BigPatents India

Pressurised gaseous nitrogen ("GAN") is produced in a process in which liquid nitrogen ("LIN") is produced in a cryogenic air separation unit ("ASU") 124, 150. The pressure of at least a to a portion of the LIN is increased 164 to produce pressurised LIN. A fluid having an oxygen concentration at leastequal to that of air is separated in an auxiliary cryogenic distillation column 196 to produce nitrogen-rich overhead vapour and oxygen-enriched bottoms liquid. Heat and optionally mass is transferred 166, 503 between at least a portion of the nitrogen-rich overhead vapour and at least a portion of the pressurised LIN to produce nitrogen-rich liquid and pressurised GAN. At least a portion of said nitrogen-rich liquid is used as reflux to the ASU after suitable pressure adjustment 173.Such a process allows the production of high purity GAN without the 20 loss of oxygen recovery typically observed in conventional pumped LIN cycles.