What material refractory bricks are used in each part of the glass kiln? After reading it, you will be clear!
[Summary description] A glass furnace is a thermal equipment for melting glass composed of refractory materials. When choosing refractory materials for glass kilns, the type of kiln, the location of use, the damage mechanism, the variety of fused glass and the type of pigment should be considered. Refractories for glass kilns should first be able to resist the erosion of glass melts and gaseous agents, and should have a sufficiently high load softening temperature and thermal stability.
A glass furnace is a thermal equipment for melting glass composed of refractory materials. When choosing refractory materials for glass kilns, the type of kiln, the location of use, the damage mechanism, the variety of fused glass and the type of pigment should be considered. Refractories for glass kilns should first be able to resist the erosion of glass melts and gaseous agents, and should have a sufficiently high load softening temperature and thermal stability.
It is usually hoped that the refractories in various parts of the kiln will not experience local early corrosion damage to ensure a long enough service life of the entire kiln. However, due to the different mechanical, physical and chemical conditions of each part of the glass kiln, this requires that the performance of the refractory used should be adapted to it, and at the same time, it is required to not adversely affect other types of adjacent bricks.
The following analyzes the considerations for choosing refractory bricks for glass kilns from various aspects.
1. Clay bricks
Clay products are acidic refractory products, and their acidity increases with the increase of SiO2 content. It has a certain corrosion resistance to acidity, but less resistance to alkali erosion. There are different varieties of clay bricks, such as low-porosity clay bricks, ultra-low-porosity clay bricks, low creep, low-porosity, low-iron clay bricks, etc. Therefore, clay products should be used as refractory materials for acidic kilns. Large clay bricks for glass kilns are clay refractory bricks with a single weight of not less than 50kg for building glass kilns.
The use conditions of clay bricks are different due to different molding methods and the different aggregates and binders of clay bricks. According to these characteristics, different clay bricks can be used in different parts of the pool furnace due to different erosion conditions. The lower furnace bar and the lower lattice brick of the regenerator are less eroded by the dust and volatiles of the compounding material, and the temperature is also lower, and the load is heavy, so this brick requires high mechanical strength. Therefore, the combination in the brick can contain an appropriate amount of SiO2 and Fe2O3, but the clay brick used in the high temperature part mainly requires high fire resistance and less impurities in the combination.
Table 1 Technical indicators of large clay refractory bricks for glass kilns
2. Silicon brick
Silicon refractory is an acidic material. It has strong ability to resist acid slag or solution erosion, and has good high temperature performance: for example, the refractory is 1690-1730 ° C, and the softening temperature under load is 1640-1680 ° C. The volume expansion rate is large, and the total volume expansion produced when the temperature is 1450 ° C is about 1450 ° C, which is beneficial to ensure the structural strength and air tightness of masonry. Therefore, silica brick is the main material of glass kilns and is widely used in large arches, breastwalls, regenerator roofs and other parts.
Table 5 Physicochemical indicators of silicon bricks for glass kilns
Matters needing attention when baking silicon bricks in the kiln: When the silicon bricks are at 200-300 ° C and 573 ° C, the volume will suddenly expand due to the crystal transformation, so the baking is to raise the temperature below 600 ° C not too fast, and when cooling to below 600 ° C. Avoid drastic temperature changes and avoid contact with alkaline substances as much as possible.
3. Fused zirconium corundum brick
ZA series oxidized fused zirconium corundum products are made of high-quality purified raw materials, using a special electric arc furnace, and through a long arc melting and oxidation process. This electric fusion casting process has almost no carbon pollution from electrodes.
Due to the use of this casting process and the use of high-purity raw materials, ZA series oxidation fused zirconium corundum products have special and high resistance to glass liquid erosion, and the pollution to glass is also minimal.
AZS-33 products are particularly superior in preventing contamination of liquid glass. It has a small tendency to cause stones, bubbles and basic glass phases to precipitate in glass. It is suitable for the superstructure of melting pools, pool wall tiles and pavement tiles of working pools, material paths, etc.
AZS-36 is a standard oxidized fused zirconium corundum brick, which has the characteristics of high resistance to glass liquid erosion and low stain, and the performance of these two aspects is balanced. It is suitable for the parts of the glass melting kiln that are directly connected to the glass liquid, such as melting pool wall bricks, pavement bricks, feeding ports, etc.
AZS-41 is the highest grade oxidized fused zirconium corundum brick, which has the highest corrosion resistance to liquid glass and outstanding low pollution to liquid glass. It is suitable for parts of glass kilns that require particularly high corrosion resistance, such as all-electric melting kilns, liquid flow holes, kiln sills, bubbling turns, bricks at the corners of feeding ports, etc.
The properties and performance indicators of fused zirconium corundum bricks - the oblique zircon phase can withstand the erosion of liquid glass, and the glass phase can buffer the stress caused by the change of volume, which can keep the product gas-impermeable structure, but the quantity is too large, and the lower the seepage temperature, the worse the quality of the brick. The seepage of the glass phase will destroy the structure of the brick and affect the life. At the same time, bubbles will be released, and stones that are insoluble in the glass may be produced, which will seriously affect the quality of the glass. The seepage temperature is usually expressed by the foaming index.
4. Fused corundum brick
The main crystal phase of corundum brick is corundum, which has excellent properties, such as high melting point, high hardness, and is a neutral mineral, so the product has high hardness, anti-initialization, wear resistance, and anti-erosion at the same time. Melting and casting α-Al2O3 bricks are mainly tight and strong fine-grained structure entities composed of α-type corundum. Mainly used in glass kilns. It is suitable for melting borosilicate glass and opalescent glass. However, its high temperature corrosion resistance is poor. When it is at a high temperature of 1600 ° C, the corrosion resistance of liquid glass will decrease rapidly, so some borosilicate glass kilns tend to use fused quartz bricks. Melting and casting α-Al2O3 brick products have a bulk density of 3.15-3.30g/cm3, contain a small amount of glass phase (about 2%), fill the gap between crystals, and have high purity. Because it does not pollute the liquid glass, and has good corrosion resistance of liquid glass below 1350 ° C and excellent high temperature wear resistance, it is an ideal refractory for the clarification part, cooling part, working pool and other parts of the glass melting kiln.
The white product composed of β-Al2O3 coarse and bright crystals contains 92% -95% Al2O3, only a glass phase below 1%, and the structural strength of the product is low due to the porosity of the lattice. The Na2O contained in β-Al2O3 reacts with SiO2 to produce a large volume contraction, which may cause cracks and damage to the brick. Therefore, it is only suitable for the superstructure containing SiO2 fly dust in principle, such as the superstructure of the working pool, the parapet near the combustion port, the small furnace mouth and the hanging wall, etc. Because this brick does not interact with volatile alkali metal oxides, there is no need to worry about molten matter dripping from the brick surface contaminating the glass.
5. Magnesium refractory
(1) Magnesium material for glass kiln regenerator
Generally, high-grade magnesia bricks (w (MgO) > 97%) are used on the uppermost layer of the lattice body of the regenerator; medium-grade magnesia bricks (w (MgO) are about 95% to 96%) are used on the upper layer; directly bonded magnesia-chrome bricks are used in the middle layer; low-porosity clay bricks are used in the lower layer. The important properties of the lattice body are corrosion resistance and creep resistance. To improve the creep resistance, high-purity, low-iron, low-porosity and large-grain raw materials need to be used, and fully sintered at high temperature.
(2) Configuration of regenerator when alternative fuels are used
After the use of petroleum coke, the refractory material of the glass kiln regenerator is prone to erosion, of which the 95 magnesia brick is the most seriously damaged. A large amount of SiO2 and CaO invaded the brick body, destroying the original MgO-M2S bonding, and forming a continuous CMS-M2S low-melting bonding phase. On the other hand, petroleum coke is difficult to ignite and burns slowly. After using petroleum coke, the unburned components enter the regenerator and continue to burn in the regenerator, increasing the temperature of the regenerator. In this way, under the action of high temperature and erosion, the lattice softens and subsequently collapses. Due to the damage, the glass company expanded the amount of 97 magnesia bricks and directly bonded magnesia-chromium bricks in the regenerator, replaced the 95 magnesia bricks with poor performance, extended the life of the regenerator from 1 year to 3 years, and achieved preliminary success in the experiment using petroleum coke. In order to meet the needs of using alternative fuels, it is also necessary to develop high-purity magnesia-aluminum spinel materials with good corrosion resistance and adaptability to changes in the oxidation-reduction atmosphere. High-purity magnesia-aluminum spinel bricks have good creep resistance and alkali vapor erosion resistance, and can also be used in full-oxygen combustion glass furnaces.
6. Other refractory materials
Zircon stone is decomposed in large quantities by heating at 1680 ° C, and zircon stone products also have good corrosion resistance. Zircon stone bricks have excellent properties such as high temperature resistance, good thermal shock stability and glass liquid erosion resistance. Aluminum zirconium-silicon (AZS) molten bricks and fired bricks have good resistance to glass liquid erosion, and can be used in the wall and superstructure of the glass melting tank kiln.
7. Thermal insulation refractory
In order to save energy, glass kilns are increasingly equipped with thermal insulation structures. These thermal insulation materials such as clay thermal insulation refractory bricks, siliceous ones such as refractory bricks, diatomite bricks and thermal insulation ramming materials, etc.