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A nitrogen generator produces nitrogen gas on-site from your existing compressed air supply. It separates the nitrogen already in the air from the oxygen, water vapour, and other gases, then delivers high-purity nitrogen at the pressure your process needs. It replaces buying nitrogen in cylinders or bulk liquid from a gas supplier.
This guide explains how the two main types work, what purity you can expect, and when generating your own nitrogen makes financial sense.
Where the nitrogen comes from
The air around us is roughly 78% nitrogen and 21% oxygen, with argon, carbon dioxide, and water vapour making up the rest. A nitrogen generator does not create nitrogen. It takes ordinary compressed air and strips out everything that is not nitrogen, leaving a concentrated nitrogen stream behind.
That means a generator always starts with a compressed air supply. The quality of that supply matters. The air has to be clean and dry before it reaches the generator, or the separation media degrades and purity drops. This is why on-site nitrogen and good compressed air treatment go together.
The two technologies
There are two proven ways to separate nitrogen from compressed air. The right one depends on the purity and flow your application needs.
Pressure Swing Adsorption (PSA)
A PSA generator uses two towers filled with carbon molecular sieve, a material with pores sized to trap oxygen molecules while letting the smaller path of nitrogen pass through.
Here is the cycle:
- Clean, dry compressed air enters the first tower under pressure.
- The carbon molecular sieve adsorbs oxygen, carbon dioxide, and remaining moisture. Nitrogen passes through to the outlet and into a storage receiver.
- As the first tower fills with oxygen, the system switches to the second tower.
- The first tower depressurises, releasing the trapped oxygen to atmosphere so the sieve is ready to work again.
Because one tower always regenerates while the other produces, the supply is continuous. PSA is the standard choice where high purity matters, reaching up to 99.999% nitrogen.
Membrane separation
A membrane generator passes compressed air through bundles of hollow polymer fibres. The fibre walls let oxygen and water vapour permeate out through the sides while the nitrogen continues along the fibre to the outlet.
There are no moving parts and no switching cycle, so membrane units are compact, quiet, and very low maintenance. They suit lower purity needs, typically 95% to 99.5%, and smaller or remote installations.
What purity can you get?
Purity is adjustable, and higher purity costs more energy and a larger generator. Specifying the right grade is where the savings are won or lost.
- 95% to 99%: tyre inflation, general blanketing, fire prevention systems.
- 99% to 99.9%: food packaging, plastics moulding, heat treatment.
- 99.9% to 99.99%: laser cutting, electronics, chemical processing.
- 99.99% to 99.999%: pharmaceutical, semiconductor, analytical laboratories.
The goal is to match the generator to the purity your process actually needs, not the highest grade available.
When does on-site generation pay?
Buying nitrogen as cylinders or bulk liquid carries the cost of the gas, plus delivery, cylinder rental, and contract management. Those costs recur every month and rise with usage.
On-site generation replaces all of that with a single capital investment. After installation, the only ongoing cost is the electricity to run the compressed air feed. For sites with steady demand, the payback period is typically under two years, and the case is strongest where a compressed air system is already in place.
If you are weighing it up, the nitrogen generators page sets out the technologies and applications in more detail, and we can model your current nitrogen spend against on-site generation to give you a clear payback figure. We advise sensibly, we do not provide legal advice.