Methods and apparatuses for processing natural gas

Abstract

Methods and apparatuses for processing natural gas are provided. In a method for processing a natural gas stream, the natural gas stream is fractionated to form an overhead stream and a bottoms stream. The overhead stream is separated with a membrane to form a methane rich residual stream and a permeate stream.

What is claimed is: 
     
         1 . A method for processing a natural gas stream comprising:
 fractionating the natural gas stream to form an overhead stream and a bottoms stream; and   separating the overhead stream with a membrane to form a methane rich residual stream and a permeate stream.   
     
     
         2 . The method of  claim 1  wherein fractionating the natural gas stream forms the overhead stream comprising less than 25% carbon dioxide. 
     
     
         3 . The method of  claim 1  wherein separating the overhead stream with the membrane forms the methane rich residual stream comprising less than 10% carbon dioxide. 
     
     
         4 . The method of  claim 1  wherein separating the overhead stream with the membrane forms the methane rich residual stream comprising no more than about 6% carbon dioxide. 
     
     
         5 . The method of  claim 1  wherein separating the overhead stream with the membrane forms the methane rich residual stream comprising about no more than about 2% carbon dioxide. 
     
     
         6 . The method of  claim 1  wherein separating the overhead stream with the membrane forms the methane rich residual stream comprising no less than about 90% methane. 
     
     
         7 . The method of  claim 1  wherein separating the overhead stream with the membrane forms the methane rich residual stream comprising no less than about 95% methane. 
     
     
         8 . The method of  claim 1  further comprising compressing the overhead stream before separating the overhead stream. 
     
     
         9 . The method of  claim 1  further comprising removing water from the natural gas stream before fractionating. 
     
     
         10 . The method of  claim 1  further comprising removing water from the natural gas stream with a molecular sieve before fractionating. 
     
     
         11 . The method of  claim 1  further comprising mixing the permeate stream with the natural gas stream. 
     
     
         12 . The method of  claim 11  further comprising compressing the permeate stream before mixing the permeate stream with the natural gas stream. 
     
     
         13 . A method for producing a methane product comprising:
 passing a natural gas stream through a molecular sieve to remove water therefrom and to form a dried natural gas stream;   fractionating the dried natural gas stream in a fractionation unit to form an overhead stream and a bottoms stream;   compressing the overhead stream in a compressor to form a compressed stream; and   separating the compressed stream with a membrane to form a methane rich residual stream and a permeate stream.   
     
     
         14 . The method of  claim 13  further comprising compressing the permeate stream and mixing the compressed permeate stream with the dried natural gas stream upstream of the fractionation unit. 
     
     
         15 . The method of  claim 13  wherein fractionating the natural gas stream forms the overhead stream comprising less than 25% carbon dioxide. 
     
     
         16 . The method of  claim 13  wherein separating the overhead stream with the membrane forms the methane rich residual stream comprising less than about 10% carbon dioxide. 
     
     
         17 . The method of  claim 13  wherein separating the overhead stream with the membrane forms the methane rich residual stream comprising no less than about 90% methane. 
     
     
         18 . The method of  claim 13  wherein separating the overhead stream with the membrane forms the methane rich residual stream comprising no less than about 95% methane. 
     
     
         19 . An apparatus for processing a natural gas stream comprising:
 a fractionation unit configured to separate the natural gas stream into a bottoms stream and an overhead stream; and   a selective permeation membrane in fluid communication with the fractionation unit and configured to separate the overhead stream into a methane rich residual stream and a permeate stream.   
     
     
         20 . The apparatus of  claim 19  further comprising:
 a dehydration unit including a molecular sieve configured to remove water from the natural gas stream, wherein the fractionation unit is in fluid communication with the dehydration unit and receives the natural gas stream from the dehydration unit; 
 a compressor in fluid communication with the fractionation unit and configured to compress the overhead stream to form a compressed stream, wherein the selective permeation membrane is in fluid communication with the fractionation unit and receives the overhead stream from the compressor; 
 a recompressor in fluid communication with the selective permeation membrane and configured to compress the permeate stream; 
 a conduit configured to recycle the compressed permeate stream to the natural gas stream upstream of the fractionation unit; and 
 a pump configured to pressurize the bottoms stream.