DS PSA Technology
ds PSA stands for “double stage Pressure Swing Adsorption”. ds PSA works like a PSA to separate the oxygen, but then has a separate stage to separate the argon. The resulting product gas is oxygen, with only a small amount of residual argon and nitrogen which meets the pharmacopeia requirement for Oxygen 98. It vents to atmosphere to regenerate the sieves.
What is double stage Pressure Swing Adsorption?
ds PSA uses prepared ambient air as a source to produce the oxygen needed for medical purposes. Ambient air contains multiple gases: typically 21% oxygen, 78% nitrogen, 0.9% argon and 0.1% rare gases.
Pressure
ds 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.
double stage 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 zeolite is combined with a second media which is specific for separating argon from the gas mixture, hence "double stage".
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 will be regenerating the zeolite.
How does it work?
Pressure, double stage 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 zeolite is combined with a second medium, specific for separating argon from the gas mixture and concentrating the oxygen even more. 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 and the second medium in the vessels.
Venting, regenerating and ‘the swing’
The first vessel is vented to the atmosphere, which allows the zeolite and second medium to release their retained nitrogen, argon and any other gases. This venting clears out the necessary space in the 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 and argon into the zeolite & second medium matrix and depressurization allows the nitrogen and argon to escape, hence “pressure swing”.
