Refractory for Blast Furnace
Refractory industry is an important basic industry serving high-temperature technology, which is particularly closely related to the iron and steel industry. The new development of high temperature industry, especially steel smelting technology, has promoted the technological progress of refractory industry. The technical progress of refractory industry ensures the implementation of new technology in high temperature industry. In the iron and steel industry, the stable production, high yield and long life of various kilns are inseparable from refractories. Due to different uses and service conditions, various kilns have different requirements for the refractories constituting their main body, and different types of refractories also show different basic characteristics due to differences in chemical composition, microstructure and production technology. Therefore, it is necessary to understand the basic properties of refractories for industrial kilns. On this basis, this paper focuses on the refractory materials for blast furnace and hot blast stove.
1. Refractory for blast furnace body
Blast furnace is the main equipment of ironmaking. It has the advantages of large output, high productivity and low cost, which can not be compared with other ironmaking methods.
With the progress of iron and steel industry all over the world, blast furnace is developing towards large-scale, high efficiency and long life. New smelting technologies such as oxygen enriched coal injection, high air temperature operation and high-pressure furnace top are gradually adopted. The working conditions of blast furnace lining have changed greatly, and its service life is reduced greatly, generally only 5 ~ 6 years. In particular, the service life of the lower part of the blast furnace shaft, waist and Bosh is shorter. In order to adapt to this development, the refractories used in blast furnace have also changed greatly. New long-life and high-efficiency refractories have been gradually applied, and the service life of blast furnace has been gradually improved.
According to the operating conditions and corrosion characteristics of blast furnace lining, the refractory is required to have:
1). Good high temperature performance, good thermal stability under long-term high temperature.
2). The strength at room temperature and high temperature shall be high and the wear resistance shall be good.
3). High density, good thermal conductivity, low apparent porosity and small shrinkage at high temperature.
4). It can resist the severe scouring and erosion of molten iron, slag, blast furnace gas and furnace dust under high temperature and high pressure.
5). The overall dimension of refractory brick is accurate, which can ensure that the brick joint meets the specified requirements.
At present, there are many kinds of refractories for blast furnace. Clay bricks or high alumina bricks with excellent performance are generally used in the middle and upper part of the furnace body, while carbonaceous products, silicon carbide bricks, mullite bricks, corundum bricks and other special refractories are used in the lower part of the furnace body, waist and Bosh, especially the recently developed silicon carbide bricks, which have been successfully used in blast furnace. At the same time, other amorphous refractories have also been widely used.
2. Refractory for throat and roof
The furnace throat is mainly used to protect the furnace lining and distribute reasonably. When the furnace throat works normally, the temperature is 400 ~ 500 ℃, which is mainly affected by the direct impact and friction of furnace charge, but the scouring of gas flow is relatively light. Therefore, water-cooled or non water-cooled steel bricks (steel castings) are generally used for the furnace throat. Castables are filled between the water-cooled steel bricks and the furnace shell. During the installation of anhydrous cold steel bricks, castables shall be used in cooperation with the construction. The furnace top, that is, the gas seal cover, generally adopts metal anchor and wear-resistant fire-resistant spraying coating.
3. Refractory for furnace body
The furnace body is an important part of the blast furnace, which plays the role of heating, reducing and slagging. From beginning to end, it bears the scouring of gas flow and the impact of materials. However, the temperature in the upper and middle parts of the furnace body is low (400 ~ 800 ℃), and there is no harm of slag formation and slag corrosion. This part is mainly damaged by furnace charge impact, wear or thermal impact of furnace dust rise (up to 50 ℃ / min), or invasion of alkali, zinc, etc. and carbon deposition. Therefore, high-quality clay bricks and high alumina bricks with low porosity are mainly used in this part. Especially when the variety and quality of refractory products are increased, the service life of blast furnace lining is greatly prolonged.
However, with the harsh operating conditions of large and medium-sized blast furnaces and the establishment of the system of greatly prolonging the service life of blast furnaces, refractory materials with excellent spalling resistance and wear resistance are required to be used in this part. Therefore, phosphate bonded clay bricks are also used in the upper part of the furnace body, and sillimanite refractory bricks and high alumina refractory bricks with excellent spalling resistance are also used in the upper and middle parts.
The temperature at the lower part of the furnace body is relatively high. This part of the area has a lot of heat exchange, with the formation of a large number of low melting substances, the friction effect when the hot charge decreases, the scouring effect of dust and the erosion effect of alkali metal vapor when the gas rises. Therefore, this part is easily eroded. In severe cases, all coolers are eroded and maintained only by steel shell. Therefore, it is required to use high-quality clay brick, high aluminum brick, corundum brick, aluminum carbon brick or silicon carbide brick with good slag resistance, alkali resistance, high-temperature strength and wear resistance, and graphite brick is also used for the lining of cooling plate structure.
4. Refractory for furnace waist
The waist of the furnace acts as a buffer for the rising gas flow. The furnace charge has been partially reduced and slagged here, the air permeability of the material layer becomes poor, and the slag corrosion is serious. In addition, the temperature at the waist of the furnace is high (1400 ~ 1600 ℃, the high temperature radiation erosion is serious; the alkali erosion is also serious; the hot furnace gas containing dust rises, resulting in strong scouring effect on the furnace lining; the friction of coke and other materials; the rapid change of temperature caused by the passage of hot air. The joint action of the above factors causes serious damage to the refractory at this part. Therefore, slag resistance is generally selected at the furnace waist Refractory with strong erosion resistance and erosion resistance. Graphite brick is also used for the lining of cooling plate structure.
5. Refractory for bosh
The bosh connects the hearth and waist. The temperature in this area is higher, the lower charge temperature is about 1600 ~ 1650 ℃, the gas flow temperature is also high, and a large amount of intermediate slag begins to drip. The heat radiation and slag erosion of this part are very serious. In addition, the chemical action caused by alkali metal intrusion and carbon deposition, and the scouring effect of top-down melt and bottom-up hot air flow are also intensified. Therefore, the position of furnace belly has always been the key link of the shortest service life of blast furnace. Therefore, the materials in this area should have high erosion and erosion resistance, as well as certain thermal shock resistance. Therefore, it is common for modern large and medium-sized blast furnaces to use this kind of refractory in this part. Fired aluminum carbon brick and fired microporous aluminum carbon brick also have good compressive, flexural, erosion and scouring resistance, good thermal conductivity and easy slag hanging. The most important thing is strong thermal shock resistance and convenient price. They are widely used in medium and small blast furnaces in China. Graphite bricks are also used for the lining of cooling plate structure.
6. Refractory for furnace waist
The waist of the furnace acts as a buffer for the rising gas flow. The furnace charge has been partially reduced and slagged here, the air permeability of the material layer becomes poor, and the slag corrosion is serious. In addition, the temperature at the waist of the furnace is high (1400 ~ 1600 ℃, the high temperature radiation erosion is serious; the alkali erosion is also serious; the hot furnace gas containing dust rises, resulting in strong scouring effect on the furnace lining; the friction of coke and other materials; the rapid change of temperature caused by the passage of hot air. The joint action of the above factors causes serious damage to the refractory at this part. Therefore, slag resistance is generally selected at the furnace waist Refractory with strong erosion resistance and erosion resistance. Graphite brick is also used for the lining of cooling plate structure.
7. Refractory for hearth and bottom
The hearth is the place to hold molten iron and slag, and burn coke to produce a large amount of gas, which is the initial condition for blast furnace reduction and manufacturing. The hearth, especially the tuyere area, is the area with the highest temperature in the blast furnace, with a temperature of 1700 ~ 2000 ℃ and a furnace bottom temperature of 1450 ~ 1500 ℃. In addition to the high temperature, the hearth lining is mainly subject to the chemical erosion and scouring of slag iron, and the furnace bottom is mainly subject to the infiltration erosion of molten iron. While molten iron intrudes, alkali and zinc also invade. Molten iron intrusion can cause the refractory brick to float up, and chemical erosion can cause the expansion of the brittle layer of the refractory brick, resulting in serious damage to the refractory at the bottom of the blast furnace. These parts require refractory materials to have hot metal corrosion resistance, hot metal permeability resistance, alkali resistance, volume stability and appropriate thermal conductivity.
Hearth is an important part of blast furnace. The main causes of lining damage in this part are:
Erosion of slag and molten iron;
Alkali metal erosion;
Erosion of high temperature gas flow;
Failure of thermal stress;
Oxidation and erosion of CO2, O2 and H2O.
The lining damage in this part is the result of the comprehensive action of many factors, including chemical, thermal and mechanical effects.
Therefore, the performance of refractory for hearth shall meet the following requirements:
High temperature resistance, hot metal temperature is about 1500 ℃, and slag temperature is higher;
Erosion resistance, such as the erosion of high-temperature slag, especially when alkali metals and oxides in slag are stronger, followed by the erosion of molten iron, as well as the erosion of CO, CO2 and H2O;
Erosion resistance and wear resistance; Impermeability; High thermal conductivity.
8. Refractory for hearth tuyere
Corundum mullite brick, brown corundum brick and sillimanite brick can be used for hearth tuyere belt; Generally, ceramic refractory materials, i.e. corundum mullite brick or brown corundum brick, can be used on the hot surface in contact with slag and molten iron, dense carbon brick, graphitized and semi graphitized carbon brick, small microporous carbon brick and molded carbon brick can also be used on the cold surface; Semi graphite carbon brick and microporous carbon brick are selected for the furnace bottom, and a layer of graphitized carbon brick is used above the leveling layer of the furnace bottom.