Nitrogen generators - on-site nitrogen production from compressed air

Atmospheric air consists of approximately 78 percent nitrogen and 21 percent oxygen. A nitrogen generator separates oxygen from nitrogen and needs only clean, dry compressed air and electricity to operate. Two technologies are used.

PSA nitrogen generator (pressure swing adsorption)

A PSA nitrogen generator has two columns filled with CMS carbon molecular sieve. Under pressure, the bed adsorbs oxygen and traces of other gases, while nitrogen passes into the receiver. When the bed in one column becomes saturated, the column is depressurised, oxygen is released into the atmosphere and the second column takes over. Adsorption and regeneration alternate, ensuring a continuous nitrogen flow.

Membrane generator (hollow fibres)

In a membrane generator, compressed air flows through a bundle of thin, hollow polymer fibres. Oxygen, water vapour and carbon dioxide permeate the fibre walls faster than nitrogen, leaving a nitrogen-enriched stream at the outlet. The membrane has no moving parts or switching valves and is simple and compact.

The economic crossover is approximately 98 percent purity: below this, membrane technology usually wins; above it, PSA generators.

A generator does not create nitrogen from nothing: it rejects part of the feed air. The higher the purity, the more air must be compressed for each cubic metre of nitrogen.

The conclusion is simple: higher purity requires a larger compressor, more energy and higher nitrogen costs. There is no benefit in specifying a higher purity than the process actually requires.

A complete nitrogen production system consists of the following components:

Feed air should meet ISO 8573-1 class 1 for oil, with a dew point matched to the generator technology and a typical pressure of 6 to 10 bar. We build air treatment systems using components including BEKO Technologies: CLEARPOINT, DRYPOINT, BEKOMAT.

Role of air treatment components

• Coalescing filter retains oil aerosols, water and solid particles, protecting the CMS bed or membrane.
• Activated carbon filter removes oil vapour and odours that a coalescing filter cannot capture.
• Dryer lowers the dew point, as moisture shortens the life of sieves and membranes.
• Condensate drain, e.g. BEKOMAT, removes water from the receiver, dryer and filters without air loss.
• Dew point and oxygen measurement, e.g. using METPOINT instruments, enables continuous monitoring of feed air quality and nitrogen purity.

Read more about air treatment on our page compressed air filtration, and about piping on our page compressed air systems.

The largest share of generator-produced nitrogen costs is the energy needed to compress air. When selecting and operating a system, we therefore focus on several specific factors:

• Purity matched to the process, not excessive purity as a precaution. Every increase in purity means more air per 1 Nm³ of nitrogen, requiring a larger compressor and a higher electricity bill.
• No cylinder or tanker transport. On-site production eliminates deliveries and liquid nitrogen evaporation losses, reducing the CO₂ footprint associated with gas supply.
• Produce only what is needed. The generator produces nitrogen according to current demand, and the controls stop the system when demand ceases, avoiding unnecessary energy use.

Heat from the compressor supplying the generator can be recovered and used for building heating or domestic hot water. We explain the details on our page compressor heat recovery.

A leak-tight system reduces the cost of each Nm³ of nitrogen, as air lost through leaks has to be produced again. Estimate the losses with our leak cost calculator, while a complete picture of energy consumption is provided by a compressed air audit.

Regular servicing maintains nitrogen purity and output. Our inspections include:

• periodic inspections and checks of nitrogen purity and output
• replacement of CMS beds and membrane modules
• replacement of coalescing and activated carbon filter elements
• oxygen sensor calibration.

We service nitrogen generators from various manufacturers and air treatment systems, including during compressor and dryer inspections. See also compressed air dryer servicing.