PSA Nitrogen and Oxygen Generation

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Adsorptive Generation of Nitrogen

Air Compression and Treatment

Dry and clean ambient air, compressed by an air compressor, is passing through a cyclone water separator, a refrigeration compressed air dryer and an arrangement of fine dust, coarse dust and activated charcoal filters. The condensate collected at these treatment stages is discharged by automatic  condensate drain units with no pressure loss.

Tower Filling and Adsorption

The dehydrated and purified air is passing the PLC operated air inlet valve and gets into the first of two adsorber towers filled with an adsorbent of type Carbon Molecular Sieve (CMS). The adsorbent used is selected depending on the purpose of the PSA System e.g. medium or high purity nitrogen production. While the CMS bed is pressurised oxygen is adsorbed with preference on the large inner surface of the carbon pellets thus retaining nitrogen in the feed gas flow. The oxygen separation process is stopped before the CMS comes to the adsorption capacity limit and the feed air supply is switched over to the second adsorber tower.

Desorption

For regeneration of the saturated CMS in the first vessel the corresponding control valve is opened until the pressure has dropped to a calculated lower level. The adsorbed gas is removed from the CMS and released through a vent line to atmosphere. The regenerated absorbent is now prepared for the next CMS tower filling step.

Pressure Swing Procedure

The PLC is controlling the valve set so that adsorption and desorption are alternated between the two CMS towers with a “swing” of equal time intervals which finally results in a continuous nitrogen generation.

Nitrogen Quality Adjustment

A surge tank is included in the PSA generation system to store the nitrogen produced. This buffer vessel is needed to receive steady product flow and purity, which can be adjusted to reach 99,995 % Vol. at up to 7 bar g.

Nitrogen Storage

If the nitrogen product shall be stored after generation another receiver vessel must be installed downstream the described arrangement.

 

Adsorptive Generation of Oxygen

Arrangement and Operation

Also oxygen can be separated from ambient air with PSA technology. The PSA generation system for oxygen is working with the same principle like described above for nitrogen, but in this case an adsorbent of the type Zeolite Molecular Sieve (ZMS) is used. Nitrogen and other gases are adsorbed while oxygen remains in the feedgas flow.

Performance and Oxygen Quality

Oxygen PSA systems are able to generate oxygen with a maximum purity of 95 % Vol. at a delivery pressure of max. 4 bar g. The rest of the gas composition consists of minimum 0,2 % Vol. of nitrogen but mainly argon which can not be separated completely.

 

Simplified PSA schematic