There are two main types of nitrogen generators based on different principles:
- Nitrogen Membrane Separator
- Pressure Swing Adsorption (PSA) generators.
The heart of a nitrogen generator using the Membrane Separation technique is, of course, the membrane separator: air flows into each membrane and the separation is performed by the hollow fibers contained within each membrane module during air flowing in. Due to molecular sizes, the nitrogen remains into the fibers and is collected at membrane module outlet, while oxygen enriched air permeates outside fibers and is vented through the membrane Enriched Air outlet. Each membrane module enclosure is provided with relevant outlet to safe location for enriched air discharge. The inlet pressure at membrane module is function of inlet pressure of the package and of pressure drops of equipment.
PSA nitrogen generators utilize Carbon Molecular Sieve (CMS) material to separate oxygen from the source compressed air. CMS material consists of porous carbon with finely controlled pore size. As compressed air passes over the material, oxygen molecules are adsorbed into the pores, while the larger nitrogen molecules can pass through to the exhaust gas. Eventually, the CMS will become saturated with oxygen molecules and gas separation will no longer occur.
PSA generators are designed typically of two towers, one in operation and one in regeneration phase, the operation cycle is repetitive and controlled by a timer. A nitrogen buffer tank is typically required to ensure a constant pressure and flow rate during the switching between the two adsorption columns. Each generator (membrane or PSA) includes a prefiltration of air prior to entering in the separator to remove particulate, liquid water, and carry over hydrocarbons, in order to protect membranes or CMS; PSA system includes also a post filtration to protect downstream equipment from desiccant dust. Membrane generators requires few moving parts while PSA generators result heavier and bulkier equipment; in the other hand PSA is able to reach a purity level higher.