Application Mechanism of Magnesia Chrome Bricks in Cement Rotary Kiln

Magnesia chrome refractories have the advantages of high refractoriness, high-temperature strength, strong corrosion resistance to alkaline slag, and excellent thermal stability. The magnesia chrome bricks are also have certain adaptability to acid slag and is widely used in the burning zone of cement kilns.

Refractories for Cement Kilns

Refractories for the cement industry account for about 13% of all refractories. Refractories, as an indispensable lining material in the cement firing process, are also the material support conditions for the second-generation new dry cement process, and the use of refractory materials for the firing zone is particularly important. The main mineral components of Portland cement are CaO·SiO2, 3CaO·Al2O3 and 4CaO·Al2O3·Fe2O3. The most suitable refractory material for the transition zone and firing zone of the cement kiln can only be alkaline magnesia refractory.

Application Mechanism of Magnesia Chrome Bricks in Cement Rotary Kiln

In the past, magnesia chrome bricks were commonly used in the firing zone, which can resist the erosion of cement components. CaO from cement clinker reacts with Fe2O3 in the brick to form 4CaO·Al2O3·Fe2O3, which makes the brick easy to adhere to the clinker. The Cr2O3 released by the bricks has the effect of stabilizing the 2CaO·SiO2 in the kiln skin, so chromite plays an important role in improving the fire resistance, erosion resistance, thermal shock resistance and kiln skin resistance of alkaline refractories. The firing zone is in a high-temperature chemical atmosphere, the charge temperature is 1400~1500℃, and molten liquid is produced. Refractory materials are usually covered by raw materials, coupled with the rotation of the kiln body, so the kiln skin often peels off. The molten cement material reacts with the brick and the molten liquid penetrates into the brick, causing melting loss and structural peeling. The transition zone is also roughly the same.

Austria's Olbrich, Germany's Bonn Refractories Company and Refa's Kun-neck, etc. believe that magnesia chrome bricks will be subjected to a series of thermal stress, mechanical stress and chemical erosion in a cement rotary kiln. The temperature gradient in the magnesia chrome brick(https://cheapfirebricks.com/magnesia-chrome-brick/) will cause the local concentration of thermal stress and easily cause cracks.

The Mechanism of Magnesia Chrome Brick being Corroded in Cement Kiln

The corrosion caused by the mechanical stress of magnesia chrome bricks includes: wear caused by the relative movement of brick and clinker, deformation of the kiln shell caused by ovality, and spalling caused by groove formation. Corrosion effects include melting erosion, liquid phase erosion, overheating load, penetration of alkali salt, erosion of clinker, and reduction of iron causing structural spalling.

Qotaibi analyzed the magnesia-chrome residual bricks after use in the burning zone of cement rotary kiln, and found that there was no Mg-SiO4 and Mg(Al1.5Cr0.5)O4 in the interface between the hot surface of the magnesia chrome brick and the slag layer. The 3CaO·SiO2, 2CaO·SiO2 and 3CaO·Al2O3 in the cement clinker have penetrated into the hot surface. At the same time, the formation of Cr6+ was detected.

Yun Sining's research believes that structural spalling caused by cement clinker erosion mainly occurs at the hot end of magnesia chrome bricks. The erosion channels of cement clinker liquid phase and alkali salt (formed by the potassium, sodium, sulfur, and chlorine compounds in cement raw materials and fuel) at high temperature are all open pores directly combined with magnesia chrome bricks. Therefore, reducing the open porosity of directly bonded magnesia chrome bricks can effectively reduce the rate of damage on the burning zone of dry-process cement rotary kilns.

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