Liquefied natural gas and hydrocarbon gas processing

• US 8,850,849 B2
• Filed: 11/27/2012
• Issued: 10/07/2014
• Est. Priority Date: 05/16/2008
• Status: Expired due to Fees

• Current Assignee: Ortloff Enigneers, Ltd.
• Original Assignee: Ortloff Enigneers, Ltd.
• Inventors: Martinez, Tony L., Wilkinson, John D., Hudson, Hank M., Cuellar, Kyle T.
• Primary Examiner(s): Pettitt, John
• Assistant Examiner(s): LANDEROS, IGNACIO EMMANUEL
• Application Number:
  US13/686,641
• Publication Number:
  US 20130125582A1
• Time in Patent Office: 679 Days
• Field of Search: 626/17, 626/18, 626/20, 626/30, 626/32
• US Class Current: 62/620
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/38 using pre-separation or distributed distillation before a main column system, e.g. in a at least a double column system
• CPC Class Codes: F25J 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• CPC Class Codes: F25J 2200/76 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 2210/02 Multiple feed streams, e.g. originating from different sources
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2210/62 Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
• 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 2270/904 by liquid or gaseous cryogen in an open loop
• CPC Class Codes: F25J 2290/50 Arrangement of multiple equipments fulfilling the same process step in parallel
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0214 Liquefied 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

Abstract

A process for recovering ethane and heavier hydrocarbons from LNG and a hydrocarbon gas stream is disclosed. The LNG feed stream is divided into two portions. The first is supplied to a fractionation column as a first upper mid-column feed. The second portion is heated while condensing a portion of a column distillation stream, thereby producing a “lean” LNG stream and a reflux stream. The reflux stream is supplied as top column feed. The second portion of LNG feed is heated further and supplied to the column as a first lower mid-column feed. The gas stream is divided into two portions. The second is expanded, then both portions are cooled while vaporizing the lean LNG stream and heating another portion of the distillation stream. The colder first portion is supplied to the column as a second upper mid-column feed, and the second is supplied as a second lower mid-column feed.

Claims

1. A process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components and a gas stream containing methane and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile liquid fraction containing a major portion of said heavier hydrocarbon components wherein

(a) said liquefied natural gas is divided into at least a first liquid stream and a second liquid stream;

(b) said first liquid stream is expanded to lower pressure and is thereafter supplied to a distillation column at an upper mid-column feed position;

(c) said second liquid stream is heated sufficiently to vaporize it, thereby forming a vapor stream;

(d) said vapor stream is expanded to said lower pressure and is supplied to said distillation column at a lower mid-column feed position;

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

(f) said first gaseous stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;

(g) said expanded substantially condensed first gaseous stream is thereafter supplied to said distillation column at an additional upper mid-column feed position;

(h) said second gaseous stream is expanded to said lower pressure, is cooled, and is thereafter supplied to said distillation column at an additional lower mid-column feed position;

(i) an overhead distillation stream is withdrawn from an upper region of said distillation column and divided into at least a first portion and a second portion, whereupon said first portion is compressed to higher pressure;

(j) said compressed first portion is cooled sufficiently to at least partially condense it and form thereby a condensed stream, with said cooling supplying at least a portion of said heating of said second liquid stream;

(k) said condensed stream is divided into at least a volatile liquid stream and a reflux stream;

(l) said reflux stream is further cooled, with said cooling supplying at least a portion of said heating of said second liquid stream;

(m) said further cooled reflux stream is supplied to said distillation column at a top column feed position;

(n) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;

(o) said second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream and said expanded second gaseous stream;

(p) said vaporized volatile liquid stream and said heated second portion are combined to form said volatile residue gas fraction containing a major portion of said methane; and

(q) the quantity and temperature of said reflux stream and the temperatures of said feeds to said distillation column are effective to maintain the overhead temperature of said distillation column at a temperature whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile liquid fraction by fractionation in said distillation column.

2. The process according to claim 1 wherein

(a) said expanded second gaseous stream is cooled sufficiently to partially condense it;

(b) said partially condensed expanded second gaseous stream is separated thereby to provide an additional vapor stream and a third liquid stream;

(c) said additional vapor stream is further cooled and thereafter supplied to said distillation column at said additional lower mid-column feed position;

(d) said third liquid stream is supplied to said distillation column at another lower mid-column feed position;

(e) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said additional vapor stream; and

(f) said second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said additional vapor stream.

3. The process accordingly to claim 1 wherein

(a) said second liquid stream is heated sufficiently to partially vaporize it;

(b) said partially vaporized second liquid stream is separated thereby to provide said vapor stream and a third liquid stream; and

(c) said third liquid stream is expanded to said lower pressure and thereafter supplied to said distillation column at another lower mid-column feed position.

4. The process according to claim 3 wherein

(a) said expanded second gaseous stream is cooled sufficiently to partially condense it;

(b) said partially condensed expanded second gaseous stream is separated thereby to provide an additional vapor stream and a fourth liquid stream;

(c) said additional vapor stream is further cooled and thereafter supplied to said distillation column at said additional lower mid-column feed position;

(d) said fourth liquid stream is supplied to said distillation column at a further lower mid-column feed position;

(e) said volatile liquid stream is heated sufficiently to vaporize it, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said additional vapor stream; and

(f) said second portion is heated, with said heating supplying at least a portion of said cooling of one or more of said first gaseous stream, said expanded second gaseous stream, and said additional vapor stream.

5. The process according to claim 1, 2, 3 or 4 wherein

(a) said liquefied natural gas is heated and thereafter divided into at least said first liquid stream and said second liquid stream;

and

(b) said cooling of said compressed first portion and said reflux stream supply at least a portion of said heating of said liquefied natural gas.