The purity of {HEAD ~ the gas product stream} or sales gas product is achieved by controlling a reflux stream returned to {TAIL ~ a purification zone} 
The purity of { HEAD ~ the gas product stream } or sales gas product is achieved by controlling a reflux stream returned to { TAIL ~ a purification zone }
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL