US20060130521A1 - Method for recovery of natural gas liquids for liquefied natural gas - Google Patents
Method for recovery of natural gas liquids for liquefied natural gas Download PDFInfo
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- US20060130521A1 US20060130521A1 US11/300,768 US30076805A US2006130521A1 US 20060130521 A1 US20060130521 A1 US 20060130521A1 US 30076805 A US30076805 A US 30076805A US 2006130521 A1 US2006130521 A1 US 2006130521A1
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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
- 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
- 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
- F25J2200/50—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the 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
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/74—Refluxing the column with at least a part of the partially 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
- 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
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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
- 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
- F25J2245/00—Processes or apparatus involving steps for recycling of process streams
- F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2270/00—Refrigeration techniques used
- F25J2270/04—Internal refrigeration with work-producing gas expansion loop
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2270/00—Refrigeration techniques used
- F25J2270/88—Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided
Definitions
- the present invention relates to the recovery of natural gas liquids (NGL) from liquefied natural gas (LNG) streams.
- NNL natural gas liquids
- LNG liquefied natural gas
- McCartney describes a process, as shown in FIG. 4 of the present application, that uses of an overhead compressor to increase the bubble point of a lean gas stream exiting a fractionation tower 10 .
- a rich low pressure LNG stream 1 is pumped in pump 2 to 450 psia.
- LNG stream 3 exiting pump 2 is heated in exchanger 5 to ⁇ 132.5° F. to produce a heated LNG stream 6 .
- Heated LNG stream 6 is introduced to fractionation tower 10 as a top tower feed stream.
- Fractionation tower 10 is a distillation tower that produces a tower bottoms stream 12 and a tower overhead stream 14 .
- Tower bottoms stream 12 is sent to a tower reboiler 13 that is used to maintain an amount of methane in an NGL product stream 12 .
- a vapor return stream from reboiler 13 is sent to fractionation tower 10 , while NGL product is drawn off as NGL product stream 12 .
- Tower overhead stream 14 is compressed in lean gas compressor 27 to 500 psia to produce a partially boosted stream 28 .
- Partially boosted stream 28 is cooled to ⁇ 137° F. and completely condensed in first exchanger 5 to produce a low pressure lean LNG stream 21 .
- Low pressure lean LNG stream 21 is then pumped by pump 22 to elevate its pressure to 1422 psia to produce a high pressure lean LNG product stream 23 , which is the high pressure lean LNG product that is sent for vaporization and/or energy recovery.
- FIG. 2 illustrates one scheme that uses subcooled rich LNG to increase NGL recovery.
- rich low pressure LNG stream 1 is pumped in pump 2 to about 525 psia to produce LNG stream 3 .
- LNG stream 3 is then split into two streams, a first feed stream 4 and a second feed stream 24 .
- First feed stream 4 which is the larger of the two streams and contains about 93% of LNG stream 3 , is heated in first exchanger 5 to ⁇ 132.5° F. to produce a heated first feed stream 6 .
- Heated first feed stream 6 which is still all liquid, is introduced to fractionation tower 10 as a tower bottom feed stream.
- Second feed stream 24 is sent as a top feed stream to fractionation tower 10 .
- fractionation tower 10 is a distillation tower that produces a tower overhead stream 14 and a tower bottom stream 12 .
- Tower bottom stream 12 is sent to a tower reboiler 13 that is used to maintain an amount of methane in NGL product stream 12 .
- Reboiler vapor stream returns to fractionation tower 10 , while NGL product is drawn off of reboiler 13 as NGL product stream 12 .
- Tower overhead stream 14 is cooled to ⁇ 133.7° F. and completely condensed in first exchanger 5 to produce low pressure lean LNG stream 21 .
- Low pressure lean LNG stream 21 is pumped in pump 22 to elevate its pressure to 1422 psia to produce high pressure lean LNG product stream 23 , which is the high pressure lean LNG product that is sent for vaporization and/or energy recovery.
- the present invention includes a process and apparatus to increase the recovery of NGL.
- a process is provided for separating a liquefied natural gas (LNG) stream into a more volatile gas fraction containing a substantial amount of methane and lighter components and a less volatile fraction containing a large portion of heavy hydrocarbon components is advantageously provided.
- the LNG stream is split into a first feed stream and a second feed stream. At least a portion of the first feed stream is preheated and supplied to a fractionation tower as a first tower feed stream.
- fractionation tower produces a tower overhead stream and a tower bottoms stream.
- Tower overhead stream preferably includes the more volatile fraction of the LNG stream that contains a substantial amount of methane and lighter components.
- Tower bottoms stream preferably includes the less volatile fraction of the LNG stream that contains the heavy hydrocarbon components.
- At least a portion of the second feed stream is heated and supplied to the fractionation tower as a second tower feed stream. At least a portion of the tower overhead stream is cooled and partially condensed to produce a partially condensed tower overhead stream. Partially condensed tower overhead stream is separated into a lean vapor stream and a tower reflux stream being sent to the fractionation tower. Lean vapor stream is subcooled so that the lean vapor stream is substantially condensed thereby producing a lean LNG stream. Lean LNG stream is then pumped to a high pressure.
- the liquefied natural gas (LNG) stream is split into a first feed stream and a second feed stream.
- the feed streams define, respectively, a first feed stream enthalpy and a second feed stream enthalpy. At least a portion of the first feed stream is preheated and provided to the fractionation tower as the first tower feed stream. From the fractionation tower, the tower overhead stream is produced containing the more volatile fraction. The tower bottoms stream containing the less volatile fraction is also produced from the fractionation tower.
- the second feed stream is supplied to the fractionation tower such that the first feed stream and the second tower feed stream have a substantially common composition but the first tower feed stream enthalpy differs from the second feed stream enthalpy.
- the tower overhead stream is compressed to produce a compressed overhead stream.
- the compressed overhead stream is cooled until it is at least substantially condensed thereby producing a lean LNG stream.
- the compressed overhead stream is cooled until it is subcooled.
- the lean LNG stream is pumped to a higher pressure thereby creating a high pressure lean LNG stream.
- the process for separating the liquefied natural (LNG) stream includes preheating at least a portion of the LNG stream to produce first tower feed stream.
- the first tower feed stream is supplied to the fractionation tower that produces the tower overhead stream and tower bottoms stream.
- At least a portion of the tower overhead stream is cooled so that the portion of the tower overhead stream is at least substantially condensed thereby producing the lean LNG stream.
- the tower overhead stream can be subcooled.
- the lean LNG stream is pumped to a higher pressure to produce a high pressure lean LNG stream.
- the high pressure lean LNG stream is split into a lean tower reflux stream and a lean LNG product stream.
- the lean tower reflux stream is cooled to produce a cooled lean tower reflux stream and the cooled lean tower reflux stream is supplied to the fractionation tower.
- Yet another preferred embodiment includes a process for separating the liquefied natural gas (LNG) stream including splitting the LNG stream into first feed stream and second feed stream.
- the second feed stream is supplied to the fractionation tower as second tower feed stream to produce the tower overhead stream and the tower bottoms stream 12 including the less volatile fraction containing the heavy hydrocarbon components.
- At least a portion of the first feed stream is preheated to produce the first tower feed stream.
- the first tower feed stream is supplied to the fractionation tower.
- the tower overhead stream is compressed to produce compressed overhead stream.
- the compressed overhead stream is cooled such that the compressed overhead stream is substantially condensed thereby producing lean LNG stream.
- the lean LNG stream is pumped to a higher pressure to produce high pressure lean LNG stream.
- the high pressure lean LNG stream is split into lean tower reflux stream and lean LNG product stream.
- the lean tower reflux stream is cooled to produce cooled lean tower reflux stream that is supplied to the fractionation tower.
- Yet another embodiment of the invention includes a process for separating a liquefied natural gas (LNG) stream including preheating at least a portion of the LNG stream and supplying the at least a portion of the LNG stream to fractionation tower as first tower feed stream.
- the fractionation tower produces tower overhead stream and tower bottoms stream.
- At least a portion of the tower overhead stream is expanded to a lower pressure such that the at least a portion of the tower overhead stream is partially condensed to produce a partially condensed low pressure vapor stream.
- the partially condensed low pressure vapor stream is separated into a lean vapor stream and tower reflux stream 18 .
- the lean vapor stream is compressed and cooled to create lean LNG stream.
- the tower reflux stream is cooled thereby producing a cooled lean tower reflux stream and the lean LNG stream is pumped to a higher pressure creating high pressure lean LNG stream.
- the process for separating a liquefied natural gas (LNG) stream includes preheating at least a portion of the LNG stream to produce first tower feed and supplying the first tower feed to fractionation tower. From the fractionation tower is produced tower overhead stream and tower bottoms stream. At least a portion of the tower overhead stream is cooled and thereby partially condensing to produce partially condensed tower overhead stream. The partially condensed tower overhead stream is separated into lean vapor stream and lean LNG stream.
- the lean LNG stream is pumped to a high pressure to produce high pressure lean LNG stream.
- the high pressure lean LNG stream is split into a lean tower reflux stream 25 and lean LNG product stream.
- the lean tower reflux stream is cooled to produce cooled lean tower reflux stream.
- the cooled lean tower reflux stream is supplied to the fractionation tower.
- the lean vapor stream is compressed to high pressure to produce compressed second lean vapor stream.
- the compressed second lean vapor stream is combined with the lean LNG product stream.
- the invention includes an apparatus for separating a liquefied natural gas (LNG) stream, the apparatus including means for splitting the LNG stream into a first feed stream and a second feed stream. Also included is a first exchanger operable to preheat the first feed stream to provide a first tower feed stream. A fractionation tower is included for receiving the first tower feed stream and to produce tower overhead stream and tower bottoms stream. A first cooler is provided that is operable to cool and partially condense at least a portion of the tower overhead stream to produce a partially condensed tower overhead stream. The first cooler is operable to allow for heat exchange between the portion of the tower overhead stream and the second feed stream.
- LNG liquefied natural gas
- a separator is operable to separate the partially condensed overhead tower stream into lean vapor stream and tower reflux stream, the tower reflux stream returning to the fractionation tower.
- the first exchanger is operable to allow for heat exchange between the lean vapor stream and the first feed stream, the lean vapor stream being cooled in the first exchanger to provide lean LNG stream.
- a pump operable for pumping the lean LNG stream to high pressure LNG stream is provided.
- FIG. 1 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of a split feed stream and lean tower reflux stream in accordance with an embodiment of the present invention
- FIG. 2 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of a split feed stream in accordance with an embodiment of a process described in co-pending U.S. patent application Ser. No. 10/651,178 titled Optimized Heating Value in Natural Gas Liquids Recovery Scheme;
- FIG. 3 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of a lean LNG reflux stream in accordance with an embodiment of the present invention
- FIG. 4 is a simplified flow diagram of a prior art process as shown in U.S. Pat. No. 6,564,579 issued to McCartney, which illustrates a typical system and process for vaporizing LNG and separating natural gas liquids from the LNG stream in accordance with prior art;
- FIG. 5 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of an overhead compressor in accordance with an embodiment of the present invention.
- FIG. 6 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of an overhead compressor and a lean LNG reflux stream in accordance with an embodiment of the present invention.
- FIG. 7 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of an overhead condenser and an overhead compressor in accordance with an embodiment of the present invention.
- FIG. 8 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of an overhead expander reflux stream in accordance with an embodiment of the present invention.
- FIG. 9 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of a partial flow compressor in accordance with an embodiment of the present invention.
- Embodiments of the present invention have been compared with prior art processes to illustrate improvements in either yield or power consumptions.
- the processes described herein were compared using the inlet LNG stream composition and conditions shown in Table I. TABLE I Component Units Nitrogen Mol % 0.46 Methane Mol % 89.79 Ethane Mol % 6.47 Propane Mol % 2.23 i-Butane Mol % .42 n-Butane Mol % .63 Temperature F. ⁇ 241.6 Pressure Psia 71.6 Flow MMTPA 5
- liquefied natural gas (LNG) stream 3 contains methane and lighter components and heavy hydrocarbon components.
- LNG stream 3 is separated into a more volatile gas fraction that contains a substantial amount of the methane and lighter components and a less volatile gas fraction that contains a large potion of the heavy hydrocarbon components.
- FIG. 1 shows a process scheme embodiment of the present invention that is used to recover NGL products.
- LNG inlet stream 1 is pumped by LNG pump 2 to about 525 psia.
- LNG stream 3 exiting LNG pump 2 is split into two streams, first feed stream 4 and second feed stream 7 .
- First feed stream 4 which is typically the larger of the two streams and contains about 95% of LNG stream 3 , is preheated in first heater or first exchanger 5 to about ⁇ 133.5° F. to provide first tower feed stream 6 .
- First tower feed stream 6 which is still substantially all liquid, is introduced into fractionation or distillation tower 10 .
- Second feed stream 7 is heated in first cooler 8 to about ⁇ 132.9° F.
- fractionation tower 10 produces a tower overhead stream 14 and a tower bottoms stream 12 .
- Tower overhead stream 14 contains the more volatile fraction containing a substantial amount of methane contained within LNG stream 3 .
- Tower bottoms stream 12 contains the less volatile fraction containing the heavy hydrocarbon component.
- bottom liquid stream 11 is sent to reboiler 13 to produce tower bottoms stream 12 . Vapor stream from tower reboiler 13 returns to fractionation tower 10 .
- the reboiler can be used maintain methane content in a NGL product stream 12 . Alternate embodiments include substituting other heat sources known in the art to the bottom of the fractionation column 10 .
- Tower overhead stream 14 is cooled to about ⁇ 128.5° F. in first cooler 8 . This partially condenses at least a portion of the tower overhead stream 14 to produce a partially condensed tower overhead stream 15 .
- Partially condensed tower overhead stream 15 is sent to reflux accumulator or separator 16 .
- Partially condensed tower overhead stream 15 is separated into a lean vapor stream 17 and a tower reflux stream 18 .
- Tower reflux stream 18 is sent to fractionation tower 10 preferably at a top tower feed location.
- Tower reflux stream 18 can be cooled prior to sending tower reflux stream 18 to fractionation tower 10 .
- Tower reflux stream 18 is sent to fractionation tower 10 preferably by pumping with reflux pump 19 .
- Lean vapor or residue stream 17 is cooled to about ⁇ 134.5° F. and substantially completely condensed in first exchanger 5 thereby producing lean LNG stream 21 .
- Lean LNG stream 21 is then pumped preferably by pump 22 to elevate its pressure to about 1422 psia.
- High pressure lean LNG stream 23 leaving the pump is a product stream that can be sent for vaporization and/or energy recovery.
- the process shown in FIG. 1 can be used when the heavy hydrocarbon components include C 2 components, C 3 components, and heavier components, i.e., ethane recovery.
- the process shown in FIG. 1 can also be used when the heavy hydrocarbon components include C 3 components, and heavier components, i.e., propane recovery.
- the step of cooling at least a portion of tower overhead stream 14 includes cooling at least a portion of tower overhead stream 14 by heat exchange contact with at least a portion of the second feed stream 7 thereby providing at least a portion of duty for the step of preheating the at least a portion of the second feed stream.
- Heat exchange contact between second feed stream 7 and tower overhead stream 14 can be performed in first cooler 8 .
- the step of cooling lean vapor stream 17 includes cooling lean vapor stream 17 by heat exchange contact with at least a portion of first feed stream 4 in first exchanger 5 thereby providing at least a portion of the duty for the step of preheating at least a portion of first feed stream 4 .
- the embodiments described above in reference to FIG. 1 further include the step of compressing the lean vapor stream 17 prior to the step of cooling the lean vapor stream.
- the tower reflux stream 18 is cooled to create cooled tower reflux stream 26 , which is then supplied to the fractionation tower.
- the cooled tower reflux stream 26 is preferably supplied to the fractionation tower at a top feed position.
- the tower reflux stream 18 is cooled by heat exchange contact with at least a portion of second feed stream 7 thereby providing at least a portion of the duty for the step of preheating at least a portion of second feed stream 7 .
- the tower reflux stream 18 is cooled by heat exchange contact with at least a portion of the first feed stream 4 thereby providing at least a portion of the duty for the step of preheating at least a portion of the first feed stream 4 .
- the step of preheating at least a portion of the first feed stream 4 to create first tower feed stream 6 advantageously includes supplying the first tower feed stream 6 to the fractionation tower 10 as a tower bottom feed stream.
- various means of providing heat or energy to the bottom of the fractionation tower are encompassed.
- An alternate embodiment includes providing the first tower feed stream at a position in the column lower than the position where the second tower feed stream enters the fractionation tower 10 . This advantageously provides a driving force to the separation in the fractionation tower 10 .
- FIG. 3 shows a scheme that uses cooled lean tower reflux stream 26 to increase NGL recovery in NGL product stream 12 .
- cooled lean tower reflux stream 26 be subcooled. Rich low pressure LNG stream 1 is pumped in LNG pump 2 to about 525 psia. LNG stream 3 exiting LNG pump 2 is heated in first exchanger 5 to about ⁇ 133.2° F. to produce first tower feed stream 6 .
- First tower feed stream 6 which is still substantially all liquid, is introduced into fractionation tower 10 preferably as a bottom feed stream.
- tower overhead stream 14 is cooled to about ⁇ 133.7° F. and is substantially completely condensed in first exchanger 5 to produce a low pressure lean LNG stream 21 .
- Lean LNG stream 21 exiting exchanger 5 is elevated in pressure preferably by pump 22 to about 1422 psia to produce high pressure lean LNG stream 23 .
- High pressure lean LNG stream 23 is then split into lean tower reflux stream 25 and lean LNG product stream 48 .
- Lean LNG stream 48 can be sent for vaporization and/or energy recovery.
- Lean tower stream 25 is cooled in first exchanger 5 to about ⁇ 233° F. and is then sent, preferably as a top feed stream, to fractionation tower 10 .
- the process described above and its various alternate embodiments can be used when the heavy hydrocarbon components include C 2 components, C 3 components, and heavier components, i.e., ethane recovery. Similarly, the process described above and its various alternate embodiments can also be used when the heavy hydrocarbon components include C 3 components, and heavier components, i.e., propane recovery.
- the step of cooling at least a portion of the tower overhead stream 14 includes cooling the portion of the tower overhead stream by heat exchange contact with at least a portion of LNG stream 3 thereby providing at least a portion of the duty for the step of preheating the LNG stream 3 .
- lean tower reflux stream 25 is cooled by heat exchange contact with LNG stream 3 thereby providing at least a portion of the duty for the step of preheating the LNG stream 3 .
- the first tower feed stream 6 is introduced to the fractionation tower below cooled lean tower reflux stream 26 to provide additional driving force due to enthalpy differences.
- the cooled lean tower reflux stream 26 is preferably supplied to the fractionation tower as a tower top feed stream.
- first exchanger 5 can act as a critical path element possibly limiting recoveries due to the need to produce a completely liquid lean LNG stream from the exchanger that can be pumped. Attempts to increase recoveries can result in exchanger pinch on first exchanger 5 and/or possibly result in a two phase lean LNG stream at the outlet of first exchanger 5 , which would then require further processing.
- lean gas compressor 27 is introduced to avoid such a pinch and to avoid a two phase stream at the first exchanger 5 outlet. The bubble point of the lean residue gas stream leaving the tower is increased in this manner. Tower overhead stream 14 can be compressed, and then condensed at a higher temperature.
- FIG. 5 shows another scheme that can be used to separate LNG stream 3 into the more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components.
- LNG inlet stream 1 is pumped by LNG pump 2 to about 475 psia.
- LNG stream 3 exiting LNG pump 2 is split into two streams, first feed stream 4 and second feed stream 7 defining a second feed stream enthalpy.
- First feed stream 4 which is the larger of the two streams and contains about 82% of LNG stream 3 , is heated in first exchanger 5 to about ⁇ 129° F. to produce first tower feed stream 6 defining a first tower feed stream enthalpy.
- First tower feeds stream, which is still substantially all-liquid, and second feed stream 7 are sent to fractionation tower 10 .
- second feed stream 7 is introduced to fractionation tower 10 at a position above the first tower feed stream.
- second feed stream 7 is introduced as a top feed to the fractionation tower 10 .
- first tower feed stream 6 is introduced as a bottom feed to the fractionation tower.
- tower overhead stream 14 is compressed in lean gas compressor 27 to about 534 psia.
- the partially boosted tower overhead stream 28 is then cooled to about ⁇ 131.1° F. and is completely condensed in first exchanger 5 to produce low-pressure lean LNG stream 21 .
- Low pressure lean LNG stream 21 is then pumped preferably by pump 22 to elevate its pressure to about 1422 psia.
- Stream 23 leaving pump 22 is the high pressure lean LNG product stream that can be sent for vaporization and/or energy recovery.
- FIG. 6 shows a dual lean reflux scheme that utilizes a side reboiler 31 to increase NGL recovery from LNG stream 1 .
- side reboiler 31 introduced in FIG. 6 advantageously maximizes utilization of cold streams and also minimizes compressor power requirements.
- rich low pressure LNG stream 1 is pumped by LNG pump 2 to about 485 psia.
- LNG stream 3 is then split into two streams, first feed stream 4 and second feed stream 7 .
- First feed stream 4 which is the larger of the two streams and contains about 92% of LNG stream 3 , is heated in first exchanger or heater 5 to about ⁇ 128.4° F. to produce first tower feed stream 6 .
- First tower feed stream which is still substantially all liquid, is sent to fractionation tower 10 .
- first tower feed stream is fed to the fractionation tower as a bottom feed stream.
- Second feed stream 7 is introduced preferably as a middle feed stream to fractionation tower 10 .
- Tower overhead stream 14 is compressed in lean gas compressor 27 to about 543 psia.
- the partially boosted tower overhead stream 28 is then cooled in side reboiler 31 to about ⁇ 124.1° F.
- side reboiler 31 is utilized in this embodiment.
- Cold tower liquid stream or tower side reboiler stream 29 is heated in side reboiler 31 and returned to fractionation tower 10 as stream 30 .
- Partially cooled stream 32 is then further cooled to about ⁇ 130.7° F. and completely condensed in first exchanger 5 to produce low pressure lean LNG stream 21 .
- two separate exchangers are shown to provide cooling for tower overhead stream 28 , a single exchanger can be used.
- Low pressure lean LNG stream 21 is then pumped, preferably by pump 22 , to elevate its pressure to about 1422 psia to produce high pressure lean LNG stream 23 .
- Lean LNG stream 23 is then split into a lean tower reflux stream 25 and lean LNG product stream 48 .
- Lean LNG product stream 48 is sent for vaporization and/or energy recovery.
- Lean tower reflux stream 25 is then cooled in first exchanger 5 to about ⁇ 232° F. and is then sent to fractionation tower 10 , preferably as top feed stream 26 .
- the compressed tower overhead stream 28 can cooled by heat exchange with at least a portion of the first feed stream 4 thereby providing at least a portion of the duty for the step of preheating at least a portion of the first feed stream 4 .
- FIG. 6 demonstrates an embodiment including splitting the high pressure lean LNG stream 23 to create a lean tower reflux stream 25 and a lean LNG product stream 48 .
- the lean tower reflux stream 25 is then cooled to produce a cooled lean tower reflux stream 26 , which is fed to the fractionation tower 10 .
- the embodiments of the invention described herein are applicable when the heavy hydrocarbon components include C 2 components, C 3 components, and heavier components, i.e., ethane recovery.
- the embodiments described herein are applicable also when the heavy hydrocarbon components include C 3 components, and heavier components, i.e., propane recovery. 10050 ]
- Higher recoveries are made possible by increasing amount of flow in first tower feed stream 6 , which is cold and rich in the embodiments shown in FIG. 5 and FIG. 6 .
- Recoveries are also enhanced by increase in amount of cooled lean tower reflux stream 26 that is returned to fractionation tower 10 .
- Increasing the discharge pressure of lean gas compressor 27 eliminates exchanger pinch in first exchanger 5 and avoids two phase LNG stream from reaching pump 22 .
- the tower pressure can also be lowered to increase recovery, at the cost of higher compression power.
- This scheme is able to give high ethane recovery with very high propane recovery. Comparing results through process simulation with prior art, it can be seen that for a modest increase in power, the process in FIG. 6 recovers more ethane. In addition, the recovery of propane is also increased. Although the simulations have been carried out for C 2 + (ethane, ethylene, propane, propylene and heavier hydrocarbons) component recovery, the same process can be used for C 3 + (propane, propylene and heavier hydrocarbons) component recovery.
- FIG. 7 shows a scheme that uses first cooler 8 as an overhead condenser along with a lean gas compressor 27 to recover NGL from rich low pressure LNG 1 .
- rich low pressure LNG 1 is pumped by LNG pump 2 to about 525 psia.
- LNG stream 3 is then split into two streams, first feed stream 4 and second feed stream 7 .
- First feed stream 4 which is the larger of the two streams and contains about 61% of LNG stream 3 , is heated in first exchanger 5 to about ⁇ 126.8° F. to produce first tower feed stream 6 .
- First tower feed stream 6 which is substantially all liquid, is introduced to fractionation tower 10 , preferably as a bottom feed stream.
- Second feed stream 7 is heated in first cooler 8 to about ⁇ 10° F. to produce second tower feed stream 9 .
- Second tower feed stream 9 is sent, preferably at a position lower than first tower feed stream 7 , to fractionation tower 10 .
- second tower feed stream 9 is a bottom feed.
- Tower overhead stream 14 is cooled to about ⁇ 133.3° F. in first cooler 8 thereby partially condensing tower overhead stream.
- Partially condensed tower overhead stream 15 is sent to reflux accumulator or separator 16 .
- Partially condensed tower overhead stream 15 is then separated into lean vapor stream 17 and tower reflux stream 18 .
- Tower reflux stream 18 is pumped by pump 19 and is sent to fractionation tower 10 , preferably as a top feed stream.
- Lean vapor or residue stream 17 is compressed in lean gas compressor 27 to about 596 psia to produce partially boosted compressed overhead stream 28 .
- Partially boosted compressed overhead stream 28 is cooled, preferably in side reboiler 31 (see FIG. 6 ), to about ⁇ 121.5° F.
- partially boosted compressed overhead stream 28 can be cooled in first cooler 8 to produce partially cooled stream 32 .
- Cold tower side reboiler stream 29 exchanges heat in first cooler 8 and returned to fractionation tower 10 as return stream 30 .
- Partially cooled stream 32 is then further cooled to about ⁇ 125.3° F. and completely condensed in first exchanger 5 to produce low pressure lean LNG stream 21 .
- Lean LNG stream 21 is then pumped preferably by pump 22 to elevate its pressure to about 1422 psia to produce lean LNG product stream 23 .
- Stream 23 is the high pressure lean LNG product that is sent for vaporization and/or energy recovery.
- Tower reflux stream 18 can be subcooled to enhance recovery. This subcooling can take place in first exchanger 5 .
- FIG. 8 illustrates another embodiment for recovery of NGL products from a rich lower pressure LNG stream.
- overhead expander 33 is used to generate reflux for fractionation tower 10 to recover NGL.
- Rich low pressure LNG stream 1 is pumped in LNG pump 2 to about 550 psia.
- LNG stream 3 exiting pump 2 is heated in first exchanger 5 to about ⁇ 125.5° F.
- LNG stream 3 which is still all liquid, is introduced to fractionation tower 10 .
- LNG stream 3 is introduced to fractionation tower 10 as a bottom feed stream.
- At least a portion of tower overhead stream 14 is expanded in expander 33 to about 365 psia so that tower overhead stream 14 is at least partially condensed thereby producing partially condensed low pressure vapor stream 35 .
- Partially condensed low pressure vapor stream 35 is then sent to reflux accumulator or separator 16 where the stream is separated into lean vapor stream 17 and tower reflux stream 18 .
- Tower reflux stream 18 is pumped by pump 19 .
- Tower reflux stream 18 is then subcooled in first exchanger 5 to about ⁇ 232° F. to produce lean tower reflux stream 26 .
- Lean tower reflux stream 26 is then sent to fractionation tower 10 , preferably as a top feed stream.
- Lean vapor stream 17 is boosted in pressure booster compressor 34 , which is driven off or powered by the power of expander 33 , and then further compressed in lean compressor 27 to about 526 psia.
- Compressed and warm residue gas stream 28 is cooled in side reboiler 31 to about ⁇ 115.8° F. to produce partially cooled stream 32 .
- Cold tower side reboiler stream 29 is heated in side reboiler 31 and returned to fractionation tower 10 as return stream 30 .
- Partially cooled stream 32 is then further cooled to about ⁇ 132.6° F. and completely condensed in first exchanger 5 to produce lean LNG stream 21 .
- Lean LNG stream 21 is pumped by pump 22 to elevate its pressure to about 1422 psia.
- Lean LNG product stream 23 is the high pressure lean LNG product that is sent for vaporization and/or energy recovery.
- FIG. 9 illustrates yet another embodiment that is used to separate rich, low pressure LNG stream 1 by utilizing a subcooled lean LNG stream to increase NGL recovery and lean gas compressor 27 for a portion of a second lean vapor stream 17 .
- rich low pressure LNG stream 1 is pumped, preferably by pump 2 , to about 535 psia.
- LNG stream 3 exiting pump 2 is then heated in first exchanger 5 to about ⁇ 133.4° F. to produce first tower feed stream 6 .
- First tower feed stream 6 which is still all liquid, is introduced to fractionation tower 10 , preferably as a bottom tower feed stream.
- Tower overhead stream 14 is cooled to about ⁇ 133° F. and partially condensed in first exchanger 5 to produce two phase stream or partially condensed tower overhead stream 15 .
- Two phase stream 15 is sent to suction scrubber or second separator 38 that separates two phase stream 15 into second lean vapor stream 17 and lean LNG stream 21 , which is liquid.
- Lean LNG stream 21 is elevated in pressure, preferably by pump 22 , to 1422 psia to produce a high pressure lean LNG stream 23 .
- High pressure lean LNG stream 23 is then split into lean tower reflux stream 25 and lean LNG product stream 48 .
- Lean tower reflux stream 25 is cooled in first exchanger 5 to about ⁇ 232° F. and is then sent, preferably as lean tower reflux stream 26 as a top feed to fractionation tower 10 .
- Second lean vapor stream 17 is compressed in lean gas compressor 27 to produce a compressed second lean vapor stream 37 .
- Compressed second lean vapor stream 37 is then combined with lean LNG product stream 48 to produce the lean LNG product that is sent for vaporization and/or energy recovery.
- second lean vapor stream 17 can be cooled in side reboilers that can be added to fractionation tower 10 , similar to that shown in FIG. 6 . With the additional cooling for second lean vapor stream 17 , energy recovery will be more efficient due to the stream being colder.
- Table II provides a side-by-side comparison of prior art processes and described embodiment of the present invention. As can be seen in Table II, the prior art process shown in FIG. 4 has the lowest recovery rates for both C 2 and C 3 recoveries when compared to the process embodiments described herein.
- a preferred embodiment of the apparatus for separating a liquefied natural gas (LNG) stream into a more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components includes means for splitting LNG stream 3 into a first feed stream 4 and a second feed stream 7 .
- LNG liquefied natural gas
- First exchanger 5 is operable to preheat first feed stream 4 thereby creating first tower feed stream 6 .
- First tower feed stream is fed into fractionation tower 10 .
- Fractionation tower 10 produces tower overhead stream 14 including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream 12 including the less volatile fraction containing the heavy hydrocarbon components. At least a portion of tower overhead stream 14 is cooled by first cooler 8 , which is operable to cool and partially condense at least a portion of the tower overhead stream 14 to produce a partially condensed tower overhead stream 15 . In a preferred embodiment, first cooler 8 is operable to allow for heat exchange between the portion of the tower overhead stream 14 and the second feed stream 7 . Separator 16 is provided which is operable to separate the partially condensed overhead tower stream 15 into a lean vapor stream 17 and a tower reflux stream 18 .
- Tower reflux stream 18 returns to and is fed to the fractionation tower 10 .
- first exchanger 5 is operable to allow for heat exchange between the lean vapor stream 17 and the first feed stream 4 , the lean vapor stream 17 being cooled in the first exchanger 5 to provide a lean LNG stream 21 .
- Pump 22 is operable for pumping the lean LNG stream 21 to a higher pressure to produce high pressure LNG stream 23 .
- first compressor 27 is operable to receive lean vapor stream 17 and boost the pressure to produce compressed overhead stream 28 .
- Another embodiment includes side reboiler for supplying at least a portion of reboiling requirements for the fractionation tower.
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Abstract
The invention includes a process and apparatus for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components. The process includes splitting the LNG stream, preheating and providing to a fractionation tower at two locations. A tower reflux stream is utilized.
Description
- This patent application claims priority to U.S. Provisional Patent Application Ser. No. 60/637,353, filed on Dec. 17, 2004, which is incorporated by reference in its entirety. Also claiming priority to U.S. applications of the same title filed on the same date as the current application.
- 1. Technical Field of the Invention
- The present invention relates to the recovery of natural gas liquids (NGL) from liquefied natural gas (LNG) streams.
- 2. Description of the Related Art
- Many attempts have been made to recover NGL from LNG streams. One such example can be found in U.S. Pat. No. 6,564,579 issued to McCartney titled Method for Vaporizing and Recovery of Natural Gas Liquids from Liquefied Natural Gas Streams (hereinafter “McCartney”). McCartney describes a process, as shown in
FIG. 4 of the present application, that uses of an overhead compressor to increase the bubble point of a lean gas stream exiting afractionation tower 10. In this prior art process, a rich low pressure LNG stream 1 is pumped inpump 2 to 450 psia.LNG stream 3 exitingpump 2 is heated in exchanger 5 to −132.5° F. to produce a heated LNG stream 6. Heated LNG stream 6 is introduced tofractionation tower 10 as a top tower feed stream. -
Fractionation tower 10 is a distillation tower that produces atower bottoms stream 12 and atower overhead stream 14.Tower bottoms stream 12 is sent to atower reboiler 13 that is used to maintain an amount of methane in anNGL product stream 12. A vapor return stream fromreboiler 13 is sent tofractionation tower 10, while NGL product is drawn off asNGL product stream 12.Tower overhead stream 14 is compressed inlean gas compressor 27 to 500 psia to produce a partiallyboosted stream 28. Partially boostedstream 28 is cooled to −137° F. and completely condensed in first exchanger 5 to produce a low pressurelean LNG stream 21. Low pressurelean LNG stream 21 is then pumped bypump 22 to elevate its pressure to 1422 psia to produce a high pressure leanLNG product stream 23, which is the high pressure lean LNG product that is sent for vaporization and/or energy recovery. - As can be seen in Table II, recovery of LNG products is limited in the prior art. Simulation results of the embodiments of the current invention compared to alternate schemes show that for lower recoveries and NGL production, there is an increase in capital cost due to the addition of a compressor and increased heat exchanger area for prior art. Utility consumption is also affected.
- Co-pending U.S. patent application Ser. No. 10/651,178 titled Optimized Heating Value in Natural Gas Liquids Recovery Scheme illustrates another attempt at recovering NGL products from LNG streams.
FIG. 2 illustrates one scheme that uses subcooled rich LNG to increase NGL recovery. In this related process, rich low pressure LNG stream 1 is pumped inpump 2 to about 525 psia to produceLNG stream 3.LNG stream 3 is then split into two streams, afirst feed stream 4 and asecond feed stream 24.First feed stream 4, which is the larger of the two streams and contains about 93% ofLNG stream 3, is heated in first exchanger 5 to −132.5° F. to produce a heated first feed stream 6. Heated first feed stream 6, which is still all liquid, is introduced tofractionation tower 10 as a tower bottom feed stream.Second feed stream 24 is sent as a top feed stream tofractionation tower 10. - As in the prior art process shown in
FIG. 4 ,fractionation tower 10 is a distillation tower that produces atower overhead stream 14 and atower bottom stream 12.Tower bottom stream 12 is sent to atower reboiler 13 that is used to maintain an amount of methane in NGLproduct stream 12. Reboiler vapor stream returns tofractionation tower 10, while NGL product is drawn off ofreboiler 13 asNGL product stream 12. -
Tower overhead stream 14 is cooled to −133.7° F. and completely condensed in first exchanger 5 to produce low pressurelean LNG stream 21. Low pressurelean LNG stream 21 is pumped inpump 22 to elevate its pressure to 1422 psia to produce high pressure leanLNG product stream 23, which is the high pressure lean LNG product that is sent for vaporization and/or energy recovery. - The present invention includes a process and apparatus to increase the recovery of NGL. As an embodiment of the present invention, a process is provided for separating a liquefied natural gas (LNG) stream into a more volatile gas fraction containing a substantial amount of methane and lighter components and a less volatile fraction containing a large portion of heavy hydrocarbon components is advantageously provided. In this embodiment, the LNG stream is split into a first feed stream and a second feed stream. At least a portion of the first feed stream is preheated and supplied to a fractionation tower as a first tower feed stream.
- In preferred embodiments of the present invention, fractionation tower produces a tower overhead stream and a tower bottoms stream. Tower overhead stream preferably includes the more volatile fraction of the LNG stream that contains a substantial amount of methane and lighter components. Tower bottoms stream preferably includes the less volatile fraction of the LNG stream that contains the heavy hydrocarbon components.
- At least a portion of the second feed stream is heated and supplied to the fractionation tower as a second tower feed stream. At least a portion of the tower overhead stream is cooled and partially condensed to produce a partially condensed tower overhead stream. Partially condensed tower overhead stream is separated into a lean vapor stream and a tower reflux stream being sent to the fractionation tower. Lean vapor stream is subcooled so that the lean vapor stream is substantially condensed thereby producing a lean LNG stream. Lean LNG stream is then pumped to a high pressure.
- In another embodiment of the invention, the liquefied natural gas (LNG) stream is split into a first feed stream and a second feed stream. The feed streams define, respectively, a first feed stream enthalpy and a second feed stream enthalpy. At least a portion of the first feed stream is preheated and provided to the fractionation tower as the first tower feed stream. From the fractionation tower, the tower overhead stream is produced containing the more volatile fraction. The tower bottoms stream containing the less volatile fraction is also produced from the fractionation tower. The second feed stream is supplied to the fractionation tower such that the first feed stream and the second tower feed stream have a substantially common composition but the first tower feed stream enthalpy differs from the second feed stream enthalpy. The tower overhead stream is compressed to produce a compressed overhead stream. The compressed overhead stream is cooled until it is at least substantially condensed thereby producing a lean LNG stream. In one preferred embodiment, the compressed overhead stream is cooled until it is subcooled. The lean LNG stream is pumped to a higher pressure thereby creating a high pressure lean LNG stream.
- In yet another embodiment of the invention, the process for separating the liquefied natural (LNG) stream includes preheating at least a portion of the LNG stream to produce first tower feed stream. The first tower feed stream is supplied to the fractionation tower that produces the tower overhead stream and tower bottoms stream. At least a portion of the tower overhead stream is cooled so that the portion of the tower overhead stream is at least substantially condensed thereby producing the lean LNG stream. The tower overhead stream can be subcooled. The lean LNG stream is pumped to a higher pressure to produce a high pressure lean LNG stream. The high pressure lean LNG stream is split into a lean tower reflux stream and a lean LNG product stream. The lean tower reflux stream is cooled to produce a cooled lean tower reflux stream and the cooled lean tower reflux stream is supplied to the fractionation tower.
- Yet another preferred embodiment includes a process for separating the liquefied natural gas (LNG) stream including splitting the LNG stream into first feed stream and second feed stream. The second feed stream is supplied to the fractionation tower as second tower feed stream to produce the tower overhead stream and the tower bottoms stream 12 including the less volatile fraction containing the heavy hydrocarbon components. At least a portion of the first feed stream is preheated to produce the first tower feed stream. The first tower feed stream is supplied to the fractionation tower. The tower overhead stream is compressed to produce compressed overhead stream. The compressed overhead stream is cooled such that the compressed overhead stream is substantially condensed thereby producing lean LNG stream. The lean LNG stream is pumped to a higher pressure to produce high pressure lean LNG stream. The high pressure lean LNG stream is split into lean tower reflux stream and lean LNG product stream. The lean tower reflux stream is cooled to produce cooled lean tower reflux stream that is supplied to the fractionation tower.
- Yet another embodiment of the invention includes a process for separating a liquefied natural gas (LNG) stream including preheating at least a portion of the LNG stream and supplying the at least a portion of the LNG stream to fractionation tower as first tower feed stream. The fractionation tower produces tower overhead stream and tower bottoms stream. At least a portion of the tower overhead stream is expanded to a lower pressure such that the at least a portion of the tower overhead stream is partially condensed to produce a partially condensed low pressure vapor stream. The partially condensed low pressure vapor stream is separated into a lean vapor stream and
tower reflux stream 18. The lean vapor stream is compressed and cooled to create lean LNG stream. The tower reflux stream is cooled thereby producing a cooled lean tower reflux stream and the lean LNG stream is pumped to a higher pressure creating high pressure lean LNG stream. - In yet another embodiment of the present invention, the process for separating a liquefied natural gas (LNG) stream includes preheating at least a portion of the LNG stream to produce first tower feed and supplying the first tower feed to fractionation tower. From the fractionation tower is produced tower overhead stream and tower bottoms stream. At least a portion of the tower overhead stream is cooled and thereby partially condensing to produce partially condensed tower overhead stream. The partially condensed tower overhead stream is separated into lean vapor stream and lean LNG stream. The lean LNG stream is pumped to a high pressure to produce high pressure lean LNG stream. The high pressure lean LNG stream is split into a lean
tower reflux stream 25 and lean LNG product stream. The lean tower reflux stream is cooled to produce cooled lean tower reflux stream. The cooled lean tower reflux stream is supplied to the fractionation tower. The lean vapor stream is compressed to high pressure to produce compressed second lean vapor stream. The compressed second lean vapor stream is combined with the lean LNG product stream. - In another preferred embodiment, the invention includes an apparatus for separating a liquefied natural gas (LNG) stream, the apparatus including means for splitting the LNG stream into a first feed stream and a second feed stream. Also included is a first exchanger operable to preheat the first feed stream to provide a first tower feed stream. A fractionation tower is included for receiving the first tower feed stream and to produce tower overhead stream and tower bottoms stream. A first cooler is provided that is operable to cool and partially condense at least a portion of the tower overhead stream to produce a partially condensed tower overhead stream. The first cooler is operable to allow for heat exchange between the portion of the tower overhead stream and the second feed stream. A separator is operable to separate the partially condensed overhead tower stream into lean vapor stream and tower reflux stream, the tower reflux stream returning to the fractionation tower. The first exchanger is operable to allow for heat exchange between the lean vapor stream and the first feed stream, the lean vapor stream being cooled in the first exchanger to provide lean LNG stream. A pump operable for pumping the lean LNG stream to high pressure LNG stream is provided.
- So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, may be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof that is illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of the invention's scope as it may admit to other equally effective embodiments.
-
FIG. 1 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of a split feed stream and lean tower reflux stream in accordance with an embodiment of the present invention; -
FIG. 2 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of a split feed stream in accordance with an embodiment of a process described in co-pending U.S. patent application Ser. No. 10/651,178 titled Optimized Heating Value in Natural Gas Liquids Recovery Scheme; -
FIG. 3 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of a lean LNG reflux stream in accordance with an embodiment of the present invention; -
FIG. 4 is a simplified flow diagram of a prior art process as shown in U.S. Pat. No. 6,564,579 issued to McCartney, which illustrates a typical system and process for vaporizing LNG and separating natural gas liquids from the LNG stream in accordance with prior art; -
FIG. 5 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of an overhead compressor in accordance with an embodiment of the present invention. -
FIG. 6 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of an overhead compressor and a lean LNG reflux stream in accordance with an embodiment of the present invention. -
FIG. 7 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of an overhead condenser and an overhead compressor in accordance with an embodiment of the present invention. -
FIG. 8 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of an overhead expander reflux stream in accordance with an embodiment of the present invention. -
FIG. 9 is a simplified flow diagram of a hydrocarbon recovery process that is configured for increased recovery of heavy components from an inlet LNG stream through the use of a partial flow compressor in accordance with an embodiment of the present invention. - In the description of the figures, the same numbers are used to refer to similar or same components in all figures. For clarity and simplicity, not all equipment is shown as they are considered known to those skilled in the art. For consistency, the same equipment parameters such as number of trays, efficiencies, pressure drops, product specifications etc have been used to compare processes.
- Embodiments of the present invention have been compared with prior art processes to illustrate improvements in either yield or power consumptions. The processes described herein were compared using the inlet LNG stream composition and conditions shown in Table I.
TABLE I Component Units Nitrogen Mol % 0.46 Methane Mol % 89.79 Ethane Mol % 6.47 Propane Mol % 2.23 i-Butane Mol % .42 n-Butane Mol % .63 Temperature F. −241.6 Pressure Psia 71.6 Flow MMTPA 5 - In all embodiments of the process, liquefied natural gas (LNG)
stream 3 contains methane and lighter components and heavy hydrocarbon components. In order to recover NGL products,LNG stream 3 is separated into a more volatile gas fraction that contains a substantial amount of the methane and lighter components and a less volatile gas fraction that contains a large potion of the heavy hydrocarbon components. - Referring to the drawings,
FIG. 1 shows a process scheme embodiment of the present invention that is used to recover NGL products. LNG inlet stream 1 is pumped byLNG pump 2 to about 525 psia.LNG stream 3 exitingLNG pump 2 is split into two streams,first feed stream 4 andsecond feed stream 7.First feed stream 4, which is typically the larger of the two streams and contains about 95% ofLNG stream 3, is preheated in first heater or first exchanger 5 to about −133.5° F. to provide first tower feed stream 6. First tower feed stream 6, which is still substantially all liquid, is introduced into fractionation ordistillation tower 10.Second feed stream 7 is heated in first cooler 8 to about −132.9° F. to produce second tower feed stream 9, which is introduced into thefractionation tower 10. In preferred embodiments of the present invention,fractionation tower 10 produces atower overhead stream 14 and a tower bottoms stream 12. Toweroverhead stream 14 contains the more volatile fraction containing a substantial amount of methane contained withinLNG stream 3. Tower bottoms stream 12 contains the less volatile fraction containing the heavy hydrocarbon component. In a preferred embodiment,bottom liquid stream 11 is sent to reboiler 13 to produce tower bottoms stream 12. Vapor stream fromtower reboiler 13 returns tofractionation tower 10. In this embodiment, the reboiler can be used maintain methane content in aNGL product stream 12. Alternate embodiments include substituting other heat sources known in the art to the bottom of thefractionation column 10. - Tower
overhead stream 14 is cooled to about −128.5° F. in first cooler 8. This partially condenses at least a portion of thetower overhead stream 14 to produce a partially condensedtower overhead stream 15. Partially condensedtower overhead stream 15 is sent to reflux accumulator orseparator 16. Partially condensedtower overhead stream 15 is separated into a lean vapor stream 17 and atower reflux stream 18.Tower reflux stream 18 is sent tofractionation tower 10 preferably at a top tower feed location.Tower reflux stream 18 can be cooled prior to sendingtower reflux stream 18 tofractionation tower 10.Tower reflux stream 18 is sent tofractionation tower 10 preferably by pumping withreflux pump 19. - Lean vapor or residue stream 17 is cooled to about −134.5° F. and substantially completely condensed in first exchanger 5 thereby producing
lean LNG stream 21.Lean LNG stream 21 is then pumped preferably bypump 22 to elevate its pressure to about 1422 psia. High pressurelean LNG stream 23 leaving the pump is a product stream that can be sent for vaporization and/or energy recovery. - The process shown in
FIG. 1 can be used when the heavy hydrocarbon components include C2 components, C3 components, and heavier components, i.e., ethane recovery. The process shown inFIG. 1 can also be used when the heavy hydrocarbon components include C3 components, and heavier components, i.e., propane recovery. - In embodiments of the present invention, the step of cooling at least a portion of
tower overhead stream 14 includes cooling at least a portion oftower overhead stream 14 by heat exchange contact with at least a portion of thesecond feed stream 7 thereby providing at least a portion of duty for the step of preheating the at least a portion of the second feed stream. Heat exchange contact betweensecond feed stream 7 and toweroverhead stream 14 can be performed in first cooler 8. In alternate embodiments, such as demonstrated inFIG. 5 , In embodiments of the present invention, the step of cooling lean vapor stream 17 includes cooling lean vapor stream 17 by heat exchange contact with at least a portion offirst feed stream 4 in first exchanger 5 thereby providing at least a portion of the duty for the step of preheating at least a portion offirst feed stream 4. - In another embodiment of the present invention, such as is demonstrated in
FIG. 7 , the embodiments described above in reference toFIG. 1 further include the step of compressing the lean vapor stream 17 prior to the step of cooling the lean vapor stream. - In embodiments of the present invention, the
tower reflux stream 18 is cooled to create cooledtower reflux stream 26, which is then supplied to the fractionation tower. The cooledtower reflux stream 26 is preferably supplied to the fractionation tower at a top feed position. Thetower reflux stream 18 is cooled by heat exchange contact with at least a portion ofsecond feed stream 7 thereby providing at least a portion of the duty for the step of preheating at least a portion ofsecond feed stream 7. In an alternate embodiment, thetower reflux stream 18 is cooled by heat exchange contact with at least a portion of thefirst feed stream 4 thereby providing at least a portion of the duty for the step of preheating at least a portion of thefirst feed stream 4. - In certain embodiments, the step of preheating at least a portion of the
first feed stream 4 to create first tower feed stream 6 advantageously includes supplying the first tower feed stream 6 to thefractionation tower 10 as a tower bottom feed stream. As noted previously, various means of providing heat or energy to the bottom of the fractionation tower are encompassed. An alternate embodiment includes providing the first tower feed stream at a position in the column lower than the position where the second tower feed stream enters thefractionation tower 10. This advantageously provides a driving force to the separation in thefractionation tower 10. - As another embodiment of the present invention,
FIG. 3 shows a scheme that uses cooled leantower reflux stream 26 to increase NGL recovery inNGL product stream 12. In this embodiment, it is advantageous that cooled leantower reflux stream 26 be subcooled. Rich low pressure LNG stream 1 is pumped inLNG pump 2 to about 525 psia.LNG stream 3 exitingLNG pump 2 is heated in first exchanger 5 to about −133.2° F. to produce first tower feed stream 6. First tower feed stream 6, which is still substantially all liquid, is introduced intofractionation tower 10 preferably as a bottom feed stream. - In this embodiment, tower
overhead stream 14 is cooled to about −133.7° F. and is substantially completely condensed in first exchanger 5 to produce a low pressurelean LNG stream 21.Lean LNG stream 21 exiting exchanger 5 is elevated in pressure preferably bypump 22 to about 1422 psia to produce high pressurelean LNG stream 23. High pressurelean LNG stream 23 is then split into leantower reflux stream 25 and leanLNG product stream 48.Lean LNG stream 48 can be sent for vaporization and/or energy recovery.Lean tower stream 25 is cooled in first exchanger 5 to about −233° F. and is then sent, preferably as a top feed stream, tofractionation tower 10. The process described above and its various alternate embodiments can be used when the heavy hydrocarbon components include C2 components, C3 components, and heavier components, i.e., ethane recovery. Similarly, the process described above and its various alternate embodiments can also be used when the heavy hydrocarbon components include C3 components, and heavier components, i.e., propane recovery. - In one embodiment shown in
FIG. 3 , the step of cooling at least a portion of thetower overhead stream 14 includes cooling the portion of the tower overhead stream by heat exchange contact with at least a portion ofLNG stream 3 thereby providing at least a portion of the duty for the step of preheating theLNG stream 3. Alternately or in addition, leantower reflux stream 25 is cooled by heat exchange contact withLNG stream 3 thereby providing at least a portion of the duty for the step of preheating theLNG stream 3. In one embodiment, the first tower feed stream 6 is introduced to the fractionation tower below cooled leantower reflux stream 26 to provide additional driving force due to enthalpy differences. The cooled leantower reflux stream 26 is preferably supplied to the fractionation tower as a tower top feed stream. - In certain instances, first exchanger 5 can act as a critical path element possibly limiting recoveries due to the need to produce a completely liquid lean LNG stream from the exchanger that can be pumped. Attempts to increase recoveries can result in exchanger pinch on first exchanger 5 and/or possibly result in a two phase lean LNG stream at the outlet of first exchanger 5, which would then require further processing. Regarding
FIG. 5 ,lean gas compressor 27 is introduced to avoid such a pinch and to avoid a two phase stream at the first exchanger 5 outlet. The bubble point of the lean residue gas stream leaving the tower is increased in this manner. Toweroverhead stream 14 can be compressed, and then condensed at a higher temperature. - As another embodiment of the present invention,
FIG. 5 shows another scheme that can be used toseparate LNG stream 3 into the more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components. In this embodiment, LNG inlet stream 1 is pumped byLNG pump 2 to about 475 psia.LNG stream 3 exitingLNG pump 2 is split into two streams,first feed stream 4 andsecond feed stream 7 defining a second feed stream enthalpy.First feed stream 4, which is the larger of the two streams and contains about 82% ofLNG stream 3, is heated in first exchanger 5 to about −129° F. to produce first tower feed stream 6 defining a first tower feed stream enthalpy. First tower feeds stream, which is still substantially all-liquid, andsecond feed stream 7 are sent tofractionation tower 10. In a preferred embodiment,second feed stream 7 is introduced tofractionation tower 10 at a position above the first tower feed stream. In one embodiment,second feed stream 7 is introduced as a top feed to thefractionation tower 10. In one embodiment, first tower feed stream 6 is introduced as a bottom feed to the fractionation tower. - In
FIG. 5 , toweroverhead stream 14 is compressed inlean gas compressor 27 to about 534 psia. The partially boostedtower overhead stream 28 is then cooled to about −131.1° F. and is completely condensed in first exchanger 5 to produce low-pressurelean LNG stream 21. Low pressurelean LNG stream 21 is then pumped preferably bypump 22 to elevate its pressure to about 1422 psia.Stream 23 leavingpump 22 is the high pressure lean LNG product stream that can be sent for vaporization and/or energy recovery. - As another embodiment of the present invention,
FIG. 6 shows a dual lean reflux scheme that utilizes aside reboiler 31 to increase NGL recovery from LNG stream 1. In addition to the elements shown inFIG. 5 ,side reboiler 31 introduced inFIG. 6 advantageously maximizes utilization of cold streams and also minimizes compressor power requirements. As in other embodiments described herein, rich low pressure LNG stream 1 is pumped byLNG pump 2 to about 485 psia.LNG stream 3 is then split into two streams,first feed stream 4 andsecond feed stream 7.First feed stream 4, which is the larger of the two streams and contains about 92% ofLNG stream 3, is heated in first exchanger or heater 5 to about −128.4° F. to produce first tower feed stream 6. First tower feed stream, which is still substantially all liquid, is sent tofractionation tower 10. IN one embodiment first tower feed stream is fed to the fractionation tower as a bottom feed stream.Second feed stream 7 is introduced preferably as a middle feed stream tofractionation tower 10. Toweroverhead stream 14 is compressed inlean gas compressor 27 to about 543 psia. The partially boostedtower overhead stream 28 is then cooled inside reboiler 31 to about −124.1° F. - To provide a portion of the reboiling energy for
fractionation tower 10,side reboiler 31 is utilized in this embodiment. Cold tower liquid stream or towerside reboiler stream 29 is heated inside reboiler 31 and returned tofractionation tower 10 asstream 30. Partially cooledstream 32 is then further cooled to about −130.7° F. and completely condensed in first exchanger 5 to produce low pressurelean LNG stream 21. Although two separate exchangers are shown to provide cooling fortower overhead stream 28, a single exchanger can be used. Low pressurelean LNG stream 21 is then pumped, preferably bypump 22, to elevate its pressure to about 1422 psia to produce high pressurelean LNG stream 23.Lean LNG stream 23 is then split into a leantower reflux stream 25 and leanLNG product stream 48. LeanLNG product stream 48 is sent for vaporization and/or energy recovery. Leantower reflux stream 25 is then cooled in first exchanger 5 to about −232° F. and is then sent tofractionation tower 10, preferably astop feed stream 26. - In this embodiment, the compressed
tower overhead stream 28 can cooled by heat exchange with at least a portion of thefirst feed stream 4 thereby providing at least a portion of the duty for the step of preheating at least a portion of thefirst feed stream 4. -
FIG. 6 demonstrates an embodiment including splitting the high pressurelean LNG stream 23 to create a leantower reflux stream 25 and a leanLNG product stream 48. The leantower reflux stream 25 is then cooled to produce a cooled leantower reflux stream 26, which is fed to thefractionation tower 10. - J The embodiments of the invention described herein are applicable when the heavy hydrocarbon components include C2 components, C3 components, and heavier components, i.e., ethane recovery. The embodiments described herein are applicable also when the heavy hydrocarbon components include C3 components, and heavier components, i.e., propane recovery. 10050] Higher recoveries are made possible by increasing amount of flow in first tower feed stream 6, which is cold and rich in the embodiments shown in
FIG. 5 andFIG. 6 . Recoveries are also enhanced by increase in amount of cooled leantower reflux stream 26 that is returned tofractionation tower 10. Increasing the discharge pressure oflean gas compressor 27 eliminates exchanger pinch in first exchanger 5 and avoids two phase LNG stream from reachingpump 22. The tower pressure can also be lowered to increase recovery, at the cost of higher compression power. This scheme is able to give high ethane recovery with very high propane recovery. Comparing results through process simulation with prior art, it can be seen that for a modest increase in power, the process inFIG. 6 recovers more ethane. In addition, the recovery of propane is also increased. Although the simulations have been carried out for C2+ (ethane, ethylene, propane, propylene and heavier hydrocarbons) component recovery, the same process can be used for C3+ (propane, propylene and heavier hydrocarbons) component recovery. - As yet another embodiment of the present invention,
FIG. 7 shows a scheme that uses first cooler 8 as an overhead condenser along with alean gas compressor 27 to recover NGL from rich low pressure LNG 1. In this embodiment, rich low pressure LNG 1 is pumped byLNG pump 2 to about 525 psia.LNG stream 3 is then split into two streams,first feed stream 4 andsecond feed stream 7.First feed stream 4, which is the larger of the two streams and contains about 61% ofLNG stream 3, is heated in first exchanger 5 to about −126.8° F. to produce first tower feed stream 6. First tower feed stream 6, which is substantially all liquid, is introduced tofractionation tower 10, preferably as a bottom feed stream.Second feed stream 7 is heated in first cooler 8 to about −10° F. to produce second tower feed stream 9. Second tower feed stream 9 is sent, preferably at a position lower than firsttower feed stream 7, tofractionation tower 10. In one embodiment, second tower feed stream 9 is a bottom feed. - Tower
overhead stream 14 is cooled to about −133.3° F. in first cooler 8 thereby partially condensing tower overhead stream. Partially condensedtower overhead stream 15 is sent to reflux accumulator orseparator 16. Partially condensedtower overhead stream 15 is then separated into lean vapor stream 17 andtower reflux stream 18.Tower reflux stream 18 is pumped bypump 19 and is sent tofractionation tower 10, preferably as a top feed stream. Lean vapor or residue stream 17 is compressed inlean gas compressor 27 to about 596 psia to produce partially boosted compressedoverhead stream 28. Partially boosted compressedoverhead stream 28 is cooled, preferably in side reboiler 31 (seeFIG. 6 ), to about −121.5° F. Alternately, as shown inFIG. 7 , partially boosted compressedoverhead stream 28 can be cooled in first cooler 8 to produce partially cooledstream 32. Cold towerside reboiler stream 29 exchanges heat in first cooler 8 and returned tofractionation tower 10 asreturn stream 30. Partially cooledstream 32 is then further cooled to about −125.3° F. and completely condensed in first exchanger 5 to produce low pressurelean LNG stream 21.Lean LNG stream 21 is then pumped preferably bypump 22 to elevate its pressure to about 1422 psia to produce leanLNG product stream 23.Stream 23 is the high pressure lean LNG product that is sent for vaporization and/or energy recovery. -
Tower reflux stream 18 can be subcooled to enhance recovery. This subcooling can take place in first exchanger 5. -
FIG. 8 illustrates another embodiment for recovery of NGL products from a rich lower pressure LNG stream. In this embodiment,overhead expander 33 is used to generate reflux forfractionation tower 10 to recover NGL. Rich low pressure LNG stream 1 is pumped inLNG pump 2 to about 550 psia.LNG stream 3 exitingpump 2 is heated in first exchanger 5 to about −125.5°F. LNG stream 3, which is still all liquid, is introduced tofractionation tower 10. In one preferred embodiment,LNG stream 3 is introduced tofractionation tower 10 as a bottom feed stream. - At least a portion of
tower overhead stream 14 is expanded inexpander 33 to about 365 psia so thattower overhead stream 14 is at least partially condensed thereby producing partially condensed lowpressure vapor stream 35. Partially condensed lowpressure vapor stream 35 is then sent to reflux accumulator orseparator 16 where the stream is separated into lean vapor stream 17 andtower reflux stream 18.Tower reflux stream 18 is pumped bypump 19.Tower reflux stream 18 is then subcooled in first exchanger 5 to about −232° F. to produce leantower reflux stream 26. Leantower reflux stream 26 is then sent tofractionation tower 10, preferably as a top feed stream. Lean vapor stream 17 is boosted inpressure booster compressor 34, which is driven off or powered by the power ofexpander 33, and then further compressed inlean compressor 27 to about 526 psia. Compressed and warmresidue gas stream 28 is cooled inside reboiler 31 to about −115.8° F. to produce partially cooledstream 32. Cold towerside reboiler stream 29 is heated inside reboiler 31 and returned tofractionation tower 10 asreturn stream 30. Partially cooledstream 32 is then further cooled to about −132.6° F. and completely condensed in first exchanger 5 to producelean LNG stream 21.Lean LNG stream 21 is pumped bypump 22 to elevate its pressure to about 1422 psia. LeanLNG product stream 23 is the high pressure lean LNG product that is sent for vaporization and/or energy recovery. -
FIG. 9 illustrates yet another embodiment that is used to separate rich, low pressure LNG stream 1 by utilizing a subcooled lean LNG stream to increase NGL recovery andlean gas compressor 27 for a portion of a second lean vapor stream 17. In this embodiment, rich low pressure LNG stream 1 is pumped, preferably bypump 2, to about 535 psia.LNG stream 3 exitingpump 2 is then heated in first exchanger 5 to about −133.4° F. to produce first tower feed stream 6. First tower feed stream 6, which is still all liquid, is introduced tofractionation tower 10, preferably as a bottom tower feed stream. - Tower
overhead stream 14 is cooled to about −133° F. and partially condensed in first exchanger 5 to produce two phase stream or partially condensedtower overhead stream 15. Twophase stream 15 is sent to suction scrubber orsecond separator 38 that separates twophase stream 15 into second lean vapor stream 17 andlean LNG stream 21, which is liquid. -
Lean LNG stream 21 is elevated in pressure, preferably bypump 22, to 1422 psia to produce a high pressurelean LNG stream 23. High pressurelean LNG stream 23 is then split into leantower reflux stream 25 and leanLNG product stream 48. Leantower reflux stream 25 is cooled in first exchanger 5 to about −232° F. and is then sent, preferably as leantower reflux stream 26 as a top feed to fractionationtower 10. - Second lean vapor stream 17 is compressed in
lean gas compressor 27 to produce a compressed secondlean vapor stream 37. Compressed secondlean vapor stream 37 is then combined with leanLNG product stream 48 to produce the lean LNG product that is sent for vaporization and/or energy recovery. If high pressurelean LNG stream 23 is sent for energy recovery, then second lean vapor stream 17 can be cooled in side reboilers that can be added tofractionation tower 10, similar to that shown inFIG. 6 . With the additional cooling for second lean vapor stream 17, energy recovery will be more efficient due to the stream being colder. -
TABLE II POWER Tower C2 C3 Pump Compressor Total UA Power LP LNG FIG. RECOVERY % RECOVERY % NGL BPD hp hp hp Btu/hr-F Psia ° F. Hp/gpm 1 87.63 98.48 41271 8047 8047 4.44E+06 510 −134.5 6.69 2 88.87 97.73 41520 8055 8055 4.25E+06 510 −133.7 6.65 3 88.57 99.32 41635 8304 8304 4.54E+06 510 −133.7 6.84 4 88.05 97.68 41282 7528 2195 9723 5.43E+06 435 −137 8.08 5 92.48 98.41 42658 7789 2195 9984 5.48E+06 460 −131.1 8.02 6 94.74 99.62 43464 8279 2195 10474 5.93E+06 470 −130.7 8.26 7 98 99.99 44457 8257 2195 10452 5.30E+06 510 −125.3 8.06 8 96.83 100 44116 8161 2195 10356 6.98E+06 535 −132.6 8.05 9 96.03 99.99 43882 8097 2186 10283 4.73E+06 520 −133 8.03 - Table II provides a side-by-side comparison of prior art processes and described embodiment of the present invention. As can be seen in Table II, the prior art process shown in
FIG. 4 has the lowest recovery rates for both C2 and C3 recoveries when compared to the process embodiments described herein. - The invention also encompasses the apparatus necessary for each process embodiment. A preferred embodiment of the apparatus for separating a liquefied natural gas (LNG) stream into a more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components includes means for splitting
LNG stream 3 into afirst feed stream 4 and asecond feed stream 7. Various means are known in the art from a simple T in a line to more complex vessels. First exchanger 5 is operable to preheatfirst feed stream 4 thereby creating first tower feed stream 6. First tower feed stream is fed intofractionation tower 10.Fractionation tower 10 producestower overhead stream 14 including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream 12 including the less volatile fraction containing the heavy hydrocarbon components. At least a portion oftower overhead stream 14 is cooled by first cooler 8, which is operable to cool and partially condense at least a portion of thetower overhead stream 14 to produce a partially condensedtower overhead stream 15. In a preferred embodiment, first cooler 8 is operable to allow for heat exchange between the portion of thetower overhead stream 14 and thesecond feed stream 7.Separator 16 is provided which is operable to separate the partially condensedoverhead tower stream 15 into a lean vapor stream 17 and atower reflux stream 18.Tower reflux stream 18 returns to and is fed to thefractionation tower 10. In a preferred embodiment, first exchanger 5 is operable to allow for heat exchange between the lean vapor stream 17 and thefirst feed stream 4, the lean vapor stream 17 being cooled in the first exchanger 5 to provide alean LNG stream 21.Pump 22 is operable for pumping thelean LNG stream 21 to a higher pressure to produce highpressure LNG stream 23. - In another embodiment,
first compressor 27 is operable to receive lean vapor stream 17 and boost the pressure to produce compressedoverhead stream 28. Another embodiment includes side reboiler for supplying at least a portion of reboiling requirements for the fractionation tower. - While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.
Claims (23)
1. A process for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components, the process comprising the steps of:
(a) splitting the LNG stream into a first feed stream and a second feed stream;
(b) preheating at least a portion of the first feed stream to provide first tower feed stream and supplying the first tower feed stream to a fractionation tower to produce a tower overhead stream including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream including the less volatile fraction containing the heavy hydrocarbon components;
(c) preheating at least a portion of the second feed stream to provide second tower feed stream and supplying second tower feed stream to the fractionation tower;
(d) cooling and partially condensing at least a portion of the tower overhead stream to produce a partially condensed tower overhead stream;
(e) separating the partially condensed tower overhead stream into a lean vapor stream and a tower reflux stream, and supplying the tower reflux stream to the fractionation tower;
(f) cooling the lean vapor stream such that the lean vapor stream is substantially condensed thereby producing a lean LNG stream; and
(g) pumping the lean LNG stream to a high pressure lean LNG stream.
2. The process according to claim 1 , wherein the heavy hydrocarbon components include C2 components, C3 components and heavier components.
3. The process according to claim 1 , wherein the heavy hydrocarbon components include C3 components and heavier components.
4. The process according to claim 1 , further comprising the step of compressing the lean vapor stream prior to the step of cooling the lean vapor stream.
5. The process according to claim 1 , wherein the step of cooling at least a portion of the tower overhead stream includes cooling at least a portion of the tower overhead stream by heat exchange contact with the at least a portion of the second feed stream thereby providing at least a portion of duty for the step of preheating the at least a portion of the second feed stream.
6. The process according to claim 1 , wherein the step of preheating at least a portion of the first feed stream and supplying the first tower feed stream to the fractionation tower includes supplying the first tower feed stream to the fractionation tower as a tower bottom feed stream.
7. The process according to claim 1 , wherein the step of preheating at least a portion of the first feed stream and supplying the first tower feed stream to the fractionation tower includes supplying the first tower feed stream to the fractionation tower at a position in the fractionation tower lower than the position where the second tower feed stream enters the fractionation tower.
8. The process according to claim 1 , wherein the step of separating the partially condensed tower overhead stream into the lean vapor stream and the tower reflux stream includes supplying the tower reflux stream as a top tower feed stream to the fractionation tower.
9. The process according to claim 1 , wherein the step of cooling the lean vapor stream includes cooling the lean vapor stream by heat exchange contact with at least a portion of the first feed stream thereby providing at least a portion of the duty for the step of preheating at least a portion of the first feed stream.
10. The process according to claim 1 , wherein the process further includes the step of cooling the tower reflux stream to create a cooled tower reflux stream and supplying the cooled tower reflux stream to the fractionation tower.
11. The process according to claim 10 , wherein the step of sending the cooled tower reflux stream to the fractionation tower includes sending the cooled tower reflux stream as a top feed stream to the fractionation tower.
12. The process according to claim 10 , wherein the step of cooling the tower reflux stream includes cooling the tower reflux stream by heat exchange contact with at least a portion of the first feed stream.
13. A process for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components, the process comprising the steps of:
preheating at least a portion of the LNG stream and supplying the at least a portion of the LNG stream to a fractionation tower as a first tower feed stream to produce a tower overhead stream including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream including the less volatile fraction containing the heavy hydrocarbon components;
expanding at least a portion of the tower overhead stream to a lower pressure such that the at least a portion of the tower overhead stream is partially condensed to produce a partially condensed low pressure vapor stream;
separating the partially condensed low pressure vapor stream into a lean vapor stream and a tower reflux stream;
compressing the lean vapor stream;
cooling the lean vapor stream to create a lean LNG stream;
cooling the tower reflux stream thereby producing a cooled lean tower reflux stream; and
pumping the lean LNG stream to a high pressure lean LNG stream.
14. The process according to claim 13 , where the heavy hydrocarbon components include C2 components, C3 components and heavier components.
15. The process according to claim 13 , where the heavy hydrocarbon components include C3 components and heavier components.
16. The process according to claim 13 , whereby the tower reflux stream is cooled by heat exchange contact with at least a portion of the LNG stream prior to the step of supplying the tower reflux stream 18 to the fractionation tower.
17. The process according to claim 13 , the step of supplying the tower reflux stream to the fractionation tower includes supplying the tower reflux stream to the fractionation tower as a top feed stream.
18. The process according to claim 13 , wherein the step of cooling the lean vapor stream includes cooling the lean vapor stream by heat exchange contact with at least a tower side reboiler stream thereby providing reboiling duty to the fractionation tower.
19. The process according to claim 13 , wherein the step of cooling the lean vapor stream includes cooling the lean vapor stream by heat exchange with at least a portion of the LNG stream thereby providing at least a portion of duty for the step of preheating the at least a portion of the LNG stream 3.
20. The process according to claim 13 , wherein the step of supplying the at least a portion of the LNG stream to the fractionation tower includes supplying the at least a portion of the LNG stream to the fractionation tower as a tower bottom feed stream.
21. An apparatus for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components, the apparatus comprising:
means for splitting the LNG stream into a first feed stream and a second feed stream;
a first exchanger operable to preheat the first feed stream to provide a first tower feed stream;
a fractionation tower for receiving the first tower feed stream to produce a tower overhead stream including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream including the less volatile fraction containing the heavy hydrocarbon components;
a first cooler operable to cool and partially condense at least a portion of the tower overhead stream to produce a partially condensed tower overhead stream, the first cooler operable to allow for heat exchange between the portion of the tower overhead stream and the second feed stream;
a separator operable to separate the partially condensed overhead tower stream into a lean vapor stream and a tower reflux stream, the tower reflux stream operable to return to the fractionation tower, the first exchanger being operable to allow for heat exchange between the lean vapor stream and the first feed stream, the lean vapor stream being cooled in the first exchanger to provide a lean LNG stream; and
a pump operable for pumping the lean LNG stream to a high pressure LNG stream.
22. The apparatus of claim 21 , further including a first compressor for compressing the lean vapor stream.
23. The apparatus of claim 21 , further including a side reboiler for supplying at least a portion of reboiling requirements for the fractionation tower.
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US20060260356A1 (en) * | 2002-04-03 | 2006-11-23 | Howe-Baker International | Liquid natural gas processing |
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US20090277217A1 (en) * | 2008-05-08 | 2009-11-12 | Conocophillips Company | Enhanced nitrogen removal in an lng facility |
WO2010132678A1 (en) * | 2009-05-15 | 2010-11-18 | Ortloff Engineers, Ltd. | Liquefied natural gas and hydrocarbon gas processing |
WO2010132679A1 (en) * | 2009-05-15 | 2010-11-18 | Ortloff Engineers, Ltd. | Liquefied natural gas and hydrocarbon gas processing |
WO2012058342A2 (en) * | 2010-10-26 | 2012-05-03 | Kirtikumar Natubhai Patel | Process for separating and recovering ngls from hydrocarbon streams |
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