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Process (PSA)
Pressure swing
adsorption processes rely on the fact that under pressure,
gases tend to be attracted to solid surfaces, or
"adsorbed". The higher the pressure, the more gas is
adsorbed; when the pressure is reduced, the gas is
released, or desorbed. PSA processes can be used to
separate gases in a mixture because different gases tend
to be attracted to different solid surfaces more or less
strongly. If a gas mixture such as air, for example, is
passed under pressure through a vessel containing an
adsorbent bed that attracts Nitrogen more strongly than it
does Oxygen, part or all of the Nitrogen will stay in the
bed, and the gas coming out of the vessel will be Oxygen.
When the bed reaches the end of its capacity to adsorb
Nitrogen, it can be regenerated by reducing the pressure,
thereby releasing the adsorbed Nitrogen. It is then ready
for another cycle of producing Oxygen.
Using two adsorbent vessels allows near-continuous
production of the target gas. It also permits so-called
pressure equalization, where the gas leaving the vessel
being depressurized is used to partially pressurize the
second vessel. This results in significant energy savings,
and is common industrial practice. |
