System and method for improving propane recovery and ethane rejection in a gsp/ expander system

Abstract

A system and method for enhancing propane recovery in a GSP system operated in an ethane rejection mode using an add-on system comprising a heat exchanger and a condenser and optionally a reflux column having 0-5 theoretical stages. An overhead stream from a GSP fractionation column and a subcooled expanded GSP stream are diverted from the typical GSP process for processing in the add-on system to provide an additional reflux stream that increases the amount of ethane and propane that feeds into a top level of the GSP fractionation column. In ethane rejection mode, the add-on system results in an NGL product stream preferably comprising less than 6% of the ethane and at least 97% of the propane from the GSP feed stream.

I claim: 
     
         1 . A propane recovery system for increasing propane recovery in an NGL stream produced from a feed stream comprising methane, ethane, and propane in a GSP system operated in an ethane rejection mode, the GSP system comprising a fractionation column to separate a plurality of fractionation column feed streams comprising (1) a first stream comprising a subcooled expanded first part of a separator overhead stream, (2) a second stream comprising a subcooled expanded first part of a separator bottoms stream, (3) a third stream comprising an expanded second part of the separator overhead stream, and (4) a fourth stream comprising an expanded second part of the separator bottoms stream into a fractionation column overhead stream and a fractionation column bottoms stream;
 the propane recovery system comprising:   a first heat exchanger to warm the first stream through heat exchange with a first set of streams prior to the first stream feeding into the fractionation column;   a condenser for separating a condenser feed stream into a condenser overhead stream and a condenser bottoms stream;   wherein the second stream feeds into a top level of the fractionation column;   wherein the third stream and the warmed first stream feed into an upper level of the fractionation column below where the second stream feeds into the fractionation column;   wherein the fourth stream feeds into a mid-to-upper level of the fractionation column;   wherein the NGL stream comprises less than 6% of the ethane in the feed stream and more than 98% of the propane in the feed stream.   
     
     
         2 . The propane recovery system of  claim 1  wherein the first set of streams comprises the fractionation column overhead stream and wherein the condenser feed stream comprises the fractionation column overhead stream after passing through the first heat exchanger. 
     
     
         3 . The propane recovery system of  claim 1  wherein the first set of streams consists of the fractionation column overhead stream and wherein the condenser feed stream consists of the fractionation column overhead stream after passing through the first heat exchanger. 
     
     
         4 . The propane recovery system of  claim 2  wherein the feed stream comprises 10% or more ethane. 
     
     
         5 . The propane recovery system of  claim 2  wherein the plurality of fractionation column feed streams further comprises the condenser bottoms stream, which feeds into a top level of the fractionation column. 
     
     
         6 . The propane recovery system of  claim 1  further comprising a reflux column for separating the fractionation column overhead stream and the condenser bottoms stream into a reflux column overhead stream and a reflux column bottoms stream, wherein the reflux column has 0 to 5 theoretical stages. 
     
     
         7 . The propane recovery system of  claim 6  wherein the first set of streams comprises the reflux column overhead stream and wherein the condenser feed stream comprises the reflux column overhead stream after passing through the first heat exchanger. 
     
     
         8 . The propane recovery system of  claim 6  wherein the first set of streams consists of the reflux column overhead stream and wherein the condenser feed stream consists of the reflux column overhead stream after passing through the first heat exchanger. 
     
     
         9 . The propane recovery system of  claim 7  wherein the feed stream comprises 10% or more ethane. 
     
     
         10 . The propane recovery system of  claim 7  wherein the plurality of fractionation column feed streams further comprises the reflux column bottoms stream, which feeds into a top level of the fractionation column. 
     
     
         11 . A method for increasing propane recovery in an NGL stream produced from a feed stream comprising methane, ethane, and propane in a GSP system operated in an ethane rejection mode, the method comprising:
 (1) separating the feed stream in a separator into a separator overhead stream and a separator bottoms stream;   (2) splitting the separator overhead stream into a first portion and a second portion;   (3) splitting the separator bottoms stream into a first portion and a second portion;   (4) separating a plurality of fractionation column feed streams into a fractionation column overhead stream and a fractionation column bottoms stream in a fractionation column;   (5) separating a condenser feed stream into a condenser overhead stream and a condenser bottoms stream in a condenser;   (6) cooling at least a first part of the feed stream in a first heat exchanger through heat exchange with the condenser overhead stream prior to separating the first part of the feed stream step 1;   (7) cooling a first part of the separator overhead stream and a first part of the separator bottoms stream in a second heat exchanger through heat exchange with the condenser overhead stream in a second heat exchanger prior to the condenser overhead stream undergoing heat exchange in the first heat exchanger in step 6;   (8) expanding the first part of the separator overhead stream after cooling in the second heat exchanger;   (9) warming the first part of the separator overhead stream after expanding in step 8 in a third heat exchanger through heat exchange with a first set of streams;   (10) expanding the first part of the separator bottoms stream after heat exchange in the second heat exchanger in step 6;   (11) expanding a second portion of the separator overhead stream;   (12) expanding a second part of the separator bottoms stream;   wherein the plurality of fractionation column feed streams comprise: (a) the first part of the separator bottoms stream after expanding in step 10; (b) the first part of the separator overhead stream after the heat exchange in step 9; (c) the second part of the separator overhead stream after expanding in step 11; and (d) the second part of the separator bottoms stream after expanding in step 12.   
     
     
         12 . The method for increasing propane recovery of  claim 11  wherein the first set of streams in step 9 comprises the fractionation column overhead stream and wherein the condenser feed stream comprises the fractionation column overhead stream after heat exchange in step 9. 
     
     
         13 . The method of increasing propane recovery of  claim 11  wherein the first set of streams in step 9 consists of the fractionation column overhead stream and wherein the condenser feed stream consists of the fractionation column overhead stream after heat exchange in step 9. 
     
     
         14 . The method of increasing propane recovery of  claim 12  wherein the feed stream comprises 10% or more ethane. 
     
     
         15 . The method of increasing propane recovery of  claim 12  wherein the plurality of fractionation column feed streams further comprises the condenser bottoms stream. 
     
     
         16 . The method of increasing propane recovery of  claim 11  further comprising: (13) separating the fractionation column overhead stream and the condenser bottoms stream into a reflux column overhead stream and a reflux column bottoms stream in a reflux column, wherein the reflux column has 0 to 5 theoretical stages. 
     
     
         17 . The method of increasing propane recovery of  claim 16  wherein the first set of streams in step 9 comprises the reflux column overhead stream and wherein the condenser feed stream comprises the reflux column overhead stream after heat exchange in step 9. 
     
     
         18 . The method of increasing propane recovery of  claim 16  wherein the first set of streams in step 9 consists of the reflux column overhead stream and wherein the condenser feed stream consists of the reflux column overhead stream after heat exchange in step 9. 
     
     
         19 . The method of increasing propane recovery of  claim 17  wherein the feed stream comprises 10% or more ethane. 
     
     
         20 . The method of increasing propane recovery of  claim 17  wherein the plurality of fractionation column feed streams further comprises the reflux column bottoms stream.