High temperature refractory bricks for cement kiln
1. Mechanical damage
It is subjected to the comprehensive mechanical stress of compression, tension, torsion and shear. The rotation of the kiln, the ovality of the cylinder, the extrusion, twisting, and deformation of the kiln cylinder between the lining brick and the cylinder, and between the bricks, will all generate mechanical stress between the brick linings. When the gap between the cylinder and the tire is large, the ovality of the kiln cylinder increases, the alternating stress on the lining brick increases, and the mechanical stress on the tire is the most serious. After renewing the bricks in our factory, the kiln barrel was bent, and the kiln lining was partially overheated due to severe vibration, which caused deformation of the carcass and squeezed the lining. Furthermore, the adjustment of the supporting rollers took a long time. The red kiln occurred at the belt, and the refractory bricks fell off in a large area in one part, and the kiln body was digged and repaired. The normal kiln body no longer vibrated after the supporting roller was adjusted.
2. Rapid cold and rapid heat
A large number of literatures point out that the alkali expansion coefficient is large, and huge thermal stress is generated during the heating process. Therefore, the heating should be slow during the kiln drying, so that the expansion of the kiln cylinder complements the expansion of the brick to play a compensating role in the kiln body. This is the key to using alkaline bricks. However, in actual production, it is difficult to accept the kiln time of 10-20 hours. When problems are found, the high-temperature fan is directly turned on to cool the kiln quickly. After cooling and entering the kiln, it can be found that the magnesia-chrome bricks without kiln skin are peeled and damaged, and all the 1 680 silicon molybdenum bricks have surface peeling, the surface of the fracture is hard, and some fragments are obviously stretched on the brick. The magnesia-chrome bricks in the firing zone are less damaged due to the kiln skin buffering the fluctuation of temperature rise. In order to grab the output after the maintenance, the rapid cooling of the kiln is required to inevitably lead to the damage of the bricks, which lays the incentive for the increase of the secondary carcass temperature, and the refractory bricks have frequent accidents.
3. Changes in raw fuel
Only in a kiln with stable working conditions, the brick lining can adhere and maintain a solid kiln skin, and the life of the kiln lining can be guaranteed, and the stability of the thermal system requires the stability of the raw fuel. The ash content of the kiln varies from 32% to 45%. At first, in order to adapt to the high ash coal, the kiln raw meal saturation is relatively high, but the coal ash content changes too frequently, and there is no coal homogenization yard, so that the kiln raw meal and coal ash content It is difficult to respond, and it has a great impact on the conditions in the kiln.
After the overhaul, the material is charged, and the firm kiln skin is about 20m, and the magnesia-chrome brick is completely under the kiln skin. However, due to the fluctuation of coal quality, the end of the kiln skin frequently sticks and falls off, and the kiln skin that is closely adhered to the brick to form a mechanical anchorage peels off together with the brick body layer, which makes the brick body thinner and the kiln skin shortened. To about 16m, some magnesia-chrome bricks lose the protection of the kiln skin, the end of the kiln skin is thicker due to the deposition of coal ash, and the raw meal with less liquid phase scours the abrasive magnesia bricks here.
The use of direct-bonded magnesia-chrome bricks in the firing zone is mainly due to the high temperature resistance of directly-bonded magnesia-chrome bricks and easy hanging of the kiln skin, but due to the extremely low silicate content in the bricks (0.5%~2.5%SiO2), the periclase inside the bricks, Spinel is mainly combined directly, and the silicate phase is isolated in the gap, surrounded by periclase and spinel grains, and the high temperature resistance is improved, but the microstructure toughness is very poor, which makes the thermal shock stability of the brick. The resistance to alkaline corrosion and the ability to resist changes in oxidative and reducing atmospheres are considerably reduced.
Especially when used in kilns with frequent starts and stops, the service life is greatly shortened. For magnesia-chrome bricks without kiln skin as a barrier, the surface temperature changes with the kiln conditions, and the kiln skin is frequently replaced, which will cause magnesia-chrome bricks with a large expansion coefficient to occur. Thermal fatigue, chemical erosion, and the infiltration of liquid-phase alkali salts deteriorate the brick structure, reduce the thermal fatigue resistance, and cause the carcass temperature to rise continuously at these rings of magnesia-chrome bricks. The kiln skin is forced to form the kiln skin on the fire brick by water spray, but the thermal expansion of the kiln loses the compensation effect of the compressive stress inside the brick lining, which is not conducive to the life of the brick lining. In addition, the brick body is too thin to form a stable kiln skin, and the kiln is repeatedly red. Only by digging in the kiln, the thinnest part of the brick is only about 40cm. A similar situation has also occurred with magnesia-chrome bricks at 2m at the kiln mouth.
The saturation ratio of the raw meal entering the kiln is stable and moderate, but the coal ash content is large, so that the firing zone forms a 'low temperature' kiln skin, which is loose and porous. The kiln mouth is flush and cannot be fed into the kiln, causing the kiln mouth temperature to rise, the kiln mouth ring to fall off, the "low temperature" kiln skin is unstable, plus clinker dust erosion, erosion, and the extrusion of dozens of meters of bricks in the kiln , causing the special-shaped bricks at 2m to crack, drop bricks, and red kilns.