Refractory Materials for Glass Kilns with Full Oxygen Combustion

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After adopting the full oxygen combustion technology in glass melting furnaces, the volume concentration of water vapor in the flame space significantly increases, and the volume concentration of alkali volatile substances increases by 3 to 6 times. In cases where there is a relatively large upper space in traditional air-assisted combustion kilns, siliceous materials are commonly used. The high concentration of water vapor and alkali volatile substances forms a strong alkaline atmosphere, posing a risk to the performance of silica bricks in the upper structure.

Compared to the large crown, the alkaline steam concentration in areas such as the breast wall and arch wall may be slightly lower, but they still face the reaction of acid-base neutralization. The erosion rate beyond the conventional level makes the life of the kiln unpredictable. In addition, the material eroded and peeled off falls onto the glass surface, forming floating slag, further affecting the melting performance and glass quality.

glass kiln refractories

Factors to Consider in Selection of Refractory Materials

In the selection of refractory materials, principles such as high-temperature resistance, processability, cost-effectiveness, and system compatibility are important. Additionally, consideration should be given to the characteristics of full oxygen combustion when choosing suitable refractory materials. Whether it is electrically fused AZS or electrically fused alumina products, there is already a wealth of successful experience accumulated in domestic glass furnaces using full oxygen combustion. There are also cases of using other refractory materials in China based on the different characteristics of furnaces and products. Currently, in the upper structure of glass furnaces using full oxygen combustion, refractory materials based on fused cast materials are widely used. This includes the electrically fused AZS series, electrically fused alumina series, electrically fused chrome corundum series (with a current trend of using sintered chrome corundum as a substitute), etc. In the electrically fused AZS series, in addition to common types like ER1681, ER1685, and ER1711, there are also ER1851 and ER1195. The electrically fused alumina series includes electrically fused α-β alumina and electrically fused β-alumina materials.

Low Glass Phase Product – ER1851

ER1851 Typical Chemical Composition and Crystalline Phase Analysis are shown in Figure 1.

chemical coposition of low glass phase

ER1851 is a product belonging to the low glass phase fused cast AZS series. Compared to regular AZS products, ER1851 has reduced levels of silicon dioxide and sodium oxide in its composition. This reduction typically results in a glass phase content lower than 14%. When used in furnaces, it not only reduces the contamination of glass by the glass phase but also exhibits excellent refractory properties such as strong resistance to alkali vapors, resistance to spalling, and good anti-creep properties against alkali droplet pollution. The following table illustrates the infiltration phase situation for different types of refractory materials.

Types of refractory materialsER1681ER1711ER1851LOWEXER1195Jargal MJargal H IMP

In recent years, ER1851 products have been successfully applied in some full oxygen combustion projects, demonstrating satisfactory results with good performance in low infiltration and erosion resistance. Some domestic manufacturers are actively developing similar products, indicating a broad market prospect for low glass phase products.

High Zirconia Series Refractory Materials

The high zirconia series generally refers to products with a zirconia content ranging from 85% to 95%. Despite the higher production difficulty and cost, these products find extensive applications in the glass industry due to their superior performance.

Because of their excellent characteristics, the high zirconia series helps reduce the formation of stones and bubbles in glass production. Therefore, they are more suitable for areas in contact with glass in glass furnaces and exhibit good performance in the melting furnaces of borosilicate glass, aluminosilicate glass, glass ceramics, and display glass. Depending on specific requirements, there are subdivided products with high electrical resistance.

The main components are similar, with some differences in electrical conductivity. The selection of a reasonable solution depends on the glass composition and process requirements.

Note: A: Silicate Glass, 1550 degrees Celsius, industrial use results, B: Milk Glass, 1550 degrees Celsius, industrial use results, C: Lead Glass, 1550 degrees Celsius, laboratory test results, D: Television Glass, 1550 degrees Celsius, laboratory test results.

ER1195, with a higher load softening temperature, a higher erosion resistance grade, and low infiltration characteristics close to ER1851, is widely used in various parts of the full oxygen combustion furnaces, including the sidewalls, electrode bricks, and the spout. It is also the preferred choice for the spout block of full oxygen combustion electronic microcrystalline glass furnaces.

Fused α-β Alumina Products

Comprising approximately 50% α-alumina and 50% β-alumina, these products exhibit a highly dense organizational structure with intertwined crystalline formations. They boast excellent resistance to strong alkalis and demonstrate outstanding erosion resistance at temperatures below 1350°C. Due to the absence of harmful impurities such as iron and titanium, these products have minimal glass phase content. The detachment of material from these products causes negligible pollution to glass. Apart from common applications in areas like channels, settling tanks, and lip bricks in float glass melting furnaces, they can also be utilized as the crowns of furnaces, with a primary focus on achieving an extended lifespan and addressing the issue of drip-induced glass contamination.

 fused α-β-Alumina

Fused β Alumina Products

Composed entirely of β-alumina, these products exhibit large, plate-like crystalline formations of β-alumina. The crystalline phases intertwine, and the crystals are coarse, resulting in a higher porosity and lower strength. However, these products demonstrate excellent resistance to spalling, particularly in the presence of strong alkali vapors. Due to the tendency of β-alumina to crack easily when reacting with silica and sodium oxide, these products are typically used in areas with minimal dust dispersion. They are commonly employed as the crowns of furnaces, especially towards the rear end.

Fused α-β or β-alumina products have shown exceptional resistance to erosion and minimal glass pollution on furnaces used domestically. Despite their excellent performance, their widespread usage is hindered by their relatively higher cost.

Sintered α-β Alumina Products

Sintered α-β alumina products, with a relatively lower cost, have seen successful applications in domestic furnaces in recent years. Due to their unique composition, they are a preferred choice for medium to low-temperature material passages. With technological advancements, domestically produced sintered materials with similar properties have entered the market, achieving positive results. In cases where the furnace size is smaller or the pollution requirement on the crown-induced drips is not stringent, these materials can be considered for use as crown materials.

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