Method and apparatus for producing product nitrogen gas and product argon

Abstract

An apparatus for producing product nitrogen gas and product argon, comprising: a first rectification column into which raw air is introduced; a second rectification column from which product nitrogen gas is drawn; a third rectification column from which product argon gas is drawn; and a first condenser configured to perform heat exchange between a gas accumulated in a column top portion of the first rectification column, and a liquid accumulated in a column bottom portion of the second rectification column, wherein an intermediate portion gas containing nitrogen is drawn from an intermediate portion of the second rectification column and merged with a condenser gas drawn from the first condenser. The merged gases are expanded and cooled by means of an expansion turbine whereby the cold thereof is utilized.

What is claimed is: 
     
         1 . A method for producing product nitrogen gas and product argon, the method comprising the steps of:
 providing an apparatus configured to produce the product nitrogen gas and the product argon, the apparatus comprising a main heat exchanger, a first rectification column, a second rectification column, a third rectification column, a first condenser configured to perform heat exchange between a gas accumulated in a column top portion of the first rectification column, and a liquid accumulated in a column bottom portion of the second rectification column, a second condenser configured to perform heat exchange between a gas accumulated in a column top portion of the third rectification column and an oxygen-enriched liquid, a fourth rectification column configured to rectify oxygen-enriched liquid vaporized by the second condenser, and an expansion turbine;   cooling a raw air stream from which predetermined impurities have been removed and then introducing the raw air into the first rectification column for rectification therein;   withdrawing the oxygen-enriched liquid from a column bottom portion of the first rectification column;   introducing the oxygen-enriched liquid into the fourth rectification column for rectification therein;   introducing a nitrogen-containing liquid, which was previously condensed in the first condenser, as a reflux liquid at an upper portion of the second rectification column;   introducing a second oxygen-enriched liquid from the second condenser to the second rectification column at a first intermediate point;   introducing a second nitrogen-enriched gas from the fourth rectification column to the second rectification column at a second intermediate point;   expanding at least a portion of a mixed gas in the expansion turbine to generate refrigeration and then warming the mixed gas in the main heat exchanger to produce a waste gas, wherein the mixed gas comprises an intermediate portion gas withdrawn from a third intermediate location of the second rectification column and a condenser gas withdrawn from the first condenser;   introducing an argon-containing gas drawn from a lower portion of the second rectification column into the third rectification column;   withdrawing a product nitrogen gas is drawn from a column top portion of the second rectification column; and   withdrawing a product argon from the third rectification column.   
     
     
         2 . The method as claimed in  claim 1 , wherein the first condenser is positioned intermediately between the first rectification column and the second rectification column. 
     
     
         3 . The method as claimed in  claim 1 , wherein the first intermediate point is above the second intermediate point. 
     
     
         4 . The method as claimed in  claim 1 , wherein the first intermediate location is below the upper portion of the second rectification column where the nitrogen-containing liquid is introduced. 
     
     
         5 . The method as claimed in  claim 4 , wherein the third intermediate location is located between the upper portion and the first intermediate location. 
     
     
         6 . The method as claimed in  claim 4 , wherein the intermediate portion gas has a higher nitrogen concentration as compared to the condenser gas. 
     
     
         7 . The method as claimed in  claim 4 , wherein a flow rate of the intermediate portion gas as compared to a flow rate of the condenser gas is between 0.03 and 2. 
     
     
         8 . The method as claimed in  claim 4 , wherein the mixed gas has an oxygen composition between 70% and 97%. 
     
     
         9 . The method as claimed in  claim 8 , wherein the expansion turbine comprises an absence of duralumin. 
     
     
         10 . The method as claimed in  claim 1 , wherein the intermediate portion gas withdrawn from an intermediate portion of the second rectification column and the condenser gas withdrawn from the first condenser are mixed to form the mixed gas at a location upstream a cold end of the main heat exchanger and the expansion turbine. 
     
     
         11 . The method as claimed in  claim 10 , wherein the mixed gas is first partially heated in the main heat exchanger prior to being expanded in the expansion turbine. 
     
     
         12 . The method as claimed in  claim 10 , wherein the intermediate portion gas withdrawn from an intermediate portion of the second rectification column is mixed with the condenser gas without first passing through a subcooler.