Some oxygen 24 passes through and {HEAD ~ some oxygen} and xenon and krypton are adsorbed and recovered during {TAIL ~ bed regeneration} 
adsorbed during
Some oxygen 24 passes through and { HEAD ~ some oxygen } and xenon and krypton are adsorbed and recovered during { TAIL ~ bed regeneration }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL