Method for recovery of natural gas liquids for liquefied natural gas

• US 20060130520A1
• Filed: 12/15/2005
• Published: 06/22/2006
• Est. Priority Date: 12/17/2004
• Status: Abandoned Application

• Current Assignee: ABB Lummus Global Inc. (ABB Limited)
• Original Assignee: ABB Lummus Global Inc. (ABB Limited)
• Inventors: Patel, Sanjiv N.
• Application Number:
  US11/300,742
• Publication Number:
  US 20060130520A1
• Time in Patent Office: Days
• US Class Current: 62/620
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/50 using multiple (re-)boiler-condensers at different heights of the column
• 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 2200/74 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 2205/02 using simple phase separation in a vessel or drum
• 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 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/04 Internal refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/88 Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided
• 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

The invention includes a process and apparatus for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components. The process includes splitting the LNG stream into two feed streams, preheating the resulting first feed stream and providing the feed stream to a fractionation tower at two locations.

Claims

1. A process for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components, the process comprising the steps of:

(a) splitting the LNG stream into a first feed stream and a second feed stream defining a second feed stream enthalpy;

(b) preheating at least a portion of the first feed stream to provide first tower feed stream defining a first tower feed stream enthalpy;

(c) supplying the first tower feed stream to a fractionation tower to produce a tower overhead stream including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream including the less volatile fraction containing the heavy hydrocarbon components;

(d) supplying second feed stream to the fractionation tower such that the first feed stream and the second tower feed stream have a substantially common composition and the first tower feed stream enthalpy differs from the second feed stream enthalpy;

(e) compressing the tower overhead stream to produce a compressed overhead stream;

(f) cooling the compressed overhead stream such that the compressed overhead stream is substantially condensed thereby producing a lean LNG stream; and

(g) pumping the lean LNG stream to a high pressure lean LNG stream.

2. The process according to claim 1, wherein the heavy hydrocarbon components include C2 components, C3 components and heavier components.

3. The process according to claim 1, wherein the heavy hydrocarbon components include C3 components and heavier components.

4. The process according to claim 1, wherein the step of supplying the fractionation tower with the second feed stream includes supplying the fractionation tower with the second feed stream at a position in the fractionation tower higher than the position where the first tower feed stream enters the fractionation tower.

5. The process according to claim 1, wherein the step of cooling the compressed tower overhead stream includes cooling the compressed tower overhead stream by heat exchange with at least a portion of the first feed stream thereby providing at least a portion of the duty for the step of preheating at least a portion of the first feed stream.

6. The process according to claim 1, further comprising the steps of splitting the high pressure lean LNG stream to create a lean tower reflux stream and a lean LNG product stream, cooling the lean tower reflux stream to produce a cooled lean tower reflux stream, and feeding the cooled lean tower reflux stream to the fractionation tower.

7. A process for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components, the process comprising the steps of:

(a) splitting the LNG stream into a first feed stream and a second feed stream and supplying the second feed stream to a fractionation tower as a second tower feed stream to produce a tower overhead stream including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream including the less volatile fraction containing the heavy hydrocarbon components;

(b) preheating at least a portion of the first feed stream to produce a first tower feed stream and supplying the first tower feed stream to the fractionation tower;

(c) compressing the tower overhead stream to produce compressed overhead stream;

(d) cooling the compressed overhead stream so that the compressed overhead stream is substantially condensed thereby producing a lean LNG stream;

(e) pumping the lean LNG stream to a high pressure to produce a high pressure lean LNG stream;

(f) splitting the high pressure lean LNG stream into a lean tower reflux stream and a lean LNG product stream;

(g) cooling the lean tower reflux stream to produce a cooled lean tower reflux stream; and

(h) supplying the cooled lean tower reflux stream to the fractionation tower.

8. The process according to claim 7, wherein the heavy hydrocarbon components include C2 components, C3 components and heavier components.

9. The process according to claim 7, wherein the heavy hydrocarbon components include C3 components and heavier components.

10. The process according to claim 7, wherein the step of supplying the fractionation tower with cooled lean tower reflux stream includes supplying the cooled lean tower reflux stream to a top portion of the fractionation tower.

11. The process according to claim 7, wherein the step of supplying the second tower feed stream to the fractionation tower includes supplying the second tower feed stream to the fractionation tower as a tower middle feed stream.

12. The process according to claim 7, wherein the step of supplying the cooled lean tower reflux stream to the fractionation tower includes supplying the cooled lean tower reflux stream to a top of the fractionation tower.

13. The process according to claim 7, wherein the step of cooling the tower overhead stream includes cooling the tower overhead stream by heat exchange contact with at least a portion of the first feed stream thereby providing at least a portion of the duty for the step of preheating at least a portion of the first feed stream.

14. The process according to claim 7, wherein the step of cooling the lean tower reflux stream includes cooling the lean tower reflux stream by heat exchange contact with the first feed stream thereby providing at least a portion of a duty for the step of preheating at least a portion of the first feed stream.

15. The process according to claim 7, wherein the step of cooling the tower overhead stream includes cooling the tower overhead stream by heat exchange contact with a tower side reboiler stream thereby providing at least a portion of a duty operable to provide reboiling for the fractionation tower.