The multiple hearth incinerator is a circular steel furnace containing lot of solid refractory hearths with central rotating shaft. It also consist of rabble arms that is fabricated to rake the sludge on the hearth. Rabble arm is attached to the rotating shaft. The sludge gets incinerated to a truly inert and odorless ash, which yield gas which has been burned free of all malodorous and condensable volatiles. This can be utilized for the production of trouble-free steam and in-house electric power.

Principle
Multiple hearth incinerators consist of vertically shaped hearths. The operating temperature ranges from 1400-1800 ° F. In multiple-hearth incinerators sludge is fed from the top. The sludge passes down the hearths below mechanically. By moving teeth mounted on a central rotating shaft, waste is transported through the furnace. Sludge coming down from the top gets dried from the heat that originates from the burning sludge in the middle of the incinerator. Very little additional fuel is needed to make the sludge start to burn because sludge has approximately the same BTU value as wood chips. The formed ash (out of combustion) is non-toxic and inert, and can be beneficially used to make a number of products like bricks.

Features
Following are the features of multiple hearth furnace:

• High residence time for sludge and low volatile materials
• Can handle a variety of sludges
• Large amount of water can be evaporated
• Fuel efficiency is high
• Can utilize various fuels

Applications
Multiple hearth incinerators are responsible for disposal of various materials like:

• Different forms of combustible industrial waste materials
• Solids, liquids and gases
• Sludges
• Tars