Cryogenic separation of gaseous mixtures
First Claim
1. A cryogenic separation method for recovering C1+ hydrocarbons from cracked hydrocarbon feed gas comprising methane, ethene and ethane, wherein cold pressurized gaseous streams are separated in a plurality of dephlegmator units, each of said dephlegmator units being operatively connected to accumulate condensed liquid in a lower dephlegmator drum vessel by gravity flow from an upper dephlegmator heat exchanger comprising a plurality of vertically disposed indirect heat exchange passages through which gas from the lower drum vessel passes in an upward direction for cooling with refrigerant fluid by indirect heat exchange within said heat exchange passages, whereby gas flowing upwardly is partially condensed on vertical surfaces of said passages to form a reflux liquid in direct contact with the upward flowing gas stream to provide a condensed stream of cooler liquid flowing downwardly and thereby enriching condensed dephlegmator liquid gradually with C2+ hydrocarbon components;
- comprising the steps of;
introducing dry feed gas into a primary dephlegmation zone having a plurality of serially connected, sequentially colder dephlegmator units for separation of feed gas into a primary methane-rich gas stream recovered at low temperature and at least one primary liquid condensate stream rich in C2+ hydrocarbon components and containing a minor amount of methane;
passing at least one primary liquid condensate stream from the primary dephlegmation zone to serially connected demethanizer fractionators, wherein a moderately low cryogenic temperature is employed in a first demethanizer fractionator unit to recover substantially all of the methane from the primary liquid condensate stream in a first demethanizer overhead vapor stream and to recover a first C2+ liquid demethanizer bottoms stream substantially free of methane, wherein said demethanizer overhead vapor stream is cooled with moderately low temperature coolant to provide liquid reflux for recycled to a top portion of the first demethanizer fractionator;
further separating at least a portion of the first demethanizer overhead vapor stream in an ultra-low temperature final demethanizer fractionator unit to recover a liquid ethene-rich predominantly C2 hydrocarbon crude product stream and a final demethanizer ultra-low temperature overhead vapor stream substantially free of C2+ hydrocarbons, wherein a major amount of total demethanization heat exchange duty is provided by moderately low temperature refrigerant and overall energy requirements for refrigeration utilized in separating C2+ hydrocarbons from methane and lighter components are decreased; and
fractionating said second crude ethene stream and said first ethene-rich C2 hydrocarbon crude product stream to obtain a pure ethene product.
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Abstract
A cyrogenic technique for recovering ethene from a gaseous mixture containing methane, ethane, etc. Operating methods and apparatus are provided for passing the gas feed through a chilling train having a series of dephlegmator-type exchange units to condense liquid rich in ethene and ethane, while separating a major portion of methane and lighter gas. A multizone demethanizer removes condensed methane from the C2 fraction to provide a pure product economically.
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Citations
23 Claims
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1. A cryogenic separation method for recovering C1+ hydrocarbons from cracked hydrocarbon feed gas comprising methane, ethene and ethane, wherein cold pressurized gaseous streams are separated in a plurality of dephlegmator units, each of said dephlegmator units being operatively connected to accumulate condensed liquid in a lower dephlegmator drum vessel by gravity flow from an upper dephlegmator heat exchanger comprising a plurality of vertically disposed indirect heat exchange passages through which gas from the lower drum vessel passes in an upward direction for cooling with refrigerant fluid by indirect heat exchange within said heat exchange passages, whereby gas flowing upwardly is partially condensed on vertical surfaces of said passages to form a reflux liquid in direct contact with the upward flowing gas stream to provide a condensed stream of cooler liquid flowing downwardly and thereby enriching condensed dephlegmator liquid gradually with C2+ hydrocarbon components;
- comprising the steps of;
introducing dry feed gas into a primary dephlegmation zone having a plurality of serially connected, sequentially colder dephlegmator units for separation of feed gas into a primary methane-rich gas stream recovered at low temperature and at least one primary liquid condensate stream rich in C2+ hydrocarbon components and containing a minor amount of methane; passing at least one primary liquid condensate stream from the primary dephlegmation zone to serially connected demethanizer fractionators, wherein a moderately low cryogenic temperature is employed in a first demethanizer fractionator unit to recover substantially all of the methane from the primary liquid condensate stream in a first demethanizer overhead vapor stream and to recover a first C2+ liquid demethanizer bottoms stream substantially free of methane, wherein said demethanizer overhead vapor stream is cooled with moderately low temperature coolant to provide liquid reflux for recycled to a top portion of the first demethanizer fractionator; further separating at least a portion of the first demethanizer overhead vapor stream in an ultra-low temperature final demethanizer fractionator unit to recover a liquid ethene-rich predominantly C2 hydrocarbon crude product stream and a final demethanizer ultra-low temperature overhead vapor stream substantially free of C2+ hydrocarbons, wherein a major amount of total demethanization heat exchange duty is provided by moderately low temperature refrigerant and overall energy requirements for refrigeration utilized in separating C2+ hydrocarbons from methane and lighter components are decreased; and fractionating said second crude ethene stream and said first ethene-rich C2 hydrocarbon crude product stream to obtain a pure ethene product. - View Dependent Claims (2, 3, 4)
- comprising the steps of;
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5. An improved cryogenic technique for separating and recovering C2+ hydrocarbons from a feed gas containing hydrogen, methane, ethene and ethane, comprising the steps of:
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separating cold pressurized gaseous feed gas in a series of at least three dephlegmator rectification units wherein liquid condensate is recovered from at least three serially connected dephlegmation zones, each of said dephlegmator units being operatively connected to accumulate condensed C2+ -rich liquid in a lower dephlegmator drum vessel by gravity flow from an upper dephlegmator heat exchanger comprising a plurality of vertically disposed indirect heat exchange passages through which gas from the lower drum vessel passes in an upward direction for cooling by indirect heat exchange within said heat exchange passages, whereby gas flowing upwardly is partially condensed on vertical surfaces of said passages to form a reflux liquid in direct contact with the upward flowing gas stream to provide a condensed stream of cooler liquid flowing downwardly and thereby enriching condensed dephlegmator liquid gradually with C2+ hydrocarbon components; introducing dry feed gas into a primary dephlegmation zone in said series of dephlegmation units for separation of feed gas into a primary methane-rich gas stream recovered and at least one primary liquid condensate stream rich in C2 hydrocarbon components and containing a minor amount of methane; passing at least one primary liquid condensate stream from the dephlegmation units to serially connected demethanizer fractionators, wherein a moderately low cryogenic temperature is employed in a first demethanizer fractionator unit to recover a substantially all of the methane from the primary liquid condensate stream in a first demethanizer overhead vapor stream and to recover a first C2+ liquid demethanizer bottoms stream substantially free of methane; further separating at least a portion of the first demethanizer overhead vapor stream in an ultra-low temperature final demethanizer fractionator unit to recover ethene-rich C2 hydrocarbon liquid product and a final demethanizer ultra-low temperature overhead vapor stream; contacting at least a portion of said first demethanizer overhead vapor stream in direct heat exchange relationship with an intermediate liquid stream from an intermediate dephlegmation zone in a countercurrent contact unit operatively connected between primary and secondary demethanizer fractionator zones, with liquid from said countercurrent contact zone being directed to a lower stage of the secondary demethanizer fractionator zone and vapor from said countercurrent contact zone being directed to a higher stage of the secondary demethanizer fractionator zone; and passing the final demethanizer overhead vapor stream to a final dephlegmator unit to obtain a final liquid reflux stream for recycle to a top portion of the final demethanizer fractionator and a methane-rich final dephlegmator overhead vapor stream substantially free of C2+ hydrocarbons, whereby energy requirements for refrigeration utilized in separating the C2+ hydrocarbons from methane and lighter components are low.
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6. In a cryogenic separation method for recovering purified ethene from hydrocarbon feedstock gas consisting mainly of methane, ethene and ethane, wherein cold pressurized gaseous streams are separated in a plurality of sequentially arranged rectification units, each of said rectification units being operatively connected to accumulate condensed liquid in a lower liquid accumulator portion by gravity flow from an upper vertical rectifier portion through which gas from the lower accumulator portion passes in an upward direction for direct gas-liquid contact exchange within said reactifier portion, whereby methane-rich gas flowing upwardly is partially condensed in said rectifier portion with cold refluxed liquid in direct contact with the upward flowing gas stream to provide a condensed stream of cold liquid flowing downwardly and thereby enriching condensed liquid gradually with ethene and ethane components;
- the improvement comprising;
introducing dry feed gas into a primary rectification zone having a plurality of serially connected, sequentially colder rectification units for separation of feed gas into a primary methane-rich gas stream recovered at low temperature and at least one primary liquid condensate stream rich in C2 hydrocarbon components and containing a minor amount of methane; passing at least one primary liquid condensate stream from the primary rectification zone to a fractionation system having serially connected demethanizer zones, wherein a moderately low cryogenic temperature is employed in a first demethanizer fractionation zone to recover a major amount of methane from the primary liquid condensate stream in a first demethanizer overhead vapor stream and to recover a first liquid demethanized bottoms stream rich in ethane and ethene and substantially free of methane, wherein said demethanizer overhead vapor stream is cooled with moderately low temperature coolant to provide liquid reflux for recycle to a top portion of the first demethanizer zone; further separating at least a portion of the first demethanizer overhead vapor stream in an ultra-low temperature final demethanizer zone to recover a first liquid ethene-rich C2 hydrocarbon crude product stream and a final demethanizer ultra-low temperature overhead vapor stream substantially free C2+ hydrocarbons, wherein a major amount of total demethanization heat exchange duty is provided by moderately low temperature coolant and overall energy requirements for refrigeration utilized in separating C2+ hydrocarbons from methane and lighter components are decreased; further fractionating the C2+ liquid bottoms stream from the first demethanizer zone to remove ethane and heavier hydrocarbons therefrom and provide a second crude ethene stream; and fractionating said second crude ethene stream and said first ethene-rich hydrocarbon crude product stream to obtain a purified ethene product. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
- the improvement comprising;
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19. An improved cryogenic separation system for recovering a higher-boiling first gaseous component from a lower-boiling second gaseous component in a feedstock mixture thereof comprising:
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a source of primary refrigerant, moderately low temperature refrigerant and ultra low temperature refrigerant; sequential chilling train means including a primary dephlegmator unit operatively connected in serial flow relationship with intermediate and final dephlegmator units, wherein a cold pressurized gaseous stream is separated in the series of dephlegmator units, each of said dephlegmator units having means for accumulating condensed liquid rich in higher-boiling component in a lower dephlegmator drum from an upper dephlegmator heat exchanger wherein gas flowing upwardly is partially condensed to form a reflux liquid in direct contact with upward flowing gas to provide a condensed stream of cooler liquid flowing downwardly and thereby enriching condensed dephlegmator liquid gradually with higher-boiling component; means for feeding dry pressurized feedstock to the primary dephlegmator unit for sequential chilling to separate the feedstock mixture into a primary gas stream rich in lower boiling component recovered at about primary refrigerant temperature temperature and a primary liquid condensate stream rich in higher boiling component and containing a minor amount of lower boiling component; fluid handling means for passing the primary liquid condensate stream from the primary dephlegmator unit to a low temperature fractionation system for recovering condensed lower-boiling components from condensed liquid, said fractionation system having a first fractionation zone including first reflux condenser means operatively connected to the source of moderately low temperature refrigerant to recover a major amount of lower-boiling component from the primary liquid condensate stream in a first fractionator overhead vapor stream and to recover a first liquid fractionator bottoms stream substantially free of lower-boiling component; said fractionation system having a second fractionation zone including second reflux condenser means operatively connected to the source of ultra low temperature refrigerant to recover a liquid product stream consisting essentially of higher boiling component and a second fractionator ultra-low temperature overhead vapor stream; and means for passing an intermediate liquid stream condensed from at least one intermediate dephlengmator unit to to a middle stage of the second fractionation zone. - View Dependent Claims (20, 21, 22, 23)
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Specification