System and Method for the Production of Liquefied Natural Gas

Abstract

A method for producing liquefied natural gas (LNG) and separating natural gas liquids (NGLs) from the LNG is provided. The method may include compressing natural gas to compressed natural gas, removing a non-hydrocarbon from the compressed natural gas, and cooling the compressed natural gas to a cooled, compressed natural gas. The method may also include expanding a first portion and a second portion of the cooled, compressed natural gas in a first expansion element and a second expansion element to generate a first refrigeration stream and a second refrigeration stream, respectively. The method may further include separating a third portion of the cooled, compressed natural gas into a methane lean natural gas fraction containing the NGLs and a methane rich natural gas fraction. The methane rich natural gas fraction may be cooled in a liquefaction assembly with the first and second refrigeration streams to thereby produce the LNG.

We claim: 
     
         1 . A method for producing liquefied natural gas from a natural gas source and separating natural gas liquids from the liquefied natural gas produced, comprising:
 compressing natural gas from the natural gas source in a compression assembly fluidly coupled with the natural gas source to produce a compressed natural gas;   removing a non-hydrocarbon from the compressed natural gas in a separator fluidly coupled with the compression assembly;   cooling the compressed natural gas to a cooled, compressed natural gas with a cooling assembly in thermal communication with the compression assembly;   expanding a first portion of the cooled, compressed natural gas in a first expansion element to generate a first refrigeration stream;   expanding a second portion of the cooled, compressed natural gas in a second expansion element to generate a second refrigeration stream;   feeding a third portion of the cooled, compressed natural gas to a distillation column of a distillation assembly;   separating the third portion of the cooled, compressed natural gas into a methane lean natural gas fraction and a methane rich natural gas fraction in the distillation column of the distillation assembly, the methane lean natural gas fraction containing the natural gas liquids;   feeding the methane rich natural gas fraction to a liquefaction assembly; and   cooling at least a portion of the methane rich natural gas fraction with the first refrigeration stream and the second refrigeration stream in the liquefaction assembly to thereby produce the liquefied natural gas.   
     
     
         2 . The method of  claim 1 , wherein the third portion of the cooled, compressed natural gas is flowed to a middle zone of the distillation column. 
     
     
         3 . The method of  claim 2 , further comprising storing the liquefied natural gas in a storage tank. 
     
     
         4 . The method of  claim 3 , wherein separating the third portion of the cooled, compressed natural gas into the methane lean natural gas fraction and the methane rich natural gas fraction comprises:
 at least partially cooling the third portion of the cooled, compressed natural gas in a top zone of the distillation column.   
     
     
         5 . The method of  claim 4 , wherein at least partially cooling the third portion of the cooled, compressed natural gas comprises:
 pumping a portion of the liquefied natural gas from the liquefaction assembly to the top zone of the distillation column.   
     
     
         6 . The method of  claim 5 , wherein separating the third portion of the cooled, compressed natural gas into the methane lean natural gas fraction and the methane rich natural gas fraction further comprises:
 at least partially condensing the third portion of the cooled, compressed natural gas to thereby produce the natural gas liquids; and   collecting the natural gas liquids in a bottom zone of the distillation column.   
     
     
         7 . The method of  claim 4 , wherein separating the third portion of the cooled, compressed natural gas into the methane lean natural gas fraction and the methane rich natural gas fraction comprises:
 at least partially heating the third portion of the cooled, compressed natural gas in a bottom zone of the distillation column.   
     
     
         8 . The method of  claim 7 , wherein at least partially heating the third portion of the cooled, compressed natural gas comprises:
 feeding a heat transfer medium to a heat exchanger fluidly coupled with the bottom zone of the distillation column.   
     
     
         9 . The method of  claim 7 , wherein at least partially heating the third portion of the cooled, compressed natural gas produces methane vapors. 
     
     
         10 . The method of  claim 9 , wherein separating the third portion of the cooled, compressed natural gas into the methane lean natural gas fraction and the methane rich natural gas fraction further comprises:
 collecting the methane vapors in the top zone of the distillation column.   
     
     
         11 . The method of  claim 1 , further comprising precooling the third portion of the cooled, compressed natural gas with the methane rich natural gas fraction in a heat exchanger of the distillation assembly before feeding the third portion of the cooled, compressed natural gas to the distillation column of the distillation assembly. 
     
     
         12 . The method of  claim 1 , further comprising separating a portion of the natural gas liquids from the first portion of the cooled, compressed natural gas in a liquid separator before expanding the first portion of the cooled, compressed natural gas in the first expansion element. 
     
     
         13 . The method of  claim 12 , further comprising pumping the portion of the natural gas liquids from the liquid separator to the distillation column of the distillation assembly.