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 preheating the LNG stream prior to introduction to the fractionation tower. At least part of the tower overhead stream is cooled to substantially condense that portion. This is then pumped to high pressure to produce a high pressure lean LNG stream which is then split into two streams, one of which is cooled and used as reflux to the fractionation tower.

1 . A process for separating a liquefied natural (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) preheating at least a portion of the LNG stream to produce a first tower feed stream and 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;    (b) cooling at least a portion of the tower overhead stream so that the portion of the tower overhead stream is at least substantially condensed thereby producing a lean LNG stream;    (c) pumping the lean LNG stream to a high pressure to produce a high pressure lean LNG stream;    (d) splitting the high pressure lean LNG stream into a lean tower reflux stream and a lean LNG product stream;    (e) cooling the lean tower reflux stream to produce a cooled lean tower reflux stream; and    (f) supplying the cooled lean tower reflux stream to the fractionation tower.    
   
   
       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 cooling at least a portion of the tower overhead stream includes cooling the at least a portion of the tower overhead stream by heat exchange contact with at least a portion of the LNG stream thereby providing at least a portion of the duty for the step of preheating at least a portion of the LNG stream.  
   
   
       5 . The process of  claim 1 , wherein the step of cooling the lean tower reflux stream includes cooling the lean tower reflux stream by heat exchange contact with at least a portion of the LNG stream thereby providing at least a portion of the duty for the step of preheating at least a portion of the LNG stream.  
   
   
       6 . The process according to  claim 1 , wherein the step of supplying the first tower feed stream to the fractionation tower includes supplying the first tower feed stream to the fractionation tower at a position below cooled lean tower reflux stream.  
   
   
       7 . The process according to  claim 1 , wherein the step of supplying the cooled lean tower reflux stream to the fractionation tower includes supplying the cooled lean tower reflux stream to the fractionation tower as a tower top feed stream.  
   
   
       8 . 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: 
 preheating at least a portion of the LNG stream to produce a first tower feed and supplying the first tower feed 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;    cooling and thereby partially condensing at least a portion of the tower overhead stream to produce a partially condensed tower overhead stream;    separating the partially condensed tower overhead stream into a lean vapor stream and a lean LNG stream;    pumping the lean LNG stream to a high pressure to produce a high pressure lean LNG stream;    splitting the high pressure lean LNG stream into 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;    supplying the cooled lean tower reflux stream to the fractionation tower;    compressing the lean vapor stream to high pressure to produce a compressed second lean vapor stream; and    combining the compressed second lean vapor stream with the lean LNG product stream.    
   
   
       9 . The process according to  claim 8 , wherein the heavy hydrocarbon components include C2 components, C3 components and heavier components.  
   
   
       10 . The process according to  claim 8 , wherein the heavy hydrocarbon components include C3 components and heavier components.  
   
   
       11 . The process according to  claim 8 , further including the step of removing at least a portion of the LNG stream as a second feed stream and supplying the second feed stream to the fractionation tower at a location above a feed location for the LNG stream.  
   
   
       12 . The process according to  claim 8 , 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 8 , wherein the step of supplying at least a portion of the LNG stream to the fractionation tower includes supplying at least a portion of the LNG stream to the fractionation tower as a bottom tower feed stream.  
   
   
       14 . The process according to  claim 8 , wherein the step of cooling and thereby partially condensing at least a portion of the tower overhead stream includes cooling the at least a portion of the tower overhead stream by heat exchange contact with at least a portion of the LNG stream thereby providing at least a portion of duty for the step of preheating the at least a portion of the LNG stream.  
   
   
       15 . The process according to  claim 8 , wherein the step of cooling the cooled lean tower reflux stream includes cooling the cooled lean tower reflux stream by heat exchange contact with at least a portion of the LNG stream thereby providing at least a portion of duty for the step of preheating the at least a portion of the LNG stream.  
   
   
       16 . The process according to  claim 8 , wherein the step of supplying the cooled lean tower reflux stream to the fractionation tower includes supplying the cooled lean tower reflux stream to the fractionation tower as a top tower feed stream.