Introduction of glass furnace & selection of refractory products

For large float glass lines,the glass furnace is usually composed of L-shaped backwall (usually using silica bricks), melting end (the area in direct contact with the molten glass should use AZS bricks, and the crown should use silica bricks), the neck of furnace (usually using silica bricks), the cooling end includes the auriculate bath(corundum material is usually used for the place in direct contact with themolten glass, and silica brick or corundum is used for the place not in direct contact with the molten glass ), annealing furnace, regenerator (composed of high purity magnesia bricks, clay bricks, direct combination of magnesia-chrome bricks) and other parts.

1,Furnace Crown

The crown of the melting?end?and cooling end?of the glass furnace (including the arch angle),these parts are at a working temperature of 1600°C. The refractory products used in these parts must not only be able to withstand high temperature and load, but also withstand the erosion of alkali steam and batch.Therefore, the refractory products used as the crown must have extremely high refractoriness, high load softening temperature and good creep resistance, and the thermal conductivity is small.The refractory products?at high temperature should not contaminate the molten glass, and the bulk density should be small, and the high temperature strength?should be good.

The high-purity silica bricks with high-quality just have the above characteristics:

a、The high load temperature is close to its refractoriness

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

c、Since the main component is SiO2, the rate above 96%, which is the same as the main element composition of glass, so the erosion under high temperature conditions will basically not contaminate the molten glass;

d、Cheap

Thus, for those crowns from various glass furnaces, the high-purity with high-quality silica bricks have become the first choice.

The chemical erosion caused by the high-temperature chemical reaction between?batch?waste materials and alkali vapor and refractory products, as well as the crystal transformation and structural compactness changes due to phase migration and temperature are the main reasons for the damage of the crown bricks.

The research indicates?that high-purity silica bricks with high-quality?for crowns,the alteration process under the high temperature of the furnace is basically caused by the migration and phase transformation of impurities, and the chemical erosion and melting effects can basically be ignored.The function of phase change and self-purification makes the furnace operation area gradually change its performance, and its high temperature performance is improved.

2,Side Wall

1）Parts in contact with molten glass

The part of the melting end?and the cooling end?that is in direct contact with the molten glass is subject to high temperature, chemical erosion caused by the molten glass and mechanical and physical erosion caused by the flow. The most important condition for this part of the refractory?product?is to have good corrosion resistance to the molten glass. At the same time, the molten glass cannot be contaminated.

The outside of glass furnaces is generally built with AZS bricks, α-β corundum bricks, and β corundum bricks. AZS bricks have excellent performance in high temperature and resistance to glass liquid, because it obtains the eutectic of baddeleyite and α-Al2O3, but it is impossible for sintered refractory products, so AZS be used as the side wall bricks are very suitable.

The main crystal phase of α-β corundum bricks and β corundum bricks is corundum, and the glass phase content is only 1%-2%, which has good corrosion resistance. Compared with the performance of AZS?bricks, since they do not contain ZrO2 crystals , the viscosity of the reaction layer is small, and it is not stable at high temperature, so the diffusion speed between the surface of the brick and the glass liquid is relatively large, and the furnace?lining is damaged quickly.However, when the operating temperature of the furnace?is lower than 1350 ° C, the corrosion resistance of a-β corundum bricks and β corundum bricks is better than that of AZS?bricks. Therefore, a-β corundum bricks and β corundum bricks are ideal refractory materials for cooling end?etc?when the temperature is lower than 1350 °C.

2）Parts not in direct contact with molten glass

The parts?of the side?wall of the melting end?and the cooling end?that is not in direct contact with the molten glass (also called the breast wall)?are mainly subjected to the erosion of alkali vapor and batch materials.According to different designs, some are made of corundum, and some are made of silicon bricks,both of these two materials can meet the requirements.

3,?Regenerator

1）The crown and side wall of Regenerator

The inner surface of the crown and side wall of the regenerator?are eroded by high temperature, dust and alkali vapor, and the degree of erosion gradually weakens from top to bottom.?The selection of refractory products be determined according to the temperature and erosion degree that the upper, middle and lower sections of the side wall and the crown of the glass furnace can withstand. 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 furnace.

In recent years, depending on the different designs, the upper part of the side wall generally adopts ordinary magnesia-chrome bricks and direct combination magnesia-chrome bricks, and alkaline bricks such as magnesia-alumina bricks have also all achieved good results.

2) Checker

Because the whole brick body of the checker is under the action of high temperature load, dust and alkali vapor, the degree of erosion will be more severe than that of the side wall, so the service conditions are more harsh. The blockage and collapse of the checker is often one of the important reason for the shutdown and cold repair of the glass furnace. Therefore, the checker refractory products be required to have high physical strength, low creep rate, strong defence ability against alkali erosion due to changes in furnace temperature and atmosphere, no dust adhesion, and slow damage speed.

On the crown of the checker: the temperature is the highest, which can reach 1400-1540 ° C, and it is also most severely eroded by alkali steam and dust. Generally, fuse-rebonded magnesia bricks be used. Since the silicate in the fuse-rebonded magnesia bricks is relatively small, the periclase crystals have grown up, and a direct bond has been formed between the periclase crystals, which delays and stops the gradual increase speed of the periclase crystals under the action of alkali steam so that not easy to crack and pulverize bricks.

The upper part of the checker: the temperature here can reach 1100-1430 ℃, and it is generally enough to use 95# rebonded magnesia bricks.

The middle part of the checker: the temperature is 800-1100 ° C. In this range, the alkali metal sulfate condenses, and the magnesium and calcium lattice body is severely eroded by SO3 and Na2O and undergoes a chemical reaction, which will cause a large brick body to expand, the damage is serious. So this part is not suitable for using magnesia bricks, but magnesia-alumina spinel bricks or direct combination magnesia-chrome bricks or magnesia-zirconium bricks and magnesia olivine bricks should be used.

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

THE END