Characteristics of refractory materials for blast furnaces
1.1 Tuyere composite bricks
For tuyere composite bricks for blast furnaces, attention must be paid to the masonry quality and physical quality of refractory materials. The tuyere composite bricks of a steel plant's blast furnaces use self-bonded SiC bricks, sillimanite bricks and D-grade large composite bricks. The sillimanite bricks used in No. 4 and No. 2 blast furnaces (second generation) have poor spalling resistance. The self-bonded SiC bricks used in No. 1 blast furnace (third generation) have better alkali resistance and slag erosion resistance than the former. No. 3 blast furnace uses D-grade large composite bricks.
1.2 Furnace body refractory materials
As the times change and metallurgical technology continues to improve, the selection of furnace body refractory materials in the design of a steel plant's blast furnace has undergone major changes. In the configuration of furnace body refractory materials, the inlay bricks of the furnace cooling wall of No. 3 blast furnace are mainly silicon carbide combined with silicon nitride bricks, which have good wear resistance; the furnace body uses wear-resistant Sailong SIC bricks, and the furnace bodies of No. 4 blast furnace, No. 2 blast furnace (second generation) and No. 1 blast furnace (third generation) use a combination of graphite bricks with good thermal conductivity and silicon carbide. The lining from the furnace belly to the middle and lower part of the furnace body is harsh, but the copper cooling wall forms a stable slag skin on the hot surface with its excellent thermal conductivity, which better protects the cooling equipment. Therefore, the design fully inlays the hot surface of the copper cooling wall with silicon nitride combined with silicon carbide bricks with high thermal conductivity. The lining of the furnace belly is subjected to chemical erosion, scouring, and thermal shock. Its working conditions are harsh and have a great impact on the life of the blast furnace. The design uses silicon nitride combined with silicon carbide bricks with good wear resistance and resistance to slag alkali erosion in this area. The lining of the middle and upper part of the furnace body is mainly affected by the scouring of the charge and gas flow and the chemical erosion caused by the deposition of alkali metals. The working conditions are better than those of the furnace belly and the lower part of the furnace body. The blast furnace body of a steel plant uses corundum bricks, Sialon combined with corundum bricks, cooling walls inlaid with SiC bricks, Sialon combined with SiC bricks, Si3N4 combined with SiC bricks, graphite bricks, etc.
1.3 Refractory materials for the furnace bottom and furnace hearth
For the furnace hearth and furnace bottom, which are susceptible to the penetration of molten iron, zinc and alkali, the most important thing is to choose refractory bricks with fine pores. Since the pores of the commonly used carbon bricks are large in diameter, the penetration of molten iron is very serious. The average diameter of the pores of microporous carbon bricks is reduced from 4 to 5μm of the original general carbon bricks to 0.3μm, and to 0.05μm, which is called ultra-microporous carbon bricks, and its mechanical strength, resistance to molten iron, and high temperature performance are improved accordingly. Table 4 compares the performance of ordinary carbon bricks and microporous carbon bricks. The furnace bottom and hearth structures of a steel plant include the large carbon brick structure of Japan NDK, the large carbon block heated and pressed small carbon brick structure of the United States UCAR, the ceramic cup plus the large carbon block structure of Japan NDK of France SAVOIE, and the large carbon brick plus the large carbon brick of Germany SGL plus the hot pressed small carbon brick structure of the United States UCAR. With the development of blast furnace smelting technology, the selection of furnace hearth refractory materials in the design of blast furnaces in a steel plant has undergone major changes. The blast furnace bottom uses ceramic pads, graphite carbon bricks combined with large carbon bricks, and the side walls of the furnace hearth are hot pressed small carbon bricks. Hot pressed small carbon bricks can use brick joint glue to absorb the high temperature thermal expansion of refractory bricks, thereby reducing the high temperature thermal stress of bricks.
Refractory materials for blast furnace maintenance
Refractory materials for blast furnace maintenance are mainly amorphous refractory materials such as spray coatings, grouting materials and hard pressed materials.
2.1 Spraying materials
With the advancement of refractory technology and automation equipment technology, wet spraying materials and hot remote control automatic spraying technology can now be used, which can not only repair the lining of the furnace body, but also make lining, greatly extending the service life of the blast furnace. The combination of the two has become the development trend of advanced blast furnace spraying technology. The exposed furnace wall is usually sprayed and lined under the condition of lowering the material line. It is particularly suitable for repairing the unfilled parts of the upper part of the blast furnace and the large area of the furnace wall. If necessary, the material line can be lowered below the tuyere to spray and line the entire furnace wall. Since the 1980s, blast furnace spraying has been widely used in companies such as Japan and Western Europe. Morgan, Palico, American Mind, American Meigumet, Japanese Kurosaki and other companies have advanced blast furnace spraying technology. Blast furnace spraying is carried out in cold or hot state, and there are two types of semi-dry spraying and wet spraying. Semi-dry gunning: The gunning material (aggregate, powder, binder, additive) is sent to the vicinity of the gun muzzle by high-pressure air, and water is also delivered there. The water and material are quickly mixed and sprayed onto the surface of the blast furnace lining to be repaired. Wet spraying: The gunning material and water are mixed in a mixer in advance to become a self-flowing material that can be pumped, and then transported to the gun head through a high-pressure pump, pipeline, etc. A liquid coagulant is added at the same time as the gun head is sprayed, and it is quickly mixed with the wet material and sprayed onto the repair surface.
2.2 Grouting material
After the blast furnace is produced, the carbon bricks around the furnace are gradually eroded. When the temperature of the furnace side wall galvanic couple rises or the gas fire around the iron mouth is large, it is necessary to grout the furnace bottom (grout between the refractory bricks and the furnace skin). The purpose is to prevent the gap between the furnace shell and the refractory bricks, ensure good thermal conductivity, so that the cooling effect can be achieved. The press-in material can be divided into aluminum silicon system, aluminum silicon insulation system, carbon-silicon carbide system, and carbonaceous system according to the different parts of use and different refractory linings. It can be divided into water system and non-water system in the upper part of the furnace body and non-water system in the lower part of the furnace body to the furnace cylinder according to the use part.
2.3 Hard press-in material
Traditional press-in maintenance: Generally, high-aluminum press-in material combined with cement is used. The pump side pressure is generally 2-3MPa, and the furnace side pressure is generally less than 0.5MPa. The press-in material construction body hardens slowly, high water vaporization is easy to burst, the material has high porosity and low strength, and thus has a short life. Since the press-in material is limited by the temperature and pressure equipment in the furnace, the part for press-in maintenance is all the parts with furnace charge above the middle of the blast furnace body. Hard press-in maintenance: machine side pressure is 18.8MPa, furnace side pressure is 5MPa, equivalent to 10 times of ordinary press-in equipment, the service life after press-in maintenance is more than 3 months, used in the middle and lower parts of the furnace body, furnace waist, and furnace belly where there are furnace charges, composite resin is used as a binder, emphasizing the wear resistance, construction workability, appropriate hardening time, expansibility and good adhesion with the lining. In 1992, a steel plant introduced hard press-in technology from Japan, and used the blast furnace regular maintenance to press-in lining operations on the red-hot iron shell and high-temperature parts (middle and lower parts of the furnace body). With the extension of the blast furnace wind-out period of a steel plant (from the initial 1 month to the current 4 months), the press-in process has also been improved to a certain extent, which is reflected in: the improvement of press-in equipment, the improvement of press-in materials, etc. The hard press-in lining technology, with its simple, fast and effective characteristics, has become one of the most commonly used means for daily maintenance of the blast furnace lining of a steel plant. Every time the blast furnace is shut down, the furnace body is opened and hard press-in materials are pressed in. The hard pressing technology of a steel plant is not only applicable to cooling plate blast furnaces, but also, after years of efforts, has been applicable to cooling wall blast furnaces. Combined with the application of micro cooler technology, the application scope and lining effect of hard pressing lining technology have been greatly improved.
The purpose of improving blast furnace refractory materials is to make the blast furnace longer, safer and accident-free. The selection of blast furnace refractory materials is consistent with the cooling system of the blast furnace bottom, furnace hearth and furnace body.
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