The traditional process of pure nitrogen equipment with a small amount of sample oxygen product is a single tower of exhaust gas reflux expansion nitrogen with pure oxygen tower process, widely used in nitrogen equipment with a production capacity of less than 6000 Nm³ / h. The pressure level of the nitrogen product is 0.45-0.9 Mpa. The pressure level of the nitrogen product is 0.45-0.9 Mpa, and the nitrogen product is used directly by the customer's pipeline network after leaving the cold box.