ITP Metal Casting: Advanced Melting Technologies: Energy Saving ...

Cokeless Cupola: Iron is melted in this cupola
using fuels such as natural gas, propane, diesel
oil or pulverized coal in place of coke. Although
invented over 30 years ago, only a few large
foundries in Europe and India have adopted the
technology. A water-cooled grate supports
specially developed refractory spheres, which
act as heat exchangers in a cokeless cupola
(Exhibit 11). Below the grate are burners, which
are operated to impart partially reducing
conditions inside the cupola to reduce oxidation
losses. The hot gases from the burners maintain
the bed of spheres at high temperature, and
preheat and melt the scrap in the shaft. The
metal is superheated in passing through the bed
and is then collected in the well prior to tapping.
A carburizer is continually injected into the well
13
Source: DOE, EERE Energy Environmental Profile of the
U.S. Metal Casting Industry
Exhibit 11: Cokeless gas-melting
cupola
to give the correct carbon analysis. Elimination of coke decreases the CO content in the waste
gas to 1%, indicating more efficient energy use when compared with the 12 to 20% CO emission
typical in a conventional cupola. Use of cokeless cupolas simplifies the emission control system
and results in lower sulfur content in metal and reduced slag production.
Cokeless cupolas are typically operated at relatively low tapping temperatures of about 1,400 o C
(2,550°F) to extend the refractory life, followed by superheating and re-carburization in an
electric furnace. Cokeless cupolas duplexing through electric furnaces are presently in use in
Germany, Spain, Japan, Austria, and Korea. In terms of energy efficiency, a typical cold blast
cupola averaging 12% coke consumption and 1,450°C (2,640°F) tap temperature effectively
utilizes 40% of the energy input while a cokeless cupola with natural gas consumption of 50
Nm 3 /t (1,770Nft 3 /t) and an iron temperature of 1,380°C (2,520°F) utilizes 72% of the available
energy. 20
4.1.3 Electric Arc Furnaces
Steel automobile shredded scrap with high residual elements and virgin iron raw materials, such
as direct reduced iron, are difficult to melt efficiently in a cupola or coreless induction furnace.
Cupola melting requires clean steel scrap and coke, materials that are becoming increasingly
scarce and expensive. Electric arc furnaces are well suited for these purposes. Almost 87% of the
electric arc furnaces are used to melt steel (or iron and steel) and 13% to melt iron. 21
Electric arc furnace uses electrodes that are lowered to strike an arc on the cold scrap; the
electrical system automatically controls the level of the electrode, lifting and lowering each
individual electrode according to the electrical settings. The arc provides heat by radiation and
current resistance (through the metal) to melt the scrap. 22 An intrinsic advantage of electrical
heating is the lower metal loss.