All-oxygen combustion technology is a combustion mode that uses "oxygen + fuel" instead of "air + fuel". Adopting all-oxygen combustion technology can achieve energy conservation and emission reduction in glass melting furnaces, improving the melting capacity and quality. By analyzing the characteristics of all-oxygen combustion technology and summarizing the application and selection principles of fused cast AZS blocks in the key parts of all-oxygen combustion glass furnaces.
All-oxygen combustion technology
Traditional glass melting uses air as the combustion-supporting medium. When air is used for combustion assistance, over 78% of nitrogen and other components fail to generate heat and consume and carry away a large amount of heat during the combustion process. Due to the passive involvement of nitrogen, not only is energy consumption increased, but also pollutants such as NOX are produced during high-temperature combustion. The combustion mode of all-oxygen combustion technology is fuel + oxygen. With the development of oxygen production technology and the reduction of electricity costs, the oxygen combustion technology of glass melting furnaces has performed outstandingly in many aspects such as environmental protection, energy conservation, output, quality, reduction of equipment investment, and saving of factory space.
Advantages of all-oxygen combustion in glass furnaces
Energy conservation, consumption reduction, and economic benefits are outstanding. Due to the absence of a regenerator and reversing system, the structure of the furnace is simplified, the occupied area is reduced by approximately 30%, and the initial investment cost is significantly lowered. Meanwhile, pure oxygen combustion assistance increases the combustion temperature by approximately 200℃, and the flue gas volume sharply reduces to 30% of that of traditional furnaces.
It has outstanding environmental protection performance. The concentration of nitrogen oxides in the flue gas is high but the total amount is small. It can be efficiently treated without a catalyst, and the amount of waste gas emissions is significantly reduced, significantly lowering the investment and operation costs of denitrification equipment.
The quality of glass melting has been improved, and the oxidizing atmosphere of the flame is intense. Combined with the high hydroxyl group environment in the furnace, when producing high white materials and crystal white materials, there is no need to add clarifying agents such as nitrates, reducing raw material costs. Moreover, the light transmittance and whiteness of the glass liquid are better.
The operation is stable and the service life is extended. The absence of a regenerator avoids the risks of grid body blockage, collapse, and groundwater seepage corrosion. The use of fused cast AZS blocks in key parts eliminates the cross-fire of the furnace cover. The service life of the furnace can be extended to 7-10 years, the failure rate decreases, the defects of stones and stripes in the products are reduced, and the qualification rate is improved.
It has strong adaptability, and simple management, is not affected by fluctuations in groundwater levels, and has low maintenance costs, providing core technical support for the green transformation of the glass industry.
Characteristics of refractory materials
Refractory materials are an important component of glass furnaces. The designers of the furnaces need to use refractory materials to construct the furnace structure that meets the requirements of the glass melting process, including suitable flame spaces, melting areas, forming areas, and structures for the emission or heat exchange of flue gas (regenerator or flues). The selection of refractory materials for glass furnaces comes first.
The following requirements should be met:
(1) High-temperature resistance
The refractory materials for glass furnaces need to have the characteristics of being resistant to erosion and scouring at a certain temperature, a load-softening temperature, and a main composition close to that of glass. Ensure that the glass is not contaminated as much as possible (minimize or eliminate components that may contaminate the glass), the characteristics of high-temperature expansion and contraction (expansion coefficient), thermal shock resistance, and no cross-reaction with other adjacent refractory materials that affect the properties of the refractory materials, etc.
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(2) Processability
Conventional processing equipment can be used to process the required size and shape, minimizing the use of super-large and super-irregular brick materials, and reducing the types and quantities of manual processing. At the same time, the convenience of production, assembly, packaging, transportation, and masonry should be taken into consideration.
(3) Economy
Under the condition of meeting the basic needs, try to minimize the usage and choose the appropriate specification.
(4) Systematicness
Reasonably match the specifications and quantities of refractory materials in different parts to achieve the same service life of refractory materials in the glass melting furnace as much as possible. Based on application experience, after the traditional air-assisted combustion glass furnace is converted to an all-oxygen combustion furnace, there is no significant change in the selection of refractory materials for the lower structure. The main focus is on the selection and use of refractory materials for the upper space.
Fused cast AZS blocks play a crucial role in the core part of all-oxygen combustion glass furnaces, and their performance directly determines the service life, production efficiency, and glass quality of the furnaces. All-oxygen combustion technology is becoming increasingly popular due to its advantages such as energy conservation, environmental protection, and improvement of glass quality. However, it also poses more stringent requirements for refractory materials, especially those in the core parts.
The application of fused cast AZS blocks in the core part of all-oxygen furnaces
►The hot spot area of the melting end
Challenge: This is the area where the furnace temperature is the highest (usually >1600°C) and the convection of glass liquid is the most intense. The high-temperature glass liquid continuously erodes, the concentration of alkali vapor is high, and the erosion is severe. The flame temperature of all-oxygen combustion is higher and the local heat load is greater.
Application: Fused cast AZS blocks (such as 41# AZS) are the absolute main force. Its excellent resistance to glass liquid erosion, high-temperature structural strength, and low pollution to glass (low exudate phase) are the keys to ensuring the lifespan of the hot spot area. Shrinkage pore-free blocks are usually cast at an incline or in a dense manner to reduce weak points.
►Throat
Challenge: The glass liquid passes through the narrow channel at high speed with extremely strong scouring force. The temperature gradient here is large and the thermal stress is concentrated. The flow rate of the glass liquid is fast, and the erosion intensifies. It simultaneously bears the pressure difference from both sides of the melting end and the cooling section.
Application: Non-shrinkage pore-free fused cast AZS blocks (such as 41# AZS) are the standard configuration and even the only reliable option. High-quality, dense bricks without internal defects (shrinkage cavities) must be selected to ensure structural integrity and resist the erosion of high-speed glass liquid. Usually, the masonry method also needs to be carefully designed.
►Weir
Challenge: Partially immersed in the glass liquid, subjected to erosion from both the upper and lower sides of the glass liquid and temperature differences; Promote the homogenization of the glass liquid and be itself in the strong convection area; Precise control of the liquid flow is required.
Application: Fused cast AZS blocks (33# or 41#) are the mainstream choice. Different grades should be selected based on the depth, position, and design of the furnace embankment. Also, emphasize high quality and low defect rate.
►Near the chest wall/port opening
Challenge: Direct exposure to high-temperature all-oxygen flames and combustion products (high-concentration water vapor, alkali vapor, volatile substances); Exposed to high-temperature flame impact, chemical erosion (condensation erosion of alkali vapor, volatile substance reaction) and dust scouring; Frequent thermal shocks (temperature fluctuations).
Application: Electrically fused α/β -alumina bricks are increasingly widely used here. Its advantages lie in:
•Extremely high refractoriness: Melting point exceeds 1800°C.
•Excellent resistance to alkali vapor erosion: The main component is Al2O3, without SiO2, and it will not react with alkali vapor to form low-melting-point cabernet and cause peeling.
•Good thermal shock resistance: Compared with sintered zirconium materials, it has a lower coefficient of thermal expansion and better thermal shock stability.
•Low pollution: It causes minimal pollution to the glass liquid.
►The side wall/corner of the doghouse
Challenges: Understand the erosion of compound material dust, the friction and scouring of unmelted materials, temperature fluctuations, and the erosion of volatile components in compound materials.
Application: Fused cast AZS blocks (33# or 41#) or fused α/β -alumina bricks. AZS has a strong ability to resist wear and erosion by initial compounding materials. α/β-Al2O3 is more resistant to the erosion of volatile components. The choice depends on the specific compound composition and design.
Why are fused cast AZS blocks the preferred choice for core parts?
Extremely high density: The melt casting process makes its structure extremely dense, with an extremely low porosity (usually <5%), which greatly hinders the penetration of glass liquid and corrosive gases.
Outstanding resistance to glass liquid erosion: Especially for AZS blocks, the zircon phase (ZrO2) has poor wettability with the glass liquid, forming a high-viscosity protective layer (boundary layer), which significantly slows down the erosion rate. α/β-Al2O3 also has a strong resistance to the erosion of glass liquid and causes less pollution.
Outstanding high-temperature structural strength: It can maintain sufficient mechanical strength at high temperatures, and resist the erosion of glass liquid flow and structural stress.
Low exudation/low pollution: High-quality AZS (such as 41#) and α/β-Al2O3 bricks precipitate very little glass phase or impurities at high temperatures, having a minimal impact on the quality of the glass liquid. They are particularly suitable for the production of high-quality glass (such as electronic, optical, and medical glass).
Special precautions for the application of fused cast AZS blocks in all-oxygen furnaces
The concentration of alkali vapor increases: The amount of water vapor produced by all-oxygen combustion is several times that of air combustion. Water vapor will accelerate the volatilization of alkali metal oxides in the compound materials, resulting in a significant increase in the concentration of alkali vapor (NaOH, KOH) in the gas phase of the furnace. This intensifies the erosion of SiO2-containing materials (including AZS), highlighting the advantages of α/β-Al2O3 in gas-phase regions such as the chest wall.
Higher heat load: The temperature of the all-oxygen flame is higher, and the local heat load is greater, which requires refractory materials to have higher refractoriness and high-temperature strength.
More severe working conditions: Energy conservation and high efficiency often mean that the furnace is more compact and has a higher melting rate, further intensifying the erosion of refractory materials.
Problems that are prone to occur in the application of refractory materials in all-oxygen combustion furnaces
►Deformation of the crown
There have been cases of excessive arch deformation in both electrofusion and sintering materials of all-oxygen combustion furnaces. In mild cases, it led to production suspension and renovation; in severe cases, it directly collapsed. Based on the statistics of known faults in all-oxygen combustion glass furnaces, many furnaces have already experienced similar situations such as large arch deformation and collapse. This not only affects the lifespan, cost, and quality of the glass of the furnaces but also influences the success or failure of the entire project. The deformation of the crown is conventionally called saddle-shaped or M-shaped deformation. The deformation can be divided into two situations: parallel and vertical along the axis of the furnace. Deformation usually occurs in areas with higher temperatures. Figure 1 shows the variation legend of the crown.
Deformation is usually caused by the selection of materials with a load-softening temperature that does not meet the standard, or by local combustion temperatures exceeding the rated load-softening temperature of the selected materials. There are also accidents caused by substandard masonry.
►Collapse of the chest wall
In recent years, there have also been incidents of partial or total collapse of the chest wall in all-oxygen combustion furnaces. This not only poses requirements for the furnace design units in terms of material selection and masonry but also puts forward new demands for furnace usage and process control parties.
►Local burning damage
It mainly occurs near the fire port neck or opposite the firing gun. The reason for this is that the flame of all-oxygen combustion is relatively hard and the furnace pressure is relatively large. Correct operation and inspection can reduce or eliminate local burning damage.
►Material Leakage
There was once an accident of perforation and material leakage in the sidewall of the all-oxygen combustion furnace. The causes of the accident included factors related to the quality of refractory materials, as well as inadequate inspection by the production enterprise, and low daily control levels.
The application of fused cast AZS blocks in all-oxygen combustion glass furnaces not only extends the service life and production efficiency of the furnaces but also significantly improves the quality of the glass. When choosing fused cast AZS blocks, their performance characteristics and applicable parts should be fully considered to ensure the stable operation and efficient production of the furnace.
Henan SNR Refractory Co., Ltd（SNR） produces a variety of high-quality fused cast AZS blocks. If you have any needs, please contact me.
