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.