Process for supplying nitrogen by means of semi-permeable membranes or of separators of gases by adsorption

A process for supplying nitrogen to at least two user stations, whose requirements as to nitrogen purity are different, comprising the following steps:

• a) passing compressed air to at least one air treatment station permitting effecting at least one of the following treatments of said compressed air:
• oil removal;
• filtering out a major portion of particles contained in said compressed air;
• drying;
• bringing said compressed air to a desired temperature;
• b) sending the compressed air from step a) to a centralized gas separation unit, in order to produce, at an outlet of said centralized unit, an impure nitrogen gas of intermediate purity;
• and
• c) directing said impure nitrogen gas from said centralized unit to at least two utilization lines, each line having at its end one of the said user stations, and each line comprising a local gas separation unit, in which said impure nitrogen gas is treated, in order to obtain, at an outlet of each local gas separation unit, nitrogen of a purity suitable for the uses of said user station located at the end of said line.