The roof of a blast furnace represents a high-temperature zone within the furnace. The refractories used at the top, particularly the layers of bricks directly exposed to hot air and gases, must have excellent thermal shock resistance and creep resistance. Silica bricks or low-creep high-alumina bricks are typically used for the working layer, while insulating layers are generally made from clay insulating bricks. When selecting insulation materials, particular attention should be paid to ensuring that the working surface temperature does not exceed the material’s maximum allowable usage temperature.
The sidewalls of the blast furnace, also known as the furnace body’s walls, consist of several layers, including the working layer, insulating bricks, and fill materials. The upper part of the sidewall is exposed to higher temperatures, while the middle and lower parts are exposed to lower blast temperatures. The upper section’s working layer typically uses low-creep high-alumina bricks or silica bricks, while the middle and lower parts use high-alumina or clay bricks. The insulating layer is generally composed of insulating bricks, refractory ceramic fibers, or fill materials, depending on the specific area’s temperature conditions.
Partition walls separate the combustion chamber from the regenerator chamber in a blast furnace. These walls should not be fully sealed against the furnace roof to allow for proper expansion and contraction (typically a gap of 200–250mm). To ensure uniform airflow, the partition wall should extend 400–700mm higher than the regenerator checker bricks. The temperature difference between the lower and upper parts of the partition wall, as well as the thermal expansion discrepancy, can cause cracking in the structure. The upper portion is generally constructed using low-creep high-alumina or silica bricks, while the middle and lower sections are built with high-alumina and clay bricks.
Burners are devices that mix gas and air before introducing them into the combustion chamber. There are two primary types of burners: metal (mechanical) and ceramic burners, with ceramic burners being more commonly used. During the blowing period, the temperature on the upper surface of the ceramic burner is slightly lower than the blast temperature; during combustion, it is slightly higher than the temperature of the incoming air and gas. This temperature fluctuation, particularly during furnace startup, requires the burner to be built with materials that exhibit low thermal expansion and excellent creep resistance. Historically, high-alumina phosphate refractory castables and bauxite-based refractories were used for smaller blast furnaces. However, with the increase in furnace size and higher wind temperatures, materials such as high-alumina cordierite refractories and, in some cases, mullite-cordierite refractories are now used in modern systems.
Checker bricks in the regenerator chamber’s high-temperature zone must exhibit good high-temperature volumetric stability, resistance to corrosion, and creep resistance. Silica bricks possess these qualities and are widely used in both domestic and international high-blast furnaces. When the design temperature of the blast furnace roof is at least 1400°C, silica bricks are the preferred choice, with the residual quartz content controlled to be no more than 2%. For furnaces using silica bricks, a reliable temperature detection system must be in place to ensure that the minimum temperature of the silica bricks is never lower than 800°C during furnace operation, including during rest periods and furnace shutdowns.
Blast furnace holes, which endure extreme working conditions, are often a weak link in the overall structure. The use of composite brick technology improves the overall stability, integrity, and high-temperature characteristics of the furnace. Composite bricks integrate multiple measures to increase the overall performance, enhancing the furnace’s lifespan and efficiency.
To reduce the temperature of the furnace shell and various pipelines, thus extending their service life and minimizing heat loss, many blast furnaces now use various materials for refractory spraying. For example, at Baosteel’s 4000m³ blast furnace, acid-resistant spraying materials (50–70mm thick) are used in the combustion chamber, regenerator ball tops, and connecting pipes. Other parts of the furnace are sprayed with medium-heavy refractory materials (45–77mm thick), and the lower part of the regenerator is sprayed with slag wool materials (46–51mm thick). This advanced spraying technology helps enhance the efficiency and longevity of the furnace.
In summary, selecting the appropriate refractory materials for a blast furnace is essential for ensuring optimal furnace performance, longevity, and efficiency. Whether you’re dealing with high-temperature zones, blast furnace sidewalls, or furnace roof areas, understanding the different types of refractories and their specific applications will help you make the best choices for your operation.
At Firebird Refractory, we specialize in providing high-quality refractory materials designed to withstand extreme conditions. Our products, including high-alumina bricks, mullite bricks, and silica bricks, are used in various high-temperature applications across multiple industries, including steel manufacturing and high-temperature processing. Contact us today to learn more about how our refractory solutions can improve your blast furnace efficiency and reliability.
