Damage analysis of magnesia fire brick during co-processing in cement kilns

The damage caused by the construction quality is mainly reflected in the additional mechanical stress on the lining bricks during the working conditions, and the damage caused by the harmful components caused by the co-processing aggravates this damage. There are three main situations. A common type of peeling groove with a locking brick area, the locking seam steel plate in the groove can be clearly seen. It is also common that the two ends are peeled off and the middle bulge is damaged, which is shaped like a bishop's hat, so it is vividly called "bishop's hat". The main reason is that the axial expansion of the kiln is not enough, and the extrusion causes the brick feet to fall. The main reason is that the expansion joints at the first ring of bricks are unreasonably left during construction, or the mechanical strength of the lining bricks is not enough to withstand the downward movement of the lining bricks. The force causes the corners to crack. Others are basically rare due to structural problems of the blocking ring.

The failure phenomenon of magnesia fire brick interacting with the working medium is the main way of damage to the lining bricks.

1) Salt attack by harmful components

The penetration and erosion of harmful components such as alkali, chlorine, and sulfur on magnesia fire brick are similar to that of high alumina bricks, but because the strength of magnesia fire brick is higher than that of alumina bricks, it is generally about 20MPa lower than that of high alumina bricks, so the probability of brick breaking is higher than that of high alumina bricks.

2) High-temperature liquid phase erosion

For kilns with the unstable operation, the hot end of the upper transition zone is prone to drift, and the lining bricks are eroded by the high-temperature liquid phase and then peel off with the fluctuation of kiln conditions, while the risk in the lower transition zone and firing zone is relatively small. The thickness of the lining brick damaged by the high-temperature clinker liquid phase is small, and the thickness is generally not more than 20mm, which is different from the damage caused by the corrosion of harmful components. Figure 5 shows the condition of peeling off the lining brick at the hot end of the transition zone.

3) Other damage reasons

In addition to the above reasons, there are overheating damage, thermal shock damage, and redox reaction damage of magnesia-iron spinel bricks. The redox reaction damage of magnesia-iron spinel is rare in China, mainly due to the mutual conversion of ferric iron and ferrous iron and the damage to the lining brick caused by the volume change of 20%. This damage occurs in the firing zone, especially if the kiln head is heavily used with alternative fuels.