Innovation and Technology


Refractory Material Technology for Oxy-Fuel Fired Glass Furnaces

Original Paper | Published: 29th March 2015
Author: kakugy Guo
15k Accesses | 104 Citations | 429 Altmetric | Metrics


Oxy-fuel combustion technology is one of the effective means to improve the level of glass melting furnaces. Oxy-fuel combustion offers several advantages, including reduced NOx and dust emissions, energy savings, increased glass production yield and quality, and reduced environmental investment. Oxy-fuel combustion technology represents a new revolution in glass melting techniques. In the context of China’s tight energy supply and significant environmental burdens, promoting the use of oxy-fuel combustion technology holds great significance.
After adopting oxy-fuel combustion, the water vapor content inside the glass furnace can reach as high as 42% to 53%, and the volume concentration of alkali volatiles can increase three to six times, causing severe erosion of refractory materials. To reduce the erosion of furnace lining materials, improve glass quality, and extend the furnace’s service life, oxy-fuel combustion glass melting furnaces require a large quantity of new high-quality refractory materials, such as fused α-β Al2O3 bricks, high-purity dense silica bricks, premium fused AZS bricks, and fused recombined magnesia-alumina spinel bricks.
In order to develop oxy-fuel combustion technology, the “Green Manufacturing Process and Equipment” major project under China’s 11th Five-Year Plan for Science and Technology Support established a topic on “Oxy-Fuel Combustion Technology in Glass Melting Furnaces.” Ruitech Technology Co., Ltd. is responsible for research on related refractory materials. After three years of research, they have successfully addressed a series of technical challenges, significantly improved the performance of fused α-β Al2O3 bricks, and successfully researched new high-quality refractory materials, such as high-purity dense silica bricks, low-glass-phase fused AZS, and fused recombined high-purity magnesia-alumina spinel bricks, which have been applied successfully in production practice.

Advantages of Oxy-Fuel Combustion Glass Melting Technology

Oxy-fuel combustion kilns are furnaces that use oxygen as the assisting combustion gas. Their characteristics include a long residence time for the combustion gas, stable flame, kiln temperature, and kiln pressure, which are conducive to glass melting and clarification.

  1. Improved Glass Melting Quality: Using oxy-fuel combustion, the exhaust gas composition inside the kiln contains a high water vapor content, ranging from 42% to 53%. The increase in OH- content in the glass melt reduces the viscosity of the glass, making it easier for the glass to melt and clarify.
  2. Energy Efficiency and Reduced Consumption: Oxy-fuel combustion reduces the heat carried away by exhaust gases and the heat dissipated from the kiln body. Research and practice have shown that oxy-fuel combustion can result in energy savings of over 30% when melting standard soda-lime flat glass.
  3. Enhanced Combustion: Complete combustion of the fuel results in a significant increase in flame blackness and temperature. This, in conjunction with a faster rate of raw material melting, can increase the melting rate by more than 10%.
  4. Lower Furnace Construction Costs: The kiln structure of oxy-fuel combustion furnaces is similar to a unit kiln, without small furnaces or regenerators. The kiln body is a monolithic structure for the melting section, occupying less space and leading to lower initial construction costs.
  5. Extended Kiln Service Life: Oxy-fuel combustion can create two distinct flame regions within the kiln. The lower part of the flame experiences higher temperatures due to the injection of oxygen, while the upper part has slightly lower temperatures. This design can prevent excessive wear on the kiln crown, reducing crown damage. Additionally, high-quality refractory materials are used in the flame space, which can extend the kiln’s lifespan to more than 10 years.
  6. Reduced NOx Emissions and Overall Production Cost Reduction: Oxy-fuel combustion significantly reduces NOx emissions in kiln exhaust gases, lowering them from 1550-2200 mg/m³ (standard conditions) in regenerative kilns to below 500 mg/m³ (standard conditions) in oxy-fuel kilns. Furthermore, dust emissions are reduced by approximately 80%, and SO2 emissions decrease by 30%, resulting in a substantial reduction in harmful emissions and a decrease in overall production costs.
Usage Requirements for Refractory Materials in Oxy-Fuel Combustion glass Furnace
  1. Chemical Erosion in Oxy-Fuel glass Furnace: Oxy-fuel technology significantly reduces the concentration of N2 in the furnace, leading to a substantial increase in water vapor and volatile component concentrations. The increased alkali components in the glass raw materials, glass melt, kiln atmosphere, and refractory materials trigger a series of chemical reactions. The released R2O or ROH compounds severely erode any substances containing SiO2 in refractory materials, resulting in rapid damage to the kiln lining.
  2. Higher Purity Silica Refractory Materials: Silica bricks, known for their resistance to creep, low thermal conductivity, low density, affordability, and low pollution of glass in traditional glass Furnace, have a significantly reduced lifespan in oxy-fuel glass Furnace, making them the weakest link in the furnace. However, there is still a desire among users and researchers to use silica bricks. Silica bricks can be used in sections where erosion is not severe, and their quality can also be substantially improved.Increasing the purity of silica bricks and reducing their apparent porosity and thermal expansion can greatly enhance their resistance to alkali vapor erosion. For instance, reports suggest that using low-calcium, low-porosity silica bricks with 0.8% CaO content and an 18% apparent porosity in the melting section of a 150-ton-per-day oxy-fuel combustion glass Furnace resulted in a relatively even refractory surface without erosion or significant damage after 3.5 years of use. Thus, modified high-purity silica bricks can be used in oxy-fuel glass melting furnaces.
  3. Lower Glass Phase Fused AZS Refractory Materials: The erosion process of fused AZS refractory materials involves the leaching of glass phase from the bricks, gradual replacement of the glass phase by kiln glass, transformation of α-β Al2O3 into α-β Al2O3, consumption of corundum, disintegration of the refractory materials, and residual baddeleyite entering the kiln glass. Due to the high concentration of alkali vapor, fused AZS materials are subjected to stronger erosion. Therefore, it is advisable to reduce the usage of common fused zirconia-corundum refractory materials in oxy-fuel combustion kilns and instead use fused zirconia-corundum refractory materials with lower glass phase content.
  4. Fused α-β Al2O3 Refractory Materials with Improved Crystal Structure: Fused α-β Al2O3 refractory materials have an ideal mineralogical structure, consisting of approximately 45% α-Al2O3 and 55% β-Al2O3 phases, with impurities at around 1% and porosity at about 2%. They lack silicate phases and contain alkali-saturated β-Al2O3 phases interspersed with α-Al2O3, forming a dense structure. This excellent crystal structure makes them highly resistant to alkali vapor erosion and virtually non-polluting to the glass, making them one of the preferred main materials for oxy-fuel combustion glass Furnace. Therefore, it is recommended to increase the usage of fused α-βAl2O3 refractory materials in oxy-fuel combustion glass Furnace.
  5. Fused Recombined Magnesia-Alumina Spinel Materials: Fused recombined magnesia-alumina spinel materials, produced by high-temperature sintering of high-purity fused magnesia-alumina spinel sand, exhibit good resistance to erosion and creep. These materials have begun to be used in oxy-fuel combustion glass Furnace.
New Refractory Materials for Oxy-Fuel glass Furnace

Low Glass Phase Leaching Fused AZS: Ruitech Technology Co., Ltd. has made significant investments and developed advanced equipment specifically for the production of fused refractory materials, significantly enhancing the production level of fused refractory materials and laying the material foundation for manufacturing high-quality fused refractories.

  • Ruitech Technology first established a computer-controlled arc furnace dedicated to fused refractory materials, replacing manual control to improve precision and stability in the melting process. They also implemented more rational melting procedures, resulting in energy savings and improved product quality.
  • The company developed a dedusting system specific to fused arc furnaces, which, by altering the ventilation, exhaust, and dust collection of the oxidation process, reduced material loss and improved the working environment. This system also increased the stability of the chemical composition of the molten material, playing a crucial role in enhancing product quality and yield.
  • Ruitech Technology created resin-bonded sand with a softening temperature raised from around 1000°C to nearly 1700°C. This innovation significantly reduced sand sticking and casting defects and expanded the cooling rate range. By implementing enhanced insulation and reduced temperature differentials, they reduced thermal stress and casting cracks. These measures greatly improved the quality and stability of the fused AZS refractory materials, resulting in reduced processing volume and the production of high-quality fused zirconia-corundum refractory materials.

High-Quality Fused α-β Al2O3 Refractory Materials: Ruitech Technology has long been dedicated to improving the quality of fused α-β Al2O3 refractory materials. They overcame technical challenges in large-scale manufacturing of α-β Al2O3 refractory materials, producing complex, uniformly crystalline, high-grade fused α-β Al2O3 refractory materials with superior physical and chemical properties.

High-Purity, Low Porosity Silica Bricks: Through the use of special chemical additives, Ruitech Technology significantly reduced the dosage of mineralizers. By applying computer-assisted techniques, they rapidly optimized the overall process and developed low-porosity, low true density, low residual quartz, and high-strength high-purity silica bricks.

Fused Recombined Magnesia-Alumina Spinel Bricks: By adjusting particle size distribution and adding appropriate additives, Ruitech Technology created magnesia-alumina spinel bricks with excellent resistance to alkali erosion and thermal shock. These bricks are suitable for use in oxy-fuel and oxygen-rich glass Furnace.

Refractory Materials in Oxy-Fuel Glass Furnaces: Several Chinese enterprises, such as Baoshi Electronics Group’s glass tube factory, adopted Ruitech Technology’s fused AZS and α-β Al2O3 refractory materials in their 35m2 oxy-fuel combustion kiln. After years of use, Ruitech Technology’s products have proven to be comparable to imported products, meeting the requirements of oxy-fuel combustion glass Furnace.

Many other companies, including Fangxing Technology, have extensively used domestic refractory materials in their 500-ton-per-day oxy-fuel combustion glass Furnace, achieving production targets and maintaining excellent operating conditions.

Various enterprises, such as Daming Glass, have invested in the construction of oxy-fuel combustion glass Furnace, using Ruitech Technology’s fused AZS and fused α-β Al2O3 refractory materials in critical parts of the kilns. New projects, like Hunan Puzhao Technology Development Co., Ltd., and Jiangsu Yixing Jingyuan Co., Ltd., have similarly adopted Ruitech Technology’s fused materials in their oxy-fuel combustion glass Furnace.

Comparison of Refractory Material Performance and Prices

Comparing the performance of refractory materials is essential when selecting materials for oxy-fuel combustion glass Furnaces. Over the years, extensive research has been conducted both domestically and internationally. Here’s a summary of key factors:

  • Silica Bricks: Silica bricks have a low potential for contaminating glass, but they exhibit poor resistance to erosion. They are less durable in oxy-fuel kilns.
  • Fused AZS Bricks: Fused AZS bricks offer excellent resistance to erosion but have a higher potential for contaminating glass. Their high performance comes at a cost.
  • Fused Recombined Spinel Bricks: These bricks offer excellent erosion resistance and a lower tendency to contaminate glass but have less-than-ideal resistance to thermal shock.
  • Imported Spinel Bricks: Imported spinel bricks are characterized by high prices, making them less commonly used in domestic kilns.
  • Fused α-β Al2O3 Bricks: These bricks exhibit the best erosion resistance, a lower tendency to cause defects, and a high cost-effectiveness. They are maturely used and recommended for upper structures in oxy-fuel combustion glass Furnace, with a continuous usage period of more than two kiln cycles.

In terms of pricing, the order from lowest to highest is usually silica bricks, fused recombined spinel bricks, fused AZS, and fused α-β Al2O3.

Currently, domestic refractory materials have a significant price advantage in both domestic and international markets. For example, the price comparison between imported and domestic refractory materials for a 200-ton/day daily glass Furnace is shown in Table 3.

Savings for an 800-ton/day float glass Furnace can exceed 30 million RMB, a substantial sum for glass enterprises. Hence, the price advantage of domestic refractory materials over imported ones is evident.

Chinese-manufactured refractory materials are internationally competitive. On one hand, they offer a clear cost-performance advantage. On the other hand, the quality of domestically manufactured refractory materials continues to improve. The use of computer technology and optimization processes allows for efficient development of new products or improvement of existing ones. By updating equipment, employing advanced management techniques, and continuously enhancing manufacturing capabilities, the quality gap between domestic and imported refractory materials is narrowing. China-made refractory materials are becoming increasingly cost-effective. There is no doubt that Chinese-manufactured refractory materials have a promising future ahead.

About the Authors . . .

kakugy Guo Senior Engineer

CEO & Author Introduction
Advanced Refractory Materials and Furnace Technology
Leader in Oxygen Combustion Technology

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