Herreshoff multilevel furnace

Fig. 1.9. Herreshoff multilevel furnace for roasting ores, calcining kaolin, regenerating carbon, and incinerating sewage sludge. Courtesy of reference 50.

Herreshoff multilevel furnace = a vertical cylindrical furnace with many circular hearths attached to a central vertical drive shaft, and with plows to move granular load material across each hearth to expose all particles to furnace gases and to cause them to eventually drop to the next hearth level. Burners fire horizontally below and between the hearths. Used for drying sewage sludge, and for drying and pyrolizing ores. 

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