The Air and Ice Machine: A Look at How Cryogenic Nitrogen Generators Work

by Bronson Motor Speedway | Friday, Nov 11, 2016 | 472 views

IceSeparating air and all the manners of matter that constitute it may seem too ambitious a scientific pursuit, given air’s invisible and intangible characteristics. But, as you may have already noticed, ‘ambitious’ has never been a word to discourage the world’s thinkers and tinkerers alike.

Air separation has been an industrial process since 1895. Back then, all it took was taking the temperature down.

Cold Frontier

A cryogenic nitrogen gas generation system, as its name suggests, freezes pressurised air to separate nitrogen from the various other gases in the atmosphere. This is not the only method by which industries extract nitrogen from the air, however; nitrogen generators based on membrane and adsorption technologies also produce nitrogen at more than 99 per cent purity.

The distinction of the early cryogenic technology to more modern nitrogen gas generation systems is its reliance on the varying freezing points of atmospheric gases, unlike membrane- and adsorption-based generators that take advantage of the gases’ varying molecular sizes — like a sieve, but for air.

How It Works

A machine draws in air, leading it to a compressor that filters and pressurises it. The Warm End process begins when the air, now at 10°C, undergoes multiple filtration stages, mainly to eliminate hydrocarbons and other related compounds. Finally, an air purification unit removes any residual water vapour, carbon dioxide and hydrocarbons. This produces is an oxygen-rich by-product the machine vents back into the environment.

By this point, only nitrogen, carbon dioxide and other trace gases will remain inside the generator’s Warm End container. In order to isolate nitrogen at 99.99 per cent purity, the processed air enters the system’s Coldbox component, which rapidly lowers its temperature to -165°C. This is ways short of the freezing point of nitrogen (-210°C) and ways beyond that of carbon dioxide (-78.5°C), allowing pure nitrogen to leave the Coldbox only partially liquefied.

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Nitrogen is a gas as versatile as it is abundant. Countless industries rely on pure nitrogen to keep themselves operational, which makes the cryogenic nitrogen generator’s 19th century invention not early but rather just in time.

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