Calcination process in rotary kiln refer to the process to calcine lump, bulk, slurry and other materials in a certain temperature, is mainly to remove the chemical-bound water, CO2, NOx and other volatile impurities. The process means to change the chemical composition by a thermal process or to drive off a volatile fraction.

The calcination process in rotary kiln adopt the rotary kiln with vertical preheater and vertical cooler for the calcination to achieve the requirements of energy saving, environmental protection, high activity. The precalcining kiln makes the preheating process of the material move to the preheater, the decomposition of the carbonate to the decomposition furnace, which makes the process and the thermal performance of the rotary kiln change greatly. There are only a small part of the decomposition reaction, exothermic reaction, sintering reaction and clinker cooling in the kiln. Therefore, the predecomposition kiln is generally divided into three processes: the transition zone, the burning zone and the cooling zone.

The transitional zone refers to the zone from the kiln tail to the material temperature around 1280 degrees. The main task is to heat up the material and a small part of the carbonate decomposition and solid phase reaction. The burning zone refers to the temperature range of 1280℃～1450℃～1300℃, to accomplish the sintering process of the clinker. The head end of the kiln is cooling belt.

Generally, the raw material temperature is around 850℃when fed into the rotary kiln from the lowest level cyclone. The decomposition rate is 85% - 95%, which still continue to decompose in the kiln. When fed into the kiln, the raw material sedimentate in the bottom of the furnace due to the action of gravity, and then form accumulation layer. Thus only material layer on the surface can be further decomposed, and the internal granular layer material is surrouned by CO2 gas film package. Meanwhile, the partial pressure of the particles CO2 reached to around 0.1 MPa  influenced by the pressure of the upper material layer. Even if the kiln flue gas temperature up to 1000℃, the decomposition reaction will also be temporarily stopped, due to the temperature of the material is lower than 900 ℃.

When the materials move to the kiln head, the internal layer produce violent decomposition reaction by the heating of airflow and the kiln, when the temperature rose to 900℃. When continue to decompose, the internal temperature of the material layer will be maintained at about 900℃ until the decomposition reaction is completed. Due to the greatly reducing of the total amount of material decomposition, the length of the decomposition area of the kiln is greatly shortened, comparing with the suspension preheater.

When the decomposition reaction was completed, the temperature of the material gradually increased, and then produce the solid phase reaction. Generally, the primary solid phase reaction begins in the furnace at 800℃. However, due to the suspended state in the decomposition furnace and the contact between the two groups is not tight, the main solid phase reaction will carry out after enter into the rotary kiln and the material temperature rise, and finally generate C2S、C3A and C4AF.