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, comprising:
 a cooling step in which raw air from which predetermined impurities have been removed is cooled;   a raw air introduction step in which the raw air cooled in the cooling step is introduced into a first rectification column;   a first oxygen-enriched liquid introduction step in which an oxygen-enriched liquid drawn from a column bottom portion of the first rectification column is introduced into a second rectification column;   a second oxygen-enriched liquid introduction step in which at least a portion of the oxygen-enriched liquid drawn from the column bottom portion of the first rectification column is introduced into a second condenser disposed in a third rectification column;   a nitrogen-containing liquid introduction step in which a nitrogen-containing liquid condensed in the first rectification column is introduced as a reflux liquid at an upper portion of the second rectification column;   an expansion step in which at least a portion of a mixed gas is expanded to generate cold, the mixed gas comprising an intermediate portion gas drawn from an intermediate portion of the second rectification column and a condenser gas drawn from a condenser positioned intermediately between the first rectification column and the second rectification column, the condenser being 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;   an argon-containing gas introduction step in which an argon-containing gas drawn from a lower portion of the second rectification column is introduced into the third rectification column;   a product nitrogen gas drawing step in which product nitrogen gas is drawn from a column top portion of the second rectification column; and   a product argon drawing step in which product argon is drawn from the intermediate portion of the second rectification column.   
     
     
         2 . An apparatus for producing product nitrogen gas and product argon, comprising:
 a main heat exchanger for cooling raw air from which predetermined impurities have been removed;   a first rectification column into which the cooled raw air is introduced;   a second rectification column from which product nitrogen gas is drawn;   a third rectification column from which product argon is drawn;   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 nitrogen-containing liquid introduction pipe for introducing at least a portion of a nitrogen-containing liquid condensed in the first condenser into the second rectification column as a reflux liquid;   an argon-containing gas introduction pipe for introducing an argon-containing gas into the third rectification column from a lower portion of the second rectification column;   an argon-containing liquid drawing pipe for introducing an argon-containing liquid into the second rectification column from a column bottom portion of the third rectification column;   a condenser gas drawing pipe for drawing a condenser gas from a gas-phase portion of the first condenser;   an intermediate portion gas drawing pipe for drawing an intermediate portion gas from an intermediate portion of the second rectification column;   an expansion turbine for expanding and cooling a mixed gas comprising the condenser gas and the intermediate portion gas;   a product nitrogen gas drawing pipe for drawing the product nitrogen gas from the second rectification column; and   a product argon drawing pipe for drawing the product argon from an intermediate portion of the third rectification column.   
     
     
         3 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 2 , further comprising:
 an oxygen-enriched liquid drawing pipe for drawing, from a column bottom portion of the first rectification column, an oxygen-enriched liquid accumulated in the column bottom portion of the first rectification column;   a second oxygen-enriched liquid introduction pipe for introducing, into a second condenser disposed in the third rectification column, the oxygen-enriched liquid drawn from the oxygen-enriched liquid drawing pipe; and   a third oxygen-enriched liquid introduction pipe for introducing the oxygen-enriched liquid drawn from the second condenser into the second rectification column.   
     
     
         4 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 3 , wherein the third oxygen-enriched liquid introduction pipe introduces the oxygen-enriched liquid in a gaseous state from a gas-phase portion of the second condenser into the second rectification column. 
     
     
         5 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 2 , further comprising:
 a fourth rectification column disposed at an upper portion of the second condenser; and   a fourth rectification column column-top-portion gas introduction pipe for introducing, into the second rectification column, a fourth rectification column column-top-portion gas extracted from a column top portion of the fourth rectification column,   wherein the third enriched-oxygen liquid introduction pipe introduces the oxygen-enriched liquid in a liquid state from a liquid-phase portion of the second condenser into the second rectification column, and   the oxygen-enriched liquid accumulated in the column bottom portion of the first rectification column is introduced into the second condenser via a gas-phase portion of the fourth rectification column.   
     
     
         6 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 2 , further comprising a first oxygen-enriched liquid introduction pipe for introducing, into the second rectification column, at least a portion of the oxygen-enriched liquid accumulated in the column bottom portion of the first rectification column. 
     
     
         7 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 2 , wherein the mixed gas is a mixed gas comprising the condenser gas directly extracted from the gas-phase portion of the first condenser, and the intermediate portion gas directly extracted from the intermediate portion of the second rectification column. 
     
     
         8 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 2 , wherein the mixed gas is a mixed gas in which the condenser gas directly extracted from the gas-phase portion of the first condenser, and the intermediate portion gas directly extracted from the intermediate portion of the second rectification column are mixed, after which the mixture is made to pass through the main heat exchanger. 
     
     
         9 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 2 , wherein at least either one of the nitrogen-containing liquid pipe and the oxygen-enriched liquid drawing pipe, and the product nitrogen gas drawing pipe pass through a sub-cooler. 
     
     
         10 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 9 , wherein the intermediate portion gas drawing pipe, after being introduced into the sub-cooler, is connected to the condenser gas drawing pipe at a first merging point, the first merging point being at a stage after the sub-cooler and before the expansion turbine. 
     
     
         11 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 2 , wherein the intermediate portion of the second rectification column is below an attachment position of the nitrogen-containing liquid introduction pipe on the second rectification column side, and is above an attachment position of the first oxygen-enriched liquid introduction pipe on the second rectification column side. 
     
     
         12 . The apparatus for producing product nitrogen gas and product argon as claimed in  claim 2 , wherein the ratio of the drawing flow rate of the intermediate portion gas drawn from the intermediate portion gas drawing pipe to the drawing flow rate of the condenser gas drawn from the condenser gas drawing pipe is between 0.03 and 2.