Generally, glass kilns use refractory materials such as fused zirconium corundum bricks, fused corundum bricks, zircon bricks, high-purity magnesium bricks, directly bonded magnesium bricks, high-alumina bricks, sillimanite bricks, clay bricks, silica bricks, lightweight and amorphous refractory materials.
After the glass melting furnace adopts all-oxygen combustion technology, the volume concentration of water vapor in the flame space is greatly increased, and the volume concentration of alkali volatiles increases by 3 to 6 times. In the case of more upper space in traditional air-assisted combustion kilns, siliceous materials will be used. High-concentration water-based gas and high-concentration alkali volatiles form a strong alkaline atmosphere, which harms the performance of silica bricks in the upper structure.
Si02+2Na0H+02-Na2Si04+H20
Compared with the arch, the concentration of alkali vapor in breast walls, gables and other parts will be slightly lower, but they are also facing acid-base neutralization reactions. The erosion rate beyond the norm makes the life of the kiln unpredictable. In addition, the eroded and peeled materials fall onto the glass surface to form scum, which further affects the melting performance and glass quality.
1. Factors to be considered in material selection
In the principle of selecting refractory materials, in addition to high temperature resistance, processability, economy, and systematization, suitable refractory materials should also be selected according to the characteristics of oxy-fuel combustion. Whether it is fused AZS or fused alumina products, domestic oxy-fuel combustion glass furnaces have accumulated relatively rich successful experience. According to the characteristics of the furnace and the characteristics of the product, there are also cases of using other refractory materials in China.
At present, the refractory materials used in the upper structure of oxy-fuel combustion glass furnaces are mainly fused casting materials, such as fused AZS series, fused alumina series, fused chrome corundum series (there is a tendency to use sintered chrome corundum instead recently). In the fused AZS series, in addition to the common ER1681, ER1685 and ER1711, it also includes ER1851 and ER1195. The fused alumina series includes fused α-β alumina and fused B-alumina materials.
2. Low glass phase product-ER1851
This is a low glass phase fused cast AZS series product. Compared with ordinary AZS products, the content of silica and sodium oxide in its composition is reduced to a certain extent, so that the glass phase content in the product is usually less than 14%. Using it in the kiln can not only reduce the pollution of glass phase to glass, but also its good resistance to alkali vapor, flying material and creep resistance is an excellent refractory material for anti-drop pollution.
In recent years, ER1851 series products have been used in some oxy-fuel combustion projects and achieved satisfactory results. They have good performance in low permeation and erosion resistance. Some domestic manufacturers are also actively developing such products, and the market prospects of low glass phase products are broad.
3. High zirconium series refractory materials
High zirconium series products usually refer to products with a zirconium oxide content of 85%~95%. Although it is difficult to produce and has a high price, it is widely used in many glass industries due to its superior performance.
Due to its excellent properties, it reduces the generation of stones and bubbles in glass production, so it is more suitable for the parts in contact with glass in glass kilns. It has good performance in melting furnaces for borosilicate glass, aluminosilicate glass, glass ceramics and display glass. According to different requirements, there are also subdivided products with high resistivity.
ER1195 has a higher load softening temperature, a higher corrosion resistance level, and low permeation characteristics close to ER1851. It is widely used in pool walls, electrode bricks, and flow holes in oxy-fuel kilns. It is also the preferred choice for flow hole bricks in oxy-fuel electronic microcrystalline glass kilns.
4. Electric fused α-B alumina products
It is composed of about 50% a-alumina and β-alumina, and the crystals of the two are interlaced to form a very dense organizational structure. It has very good alkali resistance and has very good corrosion resistance below 1350℃. Because it does not contain harmful impurities such as iron and titanium, the glass phase content is very small, and the pollution of its flakes to the glass is negligible. In addition to being used in common flow channels, clarification tanks, lip bricks of float glass melting furnaces and other parts, it can also be used as the top of the kiln (the main consideration is the longer service life and the pollution of the glass liquid by the suspension).
5. Fused B-alumina products
It is composed of β-alumina, with large flat β-alumina crystals, the crystals are interlaced and the crystal phase is very coarse, the porosity is high and the strength is low. However, it has good anti-flaking properties, especially high corrosion resistance to strong alkali vapor. Since β-alumina is easy to break with α-alumina and sodium oxide after reacting with silica, it should be used in parts with lighter dust flying. As the top of the kiln, it is generally used at the back end.
Fused a-B or B-alumina products show ideal corrosion resistance and little pollution to glass in kilns that have been used in China, and the application effect is very good. The high price is an obstacle to its widespread use.
6. Sintered α-β alumina products
Sintered a-β alumina products are relatively cheap. In recent years, there have been successful cases of use in domestic kilns. Due to its special composition, it has become a better choice for medium and low temperature channels. With the advancement of technology, similar domestic sintering materials have also been launched and have achieved good results. For smaller furnaces or when the requirements for the crown droplet pollution formed on the crown top are not very high, it can be considered as the top material.
7. Application of new refractory materials
7.1 High-purity magnesium aluminum spinel
The chemical formula of magnesium aluminum spinel is MGO-AI203, containing 28.3% MgO and 71.7% AI203 (local data, for reference only). Its main advantages are strong corrosion resistance to reducing atmospheres such as free CO2, free SOX and free K20/Na20, and good thermal stability and wear resistance. Magnesium aluminum spinel has a high melting point, a small thermal expansion coefficient, low thermal stress, good thermal shock stability, a smaller volume density than electric melting materials (2.7g/cm3), and has a strong resistance to alkaline atmosphere.
There are actual cases of using magnesium aluminum spinel in domestic air-assisted combustion and full oxygen combustion glass kilns, but there are many problems with large crown saddle deformation.
7.2 Isostatic Pressed High Zirconium Bricks
Isostatic pressed high zirconium bricks have been used in oxygen combustion kilns due to their excellent density, corrosion resistance and lower price than electric fused high zirconium bricks, and the application effect is good.
7.3 Dense chromium oxide bricks
Dense chromium bricks have been widely used in glass fiber kilns due to their excellent thermal shock resistance, alkali resistance and erosion resistance, including the flame space of oxygen combustion glass fiber kilns. The chromium content in dense chromium bricks is different according to different parts of use. Generally, Cr203>90% and bulk density>4.0g/cm3.
It is composed of about 50% a-alumina and β-alumina, and the crystals of the two are interlaced to form a very dense organizational structure. It has very good alkali resistance and very good corrosion resistance below 1350℃. Because it does not contain harmful impurities such as iron and titanium, the glass phase content is very small, and the pollution of its flakes to the glass is negligible. In addition to being used in common flow channels, clarification tanks, lip bricks of float glass melting furnaces and other parts, it can also be used as the top of the kiln (the main consideration is the longer service life and the pollution of the glass liquid by the suspension).
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