introducing alumina into {HEAD ~ the tank} at {TAIL ~ a slow rate CL} which is from 15 to 50% below the normal rate of alumina consumption CN 
at
introducing alumina into { HEAD ~ the tank } at { TAIL ~ a slow rate CL } which is from 15 to 50 % below the normal rate of alumina consumption CN
OTH OTH OTH 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