Refractory Configuration and Optimization for a 5000t/d Clinker Line (2)

Refractory materials are developing towards environmental friendliness, strong adaptability, and long service life. Rongsheng Refractory Materials Factory supplies refractory materials for kilns used in 5,000 t/d clinker production lines. Rongsheng Refractory Materials Manufacturer leverages its innovative capabilities in refractory castables while focusing on customer needs, aiming to provide high-quality, long-life refractory lining materials for high-temperature industrial furnaces. Contact Rongsheng for free solutions.

Refractory Lining Configuration for a 5,000 t/d Cement Clinker Production Line

This article focuses on the refractory configuration for a 5,000 t/d cement clinker production line. The cement firing system involves a complex chemical process from raw meal to clinker, going through stages such as preheating in the preheater, decomposition in the calciner, high-temperature calcination, and cooling. The refractory materials used in each stage must be adapted to this process.

(3) Kiln Head Hood

The kiln head hood connects the rotary kiln to the cooler and serves as the inlet for kiln air and tertiary air. Air pressure is extremely unstable, making positive pressure a common feature of the entire kiln system. Gas temperatures range from 800-1300°C, with significant temperature fluctuations. Furthermore, the impact of clinker particles is intense, making the top and inlet areas susceptible to damage. Therefore, thermal shock resistance and wear resistance should be considered when selecting materials.

1. High-Alumina High-Strength Wear-Resistant Castable

Amount: 180 tons

Technical Performance:

Application Location: Round top

2. Calcium Silicate Board

Amount: 7.2 tons

Technical Performance: See above

Application Location: All refractory linings

(4) Burner

Because the burner is located in the high-temperature gas between the kiln mouth and the cooler, and the pulverized coal burns near the burner head, it is significantly affected by the high-temperature radiation and reducing atmosphere. The chemical composition of coal significantly influences combustion, making the burner head plate susceptible to damage. The refractory material used in this area requires high refractoriness and wear resistance, as well as enhanced thermal shock stability and spalling resistance.

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1. Mullite Castable

Quantity: 5 tons

Technical Performance:

Application Area: Burner head hood where it enters the kiln

(5) Rotary Kiln

As a rotating drum that calcines raw materials into clinker at high temperatures, the lifespan of its refractory materials often determines the production cycle, making it a key and challenging aspect of refractory material management in cement plants. After preheating and approximately 90% decomposition, the raw material enters the kiln from the kiln outlet, where its temperature gradually rises to over 1450°C, completing the calcination process and entering the cooler. A 74-meter rotary kiln can be broadly divided into five thermal stages. Because the refractory materials within the rotary kiln must be fixed to the continuously rotating drum, the strength of the refractory bricks must not fall below a certain threshold due to the following factors:

1. There is a certain degree of slippage or sliding tendency between the refractory bricks and the shell, generating friction. The refractory bricks must possess a certain strength to resist damage from this friction.
2. A rotary kiln is not an absolutely rigid structure when viewed axially. Because the rotary kiln drum has a certain curvature between its support points, it experiences periodic bending in sync with its rotation during operation. Because the three-roller rotary kiln utilizes a statically indeterminate structure, the different expansion rates of each roller group due to temperature differences can cause deviations in the kiln shell’s coaxiality, generating significant additional loads. Furthermore, the 4% inclination of the kiln shell also generates downward stress during rotation.
3. The shell is not a perfect circle in the radial direction, but rather an elliptical shape. Deformation is greatest at the wheel belts, and this deformation places additional pressure on the refractory bricks. Due to the kiln’s own weight and rotation, the kiln undergoes periodic elliptical deformation, synchronized with the rotation, placing alternating loads on the refractory bricks. When this deformation or elliptical deformation reaches a certain value, it can exceed the internal stresses in the refractory bricks, causing premature failure. Therefore, refractory materials with insufficient strength must be used in rotary kilns; they must meet basic strength requirements.
4. In addition to the aforementioned mechanical stresses, the refractory materials within the kiln are also subject to the effects of high-temperature gases and liquid clinker. It can be roughly divided into five or six working zones, which require different refractory materials for laying.

Refractory Configuration for a 5,000-ton Rotary Kiln:

1. Mullite Castable

Usage: 15 tons

Technical Performance: See above (RT-70MC)

Applicable Area: 0-0.6 m

2. High-Abrasion-Resistant Bricks

Usage: 8 tons

Technical Performance:

Applicable Area: 0.6-1.6 m

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3. Direct-Bonded Magnesia-Chrome Bricks

Usage: 340 tons

Technical Performance:

Applicable Area: 1.6-25 m/35-45 m

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4. Spinel Bricks

Usage: 99 tons

Applicable Area: 25-35 m

5. Anti-Spalling Bricks

Usage: 242 tons

Applicable Area: 45-73.2 m

6. High-Alumina Castables

Usage: 8.5 tons

Technical Performance: See above

Applicable Area: 73.2-74 m

(6) Cooler

The cooler uses air to cool the hot clinker leaving the kiln from 1400°C to below 80°C. Due to the large temperature difference between the front and rear sections, the most vulnerable parts are concentrated in the front wall and the lower wall. Furthermore, the overhanging beams at the interface with the kiln head are also susceptible to premature damage due to the erosion of high-temperature gases.

Grate coolers are stationary relative to the refractory shell, so insulation materials with low strength but low thermal conductivity can be used on the outer layer. The cooler’s inner surface must withstand thermal erosion and high-temperature abrasion caused by contact with high-temperature clinker at 300-1450°C, so the selected refractory materials must have strong wear resistance. Furthermore, the first stage cooler must also withstand high thermal loads.

Because the grate cooler has large vertical walls, the use of special anchoring refractory bricks is crucial when constructing the refractory brickwork to strengthen the connection between the bricks and the shell to prevent collapse of the vertical walls.

Currently, the most commonly used refractory castables are:

1. High-strength alkali-resistant castable

Usage: 20 tons

Technical properties: See above (RT-13NL)

Application: Section 3 and top

2. High-alumina castable

Usage: 106 tons

Technical properties: See above (RT-16)

Application: Section 2 and 3 side walls and parapet

3. High-heat high-alumina castable

Usage: 183 tons

Application: Cooler front wall and Section 1 parapet

(To be continued…3)

Refractory Configuration and Optimization for a 5000t/d Clinker Line (1)

Refractory materials are developing towards environmental friendliness, strong adaptability, and long service life. Rongsheng Refractory Materials Factory supplies refractory materials for kilns used in 5,000 t/d clinker production lines. Rongsheng Refractory Materials Manufacturer leverages its innovative capabilities in refractory castables while focusing on customer needs, aiming to provide high-quality, long-life refractory lining materials for high-temperature industrial furnaces. Contact Rongsheng for free solutions.

Refractory Lining Configuration for a 5,000 t/d Cement Clinker Production Line

This article focuses on the refractory configuration for a 5,000 t/d cement clinker production line. The cement firing system involves a complex chemical process from raw meal to clinker, going through stages such as preheating in the preheater, decomposition in the calciner, high-temperature calcination, and cooling. The refractory materials used in each stage must be adapted to this process.

(1) Preheater System

This system utilizes kiln exhaust gas to gradually heat the raw meal from ambient temperature in a suspended state to above 750°C before entering the precalciner system for decomposition. The amount of refractory material used in this system accounts for nearly two-thirds of the total refractory material used. Its thermal characteristics are:

1. 60% of the fuel and the preheated raw meal are thoroughly mixed in the precalciner for flameless combustion. Wall and flue gas temperatures are generally controlled below 1000°C. The temperatures of the other cyclones, from the first to the fifth stage, are not higher than 450°C, 650°C, 750°C, 900°C, 1000°C, and 1100°C, respectively.
2. The preheater system calcines the material with virtually no liquid phase, resulting in minimal agglomeration and sintering, and therefore requires less refractoriness. Furthermore, the overall system temperature is relatively stable, requiring less thermal shock resistance from the refractory material.
3. The preheater system is a stationary device, but its size is relatively large, requiring insulation materials with low thermal conductivity to reduce the outer shell temperature.
4. Due to the complex shape of the preheater system, including cones, cyclone inlet and outlet diameter changes, thin feed pipes, and numerous measuring holes, it is more convenient to use on-site formed refractory castables in these areas.
5. When using raw materials and fuels with high alkali content, the refractory materials in the preheater must withstand not only high-temperature corrosion but also chemical attack from alkali metal oxides.

The aforementioned thermal environment generally determines the configuration of refractory materials for each stage of the preheater, and the following principles should be followed:

1. Refractory materials with low thermal conductivity, good insulation, and a working surface with sufficient strength and resistance to alkali corrosion should be used.
2. Castables should be used for sections with complex shapes and a large number of thin pipes, while alkali-resistant bricks should be used for straight tubes and regular sections.
3. Different materials should be designed for different sections based on the different temperatures of the cyclones and to save costs. For example, for the first and second stage cyclones, a combination of refractory and insulation considerations can be considered, and clay-based alkali-resistant refractory materials can be selected. For preheaters below the third stage, alkali-resistant materials capable of temperatures exceeding 1100°C should be used.
4. Anti-scaling castables should be used for the refractory castables from the fifth stage to the smoke chamber and below the calciner, as the surface is prone to scaling.

The following is a brief introduction to the selection and dosage of refractory materials for the preheater of a 5000t/d production line:

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1. RK-H High-Strength Alkali-Resistant Bricks

Quantity: 569 tons

Performance:

Application Areas: Vertical ascending flues, cyclone tubes, and cones

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2. High-strength alkali-resistant castable

Usage: 850 tons

Performance:

Construction method:

Application: Tops of preheater stages 1-4, irregular shapes, etc.

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3. High-alumina low-cement castable

Usage: 200 tons

Performance:

Application: Precalciner, fifth-stage drum

4. Anti-scaling castable

Usage: 112 tons

Performance:

Application Area: Kiln tail flue chamber

5. Calcium Silicate Board

Consumables: 156 tons

Performance:

Application area: All refractory linings

(2) Tertiary Air Ducts

Tertiary air ducts utilize high-temperature, oxygen-rich gases from the kiln head to guide the ducting channels of the precalciner. At temperatures of 800-900°C, these gases contain a large amount of clinker particles, which can severely erode and wear the refractory materials at the bends. Therefore, the system’s alkali resistance and wear resistance must be considered. High-strength alkali-resistant bricks and calcium silicate board are used in the straight sections, while high-wear-resistant castables and calcium silicate board are used in the irregular sections.

Currently, two types of tertiary air ducts are used: parallel ducts and V-shaped ducts. Parallel ducts are arranged almost parallel to the kiln, while V-shaped ducts are V-shaped, with a settling chamber and discharge gate valve located at the lower end of the duct.

Parallel ducts are simple in design, aesthetically pleasing, and require minimal investment. However, to prevent clinker particles from settling in the tertiary duct, higher operating air velocities are required, resulting in greater resistance in the tertiary duct. This higher air velocity also requires higher wear resistance from the refractory materials. The V-type duct is more complicated and requires a large investment. It also requires regular dust discharge from the discharge gate valve. However, the V-type duct can adopt a lower operating wind speed, so the system resistance is low, and the wind speed wear is small.

The refractory material usage and performance requirements are as follows:

1. RK-H High-Strength Alkali-Resistant Bricks

Usage: 140 tons

Performance: See above

Application: Straight sections of air ducts

2. Ultra-High-Strength Wear-Resistant Castable

Usage: 70 tons

Performance:

Application Area: Tertiary duct bends and gates

3. Calcium Silicate Board

Consumables: 17 tons

Performance: See above

Application Area: All refractory linings

( To be continued…2)

Suitable for Aluminum Alloy Smelting – Unshaped Refractories Medium Temperature Low Cement Castable

The aluminum alloy melting process poses unique and demanding challenges to refractory materials, stemming from the physical and chemical properties of molten aluminum and its alloys. While the combustion chamber of an aluminum melting furnace can reach temperatures of approximately 1200°C, the furnace chamber area in direct contact with the molten aluminum typically only reaches temperatures of 700-800°C (the casting temperature for 6063 aluminum alloy is 720-740°C).

This means that the furnace lining material spends most of its time in a medium-temperature range, rather than a traditionally high-temperature state. In this temperature range, traditional refractories often experience a strength dip due to bonding phase transitions. For example, hydration products (such as CAH₁₀ and C₂AH₈) in cement-bonded Unshaped Refractories Castables begin to dehydrate at 300-400°C, losing their bonding properties while the ceramic bond is not yet fully formed, resulting in a significant drop in strength.

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Low-Cement Castables: Medium- and Low-Temperature Strength Properties

Low-cement castables exhibit unique strength properties in the medium- and low-temperature ranges, distinct from conventional castables. During heating, conventional aluminate cement unshaped refractories castables typically experience a decrease in strength (due to hydrate dehydration) followed by an increase (due to ceramic bonding), with a distinct strength dip occurring in the 800-1000°C range. Low-cement refractory castables, however, exhibit a significant increase in strength at medium temperatures, rather than a decrease in strength.

The research examples in the table below demonstrate that the hot flexural strength of low-cement castables at 800°C is significantly higher than that at room temperature. Low-cement castables made primarily of kyanite-mullite (M45 and M60) exhibit the greatest increase in hot flexural strength with increasing treatment temperature. Low-cement castables made primarily of high-alumina bauxite (M85) exhibit the second-highest increase. Conventional Unshaped Refractories castables using CA-50 cement as a binder exhibit a distinct strength dip after firing at 800°C.

Table: Changes in hot flexural strength after treatment at different temperatures (MPa)

The mechanism of this anomaly is that the dehydration of calcium aluminate hydrate in low-cement castables is slow and continuous, with minimal damage to the crystal structure. Simultaneously, the ultrafine powder begins to sinter at moderate temperatures, forming a preliminary ceramic bond.

Core Characteristics and Advantages of Low-Cement Castables

Low-Cement Castables (LCC) are a new generation of unshaped refractory materials developed in the 1980s. Compared to traditional aluminate cement Unshaped Refractories castables, their core characteristic lies in a significant reduction in the amount of calcium cement (typically from 12-20% to 3-8%). Furthermore, through the introduction of ultrafine powder technology and high-efficiency admixtures, they achieve a comprehensive performance optimization of high density, low porosity, and high strength.

The revolutionary breakthrough in low-cement castables stems from the application of ultrafine powder technology. Ultrafine powders (such as reactive SiO₂ powder and α-Al₂O₃ powder) with particle sizes less than 1.0μm can exceed 71%. These ultrafine particles possess an extremely high specific surface area and reactivity, effectively filling the gaps between aggregate particles and achieving the densest packing. It prevents particle size segregation, reduces porosity and pore diameter, ensures the fluidity of the mixture, and improves the density and bonding strength of the Unshaped Refractories castable. More importantly, the high specific surface area and reactivity of ultrafine powder significantly reduce sintering temperatures and promote sintering at medium and low temperatures.

Active SiO₂ ultrafine powder not only improves the fluidity of the castable but is also one of the most effective sintering accelerators. At temperatures above 900°C, SiO₂ ultrafine powder reacts with Al₂O₃ to form mullite (3Al₂O₃·2SiO₂), accompanied by a volume expansion of approximately 10.5%. This volume effect effectively offsets some of the volume shrinkage of the unshaped refractory castable, promoting strength improvement. Furthermore, the mullite phase forms at a relatively low temperature (beginning to form in large quantities at approximately 1000°C), and its needle-shaped or columnar crystal structure forms a cross-linked skeleton, significantly enhancing the material’s strength.

Ultrafine α-Al₂O₃ powder strengthens the material through a different mechanism. It promotes the formation of calcium hexaaluminate (CA₆) from calcium aluminate at high temperatures, along with smaller amounts of mullite, anorthite, CA, and CA₂. These minerals have large molar volumes, which prevent volume shrinkage. Furthermore, CA₆ crystals are small columnar and needle-shaped, while anorthite crystals are fine columnar. Together, they form a cross-linked structure of fine columnar and needle-shaped structures, resulting in a strong and dense structure that can reach strengths of around 100 MPa.

The setting and hardening mechanism of low-cement castables is also fundamentally different from that of traditional Unshaped Refractories castables. Traditional castables primarily derive their strength from hydration products (such as CAH₁₀ and C₂AH₈) produced by cement hydration. However, these hydrates dehydrate and decompose during heating, significantly reducing their strength at medium temperatures. Low-cement castables, on the other hand, rely primarily on a cohesive bonding mechanism: ultrafine powder particles form colloidal particles in water, which form a three-dimensional network structure through van der Waals forces and chemical bonds, tightly binding the aggregate particles together. Cement acts only as a delayed-acting setting accelerator. This cohesive mechanism ensures that the strength of low-cement castables does not decrease due to hydrate decomposition during heating, but instead continues to increase due to sintering.

By carefully controlling the type, particle size distribution, and additive amount of fine powder, low-cement castables achieve an ideal strength development curve within the operating temperature range of aluminum alloy smelting (700-900°C). This avoids the mid-temperature strength trough common in traditional Unshaped Refractories castables while providing sufficient high-temperature performance, perfectly adapting to the unique operating conditions of aluminum melting furnaces.

However, there are downsides. Low porosity and high densification also result in poor air permeability. During baking and heating, steam generated by internal moisture cannot be promptly dissipated, easily building up high pressure within the lining, causing it to spall or crack. Therefore, when using low-cement castables, a reasonable baking system and the addition of explosion-proof agents must be used.

Conclusion

From the “medium-temperature dilemma” of traditional Unshaped Refractories castables to the “precise breakthrough” of low-cement castables, the path to upgrading refractory materials is essentially a matter of precisely matching material properties with operating requirements. For the unique application of aluminum alloy smelting, low-cement castables restructure their strength formation mechanism through ultrafine powder technology. This not only addresses the strength limitations of the medium-temperature range, but also addresses the core requirements of high density and corrosion resistance. This makes them a key material support for the longevity and high efficiency of aluminum industry furnaces.