Principles for selecting refractory materials for various parts of cement kilns

1. Pre tropical zone and decomposition zone: These two areas have relatively low temperatures and require low thermal conductivity and good wear resistance of the brick lining. In this area, sulfuric acid alkali and chloride alkali from raw materials and fuels begin to evaporate, condense and accumulate in the kiln, and infiltrate into the interior of the brick. Ordinary clay bricks react with alkali to form potassium garnet and white garnet, causing the brick surface to become crispy and the brick body to expand, leading to cracking and peeling. When alkali resistant bricks or alkali resistant insulation bricks containing around Al2O325% to 28% and SiO265% to 70% react with alkali at a certain temperature, a high viscosity glaze layer is immediately formed on the surface of the brick to prevent peeling, but this type of brick cannot withstand operating temperatures above 1200 ℃. So pre heating zones generally use phosphate bonded high alumina bricks, anti stripping high alumina bricks, or alkali resistant bricks.
2. Decomposition zone: High alumina bricks with good anti stripping properties are generally used, and silica bricks have better performance than high alumina bricks with good anti stripping properties. The service life is about twice as long as high alumina bricks with anti stripping properties, but the price is higher. Therefore, anti stripping silicon carbide castables should be used at the kiln tail inlet.
3. Transition zone and firing zone: The kiln skin in the transition zone is unstable, requiring the kiln lining to have good resistance to atmospheric changes, good thermal shock resistance, low thermal conductivity, and wear resistance. It is recommended to use magnesia alumina spinel bricks abroad, but this brick has a high thermal conductivity, high cylinder temperature, and relatively high heat consumption, which is not conducive to reducing energy consumption. The thermal conductivity and wear resistance of domestic silicon-based bricks are small, and their performance can be comparable to imported materials to a certain extent.
4. Burning zone: The burning zone has high temperature and intense chemical reactions, requiring brick lining to have strong resistance to clinker erosion, SO3, and CO2. Magnesium aluminum spinel bricks are generally used abroad, but it is difficult to hang them on the kiln skin, while dolomite bricks have poor thermal shock resistance and are prone to hydration; The magnesium iron spinel bricks from abroad have a better effect on the kiln skin, but the cost is too high. The use of low chromium magnesia spinel composite bricks newly adopted domestically is relatively good.
5. Cooling zone and kiln mouth: The temperature at the cooling zone and kiln mouth can reach around 1400 ℃, with significant temperature fluctuations. The grinding of clinker and the erosion of airflow are both severe. Require the brick lining to have a low thermal conductivity, good wear resistance, and thermal shock resistance; Alkaline bricks with excellent thermal shock resistance, such as spinel bricks or high alumina bricks, are suitable for use in cooling zones. It is generally recommended to use spinel bricks abroad, but spinel bricks have a high thermal conductivity and poor wear resistance. In recent years, silicon polished bricks and wear-resistant bricks with good anti stripping properties have been mostly used domestically.
The kiln mouth often uses castables with good thermal shock resistance. For example, wear-resistant and heat-resistant high alumina bricks or steel fiber reinforced castables, as well as low cement high alumina castables, are used. However, in large kilns with extremely high kiln temperatures, ordinary or steel fiber reinforced corundum castables are used.