Lime-kiln linings under thermal load and chemical attack

A lime kiln decomposes calcium carbonate to calcium oxide. The hot face lives at high temperature in a carbon-dioxide-rich atmosphere, and is in continual contact with fuel ash and the burden. The lining has to protect the shell in that environment, and to keep both heat flow and chemical attack within acceptable bounds. Once the material fails, the cost of a stop for repair quickly outweighs the cost of the brick.

MgO-based brick is a usual working lining in the hot zone of a lime rotary kiln. Molten silicates from coal ash infiltrate along pores and grain boundaries, and react with magnesia to form forsterite (Mg₂SiO₄); monticellite (CaMgSiO₄) may appear as well. Exposure to coal ash alone is more likely to dissolve the brick and to open cracks at the hot face; ash together with quicklime often produces less slag intrusion. Potassium-rich biomass ash can go further and attack spinel, forming KAlO₂ inside the brick. Once the fuel shifts from coal toward biomass, the lining is no longer facing the same chemistry.

Shaft kilns and rotary kilns follow different thermal paths, but the picture of attack is the same: high temperature, ash and calcium oxide act together, and porosity and phase composition decide how far infiltration can go. The choice of lining starts from the fuel, the burden and the kiln type together.