We are facing the problem of a kiln ring at the 10-12m mark (from kiln outlet) There has been no significant raw meal chemistry change: CaO 42.5% Fe2O3 2% Al2O3 3% SiO2 13.7%. When the ring forms, we clear it by substituting the corrective material with 100% pitsand~80% silica. However this compromises clinker quality and the ring resurfaces after a couple of days running. We cannot produce high quality clinker with C3S above 50% without suffering this phenomenon. What could be the primary cause and remedial action? Thank you and best regards