Nitrogen production method

A method for producing nitrogen wherein air is compressed, is removed of water and carbon contained therein, cooled to a temperature close to the liquefying point, is then fed into a rectifying column for rectification and from the overhead of said rectifying column high purity nitrogen is withdrawn;

• and wherein oxygen-enriched liquid air, fed from the bottom of said rectifying column, is expanded and fed into a condensation step whereafter said expanded oxygen-enriched liquid air is used as a source of reflux producing cold for said rectifying column and adiabatic expansion is effected on the evaporated gas to produce cold, so that heat exchange with raw air is conducted,
• said method for producing nitrogen being provided with a closed cycle comprising the step of:
• compressing a circulating gas;
• cooling a compressed circulating gas by heat exchange with a circulating gas fed back into said compressing step;
• vaporizing a bottom liquid in said rectifying column by supplying said cooled circulating gas into a reboiler at the bottom of said rectifying column to thereby liquefy the cooled circulating gas;
• expanding said liquefied circulating gas;
• thereafter feeding an expanded circulating gas into said condensation step to vaporize the same by heat exchange with said high purity nitrogen withdrawn from the rectifying column overhead;
• thereafter feeding said vaporized circulating gas into said cooling step before the same is fed back into said compressing step, to heat the same by heat exchange with said compressed circulating gas;
• and returning said heated circulating gas into said compressing step for circulation.