What are the refractory materials used in oxy-combustion glass kiln?
The main problem with oxy-combustion refractory materials is the refractory materials inside the kiln. The refractory materials in the flame space of traditional air-assisted combustion furnaces are generally mainly siliceous materials. The use of electric, fused or other refractory materials is common in special glass furnaces. After the glass melting furnace adopts full 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. Traditional air-assisted combustion kilns use siliceous materials when there is a lot of space in the upper part. High-concentration water vapor and high-concentration alkali volatiles form a strong alkaline atmosphere, which harms the performance of the silica bricks in the superstructure.
Si02+2Na0H+02-Na2Si04+H20
Compared with the large kiln, the concentration of alkali vapor in breast walls, gables and other parts will be slightly lower, but they also face acid-base neutralization reactions, and the exceeding normal erosion rate makes the life of the kiln unpredictable. In addition, the eroded and peeled materials fall on the glass surface to form scum, which further affects the melting performance and glass quality.
1. Factors to consider when selecting materials
In principle, in the selection of refractory materials, in addition to high temperature resistance, processability, economy, systematization, etc., suitable refractory materials should also be selected based on the characteristics of oxy-combustion, whether it is fused AZS or fused alumina products. Domestic oxy-combustion glass kilns have accumulated relatively rich successful experience. Depending on the characteristics of the kiln and product characteristics, there are also domestic examples of using other refractory materials.
At present, the refractory materials used more in the superstructure of oxy-combustion glass furnaces are mainly fused casting materials, such as fused AZS series, fused alumina series, fused chromium corundum series (currently there is a tendency to use sintered chromium corundum instead), etc. . In addition to the common ER1681, ER1685 and ER1711, the electrofusion AZS series also includes ER1851 and ER1195. The fused alumina series includes fused ab 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 ingredients has been reduced to a certain extent, so that the glass phase content in the product is usually less than 14%. Used in furnaces, it can not only reduce the pollution of glass relative to glass, but its extremely strong resistance to alkali vapor, resistance to flying materials, and good anti-shake performance make it an excellent refractory material that can resist dripping pollution.
In recent years, ER1851 series products have been used in some oxy-combustion projects and achieved satisfactory results, with good performance in low leakage and corrosion resistance. Some domestic manufacturers are also actively developing such products, and the market prospects for low glass phase products are broad.
3. High zirconium series refractory materials (1195 or 950 series)
High-zirconium series products usually refer to products with a zirconium oxide content of 85% to 95%. Although its production is difficult and its price is high, it is widely used in many glass industries due to its superior performance. The typical chemical composition and crystal phase analysis of high zirconium series refractory materials are shown in Figure 3.
Currently known manufacturers that can mass produce high zirconium series include: Xiyin, Asahi Glass, and MONOFRAX. Due to its excellent characteristics, it reduces the generation of stones and bubbles in glass production, so it is more suitable for parts in contact with glass in glass furnaces, such as borosilicate glass, aluminosilicate glass, glass ceramics and display glass. It has good performance in the melting furnace, and there are subdivided products with high resistivity according to different requirements.
ER1195 has a higher load softening temperature (load softening temperature) corrosion resistance level and low leakage characteristics close to ER1851. It is widely used in the electrode bricks of the tank cavity and the liquid hole in the oxy-combustion kiln. It is also an oxy-combustion electronic product. The preferred choice of glass-ceramic kiln liquid hole blocking bricks.
4. Fused α-β alumina products
It is composed of about 50% each of α-alumina and β-alumina. The two crystals are interlaced to form a very dense structure. It has very good resistance to strong alkali and has very good corrosion resistance below 1350°C. Because it does not contain harmful impurities such as iron and titanium, the glass phase content is very small, and the contamination of the glass by its exfoliation is minimal. In addition to being used in common flow channels, clarifiers, lip bricks of float glass melting furnaces, etc., it can also be used in Used as the roof of the kiln (the main consideration is the long service life and the pollution of the glass liquid)
5. Fused B-alumina products
It is composed of 100% B-alumina and has a large plate-shaped B-alumina crystal structure. The crystals are staggered and the crystal phase is very coarse. The porosity is high and the strength is low. However, it has good peeling resistance, especially against strong alkali vapor, and has high corrosion resistance. Since β-alumina is easy to crack with α-alumina and sodium oxide after reacting with silica, it must be used in dusty environments. The lighter part is generally used at the rear end as the top of the furnace.
Fused α-β or β-alumina products have excellent corrosion resistance and little pollution to glass in the kilns already used in China, and the application effect is very good. The higher price is the biggest obstacle to its widespread use,
6. Sintered α-β alumina products
Sintered α-β alumina products are relatively cheap and have been successfully used in domestic kilns in recent years. Due to their special components, they have become a better choice for medium and low temperature forehearths. With the advancement of technology, similar domestically produced sintered materials have also been put on the market and have achieved good results. It can be considered as the roof material for smaller furnace types or when the requirements for droplet pollution formed by the roof are not very high.
7. Application of new refractory materials
7.1 High purity magnesium aluminum spinel
The chemical formula of magnesia-aluminum spinel is MqO-AI203, containing 28.3% MqO and 71.7% AI203 (atypical data, for reference only). Its main advantages are strong corrosion resistance to reducing xenon gases such as free CO2, free SOX and free K20/Na20, and good thermal stability and wear resistance. Magnesia-aluminum spinel has a higher melting point, small thermal expansion coefficient, low thermal stress, good thermal shock stability, smaller volume density (2.7g/cm3) than electrofusion materials, and has strong resistance to alkaline atmospheres. Resistance.
There are actual cases of using magnesium-aluminum spinel in domestic air-assisted combustion and full-oxygen combustion glass kilns, but the saddle-shaped deformation problem often occurs.
7.2 Isostatic pressing high zirconium bricks
Isostatically pressed high zirconium bricks have been used in oxy-combustion kilns with good results due to their excellent density, corrosion resistance and lower price than fused high zirconium bricks.
7.3 Dense chromium oxide bricks
Due to its excellent thermal shock performance, alkali resistance and erosion resistance, dense chrome bricks have been widely used in fiberglass kilns, including the flame space of all-oxygen combustion fiberglass kilns. The chromium in dense chrome bricks adopts different chromium contents according to different parts of use. Generally, Cr203>90% and bulk density>4.0g/cm3.
At present, in addition to foreign and joint venture production, many domestic companies can also provide the same products, but the quality and physical and chemical stability vary greatly. The pollution problem of phosphorus is difficult to solve. Many European and American countries have many restrictions on the production and application of products containing phosphorus. Chromium oxide has strong coloring ability. Generally, it is not recommended to use chromium-containing refractory materials for high-white or higher-quality glass, especially in parts that are in contact with the glass liquid. For colored glass or green and white materials with lower quality requirements, it can be considered to extend the life of the kiln.
7.4 Electric fusion and re-sintered mullite
Typical product data of electrofusion resintered mullite bricks are: AI20376%, Fe2030.1%, Si0223%. Load softening temperature T0.5>1700℃, bulk density 2.66g/cm3, normal temperature compressive strength 1100N/mm2, glass phase content <4%. Due to its relatively neutral characteristics, large furnaces for oxy-fuel fiberglass furnaces are currently used more frequently.
7.5 calcium-free silica brick
The advantages of its products are: ① It uses fused silicon oxide as a binding phase, does not contain calcium oxide, and the silica content can reach more than 98.5%; ② The density is smaller (1.8gcm3), which reduces the weight of the entire rice bowl; ③ Price Lower than electrofusion materials of the same level; ④ Lower expansion coefficient (0.6% at 650°C) and higher operating temperature (T0.5 is 1690°C) than silica bricks; ⑤ Better volume stability . It has been used in domestic oxy-combustion kilns, but there have been deformation problems that threaten the safety of the kiln.
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