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Multiple Hearth Furnaces


  • Carbonisation/production and regeneration of activated carbon.
  • Roasting of concentrates and metallurgical by-products.
  • Drying and calcination of magnesium/calcium /manganese carbonates, phosphates, kaolin, sulphates, dolomite, etc.
  • Pyrolysis-incineration of industrial/municipal sludges. (see the list here for more products treated in a multiple hearth furnace)


  • great flexibility in feed size (0.01 to 25 mm)
  • exact temperature profile
  • atmosphere control
  • tailor made products
  • exact adjustment of activity
  • exact adjustment of specific area
  • high fuel efficiency
  • high availability of more than 95%


    The FGC Multiple Hearth Furnace consists of a series of circular hearths, placed one above the other and enclosed in a refractory-lined steel shell.  A vertical rotating shaft through the centre of the furnace carries arms with rabble blades which stir the charge and move it in a spiral path across each hearth.  Material is fed to the top hearth, and rabbled across it to pass through drop holes to the hearth below.  It passes in this way over and across each hearth to the bottom where the product is discharged through one or more ports.  Heated gases flow counter-currently to heat the charge to reaction temperature and to carry on the desired reaction.  In some operation, combustion of charge-elements supplies the heat.  In other cases it is furnished by combustion of auxiliary fuel in burners on certain hearths (direct firing), or in a separate combustion chamber (indirect firing).
    The extreme flexibility of the FGC Multiple Hearth Furnace permits a wide range of processing and in addition allow for many structural variations to accommodate special operations.  Temperature and residence time of treatment can be closely controlled and can be varied within wide limits.  Fresh feeds can be admitted at the top or at any other hearth.  Heat can be supplied where it is most effective.  Gases can be withdrawn from the top, bottom or from intermediate hearths, or any combination of these.  Atmosphere can be oxidising, reducing or neutral and can be varied in different parts of the same furnace.
    Furnace area, upon which heat transfer and mass transfer between the solids and gas phases depend, is provided in the most economical form.  The processing of solids in a thin layer improves gas-solid contact, while temperature difference between the top and the bottom of the material is minimised.
    Mixing and turning the material by gentle rabbling insure uniformity of product, aid mass transfer, and contribute to even temperature throughout the bed.  Where rapid mixing is desired, four rabble arms per hearth may be used in place of the usual two.
    Time of residence is accurately controlled because of the mechanical movement of material through the furnace.  Material can be held for any specified time at each temperature level and in
    Compartmenting by hearths permits multiple zoning with variations in flow and volume.  Where a reducing atmosphere is required in one hearth, exhaust gases may be burned in another to utilise their heating value.
    Counter-current, co-current or cross gas flows are possible, and can be combined in the several zones of a single unit.  Process material can be fed to, or withdrawn from, several hearths if desired.
  • Multiple Hearth Furnace Site Construction
  • Multiple Hearth Furnace Central Shaft Assembly
  • Multiple Hearth Furnace Fuel Burner
  • Inside the Multiple Hearth Furnace (Pyrolysis Incineration)
  • Multiple Hearth Furnace Rabble Arm and Teeth