Multiple hearth furnace are important device used for various industrial applications. These furnace consist of multiple hearths that treat the materials without any wastage. They are highly versatile device that are used to treat the materials of different sizes. The furnaces are demanded highly because of their ability to process both the dry and the materials having high moisture content.

Operation and Configuration
Multiple Hearth Furnace are important furnace consisting of a steel shell lined with refractory bricks and refractory lined hearths. The materials in the furnace is moved by the rabble teeth supported by rabble arms which are attached to a central rotating shaft supported between bearings and driven by an external drive mechanism. The rabble system is cooled by air so that it can withstand the high temperatures. The heated-up air is recycled to the burner system by a fan for further use as combustion air. The design ensure the contact between solids and gases. Depending on the way they are charged, the furnaces are designed as outhearths and in-hearths.

The outhearth being situated at the bottom receives the materials which is charged from inhearth. From outhearth the material is spirally rabbled outwards after which it falls through the"out-drop hole" onto the following "in-hearth".

This process is repeated until the calcined material is discharged from the periphery of the bottom hearth. The product quality can be adjusted by controlling and varying the temperatures hearth by hearth. The dust collected in a precipitator during the process can be returned through a conveying system to one or several hearths of the furnace thus reducing the product losses with the exhaust gases.

Features

• The furnace can accept the feed material having moisture content upto 50%.
  
  
• They are highly flexible and their temperature profile can be controlled easily.
  
  
• They can also process materials of very small sizes.
  
  
• The furnace is not affected by the changes to fluctuations in chemical and physical properties and moisture content of the feed.
  
  
• The temperature at which they can be applied is high.
  
  
• These furnace can also be applied for oxidation and reduction processes.
  
  
• For solid and liquid fuels these furnace are suitable.
  
  
• The cost of maintaining the furnace is low.

Applications
Following are the applications of the multiple hearth furnace:

• Calcining filter cakes from synthetic MgO processes etc.
• Thermal treatment of ores, minerals, earths and sands.
• Calcination of industrial minerals like:
  • Magnesite
  • Dolomite
  • Limestone
  • Clay