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The refractory lining inside the cement rotary kiln plays an indispensable and key role in ensuring the efficient operation of the kiln and preventing the kiln shell from being melted down by high temperature.
There are many types of refractory materials that can be used to construct the refractory lining of cement rotary kiln. In view of the significant differences in the working conditions faced by various parts of the rotary kiln during operation, in order to achieve a more ideal effect, it is necessary to accurately select suitable refractory materials to construct the refractory lining for different areas of the rotary kiln.
The temperature in this area changes dramatically. When the material just enters the kiln, the kiln mouth has to withstand the erosion of high-temperature materials and the radiation of flames. The cooling zone is at the discharge end, with a large temperature gradient. Frequent temperature changes will cause thermal stress in the refractory material
New Tabular Corundum Castable orCastable for Kiln Outlet are usually used. New Tabular Corundum Castablehave have good high temperature resistance and thermal shock resistance.
The operating temperature of the coal injection pipe in cement kiln is relatively high, and the flame temperature may reach about 1600-1800℃. There will be some chemical corrosion. The ash produced by coal combustion contains various oxides. When the coal injection amount is adjusted, the ventilation in the kiln changes, etc., the flame temperature will change rapidly, causing the refractory lining to suffer thermal shock.
New Tabular Corundum Castable or Castable for Burner Pipe have high refractoriness, which can reach over 1800℃; they have high hardness and good wear resistance, and can resist the erosion of coal flow. For example, the front end of the coal injection pipe in some large cement kilns uses corundum refractory lining, which effectively extends the service life of the coal injection pipe.
The temperature in the Precalciner is high, and there is a large amount of airflow and material reaction, so the refractory material needs to have good wear resistance and spalling resistance
The Precalciner adopts Steel Fiber Castable or silicon carbide castable. Silicon carbide castable has excellent thermal conductivity and wear resistance, which can improve the thermal efficiency of the decomposition furnace and resist the erosion of materials.
The temperature inside the rotary kiln is extremely high, reaching a maximum temperature of 1450 - 1650℃. In the firing zone of the kiln, the temperature remains high for a long time. Therefore, the refractory lining material needs to have high refractoriness. Generally, materials with a refractoriness of not less than 1700℃ are selected, such as magnesia-alumina spinel bricks, which have a refractoriness of about 1800℃ and can withstand the high temperature in the rotary kiln well.
Excellent resistance to alkaline erosion, this is because the structure of magnesia alumina spinel (MgAl₂O₄)or Magnesia Iron Spinel Brick is stable and can effectively resist the alkaline components in cement raw materials. Good thermal shock stability, can maintain good performance in areas where the temperature of the rotary kiln changes frequently. For example, using magnesia alumina spinel bricks in the transition zone of the kiln can reduce damage caused by thermal shock and alkaline erosion.
The general operating temperature of cement kiln preheaters is between 300 and 1000℃, and the temperatures of different stages vary. For example, the temperature of the top few stages of preheaters is relatively low, usually around 300-600℃; while the temperature of the stages close to the rotary kiln will increase, up to around 1000℃. Therefore, the refractory lining material needs to be able to adapt to this temperature range.
The refractoriness of high-strength alkali-resistant bricks is generally between 1610 and 1730°C, which can meet the temperature requirements of most areas of the preheater. It has good acid resistance and has a certain resistance to the acidic gas that may be produced. In the lower temperature levels of the preheater (such as the top one and two levels), high-strength alkali-resistant bricks are an economical choice。Castable silicon carbide castable and steel fiber castable have good integrity and sealing properties and can withstand the high temperature under the preheater. Through on-site casting, a lining that fits closely with the internal structure of the preheater can be formed, which can effectively prevent the leakage of materials and gases.
The temperature at the grate cooler inlet is relatively high, reaching about 1300-1400℃. As the cooling process proceeds, the temperature gradually decreases, and the temperature at the outlet may drop to 100-200℃. This large temperature change requires the refractory lining to have good thermal shock resistance.
Corundum wear-resistant castable has good integrity and sealing. Corundum wear-resistant castable uses corundum as the main raw material and has high refractoriness, generally reaching above 1790℃. It can be cast on site to form a lining that fits tightly with the internal structure of the grate cooler, which can effectively prevent the penetration of clinker and airflow. In some areas with complex shapes that are difficult to build with bricks, such as the corners and pipe interfaces of the grate cooler, castables can better play their advantages and provide continuous and uniform protection.
The 5,000t/d new dry-process production line for treating hazardous solid waste at Beijing Lan Cement Plant in Hebei Province previously used kiln mouth castables from multiple manufacturers at home and abroad, but the effect was not ideal and the castables were corroded and fell off. After using the kiln mouth castables produced by Luoyang Shengjie in early 2022, the castables did not show any damage until the end of 2023, and were used until August 2024 before the kiln mouth castables were replaced, with a service life of up to 18 months. Luoyang Shengjie's kiln mouth-specific castables are specially developed and designed for cement kiln mouths. They use advanced production technology and high-quality raw materials to solve the problem of damage to cement kiln mouths caused by hazardous solid waste.
The main function of refractory materials for cement kilns is to serve as the lining of the cement kiln. It should maintain the high temperature required for firing cement clinker, while protecting the kiln equipment and reducing the heat loss of the kiln. In terms of refractory materials technology, refractory materials for cement kilns have developed from a few varieties such as clay bricks and high alumina bricks to a family of nearly a hundred materials. Today, refractory materials for cement kilns include sintered alkaline refractory materials, sintered aluminosilicate refractory materials, monolithic refractory materials and prefabricated parts, and insulated refractory products.
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