According to the working principle of the vertical preheater, the limestone produced a partial decomposition at the same time of completing the drying and preheating. In the convective effect of waste gas heat, the decomposition is still processing when the limestone particles enter into the rotary kiln before touching the high temperature zone of the flame. This is to say, this refers to the decomposition phase of the material in theory.

In the rotary kiln, the so-called sintering or sintering phase refers to the process that the preheated limestone particles in the rotary kiln receive the radiation heat transfer from the flame at the beginning, and then get through to the whole flame radiation zone. With the effect of high temperature, the fierce chemical reaction is conducted and eventually burned to the lime. This phase is generally completed within 30 to 40 minutes.

In the rotary kiln with a vertical preheater, the burned area is generally set in the position of around 10 meters from the kiln discharge end, within 20～25 meters extended from the feeding part of rotary kiln. The flame length should also be distributed in this area. It’s commonly referred to the sintering zone.

As the calcination process of rotary kiln is influenced by many factors, which are mutual interdependent, interacted, flexible. Therefore, there is no strict distinction on the division of the rotary kiln burning zone and other zones.

However, the sintering stage plays an important role in the whole process of the calcination, due to the characteristics of the rotary kiln calcinations. The reason is that the active property of the active lime is finally performed in this phase through the rapid sintering. Although this phase is not very long, it has a great significance for the active lime calcinations.

In the rotary kiln with vertical preheater, the reasons why active lime products cannot be sintered for a long time are as follows:

Lime raw materials are preheated with a full preparation before the sintering

Specific relationship among kiln length, flame length, and length of sintering zone;

The specific requirement of “quick burning and cooling” determined by the product property of active lime.