Systems and methods for removing nitrogen during liquefaction of natural gas

Abstract

Implementations described and claimed herein provide systems and methods for removing nitrogen during liquefaction of natural gas. In one implementation, a nitrogen rejection unit is used in an LNG facility to remove nitrogen from natural gas during an LNG liquefaction process. The nitrogen rejection unit contains at least two columns and at least one 3-stream condenser, 2-stream condenser or a two 2-stream condenser.

What is claimed is: 
     
         1 . A method for removing nitrogen from a natural gas stream using a nitrogen rejection unit, the method comprising:
 routing the natural gas stream to an upstream nitrogen removal column;   forming a first top stream and a first bottom stream in the upstream nitrogen removal column;   routing a first portion of the first top stream to a first condenser;   condensing, at least partially via indirect heat exchange, the first portion of the first top stream using the first condenser;   routing a second portion of the first top stream to an intermediate nitrogen removal column, where a second top stream and a second bottom stream are formed;   routing at least a portion of the second top stream to a second condenser;   condensing, at least partially via indirect heat exchange, the portion of the second top stream using the second condenser before routing to a downstream nitrogen removal column;   forming a third top stream and a third bottom stream in the downstream nitrogen removal column, wherein the third top stream includes nitrogen; and   removing at least a portion of the third top stream from the nitrogen rejection unit.   
     
     
         2 . The method of  claim 1 , wherein each of the first condenser and the second condenser is a printed circuit heat exchanger. 
     
     
         3 . The method of  claim 1 , further comprising:
 condensing, at least partially, the natural gas stream using a heat exchanger prior to routing the natural gas stream to the upstream nitrogen removal column.   
     
     
         4 . The method of  claim 3 , wherein the heat exchanger is a printed circuit heat exchanger. 
     
     
         5 . The method of  claim 1 , wherein nitrogen concentration of the first top stream is at least 50%. 
     
     
         6 . The method of  claim 1 , further comprising:
 removing at least a portion of the first bottom stream from the nitrogen rejection unit.   
     
     
         7 . The method of  claim 1 , wherein each of the first condenser and the second condenser is independently a 3-stream condenser or a 2-stream condenser. 
     
     
         8 . A liquefied natural gas system comprising:
 an upstream nitrogen removal column of a nitrogen rejection unit forming a first top stream and a first bottom stream from a natural gas stream;   an intermediate nitrogen removal column of the nitrogen rejection unit forming a second top stream and a second bottom stream;   a downstream nitrogen removal column of the nitrogen rejection unit forming a third top stream and a third bottom stream, the third top stream including nitrogen, at least a portion of the third top stream being removed from the nitrogen rejection unit;   a first condenser of the nitrogen rejection unit condensing, at least partially via indirect heat exchange, a portion of the first top stream; and   a second condenser of the nitrogen rejection unit condensing, at least partially via indirect heat exchange, at least a portion of the second top stream before routing the portion of the second top stream to the downstream nitrogen removal column.   
     
     
         9 . The liquefied natural gas system of  claim 8 , wherein each of the first condenser and the second condenser is a printed circuit heat exchanger. 
     
     
         10 . The liquefied natural gas system of  claim 8 , further comprising:
 a heat exchanger condensing, at least partially, the natural gas stream prior to routing the natural gas stream to the upstream nitrogen removal column.   
     
     
         11 . The liquefied natural gas system of  claim 10 , wherein the heat exchanger is a printed circuit heat exchanger. 
     
     
         12 . The liquefied natural gas system of  claim 8 , wherein nitrogen concentration of the first top stream is at least 50%. 
     
     
         13 . The liquefied natural gas system of  claim 8 , wherein each of the first condenser and the second condenser is independently a 3-stream condenser or a 2-stream condenser. 
     
     
         14 . The liquefied natural gas system of  claim 8 , further comprising:
 an expansion drum of the nitrogen rejection unit configured to receive the portion of the third top stream before being removed from the nitrogen rejection unit, the expansion drum forming a liquid stream and a gas stream.   
     
     
         15 . The liquefied natural gas system of  claim 8 , further comprising:
 one or more refrigeration cycles successively cooling the natural gas stream before being routed to the upstream nitrogen removal column.   
     
     
         16 . The liquefied natural gas system of  claim 8 , further comprising:
 one or more reboilers providing heating duty to at least one of the upstream nitrogen removal column, the intermediate nitrogen removal column, or the downstream nitrogen removal column.   
     
     
         17 . A nitrogen rejection unit comprising:
 an upstream nitrogen removal column forming a first top stream and a first bottom stream from a natural gas stream;   an intermediate nitrogen removal column forming a second top stream and a second bottom stream;   a downstream nitrogen removal column forming a third top stream and a third bottom stream, the third top stream including nitrogen;   a first condenser condensing, at least partially, a portion of the first top stream; and   a second condenser condensing, at least partially, at least a portion of the second top stream before routing the portion of the second top stream to the downstream nitrogen removal column.   
     
     
         18 . The nitrogen rejection unit of  claim 17 , wherein each of the first condenser and the second condenser is a printed circuit heat exchanger. 
     
     
         19 . The nitrogen rejection unit of  claim 17 , wherein the natural gas stream is condensed, at least partially, using a heat exchanger prior to routing the natural gas stream to the upstream nitrogen removal column. 
     
     
         20 . The nitrogen rejection unit of  claim 19 , wherein the heat exchanger is a printed circuit heat exchanger.