Process and Apparatus for Nitrogen Production

Abstract

A process and apparatus for producing nitrogen by which product nitrogen can be efficiently supplied. The nitrogen producing process comprises: a first separation step in which feed air is distilled at a low temperature; a first indirect heat exchange step in which a first nitrogen gas and a first oxygen-enriched liquefied fluid which have been separated in the first separation step are subjected to indirect heat exchange to obtain a first liquefied nitrogen and a first oxygen-enriched gas fluid; a second separation step in which the first oxygen-enriched gas fluid is distilled at a low temperature; a second indirect heat exchange step in which a second nitrogen gas and a second oxygen-enriched liquefied fluid which have been separated in the second separation step are subjected to indirect heat exchange to obtain a second liquefied nitrogen and a second oxygen-enriched gas fluid; a cold generating step in which the second oxygen-enriched gas fluid is adiabatically expanded to generate cold; a first product recovery step in which part of the first nitrogen gas is discharged as a first product nitrogen gas; and a second product recovery step in which part of the second nitrogen gas is discharged as a second product nitrogen gas after the cold is recovered.

1 : A nitrogen producing process for collecting product nitrogen by performing cryogenic liquefaction separation of feed air, the nitrogen producing process comprising:
 a first separation step of performing low temperature distillation of compressed, purified and cooled feed air at a pressure of 0.8 MPa or higher and 1.1 MPa or lower to separate the feed air into a first nitrogen gas and a first oxygen-enriched liquefied fluid;   a first indirect heat exchange step of performing an indirect heat exchange between the first nitrogen gas and the first oxygen-enriched liquefied fluid to condense the first nitrogen gas to obtain a first liquefied nitrogen and, at the same time, vaporize the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid;   a second separation step of performing low temperature distillation of the first oxygen-enriched gas fluid at a pressure of 0.4 MPa or higher and lower than the pressure in the first separation step to separate the first oxygen-enriched gas fluid into a second nitrogen gas and a second oxygen-enriched liquefied fluid;   a second indirect heat exchange step of performing an indirect heat exchange between the second nitrogen gas and the second oxygen-enriched liquefied fluid to condense the second nitrogen gas to obtain a second liquefied nitrogen and, at the same time, vaporize the second oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid;   a cold generating step of generating cold needed for the operation by performing adiabatic expansion of the second oxygen-enriched gas fluid;   a first product recovery step of discharging a part of the first nitrogen gas as a first product nitrogen gas after cold recovery; and   a second product recovery step of discharging a part of the second nitrogen gas as a second product nitrogen gas after cold recovery.   
     
     
         2 : A nitrogen producing process for collecting product nitrogen by performing cryogenic liquefaction separation of feed air, the nitrogen producing process comprising:
 a first separation step of performing low temperature distillation of compressed, purified and cooled feed air at a pressure of 0.6 MPa or higher and 1.1 MPa or lower to separate the feed air into a first nitrogen gas and a first oxygen-enriched liquefied fluid;   a first indirect heat exchange step of performing an indirect heat exchange between the first nitrogen gas and the first oxygen-enriched liquefied fluid to condense the first nitrogen gas to obtain a first liquefied nitrogen and, at the same time, vaporize the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid;   a second separation step of performing low temperature distillation of the first oxygen-enriched gas fluid at a pressure of 0.3 MPa or higher and lower than the pressure in the first separation step to separate the first oxygen-enriched gas fluid into a second nitrogen gas and a second oxygen-enriched liquefied fluid;   a second indirect heat exchange step of performing an indirect heat exchange between the second nitrogen gas and the second oxygen-enriched liquefied fluid to condense the second nitrogen gas to obtain a second liquefied nitrogen and, at the same time, vaporize the second oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid;   a cold generating step of generating cold needed for the operation by performing adiabatic expansion of a part of the feed air;   an air feeding step of introducing the feed air undergone the cold generating step to an intermediate stage of the second separation step;   a first product recovery step of discharging a part of the first nitrogen gas as a first product nitrogen gas after cold recovery; and   a second product recovery step of discharging a part of the second nitrogen gas as a second product nitrogen gas after cold recovery.   
     
     
         3 : The nitrogen producing process according to  claim 1 , comprising a step of compressing the second product nitrogen gas. 
     
     
         4 : A nitrogen producing apparatus for collecting product nitrogen by performing cryogenic liquefaction separation of feed air, the nitrogen producing apparatus comprising:
 a first rectification column which performs low temperature distillation of compressed, purified and cooled feed air at a pressure of 0.8 MPa or higher and 1.1 MPa or lower to separate the feed air into a first nitrogen gas at the upper portion of the column and a first oxygen-enriched liquefied fluid at the bottom portion of the column;   a first condenser which performs an indirect heat exchange between the first nitrogen gas and the first oxygen-enriched liquefied fluid to condense the first nitrogen gas to obtain a first liquefied nitrogen and, at the same time, vaporize the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid;   a second rectification column which performs low temperature distillation of the first oxygen-enriched gas fluid at a pressure of 0.4 MPa or higher and lower than the pressure of the first rectification column to rectify and separate the first oxygen-enriched gas fluid into a second nitrogen gas at the upper portion of the column and a second oxygen-enriched liquefied fluid at a bottom portion of the column;   a second condenser which performs an indirect heat exchange between the second nitrogen gas and the second oxygen-enriched liquefied fluid to condense the second nitrogen gas to obtain a second liquefied nitrogen and, at the same time, vaporize the second oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid;   an expansion turbine which generates cold needed for the operation of the apparatus by performing adiabatic expansion of the second oxygen-enriched gas fluid;   a first product recovery passage for discharging a part of the first nitrogen gas as a first product nitrogen gas after cold recovery; and   a second product recovery passage for discharging a part of the second nitrogen gas as a second product nitrogen gas after cold recovery.   
     
     
         5 : A nitrogen producing apparatus for collecting product nitrogen by performing cryogenic liquefaction separation of feed air, the nitrogen producing apparatus comprising:
 a first rectification column which performs low temperature distillation of compressed, purified and cooled feed air at a pressure of 0.6 MPa or higher and 1.1 MPa or lower to separate the feed air into a first nitrogen gas at the upper portion of the column and a first oxygen-enriched liquefied fluid at the bottom portion of the column;   a first condenser which performs an indirect heat exchange between the first nitrogen gas and the first oxygen-enriched liquefied fluid to condense the first nitrogen gas to obtain a first liquefied nitrogen and, at the same time, vaporize the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid;   a second rectification column which performs low temperature distillation of the first oxygen-enriched gas fluid at a pressure of 0.3 MPa or higher and lower than the pressure of the first rectification column to rectify and separate the first oxygen-enriched gas fluid into a second nitrogen gas at the upper portion of the column and a second oxygen-enriched liquefied fluid at the bottom portion of the column;   a second condenser which performs an indirect heat exchange between the second nitrogen gas and the second oxygen-enriched liquefied fluid to condense the second nitrogen gas to obtain a second liquefied nitrogen and, at the same time, vaporize the second oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid;   an expansion turbine which generates cold needed for the operation of the apparatus by performing adiabatic expansion of a part of the feed air;   an air feeding passage for introducing the feed air passed through the expansion turbine to an intermediate stage of the second rectification column;   a first product recovery passage for discharging a part of the first nitrogen gas as a first product nitrogen gas after cold recovery; and   a second product recovery passage for discharging a part of the second nitrogen gas as a second product nitrogen gas after cold recovery.   
     
     
         6 : The nitrogen producing apparatus according to  claim 4 , comprising a nitrogen compressor which compresses the second product nitrogen gas. 
     
     
         7 : The nitrogen producing apparatus according to  claim 4 , wherein the second rectification column has a liquefied nitrogen feeding passage for introducing liquefied nitrogen from outside the apparatus. 
     
     
         8 : The nitrogen producing process according to  claim 2 , comprising a step of compressing the second product nitrogen gas. 
     
     
         9 : The nitrogen producing apparatus according to  claim 5 , comprising a nitrogen compressor which compresses the second product nitrogen gas. 
     
     
         10 : The nitrogen producing apparatus according to  claim 5 , wherein the second rectification column has a liquefied nitrogen feeding passage for introducing liquefied nitrogen from outside the apparatus.