Integrated NGL recovery and liquefied natural gas production

Abstract

The separation of methane from an admixture ( 110 ) with ethane and higher hydrocarbons, especially natural gas, using a scrub column ( 114 ), in which the admixture is separated into a methane-rich overhead ( 116 ) that is partially condensed ( 122 ) to provide reflux to the column ( 114 ) and liquid methane-depleted bottoms liquid ( 126 ), is improved by providing additional reflux ( 136 ) derived from an ethane enriched stream ( 130 ) from fractionation ( 128 ) of the bottoms liquid. Preferably, absorber liquid ( 140 ) from the fractionation ( 128 ) also is introduced into the scrub column. The vapor fraction ( 120 ) remaining after partial condensation can be liquefied ( 122 ) to provide LNG product ( 124 ).

1 . In a process for recovery of components heavier than methane from a feed of methane in admixture with ethane and heavier hydrocarbon(s) by a process comprising: 
 introducing the feed into a scrub column at a first location;    withdrawing from the scrub column a first overhead vapor stream depleted in components heavier than methane and a bottoms stream enriched in components heavier than methane;    cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;    separating the first two-phase stream to provide a second overhead vapor stream and a methane-rich first reflux stream;    introducing the methane-rich first reflux stream at a second location in the scrub column above the first location; and    separating the bottoms stream into an ethane-enriched stream and one or more streams enriched in components heavier than ethane;    the improvement consisting in that an ethane-enriched second reflux stream is derived from the ethane-enriched stream and introduced into the scrub column at a location selected from the second location and a third location above the first location.    
     
     
         2 . The process of  claim 1 , wherein the ethane-enriched stream is condensed at temperature below that of the feed to the scrub column and the condensed stream pumped prior to introduction into the scrub column as the ethane-enriched second reflux stream.  
     
     
         3 . The process of  claim 2 , wherein said temperature is below −32° F.  
     
     
         4 . The process of  claim 1 , wherein the feed is a cooled natural gas feed.  
     
     
         5 . The process of  claim 1 , wherein the ethane-enriched second reflux stream is fed to the scrub column separately from the methane-rich first reflux stream.  
     
     
         6 . The process of  claim 1 , wherein the ethane-enriched second reflux stream is mixed with the methane-rich first reflux stream before introducing into the scrub column.  
     
     
         7 . The process of  claim 6 , wherein the ethane-enriched second reflux stream is combined with the first two-phase stream at a location selected from upstream of and in a reflux drum.  
     
     
         8 . The process of  claim 6 , wherein the first two-phase stream is fed to the bottom of an absorption column to which the ethane-enriched second reflux stream is fed as reflux.  
     
     
         9 . The process of  claim 6 , wherein the ethane-enriched stream is fully condensed before mixing with the methane-rich first reflux stream.  
     
     
         10 . The process of  claim 1 , wherein the ethane-enriched stream is the vapor overhead of a deethanizer.  
     
     
         11 . The process of  claim 1 , wherein an absorber liquid derived from the one or more streams enriched in components heavier than ethane is introduced into the scrub column at a location selected from the second location, the third location and a fourth location above the first location.  
     
     
         12 . The process of  claim 11 , wherein the absorber liquid ( 140 ) comprises pentane and isopentane.  
     
     
         13 . The process of  claim 11 , wherein the absorber liquid comprises C 4  hydrocarbon(s).  
     
     
         14 . The process of  claim 11 , wherein the absorber liquid comprises C 5+  hydrocarbon(s).  
     
     
         15 . The process of  claim 11 , wherein the absorber liquid is fed to the scrub column separately from either the ethane-enriched second reflux stream or the methane-rich first reflux stream.  
     
     
         16 . The process of  claim 11 , wherein the absorber liquid is combined with at least one of the methane-rich first reflux stream and the ethane-enriched second reflux stream before introducing into the scrub column.  
     
     
         17 . The process of  claim 16 , wherein the absorber liquid is combined with at least one of the first two-phase stream and the ethane-enriched second reflux stream at a location selected from upstream of and in a reflux drum.  
     
     
         18 . The process of  claim 16 , wherein the first two-phase stream is fed to the bottom of an absorption column to which at least one of the absorber liquid and the ethane-enriched second reflux stream is fed as reflux.  
     
     
         19 . The process of  claim 16 , wherein the absorber liquid is combined with the first overhead vapor stream before partial condensation of said stream to form the first two-phase stream.  
     
     
         20 . The process of  claim 11 , wherein the absorber liquid is combined with gaseous ethane-enriched stream before condensation of said stream to provide the second reflux stream.  
     
     
         21 . The process of  claim 20 , wherein the combined absorber liquid and gaseous ethane-enriched stream is phase separated and the liquid fraction is fed to the scrub column above the first location.  
     
     
         22 . The process of  claim 21 , wherein the vapor fraction is condensed and fed to the scrub column above the first location.  
     
     
         23 . The process of  claim 21 , wherein the liquid fraction is combined with the first overhead stream before partial condensation of that overhead stream to provide the first two-phase stream.  
     
     
         24 . The process of  claim 21 , wherein the condensed vapor fraction is combined with the first overhead stream before partial condensation of that overhead stream to provide the first two-phase stream.  
     
     
         25 . The process of  claim 24 , wherein both the condensed vapor fraction and the liquid fraction are combined with the first overhead stream before partial condensation of that overhead stream to provide the first two-phase stream.  
     
     
         26 . The process of  claim 1 , wherein the first overhead stream is partially condensed in two stages and liquid fraction from each condensation is fed to the scrub column as reflux.  
     
     
         27 . The process of  claim 1 , wherein the methane-rich first reflux stream constitutes at least about 80% of the total reflux (i.e. liquid fed to the scrub column above the first location).  
     
     
         28 . The process of  claim 1 , wherein the second reflux stream is less than about 20% of the total reflux (i.e. liquid fed to the scrub column above the first location).  
     
     
         29 . The process of  claim 11 , wherein the absorber liquid is less than about 10% of the total reflux (i.e. liquid fed to the scrub column above the first location).  
     
     
         30 . The process of  claim 1 , wherein the second reflux stream contains less than about 0.05% of propane.  
     
     
         31 . The process of  claim 1 , wherein methane is removed from the ethane-enriched stream whereby the second reflux stream consists essentially of ethane.  
     
     
         32 . The process of  claim 1 , wherein more than 90% of propane is recovered from the bottoms stream as product.  
     
     
         33 . The process of  claim 1 , wherein more than 90% of butane is recovered from the bottoms stream as product.  
     
     
         34 . The process of  claim 1 , wherein second overhead vapor is liquefied to provide liquefied natural gas (LNG) product.  
     
     
         35 . An apparatus for recovery of components heavier than methane from a feed of methane in admixture with ethane and heavier hydrocarbon(s) by a process of  claim 1 , said apparatus comprising: 
 a scrub column;    conduit means for introducing the feed into the scrub column at a first location;    conduit means for withdrawing from the scrub column a first overhead vapor stream depleted in components heavier than methane and a bottoms stream enriched in components heavier than methane;    heat exchanger means for cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;    separation means for separating the first two-phase stream to provide a second overhead vapor stream and a methane-rich first reflux stream;    conduit means for introducing the methane-rich first reflux stream at a second location in the scrub column above the first location;    separation means for separating the bottoms stream into an ethane-enriched stream and one or more streams enriched in components heavier than ethane; and    conduit means for introducing into the scrub column, at a location selected from the second location and a third location above the first location, an ethane-enriched second reflux stream derived from the ethane-enriched stream.    
     
     
         36 . The apparatus of  claim 35 , comprising heat exchange means for condensing the ethane-enriched stream at temperature below that of the feed to the scrub column and pumping means for pumping the condensed stream prior to introduction into the scrub column as the ethane-enriched second reflux stream.  
     
     
         37 . The apparatus of  claim 35 , comprising a reflux drum from which a mixture of the ethane-enriched second reflux stream and the methane-rich first reflux stream is fed to the scrub column.  
     
     
         38 . The apparatus of  claim 35 , comprising an absorption column which receives the first two-phase stream as a bottom feed and the ethane-enriched second reflux stream as reflux and from which the bottoms liquid is fed to the scrub column.  
     
     
         39 . The apparatus of  claim 35 , comprising conduit means for introducing into the scrub column, at a location selected from the second location, the third location and a fourth location above the first location, an absorber liquid enriched in component(s) heavier than ethane and provided by the separation means for separating the bottoms stream of the scrub column.  
     
     
         40 . The apparatus of  claim 39 , comprising a reflux drum from which a mixture of the absorber liquid and at least one of the methane-rich first reflux stream and the ethane-enriched second reflux stream is fed to the scrub column.  
     
     
         41 . The apparatus of  claim 39 , comprising an absorption column which receives the first two-phase stream as a bottom feed and at least one of the absorber liquid and the ethane-enriched second reflux stream as reflux and from which the bottoms liquid is fed to the scrub column.  
     
     
         42 . The apparatus of  claim 39 , comprising means for combining the absorber liquid with the first overhead vapor stream before partial condensation of said stream to form the first two-phase stream.  
     
     
         43 . The apparatus of  claim 39 , comprising means for combining the absorber liquid with gaseous ethane-enriched stream before condensation of said stream to provide the second reflux stream.  
     
     
         44 . The apparatus of  claim 43 , comprising separator means for phase separating the combined absorber liquid and gaseous ethane-enriched stream and conduit means for feeding the liquid fraction to the scrub column above the first location.  
     
     
         45 . The apparatus of  claim 44 , comprising heat exchange means for condensing the vapor fraction and conduit means for feeding the condensed vapor to the scrub column above the first location.  
     
     
         46 . The apparatus of  claim 44 , comprising means for combining the liquid fraction with the first overhead stream before partial condensation of that overhead stream to provide the first two-phase stream.  
     
     
         47 . The apparatus of  claim 45 , comprising means for combining the condensed vapor fraction with the first overhead stream before partial condensation of that overhead stream to provide the first two-phase stream.  
     
     
         48 . The apparatus of  claim 47 , comprising means for combining both the condensed vapor fraction and the liquid fraction with the first overhead stream before partial condensation of that overhead stream to provide the first two-phase stream.  
     
     
         49 . The apparatus of  claim 35 , comprising means for partially condensing the first overhead stream in two stages and feeding the liquid fraction from each condensation to the scrub column as reflux.