According to the temperature of the materials in the kiln, the cement rotary kiln system can be divided into: drying zone, preheating zone, decomposition zone, exothermic reaction zone, burning zone and cooling zone.
The drying zone is a short part at the raw material entrance. For the new dry process cement rotary kiln, there is basically not a drying zone. For the traditional cement rotary kiln, the temperature of the material in the drying zone is about 20℃～150℃, and the gas temperature is about 250℃～400℃.
In the preheating zone, the organic part of the raw materials begins to decompose, and the clay begins to dehydrate, preparing for the decomposition of calcium carbonate.
In the decomposition zone, the decomposition reaction of calcium carbonate mainly proceeds.
For these parts, silicon mullite brick and anti-stripping high alumina bricks are the main refractories for the kiln building.These bricks have good chemical and physical properties.
The exothermic reaction zone is also called the upper transition zone. In a traditional cement rotary kiln, the temperature of the materials in the exothermic reaction zone is 1000°C to 1300°C, and the gas temperature is 1400°C to 1600°C. For the new dry process cement kiln, about 7D~4D from the kiln head is the transition zone.The magnesia spinel brick is the best choice for this section.This kind of brick has good performance in slag resistance and abrasion resistance.The thermal shock resistance can be about 100 cycles.
In the burning zone,the material temperature is between 1300℃～1450℃, and the
flame temperature can reach 1700℃. When the material temperature is close to 1300℃, C3A and C4AF begin to melt and become liquid, CaO and Ca2Si04 decompose, and C3S will be precipitated when the saturation concentration reaches a certain amount.Increasing the temperature of the burning zone properly will help the formation of C3S, which can improve the quality of the clinker.
In the burning zone, the magnesia iron spinel brick and magnesia chrome brick are the main construction materials.This part of the kiln is a very important part of the cement kiln.The materials need to be good in abrasion resistance and alkali resistance.The magnesia chrome brick and magnesia spinel brick are most suitable products.
In the cooling zone(also called the lower transition zone), the temperature of the material is about 1100℃～1300℃.After the clinker comes out of the burning zone, it is initially solidified in the cooling zone and enters the cooler for further cooling. If the clinker temperature is too high or too low when exiting the kiln, the clinker will corrode and wear the refractory materials at the kiln mouth. If the temperature of the kiln mouth changes too fast, the clinker will cause thermal shock damage to the kiln mouth refractories.So the refractory products is important, in this section,the silicon mullite brick and fused magnesia alumina spinel bricks are the best choice.They are good in thermal shock resistance.
However, the length of each "temperature zone" of a cement rotary kiln is not fixed, and they will be affected by factors such as the pre-heating of raw materials, the length of the flame and whether the raw materials are easy to burn. The distribution of each working zone should be adjusted according to the changes of production conditions.
