The gas and {HEAD ~ vapor} evolved in these zones passes upwardly through {TAIL ~ the vents} 94 into the vapor collection region 89 and is removed 
The gas and { HEAD ~ vapor } evolved in these zones passes upwardly through { TAIL ~ the vents } 94 into the vapor collection region 89 and is removed
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH