The bottom bubbling technology is to set up one or two rows of bubbling points at the bottom of the tank between the melting zone and the clarification zone of the glass melting furnace, thereby blowing a certain pressure of gas into the kiln without destroying the normal convection of the glass liquid. In this case, the rising movement of the bubbles drives the movement of the surrounding glass liquid, thus promoting the clarification and homogenization of the glass liquid.
Advantages of bubbling technology
After bubbling, a bottom-up annular liquid flow is added near the hot spot of the glass melting furnace, as shown in Figure 1, which strengthens the heat convection formed by the hot spot and can effectively block the unmelted scum from flowing to the clarification zone. . The rise of bubbles drives the surrounding glass liquid to move, promoting the elimination of bubbles in the glass liquid. The bubbling stirring effect increases the temperature of the glass liquid at the bottom of the pool, strengthens the heat exchange between the glass liquids, can significantly improve the chemical uniformity and thermal uniformity of the glass liquid, improves the uniformity of the glass products, and makes the product bubbles Defects such as , stones and streaks are greatly reduced. Bubbles can also increase the output and save energy. It is better to use bubbling technology in the production of various glass products, especially in the melting process of brown, green and other color glass with poor heat transmittance.
Bubble technical parameters
Although pool bottom bubbling has many advantages, if not properly designed or operated, it can be counterproductive and increase defects such as bubbles in the glass. Therefore, it is very important to properly design the bubbling device and control the bubbling parameters.
①The location, number, distance and arrangement of bubble points
The more suitable bubbling position is at the hot spot in the kiln or a little behind the hot spot. The backflow of the molten glass formed in this way basically coincides with the backflow formed by the hot spot, which can better play the role of blocking and stirring. Otherwise, the flow of the molten glass in the kiln will be destroyed. field, it is easy to produce bubbles and stones.
The number of bubble points is related to factors such as the size of the bubble diameter, the distance between bubble points, and the width of the kiln. Generally, one bubble point is set for every 6~10m2 melting area. The distance between bubble points is 0.4~0.8m. The larger the bubble diameter, the smaller the number of bubble points and the greater the distance between bubble points. In order to prevent excessive damage to the pool wall, the distance between the bubbling point on the edge and the pool wall should not be less than 0.8~1m.
The arrangement of bubble points is related to the number of bubble points and the size of the furnace. Smaller furnaces are mostly arranged in a single row, while large kilns are arranged in staggered double rows. Bubble points are mostly arranged in a straight line, and sometimes they can be arranged according to the shape of the bubble boundary.
②Bubbling method, speed, size and pressure
There are two bubbling modes: low-pressure continuous bubbling and high-pressure pulse bubbling.
The pressure used for low-pressure continuous bubbling and the diameter of the resulting bubbles are smaller than those of high-pressure pulse bubbling, and the bubbling speed is faster. The bubbling speed depends on the stirring intensity of the glass liquid, usually 20~40 bubbles/min.
During high-pressure pulse bubbling, the bubbling speed is slow, 2~15/min, and the bubble diameter is approximately 100~250mm.
The bubbling pressure depends on the viscosity and depth of the glass liquid and the method of gas supply. When the pressure and gas flow are too large, the normal bubble shape turns into a jet shape. In addition to large bubbles, small bubbles will also appear in the glass liquid, which is not conducive to clarification. The bubbling pressure of low-pressure continuous bubbling is 0.03~0.05MPa. When the pressure is less than 0.02MPa, the bubbling operation is difficult to stabilize and is easy to "extinguish". The bubbling pressure of high-pressure pulse bubbling is 0.2~0.4MPa. In order to prevent the glass liquid from flowing back into the bubble nozzle during the interval, a balance pressure of 0.01~0.02MPa needs to be maintained.
Structure and installation of bubble nozzles
Since the temperature of the molten glass at the bottom of the pool increases significantly after bubbling, the flow rate of the molten glass near the nozzle accelerates, especially the immobile layer of molten glass at the bottom of the pool also participates in the flow, thus intensifying the erosion of the refractory materials at the bottom of the pool near the bubbling point. If not handled properly, it will easily cause material leakage and shorten the kiln life. Therefore, the bubbling nozzle should be resistant to high temperatures, corrosion, high strength, and not easily oxidized. Commonly used materials include platinum and platinum-rhodium (for the head of the nozzle), heat-resistant steel, corundum, silicon molybdenum, cermet, etc. The inner diameter of the bubble nozzle is generally 1~3mm, and a number of small holes are usually opened on the nozzle, which not only facilitates the formation of bubbles, but also prevents the glass liquid from flowing back into the bubble nozzle.
The nozzle bricks should be made of No. 41 oxidation method AZS bricks, which are highly resistant to corrosion. Moreover, the two rows of pool bottom bricks in front and behind the nozzle bricks should be 50~100mm higher than other pool bottom bricks. The nozzle bricks should be 50mm higher than the two rows of pool bottom bricks in front and back. ~100mm, forming a stepped shape.
The depth of the bubbling nozzle into the glass liquid is very important for bubbling. If the depth is too deep, the stirring effect of the glass liquid is not strong enough, and the viscosity of the glass is small, and the glass liquid will easily flow back into the nozzle during the bubbling interval; if the depth is too little, the corrosion of the refractory material at the bottom of the pool will be too severe, which will affect the life of the furnace. . The nozzle is generally 200~500mm higher than the bottom of the pool, and 50~100mm higher than the nozzle brick to prevent the glass liquid from flowing too fast, causing erosion of the bubbler nozzle and clogging of the bubbler tube.
Bubble air source
The bubbling air source generally uses purified compressed air. The air from the non-lubricated air compressor is freeze-dried to remove moisture, and then purified by a coarse filter and a fine filter. Because the bubbling nozzle continuously operates in high-temperature glass liquid during the entire kiln cycle, impurities such as water, oil, and dust in the poorly purified air will form scale on the small inner wall of the bubbling nozzle, causing it to become blocked. Air outlet, causing "scaling and clogging". The air supply pressure must be stable, and a backup air source must be available to prevent emergencies such as power outages.
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