PSA vs VSA (Pressure /Vacuum Swing adsorption)

[zacharialamsyah]

Dear all

Can anyone explain me the differences between PSA (Pressure Swing adsorption) and VSA (Vaccum Swing Adsorption), and when these processes can be applied, because i think these 2 process have some functions such as CO2 Removal in H2 Production, are there any special condition required.

Thank you for Your comment and opinion
best regards
Zachari Alamsyah

 

[bcd]

You can learn a lot about each if you search the terms on Google. PSA is a common process used to purify Hydrogen. It operates at elevated pressures.

VSA is a process commonly used to remove Oxygen from air. The pressure cycles from very low positive pressure down to vacuum. In each process, the gas is feed thorugh vessels pack with material that adsorb impurities at one pressure, then release them at a lower pressure. When adsorbing, nearly pure product flows out the top of the vessel. Once the vessel is nearly saturated with impurities, the vessel is isolated and the pressure changed so the impurities are released and flushed from the vessel so it can be used to purify again. They are both cyclical processes that usually use multiple vessels so there is always on that is producing purified product.

In PSA, the pressure is always postive. In VSA (or sometimes called VPSA), the pressure changes from positive to negative.

 

[poli60]

bcd description is right with an exception. In some PSA units, "the pressure changes from positive to negative" mainly in order to increase the recovery. The vacuum conditions are applied by installing a vacuum compressore on the waste gas side. The recovery (of H2) increases with the increase of the pressure ratio between the absorption and the desorption stages. A typical application for H2 recovery in Refineries foreseen about 30 barg as inlet pressure and about -0.5 barg as outlet pressure of the waste gas (there's only a slight pressure drop on the Purified H2). At PSA outlet the Waste Gas is recompressed to the pressure required to enter the Refinery Fuel Gas network (usually about 5 barg). The high compression ratio is usually covered by a screw machine.