Degradation of Refractory Bricks Used as Thermal Insulation in Rotary Kilns for Iron Ore Pellet Production

Degradation of bricks in an iron ore pellet producing kiln has been investigated. Lab-scale tests of brick/slag interaction performed under different temperatures, atmospheres, and alkali additions show that addition of alkali dissolves the mullite in the brick and leads to formation of the phase nepheline (Na2O center dot Al2O3 center dot 2SiO(2)). At a high temperature, the grain boundary where nepheline is formed disintegrates due to volume expansion. At increased temperature, the nepheline transforms to an amorphous phase. Thus, a wear mechanism is proposed in the kiln using these bricks that involves these chemical reactions in combination with erosion by the continuously flowing slag.