What are the characteristics of silica bricks for use in glass kilns?

With the progress of process engineering, the quality and technical performance of silica brick products have been significantly improved. The silica bricks for use in the glass kilns emerge in the response to adapt to the working conditions of different parts of the cement rotary kiln. Their characteristics are as follows:

(1) The products have dense structure and good wear resistance

The main crystalline phase of silica bricks for glass kiln is composed of mineral corundum (Mohs hardness 9.0-9.2), silicon carbide (Mohs hardness 9.0-9.5) and mullite (Mohs hardness 7.0-7.5) with high hardness. The structure of finished products is dense, and the bulk density is generally 2.7-3.0 g/cm3.The normal temperature wear resistance of refractory materials depend on their strength and structural compactness, and the materials with high strength and compactness usually have better wear resistance. Cement rotary kiln lining is subject to long-term rolling friction of materials, therefore abrasion is one of the main reasons for the damage of refractory lining. Its density, strength and abrasion resistance are significantly better than that of spalling-resistant high alumina bricks and magnesia-alumina spinel bricks. Guimo refractory bricks are of good use in the sub-clinkering zone, filter zone and other parts of the cement rotary kiln, which benefits by its good wear resistance to a large extent.

(2) High refractoriness under load, and good performance under high temperature 

The refractoriness under load (RUL) of silica bricks are usually above 1450°C, sometimes even higher than 1650°C. There are certain differences in RUL for different brands. The refractory bricks used for different parts of the cement rotary kiln lining vary in temperature. Brick surface temperature of the sub-clinkering zone and the front transition zone are up to about 1400℃, higher than that of the clinkering zone of glass kiln (because the clinkering zone is protected by the kiln skin, and refractory brick surface temperature is 900-1000℃). Even the RUL indicators of these bricks are more than those of the commonly-used spalling-resistant high alumina bricks and phosphate high alumina refractory bricks (RUL is 1300-1520℃).

The transition zone is not protected by the kiln skin like the clinkering zone, so it’s vulnerable to the reducing atmosphere and heat load. Its service life has been a bottleneck problem of the cement rotary kiln, so some cement plants choose to use the magnesia-alumina spinel bricks in the transition zone. The study of some factory’s use of magnesia-alumina spinel bricks for the transition zone of the 5000 t/d large-scale cement rotary kiln shows that: The front transition zone using magnesia aluminum spinel refractory brick is basically uneroded, but due to alkali deposition in the open pores causing structural densification, the same piece of refractory brick may form different segments, and result in hot surface flaking and cracks of the refractory bricks, and then damage of the lining. The Guimo refractory bricks have strong erosion resistance which benefits from their structural compactness, especially the continuous SiO2 compact layer on brick surface to prevent the penetration of molten materials; and chemically-stable Al2O3, SiC and SiO2 which do not react violently with SO2, O2, CO2 and other gases generated in the kiln, and do not react with cement materials. Secondly, the silica bricks for glass kiln have good thermal shock stability. As it contains a certain amount of SiC, which as it’s known to all has high thermal conductivity and relatively small coefficient of thermal expansion, and makes the thermal shock stability of the products be significantly improved, and be able to bear more than 10 times (sometimes even up to 46 times) of 1100℃ water cooling test, so the silica bricks for cement rotary kiln do not flake or fracture, and their service life are significantly improved.

(3) Lowering kiln temperature and good heat-proof performance

The thermal conductivity of silica bricks [2.3-2.5 W/(m·K)] is lower than that of alkaline products [2.69-2.74 W/(m·K)], so the heat-proof effect of silica bricks is better. In the sub-clinkering zone, transition zone, pre-heat zone, kiln tail, tertiary air duct, decomposint furnace and other parts of large rotary kiln, the use of silica bricks for glass kiln, compared with alkaline bricks, can reduce the surface temperature of the kiln shell by more than 100℃.