Methods and Systems for Recovering Liquified Petroleum Gas from Natural Gas

• US 20120000245A1
• Filed: 06/30/2011
• Published: 01/05/2012
• Est. Priority Date: 07/01/2010
• Status: Abandoned Application

• Current Assignee: Black & Veatch International Company (Black & Veatch Corporation)
• Original Assignee: Black & Veatch Corporation
• Inventors: Mortko, Robert A., Currence, Kevin L.
• Application Number:
  US13/174,002
• Publication Number:
  US 20120000245A1
• Time in Patent Office: Days
• US Class Current: 62/620
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• 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 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 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• 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 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 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

A process and system is provided for separating a feed gas stream containing methane, at least one C₂ component, at least one C₃ component, and optionally heavier components, into a volatile gas stream containing a major portion of the methane and at least one C₂ component and a less volatile stream containing a major portion of the at least one C₃ and heavier components. The feed stream is cooled, at least partially condensed, and fed to a fractionation column wherein the feed stream is separated into an overhead vapor stream comprising primarily the lighter components of the feed stream and a bottoms liquid stream comprising primarily the heavier components of the feed stream. The introduction of a reboiler onto the fractionation column assists in removing co-absorbed C₂ and lighter components from the fractionation column bottoms thereby facilitating more efficient operation of a downstream deethanizer column. Addition of residue recycle can further supplement recovery of desired components.

Claims

1. A process for separating a feed gas stream containing methane, at least one C₂ component, and at least one C₃ component into a volatile gas stream containing a major portion of the methane and at least one C₂ component and a less volatile stream containing a major portion of the at least one C₃ component, the process comprising:

a) cooling the feed gas stream to a temperature sufficient to condense the majority of the at least one C₃ component in the feed gas stream to produce a cooled feed stream;

b) introducing the cooled feed stream into a separator vessel to separate the cooled feed stream into a separator gas stream and a separator liquid stream;

c) introducing at least a portion of both of the separator gas and liquid streams from the separator vessel into a fractionation column to produce a fractionation column bottoms product and a fractionation column overhead residue gas stream;

d) introducing the fractionation column bottoms product into a deethanizer tower and producing a deethanizer bottoms stream comprising a majority of the at least one C₃ component and a deethanizer overhead gas stream;

e) cooling and at least partially condensing the deethanizer overhead gas stream thereby producing a deethanizer liquid reflux stream and a deethanizer residue gas stream; and

f) introducing at least a portion of the deethanizer liquid reflux stream into the fractionation column.

2. The process according to claim 1, wherein the fractionation column further includes a reboiler operable to vaporize at least a portion of a fractionation column liquid, the vaporized fractionation column liquid being reintroduced into the fractionation column.

3. The process according to claim 1, further comprising:

g) combining the fractionation column overhead residue gas stream with at least a portion of the deethanizer residue gas stream to form a combined residue gas stream;

h) compressing and cooling at least a portion of the combined residue gas stream to produce a residue gas reflux stream; and

i) introducing the residue gas reflux stream into the fractionation column.

4. The process according to claim 1, wherein the process further comprises:

g) compressing and cooling at least a portion of the fractionation column overhead residue gas stream to produce a residue gas reflux stream; and

h) introducing the residue gas reflux stream into the fractionation column.

5. A process for separating a feed gas stream containing methane, at least one C2 component, and at least one C3 component into a volatile gas stream containing a major portion of the methane and at least one C2 component and a less volatile stream containing a major portion of the at least one C3 component, the process comprising:

a) cooling the feed gas stream to a temperature sufficient to condense the majority of the at least one C3 component in the feed gas stream to produce a cooled feed stream;

b) passing the cooled feed stream to a fractionation column to produce a liquid fractionation column bottoms product and a fractionation column overhead residue gas stream, the fractionation column including a reboiler operable to vaporize at least a portion of a fractionation column liquid, the vaporized fractionation column liquid being reintroduced into the fractionation column;

c) introducing the fractionation column bottoms product into a deethanizer tower and producing a deethanizer bottoms stream comprising a majority of the at least one C₃ component and a deethanizer overhead gas stream;

d) cooling and at least partially condensing the deethanizer overhead gas stream thereby producing a deethanizer liquid reflux stream and a deethanizer residue gas stream; and

e) introducing at least a portion of the deethanizer liquid reflux stream into the fractionation column.

6. The process according to claim 5, wherein the process further comprises:

f) compressing and cooling at least a portion of the fractionation column overhead residue gas stream to produce a residue gas reflux stream; and

g) introducing the residue gas reflux stream into the fractionation column.

7. The process according to claim 6, wherein prior to step (b) introducing the cooled feed stream into a separator vessel to separate the cooled feed stream into a separator gas stream and a separator liquid stream.

8. The process according to claim 6, wherein the process further comprises, prior to step (f), combining at least a portion of the deethanizer residue gas stream with the at least a portion of the fractionation column overhead gas residue stream.

9. The process according to claim 9, wherein prior to step (b) introducing the cooled feed stream into a separator vessel to separate the cooled feed stream into a separator gas stream and a separator liquid stream.

10. A process for separating a feed gas stream containing methane, at least one C₂ component, and at least one C₃ component into a volatile gas stream containing a major portion of the methane and at least one C₂ component and a less volatile stream containing a major portion of the at least one C₃ component, the process comprising:

a) cooling the feed gas stream to a temperature sufficient to condense the majority of the at least one C₃ component in the feed gas stream to produce a cooled feed stream;

b) passing the cooled feed stream to a fractionation column to produce a liquid fractionation column bottoms product and a fractionation column overhead residue gas stream,

c) introducing the fractionation column bottoms product into a deethanizer tower and producing a deethanizer bottoms stream comprising a majority of the at least one C₃ component and a deethanizer overhead gas stream;

d) cooling and at least partially condensing the deethanizer overhead gas stream thereby producing a deethanizer liquid reflux stream and a deethanizer residue gas stream;

e) introducing at least a portion of the deethanizer liquid reflux stream into the fractionation column;

f) compressing and cooling at least a portion of the fractionation column over-head residue gas stream to produce a residue gas reflux stream; and

g) introducing the residue gas reflux stream into the fractionation column.

11. The process according to claim 10, wherein prior to step (f), at least a portion of the deethanizer overhead gas stream is combined with the fractionation column overhead residue gas stream.

12. A system for separating a feed gas stream containing methane, at least one C₂ component, and at least one C₃ component into a volatile gas stream containing a major portion of the methane and at least one C₂ component and a less volatile stream containing a major portion of the at least one C₃ component, the system comprising:

a) a feed stream heat exchanger configured to cool the feed gas stream to a temperature sufficient to condense the majority of the at least one C₃ component in the feed gas stream to produce a cooled feed stream;

b) a separator vessel located downstream from the first heat exchanger and configured to separate the cooled feed stream into a separator gas stream and a separator liquid stream;

c) a fractionation column located downstream from the separator vessel and configured to receive at least a portion of both the separator gas and liquid streams and produce a fractionation column bottoms product and a fractionation column overhead residue gas stream;

d) a deethanizer tower located downstream from the separator vessel and configured to receive at least a portion of the fractionation column bottoms product and produce a deethanizer bottoms stream comprising a majority of the at least one C₃ component and a deethanizer overhead gas stream;

e) a deethanizer heat exchanger configured to receive and cool the deethanizer overhead gas stream; and

f) a deethanizer separation vessel configured to separate the cooled deethanizer overhead gas stream into a deethanizer liquid reflux stream and a deethanizer residue gas stream.

13. The system according to claim 12, wherein the fractionation column further includes a reboiler configured to vaporize at least a portion of a fractionation column liquid and reintroduce the vaporized fractionation column liquid back into the fractionation column.

14. The system according to claim 12, further comprising:

g) conduit configured to merge at least a portion of the deethanizer residue gas stream with at least a portion of the fractionation column overhead residue gas stream to form a combined residue gas stream;

h) a residue gas heat exchanger configured to receive at least a portion of the combined residue gas stream and to produce a residue gas reflux stream; and

i) conduit configured to deliver at least a portion of the residue gas reflux stream from the residue gas heat exchanger to the fractionation column.

15. The system according to claim 12, further comprising:

g) a compressor located upstream from the residue gas heat exchanger and configured to compress the combined residue gas stream.

16. A system for separating a feed gas stream containing methane, at least one C₂ component, and at least one C₃ component into a volatile gas stream containing a major portion of the methane and at least one C₂ component and a less volatile stream containing a major portion of the at least one C₃ component, the system comprising:

a) a feed stream heat exchanger configured to cool the feed gas stream to a temperature sufficient to condense the majority of the at least one C₃ component in the feed gas stream to produce a cooled feed stream;

b) a fractionation column configured to receive the cooled feed stream and produce a fractionation column bottoms product and a fractionation column overhead residue gas stream, the fractionation column including a reboiler configured to vaporize at least a portion of a fractionation column liquid and reintroduce the vaporized fractionation column liquid back into the fractionation column;

c) a deethanizer tower located downstream from the fractionation column and configured to receive at least another portion of the fractionation column bottoms product and produce a deethanizer bottoms stream comprising a majority of the at least one C₃ component and a deethanizer overhead gas stream;

d) a deethanizer heat exchanger configured to receive and cool the deethanizer overhead gas stream; and

e) a deethanizer separation vessel configured to separate the cooled deethanizer overhead gas stream into a deethanizer liquid reflux stream and a deethanizer residue gas stream.

17. The system according to claim 16, the system further comprising:

f) a residue gas heat exchanger configured to condense at least a portion of the fractionation column overhead residue gas stream to form a residue gas reflux stream; and

g) conduit configured to deliver at least a portion of the residue gas reflux stream from the residue gas heat exchanger to the fractionation column.

18. The system according to claim 16, further comprising:

f) a compressor located upstream from the residue gas heat exchanger and configured to compress the fractionation column overhead residue gas stream.

19. The system according to claim 16, further comprising:

f) conduit configured to merge at least a portion of the deethanizer residue gas stream with at least the fractionation column overhead residue gas stream to form a combined residue gas stream.

20. A system for separating a feed gas stream containing methane, at least one C₂ component, and at least one C₃ component into a volatile gas stream containing a major portion of the methane and at least one C₂ component and a less volatile stream containing a major portion of the at least one C₃ component, the system comprising:

a) a feed stream heat exchanger configured to cool the feed gas stream to a temperature sufficient to condense the majority of the at least one C₃ component in the feed gas stream to produce a cooled feed stream;

b) a fractionation column configured to receive the cooled feed stream and produce a fractionation column bottoms product and a fractionation column overhead residue gas stream;

c) a deethanizer tower located downstream from the fractionation column and configured to receive at least a portion of the fractionation column bottoms product and produce a deethanizer bottoms stream comprising a majority of the at least one C₃ component and a deethanizer overhead gas stream;

d) a deethanizer heat exchanger configured to receive and cool the deethanizer overhead gas stream;

e) a deethanizer separation vessel configured to separate the cooled deethanizer overhead gas stream into a deethanizer liquid reflux stream and a deethanizer residue gas stream;

f) conduit configured to deliver at least a portion of the deethanizer liquid reflux stream to the fractionation column;

g) a residue gas heat exchanger configured to condense at least a portion of the fractionation column overhead residue gas stream; and

h) conduit configured to deliver at least a portion of the condensed fractionation column overhead residue gas stream to the fractionation column.

21. The system according to claim 20, further comprising:

i) conduit configured to merge at least a portion of the deethanizer residue gas stream with at least the fractionation column overhead residue gas stream to form a combined residue gas stream.