Systems and methods for removal of nitrogen from lng

Abstract

A system for the removal of nitrogen from a liquid natural gas (LNG) stream. The system. comprises a feed heat changer and a stripper column. The heat receives the LNG stream and cools the LNG stream via heat exchange with a stripper column side-draw stream to yield a cooled LNG stream and a heated side-draw stream. The stripper column receives the cooled LNG stream at a first tray and the heated side-draw stream. The stripper column produces the stripper column side-draw stream, a stripper column overhead stream, and a stripper column bottom stream. The stripper column side-draw stream is taken from the stripper column at a second tray. The second tray is at least about 15 feet higher than the feed heat exchanger.

What is claimed is: 
     
         1 . A system for the removal of nitrogen from a liquid natural gas (LNG) stream, the system comprising:
 a feed heat exchanger, wherein the heat is configured to receive the LNG stream and to cool the LNG stream via heat exchange with a stripper column side-draw stream to yield a cooled LNG stream and a heated side-draw stream; and   a stripper column, wherein the stripper column is configured to receive the cooled LNG stream at a first tray and the heated side-draw stream, and wherein the stripper column is configured to produce the stripper column side-draw stream, a stripper column overhead stream, and a stripper column bottom stream,   wherein the stripper column is configured such that the stripper column side-draw stream is taken from the stripper column at a second tray, wherein the second tray is at least about 15 feet higher than the feed heat exchanger.   
     
     
         2 . The system of  claim 1 , further comprising a pressure reduction device, wherein the pressure reduction device is configured to reduce the pressure of the stripper column side-draw stream prior to introduction into the feed heat exchanger. 
     
     
         3 . The system of  claim 2 , wherein the pressure reduction device is a valve. 
     
     
         4 . The system of  claim 2 , further comprising a control device, wherein the control device is configured to control the flow of the heated side-draw stream prior to introduction into the feed heat exchanger 
     
     
         5 . The system of  claim 4 , wherein the control device is a flow control valve. 
     
     
         6 . The system of  claim 1 , wherein the system is configured to receive the LNG stream from a LNG liquefaction plant. 
     
     
         7 . The system of  claim 1 , wherein the LNG stream is characterized as a relatively-high nitrogen content LNG stream. 
     
     
         8 . The system of  claim 7 , wherein the stripper column bottom stream has less than about 0.9 mole % nitrogen. 
     
     
         9 . The system of  claim 1 , wherein the cooled LNG stream has a temperature of from about 256° F. to −275° F. 
     
     
         10 . The system of  claim 1 , wherein the second tray is at least about 20 feet higher than the feed heat exchanger. 
     
     
         11 . A method for the removal of nitrogen from a liquid natural gas (LNG) stream, the method comprising:
 receiving, at a feed heat exchanger, the LNG stream;   cooling the LNG stream via heat exchange with a stripper column side-draw stream to yield a cooled LNG stream and a heated side-draw stream;   receiving, at a stripper column, the cooled LNG stream at a first tray and the heated side-draw stream;   producing the stripper column side-draw stream from the stripper column at a second tray that is at least about 15 feet higher than the feed heat exchanger; and   producing a stripper column overhead stream and a stripper column bottom stream.   
     
     
         12 . The method of  claim 11 , further comprising controlling the flow of the stripper column side-draw stream prior to introducing the stripper column side-draw stream into the feed heat exchanger. 
     
     
         13 . The method of  claim 12 , wherein controlling the flow of the stripper column side-draw stream comprises passing the stripper column side-draw stream through a first valve. 
     
     
         14 . The method of  claim 11 , further comprising controlling the flow of the heated side-draw stream prior to introducing the heated side-draw stream into the feed heat exchanger. 
     
     
         15 . The method of  claim 14 , wherein controlling the flow of the heated side-draw stream comprising passing the heated side-draw stream through a second valve. 
     
     
         16 . The method of  claim 11 , wherein receiving the LNG stream comprises receiving the LNG stream from a LNG liquefaction plant. 
     
     
         17 . The method of  claim 11 , wherein the LNG stream is characterized as a relatively-high nitrogen content LNG stream. 
     
     
         18 . The method of  claim 17 , wherein the s column bottom stream has less than about 0.9 mole % nitrogen. 
     
     
         19 . The method of  claim 11 , wherein cooling the LNG stream comprises cooling the LNG stream to a temperature of from about −256° F. to −275° F. 
     
     
         20 . The method of  claim 11 , wherein the second tray is at least about 20 feet higher than the feed heat exchanger.