Reasonable allocation of refractory materials for glass melting furnace
The reasonable configuration of refractory materials in each part of the furnace refers to the selection of the most suitable refractory material according to the working environment and the damage mechanism of the refractory material in each part of the furnace, so as to give full play to the characteristics of different refractory materials. In this way, the life of each part of the kiln body is balanced, glass defects caused by refractory materials are minimized, the life of the furnace is long, various technical and economic indicators are advanced, and the entire furnace is in a stable and optimal operating state.
As mentioned earlier, in recent years, the production of refractory materials for glass melting furnaces in China has made great progress, with basically complete varieties and improved quality. In addition, the reasonable selection of refractory materials in the regenerator and other parts and the damage mechanism of the service process have also been studied. Each factory has also accumulated a wealth of experience in the use of refractory materials, all of which are prepared for the reasonable configuration of refractory materials in the glass melting furnace. Necessary conditions. However, the reasonable allocation of refractory materials in various parts of the furnace is a very complex subject, which involves the structure of the furnace, glass composition, thermal system, fuel type and composition, and related process technical parameters. Therefore, it needs to be considered comprehensively according to the actual situation. The following only discusses the working environment of refractory materials in various parts of the glass melting furnace, the reasons for damage, and the requirements for refractory materials.
Part one: The part in contact with glass liquid
Including the melting part and cooling part of the pool wall, pool bottom, feeding port, corners, necks and other parts.
1. Melting department
This part is the high temperature zone of the melting furnace, and the temperature of melting the soda-lime glass is as high as 1550～1590℃. In addition, due to the temperature difference between the continuous feeding and the molten glass, the molten glass will flow vertically and horizontally. Therefore, the refractory material in this part is not only subject to the chemical attack caused by the chemical reaction of the high temperature molten glass, but also the mechanical and physical attack caused by the flow of the molten glass. Erosion is the main reason for the damage of refractory materials in this part. The erosion of refractory materials in molten glass is a process of dissolving solids in liquids, and is a problem of liquid-solid reaction kinetics. Many studies have shown that Na20 in soda-lime glass is the main corrosive component. It penetrates along the glass phase and pores of commonly used fused-cast zirconium corundum bricks by means of penetration and diffusion, so that the corundum crystals will dissolve under the diffusion action of Naz0. And it generates nepheline (Naz0 · AIz03 · SiOz) and eventually leads to the damage of the bricks. The erosion of the fused cast zirconium corundum material is the change of its transition to the equilibrium state under the use environment. The interfacial reaction caused by the diffusion of the glass liquid alkali component on the surface of the material dissolves the corundum, and at the same time forms a series of low melting point compounds with the characteristics of the feldspar group structure. Layer, its assimilation with glass leads to the gradual dissolution of the material. The main mechanism of erosion is the dissolution of the crystalline phase. Therefore, the dissolution of corundum crystals under the action of alkali diffusion and the formation of feldspar compounds are the chemical nature of the corrosion of fused cast zirconium corundum bricks. The corrosion of the refractory surface in contact with molten glass is very uneven (see Figure 1), and the corrosion is intensified at the liquid surface of the glass. This is the so-called gas-liquid-solid three-phase interface. Its erosion rate is higher than that of the molten glass. The erosion rate of the lower part of the surface is several times larger. This is because at the liquid-solid two-phase interface below the glass surface, a reaction layer will be formed during the erosion process to prevent further erosion reactions until the balance is broken, the reaction layer is destroyed, and the erosion restarts. At the three-phase interface, the reaction layer is agitated due to the surface power generated by the presence of the gas phase, which greatly accelerates the diffusion rate and intensifies erosion. The so-called upward drilling erosion phenomenon under the liquid surface is due to the presence of gas at the reaction interface, and the reaction layer is agitated by the action of the gas surface tension, which accelerates the diffusion rate. In addition, it is believed that the specific gravity of the reaction layer is larger than that of the base glass liquid, the reaction layer falls off, and the reaction interface is always in contact with the fresh glass liquid, which accelerates the diffusion reaction. Therefore, foreign pool wall bricks are erected with inclined cast bricks to reduce horizontal brick joints and avoid upward drilling erosion. In addition, the erosion rate is very sensitive to temperature. Within the normal operating temperature range, the erosion rate of refractory materials usually increases with the increase in temperature (see Figure 2).
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Figure 1. Schematic diagram of the erosion of pool wall bricks in the melting part
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Figure 2. The relationship between erosion rate and temperature
It can be seen from the figure that the corrosion rate of refractory materials increases sharply as the temperature rises. According to experience, within the normal operating temperature range, the corrosion rate of refractory materials will double for every increase of 50°C. Therefore, the melting temperature should be appropriate, otherwise it will affect the life of the furnace. The most important requirement for refractory materials in this area is good resistance to corrosion by molten glass. Therefore, melting and casting 33 #zirconium corundum brick or melting and casting 41# zirconium corundum brick are generally used as pool wall tiles and bottom tiles. The chromium-containing fused cast zirconium corundum bricks have better resistance to molten glass corrosion, but due to coloring, flat glass melting furnaces are generally not used, but only a small amount of use has begun in recent years.
2. Cooling department
The working environment of this part is basically the same as the part where the melting part is in contact with the glass liquid, but the temperature is much lower than that of the melting part, generally below 1400°C. Therefore, the corrosion rate of refractory materials is also much smaller. However, the more molten glass flows to the forming end, the more it is susceptible to the formation of defects due to the influence of refractory materials. This is because in the lower temperature zone, it is difficult to melt or eliminate solid defects derived from refractory materials. Therefore, the choice of refractory materials for this part must be very careful. The main performance requirements of refractories in this part are good corrosion resistance and minimal tendency to produce stones and bubbles. The cast α-β alumina brick has excellent resistance to glass corrosion at 1350℃, and its glass phase content is only 1% to 2%, and the bubble precipitation index is close, which will not cause pollution to the clarified molten glass. Therefore, It is an ideal refractory material for contact with molten glass in this part.
Part two: Molten glass, various parts of the upper structure of the upper melting furnace
This part includes the dome of the melting part and the cooling part, the breast wall, the small furnace mouth and so on. The surface temperature in this area is 60% to 90% higher than the surface temperature of the refractory material in contact with the molten glass, and it varies greatly. The highest temperature is generally in the hot spot area in the latter half of the length of the melting pool. In this area, refractory materials are not only attacked by batch fly materials, but also attacked by alkali vapor.
1. Melting department
(1) Dome
This part is at a high temperature of 1550～1650℃, and chemical attack caused by the high-temperature chemical reaction of batch materials, flying materials and alkali vapor with refractory materials is the main corrosion method. The requirements for refractory materials in this part are good resistance to the erosion of batch materials and alkali vapor, high softening temperature under load, and no pollution to the glass liquid. Silica brick has the above-mentioned properties. It has corrosion resistance to low-concentration alkali vapor, and the erosion only proceeds very slowly from the surface. But the main component of silica brick is SiO2, even if it is corroded, it will not pollute the molten glass. In addition, the load softening temperature of silica bricks is very high, and high-grade silica bricks can reach 1690°C. However, it should be noted that the load softening temperature of silica brick is already close to the melting point, and as long as it slightly exceeds this temperature, it will soften sharply or even collapse. The collapse of the silicon brick roof has also occurred in our country. Therefore, do not allow the silica brick to exceed the operating temperature, and do not allow the flame to directly contact the surface of the dome-top silica brick. Silica bricks used for the top of the dome require precise dimensions and tight masonry cracks, otherwise the alkali vapor will invade the cracks, and when it overflows to a low temperature, it will become liquid, causing strong erosion and producing the so-called "rat hole" abnormal erosion phenomenon. After the dome is insulated, this phenomenon has improved. In addition to the use of silica bricks for the roof, there are also fused cast zirconium corundum bricks and synthetic mullite bricks. The fused cast zirconium corundum brick contains 33% ZrO2. Using the casting process, the material does not have concentrated shrinkage cavities, but forms uniform micropores. This improves the thermal shock resistance of the bricks and reduces the bulk density. This kind of brick has better resistance to alkali vapor and the corrosiveness of batch fly material than silica brick, and the load softening temperature is also high. If it is made into a trough shape, the middle filling insulation material can be used for insulation, but its own weight is too large, and the price is higher than that of silicon. The bricks are much higher. Therefore, only special glass furnaces with the maximum span of the dome roof are used within 7m.
(2) Breast wall, small furnace mouth, etc.
The working environment of this part is basically the same as that of the dome. The main cause of refractory damage is the erosion of batch fly material and alkali vapor. The upper structure of the first, second, and third pairs of small furnaces of large and medium-sized plate glass furnaces is more severely corroded by batch materials and flying materials. After the fourth pair of small furnaces, the corrosion of alkali vapor increases. Therefore, the breast wall and the small furnace mouth (including the small furnace flat chute) are usually constructed by oxidation method 33# zirconium corundum bricks, but the fifth and sixth pairs of small furnaces are made of cast β-alumina bricks for the furnace mouth and flat strings. For appropriate. Because the refractory materials in this area are mainly corroded by high-temperature alkali vapor, the fused-cast β-alumina brick is saturated with Na2O (molecular formula is Na2O·11Al203), so it has good resistance to alkali vapor erosion. The last pair of small furnace to the breast wall of the neck is usually made of silica bricks.
2. Cooling department
The temperature of this part is much lower than that of the melting part, and its operating environment largely depends on the separation method of the end wall. If the separation between the melting part and the cooling part is not complete, the alkali vapor in the melting part will enter the cooling part and cause condensation and erosion on the surface of the superstructure refractory; if the melting part and the cooling part are completely isolated, only a small amount of alkali vapor will be removed The surface of the molten glass overflows (this refers to soda-lime glass, the surface of borosilicate glass continuously releases volatile sodium borate, even in the forehearth). Plate glass melting furnace partition devices generally use partition walls or hanging walls, which are all made of silica bricks: The lower part of U-shaped hanging walls generally use mullite bricks or sintered zirconium corundum bricks; the cooling part roof and parapet walls are all made of silica bricks. The effect is good.
