The PSA process itself is strongly influenced by certain process parameters like tail gas pressure, number of pressure equalization steps etc. PSA units can handle growing throughputs meanwhile they are getting specifically smaller. Sophisticated control systems enhance the performance, flexibility and automation.
The adsorption characteristics are considered while choosing the adsorbents. It is considered that the adsorbent would have much greater affinity for non-product molecules than for the product gas (Nitrogen or Oxygen). This characteristic results in most of the desired molecules passing through the bed and into the product stream, while undesired components (product impurities) are captured by the adsorbent.
The PSA process is inherently a batch process because the adsorbent bed requires periodic desorption while production of gas. The PSA systems usually have two adsorbent vessels which allows the continuous operation. At any time, one of the vessels is supposed to make product by adsorbing undesired components of air; while the other vessel would undergo regeneration by de-pressurization to atmospheric pressure. Whenever, the adsorbing vessel gets saturated, there is a set of valves quick in switching the services. It is equipped with a surge vessel (buffer vessel) downstream of the adsorbers ensuring the continuous delivery of the product. Generally, two-bed system is used but mono-bed and three-bed configurations are sometimes used for greater capital savings or greater production continuity, respectively.
Technology
PSA nitrogen vessels contain an activated carbon molecular sieve material which actively removes oxygen and other undesired components by adsorption during the process. The nitrogen is typically delivered from the gas production unit at pressures of six to eight atmospheres and with the purity ranging from 95 to 99.5%. If one needs higher purity of nitrogen, a "de-oxo" unit can be added that catalytically combines hydrogen with the oxygen in the nitrogen product leaving the PSA, producing water, which is removed by cooling and additional adsorption. The waste stream from a nitrogen membrane or PSA plant is enriched in oxygen - often to about 40% Oxygen. This stream could be compressed and can suitably used for combustion enhancement or waste treatment at the same site.