Abstract
There are many cases observed in the burning zone of rotary cement kiln that wear of the direct-bonded magnesia chrome refractories has been increased due to fuel conversion from oil to coal. Two used bricks taken from the most severest part of the burning zone were analyzed by X-ray deffraction, microscope, chemical composition and thermal expansion respectively.
In addition to the textural changes in the used brick which were commonly observed due to migration of cement components, it was found that alkalis in the used brick played important role in wear mechanism. The brick peeled off with 32 mm thick showed large quantity of K3Na (SO4) 2 and KCl in the range of 20 to 32 mm from the hot face. On the other hand, the brick which remained on the kiln shell contained a lot of K3Na (SO4) 2 and KCl in the range of 0 to 20 mm from the surface as well.
From the thermal expansion test these two layers that contained more alkalis than other layers showed larger thermal expansion with 1. 84% and 1.63% respectively while original brick showed 1.20% at 1100°C.
It was assumed that the crack came out between the two layers due to higher thermal expansion.
From the results, it was learned that well developed direct bond and increase of the density of brick give better characteristic to increase resistance to alkali attack.
