Refractory Materials Used In Rotary Kilns

The high temperature in a rotary kiln can severely exacerbate the damage to refractory materials. C3A and C4AF in the melt of cement clinkers are corrosive. The overheating in the kiln can severely exacerbate the damage of thermal stress.

The higher the kiln speed is, the higher the output is, the bigger the damage of mechanical stress and fatigue.

Components such as alkali, chlorine and sulfur are corrosive. Sulfates and chlorides are volatile chemicals. They volatize and are enriched via repeated cycle. This exacerbates the potential of structural spalling.

Since the diameter of the kiln is large, the skin of the kiln is not stable.

The structure of the kiln is complex. The mechanical and electrical failures increase. The frequent turning on and shutdown of the kiln exacerbates the damage.

Refractory bricks used in the rotary kiln include high alumina bricks, alkali resistant bricks and basic refractory bricks.1.High alumina bricks

Non-basic bricks are silicate alumina refractory products contain more than 48% Al2O3. It is composed of?-Al2O3, mullite and glass phase. Its content is up to the ratio of Al2O3/SiO2 and the types and amount of impurities.

According to the content of Al2O3, non-basic bricks can be divided into Grade? (Al2O365%-70%), Grade? (Al2O355%-65%) and Grade? (Al2O348%-55%).

Wear resistant bricks, mullite red bricks, silica mullite bricks and spalling resistant bricks used in the rotary kiln belong to high alumina bricks.

2. Basic bricks

Basic bricks used in the rotary kiln include magnesia alumina spinel bricks, magnesia iron spinel bricks and direct bonded magnesia chrome bricks.

In order to improve the thermal stability of magnesia bricks, aluminum oxide or iron oxide is added to the raw materials to produce magnesia bricks with spinel as the main structure. A thin protective layer of calcium aluminate is generated when the oxides react with the clinker. Liquid phase cannot penetrate into the bricks with the protection of the layer.

The direct bonded magnesia chrome brick is fired at 1750-1850? in a tunnel kiln. It has good chemical corrosion resistance. Compared to spinel bricks, it has good thermal stability and spalling resistance, but poorer chemical corrosion resistance than spinel bricks.

3. Alkali resistant bricks

They are used in tertiary air pipes and whirlwind tubes. They are composed of 25%-30% Al2O3 and more than 65% SiO2. When alkalis in the air are agglutinated on the surface of bricks, they can form a viscous glaze layer. This layer can enclose pores through which alkalis can penetrate into the bricks.

Refractory castables belongs to monolithic materials. They are a mixture of refractory aggregates and binders. They are dry material before use. During use, water or other liquid is added. The binders are hydraulically settable binding agents or chemical binding agents. The common construction methods are casting, vibration or tamping method. they can be cured without heating.

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