Method for the integration of a nitrogen liquefier and letdown of natural gas for the production of liquid nitrogen and lower pressure natural gas

Abstract

A method describing the integration of a nitrogen liquefier and letdown of natural gas for the production of liquid nitrogen and lower pressure natural gas is provided. The method may include: providing a nitrogen liquefier having a nitrogen refrigeration cycle, wherein the nitrogen liquefier comprises a nitrogen compressor, a nitrogen recycle compressor, a heat exchanger, and at least a first turbine booster and introducing a nitrogen gas stream to the nitrogen liquefier under conditions effective for liquefying the nitrogen to produce a liquid nitrogen product. The refrigeration needed to liquefy the nitrogen is provided for by the nitrogen refrigeration cycle and letdown of a high pressure natural gas stream.

We claim: 
     
         1 . A method for the integration of a nitrogen liquefier and letdown of natural gas for the production liquid nitrogen (“LIN”), the method comprising the steps of:
 a) providing a nitrogen liquefier having a nitrogen refrigeration cycle, wherein the nitrogen liquefier comprises a nitrogen recycle compressor, a heat exchanger, and a first turbine booster; 
 b) introducing a nitrogen gas stream to the nitrogen liquefier under conditions effective for liquefying the nitrogen to produce a liquid nitrogen product; 
 c) withdrawing a natural gas stream from a source operating at a first pressure P H ; 
 d) purifying the natural gas stream in a purification unit to produce a purified natural gas; 
 e) partially cooling the purified natural gas in the heat exchanger; 
 withdrawing the partially cooled natural gas from an intermediate section of the heat exchanger; 
 g) expanding the partially cooled natural gas to a medium pressure P M  in a natural gas expansion turbine to form a cold natural gas stream, wherein the medium pressure P M  is at a pressure lower than the first pressure P H ; and 
 h) warming the cold natural gas stream in the heat exchanger by heat exchange against nitrogen from the nitrogen refrigeration cycle to produce a warm natural gas stream from a warm end of the heat exchanger, 
 wherein step h) provides additional refrigeration to the nitrogen liquefier such that additional liquid nitrogen can be produced as compared to a method having an absence of steps c)-i), 
 wherein the natural gas expansion turbine drives a first gas booster. 
 
     
     
         2 . The method as claimed in  claim 1 , wherein the first gas booster is configured to compress the natural gas stream or a stream derived therefrom. 
     
     
         3 . The method as claimed in  claim 1 , wherein the first gas booster is configured to compress a stream selected from the group consisting of the natural gas stream, the purified natural gas stream, the partially cooled natural gas stream, the warm natural gas stream, and a nitrogen fluid within the nitrogen refrigeration cycle. 
     
     
         4 . The method as claimed in  claim 1 , wherein the purification unit is configured to remove at least water from the natural gas stream. 
     
     
         5 . The method as claimed in  claim 1 , wherein the nitrogen refrigeration cycle further comprises a nitrogen feed compressor. 
     
     
         6 . The method as claimed in  claim 1 , wherein the nitrogen liquefier further comprises a subcooler. 
     
     
         7 . The method as claimed in  claim 1 , wherein the source of the natural gas comprises a natural gas pipeline. 
     
     
         8 . The method as claimed in  claim 7 , wherein the natural gas pipeline has a pressure between 15 and 100 bara. 
     
     
         9 . A method for the integration of a nitrogen liquefier and letdown of natural gas for the production of liquid nitrogen (“LIN”), the method comprising the steps of:
 a) providing a nitrogen liquefier having a nitrogen refrigeration cycle, wherein the nitrogen liquefier comprises a nitrogen recycle compressor, a heat exchanger, and at least one turbine booster; 
 b) introducing a nitrogen gas stream to the nitrogen liquefier under conditions effective for liquefying the nitrogen to produce a liquid nitrogen product; 
 c) recovering a natural gas stream from a high pressure source, wherein the natural gas stream is at a first pressure; 
 d) expanding the natural gas stream to a second pressure to produce an expanded natural gas stream, wherein the second pressure is a pressure that is lower than the first pressure; and 
 e) warming the expanded natural gas stream in the heat exchanger to produce a warmed natural gas stream, 
 wherein step e) provides additional refrigeration to the nitrogen liquefier such that additional liquid nitrogen can be produced as compared to a method having an absence of steps d) through e).