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Damage characteristics and selection of refractory materials in contact with glass liquid in glass melting furnace
Jan 08, 2019

In the glass melting furnace, the kiln lining is in contact with the high temperature glass liquid phase from the melting portion, the cooling portion to the forming portion, except for the contact with the flame as described before. The temperature range of the molten glass is 1200~1600°C, and it is in a convective state, and has various flow modes, and the flow velocity of each part is different, and a combustion gas flow flows above the liquid surface of the glass. Therefore, it has strong erosion properties. The bricks in contact with this part can be divided into a pool wall, a pool bottom, a feeding tank, a cooling part (or a working part), a flow path, and the like.


First, the damage characteristics of various parts and commonly used materials.


(1) Pool wall brick


At present, the wall bricks mainly use fused zirconium corundum bricks. The damage mechanism of the brick is the melting process of the multiphase material. The damage process is roughly divided into three steps:


1 High-temperature glass phase oozing The melting of AZS brick depends on the high temperature glass phase oozing temperature (at 1320~1420 °C). The glass phase in the brick oozes out to form a high-viscosity glass liquid with the nearby glass liquid, preventing the brick from being further quilted. erosion. However, holes were left in the fused brick. Since the surface tension of the fused brick is smaller than that of the molten glass, the fused brick is always wetted by the molten glass. The rate of melting depends on the glass phase bleed temperature, the number of glass phases, and the viscosity of the agglomerate.


2 The molten layer leaves the high-viscosity glass liquid layer on the surface of the fused brick from the original position and enters the molten glass due to the flow and scouring of the molten glass. Expose the remaining holes.


3 After the molten glass penetrates into the molten layer, the new molten glass penetrates into the exposed new surface and pores, reacts with the phase around the pores, and continues to melt the fused silica. First, the mullite in the structure is decomposed to form an aluminum oxide and a new glass phase, which further dissolves the oblique zircon and corundum fine particles in the structure, and finally completely disintegrates the brick structure. The rate of penetration depends on the rate of diffusion and the structure of the brick (such as the size, shape, number and distribution of the pores).


The above three-step process is continuously repeated, so that the fused brick is continuously eroded. When the temperature of the molten glass rises, the erosion will increase. When the outer surface of the brick wall is cooled by air, the erosion will be slowed down. When the glass composition is different, the erosion condition is also different. For example, when the mirabilite is used, the liquid surface will have “nitrogen water”, and the erosion of the pool wall brick is intensified, and the fluoride loss is extremely fast.


The brick joints of the pool wall bricks are very susceptible to erosion, which is due to the flow of glass and upward drilling. Here, it is also a gas, liquid and solid three-phase interface. The bubbles on the interface promote liquid phase agitation, accelerate the solid phase dissolution, and the reaction layer is easily washed away by the glass liquid. As the material of the pool wall brick, it is required to be resistant to corrosion, not to cause any defects (such as streaks, stones, bubbles) to the glass liquid, not to color the glass liquid, and to have certain thermal shock resistance and low thermal conductivity. The ideal pool wall brick is fused zirconium corundum brick. The wall of the melting part is usually made of fused alumina AZS brick containing 41% zirconia, and the cooling part is made of fused oxide AZS brick containing 33% zirconia. For fused AZS products, attention should be paid to the abnormal volume change accompanying the crystal transformation at 1050 to 1150 °C.


Some companies have chosen to use α-β-electrofused corundum products, which are composed of closely intertwined α-alumina (53%) and β-alumina (45%) fine particles. Phase (2%) filling, can be used as a cooling brick wall vertical brick and cooling section bottoming brick and cover seam brick. In the material of the superstructure, a product of β-electrofused corundum is also introduced, which is composed of large crystal grains of β-alumina, which contains a certain amount of pores inside, but almost no glass phase exists, so the brick Excellent resistance to thermal shock and resistance to alkali vapor attack.


(2) Pool bottom brick


The condition of the bottom brick is that the temperature of the glass liquid is low and the flow is weak. It has the following three damage features.


1 Drilling down the metal impurities (mainly iron, the order of strong metal erosion: Sn, Pb, Cu, Al, Zn) and the melting from glass reduction are carried out by the batch material (mainly cullet). The metal sinks to the bottom of the pool and forms a spherical or flat annular melt. Due to the large surface tension, they form a wedge-shaped opening between the glass liquid and the bottom brick, which causes the downward drilling to erode, especially into the brick bottom. Drilling in, eroding, and extending to the non-corrosive bottom of the pool (such as clay bricks, or even lightweight insulation bricks), in severe cases, most of the bottom bricks (below the paving bricks) can be emptied.


2 Upward drilling When the glass liquid and the metal liquid smear the brick joint material and penetrate into the cushion layer under the paving brick, the cushion layer is damaged by the corrosion. The glass liquid and the molten metal are vertical upward crater erosion of the paving brick, that is, upward drilling. Clamp up and down until the paving bricks are melted through.


3 When the mechanical wear bottom is kept warm, the bottom glass liquid is in a convection state. The circulating flow wears the bottom of the tank, especially in the feed zone, where convection is severe and wear is heavy.


In view of the above-mentioned damage characteristics, the bottom brick is required to be wear-resistant and integral. Nowadays, the multi-layer composite pool bottom structure is generally used, which is generally a protective layer underneath the bottom brick (clay brick). The clay brick is provided with zircon sand or fused zirconium corundum. it is good. This layer of ramming material and the bottom of the pool are sintered together, requiring no shrinkage or expansion, no cracks, and very dense, maximally preventing the leakage of the molten glass, forming a strong underlying structure with sufficient strength.


The paving brick is directly in contact with the glass liquid, which can well protect the bottom of the ramming material pool. The fused AZS brick with good corrosion resistance and wear resistance is also used. (The high quality sintered AZS brick can also be used. The disadvantage is that the size is small. More brick joints). The use of the composite pool bottom structure is: reducing heat loss, extending the life of the pool bottom, and improving the quality of the glass liquid.


(3) Feeding pool brick


The feeding pool brick is affected by the erosion of the powder and the glass liquid, the wear of the material layer, the flushing of the liquid flow, and the flame. Therefore, the damage is more serious, especially the corner brick of the feeding pool, and the convex portion of the corner is subjected to strong abrasion and Scouring, there is a large temperature difference between the inner and outer surfaces of the brick, which generates large mechanical stress, and the part has a certain temperature fluctuation, so it is easily damaged.


It is regarded as one of the weak parts of the pool kiln. It must be made of high-temperature wear-resistant and corrosion-resistant materials. It is usually made of ZrO2: 41% fused zirconium corundum brick without shrinkage, and the brick thickness is increased to enhance air cooling. In addition to the corner bricks, other parts can be cast AZS-33 bricks.


(4) Brick for cooling department


The cooling part is a molten glass that has been melted and clarified. It has entered the later stage of the melting process and must not cause any defects (including stones, streaks, bubbles) to the glass. Since the temperature of the molten glass is lower than that of the molten portion, the erosion of the brick is lighter. The AZS-33 brick produced by the oxidation method is required for the cooling part, and the glass phase has a high precipitation temperature and does not cause bubbles to the glass liquid.


(5) Flow path brick


The flow channel uses electrofusion AZS-3 brick or fused alpha-Al2O3 brick. These materials are in a fine-grained and dense structure. The glass phase filled between the crystals is very small, and the contamination to the glass liquid is the least. The erosion resistance at 1300 ° C or lower is better than that of the AZS brick. Flow channels and runner bricks (1100~1200°C, glass flow rate 0.83~1.67m/min or higher) are easy to wear and require high quality materials. Practice has proved that the channel can also be made of sillimanite bricks and mullite bricks. Because of their dense fine-grained structure, it is not easy to cause bubbles in the glass.


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