Reasons for severe corrosion of fused AZS bricks in glass melting furnaces and methods to extend service life

01. Erosion mechanism

Chemical action is more complex and severe for fused AZS bricks, which can be divided into four aspects:

1. Precipitation of glass phase

The fused AZS bricks on the pool wall are subjected to the action of high-temperature glass liquid for a long time (>1500℃). On the one hand, the glass phase in the brick will gradually melt and precipitate (the lowest precipitation temperature is about 1150℃); on the other hand, the alkaline glass liquid containing Na2O will invade the brick along the pores and cracks of the brick body, diffuse and penetrate each other with the precipitated glass phase, thereby reducing the viscosity of the precipitated glass liquid and increasing its fluidity, thereby intensifying the corrosion behavior and extending it in depth.

2. Damage to the skeleton

As the erosion of the glass liquid intensifies in depth, the skeleton minerals that constitute the brick body are gradually infiltrated and surrounded by the glass liquid containing Na2O, and the skeleton begins to be eroded. First, the dissolved mullite decomposes into α-Al2O3 and SiO2, which in turn promotes the conversion of α-Al2O3 into β-Al2O3. As the temperature rises, β-Al2O3 is completely dissolved in the glass liquid, and the baddeleyite and corundum lattices are also destroyed, and then broken, disintegrated, and partially melted. β-Al2O3 gradually dissolves in the glass at high temperature, and very little is retained. As the glass continues to diffuse and penetrate, the baddeleyite microcrystals become free, part of which is taken away with the glass liquid and may become glass stones, and part of which is retained. Although baddeleyite can be dissolved in glass, its solubility is very small. As the temperature fluctuates, ZrO2 quickly crystallizes from the glass liquid to form skeleton-like or beaded baddeleyite crystals.

3. Crystallization of new minerals

Since the skeleton minerals of the brick body are partially melted in the glass liquid, the composition of the original glass liquid is changed. Therefore, when the ratio of SiO2-Al2O3-Na2O in the glass liquid is close to the theoretical composition of nepheline, a large amount of nepheline crystals will precipitate.

Al2O3+2SiO2+Na2O→2NaAlSiO4 (nepheline)

4. Nepheline damage

Since the density of nepheline is less than that of the brick body, the precipitation of nepheline crystals is accompanied by a large volume expansion, making the brick body structure loose. Although the melting of part of the crystalline phase in the brick at this time will increase the viscosity of the glass liquid and have a certain bonding and protective effect on the loose structure, it still cannot completely block the airflow, material and glass liquid scouring and gravity in the kiln, and cracks and peels into the glass liquid to form glass stones. The wound surface after peeling continues to be eroded and scour by the glass liquid and continues to peel. The result will inevitably lead to the erosion and disintegration of the fused zirconium corundum brick.

02. Extend the service life in the glass electric melting furnace

Picture

The glass tank furnace melts horizontally, and the material liquid level moves horizontally. In addition to the flow hole, the three-phase interface is severely eroded, as shown in Figure 1. The glass electric melting furnace is vertically melted, and most of them are cold top melting. The glass liquid surface is covered by a layer of raw material, and there are fewer three-phase interfaces. Because it is vertically melted, the erosion of the pool wall bricks is no longer concentrated on the three-phase interface, but the overall erosion, so the weak link of the fused corundum brick is the breakthrough of erosion.

For the erosion mechanism of fused AZS bricks, the content of Na2O in the raw material composition of fused AZS bricks must be strictly controlled first. The national standard requires that the content of Na2O in 33#WS is less than 1.45%, and the content of Na2O in 41#WS is less than 1.3%. The standard of our company's electric melting furnace requires that the content of Na2O in 33WS is less than 1.35%, and the content of Na2O in 41#WS is less than 1.05%.

For the erosion parts 2, the ratio of riser to brick material must reach 1.5:1. Through the pressure of riser material, the residual pores in the brick material are effectively reduced, the anti-erosion ability of the brick material at the injection port is enhanced, and no obvious shrinkage cavities are required at the injection port.

For the erosion parts 3, the brick joints are strictly inspected during the assembly process of fused AZS bricks, and the thickness is required to be less than 0.3mm. The expansion difference of each part is strictly controlled during the kiln baking process to ensure the tightness of the brick joints during the process, thereby reducing the entry of gas, preventing the formation of three-phase interface at the brick joints, and reducing the erosion of the parts in Figure 3.

For the erosion 4, the width of the brick is required to be less than 400mm during the design process. Too wide will cause the shrinkage cavities to remain inside the brick material and the internal looseness; the ratio of riser to brick material must reach 1.5:1, and the internal quality of the brick material is improved through pressure and exhaust gas rate; the insulation is reduced in the later stage of kiln operation, and the erosion rate is reduced by reducing the temperature of the brick material.