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, preheating and providing to a fractionation tower at two locations. A tower reflux stream is utilized.

1 . A process 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 comprising the steps of: 
 (a) splitting the LNG stream into a first feed stream and a second feed stream;    (b) preheating at least a portion of the first feed stream to provide 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;    (c) preheating at least a portion of the second feed stream to provide second tower feed stream and supplying second tower feed stream to the fractionation tower;    (d) cooling and partially condensing at least a portion of the tower overhead stream to produce a partially condensed tower overhead stream;    (e) separating the partially condensed tower overhead stream into a lean vapor stream and a tower reflux stream, and supplying the tower reflux stream to the fractionation tower;    (f) cooling the lean vapor stream such that the lean vapor 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 C 2  components, C 3  components and heavier components.  
   
   
       3 . The process according to  claim 1 , wherein the heavy hydrocarbon components include C 3  components and heavier components.  
   
   
       4 . The process according to  claim 1 , further comprising the step of compressing the lean vapor stream prior to the step of cooling the lean vapor stream.  
   
   
       5 . The process according to  claim 1 , wherein the step of cooling at least a portion of the tower overhead stream includes cooling at least a portion of the tower overhead stream by heat exchange contact with the at least a portion of the second feed stream thereby providing at least a portion of duty for the step of preheating the at least a portion of the second feed stream.  
   
   
       6 . The process according to  claim 1 , wherein the step of preheating at least a portion of the first feed stream and supplying the first tower feed stream to the fractionation tower includes supplying the first tower feed stream to the fractionation tower as a tower bottom feed stream.  
   
   
       7 . The process according to  claim 1 , wherein the step of preheating at least a portion of the first feed stream and supplying the first tower feed stream to the fractionation tower includes supplying the first tower feed stream to the fractionation tower at a position in the fractionation tower lower than the position where the second tower feed stream enters the fractionation tower.  
   
   
       8 . The process according to  claim 1 , wherein the step of separating the partially condensed tower overhead stream into the lean vapor stream and the tower reflux stream includes supplying the tower reflux stream as a top tower feed stream to the fractionation tower.  
   
   
       9 . The process according to  claim 1 , wherein the step of cooling the lean vapor stream includes cooling the lean vapor 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.  
   
   
       10 . The process according to  claim 1 , wherein the process further includes the step of cooling the tower reflux stream to create a cooled tower reflux stream and supplying the cooled tower reflux stream to the fractionation tower.  
   
   
       11 . The process according to  claim 10 , wherein the step of sending the cooled tower reflux stream to the fractionation tower includes sending the cooled tower reflux stream as a top feed stream to the fractionation tower.  
   
   
       12 . The process according to  claim 10 , wherein the step of cooling the tower reflux stream includes cooling the tower reflux stream by heat exchange contact with at least a portion of the first feed stream.  
   
   
       13 . A process 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 comprising the steps of: 
 preheating at least a portion of the LNG stream and supplying the at least a portion of the LNG stream to a fractionation tower as a first 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;    expanding at least a portion of the tower overhead stream to a lower pressure such that the at least a portion of the tower overhead stream is partially condensed to produce a partially condensed low pressure vapor stream;    separating the partially condensed low pressure vapor stream into a lean vapor stream and a tower reflux stream;    compressing the lean vapor stream;    cooling the lean vapor stream to create a lean LNG stream;    cooling the tower reflux stream thereby producing a cooled lean tower reflux stream; and    pumping the lean LNG stream to a high pressure lean LNG stream.    
   
   
       14 . The process according to  claim 13 , where the heavy hydrocarbon components include C 2  components, C 3  components and heavier components.  
   
   
       15 . The process according to  claim 13 , where the heavy hydrocarbon components include C 3  components and heavier components.  
   
   
       16 . The process according to  claim 13 , whereby the tower reflux stream is cooled by heat exchange contact with at least a portion of the LNG stream prior to the step of supplying the tower reflux stream  18  to the fractionation tower.  
   
   
       17 . The process according to  claim 13 , the step of supplying the tower reflux stream to the fractionation tower includes supplying the tower reflux stream to the fractionation tower as a top feed stream.  
   
   
       18 . The process according to  claim 13 , wherein the step of cooling the lean vapor stream includes cooling the lean vapor stream by heat exchange contact with at least a tower side reboiler stream thereby providing reboiling duty to the fractionation tower.  
   
   
       19 . The process according to  claim 13 , wherein the step of cooling the lean vapor stream includes cooling the lean vapor stream by heat exchange 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  3 .  
   
   
       20 . The process according to  claim 13 , wherein the step of supplying the at least a portion of the LNG stream to the fractionation tower includes supplying the at least a portion of the LNG stream to the fractionation tower as a tower bottom feed stream.  
   
   
       21 . An 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 apparatus comprising: 
 means for splitting the LNG stream into a first feed stream and a second feed stream;    a first exchanger operable to preheat the first feed stream to provide a first tower feed stream;    a fractionation tower for receiving the first 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;    a first cooler operable to cool and partially condense at least a portion of the tower overhead stream to produce a partially condensed tower overhead stream, the first cooler operable to allow for heat exchange between the portion of the tower overhead stream and the second feed stream;    a separator operable to separate the partially condensed overhead tower stream into a lean vapor stream and a tower reflux stream, the tower reflux stream operable to return to the fractionation tower, the first exchanger being operable to allow for heat exchange between the lean vapor stream and the first feed stream, the lean vapor stream being cooled in the first exchanger to provide a lean LNG stream; and    a pump operable for pumping the lean LNG stream to a high pressure LNG stream.    
   
   
       22 . The apparatus of  claim 21 , further including a first compressor for compressing the lean vapor stream.  
   
   
       23 . The apparatus of  claim 21 , further including a side reboiler for supplying at least a portion of reboiling requirements for the fractionation tower.