Environmental Engineering Reference
In-Depth Information
for about 76% of the world's total coal and for 73% of all
bituminous coal. The United States leads, with 247 Gt of
the total and 111 Gt of bituminous coal, followed by
Russia (157 Gt and 49 Gt), China (@115 Gt and 62
Gt), India (92 Gt and 90 Gt), and Australia (79 Gt and
39 Gt). Asia, Europe, including Asian Russia, and North
America have very similar shares (roughly one-third of
global reserves each), and South America, with only
about 2%, is coal-poor. In 2005 the reserves to produc-
tion ratio (R/P) was 165 years globally, and the ratios
for the countries with the largest reserves and high ex-
traction were more than 500 years for Russia, 245 years
for the United States, about 230 years for India, 215 for
Australia, and 60 years for China.
Differences in reporting criteria (there is no uniformity
in defining maximum depth and minimum thickness of
potentially recoverable seams) and in accuracy of national
estimates make the resource totals unreliable (Fettweis
1979). The United States and Russia, thanks to its huge
but low-quality Siberian deposits, have the world's larg-
est coal resources. The WEC (2001) survey lists the fol-
lowing quantities of additional U.S. coal resources in
place: 445 Gt for U.S. bituminous coal (vs. 250 Gt
of reserves), 274 Gt of subbituminous fuel (vs. 167 Gt
of reserves), and 394 Gt of lignite (vs. 40 Gt of reserves).
Australia and Germany have proportionately similar or
even larger increments. Global coal resources are on the
order of 3 Gt, but knowing their precise total is irrelevant
because most of them will always remain undisturbed, ei-
ther because they would be too expensive to extract or
because the environmental consequences of coal com-
bustion will continue to be much more important in
determining the extent of production than concerns
about its physical availability.
The major products of coal combustion include CO
2
,
H
2
O, SO
2
, and nitrogen oxides (NO and NO
2
, com-
monly labeled NO
x
, mostly from the splitting and subse-
quent oxidation of atmospheric N
2
). Most coals have
always been used directly to produce heat, but they can
be also used as feedstocks for conversions producing sec-
ondary fuels in all three states. Metallurgical coke, pro-
duced by carbonization of low-ash, low-S bituminous
coals in the absence of oxygen at temperatures up to
1400
C, is a highly porous solid fusion of carbon and re-
sidual ash strong enough to support ore and limestone
charges. Its high heating value (29.6 MJ/kg) provides
energy for reducing the ore. Briquetting, making solid
shapes from coal dust or crushed and dried lignites by
pressure molding, uses otherwise unwanted waste or in-
ferior fuel.
The first coal-derived gaseous fuel was the low-energy
town (coal) gas, first produced in 1812 in London by
gasification of the fuel in closed retorts (net heating
values 16-19 MJ/m
3
). This gas was used for urban
lighting until the early twentieth century before it was
displaced by electricity. High-energy synthetic gas (net
heating values equal to that of natural gas, 30-38
MJ/m
3
) is made by a variety of gasification processes;
the leading ones are Lurgi, Koppers-Totzek, and Win-
kler. Less than a stoichiometric supply of O
2
and com-
bustion temperatures above 700
C produce CO- and
H-rich gas that can be used directly as an energy source
or as a feedstock for the catalytic Fischer-Tropsch process
to produce liquid hydrocarbons, synthetic substitutes
for crude oil-derived fuels. This method, as well as di-
rect hydrogenation (Bergius process, the reaction with
H
2
under elevated pressure and temperature), was
deployed on a large scale by Germany during WW II.
