EP3482146B1 - Method for liquefying natural gas and for recovering possible liquids from the natural gas, comprising two refrigerant cycles semi-open to the natural gas and a refrigerant cycle closed to the refrigerant gas - Google Patents
Method for liquefying natural gas and for recovering possible liquids from the natural gas, comprising two refrigerant cycles semi-open to the natural gas and a refrigerant cycle closed to the refrigerant gas Download PDFInfo
- Publication number
- EP3482146B1 EP3482146B1 EP17745789.2A EP17745789A EP3482146B1 EP 3482146 B1 EP3482146 B1 EP 3482146B1 EP 17745789 A EP17745789 A EP 17745789A EP 3482146 B1 EP3482146 B1 EP 3482146B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- natural gas
- stream
- refrigerant
- temperature
- main
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims description 580
- 239000003345 natural gas Substances 0.000 title claims description 276
- 239000003507 refrigerant Substances 0.000 title claims description 154
- 239000007789 gas Substances 0.000 title claims description 124
- 238000000034 method Methods 0.000 title claims description 77
- 239000007788 liquid Substances 0.000 title claims description 48
- 230000008569 process Effects 0.000 claims description 69
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 32
- 238000001816 cooling Methods 0.000 claims description 29
- 229930195733 hydrocarbon Natural products 0.000 claims description 18
- 150000002430 hydrocarbons Chemical class 0.000 claims description 18
- 229910052757 nitrogen Inorganic materials 0.000 claims description 16
- 238000010521 absorption reaction Methods 0.000 claims description 14
- 238000011144 upstream manufacturing Methods 0.000 claims description 10
- 239000012530 fluid Substances 0.000 claims description 7
- 239000002253 acid Substances 0.000 claims description 6
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 230000006835 compression Effects 0.000 claims description 5
- 238000007906 compression Methods 0.000 claims description 5
- 238000009833 condensation Methods 0.000 claims description 5
- 230000005494 condensation Effects 0.000 claims description 5
- 229910052753 mercury Inorganic materials 0.000 claims description 5
- 238000011143 downstream manufacturing Methods 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims description 2
- 239000004215 Carbon black (E152) Substances 0.000 claims 1
- 239000003949 liquefied natural gas Substances 0.000 description 26
- 230000004907 flux Effects 0.000 description 25
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 24
- 238000005057 refrigeration Methods 0.000 description 24
- 238000000605 extraction Methods 0.000 description 20
- 238000009434 installation Methods 0.000 description 20
- 238000010992 reflux Methods 0.000 description 12
- 208000003173 lipoprotein glomerulopathy Diseases 0.000 description 9
- 238000011282 treatment Methods 0.000 description 9
- 238000011084 recovery Methods 0.000 description 7
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 description 6
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 6
- OFBQJSOFQDEBGM-UHFFFAOYSA-N Pentane Chemical class CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 5
- 150000001491 aromatic compounds Chemical class 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000012856 packing Methods 0.000 description 5
- 238000000926 separation method Methods 0.000 description 5
- 235000013844 butane Nutrition 0.000 description 4
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical class CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 230000000295 complement effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000007710 freezing Methods 0.000 description 3
- 230000008014 freezing Effects 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000003915 liquefied petroleum gas Substances 0.000 description 3
- 239000001294 propane Substances 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 239000010779 crude oil Substances 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 238000009776 industrial production Methods 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical class CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 2
- 238000002203 pretreatment Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 239000013535 sea water Substances 0.000 description 2
- 208000005156 Dehydration Diseases 0.000 description 1
- 239000003570 air Substances 0.000 description 1
- 239000012080 ambient air Substances 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 239000013505 freshwater Substances 0.000 description 1
- 239000003502 gasoline Substances 0.000 description 1
- 230000008676 import Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- -1 methane Chemical class 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000003129 oil well Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 230000008016 vaporization Effects 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
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- 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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- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
- F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
- F25J1/0035—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by gas expansion with extraction of work
- F25J1/0037—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by gas expansion with extraction of work of a return stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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- 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"
- F25J1/004—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 flash gas recovery
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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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- 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
- F25J1/0095—Oxides of carbon, e.g. CO2
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- 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
- F25J1/0097—Others, e.g. F-, Cl-, HF-, HClF-, HCl-hydrocarbons etc. or mixtures thereof
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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- 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
- F25J1/0208—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 in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle 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
- F25J1/0203—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
- F25J1/0208—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 in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop
- F25J1/0209—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 in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop as at least a three level refrigeration cascade
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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- 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
- F25J1/0229—Integration with a unit for using hydrocarbons, e.g. consuming hydrocarbons as feed stock
- F25J1/0231—Integration with a unit for using hydrocarbons, e.g. consuming hydrocarbons as feed stock for the working-up of the hydrocarbon feed, e.g. reinjection of heavier hydrocarbons into the liquefied gas
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- 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
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- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
- F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
- F25J1/0277—Offshore use, e.g. during shipping
- F25J1/0278—Unit being stationary, e.g. on floating barge or fixed platform
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- 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
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- F25J1/0285—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings
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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
- F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air
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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
-
- 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
Definitions
- the present invention relates to the general field of the liquefaction of natural gas based mainly on methane to produce LNG, for Liquefied Natural Gas, also called LNG in English (for “Liquefied Natural Gas”).
- a particular but non-limiting field of application of the invention is that of floating natural gas liquefaction installations, called FLNG in English (for “Floating Liquefaction of Natural Gas”), which allow liquefaction of natural gas offshore, on a ship or on any other floating medium at sea.
- FLNG floating natural gas liquefaction installations
- the predominantly methane-based natural gas that is used to produce LNG is either a by-product from oil fields, that is to say produced in combination with crude oil, in which case it is in low or medium quantity , or a major product from gas fields.
- LNG carriers specialized transport vessels
- cryogenic liquid at a temperature of around -160 ° C
- the liquefaction of natural gas for transport is generally carried out near the gas production site and requires large-scale installations and considerable amounts of mechanical energy for production capacities of up to several million tonnes per year.
- the mechanical energy required for the liquefaction process can be produced on the site of the liquefaction plant using part of the natural gas as fuel.
- Natural gas must undergo treatment prior to its liquefaction in order to extract the acid gases (in particular carbon dioxide), water (to prevent it from freezing in the liquefaction installation), mercury ( to avoid the risk of degradation of the aluminum equipment of the liquefaction plant) and part of the natural gas liquids, also called NGLs in English (for “Natural Gas Liquids”).
- NGLs include all the hydrocarbons heavier than methane present in natural gas and liable to be condensed.
- the NGLs include in particular ethane, LPGs (propane and butanes) for Liquefied Petroleum Gas, also called LPGs in English (for “Liquefied Petroleum Gas”), pentanes and hydrocarbons heavier than the pentanes present in the gas natural.
- NGLs are either integrated into the natural gas liquefaction installation, or carried out in a dedicated unit upstream of the liquefaction installation. In the first case, this extraction is generally carried out at a relatively high pressure (of the order of 4 to 5 MPa) while in the second case, it is most of the time carried out at a lower pressure (of the order of from 2 to 4 MPa).
- NGLs integrated with the liquefaction of natural gas as described for example in the publication US 4,430,103 has the advantage of being simple. However, this type of process only operates at a pressure below the critical pressure of the gas to be liquefied, which affects the efficiency of the liquefaction. In addition, this type of process typically performs the separation of natural gas and NGLs at a pressure of the order of 4 to 5 MPa. However, at these pressures, the selectivity of the extraction of NGLs is low. Indeed, a significant portion of methane is extracted at the same time as the NGLs. Downstream treatment is then generally necessary to release this methane.
- NGLs NGLs
- the way in which NGLs are extracted has a significant impact on the cost and degree of complexity of the liquefaction plant, on the performance of the liquefaction and on the energy efficiency of the liquefaction plant as a whole.
- thermodynamic cycle the compressed refrigerant (in the form of gas) is cooled (and possibly condensed) by a thermal source having a temperature higher than that of the refrigerated fluid and called "hot source" (water, air).
- hot source water, air
- another refrigeration cycle then further cooled by a flow of cold gas generated by the thermodynamic cycle itself before being relaxed.
- the low temperature cold refrigerant stream resulting from this expansion is used to cool the natural gas and pre-cool the refrigerant.
- the low-pressure gaseous refrigerant is again compressed to its original pressure level (via compressors driven by gas turbines, steam turbines or electric motors).
- the power required for the refrigeration and liquefaction of natural gas can be supplied either by the vaporization and heating of a liquid refrigerant, most of the refrigeration heat being produced by the latent heat brought into play during the change of state, either by the heating of a cold refrigerant in the form of gas.
- a refrigerant gas the temperature of the refrigerant is typically lowered by pressure reduction through an expansion turbine (in English "gas expander").
- the cooling effect produced by the refrigerant is mainly in the form of sensible heat.
- the temperature of the refrigerant is generally lowered by expansion through a valve and / or a liquid expansion turbine (in English "liquid expander").
- the cooling effect produced by the refrigerant is mainly in the form of latent heat (and, to a lesser extent, in the form of sensible heat).
- latent heat is much higher than the sensible heat
- the refrigerant flow rates which are necessary to obtain the same refrigeration capacity are higher for thermodynamic cycles using a refrigerant in the form of gas than for thermodynamic cycles using a gas. refrigerant in liquid form.
- thermodynamic refrigeration cycles using a gas as refrigerant require higher capacity refrigeration compressors and larger diameter pipes than for thermodynamic refrigeration cycles using a liquid as refrigerant.
- Gaseous refrigerant thermodynamic cycles are also generally less efficient than liquid refrigerant thermodynamic cycles, in particular because the temperature difference between the fluid undergoing refrigeration and the refrigerant is on average greater. high for a gaseous refrigerant cycle, which contributes to increasing the efficiency losses by irreversibility.
- thermodynamic cycles of refrigeration with liquid refrigerant implement mass refrigerant inventories higher than thermodynamic cycles with gaseous refrigerant.
- thermodynamic cycles with liquid refrigerant have a lower level of intrinsic safety than processes with gaseous refrigerant, in particular when comparing thermodynamic cycles with liquid refrigerant using hydrocarbons as refrigerant with thermodynamic cycles which use an inert gas such as nitrogen as refrigerant.
- This point is particularly critical in an environment where a great deal of equipment is concentrated in a small space and in particular on an offshore installation. Thermodynamic refrigeration cycles using liquid refrigerants are thus efficient but present a certain number of drawbacks, in particular for an offshore application on a floating support.
- the main aim of the present invention is therefore to overcome such drawbacks by proposing a liquefaction process using thermodynamic cycles with gaseous refrigerant and having a higher efficiency than the liquefaction processes of the prior art while proposing a simple and compact method. extraction of any NGLs, which is integrated into the liquefaction process and which offers better overall energy optimization than the processes of the prior art.
- the liquefaction process according to the invention comprises two semi-open refrigerant cycles with natural gas and a single refrigerant cycle closed with refrigerant gas.
- the function of the first semi-open refrigerant cycle using natural gas is to extract the heavy natural gas liquids (NGLs) that may be present in the natural gas to avoid freezing problems in the cold section of the liquefaction plant, and to pre-cool natural gas and refrigerant gas.
- the function of the second semi-open refrigerant cycle using natural gas is to contribute to pre-cooling of natural gas and refrigerant gas as well as for the liquefaction of natural gas.
- the function of the refrigerant cycle closed to refrigerant gas is to sub-cool the liquefied natural gas and to supply additional refrigeration power to the other two cycles.
- the refrigerant gas used is typically nitrogen.
- the process according to the invention exhibits a ratio of mechanical power consumed per tonne of LNG produced for equivalent conditions of the order of 15% lower than a process with two refrigerant cycles using nitrogen, 10 % lower than a three-cycle nitrogen refrigerant process, and 8% lower than a one-cycle natural gas refrigerant and two nitrogen refrigerant cycle process when these processes are combined with a unit of extraction of NGL upstream of the liquefaction requiring recompression of the gas (this recompression power being taken into account in the comparison).
- the power consumed per tonne of LNG produced by the process according to the invention is thus lower than for the processes known from the prior art, which shows a higher efficiency for this process.
- the process according to the invention integrates the liquefaction with the extraction of heavy natural gas liquids (NGLs), which improves the overall energy efficiency of the natural gas liquefaction plant and eliminates the need to resort to installations. dedicated to this extraction. This simplifies the natural gas pretreatment process.
- NGLs heavy natural gas liquids
- the extraction being carried out at low pressure, few light hydrocarbons (in particular methane) are entrained during this extraction process, which makes it possible to treat the heavy NGLs using a simple process of placing. artwork.
- the single refrigerant gas cycle of the process according to the invention is closed. Also, the only additional refrigerant gas that is necessary can be easily produced (in this case when the refrigerant gas mainly comprises nitrogen). In particular, no dedicated unit is required for the import, production, treatment or storage of liquid hydrocarbons used as refrigerant. The implementation of the method according to the invention is thus greatly facilitated.
- the method according to the invention has a high level of intrinsic safety. Indeed, the mass inventories of hydrocarbons are limited (in particular compared to a process using hydrocarbons in liquid form as refrigerant). The implementation of the method according to the invention is thereby facilitated.
- the process is particularly suitable for an installation for the liquefaction of natural gas at sea, such as for example on board an FLNG, because of its high level of intrinsic safety and the fact that it does not require storage of gas. refrigerants.
- auxiliary pre-cooling by auxiliary refrigerant cycle during the first semi-open refrigerant cycle to natural gas, the flow of natural gas feed to the inlet of the expansion turbine at ambient temperature is further cooled in an auxiliary heat exchanger.
- an auxiliary refrigeration cycle provides the refrigeration power necessary for the operation of the auxiliary heat exchanger.
- the third flow of natural gas to the exhaust of the intermediate expansion turbine is directed to a separator auxiliary at the outlet of which the flow of natural gas is reintroduced into the main cryogenic heat exchanger, the flow of natural gas liquids at the outlet of the auxiliary separator being pumped in whole or in part to the main separator to contribute to the absorption of natural gas liquids.
- the contact between the natural gas to be treated and the sub-cooled reflux can for example be carried out against the current.
- the main separator can be equipped with a packing bed.
- the main cryogenic heat exchanger in order to to be cooled there is extracted from said main cryogenic heat exchanger at a temperature T11 above the temperature T3 to be directed to the main separator so as to contribute to the absorption of liquids from the natural gas.
- the contact between the natural gas to be treated and the LNG reflux can for example be carried out against the current.
- the main separator can be equipped with a packing bed.
- the natural gas feed stream is advantageously mixed with lighter natural gas coming from the discharge of the natural gas compressor before being expanded in the turbine to room temperature without pre-cooling in the main cryogenic exchanger, which makes it possible to efficiently produce a cold flow ensuring the pre-cooling of the natural gas and the refrigerant gas and to extract any NGLs with excellent selectivity.
- the natural gas feed stream to the exhaust of the expansion turbine at room temperature is introduced into the main separator at the outlet of which a stream of heavy gas liquids is recovered.
- a fraction of the liquid stream of the recovered natural gas is reheated and partially vaporized in order to facilitate its downstream processing.
- the pressure of the main natural gas stream is greater than the critical pressure of natural gas, which makes it possible to maximize the efficiency of the liquefaction and ensures that the liquefaction takes place without a phase change.
- the subject of the invention is also a natural gas liquefaction installation according to claim 14 for implementing the method as defined above, the installation comprising an expansion turbine at ambient temperature intended to receive a feed stream of natural gas as well as part of a second natural gas stream coming from the discharge of a natural gas compressor and having an exhaust connected to an inlet of a main separator, a main cryogenic heat exchanger intended to receive the streams of natural gas and refrigerant gas, a compressor driven by the expansion turbine at ambient temperature intended to receive a first flow of natural gas coming from the main separator and having an outlet connected to the suction of the natural gas compressor, a turbine of intermediate temperature expansion designed to receive part of a main flow of natural gas coming from the discharge of the natural gas compressor and connected e at the inlet and outlet to the main cryogenic heat exchanger, a compressor driven by the expansion turbine at intermediate temperature intended to receive a third flow of natural gas coming from the main cryogenic heat exchanger, an expansion turbine at low temperature for refrigerant gas connected at the inlet and at the outlet to the main cry
- the natural gas compressor and the refrigerant gas compressor are driven by the same drive machine providing the power necessary for increasing the pressure of the natural gas to be liquefied as well as for compressing the fluids circulating in the three cooling cycles.
- the mechanical power consumption required for these functions is thus optimized so as to maximize LNG production while minimizing the number of equipment.
- the natural gas compressor is downstream of the compressors driven by the expansion turbine at ambient temperature and the expansion turbine at intermediate temperature
- the refrigerant gas compressor is downstream of the compressor driven by the expansion turbine at ambient temperature. low temperature.
- the liquefaction process according to the invention applies in particular (but not exclusively) to natural gas coming from gas fields.
- this natural gas mainly comprises methane and is found in combination with other gases, mainly C2, C3, C4, C5, C6 hydrocarbons, acid gases, water, and inert gases including nitrogen, as well as various impurities including mercury.
- the figure 1 shows an example of installation 2 for implementing the natural gas liquefaction process according to the invention.
- thermodynamic refrigeration cycles namely two refrigerant cycles semi-open to natural gas and a single refrigerant cycle closed to refrigerant gas.
- the process according to the invention preferably uses as refrigerant gas a gas comprising mainly nitrogen, which makes the process particularly suitable for offshore implementation, typically on a floating natural gas liquefaction installation (called in English FLNG for “Floating Liquefaction of Natural Gas”).
- this liquefaction installation 2 requires only one main cryogenic heat exchanger 4, the latter possibly consisting of an assembly of brazed aluminum heat exchangers which is installed in a cold box (called “cold box” in English).
- the liquefaction installation 2 also requires three turbo-expander (called “turbo-expander” in English), namely an ambient temperature turbo expander 6 dedicated to natural gas, an intermediate temperature turbo expander 8 dedicated to natural gas, and a low-temperature turbo-expander 10 dedicated to the refrigerant gas.
- turbo-expander three turbo-expander (called “turbo-expander” in English), namely an ambient temperature turbo expander 6 dedicated to natural gas, an intermediate temperature turbo expander 8 dedicated to natural gas, and a low-temperature turbo-expander 10 dedicated to the refrigerant gas.
- a turbo-expander is a rotating machine which is composed of a gas expansion turbine (here respectively an expansion turbine at ambient temperature 6a, an expansion turbine at intermediate temperature 8a and a low-temperature expansion turbine 10a and a gas compressor (here respectively a compressor 6b, a compressor 8b and a compressor 10b) driven by the gas expansion turbine.
- a gas expansion turbine here respectively an expansion turbine at ambient temperature 6a, an expansion turbine at intermediate temperature 8a and a low-temperature expansion turbine 10a
- a gas compressor here respectively a compressor 6b, a compressor 8b and a compressor 10b driven by the gas expansion turbine.
- the liquefaction installation 2 also comprises a natural gas compressor 12 and a refrigerant gas compressor 14, these two compressors 12, 14 preferably being driven by the same drive machine ME, for example a turbine with gas supplying the power necessary for increasing the pressure of the natural gas to be liquefied as well as for compressing the fluids circulating in the three refrigerant cycles.
- a natural gas compressor 12 and a refrigerant gas compressor 14, these two compressors 12, 14 preferably being driven by the same drive machine ME, for example a turbine with gas supplying the power necessary for increasing the pressure of the natural gas to be liquefied as well as for compressing the fluids circulating in the three refrigerant cycles.
- the natural gas compressor fulfills a threefold function: to pressurize and ensure the circulation of natural gas in such a way as to provide sufficient refrigeration power to contribute to the cooling and liquefaction of natural gas and refrigerant gas, re - compress the natural gas that has been relaxed for the extraction of heavy NGLs, and ensure that the natural gas to be liquefied is at the optimum pressure to maximize the efficiency of the liquefaction.
- the refrigerant gas compressor its function is to pressurize and ensure the circulation of the refrigerant gas so as to obtain the refrigeration power necessary to contribute to the cooling of the refrigerant gas, to contribute to the pre-cooling and liquefaction. natural gas and ensure the sub-cooling of natural gas.
- the liquefaction installation 2 also comprises a main separator 16 intended for the separation of the NGLs possibly contained in the natural gas, and a balloon 18 intended to allow a separation between the final flash gases and the liquefied natural gas (LNG).
- a main separator 16 intended for the separation of the NGLs possibly contained in the natural gas
- a balloon 18 intended to allow a separation between the final flash gases and the liquefied natural gas (LNG).
- the natural gas Prior to the first semi-open refrigerant cycle with natural gas, the natural gas undergoes a pretreatment intended to make it suitable for liquefaction.
- This pretreatment comprises in particular a treatment for extracting acid gases (including carbon dioxide) from natural gas, these acid gases being able in particular to freeze in the liquefaction installation.
- the pre-treatment also includes a dehydration treatment to extract water from natural gas and a demercurization treatment, as the mercury risks degrading the aluminum equipment of the liquefaction plant (including the main cryogenic heat exchanger 4).
- the natural gas feed stream F-0 leaves this preliminary pre-treatment phase, typically at a pressure P0 of between 5 and 10 MPa and a temperature T0 close (namely here slightly higher) to the temperature of the hot source.
- hot source is meant here the thermal source which is used to cool the non-cryogenic streams of the liquefaction process.
- This hot source can typically be ambient air, sea water, fresh water cooled by sea water, a fluid cooled by an auxiliary refrigerant cycle or a combination of several of these sources.
- This flow F-0 is mixed with the flow of natural gas F-2-1 coming from the liquefaction plant (and described later) and supplies the first semi-open refrigerant cycle with natural gas.
- this first semi-open refrigerant cycle with natural gas has the function of extracting the heavy NGLs possibly present in the natural gas, and of pre-cooling the natural gas and the refrigerant gas.
- the natural gas feed stream F-0 (combined with the natural gas stream F-2-1 described later) passes through the expansion turbine at ambient temperature 6a at the exhaust (ie outlet) from which its pressure P1 is lowered to a pressure between 1 and 3 MPa and its temperature T1 is lowered to a temperature between -40 ° C and -60 ° C.
- This phase of expansion of the natural gas supply flow leads to condensation of any heavy NGLs (for “Natural Gas Liquids”) contained in the natural gas.
- the flow of natural gas at the exhaust of the expansion turbine at room temperature 6a is directed to the inlet of the main separator 16.
- the flow of liquids from the gas natural F-HL is reheated, for example by circulating in the main cryogenic heat exchanger 4 (as shown in the figure) or by passing through a dedicated NGLs reboiler, then it is directed to an NGLs processing unit 20.
- the flow of F-HL natural gas liquids is two-phase and can either be sent directly to the NGLs processing unit 20 (as shown in the figure) or be subjected to gas-liquid separation, the evaporated gases being returned to the main separator 16.
- the NGLs 20 treatment unit is a unit which makes it possible to treat heavy NGLs, and in particular to separate the butanes and lighter hydrocarbons from the pentanes and heavier hydrocarbons to form at the outlet a flow of light natural gas liquids FG (also referred to as FG light NGLs stream) and a natural gas gasoline stream.
- FG also referred to as FG light NGLs stream
- this flow of light FG NGLs which mainly comprises ethane, propane and butanes is intended to be reinjected into the gas to be liquefied if this is compatible with the LNG specification targeted (or upgraded outside the liquefaction plant if this is not the case).
- a fraction F-HL-1 of the flow of heavy natural gas liquids F-HL can be directed to an NGLs cooler 19 to provide the thermal power necessary for the operation of this exchanger.
- the stream of FG light natural gas liquids from the NGLs processing unit 20 is cooled in the NGLs cooler 19.
- a fraction FG-1 of the cooled FG light NGLs stream is reinjected into the main separator 16. .
- the fraction of the cooled light NGLs F-G stream which is not reinjected into the main separator 16 is reinjected into the main natural gas stream F-P, downstream of the withdrawal feeding the intermediate temperature turbine 8a (mentioned later).
- the injection of the flow of light F-G NGLs can be carried out either cocurrently or countercurrently.
- the flow of light F-G NGLs is reinjected against the current into the main separator 16
- the latter may optionally be equipped with a packing bed to improve the efficiency of the extraction of the NGLs.
- the flow of natural gas freed from heavy hydrocarbons is at an acceptable temperature to ensure pre-cooling of the gas to be liquefied and of the gas. refrigerant gas.
- this gas residue forms a first flow of natural gas F-1 which passes through the main cryogenic heat exchanger.
- the first flow of natural gas F-1 cools by heat exchange, on the one hand a main flow of natural gas FP flowing countercurrently in the main cryogenic heat exchanger , and on the other hand the initial flow of refrigerant gas G-0 (mentioned later) circulating in countercurrent in the main cryogenic heat exchanger.
- the first flow of natural gas F-1 is at a temperature T2 greater than T1 and close to the temperature of the hot source. It is sent to the compressor 6b driven by the expansion turbine at ambient temperature 6a to be compressed there to a pressure P2, typically between 2 and 4 MPa.
- the natural gas flow passes through a natural gas cooler 21 then is admitted to the suction (ie at the inlet) of the natural gas compressor 12 in order to be further compressed there to a pressure P3 greater than P2 and P0 (and preferably greater than the critical pressure of natural gas) and form at the outlet a second flow of natural gas F-2.
- the pressure P3 may be between 6 and 10 MPa.
- the natural gas flow can be compressed in two successive compression phases between which the natural gas flow can be cooled by a natural gas cooler 22.
- the second natural gas stream F-2 passes through another natural gas cooler 24 and is then separated into two stream fractions: a stream fraction F-2-1 is expanded and mixed with the gas feed stream natural gas F-0 upstream of the expansion turbine at ambient temperature 6a (as described above), and the remaining fraction of this flow forms the main flow of natural gas FP which passes through the main cryogenic heat exchanger 4.
- the expansion of the flow F-2-1 can be done either by means of a simple control valve 23 (as shown in the figure), or by means of an expansion turbine.
- a fraction of this main flow of natural gas FP passes through the main cryogenic heat exchanger in order to be cooled there to a temperature T3 (typically between -140 ° C and -160 ° C) sufficiently low to ensure liquefaction. natural gas.
- T3 typically between -140 ° C and -160 ° C
- Another fraction of the main stream of natural gas F-P is subjected to a second semi-open natural gas cycle.
- the objective of this second cycle is to contribute to the cooling of the refrigerant gas and to contribute to the pre-cooling of the natural gas and its liquefaction.
- the fraction of the main flow of natural gas FP subjected to this second semi-open cycle is extracted from the main cryogenic heat exchanger at a temperature T4 (typically between -10 ° C and -40 ° C) above the temperature T3 to be directed towards the expansion turbine at intermediate temperature 8a in order to lower its temperature by expansion to a temperature T5 (typically between -80 ° C and -110 ° C) lower than the temperature T4 and form a third flow of natural gas F-3.
- a temperature T4 typically between -10 ° C and -40 ° C
- T5 typically between -80 ° C and -110 ° C
- the third stream of natural gas F-3 which may optionally contain a variable fraction of condensed liquid is then reintroduced into the main cryogenic heat exchanger to cool by heat exchange the initial stream of refrigerant gas G-0 and the stream of natural gas.
- main FP passing through the main cryogenic heat exchanger against the current.
- the third flow of natural gas F-3 in gas phase and at a temperature T6 close to the temperature of the hot source is directed to a compressor 8b driven by the expansion turbine at intermediate temperature 8a to be compressed therein. It is then cooled by a natural gas cooler 26 before being mixed with the first flow of natural gas F-1 upstream of the natural gas compressor 12.
- the main flow of natural gas FP is cooled by heat exchange with the first flow of natural gas F-1, the third flow of natural gas F3, and by a first flow of refrigerant gas G-1 (described later) all three flow countercurrently through the main cryogenic heat exchanger 4.
- the main stream of natural gas F-P has thus been cooled to a temperature allowing its liquefaction. This undergoes a Joule-Thomson expansion by passing through a valve 28 until it reaches a pressure close to atmospheric pressure. Alternatively, this expansion could be carried out by means of a liquid expansion turbine to improve its efficiency.
- the expansion of the liquefied natural gas has the effect of generating flash gases which are separated from the liquefied natural gas in the balloon 18 dedicated for this purpose.
- the flow of liquefied natural gas LNG freed from flash gas is sent to the LNG storage tanks.
- the FF flash gases are sent to the main cryogenic heat exchanger to be reheated to a temperature T11 typically between -50 ° C and -110 ° C, then to a flash gas treatment unit, this which reduces the refrigeration power requirements in the cold section of the main cryogenic heat exchanger.
- refrigerant gas here mainly nitrogen
- purpose of which is to provide the additional thermal power to the other two refrigerant cycles and to ensure the sub-cooling of the liquefied natural gas.
- the refrigerant gas compressor 14 delivers an initial flow of refrigerant gas G-0 which, after cooling in a refrigerant gas cooler 32, is at a temperature T7 close to the temperature of the hot source.
- This initial flow of refrigerant gas G-0 is mainly circulated in the main cryogenic heat exchanger 4 to be pre-cooled there by heating the first flow of natural gas F-1, a third flow of natural gas F-3 as well as the first flow of refrigerant gas G-1 mentioned later circulating in countercurrent in the main cryogenic heat exchanger.
- the initial flow of refrigerant gas G-0 is at a temperature T8 (for example between -80 ° C and -110 ° C) which is lower than the temperature T7.
- This flow is directed towards the expansion turbine at low temperature 10a to be further cooled there to a temperature T9 (for example between -140 ° C and -160 ° C) lower than the temperature T8 before being reintroduced into the main cryogenic heat exchanger to form a first refrigerant gas flow G-1.
- the circulation of this first flow of refrigerant gas G-1 in the main cryogenic heat exchanger makes it possible to ensure by heat exchange a cooling of the main flow of natural gas FP and of the initial flow of refrigerant gas G-0 flowing countercurrently through the main cryogenic heat exchanger.
- the first flow of refrigerant gas G-1 is at a temperature T10 greater than T9 and close to the temperature of the hot source. This flow is directed to the compressor 10b driven by the low-temperature expansion turbine 10a to be compressed there before being cooled by a refrigerant gas cooler 34 and then reinjected as suction from the refrigerant gas compressor 14.
- the first refrigerant gas flow G-1 can be compressed in two successive compression phases between which the refrigerant gas flow can be cooled by another refrigerant gas cooler 30.
- the figure 2 illustrates a variant of the liquefaction process according to the invention known as “serial recompression”.
- This variant differs from the embodiment of the figure 1 in that the current at the discharge of the compressor 8b driven by the intermediate temperature expansion turbine 8a is directed to the suction of the compressor 6b driven by the ambient temperature expansion turbine 6a (instead of being directly admitted to the suction of the natural gas compressor 12 as described in the embodiment of the figure 1 ).
- this natural gas stream passes through the natural gas cooler 21 and is then admitted to the suction of the natural gas compressor.
- This variant thus makes it possible to achieve a staged compression of the natural gas which is more efficient than that described in connection with the figure 1 .
- the figure 3 illustrates another variant of the liquefaction process according to the invention known as “complementary pre-cooling by auxiliary refrigerant cycle”.
- This variant differs from the embodiment of the figure 1 in that during the first semi-open refrigerant cycle with natural gas, the natural gas feed stream to the inlet of the ambient temperature expansion turbine 6a is further cooled in an auxiliary heat exchanger 36.
- an auxiliary refrigeration cycle 38 supplies the refrigeration power necessary for the operation of the auxiliary heat exchanger 36.
- This cycle can be for example a cycle with Hydro-Fluoro-Carbon (HFC) or carbon dioxide.
- the temperature in the main separator 16 is lowered, which makes it possible to obtain better recovery of the NGLs.
- the figure 4 illustrates another variant of the liquefaction process according to the invention known as “absorption of NGL by sub-cooled reflux”.
- the third flow of natural gas F-3 at the exhaust of the intermediate expansion turbine 8a is directed to an auxiliary separator 40 at the outlet of which the flow of natural gas is reintroduced into the main cryogenic heat exchanger 4, the flow of natural gas liquids at the outlet of the auxiliary separator 40 being pumped in whole or in part to the main separator 16 to contribute to the absorption of liquids from the natural gas.
- the contact between the natural gas to be treated and the sub-cooled reflux can for example be carried out against the current.
- the main separator can for example be equipped with a packing bed.
- the figure 5 illustrates another variant of the liquefaction process according to the invention known as “absorption of NGL by reflux of LNG”.
- a part FI of the fraction of the main natural gas flow FP which passes through the main cryogenic heat exchanger 4 in order to be cooled there is extracted from said exchanger of main cryogenic heat at a temperature T11 to be directed to the main separator 16 so as to contribute to the absorption of liquids from the natural gas.
- the temperature T11 for extracting the stream F-I is higher than the temperature T3. It is for example between -70 ° C and -110 ° C.
- the contact between the natural gas to be treated and the LNG reflux can for example be carried out against the current.
- the main separator can for example be equipped with a packing bed.
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- Separation By Low-Temperature Treatments (AREA)
Description
La présente invention se rapporte au domaine général de la liquéfaction de gaz naturel à base majoritairement de méthane pour produire du GNL, pour Gaz Naturel Liquéfié, appelé également LNG en anglais (pour « Liquefied Natural Gas »).The present invention relates to the general field of the liquefaction of natural gas based mainly on methane to produce LNG, for Liquefied Natural Gas, also called LNG in English (for “Liquefied Natural Gas”).
Un domaine particulier mais non limitatif d'application de l'invention est celui des installations flottantes de liquéfaction de gaz naturel, appelées FLNG en anglais (pour « Floating Liquefaction of Natural Gas »), qui permettent de réaliser une liquéfaction du gaz naturel offshore, sur un navire ou sur tout autre support flottant en mer.A particular but non-limiting field of application of the invention is that of floating natural gas liquefaction installations, called FLNG in English (for “Floating Liquefaction of Natural Gas”), which allow liquefaction of natural gas offshore, on a ship or on any other floating medium at sea.
Le gaz naturel à base majoritairement de méthane qui est utilisé pour produire du GNL est soit un sous-produit issu des champs pétroliers, c'est-à-dire produit en association avec du pétrole brut, auquel cas il est en quantité faible ou moyenne, soit un produit majeur issu de champs de gaz.The predominantly methane-based natural gas that is used to produce LNG is either a by-product from oil fields, that is to say produced in combination with crude oil, in which case it is in low or medium quantity , or a major product from gas fields.
Lorsque le gaz naturel est associé en faible quantité avec du pétrole brut, il est généralement traité et séparé puis réinjecté dans les puits de pétrole, exporté par pipeline et/ou utilisé sur place, notamment comme carburant pour alimenter des générateurs de puissance électrique, des fours ou des chaudières.When natural gas is combined in small quantities with crude oil, it is generally treated and separated then reinjected into oil wells, exported by pipeline and / or used on site, in particular as fuel to supply electric power generators, ovens or boilers.
Lorsque le gaz naturel est issu de champs de gaz et produit en haute quantité, on cherche à l'inverse à le transporter de manière à pouvoir l'utiliser dans d'autres régions que celles dans laquelle il a été produit. A cet effet, le gaz naturel peut être transporté dans des cuves de navires de transport spécialisés (appelés « méthaniers ») sous forme de liquide cryogénique (à une température de l'ordre de -160°C) et à une pression proche de la pression atmosphérique ambiante.When natural gas comes from gas fields and produced in large quantities, the reverse is true of transporting it so that it can be used in regions other than those in which it was produced. For this purpose, natural gas can be transported in the tanks of specialized transport vessels (called "LNG carriers") in the form of cryogenic liquid (at a temperature of around -160 ° C) and at a pressure close to ambient atmospheric pressure.
La liquéfaction du gaz naturel en vue de son transport s'effectue généralement à proximité du site de production de gaz et nécessite des installations de grande échelle et des quantités d'énergie mécanique considérables pour des capacités de production pouvant atteindre plusieurs millions de tonnes par an. L'énergie mécanique nécessaire au procédé de liquéfaction peut être produite sur le site de l'installation de liquéfaction en utilisant une partie du gaz naturel comme combustible.The liquefaction of natural gas for transport is generally carried out near the gas production site and requires large-scale installations and considerable amounts of mechanical energy for production capacities of up to several million tonnes per year. The mechanical energy required for the liquefaction process can be produced on the site of the liquefaction plant using part of the natural gas as fuel.
Le gaz naturel doit subir un traitement préalablement à sa liquéfaction afin d'en extraire les gaz acides (en particulier le dioxyde de carbone), l'eau (pour éviter qu'elle ne gèle dans l'installation de liquéfaction), le mercure (pour éviter les risques de dégradation des équipements en aluminium de l'installation de liquéfaction) et une partie des liquides du gaz naturel, appelés également NGLs en anglais (pour « Natural Gas Liquids »). Les NGLs comprennent l'ensemble des hydrocarbures plus lourds que le méthane présents dans le gaz naturel et susceptibles d'être condensés. Les NGLs comprennent notamment de l'éthane, des GPLs (propane et butanes) pour Gaz de Pétrole Liquéfié, appelés également LPGs en anglais (pour « Liquefied Petroleum Gas »), des pentanes et des hydrocarbures plus lourds que les pentanes présents dans le gaz naturel. Parmi ces hydrocarbures, il est en particulier critique d'extraire en amont des installations de liquéfaction le benzène, la plus grande partie des pentanes et les autres hydrocarbures plus lourds pour éviter qu'ils ne gèlent dans l'installation de liquéfaction. Par ailleurs, l'extraction de GPL et d'éthane peut être elle aussi nécessaire pour que le GNL satisfasse la spécification commerciale de pouvoir calorifique ou afin d'assurer une production commerciale de ces produits.Natural gas must undergo treatment prior to its liquefaction in order to extract the acid gases (in particular carbon dioxide), water (to prevent it from freezing in the liquefaction installation), mercury ( to avoid the risk of degradation of the aluminum equipment of the liquefaction plant) and part of the natural gas liquids, also called NGLs in English (for “Natural Gas Liquids”). NGLs include all the hydrocarbons heavier than methane present in natural gas and liable to be condensed. The NGLs include in particular ethane, LPGs (propane and butanes) for Liquefied Petroleum Gas, also called LPGs in English (for “Liquefied Petroleum Gas”), pentanes and hydrocarbons heavier than the pentanes present in the gas natural. Among these hydrocarbons, it is in particular critical to extract benzene, most of the pentanes and other heavier hydrocarbons upstream from the liquefaction installations, to prevent them from freezing in the liquefaction installation. In addition, the extraction of LPG and ethane may also be necessary for the LNG to meet the commercial calorific value specification or to ensure commercial production of these products.
L'extraction de NGLs est soit intégrée à l'installation de liquéfaction du gaz naturel, soit effectuée dans une unité dédiée en amont de l'installation de liquéfaction. Dans le premier cas, cette extraction est généralement réalisée à une pression relativement élevée (de l'ordre de 4 à 5 MPa) alors que dans le second cas, elle est la plupart du temps réalisée à une pression plus basse (de l'ordre de 2 à 4 MPa).The extraction of NGLs is either integrated into the natural gas liquefaction installation, or carried out in a dedicated unit upstream of the liquefaction installation. In the first case, this extraction is generally carried out at a relatively high pressure (of the order of 4 to 5 MPa) while in the second case, it is most of the time carried out at a lower pressure (of the order of from 2 to 4 MPa).
Une extraction de NGLs intégrée à la liquéfaction du gaz naturel comme décrite par exemple dans la publication
Par ailleurs, à une pression de l'ordre de 4 à 5 MPa, les densités du liquide et du gaz naturel sont relativement proches, ce qui rend la conception et l'opération de ballons séparateurs et de colonnes à distiller délicate (en particulier dans le cadre d'une application sur un support flottant).Moreover, at a pressure of the order of 4 to 5 MPa, the densities of the liquid and of the natural gas are relatively close, which makes the design and operation of separator flasks and distillation columns difficult (particularly in as part of an application on a floating medium).
Une extraction de NGLs à une pression de l'ordre de 2 à 4 MPa en amont de l'installation de liquéfaction dans une unité dédiée comme décrite par exemple dans la publication
Aussi, la façon dont les NGLs sont extraits a un impact significatif sur le coût et le degré de complexité de l'usine de liquéfaction, sur les performances de la liquéfaction et sur l'efficacité énergétique de l'usine de liquéfaction dans son ensemble.Also, the way in which NGLs are extracted has a significant impact on the cost and degree of complexity of the liquefaction plant, on the performance of the liquefaction and on the energy efficiency of the liquefaction plant as a whole.
Différents procédés de liquéfaction du gaz naturel ont été développés afin d'optimiser leur rendement énergétique global. Dans leur principe, ces procédés de liquéfaction reposent typiquement sur une réfrigération mécanique du gaz naturel obtenue grâce à un ou plusieurs cycles thermodynamiques de réfrigération fournissant la puissance thermique nécessaire au refroidissement et à la liquéfaction du gaz naturel. Dans chaque cycle thermodynamique mis en œuvre par ces procédés, le réfrigérant comprimé (sous forme de gaz) est refroidi (et éventuellement condensé) par une source thermique ayant une température supérieure à celle du fluide réfrigéré et appelée « source chaude » (eau, air, autre cycle de réfrigération) puis davantage refroidi par un flux de gaz froid généré par le cycle thermodynamique lui-même avant d'être détendu. Le flux de réfrigérant froid à basse température résultant de cette détente est utilisé pour refroidir le gaz naturel et pré-refroidir le réfrigérant. Le réfrigérant gazeux à basse pression est à nouveau comprimé à son niveau de pression initial (par l'intermédiaire de compresseurs entraînés par des turbines à gaz, des turbines à vapeur ou des moteurs électriques).Different natural gas liquefaction processes have been developed in order to optimize their overall energy efficiency. In principle, these liquefaction processes are typically based on mechanical refrigeration of natural gas obtained by means of one or more thermodynamic refrigeration cycles providing the thermal power necessary for cooling and liquefaction of natural gas. In each thermodynamic cycle implemented by these processes, the compressed refrigerant (in the form of gas) is cooled (and possibly condensed) by a thermal source having a temperature higher than that of the refrigerated fluid and called "hot source" (water, air). , another refrigeration cycle) then further cooled by a flow of cold gas generated by the thermodynamic cycle itself before being relaxed. The low temperature cold refrigerant stream resulting from this expansion is used to cool the natural gas and pre-cool the refrigerant. The low-pressure gaseous refrigerant is again compressed to its original pressure level (via compressors driven by gas turbines, steam turbines or electric motors).
Au cours de ces cycles thermodynamiques de réfrigération, la puissance nécessaire à la réfrigération et la liquéfaction du gaz naturel peut être fournie soit par la vaporisation et l'échauffement d'un réfrigérant liquide, l'essentiel de la chaleur de réfrigération étant produite par la chaleur latente mise en jeu lors du changement d'état, soit par l'échauffement d'un réfrigérant froid sous forme de gaz. Dans le cas d'un gaz réfrigérant, la température du réfrigérant est typiquement abaissée par détente de pression au travers d'une turbine de détente (en anglais « gas expander »). L'effet de refroidissement produit par le réfrigérant se présente majoritairement sous la forme d'une chaleur sensible.During these thermodynamic refrigeration cycles, the power required for the refrigeration and liquefaction of natural gas can be supplied either by the vaporization and heating of a liquid refrigerant, most of the refrigeration heat being produced by the latent heat brought into play during the change of state, either by the heating of a cold refrigerant in the form of gas. In the case of a refrigerant gas, the temperature of the refrigerant is typically lowered by pressure reduction through an expansion turbine (in English "gas expander"). The cooling effect produced by the refrigerant is mainly in the form of sensible heat.
Dans le cas d'un réfrigérant liquide, la température du réfrigérant est généralement abaissée par détente au travers d'une vanne et/ou d'une turbine de détente liquide (en anglais « liquid expander »). L'effet de refroidissement produit par le réfrigérant se présente principalement sous la forme d'une chaleur latente (et, dans une moindre mesure, sous la forme d'une chaleur sensible). Comme la chaleur latente est bien plus élevée que la chaleur sensible, les débits de réfrigérant qui sont nécessaires pour obtenir une même puissance de réfrigération sont plus élevés pour les cycles thermodynamiques recourant à un réfrigérant sous forme de gaz que pour les cycles thermodynamiques recourant à un réfrigérant sous forme de liquide.In the case of a liquid refrigerant, the temperature of the refrigerant is generally lowered by expansion through a valve and / or a liquid expansion turbine (in English "liquid expander"). The cooling effect produced by the refrigerant is mainly in the form of latent heat (and, to a lesser extent, in the form of sensible heat). As the latent heat is much higher than the sensible heat, the refrigerant flow rates which are necessary to obtain the same refrigeration capacity are higher for thermodynamic cycles using a refrigerant in the form of gas than for thermodynamic cycles using a gas. refrigerant in liquid form.
Aussi, pour une même capacité de liquéfaction, les cycles thermodynamiques de réfrigération utilisant comme réfrigérant un gaz nécessitent des compresseurs de réfrigération de plus haute capacité et des conduites de diamètre plus élevés que pour les cycles thermodynamiques de réfrigération utilisant comme réfrigérant un liquide. Les cycles thermodynamiques à réfrigérant gazeux sont également généralement moins efficaces que les cycles thermodynamiques à réfrigérant liquide, notamment parce que l'écart de température entre le fluide subissant la réfrigération et le fluide réfrigérant est en moyenne plus élevé pour un cycle à réfrigérant gazeux ce qui contribue à accroitre les pertes d'efficacité par irréversibilité.Also, for the same liquefaction capacity, thermodynamic refrigeration cycles using a gas as refrigerant require higher capacity refrigeration compressors and larger diameter pipes than for thermodynamic refrigeration cycles using a liquid as refrigerant. Gaseous refrigerant thermodynamic cycles are also generally less efficient than liquid refrigerant thermodynamic cycles, in particular because the temperature difference between the fluid undergoing refrigeration and the refrigerant is on average greater. high for a gaseous refrigerant cycle, which contributes to increasing the efficiency losses by irreversibility.
D'un autre côté, les cycles thermodynamiques de réfrigération à réfrigérant liquide mettent en œuvre des inventaires massiques de réfrigérant plus élevés que les cycles thermodynamiques à réfrigérant gazeux. Lorsque les fluides réfrigérant utilisés sont inflammables ou toxiques, les cycles thermodynamiques à réfrigérant liquide ont un niveau de sécurité intrinsèque plus faible que les procédés à réfrigérant gazeux, en particulier si l'on compare des cycles thermodynamiques à réfrigérant liquide utilisant des hydrocarbures comme réfrigérant avec des cycles thermodynamiques qui utilisent comme réfrigérant un gaz inerte comme l'azote. Ce point est particulièrement critique dans un environnement où de nombreux équipements sont concentrés dans un espace restreint et notamment sur une installation offshore. Les cycles thermodynamiques de réfrigération utilisant des réfrigérants liquides sont ainsi efficaces mais présentent un certain nombre d'inconvénients, en particulier pour une application offshore sur un support flottant.On the other hand, thermodynamic cycles of refrigeration with liquid refrigerant implement mass refrigerant inventories higher than thermodynamic cycles with gaseous refrigerant. When the refrigerant fluids used are flammable or toxic, thermodynamic cycles with liquid refrigerant have a lower level of intrinsic safety than processes with gaseous refrigerant, in particular when comparing thermodynamic cycles with liquid refrigerant using hydrocarbons as refrigerant with thermodynamic cycles which use an inert gas such as nitrogen as refrigerant. This point is particularly critical in an environment where a great deal of equipment is concentrated in a small space and in particular on an offshore installation. Thermodynamic refrigeration cycles using liquid refrigerants are thus efficient but present a certain number of drawbacks, in particular for an offshore application on a floating support.
Différents procédés de liquéfaction utilisant des cycles thermodynamiques de réfrigération à réfrigérant gazeux ont été proposés. On connaît par exemple des documents
De tels procédés de liquéfaction à détente d'azote présentent des avantages certains en termes de simplicité, de sécurité intrinsèque et de robustesse qui les rendent particulièrement appropriés à une application sur un support flottant offshore. Néanmoins, ces procédés sont également peu efficaces. Ainsi un procédé utilisant des réfrigérants liquides produit typiquement de l'ordre de 30% de GNL de plus qu'un procédé à double détente d'azote (à puissance mécanique dépensée équivalente).Such nitrogen expansion liquefaction processes have certain advantages in terms of simplicity, intrinsic safety and robustness which make them particularly suitable for application on an offshore floating support. However, these methods are also inefficient. Thus, a process using liquid refrigerants typically produces around 30% more LNG than a process with double nitrogen expansion (at equivalent mechanical power expended).
On connaît par ailleurs des documents
On connait enfin des documents
La présente invention a donc pour but principal de pallier de tels inconvénients en proposant un procédé de liquéfaction utilisant des cycles thermodynamiques à réfrigérant gazeux et ayant une efficacité plus élevée que les procédés de liquéfaction de l'art antérieur tout en proposant une méthode simple et compacte d'extraction d'éventuels NGLs, qui soit intégrée au procédé de liquéfaction et qui offre une meilleure optimisation énergétique globale que les procédés de l'art antérieur.The main aim of the present invention is therefore to overcome such drawbacks by proposing a liquefaction process using thermodynamic cycles with gaseous refrigerant and having a higher efficiency than the liquefaction processes of the prior art while proposing a simple and compact method. extraction of any NGLs, which is integrated into the liquefaction process and which offers better overall energy optimization than the processes of the prior art.
Conformément à l'invention, ce but est atteint grâce à un procédé de liquéfaction d'un gaz naturel selon la revendication 1 comprenant un mélange d'hydrocarbures dont majoritairement du méthane, le procédé comprenant :
- a) un premier cycle semi-ouvert au gaz naturel dans lequel, successivement :
- un flux d'alimentation de gaz naturel à une pression P0 préalablement traité pour en extraire les gaz acides, l'eau et le mercure est mélangé à un flux de gaz naturel, détendu à une pression P1 et sa température abaissée à une température T1 au moyen d'une turbine de détente à température ambiante de sorte à obtenir une condensation d'éventuels liquides du gaz naturel contenus dans le gaz naturel,
- les éventuels liquides du gaz naturel qui ont été condensés sont séparés dans un séparateur principal du flux d'alimentation de gaz naturel, ce dernier traversant alors un échangeur de chaleur cryogénique principal pour former un premier flux de gaz naturel contribuant par échange thermique, d'une part au pré-refroidissement d'un flux principal de gaz naturel circulant à contre-courant au travers de l'échangeur de chaleur cryogénique principal, et d'autre part, au refroidissement d'un flux initial de gaz réfrigérant circulant à contre-courant dans l'échangeur de chaleur cryogénique principal,
- en sortie de l'échangeur de chaleur cryogénique principal, le premier flux de gaz naturel qui est à une température T2 supérieure à T1 et voisine de la température d'une source chaude est comprimé à une pression P2 au moyen d'un compresseur entraîné par la turbine de détente à température ambiante avant d'être admis à l'aspiration d'un compresseur de gaz naturel pour y être davantage comprimé à une pression P3 supérieure à P2 et former un deuxième flux de gaz naturel,
- le deuxième flux de gaz naturel au refoulement du compresseur de gaz naturel est pour partie détendu et mélangé au flux d'alimentation de gaz naturel en amont de la turbine de détente à température ambiante, et pour partie forme le flux principal de gaz naturel,
- une fraction de ce flux principal de gaz naturel traverse l'échangeur de chaleur cryogénique principal afin d'y être refroidi jusqu'à une température T3 suffisamment basse pour permettre la liquéfaction du gaz naturel ;
- b) un second cycle réfrigérant semi-ouvert au gaz naturel dans lequel, successivement :
- une autre fraction du flux principal de gaz naturel est extraite de l'échangeur de chaleur cryogénique principal à une température T4 supérieure à T3 pour être dirigée vers une turbine de détente intermédiaire afin que sa température soit abaissée par détente jusqu'à une température T5 inférieure à T4 et former un troisième flux de gaz naturel,
- le troisième flux de gaz naturel est réintroduit dans l'échangeur de chaleur cryogénique principal pour refroidir par échange thermique le flux de gaz naturel principal et le flux initial de gaz réfrigérant circulant à contre-courant dans l'échangeur de chaleur cryogénique principal,
- en sortie de l'échangeur de chaleur cryogénique principal, le troisième flux de gaz naturel qui est à une température T6 voisine de la température de la source chaude est dirigé vers un compresseur entraîné par la turbine de détente intermédiaire pour y être comprimé puis il est refroidi avant d'être mélangé au premier flux de gaz naturel en amont du compresseur de gaz naturel;
- c) un cycle réfrigérant fermé au gaz réfrigérant dans lequel, successivement :
- un flux initial de gaz réfrigérant avec une température T7 voisine de la température de la source chaude et préalablement comprimé par un compresseur de gaz réfrigérant est circulé dans l'échangeur de chaleur cryogénique principal pour y être pré-refroidi,
- à la sortie de l'échangeur de chaleur cryogénique principal, le flux initial de gaz réfrigérant qui est à une température T8 inférieure à T7 est dirigé vers une turbine de détente à basse température afin que sa température soit abaissée par détente jusqu'à une température T9 inférieure à T8, le premier flux de gaz réfrigérant ainsi formé étant réintroduit dans l'échangeur de chaleur cryogénique principal pour contribuer au refroidissement du flux principal de gaz naturel et du flux initial de gaz réfrigérant ;
- à la sortie de l'échangeur de chaleur cryogénique principal, le premier flux de gaz réfrigérant qui est à une température T10 voisine de la température de la source chaude est dirigé vers un compresseur entraîné par la turbine de détente à basse température pour y être comprimé avant d'être refroidi puis dirigé vers l'aspiration du compresseur de gaz réfrigérant.
- a) a first semi-open natural gas cycle in which, successively:
- a natural gas feed stream at a pressure P0 previously treated to extract the acid gases, water and mercury therefrom is mixed with a natural gas stream, expanded to a pressure P1 and its temperature lowered to a temperature T1 at means of an expansion turbine at room temperature so as to obtain condensation of any natural gas liquids contained in the natural gas,
- any natural gas liquids which have been condensed are separated in a main separator from the natural gas feed stream, the latter then passing through a main cryogenic heat exchanger to form a first natural gas stream contributing by heat exchange, of on the one hand to the pre-cooling of a main flow of natural gas circulating in counter-current through the main cryogenic heat exchanger, and on the other hand, to the cooling of an initial flow of refrigerant gas flowing against current in the main cryogenic heat exchanger,
- at the outlet of the main cryogenic heat exchanger, the first flow of natural gas which is at a temperature T2 greater than T1 and close to the temperature of a hot source is compressed to a pressure P2 by means of a compressor driven by the expansion turbine at ambient temperature before being admitted to the intake of a natural gas compressor in order to be further compressed there to a pressure P3 greater than P2 and to form a second flow of natural gas,
- the second natural gas flow at the discharge from the natural gas compressor is partly expanded and mixed with the natural gas feed stream upstream of the expansion turbine at ambient temperature, and partly forms the main natural gas stream,
- a fraction of this main flow of natural gas passes through the main cryogenic heat exchanger in order to be cooled there to a temperature T3 sufficiently low to allow liquefaction of the natural gas;
- b) a second semi-open refrigerant cycle with natural gas in which, successively:
- another fraction of the main flow of natural gas is extracted from the main cryogenic heat exchanger at a temperature T4 higher than T3 to be directed to an intermediate expansion turbine so that its temperature is lowered by expansion to a lower temperature T5 at T4 and form a third flow of natural gas,
- the third natural gas stream is reintroduced into the main cryogenic heat exchanger to cool by heat exchange the main natural gas stream and the initial gas stream refrigerant circulating in counter-current in the main cryogenic heat exchanger,
- at the outlet of the main cryogenic heat exchanger, the third flow of natural gas which is at a temperature T6 close to the temperature of the hot source is directed towards a compressor driven by the intermediate expansion turbine to be compressed therein, then it is cooled before being mixed with the first flow of natural gas upstream of the natural gas compressor;
- c) a refrigerant cycle closed to refrigerant gas in which, successively:
- an initial flow of refrigerant gas with a temperature T7 close to the temperature of the hot source and previously compressed by a refrigerant gas compressor is circulated in the main cryogenic heat exchanger to be pre-cooled there,
- at the outlet of the main cryogenic heat exchanger, the initial flow of refrigerant gas which is at a temperature T8 lower than T7 is directed to an expansion turbine at low temperature so that its temperature is lowered by expansion to a temperature T9 less than T8, the first flow of refrigerant gas thus formed being reintroduced into the main cryogenic heat exchanger to help cool the main flow of natural gas and the initial flow of refrigerant gas;
- at the outlet of the main cryogenic heat exchanger, the first flow of refrigerant gas which is at a temperature T10 close to the temperature of the hot source is directed to a compressor driven by the expansion turbine at low temperature to be compressed there before being cooled and then directed to the suction of the refrigerant gas compressor.
Le procédé de liquéfaction selon l'invention comprend deux cycles réfrigérant semi-ouverts au gaz naturel et un unique cycle réfrigérant fermé au gaz réfrigérant. Le premier cycle réfrigérant semi-ouvert au gaz naturel a pour fonction d'extraire les liquides du gaz naturel (NGLs) lourds éventuellement présents dans le gaz naturel pour éviter les problèmes de gel dans la section froide de l'installation de liquéfaction, et de pré-refroidir le gaz naturel et le gaz réfrigérant. Le second cycle réfrigérant semi-ouvert au gaz naturel a pour fonction de contribuer au pré-refroidissement du gaz naturel et du gaz réfrigérant ainsi qu'à la liquéfaction du gaz naturel. Le cycle réfrigérant fermé au gaz réfrigérant a pour fonction d'assurer le sous-refroidissement du gaz naturel liquéfié et de fournir une puissance de réfrigération complémentaire aux deux autres cycles. Le gaz réfrigérant utilisé est typiquement de l'azote.The liquefaction process according to the invention comprises two semi-open refrigerant cycles with natural gas and a single refrigerant cycle closed with refrigerant gas. The function of the first semi-open refrigerant cycle using natural gas is to extract the heavy natural gas liquids (NGLs) that may be present in the natural gas to avoid freezing problems in the cold section of the liquefaction plant, and to pre-cool natural gas and refrigerant gas. The function of the second semi-open refrigerant cycle using natural gas is to contribute to pre-cooling of natural gas and refrigerant gas as well as for the liquefaction of natural gas. The function of the refrigerant cycle closed to refrigerant gas is to sub-cool the liquefied natural gas and to supply additional refrigeration power to the other two cycles. The refrigerant gas used is typically nitrogen.
Il a été calculé que le procédé selon l'invention présente un rapport de puissance mécanique consommée par tonne de GNL produit pour des conditions équivalentes de l'ordre de 15% plus faible qu'un procédé à deux cycles réfrigérant à l'azote, 10% plus faible qu'un procédé à trois cycles réfrigérant à l'azote, et 8% plus faible qu'un procédé à un cycle réfrigérant au gaz naturel et deux cycles réfrigérant à l'azote lorsque ces procédés sont associés à une unité d'extraction de NGL en amont de la liquéfaction nécessitant une re-compression du gaz (cette puissance de re-compression étant prise en compte dans la comparaison). La puissance consommée par tonne de GNL produit par le procédé selon l'invention est ainsi plus basse que pour les procédés connus de l'art antérieur, ce qui montre une efficacité plus élevée pour ce procédé.It has been calculated that the process according to the invention exhibits a ratio of mechanical power consumed per tonne of LNG produced for equivalent conditions of the order of 15% lower than a process with two refrigerant cycles using nitrogen, 10 % lower than a three-cycle nitrogen refrigerant process, and 8% lower than a one-cycle natural gas refrigerant and two nitrogen refrigerant cycle process when these processes are combined with a unit of extraction of NGL upstream of the liquefaction requiring recompression of the gas (this recompression power being taken into account in the comparison). The power consumed per tonne of LNG produced by the process according to the invention is thus lower than for the processes known from the prior art, which shows a higher efficiency for this process.
Le procédé selon l'invention intègre à la liquéfaction l'extraction des liquides du gaz naturel (NGLs) lourds, ce qui améliore l'efficacité énergétique globale de l'usine de liquéfaction de gaz naturel et permet de se dispenser de recourir à des installations dédiées à cette extraction. Le procédé de prétraitement du gaz naturel s'en trouve simplifié. De plus, l'extraction étant réalisée à basse pression, peu d'hydrocarbures légers (en particulier le méthane) sont entraînées au cours de ce processus d'extraction, ce qui permet de traiter les NGLs lourds en utilisant un procédé simple de mise en œuvre.The process according to the invention integrates the liquefaction with the extraction of heavy natural gas liquids (NGLs), which improves the overall energy efficiency of the natural gas liquefaction plant and eliminates the need to resort to installations. dedicated to this extraction. This simplifies the natural gas pretreatment process. In addition, the extraction being carried out at low pressure, few light hydrocarbons (in particular methane) are entrained during this extraction process, which makes it possible to treat the heavy NGLs using a simple process of placing. artwork.
L'unique cycle au gaz réfrigérant du procédé selon l'invention est fermé. Aussi, le seul appoint en gaz réfrigérant qui soit nécessaire peut être facilement produit (en l'occurrence lorsque le gaz réfrigérant comprend majoritairement de l'azote). En particulier, aucune unité dédiée n'est requise pour l'importation, la production, le traitement ou le stockage d'hydrocarbures liquides utilisés comme réfrigérant. L'implantation du procédé selon l'invention s'en trouve ainsi grandement facilitée.The single refrigerant gas cycle of the process according to the invention is closed. Also, the only additional refrigerant gas that is necessary can be easily produced (in this case when the refrigerant gas mainly comprises nitrogen). In particular, no dedicated unit is required for the import, production, treatment or storage of liquid hydrocarbons used as refrigerant. The implementation of the method according to the invention is thus greatly facilitated.
Le procédé selon l'invention présente un niveau élevé de sécurité intrinsèque. En effet, les inventaires massiques d'hydrocarbures sont limités (en particulier par rapport à un procédé utilisant des hydrocarbures sous forme liquide comme réfrigérant). L'implantation du procédé selon l'invention s'en trouve facilitée.The method according to the invention has a high level of intrinsic safety. Indeed, the mass inventories of hydrocarbons are limited (in particular compared to a process using hydrocarbons in liquid form as refrigerant). The implementation of the method according to the invention is thereby facilitated.
Enfin, le procédé est particulièrement approprié à une installation de liquéfaction du gaz naturel en mer, telle que par exemple à bord d'un FLNG, en raison de son haut niveau de sécurité intrinsèque et du fait qu'il ne requiert pas de stockage de réfrigérants.Finally, the process is particularly suitable for an installation for the liquefaction of natural gas at sea, such as for example on board an FLNG, because of its high level of intrinsic safety and the fact that it does not require storage of gas. refrigerants.
Selon une variante dite de « recompression en série », au cours du second cycle réfrigérant semi-ouvert au gaz naturel, le flux de gaz naturel en sortie du compresseur entraîné par la turbine de détente intermédiaire est refroidi puis mélangé au premier flux de gaz naturel avant d'être dirigé vers l'entrée du compresseur entraîné par la turbine de détente à température ambiante. Cette variante permet de réaliser une compression étagée du gaz naturel de sorte à rendre cette dernière plus efficace.According to a variant known as "series recompression", during the second refrigerant cycle semi-open to natural gas, the flow of natural gas leaving the compressor driven by the intermediate expansion turbine is cooled and then mixed with the first flow of natural gas before being directed to the inlet of the compressor driven by the expansion turbine at room temperature. This variant makes it possible to achieve staged compression of the natural gas so as to make the latter more efficient.
Selon une variante dite à « pré-refroidissement complémentaire par cycle réfrigérant auxiliaire », au cours du premier cycle réfrigérant semi-ouvert au gaz naturel, le flux d'alimentation de gaz naturel à l'admission de la turbine de détente à température ambiante est davantage refroidi dans un échangeur de chaleur auxiliaire. Dans cette variante, un cycle de réfrigération auxiliaire fournit la puissance de réfrigération nécessaire au fonctionnement de l'échangeur de chaleur auxiliaire. Il résulte de cet arrangement que la température dans le séparateur principal est abaissée, ce qui permet d'obtenir une meilleure récupération des NGLs.According to a variant known as "complementary pre-cooling by auxiliary refrigerant cycle", during the first semi-open refrigerant cycle to natural gas, the flow of natural gas feed to the inlet of the expansion turbine at ambient temperature is further cooled in an auxiliary heat exchanger. In this variant, an auxiliary refrigeration cycle provides the refrigeration power necessary for the operation of the auxiliary heat exchanger. As a result of this arrangement, the temperature in the main separator is lowered, which makes it possible to obtain better recovery of the NGLs.
Selon une variante dite à « absorption de NGL par reflux sous-refroidi », au cours du second cycle réfrigérant semi-ouvert au gaz naturel, le troisième flux de gaz naturel à l'échappement de la turbine de détente intermédiaire est dirigé vers un séparateur auxiliaire à la sortie duquel le flux de gaz naturel est réintroduit dans l'échangeur de chaleur cryogénique principal, le flux de liquides du gaz naturel à la sortie du séparateur auxiliaire étant pompé en totalité ou en partie vers le séparateur principal pour contribuer à l'absorption de liquides du gaz naturel. Le contact entre le gaz naturel à traiter et le reflux sous-refroidi peut par exemple être réalisé à contre-courant. A cet effet, le séparateur principal peut être équipé d'un lit de garnissage. Avec cette variante, il est possible de traiter facilement des gaz légers avec une haute teneur en composés aromatiques (par exemple le benzène) ou d'extraire des GPLs avec un taux de récupération élevé (par exemple pour assurer une production industrielle de GPLs).According to a variant known as "absorption of NGL by sub-cooled reflux", during the second refrigerant cycle semi-open to natural gas, the third flow of natural gas to the exhaust of the intermediate expansion turbine is directed to a separator auxiliary at the outlet of which the flow of natural gas is reintroduced into the main cryogenic heat exchanger, the flow of natural gas liquids at the outlet of the auxiliary separator being pumped in whole or in part to the main separator to contribute to the absorption of natural gas liquids. The contact between the natural gas to be treated and the sub-cooled reflux can for example be carried out against the current. For this purpose, the main separator can be equipped with a packing bed. With this variant it is possible to easily process light gases with a high content of aromatic compounds (eg benzene) or extract LPGs with a high recovery rate (eg to ensure industrial production of LPGs).
Selon une variante dite à « absorption de NGL par reflux de GNL », au cours du premier cycle réfrigérant semi-ouvert au gaz naturel, une partie de la fraction de flux principal de gaz naturel qui traverse l'échangeur de chaleur cryogénique principal afin d'y être refroidi est extraite dudit échangeur de chaleur cryogénique principal à une température T11 supérieure à la température T3 pour être dirigée vers le séparateur principal de façon à contribuer à l'absorption de liquides du gaz naturel. Le contact entre le gaz naturel à traiter et le reflux de GNL peut par exemple être réalisé à contre-courant. A cet effet, le séparateur principal peut être équipé d'un lit de garnissage. Avec cette variante, il est possible de traiter des gaz légers avec une teneur en composés aromatiques (par exemple benzène) ou d'extraire notamment des GPLs avec un taux de récupération élevé et de l'éthane.According to a variant known as “absorption of NGL by LNG reflux”, during the first semi-open refrigerant cycle with natural gas, part of the fraction of the main flow of natural gas which passes through the main cryogenic heat exchanger in order to to be cooled there is extracted from said main cryogenic heat exchanger at a temperature T11 above the temperature T3 to be directed to the main separator so as to contribute to the absorption of liquids from the natural gas. The contact between the natural gas to be treated and the LNG reflux can for example be carried out against the current. For this purpose, the main separator can be equipped with a packing bed. With this variant, it is possible to treat light gases with a content of aromatic compounds (for example benzene) or to extract in particular LPGs with a high recovery rate and ethane.
Au cours du premier cycle réfrigérant semi-ouvert au gaz naturel, le flux d'alimentation de gaz naturel est avantageusement mélangé avec du gaz naturel plus léger provenant du refoulement du compresseur de gaz naturel avant d'être détendu dans la turbine à température ambiante sans pré-refroidissement dans l'échangeur cryogénique principal, ce qui permet de produire de manière efficace un flux froid assurant le pré-refroidissement du gaz naturel et du gaz réfrigérant et d'extraire d'éventuels NGLs avec une excellente sélectivité.During the first semi-open refrigerant cycle with natural gas, the natural gas feed stream is advantageously mixed with lighter natural gas coming from the discharge of the natural gas compressor before being expanded in the turbine to room temperature without pre-cooling in the main cryogenic exchanger, which makes it possible to efficiently produce a cold flow ensuring the pre-cooling of the natural gas and the refrigerant gas and to extract any NGLs with excellent selectivity.
Au cours du premier cycle réfrigérant semi-ouvert au gaz naturel, le flux d'alimentation de gaz naturel à l'échappement de la turbine de détente à température ambiante est introduit dans le séparateur principal à la sortie duquel un flux de liquides de gaz lourds est récupéré. Dans ce cas, une fraction du flux de liquides du gaz naturel récupéré est réchauffée et partiellement vaporisée en vue de faciliter son traitement en aval.During the first semi-open refrigerant cycle with natural gas, the natural gas feed stream to the exhaust of the expansion turbine at room temperature is introduced into the main separator at the outlet of which a stream of heavy gas liquids is recovered. In this case, a fraction of the liquid stream of the recovered natural gas is reheated and partially vaporized in order to facilitate its downstream processing.
Selon une disposition avantageuse, la pression du flux de gaz naturel principal est supérieure à la pression critique du gaz naturel, ce qui permet de maximiser l'efficacité de la liquéfaction et assure que la liquéfaction se fasse sans changement de phase.According to an advantageous arrangement, the pressure of the main natural gas stream is greater than the critical pressure of natural gas, which makes it possible to maximize the efficiency of the liquefaction and ensures that the liquefaction takes place without a phase change.
L'invention a également pour objet une installation de liquéfaction de gaz naturel selon la revendication 14 pour la mise en œuvre du procédé tel que défini précédemment, l'installation comprenant une turbine de détente à température ambiante destinée à recevoir un flux d'alimentation de gaz naturel ainsi qu'une partie d'un deuxième flux de gaz naturel provenant du refoulement d'un compresseur de gaz naturel et ayant un échappement relié à une entrée d'un séparateur principal, un échangeur de chaleur cryogénique principal destiné à recevoir les flux de gaz naturels et de gaz réfrigérant, un compresseur entraîné par la turbine de détente à température ambiante destiné à recevoir un premier flux de gaz naturel issu du séparateur principal et ayant une sortie reliée à l'aspiration du compresseur de gaz naturel, une turbine de détente à température intermédiaire destinée à recevoir une partie d'un flux principal de gaz naturel provenant du refoulement du compresseur de gaz naturel et reliée en entrée et en sortie à l'échangeur de chaleur cryogénique principal, un compresseur entraîné par la turbine de détente à température intermédiaire destiné à recevoir un troisième flux de gaz naturel issu de l'échangeur de chaleur cryogénique principal, une turbine de détente à basse température pour du gaz réfrigérant reliée en entrée et en sortie à l'échangeur de chaleur cryogénique principal, et un compresseur entraîné par la turbine de détente à basse température et ayant une sortie reliée à l'aspiration d'un compresseur de gaz réfrigérant.The subject of the invention is also a natural gas liquefaction installation according to claim 14 for implementing the method as defined above, the installation comprising an expansion turbine at ambient temperature intended to receive a feed stream of natural gas as well as part of a second natural gas stream coming from the discharge of a natural gas compressor and having an exhaust connected to an inlet of a main separator, a main cryogenic heat exchanger intended to receive the streams of natural gas and refrigerant gas, a compressor driven by the expansion turbine at ambient temperature intended to receive a first flow of natural gas coming from the main separator and having an outlet connected to the suction of the natural gas compressor, a turbine of intermediate temperature expansion designed to receive part of a main flow of natural gas coming from the discharge of the natural gas compressor and connected e at the inlet and outlet to the main cryogenic heat exchanger, a compressor driven by the expansion turbine at intermediate temperature intended to receive a third flow of natural gas coming from the main cryogenic heat exchanger, an expansion turbine at low temperature for refrigerant gas connected at the inlet and at the outlet to the main cryogenic heat exchanger, and a compressor driven by the low temperature expansion turbine and having an outlet connected to the suction of a refrigerant gas compressor.
De préférence, le compresseur de gaz naturel et le compresseur de gaz réfrigérant sont entraînés par une même machine d'entraînement fournissant la puissance nécessaire à l'augmentation de pression du gaz naturel à liquéfier ainsi qu'à la compression des fluides circulants dans les trois cycles réfrigérants. La consommation de puissance mécanique nécessaire pour ces fonctions est ainsi optimisée de manière à maximiser la production de GNL tout en minimisant le nombre d'équipements.Preferably, the natural gas compressor and the refrigerant gas compressor are driven by the same drive machine providing the power necessary for increasing the pressure of the natural gas to be liquefied as well as for compressing the fluids circulating in the three cooling cycles. The mechanical power consumption required for these functions is thus optimized so as to maximize LNG production while minimizing the number of equipment.
De préférence également, le compresseur de gaz naturel est en aval des compresseurs entrainés par la turbine de détente à température ambiante et la turbine de détente à température intermédiaire, et le compresseur de gaz réfrigérant est en aval du compresseur entrainé par la turbine de détente à basse température.Also preferably, the natural gas compressor is downstream of the compressors driven by the expansion turbine at ambient temperature and the expansion turbine at intermediate temperature, and the refrigerant gas compressor is downstream of the compressor driven by the expansion turbine at ambient temperature. low temperature.
D'autres caractéristiques et avantages de la présente invention ressortiront de la description faite ci-dessous, en référence aux dessins annexés qui en illustrent des exemples de réalisation dépourvus de tout caractère limitatif. Sur les figures :
- la
figure 1 représente de façon schématique un exemple de mise en œuvre du procédé de liquéfaction selon l'invention ; - la
figure 2 représente une variante de mise en œuvre du procédé de liquéfaction selon l'invention dite de « recompression en série » ; - la
figure 3 représente une autre variante de mise en œuvre du procédé de liquéfaction selon l'invention dite à « pré-refroidissement complémentaire par cycle réfrigérant auxiliaire » ; - la
figure 4 représente une autre variante de mise en œuvre du procédé de liquéfaction selon l'invention dite à « absorption de NGL par reflux sous-refroidi » ; et - la
figure 5 représente une autre variante de mise en œuvre du procédé de liquéfaction selon l'invention dite à « absorption de NGL par reflux de GNL ».
- the
figure 1 schematically represents an example of implementation of the liquefaction process according to the invention; - the
figure 2 represents an implementation variant of the liquefaction process according to the invention known as “series recompression”; - the
figure 3 shows another variant of the implementation of the liquefaction process according to the invention, known as “complementary pre-cooling by an auxiliary refrigerant cycle”; - the
figure 4 represents another variant of implementation of the liquefaction process according to the invention known as “absorption of NGL by sub-cooled reflux”; and - the
figure 5 represents another variant implementation of the liquefaction process according to the invention known as “absorption of NGL by reflux of LNG”.
Le procédé de liquéfaction selon l'invention s'applique notamment (mais pas exclusivement) au gaz naturel provenant de champs de gaz. Typiquement, ce gaz naturel comprend majoritairement du méthane et se trouve en combinaison avec d'autres gaz, principalement des hydrocarbures en C2, C3, C4, C5, C6, des gaz acides, de l'eau, et des gaz inertes dont l'azote, ainsi que diverses impuretés dont le mercure.The liquefaction process according to the invention applies in particular (but not exclusively) to natural gas coming from gas fields. Typically, this natural gas mainly comprises methane and is found in combination with other gases, mainly C2, C3, C4, C5, C6 hydrocarbons, acid gases, water, and inert gases including nitrogen, as well as various impurities including mercury.
La
En substance, le procédé de liquéfaction selon l'invention recourt à trois cycles thermodynamiques de réfrigération, à savoir deux cycles réfrigérant semi-ouverts au gaz naturel et un unique cycle réfrigérant fermé au gaz réfrigérant.In essence, the liquefaction process according to the invention uses three thermodynamic refrigeration cycles, namely two refrigerant cycles semi-open to natural gas and a single refrigerant cycle closed to refrigerant gas.
Par ailleurs, le procédé selon l'invention utilise comme gaz réfrigérant de préférence un gaz comprenant majoritairement de l'azote, ce qui rend le procédé particulièrement adapté à une mise en œuvre offshore, typiquement sur une installation flottante de liquéfaction de gaz naturel (appelée en anglais FLNG pour « Floating Liquefaction of Natural Gas »).Furthermore, the process according to the invention preferably uses as refrigerant gas a gas comprising mainly nitrogen, which makes the process particularly suitable for offshore implementation, typically on a floating natural gas liquefaction installation (called in English FLNG for “Floating Liquefaction of Natural Gas”).
Comme représenté sur la
L'installation de liquéfaction 2 selon l'invention nécessite également trois turbodétendeurs (appelés « turbo-expander » en anglais), à savoir un turbodétendeur à température ambiante 6 dédié au gaz naturel, un turbodétendeur à température intermédiaire 8 dédié au gaz naturel, et un turbodétendeur à basse température 10 dédié au gaz réfrigérant.The
De manière connue, un turbodétendeur est une machine tournante qui est composée d'une turbine de détente de gaz (ici respectivement une turbine de détente à température ambiante 6a, une turbine de détente à température intermédiaire 8a et une turbine de détente à basse température 10a et d'un compresseur de gaz (ici respectivement un compresseur 6b, un compresseur 8b et un compresseur 10b) entraîné par la turbine de détente de gaz.In a known manner, a turbo-expander is a rotating machine which is composed of a gas expansion turbine (here respectively an expansion turbine at
L'installation de liquéfaction 2 selon l'invention comprend encore un compresseur de gaz naturel 12 et un compresseur de gaz réfrigérant 14, ces deux compresseurs 12, 14 étant de préférence entraînés par une même machine d'entraînement ME, par exemple une turbine à gaz fournissant la puissance nécessaire à l'augmentation de pression du gaz naturel à liquéfier ainsi qu'à la compression des fluides circulants dans les trois cycles réfrigérants.The
Comme il sera détaillé ultérieurement, le compresseur de gaz naturel remplit une triple fonction : pressuriser et assurer la circulation du gaz naturel de manière à fournir suffisamment de puissance de réfrigération pour contribuer au refroidissement et à la liquéfaction du gaz naturel et du gaz réfrigérant, re-comprimer le gaz naturel qui a été détendu pour l'extraction des NGLs lourds, et assurer que le gaz naturel à liquéfier soit à la pression optimale pour maximiser l'efficacité de la liquéfaction.As will be detailed later, the natural gas compressor fulfills a threefold function: to pressurize and ensure the circulation of natural gas in such a way as to provide sufficient refrigeration power to contribute to the cooling and liquefaction of natural gas and refrigerant gas, re - compress the natural gas that has been relaxed for the extraction of heavy NGLs, and ensure that the natural gas to be liquefied is at the optimum pressure to maximize the efficiency of the liquefaction.
Quant au compresseur de gaz réfrigérant, il a pour fonction de pressuriser et d'assurer la circulation du gaz réfrigérant de manière à permettre d'obtenir la puissance de réfrigération nécessaire pour contribuer au refroidissement du gaz réfrigérant, contribuer au pré-refroidissement et la liquéfaction du gaz naturel et assurer le sous-refroidissement du gaz naturel.As for the refrigerant gas compressor, its function is to pressurize and ensure the circulation of the refrigerant gas so as to obtain the refrigeration power necessary to contribute to the cooling of the refrigerant gas, to contribute to the pre-cooling and liquefaction. natural gas and ensure the sub-cooling of natural gas.
L'installation de liquéfaction 2 comprend encore un séparateur principal 16 destiné à la séparation des NGLs éventuellement contenus dans le gaz naturel, et un ballon 18 destiné à permettre une séparation entre les gaz de flash final et le gaz naturel liquéfié (GNL).The
On décrira maintenant les différentes étapes du procédé de liquéfaction de gaz naturel selon l'invention.The various stages of the natural gas liquefaction process according to the invention will now be described.
Préalablement au premier cycle réfrigérant semi-ouvert au gaz naturel, le gaz naturel subit un prétraitement destiné à le rendre propre à la liquéfaction. Ce prétraitement comprend notamment un traitement pour extraire du gaz naturel les gaz acides (dont le dioxyde de carbone), ces gaz acides pouvant notamment geler dans l'installation de liquéfaction. Le prétraitement comprend également un traitement de déshydratation pour extraire du gaz naturel l'eau et un traitement de démercurisation, le mercure risquant de dégrader les équipements en aluminium de l'installation de liquéfaction (dont l'échangeur de chaleur cryogénique principal 4).Prior to the first semi-open refrigerant cycle with natural gas, the natural gas undergoes a pretreatment intended to make it suitable for liquefaction. This pretreatment comprises in particular a treatment for extracting acid gases (including carbon dioxide) from natural gas, these acid gases being able in particular to freeze in the liquefaction installation. The pre-treatment also includes a dehydration treatment to extract water from natural gas and a demercurization treatment, as the mercury risks degrading the aluminum equipment of the liquefaction plant (including the main cryogenic heat exchanger 4).
Le flux d'alimentation de gaz naturel F-0 sort de cette phase préalable de prétraitement typiquement à une pression P0 comprise entre 5 et 10 MPa et une température T0 voisine (à savoir ici légèrement supérieure) de la température de la source chaude. Par « source chaude », on entend ici la source thermique qui est utilisée pour refroidir les flux non cryogéniques du procédé de liquéfaction. Cette source chaude peut typiquement être l'air ambiant, l'eau de mer, de l'eau douce refroidie par l'eau de mer, un fluide refroidi par un cycle réfrigérant auxiliaire ou une combinaison de plusieurs de ces sources.The natural gas feed stream F-0 leaves this preliminary pre-treatment phase, typically at a pressure P0 of between 5 and 10 MPa and a temperature T0 close (namely here slightly higher) to the temperature of the hot source. By “hot source” is meant here the thermal source which is used to cool the non-cryogenic streams of the liquefaction process. This hot source can typically be ambient air, sea water, fresh water cooled by sea water, a fluid cooled by an auxiliary refrigerant cycle or a combination of several of these sources.
Ce flux F-0 est mélangé au flux de gaz naturel F-2-1 provenant de l'installation de liquéfaction (et décrit ultérieurement) et alimente le premier cycle réfrigérant semi-ouvert au gaz naturel.This flow F-0 is mixed with the flow of natural gas F-2-1 coming from the liquefaction plant (and described later) and supplies the first semi-open refrigerant cycle with natural gas.
Comme indiqué précédemment, ce premier cycle réfrigérant semi-ouvert au gaz naturel a pour fonction d'extraire les NGLs lourds éventuellement présents dans le gaz naturel, et de pré-refroidir le gaz naturel et le gaz réfrigérant.As indicated above, this first semi-open refrigerant cycle with natural gas has the function of extracting the heavy NGLs possibly present in the natural gas, and of pre-cooling the natural gas and the refrigerant gas.
A cet effet, le flux d'alimentation de gaz naturel F-0 (combiné au au flux de gaz naturel F-2-1 décrit ultérieurement) traverse la turbine de détente à température ambiante 6a à l'échappement (i.e. sortie) de laquelle sa pression P1 est abaissée à une pression comprise entre 1 et 3 MPa et sa température T1 est abaissée à une température comprise entre -40°C et -60°C. Cette phase de détente du flux d'alimentation de gaz naturel conduit à une condensation d'éventuels NGLs (pour « Natural Gas Liquids » en anglais) lourds contenus dans le gaz naturel.To this end, the natural gas feed stream F-0 (combined with the natural gas stream F-2-1 described later) passes through the expansion turbine at
Par NGLs lourds, on entend ici l'essentiel des hydrocarbures en C5 (pentanes), C6 (hexanes, benzène) et plus qui sont contenus dans le gaz naturel, ainsi qu'une portion plus restreinte et variable d'éthane, de propane et de butanes et une portion très limitée de méthane.By heavy NGLs, one understands here the main part of the hydrocarbons in C5 (pentanes), C6 (hexanes, benzene) and more which are contained in natural gas, as well as a more restricted and variable portion of ethane, propane and of butanes and a very limited portion of methane.
Avec la condensation des NGLs lourds, le flux de gaz naturel à l'échappement de la turbine de détente à température ambiante 6a est dirigé vers l'entrée du séparateur principal 16. A la sortie du séparateur principal 16, le flux de liquides du gaz naturel F-HL est réchauffé, par exemple en circulant dans l'échangeur de chaleur cryogénique principal 4 (comme représenté sur la figure) ou en passant par un rebouilleur de NGLs dédié, puis il est dirigé vers une unité de traitement des NGLs 20. Après avoir été réchauffé, le flux de liquides du gaz naturel F-HL est diphasique et peut soit être envoyé directement à l'unité de traitement des NGLs 20 (comme représenté sur la figure) soit être soumis à une séparation gaz-liquide, les gaz évaporés étant renvoyés dans le séparateur principal 16.With the condensation of heavy NGLs, the flow of natural gas at the exhaust of the expansion turbine at
L'unité de traitement des NGLs 20 est une unité qui permet de traiter les NGLs lourds, et notamment de séparer les butanes et hydrocarbures plus légers des pentanes et hydrocarbures plus lourds pour former en sortie un flux de liquides du gaz naturel légers F-G (aussi appelé flux de NGLs légers F-G) et un flux d'essences de gaz naturel. En sortie de l'unité de traitement des NGLs, ce flux de NGLs légers F-G qui comprend majoritairement de l'éthane, du propane et des butanes est destiné à être réinjecté dans le gaz à liquéfier si cela est compatible avec la spécification de GNL visée (ou valorisé hors de l'installation de liquéfaction si ce n'est pas le cas).The
Par ailleurs, une fraction F-HL-1 du flux de liquides du gaz naturel lourds F-HL peut être dirigée vers un refroidisseur de NGLs 19 pour fournir la puissance thermique nécessaire à l'opération de cet échangeur. En particulier, le flux de liquides du gaz naturel légers F-G provenant de l'unité de traitement des NGLs 20 est refroidie dans le refroidisseur de NGLs 19. Une fraction F-G-1 du flux de NGLs légers F-G refroidi est réinjectée dans le séparateur principal 16.Furthermore, a fraction F-HL-1 of the flow of heavy natural gas liquids F-HL can be directed to an NGLs cooler 19 to provide the thermal power necessary for the operation of this exchanger. In particular, the stream of FG light natural gas liquids from the
En contrôlant le débit de réinjection de ce flux F-G-1 dans le séparateur principal, il est ainsi possible d'améliorer l'extraction de NGLs lourds et en particulier de réduire la quantité résiduelle de benzène et d'hydrocarbures lourds dans le gaz de sortie du séparateur principal.By controlling the reinjection rate of this FG-1 stream into the main separator, it is thus possible to improve the extraction of heavy NGLs and in particular to reduce the residual amount of benzene and heavy hydrocarbons in the outlet gas. of the main separator.
La fraction du flux de NGLs légers F-G refroidi qui n'est pas réinjectée dans le séparateur principal 16 est réinjectée dans le flux principal de gaz naturel F-P, en aval du soutirage alimentant la turbine à température intermédiaire 8a (mentionnée ultérieurement).The fraction of the cooled light NGLs F-G stream which is not reinjected into the
On notera que la réinjection de la fraction F-G-1 du flux de NGLs légers F-G refroidie dans le séparateur principal 16 n'est pas nécessaire si les quantités de benzène et d'hydrocarbures en C5 et plus dans le flux d'alimentation de gaz naturel sont faibles. On notera également que le refroidissement du flux de NGLs légers F-G peut être réalisé directement dans l'échangeur cryogénique principal 4 si un échangeur dédié à cet effet n'est pas prévu.It will be noted that the reinjection of the FG-1 fraction of the cooled light FG NGLs stream into the
On notera enfin que l'injection du flux de NGLs légers F-G peut être réalisée soit à co-courant soit à contre-courant. Dans le cas où le flux de NGLs légers F-G est réinjecté à contre-courant dans le séparateur principal 16, celui-ci pourra éventuellement être équipé d'un lit de garnissage pour améliorer l'efficacité de l'extraction des NGLs.Finally, it will be noted that the injection of the flow of light F-G NGLs can be carried out either cocurrently or countercurrently. In the case where the flow of light F-G NGLs is reinjected against the current into the
En sortie du séparateur principal 16, le flux de gaz naturel débarrassé des hydrocarbures lourds (résidu gaz) est à une température acceptable pour assurer un pré-refroidissement du gaz à liquéfier et du gaz réfrigérant. A cet effet, ce résidu gaz forme un premier flux de gaz naturel F-1 qui traverse l'échangeur de chaleur cryogénique principal.At the outlet of the
Lorsqu'il traverse l'échangeur de chaleur cryogénique principal, le premier flux de gaz naturel F-1 refroidit par échange thermique, d'une part un flux principal de gaz naturel F-P circulant à contre-courant dans l'échangeur de chaleur cryogénique principal, et d'autre part le flux initial de gaz réfrigérant G-0 (mentionné ultérieurement) circulant à contre-courant dans l'échangeur de chaleur cryogénique principal.When it passes through the main cryogenic heat exchanger, the first flow of natural gas F-1 cools by heat exchange, on the one hand a main flow of natural gas FP flowing countercurrently in the main cryogenic heat exchanger , and on the other hand the initial flow of refrigerant gas G-0 (mentioned later) circulating in countercurrent in the main cryogenic heat exchanger.
En sortie de l'échangeur de chaleur cryogénique principal, le premier flux de gaz naturel F-1 est à une température T2 supérieure à T1 et voisine de la température de la source chaude. Il est envoyé vers le compresseur 6b entraîné par la turbine de détente à température ambiante 6a pour y être comprimé à une pression P2, typiquement comprise entre 2 et 4 MPa .At the outlet of the main cryogenic heat exchanger, the first flow of natural gas F-1 is at a temperature T2 greater than T1 and close to the temperature of the hot source. It is sent to the
Au refoulement (i.e. en sortie) du compresseur 6b, le flux de gaz naturel traverse un refroidisseur de gaz naturel 21 puis est admis à l'aspiration (i.e. en entrée) du compresseur de gaz naturel 12 pour y être davantage comprimé à une pression P3 supérieure à P2 et P0 (et de préférence supérieure à la pression critique du gaz naturel) et former à la sortie un deuxième flux de gaz naturel F-2. Typiquement, la pression P3 pourra être comprise entre 6 et 10 MPa.At the discharge (ie at the outlet) of the
Dans ce compresseur de gaz naturel 12, le flux de gaz naturel pourra être comprimé en deux phases successives de compression entre lesquelles le flux de gaz naturel pourra être refroidi par un refroidisseur de gaz naturel 22.In this
Le deuxième flux de gaz naturel F-2 passe au travers d'un autre refroidisseur de gaz naturel 24 puis est séparé en deux fractions de flux : une fraction de flux F-2-1 est détendue et mélangée au flux d'alimentation de gaz naturel F-0 en amont de la turbine de détente à température ambiante 6a (comme décrit précédemment), et la fraction restante de ce flux forme le flux principal de gaz naturel F-P qui traverse l'échangeur de chaleur cryogénique principal 4.The second natural gas stream F-2 passes through another
On notera que la détente du flux F-2-1 peut se faire soit au moyen d'une simple vanne de contrôle 23 (comme représenté sur la figure), soit au moyen d'une turbine de détente.It will be noted that the expansion of the flow F-2-1 can be done either by means of a simple control valve 23 (as shown in the figure), or by means of an expansion turbine.
Une fraction de ce flux principal de gaz naturel F-P traverse l'échangeur de chaleur cryogénique principal afin d'y être refroidi jusqu'à une température T3 (typiquement comprise entre -140°C et -160°C) suffisamment basse pour assurer la liquéfaction du gaz naturel.A fraction of this main flow of natural gas FP passes through the main cryogenic heat exchanger in order to be cooled there to a temperature T3 (typically between -140 ° C and -160 ° C) sufficiently low to ensure liquefaction. natural gas.
Une autre fraction du flux principal de gaz naturel F-P est soumise à un second cycle semi-ouvert au gaz naturel. L'objectif de ce second cycle est de contribuer au refroidissement du gaz réfrigérant et de contribuer au pré-refroidissement du gaz naturel et à sa liquéfaction.Another fraction of the main stream of natural gas F-P is subjected to a second semi-open natural gas cycle. The objective of this second cycle is to contribute to the cooling of the refrigerant gas and to contribute to the pre-cooling of the natural gas and its liquefaction.
La fraction du flux principal de gaz naturel F-P soumise à ce second cycle semi-ouvert est extraite de l'échangeur de chaleur cryogénique principal à une température T4 (typiquement comprise entre -10°C et -40°C) supérieure à la température T3 pour être dirigé vers la turbine de détente à température intermédiaire 8a afin d'abaisser sa température par détente jusqu'à une température T5 (typiquement comprise entre -80°C et -110°C) inférieure à la température T4 et former un troisième flux de gaz naturel F-3.The fraction of the main flow of natural gas FP subjected to this second semi-open cycle is extracted from the main cryogenic heat exchanger at a temperature T4 (typically between -10 ° C and -40 ° C) above the temperature T3 to be directed towards the expansion turbine at
Le troisième flux de gaz naturel F-3 qui peut éventuellement contenir une fraction variable de liquide condensé est ensuite réintroduit dans l'échangeur de chaleur cryogénique principal pour refroidir par échange thermique le flux initial de gaz réfrigérant G-0 et le flux de gaz naturel principal F-P traversant l'échangeur de chaleur cryogénique principal à contre-courant.The third stream of natural gas F-3 which may optionally contain a variable fraction of condensed liquid is then reintroduced into the main cryogenic heat exchanger to cool by heat exchange the initial stream of refrigerant gas G-0 and the stream of natural gas. main FP passing through the main cryogenic heat exchanger against the current.
A la sortie de l'échangeur de chaleur cryogénique principal, le troisième flux de gaz naturel F-3 en phase gaz et à une température T6 voisine de la température de la source chaude est dirigé vers un compresseur 8b entraîné par la turbine de détente à température intermédiaire 8a pour y être comprimé. Il est alors refroidi par un refroidisseur de gaz naturel 26 avant d'être mélangé au premier flux de gaz naturel F-1 en amont du compresseur de gaz naturel 12.At the outlet of the main cryogenic heat exchanger, the third flow of natural gas F-3 in gas phase and at a temperature T6 close to the temperature of the hot source is directed to a
Lors de son passage dans l'échangeur de chaleur cryogénique principal, le flux principal de gaz naturel F-P est refroidi par échange thermique avec le premier flux de gaz naturel F-1, le troisième flux de gaz naturel F3, et par un premier flux de gaz réfrigérant G-1 (décrit ultérieurement) circulant tous les trois à contre-courant dans l'échangeur de chaleur cryogénique principal 4.During its passage through the main cryogenic heat exchanger, the main flow of natural gas FP is cooled by heat exchange with the first flow of natural gas F-1, the third flow of natural gas F3, and by a first flow of refrigerant gas G-1 (described later) all three flow countercurrently through the main
A la sortie de l'échangeur de chaleur cryogénique principal, le flux principal de gaz naturel F-P a ainsi été refroidi à une température permettant sa liquéfaction. Celui-ci subit une détente de Joule-Thomson en traversant une vanne 28 jusqu'à atteindre une pression voisine de la pression atmosphérique. Alternativement, cette détente pourrait être réalisée au moyen d'une turbine de détente liquide pour améliorer son efficacité.At the outlet of the main cryogenic heat exchanger, the main stream of natural gas F-P has thus been cooled to a temperature allowing its liquefaction. This undergoes a Joule-Thomson expansion by passing through a
La détente du gaz naturel liquéfié a pour effet de générer des gaz de flash qui sont séparés du gaz naturel liquéfié dans le ballon 18 dédié à cet effet. En sortie du ballon, le flux de gaz naturel liquéfié GNL débarrassé des gaz de flash est envoyé vers les cuves de stockage de GNL.The expansion of the liquefied natural gas has the effect of generating flash gases which are separated from the liquefied natural gas in the
Quant aux gaz de flash F-F, ils sont envoyés dans l'échangeur de chaleur cryogénique principal pour être réchauffés à une température T11 typiquement comprise entre -50°C et -110°C, puis vers une unité de traitement du gaz de flash, ce qui permet de réduire les besoins en puissance de réfrigération dans la section froide de l'échangeur de chaleur cryogénique principal.As for the FF flash gases, they are sent to the main cryogenic heat exchanger to be reheated to a temperature T11 typically between -50 ° C and -110 ° C, then to a flash gas treatment unit, this which reduces the refrigeration power requirements in the cold section of the main cryogenic heat exchanger.
On décrira maintenant l'unique cycle réfrigérant fermé au gaz réfrigérant (ici majoritairement de l'azote) qui a pour but de fournir la puissance thermique complémentaire aux deux autres cycles réfrigérant et d'assurer le sous-refroidissement du gaz naturel liquéfié.The single refrigerant cycle closed to refrigerant gas (here mainly nitrogen) will now be described, the purpose of which is to provide the additional thermal power to the other two refrigerant cycles and to ensure the sub-cooling of the liquefied natural gas.
Le compresseur de gaz réfrigérant 14 délivre un flux initial de gaz réfrigérant G-0 qui, après refroidissement dans un refroidisseur de gaz réfrigérant 32, se trouve à une température T7 voisine de la température de la source chaude.The
Ce flux initial de gaz réfrigérant G-0 est majoritairement circulé dans l'échangeur de chaleur cryogénique principal 4 pour y être pré-refroidi en réchauffant le premier flux de gaz naturel F-1, un troisième flux de gaz naturel F-3 ainsi que le premier flux de gaz réfrigérant G-1 mentionné ultérieurement circulant à contre-courant dans l'échangeur de chaleur cryogénique principal.This initial flow of refrigerant gas G-0 is mainly circulated in the main
A la sortie de l'échangeur de chaleur cryogénique principal, le flux initial de gaz réfrigérant G-0 se trouve à une température T8 (par exemple comprise entre -80°C et -110°C) qui est inférieure à la température T7. Ce flux est dirigé vers la turbine de détente à basse température 10a pour y être davantage refroidi jusqu'à une température T9 (par exemple comprise entre -140°C et -160°C) inférieure à la température T8 avant d'être réintroduite dans l'échangeur de chaleur cryogénique principal pour former un premier flux de gaz réfrigérant G-1.At the outlet of the main cryogenic heat exchanger, the initial flow of refrigerant gas G-0 is at a temperature T8 (for example between -80 ° C and -110 ° C) which is lower than the temperature T7. This flow is directed towards the expansion turbine at
Comme décrit précédemment, la circulation de ce premier flux de gaz réfrigérant G-1 dans l'échangeur de chaleur cryogénique principal permet d'assurer par échange thermique un refroidissement du flux principal de gaz naturel F-P et du flux initial de gaz réfrigérant G-0 circulant à contre-courant dans l'échangeur de chaleur cryogénique principal.As described above, the circulation of this first flow of refrigerant gas G-1 in the main cryogenic heat exchanger makes it possible to ensure by heat exchange a cooling of the main flow of natural gas FP and of the initial flow of refrigerant gas G-0 flowing countercurrently through the main cryogenic heat exchanger.
A la sortie de l'échangeur de chaleur cryogénique principal 4, le premier flux de gaz réfrigérant G-1 est à une température T10 supérieure à T9 et voisine de la température de la source chaude. Ce flux est dirigé vers le compresseur 10b entraîné par la turbine de détente à basse température 10a pour y être comprimé avant d'être refroidi par un refroidisseur de gaz réfrigérant 34 puis réinjecté en aspiration du compresseur de gaz réfrigérant 14.At the outlet of the main
On notera que dans le compresseur de gaz réfrigérant 14, le premier flux de gaz réfrigérant G-1 pourra être comprimé en deux phases successives de compression entre lesquelles le flux de gaz réfrigérant pourra être refroidi par un autre refroidisseur de gaz réfrigérant 30.It will be noted that in the
En liaison avec les
La
Cette variante se distingue du mode de réalisation de la
Cette variante permet ainsi de réaliser une compression étagée du gaz naturel qui est plus efficace que celle décrite en liaison avec la
La
Cette variante se distingue du mode de réalisation de la
Comme représenté sur la
Dans cette variante, la température dans le séparateur principal 16 est abaissée, ce qui permet d'obtenir une meilleure récupération des NGLs.In this variant, the temperature in the
La
Dans cette variante, au cours du second cycle réfrigérant semi-ouvert au gaz naturel, le troisième flux de gaz naturel F-3 à l'échappement de la turbine de détente intermédiaire 8a est dirigé vers un séparateur auxiliaire 40 à la sortie duquel le flux de gaz naturel est réintroduit dans l'échangeur de chaleur cryogénique principal 4, le flux de liquides du gaz naturel à la sortie du séparateur auxiliaire 40 étant pompé en totalité ou en partie vers le séparateur principal 16 pour contribuer à l'absorption de liquides du gaz naturel.In this variant, during the second semi-open refrigerant cycle with natural gas, the third flow of natural gas F-3 at the exhaust of the
Le contact entre le gaz naturel à traiter et le reflux sous-refroidi peut par exemple être réalisé à contre-courant. A cet effet, le séparateur principal peut par exemple être équipé d'un lit de garnissage. Avec cette variante, il est possible de traiter des gaz légers avec une haute teneur en composés aromatiques (par exemple le benzène) ou extraire les LPGs avec un taux de récupération élevé (par exemple pour assurer une production industrielle de GPLs).The contact between the natural gas to be treated and the sub-cooled reflux can for example be carried out against the current. For this purpose, the main separator can for example be equipped with a packing bed. With this variant, it is possible to treat light gases with a high content of aromatic compounds (for example benzene) or to extract the LPGs with a high recovery rate (for example to ensure industrial production of LPGs).
La
Dans cette variante, au cours du premier cycle réfrigérant semi-ouvert au gaz naturel, une partie F-I de la fraction de flux principal de gaz naturel F-P qui traverse l'échangeur de chaleur cryogénique principal 4 afin d'y être refroidi est extraite dudit échangeur de chaleur cryogénique principal à une température T11 pour être dirigée vers le séparateur principal 16 de façon à contribuer à l'absorption de liquides du gaz naturel.In this variant, during the first semi-open refrigerant cycle with natural gas, a part FI of the fraction of the main natural gas flow FP which passes through the main
La température T11 d'extraction du flux F-I est supérieure à la température T3. Elle est par exemple comprise entre -70°C et -110°C.The temperature T11 for extracting the stream F-I is higher than the temperature T3. It is for example between -70 ° C and -110 ° C.
Le contact entre le gaz naturel à traiter et le reflux de GNL peut par exemple être réalisé à contre-courant. A cet effet, le séparateur principal peut par exemple être équipé d'un lit de garnissage. Avec cette variante, il est possible de traiter des gaz légers avec une haute teneur en composés aromatiques en composés aromatiques (par exemple le benzène) ou d'extraire notamment des GPLs avec un taux de récupération élevé et de l'éthane.The contact between the natural gas to be treated and the LNG reflux can for example be carried out against the current. For this purpose, the main separator can for example be equipped with a packing bed. With this variant, it is possible to treat light gases with a high content of aromatic compounds in aromatic compounds (for example benzene) or to extract in particular LPGs with a high recovery rate and ethane.
Claims (16)
- A process for liquefying a natural gas comprising a hydrocarbon mixture, mainly methane, the process comprising:a) a first refrigerant cycle semi-open to the natural gas in which, successively:a natural gas feed stream (F-0) at a pressure P0 pre-treated to extract therefrom acid gases, water and mercury is mixed with a natural gas stream, expanded to a pressure P1 and its temperature lowered to a temperature T1 by means of an expansion turbine at room temperature (6a) so as to obtain a condensation of possible natural gas liquids contained in the natural gas,the possible natural gas liquids that have been condensed are separated in a main separator (16) from the natural gas feed stream, the latter then passing through a main cryogenic heat exchanger (4) in order to form a first stream of natural gas (F-1) contributing by heat exchange, on the one hand to the pre-cooling of a main stream of natural gas (F-P) flowing countercurrent through the main cryogenic heat exchanger, and on the other hand, to the cooling of an initial stream of refrigerant gas (G-0) flowing countercurrent in the main cryogenic heat exchanger,at the outlet of the main cryogenic heat exchanger, the first natural gas stream (F-1) which is at a temperature T2 greater than T1 and close to the temperature of a hot source, is compressed at a pressure P2 by means of a compressor (6b) driven by the room temperature expansion turbine (6a) before being admitted to the suction of a natural gas compressor (12) to be further compressed therein at a pressure P3 greater than P2 and form a second stream of natural gas (F-2),the second natural gas stream (F-2) at the discharge of the natural gas compressor (12) is partly expanded and mixed with the natural gas feed stream (F-0) upstream of the room temperature expansion turbine, and partly forms the main stream of natural gas (F-P),a fraction of this main stream of natural gas (F-P) passes through the main cryogenic heat exchanger in order to be cooled to a temperature T3 low enough to allow the liquefaction of the natural gas;b) a second refrigerant cycle semi-open to the natural gas in which, successively:another fraction of the main stream of natural gas (F-P) is extracted from the main cryogenic heat exchanger at a temperature T4 greater than T3 to be directed to an intermediate expansion turbine (8a) so that its temperature is lowered by expansion to a temperature T5 lower than T4 and form a third stream of natural gas (F-3),the third natural gas stream (F-3) is reintroduced into the main cryogenic heat exchanger to cool by heat-exchange the main natural gas stream and the initial stream of refrigerant gas countercurrent circulating into the main cryogenic heat exchanger,at the outlet of the main cryogenic heat exchanger, the third natural gas stream (F-3) which is at a temperature T6 close to the temperature of the hot source is directed to a compressor (8b) driven by the intermediate expansion turbine (8a) to be compressed therein and then it is cooled before being mixed with the first stream of natural gas upstream of the natural gas compressor (12);c) a refrigerant cycle closed to the refrigerant gas in which, successively:an initial stream of refrigerant gas (G-0) with a temperature T7 close to the temperature of the hot source and previously compressed by a refrigerant gas compressor (14) is circulated in the main cryogenic heat exchanger (4) to be pre-cooled therein,at the outlet of the main cryogenic heat exchanger, the initial stream of refrigerant gas (G-0) which is at a temperature T8 lower than T7 is directed to a low temperature expansion turbine (10a) so that its temperature is lowered by expansion to a temperature T9 lower than T8, the first stream of refrigerant gas (G-1) thus formed being reintroduced into the main cryogenic heat exchanger to contribute to the cooling of the main stream of natural gas (F-P) and the initial stream of refrigerant gas (G-0);at the outlet of the main cryogenic heat exchanger, the first stream of refrigerant gas (G-1) which is at a temperature T10 close to the temperature of the hot source is directed to a compressor (10b) driven by the low temperature expansion turbine (10a) to be compressed therein before being cooled and then directed to the suction of the refrigerant gas compressor (14).
- The process according to claim 1, wherein during the second refrigerant cycle semi-open to the natural gas, the natural gas stream at the outlet of the compressor (8b) driven by the intermediate expansion turbine (8a) is cooled and then mixed to the first natural gas stream before being directed to the inlet of the compressor (6b) driven by the room temperature expansion turbine (6a).
- The process according to one of claims 1 and 2, wherein during the first refrigerant cycle semi-open to the natural gas, the natural gas feed stream at the inlet of the room temperature expansion turbine (6a) is further cooled in an auxiliary heat exchanger (36).
- The process according to any one of claims 1 to 3, wherein during the second refrigerant cycle semi-open to the natural gas, the third natural gas stream (F-3) at the exhaust of the intermediate expansion turbine (8a) is directed to an auxiliary separator (40) at the outlet of which the stream of natural gas is reintroduced into the main cryogenic heat exchanger (4), the stream of liquids of the natural gas at the outlet of the auxiliary separator ( 40) being pumped in whole or in part to the main separator (16) to contribute to the absorption of liquids from the natural gas.
- The process according to any one of claims 1 to 4, wherein during the first refrigerant cycle semi-open to the natural gas, a portion of the fraction of main natural gas stream (F-P) which passes through the main cryogenic heat exchanger (4) in order to be cooled therein is extracted from said main cryogenic heat exchanger at a temperature T11 greater than the temperature T3 to be directed to the main separator (16) so as to contribute to the absorption of liquids from the natural gas.
- The process according to any one of claims 1 to 5, wherein during the first refrigerant cycle semi-open to the natural gas, the natural gas feed stream (F-0) is expanded and its temperature lowered by means of the room temperature expansion turbine (6a) without prior pre-cooling in the main cryogenic heat exchanger.
- The process according to any one of claims 1 to 6, wherein during the first refrigerant cycle semi-open to the natural gas, the natural gas feed stream at the exhaust of the expansion turbine at room temperature (6a) is introduced into the main separator (16) at the outlet of which a stream of natural gas liquids (F-HL) is recovered.
- The process according to claim 7, wherein the recovered stream of natural gas liquids (F-HL) is reheated and partially vaporized in order to facilitate its downstream processing.
- The process according to one of claims 7 and 8, wherein the thermal power required to reheat the stream of natural gas liquids (F-HL) comes from the cooling of the main stream of natural gas (F-P) and/or the initial stream of refrigerant gas (G-0).
- The process according of any one of claims 1 to 9, wherein the pressure of the main stream of natural gas (F-P) is greater than the critical pressure of the natural gas.
- The process according to any one of claims 1 to 10, wherein:the temperature T1 ranges between -40°C and -60°C;the temperature T3 ranges between -140°C and -160°C;the temperature T4 ranges between -10°C and -40°C;the temperature T5 ranges between -80°C and -110°C;the temperature T8 ranges between -80°C and -110°C;the temperature T9 ranges between -140°C and -160°C;the pressure P0 ranges between 5 and 10 MPa;the pressure P1 ranges between 1 and 3 MPa;the pressure P2 ranges between 2 and 4 MPa; andthe pressure P3 ranges between 6 and 10 MPa.
- The process according to any one of claims 1 to 11, wherein the refrigerant gas mainly comprises nitrogen.
- The process according to any one of claims 1 to 12, wherein it is implemented on board an offshore natural gas liquefaction facility.
- A natural gas liquefaction facility for the implementation of the process according to any one of claims 1 to 13, comprising:a room temperature expansion turbine (6a) for receiving a natural gas feed stream (F-0) as well as a portion of a second natural gas stream (F-2) from the discharge of a natural gas compressor (12) and having an exhaust connected to an inlet of a main separator (16);a main cryogenic heat exchanger (4) for receiving streams of natural gases (F-P, F-1, F-3) and refrigerant gas;a compressor (6b) driven by the room temperature expansion turbine (6a) for receiving a first natural gas stream (F-1) from a main separator (16) and having an output connected to the suction of the natural gas compressor (12);an intermediate temperature expansion turbine (8a) for receiving a portion of a main stream of natural gas (F-P) from the discharge of the natural gas compressor (12) and connected at the inlet and the outlet to the main cryogenic heat exchanger (4);a compressor (8b) driven by the intermediate temperature expansion turbine (8a) for receiving a third natural gas stream (F-3) from the main cryogenic heat exchanger (4);a low temperature expansion turbine (10a) for refrigerant gas connected at the inlet and the outlet to the main cryogenic heat exchanger (4); anda compressor (10b) driven by the low temperature expansion turbine (10a) and having an outlet connected to the suction of a refrigerant gas compressor (14).
- The facility according to claim 14, wherein the natural gas compressor (12) and the refrigerant gas compressor (14) are driven by a same driving machine (ME) providing the power required for the pressure increase of the natural gas to be liquefied as well as the compression of circulating fluids in the three refrigerant cycles.
- The facility according to one of claims 14 and 15, wherein the natural gas compressor (12) is downstream of the compressors driven by the room temperature expansion turbine (6a) and the intermediate temperature expansion turbine (8a), and wherein the refrigerant gas compressor (14) is downstream of the compressor driven by the low temperature expansion turbine (10a).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP21155666.7A EP3839392A1 (en) | 2016-07-06 | 2017-06-20 | Method for liquefying natural gas and for recovering any liquid from the natural gas comprising two coolant cycles semi-open to the natural gas and a coolant cycle closed to the coolant gas |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR1656460A FR3053771B1 (en) | 2016-07-06 | 2016-07-06 | METHOD FOR LIQUEFACTING NATURAL GAS AND RECOVERING LIQUID EVENTS OF NATURAL GAS COMPRISING TWO NATURAL GAS SEMI-OPENING REFRIGERANT CYCLES AND A REFRIGERANT GAS REFRIGERANT CYCLE |
| PCT/FR2017/051630 WO2018007710A1 (en) | 2016-07-06 | 2017-06-20 | Method for liquefying natural gas and for recovering possible liquids from the natural gas, comprising two refrigerant cycles semi-open to the natural gas and a refrigerant cycle closed to the refrigerant gas |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP21155666.7A Division EP3839392A1 (en) | 2016-07-06 | 2017-06-20 | Method for liquefying natural gas and for recovering any liquid from the natural gas comprising two coolant cycles semi-open to the natural gas and a coolant cycle closed to the coolant gas |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP3482146A1 EP3482146A1 (en) | 2019-05-15 |
| EP3482146B1 true EP3482146B1 (en) | 2021-02-24 |
Family
ID=57045120
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP17745789.2A Active EP3482146B1 (en) | 2016-07-06 | 2017-06-20 | Method for liquefying natural gas and for recovering possible liquids from the natural gas, comprising two refrigerant cycles semi-open to the natural gas and a refrigerant cycle closed to the refrigerant gas |
| EP21155666.7A Withdrawn EP3839392A1 (en) | 2016-07-06 | 2017-06-20 | Method for liquefying natural gas and for recovering any liquid from the natural gas comprising two coolant cycles semi-open to the natural gas and a coolant cycle closed to the coolant gas |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP21155666.7A Withdrawn EP3839392A1 (en) | 2016-07-06 | 2017-06-20 | Method for liquefying natural gas and for recovering any liquid from the natural gas comprising two coolant cycles semi-open to the natural gas and a coolant cycle closed to the coolant gas |
Country Status (21)
| Country | Link |
|---|---|
| US (1) | US11255602B2 (en) |
| EP (2) | EP3482146B1 (en) |
| JP (1) | JP6985306B2 (en) |
| KR (1) | KR102413811B1 (en) |
| CN (1) | CN109564057B (en) |
| AU (1) | AU2017294126B2 (en) |
| BR (1) | BR112019000141B1 (en) |
| CA (1) | CA3029464C (en) |
| CO (1) | CO2018013887A2 (en) |
| CY (1) | CY1123975T1 (en) |
| DK (1) | DK3482146T3 (en) |
| ES (1) | ES2862304T3 (en) |
| FR (1) | FR3053771B1 (en) |
| IL (1) | IL264067B (en) |
| MA (1) | MA44302B1 (en) |
| MX (1) | MX2019000197A (en) |
| MY (1) | MY195636A (en) |
| PH (1) | PH12018502729A1 (en) |
| RU (1) | RU2743095C2 (en) |
| SG (1) | SG11201811359VA (en) |
| WO (1) | WO2018007710A1 (en) |
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| US11555651B2 (en) * | 2018-08-22 | 2023-01-17 | Exxonmobil Upstream Research Company | Managing make-up gas composition variation for a high pressure expander process |
| US20220186986A1 (en) * | 2019-04-01 | 2022-06-16 | Samsung Heavy Ind. Co.,Ltd. | Cooling system |
| FR3099817B1 (en) * | 2019-08-05 | 2022-11-04 | Air Liquide | Process and installation for cooling and/or liquefaction. |
| JP7355979B2 (en) * | 2019-09-26 | 2023-10-04 | レール・リキード－ソシエテ・アノニム・プール・レテュード・エ・レクスプロワタシオン・デ・プロセデ・ジョルジュ・クロード | gas liquefaction equipment |
| CZ2019618A3 (en) * | 2019-10-04 | 2020-12-16 | Siad Macchine Impianti S.P.A. | Natural gas processing equipment |
| IT202000026978A1 (en) * | 2020-11-11 | 2022-05-11 | Saipem Spa | INTEGRATED PROCESS FOR PURIFICATION AND LIQUEFACTION OF NATURAL GAS |
| US20220333855A1 (en) * | 2021-04-15 | 2022-10-20 | Henry Edward Howard | System and method to produce liquefied natural gas using two distinct refrigeration cycles with an integral gear machine |
| US20220333856A1 (en) * | 2021-04-15 | 2022-10-20 | Henry Edward Howard | System and method to produce liquefied natural gas using two distinct refrigeration cycles with an integral gear machine |
| US20220333858A1 (en) * | 2021-04-15 | 2022-10-20 | Henry Edward Howard | System and method to produce liquefied natural gas using two distinct refrigeration cycles with an integral gear machine |
| US20220333853A1 (en) * | 2021-04-16 | 2022-10-20 | Henry Edward Howard | System and method to produce liquefied natural gas using a three pinion integral gear machine |
| US20230115492A1 (en) * | 2021-10-13 | 2023-04-13 | Henry Edward Howard | System and method to produce liquefied natural gas |
| US20230129424A1 (en) * | 2021-10-21 | 2023-04-27 | Henry Edward Howard | System and method to produce liquefied natural gas |
| US20240125549A1 (en) * | 2022-10-14 | 2024-04-18 | Air Products And Chemicals, Inc. | Open Loop Liquefaction Process with NGL Recovery |
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| US5036671A (en) * | 1990-02-06 | 1991-08-06 | Liquid Air Engineering Company | Method of liquefying natural gas |
| WO1997013109A1 (en) * | 1995-10-05 | 1997-04-10 | Bhp Petroleum Pty. Ltd. | Liquefaction process |
| US6158240A (en) * | 1998-10-23 | 2000-12-12 | Phillips Petroleum Company | Conversion of normally gaseous material to liquefied product |
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| AU2006215629C1 (en) * | 2005-02-17 | 2011-03-31 | Shell Internationale Research Maatschappij B.V. | Plant and method for liquefying natural gas |
| RU2406949C2 (en) * | 2005-08-09 | 2010-12-20 | Эксонмобил Апстрим Рисерч Компани | Method of liquefying natural gas |
| NO329177B1 (en) | 2007-06-22 | 2010-09-06 | Kanfa Aragon As | Process and system for forming liquid LNG |
| WO2009029140A1 (en) * | 2007-08-24 | 2009-03-05 | Exxonmobil Upstream Research Company | Natural gas liquefaction process |
| GB2459484B (en) | 2008-04-23 | 2012-05-16 | Statoilhydro Asa | Dual nitrogen expansion process |
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| FR2977015B1 (en) * | 2011-06-24 | 2015-07-03 | Saipem Sa | METHOD FOR LIQUEFACTING NATURAL GAS WITH TRIPLE FIRM CIRCUIT OF REFRIGERATING GAS |
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| CN102564059A (en) * | 2012-02-19 | 2012-07-11 | 中国石油集团工程设计有限责任公司 | Twin-stage multi-component mixed refrigerant refrigeration natural gas liquefaction system and method |
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| JP6225049B2 (en) * | 2013-12-26 | 2017-11-01 | 千代田化工建設株式会社 | Natural gas liquefaction system and method |
| GB2541464A (en) | 2015-08-21 | 2017-02-22 | Frederick Skinner Geoffrey | Process for producing Liquefied natural gas |
| CN105627693B (en) * | 2016-03-11 | 2019-03-01 | 重庆耐德能源装备集成有限公司 | A kind of processing unit and method of natural gas |
-
2016
- 2016-07-06 FR FR1656460A patent/FR3053771B1/en not_active Expired - Fee Related
-
2017
- 2017-06-20 ES ES17745789T patent/ES2862304T3/en active Active
- 2017-06-20 EP EP17745789.2A patent/EP3482146B1/en active Active
- 2017-06-20 MX MX2019000197A patent/MX2019000197A/en unknown
- 2017-06-20 CA CA3029464A patent/CA3029464C/en active Active
- 2017-06-20 KR KR1020197002719A patent/KR102413811B1/en active IP Right Grant
- 2017-06-20 JP JP2018568282A patent/JP6985306B2/en active Active
- 2017-06-20 RU RU2019101462A patent/RU2743095C2/en active
- 2017-06-20 CN CN201780042291.2A patent/CN109564057B/en active Active
- 2017-06-20 WO PCT/FR2017/051630 patent/WO2018007710A1/en unknown
- 2017-06-20 BR BR112019000141-7A patent/BR112019000141B1/en active IP Right Grant
- 2017-06-20 EP EP21155666.7A patent/EP3839392A1/en not_active Withdrawn
- 2017-06-20 MY MYPI2019000005A patent/MY195636A/en unknown
- 2017-06-20 US US16/315,115 patent/US11255602B2/en active Active
- 2017-06-20 DK DK17745789.2T patent/DK3482146T3/en active
- 2017-06-20 SG SG11201811359VA patent/SG11201811359VA/en unknown
- 2017-06-20 MA MA44302A patent/MA44302B1/en unknown
- 2017-06-20 AU AU2017294126A patent/AU2017294126B2/en active Active
-
2018
- 2018-12-20 CO CONC2018/0013887A patent/CO2018013887A2/en unknown
- 2018-12-21 PH PH12018502729A patent/PH12018502729A1/en unknown
-
2019
- 2019-01-03 IL IL264067A patent/IL264067B/en unknown
-
2021
- 2021-03-22 CY CY20211100243T patent/CY1123975T1/en unknown
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