Environmental Engineering Reference
In-Depth Information
substituted for wood or charcoal in many manufactures,
but its direct use, imparting undesirable impurities to
the final product, was impossible in glass making, malt
drying, and, most important, iron smelting.
Glassmakers solved the problem by introducing rever-
berating (heat-reflecting) furnaces, where the raw mate-
rials were heated in closed vessels. Coke was first used in
malt drying during the 1640s. In 1709, Abraham Darby
succeeded in smelting pig iron with it, but charcoal use
persisted to the end of the eighteenth century (Harris
1988). Blast furnaces charged with coke could be built
taller and more voluminous, raising productivity and cre-
ating more demand for the fuel. But by far the greatest
boost for coal extraction came with James Watt's
improved steam engine, patented in 1769. At that time
Britain was still producing more than 90% of world coal
output, and it dominated global extraction until the late
1870s. Its share of global extraction was about 53% in
1870 and 36% in 1890, when it was still about 30%
ahead of the rising U.S. output, which became the
world's largest just at the century's turn. Greater avail-
ability of wood and water power in the United States
and in parts of Europe made the process slower than in
the United Kingdom. For example, in Germany the
switch required state subsidies to favor coal (Sieferle
2001), and U.S. energy use was dominated by wood un-
til the 1880s, Russian energy use until the early twentieth
century (Smil 1994).
The first detailed global survey of coal deposits was
prepared for the Thirteenth International Congress
of Geologists (McInnes 1913); it listed 6.402 Tt of
resources and 671 Gt of recoverable reserves. By the
year 2004 the global total of proved recoverable coal
reserves stood at 909 Gt, with 479 Gt (about 53%) in bi-
tuminous coals, nearly 30% in subbituminous deposits,
and the remainder in lignites (WEC 2004). The energy
density of recoverable reserves varies with the thickness
of seams and the heat content of the fuel. A 1-m-thick
seam of poor lignite (Germany's Braunkohle with 8.5
MJ/kg and specific density of 1.4) stores no more than
12 GJ/m
2
; the same thickness of excellent bituminous
coal (29.3 MJ/kg) contains up to 40 GJ/m
2
; and an-
thracite has about 50 GJ/m
2
.
Seams range from less than 30 cm (the usual minimum
for reserve accounts) to over 100 m, with modal values
between 0.5 m and 2 m (for example, Appalachia's aver-
age is 1.5 m). Typical energy densities of large coal basins
are 10
1
GJ/m
2
. The Pittsburgh bituminous bed and the
huge North Plains lignites and subbituminous deposits
(nearly 100,000 km
2
in the Dakotas, Montana, and Wyo-
ming, with some 40% of the U.S. coal reserves) average
around 50 GJ/m
2
. The richest mines have densities 1-2
OM higher. Those in Wyoming's Powder Basin (Wyo-
dak seam) rate about 450 GJ/m
2
. Fortuna/Garsdorf,
the Rhineland's largest brown coal mine during the
1980s, came close, with 430 GJ/m
2
, and Garzweiler
and Hambach, the largest German opencast lignite mines
of the early 2000s, have reserves of around 200 GJ/m
2
.
Arizona's Black Mesa rates about 200 GJ/m
2
, Mon-
tana's Ashland 415 GJ/m
2
, and parts of Victoria's
Gippsland Basin (up to 100-m-thick lignite seams of the
Latrobe Valley) about 1 TJ/m
2
. So does the Number 3
seam of Queensland's Blair Athol, which averages 29 m;
in parts it is 32 m thick, which means that with high-
quality bituminous coal of 24.5 GJ/t, its energy density
is up to 1.1 TJ/m
2
.
Coal reserves are actually distributed more unevenly
than the reserves of crude oil. Just five nations account
