Refractory materials for oxy-combustion glass kiln
So far, refractory materials such as silicon (Si02), corundum, and magnesia-aluminum spinel have been widely used in the main part of the glass kiln.
1.Silicon refractory materials
The advantages of using silicon refractory materials are: ① High temperature volume stability. Silicone refractory materials have a high load softening temperature, a small high-temperature creep rate, and good structural stability. ②No pollution to glass liquid. Since the main component of siliceous refractory material is Si02, which is the same as the main component of glass, it will not affect the quality of the glass liquid. ③The volume density is small, and the use of silicon refractory materials can reduce the mass of the furnace body.
Traditional glass melting furnaces mainly use siliceous refractory materials, and predecessors have done a lot of research. BennettPl et al. simulated the erosion of several cast refractory materials and siliceous refractory materials, and analyzed the diffusion theory. When siliceous refractory materials are used in large quantities, the surface of the refractory material is eroded under the action of alkali vapor, and the reaction forms a high-viscosity glass phase containing Si02, which can block the pores and hinder the further diffusion of alkali vapor. In addition, because SiO2 will produce polycrystalline transformation with temperature changes, the volume change accompanying this process will make the bricks loose. The alkali vapor concentration of oxygen combustion has increased by 4 to 5 times, and the impact of the air flow is very large, which greatly accelerates the enrichment of the glass phase in the refractory materials on the top of the kiln. Under the influence of gravity and environmental conditions, it will accelerate the destruction of siliceous refractory materials. Erosion of materials. However, some researchers believe that the advantage of siliceous refractory materials is that they are cheap and lightweight, and they can be fully utilized if their microstructure and composition are optimized. Wang Jie and others have prepared an improved silica refractory material after many experiments. It has a dense structure and the main components of the glass phase are CaO and Si02. It has a high melting temperature and good alkali corrosion resistance.
2.Corundum refractory material
The advantages of corundum refractory materials are: high melting point, good chemical stability, and excellent high-temperature mechanical properties. Commonly used corundum refractory materials for glass furnaces include cast AZS, cast α-β alumina, fused corundum and fused zirconium corundum. The protective effect of the high-viscosity liquid phase produced on the surface of the cast AZS refractory material is the key to ensuring its service life. However, AZS materials contain a large amount of Si02 and will also be corroded by alkali vapor. Cast α-β alumina refractory material is suitable for most parts of the furnace, but it is expensive.
Among the refractory materials for glass kilns, the most technically difficult and technically content is fused corundum. The main products include fused a-β alumina and fused B-AL203. The fused corundum refractory material has a dense structure, can effectively resist the erosion of molten glass or alkali vapor at high temperatures, and hardly contaminates molten glass. It is an indispensable material for oxy-fuel furnaces. Fused α-β alumina is often used in large bricks of oxygen-fired glass melting furnaces. It is similar to fused β-AL203 bricks. It has a low glass phase content and is not easy to form liquid phase and impurities. The electrofused B-AL203 shows excellent alkali corrosion resistance when used in the glass liquid cooling area, but if used in the upper structure of the feeding area, it is easily eroded by dust particles.
In addition, the low glass phase fused zirconium corundum has very low glass phase exudation at high temperatures, which makes it have higher creep resistance and can increase the operating temperature of the furnace from 1600°C to 1650°C, which is beneficial to the whole industry. The upper structure of oxygen combustion glass melting furnace is stable, so low glass phase fused zirconium corundum material is widely used in this part.
3. Magnesia-aluminum spinel refractory material
The special operating conditions of the oxy-combustion glass kiln require that the refractory materials used for the top of the furnace have good resistance to alkali erosion and a small high-temperature creep rate. Table 1.1 lists the costs and properties of silicon, spinel, and corundum refractories. Among them, spinel and α-β alumina refractory materials have the greatest alkali corrosion resistance and good thermomechanical properties. They are more suitable refractory materials for large furnaces of all-oxygen combustion glass melting furnaces. However, spinel material is preferred due to its lower cost.
At present, there are many applications of magnesia-aluminum spinel as refractory materials for glass kilns at home and abroad, and good results have been achieved.
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