PSA technology
PSA stands for “Pressure Swing Adsorption”. Oxygen is separated from a mixture of gases under pressure using zeolite; then the system ‘swings’ to atmospheric pressure to desorb the adsorbed nitrogen. Two vessels are used to ensure continuous flow.
What is Pressure Swing Adsorption?
PSA uses prepared ambient air as a source to produce medical-grade oxygen. Ambient air contains multiple gases: typically 21% oxygen, 78% nitrogen, 0.9% argon and 0.1% rare gases. PSA uses pressure and a molecular sieve to separate the oxygen. The resulting product gas is oxygen, argon and a little nitrogen which meets the pharmacopeia requirement for Oxygen 93. It then vents pressure to atmosphere to regenerate the molecular sieve.
Pressure
PSA concentrators typically are comprised of two identical vessels filled with zeolite media. These two vessels are put under pressure (usually a screw type compressor) in an alternating pattern.
Swing
The alternating pattern of the pressure (the swing) is needed to ensure a nearly continuous output flow. One vessel will be concentrating the oxygen while the other regenerates the zeolite.
Adsorption
As the air flows through the vessel, the zeolite holds back the nitrogen molecules, water vapor and pollutants. Only oxygen and argon molecules are allowed to flow through the vessel and out to the system.
How does it work?
Pressure, adsorption and a switch
Air is compressed by an air compressor and passed into one of the two concentrating vessels. As the air flows through, the zeolite acts as a molecular sieve, allowing only oxygen and argon molecules to flow through the vessel and out to the system. Gradually, the nitrogen saturates the zeolite. If nothing were done, the concentration of oxygen would fall off, but before this can happen, the air supply is switched to the other vessel. This alternation is controlled by multiple valves and can be on a timed cycle or controlled by instrumentation monitoring saturation of the zeolite in the vessels.
Venting, regenerating and ‘the swing’
Simultaneously, the first vessel is vented to the atmosphere, which allows the zeolite to release its retained nitrogen and any other gases. This venting clears out the necessary space in the zeolite matrix for another cycle. The process relies on the pressure during the concentration cycle in the vessel being elevated and during regeneration being very close to atmospheric. Pressurization packs nitrogen into the zeolite matrix and depressurization allows the nitrogen to escape, hence “pressure swing”.
