US20140060114A1 - Configurations and methods for offshore ngl recovery - Google Patents

Configurations and methods for offshore ngl recovery Download PDF

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US20140060114A1
US20140060114A1 US14/014,226 US201314014226A US2014060114A1 US 20140060114 A1 US20140060114 A1 US 20140060114A1 US 201314014226 A US201314014226 A US 201314014226A US 2014060114 A1 US2014060114 A1 US 2014060114A1
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absorber
natural gas
stream
fractionator
overhead product
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John Mak
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Fluor Technologies Corp
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Fluor Technologies Corp
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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
    • 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
    • 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
    • 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
    • F25J3/0242—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 3 carbon atoms 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/04—Processes or apparatus using separation by rectification in a dual 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
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
    • F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
    • 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
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
    • 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
    • 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
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/72—Processing device is used off-shore, e.g. on a platform or floating on a ship or barge

Definitions

  • the field of the invention is removal and recovery of natural gas liquids (NGL) from feed gases to meet pipeline hydrocarbon dew point and heating value specifications, especially for offshore applications.
  • NTL natural gas liquids
  • Numerous NGL processing plants with high NGL recovery from a feed gas include cryogenic fractionation and turbo-expansion processes as described in U.S. Pat. No. 4,157,904 to Campbell et al., U.S. Pat. No. 4,251,249 to Gulsby, U.S. Pat. No. 4,617,039 to Buck, U.S. Pat. No. 4,690,702 to Paradowski et al., U.S. Pat. No. 5,275,005 to Campbell et al., U.S. Pat. No. 5,799,507 to Wilkinson et al., and U.S. Pat. No. 5,890,378 to Rambo et al., and U.S. Pat. App. No.
  • NGL recovery processes use high expansion ratio turboexpanders to produce low levels of refrigeration, which requires recompression of the residue gas.
  • additional external refrigeration is often required.
  • process configurations are complex and are difficult to operate.
  • Campbell et al. describe in U.S. Pat. No. 6,182,469 a plant in which feed gas is cooled in a heat exchanger using cold residue gas and side reboilers as depicted in Prior Art FIG. 1 .
  • the condensed feed gas liquids are then separated in a separator and fed to the demethanizer.
  • an absorber may be added upstream of a demethanizer as depicted in Prior Art FIG. 2 .
  • the liquids from the feed separator and the absorber bottoms are fed to the demethanizer.
  • the absorber overhead is cooled and refluxed by chilling with the demethanizer overhead vapor.
  • the inventive subject matter is directed to configurations and methods of recovery of C4 and heavier hydrocarbons, and moderate recovery (up to 90%) of C3 from a gas stream to meet hydrocarbon dew point and heating value specification of a pipeline gas produced from the gas stream.
  • two columns are operated at different pressures with the first column (absorber) operating at a relatively high pressure of about 550 psig and with the second column (fractionator) operating at about 450 psig.
  • the absorber By operating the absorber at relatively high pressure, the compression ratio of the residue gas is reduced, thereby minimizing the overall compression horsepower.
  • the fractionator operating at about 450 psig, it should be noted that the separation of methane from the ethane and heavier components can be accomplished with less heating requirement due to the favorable relative volatility between components, resulting in a smaller diameter column.
  • the vapor stream from the fractionator overhead is advantageously utilized for stripping in the absorber.
  • the fractionator overhead stream is compressed and the “free” heat of compression is used to efficiently remove the methane components from the NGL from the absorber.
  • the liquid portion of the expander discharge is used as reflux to the absorber, which is entirely different from heretofore known configurations and methods, which require the expander discharge to be fed to the mid or the lower section of the absorber, as illustrated in FIGS. 1-4 .
  • the expander discharge typically contains about 80% vapor, and by feeding the vapor portion in the top of the absorber, the vapor traffic in the mid- and lower portion of the absorber is significantly reduced, and hence the size of the absorber is smaller.
  • the column has to be designed to handle the total flow, and not just the liquid flow as presented herein.
  • the size of the absorber in a currently known gas plant is typically 12 ft in diameter for a 1,000 MMscfd feed gas as compared to the absorber size of 10 ft in diameter using configurations and methods presented herein, which significantly reduces space requirement, associated equipment cost and weight, which are of primary importance in an offshore environment.
  • the second fractionator operates at a lower pressure and temperature, which is not only more efficient in terms of separation, but also allows the use of residue gas compression heat for reboiling the fractionator, thereby eliminating steam requirement or hot oil heating of heretofore known systems and methods.
  • the fractionator is operated at a pressure between 450 to 550 psig, and that the overhead vapor is compressed to the absorber pressure that is at least 50 psi, and more typically at least 100 psi, and mostly typically at 155 psi higher than the absorber, and that the compressor discharge vapor has a temperature and volume that is sufficient for use as a stripping vapor to the absorber.
  • contemplated methods will also include a step of expanding the vapor phase in a turbo expander and reducing pressure of the liquid phase in a second expansion device before feeding the liquid phase to a feed exchanger. While not limiting to the inventive subject matter, it is typically preferred that the feed gas cooling is performed without use of external refrigeration. In yet another step, the bottom of the absorber is also letdown in pressure via a JT valve providing additional chilling to the feed gas in the feed exchanger.
  • a processing plant for hydrocarbon dew point control of a natural gas feed gas delivered from a feed gas source will include a feed gas exchanger that is fluidly coupled to the feed gas source and configured to cool the feed gas using a liquid phase of the cooled feed gas and an bottom product of an absorber.
  • Contemplated plants will also include a phase separator that is fluidly coupled to the feed gas exchanger and that is configured to separate the cooled feed gas into the liquid phase and a vapor phase.
  • the fractionator comprises a top section that is configured to produce a vapor phase that is compressed and used as a stripping gas in the absorber.
  • FIG. 1 is a schematic of one known configuration for NGL recovery in which feed gas is cooled in a heat exchanger using cold residue gas and side reboilers.
  • FIG. 2 is a schematic of another known configuration for NGL recovery in which an absorber/fractionator column is positioned upstream of a demethanizer.
  • FIG. 3 is a schematic of yet another known configuration for NGL recovery in which reboiler and feed gas compression are integrated in feed chilling.
  • FIG. 4 is a schematic of a further known configuration for NGL recovery in which reboiler and compressed residue gas recycle are integrated in feed chilling.
  • FIG. 5 is a schematic of an exemplary configuration for NGL recovery according to the inventive subject matter.
  • FIG. 6 is a table listing calculated compositions of gas streams in the exemplary NGL recovery plant of FIG. 5 .
  • the inventor has discovered various configurations and methods of NGL recovery in which capital and operating cost can be significantly reduced, and especially in offshore applications, where a rich feed gas is processed and where C4+ recovery with moderate C2 and C3 recovery is required.
  • contemplated configurations and methods significantly reduce complexity and cost by reducing the number of equipment services, by elimination of external refrigeration and external heating while lowering residue gas compression requirements.
  • the feed gas (typically a natural gas comprising C1, C2, C3, and C4, and heavier components) is cooled at relatively high pressure to thereby effect partial condensation.
  • the vapor and liquid phases are then separated, with the liquid phase being expanded to a lower pressure to so provide cooling to the feed gas.
  • the liquid phase is fed to the lower section of a fractionation column, while the vapor phase is expanded via a turboexpander and fed into the top section of a first fractionator (absorber).
  • relatively high pressures typically 550 to 650 psig
  • residue gas recompression requirements are significantly reduced.
  • FIG. 5 One exemplary plant configuration is depicted in FIG. 5 , in which wet feed gas 1 at a pressure of about 1,000 psig and a temperature of about 100° F., having a typical composition as shown in the table of FIG. 6 , is dried in a molecular sieve drier 51 , forming stream 2 .
  • the so dried gas stream 2 is cooled to a temperature of about ⁇ 65° F. in exchanger 52 , forming stream 3 , utilizing the refrigeration content from residue gas stream 9 and liquid streams 6 and 11 .
  • the so chilled gas stream 3 is then separated in phase separator 53 into a liquid portion, stream 5 , and a vapor portion, stream 4 .
  • the liquid portion 5 is letdown in pressure via JT valve 54 to a pressure of about 475 psig, chilled to about ⁇ 106° F. forming stream 6 , which is heated in exchanger 52 to about 70° F. prior to entering as stream 7 to the lower section of fractionator 59 .
  • the vapor portion 4 is expanded via the turboexpander 55 to about 550 psig at about ⁇ 109° F. to form stream 8 , which is fed to the top of absorber 70 .
  • the term “about” in conjunction with a numeral refers to a range of that numeral starting from 20% below the absolute of the numeral to 20% above the absolute of the numeral, inclusive.
  • turboexpander 55 the energy of expansion of gas within the turboexpander 55 may used to drive compressor 56 or other device to recover expansion energy. In some embodiments, the energy of expansion in turboexpander 55 can be used to also drive compressor 57 .
  • the vapor portion 4 is being expanded via the turboexpander 55 in such a way that partially condenses vapor portion 4 to produce a two-phase stream 8 comprising a vapor phase and a liquid phase.
  • at least 5 vol. % of stream 8 is in the vapor phase.
  • at least 10 vol. % of stream 8 is in the vapor phase.
  • at least 20 vol % of stream 8 is in the vapor phase.
  • at least 30 vol % of stream 8 is in the vapor phase.
  • at least 40 vol % of stream 8 is in the vapor phase.
  • at least 60 vol % of stream 8 is in the vapor phase.
  • At least 80 vol % of stream 8 is in the vapor phase.
  • the remainder of the expanded stream is in the liquid phase to serve as a reflux stream. Therefore, in some embodiments, at least 5 vol % of stream 8 is in a liquid phase. In yet some embodiments, at least 20 vol % of stream 8 is in a liquid phase. In yet some other embodiments, at least 30 vol % of stream 8 is in a liquid phase. In yet some embodiments, at least 40 vol % of stream 8 is in a liquid phase. In yet some embodiments, at least 60 vol % of stream 8 is in a liquid phase. In yet some embodiments, at least 80 vol % of stream 8 is in a liquid phase.
  • the operating pressure of the absorber 70 is in the range of about 550 to about 650 psig or higher, and the top section temperature is about ⁇ 100° F., and the bottom section is about ⁇ 15° F. It should be noted that only the liquid portion from the expander discharge is used as the reflux and the vapor portion forms part of the residue gas.
  • the absorber is stripped with hot compressor discharge stream 16 from the fractionator column 59 .
  • the overhead gas stream 9 comprises the residue gas from the absorber 70 and at least some of the vapor portion of stream 8 .
  • overhead gas stream 9 has a methane content of about 95 mol %.
  • Overhead gas stream 9 that comes out of absorber 70 has a low temperature (at about ⁇ 100° F.), and the refrigeration content of the overhead gas stream 9 is used to chill natural gas feed 2 .
  • the absorber bottom stream 10 is letdown in pressure to about 450 psig and chilled to ⁇ 14° F., forming stream 11 , and the refrigerant content is used to chill the feed gas in exchanger 52 to form stream 21 .
  • the heated gas is flashed to the top of the fractionator column 59 .
  • the warmed gas stream 17 that comes out of the heat exchanger 52 is being compressed by compressor 56 , and turns into compressed gas stream 18 .
  • gas stream 18 is further compressed by compressor 57 to form compressed gas stream 19 , which is used for reboiling products from the fractionator 59 in reboiler 62 .
  • So cooled residue gas stream 15 is then fed to air cooler 58 prior to leaving the plant as residue gas stream 20 (e.g., as pipeline gas). It should be recognized that such configuration does not require external heating or fuel gas heater while producing on spec product which is advantageous for offshore operation and eliminating noxioius or otherwise undesireable emissions.
  • Fractionator 59 uses reboiler 62 to maintain the methane content in the bottom liquid stream 12 to preferably no more than 2 mol % or as required to meet the vapor pressure specification of the NGL product. Because of the relatively low operating pressure in the fractionator, the reboiler can use the low temperature compression heat from the residue gas compressor discharge stream 19 for reboiling fractionator bottom product 13 , eliminating external heating requirement.
  • the fractionator 59 is configured to produce a fractionator overhead product 14 that is passed to compressor 63 . As mentioned above, the compressed stream 16 is then passed into the bottom section of the absorber 70 , while a portion of the bottom product leaves as C2+ NGL product stream 12 .
  • suitable feed gases will include C1, C2 and C3+, and may further comprise N2 and CO2. Consequently, it should be appreciated that the nature of the feed gas may vary considerably, and all feed gases in plants are considered suitable feed gases no long as they comprise C1 and C3 components, and more typically C1 to C5 and heavier components, and most typically C1 to C6 and heavier components. Therefore, particularly preferred feed gases include natural gas (e.g., after regasification from LNG, after CO2 removal where produced from a gas well), refinery gas, and synthetic gas streams obtained from other hydrocarbon materials such as coal, crude oil, naphtha, oil shale, tar sands, and lignite.
  • natural gas e.g., after regasification from LNG, after CO2 removal where produced from a gas well
  • refinery gas e.g., after regasification from LNG, after CO2 removal where produced from a gas well
  • synthetic gas streams obtained from other hydrocarbon materials such as coal, crude oil, naphtha, oil shale
  • Suitable gases may also contain relatively lesser amounts of heavier hydrocarbons such as propane, butanes, pentanes and the like, as well as hydrogen, nitrogen, carbon dioxide and other gases.
  • the pressure of the feed gas may vary. However, it is generally preferred that the feed gas has a pressure between about 700 psig to about 1400 psig, and more typically between about 900 psig to about 1200 psig.
  • contemplated configurations and methods use a single fractionator to recover at least 95% of the C4 and heavier hydrocarbons, and 60% to 80% of the C3 component, and 20% to 50% C2 component, without the use of external refrigeration. Therefore, it should be noted that feed gas cooling and/or cooling of the vapor product are performed without use of external refrigeration (e.g., at least 90% of refrigeration requirements are produced from expansion of process streams). It should also be recognized that white a single column configuration can also be used with two separate columns stacked on top of each other, with functions corresponding to the absorber and fractionator are also deemed suitable for use herein. It is still further contemplated that the dryer, separator, fractionator, heat exchanger, JT-valves, residue gas compressor, and turboexpander used in present configurations and methods are conventional devices well known to the skilled artisan.
  • the phase separator produces a C5+ enriched liquid and a C5+ depleted vapor from a feed gas.
  • C5 enriched liquids may advantageously be fractionated in the lower section of the fractionator to meet the product liquid specification.
  • contemplated configurations and processes allow handling of a rich feed gas composition, thereby eliminating the complexity of a refrigeration unit of most prior arts.
  • contemplated processes maintain constant operating conditions for the NGL recovery plant by removal of the C5+ components in the feed gas.
  • contemplated configurations will achieve at least 60%, and more typically 78% propane recovery, and at least 85%, and more typically 95% butane recovery (see FIG. 6 ).
  • Further contemplations, configurations, and methods suitable for use herein are described in U.S. Pat. Nos. 6,601,406, 6,837,7070, 7,051,552, 7,051,552 and 7,377,127, all of which are incorporated by reference herein.
  • a natural gas processing plant does not have to include all of the features described above to achieve efficiency in NGL recovery.
  • a natural processing plant may include only a subset of the features described above. In some of these embodiments, the natural processing, plant may also include additional features that are not disclosed herein.
  • a natural gas processing plant of some embodiments may include a turboexpander and an absorber.
  • the turboexpander is configured to reduce pressure of a vapor stream to generate a two-phase stream having a liquid phase and a vapor phase.
  • the absorber is configured to receive the two phase stream in a position such as to allow use of the liquid phase as a reflux.
  • the absorber is further configured to produce an absorber overhead product and an absorber bottom product.
  • the vapor stream that enters into the turboexpander comprises natural gas feed that is cooled by a heat exchanger.
  • the absorber overhead product is led back into the heat exchanger in which refrigeration content of the absorber overhead product is used to chill the natural gas stream.
  • the absorber overhead product is being compressed and used to reboil content within a fractionator.
  • the vapor stream that enters into the turboexpander comprises natural gas feed that is cooled by a heat exchanger.
  • the absorber bottom product is recycled back into the heat exchanger in which refrigeration content of the absorber bottom product is used to chill the natural gas stream.

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