{HEAD ~ The primary gas flow} is subjected to {TAIL ~ a final treatment stage} similar to the initial heat exchange treatment 
{ HEAD ~ The primary gas flow } is subjected to { TAIL ~ a final treatment stage } similar to the initial heat exchange treatment
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH