Refractory material selection for heating furnaces (including industrial kilns, boilers, metallurgical furnaces, etc.) shall be precisely matched according to core operating conditions such as working temperature, thermal load, medium corrosiveness and mechanical stress, as well as the functional differences of each component. Below are the refractory material types and selection logic for key sections of heating furnaces, covering common industrial scenarios such as iron & steel, chemical, power and building‑material industries.
I,Correspondence Table of Furnace Key Zones and Refractory Materials
| Section | Core Service Condition Characteristics | Recommended Refractory Types | Typical Materials / Product Forms |
| Furnace Roof (Suspended Roof / Arch Roof) | High temperature (1200‑1800 °C), low load‑bearing capacity, frequent thermal shock | Refractory bricks (clay, high‑alumina, silica), refractory castables | High‑alumina bricks (Al₂O₃ 60%‑85%), corundum‑mullite castables, silica bricks (SiO₂≥93%, for service above 1600 °C) |
| Furnace Wall (Side Wall / End Wall) | Medium‑high Temp. (1000‑1600 °C), Medium Corrosion, Mechanical Impact | Refractory bricks, refractory castables, refractory fibre products | Clay bricks (Al₂O₃ 30%‑45%), high‑alumina castables, lightweight insulating refractory bricks, ceramic fibre modules |
| Furnace Bottom (Load‑Bearing Layer / Working Layer) | High temperature, load‑bearing service, material abrasion / corrosion, thermal shock | High‑abrasion‑resistant refractory bricks, refractory castables, ramming mixes | Phosphate‑bonded abrasion‑resistant castables, corundum ramming mixes, magnesia‑alumina spinel bricks (for metallurgical furnaces), silicon carbide bricks (for severe corrosion conditions) |
| Burner Block / Burner Outlet | Local ultra‑high temperature (1600‑1800 °C), flame scouring, severe thermal shock | Corundum & mullite refractory bricks / castables | Corundum bricks (Al₂O₃ ≥90%), mullite‑corundum castables, zircon bricks (resistant to high‑temperature scouring) |
| Flue / Chimney | Medium‑low temperature (600‑1200 °C), flue gas corrosion, abrasion resistance | Clay bricks, lightweight refractory bricks, refractory castables | Clay refractory bricks, lightweight high‑alumina bricks, acid‑resistant castables (for chemical furnace flues) |
| Furnace Door / Sight Hole | Wide temperature fluctuation, mechanical abrasion, thermal shock | High‑alumina bricks, refractory castables, refractory fibres | High‑alumina castables, ceramic fibre blanket plus corundum inserts |
| Water‑cooled Wall / Furnace Tube Wrapping | Thermal insulation, abrasion resistance, high‑temperature radiation resistance | Refractory castables, plastic refractories, refractory fibres | Lightweight insulating castables, corundum plastic refractories, ceramic fibre modules |
| Taphole / Discharge Outlet | High temperature, material scouring, corrosion | Corundum & silicon carbide refractories | Corundum‑silicon carbide castables, silicon nitride‑bonded silicon carbide bricks |
II,In‑depth Analysis on Material Selection for Key Furnace Sections
1. Furnace Roof: Priority to high‑temperature resistance and thermal‑shock resistance
Suspended Ceiling (hanging‑type): High‑alumina bricks and corundum‑mullite castables are commonly adopted. It avoids load‑bearing cracking of arch crowns, suitable for industrial furnaces at 1200‑1600 ℃.
Arch Crown (curved‑type): Silica bricks (above 1600 ℃, e.g. glass furnaces) and high‑alumina bricks (1400‑1600 ℃). Good sealing by proper brick shape masonry shall be guaranteed to prevent high‑temperature gas leakage.
Low‑temperature furnace roof (≤1200 ℃): Composite structure of clay bricks plus lightweight insulating bricks, balancing thermal insulation and cost‑effectiveness.
2. Furnace Hearth: Core requirements: abrasion resistance and erosion resistance
General‑purpose industrial furnaces (e.g. boilers, heat‑treatment furnaces): Phosphate‑bonded abrasion‑resistant castables and high‑alumina bricks, resistant to friction from accumulated materials.
Metallurgical furnaces (e.g. blast furnaces, converters): Magnesia‑alumina spinel bricks and silicon carbide bricks to withstand chemical erosion from molten iron and slags.
Heavy‑load service conditions: Adopt composite structure of clay bricks for load‑bearing layer + high‑alumina bricks for working layer. An additional insulating layer (e.g. ceramic fibre boards) shall be arranged at the bottom to reduce heat loss.
3. Burner Block: Core requirement: extreme resistance against high‑temperature scouring
The burner zone features the local maximum temperature inside the heating furnace (flame core temperature up to 1800 ℃). High‑purity and high‑density materials must be selected for this area：
Natural gas / Heavy‑oil burners: Pre‑cast high‑alumina corundum castable inserts for quick replacement.
Pulverized‑coal burners: Mullite‑corundum bricks plus silicon‑carbide inserts to resist scouring by coal‑powder particles.
Key requirements: Thermal‑shock stability (no cracking under rapid cooling by water cooling), volume stability (no shrinkage or deformation at high temperature).
4. Insulation Zones (Flues, Outer Furnace Wall): Balance thermal insulation and mechanical strength
Medium‑low temperature flues (≤800 ℃): Lightweight insulating refractory bricks (bulk density ≤1.2 g/cm³) with low thermal conductivity (≤0.4 W/(m·K)) to reduce heat dissipation loss.
Chemical furnace flues (with acidic gas): Acid‑resistant castables (e.g. quartz sand bonded with phenolic resin) to prevent brick corrosion by flue gas.
Inner furnace wall (working layer): Dense refractory bricks (clay / high‑alumina). Outer layer: lightweight insulating bricks plus thermal‑insulation fibres. Composite "refractory + thermal‑insulation" structure achieves over 30 % improvement in energy‑saving performance.
5. Refractory Fibre Products: Suitable for conditions with frequent thermal shock and lightweight‑demand requirements
Ceramic fibre blankets / modules (service temperature: 1000‑1400 ℃): Applied for furnace doors, furnace wall interlayers and water‑cooled wall wrapping. Their weight is only 1/5 of refractory bricks, with excellent thermal‑shock stability (resistant to rapid heating and cooling).
Note: Fibre products are not suitable for load‑bearing zones (e.g. furnace roof, furnace hearth), and shall be used together with rigid refractory materials.
III,Comparison of Material Properties for Common Refractories
| Material Type | Maximum Service Temperature (℃) | Key Properties | Application |
| Clay‑based | 1200-1400 | Low cost, good thermal‑shock resistance, moderate mechanical strength | Furnace walls, flues, low‑temperature furnace roof |
| High‑alumina (Al₂O₃: 60%‑85%) | 1400-1600 | High mechanical strength, erosion resistance and high‑temperature resistance | Furnace roof, furnace walls, furnace doors |
| Corundum‑based (Al₂O₃ ≥90 %) | 1600-1800 | High‑temperature resistance, scouring resistance, high hardness | Burner blocks, tap‑holes, key wear‑resistant sections |
| Silica‑based (SiO₂ ≥93 %) | 1600-1750 | High‑temperature resistance, good volume stability, acid‑gas corrosion resistance | High‑temperature arch roofs, glass furnaces |
| Silicon‑carbide‑based (SiC ≥80 %) | 1400-1600 | Excellent wear resistance, erosion resistance and good thermal conductivity | Furnace hearth, tap‑holes, pulverized‑coal furnace burners |
| Ceramic fiber | 1000-1400 | Light‑weight, heat‑insulating, good thermal‑shock resistance | Thermal insulation layers, furnace doors, water‑wall wrapping |
IV,Key Principles for Material Selection
Temperature matching: The operating temperature shall be 50‑100 ℃ lower than the maximum service temperature of the material for safety margin. For example, for furnace walls working at 1200 ℃, avoid clay bricks with max service temperature of 1200 ℃; high‑alumina bricks rated at 1400 ℃ are preferred.
Medium compatibility: For acidic media (e.g., flue gas containing SO₂, HCl), select silica‑based materials and acid‑resistant castables. For alkaline media (e.g., slags containing CaO, MgO), select magnesia‑based bricks and magnesia‑alumina spinel bricks.
Cost balance: For non‑critical areas (e.g., flues, outer layers of furnace walls), adopt clay bricks and lightweight bricks. For key parts (burner blocks, furnace hearth), adopt high‑performance materials such as corundum‑based and silicon‑carbide‑based products.
Constructability: For complex‑shape sections (e.g., burner blocks, tap‑holes), use castables for on‑site monolithic casting. For regular‑structure sections (furnace walls, furnace roofs), use refractory bricks for high masonry efficiency.
V,Typical Industry Application Cases
Iron & Steel Industry (Converter / Reheating Furnace): High‑alumina bricks + corundum castables for furnace roof; magnesia‑alumina spinel bricks for furnace hearth; corundum‑SiC precast blocks for burners.
Power Industry (Boiler): Clay bricks + lightweight insulating bricks for furnace walls; phosphate‑bonded wear‑resistant castables for furnace hearth; acid‑resistant castables for flues.
Chemical Industry (Cracking Furnace / Reactor Furnace): Ceramic fiber modules for furnace tube wrapping; corundum‑mullite castables for furnace roof; acid‑resistant bricks for flues.
Building‑material Industry (Cement Rotary Kiln): Corundum‑SiC castables for kiln inlet; high‑alumina bricks + magnesia‑alumina spinel bricks for kiln shell; lightweight insulating bricks for preheater.
