHFFFAOYSA-N Pentane Chemical class CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 239000012080 ambient air Substances 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229940112112 capex Drugs 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000002860 competitive effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 230000006837 decompression Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000002360 explosive Substances 0.000 description 1
- 238000007667 floating Methods 0.000 description 1
- FEBLZLNTKCEFIT-VSXGLTOVSA-N fluocinolone acetonide Chemical compound C1([C@@H](F)C2)=CC(=O)C=C[C@]1(C)[C@]1(F)[C@@H]2[C@@H]2C[C@H]3OC(C)(C)O[C@@]3(C(=O)CO)[C@@]2(C)C[C@@H]1O FEBLZLNTKCEFIT-VSXGLTOVSA-N 0.000 description 1
- 239000001282 iso-butane Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 238000009491 slugging Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002918 waste heat 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
- F25J1/02—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
- F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
- F25J1/0235—Heat exchange integration
- F25J1/0237—Heat exchange integration integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas
- F25J1/0239—Purification or treatment step being integrated between two refrigeration cycles of a refrigeration cascade, i.e. first cycle providing feed gas cooling and second cycle providing overhead gas cooling
- F25J1/0241—Purification or treatment step being integrated between two refrigeration cycles of a refrigeration cascade, i.e. first cycle providing feed gas cooling and second cycle providing overhead gas cooling wherein the overhead cooling comprises providing reflux for a fractionation step
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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
- F25J1/0032—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
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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
- F25J1/0052—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 vaporising a liquid refrigerant 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
- F25J1/0211—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 multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
- F25J1/0212—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 multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a single flow MCR 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
- F25J1/0243—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
- F25J1/0247—Different modes, i.e. 'runs', of operation; Process control start-up of the process
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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
- F25J1/0254—Operation; Control and regulation; Instrumentation controlling particular process parameter, e.g. pressure, temperature
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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
- F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
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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.
- F25J1/0281—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc. characterised by the type of prime driver, e.g. hot gas expander
- F25J1/0283—Gas turbine as the prime mechanical driver
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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
- F25J2210/04—Mixing or blending of fluids with the feed 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
- 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
- F25J2220/00—Processes or apparatus involving steps for the removal of impurities
- F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
- F25J2220/64—Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
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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
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/20—Integrated compressor and process expander; Gear box arrangement; Multiple compressors on a common shaft
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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
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/30—Compression of the feed 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
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/60—Processes or apparatus involving steps for increasing the pressure of gaseous process streams the fluid being hydrocarbons or a mixture of hydrocarbons
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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
- F25J2240/00—Processes or apparatus involving steps for expanding of process streams
- F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed 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
- F25J2245/00—Processes or apparatus involving steps for recycling of process streams
- F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
Definitions
- This disclosure relates to a process for producing Liquid Natural Gas (LNG) from natural gas feedstock delivered at customary pipeline conditions to LNG process sites.
- LNG Liquid Natural Gas
- a third method economically used on smaller installations is derived from the Claude process where fractional side streams of the feedstock expand through pressure restrictors to provide a chilled heat exchanger sink. Passing the remaining main gas stream through the heat exchanger prechills it prior to it then expanding further reduce its temperature. Repeated cycles reduce rate of flow of the main gas stream while providing stepped reduction in temperatures of main gas stream to provide liquefaction of the gas.
- the cascade chilling process is the more widely used method amongst large industrial installations, and at one time was the preferred configuration in large scale commercial service.
- a series of chilling stages use heat exchange from the process gas passing through “cold boxes”.
- Each of the series of cold boxes is serviced by an externally refrigerated loop employing a refrigerant specifically suited to the particular stage of temperature reduction.
- the refrigerants suited to progressively colder temperature bands are most often single component propane, ethylene and methane products.
- Modifications of the Claude process forming the third category of installations uses the J-T effect of chilling through pressure drop of the actual feed gas flow as well as in an extracted split flow stream where the gas acts as a refrigerant to external heat exchanger by passing it through a series of pressure reducing orifices/flow restrictors that are variants of system originally proposed by Claude for liquefaction of a multitude of gasses including air.
- expanded split side streams acting as refrigerants in heat exchanger loops prechill the remaining mainstream stream gas prior to direct cryogenic expansion chilling. Repeated energy intensive recompression and orifice expansion further chills the flowstream towards liquefaction threshold conditions.
- NNL Natural Gas Liquid
- a common way to measure LNG plant performance is to compare the tonnage of CO2 emissions from hydrocarbon fuel burned in providing plant power needs to the tonnage of LNG produced by the plant. This ratio is known as the “Carbon Intensity” factor. Early plants offered a ratio of 0.30 or higher. Modem day plants aim at a level of 0.22 to achieve a “Good” rating. A present-day watermark of a Carbon Intensity of 0.18 has been achieved by the offshore Norwegian Snovit LNG Installation by using efficient aero-derivative gas turbine power generation and electric motors for process equipment drivers.
- a process for producing liquefied natural gas from a natural gas feedstock of a pipeline comprising: a) compressing and/or heating the natural gas feedstock upstream of an inlet of a turbo expander, to form a conditioned feedstock with a pressure and temperature that will enable chilling of the flow stream through J-T expansion along an offset chilling curve profile that terminates at the lower pressure levels of the gaseous region of its phase envelope; b) delivering the conditioned feedstock to the inlet of the turbo expansion device at the elevated temperature and elevated pressure; and c) expanding the conditioned feedstock in the turbo expansion device; and d) discharging an expanded gas, from an outlet of the turbo expansion device at a temperature of between about -175°F and about -262°F for pure methane or light NGL gas mixtures and between about -145°F and about -175°F for rich NGL mixes and at a pressure of between about 5 and about 15 psig, wherein the conditioned feedstock gas is not further compressed after delivery to the
- turbo expansion device is a stepped series of turbo expansion devices.
- the final temperature of the expanded gas leaving the turbo expansion device is above about -262°F, the expanded gas is further subjected to extraction of sensible heat to render the liquid state at a temperature of about -262°F.
- the conditioned feedstock at the turbo expansion device inlet is 100% methane, or it is a mixture of methane or methane and NGLs that has been preconditioned to remove undesirable quantities of water vapor, acid gas, excess NGLs and heavier hydrocarbon liquids, CO2, N2, and mercury.
- the feedstock comprises up to: a) 100 mol% methane; b) about 25 mol% ethane; c) about 12.5 mol% propane; and d) about 8.5 mol% i-butane and/or n-butane
- the molecular weight of the feedstock does not exceed about 23.2, HHV of the feedstock does not exceed about 1395BTU/ft3, and modified Wobbe Index of the feedstock as calculated for 60°F does not exceed about 62.20.
- the elevated pressure of the conditioned feedstock is between about 3400 psig and about 600 psig
- the elevated temperature of the conditioned feedstock is between about -20°F and about 210°F
- the elevated temperature and the elevated pressure of the conditioned feedstock intersect on the offset turbo expansion chilling curve profile to provide an expanded gas having a temperature of between about -145°F and about -262°F and a terminal pressure of between about 5 and about 15 psig.
- the offset turbo expansion chilling curve profile is the 170°F curve or 190°F curve of Figure 5.
- turbo expansion device is coupled to a shaft, to recover energy released by the expansion.
- the shaft is either a single shaft or a multi shaft configuration wherein the shafts operate at different or the same speeds.
- the process further comprises the step of interrupting the expansion of the conditioned feedstock step to remove excess liquid fractions formed during the process.
- the step of interrupting the expansion includes the introduction of guide vanes within liquid bleed off chambers.
- the expanded gas is further cooled using externally refrigerated heat exchange equipment situated downstream of the outlet of the turbo expansion device to extract sensible heat for final liquefaction of the expanded gas.
- a condensation loop of refrigerant in the heat exchange equipment is integrated with the turbo expansion device or with the expanded gas emerging flowstream.
- the process further comprises chilling a stream of NGLs with the heat exchange equipment, to enhance the HHV heat content of the produced LNG by intermixing of the streams.
- Figure 1 Process flow diagram of the prior art cascade chilling process to yield LNG.
- Figure 2 Process flow diagram of the prior art mixed refrigerant chilling process to yield LNG.
- FIG. 3 Process flow diagram of an embodiment of the process to yield LNG described herein.
- Figures 4A-4D Representative heat flow rates for the processes shown in Figs. 1-3, showing the proximity of the chilling demand of each process to that of pure methane gas as it chills to the LNG state.
- Figure 5 Illustrative pressure/temperature chilling curves relating to the process described herein operating with near pure methane feedstock and showing practical expansion start points at process start intercepts to offset curves (arrow).
- Figure 6 Temperature sensitive changes in values of the pressure dependant heat coefficient (Cp) for methane (critical pressure 673 psia, critical temperature -116°) that effect heat of compression. In particular, the extreme spiked values are noted as the conditions approach the critical point of the gas.
- Figure 7 Trends of Joule-Thomson chilling coefficient for methane relative to changes in temperature and pressure as considered by the process herein.
- Figure 8 Indicated chilling performance limits achievable at turbo expander outlet temperature relative to an elevated inlet temperature considered in the process described herein. The inflection point limiting improvements is shown. Fixed Methane Gas Pressure @ 3400 PSIG; Turbo Expander Efficiency of 83%.
- LNG Liquefied Natural Gas
- Offset chilling curve refers to a deeper cut in the turbo expansion chilling curve profile that terminates at the lower pressure levels of the gaseous region of the feedstock natural gas phase envelope, thus reducing the amount of heat transfer required for the transition of the feedstock to the LNG state.
- the offset chilling curve profile is created by increasing the temperature and pressure of the feedstock.
- the process uses compression of transmission gas to induce uncommon high pressure hot entry conditions into an expansion chilling device, such as a J-T device or turbo-expansion device, and by subsequent expansion provides the primary method of chilling by using the inherent Joule-Thomson (J-T) properties of this feedstock. Best performance is achieved when the LNG feedstock is close to pure methane, and methane is the preferred feedstock for the process described herein.
- J-T Joule-Thomson
- a single step chilling (turbo expansion) stage takes the feedstock from selected high temperature and high pressure inlet conditions to near atmospheric low pressure and cryogenic temperature outlet conditions. Subject to the efficiency of turbo expansion, a small capacity external refrigeration loop may then be the only additional requirement to complete the phase change to LNG.
- the feedstock is not further compressed during the single step chilling stage, nor is any other means of chilling used during the single step expansion chilling stage.
- the method described herein may use off-the-shelf components.
- the higher temperatures used for this process can be obtained for example, in a preferred embodiment, purely by heat of compression provided by pipeline station spec compressors and modulated with air coolers.
- the specifications of the compressor and related size specification of air coolers can be selected by a person of skill in the art depending on the capacity required,
- a source heat may be provided to raise the temperature as required. This option is attractive if waste heat is available,
- the expansion chilling profiles of natural gas used in the proposed method generally can be considered to begin at a pressure of 3400 psig where temperatures may range between 95°F and 250°F. Lower temperatures are preferable for pure methane mixtures and higher temperatures are preferable for mixtures of higher NGL content. Chilling performance along these curves can be subject to interception at any lower pressure and temperature provided by inlet conditioning.
- the chilling profile provided by external heat exchange or self-chilling in contemporary LNG processing starts at pipeline delivery pressures of 1100 psig or less, preferably at between 800 and 600 psig.
- Process entry temperatures in general are those provided by the feedstock supply pipeline and are at 105°F or less depending on the temperature surroundings of the pipeline, and preferably between 68°F and 75°F.
- Pre-cooling by heat exchanger or small AP reduction through turbo expansion prior to first cold box entry or self-chilling would typically be to the 45°F region with air coolers, and to -31 °F region using external propane chilling loops.
- Minta US Patent 9,140,490
- pressures between 1000 psia and 5000 psia were investigated.
- benefits of thermal heat transfer for plate exchangers were found to be optimal where refrigerant and process gas pressures were between 1500 psia and 3000 psia.
- Minta s final high pressure to atmospheric pressure reduction in a liquid state for the delivered LNG takes place from cryogenic temperatures. This offers minimal J-T temperature reduction for feedstock in the gaseous state and no J-T temperature reduction for feedstock in the PLNG (pressurized liquefied natural gas) state.
- the present disclosure exhibits high values of J-T coefficient in a gaseous state at cryogenic temperatures at pressures less than 1000 psig.
- Embodiments of the present method contemplate fluctuations in the constituents of the feedstock and make allowance for a final external chilling loop for the last few degrees of temperature drop and removal of sensible heat from the flowstream to convert it to LNG.
- This loop ideally uses nitrogen as the refrigerant best suited to offshore needs of non-explosive specifications.
- Methane or mixed refrigerant also remains as a convenient and slightly more efficient refrigerant option under selective service conditions.
- Option 1 A series arrangement of individual high efficiency turbo compressors that can yield staged reduction of pressure to the point of liquefaction - for example, a high pressure machine configuration for the first unit followed by a low pressure machine configuration for second unit to make the final transition of conditions to the LNG zone.
- Option 2 A staged wheel configuration within a single casing is a consideration, and feasible to the point of liquefaction of the process stream.
- “Sensible” heat extraction as used herein refers to the removal of latent heat causing the phase change from gas to liquid without a change in temperature.
- NGLs e.g., ethane, propane, normal butane, isobutane and pentanes
- Modem day processing for separation of liquids by front end plants upstream of the LNG process can make available an LNG feedstock of almost 100% methane devoid of acid gas, water vapor, CO2, N2 and mercury.
- these extracted constituents may be removed in the chilling process feedstock because they freeze and clog the process, reduce heat value or corrode equipment.
- the J-T coefficient of methane has its highest values at pressures below 1000 psig and at cryogenic temperatures below -120°F.
- Figure 7 shows that values of J-T coefficient to be mostly effective below about 3500 psig, and at lower temperatures - hence 3400 psig was selected as an investigative starting pressure for the traces of turbo expander chilling selected for Fig.
- the process described herein avoids recompression of the feedstock refrigerant to achieve further chilling through the temperature range of -100°F to -150°F. Offsetting the chilling curve by beginning decompression at higher temperatures steers the process conditions clear of the zone of peaking values of Cp for methane shown in Fig. 6. These high Cp values, several times the norm and typical of refrigerants used in LNG processing, result in high heats of recompression. This heat requires repeated stages of compression/interlaced external heat exchange to remove. High driver energy input would be demanded by such recompression and is contrary to the desired heat transfer objectives of the process described herein.
- a target temperature of about -262°F for the LNG state at 5 to 15 psi above atmospheric pressure is an objective of the process described herein. This process seeks to both simplify traditional LNG infrastructure and to reduce fuel consumption for LNG production.
- Target temperature and pressure conditions are also be moderated from the ideal quoted above depending on gas constituents. Starting conditions of temperature and pressure, and levels of turbo expander efficiency commensurate with developments in axial flow as well as radial flow machinery make such deep cuts in temperature practical.
- Region C shown on the diagram shows reasonable recompression from pipeline conditions of approximately 50°F and 1500 psig to approximately 105°F and 2000 psig to intercept cooling curve (3) relating to 170°F offsets at 3400psig.
- outlet conditions of the compressor air coolers ahead of the turbo expander could typically be expanded from the point of interception with the 170°F chilling line.
- turbo expansion efficiency of 83% these conditions would result in an outlet temperature of -245°F at 5 psig, clear of any vapor fraction, and at -255°F at 3 psig where the vapor fraction begins to form.
- the dew point line of either the phase diagram of pure methane or phase envelopes of light hydrocarbon mixes of transmission specification gas can be intercepted by the cooling trace from the air-cooled starting conditions.
- the terminal expansion conditions fall short of target cryogenic temperature at higher than desired pressures once the dew point is reached (indicated by the methane phase diagram A-B).
- Pre-chilling associated with traditional LNG processing for near 100% methane feedstock is not required for the process described herein.
- a starting condition of 170°F at 3400 psig offers the optimal starting position to turbo expand to attain the highest temperature reduction without exhibiting a vapor fraction for a pure methane feedstock depressured to near atmospheric pressure.
- FIG. 1 shows a simplified flow diagram of the prior art cascade chilling process for making LNG.
- the process comprises a series of cold box heat exchangers (101 , 201 and 301 ) that step the temperature of the feedstock from receipt temperatures down to the -262°F region required for liquefaction.
- the feedstock flows from A (treated gas inlet) to B (LNG outlet) through these units where its heat is extracted by exchange with refrigeration loops running through the boxes.
- These external chilling loops use propane, ethylene and methane as refrigerants, for successively colder steps of temperature reduction.
- Each loop has 4 stages of treating the working refrigerant:
- the propane loop (C-D-E-F-C) comprises a compressor (102), a condensing cooler (103), throttle (104) and heat exchange passage (101 ).
- the ethylene loop (H-l-J- K-H) comprises a compressor (202), condensing cooler (203), throttle (204) and pre chilling passage through (101 ) prior to heat exchange through (201 ).
- the methane loop (L-M-N-O-L) comprises a compressor (302), condensing cooler (303), throttle (304) and pre chilling passage through both (101 ) and (201 ) prior to heat exchange through (301 ).
- the propane loop cooler (103) uses air as its heat sink while the ethylene loop cooler (203) and methane loop cooler (303) each use the lower temperature preceding cold boxes (101 ) and (201 ) as their heat sinks.
- FIG. 1 shows a simplified flow diagram of the more efficient prior art mixed refrigerant process for making LNG.
- the process uses a single large vessel as a contiguous cold box (100). Heat exchange is provided by two external refrigeration loops (HMR) and (LMR) sequentially carrying a heavy mixed refrigerant and light mixed refrigerant through the stepdown temperature steps to cryogenic LNG conditions.
- the first loop uses a compressor (101 ) and condenser/cooler (102) to move and thermally condition refrigerant through the cold box prior to throttling and expansion. It uses staged chilling steps by splitting the refrigerant into 3 flow streams: Stream A-B-C-D-E-A, Stream A-B-C-F-G-H-A, and Stream A-B-C-F-l-J-K-A.
- the first stream comprises the compressor (101 ), condenser/cooler (102), branching at C to throttle (103), followed by a heat exchange loop through the coldbox to point E where the stream re-enters the compressor (101 )
- the second stream comprises the compressor (101 ), condenser/cooler (102), branching at F to throttle (203), followed by a heat exchange loop through the coldbox to point H where the stream re-enters the compressor (101 )
- the third stream comprises the compressor (101 ), condenser/cooler (102), branching at I to throttle (103), followed by a heat exchange loop through the coldbox to point E where the stream re-enters the compressor (101 ).
- the second refrigeration loop (LMR) running from L-M-N-O-P-Q-L provides the final chilling to liquefaction of the feedstock. A lighter refrigerant mix works at these low temperatures.
- the compressor (201 ), and condenser/cooler (202) move and thermally condition refrigerant through the cold box prior to passing through throttle (203). This throttling provides the pressure reduction and expansion of the refrigerant prior to its heat exchange passage back through the cold box on its way to re-enter the compressor (201 ) at point Q.
- the feedstock gas is pretreated upstream of this liquefaction process for reduction or removal of undesirable amounts of constituents such as acid gas, water vapor, CO2, N2 and mercury.
- Treated gas enters the process at point R, from where it passes into the cold box vessel (100) and is chilled as far as Point S from where it is withdrawn at pressure and temperature conditions conducive to entering separator vessel (300) at point T.
- residual NGL condensates fall out of phase and are withdrawn from the feedstock at point Z to flow to storage via point AA.
- FIG 4C shows improved efficiency of the new configuration for a Mixed Refrigerant process.
- FIG. 3 shows an embodiment of a process flow diagram for the production of LNG described herein.
- Process start conditions receive pipeline gas at a customary LNG plant inlet pressure of 800 psi at point B.
- the inlet gas to the process at point A (treated gas inlet) may be preconditioned to remove/reduce disruptive components of water vapor, N2, CO2, other acid gas, NGLs and mercury at upstream facilities.
- This layout is intended for near pure methane feedstock.
- a staged compression (101 ) ahead of the turbo expansion inlet (D) may be performed.
- the supply temperature at the inlet of the turbo expander (202-203) is set to a higher than ambient temperature, to offset the cooling curve as illustrated in Fig. 5. This offset then allows the final onset of the vapor fraction to occur at -255°F when pressure drops to 3 psi above atmospheric pressure using traditional turbo expander efficiency.
- Loop LR comprises a compressor (102), condenser/cooler (402) linked to the cold flow through turbo expander stage (203), a throttle (403) and heat exchanger between S and T in the coldbox (401).
- the path N-0 takes the production stream through the separator 502 where under start up or upset conditions the gas phase is split from the liquid phase.
- the gas is recycled back to the inlet of compressor 101 via Q-R-S-T that contains compressor 103 to bring up the pressure to entry conditions for compressor 101.
- the turbo expander start conditions of temperature and pressure will depend on the climatic region in which the plant is located. Minimum air temperatures in different regions will determine the approach temperature of air cooling that the compressed feedstock can be subjected to.
- Shaft power recovery (301 ) from the turbo expander will vary depending on the start conditions set for the process. Under most conditions it will be substantial and able to cover the power needs of the final liquefaction stage, and/or contribute to the process energy for preconditioning the feedstock, should this plant be located adjacent to the LNG process.
- the final chilling stage (LR Loop) is also an assurance that sufficient chilling capacity is available to produce LNG should an upstream process fluctuation in gas composition or conditions introduce small quantities of NGL (primarily trace ethane) into the flow-stream. This could result in an earlier onset of the vapor fraction, slowing down the J-T effect of the remaining methane gas phase and raising the temperature of the product produced by the turbo expander chilling.
- NGL primarily trace ethane
- turbo expander wheels between sections (202) and (203). This break allows for the extraction of the flow-stream via line E-F to the separator (501 ). When conditions warrant, NGLs can be removed via line G- H and the drier gas directed back into the turbo expander section (203).
- the break between turbo expander sections also permits the mixed use of radial and axial flow wheels in the turbo expander configuration. Should different shaft speeds be required between (202) and (203), a physical break or speed compensating gearing can be added at this location.
- Figures 4A to 4D show a side-by-side summary of heat flow attributes of the two prior art LNG processes and the LNG process described herein. Delivery of feedstock is standardized to all sites represented here at 600 psi.
- the prior art LNG processes begin with entry temperatures of 100°F.
- the LNG process described herein ( Figure 4D) uses a comparative air cooled entry temperature of 105°F at a compression boosted 2000 psig start condition for turbo expansion. This is a median point for the range of approach temperatures that prevail in specific climatic zones (e.g.: 137°F at 2500 psig in hot desert conditions (Air Temp 117°F) and 62°F at 1400 psig in temperate regions (Air Temp 42°F)). Delivery of turbo expander chilling drops to just above atmospheric pressure during the production process prior to removal of sensible heat for liquefaction.
- the cascade process is represented by two trace lines shown in Fig. 4A and Fig. 4B.
- the basic process illustrated in Fig. 1 is reflected in Fig. 4A and more advanced split refrigerant version reflected in Fig. 4B.
- the propane, ethylene, and methane chilling steps are shown. It will be noted that the space between the stepped process trace lines (solid) and demand line (dashed) for pure methane heat transfer rate is reduced in the more advanced version of the process.
- the mixed refrigerant process is represented by Fig. 4C.
- the heat transfer differential space between the mixed refrigerant steps of the process and pure methane is seen to be even more reduced reflecting the improvements from earlier technology and recent heat exchanger configurations.
- Figure 5 shows the turbo expansion chilling paths of pure methane at various starting temperatures from a common starting pressure of 3400 psig. It also includes the phase diagram (A to B) for pure methane, which also represents the dew point boundary between the gas phase and the liquid phase. It exhibits a sharper curve at low pressures and temperatures, leaving very little space between itself and the horizontal X axis for termination of the chilling curves at low temperatures. The deepest uninterrupted delta P pressure differential during completion of the gas phase expansion chilling through this low temperature region will result in the lowest finish temperature experienced by the flow-stream.
- Curve (1 ) starting at 95°F shows the extended profile along the lines of that advocated by US Patent Publication 2019/0257579 falling short of the target temperature upon striking the dew point curve.
- Curve (2) starting at 120°F shows the profile of a “pre-chilled” start to the expansion from the same high pressure turbo expander inlet condition in this attempt at lowering temperature at the point of contact with the dew point curve.
- the appearance of the vapor fraction culminating in compressed LNG at the elevated pressure again causes the cooling trace to fall short of the target temperature.
- Curve (3) starting at 170°F shows the profile of the chilling curve when it is deliberately, and counter-intuitively, displaced to commence at a hotter temperature than normally considered by the natural gas industry. This has the effect of moving the finish point at low pressure deep into the cryogenic temperature region before running low on pressure just before the dew point trace line. The complication of recompression of the flowstream in the cryogenic region of high Cp values is thereby sidestepped. Liquefaction can now be achieved with a controlled heat exchange step over a small AT.
- Curve (4) starting at 190°F shows the profile of the chilling curve when it is deliberately moved to a higher temperature zone.
- the termination condition impacts the X axis of the graph, and while good is not as good as the termination condition of Curve (3).
- FIG. 6 shows that high values of the heat coefficient Cp occur at low pressure conditions in the cryogenic zone of pure methane (-120°F to -190°F). Below -100°F, excessive values of Cp are observed, peaking 5 or 6 times the norm for common LNG process pressures below 800 psi.
- FIG. 7 shows that the Joule-Thomson coefficient for pure methane adopts a “Z“ or “S” shaped profile for pressures between 0 and up to about 4500 psi. Reading the graph from right to left: - Higher temperatures at higher pressures have higher J-T coefficient values. This is the region to consider for the process starting point.
- the process fuel energy is primarily entered at the pipeline compressor, and the process compressor upstream of the LNG chilling plant.
- the turbo expander recovers both the pipeline and process compressor energy - sufficient to power both the second step liquefaction chiller and the gas conditioning plant, however it is distributed.
- Figure 7 shows temperature conditions between 83°F and -9°F which are in common use by the gas production industry.
- Figure 8 shows the reason for selecting 170°F start temperature for chilling curve profile from 3400 psig as the optimal pure methane chilling curve. From 120°F to 190°F start temperatures an inflection trend is noted with the 170°F condition showing the lowest achievable temperature cut for a turbo expansion at 83% efficiency.
- LNG liquefied natural gas
- the increased pressure and increased temperature are selected to be at a level such that the conditioned feedstock has an offset turbo expansion chilling curve profile that will enable chilling of the flow stream through J-T expansion along an offset chilling curve profile that terminates at the lower pressure levels of the gaseous region of its phase envelope, thus easing the amount of heat transfer for the transition of the feed gas to the LNG state.
- Fig. 5 shows, in area C, a turbo expander entry condition for the 170°F chilling curve at 105°F and 2000 psig,
- the “termination” of the offset curve is the point at which the Dew Point of the feedstock gas on a phase diagram is struck by the offset chilling curve, or when the horizontal zero pressure axis is struck by a chilling curve having a higher start temperature.
- termination of the offset chilling curves (1 ), (2) and (3) occurs when Dew Point curve (A-B) is struck by the chilling curves, or when chilling curve (4) intersects the horizontal axis (0 psig).
- an offset chilling curve that strikes the Dew Point at atmospheric pressure (0 psig) may be achieved.
- lower pressure refers to a pressure of less than about 20 psig, less than about 15 psig, less than about 10 psig, less than about 5 psig; between about 0 to about 20 psig, about 0 to about 10 psig, about 0 to about 5 psig, about 1 to about 5 psig, about 1 to about 10 psig, about 5 to about 10 psig, about 10 to about 20 psig, about 15 to about 20 psig.
- the lower pressure level is the pressure typically used for industrial storage of LNG.
- the next step is delivering the conditioned feedstock to the inlet of a turbo expansion device at the selected elevated temperature and selected elevated pressure.
- a turbo expansion device may be a stepped series of turbo expansion devices.
- the next step is expanding the conditioned feedstock in the turbo expansion device.
- the next step is discharging the expanded gas from an outlet of the turbo expansion device at a temperature of between about -175°F and about -262°F for pure methane or light NGL gas mixtures and between about -145°F and -175°F for rich NGL mixes and at a pressure of between about 5 and about 15 psig.
- the conditioned feedstock gas is not compressed again (it is not further compressed) after it is delivered to the inlet of the turbo expansion device and before it is discharged from the turbo expansion device.
- any other means of chilling the gas used is any other means of chilling the gas used, after the feedstock gas is delivered to the inlet of the turbo expansion device and before it is discharged from the turbo expansion device.
- the expanded gas may be further subjected to extraction of sensible heat to render the liquid state at a temperature of about -262°F.
- the preferable feedstock at the turbo expander inlet is 100% methane, or a mixture of methane or methane and NGLs that has been preconditioned to remove/reduce undesirable quantities of water vapor, acid gas, excess NGLs and heavier hydrocarbon liquids, CO2, N2 and mercury that would otherwise inhibit the chilling process.
- the standalone unrelated maximum content of the constituents is: a. methane 100.0 mol% b. ethane 25.0 mol% c. propane 12.5 mol% d. i-Butane (Combined e. n-Butane 8.5 mol%) with the total of these constituents being 100%.
- the molecular weight of the feedstock does not exceed 23.2, HHV does not exceed 1395BTU/ft3, and modified Wobbe Index as calculated for 60°F does not exceed 62.20.
- phase at turbo expander entry conditions of such mixtures is gaseous. It is possible, subject to delivery conditions of temperature from the pipeline, and compression ahead of the turboexpander that the preferred offset chilling curve can be intercepted at pressures lower than the aforementioned 3400 psig.
- the starting pressure for turbo expansion is between 3400 psig and 600 psig depending on climatic location of the process plant and the constituent makeup of the gas feedstock.
- the corresponding start temperatures to these pressures lie between 250°F and -40°F. Higher temperatures are considered for NGL rich gas mixes to allow for liquid extraction, and a staged final expansion of the separated stream of near methane gas to the liquefaction region at the lower reaches of its dew point curve.
- cryogenic temperature achieved on exit from the turbo expander is between -175°F and -262°F for feedstock light in NGL constituents.
- NGLs are allowed to fall out at a break point in the turbo expansion, the near methane mix emerging to enter the final expander step was found to achieve temperatures between -145°F and -175°F depending on start mixture and turbo expander efficiency.
- turbo expansion can be coupled to recovered shaft energy. This can be either single shaft or multi shaft configuration operating at different or same speeds to suit axial or radial flow blade and wheel selection.
- the turbo expansion step are interrupted for liquids removal. This interruption may include the introduction of guide vanes within liquid bleed off chambers. These chambers may be located at certain process encompassed pressure and temperature points within or in a branch connection outside of the turbo expander that are attributed to specific fallout properties of constituent NGLs. After the withdrawal of liquids from these operational points, the remaining gas stream may be subjected to further turbo expansion to low temperatures.
- externally refrigerated heat exchange equipment is situated downstream of the turbo expansion unit, to extract sensible heat for final liquefaction of the gas mixture. The condensation loop of the refrigerant of such equipment may be integrated with the turbo expander or emerging flow-stream.
- heat exchange equipment may be used to further chill a stream of NGLs, enabling enhanced HHV heat content of the produced LNG by intermixing of the streams.
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- 2021-12-17 CA CA3201763A patent/CA3201763A1/en active Pending
- 2021-12-17 US US18/257,093 patent/US20240102729A1/en active Pending
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- 2021-12-17 WO PCT/CA2021/051842 patent/WO2022126282A1/en active Application Filing
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US20200386473A1 (en) * | 2017-04-26 | 2020-12-10 | Excelerate Energy Limited Partnership | Apparatus, system and method for reliquefaction of previously regasified lng |
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