The refractory lining on the interior of the cement rotary kiln is a crucial component in ensuring the kiln’s working efficiency and protecting the kiln shell from melting down.
There are many refractory materials that can be used to form the refractory lining of cement rotary kilns. For different parts of the rotary kiln, we may need to choose different materials as refractory linings to achieve better effectiveness.
Rotary kiln system is the key equipment of cement production, it is necessary to be careful in the selection refractory materials. Wrong refractory materials will not only affect the operation of the cement plant, but also cause production accidents. Here are some principles when we choose refractory materials for each part of the kiln:
1. The Discharge Port and Discharging Zone
The refractory lining used in these two parts of the rotary kiln suffers both severe mechanical wear and chemical erosion. Therefore, the lining materials for these parts must have characteristics of abrasion resistance and temperature change resistance.
The refractory lining materials generally used in the discharging zone are high alumina brick and heat shock resistant high alumina brick with 70-80% Al2O3 content, spinel brick, and magnesia chrome brick. High alumina brick, heat-resistant concrete with corundum as aggregate, or silicon carbide brick are mainly used at the discharge outlet as refractory lining materials.
2. The Sintering Zone
In general, the refractory lining of the sintering zone is directly bonded mag-cr brick fired at high or ultra-high temperature, such as sodium polyphosphate bonded magnesia brick and alkali resistant brick. These materials have been widely used because of their high temperature calcination, direct combination of spinel and periclase, high cold and hot strength and good thermal shock stability.
3. The Transition Zone
The transition zone is adjacent to the sintering zone. In this zone, the temperature changes frequently, the temperature of the cylinder is high, the kiln skin may be hanging or falling off, and the chemical erosion is also serious.
The suitable refractory lining materials for the transition zone include high alumina brick made of corundum and bauxite with 50-80% Al2O3, directly bonded mag-cr brick, ordinary mag-cr brick, and spinel brick.
4. The Cooling Zone
The temperature in the cooling zone is still relatively high, but the chemical erosion is not so severe compared to other zones. The refractory lining materials for the cooling zone can be mag-cr brick, high alumina brick, phosphate bonded high alumina brick and magnesia alumina spinel brick, etc.
5. The Calcining Zone
In the part where the calcining zone is connected with the preheating zone, due to the small thermal and chemical stress, clay bricks, high alumina bricks, light bricks calcined into chemical combination or ordinary magnesia chrome bricks can be used as the refractory lining;
In the high wear and high temperature part where it is connected with the transition zone, high alumina brick with 50-60% Al2O3 content, ordinary magnesia chrome brick or spinel brick can be used as the refractory lining;
6. The Preheating Zone
The lining material used in the preheating zone should have sufficient alkali resistance and heat insulation performance. The ideal lining material is alkali resistant and heat insulation clay brick. When light brick is used, the temperature of the kiln shell can be reduced by 60-100 ℃ compared with clay brick with the same thickness. For dry process kiln, the unit heat consumption can be reduced by 21-38kj/kg clinker.
7. The Preheater System
The refractory used in preheater system should have good alkali resistance and heat insulation performance. Alkali resistant clay brick is used in the straight tube, cone part and connecting pipe of preheater and calciner, and heat insulation composite layer is added to build with fire source.
8. The Cooler System
Because the change of material temperature in grate cooler is the biggest in the whole process of rotary kiln, the erosion of refractory lining in every part of the cooler is not uniform. In general, the lining material located at places around the cooler inlet and between it and the inlet of the tertiary air duct suffers the most severe erosion.
The refractory materials can be used in the grate cooler system include refractory brick, light castable, heat insulation brick, etc. The common mag-cr brick and high alumina brick can be used in the cutting throat area and high temperature area; clay brick can be used in the medium and low temperature area.
Conclusion
We have introduced the refractory materials applicable to each part of the cement rotary kiln, but to decide which kind of material is the best one to be used as the refractory lining for a certain part of the kiln, we still need to refer to the overall situation of the specific project, and consider the production environment, investment cost, maintenance cost, and other factors.
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