Hach BioTector B3500s, User Manual

Page: 45 / 166

Page 45
4.2.3 BioTector Oxygen Concentrator
The operation of BioTector oxygen concentrator is based on the crystalline zeolite molecular sieves, which
permits the separation of oxygen gas from the mixture of gases that comprise air. As air flows through a
column or bed of molecular sieve, the component gases it contains are adsorbed and stratified in the order of
their relative affinity to the molecular sieve material. The process may continue until the next to last gas
component stratifies near the end of the bed. Once the full bed length is used, the bed must be regenerated
by desorbing (or purging) the adsorbed gases. Purging is accomplished by reducing the pressure in the bed
and back-flushing with some of the concentrated gas product. Adsorption and desorption are completely
reversible processes and are carried out indefinitely.
The theory behind the operation of the oxygen concentrator is Pressure Swing Adsorption (PSA). This is
based on flowing air through the column (the sieve bed) packed with molecular sieve material. The
components of the air (Water Vapor, Carbon Dioxide, Carbon Monoxide, Hydrocarbons, Nitrogen, Oxygen
and Argon) are adsorbed in order of their relative affinity to the molecular sieve material. Figure 5 shows the
adsorption of air components inside the molecular sieves.
Figure 5 Adsorption of air components in oxygen concentrator molecular sieves.
Once the sieve bed is used, then it is re-generated by purging the adsorbed gasses from the molecular sieve.
This is achieved by removing the air supply from the inlet to the sieve bed, and back-flushing the sieve bed
with some of the concentrated gas product. The typical oxygen purity obtained from a PSA oxygen
concentrator is 93% (±3%) with balance gas Argon.
Figure 6 below shows the layout of BioTector oxygen concentrator and the operation of the Rotary Valve used
for the PSA process.