Configuration and characteristics of refractory materials in various zones of the blast furnace

01 Tuyere Composite Bricks
For blast furnace tuyere composite bricks, close attention must be paid to both the quality of the refractory masonry and the quality of the bricks themselves. A certain steel plant has utilized various types of tuyere composite bricks for its blast furnaces, including self-bonded SiC bricks, sillimanite bricks, and large-scale Grade D composite bricks. The sillimanite bricks used in Blast Furnaces No. 4 and No. 2 (second generation) exhibited unsatisfactory spalling resistance; the self-bonded SiC bricks used in Blast Furnace No. 1 (third generation) demonstrated superior alkali and slag erosion resistance compared to the sillimanite bricks; and large-scale Grade D composite bricks were used in Blast Furnace No. 3.

02 Blast Furnace Shaft Refractories
With the continuous evolution of the times and advancements in metallurgical technology, the selection of refractory materials for the blast furnace shaft at a specific steel plant has undergone significant changes. For Blast Furnace No. 3, the cooling staves in the shaft were lined primarily with silicon nitride-bonded silicon carbide (Si3N4-SiC) bricks, which offer superior wear resistance; wear-resistant Sialon-bonded SiC bricks were also utilized. In Blast Furnaces No. 4, No. 2 (second generation), and No. 1 (third generation), a combination of graphite bricks (offering high thermal conductivity) and silicon carbide bricks was employed for the lining extending from the bosh to the lower-middle section of the shaft. Although operating conditions in this zone are harsh, the copper cooling staves—thanks to their excellent thermal conductivity—facilitate the formation of a stable slag layer on the hot face, thereby effectively protecting the cooling equipment. Consequently, the design specified the full lining of the copper cooling staves' hot faces with high-thermal-conductivity Si3N4-SiC bricks. The lining in the bosh region is subjected to chemical erosion, abrasion, and thermal shock; these severe operating conditions significantly impact the furnace's service life. Therefore, Si3N4-SiC bricks—characterized by excellent wear resistance and resistance to slag and alkali erosion—were selected for this area. The lining in the upper-middle section of the shaft is primarily exposed to abrasion from the furnace burden and gas flow, as well as chemical erosion caused by alkali metal deposition; however, operating conditions here are less severe than in the bosh and lower shaft. Materials utilized in the shaft sections of the steel plant's blast furnaces have included corundum bricks, Sialon-bonded corundum bricks, cooling staves inlaid with SiC bricks, Sialon-bonded SiC bricks, Si3N4-bonded SiC bricks, and graphite bricks.

03 Taphole Composite Bricks
The taphole composite bricks currently used in four blast furnaces at a certain steel plant consist of hot-pressed small carbon bricks; however, there is a difference in construction: the taphole channels of Blast Furnaces No. 3 and No. 1 (third generation) are built directly from these bricks, whereas the channels for Blast Furnaces No. 4 and No. 2 are formed by drilling through the brickwork after it has been laid. While their oxidation resistance is slightly inferior, hot-pressed small carbon bricks exhibit excellent alkali resistance and spalling resistance. The blast furnace taphole composite bricks at this plant have previously included sillimanite bricks, Al2O3-SiC-C bricks, large-format ultra-microporous carbon bricks (BC-8SR), and hot-pressed small carbon bricks.

04 Refractories for the Furnace Bottom and Hearth
Given the susceptibility of the hearth and bottom to penetration by molten iron, zinc, and alkalis, the selection of refractory bricks with fine porosity is paramount. Conventional carbon bricks typically feature large pore diameters, leading to severe molten iron penetration. In contrast, microporous carbon bricks reduce the average pore diameter from the 4–5 μm found in standard bricks to 0.3 μm; those with a diameter of 0.05 μm are classified as "ultramicroporous" carbon bricks. These bricks exhibit superior mechanical strength, resistance to molten iron penetration, and high-temperature performance. Specific hearth and bottom configurations employed by the steel plant include: large carbon block structures from Japan's NDK; hot-pressed small carbon block structures from the USA's UCAR; "ceramic cup" designs combined with NDK large carbon blocks; and SGL (Germany) large carbon blocks combined with UCAR hot-pressed small carbon blocks. With advancements in blast furnace smelting technology, the plant's material selection evolved: the furnace bottom now utilizes a combination of ceramic pads, graphite carbon bricks, and large carbon blocks, while the hearth sidewalls employ hot-pressed small carbon bricks. The use of hot-pressed small carbon bricks allows the jointing paste to absorb thermal expansion at high temperatures, thereby mitigating thermal stress within the bricks.

Refractories used for blast furnace maintenance primarily consist of unshaped materials, such as gunning mixes, grouting materials, and hard injection masses.

05 Spraying Materials
With advancements in refractory technology and automated equipment, it is now possible to utilize wet-method spraying materials alongside remote-controlled, automated hot-repair spraying techniques. These methods allow for both the repair of furnace linings and the creation of new lining layers, significantly extending the service life of blast furnaces; the combination of these two approaches represents the prevailing trend in advanced blast furnace spray-repair technology. Spray-repairing and lining exposed furnace walls is typically performed while lowering the stock line; this method is particularly suitable for repairing large areas of the furnace wall, especially in the upper sections where the burden is absent. When necessary, the stock line can be lowered below the tuyere level to facilitate spray-repairing and lining of the entire furnace wall. Blast furnace spray-repair technology has been widely adopted by enterprises in Japan and Western Europe since the 1980s. Companies such as Morgan, Plibrico, Minteq, Magneco/Metrel, and Krosaki possess advanced capabilities in this field. Whether performed under cold or hot conditions, blast furnace spray-repairing employs two primary methods: semi-dry spraying and wet spraying. In semi-dry spraying, the spray material (comprising aggregates, powders, binders, and additives) is conveyed via high-pressure air to the vicinity of the nozzle, where water is simultaneously introduced; the water and material mix rapidly before being projected onto the furnace lining surface requiring repair. In wet spraying, the spray material and water are pre-mixed in a mixer to form a pumpable, self-flowing slurry, which is then transported via high-pressure pumps and piping to the spray nozzle. A liquid accelerator is injected at the nozzle tip, mixing rapidly with the wet material as it is sprayed onto the repair surface.

06 Grouting Materials
During blast furnace operations, the carbon bricks surrounding the hearth gradually undergo erosion. When thermocouple readings in the hearth sidewalls rise or intense gas flames appear around the taphole, grouting of the furnace bottom and hearth becomes necessary (injecting grout into the space between the refractory bricks and the furnace shell). The objective is to prevent the formation of gaps between the furnace shell and the refractory bricks, thereby ensuring effective heat conduction for optimal cooling performance. Depending on the application area and the specific refractory lining involved, the injection materials can be categorized by composition into: alumina-silica, alumina-silica insulating, carbon-silicon carbide, and carbon-based types. Categorized by application zone, they include water-based and non-water-based types for the upper furnace shaft, and non-water-based types for the area extending from the lower furnace shaft down to the hearth.

07 Rigid Injection Material
Traditional injection repair typically employs cement-bonded high-alumina injection materials; the injection pressure is generally 2–3 MPa on the pump side and less than 0.5 MPa on the furnace side. These materials harden slowly, are prone to cracking due to rapid evaporation of high moisture content, and exhibit high porosity and low strength, resulting in a short service life. Due to limitations regarding furnace temperatures and equipment pressure capabilities, traditional injection repairs are generally restricted to areas above the middle section of the furnace shaft where burden material is present. In contrast, rigid injection repair utilizes pressures of 18.8 MPa on the pump side and 5 MPa on the furnace side—approximately ten times that of standard equipment—yielding a service life exceeding three months. Applied in burden-filled zones such as the lower-middle shaft, the bosh, and the belly, this method uses a composite resin binder and prioritizes wear resistance, workability, appropriate hardening time, flowability, and strong adhesion to the lining. In 1992, a steel plant imported rigid injection technology from Japan and utilized scheduled blast furnace maintenance periods to perform injection-based lining formation on areas of the steel shell exhibiting red-hot spots or high temperatures (specifically the lower-middle shaft). As the blast furnace shutdown cycle at the plant extended (from an initial one month to the current four months), the injection process underwent improvements—including upgrades to injection equipment and material formulations. Characterized by its simplicity, speed, and effectiveness, rigid injection lining technology has become a primary method for routine blast furnace lining maintenance at the plant. Rigid injection material is injected through holes drilled in the furnace shaft during each shutdown period. The plant's rigid injection technology is suitable not only for cooling-plate blast furnaces but—following years of development—also for cooling-stave blast furnaces; the integration of micro-cooler technology has further significantly expanded the application scope and improved the lining formation results.

To extend the service life of its blast furnaces, a certain steel plant prioritizes research into refractories for both repair and initial furnace construction. Research into the quality and masonry techniques of carbon bricks used in the hearth and below-hearth areas forms the foundation for extending the service life of the blast furnace hearth and bottom to over 15 years. Improvements in blast furnace refractories aim to achieve a longer service life, enhanced safety, and accident-free operation. The selection of refractories is aligned with the cooling systems installed in the various sections of the blast furnace, including the bottom, hearth, and shaft.

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