Process and apparatus for separation of hydrocarbons from liquefied natural gas

Abstract

An apparatus and process for separating a feed liquefied natural gas containing at least methane and a hydrocarbon less volatile the methane, into a product natural gas enriched with methane and lean in hydrocarbon less volatile than methane and a heavier fraction lean in methane and enriched with hydrocarbon less volatile than methane. The process includes heating the feed liquefied natural gas in a heat exchanger, passing the heated fluid into a distillation column, withdrawing the heavier fraction from a bottom of the column, and withdrawing a residue gas from a top of the column. The process also includes liquefying at least part of the residue gas in the heat exchanger, refluxing a part of the liquid portion of the fluid obtained in the liquefying step into the column, and withdrawing, as the product natural gas, the remainder of the liquid portion.

1 . A process for separating a liquefied natural gas into a product natural gas and a heavier fraction, said process comprising: 
 (a) heating the liquefied feed natural gas in a first heat exchanger;    (b) passing the heated feed natural gas into a distillation column;    (c) heating liquid from the heated liquefied feed natural gas that is received within a bottom part of the distillation column using a reboiler;    (d) withdrawing the heavier fraction from the bottom part of the distillation column;    (e) withdrawing a residue gas from a top part of the distillation column;    (f) liquefying at least a part of the residue gas in the first heat exchanger to form a fluid having a liquid portion;    (g) refluxing a part of the liquid portion into the distillation column; and    (h) withdrawing, as the product natural gas, a remainder of the liquid portion, which has not been fed into the distillation column in step (g).    
   
   
       2 . The process according to  claim 1 , further comprising: 
 (i) heating the heated liquefied feed natural gas from step (a), in a second heat exchanger, prior to step (b).    
   
   
       3 . The process according to  claim 2 , wherein a part of the residue gas is liquefied in step (f), and further comprising: 
 (j) separating a gas portion from the fluid obtained in step (f) and then pressurizing the gas portion;    (k) liquefying the gas portion obtained in step (j), in the second heat exchanger; and    (l) withdrawing the liquid obtained in step (k) as the product natural gas.    
   
   
       4 . The process according to  claim 3 , wherein an entirety of the gas portion obtained in step (j) is liquefied in step (k) and withdrawn in step (l).  
   
   
       5 . The process according to  claim 2 , further comprising heating the liquefied feed natural gas from step (i), prior to step (b).  
   
   
       6 . The process according to  claim 5 , wherein a part of the residue gas is liquefied in step (f), and further comprising: 
 (j) separating a gas portion from the fluid obtained in step (f) and then pressurizing the gas portion;    (k) liquefying the gas portion obtained in step (j), in the second heat exchanger; and    (l) withdrawing the liquid obtained in step (k) as the product natural gas.    
   
   
       7 . The process according to  claim 6 , wherein an entirety of the gas portion obtained in step (j) is liquefied in step (k) and withdrawn in step (l).  
   
   
       8 . The process according to  claim 1 , wherein the distillation column is a demethanizer.  
   
   
       9 . The process according to  claim 1 , further comprising supplying to the first heat exchanger, as the liquefied feed natural gas, a feed natural gas containing at least methane and a hydrocarbon less volatile than methane, 
 wherein the heavier fraction withdrawn in step (d) is lean in methane and enriched with the hydrocarbon less volatile than methane, and    wherein the product natural gas withdrawn in step (h) is enriched with methane and lean in the hydrocarbon less volatile than methane.    
   
   
       10 . The process according to  claim 1 , further comprising supplying to the first heat exchanger, as the liquefied feed natural gas, a feed natural gas containing at least methane, ethane, and a hydrocarbon less volatile than ethane, 
 wherein the heavier fraction withdrawn in step (d) is lean in methane and ethane, and enriched with the hydrocarbon less volatile than ethane, and    wherein the product natural gas withdrawn in step (h) is enriched with methane and ethane, and lean in the hydrocarbon less volatile than ethane.    
   
   
       11 . An apparatus for separating a liquefied feed natural gas into a product natural gas and a heavier fraction, said apparatus comprising: 
 a first heat exchanger configured to receive and heat the liquefied feed natural gas;    a distillation column configured to receive a heated liquefied feed natural gas via said first heat exchanger, said distillation column having a bottom part with a lower outlet configured to discharge the heavier fraction therefrom, said distillation column having a top part with an upper outlet configured to discharge a residue gas to said first heat exchanger such that said first heat exchanger can cool at least a part of the residue gas to form a fluid including a liquid portion thereof;    a reflux device configured to feed at least a part of the liquid portion of the residue gas into said distillation column;    a line configured to discharge a remainder of the liquid portion of the residue gas as the product natural gas; and    a reboiler configured to heat liquid from the heated liquefied feed natural gas that is received within said bottom part of said distillation column.    
   
   
       12 . The apparatus according to  claim 11 , further comprising a second heat exchanger configured to receive and heat the liquefied feed natural gas from said first heat exchanger, wherein said distillation column is configured to receive the heated liquefied feed natural gas via said first heat exchanger and said second heat exchanger.  
   
   
       13 . The apparatus according to  claim 12 , wherein said first heat exchanger is configured to liquefy a part of the residue gas, further comprising: 
 a gas-liquid separator configured to receive the fluid from said first heat exchanger and separate the fluid into the liquid portion and a gas portion;    a pressurization device configured to pressurize the gas portion and feed the pressurized gas portion to said second heat exchanger so that said second heat exchanger can liquefy the pressurized gas portion; and    a line configured to discharge liquid liquefied from the pressurized gas portion in said second heat exchanger as the product natural gas.    
   
   
       14 . The apparatus according to  claim 13 , wherein said second heat exchanger is configured to liquefy an entirety of the pressurized gas portion.  
   
   
       15 . The apparatus according to  claim 12 , further comprising a heater configured to receive and heat the liquefied feed natural gas from said second heat exchanger, wherein said distillation column is configured to receive the heated liquefied feed natural gas via said first heat exchanger, said second heat exchanger, and said heater.  
   
   
       16 . The apparatus according to  claim 15 , wherein said first heat exchanger is configured to liquefy a part of the residue gas, further comprising: 
 a gas-liquid separator configured to receive the fluid from said first heat exchanger and separate the fluid into the liquid portion and a gas portion;    a pressurization device configured to pressurize the gas portion and feed the pressurized gas portion to said second heat exchanger so that said second heat exchanger can liquefy the pressurized gas portion; and    a line configured to discharge liquid liquefied from the pressurized gas portion in said second heat exchanger as the product natural gas.    
   
   
       17 . The apparatus according to  claim 16 , wherein said second heat exchanger is configured to liquefy an entirety of the pressurized gas portion.  
   
   
       18 . The apparatus according to  claim 11 , wherein said distillation column is a demethanizer.  
   
   
       19 . The apparatus according to  claim 11 , wherein: 
 said first heat exchanger is configured to receive, as the liquefied feed natural gas, a feed natural gas containing at least methane and a hydrocarbon less volatile than methane;    said lower outlet of said distillation column is configured to discharge, as the heavier fraction, a heavier fraction lean in methane and enriched with the hydrocarbon less volatile than methane; and    said line is configured to discharge, as the product natural gas, a product natural gas enriched with methane and lean in the hydrocarbon less volatile than methane.    
   
   
       20 . The apparatus according to  claim 11 , wherein: 
 said first heat exchanger is configured to receive, as the liquefied feed natural gas, a feed natural gas containing at least methane, ethane, and a hydrocarbon less volatile than ethane;    said lower outlet of said distillation column is configured to discharge, as the heavier fraction, a heavier fraction lean in methane and ethane, and enriched with the hydrocarbon less volatile than ethane; and    said line is configured to discharge, as the product natural gas, a product natural gas enriched with methane and ethane, and lean in the hydrocarbon less volatile than ethane.