US20080314079A1 - Nitrogen Rejection Column Reboiler Configuration - Google Patents

Nitrogen Rejection Column Reboiler Configuration Download PDF

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Publication number
US20080314079A1
US20080314079A1 US11/764,975 US76497507A US2008314079A1 US 20080314079 A1 US20080314079 A1 US 20080314079A1 US 76497507 A US76497507 A US 76497507A US 2008314079 A1 US2008314079 A1 US 2008314079A1
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Prior art keywords
stream
lng
column
nitrogen
heat exchanger
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US11/764,975
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English (en)
Inventor
Adam Adrian Brostow
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Air Products and Chemicals Inc
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Air Products and Chemicals Inc
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Priority to US11/764,975 priority Critical patent/US20080314079A1/en
Assigned to AIR PRODUCTS AND CHEMICALS, INC. reassignment AIR PRODUCTS AND CHEMICALS, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BROSTOW, ADAM ADRIAN
Priority to PCT/IB2008/001742 priority patent/WO2008155653A2/fr
Priority to CA002687886A priority patent/CA2687886A1/fr
Priority to RU2010101417/06A priority patent/RU2010101417A/ru
Priority to CN200880020926XA priority patent/CN102084199A/zh
Priority to KR1020097025820A priority patent/KR20100021443A/ko
Priority to AU2008264885A priority patent/AU2008264885A1/en
Priority to EP08762994A priority patent/EP2179235A2/fr
Priority to BRPI0812568-6A2A priority patent/BRPI0812568A2/pt
Priority to JP2010512805A priority patent/JP2011513503A/ja
Priority to TW097122607A priority patent/TW200902703A/zh
Priority to PE2008001043A priority patent/PE20090450A1/es
Publication of US20080314079A1 publication Critical patent/US20080314079A1/en
Abandoned legal-status Critical Current

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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
    • 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
    • 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
    • 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
    • F25J3/0257—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of nitrogen
    • 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
    • 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
    • F25J2200/40—Features relating to the provision of boil-up in the bottom of a column
    • 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
    • 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
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/04—Recovery of liquid products
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/30—Dynamic liquid or hydraulic expansion with extraction of work, e.g. single phase or two-phase turbine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/40—Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/02—Bath type boiler-condenser using thermo-siphon effect, e.g. with natural or forced circulation or pool boiling, i.e. core-in-kettle heat exchanger
    • 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
    • F25J2270/02—Internal refrigeration with liquid vaporising loop

Definitions

  • This invention relates to a process for the separation of nitrogen from a liquid natural gas stream comprising nitrogen, methane, and possibly heavier hydrocarbons.
  • Crude natural gas is often liquefied to enable storage of larger quantities in the form of liquid natural gas (LNG). Because natural gas may be contaminated with nitrogen, nitrogen is advantageously removed from LNG to produce a nitrogen-diminished LNG product that will meet desired product specifications. Several methods of effectuating nitrogen removal from LNG have been disclosed in the prior art.
  • One simple method for separating nitrogen from a LNG stream is to isentropically expand the crude LNG stream in a turbine and then inject the stream into a flash separator.
  • the liquid product removed from the flash separator will contain less nitrogen than the crude LNG stream, whereas the vapor product will contain a higher proportion of nitrogen.
  • a liquid stream is withdrawn and passed through the heat exchanger to cool the feed and then reinjected into the column at a level below that at which it had been withdrawn, to provide boilup to the column.
  • the passage of the withdrawn stream through the heat exchanger provides an additional equilibrium stage of separation.
  • a similar method for separating nitrogen from an LNG stream replaces the turbine driven dynamic decompression with a valve for static decompression, such that the expansion takes place isenthalpically rather than isentropically.
  • the use of the isentropic expansion in the process of the '165 patent allegedly permits greater methane recovery.
  • the sump of the column is divided by a baffle, one side of which is filled with liquid from the lowest tray of the column.
  • This bottoms liquid is withdrawn and at least partially vaporized in the heat exchanger, while condensing the vapor stream from the phase separator, and returned to the column as a reflux stream to provide boilup.
  • the liquid remaining in the reflux stream falls to the other side of the baffle in the sump.
  • This liquid reflux is then removed as a nitrogen-diminished product stream, pumped to a higher pressure, warmed and vaporized, and then dynamically expanded to reduce the temperature and pressure of the vapor product. Similar to the reboiler heat exchange of the '165 patent, the reflux of the bottoms liquid serves as an additional equilibrium stage of separation.
  • Another similar, but thermodynamically distinct method of nitrogen separation involves isentropically expanding the crude LNG stream in a turbine, cooling the expanded stream in a reboiler heat exchanger, and then injecting the cooled, expanded stream into a thermosiphon system.
  • the liquid from the bottom of the column is withdrawn, and a portion of it is withdrawn and pumped away as the LNG product.
  • a second portion is recycled through the reboiler heat exchanger where it is at least partially vaporized.
  • the partially vaporized stream is then reinjected into the column, where the vapor portion of the stream provides boilup; the liquid portion of the stream mixes with the liquid coming off the bottom tray to provide the source of the withdrawn bottoms stream.
  • a disadvantage of these prior art nitrogen separation methods is that they are each dependent upon liquid head to drive the flow of the reboiler stream.
  • This attribute has the adverse effect of limiting the flexibility of the overall process design.
  • the available head of the column will directly affect the design of the reboiler heat exchanger, wherein the pressure drop within the heat exchanger cannot be so great as to overcome the available flow.
  • This design limitation tends to result in the implementation of larger, more expensive heat exchangers that will have a lower pressure drop, thus allowing the column's head to drive the reboiler flow.
  • the large capital costs of the process equipment required to effectuate nitrogen removal can have a substantial effect on the profitability of the production of LNG.
  • the present invention provides an improved process for the denitrogenation of an LNG stream contaminated by nitrogen. This process allows for economic benefits by permitting a greater flexibility in the process design.
  • a crude LNG stream comprising between about 1% and 10% nitrogen, and the remainder methane and heavier hydrocarbons, is expanded in a means for expansion, and cooled in a reboiler heat exchanger.
  • the resultant crude LNG stream is introduced into a nitrogen rejection column, wherein the nitrogen content of the LNG is reduced as the liquid flows down the column.
  • a nitrogen-enriched vapor stream is withdrawn from the top of the column, and a nitrogen-diminished liquid stream is withdrawn from the bottom of the column.
  • the nitrogen-diminished bottoms LNG stream is pumped to a higher pressure and then divided into two streams, and the first stream may be collected as an LNG product if desired.
  • the second stream is reduced in pressure and then passed through the reboiler heat exchanger, thus cooling the crude LNG stream, the pressure reduction being to a level such that the second stream is at least partially vaporized in the reboiler heat exchanger.
  • the partially vaporized second stream is reinjected into the column at a level above the level of withdrawal of the nitrogen-diminished bottoms LNG stream and below the level of introduction of the crude LNG feed stream to provide column boilup.
  • the initial crude LNG stream is expanded in a dense fluid expander, which may be placed either upstream or downstream of the reboiler heat exchanger.
  • the reduction in pressure of the second stream may be accomplished through the use of a Joule-Thomson valve.
  • a valve may also be placed immediately upstream of the nitrogen rejection column, such that the crude LNG stream is throttled through the valve prior to injection into the column.
  • FIG. 1 is a schematic diagram illustrating a process for removing nitrogen from an LNG stream in accordance with one embodiment of the present invention.
  • the present invention achieves flexibility of design and process economic advantages in an LNG denitrogenation operation by using, in part, a pump to drive the reboiler stream, thus permitting a higher pressure drop within the reboiler heat exchanger. This, in turn, allows a higher velocity for the reboiler stream, and, consequently, higher heat transfer coefficients in the heat exchanger can be realized, permitting the use of a smaller heat exchanger.
  • thermodynamic inefficiency As will be clarified in the following description, achieving this flexibility without the need for additional equipment, and maintaining output levels and energy requirements, involves the introduction of a small thermodynamic inefficiency.
  • the initial capital savings afforded by the present invention more than compensates for this thermodynamic inefficiency, especially given the ease and low expense with which it may be remedied.
  • nitrogen-enriched stream is used herein to mean a stream containing a higher concentration of nitrogen when compared with an initial feed stream.
  • nitrogen-diminished stream is used herein to mean a stream containing a lower concentration of nitrogen when compared with an initial feed stream.
  • below is used herein to mean at a position of lesser height, i.e., closer to the ground.
  • FIG. 1 A preferred embodiment of the invention will now be described in detail with reference to FIG. 1 .
  • the following embodiments are not intended to limit the scope of the invention, and it should be recognized by those skilled in the art that there are other embodiments within the scope of the claims.
  • high-pressure LNG stream 100 is expanded via means for expanding the LNG stream 102 to produce lower-pressure LNG stream 104 .
  • the expansion is preferably performed isentropically, and the means for expanding the LNG stream is preferably a dense fluid expander (also known as a hydraulic turbine), but may also be a valve or other known means for expanding a fluid.
  • Lower-pressure LNG stream 104 is cooled in reboiler heat exchanger 106 to produce cooled, expanded LNG stream 108 .
  • Reboiler heat-exchanger 106 is preferably a plate-fin heat exchanger, but may be a shell-and-tube design, or any other known means for bringing two fluid streams into a heat exchange relation with each other, without mixing the fluids. Cooled, expanded LNG stream 108 is then substantially isenthalpically expanded through valve 109 and injected into nitrogen rejection column 150 , this injection preferably taking place at the top of the column. Nitrogen rejection column 150 is preferably a tray column, but may be a packed column or any other mass transfer device suitable for fractionation. A nitrogen-enriched vapor stream 130 is withdrawn from the top of column 150 . By “nitrogen-enriched,” it is herein understood to mean containing a higher concentration of nitrogen than that of high-pressure LNG stream 100 , and will typically contain more than about 30% N 2 and less than about 70% methane.
  • Nitrogen-diminished liquid stream 110 is withdrawn from the bottom of column 150 and pumped through pump 112 to a desired pressure.
  • nitrogen-diminished it is herein understood to mean containing a lower concentration of nitrogen than that of high-pressure LNG stream 100 .
  • Stream 114 may be recovered as a product LNG stream.
  • Stream 116 is substantially isenthalpically expanded through valve 117 , typically a Joule-Thomson valve, to produce low-pressure reboiler stream 118 .
  • Valve 117 may be located at any position between the point of separation of streams 114 and 116 and the reboiler heat exchanger 106 .
  • Low-pressure reboiler stream 118 is at least partially vaporized in reboiler heat exchanger 106 to produce partially vaporized reboiler stream 120 , which is then injected into the bottom of column 150 , below the lowest tray in the case of a tray column, or below the packing material in the case of a packed column, to provide boilup.
  • the means for expanding the LNG stream 102 may be placed downstream of reboiler heat exchanger 106 . In this manner, high-pressure stream 100 is cooled in reboiler heat exchanger 106 prior to undergoing expansion in the means for expanding the LNG stream 102 .
  • valve 109 is optional, and, in the alternative, cooled LNG stream 108 can be directly injected into nitrogen rejection column 150 .
  • a particularly preferred embodiment is herein provided wherein a crude LNG stream 100 is substantially isentropically expanded in a dense fluid expander 102 and cooled in a reboiler heat exchanger 106 .
  • This cooled, expanded LNG stream 108 is substantially isenthalpically expanded through valve 109 and injected into a nitrogen rejection column 150 .
  • rising vapor strips the nitrogen from the falling liquid, and a nitrogen-enriched stream 130 is withdrawn from the top of the column.
  • a nitrogen-diminished liquid stream 110 is withdrawn from the bottom of the column and its pressure is increased by passage through a pump 112 . After pumping, the liquid stream is divided into a first stream 114 and a second stream 116 .
  • the second stream 116 is reduced in pressure by passage through a valve 117 to a pressure that allows low-pressure reboiler stream 118 to at least partially vaporize during its subsequent passage through the reboiler heat exchanger 106 .
  • the reboiler stream 120 is reinjected into the nitrogen rejection column 150 to provide boilup.
  • the liquid portion of the reboiler stream mixes with the liquid from the lowest column stage upon reinjection such that the nitrogen-diminished liquid stream 110 is not exclusively the liquid from the bottom stage of the rejection column 150 , or from the reboiler 106 , but rather a mixture of both.
  • this can easily and cheaply be compensated for by the addition of a stage or stages to the nitrogen rejection column 150 .
  • the flow through the reboiler heat exchanger 106 is driven by a pump 112 that would already be available to pump the LNG product, first stream 114 .
  • the reboiler heat exchanger 106 can be designed for a broad range of pressure drops based on considerations such as capital cost, and the appropriate pressure of the reboiler stream 118 can be attained by adjusting valve 117 upstream of the reboiler heat exchanger 106 .
  • the flow rate of the second stream 116 can be any amount up to the total flow of the nitrogen-diminished liquid stream 110 , but is preferably less than about 20% of the flow rate of the first stream 114 , and may be easily optimized for the particular process. This is in contrast with the process of the '165 patent, which requires 100% of the liquid flow off of a tray to be directed through the reboiler.
  • the smaller flow rate of the reboiler stream compared with the prior art allows the reboiler heat exchanger 106 to be reduced in size.
  • the present invention has the additional advantage of eliminating the nozzle required for the withdrawal of the reboiler liquid stream from the column, since bottoms liquid that would be withdrawn anyway as LNG product is employed for column reboil.
  • the present invention provides a significant improvement in the adaptability and flexibility of a LNG denitrogenation process through the implementation of a hydraulically different process from those of the prior art.
  • a pump 112 to drive the reboiler heat exchanger 106 , rather than relying on the column head, and including the valve 117 to control mass flow, the process may be designed to optimally perform in conjunction with a chosen reboiler heat exchanger 106 design. This flexibility can lead to a smaller capital expense at the remediable cost of a minor thermodynamic loss.
  • process simulations were run, using an ASPEN process simulator, comparing an embodiment of the invention (“current process”) with the process disclosed in the '165 patent.
  • the comparison basis is an equal LNG production and a satisfied fuel balance (the amount of LNG product flash required to drive a gas turbine driving the process).
  • the respective reference numerals used in this example refer to FIG. 1 , as described above, and the '165 patent (see, e.g., FIG. 1 therein).
  • low pressure LNG stream 104 following expansion in dense fluid expander 102 , low pressure LNG stream 104 , at a flow rate of 125,450 lbmol/hr, a pressure of 71.62 psi, a temperature of ⁇ 243° F., and containing 2.96% N 2 , 95.47% methane, 1.10% C 2 hydrocarbons, and 0.47% heavier hydrocarbons, is cooled in reboiler heat exchanger 106 to produce cooled, expanded LNG stream 108 at a temperature of ⁇ 252.5° F. Cooled, expanded stream 108 is throttled through valve 109 and introduced into a denitrogenation column 150 comprising 6 trays, at a pressure of 18 psi.
  • An overhead vapor stream 130 is withdrawn from the top of the column 150 at a flow rate of 8,123 lbmol/hr, and contains 31.06% N 2 , 68.94% methane, and trace amounts of heavier hydrocarbons, at a pressure of 18 psi and a temperature of ⁇ 261.9° F.
  • Bottoms stream 110 is withdrawn from the column 150 at a flowrate of 136,071 lbmol/hr, a pressure of 19.45 psi, a temperature of ⁇ 256.8° F., and contains 1.01% N 2 , 97.31% methane, 1.17% C 2 hydrocarbons, and 0.51% heavier hydrocarbons.
  • Bottoms stream 110 is pumped to a pressure of 75 psi and divided into a first stream 114 and a second stream 116 .
  • the first stream 114 at a flow rate of 117,327 lbmol/hr, a pressure of 75 psi, a temperature of ⁇ 256.6° F., and containing 1.01% N 2 , 97.31% methane, 1.17% C 2 hydrocarbons, and 0.51% heavier hydrocarbons, is recovered as the final LNG product.
  • the second stream 116 at a flow rate of 18,744 lbmol/hr is throttled through valve 117 to a pressure of 19.74 psi to produce low pressure reboiler stream 118 , which is then introduced to reboiler heat exchanger 106 at a temperature of ⁇ 256.4° F., where it is partially vaporized to produce vaporized reboiler stream 120 .
  • Vaporized reboiler stream 120 which is at a temperature of ⁇ 252.7° F., a pressure of 19.45 psi, and has a vapor fraction of 23.7%, is injected into the bottom of column 150 to provide boilup. This process requires approximately 229 MW of power.
  • An overhead vapor stream 10 is withdrawn from the top of the column 5 at a flow rate of 8,122 lbmol/hr, and contains 31.17% N 2 , 68.83% methane, and trace amounts of heavier hydrocarbons, at a pressure of 18 psi and a temperature of ⁇ 261.9° F.
  • Bottoms stream 11 is withdrawn from the column 5 at a flowrate of 117,329 lbmol/hr, a pressure of 19.45 psi, a temperature of ⁇ 256.8° F., and contains 1.01% N2, 97.32% methane, 1.17% C 2 hydrocarbons, and 0.50% heavier hydrocarbons.
  • First LNG fraction 6 is withdrawn from the lowest tray of the column at a flow rate of 121,047 lbmol/hr, a temperature of ⁇ 259.7° F., a pressure of 19.74 psi, and contains 1.56% N 2 , 96.81% methane, 1.14% C 2 hydrocarbons, and 0.49% heavier hydrocarbons.
  • This first LNG fraction 6 is passed through indirect heat exchanger 2 to produce stream 7 , which is at a temperature of ⁇ 256.8° F., a pressure of 19.45 psi, and has a vapor fraction of 3.1%.
  • Stream 7 is returned to column 5 under the lowest tray to provide boilup. This process also requires approximately 229 MW of power.
  • Table 1 sets forth data of corresponding streams of these two processes in order to more clearly illustrate the comparison.
  • the respective feed streams, 104 and 22 , and the respective product streams, 114 and 11 , and 130 and 10 are substantially identical with respect to all relevant properties. This equivalency of feed streams and product streams enables a valid comparison of the two processes.
  • a significant difference between the two processes is that the reboiler stream of the current process 118 is at a flow rate of 18,744 lbmol/hr, which is only 15.5% of the flow rate of the reboiler stream 6 of the '165 patent process, 121,047 lbmol/hr.
  • This difference is attributable to the fact that, while the '165 patent process requires that the entire liquid flow off of a column tray be recycled through the reboiler heat exchanger, the current process optimizes the amount of flow necessary to achieve the desired separation, and therefore only recycles the amount of bottoms liquid necessary to produce the required product.
  • valve 117 can be adjusted to compensate for a greater pressure drop in the heat exchanger. This additional flexibility may be reflected not only in the initial design of the heat exchanger, but also may be advantageously employed to compensate for unexpected process conditions.

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  • Engineering & Computer Science (AREA)
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  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
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  • Oil, Petroleum & Natural Gas (AREA)
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US11/764,975 2007-06-19 2007-06-19 Nitrogen Rejection Column Reboiler Configuration Abandoned US20080314079A1 (en)

Priority Applications (12)

Application Number Priority Date Filing Date Title
US11/764,975 US20080314079A1 (en) 2007-06-19 2007-06-19 Nitrogen Rejection Column Reboiler Configuration
JP2010512805A JP2011513503A (ja) 2007-06-19 2008-06-16 窒素除去塔リボイラーの構成
AU2008264885A AU2008264885A1 (en) 2007-06-19 2008-06-16 Nitrogen rejection column reboiler configuration
CA002687886A CA2687886A1 (fr) 2007-06-19 2008-06-16 Configuration de rebouilleur d'une colonne de rejet d'azote
RU2010101417/06A RU2010101417A (ru) 2007-06-19 2008-06-16 Конструкция ребойлера колонны деазотирования
CN200880020926XA CN102084199A (zh) 2007-06-19 2008-06-16 脱氮气塔再沸器构造
KR1020097025820A KR20100021443A (ko) 2007-06-19 2008-06-16 질소 제거 칼럼의 리보일러 구조
PCT/IB2008/001742 WO2008155653A2 (fr) 2007-06-19 2008-06-16 Configuration de rebouilleur d'une colonne de rejet d'azote
EP08762994A EP2179235A2 (fr) 2007-06-19 2008-06-16 Configuration de rebouilleur d'une colonne de rejet d'azote
BRPI0812568-6A2A BRPI0812568A2 (pt) 2007-06-19 2008-06-16 Processo para a desnitrogenação de uma corrente de alimentação de gás natural liquefeito (gnl), equipamento para o desnitrogenação de uma corrente de alimentação de gás natural liquefeito (gnl) por meio de processo
TW097122607A TW200902703A (en) 2007-06-19 2008-06-17 Nitrogen rejection column reboiler configuration
PE2008001043A PE20090450A1 (es) 2007-06-19 2008-06-18 Configuracion de caldera para columna de eliminacion de nitrogeno

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US11/764,975 US20080314079A1 (en) 2007-06-19 2007-06-19 Nitrogen Rejection Column Reboiler Configuration

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EP (1) EP2179235A2 (fr)
JP (1) JP2011513503A (fr)
KR (1) KR20100021443A (fr)
CN (1) CN102084199A (fr)
AU (1) AU2008264885A1 (fr)
BR (1) BRPI0812568A2 (fr)
CA (1) CA2687886A1 (fr)
PE (1) PE20090450A1 (fr)
RU (1) RU2010101417A (fr)
TW (1) TW200902703A (fr)
WO (1) WO2008155653A2 (fr)

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US8522574B2 (en) * 2008-12-31 2013-09-03 Kellogg Brown & Root Llc Method for nitrogen rejection and or helium recovery in an LNG liquefaction plant
CN102994184B (zh) * 2012-12-03 2013-10-30 中国石油集团工程设计有限责任公司 一种液化天然气联产液氮的装置及方法
WO2017105679A1 (fr) * 2015-12-14 2017-06-22 Exxonmobil Upstream Research Company Procédé et système pour séparer l'azote d'un gaz naturel liquéfié à l'aide d'azote liquéfié
FR3075658B1 (fr) * 2017-12-21 2022-01-28 Air Liquide Procede de limitation de la concentration d'oxygene contenu dans un courant de biomethane
US11221176B2 (en) * 2018-08-14 2022-01-11 Air Products And Chemicals, Inc. Natural gas liquefaction with integrated nitrogen removal
US20200378682A1 (en) * 2019-05-29 2020-12-03 Uop Llc Use of dense fluid expanders in cryogenic natural gas liquids recovery

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TW200902703A (en) 2009-01-16
WO2008155653A2 (fr) 2008-12-24
JP2011513503A (ja) 2011-04-28
AU2008264885A1 (en) 2008-12-24
CA2687886A1 (fr) 2008-12-24
WO2008155653A3 (fr) 2011-04-07
EP2179235A2 (fr) 2010-04-28
RU2010101417A (ru) 2011-07-27
BRPI0812568A2 (pt) 2015-02-18
PE20090450A1 (es) 2009-04-27
CN102084199A (zh) 2011-06-01
KR20100021443A (ko) 2010-02-24

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