EP0054367A2 - Verfahren und Vorrichtung zur Abtrennung von Leichtfraktionen aus einem Einsatzgemisch aus Kohlenwasserstoffen - Google Patents

Verfahren und Vorrichtung zur Abtrennung von Leichtfraktionen aus einem Einsatzgemisch aus Kohlenwasserstoffen Download PDF

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Publication number
EP0054367A2
EP0054367A2 EP81305585A EP81305585A EP0054367A2 EP 0054367 A2 EP0054367 A2 EP 0054367A2 EP 81305585 A EP81305585 A EP 81305585A EP 81305585 A EP81305585 A EP 81305585A EP 0054367 A2 EP0054367 A2 EP 0054367A2
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EP
European Patent Office
Prior art keywords
tower
vapour
feed
bottoms
distillate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP81305585A
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English (en)
French (fr)
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EP0054367A3 (de
Inventor
Thomas A. Devine
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ExxonMobil Technology and Engineering Co
Original Assignee
Exxon Research and Engineering Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Exxon Research and Engineering Co filed Critical Exxon Research and Engineering Co
Publication of EP0054367A2 publication Critical patent/EP0054367A2/de
Publication of EP0054367A3 publication Critical patent/EP0054367A3/de
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G7/00—Distillation of hydrocarbon oils
    • C10G7/02—Stabilising gasoline by removing gases by fractioning

Definitions

  • This invention relates to a method and apparatus for fractionating a hydrocarbon feed to remove light ends, and is particularly but not exclusively concerned with a fractionating method which has a reduced tendency for fouling the fractionation tower and which generally has a lower energy consumption than the conventional method.
  • Bottoms temperature can be reduced by lowering the pressure within the tower, but a significant lowering of tower pressure is required in order to achieve a significant temperature reduction. Any reduction in tower pressure reduces overhead temperature, which results in a greater energy expenditure for refrigeration. A large reduction in tower pressure may cause the tower to flood and become inoperative, i.e. the vapour expands and its velocity increases to a point where heavy ends are entrained and carried off overhead. Therefore, simply lowering tower pressure is not an acceptable solution to tower fouling.
  • an energy efficient fractionation of hydrocarbon feeds may be achieved at a reduced bottoms temperature in the tower by first removing the major part of the lighter materials from only the vapour portion of the feed, in a first, relatively "coarse” fractionation.
  • a method of separating light ends from a mixed hydrocarbon feed comprising liquid and vapour portions in which method the vapour portion of the feed is fractionated in a first tower so as to provide the desired light ends cut as the vapour distillate thereof, and the bottoms of the first tower and the liquid portion of the feed are fractionated in a second tower operating at a lower pressure than the first to provide a further amount of the desired light ends cut as the vapour distillate.
  • a method of separating C 3 - materials from a steam cracked naphtha in the production of ethylene characterised in that the steam cracked naphtha feed is depropanized by delivering the vapour portion of the feed to a first tower to give a vapour distillate containing the majority of the C 3 - materials from the feed, combining the bottoms of the first tower and the liquid from the feed, fractionating the combined bottoms and liquid in a second tower operating at a lower pressure than the first tower to separate the remaining C 3 - materials as the vapour distillate of the second tower, compressing the vapour distillate from the second tower and combining it with the vapour distillate from the first tower to form a feed for the subsequent stages of ethylene recovery.
  • apparatus for separating light ends from a mixed hydrocarbon feed containing liquid and vapour portions by fractionation to obtain a light end cut and bottoms, which apparatus comprises.
  • the method of the invention is generally applicable to mixed hydrocarbon feeds where it is desired to remove the light ends.
  • the method has been found to have particular energy saving advantages in relation to a depropanizer, and will be described principally in that connection. However, it is to be understood that the method is of more general applicability: for example it may be used in deethanizers and debutanizers with considerable energy savings under certain preferred conditions discussed hereinafter.
  • the mixed hydrocarbon feed fractionated in accordance with the invention may be taken from a wide variety of products resulting from the steam cracking or catalytic cracking of the range of feedstocks from ethane and propane through to naphtha and gas oil.
  • the method has particular application to the separation of steam cracked naphtha in the production of ethylene.
  • the feed to be treated in accordance with the method is in liquid and vapour portions. Separation into these portions may be achieved in a conventional separation apparatus such as a flash drum, with a preceding cooling stage if necessary.
  • the principle of the method is that by separating light materials (C 3 - in the case of a depropanizing operation) from the vapour in the first tower, the loading on the second tower is reduced relative to that of the conventional single fractionation tower; thus the light material (e.g. hydrogen and methane) in the second tower is reduced, which means that the pressure therein may be reduced without flooding (due to gas expansion) and reduced overhead temperature becoming problems.
  • the light material e.g. hydrogen and methane
  • only the bottoms from the first tower and the liquid portion of the feed is fractionated in the second tower.
  • the second tower produces a further amount of light materials as vapour distillate since not all of the desired light end cut is removed in the first tower (this light end cut being C 3 - in the case of a depropanizer).
  • the bottoms temperature is lower than in a conventional single tower so that hot water (condensate) may be used in the reboiler instead of steam (an expensive primary heat source), with savings in energy.
  • the lower temperature means less polymerization and hence less fouling. Further energy savings may result from an increase in the overhead temperature of the second tower which may allow a higher temperature refrigerant to be used in the condenser and from the increase in efficiency due to a greater number of trays in two towers than one conventional tower.
  • the first tower is operated at a pressure of from 150 to 180, say 165 psia; the bottoms temperatures may be, say 39°F, whilst the overheads temperature in the first tower may be from -30 to -15°F.
  • the second tower preferably operates at a pressure of 150 psia or less, for example from 75 to 150 psia. It is preferred to operate the second tower at a bottoms temperature of up to 180°F (which is the temperature of the heating water in the reboiler), more preferably from 130 to 170°F, say 150°F.
  • the overheads temperature in the second tower is preferably some 35 degrees F greater than in the first, say 5 to 20°F, for example 10°F.
  • the overheads from the first and second towers may be combined, but to do this the second tower distillate needs compression since the second tower operates at a lower pressure than the first.
  • the overheads stream from the second tower is of relatively smaller,volume than the higher pressure overheads from the first tower, so the additional energy required for this compression stage is minor.
  • the method of the invention is advantageously applied to a system wherein the major portion of the desired light end (e.g. C 3 -) is separated in the first tower; the overhead temperature of the first tower exceeds the refrigerant temperature used in the conventional system; and the overhead temperature of the second tower is increased, and/or the bottoms temperature is reduced.
  • the major portion of the desired light end e.g. C 3 -
  • the overhead temperature of the first tower exceeds the refrigerant temperature used in the conventional system
  • the overhead temperature of the second tower is increased, and/or the bottoms temperature is reduced.
  • a feedstock containing hydrogen and C 1 to C 10 hydrocarbons is compressed at 1, to separate some C 5 -C 10 hydrocarbons.
  • the remaining H 2 -C 8 mixture is fed to depropanizer 2, which produces a H 2 -C 3 mixture overhead which is fed to compression and acetylene conversion stage 3.
  • the C 4 -C 8 bottoms from depropanizer 2 is fed to debutanizer 4 and further separated into C 4 hydrocarbons (overhead) and C 5 -C 8 (bottoms).
  • stage 3 The product of stage 3 is chilled and demethanized at 5 to give an H 2/ CH 4 mixture overhead and C 2/ C 3 bottoms. The latter is then fed to deethanizer 6 where the C 3 hydrocarbons are removed as bottoms, and finally the C 2 hydrocarbons are separated in ethylene fractionator 7 to yield ethylene (C 2 H 4 ) and ethane (C 2 H 6 ).
  • a depropanizer such as is conventionally used in a circuit such as the one outlined above is shown in Figure 2.
  • the feed is chilled in a heat exchanger 10 using 4.5°C propylene before being fed to a single tower 11, in which it is fractionated to yield C 3 - overhead and C 4 + bottoms.
  • the overhead is passed to a heat exchanger 12 where it is condensed using -37.8°C propylene, and then fed to reflux drum 13, from which part is refluxed back to the tower and part is fed to the compression and acetylene conversion stage 3 ( Figure 1).
  • a steam heated reboiler 14 is provided to heat the feed and so produce the necessary vapour in the tower.
  • the depropanizer would have to be operated at a pressure in the range 9-13 bar, for example at 11.4 bar (11.6 x 10 4 kgm- 2 , 165 psia) with a bottom temperature of 98°C.
  • the method of the invention utilizes the arrangement shown in Figure 3 in which the feed is again cooled in heat exchanger 10, but then separated into vapour and liquid components in a flash drum 20.
  • the vapour which may be for example some 90% of the total, is fed to a first tower 21 where it is separated into a C 3- overhead and bottoms containing C 2 -C 4 with some H 2 and CH 4 .
  • the overhead is cooled in a heat exchanger 22 with -37.8° C propylene and fed to a reflux drum 23, from which some is refluxed through the first tower 21, and some is taken off to the compression and acetylene conversion stage 3 ( Figure 1).
  • the bottoms of the first tower 21 is combined with the liquid portion of the feed from flash drum 20 and fed to the second tower 24, in this embodiment a depropanizer, in which it is separated into C 3- overhead and C 4+ bottoms.
  • the second tower 24 typically operates at 6.7 kgm-2 (96 psia) with a bottoms temperature of 63°C, a considerably lower temperature resulting in considerably less fouling.
  • the second tower 24 is provided with a reboiler 25 which need only be heated by hot water rather than steam because of the lower pressure and bottoms temperature at which the tower is operated.
  • the overhead from tower 24 is cooled in a heat exchanger 26 using -18°C propylene and fed to a reflux drum 27 from which some is returned to the tower, and some is fed via a compressor 28 to the next stage 3 ( Figure 1).
  • the reduced bottoms temperature resulting from the lower pressure operation of the second tower means less polymerisation and hence less fouling.
  • the tower operating temperature permits the use of a cheap secondary heat source (hot water) in the reboiler, rather than the hitherto necessary use of the expensive primary heat source, steam.
  • the overhead from the second tower is condensed using higher temperature, and hence cheaper, propylene refrigeration.
  • the reduced pressure of the overheads does, though, mean that compression is required before the overheads of the first and second towers can be combined.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
EP81305585A 1980-12-12 1981-11-26 Verfahren und Vorrichtung zur Abtrennung von Leichtfraktionen aus einem Einsatzgemisch aus Kohlenwasserstoffen Withdrawn EP0054367A3 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB8039998 1980-12-12
GB8039998 1980-12-12
GB8107255 1981-03-09
GB8107255 1981-03-09

Publications (2)

Publication Number Publication Date
EP0054367A2 true EP0054367A2 (de) 1982-06-23
EP0054367A3 EP0054367A3 (de) 1982-09-15

Family

ID=26277839

Family Applications (1)

Application Number Title Priority Date Filing Date
EP81305585A Withdrawn EP0054367A3 (de) 1980-12-12 1981-11-26 Verfahren und Vorrichtung zur Abtrennung von Leichtfraktionen aus einem Einsatzgemisch aus Kohlenwasserstoffen

Country Status (2)

Country Link
EP (1) EP0054367A3 (de)
AU (1) AU7846781A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0188124A3 (en) * 1984-12-31 1987-12-09 Mobil Oil Corporation Method and apparatus for minimizing recycling in an unsaturated gas plant
WO1994006890A1 (en) * 1992-09-24 1994-03-31 Exxon Chemical Patents Inc. Fouling reducing dual pressure fractional distillator

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2364660A (en) * 1939-01-20 1944-12-12 Laurance S Reid Method of and apparatus for recovering desirable petroleum hydrocarbon fractions from high pressure wells
US2871275A (en) * 1953-08-17 1959-01-27 Universal Oil Prod Co Separation of selected components from hydrocarbon mixtures
GB1373124A (en) * 1971-12-13 1974-11-06 Shell Int Research Liquefaction of natural gas

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0188124A3 (en) * 1984-12-31 1987-12-09 Mobil Oil Corporation Method and apparatus for minimizing recycling in an unsaturated gas plant
WO1994006890A1 (en) * 1992-09-24 1994-03-31 Exxon Chemical Patents Inc. Fouling reducing dual pressure fractional distillator
US5342509A (en) * 1992-09-24 1994-08-30 Exxon Chemical Patents Inc. Fouling reducing dual pressure fractional distillator

Also Published As

Publication number Publication date
EP0054367A3 (de) 1982-09-15
AU7846781A (en) 1982-06-17

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Inventor name: DEVINE, THOMAS A.