Method for recovery of natural gas liquids for liquefied natural gas

Abstract

The invention includes a process and apparatus for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components. The process includes splitting the LNG stream into two feed streams, preheating the resulting first feed stream and providing the feed stream to a fractionation tower at two locations.

1 . A process for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components, the process comprising the steps of: 
 (a) splitting the LNG stream into a first feed stream and a second feed stream defining a second feed stream enthalpy;    (b) preheating at least a portion of the first feed stream to provide first tower feed stream defining a first tower feed stream enthalpy;    (c) supplying the first tower feed stream to a fractionation tower to produce a tower overhead stream including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream including the less volatile fraction containing the heavy hydrocarbon components;    (d) supplying second feed stream to the fractionation tower such that the first feed stream and the second tower feed stream have a substantially common composition and the first tower feed stream enthalpy differs from the second feed stream enthalpy;    (e) compressing the tower overhead stream to produce a compressed overhead stream;    (f) cooling the compressed overhead stream such that the compressed overhead stream is substantially condensed thereby producing a lean LNG stream; and    (g) pumping the lean LNG stream to a high pressure lean LNG stream.    
   
   
       2 . The process according to  claim 1 , wherein the heavy hydrocarbon components include C2 components, C3 components and heavier components.  
   
   
       3 . The process according to  claim 1 , wherein the heavy hydrocarbon components include C3 components and heavier components.  
   
   
       4 . The process according to  claim 1 , wherein the step of supplying the fractionation tower with the second feed stream includes supplying the fractionation tower with the second feed stream at a position in the fractionation tower higher than the position where the first tower feed stream enters the fractionation tower.  
   
   
       5 . The process according to  claim 1 , wherein the step of cooling the compressed tower overhead stream includes cooling the compressed tower overhead stream by heat exchange with at least a portion of the first feed stream thereby providing at least a portion of the duty for the step of preheating at least a portion of the first feed stream.  
   
   
       6 . The process according to  claim 1 , further comprising the steps of splitting the high pressure lean LNG stream to create a lean tower reflux stream and a lean LNG product stream, cooling the lean tower reflux stream to produce a cooled lean tower reflux stream, and feeding the cooled lean tower reflux stream to the fractionation tower.  
   
   
       7 . A process for separating a liquefied natural gas (LNG) stream containing methane and lighter components and heavy hydrocarbon components into a more volatile fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of the heavy hydrocarbon components, the process comprising the steps of: 
 (a) splitting the LNG stream into a first feed stream and a second feed stream and supplying the second feed stream to a fractionation tower as a second tower feed stream to produce a tower overhead stream including the more volatile fraction containing the substantial amount of the methane and lighter components and a tower bottoms stream including the less volatile fraction containing the heavy hydrocarbon components;    (b) preheating at least a portion of the first feed stream to produce a first tower feed stream and supplying the first tower feed stream to the fractionation tower;    (c) compressing the tower overhead stream to produce compressed overhead stream;    (d) cooling the compressed overhead stream so that the compressed overhead stream is substantially condensed thereby producing a lean LNG stream;    (e) pumping the lean LNG stream to a high pressure to produce a high pressure lean LNG stream;    (f) splitting the high pressure lean LNG stream into a lean tower reflux stream and a lean LNG product stream;    (g) cooling the lean tower reflux stream to produce a cooled lean tower reflux stream; and    (h) supplying the cooled lean tower reflux stream to the fractionation tower.    
   
   
       8 . The process according to  claim 7 , wherein the heavy hydrocarbon components include C2 components, C3 components and heavier components.  
   
   
       9 . The process according to  claim 7 , wherein the heavy hydrocarbon components include C3 components and heavier components.  
   
   
       10 . The process according to  claim 7 , wherein the step of supplying the fractionation tower with cooled lean tower reflux stream includes supplying the cooled lean tower reflux stream to a top portion of the fractionation tower.  
   
   
       11 . The process according to  claim 7 , wherein the step of supplying the second tower feed stream to the fractionation tower includes supplying the second tower feed stream to the fractionation tower as a tower middle feed stream.  
   
   
       12 . The process according to  claim 7 , wherein the step of supplying the cooled lean tower reflux stream to the fractionation tower includes supplying the cooled lean tower reflux stream to a top of the fractionation tower.  
   
   
       13 . The process according to  claim 7 , wherein the step of cooling the tower overhead stream includes cooling the tower overhead stream by heat exchange contact with at least a portion of the first feed stream thereby providing at least a portion of the duty for the step of preheating at least a portion of the first feed stream.  
   
   
       14 . The process according to  claim 7 , wherein the step of cooling the lean tower reflux stream includes cooling the lean tower reflux stream by heat exchange contact with the first feed stream thereby providing at least a portion of a duty for the step of preheating at least a portion of the first feed stream.  
   
   
       15 . The process according to  claim 7 , wherein the step of cooling the tower overhead stream includes cooling the tower overhead stream by heat exchange contact with a tower side reboiler stream thereby providing at least a portion of a duty operable to provide reboiling for the fractionation tower.