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PSA Technology.

What is PSA?

Pressure-Swing Adsorption.

PSA is an economical alternative for on-site production of oxygen or nitrogen (and other gases) for medical and industrial purposes.

Along this process, ambient air is compressed, conditioned, and filtered through synthetic minerals (zeolites) under pressure, where nitrogen is selectively adsorbed while the oxygen and argon are not, and pass through the zeolites stored in buffer tank to be used directly by the end user on demand.

PSA Diagram

Ambient air fed into the compressors is 78% nitrogen, 21% oxygen, less than 1% argon and other gases. As nitrogen is separated, the resulting gas is up to 95.5% oxygen purity. This maximum purity is the theoretical maximum; as nitrogen is adsorbed, the remaining gas can only contain the remaining 1% argon and other trace gases and 21% oxygen, therefore the limiting concentration of the impurities will be 1/22 or 4.5% maximum. This leaves the ultimate maximum oxygen purity at 95.5% actual concentration of gases varies slightly, so the above is an approximation to within ½%.

This process is based on the fact that different gases have the propensity to be attracted to different solid surfaces more or less strongly. This happens with nitrogen, which is attracted to the zeolites. As the air is compressed, the nitrogen is forced into the cristaline cages of the zeolite, and the oxygen is less adsorbed and conveyed to the end of the zeolite bed and ultimately recovered in the oxygen buffer tank.

Two zeolite beds are used together: One filters air and under pressure until it gets saturated with nitrogen while oxygen passes through. The second filter begins to do the same while the first one is regenerated as nitrogen is expulsed (desorbed) by releasing the pressure. The process repeats again, storing the oxygen and argon in a tank.

The argon could be separated afterwards increasing the amount of oxygen up to 99.5%. Using a carbon molecular sieve (CMS) based adsorbent, which adsorbs the oxygen, allowing the impurities to be scrubbed.

The maximum purity achievable in such systems is 99.5%. Typically the system is operated at a design point of 99.1% to optimize the output. In such a system there is about a 35% loss in the 94% feed product gas. This loss product is sensitive to the purity level: lower purity, less product loss.