Tonnage nitrogen generator

A process for producing substantially pure gaseous nitrogen product which comprises:

• (a) removing substantially all of the carbon dioxide and water vapor from a feed air stream;
• (b) introducing said dry, carbon dioxide-free feed air stream into a first distillation column and forming an overhead vapor fraction and a bottom liquid fraction;
• (c) expanding at least part of said overhead vapor fraction in a work expansion engine to a second, lower pressure;
• (d) expanding at least part of said bottoms liquid fraction to a second, lower pressure;
• (e) introducing at least part of both expanded lower pressure fractions into a second distillation column;
• (f) providing a condenser-reboiler at least partially submerged in the liquid bottom product of said second distillation column and providing reflux to said first distillation column from said condenser-reboiler;
• (g) expanding at least a portion of the liquid bottom product of said second distillation column to a further lower pressure;
• (h) utilizing said expanded, further lower pressure liquid bottom product from said second distillation column to provide refrigeration for supplying reflux to said second distillation column;
• and
• (i) collecting substantially pure gaseous nitrogen product from the top of said second distillation column.