US20090282865A1 - Liquefied Natural Gas and Hydrocarbon Gas Processing - Google Patents
Liquefied Natural Gas and Hydrocarbon Gas Processing Download PDFInfo
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- US20090282865A1 US20090282865A1 US12/423,306 US42330609A US2009282865A1 US 20090282865 A1 US20090282865 A1 US 20090282865A1 US 42330609 A US42330609 A US 42330609A US 2009282865 A1 US2009282865 A1 US 2009282865A1
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- 239000003949 liquefied natural gas Substances 0.000 title claims abstract description 180
- 239000007789 gas Substances 0.000 title claims abstract description 167
- 229930195733 hydrocarbon Natural products 0.000 title claims abstract description 71
- 150000002430 hydrocarbons Chemical class 0.000 title claims abstract description 71
- 239000004215 Carbon black (E152) Substances 0.000 title claims abstract description 54
- 238000012545 processing Methods 0.000 title description 16
- 238000004821 distillation Methods 0.000 claims abstract description 217
- 238000000034 method Methods 0.000 claims abstract description 130
- 230000008569 process Effects 0.000 claims abstract description 127
- 238000010992 reflux Methods 0.000 claims abstract description 108
- 238000005194 fractionation Methods 0.000 claims abstract description 93
- 239000007788 liquid Substances 0.000 claims description 278
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 182
- 238000001816 cooling Methods 0.000 claims description 102
- 238000010438 heat treatment Methods 0.000 claims description 78
- 238000000926 separation method Methods 0.000 claims description 11
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 abstract description 38
- 238000011084 recovery Methods 0.000 abstract description 37
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 abstract description 34
- 230000000630 rising effect Effects 0.000 abstract description 20
- 239000001294 propane Substances 0.000 abstract description 19
- 239000012263 liquid product Substances 0.000 abstract description 11
- 238000009833 condensation Methods 0.000 abstract description 6
- 230000005494 condensation Effects 0.000 abstract description 6
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 abstract description 3
- 239000005977 Ethylene Substances 0.000 abstract description 3
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 abstract description 2
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 abstract description 2
- 239000000047 product Substances 0.000 description 22
- 239000003345 natural gas Substances 0.000 description 20
- 239000000203 mixture Substances 0.000 description 13
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical class CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 13
- 238000012856 packing Methods 0.000 description 13
- 235000013844 butane Nutrition 0.000 description 12
- 238000004088 simulation Methods 0.000 description 11
- 238000005057 refrigeration Methods 0.000 description 10
- 230000000153 supplemental effect Effects 0.000 description 10
- 238000005265 energy consumption Methods 0.000 description 9
- 230000008016 vaporization Effects 0.000 description 9
- 230000008901 benefit Effects 0.000 description 7
- 238000010586 diagram Methods 0.000 description 7
- 238000009834 vaporization Methods 0.000 description 7
- QUJJSTFZCWUUQG-UHFFFAOYSA-N butane ethane methane propane Chemical class C.CC.CCC.CCCC QUJJSTFZCWUUQG-UHFFFAOYSA-N 0.000 description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 5
- 238000009826 distribution Methods 0.000 description 5
- 239000000446 fuel Substances 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 239000013529 heat transfer fluid Substances 0.000 description 2
- -1 i.e. Chemical compound 0.000 description 2
- NNPPMTNAJDCUHE-UHFFFAOYSA-N isobutane Chemical compound CC(C)C NNPPMTNAJDCUHE-UHFFFAOYSA-N 0.000 description 2
- 239000003915 liquefied petroleum gas Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 150000003464 sulfur compounds Chemical class 0.000 description 2
- OFBQJSOFQDEBGM-UHFFFAOYSA-N Pentane Chemical class CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000002274 desiccant Substances 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 239000001282 iso-butane Substances 0.000 description 1
- 235000013847 iso-butane Nutrition 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 1
- 238000011027 product recovery Methods 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 239000006200 vaporizer Substances 0.000 description 1
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- 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
- F25J3/0204—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 feed stream
- F25J3/0209—Natural gas or substitute natural gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- 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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- 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
- 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
- F25J3/0204—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 feed stream
- F25J3/0209—Natural gas or substitute natural gas
- F25J3/0214—Liquefied natural gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- 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
- F25J3/0233—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
- 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
- F25J3/0238—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 2 carbon atoms 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
- F25J2200/38—Processes or apparatus using separation by rectification using pre-separation or distributed distillation before a main column system, e.g. in a at least a double 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
- F25J2200/72—Refluxing the column with at least a part of the totally condensed overhead gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/76—Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/78—Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
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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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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/02—Multiple feed streams, e.g. originating from different sources
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/62—Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/08—Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/60—Processes or apparatus involving steps for increasing the pressure of gaseous process streams the fluid being hydrocarbons or a mixture of hydrocarbons
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
- F25J2235/60—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being (a mixture of) hydrocarbons
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2240/00—Processes or apparatus involving steps for expanding of process streams
- F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2270/00—Refrigeration techniques used
- F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
- F25J2270/904—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration by liquid or gaseous cryogen in an open 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
- F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
- F25J2290/50—Arrangement of multiple equipments fulfilling the same process step in parallel
Definitions
- This invention relates to a process for the separation of ethane and heavier hydrocarbons or propane and heavier hydrocarbons from liquefied natural gas (hereinafter referred to as LNG) combined with the separation of a gas containing hydrocarbons to provide a volatile methane-rich gas stream and a less volatile natural gas liquids (NGL) or liquefied petroleum gas (LPG) stream.
- LNG liquefied natural gas
- NNL natural gas liquids
- LPG liquefied petroleum gas
- LNG usually has a major proportion of methane, i.e., methane comprises at least 50 mole percent of the LNG, it also contains relatively lesser amounts of heavier hydrocarbons such as ethane, propane, butanes, and the like, as well as nitrogen. It is often necessary to separate some or all of the heavier hydrocarbons from the methane in the LNG so that the gaseous fuel resulting from vaporizing the LNG conforms to pipeline specifications for heating value. In addition, it is often also desirable to separate the heavier hydrocarbons from the methane and ethane because these hydrocarbons have a higher value as liquid products (for use as petrochemical feedstocks, as an example) than their value as fuel.
- the present invention is generally concerned with the integrated recovery of ethylene, ethane, propylene, propane, and heavier hydrocarbons from such LNG and gas streams. It uses a novel process arrangement to integrate the heating of the LNG stream and the cooling of the gas stream to eliminate the need for a separate vaporizer and the need for external refrigeration, allowing high C 2 component recovery while keeping the processing equipment simple and the capital investment low. Further, the present invention offers a reduction in the utilities (power and heat) required to process the LNG and gas streams, resulting in lower operating costs than other processes, and also offering significant reduction in capital investment.
- a typical analysis of an LNG stream to be processed in accordance with this invention would be, in approximate mole percent, 92.2% methane, 6.0% ethane and other C 2 components, 1.1% propane and other C 3 components, and traces of butanes plus, with the balance made up of nitrogen.
- a typical analysis of a gas stream to be processed in accordance with this invention would be, in approximate mole percent, 80.1% methane, 9.5% ethane and other C 2 components, 5.6% propane and other C 3 components, 1.3% iso-butane, 1.1% normal butane, 0.8% pentanes plus, with the balance made up of nitrogen and carbon dioxide. Sulfur containing gases are also sometimes present.
- FIG. 1 is a flow diagram of a base case natural gas processing plant using LNG to provide its refrigeration
- FIG. 2 is a flow diagram of base case LNG and natural gas processing plants in accordance with U.S. Pat. Nos. 7,216,507 and 5,568,737, respectively;
- FIG. 3 is a flow diagram of an LNG and natural gas processing plant in accordance with the present invention.
- FIGS. 4 through 8 are flow diagrams illustrating alternative means of application of the present invention to LNG and natural gas streams.
- FIGS. 1 and 2 are provided to quantify the advantages of the present invention.
- FIG. 1 is a flow diagram showing the design of a processing plant to recover C 2 + components from natural gas using an LNG stream to provide refrigeration.
- inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] as stream 31 .
- the sulfur compounds are removed by appropriate pretreatment of the feed gas (not illustrated).
- the feed stream is usually dehydrated to prevent hydrate (ice) formation under cryogenic conditions. Solid desiccant has typically been used for this purpose.
- the inlet gas stream 31 is cooled in heat exchanger 12 by heat exchange with a portion (stream 72 a ) of partially warmed LNG at ⁇ 174° F. [ ⁇ 114° C.] and cool distillation stream 38 a at ⁇ 107° F. [ ⁇ 77° C.].
- the cooled stream 31 a enters separator 13 at ⁇ 79° F. [ ⁇ 62° C.] and 584 psia [4,027 kPa(a)] where the vapor (stream 34 ) is separated from the condensed liquid (stream 35 ).
- Liquid stream 35 is flash expanded through an appropriate expansion device, such as expansion valve 17 , to the operating pressure (approximately 430 psia [2,965 kPa(a)]) of fractionation tower 20 .
- the expanded stream 35 a leaving expansion valve 17 reaches a temperature of ⁇ 93° F. [ ⁇ 70° C.] and is supplied to fractionation tower 20 at a first mid-column feed point.
- the vapor from separator 13 enters a work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 10 expands the vapor substantially isentropically to slightly above the tower operating pressure, with the work expansion cooling the expanded stream 34 a to a temperature of approximately ⁇ 101° F. [ ⁇ 74° C.].
- the typical commercially available expanders are capable of recovering on the order of 80-88% of the work theoretically available in an ideal isentropic expansion.
- the work recovered is often used to drive a centrifugal compressor (such as item 11 ) that can be used to re-compress the heated distillation stream (stream 38 b ), for example.
- the expanded stream 34 a is further cooled to ⁇ 124° F.
- the demethanizer in tower 20 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing to provide the necessary contact between the liquids falling downward and the vapors rising upward.
- the column also includes reboilers (such as reboiler 19 ) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column to strip the liquid product, stream 41 , of methane and lighter components.
- Liquid product stream 41 exits the bottom of the tower at 99° F. [37° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.
- Overhead distillation stream 43 is withdrawn from the upper section of fractionation tower 20 at ⁇ 143° F. [ ⁇ 97° C.] and is divided into two portions, streams 44 and 47 .
- the first portion, stream 44 flows to reflux condenser 22 where it is cooled to ⁇ 237° F. [ ⁇ 149° C.] and totally condensed by heat exchange with a portion (stream 72 ) of the cold LNG (stream 71 a ).
- Condensed stream 44 a enters reflux separator 23 wherein the condensed liquid (stream 46 ) is separated from any uncondensed vapor (stream 45 ).
- the liquid stream 46 from reflux separator 23 is pumped by reflux pump 24 to a pressure slightly above the operating pressure of demethanizer 20 and stream 46 a is then supplied as cold top column feed (reflux) to demethanizer 20 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in the upper section of demethanizer 20 .
- the second portion (stream 47 ) of overhead vapor stream 43 combines with any uncondensed vapor (stream 45 ) from reflux separator 23 to form cold distillation stream 38 at ⁇ 143° F. [ ⁇ 97° C.].
- Distillation stream 38 passes countercurrently to expanded stream 34 a in heat exchanger 14 where it is heated to ⁇ 107° F. [ ⁇ 77° C.] (stream 38 a ), and countercurrently to inlet gas in heat exchanger 12 where it is heated to 47° F. [8° C.] (stream 38 b ).
- the distillation stream is then re-compressed in two stages.
- the first stage is compressor 11 driven by expansion machine 10 .
- the second stage is compressor 21 driven by a supplemental power source which compresses stream 38 c to sales line pressure (stream 38 d ).
- stream 38 e After cooling to 126° F. [52° C.] in discharge cooler 22 , stream 38 e combines with warm LNG stream 71 b to form the residue gas product (stream 42 ).
- Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements.
- the LNG (stream 71 ) from LNG tank 50 enters pump 51 at ⁇ 251° F. [ ⁇ 157° C.].
- Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence to the sales gas pipeline.
- Stream 71 a exits the pump 51 at ⁇ 242° F. [ ⁇ 152° C.] and 1364 psia [9,401 kPa(a)] and is divided into two portions, streams 72 and 73 .
- the first portion, stream 72 is heated as described previously to ⁇ 174° F. [ ⁇ 114° C.] in reflux condenser 22 as it provides cooling to the portion (stream 44 ) of overhead vapor stream 43 from fractionation tower 20 , and to 43° F.
- the recoveries reported in Table I are computed relative to the total quantities of ethane, propane, and butanes+ contained in the gas stream being processed in the plant and in the LNG stream. Although the recoveries are quite high relative to the heavier hydrocarbons contained in the gas being processed (99.58%, 100.00%, and 100.00%, respectively, for ethane, propane, and butanes+), none of the heavier hydrocarbons contained in the LNG stream are captured in the FIG. 1 process. In fact, depending on the composition of LNG stream 71 , the residue gas stream 42 produced by the FIG. 1 process may not meet all pipeline specifications.
- the specific power reported in Table I is the power consumed per unit of liquid product recovered, and is an indicator of the overall process efficiency.
- FIG. 2 is a flow diagram showing processes to recover C 2 + components from LNG and natural gas in accordance with U.S. Pat. Nos. 7,216,507 and 5,568,737, respectively, with the processed LNG stream used to provide refrigeration for the natural gas plant.
- the processes of FIG. 2 have been applied to the same LNG stream and inlet gas stream compositions and conditions as described previously for FIG. 1 .
- the LNG to be processed (stream 71 ) from LNG tank 50 enters pump 51 at ⁇ 251° F. [ ⁇ 157° C.].
- Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence to expansion machine 55 .
- Stream 71 a exits the pump at ⁇ 242° F. [ ⁇ 152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 75 and 76 .
- the first portion, stream 75 is expanded to the operating pressure (approximately 415 psia [2,859 kPa(a)]) of fractionation column 62 by expansion valve 58 .
- the expanded stream 75 a leaves expansion valve 58 at ⁇ 238° F. [ ⁇ 150° C.] and is thereafter supplied to tower 62 at an upper mid-column feed point.
- the second portion, stream 76 is heated to ⁇ 79° F. [ ⁇ 62° C.] in heat exchanger 52 by cooling compressed overhead distillation stream 79 a at ⁇ 70° F. [ ⁇ 57° C.] and reflux stream 82 at ⁇ 128° F. [ ⁇ 89° C.].
- the partially heated stream 76 a is further heated and vaporized in heat exchanger 53 using low level utility heat.
- the heated stream 76 b at ⁇ 5° F. [ ⁇ 20° C.] and 1334 psia [9,195 kPa(a)] enters work expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 76 c to a temperature of approximately ⁇ 107° F. [ ⁇ 77° C.] before it is supplied as feed to fractionation column 62 at a lower mid-column feed point.
- the demethanizer in fractionation column 62 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing consisting of two sections.
- the upper absorbing (rectification) section contains the trays and/or packing to provide the necessary contact between the vapors rising upward and cold liquid falling downward to condense and absorb the ethane and heavier components;
- the lower stripping (demethanizing) section contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward.
- the demethanizing section also includes one or more reboilers (such as side reboiler 60 using low level utility heat, and reboiler 61 using high level utility heat) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column.
- the column liquid stream 80 exits the bottom of the tower at 54° F. [12° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.
- Overhead distillation stream 79 is withdrawn from the upper section of fractionation tower 62 at ⁇ 144° F. [ ⁇ 98° C.] and flows to compressor 56 driven by expansion machine 55 , where it is compressed to 807 psia [5,567 kPa(a)] (stream 79 a ). At this pressure, the stream is totally condensed as it is cooled to ⁇ 128° F. [ ⁇ 89° C.] in heat exchanger 52 as described previously. The condensed liquid (stream 79 b ) is then divided into two portions, streams 83 and 82 .
- the first portion (stream 83 ) is the methane-rich lean LNG stream, which is pumped by pump 63 to 1270 psia [8,756 kPa(a)] for subsequent vaporization in heat exchanger 12 , heating stream 83 a to 40° F. [4° C.] as described in paragraph [0032] below to produce warm lean LNG stream 83 b.
- the remaining portion of condensed liquid stream 79 b, reflux stream 82 flows to heat exchanger 52 where it is subcooled to ⁇ 237° F. [ ⁇ 149° C.] by heat exchange with a portion of the cold LNG (stream 76 ) as described previously.
- the subcooled stream 82 a is then expanded to the operating pressure of demethanizer 62 by expansion valve 57 .
- the expanded stream 82 b at ⁇ 236° F. [ ⁇ 149° C.] is then supplied as cold top column feed (reflux) to demethanizer 62 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section of demethanizer 62 .
- inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] as stream 31 .
- the feed stream 31 is cooled in heat exchanger 12 by heat exchange with cold lean LNG (stream 83 a ) at ⁇ 116° F. [ ⁇ 82° C.], cool distillation stream 38 a at ⁇ 96° F. [ ⁇ 71° C.], and demethanizer liquids (stream 39 ) at ⁇ 3° F. [ ⁇ 20° C.].
- the cooled stream 31 a enters separator 13 at ⁇ 67° F.
- Liquid stream 35 is flash expanded through an appropriate expansion device, such as expansion valve 17 , to the operating pressure (approximately 375 psia [2,583 kPa(a)]) of fractionation tower 20 .
- the expanded stream 35 a leaving expansion valve 17 reaches a temperature of ⁇ 86° F. [ ⁇ 65° C.] and is supplied to fractionation tower 20 at a first lower mid-column feed point.
- Vapor stream 33 from separator 13 is divided into two streams, 32 and 34 .
- Stream 32 containing about 22% of the total vapor, passes through heat exchanger 14 in heat exchange relation with cold distillation stream 38 at ⁇ 150° F. [ ⁇ 101° C.] where it is cooled to substantial condensation.
- the resulting substantially condensed stream 32 a at ⁇ 144° F. [ ⁇ 98° C.] is then flash expanded through an appropriate expansion device, such as expansion valve 16 , to the operating pressure of fractionation tower 20 , cooling stream 32 b to ⁇ 148° F. [ ⁇ 100° C.] before it is supplied to fractionation tower 20 at an upper mid-column feed point.
- the remaining 78% of the vapor from separator 13 enters a work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 10 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 34 a to a temperature of approximately ⁇ 100° F. [ ⁇ 73° C.].
- the partially condensed expanded stream 34 a is thereafter supplied as feed to fractionation tower 20 at a second lower mid-column feed point.
- the demethanizer in fractionation column 20 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing consisting of two sections.
- the upper absorbing (rectification) section contains the trays and/or packing to provide the necessary contact between the vapors rising upward and cold liquid falling downward to condense and absorb the ethane and heavier components;
- the lower stripping (demethanizing) section contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward.
- the demethanizing section also includes one or more reboilers (such as the side reboiler in heat exchanger 12 described previously, and reboiler 19 using high level utility heat) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column.
- the column liquid stream 40 exits the bottom of the tower at 85° F. [30° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product, and combines with stream 80 to form the liquid product (stream 41 ).
- Overhead distillation stream 38 is withdrawn from the upper section of fractionation tower 20 at ⁇ 150° F. [ ⁇ 101° C.]. It passes countercurrently to vapor stream 32 and recycle stream 36 a in heat exchanger 14 where it is heated to ⁇ 96° F. [ ⁇ 71° C.] (stream 38 a ), and countercurrently to inlet gas stream 31 and recycle stream 36 in heat exchanger 12 where it is heated to 6° F. [ ⁇ 15° C.] (stream 38 b ). The distillation stream is then re-compressed in two stages. The first stage is compressor 11 driven by expansion machine 10 . The second stage is compressor 21 driven by a supplemental power source which compresses stream 38 c to sales line pressure (stream 38 d ). After cooling to 126° F.
- stream 38 e is divided into two portions, stream 37 and recycle stream 36 .
- Stream 37 combines with warm lean LNG stream 83 b to form the residue gas product (stream 42 ).
- Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements.
- Recycle stream 36 flows to heat exchanger 12 and is cooled to ⁇ 102° F. [ ⁇ 75° C.] by heat exchange with cool lean LNG (stream 83 a ), cool distillation stream 38 a, and demethanizer liquids (stream 39 ) as described previously.
- Stream 36 a is further cooled to ⁇ 144° F. [ ⁇ 98° C.] by heat exchange with cold distillation stream 38 in heat exchanger 14 as described previously.
- the substantially condensed stream 36 b is then expanded through an appropriate expansion device, such as expansion valve 15 , to the demethanizer operating pressure, resulting in cooling of the total stream to ⁇ 152° F. [ ⁇ 102° C.].
- the expanded stream 36 c is then supplied to fractionation tower 20 as the top column feed.
- the vapor portion of stream 36 c combines with the vapors rising from the top fractionation stage of the column to form distillation stream 38 , which is withdrawn from an upper region of the tower as described above.
- FIG. 3 illustrates a flow diagram of a process in accordance with the present invention.
- the LNG stream and inlet gas stream compositions and conditions considered in the process presented in FIG. 3 are the same as those in the FIG. 1 and FIG. 2 processes. Accordingly, the FIG. 3 process can be compared with the FIG. 1 and FIG. 2 processes to illustrate the advantages of the present invention.
- the LNG to be processed (stream 71 ) from LNG tank 50 enters pump 51 at ⁇ 251° F. [ ⁇ 157° C.].
- Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence to separator 54 .
- Stream 71 a exits the pump at ⁇ 242° F. [ ⁇ 152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 72 and 73 .
- the first portion, stream 72 becomes stream 75 and is expanded to the operating pressure (approximately 415 psia [2,859 kPa(a)]) of fractionation column 62 by expansion valve 58 .
- the expanded stream 75 a leaves expansion valve 58 at ⁇ 238° F. [ ⁇ 150C.] and is thereafter supplied to tower 62 at an upper mid-column feed point.
- stream 73 is heated prior to entering separator 54 so that all or a portion of it is vaporized.
- stream 73 is first heated to ⁇ 77° F. [ ⁇ 61 ° C.] in heat exchanger 52 by cooling compressed overhead distillation stream 79 a at ⁇ 70° F. [ ⁇ 57° C.] and reflux stream 81 at ⁇ 16° F. [ ⁇ 82° C.].
- the partially heated stream 73 a becomes stream 76 and is further heated in heat exchanger 53 using low level utility heat.
- exchangers 52 and 53 are representative of either a multitude of individual heat exchangers or a single multi-pass heat exchanger, or any combination thereof. (The decision as to whether to use more than one heat exchanger for the indicated heating services will depend on a number of factors including, but not limited to, inlet LNG flow rate, heat exchanger size, stream temperatures, etc.)
- the heated stream 76 a enters separator 54 at ⁇ 5° F. [ ⁇ 20° C.] and 1334 psia [9,195 kPa(a)] where the vapor (stream 77 ) is separated from any remaining liquid (stream 78 ).
- Vapor stream 77 enters a work expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 77 a to a temperature of approximately ⁇ 107° F. [ ⁇ 77° C.].
- the work recovered is often used to drive a centrifugal compressor (such as item 56 ) that can be used to re-compress the column overhead vapor (stream 79 ), for example.
- the partially condensed expanded stream 77 a is thereafter supplied as feed to fractionation column 62 at a lower mid-column feed point.
- the separator liquid (stream 78 ), if any, is expanded to the operating pressure of fractionation column 62 by expansion valve 59 before expanded stream 78 a is supplied to fractionation tower 62 at a second lower mid-column feed point.
- the demethanizer in fractionation column 62 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing.
- the fractionation tower 62 may consist of two sections.
- the upper absorbing (rectification) section contains the trays and/or packing to provide the necessary contact between the vapors rising upward and cold liquid falling downward to condense and absorb the ethane and heavier components;
- the lower stripping (demethanizing) section contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward.
- the demethanizing section also includes one or more reboilers (such as side reboiler 60 using low level utility heat, and reboiler 61 using high level utility heat) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column.
- the column liquid stream 80 exits the bottom of the tower at 54° F. [12° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.
- Overhead distillation stream 79 is withdrawn from the upper section of fractionation tower 62 at ⁇ 144° F. [ ⁇ 98° C.] and flows to compressor 56 driven by expansion machine 55 , where it is compressed to 805 psia [5,554 kPa(a)] (stream 79 a ). At this pressure, the stream is totally condensed as it is cooled to ⁇ 116° F. [ ⁇ 82° C.] in heat exchanger 52 as described previously. The condensed liquid (stream 79 b ) is then divided into two portions, streams 83 and 81 .
- the first portion (stream 83 ) is the methane-rich lean LNG stream, which is pumped by pump 63 to 1275 psia [8,791 kPa(a)] for subsequent vaporization in heat exchangers 14 and 12 , heating stream 83 a to ⁇ 94° F. [ ⁇ 70° C.] and 40° F. [4° C.], respectively, as described in paragraphs [0047] and [0049] below to produce warm lean LNG stream 83 c.
- the remaining portion of condensed liquid stream 79 b, stream 81 flows to heat exchanger 52 where it is subcooled to ⁇ 237° F. [ ⁇ 149° C.] by heat exchange with a portion of the cold LNG (stream 73 ) as described previously.
- the subcooled stream 81 a is then divided into two portions, streams 82 and 36 .
- the first portion, reflux stream 82 is expanded to the operating pressure of demethanizer 62 by expansion valve 57 .
- the expanded stream 82 a at ⁇ 236° F. [ ⁇ 149° C.] is then supplied as cold top column feed (reflux) to demethanizer 62 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section of demethanizer 62 .
- the disposition of the second portion, reflux stream 36 for demethanizer 20 is described in paragraph [0050] below.
- inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] as stream 31 .
- the feed stream 31 is divided into two portions, streams 32 and 33 .
- the first portion, stream 32 is cooled in heat exchanger 12 by heat exchange with cool lean LNG (stream 83 b ) at ⁇ 94° F. [ ⁇ 70° C.], cool distillation stream 38 a at ⁇ 94° F. [ ⁇ 70° C.], and demethanizer liquids (stream 39 ) at ⁇ 78° F. [ ⁇ 61° C.].
- the partially cooled stream 32 a is further cooled from ⁇ 89° F.
- exchangers 12 and 14 are representative of either a multitude of individual heat exchangers or a single multi-pass heat exchanger, or any combination thereof.
- the substantially condensed stream 32 b is then flash expanded through an appropriate expansion device, such as expansion valve 16 , to the operating pressure (approximately 415 psia [2,861 kPa(a)]) of fractionation tower 20 , cooling stream 32 c to ⁇ 132° F. [ ⁇ 91° C.] before it is supplied to fractionation tower 20 at an upper mid-column feed point.
- an appropriate expansion device such as expansion valve 16
- the second portion of feed stream 31 , stream 33 enters a work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 10 expands the vapor substantially isentropically to a pressure slightly above the operating pressure of fractionation tower 20 , with the work expansion cooling the expanded stream 33 a to a temperature of approximately 92° F. [33° C.].
- the work recovered is often used to drive a centrifugal compressor (such as item 11 ) that can be used to re-compress the heated distillation stream (stream 38 b ), for example.
- the expanded stream 33 a is further cooled in heat exchanger 12 by heat exchange with cool lean LNG (stream 83 b ), cool distillation stream 38 a, and demethanizer liquids (stream 39 ) as described previously.
- the further cooled stream 33 b enters separator 13 at ⁇ 84° F. [ ⁇ 65° C.] and 423 psia [2,916 kPa(a)] where the vapor (stream 34 ) is separated from the condensed liquid (stream 35 ).
- Vapor stream 34 is cooled to ⁇ 120° F. [ ⁇ 85° C.] in heat exchanger 14 by heat exchange with cold lean LNG (stream 83 a ) and cold distillation stream 38 as described previously.
- the partially condensed stream 34 a is then supplied to fractionation tower 20 at a first lower mid-column feed point.
- Liquid stream 35 is flash expanded through an appropriate expansion device, such as expansion valve 17 , to the operating pressure of fractionation tower 20 .
- the expanded stream 35 a leaving expansion valve 17 reaches a temperature of ⁇ 85° F. [ ⁇ 65° C.] and is supplied to fractionation tower 20 at a second lower mid-column feed point.
- the second portion of subcooled stream 81 a, reflux stream 36 is expanded to the operating pressure of demethanizer 20 by expansion valve 15 .
- the expanded stream 36 a at ⁇ 236° F. [ ⁇ 149° C.] is then supplied as cold top column feed (reflux) to demethanizer 20 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in upper rectification section 20 a of demethanizer 20 .
- the demethanizer in fractionation column 20 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing.
- the fractionation tower 20 may consist of two sections.
- the upper absorbing (rectification) section 20 a contains the trays and/or packing to provide the necessary contact between the vapors rising upward and cold liquid falling downward to condense and absorb the ethane and heavier components;
- the lower stripping (demethanizing) section 20 b contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward.
- Demethanizing section 20 b also includes one or more reboilers (such as the side reboiler in heat exchanger 12 described previously, and reboiler 19 using high level utility heat) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column.
- the column liquid stream 40 exits the bottom of the tower at 95° F. [35° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product, and combines with stream 80 to form the liquid product (stream 41 ).
- Overhead distillation stream 38 is withdrawn from the upper section of fractionation tower 20 at ⁇ 144° F. [ ⁇ 98° C.]. It passes countercurrently to the first portion (stream 32 a ) of inlet gas stream 31 and vapor stream 34 in heat exchanger 14 where it is heated to ⁇ 94° F. [ ⁇ 70° C.] (stream 38 a ), and countercurrently to the first portion (stream 32 ) of inlet gas stream 31 and expanded second portion (stream 33 a ) in heat exchanger 12 where it is heated to 13° F. [ ⁇ 11° C.] (stream 38 b ). The distillation stream is then re-compressed in two stages. The first stage is compressor 11 driven by expansion machine 10 .
- the second stage is compressor 21 driven by a supplemental power source which compresses stream 38 c to sales gas line pressure (stream 38 d ).
- stream 38 e After cooling to 126° F. [52° C.] in discharge cooler 22 , stream 38 e combines with warm lean LNG stream 83 c to form the residue gas product (stream 42 ).
- Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements.
- FIG. 3 embodiment of the present invention improves the ethane recovery from 65.37% to 99.55%, the propane recovery from 85.83% to 100.00%, and the butanes+ recovery from 99.83% to 100.00%. Further, comparing the utilities consumptions in Table III with those in Table I shows that although the power required for the FIG. 3 embodiment of the present invention is approximately 7% higher than the FIG. 1 process, the process efficiency of the FIG. 3 embodiment of the present invention is significantly better than that of the FIG. 1 process.
- the present invention does not depend on the LNG feed itself to directly serve as the reflux for fractionation column 62 . Rather, the refrigeration inherent in the cold LNG is used in heat exchanger 52 to generate a liquid reflux stream (stream 82 ) that contains very little of the C 2 components and heavier hydrocarbon components that are to be recovered, resulting in efficient rectification in the absorbing section of fractionation tower 62 and avoiding the equilibrium limitations of such prior art processes.
- Second, splitting the LNG feed into two portions before feeding fractionation column 62 allows more efficient use of low level utility heat, thereby reducing the amount of high level utility heat consumed by reboiler 61 .
- the cold portion of the LNG feed serves as a supplemental reflux stream for fractionation tower 62 , providing partial rectification of the vapors in the expanded vapor and liquid streams (streams 77 a and 78 a, respectively) so that heating and at least partially vaporizing the other portion (stream 73 ) of the LNG feed does not unduly increase the condensing load in heat exchanger 52 .
- using a portion of the cold LNG feed (stream 75 a ) as a supplemental reflux stream allows using less top reflux (stream 82 a ) for fractionation tower 62 .
- the lower top reflux flow plus the greater degree of heating using low level utility heat in heat exchanger 53 , results in less total liquid feeding fractionation column 62 , reducing the duty required in reboiler 61 and minimizing the amount of high level utility heat needed to meet the specification for the bottom liquid product from demethanizer 62 .
- integrating the LNG plant with the gas plant allows using a portion (stream 36 ) of the lean LNG as reflux for demethanizer 20 .
- the resulting stream 36 a is very cold and contains very little of the C 2 components and heavier hydrocarbon components that are to be recovered, resulting in very efficient rectification in absorbing section 20 a and further minimizing the quantity of reflux required for demethanizer 20 .
- FIG. 4 An alternative method of processing natural gas is shown in another embodiment of the present invention as illustrated in FIG. 4 .
- the LNG stream and inlet gas stream compositions and conditions considered in the process presented in FIG. 4 are the same as those in FIGS. 1 through 3 . Accordingly, the FIG. 4 process can be compared with the FIGS. 1 and 2 processes to illustrate the advantages of the present invention, and can likewise be compared to the embodiment displayed in FIG. 3 .
- the LNG to be processed (stream 71 ) from LNG tank 50 enters pump 51 at ⁇ 251° F. [ ⁇ 157° C.].
- Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence to separator 54 .
- Stream 71 a exits the pump at ⁇ 242° F. [ ⁇ 152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 72 and 73 .
- the first portion, stream 72 becomes stream 75 and is expanded to the operating pressure (approximately 415 psia [2,859 kPa(a)]) of fractionation column 62 by expansion valve 58 .
- the expanded stream 75 a leaves expansion valve 58 at ⁇ 238° F. [ ⁇ 150C.] and is thereafter supplied to tower 62 at an upper mid-column feed point.
- stream 73 is heated prior to entering separator 54 so that all or a portion of it is vaporized.
- stream 73 is first heated to ⁇ 77° F. [ ⁇ 61 ° C.] in heat exchanger 52 by cooling compressed overhead distillation stream 79 a at ⁇ 70° F. [ ⁇ 57° C.] and reflux stream 81 at ⁇ 15° F. [ ⁇ 82° C].
- the partially heated stream 73 a becomes stream 76 and is further heated in heat exchanger 53 using low level utility heat.
- the heated stream 76 a enters separator 54 at ⁇ 5° F.
- Vapor stream 77 enters a work expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 77 a to a temperature of approximately ⁇ 107° F. [ ⁇ 77° C.].
- the partially condensed expanded stream 77 a is thereafter supplied as feed to fractionation column 62 at a lower mid-column feed point.
- the separator liquid (stream 78 ), if any, is expanded to the operating pressure of fractionation column 62 by expansion valve 59 before expanded stream 78 a is supplied to fractionation tower 62 at a second lower mid-column feed point.
- the column liquid stream 80 exits the bottom of the tower at 54° F. [12° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.
- Overhead distillation stream 79 is withdrawn from the upper section of fractionation tower 62 at ⁇ 144° F. [ ⁇ 98° C.] and flows to compressor 56 driven by expansion machine 55 , where it is compressed to 805 psia [5,554 kPa(a)] (stream 79 a ). At this pressure, the stream is totally condensed as it is cooled to ⁇ 115° F. [ ⁇ 82° C.] in heat exchanger 52 as described previously.
- the condensed liquid (stream 79 b ) is then divided into two portions, streams 83 and 81 .
- the first portion (stream 83 ) is the methane-rich lean LNG stream, which is pumped by pump 63 to 1270 psia [8,756 kPa(a)] for subsequent vaporization in heat exchanger 12 , heating stream 83 a to 40° F. [4° C.] as described in paragraph [0063] below to produce warm lean LNG stream 83 b.
- the remaining portion of condensed liquid stream 79 b, stream 81 flows to heat exchanger 52 where it is subcooled to ⁇ 237° F. [ ⁇ 149° C.] by heat exchange with a portion of the cold LNG (stream 73 ) as described previously.
- the subcooled stream 81 a is then divided into two portions, streams 82 and 36 .
- the first portion, reflux stream 82 is expanded to the operating pressure of demethanizer 62 by expansion valve 57 .
- the expanded stream 82 a at ⁇ 236° F. [ ⁇ 149° C.] is then supplied as cold top column feed (reflux) to demethanizer 62 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section of demethanizer 62 .
- the disposition of the second portion, reflux stream 36 for demethanizer 20 is described in paragraph [0066] below.
- inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] as stream 31 .
- the feed stream 31 is divided into two portions, streams 32 and 33 .
- the first portion, stream 32 is cooled in heat exchanger 12 by heat exchange with cold lean LNG (stream 83 a ) at ⁇ 96° F. [ ⁇ 71° C.], cool compressed distillation stream 38 b at ⁇ 109° F. [ ⁇ 78° C.], and demethanizer liquids (stream 39 ) at ⁇ 63° F. [ ⁇ 53° C.].
- the partially cooled stream 32 a is further cooled from ⁇ 96° F.
- the substantially condensed stream 32 b is then flash expanded through an appropriate expansion device, such as expansion valve 16 , to the operating pressure (approximately 443 psia [3,052 kPa(a)]) of fractionation tower 20 , cooling stream 32 c to ⁇ 129° F. [ ⁇ 90° C.] before it is supplied to fractionation tower 20 at an upper mid-column feed point.
- expansion valve 16 the operating pressure of fractionation tower 20
- cooling stream 32 c to ⁇ 129° F. [ ⁇ 90° C.] before it is supplied to fractionation tower 20 at an upper mid-column feed point.
- the second portion of feed stream 31 , stream 33 is cooled in heat exchanger 12 by heat exchange with cold lean LNG (stream 83 a ), cool compressed distillation stream 38 b, and demethanizer liquids (stream 39 ) as described previously.
- the cooled stream 33 a enters separator 13 at ⁇ 86° F. [ ⁇ 65° C.] and 584 psia [4,027 kPa(a)] where the vapor (stream 34 ) is separated from the condensed liquid (stream 35 ).
- Liquid stream 35 is flash expanded through an appropriate expansion device, such as expansion valve 17 , to the operating pressure of fractionation tower 20 .
- the expanded stream 35 a leaving expansion valve 17 reaches a temperature of ⁇ 100° F. [ ⁇ 73° C.] and is supplied to fractionation tower 20 at a first lower mid-column feed point.
- the vapor from separator 13 enters a work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 10 expands the vapor substantially isentropically to slightly above the tower operating pressure, with the work expansion cooling the expanded stream 34 a to a temperature of approximately ⁇ 106° F. [ ⁇ 77° C.].
- the expanded stream 34 a is further cooled to ⁇ 121° F. [ ⁇ 85° C.] in heat exchanger 14 by heat exchange with cold compressed distillation stream 38 a as described previously, whereupon the partially condensed expanded stream 34 b is thereafter supplied to fractionation tower 20 at a second lower mid-column feed point.
- the second portion of subcooled stream 81 a, reflux stream 36 is expanded to the operating pressure of demethanizer 20 by expansion valve 15 .
- the expanded stream 36 a at ⁇ 236° F. [ ⁇ 149° C.] is then supplied as cold top column feed (reflux) to demethanizer 20 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section of demethanizer 20 .
- the column liquid stream 40 exits the bottom of the tower at 102° F. [39° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product, and combines with stream 80 to form the liquid product (stream 41 ).
- Overhead distillation stream 38 is withdrawn from the upper section of fractionation tower 20 at ⁇ 141° F. [ ⁇ 96° C.] and flows to compressor 11 driven by expansion machine 10 , where it is compressed to 501 psia [3,452 kPa(a)].
- the cold compressed distillation stream 38 a passes countercurrently to the first portion (stream 32 a ) of inlet gas stream 31 and expanded vapor stream 34 a in heat exchanger 14 where it is heated to ⁇ 109° F. [ ⁇ 78° C.] (stream 38 b ), and countercurrently to the first portion (stream 32 ) and second portion (stream 33 ) of inlet gas stream 31 in heat exchanger 12 where it is heated to 31° F. [ ⁇ 1° C.] (stream 38 c ).
- the heated distillation stream then enters compressor 21 driven by a supplemental power source which compresses stream 38 c to sales line pressure (stream 38 d ). After cooling to 126° F.
- stream 38 e combines with warm lean LNG stream 83 b to form the residue gas product (stream 42 ).
- Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements.
- FIG. 4 embodiment of the present invention achieves essentially the same liquids recovery as the FIG. 3 embodiment.
- the FIG. 4 embodiment uses less power than the FIG. 3 embodiment, improving the specific power by slightly more than 1%.
- the high level utility heat required for the FIG. 4 embodiment of the present invention is about 8% less than that of the FIG. 3 embodiment.
- FIG. 5 Another alternative method of processing natural gas is shown in the embodiment of the present invention as illustrated in FIG. 5 .
- the LNG stream and inlet gas stream compositions and conditions considered in the process presented in FIG. 5 are the same as those in FIGS. 1 through 4 . Accordingly, the FIG. 5 process can be compared with the FIGS. 1 and 2 processes to illustrate the advantages of the present invention, and can likewise be compared to the embodiments displayed in FIGS. 3 and 4 .
- the LNG to be processed (stream 71 ) from LNG tank 50 enters pump 51 at ⁇ 251° F. [ ⁇ 157° C.].
- Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence to separator 54 .
- Stream 71 a exits the pump at ⁇ 242° F. [ ⁇ 152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 72 and 73 .
- the first portion, stream 72 becomes stream 75 and is expanded to the operating pressure (approximately 415 psia [2,859 kPa(a)]) of fractionation column 62 by expansion valve 58 .
- the expanded stream 75 a leaves expansion valve 58 at ⁇ 238° F. [ ⁇ 150C] and is thereafter supplied to tower 62 at an upper mid-column feed point.
- stream 73 is heated prior to entering separator 54 so that all or a portion of it is vaporized.
- stream 73 is first heated to ⁇ 77° F. [ ⁇ 61° C.] in heat exchanger 52 by cooling compressed overhead distillation stream 79 a at ⁇ 70° F. [ ⁇ 57° C.] and reflux stream 81 at ⁇ 12° F. [ ⁇ 80° C].
- the partially heated stream 73 a becomes stream 76 and is further heated in heat exchanger 53 using low level utility heat.
- the heated stream 76 a enters separator 54 at ⁇ 5° F.
- Vapor stream 77 enters a work expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 77 a to a temperature of approximately ⁇ 107° F. [ ⁇ 77° C.].
- the partially condensed expanded stream 77 a is thereafter supplied as feed to fractionation column 62 at a lower mid-column feed point.
- the separator liquid (stream 78 ), if any, is expanded to the operating pressure of fractionation column 62 by expansion valve 59 before expanded stream 78 a is supplied to fractionation tower 62 at a second lower mid-column feed point.
- the column liquid stream 80 exits the bottom of the tower at 54° F. [12° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.
- Overhead distillation stream 79 is withdrawn from the upper section of fractionation tower 62 at ⁇ 144° F. [ ⁇ 98° C.] and flows to compressor 56 driven by expansion machine 55 , where it is compressed to 805 psia [5,554 kPa(a)] (stream 79 a ). At this pressure, the stream is totally condensed as it is cooled to ⁇ 112° F. [ ⁇ 80° C.] in heat exchanger 52 as described previously.
- the condensed liquid (stream 79 b ) is then divided into two portions, streams 83 and 81 .
- the first portion (stream 83 ) is the methane-rich lean LNG stream, which is pumped by pump 63 to 1270 psia [8,756 kPa(a)] for subsequent vaporization in heat exchanger 12 , heating stream 83 a to 40° F. [4° C.] as described in paragraph [0075] below to produce warm lean LNG stream 83 b.
- the remaining portion of condensed liquid stream 79 b, stream 81 flows to heat exchanger 52 where it is subcooled to ⁇ 237° F. [ ⁇ 149° C.] by heat exchange with a portion of the cold LNG (stream 73 ) as described previously.
- the subcooled stream 81 a is then divided into two portions, streams 82 and 36 .
- the first portion, reflux stream 82 is expanded to the operating pressure of demethanizer 62 by expansion valve 57 .
- the expanded stream 82 a at ⁇ 236° F. [ ⁇ 149° C.] is then supplied as cold top column feed (reflux) to demethanizer 62 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section of demethanizer 62 .
- the disposition of the second portion, reflux stream 36 for demethanizer 20 is described in paragraph [0078] below.
- inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] as stream 31 .
- the feed stream 31 is divided into two portions, streams 32 and 33 .
- the first portion, stream 32 is cooled in heat exchanger 12 by heat exchange with cold lean LNG (stream 83 a ) at ⁇ 89° F. [ ⁇ 67° C.], cool compressed distillation stream 38 b at ⁇ 91° F. [ ⁇ 68° C.], and demethanizer liquids (stream 39 ) at ⁇ 89° F. [ ⁇ 67° C.].
- the partially cooled stream 32 a is further cooled from ⁇ 86° F.
- the substantially condensed stream 32 b is then flash expanded through an appropriate expansion device, such as expansion valve 16 , to the operating pressure (approximately 428 psia [2,949 kPa(a)]) of fractionation tower 20 , cooling stream 32 c to ⁇ 117° F. [ ⁇ 83° C.] before it is supplied to fractionation tower 20 at an upper mid-column feed point.
- expansion valve 16 the operating pressure of fractionation tower 20
- cooling stream 32 c to ⁇ 117° F. [ ⁇ 83° C.] before it is supplied to fractionation tower 20 at an upper mid-column feed point.
- the second portion of feed stream 31 , stream 33 enters a work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 10 expands the vapor substantially isentropically to a pressure slightly above the operating pressure of fractionation tower 20 , with the work expansion cooling the expanded stream 33 a to a temperature of approximately 95° F. [35° C.].
- the expanded stream 33 a is further cooled in heat exchanger 12 by heat exchange with cold lean LNG (stream 83 a ), cool compressed distillation stream 38 b, and demethanizer liquids (stream 39 ) as described previously.
- the further cooled stream 33 b enters separator 13 at ⁇ 85° F. [ ⁇ 65° C.] and 436 psia [3,004 kPa(a)] where the vapor (stream 34 ) is separated from the condensed liquid (stream 35 ).
- Vapor stream 34 is cooled to ⁇ 100° F. [ ⁇ 74° C.] in heat exchanger 14 by heat exchange with cold compressed distillation stream 38 a as described previously.
- the partially condensed stream 34 a is then supplied to fractionation tower 20 at a first lower mid-column feed point.
- Liquid stream 35 is flash expanded through an appropriate expansion device, such as expansion valve 17 , to the operating pressure of fractionation tower 20 .
- the expanded stream 35 a leaving expansion valve 17 reaches a temperature of ⁇ 86° F. [ ⁇ 65° C.] and is supplied to fractionation tower 20 at a second lower mid-column feed point.
- the second portion of subcooled stream 81 a, reflux stream 36 is expanded to the operating pressure of demethanizer 20 by expansion valve 15 .
- the expanded stream 36 a at ⁇ 236° F. [ ⁇ 149° C.] is then supplied as cold top column feed (reflux) to demethanizer 20 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section of demethanizer 20 .
- the column liquid stream 40 exits the bottom of the tower at 98° F. [37° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product, and combines with stream 80 to form the liquid product (stream 41 ).
- Overhead distillation stream 38 is withdrawn from the upper section of fractionation tower 20 at ⁇ 143° F. [ ⁇ 97° C.] and flows to compressor 11 driven by expansion machine 10 , where it is compressed to 573 psia [3,950 kPa(a)].
- the cold compressed distillation stream 38 a passes countercurrently to the first portion (stream 32 a ) of inlet gas stream 31 and vapor stream 34 in heat exchanger 14 where it is heated to ⁇ 91° F. [ ⁇ 68° C.] (stream 38 b ), and countercurrently to the first portion (stream 32 ) and expanded second portion (stream 33 a ) of inlet gas stream 31 in heat exchanger 12 where it is heated to 67° F. [19° C.] (stream 38 c ).
- the heated distillation stream then enters compressor 21 driven by a supplemental power source which compresses stream 38 c to sales line pressure (stream 38 d ). After cooling to 126° F.
- stream 38 e combines with warm lean LNG stream 83 b to form the residue gas product (stream 42 ).
- Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements.
- FIG. 5 embodiment of the present invention achieves essentially the same liquids recovery as the FIG. 3 and FIG. 4 embodiments.
- the FIG. 5 embodiment uses less power than the FIG. 3 and FIG. 4 embodiments, improving the specific power by over 5% relative to the FIG. 3 embodiment and nearly 4% relative to the FIG. 4 embodiment.
- the high level utility heat required for the FIG. 5 embodiment of the present invention is somewhat higher than that of the FIG. 3 and FIG. 4 embodiments (by 24% and 35%, respectively).
- the choice of which embodiment to use for a particular application will generally be dictated by the relative costs of power and high level utility heat and the relative capital costs of pumps, heat exchangers, and compressors.
- FIG. 6 An alternative method of processing LNG and natural gas is shown in the embodiment of the present invention as illustrated in FIG. 6 .
- the LNG stream and inlet gas stream compositions and conditions considered in the process presented in FIG. 6 are the same as those in FIGS. 1 through 5 . Accordingly, the FIG. 5 process can be compared with the FIGS. 1 and 2 processes to illustrate the advantages of the present invention, and can likewise be compared to the embodiments displayed in FIGS. 3 through 5 .
- the LNG to be processed (stream 71 ) from LNG tank 50 enters pump 51 at ⁇ 251° F. [ ⁇ 157° C.].
- Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence to separator 54 .
- Stream 71 a exits the pump at ⁇ 242° F. [ ⁇ 152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 72 and 73 .
- the first portion, stream 72 becomes stream 75 and is expanded to the operating pressure (approximately 435 psia [2,997 kPa(a)]) of fractionation column 20 by expansion valve 58 .
- the expanded stream 75 a leaves expansion valve 58 at ⁇ 238° F. [ ⁇ 150° C.] and is thereafter supplied to tower 20 at a first upper mid-column feed point.
- stream 73 is heated prior to entering separator 54 so that all or a portion of it is vaporized.
- stream 73 is first heated to ⁇ 76° F. [ ⁇ 60° C.] in heat exchanger 52 by cooling compressed overhead distillation stream 81 a at ⁇ 65° F. [ ⁇ 54° C.] and reflux stream 82 at ⁇ 117° F. [ ⁇ 82° C.], exchanger 14 as described in paragraph [0085] below.
- the partially heated stream 73 b becomes stream 76 and is further heated in heat exchanger 53 using low level utility heat.
- the heated stream 76 a enters separator 54 at ⁇ 5° F.
- Vapor stream 77 enters a work expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 77 a to a temperature of approximately ⁇ 104° F. [ ⁇ 76° C.].
- the partially condensed expanded stream 77 a is thereafter supplied as feed to fractionation column 20 at a first lower mid-column feed point.
- the separator liquid (stream 78 ), if any, is expanded to the operating pressure of fractionation column 20 by expansion valve 59 before expanded stream 78 a is supplied to fractionation tower 20 at a second lower mid-column feed point.
- inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] as stream 31 .
- the feed stream 31 is divided into two portions, streams 32 and 33 .
- the first portion, stream 32 is cooled in heat exchanger 12 by heat exchange with cold lean LNG (stream 83 a ) at ⁇ 103° F. [ ⁇ 75° C.], cool compressed distillation stream 38 b at ⁇ 92° F. [ ⁇ 69° C.], and demethanizer liquids (stream 39 ) at ⁇ 78° F. [ ⁇ 61° C.].
- the partially cooled stream 32 a is further cooled from ⁇ 94° F.
- the second portion of feed stream 31 , stream 33 enters a work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed.
- the machine 10 expands the vapor substantially isentropically to a pressure slightly above the operating pressure of fractionation tower 20 , with the work expansion cooling the expanded stream 33 a to a temperature of approximately 96° F. [36° C.].
- the expanded stream 33 a is further cooled in heat exchanger 12 by heat exchange with cold lean LNG (stream 83 a ), cool compressed distillation stream 38 b, and demethanizer liquids (stream 39 ) as described previously.
- the further cooled stream 33 b enters separator 13 at ⁇ 90° F. [ ⁇ 68° C.] and 443 psia [3,052 kPa(a)] where the vapor (stream 34 ) is separated from the condensed liquid (stream 35 ).
- Vapor stream 34 is cooled to ⁇ 101° F. [ ⁇ 74° C.] in heat exchanger 14 by heat exchange with the partially heated second portion (stream 73 a ) of the LNG stream and with cold compressed distillation stream 38 a as described previously.
- the partially condensed stream 34 a is then supplied to fractionation tower 20 at a third lower mid-column feed point.
- Liquid stream 35 is flash expanded through an appropriate expansion device, such as expansion valve 17 , to the operating pressure of fractionation tower 20 .
- the expanded stream 35 a leaving expansion valve 17 reaches a temperature of ⁇ 90° F. [ ⁇ 68° C.] and is supplied to fractionation tower 20 at a fourth lower mid-column feed point.
- the liquid product stream 41 exits the bottom of the tower at 89° F. [32° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.
- Overhead distillation stream 79 is withdrawn from the upper section of fractionation tower 20 at ⁇ 142° F. [ ⁇ 97° C.] and is divided into two portions, stream 81 and stream 38 .
- the first portion (stream 81 ) flows to compressor 56 driven by expansion machine 55 , where it is compressed to 864 psia [5,955 kPa(a)] (stream 81 a ). At this pressure, the stream is totally condensed as it is cooled to ⁇ 117° F.
- the condensed liquid (stream 81 b ) is then divided into two portions, streams 83 and 82 .
- the first portion (stream 83 ) is the methane-rich lean LNG stream, which is pumped by pump 63 to 1270 psia [8,756 kPa(a)] for subsequent vaporization in heat exchanger 12 , heating stream 83 a to 40° F. [4° C.] as described previously to produce warm lean LNG stream 83 b.
- stream 81 b flows to heat exchanger 52 where it is subcooled to ⁇ 237° F. [ ⁇ 149° C.] by heat exchange with a portion of the cold LNG (stream 73 ) as described previously.
- the subcooled stream 82 a is expanded to the operating pressure of fractionation column 20 by expansion valve 57 .
- the expanded stream 82 b at ⁇ 236° F. [ ⁇ 149° C.] is then supplied as cold top column feed (reflux) to demethanizer 20 .
- This cold liquid reflux absorbs and condenses the C 2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section of demethanizer 20 .
- the second portion of distillation stream 79 flows to compressor 11 driven by expansion machine 10 , where it is compressed to 604 psia [4,165 kPa(a)].
- the cold compressed distillation stream 38 a passes countercurrently to the first portion (stream 32 a ) of inlet gas stream 31 and vapor stream 34 in heat exchanger 14 where it is heated to ⁇ 92° F. [ ⁇ 69° C.] (stream 38 b ), and countercurrently to the first portion (stream 32 ) and expanded second portion (stream 33 a ) of inlet gas stream 31 in heat exchanger 12 where it is heated to 48° F. [9° C.] (stream 38 c ).
- the heated distillation stream then enters compressor 21 driven by a supplemental power source which compresses stream 38 c to sales line pressure (stream 38 d ).
- stream 38 e After cooling to 126° F. [52° C.] in discharge cooler 22 , stream 38 e combines with warm lean LNG stream 83 b to form the residue gas product (stream 42 ).
- Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements.
- FIG. 6 embodiment of the present invention achieves essentially the same liquids recovery as the FIGS. 3 , 4 , and 5 embodiments.
- the reduction in the energy consumption of the FIG. 6 embodiment of the present invention relative to the embodiments in FIGS. 3 through 5 is unexpectedly large.
- the FIG. 6 embodiment uses less power than the FIGS. 3 , 4 , and 5 embodiments, reducing the specific power by 14%, 12%, and 9%, respectively.
- the high level utility heat required for the FIG. 6 embodiment of the present invention is also lower than that of the FIGS. 3 , 4 , and 5 embodiments (by 21%, 14%, and 37%, respectively).
- FIG. 6 embodiment of the present invention will generally be less than that of the FIGS. 3 , 4 , and 5 embodiments since it uses only one fractionation column, and due to the reduction in power and high level utility heat consumption.
- the choice of which embodiment to use for a particular application will generally be dictated by the relative costs of power and high level utility heat and the relative capital costs of columns, pumps, heat exchangers, and compressors.
- separator 13 in FIGS. 3 through 8 may not be needed.
- the cooled stream 33 b ( FIGS. 3 , 5 , 6 , and 7 ) or cooled stream 33 a ( FIGS. 4 and 8 ) leaving heat exchanger 12 may not contain any liquid (because it is above its dewpoint, or because it is above its cricondenbar), so that separator 13 may not be justified. In such cases, separator 13 and expansion valve 17 may be eliminated as shown by the dashed lines.
- the heated LNG stream leaving heat exchanger 53 may not contain any liquid (because it is above its dewpoint, or because it is above its cricondenbar). In such cases, separator 54 and expansion valve 59 may be eliminated as shown by the dashed lines.
- total condensation of stream 79 b in FIGS. 3 through 5 and stream 81 b in FIGS. 6 through 8 is shown. Some circumstances may favor subcooling these streams, while other circumstances may favor only partial condensation. Should partial condensation of these streams be achieved, processing of the uncondensed vapor may be necessary, using a compressor or other means to elevate the pressure of the vapor so that it can join the pumped condensed liquid. Alternatively, the uncondensed vapor could be routed to the plant fuel system or other such use.
- Feed gas conditions, LNG conditions, plant size, available equipment, or other factors may indicate that elimination of work expansion machines 10 and/or 55 , or replacement with an alternate expansion device (such as an expansion valve), is feasible.
- an alternate expansion device such as an expansion valve
- individual stream expansion is depicted in particular expansion devices, alternative expansion means may be employed where appropriate.
- FIGS. 3 through 8 individual heat exchangers have been shown for most services. However, it is possible to combine two or more heat exchange services into a common heat exchanger, such as combining heat exchangers 12 and 14 in FIGS. 3 through 8 into a common heat exchanger. In some cases, circumstances may favor splitting a heat exchange service into multiple exchangers. The decision as to whether to combine heat exchange services or to use more than one heat exchanger for the indicated service will depend on a number of factors including, but not limited to, inlet gas flow rate, LNG flow rate, heat exchanger size, stream temperatures, etc.
- the use and distribution of the methane-rich lean LNG and tower overhead streams for process heat exchange, and the particular arrangement of heat exchangers for heating the LNG streams and cooling the feed gas streams, must be evaluated for each particular application, as well as the choice of process streams for specific heat exchange services.
- lean LNG stream 83 a is used directly to provide cooling in heat exchanger 12 or heat exchangers 12 and 14 .
- some circumstances may favor using the lean LNG to cool an intermediate heat transfer fluid, such as propane or other suitable fluid, whereupon the cooled heat transfer fluid is then used to provide cooling in heat exchanger 12 or heat exchangers 12 and 14 .
- This alternative means of indirectly using the refrigeration available in lean LNG stream 83 a accomplishes the same process objectives as the direct use of stream 83 a for cooling in the FIGS. 3 through 8 embodiments of the present invention.
- the choice of how best to use the lean LNG stream for refrigeration will depend mainly on the composition of the inlet gas, but other factors may affect the choice as well.
- each branch of the split LNG feed to fractionation column 62 in each branch of the split inlet gas to fractionation column 20 , and in each branch of the split LNG feed and the split inlet gas to fractionation column 20 will depend on several factors, including inlet gas composition, LNG composition, the amount of heat which can economically be extracted from the feed, and the quantity of horsepower available. More feed to the top of the column may increase recovery while increasing the duty in reboilers 61 and/or 19 and thereby increasing the high level utility heat requirements. Increasing feed lower in the column reduces the high level utility heat consumption but may also reduce product recovery.
- the relative locations of the mid-column feeds may vary depending on inlet gas composition, LNG composition, or other factors such as the desired recovery level and the amount of vapor formed during heating of the LNG streams.
- two or more of the feed streams, or portions thereof, may be combined depending on the relative temperatures and quantities of individual streams, and the combined stream then fed to a mid-column feed position.
- stream 75 a it may be desirable to recover refrigeration from the portion (stream 75 a ) of LNG feed stream 71 that is fed to an upper mid-column feed point on demethanizer 62 ( FIGS. 3 through 5 ) and demethanizer 20 ( FIGS. 6 through 8 ).
- all of stream 71 a would be directed to heat exchanger 52 (stream 73 ) and the partially heated LNG stream (stream 73 a in FIGS. 3 through 5 and stream 73 b in FIGS. 6 through 8 ) would then be divided into stream 76 and stream 74 (as shown by the dashed lines), whereupon stream 74 would be directed to stream 75 .
- FIGS. 3 through 6 embodiments recovery of C 2 components and heavier hydrocarbon components is illustrated. However, it is believed that the FIGS. 3 through 8 embodiments are also advantageous when recovery of only C 3 components and heavier hydrocarbon components is desired.
- the present invention provides improved recovery of C 2 components and heavier hydrocarbon components or of C 3 components and heavier hydrocarbon components per amount of utility consumption required to operate the process.
- An improvement in utility consumption required for operating the process may appear in the form of reduced power requirements for compression or pumping, reduced energy requirements for tower reboilers, or a combination thereof.
- the advantages of the present invention may be realized by accomplishing higher recovery levels for a given amount of utility consumption, or through some combination of higher recovery and improvement in utility consumption.
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Abstract
A process for the recovery of ethane, ethylene, propane, propylene, and heavier hydrocarbons from a liquefied natural gas (LNG) stream and a hydrocarbon gas stream is disclosed. The LNG feed stream is divided into two portions. The first portion is supplied to a fractionation column at a first upper mid-column feed point. The second portion is directed in heat exchange relation with a first portion of a warmer distillation stream rising from the fractionation stages of the column, whereby the LNG feed stream is partially heated and the distillation stream is totally condensed. The condensed distillation stream is divided into a “lean” LNG stream and a reflux stream, whereupon the reflux stream is supplied to the column at a top column feed position. The second portion of the LNG feed stream is heated further to partially or totally vaporize it and thereafter supplied to the column at a first lower mid-column feed position. The gas stream is divided into two portions. The second portion is expanded to the operating pressure of the column, then both portions are directed in heat exchange relation with the lean LNG stream and the second portion of the warmer distillation stream, whereby both portions of the gas stream are cooled, the lean LNG stream is vaporized, and the second portion of the distillation stream is heated. The first portion of the gas stream, which has been cooled to substantial condensation, is supplied to the column at a second upper mid-column feed point, and the second portion is supplied to the column at a second lower mid-column feed point. The quantities and temperatures of the feeds to the column are effective to maintain the column overhead temperature at a temperature whereby the major portion of the desired components is recovered in the bottom liquid product from the column.
Description
- This invention relates to a process for the separation of ethane and heavier hydrocarbons or propane and heavier hydrocarbons from liquefied natural gas (hereinafter referred to as LNG) combined with the separation of a gas containing hydrocarbons to provide a volatile methane-rich gas stream and a less volatile natural gas liquids (NGL) or liquefied petroleum gas (LPG) stream. The applicants claim the benefits under
Title 35, United States Code, Section 119(e) of prior U.S. Provisional Application No. 61/053,814 which was filed on May 16, 2008. - As an alternative to transportation in pipelines, natural gas at remote locations is sometimes liquefied and transported in special LNG tankers to appropriate LNG receiving and storage terminals. The LNG can then be re-vaporized and used as a gaseous fuel in the same fashion as natural gas. Although LNG usually has a major proportion of methane, i.e., methane comprises at least 50 mole percent of the LNG, it also contains relatively lesser amounts of heavier hydrocarbons such as ethane, propane, butanes, and the like, as well as nitrogen. It is often necessary to separate some or all of the heavier hydrocarbons from the methane in the LNG so that the gaseous fuel resulting from vaporizing the LNG conforms to pipeline specifications for heating value. In addition, it is often also desirable to separate the heavier hydrocarbons from the methane and ethane because these hydrocarbons have a higher value as liquid products (for use as petrochemical feedstocks, as an example) than their value as fuel.
- Although there are many processes which may be used to separate ethane and/or propane and heavier hydrocarbons from LNG, these processes often must compromise between high recovery, low utility costs, and process simplicity (and hence low capital investment). U.S. Pat. Nos. 2,952,984; 3,837,172; 5,114,451; and 7,155,931 describe relevant LNG processes capable of ethane or propane recovery while producing the lean LNG as a vapor stream that is thereafter compressed to delivery pressure to enter a gas distribution network. However, lower utility costs may be possible if the lean LNG is instead produced as a liquid stream that can be pumped (rather than compressed) to the delivery pressure of the gas distribution network, with the lean LNG subsequently vaporized using a low level source of external heat or other means. U.S. Pat. Nos. 6,604,380; 6,907,752; 6,941,771; 7,069,743; and 7,216,507 and co-pending application Ser. Nos. 11/749,268 and 12/060,362 describe such processes.
- Economics and logistics often dictate that LNG receiving terminals be located close to the natural gas transmission lines that will transport the re-vaporized LNG to consumers. In many cases, these areas also have plants for processing natural gas produced in the region to recover the heavier hydrocarbons contained in the natural gas. Available processes for separating these heavier hydrocarbons include those based upon cooling and refrigeration of gas, oil absorption, and refrigerated oil absorption. Additionally, cryogenic processes have become popular because of the availability of economical equipment that produces power while simultaneously expanding and extracting heat from the gas being processed. Depending upon the pressure of the gas source, the richness (ethane, ethylene, and heavier hydrocarbons content) of the gas, and the desired end products, each of these processes or a combination thereof may be employed.
- The cryogenic expansion process is now generally preferred for natural gas liquids recovery because it provides maximum simplicity with ease of startup, operating flexibility, good efficiency, safety, and good reliability. U.S. Pat. Nos. 3,292,380; 4,061,481; 4,140,504; 4,157,904; 4,171,964; 4,185,978; 4,251,249; 4,278,457; 4,519,824; 4,617,039; 4,687,499; 4,689,063; 4,690,702; 4,854,955; 4,869,740; 4,889,545; 5,275,005; 5,555,748; 5,566,554; 5,568,737; 5,771,712; 5,799,507; 5,881,569; 5,890,378; 5,983,664; 6,182,469; 6,578,379; 6,712,880; 6,915,662; 7,191,617; 7,219,513; reissue U.S. Pat. No. 33,408; and co-pending application Ser. Nos. 11/430,412; 11/839,693; 11/971,491; and 12/206,230 describe relevant processes (although the description of the present invention is based on different processing conditions than those described in the cited U.S. patents).
- The present invention is generally concerned with the integrated recovery of ethylene, ethane, propylene, propane, and heavier hydrocarbons from such LNG and gas streams. It uses a novel process arrangement to integrate the heating of the LNG stream and the cooling of the gas stream to eliminate the need for a separate vaporizer and the need for external refrigeration, allowing high C2 component recovery while keeping the processing equipment simple and the capital investment low. Further, the present invention offers a reduction in the utilities (power and heat) required to process the LNG and gas streams, resulting in lower operating costs than other processes, and also offering significant reduction in capital investment.
- Heretofore, assignee's U.S. Pat. No. 7,216,507 has been used to recover C2 components and heavier hydrocarbon components in plants processing LNG, while assignee's U.S. Pat. No. 5,568,737 has been used to recover C2 components and heavier hydrocarbon components in plants processing natural gas. Surprisingly, applicants have found that by integrating certain features of the assignee's U.S. Pat. No. 7,216,507 invention with certain features of the assignee's U.S. Pat. No. 5,568,737, extremely high C2 component recovery levels can be accomplished using less energy than that required by individual plants to process the LNG and natural gas separately.
- A typical analysis of an LNG stream to be processed in accordance with this invention would be, in approximate mole percent, 92.2% methane, 6.0% ethane and other C2 components, 1.1% propane and other C3 components, and traces of butanes plus, with the balance made up of nitrogen. A typical analysis of a gas stream to be processed in accordance with this invention would be, in approximate mole percent, 80.1% methane, 9.5% ethane and other C2 components, 5.6% propane and other C3 components, 1.3% iso-butane, 1.1% normal butane, 0.8% pentanes plus, with the balance made up of nitrogen and carbon dioxide. Sulfur containing gases are also sometimes present.
- For a better understanding of the present invention, reference is made to the following examples and drawings. Referring to the drawings:
-
FIG. 1 is a flow diagram of a base case natural gas processing plant using LNG to provide its refrigeration; -
FIG. 2 is a flow diagram of base case LNG and natural gas processing plants in accordance with U.S. Pat. Nos. 7,216,507 and 5,568,737, respectively; -
FIG. 3 is a flow diagram of an LNG and natural gas processing plant in accordance with the present invention; and -
FIGS. 4 through 8 are flow diagrams illustrating alternative means of application of the present invention to LNG and natural gas streams. -
FIGS. 1 and 2 are provided to quantify the advantages of the present invention. - In the following explanation of the above figures, tables are provided summarizing flow rates calculated for representative process conditions. In the tables appearing herein, the values for flow rates (in moles per hour) have been rounded to the nearest whole number for convenience. The total stream rates shown in the tables include all non-hydrocarbon components and hence are generally larger than the sum of the stream flow rates for the hydrocarbon components. Temperatures indicated are approximate values rounded to the nearest degree. It should also be noted that the process design calculations performed for the purpose of comparing the processes depicted in the figures are based on the assumption of no heat leak from (or to) the surroundings to (or from) the process. The quality of commercially available insulating materials makes this a very reasonable assumption and one that is typically made by those skilled in the art.
- For convenience, process parameters are reported in both the traditional British units and in the units of the Système International d'Unites (SI). The molar flow rates given in the tables may be interpreted as either pound moles per hour or kilogram moles per hour. The energy consumptions reported as horsepower (HP) and/or thousand British Thermal Units per hour (MBTU/Hr) correspond to the stated molar flow rates in pound moles per hour. The energy consumptions reported as kilowatts (kW) correspond to the stated molar flow rates in kilogram moles per hour.
-
FIG. 1 is a flow diagram showing the design of a processing plant to recover C2+ components from natural gas using an LNG stream to provide refrigeration. In the simulation of theFIG. 1 process, inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] asstream 31. If the inlet gas contains a concentration of sulfur compounds which would prevent the product streams from meeting specifications, the sulfur compounds are removed by appropriate pretreatment of the feed gas (not illustrated). In addition, the feed stream is usually dehydrated to prevent hydrate (ice) formation under cryogenic conditions. Solid desiccant has typically been used for this purpose. - The
inlet gas stream 31 is cooled inheat exchanger 12 by heat exchange with a portion (stream 72 a) of partially warmed LNG at −174° F. [−114° C.] andcool distillation stream 38 a at −107° F. [−77° C.]. The cooledstream 31 aenters separator 13 at −79° F. [−62° C.] and 584 psia [4,027 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 35).Liquid stream 35 is flash expanded through an appropriate expansion device, such asexpansion valve 17, to the operating pressure (approximately 430 psia [2,965 kPa(a)]) offractionation tower 20. The expandedstream 35 a leavingexpansion valve 17 reaches a temperature of −93° F. [−70° C.] and is supplied tofractionation tower 20 at a first mid-column feed point. - The vapor from separator 13 (stream 34) enters a
work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 10 expands the vapor substantially isentropically to slightly above the tower operating pressure, with the work expansion cooling the expandedstream 34 a to a temperature of approximately −101° F. [−74° C.]. The typical commercially available expanders are capable of recovering on the order of 80-88% of the work theoretically available in an ideal isentropic expansion. The work recovered is often used to drive a centrifugal compressor (such as item 11) that can be used to re-compress the heated distillation stream (stream 38 b), for example. The expandedstream 34 a is further cooled to −124° F. [−87° C.] inheat exchanger 14 by heat exchange withcold distillation stream 38 at −143° F. [−97° C.], whereupon the partially condensed expandedstream 34 b is thereafter supplied tofractionation tower 20 at a second mid-column feed point. - The demethanizer in
tower 20 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing to provide the necessary contact between the liquids falling downward and the vapors rising upward. The column also includes reboilers (such as reboiler 19) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column to strip the liquid product,stream 41, of methane and lighter components.Liquid product stream 41 exits the bottom of the tower at 99° F. [37° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product. -
Overhead distillation stream 43 is withdrawn from the upper section offractionation tower 20 at −143° F. [−97° C.] and is divided into two portions, streams 44 and 47. The first portion,stream 44, flows to refluxcondenser 22 where it is cooled to −237° F. [−149° C.] and totally condensed by heat exchange with a portion (stream 72) of the cold LNG (stream 71 a).Condensed stream 44 a entersreflux separator 23 wherein the condensed liquid (stream 46) is separated from any uncondensed vapor (stream 45). Theliquid stream 46 fromreflux separator 23 is pumped byreflux pump 24 to a pressure slightly above the operating pressure ofdemethanizer 20 andstream 46 a is then supplied as cold top column feed (reflux) todemethanizer 20. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising in the upper section ofdemethanizer 20. - The second portion (stream 47) of
overhead vapor stream 43 combines with any uncondensed vapor (stream 45) fromreflux separator 23 to formcold distillation stream 38 at −143° F. [−97° C.].Distillation stream 38 passes countercurrently to expandedstream 34 a inheat exchanger 14 where it is heated to −107° F. [−77° C.] (stream 38 a), and countercurrently to inlet gas inheat exchanger 12 where it is heated to 47° F. [8° C.] (stream 38 b). The distillation stream is then re-compressed in two stages. The first stage iscompressor 11 driven byexpansion machine 10. The second stage iscompressor 21 driven by a supplemental power source which compressesstream 38 c to sales line pressure (stream 38 d). After cooling to 126° F. [52° C.] in discharge cooler 22,stream 38 e combines withwarm LNG stream 71 b to form the residue gas product (stream 42).Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements. - The LNG (stream 71) from
LNG tank 50 enterspump 51 at −251° F. [−157° C.].Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence to the sales gas pipeline.Stream 71 a exits thepump 51 at −242° F. [−152° C.] and 1364 psia [9,401 kPa(a)] and is divided into two portions, streams 72 and 73. The first portion,stream 72, is heated as described previously to −174° F. [−114° C.] inreflux condenser 22 as it provides cooling to the portion (stream 44) ofoverhead vapor stream 43 fromfractionation tower 20, and to 43° F. [6° C.] inheat exchanger 12 as it provides cooling to the inlet gas. The second portion,stream 73, is heated to 35° F. [2° C.] inheat exchanger 53 using low level utility heat. Theheated streams warm LNG stream 71 b at 40° F. [4° C.], which thereafter combines withdistillation stream 38 e to formresidue gas stream 42 as described previously. - A summary of stream flow rates and energy consumption for the process illustrated in
FIG. 1 is set forth in the following table: -
TABLE I (FIG. 1) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 42,545 5,048 2,972 1,658 53,145 34 33,481 1,606 279 39 36,221 35 9,064 3,442 2,693 1,619 16,924 43 50,499 25 0 0 51,534 44 8,055 4 0 0 8,221 45 0 0 0 0 0 46 8,055 4 0 0 8,221 47 42,444 21 0 0 43,313 38 42,444 21 0 0 43,313 71 40,293 2,642 491 3 43,689 72 27,601 1,810 336 2 29,927 73 12,692 832 155 1 13,762 42 82,737 2,663 491 3 87,002 41 101 5,027 2,972 1,658 9,832 Recoveries* Ethane 65.37% Propane 85.83% Butanes+ 99.83% Power LNG Feed Pump 3,561 HP [ 5,854 kW] Reflux Pump 23 HP [ 38 kW] Residue Gas Compressor 24,612 HP [ 40,462 kW] Totals 28,196 HP [ 46,354 kW] Low Level Utility Heat LNG Heater 68,990 MBTU/Hr [ 44,564 kW] High Level Utility Heat Demethanizer Reboiler 80,020 MBTU/Hr [ 51,689 kW] Specific Power HP-Hr/Lb. Mole 2.868 [kW-Hr/kg mole] [ 4.715 ] *(Based on un-rounded flow rates) - The recoveries reported in Table I are computed relative to the total quantities of ethane, propane, and butanes+ contained in the gas stream being processed in the plant and in the LNG stream. Although the recoveries are quite high relative to the heavier hydrocarbons contained in the gas being processed (99.58%, 100.00%, and 100.00%, respectively, for ethane, propane, and butanes+), none of the heavier hydrocarbons contained in the LNG stream are captured in the
FIG. 1 process. In fact, depending on the composition ofLNG stream 71, theresidue gas stream 42 produced by theFIG. 1 process may not meet all pipeline specifications. The specific power reported in Table I is the power consumed per unit of liquid product recovered, and is an indicator of the overall process efficiency. -
FIG. 2 is a flow diagram showing processes to recover C2+ components from LNG and natural gas in accordance with U.S. Pat. Nos. 7,216,507 and 5,568,737, respectively, with the processed LNG stream used to provide refrigeration for the natural gas plant. The processes ofFIG. 2 have been applied to the same LNG stream and inlet gas stream compositions and conditions as described previously forFIG. 1 . - In the simulation of the
FIG. 2 process, the LNG to be processed (stream 71) fromLNG tank 50 enterspump 51 at −251° F. [−157° C.].Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence toexpansion machine 55.Stream 71 a exits the pump at −242° F. [−152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 75 and 76. The first portion,stream 75, is expanded to the operating pressure (approximately 415 psia [2,859 kPa(a)]) offractionation column 62 byexpansion valve 58. The expandedstream 75 aleaves expansion valve 58 at −238° F. [−150° C.] and is thereafter supplied to tower 62 at an upper mid-column feed point. - The second portion,
stream 76, is heated to −79° F. [−62° C.] inheat exchanger 52 by cooling compressedoverhead distillation stream 79 a at −70° F. [−57° C.] andreflux stream 82 at −128° F. [−89° C.]. The partiallyheated stream 76 a is further heated and vaporized inheat exchanger 53 using low level utility heat. Theheated stream 76 b at −5° F. [−20° C.] and 1334 psia [9,195 kPa(a)] enterswork expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expandedstream 76 c to a temperature of approximately −107° F. [−77° C.] before it is supplied as feed tofractionation column 62 at a lower mid-column feed point. - The demethanizer in
fractionation column 62 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing consisting of two sections. The upper absorbing (rectification) section contains the trays and/or packing to provide the necessary contact between the vapors rising upward and cold liquid falling downward to condense and absorb the ethane and heavier components; the lower stripping (demethanizing) section contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward. The demethanizing section also includes one or more reboilers (such asside reboiler 60 using low level utility heat, andreboiler 61 using high level utility heat) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column. Thecolumn liquid stream 80 exits the bottom of the tower at 54° F. [12° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product. -
Overhead distillation stream 79 is withdrawn from the upper section offractionation tower 62 at −144° F. [−98° C.] and flows tocompressor 56 driven byexpansion machine 55, where it is compressed to 807 psia [5,567 kPa(a)] (stream 79 a). At this pressure, the stream is totally condensed as it is cooled to −128° F. [−89° C.] inheat exchanger 52 as described previously. The condensed liquid (stream 79 b) is then divided into two portions, streams 83 and 82. The first portion (stream 83) is the methane-rich lean LNG stream, which is pumped bypump 63 to 1270 psia [8,756 kPa(a)] for subsequent vaporization inheat exchanger 12,heating stream 83 a to 40° F. [4° C.] as described in paragraph [0032] below to produce warmlean LNG stream 83 b. - The remaining portion of condensed
liquid stream 79 b,reflux stream 82, flows toheat exchanger 52 where it is subcooled to −237° F. [−149° C.] by heat exchange with a portion of the cold LNG (stream 76) as described previously. Thesubcooled stream 82 a is then expanded to the operating pressure ofdemethanizer 62 byexpansion valve 57. The expandedstream 82 b at −236° F. [−149° C.] is then supplied as cold top column feed (reflux) todemethanizer 62. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section ofdemethanizer 62. - In the simulation of the
FIG. 2 process, inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] asstream 31. Thefeed stream 31 is cooled inheat exchanger 12 by heat exchange with cold lean LNG (stream 83 a) at −116° F. [−82° C.],cool distillation stream 38 a at −96° F. [−71° C.], and demethanizer liquids (stream 39) at −3° F. [−20° C.]. The cooledstream 31 a entersseparator 13 at −67° F. [−55° C.] and 584 psia [4,027 kPa(a)] where the vapor (stream 33) is separated from the condensed liquid (stream 35).Liquid stream 35 is flash expanded through an appropriate expansion device, such asexpansion valve 17, to the operating pressure (approximately 375 psia [2,583 kPa(a)]) offractionation tower 20. The expandedstream 35 a leavingexpansion valve 17 reaches a temperature of −86° F. [−65° C.] and is supplied tofractionation tower 20 at a first lower mid-column feed point. -
Vapor stream 33 fromseparator 13 is divided into two streams, 32 and 34.Stream 32, containing about 22% of the total vapor, passes throughheat exchanger 14 in heat exchange relation withcold distillation stream 38 at −150° F. [−101° C.] where it is cooled to substantial condensation. The resulting substantially condensedstream 32 a at −144° F. [−98° C.] is then flash expanded through an appropriate expansion device, such asexpansion valve 16, to the operating pressure offractionation tower 20, coolingstream 32 b to −148° F. [−100° C.] before it is supplied tofractionation tower 20 at an upper mid-column feed point. - The remaining 78% of the vapor from separator 13 (stream 34) enters a
work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 10 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expandedstream 34 a to a temperature of approximately −100° F. [−73° C.]. The partially condensed expandedstream 34 a is thereafter supplied as feed tofractionation tower 20 at a second lower mid-column feed point. - The demethanizer in
fractionation column 20 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing consisting of two sections. The upper absorbing (rectification) section contains the trays and/or packing to provide the necessary contact between the vapors rising upward and cold liquid falling downward to condense and absorb the ethane and heavier components; the lower stripping (demethanizing) section contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward. The demethanizing section also includes one or more reboilers (such as the side reboiler inheat exchanger 12 described previously, andreboiler 19 using high level utility heat) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column. Thecolumn liquid stream 40 exits the bottom of the tower at 85° F. [30° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product, and combines withstream 80 to form the liquid product (stream 41). -
Overhead distillation stream 38 is withdrawn from the upper section offractionation tower 20 at −150° F. [−101° C.]. It passes countercurrently tovapor stream 32 and recyclestream 36 a inheat exchanger 14 where it is heated to −96° F. [−71° C.] (stream 38 a), and countercurrently toinlet gas stream 31 and recyclestream 36 inheat exchanger 12 where it is heated to 6° F. [−15° C.] (stream 38 b). The distillation stream is then re-compressed in two stages. The first stage iscompressor 11 driven byexpansion machine 10. The second stage iscompressor 21 driven by a supplemental power source which compressesstream 38 c to sales line pressure (stream 38 d). After cooling to 126° F. [52° C.] in discharge cooler 22,stream 38 e is divided into two portions,stream 37 and recyclestream 36.Stream 37 combines with warmlean LNG stream 83 b to form the residue gas product (stream 42).Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements. -
Recycle stream 36 flows toheat exchanger 12 and is cooled to −102° F. [−75° C.] by heat exchange with cool lean LNG (stream 83 a),cool distillation stream 38 a, and demethanizer liquids (stream 39) as described previously.Stream 36 a is further cooled to −144° F. [−98° C.] by heat exchange withcold distillation stream 38 inheat exchanger 14 as described previously. The substantially condensedstream 36 b is then expanded through an appropriate expansion device, such asexpansion valve 15, to the demethanizer operating pressure, resulting in cooling of the total stream to −152° F. [−102° C.]. The expandedstream 36 c is then supplied tofractionation tower 20 as the top column feed. The vapor portion ofstream 36 c combines with the vapors rising from the top fractionation stage of the column to formdistillation stream 38, which is withdrawn from an upper region of the tower as described above. - A summary of stream flow rates and energy consumption for the process illustrated in
FIG. 2 is set forth in the following table: -
TABLE II (FIG. 2) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 42,545 5,048 2,972 1,658 53,145 33 36,197 2,152 429 64 39,690 35 6,348 2,896 2,543 1,594 13,455 32 8,027 477 95 14 8,801 34 28,170 1,675 334 50 30,889 38 52,982 30 0 0 54,112 36 10,537 6 0 0 10,762 37 42,445 24 0 0 43,350 40 100 5,024 2,972 1,658 9,795 71 40,293 2,642 491 3 43,689 75 4,835 317 59 0 5,243 76 35,458 2,325 432 3 38,446 79 45,588 16 0 0 45,898 82 5,348 2 0 0 5,385 83 40,240 14 0 0 40,513 80 53 2,628 491 3 3,176 42 82,685 38 0 0 83,863 41 153 7,652 3,463 1,661 12,971 Recoveries* Ethane 99.51% Propane 100.00% Butanes+ 100.00% Power LNG Feed Pump 3,561 HP [ 5,854 kW] LNG Product Pump 1,746 HP [ 2,870 kW] Residue Gas Compressor 31,674 HP [ 52,072 kW] Totals 36,981 HP [ 60,796 kW] Low Level Utility Heat Liquid Feed Heater 66,200 MBTU/Hr [ 42,762 kW] Demethanizer Reboiler 6023,350 MBTU/Hr [ 15,083 kW] Totals 89,550 MBTU/Hr [ 57,845 kW] High Level Utility Heat Demethanizer Reboiler 19 20,080 MBTU/Hr [ 12,971 kW] Demethanizer Reboiler 613,400 MBTU/Hr [ 2,196 kW] Totals 23,480 MBTU/Hr [ 15,167 kW] Specific Power HP-Hr/Lb. Mole 2.851 [kW-Hr/kg mole] [ 4.687 ] *(Based on un-rounded flow rates) - Comparison of the recovery levels displayed in Tables I and II shows that the liquids recovery of the
FIG. 2 processes is much higher than that of theFIG. 1 process due to the recovery of the heavier hydrocarbon liquids contained in the LNG stream infractionation tower 62. The ethane recovery improves from 65.37% to 99.51%, the propane recovery improves from 85.83% to 100.00%, and the butanes+ recovery improves from 99.83% to 100.00%. In addition, the process efficiency of theFIG. 2 processes is improved by about 1% in terms of the specific power relative to theFIG. 1 process. -
FIG. 3 illustrates a flow diagram of a process in accordance with the present invention. The LNG stream and inlet gas stream compositions and conditions considered in the process presented inFIG. 3 are the same as those in theFIG. 1 andFIG. 2 processes. Accordingly, theFIG. 3 process can be compared with theFIG. 1 andFIG. 2 processes to illustrate the advantages of the present invention. - In the simulation of the
FIG. 3 process, the LNG to be processed (stream 71) fromLNG tank 50 enterspump 51 at −251° F. [−157° C.].Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence toseparator 54.Stream 71 a exits the pump at −242° F. [−152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 72 and 73. The first portion,stream 72, becomesstream 75 and is expanded to the operating pressure (approximately 415 psia [2,859 kPa(a)]) offractionation column 62 byexpansion valve 58. The expandedstream 75 aleaves expansion valve 58 at −238° F. [−150C.] and is thereafter supplied to tower 62 at an upper mid-column feed point. - The second portion,
stream 73, is heated prior to enteringseparator 54 so that all or a portion of it is vaporized. In the example shown inFIG. 3 ,stream 73 is first heated to −77° F. [−61 ° C.] inheat exchanger 52 by cooling compressedoverhead distillation stream 79 a at −70° F. [−57° C.] andreflux stream 81 at −16° F. [−82° C.]. The partiallyheated stream 73 a becomesstream 76 and is further heated inheat exchanger 53 using low level utility heat. (High level utility heat, such as the heating medium used intower reboiler 61, is normally more expensive than low level utility heat, so lower operating cost is usually achieved when use of low level heat, such as sea water, is maximized and the use of high level utility heat is minimized.) Note that in all cases exchangers 52 and 53 are representative of either a multitude of individual heat exchangers or a single multi-pass heat exchanger, or any combination thereof. (The decision as to whether to use more than one heat exchanger for the indicated heating services will depend on a number of factors including, but not limited to, inlet LNG flow rate, heat exchanger size, stream temperatures, etc.) - The
heated stream 76 a entersseparator 54 at −5° F. [−20° C.] and 1334 psia [9,195 kPa(a)] where the vapor (stream 77) is separated from any remaining liquid (stream 78).Vapor stream 77 enters awork expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expandedstream 77 a to a temperature of approximately −107° F. [−77° C.]. The work recovered is often used to drive a centrifugal compressor (such as item 56) that can be used to re-compress the column overhead vapor (stream 79), for example. The partially condensed expandedstream 77 a is thereafter supplied as feed tofractionation column 62 at a lower mid-column feed point. The separator liquid (stream 78), if any, is expanded to the operating pressure offractionation column 62 byexpansion valve 59 before expandedstream 78 a is supplied tofractionation tower 62 at a second lower mid-column feed point. - The demethanizer in
fractionation column 62 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing. Thefractionation tower 62 may consist of two sections. The upper absorbing (rectification) section contains the trays and/or packing to provide the necessary contact between the vapors rising upward and cold liquid falling downward to condense and absorb the ethane and heavier components; the lower stripping (demethanizing) section contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward. The demethanizing section also includes one or more reboilers (such asside reboiler 60 using low level utility heat, andreboiler 61 using high level utility heat) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column. Thecolumn liquid stream 80 exits the bottom of the tower at 54° F. [12° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product. -
Overhead distillation stream 79 is withdrawn from the upper section offractionation tower 62 at −144° F. [−98° C.] and flows tocompressor 56 driven byexpansion machine 55, where it is compressed to 805 psia [5,554 kPa(a)] (stream 79 a). At this pressure, the stream is totally condensed as it is cooled to −116° F. [−82° C.] inheat exchanger 52 as described previously. The condensed liquid (stream 79 b) is then divided into two portions, streams 83 and 81. The first portion (stream 83) is the methane-rich lean LNG stream, which is pumped bypump 63 to 1275 psia [8,791 kPa(a)] for subsequent vaporization inheat exchangers heating stream 83 a to −94° F. [−70° C.] and 40° F. [4° C.], respectively, as described in paragraphs [0047] and [0049] below to produce warmlean LNG stream 83 c. - The remaining portion of condensed
liquid stream 79 b,stream 81, flows toheat exchanger 52 where it is subcooled to −237° F. [−149° C.] by heat exchange with a portion of the cold LNG (stream 73) as described previously. Thesubcooled stream 81 a is then divided into two portions, streams 82 and 36. The first portion,reflux stream 82, is expanded to the operating pressure ofdemethanizer 62 byexpansion valve 57. The expandedstream 82 a at −236° F. [−149° C.] is then supplied as cold top column feed (reflux) todemethanizer 62. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section ofdemethanizer 62. The disposition of the second portion,reflux stream 36 fordemethanizer 20, is described in paragraph [0050] below. - In the simulation of the
FIG. 3 process, inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] asstream 31. Thefeed stream 31 is divided into two portions, streams 32 and 33. The first portion,stream 32, is cooled inheat exchanger 12 by heat exchange with cool lean LNG (stream 83 b) at −94° F. [−70° C.],cool distillation stream 38 a at −94° F. [−70° C.], and demethanizer liquids (stream 39) at −78° F. [−61° C.]. The partially cooledstream 32 a is further cooled from −89° F. [−67° C.] to −120° F. [−85° C.] inheat exchanger 14 by heat exchange with cold lean LNG (stream 83 a) at −97° F. [−72° C.] andcold distillation stream 38 at −144° F. [−98° C.]. Note that in all cases exchangers 12 and 14 are representative of either a multitude of individual heat exchangers or a single multi-pass heat exchanger, or any combination thereof. (The decision as to whether to use more than one heat exchanger for the indicated heating services will depend on a number of factors including, but not limited to, inlet gas flow rate, heat exchanger size, stream temperatures, etc.) The substantially condensedstream 32 b is then flash expanded through an appropriate expansion device, such asexpansion valve 16, to the operating pressure (approximately 415 psia [2,861 kPa(a)]) offractionation tower 20, coolingstream 32 c to −132° F. [−91° C.] before it is supplied tofractionation tower 20 at an upper mid-column feed point. - The second portion of
feed stream 31,stream 33, enters awork expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 10 expands the vapor substantially isentropically to a pressure slightly above the operating pressure offractionation tower 20, with the work expansion cooling the expandedstream 33 a to a temperature of approximately 92° F. [33° C.]. The work recovered is often used to drive a centrifugal compressor (such as item 11) that can be used to re-compress the heated distillation stream (stream 38 b), for example. The expandedstream 33 a is further cooled inheat exchanger 12 by heat exchange with cool lean LNG (stream 83 b),cool distillation stream 38 a, and demethanizer liquids (stream 39) as described previously. The further cooledstream 33 b entersseparator 13 at −84° F. [−65° C.] and 423 psia [2,916 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 35). -
Vapor stream 34 is cooled to −120° F. [−85° C.] inheat exchanger 14 by heat exchange with cold lean LNG (stream 83 a) andcold distillation stream 38 as described previously. The partially condensedstream 34 a is then supplied tofractionation tower 20 at a first lower mid-column feed point.Liquid stream 35 is flash expanded through an appropriate expansion device, such asexpansion valve 17, to the operating pressure offractionation tower 20. The expandedstream 35 a leavingexpansion valve 17 reaches a temperature of −85° F. [−65° C.] and is supplied tofractionation tower 20 at a second lower mid-column feed point. - The second portion of
subcooled stream 81 a,reflux stream 36, is expanded to the operating pressure ofdemethanizer 20 byexpansion valve 15. The expandedstream 36 a at −236° F. [−149° C.] is then supplied as cold top column feed (reflux) todemethanizer 20. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising inupper rectification section 20 a ofdemethanizer 20. - The demethanizer in
fractionation column 20 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing. Thefractionation tower 20 may consist of two sections. The upper absorbing (rectification)section 20 a contains the trays and/or packing to provide the necessary contact between the vapors rising upward and cold liquid falling downward to condense and absorb the ethane and heavier components; the lower stripping (demethanizing)section 20 b contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward.Demethanizing section 20 b also includes one or more reboilers (such as the side reboiler inheat exchanger 12 described previously, andreboiler 19 using high level utility heat) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column. Thecolumn liquid stream 40 exits the bottom of the tower at 95° F. [35° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product, and combines withstream 80 to form the liquid product (stream 41). -
Overhead distillation stream 38 is withdrawn from the upper section offractionation tower 20 at −144° F. [−98° C.]. It passes countercurrently to the first portion (stream 32 a) ofinlet gas stream 31 andvapor stream 34 inheat exchanger 14 where it is heated to −94° F. [−70° C.] (stream 38 a), and countercurrently to the first portion (stream 32) ofinlet gas stream 31 and expanded second portion (stream 33 a) inheat exchanger 12 where it is heated to 13° F. [−11° C.] (stream 38 b). The distillation stream is then re-compressed in two stages. The first stage iscompressor 11 driven byexpansion machine 10. The second stage iscompressor 21 driven by a supplemental power source which compressesstream 38 c to sales gas line pressure (stream 38 d). After cooling to 126° F. [52° C.] in discharge cooler 22,stream 38 e combines with warmlean LNG stream 83 c to form the residue gas product (stream 42).Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements. - A summary of stream flow rates and energy consumption for the process illustrated in
FIG. 3 is set forth in the following table: -
TABLE III (FIG. 3) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 42,545 5,048 2,972 1,658 53,145 32 5,531 656 386 215 6,909 33 37,014 4,392 2,586 1,443 46,236 34 32,432 1,703 255 29 35,166 35 4,582 2,689 2,331 1,414 11,070 36 7,720 2 0 0 7,773 38 50,165 24 0 0 51,078 40 100 5,026 2,972 1,658 9,840 71 40,293 2,642 491 3 43,689 72/75 4,916 322 60 0 5,330 73/76 35,377 2,320 431 3 38,359 77 35,377 2,320 431 3 38,359 78 0 0 0 0 0 79 45,682 14 0 0 45,990 81 13,162 4 0 0 13,251 83 32,520 10 0 0 32,739 82 5,442 2 0 0 5,478 80 53 2,630 491 3 3,177 42 82,685 34 0 0 83,817 41 153 7,656 3,463 1,661 13,017 Recoveries* Ethane 99.55% Propane 100.00% Butanes+ 100.00% Power LNG Feed Pump 3,561 HP [ 5,854 kW] LNG Product Pump 1,740 HP [ 2,861 kW] Residue Gas Compressor 24,852 HP [ 40,856 kW] Totals 30,153 HP [ 49,571 kW] Low Level Utility Heat Liquid Feed Heater 65,000 MBTU/Hr [ 41,987 kW] Demethanizer Reboiler 60 19,000 MBTU/Hr [ 12,273 kW] Totals 84,000 MBTU/Hr [ 54,260 kW] High Level Utility Heat Demethanizer Reboiler 19 41,460 MBTU/Hr [ 26,781 kW] Demethanizer Reboiler 61 8,400 MBTU/Hr [ 5,426 kW] Totals 49,860 MBTU/Hr [ 32,207 kW] Specific Power HP-Hr/Lb. Mole 2.316 [kW-Hr/kg mole] [ 3.808 ] *(Based on un-rounded flow rates) - The improvement offered by the
FIG. 3 embodiment of the present invention is astonishing compared to theFIG. 1 andFIG. 2 processes. Comparing the recovery levels displayed in Table III above for theFIG. 3 embodiment with those in Table I for theFIG. 1 process shows that theFIG. 3 embodiment of the present invention improves the ethane recovery from 65.37% to 99.55%, the propane recovery from 85.83% to 100.00%, and the butanes+ recovery from 99.83% to 100.00%. Further, comparing the utilities consumptions in Table III with those in Table I shows that although the power required for theFIG. 3 embodiment of the present invention is approximately 7% higher than theFIG. 1 process, the process efficiency of theFIG. 3 embodiment of the present invention is significantly better than that of theFIG. 1 process. The gain in process efficiency is clearly seen in the drop in the specific power, from 2.868 HP-Hr/Lb. Mole [4.715 kW-Hr/kg mole] for theFIG. 1 process to 2.316 HP-Hr/Lb. Mole [3.808 kW-Hr/kg mole] for theFIG. 3 embodiment of the present invention, an increase of more than 19% in the production efficiency. - Comparing the recovery levels displayed in Table III for the
FIG. 3 embodiment with those in Table II for theFIG. 2 processes shows that the liquids recovery levels are essentially the same. However, comparing the utilities consumptions in Table III with those in Table II shows that the power required for theFIG. 3 embodiment of the present invention is about 18% lower than theFIG. 2 processes. This results in reducing the specific power from 2.851 HP-Hr/Lb. Mole [4.687 kW-Hr/kg mole] for theFIG. 2 processes to 2.316 HP-Hr/Lb. Mole [3.808 kW-H/kg mole] for theFIG. 3 embodiment of the present invention, an improvement of nearly 19% in the production efficiency. - There are six primary factors that account for the improved efficiency of the present invention. First, compared to many prior art processes, the present invention does not depend on the LNG feed itself to directly serve as the reflux for
fractionation column 62. Rather, the refrigeration inherent in the cold LNG is used inheat exchanger 52 to generate a liquid reflux stream (stream 82) that contains very little of the C2 components and heavier hydrocarbon components that are to be recovered, resulting in efficient rectification in the absorbing section offractionation tower 62 and avoiding the equilibrium limitations of such prior art processes. Second, splitting the LNG feed into two portions before feedingfractionation column 62 allows more efficient use of low level utility heat, thereby reducing the amount of high level utility heat consumed byreboiler 61. The cold portion of the LNG feed (stream 75 a) serves as a supplemental reflux stream forfractionation tower 62, providing partial rectification of the vapors in the expanded vapor and liquid streams (streams 77 a and 78 a, respectively) so that heating and at least partially vaporizing the other portion (stream 73) of the LNG feed does not unduly increase the condensing load inheat exchanger 52. Third, using a portion of the cold LNG feed (stream 75 a) as a supplemental reflux stream allows using less top reflux (stream 82 a) forfractionation tower 62. The lower top reflux flow, plus the greater degree of heating using low level utility heat inheat exchanger 53, results in less total liquidfeeding fractionation column 62, reducing the duty required inreboiler 61 and minimizing the amount of high level utility heat needed to meet the specification for the bottom liquid product fromdemethanizer 62. - Fourth, using the cold
lean LNG stream 83 a to provide “free” refrigeration to the gas streams inheat exchangers heat exchanger 53 in theFIG. 1 process) to re-vaporize the LNG prior to delivery to the sales gas pipeline. Fifth, cooling a portion (stream 32) ofinlet gas stream 31 to substantial condensation prior to expansion to the operating pressure ofdemethanizer 20 allows the expanded substantially condensedstream 32 c to serve as a supplemental reflux stream forfractionation tower 20, providing partial rectification of the vapors in the partially condensed vapor and expanded liquid streams (streams 34 a and 35 a, respectively) so that less top reflux (stream 36 a) is needed forfractionation tower 20. Sixth, integrating the LNG plant with the gas plant allows using a portion (stream 36) of the lean LNG as reflux fordemethanizer 20. The resultingstream 36 a is very cold and contains very little of the C2 components and heavier hydrocarbon components that are to be recovered, resulting in very efficient rectification in absorbingsection 20 a and further minimizing the quantity of reflux required fordemethanizer 20. - An alternative method of processing natural gas is shown in another embodiment of the present invention as illustrated in
FIG. 4 . The LNG stream and inlet gas stream compositions and conditions considered in the process presented inFIG. 4 are the same as those inFIGS. 1 through 3 . Accordingly, theFIG. 4 process can be compared with theFIGS. 1 and 2 processes to illustrate the advantages of the present invention, and can likewise be compared to the embodiment displayed inFIG. 3 . - In the simulation of the
FIG. 4 process, the LNG to be processed (stream 71) fromLNG tank 50 enterspump 51 at −251° F. [−157° C.].Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence toseparator 54.Stream 71 a exits the pump at −242° F. [−152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 72 and 73. The first portion,stream 72, becomesstream 75 and is expanded to the operating pressure (approximately 415 psia [2,859 kPa(a)]) offractionation column 62 byexpansion valve 58. The expandedstream 75 aleaves expansion valve 58 at −238° F. [−150C.] and is thereafter supplied to tower 62 at an upper mid-column feed point. - The second portion,
stream 73, is heated prior to enteringseparator 54 so that all or a portion of it is vaporized. In the example shown inFIG. 4 ,stream 73 is first heated to −77° F. [−61 ° C.] inheat exchanger 52 by cooling compressedoverhead distillation stream 79 a at −70° F. [−57° C.] andreflux stream 81 at −15° F. [−82° C]. The partiallyheated stream 73 a becomesstream 76 and is further heated inheat exchanger 53 using low level utility heat. Theheated stream 76 a entersseparator 54 at −5° F. [−20° C.] and 1334 psia [9,195 kPa(a)] where the vapor (stream 77) is separated from any remaining liquid (stream 78).Vapor stream 77 enters awork expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expandedstream 77 a to a temperature of approximately −107° F. [−77° C.]. The partially condensed expandedstream 77 a is thereafter supplied as feed tofractionation column 62 at a lower mid-column feed point. The separator liquid (stream 78), if any, is expanded to the operating pressure offractionation column 62 byexpansion valve 59 before expandedstream 78 a is supplied tofractionation tower 62 at a second lower mid-column feed point. - The
column liquid stream 80 exits the bottom of the tower at 54° F. [12° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.Overhead distillation stream 79 is withdrawn from the upper section offractionation tower 62 at −144° F. [−98° C.] and flows tocompressor 56 driven byexpansion machine 55, where it is compressed to 805 psia [5,554 kPa(a)] (stream 79 a). At this pressure, the stream is totally condensed as it is cooled to −115° F. [−82° C.] inheat exchanger 52 as described previously. The condensed liquid (stream 79 b) is then divided into two portions, streams 83 and 81. The first portion (stream 83) is the methane-rich lean LNG stream, which is pumped bypump 63 to 1270 psia [8,756 kPa(a)] for subsequent vaporization inheat exchanger 12,heating stream 83 a to 40° F. [4° C.] as described in paragraph [0063] below to produce warmlean LNG stream 83 b. - The remaining portion of condensed
liquid stream 79 b,stream 81, flows toheat exchanger 52 where it is subcooled to −237° F. [−149° C.] by heat exchange with a portion of the cold LNG (stream 73) as described previously. Thesubcooled stream 81 a is then divided into two portions, streams 82 and 36. The first portion,reflux stream 82, is expanded to the operating pressure ofdemethanizer 62 byexpansion valve 57. The expandedstream 82 a at −236° F. [−149° C.] is then supplied as cold top column feed (reflux) todemethanizer 62. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section ofdemethanizer 62. The disposition of the second portion,reflux stream 36 fordemethanizer 20, is described in paragraph [0066] below. - In the simulation of the
FIG. 4 process, inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] asstream 31. Thefeed stream 31 is divided into two portions, streams 32 and 33. The first portion,stream 32, is cooled inheat exchanger 12 by heat exchange with cold lean LNG (stream 83 a) at −96° F. [−71° C.], coolcompressed distillation stream 38 b at −109° F. [−78° C.], and demethanizer liquids (stream 39) at −63° F. [−53° C.]. The partially cooledstream 32 a is further cooled from −96° F. [−71° C.] to −121° F. [−85° C.] inheat exchanger 14 by heat exchange with coldcompressed distillation stream 38 a at −128° F. [−89° C.]. The substantially condensedstream 32 b is then flash expanded through an appropriate expansion device, such asexpansion valve 16, to the operating pressure (approximately 443 psia [3,052 kPa(a)]) offractionation tower 20, coolingstream 32 c to −129° F. [−90° C.] before it is supplied tofractionation tower 20 at an upper mid-column feed point. - The second portion of
feed stream 31,stream 33, is cooled inheat exchanger 12 by heat exchange with cold lean LNG (stream 83 a), coolcompressed distillation stream 38 b, and demethanizer liquids (stream 39) as described previously. The cooledstream 33 a entersseparator 13 at −86° F. [−65° C.] and 584 psia [4,027 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 35).Liquid stream 35 is flash expanded through an appropriate expansion device, such asexpansion valve 17, to the operating pressure offractionation tower 20. The expandedstream 35 a leavingexpansion valve 17 reaches a temperature of −100° F. [−73° C.] and is supplied tofractionation tower 20 at a first lower mid-column feed point. - The vapor from separator 13 (stream 34) enters a
work expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 10 expands the vapor substantially isentropically to slightly above the tower operating pressure, with the work expansion cooling the expandedstream 34 a to a temperature of approximately −106° F. [−77° C.]. The expandedstream 34 a is further cooled to −121° F. [−85° C.] inheat exchanger 14 by heat exchange with coldcompressed distillation stream 38 a as described previously, whereupon the partially condensed expandedstream 34 b is thereafter supplied tofractionation tower 20 at a second lower mid-column feed point. - The second portion of
subcooled stream 81 a,reflux stream 36, is expanded to the operating pressure ofdemethanizer 20 byexpansion valve 15. The expandedstream 36 a at −236° F. [−149° C.] is then supplied as cold top column feed (reflux) todemethanizer 20. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section ofdemethanizer 20. - The
column liquid stream 40 exits the bottom of the tower at 102° F. [39° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product, and combines withstream 80 to form the liquid product (stream 41).Overhead distillation stream 38 is withdrawn from the upper section offractionation tower 20 at −141° F. [−96° C.] and flows tocompressor 11 driven byexpansion machine 10, where it is compressed to 501 psia [3,452 kPa(a)]. The coldcompressed distillation stream 38 a passes countercurrently to the first portion (stream 32 a) ofinlet gas stream 31 and expandedvapor stream 34 a inheat exchanger 14 where it is heated to −109° F. [−78° C.] (stream 38 b), and countercurrently to the first portion (stream 32) and second portion (stream 33) ofinlet gas stream 31 inheat exchanger 12 where it is heated to 31° F. [−1° C.] (stream 38 c). The heated distillation stream then enterscompressor 21 driven by a supplemental power source which compressesstream 38 c to sales line pressure (stream 38 d). After cooling to 126° F. [52° C.] in discharge cooler 22,stream 38 e combines with warmlean LNG stream 83 b to form the residue gas product (stream 42).Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements. - A summary of stream flow rates and energy consumption for the process illustrated in
FIG. 4 is set forth in the following table: -
TABLE IV (FIG. 4) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 42,545 5,048 2,972 1,658 53,145 32 3,404 404 238 133 4,251 33 39,141 4,644 2,734 1,525 48,894 34 28,606 1,181 191 26 30,730 35 10,535 3,463 2,543 1,499 18,164 36 8,046 2 0 0 8,101 38 50,491 27 0 0 51,413 40 100 5,023 2,972 1,658 9,833 71 40,293 2,642 491 3 43,689 72/75 4,916 322 60 0 5,330 73/76 35,377 2,320 431 3 38,359 77 35,377 2,320 431 3 38,359 78 0 0 0 0 0 79 45,682 14 0 0 45,990 81 13,488 4 0 0 13,579 83 32,194 10 0 0 32,411 82 5,442 2 0 0 5,478 80 53 2,630 491 3 3,177 42 82,685 37 0 0 83,824 41 153 7,653 3,463 1,661 13,010 Recoveries* Ethane 99.51% Propane 100.00% Butanes+ 100.00% Power LNG Feed Pump 3,561 HP [ 5,854 kW] LNG Product Pump 1,727 HP [ 2,839 kW] Residue Gas Compressor 24,400 HP [ 40,113 kW] Totals 29,688 HP [ 48,806 kW] Low Level Utility Heat Liquid Feed Heater 65,000 MBTU/Hr [ 41,987 kW] Demethanizer Reboiler 60 19,000 MBTU/Hr [ 12,273 kW] Totals 84,000 MBTU/Hr [ 54,260 kW] High Level Utility Heat Demethanizer Reboiler 19 37,360 MBTU/Hr [ 24,133 kW] Demethanizer Reboiler 61 8,400 MBTU/Hr [ 5,426 kW] Totals 45,760 MBTU/Hr [ 29,559 kW] Specific Power HP-Hr/Lb. Mole 2.282 [kW-Hr/kg mole] [ 3.751 ] *(Based on un-rounded flow rates) - A comparison of Tables III and IV shows that the
FIG. 4 embodiment of the present invention achieves essentially the same liquids recovery as theFIG. 3 embodiment. However, theFIG. 4 embodiment uses less power than theFIG. 3 embodiment, improving the specific power by slightly more than 1%. In addition, the high level utility heat required for theFIG. 4 embodiment of the present invention is about 8% less than that of theFIG. 3 embodiment. - Another alternative method of processing natural gas is shown in the embodiment of the present invention as illustrated in
FIG. 5 . The LNG stream and inlet gas stream compositions and conditions considered in the process presented inFIG. 5 are the same as those inFIGS. 1 through 4 . Accordingly, theFIG. 5 process can be compared with theFIGS. 1 and 2 processes to illustrate the advantages of the present invention, and can likewise be compared to the embodiments displayed inFIGS. 3 and 4 . - In the simulation of the
FIG. 5 process, the LNG to be processed (stream 71) fromLNG tank 50 enterspump 51 at −251° F. [−157° C.].Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence toseparator 54.Stream 71 a exits the pump at −242° F. [−152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 72 and 73. The first portion,stream 72, becomesstream 75 and is expanded to the operating pressure (approximately 415 psia [2,859 kPa(a)]) offractionation column 62 byexpansion valve 58. The expandedstream 75 aleaves expansion valve 58 at −238° F. [−150C] and is thereafter supplied to tower 62 at an upper mid-column feed point. - The second portion,
stream 73, is heated prior to enteringseparator 54 so that all or a portion of it is vaporized. In the example shown inFIG. 5 ,stream 73 is first heated to −77° F. [−61° C.] inheat exchanger 52 by cooling compressedoverhead distillation stream 79 a at −70° F. [−57° C.] andreflux stream 81 at −12° F. [−80° C]. The partiallyheated stream 73 a becomesstream 76 and is further heated inheat exchanger 53 using low level utility heat. Theheated stream 76 a entersseparator 54 at −5° F. [−20° C.] and 1334 psia [9,195 kPa(a)] where the vapor (stream 77) is separated from any remaining liquid (stream 78).Vapor stream 77 enters awork expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expandedstream 77 a to a temperature of approximately −107° F. [−77° C.]. The partially condensed expandedstream 77 a is thereafter supplied as feed tofractionation column 62 at a lower mid-column feed point. The separator liquid (stream 78), if any, is expanded to the operating pressure offractionation column 62 byexpansion valve 59 before expandedstream 78 a is supplied tofractionation tower 62 at a second lower mid-column feed point. - The
column liquid stream 80 exits the bottom of the tower at 54° F. [12° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.Overhead distillation stream 79 is withdrawn from the upper section offractionation tower 62 at −144° F. [−98° C.] and flows tocompressor 56 driven byexpansion machine 55, where it is compressed to 805 psia [5,554 kPa(a)] (stream 79 a). At this pressure, the stream is totally condensed as it is cooled to −112° F. [−80° C.] inheat exchanger 52 as described previously. The condensed liquid (stream 79 b) is then divided into two portions, streams 83 and 81. The first portion (stream 83) is the methane-rich lean LNG stream, which is pumped bypump 63 to 1270 psia [8,756 kPa(a)] for subsequent vaporization inheat exchanger 12,heating stream 83 a to 40° F. [4° C.] as described in paragraph [0075] below to produce warmlean LNG stream 83 b. - The remaining portion of condensed
liquid stream 79 b,stream 81, flows toheat exchanger 52 where it is subcooled to −237° F. [−149° C.] by heat exchange with a portion of the cold LNG (stream 73) as described previously. Thesubcooled stream 81 a is then divided into two portions, streams 82 and 36. The first portion,reflux stream 82, is expanded to the operating pressure ofdemethanizer 62 byexpansion valve 57. The expandedstream 82 a at −236° F. [−149° C.] is then supplied as cold top column feed (reflux) todemethanizer 62. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section ofdemethanizer 62. The disposition of the second portion,reflux stream 36 fordemethanizer 20, is described in paragraph [0078] below. - In the simulation of the
FIG. 5 process, inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] asstream 31. Thefeed stream 31 is divided into two portions, streams 32 and 33. The first portion,stream 32, is cooled inheat exchanger 12 by heat exchange with cold lean LNG (stream 83 a) at −89° F. [−67° C.], coolcompressed distillation stream 38 b at −91° F. [−68° C.], and demethanizer liquids (stream 39) at −89° F. [−67° C.]. The partially cooledstream 32 a is further cooled from −86° F. [−65° C.] to −100° F. [−74° C.] inheat exchanger 14 by heat exchange with coldcompressed distillation stream 38 a at −112° F. [−80° C.]. The substantially condensedstream 32 b is then flash expanded through an appropriate expansion device, such asexpansion valve 16, to the operating pressure (approximately 428 psia [2,949 kPa(a)]) offractionation tower 20, coolingstream 32 c to −117° F. [−83° C.] before it is supplied tofractionation tower 20 at an upper mid-column feed point. - The second portion of
feed stream 31,stream 33, enters awork expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 10 expands the vapor substantially isentropically to a pressure slightly above the operating pressure offractionation tower 20, with the work expansion cooling the expandedstream 33 a to a temperature of approximately 95° F. [35° C.]. The expandedstream 33 a is further cooled inheat exchanger 12 by heat exchange with cold lean LNG (stream 83 a), coolcompressed distillation stream 38 b, and demethanizer liquids (stream 39) as described previously. The further cooledstream 33 b entersseparator 13 at −85° F. [−65° C.] and 436 psia [3,004 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 35). -
Vapor stream 34 is cooled to −100° F. [−74° C.] inheat exchanger 14 by heat exchange with coldcompressed distillation stream 38 a as described previously. The partially condensedstream 34 a is then supplied tofractionation tower 20 at a first lower mid-column feed point.Liquid stream 35 is flash expanded through an appropriate expansion device, such asexpansion valve 17, to the operating pressure offractionation tower 20. The expandedstream 35 a leavingexpansion valve 17 reaches a temperature of −86° F. [−65° C.] and is supplied tofractionation tower 20 at a second lower mid-column feed point. - The second portion of
subcooled stream 81 a,reflux stream 36, is expanded to the operating pressure ofdemethanizer 20 byexpansion valve 15. The expandedstream 36 a at −236° F. [−149° C.] is then supplied as cold top column feed (reflux) todemethanizer 20. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section ofdemethanizer 20. - The
column liquid stream 40 exits the bottom of the tower at 98° F. [37° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product, and combines withstream 80 to form the liquid product (stream 41).Overhead distillation stream 38 is withdrawn from the upper section offractionation tower 20 at −143° F. [−97° C.] and flows tocompressor 11 driven byexpansion machine 10, where it is compressed to 573 psia [3,950 kPa(a)]. The coldcompressed distillation stream 38 a passes countercurrently to the first portion (stream 32 a) ofinlet gas stream 31 andvapor stream 34 inheat exchanger 14 where it is heated to −91° F. [−68° C.] (stream 38 b), and countercurrently to the first portion (stream 32) and expanded second portion (stream 33 a) ofinlet gas stream 31 inheat exchanger 12 where it is heated to 67° F. [19° C.] (stream 38 c). The heated distillation stream then enterscompressor 21 driven by a supplemental power source which compressesstream 38 c to sales line pressure (stream 38 d). After cooling to 126° F. [52° C.] in discharge cooler 22,stream 38 e combines with warmlean LNG stream 83 b to form the residue gas product (stream 42).Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements. - A summary of stream flow rates and energy consumption for the process illustrated in
FIG. 5 is set forth in the following table: -
TABLE V (FIG. 5) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 42,545 5,048 2,972 1,658 53,145 32 14,465 1,716 1,010 564 18,069 33 28,080 3,332 1,962 1,094 35,076 34 24,317 1,236 184 21 26,322 35 3,763 2,096 1,778 1,073 8,754 36 10,372 3 0 0 10,442 38 52,817 30 0 0 53,749 40 100 5,021 2,972 1,658 9,838 71 40,293 2,642 491 3 43,689 72/75 4,916 322 60 0 5,330 73/76 35,377 2,320 431 3 38,359 77 35,377 2,320 431 3 38,359 78 0 0 0 0 0 79 45,682 14 0 0 45,990 81 15,814 5 0 0 15,920 83 29,868 9 0 0 30,070 82 5,442 2 0 0 5,478 80 53 2,630 491 3 3,177 42 82,685 39 0 0 83,819 41 153 7,651 3,463 1,661 13,015 Recoveries* Ethane 99.48% Propane 100.00% Butanes+ 100.00% Power LNG Feed Pump 3,561 HP [ 5,854 kW] LNG Product Pump 1,778 HP [ 2,923 kW] Residue Gas Compressor 23,201 HP [ 38,142 kW] Totals 28,540 HP [ 46,919 kW] Low Level Utility Heat Liquid Feed Heater 65,000 MBTU/Hr [ 41,987 kW] Demethanizer Reboiler 60 19,000 MBTU/Hr [ 12,273 kW] Totals 84,000 MBTU/Hr [ 54,260 kW] High Level Utility Heat Demethanizer Reboiler 19 53,370 MBTU/Hr [ 34,475 kW] Demethanizer Reboiler 61 8,400 MBTU/Hr [ 5,426 kW] Totals 61,770 MBTU/Hr [ 39,901 kW] Specific Power HP-Hr/Lb. Mole 2.193 [kW-Hr/kg mole] [ 3.605 ] *(Based on un-rounded flow rates) - A comparison of Tables III, IV, and V shows that the
FIG. 5 embodiment of the present invention achieves essentially the same liquids recovery as theFIG. 3 andFIG. 4 embodiments. TheFIG. 5 embodiment uses less power than theFIG. 3 andFIG. 4 embodiments, improving the specific power by over 5% relative to theFIG. 3 embodiment and nearly 4% relative to theFIG. 4 embodiment. However, the high level utility heat required for theFIG. 5 embodiment of the present invention is somewhat higher than that of theFIG. 3 andFIG. 4 embodiments (by 24% and 35%, respectively). The choice of which embodiment to use for a particular application will generally be dictated by the relative costs of power and high level utility heat and the relative capital costs of pumps, heat exchangers, and compressors. - An alternative method of processing LNG and natural gas is shown in the embodiment of the present invention as illustrated in
FIG. 6 . The LNG stream and inlet gas stream compositions and conditions considered in the process presented inFIG. 6 are the same as those inFIGS. 1 through 5 . Accordingly, theFIG. 5 process can be compared with theFIGS. 1 and 2 processes to illustrate the advantages of the present invention, and can likewise be compared to the embodiments displayed inFIGS. 3 through 5 . - In the simulation of the
FIG. 6 process, the LNG to be processed (stream 71) fromLNG tank 50 enterspump 51 at −251° F. [−157° C.].Pump 51 elevates the pressure of the LNG sufficiently so that it can flow through heat exchangers and thence toseparator 54.Stream 71 a exits the pump at −242° F. [−152° C.] and 1364 psia [9,401 kPa(a)] and is split into two portions, streams 72 and 73. The first portion,stream 72, becomesstream 75 and is expanded to the operating pressure (approximately 435 psia [2,997 kPa(a)]) offractionation column 20 byexpansion valve 58. The expandedstream 75 aleaves expansion valve 58 at −238° F. [−150° C.] and is thereafter supplied to tower 20 at a first upper mid-column feed point. - The second portion,
stream 73, is heated prior to enteringseparator 54 so that all or a portion of it is vaporized. In the example shown inFIG. 6 ,stream 73 is first heated to −76° F. [−60° C.] inheat exchanger 52 by cooling compressedoverhead distillation stream 81 a at −65° F. [−54° C.] andreflux stream 82 at −117° F. [−82° C.],exchanger 14 as described in paragraph [0085] below. The partiallyheated stream 73 b becomesstream 76 and is further heated inheat exchanger 53 using low level utility heat. Theheated stream 76 a entersseparator 54 at −5° F. [−20° C.] and 1334 psia [9,195 kPa(a)] where the vapor (stream 77) is separated from any remaining liquid (stream 78).Vapor stream 77 enters awork expansion machine 55 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 55 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expandedstream 77 a to a temperature of approximately −104° F. [−76° C.]. The partially condensed expandedstream 77 a is thereafter supplied as feed tofractionation column 20 at a first lower mid-column feed point. The separator liquid (stream 78), if any, is expanded to the operating pressure offractionation column 20 byexpansion valve 59 before expandedstream 78 a is supplied tofractionation tower 20 at a second lower mid-column feed point. - In the simulation of the
FIG. 6 process, inlet gas enters the plant at 126° F. [52° C.] and 600 psia [4,137 kPa(a)] asstream 31. Thefeed stream 31 is divided into two portions, streams 32 and 33. The first portion,stream 32, is cooled inheat exchanger 12 by heat exchange with cold lean LNG (stream 83 a) at −103° F. [−75° C.], coolcompressed distillation stream 38 b at −92° F. [−69° C.], and demethanizer liquids (stream 39) at −78° F. [−61° C.]. The partially cooledstream 32 a is further cooled from −94° F. [−70° C.] to −101° F. [−74° C.] inheat exchanger 14 by heat exchange with the partially heated second portion (stream 73 a) of the LNG stream and with coldcompressed distillation stream 38 a at −106° F. [−77° C.]. The substantially condensedstream 32 b is then flash expanded through an appropriate expansion device, such asexpansion valve 16, to the operating pressure offractionation tower 20, coolingstream 32 c to −117° F. [−83° C.] before it is supplied tofractionation tower 20 at a second upper mid-column feed point. - The second portion of
feed stream 31,stream 33, enters awork expansion machine 10 in which mechanical energy is extracted from this portion of the high pressure feed. Themachine 10 expands the vapor substantially isentropically to a pressure slightly above the operating pressure offractionation tower 20, with the work expansion cooling the expandedstream 33 a to a temperature of approximately 96° F. [36° C.]. The expandedstream 33 a is further cooled inheat exchanger 12 by heat exchange with cold lean LNG (stream 83 a), coolcompressed distillation stream 38 b, and demethanizer liquids (stream 39) as described previously. The further cooledstream 33 b entersseparator 13 at −90° F. [−68° C.] and 443 psia [3,052 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 35). -
Vapor stream 34 is cooled to −101° F. [−74° C.] inheat exchanger 14 by heat exchange with the partially heated second portion (stream 73 a) of the LNG stream and with coldcompressed distillation stream 38 a as described previously. The partially condensedstream 34 a is then supplied tofractionation tower 20 at a third lower mid-column feed point.Liquid stream 35 is flash expanded through an appropriate expansion device, such asexpansion valve 17, to the operating pressure offractionation tower 20. The expandedstream 35 a leavingexpansion valve 17 reaches a temperature of −90° F. [−68° C.] and is supplied tofractionation tower 20 at a fourth lower mid-column feed point. - The
liquid product stream 41 exits the bottom of the tower at 89° F. [32° C.], based on a typical specification of a methane to ethane ratio of 0.020:1 on a molar basis in the bottom product.Overhead distillation stream 79 is withdrawn from the upper section offractionation tower 20 at −142° F. [−97° C.] and is divided into two portions,stream 81 andstream 38. The first portion (stream 81) flows tocompressor 56 driven byexpansion machine 55, where it is compressed to 864 psia [5,955 kPa(a)] (stream 81 a). At this pressure, the stream is totally condensed as it is cooled to −117° F. [−83° C.] inheat exchanger 52 as described previously. The condensed liquid (stream 81 b) is then divided into two portions, streams 83 and 82. The first portion (stream 83) is the methane-rich lean LNG stream, which is pumped bypump 63 to 1270 psia [8,756 kPa(a)] for subsequent vaporization inheat exchanger 12,heating stream 83 a to 40° F. [4° C.] as described previously to produce warmlean LNG stream 83 b. - The remaining portion of
stream 81 b (stream 82) flows toheat exchanger 52 where it is subcooled to −237° F. [−149° C.] by heat exchange with a portion of the cold LNG (stream 73) as described previously. Thesubcooled stream 82 a is expanded to the operating pressure offractionation column 20 byexpansion valve 57. The expandedstream 82 b at −236° F. [−149° C.] is then supplied as cold top column feed (reflux) todemethanizer 20. This cold liquid reflux absorbs and condenses the C2 components and heavier hydrocarbon components from the vapors rising in the upper rectification section ofdemethanizer 20. - The second portion of distillation stream 79 (stream 38) flows to
compressor 11 driven byexpansion machine 10, where it is compressed to 604 psia [4,165 kPa(a)]. The coldcompressed distillation stream 38 a passes countercurrently to the first portion (stream 32 a) ofinlet gas stream 31 andvapor stream 34 inheat exchanger 14 where it is heated to −92° F. [−69° C.] (stream 38 b), and countercurrently to the first portion (stream 32) and expanded second portion (stream 33 a) ofinlet gas stream 31 inheat exchanger 12 where it is heated to 48° F. [9° C.] (stream 38 c). The heated distillation stream then enterscompressor 21 driven by a supplemental power source which compressesstream 38 c to sales line pressure (stream 38 d). After cooling to 126° F. [52° C.] in discharge cooler 22,stream 38 e combines with warmlean LNG stream 83 b to form the residue gas product (stream 42).Residue gas stream 42 flows to the sales gas pipeline at 1262 psia [8,701 kPa(a)], sufficient to meet line requirements. - A summary of stream flow rates and energy consumption for the process illustrated in
FIG. 6 is set forth in the following table: -
TABLE VI (FIG. 6) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 42,545 5,048 2,972 1,658 53,145 32 7,871 934 550 307 9,832 33 34,674 4,114 2,422 1,351 43,313 34 29,159 1,328 185 21 31,380 35 5,515 2,786 2,237 1,330 11,933 71 40,293 2,642 491 3 43,689 72/75 5,037 330 61 0 5,461 73/76 35,256 2,312 430 3 38,228 77 35,256 2,312 430 3 38,228 78 0 0 0 0 0 79 97,329 46 0 0 98,696 38 54,991 26 0 0 55,763 81 42,338 20 0 0 42,933 82 14,644 7 0 0 14,850 83 27,694 13 0 0 28,083 42 82,685 39 0 0 83,846 41 153 7,651 3,463 1,661 12,988 Recoveries* Ethane 99.48% Propane 100.00% Butanes+ 100.00% Power LNG Feed Pump 3,561 HP [ 5,854 kW] LNG Product Pump 1,216 HP [ 1,999 kW] Residue Gas Compressor 21,186 HP [ 34,829 kW] Totals 25,963 HP [ 42,682 kW] Low Level Utility Heat Liquid Feed Heater 70,000 MBTU/Hr [ 45,217 kW] Demethanizer Reboiler 1830,000 MBTU/Hr [ 19,378 kW] Totals 100,000 MBTU/Hr [ 64,595 kW] High Level Utility Heat Demethanizer Reboiler 19 39,180 MBTU/Hr [ 25,308 kW] Specific Power HP-Hr/Lb. Mole 1.999 [kW-Hr/kg mole] [ 3.286 ] *(Based on un-rounded flow rates) - A comparison of Tables III, IV, V, and VI shows that the
FIG. 6 embodiment of the present invention achieves essentially the same liquids recovery as theFIGS. 3 , 4, and 5 embodiments. However, the reduction in the energy consumption of theFIG. 6 embodiment of the present invention relative to the embodiments inFIGS. 3 through 5 is unexpectedly large. TheFIG. 6 embodiment uses less power than theFIGS. 3 , 4, and 5 embodiments, reducing the specific power by 14%, 12%, and 9%, respectively. The high level utility heat required for theFIG. 6 embodiment of the present invention is also lower than that of theFIGS. 3 , 4, and 5 embodiments (by 21%, 14%, and 37%, respectively). These large gains in process efficiency are mainly due to the more optimal distribution of the column feeds afforded by integrating the LNG processing and the natural gas processing into a single fractionation column,demethanizer 20. For instance, the relative distribution of theinlet gas stream 31 between stream 32 (which forms the substantially condensed expandedstream 32 c) andstream 33 supplied toexpansion machine 10 can be optimized for power production, sincestream 75 a fromLNG stream 71 provides part of the supplemental rectification forcolumn 20 that must be provided entirely bystream 32 c in theFIGS. 3 through 5 embodiments. - The capital cost of the
FIG. 6 embodiment of the present invention will generally be less than that of theFIGS. 3 , 4, and 5 embodiments since it uses only one fractionation column, and due to the reduction in power and high level utility heat consumption. The choice of which embodiment to use for a particular application will generally be dictated by the relative costs of power and high level utility heat and the relative capital costs of columns, pumps, heat exchangers, and compressors. - Some circumstances may favor using
cold distillation stream 38 in theFIG. 6 embodiment for heat exchange prior to compression as shown in the embodiment displayed inFIG. 7 . In other instances, work expansion of the high pressure inlet gas may be more advantageous after cooling and separation of any liquids, as shown in the embodiment displayed inFIG. 8 . The choices regarding the streams used for work expansion and where best to apply the power generated in compressing the process streams will depend on such factors as inlet gas pressure and composition, and must be determined for each application. - When the inlet gas is leaner,
separator 13 inFIGS. 3 through 8 may not be needed. Depending on the quantity of heavier hydrocarbons in the feed gas and the feed gas pressure, the cooledstream 33 b (FIGS. 3 , 5, 6, and 7) or cooledstream 33 a (FIGS. 4 and 8) leavingheat exchanger 12 may not contain any liquid (because it is above its dewpoint, or because it is above its cricondenbar), so thatseparator 13 may not be justified. In such cases,separator 13 andexpansion valve 17 may be eliminated as shown by the dashed lines. When the LNG to be processed is lean or when complete vaporization of the LNG inheat exchangers separator 54 inFIGS. 3 through 8 may not be justified. Depending on the quantity of heavier hydrocarbons in the inlet LNG and the pressure of the LNG stream leavingfeed pump 51, the heated LNG stream leavingheat exchanger 53 may not contain any liquid (because it is above its dewpoint, or because it is above its cricondenbar). In such cases,separator 54 andexpansion valve 59 may be eliminated as shown by the dashed lines. - In the embodiments of the present invention illustrated in
FIGS. 4 and 8 , the expanded substantially condensedstream 32 c is formed using a portion (stream 32) ofinlet gas stream 31. Depending on the feed gas composition and other factors, some circumstances may favor using a portion of the vapor (stream 34) fromseparator 13 instead. In such instances, a portion of theseparator 13 vapor forms stream 32 a as shown by the dashed lines inFIGS. 4 and 8 , with the remaining portion forming thestream 34 that is fed toexpansion machine 10. - In the examples shown, total condensation of
stream 79 b inFIGS. 3 through 5 andstream 81 b inFIGS. 6 through 8 is shown. Some circumstances may favor subcooling these streams, while other circumstances may favor only partial condensation. Should partial condensation of these streams be achieved, processing of the uncondensed vapor may be necessary, using a compressor or other means to elevate the pressure of the vapor so that it can join the pumped condensed liquid. Alternatively, the uncondensed vapor could be routed to the plant fuel system or other such use. - Feed gas conditions, LNG conditions, plant size, available equipment, or other factors may indicate that elimination of
work expansion machines 10 and/or 55, or replacement with an alternate expansion device (such as an expansion valve), is feasible. Although individual stream expansion is depicted in particular expansion devices, alternative expansion means may be employed where appropriate. - In
FIGS. 3 through 8 , individual heat exchangers have been shown for most services. However, it is possible to combine two or more heat exchange services into a common heat exchanger, such as combiningheat exchangers FIGS. 3 through 8 into a common heat exchanger. In some cases, circumstances may favor splitting a heat exchange service into multiple exchangers. The decision as to whether to combine heat exchange services or to use more than one heat exchanger for the indicated service will depend on a number of factors including, but not limited to, inlet gas flow rate, LNG flow rate, heat exchanger size, stream temperatures, etc. In accordance with the present invention, the use and distribution of the methane-rich lean LNG and tower overhead streams for process heat exchange, and the particular arrangement of heat exchangers for heating the LNG streams and cooling the feed gas streams, must be evaluated for each particular application, as well as the choice of process streams for specific heat exchange services. - In the embodiments of the present invention illustrated in
FIGS. 3 through 8 ,lean LNG stream 83 a is used directly to provide cooling inheat exchanger 12 orheat exchangers heat exchanger 12 orheat exchangers lean LNG stream 83 a accomplishes the same process objectives as the direct use ofstream 83 a for cooling in theFIGS. 3 through 8 embodiments of the present invention. The choice of how best to use the lean LNG stream for refrigeration will depend mainly on the composition of the inlet gas, but other factors may affect the choice as well. - It will be recognized that the relative amount of feed found in each branch of the split LNG feed to
fractionation column 62, in each branch of the split inlet gas tofractionation column 20, and in each branch of the split LNG feed and the split inlet gas tofractionation column 20 will depend on several factors, including inlet gas composition, LNG composition, the amount of heat which can economically be extracted from the feed, and the quantity of horsepower available. More feed to the top of the column may increase recovery while increasing the duty inreboilers 61 and/or 19 and thereby increasing the high level utility heat requirements. Increasing feed lower in the column reduces the high level utility heat consumption but may also reduce product recovery. The relative locations of the mid-column feeds may vary depending on inlet gas composition, LNG composition, or other factors such as the desired recovery level and the amount of vapor formed during heating of the LNG streams. Moreover, two or more of the feed streams, or portions thereof, may be combined depending on the relative temperatures and quantities of individual streams, and the combined stream then fed to a mid-column feed position. - In some circumstance it may be desirable to recover refrigeration from the portion (
stream 75 a) ofLNG feed stream 71 that is fed to an upper mid-column feed point on demethanizer 62 (FIGS. 3 through 5 ) and demethanizer 20 (FIGS. 6 through 8 ). In such cases, all ofstream 71 a would be directed to heat exchanger 52 (stream 73) and the partially heated LNG stream (stream 73 a inFIGS. 3 through 5 andstream 73 b inFIGS. 6 through 8 ) would then be divided intostream 76 and stream 74 (as shown by the dashed lines), whereuponstream 74 would be directed to stream 75. - In the examples given for the
FIGS. 3 through 6 embodiments, recovery of C2 components and heavier hydrocarbon components is illustrated. However, it is believed that theFIGS. 3 through 8 embodiments are also advantageous when recovery of only C3 components and heavier hydrocarbon components is desired. The present invention provides improved recovery of C2 components and heavier hydrocarbon components or of C3 components and heavier hydrocarbon components per amount of utility consumption required to operate the process. An improvement in utility consumption required for operating the process may appear in the form of reduced power requirements for compression or pumping, reduced energy requirements for tower reboilers, or a combination thereof. Alternatively, the advantages of the present invention may be realized by accomplishing higher recovery levels for a given amount of utility consumption, or through some combination of higher recovery and improvement in utility consumption. - While there have been described what are believed to be preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto, e.g. to adapt the invention to various conditions, types of feed, or other requirements without departing from the spirit of the present invention as defined by the following claims.
Claims (45)
1. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein
(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;
(b) said first liquid stream is expanded to lower pressure and is thereafter supplied to a distillation column at a first upper mid-column feed position;
(c) said second liquid stream is heated sufficiently to vaporize it, thereby forming a vapor stream;
(d) said vapor stream is expanded to said lower pressure and is supplied to said distillation column at a first lower mid-column feed position;
(e) said gas stream is divided into at least a first gaseous stream and a second gaseous stream;
(f) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;
(g) said expanded substantially condensed first gaseous stream is thereafter supplied to said distillation column at a second upper mid-column feed position;
(h) said second gaseous stream is expanded to said lower pressure, is cooled, and is thereafter supplied to said distillation column at a second lower mid-column feed position;
(i) an overhead distillation stream is withdrawn from an upper region of said distillation column and divided into at least a first portion and a second portion, whereupon said first portion is compressed to higher pressure;
(j) said compressed first portion is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;
(k) said condensed stream is divided into at least a volatile liquid stream and a reflux stream;
(l) said reflux stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;
(m) said further cooled reflux stream is supplied to said distillation column at a top column feed position;
(n) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;
(o) said second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;
(p) said vaporized volatile liquid stream and said heated second portion are combined to form said volatile residue gas fraction containing a major portion of said methane; and
(q) the quantity and temperature of said reflux stream and the temperatures of said feeds to said distillation column are effective to maintain the overhead temperature of said distillation column at a temperature whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said distillation column.
2. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein
(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;
(b) said first liquid stream is expanded to lower pressure and is thereafter supplied to a distillation column at a first upper mid-column feed position;
(c) said second liquid stream is heated sufficiently to vaporize it, thereby forming a first vapor stream;
(d) said first vapor stream is expanded to said lower pressure and thereafter supplied to said distillation column at a first lower mid-column feed position;
(e) said gas stream is divided into at least a first gaseous stream and a second gaseous stream;
(f) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;
(g) said expanded substantially condensed first gaseous stream is thereafter supplied to said distillation column at a second upper mid-column feed position;
(h) said second gaseous stream is expanded to said lower pressure and is thereafter cooled sufficiently to partially condense it;
(i) said partially condensed expanded second gaseous stream is separated thereby to provide a second vapor stream and a third liquid stream;
(j) said second vapor stream is further cooled and thereafter supplied to said distillation column at a second lower mid-column feed position;
(k) said third liquid stream is supplied to said distillation column at a third lower mid-column feed position;
(l) an overhead distillation stream is withdrawn from an upper region of said distillation column and divided into at least a first portion and a second portion, whereupon said first portion is compressed to higher pressure;
(m) said compressed first portion is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;
(n) said condensed stream is divided into at least a volatile liquid stream and a reflux stream;
(o) said reflux stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;
(p) said further cooled reflux stream is supplied to said distillation column at a top column feed position;
(q) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream;
(r) said second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream;
(s) said vaporized volatile liquid stream and said heated second portion are combined to form said volatile residue gas fraction containing a major portion of said methane; and
(t) the quantity and temperature of said reflux stream and the temperatures of said feeds to said distillation column are effective to maintain the overhead temperature of said distillation column at a temperature whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said distillation column.
3. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein
(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;
(b) said first liquid stream is expanded to lower pressure and is thereafter supplied to a distillation column at a first upper mid-column feed position;
(c) said second liquid stream is heated sufficiently to partially vaporize it;
(d) said partially vaporized second liquid stream is separated thereby to provide a vapor stream and a third liquid stream;
(e) said vapor stream is expanded to said lower pressure and is supplied to said distillation column at a first lower mid-column feed position;
(f) said gas stream is divided into at least a first gaseous stream and a second gaseous stream;
(g) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;
(h) said expanded substantially condensed first gaseous stream is thereafter supplied to said distillation column at a second upper mid-column feed position;
(i) said second gaseous stream is expanded to said lower pressure, is cooled, and is thereafter supplied to said distillation column at a second lower mid-column feed position;
(j) said third liquid stream is expanded to said lower pressure and thereafter supplied to said distillation column at a third lower mid-column feed position;
(k) an overhead distillation stream is withdrawn from an upper region of said distillation column and divided into at least a first portion and a second portion, whereupon said first portion is compressed to higher pressure;
(l) said compressed first portion is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;
(m) said condensed stream is divided into at least a volatile liquid stream and a reflux stream;
(n) said reflux stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;
(o) said further cooled reflux stream is supplied to said distillation column at a top column feed position;
(p) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;
(q) said second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;
(r) said vaporized volatile liquid stream and said heated second portion are combined to form said volatile residue gas fraction containing a major portion of said methane; and
(s) the quantity and temperature of said reflux stream and the temperatures of said feeds to said distillation column are effective to maintain the overhead temperature of said distillation column at a temperature whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said distillation column.
4. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein
(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;
(b) said first liquid stream is expanded to lower pressure and is thereafter supplied to a distillation column at a first upper mid-column feed position;
(c) said second liquid stream is heated sufficiently to partially vaporize it;
(d) said partially vaporized second liquid stream is separated thereby to provide a first vapor stream and a third liquid stream;
(e) said first vapor stream is expanded to said lower pressure and thereafter supplied to said distillation column at a first lower mid-column feed position;
(f) said gas stream is divided into at least a first gaseous stream and a second gaseous stream;
(g) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;
(h) said expanded substantially condensed first gaseous stream is thereafter supplied to said distillation column at a second upper mid-column feed position;
(i) said second gaseous stream is expanded to said lower pressure;
(j) said expanded second gaseous stream is cooled sufficiently to partially condense it;
(k) said partially condensed expanded second gaseous stream is separated thereby to provide a second vapor stream and a fourth liquid stream;
(l) said second vapor stream is further cooled and thereafter supplied to said distillation column at a second lower mid-column feed position;
(m) said third liquid stream is expanded to said lower pressure and thereafter supplied to said distillation column at a third lower mid-column feed position;
(n) said fourth liquid stream is supplied to said distillation column at a fourth lower mid-column feed position;
(o) an overhead distillation stream is withdrawn from an upper region of said distillation column and divided into at least a first portion and a second portion, whereupon said first portion is compressed to higher pressure;
(p) said compressed first portion is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;
(q) said condensed stream is divided into at least a volatile liquid stream and a reflux stream;
(r) said reflux stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;
(s) said further cooled reflux stream is supplied to said distillation column at a top column feed position;
(t) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream;
(u) said second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream;
(v) said vaporized volatile liquid stream and said heated second portion are combined to form said volatile residue gas fraction containing a major portion of said methane; and
(w) the quantity and temperature of said reflux stream and the temperatures of said feeds to said distillation column are effective to maintain the overhead temperature of said distillation column at a temperature whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said distillation column.
5. The process according to claim 1 or 3 wherein
(a) said second portion is compressed to higher pressure;
(b) said compressed second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream; and
(c) said vaporized volatile liquid stream and said heated compressed second portion are combined to form said volatile residue gas fraction.
6. The process according to claim 2 or 4 wherein
(a) said second portion is compressed to higher pressure;
(b) said compressed second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream; and
(c) said vaporized volatile liquid stream and said heated compressed second portion are combined to form said volatile residue gas fraction.
7. The process according to claim 1 or 3 wherein
(a) said second gaseous stream is cooled prior to said expansion;
(b) said second portion is compressed to higher pressure;
(c) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second gaseous stream;
(d) said compressed second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second gaseous stream; and
(e) said vaporized volatile liquid stream and said heated compressed second portion are combined to form said volatile residue gas fraction.
8. The process according to claim 2 wherein
(a) said second gaseous stream is cooled sufficiently to partially condense it;
(b) said partially condensed second gaseous stream is separated thereby to provide said second vapor stream and said third liquid stream;
(c) said second vapor stream is expanded to said lower pressure, is cooled, and is thereafter supplied to said distillation column at said second lower mid-column feed position;
(d) said third liquid stream is expanded to said lower pressure and thereafter supplied to said distillation column at said third lower mid-column feed position;
(e) said second portion is compressed to higher pressure;
(f) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second vapor stream;
(g) said compressed second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second vapor stream; and
(h) said vaporized volatile liquid stream and said heated compressed second portion are combined to form said volatile residue gas fraction.
9. The process according to claim 4 wherein
(a) said second gaseous stream is cooled sufficiently to partially condense it;
(b) said partially condensed second gaseous stream is separated thereby to provide said second vapor stream and said fourth liquid stream;
(c) said second vapor stream is expanded to said lower pressure, is cooled, and is thereafter supplied to said distillation column at said second lower mid-column feed position;
(d) said fourth liquid stream is expanded to said lower pressure and thereafter supplied to said distillation column at said fourth lower mid-column feed position;
(e) said second portion is compressed to higher pressure;
(f) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second vapor stream;
(g) said compressed second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second vapor stream; and
(h) said vaporized volatile liquid stream and said heated compressed second portion are combined to form said volatile residue gas fraction.
10. The process according to claim 8 wherein
(a) said gas stream is cooled sufficiently to partially condense it;
(b) said partially condensed gas stream is separated thereby to provide said second vapor stream and said third liquid stream;
(c) said second vapor stream is divided into at least said first gaseous stream and said second gaseous stream;
(d) said second gaseous stream is expanded to said lower pressure, is cooled, and is thereafter supplied to said distillation column at said second lower mid-column feed position;
(e) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said gas stream, said first gaseous stream, and said expanded second gaseous stream; and
(f) said compressed second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said gas stream, said first gaseous stream, and said expanded second gaseous stream.
11. The process according to claim 9 wherein
(a) said gas stream is cooled sufficiently to partially condense it;
(b) said partially condensed gas stream is separated thereby to provide said second vapor stream and said fourth liquid stream;
(c) said second vapor stream is divided into at least said first gaseous stream and said second gaseous stream;
(d) said second gaseous stream is expanded to said lower pressure, is cooled, and is thereafter supplied to said distillation column at said second lower mid-column feed position;
(e) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said gas stream, said first gaseous stream, and said expanded second gaseous stream; and
(f) said compressed second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said gas stream, said first gaseous stream, and said expanded second gaseous stream.
12. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein
(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;
(b) said first liquid stream is expanded to a first lower pressure and is thereafter supplied to a first distillation column at an upper mid-column feed position;
(c) said second liquid stream is heated sufficiently to vaporize it, thereby forming a vapor stream;
(d) said vapor stream is expanded to said first lower pressure and is supplied to said first distillation column at a lower mid-column feed position;
(e) a first overhead distillation stream is withdrawn from an upper region of said first distillation column and compressed to higher pressure;
(f) said compressed first overhead distillation stream is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;
(g) said condensed stream is divided into at least a volatile liquid stream and a reflux liquid stream;
(h) said reflux liquid stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;
(i) said further cooled reflux liquid stream is divided into at least a first reflux stream and a second reflux stream;
(j) said first reflux stream is supplied to said first distillation column at a top column feed position;
(k) said gas stream is divided into at least a first gaseous stream and a second gaseous stream;
(l) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to a second lower pressure whereby it is further cooled;
(m) said expanded substantially condensed first gaseous stream is thereafter supplied to a second distillation column at an upper mid-column feed position;
(n) said second gaseous stream is expanded to said second lower pressure, is cooled, and is thereafter supplied to said second distillation column at a lower mid-column feed position;
(o) said second reflux stream is supplied to said second distillation column at a top column feed position;
(p) a second overhead distillation stream is withdrawn from an upper region of said second distillation column;
(q) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;
(r) said second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;
(s) said vaporized volatile liquid stream and said heated second overhead distillation stream are combined to form said volatile residue gas fraction containing a major portion of said methane;
(t) a first bottom liquid from said first distillation column and a second bottom liquid from said second distillation column are combined to form said relatively less volatile liquid fraction; and
(u) the quantities and temperatures of said first and second reflux streams and the temperatures of said feeds to said first and second distillation columns are effective to maintain the overhead temperatures of said first and second distillation columns at temperatures whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said first and second distillation columns.
13. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein
(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;
(b) said first liquid stream is expanded to a first lower pressure and is thereafter supplied to a first distillation column at an upper mid-column feed position;
(c) said second liquid stream is heated sufficiently to vaporize it, thereby forming a first vapor stream;
(d) said first vapor stream is expanded to said first lower pressure and thereafter supplied to said first distillation column at a lower mid-column feed position;
(e) a first overhead distillation stream is withdrawn from an upper region of said first distillation column and compressed to higher pressure;
(f) said compressed first overhead distillation stream is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;
(g) said condensed stream is divided into at least a volatile liquid stream and a reflux liquid stream;
(h) said reflux liquid stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;
(i) said further cooled reflux liquid stream is divided into at least a first reflux stream and a second reflux stream;
(j) said first reflux stream is supplied to said first distillation column at a top column feed position;
(k) said gas stream is divided into at least a first gaseous stream and a second gaseous stream;
(l) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to a second lower pressure whereby it is further cooled;
(m) said expanded substantially condensed first gaseous stream is thereafter supplied to a second distillation column at an upper mid-column feed position;
(n) said second gaseous stream is expanded to said second lower pressure and is thereafter cooled sufficiently to partially condense it;
(o) said partially condensed expanded second gaseous stream is separated thereby to provide a second vapor stream and a third liquid stream;
(p) said second vapor stream is further cooled and thereafter supplied to said second distillation column at a first lower mid-column feed position;
(q) said third liquid stream is supplied to said second distillation column at a second lower mid-column feed position;
(r) said second reflux stream is supplied to said second distillation column at a top column feed position;
(s) a second overhead distillation stream is withdrawn from an upper region of said second distillation column;
(t) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream;
(u) said second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream;
(v) said vaporized volatile liquid stream and said heated second overhead distillation stream are combined to form said volatile residue gas fraction containing a major portion of said methane;
(w) a first bottom liquid from said first distillation column and a second bottom liquid from said second distillation column are combined to form said relatively less volatile liquid fraction; and
(x) the quantities and temperatures of said first and second reflux streams and the temperatures of said feeds to said first and second distillation columns are effective to maintain the overhead temperatures of said first and second distillation columns at temperatures whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said first and second distillation columns.
14. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein
(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;
(b) said first liquid stream is expanded to a first lower pressure and is thereafter supplied to a first distillation column at an upper mid-column feed position;
(c) said second liquid stream is heated sufficiently to partially vaporize it;
(d) said partially vaporized second liquid stream is separated thereby to provide a vapor stream and a third liquid stream;
(e) said vapor stream is expanded to said first lower pressure and is supplied to said first distillation column at a first lower mid-column feed position;
(f) said third liquid stream is expanded to said first lower pressure and thereafter supplied to said first distillation column at a second lower mid-column feed position;
(g) a first overhead distillation stream is withdrawn from an upper region of said first distillation column and compressed to higher pressure;
(h) said compressed first overhead distillation stream is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;
(i) said condensed stream is divided into at least a volatile liquid stream and a reflux liquid stream;
(j) said reflux liquid stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;
(k) said further cooled reflux liquid stream is divided into at least a first reflux stream and a second reflux stream;
(l) said first reflux stream is supplied to said first distillation column at a top column feed position;
(m) said gas stream is divided into at least a first gaseous stream and a second gaseous stream;
(n) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to a second lower pressure whereby it is further cooled;
(o) said expanded substantially condensed first gaseous stream is thereafter supplied to a second distillation column at an upper mid-column feed position;
(p) said second gaseous stream is expanded to said second lower pressure, is cooled, and is thereafter supplied to said second distillation column at a lower mid-column feed position;
(q) said second reflux stream is supplied to said second distillation column at a top column feed position;
(r) a second overhead distillation stream is withdrawn from an upper region of said second distillation column;
(s) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;
(t) said second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;
(u) said vaporized volatile liquid stream and said heated second overhead distillation stream are combined to form said volatile residue gas fraction containing a major portion of said methane;
(v) a first bottom liquid from said first distillation column and a second bottom liquid from said second distillation column are combined to form said relatively less volatile liquid fraction; and
(w) the quantities and temperatures of said first and second reflux streams and the temperatures of said feeds to said first and second distillation columns are effective to maintain the overhead temperatures of said first and second distillation columns at temperatures whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said first and second distillation columns.
15. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein
(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;
(b) said first liquid stream is expanded to a first lower pressure and is thereafter supplied to a first distillation column at an upper mid-column feed position;
(c) said second liquid stream is heated sufficiently to partially vaporize it;
(d) said partially vaporized second liquid stream is separated thereby to provide a first vapor stream and a third liquid stream;
(e) said first vapor stream is expanded to said first lower pressure and thereafter supplied to said first distillation column at a first lower mid-column feed position;
(f) said third liquid stream is expanded to said first lower pressure and thereafter supplied to said first distillation column at a second lower mid-column feed position;
(g) a first overhead distillation stream is withdrawn from an upper region of said first distillation column and compressed to higher pressure;
(h) said compressed first overhead distillation stream is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;
(i) said condensed stream is divided into at least a volatile liquid stream and a reflux liquid stream;
(j) said reflux liquid stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;
(k) said further cooled reflux liquid stream is divided into at least a first reflux stream and a second reflux stream;
(l) said first reflux stream is supplied to said first distillation column at a top column feed position;
(m) said gas stream is divided into at least a first gaseous stream and a second gaseous stream;
(n) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to a second lower pressure whereby it is further cooled;
(o) said expanded substantially condensed first gaseous stream is thereafter supplied to a second distillation column at an upper mid-column feed position;
(p) said second gaseous stream is expanded to said second lower pressure and is thereafter cooled sufficiently to partially condense it;
(q) said partially condensed expanded second gaseous stream is separated thereby to provide a second vapor stream and a fourth liquid stream;
(r) said second vapor stream is further cooled and thereafter supplied to said second distillation column at a first lower mid-column feed position;
(s) said fourth liquid stream is supplied to said second distillation column at a second lower mid-column feed position;
(t) said second reflux stream is supplied to said second distillation column at a top column feed position;
(u) a second overhead distillation stream is withdrawn from an upper region of said second distillation column;
(v) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream;
(w) said second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream;
(x) said vaporized volatile liquid stream and said heated second overhead distillation stream are combined to form said volatile residue gas fraction containing a major portion of said methane;
(y) a first bottom liquid from said first distillation column and a second bottom liquid from said second distillation column are combined to form said relatively less volatile liquid fraction; and
(z) the quantities and temperatures of said first and second reflux streams and the temperatures of said feeds to said first and second distillation columns are effective to maintain the overhead temperatures of said first and second distillation columns at temperatures whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said first and second distillation columns.
16. The process according to claim 12 or 14 wherein
(a) said second overhead distillation stream is compressed to higher pressure;
(b) said compressed second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream; and
(c) said vaporized volatile liquid stream and said heated compressed second overhead distillation stream are combined to form said volatile residue gas fraction.
17. The process according to claim 13 or 15 wherein
(a) said second overhead distillation stream is compressed to higher pressure;
(b) said compressed second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said second vapor stream; and
(c) said vaporized volatile liquid stream and said heated compressed second overhead distillation stream are combined to form said volatile residue gas fraction.
18. The process according to claim 12 or 14 wherein
(a) said second gaseous stream is cooled prior to said expansion;
(b) said second overhead distillation stream is compressed to higher pressure;
(c) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second gaseous stream;
(d) said compressed second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second gaseous stream; and
(e) said vaporized volatile liquid stream and said heated compressed second overhead distillation stream are combined to form said volatile residue gas fraction.
19. The process according to claim 13 wherein
(a) said second gaseous stream is cooled sufficiently to partially condense it;
(b) said partially condensed second gaseous stream is separated thereby to provide said second vapor stream and said third liquid stream;
(c) said second vapor stream is expanded to said second lower pressure, is cooled, and is thereafter supplied to said second distillation column at said first lower mid-column feed position;
(d) said third liquid stream is expanded to said second lower pressure and thereafter supplied to said second distillation column at said second lower mid-column feed position;
(e) said second overhead distillation stream is compressed to higher pressure;
(f) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second vapor stream;
(g) said compressed second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second vapor stream; and
(h) said vaporized volatile liquid stream and said heated compressed second overhead distillation stream are combined to form said volatile residue gas fraction.
20. The process according to claim 15 wherein
(a) said second gaseous stream is cooled sufficiently to partially condense it;
(b) said partially condensed second gaseous stream is separated thereby to provide said second vapor stream and said fourth liquid stream;
(c) said second vapor stream is expanded to said second lower pressure, is cooled, and is thereafter supplied to said second distillation column at said first lower mid-column feed position;
(d) said fourth liquid stream is expanded to said second lower pressure and thereafter supplied to said second distillation column at said second lower mid-column feed position;
(e) said second overhead distillation stream is compressed to higher pressure;
(f) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second vapor stream;
(g) said compressed second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said second gaseous stream, and said expanded second vapor stream; and
(h) said vaporized volatile liquid stream and said heated compressed second overhead distillation stream are combined to form said volatile residue gas fraction.
21. The process according to claim 19 wherein
(a) said gas stream is cooled sufficiently to partially condense it;
(b) said partially condensed gas stream is separated thereby to provide said second vapor stream and said third liquid stream;
(c) said second vapor stream is divided into at least said first gaseous stream and said second gaseous stream;
(d) said second gaseous stream is expanded to said second lower pressure, is cooled, and is thereafter supplied to said second distillation column at said first lower mid-column feed position;
(e) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said gas stream, said first gaseous stream, and said expanded second gaseous stream; and
(f) said compressed second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said gas stream, said first gaseous stream, and said expanded second gaseous stream.
22. The process according to claim 20 wherein
(a) said gas stream is cooled sufficiently to partially condense it;
(b) said partially condensed gas stream is separated thereby to provide said second vapor stream and said fourth liquid stream;
(c) said second vapor stream is divided into at least said first gaseous stream and said second gaseous stream;
(d) said second gaseous stream is expanded to said second lower pressure, is cooled, and is thereafter supplied to said second distillation column at said first lower mid-column feed position;
(e) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said gas stream, said first gaseous stream, and said expanded second gaseous stream; and
(f) said compressed second overhead distillation stream is heated, with said heating supplying at least a portion of said cooling of one or more of said gas stream, said first gaseous stream, and said expanded second gaseous stream.
23. The process according to claim 1 , 2 , 3 , 4 , 8 , 9 , 10 , or 11 wherein
(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream; and
(b) said cooling of said compressed first portion and said reflux stream supply at least a portion of said heating of said liquefied natural gas.
24. The process according to claim 5 wherein
(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream; and
(b) said cooling of said compressed first portion and said reflux stream supply at least a portion of said heating of said liquefied natural gas.
25. The process according to claim 6 wherein
(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream; and
(b) said cooling of said compressed first portion and said reflux stream supply at least a portion of said heating of said liquefied natural gas.
26. The process according to claim 7 wherein
(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream; and
(b) said cooling of said compressed first portion and said reflux stream supply at least a portion of said heating of said liquefied natural gas.
27. The process according to claim 12 , 13 , 14 , 15 , 19 , 20 , 21 , or 22 wherein
(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream; and
(b) said cooling of said compressed first overhead distillation stream and said reflux liquid stream supply at least a portion of said heating of said liquefied natural gas.
28. The process according to claim 16 wherein
(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream; and
(b) said cooling of said compressed first overhead distillation stream and said reflux liquid stream supply at least a portion of said heating of said liquefied natural gas.
29. The process according to claim 17 wherein
(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream; and
(b) said cooling of said compressed first overhead distillation stream and said reflux liquid stream supply at least a portion of said heating of said liquefied natural gas.
30. The process according to claim 18 wherein
(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream; and
(b) said cooling of said compressed first overhead distillation stream and said reflux liquid stream supply at least a portion of said heating of said liquefied natural gas.
31. The process according to claim 1 , 2 , 3 , 4 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 19 , 20 , 21 , or 22 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
32. The process according to claim 5 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
33. The process according to claim 6 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
34. The process according to claim 7 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
35. The process according to claim 16 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components
36. The process according to claim 17 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
37. The process according to claim 18 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
38. The process according to claim 23 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
39. The process according to claim 24 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
40. The process according to claim 25 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
41. The process according to claim 26 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
42. The process according to claim 27 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
43. The process according to claim 28 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
44. The process according to claim 29 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
45. The process according to claim 30 wherein said volatile residue gas fraction contains a major portion of said methane and C2 components.
Priority Applications (9)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US12/423,306 US20090282865A1 (en) | 2008-05-16 | 2009-04-14 | Liquefied Natural Gas and Hydrocarbon Gas Processing |
MYPI20105352 MY150987A (en) | 2008-05-16 | 2009-04-15 | Liquefied natural gas and hydrocarbon gas processing |
GB1019307.6A GB2472170B (en) | 2008-05-16 | 2009-04-15 | Liquefied natural gas and hydrocarbon gas processing |
PCT/US2009/040639 WO2009140014A1 (en) | 2008-05-16 | 2009-04-15 | Liquefied natural gas and hydrocarbon gas processing |
CA2723965A CA2723965A1 (en) | 2008-05-16 | 2009-04-15 | Liquefied natural gas and hydrocarbon gas processing |
MX2010011992A MX2010011992A (en) | 2008-05-16 | 2009-04-15 | Liquefied natural gas and hydrocarbon gas processing. |
CN200980117517.6A CN102027304B (en) | 2008-05-16 | 2009-04-15 | Liquefied natural gas and hydrocarbon gas processing |
CO10155774A CO6311034A2 (en) | 2008-05-16 | 2010-12-10 | INTEGRATED PROCESSING OF LIQUID NATURAL GAS AND HYDROCARBON GAS CURRENTS TO RECOVER HEAVY HYDROCARBONS |
US13/686,641 US8850849B2 (en) | 2008-05-16 | 2012-11-27 | Liquefied natural gas and hydrocarbon gas processing |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US5381408P | 2008-05-16 | 2008-05-16 | |
US12/423,306 US20090282865A1 (en) | 2008-05-16 | 2009-04-14 | Liquefied Natural Gas and Hydrocarbon Gas Processing |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US13/686,641 Continuation US8850849B2 (en) | 2008-05-16 | 2012-11-27 | Liquefied natural gas and hydrocarbon gas processing |
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Also Published As
Publication number | Publication date |
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GB2472170B (en) | 2013-03-20 |
GB201019307D0 (en) | 2010-12-29 |
WO2009140014A1 (en) | 2009-11-19 |
CN102027304B (en) | 2014-03-12 |
US20130125582A1 (en) | 2013-05-23 |
CO6311034A2 (en) | 2011-08-22 |
MY150987A (en) | 2014-03-31 |
US8850849B2 (en) | 2014-10-07 |
MX2010011992A (en) | 2010-11-30 |
US20140096563A2 (en) | 2014-04-10 |
CN102027304A (en) | 2011-04-20 |
GB2472170A (en) | 2011-01-26 |
CA2723965A1 (en) | 2009-11-19 |
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