Herreshoff furnace

Charcoal is produced commercially from primary wood-processing residues and low quaUty roundwood in either kilns or continuous furnaces. A kiln is used if the raw material is in the form of roundwood, sawmill slabs, or edgings. In the United States, most kilns are constmcted of poured concrete with a capacity of 40 to 100 cords of wood and operating on a 7- to 12-d cycle. Sawdust, shavings, or milled wood and bark are converted to charcoal in a continuous multiple-hearth furnace commonly referred to as a Herreshoff furnace. The capacity is usually at least 1 ton of charcoal per hour. The yield is - 25% by weight on a dry basis. 

Herreshoff Furnace. A multiple-hearth cylindrical muffle roasting furnace such a furnace has been used to calcine of fireclay. 

The multiple-hearth incinerator (commonly called the Herreshoff furnace) is a flexible unit that has been utilized to dispose of sewage sludges, tars, solids. 

Multiple-Hea.rth Roasters. The circular types consist of a series of hearths arranged vertically in such a way that the ore entering the top is rabbled and dropped down from hearth to hearth, until it is completely oxidized. The hearths are usually stationary and the plows revolve, such as in the Wedge, Herreshoff, Ord, Skinner, and other roasters (21). In other furnaces, the hearths revolve and the rabbles are fixed, eg, the deSpirlet and its modification, the Barrier. 

Continuous production ol charcoal is typically performed in multiple hearth furnaces, as illustrated in the Herreshoff patent shown in Figure 2. Raw material is carried by a screw conveyor to the uppermost of a series of hearths, /kir is supplied counter-currently and burns some of the wood to supply process heat. As the layers of wood carbonize, they are transported to the lower (hotter) hearths by rakes. The hot charcoal product is discharged onto a conveyor belt and cooled with a water spray. 

The production of chemical-grade magnesia or light-burned MgO requires careful control of the calcination temperature to achieve the required specific surface area of the finished product. A furnace well suited to this requirement is the multiple-hearths Herreshoff-type. For the production of dead-burned magnesia typically shaft or rotary kilns are employed. See Chapter 5 for furnaces used in MgO production. 

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

Continuous dryers, ovens, incinerators, and furnaces take any of a variety of forms such as rotary drum, tower, shaft, tunnel oven, multihearth (Herreshoff) kiln, and fluidized bed. As with all continuous furnaces, their design is very dependent on how the load(s) can be moved through the furnace (or occasionally, how the furnace can be moved over the loads). 

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. 

Roasted pyrites release sulfur dioxide, which can then be converted to sulfuric acid. Commercial scale production of sulfuric acid from pyrites had taken place back in 1793, by M. Dartigues of France. To produce sulfuric acid from pyrites, the critical technology was the pyrites burner. A major technical breakthrough was an improved furnace, invented by Michel Ferret (1813 - 1900) in 1832 (Fr. Patent No. 1094, 1836 another modification by Ferret was made in 1845). Ferret built a sulfuric acid plant in Saint-Fons, near Lyons, in 1837. Later burner developments came from MacDougall Bros, of Liverpool and James Brown Herreshoff Sr. (1831 - 1930), brother of John Brown Herreshoff. 

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