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Air enters the generator via an inlet vent, passes through
the four way valve V-1, through a single stage, dry rotary
lobe blower, an air cooler and then into the adsorber bed,
again via valve V-1. On entering the adsorber vessel water
vapour, carbon dioxide and hydrocarbons are removed in a desiccant
layer. Thus only oxygen and nitrogen molecules flow over the
sieve bed, where the nitrogen is adsorbed and the oxygen passes
out of the vessel and through the open valve CV-2 to fill
the O2 buffer tank.
The bed quickly becomes saturated with nitrogen molecules.
These now have to be removed in a vacuum step to regenerate
the bed. Valves CV-1 and CV-2 are closed, and the four way
valve V-1 rotates such that the blower now acts in reverse
and "sucks" nitrogen molecules off the sieve bed,
in addition to removing water vapour, carbon dioxide and hydrocarbons
off the desiccant layer. All these are exhaust gases that
are vented out of the system through the same blower (now
acting as a vacuum blower) that the air originally entered.
In the purge step valve CV-2 opens to allow oxygen molecules
to flow back into the adsorber vessel to help remove any last
traces of nitrogen in the system.
Finally, in the re-pressurisation step, the whole system
is brought back up to atmospheric pressure by valve V-1 rotating
into a position such that air can rush back into the inlet.
At the same time oxygen is allowed into the top of the bed,
thus ensuring that there is no movement of the sieve bed (sometimes
a problem in PSA systems). The product valve PIC-1 remains
open throughout the whole of the above cycle so that a continuous
flow of oxygen product is maintained.
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