In the rotary kiln with the vertical preheater, the preheating process before sintering is the important part of the calcinations of rotary kiln, because the limestone cannot be sintered directly under the temperature of 900—1000℃.
For many different types of kiln without preheated device, the active lime also could be calcinated with a certain quality. However, compared with kiln with the preheated device, the difference is on the feature of low activity and unstable, much residual of CO2, poor texture and appearance and so on, not considering the detailed comparison on the physical and chemical technology index.
On the effect of smoke discharge and draft fraught, the limestone in the preheater device makes the hot airflow from the rotary kiln go up from the bottom of preheater. The limestone is heated from when it moves down continuously, which is gradually transformed from the low temperature to the high temperature（200～900℃）until to the temperature can be dissolved. However the heat source is mainly depending on the waste gas heat.
After entering into the preheater, the limestone is firstly dried under the influence of hot air flow and removed their owned and entrained moisture. Along with the continuous downward movement, the air temperature becomes higher and higher while the limestone particles begin to be heated. Once heated to above 800℃, the surface layer of the particles will conduct the decomposition reaction. CO2 (gas) will be separated from the CaCO3 while the “white coating” phenomenon appears on the surface of limestone particles.
The result of theory and practice shows that the decomposition temperature of CaCO3 is about 870——920℃. In the bottom of the vertical preheater, the temperature of exhaust flow is around 950℃. This means that the partial decomposition reaction of the limestone surface begins when the limestone particles enter into this temperature area and complete the preheating phase at the same time. In the rotary kiln with vertical preheater, the preheating phase usually takes about 120 minutes.
