Why is Transition Zone using Silicon Mullite Bricks?
Silicon mullite bricks are produced by high temperature firing of main raw materials such as high quality mullite and silicon carbide. Because there is no kiln skin protection, the transition zone is easily affected by the reducing atmosphere and high heat load, and is easily subject to material wear. In order to require a high temperature environment, silicon mullite brick can meet the above requirements. Silicon mullite brick has excellent wear resistance, good resistance to spalling and thermal shock resistance, and is suitable for use at the end of the transition zone of cement kiln. Silicon mullite brick has achieved good results.
The application of silicon mullite brick in cement rotary kiln has been rapidly developed, especially the emergence and enlargement of new dry process kiln. The rotational speed of kiln and the thermal stress intensity in kiln have been greatly improved, and new materials have been proposed for the material and physical and chemical properties of refractory materials. High requirements. Therefore, in addition to the magnesia chrome bricks, the cement rotary kiln is used in the kiln skin under the protection of the kiln skin. The secondary firing zone, the transition zone and the cooling zone are obviously better than the magnesia chrome bricks.
The silica mullite brick configuration is adaptable. The traditional configuration of refractory materials is usually refractory materials with different properties such as spinel brick, magnesia chrome brick and anti stripping brick in the kiln mouth, the front transition zone, the rear transition zone and the decomposition zone. The silicon molybdenum brick can cover all the process belts except the firing zone.
The main crystal phase of silica mullite brick consists of high hardness mineral corundum (Mohs hardness 9.0-9.2), silicon carbide (Mohs hardness 9.0-9.5), and mullite (Mohs hardness 7.0-7.5). The structure of the product has a high density, and the bulk density is generally between 2.7 and 3.0 g/cm3. The normal temperature wear resistance of the refractory material depends on its strength and compactness of the structure, and the material with high strength and high density has good wear resistance. The lining of cement rotary kiln has been subjected to rolling friction of materials for a long time, and wear is one of the main reasons for the damage of refractory lining. The density, strength and wear resistance of silica bricks are significantly better than those of anti flaking high alumina bricks and magnesium aluminum spinel bricks. Silica mullite brick is used in the secondary firing zone of the cement rotary kiln, the filter belt and the like, and it can be said that the wear resistance plays an important role.
The secondary firing zone or the upper and lower transition zone is not affected by the kiln skin protection, and is easily affected by the reducing atmosphere and high heat load. Its service life has always been a bottleneck problem of the cement rotary kiln. Therefore, some cement plants use magnesia alumina spinel in the transition zone. brick. The 5000t·d-1 large kiln transition zone of a factory uses magnesia alumina spinel bricks, and the following conclusions are drawn: the magnesium aluminum spinel bricks in the lower transition zone are basically non erosion, but the alkali is deposited in the open pores to make the structure dense. The same refractory bricks are formed into different sections, and the hot surface of the refractory brick is peeled off and cracks are generated, causing the inner liner to be damaged. Due to its compact structure, the silica mullite bricks form a continuous SiO2 dense layer, which prevents the penetration of molten material, and the chemical substances of Al2O3, SiC and SiO2 are stable, and do not react violently with SO2, C and other gases generated in the kiln. It does not react chemically with cement materials, so the silica brick has strong erosion resistance.
The working temperature of the cement rotary kiln varies greatly, the kiln is frequently shut down for maintenance or handling accidents, and the lining is subject to severe temperature fluctuations. Silica mullite brick contains certain SiC, SiC has high thermal conductivity and relatively small thermal expansion coefficient, which makes the thermal shock stability of the product significantly improved. The water temperature test at 10 °C is more than the next time, up to 46 times, so the silica mullite brick is in cement. The use of the rotary kiln does not peel off, does not break, significantly improves the service life.
Spinel brick used in the transition zone of cement rotary kiln, due to the high thermal conductivity, increases the heat loss and affects the life of the kiln. It causes the kiln to be shut down for 2-3 times a year and replace the refractory material. The thermal conductivity of silica brick is lower than that of spinel brick, so the thermal insulation effect of silica brick is better. In the large rotary kiln sub baking zone, transition zone, cooling zone, pre-tropic zone, decomposition zone and other parts, the surface temperature of the silica brick is lower than 0 ° C than the cylinder surface using spinel refractory brick.
