After decades of development, the melting capacity of China's glass industry has expanded from a small 150 t/d to today's 1600t/d or even larger super-large tonnage production lines.
Along with the development of the glass industry, the bottom structure of the glass melting furnace has also gradually developed from the early flat bottom structure of the whole furnace to a structure with one step or multiple steps. According to the different types of glass produced, the depth of the furnace pool is different, so that the melting zone of the furnace has the production capacity to melt enough glass liquid within a certain melting area. For the production of certain types of glass melting furnaces, deepening the melting zone pool can reduce the bottom temperature and slow down the erosion rate of the bottom; while the rear end neck, cooling part and other parts do not require too deep a furnace pool depth, so it is necessary to design one or more bottom steps to meet the melting needs and save energy and reduce consumption.
arly float glass melting furnaces were mostly flat-bottomed structures with a pool depth of 1.2m, as shown in the figure below. Float glass melting furnaces before the beginning of 2000 were generally of this structure. The characteristics of this structure are relatively stable production, especially in the cooling section, due to the deep pool depth, the relatively low pool bottom temperature, the thicker pool bottom immovable layer, the homogenization quality of the middle and upper layers of glass liquid, and fewer glass defects such as bubbles and inclusions. The disadvantage is that the pool depth before and after the melting furnace is the same, resulting in a relatively shallow pool depth in the melting zone and a relatively high pool bottom temperature, which is not conducive to melting. The pool depth after the clarification section is deeper, and the reflux of glass liquid is larger, resulting in a higher proportion of glass liquid that is repeatedly heated, and the unit heat consumption of the melting furnace will be higher.
Since the beginning of 2000, with the introduction of some advanced foreign glass melting furnace technologies, especially the glass melting furnace technology of PPG Company in the United States, domestic glass companies and scientific research and design units began to set up step structures on the glass melting furnaces of newly built production lines. At this time, most of them were one-step structures, as shown in the figure below.
The characteristic of this structure is that it can increase the depth of the glass liquid pool in the melting section and reduce the depth of the cooling section pool. The advantage is that the increased depth of the melting section pool can provide better conditions for glass liquid melting, while reducing the depth of the cooling section pool, reducing the reflux of glass liquid and reducing the unit heat consumption of the melting furnace. The disadvantage is that the pool depth of the melting section is the same, and the pool depth before the hot spot cannot be increased too much. In addition, the pool depth at the end of the clarification zone can also be reduced to reduce the reflux of glass liquid because the quality of the glass liquid is better at this time.
After the promotion of the melting furnace step structure, with the continuous advancement of glass melting furnace technology, multi-step structures such as two-step and three-step began to be used.
The characteristic of the multi-step pool bottom structure is that multiple steps can be set in the melting section as needed to increase the pool depth of the glass liquid in the melting section, while reducing the pool depth of the clarification zone and the cooling section. Its advantage is that the pool depth of the melting zone can be increased as needed, providing better melting conditions for the glass liquid, which can effectively reduce the pool bottom temperature and have a good protective effect on the pool bottom. Setting one or more steps in the clarification zone can reduce the depth of the glass liquid in the clarification zone, further reduce the amount of glass liquid reflux, and reduce the unit heat consumption of the melting furnace. The disadvantage is that the number of steps in the melting section is large, resulting in a relatively complex structure of the melting furnace, and at the same time, the glass liquid flow is prone to produce micro defects at the steps, thereby affecting the quality of the glass liquid.
Practice and research results have proved that the use of a stepped bottom structure in a glass melting furnace can effectively limit the amount of glass liquid reflux in the clarification and cooling sections and reduce the amount of repeated heating of the glass liquid. Under specific melting temperature systems and the insertion depth of the neck water bag, the glass melting furnace with steps at the bottom of the melting furnace has a relatively high temperature for the upper layer of the glass liquid, and the melting time of the material particles is greatly shortened. Moreover, as the number of steps increases and the depth of the pool deepens, the melting time of the material particles is significantly reduced. The "immobile zone" of the glass liquid at the bottom of the melting furnace pool becomes smaller, thereby reducing the probability of taking away the bad glass liquid that stays in the "immobile zone" due to the temperature fluctuation of the bottom of the pool, reducing the proportion of inclusions in the glass liquid, and improving the quality of the glass liquid. The flow rate of the middle and upper layers of the multi-step melting furnace is relatively slow, thereby increasing the clarification and homogenization time of the glass liquid in the high temperature zone, improving the quality of the glass liquid, and at the same time significantly reducing the reflux in the neck section, and the heat consumption of the neck reflux is significantly lower than that of the melting furnace with a flat bottom structure, which is conducive to energy saving and consumption reduction.
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