In iron-making enterprises, the ball-type hot blast stove is a blast furnace blast heating device. The core of the technical problem of the ball-type hot blast stove is the ball bed. The ball bed is naturally piled up by equal-diameter refractory balls. Generally, it is divided into upper and lower stages according to the ball diameter and material. There are three main types of refractory balls used as heat medium materials in the high temperature zone of the ball bed, including high alumina refractory balls, silicon refractory balls and magnesium aluminum refractory balls.
1. High aluminum refractory ball
Where the mass fraction of Al2O3 is more than 45%, the refractory material mainly composed of alumina or aluminosilicate is called high alumina refractory . The mineral composition of the product differs depending on the Al2O3 content. As the content of Al2O3 increases, the crystallization phase of mullite and corundum increases, while the glass phase decreases correspondingly, and the fire resistance performance increases. Generally, the high alumina refractory ball has a refractoriness of not less than 1750 to 1790, and the load softening start temperature is not less than 1 400 to 1 530. Al2O3 belongs to amphoteric oxide, so it has better resistance to acid slag, but weaker than siliceous refractory ball. Its resistance to alkaline slag is better, but weaker than that of magnesium-aluminum refractory ball [4]. The higher the Al2O3 content of the article, the lower its thermal stability. During the working process of the ball type hot blast stove, the refractory ball will be affected by the alternating periodic hot and cold at high temperature and the erosion or slag bonding of the alkaline gas dust. The production practice shows that the high-aluminum refractory ball is used in the high temperature zone of the ball bed, and its refractoriness and load softening temperature can meet the requirements, but the thermal stability and slag resistance are insufficient. Therefore, surface cracking and slag bonding often occur, resulting in poor gas permeability of the bed and shortening of the clearing cycle.
2, silicon refractory ball
The siliceous refractory ball is an acidic refractory material. The mass fraction of SiO2 is more than 93% and has the characteristics of polycrystal. The other components are mainly Al2O3, Fe2O3, CaO, MgO and some alkali metal oxides. The refractoriness of the siliceous refractory ball is generally 1710~1750, and the load softening temperature is relatively high, up to 1640~1650; its acid slag corrosion resistance is strong, and the resistance to alkali slag corrosion is very poor. The mineral phase composition of siliceous refractory spheres is mainly tridymite and cristobalite. Quartz, cristobalite and residual quartz change in crystal form at low temperature, and the volume changes greatly, so the thermal stability at low temperature is poor [5] ]. Under the working conditions of the spherical hot blast stove, the silicon refractory ball is used in the high temperature zone of the ball bed. Under the conditions of high temperature and large gradient temperature change, the surface of the sphere is severely cracked, and the resistance to alkaline gas dust erosion is poor, and the slag bonding phenomenon Serious, clearing the ball is more difficult.
3, magnesium-aluminum refractory ball
Magnesium refractory balls generally have a refractoriness of more than 2,000, and the load softening temperature is generally not higher than 1550, and the resistance to alkali slag is strong. Compared with clay bricks, it has poor thermal stability and volume stability, but its thermal conductivity is very strong. Magnesium-aluminum refractory ball is a refractory product containing periclase as the main mineral component and magnesium-aluminum spinel as the main component. In addition to the advantages of magnesium refractory products, it also has the advantages of good thermal stability and high load softening temperature. Compared with ordinary magnesia bricks, the main characteristics of the production process are: the quality of the raw materials is relatively strict, and the purity of the first-grade magnesia, raw clay and bauxite clinker is relatively high; Tight, high bulk density can be obtained, and the thermal stability and sintering performance of the product, as well as the reduction of porosity and the softening temperature of the product, will have a good effect; 5%~10% of Al2O3 is introduced into the ingredients. Afterwards, it is beneficial to the formation of magnesium aluminate spinel, reducing harmful components such as calcium forsterite and magnesium ferrite, thereby improving the thermal stability of the refractory ball, reducing the thermal expansion rate, and increasing the load softening temperature; The periclase and magnesia-alumina spinel in the refractory ball are both hard-to-sinter minerals, so the firing temperature is higher than that of ordinary magnesia bricks. The higher firing temperature can effectively reduce the re-sintering shrinkage of the product, increase the density of the product, and improve the thermal stability and high-temperature structural strength of the product.
It can be seen that the production process of magnesium-aluminum refractory ball is more precise and stricter than ordinary magnesia brick, and its performance is better than ordinary magnesia refractory products, such as high load softening temperature, up to about 1620; thermal stability Well, the number of heat exchanges in 850 water can reach more than 20 times; the slag resistance is good, especially the ability to resist Fe2O3 erosion is greatly improved. The above characteristics indicate that the magnesia-alumina refractory ball is suitable for use on a ball bed with high operating temperature and frequent fluctuations.
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