When it comes to thermal processing, how do you know if you need a rotary kiln or a rotary kiln dryer? Though both of them have almost the same appearance and share similar thermal processing principles, there are essential differences between the two products. In addition to the slight difference in structure details, appearance, and technological design, they are used in very different applications.
In the cement industry, rotary kiln and dryer are commonly used cement equipment in cement plants, which play a very important role in the stage of clinker calcination and raw material preparation respectively. In principle, they all play a role in drying materials by using high temperatures, but their purposes are different. While cement rotary kiln can dry materials, but its main concern is not drying, but heating.
Next, we will keep talking about the difference between the rotary kiln and dryer when they applied in the cement production line.
What’s their main difference?
One of the essential differences between the cement rotary kiln and dryer is that the cement rotary kiln can withstand a higher temperature than rotary kiln dryer, operating between 800℃-1300℃, while in the rotary kiln dryer, the heating temperature is only about 300℃.
Both cement rotary kiln and rotary dryer rely on the heat transfer between the material and hot gas to realize drying, while the special internal structure of rotary kiln makes it able to withstand a higher temperature than the dryer, like direct fired rotary kilns, their inwall is lined with refractory lining bricks or castable interior. This design protects the cylinder from high-temperature damage. The indirect fired rotary kilns do not have the protective refractory liner so the shell of the cylinder should be made from high-temperature resistant alloy, not steel.
As we mentioned above, the heating temperature of the rotary kiln dryer is low, it is not necessary to arrange high-temperature resistant lining in the cylinder, so various internal components can be installed to improve heat transfer. One of the most common internal components is flight plates. They are installed on the wall of the cylinder and rotate continuously with the cylinder body, lifting the materials and then sprinkling them so that the material can fully contact with the hot gas, conduct heat and achieve the purpose of drying.
Although there is some overlap between the functions of rotary kiln and dryer, they are usually used for different purposes. Rotary kiln dryer is a heat transfer device applied in low-temperature applications. It is capable to reduce the water content of raw materials. In the cement production line, a rotary kiln dryer is an indispensable device in the material preparation stage. In order to ensure a high-efficiency of the grinding mill and the quality of cement products, it is necessary to dry the excess water before grinding clay, coal, and other raw materials. On the contrary, the cement rotary kiln is mainly used for high-temperature applications, the purpose of which is to cause physical changes or chemical reactions of materials. Different from the rotary dryer, cement rotary kiln is usually set in the clinker calcination stage of the cement production line. Raw materials are heated by the rising temperature in the kiln cylinder and then cooled to form the clinker after reaching a boundary point.
Many raw materials calcined in rotary kilns will undergo both physical and chemical changes, such as limestone. When it is heated by extreme high-temperature in cement rotary kiln, a series of physical changes (water evaporation) and chemical reactions (calcium carbonate decomposes into calcium oxide) will be triggered. This process realizes the convert of material properties, which we usually say a new product is created. However, the rotary dryer can only evaporate the moisture inside the material, turning the wet material into the dry material, and the material essence has not changed.
The diameter ratio and length ratio of cement rotary kiln are generally more than 10, while the dryer is less than 8. Therefore, the cylinder body of rotary kiln is mostly long and thin, the rotary kiln dryer is relatively thick and short.
The steel plate used in the production of cement rotary kiln is much thicker than that used in the dryer, so the rotary kiln is relatively heavier. Besides, both of the two machines adopt the supporting roller device, while the roller equipped on the rotary kiln is obviously heavier than that of the dryer.
The cement rotary kiln is much more expensive than the cement kiln dryer.
AGICO has been a leading manufacturer for the cement rotary kiln and rotary kiln dryer industries for many years. We offer one-stop service capable of fabricating kilns and dryers of all sizes, as well as providing other kinds of cement equipment used in cement plants. For more information on cement plant equipment, please contact us!