Refractory brick linings are the core heat-resistant protective structures for equipment such as industrial kilns and high-temperature vessels. Through specific brick shape design, masonry methods, and material combinations, they protect the equipment shell and maintain the process temperature. The structural design of refractory brick linings is highly matched to their functions, and customization is required based on the application scenarios (e.g., kiln type, temperature, and medium corrosiveness).
I. Structural Composition of Refractory Brick Linings
A refractory brick lining is not a simple “stack of bricks” but a collaborative structure composed of multiple functional layers. From the equipment shell to the high-temperature side (hot face), it is usually divided into 3 layers, and additional auxiliary layers may be added in some complex scenarios.
| Structural Layer | Core Materials | Reference Thickness Range | Core Function |
| Insulation Layer | Lightweight insulation bricks (high-alumina insulation bricks, fire clay insulation bricks), insulating castables | 50-200mm | Reduces heat transfer to the equipment shell, lowers the shell temperature(usually controlled below 200℃) reduces energy consumption |
| Working Layer | Heavy refractory bricks (high-alumina bricks, silica bricks,magnesia bricks, corundum bricks) | 100-300mm | Directly contacts high-temperature flames/materials (with temperatures up to 800-1800℃) withstands high-temperature scouringchemical erosion, and mechanical wear |
| Transition Layer | Medium-weight refractory bricks (fire clay-alumina composite brick) | 50-100mm | Alleviates the temperature gradient and thermalexpansion difference between the working layer and the insulation layer, preventing the lining fromcracking due to thermal stress |
| Auxiliary Structures | Refractory mortarexpansion joint fillers, anchors | – | Bonds bricks together, absorbs thermal expansionand fixes the lining (to prevent falling off) |
Key Structural Details of Refractory Brick Linings
Brick Shape Design: Adapting to Equipment Form and Stress Requirements
Refractory bricks are not all “standard rectangles”; special brick shapes need to be designed according to the equipment structure (e.g., circular kilns, square furnace chambers, inner walls of pipelines). The core types include:
- Standard straight bricks: Used for flat walls and floors, accounting for 70%-80% of the total.
- Special-shaped bricks: Such as wedge-shaped bricks (used for the arch roof of circular kilns to achieve “arch load-bearing” and distribute weight), cut bricks (for filling non-standard gaps), and grooved bricks (for fixing anchors).
- Extra-special-shaped bricks: Custom-made for complex parts (e.g., kiln mouths, around burners), which need to withstand higher temperatures and air flow scouring.
Masonry Methods for Refractory Brick Linings: Ensuring Sealing Performance and Structural Stability
The quality of masonry directly affects the service life of the lining, with core requirements including:
Mortar Joint Control: The mortar joints of the working layer are usually ≤ 2mm (using high-density refractory mortar), and those of the insulation layer are ≤ 3mm (using lightweight mortar). This prevents high-temperature gas from penetrating through the mortar joints (which would cause burnout of the insulation layer).
Staggered Joint Masonry: The mortar joints of adjacent brick layers are staggered (similar to the “header-stretcher masonry” of brick walls), avoiding the formation of through cracks and enhancing the structural integrity.
Arch Roof Masonry: A “radial arrangement” is adopted, where the small end of each wedge-shaped brick faces the center of the circle. A self-supporting structure is formed through the extrusion between bricks, requiring no additional supports.
Expansion Joint Design: Preventing Cracking Due to Thermal Expansion
Refractory bricks expand at high temperatures (with a linear expansion rate typically ranging from 0.5% to 2%). Without expansion joints, the lining will crack due to “thermal stress”, so they must be installed in accordance with specifications:
- Spacing: Along the length/height of the furnace chamber, a longitudinal/transverse expansion joint is installed every 3-5 meters, with a width of 20-50mm.
- Fillers: Compressible, high-temperature-resistant materials (e.g., ceramic fiber ropes, refractory cotton dedicated for expansion joints) are used for filling. This prevents air leakage in the cold state and extrusion in the hot state.
II. Core Functions of Refractory Brick Linings
The functions of refractory brick linings revolve around three core goals: “protecting equipment”, “ensuring process stability”, and “reducing energy consumption”.
1. High-Temp Protection Function of Refractory Brick Linings: Safeguarding the Equipment Shell
The shells of industrial kilns are mostly made of steel (e.g., Q235 steel), which can only withstand temperatures of 300-400°C, while the temperature inside the furnace chamber often exceeds 1000°C. The refractory brick lining (especially the working layer) can directly withstand high temperatures, reducing the shell temperature to a safe range (usually ≤ 180°C). This prevents the shell from high-temperature deformation and oxidative corrosion, and extends the overall service life of the equipment.
2. Refractory Brick Linings Maintain Process Temperature and Stabilize Production Conditions
Most high-temperature processes (such as iron and steel smelting, cement calcination, and ceramic sintering) have extremely high requirements for temperature stability (temperature difference needs to be controlled within ±50°C). The stable thermal conductivity and low heat dissipation of refractory brick linings (thanks to the insulation layer) can reduce heat loss inside the furnace chamber. This helps the equipment quickly heat up to the process temperature and maintain stability, avoiding product quality disqualification caused by temperature fluctuations (e.g., underfired ceramics, insufficient cement strength grade).
3. Corrosion and Wear Resistance Function of Refractory Brick Linings: Withstanding Harsh Working Conditions
In addition to high temperatures, there are various “destructive factors” inside the furnace chamber, and the refractory brick lining must resist them in a targeted manner:
- Chemical corrosion: For example, alkaline clinker (CaO) in cement kilns can corrode fire clay bricks, so alkali-resistant magnesia-alumina spinel bricks are required; molten iron and slag in ironmaking blast furnaces can erode the brick body, so high-alumina or carbon composite refractory bricks are needed.
- Mechanical wear: For example, when a rotary kiln rotates, materials (ore, clinker) scour the lining bricks. High-density and high-hardness wear-resistant refractory bricks (e.g., corundum-mullite bricks) are required.
- Thermal shock impact: For example, in the “heating-cooling” cycle of intermittent kilns (e.g., down-draft kilns), refractory bricks with good thermal shock resistance (e.g., fire clay bricks with thermal shock stability ≥ 15 times) are required to prevent the brick body from cracking due to sudden temperature changes.
4. Refractory Brick Linings Achieve Thermal Insulation and Energy Conservation, Reducing Energy Consumption
The energy consumption of industrial kilns accounts for 20%-30% of the total industrial energy consumption. The insulation layer of the refractory brick lining is the “key to energy conservation”: through the low thermal conductivity of lightweight insulation bricks (usually 0.2-0.8W/(m·K), much lower than the 1.5-3.0W/(m·K) of heavy bricks), heat loss through the furnace wall is reduced. Taking a Φ3×50m rotary kiln as an example, a high-quality lining can reduce heat loss by 15%-20%, saving more than 100,000 cubic meters/ton of natural gas/coal consumption annually.
5. Refractory Brick Linings Realize Sealing and Gas Control, Ensuring the Process Environment
Some processes (such as ceramic glaze firing and metal heat treatment) need to be carried out under an “inert atmosphere” or “slight positive pressure”. The staggered joint masonry and mortar joint sealing of the refractory brick lining can prevent external air from infiltrating (avoiding oxidation) and at the same time prevent harmful gases (e.g., S2, NOₓ) inside the furnace chamber from leaking. This not only ensures product quality but also reduces environmental pollution.
