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