Compared with traditional cement kilns, large-scale cement rotary kiln has higher sintering temperatures and more severe damage. Moreover, it is more severely corroded by alkali, sulfur, chlorine and other volatile components. This requires refractory materials to have higher overall stability and stress resistance.
Cement rotary kiln is generally composed of preheating zone, decomposition zone, transition zone, burning zone, cooling zone, kiln mouth, etc.
Preheat zone and decomposition zone: alkali-resistant materials with Al2O3 content of 25%~28% and SiO2 content of about 65%~70% should be used in both rotary kiln brick lining. For example, anti-stripping high alumina bricks, magnesia alumina spinel bricks, silica-molybdenum bricks and high alumina bricks. This type of refractory brick can form a glaze layer on the surface during operation. It can reduce the porosity and prevent “alkali cracking”.
Transition zone: most of the transition zone uses magnesia-alumina spinel bricks. In addition, for new dry-process cement kilns with a capacity of less than 2500t/d or relatively stable firing conditions, high-quality silica-molybdenum bricks can also be used as refractory materials for the transition zone. Such as 1680 silica-molybdenum bricks and silica-molybdenum red bricks.
Burning zone: the firing zone of rotary kiln calcined bauxite has relatively high requirements on the performance of refractory kiln lining. Commonly used refractory materials include direct bonded magnesia chrome bricks, magnesia iron spinel bricks, dolomite bricks and magnesia calcium bricks. However, dolomite bricks must be used in the section with stable kiln lining.
Cooling zone: the temperature of the cooling zone is as high as about 1400℃ and the temperature fluctuates greatly. Alkaline bricks with good heat shock resistance such as phosphate bricks or high-alumina bricks are suitable for cooling zones.
Kiln mouth: the kiln mouth part mostly uses castables with good heat shock resistance. Such as steel fiber castables and high aluminum castables.
These parts are different in temperature and purpose. So the refractory materials used in rotary kiln refractory lining are also different.