Rotary kiln is a kind of inclined long cylindrical cement equipment. Raw materials will convert into clinker after being heated and calcined in the kiln. Through our years of experience in cement production, we have come to the conclusion that a high-efficiency clinker production requires a stable sintering zone and kiln skin, a stable material flow temperature and flue gas, and the most important one, a stable clinker output. However, in fact, the composition and quantity of the raw material sent into the rotary kiln are variable, and the calorific value, ash content, volatile content and water content of fuel are also different. Therefore, there are many factors affecting the stable production of rotary kiln.
Rotating Speed and Materials Residence Time
The diameter, length and inclination of the rotary kiln are all fixed. The only change is the rotational speed. While, the residence time of materials in the kiln is related to the rotational speed, and also related to the diameter, length and inclination of the kiln. Some people believe that in the production process, the kiln rotation speed controls the material flow. If the speed is relatively stable, the kiln material layer thickness will also maintain stable. That is to say, if the amount of material entering the kiln decreases, the kiln speed will decrease correspondingly, and the material residence time will increase.
From the production practice, the temperature of materials delivered from the precalciner kiln is about 900℃. Some melts of these raw materials will affect its surface viscosity and running speed in the rotary kiln to some extent. In addition, the crusting and ring-forming of materials in the kiln will also affect its running speed. In recent years, with the increase of decomposition rate of materials, the kiln rotation speed has increased from 3 r/min in the early stage to more than 5r/min, and the residence time of materials in the kiln has decreased.
Kiln Skin and Refractory Bricks
During the heating process of raw materials in the rotary kiln, some minerals melt and adhere to the surface of firebrick to form kiln skin, and the kiln skin will hang on firebrick from the upper transition zone to lower transition zone. As shown in the figure below, the thickest part of the kiln skin is in the sintering zone, about 30-40 cm.
The maintenance of refractory bricks will not only reduce clinker production but also consume materials and labor costs. However, refractory bricks have the property of adhering kiln skin, which is related to the composition of clinker and itself. For example, the raw material contains a small amount of elemental compounds such as alkali and sulfur, which have a greater impact on refractories. In order to reduce the damage of refractory bricks in kilns, refractories should be selected according to the chemical properties of raw materials and technological conditions. For another, make a good record of refractory damage in production, and analyze the cause of damage. If it is difficult to find out the cause, we can send the refractories to the relevant departments for quality inspection, and inspect the masonry at the same time. In addition, if the used refractories are found to be inappropriate, they can be re-selected after optimization, or we can also adjust the composition of clinker appropriately to prolong the use of refractory bricks.
The Thermal Intensity
The fuel system and burner type directly affect the temperature of materials in rotary kiln and the performance of clinker. If the kiln profile temperature is low, the fCaO in clinker will be high. If the temperature is too high, the large lattice C3S clinker will easily be formed, which will affect its granulation and strength. In addition, the research shows that if the flame in the kiln is short, the clinker residence time in the high-temperature zone is short, the temperature will rise, the granulation will be more uniform, the cooling speed will be faster and the strength will be higher.
Fuel combustion in the kiln cannot leave without oxygen, and the high-temperature flue gas produced by combustion will be pulled back by the sintering system fan. In this process, the raw material is heated by the flue gas and calcinated into clinker. Heat transfer lowers the temperature of the flue gas, which is then discharged into the atmosphere from the chimney.
To ensure the adequate combustion of fuel, there must be enough oxygen in the air. Moreover, the pulling force of the fan to the airflow must also be appropriate. If the air pressure is too high and the flow rate is too large, the flame will grow and the fuel consumption will increase. When the air pressure and flow rate are low, it will cause insufficient combustion of fuel and form a reducing atmosphere in the rotary kiln, which reduces the iron content in the clinker and causes the center of the clinker ball to be brown.
AGICO, as one of the leading cement plant and cement equipment suppliers in China, provides high-quality rotary kilns. We also offer cement plant design service, equipment installation and commissioning service and after-sales service. If you are interested in our products, please feel free to contact us!