The Role of Blast Furnace Refractory Materials in Ironmaking Production

Main Equipment and Operating Conditions of Blast Furnaces

The blast furnace is a crucial piece of equipment in steel metallurgy, responsible for approximately 73% of the total energy consumption in producing usable metal. To produce 1 ton of iron, about 0.5 tons of coke is consumed, and approximately 1.6 kg of refractory materials are used. Although the consumption of refractory materials may seem minimal, the degradation of refractory linings often leads to furnace shutdowns for maintenance, significantly impacting productivity.

To enhance blast furnace productivity and reduce fuel consumption, the key measures include increasing furnace volume, raising blast air temperature, and injecting auxiliary fuels such as heavy oil, natural gas, pulverized coal, coal-oil slurries, or hot reducing gases. Using more durable refractory materials and ensuring their protection is also essential.

For instance, a blast furnace with a volume of 5000 m³ consumes about 3.5 kt of refractory materials for its lining, while its three hot stoves and other auxiliary equipment require an additional 27.5 kt. Based on operating conditions and interactions between the linings and erosive agents, the refractory lining is divided into eight zones, as illustrated in Figure 11-1:

1. Throat: Located at the uppermost part of the furnace, where raw materials are preheated.
2. Furnace Body: Comprised of two sections—an uncooled upper portion and a water-cooled lower portion using specialized plate coolers. The throat and body rest on support rings.
3. Belly: Known as the reduction zone.
4. Boshes: This region houses the tuyere zone, where air is blown into the furnace, and combustion occurs.
5. Hearth: The circular portion below the boshes.
6. Slag Outlet: Positioned in the upper hearth region.
7. Taphole: Found in the lower hearth area.
8. Bottom and Furnace Floor: Constituting the lowest section of the furnace.

Operating Temperatures by Zone

• Upper Furnace Body and Gas Pipelines: 300–400°C
• Lower Furnace Body: 1200–1250°C
• Boshes: 1710–1750°C
• Hearth: 1550–1600°C
• Furnace Floor: 1300°C
• Inclined Chutes: 1500°C

The highest wear and tear occur in the lower furnace body and boshes, making the lifespan of the refractory lining in these areas critical to the overall service life of the furnace.

Causes of Refractory Damage

1. Chemical Erosion: Intense chemical reactions caused by slag, especially in the lower furnace body, involving alkali vapors, carbon monoxide, and zinc.
2. Thermal Shock: Significant temperature fluctuations induce thermal stress.
3. Mechanical Abrasion: Wear due to the descending raw materials.
4. Erosion: Gas and liquid iron erode solid particles.

Solutions and Materials

To combat these challenges, blast furnace refractory materials must exhibit excellent resistance to wear, thermal creep (200 hours at 450°C), and stability against carbon monoxide and thermal cycling. However, even large blast furnaces producing 2–2.5 tons of pig iron per unit require additional measures when gas pressure at the throat reaches 0.2–0.25 MPa.

Refractory materials commonly used include:

• Sintered Corundum Bricks with Mullite Bond: Al₂O₃ content 88–94%, apparent porosity 15–13.5%.
• Sintered Corundum Bricks with Bauxite Bond: Al₂O₃ content 88%, apparent porosity 13–16%.
• Sintered Chrome-Corundum Bricks: Al₂O₃ content 92%, Cr₂O₃ content 7.5%, apparent porosity 16–19%.

These high-alumina refractories with low apparent porosity are vital for maintaining the furnace's operational stability and extending its service life.