Each gas has its own advantages in respective applications. If we wish to use air as a raw material to get the pure gases it contains, we should use air separation industrial process i.e. cryogenic air separation. At the end of the cryogenic air separation process, all its constituents gas separated in either gas or liquid phases based on its temperature.
Table of Contents
What is Cryogenic Air Separation?
To, start air separation, one should use fractional distillation process.
The air contains many gases in it and they are having its own boiling points (at cryogenics temperature range, less than -150 °C). For example,
- Nitrogen: -195.8 °C
- Argon: -185.9 °C
- Oxygen: -183.0 °C
This means, if you pass air through a surface whose temperature is less than -183.0°C, first oxygen gets condensed on that surface, once the temperature of that surface reaches below -185.9°C, Argon gets separated and then at temperature below -195.8°C, nitrogen gets separated.
Thus, By cooling air to cryogenic temperatures, the gases liquefy and can be separated based on their boiling points through fractional distillation.
Cryogenic Air Separation Process:
The process handles air in different components of the system. The air first sucked from the atmosphere and filtered through filters. This raw air now sent to compressor where it gets compressed to high pressure. The gas is now sent for purification. The carbon dioxide and other impurities are separated from it. The moisture is also absorbed at this stage.
The air is now sent for cooling and liquefaction. The gaseous air passes through series of heat exchangers so that its temperature can be lowered to cryogenic temperature range below -196 °C (boiling point of air).
This liquid air is now poured to distillation column.
- Top of the Column: Nitrogen, having the lowest boiling point, rises to the top and is extracted as a gas.
- Middle Section: Argon is extracted from the middle section of the column and also separation of residual oxygen from it.
- Bottom of the Column: Oxygen, with the highest boiling point, remains at the bottom and is collected in liquid form.
These separated gases now sent for storage where they are now ready to use for various applications.
Thus, cryogenic air separation involves separating dust, moisture, oxygen, nitrogen and argon from it through filtration, compression, purification and cooling with distillation separation.
Storage in Cryogenic vessels:
The different liquefied gases like liquid oxygen, liquid nitrogen and liquid argon are stored in specially designed cryogenic vessel known as Dewar vessel. The vessel is one kind of cylindrical double walled vessel. The vacuum is maintained in between the two walls of this vessel. This prevents the heat transfer and kept the atmospheric energy to come in contact with cryogen (liquid oxygen, liquid nitrogen and liquid argon).
Though, there can never be a vessel with 100% insulation. There will always have a heat transfer into the vessel. This energy boils off the liquid gases and convert it to again in vapors. There is a boil off valve, which operates and release the gas during high pressure vapor accumulation in the Dewar vessel. One has to take very good care of yourself by using cryogenic safety gloves while handling cryogenic fluid. They can cause severe cold burn and harm your skin.
Applications of cryogenic air separation
Cryogenic air separation is very useful for various industrial purposes including food preservation, healthcare, welding and metal cutting, electronic, oil and gas operation.