The
most economical form of oxygen supply for environmental applications is, in
general, an on-site oxygen generation system. These systems are highly reliable
and have been supplying oxygen economically and safely to treatment facilities
ranging in size from one to 500 million gallons per day. Two basic types of
technology are employed to separate oxygen from air. Adsorption type
systems are generally used for small to medium size plants. Cryogenic type systems
are used for larger size plants. For some special cases, including small treatment
plants, liquid oxygen may be delivered to and stored on the site.
Linde
PP
Linde
Process Plants (Tulsa,OK) and M2T Technologies are affiliated.
offers three oxygen supply
options, consisting of Pressure Swing Adsorption (PSA) Systems, Vacuum Swing
Adsorption (VSA) Sys-tems and Cryogenic Sys-tems. The choice of system depends
on a number of fac-tors, including space avail-able, quantity of oxygen re-quired,
oxygen demand vari-ations and utility costs. All of these oxygen supply systems
can be operated in a turn-down mode yielding cost sav-ings when not operating
at full capacity. They are all very reliable with unscheduled downtime averaging
less than about one percent.
The
PSA System is generally applicable for systems requiring less than about 30
tons per day of oxygen. As shown in Figure 1, ambient air is compressed and
flows to a vessel that contains a molecular sieve adsorbent. The adsorbent selectively
re-moves water, carbon dioxide and most of the nitrogen pro-ducing a high purity
oxygen gas (typically 90%) from the adsorber vessel. Once the adsorbent is loaded
with im-purities the adsorber bed is depressurized to atmospheric pressure whereby
the impurities are removed from the adsorbent in preparation for the next adsorption
cycle.