Introduction

Coke dry quenching (CDQ) technology is a core environmental protection technology in modern coking industry. It plays an irreplaceable role in energy conservation, emission reduction, and energy recycling. In recent years, environmental policies have promoted CDQ installations to replace traditional wet quenching methods. The technology has gained market favor due to its high efficiency and environmental advantages.

However, premature damage to refractory materials in the CDQ chute area has been a key bottleneck. This issue constrains the widespread application of the technology. Many installations experience problems within one year of operation. Cracks, fractures, and other issues in refractory materials appear frequently. These problems seriously affect production continuity and economic benefits.

This article systematically analyzes the root causes of refractory material damage in the CDQ chute area. It combines engineering practice to propose comprehensive quality control strategies. These strategies cover the entire process from raw material selection to operation management. The goal is to provide technical reference for extending the service life of refractory materials.

Analysis of Damage Mechanisms in Chute Area Refractory Materials

Challenges from Complex Working Conditions

The CDQ chute area is located at a critical position. Hot coke falls down while circulating gas flows through this area. The working environment is extremely harsh. Under normal operating conditions, circulating gas flows through the cooling section. It then enters the ash duct from the chute area. During this process, it carries some hot coke particles.

This process subjects the refractory materials to multiple stresses simultaneously. First is mechanical impact stress. Coke flows downward at a certain speed. It produces continuous wear and impact on the refractory material surface. When the flow rate is unstable, local wear intensifies. Second is thermal stress. The temperature in the lower part of the chute area varies drastically between 300-700°C. These temperature fluctuations generate enormous thermal stress inside the material. This leads to the initiation and propagation of micro-cracks.

In addition, the adhesion and obstruction of coke particles carried by circulating gas also change the stress distribution on the refractory material surface. When these combined stresses exceed the material’s load-bearing limit, macroscopic damage occurs. This includes cracking and spalling.

Acceleration Effect of Improper Operation

Unreasonable control of operating parameters significantly accelerates the damage process of refractory materials. Problems arise when the coke discharge rate suddenly increases. If the circulating air volume adjustment is not timely or the adjustment range is too large, it causes severe fluctuations in the temperature and flow fields inside the furnace. This makes the refractory materials bear greater thermal shock.

The mismatch between circulating air volume and coke discharge rate may also cause local overheating or overcooling. This further deteriorates the working conditions of the materials.

Construction of Full-Process Quality Control System

Strict Control of Raw Material Quality

The performance of refractory materials depends first on the quality of raw materials. The main raw materials for producing mullite silicon carbide bricks include mullite, silicon carbide, and alumina powder. Mullite can be classified into different types according to its source. These include sintered mullite, brown mullite, and fused mullite. Different types show significant performance differences.

Silicon carbide requires high-quality products with purity above 97%. When combined with ultrafine α-Al₂O₃ and other raw materials, it ensures that the products meet design requirements. It also satisfies actual production needs.

The purity of raw materials directly affects the physical and chemical indicators of final products. It also impacts service life. Excessive impurity content will form low-melting phases at high temperatures. This reduces the refractoriness and corrosion resistance of materials. Therefore, a strict raw material inspection system must be established. Comprehensive testing should be conducted on key indicators of each batch of raw materials. These include chemical composition, particle size distribution, and purity.

Mechanized Production Ensures Consistency

The traditional manual ramming brick-making method has many drawbacks. The chute area requires many brick varieties with complex specifications and large dimensions. Manual operation cannot guarantee product quality consistency. The limitations of testing equipment and methods make quality labeling inaccurate. This leads to physical and chemical indicators and dimensional errors that cannot meet strict requirements.

Adopting mechanized production is an effective way to solve this problem. Using a press with a capacity of 1000 tons or more for molding ensures uniform raw material distribution and consistent density. Selecting dry pressing or wet pressing processes according to brick shape characteristics achieves significant quality improvement. Secondary ratio optimization is also important.

After production molding, strict control of the firing temperature curve and heat preservation system in the temperature-controlled kiln is necessary. This ensures the density and stability of the organizational structure. For products with dimensional deviations or unqualified physical and chemical indicators, they must be returned to the factory for rework. This fundamentally guarantees product quality.

Fine Management of Masonry Quality

CDQ masonry is an integral structure. The chute area starts with variable angle connections from the beginning. This requires extremely high construction accuracy. The quality of construction directly determines whether refractory materials can form an effective overall load-bearing system.

During the masonry process, the rationality of load-bearing must be fully considered. Special attention should be paid to the hardening and compressive strength of refractory mortar after 24 hours at room temperature. In actual construction, this key factor is often neglected due to rushing the schedule. During masonry, displacement and sliding are likely to occur. This causes uneven force on each chute area. The symmetry and stability of the overall structure are greatly reduced.

To ensure masonry quality, the following key points should be strictly controlled. First, evenly distribute the center and circumferential distribution angles that support the chute area. This ensures balanced force distribution. Second, strictly control the joint error within ±0.5mm. The mortar must be full. Brick joints and levelness should be reasonably controlled.

Third, once any inclination or distortion is found, masonry should be stopped immediately and adjusted promptly. Fourth, reasonably control the construction schedule. It is recommended to lay one layer per day. This ensures that the mortar obtains sufficient cold strength. Finally, after masonry is completed, it should be dried for more than three days. This ensures that the strength meets standards and the chute area forms an integral structure. In addition, climate factors should be comprehensively considered. Construction should be carried out in summer and autumn seasons when possible.

Scientific Formulation of Baking System

Baking is a key link in ensuring the service life of CDQ refractory materials. New reverse baking methods can effectively suppress refractory material damage during baking. This significantly extends service life. Refractory materials usually contain a certain amount of moisture. Before production, most of the moisture in the masonry must be fully discharged. This process is mainly achieved through surface evaporation. The evaporation rate decreases as the moisture content inside the material decreases.

The heating rate must be strictly controlled in the early stage of baking. Generally, the heating rate per hour should be controlled at about 10°C. The maximum should not exceed 20°C. Too fast heating will cause a large temperature difference and water vapor pressure difference between the surface and interior of the material. This causes thermal stress concentration and internal cracks.

At the same time, temperature fluctuations must be strictly prohibited. Sufficient heat preservation time should be ensured. This allows moisture to be evenly discharged and the temperature field to stabilize. It avoids irreversible damage to refractory materials.

Stable Operation and Continuous Maintenance

The stable operation of the CDQ furnace is of great significance for extending the service life of refractory materials in the chute area. A reasonable operation management system must be established. System parameters should be precisely controlled. This keeps the device in thermal balance.

Controlling a relatively stable coke discharge rate is the core point. A stable coke discharge rate ensures that coke flows downward at a relatively constant speed in the CDQ furnace. This reduces mechanical wear on refractory materials. It is also conducive to the stable distribution of temperature inside the furnace. This reduces the risk of cracks and spalling caused by drastic temperature changes.

Magscie strictly implemented the aforementioned measures throughout all stages of refractory material production, masonry work, furnace drying, and operational processes for dry quenching furnaces, effectively ensuring the quality of the refractory lining.

Refractory Material Selection and Technical Progress

Comparison of Mainstream Material Systems

Currently, there are three main types of refractory materials for the CDQ chute area. The mullite silicon carbide series is the most widely used material at present. It has good thermal shock resistance and wear resistance. It also has high flexural strength and excellent corrosion resistance. Good thermal shock stability and wear resistance of the column bricks in the chute area are the main conditions for meeting long service life requirements.

The silicon nitride bonded silicon carbide series has theoretically superior performance. CDQ installations use nitrogen to cool red coke. The compatibility of materials makes its theoretical service life longer. Its strength is also relatively high. However, the production cost of this material is about three times that of mullite silicon carbide bricks or more. The one-time investment is relatively high. Under the current situation of the coking industry, it is difficult for most enterprises to accept.

Although clay series materials have good thermal shock resistance, their comprehensive performance is not ideal. Early CDQ furnaces used this type of material. Currently, it is being gradually phased out.

Technical Development Direction

Ultra-large CDQ installations have achieved a processing capacity of 260t/h. Through technological innovation, major technical problems have been solved. These include floating coke control, deterioration of cooling characteristics, and high-temperature sulfur corrosion of boiler superheaters. In the field of refractory materials, new materials such as low internal stress mullite andalusite bricks show promising characteristics. They exhibit extremely low high-temperature internal stress. They also have excellent thermal shock stability and good wear resistance. These materials can better meet the long-life requirements of CDQ furnaces.

From a long-term development perspective, capable enterprises can consider using high-performance materials such as silicon nitride bonded silicon carbide bricks. However, for enterprises using mullite silicon carbide bricks, stable operation for more than one year is completely feasible. This requires strict quality control and standardized management in all aspects. These include structural design, raw material selection, formula optimization, mechanical manufacturing, construction management, baking system, and operation maintenance.

Conclusion

The damage to refractory materials in the CDQ chute area is the result of multiple factors acting together. There are limitations in the performance of the materials themselves. More importantly, human factors cause the problems. By establishing a full-process quality control system, the service life of refractory materials can be effectively extended. This system covers raw material selection, manufacturing process, construction quality, baking system, and operation management. It improves the operational stability and economic benefits of CDQ installations.

Practice shows that five aspects of measures are effective. These include emphasizing the purity and physical-chemical indicators of raw materials, adopting mechanized production to ensure product consistency, strictly controlling masonry quality, scientifically formulating baking plans, and maintaining stable operation of installations. These measures can fundamentally guarantee the quality of refractory materials in the chute area.

China’s CDQ technology has reached the international advanced level. The serialization and large-scale development of installations has been achieved. Continuous improvement in refractory material quality control will further enhance the overall competitiveness of CDQ technology.

With the research and application of new refractory materials, and the continuous improvement of quality management levels, the service life of refractory materials in the CDQ chute area is expected to be further extended. This will provide more solid technical support for the promotion and application of CDQ technology and the green development of the coking industry.