| Two Bed PSA Process |  |
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| Two Bed PSA Process |
| Using Double bed PSA
for Helium Purification Helium owing to its unique properties is gaining ground for its use in high profile technologies like Nuclear power plants, as a refrigerant for superconducting magnets, or transfer of energy to lasing gases. Using Double bed PSA system for purification makes it possible to enhance the performance of Helium enrichment plant. The PSA system has been able to reduce impurities like nitrogen, which has led to obtaining pre-enriced helium concentration to the tune of 15 vol % from about 1.4 vol % earlier. One of the primary benefits of using PSA system has been that unlike the enrichment and purification plants where nitrogen in the liquid form is used as an external refrigerant here liquid nitrogen is not needed to pre enrich helium. |
Using simple two bed PSA process high purity Oxygen, Nitrogen and Hydrogen could be obtained. From the economic point of view, for Oxygen production less than 700 Nm3/hr the 2-bed PSA process is conformed as a more feasible option. Generally Two adsorbent beds are arranged in parallel. One bed is made on-line while the other gets regenerated. Each bed then undergoes a cycle of phases.
The PSA process takes the following cyclic sequence of Pressurization with the feed gas (PR), High-pressure adsorption (AD), Depressurizing pressure equalization (DPE), Countercurrent depressurization (DP), Purge (PG), and lastly Pressurizing pressure equalization (PPE).
Each step of Two Bed PSA Process is described in the following table:
| Elementary steps | Mode of operation | Principal features |
| Pressurization | Pressurization with feeding
from the feed end Pressurization with raffinate product from the product end before feed pressurization |
Enrichment completed, of the 'less selectively
adsorbed species' in the gas phase at product end Sharpens the concentration front, that improves purity and recovery process of raffinate product |
| High-pressure adsorption | Product (raffinate) withdrawal is done at
constant bed pressure The bed pressure is allowed to lessen as the raffinate product is drawn from the product end |
Raffinate product gets delivered at high
pressure Considerable recovery of the less selectively adsorbed species is achieved, but the end product is delivered at low pressure |
| Blowdown | Counter-current blowdown to very low pressure Co-current blowdown to an intermediate pressure before counter-current blowdown |
Applicable only when raffinate product is
required at high purity; can prevent contamination of the product
end with more strongly adsorbed species Used when extract product is also needed with high purity; enhances extract product purity; can also increase raffiante recovery |
| Desorption at low pressure | Counter-current desorption with
product purge Counter-current desorption without external purge Evacuation |
Enhances raffinate product but at the expense
of lower recovery; purge at sub atmospheric pressure reduces
raffinate product loss but energy cost goes up Recovery enhancement while maintaining high product purity is possible only during certain type of kinetic separation High purity obtainable of both extract and raffinate products; advantage over product purge when the adsorbed phase is very held strongly |
| Pressure equalization | The low and high pressure beds are connected through their product ends or through feed end. Product ends of the high-pressure bed are joined to the respective ends of the low-pressure bed | Conserves energy and separative work |