The concentrated black liquor is taken to be combusted in {TAIL ~ a recovery boiler}, into which {HEAD ~ combustion air} is fed at several levels for the combustion process 
into is fed
The concentrated black liquor is taken to be combusted in { TAIL ~ a recovery boiler } , into which { HEAD ~ combustion air } is fed at several levels for the combustion process
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH REL OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH OTH OTH