Selection of refractory materials for each section of rotary kiln

Selection of refractory materials for each section of rotary kiln

Selection of refractory materials from the kiln tail feeding belt to the preheating belt

In the part close to the kiln tail or small rotary kiln, from the perspective of user cost, we recommend the use of high-alumina bricks with high compressive strength and good anti-stripping performance. The service life of high-alumina bricks with anti-stripping in the kiln tail is generally more than 2 years.

At about 1 meter from the tail of the rotary kiln, since it is at the end of the rotary kiln, the refractory bricks need to be fixed, so only castables can be used for masonry. Generally, special castables for the kiln mouth or steel fiber wear-resistant castables can be selected.

Selection of refractory materials for the transition zone

In general, we usually divide the transition zone into two sections, the upper transition zone and the lower transition zone. The part close to the preheating zone is generally called the upper transition zone, and the part close to the firing zone is called the lower transition zone. In the upper transition zone, 1650 silica-molybdenum bricks (silicon-molybdenum red bricks) are generally used. Because the temperature in the lower transition zone is relatively high, only magnesia-alumina spinel bricks or 1680 silica-molybdenum bricks (silicon-molybdenum red bricks) can be used. Due to the high temperature in this area, the service life of the refractory materials used in the transition zone is generally about 12 months.

Compared with magnesia-alumina spinel bricks, silica-molybdenum bricks have the advantages of low thermal conductivity, good thermal shock stability and high cost performance. Compared with silica-molybdenum bricks, magnesia-alumina spinel bricks have the advantages of stronger anti-corrosion performance and high thermal conductivity. In the system of garbage cement rotary kiln, magnesia-alumina spinel bricks have better anti-alkali sulfur erosion effect, so in large rotary kilns, considering the safety factor, magnesia-alumina spinel bricks are still mostly used for masonry.

On the whole, due to its cost-effectiveness, silica-molybdenum bricks tend to replace magnesia-alumina spinel bricks in cement rotary kilns in China.

Selection of refractory materials for firing zone

Magnesia-iron spinel bricks not only have the characteristics of high compressive strength, good thermal shock stability, good flexibility, and high load softening temperature, but also have the characteristics of being directly combined with magnesia-chrome bricks and easy to stick to the kiln lining, which effectively solves the pollution problem of magnesia-chrome bricks used in cement kilns, meets the market demand of the cement industry for chrome-free alkaline refractory materials under the new situation, and also changes the demand elasticity of imported alkaline refractory materials, realizing the localization of chrome-free for cement kilns, and has been widely recognized in the cement industry.

In practice, combined with the industry status that the ferromagnesia spinel bricks and silica-molybdenum bricks used in the connection area between the firing zone and the transition zone are prone to peeling and damage due to frequent changes in the temperature field, the ferromagnesia spinel brick process has been optimized and improved. According to the characteristics of various raw materials, a special process of compounding synthetic ferroaluminum spinel and magnesia-aluminum spinel has been adopted to develop and produce magnesia-ferroaluminum composite spinel bricks, so that the excellent characteristics of ferroaluminum spinel and magnesia-aluminum spinel are complementary. This product has good alkali erosion resistance and wear resistance. At high temperatures, a layer of kiln skin can be quickly attached to protect the lining bricks from high-temperature flame erosion. At low temperatures, it has good wear resistance and is not worn, and can be applied to the entire rotary kiln.

Selection of refractory materials for cooling belt

In the production of large-scale dry kilns, the cooling zone kiln lining is one of the weakest kiln linings in large rotary kilns. In the cooling zone, although the ambient temperature is not as high as that in the high-temperature zone and there is no smoke corrosion, the cooling zone of the cement rotary kiln is very short due to the production process. The temperature of the clinker at the kiln mouth of the rotary kiln is as high as 1400℃, and the temperature of the secondary air entering the kiln is as high as 1200℃. The kiln mouth is almost completely exposed to the radiation of the 1700℃ high-temperature flame. At present, the cooling zone of the cement rotary kiln, except for the 0-0.6m position of the kiln mouth, is built with refractory bricks, and most of them are built with magnesia-alumina spinel bricks and silica-molybdenum bricks. In comparison, magnesium-aluminum spinel bricks have better corrosion resistance than silica-methane bricks, but higher thermal conductivity. Silica-methane bricks have lower thermal conductivity, but their alkali corrosion resistance is not as good as magnesium-aluminum spinel bricks. Therefore, in this area, if the alkali-sulfur content in the user’s raw materials is not high, silica-methane bricks can be used. If the peeling phenomenon caused by excessive alkali-sulfur content often occurs, magnesium-aluminum spinel bricks should be used.

Selection of refractory materials at the kiln mouth

After the cement clinker is cooled, it is discharged to the grate cooler through the kiln mouth. The kiln barrel is inclined at 3.5% to 4% with the horizontal line. When the kiln is running, the material in the kiln moves from the kiln tail to the kiln head. Under the combined action of the thrust of the moving material and the axial stress of the refractory bricks in the kiln, there is a tendency to move toward the kiln head, resulting in a very large axial extrusion stress at the kiln mouth. In order to prevent the displacement of the overall refractory bricks, the kiln mouth can only be constructed with castables. The kiln mouth here refers only to the 0-1 meter position of the material end, also known as the front kiln mouth.

The front kiln mouth castable should have sufficient refractoriness, mechanical strength, thermal shock stability and wear resistance under high temperature environment. In view of the weak characteristics of the kiln mouth, special kiln mouth castables with excellent thermal shock resistance, impact resistance and wear resistance are often used. The special kiln mouth castable developed by the company adopts advanced process formula and is made of high-quality corundum, silicon carbide, imported andalusite and additives. It has the advantages of good volume stability, thermal shock resistance, erosion resistance and wear resistance. Under normal operation, the life of the special kiln mouth castable can reach more than 12 months.