Natural gas liquefaction

• US 7,210,311 B2
• Filed: 07/22/2005
• Issued: 05/01/2007
• Est. Priority Date: 06/08/2001
• Status: Expired due to Term

• Current Assignee: UOP Llc (Honeywell International Inc.)
• Original Assignee: Ortloff Enigneers, Ltd.
• Inventors: Hudson, Hank M., Cuellar, Kyle T., Wilkinson, John D.
• Primary Examiner(s): Doerrler; William C.
• Application Number:
  US11/188,297
• Publication Number:
  US 20050268649A1
• Time in Patent Office: 648 Days
• Field of Search: 626/11, 626/12, 626/20, 626/21
• US Class Current: 62/611
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0042 by liquid expansion with extraction of work
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0057 after expansion of the liquid refrigerant stream with extraction of work
• CPC Class Codes: F25J 1/0205 as a dual level SCR refrigeration cascade
• CPC Class Codes: F25J 1/0214 as a dual level refrigeration cascade with at least one MCR cycle
• CPC Class Codes: F25J 1/0216 using a C3 pre-cooling cycle
• CPC Class Codes: F25J 1/0239 Purification or treatment step being integrated between two refrigeration cycles of a refrigeration cascade, i.e. first cycle providing feed gas cooling and second cycle providing overhead gas cooling
• CPC Class Codes: F25J 1/0241 wherein the overhead cooling comprises providing reflux for a fractionation step
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• CPC Class Codes: F25J 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2230/08 Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2235/60 the fluid being (a mixture of) hydrocarbons
• CPC Class Codes: F25J 2240/02 : Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• CPC Class Codes: F25J 2240/30 : Dynamic liquid or hydraulic expansion with extraction of work, e.g. single phase or two-phase turbine
• CPC Class Codes: F25J 2240/40 : Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
• CPC Class Codes: F25J 2245/02 : Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/02 : Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/12 : External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/60 : Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• CPC Class Codes: F25J 2270/66 : Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• CPC Class Codes: F25J 2290/40 : Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.
• CPC Class Codes: F25J 2290/62 : Details of storing a fluid in a tank
• CPC Class Codes: F25J 3/0209 : Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0233 : separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 : separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0242 : separation of CnHm with 3 carbon atoms or more
• CPC Class Codes: F25J 3/0247 : separation of CnHm with 4 carbon atoms or more

Abstract

A process for liquefying natural gas in conjunction with producing a liquid stream containing predominantly hydrocarbons heavier than methane is disclosed. In the process, the natural gas stream to be liquefied is partially cooled, expanded to an intermediate pressure, and supplied to a distillation column. The bottom product from this distillation column preferentially contains the majority of any hydrocarbons heavier than methane that would otherwise reduce the purity of the liquefied natural gas. The residual gas stream from the distillation column is compressed to a higher intermediate pressure, cooled under pressure to condense it, and then expanded to low pressure to form the liquefied natural gas stream.

Claims

1. In a process for liquefying a natural gas stream containing methane and heavier hydrocarbon components wherein

(a) said natural gas stream is cooled under pressure to condense at least a portion of it and form a condensed stream;

and

(b) said condensed stream is expanded to lower pressure to form said liquefied natural gas stream;

the improvement wherein

(1) said natural gas stream is treated in one or more cooling steps by a closed loop refrigeration cycle;

(2) said cooled natural gas stream is divided into at least a first gaseous stream and a second gaseous stream;

(3) said first gaseous stream is cooled by a closed loop refrigeration cycle to condense substantially all of it and thereafter expanded to an intermediate pressure;

(4) said second gaseous stream is expanded to said intermediate pressure;

(5) said expanded substantially condensed gaseous first stream and said expanded gaseous second stream are directed into a distillation column wherein said streams are separated into a volatile residue gas fraction containing a major portion of said methane and lighter components and a relatively less volatile fraction containing a major portion of said heavier hydrocarbon components; and

(6) said volatile residue gas fraction is cooled under pressure to condense at least a portion of it and form thereby said condensed stream.

4. The improvement according to claim 1, 2, or 3 wherein said volatile residue gas fraction is compressed and thereafter cooled under pressure to condense at least a portion of it and form thereby said condensed stream.

5. The improvement according to claim 1, 2, or 3 wherein said volatile residue gas fraction is heated by means other than with heat exchange with said natural gas stream, compressed, and thereafter cooled under pressure to condense at least a portion of it and form thereby said condensed stream.

6. The improvement according to claim 1, 2, or 3 wherein said volatile residue gas fraction contains a major portion of said methane, lighter components, and C₂ components.

7. The improvement according to claim 1, 2, or 3 wherein said volatile residue gas fraction contains a major portion of said methane, lighter components, C₂ components, and C₃ components.

2. In a process for liquefying a natural gas stream containing methane and heavier hydrocarbon components wherein

(a) said natural gas stream is cooled under pressure to condense at least a portion of it and form a condensed stream;

and

(b) said condensed stream is expanded to lower pressure to form said liquefied natural gas stream;

the improvement wherein

(1) said natural gas stream is treated in one or more cooling steps by a closed loop refrigeration cycle to partially condense it;

(2) said partially condensed natural gas stream is separated to provide thereby a vapor stream and a liquid stream;

(3) said vapor stream is divided into at least a first gaseous stream and a second gaseous stream;

(4) said first gaseous stream is cooled by a closed loop refrigeration cycle to condense substantially all of it and thereafter expanded to an intermediate pressure;

(5) said second gaseous stream is expanded to said intermediate pressure;

(6) said liquid stream is expanded to said intermediate pressure;

(7) said expanded substantially condensed gaseous first stream, said expanded gaseous second stream, and said expanded liquid stream are directed into a distillation column wherein said streams are separated into a volatile residue gas fraction containing a major portion of said methane and lighter components and a relatively less volatile fraction containing a major portion of said heavier hydrocarbon components; and

(8) said volatile residue gas fraction is cooled under pressure to condense at least a portion of it and form thereby said condensed stream.

3. In a process for liquefying a natural gas stream containing methane and heavier hydrocarbon components wherein

(a) said natural gas stream is cooled under pressure to condense at least a portion of it and form a condensed stream;

and

(b) said condensed stream is expanded to lower pressure to form said liquefied natural gas stream;

the improvement wherein

(1) said natural gas stream is treated in one or more cooling steps by a closed loop refrigeration cycle to partially condense it;

(2) said partially condensed natural gas stream is separated to provide thereby a vapor stream and a liquid stream;

(3) said vapor stream is divided into at least a first gaseous stream and a second gaseous stream;

(4) said first gaseous stream is combined with at least a portion of said liquid stream, forming thereby a combined stream;

(5) said combined stream is cooled by a closed loop refrigeration cycle to condense substantially all of it and thereafter expanded to an intermediate pressure;

(6) said second gaseous stream is expanded to said intermediate pressure;

(7) any remaining portion of said liquid stream is expanded to said intermediate pressure;

(8) said expanded substantially condensed combined stream, said expanded gaseous second stream, and said remaining portion of said liquid stream are directed into a distillation column wherein said streams are separated into a volatile residue gas fraction containing a major portion of said methane and lighter components and a relatively less volatile fraction containing a major portion of said heavier hydrocarbon components; and

(9) said volatile residue gas fraction is cooled under pressure to condense at least a portion of it and form thereby said condensed stream.