With the continuous improvement of photovoltaic module manufacturers' requirements for glass, the demand for large-scale and thin-sheet photovoltaic rolled glass furnaces has become an inevitable trend. At present, the scale of photovoltaic rolled glass melting furnace has been developed to the level of 1000~1200t/d. In the future, as photovoltaic module manufacturers gradually develop and apply large-scale photovoltaic glass with thicknesses of 2.5mm, 2mm and 1.6mm, photovoltaic glass suppliers will inevitably adjust their production, especially changes in forming and temperature requirements, which will inevitably affect the design of the channel And production adjustments.
Due to the extremely low iron content in photovoltaic rolled glass, the glass liquid has high light transmittance, strong heat permeability, and high convection intensity in the horizontal direction. However, the use of agitators at the neck of the photovoltaic calendering furnace is rarely used, and the neck is locked. Gradually developing in the direction of shortening and narrowing, this results in a limited cooling range of the molten glass at the position of the neck, making the temperature of the molten glass near the outlet of the neck higher, which affects the choice of the material of the channel wall bricks near the outlet of the neck.
Some photovoltaic calendering kilns completely use fused α-β corundum bricks for the wall of the passage, and the high temperature near the exit of the neck is severely corroded by the fused α-β corundum bricks, and there may be hidden dangers. The author recommends that fused zirconia corundum bricks be appropriately selected on the pool wall downstream near the outlet of the card neck to achieve an optimized and reasonable configuration, so as to more flexibly adapt to changes in temperature and product specifications.
1. Two configurations and advantages and disadvantages of the wall brick material of the access pool
1.1 Two configurations of wall bricks
The pool wall bricks near the exit of the card neck have not been unified in material selection. Some photovoltaic calendering kilns all use fused α-β corundum bricks; some photovoltaic calendering kilns use 33# oxidized fused zirconium without shrinkage holes Corundum bricks are used in combination with fused α-β corundum bricks, but the ratio and the position of the distance from the neck when used together are yet to be discussed.
The advantages and disadvantages of 1.22 different materials of fused cast bricks
The pool wall bricks of photovoltaic calendering kiln generally choose the products of high-quality mainstream brand manufacturers. The price of ordinary cast fused α-β corundum pool wall bricks is about 40,000/t, while 33# oxidized fused zirconia corundum without shrinkage holes The price of pool wall bricks is around 35,000/t. This is because the manufacturing difficulty and technical input of fused α-β corundum bricks are higher than those of fused zirconium corundum bricks. Therefore, in terms of the price of pool wall bricks, the price of fused α-β corundum bricks is slightly higher than that of 33# oxidation method. Hole fused zirconia corundum brick.
The pollution resistance of fused zirconia corundum bricks is not as good as that of fused α-β corundum bricks. This is because the alumina-based fused bricks are very pure and the content of Al2O3 accounts for more than 90%. The metamorphic layer of nepheline formed on the surface of the brick body in the glass The viscosity is not as high as the nepheline metamorphic layer containing ZrO2. It is more viscous and easier to dissolve. Therefore, the corrosion resistance at high temperature is not as good as that of fused zirconium corundum bricks. The nepheline metamorphic layer of aluminum brick has low viscosity and is easily soluble in molten glass, so it has little pollution to molten glass
Therefore, in the high temperature area (>1350℃), the fused zirconia corundum brick without shrinkage by oxidation method is stronger than the fused α-β corundum brick in the corrosion resistance of molten glass; in the low temperature area (<1350℃), the fused α-β corundum brick Compared with fused zirconia corundum bricks, β corundum bricks have little difference in corrosion resistance, even slightly better than the latter. Fused α-β corundum bricks contain very little glass phase and have less pollution to the molten glass, so they are better used in places where the temperature is lower than 1350°C.
2. The temperature drop of glass liquid at the neck
There are many calculation methods for the temperature drop of glass liquid passing through the neck, such as actual measurement, simulation or theoretical calculation. Simulation and theoretical calculations are relatively cumbersome, and there will be varying degrees of error. The author chooses the actual measurement method and uses the thermometer to measure the temperature of furnace A and furnace B.
Different furnaces have different options for monitoring the temperature of the molten glass during production. The position selected here is based on the temperature of the molten glass at the inlet and outlet of the neck as the temperature monitoring point, and the two furnaces A and B are used as a comparison. The temperature of the molten glass at the entrance and exit of the neck is measured accordingly. Three different high-temperature thermometers are used to verify the temperature. After measuring the temperature in the same place, the error is within 5℃, so as to prevent errors in the measurement. Larger, ensuring the accuracy of temperature measurement of 3 thermometers.
The structure and size of the two kilns in Table 1 are exactly the same. The pool wall bricks near the exit of the necks of the two kilns are all fused α-β corundum bricks. Kiln Volume 48, Issue 5 The temperature at the outlet of the glass enamel and glasses A collar is close to 1370℃, and the outlet temperature of the kiln B collar is about 1350℃. The temperature process system adopted when the same furnace produces the same specifications of glass The difference is quite obvious. The temperature of the molten glass near the outlet of the neck of the kiln A is significantly higher than 1350℃, and the wall brick near the outlet of the neck is made of fused α-β corundum bricks. The same drawing amount, the higher the temperature, the molten glass is opposite to the pool. The wall bricks will erode faster, so it is necessary to strengthen the monitoring of the pool wall bricks near the card neck exit, especially the channel wall closest to the corner brick of the card neck exit. At the same time, appropriate protective measures should be taken, such as blowing and cooling the pool wall bricks to slow down the erosion of the pool wall. We found that the temperature of the molten glass at the entrance of the kiln A was about 20℃ higher than that of the furnace B, and the temperature drop of the molten glass in the two furnaces reached the exit of the kiln after the heat dissipation of the kiln and the deep water bag of the kiln. The temperature difference is not big, the same is about 20℃. The main difference in the temperature of the molten glass at the neck of the two furnaces is the setting of the clarification temperature. The author suggests that the clarification temperature of kiln A can be appropriately lowered, and the heat dissipation of the horizontal and branch passages can be appropriately reduced. This not only satisfies the forming temperature, but also reduces the corrosion of the kiln, and also achieves the purpose of energy saving and consumption reduction.
From Table 1, we also find that the temperature drop of the molten glass in furnace A and furnace B through the neck is about 90℃, while the temperature drop of the molten glass in the float glass furnace is about 110°C. This is because in addition to the neck deep water ladle in the float glass furnace, there is also a horizontal or vertical agitator. At the same time, the cooling part has temperature adjustment methods such as dilution air and space cooling water ladle, and many photovoltaic rolled glass On the basis of eliminating the agitator and dilution wind, the kiln has strengthened the heat preservation of the passage, resulting in a small temperature drop of the molten glass in the photovoltaic calendering kiln after passing through the collar. Therefore, special attention should be paid to the material selection of pool wall bricks near the exit of the neck of the photovoltaic calendering kiln.
3. The necessity of installing fused zirconia corundum bricks on the wall of the channel near the exit of the card neck
3.1 Higher clarification temperature
Nowadays, many furnaces generally adopt the "double high" operation system, namely "high temperature melting" and "high temperature clarification". The photovoltaic rolled glass has strong heat permeability, the temperature difference between the upper and lower layers of the glass is small, and the deep bubbles in the clarification zone are more difficult to clarify. , The clarification temperature will be increased accordingly when the general temperature process is set. As shown in Table 1 above, the temperature of furnace A at the inlet of the collar is higher than 1455°C. Setting such a high clarification temperature will inevitably lead to an increase in the temperature of the molten glass at the outlet of the collar.
3.2 Gradually shorten the narrow neck
The necks of the kilns generally adopt a narrow and long form. At present, the size of the necks of the kilns is gradually shortening and narrowing. The length of the necks of the two kilns in Table 1 is 7500mm and the width is 4000mm. However, the current kiln cards of the same scale The length of the neck is 5000mm and the width is 2200mm. Under the same other conditions, the temperature drop of the glass liquid when it passes through the latter's narrow neck will be less than 90℃. The narrower collar reduces the backflow of the glass liquid in the passage, which also reduces secondary heating, which is conducive to energy saving and consumption reduction. However, the flow rate of the glass liquid through the shorter and narrower collar is faster and the heat dissipation area is reduced. , The temperature drop of the molten glass after passing through the neck of the collar will be smaller, which will cause the temperature of the molten glass at the outlet of the neck of the collar to increase.
3.3 The need for energy saving and insulation
The measures for channel temperature adjustment are generally to switch the observation hole of the heat dissipation hole, the increase or decrease of the dilution wind or the insulation layer, and the use of a space water bag or baffle. In order to save energy and reduce consumption, the passage of the photovoltaic calendering kiln will try to take good heat preservation measures, and suitable slow cooling, which is conducive to the stability of the molten glass flow and the absorption of microbubbles by the molten glass. Good heat preservation measures will also cause higher temperature of the molten glass at the outlet of the neck.
According to experience, the larger the furnace tonnage, the slower the cooling rate of molten glass. Taking a 700t/d furnace as an example, the average temperature drop of the molten glass from the hot spot to the neck is about 7.5℃/m, and under the same cooling intensity or the same heat preservation, the temperature drop at high temperature is greater than that at low temperature. For the sake of safety and conservativeness, the author set the temperature drop of the molten glass near the exit of the neck to 6℃/m. At the same time, 33# oxidation method non-shrinkage fused zirconia corundum bricks have a glass phase primary precipitation temperature not lower than 1400℃, and the author sets a higher temperature of the glass at the outlet of the neck to 1400℃, taking a temperature drop of 6℃/m , When the temperature drops below 1350℃, it is regarded as a safe temperature. Therefore, the author believes that from the perspective of temperature, it is not suitable to use fused zirconia corundum bricks at a distance of 9000mm downstream from the corner bricks at the exit of the collar.
Take a typical one-kiln four-line kiln and one kiln five-line kiln to briefly explain. Figure 1 shows a one-kiln and four-line kiln. The two corner bricks at the exit of the neck are drawn as the center and the length of 9000mm is the radius. The pool walls indicated by thick red lines in these two circles are all made of 33# oxidation method non-shrinkage fused zirconia corundum bricks. When the molten glass reaches the nearest branch passage after it exits the neck, its actual temperature has dropped below 1350℃, and the erosion of the molten glass on the wall bricks of the branch passage has been significantly weakened. Therefore, the branch passage of a kiln with four lines All pool walls are made of fused α-β corundum bricks. Figure 2 shows a five-line kiln with one kiln. The two corner bricks at the exit of the neck are also drawn as a circle with a length of 9000mm as the radius. The pool walls indicated by thick red lines in these two circles are all 33#. Oxidation method non-shrinkage fused zirconia corundum brick. The width of the horizontal passage is generally in the range of 3500~7000mm. The temperature of the molten glass is relatively high when it enters the middle branch passage. At the same time, the erosion and erosion of the brick wall near the branch passage entrance by the molten glass will be more serious, so the branch passage entrance Part of the pool wall should be 33# oxidized non-shrinkage fused zirconia corundum bricks, and the other 4 branch channels should be fused α-β corundum bricks.
5. Suggestions for the production of kilns that have been put into operation
Based on the consideration of the corrosion resistance of fused α-β corundum bricks, the author recommends that the temperature of the molten glass at the outlet of the neck should be controlled to be as low as 1350℃, especially for the wall of the channel, all fused α-β corundum bricks The kiln can start from the following aspects:
(1) Appropriately reduce the clarification temperature. Too high a clarification temperature does not improve the clarification effect of the glass liquid, but increases energy consumption, and also increases the corrosion of the refractory materials of the furnace, which affects the quality of the glass.
(2) Strengthen the cooling strength and heat dissipation of the card neck deep water bag, and add other cooling methods when necessary. Appropriately increasing the pressing depth of the card neck deep-layer water bag has a significant effect on the cooling of the glass liquid, and it is also beneficial in energy saving and improving the quality of the glass. The pressing depth should not be too deep. It can be made according to the specific furnace structure size. Adjust accordingly, the pressing depth is about 35%~50% of the neck depth.
(3) Strengthen the heat dissipation and cooling of the outer surface of the channel wall near the outlet of the neck, especially near the liquid level line, where the gas-solid-liquid 3-phase junction is the fastest erosion. Air cooling is a better way. If necessary, tie bricks to the upper part of the pool wall to extend the life of the pool wall bricks.
For kilns that use fused zirconia corundum bricks and fused α-β corundum bricks on the wall of the channel near the exit of the card neck, the temperature should be appropriately lowered when high-quality glass can be produced. Both have benefits in terms of furnace erosion. Experience has proved that within the normal melting temperature range, every 50°C increase in the temperature in the kiln will double the corrosion rate of refractory materials, which is also not conducive to glass quality and furnace safety.
6 Conclusion
In summary, in order to adapt to the large-scale photovoltaic rolled glass melting furnace and the general trend of product thinning, the forming of photovoltaic glass and its temperature requirements have changed, so in the design and production, it is necessary to configure the refractory material for the passage Making corresponding adjustments to make full use of the advantages of the two types of bricks is not only beneficial to the adjustment of the process, but also does not increase the investment in the kiln.
Based on the analysis of the temperature drop range of the molten glass through the neck, it is recommended to use 33# oxidation method non-shrinkage fused zirconium corundum bricks on the pool wall within 9000mm downstream of the junction between the neck and the passage, and use fused α- for other parts. The configuration of β corundum bricks. Through the optimized configuration of these two types of bricks, it is possible to flexibly adapt to the adjustment and operation of the production process of different thicknesses of glass, thereby facilitating the exploration of the melting process and the calendering process for the production of thin plates.
For the kiln that has been put into production, according to the existing pool wall brick configuration of the passage, adjust the temperature system through different means to seek to reduce the corrosion of the kiln, save energy and reduce consumption, and maintain a long-term stable balance of melting quality, so as to achieve safety, energy saving and high quality The goal of high productivity.
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