The Liquid Nitrogen Plant consists of Cryogenerator, which is provided with a condenser. The rectification column is connected to the condenser. The column is provided with an inlet opening for the intake of ambient air, owing to the condensation, a pressure drop arises around the cold exchanger in the condenser as a result of which the correct quantity of air is sucked in automatically. The impurities in the intake air (Water vapours, carbon dioxide etc.) are separated in the column and stored in the form of snow. After the end of the production period this snow must be removed by defrosting. Traces of noble gases present in the air (non condensable gases) can only be removed via flow meter and the water jet pump. The oxygen is blown off from the column, this blow off is controlled by adjusting the blow-off pressure by means of oxygen adjusting valve. The blow -off rate is set in accordance to the indication of the flow meters for the intake air and for the oxygen exhaust.
The cryogenerator is filled by hydrogen or helium under high pressure which effects the cooling process in a closed cycle. In the internal process it is, of course, required to use a gas which does not liquify at the operating temperature of the cryogenerator. For this reason either hydrogen or helium can be used as the cooling medium.
Cooling water system
The cooling water is needed for removing the compression heat and the heat absorbed by the cryogenic head. The cooling water first flows through the oil cooler
and then through the main cooler. In the drain the water safety switch is mounted which trips the installation if the water flow becomes less than 0.5 cu.m/hr. The
normally required quantity of water is 0.75 cu.m/hr. with a pressure of 1.7–2.5 bar at the inlet and the maximum inlet temperature of 25°C.