(I) Mixed iron furnace and mixed iron type molten iron tank
(1) Mixed iron furnace
The mixed iron furnace is a thermal equipment used to accumulate, store and maintain a certain temperature (1250~1300℃) and mix iron components. The lining of the mixed iron furnace is built with refractory materials. The main reason for the damage of the refractory lining is the penetration of molten iron into the cracks of brick joints, and also due to the floating of bricks, slag erosion and peeling.
According to the alkali content in the slag, the mixed iron furnace is built with magnesia bricks, forsterite bricks or high-alumina bricks with high alumina content. When the alkali content in the slag is low, aluminum silicate products are used. When the slag contains Na2O>2%~3%, the aluminum silicate products become loose and are destroyed. In this case, magnesium bricks or forsterite refractory materials are used. Special attention should be paid to the life of the fire mud, which should have the ability to make the brick joints dense. The working layer of the lining of the acidic mixed iron furnace is generally built with silica bricks.
(2) Mixed iron type hot metal ladle
Due to the increase in steel production, the mixed iron furnace has lost its unique role as a storage for hot metal and has been replaced by a mixed iron type hot metal ladle. The mixed iron type ordinary torpedo ladle is shown in Figure 11-2. The use conditions of the refractory materials here are roughly the same as those of the ordinary mixed iron furnace. From the perspective of the material stress of the torpedo ladle, it is a problem of uniform distribution of the load on the two supporting beams. Even the slight bending of this beam causes the mechanical process load of 0.2MPa and above in some areas of the lining. This situation causes the application of refractory materials due to creep limitation. It is believed that the creep at 1300℃ under a load of 0.2MPa should not be ≥0.03%/h. When using tar-impregnated refractory materials, the lining life of the mixed iron ladle is greatly improved. The lining of the mixed iron ladle is usually implemented in three layers: working layer, protective layer and thermal insulation layer.
Due to the development of hot metal pretreatment technology, the mixed iron type ladle is used not only as a tool for transporting liquid iron from the blast furnace to the steelmaking equipment, but also as a container for refining outside the blast furnace, including hot metal desulfurization. Lime is used as a desulfurizing agent, which is blown into the iron and mixed with the subsequent gas in the nitrogen current. In this case, the mixed iron furnace is built with magnesia or alumina silicon carbide refractory materials. When the molten iron is desulfurized with calcium carbide, the mixed iron furnace lining with unburned magnesium calcium products combined with asphalt is used to achieve relatively good results. Japan carries out desulfurization, dephosphorization and desiliconization in torpedo tanks, and the use of Al2O3-SiC-C products has a good effect. my country uses high-alumina bricks soaked in asphalt, or adds SiC or C to the ingredients, or both at the same time, to improve the corrosion resistance and thermal shock resistance. Some also use dolomite refractory materials.
(II) Coke oven
The coke oven has its own complex refractory masonry structure. The most important part of the masonry is the combustion chamber wall. It works under the following conditions: the temperature during coking is about 1300℃, and the change is very small; the coking temperature starts from 500~600℃ coking cycle and rises to 1200~1250℃ at the end of coking. At the same time, the temperature at the center of the coke cake reaches 1100℃, the chamber width is 400~450mm, and the coking period lasts 14~17h. It is very important for the coke oven to work properly, so that the wall and furnace masonry generally maintain high airtightness. The refractory masonry is subjected to the compressive stress of the mass of the masonry itself and the weight of the coal car on the furnace. Perhaps only silica bricks can meet these conditions. Some coke ovens using silica bricks have been used for 40 years. However, the thermal conductivity of silica bricks at coking temperature is relatively low, about 1.9W/(m·K). Due to its high volatility, the temperature is not allowed to exceed 1250℃. More effective refractory materials to replace silica bricks are in the determination stage, such as the wall structure of magnesium-silica products, and silicon carbide bricks, corundum refractory materials, iron-containing silica bricks, etc. have also been tested. Refractory castables (large wall panels) are used instead of small products of complex shapes.
(III) Refractory materials for direct ironmaking
The process of directly making iron from ore is in the form of sponge iron, granular iron or liquid iron, which is heated in a reducing gas medium (H₂, CO), mainly to reduce iron oxide to metallic iron. The production of sponge iron is carried out in a vertical furnace at a temperature of less than 1000°C. Ordinary clay refractory materials can be used in this furnace.
The reducing gas is produced by natural gas (CH₄) conversion and treated in a special gas heater according to the heat storage principle. The gas heater is similar to the hot blast furnace of a blast furnace in terms of structure. Nickel is used to catalyze the conversion of natural gas. The grid room of the gas heater also plays an important role as a catalyst and works under variable temperature and gas medium under changing conditions from oxidation to reduction. The problem here is the thermal shock resistance of the refractory and its chemical stability to the catalyst.
According to relevant information: Al₂O₃-C bricks and MgO-Cr₂O₃ products are generally better. Since the new smelting ironmaking process is a new technology under development, the refractory materials used are also being explored.
(IV) Refractory materials for iron ore raw material sintering equipment
Intensified metallurgical production has led to the use of various methods and equipment for pre-heat treatment of iron ore raw materials: conveyor belt sintering machine and roasting machine; grate plate-tube furnace-ring cooler. Combined equipment: vertical furnace, boiling furnace and other thermal equipment. The furnace lining is mainly high-aluminum products with an Al2O2 content of 85% and refractory castables of various compositions, as well as heat-insulating mullite, siliceous plates, floating beads bricks or refractory fibers. The damaged refractory lining is repaired and repaired by the gunning method to extend its life.
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