Nitrogen generator vs liquid nitrogen: which costs less?

For a steady, all-day demand for nitrogen gas, an on-site nitrogen generator costs far less than a liquid nitrogen tank. You pay for electricity and servicing instead of delivered gas, tank rental and boil-off. Liquid nitrogen is the only choice for cryogenic uses.

How each supply works

What you pay for with liquid nitrogen

The price per litre or per cubic metre is only part of a liquid nitrogen bill. Check your contract and invoices for:

• the gas itself, usually priced per unit delivered
• tank and vaporiser rental, charged whether you use gas or not
• delivery charges, minimum drop sizes and any fuel or energy surcharges
• telemetry that tells the supplier when to refill
• floor space for the tank and vaporiser, plus clear access for the tanker
• the environmental cost: every refill is a diesel tanker journey to your site, and the nitrogen was liquefied at an air separation plant that uses a great deal of electricity
• boil-off, because heat still reaches the liquid through the insulation and some is vented as gas even on days when you draw none

Boil-off hits hardest on sites that use little nitrogen, or none at weekends and over shutdowns. You are still paying for gas that leaves through the relief valve.

What you pay for with a generator

• The generator, bought outright, financed or leased.
• Compressed air, which means electricity. This is the main running cost.
• Servicing: filter elements, valve kits, analyser checks and an annual service.
• Compressor capacity. If your existing compressors have no spare air, you may need a compressor for the generator.
• Floor space for the generator, its filtration and a nitrogen buffer vessel.

There is no rental, no delivery and no boil-off. The generator only uses air while it is making nitrogen, and Parker’s NITROSource Plus generators use Energy Saving Technology to cut air use when nitrogen demand falls.

Working out the cost of generated nitrogen

The electricity cost of each cubic metre of nitrogen comes from two figures: how much compressed air the generator needs for each cubic metre of nitrogen (the air to nitrogen ratio), and how much electricity your compressor uses to make each cubic metre of air.

Add servicing spread over the year’s output. Then compare the total with what your liquid nitrogen invoices work out at per cubic metre once rental, delivery and boil-off are included. Our article on the financial case for on-site nitrogen generation goes further into return on investment.

Published case studies from UK sites that replaced bulk liquid with a generator show how wide the gap is. Their all-in cost of nitrogen fell from between 29p and 40p a cubic metre to between 4p and 7p.

The only reason to choose liquid nitrogen

The only reason to choose liquid nitrogen is that you use it as a liquid, for freezing, cryogenic grinding or liquid dosing into cans and bottles. A gas generator cannot do that. Wherever your process uses nitrogen as a gas, a correctly specified generator is the better choice.

Liquid nitrogen is often kept as a standby supply, but it is an expensive one. The tank boils off gas whether you use it or not. A well specified generator system builds the standby in instead, on both the compressed air supply and the generator, so a service or a fault on one machine does not stop production.

How to compare the two for your site

1. Collect 12 months of nitrogen invoices, including rental, delivery and surcharges.
2. Work out the real usage: how much and at what flow. Note the times of day and week too.
3. Confirm the purity and pressure each process needs. Asking for more than you need costs compressed air.
4. Check how much spare capacity your compressors have.
5. Price the generator option with servicing included, and with standby on the compressed air and the generator.

Our compressed air and nitrogen audit measures the flow, purity and compressor capacity for you, so the comparison rests on your figures, not estimates.

Frequently asked questions

Is a nitrogen generator cheaper than liquid nitrogen?

Yes, by a wide margin, for any process that uses nitrogen as a gas. A generator’s main running cost is the electricity for its compressed air, while liquid nitrogen carries the gas price, tank rental, delivery charges and boil-off.

How much nitrogen gas does one litre of liquid nitrogen make?

One litre of liquid nitrogen gives about 0.65 normal cubic metres of nitrogen gas, measured at 0°C and atmospheric pressure. That is roughly 650 litres of gas, which is why liquid is an efficient way to deliver and store nitrogen in bulk.

Can a nitrogen generator replace a liquid nitrogen tank?

Yes, where the process uses nitrogen as a gas and the generator is sized for the peak flow, purity and pressure. It cannot replace liquid nitrogen used as a liquid, for example for freezing or liquid dosing.

Do I still need a backup nitrogen supply with a generator?

If stopping production would be costly, yes, but a liquid nitrogen tank is an expensive way to provide it, because it boils off gas while it waits. A better answer is a generator system specified with standby on both the compressed air supply and the generator, so servicing or a fault on one machine does not stop production.