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