In pyrometallurgical processes, the service life of refractory materials is an important production indicator that greatly affects furnace operation efficiency and production costs. Refractory materials need to withstand temperature damage, thermal stress, and corrosion from media in their operating environment. Therefore, the selection of suitable refractory bricks and extending their lifespan play a crucial role in improving production efficiency and reducing costs.
1.Types of Refractory Bricks
Currently, refractory materials are commonly classified based on their chemical composition. They can be categorized into silica, alumina-silicate, magnesia, dolomite, and carbon composite refractory materials.
1.1 Silica Refractory Materials
Silica refractory materials are primarily composed of SiO₂, with a mass fraction of SiO₂ not less than 93%. They can be either shaped or unshaped refractory materials. These materials have advantages such as high thermal conductivity, high load softening point, and strong resistance to acidic slag erosion. However, their major drawback is low resistance to thermal shock. As a result, silica refractory materials are mainly used as structural materials in coke ovens, glass melting furnaces, acid steelmaking furnaces, and other thermal equipment.
1.2 Alumina-Silicate Refractory Materials
Alumina-silicate refractory materials are composed mainly of AI₂O₃ and SiO₂. Depending on the AI₂O₃ content in the refractory materials, they can be classified as semi-siliceous (with a mass fraction of 15%~30%), clayey (with a mass fraction of 30%~48%), or high-alumina (with a mass fraction above 48%) refractory materials. These materials have advantages such as lightweight, thermal stability, and good insulation performance. However, their deformation starts at 1400℃. Therefore, alumina-silicate refractory materials are generally used as insulation materials in the metallurgical industry and not in the working layer.
1.3 Magnesia Refractory Materials
Magnesia refractory materials are primarily composed of periclase (MgO) as the main crystal phase, with a mass fraction of MgO greater than 80%. Due to the influence of magnesia raw material composition, the main components of magnesia refractory materials include MgO, FeO, Fe₂O₃, AI₂O₃, SiO₂, CaO, and Cr₂O₃. With a melting point as high as 2800℃, magnesia refractory materials have a refractoriness of 2000℃, exhibiting excellent high-temperature resistance. Magnesia refractory materials include magnesia bricks, magnesia olivine refractory materials, magnesia-alumina spinel refractory materials, magnesia-chrome refractory materials, and magnesia-dolomite refractory materials. Among them, magnesia-chrome refractory materials are made from magnesite and chromite, with magnesite being the main component. Compared to traditional magnesia bricks, magnesia-chrome refractory materials have stronger thermal stability and are widely used in non-ferrous smelting furnaces. However, hexavalent chromium is severely harmful to the environment and human health, especially causing serious water pollution. Therefore, during production and manufacturing processes, it is necessary to strictly control alkaline media and oxygen partial pressure.
1.4 Dolomite Refractory Materials
Dolomite refractory materials are alkaline refractory materials primarily made from dolomite as the main raw material. The main components include MgO and CaO. The mass fraction of CaO ranges from 40% to 60%, while the mass fraction of magnesia oxide (MgO) ranges from 30% to 40%. Dolomite refractory materials have a refractory temperature exceeding 1780°C, and the onset temperature of softening under a 0.2MPa load is 1550°C. It is evident that dolomite refractory materials exhibit excellent high-temperature stability. They belong to strong alkaline refractory materials and have good resistance to alkaline slag. However, their resistance to acidic slag is comparatively poor. Therefore, dolomite refractory materials are primarily used in the furnace walls, hearths, and burners of rotary kilns and other applications.
1.5 Carbon Composite Refractory Materials
Carbon composite refractory materials, also known as carbon-containing refractory materials, are multi-phase composite refractory materials made from two or more different types of refractory oxides (such as MgO, CaO, Al₂O₃, ZrO₂, etc.), carbon materials, and non-oxide materials. Carbon materials are used as binders. Carbon composite refractory materials have high refractoriness, good thermal conductivity, electrical conductivity, excellent load deformation temperature, high-temperature strength, and superior resistance to slag and thermal shock compared to other refractory materials. However, one disadvantage of this category of products is their susceptibility to oxidation. Therefore, carbon composite refractory materials are primarily used in the smelting of stainless steel, pure steel, low-sulfur steel, and other high-quality steel grades.
2.Selection of Refractory Materials for Side-Blown Furnace
2.1 Introduction to Side-Blown Furnace
The side-blown furnace is a smelting equipment used for producing crude copper. Oxygen-enriched air is injected into the furnace through the primary tuyere located in the slag line area. Under high-temperature conditions, reactions take place, with crude copper settling at the bottom of the molten pool and being discharged to the electric furnace, while the furnace slag accumulates at the upper part of the molten pool and is discharged through overflow into the electric furnace. The reaction gases are emitted through the flue to the boiler process gas.
The structure of the side-blown furnace adopts a fixed rectangular furnace type, composed of a copper water jacket, refractory materials, and steel structures. The furnace is divided into four parts from bottom to top: the crucible, furnace body, furnace top, and flue. The crucible, which is used to store the generated crude copper and slag, is constructed with refractory bricks, and a slag chamber is set at the end of the crucible for copper-slag separation. The furnace body is further divided into a reaction zone and a flue gas zone. The reaction zone consists of a copper water jacket and a primary tuyere, while the flue gas zone consists of slotted copper water jackets that facilitate slag hanging protection and secondary tuyeres. The reaction gases are discharged through the exhaust port composed of the water jackets and enter the flue. The dimensions of the flue space are calculated based on the flue gas velocity to ensure a residence time of at least 2 seconds. The main reaction zone of the side-blown furnace is located in the copper water jacket protection position, and the refractory materials are mainly used in the crucible, slag chamber, and flue.
2.2 Selection of Refractory Material Composition for Side-Blown Furnace
Based on the working principle of the side-blown furnace, it can be inferred that the crucible, slag chamber, and flue of the side-blown furnace will be subjected to erosion and erosion by the molten metal, as well as irrigation erosion by a small amount of molten slag and scouring by dusty flue gases. Under normal operating conditions, the temperature in these three areas ranges from 1100 to 1300°C. However, under unstable operating conditions, the temperature in these areas can exceed 1400°C. During actual production, the side-blown furnace requires the injection of oxygen-enriched primary and secondary air, which creates a strongly oxidizing atmosphere locally. Therefore, refractory bricks that are resistant to oxidation should be selected for the side-blown furnace. The main components of the furnace slag are FeO, SiO₂, CaO, and AI₂O₃. High alumina and silica refractory materials participate in slag formation and are not suitable for use in the side-blown furnace. Therefore, the refractory materials for the side-blown furnace need to have characteristics such as high temperature resistance, strong thermal stability, high load deformation temperature, high compressive strength, oxidation resistance, and non-participation in slag formation. Considering the characteristics of refractory materials, magnesia refractory materials should be selected for the side-blown furnace. Increasing the content of Cr₂O₃ in magnesia refractory materials can enhance their resistance to slag erosion. Therefore, refractory bricks with a higher Cr₂O₃ content in magnesia-chrome refractory materials should be chosen for the crucible, slag chamber, and flue of the side-blown furnace.
2.3 Selection of Refractory Material Bonding Forms for Side-Blown Furnace
The bonding forms of magnesia-chrome refractory materials for the side-blown furnace include direct bonding, semi-rebonding, and electrofusion rebonding. Among them, direct bonding magnesia-chrome refractory materials are produced by directly sintering high-purity sintered magnesia and chromite ore, where electrofused magnesia and chromite ore are sintered directly. Semi-rebonding magnesia-chrome refractory materials are produced by using electrofused magnesia-chrome sand as the main granule, adding a certain amount of chromite ore and magnesia sand, or sintering them together to form fine magnesia-chrome powder, which is then sintered at high temperatures. Electrofusion rebonding magnesia-chrome refractory materials are produced by melting chromite ore and electrofused magnesia sand in an electric furnace to obtain electrofused magnesia-chrome sand, which is then sintered at high temperatures.
Electrofusion rebonding magnesia-chrome refractory materials exhibit the best performance, followed by semi-rebonding magnesia-chrome refractory materials. Taking into account the wear of refractory materials in the crucible, slag chamber, and flue areas of the side-blown furnace, semi-rebonding, electrofusion rebonding, and direct bonding magnesia-chrome refractory materials are respectively used in these areas.
The service life of refractory materials directly affects production efficiency and production costs. It is necessary to select the appropriate type of refractory materials and bonding forms based on the working environment of different areas. This is the most effective way to improve the service life of refractory materials.