Discussion on the design of step structure at the bottom of glass melting furnace

In the production of glass melting furnaces, the flame transfers heat to the material in a radiant way. Part or most of the heat absorbed by the material is used to melt glass, while the other part is used to reheat the refluxed glass liquid. In addition to the heat dissipated by the melting furnace and the heat taken away by the exhaust gas, this results in the effective thermal efficiency of the glass melting furnace being only 30%~40%. By calculation, the heat of repeated heating of the refluxed glass liquid accounts for about 10% of the total heat. Therefore, a reasonable pool bottom structure can reduce part of the heat required for repeated heating of the glass liquid, which is very necessary for energy saving and consumption reduction of the melting furnace.

After decades of development of my country's glass industry, the melting capacity of the melting furnace has expanded from a small 150 t/d to today's 1600t/d or even larger super-large tonnage production line.

Along with the development of the glass industry, the bottom structure of the glass melting furnace has also gradually developed from the early full-kiln flat bottom structure to a single step, multiple steps and other structural forms. 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 pool depth in the melting zone can reduce the pool bottom temperature and slow down the erosion rate of the pool bottom; while the rear end of the neck, cooling part and other parts do not require too deep a furnace pool depth, so it is necessary to design one or more pool bottom steps to meet the melting needs and save energy and reduce consumption.

Flat bottom structure of glass melting furnace Early float glass melting furnaces were mostly flat bottom structures, and the pool depth was generally 1.2m, as shown in the figure below. Float glass melting furnaces before the beginning of 2000 generally had this structure. The characteristics of this structure are relatively stable production, especially the cooling part due to the deep pool depth, relatively low pool bottom temperature, thicker pool bottom immovable layer, good 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 glass liquid reflux volume is larger, resulting in a higher proportion of repeatedly heated glass liquid, and the unit heat consumption of the melting furnace will be higher.

The single-step structure of the bottom of the glass melting furnace began in the early 2000s. With the introduction of some advanced foreign glass melting furnace technologies, especially the introduction of the glass melting furnace technology of the American PPG company, domestic glass companies and scientific research and design units began to set up step structures on the glass melting furnaces of new production lines. At this time, it is mostly a step structure, 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 depth of the melting section pool is increased, which can provide better conditions for glass liquid melting, while reducing the depth of the cooling section pool, reducing the reflux volume 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 volume of glass liquid because the quality of the glass liquid is better at this time.

After the promotion of the step structure of the melting furnace, 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 reflux of the glass liquid, 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 the glass liquid flow is prone to produce micro defects at the steps, thereby affecting the quality of the glass liquid.

The summary of practice and research results proves that the use of a stepped pool bottom structure in a glass melting furnace can effectively limit the reflux of the glass liquid in the clarification section and the cooling section, and reduce the amount of repeated heating of the glass liquid. Under the conditions of a specific melting temperature system 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 of the upper 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 range of the "immobile zone" of the glass liquid at the bottom of the melting furnace pool becomes smaller, thereby reducing the probability of carrying away the bad glass liquid that stays in the "immobile zone" due to the temperature fluctuation at 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.