According to the requirements of the furnace design for the synchronous loss of refractory bricks, the corrosion damage of each part of the furnace should be basically similar at the end of the kiln period to achieve economical and reasonable results. The large sill, pool wall and breast wall are listed as the key parts of the oxy-combustion glass melting furnace, and the quality of the material selection also directly affects the life of the melting furnace and the overall interests of the glass enterprise. Zhengzhou Shennan Refractory Factory analyzes the selection of refractory materials for glass melting furnaces from the following aspects.
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1.1 Selection of materials for the dome
Traditionally, the main use of dome is silica brick. Erosion of several fused cast products and silica bricks was investigated in both "short-term" laboratory simulation tests and "long-term" masonry actual test samples, and diffusion theoretical analysis was carried out. Silica brick has a high softening temperature under load and is relatively cheap. When used as a large sill, under the action of alkaline components, the surface of the brick body is eroded to form a new glass phase rich in SiO2. Due to its high viscosity, it not only blocks the pores, but also hinders the further diffusion of alkaline components into the brick. Only when the high-viscosity glass phase on the surface of the brick is lost, the brick body will be further eroded. In addition, the polycrystalline transformation due to temperature change is accompanied by volume change, which loosens the brick body. In the oxy-fuel combustion kiln, the temperature of the inner surface of the kiln dome is 25-50°C lower than that of the air flame retardant, but the alkali vapor concentration is correspondingly 4-5 times higher, and the airflow impulse is large, which greatly accelerates the kiln. The corrosion of the top silica brick, the chemical reaction of its erosion is as follows. The low melting point silicate glass phase is enriched on the surface of silicon. Under the influence of gravity and changes in environmental conditions, especially when the concentration of alkali vapor is high and the airflow impulse is large, the reactants on the surface of the silica brick will melt droplets. In the form of dripping, the alkali vapor takes the opportunity to diffuse into the interior of the silica brick, which accelerates the erosion of the silica brick. At the same time, due to the erosion and damage of the silica brick, the "silicon flow erosion" phenomenon will occur in the cast AZS brick under the silica brick, which will shorten the service life of the furnace and bring refractory stones to the glass liquid, making the glass yield decreased. Therefore, silica bricks are not suitable for large sill materials for long kiln age furnaces. Using fused AZS bricks as the dome material, usually an important indicator for evaluating the quality of conventional fused AZS bricks is the exudation of the glass phase, and the barrier effect of the high viscosity liquid phase near the surface of the fused AZS bricks is the key to further ensure its life. . However, the AZS material contains a large amount of SiO2, and the high alkali vapor concentration will increase the intrusion of alkali species, reduce the viscosity of the glass phase in the brick, and cause severe exudation. Therefore, if the fused AZS brick is used as the dome material, it must be greatly improved. Moore et al. compared and analyzed the erosion behavior of silica bricks and AZS bricks on the dome by two combustion methods of air 2 fuel and oxygen 2 fuel, but did not conduct experimental analysis. Japan's Asahi Glass Co., Ltd. has obtained through simulation tests that α2β corundum bricks and fused zirconium corundum bricks with low glass phase exudation are more suitable for full-oxygen combustion furnaces. When αβ2 corundum brick is used as the dome material, special attention should be paid to its assembly quality, and the requirements for size are also very strict, and the sealing material should be developed accordingly. In addition, the relatively expensive price also limits it to oxy-fuel glass melting furnaces for the production of high-grade glass. Using fused zirconium corundum bricks with low glass phase exudation as the dome material, the processing, sealing and size specifications of the expansion joints, the matching of materials and the cost are also a big problem. In addition, β2Al2O3 brick is also a refractory material with better resistance to alkali vapor corrosion, but its compressive strength and resistance to flying material corrosion are poor. At the same time, British scientists believe that the advantage of silica brick is that it is cheap and light, and it can continue to be used if the structure and glass phase composition are improved. After many tests, an improved silica brick was obtained, which has a dense structure, a glass phase of CaO·SiO2, a melting temperature of 1520℃, and is resistant to the erosion of high-concentration alkali vapor. American scientists believe that the use of fused zirconium corundum bricks may cause droplets to fall, and they prefer to use fused alumina bricks (α2βAl2O3). α2βAl2O3 contains about 45% α2Al2O3 phase and 55% β2Al2O3 phase, impurity phase is about 1%, and pores are 2%. During air combustion and total oxygen combustion (no dust), α2Al2O3 layers and pores are formed on the surface; Na is lost from β2Al2O3 to form NaOH with a 17% volume reduction and finely dispersed pores. α2βAl2O3 bricks are suitable for most occasions. If α2βAl2O3 bricks are expensive and unaffordable, α2βAl2O3 bricks must be used from the hot spot to the bridge wall.
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1.2 Selection of breast wall materials
Usually, the breast wall of all-oxygen melting furnace is made of fused AZS bricks. The erosion of the flame in the kiln causes mechanical wear of the breast wall bricks. The parapet surface continuously reacts with certain components of the parapet tiles, causing chemical attack. In addition, the alkali vapor in the flame space directly enters the interior of the brick from the brick joints and open pores, and chemical attack occurs. As far as the brick body itself is concerned, the gas formed by the closed pores and the residual carbon oxidation in the brick will expand rapidly at high temperature to extrude the liquid phase in the brick. This process is related to the combined action of temperature and alkali vapor, which causes a large amount of liquid phase to seep out of the refractory brick, which aggravates the peeling of the brick body. Mackintosh et al. pointed out that the corrosion of AZS bricks is mainly due to the diffusion of univalent and divalent ions R+ and R2+ in the glass liquid to the matrix in the brick, and the glass phase in the brick meets Provide a channel for this expansion; the highly alkaline liquid phase promotes the dissolution of corundum; and the increase of Al3+ concentration in the liquid phase can reduce the solubility of ZrO2. Therefore, in the oxygen-fired glass melting furnace, the necessary improvements should also be made to the cast AZS bricks in the breast wall, mainly to reduce the glass phase content, so that the exudation of the glass phase is less when used in the upper structure; Improve its creep resistance and increase the normal operating temperature from 1600 ℃ to 1650 ℃.
1.3 Selection of pool wall materials
Usually, the pool wall in the oxy-fuel combustion kiln is also made of fused AZS bricks. Gupta et al. have studied the erosion change of liquid level after using AZS pool bricks in three furnaces. There is a lot of glass in the fused AZS brick. This glass phase has a low melting point and seeps out of the brick at high temperature. Due to the full oxygen combustion, a large amount of water vapor is generated, accounting for 67% of the entire flue gas volume. At the same time, it makes The increase of OH- concentration in the glass liquid reduces the viscosity of the glass, improves the separation and crystallization tendency of the glass phase in the glass, and increases the convection speed of the glass liquid. The exudation temperature of the glass phase of ordinary cast AZS bricks is about 1400 ° C, but in the high temperature full oxygen combustion furnace of about 1600 ° C, a large amount of glass phase will continue to exude, so that the crystalline phase in the brick becomes isolated. It falls into the glass under the action of its own weight and liquid flow. Alkaline oxides such as Na2O and K2O in the glass liquid continuously react with Al2O3 in the AZS brick to produce nepheline and β2 alumina; ZrO2 and Al2O3 in the brick continue to precipitate on the surface of the brick body to form a high-viscosity protective layer, preventing further erosion of the molten glass. However, erosion and its own bulk density make this protective layer gradually updated, and the erosion will further intensify. A large amount of water vapor in the all-oxygen combustion product reacts with the components of the liquid glass surface layer to form volatile hydroxides that continuously escape from the surface of the glass liquid, which intensifies the erosion at the three-phase liquid surface line of the pool wall. According to the research of a refractory company in the United States, the erosion rate of the pool wall bricks in the oxygen-burning kiln is 25% faster than that in the air-burning kiln. Therefore, ordinary fused-cast AZS bricks are not suitable for use in the wall of oxyfuel combustion pools, and a new type of refractory material with good chemical stability, low glass phase content and high liquid phase exudation temperature must be developed.
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