{TAIL ~ A portion} of {HEAD ~ the hydrogen gas} introduced at the inlet to the preheater is ultimately consumed either to replenish hydrogen stripped from solvent or to actually stabilize coal free radicals 
{ TAIL ~ A portion } of { HEAD ~ the hydrogen gas } introduced at the inlet to the preheater is ultimately consumed either to replenish hydrogen stripped from solvent or to actually stabilize coal free radicals
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH