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