PSA in Pollution Control

Volatile Organic Compounds (VOCs) are almost found in everything. Common items like paints and coatings to deodorants and cleaning fluids all have some quantity of volatile organic compounds. With strict pollution norms. They are in the scanner for all major Environmental Protection Agencies and Air quality boards all over the world. VOCs are a significant contributing factor to ozone, an air pollutant.

The basic unit of a Vapor Recovery Unit comprises of a PSA (Pressure Swing Adsorption) process that has two numbers activated carbon bed vessels. This alternate on a time cycle of 15 minutes. Carbon reactors are Regenerated through vessel evacuation. It employs two stage liquid ring vacuum pumps to raise a pressure level of 27”Hg. Regeneration is also accomplished secondarily, with a controlled ambient air purge input to the bed. This is generally done during the last quarter of the regeneration cycle.

The Volatile Organic Compounds or VOCs that gets desorbed from the carbon during the process of reactor regeneration are efficiently recovered in a two step process. This includes condensation to occurring in the liquid ring vacuum pump and absorption happening in a packed tower that has counter current flow absorber. Gasoline from the Supply tank is pumped on skid, for use as a lean oil in the absorber. Also, this acts as a heat exchange fluid required for in the liquid ring vacuum pump seal fluid.

Finally all the product that is recovered by the system is again pumped back into the supply tank of gasoline. The enriched liquid gasoline is directed to spread throughout the supply tank. This causes a very negligible change in product characteristics.

Diagram of a PSA operated Vapour Recovery Unit