EP0687353B1 - Method and apparatus for liquefying natural gas - Google Patents
Method and apparatus for liquefying natural gas Download PDFInfo
- Publication number
- EP0687353B1 EP0687353B1 EP95905171A EP95905171A EP0687353B1 EP 0687353 B1 EP0687353 B1 EP 0687353B1 EP 95905171 A EP95905171 A EP 95905171A EP 95905171 A EP95905171 A EP 95905171A EP 0687353 B1 EP0687353 B1 EP 0687353B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- natural gas
- fraction
- liquefying
- liquid
- gas
- 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.)
- Expired - Lifetime
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 346
- 239000003345 natural gas Substances 0.000 title claims abstract description 150
- 238000000034 method Methods 0.000 title claims abstract description 62
- 239000012071 phase Substances 0.000 claims abstract description 98
- 239000007789 gas Substances 0.000 claims abstract description 79
- 239000007791 liquid phase Substances 0.000 claims abstract description 32
- 230000008569 process Effects 0.000 claims abstract description 27
- 238000001816 cooling Methods 0.000 claims abstract description 20
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 91
- 239000000203 mixture Substances 0.000 claims description 65
- 239000007788 liquid Substances 0.000 claims description 55
- 229910052757 nitrogen Inorganic materials 0.000 claims description 45
- 238000007906 compression Methods 0.000 claims description 29
- 230000006835 compression Effects 0.000 claims description 29
- 229930195733 hydrocarbon Natural products 0.000 claims description 21
- 150000002430 hydrocarbons Chemical class 0.000 claims description 21
- 239000003949 liquefied natural gas Substances 0.000 claims description 20
- 239000012530 fluid Substances 0.000 claims description 6
- 239000000463 material Substances 0.000 claims description 6
- 238000001179 sorption measurement Methods 0.000 claims description 6
- 239000002826 coolant Substances 0.000 claims description 5
- 238000009833 condensation Methods 0.000 claims description 4
- 230000005494 condensation Effects 0.000 claims description 4
- 238000000926 separation method Methods 0.000 claims description 4
- 239000002131 composite material Substances 0.000 claims description 3
- 238000001704 evaporation Methods 0.000 claims 1
- 230000007704 transition Effects 0.000 abstract description 18
- 238000005057 refrigeration Methods 0.000 description 24
- 239000003507 refrigerant Substances 0.000 description 15
- 238000010586 diagram Methods 0.000 description 10
- 239000003570 air Substances 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 239000012808 vapor phase Substances 0.000 description 6
- 230000008016 vaporization Effects 0.000 description 5
- 239000003463 adsorbent Substances 0.000 description 3
- 238000003795 desorption Methods 0.000 description 3
- 239000007792 gaseous phase Substances 0.000 description 3
- 230000002040 relaxant effect Effects 0.000 description 3
- 239000011555 saturated liquid Substances 0.000 description 3
- 238000009834 vaporization Methods 0.000 description 3
- FGUUSXIOTUKUDN-IBGZPJMESA-N C1(=CC=CC=C1)N1C2=C(NC([C@H](C1)NC=1OC(=NN=1)C1=CC=CC=C1)=O)C=CC=C2 Chemical compound C1(=CC=CC=C1)N1C2=C(NC([C@H](C1)NC=1OC(=NN=1)C1=CC=CC=C1)=O)C=CC=C2 FGUUSXIOTUKUDN-IBGZPJMESA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 241001080024 Telles Species 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 239000012809 cooling fluid Substances 0.000 description 2
- 238000004821 distillation Methods 0.000 description 2
- 239000002609 medium Substances 0.000 description 2
- 150000002829 nitrogen Chemical class 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 238000011144 upstream manufacturing Methods 0.000 description 2
- FNYLWPVRPXGIIP-UHFFFAOYSA-N Triamterene Chemical compound NC1=NC2=NC(N)=NC(N)=C2N=C1C1=CC=CC=C1 FNYLWPVRPXGIIP-UHFFFAOYSA-N 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000001174 ascending effect Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 238000003486 chemical etching Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- YWXYYJSYQOXTPL-SLPGGIOYSA-N isosorbide mononitrate Chemical compound [O-][N+](=O)O[C@@H]1CO[C@@H]2[C@@H](O)CO[C@@H]21 YWXYYJSYQOXTPL-SLPGGIOYSA-N 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
Images
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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
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
- F25J3/0257—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of nitrogen
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- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
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- 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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- 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"
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- 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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- 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"
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- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
- F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
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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
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
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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
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
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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
- F25J2205/00—Processes or apparatus using other separation and/or other processing means
- F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
- F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
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- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
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- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/20—Integrated compressor and process expander; Gear box arrangement; Multiple compressors on a common shaft
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2240/00—Processes or apparatus involving steps for expanding of process streams
- F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
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- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2240/00—Processes or apparatus involving steps for expanding of process streams
- F25J2240/30—Dynamic liquid or hydraulic expansion with extraction of work, e.g. single phase or two-phase turbine
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2240/00—Processes or apparatus involving steps for expanding of process streams
- F25J2240/40—Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2245/00—Processes or apparatus involving steps for recycling of process streams
- F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2270/00—Refrigeration techniques used
- F25J2270/04—Internal refrigeration with work-producing gas expansion loop
- F25J2270/06—Internal refrigeration with work-producing gas expansion loop with multiple gas expansion loops
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2270/00—Refrigeration techniques used
- F25J2270/12—External refrigeration with liquid vaporising 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
- F25J2270/00—Refrigeration techniques used
- F25J2270/88—Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided
Definitions
- Natural gas liquefaction is an industrial operation important for transporting natural gas over long periods distances by LNG carrier, or to store them in liquid form.
- an external refrigeration cycle using as refrigerant a mixture of fluids is used.
- Such vaporizing mixture may refrigerate and liquefy gas under pressure. After vaporization, the mixture is compressed, condensed into exchanging heat with an ambient medium such as water or the air.
- a first refrigeration step of refrigerate and liquefy natural gas directly by relaxing through a turbine from a "dense" phase denotes a phase obtainable from a gas phase initial by an isobaric evolution without phase transition and leading by isentropic expansion to a liquid phase without phase transition. At at least part of the liquefaction process takes place without transition from phase, i.e. the transition from the gas phase to the liquid phase takes place continuously, without transformation during which it two different phases would coexist. Natural gas is brought in "dense phase” before expansion, operating at a pressure at least higher than the critical methane pressure, and lowering the "natural gas" temperature.
- the present invention relates to a process for liquefying a gas natural. It is characterized in that it comprises a step according to which at least partially liquefies said gas by expansion with supply of mechanical energy, this relaxation taking it from a state or phase dense to a liquid state or phase.
- the first relaxed majority fraction is preferably greater than two thirds of the dense phase natural gas from the first stage.
- a turbine is used as a device to relax the gas and move it from the dense phase state to the phase state liquid.
- natural gas can be cooled by exchange thermal using a gaseous fraction from said natural gas, said gas fraction being expanded in a turbine, said fraction expanded gas being at least partly recompressed in a stage of compression and recycled.
- At least one recycled gas fraction is compressed using at least two stages, the gas being cooled at the outlet of each of the stages of compression by an ambient medium of refrigeration available.
- natural gas can also be cooled by vaporization of a mixture of refrigerants, the mixture thus obtained present in vapor or gas phase. It is then compressed, condensed by a heat exchange with the ambient medium of refrigeration available, relaxed and recycled.
- the refrigerant mixture can be expanded and vaporized to at least two pressure levels.
- Step a) is carried out at a pressure higher than the pressure critical of methane and preferably higher than the critical pressure of natural gas, to be liquefied.
- step a) is carried out at a pressure value higher than the gas cricondenbar natural to liquefy.
- Step a) is carried out at a pressure that is preferably understood to be between 7 and 20 MPa.
- the temperature that natural gas has at the end of step a) is preferably between 165 and 230 K.
- Natural gas during step a) is expanded to a pressure such that after expansion, a liquid fraction concentrated in hydrocarbons heavier than methane is produced, said fraction liquid then being separated.
- Step b) is, for example, carried out by expansion in a turbine whose elements are thermally insulated from gas, at least one of the elements being made of a material little conductor of heat.
- Step b) is, for example, carried out by expansion in a turbine having a rotor made of composite material, not very conductive of heat.
- the heat exchanges during steps a) and d) can be carried out by passing the gas through exchangers operating against the current.
- the heat exchange in step d) can be carried out by passing the gas in an exchanger with a temperature difference on the side cooler of the exchanger less than 5 K and a temperature difference on the side the hottest heat exchanger less than 10 K.
- the relaxation can be achieved during step b) by means of minus two successive turbines, the liquid-vapor mixture coming from the first partial expansion being separated, into a gaseous fraction and a liquid fraction, said gaseous fraction being sent to carry out the step d) and said resulting liquid fraction being expanded in the second turbine, the liquid fraction at the end of this second expansion forming a part of the liquefied natural gas produced by the process.
- At least part of the gaseous fraction from step b) is put, for example, in counter-current contact with the liquid fraction from step e), the resulting liquid fraction being sent to step f) and the resulting gas fraction being combined with the fraction gas from step e) to form at least in part a gas fraction rich in nitrogen which is evacuated.
- the present invention also relates to an apparatus for liquefaction of a natural gas according to the method described above, comprising a natural gas inlet pipe and preferably a conduit for a recycled gas, said conduits being connected to a device allowing to cool natural gas, a conduit allowing the passage refrigeration fluid, inside the device, an outlet duct connected to the cooled natural gas device and in the form of dense phase, a compression and condensation circuit.
- the duct is separated in two under conduits, said first under conduit being connected to a first expansion device, said second under conduit being directly connected to a refrigeration device, having a gas fraction outlet pipe natural refrigerated, said duct being connected to an expansion means, said duct being connected to a expansion device, said expansion devices being connected to a means for separation of the expanded natural gas fractions from devices by conduits respectively, said separation means being provided with at least one vapor phase evacuation pipe and minus a liquefied natural gas discharge pipe.
- the means capable of relaxing natural gas in the form of a phase dense consists of at least one expansion turbine of which at least one elements is made of a material which is not very conductive of heat.
- the present invention offers many advantages over to the methods usually used in the prior art. Indeed, the fact of work at an initial pressure value for the gas greater than values used by the processes mentioned in the prior art allows reduce the energy required for liquefying natural gas.
- Figure 1 shows a block diagram of a process used according to the prior art for liquefying a natural gas, for example.
- the liquefaction process involves a precooling cycle which allows the mixture used in the refrigeration cycle to be condensed main.
- the pre-refrigeration cycle and the main refrigeration cycle use a mixture of fluids as refrigerant.
- a mixture in vaporizing is likely to refrigerate and liquefy the gas under pressure.
- the mixture is compressed, condensed into exchanging heat with the surrounding environment, such as water or air, available and recycled.
- Natural gas comes under pressure through line 1. It then passes in the exchanger E1 in which it is liquefied and cooled. At the exit of exchanger E1, liquefied natural gas is expanded to a value of pressure close to atmospheric pressure by passing through a expansion valve V1 and then discharged through line 2.
- Natural gas is cooled by a permanent gas circulating in the refrigeration cycle consisting of a turbine T 1 , a duct 4 connecting the turbine T 1 to the exchanger E1, and a duct 5 allowing passage permanent gas from the exchanger to a series of compressors and cooling means arranged in cascade K1, C1, K2, C2 for example.
- the permanent gas circulating in the refrigeration cycle is compressed in the compression stage K1, cooled by passage through the cooling means C1 and then passes into the compression stage K2 in which it is compressed to be subsequently cooled by passage through the cooling stage C2.
- the permanent gas, thus compressed and cooled is sent via line 3 to the turbine T 1 in which it undergoes expansion and from which it emerges cooled before being sent to the exchanger E1 via line 4.
- the permanent gas thus refrigerated cools the natural gas when brought into contact in the exchanger E1. At the outlet of this exchanger and after having cooled the natural gas, the permanent gas is sent again and recycled in the compression and cooling stages via the conduit 5.
- Such a cycle is used for small capacity units, in particular because of its simplicity. However, it is recognized that its performance is significantly lower than a cycle using a mixture of refrigerants. In addition, it involves the recirculation of a very large flow of refrigerant gas.
- the principle implemented according to the invention described below consists, from a dense phase natural gas, to arrive at least in part at its liquefaction without phase transition, i.e. at least part of the liquefaction process takes place without phase transition during of which there would be coexistence between two phases of natures different. So, throughout the liquefaction process the passage of the dense phase to the liquid phase takes place continuously, a phase transition involving discontinuous passage.
- the method relies on the implementation, essentially of at least two stages, the first consisting in bringing natural gas into phase dense and the second to produce a trigger with energy supply mechanical, for example a substantially isentropic expansion, making pass the natural gas in dense phase in liquid phase.
- the gas arrives via the conduit 7 (FIG. 3A) in the gas phase, in a thermodynamic state represented by the point G1 (FIG. 3B), in an exchanger E2 in which it is precooled to a given temperature, in contact with a coolant from a refrigeration cycle R1.
- Natural gas is present at the outlet of the exchanger E2, in dense phase, at point G2 (Fig.3B). It is then transmitted from the exchanger E2 to the turbine T 4 in which it is expanded by the conduit 15. After passing through the turbine T 4 , it is at least partly in the liquid phase at point G3.
- the transformation from the dense phase to the liquid phase is carried out by expansion with supply of mechanical energy and without phase transition.
- the liquid phase obtained at point G3 after expansion is, for example, a saturated liquid phase.
- a gaseous fraction or steam which, after heat exchange, can be recycled or used otherwise. It is, for example, used as fuel on the site of the liquefaction facility.
- the process is illustrated in a coordinate diagram pressure (P) and temperature (T) shown in Figure 3B.
- P coordinate diagram pressure
- T temperature
- the gas phase domain is delimited by the vapor branch v (dew curve) of the two-phase domain and the isentrope s passing through the critical point C.
- the domain of the dense phase is delimited on the one hand by the isentrope s and on the other hand by the isobaric p passing by the critical point C.
- the domain of the liquid phase is delimited by a leaves by the isobar p and by the liquid branch I (bubble curve) of the domain two-phase.
- the natural gas to be liquefied is initially in a gas phase state represented by a point G1 at a temperature T G1 and at a pressure P G1 . It is then cooled in a substantially isobaric manner so as to bring it into a dense phase state represented by the point G2, at a pressure and a temperature respectively P G2 and T G2 .
- the transition from G1 to G2 takes place, for example, continuously, without phase transition, passing through the point F1 of the isentrope p delimiting the gas phase domain from the dense phase domain.
- the natural gas in dense phase, point G2 is then expanded in a substantially isentropic manner to pass it into a liquid phase state, and preferably in a saturated liquid phase state represented by a point G3 located, for example, on the liquid branch I of the two-phase domain, corresponding to temperature and pressure values T G3 and P G3 .
- the value of the pressure P G3 is preferably substantially equal to that of the atmospheric pressure.
- the transition from the state represented by the point G2 to the state represented by the point G3 is effected by passing through the point F2 of the isobare p delimiting the dense phase domain from the liquid phase domain, continuously without phase transition, that is to say without coexistence between two different phases.
- the trigger can be continued in the two-phase field by generating a vapor fraction or carbonated.
- the temperature at the end of the refrigeration stage preceding the stage of trigger is between 165 and 230K.
- FIG. 3C illustrates the application of the process to the liquefaction of a gas natural.
- Natural gas arrives via a pipe 7 to an exchanger E2 under a pressure greater than at least the critical pressure value of methane, in which it is cooled to a temperature, for example between 165 K and 230 K.
- This step of pre refrigeration of the gas is ensured, for example, by a fraction of the natural gas withdrawn before it enters an exchanger E2 via a pipe 8 which transfers this fraction withdrawn to an expansion turbine T 2 .
- the withdrawn fraction is cooled during expansion, carried out and operated in the gas phase in the turbine T 2 , it is then sent to the exchanger E2 by a conduit 9.
- the withdrawn and cooled gaseous fraction thus acts as an agent cooling and lowers the temperature of the natural gas entering the exchanger E2. Any external refrigerant with characteristics allowing to cool a gas can replace the fraction of natural gas withdrawn and cooled.
- the natural gas thus leaves the exchanger E2 cooled in the "dense" phase by a conduit 10.
- a fraction of this "dense" phase is sent directly by a conduit 11, for example, to an expansion turbine T 3 .
- a mixture composed mainly of liquid phase is obtained.
- the mixture is discharged through a line 12, at a pressure close to atmospheric pressure, from the turbine T 3 to a separator flask B1 in which the liquid and gaseous fractions are separated.
- the gaseous fraction taken from the balloon B1 is sent through a line 13 into an exchanger E3.
- the fraction of natural gas cooled in the "dense" phase from the exchanger E2 which has not been sent to the turbine T 3 passes through a pipe 14 in an exchanger E3 in which it is refrigerated by heat exchange with the gaseous fraction arriving via line 13.
- the natural gas thus refrigerated leaves the exchanger E3 at a temperature lower than the temperature which it has at the inlet of this exchanger, for example at a temperature close to the temperature of the arriving gaseous fraction via line 13. It is then sent via line 15 to a turbine T 4 in which it is expanded. At the outlet of the turbine T 4 , the majority mixture is obtained in the liquid phase which is sent via a line 16 to the separator flask B1.
- the two liquid phase fractions collected in the flask B1 form the liquefied natural gas discharged through a line 17.
- the gaseous fraction coming from the separator flask B1 passes into the exchanger E3 by a conduit 13 and is sent to the exchanger E2 by a conduit 18 from which it emerges at a temperature close to the inlet temperature of the natural gas to be liquefied. It is then sent to a compression stage K3 via a conduit 19.
- the gaseous fraction is cooled by heat exchange with the ambient medium, water or air, available in a heat exchanger C3, then it is mixed with a gaseous fraction coming from the expansion through the turbine T 2 of the gaseous part initially removed before the exchanger E2, said gaseous fraction coming from the exchanger E2 by a conduit 20 connected and opening into the conduit 19, for example between the exchanger C3 and a compression stage K4.
- the gas mixture thus obtained is compressed in the compression stage K4 and then cooled by heat exchange with the ambient medium, water or air available.
- the gas mixture thus compressed and cooled is recycled via line 21 and mixed with the natural gas to be liquefied arriving via line 7.
- Each of the compression stages K3 and K4 can be advantageously replaced by a succession of compression stages, the gas mixture leaving a compression stage being cooled by heat exchange with the surrounding environment, water or air, available, before to be sent to the next floor so as to bring the compression closer operated by an isothermal compression carried out at a neighboring temperature the ambient temperature, water or air, available.
- the critical pressure of the mixture forming the natural gas is higher than the critical methane pressure.
- the pressure at which is carried out step a) is preferably greater than the pressure critical of said mixture.
- the pressure at which step a) is carried out is also, from preferably greater than the defined cricondenbar for a mixture like being the pressure above which two phases cannot coexist.
- the fraction of natural gas in the "dense" phase which is not expanded in the turbine T 3 is cooled in the exchanger E3 to a temperature close to the final temperature of the natural gas liquefied product.
- the fraction of natural gas expanded in the expansion turbine T 3 represents a majority fraction of the natural gas present at the inlet, this fraction preferably being greater than two thirds of the natural gas present at the inlet of the exchanger E3 and arriving via line 10.
- the expansion work used to relax the natural gas is, for example, recovered in the turbines T 3 and T 4 and used, for example, to drive the compression stages K3 and K4 and / or, in the case of the diagram in the figures 5 and 6, the compression stages K5 and K6.
- the additional mechanical energy that may be required is supplied, for example, by a steam turbine or, preferably, by a gas turbine.
- step a) By increasing the pressure level at which step a) is carried out, it is possible to reduce the additional mechanical energy required to liquefy natural gas.
- the method according to the invention is all the more advantageous since the pressure at which step a) is carried out is high.
- the pressure used must be at least equal to the critical pressure of methane (4.6 MPa) and, preferably greater than the cricondenbar of the mixture which constitutes the gas natural to liquefy. It is situated, advantageously in an interval for example between 7 and 20 MPa.
- the quantity of gaseous phase recycled after the expansion carried out at during step c is preferably between 165 K and 230K.
- hydrocarbons When natural gas contains heavier hydrocarbons than methane, these hydrocarbons are, for example, at least in part separated from natural gas before the liquefaction operation, in particular for avoid any risk of crystallization during liquefaction.
- the Hydrocarbons heavier than methane cannot be condensed by refrigeration. It was discovered that, in this case, they are advantageously separated by an adsorption step on an adsorbent constituted for example by an alumina, a zeolite or an activated carbon.
- the adsorbent is used, for example, in at least two beds fixed operating in parallel.
- a bed operates, for example, in adsorption while another bed is operating in desorption.
- Desorption is carried out, by for example, by decreasing the pressure and / or increasing the temperature. Hydrocarbons heavier than methane which must be separated, attach to the adsorbent during the adsorption step, then they are separated during the desorption step.
- step a Another way to proceed when natural gas contains heavy hydrocarbons, consists, during step a) in cooling the gas natural at a temperature such that after a relaxation substantially isentropic having brought the gas to a pressure below the cricondenbar of the mixture, a liquid phase is formed by condensation retrograde.
- the expanded mixture is then cooled to a pressure substantially constant.
- the liquid phase comprising the hydrocarbons heavier than methane, to be separated, is then removed after the expansion operation and / or during the subsequent cooling of the mixture operated at a substantially constant pressure.
- the gas can be compressed, at the by means of a compression step carried out under conditions also as close as possible to that of isothermal compression using compression stages alternating with cooling stages, the cooling being carried out using a cooling fluid, water or air available, for example at the liquefaction site.
- such a compression step can become necessary when the gas pressure at the head of the well becomes too low, for example, after a period of exploitation of the gas field natural.
- the natural gas to be liquefied contains nitrogen, and when this is necessary, it is possible to at least partially separate this nitrogen.
- Natural gas is sent to the exchanger E2 via line 7. A the end of the cooling step in the exchanger E2, natural gas comes out as a "dense" phase. The fraction of this "dense" phase can be relaxed directly, by at least two relaxation steps described below.
- a first fraction of the dense phase is sent via the conduit 11 from the outlet of the exchanger E2 to a turbine T 31 in which it is expanded.
- the mixture obtained by expansion is evacuated via a pipe 30 from the turbine T 31 to a separator flask B2 in which the liquid and gaseous fractions of the mixture are separated.
- the gaseous fraction is, for example, sent or recycled through a conduit 31 in the exchanger E3.
- the liquid fraction separated in the separator flask B2 is depleted in nitrogen, then discharged through a conduit 32 to a turbine T 32 where it is expanded and from which it emerges in the form of a liquid-vapor mixture.
- this liquid-vapor mixture obtained is sent to the base or lower part of a contactor S1 via a pipe 35.
- the fraction of natural gas cooled in dense phase from the exchanger E2 and not diverted to the turbine T 31 is sent through a pipe 14 to the exchanger E3. It is refrigerated in this exchanger by heat exchange with the gaseous fraction coming from the duct 31. At the outlet of the exchanger E3, the fraction in dense phase is at a temperature below its initial temperature of entry into the exchanger E3, substantially close of the temperature of the gaseous fraction arriving via the pipe 31.
- This dense phase fraction coming from the exchanger E3 is sent by a pipe 15, in a turbine T 4 , in which it is expanded.
- the liquid-vapor mixture mainly composed of liquid phase obtained after expansion at the outlet of the turbine T 4 is sent to the head of the contactor S1, upper part of the contactor, through a conduit 36.
- the liquid phase leaving the turbine T 4 is relatively concentrated in nitrogen.
- it is contacted against the current with the gaseous fraction arriving at the base of the contactor S1 via the conduit 35 whose composition is close to equilibrium with a liquid phase relatively poor in nitrogen.
- the liquid phase which descends becomes depleted in nitrogen and the gaseous phase which rises is enriched in nitrogen. It is thus possible to obtain, at the base of the contactor S1, a liquid fraction relatively poor in nitrogen and at the head of the contactor S1 a gaseous fraction relatively rich in nitrogen.
- the liquid fraction collected at the base of the contactor S1 forms the liquefied natural gas discharged through a conduit 38.
- the gaseous fraction collected at the head of the contactor S1 forms the gaseous fraction concentrated in nitrogen which is separated from the natural gas.
- This gaseous fraction concentrated in nitrogen is removed by a conduit 34 and sent to an exchanger E4 from which it emerges through a conduit 37.
- the gaseous fraction concentrated in nitrogen is heated by heat exchange with a fraction of natural gas derived from the natural gas introduced arriving via a conduit 33 connecting directly the conduit 7 for introducing natural gas to the exchanger E4.
- This fraction of natural gas directly derived from the introduction conduit 7 is cooled in the exchanger E4, then expanded through an expansion valve V3 located on the conduit 36 connecting the exchanger E4 to the contactor S1.
- the fraction of natural gas derived and expanded is then mixed with the liquid-vapor mixture coming from the turbine T 4 , and sent to the contactor S1, the mixing of the two liquid vapor fractions being carried out at the level of the conduit 36.
- the contactor S1 is formed for example of a column element with packing or column trays.
- the number of theoretical stages of the contactor S1 is for example 3 or 4.
- a first fraction f1 of this natural gas is cooled by the exchangers E2 and E3 to a temperature of 122 K.
- the natural gas is thus found at the outlet of the exchanger E3 in a "dense" phase state. It is then at least partially liquefied by expansion in the turbine T 4 , for example, at atmospheric pressure and is then introduced through the conduit 16 at the head of the contactor S1.
- a second fraction f2 taken upstream of the exchanger E2 is cooled to 185 K by a substantially isentropic expansion in the turbine T 2 to the vicinity of its dew pressure.
- This cooled and expanded fraction is then introduced via line 9 into the exchanger E2 where it heats up against the current with the first fraction f1.
- the fraction f2 passes through a train of compressors refrigerated by the ambient medium K4, C4, in which it is compressed and cooled, then is mixed with the natural gas to be liquefied introduced by the conduit 7.
- a third fraction f3 is taken and cooled, for example, to 117 K by a substantially isentropic expansion in a turbine T 31 .
- the gaseous fraction is separated from the gas / liquid mixture obtained by expansion of the fraction f3 in the cylinder B2, and introduced by the conduit 31 in the exchanger E3, then by the conduit 18 in the exchanger E2 where it heats up against current with the first fraction f1.
- the fraction f3 passes through a train of compressors K3, C3, refrigerated, for example, by the ambient medium and is then mixed with the second fraction f2 upstream of the train of compressors K4, C4 also refrigerated. , for example, by the surrounding environment.
- the liquid fraction coming from the balloon B2 is expanded by passing through the turbine T 32 at atmospheric pressure and introduced into the lower part, for example, at the bottom of the contactor S1.
- the vapor fraction or gaseous fraction is enriched in nitrogen.
- the vapor fraction contains 66% by mass of nitrogen and liquefied natural gas 1.3% by mass of nitrogen. This vapor fraction is warmed up to room temperature with a fraction f4 of the natural gas to be treated, is introduced at the top of the contactor before being discharged.
- fractions f1, f2, f3 and f4 are chosen so that the thermal approaches to the exchangers are minimal.
- the methane losses in the purged gas are 3.5%.
- step b) The relaxation carried out during step b) is accompanied by a significant variation in temperature which is, for example, greater than 50 ° C. In the case where the expansion is carried out in two or more successive turbines, this results in a relatively large difference between the inlet and outlet temperatures for each turbine.
- the trigger is operated in the "dense" or liquid phase. Thermal exchanges between the fluid being expanded and the elements of the turbine can, under these conditions, reduce the effectiveness of the trigger.
- These elements can be coated metallic components a thermally insulating layer. These elements, and in particular the rotor, can also be made of a composite material poor conductor of heat.
- the heat exchanges carried out during steps a) and d) are carried out in heat exchangers operating against the current.
- These heat exchangers are, for example, pass exchangers multiple and are preferably constituted by plate heat exchangers.
- These plate exchangers can be, for example, heat exchangers brazed aluminum. It is also possible to use heat exchangers stainless steel with plates welded together.
- the channels in which the fluids participating in the exchange circulate heat can be obtained by different means by arranging between the plates of the corrugated intermediate plates, forming the plates, for example by explosion, by grooving the plates, for example by chemical etching.
- step e) The heat exchange carried out during step e) is then carried out with a temperature difference on the coldest side of the heat exchanger preferably less than 5K and a temperature difference on the hottest side of the exchanger preferably less than 10K.
- stage a) of refrigeration by means of an external cycle operating with a mixture of refrigerants.
- the operating principle of the process in this case is illustrated, for example in FIG. 5.
- the first stage of refrigeration of natural gas is then carried out in the exchanger E2, such as a plate exchanger, not by an exchange thermal with a gaseous fraction refrigerated by expansion as it is described above, but. with a mixture of refrigerants which vaporizes in the exchanger E2.
- the exchanger E2 such as a plate exchanger
- the refrigerant mixture comes from cycle A comprising, by example, a set of pipes, compressors, exchangers and valves as described below.
- the refrigerant mixture is vaporized at two pressure levels which can be successive to widen the temperature range for which performs the refrigeration.
- This mixture is, for example, introduced into the exchanger E2 by a conduit 27 which separates into two conduits 27a and 27b.
- a first part mixture of refrigerants in liquid phase is first evacuated by a conduit 23 extending conduit 27a from exchanger E2 to a first expansion valve V20, in which it is vaporized, for example, at a temperature between 238 and 303K, pass through the exchanger E2 and comes out in gaseous or vapor form to be sent to a compressor K6 through a pipe 24.
- a second part of the mixture passes through the sub-conduit 27b, then is evacuated from the exchanger E2 to a valve V30 located on a conduit 25 extending the sub duct 27b.
- the mixture is expanded by the valve V30 up to a pressure close to atmospheric pressure and vaporized, for example, at a temperature between 173 and 238K.
- the vapor phase thus obtained is sent from the E2 exchanger to the inlet of a K5 compressor, then cools in a C5 exchanger located after the compressor K5 and mixed with the steam fraction arriving through the pipe 24.
- the vapor phase mixture thus obtained is then compressed in the K6 compressor, cooled and condensed by passing through an exchanger C6 before being sent via line 27 into the exchanger E2, where it is sub-cooled before being relaxed and vaporized.
- Natural gas arrives via line 7 and leaves the exchanger E2 cooled by a line 11, it has, at the outlet of exchanger E2, a temperature close to, for example, 178K in the form of a mixture. Most of this mixture passes through a turbine T 3 in which it is expanded and from which it emerges in the form of a liquid-vapor mixture which is then sent by a conduit 12 to the base of a contactor S1.
- the other part of the natural gas having passed through the turbine T 3 passes directly from the exchanger E2 to a plate exchanger E3 by a conduit 14 in which it is cooled for example by exchange with the fraction in vapor phase coming from the contactor S1 by a conduit 13, up to a temperature close to the final temperature of the liquefied natural gas produced.
- the gas fraction cooled in the exchanger E3 leaves this exchanger through a conduit 15 and expanded through an expansion valve V4.
- the liquid fraction obtained by expansion is sent to the top of the contactor S1.
- this liquid phase is depleted in nitrogen, while the vapor phase fraction introduced at the bottom of the contactor S1 goes back into the contactor, enriched with nitrogen. Fraction in the vapor phase which leaves the contactor S1 is thus charged with nitrogen, this which thus allows most of the nitrogen contained to be removed initially in natural gas.
- the nitrogen-rich gas fraction passes through the exchanger E3, then via the conduit 18 in the exchanger E2 from which it emerges by a duct 19.
- the contactor S1 can be constituted for example by a column with trays or a packed column.
- the lining may advantageously be of the "structured" type.
- V20, V30 and V4 expansion valves can be replaced by in whole or in part by drive expansion turbines.
- the E2 and E3 exchangers can be made with materials and / or different assembly methods. It is also possible to carry out all of the heat exchanges in a heat exchanger single plate.
- K5 and K6 compressors can each have a series of floors. Between two successive stages, it is possible to plan a stage intermediate cooling.
- the low-pressure gas fraction discharged through line 19 can be at least partially recompressed and recycled. It is clear, however, that if the gaseous fraction thus obtained can be used at low pressure, without be recycled, it is possible to significantly reduce costs investment and the necessary operating costs.
- the natural gas leaving the exchanger E2 via the conduit 11 undergoes a first expansion in the turbine T 31 .
- a liquid fraction is collected by a balloon B3 then evacuated by the conduit 42 preferably located in the lower part of this balloon towards a turbine T 32 where it undergoes a second expansion.
- a gaseous fraction relatively rich in nitrogen sent by a pipe 40 in a turbine T 4 where it is expanded before being sent into the contactor S1, preferably in its lower part.
- the expanded mixture obtained is evacuated by a conduit 43 and separated in a flask 84 into a liquid fraction depleted in nitrogen which is evacuated by a conduit 45 located in the lower part of the flask B, preferably , and which constitutes part of the liquefied natural gas produced and a gaseous fraction taken from the upper part of the balloon relatively poor in nitrogen sent by a conduit 44 to the exchanger E3, then by the conduit 18 to the exchanger E2 from where it comes out through the conduit 19.
- the conduit 19 is connected to a compressor K3 which recompresses, for example, said gaseous fraction relatively poor in nitrogen before passing through an exchanger C3 where it is cooled with the cooling fluid, which can be of the water or air.
- the compressor K3 preferably comprises several compression stages between which are placed, for example, cooling stages.
- Natural gas under pressure leaving the exchanger E3 via the pipe 15 is, for example, relaxed in an expansion valve V11 before being sent at the head of contactor S1.
- the non-recycled fraction is evacuated via conduit 49.
- Via conduit 47 arrives in the exchanger E4 a fraction of the pressurized natural gas that is cooled in the exchanger E4 and exits through the conduit 48 at a temperature close to the final temperature of the LNG produced. Said fraction is then relaxed to through valve V10 and sent to the head of contactor S1.
- a liquid fraction is collected which is mixed with the liquid fraction arriving via line 45 to form the liquefied natural gas produced, which is discharged through line 50.
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Abstract
Description
La liquéfaction du gaz naturel est une opération industrielle importante qui permet de transporter le gaz naturel sur de longues distances par méthanier, ou de les stocker sous forme liquide.Natural gas liquefaction is an industrial operation important for transporting natural gas over long periods distances by LNG carrier, or to store them in liquid form.
Les procédés utilisés actuellement réalisent l'opération de liquéfaction d'un "gaz naturel" en faisant passer ce gaz naturel à travers des échangeurs et en les réfrigérant au moyen d'un cycle frigorifique externe. Ainsi, les brevets US-3.735.600 et US-3.433.026 décrivent des procédés de liquéfaction au cours desquels le gaz est envoyé à travers un ou plusieurs échangeurs de chaleur de manière à obtenir sa liquéfaction. Par "gaz naturel", nous entendons par la suite un mélange formé majoritairement de méthane mais pouvant contenir également d'autres hydrocarbures et de l'azote, sous quelque forme qu'il se trouve (gazeuse, liquide ou diphasique). Le gaz naturel au départ se présente majoritairement sous une forme gazeuse, et au coursde l'étape de liquéfaction, il peut se présenter sous différentes formes, liquide et gazeuse qui peuvent coexister à un instant donné.The methods currently used carry out the operation of liquefaction of a "natural gas" by passing this natural gas through exchangers and refrigerating them by means of a refrigeration cycle external. Thus, the patents US-3,735,600 and US-3,433,026 describe liquefaction processes in which gas is sent through a or several heat exchangers so as to obtain its liquefaction. By "natural gas" we mean afterwards a mixture formed mostly methane but may also contain other hydrocarbons and nitrogen, in whatever form (gaseous, liquid or two-phase). Natural gas at the start mostly in gaseous form, and during the liquefaction, it can come in different forms, liquid and gaseous which can coexist at a given time.
Dans de tels procédés, un cycle de réfrigération externe utilisant comme fluide réfrigérant un mélange de fluides est mis en oeuvre. Un tel mélange en se vaporisant est susceptible de réfrigérer et de liquéfier le gaz sous pression. Après vaporisation, le mélange est comprimé, condensé en échangeant de la chaleur avec un milieu ambiant tel que de l'eau ou de l'air.In such processes, an external refrigeration cycle using as refrigerant a mixture of fluids is used. Such vaporizing mixture may refrigerate and liquefy gas under pressure. After vaporization, the mixture is compressed, condensed into exchanging heat with an ambient medium such as water or the air.
De tels procédés sont complexes et mettent en jeu des surfaces d'échange élevées ainsi que des puissances de compression importantes. De ce fait, ils conduisent à des coûts d'investissement élevés.Such processes are complex and involve surfaces high exchange rates as well as high compression powers. Therefore, they lead to high investment costs.
L'art antérieur mentionne aussi d'autres manières de procéder.The prior art also mentions other ways of proceeding.
Le brevet US-3.616.652 décrit un procédé de liquéfaction d'un gaz naturel. Le gaz naturel se présente dans un état de phase dense, l'étape de détente et l'étape de réfrigération sont effectuées sur la totalité du flux du gaz naturel.US Patent 3,616,652 describes a process for liquefying a gas natural. Natural gas is in a dense phase state, the stage expansion and the cooling step are performed on the entire flow natural gas.
Dans le brevet US-4.778.497, le gaz naturel est transformé sous une forme de phase dense en utilisant un dispositif dont la fonction est de sous refroidir un gaz supercritique. L'étape de détente suivante est ensuite effectuée sur la totalité du flux de gaz.In US Pat. No. 4,778,497, natural gas is transformed under a dense phase form using a device whose function is to under cool a supercritical gas. The next relaxation step is then performed on the entire gas flow.
Il a été découvert, et c'est là un des objets de la présente invention, qu'il est possible à l'issue d'une première étape de réfrigération de réfrigérer et de liquéfier le gaz naturel directement par détente à travers une turbine à partie d'une phase "dense". L'expression "phase dense" désigne une phase pouvant être obtenue à partir d'une phase gazeuse initiale par une évolution isobare sans transition de phase et conduisant par détente isentropique à une phase liquide sans transition de phase. Au moins une partie du procédé de liquéfaction s'effectue sans transition de phase, c'est-à-dire que le passage de la phase gazeuse à la phase liquide s'effectue de manière continue, sans transformation au cours de laquelle il y aurait coexistence de deux phases différentes. Le gaz naturel est amené en "phase dense" avant détente, en opérant à une pression au moins supérieure à la pression critique du méthane, et en abaissant la température du "gaz naturel".It was discovered, and this is one of the objects of the present invention, that it is possible after a first refrigeration step of refrigerate and liquefy natural gas directly by relaxing through a turbine from a "dense" phase. The expression "dense phase" denotes a phase obtainable from a gas phase initial by an isobaric evolution without phase transition and leading by isentropic expansion to a liquid phase without phase transition. At at least part of the liquefaction process takes place without transition from phase, i.e. the transition from the gas phase to the liquid phase takes place continuously, without transformation during which it two different phases would coexist. Natural gas is brought in "dense phase" before expansion, operating at a pressure at least higher than the critical methane pressure, and lowering the "natural gas" temperature.
La présente invention concerne un procédé de liquéfaction d'un gaz naturel. II est caractérisé en ce qu'il comporte une étape selon laquelle on liquéfie au moins en partie ledit gaz par détente avec fourniture d'énergie mécanique, cette détente le faisant passer d'un état ou phase dense vers un état ou une phase liquide.The present invention relates to a process for liquefying a gas natural. It is characterized in that it comprises a step according to which at least partially liquefies said gas by expansion with supply of mechanical energy, this relaxation taking it from a state or phase dense to a liquid state or phase.
Le passage entre ces deux états s'effectue sans coexistence simultanée de deux phases différentes.The transition between these two states takes place without coexistence two different phases simultaneously.
Le procédé selon l'invention comporte en combinaison les
étapes suivantes:
La première fraction majoritaire détendue est de préférence supérieure aux deux tiers du gaz naturel en phase dense issu de la première étape.The first relaxed majority fraction is preferably greater than two thirds of the dense phase natural gas from the first stage.
La détente sur la phase liquide obtenue au cours de l'étape b) étant poursuivie jusqu'à l'apparition d'une fraction gazeuse, l'on procède aux étapes suivantes :
- on sépare la fraction liquide et la fraction gazeuse au cours de l'étape c),
- la fraction gazeuse résultant de l'étape c) est échangée thermiquement avec une fraction non détendue du gaz naturel au cours de l'étape d), ladite fraction non détendue étant détendue à l'issue de cette opération d'échange thermique au cours de l'étape e) en formant un mélange liquide-vapeur qui est séparé en une fraction liquide et une fraction gazeuse,
- on réunit les fractions liquides provenant des étapes c) et e) pour former le gaz naturel liquéfié, et
- on recomprime et on recycle au moins en partie les fractions gazeuses provenant des étapes c) et e) à l'étape a).
- the liquid fraction and the gaseous fraction are separated during step c),
- the gaseous fraction resulting from step c) is thermally exchanged with an unexpanded fraction of natural gas during step d), said unexpanded fraction being expanded at the end of this heat exchange operation during step e) by forming a liquid-vapor mixture which is separated into a liquid fraction and a gaseous fraction,
- the liquid fractions coming from steps c) and e) are combined to form the liquefied natural gas, and
- the gaseous fractions from steps c) and e) in step a) are recompressed and at least partially recycled.
On utilise, par exemple, comme dispositif une turbine pour détendre le gaz et le faire passer de l'état en phase dense vers l'état en phase liquide.For example, a turbine is used as a device to relax the gas and move it from the dense phase state to the phase state liquid.
Au cours de l'étape a), on peut refroidir le gaz naturel par échange thermique en utilisant une fraction gazeuse provenant dudit gaz naturel, ladite fraction gazeuse étant détendue dans une turbine, ladite fraction gazeuse détendue étant au moins en partie recomprimée dans un étage de compression et recyclée.During step a), natural gas can be cooled by exchange thermal using a gaseous fraction from said natural gas, said gas fraction being expanded in a turbine, said fraction expanded gas being at least partly recompressed in a stage of compression and recycled.
On comprime, par exemple, au moins une fraction gazeuse recyclée en mettant en oeuvre au moins deux étages, le gaz étant refroidi à la sortie de chacun des étages de compression par un milieu ambiant de réfrigération disponible.For example, at least one recycled gas fraction is compressed using at least two stages, the gas being cooled at the outlet of each of the stages of compression by an ambient medium of refrigeration available.
Au cours de l'étape a), on peut aussi refroidir le gaz naturel par vaporisation d'un mélange de réfrigérants, le mélange ainsi obtenu se présente en phase vapeur ou phase gazeuse. Il est ensuite comprimé, condensé par un échange thermique avec le milieu ambiant de réfrigération disponible, détendu et recyclé.During step a), natural gas can also be cooled by vaporization of a mixture of refrigerants, the mixture thus obtained present in vapor or gas phase. It is then compressed, condensed by a heat exchange with the ambient medium of refrigeration available, relaxed and recycled.
Le mélange de réfrigérants peut être détendu et vaporisé à au moins deux niveaux de pression.The refrigerant mixture can be expanded and vaporized to at least two pressure levels.
Lorsque le gaz naturel comporte des hydrocarbures lourds, on peut séparer les hydrocarbures les plus lourds contenus dans le gaz naturel à liquéfier préalablement à l'étape a) au moyen d'un étape d'adsorption.When natural gas contains heavy hydrocarbons, we can separate the heaviest hydrocarbons contained in natural gas to liquefy before step a) by means of an adsorption step.
On réalise l'étape a) à une de pression supérieure à la pression critique du méthane et de préférence supérieure à la pression critique du gaz naturel, à liquéfier. Step a) is carried out at a pressure higher than the pressure critical of methane and preferably higher than the critical pressure of natural gas, to be liquefied.
De préférence, encore, on réalise l'étape a) à une valeur de pression supérieure au cricondenbar du gaz naturel à liquéfier.Preferably, again, step a) is carried out at a pressure value higher than the gas cricondenbar natural to liquefy.
L'étape a) est réalisée à une pression comprise, de préférence, entre 7 et 20 MPa.Step a) is carried out at a pressure that is preferably understood to be between 7 and 20 MPa.
La température que possède le gaz naturel à l'issu de l'étape a) est de préférence, comprise entre 165 et 230 K.The temperature that natural gas has at the end of step a) is preferably between 165 and 230 K.
Pour un gaz naturel comportant des hydrocarbures plus lourds que le méthane, on sépare les hydrocarbures au monis en partie au cours d'une étape préliminaire opérée à une pression inférieure à la pression de l'étape a).For a natural gas containing heavier hydrocarbons than methane, we separate the hydrocarbons to monis partly during of a preliminary stage operated at a pressure lower than the pressure of step a).
Le gaz naturel au cours de l'étape a) est détendu jusqu'à une pression telle qu'après détente, une fraction liquide concentrée en hydrocarbures plus lourds que le méthane est produite, ladite fraction liquide étant alors séparée.Natural gas during step a) is expanded to a pressure such that after expansion, a liquid fraction concentrated in hydrocarbons heavier than methane is produced, said fraction liquid then being separated.
L'étape b) est, par exemple, réalisée par détente dans une turbine dont les éléments sont isolés thermiquement du gaz, au moins un des éléments étant réalisé en un matériau peu conducteur de la chaleur.Step b) is, for example, carried out by expansion in a turbine whose elements are thermally insulated from gas, at least one of the elements being made of a material little conductor of heat.
L'étape b) est, par exemple, réalisée par détente dans une turbine ayant un rotor réalisé en matériau composite, peu conducteur de la chaleur.Step b) is, for example, carried out by expansion in a turbine having a rotor made of composite material, not very conductive of heat.
Les échanges de chaleur au cours des étapes a) et d) peuvent être effectués en faisant passer le gaz dans des échangeurs opérant à contre-courant.The heat exchanges during steps a) and d) can be carried out by passing the gas through exchangers operating against the current.
On peut réaliser l'échange thermique de l'étape d) en faisant passer le gaz dans un échangeur présentant un écart de température du côté le plus froid de l'échangeur inférieur à 5 K et un écart de température du côté le plus chaud de l'échangeur inférieur à 10 K.The heat exchange in step d) can be carried out by passing the gas in an exchanger with a temperature difference on the side cooler of the exchanger less than 5 K and a temperature difference on the side the hottest heat exchanger less than 10 K.
On peut réaliser la détente au cours de l'étape b) au moyen d'au moins deux turbines successives, le mélange liquide-vapeur provenant de la première détente partielle étant séparé, en une fraction gazeuse et une fraction liquide, ladite fraction gazeuse étant envoyée pour réaliser l'étape d) et ladite fraction liquide résultante étant détendue dans la deuxième turbine, la fraction liquide à l'issue de cette deuxième détente formant une partie du gaz naturel liquéfié produit par le procédé.The relaxation can be achieved during step b) by means of minus two successive turbines, the liquid-vapor mixture coming from the first partial expansion being separated, into a gaseous fraction and a liquid fraction, said gaseous fraction being sent to carry out the step d) and said resulting liquid fraction being expanded in the second turbine, the liquid fraction at the end of this second expansion forming a part of the liquefied natural gas produced by the process.
Au moins une partie de la fraction gazeuse provenant de l'étape b) est mis, par exemple, en contact à contre-courant avec la fraction liquide provenant de l'étape e), la fraction liquide résultante étant envoyée à l'étape f) et la fraction gazeuse résultante étant réunie avec la fraction gazeuse provenant de l'étape e) pour former au moins en partie une fraction gazeuse riche en azote qui est évacuée.At least part of the gaseous fraction from step b) is put, for example, in counter-current contact with the liquid fraction from step e), the resulting liquid fraction being sent to step f) and the resulting gas fraction being combined with the fraction gas from step e) to form at least in part a gas fraction rich in nitrogen which is evacuated.
La présente invention concerne aussi un appareil pour la liquéfaction d'un gaz naturel selon le procédé décrit précédemment, comportant un conduit d'arrivée du gaz naturel et de préférence un conduit d'un gaz recyclé, lesdits conduits étant reliés à un dispositif permettant de refroidir le gaz naturel, un conduit permettant le passage d'un fluide de réfrigération, à l'intérieur du dispositif, un conduit de sortie relié au dispositif du gaz naturel refroidi et se présentant sous forme de phase dense, un circuit de compression et de condensation.The present invention also relates to an apparatus for liquefaction of a natural gas according to the method described above, comprising a natural gas inlet pipe and preferably a conduit for a recycled gas, said conduits being connected to a device allowing to cool natural gas, a conduit allowing the passage refrigeration fluid, inside the device, an outlet duct connected to the cooled natural gas device and in the form of dense phase, a compression and condensation circuit.
Il est caractérisé en ce que le conduit est séparé en deux sous conduits, ledit premier sous conduit étant relié à un premier dispositif de détente, ledit second sous conduit étant relié directement à un dispositif de réfrigération, comportant un conduit de sortie de la fraction de gaz naturel réfrigérée, ledit conduit étant relié à un moyen de détente, ledit conduit étant relié à un dispositif de détente, lesdits dispositifs de détente étant reliés à un moyen de séparation des fractions de gaz naturels détendus et issus des dispositifs par des conduits respectivement, ledit moyen de séparation étant pourvu d'au moins un conduit d'évacuation de la phase vapeur et d'au moins un conduit d'évacuation du gaz naturel liquéfié.It is characterized in that the duct is separated in two under conduits, said first under conduit being connected to a first expansion device, said second under conduit being directly connected to a refrigeration device, having a gas fraction outlet pipe natural refrigerated, said duct being connected to an expansion means, said duct being connected to a expansion device, said expansion devices being connected to a means for separation of the expanded natural gas fractions from devices by conduits respectively, said separation means being provided with at least one vapor phase evacuation pipe and minus a liquefied natural gas discharge pipe.
Le moyen capable de détendre le gaz naturel sous forme de phase dense est constitué d'au moins une turbine de détente dont au moins un des éléments est réalisé en un matériau peu conducteur de la chaleur.The means capable of relaxing natural gas in the form of a phase dense consists of at least one expansion turbine of which at least one elements is made of a material which is not very conductive of heat.
Ainsi, la présente invention offre de nombreux avantages par rapport aux procédés habituellement utilisés dans l'art antérieur. En effet, le fait de travailler à une valeur de pression initiale pour le gaz supérieure aux valeurs utilisées par les procédés mentionnés dans l'art antérieur permet de réduire l'énergie nécessaire pour la liquéfaction du gaz naturel. Thus, the present invention offers many advantages over to the methods usually used in the prior art. Indeed, the fact of work at an initial pressure value for the gas greater than values used by the processes mentioned in the prior art allows reduce the energy required for liquefying natural gas.
De plus, la liquéfaction directe du gaz naturel par détente permet de réduire les surfaces d'échangeurs de chaleur nécessaires et de simplifier le procédé, en réduisant ainsi les coûts d'investissements induites.In addition, the direct liquefaction of natural gas by expansion makes it possible to reduce the areas of heat exchangers required and simplify the process, thereby reducing the investment costs involved.
La présente invention sera mieux comprise et ses avantages apparaítront clairement à la lecture de quelques exemples, non limitatifs, illustrés par les figures suivantes parmi lesquelles :
- la figure 1 schématise un exemple de cycle de réfrigération tel que décrit dans l'art antérieur comportant un cycle de préréfrigération,
- la figure 2 décrit un exemple de cycle de l'art antérieur utilisant un gaz permanent,
- les figures 3A, 3B et 3C schématisent respectivement le principe de base utilisé selon l'invention, un diagramme pression température des différentes phases pour un gaz naturel, par exemple, et un exemple particulier de réalisation.
- la figure 4 décrit un exemple de réalisation adaptée à la liquéfaction d'un gaz comportant de l'azote, et séparant partiellement l'azote,
- la figure 5 décrit un exemple de réalisation pour lequel l'étape de préréfrigération est assurée par un mélange de réfrigérants, et
- la figure 6 décrit un exemple de réalisation pour la liquéfaction d'un gaz naturel contenant de l'azote, dans lequel une partie de la fraction gazeuse produite par détente est recyclée, et l'étape de réfrigération est effectuée par un mélange de réfrigérants.
- FIG. 1 shows schematically an example of a refrigeration cycle as described in the prior art comprising a pre-refrigeration cycle,
- FIG. 2 describes an example of a cycle of the prior art using a permanent gas,
- FIGS. 3A, 3B and 3C respectively diagram the basic principle used according to the invention, a pressure-temperature diagram of the different phases for a natural gas, for example, and a particular example of embodiment.
- FIG. 4 describes an exemplary embodiment suitable for the liquefaction of a gas comprising nitrogen, and partially separating the nitrogen,
- FIG. 5 describes an exemplary embodiment for which the pre-cooling step is provided by a mixture of refrigerants, and
- FIG. 6 describes an exemplary embodiment for the liquefaction of a natural gas containing nitrogen, in which a part of the gaseous fraction produced by expansion is recycled, and the refrigeration step is carried out by a mixture of refrigerants.
La figure 1 représente un schéma de principe d'un procédé utilisé selon l'art antérieur pour liquéfier un gaz naturel, par exemple.Figure 1 shows a block diagram of a process used according to the prior art for liquefying a natural gas, for example.
Le procédé de liquéfaction comporte un cycle de préréfrigération qui permet de condenser le mélange utilisé dans le cycle de réfrigération principal.The liquefaction process involves a precooling cycle which allows the mixture used in the refrigeration cycle to be condensed main.
Le cycle de préréfrigération et le cycle de réfrigération principal utilisent comme fluide réfrigérant un mélange de fluides. Un tel mélange en se vaporisant est susceptible de réfrigérer et de liquéfier le gaz sous pression. Après vaporisation, le mélange est comprimé, condensé en échangeant de la chaleur avec le milieu ambiant, tel que de l'eau ou de l'air, disponible et recyclé.The pre-refrigeration cycle and the main refrigeration cycle use a mixture of fluids as refrigerant. Such a mixture in vaporizing is likely to refrigerate and liquefy the gas under pressure. After vaporization, the mixture is compressed, condensed into exchanging heat with the surrounding environment, such as water or air, available and recycled.
Une autre manière de procéder selon l'art antérieur consiste à utiliser un cycle fonctionnant avec un gaz permanent tel que de l'azote. Un tel schéma est décrit dans la figure 2.Another way of proceeding according to the prior art consists in using a cycle operating with a permanent gas such as nitrogen. Such diagram is described in figure 2.
Le gaz naturel arrive sous pression par le conduit 1. Il passe ensuite dans l'échangeur E1 dans lequel il est liquéfié et refroidi . A la sortie de l'échangeur E1, le gaz naturel liquéfié est détendu jusqu'à une valeur de pression voisine de la pression atmosphérique par passage dans une vanne de détente V1 et évacué ensuite par le conduit 2.Natural gas comes under pressure through line 1. It then passes in the exchanger E1 in which it is liquefied and cooled. At the exit of exchanger E1, liquefied natural gas is expanded to a value of pressure close to atmospheric pressure by passing through a expansion valve V1 and then discharged through line 2.
Le refroidissement du gaz naturel est assuré par un gaz permanent
circulant dans le cycle de réfrigération constitué d'une turbine T1, d'un
conduit 4 reliant la turbine T1 à l'échangeur E1, et d'un conduit 5
permettant le passage du gaz permanent de l'échangeur vers une série de
compresseurs et de moyens de refroidissement agencés en cascade K1,
C1, K2, C2 par exemple. Ainsi, le gaz permanent circulant dans le cycle de
réfrigération est comprimé dans l'étage de compression K1, refroidi par
passage dans le moyen de refroidissement C1 puis passe ensuite dans
l'étage de compression K2 dans lequel il est comprimé pour être refroidi
ensuite par passage dans l'étage de refroidissement C2. Le gaz
permanent ainsi comprimé et refroidi, est envoyé par le conduit 3 vers la
turbine T1 dans laquelle il subit une détente et d'où il ressort refroidi avant
d'être envoyé dans l'échangeur E1 par le conduit 4. Le gaz permanent
ainsi réfrigéré refroidit le gaz naturel lors de leur mise en contact dans
l'échangeur E1. A la sortie de cet échangeur et après avoir réalisé le
refroidissement du gaz naturel, le gaz permanent est envoyé à nouveau et
recyclé dans les étages de compression et de refroidissement par le
conduit 5.Natural gas is cooled by a permanent gas circulating in the refrigeration cycle consisting of a turbine T 1 , a duct 4 connecting the turbine T 1 to the exchanger E1, and a
Un tel cycle est utilisé pour des unités de petite capacité, notamment du fait de sa simplicité. Il est toutefois reconnu que ses performances sont nettement inférieures à celles d'un cycle utilisant un mélange de réfrigérants. De plus, il implique la recirculation d'un débit très important de gaz réfrigérant.Such a cycle is used for small capacity units, in particular because of its simplicity. However, it is recognized that its performance is significantly lower than a cycle using a mixture of refrigerants. In addition, it involves the recirculation of a very large flow of refrigerant gas.
On peut remplacer le gaz permanent auxiliaire utilisé comme réfrigérant, tel que de l'azote, par une fraction du gaz à liquéfier exerçant alors la même fonction. Le principe de fonctionnement du cycle représenté sur la figure 2 reste identique au principe décrit précédemment.It is possible to replace the auxiliary permanent gas used as refrigerant, such as nitrogen, by a fraction of the liquefying gas exerting then the same function. The operating principle of the represented cycle in Figure 2 remains identical to the principle described above.
Le principe mis en oeuvre selon l'invention décrite ci-après consiste, à partir d'un gaz naturel en phase dense, à arriver au moins en partie à sa liquéfaction sans transition de phase, c'est-à-dire qu'au moins une partie du processus de liquéfaction s'effectue sans transition de phase au cours de laquelle il y aurait coexistence entre deux phases de natures différentes. Ainsi, tout au long du processus de liquéfaction le passage de la phase dense à la phase liquide s'effectue de manière continue, une transition de phase impliquant un passage discontinu.The principle implemented according to the invention described below consists, from a dense phase natural gas, to arrive at least in part at its liquefaction without phase transition, i.e. at least part of the liquefaction process takes place without phase transition during of which there would be coexistence between two phases of natures different. So, throughout the liquefaction process the passage of the dense phase to the liquid phase takes place continuously, a phase transition involving discontinuous passage.
Le procédé repose sur la mise en oeuvre, essentiellement d'au moins deux étapes, la première consistant à amener le gaz naturel en phase dense et la seconde à produire une détente avec fourniture d'énergie mécanique, par exemple une détente sensiblement isentropique, faisant passer le gaz naturel en phase dense en phase liquide.The method relies on the implementation, essentially of at least two stages, the first consisting in bringing natural gas into phase dense and the second to produce a trigger with energy supply mechanical, for example a substantially isentropic expansion, making pass the natural gas in dense phase in liquid phase.
Le gaz arrive par le conduit 7 (Fig. 3A) en phase gazeuse, dans un
état thermodynamique représenté par le point G1 (Fig.3B), dans un
échangeur E2 dans lequel il est pré refroidi à une température donnée, au
contact d'un agent de refroidissement provenant d'un cycle de réfrigération
R1. Le gaz naturel se présente en sortie de l'échangeur E2, en phase
dense, au point G2 (Fig.3B). Il est ensuite transmis de l'échangeur E2 vers
la turbine T4 dans laquelle il est détendu par le conduit 15. Après passage
dans la turbine T4, il se trouve au moins en partie en phase liquide au
point G3. La transformation de la phase dense à la phase liquide s'effectue
par détente avec fourniture d'énergie mécanique et sans transition de
phase. The gas arrives via the conduit 7 (FIG. 3A) in the gas phase, in a thermodynamic state represented by the point G1 (FIG. 3B), in an exchanger E2 in which it is precooled to a given temperature, in contact with a coolant from a refrigeration cycle R1. Natural gas is present at the outlet of the exchanger E2, in dense phase, at point G2 (Fig.3B). It is then transmitted from the exchanger E2 to the turbine T 4 in which it is expanded by the
La phase liquide obtenue au point G3 après détente est, par exemple, une phase liquide saturée. Lorsque l'on poursuit l'opération de détente à partir de cette phase liquide saturée, il apparaít une fraction gazeuse ou vapeur qui, après échange thermique peut être recyclée, ou encore utilisée par ailleurs. Elle est, par exemple, employée comme combustible sur le site de l'installation de liquéfaction.The liquid phase obtained at point G3 after expansion is, for example, a saturated liquid phase. When the expansion operation is continued at from this saturated liquid phase, it appears a gaseous fraction or steam which, after heat exchange, can be recycled or used otherwise. It is, for example, used as fuel on the site of the liquefaction facility.
Le processus est illustré dans un diagramme de coordonnées pression (P) et température (T) représenté sur la figure 3B. Dans ce diagramme, à l'intérieur du domaine diphasique coexistent une phase liquide et une phase gazeuse. A l'extérieur de ce domaine diphasique, on définit trois domaines. Le domaine de la phase gazeuse est délimité par la branche vapeur v (courbe de rosée) du domaine diphasique et l'isentrope s passant par le point critique C. Le domaine de la phase dense est délimité d'une part par l'isentrope s et d'autre part par l'isobare p passant par le point critique C. Le domaine de la phase liquide est délimité d'une part par l'isobare p et par la branche liquide I (courbe de bulle) du domaine diphasique.The process is illustrated in a coordinate diagram pressure (P) and temperature (T) shown in Figure 3B. In this diagram, inside the two-phase domain coexist a phase liquid and a gas phase. Outside this two-phase domain, we defines three areas. The gas phase domain is delimited by the vapor branch v (dew curve) of the two-phase domain and the isentrope s passing through the critical point C. The domain of the dense phase is delimited on the one hand by the isentrope s and on the other hand by the isobaric p passing by the critical point C. The domain of the liquid phase is delimited by a leaves by the isobar p and by the liquid branch I (bubble curve) of the domain two-phase.
L'évolution suivie par le gaz naturel au cours du processus selon l'invention se déroule de la manière suivante :The evolution followed by natural gas during the process according to the invention proceeds as follows:
Le gaz naturel à liquéfier se trouve initialement dans un état en phase gazeuse représenté par un point G1 à une température TG1 et à une pression PG1. Il est ensuite refroidi de manière sensiblement isobare de manière à l'amener dans un état en phase dense représenté par le point G2, à une pression et une température respectivement PG2 et TG2. Le passage de G1 à G2 s'effectue, par exemple, de manière continue, sans transition de phase, en passant par le point F1 de l'isentrope p délimitant le domaine de phase gazeuse du domaine de phase dense. Le gaz naturel en phase dense, point G2, est alors détendu de manière sensiblement isentropique pour le faire passer dans un état en phase liquide, et de préférence dans un état en phase liquide saturé représenté par un point G3 se trouvant, par exemple, sur la branche liquide I du domaine diphasique, correspondant à des valeurs de température et de pression TG3 et PG3. La valeur de la pression PG3 est, de préférence, sensiblement égale à celle de la pression atmosphérique. Le passage de l'état représenté par le point G2 à l'état représenté par le point G3 s'effectue en passant par le point F2 de l'isobare p délimitant le domaine de phase dense du domaine de phase liquide, de manière continue sans transition de phase, c'est-à-dire sans coexistence entre deux phases différentes.The natural gas to be liquefied is initially in a gas phase state represented by a point G1 at a temperature T G1 and at a pressure P G1 . It is then cooled in a substantially isobaric manner so as to bring it into a dense phase state represented by the point G2, at a pressure and a temperature respectively P G2 and T G2 . The transition from G1 to G2 takes place, for example, continuously, without phase transition, passing through the point F1 of the isentrope p delimiting the gas phase domain from the dense phase domain. The natural gas in dense phase, point G2, is then expanded in a substantially isentropic manner to pass it into a liquid phase state, and preferably in a saturated liquid phase state represented by a point G3 located, for example, on the liquid branch I of the two-phase domain, corresponding to temperature and pressure values T G3 and P G3 . The value of the pressure P G3 is preferably substantially equal to that of the atmospheric pressure. The transition from the state represented by the point G2 to the state represented by the point G3 is effected by passing through the point F2 of the isobare p delimiting the dense phase domain from the liquid phase domain, continuously without phase transition, that is to say without coexistence between two different phases.
Comme celà a été indiqué précédemment, la détente peut être poursuivie dans le domaine diphasique en générant une fraction vapeur ou gazeuse.As indicated above, the trigger can be continued in the two-phase field by generating a vapor fraction or carbonated.
Dans une version préférée du procédé selon l'invention, la température à l'issue de l'étape de réfrigération précédent l'étape de détente est comprise entre 165 et 230K.In a preferred version of the method according to the invention, the temperature at the end of the refrigeration stage preceding the stage of trigger is between 165 and 230K.
Il a été découvert que pour opérer dans de telles conditions tout en maintenant la pression au cours de l'étape a) de préférence entre 7 et 20 MPa, il est nécessaire d'admettre une valeur de la fraction gazeuse à l'issue de l'étape de détente supérieure à une valeur minimale, par exemple 20 %.It has been discovered that to operate under such conditions while maintaining the pressure during step a) preferably between 7 and 20 MPa, it is necessary to admit a value of the gas fraction to the outcome of the expansion step greater than a minimum value, by example 20%.
La description ci-après du procédé selon l'invention en relation avec la figure 3C illustre l'application du procédé à la liquéfaction d'un gaz naturel.The following description of the process according to the invention in relation to FIG. 3C illustrates the application of the process to the liquefaction of a gas natural.
Le gaz naturel arrive par une conduite 7 vers un échangeur E2 sous
une pression supérieure au moins à la valeur de pression critique du
méthane, dans lequel il est refroidi à une température, par exemple
comprise entre 165 K et 230 K. Cette étape de pré réfrigération du gaz est
assurée, par exemple, par une fraction du gaz naturel prélevé avant son
entrée dans un échangeur E2 par une conduite 8 qui transfère cette
fraction prélevée à une turbine de détente T2. La fraction prélevée est
refroidie au cours de la détente, effectuée et opérée en phase gazeuse
dans la turbine T2, elle est ensuite envoyée dans l'échangeur E2 par un
conduit 9. La fraction gazeuse prélevée et refroidie joue ainsi le rôle
d'agent de refroidissement et permet d'abaisser la température du gaz
naturel pénétrant dans l'échangeur E2. Tout réfrigérant externe présentant
des caractéristiques permettant de refroidir un gaz peut remplacer la
fraction du gaz naturel prélevée et refroidie.Natural gas arrives via a pipe 7 to an exchanger E2 under a pressure greater than at least the critical pressure value of methane, in which it is cooled to a temperature, for example between 165 K and 230 K. This step of pre refrigeration of the gas is ensured, for example, by a fraction of the natural gas withdrawn before it enters an exchanger E2 via a
Le gaz naturel sort ainsi de l'échangeur E2 refroidi en phase "dense"
par un conduit 10. Une fraction de cette phase "dense" est envoyée
directement par un conduit 11, par exemple, à une turbine de détente T3. A
la sortie de la turbine T3, on obtient, par exemple, un mélange composé
majoritairement de phase liquide. Le mélange est évacué par un conduit
12, à une pression voisine de la pression atmosphérique, de la turbine T3
vers un ballon séparateur B1 dans lequel les fractions liquide et gazeuse
sont séparées. La fraction gazeuse prélevée du ballon B1 est envoyée par
un conduit 13 dans un échangeur E3.The natural gas thus leaves the exchanger E2 cooled in the "dense" phase by a
La fraction de gaz naturel refroidi en phase "dense" provenant de
l'échangeur E2 qui n'a pas été envoyée à la turbine T3 passe par un
conduit 14 dans un échangeur E3 dans laquelle elle est réfrigérée par
échange thermique avec la fraction gazeuse arrivant par le conduit 13. Le
gaz naturel ainsi réfrigéré sort de l'échangeur E3 à une température plus
basse que la température qu'il possède à l'entrée de cet échangeur par
exemple à une température voisine de la température de la fraction
gazeuse arrivant par le conduit 13. Elle est ensuite envoyée par un conduit
15 à une turbine T4 dans laquelle elle est détendue. A la sortie de la
turbine T4, on obtient le mélange majoritaire en phase liquide qui est
envoyé par un conduit 16 au ballon séparateur B1. Les deux fractions de
phase liquide recueillies dans le ballon B1 forment le gaz naturel liquéfié
évacué par un conduit 17.The fraction of natural gas cooled in the "dense" phase from the exchanger E2 which has not been sent to the turbine T 3 passes through a
En détendant une telle phase dense, c'est-à-dire une phase obtenue après la mise en oeuvre de la première étape selon l'invention, dans une ou plusieurs turbine(s), la réfrigération est poursuivie et on obtient, par exemple, directement à la sortie du dernier étage de détente un mélange contenant une phase liquide majoritaire à une pression voisine de la pression atmosphérique et à une température voisine de la température d'ébullition du méthane (111,66K).By relaxing such a dense phase, that is to say a phase obtained after the implementation of the first step according to the invention, in a or more turbine (s), the refrigeration is continued and one obtains, by example, directly at the exit of the top trigger stage, a mixture containing a majority liquid phase at a pressure close to the atmospheric pressure and at a temperature close to the temperature of boiling methane (111.66K).
La fraction gazeuse provenant du ballon séparateur B1, après
séparation ainsi qu'il a été mentionné ci-dessus, passe dans l'échangeur
E3 par un conduit 13 et est envoyée à l'échangeur E2 par un conduit 18
d'où elle ressort à une température voisine de la température d'entrée du
gaz naturel à liquéfier. Elle est alors envoyée à un étage de compression
K3 par un conduit 19. A la sortie de l'étage de compression K3, la fraction
gazeuse est refroidie par échange thermique avec le milieu ambiant, eau
ou air, disponible dans un échangeur C3, puis elle est mélangée avec une
fraction gazeuse provenant de la détente à travers la turbine T2 de la partie
gazeuse initialement prélevée avant l'échangeur E2, ladite fraction
gazeuse venant de l'échangeur E2 par un conduit 20 relié et débouchant
dans le conduit 19, par exemple entre l'échangeur C3 et un étage de
compression K4. Le mélange gazeux ainsi obtenu est comprimé dans
l'étage de compression K4 puis refroidi par échange thermique avec le
milieu ambiant, eau ou air disponible. Le mélange gazeux ainsi comprimé
et refroidi est recyclé par le conduit 21 et mélangé avec le gaz naturel à
liquéfier arrivant par le conduit 7.The gaseous fraction coming from the separator flask B1, after separation as mentioned above, passes into the exchanger E3 by a
Chacun des étages de compression K3 et K4 peut être avantageusement remplacé par une succession d'étages de compression, le mélange gazeux sortant d'un étage de compression étant refroidi par échange thermique avec le milieu ambiant, eau ou air, disponible, avant d'être envoyé à l'étage suivant de manière à rapprocher la compression opérée d'une compression isotherme effectuée à une température voisine de la température du milieu ambiant, eau ou air, disponible.Each of the compression stages K3 and K4 can be advantageously replaced by a succession of compression stages, the gas mixture leaving a compression stage being cooled by heat exchange with the surrounding environment, water or air, available, before to be sent to the next floor so as to bring the compression closer operated by an isothermal compression carried out at a neighboring temperature the ambient temperature, water or air, available.
Le procédé selon l'invention met au moins en oeuvre les deux étapes
suivantes :
Lorsque l'opération de détente se poursuit jusqu'à l'apparition d'une
fraction gazeuse, le procédé inclut par exemple, les étapes suivantes :
Lorsque le gaz naturel contient des hydrocarbures plus lourds que le méthane, la pression critique du mélange formant le gaz naturel est supérieure à la pression critique du méthane. Dans ce cas, la pression à laquelle est effectuée l'étape a) est de préférence supérieure à la pression critique dudit mélange.When natural gas contains heavier hydrocarbons than methane, the critical pressure of the mixture forming the natural gas is higher than the critical methane pressure. In this case, the pressure at which is carried out step a) is preferably greater than the pressure critical of said mixture.
La pression à laquelle est effectuée l'étape a) est également, de préférence, supérieure au cricondenbar défini pour un mélange comme étant la pression au-dessus de laquelle deux phases ne peuvent coexister.The pressure at which step a) is carried out is also, from preferably greater than the defined cricondenbar for a mixture like being the pressure above which two phases cannot coexist.
Dans le cas illustré par la figure 3C, la fraction de gaz naturel en phase "dense" qui n'est pas détendue dans la turbine T3 est refroidie dans l'échangeur E3 jusqu'à une température proche de la température finale du gaz naturel liquéfié produit.In the case illustrated in FIG. 3C, the fraction of natural gas in the "dense" phase which is not expanded in the turbine T 3 is cooled in the exchanger E3 to a temperature close to the final temperature of the natural gas liquefied product.
La fraction de gaz naturel détendue dans la turbine de détente T3
représente une fraction majoritaire du gaz naturel présent à l'entrée, cette
fraction étant de préférence supérieure aux deux tiers du gaz naturel
présent à l'entrée de l'échangeur E3 et arrivant par le conduit 10.The fraction of natural gas expanded in the expansion turbine T 3 represents a majority fraction of the natural gas present at the inlet, this fraction preferably being greater than two thirds of the natural gas present at the inlet of the exchanger E3 and arriving via
Le travail de détente utilisé pour détendre le gaz naturel est, par exemple, récupéré dans les turbines T3 et T4 et utilisé, par exemple, pour entraíner les étages de compression K3 et K4 et/ou, dans le cas du schéma des figures 5 et 6, les étages de compression K5 et K6. Le complément d'énergie mécanique éventuellement nécessaire est fourni, par exemple, par une turbine à vapeur ou, de préférence, par une turbine à gaz.The expansion work used to relax the natural gas is, for example, recovered in the turbines T 3 and T 4 and used, for example, to drive the compression stages K3 and K4 and / or, in the case of the diagram in the figures 5 and 6, the compression stages K5 and K6. The additional mechanical energy that may be required is supplied, for example, by a steam turbine or, preferably, by a gas turbine.
Il peut être avantageux de placer sur un même arbre deux ou plusieurs étages de compression ainsi que deux ou plusieurs turbines.It may be advantageous to place on the same tree two or several compression stages as well as two or more turbines.
En augmentant le niveau de pression auquel est réalisée l'étape a), il est possible de réduire le complément d'énergie mécanique nécessaire pour liquéfier le gaz naturel.By increasing the pressure level at which step a) is carried out, it is possible to reduce the additional mechanical energy required to liquefy natural gas.
Le procédé selon l'invention est d'autant plus avantageux que la pression à laquelle on effectue l'étape a) est élevée. La pression utilisée doit être au moins égale à la pression critique du méthane (4,6 MPa) et, de préférence, supérieure au cricondenbar du mélange qui constitue le gaz naturel à liquéfier. Elle se situe, avantageusement dans un intervalle compris par exemple entre 7 et 20 MPa.The method according to the invention is all the more advantageous since the pressure at which step a) is carried out is high. The pressure used must be at least equal to the critical pressure of methane (4.6 MPa) and, preferably greater than the cricondenbar of the mixture which constitutes the gas natural to liquefy. It is situated, advantageously in an interval for example between 7 and 20 MPa.
En abaissant la température à l'issue de l'étape a), on réduit la quantité de phase gazeuse recyclée à l'issue de la détente opérée au cours de l'étape c). Comme cela a été indiqué précédemment, la température est, de préférence, comprise entre 165 K et 230K.By lowering the temperature at the end of step a), the quantity of gaseous phase recycled after the expansion carried out at during step c). As noted earlier, the temperature is preferably between 165 K and 230K.
Lorsque le gaz naturel contient des hydrocarbures plus lourds que le méthane, ces hydrocarbures sont, par exemple, au moins en partie séparés du gaz naturel avant l'opération de liquéfaction, notamment pour éviter tout risque de cristallisation au cours de la liquéfaction.When natural gas contains heavier hydrocarbons than methane, these hydrocarbons are, for example, at least in part separated from natural gas before the liquefaction operation, in particular for avoid any risk of crystallization during liquefaction.
Dans le cas où la pression est supérieure au cricondenbar, les hydrocarbures plus lourds que le méthane ne peuvent pas être condensés par réfrigération. Il a été découvert que, dans ce cas, ils sont avantageusement séparés par une étape d'adsorption sur un adsorbant constitué par exemple par une alumine, une zéolithe ou un charbon actif.If the pressure is higher than the cricondenbar, the Hydrocarbons heavier than methane cannot be condensed by refrigeration. It was discovered that, in this case, they are advantageously separated by an adsorption step on an adsorbent constituted for example by an alumina, a zeolite or an activated carbon.
L'adsorbant est mis en oeuvre, par exemple, dans au moins deux lits fixes opérant en parallèle. Un lit opère, par exemple, en adsorption pendant qu'un autre lit opère en désorption. La désorption est réalisée, par exemple, par diminution de la pression et/ou augmentation de la température. Les hydrocarbures plus lourds que le méthane qui doivent être séparés, se fixent sur l'adsorbant au cours de l'étape d'adsorption, puis ils sont séparés au cours de l'étape de désorption.The adsorbent is used, for example, in at least two beds fixed operating in parallel. A bed operates, for example, in adsorption while another bed is operating in desorption. Desorption is carried out, by for example, by decreasing the pressure and / or increasing the temperature. Hydrocarbons heavier than methane which must be separated, attach to the adsorbent during the adsorption step, then they are separated during the desorption step.
Une autre manière de procéder lorsque le gaz naturel comporte des hydrocarbures lourds, consiste, au cours de l'étape a) à refroidir le gaz naturel à une température telle qu'à l'issue d'une détente sensiblement isentropique ayant amené le gaz à une pression inférieure au cricondenbar du mélange, il se forme une phase liquide par condensation rétrograde. Le mélange détendu est ensuite refroidi à une pression sensiblement constante. La phase liquide comprenant les hydrocarbures plus lourds que le méthane, à séparer, est alors prélevée à l'issue de l'opération de détente et/ou au cours du refroidissement ultérieur du mélange opéré à une pression sensiblement constante.Another way to proceed when natural gas contains heavy hydrocarbons, consists, during step a) in cooling the gas natural at a temperature such that after a relaxation substantially isentropic having brought the gas to a pressure below the cricondenbar of the mixture, a liquid phase is formed by condensation retrograde. The expanded mixture is then cooled to a pressure substantially constant. The liquid phase comprising the hydrocarbons heavier than methane, to be separated, is then removed after the expansion operation and / or during the subsequent cooling of the mixture operated at a substantially constant pressure.
Lorsque le gaz naturel comporte des hydrocarbures plus lourds que le méthane, il est également possible de séparer ces hydrocarbures au cours d'une étape préalable effectuée à une pression inférieure à la pression à laquelle on réalise l'étape a). Dans ce cas, si la pression au cours de ladite étape préalable est inférieure au cricondenbar, les hydrocarbures plus lourds que le méthane peuvent être séparés par différents moyens connus tels que des moyens de condensation, distillation et/ou adsorption dans un solvant, par exemple, à une température inférieure à la température ambiante.When natural gas contains heavier hydrocarbons than methane, it is also possible to separate these hydrocarbons during a previous step carried out at a pressure below the pressure at which step a) is carried out. In this case, if the pressure at during said prior step is less than the cricondenbar, the heavier hydrocarbons than methane can be separated by various known means such as condensation means, distillation and / or adsorption in a solvent, for example, at a temperature below room temperature.
A l'issue de cette étape préalable, le gaz peut être comprimé, au moyen d'une étape de compression réalisée dans des conditions aussi proches que possible que celles d'une compression isotherme au moyen d'étages de compression alternant avec des étages de refroidissement, le refroidissement étant opéré à l'aide d'un fluide de refroidissement, eau ou air disponible, par exemple sur le site de liquéfaction.At the end of this preliminary step, the gas can be compressed, at the by means of a compression step carried out under conditions also as close as possible to that of isothermal compression using compression stages alternating with cooling stages, the cooling being carried out using a cooling fluid, water or air available, for example at the liquefaction site.
De manière générale, une telle étape de compression préalable est prévue lorsque la pression du gaz à liquéfier est insuffisante pour effectuer l'étape a) dans des conditions satisfaisantes.Generally, such a prior compression step is provided when the pressure of the gas to be liquefied is insufficient to carry out step a) under satisfactory conditions.
En particulier, une telle étape de compression peut devenir nécessaire lorsque la pression du gaz en tête du puits devient trop faible, par exemple, à l'issue d'une période d'exploitation du gisement de gaz naturel.In particular, such a compression step can become necessary when the gas pressure at the head of the well becomes too low, for example, after a period of exploitation of the gas field natural.
Dans le cas où le gaz naturel à liquéfier contient de l'azote, et lorsque cela s'avère nécessaire, il est possible de séparer au moins en partie cet azote.In the case where the natural gas to be liquefied contains nitrogen, and when this is necessary, it is possible to at least partially separate this nitrogen.
On procède par exemple de la façon suivante :For example, we proceed as follows:
Il a été découvert qu'il est possible d'obtenir à l'issue de la détente opérée au cours de l'étape b) une phase gazeuse concentrée en azote et, de séparer ainsi au moins une fraction de l'azote contenue dans le gaz naturel à liquéfier sans avoir à liquéfier cette fraction d'azote, en mélange avec le gaz naturel. En effet, liquéfier le gaz naturel en présence de cette fraction d'azote est doublement pénalisant puisque la présence de cette fraction d'azote rend l'opération de liquéfaction plus difficile et qu'ensuite, cette fraction d'azote doit être séparé de la phase liquide obtenue, par exemple par un processus de distillation.It was discovered that it is possible to obtain after the trigger operated during step b) a gaseous phase concentrated in nitrogen and, to thus separate at least a fraction of the nitrogen contained in the gas natural to liquefy without having to liquefy this fraction of nitrogen, mixed with natural gas. Indeed, liquefying natural gas in the presence of this fraction of nitrogen is doubly penalizing since the presence of this fraction of nitrogen makes the liquefaction operation more difficult and then, this nitrogen fraction must be separated from the liquid phase obtained, by example by a distillation process.
Le procédé dans ce cas est réalisé, par exemple selon le schéma de principe représenté sur la figure 4.The process in this case is carried out, for example according to the scheme of principle shown in figure 4.
Le gaz naturel est envoyé dans l'échangeur E2 par le conduit 7. A l'issue de l'étape de refroidissement dans l'échangeur E2, le gaz naturel sort sous une forme de phase "dense". La fraction de cette phase "dense" peut être détendue directement, par au moins deux étapes de détente successives décrites ci-après.Natural gas is sent to the exchanger E2 via line 7. A the end of the cooling step in the exchanger E2, natural gas comes out as a "dense" phase. The fraction of this "dense" phase can be relaxed directly, by at least two relaxation steps described below.
Une première fraction de la phase dense est envoyée par le conduit
11 de la sortie de l'échangeur E2 vers une turbine T31 dans laquelle elle
est détendue. A l'issue de cette première étape de détente, le mélange
obtenu par détente est évacué par un conduit 30 de la turbine T31 vers un
ballon séparateur B2 dans lequel les fractions liquide et gazeuse du
mélange sont séparées. La fraction gazeuse est, par exemple, envoyée ou
recyclée par un conduit 31 dans l'échangeur E3. A first fraction of the dense phase is sent via the
La fraction liquide séparée dans le ballon séparateur B2 est
appauvrie en azote, puis évacuée par un conduit 32 vers une turbine T32
où elle est détendue et d'où elle ressort sous la forme d'un mélange
liquide-vapeur. A la sortie de la turbine T32, ce mélange liquide-vapeur
obtenu est envoyé à la base ou partie inférieure d'un contacteur S1 par
une conduite 35.The liquid fraction separated in the separator flask B2 is depleted in nitrogen, then discharged through a
La fraction de gaz naturel refroidi en phase dense provenant de
l'échangeur E2 et non dérivée vers la turbine T31 est envoyée par un
conduit 14 vers l'échangeur E3. Elle est réfrigérée dans cet échangeur par
échange thermique avec la fraction gazeuse provenant du conduit 31. En
sortie d'échangeur E3, la fraction en phase dense est à une température
inférieure à sa température initiale d'entrée dans l'échangeur E3,
sensiblement voisine de la température de la fraction gazeuse arrivant par
le conduit 31. Cette fraction en phase dense issue de l'échangeur E3 est
envoyée par un conduit 15, dans une turbine T4, dans laquelle elle est
détendue. Le mélange liquide-vapeur, composé en majorité de phase
liquide obtenu après détente à la sortie de la turbine T4 est envoyé en tête
du contacteur S1, partie supérieure du contacteur, par un conduit 36. La
phase liquide sortant de la turbine T4 est relativement concentrée en
azote. Dans le contacteur S1, elle est contactée à contre-courant avec la
fraction gazeuse arrivant à la base du contacteur S1 par le conduit 35 dont
la composition est proche de l'équilibre avec une phase liquide
relativement pauvre en azote. Dans le contacteur S1, la phase liquide qui
descend s'appauvrit en azote et la phase gazeuse qui monte s'enrichit en
azote. Il est ainsi possible d'obtenir, à la base du contacteur S1, une
fraction liquide relativement pauvre en azote et en tête du contacteur S1
une fraction gazeuse relativement riche en azote. La fraction liquide
recueillie à la base du contacteur S1 forme le gaz naturel liquéfié évacué
par un conduit 38. La fraction gazeuse recueillie en tête du contacteur S1
forme la fraction gazeuse concentrée en azote qui est séparée du gaz
naturel.The fraction of natural gas cooled in dense phase from the exchanger E2 and not diverted to the turbine T 31 is sent through a
Cette fraction gazeuse concentrée en azote est évacuée par un
conduit 34 et envoyée à un échangeur E4 d'où elle ressort par un conduit
37. Dans l'échangeur E4, la fraction gazeuse concentrée en azote est
réchauffée par échange thermique avec une fraction du gaz naturel
dérivée du gaz naturel introduit arrivant par un conduit 33 reliant
directement le conduit d'introduction 7 du gaz naturel à l'échangeur E4. This gaseous fraction concentrated in nitrogen is removed by a
Cette fraction du gaz naturel dérivée directement du conduit
d'introduction 7 est refroidie dans l'échangeur E4, puis détendue à travers
une vanne de détente V3 située sur le conduit 36 reliant l'échangeur E4 au
contacteur S1. La fraction de gaz naturel dérivée et détendue est ensuite
mélangée avec le mélange liquide-vapeur provenant de la turbine T4, et
envoyée au contacteur S1, le mélange des deux fractions liquide vapeur
s'effectuant au niveau du conduit 36.This fraction of natural gas directly derived from the introduction conduit 7 is cooled in the exchanger E4, then expanded through an expansion valve V3 located on the
Il est également possible d'envoyer la fraction gazeuse sortant en tête du contacteur S1 aux échangeurs de chaleur E3 et E2, qui doivent dans ce cas, comporter des moyens d'échange complémentaires.It is also possible to send the gaseous fraction leaving the head from contactor S1 to heat exchangers E3 and E2, which must in this case, include additional means of exchange.
Le contacteur S1 est formé par exemple d'un élément de colonne à garnissage ou de colonne à plateaux. Le nombre d'étages théoriques du contacteur S1 est par exemple de 3 ou de 4.The contactor S1 is formed for example of a column element with packing or column trays. The number of theoretical stages of the contactor S1 is for example 3 or 4.
Un exemple de fonctionnement du procédé selon l'invention est présenté par la suite.An example of operation of the method according to the invention is presented later.
Pour un gaz naturel à liquéfier disponible à une valeur de température de 308 K, ayant une valeur de pression de 150 bars et contenant 7,7 % masse d'azote :For a natural gas to be liquefied available at a value of temperature of 308 K, having a pressure value of 150 bars and containing 7.7% mass of nitrogen:
Une première fraction f1 de ce gaz naturel est refroidie par les
échangeurs E2 et E3 jusqu'à une température de 122 K. Le gaz naturel se
trouve ainsi en sortie de l'échangeur E3 dans un état en phase "dense". Il
est ensuite liquéfié au moins partiellement par une détente dans la turbine
T4, par exemple, à pression atmosphérique puis est introduit par le conduit
16 en tête du contacteur S1.A first fraction f1 of this natural gas is cooled by the exchangers E2 and E3 to a temperature of 122 K. The natural gas is thus found at the outlet of the exchanger E3 in a "dense" phase state. It is then at least partially liquefied by expansion in the turbine T 4 , for example, at atmospheric pressure and is then introduced through the
Une deuxième fraction f2 prélevée en amont de l'échangeur E2 est
refroidie jusqu'à 185 K par une détente sensiblement isentropique dans la
turbine T2 jusqu'au voisinage de sa pression de rosée. Cette fraction
refroidie et détendue est ensuite introduite par le conduit 9 dans
l'échangeur E2 où elle se réchauffe à contre courant avec la première
fraction f1. A l'issue de cet échange, la fraction f2 passe dans un train de
compresseurs réfrigérés par le milieu ambiant K4, C4, dans laquelle elle
est comprimée et refroidie, puis est mélangée au gaz naturel à liquéfier
introduit par le conduit 7.A second fraction f2 taken upstream of the exchanger E2 is cooled to 185 K by a substantially isentropic expansion in the turbine T 2 to the vicinity of its dew pressure. This cooled and expanded fraction is then introduced via
En sortie de l'échangeur E2, une troisième fraction f3 est prélevée et
refroidie, par exemple, jusqu'à 117 K par une détente sensiblement
isentropique dans une turbine T31. La fraction gazeuse est séparée du
mélange gaz/liquide obtenue par détente de la fraction f3 dans le ballon
B2, et introduite par le conduit 31 dans l'échangeur E3, puis par le conduit
18 dans l'échangeur E2 où elle se réchauffe à contre courant avec la
première fraction f1. A l'issue de ce réchauffement, la fraction f3 passe
dans un train de compresseurs K3, C3, réfrigérés, par exemple, par le
milieu ambiant puis est mélangée à la deuxième fraction f2 en amont du
train de compresseurs K4, C4 réfrigérés eux aussi, par exemple, par le
milieu ambiant.At the outlet of the exchanger E2, a third fraction f3 is taken and cooled, for example, to 117 K by a substantially isentropic expansion in a turbine T 31 . The gaseous fraction is separated from the gas / liquid mixture obtained by expansion of the fraction f3 in the cylinder B2, and introduced by the
La fraction liquide provenant du ballon B2 est détendue par passage dans la turbine T32 à pression atmosphérique et introduite dans la partie inférieure, par exemple, au fond du contacteur S1. Au contact du liquide situé dans la partie supérieure du contacteur, riche en azote (6,7 % masse), la fraction vapeur ou fraction gazeuse s'enrichit en azote. A la sorite du contacteur S1, la fraction vapeur contient 66 % en masse d'azote et le gaz naturel liquéfié 1,3 % en masse d'azote. Cette fraction vapeur est réchauffée jusqu'à la température ambiante par une fraction f4 du gaz naturel à traiter, est introduite en tête du contacteur avant d'être rejetée..The liquid fraction coming from the balloon B2 is expanded by passing through the turbine T 32 at atmospheric pressure and introduced into the lower part, for example, at the bottom of the contactor S1. On contact with the liquid located in the upper part of the contactor, rich in nitrogen (6.7% by mass), the vapor fraction or gaseous fraction is enriched in nitrogen. At the output of contactor S1, the vapor fraction contains 66% by mass of nitrogen and liquefied natural gas 1.3% by mass of nitrogen. This vapor fraction is warmed up to room temperature with a fraction f4 of the natural gas to be treated, is introduced at the top of the contactor before being discharged.
Les fractions f1, f2, f3 et f4 sont choisies de telle sorte que les approches thermiques aux échangeurs soient minimales.The fractions f1, f2, f3 and f4 are chosen so that the thermal approaches to the exchangers are minimal.
Les pertes en méthane dans le gaz purgé sont de 3,5 %.The methane losses in the purged gas are 3.5%.
La détente effectuée au cours de l'étape b) s'accompagne d'une variation importante de température qui est, par exemple, supérieure à 50°C. Dans le cas où la détente est réalisée dans deux ou plusieurs turbines successives, il en résulte un écart relativement important entre les températures d'entrée et de sortie pour chaque turbine. En outre, la détente est opérée en phase "dense" ou liquide. Les échanges thermiques entre le fluide en cours de détente et les éléments de la turbine peuvent, dans ces conditions, réduire l'efficacité de la détente.The relaxation carried out during step b) is accompanied by a significant variation in temperature which is, for example, greater than 50 ° C. In the case where the expansion is carried out in two or more successive turbines, this results in a relatively large difference between the inlet and outlet temperatures for each turbine. In addition, the trigger is operated in the "dense" or liquid phase. Thermal exchanges between the fluid being expanded and the elements of the turbine can, under these conditions, reduce the effectiveness of the trigger.
Il a été découvert qu'il est avantageux de réaliser la détente dans une turbine dont les éléments sont réalisés en matériaux peu conducteurs de la chaleur. Ils sont ainsi isolés thermiquement du gaz naturel.It has been discovered that it is advantageous to achieve relaxation in a turbine whose elements are made of materials which are not very conductive of the heat. They are thus thermally isolated from natural gas.
Ces éléments peuvent être des composants métalliques revêtus d'une couche thermiquement isolante. Ces éléments, et notamment le rotor, peuvent également être réalisés en un matériau composite faiblement conducteur de la chaleur.These elements can be coated metallic components a thermally insulating layer. These elements, and in particular the rotor, can also be made of a composite material poor conductor of heat.
Les échanges de chaleur réalisés au cours des étapes a) et d) sont effectués dans des échangeurs de chaleur opérant à contre-courant. Ces échangeurs de chaleur sont, par exemple, des échangeurs à passes multiples et sont, de préférence, constitués par des échangeurs à plaques. Ces échangeurs à plaques peuvent être, par exemple, des échangeurs en aluminium brasé. Il est également possible d'utiliser des échangeurs en acier inoxydable dont les plaques sont soudées entre elles.The heat exchanges carried out during steps a) and d) are carried out in heat exchangers operating against the current. These heat exchangers are, for example, pass exchangers multiple and are preferably constituted by plate heat exchangers. These plate exchangers can be, for example, heat exchangers brazed aluminum. It is also possible to use heat exchangers stainless steel with plates welded together.
Les canaux dans lesquels circulent les fluides participant à l'échange de chaleur peuvent être obtenus par différents moyens en disposant entre les plaques des plaques intercalaires ondulées, en formant les plaques, par exemple par explosion, en rainurant les plaques, par exemple par gravure chimique.The channels in which the fluids participating in the exchange circulate heat can be obtained by different means by arranging between the plates of the corrugated intermediate plates, forming the plates, for example by explosion, by grooving the plates, for example by chemical etching.
Il est également possible d'utiliser des échangeurs bobinés. L'échange de chaleur effectué au cours de l'étape e) est alors effectué avec un écart de température du côté le plus froid de l'échangeur de préférence inférieur à 5K et un écart de température du côté le plus chaud de l'échangeur de préférence inférieur à 10K.It is also possible to use wound exchangers. The heat exchange carried out during step e) is then carried out with a temperature difference on the coldest side of the heat exchanger preferably less than 5K and a temperature difference on the hottest side of the exchanger preferably less than 10K.
Il est également possible, dans le cadre de l'invention, d'effectuer l'étape a) de réfrigération au moyen d'un cycle extérieur opérant avec un mélange de réfrigérants. Le principe de fonctionnement du procédé dans ce cas est illustré, par exemple sur la figure 5.It is also possible, within the framework of the invention, to carry out stage a) of refrigeration by means of an external cycle operating with a mixture of refrigerants. The operating principle of the process in this case is illustrated, for example in FIG. 5.
La première étape de réfrigération du gaz naturel est alors réalisée dans l'échangeur E2, tel qu'un échangeur à plaques, non par un échange thermique avec une fraction gazeuse réfrigérée par détente comme il est décrit précédemment, mais. avec un mélange de réfrigérants qui se vaporise dans l'échangeur E2.The first stage of refrigeration of natural gas is then carried out in the exchanger E2, such as a plate exchanger, not by an exchange thermal with a gaseous fraction refrigerated by expansion as it is described above, but. with a mixture of refrigerants which vaporizes in the exchanger E2.
Le mélange de réfrigérants provient du cycle A comportant, par exemple, un ensemble de conduites, de compresseurs, d'échangeurs et de vannes tel que décrit ci-après.The refrigerant mixture comes from cycle A comprising, by example, a set of pipes, compressors, exchangers and valves as described below.
Le mélange de réfrigérants est vaporisé à deux niveaux de pression qui peuvent être successifs pour élargir l'intervalle de température pour lequel s'effectue la réfrigération.The refrigerant mixture is vaporized at two pressure levels which can be successive to widen the temperature range for which performs the refrigeration.
Ce mélange est, par exemple, introduit dans l'échangeur E2 par un
conduit 27 qui se sépare en deux conduits 27a et 27b. Une première partie
du mélange de réfrigérants en phase liquide est d'abord évacué par un
conduit 23 prolongeant le conduit 27a de l'échangeur E2 vers une
première vanne V20 de détente, dans laquelle il est vaporisé, par exemple,
à une température comprise entre 238 et 303K, repasse par l'échangeur
E2 et ressort sous forme gazeuse ou vapeur pour être envoyé à un
compresseur K6 par un conduit 24. This mixture is, for example, introduced into the exchanger E2 by a
Une seconde partie du mélange passe par le sous conduit 27b, puis
est évacué de l'échangeur E2 vers une vanne V30 située sur un conduit 25
prolongeant le sous conduit 27b. Le mélange est détendu par la vanne
V30 jusqu'à une pression proche de la pression atmosphérique et
vaporisé, par exemple, à une température comprise entre 173 et 238K. La
phase vapeur ainsi obtenue est envoyée de l'échangeur E2 vers l'entrée
d'un compresseur K5, puis refroidit dans un échangeur C5 situé après le
compresseur K5 et mélangée avec la fraction vapeur arrivant par le conduit
24. Le mélange en phase vapeur ainsi obtenu est ensuite comprimé dans
le compresseur K6, refroidi et condensé par passage dans un échangeur
C6 avant d'être envoyé par le conduit 27 dans l'échangeur E2, où il est
sous-refroidi avant d'être détendu et vaporisé.A second part of the mixture passes through the sub-conduit 27b, then
is evacuated from the exchanger E2 to a valve V30 located on a
Le gaz naturel arrive par le conduit 7 et sort refroidi de l'échangeur E2
par un conduit 11, il possède en sortie d'échangeur E2 une température
voisine, par exemple, de 178K sous forme de mélange. La majeure partie
de ce mélange passe à travers une turbine T3 dans laquelle il est détendu
et d'où il ressort sous forme d'un mélange liquide-vapeur qui est ensuite
envoyé par un conduit 12 à la base d'un contacteur S1.Natural gas arrives via line 7 and leaves the exchanger E2 cooled by a
L'autre partie du gaz naturel ayant traversé la turbine T3 passe
directement de l'échangeur E2 vers un échangeur à plaques E3 par un
conduit 14 dans lequel elle est refroidie par exemple par échange avec la
fraction en phase vapeur provenant du contacteur S1 par un conduit 13,
jusqu'à une température proche de la température finale du gaz naturel
liquéfié produit.The other part of the natural gas having passed through the turbine T 3 passes directly from the exchanger E2 to a plate exchanger E3 by a
La fraction gazeuse refroidie dans l'échangeur E3 sort de cet
échangeur par un conduit 15 et détendue à travers une vanne de détente
V4. La fraction liquide obtenue par détente est envoyée en tête du
contacteur S1.The gas fraction cooled in the exchanger E3 leaves this
exchanger through a
A l'intérieur du contacteur S1, cette phase liquide s'appauvrit en azote, alors que la fraction en phase vapeur introduite en bas du contacteur S1 remonte dans le contacteur, s'enrichit en azote. La fraction en phase vapeur qui sort du contacteur S1 est ainsi chargée en azote, ce qui permet d'évacuer ainsi la majeure partie de l'azote contenue initialement dans le gaz naturel.Inside the contactor S1, this liquid phase is depleted in nitrogen, while the vapor phase fraction introduced at the bottom of the contactor S1 goes back into the contactor, enriched with nitrogen. Fraction in the vapor phase which leaves the contactor S1 is thus charged with nitrogen, this which thus allows most of the nitrogen contained to be removed initially in natural gas.
La fraction gazeuse riche en azote passe dans l'échangeur E3, puis
par l'intermédiaire du conduit 18 dans l'échangeur E2 d'où elle ressort par
un conduit 19. The nitrogen-rich gas fraction passes through the exchanger E3, then
via the
Le gaz naturel liquéfié résultant de la fraction liquide appauvrie en azote est extrait dans la partie inférieure du contacteur S1.Liquefied natural gas resulting from the depleted liquid fraction in nitrogen is extracted in the lower part of contactor S1.
Le contacteur S1 peut être constitué par exemple par une colonne à plateaux ou une colonne à garnissage. Dans le cas d'une colonne à garnissage, le garnissage peut être avantageusement de type "structuré".The contactor S1 can be constituted for example by a column with trays or a packed column. In the case of a column to lining, the lining may advantageously be of the "structured" type.
Différentes modifications du schéma présenté sur la figure 5 à titre d'exemple de réalisation peuvent être considérées en restant dans le cadre de l'invention.Different modifications of the diagram shown in Figure 5 as examples can be considered by staying in the part of the invention.
Il est notamment possible au cours de l'étape de réfrigération réalisée dans l'échangeur E2 de modifier le nombre de niveaux de pression auxquels le mélange en phase liquide est détendu. Dans le schéma représenté sur la figure 5, ce nombre est de deux, mais il peut être réduit à un ou au contraire être fixé à trois ou plus. En augmentant le nombre de niveaux de pression de détente, on réduit, par exemple, la puissance de compression nécessaire, mais on augmente la complexité de l'installation. Le choix du nombre de niveaux de pression de détente résulte par conséquent d'une optimisation technicoéconomique.It is in particular possible during the refrigeration stage carried out in the exchanger E2 to modify the number of pressure levels to which the liquid phase mixture is expanded. In the diagram shown in Figure 5, this number is two, but it can be reduced to one or on the contrary be fixed at three or more. By increasing the number of trigger pressure levels, for example, the power of compression required, but the complexity of the installation is increased. The choice of the number of trigger pressure levels results in consequence of a technical and economic optimization.
Les vannes de détente V20, V30 et V4 peuvent être remplacées en totalité ou en partie par des turbines de détente motrices.The V20, V30 and V4 expansion valves can be replaced by in whole or in part by drive expansion turbines.
Les échangeurs E2 et E3 peuvent être réalisés avec des matériaux et/ou des modes d'assemblages différents. Il est également possible de réaliser l'ensemble des échanges thermiques dans un échangeur à plaque unique.The E2 and E3 exchangers can be made with materials and / or different assembly methods. It is also possible to carry out all of the heat exchanges in a heat exchanger single plate.
Les compresseurs K5 et K6 peuvent comporter chacun une série d'étages. Entre deux étages successifs, il est possible de prévoir une étape de refroidissement intermédiaire.K5 and K6 compressors can each have a series of floors. Between two successive stages, it is possible to plan a stage intermediate cooling.
La fraction gazeuse à basse pression évacuée par le conduit 19 peut
être au moins en partie recomprimée et recyclée. Il est clair toutefois que si
la fraction gazeuse ainsi obtenue peut être utilisée à basse pression, sans
être recyclée, il est possible de réduire sensiblement les coûts
d'investissement et les frais opératoires nécessaires.The low-pressure gas fraction discharged through
Lorsque le gaz naturel contient de l'azote, il est avantageux de recycler une fraction gazeuse relativement pauvre en azote et d'évacuer une fraction gazeuse relativement riche en azote. On peut dans ce cas opérer, par exemple, selon le schéma représenté sur la figure 6.When natural gas contains nitrogen, it is advantageous to recycle a gaseous fraction relatively poor in nitrogen and evacuate a gaseous fraction relatively rich in nitrogen. We can in this case operate, for example, according to the diagram shown in Figure 6.
Dans la disposition schématisée sur la figure 6, le gaz naturel sortant
de l'échangeur E2 par le conduit 11 subit une première détente dans la
turbine T31. A la sortie de la turbine T31, une fraction liquide est recueillie
par un ballon B3 puis évacuée par le conduit 42 situé de préférence dans
la partie inférieure de ce ballon vers une turbine T32 où il subit une
deuxième détente. On recueille également dans la partie supérieure du
ballon une fraction gazeuse relativement riche en azote envoyée par un
conduit 40 dans une turbine T4 où elle est détendue avant d'être envoyée
dans le contacteur S1, de préférence dans sa partie inférieure. A la sortie
de la turbine T32, le mélange détendu obtenu est évacué par un conduit
43 et séparé dans un ballon 84 en une fraction liquide appauvrie en azote
qui est évacuée par un conduit 45 situé dans la partie inférieure du ballon
B, de préférence, et qui constitue une partie du gaz naturel liquéfié produit
et une fraction gazeuse prélevée en partie supérieure du ballon
relativement pauvre en azote envoyée par un conduit 44 à l'échangeur E3,
puis par le conduit 18 à l'échangeur E2 d'où elle ressort par le conduit 19.
Le conduit 19 est relié à un compresseur K3 qui recomprime, par exemple,
ladite fraction gazeuse relativement pauvre en azote avant son passage
dans un échangeur C3 où elle est refroidie avec le fluide de
refroidissement, qui peut être de l'eau ou de l'air. Le compresseur K3
comporte, de préférence, plusieurs étages de compression entre lesquels
sont placés par exemple des étages de refroidissement.In the arrangement shown diagrammatically in FIG. 6, the natural gas leaving the exchanger E2 via the
Le gaz naturel sous pression sortant de l'échangeur E3 par le conduit
15 est, par exemple, détendu dans une vanne de détente V11 avant d'être
envoyé en tête du contacteur S1.Natural gas under pressure leaving the exchanger E3 via the
La fraction gazeuse enrichie en azote par son passage ascendant au
contact de la phase liquide dans le contacteur S1, sort du contacteur par
un conduit 46, est envoyée dans un échangeur E4 d'où elle peut être
partiellement recyclée par le conduit 51. La fraction non recyclée est
évacuée par le conduit 49. Par le conduit 47 arrive dans l'échangeur E4
une fraction du gaz naturel sous pression qui est refroidie dans
l'échangeur E4 et ressort par le conduit 48 à une température proche de la
température finale du GNL produit. Ladite fraction est alors détendue à
travers la vanne V10 et envoyée en tête du contacteur S1.The gaseous fraction enriched in nitrogen by its ascending passage to
liquid phase contact in contactor S1, exit from contactor by
a
A la base du contacteur S1, on recueille une fraction liquide qui est
mélangée avec la fraction liquide arrivant par le conduit 45 pour former le
gaz naturel liquéfié produit, qui est évacué par le conduit 50. At the base of the contactor S1, a liquid fraction is collected which is
mixed with the liquid fraction arriving via
On peut sans sortir de l'invention utiliser à la place d'une turbine un autre équipement permettant de réaliser une détente avec fourniture d'énergie mécanique.Without departing from the invention, it is possible to use instead of a turbine a other equipment to achieve relaxation with supply mechanical energy.
Claims (24)
- A method of liquefying a natural gas, consisting of a combination of the following steps:a) the natural gas is cooled at a pressure at least greater than or equal to the critical pressure of methane and at a temperature such that said natural gas is in dense phase at the end of this cooling step and said gas is mixed alternately with a recycled gaseous fraction,a') the cooled natural gas in dense phase is separated into two fractions, a first larger fraction (11) and a second remaining fraction (14),b) the first larger fraction from step a) is expanded and liquefied by means of a device (T3) set up to decrease the pressure of the natural gas by expansion with mechanical energy in order to obtain a liquid fraction and a gaseous fraction at the end of this step b),c) the liquid fraction and the gaseous fraction (13) obtained during step b) are separated (B1),d) the gaseous fraction (13) resulting from step c) is put through a process of heat exchange (E3) with the second remaining fraction (14) of natural gas that was not expanded, said non-expanded and cooled fraction at the end of this operation being expanded in an expansion device (T4) to form a liquid-vapour mixture which is separated (B1) into a liquid fraction and a gaseous fraction,e) the liquid fractions from steps c) and d) are reunited to form the liquefied natural gas andf) the gaseous fractions from steps c) and d) at step a) are at least partially re-compressed and recycled, thus forming said fraction of gas recycled to step a) and the non-recycled fractions are evacuated.
- A method as claimed in claim 1, characterised in that the first, larger expanded fraction (11) is preferably more than two thirds of the natural gas in dense phase resulting from step a).
- A method of liquefying a natural gas as claimed in claim 2, characterised in that the expansion applied to the liquid phase obtained during step b) is continued until a gaseous fraction appears and the following steps are then performed:the liquid fraction and the gaseous fraction are separated during step c),the gaseous fraction resulting from step c) is put through a process of heat exchange with a non-expanded fraction of natural gas during step d), said non-expanded fraction being expanded at the end of this heat exchange operation during step e) to form a liquid-vapour mixture which is separated into a liquid fraction and a gaseous fraction,the liquid fractions from steps c) and e) are reunited to form the liquefied natural gas andat least some of the gaseous fractions from steps c) and e) are re-compressed and recycled to step a).
- A method of liquefying a natural gas as claimed in one of claims 2 to 3, characterised in that the device used to expand the natural gas from the dense phase state to the liquid phase state is a turbine.
- A method of liquefying a natural gas as claimed in one of claims 2 to 4, characterised in that during step a), the natural gas is cooled by a process of heat exchange using a gaseous fraction from said natural gas, said gaseous fraction being expanded in a turbine (T2), said expanded gaseous fraction being at least partially re-compressed in a compression stage and recycled.
- A method of liquefying a natural gas as claimed in one of claims 2 to 5, characterised in that at least one fraction of recycled gas is compressed using at least two stages, the gas being cooled at the output of each of the compression stages by an available ambient cooling medium.
- A method of liquefying a natural gas as claimed in one of claims 2 to 6, characterised in that the natural gas is cooled during step a) by evaporating a mixture of coolants.
- A method as claimed in claim 7, characterised in that the mixture of coolants is expanded and evaporated at two different pressure levels at least.
- A method of liquefying a natural gas as claimed in one of claims 2 to 8, characterised in that if the natural gas contains heavy hydrocarbons, the heaviest hydrocarbons contained in the natural gas to be liquefied are separated by means of an adsorption stage prior to step a).
- A method of liquefying a natural gas as claimed in one of claims 2 to 9, characterised in that step a) is operated at a pressure in excess of the critical pressure of the natural gas to be liquefied.
- A method of liquefying a natural gas as claimed in claim 10, characterised in that step a) is operated at a pressure greater than the cricondenbar of the natural gas to be liquefied.
- A method of liquefying a natural gas as claimed in claims 10 and 11, characterised in that step a) is operated at a pressure within the range of between 7 and 20 MPa.
- A method of liquefying a natural gas as claimed in one of claims 2 to 10, characterised in that the temperature of the natural gas is within the range between 165 K and 230 K at the end of step a).
- A method of liquefying a natural gas as claimed in claim 3, characterised in that the gaseous fraction obtained at the end of step b) is greater than or equal to 20%.
- A method of liquefying a natural gas as claimed in one of claims 2 to 10, characterised in that if the natural gas contains hydrocarbons heavier than methane, these hydrocarbons are at least partially separated during a preliminary step operated at a pressure that is lower than the pressure of step a).
- A method of liquefying a natural gas as claimed in one of claims 2 to 10 and 13 to 15, characterised in that the natural gas is cooled during step a) to a temperature such that after producing a liquid fraction with a high concentration of hydrocarbons heavier than methane, the liquid fraction is then separated.
- A method of liquefying a natural gas as claimed in one of claims 2 to 10 and 13, characterised in that step b) is operated by means of a turbine in which at least one of the elements is made from a material that is not very heat conductive.
- A method of liquefying a natural gas as claimed in claim 17, characterised in that the rotor of the turbine is made from a composite material that is not very heat conductive.
- A method of liquefying a natural gas as claimed in claims 2 to 10 and 13 and 17, characterised in that the exchanges of heat during steps a) and d) are conducted in counter-flow exchangers.
- A method of liquefying a natural gas as claimed in one of claims 2 to 10 and 13 and 17, characterised in that the heat exchange process of step d) is conducted by feeding the natural gas into an exchanger in which there is a temperature difference of less than 5K on the coldest side of the exchanger and a temperature difference of less than 10K on the hottest side of the exchanger.
- A method of liquefying a natural gas as claimed in one of claims 2 to 10 and 13 and 17, characterised in that the expansion during step b) is conducted by means of at least two successive turbines, the liquid-vapour mixture from the first partial expansion being separated into a gaseous fraction and a liquid fraction, said gaseous fraction being sent to undergo step d) and said resulting liquid fraction being expanded in the second turbine, the liquid fraction at the end of this second expansion forming a part of the liquefied natural gas produced by the method.
- A method of liquefying a natural gas as claimed in one of claims 2 to 10 and 13 and 17, characterised in that at least a part of the gaseous fraction from step b) is brought into counter-flow contact with the liquid fraction from step e), the resulting liquid fraction being reunited with the liquid fraction from step b) to form the liquefied natural gas and the resultant gaseous fraction being reunited with the gaseous fraction from step e) to form at least a part of a gaseous fraction with a high nitrogen content which is evacuated.
- A system for liquefying a natural gas as claimed by the method having the characteristics claimed in any one of the preceding claims consisting of an inlet pipe (7) for the natural gas (1), and preferably a pipe (21) for a recycled gas, said pipes being connected to a device (E2) for cooling the natural gas, a pipe enabling a coolant fluid (9) to be circulated inside the device (E2), an outlet pipe (10) connected to the device (E2) in which the natural gas is cooled and is present in the form of dense phase, a compression and condensation circuit (K3, C3, ...,) characterised in that the pipe 10 is separated into two sub-pipes (11, 14), first said sub-pipe (11) being connected to a first expansion device (T3), said second sub-pipe (14) being directly connected to a cooling device (E3) with an outlet pipe (15) for the cooled fraction of natural gas, said pipe (15) being connected to a second expansion device (T4), said expansion devices (T3, T4) being connected to a means for separating (B1) the expanded fractions of gas leaving the expansion devices (T3, T4) respectively via pipes (12, 16), said separation means (B1) being provided with at least one pipe (13) for evacuating the vapour phase and at least one pipe (17) for evacuating the liquefied natural gas.
- A system for liquefying a natural gas as claimed in claim 23, characterised in that said expansion devices are at least one expansion turbine, at least one of the elements of which is made from a material that is not very heat conductive.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR9315924 | 1993-12-30 | ||
FR9315924A FR2714720B3 (en) | 1993-12-30 | 1993-12-30 | Method and apparatus for liquefying a natural gas. |
FR9402024A FR2714722B1 (en) | 1993-12-30 | 1994-02-21 | Method and apparatus for liquefying a natural gas. |
FR9402024 | 1994-02-21 | ||
PCT/FR1994/001535 WO1995018345A1 (en) | 1993-12-30 | 1994-12-26 | Method and apparatus for liquefying natural gas |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0687353A1 EP0687353A1 (en) | 1995-12-20 |
EP0687353B1 true EP0687353B1 (en) | 1998-11-11 |
Family
ID=26230869
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP95905171A Expired - Lifetime EP0687353B1 (en) | 1993-12-30 | 1994-12-26 | Method and apparatus for liquefying natural gas |
Country Status (10)
Country | Link |
---|---|
US (1) | US5651269A (en) |
EP (1) | EP0687353B1 (en) |
JP (1) | JP3602130B2 (en) |
KR (1) | KR100356093B1 (en) |
AU (1) | AU684885B2 (en) |
CA (1) | CA2156249C (en) |
ES (1) | ES2126876T3 (en) |
FR (1) | FR2714722B1 (en) |
NO (1) | NO303850B1 (en) |
WO (1) | WO1995018345A1 (en) |
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- 1994-02-21 FR FR9402024A patent/FR2714722B1/en not_active Expired - Fee Related
- 1994-12-26 JP JP51781795A patent/JP3602130B2/en not_active Expired - Lifetime
- 1994-12-26 WO PCT/FR1994/001535 patent/WO1995018345A1/en active IP Right Grant
- 1994-12-26 CA CA002156249A patent/CA2156249C/en not_active Expired - Lifetime
- 1994-12-26 KR KR1019950703632A patent/KR100356093B1/en not_active IP Right Cessation
- 1994-12-26 EP EP95905171A patent/EP0687353B1/en not_active Expired - Lifetime
- 1994-12-26 ES ES95905171T patent/ES2126876T3/en not_active Expired - Lifetime
- 1994-12-26 US US08/507,277 patent/US5651269A/en not_active Expired - Lifetime
- 1994-12-26 AU AU13883/95A patent/AU684885B2/en not_active Expired
-
1995
- 1995-08-29 NO NO953377A patent/NO303850B1/en not_active IP Right Cessation
Also Published As
Publication number | Publication date |
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EP0687353A1 (en) | 1995-12-20 |
FR2714722A1 (en) | 1995-07-07 |
AU1388395A (en) | 1995-07-17 |
JPH08507364A (en) | 1996-08-06 |
WO1995018345A1 (en) | 1995-07-06 |
CA2156249C (en) | 2006-03-21 |
NO303850B1 (en) | 1998-09-07 |
NO953377L (en) | 1995-08-29 |
US5651269A (en) | 1997-07-29 |
CA2156249A1 (en) | 1995-07-06 |
AU684885B2 (en) | 1998-01-08 |
KR960701346A (en) | 1996-02-24 |
FR2714722B1 (en) | 1997-11-21 |
NO953377D0 (en) | 1995-08-29 |
JP3602130B2 (en) | 2004-12-15 |
KR100356093B1 (en) | 2003-01-29 |
ES2126876T3 (en) | 1999-04-01 |
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