Problems appear to be caused by hot spots, short circuits or {HEAD ~ fluid composition deviations} coming from {TAIL ~ the upper reaction bed} 
Problems appear to be caused by hot spots , short circuits or { HEAD ~ fluid composition deviations } coming from { TAIL ~ the upper reaction bed }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL