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Filtration, Compressions and Cooling
The cryogenic process starts by filtering out the air from the atmosphere to remove any type of debris that it may contain. Once it passes the filters, the air goes through a compressor, which compresses the air to around five to eight bar. Compressing air makes it hot and it needs to be cooled down before it can be purified. To do this, the air passes through a refrigeration system.
Purification
In the purification process, other elements, such as carbon dioxide and water vapor, are separated from the main gas where oxygen and nitrogen will be extracted. There are two typical systems that do this: prepurification units and reversing exchangers. Prepurification units use molecular sieves that filter molecules of water vapor and carbon dioxide while the air passes. On the other hand, reversing exchangers use chambers that can release hot or cold air. First, the chamber blasts cold air to freeze carbon dioxide and water vapor. Once the purified gas leaves the chamber, a blast of hot air is sent to the chamber to melt the frozen vapor and carbon dioxide. The chamber then releases this "waste" to the atmosphere.
Cooling and Distillation
After the purification stage, the processed air only contains oxygen, nitrogen and argon. Before distillation, the air is cooled to very low temperatures (about -300 degrees Fahrenheit) and is then sent to the distillation columns. Distillation columns have two exit points: low and high. The low exit point is the area where the oxygen goes, while the high exit point is the area where the nitrogen goes. The oxygen produced in this process is still impure and contains argon. To create pure oxygen, the air goes into another pressure column where the argon and the oxygen are separated.
Storage
Some cryogenic distillation factories have pipelines that directly deliver processed products to their clients, while most store purified gases in liquid form through the use of high-pressure tanks. When delivering small quantities, these purified gases are often put in dewar flasks or gas cylinders. Both storage devices are pressurized vacuums with stoppers and control knobs to regulate the release of the stored gas.