The compressed air is passed through a Twin Tower PSA module interconnected with automatic change over valves. After passing through a Refrigerated Dryer air gets dried. Dried compressed air will now come in contact with bed of Zeolite molecular sieves(ZMS). Zeolite Molecular Sieves are special grade of adsorbent which have the property of preferential adsorption of nitrogen molecules. At a time one tower remains under nitrogen production cycle, whereas the other tower undergoes regeneration which is achieved through depressurization of the tower to atmospheric pressure. The outgoing oxygen gas is sent to a surge vessel where the minimum pressure will be maintained with the help of Back Pressure Regulator.