{HEAD ~ The burner} is {TAIL ~ a gas fired burner} whose flame is encapsulated in a layer of cool air due to the effect of the induction blower drawing air through the tube bundle from the exhaust outlet, so that the flame does not melt or burn through the tubes 
is
{ HEAD ~ The burner } is { TAIL ~ a gas fired burner } whose flame is encapsulated in a layer of cool air due to the effect of the induction blower drawing air through the tube bundle from the exhaust outlet , so that the flame does not melt or burn through the tubes
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH