Electric furnace technology

Almost all battery scrap and paste is converted to impure lead or lead alloys by pyrometaHurgical processes employing blast, reverberatory, rotary, Isasmelt, or electric furnaces. In many plants, a furnace combination is used. PIectrowinning technologies have also been developed but as of this writing none is yet in fliU commercial operation. 

The earliest method for manufacturiag carbon disulfide involved synthesis from the elements by reaction of sulfur and carbon as hardwood charcoal in externally heated retorts. Safety concerns, short Hves of the retorts, and low production capacities led to the development of an electric furnace process, also based on reaction of sulfur and charcoal. The commercial use of hydrocarbons as the source of carbon was developed in the 1950s, and it was still the predominate process worldwide in 1991. That route, using methane and sulfur as the feedstock, provides high capacity in an economical, continuous unit. Retort and electric furnace processes are stiU used in locations where methane is unavailable or where small plants are economically viable, for example in certain parts of Africa, China, India, Russia, Eastern Europe, South America, and the Middle East. Other technologies for synthesis of carbon disulfide have been advocated, but none has reached commercial significance. 

Source of Heat Industrial furnaces are either fuel-fired or electric, and the first decision that a prospective furnace user must make is between these two. Although elecdric furnaces are uniquely suited to a few apphcations in the chemical industiy (manufacture of sihcon carbide, calcium carbide, and graphite, for example), their principal use is in the metallurgical and metal-treatment industries. In most cases the choice between elecdric and fuel-fired is economic or custom-dictated, because most tasks that can be done in one can be done equally well in the other. Except for an occasional passing reference, electric furnaces will not be considered further here. The interested reader will find useful reviews of them in Kirk-Othmer Encyclopedia of Chemical Technology (4th ed., vol. 12, articles by Cotchen, Sommer, and Walton, pp. 228-265, Wiley, New York, 1994) and in Marks Standard Handbook for Mechanical Engineers (9th ed., article by Lewis, pp. 7.59-7.68, McGraw-Hill, New York, 1987). 

The conventional industrial method for the synthesis of a-silicon carbide is to heat silica (sand) with coke in an electric furnace at 2,000-2,500 °C. However, because of the high melting point of the product, it is difficult to fabricate by sintering or melt techniques. Thus, the discovery of a lower temperature fabrication and synthesis route to silicon carbide by Yajima and coworkers in 197526,27 proved to be an important technological breakthrough. This is a preceramic polymer pyrolysis route that has been developed commercially for the production of ceramic fibers. 

In 1990, there were about eight plants in operation, some with multiple furnaces, in the United States. By 2000-2001, only one plant remained. New emission standards, high capital and operating costs, and competitive lower-cost wet acid purification technology have spelled doom for most of the furnace plants. A more thorough discussion of electric furnace processing is to be found in the ninth edition of this Handbook. 

Virtually all segments of the glass industry have now implemented 100% oxy/fuel furnace technology. Table 7.1 summarizes the completed conversions in North America. The table includes mixed melters, so-called because they get a large portion of their total melting energy from electricity. 

J. Dableh, Formulation for the Electromagnetic Field Problem in an Electrical Furnace, Internal Report. April 1998, LRT Technologies Inc., Mississauga, Ontario. 

FIGURE 4.1 Phosphorus electric furnace (simplified). (Reprinted from Phosphorus An Outline of Its Chemistry, Biochemistry and Technology, 3rd Ed., Chapter 2, D.E.C. Corbridge, Elsevier, Amsterdam, 1985. Copyright 1985, with permission from Elsevier.)... 

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