Rotary kilns are available in both direct-fired and indirect-fired configurations. Each type offers its own unique advantages and disadvantages. Both kinds of rotary kilns run on the same thermal processing principles, but they are better suited for certain applications. The main difference between the two, is how the heat is introduced to the material.
Indirect-fired rotary kilns
Rotary kilns (furnaces) of indirect heating are used for drying different friable materials as well as heating them up to temperatures required for different technological processes. In rotary kilns of indirect heating processes of heat production take place outside the case of the rotating furnace. So, the processed material does not come into contact with combustion gases which can be important for the product quality.
Indirect-fired rotary kilns is used in:
Food, chemical, petrochemical or pharmaceutical industries, metallurgy and rock treatment;
For processing and production of mineral resources;
Construction and operation
The rotary kiln of indirect heating is a cylinder rotating on bearing rims mounted on the frame and covered by a fixed case where hot gases are pumped during the kiln operation. These gases heat up the outer surface of the rotary cylinder when touching it and provide transmission of heat to the processed material without any direct contact with it. The outer case is insulated which allows to minimize energy loss.
Inclination of the case together with rotation round the axis provides the move of the processed material in the direction of the discharge chamber.
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