GB2110808A - Cryogenic gas plant - Google Patents

Cryogenic gas plant Download PDF

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Publication number
GB2110808A
GB2110808A GB08233219A GB8233219A GB2110808A GB 2110808 A GB2110808 A GB 2110808A GB 08233219 A GB08233219 A GB 08233219A GB 8233219 A GB8233219 A GB 8233219A GB 2110808 A GB2110808 A GB 2110808A
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GB
United Kingdom
Prior art keywords
stream
column
reflux
ethane
feedstream
Prior art date
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Granted
Application number
GB08233219A
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GB2110808B (en
Inventor
John Michael Harryman
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.)
Shell Internationale Research Maatschappij BV
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Shell Internationale Research Maatschappij BV
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Filing date
Publication date
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Publication of GB2110808A publication Critical patent/GB2110808A/en
Application granted granted Critical
Publication of GB2110808B publication Critical patent/GB2110808B/en
Expired legal-status Critical Current

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Classifications

    • 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
    • F25J3/0204—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
    • 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
    • F25J2200/30—Processes or apparatus using separation by rectification using a side column in a single pressure 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
    • F25J2200/76—Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
    • 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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/40—Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Separation By Low-Temperature Treatments (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

A process for separating substantially all of the C3 and heavier components and a major portion of the C2 component from a natural gas stream using a cryogenic process. The process uses a rectifying column 12 which provides an overhead stream of methane in combination with a demethanizing column 22 to separate the C2 and heavier components. A reflux for the rectifying column is supplied by compressing a small portion of the overhead stream 11 and condensing it via heat exchange with the overhead stream. <IMAGE>

Description

SPECIFICATION Cryogenic gas plant The present invention relates to a cryogenic gas plant and particularly to a gas plant which is designed to separate natural gas liquids (NGL), which contain ethane and higher boiling hydrocarbony from a natural gas feedstream.
The evolution of cryogenic gas plants is reviewed in a paper presented at the 1977 Gas Processing Association Convention entitled "Evolution in Design" by R.L. McKee. This paper described the use of turbo-expanders to increase the thermodynamic efficiency of a gas plant and thus improve its overall economics. A similar type of cryogenic system for recovering ethane and higher boiling hydrocarbons from a natural gas stream is described in U.S. Patent Specification No. 3,292,380. A more recent descrip ticn of cryogenic gas processing plants appears in the July14, 1980 edition ofthe"Oil and Gas Journal" at page 76 et. seq.All of these references describe the use of a turbo-expander for supplying the feedstockto a demethanizing column where the methane is separated from the ethane and the higher boiling hydrocarbons.
While these systems have been satisfactory, they do not recover all the ethane and higher boiling point liquids. The ethane and higher boiling point liquids are used as chemical feedstocks which have more value in today's markets as chemical feedstocks than as natural gas. The lack of complete recovery of the ethane partially is due to the relative volatility of methane to ethane and to the fact that a considerable amount of the ethane is contained as a vapour in the methane when it enters the demethanizing column. The portion of the ethane contained as vapour remains in the gas phase and is discharged from the top of the column as pipeline gas.
A further problem arises when attempts are made to operate plants near their capacity or beyond.
When operating plants at or above their capacity, flooding of the demethanizing column with liquid occurs. When this occurs, additional ethane and higher boiling point liquids are lost to the natural gas stream instead of being condensed and removed as liquid from the bottom of the column.
The object of the present invention is to solve the above problems.
The process for separating ethane and heavier components from a natural gas feedstream utilizing a cryogenic plant having a cold feedstream thereto comprises according to the invention introducing the feedstream into a rectifier column to recover ethane from the feedstream and withdrawing methane as a overhead stream; passing a portion of the overhead stream back to the top of said rectifier column as a reflux stream, the pressure of said reflux stream being increased above the pressure of said overhead stream; introducing the bottom stream of said rectifier column as a feed to a demethanizer column; and returning the top stream of said demethanizer column as a bottom feed to said rectifier column.
According to the invention the aforementioned problems are solved by placing a rectifying column ahead of the demethanizing column. The rectifying column is provided with a reflux system while the liquefied bottom stream from the rectifying column is used as a feed for the demethanizing column. The combination of the rectifying column and the demethanizing column can provide essentially 100% recovery of the ethane and higher boiling point liquids from a natural gas stream. The reflux of the rectifying column uses a small portion of the overhead stream from the rectifying column, about 10% to 17%. The reflux stream is produced by a com pressorand a condenser which is cooled by the overhead stream from the rectifying column.The use of a liquid reflux stream increases recovery of NGL, the ethane and higher boiling point liquids, while the use of the demethanizing column insures that sufficient methane will be removed from the NGL product. It is to be noted that the rectifying column also can be placed on top of the demethanizing stripper column, both being one common vessel, in order to reduce equipment costs and complexity, including elimination of the need to pump liquid from the bottom of the rectifying column to the top of the demethanizing column.
The present invention will be more easily understood from the following detailed description of a preferred embodiment when taken in conjunction with the attached drawing showing schematically a gas processing system constructed according to the present invention.
Referring to the attached drawing, there is shown a rectifying column 12 that has been added ahead of a demethanizing stripper column 22. In known gas plants the demethanising column is supplied with a partially liquefied feedstream 10 from a turboexpander not shown in the drawing. Such a known plant without a rectifying column will recover approximately 76% of the ethane while the present invention provides a plant enabling the recovery of approximately 93% of the ethane and essentially all of the higher boiling liquids.
Apart from a turbo-expander for supplying the feedstream 10 other systems could be used to supply the cold vapour liquid feedstream. For example, refrigeration systems could be used to supply the feedstream. The feedstream should have a temperature in the range of -73 C to -115"C and a pressure in the range of 1720 kPa to 3100 kPa. In an existing plant the feedstream from the turbo- expander has a pressure of 2654 kPa and a temperature of -93"C.
Rectifying column 12 is supplied with the feedstream 10, formerly supplied in the demethanizing column 22, having a temperature of approximately minus 94"C and comprising essentially methane gas and higher boiling point liquid hydrocarbons. The ethane and higher boiling point liquids are stripped from the feedstream and removed from the bottom of the rectifying column while the methane is withdrawn as an overhead stream 11. A small portion of the overhead stream of the column 12 is taken off as a reflux stream 13 and compressed by compressor 14. As explained above, the reflux should comprise a small portion of the total flow, approximately 10% to 17%, of the overhead stream.
The compressed reflux stream is passed through a condenser 15 where it is condensed by the overhead stream 11 with the flow of the overhead stream through the condenser being controlled by bypass valve 17. A valve 16 controls the condensing pressure and the flow of reflux to the rectifying column 12.
The liquid reflux suppled to the rectifying column effects recovery of most of the ethane and essentially all the higher boiling point hydrocarbon from the feedstream 10. The liquid bottom stream 20, including a substantial quantity of methane, is pumped to the demethanizing column 22 by a pump 21.
The top stream 23 from the demethanizing column, consisting of methane and a smaller amount of ethane and higher boiling liquids, flows into the bottom part of the rectifying column 12. The rectifying column 12 and the demethanizing column 22 are reboiled by warmer portions of the gas stream upstream of the turbo-expander, not shown in the drawing.
NGL product is withdrawn from the bottom of demethanizing column 22 through a line 30 and supplied by pump 31 as a chemical feedstock to other processing units not shown. The bottom reboiler 32 and sale reboilers 24 and 25 ensure that sufficient methane is removed from the NGL product.
From the above description, it is seen that only a small portion of the overhead stream of the rectifying column is used as reflux. Further, a compressor can be used to compress this fluid to higher pressure which permits its condensation to a liquid using the overhead stream from the column as the cooling medium. Thus, a liquid reflux is obtained with minimum expenditure of energy in contrast to the use of turbo-expanders in prior systems. The use of a liquid reflux in the rectifying column ensures that more than 90% of the ethane and essentially 100% of the higher boiling point liquids are removed from the feedstream 10. By removing some of the methane from the liquid in the rectifying column, the load on the demethanizing column 22 is reduced with the net result that the throughput of the plant can be increased if one so desires.

Claims (7)

1. A process for separating ethane and heavier components from a natural gas feed stream utilizing a cryogenic plant having a cold feedstream, said process comprising: introducing the feedstream into a rectifier column to recover ethane from the feedstream and withdrawing methane as a overhead stream; passing a portion of the overhead stream back to the top of said rectifier column as a reflux stream, the pressure of said reflux stream being increased above the pressure of said overhead stream; introducing the bottom stream of said rectifier column as the feed to a demethanizer column; and returning the top stream of said demethanizer column as a bottom feed to said rectifier column.
2. The process according to claim 1 and in addition, condensing a portion of said reflux stream after the pressure of said stream is increased.
3. The process according to claim 2, wherein said portion of the reflux stream is condensed by cooling with the overhead stream of said rectifier column.
4. The process according to any one of the claims 1-3, wherein the rectifier column and demethanizer column are separate vessels.
5. The process according to any one of the claims 1-3, wherein the rectifier column and demethanizer column are part of a common vessel.
6. The process according to any one of claims 1-5, wherein the reflux stream comprises less than 25% of the overhead stream.
7. A process for separating ethane and heavier components from a natural gas feed stream substantially as described with particular reference to the accompanying drawing.
GB08233219A 1981-11-24 1982-11-22 Cryogenic gas plant Expired GB2110808B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US32436181A 1981-11-24 1981-11-24

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GB2110808A true GB2110808A (en) 1983-06-22
GB2110808B GB2110808B (en) 1985-04-17

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2146751A (en) * 1983-09-20 1985-04-24 Petrocarbon Dev Ltd Separation of hydrocarbon mixtures
US4622053A (en) * 1983-09-20 1986-11-11 Petrocarbon Developments Limited Separation of hydrocarbon mixtures
WO1988000936A1 (en) * 1986-08-06 1988-02-11 Linde Aktiengesellschaft PROCESS FOR SEPARATING A GAS MIXTURE OF C2+ OR C3+ or C4 HYDROCARBONS
US5030339A (en) * 1988-10-21 1991-07-09 Costain Engineering Limited Separation of gas and oil mixtures
US5673571A (en) * 1996-03-06 1997-10-07 Manley; David B. Deethanizer/depropanizer sequences with thermal and thermo-mechanical coupling and component distribution

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2146751A (en) * 1983-09-20 1985-04-24 Petrocarbon Dev Ltd Separation of hydrocarbon mixtures
US4622053A (en) * 1983-09-20 1986-11-11 Petrocarbon Developments Limited Separation of hydrocarbon mixtures
WO1988000936A1 (en) * 1986-08-06 1988-02-11 Linde Aktiengesellschaft PROCESS FOR SEPARATING A GAS MIXTURE OF C2+ OR C3+ or C4 HYDROCARBONS
AU592227B2 (en) * 1986-08-06 1990-01-04 Linde Aktiengesellschaft Process for separating a gas mixture of c2+ or c3+ or c4 hydrocarbons
US5026952A (en) * 1986-08-06 1991-06-25 Linde Aktiengesellschaft Process for separating C2 + or C3 + or C4 hydrocarbons from a gaseous mixture
US5030339A (en) * 1988-10-21 1991-07-09 Costain Engineering Limited Separation of gas and oil mixtures
US5673571A (en) * 1996-03-06 1997-10-07 Manley; David B. Deethanizer/depropanizer sequences with thermal and thermo-mechanical coupling and component distribution

Also Published As

Publication number Publication date
CA1184210A (en) 1985-03-19
GB2110808B (en) 1985-04-17

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PCNP Patent ceased through non-payment of renewal fee