In cement clinker production, the tertiary air duct plays an important role in transporting high-temperature air. During long-term operation, its refractory lining is exposed to high-temperature airflow, dust erosion, temperature fluctuations and local mechanical stress.

Therefore, the selection of refractory materials for a tertiary air duct should not be based only on the refractoriness of the material. Operating temperature, airflow velocity, dust concentration, wear conditions, structural design and construction quality should also be considered.

1. Common Causes of Refractory Lining Damage

1. High-Temperature Airflow and Dust Erosion

High-temperature airflow continuously passes through the tertiary air duct, and the airflow may contain dust and solid particles.

Over time, these particles can continuously erode the surface of the refractory lining. Elbows, reducers, connections and areas where the airflow direction changes may experience more severe local erosion.

If the wear resistance of the refractory material is insufficient, the lining may gradually become thinner and eventually develop local damage or spalling.

2. Thermal Stress Caused by Temperature Changes

During kiln start-up, shutdown and operating-condition adjustments, the tertiary air duct may experience repeated temperature changes.

If the refractory material has insufficient thermal shock resistance, repeated heating and cooling can generate thermal stress inside the lining. Microcracks may gradually develop and eventually result in cracking or spalling.

3. Local Stress at Structural Changes

Tertiary air ducts commonly include elbows, tees, expansion joints, inspection openings and sections with different cross-sections.

These areas have relatively complex structures and may be exposed to different types of mechanical stress. Improper refractory selection, lining thickness or anchoring design can increase the risk of local cracking and detachment.

4. Construction and Drying Quality

The performance of refractory castables depends not only on the material itself but also on installation quality.

For example:

• Excessive mixing water;

• Insufficient mixing;

• Inadequate vibration;

• Improper anchoring;

• Insufficient curing;

• Excessively rapid heating during drying.

These problems may create internal pores or structural defects and reduce the overall stability of the refractory lining.

2. How to Select Refractory Materials for Different Areas?

Different sections of a tertiary air duct have different operating conditions. Therefore, using exactly the same refractory material throughout the entire duct may not always be appropriate.

1. Straight Sections

Straight sections are generally affected by high-temperature airflow and dust erosion.

Depending on the actual operating temperature and wear conditions, high alumina refractory castables or wear-resistant castables can be considered.

For areas exposed to significant erosion, attention should be paid to wear resistance, dimensional stability and thermal shock resistance.

2. Elbows and Airflow Direction Changes

Elbows may experience stronger particle erosion because of changes in airflow direction.

For these areas, wear resistance and thermal shock resistance are particularly important.

Depending on the specific operating conditions, high alumina wear-resistant castables, steel fiber reinforced castables or other suitable monolithic refractory materials may be considered.

3. Connections and Complex Structural Areas

For tees, reducers, inspection openings and other complex sections, the compatibility between the refractory lining and the equipment structure should be carefully considered.

If the lining is exposed to significant mechanical stress, material selection should be combined with anchoring design, lining thickness and shrinkage characteristics rather than simply selecting a material with a higher temperature rating.

4. Local Repair Areas

When local wear or spalling has already occurred, the damaged section can be repaired according to the actual condition.

In addition to temperature and wear resistance, repair materials should also provide suitable workability and good compatibility with the existing lining.

3. How to Reduce Damage to the Tertiary Air Duct Refractory Lining?

In addition to proper material selection, installation and maintenance are also important.

First, refractory materials should be selected according to the actual conditions of different sections of the tertiary air duct rather than applying exactly the same material everywhere.

Second, the amount of mixing water, mixing process, vibration and curing should be strictly controlled during castable installation. After construction, controlled drying and heating should be carried out according to the material requirements to reduce excessive thermal stress.

During operation, the external surface temperature of the tertiary air duct can be inspected periodically. If abnormal hot spots, cracks or refractory material loss are detected, the internal lining should be inspected as soon as possible.

For locations where refractory damage repeatedly occurs, the root cause should also be investigated, including airflow erosion, structural deformation, anchoring design and construction quality, instead of simply replacing the same material repeatedly.

4. Conclusion

Damage to the refractory lining of a cement rotary kiln tertiary air duct is usually caused by a combination of factors, including high-temperature airflow, dust erosion, temperature fluctuations, structural stress and construction quality.

Therefore, refractory material selection should be based on actual operating conditions. High alumina castables, wear-resistant castables, steel fiber castables and other monolithic refractories can be selected according to the temperature, wear conditions and structural characteristics of different areas.

Proper material selection, standardized installation and regular inspection can help reduce the risk of severe wear, cracking and spalling and provide more reliable refractory protection for stable cement production.