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