How does Pressure Swing Adsorption work?
When producing your own nitrogen, it is important to know and understand the purity level you want to achieve. Some applications require low purity levels (between 90 and 99%), such as tire inflation and fire prevention, while others, such as applications in the food and beverage industry or plastic molding, require high levels (from 97 to 99.999%). In these cases PSA technology is the ideal and easiest way to go. 

In essence a nitrogen generator works by separating nitrogen molecules from the oxygen molecules within the compressed air. Pressure Swing Adsorption does this by trapping oxygen from the compressed air stream using adsorption. Adsorption takes place when molecules bind themselves to an adsorbent, in this case the oxygen molecules attach to a carbon molecular sieve (CMS). This happens in two separate pressure vessels, each filled with a CMS, that switch between the separation process and the regeneration process. For the time being, let us call them tower A and tower B. 

For starters, clean and dry compressed air enters tower A and since oxygen molecules are smaller than nitrogen molecules, they will enter the pores of the carbon sieve. Nitrogen molecules on the other hand cannot fit into the pores so they will bypass the carbon molecular sieve. As a result, you end up with nitrogen of desired purity. This phase is called the adsorption or separation phase. 

It does not stop there however. Most of the nitrogen produced in tower A exits the system (ready for direct use or storage), while a small portion of the generated nitrogen is flown into tower B in the opposite direction (from top to bottom). This flow is required to push out the oxygen that was captured in the previous adsorption phase of tower B. By releasing the pressure in tower B, the carbon molecular sieves lose their ability to hold the oxygen molecules. They will detach from the sieves and get carried away through the exhaust by the small nitrogen flow coming from tower A. By doing that the system makes room for new oxygen molecules to attach to the sieves in a next adsorption phase. We call this process of ‘cleaning’ an oxygen saturated tower regeneration.




First, tank A is in the adsorption phase while tank B regenerates. In the second stage both vessels equalize pressure to prepare for the switch. After the switch, tank A starts regenerating while tank B generates nitrogen.
At this point, the pressure in both towers will equalize and they will change phases from adsorbing to regenerating and vice versa. The CMS in tower A will get saturated, while tower B, due to the depressurization, will be able to restart the adsorption process. This process is also referred to as ‘swing of pressure’ , which means that it allows for certain gases to be captured at higher pressure and released at lower pressure. The two tower PSA system allows for continuous nitrogen production at a desired purity level.