Methods and Systems for Recovering Liquified Petroleum Gas from Natural Gas

Abstract

A process and system is provided for separating a feed gas stream containing methane, at least one C 2 component, at least one C 3 component, and optionally heavier components, into a volatile gas stream containing a major portion of the methane and at least one C 2 component and a less volatile stream containing a major portion of the at least one C 3 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 C 2 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.

1 . A process for separating a feed gas stream containing methane, at least one C 2  component, and at least one C 3  component into a volatile gas stream containing a major portion of the methane and at least one C 2  component and a less volatile stream containing a major portion of the at least one C 3  component, the process comprising:
 a) cooling the feed gas stream to a temperature sufficient to condense the majority of the at least one C 3  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 C 3  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 C 3  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 C 2  component, and at least one C 3  component into a volatile gas stream containing a major portion of the methane and at least one C 2  component and a less volatile stream containing a major portion of the at least one C 3  component, the process comprising:
 a) cooling the feed gas stream to a temperature sufficient to condense the majority of the at least one C 3  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 C 3  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 C 2  component, and at least one C 3  component into a volatile gas stream containing a major portion of the methane and at least one C 2  component and a less volatile stream containing a major portion of the at least one C 3  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 C 3  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 C 3  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 C 2  component, and at least one C 3  component into a volatile gas stream containing a major portion of the methane and at least one C 2  component and a less volatile stream containing a major portion of the at least one C 3  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 C 3  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 C 3  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 C 2  component, and at least one C 3  component into a volatile gas stream containing a major portion of the methane and at least one C 2  component and a less volatile stream containing a major portion of the at least one C 3  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 C 3  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 C 3  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.