Introduction to glass kiln and selection of refractory materials

Introduction to glass kiln and selection of refractory materials

For large float lines, the glass furnace usually consists of an L-shaped hanging wall (usually using silica bricks), a melting section (the area in direct contact with the glass liquid uses electric fused bricks, and the top part uses silica bricks or electric fused bricks),clamping neck (silica bricks are usually used), cooling section including ear pool (corundum material is usually used in places that are in direct contact with the glass liquid, and silica bricks or corundum are used in places that are not in direct contact with the glass liquid), annealing kiln, the regenerator (composed of high alumina bricks, clay bricks, direct bonded magnesia chromium bricks) and other parts.

1. Crown

The roofs (including arch angles) of the melting and cooling parts of the glass melting furnace are at a working temperature of 1600°C. The refractory materials used in these parts must be able to withstand high temperatures and loads as well as alkali vapor and batch materials. Therefore, the refractory material used as the top must have high refractoriness, high load softening temperature and good creep resistance, and have a small thermal conductivity. The refractory material at high temperature cannot pollute the glass liquid. The bulk density of the material It should also be small and have good high-temperature strength and other characteristics.

High-performance high-purity silica bricks have the above characteristics:

a. The load temperature is high and close to its refractoriness;

b. Good stability under high temperature and high compressive strength;

c. Since the main component SiO2, with a content of >96%, is the same as the main element of glass, corrosion products under high temperature conditions will basically not contaminate the glass liquid;

d. Cheap price.

Therefore, high-purity silica bricks have become an ideal product in the production process of various glass bridges.

Chemical erosion caused by the high-temperature chemical reaction of waste materials and alkali vapor with refractory materials, as well as crystal transformation and structural density changes due to phase migration and temperature are the main reasons for the damage of the roof bricks.

The research results show that the alteration process of glass kiln silica bricks used in the roof under the action of high temperature in the kiln is basically caused by impurity migration and impurity phase change, and chemical erosion and melting can basically be ignored. The effects of phase change and self-purification gradually change the performance of the kiln operating zone, and its high-temperature performance is improved.

2. Pool wall

1) Parts in contact with glass liquid

The parts of the melting part and the cooling part where the pool wall is in direct contact with the molten glass are subject to high temperatures, chemical erosion caused by the molten glass, and mechanical and physical erosion caused by the flow. The main condition for the refractory material in this part is to have good resistance to the erosion of the molten glass. At the same time, Do not contaminate the glass liquid.

Fused zirconium corundum bricks, α-β corundum bricks, and β corundum bricks are commonly used outside domestic glass kilns. Fused zirconium corundum brick has excellent high temperature and resistance to glass liquid. This is because it has excellent corrosion resistance that is impossible to obtain with sintered refractory materials. It is a eutectic of baddeleyite and α-Al2O3, so it is used as a glass kiln. Pool wall tiles in the furnace melting section are very suitable.

The main crystal phase of α-β corundum bricks and β-corundum bricks is corundum, with a glass phase content of only 1%-2%, which has good corrosion resistance. Compared with the performance of fused zirconium corundum bricks, it does not contain ZrO2 crystals. , the viscosity of the reaction layer is small and unstable at high temperatures, so the gap between the surface of the brick and the glass liquid

The diffusion speed is relatively large, and the kiln lining is damaged quickly. However, when the operating temperature of the kiln is lower than 1350°C, the corrosion resistance of a-β corundum bricks and β-corundum bricks

The performance is better than that of fused zirconium corundum bricks. Therefore, a-β corundum bricks and β-corundum bricks are ideal refractory materials for cooling parts and other parts when the temperature is lower than 1350°C.

2) Parts that are not in direct contact with the glass liquid

 

The part of the melting part and cooling part wall that is not in direct contact with the glass liquid (also called the parapet). This area is mainly affected by the erosion of alkali steam and batch materials. Depending on the design, some use corundum material, and some use silicon. Brick, these two materials can meet the requirements. Therefore, hook bricks and straight bricks are often used in this location.



3. Regenerator

1) Regenerator vents and side walls

The inner surfaces of the regenerator and side walls are corroded by high temperature, dust, and alkali vapor. From top to bottom, the degree of erosion gradually weakens. The selection of refractory materials is based on the top, middle, and lower sections of the glass kiln regenerator, side walls, and side walls. It is determined by the temperature and degree of erosion it endures. Silica bricks are generally used for the top and side walls, and low porosity clay bricks and high alumina bricks are generally recommended for the middle side walls. Ordinary clay bricks and low porosity clay bricks are generally used for the lower part of the kiln. Depending on the design, in recent years, ordinary magnesia-chrome bricks and directly bonded magnesia-chrome bricks, magnesia-alumina bricks and other alkaline bricks have been used in the upper part of the side walls, and have also achieved good results.

2) Grid body

Because all the bricks are under high temperature load, the grid body will be corroded more severely than the crown and side walls under the action of dust and alkali vapor, so the usage conditions are more stringent. The blockage and collapse of the lattice body are often one of the important reasons for the shutdown of the glass kiln for cold repairs. Therefore, the grid refractory materials are required to have high physical strength, low creep rate, strong defense ability against alkali erosion due to changes in kiln temperature and atmosphere, no dust adhesion, and slow damage rate.

At the top of the lattice body: the temperature is high, reaching 1400-1540°C, and it is also severely corroded by alkali steam and dust. Generally, electrofused magnesia bricks are used. Since there are relatively few silicates in the electrofused rebonded magnesia bricks, the periclase crystals have grown and direct bonds have been formed between the periclase bricks.

Combined, it delays and stops the gradual growth rate of periclase crystals under the action of alkali vapor, making it difficult for bricks to crack and pulverize.

The upper part of the grid body: the temperature here can reach 1100-1430°C. Generally, 95# combined with magnesia bricks will suffice.

The middle part of the lattice body: the temperature is 800-1100°C. In the range of 800-1100°C, alkali metal sulfates condense. The magnesium and calcium lattice bodies are severely corroded by SO3 and Na2O and undergo chemical reactions, which will lead to larger bricks. The body will expand and cause serious damage, so magnesia bricks are not suitable for this part. Instead, magnesia-alumina spinel bricks or magnesia-chrome bricks or magnesia-zirconium bricks and forsterite bricks should be directly combined.

Lower part of the lattice body: This section has low operating temperature, heavy load, and is less susceptible to alkali erosion. However, it is relatively close to the flue and is directly affected by cold air. The required material should be able to withstand rapid cooling and rapid heating, and it should be chosen at a low price. Therefore, low-porous clay bricks, which are relatively cheap, are generally used.

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