Introduction to glass kilns and selection of refractory materials

For large float glass lines, the structure of glass kilns is usually composed of L-shaped hanging walls (usually using silica bricks), melting parts (the area in direct contact with the glass liquid should use electric fused bricks, and the area near the top should use silica bricks or electric fused bricks), necks (usually using silica bricks), cooling parts including ear pools (the area in direct contact with the glass liquid usually uses corundum materials, and the area not in direct contact with the glass liquid uses silica bricks or corundum), annealing kilns, heat storage chambers (made of high-alumina bricks, clay bricks, and directly bonded magnesia-chrome bricks) and other parts.

01. Arch top

The arch top (including arch angle) of the melting part and cooling part of the glass melting furnace is at a working temperature of 1600℃. The refractory materials used in these parts must be able to withstand high temperature, load and scouring of alkali vapor and batch materials. Therefore, the refractory materials used as the top must have extremely high refractoriness, high load softening temperature and good creep resistance, and low thermal conductivity. The refractory materials at high temperature cannot pollute the glass liquid. The bulk density of the material must also be small and the high temperature strength is good.

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

a. The load temperature is close to its refractoriness;

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

c. Since the main component SiO2, the content is >96%, which is the same as the main element composition of glass, the corrosive materials under high temperature conditions will basically not pollute the glass liquid;

d. Cheap price.

Therefore, in various glass bridge tops, high-purity and high-quality silica bricks have become the first choice in the production process of various glasses.

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

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

02. Pool wall

1) Parts in contact with glass liquid

The parts of the pool wall of the melting part and the cooling part that are in direct contact with the glass liquid are subject to high temperature, chemical erosion caused by the glass liquid and mechanical and physical scouring caused by the flow. The most important condition for the refractory material in this part is to have good resistance to glass liquid erosion and not to pollute the glass liquid.

Domestic glass kilns are generally built with fused zirconium corundum bricks, α-β corundum bricks, and β corundum bricks. Fused zirconium corundum bricks have excellent high temperature and glass liquid resistance. This is because they have obtained the eutectic of baddeleyite and α-Al2O3 with very good corrosion resistance that sintered refractory materials cannot obtain, so it is very suitable as a pool wall brick for the melting part of the glass kiln.

The main crystal phase of α-β corundum bricks and β corundum bricks is corundum, and the glass phase content is only 1%-2%. They have good corrosion resistance. Compared with the performance of fused zirconium corundum bricks, because they do not contain ZrO2 crystals, their reaction layer viscosity is small and not very stable at high temperatures, so the diffusion rate between the surface of the brick and the glass liquid is relatively large, and the kiln lining is damaged faster. However, when the operating temperature of the kiln is lower than 1350℃, the corrosion resistance of a-β corundum bricks and β corundum bricks 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℃.

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

The part of the melting and cooling pool wall that is not in direct contact with the glass liquid (also called the breast wall) is mainly affected by the scouring of alkali vapor and batch materials. Depending on the design, some use corundum materials, and some use silica bricks. Both materials can meet the requirements. Therefore, hook bricks and straight bricks are often used in this part.

1) Regenerator arch and side walls

The inner surface of the regenerator arch and side walls is eroded by high temperature, dust, and alkali vapor. From top to bottom, the degree of erosion gradually decreases. The selection of refractory materials is determined according to the temperature and erosion degree of the top, middle and lower sections of the regenerator of the glass kiln. 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; general clay bricks and low-porosity clay bricks are generally used for the lower part of the kiln. According to different designs, in recent years, the upper part of the side wall generally uses ordinary magnesia-chrome bricks and directly bonded magnesia-chrome bricks, and magnesia-alumina bricks and other alkaline bricks have also achieved good results.

2) Lattice body

Because the entire brick body is under high temperature load, dust and alkali vapor, the erosion degree of the lattice body will be more serious than that of the lattice body and the side wall, so the use conditions are more stringent. The blockage and collapse of the lattice body are often one of the important reasons for the shutdown and cold repair of the glass kiln. Therefore, the refractory material of the lattice body is required to have high physical strength, low creep rate, strong defense against alkali erosion caused by changes in kiln temperature and atmosphere, no dust adhesion, and slow damage.

At the top of the lattice body: the temperature is the highest, which can reach 1400-1540℃, and the erosion by alkali vapor and dust is also the most serious. Generally, electric melting and combined magnesia bricks are used. Since there are relatively few silicates in the fused rebonded magnesium brick, the periclase crystals have grown up, and the periclase has formed a direct bond, which slows down and stops the rate at which the periclase crystals gradually grow under the action of alkali vapor, and it is not easy for the brick to crack or pulverize.

Upper part of the lattice: The temperature here can reach 1100-1430℃, and 95# rebonded magnesium bricks are generally used.

Middle part of the lattice: The temperature is 800-1100℃. In the range of 800-1100℃, alkali metal sulfates condense, and magnesium and calcium lattices are severely eroded by SO3 and Na2O and chemical reactions occur, which will cause large brick expansion and serious damage. Therefore, this part is not suitable for the use of magnesium bricks, but magnesium-aluminum spinel bricks or directly bonded magnesium-chrome bricks or magnesium-zirconium bricks and forsterite bricks should be used.

The lower part of the grid body: This section has low operating temperature, heavy load, and little alkali erosion, but it is close to the flue and directly affected by cold air. The required material should be able to withstand rapid cooling and heating, and the price should be low. Therefore, low-porosity clay bricks with relatively low prices are generally used.