In the smelting of fire method, the service life of refractory materials is an important production indicator, which seriously affects the operating rate and production cost of the furnace. The use environment of refractory materials requires that it can resist the damage of temperature, the damage of thermal stress, and the corrosion of the medium. Therefore, choosing a suitable refractory brick, extending the life of refractory bricks, play a vital role in improving production efficiency and reducing production costs.
1. Types of refractory bricks
At present, the most common classification of refractory materials is chemical composition classification, which can be divided into silica, aluminosilicate, magnesia, dolomite and carbon composite refractory materials.
1.1 Silica refractories
Silica refractory material is a refractory material with SiO₂ as the main component, and the mass fraction of SiO₂ is not less than 93%. It can be shaped or unshaped refractory material. The refractory material has the advantages of thermal conductivity, high softening point under load, strong resistance to acid slag erosion, etc., but the biggest disadvantage is low thermal shock resistance. Therefore, the refractory material is mainly used as structural materials for coke ovens, glass melting furnaces, acid steelmaking furnaces and other thermal equipment.
1.2 Aluminosilicate refractories
Aluminosilicate refractories are refractory materials with AI₂O₃ and SiO₂ as the main components. According to the content of AI₂O₃ in refractories, they can be divided into semi-silicon (mass fraction 15%~30%), clay (mass fraction 30%~48%) and high alumina (mass fraction> 48%) refractories. The refractory material has the advantages of light weight, thermal stability, and good thermal insulation performance, but its deformation temperature is 1400°C. Therefore, aluminosilicate refractories are generally used as insulation materials in the metallurgical industry, not for working layers.
1.3 Magnesia refractories
Magnesia refractories are refractories with periclase as the main crystal phase and MgO mass fraction greater than 80%. Affected by the composition of magnesia raw materials, the main components of magnesia refractories are MgO, FeO, Fe₂O₃, AI₂O₃, SiO₂, CaO, Cr₂O₃. The melting point of MgO is as high as 2800°C, and the refractoriness of magnesia refractories reaches 2000°C, so magnesia refractories have good high temperature resistance. Magnesia refractories include magnesia bricks, forsterite refractories, magnesia-aluminum spinel refractories, magnesia-chrome refractories, and white jade refractories. Among them, the magnesia-chromium refractory material is made of magnesia and chromite, and the main component is magnesia. Compared with traditional magnesia bricks, magnesia-chrome refractories have stronger thermal stability and are widely used in non-ferrous smelting furnaces. However, because hexavalent chromium has serious harm to the environment and human health, especially to water, it is necessary to strictly control the alkaline medium and oxygen partial pressure in the production and production process.
1.4 Dolomite refractories
Dolomite refractories are alkaline refractories with dolomite as the main raw material and MgO and CaO as the main components. The mass fraction of CaO is 40%~60%, and the mass fraction of magnesium oxide is 30%~40%. The refractory temperature of dolomite refractories is above 1780°C, and the softening temperature under 0.2MPa load is 1550°C, which shows that it has good high temperature stability. Dolomite refractories are strong alkaline refractories, which have strong slag resistance to alkaline slag, but poor slag resistance to acid slag. Therefore, this refractory material is mainly used for the furnace wall and bottom of the open hearth furnace, the firing zone of the rotary kiln, etc.
1.5 Carbon composite refractories
Carbon composite refractories, also known as carbon-containing refractories, are made of two or more refractory oxides (MgO, CaO, Al₂O₃, ZrO₂, etc.) A multi-phase composite refractory material made of plain materials as a binder. Carbon composite refractories have high refractoriness, good thermal conductivity and electrical conductivity, excellent load deformation temperature and high temperature strength, and better slag resistance and thermal shock resistance than other refractory materials, but this type of products are easy to oxidize shortcoming. Therefore, this refractory material is mainly used in the field of high-quality steel such as smelting stainless steel, pure steel and low-sulfur steel.
2. Selection of refractory materials for side blowing furnace
2.1 Brief introduction of side blowing furnace
The side-blowing furnace is a smelting equipment for producing blister copper. Oxygen-enriched air is blown into the furnace through the primary tuyeres in the slag line area, and reacts under the action of high temperature. The blister copper sinks into the lower part of the molten pool and is discharged into the electric furnace. The slag is Accumulated in the upper part of the molten pool, discharged to the electric furnace through the overflow, and the reaction flue gas is discharged from the flue to the boiler process gas
The body structure of the side-blowing furnace adopts a fixed rectangular furnace type, which is composed of copper water jacket, refractory material and steel structure. The furnace body is divided into four parts from bottom to top: hearth, furnace body, furnace roof and flue. The hearth used to store the blister copper and slag produced by the reaction is made of refractory bricks, and a slag chamber is set at the end of the hearth to separate the copper slag. The furnace body is divided into reaction zone and flue gas zone. The reaction zone is composed of copper water jacket and primary tuyere, and the flue gas zone is composed of slotted copper water jacket and secondary tuyere for slag hanging protection. The reaction flue gas is discharged from the flue gas outlet formed by the water jacket and enters the flue. The size of the flue space is calculated according to the flue gas flow rate to ensure that the flue gas stays in the flue for more than 2s. The main reaction area of the side-blowing furnace belongs to the protection position of the copper water jacket, and the refractory materials are mainly used in the furnace hearth, slag chamber and flue.
2.2 Selection of refractory components for side-blown furnaces
From the working principle of the side-blowing furnace, it can be seen that the hearth and slag chamber of the side-blowing furnace will be eroded and washed by the melt, and the flue will be eroded by a small amount of molten slag spray and washed by dusty flue gas. Under normal furnace conditions, the temperature in these three areas is 1100~1300°C; but in the case of unstable furnace conditions, the temperature in these three areas can reach above 1400°C. In the actual production process, the side-blowing furnace needs to be supplied with oxygen-enriched primary air and secondary air, and forms a strong oxidizing atmosphere locally, so the side-blowing furnace should choose refractory bricks that are not easily oxidized. The main components of slag are FeO, SiO₂, CaO, AI₂O₃, high alumina refractory materials and silica refractory materials will participate in slagging, which is not suitable for side blowing furnaces. Therefore, the refractory materials for side-blown furnaces need to have the characteristics of high temperature resistance, strong thermal stability, high load deformation temperature, high compressive strength, oxidation resistance, and not participating in slagging. Combined with the characteristics of refractory materials, magnesia refractory materials should be selected for side blowing furnaces. The increase of Cr₂O₃ content in magnesia refractories can improve the slag erosion resistance of materials, so the refractory bricks of side blowing furnace hearth, slag chamber and flue should choose magnesia chromium refractories with higher Cr₂O₃ content.
2.3 Selection of combination form of refractories for side-blowing furnace
According to the different bonding forms of magnesia-chromium refractory materials, it includes magnesia-chromium refractory materials such as direct bonding, semi-recombination, and electrofusion recombination. Among them, the directly combined magnesia-chrome refractory material is made of high-purity sintered magnesia and chromite ore, and the fused magnesia and chromite ore are directly sintered; the semi-recombined magnesia-chrome refractory material is made of fused magnesia-chromite Particles are made by adding part of chromium ore and magnesia or sintering to form magnesia-chrome material as fine powder, and sintering at high temperature; the electric melting recombination of magnesia-chromium refractory material is to melt chromium ore and fused magnesia in an electric furnace to produce It is made of fused magnesia-chrome sand and then sintered at high temperature.
3. Conclusion
The service life of refractory materials directly affects the production rate and production cost. It is necessary to select the appropriate type and combination of refractory materials according to the working environment in different regions. This is the most effective means to improve the service life of refractory materials.
