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 . An apparatus for producing natural gas liquids (NGL) and liquefied natural gas (LNG) from a natural gas feed of methane in admixture with ethane and heavier hydrocarbon(s), comprising:
 a scrub column;   a first conduit for introducing a natural gas feed of methane in admixture with ethane and heavier hydrocarbon(s) into the scrub column at a first location;   a second conduit for withdrawing from the scrub column a first overhead vapor stream depleted in components heavier than methane   a third conduit for withdrawing from the scrub column a bottoms stream enriched in components heavier than methane;   a first heat exchanger for cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;   a first separator for separating the first two-phase stream to provide a second overhead vapor stream and a methane-rich first reflux stream;   a fourth conduit for introducing the methane-rich first reflux stream at a second location in the scrub column above the first location;   a second heat exchanger for liquefying the second overhead vapor stream to provide a LNG product stream and fully condensing, at temperature below that of the natural gas feed to the scrub column, an ethane-enriched stream;   a second separator for separating the bottoms stream to provide the ethane-enriched stream and one or more NGL streams enriched in components heavier than ethane;   a fifth conduit for feeding the ethane-enriched stream into the second heat exchanger;   a sixth conduit for feeding into the scrub column, as a second reflux stream at a location above the first location, the condensed ethane-enriched stream; and   a pump for pumping the condensed ethane-enriched stream prior to introduction into the scrub column.   
     
     
         2 . The apparatus of  claim 1 , wherein the first heat exchanger for cooling and partially condensing the first overhead vapor stream is the warm bundle of the second heat exchanger. 
     
     
         3 . The apparatus of  claim 1 , wherein the first separator is a reflux drum. 
     
     
         4 . The apparatus of  claim 1 , wherein the first separator is an absorption column which receives the first two-phase stream as a bottom feed stream and the ethane-enriched second reflux stream as a reflux stream and from which the bottoms liquid is fed to the scrub column. 
     
     
         5 . The apparatus of  claim 1 , wherein an absorber liquid stream enriched in component(s) heavier than ethane and provided by the second separator is introduced into the scrub column at a location above the first location. 
     
     
         6 . The apparatus of  claim 5 , wherein the first separator is a reflux drum from which a mixture of the absorber liquid stream and at least one of the methane-rich first reflux stream and the ethane-enriched second reflux stream is fed to the scrub column. 
     
     
         7 . The apparatus of  claim 5 , wherein the first separator is an absorption column which receives the first two-phase stream as a bottom feed stream and at least one of the absorber liquid stream and the ethane-enriched second reflux stream as a reflux stream and from which the bottoms liquid stream is fed to the scrub column. 
     
     
         8 . The apparatus of  claim 5 , wherein the absorber liquid stream is combined with the first overhead vapor stream before partial condensation of the first overhead vapor stream to form the first two-phase stream. 
     
     
         9 . The apparatus of  claim 5 , wherein the absorber liquid stream is combined with a gaseous ethane-enriched stream before condensation of the gaseous ethane-enriched stream to provide the second reflux stream. 
     
     
         10 . The apparatus of  claim 9 , further comprising a third separator for phase separating a combined stream of the absorber liquid stream and the gaseous ethane-enriched stream and a seventh conduit for feeding a liquid fraction stream from the third separator to the scrub column above the first location. 
     
     
         11 . The apparatus of  claim 10 , further comprising a third heat exchanger for condensing a vapor fraction stream from the third separator and an eight conduit for feeding the condensed vapor stream to the scrub column above the first location. 
     
     
         12 . The apparatus of  claim 10 , wherein the liquid fraction stream is combined with the first overhead stream before partial condensation of the first overhead stream to provide the first two-phase stream. 
     
     
         13 . The apparatus of  claim 11 , wherein the condensed vapor fraction stream is combined with the first overhead stream before partial condensation of the first overhead stream to provide the first two-phase stream. 
     
     
         14 . The apparatus of  claim 13 , wherein both the condensed vapor fraction stream and the liquid fraction stream are combined with the first overhead stream before partial condensation of the first overhead stream to provide the first two-phase stream. 
     
     
         15 . The apparatus of  claim 5 , wherein the first overhead stream is partially condensed in two stages and the liquid fraction stream from each condensation is fed to the scrub column as a reflux stream. 
     
     
         16 . An apparatus for producing natural gas liquids (NGL) and liquefied natural gas (LNG) from a natural gas feed of methane in admixture with ethane and heavier hydrocarbon(s), comprising:
 a scrub column;   a first conduit fluidly connected to the scrub column for introducing a natural gas feed of methane in admixture with ethane and heavier hydrocarbon(s) into the scrub column at a first location;   a second conduit fluidly connected to the scrub column for withdrawing a first overhead vapor stream depleted in components heavier than methane;   a third conduit fluidly connected to the scrub column for withdrawing a bottoms stream enriched in components heavier than methane;   a first heat exchanger fluidly connected to the second conduit for cooling and partially condensing the first overhead vapor stream to form a first two-phase stream;   a first separator fluidly connected to the first heat exchanger for separating the first two-phase stream to provide a second overhead vapor stream and a methane-rich first reflux stream;   a fourth conduit fluidly connected to the first separator for introducing the methane-rich first reflux stream at a second location in the scrub column above the first location;   a second heat exchanger for liquefying the second overhead vapor stream to provide a LNG product stream and fully condensing, at temperature below that of the natural gas feed to the scrub column, an ethane-enriched stream;   a second separator for separating the bottoms stream to provide the ethane-enriched stream and one or more NGL streams enriched in components heavier than ethane;   a fifth conduit fluidly connected to the second separator for feeding the ethane-enriched stream into the first heat exchanger;   a sixth conduit fluidly connected to the first heat exchanger for feeding into the scrub column, as a second reflux stream at a location above the first location, the condensed ethane-enriched stream,   wherein a pump, fluidly connected to the sixth conduit, pressurizes the condensed ethane-enriched stream prior to introduction into the scrub column.   
     
     
         17 . The apparatus of  claim 16 , wherein the first heat exchanger and the second heat exchanger are a single main heat exchanger. 
     
     
         18 . The apparatus of  claim 16 , wherein the first separator is a reflux drum. 
     
     
         19 . The apparatus of  claim 16 , wherein the first separator is an absorption column. 
     
     
         20 . The apparatus of  claim 17 , further comprising a seventh conduit for providing a mixed refrigerant stream to the main heat exchanger to provide refrigeration.