An apparatus 30, wherein said mechanism for regenerating {HEAD ~ the first adsorbent bed} comprises a mechanism for passing a regeneration gas through {TAIL ~ the bed} 
An apparatus 30 , wherein said mechanism for regenerating { HEAD ~ the first adsorbent bed } comprises a mechanism for passing a regeneration gas through { TAIL ~ the bed }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL