Air can be separated into oxygen,
nitrogen and argon by fractional distillation.
Oxygen is used in a number of chemical processes
including steel making and metal cutting. Nitrogen gas is used
as an inert atmosphere for storing food.
Argon is used for filling light bulbs.
Air, the raw material for this process, is everywhere and so plants are sited for
the convenience of distributing
the products. The principle of the process is straightforward.
Air is cooled until it becomes liquid. Nitrogen has a lower boiling point than oxygen
so it rises as a gas up the distillation column.
Liquid oxygen collects at the bottom. On this site
air is drawn in and compressed at this point.
The air is cleaned.
After further compression it's fed into the distillation column
as a liquid. The liquid air products are stored on the site
before delivery to customers.
Air is the raw material of the process. It is drawn in here
and then drawn through filters to remove dust. The filtered air
is then compressed and this powerful compressor forces the gas stream
through the process.
The air is chilled to 6 degrees Celsius. Most of the moisture condenses out.
The cooled air passes through chemicals which absorb the carbon dioxide
and any remaining water. Further cooling takes place in a heat exchanger
using cold gases from the distillation column. The air is cooled even more by
compression followed by expansion. The energy from the expanding gas
spins a turbine and that in turn provides some of the energy
for the compressors.
Final cooling takes place here.
Eventually the liquid air is led into the fractional distillation column.
This tall fractional distillation column is in fact two columns
with a low pressure unit sitting on top of a high pressure one.
The double column works like this.
Air enters the high-pressure column as a liquid. Nitrogen boils off and rises
as a gas to the top of the column
where it's condensed. A liquid rich in oxygen
condenses at the bottom of the column. The oxygen-rich liquid
is fed to the low pressure column. Any nitrogen boils off
and almost pure liquid oxygen condenses.
Argon is separated as a byproduct from the oxygen-rich liquid
in a side column by further fractional distillation.
Small quantities of gases can be supplied to customers
in cylinders.
Larger quantities of air products are supplied as liquids
in refrigerated tankers.