Environmental Engineering Reference
In-Depth Information
The electric arc furnace traces back to William Sie-
mens, one of the greatest innovators of the nineteenth
century, but the high cost and limited availability of elec-
tricity limited its adoption for many decades. The shift
from BOFs to EAFs severed the link between steelmak-
ing, blast furnaces, and coking and made it possible to
set up smaller mills whose location did not have to take
into account the supplies of coal, ore, and limestone.
These minimills, with annual capacities of less than
50,000 t to as much as 600,000 t, combine EAFs
with continuous casting and rolling (Szekely 1987; Hall
1997). By the year 2000 one-third of the world's steel
came from EAFs. The United States, with 47% of total
output, had the highest share among major producers;
China's share was 16%, Japan's 29%, and Russia's less
than 15% (IISI 2005). In 1965 the best furnaces needed
about 630 kWh/t of crude steel; 25 years later the best
rate, with the help of oxygen blowing, was down to 350
kWh/t (de Beer, Worrell, and Blok 1998), and IISI
(2005) reported that during the 1990s the global mean
fell from 450 to about 390 kWh/t.
The subsequent processing of steel has also undergone
a fundamental change. The traditional process involved
first the production of steel ingots, oblong pieces weigh-
ing 50-100 t that had to be reheated before further
processing into standard semifinished products: slabs (5-
25 cm thick), billets (square profiles used mainly to pro-
duce bars), and blooms (rectangular profiles wider than
20 cm used to roll beams), which were then converted
by hot or cold rolling into finished plates and coils, struc-
tural pieces (bars, beams, rods), rails, and wire. This
inefficient sequence often consumed as much energy as
steelmaking itself, and it was eventually replaced by con-
tinuous casting of steel, the process pioneered by Sieg-
fried Junghans, promoted by Irving Rossi, and first
adopted by Japanese steelmakers (Morita and Toshihiko
2003; Luiten 2001; Tanner 1998; Fruehan 1998).
By the year 2000 more than 85% of the world's steel
was cast continuously, with the shares (96%-97%) basi-
cally identical in Europe, the United States, and Japan.
In China, now the world's largest steel producer, contin-
uous casting accounted for nearly 90%; among the major
steelmakers, only Russia (50%) and the Ukraine (20%)
still lagged behind. The advantages of continuous casting
are many: much faster production (
<
1 h vs. 1-2 days),
higher yields of metal (up to 99% vs. less than 90% of
steel to slab), energy savings of 50%-75%, and labor sav-
ings of the same magnitude. Earlier methods involving
decarburization of iron in OHFs and the subsequent
shaping of steel doubled the energy cost of traditionally
finished products compared to modern ones; in 1950
even the best-integrated steel mills typically consumed
more than 40 GJ/t.
According to Leckie, Millar, and Medley (1982), typi-
cal gains from process innovations in steelmaking and
casting were (per tonne of liquid metal) more than 3 GJ
from replacing OHF (4 GJ) with BOF (600 MJ) and
nearly 1 GJ from substituting continuous casting (300
MJ) for rolling semifinished products from ingots (1.2
GJ). (The 600 MJ figure for BOF represents the cost of
electricity to make oxygen; the smelting process itself is
exothermic.) Innovations combined to bring energy
costs of modern steelmaking down to 25 GJ/t by 1975
and just below 20 GJ/t during the late 1990s, with
about 65% of that total used by blast furnaces. The U.S.
average fell to about 19 GJ/t by the mid-1990s, and
Japan's consumption averaged 19.4 GJ/t of crude steel
in 2000 (AISI 2002; JISF 2003). In contrast, the most
efficient EAF-based producers needed about 7 GJ/t in
the late 1990s.
