Separating Air to Produce Gases

Separating air to produce gases.

What is air? And what is air separation? Air is a mixture of gases, consisting primarily of nitrogen Air can be separated into its components by (78 %), oxygen (21 %) and the inert gas argon (0.9 %). means of distillation in special units. So-called air The remaining 0.1 % is made up mostly of carbon dioxide fractionating plants employ a thermal process and the inert gases neon, helium, krypton and xenon. known as cryogenic rectification to separate the individual components from one another in order to produce high-purity nitrogen, oxygen and argon in liquid and gaseous form.

N2 Compression of air Cooling of air Ar Separation of air Withdrawal and storage O Ambient air is drawn in, filtered and Because the gases which make 2 Separation of air into pure oxygen Gaseous oxygen and nitrogen are compressed to approx. 6 bar by a compressor. up air only liquefy at very low temperatures, and pure nitrogen is performed in two fed into pipelines for transport to the purified air in the main heat exchanger columns, the medium-pressure and the low- users, e.g. steelworks. In liquid is cooled to approx. -175 °C. The cooling pressure columns. The difference in boiling form, oxygen, nitrogen and argon Precooling of air is achieved by means of internal heat point of the constituents is exploited for are stored in tanks and transported to To separate air into its components, exchange, in which the flows of cold gas the separation process. Oxygen becomes customers by road tankers. it must first be liquefied at an extremely low generated during the process cool the a liquid at -183 °C and nitrogen at -196 °C. temperature. As a first step, the compressed compressed air. Rapid reduction of the The continuous evaporation and condensation air is precooled with chilled water. pressure then causes the compressed air brought about by the intense exchange of to cool further, whereby it undergoes partial matter and heat between the rising steam liquefaction. Now the air is ready for the and the descending liquid produces pure Purification of air separating column, where the actual nitrogen at the top of the low-pressure Impurities such as water vapour separation takes place. column and pure oxygen at the bottom. and carbon dioxide are then removed from Argon is separated in additional columns and the air in a so-called molecular sieve. involves some extra steps in the process.

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