NGL Extraction from Liquefied Natural Gas

Abstract

A process of extraction of natural gas liquids from a liquefied natural gas stream is disclosed.

1 . A process for the separation of C 2 + or C 3 + hydrocarbons from a liquefied natural gas (LNG) stream, comprising:
 providing a first stream of liquid LNG having a pressure of at least 600 psig;   passing the first stream through a first heat exchanger to vaporize the LNG and form a second stream;   expanding the second stream in an turbo-expander to form a third stream having reduced pressure and temperature as compared to the second stream;   introducing a first portion of the third stream to a distillation column at one or more feed trays;   passing a second portion of the third stream through the first heat exchanger to be cooled by heat exchange with the first stream to form a fourth stream;   introducing the fourth stream to the distillation column at a point higher than the first portion of the third stream inlet;   withdrawing a fifth stream of vapor hydrocarbon from an upper portion of the distillation column having a reduced content of C 2 + or C 3 + hydrocarbons as compared to the first stream;   compressing the fifth stream in a turbo-compressor coupled to and powered by the turbo-expander;   withdrawing a sixth stream of liquid hydrocarbon from a lower portion of the distillation column having an increased content of C 2 + or C 3 + hydrocarbons as compared to the first stream.   
   
   
       2 . The process of  claim 1 , wherein said distillation column is operated with a bottom temperature of about 0° F. to about 250° F. and a top temperature of about −200° F. to about 0° F. 
   
   
       3 . The process of  claim 1 , wherein said column is operated at a pressure of about 150 psig to about 550 psig. 
   
   
       4 . The process of  claim 1 , wherein the fourth stream provides from 1% to 50% of the total feed to the distillation column. 
   
   
       5 . The process of  claim 1 , wherein the fourth stream provides from 20% to 40% of the total feed to the distillation column. 
   
   
       6 . The process of  claim 1 , wherein the expansion of the second stream in the turbo-expander to form the third stream generates work and said work is utilized to compress the fifth stream in the turbo-compressor. 
   
   
       7 . The process of  claim 1 , wherein the turbo-compressor provides at least 30% of the required compression for the fifth stream to reach a pipeline pressure. 
   
   
       8 . The process of  claim 1 , wherein the turbo-compressor provides at least 50% of the required compression for the fifth stream to reach a pipeline pressure. 
   
   
       9 . The process of  claim 1 , wherein the turbo-compressor provides less than 100% of the required compression for the fifth stream to reach a pipeline pressure. 
   
   
       10 . The process of  claim 1 , wherein the second stream entering the turbo-expander is at a higher temperature than the fifth stream entering the turbo-compressor. 
   
   
       11 . The process of  claim 1 , wherein the temperature of the second stream entering the turbo-expander is at least 50° F. higher temperature than the fifth stream entering the turbo-compressor. 
   
   
       12 . The process of  claim 1 , wherein the temperature of the second stream entering the turbo-expander is at least 100° F. higher temperature than the fifth stream entering the turbo-compressor. 
   
   
       13 . The process of  claim 1 , wherein the fifth stream before and after the turbo-compressor has either a pressure of at least 700 psig, or a temperature greater than −50° F., or both. 
   
   
       14 . A process for the separation of C 2 + or C 3 + hydrocarbons from a liquefied natural gas (LNG) stream, comprising:
 vaporizing a first LNG stream to provide a first stream of vaporized natural gas having a pressure of at least 600 psig;   expanding the first stream in an turbo-expander to form a second stream having reduced pressure and temperature as compared to the first stream;   introducing the second stream to a distillation column at one or more feed trays;   providing a third stream of liquid LNG having a pressure of at least 150 psig;   introducing the third stream to the distillation column at a point higher than the second stream inlet;   withdrawing a fourth stream of vapor hydrocarbon from an upper portion of the distillation column having a reduced content of C 2 + or C 3 + hydrocarbons as compared to the first stream;   compressing the fourth stream in a turbo-compressor coupled to and powered by the turbo-expander;   withdrawing a fifth stream of liquid NGL hydrocarbon from a lower portion of said distillation column having an increased content of C 2 + or C 3 + hydrocarbons as compared to the first stream.   
   
   
       15 . The process of  claim 14 , wherein said distillation column is operated with a bottom temperature of about 0° F. to about 250° F. and a top temperature of about −200° F. to about 0° F. 
   
   
       16 . The process of  claim 14 , wherein said column is operated at a pressure of about 150 psig to about 550 psig. 
   
   
       17 . The process of  claim 14 , wherein the second stream provides from 1% to 50% of the total feed to the distillation column. 
   
   
       18 . The process of  claim 14 , wherein the second stream provides from 20% to 40% of the total feed to the distillation column. 
   
   
       19 . The process of  claim 14 , wherein the expansion of the first stream in the turbo-expander to form the second stream generates work and said work is utilized to compress the fourth stream in the turbo-compressor. 
   
   
       20 . The process of  claim 14 , wherein the turbo-compressor provides at least 30% of the required compression for the fourth stream to reach a pipeline pressure. 
   
   
       21 . The process of  claim 14 , wherein the turbo-compressor provides at least 50% of the required compression for the fourth stream to reach a pipeline pressure. 
   
   
       22 . The process of  claim 14 , wherein the turbo-compressor provides less than 100% of the required compression for the fourth stream to reach a pipeline pressure. 
   
   
       23 . The process of  claim 14 , wherein the first stream entering the turbo-expander is at a higher temperature than the fourth stream entering the turbo-compressor. 
   
   
       24 . The process of  claim 14 , wherein the temperature of the first stream entering the turbo-expander is at least 50° F. higher temperature than the fourth stream entering the turbo-compressor. 
   
   
       25 . The process of  claim 14 , wherein the temperature of the first stream entering the turbo-expander is at least 100° F. higher temperature than the fourth stream entering the turbo-compressor. 
   
   
       26 . The process of  claim 14 , wherein the fourth stream before and after the turbo-compressor has either a pressure of at least 700 psig, or a temperature greater than −50° F., or both.