The cement rotary kiln is a key equipment in the cement production process, and the refractory lining is an important part of the rotary kiln, which plays a role in protecting the kiln body and maintaining the high-temperature working environment in the kiln. Damage to the refractory lining not only affects production efficiency, but may also cause serious damage to the equipment. The following is an analysis of common causes of damage to the refractory lining of the cement rotary kiln and corresponding countermeasures:
1. Thermal expansion squeezes refractory bricks
When the kiln temperature rises to a certain level, thermal expansion will generate pressure in the axial direction of the kiln, causing adjacent refractories bricks to squeeze each other. When the pressure is greater than the strength of the refractory fire bricks, it will cause the brick surface to peel off. The following measures should be taken:
(1) Dry-lay refractory firebricks, set reasonable side paperboards, and leave 2mm fire mud joints for wet-lay refractories bricks.
(2) Leave a suitable brick retaining ring.
2. Iron plate stress damage
At the hot end of the refractory brick, the veneer iron plate reacts chemically with the magnesium oxide in the magnesia brick at high temperature to form magnesia-iron compounds, which increase the volume and squeeze the refractory fire brick, causing horizontal fractures. In view of this situation, the practice of veneer iron on refractory firebricks should be changed or replaced with fire clay.
3. Large-area twisting and dislocation of fire bricks
Due to loose masonry and frequent kiln opening and closing, the kiln shell is deformed, causing the kiln shell and the cold surface of the lining brick to move relative to each other, causing the lining brick to twist and dislocate, and the brick surface to crack and fall off. The following measures should be taken:
(1) During masonry, the large surface of the refractory fire brick should be hammered solid with a wooden hammer, the locking brick should be locked, and a wedge iron should be added for the second time.
(2) Maintain a stable thermal system.
(3) The deformed part of the kiln shell should be leveled with high-temperature cement.
4. Ovality stress extrusion
Due to the increase in the gap between the rotary kiln wheel shims, the shell has a larger ovality, causing the refractory brick to be squeezed. The ovality of the cylinder should be checked regularly. If the ovality value exceeds 1/10 of the kiln diameter, the pad should be replaced or the pad iron should be added to adjust the wheel gap.
5. Locking iron stress extrusion
When locking bricks, too many locking irons are too tight, which will cause brick grooves at the locking point. The following measures should be taken:
(1) At the same locking point, the number of locking irons should not exceed 3.
(2) The spacing between locking irons should be as dispersed as possible.
(3) The tightness of the inner and outer openings should be consistent when locking bricks.
(4) The locking iron should be kept as far away from thin locking bricks as possible.
6. Brick retaining ring squeezes refractory bricks
The retaining bricks (special-shaped bricks) at the brick retaining ring are broken and cracked due to extrusion. In this case, the single-track brick retaining ring should be changed to a double-track brick retaining ring, and whole bricks should be laid on the brick retaining ring to avoid processing special-shaped bricks.
7. Overheating
The local overheating of the temperature in the kiln causes the refractory bricks to melt and form pits. In order to avoid this situation, the burner should be adjusted correctly and reasonable refractory materials should be selected in different parts.
8. Thermal shock phenomenon
The thermal stress caused by sudden temperature changes causes the brick surface to peel and crack, which is mainly caused by frequent opening and closing of extreme cold and heat. The production operation should be stabilized and a reasonable heating and cooling kiln system should be formulated.
9. Chemical erosion damage
The gas phase alkali salt compounds penetrate into the gaps of the brick body, condense and solidify, and form a horizontal permeable layer of alkali salts in the brick body. The alkali salt content entering the kiln should be reduced during production.
From the above damage mechanism of refractory bricks, it can be seen that the standardization of refractory material construction can effectively extend the service life of refractory materials, and professional and dedicated masonry personnel are important factors in ensuring the quality of refractory material construction.
Principles of refractory material selection
When selecting refractory materials, the following requirements should be met:
(1) High temperature resistance. It can be operated in an environment above 800T for a long time.
(2) High strength and good wear resistance. The refractory materials in the rotary kiln must have a certain mechanical strength to withstand the expansion stress at high temperature and the stress caused by the deformation of the rotary kiln shell. At the same time, due to the wear of the furnace charge and flue gas on the refractory material, the refractory material needs to have good wear resistance.
(3) Good chemical stability. To resist the erosion of chemical substances in the flue gas.
(4) Good thermal stability. Able to withstand the alternating stress under the burning state. When the furnace is stopped, started, and the rotating operation is unstable, the temperature in the kiln changes greatly, and there should be no cracking or peeling.
(5) Thermal expansion stability. Although the thermal expansion coefficient of the rotary kiln shell is greater than the expansion coefficient of the rotary kiln refractory material, the shell temperature is generally around 10000℃, while the temperature of the refractory material is generally above 8001℃. This may cause the refractory material to expand more than the rotary kiln shell and fall off easily.
(6) Low porosity. If the porosity is high, the flue gas will penetrate into the refractory material and erode the refractory material.
