A Complete Guide to Kiln Firebrick
Kiln Firebrick is a refractory material specially designed for industrial kilns. Usually made of sintered high-temperature resistant minerals. It can maintain a stable structure in high-temperature environments and chemical corrosion environments. It can insulate against high temperatures, reduce heat loss, resist chemical corrosion, and withstand the impact of thermal stress. When limestone is calcined in a vertical lime kiln or limestone rotary kiln, temperatures reach 1200°C or even higher. Therefore, there are extremely high requirements for refractory materials to ensure that the lime calcination kiln can operate stably. Ordinary refractory materials cannot meet the criteria. The choice of kiln firebrick is extremely important. This article will take you to know more about kiln firebrick and help you choose the most suitable kiln firebrick.
Kiln Firebrick Categories
1. Magnesia Brick
Magnesia bricks are alkaline refractory bricks with magnesium oxide as the main component. It has excellent resistance to alkaline corrosion and can effectively resist high-temperature corrosion of CaO in lime kilns. Its refractoriness exceeds 2000℃, and its high-temperature strength is good, but its thermal shock resistance is poor.
2. Magnesia Chrome Brick:
Magnesia-chrome bricks are made of magnesium oxide and chromite, combining the alkali resistance of magnesia bricks and the thermal shock stability of chromite. However, attention should be paid to environmental issues, as harmful Cr⁶⁺ may be generated.
3. Dolomite Brick:
Dolomite bricks are made from natural dolomite. Because its composition is similar to lime, it has good compatibility with the kiln environment at high temperatures. However, it easily absorbs moisture and turns into powder, so it needs to be stored in a moisture-proof manner and used with sealing measures.
4. High Alumina Brick:
High alumina bricks are divided into different grades according to the alumina content. It has high refractoriness and good resistance to chemical corrosion and is cost-effective.
5. Silica Brick:
Silica-molybdenum bricks are composite refractory materials with silicon carbide added to a high-alumina matrix. It has both the high-temperature resistance of high alumina bricks and the wear resistance and high thermal conductivity of silicon carbide.
6. Lightweight Clay Brick:
Lightweight clay bricks are characterized by a porous structure and low thermal conductivity. It has poor mechanical strength and corrosion resistance, does not directly contact high-temperature materials, and is often used in conjunction with working layer refractory bricks to optimize energy efficiency.
Applicable Areas of Various Types of Kiln Firebrick
1. Magnesia bricks: suitable for high-temperature calcining zone of lime kiln, especially the area in direct contact with lime.
2. Magnesia-chrome bricks: suitable for use in the transition zone of the rotary kiln, the area connecting the preheating and calcining zones.
3. Dolomite bricks: suitable for use in the calcining zone of static kilns, such as the high-temperature area of vertical lime kilns.
4. High alumina brick: Ordinary high alumina bricks are suitable for the preheating zone and cooling zone. High-purity high alumina bricks are suitable for small lime kiln calcining zones.
5. Silica-molybdenum bricks: suitable for use in the rolling friction area of limestone rotary kiln materials.
6. Lightweight clay bricks: suitable for the outer insulation layer of the kiln body without direct contact with flames or materials.
They can be Used in These Kilns
- Glass melting furnace
- lime calcination kiln
- Pet cremation incinerator
- Garbage incinerator
- Activated carbon furnace
Kiln Firebrick Selection Guide
- Operating Temperature
When selecting kiln linings fire bricks, firstly, the operating temperature range of each part of the kiln should be accurately determined to ensure that the refractoriness of the selected material is at least 100-200℃ higher than the maximum operating temperature.
- Chemical Environment
The chemical medium characteristics in the kiln must be analyzed, including acidity, alkalinity, redox properties, and corrosive gas composition.
- Mechanical Stress
Select corresponding kiln linings fire bricks according to the mechanical loads borne by different parts of the kiln. For equipment with large vibrations, the flexural strength and toughness of the bricks must also be considered.
- Thermal Properties
The thermal properties of kiln linings fire bricks directly affect the kiln energy efficiency and operational stability. For areas with large temperature gradients, a gradient composite lining design may be considered.
- Economic Considerations
Under the premise of meeting the technical requirements, the balance between initial cost and service life needs to be comprehensively evaluated. The most economical kiln linings fire bricks should be selected.
Kiln Firebrick Construction and Installation
1. Preparation work before masonry:
Before the construction of refractory bricks, the material quality must be strictly checked to ensure that the bricks have no cracks or missing corners and that the size meets the design requirements. Clean the surface of the kiln steel structure, remove rust, oil stains, and old brick residues, and spray the anti-rust layer if necessary. Prepare special refractory slurry, ceramic fiber expansion joint materials, and construction tools. The ambient temperature should be kept at 5-35℃ to avoid humid or low-temperature operations that affect mud solidification.
2. Masonry technology:
Staggered overlap is required during masonry, with brick joints staggered by 1/2 or 1/3 of the brick length. Use matching refractory slurry for wet masonry, control the mortar joints at 1-3mm, and use the slurry extrusion method to ensure that the fullness is >95%. The deviation between verticality and horizontality must be ≤2mm/m, and should be checked every 3-5 layers. The anchors should be welded firmly in advance and embedded in the bricks to a depth of ≥ 2/3 of the brick thickness. The top of the arch needs to be supported by formwork, and locked with bricks after symmetrical masonry.
3. Expansion joint treatment:
The expansion joint width is reserved at 1%-1.5% of the brick lining length. One is set every 1-1.5m horizontally, and an oblique seam is added at the corner of the kiln body. Fill the seams with ceramic fiber blankets or compressible refractory boards to prevent lining extrusion and cracking due to thermal expansion. The joints of bricks of different materials must be separated to prevent structural damage due to differences in thermal expansion coefficients. After construction, the sealing of the gaps needs to be checked to ensure that no refractory mud has penetrated and affected the expansion and contraction function.
Kiln Firebrick FAQ
- Brick Cracking or Peeling
It may be caused by excessive thermal stress, insufficient expansion joints, mechanical stress, material mismatch, etc.
- Surface Melting or Chemical Corrosion
It may be alkaline or acidic corrosion, slag penetration leading to loose structure, and corrosive gases reacting chemically with refractory materials.
- Local Wear is Too Fast
The friction of hard particles such as materials in the kiln, the high-speed and high-temperature airflow erodes the brick surface, and the density of the brick body is insufficient.
- Deformation or Collapse of the Overall Structure
This may be caused by construction problems such as failure of the anchoring system, long-term use at temperatures exceeding the design temperature, loose brick locks, insufficient arch support, etc.
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