When the share of calcination happening at the bottom-stage cyclone climbs above its design figure — meaning the calciner is sending meal to the kiln inlet that has not been fully decomposed upstream — the calciner is no longer doing its share of the work. The reaction has shifted into a stage that was not designed for the heat duty, or the calciner is short of fuel, air, or residence time and the meal arrives incompletely calcined. Either way, the kiln burning zone has to pick up the slack, and the operating margin everyone else relied on quietly disappears.
Why this matters in the preheater
The calciner exists to take 90–95% of the calcination load off the kiln, so the kiln can use its heat for combination reactions in the burning zone. When that split shifts — calciner doing less, kiln doing more — heat consumption rises, free lime gets harder to control, and the kiln's effective capacity falls. Bottom-stage cyclones run hotter than design, which accelerates dip-tube erosion and refractory wear in a part of the tower not built for that thermal duty.
A persistent calcination shift also unbalances the volatile cycle, because more material is decomposing in the wrong location at the wrong temperature. SO₃ and chloride condensation patterns move with it, and string formation becomes more likely a few weeks later.